Melting in super-earths.

PubMed

Stixrude, Lars

2014-04-28

We examine the possible extent of melting in rock-iron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of super-earths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of super-earth interiors based on existing experimental and ab initio results and scaling laws. We construct super-earth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

The influence of melting on the kinematic development of the Himalayan crystalline core

NASA Astrophysics Data System (ADS)

Webb, Alexander

2016-04-01

Current hypotheses for the development and emplacement of the Himalayan crystalline core are 1) models with intense upper plate out-of-sequence activity (i.e., tunneling of channel flow, and some modes of critical taper wedge behavior) and 2) models in which the upper plate mainly records basal accretion of horses (i.e., duplexing). The two concepts can be considered end-members. A signal difference between these two models is the role of melting. The intense upper plate deformation envisioned in the first set of models has been hypothesized to be largely a product of partial melting, particularly in channel flow models. Specifically, the persistent presence of melt in the middle crust of the upper plate may dramatically lower the viscosity of these rocks, allowing distributed deformation. The second set of models - duplexing - predicts in-sequence thrusting with only minor out-of-sequence deformation. Stacking of a duplex acts like a deli cheese-slicing machine: slice after slice is cut from the intact block to a stack of slices, but neither the block (~down-going plate) nor the stack (~upper plate) features much internal deformation. In this model, partial melting produces no significant kinematic impact. The dominant preserved structural elements across the Himalayan crystalline core rocks are flattening and L-S fabrics. Structurally high portions of the crystalline core locally display complex outcrop-scale deformation associated with migmatitic rocks, and contain km-scale leucogranite bodies; both features developed in the early to middle Miocene. The flattening and L-S fabrics have been interpreted to record either (A) southwards channel tunneling across the upper plate, or (B) fabric development during metamorphism of the down-going plate, prior to accretion to the upper plate. The deformation of migmatitic rock and emplacement of leucogranite have been interpreted in support of widespread distributed deformation. Alternatively, these features may have accumulated from increments of melting and crystallization which did not produce sufficient melt during any one period to significantly alter viscosity at >100 m scales. Recent work integrating monazite and zircon geochronology with structural records shows that the Himalayan middle crust has been assembled along a series of mainly southwards-younging thrust faults throughout the early to middle Miocene. The thrust faults separate 1-5 km thick panels that experienced similar metamorphic cycles during different time periods. At this scale, out-of-sequence deformation is rare, with its apparent significance enhanced because of the high throw-to-heave ratio of out-of-sequence thrusting. These findings support the duplexing model and indicate that melting did not have a significant impact on the kinematic development of the Himalayan crystalline core.

Melting-induced stratification above the Earth's inner core due to convective translation.

PubMed

Alboussière, Thierry; Deguen, Renaud; Melzani, Mickaël

2010-08-05

In addition to its global North-South anisotropy, there are two other enigmatic seismological observations related to the Earth's inner core: asymmetry between its eastern and western hemispheres and the presence of a layer of reduced seismic velocity at the base of the outer core. This 250-km-thick layer has been interpreted as a stably stratified region of reduced composition in light elements. Here we show that this layer can be generated by simultaneous crystallization and melting at the surface of the inner core, and that a translational mode of thermal convection in the inner core can produce enough melting and crystallization on each hemisphere respectively for the dense layer to develop. The dynamical model we propose introduces a clear asymmetry between a melting and a crystallizing hemisphere which forms a basis for also explaining the East-West asymmetry. The present translation rate is found to be typically 100 million years for the inner core to be entirely renewed, which is one to two orders of magnitude faster than the growth rate of the inner core's radius. The resulting strong asymmetry of buoyancy flux caused by light elements is anticipated to have an impact on the dynamics of the outer core and on the geodynamo.

Stability of the body-centred-cubic phase of iron in the Earth's inner core.

PubMed

Belonoshko, Anatoly B; Ahuja, Rajeev; Johansson, Börje

2003-08-28

Iron is thought to be the main constituent of the Earth's core, and considerable efforts have therefore been made to understand its properties at high pressure and temperature. While these efforts have expanded our knowledge of the iron phase diagram, there remain some significant inconsistencies, the most notable being the difference between the 'low' and 'high' melting curves. Here we report the results of molecular dynamics simulations of iron based on embedded atom models fitted to the results of two implementations of density functional theory. We tested two model approximations and found that both point to the stability of the body-centred-cubic (b.c.c.) iron phase at high temperature and pressure. Our calculated melting curve is in agreement with the 'high' melting curve, but our calculated phase boundary between the hexagonal close packed (h.c.p.) and b.c.c. iron phases is in good agreement with the 'low' melting curve. We suggest that the h.c.p.-b.c.c. transition was previously misinterpreted as a melting transition, similar to the case of xenon, and that the b.c.c. phase of iron is the stable phase in the Earth's inner core.

Interpretation of the results of the CORA-33 dry core BWR test

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ott, L.J.; Hagen, S.

All BWR degraded core experiments performed prior to CORA-33 were conducted under ``wet`` core degradation conditions for which water remains within the core and continuous steaming feeds metal/steam oxidation reactions on the in-core metallic surfaces. However, one dominant set of accident scenarios would occur with reduced metal oxidation under ``dry`` core degradation conditions and, prior to CORA-33, this set had been neglected experimentally. The CORA-33 experiment was designed specifically to address this dominant set of BWR ``dry`` core severe accident scenarios and to partially resolve phenomenological uncertainties concerning the behavior of relocating metallic melts draining into the lower regions ofmore » a ``dry`` BWR core. CORA-33 was conducted on October 1, 1992, in the CORA tests facility at KfK. Review of the CORA-33 data indicates that the test objectives were achieved; that is, core degradation occurred at a core heatup rate and a test section axial temperature profile that are prototypic of full-core nuclear power plant (NPP) simulations at ``dry`` core conditions. Simulations of the CORA-33 test at ORNL have required modification of existing control blade/canister materials interaction models to include the eutectic melting of the stainless steel/Zircaloy interaction products and the heat of mixing of stainless steel and Zircaloy. The timing and location of canister failure and melt intrusion into the fuel assembly appear to be adequately simulated by the ORNL models. This paper will present the results of the posttest analyses carried out at ORNL based upon the experimental data and the posttest examination of the test bundle at KfK. The implications of these results with respect to degraded core modeling and the associated safety issues are also discussed.« less

Temperature of Earth's core constrained from melting of Fe and Fe0.9Ni0.1 at high pressures

NASA Astrophysics Data System (ADS)

Zhang, Dongzhou; Jackson, Jennifer M.; Zhao, Jiyong; Sturhahn, Wolfgang; Alp, E. Ercan; Hu, Michael Y.; Toellner, Thomas S.; Murphy, Caitlin A.; Prakapenka, Vitali B.

2016-08-01

The melting points of fcc- and hcp-structured Fe0.9Ni0.1 and Fe are measured up to 125 GPa using laser heated diamond anvil cells, synchrotron Mössbauer spectroscopy, and a recently developed fast temperature readout spectrometer. The onset of melting is detected by a characteristic drop in the time-integrated synchrotron Mössbauer signal which is sensitive to atomic motion. The thermal pressure experienced by the samples is constrained by X-ray diffraction measurements under high pressures and temperatures. The obtained best-fit melting curves of fcc-structured Fe and Fe0.9Ni0.1 fall within the wide region bounded by previous studies. We are able to derive the γ-ɛ-l triple point of Fe and the quasi triple point of Fe0.9Ni0.1 to be 110 ± 5GPa, 3345 ± 120K and 116 ± 5GPa, 3260 ± 120K, respectively. The measured melting temperatures of Fe at similar pressure are slightly higher than those of Fe0.9Ni0.1 while their one sigma uncertainties overlap. Using previously measured phonon density of states of hcp-Fe, we calculate melting curves of hcp-structured Fe and Fe0.9Ni0.1 using our (quasi) triple points as anchors. The extrapolated Fe0.9Ni0.1 melting curve provides an estimate for the upper bound of Earth's inner core-outer core boundary temperature of 5500 ± 200K. The temperature within the liquid outer core is then approximated with an adiabatic model, which constrains the upper bound of the temperature at the core side of the core-mantle boundary to be 4000 ± 200K. We discuss a potential melting point depression caused by light elements and the implications of the presented core-mantle boundary temperature bounds on phase relations in the lowermost part of the mantle.

Temperature of Earth's core constrained from melting of Fe and Fe 0.9Ni 0.1 at high pressures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Dongzhou; Jackson, Jennifer M.; Zhao, Jiyong

The melting points of fcc- and hcp-structured Fe 0.9Ni 0.1 and Fe are measured up to 125 GPa using laser heated diamond anvil cells, synchrotron Mossbauer spectroscopy, and a recently developed fast temperature readout spectrometer. The onset of melting is detected by a characteristic drop in the time integrated synchrotron Mfissbauer signal which is sensitive to atomic motion. The thermal pressure experienced by the samples is constrained by X-ray diffraction measurements under high pressures and temperatures. The obtained best-fit melting curves of fcc-structured Fe and Fe 0.9Ni 0.1 fall within the wide region bounded by previous studies. We are ablemore » to derive the gamma-is an element of-1 triple point of Fe and the quasi triple point of Fe0.9Ni0.1 to be 110 ± 5 GPa, 3345 ± 120 K and 116 ± 5 GPa, 3260 ± 120 K, respectively. The measured melting temperatures of Fe at similar pressure are slightly higher than those of Fe 0.9Ni 0.1 while their one sigma uncertainties overlap. Using previously measured phonon density of states of hcp-Fe, we calculate melting curves of hcp-structured Fe and Fe 0.9Ni 0.1 using our (quasi) triple points as anchors. The extrapolated Fe 0.9Ni 0.1 melting curve provides an estimate for the upper bound of Earth's inner core-outer core boundary temperature of 5500 ± 200 K. The temperature within the liquid outer core is then approximated with an adiabatic model, which constrains the upper bound of the temperature at the core side of the core -mantle boundary to be 4000 ± 200 K. We discuss a potential melting point depression caused by light elements and the implications of the presented core -mantle boundary temperature bounds on phase relations in the lowermost part of the mantle.« less

Near-Melting Condition of the Inner Core Boundary Revealed from Antipodal Seismic Waves

NASA Astrophysics Data System (ADS)

Cormier, V. F.; Attanayake, J.; de Silva, S. M. S.; Miller, M. S.; Thomas, C.

2014-12-01

First-principles calculations1 have suggested that the inner core's low shear velocity (3.5 km/sec) is a consequence of its temperature being very close to its melting temperature throughout its volume. Near the inner core's freezing or melting boundary, the shear modulus could possibly approach zero. A test of this is made from observations of the amplitude of PKIIKP waves at antipodal (>175o) ranges. These underside reflections are very sensitive to the S velocity beneath the inner core boundary due to energy subtracted from PKIIKP by converted S energy. This sensitivity is exploited by modeling PKIIKP waveforms observed by a transportable array in Morocco, which recorded many high-quality antipodal waveforms from Tonga. Differences in the in the sampling of the upper inner core between PKIIKP arriving from the short (<180o) and long (>180o) distances make it feasible to investigate lateral differences in the elastic and anelastic states of uppermost inner core from the amplitude and frequency content of the waveforms. In computational experiments, we show that a zero or small shear modulus in the uppermost inner core is the most effective way of matching large amplitude PKIIKP's observed from antipodal paths from Tonga to Morocco. The correlation of this bright spot in the PKIIKP reflection with a thin zone of low P velocity identified from multi-pathed PKIKP waves sampling a portion of the equatorial eastern hemisphere2suggests that at least this region of the inner core is near its melting temperature. Waveform modeling of PKIKP and PKIIKP from the combined effects of viscoelasticity and forward scattering is performed to determine whether this region of low shear modulus is consistent with freezing or melting. 1Martorell, B., L. Vocadlo, J.P. Brodholt, and I.G.Wood, (2013) Science, 342 (6157), doi: 10.1126/science.1243651. 2Stroujkova, A., and V.F. Cormier (2004), J. Geophys. Res., 109(B10), doi:10.1029/2004JB002976.

Platinum Partitioning at Low Oxygen Fugacity: Implications for Core Formation Processes

NASA Technical Reports Server (NTRS)

Medard, E.; Martin, A. M.; Righter, K.; Lanziroti, A.; Newville, M.

2016-01-01

Highly siderophile elements (HSE = Au, Re, and the Pt-group elements) are tracers of silicate / metal interactions during planetary processes. Since most core-formation models involve some state of equilibrium between liquid silicate and liquid metal, understanding the partioning of highly siderophile elements (HSE) between silicate and metallic melts is a key issue for models of core / mantle equilibria and for core formation scenarios. However, partitioning models for HSE are still inaccurate due to the lack of sufficient experimental constraints to describe the variations of partitioning with key variable like temperature, pressure, and oxygen fugacity. In this abstract, we describe a self-consistent set of experiments aimed at determining the valence of platinum, one of the HSE, in silicate melts. This is a key information required to parameterize the evolution of platinum partitioning with oxygen fugacity.

Applications of liquid state physics to the earth's core

NASA Technical Reports Server (NTRS)

Stevenson, D. J.

1980-01-01

New results derived for application to the earth's outer core using the modern theory of liquids and the hard-sphere model of liquid structure are presented. An expression derived in terms of the incompressibility and pressure is valid for a high-pressure liquid near its melting point, provided that the pressure is derived from a strongly repulsive pair potential; a relation derived between the melting point and density leads to a melting curve law of essentially the same form as Lindemann's law. Finally, it is shown that the 'core paradox' of Higgins and Kennedy (1971) can occur only if the Gruneisen parameter is smaller than 2/3, and this constant is larger than this value in any liquid for which the pair potential is strongly repulsive.

An Iron-Rain Model for Core Formation on Asteroid 4 Vesta

NASA Technical Reports Server (NTRS)

Kiefer, Walter S.; Mittlefehldt, David W.

2016-01-01

Asteroid 4 Vesta is differentiated into a crust, mantle, and core, as demonstrated by studies of the eucrite and diogenite meteorites and by data from NASA's Dawn spacecraft. Most models for the differentiation and thermal evolution of Vesta assume that the metal phase completely melts within 20 degrees of the eutectic temperature, well before the onset of silicate melting. In such a model, core formation initially happens by Darcy flow, but this is an inefficient process for liquid metal and solid silicate. However, the likely chemical composition of Vesta, similar to H chondrites with perhaps some CM or CV chondrite, has 13-16 weight percent S. For such compositions, metal-sulfide melting will not be complete until a temperature of at least 1350 degrees Centigrade. The silicate solidus for Vesta's composition is between 1100 and 1150 degrees Centigrade, and thus metal and silicate melting must have substantially overlapped in time on Vesta. In this chemically and physically more likely view of Vesta's evolution, metal sulfide drops will sink by Stokes flow through the partially molten silicate magma ocean in a process that can be envisioned as "iron rain". Measurements of eucrites show that moderately siderophile elements such as Ni, Mo, and W reached chemical equilibrium between the metal and silicate phases, which is an important test for any Vesta differentiation model. The equilibration time is a function of the initial metal grain size, which we take to be 25-45 microns based on recent measurements of H6 chondrites. For these sizes and reasonable silicate magma viscosities, equilibration occurs after a fall distance of just a few meters through the magma ocean. Although metal drops may grow in size by merger with other drops, which increases their settling velocities and decreases the total core formation time, the short equilibration distance ensures that the moderately siderophile elements will reach chemical equilibrium between metal and silicate before metal drop merger becomes important. In this model, there must be at least 30 percent melting of the silicate phase when metal melting is complete, corresponding to a crust thickness of at least 30 kilometers on Vesta, consistent with Dawn gravity observations. Greater degrees of silicate melting and a correspondingly thicker crust are possible if Vesta accreted sufficiently rapidly.

Polychlorinated Biphenyls in a Temperate Alpine Glacier: 2. Model Results of Chemical Fate Processes.

PubMed

Steinlin, Christine; Bogdal, Christian; Pavlova, Pavlina A; Schwikowski, Margit; Lüthi, Martin P; Scheringer, Martin; Schmid, Peter; Hungerbühler, Konrad

2015-12-15

We present results from a chemical fate model quantifying incorporation of polychlorinated biphenyls (PCBs) into the Silvretta glacier, a temperate Alpine glacier located in Switzerland. Temperate glaciers, in contrast to cold glaciers, are glaciers where melt processes are prevalent. Incorporation of PCBs into cold glaciers has been quantified in previous studies. However, the fate of PCBs in temperate glaciers has never been investigated. In the model, we include melt processes, inducing elution of water-soluble substances and, conversely, enrichment of particles and particle-bound chemicals. The model is validated by comparing modeled and measured PCB concentrations in an ice core collected in the Silvretta accumulation area. We quantify PCB incorporation between 1900 and 2010, and discuss the fate of six PCB congeners. PCB concentrations in the ice core peak in the period of high PCB emissions, as well as in years with strong melt. While for lower-chlorinated PCB congeners revolatilization is important, for higher-chlorinated congeners, the main processes are storage in glacier ice and removal by particle runoff. This study gives insight into PCB fate and dynamics and reveals the effect of snow accumulation and melt processes on the fate of semivolatile organic chemicals in a temperate Alpine glacier.

Ice Core Records of West Greenland Melt and Climate Forcing

NASA Astrophysics Data System (ADS)

Graeter, K. A.; Osterberg, E. C.; Ferris, D. G.; Hawley, R. L.; Marshall, H. P.; Lewis, G.; Meehan, T.; McCarthy, F.; Overly, T.; Birkel, S. D.

2018-04-01

Remote sensing observations and climate models indicate that the Greenland Ice Sheet (GrIS) has been losing mass since the late 1990s, mostly due to enhanced surface melting from rising summer temperatures. However, in situ observational records of GrIS melt rates over recent decades are rare. Here we develop a record of frozen meltwater in the west GrIS percolation zone preserved in seven firn cores. Quantifying ice layer distribution as a melt feature percentage (MFP), we find significant increases in MFP in the southernmost five cores over the past 50 years to unprecedented modern levels (since 1550 CE). Annual to decadal changes in summer temperatures and MFP are closely tied to changes in Greenland summer blocking activity and North Atlantic sea surface temperatures since 1870. However, summer warming of 1.2°C since 1870-1900, in addition to warming attributable to recent sea surface temperature and blocking variability, is a critical driver of high modern MFP levels.

Pre-Melting in Iron and Iron Alloys at Earth's Core Conditions: Results from Ab Initio Molecular Dynamics Calculations

NASA Astrophysics Data System (ADS)

Vocadlo, L.; Martorell, B.; Brodholt, J. P.; Wood, I. G.

2014-12-01

Seismically determined S-wave velocities in the Earth's inner core are observed to be much lower (10-30%) than those generally inferred from mineral physics. This is a remarkably large discrepancy - mineralogical models for the mantle and the outer core match the observed velocities to around 1%. In no other large volume of the Earth does such a difference exist. There have been a number of arguments put forward over the years to account for the difference, but none have been universally accepted and our inability to explain the seismic velocities of the inner core remains an uncomfortable truth. Here, we present results from ab initio molecular dynamics calculations performed at 360 GPa and core temperatures on hcp and fcc iron, and on fcc-Fe alloyed with nickel and hcp-Fe alloyed with silicon. The calculated shear modulus, and therefore seismic velocities, of pure hcp-Fe reduces dramatically just prior to melting, providing an elegant explanation for the observed velocities. Calculations on fcc-Fe show no such strong reduction in VS, with a transformation to an hcp-type structure prior to melting; addition of 6.5 atm% and 13 atm% Ni to fcc-Fe raises the temperature of this transition. When silicon is added to hcp-Fe, the pre-melting behaviour is found to be very similar to that of pure hcp-Fe with a strong nonlinear shear weakening just before melting and a corresponding reduction in VS. Because temperatures range from T/Tm = 1 at the inner-outer core boundary to T/Tm ≈ 0.99 at the centre, this strong nonlinear effect on VS should occur in the inner core, providing a compelling explanation for the low VS observed.

Post-impact alteration of the Manson impact structure

NASA Technical Reports Server (NTRS)

Crossey, L. J.; Mccarville, P.

1993-01-01

Core materials from the Manson impact site (Manson, Iowa) are examined in order to evaluate post-impact alteration processes. Diagenetic interpretation of post-impact events is based on petrologic, mineralogic, and geochemical investigation of core materials including the following: target strata, disturbed and disrupted strata, ejecta, breccias, microbreccias, and impact melt. The diagenetic study utilizes research cores obtained by the continental scientific drilling project (CSDP) at the Manson structure, as well as core and cuttings of related materials. Samples include impactites (breccias, microbreccias, and melt material), crater fill material (sedimentary clast breccias), disturbed and disrupted target rocks, and reference target material (Amoco Eisheid No. 1 materials). The study of multiple cores will permit development of a regional picture of post-impact thermal history. The specific objectives are as follows: (1) provide a detailed description of authigenic and alteration mineralogy from diverse lithologies encountered in research drill cores at the Manson impact structure, and (2) identify and relate significant post-impact mineral alteration to post-impact thermal regime (extent and duration). Results will provide mineralogical and geochemical constraints on models for post-impact processes including the following: infilling of the crater depression; cooling and hydrothermal alteration of melt rocks; and subsequent long-term, low-temperature alteration of target rocks, breccias, and melt rocks. Preliminary petrologic and x-ray diffraction examination of fracture linings and void fillings from research core M1 indicate the presence of quartz, chlorite, mixed-layer clays, gypsum/anhydrite, calcite, and minor pyrite.

Inflation of a magma chamber surrounded by poroelastic mush shell

NASA Astrophysics Data System (ADS)

Liao, Y.; Soule, S. A.; Jones, M.

2017-12-01

Recent studies have highlighted the importance of crystal-rich mush in crustal magmatic system [Cashman et. al. 2017]. This potential paradigm shift from isolated melt bodies in elastic crust poses new challenges to our previous understanding of igneous processes. Existing models describing the physical processes in a conventional magma plumbing system may require modification to account for the properties of mush. In this study, we demonstrate that the abundance of very crystalline mush between magma lenses and the crustal rocks influences the mechanical coupling between pressurized magma lenses and their surroundings with regard to deformation and melt transport. We develop a conceptual model invoking a simplified geometry and presumed rheological properties of liquid magma, mush and country rock. In our preliminary study, a magma chamber is modeled as a spherical liquid core enveloped by a shell of poroelastic, magma-(and/or)-gas-bearing mush in an infinite domain of elastic country rock. We interrogate the effect of varying physical properties of the system (e.g., geometry) and mush material (e.g., elastic moduli) on the deformation in the liquid core, mush shell and host rock, as well as pressure built-up in the chamber, upon injection of magma into the liquid core. When we allow the pore spaces to be connected in the mush shell, melt can migrate within the permeable matrix, thereby promoting melt segregation or `leaking' from the core to the shell. These initial results highlight the importance of constraining the physical properties of crystal mush in order for us to properly evaluate the mechanics of magmatic system.

In situ recovery of water from dormant comet cores and CI carbonaceous chondrites

NASA Astrophysics Data System (ADS)

Kuck, David L.

A model is presented for the derivation of water and volatiles from drill holes in dormant comet cores and class CI or CM asteroids, as in the Frasch process applied to sulfur mines. Hot gas is injected to melt ice, as well as to blow water and/or steam from the hole; heating to over 393 K removes six of the seven water molecules from epsomite, and melts elemental sulfur; a temperature above 573 K can drive water from hydrated phylosilicates.

Anionic Pt in Silicate Melts at Low Oxygen Fugacity: Speciation, Partitioning and Implications for Core Formation Processes on Asteroids

NASA Technical Reports Server (NTRS)

Medard, E.; Martin, A. M.; Righter, K.; Malouta, A.; Lee, C.-T.

2017-01-01

Most siderophile element concentrations in planetary mantles can be explained by metal/ silicate equilibration at high temperature and pressure during core formation. Highly siderophile elements (HSE = Au, Re, and the Pt-group elements), however, usually have higher mantle abundances than predicted by partitioning models, suggesting that their concentrations have been set by late accretion of material that did not equilibrate with the core. The partitioning of HSE at the low oxygen fugacities relevant for core formation is however poorly constrained due to the lack of sufficient experimental constraints to describe the variations of partitioning with key variables like temperature, pressure, and oxygen fugacity. To better understand the relative roles of metal/silicate partitioning and late accretion, we performed a self-consistent set of experiments that parameterizes the influence of oxygen fugacity, temperature and melt composition on the partitioning of Pt, one of the HSE, between metal and silicate melts. The major outcome of this project is the fact that Pt dissolves in an anionic form in silicate melts, causing a dependence of partitioning on oxygen fugacity opposite to that reported in previous studies.

Partitioning of Moderately Siderophile Elements Among Olivine, Silicate Melt, and Sulfide Melt: Constraints on Core Formation in the Earth and Mars

NASA Technical Reports Server (NTRS)

Gaetani, Glenn A.; Grove, Timothy L.

1997-01-01

This study investigates the effects of Variations in the fugacities of oxygen and sulfur on the partitioning of first series transition metals (V, Cr, Mn, Fe, Co, Ni. and Cu) and W among coexisting sulfide melt, silicate melt, and olivine. Experiments were performed at 1 atm pressure, 1350 C, with the fugacities of oxygen and sulfur controlled by mixing CO2, CO, and SO2 gases. Starting compositions consisted of a CaO-MgO-Al2O3-SiO2-FeO-Na2O analog for a barred olivine chondrule from an ordinary chondrite and a synthetic komatiite. The f(sub O2)/f(sub S2), conditions ranged from log of f(sub O2) = -7.9 to - 10.6, with log of f(sub S2) values ranging from - 1.0 to -2.5. Our experimental results demonstrate that the f(sub O2)/f(sub S2) dependencies of sulfide melt/silicate melt partition coefficients for the first series transition metals arc proportional to their valence states. The f(sub O2)/f(sub S2) dependencies for the partitioning of Fe, Co, Ni, and Cu are weaker than predicted on the basis of their valence states. Variations in conditions have no significant effect on olivine/melt partitioning other than those resulting from f(sub O2)-induced changes in the valence state of a given element. The strong f(sub O2)/f(sub S2) dependence for the olivine/silicate melt partitioning of V is attributable to a change of valence state, from 4+ to 3+, with decreasing f(sub O2). Our experimentally determined partition coefficients are used to develop models for the segregation of sulfide and metal from the silicate portion of the early Earth and the Shergottite parent body (Mars). We find that the influence of S is not sufficient to explain the overabundance of siderophile and chalcophile elements that remained in the mantle of the Earth following core formation. Important constraints on core formation in Mars are provided by our experimental determination of the partitioning of Cu between silicate and sulfide melts. When combined with existing estimates for siderophile element abundances in the Martian mantle and a mass balance constraint from Fe, the experiments allow a determination of the mass of the Martian core (approx. 17 to 22 wt% of the planet) and its S content (approx.0.4 wt%). These modeling results indicate that Mars is depleted in S, and that its core is solid.

Geochemical Comparison of Four Cores from the Manson Impact Structure

NASA Technical Reports Server (NTRS)

Korotev, Randy L.; Rockow, Kaylynn M.; Jolliff, Bradley L.; Haskin, Larry A.; McCarville, Peter; Crossey, Laura J.

1996-01-01

Concentrations of 33 elements were determined in relatively unaltered, matrix-rich samples of impact breccia at approximately 3-m-depth intervals in the M-1 core from the Manson impact structure, Iowa. In addition, 46 matrix-rich samples from visibly altered regions of the M-7, M-8, and M-10 cores were studied, along with 42 small clasts from all four cores. Major element compositions were determined for a subset of impact breccias from the M-1 core, including matrix-rich impact-melt breccia. Major- and trace-element compositions were also determined for a suite of likely target rocks. In the M-1 core, different breccia units identified from lithologic examination of cores are compositionally distinct. There is a sharp compositional discontinuity at the boundary between the Keweenawan-shale-clast breccia and the underlying unit of impact-melt breccia (IMB) for most elements, suggesting minimal physical mixing between the two units during emplacement. Samples from the 40-m-thick IMB (M-1) are all similar to each other in composition, although there are slight increases in concentration with depth for those elements that have high concentrations in the underlying fragmental-matrix suevite breccia (SB) (e.g., Na, Ca, Fe, Sc), presumably as a result of greater clast proportions at the bottom margin of the unit of impact-melt breccia. The high degree of compositional similarity we observe in the impact-melt breccias supports the interpretation that the matrix of this unit represents impact melt. That our analyses show such compositional similarity results in part from our technique for sampling these breccias: for each sample we analyzed a few small fragments (total mass: approximately 200 mg) selected to be relatively free of large clasts and visible signs of alteration instead of subsamples of powders prepared from a large mass of breccia. The mean composition of the matrix-rich part of impact-melt breccia from the M-1 core can be modeled as a mixture of approximately 35% shale and siltstone (Proterozoic "Red Clastics"), 23% granite, 40% hornblende-biotite gneiss, and a small component (less than 2%) of mafic-dike rocks.

Molybdenum Valence in Basaltic Silicate Melts: Effects of Temperature and Pressure

NASA Technical Reports Server (NTRS)

Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Choi, Y.; Pando, K.

2011-01-01

The metal-silicate partitioning behavior of molybdenum has been used as a test for equilibrium core formation hypotheses [for example, 1-6]. However, current models that apply experimental data to equilibrium core-mantle differentiation infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Molybdenum, a multi-valent element with a valence transition near the fO2 of interest for core formation (approx.IW-2) will be sensitive to changes in fO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo(6+) can be either octahedrally or tetrahedrally coordinated. Here we present X-ray absorption near edge structure (XANES) measurements of Mo valence in basaltic run products at a range of P, T, and fO2 and further quantify the valence transition of Mo.

Thermal evolution and core formation of planetesimals

NASA Astrophysics Data System (ADS)

Suwa, Taichi; Nagahara, Hiroko

2017-04-01

Planetesimals did not get an adequate thermal energy by accretion to form large scale magma ocean because of smaller radii, masses, gravity and accretion energy, however, there are various evidences for the presence of core in planetesimals: 4-Vesta has a core and non-magmatic iron meteorites were segregated metal in bodies that did not experience silicate melting. It has been pointed out that accretion time of planetesimals controls melting and differentiation, because short lived nuclides are plausible heat source. Other factors such as radiative cooling from the surface and thermal conductivity, would also affect thermal evolution of planetesimals. Furthermore, percolation of Fe-S melt through silicate matrix is controlled by the porosity and grain size of silicates and dihedral angle between the melt and silicates. Therefore, the interior structure of planetesimals should be considered by taking the accretion, growth, and thermal evolution of the interior simultaneously. We make a numerical simulation with a spherical 1D model on the basis of the model by Neuman, which is a non-stationary heat conduction equation. We specifically pay attention to the process at temperatures between eutectic temperature Fe-FeS (1213K) and silicate solidus (1425K) and the surface tension of the melt that governs percolation. The model contains three free parameters, formation time, accretion duration, and final size of the planetesimals. The results show that the interior structure can be divided to four types: Type A is undifferentiated, Type B is differentiated to core and mantle of which core was formed by Fe-S melt percolation, Type C is partially differentiated to FeS core and mantle, where mantle retains residual Fe metal, and Type D is differentiated to core and mantle by metal separation in silicate magma. Type A would correspond to the parent bodies of chondrites, and Type B (and Type C?) core would be the source of non-magmatic iron meteorites. Type D would be parent bodies for 4 Vesta and angrites. The conditions for the four types of planetesimals are throuly investigated as a function of the three parameters, accretion time, accreting duration, and palnetesimal size. We found that the planetesimal interior is strongly controlled by the formation time: planetesimals formed after 3 Ma after CAIs would be undifferentiated (Type A) regardless of the planetary size, whereas most of them formed within 1 Ma are Type D (differentiated bodies with magmatically formed core). Types B and C bodies are preferentially formed between 1 and 3 Ma after CAIs. Longer accretion duration tends to be resulted in formation of Types A, B and C. The present work predicts the planetesimal interior structure if we know the formation age with the isotopic measurements of samples and the size of the body, which would be a very powerful tool for future explorations of small bodies except for very small (< 20 km) bodies.

Surface Melt and Firn Density Evolution in the Western Greenland Percolation Zone Over the Past 50 Years

NASA Astrophysics Data System (ADS)

Graeter, K.; Osterberg, E. C.; Hawley, R. L.; Thundercloud, Z. R.; Marshall, H. P.; Ferris, D. G.; Lewis, G.

2016-12-01

Predictions of the Greenland Ice Sheet's (GIS) contribution to sea-level rise in a warming climate depend on our ability to model the surface mass balance (SMB) processes occurring across the ice sheet. These processes are poorly constrained in the percolation zone, the region of the ice sheet where surface melt refreezes in the firn, thus preventing that melt from directly contributing to GIS mass loss. In this way, the percolation zone serves as a buffer to higher temperatures increasing mass loss. However, it is unknown how the percolation zone is evolving in a changing climate and to what extent the region will continue to serve as a buffer to future runoff. We collected seven shallow ( 22-30 m) firn cores from the Western Greenland percolation zone in May-June 2016 as part of the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) project. Here we present data on melt layer stratigraphy, density, and annual accumulation for each core to determine: (1) the temporal and spatial accumulation and melt refreeze patterns in the percolation zone of W. Greenland over the past 40 - 55 years, and (2) the impacts of changing melt and refreeze patterns on the near-surface density profile of the percolation zone. Three of the GreenTrACS firn cores re-occupy firn core sites collected in the 1970's-1990's, allowing us to more accurately quantify the evolution of the percolation zone surface melt and firn density during the most recent decades of summertime warming. This work is the basis for broader investigations into how changes in W. Greenland summertime climate are impacting the SMB of the Greenland Ice Sheet.

The MELTSPREAD Code for Modeling of Ex-Vessel Core Debris Spreading Behavior, Code Manual – Version3-beta

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farmer, M. T.

MELTSPREAD3 is a transient one-dimensional computer code that has been developed to predict the gravity-driven flow and freezing behavior of molten reactor core materials (corium) in containment geometries. Predictions can be made for corium flowing across surfaces under either dry or wet cavity conditions. The spreading surfaces that can be selected are steel, concrete, a user-specified material (e.g., a ceramic), or an arbitrary combination thereof. The corium can have a wide range of compositions of reactor core materials that includes distinct oxide phases (predominantly Zr, and steel oxides) plus metallic phases (predominantly Zr and steel). The code requires input thatmore » describes the containment geometry, melt “pour” conditions, and cavity atmospheric conditions (i.e., pressure, temperature, and cavity flooding information). For cases in which the cavity contains a preexisting water layer at the time of RPV failure, melt jet breakup and particle bed formation can be calculated mechanistically given the time-dependent melt pour conditions (input data) as well as the heatup and boiloff of water in the melt impingement zone (calculated). For core debris impacting either the containment floor or previously spread material, the code calculates the transient hydrodynamics and heat transfer which determine the spreading and freezing behavior of the melt. The code predicts conditions at the end of the spreading stage, including melt relocation distance, depth and material composition profiles, substrate ablation profile, and wall heatup. Code output can be used as input to other models such as CORQUENCH that evaluate long term core-concrete interaction behavior following the transient spreading stage. MELTSPREAD3 was originally developed to investigate BWR Mark I liner vulnerability, but has been substantially upgraded and applied to other reactor designs (e.g., the EPR), and more recently to the plant accidents at Fukushima Daiichi. The most recent round of improvements that are documented in this report have been specifically implemented to support industry in developing Severe Accident Water Management (SAWM) strategies for Boiling Water Reactors.« less

Experimental alteration of artificial and natural impact melt rock from the Chesapeake Bay impact structure

USGS Publications Warehouse

Declercq, J.; Dypvik, H.; Aagaard, Per; Jahren, J.; Ferrell, R.E.; Horton, J. Wright

2009-01-01

The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mj??lnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 ??C) in order to reproduce conditions found in meltbearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples. In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment. ?? 2009 The Geological Society of America.

The evolution of complex type B Allende inclusion - An ion microprobe trace element study

NASA Technical Reports Server (NTRS)

Macpherson, Glenn J.; Crozaz, Ghislaine; Lundberg, Laura L.

1989-01-01

Results are presented of a detailed trace-element and isotopic analyses of the constituent phases in each of the major textural parts (mantle, core, and islands) of a Type B refractory inclusion, the USNM 5241 inclusion from Allende, first described by El Goresy et al. (1985). The REE data on 5241 were found to be largely consistent with a model in which the mantle and the core of 5241 formed sequentially out of a single melt by fractional crystallization. The numerical models of REE evolution in the 5241 melt, especially that of Eu, require that a significant mass of spinel-free island material was assimilated into the evolving melt during the last half of the solidification history of 5241. The trace element results pbtained thus strongly support the interpretation of El Goresy et al. (1985) that the spinel-free islands in the 5241 are trapped xenoliths.

Core-melt source reduction system

DOEpatents

Forsberg, C.W.; Beahm, E.C.; Parker, G.W.

1995-04-25

A core-melt source reduction system for ending the progression of a molten core during a core-melt accident and resulting in a stable solid cool matrix. The system includes alternating layers of a core debris absorbing material and a barrier material. The core debris absorbing material serves to react with and absorb the molten core such that containment overpressurization and/or failure does not occur. The barrier material slows the progression of the molten core debris through the system such that the molten core has sufficient time to react with the core absorbing material. The system includes a provision for cooling the glass/molten core mass after the reaction such that a stable solid cool matrix results. 4 figs.

Core-melt source reduction system

DOEpatents

Forsberg, Charles W.; Beahm, Edward C.; Parker, George W.

1995-01-01

A core-melt source reduction system for ending the progression of a molten core during a core-melt accident and resulting in a stable solid cool matrix. The system includes alternating layers of a core debris absorbing material and a barrier material. The core debris absorbing material serves to react with and absorb the molten core such that containment overpressurization and/or failure does not occur. The barrier material slows the progression of the molten core debris through the system such that the molten core has sufficient time to react with the core absorbing material. The system includes a provision for cooling the glass/molten core mass after the reaction such that a stable solid cool matrix results.

Melting of Iron to 290 Gigapascals

NASA Astrophysics Data System (ADS)

Sinmyo, R.; Hirose, K.; Ohishi, Y.

2017-12-01

The Earth's core is composed mainly of iron. Since liquid core coexists with solid core at the inner core boundary (ICB), the melting point of iron at 330 gigapascals offers a key constraint on core temperatures. However, previous results using a laser-heated diamond-anvil cell (DAC) have been largely inconsistent with each other, likely because of an intrinsic large temperature gradient and its temporal fluctuation. Here we employed an internal-resistance-heated DAC and determined the melting temperature of pure iron up to 290 gigapascals, the highest ever in static compression experiments. A small extrapolation indicates a melting point of 5500 ± 80 kelvin at the ICB, about 500-1000 degrees lower than earlier shock-compression data. It suggests a relatively low temperature for the core-mantle boundary, which avoids global melting of the lowermost mantle in the last more than 1.5 billion years.

The melting curve of iron to 250 gigapascals - A constraint on the temperature at earth's center

NASA Technical Reports Server (NTRS)

Williams, Quentin; Jeanloz, Raymond; Bass, Jay; Svendsen, Bob; Ahrens, Thomas J.

1987-01-01

The melting curve of iron, the primary constituent of earth's core, has been measured to pressures of 250 gigapascals with a combination of static and dynamic techniques. The melting temperature of iron at the pressure of the core-mantle boundary (136 GPa) is 4800 + or - 200 K, whereas at the inner core-outer core boundary (330 GPa), it is 7600 + or - 500 K. A melting temperature for iron-rich alloy of 6600 K at the inner core-outer core boundary and a maximum temperature of 6900 K at earth's center are inferred. This latter value is the first experimental upper bound on the temperature at earth's center, and these results imply that the temperature of the lower mantle is significantly less than that of the outer core.

Fukushima Daiichi Unit 1 ex-vessel prediction: Core melt spreading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farmer, M. T.; Robb, K. R.; Francis, M. W.

Lower head failure and corium-concrete interaction were predicted to occur at Fukushima Daiichi Unit 1 (1F1) by several different system-level code analyses, including MELCOR v2.1 and MAAP5. Although these codes capture a wide range of accident phenomena, they do not contain detailed models for ex-vessel core melt behavior. However, specialized codes exist for analysis of ex-vessel melt spreading (e.g., MELTSPREAD) and long-term debris coolability (e.g., CORQUENCH). On this basis, an analysis has been carried out to further evaluate ex-vessel behavior for 1F1 using MELTSPREAD and CORQUENCH. Best-estimate melt pour conditions predicted by MELCOR v2.1 and MAAP5 were used as input.more » MELTSPREAD was then used to predict the spatially-dependent melt conditions and extent of spreading during relocation from the vessel. Lastly, this information was then used as input for the long-term debris coolability analysis with CORQUENCH that is reported in a companion paper.« less

Fukushima Daiichi Unit 1 ex-vessel prediction: Core melt spreading

DOE PAGES

Farmer, M. T.; Robb, K. R.; Francis, M. W.

2016-10-31

Lower head failure and corium-concrete interaction were predicted to occur at Fukushima Daiichi Unit 1 (1F1) by several different system-level code analyses, including MELCOR v2.1 and MAAP5. Although these codes capture a wide range of accident phenomena, they do not contain detailed models for ex-vessel core melt behavior. However, specialized codes exist for analysis of ex-vessel melt spreading (e.g., MELTSPREAD) and long-term debris coolability (e.g., CORQUENCH). On this basis, an analysis has been carried out to further evaluate ex-vessel behavior for 1F1 using MELTSPREAD and CORQUENCH. Best-estimate melt pour conditions predicted by MELCOR v2.1 and MAAP5 were used as input.more » MELTSPREAD was then used to predict the spatially-dependent melt conditions and extent of spreading during relocation from the vessel. Lastly, this information was then used as input for the long-term debris coolability analysis with CORQUENCH that is reported in a companion paper.« less

Melting curve of SiO2 at multimegabar pressures: implications for gas giants and super-Earths.

PubMed

González-Cataldo, Felipe; Davis, Sergio; Gutiérrez, Gonzalo

2016-05-23

Ultrahigh-pressure phase boundary between solid and liquid SiO2 is still quite unclear. Here we present predictions of silica melting curve for the multimegabar pressure regime, as obtained from first principles molecular dynamics simulations. We calculate the melting temperatures from three high pressure phases of silica (pyrite-, cotunnite-, and Fe2P-type SiO2) at different pressures using the Z method. The computed melting curve is found to rise abruptly around 330 GPa, an increase not previously reported by any melting simulations. This is in close agreement with recent experiments reporting the α-PbO2-pyrite transition around this pressure. The predicted phase diagram indicates that silica could be one of the dominant components of the rocky cores of gas giants, as it remains solid at the core of our Solar System's gas giants. These results are also relevant to model the interior structure and evolution of massive super-Earths.

Melting curve of SiO2 at multimegabar pressures: implications for gas giants and super-Earths

PubMed Central

González-Cataldo, Felipe; Davis, Sergio; Gutiérrez, Gonzalo

2016-01-01

Ultrahigh-pressure phase boundary between solid and liquid SiO2 is still quite unclear. Here we present predictions of silica melting curve for the multimegabar pressure regime, as obtained from first principles molecular dynamics simulations. We calculate the melting temperatures from three high pressure phases of silica (pyrite-, cotunnite-, and Fe2P-type SiO2) at different pressures using the Z method. The computed melting curve is found to rise abruptly around 330 GPa, an increase not previously reported by any melting simulations. This is in close agreement with recent experiments reporting the α-PbO2–pyrite transition around this pressure. The predicted phase diagram indicates that silica could be one of the dominant components of the rocky cores of gas giants, as it remains solid at the core of our Solar System’s gas giants. These results are also relevant to model the interior structure and evolution of massive super-Earths. PMID:27210813

A Model of the Chicxulub Impact Basin Based on Evaluation of Geophysical Data, Well Logs, and Drill Core Samples

NASA Technical Reports Server (NTRS)

Sharpton, Virgil L.; Marin, Luis E.; Carney, John D.; Lee, Scott; Ryder, Graham; Schuraytz, Benjamin C.; Sikora, Paul; Spudis, Paul D.

1996-01-01

Abundant evidence now shows that the buried Chicxulub structure in northern Yucatan, Mexico, is indeed the intensely sought-after source of the ejecta found world-wide at the Cretaceous-Tertiary (K/T) boundary. In addition to large-scale concentric patterns in gravity and magnetic data over the structure, recent analyses of drill-core samples reveal a lithological assemblage similar to that observed at other terrestrial craters. This assemblage comprises suevite breccias, ejecta deposit breccias (Bunte Breccia equivalents), fine-grained impact melt rocks, and melt-matrix breccias. All these impact-produced lithologies contain diagnostic evidence of shock metamorphism, including planar deformation features in quartz, feldspar, and zircons; diaplectic glasses of quartz and feldspar; and fused mineral melts and whole-rock melts. In addition, elevated concentrations of Ir, Re, and Os, in meteoritic relative proportions, have been detected in some melt-rock samples from the center of the structure. Isotopic analyses, magnetization of melt-rock samples, and local stratigraphic constraints identify this crater as the source of K/T boundary deposits.

Partial melting of a Pb-Sn mushy layer due to heating from above, and implications for regional melting of Earth's directionally solidified inner core

NASA Astrophysics Data System (ADS)

Yu, James; Bergman, Michael I.; Huguet, Ludovic; Alboussiere, Thierry

2015-09-01

Superimposed on the radial solidification of Earth's inner core may be hemispherical and/or regional patches of melting at the inner-outer core boundary. Little work has been carried out on partial melting of a dendritic mushy layer due to heating from above. Here we study directional solidification, annealing, and partial melting from above of Pb-rich Sn alloy ingots. We find that partial melting from above results in convection in the mushy layer, with dense, melted Pb sinking and resolidifying at a lower height, yielding a different density profile than for those ingots that are just directionally solidified, irrespective of annealing. Partial melting from above causes a greater density deeper down and a corresponding steeper density decrease nearer the top. There is also a change in microstructure. These observations may be in accordance with inferences of east-west and perhaps smaller-scale variations in seismic properties near the top of the inner core.

Sulfur Saturation Limits in Silicate Melts and their Implications for Core Formation Scenarios for Terrestrial Planets

NASA Technical Reports Server (NTRS)

Holzheid, Astrid; Grove, Timothy L.

2002-01-01

This study explores the controls of temperature, pressure, and silicate melt composition on S solubility in silicate liquids. The solubility of S in FeO-containing silicate melts in equilibrium with metal sulfide increases significantly with increasing temperature but decreases with increasing pressure. The silicate melt structure also exercises a control on S solubility. Increasing the degree of polymerization of the silicate melt structure lowers the S solubility in the silicate liquid. The new set of experimental data is used to expand the model of Mavrogenes and O'Neill(1999) for S solubility in silicate liquids by incorporating the influence of the silicate melt structure. The expected S solubility in the ascending magma is calculated using the expanded model. Because the negative pressure dependence of S solubility is more influential than the positive temperature dependence, decompression and adiabatic ascent of a formerly S-saturated silicate magma will lead to S undersaturation. A primitive magma that is S-saturated in its source region will, therefore, become S-undersaturated as it ascends to shallower depth. In order to precipitate magmatic sulfides, the magma must first cool and undergo fractional crystallization to reach S saturation. The S content in a metallic liquid that is in equilibrium with a magma ocean that contains approx. 200 ppm S (i.e., Earth's bulk mantle S content) ranges from 5.5 to 12 wt% S. This range of S values encompasses the amount of S (9 to 12 wt%) that would be present in the outer core if S is the light element. Thus, the Earth's proto-mantle could be in equilibrium (in terms of the preserved S abundance) with a core-forming metallic phase.

The WAIS Melt Monitor: An automated ice core melting system for meltwater sample handling and the collection of high resolution microparticle size distribution data

NASA Astrophysics Data System (ADS)

Breton, D. J.; Koffman, B. G.; Kreutz, K. J.; Hamilton, G. S.

2010-12-01

Paleoclimate data are often extracted from ice cores by careful geochemical analysis of meltwater samples. The analysis of the microparticles found in ice cores can also yield unique clues about atmospheric dust loading and transport, dust provenance and past environmental conditions. Determination of microparticle concentration, size distribution and chemical makeup as a function of depth is especially difficult because the particle size measurement either consumes or contaminates the meltwater, preventing further geochemical analysis. Here we describe a microcontroller-based ice core melting system which allows the collection of separate microparticle and chemistry samples from the same depth intervals in the ice core, while logging and accurately depth-tagging real-time electrical conductivity and particle size distribution data. This system was designed specifically to support microparticle analysis of the WAIS Divide WDC06A deep ice core, but many of the subsystems are applicable to more general ice core melting operations. Major system components include: a rotary encoder to measure ice core melt displacement with 0.1 millimeter accuracy, a meltwater tracking system to assign core depths to conductivity, particle and sample vial data, an optical debubbler level control system to protect the Abakus laser particle counter from damage due to air bubbles, a Rabbit 3700 microcontroller which communicates with a host PC, collects encoder and optical sensor data and autonomously operates Gilson peristaltic pumps and fraction collectors to provide automatic sample handling, melt monitor control software operating on a standard PC allowing the user to control and view the status of the system, data logging software operating on the same PC to collect data from the melting, electrical conductivity and microparticle measurement systems. Because microparticle samples can easily be contaminated, we use optical air bubble sensors and high resolution ice core density profiles to guide the melting process. The combination of these data allow us to analyze melt head performance, minimize outer-to-inner fraction contamination and avoid melt head flooding. The WAIS Melt Monitor system allows the collection of real-time, sub-annual microparticle and electrical conductivity data while producing and storing enough sample for traditional Coulter-Counter particle measurements as well long term acid leaching of bioactive metals (e.g., Fe, Co, Cd, Cu, Zn) prior to chemical analysis.

Differentiation of Asteroid 4 Vesta: Core Formation by Iron Rain in a Silicate Magma Ocean

NASA Technical Reports Server (NTRS)

Kiefer, Walter S.; Mittlefehldt, David W.

2017-01-01

Geochemical observations of the eucrite and diogenite meteorites, together with observations made by NASA's Dawn spacecraft while orbiting asteroid 4 Vesta, suggest that Vesta resembles H chondrites in bulk chemical composition, possible with about 25 percent of a CM-chondrite like composition added in. For this model, the core is 15 percent by mass (or 8 percent by volume) of the asteroid, with a composition of 73.7 percent by weight Fe, 16.0 percent by weight S, and 10.3 percent by weight Ni. The abundances of moderately siderophile elements (Ni, Co, Mo, W, and P) in eucrites require that essentially all of the metallic phase in Vesta segregated to form a core prior to eucrite solidification. The combination of the melting phase relationships for the silicate and metal phases, together with the moderately siderophile element concentrations together require that complete melting of the metal phase occurred (temperature is greater than1350 degrees Centigrade), along with substantial (greater than 40 percent) melting of the silicate material. Thus, core formation on Vesta occurs as iron rain sinking through a silicate magma ocean.

On the Composition and Temperature of the Terrestrial Planetary Core

NASA Astrophysics Data System (ADS)

Fei, Yingwei

2013-06-01

The existence of liquid cores of terrestrial planets such as the Earth, Mar, and Mercury has been supported by various observation. The liquid state of the core provides a unique opportunity for us to estimate the temperature of the core if we know the melting temperature of the core materials at core pressure. Dynamic compression by shock wave, laser-heating in diamond-anvil cell, and resistance-heating in the multi-anvil device can melt core materials over a wide pressure range. There have been significant advances in both dynamic and static experimental techniques and characterization tool. In this tal, I will review some of the recent advances and results relevant to the composition and thermal state of the terrestrial core. I will also present new development to analyze the quenched samples recovered from laser-heating diamond-anvil cell experiments using combination of focused ion beam milling, high-resolution SEM imaging, and quantitative chemical analysi. With precision milling of the laser-heating spo, the melting point and element partitioning between solid and liquid can be precisely determined. It is also possible to re-construct 3D image of the laser-heating spot at multi-megabar pressures to better constrain melting point and understanding melting process. The new techniques allow us to extend precise measurements of melting relations to core pressures, providing better constraint on the temperature of the cor. The research is supported by NASA and NSF grants.

Approach to numerical safety guidelines based on a core melt criterion. [PWR; BWR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Azarm, M.A.; Hall, R.E.

1982-01-01

A plausible approach is proposed for translating a single level criterion to a set of numerical guidelines. The criterion for core melt probability is used to set numerical guidelines for various core melt sequences, systems and component unavailabilities. These guidelines can be used as a means for making decisions regarding the necessity for replacing a component or improving part of a safety system. This approach is applied to estimate a set of numerical guidelines for various sequences of core melts that are analyzed in Reactor Safety Study for the Peach Bottom Nuclear Power Plant.

The high-pressure phase diagram of Fe(0.94)O - A possible constituent of the earth's core

NASA Technical Reports Server (NTRS)

Knittle, Elise; Jeanloz, Raymond

1991-01-01

Electrical resistivity measurements to pressures of 83 GPa and temperatures ranging from 300 K to 4300 K confirm the presence of both crystalline and liquid metallic phases of FeO at pressures above 60-70 GPa and temperatures above 1000 K. By experimentally determinig the melting temperature of FeO to 100 GPa and of a model-core composition at 83 GPa, it is found that the solid-melt equilibria can be described by complete solid solution across the Fe-FeO system at pressures above 70 GPa. The results indicate that oxygen is a viable and likely candidate for the major light alloying element of the earth's liquid outer core. The data suggest that the temperature at the core-mantle boundary is close to 4800 K and that heat lost out of the core accounts for more than 20 percent of the heat flux observed at the surface.

Melting and solidification behavior of Cu/Al and Ti/Al bimetallic core/shell nanoparticles during additive manufacturing by molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Rahmani, Farzin; Jeon, Jungmin; Jiang, Shan; Nouranian, Sasan

2018-05-01

Molecular dynamics (MD) simulations were performed to investigate the role of core volume fraction and number of fusing nanoparticles (NPs) on the melting and solidification of Cu/Al and Ti/Al bimetallic core/shell NPs during a superfast heating and slow cooling process, roughly mimicking the conditions of selective laser melting (SLM). One recent trend in the SLM process is the rapid prototyping of nanoscopically heterogeneous alloys, wherein the precious core metal maintains its particulate nature in the final manufactured part. With this potential application in focus, the current work reveals the fundamental role of the interface in the two-stage melting of the core/shell alloy NPs. For a two-NP system, the melting zone gets broader as the core volume fraction increases. This effect is more pronounced for the Ti/Al system than the Cu/Al system because of a larger difference between the melting temperatures of the shell and core metals in the former than the latter. In a larger six-NP system (more nanoscopically heterogeneous), the melting and solidification temperatures of the shell Al roughly coincide, irrespective of the heating or cooling rate, implying that in the SLM process, the part manufacturing time can be reduced due to solidification taking place at higher temperatures. The nanostructure evolution during the cooling of six-NP systems is further investigated. [Figure not available: see fulltext.

Transient experiments with thermite melts for a core catcher concept based on water addition from below

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tromm, W.; Alsmeyer, H.

1995-09-01

A core catcher concept is proposed to be integrated into a new pressurized water reactor. The core catcher achieves coolability by spreading and fragmentation of the ex-vessel core melt based on a process of water inlet from the bottom through the melt. By highly effective heat removal that uses evaporating water in direct contact with the fragmented melt, the corium melt would solidify in a short time period, and long-term cooling could be maintained by continuous water evaporation from the flooded porous or fragmented corium bed. The key process for obtaining coolability is the coupling of the three effects: (a)more » water ingression from below and its evaporation, (b) break up and fragmentation of the corium layer, and (c) heat transfer and solidification of the let. These mechanisms are investigated in transient medium-scale experiments with thermite melts. The experimental setup represents a section of the proposed core catcher design. A thermite melt is located on the core catcher plate with a passive water supply from the bottom. After generation of the melt, the upper sacrificial layer is eroded until water penetrates into the melt for the bottom through plugs in the supporting plate. Fragmentation and fast solidification of the melt are observed, and long-term heat removal is guaranteed by the coolant water flooding the porous melt. Water inflow is sufficient to safely remove the decay heat in a comparable corium layer. The open porosity is created by the vapor streaming through the melt during the solidification process. Fracture of the solid by thermomechanical stresses is not observed. The experiments in their current stage show the principal feasibility of the proposed cooling concept and are used to prepare large-scale experiments to be performed in the modified BETA facility with sustained heating of the melt.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walston, S; Rowland, M; Campbell, K

It is difficult to track to the location of a melted core in a GE BWR with Mark I containment during a beyond-design-basis accident. The Cooper Nuclear Station provided a baseline of normal material distributions and shielding configurations for the GE BWR with Mark I containment. Starting with source terms for a design-basis accident, methods and remote observation points were investigated to allow tracking of a melted core during a beyond-design-basis accident. The design of the GE BWR with Mark-I containment highlights an amazing poverty of expectations regarding a common mode failure of all reactor core cooling systems resulting inmore » a beyond-design-basis accident from the simple loss of electric power. This design is shown in Figure 1. The station blackout accident scenario has been consistently identified as the leading contributor to calculated probabilities for core damage. While NRC-approved models and calculations provide guidance for indirect methods to assess core damage during a beyond-design-basis loss-of-coolant accident (LOCA), there appears to be no established method to track the location of the core directly should the LOCA include a degree of fuel melt. We came to the conclusion that - starting with detailed calculations which estimate the release and movement of gaseous and soluble fission products from the fuel - selected dose readings in specific rooms of the reactor building should allow the location of the core to be verified.« less

The Effect of Inner Core Translation on Outer Core Flow and the Geomagnetic Field

NASA Astrophysics Data System (ADS)

Mound, J. E.; Davies, C. J.; Silva, L.

2015-12-01

Bulk translation of the inner core has been proposed to explain quasi-hemispheric patterns of seismic heterogeneity. Such a translation would result in differential melting and freezing at the inner core boundary (ICB) and hence a heterogeneous pattern of buoyancy flux that could influence convection in the outer core. This heterogeneous flux at the ICB will tend to promote upwelling on the trailing hemisphere, where enhanced inner core growth results in increased latent heat and light element release, and inhibit upwelling on the leading hemisphere, where melting of the inner core occurs. If this difference in convective driving between the two hemispheres propagated across the thickness of the outer core, then flows near the surface of the core could be linked to the ICB heterogeneity and result in a hemispheric imbalance in the geomagnetic field. We have investigated the influence of such ICB boundary conditions on core flows and magnetic field structure in numerical geodynamo models and analysed the resultant hemispheric imbalance relative to the hemispheric structure in models constructed from observations of Earth's field. Inner core translation at rates consistent with estimates for the Earth produce a strong hemispheric bias in the field, one that should be readily apparent in averages of the field over tens of thousands of years. Current models of the field over the Holocene may be able to rule out the most extreme ICB forcing scenarios, but more information on the dynamic structure of the field over these time scales will be needed to adequately test all cases.

Zircon U-Pb ages and Hf-O isotopic composition of migmatites from the Zanjan-Takab complex, NW Iran: Constraints on partial melting of metasediments

NASA Astrophysics Data System (ADS)

Moghadam, Hadi Shafaii; Li, Xian-Hua; Stern, Robert J.; Ghorbani, Ghasem; Bakhshizad, Farzaneh

2016-01-01

We study migmatites and other metamorphic rocks in the Zanjan-Takab region of NW Iran and use these results to report the first evidence of Oligocene core complex formation in Iran. Four samples of migmatites associated with paragneisses, including leucosomes and associated para-amphibolite melanosomes were selected for U-Pb dating and Hf-O isotopic analysis. Zircon cores - interpreted as originally detrital zircons - have variable ages that peak at ca. 100-110 Ma, but their sedimentation age - indicated by the youngest 206Pb/238U ages - is ca. 35-40 Ma. New zircons associated with incipient melting occur as overgrowths around zircon cores and/or as newly grown grains. Morphologies and internal structures suggest that rim growth and formation of new zircons were associated with partial melting. All four samples contain zircons with rims that yield 206Pb/238U ages of 28-25 Ma, indicating that partial melting occurred in Late Oligocene time. δ18O values for zircon rims vary between 8.2 and 12.3‰, significantly higher than expected for mantle inputs (δ18O 6‰) and consistent with equilibrium with surface materials. Zircon rims yield εHf(t) between 2.2 and 12.4 and two-stage Hf model ages of 448-562 Ma, indicating that the region is underlain by Cadomian-Caledonian crust. According to the Hf-O isotopic values, the main mechanism forming zircon rims was dissolution of pre-existing detrital zircons with reprecipitation of new zircon shortly thereafter. Oligocene ages indicate that partial melting accompanied core complex formation in the Zanjan-Takab region. Extension, melting, and core complex formation in south-central Iran are Eocene in age, but younger ages of Oligocene-Miocene in NW Iran and Turkey indicate that extension was distributed throughout the region during Cenozoic time.

The Gao-Guenie impact melt breccia—Sampling a rapidly cooled impact melt dike on an H chondrite asteroid?

NASA Astrophysics Data System (ADS)

Schmieder, Martin; Kring, David A.; Swindle, Timothy D.; Bond, Jade C.; Moore, Carleton B.

2016-06-01

The Gao-Guenie H5 chondrite that fell on Burkina Faso (March 1960) has portions that were impact-melted on an H chondrite asteroid at ~300 Ma and, through later impact events in space, sent into an Earth-crossing orbit. This article presents a petrographic and electron microprobe analysis of a representative sample of the Gao-Guenie impact melt breccia consisting of a chondritic clast domain, quenched melt in contact with chondritic clasts, and an igneous-textured impact melt domain. Olivine is predominantly Fo80-82. The clast domain contains low-Ca pyroxene. Impact melt-grown pyroxene is commonly zoned from low-Ca pyroxene in cores to pigeonite and augite in rims. Metal-troilite orbs in the impact melt domain measure up to ~2 mm across. The cores of metal orbs in the impact melt domain contain ~7.9 wt% of Ni and are typically surrounded by taenite and Ni-rich troilite. The metallography of metal-troilite droplets suggest a stage I cooling rate of order 10 °C s-1 for the superheated impact melt. The subsolidus stage II cooling rate for the impact melt breccia could not be determined directly, but was presumably fast. An analogy between the Ni rim gradients in metal of the Gao-Guenie impact melt breccia and the impact-melted H6 chondrite Orvinio suggests similar cooling rates, probably on the order of ~5000-40,000 °C yr-1. A simple model of conductive heat transfer shows that the Gao-Guenie impact melt breccia may have formed in a melt injection dike ~0.5-5 m in width, generated during a sizeable impact event on the H chondrite parent asteroid.

Melting and Crystallization at Core Mantle Boundary

NASA Astrophysics Data System (ADS)

Fiquet, G.; Pradhan, G. K.; Siebert, J.; Auzende, A. L.; Morard, G.; Antonangeli, D.; Garbarino, G.

2015-12-01

Early crystallization of magma oceans may generate original compositional heterogeneities in the mantle. Dense basal melts may also be trapped in the lowermost mantle and explain mantle regions with ultralow seismic velocities (ULVZs) near the core-mantle boundary [1]. To test this hypothesis, we first constructed the solidus curve of a natural peridotite between 36 and 140 gigapascals using laser-heated diamond anvil cells. In our experiments, melting at core-mantle boundary pressures occurs around 4100 ± 150 K, which is a value that can match estimated mantle geotherms. Similar results were found for a chondritic mantle [2] whereas much lower pyrolitic melting temperatures were recently proposed from textural and chemical characterizations of quenched samples [3]. We also investigated the melting properties of natural mid ocean ridge basalt (MORB) up to core-mantle boundary (CMB) pressures. At CMB pressure (135 GPa), we obtain a MORB solidus temperature of 3950 ±150 K. If our solidus temperatures are in good agreement with recent results proposed for a similar composition [4], the textural and chemical characterizations of our recovered samples made by analytical transmission electron microscope indicate that CaSiO3 perovskite (CaPv) is the liquidus phase in the entire pressure range up to CMB. The partial melt composition is enriched in FeO, which suggests that such partial melts could be gravitationnally stable at the core mantle boundary. Our observations are tested against calculations made using a self-consistent thermodynamic database for the MgO-FeO-SiO2 system from 20 GPa to 140 GPa [5]. These observations and calculations provide a first step towards a consistent thermodynamic modelling of the crystallization sequence of the magma ocean, which shows that the existence of a dense iron rich and fusible layer above the CMB at the end of the crystallization is plausible [5], which is in contradiction with the conclusions drawn in [4]. [1] Williams & Garnero (1996) Science 273, 1528. [2] Andrault et al. (2011), EPSL 304, 251. [3] Nomura et al. (2014) Science 343, 522. [4] Andrault et al. (2014) Science 344, 892. [5] Boukaré et al (2015) J.Geophys. Res, in press.

The effect of changing wind forcing on Antarctic ice shelf melting in high-resolution, global sea ice-ocean simulations with the Accelerated Climate Model for Energy (ACME)

NASA Astrophysics Data System (ADS)

Asay-Davis, Xylar; Price, Stephen; Petersen, Mark; Wolfe, Jonathan

2017-04-01

The capability for simulating sub-ice shelf circulation and submarine melting and freezing has recently been added to the U.S. Department of Energy's Accelerated Climate Model for Energy (ACME). With this new capability, we use an eddy permitting ocean model to conduct two sets of simulations in the spirit of Spence et al. (GRL, 41, 2014), who demonstrate increased warm water upwelling along the Antarctic coast in response to poleward shifting and strengthening of Southern Ocean westerly winds. These characteristics, symptomatic of a positive Southern Annular Mode (SAM), are projected to continue into the 21st century under anthropogenic climate change (Fyfe et al., J. Clim., 20, 2007). In our first simulation, we force the climate model using the standard CORE interannual forcing dataset (Large and Yeager; Clim. Dyn., 33, 2009). In our second simulation, we force our climate model using an altered version of CORE interannual forcing, based on the latter half of the full time series, which we take as a proxy for a future climate state biased towards a positive SAM. We compare ocean model states and sub-ice shelf melt rates with observations, exploring sources of model biases as well as the effects of the two forcing scenarios.

Model for the formation of the earth's core

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCammon, C.A.; Ringwood, A.E.; Jackson, I.

1983-02-15

The recent discovery of a phase transformation in Fe/sub 0.94/O by Jeanloz and Ahrens has allowed a more detailed development of a model for core formation involving oxygen as the principal light alloying element in the core. It is predicted, based on calculations, that an increasing pressure in the system FeO-MgO will result in a gradual exsolution of an almost pure high-pressure phase FeO(hpp), leaving an iron-depleted (Fe,Mg)O rocksalt (B1) phase. We also predict that FeO(hhp) will form a low-melting point alloy with Fe at high temperature and high pressure. On the basis of our interpretations, we have constructed amore » model for core segregation. Assuming the earth to have accreted from the primordial solar nebula as a relatively homogeneous mixture of metallic iron and silicate-oxide phases, core segregation involving oxygen would commence at a depth where pressure is sufficiently high to cause exsolution of FeO(hpp) from the rocksalt phase, and temperature is sufficiently high to allow formation of an Fe-FeO(hpp) melt. A gravitational instability arises, leading to vertical differentiation of the earth as molten blobs of the metal sink downwards to form the core and the residual depleted silicate material coalesces to form large bodies which rise diapirically upwards to form the mantle.« less

A scaling relationship for impact-induced melt volume

NASA Astrophysics Data System (ADS)

Nakajima, M.; Rubie, D. C.; Melosh, H., IV; Jacobson, S. A.; Golabek, G.; Nimmo, F.; Morbidelli, A.

2016-12-01

During the late stages of planetary accretion, protoplanets experience a number of giant impacts and extensive mantle melting. The impactor's core sinks through the molten part of the target mantle (magma ocean) and experiences metal-silicate partitioning (e.g., Stevenson, 1990). For understanding the chemical evolution of the planetary mantle and core, we need to determine the impact-induced melt volume because the partitioning strongly depends on the ranges of the pressures and temperatures within the magma ocean. Previous studies have investigated the effects of small impacts (i.e. impact cratering) on melt volume, but those for giant impacts are not well understood yet. Here, we perform giant impact simulations to derive a scaling law for melt volume as a function of impact velocity, impact angle, and impactor-to-target mass ratio. We use two different numerical codes, namely smoothed particle hydrodynamics we developed (SPH, a particle method) and the code iSALE (a grid-based method) to compare their outcomes. Our simulations show that these two codes generally agree as long as the same equation of state is used. We also find that some of the previous studies developed for small impacts (e.g., Abramov et al., 2012) overestimate giant impact melt volume by orders of magnitudes partly because these models do not consider self-gravity of the impacting bodies. Therefore, these models may not be extrapolated to large impacts. Our simulations also show that melt volume can be scaled by the total mass of the system. In this presentation, we further discuss geochemical implications for giant impacts on planets, including Earth and Mars.

Thermal Modeling of the Injection of Standard and Thermally Insulated Cored Wire

NASA Astrophysics Data System (ADS)

Castro-Cedeno, E.-I.; Jardy, A.; Carré, A.; Gerardin, S.; Bellot, J. P.

2017-12-01

Cored wire injection is a widespread method used to perform alloying additions during ferrous and non-ferrous liquid metal treatment. The wire consists of a metal casing that is tightly wrapped around a core of material; the casing delays the release of the material as the wire is immersed into the melt. This method of addition presents advantages such as higher repeatability and yield of cored material with respect to bulk additions. Experimental and numerical work has been performed by several authors on the subject of alloy additions, spherical and cylindrical geometries being mainly considered. Surprisingly this has not been the case for cored wire, where the reported experimental or numerical studies are scarce. This work presents a 1-D finite volume numerical model aimed for the simulation of the thermal phenomena which occurs when the wire is injected into a liquid metal bath. It is currently being used as a design tool for the conception of new types of cored wire. A parametric study on the effect of injection velocity and steel casing thickness for an Al cored wire immersed into a steel melt at 1863 K (1590 °C) is presented. The standard single casing wire is further compared against a wire with multiple casings. Numerical results show that over a certain range of injection velocities, the core contents' release is delayed in the multiple casing when compared to a single casing wire.

Fukushima Daiichi Unit 1 Ex-Vessel Prediction: Core Concrete Interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robb, Kevin R; Farmer, Mitchell; Francis, Matthew W

Lower head failure and corium concrete interaction were predicted to occur at Fukushima Daiichi Unit 1 (1F1) by several different system-level code analyses, including MELCOR v2.1 and MAAP5. Although these codes capture a wide range of accident phenomena, they do not contain detailed models for ex-vessel core melt behavior. However, specialized codes exist for analysis of ex-vessel melt spreading (e.g., MELTSPREAD) and long-term debris coolability (e.g., CORQUENCH). On this basis, an analysis was carried out to further evaluate ex-vessel behavior for 1F1 using MELTSPREAD and CORQUENCH. Best-estimate melt pour conditions predicted by MELCOR v2.1 and MAAP5 were used as input.more » MELTSPREAD was then used to predict the spatially dependent melt conditions and extent of spreading during relocation from the vessel. The results of the MELTSPREAD analysis are reported in a companion paper. This information was used as input for the long-term debris coolability analysis with CORQUENCH.« less

From Mush to Eruption in 1000 Years: Rapid Assembly of the Super-Sized Oruanui Magma Body

NASA Astrophysics Data System (ADS)

Allan, A. S.; Morgan, D. J.; Wilson, C. J.; Millet, M.

2012-12-01

The mush model is useful in explaining how large volumes of evolved silicic melt can be generated in and extracted from a crystal-rich source to form crystal-poor rhyolite magma bodies at shallow crustal levels. It is unclear, however, how processes of melt extraction and/or formation of the melt-dominant magma body might be reflected in the crystal record, and what physical and temporal constraints can be applied. Textural observations and in situ geochemical fingerprints in crystals from pumices of the ~25.4 ka Oruanui eruption (Taupo, New Zealand), offer new perspectives on the processes, physical conditions and timing of the melt extraction and accumulation. Almost all orthopyroxene (opx) and plagioclase (plag) cores have textures showing a period of disequilibrium (partial dissolution and/or resorption) followed by stable conditions (infilling of raddled cores; euhedral rim overgrowths). Trace element contents in amphibole (amph), which was stable and actively crystallizing in all but the most evolved parcels of Oruanui magma, complement textural evidence showing that Mn and Zn liberated by opx dissolution were preferentially sequestered in amph. Concentrations of these opx-loving elements show a prominent inflection when plotted against indices of melt evolution (e.g. Eu/Eu* in amph) marking a return to opx stability and subsequent crystallization. Plagioclase, the most abundant crystal phase, records a more complex history with significant inheritance, but textural and chemical evidence suggests that at least some of Oruanui plag crystals experienced the same departure from and return to stability as the opx. Amphibole trace element data are linked to in situ estimates of P-T-fO2 and melt H2O determined via the Ridolfi et al. (2010: Contrib Mineral Petrol 160, 45) thermobarometer. Textural and geochemical evidence combined with P-T-H2O model values indicate that three major Oruanui crystal phases (opx, amph, plag) record a significant decompression event (from ~250 to ~150 MPa) with associated cooling (from ~900 to 820°C) coupled with the destabilization of opx. We interpret this event to reflect the extraction of rhyolitic melt plus crystals from a mush-like reservoir to form the Oruanui melt-dominant body. This body grew within model pressures of 90-150 MPa (~4-6 km depth) held at 760-800°C, with a generally homogeneous melt composition, as reflected in the consistent rim compositions of the three mineral phases. Fe-Mg diffusion modelling of core-rim boundaries in opx implies that accumulation of the ~530 km3 melt dominant body began only ca. 1000 years before eruption. The traditionally envisaged quasi-static drivers of the mush model (crystal settling, gas sparging, etc.) are difficult to reconcile with the rapidity of this timeframe, and a more dynamic, external influence (e.g. from extensional tectonics) is implied.

Experimental constraints on melting temperatures in the MgO-SiO2 system at lower mantle pressures

NASA Astrophysics Data System (ADS)

Baron, Marzena A.; Lord, Oliver T.; Myhill, Robert; Thomson, Andrew R.; Wang, Weiwei; Trønnes, Reidar G.; Walter, Michael J.

2017-08-01

Eutectic melting curves in the system MgO-SiO2 have been experimentally determined at lower mantle pressures using laser-heated diamond anvil cell (LH-DAC) techniques. We investigated eutectic melting of bridgmanite plus periclase in the MgO-MgSiO3 binary, and melting of bridgmanite plus stishovite in the MgSiO3-SiO2 binary, as analogues for natural peridotite and basalt, respectively. The melting curve of model basalt occurs at lower temperatures, has a shallower dT / dP slope and slightly less curvature than the model peridotitic melting curve. Overall, melting temperatures detected in this study are in good agreement with previous experiments and ab initio simulations at ∼25 GPa (Liebske and Frost, 2012; de Koker et al., 2013). However, at higher pressures the measured eutectic melting curves are systematically lower in temperature than curves extrapolated on the basis of thermodynamic modelling of low-pressure experimental data, and those calculated from atomistic simulations. We find that our data are inconsistent with previously computed melting temperatures and melt thermodynamic properties of the SiO2 endmember, and indicate a maximum in short-range ordering in MgO-SiO2 melts close to Mg2SiO4 composition. The curvature of the model peridotite eutectic relative to an MgSiO3 melt adiabat indicates that crystallization in a global magma ocean would begin at ∼100 GPa rather than at the bottom of the mantle, allowing for an early basal melt layer. The model peridotite melting curve lies ∼ 500 K above the mantle geotherm at the core-mantle boundary, indicating that it will not be molten unless the addition of other components reduces the solidus sufficiently. The model basalt melting curve intersects the geotherm at the base of the mantle, and partial melting of subducted oceanic crust is expected.

Overturn of magma ocean ilmenite cumulate layer: Implications for lunar magmatic evolution and formation of a lunar core

NASA Technical Reports Server (NTRS)

Hess, P. C.; Parmentier, E. M.

1993-01-01

We explore a model for the chemical evolution of the lunar interior that explains the origin and evolution of lunar magmatism and possibly the existence of a lunar core. A magma ocean formed during accretion differentiates into the anorthositic crust and chemically stratified cumulate mantle. The cumulative mantle is gravitationally unstable with dense ilmenite cumulate layers overlying olivine-orthopyroxene cumulates with Fe/Mg that decreases with depth. The dense ilmenite layer sinks to the center of the moon forming the core. The remainder of the gravitationally unstable cumulate pile also overturns. Any remaining primitive lunar mantle rises to its level of neutral buoyancy in the cumulate pile. Perhaps melting of primitive lunar mantle due to this decompression results in early lunar Mg-rich magmatism. Because of its high concentration of incompatible heat producing elements, the ilmenite core heats the overlying orthopyroxene-bearing cumulates. As a conductively thickening thermal boundary layer becomes unstable, the resulting mantle plumes rise, decompress, and partially melt to generate the mare basalts. This model explains both the timing and chemical characteristics of lunar magmatism.

Triple point fcc-hcp-liquid in the Fe phase diagram determined by in-situ XANES diagnostic and post-mortem XRD and FIB-SEM analysis.

NASA Astrophysics Data System (ADS)

Morard, G.; Boccato, S.; Rosa, A. D.; Anzellini, S.; Miozzi Ferrini, F.; Laura, H.; Garbarino, G.; Harmand, M.; Guyot, F. J.; Boulard, E.; Kantor, I.; Irifune, T.; Torchio, R.

2017-12-01

Iron is the main constituent of planetary cores. Studying its phase diagram under high pressure is necessary to constrain properties of planetary interiors, and to model key parameters such as the generation of magnetic field. Though, strong controversy on the melting curve of pure Fe still remains. Recently, Aquilanti et al, (PNAS, 2015) reported a Fe melting curved based on XANES measurements which is in open disagreement with previous X-ray diffraction results (Anzellini et al, Science, 2013). Discrepancies in the melting temperature exceed several hundred degrees close to Mbar pressures, which may be related to differences in temperature measurement techniques, melting diagnostics, or to chemical reactions of the sample with the surrounding medium. We therefore performed new in situ high P/T XANES experiments on pure Fe (up to 115 GPa and 4000 K) at the ESRF beamline ID24, combining the energy dispersive absorption set up with laser heated diamond anvil cells. X-ray diffraction maps were collected from all recovered samples in order to identify and characterize laser-heated spots. The XANES melting criterion was further cross checked by analyzing the recovered sample textures using FIB cutting techniques and SEM imaging. We found systematically that low melting temperatures are related to the presence of Fe3C, implying that in those cases chemical reactions occurred during heating resulting in carbon contamination from the diamonds. These low melting points fall onto the melting line reported by Aquilanti et al, (2015). Uncontaminated points are in agreement with the melting curve of Anzellini et al, (2013) within their uncertainties. Moreover, this data set allowed us to refine the location of the triple point in the Fe phase diagram at 105 (±10) GPa and 3600 (±200) K, which may imply a small kink in the melting curve around this point. This refined Fe phase diagram could be then used to compute thermodynamic models for planetary cores.

Translation and convection of Earth's inner core

NASA Astrophysics Data System (ADS)

Monnereau, M.; Calvet, M.; Margerin, L.; Mizzon, H.; Souriau, A.

2012-12-01

The image of the inner core growing slowly at the center of the Earth by gradual cooling and solidification of the surrounding liquid outer core is being replaced by the more vigorous image of a ``deep foundry'', where melting and crystallization rates exceed by many times the net growth rate. Recently, a particular mode of convection, called translation, has been put forward as an important mode of inner core dynamics because this mechanism is able to explain the observed East-West asymmetry of P-wave velocity and attenuation (Monnereau et al. 2010). Translation is a pure solid displacement of the inner core material (solid iron) within its envelop, implying crystallization of entering iron on one side of the inner core and melting on the opposite side. Translation is consistent with multiple scattering models of wave propagation. If they do not experience deformation, iron crystals grow as they transit from one hemisphere to the other. Larger crystals constituting a faster and more attenuating medium, a translation velocity of some cm/yr (about ten times the growth rate) is enough to account for the superficial asymmetry observed for P-wave velocity and attenuation, with grains of a few hundred meters on the crystallizing side (West) growing up to a few kilometers before melting on the East side, and a drift direction located in the equatorial plane. Among all hypotheses that have been proposed to account for the seismic asymmetry, translation is the only one based on a demonstrated link between the seismic data and the proposed dynamics, notably through a model of seismic wave propagation. This mechanism was also proposed to be responsible for the formation of a dense layer at the bottom of the outer core, since the high rate of melting and crystallization would release a liquid depleted in light elements at the surface of the inner core (Alboussiere et al 2010). This would explain the anomalously low gradient of P wave velocity in the lowermost 200 km of the outer core. Translation is a particular solution of Navier-Stokes equation with permeable boundary conditions, but depending on the viscosity of the solid core, modes with higher spherical harmonics degree can develop. At low viscosity, these modes can be dominant and dissipate the degree l=1 of thermal heterogeneities. Hence, a viscosity threshold may be expected below which translation cannot take place, thereby constraining the viscosity of iron at inner core conditions. Using a hybrid finite-difference spherical harmonics Navier-Stokes solver, we investigate the interplay between translation and convection in a 3D spherical model with permeable boundary conditions. Our numerical simulations show the dominance of pure translation for viscosities of the inner core higher than 5 x 1018 Pas. Translation is almost completely hampered by convective motions for viscosities lower than 1017 Pas and the phase change becomes an almost impermeable boundary. Between these values, a well developed circulation at the harmonic degree l=1 persists, but composed of localized cold downwellings, a passive upward flow taking place on the opposite side (the melting side). Such a convective structure remains compatible with the seismic asymmetry. Alboussiere, T., Deguen, R., Melzani, M., 2010. Nature 466 (7307), 744-U9. Monnereau, M., Calvet, M., Margerin, L., Souriau, A., 2010. Science 328 (5981), 1014-1017.

Melt in the impact breccias from the Eyreville drill cores, Chesapeake Bay impact structure, USA

NASA Astrophysics Data System (ADS)

Bartosova, Katerina; Hecht, Lutz; Koeberl, Christian; Libowitzky, Eugen; Reimold, Wolf Uwe

2011-03-01

The center of the 35.3 Ma Chesapeake Bay impact structure (85 km diameter) was drilled during 2005/2006 in an ICDP-0USGS drilling project. The Eyreville drill cores include polymict impact breccias and associated rocks (1397-01551 m depth). Tens of melt particles from these impactites were studied by optical and electron microscopy, electron microprobe, and microRaman spectroscopy, and classified into six groups: m1—clear or brownish melt, m2—brownish melt altered to phyllosilicates, m3—colorless silica melt, m4—melt with pyroxene and plagioclase crystallites, m5—dark brown melt, and m6—melt with globular texture. These melt types have partly overlapping major element abundances, and large compositional variations due to the presence of schlieren, poorly mixed melt phases, partly digested clasts, and variable crystallization and alteration. The different melt types also vary in their abundance with depth in the drill core. Based on the chemical data, mixing calculations were performed to determine possible precursors of these melt particles. The calculations suggest that most melt types formed mainly from the thick sedimentary section of the target sequence (mainly the Potomac Formation), but an additional crystalline basement (schist/gneiss) precursor is likely for the most abundant melt types m2 and m5. Sedimentary rocks with compositions similar to those of the melt particles are present among the Eyreville core samples. Therefore, sedimentary target rocks were the main precursor of the Eyreville melt particles. However, the composition of the melt particles is not only the result of the precursor composition but also the result of changes during melting and solidification, as well as postimpact alteration, which must also be considered. The variability of the melt particle compositions reflects the variety of target rocks and indicates that there was no uniform melt source. Original heterogeneities, resulting from melting of different target rocks, may be preserved in impactites of some large impact structures that formed in volatile-rich targets, because no large melt body exists, in which homogenization would have taken place.

Ocean interactions with the base of Amery Ice Shelf, Antarctica

NASA Technical Reports Server (NTRS)

Hellmer, Hartmut H.; Jacobs, Stanley S.

1992-01-01

Using a two-dimensional ocean themohaline circulation model, we varied the cavity shape beneath Amery Ice Shelf in an attempt to reproduce the 150-m-thick marine ice layer observed at the 'G1' ice core site. Most simulations caused melting rates which decrease the ice thickness by as much as 400 m between grounding line and G1, but produce only minor accumulation at the ice core site and closer to the ice front. Changes in the sea floor and ice topographies revealed a high sensitivity of the basal mass balance to water column thickness near the grounding line, to submarine sills, and to discontinuities in ice thickness. Model results showed temperature/salinity gradients similar to observations from beneath other ice shelves where ice is melting into seawater. Modeled outflow characteristics at the ice front are in general agreement with oceanographic data from Prydz Bay. We concur with Morgan's inference that the G1 core may have been taken in a basal crevasse filled with marine ice. This ice is formed from water cooled by ocean/ice shelf interactions along the interior ice shelf base.

Partial melting of lower oceanic crust gabbro: Constraints from poikilitic clinopyroxene primocrysts

NASA Astrophysics Data System (ADS)

Leuthold, Julien; Lissenberg, C. Johan; O'Driscoll, Brian; Karakas, Ozge; Falloon, Trevor; Klimentyeva, Dina N.; Ulmer, Peter

2018-03-01

Successive magma batches underplate, ascend, stall and erupt along spreading ridges, building the oceanic crust. It is therefore important to understand the processes and conditions under which magma differentiates at mid ocean ridges. Although fractional crystallization is considered to be the dominant mechanism for magma differentiation, open-system igneous complexes also experience Melting-Assimilation-Storage-Hybridization (MASH, Hildreth and Moorbath, 1988) processes. Here, we examine crystal-scale records of partial melting in lower crustal gabbroic cumulates from the slow-spreading Atlantic oceanic ridge (Kane Megamullion; collected with Jason ROV) and the fast-spreading East Pacific Rise (Hess Deep; IODP expedition 345). Clinopyroxene oikocrysts in these gabbros preserve marked intra-crystal geochemical variations that point to crystallization-dissolution episodes of the gabbro eutectic assemblage. Kane Megamullion and Hess Deep clinopyroxene core1 primocrysts and their plagioclase inclusions indicate crystallization from high temperature basalt (>1160 and >1200°C, respectively), close to clinopyroxene saturation temperature (<50% and <25% crystallization). Step-like compatible Cr (and co-varying Al) and incompatible Ti, Zr, Y and rare earth elements (REE) decrease from anhedral core1 to overgrown core2, while Mg# and Sr/Sr* ratios increase. We show that partial resorption textures and geochemical zoning result from partial melting of REE-poor lower oceanic crust gabbroic cumulate (protolith) following intrusion by hot primitive mantle-derived melt, and subsequent overgrowth crystallization (refertilization) from a hybrid melt. In addition, towards the outer rims of crystals, Ti, Zr, Y and the REE strongly increase and Al, Cr, Mg#, Eu/Eu* and Sr/Sr* decrease, suggesting crystallization either from late-stage percolating relatively differentiated melt or from in situ trapped melt. Intrusion of primitive hot reactive melt and percolation of interstitial differentiated melt are two distinct MASH processes in the lower oceanic crust. They are potentially fundamental mechanisms for generating the wide compositional variation observed in mid-ocean ridge basalts. We furthermore propose that such processes operate at both slow- and fast-spreading ocean ridges. Thermal numerical modelling shows that the degree of lower crustal partial melting at slow-spreading ridges can locally increase up to 50%, but the overall crustal melt volume is low (less than ca. 5% of total mantle-derived and crustal melts; ca. 20% in fast-spreading ridges).

Detectability of temporal changes in fine structures near the inner core boundary beneath the eastern hemisphere

NASA Astrophysics Data System (ADS)

Yu, Wen-che

2016-04-01

The inner core boundary (ICB), where melting and solidification of the core occur, plays a crucial role in the dynamics of the Earth's interior. To probe temporal changes near the ICB beneath the eastern hemisphere, I analyze differential times of PKiKP (dt(PKiKP)), double differential times of PKiKP-PKPdf, and PKiKP coda waves from repeating earthquakes in the Southwest Pacific subduction zones. Most PKiKP differential times are within ±30 ms, comparable to inherent travel time uncertainties due to inter-event separations, and suggest no systematic changes as a function of calendar time. Double differential times measured between PKiKP codas and PKiKP main phases show promising temporal changes, with absolute values of time shifts of >50 ms for some observations. However, there are discrepancies among results from different seismographs in the same calendar time window. Negligible changes in PKiKP times, combined with changes in PKiKP coda wave times on 5 year timescales, favor a smooth inner core boundary with fine-scale structures present in the upper inner core. Differential times of PKiKP can be interpreted in the context of either melting based on translational convection, or growth based on thermochemical mantle-inner core coupling. Small dt(PKiKP) values with inherent uncertainties do not have sufficient resolution to distinguish the resultant longitudinal (melting) and latitudinal (growth) dependencies predicted on the basis of the two models on 5 year timescales.

Molybdenum Valence in Basaltic Silicate Melts

NASA Technical Reports Server (NTRS)

Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Pando, K.

2010-01-01

The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

Fukushima Daiichi Unit 1 Ex-Vessel Prediction: Core-Concrete Interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robb, Kevin R.; Farmer, Mitchell T.; Francis, Matthew W.

Lower head failure and corium-concrete interaction were predicted to occur at Fukushima Daiichi Unit 1 (1F1) by several different system-level code analyses, including MELCOR v2.1 and MAAP5. Although these codes capture a wide range of accident phenomena, they do not contain detailed models for ex-vessel core melt behavior. However, specialized codes exist for the analysis of ex-vessel melt spreading (e.g., MELTSPREAD) and long-term debris coolability (e.g., CORQUENCH). On this basis, in this paper an analysis was carried out to further evaluate ex-vessel behavior for 1F1 using MELTSPREAD and CORQUENCH. Best-estimate melt pour conditions predicted by MELCOR v2.1 and MAAP5 weremore » used as input. MELTSPREAD was then used to predict the spatially dependent melt conditions and extent of spreading during relocation from the vessel. The results of the MELTSPREAD analysis are reported in a companion paper. This information was used as input for the long-term debris coolability analysis with CORQUENCH. For the MELCOR-based melt pour scenario, CORQUENCH predicted the melt would readily cool within 2.5 h after the pour, and the sumps would experience limited ablation (approximately 18 cm) under water-flooded conditions. Finally, for the MAAP-based melt pour scenarios, CORQUENCH predicted that the melt would cool in approximately 22.5 h, and the sumps would experience approximately 65 cm of concrete ablation under water-flooded conditions.« less

Fukushima Daiichi Unit 1 Ex-Vessel Prediction: Core-Concrete Interaction

DOE PAGES

Robb, Kevin R.; Farmer, Mitchell T.; Francis, Matthew W.

2016-10-31

Lower head failure and corium-concrete interaction were predicted to occur at Fukushima Daiichi Unit 1 (1F1) by several different system-level code analyses, including MELCOR v2.1 and MAAP5. Although these codes capture a wide range of accident phenomena, they do not contain detailed models for ex-vessel core melt behavior. However, specialized codes exist for the analysis of ex-vessel melt spreading (e.g., MELTSPREAD) and long-term debris coolability (e.g., CORQUENCH). On this basis, in this paper an analysis was carried out to further evaluate ex-vessel behavior for 1F1 using MELTSPREAD and CORQUENCH. Best-estimate melt pour conditions predicted by MELCOR v2.1 and MAAP5 weremore » used as input. MELTSPREAD was then used to predict the spatially dependent melt conditions and extent of spreading during relocation from the vessel. The results of the MELTSPREAD analysis are reported in a companion paper. This information was used as input for the long-term debris coolability analysis with CORQUENCH. For the MELCOR-based melt pour scenario, CORQUENCH predicted the melt would readily cool within 2.5 h after the pour, and the sumps would experience limited ablation (approximately 18 cm) under water-flooded conditions. Finally, for the MAAP-based melt pour scenarios, CORQUENCH predicted that the melt would cool in approximately 22.5 h, and the sumps would experience approximately 65 cm of concrete ablation under water-flooded conditions.« less

Preparation and evaluation of metoprolol tartrate sustained-release pellets using hot melt extrusion combined with hot melt coating.

PubMed

Yang, Yan; Shen, Lian; Li, Juan; Shan, Wei-Guang

2017-06-01

The objective of this study was to prepare and evaluate metoprolol tartrate sustained-release pellets. Cores were prepared by hot melt extrusion and coated pellets were prepared by hot melt coating. Cores were found to exist in a single-phase state and drug in amorphous form. Plasticizers had a significant effect on torque and drug content, while release modifiers and coating level significantly affected the drug-release behavior. The mechanisms of drug release from cores and coated pellets were Fickian diffusion and diffusion-erosion. The coated pellets exhibited sustained-release properties in vitro and in vivo.

Some aspects of core formation in Mercury

NASA Technical Reports Server (NTRS)

Solomon, S. C.

1976-01-01

Some questions dealing with the nature and history of a large metallic core within Mercury are considered. These include the existence of a core, its size, whether it is fluid or solid, the timescale for core formation, the geological consequences of core formation, and whether such consequences are consistent with the surface geology. Several indirect lines of evidence are discussed which suggest the presence of a large iron-rich core. A core-formation model is examined in which core infall is accompanied by an increase of 17 km in planetary radius, an increase of 700 K in mean internal temperature, and substantial melting of the mantle. It is argued that if the core differentiated from an originally homogeneous planet, that event must have predated the oldest geological units comprising most of the planetary surface. A convective dynamo model for the source of Mercury's magnetic field is shown to conflict with cosmochemical models that do not predict a substantial radiogenic heat source in the core.

Core segregation mechanism and compositional evolution of terretrial planets

NASA Astrophysics Data System (ADS)

Petford, N.; Rushmer, T.

2009-04-01

A singular event in the formation of the earth and terrestrial planets was the separation iron-rich melt from mantle silicate to form planetary cores. On Earth, and by implication other rocky planets, this process induced profound internal chemical fractionation, with siderophile elements (Ni, Co, Au, Pt, W, Re) following Fe into the core, leaving the silicate crust and mantle with strong depletions of these elements relative to primitive planetary material. Recent measurements of radiogenic 182W anomalies in the silicate Earth, Mars and differentiated meteorites imply that planetesimals segregated metallic cores within a few Myr of the origin of the solar system. Various models have been put forward to explain the physical nature of the segregation mechanism (Fe-diapirs, ‘raining' through a magma ocean), and more recently melt flow via fractures. In this contribution we present the initial results of a numerical study into Fe segregation in a deforming silicate matrix that captures the temperature-dependent effect of liquid metal viscosity on the transport rate. Flow is driven by pressure gradients associated with impact deformation in a growing planetesimal and the fracture geometry is constrained by experimental data on naturally deformed H6 chondrite. Early results suggest that under dynamic conditions, fracture-driven melt flow can in principle be extremely rapid, leading to a significant draining of the Fe-liquid metal and siderophile trace element component on a timescale of hours to days. Fluid transport in planetesimals where deformation is the driving force provides an attractive and simple way of segregating Fe from host silicate as both precursor and primary agent of core formation. The potential for flow of metal-rich melt to induce local magnetic anomalies will also be addressed.

Heat transport in the high-pressure ice mantle of large icy moons

NASA Astrophysics Data System (ADS)

Choblet, Gael; Tobie, Gabriel; Sotin, Christophe; Kalousova, Klara; Grasset, Olivier

2017-04-01

While the existence of a buried ocean sandwiched between surface ice and high-pressure (HP) polymorphs of ice emerges as the most plausible structure for the hundreds-of-kilometers thick hydrospheres within large icy moons of the Solar System (Ganymede, Callisto, Titan), little is known about the thermal structure of the deep HP ice mantle and its dynamics, possibly involving melt production and extraction. This has major implications for the thermal history of these objects as well as on the habitability of their ocean as the HP ice mantle is presumed to limit chemical transport from the rock component to the ocean. Here, we describe 3D spherical simulations of subsolidus thermal convection tailored to the specific structure of the HP ice mantle of large icy moons. Melt production is monitored and melt transport is simplified by assuming instantaneous extraction to the ocean above. The two controlling parameters for these models are the rheology of ice VI and the heat flux from the rock core. Reasonable end-members are considered for both parameters as disagreement remains on the former (especially the pressure effect on viscosity) and as the latter is expected to vary significantly during the moon's history. We show that the heat power produced by radioactive decay within the rock core is mainly transported through the HP ice mantle by melt extraction to the ocean, with most of the melt produced directly above the rock/water interface. While the average temperature in the bulk of the HP ice mantle is always relatively cool when compared to the value at the interface with the rock core (˜ 5 K above the value at the surface of the HP ice mantle), maximum temperatures at all depths are close to the melting point, often leading to the interconnection of a melt path via hot convective plume conduits throughout the HP ice mantle. Overall, we predict long periods of time during these moons' history where water generated in contact with the rock core is transported to the above ocean.

Heat transport in the high-pressure ice mantle of large icy moons

NASA Astrophysics Data System (ADS)

Choblet, G.; Tobie, G.; Sotin, C.; Kalousová, K.; Grasset, O.

2017-03-01

While the existence of a buried ocean sandwiched between surface ice and high-pressure (HP) polymorphs of ice emerges as the most plausible structure for the hundreds-of-kilometers thick hydrospheres within large icy moons of the Solar System (Ganymede, Callisto, Titan), little is known about the thermal structure of the deep HP ice mantle and its dynamics, possibly involving melt production and extraction. This has major implications for the thermal history of these objects as well as on the habitability of their ocean as the HP ice mantle is presumed to limit chemical transport from the rock component to the ocean. Here, we describe 3D spherical simulations of subsolidus thermal convection tailored to the specific structure of the HP ice mantle of large icy moons. Melt production is monitored and melt transport is simplified by assuming instantaneous extraction to the ocean above. The two controlling parameters for these models are the rheology of ice VI and the heat flux from the rock core. Reasonable end-members are considered for both parameters as disagreement remains on the former (especially the pressure effect on viscosity) and as the latter is expected to vary significantly during the moon's history. We show that the heat power produced by radioactive decay within the rock core is mainly transported through the HP ice mantle by melt extraction to the ocean, with most of the melt produced directly above the rock/water interface. While the average temperature in the bulk of the HP ice mantle is always relatively cool when compared to the value at the interface with the rock core (∼ 5 K above the value at the surface of the HP ice mantle), maximum temperatures at all depths are close to the melting point, often leading to the interconnection of a melt path via hot convective plume conduits throughout the HP ice mantle. Overall, we predict long periods of time during these moons' history where water generated in contact with the rock core is transported to the above ocean.

Multistage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf-W Chronometry of Iron Meteorites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neumann, W.; Kruijer, T. S.; Breuer, D.

Iron meteorites provide some of the most direct insights into the processes and timescales of core formation in planetesimals. Of these, group IVB irons stand out by having one of the youngest 182Hf- 182W model ages for metal segregation (2.9 ± 0.6 Ma after solar system formation), as well as the lowest bulk sulfur content and hence highest liquidus temperature. Here in this paper, using a new model for the internal evolution of the IVB parent body, we show that a single stage of metal-silicate separation cannot account for the complete melting of pure Fe metal at the relatively latemore » time given by the Hf-W model age. Instead, a complex metal-silicate separation scenario is required that includes migration of partial silicate melts, formation of a shallow magma ocean, and core formation in two distinct stages of metal segregation. In the first stage, a protocore formed at ≈1.5 Ma via settling of metal particles in a mantle magma ocean, followed by metal segregation from a shallow magma ocean at ≈5.4 Ma. As these stages of metal segregation occurred at different times, the two metal fractions had different 182W compositions. Consequently, the final 182W composition of the IVB core does not correspond to a single differentiation event, but represents the average composition of early- and late-segregated core fractions. Our best fit model indicates an ≈100 km radius for the IVB parent body and provides an accretion age of ≈0.1–0.5 Ma after solar system formation. The computed solidification time is, furthermore, consistent with the Re-Os age for crystallization of the IVB core.« less

Multistage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf-W Chronometry of Iron Meteorites

DOE PAGES

Neumann, W.; Kruijer, T. S.; Breuer, D.; ...

2018-02-01

Iron meteorites provide some of the most direct insights into the processes and timescales of core formation in planetesimals. Of these, group IVB irons stand out by having one of the youngest 182Hf- 182W model ages for metal segregation (2.9 ± 0.6 Ma after solar system formation), as well as the lowest bulk sulfur content and hence highest liquidus temperature. Here in this paper, using a new model for the internal evolution of the IVB parent body, we show that a single stage of metal-silicate separation cannot account for the complete melting of pure Fe metal at the relatively latemore » time given by the Hf-W model age. Instead, a complex metal-silicate separation scenario is required that includes migration of partial silicate melts, formation of a shallow magma ocean, and core formation in two distinct stages of metal segregation. In the first stage, a protocore formed at ≈1.5 Ma via settling of metal particles in a mantle magma ocean, followed by metal segregation from a shallow magma ocean at ≈5.4 Ma. As these stages of metal segregation occurred at different times, the two metal fractions had different 182W compositions. Consequently, the final 182W composition of the IVB core does not correspond to a single differentiation event, but represents the average composition of early- and late-segregated core fractions. Our best fit model indicates an ≈100 km radius for the IVB parent body and provides an accretion age of ≈0.1–0.5 Ma after solar system formation. The computed solidification time is, furthermore, consistent with the Re-Os age for crystallization of the IVB core.« less

Multistage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf-W Chronometry of Iron Meteorites

NASA Astrophysics Data System (ADS)

Neumann, W.; Kruijer, T. S.; Breuer, D.; Kleine, T.

2018-02-01

Iron meteorites provide some of the most direct insights into the processes and timescales of core formation in planetesimals. Of these, group IVB irons stand out by having one of the youngest 182Hf-182W model ages for metal segregation (2.9 ± 0.6 Ma after solar system formation), as well as the lowest bulk sulfur content and hence highest liquidus temperature. Here, using a new model for the internal evolution of the IVB parent body, we show that a single stage of metal-silicate separation cannot account for the complete melting of pure Fe metal at the relatively late time given by the Hf-W model age. Instead, a complex metal-silicate separation scenario is required that includes migration of partial silicate melts, formation of a shallow magma ocean, and core formation in two distinct stages of metal segregation. In the first stage, a protocore formed at ≈1.5 Ma via settling of metal particles in a mantle magma ocean, followed by metal segregation from a shallow magma ocean at ≈5.4 Ma. As these stages of metal segregation occurred at different times, the two metal fractions had different 182W compositions. Consequently, the final 182W composition of the IVB core does not correspond to a single differentiation event, but represents the average composition of early- and late-segregated core fractions. Our best fit model indicates an ≈100 km radius for the IVB parent body and provides an accretion age of ≈0.1-0.5 Ma after solar system formation. The computed solidification time is, furthermore, consistent with the Re-Os age for crystallization of the IVB core.

Emergency deployable core catcher

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosewell, M.P.

An emergency melt down core catcher apparatus for a nuclear reactor having a retrofitable eutectic solute holding vessel connected to a core containment vessel with particle transferring fluid and particles or granules of solid eutectic solute materials contained therein and transferable by automatically operated valve means to transport and position the solid eutectic solute material in a position below the core to catch and react with any partial or complete melt down of the fuel core.

Effects of water, depth and temperature on partial melting of mantle-wedge fluxed by hydrous sediment-melt in subduction zones

NASA Astrophysics Data System (ADS)

Mallik, Ananya; Dasgupta, Rajdeep; Tsuno, Kyusei; Nelson, Jared

2016-12-01

This study investigates the partial melting of variable bulk H2O-bearing parcels of mantle-wedge hybridized by partial melt derived from subducted metapelites, at pressure-temperature (P-T) conditions applicable to the hotter core of the mantle beneath volcanic arcs. Experiments are performed on mixtures of 25% sediment-melt and 75% fertile peridotite, from 1200 to 1300 °C, at 2 and 3 GPa, with bulk H2O concentrations of 4 and 6 wt.%. Combining the results from these experiments with previous experiments containing 2 wt.% bulk H2O (Mallik et al., 2015), it is observed that all melt compositions, except those produced in the lowest bulk H2O experiments at 3 GPa, are saturated with olivine and orthopyroxene. Also, higher bulk H2O concentration increases melt fraction at the same P-T condition, and causes exhaustion of garnet, phlogopite and clinopyroxene at lower temperatures, for a given pressure. The activity coefficient of silica (ϒSiO2) for olivine-orthopyroxene saturated melt compositions (where the activity of silica, aSiO2 , is buffered by the reaction olivine + SiO2 = orthopyroxene) from this study and from mantle melting studies in the literature are calculated. In melt compositions generated at 2 GPa or shallower, with increasing H2O concentration, ϒSiO2 increases from <1 to ∼1, indicating a transition from non-ideal mixing as OH- in the melt (ϒSiO2 <1) to ideal mixing as molecular H2O (ϒSiO2 ∼1). At pressures >2 GPa, ϒSiO2 >1 at higher H2O concentrations in the melt, indicate requirement of excess energy to incorporate molecular H2O in the silicate melt structure, along with a preference for bridging species and polyhedral edge decorations. With vapor saturation in the presence of melt, ϒSiO2 decreases indicating approach towards ideal mixing of H2O in silicate melt. For similar H2O concentrations in the melt, ϒSiO2 for olivine-orthopyroxene saturated melts at 3 GPa is higher than melts at 2 GPa or shallower. This results in melts generated at 3 GPa being more silica-poor than melts at 2 GPa. Thus, variable bulk H2O and pressure of melt generation results in the partial melts from this study varying in composition from phonotephrite to basaltic andesite at 2 GPa and foidite/phonotephrite to basalt at 3 GPa, forming a spectrum of arc magmas. Modeling suggests that the trace element patterns of sediment-melt are unaffected by the process of hybridization within the hotter core of the mantle-wedge. K2O/H2O and H2O/Ce ratios of the sediment-melts are unaffected, within error, by the process of hybridization of the mantle-wedge. This implies that thermometers based on K2O/H2O and H2O/Ce ratios of arc lavas may be used to estimate slab-top temperatures when (a) sediment-melt from the slab reaches the hotter core of the mantle-wedge by focused flow (b) sediment-melt freezes in the overlying mantle at the slab-mantle interface and the hybridized package rises as a mélange diapir and partially melts at the hotter core of the mantle-wedge. Based on the results from this study and previous studies, both channelized and porous flow of sediment-melt/fluid through the sub-arc mantle can explain geochemical signatures of arc lavas under specific geodynamic scenarios of fluid/melt fluxing, hybridization, and subsequent mantle melting.

A Melting Layer Model for Passive/Active Microwave Remote Sensing Applications. Part 1; Model Formulation and Comparison with Observations

NASA Technical Reports Server (NTRS)

Olson, William S.; Bauer, Peter; Viltard, Nicolas F.; Johnson, Daniel E.; Tao, Wei-Kuo

2000-01-01

In this study, a 1-D steady-state microphysical model which describes the vertical distribution of melting precipitation particles is developed. The model is driven by the ice-phase precipitation distributions just above the freezing level at applicable gridpoints of "parent" 3-D cloud-resolving model (CRM) simulations. It extends these simulations by providing the number density and meltwater fraction of each particle in finely separated size categories through the melting layer. The depth of the modeled melting layer is primarily determined by the initial material density of the ice-phase precipitation. The radiative properties of melting precipitation at microwave frequencies are calculated based upon different methods for describing the dielectric properties of mixed phase particles. Particle absorption and scattering efficiencies at the Tropical Rainfall Measuring Mission Microwave Imager frequencies (10.65 to 85.5 GHz) are enhanced greatly for relatively small (approx. 0.1) meltwater fractions. The relatively large number of partially-melted particles just below the freezing level in stratiform regions leads to significant microwave absorption, well-exceeding the absorption by rain at the base of the melting layer. Calculated precipitation backscatter efficiencies at the Precipitation Radar frequency (13.8 GHz) increase in proportion to the particle meltwater fraction, leading to a "bright-band" of enhanced radar reflectivities in agreement with previous studies. The radiative properties of the melting layer are determined by the choice of dielectric models and the initial water contents and material densities of the "seeding" ice-phase precipitation particles. Simulated melting layer profiles based upon snow described by the Fabry-Szyrmer core-shell dielectric model and graupel described by the Maxwell-Garnett water matrix dielectric model lead to reasonable agreement with radar-derived melting layer optical depth distributions. Moreover, control profiles that do not contain mixed-phase precipitation particles yield optical depths that are systematically lower than those observed. Therefore, the use of the melting layer model to extend 3-D CRM simulations appears justified, at least until more realistic spectral methods for describing melting precipitation in high-resolution, 3-D CRM's are implemented.

Asteroid 4 Vesta: A Fully Differentiated Dwarf Planet

NASA Technical Reports Server (NTRS)

Mittlefehldt, David

2014-01-01

One conclusion derived from the study of meteorites is that some of them - most irons, stony irons, some achondrites - hail from asteroids that were heated to the point where metallic cores and basaltic crusts were formed. Telescopic observations show that there remains only one large asteroid with a basaltic crust, 4 Vesta; present day mean radius 263 km. The largest clan of achondrites, the howardite, eucrite and diogenite (HED) meteorites, represent the crust of their parent asteroid. Diogenites are cumulate harzburgites and orthopyroxenites from the lower crust whilst eucrites are cumulate gabbros, diabases and basalts from the upper crust. Howardites are impact-engendered breccias of diogenites and eucrites. A strong case can be made that HEDs are derived from Vesta. The NASA Dawn spacecraft orbited Vesta for 14 months returning data allowing geological, mineralogical, compositional and geophysical interpretations of Vesta's surface and structure. Combined with geochemical and petrological observations of HED meteorites, differentiation models for Vesta can be developed. Proto-Vesta probably consisted of primitive chondritic materials. Compositional evidence, primarily from basaltic eucrites, indicates that Vesta was melted to high degree (>=50%) which facilitated homogenization of the silicate phase and separation of immiscible Fe,Ni metal plus Fe sulphide into a core. Geophysical models based on Dawn data support a core of 110 km radius. The silicate melt vigorously convected and initially followed a path of equilibrium crystallization forming a harzburgitic mantle, possibly overlying a dunitic restite. Once the fraction of crystals was sufficient to cause convective lockup, the remaining melt collected between the mantle and the cool thermal boundary layer. This melt undergoes fractional crystallization to form a dominantly orthopyroxenite (diogenite) lower crust. The initial thermal boundary layer of primitive chondritic material is gradually replaced by a mafic crust through impact disruption and foundering. The quenched mafic crust thickens over time through magma extrusion/intrusion. Melt from the residual magma ocean intrudes and penetrates the mafic crust forming cumulate eucrite plutons, and dikes, sills and flows of basaltic eucrite composition. The post-differentiation vestan structure is thus not too dissimilar from that of terrestrial planets: (i) a metallic core; (ii) an ultramafic mantle comprised of a lower dunitic layer (if melting was substantially <100%) and an upper cumulate harzburgitic layer; (iii) a lower crust of harzburgitic and orthopyroxenitic cumulates; and (iv) an upper mafic crust of basalts and diabases (melt compositions) with cumulate gabbro intrusions. Impacts have excavated to the lower crust and delivered howardites, eucrites and diogenites to Earth, but there is yet no evidence demonstrating excavation of the vestan mantlle.

Melting Penetration Simulation of Fe-U System at High Temperature Using MPS_LER

NASA Astrophysics Data System (ADS)

Mustari, A. P. A.; Yamaji, A.; Irwanto, Dwi

2016-08-01

Melting penetration information of Fe-U system is necessary for simulating the molten core behavior during severe accident in nuclear power plants. For Fe-U system, the information is mainly obtained from experiment, i.e. TREAT experiment. However, there is no reported data on SS304 at temperature above 1350°C. The MPS_LER has been developed and validated to simulate melting penetration on Fe-U system. The MPS_LER modelled the eutectic phenomenon by solving the diffusion process and by applying the binary phase diagram criteria. This study simulates the melting penetration of the system at higher temperature using MPS_LER. Simulations were conducted on SS304 at 1400, 1450 and 1500°C. The simulation results show rapid increase of melting penetration rate.

Two-Phase Dynamics Simulations of the Growth and Instability of Earth's Inner Core

NASA Astrophysics Data System (ADS)

Hernlund, J. W.; Jellinek, M.; Labrosse, S.

2008-12-01

When the center of Earth's core began to freeze from a homogeneous liquid 1-2 billion years ago, its constitution was very likely that of a mushy region. As this incipient inner core grew by further crystallization of the outer core, an increase in gravity force allowed for the solid grains to compress against one another, undergo viscous compaction, and begin to expel remnant fluid out of the inner core by percolation. Meanwhile, inside the inner core the residual fluid and solid remained in equilibrium, and any perturbations that resulted in upwelling of the deformable mush would also be accompanied by decompression melting. Upwelling and melting regions might then increase in liquid fraction, become less dense, and hence buoyant in a way that would propel them upward at a faster rate, setting up a runaway instability and partial Rayleigh-Taylor-like overturn of Earth's inner core. Structures inherited from this event possibly include the distinct innermost inner core posited by seismologists to exist at Earth's centermost 300-600 km. We use a new two-phase dynamics code to model this scenario in axi-symmetric geometry in order to understand whether and when such an instability occurred, what size the core will have been at the onset of instability, and the degree and style of deformation that would have accompanied this episode. We have found that the growth of instability competes with the rate of background melt percolation, such that the instability would only have occurred after the inner core reaches a critical size and expelled a certain amount of liquid from its interior. A linear stability analysis confirms that there is a critical Rayleigh number for the onset of instability at a given radius. The combined constraints show that the inner core is guaranteed to have undergone this kind of instability, at a time and strength governed solely by physical properties such as grain size, density differences between liquid and solid, and viscosities of the phases.

A model that helps explain Sr-isotope disequilibrium between feldspar phenocrysts and melt in large-volume silicic magma systems

USGS Publications Warehouse

Duffield, W.A.; Ruiz, J.

1998-01-01

Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a model by which either more- or less-radiogenic feldspar (or even both within a single eruptive unit) can originate. The model requires a magma body open to interaction with biotite- and feldspar-bearing wall rock. Magma is incrementally contaminated as wall rock melts incongruently. Biotite preferentially melts first, followed by feldspar. Such melting behavior, which is supported by both field and experimental studies, first contaminates magma with a relatively radiogenic addition, followed by a less-radiogenic addition. Feldspar phenocrysts lag behind melt (groundmass of volcanic rock) in incorporating the influx of contaminant, thus resulting in Sr-isotopic disequilibrium between the crystals and melt. The sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process. This model is testable by isotopic fingerprinting of individual feldspar crystals. For a given set of geologic boundary conditions, specific core-to-rim Sr-isotopic profiles are expectable. Moreover, phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history. Initial results of Sr-isotopic fingerprinting of sanidine phenocrysts from the Taylor Creek Rhyolite are consistent with the model. More tests of the model are desirable.Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a model by which either more- or less-radiogenic feldspar (or even both within a single eruptive unit) can originate. The model requires a magma body open to interaction with biotite- and feldspar-bearing wall rock. Magma is incrementally contaminated as wall rock melts incongruently. Biotite preferentially melts first, followed by feldspar. Such melting behavior, which is supported by both field and experimental studies, first contaminates magma with a relatively radiogenic addition, followed by a less-radiogenic addition. Feldspar phenocrysts lag behind melt (groundmass of volcanic rock) in incorporating the influx of contaminant, thus resulting in Sr-isotopic disequilibrium between the crystals and melt. The sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process. This model is testable by isotopic fingerprinting of individual feldspar crystals. For a given set of geologic boundary conditions, specific core-to-rim Sr-isotopic profiles are expectable. Moreover, phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history. Initial results of Sr-isotopic fingerprinting of sanidine phenocrysts from the Taylor Creek Rhyolite are consistent with the model. More tests of the model are desirable.

A Model for Siderophile Element Distribution in Planetary Differentiation

NASA Technical Reports Server (NTRS)

Humayun, M.; Rushmer, T.; Rankenburg, K.; Brandon, A. D.

2005-01-01

Planetary differentiation begins with partial melting of small planetesimals. At low degrees of partial melting, a sulfur-rich liquid segregates by physical mechanisms including deformation-assisted porous flow. Experimental studies of the physical mechanisms by which Fe-S melts segregate from the silicate matrix of a molten H chondrite are part of a companion paper. Geochemical studies of these experimental products revealed that metallic liquids were in equilibrium with residual metal in the H chondrite matrix. This contribution explores the geochemical signatures produced by early stages of core formation. Particularly, low-degree partial melt segregation of Fe-S liquids leaves residual metal in the silicate matrix. Some achondrites appear to be residues of partial melting, e.g., ureilites, which are known to contain metal. The metal in these achondrites may show a distinct elemental signature. To quantify the effect of sulfur on siderophile element contents of residual metal we have developed a model based on recent parametrizations of equilibrium solid metal-liquid metal partitioning experiments.

Drilling into Magma: Experiences at Kīlauea Iki Lava Lake, Hawaii

NASA Astrophysics Data System (ADS)

Helz, R. L.

2017-12-01

Several historic lava lakes (1959 Kīlauea Iki, 1963 Alae, and 1965 Makaopuhi) were drilled in the 20th century, and molten core recovered from them. Kīlauea Iki lava lake, the most extensively studied, was drilled in 1960-62, 1967, 1965, 1976, 1979, 1981 and 1988. A total of 1400 m feet of core was recovered, about 210 m of which was partially molten. The melt fraction varied from near zero to 40-45% by volume, with higher fractions in glassy ooze from below the crust/melt interface. Most of the 1960-1979 drill holes terminated in pre-existing melt-rich internal differentiates; the later (1981, 1988) drill holes were mostly stopped arbitrarily. When melt was reached and the string backed off to wireline the last interval of core, black glassy ooze immediately moved up the borehole. Repeated re-entry and ooze recovery never exhausted the melt-rich sources. The first deep hole that did not hit melt was KI79-1, which was stopped at 62.2 m after recovering 12 m of molten mush. Here the uncased drill hole backfilled not with black glassy ooze but with olivine-rich, partly crystalline mush. The first redrilled core (recovered between 50.8 and 53.9 m), which moved up over a period of 16 days after termination of the original hole, underwent extensive separation of melt from crystals as it flowed upward. After this interval was pulled, drilling resumed with the bottom of the hole at 52.9 m, and uniform olivine-rich mush was recovered from 52.9-54.25 m. Drilling resumed once more at 52.9 m and a further 3 m of ooze recovered. The bit reached a depth of 55.4 m when the core barrel was full, suggesting that the crystal-rich mush was rising into the core barrel spontaneously during drilling. The three cores recovered in reentering KI79-1 show the effect of unloading the confining pressure on mush layers, with melt moving toward the low-pressure area (the bottom of the hole) relative to crystals. All of the crystal-rich mushes are more melt-rich than the original core, with elevated TiO2, K2O and P2O5 levels at the same bulk MgO content. Grain-to-grain contacts were progressively eroded in the melt-inflated mushes, so that the mushes had no internal cohesion. Although their melt contents never reached 50% by volume, they were extremely mobile, rising into the drill hole in minutes rather than the days required for the initial backfilling of the hole.

An early geodynamo driven by exsolution of mantle components from Earth’s core

PubMed Central

Badro, James; Siebert, Julien; Nimmo, Francis

2016-01-01

Terrestrial core formation occurred in the early molten Earth by gravitational segregation of immiscible metal and silicate melts, stripping iron-loving elements from the silicate mantle to the metallic core1–3, and leaving rock-loving components behind. Here we performed experiments showing that at high enough temperature, Earth’s major rock-loving component, magnesium oxide, can also dissolve in core-forming metallic melts. Our data clearly point to a dissolution reaction, and are in agreement with recent DFT calculations4. Using core formation models5, we further show that a high-temperature event during Earth’s accretion (such as the Moon-forming giant impact6) can contribute significant amounts of magnesium to the early core. As it subsequently cools, the ensuing exsolution7 of buoyant magnesium oxide generates a substantial amount of gravitational energy. This energy is comparable to if not significantly higher than that produced by inner core solidification8 — the primary driver of the Earth’s current magnetic field9–11. Since the inner core is too young12 to explain the existence of an ancient field prior to ~1 billion years, our results solve the conundrum posed by the recent paleomagnetic observation13 of an ancient field at least 3.45 Gyr old. PMID:27437583

Nuclear reactor melt-retention structure to mitigate direct containment heating

DOEpatents

Tutu, Narinder K.; Ginsberg, Theodore; Klages, John R.

1991-01-01

A light water nuclear reactor melt-retention structure to mitigate the extent of direct containment heating of the reactor containment building. The structure includes a retention chamber for retaining molten core material away from the upper regions of the reactor containment building when a severe accident causes the bottom of the pressure vessel of the reactor to fail and discharge such molten material under high pressure through the reactor cavity into the retention chamber. In combination with the melt-retention chamber there is provided a passageway that includes molten core droplet deflector vanes and has gas vent means in its upper surface, which means are operable to deflect molten core droplets into the retention chamber while allowing high pressure steam and gases to be vented into the upper regions of the containment building. A plurality of platforms are mounted within the passageway and the melt-retention structure to direct the flow of molten core material and help retain it within the melt-retention chamber. In addition, ribs are mounted at spaced positions on the floor of the melt-retention chamber, and grid means are positioned at the entrance side of the retention chamber. The grid means develop gas back pressure that helps separate the molten core droplets from discharged high pressure steam and gases, thereby forcing the steam and gases to vent into the upper regions of the reactor containment building.

Characterisation of Ceramic-Coated 316LN Stainless Steel Exposed to High-Temperature Thermite Melt and Molten Sodium

NASA Astrophysics Data System (ADS)

Ravi Shankar, A.; Vetrivendan, E.; Shukla, Prabhat Kumar; Das, Sanjay Kumar; Hemanth Rao, E.; Murthy, S. S.; Lydia, G.; Nashine, B. K.; Mallika, C.; Selvaraj, P.; Kamachi Mudali, U.

2017-11-01

Currently, stainless steel grade 316LN is the material of construction widely used for core catcher of sodium-cooled fast reactors. Design philosophy for core catcher demands its capability to withstand corium loading from whole core melt accidents. Towards this, two ceramic coatings were investigated for its application as a layer of sacrificial material on the top of core catcher to enhance its capability. Plasma-sprayed thermal barrier layer of alumina and partially stabilised zirconia (PSZ) with an intermediate bond coat of NiCrAlY are selected as candidate material and deposited over 316LN SS substrates and were tested for their suitability as thermal barrier layer for core catcher. Coated specimens were exposed to high-temperature thermite melt to simulate impingement of molten corium. Sodium compatibility of alumina and PSZ coatings were also investigated by exposing samples to molten sodium at 400 °C for 500 h. The surface morphology of high-temperature thermite melt-exposed samples and sodium-exposed samples was examined using scanning electron microscope. Phase identification of the exposed samples was carried out by x-ray diffraction technique. Observation from sodium exposure tests indicated that alumina coating offers better protection compared to PSZ coating. However, PSZ coating provided better protection against high-temperature melt exposure, as confirmed during thermite melt exposure test.

Melting of Fe-Si-O alloys: the Fate of Coexisting Si and O in the Core

NASA Astrophysics Data System (ADS)

Arveson, S. M.; Lee, K. K. M.

2017-12-01

The light element budget of Earth's core plays an integral role in sustaining outer core convection, which powers the geodynamo. Many experiments have been performed on binary iron compounds, but the results do not robustly agree with seismological observations and geochemical constraints. Earth's core is almost certainly made up of multiple light elements, so the future of core composition studies lies in ternary (or higher order) systems in order to examine interactions between light elements. We perform melting experiments on Fe-Si-O alloys in a laser-heated diamond-anvil cell to 80 GPa and 4000 K. Using 2D multi- wavelength imaging radiometry together with textural and chemical analysis of quenched samples, we measure the high-pressure melting curves and determine partitioning of light elements between the melt and the coexisting solid. Quenched samples are analyzed both in map view and in cross section using scanning electron microscopy (SEM) and electron microprobe analysis (EPMA) to examine the 3D melt structure and composition. Partitioning of light elements between molten and solid alloys dictates (1) the density contrast at the ICB, which drives compositional convection in the outer core and (2) the temperature of the CMB, an integral parameter for understanding the deep Earth. Our experiments suggest silicon and oxygen do not simply coexist in the melt and instead show complex solubility based on temperature. Additionally, we do not find evidence of crystallization of SiO2 at low oxygen content as was recently reported.11 Hirose, K., et al., Crystallization of silicon dioxide and compositional evolution of the Earth's core. Nature, 2017. 543(7643): p. 99-102.

Divertor tungsten tile melting and its effect on core plasma performance

NASA Astrophysics Data System (ADS)

Lipschultz, B.; Coenen, J. W.; Barnard, H. S.; Howard, N. T.; Reinke, M. L.; Whyte, D. G.; Wright, G. M.

2012-12-01

For the 2007 and 2008 run campaigns, Alcator C-Mod operated with a full toroidal row of tungsten tiles in the high heat flux region of the outer divertor; tungsten levels in the core plasma were below measurement limits. An accidental creation of a tungsten leading edge in the 2009 campaign led to this study of a melting tungsten source: H-mode operation with strike point in the region of the melting tile was immediately impossible due to some fraction of tungsten droplets reaching the main plasma. Approximately 15 g of tungsten was lost from the tile over ˜100 discharges. Less than 1% of the evaporated tungsten was found re-deposited on surfaces, the rest is assumed to have become dust. The strong discharge variability of the tungsten reaching the core implies that the melt layer topology is always varying. There is no evidence of healing of the surface with repeated melting. Forces on the melted tungsten tend to lead to prominences that extend further into the plasma. A discussion of the implications of melting a divertor tungsten monoblock on the ITER plasma is presented.

Quantifying Textures of Rapakivi Granites and Mantle Formation Insights

NASA Astrophysics Data System (ADS)

Ashauer, Z.; Currier, R. M.

2017-12-01

Rapakivi texture, the mantling of plagioclase on alkali feldspar, is a common occurrence in granitoids derived from crustal melting. Presented here, are several textural analyses that quantify mantle thickness and the overall distribution of crystal populations. Analyses were performed on outcrops and slabbed samples from the Wolf River Batholith, Wisconsin, USA and the Wiborg Batholith, Finland. Both localities are "classical" rapakivi granites of Proterozoic age associated with incipient rifting of the supercontinent Nuna/Columbia. Mantle thickness analysis reveals a relationship between the characteristic size of the mantle and the size of the core. The thickest mantles tend to be on relatively small cores while relatively large cores display thin mantles. This relationship is consistent with a replacement origin as a result of alkali feldspar dissolution with concomitant reprecipitation of plagioclase, due to disequilibrium between crystal and melt. If this is the case then crystal size distributions should be similar between unmantled and mantled megacrysts. Preliminary results confirm this supposition: rapakivi mantle formation in these classical systems appear to be the result of replacement. These textural analyses immediately call into question the viability of epitaxial growth models. A certain amount of disequilibrium is required to drive the replacement reaction. Two potential mechanisms are 1) mechanical transfer of crystals into a magma of more mafic composition (i.e., magma mixing), and 2) the production of a heterogeneous melt during rapid melting of granitic rock and reaction between unmelted crystals and partial melt. The classical rapakivi granites are associated with prolonged bimodal magmatism, and so there is clear potential to drive either of these mantling mechanisms.

A Reevaluation of Impact Melt Production

NASA Astrophysics Data System (ADS)

Pierazzo, E.; Vickery, A. M.; Melosh, H. J.

1997-06-01

The production of melt and vapor is an important process in impact cratering events. Because significant melting and vaporization do not occur in impacts at velocities currently achievable in the laboratory, a detailed study of the production of melt and vapor in planetary impact events is carried out with hydrocode simulations. Sandia's two-dimensional axisymmetric hydrocode CSQ was used to estimate the amount of melt and vapor produced for widely varying initial conditions: 10 to 80 km/sec for impact velocity, 0.2 to 10 km for the projectile radius. Runs with different materials demonstrate the material dependency of the final result. These results should apply to any size projectile (for given impact velocity and material), since the results can be dynamically scaled so long as gravity is unimportant in affecting the early-time flow. In contrast with the assumptions of previous analytical models, a clear difference in shape, impact-size dependence, and depth of burial has been found between the melt regions and the isobaric core. In particular, the depth of the isobaric core is not a good representation of the depth of the melt regions, which form deeper in the target. While near-surface effects cause the computed melt region shapes to look like “squashed spheres” the spherical shape is still a good analytical analog. One of the goals of melt production studies is to find proper scaling laws to infer melt production for any impact event of interest. We tested the point source limit scaling law for melt volumes (μ = 0.55-0.6) proposed by M. D. Bjorkman and K. A. Holsapple (1987,Int. J. Impact Eng.5, 155-163). Our results indicate that the point source limit concept does not apply to melt and vapor production. Rather, melt and vapor production follows an energy scaling law (μ = 0.67), in good agreement with previous results of T. J. Ahrens and J. D. O'Keefe [1977, inImpact and Explosion Cratering(D. J. Roddy, R. O. Pepin, and R. B. Merrill, Eds.), pp. 639-656, Pergamon Press, Elmsford, NY]. Finally we tested the accuracy of our melt production calculation against a terrestrial dataset compiled by R. A. F. Grieve and M. J. Cintala (1992,Meteorities27, 526-538). The hydrocode melt volumes are in good agreement with the estimated volumes of that set of terrestrial craters on crystalline basements. At present there is no good model for melt production from impact craters on sedimentary targets.

Models for viscosity and shear localization in bubble-rich magmas

NASA Astrophysics Data System (ADS)

Vona, Alessandro; Ryan, Amy G.; Russell, James K.; Romano, Claudia

2016-09-01

Bubble content influences magma rheology and, thus, styles of volcanic eruption. Increasing magma vesicularity affects the bulk viscosity of the bubble-melt suspension and has the potential to promote non-Newtonian behavior in the form of shear localization or brittle failure. Here, we present a series of high temperature uniaxial deformation experiments designed to investigate the effect of bubbles on the magma bulk viscosity. The starting materials are cores of natural rhyolitic obsidian synthesized to have variable vesicularity (ϕ = 0- 66%). The foamed cores were deformed isothermally (T = 750 °C) at atmospheric conditions using a high-temperature uniaxial press under constant displacement rates (strain rates between 0.5- 1 ×10-4 s-1) and to total strains of 10-40%. The viscosity of the bubble-free melt (η0) was measured by micropenetration and parallel plate methods to establish a baseline for experiments on the vesicle rich cores. At the experimental conditions, rising vesicle content produces a marked decrease in bulk viscosity that is best described by a two-parameter empirical equation: log10 ⁡ηBulk =log10 ⁡η0 - 1.47[ ϕ / (1 - ϕ) ] 0.48. Our parameterization of the bubble-melt rheology is combined with Maxwell relaxation theory to map the potential onset of non-Newtonian behavior (shear localization) in magmas as a function of melt viscosity, vesicularity, and strain rate. For low degrees of strain (i.e. as in our study), the rheological properties of vesicular magmas under different flow types (pure vs. simple shear) are indistinguishable. For high strain or strain rates where simple and pure shear viscosity values may diverge, our model represents a maximum boundary condition. Vesicular magmas can behave as non-Newtonian fluids at lower strain rates than unvesiculated melts, thereby, promoting shear localization and (explosive or non-explosive) magma fragmentation. The extent of shear localization in magma influences outgassing efficiency, thereby, affecting magma ascent and the potential for explosivity.

Electrical Resistivity Measurement of Cu and Zn on the Pressure-Dependent Melting Boundary

NASA Astrophysics Data System (ADS)

Secco, R. A.; Ezenwa, I.; Yong, W.

2016-12-01

Understanding how the core cools through heat conduction and modelling the geodynamo requires knowledge of the thermal and electrical conductivity of solid and liquid Fe and its relevant alloys at high pressures. It has been proposed that electrical resistivity of a pure metal is constant along its P-dependent melting boundary (Stacey and Anderson, PEPI, 2001). If confirmed, this invariant behavior could serve as a practical tool for low P studies to assess electrical resistivity of Earth's core. Since Earth's inner core boundary (ICB) is a melting boundary of mainly Fe, measurements of electrical resistivity of Fe at the melting boundary, under any P, would serve as a proxy for the resistivity at the ICB. A revised treatment (Stacey and Loper, PEPI, 2007) accounted for s-d scattering in transition metals with unfilled d-bands and limited the proposal to metals with electrons of the same type in filled d-band metals. To test this proposal, we made high P, T measurements of electrical resistivity of d-band filled Cu and Zn in solid and liquid states. Experiments were carried out in a 1000 ton cubic anvil press up to 5 GPa and 300K above melting temperatures. Two thermocouples placed at opposite ends of the wire sample served as T probes as well as 4-wire resistance electrodes in a switched circuit. A polarity switch was used to remove any bias voltage measurement using thermocouple legs. Electron microprobe analyses were used to check the compositions of the recovered samples. The expected resistivity decrease with P and increase with T were found and comparisons with 1atm data are in very good agreement. Within the error of measurement, the resistivity values of Cu decrease along the melting boundary while Zn appears to support the hypothesis of constant resistivity along the melting boundary.

Eutectic melting in the MgO-SiO2 system and its implication to Earth's lower mantle evolution

NASA Astrophysics Data System (ADS)

Baron, M. A.; Lord, O. T.; Myhill, R.; Thomson, A.; Wang, W.; Tronnes, R. G.; Walter, M. J.

2017-12-01

Eutectic melting curves in the system MgO-SiO2 have been experimentally studied at lower mantle pressures using laser-heated diamond anvil cell (LH-DAC) techniques. We investigated eutectic melting of bridgmanite plus periclase in the MgO-MgSiO3 binary and bridgmanite plus stishovite in the MgSiO3-SiO2 sub-system as the simplest models of natural peridotite and basalt. The eutectic melting have been detected on the basis of the thermal perturbations (i.e. melting plateau) during the experiment but also post-experimental textural and chemical analyses of the recovered samples. We also performed a suite of sub-solidus experiments in order to compare and bracket the eutectic melting experiments. The melting curve of model basalt occurs at lower temperatures, has a shallower dT/dP slope and slightly less curvature than the model peridotitic melting curve. Overall, melting temperatures detected in this study are in good agreement with previous experiments and ab initio simulations at 25 GPa (Liebske and Frost, 2012; de Koker et al., 2013). However, at higher pressures the measured eutectic melting curves are systematically lower in temperature than curves extrapolated on the basis of thermodynamic modelling of low-pressure experimental data, and those calculated from atomistic simulations. In turn, when comparing with previously published solidus curves obtained for natural basalt and peridotite (e.g. Fiquet et al., 2010; Andrault et al. 2011; Nomura et al. 2014; Hirose et al. 1999; Andrault et al. 2014 and Pradhan et al. 2015) the melting curves from this study are higher. However, the difference in temperature is less significant than previously though. Based on the comparison of the curvature of the model peridotite eutectic relative to an MgSiO3 melt adiabat we infer that crystallization in a global magma ocean would begin at 100 GPa rather than at the bottom of the mantle, allowing for an early basal melt layer. The model peridotite melting curve lies 500 K above the mantle geotherm at the core-mantle boundary, indicating that it will not be molten. The model basalt melting curve intersects the geotherm at the base of the mantle, and partial melting of subducted oceanic crust is therefore expected.

The melting mechanism in binary Pd0.25Ni0.75 nanoparticles: molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Domekeli, U.; Sengul, S.; Celtek, M.; Canan, C.

2018-02-01

The melting mechanism for Pd0.25Ni0.75 alloy nanoparticles (NPs) was investigated using molecular dynamics (MD) simulations with quantum Sutton-Chen many-body potentials. NPs of six different sizes ranging from 682 to 22,242 atoms were studied to observe the effect of size on the melting point. The melting temperatures of the NPs were estimated by following the changes in both the thermodynamic and structural quantities such as the total energy, heat capacity and Lindemann index. We also used a thermodynamics model to better estimate the melting point and to check the accuracy of MD simulations. We observed that the melting points of the NPs decreased as their sizes decreased. Although the MD simulations for the bulk system yielded higher melting temperatures because of the lack of a seed for the liquid phase, the melting temperatures determined for both the bulk material and the NPs are in good agreement with those predicted from the thermodynamics model. The melting mechanism proceeds in two steps: firstly, a liquid-like shell is formed in the outer regions of the NP with increasing temperature. The thickness of the liquid-like shell increases with increasing temperature until the shell reaches a critical thickness. Then, the entire Pd-Ni NP including core-related solid-like regions melts at once.

Fukushima Daiichi unit 1 uncertainty analysis--Preliminary selection of uncertain parameters and analysis methodology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cardoni, Jeffrey N.; Kalinich, Donald A.

2014-02-01

Sandia National Laboratories (SNL) plans to conduct uncertainty analyses (UA) on the Fukushima Daiichi unit (1F1) plant with the MELCOR code. The model to be used was developed for a previous accident reconstruction investigation jointly sponsored by the US Department of Energy (DOE) and Nuclear Regulatory Commission (NRC). However, that study only examined a handful of various model inputs and boundary conditions, and the predictions yielded only fair agreement with plant data and current release estimates. The goal of this uncertainty study is to perform a focused evaluation of uncertainty in core melt progression behavior and its effect on keymore » figures-of-merit (e.g., hydrogen production, vessel lower head failure, etc.). In preparation for the SNL Fukushima UA work, a scoping study has been completed to identify important core melt progression parameters for the uncertainty analysis. The study also lays out a preliminary UA methodology.« less

Heat up and failure of BWR upper internals during a severe accident

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robb, Kevin R.

In boiling water reactors, the shroud dome, separators, and dryers above the core are made of approximately 100,000 kg of stainless steel. During a severe accident in which the coolant boils away and exothermic oxidation of zirconium occurs, gases (steam and hydrogen) are superheated in the core region and pass through the upper internals. In this scenario, the upper internals can also be heated by thermal radiation from the hot degrading core. Historically, models of the upper internals have been relatively simple in severe accident codes. The upper internals are typically modeled in MELCOR as two lumped volumes with simplifiedmore » heat transfer characteristics and no structural integrity considerations, and with limited ability to oxidize, melt, and relocate. The potential for and the subsequent impact of the upper internals to heat up, oxidize, fail, and relocate during a severe accident was investigated. A higher fidelity representation of the shroud dome, steam separators, and steam driers was developed in MELCOR v1.8.6 by extending the core region upwards. The MELCOR modeling effort entailed adding 45 additional core cells and control volumes, 98 flow paths, and numerous control functions. The model accounts for the mechanical loading and structural integrity, oxidation, melting, flow area blockage, and relocation of the various components. Consistent with a previous study, the results indicate that the upper internals can reach high temperatures during a severe accident sufficient to lose their structural integrity and relocate. Finally, the additional 100 metric tons of stainless steel debris influences the subsequent in-vessel and ex-vessel accident progression.« less

Heat up and failure of BWR upper internals during a severe accident

DOE PAGES

Robb, Kevin R.

2017-02-21

In boiling water reactors, the shroud dome, separators, and dryers above the core are made of approximately 100,000 kg of stainless steel. During a severe accident in which the coolant boils away and exothermic oxidation of zirconium occurs, gases (steam and hydrogen) are superheated in the core region and pass through the upper internals. In this scenario, the upper internals can also be heated by thermal radiation from the hot degrading core. Historically, models of the upper internals have been relatively simple in severe accident codes. The upper internals are typically modeled in MELCOR as two lumped volumes with simplifiedmore » heat transfer characteristics and no structural integrity considerations, and with limited ability to oxidize, melt, and relocate. The potential for and the subsequent impact of the upper internals to heat up, oxidize, fail, and relocate during a severe accident was investigated. A higher fidelity representation of the shroud dome, steam separators, and steam driers was developed in MELCOR v1.8.6 by extending the core region upwards. The MELCOR modeling effort entailed adding 45 additional core cells and control volumes, 98 flow paths, and numerous control functions. The model accounts for the mechanical loading and structural integrity, oxidation, melting, flow area blockage, and relocation of the various components. Consistent with a previous study, the results indicate that the upper internals can reach high temperatures during a severe accident sufficient to lose their structural integrity and relocate. Finally, the additional 100 metric tons of stainless steel debris influences the subsequent in-vessel and ex-vessel accident progression.« less

Toward a coherent model for the melting behavior of the deep Earth's mantle

NASA Astrophysics Data System (ADS)

Andrault, D.; Bolfan-Casanova, N.; Bouhifd, M. A.; Boujibar, A.; Garbarino, G.; Manthilake, G.; Mezouar, M.; Monteux, J.; Parisiades, P.; Pesce, G.

2017-04-01

Knowledge of melting properties is critical to predict the nature and the fate of melts produced in the deep mantle. Early in the Earth's history, melting properties controlled the magma ocean crystallization, which potentially induced chemical segregation in distinct reservoirs. Today, partial melting most probably occurs in the lowermost mantle as well as at mid upper-mantle depths, which control important aspects of mantle dynamics, including some types of volcanism. Unfortunately, despite major experimental and theoretical efforts, major controversies remain about several aspects of mantle melting. For example, the liquidus of the mantle was reported (for peridotitic or chondritic-type composition) with a temperature difference of ∼1000 K at high mantle depths. Also, the Fe partitioning coefficient (DFeBg/melt) between bridgmanite (Bg, the major lower mantle mineral) and a melt was reported between ∼0.1 and ∼0.5, for a mantle depth of ∼2000 km. Until now, these uncertainties had prevented the construction of a coherent picture of the melting behavior of the deep mantle. In this article, we perform a critical review of previous works and develop a coherent, semi-quantitative, model. We first address the melting curve of Bg with the help of original experimental measurements, which yields a constraint on the volume change upon melting (ΔVm). Secondly, we apply a basic thermodynamical approach to discuss the melting behavior of mineralogical assemblages made of fractions of Bg, CaSiO3-perovskite and (Mg,Fe)O-ferropericlase. Our analysis yields quantitative constraints on the SiO2-content in the pseudo-eutectic melt and the degree of partial melting (F) as a function of pressure, temperature and mantle composition; For examples, we find that F could be more than 40% at the solidus temperature, except if the presence of volatile elements induces incipient melting. We then discuss the melt buoyancy in a partial molten lower mantle as a function of pressure, F and DFeBg/melt. In the lower mantle, density inversions (i.e. sinking melts) appear to be restricted to low F values and highest mantle pressures. The coherent melting model has direct geophysical implications: (i) in the early Earth, the magma ocean crystallization could not occur for a core temperature higher than ∼5400 K at the core-mantle boundary (CMB). This temperature corresponds to the melting of pure Bg at 135 GPa. For a mantle composition more realistic than pure Bg, the right CMB temperature for magma ocean crystallization could have been as low as ∼4400 K. (ii) There are converging arguments for the formation of a relatively homogeneous mantle after magma ocean crystallization. In particular, we predict the bulk crystallization of a relatively large mantle fraction, when the temperature becomes lower than the pseudo-eutectic temperature. Some chemical segregation could still be possible as a result of some Bg segregation in the lowermost mantle during the first stage of the magma ocean crystallization, and due to a much later descent of very low F, Fe-enriched, melts toward the CMB. (iii) The descent of such melts could still take place today. There formation should to be related to incipient mantle melting due to the presence of volatile elements. Even though, these melts can only be denser than the mantle (at high mantle depths) if the controversial value of DFeBg/melt is indeed as low as suggested by some experimental studies. This type of melts could contribute to produce ultra-low seismic velocity anomalies in the lowermost mantle.

The effect of melt composition on metal-silicate partitioning of siderophile elements and constraints on core formation in the angrite parent body

NASA Astrophysics Data System (ADS)

Steenstra, E. S.; Sitabi, A. B.; Lin, Y. H.; Rai, N.; Knibbe, J. S.; Berndt, J.; Matveev, S.; van Westrenen, W.

2017-09-01

We present 275 new metal-silicate partition coefficients for P, S, V, Cr, Mn, Co, Ni, Ge, Mo, and W obtained at moderate P (1.5 GPa) and high T (1683-1883 K). We investigate the effect of silicate melt composition using four end member silicate melt compositions. We identify possible silicate melt dependencies of the metal-silicate partitioning of lower valence elements Ni, Ge and V, elements that are usually assumed to remain unaffected by changes in silicate melt composition. Results for the other elements are consistent with the dependence of their metal-silicate partition coefficients on the individual major oxide components of the silicate melt composition suggested by recently reported parameterizations and theoretical considerations. Using multiple linear regression, we parameterize compiled metal-silicate partitioning results including our new data and report revised expressions that predict their metal-silicate partitioning behavior as a function of P-T-X-fO2. We apply these results to constrain the conditions that prevailed during core formation in the angrite parent body (APB). Our results suggest the siderophile element depletions in angrite meteorites are consistent with a CV bulk composition and constrain APB core formation to have occurred at mildly reducing conditions of 1.4 ± 0.5 log units below the iron-wüstite buffer (ΔIW), corresponding to a APB core mass of 18 ± 11%. The core mass range is constrained to 21 ± 8 mass% if light elements (S and/or C) are assumed to reside in the APB core. Incorporation of light elements in the APB core does not yield significantly different redox states for APB core-mantle differentiation. The inferred redox state is in excellent agreement with independent fO2 estimates recorded by pyroxene and olivine in angrites.

Permeability and 3-Dimensional Melt Distribution in Partially Molten Rocks

NASA Astrophysics Data System (ADS)

Zhu, Wen-Lu; Gaetani, Glenn; Fusseis, Florian

2010-05-01

Quantitative knowledge of the distribution of small amounts of silicate melt in peridotite and of its influence on permeability are critical to our understanding of melt migration and segregation processes in the upper mantle, as well as interpretations of the geochemical and geophysical observations at ocean ridges. For a system containing a single solid phase of isotropic interfacial energy, chemical and mechanical equilibrium requires a constant mean curvature of solid-melt interfaces and a single dihedral angle. Under these conditions, a simple power-law relationship between permeability, grain size and melt fraction, has been derived [e.g., von Bargen and Waff, 1986]. However, microstructural observations on texturally equilibrated, partially molten rocks reveal that the melt distribution is more complex than predicted by the isotropic model. Several factors, such as non-hydrostatic stress, anisotropic interfacial energy, or the presence of a second solid phase, will alter the power-law relationship. Better estimates for the permeability of partially molten rock require an accurate assessment of 3-dimensional melt distribution at the grain-scale. Existing studies of melt distribution, carried out on 2-D slices through experimental charges, have produced divergent models for melt distribution at small melt fractions. While some studies conclude that small amounts of melt are distributed primarily along 3-grain junctions [e.g., Wark et al., 2003], others predict an important role for melt distribution along grain boundaries at low melt fractions [e.g., Faul 1997]. Using X-ray synchrotron microtomography, we have carried out the first high quality non-destructive imaging of 3-dimensional melt distribution in experimentally equilibrated olivine-basalt aggregates [Zhu et al., 2009]. Microtomographic images of melt distribution were obtained on 1 mm cylindrical cores with melt fractions of 0.2, 0.1, and 0.02, at a spatial resolution of 0.7 microns. Textual information such as melt channel size and channel connectivity was determined using AVIZO and MATLAB. Our data indicate that as melt fraction decreases from 0.2 to 0.02, grain size increases slightly whereas melt interconnectivity decreases. Network modeling and the Lattice Boltzmann method provide a quantitative link between the macroscale transport properties and microscale melt distribtution. Incorporating our quantitative 3-D melt distribution data into these models allow us to simulate melt transport and, thereby, calculate the permeability and electrical conductivity of partially molten peridotite, especially at low melt fractions.

Experimental determination of the partitioning of gallium between solid iron metal and synthetic basaltic melt Electron and ion microprobe study

NASA Technical Reports Server (NTRS)

Drake, M. J.; Newsom, H. E.; Reed, S. J. B.; Enright, M. C.

1984-01-01

The distribution of Ga between solid Fe metal and synthetic basaltic melt is investigated experimentally at temperatures of 1190 and 1330 C, and over a narrow range of oxygen fugacities. Metal-silicate reversal experiments were conducted, indicating a close approach to equilibrium. The analysis of the partitioned products was performed using electron and ion microprobes. At one bar total pressure, the solid metal/silicate melt partition coefficient D(Ga) is used to evaluate metal-silicate fractionation processes in the earth, moon, and Eucrite Parent Body (EPB). It is found that the depletion of Ga abundances in the EPB is due to the extraction of Ga into a metallic core. Likewise, the depletion of Ga in the lunar mantle is consistent with the extraction of Ga into a smaller lunar core if Ga was originally present in a subchondritic concentration. The relatively high Ga abundances in the earth's mantle are discussed, with reference to several theoretical models.

Wire Composition: Its Effect on Metal Disintegration and Particle Formation in Twin-Wire Arc-Spraying Process

NASA Astrophysics Data System (ADS)

Tillmann, W.; Abdulgader, M.

2013-03-01

The wire tips in twin-wire arc-spraying (TWAS) are heated in three different zones. A high-speed camera was used to observe the melting behavior, metal breakup, and particle formation under different operating conditions. In zone (I), the wire tips are melted (liquidus metal) and directly atomized in the form of smaller droplets. Their size is a function of the specific properties of the molten metal and the exerting aerodynamic forces. Zone (II) is directly beneath zone (I) and the origin of the extruded metal sheets at the wire tips. The extruded metal sheets in the case of cored wires are shorter than those observed while using solid wires. In this study, the effects of adjustable parameters and powder filling on melting behavior, particle formation, and process instability were revealed, and a comparison between solid and cored wires was made. The findings can improve the accuracy of the TWAS process modeling.

Experiments on the rheology of vesicle-bearing magmas

NASA Astrophysics Data System (ADS)

Vona, Alessandro; Ryan, Amy G.; Russell, James K.; Romano, Claudia

2016-04-01

We present a series of high temperature uniaxial deformation experiments designed to investigate the effect of bubbles on the magma bulk viscosity. Starting materials having variable vesicularity (φ = 0 - 66%) were synthesized by high-temperature foaming (T = 900 - 1050 ° C and P = 1 bar) of cores of natural rhyolitic obsidian from Hrafntinnuhryggur, Krafla, Iceland. These cores were subsequently deformed using a high-temperature uniaxial press at dry atmospheric conditions. Each experiment involved deforming vesicle-bearing cores isothermally (T = 750 ° C), at constant displacement rates (strain rates between 0.5-1 x 10-4 s-1), and to total strains (ɛ) of 10-40%. The viscosity of the bubble-free melt (η0) was measured by micropenetration and parallel plate methods and establishes a baseline for comparing data derived from experiments on vesicle rich cores. At the experimental conditions, the presence of vesicles has a major impact on the rheological response, producing a marked decrease of bulk viscosity (maximum decrease of 2 log units Pa s) that is best described by a two-parameter empirical equation: log ηBulk = log η0 - 1.47 * [φ/(1-φ)]0.48. Our model provides a means to compare the diverse behaviour of vesicle-bearing melts reported in the literature and reflecting material properties (e.g., analogue vs. natural), geometry and distribution of pores (e.g. foamed/natural vs. unconsolidated/sintered materials), and flow regime. Lastly, we apply principles of Maxwell relaxation theory, combined with our parameterization of bubble-melt rheology, to map the potential onset of non-Newtonian behaviour (strain localization) in vesiculated magmas and lavas as a function of melt viscosity, vesicularity, strain rate, and geological condition. Increasing vesicularity in magmas can initiate non-Newtonian behaviour at constant strain rates. Lower melt viscosity sustains homogeneous Newtonian flow in vesiculated magmas even at relatively high strain rates.

Melting relations in the iron-sulfur system at ultra-high pressures - Implications for the thermal state of the earth

NASA Technical Reports Server (NTRS)

Williams, Quentin; Jeanloz, Raymond

1990-01-01

The melting temperatures of FeS-troilite and of a 10-wt-pct sulfur iron alloy have been measured to pressures of 120 and 90 GPa, respectively. The results document that FeS melts at a temperature of 4100 (+ or - 300) K at the pressure of the core-mantle boundary. Eutecticlike behavior persists in the iron-sulfur system to the highest pressures of measurements, in marked contrast to the solid-solutionlike behavior observed at high pressures in the iron-iron oxide system. Iron with 10-wt-pct sulfur melts at a similar temperature as FeS at core-mantle boundary conditions. If the sole alloying elements of iron within the core are sulfur and oxygen and the outer core is entirely liquid, the minimum temperature at the top of the outer core is 4900 (+ or - 400) K. Calculations of mantle geotherms dictate that there must be a temperature increase of between 1000 and 2000 K across thermal boundary layers within the mantle. If D-double-prime is compositionally stratified, it could accommodate the bulk of this temperature jump.

Heat up and potential failure of BWR upper internals during a severe accident

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robb, Kevin R

2015-01-01

In boiling water reactors, the steam dome, steam separators, and dryers above the core are comprised of approximately 100 tons of stainless steel. During a severe accident in which the coolant boils away and exothermic oxidation of zirconium occurs, gases (steam and hydrogen) are superheated in the core region and pass through the upper internals. Historically, the upper internals have been modeled using severe accident codes with relatively simple approximations. The upper internals are typically modeled in MELCOR as two lumped volumes with simplified heat transfer characteristics, with no structural integrity considerations, and with limited ability to oxidize, melt, andmore » relocate. The potential for and the subsequent impact of the upper internals to heat up, oxidize, fail, and relocate during a severe accident was investigated. A higher fidelity representation of the shroud dome, steam separators, and steam driers was developed in MELCOR v1.8.6 by extending the core region upwards. This modeling effort entailed adding 45 additional core cells and control volumes, 98 flow paths, and numerous control functions. The model accounts for the mechanical loading and structural integrity, oxidation, melting, flow area blockage, and relocation of the various components. The results indicate that the upper internals can reach high temperatures during a severe accident; they are predicted to reach a high enough temperature such that they lose their structural integrity and relocate. The additional 100 tons of stainless steel debris influences the subsequent in-vessel and ex-vessel accident progression.« less

A multiphysics phase field model on melting and kinetic superheating of aluminum nanolayer and nanoparticle

NASA Astrophysics Data System (ADS)

Hwang, Yong Seok

It has been found during the last decade that a nanoscale melting of metal has very distinctive features compared to its microscale counterpart. It has been observed that a highly non-equilibrium state can result in extreme superheating of a solid state, which cannot be explained well by thermodynamic theories based on equilibrium or nucleation. An endeavor to find the superheating limit and mechanisms of melting and superheating becomes more complicated when various physical phenomena are involved at the similar scales. The main goal of this research is to establish a multiphysics model and to reveal the mechanism of melting and kinetic superheating of a metal nanostructure at high heating rates. The model includes elastodynamics, a fast heating of metal considering a delayed heat transfer between electron gas and lattice phonon and couplings among physical phenomena, and phase transformation incorporated with thermal fluctuation. The model successfully reproduces two independent experiments and several novel nanoscale physical phenomena are discovered. For example, the depression of the melting temperature of Al nanolayer under plane stress condition, the threshold heating rate, 1011 K/s, for kinetic superheating, a large temperature drop in a 5 nm collision region of the two solid-melt interfaces, and a strong effect of geometry on kinetic superheating in Al core-shell nanostructure at high heating rate.

Origins of ultralow velocity zones through slab-derived metallic melt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jiachao; Li, Jie; Hrubiak, Rostislav

2016-05-03

Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth’s core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce themore » seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich post-bridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth’s core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.« less

“Skin-Core-Skin” Structure of Polymer Crystallization Investigated by Multiscale Simulation

PubMed Central

Ruan, Chunlei

2018-01-01

“Skin-core-skin” structure is a typical crystal morphology in injection products. Previous numerical works have rarely focused on crystal evolution; rather, they have mostly been based on the prediction of temperature distribution or crystallization kinetics. The aim of this work was to achieve the “skin-core-skin” structure and investigate the role of external flow and temperature fields on crystal morphology. Therefore, the multiscale algorithm was extended to the simulation of polymer crystallization in a pipe flow. The multiscale algorithm contains two parts: a collocated finite volume method at the macroscopic level and a morphological Monte Carlo method at the microscopic level. The SIMPLE (semi-implicit method for pressure linked equations) algorithm was used to calculate the polymeric model at the macroscopic level, while the Monte Carlo method with stochastic birth-growth process of spherulites and shish-kebabs was used at the microscopic level. Results show that our algorithm is valid to predict “skin-core-skin” structure, and the initial melt temperature and the maximum velocity of melt at the inlet mainly affects the morphology of shish-kebabs. PMID:29659516

A 400-Year Ice Core Melt Layer Record of Summertime Warming in the Alaska Range

NASA Astrophysics Data System (ADS)

Winski, Dominic; Osterberg, Erich; Kreutz, Karl; Wake, Cameron; Ferris, David; Campbell, Seth; Baum, Mark; Bailey, Adriana; Birkel, Sean; Introne, Douglas; Handley, Mike

2018-04-01

Warming in high-elevation regions has societally important impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high-elevation temperature records exist from the middle or high latitudes. While a variety of paleoproxy records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually resolved temperature records from high elevations. Here we present a 400-year temperature proxy record based on the melt layer stratigraphy of two ice cores collected from Mt. Hunter in Denali National Park in the central Alaska Range. The ice core record shows a sixtyfold increase in water equivalent total annual melt between the preindustrial period (before 1850 Common Era) and present day. We calibrate the melt record to summer temperatures based on weather station data from the ice core drill site and find that the increase in melt production represents a summer warming rate of at least 1.92 ± 0.31°C per century during the last 100 years, exceeding rates of temperature increase at most low-elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p < 0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby wave-like pattern that enhances high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century and that conditions in the tropical oceans contribute to this warming.

Computer Simulation To Assess The Feasibility Of Coring Magma

NASA Astrophysics Data System (ADS)

Su, J.; Eichelberger, J. C.

2017-12-01

Lava lakes on Kilauea Volcano, Hawaii have been successfully cored many times, often with nearly complete recovery and at temperatures exceeding 1100oC. Water exiting nozzles on the diamond core bit face quenches melt to glass just ahead of the advancing bit. The bit readily cuts a clean annulus and the core, fully quenched lava, passes smoothly into the core barrel. The core remains intact after recovery, even when there are comparable amounts of glass and crystals with different coefficients of thermal expansion. The unique resulting data reveal the rate and sequence of crystal growth in cooling basaltic lava and the continuous liquid line of descent as a function of temperature from basalt to rhyolite. Now that magma bodies, rather than lava pooled at the surface, have been penetrated by geothermal drilling, the question arises as to whether similar coring could be conducted at depth, providing fundamentally new insights into behavior of magma. This situation is considerably more complex because the coring would be conducted at depths exceeding 2 km and drilling fluid pressures of 20 MPa or more. Criteria that must be satisfied include: 1) melt is quenched ahead of the bit and the core itself must be quenched before it enters the barrel; 2) circulating drilling fluid must keep the temperature of the coring assembling cooled to within operational limits; 3) the drilling fluid column must nowhere exceed the local boiling point. A fluid flow simulation was conducted to estimate the process parameters necessary to maintain workable temperatures during the coring operation. SolidWorks Flow Simulation was used to estimate the effect of process parameters on the temperature distribution of the magma immediately surrounding the borehole and of drilling fluid within the bottom-hole assembly (BHA). A solid model of the BHA was created in SolidWorks to capture the flow behavior around the BHA components. Process parameters used in the model include the fluid properties and temperature of magma, coolant flow rate, rotation speed, and rate of penetration (ROP). The modeling results indicate that there are combinations of process parameters that will provide sufficient cooling to enable the desired coring process in magma.

In situ TEM and analytical STEM studies of ZnO nanotubes with Sn cores and Sn nanodrops

NASA Astrophysics Data System (ADS)

Ortega, Y.; Jäger, W.; Piqueras, J.; Häussler, D.; Fernández, P.

2013-10-01

ZnO nanorods with Sn core regions grown by a thermal evaporation-deposition method from a mixture of SnO2 and ZnS powders as precursors, are used to study the behaviour of liquid metal in the nanotubes' core regions and the formation of liquid metal nanodrops at the tube ends by in situ TEM experiments. The compositions of the core materials and of the nanodrops were assessed by employing HAADF-STEM imaging and spatially resolved EDXS measurements. By applying variable thermal load through changing the electron-beam flux of the electron microscope, melting of the metallic core can be induced and the behaviour of the liquid metal of the nanorods can be monitored locally. Within the nanorod core, melting and reversible thermal expansion and contraction of Sn core material is reproducibly observed. For nanotubes with core material near-tip regions, a nanodrop emerges from the tip upon melting the core material, followed by reabsorption of the melt into the core and re-solidification upon decreasing the heat load, being reminiscent of a ‘soldering nanorod’. The radius of the liquid nanodrop can reach a few tens of nanometres, containing a total volume of 10-20 up to 10-18 l of liquid Sn. In situ TEM confirms that the radius of the nanodrop can be controlled via the thermal load: it increases with increasing temperature and decreases with decreasing temperature. In addition, some phenomena related to structure modifications during extended electron-beam exposure are also described.

The SAS4A/SASSYS-1 Safety Analysis Code System, Version 5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fanning, T. H.; Brunett, A. J.; Sumner, T.

The SAS4A/SASSYS-1 computer code is developed by Argonne National Laboratory for thermal, hydraulic, and neutronic analysis of power and flow transients in liquidmetal- cooled nuclear reactors (LMRs). SAS4A was developed to analyze severe core disruption accidents with coolant boiling and fuel melting and relocation, initiated by a very low probability coincidence of an accident precursor and failure of one or more safety systems. SASSYS-1, originally developed to address loss-of-decay-heat-removal accidents, has evolved into a tool for margin assessment in design basis accident (DBA) analysis and for consequence assessment in beyond-design-basis accident (BDBA) analysis. SAS4A contains detailed, mechanistic models of transientmore » thermal, hydraulic, neutronic, and mechanical phenomena to describe the response of the reactor core, its coolant, fuel elements, and structural members to accident conditions. The core channel models in SAS4A provide the capability to analyze the initial phase of core disruptive accidents, through coolant heat-up and boiling, fuel element failure, and fuel melting and relocation. Originally developed to analyze oxide fuel clad with stainless steel, the models in SAS4A have been extended and specialized to metallic fuel with advanced alloy cladding. SASSYS-1 provides the capability to perform a detailed thermal/hydraulic simulation of the primary and secondary sodium coolant circuits and the balance-ofplant steam/water circuit. These sodium and steam circuit models include component models for heat exchangers, pumps, valves, turbines, and condensers, and thermal/hydraulic models of pipes and plena. SASSYS-1 also contains a plant protection and control system modeling capability, which provides digital representations of reactor, pump, and valve controllers and their response to input signal changes.« less

Microstructures and Petrology of Melt Inclusions in the Anatectic Sequence of Jubrique (Betic Cordillera, S Spain): Implications for Crustal Anatexis

NASA Astrophysics Data System (ADS)

Acosta-vigil, A.; Barich, A.; Garrido, C. J.; Cesare, B.; Tajčmanová, L.; Bartoli, O.

2014-12-01

We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence garnet decreases whereas biotite increases in proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ≈5 to 200 micrometers, with a mean size of ≈30-40 micrometers. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ≈850 ºC and 12-14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ≈800-850 ºC and 5-6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous conventional petrologic studies on these strongly deformed rocks have proposed that anatexis started during decompression from peak to post-peak conditions and in the field of sillimanite. The study of melt inclusions shows, however, that melt was already present in the system at peak conditions, and that most garnet grew in the presence of melt.

Stability and melting of Fe3C at high pressure and temperature: Implication for the carbon in the Earth's core

NASA Astrophysics Data System (ADS)

Takahashi, S.; Ohtani, E.; Sakai, T.; Hirao, N.; Ohishi, Y.

2012-12-01

The Earth's core is regarded as an Fe-Ni alloy but its density is lower than that of pure Fe at the core conditions. Therefore, the Earth's core is supposed to contain light elements and carbon is one of the candidates of the light elements to explain the density deficit of the Earth's core. Nakajima et al. (2009) reported the melting temperature of Fe3C up to around 30 GPa based on textual observations, the chemical analysis of the quenched run products and in situ X-ray diffraction experiments using a Kawai-type multi anvil apparatus. Lord et al. (2009) reported melting temperatures of Fe3C up to 70 GPa, which was determined by the temperature plateau during increasing laser power using a laser-heated diamond anvil cell. They also suggested Fe+Fe7C3 is a stable subsolidus phase. There are obvious discrepancies between the melting curve and the stable subsolidus phase reported by Nakajima et al. (2009) and those reported by Lord et al. (2009). In this study, the melting temperatures of Fe3C and a subsolidus phase relation were determined based on in situ X-ray diffraction experiments. This study aims to reveal the stability field of Fe3C and the melting temperature of Fe3C and to discuss the behaviors of carbon in the Earth's core. We have performed experiments using a laser-heated diamond anvil cell combined with in situ X-ray diffraction experiment at BL10XU beamline, SPring-8 synchrotron facility. An NaCl powder and a rhenium or tungsten foil were used for the insulator and gasket, respectively. Melting of the sample was determined by disappearance of the X-ray diffraction peaks. We determined the melting relation of Fe3C up to 145 GPa by in situ X-ray diffraction experiments. Present results are close to Nakajima et al. (2009) up to 30 GPa but become close to that reported by Lord et al. (2009) at higher pressure conditions. The solidus temperature extrapolated to the ICB pressure, 330 GPa, is 5400 K. We also confirmed that Fe3C is stable as a subsolidus phase at least up to 237 GPa and 4100 K. This strongly suggests that Fe3C is a potential candidate of the Earth's inner core although we need further studies at the inner core conditions.

Melting relations in the Fe-S-Si system at high pressure and temperature: implications for the planetary core

NASA Astrophysics Data System (ADS)

Sakairi, Takanori; Ohtani, Eiji; Kamada, Seiji; Sakai, Takeshi; Sakamaki, Tatsuya; Hirao, Naohisa

2017-12-01

The phase and melting relations in the Fe-S-Si system were determined up to 60 GPa by using a double-sided laser-heated diamond anvil cell combined with X-ray diffraction. On the basis of the X-ray diffraction patterns, we confirmed that hcp/fcc Fe-Si alloys and Fe3S are stable phases under subsolidus conditions in the Fe-S-Si system. Both solidus and liquidus temperatures are significantly lower than the melting temperature of pure Fe and both increase with pressure. The slopes of the Fe-S-Si liquidus and solidus curves determined here are smaller than the adiabatic temperature gradients of the liquid cores of Mercury and Mars. Thus, crystallization of their cores started at the core-mantle boundary region.

Molecular dynamics simulation of Coulomb explosion, melting and shock wave creation in silicon after an ionization pulse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhongyu; Shao, Lin, E-mail: lshao@tamu.edu; Chen, Di

Strong electronic stopping power of swift ions in a semiconducting or insulating substrate can lead to localized electron stripping. The subsequent repulsive interactions among charged target atoms can cause Coulomb explosion. Using molecular dynamics simulation, we simulate Coulomb explosion in silicon by introducing an ionization pulse lasting for different periods, and at different substrate temperatures. We find that the longer the pulse period, the larger the melting radius. The observation can be explained by a critical energy density model assuming that melting required thermal energy density is a constant value and the total thermal energy gained from Coulomb explosion ismore » linearly proportional to the ionization period. Our studies also show that melting radius is larger at higher substrate temperatures. The temperature effect is explained due to a longer structural relaxation above the melting temperature at original ionization boundary due to lower heat dissipation rates. Furthermore, simulations show the formation of shock waves, created due to the compression from the melting core.« less

Bernard J. Wood Receives 2013 Harry H. Hess Medal: Citation

NASA Astrophysics Data System (ADS)

Hofmann, Albrecht W.

2014-01-01

As Harry Hess recognized over 50 years ago, mantle melting is the fundamental motor for planetary evolution and differentiation. Melting generates the major divisions of crust mantle and core. The distribution of chemical elements between solids, melts, and gaseous phases is fundamental to understanding these differentiation processes. Bernie Wood, together with Jon Blundy, has combined experimental petrology and physicochemical theory to revolutionize the understanding of the distribution of trace elements between melts and solids in the Earth. Knowledge of these distribution laws allows the reconstruction of the source compositions of the melts (deep in Earth's interior) from their abundances in volcanic rocks. Bernie's theoretical treatment relates the elastic strain of the lattice caused by the substitution of a trace element in a crystal to the ionic radius and charge of this element. This theory, and its experimental calibrations, brought order to a literature of badly scattered, rather chaotic experimental data that allowed no satisfactory quantitative modeling of melting processes in the mantle.

Non-chondritic iron isotope ratios in planetary mantles as a result of core formation

NASA Astrophysics Data System (ADS)

Elardo, Stephen M.; Shahar, Anat

2017-02-01

Information about the materials and conditions involved in planetary formation and differentiation in the early Solar System is recorded in iron isotope ratios. Samples from Earth, the Moon, Mars and the asteroid Vesta reveal significant variations in iron isotope ratios, but the sources of these variations remain uncertain. Here we present experiments that demonstrate that under the conditions of planetary core formation expected for the Moon, Mars and Vesta, iron isotopes fractionate between metal and silicate due to the presence of nickel, and enrich the bodies' mantles in isotopically light iron. However, the effect of nickel diminishes at higher temperatures: under conditions expected for Earth's core formation, we infer little fractionation of iron isotopes. From our experimental results and existing conceptual models of magma ocean crystallization and mantle partial melting, we find that nickel-induced fractionation can explain iron isotope variability found in planetary samples without invoking nebular or accretionary processes. We suggest that near-chondritic iron isotope ratios of basalts from Mars and Vesta, as well as the most primitive lunar basalts, were achieved by melting of isotopically light mantles, whereas the heavy iron isotope ratios of terrestrial ocean floor basalts are the result of melting of near-chondritic Earth mantle.

A volatile rich Earth's core?

NASA Astrophysics Data System (ADS)

Morard, G.; Antonangeli, D.; Andrault, D.; Nakajima, Y.

2017-12-01

The composition of the Earth's core is still an open question. Although mostly composed of iron, it contains impurities that lower its density and melting point with respect to pure Fe. Knowledge of the nature and abundance of light elements (O, S, Si, C or H) in the core has major implications for establishing the bulk composition of the Earth and for building the model of Earth's differentiation. Geochemical models of the Earth's formation point out that its building blocks were depleted in volatile elements compared to the chondritic abundance, therefore light elements such as S, H or C cannot be the major elements alloyed with iron in the Earth's core. However, such models should be compatible with the comparison of seismic properties of the Earth's core and physical properties of iron alloys under extreme conditions, such as sound velocity or density of solid and liquid. The present work will discuss the recent progress for compositional model issued from studies of phase diagrams and elastic properties of iron alloys under core conditions and highlight the compatibility of volatile elements with observed properties of the Earth's core, in potential contradiction with models derived from metal-silicate partitioning experiments.

Possible Role of Hydrogen in the Earth Core

NASA Astrophysics Data System (ADS)

Takahashi, E.; Imai, T.

2011-12-01

Possible role of hydrogen in the Earth core has been discussed by Stevenson (1977) and demonstrated experimentally by Fukai (1984), Okuchi (1997) and others. Planetary theory proposes a possibility of hydrogen incorporation in Earth's magma ocean from ambient solar nebula gas (Ikoma & Genda 2005, Genda & Ikoma 2008). More recently, migration of snow line during planet formation was examined (Min et al., 2010; Oka et al, 2011) and it was proposed that the Earth building material originally contained abundant water as ice and hydrous minerals. Therefore, it is very important to investigate the fate of water in the planet building process and clarify the role of hydrogen in the planetary core. Using SPring-8 synchrotron (NaCl capsule, LiAlH4 as hydrogen source), we determined the melting curve of FeH up to 20 GPa under hydrogen saturated conditions (Sakamaki, Takahashi et al, 2009). Observed melting point is below 1300C and has a very small dT/dP slope. By extrapolating the melting curve using Lindeman's law, we proposed that hydrogen could lower the melting temperature of the Earth core by more than 1500K than current estimate. Here we report our new experiments using SPring-8 synchrotron (single crystal diamond capsule, water as hydrogen source). Hydrogen concentration and melting temperature of FeHx that coexists with hydrous mantle minerals were determined at 15-20GPa and 1000-1600C. We show that 1) hydrogen concentration in FeHx at 1000C, coexisting with hydrous-B and ringwoodite is approximately X=0.6. 2) Upon heating, hydrous-B decomposes and hydrogen strongly partitions into FeHx (X=0.8~1.0) than ringwoodite. 3) FeHx that coexists with ringwoodite melts between ~1300C (solidus) and ~1600C (liquidus). Combined our new experiments with those by Sakamaki et al (2009) and Shibazaki et al (2009), partitioning of hydrogen between proto-core and primitive mantle is discussed. We propose that >90% of water in the source material may have entered the Earth core. Given large hydrogen concentration in the Earth core, temperature of the outermost core could be as low as that of lower mantle adiabat. Presence of the light element-rich layer at the top 300km layer of the outer core (Helffrich & Kaneshima, 2010) may be easily understood if there is no temperature gap between the core and the lower mantle.

Effect of Hydrogen and Carbon on the Melting Temperature of the Core

NASA Astrophysics Data System (ADS)

Nakajima, Y.; Sakamaki, K.; Takahashi, E.; Fukai, Y.; Suzuki, T.; Funakoshi, K.

2007-12-01

The temperature of the Earth's outer core has been discussed based on the melting temperature of Fe- O-S alloys (e.g., Boehler, 1996). Although hydrogen and carbon are the possible candidates of the core component, their effects on the melting temperature of iron at high-pressures are unclear. Using a Kawai-type multi-anvil apparatus at SPring-8 synchrotron, we carried out a series of melting experiments on FeH and Fe3C up to 20 and 28 GPa, respectively. In the experiments on FeH, Fe sponge mixed with MgO was packed into a NaCl container with a hydrogen source, LiAlH4 (e.g., Fukai et al., 1989). During heating under high-pressures, hydrogenation of iron was observed by volume change. The phase boundary between ɛ'-phase (low-temperature phase) and γ-phase (high-temperature phase) of iron-hydride was determined using both cooling and heating experiments. Hydrogen concentrations in the γ-FeHx and ɛ'-FeHx were calculated based on the excess volume data from that of pure iron. It is found that γ-FeHx and ɛ'-FeHx synthesized in our experiments at pressures between 10 and 20 GPa are nearly stoichiometric FeH. Melting temperature of the γ-FeH was determined by the abrupt change in the X-ray diffraction patterns (crystalline to amorphous). The melting temperatures were determined to be 1473, 1473, 1493, 1573 and 1593 K at 10, 11.5, 15, 18 and 20 GPa, respectively. In the experiments using Fe3C, the synthesized Fe3C powder was encapsulated in a MgO container. In the diffraction sequences during heating, the peaks of Fe3C disappeared, and the new peaks identified as those of Fe7C3 were observed with halo caused by liquid. Finally, the Fe7C3 peaks disappeared, and only the halo pattern was observed. Based on these observations, the incongruent melting of Fe3C to Fe7C3 and liquid is estimated to occur at 1823 and 1923 K at 19.7 and 27.0 GPa, respectively. The liquidus temperatures of the Fe3C composition are found to be at 2098 and 2198 K at 19.5 and 26.8 GPa, respectively. The melting temperatures of Fe3C determined by our experiments are >700 K lower than that of the previous estimation based on thermodynamic calculation (Wood, 1993). Our experimental results show a possibility that the hydrogen and carbon lower the melting temperature of iron (outer core) dramatically. The melting temperatures of γ-FeH and Fe3C at 20 GPa are already 500 K lower than that of pure iron estimated by Anderson and Isaak (2000). Extrapolating our experimental melting curves for FeH and Fe3C to core pressures using Lindemann's melting law, we obtained the melting temperatures to be ~2600 and ~2900 K at the core-mantle boundary (CMB), respectively. In the presence of both hydrogen and carbon, melting temperature of the Earth's outer core could be >1500 K lower than that of the previous estimates, implying that the temperature gap at CMB could be much smaller than the current estimates.

The structure of melting mushy zones, with implications for Earth's inner core (Invited)

NASA Astrophysics Data System (ADS)

Bergman, M. I.; Huguet, L.; Alboussiere, T.

2013-12-01

Seismologists have inferred hemispherical differences in the isotropic wavespeed, the elastic anisotropy, the attenuation, and the attenuation anisotropy of Earth's inner core. One hypothesis for these hemispherical differences involves an east-west translation of the inner core, with enhanced solidification on one side and melting on the other. Another hypothesis is that long term mantle control over outer core convection can lead to hemispherical variations in solidification that could even result in melting in some regions of the inner core boundary. It has also been hypothesized that the inner core is growing dendritically, resulting in an inner core that has the structure of a mushy zone (albeit one with a high solid fraction). It would therefore be helpful to understand how the structure of a melting mushy zone might look in comparison with one that is solidifying, in an effort to help interpret the seismic inferences. We have carried out experiments on the solidification of ammonium chloride from an aqueous solution, yielding a mushy zone. The experiments run in a centrifuge, in order to reach a more realistic ratio of convective velocity to phase change rate, expected to be very large at the boundary of the inner core. Hypergravity thus increases the experimental solid fraction of the mush. So far the maximum gravity we have achieved is 200 g. A Peltier cell provides cooling at one end of the cell, and after the mushy zone has grown we turn on a heater at the other end. Probes monitor the temperature along the height of the cell. As ammonium chloride in the mushy zone melts it produces more dense fluid, which results in convection in the mushy zone, a greater ammonium chloride concentration deeper in the mushy zone, and hence enhanced solidification there. This thus changes the solid fraction profile from that during solidification, which may be observable in the lab experiments using ultrasonic transducers and post-mortem under a microscope. The melting may also change the propagation of chimney convection. It remains unclear whether these changes will be observable seismically.

A 400-year ice core melt layer record of summertime warming in the Alaska Range

NASA Astrophysics Data System (ADS)

Winski, D.; Osterberg, E. C.; Kreutz, K. J.; Wake, C. P.; Ferris, D. G.; Campbell, S. W.; Baum, M.; Raudzens Bailey, A.; Birkel, S. D.; Introne, D.; Handley, M.

2017-12-01

Warming in high-elevation regions has socially relevant impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high-elevation temperature records exist from the middle or high latitudes. While many terrestrial paleoclimate records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually-resolved temperature records from high elevations. We present a 400-year temperature record based on the melt-layer stratigraphy in two ice cores collected from Mt. Hunter in the Central Alaska Range. The ice core record shows a 60-fold increase in melt frequency and water equivalent melt thickness between the pre-industrial period (before 1850) and present day. We calibrate the melt record to summer temperatures based on local and regional weather station analyses, and find that the increase in melt production represents a summer warming of at least 2° C, exceeding rates of temperature increase at most low elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p<0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby-wave like pattern that induces high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century, and that conditions in the tropical oceans contribute to this warming.

Drilling Magma for Science, Volcano Monitoring, and Energy

NASA Astrophysics Data System (ADS)

Eichelberger, J. C.; Lavallée, Y.; Blankenship, D.

2017-12-01

Magma chambers are central to understanding magma evolution, formation of continental crust, volcanism, and renewal of hydrothermal systems. Information from geology, petrology, laboratory experiments, and geophysical imagery has led to little consensus except a trend to see magma systems as being crystal-dominant (mush) rather than melt dominant. At high melt viscosities, crystal-liquid fractionation may be achieved by separation of melt from mush rather than crystals from liquid suspension. That the dominant volume has properties more akin to solid than liquid might explain the difficulty in detecting magma geophysically. Recently, geothermal drilling has intersected silicic magma at the following depths and SiO2 contents are: Puna, Hawaii, 2.5 km, 67 wt%; Menengai, Kenya 2.1 km, 67 wt%; Krafla, Iceland, 2.1 km, 75 wt%. Some similarities are: 1) Drillers encountered a "soft", sticky formation; 2) Cuttings or chips of clear quenched glass were recovered; 3) The source of the glass flowed up the well; 4) Transition from solid rock to recovering crystal-poor glass occurred in tens of meters, apparently without an intervening mush zone. Near-liquidus magma at the roof despite rapid heat loss there presents a paradox that may be explained by very recent intrusion of magma, rise of liquidus magma to the roof replacing partially crystallized magma, or extremely skewed representation of melt over mush in cuttings (Carrigan et al, this session). The latter is known to occur by filter pressing of ooze into lava lake coreholes (Helz, this session), but cannot be verified in actual magma without coring. Coring to reveal gradients in phase composition and proportions is required for testing any magma chamber model. Success in drilling into and controlling magma at all three locations, in coring lava lakes to over 1100 C, and in numerical modeling of coring at Krafla conditions (Su, this session) show this to be feasible. Other unprecedented experiments are using the known location and properties of magma to calibrate geophysics (Brown et al, this session) and understand signals of "unrest". How can we not make such observations when there is so much to learn, so much at stake in correctly monitoring volcanoes, and such a need for clean, renewable energy?

Sr isotope zoning in plagioclase from andesites at Cabo De Gata, Spain: Evidence for shallow and deep contamination

NASA Astrophysics Data System (ADS)

Waight, Tod E.; Tørnqvist, Jakob B.

2018-05-01

Plagioclase crystals in andesites from the Cabo De Gata region show generally radiogenic Sr isotope compositions and consistent core to rim increases in 87Sr/86Sr that are indicative of open system processes in the lithosphere and crustal contamination during crystallization. High-grade metamorphic rocks of the Alpujárride and Nevado-Filábride complexes represent the most likely crustal contaminants. The plagioclases are characterized by subtly zoned and resorbed calcic cores (An73-86). These cores also have radiogenic 87Sr/86Sr (0.7127-0.7129), although typically less radiogenic than plagioclase rims, groundmass plagioclase and whole rock compositions (up to 87Sr/86Sr = 0.7135). These cores are interpreted to represent early crystallization of plagioclase from hydrous melts emplaced into the lower crust. The parental melts to these andesites must therefore have already inherited their radiogenic Sr isotope compositions prior to entering the lower crust and before the onset of crystallization of plagioclase, which is inconsistent with previous models suggesting that the generally radiogenic nature of Sr in these volcanics reflects large amounts of crustal contamination. Instead, the isotope systematics are consistent with models invoked significant addition of a subducted sediment component to the mantle source. The high-An% plagioclase cores are characterized by resorption textures, which are consistent with dissolution during rapid decompression and/or devolatisation during magma migration from the lower crust into upper crustal magma chambers.

Effect of Ni on Fe FeS phase relations at high pressure and high temperature

NASA Astrophysics Data System (ADS)

Zhang, Li; Fei, Yingwei

2008-04-01

A series of melting experiments in the Fe-rich portion of the Fe-Ni-S system have been conducted at 19-23 GPa and 800-1100 °C. The solubility of S in the Fe-Ni solid alloy and the eutectic melting in the Fe-Ni-S system were determined as a function of Ni content. The maximum S solubility in the Fe-Ni alloy is 2.7 wt.% at 20 GPa and the eutectic temperature. The eutectic melting temperature in the Fe-Ni(5wt.%)-S system is ~ 1000 °C lower than the melting point of pure Fe at 20 GPa. We also found that Ni can substitute Fe in the Fe 3S structure to form (Fe,Ni) 3S solid solutions up to at least a Fe/Ni atomic ratio of 0.5. Similar to melting behavior in the Fe-FeS system, the eutectic melting relations in the Fe-Ni-S system could produce inner and outer cores with the right light element balance to account for the density difference between the solid inner core and the liquid outer core.

Quantitative characterization of 3-dimensional melt distribution in partially molten olivine-basalt aggregates using X-ray synchrotron microtomography

NASA Astrophysics Data System (ADS)

Zhu, W.; Gaetani, G. A.; Fusseis, F.

2009-12-01

Quantitative knowledge of the distribution of small amounts of silicate melt in peridotite and of its influence on permeability are critical to our understanding of melt migration and segregation processes in the upper mantle. Estimates for the permeability of partially molten rock require 3D melt distribution at the grain-scale. Existing studies of melt distribution, carried out on 2D slices through experimental charges, have produced divergent models for melt distribution at small melt fractions. While some studies conclude that small amounts of melt are distributed primarily along triple junctions [e.g., Wark et al., 2003], others predict an important role for melt distribution along grain boundaries at low melt fractions [e.g., Faul 1997]. Using X-ray synchrotron microtomography, we have obtained the first high quality non-destructive imaging of 3D melt distribution in olivine-basalt aggregates. Textually equilibrated partially molten samples consisting of magnesian olivine plus 2, 5, 10, or 20% primitive basalt were synthesized at 1.5 GPa and 1350°C in experiments lasting 264-336 hours. Microtomographic images of melt distribution were obtained on cylindrical cores, 1 mm in diameter, at a spatial resolution of 1 micron. Textual information such as melt channel size, dihedral angle and channel connectivity was then quantified using AVIZO and MATLAB. Our results indicate that as melt fraction decreases, melt becomes increasingly distributed along 3 grain junctions, in agreement with theoretical predictions. We do not find significant amounts of melt along grain boundaries at low melt fractions. We found that the true dihedral angle ranges from 50 to 70°, in agreements with results using 2D microcopy. Comparison between the samples provides a quantitative characterization of how melt fraction affects melt distribution including connectivity. The geometrical data have been incorporated into our network model to obtain macroscale transport properties for partially molten dunite. Results from this tomographic study thus provide constraints on rates of melt migration and melt extraction within the partially molten regions beneath ocean ridges. Fig 1. Melt channels in an olivine-basalt sample with 10 vol% melt.

Nitrogen partitioning during core-mantle differentiation

NASA Astrophysics Data System (ADS)

Speelmanns, I. M.; Schmidt, M. W.; Liebske, C.

2016-12-01

This study investiagtes nitrogen partitioing between metal and silicate melts as relevant for core segregation during the accretion of planetesimals into the Earth. On present day Earth, N belongs to the most important elements, as it is one of the key constituents of our atmosphere and forms the basis of life. However, the geochemistry of N, i.e. its distribution and isotopic fractionation between Earth's deep reservoirs is not well constrained. In order to determine the partitioning behaviour of N, a centrifuging piston cylinder was used to euqilibrate and then gravitationally separate metal-silicate melt pairs at 1250 °C, 1 GPa over the range of oxygen fugacities thought to have prevailied druing core segreagtion (IW-4 to IW). Complete segregation of the two melts was reached within 3 hours at 1000 g, the interface showing a nice meniscus The applied double capsule technique, using an outer metallic and inner non-metallic (mostly graphite) capsule, minimizes volatile loss over the course of the experiment compared to single non-metallic capsules. The two quenched melts were cut apart, cleaned at the outside and N concentrations of the melts were analysed on bulk samples by an elemental analyser. Nevertheless, the low amount of sample material and the N yield in the high pressure experiments required the developement of new analytical routines. Despite these experimental and analytical difficulties, we were able to determine a DNmetal/silicateof 13±0.25 at IW-1, N partitioning into the core froming metal. The few availible literature data [1],[2] suggest that N changes its compatibility favoring the silicate melt or magma ocean at around IW-2.5. In order to asses how much N may effectively be contained in the core and the silicate Earth, experiments characterizing N behaviour over the entire range of core formation condtitions are well under way. [1] Kadik et al., (2011) Geochemistry International 49.5: 429-438. [2] Roskosz et al., (2013) GCA 121: 15-28.

Lunar Love Numbers and the Deep Lunar Interior

NASA Technical Reports Server (NTRS)

Williams, J. G.; Boggs, D. H.; Ratcliff, J. T.; Dickey, J. O.

2002-01-01

Observationally determined values of the Love number k2 are larger than existing models of the lunar interior predict. The region between the deep moonquakes and core may be a low velocity zone from a partial melt. Additional information is contained in the original extended abstract.

Variations in Melt Generation and Migration along the Aleutian Arc (Invited)

NASA Astrophysics Data System (ADS)

Plank, T. A.; Van Keken, P. E.

2013-12-01

The generation and ascent of mantle melt beneath volcanic arcs sets the course for how magmas differentiate to form the continental crust and erupt explosively from volcanoes. Although the basic framework of melting at subduction zones is understood to involve the convective influx of hot mantle (Tp ≥ 1300°C) and advective transport of water-rich fluids from the subducting slab, the P-T paths that melts follow during melt generation and migration are still not well known. The Aleutian Arc provides an opportunity to explore the conditions of mantle melting in the context of volcanoes that span an unusually large range in the depth to the slab, from Seguam island, with among the shallowest depths to the slab worldwide (~65 km, [1]) to Bogoslof island, behind the main volcanic front and twice the depth to the slab (~130 km). Here we combine thermal models tuned to Aleutian subduction parameters [after 2] with petrological estimates of the T and P of mantle-melt equilibration, using a major element geothermometer [3] and estimates of H2O and fO2 from olivine-hosted melt inclusion measurements [4] for basaltic magmas from 6 volcanoes in the central Aleutians (Korovin, Seguam, Bogoslof, Pakushin, Akutan, Shishaldin). We find mantle-melt equilibration conditions to vary systematically as a function of the depth to the slab, from 30 km and 1220°C (for Seguam) to 60 km and 1300°C (for Bogoslof). Such shallow depths, which extend up to the Moho, define a region perched well above the hot core of the mantle wedge predicted from thermal models, even considering the shallow depths of slab-mantle coupling (< 60 km) required to supply hot mantle beneath Seguam. Thus, even though the greatest melt production will occur in the hot core of the wedge (50-100 km depth), melts apparently ascend and re-equilibrate in the shallowest mantle. Volcanoes that overlie the greatest depth to the slab, and lie furthest from the wedge corner, stall at greater depths (~60 km), at the base of the conductive upper plate (i.e., lithosphere). The conductive lid and isotherms shallow toward the wedge corner. This leads to shallower depths of melt equilibration at shallower depths to the slab. A second effect is infiltration of melt into the thinning lithosphere, likely due to the increase in strain-rate toward the wedge corner, which favors melt segregation, migration, and shallow equilibration [5]. Such a process is developed most beneath Seguam, where melts collect at the Moho (~ 30km), but are still > 1200°C. Such equilibration depths in the uppermost mantle (30-60 km) and temperatures typical of the base of the conductive lid appear to characterize most modeled primary arc magmas [6], and point to a final re-setting point in the mantle that controls the composition of bulk arc crust. [1] Syracuse & Abers, 2006, G3. [2] Syracuse, van Keken, Abers, (2010) PEPI. [3] Lee, Luffi, Plank, Dalton, Leeman (2009) EPSL. [4] Zimmer et al. (2010) J.Pet. [5] Holzman & Kendall (2010). [6] Ruscitto et al. (2012) G3.

Key findings and remaining questions in the areas of core-concrete interaction and debris coolability

DOE PAGES

Farmer, M. T.; Gerardi, C.; Bremer, N.; ...

2016-10-31

The reactor accidents at Fukushima-Dai-ichi have rekindled interest in late phase severe accident behavior involving reactor pressure vessel breach and discharge of molten core melt into the containment. Two technical issues of interest in this area include core-concrete interaction and the extent to which the core debris may be quenched and rendered coolable by top flooding. The OECD-sponsored Melt Coolability and Concrete Interaction (MCCI) programs at Argonne National Laboratory included the conduct of large scale reactor material experiments and associated analysis with the objectives of resolving the ex-vessel debris coolability issue, and to address remaining uncertainties related to long-term two-dimensionalmore » molten core-concrete interactions under both wet and dry cavity conditions. These tests provided a broad database to support accident management planning, as well as the development and validation of models and codes that can be used to extrapolate the experiment results to plant conditions. This paper provides a high level overview of the key experiment results obtained during the program. Finally, a discussion is also provided that describes technical gaps that remain in this area, several of which have arisen based on the sequence of events and operator actions during Fukushima.« less

Key findings and remaining questions in the areas of core-concrete interaction and debris coolability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farmer, M. T.; Gerardi, C.; Bremer, N.

The reactor accidents at Fukushima-Dai-ichi have rekindled interest in late phase severe accident behavior involving reactor pressure vessel breach and discharge of molten core melt into the containment. Two technical issues of interest in this area include core-concrete interaction and the extent to which the core debris may be quenched and rendered coolable by top flooding. The OECD-sponsored Melt Coolability and Concrete Interaction (MCCI) programs at Argonne National Laboratory included the conduct of large scale reactor material experiments and associated analysis with the objectives of resolving the ex-vessel debris coolability issue, and to address remaining uncertainties related to long-term two-dimensionalmore » molten core-concrete interactions under both wet and dry cavity conditions. These tests provided a broad database to support accident management planning, as well as the development and validation of models and codes that can be used to extrapolate the experiment results to plant conditions. This paper provides a high level overview of the key experiment results obtained during the program. Finally, a discussion is also provided that describes technical gaps that remain in this area, several of which have arisen based on the sequence of events and operator actions during Fukushima.« less

Modeling the early evolution of Vesta

NASA Astrophysics Data System (ADS)

Weisfeiler, Marie; Turcotte, Donald L.; Kellogg, Louise H.

2017-05-01

The early evolution of the asteroid Vesta has been extensively studied because of the availability of relevant data, especially important new studies of HED meteorites which originated from Vesta and the Dawn mission to Vesta in 2011-2012. These studies have concluded that an early melting episode led to the differentiation of Vesta into crust, mantle, and core. This melting episode is attributed to the decay of 26Al, which has a half-life of 7.17 × 105 yr. This heating produced a global magma ocean. Surface cooling of this magma ocean will produce a solid crust. In this paper, we propose a convective heat-transfer mechanism that effectively cools the asteroid when the degree of melting reaches about 50%. We propose that a cool solid surface crust, which is gravitationally unstable, will founder into the solid-liquid mix beneath and will very effectively transfer heat that prevents further melting of the interior. In this paper, we quantify this process. If Vesta had a very early formation, melting would commence at an age of about 1,30,000 yr, and solidification would occur at an age of about 10 Myr. If Vesta formed with a time delay greater than about 2 Myr, no melting would have occurred. An important result of our model is that the early melting episode is restricted to the first 10 Myr. This result is in good agreement with the radiometric ages of the HED meteorites.

An assessment of the CORCON-MOD3 code. Part 1: Thermal-hydraulic calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strizhov, V.; Kanukova, V.; Vinogradova, T.

1996-09-01

This report deals with the subject of CORCON-Mod3 code validation (thermal-hydraulic modeling capability only) based on MCCI (molten core concrete interaction) experiments conducted under different programs in the past decade. Thermal-hydraulic calculations (i.e., concrete ablation, melt temperature, melt energy, concrete temperature, and condensible and non-condensible gas generation) were performed with the code, and compared with the data from 15 experiments, conducted at different scales using both simulant (metallic and oxidic) and prototypic melt materials, using different concrete types, and with and without an overlying water pool. Sensitivity studies were performed in a few cases involving, for example, heat transfer frommore » melt to concrete, condensed phase chemistry, etc. Further, special analysis was performed using the ACE L8 experimental data to illustrate the differences between the experimental and the reactor conditions, and to demonstrate that with proper corrections made to the code, the calculated results were in better agreement with the experimental data. Generally, in the case of dry cavity and metallic melts, CORCON-Mod3 thermal-hydraulic calculations were in good agreement with the test data. For oxidic melts in a dry cavity, uncertainties in heat transfer models played an important role for two melt configurations--a stratified geometry with segregated metal and oxide layers, and a heterogeneous mixture. Some discrepancies in the gas release data were noted in a few cases.« less

Deleterious Thermal Effects Due To Randomized Flow Paths in Pebble Bed, and Particle Bed Style Reactors

NASA Technical Reports Server (NTRS)

Moran, Robert P.

2013-01-01

A review of literature associated with Pebble Bed and Particle Bed reactor core research has revealed a systemic problem inherent to reactor core concepts which utilize randomized rather than structured coolant channel flow paths. For both the Pebble Bed and Particle Bed Reactor designs; case studies reveal that for indeterminate reasons, regions within the core would suffer from excessive heating leading to thermal runaway and localized fuel melting. A thermal Computational Fluid Dynamics model was utilized to verify that In both the Pebble Bed and Particle Bed Reactor concepts randomized coolant channel pathways combined with localized high temperature regions would work together to resist the flow of coolant diverting it away from where it is needed the most to cooler less resistive pathways where it is needed the least. In other words given the choice via randomized coolant pathways the reactor coolant will take the path of least resistance, and hot zones offer the highest resistance. Having identified the relationship between randomized coolant channel pathways and localized fuel melting it is now safe to assume that other reactor concepts that utilize randomized coolant pathways such as the foam core reactor are also susceptible to this phenomenon.

Chemical layering in the upper mantle of Mars: Evidence from olivine-hosted melt inclusions in Tissint

NASA Astrophysics Data System (ADS)

Basu Sarbadhikari, A.; Babu, E. V. S. S. K.; Vijaya Kumar, T.

2017-02-01

Melting of Martian mantle, formation, and evolution of primary magma from the depleted mantle were previously modeled from experimental petrology and geochemical studies of Martian meteorites. Based on in situ major and trace element study of a range of olivine-hosted melt inclusions in various stages of crystallization of Tissint, a depleted olivine-phyric shergottite, we further constrain different stages of depletion and enrichment in the depleted mantle source of the shergottite suite. Two types of melt inclusions were petrographically recognized. Type I melt inclusions occur in the megacrystic olivine core (Fo76-70), while type II melt inclusions are hosted by the outer mantle of the olivine (Fo66-55). REE-plot indicates type I melt inclusions, which are unique because they represent the most depleted trace element data from the parent magmas of all the depleted shergottites, are an order of magnitude depleted compared to the type II melt inclusions. The absolute REE content of type II displays parallel trend but somewhat lower value than the Tissint whole-rock. Model calculations indicate two-stage mantle melting events followed by enrichment through mixing with a hypothetical residual melt from solidifying magma ocean. This resulted in 10 times enrichment of incompatible trace elements from parent magma stage to the remaining melt after 45% crystallization, simulating the whole-rock of Tissint. We rule out any assimilation due to crustal recycling into the upper mantle, as proposed by a recent study. Rather, we propose the presence of Al, Ca, Na, P, and REE-rich layer at the shallower upper mantle above the depleted mantle source region during the geologic evolution of Mars.

Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet.

PubMed

Keegan, Kaitlin M; Albert, Mary R; McConnell, Joseph R; Baker, Ian

2014-06-03

In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting.

The Deep Crust Magmatic Refinery, Part 1: A Coupled Thermodynamic and Two-phase Flow Model

NASA Astrophysics Data System (ADS)

Riel, N., Jr.; Bouilhol, P.; Van Hunen, J.; Velic, M.; Magni, V.

2016-12-01

Metamorphic and magmatic processes occurring in the deep crust ultimately control the chemical and physical characteristic of the continental crust. A complex interplay between magma intrusion, crystallization, and reaction with the pre-existing crust provide a wide range of differentiated magma and cumulates (and / or restites) that will feed the upper crustal levels with evolved melt while constructing the lower crust. With growing evidence from field and experimental studies, it becomes clearer that crystallization and melting processes are non-exclusive but should be considered together. Incoming H2O bearing mantle melts will start to fractionate to a certain extent, forming cumulates but also releasing heat and H2O to the intruded host-rock allowing it to melt in saturated conditions. The end-result of such dynamic system is a function of the amount and composition of melt input, and extent of reaction with the host which is itself dependent on the migration mode of the melts. To assess the dynamics of this deep magmatic system we developed a new 2-D two-phase flow code using finite volume method. Our formulation takes into account: (i) melt flow through a viscous porous matrix with temperature- and melt-content dependent host-rock viscosity, (ii) heat transfer, assuming local thermal equilibrium between solid and liquid, (iii) thermodynamic modelling of stable phases, (iv) injection of fractionated melt from crystallizing basalt at the Moho and (v) chemical advection of both the solid and liquid compositions. Here we present the core of our modelling approach, especially the petrological implementation. We show in details that our thermodynamic model can reproduce well both the sub- and supra solidus phase relationship and composition of the host-rock. We apply our method to an idealized amphibolite lower crust that is affected by a magmatic event represented by the intrusion of a wet mantle melt into the crust at Moho depth. The models [see Bouilhol et al. associated abstract for results] allow calculating the different proportion of phases present in the system through time.

Improvements on the interior structure of Mercury expected from geodesy measurements

NASA Astrophysics Data System (ADS)

Rivoldini, A.; van Hoolst, T.; Verhoeven, O.

2008-09-01

ABSTRACT We assess the improvements on the interior structure of Mercury provided by expected data from geodesy experiments to be performed with the MESSENGER and BepiColombo orbiters. The observation of obliquity will allow estimating the moment of inertia, whereas measurements of libration will determine the moment of inertia of the silicate shell (mantle and crust). Tidal measurements will constrain the Love numbers that characterize the response of Mercury to the solar tidal forcing. Here, we construct depth-dependent interior structure models of Mercury for several plausible chemical compositions of the core and of the mantle using recent data on core and mantle materials. In particular we study the core structure for different mantle mineralogies and two different temperature profiles. We investigate the influence of the core light element concentration, temperature, and melting law on core state and inner core size. We compute libration amplitude, obliquity, tidal deformation, and tidal changes in the external potential for our models.

The hottest lavas of the Phanerozoic from a reservoir at the core-mantle boundary

NASA Astrophysics Data System (ADS)

Gazel, E.; Trela, J.; Sobolev, A. V.; Bizimis, M.; Jicha, B. R.; Batanova, V. G.

2017-12-01

Petrologic models suggest that modern plume-derived melts generate at high mantle temperatures (>1500 °C) relative to those produced at ambient mid-ocean ridge conditions ( 1350 °C). Earth's mantle has cooled during its history due to heat loss and decrease in radioactive heat production, thus the temperatures of these modern-day basalts are substantially lower than those produced during the Archean (>2.5 Ga), as recorded by komatiites (>1700 °C). Surprisingly, we discovered that the 90 Ma Galapagos-related Tortugal Suite accreted in Costa Rica not only records mantle potential temperatures as high as ancient Archean komatiites ( 1800 °C), but also the highest olivine-spinel crystallization temperatures ever reported ( 1600 °C). These new results from Tortugal (and other anomalously hot Phanerozoic locations) imply that if the mantle is still producing melts as hot as during the Archean, then there must exist reservoirs that preserve Archean temperatures at the base of the lower mantle. These anomalously hot reservoirs could be sustained over time by the steady-state temperature conditions at the core-mantle boundary buffered by the crystallization of Earth's core. Although our results suggest that even modern plumes can produce melts at similar P-T conditions as inferred during the Archean, these occurrences are not common as plumes will likely interact with the cooler ambient mantle.

Microstructures and petrology of melt inclusions in the anatectic sequence of Jubrique (Betic Cordillera, S Spain): Implications for crustal anatexis

NASA Astrophysics Data System (ADS)

Barich, Amel; Acosta-Vigil, Antonio; Garrido, Carlos J.; Cesare, Bernardo; Tajčmanová, Lucie; Bartoli, Omar

2014-10-01

We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though strongly thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and in contact with the peridotites, and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence, garnet decreases whereas biotite increases in modal proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ≈ 5 to 200 μm, with a mean size of ≈ 30-40 μm. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ≈ 850 °C and 12-14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ≈ 800-850 °C and 5-6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous conventional petrologic studies on these strongly deformed rocks have proposed that anatexis started during decompression from peak to post-peak conditions and in the field of sillimanite. The study of melt inclusions shows, however, that melt was already present in the system at peak conditions, and that most garnet grew in the presence of melt.

The melting curve of Ni to 1 Mbar

NASA Astrophysics Data System (ADS)

Lord, Oliver T.; Wood, Ian G.; Dobson, David P.; Vočadlo, Lidunka; Wang, Weiwei; Thomson, Andrew R.; Wann, Elizabeth T. H.; Morard, Guillaume; Mezouar, Mohamed; Walter, Michael J.

2014-12-01

The melting curve of Ni has been determined to 125 GPa using laser-heated diamond anvil cell (LH-DAC) experiments in which two melting criteria were used: firstly, the appearance of liquid diffuse scattering (LDS) during in situ X-ray diffraction (XRD) and secondly, plateaux in temperature vs. laser power functions in both in situ and off-line experiments. Our new melting curve, defined by a Simon-Glatzel fit to the data where TM (K) = [ (PM/18.78 ± 10.20 + 1) ]1/2.42 ± 0.66 × 1726, is in good agreement with the majority of the theoretical studies on Ni melting and matches closely the available shock wave melting data. It is however dramatically steeper than the previous off-line LH-DAC studies in which determination of melting was based on the visual observation of motion aided by the laser speckle method. We estimate the melting point (TM) of Ni at the inner-core boundary (ICB) pressure of 330 GPa to be TM = 5800 ± 700 K (2 σ), within error of the value for Fe of TM = 6230 ± 500 K determined in a recent in situ LH-DAC study by similar methods to those employed here. This similarity suggests that the alloying of 5-10 wt.% Ni with the Fe-rich core alloy is unlikely to have any significant effect on the temperature of the ICB, though this is dependent on the details of the topology of the Fe-Ni binary phase diagram at core pressures. Our melting temperature for Ni at 330 GPa is ∼2500 K higher than that found in previous experimental studies employing the laser speckle method. We find that those earlier melting curves coincide with the onset of rapid sub-solidus recrystallization, suggesting that visual observations of motion may have misinterpreted dynamic recrystallization as convective motion of a melt. This finding has significant implications for our understanding of the high-pressure melting behaviour of a number of other transition metals.

Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling

NASA Astrophysics Data System (ADS)

Heilig, Achim; Eisen, Olaf; MacFerrin, Michael; Tedesco, Marco; Fettweis, Xavier

2018-06-01

Increasing melt over the Greenland Ice Sheet (GrIS) recorded over the past several years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as a meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness have been observed in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779° N, 46.2856° W) at 2120 m a.s.l. The radar is capable of quasi-continuously monitoring changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well for both timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg m-2 into firn beneath the summer surface of 2015. We find that continuous observations of liquid water content, percolation depths and rates for the seasonal mass fluxes are sufficiently accurate to provide valuable information for validation of model approaches and help to develop a better understanding of liquid water retention and percolation in perennial firn.

Experimental Phase Relations of Hydrous, Primitive Melts: Implications for variably depleted mantle melting in arcs and the generation of primitive high-SiO2 melts

NASA Astrophysics Data System (ADS)

Weaver, S.; Wallace, P. J.; Johnston, A.

2010-12-01

There has been considerable experimental and theoretical work on how the introduction of H2O-rich fluids into the mantle wedge affects partial melting in arcs and chemical evolution of mantle melts as they migrate through the mantle. Studies aimed at describing these processes have become largely quantitative, with an emphasis on creating models that suitably predict the production and evolution of melts and describe the thermal state of arcs worldwide. A complete experimental data set that explores the P-T conditions of melt generation and subsequent melt extraction is crucial to the development, calibration, and testing of these models. This work adds to that data set by constraining the P-T-H2O conditions of primary melt extraction from two end-member subduction zones, a continental arc (Mexico) and an intraoceanic arc (Aleutians). We present our data in context with primitive melts found worldwide and with other experimental studies of melts produced from fertile and variably depleted mantle sources. Additionally, we compare our experimental results to melt compositions predicted by empirical and thermodynamic models. We used a piston-cylinder apparatus and employed an inverse approach in our experiments, constraining the permissible mantle residues with which our melts could be in equilibrium. We confirmed our inverse approach with forced saturation experiments at the P-T-H2O conditions of melt-mantle equilibration. Our experimental results show that a primitive, basaltic andesite melt (JR-28) from monogenetic cinder cone Volcan Jorullo (Central Mexico) last equilibrated with a harzburgite mantle residue at 1.2-1.4 GPa and 1150-1175°C with H2O contents in the range of 5.5-7 wt% H2O prior to ascent and eruption. Phase relations of a tholeiitic high-MgO basaltic melt (ID-16) from the Central Aleutians (Okmok) show the conditions of last equilibration with a fertile lherzolite mantle residue at shallower (1.2 GPa) but hotter (1275°C) conditions with approximately 2 wt% H2O. Given the estimated crustal thicknesses of these two regions, our data suggest that both samples equilibrate with mantle minerals just below the Moho. Recent viscosity dependent thermal models that account for slab geometry suggest that JR-28 melts last equilibrate with harzburgite in a cooler region of the mantle wedge. In contrast, ID-16 equilibrated with a fertile source near the hotter core of the mantle wedge. Our results support the hypothesis that lherzolite melting (wet or dry) produces essentially basaltic melts, whereas more Si-rich primitive melts require shallow hydrous melting of harzburgite or reequilibration of basaltic melts with harzburgite in the uppermost part of the wedge.

Presumption of large-scale heterogeneity at the top of the outer core basal layer

NASA Astrophysics Data System (ADS)

Souriau, Annie

2015-04-01

A layer of reduced P-velocity gradient with thickness of about 100-200 km has been identified at the base of the liquid core from seismological methods. It has been interpreted as a dense layer resulting from partial re-melting of the inner core, which is depleted in light elements with respect to the liquid core during freezing. In an attempt to specify where freezing and re-melting occur, the structure of this basal layer is investigated with the seismological core phase PKPbc which has its turning point in the lower third of the outer core. The large PKPbc data set of the EHB catalog distributed by the International Seismological Centre is analyzed. In order to compensate for the uneven distribution of the data and to minimize the influence of mantle heterogeneities, the travel time anomalies are binned inside equal area and equal azimuth sectors sampling the base of the liquid core at different depths. Most of the observed variations in the binned travel time residuals are not significant according to their confidence level. The only features which could be significant are a large patch with a velocity increase of about 0.5% located at the top of the basal layer beneath the eastern hemisphere, and the complementary velocity decrease beneath the western hemisphere and the South pole. This observation suggests that some freezing or re-melting processes occur at the top of the basal layer with a hemispherical dissymmetry. If confirmed, it may give strong constraints on the fate of the light elements during the freezing and re-melting process and on their interaction with the basal layer and the overlying liquid core.

MELT Bibliography. Materials Correlated with the Core Curriculum Competencies of the Mainstream English Language Training Project, Office of Refugee Resettlement.

ERIC Educational Resources Information Center

Brod, Shirley, Comp.; Sample, Barbara J.

This bibliography is intended to assist teachers and administrators involved in competency-based, English as a second language (ESL) instruction. The materials included in the bibliography have been correlated with the core curriculum competencies of the Mainstream English Language Training (MELT) Project. The guide is divided into three parts.…

The geochemical record in rock glaciers

USGS Publications Warehouse

Steig, E.J.; Fitzpatrick, J.J.; Potter, N.; Clark, D.H.

1998-01-01

A 9.5 m ice core was extracted from beneath the surficial debris cover of a rock glacier at Galena Creek, northwestern Wyoming. The core contains clean, bubble-rich ice with silty debris layers spaced at roughly 20 cm intervals. The debris layers are similar in appearance to those in typical alpine glaciers, reflecting concentration of debris by melting at the surface during the summer ablation season. Profiles of stable isotope concentrations and electrical conductivity measurements provide independent evidence for melting in association with debris layers. These observations are consistent with a glacial origin for the ice, substantiating the glacigenic model for rock glacier formation. The deuterium excess profile in the ice indicates that the total depth of meltwater infiltration is less than the thickness of one annual layer, suggesting that isotope values and other geochemical signatures are preserved at annual resolution. This finding demonstrates the potential for obtaining useful paleoclimate information from rock glacier ice.

Sprayed skin turbine component

DOEpatents

Allen, David B

2013-06-04

Fabricating a turbine component (50) by casting a core structure (30), forming an array of pits (24) in an outer surface (32) of the core structure, depositing a transient liquid phase (TLP) material (40) on the outer surface of the core structure, the TLP containing a melting-point depressant, depositing a skin (42) on the outer surface of the core structure over the TLP material, and heating the assembly, thus forming both a diffusion bond and a mechanical interlock between the skin and the core structure. The heating diffuses the melting-point depressant away from the interface. Subsurface cooling channels (35) may be formed by forming grooves (34) in the outer surface of the core structure, filling the grooves with a fugitive filler (36), depositing and bonding the skin (42), then removing the fugitive material.

Chicxulub Impact Melts: Geochemical Signatures of Target Lithology Mixing and Post-Impact Hydrothermal Fluid Processes

NASA Technical Reports Server (NTRS)

Kring, David A.; Zurcher, Lukas; Horz, Freidrich; Mertzmann, Stanley A.

2004-01-01

Impact melts within complex impact craters are generally homogeneous, unless they differentiated, contain immiscible melt components, or were hydrothermally altered while cooling. The details of these processes, however, and their chemical consequences, are poorly understood. The best opportunity to unravel them may lie with the Chicxulub impact structure, because it is the world s most pristine (albeit buried) large impact crater. The Chicxulub Scientific Drilling Project recovered approx. 100 meters of impactites in a continuous core from the Yaxcopoil-1 (YAX-1) borehole. This dramatically increased the amount of melt available for analyses, which was previously limited to two small samples N17 and N19) recovered from the Yucatan-6 (Y-6) borehole and one sample (N10) recovered from the Chicxulub-1 (C-1) borehole. In this study, we describe the chemical compositions of six melt samples over an approx. 40 m section of the core and compare them to previous melt samples from the Y-6 and C-1 boreholes.

Low-Degree Partial Melting Experiments of CR and H Chondrite Compositions: Implications for Asteroidal Magmatism Recorded in GRA 06128 and GRA 06129 T

NASA Technical Reports Server (NTRS)

Usui, T.; Jones, John H.; Mittlefehldt, D. W.

2010-01-01

Studies of differentiated meteorites have revealed a diversity of differentiation processes on their parental asteroids; these differentiation mechanisms range from whole-scale melting to partial melting without the core formation [e.g., 1]. Recently discovered paired achondrites GRA 06128 and GRA 06129 (hereafter referred to as GRA) represent unique asteroidal magmatic processes. These meteorites are characterized by high abundances of sodic plagioclase and alkali-rich whole-rock compositions, implying that they could originate from a low-degree partial melt from a volatile-rich oxidized asteroid [e.g., 2, 3, 4]. These conditions are consistent with the high abundances of highly siderophile elements, suggesting that their parent asteroid did not segregate a metallic core [2]. In this study, we test the hypothesis that low-degree partial melts of chondritic precursors under oxidizing conditions can explain the whole-rock and mineral chemistry of GRA based on melting experiments of synthesized CR- and H-chondrite compositions.

A Model for the Thermal and Chemical Evolution of the Moon's Interior: Implications for the Onset of Mare Volcanism

NASA Technical Reports Server (NTRS)

Hess, Paul C.; Parmentier, E. M.

1995-01-01

Crystallization of the lunar magma ocean creates a chemically stratified Moon consisting of an anorthositic crust and magma ocean cumulates overlying the primitive lunar interior. Within the magma ocean cumulates the last liquids to crystallize form dense, ilmenite-rich cumulates that contain high concentrations of incompatible radioactive elements. The underlying olivine-orthopyroxene cumulates are also stratified with later crystallized, denser, more Fe-rich compositions at the top. This paper explores the chemical and thermal consequences of an internal evolution model accounting for the possible role of these sources of chemical buoyancy. Rayleigh-Taylor instability causes the dense ilmenite-rich cumulate layer and underlying Fe-rich cumulates to sink toward the center of the Moon, forming a dense lunar core. After this overturn, radioactive heating within the ilmenite-rich cumulate core heats the overlying mantle, causing it to melt. In this model, the source region for high-TiO2 mare basalts is a convectively mixed layer above the core-mantle boundary which would contain small and variable amounts of admixed ilmenite and KREEP. This deep high-pressure melting, as required for mare basalts, occurs after a reasonable time interval to explain the onset of mare basalt volcanism if the content of radioactive elements in the core and the chemical density gradients above the core are sufficiently high but within a range of values that might have been present in the Moon. Regardless of details implied by particular model parameters, gravitational overturn driven by the high density of magma ocean Fe-rich cumulates should concentrate high-TiO2 mare basalt sources, and probably a significant fraction of radioactive heating, toward the center of the Moon. This will have important implications for both the thermal evolution of the Moon and for mare basalt genesis.

Investigation of micro-injection molding based on longitudinal ultrasonic vibration core.

PubMed

Qiu, Zhongjun; Yang, Xue; Zheng, Hui; Gao, Shan; Fang, Fengzhou

2015-10-01

An ultrasound-assisted micro-injection molding method is proposed to improve the rheological behavior of the polymer melt radically, and a micro-injection molding system based on a longitudinal ultrasonic vibration core is developed and employed in the micro-injection molding process of Fresnel lenses. The verification experiments show that the filling mold area of the polymer melt is increased by 6.08% to 19.12%, and the symmetric deviation of the Fresnel lens is improved 15.62% on average. This method improved the filling performance and replication quality of the polymer melt in the injection molding process effectively.

Si and O partitioning between core metal and lower mantle minerals during core formation

NASA Astrophysics Data System (ADS)

Nakajima, Y.; Frost, D. J.; Rubie, D. C.

2010-12-01

In addition to Fe and Ni, the Earth’s core contains light alloying elements (e.g., H, C, O, Si, and/or S) in order to explain the 10% core density deficit (e.g., Birch, 1964, JGR). Experimental data on the partitioning behavior of siderophile elements such as Ni and Co between liquid Fe and mantle minerals indicate that equilibration between core-forming metal and a silicate magma ocean likely occurred at lower-mantle pressures (e.g., Li and Agee, 1996 Nature). If core-mantle differentiation has occurred under such conditions, significant quantities of O or Si could have entered the core. At these conditions the nature of the dominant light element in the core will depend strongly on the oxygen fugacity at which equilibration occurred. High pressure experiments were carried out at 25 GPa and 2400-2950 K using a Kawai-type multi-anvil apparatus in order to investigate the partitioning of Si and O between liquid Fe and (Mg,Fe)SiO3 perovskite (Pv), silicate melt, and (Mg,Fe)O ferropericlace (Fp). Starting materials consisting of metallic Fe (+-Si) and olivine (Fo70-95) were contained in single-crystal MgO capsules. Over the oxygen fugacity range IW-0.5 to -3, the Si molar partition coefficient D* (= [Si]metal /[Si]silicate) between metal and Pv increases linearly with decreasing oxygen fugacity at a fixed given temperature. The partition coefficient between metal and silicate melt is of a similar magnitude but is less dependent on the oxygen fugacity. The obtained oxygen distribution coefficient Kd (= [Fe]metal[O]metal /[FeO]Fp) is in agreement with that determined in the Fe-Fp binary system (Asahara et al., 2007 EPSL) below the silicate liquidus temperature. In contrast, a correlation between the O partitioning and Si concentration in Fe is observed above 2700 K where liquid metal coexists with silicate melt + Fp. With an increasing concentration of Si in the liquid metal, O partitioning into Fp is strongly enhanced. Five atomic% Si in the metal reduces the metal-silicate O partition coefficient by about 1 order magnitude. Near the base of a deep magma ocean where pressures exceed 20 GPa, liquid metal could have coexisted with silicate melt, Pv, and Fp. Our results show that Si would readily partitioned into core-forming metal from both perovskite and silicate liquid at a relevant oxygen fugacity (e.g., IW-2). Simultaneously, the Si solubility would hinder the dissolution of O in the liquid metal. This implies that the presence of Si in liquid metal must be included in models of O partitioning.

The Density Jump at the Inner Core Boundary in the Eastern and Western Hemispheres

NASA Astrophysics Data System (ADS)

Krasnoshchekov, D. N.; Ovtchinnikov, V. M.

2018-02-01

The results of analysis of more than 1300 new PKiKP/PcP amplitude ratios measured in Southeast Asia and South America at the epicentral distances of 3.2°-35.2° are presented. The density jump in the Eastern Hemisphere of the Earth's inner core (IC) is 0.3 g/cm3, and it is 0.9 g/cm3 in the Western one. Taking the large discrepancy in the obtained estimates into consideration, maintenance of such large lateral variations in the mosaic properties of the IC reflecting surface requires considerable variations in the thermodynamic parameters (mostly temperature) of the inner-outer core transition. However, if the observed asymmetry in the density jump distribution is of a global character, the data presented support the translation model of the IC dynamics. This model implies IC crystallization in the Western Hemisphere and melting in the Eastern one, not vice versa, as suggested by another geodynamic model based on thermochemical convection in the outer core and the thermal balance of the core-mantle system.

A massively parallel adaptive scheme for melt migration in geodynamics computations

NASA Astrophysics Data System (ADS)

Dannberg, Juliane; Heister, Timo; Grove, Ryan

2016-04-01

Melt generation and migration are important processes for the evolution of the Earth's interior and impact the global convection of the mantle. While they have been the subject of numerous investigations, the typical time and length-scales of melt transport are vastly different from global mantle convection, which determines where melt is generated. This makes it difficult to study mantle convection and melt migration in a unified framework. In addition, modelling magma dynamics poses the challenge of highly non-linear and spatially variable material properties, in particular the viscosity. We describe our extension of the community mantle convection code ASPECT that adds equations describing the behaviour of silicate melt percolating through and interacting with a viscously deforming host rock. We use the original compressible formulation of the McKenzie equations, augmented by an equation for the conservation of energy. This approach includes both melt migration and melt generation with the accompanying latent heat effects, and it incorporates the individual compressibilities of the solid and the fluid phase. For this, we derive an accurate and stable Finite Element scheme that can be combined with adaptive mesh refinement. This is particularly advantageous for this type of problem, as the resolution can be increased in mesh cells where melt is present and viscosity gradients are high, whereas a lower resolution is sufficient in regions without melt. Together with a high-performance, massively parallel implementation, this allows for high resolution, 3d, compressible, global mantle convection simulations coupled with melt migration. Furthermore, scalable iterative linear solvers are required to solve the large linear systems arising from the discretized system. Finally, we present benchmarks and scaling tests of our solver up to tens of thousands of cores, show the effectiveness of adaptive mesh refinement when applied to melt migration and compare the compressible and incompressible formulation. We then apply our software to large-scale 3d simulations of melting and melt transport in mantle plumes interacting with the lithosphere. Our model of magma dynamics provides a framework for modelling processes on different scales and investigating links between processes occurring in the deep mantle and melt generation and migration. The presented implementation is available online under an Open Source license together with an extensive documentation.

Orthopyroxene oikocrysts in the MG1 chromitite layer of the Bushveld Complex: implications for cumulate formation and recrystallisation

NASA Astrophysics Data System (ADS)

Kaufmann, Felix E. D.; Vukmanovic, Zoja; Holness, Marian B.; Hecht, Lutz

2018-02-01

Two typical mineral textures of the MG 1 chromitite of the Bushveld Complex, South Africa, were observed; one characterised by abundant orthopyroxene oikocrysts, and the other by coarse-grained granular chromitite with only minor amounts of interstitial material. Oikocrysts form elongate clusters of several crystals aligned parallel to the layering, and typically have subhedral, almost chromite-free, core zones containing remnants of olivine. The core zones are surrounded by poikilitic aureoles overgrowing euhedral to subhedral chromite chadacrysts. Chromite grains show no preferred crystal orientation, whereas orthopyroxene grains forming clusters commonly share the same crystallographic orientation. Oikocryst core zones have lower Mg# and higher concentrations of incompatible trace elements compared to their poikilitic aureoles. Core zones are relatively enriched in REE compared to a postulated parental magma (B1) and did not crystallise in equilibrium with the surrounding minerals, whereas the composition of the poikilitic orthopyroxene is consistent with growth from the B1 magma. These observations cannot be explained by the classic cumulus and post-cumulus models of oikocryst formation. Instead, we suggest that the oikocryst core zones in the MG1 chromitite layer formed by peritectic replacement of olivine primocrysts by reaction with an upwards-percolating melt enriched in incompatible trace elements. Poikilitic overgrowth on oikocryst core zones occurred in equilibrium with a basaltic melt of B1 composition near the magma-crystal mush interface. Finally, adcumulus crystallisation followed by grain growth resulted in the surrounding granular chromitite.

Fluid-mechanic/thermal interaction of a molten material and a decomposing solid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Larson, D.W.; Lee, D.O.

1976-12-01

Bench-scale experiments of a molten material in contact with a decomposing solid were conducted to gain insight into the expected interaction of a hot, molten reactor core with a concrete base. The results indicate that either of two regimes can occur: violent agitation and splattering of the melt or a very quiescent settling of the melt when placed in contact with the solid. The two regimes appear to be governed by the interface temperature condition. A conduction heat transfer model predicts the critical interface temperature with reasonable accuracy. In addition, a film thermal resistance model correlates well with the datamore » in predicting the time for a solid skin to form on the molten material.« less

Devon island ice cap: core stratigraphy and paleoclimate.

PubMed

Koerner, R M

1977-04-01

Valuable paleoclimatic information can be gained by studying the distribution of melt layers in deep ice cores. A profile representing the percentage of ice in melt layers in a core drilled from the Devon Island ice cap plotted against both time and depth shows that the ice cap has experienced a period of very warm summers since 1925, following a period of colder summers between about 1600 and 1925. The earlier period was coldest between 1680 and 1730. There is a high correlation between the melt-layer ice percentage and the mass balance of the ice cap. The relation between them suggests that the ice cap mass balance was zero (accumulation equaled ablation) during the colder period but is negative in the present warmer one. There is no firm evidence of a present cooling trend in the summer conditions on the ice cap. A comparison with the melt-layer ice percentage in cores from the other major Canadian Arctic ice caps shows that the variation of summer conditions found for the Devon Island ice cap is representative for all the large ice caps for about 90 percent of the time. There is also a good correlation between melt-layer percentage and summer sea-ice conditions in the archipelago. This suggests that the search for the northwest passage was influenced by changing climate, with the 19th-century peak of the often tragic exploration coinciding with a period of very cold summers.

The Ewing Impact Structure: Progress Report

NASA Astrophysics Data System (ADS)

Abbott, D. H.; Nunes, A. A.; Leung, I. S.; Burckle, L.; Hagstrum, J. T.

2003-12-01

We have previously reported on the discovery of the Ewing impact structure. It is 150 km in diameter and is located in the equatorial Pacific between the Clarion and Clipperton fracture zones. We have now mapped the distribution of microtektites and other types of impact spherules. The microtektite bearing cores form a half circle to the south with a straight edge that passes through the center of the crater. This pattern of tektite distribution matches the pattern that has been modeled for deep-water impacts. The impact melt bodies that are the source of the magnetic anomalies associated with the crater also lie in the southern half of the crater. Thus, the overall pattern of microtektite and impact melt distribution is consistent with an impactor on an inclined trajectory that arrived from the north and sprayed ejecta to the south. We have found an impact melt bomb that is part of the distal ejecta blanket. The impact melt bomb is about 10 cm by 6 cm in size. It contains unmelted marine sediment in the center that is surrounded by impact melt glass. So far, attempts to date glassy spherules and impact melt glass have been unsuccessful. Thus, our best estimate of the age of the impact is derived from diatom biostratigraphy, which gives an age of 7 to 11 Ma. In this time period, there are three major climatic excursions that might be related to the Ewing impact event. In most of the region, the 5000-meter water depth precludes using the more numerous foraminiferal zones and oxygen isotope stratigraphy to more precisely date the ejecta layer. Detailed studies of the mineralogy of the ejecta layer in core PLDS-111P have failed to find any quartz at all, shocked or unshocked. However, this core received its ejecta from the southern half of the crater, where the pre-impact basement was composed of normal oceanic crust. To the north, a minor fracture zone cuts the crater. This fracture zone is a potential location of plagiogranites, which are quartz normative. The fracture zone also contains local topographic highs that are shallow enough to retain foraminifera. By concentrating our efforts on carbonate rich cores that sample the ejecta from the northern half of the crater on or near the fracture zone, we hope to determine a more accurate biostratigraphic age for the Ewing impact event. We will also examine the mineralogy of these samples to see if quartz or opaque minerals are present. Both quartz and some opaques can show characteristic shock deformation features.

Boundary pressure of inter-connection of Fe-Ni-S melt in olivine based on in-situ X-ray tomography: Implication to core formation in asteroids

NASA Astrophysics Data System (ADS)

Terasaki, H.; Urakawa, S.; Uesugi, K.; Nakatsuka, A.; Funakoshi, K.; Ohtani, E.

2011-12-01

Interconnectivity of Fe-alloy melt in crystalline silicates is important property for the core formation mechanism in planetary interior. In previous studies, the interconnectivity of Fe-alloy melt has been studied based on textural observation of recovered samples from high pressure and temperature. However, there is no observation under high pressure and temperature. We have developed 80-ton uni-axial press for X-ray computed micro-tomography (X-CT) and performed X-CT measurement under high pressure (Urakawa et al. 2010). Here we report X-CT measurement of Fe-Ni-S melt in crystalline olivine and interconnectivity of the melt up to 3.5 GPa and 1273 K. X-CT measurements were carried out at BL20B2 beamline, SPring-8 synchrotron facility. The sample was powder mixture of Fe-Ni-S and olivine, which was enclosed in graphite capsule. Heating was performed using a cylindrical graphite furnace. Pressure was generated using opposed toroidal-shape WC anvil. The uni-axial press was set on the rotational stage and X-ray radiography image of the sample was collected using CCD camera from 0°to 180°with 0.3° step. 3-D image of the sample was obtained by reconstructing the 2-D radiography image. The 3-D CT image shows that the size of the Fe-Ni-S melt increased significantly compared to that before melting below 2.5 GPa, suggesting that the melt was interconnected in olivine crystals. On the other hand, 3-D texture of the sample at 3.5 GPa did not show difference from that before melting. Therefore, the boundary of inter-connection of Fe-Ni-S melt is likely to locate between 2.5 and 3.5 GPa. This result is important application for the core formation mechanism especially in small bodies, such as differentiated asteroids.

Defining the Iron-Rich Fe-Ni-S Melting Curve at 20GPa: Implications for Martian Core Solidification

NASA Astrophysics Data System (ADS)

Gilfoy, F. G.; Li, J.

2016-12-01

In 1997, the Mars Global Surveyor detected strong remnant magnetization of 4 Ga impact basins in the planet's southern highlands (Acuna et al. 1999), but the dearth of strongly magnetized rocks younger than 4 Ga in age is interpreted as evidence cataloging the death of an early Martian dynamo (Stevenson, 2001; Fassett 2011). In order to investigate the thermal evolution of the Martian core and assess the possibility of iron "snow" core crystallization to restart the dynamo, a series of multi-anvil experiments have been conducted to define the iron-rich liquidus of the Fe-Ni-S system at 20 GPa, the estimated pressure of the Martian core-mantle boundary (CMB), across its entire temperature range. Due to the fineness of features at high temperatures and low S concentrations, area analysis techniques, in additional to traditional electron microprobe analysis, were used to determine the composition of the experimental data. When fitted using an asymmetrical regular solution model, our data yields a liquidus that is significantly depressed when compared to calculations made assuming ideal behavior. Pronounced melting point depression at S contents corresponding to the likely composition of the Martian core means that the onset of crystallization will take much longer than previously thought. By comparing a calculated areotherm to liquidii interpolated between our experimental data and that from the literature, we find that the two intersect at the high-pressure end. Thus, the Martian core solidification is expected to begin at the center of planet and iron "snow" core crystallization is unlikely to occur within Mars .

Lid heater for glass melter

DOEpatents

Phillips, Terrance D.

1993-01-01

A glass melter having a lid electrode for heating the glass melt radiantly. The electrode comprises a series of INCONEL 690 tubes running above the melt across the melter interior and through the melter walls and having nickel cores inside the tubes beginning where the tubes leave the melter interior and nickel connectors to connect the tubes electrically in series. An applied voltage causes the tubes to generate heat of electrical resistance for melting frit injected onto the melt. The cores limit heat generated as the current passes through the walls of the melter. Nickel bus connection to the electrical power supply minimizes heat transfer away from the melter that would occur if standard copper or water-cooled copper connections were used between the supply and the INCONEL 690 heating tubes.

Lid heater for glass melter

DOEpatents

Phillips, T.D.

1993-12-14

A glass melter having a lid electrode for heating the glass melt radiantly. The electrode comprises a series of INCONEL 690 tubes running above the melt across the melter interior and through the melter walls and having nickel cores inside the tubes beginning where the tubes leave the melter interior and nickel connectors to connect the tubes electrically in series. An applied voltage causes the tubes to generate heat of electrical resistance for melting frit injected onto the melt. The cores limit heat generated as the current passes through the walls of the melter. Nickel bus connection to the electrical power supply minimizes heat transfer away from the melter that would occur if standard copper or water-cooled copper connections were used between the supply and the INCONEL 690 heating tubes. 3 figures.

Solidus and liquidus profiles of chondritic mantle: Implication for melting of the Earth across its history

NASA Astrophysics Data System (ADS)

Andrault, Denis; Bolfan-Casanova, Nathalie; Nigro, Giacomo Lo; Bouhifd, Mohamed A.; Garbarino, Gaston; Mezouar, Mohamed

2011-04-01

We investigated the melting properties of a synthetic chondritic primitive mantle up to core-mantle boundary (CMB) pressures, using laser-heated diamond anvil cell. Melting criteria are essentially based on the use of X-rays provided by synchrotron radiation. We report a solidus melting curve lower than previously determined using optical methods. The liquidus curve is found between 300 and 600 K higher than the solidus over the entire lower mantle. At CMB pressures (135 GPa), the chondritic mantle solidus and liquidus reach 4150 (± 150) K and 4725 (± 150) K, respectively. We discuss that the lower mantle is unlikely to melt in the D″-layer, except if the highest estimate of the temperature profile at the base of the mantle, which is associated with a very hot core, is confirmed. Therefore, recent suggestions of partial melting in the lowermost mantle based on seismic observations of ultra-low velocity zones indicate either (1) a outer core exceeding 4150 K at the CMB or (2) the presence of chemical heterogeneities with high concentration of fusible elements. Our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion. Not only complete melting of the lower mantle would require excessively high temperatures, but also, below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought. In addition, magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 GPa, as suggested by siderophile metal-silicate partitioning data. Such high surface temperature regime, where thermal blanketing is inefficient, points out to a transient character of the magma ocean, with a very fast cooling rate.

Siderophile Element Partitioning between Cohenite and Liquid in Fe-Ni-S-C System and Implications for Geochemistry of Planetary Cores and Mantles

NASA Astrophysics Data System (ADS)

Buono, A. S.; Dasgupta, R.; Walker, D.

2011-12-01

Secular cooling of terrestrial planets is known to cause crystallization of a solid inner core from metallic liquid core. Fractionation of light and siderophile elements is important during such crystallization for evolution of outer core and possible core-mantle interaction. Thus far studies focused on a pure Fe inner core in simple binary systems but the effects of possible formation of a carbide inner core component on siderophile element partitioning in a multi-component system has yet to be looked at in detail. We investigated the effects of pressure and S content on partition coefficients (D) between cohenite and liquid in the Fe-Ni-S-C system. Multi-anvil experiments were performed at 3 and 6 GPa at 1150 °C, in an Fe-rich mix containing a constant C and Ni to which S contents of 0, 5, and 14 wt.% were added. All the mixes were doped with W, Re, Os, Pt, and Co. Samples were imaged and analyzed for Fe, Ni, S, and C using an EPMA. Fe, Ni, and trace elements were analyzed using a LA-ICP-MS. All the experiments produced cohenite and Fe-Ni-C±S liquid. Compared to solid-Fe/melt Ds [1-2], cohenite/melt Ds are lower for all elements except W. The light element (S+C) content of the liquid is the dominant controlling factor in siderophile element partitioning between cohenite and liquid as it is between crystalline Fe and liquid. In the cohenite-metallic melt experiments, D Ni decreases as S+C increases. Ni is excluded from the crystallizing solid if the solid is cohenite. We also find that in the Fe-Ni-S-C system, cohenite is stabilized to higher P than in the Fe-S-C system [3-5]. Similar to the Fe-metallic liquid systems the non-metal avoidance model [6] is applicable to the Fe3C-metallic liquid system studied here. Our study has implications for both the cores of smaller planets and the mantles of larger planets. If inner core forms a cohenite layer we would predict that depletions in the outer core will be less than they might be for Fe metal crystallization. For the mantle of the earth, which is thought to become Fe-Ni metal-saturated as shallow as 250 km, the sub-system Fe-Ni + C + S becomes relevant and Fe-Ni carbide rather than metallic Fe-Ni alloy may become the crystalline phase of interest. Our study implies that because the partition coefficients between cohenite and Fe-C-S melts are significantly lower than those between Fe-metal and S-rich liquid, in the presence of cohenite and Fe-C-S melt in the mantle, the mantle budget of Ni, Co, and Pt may be dominated by Fe-C-S liquid. W, Re, and Os will also be slightly enriched in C-rich Fe-Ni liquid over cohenite if the metal sub-system of interest is S-free. [1] Chabot et al., GCA 70, 1322-1335, 2006 [2] Chabot et al., GCA 72, 4146-4158, 2008 [3] Chabot et al., Meteorit. Planet. Sci. 42, 1735-1750, 2007 [4] Stewart et al., EPSL 284, 302-309, 2009 [5] Van Orman et al., EPSL 274, 250-257, 2008 [6] Jones, J.H., Malvin, D.J., Metall Mater Trans B 21, 697-706, 1990

A Holistic Model That Physicochemically Links Iron Oxide - Apatite and Iron Oxide - Copper - Gold Deposits to Magmas

NASA Astrophysics Data System (ADS)

Simon, A. C.; Reich, M.; Knipping, J.; Bilenker, L.; Barra, F.; Deditius, A.; Lundstrom, C.; Bindeman, I. N.

2015-12-01

Iron oxide-apatite (IOA) and iron oxide-copper-gold deposits (IOCG) are important sources of their namesake metals and increasingly for rare earth metals in apatite. Studies of natural systems document that IOA and IOCG deposits are often spatially and temporally related with one another and coeval magmatism. However, a genetic model that accounts for observations of natural systems remains elusive, with few observational data able to distinguish among working hypotheses that invoke meteoric fluid, magmatic-hydrothermal fluid, and immiscible melts. Here, we use Fe and O isotope data and high-resolution trace element (e.g., Ti, V, Mn, Al) data of individual magnetite grains from the world-class Los Colorados (LC) IOA deposit in the Chilean Iron Belt to elucidate the origin of IOA and IOCG deposits. Values of d56Fe range from 0.08‰ to 0.26‰, which are within the global range of ~0.06‰ to 0.5‰ for magnetite formed at magmatic conditions. Values of δ18O for magnetite and actinolite are 2.04‰ and 6.08‰, respectively, consistent with magmatic values. Ti, V, Al, and Mn are enriched in magnetite cores and decrease systematically from core to rim. Plotting [Al + Mn] vs. [Ti + V] indicates that magnetite cores are consistent with magmatic and/or magmatic-hydrothermal (i.e., porphyry) magnetites. Decreasing Al, Mn, Ti, V is consistent with a cooling trend from porphyry to Kiruna to IOCG systems. The data from LC are consistent with the following new genetic model for IOA and IOCG systems: 1) magnetite cores crystallize from silicate melt; 2) these magnetite crystals are nucleation sites for aqueous fluid that exsolves and scavenges inter alia Fe, P, S, Cu, Au from silicate melt; 3) the magnetite-fluid suspension is less dense that the surrounding magma, allowing ascent; 4) as the suspension ascends, magnetite grows in equilibrium with the fluid and takes on a magmatic-hydrothermal character (i.e., lower Al, Mn, Ti, V); 5) during ascent, magnetite, apatite and actinolite are deposited to form IOA deposits; 6) the further ascending fluid transports Fe, Cu, Au and S toward the surface where metal-oxides and metal-sulfides precipitate to form IOCG deposits. This model is globally applicable and explains the observed temporal and spatial relationship between magmatism and formation of IOA and IOCG deposits.

Origin and Constraints on Ilmenite-rich Partial Melt in the Lunar Lower Mantle

NASA Astrophysics Data System (ADS)

Mallik, A.; Fuqua, H.; Bremner, P. M.; Panovska, S.; Diamond, M. R.; Lock, S. J.; Nishikawa, Y.; Jiménez-Pérez, H.; Shahar, A.; Panero, W. R.; Lognonne, P. H.; Faul, U.

2015-12-01

Existence of a partially molten layer at the lunar core-mantle boundary has been proposed to explain the lack of observed far-side deep moonquakes, the observation of reflected seismic phases from deep moonquakes, and the dissipation of tidal energy within the lunar interior [1,2]. However, subsequent models explored the possibility that dissipation due to elevated temperatures alone can explain the observed dissipation factor (Q) and tidal love numbers [3]. Using thermo-chemical and dynamic modeling (including models of the early lunar mantle convection), we explore the hypothesis that an ilmenite-rich layer forms below crustal anorthosite during lunar magma ocean crystallization and may sink to the base of the mantle to create a partial melt layer at the lunar core-mantle boundary. Self-consistent physical parameters (including gravity, pressure, density, VP and Vs) are forward calculated for a well-mixed mantle with uniform bulk composition versus a mantle with preserved mineralogical stratigraphy from lunar magma ocean crystallization. These parameters are compared against observed mass, moment of inertia, real and imaginary parts of the Love numbers, and seismic travel times to further limit the acceptable models for the Moon. We have performed a multi-step grid search with over twenty thousand forward calculations varying thicknesses of chemically/mineralogically distinct layers within the Moon to evaluate if a partially molten layer at the base of the lunar mantle is well-constrained by the observed data. Furthermore, dynamic mantle modeling was employed on the best-fit model versions to determine the survivability of a partially molten layer at the core-mantle boundary. This work was originally initiated at the CIDER 2014 program. [1] Weber et al. (2011). Science 331(6015), 309-12. [2] Khan et al. (2014). JGR 119. [3] Nimmo et al. (2012). JGR 117, 1-11.

A preliminary study on isotopic evolution of ice by a melting experiment

NASA Astrophysics Data System (ADS)

Ham, J. Y.; Lee, J.; Lee, W. S.; Han, Y.; Hur, S. D.

2016-12-01

Evidences of melted snow at surface were found on some ice cores. Melted layers may generate a significant error when paleo-temperature was retrieved from ice cores using stable water isotopes. To resolve this problem, it is necessary to understand the isotopic changes of ice and its meltwater that is made during the ice and snow melting. Isotopic fractionations between liquid water and snow have been discussed by Taylor et al. (2002) and Lee et al. (2009). The goal of this work is to understand isotopic evolution of ice and its meltwater. Melting experiments in a cold room were designed and conducted with heat source (infrared lamp) to mimic solar radiation. Melting rates were calculated in terms of specific discharge (g/min). To control melting rates, distances between ice surface and heat source were adjusted in various conditions (1 cm, 10 cm and 20 cm). The experiments were conducted by three different melting rates, 1.6 g/min, 3.5 g/min and 5.8 g/min. We used cubic ice that has 3 cm in width, length and height in dimension with 1.5 kg or 2 kg of ice used totally. The total time spent melting the whole ice was 592, 783, and 1180 minutes, respectively. Cold room temperature was range of -1 to 1°C, which removes an effect of air temperature. Meltwater samples were collected and isotopic compositions of oxygen and hydrogen were determined by a cavity ring down spectrometer (Picarro L-1120) installed at the Korea Polar Research Institute. We also analyzed bulk water and bulk ice to make the ice used in the experiments (-8.20 ‰ and -58.73 ‰ for oxygen and hydrogen isotopes, respectively). The isotopic compositions of meltwater increased linearly or to a second degree polynomial. The isotopic variations were larger in the lower melting rates, compared to the higher melting rates (0.65 of lower melting rates vs. 0.35 higher melting rates for oxygen isotope). The slope of linear regression between oxygen and hydrogen ranged 6.2, 7.3 and 6.2, which is less than that of the Global Meteoric Water Line (8) and the sublimation (7.7) suggested by Earman et al. (2006). We believe that isotopic exchange between liquid water and ice plays a crucial role in the variations of isotopes for the ice and its meltwater. We will modify a physically based 1-D model used in the previous studies to better understand the isotopic compositions of ice and its meltwater.

Monoclinic tridymite in clast-rich impact melt rock from the Chesapeake Bay impact structure

USGS Publications Warehouse

Jackson, John C.; Horton, J. Wright; Chou, I-Ming; Belkin, Harvey E.

2011-01-01

X-ray diffraction and Raman spectroscopy confirm a rare terrestrial occurrence of monoclinic tridymite in clast-rich impact melt rock from the Eyreville B drill core in the Chesapeake Bay impact structure. The monoclinic tridymite occurs with quartz paramorphs after tridymite and K-feldspar in a microcrystalline groundmass of devitrified glass and Fe-rich smectite. Electron-microprobe analyses revealed that the tridymite and quartz paramorphs after tridymite contain different amounts of chemical impurities. Inspection by SEM showed that the tridymite crystal surfaces are smooth, whereas the quartz paramorphs contain irregular tabular voids. These voids may represent microporosity formed by volume decrease in the presence of fluid during transformation from tridymite to quartz, or skeletal growth in the original tridymite. Cristobalite locally rims spherulites within the same drill core interval. The occurrences of tridymite and cristobalite appear to be restricted to the thickest clast-rich impact melt body in the core at 1402.02–1407.49 m depth. Their formation and preservation in an alkali-rich, high-silica melt rock suggest initially high temperatures followed by rapid cooling.

A discontinuous melt sheet in the Manson impact structure

NASA Technical Reports Server (NTRS)

Izett, G. A.; Reynolds, R. L.; Rosenbaum, J. G.; Nishi, J. M.

1993-01-01

Petrologic studies of the core recovered from holes drilled in the Manson, Iowa, buried impact structure may unravel the thermal history of the crater-fill debris. We made a cursory examination of about 200 m of core recovered from the M-1 bore hole. The M-1 bore hole was the first of 12 holes drilled as part of a cooperative drilling program between the U.S. Geological Survey and the Iowa Geological Survey Bureau. The M-1 core hole is about 6 km northeast of the center of the impact structure, apparently on the flank of its central peak. We developed a working hypothesis that a 30-m-thick breccia unit within a 53-m-thick unit previously termed the 'crystalline clast breccia with glassy matrix' is part of a discontinuous melt sheet in the crater-fill impact debris. The 30-m-thick breccia unit reached temperatures sufficient to partially melt some small breccia clasts and convert the fine-grained breccia matrix into a silicate melt that cooled to a greenish-black, flinty, microcrystalline rock. The results of the investigation of this unit are presented.

METHOD AND APPARATUS FOR EARTH PENETRATION

DOEpatents

Adams, W.M.

1963-12-24

A nuclear reactor apparatus for penetrating into the earth's crust is described. The apparatus comprises a cylindrical nuclear core operating at a temperature that is higher than the melting temperature of rock. A high-density ballast member is coupled to the nuclear core such that the overall density of the core-ballast assembly is greater than the density of molten rock. The nuclear core is thermally insulated so that its heat output is constrained to flow axially, with radial heat flow being minimized. In operation, the apparatus is placed in contact with the earth's crust at the point desired to be penetrated. The heat output of the reactor melts the underlying rock, and the apparatus sinks through the resulting magma. The fuel loading of the reactor core determines the ultimate depth of crust penetration. (AEC)

Polychlorinated Biphenyls in a Temperate Alpine Glacier: 1. Effect of Percolating Meltwater on their Distribution in Glacier Ice.

PubMed

Pavlova, Pavlina Aneva; Jenk, Theo Manuel; Schmid, Peter; Bogdal, Christian; Steinlin, Christine; Schwikowski, Margit

2015-12-15

In Alpine regions, glaciers act as environmental archives and can accumulate significant amounts of atmospherically derived pollutants. Due to the current climate-warming-induced accelerated melting, these pollutants are being released at correspondingly higher rates. To examine the effect of melting on the redistribution of legacy pollutants in Alpine glaciers, we analyzed polychlorinated biphenyls in an ice core from the temperate Silvretta glacier, located in eastern Switzerland. This glacier is affected by surface melting in summer. As a result, liquid water percolates down and particles are enriched in the current annual surface layer. Dating the ice core was a challenge because meltwater percolation also affects the traditionally used parameters. Instead, we counted annual layers of particulate black carbon in the ice core, adding the years with negative glacier mass balance, that is, years with melting and subsequent loss of the entire annual snow accumulation. The analyzed samples cover the time period 1930-2011. The concentration of indicator PCBs (iPCBs) in the Silvretta ice core follows the emission history, peaking in the 1970s (2.5 ng/L). High PCB values in the 1990s and 1930s are attributed to meltwater-induced relocation within the glacier. The total iPCB load at the Silvretta ice core site is 5 ng/cm(2). A significant amount of the total PCB burden in the Silvretta glacier has been released to the environment.

Diatoms in late Quaternary sediment from the Orca Basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klas, M.; Burckle, L.H.

1985-01-01

Diatoms and clays were studied in core EN32-PC6 from the Orca Basin. This core contains oxygen isotope evidence for increased melt-water outflow from the Mississippi River during the post-Wisconsin deglaciation. Diatoms are present in two intervals: the period of increased melt-water outflow at about 15,000 to 12,000 years BP and during the past 5000 years. The earlier interval (the melt-water spike) contains fresh and brackish water diatoms and open ocean forms that prefer lower salinities while the youngest interval is characterized by open ocean forms. The melt-water spike interval also contains fewer reworked Cretaceous and Paleogene coccoliths and has littlemore » or no quartz. A decrease in smectite in the core at about 22,000 years BP may be related to a similar decrease in the Morton loess due to the blocking and diversion of the ancient Mississippi by the advancing Woodfordian glacier of the Lake Michigan lobe. After this diversion, the Mississippi took its present-day course and continued to take outwash away from the receding glacier. In Orca Basin sediments, this is indicated by an increase in smectite. The interval of the melt-water spike seems to be characterized by increased rainfall and sheet flooding.« less

An Improved Extraction and Analysis Technique for Determination of Carbon Monoxide Stable Isotopes and Mixing Ratios from Ice Core and Atmospheric Air Samples.

NASA Astrophysics Data System (ADS)

Place, P., Jr.; Petrenko, V. V.; Vimont, I.

2017-12-01

Carbon Monoxide (CO) is an important atmospheric trace gas that affects the oxidative capacity of the atmosphere and contributes indirectly to anthropogenic radiative forcing. Carbon monoxide stable isotopes can also serve as a tracer for variations in biomass burning, particularly in the preindustrial atmosphere. A good understanding of the past variations in CO mole fractions and isotopic composition can help improve the skill of chemical transport models and constrain biomass burning changes. Ice cores may preserve a record of past atmospheric CO for analysis and interpretation. To this end, a new extraction system has been developed for analysis of stable isotopes (δ13CO and δC18O) of atmospheric carbon monoxide from ice core and atmospheric air samples. This system has been designed to measure relatively small sample sizes (80 cc STP of air) to accommodate the limited availability of ice core samples. Trapped air is extracted from ice core samples via melting in a glass vacuum chamber. This air is expanded into a glass expansion loop and then compressed into the sample loop of a Reducing Gas Detector (Peak Laboratories, Peak Performer 1 RCP) for the CO mole fraction measurement. The remaining sample gas will be expelled from the melt vessel into a larger expansion loop via headspace compression for isotopic analysis. The headspace compression will be accomplished by introduction of clean degassed water into the bottom of the melt vessel. Isotopic analysis of the sample gas is done utilizing the Schütze Reagent to convert the carbon monoxide to carbon dioxide (CO2) which is then measured using continuous-flow isotope ratio mass spectrometry (Elementar Americas, IsoPrime 100). A series of cryogenic traps are used to purify the sample air, capture the converted sample CO2, and cryofocus the sample CO2 prior to injection.

Chemical State Mapping of Degraded B4C Control Rod Investigated with Soft X-ray Emission Spectrometer in Electron Probe Micro-analysis.

PubMed

Kasada, R; Ha, Y; Higuchi, T; Sakamoto, K

2016-05-10

B4C is widely used as control rods in light water reactors, such as the Fukushima Daiichi nuclear power plant, because it shows excellent neutron absorption and has a high melting point. However, B4C can melt at lower temperatures owing to eutectic interactions with stainless steel and can even evaporate by reacting with high-temperature steam under severe accident conditions. To reduce the risk of recriticality, a precise understanding of the location and chemical state of B in the melt core is necessary. Here we show that a novel soft X-ray emission spectrometer in electron probe microanalysis can help to obtain a chemical state map of B in a modeled control rod after a high-temperature steam oxidation test.

Top-down freezing in a Fe-FeS core and Ganymede's present-day magnetic field

NASA Astrophysics Data System (ADS)

Rückriemen, Tina; Breuer, Doris; Spohn, Tilman

2018-06-01

Ganymede's core most likely possesses an active dynamo today, which produces a magnetic field at the surface of ∼ 719 nT. Thermochemical convection triggered by cooling of the core is a feasible power source for the dynamo. Experiments of different research groups indicate low pressure gradients of the melting temperatures for Fe-FeS core alloys at pressures prevailing in Ganymede's core ( < 10 GPa). This may entail that the core crystallizes from the top instead of from the bottom as is expected for Earth's core. Depending on the core sulfur concentration being more iron- or more sulfur-rich than the eutectic concentration either snowing iron crystals or a solid FeS layer can form at the top of the core. We investigate whether these two core crystallization scenarios are capable of explaining Ganymede's present magnetic activity. To do so, we set up a parametrized one-dimensional thermal evolution model. We explore a wide range of parameters by running a large set of Monte Carlo simulations. Both freezing scenarios can explain Ganymede's present-day magnetic field. Dynamos of iron snow models are rather young ( < 1 Gyr), whereas dynamos below the FeS layer can be both young and much older ( ∼ 3.8 Gyr). Successful models preferably contain less radiogenic heat sources in the mantle than the chondritic abundance and show a correlation between the reference viscosity in the mantle and the initial core sulfur concentration.

Core formation in the Moon: The mystery of the excess depletion of Mo, W and P

NASA Technical Reports Server (NTRS)

Newsom, H. E.; Maehr, S. A.

1993-01-01

We have evaluated siderophile element depletion models for the Moon in light of our improved statistical treatment of siderophile element abundance data and new information on the physics of core formation. If core formation occurred in the Moon at the large degrees of partial melting necessary for metal segregation, according to recent estimates, then a significant inconsistency (not seen in the eucrite parent body) exists in the depletion of the incompatible siderophile elements Mo, W, and P, compared to other siderophile elements in the Moon. The siderophile data, with the exception of Mo, are most consistent with terrestrial initial siderophile abundances and segregation of a very small core in the Moon. Our improved abundance estimates and possible explanations for these discrepancies are discussed.

Eutectic melting temperature of the lowermost Earth's mantle

NASA Astrophysics Data System (ADS)

Andrault, D.; Lo Nigro, G.; Bolfan-Casanova, N.; Bouhifd, M.; Garbarino, G.; Mezouar, M.

2009-12-01

Partial melting of the Earth's deep mantle probably occurred at different stages of its formation as a consequence of meteoritic impacts and seismology suggests that it even continues today at the core-mantle boundary. Melts are important because they dominate the chemical evolution of the different Earth's reservoirs and more generally the dynamics of the whole planet. Unfortunately, the most critical parameter, that is the temperature profile inside the deep Earth, remains poorly constrained accross the planet history. Experimental investigations of the melting properties of materials representative of the deep Earth at relevant P-T conditions can provide anchor points to refine past and present temperature profiles and consequently determine the degree of melting at the different geological periods. Previous works report melting relations in the uppermost lower mantle region, using the multi-anvil press [1,2]. On the other hand, the pyrolite solidus was determined up to 65 GPa using optical observations in the laser-heated diamond anvil cell (LH-DAC) [3]. Finally, the melting temperature of (Mg,Fe)2SiO4 olivine is documented at core-mantle boundary (CMB) conditions by shock wave experiments [4]. Solely based on these reports, experimental data remain too sparse to draw a definite melting curve for the lower mantle in the relevant 25-135 GPa pressure range. We reinvestigated melting properties of lower mantle materials by means of in-situ angle dispersive X-ray diffraction measurements in the LH-DAC at the ESRF [5]. Experiments were performed in an extended P-T range for two starting materials: forsterite and a glass with chondrite composition. In both cases, the aim was to determine the onset of melting, and thus the eutectic melting temperatures as a function of pressure. Melting was evidenced from drastic changes of diffraction peak shape on the image plate, major changes in diffraction intensities in the integrated pattern, disappearance of diffraction rings, and changes in the relation between sample-temperature and laser-power. In this work, we show that temperatures higher than 4000 K are necessary for melting mean mantle at the 135 GPa pressure found at the core mantle boundary (CMB). Such temperature is much higher than that from estimated actual geotherms. Therefore, melting at the CMB can only occur if (i) pyrolitic mantle resides for a very long time in contact with the outer core, (ii) the mantle composition is severely affected by additional elements depressing the solidus such as water or (iii) the temperature gradient in the D" region is amazingly steep. Other implications for the temperature state and the lower mantle properties will be presented. References (1) Ito et al., Phys. Earth Planet. Int., 143-144, 397-406, 2004 (2) Ohtani et al., Phys. Earth Planet. Int., 100, 97-114, 1997 (3) Zerr et al., Science, 281, 243-246, 1998 (4) Holland and Ahrens, Science, 275, 1623-1625, 1997 (5) Schultz et al., High Press. Res., 25, 1, 71-83, 2005.

Thermal Evolution and Crystallisation Regimes of the Martian Core

NASA Astrophysics Data System (ADS)

Davies, C. J.; Pommier, A.

2015-12-01

Though it is accepted that Mars has a sulfur-rich metallic core, its chemical and physical state as well as its time-evolution are still unconstrained and debated. Several lines of evidence indicate that an internal magnetic field was once generated on Mars and that this field decayed around 3.7-4.0 Gyrs ago. The standard model assumes that this field was produced by a thermal (and perhaps chemical) dynamo operating in the Martian core. We use this information to construct parameterized models of the Martian dynamo in order to place constraints on the thermochemical evolution of the Martian core, with particular focus on its crystallization regime. Considered compositions are in the FeS system, with S content ranging from ~10 and 16 wt%. Core radius, density and CMB pressure are varied within the errors provided by recent internal structure models that satisfy the available geodetic constraints (planetary mass, moment of inertia and tidal Love number). We also vary the melting curve and adiabat, CMB heat flow and thermal conductivity. Successful models are those that match the dynamo cessation time and fall within the bounds on present-day CMB temperature. The resulting suite of over 500 models suggest three possible crystallization regimes: growth of a solid inner core starting at the center of the planet; freezing and precipitation of solid iron (Fe- snow) from the core-mantle boundary (CMB); and freezing that begins midway through the core. Our analysis focuses on the effects of core properties that are expected to be constrained during the forthcoming Insight mission.

Frictional melt generated by the 2008 Mw 7.9 Wenchuan earthquake and its faulting mechanisms

NASA Astrophysics Data System (ADS)

Wang, H.; Li, H.; Si, J.; Sun, Z.; Zhang, L.; He, X.

2017-12-01

Fault-related pseudotachylytes are considered as fossil earthquakes, conveying significant information that provide improved insight into fault behaviors and their mechanical properties. The WFSD project was carried out right after the 2008 Wenchuan earthquake, detailed research was conducted in the drilling cores. 2 mm rigid black layer with fresh slickenlines was observed at 732.6 m in WFSD-1 cores drilled at the southern Yingxiu-Beichuan fault (YBF). Evidence of optical microscopy, FESEM and FIB-TEM show it's frictional melt (pseudotachylyte). In the northern part of YBF, 4 mm fresh melt was found at 1084 m with similar structures in WFSD-4S cores. The melts contain numerous microcracks. Considering that (1) the highly unstable property of the frictional melt (easily be altered or devitrified) under geological conditions; (2) the unfilled microcracks; (3) fresh slickenlines and (4) recent large earthquake in this area, we believe that 2-4 mm melt was produced by the 2008 Wenchuan earthquake. This is the first report of fresh pseudotachylyte with slickenlines in natural fault that generated by modern earthquake. Geochemical analyses show that fault rocks at 732.6 m are enriched in CaO, Fe2O3, FeO, H2O+ and LOI, whereas depleted in SiO2. XRF results show that Ca and Fe are enriched obviously in the 2.5 cm fine-grained fault rocks and Ba enriched in the slip surface. The melt has a higher magnetic susceptibility value, which may due to neoformed magnetite and metallic iron formed in fault frictional melt. Frictional melt visible in both southern and northern part of YBF reveals that frictional melt lubrication played a major role in the Wenchuan earthquake. Instead of vesicles and microlites, numerous randomly oriented microcracks in the melt, exhibiting a quenching texture. The quenching texture suggests the frictional melt was generated under rapid heat-dissipation condition, implying vigorous fluid circulation during the earthquake. We surmise that during earthquakes vigorous fluid influx within fault zone, likely dissipating the frictional heat and resulting in rapid temperature drop, may facilitate the solidification of melt and hamper the aftermost fault slip. Meanwhlie, the high temperature fluid-rock interaction may play an important role in the chemical elements migrating in fault zones.

Planetesimal core formation with partial silicate melting using in-situ high P, high T, deformation x-ray microtomography

NASA Astrophysics Data System (ADS)

Anzures, B. A.; Watson, H. C.; Yu, T.; Wang, Y.

2017-12-01

Differentiation is a defining moment in formation of terrestrial planets and asteroids. Smaller planetesimals likely didn't reach high enough temperatures for widescale melting. However, we infer that core formation must have occurred within a few million years from Hf-W dating. In lieu of a global magma ocean, planetesimals likely formed through inefficient percolation. Here, we used in-situ high temperature, high pressure, x-ray microtomography to track the 3-D evolution of the sample at mantle conditions as it underwent shear deformation. Lattice-Boltzmann simulations for permeability were used to characterize the efficiency of melt percolation. Mixtures of KLB1 peridotite plus 6.0 to 12.0 vol% FeS were pre-sintered to achieve an initial equilibrium microstructure, and then imaged through several consecutive cycles of heating and deformation. The maximum calculated melt segregation velocity was found to be 0.37 cm/yr for 6 vol.% FeS and 0.61 cm/year for 12 vol.% FeS, both below the minimum velocity of 3.3 cm/year required for a 100km planetesimal to fully differentiate within 3 million years. However, permeability is also a function of grain size and thus the samples having smaller grains than predicted for small planetesimals could have contributed to low permeability and also low migration velocity. The two-phase (sulfide melt and silicate melt) flow at higher melt fractions (6 vol.% and 12 vol.% FeS) was an extension of a similar study1 containing only sulfide melt at lower melt fraction (4.5 vol.% FeS). Contrary to the previous study, deformation did result in increased permeability until the sample was sheared by twisting the opposing Drickamer anvils by 360 degrees. Also, the presence of silicate melt caused the FeS melt to coalesce into less connected pathways as the experiment with 6 vol.% FeS was found to be less permeable than the one with 4.5 vol.% FeS but without any partial melt. The preliminary data from this study suggests that impacts as well as higher temperature leading to partial melting of the silicate portion of the mantle could have contributed to fast enough core formation. 1. Todd, K.A., Watson, H.C., Yu, T., Wang, Y., American Mineralogist, 101.9, 1996-2004, 2016

Simulation of the planetary interior differentiation processes in the laboratory.

PubMed

Fei, Yingwei

2013-11-15

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

PubMed Central

Fei, Yingwei

2013-01-01

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process. PMID:24326245

WCRP's Climate and Cryosphere (CliC) Project: Climate Change and Middle and Low Latitude Glaciers

NASA Astrophysics Data System (ADS)

Dick, C. A.; Clic Project, W.

2004-12-01

The newest World Climate Research Programme (WCRP) Core Project, the Climate and Cryosphere (CliC) Project, is concerned with all aspects of the interactions between the cryosphere and climate. The cryosphere, defined as those portions of the Earth's surface where water exists in solid form, is an integral part of the climate system, both responding to, and influencing climate change. The cryosphere also provides many of the best indicators of climate variability and change. In addition to a range of direct physical indicators (e.g., snow/sea ice/glacier extent and thickness, river and lake freeze-up/break-up dates, etc.), ice cores from glaciers, ice caps and ice sheets have been shown to contain a wealth of information about past climate and environmental conditions. Ice cores are of particular value, since they often come from areas that are remote and poorly observed, yet have a major effect on the climate of the rest of the globe. General Circulation Models (GCMs) usually predict that the Earth's polar regions will warm fastest with the increasing levels of atmospheric greenhouse gases. However, models also indicate that continental interiors should warm more quickly than marine areas at non-polar latitudes. In fact, while some areas in the Arctic and Antarctic have warmed rapidly over the last few decades, it has generally been in the middle and low latitudes that the greatest effects of climate change have been observed. Particularly obvious has been the widespread retreat of glaciers. This retreat, and the warming which it implies, will have not only important scientific consequences but also socio-economic consequences in areas where glacier melt-water is an important component of the water supply. Glaciers preserve records of climate and the environment through both the isotopic composition of the water molecules, and through the chemicals 'trapped' in the snow, firn and ice layers. In polythermal (i.e., cold) glaciers where only limited melt occurs, the isotopic and chemical signals remain largely undisturbed, and ice cores can provide excellent high resolution records of past conditions. In temperate glaciers, where the ice is at its pressure melting point throughout, diffusion processes are much more rapid, and summer melt and run-off can drastically alter the chemical composition. Much of the climatic and environmental information is destroyed. This presentation will discuss the very serious concern that so many middle and low latitude glaciers are retreating and warming. The CliC Project recognizes an urgent need to recover ice cores from all non-polar glaciated regions before warming affects the glaciers and removes the information they contain. Without such information our ability to understand the climate changes that have occurred in the world's mountainous regions will be restricted, and our ability to model and predict future climate will be severely impaired.

Separating Multiple Episodes of Partial Melting in Polyorogenic Crust: AN Example from the Haiyangsuo Complex, Northern Sulu Belt, Eastern China

NASA Astrophysics Data System (ADS)

Feng, P.; Wang, L.; Brown, M.; Wang, S.

2017-12-01

Determining the timing, mechanism and source of partial melts in polyorogenic crust is challenging. In the Sulu belt, the tectonic affinity of the Haiyangsuo (HYS) complex is controversial due to its polyphase metamorphic history. Here we use detailed field mapping, petrology, microstructural analysis and zircon geochronology to study thin stromatic leucosomes in host granite gneiss, and crosscutting leucogranite dykes to decipher the melting history. Zircon grains from both granite gneiss and thin leucosomes exhibit core-mantle-rim structures. Zircon cores yield protolith ages of 2.86-2.81 Ga, whereas the mantles and rims yield younger metamorphic/melt crystallization ages of ca. 1.82-1.80 Ga. The mantles are characterized by gray luminescence, flat HREE distribution patterns and relatively low Th/U ratios, indicating crystallization during granulite-facies metamorphism. Whereas rims show bright luminescence, steep HREE distribution patterns and higher Th/U ratios, suggesting they crystallized from melt. The mantles and rims have ɛHf (t) of -18.2 to -11.0. Using 176Lu/177Hf = 0.001, these data project back to the array of ɛHf (t) values for the zircon cores. This demonstrates that the thin leucosomes were derived from the gneiss without any mass input from a mantle source. These features are consistent with an origin of the HYS as part of the eastern margin of the NCC prior to juxtaposition with the Sulu belt. Zircons from the leucogranite dykes also show core-mantle-rim structure. Inherited cores yield concordant 206Pb/238U ages of 776-701 Ma consistent with the dominant age range for protoliths of the UHP metamorphic rocks in the Sulu belt. Zircon mantle and rim domains, which both contain multiphase solid inclusions (Kfs + Pl + Qz and Hem + Pl + Qz in mantles and Kfs + Pl + Qz + Bt in rims), yield melt crystallization ages of 226-217 and 169-156 Ma, respectively. High Sr, low Y and Yb contents, high Sr/Y ratios, and the range of ɛNd (t) values (-18.2- -15.0) and initial 87Sr/86Sr ratios (0.7106 - 0.7146) for the leucogranites are consistent with melting of thickened lower continental crust of the Sulu belt. We interpret the dykes to have been emplaced during post-collisional collapse of the orogenic root of this belt in the Middle-Upper Jurassic.

Fracture-induced flow and liquid metal transport during core formation

NASA Astrophysics Data System (ADS)

Jones, V.; Petford, N.; Rushmer, T.; Wertheim, D.

2008-12-01

The most important event in the early history of the earth was the separation of its iron-rich core. Core formation induced profound chemical fractionations and extracted into the core most of Earth's iron and siderophile elements (Ni, Co, Au, Pt, W, Re), leaving the silicate crust and mantle with strong depletions of these elements relative to primitive planetary material. Recent measurements of radiogenic 182W anomalies in the silicate Earth, Mars and differentiated meteorites imply that planetesimals segregated metallic cores within a few Myr of the origin of the solar system. Various models have been put forward to explain the physical nature of the segregation mechanism (Fe-diapirs, 'raining' through a magma ocean), and more recently melt flow via fractures. In this contribution we present the initial results of a numerical study into Fe segregation in a deforming silicate matrix that captures the temperature-dependent effect of liquid metal viscosity on the transport rate. Flow is driven by pressure gradients associated with impact deformation in a growing planetesimal and the fracture geometry is constrained by experimental data on naturally deformed H6 chondrite. Early results suggest that under dynamic conditions, fracture-driven melt flow can in principle be extremely rapid, leading to a significant draining of the Fe-liquid metal and siderophile trace element component on a timescale of hours to days. Fluid transport in planetesimals where deformation is the driving force provides an attractive and simple way of segregating Fe from host silicate as both precursor and primary agent of core formation

Experimental determination of CO2 content at graphite saturation along a natural basalt-peridotite melt join: Implications for the fate of carbon in terrestrial magma oceans

NASA Astrophysics Data System (ADS)

Duncan, Megan S.; Dasgupta, Rajdeep; Tsuno, Kyusei

2017-05-01

Knowledge of the carbon carrying capacity of peridotite melt at reducing conditions is critical to constrain the mantle budget and planet-scale distribution of carbon set at early stage of differentiation. Yet, neither measurements of CO2 content in reduced peridotite melt nor a reliable model to extrapolate the known solubility of CO2 in basaltic (mafic) melt to solubility in peridotitic (ultramafic) melt exist. There are several reasons for this gap; one reason is due to the unknown relative contributions of individual network modifying cations, such as Ca2+ versus Mg2+, on carbonate dissolution particularly at reducing conditions. Here we conducted high pressure, temperature experiments to estimate the CO2 contents in silicate melts at graphite saturation over a compositional range from natural basalts toward peridotite at a fixed pressure (P) of 1.0 GPa, temperature (T) of 1600 °C, and oxygen fugacity (log ⁡ fO2 ∼ IW + 1.6). We also conducted experiments to determine the relative effects of variable Ca and Mg contents in mafic compositions on the dissolution of carbonate. Carbon in quenched glasses was measured and characterized using Fourier transform infrared spectroscopy (FTIR) and Raman Spectroscopy and was found to be dissolved as carbonate (CO32-). The FTIR spectra showed CO32- doublets that shifted systematically with the MgO and CaO content of silicate melts. Using our data and previous work we constructed a new composition-based model to determine the CO2 content of ultramafic (peridotitic) melt representative of an early Earth, magma ocean composition at graphite saturation. Our data and model suggest that the dissolved CO2 content of reduced, peridotite melt is significantly higher than that of basaltic melt at shallow magma ocean conditions; however, the difference in C content between the basaltic and peridotitic melts may diminish with depth as the more depolymerized peridotite melt is more compressible. Using our model of CO2 content at graphite saturation as a function of P-T-fO2-melt composition, we predict that a superliquidus shallow magma ocean should degas CO2. Whereas if the increase of fO2 with depth is weak, a magma ocean may ingas a modest amount of carbon during crystallization. Further, using the carbon content of peridotite melt at log ⁡ fO2 of IW and the knowledge of C content of Fe-rich alloy melt, we also consider the core-mantle partitioning of carbon, showing that DCmetal/peridotite of a shallow magma ocean is generally higher than previously estimated.

About the Influence of the initial Atmosphere on the Earth's Temperature Distribution during it's Accumulation

NASA Astrophysics Data System (ADS)

Khachay, Y.; Anfilogov, V.; Antipin, A.

2012-04-01

We suggested a new model for accumulation of planets of the Earth's group [1], which is based on the contemporary results of geochemical analyses, which allow to obtain the concentrations of short living radioactive isotopes of 26Al in the matter of the pre planet cloud [2]. With use of that data new estimations of temperature distribution into the growing planetary pre planetary bodies into the Earth's nebular zone had been obtained. For the further Earth's temperature evolution, as it had been showed by the results of numerical modeling, the main role belongs to the temperature distribution in the forming Earth's core and the existence of a dense and transparent atmosphere. The shadow influence of the initial atmosphere had been researched in the paper [3]. We shall give the main consideration to these problems in that paper. It had been shown in [1], that on the earliest accumulation stage the heat release by the decay of 26Al it is sufficient for forming a central melted area and solid relatively thin mainly silicate upper envelope in the pre planetary body, with dimensions, larger than (50-100) km. The impact velocities on that stage are yet not large, therefore by the bodies impact with these or near dimensions liquid and mainly iron their parts merge, but the masses of the pre planetary bodies are not sufficient to gravitational keeping of silicate parts of the cold solid envelope. On that stage they remain into the nebular zone of the proto planet and the mechanism of matter differentiation for the future core and mantle reservoirs realizes. The process takes place yet in small bodies and is in time to finish during less than 10 million years. The next forming of the core and mantle structure continues according to all known estimations about 100 million years. Because of the merging of inner liquid parts of impacting bodies occur due to inelastic impact, the main part of potential energy transforms into heat. That continues up to that time when the iron core mass increases to the main part of the contemporary mass. The silicate particles of different dimensions remain in the proto planet cloud and in the initial atmosphere, reducing it's transparency and release of the heat radiation. On the finishing stage of the core growing the mass of the pre planetary body is sufficient for keeping of the rising part of the silicate envelope of falling bodies. The matter of the growing planet enriches more and more with a touch of silicates. The impact process of accumulated bodies gradually converts to the mechanism of elastic impact, by which only a small part of kinetic energy transforms into the merging by the pre planet body heat. The atmosphere losses the silicate particles and it's transparency exceeds. It is forming either a non melted mantle, or a mantle with a rising melted layer. That results show that the existence of a dense, nontransparent atmosphere leads to temperature growing in the inner areas of the planet during it's accumulation process. 1.Anfilogov V.N., Khachay Yu.V. A possible variant of matter differentiation on the initial stage of Earth's forming. // DAN. 2005, V. 403, N. 6, 803-806. 2.Merk R.,Breuer D., Spohn T., 2002. Numerical modeling of 26Al - Induced radioactive melting of asteroids concerning accretion, Icarus, 159, 183-191. 3.Hayashi C., Nakazawa K., Mizuno H. Earth's melting due to the blanketing effect of primordial dense atmosphere. // Earth and Plenetary Science Letters. (1979). v. 43, 22-28

Mercury's core evolution

NASA Astrophysics Data System (ADS)

Deproost, Marie-Hélène; Rivoldini, Attilio; Van Hoolst, Tim

2016-10-01

Remote sensing data of Mercury's surface by MESSENGER indicate that Mercury formed under reducing conditions. As a consequence, silicon is likely the main light element in the core together with a possible small fraction of sulfur. Compared to sulfur, which does almost not partition into solid iron at Mercury's core conditions and strongly decreases the melting temperature, silicon partitions almost equally well between solid and liquid iron and is not very effective at reducing the melting temperature of iron. Silicon as the major light element constituent instead of sulfur therefore implies a significantly higher core liquidus temperature and a decrease in the vigor of compositional convection generated by the release of light elements upon inner core formation.Due to the immiscibility in liquid Fe-Si-S at low pressure (below 15 GPa), the core might also not be homogeneous and consist of an inner S-poor Fe-Si core below a thinner Si-poor Fe-S layer. Here, we study the consequences of a silicon-rich core and the effect of the blanketing Fe-S layer on the thermal evolution of Mercury's core and on the generation of a magnetic field.

Impact-generated Hydrothermal Activity at the Chicxulub Crater

NASA Astrophysics Data System (ADS)

Kring, D. A.; Zurcher, L.; Abramov, O.

2007-05-01

Borehole samples recovered from PEMEX exploration boreholes and an ICDP scientific borehole indicate the Chicxulub impact event generated hydrothermal alteration throughout a large volume of the Maya Block beneath the crater floor and extending across the bulk of the ~180 km diameter crater. The first indications of hydrothermal alteration were observed in the crater discovery samples from the Yucatan-6 borehole and manifest itself in the form of anhydrite and quartz veins. Continuous core from the Yaxcopoil-1 borehole reveal a more complex and temporally extensive alteration sequence: following a brief period at high temperatures, impact- melt-bearing polymict breccias and a thin, underlying unit of impact melt were subjected to metasomatism, producing alkali feldspar, sphene, apatite, and magnetite. As the system continued to cool, smectite-series phyllosilicates appeared. A saline solution was involved. Stable isotopes suggest the fluid was dominated by a basinal brine created mostly from existing groundwater of the Yucatan Peninsula, although contributions from down-welling water also occurred in some parts of the system. Numerical modeling of the hydrothermal system suggests circulation occurred for 1.5 to 2.3 Myr, depending on the permeability of the system. Our understanding of the hydrothermal system, however, is still crude. Additional core recovery projects, particularly into the central melt sheet, are needed to better evaluate the extent and duration of hydrothermal alteration.

Characteristics of basal ice and subglacial water at Dome Fuji, Antarctica ice sheet

NASA Astrophysics Data System (ADS)

Motoyama, H.; Uemura, R.; Hirabayashi, M.; Miyake, T.; Kuramoto, T.; Tanaka, Y.; Dome Fuji Ice Core Project, M.

2008-12-01

(Introduction): The second deep ice coring project at Dome Fuji, Antarctica reached a depth of 3035.22 m during the austral summer season in 2006/2007. The recovered ice cores contain records of global environmental changes going back about 720,000 years. (Estimation of basal ice melt): The borehole measurement was carried out on January 2nd in 2007 when the temperature disturbance in the borehole calmed down by the rest of drilling for 2 days. Temperature measurement was performed after 0 C thermometer test was done in the ground. The temperature sensor of pt100 installed in the skate-like anti-torque was used. We did not have the enough time until the temperature of thermometer was matched with the temperature of ice sheet. Some error was included in ice temperature data. The resistance of pt100 sensor was converted to temperature in the borehole measurement machine. But we used only two electrical lines for pt100 sensor. Rate of heat flow in the ice sheet was calculated using the vertical temperature gradient of the ice sheet and rate of heat conductivity of ice. The deepest part of heat flux using temperatures at 3000m and 3030m was about 45mW/m2. We assumed that this value was the heat flux from the bedrock in the ice sheet. Heat flux to the bedrock surface in the ground was assumed 54.6mW/m2 adopted by ice sheet model (P. Huybrechts, 2006). Then the heat flux for basal ice melt was about 10mW/m2. This value was equaled to melting of 1.1mm of ice thickness per year. On the other hand, the annual layer thickness under 2500m was not changed so much and its average was 1.3mm of ice thickness. So the annual layer thickness and melting rate of basal ice was the same in ordering way. Or ice equivalent in annual layer is melting every year. The age of the deepest part of ice core is guessed at 720,000 years old and the ice older than basal ice has melted away. (The state of basal ice): When the ice core drilling depth passed 3031.44m, amount of ice chip more abundant than the cutting chips has been collected. When the drilling passed 3033.46m, the amount of ice chip was decreased. But the amount of ice chip collected increase again from 3034.59m and many large ices have taken the upper part of ice core. The temperature of ice sheet near the bedrock is the pressure melting point. So the liquid water can exist easy there. The water like groundwater infiltrated into the borehole and froze in drilling liquid from 3031.44m to 3033.46m. Under 3034.59m, the subglacial water infiltrated into the borehole and froze in drilling liquid. The existence of water channel in the ice core was found. We think that the liquid water has been flowing through the boundary of ice crystal. (Characteristics of chemical constituents): The melted ice was analyzed every 10cm per 50cm from 2400m to 3028m and continuously every 10cm from 3028m to 3034m. The analytical items were water isotopes (d18O and dD), micro particles (dust) and major ion components. The variations of water isotope and dust in ice near the bedrock have no conspicuous change. But, the concentrations of Cl- and Na+ ions had interesting behavior. The concentration of Cl- ion increased and Na+ ion was decreased deeper than 3020m. Further the concentrations of all ions were decreased suddenly deeper than 3034m. The concentration of ions will be decrease in turn according to the solubility of the ion. home/

The Pressure Dependence of Thermal Expansion of Core-Forming Alloys: A Key Parameter in Determining the Convective Style of Planetary Cores

NASA Astrophysics Data System (ADS)

Williams, Q. C.; Manghnani, M. H.

2017-12-01

The convective style of planetary cores is critically dependent on the thermal properties of iron alloys. In particular, the relation between the adiabatic gradient and the melting curve governs whether planetary cores solidify from their top down (when the adiabat is steeper than the melting curve) or the bottom up (the converse). Molten iron alloys, in general, have large, ambient pressure thermal expansions: values in excess of 1.2 x 10^-4/K are dictated by data derived from levitated and sessile drop techniques. These high values of the thermal expansion imply that the adiabatic gradients within early planetesimals and present day moons that have comparatively low-pressure, iron-rich cores are steep (typically greater than 35 K/GPa at low pressures): values, at low pressures, that are greater than the slope of the melting curve, and hence show that the cores of small solar system objects probably crystallize from the top-down. Here, we deploy a different manifestation of these large values of thermal expansion to determine the pressure dependence of thermal expansion in iron-rich liquids: a difficult parameter to experimentally measure, and critical for determining the size range of cores in which top-down core solidification predominates. In particular, the difference between the adiabatic and isothermal bulk moduli of iron liquids is in the 20-30% range at the melting temperature, and scales as the product of the thermal expansion, the Grüneisen parameter, and the temperature. Hence, ultrasonic (and adiabatic) moduli of iron alloy liquids, when coupled with isothermal sink-float measurements, can yield quantitative constraints on the pressure dependence of thermal expansion. For liquid iron alloys containing 17 wt% Si, we find that the thermal expansion is reduced by 50% over the first 8 GPa of compression. This "squeezing out" of the anomalously high low-pressure thermal expansion of iron-rich alloys at relatively modest conditions likely limits the size range over which top-down crystallizing cores are anticipated within planetary bodies.

Probing the melt zone of Kilauea Iki lava lake, Kilauea volcano, Hawaii

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hardee, H.C.; Dunn, J.C.; Hills, R.G.

1981-12-01

New drilling techniques were recently used to drill and core the melt zone of Kilauea Iki lava lake to a depth of 93 m. A partial melt zone was found to exist at depths between 58 m and 89 m consisting of 40 volume percent melt. Downhole seismic shots detonated in and below the melt zone resulted in the first in situ measurements of seismic velocity directly through well characterized partial melt zone. Periodic seismic sources were used to effectively penetrate the highly fractured hydrothermal zone of the lava lake crust. Low velocity P-wave layers (< or =2.0 km/s) weremore » found at the surface, at 40 m depth, and at 90 m depth. Thermal convective experiments in the melt zone resulted in the first controlled in situ measurements of the interaction of water with a basaltic melt zone. Transient energy rates of 900 kW (980 kW/m/sup 2/) and steady rates of 85 kW (93 kW/m/sup 2/) were observed. The full water recovery (100%), high downhole steam temperatures (670 C), and high energy transfer rates (93 to 980 kW/m/sup 2/) observed in these thermal experiments are consistent with a closed cavity model where the injected water/steam directly contacted basaltic melt or near melt. In addition to understanding lava lakes, these seismic and thermal experiments have applications for the location of magma bodies in the crust and for the efficient extraction of energy from these bodies.« less

Shock compression of stishovite and melting of silica at planetary interior conditions

NASA Astrophysics Data System (ADS)

Millot, M.; Dubrovinskaia, N.; Černok, A.; Blaha, S.; Dubrovinsky, L.; Braun, D. G.; Celliers, P. M.; Collins, G. W.; Eggert, J. H.; Jeanloz, R.

2015-01-01

Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. In particular, how much heat solids can sustain before melting under pressure is key to determining a planet’s internal structure and evolution. We report laser-driven shock experiments on fused silica, α-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of SiO2 rises to 8300 K at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5-Earth mass super-Earth. We show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets.

Planetary science. Shock compression of stishovite and melting of silica at planetary interior conditions.

PubMed

Millot, M; Dubrovinskaia, N; Černok, A; Blaha, S; Dubrovinsky, L; Braun, D G; Celliers, P M; Collins, G W; Eggert, J H; Jeanloz, R

2015-01-23

Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. In particular, how much heat solids can sustain before melting under pressure is key to determining a planet's internal structure and evolution. We report laser-driven shock experiments on fused silica, α-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of SiO2 rises to 8300 K at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5-Earth mass super-Earth. We show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets. Copyright © 2015, American Association for the Advancement of Science.

Visualizing Earth's Core-Mantle Interactions using Nanoscale X-ray Tomography

NASA Astrophysics Data System (ADS)

Mao, W. L.; Wang, J.; Yang, W.; Hayter, J.; Pianetta, P.; Zhang, L.; Fei, Y.; Mao, H.; Hustoft, J. W.; Kohlstedt, D. L.

2010-12-01

Early-stage, core-mantle differentiation and core formation represent a pivotal geological event which defined the major geochemical signatures. However current hypotheses of the potential mechanism for core-mantle separation and interaction need more experimental input which has been awaiting technological breakthroughs. Nanoscale x-ray computed tomography (nanoXCT) within a laser-heated diamond anvil cell has exciting potential as a powerful 3D petrographic probe for non-destructive, nanoscale (<40nm) resolution of multiple minerals and amorphous phases (including melts) which are synthesized under the high pressure-temperature conditions found deep within the Earth and planetary interiors. Results from high pressure-temperature experiments which illustrate the potential for this technique will be presented. By extending measurements of the texture, shape, porosity, tortuosity, dihedral angle, and other characteristics of molten Fe-rich alloys in relation to silicates and oxides, along with the fracture systems of rocks under deformation by high pressure-temperature conditions, potential mechanisms of core formation can be tested. NanoXCT can also be used to investigate grain shape, intergrowth, orientation, and foliation -- as well as mineral chemistry and crystallography at core-mantle boundary conditions -- to understand whether shape-preferred orientation is a primary source of the observed seismic anisotropy in Earth’s D” layer and to determine the textures and shapes of the melt pockets and channels which would form putative partial melt which may exist in ultralow velocity zones.

Advancing dynamic and thermodynamic modelling of magma oceans

NASA Astrophysics Data System (ADS)

Bower, Dan; Wolf, Aaron; Sanan, Patrick; Tackley, Paul

2017-04-01

The techniques for modelling low melt-fraction dynamics in planetary interiors are well-established by supplementing the Stokes equations with Darcy's Law. But modelling high-melt fraction phenomena, relevant to the earliest phase of magma ocean cooling, necessitates parameterisations to capture the dynamics of turbulent flow that are otherwise unresolvable in numerical models. Furthermore, it requires knowledge about the material properties of both solid and melt mantle phases, the latter of which are poorly described by typical equations of state. To address these challenges, we present (1) a new interior evolution model that, in a single formulation, captures both solid and melt dynamics and hence charts the complete cooling trajectory of a planetary mantle, and (2) a physical and intuitive extension of a "Hard Sphere" liquid equation of state (EOS) to describe silicate melt properties for the pressure-temperature (P-T) range of Earth's mantle. Together, these two advancements provide a comprehensive and versatile modelling framework for probing the far-reaching consequences of magma ocean cooling and crystallisation for Earth and other rocky planets. The interior evolution model accounts for heat transfer by conduction, convection, latent heat, and gravitational separation. It uses the finite volume method to ensure energy conservation at each time-step and accesses advanced time integration algorithms by interfacing with PETSc. This ensures it accurately and efficiently computes the dynamics throughout the magma ocean, including within the ultra-thin thermal boundary layers (< 2 cm thickness) at the core-mantle boundary and surface. PETSc also enables our code to support a parallel implementation and quad-precision calculations for future modelling capabilities. The thermodynamics of mantle melting are represented using a pseudo-one-component model, which retains the simplicity of a standard one-component model while introducing a finite temperature interval for melting (important for multi-component systems). Our new high P-T liquid EOS accurately captures the energetics and physical properties of the partially molten system whilst retaining the largest number of familiar EOS parameters. We demonstrate the power of our integrated dynamic and EOS model by exploring two crystallisation scenarios for Earth that are dictated by the coincidence of the liquid adiabat and melting curve. Experiments on melting of primitive chondrite composition predict that crystallisation occurs from the "bottom-up", whereas molecular dynamics simulations of MgSiO3 perovskite suggest crystallisation occurs from the "middle-out". In each case, we evaluate the lifetime of the magma ocean using our model and find that in both scenarios, initial cooling is rapid and the rheological transition (boundary between melt- and solid-like behaviour) is reached within a few kyrs. During this stage efficient mixing prevents the establishment of thermal and chemical heterogeneity, so it may be challenging to locate a signature of the earliest phase of magma ocean evolution. At the rheological transition, cooling is governed by gravitational separation and viscous creep, and even in the absence of iron partitioning our models predict long-lasting (> 500 Myr) melt at the base of the mantle.

The thermal evolution of Mercury's Fe-Si core

NASA Astrophysics Data System (ADS)

Knibbe, Jurriën Sebastiaan; van Westrenen, Wim

2018-01-01

We have studied the thermal and magnetic field evolution of planet Mercury with a core of Fe-Si alloy to assess whether an Fe-Si core matches its present-day partially molten state, Mercury's magnetic field strength, and the observed ancient crustal magnetization. The main advantages of an Fe-Si core, opposed to a previously assumed Fe-S core, are that a Si-bearing core is consistent with the highly reduced nature of Mercury and that no compositional convection is generated upon core solidification, in agreement with magnetic field indications of a stable layer at the top of Mercury's core. This study also present the first implementation of a conductive temperature profile in the core where heat fluxes are sub-adiabatic in a global thermal evolution model. We show that heat migrates from the deep core to the outer part of the core as soon as heat fluxes at the outer core become sub-adiabatic. As a result, the deep core cools throughout Mercury's evolution independent of the temperature evolution at the core-mantle boundary, causing an early start of inner core solidification and magnetic field generation. The conductive layer at the outer core suppresses the rate of core growth after temperature differences between the deep and shallow core are relaxed, such that a magnetic field can be generated until the present. Also, the outer core and mantle operate at higher temperatures than previously thought, which prolongs mantle melting and mantle convection. The results indicate that S is not a necessary ingredient of Mercury's core, bringing bulk compositional models of Mercury more in line with reduced meteorite analogues.

TEMperature Pressure ESTimation of a homogeneous boiling fuel-steel mixture in an LMFBR core. [TEMPEST code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pyun, J.J.; Majumdar, D.

The paper describes TEMPEST, a simple computer program for the temperature and pressure estimation of a boiling fuel-steel pool in an LMFBR core. The time scale of interest of this program is large, of the order of ten seconds. Further, the vigorous boiling in the pool will generate a large contact, and hence a large heat transfer between fuel and steel. The pool is assumed to be a uniform mixture of fuel and steel, and consequently vapor production is also assumed to be uniform throughout the pool. The pool is allowed to expand in volume if there is steel meltingmore » at the walls. In this program, the total mass of liquid and vapor fuel is always kept constant, but the total steel mass in the pool may change by steel wall melting. Because of a lack of clear understanding of the physical phenomena associated with the progression of a fuel-steel mixture at high temperature, various input options have been built-in to enable one to perform parametric studies. For example, the heat transfer from the pool to the surrounding steel structure may be controlled by input values for the heat transfer coefficients, or, the heat transfer may be calculated by a correlation obtained from the literature. Similarly, condensation of vapor on the top wall can be specified by input values of the condensation coefficient; the program can otherwise calculate condensation according to the non-equilibrium model predictions. Meltthrough rates of the surrounding steel walls can be specified by a fixed melt-rate or can be determined by a fraction of the heat loss that goes to steel-melting. The melted steel is raised to the pool temperature before it is joined with the pool material. Several applications of this program to various fuel-steel pools in the FFTF and the CRBR cores are discussed.« less

Greenland-Wide Seasonal Temperatures During the Last Deglaciation

NASA Astrophysics Data System (ADS)

Buizert, C.; Keisling, B. A.; Box, J. E.; He, F.; Carlson, A. E.; Sinclair, G.; DeConto, R. M.

2018-02-01

The sensitivity of the Greenland ice sheet to climate forcing is of key importance in assessing its contribution to past and future sea level rise. Surface mass loss occurs during summer, and accounting for temperature seasonality is critical in simulating ice sheet evolution and in interpreting glacial landforms and chronologies. Ice core records constrain the timing and magnitude of climate change but are largely limited to annual mean estimates from the ice sheet interior. Here we merge ice core reconstructions with transient climate model simulations to generate Greenland-wide and seasonally resolved surface air temperature fields during the last deglaciation. Greenland summer temperatures peak in the early Holocene, consistent with records of ice core melt layers. We perform deglacial Greenland ice sheet model simulations to demonstrate that accounting for realistic temperature seasonality decreases simulated glacial ice volume, expedites the deglacial margin retreat, mutes the impact of abrupt climate warming, and gives rise to a clear Holocene ice volume minimum.

Laurentide Ice-Sheet Meltwater Sources to the Gulf of Mexico During the Last Deglaciation: Assessing Data Reconstructions Using Water Isotope Enabled Simulations

NASA Astrophysics Data System (ADS)

Vetter, L.; LeGrande, A. N.; Ullman, D. J.; Carlson, A. E.

2017-12-01

Sediment cores from the Gulf of Mexico show evidence of meltwater derived from the Laurentide Ice Sheet during the last deglaciation. Recent studies using geochemical measurements of individual foraminifera suggest changes in the oxygen isotopic composition of the meltwater as deglaciation proceeded. Here we use the water isotope enabled climate model simulations (NASA GISS ModelE-R) to investigate potential sources of meltwater within the ice sheet. We find that initial melting of the ice sheet from the southern margin contributed an oxygen isotope value reflecting a low-elevation, local precipitation source. As deglacial melting proceeded, meltwater delivered to the Gulf of Mexico had a more negative oxygen isotopic value, which the climate model simulates as being sourced from the high-elevation, high-latitude interior of the ice sheet. This study demonstrates the utility of combining stable isotope analyses with climate model simulations to investigate past changes in the hydrologic cycle.

Preparation of acetaminophen capsules containing beads prepared by hot-melt direct blend coating.

PubMed

Pham, Loan; Christensen, John M

2014-02-01

Twelve hydrophobic coating agents were assessed for their effects on drug release after coating sugar cores by a flexible hot-melt coating method using direct blending. Drug-containing pellets were also produced and used as cores. The cores were coated with single or double wax layers containing acetaminophen (APAP). The harder the wax, the slower the resultant drug releases from single-coated beads. Wax coating can be deposited on cores up to 28% of the beads final weight and reaching 58% with wax and drug. Carnauba-coated beads dissolved in approximately 6 h releasing 80% of the loaded drug. Applying another wax layer extended drug release over 20 h, while still delivering 80% of the loaded drug. When drug-containing pellets (33-58% drug loading) were used as cores, double wax-coated pellets exhibited a near zero-order drug release for 16 h, releasing 80% of the loaded drug delivering 18 mg/h. The simple process of hot-melt coating by direct blending of pellet-containing drug-coated formulations provides excellent options for immediate and sustained release formulations when higher lipid coating or drug loading is warranted. Predicted plasma drug concentration time profiles using convolution and in vitro drug release properties of the beads were performed for optimal formulations.

Influence of Silicate Melt Composition on Metal/Silicate Partitioning of W, Ge, Ga and Ni

NASA Technical Reports Server (NTRS)

Singletary, S. J.; Domanik, K.; Drake, M. J.

2005-01-01

The depletion of the siderophile elements in the Earth's upper mantle relative to the chondritic meteorites is a geochemical imprint of core segregation. Therefore, metal/silicate partition coefficients (Dm/s) for siderophile elements are essential to investigations of core formation when used in conjunction with the pattern of elemental abundances in the Earth's mantle. The partitioning of siderophile elements is controlled by temperature, pressure, oxygen fugacity, and by the compositions of the metal and silicate phases. Several recent studies have shown the importance of silicate melt composition on the partitioning of siderophile elements between silicate and metallic liquids. It has been demonstrated that many elements display increased solubility in less polymerized (mafic) melts. However, the importance of silicate melt composition was believed to be minor compared to the influence of oxygen fugacity until studies showed that melt composition is an important factor at high pressures and temperatures. It was found that melt composition is also important for partitioning of high valency siderophile elements. Atmospheric experiments were conducted, varying only silicate melt composition, to assess the importance of silicate melt composition for the partitioning of W, Co and Ga and found that the valence of the dissolving species plays an important role in determining the effect of composition on solubility. In this study, we extend the data set to higher pressures and investigate the role of silicate melt composition on the partitioning of the siderophile elements W, Ge, Ga and Ni between metallic and silicate liquid.

Random pinning elucidates the nature of melting transition in two-dimensional core-softened potential system

NASA Astrophysics Data System (ADS)

Tsiok, E. N.; Fomin, Y. D.; Ryzhov, V. N.

2018-01-01

Despite about forty years of investigations, the nature of the melting transition in two dimensions is not completely clear. In the framework of the most popular Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young (BKTHNY) theory, 2D systems melt through two continuous Berezinskii-Kosterlitz-Thouless (BKT) transitions with intermediate hexatic phase. The conventional first-order transition is also possible. On the other hand, recently on the basis of computer simulations the new melting scenario was proposed with continuous BKT type solid-hexatic transition and first order hexatic-liquid transition. However, in the simulations the hexatic phase is extremely narrow that makes its study difficult. In the present paper, we propose to apply the random pinning to investigate the hexatic phase in more detail. The results of molecular dynamics simulations of two dimensional system having core-softened potentials with narrow repulsive step which is similar to the soft disk system are outlined. The system has a small fraction of pinned particles giving quenched disorder. Random pinning widens the hexatic phase without changing the melting scenario and gives the possibility to study the behavior of the diffusivity and order parameters in the vicinity of the melting transition and inside the hexatic phase.

Deformation of a crystalline olivine aggregate containing two immiscible liquids: Implications for early core-mantle differentiation

NASA Astrophysics Data System (ADS)

Cerantola, V.; Walte, N. P.; Rubie, D. C.

2015-05-01

Deformation-assisted segregation of metallic and sulphidic liquid from a solid peridotitic matrix is a process that may contribute to the early differentiation of small planetesimals into a metallic core and a silicate mantle. Here we present results of an experimental study using a simplified system consisting of a polycrystalline Fo90-olivine matrix containing a small percentage of iron sulphide and a synthetic primitive MORB melt, in order to investigate whether the silicate melt enhances the interconnection and segregation of FeS liquid under deformation conditions at varying strain rates. The experiments have been performed at 2 GPa, 1450 °C and strain rates between 1 ×10-3s-1 to 1 ×10-5s-1. Our results show that the presence of silicate melt actually hinders the migration and segregation of sulphide liquid by reducing its interconnectivity. At low to moderate strain rates the sulphide liquid pockets preserved a roundish shape, showing the liquid behavior is governed mainly by surface tension rather than by differential stress. Even at the highest strain rates, insignificant FeS segregation and interconnection were observed. On the other hand the basaltic melt was very mobile during deformation, accommodating part of the strain, which led to its segregation from the matrix at high bulk strains leaving the sulphide liquid stranded in the olivine matrix. Hence, we conclude that deformation-induced percolation of sulphide liquid does not contribute to the formation of planetary cores after the silicate solidus is overstepped. A possible early deformation enhanced core-mantle differentiation after overstepping the Fe-S solidus is not possible between the initial formation of silicate melt and the formation of a widespread magma ocean.

Effect of controlling recrystallization from the melt on the residual stress and structural properties of the Silica-clad Ge core fiber

NASA Astrophysics Data System (ADS)

Zhao, Ziwen; Cheng, Xueli; He, Ting; Xue, Fei; Zhang, Wei; Chen, Na; Wen, Jianxiang; Zeng, Xianglong; Wang, Tingyun

2017-09-01

Effect of controlling recrystallization from the melt (1000 °C) on the residual stress and structural properties of a Ge core fiber via molten core drawing (MCD) method is investigated. Ge core fibers is investigated using Raman spectroscopy, scanning electron microscope (SEM), and X-ray diffraction (XRD). Compared with the as-drawn Ge fiber, the Raman peak of the recrystallized Ge fiber shift from 300 cm-1 to 300.6 cm-1 and full width at half maximum (FWHM) decreased from 5.36 cm-1 to 4.48 cm-1. The Ge crystal grains which sizes are of 200-600 nm were formed during the process of recrystallization; the XRD peak of (1 1 1) plane is observed after recrystallization. These results show that controlling recrystallization allows the release of the thermal stress, and improvement of the crystal quality of Ge core.

Waterlike anomalies in a two-dimensional core-softened potential

NASA Astrophysics Data System (ADS)

Bordin, José Rafael; Barbosa, Marcia C.

2018-02-01

We investigate the structural, thermodynamic, and dynamic behavior of a two-dimensional (2D) core-corona system using Langevin dynamics simulations. The particles are modeled by employing a core-softened potential which exhibits waterlike anomalies in three dimensions. In previous studies in a quasi-2D system a new region in the pressure versus temperature phase diagram of structural anomalies was observed. Here we show that for the two-dimensional case two regions in the pressure versus temperature phase diagram with structural, density, and diffusion anomalies are observed. Our findings indicate that, while the anomalous region at lower densities is due the competition between the two length scales in the potential at higher densities, the anomalous region is related to the reentrance of the melting line.

Possible Mechanisms for Turbofan Engine Ice Crystal Icing at High Altitude

NASA Technical Reports Server (NTRS)

Tsao, Jen-Ching; Struk, Peter M.; Oliver, Michael

2014-01-01

A thermodynamic model is presented to describe possible mechanisms of ice formation on unheated surfaces inside a turbofan engine compression system from fully glaciated ice crystal clouds often formed at high altitude near deep convective weather systems. It is shown from the analysis that generally there could be two distinct types of ice formation: (1) when the "surface freezing fraction" is in the range of 0 to 1, dominated by the freezing of water melt from fully or partially melted ice crystals, the ice structure is formed from accretion with strong adhesion to the surface, and (2) when the "surface melting fraction" is the range of 0 to 1, dominated by the further melting of ice crystals, the ice structure is formed from accumulation of un-melted ice crystals with relatively weak bonding to the surface. The model captures important qualitative trends of the fundamental ice-crystal icing phenomenon reported earlier1,2 from the research collaboration work by NASA and the National Research Council (NRC) of Canada. Further, preliminary analysis of test data from the 2013 full scale turbofan engine ice crystal icing test3 conducted in the NASA Glenn Propulsion Systems Laboratory (PSL) has also suggested that (1) both types of ice formation occurred during the test, and (2) the model has captured some important qualitative trend of turning on (or off) the ice crystal ice formation process in the tested engine low pressure compressor (LPC) targeted area under different icing conditions that ultimately would lead to (or suppress) an engine core roll back (RB) event.

Possible Mechanisms for Turbofan Engine Ice Crystal Icing at High Altitude

NASA Technical Reports Server (NTRS)

Tsao, Jen-Ching; Struk, Peter M.; Oliver, Michael J.

2016-01-01

A thermodynamic model is presented to describe possible mechanisms of ice formation on unheated surfaces inside a turbofan engine compression system from fully glaciated ice crystal clouds often formed at high altitude near deep convective weather systems. It is shown from the analysis that generally there could be two distinct types of ice formation: (1) when the "surface freezing fraction" is in the range of 0 to 1, dominated by the freezing of water melt from fully or partially melted ice crystals, the ice structure is formed from accretion with strong adhesion to the surface, and (2) when the "surface melting fraction" is the range of 0 to 1, dominated by the further melting of ice crystals, the ice structure is formed from accumulation of un-melted ice crystals with relatively weak bonding to the surface. The model captures important qualitative trends of the fundamental ice-crystal icing phenomenon reported earlier (Refs. 1 and 2) from the research collaboration work by NASA and the National Research Council (NRC) of Canada. Further, preliminary analysis of test data from the 2013 full scale turbofan engine ice crystal icing test (Ref. 3) conducted in the NASA Glenn Propulsion Systems Laboratory (PSL) has also suggested that (1) both types of ice formation occurred during the test, and (2) the model has captured some important qualitative trend of turning on (or off) the ice crystal ice formation process in the tested engine low pressure compressor (LPC) targeted area under different icing conditions that ultimately would lead to (or suppress) an engine core roll back (RB) event.

The role of S in the evolution of the parental cores of the iron meteorites

NASA Technical Reports Server (NTRS)

Kracher, A.; Wasson, J. T.

1982-01-01

The S contents of iron meteorite parent bodies are estimated on the basis of cosmochemical relationships to undifferentiated meteorites, the results are compared to observations on the major magmatic iron meteorite groups, and evidence is presented that S/Ni ratios in their parent melts were much lower than those inferred for the parent body. Several alternative models to account for the discrepancy are offered, including volatilization of S from the IIAB parent body, liquid immiscibility, and metastable liquid layers produced by episodic melting. Finally, the fate of the S-rich meteoroidal material is discussed, as well as the question of why it seems to be missing from meteorite collections.

Structure, Frictional Melting and Fault Weakening during the 2008 Mw 7.9 Wenchuan Earthquake Slip: Observation from the WFSD Drilling Core Samples

NASA Astrophysics Data System (ADS)

Li, H.; Wang, H.; Li, C.; Zhang, J.; Sun, Z.; Si, J.; Liu, D.; Chevalier, M. L.; Han, L.; Yun, K.; Zheng, Y.

2015-12-01

The 2008 Mw7.9 Wenchuan earthquake produced two co-seismic surface ruptures along Yingxiu-Beichuan fault (~270 km) and the Guanxian-Anxian fault (~80 km) simultaneously in the Longmen Shan thrust belt. Besides, two surface rupture zones were tracked in the southern segment of the Yingxiu-Beichuan rupture zone, one along the Yingxiu fault, the other along the Shenxigou-Longchi fault, which both converged into one rupture zone at the Bajiaomiao village, Hongkou town, where one distinct fault plane with two striation orientations was exposed. The Wenchuan earthquake Fault Scientific Drilling project (WFSD) was carried out right after the earthquake to investigate its faulting mechanisms and rupture process. Six boreholes were drilled along the rupture zones with depths ranging from 600 to 2400 m. WFSD-1 and WFSD-2 are located at the Bajiaomiao area, the southern segment of the Yingxiu-Beichuan rupture zone, while WFSD-4 and WFSD-4S are in the Nanba town area, in the northern part of the rupture zone. Detailed research showed that ~1 mm thick Principal Slip Zone (PSZ) of the Wenchuan earthquake is located at ~589 m-depth in the WFSD-1 cores. Graphite present in the PSZ indicates a low fault strength. Long-term temperature monitoring shows an extremely low fault friction coefficient during the earthquake. Recently, another possible PSZ was found in WFSD-1 cores at ~732 m-depth, with a ~2 mm thick melt layer in the fault gouge, where feldspar was melted but quartz was not, indicating that the frictional melting temperature was 1230°C < T < 1720°C. These two PSZs at depth may correspond to the two co-seismic surface rupture zones. Besides, the Wenchuan earthquake PSZ was also recognized in the WFSD-4S cores, at ~1084 m-depth. About 200-400 μm thick melt layer (fault vein, mainly feldspar), as well as melt injection veins, were observed in the slip zone, where oblique distinct striations were visible on the slip surface. Therefore, there are two PSZs in the shallow crust at the southern segment along the Yingxiu-Beichuan fault, and another one along the northern segment. Melt and graphite in the PSZs indicate that the frictional melting and thermal pressurization are the main fault mechanisms during the Wenchuan earthquake. The melt and graphite can be considered as markers of large earthquakes.

Successive reactive liquid flow episodes in a layered intrusion (Unit 9, Rum Eastern Layered Intrusion, Scotland)

NASA Astrophysics Data System (ADS)

Leuthold, Julien; Blundy, Jon; Holness, Marian

2014-05-01

We will present a detailed microstructural and geochemical study of reactive liquid flow in Unit 9 of the Rum Eastern Layered Intrusion. In the study region, Unit 9 comprises an underlying lens-like body of peridotite overlain by a sequence of troctolite and gabbro (termed allivalite), with some local and minor anorthosite. The troctolite is separated from the overlying gabbro by a distinct, sub-horizontal, undulose horizon (the major wavy horizon). Higher in the stratigraphy is another, similar, horizon (the minor wavy horizon) that separates relatively clinopyroxene-poor gabbro from an overlying gabbro. To the north of the peridotite lens, both troctolite and gabbro grade into poikilitic gabbro. Clinopyroxene habit in the allivalite varies from thin rims around olivine in troctolite, to equigranular crystals in gabbro, to oikocrysts in the poikilitic gabbro. The poikilitic gabbros contain multiple generations of clinopyroxene, with Cr-rich (~1.1 wt.% Cr2O3), anhedral cores with moderate REE concentrations (core1) overgrown by an anhedral REE-depleted second generation with moderate Cr (~0.7 wt.% Cr2O3) (core2). These composite cores are rimmed by Cr-poor (~0.2 wt.% Cr2O3) and REE-poor to moderate clinopyroxene. We interpret these microstructures as a consequence of two separate episodes of partial melting triggered by the intrusion of hot olivine-phyric picrite to form the discontinuous lenses that comprise the Unit 9 peridotite. Loss of clinopyroxene-saturated partial melt from the lower part of the allivalite immediately following the early stages of sill intrusion resulted in the formation of clinopyroxene-poor gabbro. The spatial extent of clinopyroxene loss is marked by the minor wavy horizon. A further partial melting event stripped out almost all clinopyroxene from the lowest allivalite, to form a troctolite, with the major wavy horizon marking the extent of melting during this second episode. The poikilitic gabbro formed from clinopyroxene-saturated melt moving upwards and laterally through the cumulate pile. The Rum layered intrusion is an open intrusive complex, composed of individual partially molten zones, evolving independently. The Rum layered intrusion offers a direct overview of processes taking place in shallow intra-plate and ridge magma chambers. Intrusion of hot magma into a pre-existing cumulate pile results in the modification both the incoming liquid and the host-rock cumulates. Our study highlights the necessity of considering this type of process when modelling the geochemistry of lavas erupted from magma chambers subject to repeated replenishment.

Determining the Metal/Silicate Partition Coefficient of Germanium: Implications for Core and Mantle Differentiation.

NASA Technical Reports Server (NTRS)

King, C.; Righter, K.; Danielson, L.; Pando, K.; Lee, C.

2010-01-01

Currently there are several hypotheses for the thermal state of the early Earth. Some hypothesize a shallow magma ocean, or deep magma ocean, or heterogeneous accretion which requires no magma ocean at all. Previous models are unable to account for Ge depletion in Earth's mantle relative to CI chondrites. In this study, the element Ge is used to observe the way siderophile elements partition into the metallic core. The purpose of this research is to provide new data for Ge and to further test these models for Earth's early stages. The partition coefficients (D(sub Ge) = c(sub metal)/c(sub silicate), where D = partition coefficient of Ge and c = concentration of Ge in the metal and silicate, respectively) of siderophile elements were studied by performing series of high pressure, high temperature experiments. They are also dependent on oxygen fugacity, and metal and silicate composition. Ge is a moderately siderophile element found in both the mantle and core, and has yet to be studied systematically at high temperatures. Moreover, previous work has been limited by the low solubility of Ge in silicate melts (less than 100 ppm and close to detection limits for electron microprobe analysis). Reported here are results from 14 experiments studying the partitioning of Ge between silicate and metallic liquids. The Ge concentrations were then analyzed using Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) which is sensitive enough to detect ppm levels of Ge in the silicate melt.

Effect of Microstructure on Diffusional Solidification of 4343/3005/4343 Multi-Layer Aluminum Brazing Sheet

NASA Astrophysics Data System (ADS)

Tu, Yiyou; Tong, Zhen; Jiang, Jianqing

2013-04-01

The effect of microstructure on clad/core interactions during the brazing of 4343/3005/4343 multi-layer aluminum brazing sheet was investigated employing differential scanning calorimetry (DSC) and electron back-scattering diffraction (EBSD). The thickness of the melted clad layer gradually decreased during the brazing operation. It could be completely removed isothermally as a result of diffusional solidification at the brazing temperature. During the brazing cycle, the rate of loss of the melt in the brazing sheet, with small equiaxed grains' core layer, was higher than that with the core layer consisting of elongated large grains. The difference in microstructure affected the amount of liquid formed during brazing.

Chemical Convention in the Lunar Core from Melting Experiments on the Ironsulfur System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, J.; Liu, J.; Chen, B.

2012-03-26

By reanalyzing Apollo lunar seismograms using array-processing methods, a recent study suggests that the Moon has a solid inner core and a fluid outer core, much like the Earth. The volume fraction of the lunar inner core is 38%, compared with 4% for the Earth. The pressure at the Moon's core-mantle boundary is 4.8 GPa, and that at the ICB is 5.2 GPa. The partially molten state of the lunar core provides constraints on the thermal and chemical states of the Moon: The temperature at the inner core boundary (ICB) corresponds to the liquidus of the outer core composition, andmore » the mass fraction of the solid core allows us to infer the bulk composition of the core from an estimated thermal profile. Moreover, knowledge on the extent of core solidification can be used to evaluate the role of chemical convection in the origin of early lunar core dynamo. Sulfur is considered an antifreeze component in the lunar core. Here we investigate the melting behavior of the Fe-S system at the pressure conditions of the lunar core, using the multi-anvil apparatus and synchrotron and laboratory-based analytical methods. Our goal is to understand compositionally driven convection in the lunar core and assess its role in generating an internal magnetic field in the early history of the Moon.« less

How to measure heat capacity of metals at 10s to 100s of GPa

NASA Astrophysics Data System (ADS)

Geballe, Z. M.; Townley, A.; Jeanloz, R.

2014-12-01

Adapting methods of calorimetry to the diamond-anvil cell can provide important new information for understanding planetary interiors. Here we show that heat capacity of metals can be measured to the 10-100 GPa range by using AC electrical heating inside diamond anvil cells. Frequencies of f ≈ 1-100 MHz must be used to contain the heat within the sample of interest, as evidenced by numerical and physical models of heat flow: f > DinsCins2/(Csamdsam)2, where Dins is the thermal diffusivity of the insulation, Cins and Csam are specific heat capacities of insulation and metal sample, and dsam is sample thickness. Heat must be deposited uniformly (e.g. skin depth > sample thickness) for the most accurate and unambiguous measurements, thereby allowing measurement of the energetics of pre-melting, melting and partial melting of metals, including iron and its alloys. In principle, high-pressure calorimetry can be used to independently determine melting at high pressures, and also to quantify latent heats of fusion, thereby revealing the density of liquid metals at Earth core conditions.

OECD 2-D Core Concrete Interaction (CCI) tests : CCI-2 test plan, Rev. 0 January 31, 2004.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farmer, M. T.; Kilsdonk, D. J.; Lomperski, S.

The Melt Attack and Coolability Experiments (MACE) program addressed the issue of the ability of water to cool and thermally stabilize a molten core-concrete interaction when the reactants are flooded from above. These tests provided data regarding the nature of corium interactions with concrete, the heat transfer rates from the melt to the overlying water pool, and the role of noncondensable gases in the mixing processes that contribute to melt quenching. As a follow-on program to MACE, The Melt Coolability and Concrete Interaction Experiments (MCCI) project is conducting reactor material experiments and associated analysis to achieve the following objectives: (1)more » resolve the ex-vessel debris coolability issue through a program that focuses on providing both confirmatory evidence and test data for the coolability mechanisms identified in MACE integral effects tests, and (2) address remaining uncertainties related to long-term two-dimensional molten core-concrete interactions under both wet and dry cavity conditions. Achievement of these two program objectives will demonstrate the efficacy of severe accident management guidelines for existing plants, and provide the technical basis for better containment designs for future plants. In terms of satisfying these objectives, the Management Board (MB) approved the conduct of two long-term 2-D Core-Concrete Interaction (CCI) experiments designed to provide information in several areas, including: (i) lateral vs. axial power split during dry core-concrete interaction, (ii) integral debris coolability data following late phase flooding, and (iii) data regarding the nature and extent of the cooling transient following breach of the crust formed at the melt-water interface. The first of these two tests, CCI-1, was conducted on December 19, 2003. This test investigated the interaction of a fully oxidized 400 kg PWR core melt, initially containing 8 wt % calcined siliceous concrete, with a specially designed two-dimensional siliceous concrete test section with an initial cross-sectional area of 50 cm x 50 cm. The second of these two planned tests, CCI-2, will be conducted with a nearly identical test facility and experiment boundary conditions, but with a Limestone/Common Sand (LCS) concrete test section to investigate the effect of concrete type on the two-dimensional core-concrete interaction and debris cooling behavior. The objective of this report is to provide the overall test plan for CCI-2 to enable pretest calculations to be carried out. The report begins by providing a summary description of the CCI-2 test apparatus, followed by a description of the planned test operating procedure. Overall specifications for CCI-2 are provided in Table 1-1.« less

Nitrogen partitioning during Earth's accretion and core-mantle differentiation

NASA Astrophysics Data System (ADS)

Speelmanns, I. M.; Schmidt, M. W.; Liebske, C.

2017-12-01

On present day Earth, N is one of the key constituents of our atmosphere and forms the basis of life. However, the deep Earth geochemistry of N, i.e. its distribution and isotopic fractionation between Earth's deep reservoirs is not well constrained. This study investigates nitrogen partitioning between metal and silicate melts as relevant for core segregation during the accretion of planetesimals into the Earth. We have determined N-partitioning coefficients over a wide range of temperatures (1250-2000 °C), pressures (15-35 kbar) and oxygen fugacity's, the latter in the relevant range of core segregation (IW-5 to IW). Centrifuging piston cylinders were used to equilibrate and then gravitationally separate metal-silicate melt pairs. Separation of the two melts is necessary to avoid micro nugget contamination in the silicate melt at reducing conditions < IW-2.5. Complete segregation of the two melts was reached within 1 to 3 hours at 1000 g and 1600-1250 °C respectively, the interface showing a proper meniscus. The applied double capsule technique in all experiments, using an outer metallic (Pt) and inner non-metallic capsule (graphite or Al2O3), minimizes N-loss over the course of the experiments compared to single non-metallic capsules. The two quenched melts were cut apart mechanically, cleaned at the outside, their N concentrations were then analysed on bulk samples by an elemental analyser, the low abslute masses requiring careful development of analytical routines. Despite these difficulties, we were able to determine a DNmetal/silicate of 13±0.3 at IW-1 decreasing to 2.0±0.2 at IW-5.5, at 1250°C and 15 kbar, N partitioning into the core forming metal. Increasing temperature dramatically lowers the DNmetal/silicate to e.g. 0.5±0.15 at IW-4, during early core formation N was hence mildly incompatible in the metal. The results suggest that under magma ocean conditions (> 2000 oC and fO2 IW-2.5), N-partition coefficents were within a factor of 2 of unity. Hence, N did not partition into the core, which should contain negliligible quantities of N. The few available literature data [1],[2],[3] support N changing compatibility with decreasing fO2. [1] Kadik et al., (2011) Geochem Int 49.5: 429-438. [2] Roskosz et al., (2013) GCA 121: 15-28. [3] Dalou et al., (2017) EPSL 458: 141-151

OECD MCCI 2-D Core Concrete Interaction (CCI) tests : CCI-2 test data report-thermalhydraulic results, Rev. 0 October 15, 2004.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farmer, M. T.; Lomperski, S.; Kilsdonk, D. J.

The Melt Attack and Coolability Experiments (MACE) program addressed the issue of the ability of water to cool and thermally stabilize a molten core-concrete interaction when the reactants are flooded from above. These tests provided data regarding the nature of corium interactions with concrete, the heat transfer rates from the melt to the overlying water pool, and the role of noncondensable gases in the mixing processes that contribute to melt quenching. As a follow-on program to MACE, The Melt Coolability and Concrete Interaction Experiments (MCCI) project is conducting reactor material experiments and associated analysis to achieve the following objectives: (1)more » resolve the ex-vessel debris coolability issue through a program that focuses on providing both confirmatory evidence and test data for the coolability mechanisms identified in MACE integral effects tests, and (2) address remaining uncertainties related to long-term two-dimensional molten core-concrete interactions under both wet and dry cavity conditions. Achievement of these two program objectives will demonstrate the efficacy of severe accident management guidelines for existing plants, and provide the technical basis for better containment designs for future plants. In terms of satisfying these objectives, the Management Board (MB) approved the conduct of two long-term 2-D Core-Concrete Interaction (CCI) experiments designed to provide information in several areas, including: (i) lateral vs. axial power split during dry core-concrete interaction, (ii) integral debris coolability data following late phase flooding, and (iii) data regarding the nature and extent of the cooling transient following breach of the crust formed at the melt-water interface. This data report provides thermal hydraulic test results from the CCI-2 experiment, which was conducted on August 24, 2004. Test specifications for CCI-2 are provided in Table 1-1. This experiment investigated the interaction of a fully oxidized 400 kg PWR core melt, initially containing 8 wt % Limestone/Common Sand (LCS) concrete, with a specially designed two-dimensional LCS concrete test section with an initial cross-sectional area of 50 cm x 50 cm. The report begins by providing a summary description of the CCI-2 test apparatus and operating procedures, followed by presentation of the thermal-hydraulic results. Detailed posttest debris examination results will be provided in a subsequent publication. Observations drawn within this report regarding the overall cavity erosion behavior may be subject to revision once the posttest examinations are completed, since these examinations will fully reveal the final cavity shape.« less

Cooling vests with phase change materials: the effects of melting temperature on heat strain alleviation in an extremely hot environment.

PubMed

Gao, Chuansi; Kuklane, Kalev; Holmér, Ingvar

2011-06-01

A previous study by the authors using a heated thermal manikin showed that the cooling rates of phase change material (PCM) are dependent on temperature gradient, mass, and covering area. The objective of this study was to investigate if the cooling effects of the temperature gradient observed on a thermal manikin could be validated on human subjects in extreme heat. The subjects wore cooling vests with PCMs at two melting temperatures (24 and 28°C) and fire-fighting clothing and equipment, thus forming three test groups (vest24, vest28 and control group without the vest). They walked on a treadmill at a speed of 5 km/h in a climatic chamber (air temperature = 55°C, relative humidity = 30%, vapour pressure = 4,725 Pa, and air velocity = 0.4 m/s). The results showed that the PCM vest with a lower melting temperature (24°C) has a stronger cooling effect on the torso and mean skin temperatures than that with a higher melting temperature (28°C). Both PCM vests mitigate peak core temperature increase during the resting recovery period. The two PCM vests tested, however, had no significant effect on the alleviation of core temperature increase during exercise in the heat. To study the possibility of effective cooling of core temperature, cooling garments with PCMs at even lower melting temperatures (e.g. 15°C) and a larger covering area should be investigated.

Zircon (Hf, O isotopes) as melt indicator: Melt infiltration and abundant new zircon growth within melt rich layers of granulite-facies lenses versus solid-state recrystallization in hosting amphibolite-facies gneisses (central Erzgebirge, Bohemian Massif)

NASA Astrophysics Data System (ADS)

Tichomirowa, Marion; Whitehouse, Martin; Gerdes, Axel; Schulz, Bernhard

2018-03-01

In the central Erzgebirge within the Bohemian Massif, lenses of high pressure and ultrahigh pressure felsic granulites occur within meta-sedimentary and meta-igneous amphibolite-facies felsic rocks. In the felsic granulite, melt rich parts and restite form alternating layers, and were identified by petrology and bulk rock geochemistry. Mineral assemblages representing the peak P-T conditions were best preserved in melanocratic restite layers. In contrast, in the melt rich leucocratic layers, garnet and related HP minerals as kyanite are almost completely resorbed. Both layers display differences in accessory minerals: melanosomes have frequent and large monazite and Fe-Ti-minerals but lack xenotime and apatite; leucosomes have abundant apatite and xenotime while monazite is rare. Here we present a detailed petrographic study of zircon grains (abundance, size, morphology, inclusions) in granulite-facies and amphibolite-facies felsic gneisses, along with their oxygen and hafnium isotope compositions. Our data complement earlier Usbnd Pb ages and trace element data (REE, Y, Hf, U) on zircons from the same rocks (Tichomirowa et al., 2005). Our results show that the degree of melting determines the behaviour of zircon in different layers of the granulites and associated amphibolite-facies rocks. In restite layers of the granulite lenses, small, inherited, and resorbed zircon grains are preserved and new zircon formation is very limited. In contrast, new zircons abundantly grew in the melt rich leucocratic layers. In these layers, the new zircons (Usbnd Pb age, trace elements, Hf, O isotopes) best preserve the information on peak metamorphic conditions due to intense corrosion of other metamorphic minerals. The new zircons often contain inherited cores. Compared to cores, the new zircons and rims show similar or slightly lower Hf isotope values, slightly higher Hf model ages, and decreased oxygen isotope ratios. The isotope compositions (Hf, O) of new zircons indicate partial Hf isotope homogenization in the melt, and melt infiltration from an external source. New zircon was most likely formed by a peritectic reaction with melt above the wet solidus (peritectic zircon). Conversely, the amphibolite-facies host gneisses lack indications of significant melt production. Pre-metamorphic zircons experienced mainly solid-state recrystallization and variable Pb loss with only minor new zircon formation. However, subtle changes in cathodoluminescence pattern, in the Hf and O isotopes, and in the Lu/Hf, Yb/Hf ratios of zircons suggest that small volumes of melt were locally present. In difference to granulites, melt was internally produced. The detection of low degree melts (inferred from zircon geochemistry) is extremely important for the rheology because these amphibolite-facies rocks could act as large scale ductile shear zones. The new zircon data support a different P-T path for closely spaced amphibolite- and granulite-facies rocks.

Precipitation hydrometeor type relative to the mesoscale airflow in mature oceanic deep convection of the Madden-Julian Oscillation

DOE PAGES

Barnes, Hannah C.; Houze, Robert A.

2014-12-25

We present that composite analysis of mature near-equatorial oceanic mesoscale convective systems (MCSs) during the active stage of the Madden-Julian Oscillation (MJO) shows where different hydrometeor types occur relative to convective updraft and stratiform midlevel inflow layers. The National Center for Atmospheric Research (NCAR) S-PolKa radar observed these MCSs during the Dynamics of the Madden-Julian Oscillation/Atmospheric Radiation Measurement-MJO Investigation Experiment (DYNAMO/AMIE). NCAR's particle identification algorithm (PID) is applied to S-PolKa's polarimetric data to identify the dominant hydrometeor type in each radar sample volume. Combining S-PolKa's Doppler velocity data with the PID demonstrates that hydrometeors have a systematic relationship to themore » airflow within mature MCSs. In the convective region, moderate rain occurs within the updraft core; the heaviest rain occurs just downwind of the core; wet aggregates occur immediately below the melting layer; narrow zones containing graupel/rimed aggregates occur just downstream of the updraft core at midlevels; dry aggregates dominate above the melting level; and smaller ice particles occur along the edges of the convective zone. In the stratiform region, rain intensity decreases toward the anvil; melting aggregates occur in horizontally extensive but vertically thin regions at the melting layer; intermittent pockets of graupel/rimed aggregates occur atop the melting layer; dry aggregates and small ice particles occur sequentially above the melting level; and horizontally oriented ice crystals occur between -10°C and -20°C in turbulent air above the descending midlevel inflow, suggesting enhanced depositional growth of dendrites. Finally, the organization of hydrometeors within the midlevel inflow layer is insensitive to the presence or absence of a leading convective line.« less

Key characteristics of the Fe-snow regime in Ganymede's core

NASA Astrophysics Data System (ADS)

Rückriemen, Tina; Breuer, Doris; Spohn, Tilman

2014-05-01

Ganymede shows signs of an internally produced dipolar magnetic field (|Bdip|≡719 nT) [1]. For small planetary bodies such as Ganymede the Fe-snow regime, i.e. the top-down solidification of iron, has been suggested to play an important role in the core cooling history [2,3]. In that regime, iron crystals form first at the core-mantle boundary (CMB) due to shallow or negative slopes of the melting temperature [2,3]. The solid iron particles are heavier than the surrounding Fe-FeS fluid, i.e. a snow zone forms, settle to deeper core regions, where the core temperature is higher than the melting temperature, and remelt again. As a consequence, a stable chemical gradient in the Fe-FeS fluid arises within the snow zone. We speculate this style of convection via sedimentation to be small scale, therefore it lacks an important criterion necessary for dynamo action [4]. Below this zone, whose thickness increases with time, the process of remelting of iron creates a gravitationally unstable situation. We propose that this could be the driving mechanism for a potential dynamo. However, dynamo action would be restricted to the time period the snow zone needs to grow across the core. With a 1D thermo-chemical evolution model, we investigate key characteristics of the Fe-snow regime within Ganymede's core: the compositional density gradient of the fluid Fe-FeS within the snow zone and the time period necessary to grow the snow zone across the core. Additionally, we determine the dipolar magnetic field strength associated with a dynamo in Ganymede's deeper fluid core. We vary important input paramters such as the initial sulfur concentration (7-19 wt.%), the core heat flux (2-6 mW/m2) and the thermal conductivity (20-60 W/mK) with the nominal model being: xs=10 wt.%, qcmb=4 mW/m2, kc=32 W/mK. We find, that heat fluxes higher than 6 or 22 mW/m2 are required for double-diffusive or overturning convection to overcome the compositional density gradient within the snow zone, respectively. Since Ganymede's core heat flux does not exceed values of 4 mW/m2 [2], we consider the snow zone to be stable against thermal convection. The time necessary to grow the snow zone across the core is between 230-1900 Myr. For representative models we calculate the temporal evolution of the surface dipolar magnetic field strength according to [5]. All models show surface dipolar magnetic field strengths during the evolution of the snow zone that match the observed value of |Bdip|≡719 nT. In conclusion, we find that the Fe-snow regime produces a stably-stratified liquid layer in the snow zone below which a magnetic field of observed strength can be generated. Such a chemical dynamo is restricted in time and stops as soon as an inner solid core starts to grow suggesting the absence of such an inner core in Ganymede. The present model further suggests a core with high initial sulfur concentration, because this leads to a late start and a long duration of the dynamo necessary to explain the present magnetic field. References [1] Kivelson, M et al. (1996), Nature, 384(6609), [2] Hauck II, S. et al. (2006), JGR, 111(E9), [3] Williams, Q. (2009), EPSL, 284(3), [4] Christensen, U. and J. Wicht (2007), Treatise of Geophysics, Elsevier, [5] Christensen, U., and J. Aubert (2006), GJI, 166(1)

Early evolution and dynamics of Earth from a molten initial stage

NASA Astrophysics Data System (ADS)

Louro Lourenço, D. J.; Tackley, P. J.

2014-12-01

It is now well established that most of the terrestrial planets underwent a magma ocean stage during their accretion. On Earth, it is probable that at the end of accretion, giant impacts like the hypothesised Moon-forming impact, together with other sources of heat, melted a substantial part of the mantle. The thermal and chemical evolution of the resulting magma ocean most certainly had dramatic consequences on the history of the planet. Considerable research has been done on magma oceans using simple 1-D models (e.g.: Abe, PEPI 1997; Solomatov, Treat. Geophys. 2007; Elkins-Tanton EPSL 2008). However, some aspects of the dynamics may not be adequately addressed in 1-D and require the use of 2-D or 3-D models. Moreover, new developments in mineral physics that indicate that melt can be denser than solid at high pressures (e.g.: de Koker et al., EPSL 2013) can have very important impacts on the classical views of the solidification of magma oceans (Labrosse et al., Nature 2007). The goal of our study is to understand and characterize the influence of melting on the long-term thermo-chemical evolution of rocky planet interiors, starting from an initial molten state (magma ocean). Our approach is to model viscous creep of the solid mantle, while parameterizing processes that involve melt as previously done in 1-D models, including melt-solid separation at all melt fractions, the use of an effective diffusivity to parameterize turbulent mixing, coupling to a parameterized core heat balance and a radiative surface boundary condition. These enhancements have been made to the numerical code StagYY (Tackley, PEPI 2008). We will present results for the evolution of an Earth-like planet from a molten initial state to present day, while testing the effect of uncertainties in parameters such as melt-solid density differences, surface heat loss and efficiency of turbulent mixing. Our results show rapid cooling and crystallization until the rheological transition then much slower crystallization, large-scale overturn well before full solidification, the formation and subduction of an early crust while a partially-molten upper mantle is still present, transitioning to mostly-solid-state long-term mantle convection and plate tectonics.

Melting and Its Influence on the Long-term Evolution of the Lower Mantle Heterogeneities (LLSVP and ULVZ)

NASA Astrophysics Data System (ADS)

Fomin, I.; Tackley, P. J.

2017-12-01

Recent investigations have shown mantle solidus close to the range of proposed core-mantle boundary (CMB) temperatures (e.g. [Andrault et al., 2011, 2014], [de Koker et al., 2013]). Certain fraction of distinct rocks may reduce the effective melting temperature to values below the CMB temperature. It is especially true for iron enriched materials such as MORB [Nomura et al., 2011], BIF [Kato et al., 2016], iron-rich periclase [Boukare et al., 2015] and other rock species used to explain observed seismic anomalies. Computer simulations allow to study evolution and stability for chemically distinct piles proposed from geophysical data. Previous researches (e.g. [Mulyukova et al., 2015]) found those piles stirring in several hundreds of Ma. Our investigation adds influence of melting and following chemical differentiation on preservation of such structures.We present StagYY code [Tackley et al., 2008] with extended set of routines to model melting, melt redistribution and melt-dependent rheology in addition to solid-state mantle convection to reveal fate of chemically distinct piles in long-term (millions of years) perspective. A new point of our approach is usage of chemically independent oxides to describe rock composition and physical properties. Thin layers homogenize in few tens of millions of years despite whether melting happens or not. Thick structures (like periclase piles proposed for ULVZ [Wicks et al., 2010] or MORB-bearing domes for LLSVP [Ohta et al., 2008]) undergo partial melting if CMB temperature is above 3700K. Melt migration results in extraction of fusible components and therefore segregation of iron-enriched material. However, we weren't able to obtain any stabilized layer of iron-rich partially molten material at the CMB, because ongoing interaction and reequilibration of melt and solid results in buoyant liquids spreading to the adjacent mantle. Rheological influence of melt on bulk rock properties reduces time pile can exist.Our modeling puts severe constraints on the presence and fate of chemical heterogeneities in the lowermost mantle. Melting enhances stirring of such heterogeneities and generally no silicate melt can be stabilized at CMB for long time. Only low CMB temperatures (generally lower than 3700 K) allow anomalies to exist for geological periods of time (hundreds of Ma).

Megablocks and melt pockets in the Chesapeake Bay impact structure constrained by magnetic field measurements and properties of the Eyreville and Cape Charles cores

USGS Publications Warehouse

Shah, A.K.; Daniels, D.L.; Kontny, A.; Brozena, J.

2009-01-01

We use magnetic susceptibility and remanent magnetization measurements of the Eyreville and Cape Charles cores in combination with new and previously collected magnetic field data in order to constrain structural features within the inner basin of the Chesapeake Bay impact structure. The Eyreville core shows the first evidence of several-hundred-meter-thick basement-derived megablocks that have been transported possibly kilometers from their pre-impact location. The magnetic anomaly map of the structure exhibits numerous short-wavelength (<2 km) variations that indicate the presence of magnetic sources within the crater fill. With core magnetic properties and seismic reflection and refraction results as constraints, forward models of the magnetic field show that these sources may represent basementderived megablocks that are a few hundred meters thick or melt bodies that are a few dozen meters thick. Larger-scale magnetic field properties suggest that these bodies overlie deeper, pre-impact basement contacts between materials with different magnetic properties such as gneiss and schist or gneiss and granite. The distribution of the short-wavelength magnetic anomalies in combination with observations of small-scale (1-2 mGal) gravity field variations suggest that basement-derived megablocks are preferentially distributed on the eastern side of the inner crater, not far from the Eyreville core, at depths of around 1-2 km. A scenario where additional basement-derived blocks between 2 and 3 km depth are distributed throughout the inner basin-and are composed of more magnetic materials, such as granite and schist, toward the east over a large-scale magnetic anomaly high and less magnetic materials, such as gneiss, toward the west where the magnetic anomaly is lower-provides a good model fi t to the observed magnetic anomalies in a manner that is consistent with both gravity and seismic-refraction data. ?? 2009 The Geological Society of America.

Ice Particle Transport Analysis With Phase Change for the E(sup 3) Turbofan Engine Using LEWICE3D Version 3.2

NASA Technical Reports Server (NTRS)

Bidwell, Colin, S.

2012-01-01

Ice Particle trajectory calculations with phase change were made for the Energy Efficient Engine (E(sup 3)) using the LEWICE3D Version 3.2 software. The particle trajectory computations were performed using the new Glenn Ice Particle Phase Change Model which has been incorporated into the LEWICE3D Version 3.2 software. The E(sup 3) was developed by NASA and GE in the early 1980 s as a technology demonstrator and is representative of a modern high bypass turbofan engine. The E(sup 3) flow field was calculated using the NASA Glenn ADPAC turbomachinery flow solver. Computations were performed for the low pressure compressor of the E(sup 3) for a Mach 0.8 cruise condition at 11,887 m assuming a standard warm day for ice particle sizes of 5, 20, and 100 microns and a free stream particle concentration of 0.3 g/cu m. The impingement efficiency results showed that as particle size increased average impingement efficiencies and scoop factors increased for the various components. The particle analysis also showed that the amount of mass entering the inner core decreased with increased particle size because the larger particles were less able to negotiate the turn into the inner core due to particle inertia. The particle phase change analysis results showed that the larger particles warmed less as they were transported through the low pressure compressor. Only the smallest 5 micron particles were warmed enough to produce melting and the amount of melting was relatively small with a maximum average melting fraction of 0.836. The results also showed an appreciable amount of particle sublimation and evaporation for the 5 micron particles entering the engine core (22 percent).

Polymorphic Nature of Iron and Degree of Lattice Preferred Orientation Beneath the Earth's Inner Core Boundary

NASA Astrophysics Data System (ADS)

Mattesini, Maurizio; Belonoshko, Anatoly B.; Tkalčić, Hrvoje

2018-01-01

Deciphering the polymorphic nature and the degree of iron lattice-preferred orientation in the Earth's inner core holds a key to understanding the present status and evolution of the inner core. A multiphase lattice-preferred orientation pattern is obtained for the top 350 km of the inner core by means of the ab initio based Candy Wrapper Velocity Model coupled to a Monte Carlo phase discrimination scheme. The achieved geographic distribution of lattice alignment is characterized by two regions of freezing, namely within South America and the Western Central Pacific, that exhibit an uncommon high degree of lattice orientation. In contrast, widespread regions of melting of relatively weak lattice ordering permeate the rest of the inner core. The obtained multiphase lattice-preferred orientation pattern is in line with mantle-constrained geodynamo simulations and allows to setup an ad hoc mineral physics scenario for the complex Earth's inner core. It is found that the cubic phase of iron is the dominating iron polymorph in the outermost part of the inner core.

Analysis of loss-of-coolant accident for a fast-spectrum lithium-cooled nuclear reactor for space-power applications

NASA Technical Reports Server (NTRS)

Turney, G. E.; Petrik, E. J.; Kieffer, A. W.

1972-01-01

A two-dimensional, transient, heat-transfer analysis was made to determine the temperature response in the core of a conceptual space-power nuclear reactor following a total loss of reactor coolant. With loss of coolant from the reactor, the controlling mode of heat transfer is thermal radiation. In one of the schemes considered for removing decay heat from the core, it was assumed that the 4 pi shield which surrounds the core acts as a constant-temperature sink (temperature, 700 K) for absorption of thermal radiation from the core. Results based on this scheme of heat removal show that melting of fuel in the core is possible only when the emissivity of the heat-radiating surfaces in the core is less than about 0.40. In another scheme for removing the afterheat, the core centerline fuel pin was replaced by a redundant, constant temperature, coolant channel. Based on an emissivity of 0.20 for all material surfaces in the core, the calculated maximum fuel temperature for this scheme of heat removal was 2840 K, or about 90 K less than the melting temperature of the UN fuel.

An empirical method for calculating melt compositions produced beneath mid-ocean ridges: for axis and off-axis (seamounts) melting application

NASA Astrophysics Data System (ADS)

Batiza, Rodey

1991-12-01

We present a new method for calculating the major element compositions of primary melts parental to mid-ocean ridge basalt (MORB). This model is based on the experimental data of Jaques and Green (1980), Falloon et al. (1988), and Falloon and Green (1987, 1988) which are ideal for this purpose. Our method is empirical and employs solid-liquid partition coefficients (Di) from the experiments. We empirically determine Di=f(P,F) and use this to calculate melt compositions produced by decompression-induced melting along an adiabat (column melting). Results indicate that most MORBs can be generated by 10-20% partial melting at initial pressures (P0) of 12-21 kbar. Our primary MORB melts have MgO=10-12 wt %. We fractionate these at low pressure to an MgO content of 8.0 wt% in order to interpret natural MORB liquids. This model allows us to calculate Po, Pf, To, Tf, and F for natural MORB melts. We apply the model to interpret MORB compositions and mantle upwelling patterns beneath a fast ridge (East Pacific Rise (EPR) 8°N to 14°N), a slow ridge (mid-Atlantic Ridge (MAR) at 26°S), and seamounts near the EPR (Lamont seamount chain). We find mantle temperature differences of up to 50°-60°C over distances of 30-50 km both across axis and along axis at the EPR. We propose that these are due to upward mantle flow in a weakly conductive (versus adiabatic) temperature gradient. We suggest that the EPR is fed by a wide (~100 km) zone of upwelling due to plate separation but has a central core of faster buoyant flow. An along-axis thermal dome between the Siqueiros transform and the 11°45' Overlapping Spreading Center (OSC) may represent such an upwelling; however, in general there is a poor correlation between mantle temperature, topography, and the segmentation pattern at the EPR. For the Lamont seamounts we find regular across-axis changes in Po and F suggesting that the melt zone pinches out off axis. This observation supports the idea that the EPR is fed by a broad upwelling which diminishes in vigor off axis. In contrast with the EPR axis, mantle temperature correlates well with topography at the MAR, and there is less melting under offsets. The data are consistent with weaker upwelling under offsets and a adiabatic temperature gradient in the subaxial mantle away from offsets. The MAR at 26°S exhibits the so-called local trend of Klein and Langmuir (1989). Our model indicates that the local trend cannot be due solely to intracolumn melting processes. The local trend seems to be genetically associated with slow-spreading ridges, and we suggest it is due to melting of multiple individual domains that differ in initial and final melting pressure within segments fed by buoyant focused mantle flow.

An empirical method for calculating melt compositions produced beneath mid-ocean ridges: Application for axis and off-axis (seamounts) melting

NASA Astrophysics Data System (ADS)

Niu, Yaoling; Batiza, Rodey

1991-12-01

We present a new method for calculating the major element compositions of primary melts parental to mid-ocean ridge basalt (MORB). This model is based on the experimental data of Jaques and Green (1980), Falloon et al. (1988), and Falloon and Green (1987, 1988) which are ideal for this purpose. Our method is empirical and employs solid-liquid partition coefficients (Di) from the experiments. We empirically determine Di = ƒ(P,F) and use this to calculate melt compositions produced by decompression-induced melting along an adiabat (column melting). Results indicate that most MORBs can be generated by 10-20% partial melting at initial pressures (P0) of 12-21 kbar. Our primary MORB melts have MgO = 10-12 wt %. We fractionate these at low pressure to an MgO content of 8.0 wt % in order to interpret natural MORB liquids. This model allows us to calculate Po, Pƒ, To, Tƒ, and F for natural MORB melts. We apply the model to interpret MORB compositions and mantle upwelling patterns beneath a fast ridge (East Pacific Rise (EPR)8°N to 14°N), a slow ridge (mid-Atlantic Ridge (MAR) at 26°S), and seamounts near the EPR (Lament seamount chain). We find mantle temperature differences of up to 50°-60°C over distances of 30-50 km both across axis and along axis at the EPR. We propose that these are due to upward mantle flow in a weakly conductive (versus adiabatic) temperature gradient. We suggest that the EPR is fed by a wide (-100 km) zone of upwelling due to plate separation but has a central core of faster buoyant flow. An along-axis thermal dome between the Siqueiros transform and the 11°45' Overlapping Spreading center (OSC) may represent such an upwelling; however, in general there is a poor correlation between mantle temperature, topography, and the segmentation pattern at the EPR. For the Lament seamounts we find regular across-axis changes in Po and F suggesting that the melt zone pinches out off axis. This observation supports the idea that the EPR is fed by a broad upwelling which diminishes in vigor off axis. In contrast with the EPR axis, mantle temperature correlates well with topography at the MAR, and there is less melting under offsets. The data are consistent with weaker upwelling under offsets and an adiabatic temperature gradient in the sub axial mantle away from offsets. The MAR at 26°S exhibits the so-called local trend of Klein and Langmuir (1989). Our model indicates that the local trend cannot be due solely to intracolumn melting processes. The local trend seems to be genetically associated with slow-spreading ridges, and we suggest it is due to melting of multiple individual domains that differ in initial and final melting pressure within segments fed by buoyant focused mantle flow.

Bacterial Communities of Surface Mixed Layer in the Pacific Sector of the Western Arctic Ocean during Sea-Ice Melting

PubMed Central

Ha, Ho Kyung; Kim, Hyun Cheol; Kim, Ok-Sun; Lee, Bang Yong; Cho, Jang-Cheon; Hur, Hor-Gil; Lee, Yoo Kyung

2014-01-01

From July to August 2010, the IBRV ARAON journeyed to the Pacific sector of the Arctic Ocean to monitor bacterial variation in Arctic summer surface-waters, and temperature, salinity, fluorescence, and nutrient concentrations were determined during the ice-melting season. Among the measured physicochemical parameters, we observed a strong negative correlation between temperature and salinity, and consequently hypothesized that the melting ice decreased water salinity. The bacterial community compositions of 15 samples, includicng seawater, sea-ice, and melting pond water, were determined using a pyrosequencing approach and were categorized into three habitats: (1) surface seawater, (2) ice core, and (3) melting pond. Analysis of these samples indicated the presence of local bacterial communities; a deduction that was further corroborated by the discovery of seawater- and ice-specific bacterial phylotypes. In all samples, the Alphaproteobacteria, Flavobacteria, and Gammaproteobacteria taxa composed the majority of the bacterial communities. Among these, Alphaproteobacteria was the most abundant and present in all samples, and its variation differed among the habitats studied. Linear regression analysis suggested that changes in salinity could affect the relative proportion of Alphaproteobacteria in the surface water. In addition, the species-sorting model was applied to evaluate the population dynamics and environmental heterogeneity in the bacterial communities of surface mixed layer in the Arctic Ocean during sea-ice melting. PMID:24497990

Bacterial communities of surface mixed layer in the Pacific sector of the western Arctic Ocean during sea-ice melting.

PubMed

Han, Dukki; Kang, Ilnam; Ha, Ho Kyung; Kim, Hyun Cheol; Kim, Ok-Sun; Lee, Bang Yong; Cho, Jang-Cheon; Hur, Hor-Gil; Lee, Yoo Kyung

2014-01-01

From July to August 2010, the IBRV ARAON journeyed to the Pacific sector of the Arctic Ocean to monitor bacterial variation in Arctic summer surface-waters, and temperature, salinity, fluorescence, and nutrient concentrations were determined during the ice-melting season. Among the measured physicochemical parameters, we observed a strong negative correlation between temperature and salinity, and consequently hypothesized that the melting ice decreased water salinity. The bacterial community compositions of 15 samples, includicng seawater, sea-ice, and melting pond water, were determined using a pyrosequencing approach and were categorized into three habitats: (1) surface seawater, (2) ice core, and (3) melting pond. Analysis of these samples indicated the presence of local bacterial communities; a deduction that was further corroborated by the discovery of seawater- and ice-specific bacterial phylotypes. In all samples, the Alphaproteobacteria, Flavobacteria, and Gammaproteobacteria taxa composed the majority of the bacterial communities. Among these, Alphaproteobacteria was the most abundant and present in all samples, and its variation differed among the habitats studied. Linear regression analysis suggested that changes in salinity could affect the relative proportion of Alphaproteobacteria in the surface water. In addition, the species-sorting model was applied to evaluate the population dynamics and environmental heterogeneity in the bacterial communities of surface mixed layer in the Arctic Ocean during sea-ice melting.

Ho-doped Soft Glass Optical Fibers for Coherent Wavelength Sources Above 2 Micron

DTIC Science & Technology

2010-12-01

following glasses were prepared in order to fabricate a single-mode Tm-Ho doped optical fibre. Their composition is in mol% and the rare earth oxides ...in this work was 99+%. The onset melting temperature was 750 ˚C and the duration of the process 2 hours. The melt was cast in a brass mould...preheated to 300 ˚C and annealed at Tg – 10 ˚C for 2 h. Glass melting was carried out in a Pt crucible inside a chamber furnace. Core glass was melted

Application of Ti-in-quartz solubility as a thermobarometer in rutile-free rocks

NASA Astrophysics Data System (ADS)

Thomas, J. B.; Watson, E. B.

2011-12-01

Application of Ti-in-quartz solubility as a thermobarometer (TitaniQ; Thomas et al. 2010) may profoundly influence interpretations of crustal rocks. Complex Ti zoning patterns observed in cathodoluminescence (CL) images of crystals can be associated with changes in P-T conditions that prevailed during quartz crystallization. In rocks lacking rutile application of TitaniQ is challenging because Ti activity (aTiO2) during quartz crystallization must be constrained. Many felsic rocks contain minerals in which Ti is an essential stoichiometric constituent (e.g. ilmenite) that will buffer aTiO2 at a fixed value. To use Ti-in-quartz solubility in rocks lacking rutile (or sphene) the P-T dependencies of Ti-in-quartz solubility must be combined with an independent constraint on either P or T to estimate quartz crystallization conditions. Values for aTiO2 in melts can be calculated using (1) melt compositions and the rutile-saturation model of Hayden et al. (2007), (2) melt compositions and the MELTS algorithms to yield rutile affinity (i.e. degree of saturation) and liquidus T (TL; Ghiorso and Sack, 1995; Asimov and Ghiorso, 1998), and (3) mineral reaction equilibria, such as 2FeTiO3=TiO2+Fe2TiO4, measured mineral compositions, tabulated thermodynamic data, and an input temperature constrained by phase equilibria (or MELTS). The rutile-saturation model was calibrated at 10 kbar only, and intended for applications in which alternatives for calculating aTiO2 are unavailable. This should not be used for quantitative interpretations concerning rocks formed at other pressures because it is likely that Ti solubility in a melt is strongly pressure dependent. Consequently, the 10 kbar rutile-saturation model will underestimate the Ti required for rutile saturation at lower pressures, thereby yielding impossible aTiO2 values that exceed unity. We used a range of published rhyolite melt and Fe-Ti oxide compositions as inputs for aTiO2 calculations using MELTS and mineral reaction equilibria. Both approaches yield reasonable aTiO2 values. MELTS also yields TL values well aligned with phase equilibria. Rutile affinities obtained from MELTS can be used to calculate a range of aTiO2=0.2-0.5. Titanium activities calculated from mineral reaction equilibria have a range of aTiO2=0.3-0.5. Using published Ti of rhyolitic quartz and aTiO2 calculated above, TitaniQ yields P and T estimates that are strikingly similar to those expected based on phase equilibria. Many quartz crystals from rhyolites have CL dark cores with ~50 ppm Ti and CL bright rims with ~100-120 ppm Ti (e.g., Bishop, Oruanui, Yellowstone, Katmai, Bandelier). It is plausible that a common process produced quartz crystals with similar zoning patterns. Previous interpretations suggested that mafic input increased magma T and quartz rims with high Ti grew at higher temperatures. However, increasing T would cause dissolution instead of growth, at all possible CO2 contents (i.e., XH2O>0.9). TitaniQ provides a new interpretation in which the dark CL cores of quartz crystals (low Ti) grew at pressures greater than the final emplacement level, followed by entrainment during emplacement to an upper-crustal reservoir where the bright CL rims (high Ti) grew at lower P and T.

A TEM analysis of nanoparticulates in a Polar ice core

DOE Office of Scientific and Technical Information (OSTI.GOV)

Esquivel, E.V.; Murr, L.E

2004-03-15

This paper explores the prospect for analyzing nanoparticulates in age-dated ice cores representing times in antiquity to establish a historical reference for atmospheric particulate regimes. Analytical transmission electron microscope (TEM) techniques were utilized to observe representative ice-melt water drops dried down on carbon/formvar or similar coated grids. A 10,000-year-old Greenland ice core was melted, and representative water drops were transferred to coated grids in a clean room environment. Essentially, all particulates observed were aggregates and either crystalline or complex mixtures of nanocrystals. Especially notable was the observation of carbon nanotubes and related fullerene-like nanocrystal forms. These observations are similar withmore » some aspects of contemporary airborne particulates including carbon nanotubes and complex nanocrystal aggregates.« less

Chicxulub Impact Crater and Yucatan Carbonate Platform - Stratigraphy and Petrography of PEMEX Borehole Cores

NASA Astrophysics Data System (ADS)

Gutierrez-Cirlos, A. G.; Perez-Drago, G.; Perez-Cruz, L.; Urrutia-Fucugauchi, J.

2008-12-01

Chicxulub impact crater is the best preserved of the three large multi-ring structures documented in the terrestrial record. Chicxulub, formed 65 Ma ago, is associated with the Cretaceous/Tertiary (K/T) boundary layer and the impact related to the organism extinctions and events marking the boundary. The crater is buried under Tertiary sediments in the Yucatan carbonate platform in the southern Gulf of Mexico. The structure was initially recognized from gravity and magnetic anomalies in the PEMEX exploration surveys of the northwestern Yucatan peninsula. The exploration program included eight deep boreholes completed from 1952 through the 1970s. The investigations showing Chicxulub as a large complex impact crater formed at the K/T boundary have relayed on the PEMEX decades-long exploration program. However, despite frequent use of PEMEX information and core samples, significant parts of the database and cores remain to be evaluated, analyzed and incorporated with results from recent efforts. Access to PEMEX Core Repository has permitted to study the cores and collect new samples from some of the boreholes. We analyzed cores from Yucatan-6, Chicxulub-1, Sacapuc-1, Ticul-1, Yucatan-1 and Yucatan-4 boreholes to make new detailed stratigraphic correlations and petrographic characterization, using information from PEMEX database and the recent studies. In C-1 cores, breccias show 4-8 cm clasts of fine grained altered melt dispersed in a medium to coarse grained matrix composed of pyroxene and feldspar with little macroscopic alteration. Clasts contain 0.2 to 0.1 cm fragments of silicate material (basement) that show variable degrees of digestion. Melt samples from C-1 N10 comes from interval 1,393-1,394 m, and show a fine-to-medium grained coherent microcrystalline groundmass. Melt and breccias in Y-6 extend from about 1,100 m to more than 1,400 m. Sequence is well sorted, with an apparent gradation in both the lithic and melt clasts. In this presentation we report on initial results from this new joint project for the carbonate sequences and impact lithologies.

Siderophile Volatile Element Partitioning during Core Formation.

NASA Astrophysics Data System (ADS)

Loroch, D. C.; Hackler, S.; Rohrbach, A.; Klemme, S.

2017-12-01

Since the nineteen sixties it is known, that the Earth's mantle is depleted relative to CI chondrite in numerous elements as a result of accretion and core-mantle differentiation. Additionally, if we take the chondritic composition as the initial solar nebular element abundances, the Earth lacks 85 % of K and up to 98 % of other volatiles. However one potentially very important group of elements has received considerably less attention in this context and these elements are the siderophile but volatile elements (SVEs). SVEs perhaps provide important information regarding the timing of volatile delivery to Earth. Especially for the SVEs the partitioning between metal melt and silicate melt (Dmetal/silicate) at core formation conditions is poorly constrained, never the less they are very important for most of the core formation models. This study is producing new metal-silicate partitioning data for a wide range of SVEs (S, Se, Te, Tl, Ag, As, Au, Cd, Bi, Pb, Sn, Cu, Ge, Zn, In and Ga) with a focus on the P, T and fO2dependencies. The initial hypothesis that we are aiming to test uses the accretion of major portions of volatile elements while the core formation was still active. The key points of this study are: - What are the effects of P, T and fO2 on SVE metal-silicate partioning? - What is the effect of compositional complexity on SVE metal-silicate partioning? - How can SVE's D-values fit into current models of core formation? The partitioning experiments will be performed using a Walker type multi anvil apparatus in a pressure range between 10 and 20 GPa and temperatures of 1700 up to 2100 °C. To determine the Dmetal/silicate values we are using a field emission high-resolution JEOL JXA-8530F EPMA for major elements and a Photon Machines Analyte G2 Excimer laser (193 nm) ablation system coupled to a Thermo Fisher Element 2 single-collector ICP-MS (LA-ICP-MS) for the trace elements. We recently finished the first sets of experiments and can provide the corresponding datasets. Based on the general understanding of Dmetal/silicate values we expect to depend on the composition, in this particular case this means a variation in sulfur and carbon content of the core composition, and also a change of the redox conditions. The major goal however is to derive a model of core formation on Earth that includes and also explains the SVEs.

Chondritic Models of 4 Vesta: Comparison of Data from the Dawn Mission with Predicted Internal Structure and Surface Composition/Mineralogy

NASA Technical Reports Server (NTRS)

Toplis, M. J.; Mizzon, H.; Forni, O.; Monnereau, M.; Barrat, J-A.; Prettyman, T. H.; McSween, H. Y.; McCoy, T. J.; Mittlefehldt, D. W.; De Sanctis, M. C.;

Evaluation of solar flares and electron precipitation by nitrate distribution in Antarctica

NASA Astrophysics Data System (ADS)

Dreschhoff, Gisela A.; Zeller, Edward J.

1991-10-01

Most of the time devoted to project research was spent in Antarctica. A firm core was drilled by hand to a depth of 29 meters at Windless Bight on the Ross Ice Shelf. The main result is that all of the major peaks identified as resulting from ionization caused by SPEs that were found in the 1988-89 core could also be identified in the analytical sequence from the 1990-91 core. Following the Antarctic field season, a set of snow samples were obtained that had been collected by the International Trans-Antarctica Expedition. The analysis of these samples showed nitrate flux that correlates closely with known spatial distribution of electron precipitation in the south polar region. A new apparatus has been build for field analysis on a continuous basis of nitrate and conductivity in a melt derived from the vertical melting of ice cores.

Implications for the melting phase relations in the MgO-FeO system at Core-Mantle Boundary conditions

NASA Astrophysics Data System (ADS)

Deng, J.; Lee, K. K. M.

2017-12-01

At nearly 2900 km depth, the core-mantle boundary (CMB) represents the largest density increase within the Earth going from a rocky mantle into an iron-alloy core. This compositional change sets up steep temperature gradients, which in turn influences mantle flow, structure and seismic velocities. Here we compute the melting phase relations of (Mg,Fe)O ferropericlase, the second most abundant mineral in the Earth's mantle, at CMB conditions and find that ultralow-velocity zones (ULVZs) could be explained by solid ferropericlase with 35 < Mg# = 100×(Mg/(Mg+Fe) by mol%) < 65. For compositions outside of this range, a solid ferropericlase cannot explain ULVZs. Additionally, solid ferropericlase can also provide a matrix for iron infiltration at the CMB by morphological instability, providing a mechanism for a high electrical conductivity layer of appropriate length scale inferred from core nutations.

Melt coaxial electrospinning: a versatile method for the encapsulation of solid materials and fabrication of phase change nanofibers.

PubMed

McCann, Jesse T; Marquez, Manuel; Xia, Younan

2006-12-01

We have developed a method based on melt coaxial electrospinning for fabricating phase change nanofibers consisting of long-chain hydrocarbon cores and composite sheaths. This method combines melt electrospinning with a coaxial spinneret and allows for nonpolar solids such as paraffins to be electrospun and encapsulated in one step. Shape-stabilized, phase change nanofibers have many potential applications as they are able to absorb, hold, and release large amounts of thermal energy over a certain temperature range by taking advantage of the large heat of fusion of long-chain hydrocarbons. We have focused on compounds with melting points near room temperature (octadecane) and body temperature (eicosane) as these temperature ranges are most valuable in practice. We have produced thermally stable, phase change materials up to 45 wt % octadecane, as measured by differential scanning calorimetry. In addition, the resultant fibers display novel segmented morphologies for the cores due to the rapid solidification of the hydrocarbons driven by evaporative cooling of the carrier solution. Aside from the fabrication of phase change nanofibers, the melt coaxial method is promising for applications related to microencapsulation and controlled release of drugs.

Quenching behavior of molten pool with different strategies – A review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shrikant,, E-mail: 2014rmt9018@mnit.ac.in; Pandel, U.; Duchaniya, R. K.

After the major severe accident in nuclear reactor, there has been lot of concerns regarding long term core melt stabilization following a severe accident in nuclear reactors. Numerous strategies have been though for quenching and stabilization of core melt like top flooding, bottom flooding, indirect cooling, etc. However, the effectiveness of these schemes is yet to be determined properly, for which, lot of experiments are needed. Several experiments have been performed for coolability of melt pool under bottom flooding as well as for indirect cooling. Besides these tests are very scattered because they involve different simulants material initial temperatures andmore » masses of melt, which makes it very complex to judge the effectiveness of a particular technique and advantage over the other. In this review paper, a study has been carried on different cooling techniques of simulant materials with same mass. Three techniques have been compared here and the results are discussed. Under top flooding technique it took several hours to cool the melt under without decay heat condition. In bottom flooding technique was found to be the best technique among in indirect cooling technique, top flooded technique, and bottom flooded technique.« less

Preliminary Ar-40/Ar-39 age spectrum and laser probe dating of the M1 core of the Manson Impact Structure, Iowa: A K-T boundary crater candidate

NASA Technical Reports Server (NTRS)

Kunk, M. J.; Snee, L. W.; French, B. M.; Harlan, S. S.; Mcgee, J. J.

1993-01-01

Preliminary Ar-40/Ar-39 age spectrum and laser probe dating results from new drill core from the 35-km-diameter Manson Impact Structure (MIS), Iowa indicates a reasonable possibility that the MIS is a Cretaceous-Tertiary (K-T) boundary impact event. Several different types of samples from a melt-matrix breccia, a unit of apparent crater fill intersected by the M1 core, were analyzed. Ar-40/Ar-39 results from these samples indicate a maximum age for the MIS of about 65.4 plus or minus 0.4(2 sigma) Ma. Petrographic analyses of the samples indicate a high probability that all the dated samples from the melt-matrix breccia contain relict grains that were not entirely melted or degassed at the time of impact, suggesting that the actual age of the MIS could be somewhat younger than our preliminary results indicate. The results are consistent with a previously published age estimate of shocked microcline from the MIS central uplift of 65.7 plus or minus 1.0 Ma.

Core Formation Process and Light Elements in the Planetary Core

NASA Astrophysics Data System (ADS)

Ohtani, E.; Sakairi, T.; Watanabe, K.; Kamada, S.; Sakamaki, T.; Hirao, N.

2015-12-01

Si, O, and S are major candidates for light elements in the planetary core. In the early stage of the planetary formation, the core formation started by percolation of the metallic liquid though silicate matrix because Fe-S-O and Fe-S-Si eutectic temperatures are significantly lower than the solidus of the silicates. Therefore, in the early stage of accretion of the planets, the eutectic liquid with S enrichment was formed and separated into the core by percolation. The major light element in the core at this stage will be sulfur. The internal pressure and temperature increased with the growth of the planets, and the metal component depleted in S was molten. The metallic melt contained both Si and O at high pressure in the deep magma ocean in the later stage. Thus, the core contains S, Si, and O in this stage of core formation. Partitioning experiments between solid and liquid metals indicate that S is partitioned into the liquid metal, whereas O is weakly into the liquid. Partitioning of Si changes with the metallic iron phases, i.e., fcc iron-alloy coexisting with the metallic liquid below 30 GPa is depleted in Si. Whereas hcp-Fe alloy above 30 GPa coexisting with the liquid favors Si. This contrast of Si partitioning provides remarkable difference in compositions of the solid inner core and liquid outer core among different terrestrial planets. Our melting experiments of the Fe-S-Si and Fe-O-S systems at high pressure indicate the core-adiabats in small planets, Mercury and Mars, are greater than the slope of the solidus and liquidus curves of these systems. Thus, in these planets, the core crystallized at the top of the liquid core and 'snowing core' formation occurred during crystallization. The solid inner core is depleted in both Si and S whereas the liquid outer core is relatively enriched in Si and S in these planets. On the other hand, the core adiabats in large planets, Earth and Venus, are smaller than the solidus and liquidus curves of the systems. The inner core of these planets crystallized at the center of the core and it has the relatively Si rich inner core and the S enriched outer core. Based on melting and solid-liquid partitioning, the equation of state, and sound velocity of iron-light element alloys, we examined the plausible distribution of light elements in the liquid outer and solid inner cores of the terrestrial planets.

Is formation segregation melts in basaltic lava flows a viable analogue to melt generation in basaltic systems?

NASA Astrophysics Data System (ADS)

Thordarson, Thorvaldur; Sigmarsson, Olgeir; Hartley, Margaret E.; Miller, Jay

2010-05-01

Pahoehoe sheet lobes commonly exhibit a three-fold structural division into upper crust, core and lower crust, where the core corresponds to the liquid portion of an active lobe sealed by crust. Segregations are common in pahoehoe lavas and are confined to the core of individual lobes. Field relations and volume considerations indicate that segregation is initiated by generation of volatile-rich melt at or near the lower crust to core boundary via in-situ crystallization. Once buoyant, the segregated melt rises through the core during last stages of flow emplacement and accumulates at the base of the upper crust. The segregated melt is preserved as vesicular and aphyric, material within well-defined vesicle cylinders and horizontal vesicle sheets that make up 1-4% of the total lobe volume. We have undertaken a detailed sampling and chemical analysis of segregations and their host lava from three pahoehoe flow fields; two in Iceland and one in the Columbia River Basalt Group (CRBG). The Icelandic examples are: the olivine-tholeiite Thjorsa lava (24 cubic km) of the Bardarbunga-Veidivotn volcanic system and mildly alkalic Surtsey lavas (1.2 cubic km) of the Vestmannaeyjar volcanic system. The CRBG example is the tholeiitic ‘high-MgO group' Levering lava (>100? cubic km) of the N2 Grande Ronde Basalt. The thicknesses of the sampled lobes ranges from 2.3 to 14 m and each lobe feature well developed network of segregation structures [1,2,3]. Our whole-rock analyses show that the segregated melt is significantly more evolved than the host lava, with enrichment factors of 1.25 (Thjorsa) to 2.25 (Surtsey) for incompatible trace elements (Ba, Zr). Calculations indicate that the segregation melt was formed by 20 to 50% closed-system fractional crystallization of plagioclase (plus minor pyroxene and/or olivine). A more striking feature is the whole-rock composition of the segregations. In the olivine-tholeiite Thjorsa lava the segregations exhibit quartz tholeiite composition that is identical to the magma compositions produced by the nearby Grimsvotn and Kverkfjoll volcanic systems during the Holocene. The Surtsey segregations have whole-rock composition remarkably similar to the FeTi basalts from adjacent Katla volcanic system, whereas the segregations of the Levering flow are identical to the ‘low-MgO group' basalts of the CRBG. Is this a coincidence or does volatile induced liquid transfer, as inferred for the formation of the segregations, play an important role in magma differentiation in basaltic systems? [1]Thordarson & Self The Roza Member, Columbia River Basalt Group. J Geophys Res - Solid Earth [2] Sigmarsson, et al, 2009. Segregations in Surtsey lavas (Iceland). In Studies in Volcanology: The Legacy of George Walker. Special Publication of IAVCEI No 3. [3] Hartley & Thordarson, 2009, Melt segregations in a Columbia River Basalt lava flow. Lithos

Composition of Apollo 17 core 76001

NASA Technical Reports Server (NTRS)

Korotev, Randy L.; Bishop, Kaylynn M.

1993-01-01

Core 76001 is a single drive tube containing a column of regolith taken at the base of the North Massif, station 6, Apollo 17. The core material is believed to have accumulated through slow downslope mass wasting from the massif. As a consequence, the core soil is mature throughout its length. Results of INAA for samples taken every half centimeter along the length of the core indicate that there is only minor systematic compositional variation with depth. Concentrations of elements primarily associated with mare basalt (Sc, Fe) and noritic impact melt breccia (Sm) decrease slightly with depth, particularly between 20 cm and the bottom of the core at 32 cm depth. This is consistent with petrographic studies that indicate a greater proportion of basalt and melt breccia in the top part of the core. However, Sm/Sc and La/Sm ratios are remarkably constant with depth, indicating no variation in the ratio of mare material to Sm-rich highlands material with depth. Other than these subtle changes, there is no compositional evidence for the two stratigraphic units (0-20 cm and 20-32 cm) defined on the basis of modal petrography, although all samples with anomalously high Ni concentrations (Fe-Ni metal nuggets) occur above 20 cm depth.

Enhanced ice sheet melting driven by volcanic eruptions during the last deglaciation.

PubMed

Muschitiello, Francesco; Pausata, Francesco S R; Lea, James M; Mair, Douglas W F; Wohlfarth, Barbara

2017-10-24

Volcanic eruptions can impact the mass balance of ice sheets through changes in climate and the radiative properties of the ice. Yet, empirical evidence highlighting the sensitivity of ancient ice sheets to volcanism is scarce. Here we present an exceptionally well-dated annual glacial varve chronology recording the melting history of the Fennoscandian Ice Sheet at the end of the last deglaciation (∼13,200-12,000 years ago). Our data indicate that abrupt ice melting events coincide with volcanogenic aerosol emissions recorded in Greenland ice cores. We suggest that enhanced ice sheet runoff is primarily associated with albedo effects due to deposition of ash sourced from high-latitude volcanic eruptions. Climate and snowpack mass-balance simulations show evidence for enhanced ice sheet runoff under volcanically forced conditions despite atmospheric cooling. The sensitivity of past ice sheets to volcanic ashfall highlights the need for an accurate coupling between atmosphere and ice sheet components in climate models.

Contrasting accessory mineral behavior in minimum-temperature melts: Empirical constraints from the Himalayan metamorphic core

NASA Astrophysics Data System (ADS)

Cottle, John M.; Larson, Kyle P.; Yakymchuk, Chris

2018-07-01

Medium-grained leucogranite in the Tama Kosi region of the Nepalese Himalayan Metamorphic Core yields a relatively narrow range of monazite 208Pb/232Th dates with a dominant population at 21.0 Ma inferred to represent crystallization of an early plutonic phase. In contrast, the pegmatitic portion of the same intrusive complex, that cross-cuts the medium-grained leucogranite, contains zircon, monazite and xenotime that each display near-identical age spectra, recording semi-continuous (re-)crystallization from 27.5 Ma to 21.0 Ma, followed by a 2 m.y. hiatus then further (re-)crystallization between 19.4 and 18.6 Ma. The "gap" in pegmatite dates corresponds well to the crystallization age of the older leucogranite, whereas the end of accessory phase growth in the pegmatite coincides with the onset of regional-scale cooling. Detailed textural, trace element and thermochronologic data indicate that the range of zircon, monazite and xenotime dates recorded in the pegmatite reflect inherited components that underwent semi-continuous (re-)crystallization during metamorphism and/or anatexis in the source region(s), whereas dates younger than the hiatus indicate accessory phase recrystallization, related to both fluid influx and a concomitant increase in temperature. In contrast, the lack of an inherited component(s) in the medium-grained leucogranite phase is inferred to be a result of complete dissolution during partial melting. A model is proposed in which influx of heat and H2O-rich fluids associated with early leucogranite emplacement temporarily delayed zircon and monazite and xenotime crystallization, respectively. These data highlight the importance of measuring spatially resolved dates, trace elements and textural patterns from multiple accessory minerals combined with model constraints to better understand the often-complex crystallization history of anatectic melts in collisional orogens.

The chemical composition of the cores of the terrestrial planets and the moon

NASA Technical Reports Server (NTRS)

Kuskov, O. L.; Khitarov, N. I.

1977-01-01

Using models of the quasi-chemical theory of solutions, the activity coefficients of silicon are calculated in the melts Fe-Si, Ni-Si, and Fe-Ni-Si. The calculated free energies of solution of liquid nickel and silicon in liquid iron in the interval 0 to 1400 kbar and 1500 to 4000 K, shows that Fe-Ni-Si alloy is stable under the conditions of the outer core of the earth and the cores of the terrestrial planets. The oxidation-reduction conditions are studied, and the fugacity of oxygen in the mantles of the planets and at the core-mantle boundary are calculated. The mechanism of reduction of silicon is analyzed over a broad interval of p and T. The interaction between the matter of the core and mantle is studied, resulting in the extraction of silicon from the mantle and its solution in the material of the core. It is concluded that silicon can enter into the composition of the outer core of the earth and Venus, but probably does not enter into the composition of the cores of Mercury, Mars, and the moon, if in fact the latter possesses one.

Crystallization of a compositionally stratified basal magma ocean

NASA Astrophysics Data System (ADS)

Laneuville, Matthieu; Hernlund, John; Labrosse, Stéphane; Guttenberg, Nicholas

2018-03-01

Earth's ∼3.45 billion year old magnetic field is regenerated by dynamo action in its convecting liquid metal outer core. However, convection induces an isentropic thermal gradient which, coupled with a high core thermal conductivity, results in rapid conducted heat loss. In the absence of implausibly high radioactivity or alternate sources of motion to drive the geodynamo, the Earth's early core had to be significantly hotter than the melting point of the lower mantle. While the existence of a dense convecting basal magma ocean (BMO) has been proposed to account for high early core temperatures, the requisite physical and chemical properties for a BMO remain controversial. Here we relax the assumption of a well-mixed convecting BMO and instead consider a BMO that is initially gravitationally stratified owing to processes such as mixing between metals and silicates at high temperatures in the core-mantle boundary region during Earth's accretion. Using coupled models of crystallization and heat transfer through a stratified BMO, we show that very high temperatures could have been trapped inside the early core, sequestering enough heat energy to run an ancient geodynamo on cooling power alone.

Melting phase relations in the Fe-S and Fe-S-O systems at core conditions in small terrestrial bodies

NASA Astrophysics Data System (ADS)

Pommier, Anne; Laurenz, Vera; Davies, Christopher J.; Frost, Daniel J.

2018-05-01

We report an experimental investigation of phase equilibria in the Fe-S and Fe-S-O systems. Experiments were performed at high temperatures (1400-1850 °C) and high pressures (14 and 20 GPa) using a multi-anvil apparatus. The results of this study are used to understand the effect of sulfur and oxygen on core dynamics in small terrestrial bodies. We observe that the formation of solid FeO grains occurs at the Fe-S liquid - Fe solid interface at high temperature ( > 1400 °C at 20 GPa). Oxygen fugacities calculated for each O-bearing sample show that redox conditions vary from ΔIW = -0.65 to 0. Considering the relative density of each phase and existing evolutionary models of terrestrial cores, we apply our experimental results to the cores of Mars and Ganymede. We suggest that the presence of FeO in small terrestrial bodies tends to contribute to outer-core compositional stratification. Depending on the redox and thermal history of the planet, FeO may also help form a transitional redox zone at the core-mantle boundary.

OECD MCCI project 2-D Core Concrete Interaction (CCI) tests : CCI-3 test data report-thermalhydraulic results. Rev. 0 October 15, 2005.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farmer, M. T.; Lomperski, S.; Kilsdonk, D. J.

The Melt Attack and Coolability Experiments (MACE) program addressed the issue of the ability of water to cool and thermally stabilize a molten core-concrete interaction when the reactants are flooded from above. These tests provided data regarding the nature of corium interactions with concrete, the heat transfer rates from the melt to the overlying water pool, and the role of noncondensable gases in the mixing processes that contribute to melt quenching. As a follow-on program to MACE, The Melt Coolability and Concrete Interaction Experiments (MCCI) project is conducting reactor material experiments and associated analysis to achieve the following objectives: (1)more » resolve the ex-vessel debris coolability issue through a program that focuses on providing both confirmatory evidence and test data for the coolability mechanisms identified in MACE integral effects tests, and (2) address remaining uncertainties related to long-term two-dimensional molten core-concrete interactions under both wet and dry cavity conditions. Achievement of these two program objectives will demonstrate the efficacy of severe accident management guidelines for existing plants, and provide the technical basis for better containment designs for future plants. In terms of satisfying these objectives, the Management Board (MB) approved the conduct of a third long-term 2-D Core-Concrete Interaction (CCI) experiment designed to provide information in several areas, including: (i) lateral vs. axial power split during dry core-concrete interaction, (ii) integral debris coolability data following late phase flooding, and (iii) data regarding the nature and extent of the cooling transient following breach of the crust formed at the melt-water interface. This data report provides thermal hydraulic test results from the CCI-3 experiment, which was conducted on September 22, 2005. Test specifications for CCI-3 are provided in Table 1-1. This experiment investigated the interaction of a fully oxidized 375 kg PWR core melt, initially containing 15 wt% siliceous concrete, with a specially designed two-dimensional siliceous concrete test section with an initial cross-sectional area of 50 cm x 50 cm. The sand and aggregate constituents for this particular siliceous concrete were provided by CEA as an in-kind contribution to the program. The report begins by providing a summary description of the CCI-3 test apparatus and operating procedures, followed by presentation of the thermal-hydraulic results. Detailed posttest debris examination results will be provided in a subsequent publication. Observations drawn within this report regarding the overall cavity erosion behavior may be subject to revision once the posttest examinations are completed, since these examinations will fully reveal the final cavity shape.« less

Slab and Sediment Melting during Subduction Initiation: Mantle Plagiogranites from the Oman Ophiolite

NASA Astrophysics Data System (ADS)

Rollinson, H. R.

2014-12-01

Granitoid dykes up to several hundred metres wide and 2 km long are found in depleted harzburgites in the mantle section of the Oman ophiolite. They vary in composition from tonalite to potassic granite and are generally more potassic than the crustal plagiogranites found within the sheeted dyke complex higher up within the ophiolite stratigraphy. Some granites are strongly peraluminous and contain garnet and andalusite. They are geochemically variable, some with REE that are relatively unfractionated ((La/Yb)n= 3.5-6.0, flat middle to heavy REE, steep light REE) to those which are highly fractionated ((La/Yb)n= 28-220). On primitive-mantle normalised plots some have very high concentrations of fluid-mobile elements - Cs, Rb, Th, U and Pb. Few have significant Ta-Nb anomalies. On the Ca-Fe-Mg-Ti discrimination diagram of Patino Douce (J. Petrol., 1999) whole-rock compositions define a spectrum between felsic-pelite derived melts and amphibolite-derived melts. There is a chemical similarity between the least REE fractionated plagiogranites (generally tonalites and granodiorites) and melts of an amphibolitic parent. This is supported by the occurrence of mafic xenoliths in some dykes, the presence of hornblende and highly calcic cores (up to An85) in some plagioclase grains. Trace element modelling using Oman Geotimes lavas as the starting composition indicates that melting took place in the garnet stability field, although enrichment in the melt in Cs, Rb, Ba and Pb suggests that there was another component present in addition to the mafic parent. Other plagiogranites (trondhjemites and granites) have a strongly peraluminous chemistry and mineralogy and geochemical similarities with the Himalayan leucogranites implying that they were derived from a sedimentary protolith. These mantle plagiogranites are more prevalent in the northern outcrops of the ophiolite. The volume of granitoid melt and the depth of melting preclude their derivation from the sole of the ophiolite, rather they were derived during subduction by the partial melting of the slab and associated sediment and emplaced into the overlying mantle wedge. Current subduction-initiation models for supra-subduction ophiolites should integrate this process into their thinking.

Zircon from charnockite gneiss, charnockite, and leucosome of migmatite in the Nimnyr Block of the Aldan Shield

NASA Astrophysics Data System (ADS)

Glebovitsky, V. A.; Sedova, I. S.; Berezhnaya, N. G.; Skublov, S. G.; Samorukova, L. M.

2015-12-01

The microgeochemistry of zircon was studied in three samples: charnockite gneiss (1594), charnockite (1594a), and migmatite leucosome Lc4 (1594c). Prismatic (Zrn I) and oval (Zrn II) zircon morphotypes are distinguished in the first two samples. Most zircon grains consist of two-phase cores and overgrowth rims variable in thickness. The average weighted concordant U-Pb age of Zrn II cores from charnockite gneiss is 2436 ± 10 Ma. The concordant ages of Zrn I and Zrn II cores from charnockite are 2402 ± 16 Ma and 2453 ± 14 Ma, respectively. Some overgrowth rims are 1.9-2.1 Ga in age. In leucosome Lc4, all measured prismatic zircon crystals yielded a discordant age of 1942 ± 11 Ma (the upper intersection of discordia with concordia). These zircons are strongly altered and anomalously enriched in U and Th. Zrn I grains are enriched relative to Zrn II in REE, Li, Ca, Sr, Ba, Hf, Th, and U. Zrn I is considered to be a product of melt crystallization or subsolidus recrystallization in the presence of melt. Zrn II is relict or crystallizing from melt and then partly fused again. Zrn I from charnockite gneiss and especially from charnockite are markedly altered and have a more discordant age than Zrn II. This is probably related to concentration of fluid in the residual melt left after zircon crystallization.

Confirmation of a meteoritic component in impact-melt rocks of the Chesapeake Bay impact structure, Virginia, USA - Evidence from osmium isotopic and PGE systematics

USGS Publications Warehouse

Lee, S.R.; Horton, J. Wright; Walker, R.J.

2006-01-01

The osmium isotope ratios and platinum-group element (PGE) concentrations of impact-melt rocks in the Chesapeake Bay impact structure were determined. The impact-melt rocks come from the cored part of a lower-crater section of suevitic crystalline-clast breccia in an 823 m scientific test hole over the central uplift at Cape Charles, Virginia. The 187Os/188Os ratios of impact-melt rocks range from 0.151 to 0.518. The rhenium and platinum-group element (PGE) concentrations of these rocks are 30-270?? higher than concentrations in basement gneiss, and together with the osmium isotopes indicate a substantial meteoritic component in some impact-melt rocks. Because the PGE abundances in the impact-melt rocks are dominated by the target materials, interelemental ratios of the impact-melt rocks are highly variable and nonchondritic. The chemical nature of the projectile for the Chesapeake Bay impact structure cannot be constrained at this time. Model mixing calculations between chondritic and crustal components suggest that most impact-melt rocks include a bulk meteoritic component of 0.01-0.1% by mass. Several impact-melt rocks with lowest initial 187Os/188Os ratios and the highest osmium concentrations could have been produced by additions of 0.1%-0.2% of a meteoritic component. In these samples, as much as 70% of the total Os may be of meteoritic origin. At the calculated proportions of a meteoritic component (0.01-0.1% by mass), no mixtures of the investigated target rocks and sediments can reproduce the observed PGE abundances of the impact-melt rocks, suggesting that other PGE enrichment processes operated along with the meteoritic contamination. Possible explanations are 1) participation of unsampled target materials with high PGE abundances in the impact-melt rocks, and 2) variable fractionations of PGE during syn- to post-impact events. ?? The Meteoritical Society, 2006.

Mass Balance of Multiyear Sea Ice in the Southern Beaufort Sea

DTIC Science & Technology

2015-09-30

1) Determination of the net growth and melt of multiyear (MY) sea ice during its transit through the southern Beaufort Sea 2) Identification of...which we refer to as the FGIV dataset. Analysis of melt processes from ice core and IMB data (Eicken) Through stratigraphic analysis of sea ice...samples that are brought back to shore were melted and used to determine profiles of salinity and stable isotope ratios. These data allow us to identify

The Origin of the Compositional Diversity of Mercury's Surface Constrained From Experimental Melting of Enstatite Chondrites

NASA Technical Reports Server (NTRS)

Boujibar, A.; Righter, K.; Pando, K.; Danielson, L.

2015-01-01

Mercury is known as an endmember planet as it is the most reduced terrestrial planet with the highest core/mantle ratio. MESSENGER spacecraft has shown that its surface is FeO-poor (2-4 wt%) and Srich (up to 6-7 wt%), which confirms the reducing nature of its silicate mantle. Moreover, high resolution images revealed large volcanic plains and abundant pyroclastic deposits, suggesting important melting stages of the Mercurian mantle. This interpretation was confirmed by the high crustal thickness (up to 100 km) derived from Mercury's gravity field. This is also corroborated by a recent experimental result that showed that Mercurian partial melts are expected to be highly buoyant within the Mercurian mantle and could have risen from depths as high as the core-mantle boundary. In addition MESSENGER spacecraft provided relatively precise data on major elemental compositions of Mercury's surface. These results revealed important chemical and mineralogical heterogeneities that suggested several stages of differentiation and re-melting processes. However, the extent and nature of compositional variations produced by partial melting remains poorly constrained for the particular compositions of Mercury (very reducing conditions, low FeO-contents and high sulfur-contents). Therefore, in this study, we investigated the processes that lead to the various compositions of Mercury's surface. Melting experiments with bulk Mercury-analogue compositions were performed and compared to the compositions measured by MESSENGER.

An Equation Governing Ultralow-Velocity Zones: Implications for Holes in the ULVZ, Lateral Chemical Reactions at the Core-Mantle Boundary, and Damping of Heat Flux Variations in the Core

NASA Astrophysics Data System (ADS)

Hernlund, J. W.; Matsui, H.

2017-12-01

Ultralow-velocity zones (ULVZ) are increasingly illuminated by seismology, revealing surprising diversity in size, shape, and physical characteristics. The only viable hypotheses are that ULVZs are a compositionally distinct FeO-enriched dense material, which could have formed by fractional crystallization of a basal magma ocean, segregation of subducted banded iron formations, precipitation of solids from the outer core, partial melting and segregation of iron-rich melts from subducted basalts, or most likely a combination of many different processes. But many questions remain: Are ULVZ partially molten in some places, and not in others? Are ULVZ simply the thicker portions of an otherwise global thin layer, covering the entire CMB and thus blocking or moderating chemical interactions between the core and overlying mantle? Is such a layer inter-connected and able to conduct electrical currents that allow electro-magnetic coupling of core and mantle angular momentum? Are they being eroded and shrinking in size due to viscous entrainment, or is more material being added to ULVZ over time? Here we derive an advection-diffusion-like equation that governs the dynamical evolution of a chemically distinct ULVZ. Analysis of this equation shows that ULVZ should become readily swept aside by viscous mantle flows at the CMB, exposing "ordinary mantle" to the top of the core, thus inducing chemical heterogeneity that drives lateral CMB chemical reactions. These reactions are correlated with heat flux, thus maintaining large-scale pressure variations atop the core that induce cyclone-like flows centered around ULVZ and ponded subducted slabs. We suggest that turbulent diffusion across adjacent cyclone streams inside a stratified region atop the core readily accommodates lateral transport and re-distribution of components such as O and Si, in addition to heat. Our model implies that the deeper core is at least partly shielded from the influence of strong heat flux variations at the CMB which might otherwise cause problems for producing a geodynamo.

A carbon-rich region in Miller Range 091004 and implications for ureilite petrogenesis

NASA Astrophysics Data System (ADS)

Day, James M. D.; Corder, Christopher A.; Cartigny, Pierre; Steele, Andrew M.; Assayag, Nelly; Rumble, Douglas; Taylor, Lawrence A.

2017-02-01

Ureilite meteorites are partially melted asteroidal-peridotite residues, or more rarely, cumulates that can contain greater than three weight percent carbon. Here we describe an exceptional C-rich lithology, composed of 34 modal % large (up to 0.8 mm long) crystalline graphite grains, in the Antarctic ureilite meteorite Miller Range (MIL) 091004. This C-rich lithology is embedded within a silicate region composed dominantly of granular olivine with lesser quantities of low-Ca pyroxene, and minor FeNi metal, high-Ca pyroxene, spinel, schreibersite and troilite. Petrological evidence indicates that the graphite was added after formation of the silicate region and melt depletion. Associated with graphite is localized reduction of host olivine (Fo88-89) to nearly pure forsterite (Fo99), which is associated with FeNi metal grains containing up to 11 wt.% Si. The main silicate region is typical of ureilite composition, with highly siderophile element (HSE) abundances ∼0.3 × chondrite, 187Os/188Os of 0.1260-0.1262 and Δ17O of -0.81 ± 0.16‰. Mineral trace-element analyses reveal that the rare earth elements (REE) and the HSE are controlled by pyroxene and FeNi metal phases in the meteorite, respectively. Modeling of bulk-rock REE and HSE abundances indicates that the main silicate region experienced ∼6% silicate and >50% sulfide melt extraction, which is at the lower end of partial melt removal estimated for ureilites. Miller Range 091004 demonstrates heterogeneous distribution of carbon at centimeter scales and a limited range in Mg/(Mg + Fe) compositions of silicate grain cores, despite significant quantities of carbon. These observations demonstrate that silicate rim reduction was a rapid disequilibrium process, and came after silicate and sulfide melt removal in MIL 091004. The petrography and mineral chemistry of MIL 091004 is permissive of the graphite representing late-stage C-rich melt that pervaded silicates, or carbon that acted as a lubricant during anatexis and impact disruption in the parent body. Positive correlation of Pt/Os ratios with olivine core compositions, but a wide range of oxygen isotope compositions, indicates that ureilites formed from a compositionally heterogeneous parent body that experienced variable sulfide and metal melt-loss that is most pronounced in relatively oxidized ureilites with Δ17O between -1.5 and ∼0‰.

Muscovite-Dehydration Melting: A Textural Study of a Key Reaction in Transforming Continental Margin Strata Into a Migmatitic Orogenic Core

NASA Astrophysics Data System (ADS)

Dyck, B. J.; St Onge, M. R.; Waters, D. J.; Searle, M. P.

2015-12-01

Metamorphosed continental margin sedimentary sequences, which comprise the dominant tectonostratigraphic assemblage exposed in orogenic hinterlands, are crucial to understanding the architecture and evolution of collisional mountain belts. This study explores the textural effect of anatexis in amphibolite-grade conditions and documents the mineral growth mechanisms that control nucleation and growth of K-feldspar, sillimanite and silicate melt. The constrained textural evolution follows four stages: 1) Nucleation - K-feldspar is documented to nucleate epitaxially on isomorphic plagioclase in quartzofeldspathic (psammitic) domains, whereas sillimanite nucleates in the Al-rich (pelitic) domain, initially on [001] mica planes. The first melt forms at the site of muscovite breakdown. 2) Chemically driven growth - In the quartzofeldspathic domain, K-feldspar progressively replaces plagioclase by a K+ - Na+ cation transfer reaction, driven by the freeing of muscovite-bound K+ during breakdown of the mica. Sillimanite forms intergrowths with the remaining hydrous melt components, contained initially in ovoid clots. 3) Merge and coarsening - With an increase in pressure, melt and sillimanite migrate away from clots along grain boundaries. A melt threshold is reached once the grain-boundary network is wetted by melt, increasing the length-scale of diffusion, resulting in grain boundary migration and grain-size coarsening. The melt threshold denotes the transition to an open-system on the lithology scale, where melt is a transient phase. 4) Residual melt crystallization - Residual melt crystallizes preferentially on existing peritectic grains as anatectic quartz, plagioclase, and K-feldspar. As the system cools and closes, grain growth forces melt into the intersections of grain-boundaries, recognized as irregular shaped melt films, or as intergrowths of the volatile-rich phases (i.e. Tur-Ms-Ap). In the Himalayan metamorphic core these processes result in the formation of: pelitic K-feldspar augen gneiss, stockwork leucogranites, and an effective strengthening of the hinterland, as evidenced by a switch in tectonic deformation style, from thin-skinned cover sequence thrust imbrication and folding to out-of-sequence basement-involved thick-skinned thrusting and folding.

Present-day Circum-Antarctic Simulations using the POPSICLES Coupled Ice Sheet-Ocean Model

NASA Astrophysics Data System (ADS)

Asay-Davis, X.; Martin, D. F.; Price, S. F.; Maltrud, M. E.; Collins, W.

2014-12-01

We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010. Simulations are performed at 0.1o (~5 km) ocean resolution and with adaptive ice-sheet model resolution as fine as 500 m. We compare time-averaged melt rates below a number of major ice shelves with those reported by Rignot et al. (2013) as well as other recent studies. We also present seasonal variability and decadal trends in submarine melting from several Antarctic regions. Finally, we explore the influence on basal melting and system dynamics resulting from two different choices of climate forcing: a "normal-year" climatology and the CORE v. 2 forcing data (Large and Yeager 2008).POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh (2009) to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3D; Pattyn et al., 2013) and realistic configurations (Favier et al. 2014).A companion presentation, "Response of the Antarctic Ice Sheet to ocean forcing using the POPSICLES coupled ice sheet-ocean model" in session C024 covers the ice-sheet response to these melt rates in the coupled simulation. The figure shows eddy activity in the vertically integrated (barotropic) velocity nearly six years into a POPSICLES simulation of the Antarctic region.

OECD MMCI 2-D Core Concrete Interaction (CCI) tests : CCCI-1 test data report-thermalhydraulic results. Rev 0 January 31, 2004.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farmer, M. T.; Lomperski, S.; Aeschlimann, R. W.

The Melt Attack and Coolability Experiments (MACE) program addressed the issue of the ability of water to cool and thermally stabilize a molten core-concrete interaction when the reactants are flooded from above. These tests provided data regarding the nature of corium interactions with concrete, the heat transfer rates from the melt to the overlying water pool, and the role of noncondensable gases in the mixing processes that contribute to melt quenching. As a follow-on program to MACE, The Melt Coolability and Concrete Interaction Experiments (MCCI) project is conducting reactor material experiments and associated analysis to achieve the following objectives: (1)more » resolve the ex-vessel debris coolability issue through a program that focuses on providing both confirmatory evidence and test data for the coolability mechanisms identified in MACE integral effects tests, and (2) address remaining uncertainties related to long-term two-dimensional molten coreconcrete interactions under both wet and dry cavity conditions. Achievement of these two program objectives will demonstrate the efficacy of severe accident management guidelines for existing plants, and provide the technical basis for better containment designs for future plants. In terms of satisfying these objectives, the Management Board (MB) approved the conduct of two long-term 2-D Core-Concrete Interaction (CCI) experiments designed to provide information in several areas, including: (i) lateral vs. axial power split during dry core-concrete interaction, (ii) integral debris coolability data following late phase flooding, and (iii) data regarding the nature and extent of the cooling transient following breach of the crust formed at the melt-water interface. This data report provides thermal hydraulic test results from the CCI-1 experiment, which was conducted on December 19, 2003. Test specifications for CCI-1 are provided in Table 1-1. This experiment investigated the interaction of a fully oxidized 400 kg PWR core melt, initially containing 8 wt % calcined siliceous concrete, with a specially designed two-dimensional siliceous concrete test section with an initial cross-sectional area of 50 cm x 50 cm. The report begins by providing a summary description of the CCI-1 test apparatus and operating procedures, followed by presentation of the thermal-hydraulic results. The posttest debris examination results will be provided in a subsequent publication. Observations drawn within this report regarding the overall cavity erosion behavior may be subject to revision once the posttest examinations are completed, since these examinations will fully reveal the final cavity shape.« less

Global risk of radioactive fallout after nuclear reactor accidents

NASA Astrophysics Data System (ADS)

Lelieveld, J.; Kunkel, D.; Lawrence, M. G.

2011-11-01

Reactor core meltdowns of nuclear power plants are rare, yet the consequences are catastrophic. But what is meant by "rare"? And what can be learned from the Chernobyl and Fukushima incidents? Here we assess the risk of exposure to radioactivity due to atmospheric dispersion of gases and particles following severe nuclear accidents, using particulate 137Cs and gaseous 131I as proxies for the fallout. It appears that previously the occurrence of major accidents and the risks of radioactive contamination have been underestimated. Using a global model of the atmosphere we compute that on average, in the event of a core melt of any nuclear power plant worldwide, more than 90% of emitted 137Cs would be transported beyond 50km and about 50% beyond 1000 km distance. This corroborates that such accidents have large-scale and trans-boundary impacts. Although the emission strengths and atmospheric removal processes of 137Cs and 131I are quite different, the radioactive contamination patterns over land and the human deposition exposure are computed to be similar. High human exposure risks occur around reactors in densely populated regions, notably in southern Asia where a core melt can subject 55 million people to radioactive contamination. The recent decision by Germany to phase out its nuclear reactors will reduce the national risk, though a large risk will still remain from the reactors in neighbouring countries.

Global risk of radioactive fallout after nuclear reactor accidents

NASA Astrophysics Data System (ADS)

Kunkel, D.; Lelieveld, J.; Lawrence, M. G.

2012-04-01

Reactor core meltdowns of nuclear power plants are rare, yet the consequences are catastrophic. But what is meant by "rare"? And what can be learned from the Chernobyl and Fukushima incidents? Here we assess the risk of exposure to radioactivity due to atmospheric dispersion of gases and particles following severe nuclear accidents, using particulate 137Cs and gaseous 131I as proxies for the fallout. It appears that previously the occurrence of major accidents and the risks of radioactive contamination have been underestimated. Using a global model of the atmosphere we compute that on average, in the event of a core melt of any nuclear power plant worldwide, more than 90 % of emitted 137Cs would be transported beyond 50 km and about 50 % beyond 1000 km distance. This corroborates that such accidents have large-scale and trans-boundary impacts. Although the emission strengths and atmospheric removal processes of 137Cs and 131I are quite different, the radioactive contamination patterns over land and the human deposition exposure are computed to be similar. High human exposure risks occur around reactors in densely populated regions, notably in southern Asia where a core melt can subject 55 million people to radioactive contamination. The recent decision by Germany to phase out its nuclear reactors will reduce the national risk, though a large risk will still remain from the reactors in neighbouring countries.

Continuous analysis of phosphate in a Greenland shallow ice core

NASA Astrophysics Data System (ADS)

Kjær, Helle Astrid; Svensson, Anders; Bigler, Matthias; Vallelonga, Paul; Kettner, Ernesto; Dahl-Jensen, Dorthe

2010-05-01

Phosphate is an important and sometimes limiting nutrient for primary production in the oceans. Because of deforestation and the use of phosphate as a fertilizer changes in the phosphate cycle have occurred over the last centuries. On longer time scales, sea level changes are thought to have also caused changes in the phosphate cycle. Analyzing phosphate concentrations in ice cores may help to gain important knowledge about those processes. In the present study, we attach a phosphate detection line to an existing continuous flow analysis (CFA) setup for ice core analysis at the University of Copenhagen. The CFA system is optimized for high-resolution measurements of insoluble dust particles, electrolytic melt water conductivity, and the concentrations of ammonium and sodium. For the phosphate analysis we apply a continuous and highly sensitive absorption method that has been successfully applied to determine phosphate concentrations of sea water (Zhang and Chi, 2002). A line of melt water from the CFA melt head (1.01 ml per minute) is combined with a molybdate blue reagent and an ascorbic acid buffer. An uncompleted reaction takes place in five meters of heated mixing coils before the absorption measurement at a wavelength of 710 nanometer takes place in a 2 m long liquid waveguide cell (LWCC) with an inner volume of 0.5 ml. The method has a detection limit of around 0.1 ppb and we are currently investigating a possible interference from molybdate reacting with silicates that are present in low amounts in the ice. Preliminary analysis of early Holocene samples from the NGRIP ice core show phosphate concentration values of a few ppb. In this study, we will attempt to determine past levels of phosphate in a shallow Northern Greenland firn core with an annual layer thickness of about 20 cm ice equivalent. With a melt speed of 2.5 cm ice per minute our method should allow the resolution of any seasonal variability in phosphate concentrations.

Tomographic location of potential melt-bearing phenocrysts in lunar glass spherules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ebel, D.S.; Fogel, R.A.; Rivers, M.L.

2005-02-04

Apollo 17 orange glass spherules contain olivine phenocrysts with melt inclusions from depth. Tomography (<2micron/pxl) of >200 spherules located 1 phenocryst. We will try to find melt inclusions and obtain original magma volatiles and compositions. In 1971, Apollo 17 astronauts collected a 10 cm soil sample (74220) comprised almost entirely of orange glass spherules. Below this, a double drive-tube core sampled a 68 cm thick horizon comprised of orange glass and black beads (crystallized equivalents of orange glass). Primitive lunar glass spherules (e.g.-A17 orange glasses) are thought to represent ejecta from lunar mare fire fountains. The fire-fountains were apparently drivenmore » by a combination of C-O gas exsolution from orange glass melt and the oxidation of graphite. Upon eruption, magmas lost their volatiles (e.g., S, CO, CO{sub 2}) to space. Evidence for volatile escape remains as volatile-rich coatings on the exteriors of many spherules. Moreover, it showed that Type I and II Fe-Ni-rich metal particles found within orange glass olivine phenocrysts, or free-floating in the glass itself, are powerful evidence for the volatile driving force for lunar fire fountains. More direct evidence for the volatile mechanism has yet to be uncovered. Issues remaining include: the exact composition of magmatic volatiles; the hypothesized existence of graphite in the magma; the oxygen fugacity of the magma and of the lunar interior. In 1996 reported a single {approx}450 micron, equant olivine phenocryst, containing four glassy melt inclusions (or inclusion cores), the largest {approx}30micron in size, in a thin section of the 74001/2 drill core. The melt is assumed to sample the parent magma of the lunar basalts at depth, evidenced by the S content of the inclusion (600 ppm) which is 400 ppm greater than that of the orange glass host. Such melts potentially contain a full complement of the volatile components of the parent magma, which can be analyzed by infrared spectroscopy. Although the A17 orange glass magma is thought to derive from {approx} 400 km depth, the calculations imply a 4 km depth of graphite oxidation (and melt saturation in C-O volatiles) during ascent. We have imaged several hundred similar orange glass spherules, from sample 74220,764, using synchrotron x-ray computer-aided microtomography (XRCMT). Our goals: (1) locate similar phenocrysts containing melt inclusions; (2) analyze phenocrysts to understand the evolution of the magma; (3) analyze melt and fluid inclusions using EPMA and FTIR to obtain direct evidence of magmatic volatiles and pristine bulk compositions.« less

Coeval Ar-40/Ar-39 ages of 65.0 million years ago from Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites

NASA Technical Reports Server (NTRS)

Swisher, Carl C., III; Grajales-Nishimura, Jose M.; Montanari, Alessandro; Margolis, Stanley V.; Claeys, Philippe; Alvarez, Walter; Renne, Paul; Cedillo-Pardo, Esteban; Maurrasse, Florentin J.-M. R.; Curtis, Garniss H.

1992-01-01

Ar-40/Ar-39 dating of drill-core samples of a glassy melt rock recovered from beneath a massive impact breccia contained with the 180-kilometer subsurface Chicxulub crater yields well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from Ar-40/Ar-39 ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The Ar-40/Ar-39 ages, in conjunction with geochemical and petrological similarities, strengthen the suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

Carbon Solubility in Metallic Iron and Melting Relations in the Fe-C System at High Pressure and Temperature

NASA Astrophysics Data System (ADS)

Wang, Y.; Fei, Y.

2006-05-01

Carbon has been proposed to be one of the light elements in the Earth's core. Knowledge of phase relations in the Fe-C system at high pressure and temperature is needed to understand the carbon content in the core and its effect on the physical properties and the temperature of the core. Experimental data in this system at high pressure and temperature are limited. In this study we report new experimental data on melting relations up to 25 GPa. The experiments were performed using piston-cylinder and multi-anvil devices at the Geophysical Laboratory. Mixtures of fine power of pure iron and graphite with different carbon content were prepared as starting materials. The starting materials were loaded into MgO capsules and then compressed to the desired pressures, using various high-pressure cell assemblies that have been calibrated at high pressure. High temperatures were achieved using either graphite heater (<6 GPa) or rhenium heater at higher pressures and measured with a tungsten-rhenium thermocouple. Melting relations were determined with a JEOL JXA-8900 electron microprobe, based on quench textures and chemical composition of the quenched phases. Powder X- ray diffraction technique was also used to identify phases and determine unit cell parameters. A positive slope between the solubility of carbon in metallic iron and pressure was found at elevated temperatures. The eutectic temperature increases with increasing pressure. The liquidus temperature determined in this study is significantly lower than the calculated value in previous study. Our study presents directly experimental measurements of the melting relations in the Fe-C system at high pressure and temperature, which provides better constraints on composition and temperature of the Earth's core.

Metamorphism and partial melting of ordinary chondrites: Calculated phase equilibria

NASA Astrophysics Data System (ADS)

Johnson, T. E.; Benedix, G. K.; Bland, P. A.

2016-01-01

Constraining the metamorphic pressures (P) and temperatures (T) recorded by meteorites is key to understanding the size and thermal history of their asteroid parent bodies. New thermodynamic models calibrated to very low P for minerals and melt in terrestrial mantle peridotite permit quantitative investigation of high-T metamorphism in ordinary chondrites using phase equilibria modelling. Isochemical P-T phase diagrams based on the average composition of H, L and LL chondrite falls and contoured for the composition and abundance of olivine, ortho- and clinopyroxene, plagioclase and chromite provide a good match with values measured in so-called equilibrated (petrologic type 4-6) samples. Some compositional variables, in particular Al in orthopyroxene and Na in clinopyroxene, exhibit a strong pressure dependence when considered over a range of several kilobars, providing a means of recognising meteorites derived from the cores of asteroids with radii of several hundred kilometres, if such bodies existed at that time. At the low pressures (<1 kbar) that typify thermal metamorphism, several compositional variables are good thermometers. Although those based on Fe-Mg exchange are likely to have been reset during slow cooling, those based on coupled substitution, in particular Ca and Al in orthopyroxene and Na in clinopyroxene, are less susceptible to retrograde diffusion and are potentially more faithful recorders of peak conditions. The intersection of isopleths of these variables may allow pressures to be quantified, even at low P, permitting constraints on the minimum size of parent asteroid bodies. The phase diagrams predict the onset of partial melting at 1050-1100 °C by incongruent reactions consuming plagioclase, clinopyroxene and orthopyroxene, whose compositions change abruptly as melting proceeds. These predictions match natural observations well and support the view that type 7 chondrites represent a suprasolidus continuation of the established petrologic types at the extremes of thermal metamorphism. The results suggest phase equilibria modelling has potential as a powerful quantitative tool in investigating, for example, progressive oxidation during metamorphism, the degree of melting and melt loss or accumulation required to produce the spectrum of differentiated meteorites, and whether the onion shell or rubble pile model best explains the metamorphic evolution of asteroid parent bodies in the early solar system.

Heinrich-type glacial surges in a low-order dynamical climate model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verbitsky, M.; Saltzman, B.

1994-07-01

Recent studies suggest the occurrence of sporadic episodes during which the ice streams that discharge ice sheets become enormously active, producing large numbers of icebergs (reflected in North Atlantic sea cores as {open_quotes}Heinrich events{close_quotes}) and possibly causing the partial collapse of the ice sheets. To simulate the mechanism of implied internal thermo-hydrodynamical instability in the context of a more general paleoclimate dynamics model (PDM), a new sliding-catastrophe function that can account for ice-sheet surges in terms of the thickness, density, viscosity, heat-capacity. and heat-conductivity of ice is introduced. Analysis suggests these events might be of three possible kinds: the firstmore » occurs in periods of glacial maximum when temperature conditions on the ice surface are extremely cold, but internal friction within bottom boundary layer is also at its maximum and is strong enough to melt ice and cause its surge. The second may happen during an interglacial, when the ice thickness is small but relatively warm climate conditions on the upper surface of ice can be easily advected with the flow of ice to the bottom where even a small additional heating due to friction may cause melting. The third and, perhaps, most interesting type is one that may occur during ice sheet growth: in this period particles of ice reaching the bottom {open_quotes}remember{close_quotes} the warm temperature conditions of the previous interglacial and additional heating due to increasing friction associated with the growing ice sheet may again cause melting. This third introduces the interesting possibility that earlier CO{sub 2} concentrations may be as important for the present-day climate as its current value. According to our model the climate system seems more vulnerable to surges during the penultimate interglacial period than in present one contributing to an explanation of the recent results of the Greenland Ice Core Project. 18 refs., 3 figs., 1 tab.« less

Where is the 1-million-year-old ice at Dome A?

NASA Astrophysics Data System (ADS)

Zhao, Liyun; Moore, John C.; Sun, Bo; Tang, Xueyuan; Guo, Xiaoran

2018-05-01

Ice fabric influences the rheology of ice, and hence the age-depth profile at ice core drilling sites. To investigate the age-depth profile to be expected of the ongoing deep ice coring at Kunlun station, Dome A, we use the depth-varying anisotropic fabric suggested by the recent polarimetric measurements around Dome A along with prescribed fabrics ranging from isotropic through girdle to single maximum in a three-dimensional, thermo-mechanically coupled full-Stokes model of a 70 × 70 km2 domain around Kunlun station. This model allows for the simulation of the near basal ice temperature and age, and ice flow around the location of the Chinese deep ice coring site. Ice fabrics and geothermal heat flux strongly affect the vertical advection and basal temperature which consequently control the age profile. Constraining modeled age-depth profiles with dated radar isochrones to 2/3 ice depth, the surface vertical velocity, and also the spatial variability of a radar isochrones dated to 153.3 ka BP, limits the age of the deep ice at Kunlun to between 649 and 831 ka, a much smaller range than previously inferred. The simple interpretation of the polarimetric radar fabric data that we use produces best fits with a geothermal heat flux of 55 mW m-2. A heat flux of 50 mW m-2 is too low to fit the deeper radar layers, and 60 mW m-2 leads to unrealistic surface velocities. The modeled basal temperature at Kunlun reaches the pressure melting point with a basal melting rate of 2.2-2.7 mm a-1. Using the spatial distribution of basal temperatures and the best fit fabric suggests that within 400 m of Kunlun station, 1-million-year-old ice may be found 200 m above the bed, and that there are large regions where even older ice is well above the bedrock within 5-6 km of the Kunlun station.

Early evolution and dynamics of Earth from a molten initial stage

NASA Astrophysics Data System (ADS)

Lourenço, Diogo L.; Tackley, Paul J.

2014-05-01

It is now well established that most of the terrestrial planets underwent a magma ocean stage during their accretion. On Earth, it is probable that at the end of accretion, giant impacts like the hypothesised Moon-forming impact, together with other sources of heat such as conversion of gravitational energy of formation into heat, heat losses from the core at the core-mantle boundary, radioactive decay, electromagnetic induction heating and tidal heating, melted a substantial part of the mantle. The thermal and chemical evolution of the resulting magma ocean most certainly had dramatic consequences on the history of the planet, influencing the chemical composition of the mantle after differentiation, the style of tectonic regime prevailing in the solid-state mantle and its habitability. Considerable research has been done on magma oceans using 1-D models (e.g.: Abe, PEPI 1997; Solomatov, Treat. Geophys. 2007; Elkins-Tanton, EPSL 2008). However, its dynamics, evolution from a molten state to the present day solid state, and crystallisation are still not fully understood and are more complex than a 1-D formulation. Recent advances in computational methods and resources allow us to address numerically more complex problems, with higher resolution and multiple physics incorporated. Moreover, new developments in mineral physics that indicate that melt can be denser than solid at high pressures (e.g.: de Koker et al., EPSL 2013) can have very important impacts on the classical views of the solidification of magma oceans (Labrosse et al., Nature 2007). The goal of our study is to understand and characterise the influence of melting on the long-term thermo-chemical evolution of rocky planet interiors, starting from an initial molten state (magma ocean). Our approach is to test existing published 1-D parameterisations of magma ocean dynamics and extend them into 2-D models. We will address this problem using the numerical code StagYY (Tackley, PEPI 2008), which uses a finite-volume scheme for advection of temperature, a multigrid solver to obtain a velocity-pressure solution at each timestep, tracers to track composition, and a treatment of partial melting and crustal formation. Additional enhancements are needed in the code and are related to the physics and parameterisation of melting.

Accumulated phenocrysts and origin of feldspar porphyry in the Chanho area, western Yunnan, China

NASA Astrophysics Data System (ADS)

Xu, Xing-Wang; Jiang, Neng; Yang, Kai; Zhang, Bao-Lin; Liang, Guang-He; Mao, Qian; Li, Jin-Xiang; Du, Shi-Jun; Ma, Yu-Guang; Zhang, Yong; Qin, Ke-Zhang

2009-12-01

The No. 1 feldspar porphyry in the Chanho area, western Yunnan, China is characterized by the development of deformed glomeroporphyritic aggregates (GA) that contain diagnostic gravity settling textures. These textures include interlocking curved grain boundaries caused by compaction, bent twins, and arch-like structures. The GAs are accumulated phenocrysts (AP) and antecrysts. The unstable textural configurations such as extensive penetrative microfractures that are restricted within the AP and fractured cores of zircon grains, all suggest that the GAs are transported fragments of fractured cumulates that formed in a pre-emplacement magma chamber rather than form in situ at the current intrusion site. Compositions of minerals and melt as represented by different mineral aggregates formed at various stages of the magmatic process and their relations to the composition of porphyry bodies in the Chanho area indicate that the porphyritic melt for the No. 1 feldspar porphyry experienced two stages of melt mixing. Pulses of potassic melt flowed into a pre-emplacement magma chamber and mixed with crystallizing dioritic magma containing phenocrysts resulted in the first hybrid alkaline granitic melt. The mixing caused denser phenocrysts to settle and aggregate to form cumulates. Secondly, new dioritic melt was injected into the magma chamber and was mixed with the previously formed hybrid alkaline granitic melt to produce syenitic melt. Geochron data, including U-Pb age of zircon and 39Ar/ 40Ar age of hornblende and oligoclase phenocrysts, indicate that hornblende and oligoclase phenocrysts, as well as the core of zircon grains, were antecrysts that formed in a number of crystallization events between 36.3 and 32.78 Ma. Gravity settling of phenocrysts took place at about 33.1 to 32.78 Ma and melts with deformed GAs were transported upwards and emplaced into the current site at 32 Ma. Results of this research indicate that the No. 1 feldspar porphyry was a shallow intrusion of mixed melts that contained phenocrysts and GAs, both of which formed in a deeper transitional magma chamber.

On the origins of the weak folding cooperativity of a designed ββα ultrafast protein FSD-1.

PubMed

Wu, Chun; Shea, Joan-Emma

2010-11-18

FSD-1, a designed small ultrafast folder with a ββα fold, has been actively studied in the last few years as a model system for studying protein folding mechanisms and for testing of the accuracy of computational models. The suitability of this protein to describe the folding of naturally occurring α/β proteins has recently been challenged based on the observation that the melting transition is very broad, with ill-resolved baselines. Using molecular dynamics simulations with the AMBER protein force field (ff96) coupled with the implicit solvent model (IGB = 5), we shed new light into the nature of this transition and resolve the experimental controversies. We show that the melting transition corresponds to the melting of the protein as a whole, and not solely to the helix-coil transition. The breadth of the folding transition arises from the spread in the melting temperatures (from ∼325 K to ∼302 K) of the individual transitions: formation of the hydrophobic core, β-hairpin and tertiary fold, with the helix formed earlier. Our simulations initiated from an extended chain accurately predict the native structure, provide a reasonable estimate of the transition barrier height, and explicitly demonstrate the existence of multiple pathways and multiple transition states for folding. Our exhaustive sampling enables us to assess the quality of the Amber ff96/igb5 combination and reveals that while this force field can predict the correct native fold, it nonetheless overstabilizes the α-helix portion of the protein (Tm = ∼387K) as well as the denatured structures.

The 8.2 ka cooling event caused by Laurentide ice saddle collapse

NASA Astrophysics Data System (ADS)

Matero, I. S. O.; Gregoire, L. J.; Ivanovic, R. F.; Tindall, J. C.; Haywood, A. M.

2017-09-01

The 8.2 ka event was a period of abrupt cooling of 1-3 °C across large parts of the Northern Hemisphere, which lasted for about 160 yr. The original hypothesis for the cause of this event has been the outburst of the proglacial Lakes Agassiz and Ojibway. These drained into the Labrador Sea in ∼0.5-5 yr and slowed the Atlantic Meridional Overturning Circulation, thus cooling the North Atlantic region. However, climate models have not been able to reproduce the duration and magnitude of the cooling with this forcing without including additional centennial-length freshwater forcings, such as rerouting of continental runoff and ice sheet melt in combination with the lake release. Here, we show that instead of being caused by the lake outburst, the event could have been caused by accelerated melt from the collapsing ice saddle that linked domes over Hudson Bay in North America. We forced a General Circulation Model with time varying meltwater pulses (100-300 yr) that match observed sea level change, designed to represent the Hudson Bay ice saddle collapse. A 100 yr long pulse with a peak of 0.6 Sv produces a cooling in central Greenland that matches the 160 yr duration and 3 °C amplitude of the event recorded in ice cores. The simulation also reproduces the cooling pattern, amplitude and duration recorded in European Lake and North Atlantic sediment records. Such abrupt acceleration in ice melt would have been caused by surface melt feedbacks and marine ice sheet instability. These new realistic forcing scenarios provide a means to reconcile longstanding mismatches between proxy data and models, allowing for a better understanding of both the sensitivity of the climate models and processes and feedbacks in motion during the disintegration of continental ice sheets.

Direct measurement of thermal conductivity in solid iron at planetary core conditions.

PubMed

Konôpková, Zuzana; McWilliams, R Stewart; Gómez-Pérez, Natalia; Goncharov, Alexander F

2016-06-02

The conduction of heat through minerals and melts at extreme pressures and temperatures is of central importance to the evolution and dynamics of planets. In the cooling Earth's core, the thermal conductivity of iron alloys defines the adiabatic heat flux and therefore the thermal and compositional energy available to support the production of Earth's magnetic field via dynamo action. Attempts to describe thermal transport in Earth's core have been problematic, with predictions of high thermal conductivity at odds with traditional geophysical models and direct evidence for a primordial magnetic field in the rock record. Measurements of core heat transport are needed to resolve this difference. Here we present direct measurements of the thermal conductivity of solid iron at pressure and temperature conditions relevant to the cores of Mercury-sized to Earth-sized planets, using a dynamically laser-heated diamond-anvil cell. Our measurements place the thermal conductivity of Earth's core near the low end of previous estimates, at 18-44 watts per metre per kelvin. The result is in agreement with palaeomagnetic measurements indicating that Earth's geodynamo has persisted since the beginning of Earth's history, and allows for a solid inner core as old as the dynamo.

Changes in Black Carbon Deposition to Antarctica from Two Ice Core Records, A.D. 1850-2000

NASA Technical Reports Server (NTRS)

Bisiaux, Marion M.; Edward, Ross; McConnell, Joseph R.; Curran, Mark A. J.; VanOmmen, Tas D.; Smith, Andrew M.; Neumann, Thomas A.; Pasteris, Daniel R.; Penner, Joyce E.; Taylor, Kendrick

2012-01-01

Continuous flow analysis was based on a steady sample flow and in-line detection of BC and other chemical substances as described in McConnell et al. (2007). In the cold room, previously cut one meter ice core sticks of 3x3cm, are melted continuously on a heated melter head specifically designed to eliminate contamination from the atmosphere or by the external parts of the ice. The melted ice from the most inner part of the ice stick is continuously pumped by a peristaltic pump and carried to a clean lab by Teflon lines. The recorded signal is continuous, integrating a sample volume of about 0.05 mL, for which the temporal resolution depends on the speed of melting, ice density and snow accumulation rate at the ice core drilling site. For annual accumulation derived from the WAIS and Law Dome ice cores, we assumed 3.1 cm water equivalent uncertainty in each year's accumulation from short scale spatial variability (glaciological noise) which was determined from several measurements of annual accumulation in multiple parallel ice cores notably from the WAIS Divide ice core site (Banta et al., 2008) and from South Pole site (McConnell et al., 1997; McConnell et al., 2000). Refractory black carbon (rBC) concentrations were determined using the same method as in (Bisiaux et al., 2011) and adapted to continuous flow measurements as described by (McConnell et al., 2007). The technique uses a single particle intracavity laser induced incandescence photometer (SP2, Droplet Measurement Technologies, Boulder, Colorado) coupled to an ultrasonic nebulizer/desolvation (CETAC UT5000) Flow Injection Analysis (FIA). All analyses, sample preparation etc, were performed in a class 100 cleanroom using anti contamination "clean techniques". The samples were not acidified.

Rapid, dynamic segregation of core forming melts: Results from in-situ High Pressure- High Temperature X-ray Tomography

NASA Astrophysics Data System (ADS)

Watson, H. C.; Yu, T.; Wang, Y.

2011-12-01

The timing and mechanisms of core formation in the Earth, as well as in Earth-forming planetesimals is a problem of significant importance in our understanding of the early evolution of terrestrial planets . W-Hf isotopic signatures in meteorites indicate that core formation in small pre-differentiated planetesimals was relatively rapid, and occurred over the span of a few million years. This time scale is difficult to achieve by percolative flow of the metallic phase through a silicate matrix in textural equilibrium. It has been suggested that during this active time in the early solar system, dynamic processes such as impacts may have caused significant deformation in the differentiating planetesimals, which could lead to much higher permeability of the core forming melts. Here, we have measured the change in permeability of core forming melts in a silicate matrix due to deformation. Mixtures of San Carlos olivine and FeS close to the equilibrium percolation threshold (~5 vol%FeS) were pre-synthesized to achieve an equilibrium microstructure, and then loaded into the rotational Drickamer apparatus at GSE-CARS, sector 13-BMD, at the Advanced Photon Source (Argonne National Laboratory). The samples were subsequently pressed to ~2GPa, and heated to 1100°C. Alternating cycles of rotation to collect X-ray tomography images, and twisting to deform the sample were conducted until the sample had been twisted by 1080°. Qualitative and quantitative analyses were performed on the resulting 3-dimensional x-ray tomographic images to evaluate the effect of shear deformation on permeability and migration velocity. Lattice-Boltzmann simulations were conducted, and show a marked increase in the permeability with increasing deformation, which would allow for much more rapid core formation in planetesimals.

The Origin of Mercury's Surface Composition, an Experimental Investigation

NASA Technical Reports Server (NTRS)

Boujibar, A.; Righter, K.; Rapp, J. F.; Ross, D. K.; Pando, K. M.; Danielson, L. R.; Fontaine, E.

2016-01-01

Introduction: Results from MESSENGER spacecraft have confirmed the reduced nature of Mercury, based on its high core/mantle ratio and its FeO-poor and S-rich surface. Moreover, high resolution images revealed large volcanic plains and abundant pyroclastic deposits, suggesting major melting stages of the Mercurian mantle. In addition, MESSENGER has provided the most precise data to date on major elemental compositions of Mercury's surface. These results revealed considerable chemical heterogeneities that suggested several stages of differentiation and re-melting processes. This interpretation was challenged by our experimental previous study, which showed a similar compositional variation in the melting products of enstatite chondrites, which are a possible Mercury analogue. However, these experimental melts were obtained over a limited range of pressure (1 bar to 1 gigapascal) and were not compared to the most recent elemental maps. Therefore, here we extend the experimental dataset to higher pressures and perform a more quantitative comparison with Mercury's surface compositions measured by MESSENGER. In particular, we test whether these chemical heterogeneities result from mixing between polybaric melts. Our experiments and models show that the majority of chemical diversity of Mercury's surface can result from melting of a primitive mantle compositionally similar to enstatite chondrites in composition at various depths and degrees of melting. The high-Mg region's composition is reproduced by melting at high pressure (3 gigapascals) (Tab. 1), which is consistent with previous interpretation as being a large degraded impact basin based on its low elevation and thin average crust. While low-Mg NVP (North Volcanic Plains) are the result of melting at low pressure (1 bar), intermediate-Mg NVP, Caloris Basin and Rachmaninoff result from mixing of a high-pressure (3 gigapascals) and low-pressure components (1 bar for Rachmaninoff and 1 gigapascal for the other regions) (Tab. 1). Moreover, all compositions suggest mixing between low and high degree melts that indicate important differentiation processes.

Relationship Between the Melting Temperature of hcp Iron at ICB Pressure and the Light Impurity Content of Earth's Core

NASA Astrophysics Data System (ADS)

Anderson, O. L.

2001-12-01

The table below leads the reader through calculation of the core density deficit starting from the melting temperature (solidus), Tm, at the pressure, P, of the inner core boundary (ICB) (330 GPa). Tm values come from recent data of four sets of authors. Thermal pressure, Δ PTH, values were calculated in the author's laboratory. P0 = 330 - PTH is the P corresponding to the volume, V, of iron at Tm, V0 (sol.). P0 yields V0 (sol.) from an equation of state. The volume change of melting, Δ Vm, which leads to the liquidus V, V0 (liq.), was determined by the author. The liquidus density, ρ 0 (liq.), is higher than the seismic density at 330 GPa by the core density deficit. S wt.% is the amount of sulfur alone that satisfies the core ρ deficit. Δ Tf is the freezing point depression arising from impurities. %table { \\setlength{\\tabcolsep}{.05truein} \\begin{center} \\begin{tabular}{lcccc} \\multicolumn{5}{l}{ Core density deficit and freezing point depression} multicolumn{5}{l}{calculated from Tm} \\hline Tm (330)& 4800 K& 5850 K& 6700 K& 7500 K \\hline Δ PTH& 64.0& 82.0& 97.0& 112\\P0 (330 K)& 266& 248& 233& 218\\V0 (sol.)& 4.25& 4.30& 4.37& 4.43Δ Vm& .055& .055& .055& .055\\V0 (liq.)& 4.305& 4.355& 4.425& 4.485ρ (liq.)& 13.09& 12.94& 12.73& 12.48 core ρ def.& 7.1& 6& 4& 2.9 S wt.% & 7.3& 6.2& 3.8& 2.5 Δ Tf& ~ 330& ~ 300& ~ 200& ~ 150 \\hline \\multicolumn{5}{l}{Units: PTH & P0, GPa; V0 & Δ Vm, cm3mol.-1;} multicolumn{5}{l}{ρ , kg m-3x 103; core ρ def., %; Δ Tf, K.}\\ } Cosmochemists' estimates of viable amounts of S and Si in the core are most easily satisfied by the core density deficit arising from Tm = 5850 K. High Tm values result in surprisingly high values for Earth's ICB temperature, because Δ Tf is low. A large Δ PTH results in a low Δ Tf.

Early evolution and dynamics of Earth from a molten initial stage

NASA Astrophysics Data System (ADS)

Louro Lourenço, Diogo; Tackley, Paul J.

2016-04-01

It is now well established that most of the terrestrial planets underwent a magma ocean stage during their accretion. On Earth, it is probable that at the end of accretion, giant impacts like the hypothesised Moon-forming impact, together with other sources of heat, melted a substantial part of the mantle. The thermal and chemical evolution of the resulting magma ocean most certainly had dramatic consequences on the history of the planet. Considerable research has been done on magma oceans using simple 1-D models (e.g.: Abe, PEPI 1997; Solomatov, Treat. Geophys. 2007; Elkins-Tanton EPSL 2008). However, some aspects of the dynamics may not be adequately addressed in 1-D and require the use of 2-D or 3-D models. Moreover, new developments in mineral physics that indicate that melt can be denser than solid at high pressures (e.g.: de Koker et al., EPSL 2013) can have very important impacts on the classical views of the solidification of magma oceans (Labrosse et al., Nature 2007). The goal of our study is to understand and characterize the influence of melting on the long-term thermo-chemical evolution of rocky planet interiors, starting from an initial molten state (magma ocean). Our approach is to model viscous creep of the solid mantle, while parameterizing processes that involve melt as previously done in 1-D models, including melt-solid separation at all melt fractions, the use of an effective diffusivity to parameterize turbulent mixing, coupling to a parameterized core heat balance and a radiative surface boundary condition. These enhancements have been made to the numerical code StagYY (Tackley, PEPI 2008). We present results for the evolution of an Earth-like planet from a molten initial state to present day, while testing the effect of uncertainties in parameters such as melt-solid density differences, surface heat loss and efficiency of turbulent mixing. Our results show rapid cooling and crystallization until the rheological transition then much slower crystallization, large-scale overturn well before full solidification, the formation and subduction of an early crust while a partially-molten upper mantle is still present, transitioning to mostly-solid-state long-term mantle convection and plate tectonics or an episodic-lid regime.

Early evolution and dynamics of Earth from a molten initial stage

NASA Astrophysics Data System (ADS)

Lourenço, Diogo; Tackley, Paul

2015-04-01

It is now well established that most of the terrestrial planets underwent a magma ocean stage during their accretion. On Earth, it is probable that at the end of accretion, giant impacts like the hypothesised Moon-forming impact, together with other sources of heat, melted a substantial part of the mantle. The thermal and chemical evolution of the resulting magma ocean most certainly had dramatic consequences on the history of the planet. Considerable research has been done on magma oceans using simple 1-D models (e.g.: Abe, PEPI 1997; Solomatov, Treat. Geophys. 2007; Elkins-Tanton EPSL 2008). However, some aspects of the dynamics may not be adequately addressed in 1-D and require the use of 2-D or 3-D models. Moreover, new developments in mineral physics that indicate that melt can be denser than solid at high pressures (e.g.: de Koker et al., EPSL 2013) can have very important impacts on the classical views of the solidification of magma oceans (Labrosse et al., Nature 2007). The goal of our study is to understand and characterize the influence of melting on the long-term thermo-chemical evolution of rocky planet interiors, starting from an initial molten state (magma ocean). Our approach is to model viscous creep of the solid mantle, while parameterizing processes that involve melt as previously done in 1-D models, including melt-solid separation at all melt fractions, the use of an effective diffusivity to parameterize turbulent mixing, coupling to a parameterized core heat balance and a radiative surface boundary condition. These enhancements have been made to the numerical code StagYY (Tackley, PEPI 2008). We will present results for the evolution of an Earth-like planet from a molten initial state to present day, while testing the effect of uncertainties in parameters such as melt-solid density differences, surface heat loss and efficiency of turbulent mixing. Our results show rapid cooling and crystallization until the rheological transition then much slower crystallization, large-scale overturn well before full solidification, the formation and subduction of an early crust while a partially-molten upper mantle is still present, transitioning to mostly-solid-state long-term mantle convection and plate tectonics or an episodic-lid regime.

Evolution and dynamics of Earth from a molten initial stage

NASA Astrophysics Data System (ADS)

Louro Lourenço, D. J.; Tackley, P.

2016-12-01

It is now well established that most of the terrestrial planets underwent a magma ocean stage during their accretion. On Earth, it is probable that at the end of accretion, giant impacts like the hypothesised Moon-forming impact, together with other sources of heat, melted a substantial part of the mantle. The thermal and chemical evolution of the resulting magma ocean most certainly had dramatic consequences on the history of the planet. Considerable research has been done on magma oceans using simple 1-D models (e.g.: Abe, PEPI 1997; Solomatov, Treat. Geophys. 2007; Elkins-Tanton EPSL 2008). However, some aspects of the dynamics may not be adequately addressed in 1-D and require the use of 2-D or 3-D models. Moreover, new developments in mineral physics that indicate that melt can be denser than solid at high pressures (e.g.: de Koker et al., EPSL 2013) can have very important impacts on the classical views of the solidification of magma oceans (Labrosse et al., Nature 2007; Labrosse et al., The Early Earth 2015). The goal of our study is to understand and characterize the influence of melting on the long-term thermo-chemical evolution of rocky planet interiors, starting from an initial molten state (magma ocean). Our approach is to model viscous creep of the solid mantle, while parameterizing processes that involve melt as previously done in 1-D models, including melt-solid separation at all melt fractions, the use of an effective diffusivity to parameterize turbulent mixing, coupling to a parameterized core heat balance and a radiative surface boundary condition. These enhancements have been made to the numerical code StagYY (Tackley, PEPI 2008). We present results for the evolution of an Earth-like planet from a molten initial state to present day, while testing the effect of uncertainties in parameters such as melt-solid density differences, surface heat loss and efficiency of turbulent mixing. Our results show rapid cooling and crystallization until the rheological transition then much slower crystallization, large-scale overturn well before full solidification, the formation and subduction of an early crust while a partially-molten upper mantle is still present, transitioning to mostly-solid-state long-term mantle convection and plate tectonics or an episodic-lid regime.

Core Formation: an Experimental Study of Metallic Melt-Silicate Segregation

NASA Astrophysics Data System (ADS)

Herpfer, M. A.; Larimer, J. W.

1993-07-01

To a large extent, the question of how metallic cores form reduces to the problem of understanding the surface tension between metallic melts and silicates [1]. This problem was addressed by performing experiments to determine the surface tensions between metallic melts with variable S contents and the silicate phases (olivine and orthopyroxene) expected in planetary mantles. The experiments were conducted in a piston-cylinder apparatus at P = 1GPa and T = 1250-1450 degrees C. Textural and chemical equilibration was confirmed in several ways: theoretical estimates were checked by conducting a series of experiments at progressively longer times (up to 72 hrs) until phase composition and dihedral angle ceased to change and the distribution of measured "apparent" angles matched the standard cumulative frequency curve. The dihedral "wetting" angles (theta) were measured from high resolution photomicrgraphs using a 10X optical protractor; 100-400 measurements were made for most experiments. The dihedral angle is related to the ratio of interfacial energies: gamma(sub)ss/gamma(sub)sl = 2 cos(theta/2), where gamma(sub)ss and gamma(sub)sl are the interfacial energies between solid-solid and liquid-solid. Since data exist for the pertinent solid-solid energies, the liquid-solid interfacial energies can be computed from measured theta values. However, the important relations are best expressed in terms of theta values. The extent to which a melt is interconnected along grain boundaries, and hence able to flow and segregate depends on the value of theta and the fraction of melt present. When theta < 60 degrees, the liquid can be interconnected at all melt fractions but when theta > 60 degrees, the melt fraction must be at least 1 vol% and increses as theta increases. Actually there is a predicted effect, analogous to a hysteresis effect, where for a given theta value the amount of melt that needs to be added for interconnection is greater than the amount left when the melt disconnects (pinches off). In our experiments, where dense metallic melt drained away, the disconnect theta values match the theoretical predictions. The composition of the metallic melt in the experiments was varied from stoichiometric FeS to Fe/S ratios near the the eutectic and on to more Fe rich compositons. The theta values vary in a systematic manner; for example, for melts in contact with olivine at 1300 degrees C the theta values range from 67 degrees for FeS to 55 degrees at the eutectic and back toward higher values at higher Fe contents. Theoretical considerations indicate that eutectic compositions are expected to have the lowest theta values, just as observed. The theta values indicate that melts with eutectic composition can interconnect and segregate at 1-2 vol% melt fraction at 1300 degrees C. Some previous estimates of the melt fraction required for interconnection are much higher [2,3], but the inferences were drawn from experiments that were not designed to test for textural equilibrium, fraction of melt present, etc. The present experiments clearly show that metallic melts can readily segregate from solid silicates. Simple extrapolations to other phases, compositions and PT conditions provide a rather complete picture of how the "plumbing" worked in the mantles of planetary objects during the initial stages of core segregation. References: [1] Stevenson D. J. (1990) In Origin of the Earth, 231-249. [2] Taylor G. J. (1989) LPSC XX, 1109. [3] Walker D. and Agee C. B. Meteor. 23, 81-91.

Eemian interglacial reconstructed from a Greenland folded ice core.

PubMed

2013-01-24

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

A laboratory model for solidification of Earth's core

NASA Astrophysics Data System (ADS)

Bergman, Michael I.; Macleod-Silberstein, Marget; Haskel, Michael; Chandler, Benjamin; Akpan, Nsikan

2005-11-01

To better understand the influence of rotating convection in the outer core on the solidification of the inner core we have constructed a laboratory model for solidification of Earth's core. The model consists of a 15 cm radius hemispherical acrylic tank concentric with a 5 cm radius hemispherical aluminum heat exchanger that serves as the incipient inner core onto which we freeze ice from salt water. Long exposure photographs of neutrally buoyant particles in illuminated planes suggest reduction of flow parallel to the rotation axis. Thermistors in the tank near the heat exchanger show that in experiments with rotation the temperature near the pole is lower than near the equator, unlike for control experiments without rotation or with a polymer that increases the fluid viscosity. The photographs and thermistors suggest that our observation that ice grows faster near the pole than near the equator for experiments with rotation is a result of colder water not readily convecting away from the pole. Because of the reversal of the thermal gradient, we expect faster equatorial solidification in the Earth's core. Such anisotropy in solidification has been suggested as a cause of inner core elastic (and attenuation) anisotropy, though the plausibility of this suggestion will depend on the core Nusselt number and the slope of the liquidus, and the effects of post-solidification deformation. Previous experiments on hexagonal close-packed alloys such as sea ice and zinc-tin have shown that fluid flow in the melt can result in a solidification texture transverse to the solidification direction, with the texture depending on the nature of the flow. A comparison of the visualized flow and the texture of columnar ice crystals in thin sections from these experiments confirms flow-induced transverse textures. This suggests that the convective pattern at the base of the outer core is recorded in the texture of the inner core, and that outer core convection might contribute to the complexity in the seismically inferred pattern of anisotropy in the Earth's inner core.

Three tier transition of Neoarchean TTG-sanukitoid magmatism in the Beit Bridge Complex, Southern Africa

NASA Astrophysics Data System (ADS)

Rajesh, H. M.; Belyanin, G. A.; Van Reenen, D. D.

2018-01-01

Neoarchean TTG-sanukitoid associations of contrasting scales occur within the Beit Bridge Complex terrane of the Limpopo Complex in southern Africa. These include the smaller 2.65-2.63 Ga Avoca granitoid and the voluminous 2.73-2.64 Ga Alldays granitoid. This study characterizes the wide compositional spectrum preserved in these two granitoids. The elliptical Avoca pluton consists of a biotite-amphibole-orthopyroxene ± clinopyroxene-bearing core that is dominantly trondhjemite with less dominant tonalite and granodiorite variants, and a thin amphibole-biotite-bearing granite rim, with local occurrence of two-pyroxene-bearing metabasite boudins. While both the core and rim rocks exhibit a linear fabric, the granite in addition preserves a penetrative foliation. Field relations of granite enclaves in the core rocks together with available ages indicate that the core rocks intruded the granite. The foliated biotite ± amphibole-bearing Alldays granitoid contains inclusions of older supracrustals and rocks of the Messina layered intrusion, and is widely distributed. Compositionally, it include tonalites and granodiorites and to a lesser extent trondhjemites. Both the Avoca core and rim rocks are characterized by difference in mineral chemistry, with the mafic minerals Mg-rich in the TTG core, while they are Fe-rich in the granite and metabasite. In comparison, biotite is Mg-rich and amphibole is Fe-rich in the Alldays granitoid. Two groups of Alldays TTG can be delineated in terms of whole-rock geochemical characteristics, and are comparable to the low- to medium-pressure TTG groups delineated by Moyen (2011), while the Avoca TTG is similar to the high-pressure TTG group. The lowest silica samples from each group of granitoid have geochemical characteristics comparable to Archean sanukitoids, with those from the Avoca granitoid similar to low-Ti sanukitoids, and those from the Alldays granitoid similar to low-Ti and high-Ti sanukitoids. Separate petrogenetic models are suggested for different phases of the Avoca core, with the trondhjemite-tonalites considered as high-pressure melts of metabasalt, while the granodiorite with lower SiO2 content, higher K2O and MgO contents, and higher incompatible element contents, than the trondhjemite-tonalites, is a product of hybridization of earlier TTG melts and peridodite. Granite from the Avoca rim are low-pressure melts of pre-existing crustal lithologies. The two groups of Alldays TTG with lower Sr/Y ratios than the Avoca TTG are considered as low- to medium-pressure melts of metabasalt, whose progressive interaction with peridotitic mantle at shallower angles account for the unique composition of Alldays low-Ti and high-Ti sanukitoids. Taken together with their spatial and temporal transition from southeastern ( 2.73-2.72 Ga; low-pressure TTG-low-Ti sanukitoid) to central ( 2.65-2.64 Ga; medium-pressure TTG-high-Ti sanukitoid) to northwestern ( 2.63 Ga; high-pressure TTG-low-Ti sanukitoid) parts of the Beit Bridge Complex, the three tier transition of TTG-sanukitoid magmatism argues for the southern margin of the Beit Bridge Complex to represent an active arc in the Neoarchean.

Pu-Zr alloy for high-temperature foil-type fuel

DOEpatents

McCuaig, Franklin D.

1977-01-01

A nuclear reactor fuel alloy consists essentially of from slightly greater than 7 to about 4 w/o zirconium, balance plutonium, and is characterized in that the alloy is castable and is rollable to thin foils. A preferred embodiment of about 7 w/o zirconium, balance plutonium, has a melting point substantially above the melting point of plutonium, is rollable to foils as thin as 0.0005 inch thick, and is compatible with cladding material when repeatedly cycled to temperatures above 650.degree. C. Neutron reflux densities across a reactor core can be determined with a high-temperature activation-measurement foil which consists of a fuel alloy foil core sandwiched and sealed between two cladding material jackets, the fuel alloy foil core being a 7 w/o zirconium, plutonium foil which is from 0.005 to 0.0005 inch thick.

Pu-ZR Alloy high-temperature activation-measurement foil

DOEpatents

McCuaig, Franklin D.

1977-08-02

A nuclear reactor fuel alloy consists essentially of from slightly greater than 7 to about 4 w/o zirconium, balance plutonium, and is characterized in that the alloy is castable and is rollable to thin foils. A preferred embodiment of about 7 w/o zirconium, balance plutonium, has a melting point substantially above the melting point of plutonium, is rollable to foils as thin as 0.0005 inch thick, and is compatible with cladding material when repeatedly cycled to temperatures above 650.degree. C. Neutron flux densities across a reactor core can be determined with a high-temperature activation-measurement foil which consists of a fuel alloy foil core sandwiched and sealed between two cladding material jackets, the fuel alloy foil core being a 7 w/o zirconium, plutonium foil which is from 0.005 to 0.0005 inch thick.

Magnetic Heating of Iron Oxide Nanoparticles and Magnetic Micelles for Cancer Therapy.

PubMed

Glover, Amanda L; Bennett, James B; Pritchett, Jeremy S; Nikles, Sarah M; Nikles, David E; Nikles, Jacqueline A; Brazel, Christopher S

2013-01-01

The inclusion of magnetic nanoparticles into block copolymer micelles was studied towards the development of a targeted, magnetically triggered drug delivery system for cancer therapy. Herein, we report the synthesis of magnetic nanoparticles and poly(ethylene glycol-b-caprolactone) block copolymers, and experimental verification of magnetic heating of the nanoparticles, self-assembly of the block copolymers to form magnetic micelles, and thermally-enhanced drug release. The semicrystalline core of the micelles melted at temperatures just above physiological conditions, indicating that they could be used to release a chemotherapy agent from a thermo-responsive polymer system. The magnetic nanoparticles were shown to heat effectively in high frequency magnetic fields ranging from 30-70 kA/m. Magnetic micelles also showed heating properties, that when combined with a chemotherapeutic agent and a targeting ligand could be developed for localized, triggered drug delivery. During the magnetic heating experiments, a time lag was observed in the temperature profile for magnetic micelles, likely due to the heat of fusion of melting of polycaprolactone micelle cores before bulk solution temperatures increased. Doxorubicin, incorporated into the micelles, released faster when the micelles were heated above the core melting point.

Density Determination of Metallic Melts from Diffuse X-Ray Scattering

NASA Astrophysics Data System (ADS)

Brauser, N.; Davis, A.; Greenberg, E.; Prakapenka, V. B.; Campbell, A.

2017-12-01

Liquids comprise several important structural components of the deep Earth, for example, the present outer core and a hypothesized magma ocean early in Earth history. However, the physical properties of the constituent materials of these structures at high pressures and temperatures are less well constrained than their crystalline counterparts. Determination of the physical properties of these liquids can inform geophysical models of the composition and structure of the Earth, but methods for studying the physical properties of liquids at high pressure and temperatures are underdeveloped. One proposed method for direct determination of density of a melt requires analysis of the diffuse scattered X-ray signal of the liquid. Among the challenges to applying this technique to high-pressure melts within a laser heated diamond anvil cell are the low signal-to-noise ratio and overlapping diffraction peaks from the crystalline components of the sample assembly interfering with the diffuse scattering from the liquid. Recent advances in instrumentation at synchrotron X-ray sources have made this method more accessible for determination of density of melted material. In this work we present the technique and report the densities of three high-pressure melts of the FCC metals iron, nickel, and gold derived from diffuse scattered X-ray spectra collected from in situ laser-heated diamond anvil cell synchrotron experiments. The results are compared to densities derived from shock wave experiments.

Partitioning of light lithophile elements during basalt eruptions on Earth and application to Martian shergottites

NASA Astrophysics Data System (ADS)

Edmonds, Marie

2015-02-01

An enigmatic record of light lithophile element (LLE) zoning in pyroxenes in basaltic shergottite meteorites, whereby LLE concentrations decrease dramatically from the cores to the rims, has been interpreted as being due to partitioning of LLE into a hydrous vapor during magma ascent to the surface on Mars. These trends are used as evidence that Martian basaltic melts are water-rich (McSween et al., 2001). Lithium and boron are light lithophile elements (LLE) that partition into volcanic minerals and into vapor from silicate melts, making them potential tracers of degassing processes during magma ascent to the surface of Earth and of other planets. While LLE degassing behavior is relatively well understood for silica-rich melts, where water and LLE concentrations are relatively high, very little data exists for LLE abundance, heterogeneity and degassing in basaltic melts. The lack of data hampers interpretation of the trends in the shergottite meteorites. Through a geochemical study of LLE, volatile and trace elements in olivine-hosted melt inclusions from Kilauea Volcano, Hawaii, it can be demonstrated that lithium behaves similarly to the light to middle rare Earth elements during melting, magma mixing and fractionation. Considerable heterogeneity in lithium and boron is inherited from mantle-derived primary melts, which is dominant over the fractionation and degassing signal. Lithium and boron are only very weakly volatile in basaltic melt erupted from Kilauea Volcano, with vapor-melt partition coefficients <0.1. Degassing of LLE is further inhibited at high temperatures. Pyroxene and associated melt inclusion LLE concentrations from a range of volcanoes are used to quantify lithium pyroxene-melt partition coefficients, which correlate negatively with melt H2O content, ranging from 0.13 at low water contents to <0.08 at H2O contents >4 wt%. The observed terrestrial LLE partitioning behavior is extrapolated to Martian primitive melts through modeling. The zoning observed in the shergottite pyroxenes is only consistent with degassing of LLE from a Martian melt near its liquidus temperature if the vapor-melt partition coefficient was an order of magnitude larger than observed on Earth. The range in LLE and trace elements observed in shergottite pyroxenes are instead consistent with concurrent mixing and fractionation of heterogeneous melts from the mantle.

Increasing Sequence Diversity with Flexible Backbone Protein Design: The Complete Redesign of a Protein Hydrophobic Core

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphy, Grant S.; Mills, Jeffrey L.; Miley, Michael J.

2015-10-15

Protein design tests our understanding of protein stability and structure. Successful design methods should allow the exploration of sequence space not found in nature. However, when redesigning naturally occurring protein structures, most fixed backbone design algorithms return amino acid sequences that share strong sequence identity with wild-type sequences, especially in the protein core. This behavior places a restriction on functional space that can be explored and is not consistent with observations from nature, where sequences of low identity have similar structures. Here, we allow backbone flexibility during design to mutate every position in the core (38 residues) of a four-helixmore » bundle protein. Only small perturbations to the backbone, 12 {angstrom}, were needed to entirely mutate the core. The redesigned protein, DRNN, is exceptionally stable (melting point >140C). An NMR and X-ray crystal structure show that the side chains and backbone were accurately modeled (all-atom RMSD = 1.3 {angstrom}).« less

Melting of Fe and Fe0.9Ni0.1 alloy at high pressures

NASA Astrophysics Data System (ADS)

Zhang, D.; Jackson, J. M.; Zhao, J.; Sturhahn, W.; Alp, E. E.; Hu, M. Y.; Toellner, T.

2014-12-01

Cosmochemical studies suggest that the cores of terrestrial planets are primarily composed of Fe alloyed with about 5 to 10 wt% Ni, plus some light elements (e.g., McDonough and Sun 1995). Thus, the high pressure melting curve of Fe0.9Ni0.1 is considered to be an important reference for characterizing the cores of terrestrial planets. We have determined the melting points of fcc-structured Fe and Fe0.9Ni0.1 up to 86 GPa using an in-situ method that monitors the atomic dynamics of the Fe atoms in the sample, synchrotron Mössbauer spectroscopy (Jackson et al. 2013). A laser heated diamond anvil cell is used to provide the high pressure-high temperature environmental conditions, and in-situ X-ray diffraction is used to constrain the pressure of the sample. To eliminate the influence of temperature fluctuations experienced by the sample on the determination of melting, we develop a Fast Temperature Readout (FasTeR) spectrometer. The FasTeR spectrometer features a fast reading rate (>100 Hz), a high sensitivity, a large dynamic range and a well-constrained focus. By combining the melting curve of fcc-structured Fe0.9Ni0.1 alloy determined in our study and the fcc-hcp phase boundary from Komabayashi et al. (2012), we calculate the fcc-hcp-liquid triple point of Fe0.9Ni0.1. Using this triple point and the thermophysical parameters from a nuclear resonant inelastic X-ray scattering study on hcp-Fe (Murphy et al. 2011), we compute the melting curve of hcp-structured Fe0.9Ni0.1. We will discuss our new experimental results with implications for the cores of Venus, Earth and Mars. Select references: McDonough & Sun (1995): The composition of the Earth. Chem. Geol. 120, 223-253. Jackson et al. (2013): Melting of compressed iron by monitoring atomic dynamics, EPSL, 362, 143-150. Komabayashi et al. (2012): In situ X-ray diffraction measurements of the fcc-hcp phase transition boundary of an Fe-Ni alloy in an internally heated diamond anvil cell, PCM, 39, 329-338. Murphy et al. (2011): Melting and thermal pressure of hcp-Fe from the phonon density of states, PEPI, 188, 114-120.

Fe-Ti-oxide textures and microstructures in shear zones from oceanic gabbros at Atlantis Bank, Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Till, Jessica; Morales, Luiz F. G.; Rybacki, Erik

2016-04-01

Ocean drilling expeditions at several oceanic core complexes formed at slow- and ultra-slow-spreading ridges have recovered cores containing numerous zones of oxide-rich gabbros containing ilmenite and magnetite. In these cores, high modal concentrations of Fe-Ti-oxides are systematically associated with high-temperature plastic deformation features in silicates. We present observations of Fe-Ti-oxide mineral structures and textural characteristics from a series of oxide-rich shear zones from Atlantis Bank (ODP Site 735B) on the Southwest Indian Ridge aimed at determining how oxide mineral abundances relate to strain localization. Fe-Ti-oxide minerals in undeformed oxide gabbros and in highly deformed samples from natural shear zones generally have morphologies characteristic of crystallized melt, including highly cuspate grains and low dihedral angles. Anisotropy of magnetic susceptibility in oxide-rich shear zones is very strong, with fabrics mainly characterized by strong magnetic foliations parallel to the macroscopic foliation. Crystallographic preferred orientations (CPO) in magnetite are generally weak, with occasionally well-defined textures. Ilmenite typically displays well-developed CPOs, however, the melt-like ilmenite grain shapes indicate that at least part of the crystallographic texture results from oriented ilmenite growth during post-deformation crystallization. The oxides are hypothesized to have initially been present as isolated pockets of trapped melt (intercumulus liquid) in a load-bearing silicate framework. Progressive plastic deformation of silicate phases at high-temperature mainly produced two features: (i) elongated melt pockets, which crystallized to form strings of opaque minerals and (ii), interconnected networks of melt regions. The latter lead to intense strain localization of the rock, which appears as oxide-rich mylonites in the samples. In some samples, abundant low-angle grain boundaries in both magnetite and ilmenite suggest that deformation may have continued after crystallization of the late melt, imposing a weak strain on the oxides. Recent experimental deformation results indicate that magnetite and ilmenite should be weaker than most mafic silicates under anhydrous conditions. However, melt-like oxide morphologies observed in Atlantis Bank shear zones indicate that the redistribution of Fe-Ti-oxide melts may have more influence on the strength and strain localization behavior of oceanic gabbros than their solid-state rheology.

Evolutions of lamellar structure during melting and solidification of Fe9577 nanoparticle from molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Wu, Yongquan; Shen, Tong; Lu, Xionggang

2013-03-01

A structural evolution during solidification and melting processes of nanoparticle Fe9577 was investigated from MD simulations. A perfect lamellar structure, consisting alternately of fcc and hcp layers, was obtained from solidification process. A structural heredity of early embryo is proposed to explain the structural preference of solidification. Defects were found inside the solid core and play the same role as surface premelting on melting. hcp was found more stable than fcc in high temperature. The difference between melting and solidification points can be deduced coming fully from the overcoming of thermodynamic energy barrier, instead of kinetic delay of structural relaxation.

Isostructural solid-solid phase transition in monolayers of soft core-shell particles at fluid interfaces: structure and mechanics.

PubMed

Rey, Marcel; Fernández-Rodríguez, Miguel Ángel; Steinacher, Mathias; Scheidegger, Laura; Geisel, Karen; Richtering, Walter; Squires, Todd M; Isa, Lucio

2016-04-21

We have studied the complete two-dimensional phase diagram of a core-shell microgel-laden fluid interface by synchronizing its compression with the deposition of the interfacial monolayer. Applying a new protocol, different positions on the substrate correspond to different values of the monolayer surface pressure and specific area. Analyzing the microstructure of the deposited monolayers, we discovered an isostructural solid-solid phase transition between two crystalline phases with the same hexagonal symmetry, but with two different lattice constants. The two phases corresponded to shell-shell and core-core inter-particle contacts, respectively; with increasing surface pressure the former mechanically failed enabling the particle cores to come into contact. In the phase-transition region, clusters of particles in core-core contacts nucleate, melting the surrounding shell-shell crystal, until the whole monolayer moves into the second phase. We furthermore measured the interfacial rheology of the monolayers as a function of the surface pressure using an interfacial microdisk rheometer. The interfaces always showed a strong elastic response, with a dip in the shear elastic modulus in correspondence with the melting of the shell-shell phase, followed by a steep increase upon the formation of a percolating network of the core-core contacts. These results demonstrate that the core-shell nature of the particles leads to a rich mechanical and structural behavior that can be externally tuned by compressing the interface, indicating new routes for applications, e.g. in surface patterning or emulsion stabilization.

Constant electrical resistivity of Ni along the melting boundary up to 9 GPa

NASA Astrophysics Data System (ADS)

Silber, Reynold E.; Secco, Richard A.; Yong, Wenjun

2017-07-01

Characterization of transport properties of liquid Ni at high pressures has important geophysical implications for terrestrial planetary interiors, because Ni is a close electronic analogue of Fe and it is also integral to Earth's core. We report measurements of the electrical resistivity of solid and liquid Ni at pressures 3-9 GPa using a 3000 t multianvil large volume press. A four-wire method, in conjunction with a rapid acquisition meter and polarity switch, was used to overcome experimental challenges such as melt containment and maintaining sample geometry and to mitigate the extreme reactivity/solubility of liquid Ni with most thermocouple and electrode materials. Thermal conductivity is calculated using the Wiedemann-Franz law. Electrical resistivity of solid Ni exhibits the expected P dependence and is consistent with earlier experimental values. Within experimental uncertainties, our results indicate that resistivity of liquid Ni remains invariant along the P-dependent melting boundary, which is in disagreement with earlier prediction for liquid transition metals. The potential reasons for such behavior are examined qualitatively through the impact of P-independent local short-range ordering on electron mean free path and the possibility of constant Fermi surface at the onset of Ni melting. Correlation among metals obeying the Kadowaki-Woods ratio and the group of late transition metals with unfilled d-electron band displaying anomalously shallow melting curves suggests that on the melting boundary, Fe may exhibit the same resistivity behavior as Ni. This could have important implications for the heat flow in the Earth's core.

A Brief Review of Past INL Work Assessing Radionuclide Content in TMI-2 Melted Fuel Debris: The Use of 144Ce as a Surrogate for Pu Accountancy

DOE Office of Scientific and Technical Information (OSTI.GOV)

D. L. Chichester; S. J. Thompson

2013-09-01

This report serves as a literature review of prior work performed at Idaho National Laboratory, and its predecessor organizations Idaho National Engineering Laboratory (INEL) and Idaho National Engineering and Environmental Laboratory (INEEL), studying radionuclide partitioning within the melted fuel debris of the reactor of the Three Mile Island 2 (TMI-2) nuclear power plant. The purpose of this review is to document prior published work that provides supporting evidence of the utility of using 144Ce as a surrogate for plutonium within melted fuel debris. When the TMI-2 accident occurred no quantitative nondestructive analysis (NDA) techniques existed that could assay plutonium inmore » the unconventional wastes from the reactor. However, unpublished work performed at INL by D. W. Akers in the late 1980s through the 1990s demonstrated that passive gamma-ray spectrometry of 144Ce could potentially be used to develop a semi-quantitative correlation for estimating plutonium content in these materials. The fate and transport of radioisotopes in fuel from different regions of the core, including uranium, fission products, and actinides, appear to be well characterized based on the maximum temperature reached by fuel in different parts of the core and the melting point, boiling point, and volatility of those radioisotopes. Also, the chemical interactions between fuel, fuel cladding, control elements, and core structural components appears to have played a large role in determining when and how fuel relocation occurred in the core; perhaps the most important of these reaction appears to be related to the formation of mixed-material alloys, eutectics, in the fuel cladding. Because of its high melting point, low volatility, and similar chemical behavior to plutonium, the element cerium appears to have behaved similarly to plutonium during the evolution of the TMI-2 accident. Anecdotal evidence extrapolated from open-source literature strengthens this logical feasibility for using cerium, which is rather easy to analyze using passive nondestructive analysis gamma-ray spectrometry, as a surrogate for plutonium in the final analysis of TMI-2 melted fuel debris. The generation of this report is motivated by the need to perform nuclear material accountancy measurements on the melted fuel debris that will be excavated from the damaged nuclear reactors at the Fukushima Daiichi nuclear power plant in Japan, which were destroyed by the Tohoku earthquake and tsunami on March 11, 2011. Lessons may be taken from prior U.S. work related to the study of the TMI-2 core debris to support the development of new assay methods for use at Fukushima Daiichi. While significant differences exist between the two reactor systems (pressurized water reactor (TMI-2) versus boiling water reactor (FD), fresh water post-accident cooing (TMI-2) versus salt water (FD), maintained containment (TMI-2) versus loss of containment (FD)) there remain sufficient similarities to motivate these comparisons.« less

Equation of state and phase diagram of Fe-16Si alloy as a candidate component of Earth's core

NASA Astrophysics Data System (ADS)

Fischer, Rebecca A.; Campbell, Andrew J.; Caracas, Razvan; Reaman, Daniel M.; Dera, Przymyslaw; Prakapenka, Vitali B.

2012-12-01

The outer core of the Earth contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is critical to understand the high pressure-temperature properties and behavior of an iron-silicon alloy with a geophysically relevant composition (16 wt% silicon). We experimentally determined the melting curve, subsolidus phase diagram, and equations of state of all phases of Fe-16 wt%Si to 140 GPa, finding a conversion from the D03 crystal structure to a B2+hcp mixture at high pressures. The melting curve implies that 3520 K is a minimum temperature for the Earth's outer core, if it consists solely of Fe-Si alloy, and that the eutectic composition in the Fe-Si system is less than 16 wt% silicon at core-mantle boundary conditions. Comparing our new equation of state to that of iron and the density of the core, we find that for an Fe-Ni-Si outer core, 11.3±1.5 wt% silicon would be required to match the core's observed density at the core-mantle boundary. We have also performed first-principles calculations of the equations of state of Fe3Si with the D03 structure, hcp iron, and FeSi with the B2 structure using density-functional theory.

Decadal-Scale Response of the Antarctic Ice sheet to a Warming Ocean using the POPSICLES Coupled Ice Sheet-Ocean model

NASA Astrophysics Data System (ADS)

Martin, D. F.; Asay-Davis, X.; Cornford, S. L.; Price, S. F.; Ng, E. G.; Collins, W.

2015-12-01

We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period from 1990 to 2010. We use the CORE v. 2 interannual forcing data to force the ocean model. Simulations are performed at 0.1o(~5 km) ocean resolution with adaptive ice sheet resolution as fine as 500 m to adequately resolve the grounding line dynamics. We discuss the effect of improved ocean mixing and subshelf bathymetry (vs. the standard Bedmap2 bathymetry) on the behavior of the coupled system, comparing time-averaged melt rates below a number of major ice shelves with those reported in the literature. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and the consequent dynamic response of the grounded ice sheet.POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program, and the BISICLES ice-sheet model. POP2x includes sub-ice-shelf circulation using partial top cells and the commonly used three-equation boundary layer physics. Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP) and other continental-scale simulations and melt-rate observations. BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d) and realistic configurations.The figure shows the BISICLES-computed vertically-integrated grounded ice velocity field 5 years into a 20-year coupled full-continent Antarctic-Southern-Ocean simulation. Submarine melt rates are painted onto the surface of the floating ice shelves. Grounding lines are shown in green.

Iron snow in the Martian Core?

NASA Astrophysics Data System (ADS)

Davies, C. J.; Pommier, A.

2017-12-01

The decline of Mars' global magnetic field some 3.8-4.1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core. The termination of the dynamo is intimately tied to the thermochemical evolution of the core-mantle system and therefore to the present-day physical state of the Martian core. The standard model predicts that the Martian dynamo failed because thermal convection stopped and the core remained entirely liquid until the present. Here we consider an alternative hypothesis that the Martian core crystallized from the top down in the so-called iron snow regime. We derive energy-entropy equations describing the long-timescale thermal and magnetic evolution of the core that incorporate the self-consistent formation of a snow layer that freezes out pure iron and is assumed to be on the liquidus; the iron sinks and remelts in the deeper core, acting as a possible source for magnetic field generation. Compositions are in the FeS system, with a sulfur content up to 16 wt%. The values of the different parameters (core radius, density and CMB pressure) are varied within bounds set by recent internal structure models that satisfy existing geodetic constraints (planetary mass, moment of inertia and tidal Love number). The melting curve and adiabat, CMB heat flow and thermal conductivity were also varied, based on previous experimental and numerical works. We observe that the formation of snow zones occurs for a wide range of interior and thermal structure properties and depends critically on the initial sulfur concentration. Gravitational energy release and latent heat effects arising during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies a significant fraction of the core. Our results suggest that snow zones can be 1.5-2 Gyrs old, though thermal stratification of the uppermost core, not included in our model, likely delays onset. Models that match the available magnetic and geodetic constraints have an initial S concentration of about 10wt.% and snow zones that occupy approximately the top 100 km of the present-day Martian core.

Viscosity of rock-ice mixtures and applications to the evolution of icy satellites

NASA Technical Reports Server (NTRS)

Friedson, A. J.; Stevenson, D. J.

1983-01-01

Theory and experiments are used to establish lower and upper bounds on the ratio of actual viscosity to pure ice viscosity for a suspension of rock particles in a water ice matrix. A rheological model for rock-ice mixtures is described, establishing bounds for the range of possible viscosity enhancements provided by a suspension of silicate spheres in an ice matrix. A parametrized thermal convection model is described and used to determine a criterion for criticality, defined as the heat flow and/or silicate volume fraction for which the satellite temperature profile intercepts the melting curve of water ice. The consequences of achieving this critical state are examined, and it is shown that under certain circumstances a 'runaway' differentiation can occur in which the silicates settle to form a core and extensive melting of water ice takes place, the latent heat being supplied by the gravitational energy of differentiation. A possible application of these results to Ganymede and Callisto is described.

Holocene sea-level change and Antarctic melting history derived from geological observations and geophysical modeling along the Shimokita Peninsula, northern Japan

NASA Astrophysics Data System (ADS)

Yokoyama, Yusuke; Okuno, Jun'ichi; Miyairi, Yosuke; Obrochta, Stephen; Demboya, Nobuhiro; Makino, Yoshinori; Kawahata, Hodaka

2012-07-01

A Mid to Late Holocene sea-level record based on combined geomorphological, geological and micropaleontological observations was obtained from well-developed wave cut benches subaerially exposed along the Shimokita Peninsula, northern Japan. Results indicate that the benches were formed during mid to late Holocene sea-level transgressions, reaching a maximum highstand level of 2 m above present at about 4,000 years ago. This timing corresponds to an abrupt, order of magnitude decrease in sedimentation rate as recorded in a core recovered from proximal Mutsu Bay. In addition, glacio-hydro-isostatic adjustment due to crustal deformation in response to postglacial sea-level rise was modeled, and results are consistent with the reconstructed local 2 m highstand. Given that meltwater contributions from the major North American and European ice sheets had largely ceased by 7,000 years ago, these independent lines of evidence, taken together, indicate that melting of the Antarctic ice sheet ended by 4,000 years ago.

Experimentally determined sulfur isotope fractionation between metal and silicate and implications for planetary differentiation

NASA Astrophysics Data System (ADS)

Labidi, J.; Shahar, A.; Le Losq, C.; Hillgren, V. J.; Mysen, B. O.; Farquhar, J.

2016-02-01

The Earth's mantle displays a subchondritic 34S/32S ratio. Sulfur is a moderately siderophile element (i.e. iron-loving), and its partitioning into the Earth's core may have left such a distinctive isotope composition on the terrestrial mantle. In order to constrain the sulfur isotope fractionation occurring during core-mantle differentiation, high-pressure and temperature experiments were conducted with synthetic mixtures of metal and silicate melts. With the purpose to identify the mechanism(s) responsible for the S isotope fractionations, we performed our experiments in different capsules - namely, graphite and boron nitride capsules - and thus at different fO2, with varying major element chemistry of the silicate and metal fractions. The S isotope fractionations Δ34Smetal-silicate of equilibrated metal alloys versus silicate melts is +0.2 ± 0.1‰ in a boron-free and aluminum-poor system quenched at 1-1.5 GPa and 1650 °C. The isotope fractionation increases linearly with increasing boron and aluminum content, up to +1.4 ± 0.2‰, and is observed to be independent of the silicon abundance as well as of the fO2 over ∼3.5 log units of variations explored here. The isotope fractionations are also independent of the graphite or nitride saturation of the metal. Only the melt structural changes associated with aluminum and boron concentration in silicate melts have been observed to affect the strength of sulfur bonding. These results establish that the structure of silicate melts has a direct influence on the S2- average bonding strengths. These results can be interpreted in the context of planetary differentiation. Indeed, the structural environments of silicate evolve strongly with pressure. For example, the aluminum, iron or silicon coordination numbers increase under the effect of pressure. Consequently, based on our observations, the sulfur-bonding environment is likely to be affected. In this scheme, we tentatively hypothesize that S isotope fractionations between the silicate mantle and metallic core of terrestrial planetary bodies would depend on the average pressure at which their core-mantle differentiation occurred.

Formation of Apollo 16 impactites and the composition of late accreted material: Constraints from Os isotopes, highly siderophile elements and sulfur abundances

NASA Astrophysics Data System (ADS)

Gleißner, Philipp; Becker, Harry

2017-03-01

Fe-Ni metal-schreibersite-troilite intergrowths in Apollo 16 impact melt rocks and new highly siderophile element (HSE) and S abundance data indicate that millimeter-scale closed-system fractional crystallization processes during cooling of impactor-derived metal melt droplets in impact-melts are the main reason for compositional variations and strong differences in abundances and ratios of HSE in multiple aliquots from Apollo 16 impact melt rocks. Element ratios obtained from linear regression of such data are therefore prone to error, but weighted averages take into account full element budgets in the samples and thus represent a more accurate estimate of their impactor contributions. Modeling of solid metal-liquid metal partitioning in the Fe-Ni-S-P system and HSE patterns in impactites from different landing sites suggest that bulk compositions of ancient lunar impactites should be representative of impact melt compositions and that large-scale fractionation of the HSE by in situ segregation of solid metal or sulfide liquid in impact melt sheets most likely did not occur. The compositional record of lunar impactites indicates accretion of variable amounts of chondritic and non-chondritic impactor material and the mixing of these components during remelting of earlier ejecta deposits. The non-chondritic composition appears most prominently in some Apollo 16 impactites and is characterized by suprachondritic HSE/Ir ratios which increase from refractory to moderately volatile HSE and exhibit a characteristic enrichment of Ru relative to Pt. Large-scale fractional crystallization of solid metal from sulfur and phosphorous rich metallic melt with high P/S in planetesimal or embryo cores is currently the most likely process that may have produced these compositions. Similar materials or processes may have contributed to the HSE signature of the bulk silicate Earth (BSE).

The elastic properties of hcp-Fe alloys under the conditions of the Earth's inner core

NASA Astrophysics Data System (ADS)

Li, Yunguo; Vočadlo, Lidunka; Brodholt, John P.

2018-07-01

Geophysical and cosmochemical constraints suggest the inner-core is mainly composed of iron with a few percent of light elements. However, despite extensive studies over many years, no single alloying light-element has been found that is able to simultaneously match the observed inner-core density and both seismic velocities. This has motivated a number of suggestions of other mechanism to lower velocities, such as anelasticity or premelting. However, an unexplored possibility is that a combination of two or more light-elements might produce the desired reduction in velocities and densities of the inner core. In order to test this, we use ab initio molecular dynamics calculations to map the elastic property space of hcp-Fe alloyed with S, Si and C at 360 GPa up to the melting temperature. Based on a mixing solid solution model together with direct simulations on the ternaries, we found a number of compositions which are able to match the observed properties of the inner core. This is the first time that the density, VP, Vs and the Poisson's ratio of the inner core have been matched directly with an hcp-Fe alloy.

Fukushima Daiichi Unit 1 Uncertainty Analysis-Exploration of Core Melt Progression Uncertain Parameters-Volume II.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Denman, Matthew R.; Brooks, Dusty Marie

Sandia National Laboratories (SNL) has conducted an uncertainty analysi s (UA) on the Fukushima Daiichi unit (1F1) accident progression wit h the MELCOR code. Volume I of the 1F1 UA discusses the physical modeling details and time history results of the UA. Volume II of the 1F1 UA discusses the statistical viewpoint. The model used was developed for a previous accident reconstruction investigation jointly sponsored by the US Department of Energy (DOE) and Nuclear Regulatory Commission (NRC). The goal of this work was to perform a focused evaluation of uncertainty in core damage progression behavior and its effect on keymore » figures - of - merit (e.g., hydrogen production, fraction of intact fuel, vessel lower head failure) and in doing so assess the applicability of traditional sensitivity analysis techniques .« less

Crystallization of carbon-oxygen mixtures in white dwarf stars.

PubMed

Horowitz, C J; Schneider, A S; Berry, D K

2010-06-11

We determine the phase diagram for dense carbon-oxygen mixtures in white dwarf (WD) star interiors using molecular dynamics simulations involving liquid and solid phases. Our phase diagram agrees well with predictions from Ogata et al. and from Medin and Cumming and gives lower melting temperatures than Segretain et al. Observations of WD crystallization in the globular cluster NGC 6397 by Winget et al. suggest that the melting temperature of WD cores is close to that for pure carbon. If this is true, our phase diagram implies that the central oxygen abundance in these stars is less than about 60%. This constraint, along with assumptions about convection in stellar evolution models, limits the effective S factor for the 12C(α,γ)16O reaction to S(300)≤170  keV b.

Chemical, thermal and impact processing of asteroids

NASA Technical Reports Server (NTRS)

Scott, E. R. D.; Taylor, G. J.; Newsom, H. E.; Herbert, F.; Zolensky, M.

1989-01-01

The geological effects of impacts, heating, melting, core formation, and aqueous alteration on asteroids are reviewed. A review of possible heat sources appears to favor an important role for electrical induction heating. The effects of each geologic process acting individually and in combination with others, are considered; it is concluded that there is much evidence for impacts during alteration, metamorphism and melting. These interactions vastly increased the geologic diversity of the asteroid belt. Subsequent impacts of cool asteroids did not reduce this diversity. Instead new rock types were created by mixing, brecciation and minor melting.

The melting points of MgO up to 4 TPa predicted based on ab initio thermodynamic integration molecular dynamics

NASA Astrophysics Data System (ADS)

Taniuchi, Takashi; Tsuchiya, Taku

2018-03-01

The melting curve of MgO is extended up to 4 TPa, corresponding to the Jovian core pressure, based on the one-step thermodynamic integration method implemented on ab initio molecular dynamics. The calculated melting temperatures are 3100 and 16 000 K at 0 and 500 GPa, respectively, which are consistent with previous experimental results, and 20 600 K at 3900 GPa, which is inconsistent with a recent experimental extrapolation, which implies the molten Jovian core. A quite small Clapeyron slope (dT/dP ) of 0.0+/- 0.5 is found at 3900 GPa due to comparable densities of the liquid and B2 phases under extreme compression. The Mg-O coordination number in the liquid phase is saturated at around 7.5 above 1 TPa and remains smaller than that in the B2 phase (8) even at 4 TPa, suggesting no density crossover between liquid and crystal and thus no further denser crystalline phases. Dynamical properties (atomic diffusivity and viscosity) are also investigated along the melting curve to understand these behaviors in greater detail.

Effect of a core-softened O-O interatomic interaction on the shock compression of fused silica

NASA Astrophysics Data System (ADS)

Izvekov, Sergei; Weingarten, N. Scott; Byrd, Edward F. C.

2018-03-01

Isotropic soft-core potentials have attracted considerable attention due to their ability to reproduce thermodynamic, dynamic, and structural anomalies observed in tetrahedral network-forming compounds such as water and silica. The aim of the present work is to assess the relevance of effective core-softening pertinent to the oxygen-oxygen interaction in silica to the thermodynamics and phase change mechanisms that occur in shock compressed fused silica. We utilize the MD simulation method with a recently published numerical interatomic potential derived from an ab initio MD simulation of liquid silica via force-matching. The resulting potential indicates an effective shoulder-like core-softening of the oxygen-oxygen repulsion. To better understand the role of the core-softening we analyze two derivative force-matching potentials in which the soft-core is replaced with a repulsive core either in the three-body potential term or in all the potential terms. Our analysis is further augmented by a comparison with several popular empirical models for silica that lack an explicit core-softening. The first outstanding feature of shock compressed glass reproduced with the soft-core models but not with the other models is that the shock compression values at pressures above 20 GPa are larger than those observed under hydrostatic compression (an anomalous shock Hugoniot densification). Our calculations indicate the occurrence of a phase transformation along the shock Hugoniot that we link to the O-O repulsion core-softening. The phase transformation is associated with a Hugoniot temperature reversal similar to that observed experimentally. With the soft-core models, the phase change is an isostructural transformation between amorphous polymorphs with no associated melting event. We further examine the nature of the structural transformation by comparing it to the Hugoniot calculations for stishovite. For stishovite, the Hugoniot exhibits temperature reversal and associated phase transformation, which is a transition to a disordered phase (liquid or dense amorphous), regardless of whether or not the model accounts for core-softening. The onset pressures of the transformation predicted by different models show a wide scatter within 60-110 GPa; for potentials without core-softening, the onset pressure is much higher than 110 GPa. Our results show that the core-softening of the interaction in the oxygen subsystem of silica is the key mechanism for the structural transformation and thermodynamics in shock compressed silica. These results may provide an important contribution to a unified picture of anomalous response to shock compression observed in other network-forming oxides and single-component systems with core-softening of effective interactions.

Can Suspended Iron-Alloy Droplets Explain the Origin, Composition and Properties of Large Low Shear Velocity Provinces?

NASA Astrophysics Data System (ADS)

Zhang, Z.; Dorfman, S. M.; Labidi, J.; Zhang, S.; Manga, M.; Stixrude, L. P.; McDonough, W. F.; Williams, Q. C.

2014-12-01

The enigmatic large low shear velocity provinces (LLSVPs) identified by seismic tomography at the base of the Earth's mantle have been proposed to be reservoirs of primordial mantle composition tapped by hot spot volcanism. The LLSVPs are characterized by anomalously low shear wave speed, VS, slightly elevated bulk sound speed, VB, and high density, ρ, in piles as thick as 1000 km above the core-mantle boundary. This combination of properties could be explained by a few percent dense melt, but the solidus of the lower mantle silicate and oxide assemblage may be too high to produce melt over the large extent of these regions. Iron-rich sulfur-bearing alloy may be molten at the conditions of the LLSVPs and ~1-2% of this component could satisfy both constraints on VS and ρ. An Fe alloy phase in the LLSVPs also has the potential to explain geochemical anomalies associated with hot spot volcanism, and its existence can be constrained by geochemical mass balance. Primordial noble gases such as 3He would be preferentially dissolved in Fe-rich melt rather than crystalline silicates. The reconstructed abundances of the moderately siderophile/chalcophile elements S, Cu and Pb in iron-alloy-bearing LLSVPs do not exceed predicted losses from volatilization, though this depends on the S-content of the alloy. The alloy phase would also be expected to incorporate W, and W isotope anomalies associated with hot spots are thus expected to have important implications for the timing of LLSVP formation. We have developed a model, via CIDER-2014, for the origin and properties of LLSVPs incorporating geochemistry, mineral physics, and fluid dynamic constraints on the generation, capture, and thermoelastic properties of Fe-rich melt droplets. The solidification of a basal magma ocean would produce both solid silicates and metallic melt. The bulk of the alloy generated by this process would sink to merge with the core. However, once the density of the remnant liquid exceeds that of the solid, newly-formed crystals floating at the crystallization front may trap droplets of Fe-rich melt as inclusions or at grain boundaries. We find that a mixture of mantle silicates and ~1-2% molten Fe-rich droplets matches constraints on density and seismic velocities and could host the hidden 3He and other elements of the primordial mantle reservoir.

Realization of thermal Convection into the initial Earth's Core on the Stage of planetary Accumulation

NASA Astrophysics Data System (ADS)

Professor Khachay, Yurie

2015-04-01

Convection in the Earth's core is not only the main mechanism of heat-mass transfer, but the significant component of the MHD mechanism of geomagnetic field generation. However the research of different convection forms on the Earth's accumulation stage had been so far not produced. Regarding the convection realization into the initial core of the growing proto planet we can distinguish some qualitative different stages. The earliest from them for the area of the planets of the Earth's group had been realized in to the pre planetary bodies, when the energy dissipation by the decay of the short living radioactive, first of all 26Al, provided the melted state of the inner areas of the proto planet. By that the masses and relative velocities of body's impacts during the process of accumulation had been small. That stipulated the low temperature values of the growing proto planetary surface [1] and the background of Raleigh heat convection realization. On the next stage of the planetary accumulation the contribution of short living isotopes to the energetic process during the decay 26Al decreased, but the energy contribution from the body's impact increased. The balance of the energy on the surface of the proto planet leaded to the melted state of the upper envelope and to the inelastic character of the impact. Further during the increase of the proto planetary mass, increase of the pressure and the melting temperature with the depth and decrease of the intensity of the dissipate energy by the body's impact, which became more elastic because of the silicate part, the background of the Raleigh heat convection can be realized [2]. However the falling of accumulated bodies can lead to the random distribution of the heat anomalies, which we could research only in the frame of the 3-D model [3-4]. For researching of the MHD mechanism of geomagnetic field generation developing yet on the stage of Earth's accumulation in that paper are presented the results of numerical modeling of PT- conditions and revealed the conditions, when the random distribution of 3D thermal heterogeneities does not destroy the thermal convection into the forming outer Earth's core. Reference 1Anfilogov V.N.,Khachay Y.V.DAN (2005) ,V 403, N 6, 803-806. 2 Anfilogov V.N.,Khachay Y.V.Litosphere (2012), N6, 3-1 3.Khachay Y.V. Magnetohydrodynamics. ( 2013), 49 N 1-3, 81-86 4.Khachay Y., Antipin A.Ural'skij geofiziceskij vestnik (2014), N1,81-85

Glass-ceramic optical fiber containing Ba2TiSi2O8 nanocrystals for frequency conversion of lasers

NASA Astrophysics Data System (ADS)

Fang, Zaijin; Xiao, Xusheng; Wang, Xin; Ma, Zhijun; Lewis, Elfed; Farrell, Gerald; Wang, Pengfei; Ren, Jing; Guo, Haitao; Qiu, Jianrong

2017-03-01

A glass-ceramic optical fiber containing Ba2TiSi2O8 nanocrystals fabricated using a novel combination of the melt-in-tube method and successive heat treatment is reported for the first time. For the melt-in-tube method, fibers act as a precursor at the drawing temperature for which the cladding glass is softened while the core glass is melted. It is demonstrated experimentally that following heat treatment, Ba2TiSi2O8 nanocrystals with diameters below 10 nm are evenly distributed throughout the fiber core. Comparing to the conventional rod-in-tube method, the melt-in-tube method is superior in terms of controllability of crystallization to allow for the fabrication of low loss glass-ceramic fibers. When irradiated using a 1030 nm femtosecond laser, an enhanced green emission at a wavelength of 515 nm is observed in the glass-ceramic fiber, which demonstrates second harmonic generation of a laser action in the fabricated glass-ceramic fibers. Therefore, this new glass-ceramic fiber not only provides a highly promising development for frequency conversion of lasers in all optical fiber based networks, but the melt-in-tube fabrication method also offers excellent opportunities for fabricating a wide range of novel glass-ceramic optical fibers for multiple future applications including fiber telecommunications and lasers.

Ice core evidence for extensive melting of the greenland ice sheet in the last interglacial.

PubMed

Koerner, R M

1989-05-26

Evidence from ice at the bottom of ice cores from the Canadian Arctic Islands and Camp Century and Dye-3 in Greenland suggests that the Greenland ice sheet melted extensively or completely during the last interglacial period more than 100 ka (thousand years ago), in contrast to earlier interpretations. The presence of dirt particles in the basal ice has previously been thought to indicate that the base of the ice sheets had melted and that the evidence for the time of original growth of these ice masses had been destroyed. However, the particles most likely blew onto the ice when the dimensions of the ice caps and ice sheets were much smaller. Ice texture, gas content, and other evidence also suggest that the basal ice at each drill site is superimposed ice, a type of ice typical of the early growth stages of an ice cap or ice sheet. If the present-day ice masses began their growth during the last interglacial, the ice sheet from the earlier (Illinoian) glacial period must have competely or largely melted during the early part of the same interglacial period. If such melting did occur, the 6-meter higher-than-present sea level during the Sangamon cannot be attributed to disintegration of the West Antarctic ice sheet, as has been suggested.

Glass-ceramic optical fiber containing Ba2TiSi2O8 nanocrystals for frequency conversion of lasers

PubMed Central

Fang, Zaijin; Xiao, Xusheng; Wang, Xin; Ma, Zhijun; Lewis, Elfed; Farrell, Gerald; Wang, Pengfei; Ren, Jing; Guo, Haitao; Qiu, Jianrong

2017-01-01

A glass-ceramic optical fiber containing Ba2TiSi2O8 nanocrystals fabricated using a novel combination of the melt-in-tube method and successive heat treatment is reported for the first time. For the melt-in-tube method, fibers act as a precursor at the drawing temperature for which the cladding glass is softened while the core glass is melted. It is demonstrated experimentally that following heat treatment, Ba2TiSi2O8 nanocrystals with diameters below 10 nm are evenly distributed throughout the fiber core. Comparing to the conventional rod-in-tube method, the melt-in-tube method is superior in terms of controllability of crystallization to allow for the fabrication of low loss glass-ceramic fibers. When irradiated using a 1030 nm femtosecond laser, an enhanced green emission at a wavelength of 515 nm is observed in the glass-ceramic fiber, which demonstrates second harmonic generation of a laser action in the fabricated glass-ceramic fibers. Therefore, this new glass-ceramic fiber not only provides a highly promising development for frequency conversion of lasers in all optical fiber based networks, but the melt-in-tube fabrication method also offers excellent opportunities for fabricating a wide range of novel glass-ceramic optical fibers for multiple future applications including fiber telecommunications and lasers. PMID:28358045

Glass-ceramic optical fiber containing Ba2TiSi2O8 nanocrystals for frequency conversion of lasers.

PubMed

Fang, Zaijin; Xiao, Xusheng; Wang, Xin; Ma, Zhijun; Lewis, Elfed; Farrell, Gerald; Wang, Pengfei; Ren, Jing; Guo, Haitao; Qiu, Jianrong

2017-03-30

A glass-ceramic optical fiber containing Ba 2 TiSi 2 O 8 nanocrystals fabricated using a novel combination of the melt-in-tube method and successive heat treatment is reported for the first time. For the melt-in-tube method, fibers act as a precursor at the drawing temperature for which the cladding glass is softened while the core glass is melted. It is demonstrated experimentally that following heat treatment, Ba 2 TiSi 2 O 8 nanocrystals with diameters below 10 nm are evenly distributed throughout the fiber core. Comparing to the conventional rod-in-tube method, the melt-in-tube method is superior in terms of controllability of crystallization to allow for the fabrication of low loss glass-ceramic fibers. When irradiated using a 1030 nm femtosecond laser, an enhanced green emission at a wavelength of 515 nm is observed in the glass-ceramic fiber, which demonstrates second harmonic generation of a laser action in the fabricated glass-ceramic fibers. Therefore, this new glass-ceramic fiber not only provides a highly promising development for frequency conversion of lasers in all optical fiber based networks, but the melt-in-tube fabrication method also offers excellent opportunities for fabricating a wide range of novel glass-ceramic optical fibers for multiple future applications including fiber telecommunications and lasers.

Recovering Paleo-Records from Antarctic Ice-Cores by Coupling a Continuous Melting Device and Fast Ion Chromatography.

PubMed

Severi, Mirko; Becagli, Silvia; Traversi, Rita; Udisti, Roberto

2015-11-17

Recently, the increasing interest in the understanding of global climatic changes and on natural processes related to climate yielded the development and improvement of new analytical methods for the analysis of environmental samples. The determination of trace chemical species is a useful tool in paleoclimatology, and the techniques for the analysis of ice cores have evolved during the past few years from laborious measurements on discrete samples to continuous techniques allowing higher temporal resolution, higher sensitivity and, above all, higher throughput. Two fast ion chromatographic (FIC) methods are presented. The first method was able to measure Cl(-), NO3(-) and SO4(2-) in a melter-based continuous flow system separating the three analytes in just 1 min. The second method (called Ultra-FIC) was able to perform a single chromatographic analysis in just 30 s and the resulting sampling resolution was 1.0 cm with a typical melting rate of 4.0 cm min(-1). Both methods combine the accuracy, precision, and low detection limits of ion chromatography with the enhanced speed and high depth resolution of continuous melting systems. Both methods have been tested and validated with the analysis of several hundred meters of different ice cores. In particular, the Ultra-FIC method was used to reconstruct the high-resolution SO4(2-) profile of the last 10,000 years for the EDML ice core, allowing the counting of the annual layers, which represents a key point in dating these kind of natural archives.

Soft particles at fluid interfaces: wetting, structure, and rheology

NASA Astrophysics Data System (ADS)

Isa, Lucio

Most of our current knowledge concerning the behavior of colloidal particles at fluid interfaces is limited to model spherical, hard and uniform objects. Introducing additional complexity, in terms of shape, composition or surface chemistry or by introducing particle softness, opens up a vast range of possibilities to address new fundamental and applied questions in soft matter systems at fluid interfaces. In this talk I will focus on the role of particle softness, taking the case of core-shell microgels as a paradigmatic example. Microgels are highly swollen and cross-linked hydrogel particles that, in parallel with their practical applications, e.g. for emulsion stabilization and surface patterning, are increasingly used as model systems to capture fundamental properties of bulk materials. Most microgel particles develop a core-shell morphology during synthesis, with a more cross-linked core surrounded by a corona of loosely linked and dangling polymer chains. I will first discuss the difference between the wetting of a hard spherical colloid and a core-shell microgel at an oil-water interface, pinpointing the interplay between adsorption at the interface and particle deformation. I will then move on to discuss the interplay between particle morphology and the microstructure and rheological properties of the interface. In particular, I will demonstrate that synchronizing the compression of a core-shell microgel-laden fluid interface with the deposition of the interfacial monolayer makes it possible to transfer the 2D phase diagram of the particles onto a solid substrate, where different positions correspond to different values of the surface pressure and the specific area. Using atomic force microscopy, we analyzed the microstructure of the monolayer and discovered a phase transition between two crystalline phases with the same hexagonal symmetry, but with two different lattice constants. The two phases correspond to shell-shell or core-core inter-particle contacts, respectively, where with increasing surface pressure the former mechanically fail enabling the particle cores to come into contact. In the phase-transition region, clusters of particles in core-core contacts nucleate, melting the surrounding shell-shell crystal, until the whole monolayer moves into the second phase. We furthermore extended our analysis to measure the interfacial rheology of the monolayers as a function of the surface pressure using an interfacial microdisk rheometer; the interfaces always show a strong elastic response, with a dip in the elastic modulus in correspondence of the melting of the shell-shell phase, followed by a steep increase upon formation of a percolating network of the core-core contacts. The presented results highlight the complex interplay between the wetting and deformation of individual soft particles at fluid interfaces and the overall interface microstructure and mechanics. They show strong connections to fundamental studies on phase transitions in two-dimensional systems and pave the way for novel nanoscale surface patterning routes. The author acknowledges financial support from the Swiss National Science Foundation Grant PP00P2-144646/1.

Modelling the Thermal History of Asteroid 4 Vesta

NASA Technical Reports Server (NTRS)

Solano, James M.; Kiefer, W. S.; Mittlefehldt, D. W.

2012-01-01

The asteroid 4 Vesta is widely thought to be the source of the HED (Howardite, Eucrite and Diogenite) meteorites, with this link supported by spectroscopic and dynamical studies. The availability of the HED meteorites for study and the new data being gained from the Dawn mission provides an excellent opportunity to investigate Vesta s history. In this study, modelling of Vesta has been undertaken to investigate its evolution from an unconsolidated chondritic body to a differentiated body with an iron core. In contrast to previous modelling, both heat and mass transfer are considered as coupled processes. This work draws on models of melt segregation in terrestrial environments to inform the evolution of Vesta into the differentiated body observed today. In order for a core to form in this body, a separation of the metallic iron from the silicates must take place. Temperatures in excess of the solidus temperatures for the Fe-FeS system and the silicates are therefore required. Thermal modelling has shown accretion before 2Myr leads to temperatures in excess of the silicate solidus.

Preliminary results of sulfide melt/silicate wetting experiments in a partially melted ordinary chondrite

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, John H.

1994-01-01

Recently, mechanisms for core formation in planetary bodies have received considerable attention. Most current theories emphasize the need for large degrees of silicate partial melting to facilitate the coalescence and sinking of sulfide-metal liquid blebs through a low strength semi-crystalline silicate mush. This scenario is based upon observations that sulfide-metal liquid tends to form circular blebs in partially molten meteorites during laboratory experiments. However, recent experimental work by Herpfer and Larimer indicates that some sulfide-Fe liquids have wetting angles at and slightly below 60 deg in an olivine aggregate, implying an interconnected melt structure at any melt fraction. Such melt interconnectivity provides a means for gravitational compaction and extraction of the majority of a sulfide liquid phase in small planetary bodies without invoking large degrees of silicate partial melting. Because of the important ramifications of these results, we conducted a series of experiments using H-chondrite starting material in order to evaluate sulfide-liquid/silicate wetting behavior in a more complex natural system.

Metal-silicate partitioning of U: Implications for the heat budget of the core and evidence for reduced U in the mantle

NASA Astrophysics Data System (ADS)

Chidester, Bethany A.; Rahman, Zia; Righter, Kevin; Campbell, Andrew J.

2017-02-01

Earth's core might require an internal heat source, such as radioactive decay, to explain the presence of the magnetic field through geologic time. To investigate whether U would be an important heat source in the core, we performed metal-silicate partitioning experiments of U at P-T (up to 67 GPa and 5400 K) conditions more relevant to a magma ocean scenario than has previously been reported. This study finds the partitioning of U to be strongly dependent on ƒO2, temperature, the S content of the metal and the SiO2 content of the silicate during core-mantle differentiation. Differentiation at mean conditions of 42-58 GPa and 3900-4200 K would put 1.4-3.5 ppb U (2-8 wt% S) in the core, amounting to a maximum of 1.4 (+1/-0.7) TW of heat 4.5 billion years ago. This is likely not enough heat to mitigate early widespread mantle melting. It was also found that U likely exists in the 2+ oxidation state in silicate melts in the deep Earth, a state which has not been previously observed in nature.

Nickel and helium evidence for melt above the core-mantle boundary.

PubMed

Herzberg, Claude; Asimow, Paul D; Ionov, Dmitri A; Vidito, Chris; Jackson, Matthew G; Geist, Dennis

2013-01-17

High (3)He/(4)He ratios in some basalts have generally been interpreted as originating in an incompletely degassed lower-mantle source. This helium source may have been isolated at the core-mantle boundary region since Earth's accretion. Alternatively, it may have taken part in whole-mantle convection and crust production over the age of the Earth; if so, it is now either a primitive refugium at the core-mantle boundary or is distributed throughout the lower mantle. Here we constrain the problem using lavas from Baffin Island, West Greenland, the Ontong Java Plateau, Isla Gorgona and Fernandina (Galapagos). Olivine phenocryst compositions show that these lavas originated from a peridotite source that was about 20 per cent higher in nickel content than in the modern mid-ocean-ridge basalt source. Where data are available, these lavas also have high (3)He/(4)He. We propose that a less-degassed nickel-rich source formed by core-mantle interaction during the crystallization of a melt-rich layer or basal magma ocean, and that this source continues to be sampled by mantle plumes. The spatial distribution of this source may be constrained by nickel partitioning experiments at the pressures of the core-mantle boundary.

Thermal Constraints from Siderophile Trace Elements in Acapulcoite-Lodranite Metals

NASA Technical Reports Server (NTRS)

Herrin, Jason S.; Mittlefehldt, D. W.; Humayun, M.

2006-01-01

A fundamental process in the formation of differentiated bodies is the segregation of metal-sulfide and silicate phases, leading to the formation of a metallic core. The only known direct record of this process is preserved in some primitive achondrites, such as the acapulcoite-lodranites. Meteorites of this clan are the products of thermal metamorphism of a chondritic parent. Most acapulcoites have experienced significant partial melting of the metal-sulfide system but not of silicates, while lodranites have experienced partial melting and melt extraction of both. The clan has experienced a continuum of temperatures relevant to the onset of metal mobility in asteroidal bodies and thus could yield insight into the earliest stages of core formation. Acapulcoite GRA 98028 contains relict chondrules, high modal sulfide/metal, has the lowest 2-pyroxene closure temperature, and represents the least metamorphosed state of the parent body among the samples examined. Comparison of the metal-sulfide component of other clan members to GRA 98028 can give an idea of the effects of metamorphism.

Investigating Planetesimal Evolution by Experiments with Fe-Ni Metallic Melts: Light Element Composition Effects on Trace Element Partitioning Behavior

NASA Astrophysics Data System (ADS)

Chabot, N. L.

2017-12-01

As planetesimals were heated up in the early Solar System, the formation of Fe-Ni metallic melts was a common occurrence. During planetesimal differentiation, the denser Fe-Ni metallic melts separated from the less dense silicate components, though some meteorites suggest that their parent bodies only experienced partial differentiation. If the Fe-Ni metallic melts did form a central metallic core, the core eventually crystallized to a solid, some of which we sample as iron meteorites. In all of these planetesimal evolution processes, the composition of the Fe-Ni metallic melt influenced the process and the resulting trace element chemical signatures. In particular, the metallic melt's "light element" composition, those elements present in the metallic melt in a significant concentration but with lower atomic masses than Fe, can strongly affect trace element partitioning. Experimental studies have provided critical data to determine the effects of light elements in Fe-Ni metallic melts on trace element partitioning behavior. Here I focus on combining numerous experimental results to identify trace elements that provide unique insight into constraining the light element composition of early Solar System Fe-Ni metallic melts. Experimental studies have been conducted at 1 atm in a variety of Fe-Ni systems to investigate the effects of light elements on trace element partitioning behavior. A frequent experimental examination of the effects of light elements in metallic systems involves producing run products with coexisting solid metal and liquid metal phases. Such solid-metal-liquid-metal experiments have been conducted in the Fe-Ni binary system as well as Fe-Ni systems with S, P, and C. Experiments with O-bearing or Si-bearing Fe-Ni metallic melts do not lend themselves to experiments with coexisting solid metal and liquid metal phases, due to the phase diagrams of these elements, but experiments with two immiscible Fe-Ni metallic melts have provided insight into the qualitative effects of O and Si relative to the well-determined effects of S. Together, these experimental studies provide a robust dataset to identify key elements that are predicted to produce distinct chemical signatures as a function of different Fe-Ni metallic melt compositions during planetesimal evolution processes.

The melting curve of Ni to 125 GPa: implications for Earth's Fe rich core alloy

NASA Astrophysics Data System (ADS)

Lord, O. T.; Wood, I. G.; Dobson, D. P.; Vocadlo, L.; Thomson, A. R.; Wann, E.; Wang, W.; Edgington, A.; Morard, G.; Mezouar, N.; Walter, M. J.

2014-12-01

The melting curve of Ni has been determined to 125 GPa using laser-heated diamond anvil cell (LH-DAC) experiments and two melting criteria: the appearance of liquid diffuse scattering (LDS) during in situ X-ray diffraction (XRD) and simultaneous plateaux in temperature vs. laser power functions [1]. Our melting curve (Fig. 1) is in good agreement with most theoretical studies [e.g. 2] and the available shock wave data (Fig. 2). It is, however, dramatically steeper than the previous off-line LH-DAC studies in which the determination of melting was based on the visual observation of motion aided by the laser speckle method [e.g. 3]. We estimate the melting point of Ni at the inner-core boundary (ICB; 330 GPa) to be 5800±700 K (2σ), ~2500 K higher than the estimate based on the laser speckle method [3] and within error of Fe (6230±500 K) as determined in a similar in situ LH-DAC study [4]. We find that laser speckle based melting curves coincide with the onset of rapid sub-solidus recrystallization, suggesting that visual observations of motion may have misinterpreted dynamic recrystallization as melt convection. Our new melting curve suggests that the reduction in ICB temperature due to the alloying of Ni with Fe is likely to be significantly smaller than would be expected had the earlier experimental Ni melting studies been correct. We have applied our methodology to a range of other transition metals (Mo, Ti, V, Cu). In the case of Mo, Ti and V the melting curves are in good agreement with the shock compression and theoretical melting studies but hotter and steeper than those based on the laser speckle method, as with Ni. Cu is an exception in which all studies agree, including those employing the laser speckle method. These results go a long way toward resolving the the long-standing controversy over the phase diagrams of the transition metals as determined from static LH-DAC studies on the one hand, and theoretical and dynamic compression studies on the other. [1] Lord et al. (2014) Phys Earth Planet Inter [2] Pozzo M, Alfè D (2013) Phys Rev B, 88:024111 [3] Errandonea et al. (2001) Phys Rev B, 63:132104 [4] Anzellini et al. (2013) Science, 340:464-466

Basin-forming impacts on Mars and the coupled thermal evolution of the interior

NASA Astrophysics Data System (ADS)

Arkani-Hamed, J.; Roberts, J. H.

2015-12-01

The youngest of the Noachian giant impact basins on Mars, are either weakly magnetized or completely demagnetized, indicating that a global magnetic field was not present and that a core dynamo was not operating at the time those basins formed. Shock heating from this sequence of basin-forming impacts modified the pattern of mantle convection. The heating produced by the eight largest impacts (Acidalia, Amazonis, Ares, Chryse, Daedalia, Hellas, Scopolus, and Utopia) penetrates below the core-mantle boundary (CMB). Here, we extend previous workon coupled thermal evolution into 3D, in order to accurately model the spatial relationship between impact basins. At the time of each impact we introduce a temperature perturbation resulting from shock heating into the core and mantle. Stratification of the core occurs very quickly compared to mantle dynamics, and we horizontally average the temperature in the core.We model mantle convection using the 3D finite element code CitcomS, and the thermal evolution of the core using a 1D parameterization.Each impact alters the pattern of mantle dynamics and a significant amount of impact melt is produced in the near surface. However, only the outermost part of the core is affected; the inner core temperature is still adiabatic. Immediately following the impact, the inner core may remain convective. The top of the core will cool by conduction into the deeper core faster than across the CMB, deepening the zone of stable stratification. Further core cooling results in formation of a convecting zone at the top of the core that propagates downwards as the thermal gradient becomes adiabatic at greater depths. Our goal is to obtain a better estimate of the time scale for restoration of post-impact core dynamo activity. Because the disappearance of the magnetic field exposes the early atmosphere to solar wind activity, constraining the history of the dynamo is critical for understanding climate evolution and habitability of the surface.

Experimental segregation of iron-nickel metal, iron-sulfide, and olivine in a thermal gradient: Preliminary results

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, J. H.

1993-01-01

Speculation about the possible mechanisms for core formation in small asteroids raises more questions than answers. Petrologic evidence from iron meteorites, pallasites, and astronomical observations of M asteroids suggests that many small bodies were capable of core formation. Recent work by Taylor reviews the geochemical evidence and examines the possible physical/mechanical constraints on segregation processes. Taylor's evaluation suggests that extensive silicate partial melting (preferably 50 vol. percent or greater) is required before metal can segregate from the surrounding silicate and form a metal core. The arguments for large degrees of silicate partial melting are two-fold: (1) elemental trends in iron meteorites require that the metal was at is liquidus; and (2) experimental observations of metal/sulfide inclusions in partially molten silicate meteorites show that the metal/sulfide tends to form spherules in the liquid silicate due to surface tension effects. Taylor points out that for these metal spherules to sink through a silicate mush, high degrees of silicate partial melting are required to lower the silicate yield strength. Although some qualitative experimental data exists, little is actually known about the behavior of metals and liquid sulfides dispersed in silicate systems. In addition, we have been impressed with the ability of cumulative olivine to expel trapped liquid when placed in a thermal gradient. Consequently, we undertook to accomplish the following: (1) experimentally evaluate the potential for metal/sulfide/silicate segregation in a thermal gradient; and (2) obtain quantitative data of the wetting parameters of metal-sulfide melts among silicate grains.

Rock Magnetic Study of IODP/ICDP Expedition 364 Site M0077A Drill Cores: Post-Impact Sediments, Impact Breccias, Melt, Granitic Basement and Dikes

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Perez-Cruz, L. L.; Rebolledo-Vieyra, M.; Tikoo, S.; Zylberman, W.; Lofi, J.

2017-12-01

Drilling at Site M0077 sampled post-impact sediments overlying a peak ring consisting of impact breccias, melt rock and granitoids. Here we focus on characterizing the peak ring using magnetic properties, which vary widely and depend on mineralogy, depositional and emplacement conditions and secondary alterations. Rock magnetic properties are integrated with Multi-Sensor Core Logger (MSCL) data, vertical seismic profile, physical properties, petrographic and chemical analyses and geophysical models. We measure low-field magnetic susceptibility at low- and high-frequencies, intensity and direction of natural remanent magnetization (NRM) and laboratory-induced isothermal (IRM) and anhysteretic (ARM) magnetizations, alternating-field demagnetization of NRM, IRM and NRM, susceptibility variation with temperature, anisotropy of magnetic susceptibility, hysteresis and IRM back-field demagnetization. Post-impact carbonates show low susceptibilities and NRM intensities, variable frequency-dependent susceptibilities and multivectorial remanences residing in low and high coercivity minerals. Hysteresis loops show low coercivity saturation magnetizations and variable paramagnetic mineral contents. Impact breccias (suevites) and melt rock show higher susceptibilities, low frequency-dependent susceptibilities, high NRM, ARM and IRM intensities and moderate ARM intensity/susceptibility ratios. Magnetic signal is dominated by fine-grained magnetite and titanomagnetites with PSD domain states. Melt rocks at the base of impactite section show the highest susceptibilities and remanence intensities. Basement section is characterized by low susceptibilities in the granites and higher values in the dikes, with NRM and ARM intensities increasing towards the base. The high susceptibilities and remanence intensities correlate with high seismic velocities, density and decreased porosity and electrical resistivity. Fracturing and alteration account for the reduced seismic velocities, density and magnetic properties in the basement section. Site M0077 is in a horizontal gradient high within the semi-circular gravity low in the crater central zone. Correlation with MSCL logs and petrographic and chemical data will allow further detailed characterization of peak ring units.

Magma surge from the mantle: the Father's Day Eruption, Kīlauea Volcano, Hawai'i

NASA Astrophysics Data System (ADS)

Salem, L. C.; Edmonds, M.; Maclennan, J.; Houghton, B. F.; Poland, M. P.

2015-12-01

The geometry of the shallow plumbing system of Kīlauea Volcano, Hawai'i, is constrained by both geophysical and petrologic studies, yet the loci of lower crustal magma storage and timescales of magma ascent are almost entirely unknown. The petrography and texture of erupted magmas are largely overprinted by processes in the shallow reservoir and conduit. Direct petrological evidence for lower crustal storage and transport is enigmatic but exists in the form of fine-scale crystal zoning in the cores of olivine phenocrysts, in the geochemical heterogeneity of melt inclusions and in fluid inclusion density. The 2007 Father's Day intrusion and eruption occurred at the culmination of a surge in magma supply to the summit reservoir and during a period of heightened CO2 outgassing flux. The erupted lavas provide an opportunity to analyze atypically primitive melts, with > 8.5 wt% MgO in the whole rock, which have undergone relatively little shallow crustal processing. We characterise melt inclusions and their host olivine crystals through a detailed study of olivine morphology, diffusion modelling, and melt and fluid inclusion geochemistry. We show that the melt inclusions preserve primitive geochemical heterogeneity, which we use to reconstruct fractionation, mixing and degassing processes through the crust. We infer timescales and pressures of magma ascent, storage, and CO2 degassing through the crustal plumbing system. These observations are interpreted in the context of the exceptionally detailed set of volcano monitoring data at Kīlauea Volcano.

In situ insights to Se (S) partitioning between silicate and metallic melts at extreme conditions

NASA Astrophysics Data System (ADS)

Borchert, M.; Petitgirard, S.; Appel, K.; Watenphul, A.; Morgenroth, W.

2012-12-01

The Earth's core mainly consists of a metallic Fe-Ni mixture. However, seismic observations show that the density is about 5-10% lower than expected for an Fe-Ni alloy under similar pressure and temperature conditions (e.g., [1,2]). This discovery initiated numerous studies to identify and quantify light elements in the Earth0s core. Among others, sulphur has been suggested to be a promisingly candidate to alloy with the metallic core because of its depletion in the crust and the mantle relative to other volatile elements by several orders of magnitude (e.g., [3-5]). In the last decades, several experimental studies have aimed to quantify the sulphur content in the Earth's core and to determine its influence on the physical properties (e.g., [6]). However, experimental data on sulphur partitioning between silicate and metallic liquids at pressures and temperatures relevant for core-mantle boundary conditions are missing. This lack is due to pressure and temperature limitations of conventional experimental approaches (up to 25 GPa and 2200 K). New developments, like laser-heated diamond-anvil cells (LDAC), allow studies at core-mantle boundary conditions, but in-situ chemical analysis of sulphur in LDACs is impossible due to the high absorption of S fluorescence in the diamonds. Instead of sulphur, selenium can be used to model sulphur partitioning between silicate and metallic melts at elevated PT conditions. This is based on the fact that sulphur and selenium can be considered as geochemical twins ([7,8]). The main advantage of this approach is the much higher excitation energy of selenium compared to sulphur, which enables in-situ XRF analysis in LDACs. Here, we present preliminary data on Se partitioning between silicate and metallic melt at extreme conditions. The experiments have been performed in double-sided laser-heated LDACs at the high pressure beamlines P02.2 (DESY, Germany) and ID27 (ESRF, France) as described in [9]. Micro-XRF mappings are used to visualise changes of the Se distribution before and after laser heating. Micro-XRD is used to determine the experimental pressure, the onset of melting and also provides information on distribution of high-pressure / high temperature phases (XRD map). In order to fully apply the observed in-situ Se results to the S partitioning, the recovered samples will be additionally analysed ex-situ for Se and S by EMP, SEM and HRTEM. This will also set constraints on the effect of quenching. [1] Birch (1952) J. Geophys. Res. 57, 227-286. [2] McDonough (2003) Treatise on Geochemistry, Vol. 2, pp. 547-568. [3] Manson (1966) Nature 211, 616-618. [4] Rama Murthy and Hall (1970) Phys. Earth. Planet. Inter. 2, 276-282. [5] Dreibus and Palme (1996) Geochim. Cosmochim Acta. 60, 1125-1130. [6] Morard et al. (2008) Earth. Planet Sci Lett. 272, 620-626. [7] Jenner et al. (2009) Geostand. Geoanal. Res. 33, 309-317. [8] Wykes et al. (2010) Ontario Geological Survey, Miscellaneous Release-Data 269. [9] Petitgirard et al. (2012) Rev. Sci. Instrum. 83, 013904.

Magma Chamber of the 26.5 ka Oruanui Eruption, Taupo Volcano, New Zealand

NASA Astrophysics Data System (ADS)

Liu, Y.; Anderson, A. T.; Wilson, C. J.; Davis, A. M.

2004-12-01

We have investigated melt inclusions and their host quartz crystals from the Bishop-Tuff-sized 26.5 ka Oruanui eruption at Taupo volcano, New Zealand. Compositions (major and trace elements, H2O and CO2) of melt inclusions and cathodoluminescence (CL) images of quartz were obtained for eight individual pumices from early, middle and late depositional units. All melt inclusions are high-silica weakly peraluminous rhyolites. Melt inclusions for different eruptive phases have similar ranges of H2O contents (3.8-5.2 wt %), but late-erupted samples have higher CO2 contents (mostly > 140 ppm). A positive correlation between CO2 and compatible trace elements such as Sr suggests that crystallization and melt entrapment occurred under gas-saturated conditions. Trace elements variations in melt inclusions are consistent with fractionation of 30-40 wt % crystals (plagioclase+quartz+pyroxene+amphibole). Crystal contents in pumices, trace-element contents in melt inclusions, and CL zoning patterns of quartz show no correlation with eruptive phases, suggesting that the Oruanui magma was well mixed before eruption. Some Oruanui quartz crystals contain distinctive CL zonings with a jagged ('restitic') core mantled by a black CL zone. Trace element variations in melt inclusions in the 'restitic' cores are consistent with fractionation of Ba-bearing minerals such as sanidine and/or biotite, both of which are rare or absent in rocks erupted from Taupo volcanic center. The above evidence suggests that Oruanui rhyolite is generated by assimilation of previous intruded rocks or country rocks, differentiated by crystal fractionation, and then mixed prior to eruption. Despite the differences in trace element and volatile contents, and crystal assemblages, both Bishop Tuff and Oruanui magmas involve crystal fractionation as one of the main differentiation mechanisms during their evolution. However, there are pronounced differences in the pre-eruptive stratification of the two chambers, which may reflect the tectonic settings, eruption rates, and ages of the systems.

Timing of anatexis and melt crystallization in the Socorro-Guaxupé Nappe, SE Brazil: Insights from trace element composition of zircon, monazite and garnet coupled to Usbnd Pb geochronology

NASA Astrophysics Data System (ADS)

Rocha, B. C.; Moraes, R.; Möller, A.; Cioffi, C. R.; Jercinovic, M. J.

2017-04-01

The timing of partial melting and melt crystallization in granulite facies rocks of the Socorro-Guaxupé Nappe (SGN), Brazil is constrained using a combination of imaging techniques, LA-ICP-MS and EPMA dating, trace element geochemistry and thermobarometry. (Orthopyroxene)-garnet-bearing migmatite that records extensive biotite dehydration melting shows evidence for a clockwise P-T-t path. UHT peak conditions were attained at 1030 ± 110 °C, 11.7 ± 1.4 kbar, with post-peak cooling to 865 ± 38 °C, 8.9 ± 0.8 kbar. Cryogenian igneous inheritance of ca. 720-640 Ma is identified in oscillatory zoned zircon cores (n = 167) with steep HREE patterns. Resorbed, Y-rich monazite cores preserve a prograde growth stage at 631 ± 4 Ma prior to the partial melting event, providing an upper age limit for the granulite facies metamorphism in the SGN. REE-rich, Th-depleted monazite related to apatite records the initial stages of decompression at 628 ± 4 Ma. Multiple monazite growth episodes record melt crystallization events at 624 ± 3 Ma, 612 ± 5 Ma and 608 ± 6 Ma. Stubby, equant "soccer ball" zircon provide evidence for melt crystallization at 613 ± 2 Ma and 607 ± 4 Ma. The excess scatter in zircon and monazite age populations between 629 ± 4 and 601 ± 3 Ma is interpreted as discontinuous and episodic growth within this age range, characterizing a prolonged metamorphic event in the SGN lasting ca. 30 m.y. The development of Y + HREE-rich monazite rims at ca. 600 Ma documents retrograde garnet breakdown, extensive biotite growth and the final stages of melt crystallization. Th-rich, Y + HREE-poor monazite rims at ca. 590 Ma record monazite recrystallization.

Experimental investigation on V isotope equilibrium fractionation factor between metal and silicate melt

NASA Astrophysics Data System (ADS)

Zhang, S.; Zhang, H.; Huang, F.

2017-12-01

Equilibrium fractionation factors of stable isotopes between metal and silicate melt are of vital importance for understanding the isotope variations within meteorites and planetary bodies. The V isotope composition (reported as δ51V = 1000 × [(51V/50Vsample/51V/50VAA)-1] ) of the bulk silicate Earth (BSE) has been estimated as δ51V = -0.7 ± 0.2‰ (2sd) [1], which is significantly heavier than most meteorites by 1‰ [2]. Such isotopic offset may provide insights for the core formation and core-mantle segregation. Therefore, it is important to understand V isotope equilibrium fractionation factor between silicate melt and metal. Nielsen et al. (2014) [2] had performed 3 experiments using starting materials of pure Fe metal and An50Di28Fo22 composition, revealing no resolvable V isotope fractionation. However, it is not clear whether chemical compositions in the melts can affect V isotope fractionations. Therefore, we experimentally calibrated equilibrium V isotope fractionation between Fe metallic and basaltic melt, with particular focus on the effect of Ni and other light elements. Experiments were performed at 1 GPa and 1600 oC using a 3/4″ end-loaded piston cylinder. The starting materials consisted of 1:1 mixture of pure Fe metal and basaltic composition [3]. The isotope equilibrium was assessed using time series experiments combined with the reverse reaction method. Carbon saturation and C-free experiments were achieved by using graphite and silica capsules, respectively. The Ni series experiments were doped with 6 wt% Ni into the starting Fe metal. The metal and silicate phases of samples were mechanically separated, V was purified using a chromatographic technique, and V isotope ratios were measured using MC-ICP-MS [4]. Carbon saturation, C-free experiments and Ni series experiment all show non-resolvable V isotope fractionation between metal and basaltic melt, which indicates that the presence of C and Ni could not affect V isotope fractionation during core formation. More experiments will be performed to explore the effect of Si and S in the metal on V isotope fractionation between metal and silicate melt.References: [1] Prytulak et al. (2013) EPSL 365, 177-189 [2] Nielsen et al. (2014) EPSL 389, 167-175 [3] Cottrell et al. (2009) CG 268, 167-179 [4] Wu et al. (2016) CG 421, 17-25

Petrology of the Yamato nakhlites

NASA Astrophysics Data System (ADS)

Imae, N.; Ikeda, Y.; Kojima, H.

2005-11-01

The Yamato nakhlites, Y-000593, Y-000749, and Y-000802, were recovered in 2000 from the bare icefield around the Yamato mountains in Antarctica, consisting of three independent specimens with black fusion crusts. They are paired cumulate clinopyroxenites. We obtained the intercumulus melt composition of the Yamato nakhlites and here call it the Yamato intercumulus melt (YIM). The YIM crystallized to form the augite rims, the olivine rims and the mesostasis phases in the cumulates. The augite rims consist of two layers: inner and outer. The crystallization of the inner rim drove the interstitial melt into the plagioclase liquidus field. Subsequently, the residual melt crystallized pigeonites and plagioclase to form the outer rims and the mesostasis.Three types of inclusions were identified in olivine phenocrysts: rounded vitrophyric, angular vitrophyric, and monomineralic augite inclusions. The monomineralic augite inclusions are common and may have been captured by growing olivine phenocrysts. The rounded vitrophyric inclusions are rare and may represent the composition of middle-stage melts, whereas the angular vitrophyric inclusions seem to have been derived from fractionated late-stage melts. Glass inclusions occur in close association with titanomagnetite and ferroan augite halo in phenocryst core augites and the assemblages may be magmatic inclusions in augites. We compared the YIM with compositions of magmatic inclusions in olivine and augite. The composition of magmatic inclusions in augite is similar to the YIM.Phenocrystic olivines contain exsolution lamellae, augite-magnetite aggregates, and symplectites in the cores. The symplectites often occur at the boundaries between olivine and augite grains. The aggregates, symplectite and lamellae formed by exsolution from the host olivine at magmatic temperatures.We present a formational scenario for nakhlites as follows: (1) accumulation of augite, olivine, and titanomagnetite phenocrysts took place on the floor of a magma chamber; (2) olivine exsolved augite and magnetite as augite-magnetite aggregates, symplectites and lamellae; (3) the overgrowth on olivine phenocrysts formed their rims, and the inner rims crystallized on augite phenocryst cores; and finally, (4) the outer rim formed surrounding the inner rims of augite phenocrysts, and plagioclase and minor minerals crystallized to form mesostasis under a rapid cooling condition, probably in a lava flow or a sill.

Geophysical evidence for melt in the deep lunar interior and implications for lunar evolution (Invited)

NASA Astrophysics Data System (ADS)

Khan, A.; Connolly, J. A.; Pommier, A.

2013-12-01

Analysis of lunar seismic and lunar laser ranging data has yielded evidence that has been interpreted to indicate a molten zone in the lower-most mantle and/or the outer core of the Moon. Such a zone would provide strong constraints on models of the thermal evolution of the Moon. Here we invert lunar geophysical data in combination with phase-equilibrium modeling to derive information about the thermo-chemical and physical structure of the deep lunar interior. Specifically, we assess whether a molten layer is required by the geophysical data and, if so, its likely composition and physical properties (e.g., density and seismic wave speeds). The data considered are mean mass and moment of inertia, second-degree tidal Love number, and frequency-dependent electromagnetic sounding data. The main conclusion drawn from this study is that a region with high dissipation located deep within the Moon is indeed required to explain the geophysical data. If this dissipative region is located within the mantle, then the solidus is crossed at a depth of ~1200 km (>1600 deg C). The apparent absence of far-side deep moonquakes (DMQs) is supporting evidence for a highly dissipative layer. Inverted compositions for the partially molten layer (typically 100--200 km thick) are enriched in FeO and TiO2 relative to the surrounding mantle. While the melt phase in >95 % of inverted models is neutrally buoyant at pressures of ~4.5--4.6 GPa, the melt contains less TiO2 (>~4 wt %) than the Ti-rich (~16 wt % TiO2) melts that produced a set of high-density primitive lunar magmas (~3.4 g/ccm). Melt densities computed here range from 3.3 to 3.4 g/ccm bracketing the density of lunar magmas with moderate-to-high TiO2 contents. Our results are consistent with a model of lunar evolution in which the cumulate pile formed from crystallization of the magma ocean as it overturned, trapping heat-producing elements in the lower mantle.

Research into the rationality and the application scopes of different melting models of nanoparticles

NASA Astrophysics Data System (ADS)

Fu, Qingshan; Xue, Yongqiang; Cui, Zixiang; Duan, Huijuan

2017-07-01

A rational melting model is indispensable to address the fundamental issue regarding the melting of nanoparticles. To ascertain the rationality and the application scopes of the three classical thermodynamic models, namely Pawlow, Rie, and Reiss melting models, corresponding accurate equations for size-dependent melting temperature of nanoparticles were derived. Comparison of the melting temperatures of Au, Al, and Sn nanoparticles calculated by the accurate equations with available experimental results demonstrates that both Reiss and Rie melting models are rational and capable of accurately describing the melting behaviors of nanoparticles at different melting stages. The former (surface pre-melting) is applicable to the stage from initial melting to critical thickness of liquid shell, while the latter (solid particles surrounded by a great deal of liquid) from the critical thickness to complete melting. The melting temperatures calculated by the accurate equation based on Reiss melting model are in good agreement with experimental results within the whole size range of calculation compared with those by other theoretical models. In addition, the critical thickness of liquid shell is found to decrease with particle size decreasing and presents a linear variation with particle size. The accurate thermodynamic equations based on Reiss and Rie melting models enable us to quantitatively and conveniently predict and explain the melting behaviors of nanoparticles at all size range in the whole melting process. [Figure not available: see fulltext.

Early evolution of the Earth: Accretion, atmosphere formation, and thermal history

NASA Astrophysics Data System (ADS)

Abe, Yutaka; Matsui, Takafumi

1986-03-01

Atmospheric and thermal evolution of the earth growing by planetesimal impacts was modeled by taking into account the blanketing effect of an impact-induced H2O atmosphere and the temperature dependence of H2O degassing. When the water content of planetesimals is larger than 0.1% by weight and the accretion time of the earth is less than 5 × 107 years, the surface of the accreting earth melts and thus a “magma ocean” forms and covers the surface. The formation of a “magma ocean” will result in the initiation of core-mantle separation and mantle differentiation during accretion. Once a magma ocean is formed, the surface temperature, the degree of melting in the magma ocean, and the mass of the H2O atmosphere are nearly constant as the protoplanet grows further. The final mass of the H2O atmosphere is about 1021 kg, a value which is insensitive to variations in the model parameter values such as the accretion time and the water content of planetesimals. That the final mass of the H2O atmosphere is close to the mass of the present oceans suggests an impact origin for the earth's hydrosphere. On the other hand, most of the H2O retained in planetesimals will be deposited in the solid earth. Free water within the proto-earth may affect differentiation of the proto-mantle, in particular, the mantle FeO abundance and the incorporation of a light element in the outer core.

Thermo-Physics Technical Note No. 60: thermal analysis of SNAP 10A reactor core during atmospheric reentry and resulting core disintegration and fuel element separation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mouradian, E.M.

1966-02-16

A thermal analysis is carried out to determine the temperature distribution throughout a SNAP 10A reactor core, particularly in the vicinity of the grid plates, during atmospheric reentry. The transient temperatue distribution of the grid plate indicates when sufficient melting occurs so that fuel elements are free to be released and continue their descent individually.

Viscosity of the earth's core.

NASA Technical Reports Server (NTRS)

Gans, R. F.

1972-01-01

Calculation of the viscosity of the core at the boundary of the inner and outer core. It is assumed that this boundary is a melting transition and the viscosity limits of the Andrade (1934,1952) hypothesis (3.7 to 18.5 cp) are adopted. The corresponding kinematic viscosities are such that the precessional system explored by Malkus (1968) would be unstable. Whether it would be sufficiently unstable to overcome a severely subadiabatic temperature gradient cannot be determined.

Plastic deformation of FeSi at high pressures: implications for planetary cores

NASA Astrophysics Data System (ADS)

Kupenko, Ilya; Merkel, Sébastien; Achorner, Melissa; Plückthun, Christian; Liermann, Hanns-Peter; Sanchez-Valle, Carmen

2017-04-01

The cores of terrestrial planets is mostly comprised of a Fe-Ni alloy, but it should additionally contain some light element(s) in order to explain the observed core density. Silicon has long been considered as a likely candidate because of geochemical and cosmochemical arguments: the Mg/Si and Fe/Si ratios of the Earth does not match those of the chondrites. Since silicon preferentially partition into iron-nickel metal, having 'missing' silicon in the core would solve this problem. Moreover, the evidence of present (e.g. Mercury) or ancient (e.g. Mars) magnetic fields on the terrestrial planets is a good indicator of (at least partially) liquid cores. The estimated temperature profiles of these planets, however, lay below iron melting curve. The addition of light elements in their metal cores could allow reducing their core-alloy melting temperature and, hence, the generation of a magnetic field. Although the effect of light elements on the stability and elasticity of Fe-Ni alloys has been widely investigated, their effect on the plasticity of core materials remains largely unknown. Yet, this information is crucial for understanding how planetary cores deform. Here we investigate the plastic deformation of ɛ-FeSi up to 50 GPa at room temperature employing a technique of radial x-ray diffraction in diamond anvil cells. Stoichiometric FeSi endmember is a good first-order approximation of the Fe-FeSi system and a good starting material to develop new experimental perspectives. In this work, we focused on the low-pressure polymorph of FeSi that would be the stable phase in the cores of small terrestrial planets. We will present the analysis of measured data and discuss their potential application to constrain plastic deformation in planetary cores.

Scrap melting model for steel converter founded on interfacial solid/liquid phenomena

NASA Astrophysics Data System (ADS)

Kruskopf, Ari; Holappa, Lauri

2017-12-01

The primary goal in steel converter operation is the removal of carbon from the hot metal. This is achieved by blowing oxygen into the melt. The oxidation of carbon produces a lot of heat. To avoid too high temperatures in the melt cold scrap (recycled steel) is charged into the converter. The melting rate is affected by heat and carbon mass transfer. A process model for steel converter is in development. This model is divided into several modules, which are fluid dynamics, heat- and mass-transfer, scrap melting and chemical reactions. This article focuses on the development of the scrap melting module. A numerical model for calculating temperature and carbon concentration in the melt is presented. The melt model is connected with the solid scrap model via solid/liquid interface. The interface model can take into account solidification of iron melt, melting of solidified layer, a situation without such phase changes, and scrap melting. The aim is to predict the melting rate of the scrap including the properties of the hot metal. The model is tested by calculating the melting rates for different scrap thicknesses. All of the stages in the interface model were taking place in the test calculations.

The extreme melt across the Greenland ice sheet in 2012

NASA Astrophysics Data System (ADS)

Nghiem, S. V.; Hall, D. K.; Mote, T. L.; Tedesco, M.; Albert, M. R.; Keegan, K.; Shuman, C. A.; DiGirolamo, N. E.; Neumann, G.

2012-10-01

The discovery of the 2012 extreme melt event across almost the entire surface of the Greenland ice sheet is presented. Data from three different satellite sensors - including the Oceansat-2 scatterometer, the Moderate-resolution Imaging Spectroradiometer, and the Special Sensor Microwave Imager/Sounder - are combined to obtain composite melt maps, representing the most complete melt conditions detectable across the ice sheet. Satellite observations reveal that melt occurred at or near the surface of the Greenland ice sheet across 98.6% of its entire extent on 12 July 2012, including the usually cold polar areas at high altitudes like Summit in the dry snow facies of the ice sheet. This melt event coincided with an anomalous ridge of warm air that became stagnant over Greenland. As seen in melt occurrences from multiple ice core records at Summit reported in the published literature, such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the Medieval Warm Period. Given its rarity, the 2012 extreme melt across Greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research.

REE and Isotopic Compositions of Lunar Basalts Demonstrate Partial Melting of Hybridized Mantle Sources after Cumulate Overturn is Required

NASA Astrophysics Data System (ADS)

Dygert, N. J.; Liang, Y.

2017-12-01

Lunar basalts maintain an important record of the composition of the lunar interior. Much of our understanding of the Moon's early evolution comes from studying their petrogenesis. Recent experimental work has advanced our knowledge of major and trace element fractionation during lunar magma ocean (LMO) crystallization [e.g., 1-3], which produced heterogeneous basalt sources in the Moon's mantle. With the new experimental constraints, we can evaluate isotopic and trace element signatures in lunar basalts in unprecedented detail, refining inferences about the Moon's dynamic history. Two petrogenetic models are invoked to explain the compositions of the basalts. The assimilation model argues they formed as primitive melts of early LMO cumulates that assimilated late LMO cumulates as they migrated upward. The cumulate overturn model argues that dense LMO cumulates sank into the lunar interior, producing hybridized sources that melted to form the basalts. Here we compare predicted Ce/Yb and Hf and Nd isotopes of partial melts of LMO cumulates with measured compositions of lunar basalts to evaluate whether they could have formed by end-member petrogenetic models. LMO crystallization models suggest all LMO cumulates have chondrite normalized Ce/Yb <1. Residual liquid from the magma ocean has Ce/Yb 1.5. Many primitive lunar basalts have Ce/Yb>1.5; these could not have formed by assimilation of any LMO cumulate or residual liquid (or KREEP basalt, which has isotopically negative ɛNd and ɛHf). In contrast, basalt REE patterns and isotopes can easily be modeled assuming partial melting of hybridized mantle sources, indicating overturn may be required. A chemical requirement for overturn independently confirms that late LMO cumulates are sufficiently low in viscosity to sink into the lunar interior, as suggested by recent rock deformation experiments [4]. Overturned, low viscosity late LMO cumulates would be relatively stable around the core [5]. High Ce/Yb basalts require that overturned cumulates were mixed back into the overlying mantle by convection within a few hundred Myr. [1] Dygert et al. (2014), GCA 132, 170-186. [2] Sun et al. (2017), GCA 206, 273-295. [3] Lin et al. (2017), EPSL 471, 104-116. [4] Dygert et al. (2016), GRL 43, 10.1002/2015GL066546. [5] Zhang et al. (2017), GRL 44, 10.1002/2017GL073702.

Sulfur concentration of mare basalts at sulfide saturation at high pressures and temperatures-Implications for S in the lunar mantle

NASA Astrophysics Data System (ADS)

Ding, S.; Hough, T.; Dasgupta, R.

2016-12-01

Low estimate of S in the bulk silicate moon (BSM) [e.g., 1] suggests that sulfide in the lunar mantle is likely exhausted during melting. This agrees with estimates of HSE depletion in the BSM [2], but challenges the S-rich core proposed by previous studies [e.g., 3]. A key parameter to constrain the fate of sulfide during mantle melting is the sulfur carrying capacity of the mantle melts (SCSS). However, the SCSS of variably high-Ti lunar basalts at high P-Tare unknown. Basalt-sulfide melt equilibria experiments were run in graphite capsules using a piston cylinder at 1.0-2.5 GPa and 1400-1600 °C, on high-Ti (Apollo11, 11.1 wt.%; [4]) and intermediate-Ti (Luna16, 5 wt.%; [5]) mare basalts. At 1.5 GPa, SCSS of Apollo11 increases from 3940 ppm S to 5860 ppm, as temperature increases from 1400 °C to 1600 °C. And at 1500 °C, SCSS decreases from 5350 ppm S to 3830 ppm, as pressure increases from 1 to 2.5 GPa. SCSS of Luna16 shows a similar P-T dependence. Previous models [e.g., 6] tend to overestimate the SCSS values determined in our study, with the model overprediction increasing with increasing melt TiO2. Consequently, we derive a new SCSS parameterization for high-FeO* silicate melts of variable TiO2content. At multiple saturation points [e.g., 7], the SCSS of primary lunar melts is 3500-5500 ppm. With these values, 0.02-0.05 wt.% sulfide (70-200 ppm S) in the mantle can be consumed by 2-6% melting. In order to generate primary lunar basalts with S of 800-1000 ppm [1], sulfide in the mantle must be exhausted, and the mode of sulfide cannot exceed 0.025 wt.% (100 ppm S). This estimate corresponds with lower end values in the terrestrial mantle and further agrees with previous calculations of HSE depletion in the BSM [2]. [1] Hauri et al.,2015, EPSL; [2] Day et al.,2007, Science; [3] Jing et al., 2014, EPSL; [4] Synder et al.,1992, GCA; [5] Warren & Taylor, 2014, Treatise on Geochemistry; [6] Li & Ripley, 2009, Econ.Geol ; [7] Krawczynski & Grove, 2012, GCA.

Mantle Water Contents Beneath the Rio Grande Rift (NM, USA): FTIR Analysis of Rio Puerco and Kilbourne Hole Peridotite Xenoliths

NASA Technical Reports Server (NTRS)

Schaffer, L. A.; Peslier, A. H.; Brandon, A.; Selverstone, J.

2015-01-01

Peridotite xenoliths from the Rio Grande Rift (RGR) are being analyzed for H (sub 2) O contents by FTIR (Fourier Transform Infrared) as well as for major and trace element compositions. Nine samples are from the Rio Puerco Volcanic Field (RP) which overlaps the central RGR and southeastern Colorado Plateau; seventeen samples are from Kilbourne Hole (KH) in the southern RGR. Spinel Cr# (Cr/(Cr+Al)) (0.08-0.46) and olivine Mg# (Mg/(Mg plus Fe)) (0.883-0.911) of all RGR samples fall within the olivine-spinel mantle array from [1], an indicator that peridotites are residues of partial melting. Pyroxene H (sub 2) O in KH correlate with bulk rock and pyroxene Al (sub 2) O (sub 3).The KH clinopyroxene rare earth element (REE) variations fit models of 0-13 percent fractional melting of a primitive upper mantle. Most KH peridotites have bulk-rock light REE depleted patterns, but five are enriched in light REEs consistent with metasomatism. Variation in H (sub 2) O content is unrelated to REE enrichment. Metasomatism is seen in RP pyroxenite xenoliths [2] and will be examined in the peridotites studied here. Olivine H (sub 2) O contents are low (less than or equal to 15 parts per million), and decrease from core to rim within grains. This is likely due to H loss during xenolith transport by the host magma [3]. Diffusion models of H suggest that mantle H (sub 2) O contents are still preserved in cores of KH olivine, but not RP olivine. The average H (sub 2) O content of Colorado Plateau clinopyroxene (670 parts per million) [4] is approximately 300 parts per million higher than RGR clinopyroxene (350 parts per million). This upholds the hypothesis that hydration-induced lithospheric melting occurred during flat-slab subduction of the Farallon plate [5]. Numerical models indicate hydration via slab fluids is possible beneath the plateau, approximately 600 kilometers from the paleo-trench, but less likely approximately 850 kilometers away beneath the rift [6].

Earth's inner core nucleation paradox

NASA Astrophysics Data System (ADS)

Huguet, Ludovic; Van Orman, James A.; Hauck, Steven A.; Willard, Matthew A.

2018-04-01

The conventional view of Earth's inner core is that it began to crystallize at Earth's center when the temperature dropped below the melting point of the iron alloy and has grown steadily since that time as the core continued to cool. However, this model neglects the energy barrier to the formation of the first stable crystal nucleus, which is commonly represented in terms of the critical supercooling required to overcome the barrier. Using constraints from experiments, simulations, and theory, we show that spontaneous crystallization in a homogeneous liquid iron alloy at Earth's core pressures requires a critical supercooling of order 1000 K, which is too large to be a plausible mechanism for the origin of Earth's inner core. We consider mechanisms that can lower the nucleation barrier substantially. Each has caveats, yet the inner core exists: this is the nucleation paradox. Heterogeneous nucleation on a solid metallic substrate tends to have a low energy barrier and offers the most straightforward solution to the paradox, but solid metal would probably have to be delivered from the mantle and such events are unlikely to have been common. A delay in nucleation, whether due to a substantial nucleation energy barrier, or late introduction of a low energy substrate, would lead to an initial phase of rapid inner core growth from a supercooled state. Such rapid growth may lead to distinctive crystallization texturing that might be observable seismically. It would also generate a spike in chemical and thermal buoyancy that could affect the geomagnetic field significantly. Solid metal introduced to Earth's center before it reached saturation could also provide a nucleation substrate, if large enough to escape complete dissolution. Inner core growth, in this case, could begin earlier and start more slowly than standard thermal models predict.

Study of the preparation of Cu-TiC composites by reaction of soluble Ti and ball-milled carbon coating TiC

NASA Astrophysics Data System (ADS)

Xu, Xuexia; Li, Wenbin; Wang, Yong; Dong, Guozhen; Jing, Shangqian; Wang, Qing; Feng, Yanting; Fan, Xiaoliang; Ding, Haimin

2018-06-01

In this work, Cu-TiC composites have been successfully prepared by reaction of soluble Ti and carbon coating TiC. Firstly, the ball milling of graphite and TiC mixtures is used to obtain the carbon coating TiC which has fine size and improved reaction activity. After adding the ball milled carbon coating TiC into Cu-Ti melts, the soluble Ti will easily react with the carbon coating to form TiC. This process will also improve the wettability between Cu melts and TiC core. As a result, besides the TiC prepared by reaction of soluble Ti and carbon coating, the ball milled TiC will also be brought into the melts. Some of these ball-milled TiC particles will go on being coated by the formed TiC from the reaction of Ti and the coating carbon and left behind in the composites. However, most of TiC core will be further reacted with the excessive Ti and be transformed into the newly formed TiC with different stoichiometry. The results indicate that it is a feasible method to synthesize TiC in Cu melts by reaction of soluble Ti and ball-milled carbon coating TiC.

Spinnability and Characteristics of Polyvinylidene Fluoride (PVDF)-based Bicomponent Fibers with a Carbon Nanotube (CNT) Modified Polypropylene Core for Piezoelectric Applications

PubMed Central

Glauß, Benjamin; Steinmann, Wilhelm; Walter, Stephan; Beckers, Markus; Seide, Gunnar; Gries, Thomas; Roth, Georg

2013-01-01

This research explains the melt spinning of bicomponent fibers, consisting of a conductive polypropylene (PP) core and a piezoelectric sheath (polyvinylidene fluoride). Previously analyzed piezoelectric capabilities of polyvinylidene fluoride (PVDF) are to be exploited in sensor filaments. The PP compound contains a 10 wt % carbon nanotubes (CNTs) and 2 wt % sodium stearate (NaSt). The sodium stearate is added to lower the viscosity of the melt. The compound constitutes the fiber core that is conductive due to a percolation CNT network. The PVDF sheath’s piezoelectric effect is based on the formation of an all-trans conformation β phase, caused by draw-winding of the fibers. The core and sheath materials, as well as the bicomponent fibers, are characterized through different analytical methods. These include wide-angle X-ray diffraction (WAXD) to analyze crucial parameters for the development of a crystalline β phase. The distribution of CNTs in the polymer matrix, which affects the conductivity of the core, was investigated by transmission electron microscopy (TEM). Thermal characterization is carried out by conventional differential scanning calorimetry (DSC). Optical microscopy is used to determine the fibers’ diameter regularity (core and sheath). The materials’ viscosity is determined by rheometry. Eventually, an LCR tester is used to determine the core’s specific resistance. PMID:28811400

Equation of state and phase diagram of Fe-16Si alloy as a candidate component of Earth's core

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fischer, Rebecca A; Campbell, Andrew J; Caracas, Razvan

2016-07-29

The outer core of the Earth contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is critical to understand the high pressure–temperature properties and behavior of an iron–silicon alloy with a geophysically relevant composition (16 wt% silicon). We experimentally determined the melting curve, subsolidus phase diagram, and equations of state of all phases of Fe–16 wt%Si to 140 GPa, finding a conversion from the D0 3 crystal structure to a B2+hcp mixture at high pressures. The melting curve implies that 3520 K is a minimum temperature for the Earth's outer core, ifmore » it consists solely of Fe–Si alloy, and that the eutectic composition in the Fe–Si system is less than 16 wt% silicon at core–mantle boundary conditions. Comparing our new equation of state to that of iron and the density of the core, we find that for an Fe–Ni–Si outer core, 11.3±1.5 wt% silicon would be required to match the core's observed density at the core–mantle boundary. We have also performed first-principles calculations of the equations of state of Fe 3Si with the D0 3 structure, hcp iron, and FeSi with the B2 structure using density-functional theory.« less

Release of PCBs from Silvretta glacier (Switzerland) investigated in lake sediments and meltwater.

PubMed

Pavlova, P A; Zennegg, M; Anselmetti, F S; Schmid, P; Bogdal, C; Steinlin, C; Jäggi, M; Schwikowski, M

2016-06-01

This study is part of our investigations about the release of persistent organic pollutants from melting Alpine glaciers and the relevance of the glaciers as secondary sources of legacy pollutants. Here, we studied the melt-related release of polychlorinated biphenyls (PCBs) in proglacial lakes and glacier streams of the catchment of the Silvretta glacier, located in the Swiss Alps. To explore a spatial and temporal distribution of chemicals in glacier melt, we combined two approaches: (1) analysing a sediment record as an archive of past remobilization and (2) passive water sampling to capture the current release of PCBs during melt period. In addition, we determined PCBs in a non-glacier-fed stream as a reference for the background pollutant level in the area. The PCBs in the sediment core from the Silvretta lake generally complied with trends of PCB emissions into the environment. Elevated concentrations during the most recent ten years, comparable in level with times of the highest atmospheric input, were attributed to accelerated melting of the glacier. This interpretation is supported by the detected PCB fractionation pattern towards heavier, less volatile congeners, and by increased activity concentrations of the radioactive tracer (137)Cs in this part of the sediment core. In contrast, PCB concentrations were not elevated in the stream water, since no significant difference between pollutant concentrations in the glacier-fed and the non-glacier-fed streams was detected. In stream water, no current decrease of the PCBs with distance from the glacier was observed. Thus, according to our data, an influence of PCBs release due to accelerated glacier melt was only detected in the proglacial lake, but not in the other compartments of the Silvretta catchment.

Siderophile Element Constraints on the Conditions of Core Formation in Mars

NASA Technical Reports Server (NTRS)

Righter, K.; Humayun, M.

2012-01-01

Siderophile element concentrations in planetary basalts and mantle samples have been used to estimate conditions of core formation for many years and have included applications to Earth, Moon, Mars and asteroid 4 Vesta [1]. For Earth, we have samples of mantle and a diverse collection of mantle melts which have provided a mature understanding of the how to reconstruct the concentration of siderophile elements in mantle materials, from only concentrations in surficial basalt (e.g., [2]). This approach has led to the consensus views that Earth underwent an early magma ocean stage to pressures of 40-50 GPa (e.g., [3,4]), Moon melted extensively and formed a small (approx. 2 mass %) metallic core [5], and 4 Vesta contains a metallic core that is approximately 18 mass % [6,7]. Based on new data from newly found meteorites, robotic spacecraft, and experimental partitioning studies, [8] showed that eight siderophile elements (Ni, Co, Mo, W, Ga, P, V and Cr) are consistent with equilibration of a 20 mass% S-rich metallic core with the mantle at pressures of 14 +/- 3 GPa. We aim to test this rather simple scenario with additional analyses of meteorites for a wide range of siderophile elements, and application of new experimental data for the volatile siderophile and highly siderophile elements.

Synchronous partial melting, deformation, and magmatism: evidence from in an exhumed Proterozoic orogen

NASA Astrophysics Data System (ADS)

Levine, J. S. F.; Mosher, S.

2017-12-01

Older orogenic belts that now expose the middle and lower crust record interaction between partial melting, magmatism, and deformation. A field- and microstructural-based case study from the Wet Mountains of central Colorado, an exhumed section of Proterozoic rock, shows structures associated with anatexis and magmatism, from the grain- to the kilometer-scale, that indicate the interconnection between deformation, partial melting, and magmatism, and allow reconstructions of the processes occurring in hot active orogens. Metamorphic grade, along with the degree of deformation, partial melting, and magmatism increase from northwest to southeast. Deformation synchronous with this high-grade metamorphic event is localized into areas with greater quantities of former melt, and preferential melting occurs within high-strain locations. In the less deformed northwest, partial melting occurs dominantly via muscovite-dehydration melting, with a low abundance of partial melting, and an absence of granitic magmatism. The central Wet Mountains are characterized by biotite dehydration melting, abundant former melt and foliation-parallel inferred melt channels along grain boundaries, and the presence of a nearby granitic pluton. Rocks in the southern portion of the Wet Mountains are characterized by partial melting via both biotite dehydration and granitic wet melting, with widespread partial melting as evidenced by well-preserved former melt microstructures and evidence for back reaction between melt and the host rocks. The southern Wet Mountains has more intense deformation and widespread plutonism than other locations and two generations of dikes and sills. Recognition of textures and fabrics associated with partial melting in older orogens is paramount for interpreting the complex interplay of processes occurring in the cores of orogenic systems.

Ureilite petrogenesis: A limited role for smelting during anatexis and catastrophic disruption

NASA Astrophysics Data System (ADS)

Warren, Paul H.; Huber, Heinz

2006-06-01

A popular model for ureilites assumes that during anatexis in an asteroidal mantle, pressure-buffered equilibrium smelting (partial reduction coincident with partial melting) engendered their conspicuous mafic-silicate-core mg diversity (75-96 mol%). Several mass-balance problems arise from this hypothesis. Smelting inevitably consumes a large proportion of any plausible initial carbon while generating significant proportions of Fe metal and copious proportions of CO gas. The most serious problem concerns the yield of CO gas. If equilibrium smelting produced the ureilites' entire 21 mol% range in olivine-core mg, the proportion of gas within the asteroidal mantle (assuming plausibly low pressure <˜80 bar) should have reached ≥85 vol%. Based on the remarkably stepwise cooling history inferred from ureilite texture and mineralogy, a runaway, CO-leaky process that can loosely be termed smelting appears to have occurred, probably triggered by a major impact. The runaway scenario appears likely because, by Le Châtelier's principle, CO leakage would tend to accelerate the smelting process. Also, the copious volumes of gas produced by smelting would have led to explosive, mass-leaky eruptions into the vacuum surrounding the asteroid. Loss of mass would mean diminution of interior pressure, which would induce further smelting, leading to further loss of mass (basalt), and so on. Such a disruptive runaway process may have engendered the ureilites' distinctive reduced olivine rims. But the only smelting, according to this scenario, was a short-lived disequilibrium process that reduced only the olivine rims, not the cores; and the ureilites were cooling, not melting, during the abortive "smelting" episode.

Taxon interactions control the distributions of cryoconite bacteria colonizing a High Arctic ice cap.

PubMed

Gokul, Jarishma K; Hodson, Andrew J; Saetnan, Eli R; Irvine-Fynn, Tristram D L; Westall, Philippa J; Detheridge, Andrew P; Takeuchi, Nozomu; Bussell, Jennifer; Mur, Luis A J; Edwards, Arwyn

2016-08-01

Microbial colonization of glacial ice surfaces incurs feedbacks which affect the melting rate of the ice surface. Ecosystems formed as microbe-mineral aggregates termed cryoconite locally reduce ice surface albedo and represent foci of biodiversity and biogeochemical cycling. Consequently, greater understanding the ecological processes in the formation of functional cryoconite ecosystems upon glacier surfaces is sought. Here, we present the first bacterial biogeography of an ice cap, evaluating the respective roles of dispersal, environmental and biotic filtration occurring at local scales in the assembly of cryoconite microbiota. 16S rRNA gene amplicon semiconductor sequencing of cryoconite colonizing a Svalbard ice cap coupled with digital elevation modelling of physical parameters reveals the bacterial community is dominated by a ubiquitous core of generalist taxa, with evidence for a moderate pairwise distance-decay relationship. While geographic position and melt season duration are prominent among environmental predictors of community structure, the core population of taxa appears highly influential in structuring the bacterial community. Taxon co-occurrence network analysis reveals a highly modular community structured by positive interactions with bottleneck taxa, predominantly Actinobacteria affiliated to isolates from soil humus. In contrast, the filamentous cyanobacterial taxon (assigned to Leptolyngbya/Phormidesmis pristleyi) which dominates the community and binds together granular cryoconite are poorly connected to other taxa. While our study targeted one ice cap, the prominent role of generalist core taxa with close environmental relatives across the global cryosphere indicate discrete roles for cosmopolitan Actinobacteria and Cyanobacteria as respective keystone taxa and ecosystem engineers of cryoconite ecosystems colonizing ice caps. © 2016 John Wiley & Sons Ltd.

Crystallization in Micellar Cores: confinement effects and dynamics

NASA Astrophysics Data System (ADS)

Lund, Reidar; Zinn, Thomas; Willner, Lutz; Department of Chemistry, University of Oslo Team; Forschungszentrum Jülich Collaboration

It is well known that liquids confined to small nanoscopic pores and droplets exhibit thermal behavior very different from bulk samples. Here we demonstrate that n-alkanes forming 2-3 nm small micellar cores are considerably affected by confinement in analogue with hard confined systems. We study micelles form by self-assembly of a series of well-defined n-Alkyl-PEO polymers in aqueous solutions. By using small-angle X-ray scattering (SAXS), densiometry and differential scanning calorimetry (DSC), we show that n-alkane exhibit a first-order phase transition i.e. melting. Correlating the structural and thermodynamic data, we find that a melting depression can be accurately described by the Gibbs-Thomson equation. ∖f1 The effect of core crystallinity on the molecular exchange kinetics is investigated using time-resolved small-angle neutron scattering (TR-SANS). We show that there are considerable entropic and enthalpic contributions from the chain packing that affect the kinetic stability of micelles. ∖pard

Electrical breakdown and nanogap formation of indium oxide core/shell heterostructure nanowires.

PubMed

Jung, Minkyung; Song, Woon; Sung Lee, Joon; Kim, Nam; Kim, Jinhee; Park, Jeunghee; Lee, Hyoyoung; Hirakawa, Kazuhiko

2008-12-10

We report the electrical breakdown behavior and subsequent nanogap formation of In(2)O(3)/InO(x) core/shell heterostructure nanowires with substrate-supported and suspended structures. The radial heterostructure nanowires, composed of crystalline In(2)O(3) cores and amorphous In-rich shells, are grown by chemical vapor deposition. As the nanowires broke down, they exhibited two distinct current drops in the current-voltage characteristics. The tips of the broken nanowires were found to have a cone or a volcano shape depending on the width of the nanowire. The shape, the size, and the position of the nanogap depend strongly on the device structure and the nanowire dimensions. The substrate-supported and the suspended devices exhibit distinct breakdown behavior which can be explained by the diffusive thermal transport model. The breakdown temperature of the nanowire is estimated to be about 450 K, close to the melting temperature of indium. We demonstrated the usefulness of this technique by successful fabrication of working pentacene field-effect transistors.

Viscosity and Structure of a Late Lunar Magma Ocean Liquid: Implications for the Purity of Ferroan Anorthosites and the Dynamics of a Crystallizing Magma Ocean

NASA Astrophysics Data System (ADS)

Dygert, N. J.; Lin, J. F.; Marshall, E. W., IV; Kono, Y.; Gardner, J. E.

2016-12-01

The current paradigm argues the Moon formed after a giant impact that produced a deep lunar magma ocean (LMO). After a period of turbulent convection, the LMO experienced fractional crystallization, causing the initially peridotitic liquid to evolve to a plagioclase-saturated ferrobasalt. The lunar crust, much of which comprises 93-98% pure anorthosite [1,2], formed by flotation of positively buoyant plagioclase on the residual liquid. A flotation crust would contain some trapped melt; compaction of the melt out of the crust before solidification may be necessary to generate a very pure anorthitic crust. The efficiency of this process depends on the previously unmeasured viscosity of the residual liquid [3]. To characterize the viscosity and thermal equation of state of a late LMO liquid, we conducted experiments at the Advanced Photon Source, Beamline 16-BM-B, Argonne National Laboratory on a nominally anhydrous Ti-rich ferrobasalt [4]. X-ray radiography and diffuse scattering experiments were conducted in a Paris-Edinburgh apparatus in graphite-lined BN capsules, allowing in-situ observation of viscosity and derivation of thermal EoS at P-T conditions relevant to the Moon (1300-1600°C, 0.1-4.4GPa). We calculated viscosities of 0.23-1.45 Pa·s for the melt; based on 11 observations, we find that viscosity is pressure insensitive under the conditions explored. Viscosity can be modeled by an Arrhenius relation with an activation enthalpy of 66 kJ/mol. Composition-dependent predictive models [5] overestimate our observations by roughly a factor of 2. Preliminary analysis suggests no pressure-dependent structural transition over the conditions explored. Late LMO liquids brought to the lunar core-mantle boundary by cumulate mantle overturn may be positively buoyant, implying the seismically attenuating layer around the lunar core contains a denser, higher-Ti melt. Our results suggest that efficient phase segregation in the lunar magma ocean and compaction in the anorthositic flotation crust can produce a high-purity crust under physically reasonable conditions. [1] Warren (1990), AmMin 75, 46-58. [2] Ohtake et al. (2009), Nature 461, 236-240. [3] Piskorz, & Stevenson (2014), Icarus 239, 238-243. [4] Longhi (2003), JGR 108, doi:10.1029/2002JE001941. [5] Giordano et al. (2008), EPSL 271, 123-134.

Chemical and dynamical perspectives on accretion and differentiation

NASA Astrophysics Data System (ADS)

Nimmo, F.

2012-12-01

The initial thermal and chemical state of a planet is largely determined by how it accreted. Although large bodies rapidly lose their memory of those initial conditions, smaller bodies do not: the Martian mantle has different isotopic reservoirs that were established early in its history and not subsequently homogenized [1], while the Martian dynamo may have been driven by an initially superheated core [2]. Accretion is also inefficient; impacts can modify planetary bulk compositions in subtle [3] or dramatic [4] ways. There are two main pathways for melting and differentiation of silicate bodies. Small rapidly-accreted bodies melt from the inside out due to 26Al decay, potentially leaving an unmelted carapace [5]. Large bodies melt due to release of gravitational energy via giant impacts. Both situations likely result in magma oceans, which may crystallize to yield unstable density structures [6]. The lifetime of magma oceans is highly uncertain and depends on whether a flotation crust develops, and whether a thick primordial atmosphere is present [7]. The Hf-W [8] and Pd-Ag [9] isotopic systems provide constraints on the timing and style of core formation. For instance, the rapid growth of planets in the ``Grand Tack'' model [10] may not be consistent with these constraints. The key uncertainty is the extent to which impactor cores equilibrate with the surrounding mantle during impacts. For example, the inferred rapid accretion of Mars [11] depends on an assumption of perfect re-equilibration. The physics of re-equilibration is imperfectly understood [12], and hard to model numerically [13]; laboratory experiments may provide a better approach [14]. Dynamical models suggest that the Earth's feeding zone moved outwards with time [15]. Isotopic [9] and element partitioning [16] models are consistent with this picture, suggesting that accreted material changed from volatile-poor and reduced to volatile-rich and oxidized as time progressed. [1] Halliday et al., SSR 96, 197-230, 2001. [2] Williams & Nimmo, Geology 32, 97-100, 2004 [3] O'Neill & Palme, PTRSL 366, 4205-4238, 2008. [4] Benz et al., SSR 132, 189-202, 2007. [5] Elkins-Tanton et al., EPSL 305, 1-10, 2011. [6] Elkins-Tanton et al., MAPS 38, 1753-1771, 2003. [7] Zahnle et al., SSR 129, 35-78, 2007. [8] Kleine et al., GCA 73, 5150-5188, 2009. [9] Schonbachler et al., Science 328, 884-887, 2010. [10] Walsh et al., Nature 475, 206-209, 2011. [11] Dauphas & Pourmand, Nature 473, 489, 2011. [12] Dahl & Stevenson, EPSL 295, 177-186, 2010. [13] Kendall & Melosh, LPSC 43, 2699, 2012. [14] Deguen et al., EPSL 310, 303-313, 2011. [15] O'Brien et al., Icarus 184, 39-58, 2006. [16] Rubie et al. EPSL 301, 31-42, 2011.

Holocene sea-level change and Antarctic melting history derived from geological observations and geophysical modeling along the Shimokita Peninsula, northern Japan

NASA Astrophysics Data System (ADS)

Yokoyama, Y.; Okuno, J.; Miyairi, Y.; Obrochta, S.; Demboya, N.; Makino, Y.; Kawahata, H.

2012-12-01

A Mid to Late Holocene sea-level record based on combined geomorphological, geological and micropaleontological observations was obtained from well-developed wave cut benches subaerially exposed along the Shimokita Peninsula, northern Japan. Results indicate that the benches were formed during mid to late Holocene sea-level transgressions, reaching a maximum highstand level of 2 m above present at about 3,000 to 4,000 years ago. This timing corresponds to an abrupt, order of magnitude decrease in sedimentation rate as recorded in a core recovered from proximal Mutsu Bay. In addition, glacio-hydro-isostatic adjustment due to crustal deformation in response to postglacial sea-level rise was modeled, and results are consistent with the reconstructed local 2 m highstand. Given that meltwater contributions from the major North American and European ice sheets had largely ceased by 7,000 years ago, these independent lines of evidence, taken together, indicate that melting of the Antarctic ice sheet ended by late Holocene, around 3,000-4,000 years ago.

Manufacturing and characterization of encapsulated microfibers with different molecular weight poly(ε-caprolactone) (PCL) resins using a melt electrospinning technique

NASA Astrophysics Data System (ADS)

Lee, Jason K.; Ko, Junghyuk; Jun, Martin B. G.; Lee, Patrick C.

2016-02-01

Encapsulated structures of poly(ε-caprolactone) microfibers were successfully fabricated through two distinct melt electrospinning methods: melt coaxial and melt-blending electrospinning methods. Both methods resulted in encapsulated microfibers, but the resultant microfibers had different morphologies. Melt coaxial electrospinning formed a dual, semi-concentric structure, whereas melt-blending electrospinning resulted in an islands-in-a-sea fiber structure (i.e. a multiple-core structure). The encapsulated microfibers were produced using a custom-designed melt coaxial electrospinning device and the microfibers were characterized using a scanning electron microscope. To analyze the properties of the melt blended encapsulated fibers and coaxial fibers, the microfiber mesh specimens were collected. The mechanical properties of each microfiber mesh were analyzed through a tensile test. The coaxial microfiber meshes were post processed with a femtosecond laser machine to create dog-bone shaped tensile test specimens, while the melt blended microfiber meshes were kept as-fabricated. The tensile experiments undertaken with coaxial microfiber specimens resulted in an increase in tensile strength compared to 10 k and 45 k monolayer specimens. However, melt blended microfiber meshes did not result in an increase in tensile strength. The melt blended microfiber mesh results indicate that by using greater amounts of 45 k PCL resin within the microstructure, the resulting fibers obtain a higher tensile strength.

High-pressure melting experiments on Fe-Si alloys and implications for silicon as a light element in the core

NASA Astrophysics Data System (ADS)

Ozawa, Haruka; Hirose, Kei; Yonemitsu, Kyoko; Ohishi, Yasuo

2016-12-01

We carried out melting experiments on Fe-Si alloys to 127 GPa in a laser-heated diamond-anvil cell (DAC). On the basis of textural and chemical characterizations of samples recovered from a DAC, a change in eutectic liquid composition in the Fe-FeSi binary system was examined with increasing pressure. The chemical compositions of coexisting liquid and solid phases were quantitatively determined with field-emission-type electron microprobes. The results demonstrate that silicon content in the eutectic liquid decreases with increasing pressure to less than 1.5 ± 0.1 wt.% Si at 127 GPa. If silicon is a single light element in the core, 4.5 to 12 wt.% Si is required in the outer core in order to account for its density deficit from pure iron. However, such a liquid core, whose composition is on the Si-rich side of the eutectic point, crystallizes less dense solid, CsCl (B2)-type phase at the inner core boundary (ICB). Our data also show that the difference in silicon concentration between coexisting solid and liquid is too small to account for the observed density contrast across the ICB. These indicate that silicon cannot be the sole light element in the core. Previous geochemical and cosmochemical arguments, however, strongly require ∼6 wt.% Si in the core. It is possible that the Earth's core originally included ∼6 wt.% Si but then became depleted in silicon by crystallizing SiO2 or MgSiO3.

Generating Melt During Exhumation of Continental Crust from Ultrahigh Pressure (UHP) Conditions

NASA Astrophysics Data System (ADS)

Brown, M.; Wang, S.; Wang, L.; Piccoli, P. M.; Johnson, T. E.

2017-12-01

Hydrate breakdown rather than fluid-present melting is commonly cited during exhumation of UHP continental crust, but may have been overemphasized in relation to petrographic evidence. In this study from the central Sulu belt, China, we posit that dm- to m-scale dikes of leucosome in stromatic migmatite, formerly UHP eclogite, crystallized from hydrous melt derived by evolution of supercritical fluid as it drained through exhuming crust and increased in solute content. Leucosomes comprise Qz + Ph + Ab + Aln/Ep + Grt. Overgrowths of Zrn on inherited cores and new grains crystallized at ca. 223-219 Ma, within the age range of HP eclogite facies recrystallization in the belt. Si-in-Ph/Ti-in-Zrn thermobarometry yields crystallization conditions of 3.0-2.5 GPa at 830-770 °C. Compositions are granitic with normalized TE patterns enriched in LREE relative to HREE and enriched in LILE relative to HFSE, features consistent with crystallization from crustally derived hydrous melt. The leucosomes have Sr-Nd isotope compositions intermediate between host eclogites and surrounding gneisses. At the metamorphic peak, the source rocks were likely fluid deficient or fluid absent. During exhumation from UHP conditions, structural water stored in nominally anhydrous minerals during the prograde evolution was exsolved to form a grain boundary supercritical fluid in eclogite and gneiss. By migrating from grain boundaries into channels and draining from the volumetrically dominant gneiss through eclogite, the fluid acquired a blended Sr-Nd isotope composition intermediate between end-members. Concomitantly, the ascending fluid evolved to a denser, more viscous and more polymerized hydrous melt by dissolution of the silicate matrix. Trapped around the transition from UHP to HP eclogite facies conditions, the melt crystallized by diffusive loss of water to the host eclogite. Aggregates of Pl + Bt around Ph and thin films and cuspate veinlets/patches of Kfs along grain boundaries in leucosomes are consistent with subsequent low degrees of melting by Ph breakdown. Phase equilibria modeling indicates melting occurred during the transition from HP eclogite to amphibolite facies, with final subsolidus equilibration at 1.04-0.87 GPa and T <640 °C. However, Ph-breakdown melting was not the mechanism by which the leucosomes formed.

Crustal Structure of the Iceland Region from Spectrally Correlated Free-air and Terrain Gravity Data

NASA Technical Reports Server (NTRS)

Leftwich, T. E.; vonFrese, R. R. R. B.; Potts, L. V.; Roman, D. R.; Taylor, Patrick T.

2003-01-01

Seismic refraction studies have provided critical, but spatially restricted constraints on the structure of the Icelandic crust. To obtain a more comprehensive regional view of this tectonically complicated area, we spectrally correlated free-air gravity anomalies against computed gravity effects of the terrain for a crustal thickness model that also conforms to regional seismic and thermal constraints. Our regional crustal thickness estimates suggest thickened crust extends up to 500 km on either side of the Greenland-Scotland Ridge with the Iceland-Faeroe Ridge crust being less extended and on average 3-5 km thinner than the crust of the Greenland-Iceland Ridge. Crustal thickness estimates for Iceland range from 25-35 km in conformity with seismic predictions of a cooler, thicker crust. However, the deepening of our gravity-inferred Moho relative to seismic estimates at the thermal plume and rift zones of Iceland suggests partial melting. The amount of partial melting may range from about 8% beneath the rift zones to perhaps 20% above the plume core where mantle temperatures may be 200-400 C above normal. Beneath Iceland, areally limited regions of partial melting may also be compositionally and mechanically layered

Water generation and transport through the high-pressure ice layers of Titan and Ganymede

NASA Astrophysics Data System (ADS)

Kalousova, K.; Sotin, C.; Choblet, G.; Tobie, G.; Grasset, O.

2017-09-01

We investigate the generation and transport of water through the high-pressure (HP) ice layers of Ganymede and Titan using a numerical model of two-phase convection in 2D geometry. Our results suggest that water can be generated at the silicate/HP ice interface for small to intermediate values of Rayleigh number (Ra 1.e8-1.e10) while no melt is generated for the higher values (Ra 1.e11). If generated, water is transported through the layer by the upwelling plumes and, depending on the vigor of convection, it stays liquid (smaller Ra) or it may freeze (intermediate Ra) before melting again as the plume reaches the temperate layer at the interface with the ocean. The thickness of this layer as well as the amount of melt that is extracted from it is controlled by the HP ice permeability. This process may enable the transfer of volatiles and salts that might have been leached from silicates by the meltwater. Since the HP ice layer is much thinner on Titan than on Ganymede, it is probably more permeable for volatiles and salts leached from the silicate core.

Surface mass balance of Greenland mountain glaciers and ice caps

NASA Astrophysics Data System (ADS)

Benson, R. J.; Box, J. E.; Bromwich, D. H.; Wahr, J. M.

2009-12-01

Mountain glaciers and ice caps contribute roughly half of eustatic sea-level rise. Greenland has thousands of small mountain glaciers and several ice caps > 1000 sq. km that have not been included in previous mass balance calculations. To include small glaciers and ice caps in our study, we use Polar WRF, a next-generation regional climate data assimilation model is run at grid resolution less than 10 km. WRF provides surface mass balance data at sufficiently high resolution to resolve not only the narrow ice sheet ablation zone, but provides information useful in downscaling melt and accumulation rates on mountain glaciers and ice caps. In this study, we refine Polar WRF to simulate a realistic surface energy budget. Surface melting is calculated in-line from surface energy budget closure. Blowing snow sublimation is computed in-line. Melt water re-freeze is calculated using a revised scheme. Our results are compared with NASA's Gravity Recovery and Climate Experiment (GRACE) and associated error is calculated on a regional and local scale with validation from automated weather stations (AWS), snow pits and ice core data from various regions along the Greenland ice sheet.

Atmospheric depositions of black carbon, inorganic pollutants and mineral dust from the Ortles, Eastern European Alps ice cores during the last 3000 years

NASA Astrophysics Data System (ADS)

Bertò, Michele; Barbante, Carlo; Gabrielli, Paolo; Gabrieli, Jacopo; Spolaor, Andrea; Dreossi, Giuliano; Laj, Paolo; Zanatta, Marco; Stenni, Barbara

2017-04-01

Reconstructions of the atmospheric content of black carbon, heavy metals and mineral dust covering millennial time scales are rare, particularly in the European region. Evaluating the human impact on the environment through mining and industrial activities, road traffic, biomass and coal burning, and the naturally emitted aerosols atmospheric load, is important to know the degree of contaminations and the quality of melting water, the radiative effect on the glacier's radiative balance, the atmospheric aerosols' climatic impacts and the recent decades pollutions emissions policies' efficiencies. Four ice cores were drilled in 2011 from the "Alto dell'Ortles" (3859 m), the highest glacier of the Mt. Ortles massif (South Tirol, Italy). Three 74 m long ice cores were dated by mean of 210Pb, tritium, beta emissions and 14C analyses following also the new dating technique based on filtering the ice for extracting the carbonaceous component of the deposited aerosols. The depth-age curve was obtained by using a Monte Carlo based empirical fitting model (COPRA). The basal ice of core#2 and #3 was dated back to about 7000 years b.p., whereas that of core#1, about one meter shorter, to 3000 years before present. Below the firn-ice transition, at a depth of about 24 m, the borehole temperature revealed the presence of well-preserved cold ice (Gabrielli et al, 2012). The O and H stable isotopes profiles describe well the atmospheric warming as well as the low temperatures recorded during the Little Ice Age (LIA). The proximity of the "Alto dell'Ortles" to densely industrialized areas (Po Valley) makes these ice cores specifically suited for reconstructing the anthropogenic impacts in the Eastern European Alpine region over the last 3 millennia. The ice core#1 was analyzed with a "Continuous Flow Analysis" system (CFA). The separation between internal and external parts of the core prevents any kind of contamination. The core was melted at about 2.5 cm min-1 and simultaneous analyses of conductivity, dust concentration and size distribution (from 0.8 to 80 μm), trace elements with Inductive Coupled Plasma Mass Spectrometer (ICP-MS, Agilent 7500) and refractory black carbon (rBC) with the Single Particle Soot Photometer (SP2, Droplet Measurement Technologies) were performed. A fraction of the melt water was collected by an auto-sampler. More than 1000 samples were analyzed discreetly with a CRC-ICP-MS (with the highest resolution of about 3 cm). The rBC shows significant variability over the last century peaking in concentrations of about 10 ng g-1 from the 1920s to the 1970s, whereas very low values characterized the period from 1000 BC to 1850 AD. The seasonality appears to be preserved even in the firn temperate part of the core as argued from the comparison with the water stable isotopes ratios (δO18). The overall determined trace elements are Li, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, As, Se, Sr, Ag, Cd, Sb, Te, I, Cs, Ba, Hg, Tl, Pb, Bi, U. The Enrichment Factors (EF) for the crustal elements didn't show any particular trend. While mining and smelting activities appeared to be the most significant heavy metals sources before the 19th century, other anthropogenic heavy metals strongly increased from the onset of the Industrial Revolutions.

Properties of iron alloys under the Earth's core conditions

NASA Astrophysics Data System (ADS)

Morard, Guillaume; Andrault, Denis; Antonangeli, Daniele; Bouchet, Johann

2014-05-01

The Earth's core is constituted of iron and nickel alloyed with lighter elements. In view of their affinity with the metallic phase, their relative high abundance in the solar system and their moderate volatility, a list of potential light elements have been established, including sulfur, silicon and oxygen. We will review the effects of these elements on different aspects of Fe-X high pressure phase diagrams under Earth's core conditions, such as melting temperature depression, solid-liquid partitioning during crystallization, and crystalline structure of the solid phases. Once extrapolated to the inner-outer core boundary, these petrological properties can be used to constrain the Earth's core properties.

Phase Equilibria of a S- and C-Poor Lunar Core

NASA Technical Reports Server (NTRS)

Righter, K.; Pando, K.; Go, B. M.; Danielson, L. R.; Habermann, M.

2016-01-01

The composition of the lunar core can have a large impact on its thermal evolution, possible early dynamo creation, and physical state. Geochemical measurements have placed better constraints on the S and C content of the lunar mantle. In this study we have carried out phase equilibrium studies of geochemically plausible S- and C-poor lunar core compositions in the Fe-Ni-S-C system, and apply them to the early history of the Moon. We chose two bulk core compositions, with differing S and C content based on geochemical analyses of S and C trapped melts in Apollo samples, and on the partitioning of S and C between metal and silicate. This approach allowed calculation of core S and C contents - 90% Fe, 9% Ni, 0.5% C, and 0.375% S by weight; a second composition contained 1% each of S and C. Experiments were carried out from 1473K to 1973K and 1 GPa to 5 GPa, in piston cylinder and multi- anvil apparatuses. Combination of the thermal model of with our results, shows that a solid inner core (and therefore initiation of a dynamo) may have been possible in the earliest history of the Moon (approximately 4.2 Ga ago), in agreement with. Thus a volatile poor lunar core may explain the thermal and magnetic history of the Moon.

The effect of acidified sample storage time on the determination of trace element concentration in ice cores by ICP-SFMS

NASA Astrophysics Data System (ADS)

Uglietti, C.; Gabrielli, P.; Lutton, A.; Olesik, J.; Thompson, L. G.

2012-12-01

Trace elements in micro-particles entrapped in ice cores are a valuable proxy of past climate and environmental variations. Inductively coupled plasma sector field mass spectrometry (ICP-SFMS) is generally recognized as a sensitive and accurate technique for the quantification of ultra-trace element concentrations in ice cores. Usually, ICP-SFMS analyses of ice core samples are performed by melting and acidifying aliquots. Acidification is important to transfer trace elements from particles into solution by partial and/or complete dissolution. Only elements in solution and in sufficiently small particles will be vaporized and converted to elemental ions in the plasma for detection by ICP-SFMS. However, experimental results indicate that differences in acidified sample storage time at room temperature may lead to the recovery of different trace element fractions. Moreover, different lithologies of the relatively abundant crustal material entrapped in the ice matrix could also influence the fraction of trace elements that are converted into elemental ions in the plasma. These factors might affect the determination of trace elements concentrations in ice core samples and hamper the comparison of results obtained from ice cores from different locations and/or epochs. In order to monitor the transfer of elements from particles into solution in acidified melted ice core samples during storage, a test was performed on sections from nine ice cores retrieved from low latitude drilling sites around the world. When compared to ice cores from polar regions, these samples are characterized by a relative high content of micro-particles that may leach trace elements into solution differently. Of the nine ice cores, five are from the Tibetan Plateau (Dasuopu, Guliya, Naimonanyi, Puruogangri and Dunde), two from the Andes (Quelccaya and Huascaran), one from Africa (Kilimanjaro) and one from the Eastern Alps (Ortles). These samples were decontaminated by triple rinsing, melted and stored in pre-cleaned low-density polyethylene bottles, and kept frozen until acidification (2% v/v ultra-pure HNO3). Determination of twenty trace elements (Ag, Al, As, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Rb, Sb, Sn, Ti, Tl, U, V, and Zn) was repeated at different times after acidification using the same aliquot. Analyses show a mean increase of 40-50% in trace element concentration in all the samples during the first 15 days of storage after acidification, except Al, Fe, V and Cr, which show a larger increase (90-100%). After 15 days the trace element concentrations reach generally stable values (with small increases within measurement uncertainty), except for the Naimonanyi and Kilimanjaro samples which continue to increase. In contrast, Ag concentration decreases after one week, likely due to its low stability in the acidified solution that may depend on the Cl- concentration. We froze the samples 43 days after the acidification. After two weeks the samples were melted and re-analyzed by ICP-SFMS in two different laboratories as an inter-calibration exercise. The results show a good correspondence between the measured concentrations determined by the two instruments and a consistent additional increase of 20-30% of measured trace element concentrations in almost all samples.

Development of MPS Method for Analyzing Melt Spreading Behavior and MCCI in Severe Accidents

NASA Astrophysics Data System (ADS)

Yamaji, Akifumi; Li, Xin

2016-08-01

Spreading of molten core (corium) on reactor containment vessel floor and molten corium-concrete interaction (MCCI) are important phenomena in the late phase of a severe accident for assessment of the containment integrity and managing the severe accident. The severe accident research at Waseda University has been advancing to show that simulations with moving particle semi-implicit (MPS) method (one of the particle methods) can greatly improve the analytical capability and mechanical understanding of the melt behavior in severe accidents. MPS models have been developed and verified regarding calculations of radiation and thermal field, solid-liquid phase transition, buoyancy, and temperature dependency of viscosity to simulate phenomena, such as spreading of corium, ablation of concrete by the corium, crust formation and cooling of the corium by top flooding. Validations have been conducted against experiments such as FARO L26S, ECOKATS-V1, Theofanous, and SPREAD for spreading, SURC-2, SURC-4, SWISS-1, and SWISS-2 for MCCI. These validations cover melt spreading behaviors and MCCI by mixture of molten oxides (including prototypic UO2-ZrO2), metals, and water. Generally, the analytical results show good agreement with the experiment with respect to the leading edge of spreading melt and ablation front history of concrete. The MPS results indicate that crust formation may play important roles in melt spreading and MCCI. There is a need to develop a code for two dimensional MCCI experiment simulation with MPS method as future study, which will be able to simulate anisotropic ablation of concrete.

Mass Fluxes of Ice and Oxygen Across the Entire Lid of Lake Vostok from Observations of Englacial Radiowave Attenuation

NASA Astrophysics Data System (ADS)

Winebrenner, D. P.; Kintner, P. M. S.; MacGregor, J. A.

2017-12-01

Over deep Antarctic subglacial lakes, spatially varying ice thickness and the pressure-dependent melting point of ice result in areas of melting and accretion at the ice-water interface, i.e., the lake lid. These ice mass fluxes drive lake circulation and, because basal Antarctic ice contains air-clathrate, affect the input of oxygen to the lake, with implications for subglacial life. Inferences of melting and accretion from radar-layer tracking and geodesy are limited in spatial coverage and resolution. Here we develop a new method to estimate rates of accretion, melting, and the resulting oxygen input at a lake lid, using airborne radar data over Lake Vostok together with ice-temperature and chemistry data from the Vostok ice core. Because the lake lid is a coherent reflector of known reflectivity (at our radar frequency), we can infer depth-averaged radiowave attenuation in the ice, with spatial resolution 1 km along flight lines. Spatial variation in attenuation depends mostly on variation in ice temperature near the lid, which in turn varies strongly with ice mass flux at the lid. We model ice temperature versus depth with ice mass flux as a parameter, thus linking that flux to (observed) depth-averaged attenuation. The resulting map of melt- and accretion-rates independently reproduces features known from earlier studies, but now covers the entire lid. We find that accretion is dominant when integrated over the lid, with an ice imbalance of 0.05 to 0.07 km3 a-1, which is robust against uncertainties.

Exploration of the Eltanin Impact Area (Bellingshausen Sea): Expedition ANT XVIII5a

NASA Technical Reports Server (NTRS)

Gersonde, Rainer; Kyte, Frank T.

2001-01-01

The impact of the Eltanin asteroid into the Bellingshausen Sea (2.15 Ma) is the only known impact in a deep-ocean (approx. 5 km) basin. On 26 March 2001, the FS Polarstern returned to the impact area during expedition ANT XVIII/5a. Over a period of 14 days, this region was explored by detailed bathymetric mapping, acoustic profiling of sediment deposits, and direct sampling with 18 piston cores and four gravity cores. Preliminary shipboard examination of microfossils showed that sixteen of the piston cores and three gravity cores contained sediments at least as old as the impact event and have a high probability of containing a record of the disturbances caused by the impact. During the expedition, portions of eleven piston cores were opened for preliminary examination of the impact deposits. Visual examination of cores and microscopic identification of suspect impact melt particles were were used to identify ejecta and X-ray radiographs of the opened core segments permitted analysis of sediment structures. Impact deposits were found in nine of the eleven opened cores, and a similar success rate is anticipated in the seven cores remaining to be opened. These preliminary observations indicate that the highest concentrations of meteoritic ejecta and the largest particle sizes appear to occur in the region north of the San Martin seamounts. Recovered debris includes cm-sized melt rocks and a 2.5 cm meteorite. This expedition has confirmed the presence of high concentrations of meteoritic ejecta across a region at least as large as 10(exp 5) sq km. Quantitative analyses of ejecta distribution within this region will require further study, but previous estimates of 1 km for the minimum diameter of the Eltanin asteroid, appear safe.

Evolution of C-O-H-N volatile species in the magma ocean during core formation.

NASA Astrophysics Data System (ADS)

Dalou, C.; Le Losq, C.; Hirschmann, M. M.; Jacobsen, S. D.; Fueri, E.

2017-12-01

The composition of the Hadean atmosphere affected how life began on Earth. Magma ocean degassing of C, O, H, and N was a key influence on the composition of the Hadean atmosphere. To identify the nature of degassed C-O-H-N species, we determined their speciation in reduced basaltic glasses (in equilibrium with Fe-C-N metal alloy, synthetized at 1400 and 1600 ºC and 1.2-3 GPa) via Raman spectroscopy. We addressed the effect of oxygen fugacity (fO2) on C-O-H-N speciation between IW-2.3 and IW-0.4, representing the evolution of the shallow upper mantle fO2 during the Hadean. We observe H2, NH2, NH3, CH3, CH4, CO, N2, and OH species in all glasses. With increasing ƒO2, our results support the formation of OH groups at the expense of N-H and C-H bonds in the melt, implying the equilibria at IW-2: (1) 2OH- (melt) + ½ N2 (melt) ↔ NH2 (melt) + 2 O2- (melt) , (2) 2OH- (melt) + ½ N2 (melt) + ½ H2 (melt) ↔ NH3 (melt) + 2 O2- (melt) . With increasing fO2, eqs. (1) and (2) shift to the left. From IW-2 to IW, we also observe an increase in the intensity of the NH2 peak relative to NH3. Carbon is present as CH3, CH4, and CO in all our glasses. While CO is likely the main carbon specie under reduced conditions (e.g., Armstrong et al. 2015), CH species should remain stable from moderately (IW-0.4) to very reduced (IW-3; Ardia et al. 2014; Kadik et al. 2015, 2017) conditions in hydrous silicate glasses following the equilibria: (3) 3OH- (melt) + C (graphite) ↔ CH3 (melt) + 3O2- (melt) , (4) 4OH- (melt) + C (graphite) ↔ CH4 (melt) + 4O2- (melt) . With increasing fO2, eqs. (3) and (4) shift to the left. As metal segregation and core formation drove the ƒO2 of the magma ocean from IW-4 to IW during the Hadean (Rubie et al. 2011), the nature of species degassed by the magma ocean should have evolved during that time. The C-O-H-N species we observe dissolved in our reduced glasses may not directly correspond to those degassed (Schaeffer and Fegley, 2007), but a better understanding of species abundances and gas phase equilibria should constrain the contribution of magma ocean degassing to the Hadean atmosphere. As reactions involving CO, N2, and OH are sufficient to form amino acids, and NH2, NH3, CH3, and CH4 are amino acid components, the availability of such reduced molecules for outgassing from the magma ocean suggest a central role in the formation of the first organic molecules.

75 FR 43571 - Duke Energy Carolinas, LLC; Catawba Nuclear Station, Units 1 and 2; Environmental Assessment And...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-26

... probability of any accident. For the accidents that involve damage or melting of the fuel in the reactor core..., the probability of an accident will not be affected. For the accidents in which core remains intact... event of a serious accident, but because the radionuclides contributing most to the dose are short-lived...

Evidence for propagation of cold-adapted yeast in an ice core from a Siberian Altai glacier

NASA Astrophysics Data System (ADS)

Uetake, Jun; Kohshima, Shiro; Nakazawa, Fumio; Takeuchi, Nozomu; Fujita, Koji; Miyake, Takayuki; Narita, Hideki; Aizen, Vladimir; Nakawo, Masayoshi

2011-03-01

Cold environments, including glacier ice and snow, are known habitats for cold-adapted microorganisms. We investigated the potential for cold-adapted yeast to have propagated in the snow of the high-altitude Belukha glacier. We detected the presence of highly concentrated yeast (over 104 cells mL-1) in samples of both an ice core and firn snow. Increasing yeast cell concentrations in the same snow layer from July 2002 to July 2003 suggests that the yeast cells propagated in the glacier snow. A cold-adapted Rhodotorula sp. was isolated from the snow layer and found to be related to psychrophilic yeast previously found in other glacial environments (based on the D1/D2 26S rRNA domains). 26S rRNA clonal analysis directly amplified from meltwater within the ice core also revealed the presence of genus Rhodotorula. Analyses of the ice core showed that all peaks in yeast concentration corresponded to the peaks in indices of surface melting. These results support the hypothesis that occasional surface melting in an accumulation area is one of the major factors influencing cold-adapted yeast propagation.

Melting behavior of Earth's lower mantle minerals at high pressures

NASA Astrophysics Data System (ADS)

Fu, S.; Yang, J.; Prakapenka, V. B.; Zhang, Y.; Greenberg, E.; Lin, J. F.

2017-12-01

Melting behavior of the most abundant lower mantle minerals, bridgmanite and ferropericlase, at high pressure-temperature (P-T) conditions is of critical importance to understand the dynamic evolution of the early Earth and to explain the seismological and geochemical signatures in the present lowermost mantle. Theoretical calculations [1] and geodynamical models [2] suggested that partial melting of early Earth among MgO-FeO-SiO2 ternary could be located at the eutectic point where a pyrolitic composition formed for the Earth's lower mantle and the eutectic crystallization process could provide a plausible mechanism to the origin of the ultra-low velocity zones (ULVZs) near the core-mantle boundary. Here we have investigated the melting behavior of ferropericlase and Al,Fe-bearing bridgmanite in laser-heated diamond anvil cells coupled with in situ X-ray diffraction up to 120 GPa. Together with chemical and texture characterizations of the quenched samples, these results are analyzed using thermodynamic models to address the effects of iron on the liquidus and solidus temperatures as well as solid-liquid iron partitioning and the eutectic point in ferropericlase-bridgmanite existing system at lower-mantle pressure. In this presentation, we discuss the application of these results to better constrain the seismic observations of the deep lowermost mantle such as large low shear wave velocity provinces (LLSVPs) and ULVZs. We will also discuss the geochemical consequences of the ferropericlase-bridgmanite melting due to the changes in the electronic spin and valence states of iron in the system. ADDIN EN.REFLIST 1. Boukaré, C.E., Y. Ricard, and G. Fiquet, Thermodynamics of the MgO-FeO-SiO2 system up to 140 GPa: Application to the crystallization of Earth's magma ocean. Journal of Geophysical Research: Solid Earth, 2015. 120(9): p. 6085-6101. 2. Labrosse, S., J. Hernlund, and N. Coltice, A crystallizing dense magma ocean at the base of the Earth's mantle. Nature, 2007. 450(7171): p. 866-869.

Formation and evolution of a metasomatized lithospheric root at the motionless Antarctic plate: the case of East Island, Crozet Archipelago (Indian Ocean)

NASA Astrophysics Data System (ADS)

Meyzen, Christine; Marzoli, Andrea; Bellieni, Giuliano; Levresse, Gilles

2016-04-01

Sitting atop the nearly stagnant Antarctic plate (ca. 6.46 mm/yr), the Crozet archipelago midway between Madagascar and Antarctica constitutes a region of unusually shallow (1543-1756 m below sea level) and thickened oceanic crust (10-16.5 km), high geoid height, and deep low-velocity zone, which may reflect the surface expression of a mantle plume. Here, we present new major and trace element data for Quaternary sub-aerial alkali basalts from East Island, the easterly and oldest island (ca. 9 Ma) of the Crozet archipelago. Crystallization at uppermost mantle depth and phenocryst accumulation have strongly affected their parental magma compositions. Their trace element patterns show a large negative K anomaly relative to Ta-La, moderate depletions in Rb and Ba with respect to Th-U, and heavy rare earth element (HREE) depletions relative to light REE. These characteristics allow limits to be placed upon the composition and mineralogy of their mantle source. The average trace element spectrum of East Island basalts can be matched by melting of about 2 % of a garnet-phlogopite-bearing peridotite source. The stability field of phlogopite restricts melting depth to lithospheric levels. The modelled source composition requires a multistage evolution, where the mantle has been depleted by melt extraction before having been metasomatized by alkali-rich plume melts. The depleted mantle component may be sourced by residual mantle plume remnants stagnated at the melting locus due to a weak lateral flow velocity inside the melting regime, whose accumulation progressively edifies a depleted lithospheric root above the plume core. Low-degree alkali-rich melts are likely derived from the plume source. Such a mantle source evolution may be general to both terrestrial and extraterrestrial environments where the lateral component velocity of the mantle flow field is extremely slow.

Low-temperature hermetic sealing of optical fiber components

DOEpatents

Kramer, D.P.

1996-10-22

A method for manufacturing low-temperature hermetically sealed optical fiber components is provided. The method comprises the steps of: inserting an optical fiber into a housing, the optical fiber having a glass core, a glass cladding and a protective buffer layer disposed around the core and cladding; heating the housing to a predetermined temperature, the predetermined temperature being below a melting point for the protective buffer layer and above a melting point of a solder; placing the solder in communication with the heated housing to allow the solder to form an eutectic and thereby fill a gap between the interior of the housing and the optical fiber; and cooling the housing to allow the solder to form a hermetic compression seal between the housing and the optical fiber. 5 figs.

Low-temperature hermetic sealing of optical fiber components

DOEpatents

Kramer, Daniel P.

1996-10-22

A method for manufacturing low-temperature hermetically sealed optical fi components is provided. The method comprises the steps of: inserting an optical fiber into a housing, the optical fiber having a glass core, a glass cladding and a protective buffer layer disposed around the core and cladding; heating the housing to a predetermined temperature, the predetermined temperature being below a melting point for the protective buffer layer and above a melting point of a solder; placing the solder in communication with the heated housing to allow the solder to form an eutectic and thereby fill a gap between the interior of the housing and the optical fiber; and cooling the housing to allow the solder to form a hermetic compression seal between the housing and the optical fiber.

Holocene thinning of the Greenland ice sheet.

PubMed

Vinther, B M; Buchardt, S L; Clausen, H B; Dahl-Jensen, D; Johnsen, S J; Fisher, D A; Koerner, R M; Raynaud, D; Lipenkov, V; Andersen, K K; Blunier, T; Rasmussen, S O; Steffensen, J P; Svensson, A M

2009-09-17

On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an important concern, especially in the light of new evidence of rapidly changing flow and melt conditions at the GIS margins. Studying the response of the GIS to past climatic change may help to advance our understanding of GIS dynamics. The previous interpretation of evidence from stable isotopes (delta(18)O) in water from GIS ice cores was that Holocene climate variability on the GIS differed spatially and that a consistent Holocene climate optimum-the unusually warm period from about 9,000 to 6,000 years ago found in many northern-latitude palaeoclimate records-did not exist. Here we extract both the Greenland Holocene temperature history and the evolution of GIS surface elevation at four GIS locations. We achieve this by comparing delta(18)O from GIS ice cores with delta(18)O from ice cores from small marginal icecaps. Contrary to the earlier interpretation of delta(18)O evidence from ice cores, our new temperature history reveals a pronounced Holocene climatic optimum in Greenland coinciding with maximum thinning near the GIS margins. Our delta(18)O-based results are corroborated by the air content of ice cores, a proxy for surface elevation. State-of-the-art ice sheet models are generally found to be underestimating the extent and changes in GIS elevation and area; our findings may help to improve the ability of models to reproduce the GIS response to Holocene climate.

El'gygytgyn impact crater, Chukotka, Arctic Russia: Impact cratering aspects of the 2009 ICDP drilling project

NASA Astrophysics Data System (ADS)

Koeberl, Christian; Pittarello, Lidia; Reimold, Wolf Uwe; Raschke, Ulli; Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel

2013-07-01

The El'gygytgyn impact structure in Chukutka, Arctic Russia, is the only impact crater currently known on Earth that was formed in mostly acid volcanic rocks (mainly of rhyolitic, with some andesitic and dacitic, compositions). In addition, because of its depth, it has provided an excellent sediment trap that records paleoclimatic information for the 3.6 Myr since its formation. For these two main reasons, because of the importance for impact and paleoclimate research, El'gygytgyn was the subject of an International Continental Scientific Drilling Program (ICDP) drilling project in 2009. During this project, which, due to its logistical and financial challenges, took almost a decade to come to fruition, a total of 642.3 m of drill core was recovered at two sites, from four holes. The obtained material included sedimentary and impactite rocks. In terms of impactites, which were recovered from 316.08 to 517.30 m depth below lake bottom (mblb), three main parts of that core segment were identified: from 316 to 390 mblb polymict lithic impact breccia, mostly suevite, with volcanic and impact melt clasts that locally contain shocked minerals, in a fine-grained clastic matrix; from 385 to 423 mblb, a brecciated sequence of volcanic rocks including both felsic and mafic (basalt) members; and from 423 to 517 mblb, a greenish rhyodacitic ignimbrite (mostly monomict breccia). The uppermost impactite (316-328 mblb) contains lacustrine sediment mixed with impact-affected components. Over the whole length of the impactite core, the abundance of shock features decreases rapidly from the top to the bottom of the studied core section. The distinction between original volcanic melt fragments and those that formed later as the result of the impact event posed major problems in the study of these rocks. The sequence that contains fairly unambiguous evidence of impact melt (which is not very abundant anyway, usually less than a few volume%) is only about 75 m thick. The reason for this rather thin fallback impactite sequence may be the location of the drill core on an elevated part of the central uplift. A general lack of large coherent melt bodies is evident, similar to that found at the similarly sized Bosumtwi impact crater in Ghana that, however, was formed in a target composed of a thin layer of sediment above crystalline rocks.

El'gygytgyn impact crater, Chukotka, Arctic Russia: Impact cratering aspects of the 2009 ICDP drilling project.

PubMed

Koeberl, Christian; Pittarello, Lidia; Reimold, Wolf Uwe; Raschke, Ulli; Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel; Spray, John

2013-07-01

The El'gygytgyn impact structure in Chukutka, Arctic Russia, is the only impact crater currently known on Earth that was formed in mostly acid volcanic rocks (mainly of rhyolitic, with some andesitic and dacitic, compositions). In addition, because of its depth, it has provided an excellent sediment trap that records paleoclimatic information for the 3.6 Myr since its formation. For these two main reasons, because of the importance for impact and paleoclimate research, El'gygytgyn was the subject of an International Continental Scientific Drilling Program (ICDP) drilling project in 2009. During this project, which, due to its logistical and financial challenges, took almost a decade to come to fruition, a total of 642.3 m of drill core was recovered at two sites, from four holes. The obtained material included sedimentary and impactite rocks. In terms of impactites, which were recovered from 316.08 to 517.30 m depth below lake bottom (mblb), three main parts of that core segment were identified: from 316 to 390 mblb polymict lithic impact breccia, mostly suevite, with volcanic and impact melt clasts that locally contain shocked minerals, in a fine-grained clastic matrix; from 385 to 423 mblb, a brecciated sequence of volcanic rocks including both felsic and mafic (basalt) members; and from 423 to 517 mblb, a greenish rhyodacitic ignimbrite (mostly monomict breccia). The uppermost impactite (316-328 mblb) contains lacustrine sediment mixed with impact-affected components. Over the whole length of the impactite core, the abundance of shock features decreases rapidly from the top to the bottom of the studied core section. The distinction between original volcanic melt fragments and those that formed later as the result of the impact event posed major problems in the study of these rocks. The sequence that contains fairly unambiguous evidence of impact melt (which is not very abundant anyway, usually less than a few volume%) is only about 75 m thick. The reason for this rather thin fallback impactite sequence may be the location of the drill core on an elevated part of the central uplift. A general lack of large coherent melt bodies is evident, similar to that found at the similarly sized Bosumtwi impact crater in Ghana that, however, was formed in a target composed of a thin layer of sediment above crystalline rocks.

El'gygytgyn impact crater, Chukotka, Arctic Russia: Impact cratering aspects of the 2009 ICDP drilling project

PubMed Central

Koeberl, Christian; Pittarello, Lidia; Reimold, Wolf Uwe; Raschke, Ulli; Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel; Spray, John

2013-01-01

The El'gygytgyn impact structure in Chukutka, Arctic Russia, is the only impact crater currently known on Earth that was formed in mostly acid volcanic rocks (mainly of rhyolitic, with some andesitic and dacitic, compositions). In addition, because of its depth, it has provided an excellent sediment trap that records paleoclimatic information for the 3.6 Myr since its formation. For these two main reasons, because of the importance for impact and paleoclimate research, El'gygytgyn was the subject of an International Continental Scientific Drilling Program (ICDP) drilling project in 2009. During this project, which, due to its logistical and financial challenges, took almost a decade to come to fruition, a total of 642.3 m of drill core was recovered at two sites, from four holes. The obtained material included sedimentary and impactite rocks. In terms of impactites, which were recovered from 316.08 to 517.30 m depth below lake bottom (mblb), three main parts of that core segment were identified: from 316 to 390 mblb polymict lithic impact breccia, mostly suevite, with volcanic and impact melt clasts that locally contain shocked minerals, in a fine-grained clastic matrix; from 385 to 423 mblb, a brecciated sequence of volcanic rocks including both felsic and mafic (basalt) members; and from 423 to 517 mblb, a greenish rhyodacitic ignimbrite (mostly monomict breccia). The uppermost impactite (316–328 mblb) contains lacustrine sediment mixed with impact-affected components. Over the whole length of the impactite core, the abundance of shock features decreases rapidly from the top to the bottom of the studied core section. The distinction between original volcanic melt fragments and those that formed later as the result of the impact event posed major problems in the study of these rocks. The sequence that contains fairly unambiguous evidence of impact melt (which is not very abundant anyway, usually less than a few volume%) is only about 75 m thick. The reason for this rather thin fallback impactite sequence may be the location of the drill core on an elevated part of the central uplift. A general lack of large coherent melt bodies is evident, similar to that found at the similarly sized Bosumtwi impact crater in Ghana that, however, was formed in a target composed of a thin layer of sediment above crystalline rocks. PMID:26074719

Mineralogy and petrology of cretaceous subsurface lamproite sills, southeastern Kansas, USA

USGS Publications Warehouse

Cullers, R.L.; Dorais, M.J.; Berendsen, P.; Chaudhuri, Sambhudas

1996-01-01

Cores and cuttings of lamproite sills and host sedimentary country rocks in southeastern Kansas from up to 312 m depth were analyzed for major elements in whole rocks and minerals, certain trace elements in whole rocks (including the REE) and Sr isotopic composition of the whole rocks. The lamproites are ultrapotassic (K2O/Na2O = 2.0-19.9), alkalic [molecular (K2O/Na2O)/Al2O3 = 1.3-2.8], enriched in mantle-incompatible elements (light REE, Ba, Rb, Sr, Th, Hf, Ta) and have nearly homogeneous initial Sr isotopic compositions (0.707764-0.708114). These lamproites could have formed by variable degrees of partial melting of harzburgite country rock and cross-cutting veins composed of phlogopite, K-Ti richterite, titanite, diopside, K-Ti silicates, or K-Ba-phosphate under high H2O/CO2 ratios and reducing conditions. Variability in melting of veins and wall rock and variable composition of the metasomatized veins could explain the significantly different composition of the Kansas lamproites. Least squares fractionation models preclude the derivation of the Kansas lamproites by fractional crystallization from magmas similar in composition to higher silica phlogopite-sanidine lamproites some believe to be primary lamproite melts found elsewhere. In all but one case, least squares fractionation models also preclude the derivation of magmas similar in composition to any of the Kansas lamproites from one another. A magma similar in composition to the average composition of the higher SiO2 Ecco Ranch lamproite (237.5-247.5 m depth) could, however, have marginally crystallized about 12% richterite, 12% sanidine, 7% diopside and 6% phlogopite to produce the average composition of the Guess lamproite (305-312 m depth). Lamproite from the Ecco Ranch core is internally fractionated in K2O, Al2O3, Ba, MgO, Fe2O3, Co and Cr most likely by crystal accumulation-removal of ferromagnesian minerals and sanidine. In contrast, the Guess core (305-312 m depth) has little fractionation throughout most of the sill except in several narrow zones. Lamproite in the Guess core has large enrichments in TiO2, Ba, REE, Th, Ta and Sc and depletions in MgO, Cr, Co and Rb possibly concentrated in these narrow zones during the last dregs of crystallization of this magma. The Ecco Ranch sill did not show any evidence of loss of volatiles or soluble elements into the country rock. This contrasts to the previously studied, shallow Silver City lamproite which did apparently lose H2O-rich fluid to the country rock. Perhaps a greater confining pressure and lesser amount of H2O-rich fluid prevented it from escaping.

Chemical evolution of Himalayan leucogranites based on an O, U-Pb and Hf study of zircon

NASA Astrophysics Data System (ADS)

Hopkinson, Thomas N.; Warren, Clare J.; Harris, Nigel B. W.; Hammond, Samantha J.; Parrish, Randall R.

2015-04-01

Crustal melting is a characteristic process at convergent plate margins, where crustal rocks are heated and deformed. Miocene leucogranite sheets and plutons are found intruded into the high-grade metasedimentary core (the Greater Himalayan Sequence, GHS) across the Himalayan orogen. Previously-published Himalayan whole-rock data suggest that these leucogranites formed from a purely meta-sedimentary source, isotopically similar to those into which they now intrude. Bulk rock analyses carry inherent uncertainties, however: they may hide contributions from different contributing sources, and post-crystallization processes such as fluid interaction may significantly alter the original chemistry. In contrast, zircon is more able to retain precise information of the contributing sources of the melt from which it crystallises whilst its resistant nature is impervious to post-magmatic processes. This multi-isotope study of Oligocene-Miocene leucogranite zircons from the Bhutan Himalaya, seeks to differentiate between various geochemical processes that contribute to granite formation. Hf and O isotopes are used to detect discrete changes in melt source while U-Pb isotopes provide the timing of zircon crystallisation. Our data show that zircon rims of Himalayan age yield Hf-O signatures that lie within the previously reported whole-rock GHS field, confirming the absence of a discernible mantle contribution to the leucogranite source. Importantly, we document a decrease in the minimum ɛHf values during Himalayan orogenesis through time, correlating to a change in Hf model age from 1.4 Ga to 2.4 Ga. Nd model ages for the older Lesser Himalayan metasediments (LHS) that underthrust the GHS are significantly older than those for the GHS (2.4-2.9 Ga compared with 1.4-2.2 Ga), and as such even minor contributions of LHS material incorporated into a melt would significantly increase the resulting Hf model age. Hence our leucogranite data suggest either a change of source within the GHS over time, or an increasing contribution from older Lesser Himalayan (LHS) material in the melt. This is the first time that an evolutionary trend in the chemistry of Himalayan crustal melts has been recognized. Thus these new data show that, at least in the Himalaya, accessory phase geochemistry can provide more detailed insight into tectonic processes than bulk rock geochemistry.

Effect of carbon, sulfur and silicon on iron melting at high pressure: Implications for composition and evolution of the planetary terrestrial cores

NASA Astrophysics Data System (ADS)

Deng, Liwei; Fei, Yingwei; Liu, Xi; Gong, Zizheng; Shahar, Anat

2013-08-01

High-pressure melting experiments in the Fe-S-C ternary and Fe-S-Si-C quaternary systems have been conducted in the range of 3.5-20 GPa and 920-1700 °C in the multi-anvil press. The mutual solubility, melting relations, and crystallization sequences were systematically investigated with changes of pressure, temperature and bulk composition. Five starting materials of Fe(84.69 wt%)-C(4.35 wt%)-S(7.85 wt%), Fe(84.87 wt%)-C(2.08 wt%)-S(11.41 wt%), Fe(86.36 wt%)-C(0.96 wt%)-S(10.31 wt%), Fe(85.71 wt%)-C(0.33 wt%)-S(11.86 wt%) and Fe(82.95 wt%)-C(0.66 wt%)-S(13.7 wt%)-Si(2.89 wt%) were employed. For Fe(84.69 wt%)-C(4.35 wt%)-S(7.85 wt%), the first crystallized phase is Fe3C at 5 GPa and Fe7C3 at 10-20 GPa. For Fe(84.87 wt%)-C(2.08 wt%)-S(11.41 wt%), Fe3C is the stable carbide at subsolidus temperature at 5-15 GPa. For Fe(86.36 wt%)-C(0.96 wt%)-S(10.31 wt%) and Fe(85.71 wt%)-C(0.33 wt%)-S(11.86 wt%), the first crystallized phase is metallic Fe instead of iron carbide at 5-10 GPa. The cotectic curves in Fe-S-C ternary system indicate only a small amount of C is needed to form an iron carbide solid inner core with the presence of S. Experiments on Fe(82.95 wt%)-C(0.66 wt%)-S(13.7 wt%)-Si(2.89 wt%) showed that a small amount of C does not significantly change the closure pressure of miscibility gap compared with that in Fe-S-Si system. It is observed that S preferentially partitions into molten iron while a significant amount of Si enters the solid phase with temperature decrease. Meanwhile, the C concentration in the liquid and solid iron metal changes little with temperature variations. If S, C and Si partitioning behavior between molten iron and solid iron metal with temperature remains the same under Earth's present core pressure conditions, the solid inner core should be iron dominated with dissolved Si. On the other hand, the liquid outer core will be S rich and Si poor. Moderate carbon will be evenly present in both solid and liquid cores. Based on our melting data in a multi-component system, no layered liquid core should exist in the Earth, Mars and Mercury.

Apparatus for controlling molten core debris

DOEpatents

Golden, Martin P. [Trafford, PA; Tilbrook, Roger W. [Monroeville, PA; Heylmun, Neal F. [Pittsburgh, PA

1977-07-19

Apparatus for containing, cooling, diluting, dispersing and maintaining subcritical the molten core debris assumed to melt through the bottom of a nuclear reactor pressure vessel in the unlikely event of a core meltdown. The apparatus is basically a sacrificial bed system which includes an inverted conical funnel, a core debris receptacle including a spherical dome, a spherically layered bed of primarily magnesia bricks, a cooling system of zig-zag piping in graphite blocks about and below the bed and a cylindrical liner surrounding the graphite blocks including a steel shell surrounded by firebrick. Tantalum absorber rods are used in the receptacle and bed.

Geophysical evidence for melt in the deep lunar interior and implications for lunar evolution

NASA Astrophysics Data System (ADS)

Khan, A.; Connolly, J. A. D.; Pommier, A.; Noir, J.

2014-10-01

Analysis of lunar laser ranging and seismic data has yielded evidence that has been interpreted to indicate a molten zone in the lowermost mantle overlying a fluid core. Such a zone provides strong constraints on models of lunar thermal evolution. Here we determine thermochemical and physical structure of the deep Moon by inverting lunar geophysical data (mean mass and moment of inertia, tidal Love number, and electromagnetic sounding data) in combination with phase-equilibrium computations. Specifically, we assess whether a molten layer is required by the geophysical data. The main conclusion drawn from this study is that a region with high dissipation located deep within the Moon is required to explain the geophysical data. This region is located within the mantle where the solidus is crossed at a depth of ˜1200 km (≥1600°C). Inverted compositions for the partially molten layer (150-200 km thick) are enriched in FeO and TiO2 relative to the surrounding mantle. The melt phase is neutrally buoyant at pressures of ˜4.5-4.6 GPa but contains less TiO2 (<15 wt %) than the Ti-rich (˜16 wt %) melts that produced a set of high-density primitive lunar magmas (density of 3.4 g/cm3). Melt densities computed here range from 3.25 to 3.45 g/cm3 bracketing the density of lunar magmas with moderate-to-high TiO2 contents. Our results are consistent with a model of lunar evolution in which the cumulate pile formed from crystallization of the magma ocean as it overturned, trapping heat-producing elements in the lower mantle.

Cooling rates and crystallization dynamics of shallow level pegmatite-aplite dikes, San Diego County, California

USGS Publications Warehouse

Webber, Karen L.; Simmons, William B.; Falster, Alexander U.; Foord, Eugene E.

1999-01-01

Pegmatites of the Pala and Mesa Grande Pegmatite Districts, San Diego County, California are typically thin, sheet-like composite pegmatite-aplite dikes. Aplitic portions of many dikes display pronounced mineralogical layering referred to as "line rock," characterized by fine-grained, garnet-rich bands alternating with albite- and quartz-rich bands. Thermal modeling was performed for four dikes in San Diego County including the 1 m thick Himalaya dike, the 2 m thick Mission dike, the 8 m thick George Ashley dike, and the 25 m thick Stewart dike. Calculations were based on conductive cooling equations accounting for latent heat of crystallization, a melt emplacement temperature of 650 °C into 150 °C fractured, gabbroic country rock at a depth of 5 km, and an estimated 3 wt% initial H2O content in the melt. Cooling to -5 cm/s. Crystal size distribution (CSD) studies of garnet from layered aplites suggest growth rates of about 10-6 cm/s. These results indicate that the dikes cooled and crystallized rapidly, with variable nucleation rates but high overall crystal-growth rates. Initial high nucleation rates coincident with emplacement and strong undercooling can account for the millimeter-size aplite grains. Lower nucleation rates coupled with high growth rates can explain the decimeter-size minerals in the hanging walls, cores, and miarolitic cavities of the pegmatites. The presence of tourmaline and/or lepidolite throughout these dikes suggests that although the melts were initially H2O-undersaturated, high melt concentrations of incompatible (or fluxing) components such as B, F, and Li (±H2O), aided in the development of large pegmatitic crystals that grew rapidly in the short times suggested by the conductive cooling models.

Constraints on Earth’s inner core composition inferred from measurements of the sound velocity of hcp-iron in extreme conditions

PubMed Central

Sakamaki, Tatsuya; Ohtani, Eiji; Fukui, Hiroshi; Kamada, Seiji; Takahashi, Suguru; Sakairi, Takanori; Takahata, Akihiro; Sakai, Takeshi; Tsutsui, Satoshi; Ishikawa, Daisuke; Shiraishi, Rei; Seto, Yusuke; Tsuchiya, Taku; Baron, Alfred Q. R.

2016-01-01

Hexagonal close-packed iron (hcp-Fe) is a main component of Earth’s inner core. The difference in density between hcp-Fe and the inner core in the Preliminary Reference Earth Model (PREM) shows a density deficit, which implies an existence of light elements in the core. Sound velocities then provide an important constraint on the amount and kind of light elements in the core. Although seismological observations provide density–sound velocity data of Earth’s core, there are few measurements in controlled laboratory conditions for comparison. We report the compressional sound velocity (VP) of hcp-Fe up to 163 GPa and 3000 K using inelastic x-ray scattering from a laser-heated sample in a diamond anvil cell. We propose a new high-temperature Birch’s law for hcp-Fe, which gives us the VP of pure hcp-Fe up to core conditions. We find that Earth’s inner core has a 4 to 5% smaller density and a 4 to 10% smaller VP than hcp-Fe. Our results demonstrate that components other than Fe in Earth’s core are required to explain Earth’s core density and velocity deficits compared to hcp-Fe. Assuming that the temperature effects on iron alloys are the same as those on hcp-Fe, we narrow down light elements in the inner core in terms of the velocity deficit. Hydrogen is a good candidate; thus, Earth’s core may be a hidden hydrogen reservoir. Silicon and sulfur are also possible candidates and could show good agreement with PREM if we consider the presence of some melt in the inner core, anelasticity, and/or a premelting effect. PMID:26933678

Release of Nitrogen during Planetary Accretion Explains Missing Nitrogen in Earth's Mantle

NASA Astrophysics Data System (ADS)

Liu, J.; Dorfman, S.; Lv, M.; Li, J.; Kono, Y.

2017-12-01

Nitrogen and carbon are essential elements for life on Earth, and their relative abundances in planetary bodies (C/N ratios) are important for understanding planetary evolution and habitability1,2. However, the high C/N ratio in the bulk silicate Earth relative to CI chondrites and other volatile-rich chondrites is difficult to explain with partitioning behavior between silicate and metallic liquid or solubility in silicate melt, and has thus been a major unsolved problem in geochemistry1-5. Because core formation does not explain nitrogen depletion in the mantle, another process is required to match the observed BSE C/N ratio, such as devolatilization of metallic liquid. Previous studies have examined the Fe-C phase diagram extensively (e.g. ref. 6), but very limited melting data is available for the Fe-N system7. Here we examine melting relations for four Fe-N-C compositions with 1-7 wt% nitrogen up to 7 GPa and 2200 K in the Paris-Edinburgh press by a combination of in-situ X-ray radiography, X-ray diffraction and ex-situ electron microprobe techniques. In striking contrast to the Fe-C system, near-surface melting in all compositions in the Fe-N-C system entails release of nitrogen fluid and depletion of nitrogen from the liquid alloy. This could provide a pathway for nitrogen to escape the magma ocean in the accretion stage while carbon is retained. On the basis of our experimental results, we propose a new quantitative model of mantle nitrogen evolution during the core formation stage to explain the high BSE C/N ratios and resolve the paradox of missing mantle nitrogen1-5. Although nitrogen itself is not a greenhouse gas, the nitrogen released to the atmosphere from metallic melt early in Earth's history could amplify the greenhouse effect through collision-enhanced absorption8,9, which may help to explain warm surface temperatures during the Hadean and Archean eras on Earth when the solar luminosity was 25-30% lower than the present10. References1. Bergin et al., PNAS (2015). 2. Hirschmann, Am. Mineral. (2016). 3. Marty, EPSL (2012). 4. Halliday, GCA (2013). 5. Dalou et al., EPSL (2017). 6. Walker et al., Contrib. Mineral. Petrol. (2013). 7. Guillermet et al., Z. Metallkd. (1994). 8. Wordsworth et al., Science (2013). 9. Goldblatt et al. Nat. Geosci. (2009). 10. Gough. Sol. Phys. (1981)

The behaviour of tungsten during mantle melting revisited with implications for planetary differentiation time scales

NASA Astrophysics Data System (ADS)

Babechuk, Michael G.; Kamber, Balz S.; Greig, Alan; Canil, Dante; Kodolányi, János

2010-02-01

Tungsten is a moderately siderophile high-field-strength element that is hydrophile and widely regarded as highly incompatible during mantle melting. In an effort to extend empirical knowledge regarding the behaviour of W during the latter process, we report new high-precision trace element data (W, Th, U, Ba, La, Sm) that represent both terrestrial and planetary reservoirs: MORB (11), abyssal peridotites (8), eucrite basalts (3), and carbonaceous chondrites (8). A full trace element suite is also reported for Cordilleran Permian ophiolite peridotites (12) to better constrain the behaviour of W in the upper mantle. In addition, we report our long-term averages for a number of USGS (BIR-1, BHVO-1, BHVO-2, PCC-1, DTS-1) and GSJ (JA-3, JP-1) standard reference materials, some of which we conclude to be heterogeneous and contaminated with respect to W. The most significant finding of this study is that many of the highly depleted upper mantle peridotites contain far higher W concentrations than expected. In the absence of convincing indications for alteration, re-enrichment or contamination, we propose that the W excess was caused by retention in an Os-Ir alloy phase, whose stability is dependent on fO 2 of the mantle source region. This explanation could help to account for the particularly low W content of N-MORB and implies that the lithophile behaviour of W in basaltic rocks is not an accurate representation of the behaviour in the melt source. These findings then become relevant to the interpretation of W-isotopic data for achondrites, where the fractionation of Hf from W during melting is used to infer the Hf/W of the parent body mantle. This is exemplified by the differentiation chronology of the eucrite parent body (EPB), which has been modeled with a melt source with high Hf/W. By contrast, we explore the alternative scenario with a low mantle Hf/W on the EPB. Using available eucrite literature data, a maximum core segregation age of 1.2 ± 1.2 Myr after the closure of CAIs is calculated with a more prolonged time between core formation and mantle fractionation of ca. 2 Myr. This timeline is consistent with most recent published chronologies of the EPB differentiation based on the 53Mn- 53Cr and 26Al- 26Mg systems.

Melting and Freezing of Metals Under the High Pressures of Planetary Interiors

NASA Astrophysics Data System (ADS)

Geballe, Zachary Michael

The goal of this thesis is to help improve models of the evolution of cores of the Earth and other planets, and to improve understanding of melting transitions of metals in general. First, I present laboratory studies of high-pressure melting and near-melting phase transitions of two metals. The epsilon-to-B2 phase boundary of FeSi is constrained to 30 +/- 2 GPa with no measurable pressure-dependence from 1200 +/- 200 to 2300 +/- 200 K using x-ray diffraction in laser heated diamond anvil cells. The miscibility of Si in crystalline Fe likely increases at this transition due to the increasing effective ionic radius of Si, evidenced by the coordination change documented here. The result is that silicon is even more miscible in iron in the cores of Mercury and Mars than shown previously. Solid-solid transitions are also documented in AuGa2 from cubic (fluorite-type) to denser phases above 5.5 GPa and 600 K, in close proximity to the reversal in melting curve from negative slope to positive slope, which is also documented here. The change in melting curve therefore seems to be primarily driven by the crystallographic transitions and not the electronic transitions thought to occur at low temperatures. All transitions described here are reversed in the experiments, revealing hysteresis that ranges from 90 K to less than 15 K, and from 7 GPa to less than 2 GPa. This complexity, along with other complexities seen here and in other studies, suggest the need for new experimental techniques to make unambiguous measurements of a variety of equilibrium properties at melting and near melting. To improve future laboratory studies of melting at high pressure, I analyze several varieties of dynamic heating experiments. Laser heating experiments on metals in diamond anvil cells are shown to be at least 5 times less sensitive (and sometimes > 100 times less sensitive) to the latent heat of melting than suggested by published experimental data from pulsed-heating and continuous-heating experiments. Rather, experimentally detected plateaus in temperature likely result from changes in reflectivity of the laser absorber. To reveal a material's energetic properties (latent heat or heat capacity) in the highly conductive environment of diamond cells, heating frequencies >100 kHz should be used, and heat should be deposited uniformly through the material. Specifically, an "adiabaticity parameter'' is presented in Chapter 4 to guide experiments seeking to measure temperature plateaus that reveal the latent heats of first order phase transitions. Focusing on heat capacity alone, two experimental possibilities are described in Chapter 5: relative measures of heat capacity of metallic samples using modulated laser heating at 1 MHz to 1 GHz, and absolute measure of heat capacity using Joule-heating of metallic samples at 1 to 100 MHz frequency. Finally, Chapter 6 shows that a specific experimental design for Joule-heating is feasible: a realistic electrical circuit using two amplifiers and a Wheatstone bridge can couple electrical current into a diamond-cell-sized metal sample and output 20 mu V residual voltage oscillations induced by the sample's 1 MHz temperature oscillations, allowing measurement of the sample's heat capacity with 11% contribution from the insulation. The thermal models of Joule heating in diamond cells are validated by laboratory data of the heat capacity of a nickel foil pressed between thin glass pieces glued to a diamond: measured heat capacities decrease from 100s of % above the actual heat capacity of a 6 mu m-thick nickel sample at ≤ 1 kHz, to within ~ 20% of the actual heat capacity at 30 kHz.

Partitioning of carbon between Fe-rich alloy melt and silicate melt in a magma ocean - Implications for the abundance and origin of volatiles in Earth, Mars, and the Moon

NASA Astrophysics Data System (ADS)

Chi, Han; Dasgupta, Rajdeep; Duncan, Megan S.; Shimizu, Nobumichi

2014-08-01

The budget and origin of carbon in Earth and other terrestrial planets are debated and one of the key unknowns is the fate of carbon during early planetary processes including accretion, core formation, and magma ocean (MO) crystallization. Here we determine, experimentally, the solubility of carbon in coexisting Fe-Ni alloy melt and basaltic silicate melt in shallow MO conditions, i.e., at 1-3 GPa, 1500-1800 °C. Oxygen fugacity of the experiments, estimated based on Fe (in metallic alloy melt)-FeO (in silicate melt) equilibrium, varied between ∼IW-0.4 and IW-1.0, where IW refers to the oxygen fugacity imposed by the coexistence of iron and wüstite. Four different starting mixes, each with 7:3 silicate:metal mass ratio and silicate melt NBO/T (estimated proportion of non-bridging oxygen with respect to tetrahedral cations; NBO/T=2×/total OT -4, where T = Si + Ti + Al + Cr + P) ranging from 0.81 to 1.54 were studied. Concentrations of carbon in the alloy melt were determined using electron microprobe whereas carbon contents of quenched basaltic glasses were determined using secondary ionization mass spectrometry (SIMS). Identification of carbon and hydrogen-bearing species in silicate glasses was performed using Raman and Fourier Transformed Infrared (FTIR) spectroscopy. Our results show that carbon in the metallic melt varies between 4.4 wt.% and 7.4 wt.% and increases with increasing temperature and modestly with increasing pressure but decreases with increasing Ni content of the alloy melt. Carbon concentration in the silicate melts, on the other hand, varies from 11 ± 1 ppm to 111 ± 7 ppm and is negatively correlated with pressure but positively correlated with temperature, the NBO/T, the oxygen fugacity and the water content of the silicate melts. Raman and FTIR results show that at our experimental conditions, carbon in silicate melt is dissolved both as hydrogenated species and CO32-. The calculated carbon partition coefficient DCmetal/silicate varies from 510 ± 53 to 5369 ± 217 and varies systematically as a function of P, T, fO2, water content, the composition of the silicate melt (expressed using NBO/T), and Ni content of alloy melt (XNi). The range of DCmetal/silicate measured in our study with carbonated and hydrogenated carbon species in silicate melt is similar to that reported in the literature for experiments where carbonyl complexes are the chief carbon species in silicate melts. A parameterization was derived using the data from this and existing studies such as lnDCmetal/silicate=a/T+b·P/T+c·ln(fO2)+d·(NBO/T)+e·ln(1-XNi)+f where a = -33,510, b = 1357, c = -0.596, d = -1.182, e = 4.15, f = 13.38, the temperature is in Kelvin, and the pressure is in gigapascal. Using this parameterization and the estimated conditions for the base of the MOs, the average DCmetal/silicate value for Earth, Mars, and the Moon can be predicted. The deep MO of Earth is predicted to cause the strongest depletion of its silicate carbon budget, closely followed by Mars with intermediate depth MO, and then the Moon with a shallow MO. We predict that the lunar mantle carbon budget, similar to that of the Earth’s present-day upper mantle, might have been set by equilibrium core-mantle fractionation in MO; whereas for Earth, later processes such as ingassing from a proto-atmosphere and late-stage accretion of volatile-rich material was necessary for delivery of carbon and other volatiles. Finally, the comparison of our measured and predicted value of DCmetal/silicate for terrestrial MO with similar constraints on DNmetal/silicate from the literature suggests that the apparent depletion of nitrogen relative to carbon for the bulk silicate Earth and the Earth’s upper mantle is unlikely to be caused by preferential partitioning of nitrogen to alloy melt during core formation.

Mars’ Low Dissipation Factor at 11-h - Interpretation from Anelasticity-Based Dissipation Model

NASA Astrophysics Data System (ADS)

Castillo-Rogez, Julie; Choukroun, M.

2010-10-01

We explore the information contained in the ratio of the tidal Love number k2 to the dissipation factor Q characterizing the response of Mars to the tides exerted by its satellite Phobos (11-h period). Assuming that Mars can be approximated as a Maxwell body, Bills et al. [1] have inferred an average viscosity of the Martian mantle 8.7x1014 Pa s. Such a low viscosity appears inconsistent with Mars’ thermal evolution and current heat budget models. Alternative explanations include the presence of partial melt in the mantle [2], or the presence of an aquifer in the crust [3]. We revisit the interpretation of Mars’ k2/Q using a laboratory-based attenuation model that accounts for material viscoelasticity and anelasticity. As a first step, we have computed Mars’ k2/Q for an interior model that includes a solid inner core, a liquid core layer, a mantle, and crust (consistent with the observed moment of inertia, and k2 measured at the orbital period), and searched for the range of mantle viscosities that can explain the observed k2/Q. Successful models are characterized by an average mantle viscosity between 1018 and 1022 Pa s, which rules out the presence of partial melt in the mantle. We can narrow down that range by performing a more detailed calculation of the mineralogy and temperature profiles. Preliminary results will be presented at the meeting. References: [1] Bills et al. (2005) JGR 110, E00704; [2] Ruedas et al. (2009 White paper to the NRC Planetary Science decadal survey; [3] Bills et al. (2009) LPS 40, 1712. MC is supported by a NASA Postdoctoral Program Fellowship, administered by Oak Ridge Associated Universities. This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract to NASA. Government sponsorship acknowledged.

Modeling Specular Exchange Between Concentric Cylinders in a Radiative Shielded Furnace

NASA Technical Reports Server (NTRS)

Schunk, Richard Gregory; Wessling, Francis C.

2000-01-01

The objective of this research is to develop and validate mathematical models to characterize the thermal performance of a radiative shielded furnace, the University of Alabama in Huntsville (UAH) Isothermal Diffusion Oven. The mathematical models are validated against experimental data obtained from testing the breadboard oven in a terrestrial laboratory environment. It is anticipated that the validation will produce math models capable of predicting the thermal performance of the furnace over a wide range of operating conditions, including those for which no experimental data is available. Of particular interest is the furnace core temperature versus heater power parametric and the transient thermal response of the furnace. Application to a microgravity environment is not considered, although it is conjectured that the removal of any gravity dependent terms from the math models developed for the terrestrial application should yield adequate results in a microgravity environment. The UAH Isothermal Diffusion Oven is designed to provide a thermal environment that is conducive to measuring the diffusion of high temperature liquid metals. In addition to achieving the temperatures required to melt a sample placed within the furnace, reducing or eliminating convective motions within the melt is an important design consideration [1]. Both of these influences are reflected in the design of the furnace. Reducing unwanted heat losses from the furnace is achieved through the use of low conductivity materials and reflective shielding. As evidenced by the highly conductive copper core used to house the sample within the furnace, convective motions can be greatly suppressed by providing an essentially uniform thermal environment. An oven of this design could ultimately be utilized in a microgravity environment, presumably as a experiment payload. Such an application precipitates other design requirements that limit the resources available to the furnace such as power, mass, volume, and possibly even time. Through the experimental and numerical results obtained, the power requirements and thermal response time of the breadboard furnace are quantified.

Extensive, water-rich magma reservoir beneath southern Montserrat

NASA Astrophysics Data System (ADS)

Edmonds, M.; Kohn, S. C.; Hauri, E. H.; Humphreys, M. C. S.; Cassidy, M.

2016-05-01

South Soufrière Hills and Soufrière Hills volcanoes are 2 km apart at the southern end of the island of Montserrat, West Indies. Their magmas are distinct geochemically, despite these volcanoes having been active contemporaneously at 131-129 ka. We use the water content of pyroxenes and melt inclusion data to reconstruct the bulk water contents of magmas and their depth of storage prior to eruption. Pyroxenes contain up to 281 ppm H2O, with significant variability between crystals and from core to rim in individual crystals. The Al content of the enstatites from Soufrière Hills Volcano (SHV) is used to constrain melt-pyroxene partitioning for H2O. The SHV enstatite cores record melt water contents of 6-9 wt%. Pyroxene and melt inclusion water concentration pairs from South Soufriere Hills basalts independently constrain pyroxene-melt partitioning of water and produces a comparable range in melt water concentrations. Melt inclusions recorded in plagioclase and in pyroxene contain up to 6.3 wt% H2O. When combined with realistic melt CO2 contents, the depth of magma storage for both volcanoes ranges from 5 to 16 km. The data are consistent with a vertically protracted crystal mush in the upper crust beneath the southern part of Montserrat which contains heterogeneous bodies of eruptible magma. The high water contents of the magmas suggest that they contain a high proportion of exsolved fluids, which has implications for the rheology of the mush and timescales for mush reorganisation prior to eruption. A depletion in water in the outer 50-100 μm of a subset of pyroxenes from pumices from a Vulcanian explosion at Soufrière Hills in 2003 is consistent with diffusive loss of hydrogen during magma ascent over 5-13 h. These timescales are similar to the mean time periods between explosions in 1997 and in 2003, raising the possibility that the driving force for this repetitive explosive behaviour lies not in the shallow system, but in the deeper parts of a vertically protracted crustal magma storage system.

High Resolution Continuous Flow Analysis System for Polar Ice Cores

NASA Astrophysics Data System (ADS)

Dallmayr, Remi; Azuma, Kumiko; Yamada, Hironobu; Kjær, Helle Astrid; Vallelonga, Paul; Azuma, Nobuhiko; Takata, Morimasa

2014-05-01

In the last decades, Continuous Flow Analysis (CFA) technology for ice core analyses has been developed to reconstruct the past changes of the climate system 1), 2). Compared with traditional analyses of discrete samples, a CFA system offers much faster and higher depth resolution analyses. It also generates a decontaminated sample stream without time-consuming sample processing procedure by using the inner area of an ice-core sample.. The CFA system that we have been developing is currently able to continuously measure stable water isotopes 3) and electrolytic conductivity, as well as to collect discrete samples for the both inner and outer areas with variable depth resolutions. Chemistry analyses4) and methane-gas analysis 5) are planned to be added using the continuous water stream system 5). In order to optimize the resolution of the current system with minimal sample volumes necessary for different analyses, our CFA system typically melts an ice core at 1.6 cm/min. Instead of using a wire position encoder with typical 1mm positioning resolution 6), we decided to use a high-accuracy CCD Laser displacement sensor (LKG-G505, Keyence). At the 1.6 cm/min melt rate, the positioning resolution was increased to 0.27mm. Also, the mixing volume that occurs in our open split debubbler is regulated using its weight. The overflow pumping rate is smoothly PID controlled to maintain the weight as low as possible, while keeping a safety buffer of water to avoid air bubbles downstream. To evaluate the system's depth-resolution, we will present the preliminary data of electrolytic conductivity obtained by melting 12 bags of the North Greenland Eemian Ice Drilling (NEEM) ice core. The samples correspond to different climate intervals (Greenland Stadial 21, 22, Greenland Stadial 5, Greenland Interstadial 5, Greenland Interstadial 7, Greenland Stadial 8). We will present results for the Greenland Stadial -8, whose depths and ages are between 1723.7 and 1724.8 meters, and 35.520 to 35.636 kyr b2k 7), respectively. The results show the conductivity measured upstream and downstream of the debubbler. We will calculate the depth resolution of our system and compare it with earlier studies. 1) Bigler at al, "Optimization of High-Resolution Continuous Flow Analysis For Transient Climate Signals in Ice Cores". Environ. Sci. Technol. 2011, 45, 4483-4489 2) Kaufmann et al, "An Improved Continuous Flow Analysis System for High Resolution Field Measurements on Ice Cores". Environmental Environ. Sci. Technol. 2008, 42, 8044-8050 3) Gkinis, V., T. J. Popp, S. J. Johnsen and T, Blunier, 2010: A continuous stream flash evaporator for the calibration of an IR cavity ring down spectrometer for the isotopic analysis of water. Isotopes in Environmental and Health Studies, 46(4), 463-475. 4) McConnell et al, "Continuous ice-core chemical analyses using inductively coupled plasma mass spectrometry. Environ. Sci. Technol. 2002, 36, 7-11 5) Rhodes et al, "Continuous methane measurements from a late Holocene Greenland ice core : Atmospheric and in-situ signals" Earth and Planetary Science Letters. 2013, 368, 9-19 6) Breton et al, "Quantifying Signal Dispersion in a Hybrid Ice Core Melting System". Environ. Sci. Technol. 2012, 46, 11922-11928 7) Rasmussen et al, " A first chronology for the NEEM ice core". Climate of the Past. 2013, 9, 2967--3013

Siderophile Element Partitioning between Sulfide- and Silicate melts.

NASA Astrophysics Data System (ADS)

Hackler, S.; Rohrbach, A.; Loroch, D. C.; Klemme, S.; Berndt, J.

2017-12-01

Different theories concerning the formation of the Earth are debated. Either Earth accreted mostly `dry' or volatile elements were delivered late after core formation was largely inactive [1, 2], or volatile rich material was accreted during the main stages of accretion and core formation [3, 4, 5]. The partitioning behavior of siderophile volatile elements (SVE; S, Se, Te, Tl, Ag, Au, Cd, Bi, Pb, Sn, Cu, Ge, and In) may provide first order constraints whether these element concentrations in Earth's mantle were established before or after core-mantle differentiation or perhaps during both periods by multi stage core formation [6]. A special interest is laid into chalcophile element behavior with respective to the possible formation and segregation of a hadean matte [7]. To examine the influence of sulfur on SVE partitioning between metal-silicate melts, we performed experiments simulating a magma ocean stage evolving from sulfur poor- (low fO2) to more oxidizing sulfur rich- (Fe, Ni)-S melts ( 20 wt% S) towards the end of accretion. We carried out partitioning experiments under various P-T-fO2 conditions with a Bristol type end loaded piston cylinder apparatus (<3 GPa) and a 1000 t walker-type multi-anvil press (3-20 GPa). Our results will be presented at the meeting. References: [1] Albarède F. (2009) Nature, 461, 1227-1233. [2] Ballhaus C. et al. (2013) EPSL, 362, 237-245. [3] Fischer-Gödde M. and Kleine T. (2017) Nature, 541, 525 527. [4] Wade J. and Wood B. J. (2005) EPSL, 236, 78-95. [5] Rubie D. et al. (2016) Science, 253, 1141-1144. [6] Rubie D. et al. (2011) EPSL, 301, 31-42. [7] O'Neill H. St. C. (1991) GCA, 55, 1159-1172.

Phase relations in the Fe-FeSi system at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Fischer, Rebecca A.; Campbell, Andrew J.; Reaman, Daniel M.; Miller, Noah A.; Heinz, Dion L.; Dera, Przymyslaw; Prakapenka, Vitali B.

2013-07-01

The Earth's core is comprised mostly of iron and nickel, but it also contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is important to understand the high pressure, high temperature properties and behavior of alloys in the Fe-FeSi system, such as their phase diagrams. We determined melting temperatures and subsolidus phase relations of Fe-9 wt% Si and stoichiometric FeSi using synchrotron X-ray diffraction at high pressures and temperatures, up to ~200 GPa and ~145 GPa, respectively. Combining this data with that of previous studies, we generated phase diagrams in pressure-temperature, temperature-composition, and pressure-composition space. We find the B2 crystal structure in Fe-9Si where previous studies reported the less ordered bcc structure, and a shallower slope for the hcp+B2 to fcc+B2 boundary than previously reported. In stoichiometric FeSi, we report a wide B2+B20 two-phase field, with complete conversion to the B2 structure at ~42 GPa. The minimum temperature of an Fe-Si outer core is 4380 K, based on the eutectic melting point of Fe-9Si, and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur. At the highest pressures reached, only the hcp and B2 structures are seen in the Fe-FeSi system. We predict that alloys containing more than ~4-8 wt% silicon will convert to an hcp+B2 mixture and later to the hcp structure with increasing pressure, and that an iron-silicon alloy in the Earth's inner core would most likely be a mixture of hcp and B2 phases.

Phase relations in the Fe-FeSi system at high pressures and temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fischer, Rebecca A.; Campbell, Andrew J.; Reaman, Daniel M.

2016-07-29

The Earth's core is comprised mostly of iron and nickel, but it also contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is important to understand the high pressure, high temperature properties and behavior of alloys in the Fe–FeSi system, such as their phase diagrams. We determined melting temperatures and subsolidus phase relations of Fe–9 wt% Si and stoichiometric FeSi using synchrotron X-ray diffraction at high pressures and temperatures, up to ~200 GPa and ~145 GPa, respectively. Combining this data with that of previous studies, we generated phase diagrams in pressure–temperature, temperature–composition,more » and pressure–composition space. We find the B2 crystal structure in Fe–9Si where previous studies reported the less ordered bcc structure, and a shallower slope for the hcp+B2 to fcc+B2 boundary than previously reported. In stoichiometric FeSi, we report a wide B2+B20 two-phase field, with complete conversion to the B2 structure at ~42 GPa. The minimum temperature of an Fe–Si outer core is 4380 K, based on the eutectic melting point of Fe–9Si, and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur. At the highest pressures reached, only the hcp and B2 structures are seen in the Fe–FeSi system. We predict that alloys containing more than ~4–8 wt% silicon will convert to an hcp+B2 mixture and later to the hcp structure with increasing pressure, and that an iron–silicon alloy in the Earth's inner core would most likely be a mixture of hcp and B2 phases.« less

Complete devil's staircase and crystal-superfluid transitions in a dipolar XXZ spin chain: a trapped ion quantum simulation

NASA Astrophysics Data System (ADS)

Hauke, Philipp; Cucchietti, Fernando M.; Müller-Hermes, Alexander; Bañuls, Mari-Carmen; Cirac, J. Ignacio; Lewenstein, Maciej

2010-11-01

Systems with long-range interactions show a variety of intriguing properties: they typically accommodate many metastable states, they can give rise to spontaneous formation of supersolids, and they can lead to counterintuitive thermodynamic behavior. However, the increased complexity that comes with long-range interactions strongly hinders theoretical studies. This makes a quantum simulator for long-range models highly desirable. Here, we show that a chain of trapped ions can be used to quantum simulate a one-dimensional (1D) model of hard-core bosons with dipolar off-site interaction and tunneling, equivalent to a dipolar XXZ spin-1/2 chain. We explore the rich phase diagram of this model in detail, employing perturbative mean-field theory, exact diagonalization and quasi-exact numerical techniques (density-matrix renormalization group and infinite time-evolving block decimation). We find that the complete devil's staircase—an infinite sequence of crystal states existing at vanishing tunneling—spreads to a succession of lobes similar to the Mott lobes found in Bose-Hubbard models. Investigating the melting of these crystal states at increased tunneling, we do not find (contrary to similar 2D models) clear indications of supersolid behavior in the region around the melting transition. However, we find that inside the insulating lobes there are quasi-long-range (algebraic) correlations, as opposed to models with nearest-neighbor tunneling, that show exponential decay of correlations.

Sm-Nd Age and Nd- and Sr- Isotopic Evidence for the Petrogenesis of Dhofar 378

NASA Technical Reports Server (NTRS)

Nyquist, L. E.; Ikeda, Y.; Shih, C.-Y.; Reese, Y. D.; Nakamura, N.; Takeda, H.

2006-01-01

Dhofar 378 (hereafter Dho 378) is one of the most ferroan lithologies among martian meteorites, resembling the Los Angeles basaltic shergottite in lithology and mineral chemistry, although it is more highly shocked than Los Angeles. All plagioclase (Pl) grains in the original lithology were melted by an intense shock in the range 55-75 GPa. Clinopyroxenes (Cpx) sometimes show mosaic extinction under a microscope showing that they, too, experienced intense shock. Nevertheless, they zone from magnesian cores to ferroan rims, reflecting the original lithology. Cpx grains also often contain exsolution lamellae, showing that the original lithology cooled slowly enough for the lamellae to form. Because all plagioclase grains were melted by the intense shock and subsequently quenched, the main plagioclase component is glass (Pl-glass) rather than maskelynite. Like Los Angeles, but unlike most basaltic shergottites, Dho 378 contains approximately equal modal abundances of Cpx and Pl-glass. The grain sizes of the original minerals were comparatively large (approximately 1 mm). The original plagioclase zoning has been severely modified. Following shock melting, the plagioclase melts crystallized from the outside inward, first forming outer rims of Cpx-Pl intergrowths (approximately 10 micrometers) followed by inner rims (10's to 100 micrometers) of An(sub 40-50) feldspar, and finally Pl-gl cores of compositions An(sub 33-50) with orthoclase compositions up to Or(sub 12).

Redox Evolution in Magma Oceans Due to Ferric/Ferrous Iron Partitioning

NASA Astrophysics Data System (ADS)

Schaefer, L.; Elkins-Tanton, L. T.; Pahlevan, K.

2017-12-01

A long-standing puzzle in the evolution of the Earth is that while the present day upper mantle has an oxygen fugacity close to the QFM buffer, core formation during accretion would have occurred at much lower oxygen fugacities close to IW. We present a new model based on experimental evidence that normal solidification and differentiation processes in the terrestrial magma ocean may explain both core formation and the current oxygen fugacity of the mantle without resorting to a change in source material or process. A commonly made assumption is that ferric iron (Fe3+) is negligible at such low oxygen fugacities [1]. However, recent work on Fe3+/Fe2+ ratios in molten silicates [2-4] suggests that the Fe3+ content should increase at high pressure for a given oxygen fugacity. While disproportionation was not observed in these experiments, it may nonetheless be occurring in the melt at high pressure [5]. Therefore, there may be non-negligible amounts of Fe3+ formed through metal-silicate equilibration at high pressures within the magma ocean. Homogenization of the mantle and further partitioning of Fe2+/Fe3+ as the magma ocean crystallizes may explain the oxygen fugacity of the Earth's mantle without requiring additional oxidation mechanisms. We present here models using different parameterizations for the Fe2+/Fe3+ thermodynamic relationships in silicate melts to constrain the evolution of the redox state of the magma ocean as it crystallizes. The model begins with metal-silicate partitioning at high pressure to form the core and set the initial Fe3+ abundance. Combined with previous work on oxygen absorption by magma oceans due to escape of H from H2O [6], we show that the upper layers of solidifying magma oceans should be more oxidized than the lower mantle. This model also suggests that large terrestrial planets should have more oxidized mantles than small planets. From a redox perspective, no change in the composition of the Earth's accreting material needs to be invoked to explain mantle oxygen fugacity, although implications for trace elements in the Earth's core and mantle are still being explored. [1] Ringwood, AE (1979) [2] Armstrong, K et al (2016) LPSC, 2580 [3] Armstrong, K et al (2017) ACCRETE workshop [4] Zhang, HL et al (2017) GCA, 204, 83 [5] Frost, DJ et al (2004) Nature, 428, 409 [6] Schaefer, L et al (2016) ApJ, 829, 63

Cognate clinopyroxene from Paleogene mantle xenolith-bearing basanite lavas (East Serbia, SE Europe): the role of dissolution of mantle orthopyroxene

NASA Astrophysics Data System (ADS)

Cvetković, Vladica; Erić, Suzana; Radivojević, Maša; Šarić, Kristina

2012-11-01

The study focuses on clinopyroxene from mantle xenolith-bearing East Serbian basanites and suggests that dissolution of mantle orthopyroxene played an important role in at least some stages of the crystallization of these alkaline magmas. Five compositional types of clinopyroxene are distinguished, some of them having different textural forms: megacrysts (Type-A), green/colourless-cored phenocrysts (Type-B), overgrowths and sieve-textured cores (Type-C), rims and matrix clinopyroxene (Type-D), and clinopyroxene from the reaction rims around orthopyroxene xenocrysts (Type-E). Type-A is high-Al diopside that probably crystallized at near-liquidus conditions either directly from the host basanite or from compositionally similar magmas in previous magmatic episodes. Type-B cores show high VIAl/IVAl≥1 and low Mg# of mostly <75 and are interpreted as typical xenocrysts. Type-C, D and E are interpreted as typical cognate clinopyroxene. Type-D has Mg#<78, Al2O3 = 6-13 wt.%, TiO2 = 1.5-4.5 wt.%, and Na2O = 0.4-0.8 wt.% and compositionally similar clinopyroxene is calculated by MELTS as a phase in equilibrium with the last 30 % of melt starting from the average host lava composition. Type-C has Mg# = 72-89, Al2O3 = 4.5-9.5 wt.%, TiO2 = 1-2.5 wt.%, Na2O = 0.35-1 wt.% and Cr2O3 = 0.1-1.5 wt.%. This clinopyroxene has some compositional similarities to Type-E occurring exclusively around mantle orthopyroxene. Cr/Al vs Al/Ti and Cr/Al vs Na/Ti plots revealed that Type-C clinopyroxene can crystallize from a mixture of the host basanite magma and 2-20 wt.% mantle orthopyroxene. Sieve-textured Type-C crystals show characteristics of experimentally produced skeletal clinopyroxene formed by orthopyroxene dissolution suggesting that crystallization of Type-C was both texturally and compositionally controlled by orthopyroxene breakdown. According to FeO/MgOcpx/melt modelling the first clinopyroxene precipitating from the host basanite was Type-A (T ~ 1250 °C, p ~ 1.5 GPa). Dissolution of orthopyroxene produced decreasing FeO/MgOmelt and crystallization of Type-E and sieve-textured Type-C clinopyroxene (0.3-0.8 GPa and 1200-1050 °C). The melt composition gradually shifted towards higher FeO/MgOmelt ratios precipitating more evolved Type-C and Type-D approaching near-solidus conditions (<0.3 GPa; ~950 °C).

Silica and Pyroxene in IVA Irons; Possible Formation of the IVA Magma by Impact Melting and Reduction of L-LL-Chondrite Materials Followed by Crystallization and Cooling

NASA Technical Reports Server (NTRS)

Wasson, John T.; Matsunami, Yoshiyuki; Rubin, Alan E.

2006-01-01

Group IVA is a large magmatic group of iron meteorites. The mean DELTA O-17 (= delta O-17 - 0.52(raised dot) delta O-18) of the silicates is approx. plus or minus 1.2%o, similar to the highest values in L chondrites and the lowest values in LL chondrites; delta O-18 values are also in the L/LL range. This strongly suggests that IVA irons formed by melting L-LL parental material, but the mean Ni content of IVA irons (83 mg/g) is much lower than that of a presumed L-LL parent (approx. 170 mg/g) and the low-Ca pyroxene present in two IVA meteorites is Fs13, much lower than the Fs20-29 values in L and LL chondrites. Thus, formation from L-LL precursors requires extensive addition of metallic Fe, probably produced by reduction of FeS and FeO. Group IVA also has S/Ni, Ga/Ni, and Ge/Ni ratios that are much lower than those in L-LL chondrites or any chondrite group that preserves nebular compositions, implying loss of these volatile elements during asteroidal processing. We suggest that these reduction and loss processes occurred near the surface of the asteroid during impact heating, and resulted partly from reduction by C, and partly from the thermal dissociation of FeS and FeO with loss of O and S. The hot (approx. 1770 K) low-viscosity melt quickly moved through channels in the porous asteroid to form a core. Two members of the IVA group, Sao Joao Nepomuceno (hereafter, SJN) and Steinbach, contain moderate amounts of orthopyroxene and silica, and minor amounts of low-Ca clinopyroxene. Even though SJN formed after approx. 26% crystallization and Steinbach formed after approx. 77% Crystallization of the IVA core, both could have originated within several tens of meters of the core-mantle interface if 99% of the crystallization occurred from the center outwards. Two other members of the group (Gibeon and Bishop Canyon) contain tabular tridymite, which we infer to have initially formed as veins deposited from a cooling SiO-rich vapor. The silicates were clearly introduced into IVA irons after the initial magma crystallized. Because the y-iron crystals in SJN are typically about 5 cm across, an order of magnitude smaller than in IVA irons that do not contain massive silicates, we infer that the metal was in the gamma-iron field when the silicates were injected. The SJN and Steinbach silicate compositions are near the low-Ca-pyroxene/silica eutectic compositions. We suggest that a tectonic event produced a eutectic-like liquid and injected it together with unmelted pyroxene grains into fissures in the solid metal core. Published estimates of IVA metallographic cooling rates range from 20 to 3000 K/Ma, leading to a hypothesized breakup of the core during a major impact followed by scrambling of the core and mantle debris [Haack, H., Scott, E.R.D., Love, S.G., Brearley, A. 1996. Thermal histories of IVA stony-iron and iron meteorites: evidence for asteroid fragmentation and reaccretion. Geochim. Cosmochim. Acta 60, 3103-3113]. This scrambling model is physically implausible and cannot explain the strong correlation of estimated cooling rates with metal composition. Previous workers concluded that the low-Ca clinopyroxene in SJN and Steinbach formed from protopyroxene by quenching at a cooling rate of 10(sup 12) K/Ma, and suggested that this also supported an impact-scrambling model. This implausible spike in cooling rate by a factor of 10(sup 10) can be avoided if the low-Ca clinopyroxene were formed by a late shock event that converted orthopyroxene to clinopyroxene followed by minimal growth in the clinopyroxene field, probably because melt was also produced. We suggest that metallographic cooling-rate estimates (e.g., based on island taenite) giving similar values throughout the metal compositional range are more plausible, and that the IVA parent asteroid can be modeled by monotonic cooling followed by a high-temperature impact event that introduced silicates into the metal and a low-temperature impact event that partially converted thopyroxene into low-Ca clinopyroxene.

Double-clad nuclear fuel safety rod

DOEpatents

McCarthy, William H.; Atcheson, Donald B.; Vaidyanathan, Swaminathan

1984-01-01

A device for shutting down a nuclear reactor during an undercooling or overpower event, whether or not the reactor's scram system operates properly. This is accomplished by double-clad fuel safety rods positioned at various locations throughout the reactor core, wherein melting of a secondary internal cladding of the rod allows the fuel column therein to shift from the reactor core to place the reactor in a subcritical condition.

Double-clad nuclear-fuel safety rod

DOEpatents

McCarthy, W.H.; Atcheson, D.B.

1981-12-30

A device for shutting down a nuclear reactor during an undercooling or overpower event, whether or not the reactor's scram system operates properly. This is accomplished by double-clad fuel safety rods positioned at various locations throughout the reactor core, wherein melting of a secondary internal cladding of the rod allows the fuel column therein to shift from the reactor core to place the reactor in a subcritical condition.

Origins of ultralow velocity zones through slab-derived metallic melt

PubMed Central

Liu, Jiachao; Li, Jie; Smith, Jesse S.

2016-01-01

Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron−carbon system crosses the current geotherm near Earth’s core−mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich postbridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth's core−mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle. PMID:27143719

Zircon Hf-O isotopic constraints on the origin of Late Mesozoic felsic volcanic rocks from the Great Xing'an Range, NE China

NASA Astrophysics Data System (ADS)

Gong, Mingyue; Tian, Wei; Fu, Bin; Wang, Shuangyue; Dong, Jinlong

2018-05-01

The voluminous Late Mesozoic magmatism was related to extensive re-melting of juvenile materials that were added to the Central East Asia continent in Phanerozoic time. The most favoured magma generation mechanism of Late Mesozoic magmas is partial melting of underplated lower crust that had radiogenic Hf-Nd isotopic characteristics, but this mechanism faces difficulties when interpreting other isotopic data. The tectonic environment controlling the generation of the Late Mesozoic felsic magmas is also in dispute. In this study, we obtained new U-Pb ages, and geochemical and isotopic data of representative Jurassic (154.4 ± 1.5 Ma) and Cretaceous (140.2 ± 1.5 Ma) felsic volcanic samples. The Jurassic sample has inherited zircon cores of Permian age, with depleted mantle-like εHf(t) of +7.4 - +8.5, which is in contrast with those of the magmatic zircons (εHf(t) = +2.4 ± 0.7). Whereas the inherited cores and the magmatic zircons have identical mantle-like δ18O composition ranges (4.25-5.29‰ and 4.69-5.54‰, respectively). These Hf-O isotopic characteristics suggest a mixed source of enriched mantle materials rather than ancient crustal components and a depleted mantle source represented by the inherited Permian zircon core. This mechanism is manifested by the eruption of Jurassic alkaline basalts originated from an enriched mantle source. The Cretaceous sample has high εHf(t) of +7.0 - +10.5, suggesting re-melting of a mafic magma derived from a depleted mantle-source. However, the sub-mantle zircon δ18O values (3.70-4.58‰) suggest the depleted mantle-derived mafic source rocks had experienced high temperature hydrothermal alteration at upper crustal level. Therefore, the Cretaceous felsic magma, if not all, could be generated by re-melting of down-dropped supracrustal volcanic rocks that experienced high temperature oxygen isotope alteration. The two processes, enriched mantle-contribution and supracrustal juvenile material re-melting, are new generation mechanisms of the Late Mesozoic magmas from Central East Asia. Rift settings may have controlled these processes throughout crustal and mantle levels.

New insights into seismic faulting during the 2008 Mw7.9 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

Li, H.; Wang, H.; Si, J.; Sun, Z.; Pei, J.; Lei, Z.; He, X.

2017-12-01

The WFSD project was implemented promptly after the 2008 Mw 7.9 Wenchuan earthquake. A series of research results on the seismogenic structure, fault deformation, sliding mechanism and fault healing have been obtained, which provide new insights into seismic faulting and mechanisms of the Wenchuan earthquake. The WFSD-1 and -2 drilling core profiles reveal that the Longmen Shan thrust belt is composed of multiple thrust sheets. The 2008 Wenchuan earthquake took place in such tectonic setting with strong horizontal shortening. The two ruptured faults have different deformation mechanisms. The Yingxiu-Beichuan fault (YBF) is a stick-slip fault characterized by fault gouge with high magnetic susceptibility, Guanxian-Anxian fault (GAF) with creeping features and characterized by fault gouge with low magnetic susceptibility. Two PSZs were found in WFSD-1 and -2 cores in the southern segment of YBF. The upper PSZ1 is a low-angle thrust fault characterized by coseisimc graphitization with an extremely low frictional coefficient. The lower PSZ2 is an oblique dextral-slip thrust fault characterized by frictional melt lubrication. In the northern segment of YBF, the PSZ in WFSD-4S cores shows a high-angle thrust feature with fresh melt as well. Therefore, the oblique dextral-slip thrust faulting with frictional melt lubrication is the main faulting of Wenchuan earthquake. Fresh melt with quenching texture was formed in Wenchuan earthquake implying vigorous fluid circulation occurred during the earthquake, which quenched high-temperature melt, hamper the aftermost fault slip and welding seismic fault. Therefore, fluids in the fault zone not only promotes fault weakening, but also suppress slipping in theWenchuan earthquake. The YBF has an extremely high hydraulic diffusivity (2.4×10-2 m2s-1), implying a vigorous fluid circulation in the Wenchuan fault zone. the permeability of YBF has reduced 70% after the shock, reflecting a rapid healing for the YBF. However, the water level has not changed in the WFSD-3 borehole drilled through GAF, indicating an unchanged permeability. These results are of great significance to understanding the seismogenic mechanisms and earthquake cycle for the Wenchuan earthquake.

Melting Experiments in the Fe-FeSi System at High Pressure

NASA Astrophysics Data System (ADS)

Ozawa, H.; Hirose, K.

2013-12-01

The principal light element in the Earth's core must reproduce the density jump at the inner core boundary (ICB). Silicon is thought to be a plausible light element in the core, and the melting phase relations in Fe-FeSi binary system at the ICB pressure are of great importance. Theoretical calculations on the Fe-FeSi binary system suggested that the difference in Si content between the outer core and the inner core would be too small to satisfy the observed density jump at the ICB [Alfè et al., 2002 EPSL], which requires other light elements in addition to silicon. Here we experimentally examined partitioning of silicon between liquid and solid iron up to 97 GPa. High pressure and temperature conditions were generated in a laser-heated diamond-anvil cell. Chemical compositions of co-existing quenched liquid and solid Fe-Si alloys were determined with a field-emission-type electron probe micro-analyzer. We used Fe-Si alloy containing 9 wt% Si as a starting material. Chemical analyses on the recovered samples from 39 and 49 GPa demonstrated the coexistence of quenched Si-depleted liquid and Si-enriched solid. In contrast, silicon partitions preferentially into liquid metal at 97 GPa, suggesting the starting composition (Fe-9wt% Si) lies on the iron-rich part of the eutectic. These results indicate the eutectic composition shifts toward FeSi between 49 and 97 GPa.

Early thermal history of Rhea: the role of serpentinization and liquid state convection

NASA Astrophysics Data System (ADS)

Czechowski, Leszek; Losiak, Anna

2015-04-01

Intorduction: Thermal history of Rhea from the beginning of accretion is investigated. The numerical model of convection combined with the parameterized theory is developed. Melting of the satellite's matter, gravitational differentiation and serpentinization of silicates are included. The role of the following parameters of the model is investigated: time of beginning of accretion, duration of accretion, viscosity of ice close to the melting point, activation energy in the formula for viscosity E, thermal conductivity of silicate component, ammonia content X, and energy of serpentinization. 1. Numerical model: In our calculations we use numerical model developed by Czechowski (2012) (see e.g. description in [1]). The model is based on parameterized theory of convection combined with 1-dimensional equation of the heat transfer in spherical coordinates: δT(r,t)- ρcp δt = div(k(r,T ) gradT (r,t))+ Q(r,T), where r is the radial distance (spherical coordinate), ρ is the density [kg m-3], cp [J kg1 K-1 ] is the specific heat, Q [W kg-1] is the heating rate, and k[W m-1 K-1] is the thermal conductivity. Q(r,t) includes sources and sinks of the heat. The equation is solved in time dependent region [0, R(t)]. During accretion the radius R(t) increases in time according to formula: R(t) = atfor tini tac , i.e. after the accretion (see e.g. [2]), where tinidenotes beginning of accretion and tac denotes duration of this process. If the Rayleigh number in the considered layer exceeds its critical value Racr then convection starts. It leads to effective heat transfer. The full description of convection is given by a velocity field and temperature distribution. However, we are interested in convection as a process of heat transport only. For solid state convection (SSC) heat transport can be described by dimensionless Nusselt number Nu. We use the following definition of the Nu: Nu= (True total surface heat flow)/(Total heat flow without convection). The heat transport by SSC is modelled simply by multiplying the coefficient of the heat conduction in the considered layer, i.e.: kconv =Nu k. This approach is used successfully in parameterized theory of convection for SSC in the Earth and other planets (e.g. [3], [4]). Parameterization of liquid state convection (LSC) is even simpler. Ra in molten region is very high (usually higher than 1016). The LSC could be very intensive resulting in almost adiabatic temperature gradient given by: dT-= gαmT-, dr cpm where αm and cpm are thermal expansion coefficient and specific heat in molten region, g is the local gravity. In Enceladus and Mimas the adiabatic gradient is low and therefore LSC region is almost isothermal. 2. Results: 1. We found that time of beginning of accretion and duration of accretion are crucial for early evolution, especially for differentiation. 2. Viscosity of ice close to melting point, activation energy in formula for viscosity E, and ammonia content X are very important for evolution, but not dramatic differences are found if realistic values are considered. 3. The energy of serpentinization is important for evolution, but its role is also not dominant. 4. LSC operating in molten part could delay the differentiation and the core formation for a few hundreds Myr. 5. The gravity data could be interpreted that Rhea is fully differentiated only if its core has high porosity and low density ~1300 kg m-3. In fact, there is not mechanism that could remove the water from molten core and the core of Rhea is probably porous. Acknowledgements: The research is partly supported by National Science Centre (grant 2011/ 01/ B/ ST10/06653). References : [1] Czechowski, L. (2014) Some remarks on the early evolution of Enceladus. Planet. Sp. Sc. 104, 185-199. [2] Merk, R., Breuer, D., Spohn, T. (2002). Numerical modeling of 26Al induced radioactive melting of asteroids concerning accretion. Icarus 199, 183-191. [3] Sharpe, H.N., Peltier, W.R., (1978) Parameterized mantle convection and the Earth's thermal history. Geophys. Res. Lett. 5, 737-740.

NiO and Fe/Mn in Fo-rich olivines from OIB, MORB, and mantle peridotites

NASA Astrophysics Data System (ADS)

Li, H.; Baker, M.; Hofmann, A. E.; Clague, D.; Stolper, E.

2006-12-01

Olivines from mantle peridotites have a narrow range of NiO (0.36±0.03 [1σ] wt%), but NiO of olivines in basalts suggest NiO in mantle olivines is actually more variable: e.g., Hawaiian phenocrysts (Fo>90) have NiO >0.55%, and olivines from continental flood basalts can have >0.5% NiO. At the other end of the spectrum, some basaltic suites (e.g., Iceland, MORBs) have Fo>90 olivines with NiO >0.2%. Partial melting calculations on peridotites show it is difficult to generate liquids that crystallize Fo>90 olivines with >0.4% NiO without resorting to complex processes. Hypotheses to explain the variability of NiO in mantle-derived olivines include (1) reaction of peridotite with silica-rich melts of eclogite results in decreasing modal abundance of olivine and increasing NiO in olivine [1,2]; (2) magmas with NiO-rich olivines come from sources enriched in NiO due to a core-derived component [3]. [4] proposed that high Fe/Mn of Hawaiian vs. Icelandic and MORB lavas reflect a core-derived component in their sources. Possible core incorporation is poorly constrained but FeO and NiO are expected to increase by such processes, leading to correlations between NiO and Fe/Mn in mantle rocks with significant core-derived components. We present high-precision analyses of Fo-rich olivines from OIBs, MORBs, komatiites, and mantle peridotites, focusing on NiO contents and Fe/Mn ratios. Our goal is to test hypotheses to explain elevated NiO of Fo-rich olivines in basalts. Olivines are Fo85.1-93.4; more were analyzed, but we focused on this range to avoid complications due to decreasing NiO in olivine with crystallization. Errors (1σ) are 0.01 wt% in NiO and 1.5 in Fe/Mn (wt). Our data show several features: (1) NiO contents and Fe/Mn ratios of Fo>88 olivines are positively correlated, with the low end of the trend (NiO ~0.23%, Fe/Mn ~61) defined by MORB and Iceland and the high end of the trend (NiO ~0.55%, Fe/Mn ~80) by Reunion and Hawaii. Between these end points, there is a regular trend from MORB/Iceland, to Baffin Isl, to mantle peridotites/Juan Fernandez, to Reunion/Hawaii. This array can't be explained by simple crystallization (all have similar Fo) or by variable degrees of partial melting of a single source. The NiO-Fe/Mn correlation can be modeled by quantitative addition of 1-2% oxidized core to depleted mantle and thus is consistent with the core-addition hypothesis. However, more complex core-mantle interactions/fractionations would still be required to explain trace siderophile and chalcophile elements and isotopes. Moreover, other hypotheses to explain the observed trend (including addition of silicic melts to peridotite) cannot be ruled out. (2) The Hawaiian data, although clearly defining with Reunion the upper end of the overall NiO-Fe/Mn array, are more complex. For example, a single Mauna Kea sample has ~Fo90 phenocrysts with NiO from 0.30 to 0.54%, all with Fe/Mn=72-80, and North Arch and Loihi olivines have relatively low NiO at Fe/Mn ratios comparable to other Hawaiian olivines. Although Loihi and North Arch lavas are low in SiO2, in detail the NiO of Hawaiian olivines are not well predicted by SiO2 contents of the host lavas. (3) The Gorgona Isl komatiites fall off the overall trend, extending to NiO >0.5 wt% at Fe/Mn ~62, perhaps reflecting different sources, processes, or anomalous degrees of melting. [1] Kelemen et al (1998) EPSL 164, 387-406 [2] Sobolev et al (2005) Nature 434, 590-597 [3] Ryabchikov (2003) Doklady Earth Sci. 389A, 437-439 [4] Humayun et al (2004) Science 306, 91-94

Metal-silicate Partitioning and Its Role in Core Formation and Composition on Super-Earths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaefer, Laura; Petaev, M. I.; Sasselov, Dimitar D.

We use a thermodynamic framework for silicate-metal partitioning to determine the possible compositions of metallic cores on super-Earths. We compare results using literature values of the partition coefficients of Si and Ni, as well as new partition coefficients calculated using results from laser shock-induced melting of powdered metal-dunite targets at pressures up to 276 GPa, which approaches those found within the deep mantles of super-Earths. We find that larger planets may have little to no light elements in their cores because the Si partition coefficient decreases at high pressures. The planet mass at which this occurs will depend on themore » metal-silicate equilibration depth. We also extrapolate the equations of state (EOS) of FeO and FeSi alloys to high pressures, and present mass–radius diagrams using self-consistent planet compositions assuming equilibrated mantles and cores. We confirm the results of previous studies that the distribution of elements between mantle and core will not be detectable from mass and radius measurements alone. While observations may be insensitive to interior structure, further modeling is sensitive to compositionally dependent properties, such as mantle viscosity and core freeze-out properties. We therefore emphasize the need for additional high pressure measurements of partitioning as well as EOSs, and highlight the utility of the Sandia Z-facilities for this type of work.« less

Geochemical variability of the Yucatan basement: Constraints from crystalline clasts in Chicxulub impactites

NASA Astrophysics Data System (ADS)

Kettrup, B.; Deutsch, A.

2003-07-01

The 65 Ma old Chicxulub impact structure with a diameter of about 180 km is again in the focus of the geosciences because of the recently commenced drilling of the scientific well Yaxcopoil- 1. Chicxulub is buried beneath thick post-impact sediments, yet samples of basement lithologies in the drill cores provide a unique insight into age and composition of the crust beneath Yucatan. This study presents major element, Sr, and Nd isotope data for Chicxulub impact melt lithologies and clasts of basement lithologies in impact breccias from the PEMEX drill cores C-1 and Y-6, as well as data for ejecta material from the K/T boundaries at La Lajilla, Mexico, and Furlo, Italy. The impact melt lithologies have an andesitic composition with significantly varying contents of Al, Ca, and alkali elements. Their present day 87Sr/86Sr ratios cluster at about 0.7085, and 143Nd/144Nd ratios range from 0.5123 to 0.5125. Compared to the melt lithologies that stayed inside the crater, data for ejecta material show larger variations. The 87Sr/86Sr ratios range from 0.7081 for chloritized spherules from La Lajilla to 0.7151 for sanidine spherules from Furlo. The 143Nd/144Nd ratio is 0.5126 for La Lajilla and 0.5120 for the Furlo spherules. In an tCHUR(Nd)-tUR(Sr) diagram, the melt lithologies plot in a field delimited by Cretaceous platform sediments, various felsic lithic clasts and a newly found mafic fragment from a suevite. Granite, gneiss, and amphibolite have been identified among the fragments from crystalline basement gneiss. Their 87Sr/86Sr ratios range from 0.7084 to 0.7141, and their 143Nd/144Nd ratios range from 0.5121 to 0.5126. The TNdDM model ages vary from 0.7 to 1.4 Ga, pointing to different source terranes for these rocks. This leads us to believe that the geological evolution and the lithological composition of the Yucatàn basement is probably more complex than generally assumed, and Gondwanan as well as Laurentian crust may be present in the Yucatàn basement.

Scanning electron microscopy investigations of laboratory-grown gas clathrate hydrates formed from melting ice, and comparison to natural hydrates

USGS Publications Warehouse

Stern, L.A.; Kirby, S.H.; Circone, S.; Durham, W.B.

2004-01-01

Scanning electron microscopy (SEM) was used to investigate grain texture and pore structure development within various compositions of pure sI and sII gas hydrates synthesized in the laboratory, as well as in natural samples retrieved from marine (Gulf of Mexico) and permafrost (NW Canada) settings. Several samples of methane hydrate were also quenched after various extents of partial reaction for assessment of mid-synthesis textural progression. All laboratory-synthesized hydrates were grown under relatively high-temperature and high-pressure conditions from rounded ice grains with geometrically simple pore shapes, yet all resulting samples displayed extensive recrystallization with complex pore geometry. Growth fronts of mesoporous methane hydrate advancing into dense ice reactant were prevalent in those samples quenched after limited reaction below and at the ice point. As temperatures transgress the ice point, grain surfaces continue to develop a discrete "rind" of hydrate, typically 5 to 30 ??m thick. The cores then commonly melt, with rind microfracturing allowing migration of the melt to adjacent grain boundaries where it also forms hydrate. As the reaction continues under progressively warmer conditions, the hydrate product anneals to form dense and relatively pore-free regions of hydrate grains, in which grain size is typically several tens of micrometers. The prevalence of hollow, spheroidal shells of hydrate, coupled with extensive redistribution of reactant and product phases throughout reaction, implies that a diffusion-controlled shrinking-core model is an inappropriate description of sustained hydrate growth from melting ice. Completion of reaction at peak synthesis conditions then produces exceptional faceting and euhedral crystal growth along exposed pore walls. Further recrystallization or regrowth can then accompany even short-term exposure of synthetic hydrates to natural ocean-floor conditions, such that the final textures may closely mimic those observed in natural samples of marine origin. Of particular note, both the mesoporous and highly faceted textures seen at different stages during synthetic hydrate growth were notably absent from all examined hydrates recovered from a natural marine-environment setting.

Melting relations in the Fe-rich portion of the system FeFeS at 30 kb pressure

USGS Publications Warehouse

Brett, R.; Bell, P.M.

1969-01-01

The melting relations of FeFeS mixtures covering the composition range from Fe to Fe67S33 have been determined at 30 kb pressure. The phase relations are similar to those at low pressure. The eutectic has a composition of Fe72.9S27.1 and a temperature of 990??C. Solubility of S in Fe at elevated temperatures at 30 kb is of the same order of magnitude as at low pressure. Sulfur may have significantly lowered the melting point of iron in the upper mantle during the period of coalescence of metal prior to core formation in the primitive earth. ?? 1969.

An experimental study of steam explosions involving chemically reactive metal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, D.H.; Armstrong, D.R.; Gunther, W.H.

1997-07-01

An experimental study of molten zirconium-water explosions was conducted. A 1-kg mass of zirconium melt was dropped into a column of water. Explosions took place only when an external trigger was used. In the triggered tests, the extent of oxidation of the zirconium melt was very extensive. However, the explosion energetics estimated were found to be very small compared to the potential chemical energy available from the oxidation reaction. Zirconium is of particular interest, since it is a component of the core materials of the current nuclear power reactors. This paper describes the test apparatus and summarizes the results ofmore » four tests conducted using pure zirconium melt.« less

Preparation and characterization of Phase change material microcapsules by a core-shell-like emulsion polymerization method

NASA Astrophysics Data System (ADS)

Ding, Li-ming; Pei, Guang-ling

2015-07-01

Phase change material microcapsules (MicroPCMs) were synthesized by a coreshell-like emulsion polymerization method. Styrene and methylacrylic acid copolymer (PS- MAA) was used as a wall material, and paraffin was used as a core material in order to prepare spherical, high resistance and high enthalpy MicroPCMs. Scanning Electron Microscope (SEM), laser particle size analyzer, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetry (TG) and Differential Scanning Calorimeter (DSC) were employed to characterize the MicroPCMs. The results indicated that the average particle size of MicroPCMs was 42.29 μm, and the content of paraffin within microcapsules was 57.6%. The melting temperature and crystallization temperature were 30.7°C and 25.2°C.The melting enthalpy and crystallization enthalpy were -84.1 J/g and 91.3 J/g, respectively.

Melt migration modeling in partially molten upper mantle

NASA Astrophysics Data System (ADS)

Ghods, Abdolreza

The objective of this thesis is to investigate the importance of melt migration in shaping major characteristics of geological features associated with the partial melting of the upper mantle, such as sea-floor spreading, continental flood basalts and rifting. The partial melting produces permeable partially molten rocks and a buoyant low viscosity melt. Melt migrates through the partially molten rocks, and transfers mass and heat. Due to its much faster velocity and appreciable buoyancy, melt migration has the potential to modify dynamics of the upwelling partially molten plumes. I develop a 2-D, two-phase flow model and apply it to investigate effects of melt migration on the dynamics and melt generation of upwelling mantle plumes and focusing of melt migration beneath mid-ocean ridges. Melt migration changes distribution of the melt-retention buoyancy force and therefore affects the dynamics of the upwelling plume. This is investigated by modeling a plume with a constant initial melt of 10% where no further melting is considered. Melt migration polarizes melt-retention buoyancy force into high and low melt fraction regions at the top and bottom portions of the plume and therefore results in formation of a more slender and faster upwelling plume. Allowing the plume to melt as it ascends through the upper mantle also produces a slender and faster plume. It is shown that melt produced by decompressional melting of the plume migrates to the upper horizons of the plume, increases the upwelling velocity and thus, the volume of melt generated by the plume. Melt migration produces a plume which lacks the mushroom shape observed for the plume models without melt migration. Melt migration forms a high melt fraction layer beneath the sloping base of the impermeable oceanic lithosphere. Using realistic conditions of melting, freezing and melt extraction, I examine whether the high melt fraction layer is able to focus melt from a wide partial melting zone to a narrow region beneath the observed neo-volcanic zone. My models consist of three parts; lithosphere, asthenosphere and a melt extraction region. It is shown that melt migrates vertically within the asthenosphere, and forms a high melt fraction layer beneath the sloping base of the impermeable lithosphere. Within the sloping high melt fraction layer, melt migrates laterally towards the ridge. In order to simulate melt migration via crustal fractures and cracks, melt is extracted from a melt extraction region extending to the base of the crust. Performance of the melt focusing mechanism is not significantly sensitive to the size of melt extraction region, melt extraction threshold and spreading rate. In all of the models, about half of the total melt production freezes beneath the cooling base of the lithosphere, and the rest is effectively focused towards the ridge and forms the crust. To meet the computational demand for a precise tracing of the deforming upwelling plume and including the chemical buoyancy of the partially molten zone in my models, a new numerical method is developed to solve the related pure advection equations. The numerical method is based on Second Moment numerical method of Egan and Mahoney [1972] which is improved to maintain a high numerical accuracy in shear and rotational flow fields. In comparison with previous numerical methods, my numerical method is a cost-effective, non-diffusive and shape preserving method, and it can also be used to trace a deforming body in compressible flow fields.

MeltMigrator: A MATLAB-based software for modeling three-dimensional melt migration and crustal thickness variations at mid-ocean ridges following a rules-based approach

NASA Astrophysics Data System (ADS)

Bai, Hailong; Montési, Laurent G. J.; Behn, Mark D.

2017-01-01

MeltMigrator is a MATLAB®-based melt migration software developed to process three-dimensional mantle temperature and velocity data from user-supplied numerical models of mid-ocean ridges, calculate melt production and melt migration trajectories in the mantle, estimate melt flux along plate boundaries, and predict crustal thickness distribution on the seafloor. MeltMigrator is also capable of calculating compositional evolution depending on the choice of petrologic melting model. Programmed in modules, MeltMigrator is highly customizable and can be expanded to a wide range of applications. We have applied it to complex mid-ocean ridge model settings, including transform faults, oblique segments, ridge migration, asymmetrical spreading, background mantle flow, and ridge-plume interaction. In this technical report, we include an example application to a segmented mid-ocean ridge. MeltMigrator is available as a supplement to this paper, and it is also available from GitHub and the University of Maryland Geodynamics Group website.

Optical properties of melting first-year Arctic sea ice

NASA Astrophysics Data System (ADS)

Light, Bonnie; Perovich, Donald K.; Webster, Melinda A.; Polashenski, Christopher; Dadic, Ruzica

2015-11-01

The albedo and transmittance of melting, first-year Arctic sea ice were measured during two cruises of the Impacts of Climate on the Eco-Systems and Chemistry of the Arctic Pacific Environment (ICESCAPE) project during the summers of 2010 and 2011. Spectral measurements were made for both bare and ponded ice types at a total of 19 ice stations in the Chukchi and Beaufort Seas. These data, along with irradiance profiles taken within boreholes, laboratory measurements of the optical properties of core samples, ice physical property observations, and radiative transfer model simulations are employed to describe representative optical properties for melting first-year Arctic sea ice. Ponded ice was found to transmit roughly 4.4 times more total energy into the ocean, relative to nearby bare ice. The ubiquitous surface-scattering layer and drained layer present on bare, melting sea ice are responsible for its relatively high albedo and relatively low transmittance. Light transmittance through ponded ice depends on the physical thickness of the ice and the magnitude of the scattering coefficient in the ice interior. Bare ice reflects nearly three-quarters of the incident sunlight, enhancing its resiliency to absorption by solar insolation. In contrast, ponded ice absorbs or transmits to the ocean more than three-quarters of the incident sunlight. Characterization of the heat balance of a summertime ice cover is largely dictated by its pond coverage, and light transmittance through ponded ice shows strong contrast between first-year and multiyear Arctic ice covers.

Impact melting of carbonates from the Chicxulub crater

NASA Astrophysics Data System (ADS)

Jones, A. P.; Claeys, P.; Heuschkel, S.

We have recently interpreted distinctive feathery-textured spinifex carbonate in the upper part of the Chicxulub suevite breccia as quenched carbonate melts (Jones et al. 1998); these distinctive fragments make up to 10 vol% of the breccia. Carbonate clasts and spherules occurring in the ejecta-rich basal part of the coarse clastic sequence, which marks the K/T boundary all around the Gulf of Mexico, may represent distal quenched droplets of carbonate liquids. In seeking to explain this widespread carbonate impact-melting phenomenon, we have re-examined the available experimental evidence. The important decarbonation reaction for calcite CaCO3=CaO+CO2 is inhibited by very small pressures up to temperatures >2000 K. We conclude that massive decarbonation by direct shock pressure is unlikely without attainment of temperatures >4000 K. Therefore, decarbonation generally can only occur during post-shock cooling for carbonates at low pressure (< 10 bars). We assume that post-shock cooling is quasi-thermodynamic, and provide a general P-T model for carbonate spanning 11 orders of magnitude in pressure (atmosphere to core). Subtle differences in sample preconditioning can probably explain the wildly divergent experimental shock data. A major planetary implication for the formation of the Earth's early atmosphere is that impacts on limestone would be less likely to have contributed substantial CO2 than has previously been assumed. Lastly, we note that carbonate melts at high pressures serve as excellent catalysts for diamond growth, and may have contributed to the widespread formation of some impact diamond.

Isotopic composition of ice cores and meltwater from upper fremont glacier and Galena Creek rock glacier, Wyoming

USGS Publications Warehouse

DeWayne, Cecil L.; Green, J.R.; Vogt, S.; Michel, R.; Cottrell, G.

1998-01-01

Meltwater runoff from glaciers can result from various sources, including recent precipitation and melted glacial ice. Determining the origin of the meltwater from glaciers through isotopic analysis can provide information about such things as the character and distribution of ablation on glaciers. A 9.4 m ice core and meltwater were collected in 1995 and 1996 at the glacigenic Galena Creek rock glacier in Wyoming's Absaroka Mountains. Measurements of chlorine-36 (36Cl), tritium (3H), sulphur-35 (35S), and delta oxygen-18 (??18O) were compared to similar measurements from an ice core taken from the Upper Fremont Glacier in the Wind River Range of Wyoming collected in 1991-95. Meltwater samples from three sites on the rock glacier yielded 36Cl concentrations that ranged from 2.1 ?? 1.0 X 106 to 5.8??0.3 X 106 atoms/l. The ice-core 36Cl concentrations from Galena Creek ranged from 3.4??0.3 X 105 to 1.0??0.1 X 106 atoms/l. Analysis of an ice core from the Upper Fremont Glacier yielded 36Cl concentrations of 1.2??0.2 X 106 and 5.2??0.2 X 106 atoms/l for pre- 1940 ice and between 2 X 106 and 3 X 106 atoms/l for post-1980 ice. Purdue's PRIME Lab analyzed the ice from the Upper Fremont Glacier. The highest concentration of 36Cl in the ice was 77 ?? 2 X 106 atoms/l and was deposited during the peak of atmospheric nuclear weapons testing in the late 1950s. This is an order of magnitude greater than the largest measured concentration from both the Upper Fremont Glacier ice core that was not affected by weapons testing fallout and the ice core collected from the Galena Creek rock glacier. Tritium concentrations from the rock glacier ranged from 9.2??0.6 to 13.2??0.8 tritium units (TU) in the meltwater to -1.3??1.3 TU in the ice core. Concentrations of 3H in the Upper Fremont Glacier ice core ranged from 0 TU in the ice older than 50 years to 6-12 TU in the ice deposited in the last 10 years. The maximum 3H concentration in ice from the Upper Fremont Glacier deposited in the early 1960s during peak weapons testing fallout for this isotope was 360 TU. One meltwater sample from the rock glacier was analyzed for 35S with a measured concentration of 5.4??1.0 millibecquerel per liter (mBeq/l). Modern precipitation in the Rocky Mountains contains 35S from 10 to 40 mBeq/L. The ??18O results in meltwater from the Galena Creek rock glacier (-17.40??0.1 to -17.98??0.1 per mil) are similar to results for modern precipitation in the Rocky Mountains. Comparison of these isotopic concentrations from the two glaciers suggest that the meltwater at the Galena Creek site is composed mostly of melted snow and rain that percolates through the rock debris that covers the glacier. Additionally, this water from the rock debris is much younger (less than two years) than the reported age of about 2000 years for the subsurface ice at the mid-glacier coring site. Thus the meltwater from the Galena Creek rock glacier is composed primarily of melted surface snow and rain water rather than melted glacier ice, supporting previous estimates of slow ablation rates beneath the surface debris of the rock glacier.

Fusible core molding for the fabrication of branched, perfusable, three-dimensional microvessels for vascular tissue engineering.

PubMed

Martin, Cristina; Sofla, Aarash; Zhang, Boyang; Nunes, Sara S; Radisic, Milica

2013-03-01

A novel method for fabrication of branched, tubular, perfusable microvessels for use in vascular tissue engineering is reported. A tubular, elastomeric, biodegradable scaffold is first fabricated via a new, double fusible injection molding technique that uses a ternary alloy with a low melting temperature, Field's metal, and paraffin as sacrificial components. A cylindrical core metal of 500 μm or lower dia-meter with the target branching scaffold geometry is first constructed, then the metal structure is coated with paraffin and, finally, the metal-paraffin construct is embedded in polydimethylsiloxane (PDMS). The paraffin layer is then removed by heating and replaced by a biodegradable elastomeric pre-polymer that is subsequently UV-cured inside the PDMS. Next, the metal core is melted away and the PDMS is removed to attain the branched tubular elastomeric biodegradable scaffold. Finally, it is also demonstrated that human umbilical vein endothelial cells (HUVEC) were able to spread on the surface of the scaffold and form a confluent monolayer, confirming the potential of this new technique for making engineered blood vessels.

Melt infiltration of silicon carbide compacts. II - Evaluation of solidification microstructures

NASA Technical Reports Server (NTRS)

Asthana, Rajiv; Rohatgi, Pradeep K.

1993-01-01

Microstructural aspects of alloy solidification within the interstices of porous compacts of platelet-shaped single crystals of alpha-SiC, when the latter are infiltrated with a hot metal under pressure, have been described. Microstructural evidence is presented of selective reorientation of platelets and nonhomogeneous solute distribution under shear of pressurized melt, of constrained growth of primary solid within finite width zones, and of the modulation of coring due to microsegregation as a result of variations in the pore size of compacts.

Uranium, thorium and REE partitioning into sulfide liquids at high pressure and high temperature: Implications for reduced, S-rich planetary bodies

NASA Astrophysics Data System (ADS)

Wohlers, A.; Wood, B. J.

2017-12-01

Based on models of the young solar nebula it is likely that the inner planets went through an early reduced phase of accretion with high metal/silicate ratio and low volatile element contents. Mercury is an existing example of a large planetary embryo with these characteristics but also with a very high S content. In order to investigate the geochemical evolution of Mercury-like bodies we experimentally determined the partitioning of lithophile elements (U, Th, Eu, Sm, Nd, Zr, La, Ce, Yb) between sulfide liquid, low-S metals and silicate melt at 1.5 GPa and 1400-2100˚C. Our results, when combined with those of Wohlers and Wood (2015) show that under highly reducing conditions (FeOsilicate<1wt%) U, Sm, Nd and other lithophile elements partition strongly into FeS liquids relative to silicate melts. The dependences of D's on the FeS contents of the metal and FeO contents of the silicate may be understood in terms of exchange reactions: UO2 + 2FeS = 2FeO + US2silicate sulfide silicate sulfideHigh concentrations of FeSmetal and low FeO contents of the silicate melts drive the reaction to the right, yielding high US2 in the sulfide and high DU. A second effect which raises DU (and other lithophile D's) is the S content of the silicate melt. The latter increases rapidly at low FeO contents and reaches 11wt %. This greatly reduces the activity coefficient of FeO, displacing the reaction further to the right. At 1.5GPa and 1400˚C we obtain sulfide-silicate partitioning with DNd/DSm 1.4 and DTh 0.1DU. As temperature increases to 2100˚C, DNd/DSm declines to 1.0 and DTh/DU increases to 0.3. We estimated the effects of accreting a reduced sulfur-rich component (with FeS core) added to early Earth. The results at 1400˚C imply the possibility of a significant ( 11ppm) 142Nd anomaly in silicate Earth and the addition of >8 ppb U to the core, but require an unreasonably high Th/U of silicate Earth (4.54). Results at 2100˚C lead to a 142Nd anomaly of 0 but addition of such a reduced sulfur-rich body could add up to 10 ppb of U to the core, together with 21 ppb Th. This combination would generate 3 TW of the energy required for the geodynamo. In this case, the Th/U ratio of silicate Earth would be 4.3, within the range of some estimates. Wohlers A. & Wood B.J. (2015) A Mercury-like component of early Earth yield uranium in the core and high mantle Nd142. Nature 520, 337-340

Magma ocean formation due to giant impacts

NASA Technical Reports Server (NTRS)

Tonks, W. B.; Melosh, H. J.

1993-01-01

The thermal effects of giant impacts are studied by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths. Additionally, the effects of the planet's initial temperature on the generated melt volume are examined. The shock pressure required to completely melt the material is determined using the Hugoniot curve plotted in pressure-entropy space. Once the melting pressure is known, an impact melting model is used to estimate the radial distance melting occurred from the impact site. The melt region's geometry then determines the associated melt volume. The model is also used to estimate the partial melt volume. Magma ocean depths resulting from both excavated and retained melt are calculated, and the melt fraction not excavated during the formation of the crater is estimated. The fraction of a planet melted by the initial shock wave is also estimated using the model.

Apparatus for controlling molten core debris. [LMFBR

DOEpatents

Golden, M.P.; Tilbrook, R.W.; Heylmun, N.F.

1977-07-19

Disclosed is an apparatus for containing, cooling, diluting, dispersing and maintaining subcritical the molten core debris assumed to melt through the bottom of a nuclear reactor pressure vessel in the unlikely event of a core meltdown. The apparatus is basically a sacrificial bed system which includes an inverted conical funnel, a core debris receptacle including a spherical dome, a spherically layered bed of primarily magnesia bricks, a cooling system of zig-zag piping in graphite blocks about and below the bed and a cylindrical liner surrounding the graphite blocks including a steel shell surrounded by firebrick. Tantalum absorber rods are used in the receptacle and bed. 9 claims, 22 figures.

An ice core record of net snow accumulation and seasonal snow chemistry at Mt. Waddington, southwest British Columbia, Canada

NASA Astrophysics Data System (ADS)

Neff, P. D.; Steig, E. J.; Clark, D. H.; McConnell, J. R.; Pettit, E. C.; Menounos, B.

2011-12-01

We recovered a 141 m ice core from Combatant Col (51.39°N, 125.22°W, 3000 m asl) on the flank of Mt. Waddington, southern Coast Mountains, British Columbia, Canada. Aerosols and other impurities in the ice show unambiguous seasonal variations, allowing for annual dating of the core. Clustered melt layers, originating from summer surface heating, also aid in the dating of the core. Seasonality in water stable isotopes is preserved throughout the record, showing little evidence of diffusion at depth, and serves as an independent verification of the timescale. The annual signal of deuterium excess is especially well preserved. The record of lead deposition in the core agrees with those of ice cores from Mt. Logan and from Greenland, with a sharp drop-off in concentration in the 1970s and early 1980s, further validating the timescales. Despite significant summertime melt at this mid-latitude site, these data collectively reveal a continuous and annually resolved 36-year record of snow accumulation. We derived an accumulation time series from the Mt. Waddington ice core, after correcting for ice flow. Years of anomalously high or low snow accumulation in the core correspond with extremes in precipitation data and geopotential height anomalies from reanalysis data that make physical sense. Specifically, anomalously high accumulation years at Mt. Waddington correlate with years where "Pineapple Express" atmospheric river events bring large amounts of moisture from the tropical Pacific to western North America. The Mt. Waddington accumulation record thus reflects regional-scale climate. These results demonstrate the potential of ice core records from temperate glaciers to provide meaningful paleoclimate information. A longer core to bedrock (250-300 m) at the Mt. Waddington site could yield ice with an age of several hundred to 1000 years.

Orthopyroxenes as Recorders of Diogenite Petrogenesis: Nature and Causes of Intragrain Chemical Variability

NASA Astrophysics Data System (ADS)

Papike, J. J.; Spilde, M. N.

1993-07-01

Diogenites can as a first approximation be considered as orthopyroxene cumulates in differentiated asteroids [1]. Orthopyroxene is a very powerful mineral recorder in mafic cumulates as demonstrated by Lambert and Simmons [2], who "inverted" REE data from cores of orthopyroxene crystals to estimate the melt compositions parental to the various cumulate horizons in the Stillwater Complex, Montana. These authors demonstrated that the rims of orthopyroxene grains are enriched in REE relative to cores, most likely because of subsolidus orthopyroxene/trapped melt exchange. These authors also noted the importance of working with elements with slow diffusion rates (e.g., REE) relative to those with rapid diffusion rates (e.g., Fe^2+, Mg). In most diogenites, the primary pyroxene is orthopyroxene, while in Fe- enriched diogenites (e.g., some assemblages in Garland and Yamato 75032 [3]) the primary pyroxene phase is pigeonite. In slowly cooled cumulate assemblages, monoclinic pigeonite inverts to orthopyroxene with complex augite exsolution lamellae, and the trace-element records of the parental magmas are essentially lost. Our recent SIMS studies indicate a strong fractionation of REE into the augite lamellae. Most of the orthopyroxene grains that we examined in our original suite of 13 diogenites have fine (100) augite lamellae. These lamellae can easily be reintegrated with the host orthopyroxene by using a relatively broad EMP or SIMS beam of 15-20 micrometers. In this study, we consider the nature and causes of OPX intragrain chemical variations. Our previous studies [4] showed that Cr and Al showed significant variations among the different diogenites and that specific diogenites trend toward one of several different trajectories on a Cr-Al plot. We also found significant chemical variability in individual OPX grains. To date, we have identified three types of intragrain chemical variations: (1) smooth trends from core to rim, (2) periodic linear variations [e.g., (100) augite lamellae in an OPX host], and (3) relatively random variability (e.g., exsolution of spinel). Figure 1 (an OPX from Garland) provides evidence for smooth core-to-rim diffusion profiles. Iron and Mn increase while Mg and Cr decrease from core to rim. Also, Al remains relatively constant, Si decreases, and Ti shows an increase, near the grain edge, on the core-to-rim traverse. These chemical systematics were likely caused by a reaction between the cumulate OPX grain and trapped melt. The trapped melt was apparently enriched in Fe and Mn and depleted in Cr relative to OPX. In conclusion, postcrystallization resetting of cumulate grain chemical systematics must be carefully assessed before the data can be "inverted" to estimates of parental melt compositions. Acknowledgment: This research was supported by NASA grant NAGW-3347 and the Institute of Meteoritics. References: [1] Shearer C. K. et al. (1993) LPS XXIV, 1289-1290. [2] Lambert D. D. and Simmons E. C. (1987) Am. J. Sci., 287, 1-32. [3] Takeda H. et. al. (1979) Proc. 3rd Symp. Antarc. Met., 82-108. [4] Papike J. J. et. al. (1993) LPS XXIV, 1109-1110. Fig. 1 appears here in the hard copy.

Magnetic Signatures of Nectarian-Aged Lunar Basin-Forming Impacts: Probable Evidence for a Former Core Dynamo

NASA Astrophysics Data System (ADS)

Hood, Lon

2010-05-01

Previous analyses of Lunar Prospector magnetometer (MAG) and electron reflectometer (ER) data have shown that impact processes played an important role in producing the observed crustal magnetization. In particular, the largest areas of strong anomalies occur antipodal to the youngest large basins and correlative studies indicate that basin ejecta materials are important anomaly sources. Models suggest that transient fields generated by the expansion of impact vapor-melt clouds in the presence of an initial solar wind magnetic field are sufficient to explain the antipodal anomalies (Hood and Artemieva, Icarus, v. 193, p. 485, 2008). However, analyses of ER data have also shown that some anomalies are present within Nectarian-aged basins including Moscoviense, Mendel-Rydberg, and Crisium (Halekas et al., Meteorit. Planet. Sci., v. 38, p. 565, 2003). These latter anomalies could be due either to thermoremanence (TRM) in impact melt or to shock remanence in the central uplift. The former interpretation would require a long-lived, steady magnetizing field, consistent with a core dynamo, while the latter interpretation could in principle be explained by an impact-generated field. Here, LP MAG data are applied to produce more detailed regional maps of magnetic anomalies within selected Nectarian basins. Anomalies within the Crisium basin, in particular, are located inside the inner rim edges and are clearly genetically associated with the basin (rather than being due to ejecta from younger basins superposed on Crisium). An analysis of the vector field components shows that the directions of magnetization of the two main sources are close to parallel within the errors of the modeling. These anomalies are therefore most probably due to TRM of impact melt that cooled in a steady, large-scale field. In addition, the paleomagnetic pole position calculated for the strongest and most isolated anomaly lies close to the present rotational pole. Assuming no true polar wander since the Crisium impact and that the lunar dynamo behaved similarly to presently existing terrestrial planet dynamos, they are therefore consistent with the existence of a lunar dynamo field.

Thermal-hydraulic simulation of natural convection decay heat removal in the High Flux Isotope Reactor using RELAP5 and TEMPEST: Part 1, Models and simulation results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morris, D.G.; Wendel, M.W.; Chen, N.C.J.

A study was conducted to examine decay heat removal requirements in the High Flux Isotope Reactor (HFIR) following shutdown from 85 MW. The objective of the study was to determine when forced flow through the core could be terminated without causing the fuel to melt. This question is particularly relevant when a station blackout caused by an external event is considered. Analysis of natural circulation in the core, vessel upper plenum, and reactor pool indicates that 12 h of forced flow will permit a safe shutdown with some margin. However, uncertainties in the analysis preclude conclusive proof that 12 hmore » is sufficient. As a result of the study, two seismically qualified diesel generators were installed in HFIR. 9 refs., 4 figs.« less

The Earth's missing lead may not be in the core.

PubMed

Lagos, M; Ballhaus, C; Münker, C; Wohlgemuth-Ueberwasser, C; Berndt, J; Kuzmin, Dmitry V

2008-11-06

Relative to the CI chondrite class of meteorites (widely thought to be the 'building blocks' of the terrestrial planets), the Earth is depleted in volatile elements. For most elements this depletion is thought to be a solar nebular signature, as chondrites show depletions qualitatively similar to that of the Earth. On the other hand, as lead is a volatile element, some Pb may also have been lost after accretion. The unique (206)Pb/(204)Pb and (207)Pb/(204)Pb ratios of the Earth's mantle suggest that some lead was lost about 50 to 130 Myr after Solar System formation. This has commonly been explained by lead lost via the segregation of a sulphide melt to the Earth's core, which assumes that lead has an affinity towards sulphide. Some models, however, have reconciled the Earth's lead deficit with volatilization. Whichever model is preferred, the broad coincidence of U-Pb model ages with the age of the Moon suggests that lead loss may be related to the Moon-forming impact. Here we report partitioning experiments in metal-sulphide-silicate systems. We show that lead is neither siderophile nor chalcophile enough to explain the high U/Pb ratio of the Earth's mantle as being a result of lead pumping to the core. The Earth may have accreted from initially volatile-depleted material, some lead may have been lost to degassing following the Moon-forming giant impact, or a hidden reservoir exists in the deep mantle with lead isotope compositions complementary to upper-mantle values; it is unlikely though that the missing lead resides in the core.

Some remarks on the early evolution of Enceladus

NASA Astrophysics Data System (ADS)

Czechowski, Leszek

2014-12-01

Thermal history of Enceladus is investigated from the beginning of accretion to formation of its core (~400 My). We consider model with solid state convection (in a solid layer) as well as liquid state convection (in molten parts of the satellite). The numerical model of convection uses full conservative finite difference method. The roles of two modes of convection are considered using the parameterized theory of convection. The following heat sources are included: short lived and long lived radioactive isotopes, accretion, serpentinization, and phase changes. Heat transfer processes are: conduction, solid state convection, and liquid state convection. It is found that core formation was completed only when liquid state convection had slowed down. Eventually, the porous core with pores filled with water was formed. Recent data concerning gravity field of Enceladus confirm low density of the core. We investigated also thermal history for different values of the following parameters: time of beginning of accretion tini, duration of accretion tacr, viscosity of ice close to the melting point ηm, activation energy in formula for viscosity E, thermal conductivity of silicate component ksil, ammonia content XNH3, and energy of serpentinization cserp. All these parameters are important for evolution, but not dramatic differences are found for realistic values. Moreover, the hypothesis of proto-Enceladus (stating that initially Enceladus was substantially larger) is considered and thermal history of such body is calculated. The last subject is the Mimas-Enceladus paradox. Comparison of thermal models of Mimas and Enceladus indicates that period favorable for 'excited path of evolution' was significantly shorter for Mimas than for Enceladus.

Parallel Task Management Library for MARTe

NASA Astrophysics Data System (ADS)

Valcarcel, Daniel F.; Alves, Diogo; Neto, Andre; Reux, Cedric; Carvalho, Bernardo B.; Felton, Robert; Lomas, Peter J.; Sousa, Jorge; Zabeo, Luca

2014-06-01

The Multithreaded Application Real-Time executor (MARTe) is a real-time framework with increasing popularity and support in the thermonuclear fusion community. It allows modular code to run in a multi-threaded environment leveraging on the current multi-core processor (CPU) technology. One application that relies on the MARTe framework is the Joint European Torus (JET) tokamak WAll Load Limiter System (WALLS). It calculates and monitors the temperature on metal tiles and plasma facing components (PFCs) that can melt or flake if their temperature gets too high when exposed to power loads. One of the main time consuming tasks in WALLS is the calculation of thermal diffusion models in real-time. These models tend to be described by very large state-space models thus making them perfect candidates for parallelisation. MARTe's traditional approach for task parallelisation is to split the problem into several Real-Time Threads, each responsible for a self-contained sequential execution of an input-to-output chain. This is usually possible, but it might not always be practical for algorithmic or technical reasons. Also, it might not be easily scalable with an increase in the number of available CPU cores. The WorkLibrary introduces a “GPU-like approach” of splitting work among the available cores of modern CPUs that is (i) straightforward to use in an application, (ii) scalable with the availability of cores and all of this (iii) without rewriting or recompiling the source code. The first part of this article explains the motivation behind the library, its architecture and implementation. The second part presents a real application for WALLS, a parallel version of a large state-space model describing the 2D thermal diffusion on a JET tile.

Geoantineutrino spectrum and slow nuclear burning on the boundary of the liquid and solid phases of the Earth's core

NASA Astrophysics Data System (ADS)

Rusov, V. D.; Pavlovich, V. N.; Vaschenko, V. N.; Tarasov, V. A.; Zelentsova, T. N.; Bolshakov, V. N.; Litvinov, D. A.; Kosenko, S. I.; Byegunova, O. A.

2007-09-01

We give an alternative description of the data produced in the KamLAND experiment. Assuming the existence of a natural nuclear reactor on the boundary of the liquid and solid phases of the Earth's core, a geoantineutrino spectrum is obtained. This assumption is based on the experimental results of V. Anisichkin and his collaborators on the interaction of uranium dioxide and uranium carbide with iron-nickel and silica-alumina melts at high pressure (5-10 GPa) and temperature (1600-2200°C), which led to the proposal of the existence of an actinide shell in the Earth's core. We describe the operating mechanism of this reactor as solitary waves of nuclear burning in 238U and/or 232Th medium, in particular, as neutron fission progressive waves of Feoktistov and/or Teller et al. type. Next, we propose a simplified model for the accumulation and burn-up kinetics in Feoktistov's U-Pu fuel cycle. We also apply this model for numerical simulations of neutron fission wave in a two-phase UO2/Fe medium on the surface of the Earth's solid core. The proposed georeactor model offers a mechanism for the generation of 3He. The 3He/4He distribution in the Earth's interior is calculated, which in turn can be used as a natural quantitative criterion of the georeactor thermal power. Finally, we give a tentative estimation of the geoantineutrino intensity and spectrum on the Earth's surface. For this purpose we use the O'Nions et al. geochemical model of mantle differentiation and crust growth complemented by a nuclear energy source (georeactor with power of 30 TW).

Modeling Snow Regime in Cores of Small Planetary Bodies

NASA Astrophysics Data System (ADS)

Boukaré, C. E.; Ricard, Y. R.; Parmentier, E.; Parman, S. W.

2017-12-01

Observations of present day magnetic field on small planetary bodies such as Ganymede or Mercury challenge our understanding of planetary dynamo. Several mechanisms have been proposed to explain the origin of magnetic fields. Among the proposed scenarios, one family of models relies on snow regime. Snow regime is supported by experimental studies showing that melting curves can first intersect adiabats in regions where the solidifying phase is not gravitationaly stable. First solids should thus remelt during their ascent or descent. The effect of the snow zone on magnetic field generation remains an open question. Could magnetic field be generated in the snow zone? If not, what is the depth extent of the snow zone? How remelting in the snow zone drive compositional convection in the liquid layer? Several authors have tackled this question with 1D-spherical models. Zhang and Schubert, 2012 model sinking of the dense phase as internally heated convection. However, to our knowledge, there is no study on the convection structure associated with sedimentation and phase change at planetary scale. We extend the numerical model developped in [Boukare et al., 2017] to model snow dynamics in 2D Cartesian geometry. We build a general approach for modeling double diffusive convection coupled with solid-liquid phase change and phase separation. We identify several aspects that may govern the convection structure of the solidifying system: viscosity contrast between the snow zone and the liquid layer, crystal size, rate of melting/solidification and partitioning of light components during phase change.

A Mathematical Model of Melt Lake Development on an Ice Shelf

NASA Astrophysics Data System (ADS)

Buzzard, S. C.; Feltham, D. L.; Flocco, D.

2018-02-01

The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. Melt lakes have been implicated in ice shelf collapse; Antarctica's Larsen B Ice Shelf was observed to have a large amount of surface melt lakes present preceding its collapse in 2002. Such collapse can affect ocean circulation and temperature, cause habitat loss and contribute to sea level rise through the acceleration of tributary glaciers. We present a mathematical model of a surface melt lake on an idealized ice shelf. The model incorporates a calculation of the ice shelf surface energy balance, heat transfer through the firn, the production and percolation of meltwater into the firn, the formation of ice lenses, and the development and refreezing of surface melt lakes. The model is applied to the Larsen C Ice Shelf, where melt lakes have been observed. This region has warmed several times the global average over the last century and the Larsen C firn layer could become saturated with meltwater by the end of the century. When forced with weather station data, our model produces surface melting, meltwater accumulation, and melt lake development consistent with observations. We examine the sensitivity of lake formation to uncertain parameters and provide evidence of the importance of processes such as lateral meltwater transport. We conclude that melt lakes impact surface melt and firn density and warrant inclusion in dynamic-thermodynamic models of ice shelf evolution within climate models, of which our model could form the basis for the thermodynamic component.

The growth history of the Lago Della Vacca (Southern Adamello Massive, Italy) intrusion from field observations, thermal and rheological modelling

NASA Astrophysics Data System (ADS)

Rust, A.; Annen, C.; Blundy, J. D.; Caricchi, L.

2010-12-01

The Lago Della Vacca granitoid is an intrusive body emplaced at about 4-6 km in up to 1 My. The core of the body is characterised by the presence of dyke-like structures, enclave-swarms and randomly distributed enclaves, which appear undeformed. Enclaves become oblate with the short axis perpendicular to the foliation, which, in turn follows the margin of the plutonic body (John and Blundy, 1993). Geothermometry and experimental data have been used to constrain the temperature of injection of the mafic component (1273-1323 K), the temperature of the host granitic magma (1173-1223), and to characterise the evolution of crystallinity with temperature for both magmas (Blundy and Sparks, 1992). Based on these data thermal and rheological modelling have been combined to interpret the growth and deformation history of the Lago della Vacca intrusive body. The pluton was modeled as a series of incrementally emplaced nested cylinders with 1D-cylindrical conductive heat transfer. The evolution of temperature and melt fraction distribution in the pluton and country rock were determined and used as input parameters for the rheological modelling. The rheology of each magma depends on the viscosity of the melt and, more importantly, on crystallinity. Field observations suggest that the mafic magma was injected as dykes. Their partial or total disaggregation produced mafic enclaves. The presence of randomly distributed enclaves in the core of Lago Della Vacca body indicates that convection was active in this portion of the intrusion. The undeformed nature of the enclaves in this region also implies that the contrast in temperature between host magma and mafic material produced a sudden (hours) rheological inversion with the mafic magma becoming more viscous than the felsic end-member. In these conditions, the enclaves would be transported passively by the felsic-host without suffering any substantial deformation. Thermal modelling indicates that to maintain the core of the pluton above solidus temperature between injections requires either fast emplacement or high initial temperatures of the country rocks. The latter is unlikely for emplacement depths of 4-6 km and as a consequence we infer duration of emplacement up to few hundred thousand years. The wider range of zircon ages may reflect combined intrusion and thermal relaxation times. The extremely flattened enclaves at the rim of the pluton are the result of deformation at lower temperature as the core inflates. As magmas cool the crystallinity of host become as high as the enclaves, resulting in a small viscosity contrast between them, which can be seen as a Window of Mutual Deformability (WMD). Further straining results in a homogeneous deformation and flattening of the enclaves parallel to the margins.

Primative components, crustal assimilation, and magmatic degassing of the 2008 Kilauea summit eruption

USGS Publications Warehouse

Rowe, Michael C.; Thornber, Carl R.; Orr, Tim R.

2015-01-01

Simultaneous summit and rift zone eruptions at Kīlauea starting in 2008 reflect a shallow eruptive plumbing system inundated by a bourgeoning supply of new magma from depth. Olivine-hosted melt inclusions, host glass, and bulk lava compositions of magma erupted at both the summit and east rift zone demonstrate chemical continuity at both ends of a well-worn summit-to-rift pipeline. Analysis of glass within dense-cored lapilli erupted from the summit in March – August 2008 show these are not samplings of compositionally distinct magmas stored in the shallow summit magma reservoir, but instead result from remelting and assimilation of fragments from conduit wall and vent blocks. Summit pyroclasts show the predominant and most primitive component erupted to be a homogenous, relatively trace-element-depleted melt that is a compositionally indistinguishable from east rift lava. Based on a “top-down” model for the geochemical variation in east rift zone lava over the past 30 years, we suggest that the apparent absence of a 1982 enriched component in melt inclusions, as well as the proposed summit-rift zone connectivity based on sulfur and mineral chemistry, indicate that the last of the pre-1983 magma has been flushed out of the summit reservoir during the surge of mantle-derived magma from 2003-2007.

The Germanium Dichotomy in Martian Meteorites

NASA Technical Reports Server (NTRS)

Humayun, M.; Yang, S.; Righter, K.; Zanda, B.; Hewins, R. H.

2016-01-01

Germanium is a moderately volatile and siderophile element that follows silicon in its compatibility during partial melting of planetary mantles. Despite its obvious usefulness in planetary geochemistry germanium is not analyzed routinely, with there being only three prior studies reporting germanium abundances in Martian meteorites. The broad range (1-3 ppm) observed in Martian igneous rocks is in stark contrast to the narrow range of germanium observed in terrestrial basalts (1.5 plus or minus 0.1 ppm). The germanium data from these studies indicates that nakhlites contain 2-3 ppm germanium, while shergottites contain approximately 1 ppm germanium, a dichotomy with important implications for core formation models. There have been no reliable germanium abundances on chassignites. The ancient meteoritic breccia, NWA 7533 (and paired meteorites) contains numerous clasts, some pristine and some impact melt rocks, that are being studied individually. Because germanium is depleted in the Martian crust relative to chondritic impactors, it has proven useful as an indicator of meteoritic contamination of impact melt clasts in NWA 7533. The germanium/silicon ratio can be applied to minerals that might not partition nickel and iridium, like feldspars. We report germanium in minerals from the 3 known chassignites, 2 nakhlites and 5 shergottites by LAICP- MS using a method optimized for precise germanium analysis.

The parent magma of the nakhlite meteorites - Clues from melt inclusions

NASA Technical Reports Server (NTRS)

Harvey, Ralph P.; Mcsween, Harry Y., Jr.

1992-01-01

Several forms of trapped liquid found within nakhlite meteorites have been examined, including interstitial melt and magmatic inclusions within the cores of large olivine grains. Differences in the mineralogy and texture between two types of trapped melt inclusions, and between these inclusions and the mesostasis, indicate that vitrophyric inclusions are most appropriate for estimating the composition of a nakhlite parental magma in equilibrium with early-forming olivine and augite. Parent liquids were calculated from the mineralogy of large inclusions in Nakhla and Governador Valadares, using a system of mass-balance equations solved by linear regression methods. The chosen parental liquids were cosaturated in olivine and augite and had Mg/Fe values consistent with measured augite/liquid Kds. These parental magma compositions are similar to other published compositions for Nakhla, Chassigny, and Shergotty parental melts, and may correspond to a significant magma type on Mars.

Non-free gas of dipoles of non-singular screw dislocations and the shear modulus near the melting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malyshev, Cyril, E-mail: malyshev@pdmi.ras.ru

2014-12-15

The behavior of the shear modulus caused by proliferation of dipoles of non-singular screw dislocations with finite-sized core is considered. The representation of two-dimensional Coulomb gas with smoothed-out coupling is used, and the stress–stress correlation function is calculated. A convolution integral expressed in terms of the modified Bessel function K{sub 0} is derived in order to obtain the shear modulus in approximation of interacting dipoles. Implications are demonstrated for the shear modulus near the melting transition which are due to the singularityless character of the dislocations. - Highlights: • Thermodynamics of dipoles of non-singular screw dislocations is studied below themore » melting. • The renormalization of the shear modulus is obtained for interacting dipoles. • Dependence of the shear modulus on the system scales is presented near the melting.« less

The electronic structure of iron in rhyolitic and basaltic glasses at high pressure

NASA Astrophysics Data System (ADS)

Solomatova, N. V.; Jackson, J. M.; Sturhahn, W.; Roskosz, M.

2016-12-01

The physical properties of silicate melts within the Earth's mantle affect the chemical and thermal evolution of the Earth's interior. To understand melting processes within the Earth, it is imperative to determine the structure of silicate melts at high pressure. It has been proposed that iron-bearing silicate melts may exist in the lower mantle just above the core-mantle boundary [1]. The behavior of iron in mantle melts is poorly understood, but can be experimentally approximated by iron-bearing silicate glasses. Previous studies have conflicting conclusions on whether iron in lower mantle silicate melts goes through a high-spin to low-spin transition [2-4]. Additionally, the average coordination environment of iron in glasses is poorly constrained. XANES experiments on basaltic glasses have demonstrated that both four and six-fold coordinated iron may exist in significant amounts regardless of oxidation state [5] while conventional Mössbauer experiments have observed five-fold coordinated Fe2+ with small amounts of four and six-fold coordinated Fe2+ [6]. In an attempt to resolve these discrepancies, we have measured the hyperfine parameters of iron-bearing rhyolitic glass up to 115 GPa and basaltic glass up to 92 GPa in a neon pressure medium using time-resolved synchrotron Mössbauer spectroscopy at the Advanced Photon Source (Argonne National Laboratory, IL). We observed changes in the hyperfine parameters likely due to coordination changes as a result of increasing pressure. Our results indicate that iron does not undergo a high-spin to low-spin transition within the pressure range investigated. Changes in the electronic configuration, such as the spin state of iron affects the compressibility and thermal properties of melts. With the assumption that silica glasses can be used to model structural behavior in silicate melts, our study predicts that iron in chemically-complex silica-rich melts in the lower mantle likely exists in a high-spin state. Select references: [1] Williams and Garnero, Science 273, 1528-1530 (1996). [2] Nomura et al., Nature 473, 199-202 (2011). [3] Gu et al., Geophys. Res. Lett. 39 (2012). [4] Mao et al., Am. Mineral. 99, 415-423 (2014). [5] Wilke et al., Chem. Geology 220, 143-161 (2005). [6] Cottrell and Kelley Earth Planet. Sci. Lett. 305, 270-282 (2011).

Mantle water contents beneath the Rio Grande Rift (NM, USA): FTIR analysis of Rio Puerco and Kilbourne Hole peridotite xenoliths

NASA Astrophysics Data System (ADS)

Schaffer, L. A.; Peslier, A. H.; Brandon, A. D.; Selverstone, J.

2015-12-01

Peridotite xenoliths from the Rio Grande Rift (RGR) are being analyzed for H2O contents by FTIR as well as for major and trace element compositions. Nine samples are from the Rio Puerco Volcanic Field (RP) which overlaps the central RGR and southeastern Colorado Plateau; seventeen samples are from Kilbourne Hole (KH) in the southern RGR. Spinel Cr# (Cr/(Cr+Al) = 0.08-0.46) and olivine Mg# (Mg/(Mg+Fe) = 0.883-0.911) of samples fall within the olivine-spinel mantle array from [1], an indicator that these are residues of partial melting. Pyroxene H2O contents in KH correlate with bulk rock and pyroxene Al2O3 contents. The KH clinopyroxene rare earth element (REE) variations fit models of 0-13% fractional melting of a primitive upper mantle. Most KH peridotites have bulk-rock light REE depleted patterns, but five are enriched in light REEs consistent with metasomatism. Variation in H2O content seems unrelated to REE enrichment. Metasomatism is seen in RP pyroxenite xenoliths [2] and will be examined in the peridotites studied here. Olivine H2O contents are low (≤20 ppm), and decrease from core to rim within grains. This is likely due to H loss during xenolith transport by the host magma [3]. Diffusion models of H suggest that mantle H2O contents are still preserved in cores of KH olivine, but not those of RP olivine. The average H2O content of Colorado Plateau clinopyroxene (670 ppm) [4] is ~300 ppm higher than RGR clinopyroxene (350 ppm). This upholds the hypothesis that hydration-induced lithospheric melting occurred during flat-slab subduction of the Farallon plate [5]. Numerical models indicate hydration via slab fluids is possible beneath the plateau, ~600 km from the paleo-trench, but less likely ~850 km away beneath the rift [6]. [1]Arai, 1994 CG 113, 191-204.[2]Porreca et al., 2006 Geosp 2, 333-351.[3]Peslier and Luhr, 2006 EPSL 242, 302-319.[4]Li et al., 2008 JGR 113, 1978-2012.[5]Humphreys et al., 2003 Int Geol Rev 45, 575-595.[6]English et al., 2003 EPSL 214, 619-632.

Early metal-silicate differentiation during planetesimal formation revealed by acapulcoite and lodranite meteorites

NASA Astrophysics Data System (ADS)

Dhaliwal, Jasmeet K.; Day, James M. D.; Corder, Christopher A.; Tait, Kim T.; Marti, Kurt; Assayag, Nelly; Cartigny, Pierre; Rumble, Doug; Taylor, Lawrence A.

2017-11-01

In order to establish the role and expression of silicate-metal fractionation in early planetesimal bodies, we have conducted a highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance and 187Re-187Os study of acapulcoite-lodranite meteorites. These data are reported with new petrography, mineral chemistry, bulk-rock major and trace element geochemistry, and oxygen isotopes for Acapulco, Allan Hills (ALHA) 81187, Meteorite Hills (MET) 01195, Northwest Africa (NWA) 2871, NWA 4833, NWA 4875, NWA 7474 and two examples of transitional acapulcoite-lodranites, Elephant Moraine (EET) 84302 and Graves Nunataks (GRA) 95209. These data support previous studies that indicate that these meteorites are linked to the same parent body and exhibit limited degrees (<2-7%) of silicate melt removal. New HSE and osmium isotope data demonstrate broadly chondritic relative and absolute abundances of these elements in acapulcoites, lower absolute abundances in lodranites and elevated (>2 × CI chondrite) HSE abundances in transitional acapulcoite-lodranite meteorites (EET 84302, GRA 95209). All of the meteorites have chondritic Re/Os with measured 187Os/188Os ratios of 0.1271 ± 0.0040 (2 St. Dev.). These geochemical characteristics imply that the precursor material of the acapulcoites and lodranites was broadly chondritic in composition, and were then heated and subject to melting of metal and sulfide in the Fe-Ni-S system. This resulted in metallic melt removal and accumulation to form lodranites and transitional acapulcoite-lodranites. There is considerable variation in the absolute abundances of the HSE, both among samples and between aliquots of the same sample, consistent with both inhomogeneous distribution of HSE-rich metal, and of heterogeneous melting and incomplete mixing of silicate material within the acapulcoite-lodranite parent body. Oxygen isotope data for acapulcoite-lodranites are also consistent with inhomogeneous melting and mixing of accreted components from different nebular sources, and do not form a well-defined mass-dependent fractionation line. Modeling of HSE inter-element fractionation suggests a continuum of melting in the Fe-Ni-S system and partitioning between solid metal and sulfur-bearing mineral melt, where lower S contents in the melt resulted in lower Pt/Os and Pd/Os ratios, as observed in lodranites. The transitional meteorites, EET 84302 and GRA 95209, exhibit the most elevated HSE abundances and do not follow modelled Pt/Os and Pd/Os solid metal-liquid metal partitioning trends. We interpret this to reflect metal melt pooling into domains that were sampled by these meteorites, suggesting that they may originate from deeper within the acapulcoite-lodranite parent body, perhaps close to a pooled metallic 'core' region. Petrographic examination of transitional samples reveals the most extensive melting, pooling and networking of metal among the acapulcoite-lodranite meteorites. Overall, our results show that solid metal-liquid metal partitioning in the Fe-Ni-S system in primitive achondrites follows a predictable sequence of limited partial melting and metal melt pooling that can lead to significant HSE inter-element fractionation effects in proto-planetary materials.

Igneous Crystallization and Localized Deformation in the Shallow Mantle beneath Slow Spreading Ridges

NASA Astrophysics Data System (ADS)

Kelemen, P.; Kikawa, E.; Miller, J.

2004-05-01

Building upon previous work, and incorporating new results from ODP Leg 209, we will provide a synthesis of melt migration mechanisms beneath oceanic spreading ridges, with an emphasis on the thick conductive boundary layer extending to about 20 km depth beneath slow-spreading ridges. In adiabatically upwelling mantle, ascending melt acts as a "solvent", creating additional melt by dissolving pyroxene in surrounding wall rocks, and thus forming high porosity dissolution channels. Mature dissolution channels lack pyroxene, and allow migration of pyroxene-undersaturated melt through the shallow mantle. In conductively cooled mantle, melts begin to crystallize due to cooling, and in addition reactions with surrounding peridotite consume melt. Where melt fluxes are large, this can create a permeability barrier that ultimately leads to an upstream increase in melt pressure and, in some cases, causes hydrofracture and magma ascent in dikes. Where melt fluxes are small, porous flow of crystallizing melt continues upward into the conductive boundary layer. This leads to formation of "impregnated peridotite", with igneous plag and pyroxene precipitated along olivine grain boundaries, and forms melts that are in equilibrium with lherzolite assemblages at relatively low pressures. Impregnated peridotites from ODP Leg 209 have "equilibrated" textures and contain olivine, 2 pyroxenes, plag and Cr-rich spinel. Mg#, Cr# and Ni are high, extending to residual peridotite values. Crystallization pressure can be estimated using local lava compositions. 87 MORB glasses from 14 to 16°N with Mg# from 60 to 73 [from PetDB] could be plagioclase lherzolite saturated at 5.4 kb (+ - 1.4 kb 2 sigma) and 1220 C (+ - 16°C 2 sigma) [using Kinzler & Grove, JGR 92]. Plag ranges from An 60 to 75. Subsolidus PT for the plag spinel lherzolite assemblage are not well constrained, but are about 3 kb and 700-800 C, consistent with the conductive geotherm inferred from igneous PT estimates. Thus, melts began to cool and crystallize at depths > 15 km. Impregnated and residual peridotites in our core appear undeformed. Though they may have a strong olivine LPO, there are few shape fabrics. Instead skeletal, interstitial pyroxene and spinel extend for mm in 2D and 3D. Core from most sites includes high T mylonitic shear zones (mainly impregnated peridotite) and low T fault gouge. Shear zones and faults are not all parallel; numerous, cross-cutting planes of localized deformation formed at >1000 C to <100 C, from >15 km to the seafloor. These accommodated subsolidus deformation during corner flow and exhumation of peridotites and high P igneous rocks, in keeping with previous inferences that the thermal boundary layer beneath the MAR extends to about 20 km. Penetrative deformation of blocks between shear zones and faults was minor. Localization of deformation at high temperature may have been facilitated by the presence of melt.

Can basal magma oceans generate magnetic fields?

NASA Astrophysics Data System (ADS)

Stegman, D. R.; Ziegler, L. B.; Davies, C.

2015-12-01

Earth's magnetic field is very old, with recent data now showing the field possibly extended back to 4.1 billion years ago (Tarduno et al., Science, 2015). Yet, based upon our current knowledge there are difficulties in sustained a core dynamo over most of Earth's history. Moreover, recent estimates of thermal and electrical conductivity of liquid iron at core conditions from mineral physics experiments indicate that adiabatic heat flux is approximately 15 TW, nearly 3 times larger than previously thought, exacerbating difficulties for driving a core dynamo by convective core cooling alone throughout Earth history. A long-lived basal magma ocean in the lowermost mantle has been proposed to exist in the early Earth, surviving perhaps into the Archean. While the modern, solid lower mantle is an electromagnetic insulator, electrical conductivities of silicate melts are known to be higher, though as yet they are unconstrained for lowermost mantle conditions. Here we explore the geomagnetic consequences of a basal magma ocean layer for a range of possible electrical conductivities. For the highest electrical conductivities considered, we find a basal magma ocean could be a primary dynamo source region. This would suggest the proposed three magnetic eras observed in paleomagnetic data originate from distinct sources for dynamo generation: from 4.5-2.45 Ga within a basal magma ocean, from 2.25-0.4 Ga within a superadiabatically cooled liquid core, and from 0.4-present within a quasi-adiabatic core that includes a solidifying inner core. We have extended this work by developing a new code, Dynamantle, which is a model with an entropy-based approach, similar to those commonly used in core dynamics models. We present new results using this code to assess the conditions under which basal magma oceans can generate positive ohmic dissipation. This is more generally useful than just considering the early Earth, but also for many silicate exoplanets in which basal magma oceans are even more likely to exist.

Interpreting Continental Break-Up From Surface Observations: Analysis of 1D Partial Melting Using Synthetic Waveform Propagation

NASA Astrophysics Data System (ADS)

Franken, T.; Armitage, J. J.; Fuji, N.; Fournier, A.

2017-12-01

Low shear-wave velocity zones underneath margins of continental break-up are believed to be related to the presence of melt. Many models attempt to model the process of melt production and transportation during mantle upwelling, yet there is a disconnect between geodynamic models, seismic observations, and petrological studies of melt flow velocities. Geodynamic models that emulate melt retention of 2 %, suggested by shear-wave velocity anomalies (Forsyth & MELT Seismic Team, 1998), fail to adequately reproduce the seismic signal as seen in receiver functions (Rychert, 2012; Armitage et al., 2015). Furthermore, numerical models of melt migration conclude mean melt flow velocities up to 1,3 m yr-1(Weatherley & Katz, 2015), whereas Uranium isotope migration rates advocate velocities up to two orders of magnitude higher. This study aims to reconcile the diverting assertions on the partial melting process by analysing the effect of melt presence on the coda of the seismic signal. A 1D forward model has been created to emulate melt production and transportation in an upwelling mantle environment. Scenarios have been modelled for variable upwelling velocities v (1 - 100 mm yr-1), initial temperatures T0 (1200 - 1800 °C) and permeabilities k0 (10-9 - 10-5 m2). The 1D model parameters are converted to anharmonic seismic parameters using look-up tables from phase diagrams (Goes et al., 2012) to generate synthetic seismograms with the Direct Solution Method. The maximum frequency content of the synthetics is 1,25 Hz, sampled at 20 Hz with a low-pass filter of 0,1 Hz. A comparison between the synthetics and seismic observations of the La Reunion mantle plume from the RER Geoscope receiver is performed using a Monte-Carlo approach. The synthetic seismograms show highest sensitivity to the presence of melt in S-waves within epicentral distances of 0-20 degrees. In the 0-10 degree range only a time-shift is observed proportional to the melt fraction at the onset of melting. Within the 10-20 degree range the presence of melt causes an additional change in the coda of the signal compared to a no-melt model. By analysing these altered synthetic waveforms we search for a seismic signature corresponding to melt presence to form a benchmark for the comparison between the Monte-Carlo results and the seismic observations.

The Chicxulub crater - impact metamorphism of sulfate and carbonate lithologies

NASA Astrophysics Data System (ADS)

Deutsch, A.; Langenhorst, F.; Hornemann, U.; Ivanov, B. A.

2003-04-01

It is discussed whether in the aftermath of the Chicxulub event, impact-released CO_2 and SO_x have changed the Earth's climate, acting also as lethal thread for life. Undoubtedly, vaporization of carbonates and sulfates, which are major target lithologies at the Chicxulub impact site, occurred in the footprint of the projectile. What happened to these lithologies outside this very restricted zone was so far unconstrained. Petrologic observations on PEMEX and UNAM as well as on the CSDP cores allow to set up a general classification for shock-related pro-grade effects on sulfate and carbonate sedimentary rocks. Shock effects in lithic breccias are restricted to brecciation and formation of twins in calcite. Suevites mostly lack melted carbonate clasts; annealing effects in anhydrite fragments are absent. The underlying melt breccias contain anhydrite fragments still displaying a sedimentary texture, and limestone clasts, whose texture reflect crystallization from melt. Impact melt breccias from deeper levels frequently contain partially resorbed anhydrite clasts and a melt matrix with the Ca-rich mineral assemblage quartz + plagioclase + clinopyroxene; this mineral assemblage provides evidence for partial dissociation of CaSO_4. Large clasts of anhydrite consist of equant crystals with 120^o triple junctions, a feature indicative for re-crystallization in the solid state. Tagamites (impact melt rocks) are virtually free of clasts from sedimentary lithologies. These rocks have an extremely high formation temperature, which caused total dissociation of CaSO_4 and CaCO_3. Finally, up to 100 μm wide veins of anhydrite + calcite + quartz cut the matrix of all lithologies except the tagamites. They probably represent "degassing vents". The given scheme is in qualitative accordance with data of shock recovery and annealing experiments as well as with modeling results. In addition, it substantiates that annealing plays a fundamental role in the impact metamorphism of sedimentary rocks.

Eruption Depths, Magma Storage and Magma Degassing at Sumisu Caldera, Izu-Bonin Arc: Evidence from Glasses and Melt Inclusions

NASA Astrophysics Data System (ADS)

Johnson, E. R.

2015-12-01

Island arc volcanoes can become submarine during cataclysmal caldera collapse. The passage of a volcanic vent from atmospheric to under water environment involves complex modifications of the eruption style and subsequent transport of the pyroclasts. Here, we use FTIR measurements of the volatile contents of glass and melt inclusions in the juvenile pumice clasts in the Sumisu basin and its surroundings (Izu-Bonin arc) to investigate changes in eruption depths, magma storage and degassing over time. This study is based on legacy cores from ODP 126, where numerous unconsolidated (<65 ka), extremely thick (few m to >250 m), massive to normally graded pumice lapilli-tuffs were recovered over four cores (788C, 790A, 790B and 791A). Glass and clast geochemistry indicate the submarine Sumisu caldera as the source of several of these pumice lapilli-tuffs. Glass chips and melt inclusions from these samples were analyzed using FTIR for H2O and CO2 contents. Glass chips record variable H2O contents; most chips contain 0.6-1.6 wt% H2O, corresponding to eruption depths of 320-2100 mbsl. Variations in glass H2O and pressure estimates suggest that edifice collapse occurred prior-to or during eruption of the oldest of these samples, and that the edifice may have subsequently grown over time. Sanidine-hosted melt inclusions from two units record variably degassed but H2O-rich melts (1.1-5.6 wt% H2O). The lowest H2O contents overlap with glass chips, consistent with degassing and crystallization of melts until eruption, and the highest H2O contents suggest that large amounts of degassing accompanied likely explosive eruptions. Most inclusions, from both units, contain 2-4 wt% H2O, which further indicates that the magmas crystallized at pressures of ~50-100 MPa, or depths ~400-2800 m below the seafloor. Further glass and melt inclusion analyses, including major element compositions, will elucidate changes in magma storage, degassing and evolution over time.

Pseudotachylitic breccia from the Dhala impact structure, north-central India: Texture, mineralogy and geochemical characterization

NASA Astrophysics Data System (ADS)

Pati, J. K.; Reimold, W. U.; Greshake, A.; Schmitt, R. T.; Koeberl, C.; Pati, P.; Prakash, K.

2015-05-01

Pseudotachylitic breccia (PTB) occurs in a drill core from the crater floor of the 11 km diameter, Proterozoic Dhala impact structure, India. PTBs were intersected in late Archean granitoids between 348.15 m and 502.55 m depth in the MCB-10 drill core from the center of the Dhala structure. The breccias comprise both cataclastic-matrix as well as melt breccias. The presence of microlites and vesicles in the groundmass and a widely observed flow fabric in the PTB support the presence of melt in the groundmass of some samples. Clasts in PTB are derived from the Archean granitoid basement. PTB matrix, the matrix of impact melt breccia also occurring between 256.50 m and 502.55 m depth, and the target granitoids vary in terms of silica, total alkali, magnesium and iron oxide contents. Chondrite-normalized REE patterns of PTB and target granitoids are similar, but the elemental abundances in the PTB are lower. The restricted size of PTB as veins and pods of up to 2.5 cm width, their occurrence at varied depths over a core length of 150 m, the clast population, and the chemical relationships between PTB and their host rocks all suggest the derivation of these breccias locally from the fractured basement granitoids involving in-situ melting. We favor that this took place due to rapid decompression during the collapse and modification stage of impact cratering, with, locally, additional energy input from frictional heating. Locally, amphibolite and dioritic mylonite occur in the host granitoids and their admixture could have contributed to the comparatively more mafic composition of PTB. Alteration of these crater floor rocks could have involved preferential reduction of silica and alkali element abundances, possibly due to impact-induced hydrothermal activity at crater floor level. This process, too, could have resulted in more mafic compositions.

Distribution of some highly volatile elements in chondrules

NASA Astrophysics Data System (ADS)

Kim, J. S.; Marti, K.

1994-07-01

As chondrule apparently were melted before accretion into chondritic parent bodies, we carried out a N and Xe isotopic study to obtain information on the partitioning of some of the most volatile as well as incompatible elements: noble gases, N, I, REE, and Pu. In separated silicates in Forest Vale, consisting of mostly broken chondrules, we observed rather large Xe concentrations, and since noble gases in chondrites are associated with C-rich phases, we decided to study the core portion of a suite of chondrules after removing the chondrule rim portion and adhering matrix. We selected sets of rounded chondrules from four meteorites: Allende (CV3), Dhajala (H3.8), Forest Vale (H4), and Bjurbole (L4). We compare measured N and Xe concentrations and isotopic abundances in cores of chondrules to those obtained from unetched chondrules. We discuss results obtained from melting steps, because N and Xe in the silicate lattice are mostly released at T greater than 1000 C. All cores of chondrules contain less than 1% of the Xe in the respective bulk samples. Moreover, they released much less trapped Xe in the melting step than did untreated bulk chondrites. However, the radiogenic Xer-129 and fissiogenic Xef is not or is only slightly depleted, and spallogenic Xe is a major component, particularly in Forest Vale. We can not deduce the signature of trapped Xe in the chondrules. The release systematics are completely different from those observed in primitive achondrites, which contain noble gas in the 'dusty' silicate inclusions. Allende chondrules differ from those of ordinary chondrite in the N release pattern. This represents possibly a signature of the local environment during chondrule formation, since N may exist in chondrule minerals in chemically bound forms. In contrast, all three sets of ordinary chondrite chondrules released less than 0.6 ppm N in the melting step, and these signatures reveal substantial components of cosmic-ray-produced N.

Shock Melting of Iron Silicide as Determined by In Situ X-ray Diffraction.

NASA Astrophysics Data System (ADS)

Newman, M.; Kraus, R. G.; Wicks, J. K.; Smith, R.; Duffy, T. S.

2016-12-01

The equation of state of core alloys at pressures and temperatures near the solid-liquid coexistence curve is important for understanding the dynamics at the inner core boundary of the Earth and super-Earths. Here, we present a series of laser driven shock experiments on textured polycrystalline Fe-15Si. These experiments were conducted at the Omega and Omega EP laser facilities. Particle velocities in the Fe-15Si samples were measured using a line VISAR and were used to infer the thermodynamic state of the shocked samples. In situ x-ray diffraction measurements were used to probe the melting transition and investigate the potential decomposition of Fe-15Si in to hcp and B2 structures. This work examines the kinetic effects of decomposition due to the short time scale of dynamic compression experiments. In addition, the thermodynamic data collected in these experiments adds to a limited body of information regarding the equation of state of Fe-15Si, which is a candidate for the composition in Earth's outer core. Our experimental results show a highly textured solid phase upon shock compression to pressures ranging from 170 to 300 GPa. Below 320 GPa, we observe diffraction peaks consistent with decomposition of the D03 starting material in to an hcp and a cubic (potentially B2) structure. Upon shock compression above 320 GPa, the intense and textured solid diffraction peaks give way to diffuse scattering and loss of texture, consistent with melting along the Hugoniot. When comparing these results to that of pure iron, we can ascertain that addition of 15 wt% silicon increases the equilibrium melting temperature significantly, or that the addition of silicon significantly increases the metastability of the solid phase, relative to the liquid. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Isotopic evolution of Mauna Loa and the chemical structure of the Hawaiian plume

NASA Astrophysics Data System (ADS)

Depaolo, Donald J.; Bryce, Julia G.; Dodson, Allen; Shuster, David L.; Kennedy, B. Mack

2001-07-01

New He isotopic data from the HSDP pilot hole core, lava accumulation rate models, and data from the literature are used to develop a 200,000 year isotopic record for the lava erupted from the Mauna Loa volcano. This record, coupled with an analogous record from Mauna Kea from the Hawaii Scientific Drilling Project (HSDP) pilot hole project and other literature data from the GEOROC database, are used to construct a "map" of lava isotopic compositions for the island of Hawaii. The isotopic map is converted to a map of the He and Nd isotopic compositions of melts from the mantle plume, which can be compared with a published melt supply map derived from geodynamic modeling. The resulting map of the plume indicates that values of helium 3He/4He > 20 Ra are confined to the core of the plume (radius ≈ 20-25 km) and correspond to potential temperatures >1565°C, suggesting the He isotopic signal is derived from deep in the mantle. The 3He/4He map has closed contours down to 10 Ra; the contours are teardrop-shaped and elongated in the general direction of plate motion. The closed contours indicate that most of the plume He signal is lost during the early stages of melting, which is consistent with helium behaving as a strongly incompatible element (KHe ≤ 0.001). The ɛNd contours (and by inference the contours for Sr, Pb, Hf, and Os) do not all close on the scale of the island of Hawaii but instead partially follow material flow lines within the plume beneath the lithosphere. The plume signal for Nd extends circa 100 km in the direction of plate motion, which is consistent with the moderately incompatible behavior of Nd (KNd ≈ 0.02). Downstream from the plume core epicenter, plume Nd occurs with asthenospheric He; this could be mistaken for an additional plume component, whereas it may be only a manifestation of differing incompatibility. Data from Mauna Loa suggest the presence of a low-3He/4He plume component that has low ɛNd and high 87Sr/86Sr. The plume map suggests that this component may be a blob (circa 20 km scale), located between Mauna Loa and Hualalai and separated from the main plume core by a zone of more asthenosphere-like material. The HSDP data preclude a proposed model where this material represents a ring of entrained material from the lower mantle. The orientation of the elongation of contours on the plume He and Nd isotope maps (˜N45°W) does not match the modern plate motion as measured by GPS (N65°W) nor does it match the trend of the ridge axis between Maui and Loihi (N30°W). The geochemical evidence, as well as the locations and growth histories of the Hawaiian volcanoes, suggest that the plume, as well as the Pacific plate, has been moving at a velocity of several centimeters per year over the past 1 to 2 million years.

In situ determination of binary alloy melt compositions in the LHDAC by X- Radiography

NASA Astrophysics Data System (ADS)

Lord, O. T.; Walter, M. J.; Walker, D.; Clark, S. M.

2008-12-01

Constraining the light element in Earth's molten outer core requires an understanding of the melting phase relations in iron-light element binary systems. For example, it is critical to determine the composition of liquids at binary eutectics. Typically such measurements are carried out after the sample has been quenched in temperature and pressure. Such 'cook and look' methods possibly suffer from systematic errors introduced by exsolution of the light element from the melt on quench and error in the reintegration of the liquid composition [1]. Here, we present a novel method for the determination of melt compositions in iron-light element binary systems in situ in the LHDAC at simultaneous high-pressure, high-temperature conditions. Samples consist of a light element bearing compound, such as FeO, surrounded by a pure iron ring, forming a donut ~100 μm in diameter and ~15 μm thick. The donuts are loaded into stainless steel gaskets in the DAC, sandwiched between discs fabricated from sol-gel deposited nanocrystalline Al2O3 with similar dimensions to the donut. Pressure is monitored by ruby fluorescence during compression. The sample is heated at the boundary between the iron and light element compound using two 100 W IR lasers in a double-sided configuration at beamline 12.2.2 at the Advanced Light Source. Temperature is measured by spectroradiometry. Before, during and after melting, X-radiographic images of the sample are taken by shining a defocused beam of synchrotron X-rays through the sample and onto a CdWO4 phosphor. The visible light from the phosphor is then focused onto a high resolution CCD, where absorption contrast images are recorded. The absorption of the molten region is then determined, and it's composition calculated by linear interpolation between the absorption of the two solid end members. As a test of the reliability of the method we measured the Fe-FeS eutectic to 20 GPa and our results are in good agreement with previous studies that are based on various ex situ techniques. We measured the eutectic composition between Fe and Fe3C up to 44 GPa, and found that the carbon content of the eutectic drops rapidly above about 10 GPa, dropping to less that 1 wt% by 44 GPa. This result is generally consistent with the thermodynamic calculations of Wood [2]. Experiments on the Fe-FeSi eutectic yielded an increase in the Si content of the eutectic to 35 GPa, consistent with data from large volume press experiments [3] Notably, melting experiments at 35-43 GPa and ~2500 K on a boundary between Fe and FeO failed to yield evidence of a melt with a composition distinguishable from pure iron. However, an experiment at 12 GPa and 2700 K between Fe and FeO(OH) did yield a melt with a composition intermediate between the two end members. This suggests that O solubility in the Fe-O eutectic melt is low at mid-mantle pressures, but that H may dissolve into the melt by itself or in combination with O. [1] Walker, D., 2005. Core-Mantle chemical issues. Canad. Min., 43, 1553-1564 [2] Wood, B. J., 1993. Carbon in the core. Earth Planet Sci. Lett., 117, 593-607 [3] Kuwayama, Y. & Hirose, K., 2004. Phase relations in the system Fe-FeSi at 21 GPa. Am. Min., 89, 273-276.

Dehydration melting studies in a 'Kyanite terrain', Manali, NW Himalayas

NASA Astrophysics Data System (ADS)

Verma, Pramod; Sengupta, Susmita; Chaddha, D. K.; Pant, N. C.

2005-05-01

The Beas valley section in Himachal Pradesh is characterized by the presence of kyanite as the alumino-silicate phase and a small extent of Neogene quartzo-feldspathic intrusives. The present paper explores the reasons for the lack of extensive granite occurrences through a detailed petrologic study on samples of a drill core (200 m, inclined 60° due ESE) close to Manali, the expected highest point in P-T space in this section. The highest assemblage encountered is quartz+muscovite+biotite+garnet+plagioclase+kyanite±apatite±zircon±tourmaline±ilmenite±rutile. The chemical analyses of mineral grains were carried out on a CAMECA SX51 EPMA. The following two reactions that constrain the P-T regime of the area have been established. St+Qtz→Alm+Ky+HO Bio+Plg+Qtz+Ksp→Gar+Ky+Liq. Our result, P=8.25±1 kbar, T=638±4 °C, falls in a region between curves representing aO=1.0 and aO=0.7 of the fluid in Thompson [Trans. Royal Soc. Edinb. 87 (1996) 1] diagram. The P-T estimate falls in the kyanite field and is very close to the mica dehydration-melting curve. The studies indicate that the core samples are a part of progressive metamorphic sequence. It implies that the absence of sillimanite and large scale melting is perhaps chance brought about by thrusting and erosion. The present section experienced single stage dehydration melting.

On the melting temperature measurements of metals under shock compression by pyrometry

NASA Astrophysics Data System (ADS)

Dai, Chengda; Hu, Jianbo; Tan, Hua

2009-06-01

The high-pressure melting temperatures are of interest in validating equation of state and modeling constitutive equation. The determination of melting temperatures for metals at megabars by pyrometry experiments is principally associated with the one-dimensional models for heat flow through dissimilar media: Grover-Urtiew model (J. App. Phys. 1974, 45: 146-152) and Tan-Ahrens model (High Press. Res. 1990, 2: 159-182). In the present work, we analyzed the insufficiency of Grover-Urtiew model in determining melting temperatures from observed interface temperatures. Based on the Tan-Ahrens model, we extracted the upper and lower bound on melting temperature at interface pressure, and proposed that the median of the both bounds was a good approximation to the melting temperatures at interface pressure. Pyrometry experiments were performed on tantalum, and the high-pressure melting temperatures were evaluated by application of the proposed approximation. The obtained results were compared with available theoretical calculations.

Evidence of denser MgSiO3 glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean.

PubMed

Murakami, Motohiko; Bass, Jay D

2011-10-18

Ultralow velocity zones are the largest seismic anomalies in the mantle, with 10-30% seismic velocity reduction observed in thin layers less than 20-40 km thick, just above the Earth's core-mantle boundary (CMB). The presence of silicate melts, possibly a remnant of a deep magma ocean in the early Earth, have been proposed to explain ultralow velocity zones. It is, however, still an open question as to whether such silicate melts are gravitationally stable at the pressure conditions above the CMB. Fe enrichment is usually invoked to explain why melts would remain at the CMB, but this has not been substantiated experimentally. Here we report in situ high-pressure acoustic velocity measurements that suggest a new transformation to a denser structure of MgSiO(3) glass at pressures close to those of the CMB. The result suggests that MgSiO(3) melt is likely to become denser than crystalline MgSiO(3) above the CMB. The presence of negatively buoyant and gravitationally stable silicate melts at the bottom of the mantle, would provide a mechanism for observed ultralow seismic velocities above the CMB without enrichment of Fe in the melt. An ultradense melt phase and its geochemical inventory would be isolated from overlying convective flow over geologic time.

Dynamic melting of metals in the diamond cell: Clues for melt viscosity?

NASA Astrophysics Data System (ADS)

Boehler, R.; Karandikar, A.; Yang, L.

2011-12-01

From the observed decreasing mobility of liquid iron at high pressure in the laser-heated diamond cell and the gradual decrease in the shear modulus in shock experiments, one may derive high viscosity in the liquid outer core of the Earth. A possible explanation could be the presence of local structures in the liquid as has been observed for several transition metals. In order to bridge the large gap in the timescales between static and dynamic melting experiments, we have developed new experimental techniques to solve the large discrepancies in the melting curves of transition metals (Fe, W, Ta, Mo) measured statically in the laser-heated diamond cell and in shock experiments. The new methods employ "single-shot" laser heating in order to reduce problems associated with mechanical instabilities and chemical reactions of the samples subjected to several thousand degrees at megabar pressures. For melt detection, both synchrotron X-ray diffraction and Scanning Electron Microscopy (SEM) on recovered samples are used. A third approach is the measurement of latent heat effects associated with melting or freezing. This method employs simultaneous CW and pulse laser heating and monitoring the temperature-time history with fast photomultipliers. Using the SEM recovery method, we measured first melting temperatures of rhenium, which at high pressure may be one of the most refractory materials. From the melt textures of Re, we did not observe a significant pressure dependence of viscosity.

Evidence of denser MgSiO3 glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

PubMed Central

Murakami, Motohiko; Bass, Jay D.

2011-01-01

Ultralow velocity zones are the largest seismic anomalies in the mantle, with 10–30% seismic velocity reduction observed in thin layers less than 20–40 km thick, just above the Earth’s core-mantle boundary (CMB). The presence of silicate melts, possibly a remnant of a deep magma ocean in the early Earth, have been proposed to explain ultralow velocity zones. It is, however, still an open question as to whether such silicate melts are gravitationally stable at the pressure conditions above the CMB. Fe enrichment is usually invoked to explain why melts would remain at the CMB, but this has not been substantiated experimentally. Here we report in situ high-pressure acoustic velocity measurements that suggest a new transformation to a denser structure of MgSiO3 glass at pressures close to those of the CMB. The result suggests that MgSiO3 melt is likely to become denser than crystalline MgSiO3 above the CMB. The presence of negatively buoyant and gravitationally stable silicate melts at the bottom of the mantle, would provide a mechanism for observed ultralow seismic velocities above the CMB without enrichment of Fe in the melt. An ultradense melt phase and its geochemical inventory would be isolated from overlying convective flow over geologic time. PMID:21969547

Distribution of siderophile and other trace elements in melt rock at the Chicxulub impact structure

NASA Technical Reports Server (NTRS)

Schuraytz, B. C.; Lindstrom, D. J.; Martinez, R. R.; Sharpton, V. L.; Marin, L. E.

1994-01-01

Recent isotopic and mineralogical studies have demonstrated a temporal and chemical link between the Chicxulub multiring impact basin and ejecta at the Cretaceous-Tertiary boundary. A fundamental problem yet to be resolved, however, is identification of the projectile responsible for this cataclysmic event. Drill core samples of impact melt rock from the Chichxulub structure contain Ir and Os abundances and Re-Os isotopic ratios indicating the presence of up to approx. 3 percent meteoritic material. We have used a technique involving microdrilling and high sensitivity instrumental neutron activation analysis (INAA) in conjunction with electron microprobe analysis to characterize further the distribution of siderophile and other trace elements among phases within the C1-N10 melt rock.

Nuclear fuel in a reactor accident.

PubMed

Burns, Peter C; Ewing, Rodney C; Navrotsky, Alexandra

2012-03-09

Nuclear accidents that lead to melting of a reactor core create heterogeneous materials containing hundreds of radionuclides, many with short half-lives. The long-lived fission products and transuranium elements within damaged fuel remain a concern for millennia. Currently, accurate fundamental models for the prediction of release rates of radionuclides from fuel, especially in contact with water, after an accident remain limited. Relatively little is known about fuel corrosion and radionuclide release under the extreme chemical, radiation, and thermal conditions during and subsequent to a nuclear accident. We review the current understanding of nuclear fuel interactions with the environment, including studies over the relatively narrow range of geochemical, hydrological, and radiation environments relevant to geological repository performance, and discuss priorities for research needed to develop future predictive models.

A Little Island With A Big Secret: Isla Rábida, Galápagos

NASA Astrophysics Data System (ADS)

Bercovici, H.; Geist, D.; Harpp, K. S.; Almeida, M.; Mahr, J.; Pimentel, R.; Cleary, Z.

2016-12-01

The Galápagos Archipelago is a hotspot island chain 1000 km west of Ecuador, where the vast majority of the lavas are basaltic. Four volcanoes in the archipelago, Rábida, Santiago, Pinzón, and Alcedo, erupt rhyolites and trachytes. Isla Rábida, a small island 50 km east of the mantle plume center, is the focus of this project. It is 5 km2 in area, and lavas range from 0.9 to 1.1 Ma. About 25% of the rocks in our suite are intermediate to felsic, extending from Mg#=2 to 57. Major and trace element data indicate the evolved rocks formed by advanced crystallization of basaltic magma. One of the unique aspects of Rábida is the cumulate xenolith suite ranging from olivine gabbro to ferroan granite. The basalts have 6 to 58 modal% plagioclase phenocrysts, which we interpret as mixtures of melt and accumulated plagioclase mush at the margins of the shallow reservoir. Thus, Rábida erupts material that has undergone different extents of crystallization and crystal sorting from pure melts, to melt-mush hybrids, to solidified cumulates. This hypothesis is evaluated by comparing plagioclase compositions from the xenoliths and the lavas. Plagioclases in two of the lavas, one with Mg#=57 and the other with Mg#=36, have similar compositions and zonation patterns to each other. There is on average less than 4% change in anorthite content from the core of the plagioclases in the basalts to the rim, with the compositions overall varying between An22 and An37. Both melts likely picked up the crystals from the same plagioclase mush before eruption. In comparison to plagioclases in an olivine-gabbro xenolith from Rábida, those in the lavas are less zoned, suggesting that the lavas' plagioclases experienced a different growth environment. Plagioclases in the xenolith are normally zoned, with cores averaging An37 and rims averaging An32. The xenolith's plagioclases also have more diverse compositions than those in the lavas. The normal zoning in the xenolith's plagioclase is likely from late-stage crystallization of evolved intercumulus melt. Our results suggest that the extraordinary petrologic diversity of Rábida is attributable to crystal-liquid segregation and reincorporation of plagioclase in various melts. These processes result in the eruption of pure melt, melt mixed with mush, and cumulates.

Petrogenesis of Silicic Magmas in the Afro-Arabian Flood Volcanic Province in Yemen: A Melt Inclusion Study

NASA Astrophysics Data System (ADS)

Falkena, L. B.; Peate, D.; Ukstins Peate, I.

2009-05-01

The Oligocene (˜26-30 Ma) Afro-Arabian Flood Volcanic Province in Yemen and Ethiopia contains significant silicic material primarily deposited as large volume (>1,000 km 3 ) ignimbrites. These deposits have been correlated to tephra layers in ODP cores ˜2700 km SE of Yemen in the Indian Ocean. We are using melt inclusions (MI) in 4 ignimbrite units to model the petrogenesis and pre-eruptive volatile contents of the ignimbrites. Although quartz is a better MI host in silicic systems, these units only contain plagioclase that has the potential for degassing and leakage in cleavage planes. Through a series of experiments to investigate the rehomogenization temperature of the MI, we found inclusions were glassy at 1075 ° C after 24 hours. We also have compositional data from shorter duration runs (˜20 min.) at 1050 ° C. Reconnaissance MI data show a wide compositional variation compared to whole rock samples of the ignimbrites, and they provide a better estimate of true magmatic compositions compared to the heterogeneous whole rock samples. The inclusions are generally lower in Si (˜59-85 wt.%), yet significantly higher in Na and Al, which both decrease with increasing Si. We are currently modeling these variations to determine the petrogenesis of these silicic magmas. In terms of pre-eruptive volatiles, sulfur in the long duration experiments appears degassed (<5 ppm) yet is retained in the shorter duration runs (up to 500 ppm). Cl appears robust in the MI at ˜340 ppm and is consistent with modeled high halogen contents in such peralkaline melts. We will present estimates for the total S and Cl released during these large ignimbrite eruptions.

Composition of basaltic lavas sampled by phase-2 of the Hawaii Scientific Drilling Project: Geochemical stratigraphy and magma types

NASA Astrophysics Data System (ADS)

Rhodes, J. M.; Vollinger, M. J.

2004-03-01

This paper presents major and trace element compositions of lavas from the entire 3098 m stratigraphic section sampled by phase-2 of the Hawaii Scientific Drilling Project. The upper 245 m are lavas from Mauna Loa volcano, and the lower 2853 m are lavas and volcanoclastic rocks from Mauna Kea volcano. These intervals are inferred to represent about 100 ka and 400 ka respectively of the eruptive history of the two volcanoes. The Mauna Loa tholeiites tend to be higher in SiO2 and lower in total iron, TiO2, alkalis, and incompatible elements at a given MgO content than Mauna Kea lavas. The transition from Mauna Loa to Mauna Kea lavas is all the more pronounced because the Mauna Loa tholeiites overlie a thin sequence of postshield Mauna Kea alkalic to transitional tholeiitic lavas. The Mauna Loa tholeiites display well-developed coherent trends with MgO that are indistinguishable in most respects from modern lavas. With depth, however, there is a slight decline in incompatible element abundances, and small shifts to depleted isotopic ratios. These characteristics suggest small changes in melt production and source components over time, superimposed on shallow melt segregation. The Mauna Kea section is subdivided into a thin, upper 107 m sequence of postshield tholeiites, transitional tholeiites and alkali basalts of the Hamakua volcanics, overlying four tholeiitic magma types that are intercalated throughout the rest of the core. These four magma types are recognized on the basis of MgO-normalized SiO2 and Zr/Nb values. Type-1 lavas (high SiO2 and Zr/Nb) are ubiquitous below the postshield lavas and are the dominant magma type on Mauna Kea. They are inter-layered with the other three lava types. Type-2 lavas (low SiO2 but high Zr/Nb) are found only in the upper core, and especially above 850 m. Type-3 lavas (low SiO2 and Zr/Nb) are very similar to tholeiites from Loihi volcano and are present only below 1974 m. There are only 3 discrete samples of type-4 lavas (high SiO2 and low Zr/Nb), which are present in the upper and lower core. The differences between these magma types are inferred to reflect changes in melt production, depth of melt segregation, and differences in plume source components over about 400 ka of Mauna Kea's eruptive history. At the start of this record, eruption rates were high, and two distinct tholeiitic magmas (type-1 and 3) were erupting concurrently. These two magmas require two distinct source components, one similar to that of modern Loihi tholeiites and the other close to that of Kilauea magmas. Subsequently, the Loihi-like source of the type-3 magmas was exhausted, and these lavas are absent from the remainder of the core. For the next 200 ka or so, the eruptive sequence consists of inter-layered type-1 and -2 lavas that are derived from a common Mauna Kea source, the major difference between the two being the depth at which the melts segregated from the source. At around 440 ka (corresponding with the transition in the core from submarine to subaerial lavas) eruption rates began to decline and low-MgO lavas are suddenly much more abundant in the record. Continuing gradual decline in melting and eruption rates was accompanied by a decline in normalized SiO2 content of the type-1 magmas, and the eventual onset of postshield magmatism.

Descriptions and preliminary interpretations of cores recovered from the Manson Impact Structure (Iowa)

NASA Technical Reports Server (NTRS)

Anderson, R. R.; Witzke, B. J.; Hartung, J. B.; Shoemaker, E. M.; Roddy, D. J.

1993-01-01

A core drilling program initiated by the Iowa Geological Survey Bureau and U.S. Geological Survey in 1991 and 1992 collected 12 cores totalling over 1200 m from the Manson Impact Structure, a probable K-T boundary structure located in north-central Iowa. Cores were recovered from each of the major structural terranes, with 2 cores (M-3 and M-4) from the Terrace Terrane, 4 cores (M-2, M-2A, M-6, and M-9) from the Crater Moat, and 6 cores (M-1, M-5, M-7, M-8, M-10, and M-11) from the Central Peak. These supplemented 2 central peak cores (1-A and 2-A) drilled in 1953. The cores penetrated five major impact lithologies: (1) sedimentary clast breccia; (2) impact ejecta; (3) central peak crystallite rocks; (4) crystalline clast breccia with sandy matrix; and (5) crystallite clast breccia with a melt matrix. Descriptions and preliminary interpretations of these cores are presented.

Free-Standing and Self-Crosslinkable Hybrid Films by Core-Shell Particle Design and Processing.

PubMed

Vowinkel, Steffen; Paul, Stephen; Gutmann, Torsten; Gallei, Markus

2017-11-15

The utilization and preparation of functional hybrid films for optical sensing applications and membranes is of utmost importance. In this work, we report the convenient and scalable preparation of self-crosslinking particle-based films derived by directed self-assembly of alkoxysilane-based cross-linkers as part of a core-shell particle architecture. The synthesis of well-designed monodisperse core-shell particles by emulsion polymerization is the basic prerequisite for subsequent particle processing via the melt-shear organization technique. In more detail, the core particles consist of polystyrene (PS) or poly(methyl methacrylate) (PMMA), while the comparably soft particle shell consists of poly(ethyl acrylate) (PEA) and different alkoxysilane-based poly(methacrylate)s. For hybrid film formation and convenient self-cross-linking, different alkyl groups at the siloxane moieties were investigated in detail by solid-state Magic-Angle Spinning Nuclear Magnetic Resonance (MAS, NMR) spectroscopy revealing different crosslinking capabilities, which strongly influence the properties of the core or shell particle films with respect to transparency and iridescent reflection colors. Furthermore, solid-state NMR spectroscopy and investigation of the thermal properties by differential scanning calorimetry (DSC) measurements allow for insights into the cross-linking capabilities prior to and after synthesis, as well as after the thermally and pressure-induced processing steps. Subsequently, free-standing and self-crosslinked particle-based films featuring excellent particle order are obtained by application of the melt-shear organization technique, as shown by microscopy (TEM, SEM).

Enteric protection of naproxen in a fixed-dose combination product produced by hot-melt co-extrusion.

PubMed

Vynckier, A-K; De Beer, M; Monteyne, T; Voorspoels, J; De Beer, T; Remon, J P; Vervaet, C

2015-08-01

In this study hot-melt co-extrusion is used as processing technique to manufacture a fixed-dose combination product providing enteric protection to naproxen incorporated in the core and immediate release to esomeprazole magnesium embedded in the coat. The plasticizing effect of naproxen and triethyl citrate (TEC) was tested on the enteric polymers investigated (Eudragit(®) L100-55, HPMC-AS-LF and HPMCP-HP-50). Core matrix formulations containing HPMC-AS-LF, TEC and a naproxen load of 15, 30 and 50% were processed and characterized. The in vitro naproxen release in 0.1N HCl was prevented for 2h for all formulations. The physicochemical state of the drug in the extrudates was determined and a stability study was performed. Intermolecular interactions between naproxen and polymer were identified using attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. When esomeprazole magnesium was formulated in a polyethylene oxide 100K:polyethylene glycol 4K (1:1) matrix, separated from the naproxen-containing layer, the formulation could be easily processed and complete in vitro drug release was observed after 45 min. When co-extruding the core/coat dosage form it was observed that a third layer of polymer, separating the naproxen loaded enteric formulation in the core from the coat, is required to prevent degradation of the acid-labile esomeprazole magnesium at the core/coat interface. Copyright © 2015 Elsevier B.V. All rights reserved.

Si-depleted outer core inferred from sound velocity measurements of liquid Fe-Si alloys

NASA Astrophysics Data System (ADS)

Nakajima, Y.; Imada, S.; Hirose, K.; Kuwayama, Y.; Sinmyo, R.; Tateno, S.; Ozawa, H.; Tsutsui, S.; Uchiyama, H.; Baron, A. Q. R.

2016-12-01

Recent core formation models [1,2] suggested that a large amount of Si could have been incorporated into the core forming metals in the early stage of the Earth. These studies gave estimates for the Si content in the core, from 2 to 9 wt.%. In order to constrain the Si content of the outer core, we have determined the sound wave velocity of liquid Fe-Si alloys under high pressures and high temperatures. Starting materials of Fe-Si alloys with 6.5 and 9 wt.% Si were melted in a laser-heated diamond-anvil cell. The longitudinal acoustic phonon excitation of a liquid metal was measured up to 52 GPa and 3200 K by using high resolution inelastic X-ray scattering spectroscopy at beamline BL35XU [3] of the SPring-8 synchrotron facility. Our results show that silicon significantly increases the P-wave velocity of liquid Fe. Seismological observation shows that the P-wave velocity in the outer core is 3-4% faster than in pure iron. Comparing the present results with seismological observations, the silicon content of the outer core should be limited to be <2 wt.%, significantly lower than previous estimates based on the element partitioning between core forming mental and silicate magma ocean during core formation processes. This indicates that the present-day core is depleted in Si relative to the ancient core just after core formation, which agrees with the recent proposal [4] that the Si content in the outer core has been diminished by SiO2 crystallization through the core cooling history. [1] Rubie et al. (2011) Earth Planet. Sci. Lett. 301, 31-42. [2] Siebert et al. (2013) Science 339, 1194-1197. [3] Baron et al. (2000) J. Phys. Chem. Solids 61, 461-465 [4] Hirose et al. (2015) Abstract presented at AGU Fall Meeting 2015.

Major and trace element modeling of mid-ocean ridge mantle melting from the garnet to the plagioclase stability fields: Generating local and global compositional variability

NASA Astrophysics Data System (ADS)

Brown, S. M.; Behn, M. D.; Grove, T. L.

2017-12-01

We present results of a combined petrologic - geochemical (major and trace element) - geodynamical forward model for mantle melting and subsequent melt modification. The model advances Behn & Grove (2015), and is calibrated using experimental petrology. Our model allows for melting in the plagioclase, spinel, and garnet fields with a flexible retained melt fraction (from pure batch to pure fractional), tracks residual mantle composition, and includes melting with water, variable melt productivity, and mantle mode calculations. This approach is valuable for understanding oceanic crustal accretion, which involves mantle melting and melt modification by migration and aggregation. These igneous processes result in mid-ocean ridge basalts that vary in composition at the local (segment) and global scale. The important variables are geophysical and geochemical and include mantle composition, potential temperature, mantle flow, and spreading rate. Accordingly, our model allows us to systematically quantify the importance of each of these external variables. In addition to discriminating melt generation effects, we are able to discriminate the effects of different melt modification processes (inefficient pooling, melt-rock reaction, and fractional crystallization) in generating both local, segment-scale and global-scale compositional variability. We quantify the influence of a specific igneous process on the generation of oceanic crust as a function of variations in the external variables. We also find that it is unlikely that garnet lherzolite melting produces a signature in either major or trace element compositions formed from aggregated melts, because when melting does occur in the garnet field at high mantle temperature, it contributes a relatively small, uniform fraction (< 10%) of the pooled melt compositions at all spreading rates. Additionally, while increasing water content and/or temperature promote garnet melting, they also increase melt extent, pushing the pooled composition to lower Sm/Yb and higher Lu/Hf.

A thermodynamic recipe for baking the Earth's lower mantle and core as a whole

NASA Astrophysics Data System (ADS)

Tirone, Max; Faak, Kathi

2016-04-01

A rigorous understanding of the thermal and dynamic evolution of the core and the interaction with the silicate mantle cannot preclude a non-empirical petrological description of the problem which takes the form of a thermodynamic model. Because the Earth's core is predominantly made of iron such model may seem relatively straightforward, simply delivering a representation of the phase transformations in the P,T space. However due to well known geophysical considerations, a certain amount of light elements should be added. With the Occam's razor principle in mind, potential candidates could be the most abundant and easily accessible elements in the mantle, O, Si and Mg. Given these premises, the challenging problems on developing this type of model are: - a thermodynamic formulation should not simply describe phase equilibrium relations at least in the Fe-Si-O system (a formidable task itself) but should be also consistently applicable to evaluate thermophysical properties of liquid components and solids phases at extreme conditions (P=500-2000 kbar, T=1000-5000 K). Presently these properties are unknown for certain mineral and liquid components or partially available from scattered sources. - experimental data on the phase relations for iron rich liquid are extremely difficult to obtain and could not cover the entire P,T,X spectrum. - interaction of the outer core with the silicate mantle requires a melt model that is capable of describing a vast range of compositions ranging from metal-rich liquids to silicate liquids. The compound energy formalism for liquids with variable tendency to ionization developed by Hillert and coworkers is a sublattice model with varying stoichiometry that includes vacancies and neutral species in one site. It represents the ideal candidate for the task in hand. The thermodynamic model unfortunately is rather complex and a detailed description of the formulation for practical applications like chemical equilibrium calculations is nowhere to be found, while the model is only accessible on few commercial thermodynamic programs. The latest developments regarding all these related issues will be discussed in this contribution. In particular some self-consistent but preliminary results will be presented addressing the following topics: - some details regarding the implementation of the liquid model for Gibbs free energy minimizations, - the physically consistent behavior of thermodynamic properties of certain solid phases like (Fe,O,Si) BCC, FCC, HCP and liquid components, - selected phase diagrams at core conditions in the system Fe-Si-O, - derived geotherms linking the inner-outer core with the core-mantle boundary. - brief outline of the future geodynamic applications.

Comparative Magma Oceanography

NASA Technical Reports Server (NTRS)

Jones, J. H.

1999-01-01

The question of whether the Earth ever passed through a magma ocean stage is of considerable interest. Geochemical evidence strongly suggests that the Moon had a magma ocean and the evidence is mounting that the same was true for Mars. Analyses of martian (SNC) meteorites have yielded insights into the differentiation history of Mars, and consequently, it is interesting to compare that planet to the Earth. Three primary features of Mars contrast strongly to those of the Earth: (i) the extremely ancient ages of the martian core, mantle, and crust (about 4.55 b.y.); (ii) the highly depleted nature of the martian mantle; and (iii) the extreme ranges of Nd isotopic compositions that arise within the crust and depleted mantle. The easiest way to explain the ages and diverse isotopic compositions of martian basalts is to postulate that Mars had an early magma ocean. Cumulates of this magma ocean were later remelted to form the SNC meteorite suite and some of these melts assimilated crustal materials enriched in incompatible elements. The REE pattern of the crust assimilated by these SNC magmas was LREE enriched. If this pattern is typical of the crust as a whole, the martian crust is probably similar in composition to melts generated by small degrees of partial melting (about 5%) of a primitive source. Higher degrees of partial melting would cause the crustal LREE pattern to be essentially flat. In the context of a magma ocean model, where large degrees of partial melting presumably prevailed, the crust would have to be dominated by late-stage, LREE-enriched residual liquids. Regardless of the exact physical setting, Nd and W isotopic evidence indicates that martian geochemical reservoirs must have formed early and that they have not been efficiently remixed since. The important point is that in both the Moon and Mars we see evidence of a magma ocean phase and that we recognize it as such. Several lines of theoretical inference point to an early Earth that was also hot and, perhaps, mostly molten. The Giant Impact hypothesis for the origin of the Moon offers a tremendous input of thermal energy and the same could be true for core formation. And current solar system models favor the formation of a limited number of large (about 1000 km) planetesimals that, upon accreting to Earth, would cause great heating, being lesser versions of the Giant Impact. Several lines of geochemical evidence do not favor this hot early Earth scenario. (i) Terrestrial man-tle xenoliths are sometimes nearly chondritic in their major element compositions, suggesting that these rocks have never been much molten. Large degrees of partial melting probably promote differentiation rather than homogenization. (ii) Unlike the case of Mars, the continental crust probably did not form as a highly fractionated residual liquid from a magma ocean (about 99% crystallization), but, rather, formed in multiple steps. [The simplest model for the formation of continental crust is complicated: (a) about 10% melting of a primitive mantle, making basalt; (b) hydrothermal alteration of that basalt, converting it to greenstone; and (c) 10% partial melting of that greenstone, producing tonalite.] This model is reinforced by the recent observation from old (about 4.1 b.y.) zircons that the early crust formed from an undepleted mantle having a chondritic Lu/Hf ratio. (iii) If the mantle were once differentiated by a magma ocean, the mantle xenolith suite requires that it subsequently be homogenized. The Os isotopic compositions of fertile spinel lherzolites place constraints on the timing of that homogenization. The Os isotopic composition of spinel lherzolites approaches that of chondrites and correlates with elements such as Lu and Al. As Lu and Al concentrations approach those of the primitive mantle, Os isotopic compositions approach chondritic. The Re and Os in these xenoliths were probably added as a late veneer. Thus, the mantle that received the late veneer must have been nearly chondritic in terms of its major elements (excluding Fe). If the mantle that the veneer was mixed into was not al-ready homogenized, then Os isotopes should not correlate with incompatible elements such as Al. Consequently, either early differentiation of the mantle did not occur or the homogenization of this differentiation must have occurred before the late veneer was added. The timing of the late veneer is itself uncertain but presumably postdated core formation at about 4.45 b.y. and did not postdate the 3.8-3.9 b.y. late bombardment of the Moon. This timing based on siderophile elements is consistent with the Hf isotopic evidence cited above. If the Earth, Moon and Mars had magma oceans, the Earth subsequently rehomogenized whereas the Moon and Mars did not. The simplest solution to this observation is that homogenization of igneous differentiates was never necessary on Earth, either because the hypothetical magma ocean never occurred or because this event did not produce mantle differentiation.

Lower continental crust formation through focused flow in km-scale melt conduits: The zoned ultramafic bodies of the Chilas Complex in the Kohistan island arc (NW Pakistan)

NASA Astrophysics Data System (ADS)

Jagoutz, O.; Müntener, O.; Burg, J.-P.; Ulmer, P.; Jagoutz, E.

2006-02-01

Whole-rock and Sm-Nd isotopic data of the main units of the Chilas zoned ultramafic bodies (Kohistan paleo-island arc, NW Pakistan) indicate that ultramafic rocks and gabbronorite sequences stem from a common magma. However, field observations rule out formation of both ultramafic and mafic sequences in terms of gravitational crystal settling in a large magma chamber. Contacts between ultramafic and gabbronorite sequences show emplacement of the dunitic bodies into a semi-consolidated gabbronoritic crystal-mush, which in turn has intruded and reacted with the ultramafic rocks to produce concentric zoning. Field and petrological observations indicate a replacive origin of the dunite. Bulk Mg#'s of dunitic rocks range from 0.87-0.81 indicating that the dunite-forming melt underwent substantial fractionation-differentiation and that percolative fractional crystallization probably generated the dunitic core. The REE chemistry of clinopyroxene in primitive dunite samples and the Nd isotopic composition of ultramafic rocks are in equilibrium with the surrounding gabbronorite. Accordingly, liquids that formed the dunitic rocks and later the mafic sequence derived from a similar depleted source ( ɛNd˜4.8). We propose a mechanism for the comagmatic emplacement, where km-scale ultramafic bodies represent continuous channels reaching down into the upper mantle. The melt-filled porosity in these melt channels diminishes the mean-depth-integrated density difference to the surrounding rocks. Due to buoyancy forces, melt channels raise into the overlying crustal sequence. In the light of such processes, the ultramafic bodies are interpreted as melt channels through which the Chilas gabbronorite sequence was fed. The estimated basaltic-andesitic, low Mg# (˜0.53) bulk composition of the Chilas gabbronorite sequence closely matches estimates of lower crustal compositions. Since the mafic sequence originated from a primary, high Mg# (> 0.7) basaltic arc magma, differentiation of such high Mg# magmas within km-scale isolated melt conduits may explain the "Mg#-gap" between bulk estimates of the continental crust and primary basaltic magmas, a major paradox in the andesite model of crust formation.

Solubility of copper in silicate melts as function of oxygen and sulfur fugacities, temperature, and silicate composition

NASA Astrophysics Data System (ADS)

Holzheid, A.; Lodders, K.

2001-06-01

The solubility of Cu in silicate melts coexisting with liquid Cu(Fe) metal and liquid Cu(Fe) sulfide was determined experimentally at oxygen fugacities ranging from 10 -9.1 to 10 -13.6 bar and sulfur fugacities ranging from 10 -2.5 to 10 -6.3 bar at 1300°C. An iron oxide-free silicate of anorthite-diopside eutectic composition and a synthetic MgO-rich basaltic silicate (FeO-bearing) were used in the partitioning experiments. In S-containing systems, some of the metal reacted to metal sulfide. The silicates in the four systems investigated (Fe-free and S-free; Fe-containing and S-free; Fe-free and S-containing; Fe-containing and S-containing) had different colors depending on the dissolved Cu species and the presence of iron and/or sulfur. Irrespective of the presence of sulfur, the solubility of Cu in the silicate increases with increasing oxygen fugacity and metal/silicate partition coefficients for Cu decrease. Increasing the temperature from 1300°C to 1514°C increases the Cu solubility (decreases the metal/silicate partition coefficient) at an oxygen fugacity 0.5 log units below the iron-wüstite (IW) equilibrium in the Fe-free, S-free and Fe-containing, S-free systems. We infer the presence of monovalent Cu + ("CuO 0.5") in the silicate melt on the basis of the solubility of Cu as function of oxygen fugacity. Experiments containing iron yield a formal valence of ˜0.5 for Cu at very low oxygen fugacities, which is not observed in Fe-free systems. The low formal valence is explained by redox reactions between iron and copper in the silicate melts. There is no evidence for sulfidic dissolution of Cu in the silicates but sulfur has indirect effects on Cu partitioning. Iron metal/silicate partition coefficients depend on oxygen fugacity and on sulfur fugacity. Sulfidic dissolution of iron and oxide-sulfide exchange reactions with Cu cause a small increase in Cu metal/silicate partition coefficients. We derive an activity coefficient (γ CuO 0.5) of 10 ± 1 for liquid CuO 0.5 at 1300°C for the silicate melts used here. A comparison with literature data shows that log γ CuO 0.5 increases in proportion to the mass percentages [CaO +(Al 2O 3)/2] in silicate melts. We recommend the following equations for Cu metal/silicate and sulfide/silicate partitioning for geochemical and cosmochemical modeling if silicate composition and the activity of Cu in the metal or sulfide is known: log D met/sil = -0.48 - 0.25 · log fO 2 - log γ Cu metal + 0.02 · [CaO + (Al 2O 3)/2; wt%] silicate logD sul/sil=+0.76-0.25 · logfO 2+0.25logfS 2-logγ CS 0.5,sulfide +0.02 · [CaO+Al 2O 3/2;wt%] silicate. The derived Cu metal/silicate and metal/sulfide partition coefficients are applied to core formation in the Earth and Mars. The observed Cu abundances in the Earth cannot be easily explained by simple core-mantle equilibrium, but the observed Cu abundances for Mars are consistent with core-mantle equilibrium at low pressure and temperatures.