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Sample records for earths core mantle

  1. Sulfur in Earth's Mantle and Its Behavior During Core Formation

    Science.gov (United States)

    Chabot, Nancy L.; Righter,Kevin

    2006-01-01

    The density of Earth's outer core requires that about 5-10% of the outer core be composed of elements lighter than Fe-Ni; proposed choices for the "light element" component of Earth's core include H, C, O, Si, S, and combinations of these elements [e.g. 1]. Though samples of Earth's core are not available, mantle samples contain elemental signatures left behind from the formation of Earth's core. The abundances of siderophile (metal-loving) elements in Earth's mantle have been used to gain insight into the early accretion and differentiation history of Earth, the process by which the core and mantle formed, and the composition of the core [e.g. 2-4]. Similarly, the abundance of potential light elements in Earth's mantle could also provide constraints on Earth's evolution and core composition. The S abundance in Earth's mantle is 250 ( 50) ppm [5]. It has been suggested that 250 ppm S is too high to be due to equilibrium core formation in a high pressure, high temperature magma ocean on early Earth and that the addition of S to the mantle from the subsequent accretion of a late veneer is consequently required [6]. However, this earlier work of Li and Agee [6] did not parameterize the metalsilicate partitioning behavior of S as a function of thermodynamic variables, limiting the different pressure and temperature conditions during core formation that could be explored. Here, the question of explaining the mantle abundance of S is revisited, through parameterizing existing metal-silicate partitioning data for S and applying the parameterization to core formation in Earth.

  2. Hydrogen storage in Earth's mantle and core

    Science.gov (United States)

    Prewitt, Charles T.

    1994-01-01

    Two different approaches to explaining how hydrogen might be stored in the mantle are illustrated by a number of papers published over the past 25-30 years, but there has been little attempt to provide objective comparisons of the two. One approach invokes the presence in the mantle of dense hydrous magnesium silicates (DHMS) stable at elevated pressures and temperatures. The other involves nominally anhydrous minerals (NAM) that contain hydrogen as a minor constituent on the ppm level. Experimental studies on DHMS indicate these phases may be stable to pressures and temperatures as high at 16 GPa and 1200 C. This temperature is lower than that indicated by a mantle geotherm at 16 GPa, but may be reasonable for a subducting slab. It is possible that other DHMS could be stable to even higher pressures, but little is known about maximum temperature limits. For NAM, small amounts of hydrogen (up to several hundred ppm) have been detected in olivine, orthopyroxene, clinopyroxene, and garnet recovered from xenoliths in kimberlites, eclogites, and alkali basalts; it has been demonstrated that synthetic wadsleyite and perovskite can accommodate significant amounts of hydrogen. A number of problems are associated with each possibility. For NAM originating in the mantle, one would like to assume that the hydrogen measured in samples recovered on Earth's surface was incorporated when the phase-crystallized at high temperatures and pressures, but it could have been introduced during transport to the surface. Major problems for the DHMS proponents are that none of these phases have been found as minerals and little is yet known about their stabilities in systems containing other cations such as Fe, Al, and Ca.

  3. Iron-carbonate interaction at Earth's core-mantle boundary

    Science.gov (United States)

    Dorfman, S. M.; Badro, J.; Nabiei, F.; Prakapenka, V.; Gillet, P.

    2015-12-01

    Carbon storage and flux in the deep Earth are moderated by oxygen fugacity and interactions with iron-bearing phases. The amount of carbon stored in Earth's mantle versus the core depends on carbon-iron chemistry at the core-mantle boundary. Oxidized carbonates subducted from Earth's surface to the lowermost mantle may encounter reduced Fe0 metal from disproportionation of Fe2+ in lower mantle silicates or mixing with the core. To understand the fate of carbonates in the lowermost mantle, we have performed experiments on sandwiches of single-crystal (Ca0.6Mg0.4)CO3 dolomite and Fe foil in the laser-heated diamond anvil cell at lower mantle conditions of 49-110 GPa and 1800-2500 K. Syntheses were conducted with in situ synchrotron X-ray diffraction to identify phase assemblages. After quench to ambient conditions, samples were sectioned with a focused Ga+ ion beam for composition analysis with transmission electron microscopy. At the centers of the heated spots, iron melted and reacted completely with the carbonate to form magnesiowüstite, iron carbide, diamond, magnesium-rich carbonate and calcium carbonate. In samples heated at 49 and 64 GPa, the two carbonates exhibit a eutectoid texture. In the sample heated at 110 GPa, the carbonates form rounded ~150-nm-diameter grains with a higher modal proportion of interspersed diamonds. The presence of reduced iron in the deep lower mantle and core-mantle boundary region will promote the formation of diamonds in carbonate-bearing subducted slabs. The complete reaction of metallic iron to oxides and carbides in the presence of mantle carbonate supports the formation of these phases at the Earth's core-mantle boundary and in ultra-low velocity zones.

  4. Core cooling by subsolidus mantle convection. [thermal evolution model of earth

    Science.gov (United States)

    Schubert, G.; Cassen, P.; Young, R. E.

    1979-01-01

    Although vigorous mantle convection early in the thermal history of the earth is shown to be capable of removing several times the latent heat content of the core, a thermal evolution model of the earth in which the core does not solidify can be constructed. The large amount of energy removed from the model earth's core by mantle convection is supplied by the internal energy of the core which is assumed to cool from an initial high temperature given by the silicate melting temperature at the core-mantle boundary. For the smaller terrestrial planets, the iron and silicate melting temperatures at the core-mantle boundaries are more comparable than for the earth; the models incorporate temperature-dependent mantle viscosity and radiogenic heat sources in the mantle. The earth models are constrained by the present surface heat flux and mantle viscosity and internal heat sources produce only about 55% of the earth model's present surface heat flow.

  5. Deep mantle heat flow and thermal evolution of the Earth's core based on thermo-chemical mantle convection

    Science.gov (United States)

    Nakagawa, T.; Tackley, P.; Buffett, B.

    2004-12-01

    A coupled core-mantle evolution model that combines the global heat balance in the core with a fully-dynamical thermo-chemical mantle convection [Nakagawa and Tackley, 2004 published in EPSL] is used to investigate the deep mantle heat flow that is required to sustain the magnetic field generated by the geodynamo process. Effects of a radioactive heat source due to potassium in the core are also included in the global heat balance in the Earth??s core. Two important parameters are checked in this study; (1) density variation between depleted hartzbergite and basaltic material (0 to 3 percent) and (2) concentration of radioactive potassium in the core alloy (0ppm to 400ppm). The parameter set that most closely satisfies the criteria of size of the inner core (1220km at present time) is around 2 percent of density difference in a convecting mantle and 200ppm of radioactive heat source in the core. The concentration of potassium in the core is consistent with the geochemical approach [Murthy et al., 2003] but smaller than other successful thermal evolution models [Labrosse, 2003; Nimmo et al., 2004]. Heat flow through the core-mantle boundary and the contribution of radioactive heat sources in the core are consistent with theoretical estimates [e.g. Buffett, 2002] and geochemical constraints [Gessmann and Wood, 2002]. The power available to the geodynamo, based on the predicted heat flow through the core-mantle boundary, is approximately four times greater than the value predicted by numerical models of the geodynamo [Christensen and Kutzner, 2004] but closer to theoretical estimates [e.g. Buffett, 2002].

  6. Gravitational Core-Mantle Coupling and the Acceleration of the Earth

    Science.gov (United States)

    Rubincam, David Parry; Smith, David E. (Technical Monitor)

    2001-01-01

    Gravitational core-mantle coupling may be the cause of the observed variable acceleration of the Earth's rotation on the 1000 year timescale. The idea is that density inhomogeneities which randomly come and go in the liquid outer core gravitationally attract density inhomogeneities in the mantle and crust, torquing the mantle and changing its rotation state. The corresponding torque by the mantle on the core may also explain the westward drift of the magnetic field of 0.2 deg per year. Gravitational core-mantle coupling would stochastically affect the rate of change of the Earth's obliquity by just a few per cent. Its contribution to polar wander would only be about 0.5% the presently observed rate. Tidal friction is slowing down the rotation of the Earth, overwhelming a smaller positive acceleration from postglacial rebound. Coupling between the liquid outer core of the Earth and the mantle has long been a suspected reason for changes in the length-of-day. The present investigation focuses on the gravitational coupling between the density anomalies in the convecting liquid outer core and those in the mantle and crust as a possible cause for the observed nonsecular acceleration on the millenial timescale. The basic idea is as follows. There are density inhomogeneities caused by blobs circulating in the outer core like the blobs in a lava lamp; thus the outer core's gravitational field is not featureless. Moreover, these blobs will form and dissipate somewhat randomly. Thus there will be a time variability to the fields. These density inhomogeneities will gravitationally attract the density anomalies in the mantle.

  7. Sensitivities of Earth's core and mantle compositions to accretion and differentiation processes

    Science.gov (United States)

    Fischer, Rebecca A.; Campbell, Andrew J.; Ciesla, Fred J.

    2017-01-01

    The Earth and other terrestrial planets formed through the accretion of smaller bodies, with their core and mantle compositions primarily set by metal-silicate interactions during accretion. The conditions of these interactions are poorly understood, but could provide insight into the mechanisms of planetary core formation and the composition of Earth's core. Here we present modeling of Earth's core formation, combining results of 100 N-body accretion simulations with high pressure-temperature metal-silicate partitioning experiments. We explored how various aspects of accretion and core formation influence the resulting core and mantle chemistry: depth of equilibration, amounts of metal and silicate that equilibrate, initial distribution of oxidation states in the disk, temperature distribution in the planet, and target:impactor ratio of equilibrating silicate. Virtually all sets of model parameters that are able to reproduce the Earth's mantle composition result in at least several weight percent of both silicon and oxygen in the core, with more silicon than oxygen. This implies that the core's light element budget may be dominated by these elements, and is consistent with ≤1-2 wt% of other light elements. Reproducing geochemical and geophysical constraints requires that Earth formed from reduced materials that equilibrated at temperatures near or slightly above the mantle liquidus during accretion. The results indicate a strong tradeoff between the compositional effects of the depth of equilibration and the amounts of metal and silicate that equilibrate, so these aspects should be targeted in future studies aiming to better understand core formation conditions. Over the range of allowed parameter space, core and mantle compositions are most sensitive to these factors as well as stochastic variations in what the planet accreted as a function of time, so tighter constraints on these parameters will lead to an improved understanding of Earth's core composition.

  8. An early geodynamo driven by exsolution of mantle components from Earth's core.

    Science.gov (United States)

    Badro, James; Siebert, Julien; Nimmo, Francis

    2016-08-18

    Recent palaeomagnetic observations report the existence of a magnetic field on Earth that is at least 3.45 billion years old. Compositional buoyancy caused by inner-core growth is the primary driver of Earth's present-day geodynamo, but the inner core is too young to explain the existence of a magnetic field before about one billion years ago. Theoretical models propose that the exsolution of magnesium oxide--the major constituent of Earth's mantle--from the core provided a major source of the energy required to drive an early dynamo, but experimental evidence for the incorporation of mantle components into the core has been lacking. Indeed, terrestrial core formation occurred in the early molten Earth by gravitational segregation of immiscible metal and silicate melts, transporting iron-loving (siderophile) elements from the silicate mantle to the metallic core and leaving rock-loving (lithophile) mantle components behind. Here we present experiments showing that magnesium oxide dissolves in core-forming iron melt at very high temperatures. Using core-formation models, we show that extreme events during Earth's accretion (such as the Moon-forming giant impact) could have contributed large amounts of magnesium to the early core. As the core subsequently cooled, exsolution of buoyant magnesium oxide would have taken place at the core–mantle boundary, generating a substantial amount of gravitational energy as a result of compositional buoyancy. This amount of energy is comparable to, if not more than, that produced by inner-core growth, resolving the conundrum posed by the existence of an ancient magnetic field prior to the formation of the inner core.

  9. The source of the Earth's long wavelength geoid anomalies: Implications for mantle and core dynamics

    Science.gov (United States)

    Hager, B. H.; Richards, M. A.; Oconnell, R. J.

    1985-01-01

    The long wavelength components of the Earth's gravity field result mainly from density contrasts associated with convection in the mantle. Direct interpretation of the geoid for mantle convection is complicated by the fact that convective flow results in dynamically maintained deformation of the surface of the Earth, the core mantle boundary (CMB), and any interior chemical boundaries which might exist. These boundary deformations effect the geoid opposite in sign and are comparable in magnitude to those of the interior density contrasts driving the flow. The total difference of two relatively large quantities.

  10. Steady state toroidal magnetic field at earth's core-mantle boundary

    Science.gov (United States)

    Levy, Eugene H.; Pearce, Steven J.

    1991-01-01

    Measurements of the dc electrical potential near the top of earth's mantle have been extrapolated into the deep mantle in order to estimate the strength of the toroidal magnetic field component at the core-mantle interface. Recent measurements have been interpreted as indicating that at the core-mantle interface, the magnetic toroidal and poloidal field components are approximately equal in magnitude. A motivation for such measurements is to obtain an estimate of the strength of the toroidal magnetic field in the core, a quantity important to our understanding of the geomagnetic field's dynamo generation. Through the use of several simple and idealized calculation, this paper discusses the theoretical relationship between the amplitude of the toroidal magnetic field at the core-mantle boundary and the actual amplitude within the core. Even with a very low inferred value of the toroidal field amplitude at the core-mantle boundary, (a few gauss), the toroidal field amplitude within the core could be consistent with a magnetohydrodynamic dynamo dominated by nonuniform rotation and having a strong toroidal magnetic field.

  11. Steady state toroidal magnetic field at earth's core-mantle boundary

    Science.gov (United States)

    Levy, Eugene H.; Pearce, Steven J.

    1991-01-01

    Measurements of the dc electrical potential near the top of earth's mantle have been extrapolated into the deep mantle in order to estimate the strength of the toroidal magnetic field component at the core-mantle interface. Recent measurements have been interpreted as indicating that at the core-mantle interface, the magnetic toroidal and poloidal field components are approximately equal in magnitude. A motivation for such measurements is to obtain an estimate of the strength of the toroidal magnetic field in the core, a quantity important to our understanding of the geomagnetic field's dynamo generation. Through the use of several simple and idealized calculation, this paper discusses the theoretical relationship between the amplitude of the toroidal magnetic field at the core-mantle boundary and the actual amplitude within the core. Even with a very low inferred value of the toroidal field amplitude at the core-mantle boundary, (a few gauss), the toroidal field amplitude within the core could be consistent with a magnetohydrodynamic dynamo dominated by nonuniform rotation and having a strong toroidal magnetic field.

  12. Thermochemical flows couple the Earth's inner core growth to mantle heterogeneity.

    Science.gov (United States)

    Aubert, Julien; Amit, Hagay; Hulot, Gauthier; Olson, Peter

    2008-08-07

    Seismic waves sampling the top 100 km of the Earth's inner core reveal that the eastern hemisphere (40 degrees E-180 degrees E) is seismically faster, more isotropic and more attenuating than the western hemisphere. The origin of this hemispherical dichotomy is a challenging problem for our understanding of the Earth as a system of dynamically coupled layers. Previously, laboratory experiments have established that thermal control from the lower mantle can drastically affect fluid flow in the outer core, which in turn can induce textural heterogeneity on the inner core solidification front. The resulting texture should be consistent with other expected manifestations of thermal mantle control on the geodynamo, specifically magnetic flux concentrations in the time-average palaeomagnetic field over the past 5 Myr, and preferred eddy locations in flows imaged below the core-mantle boundary by the analysis of historical geomagnetic secular variation. Here we show that a single model of thermochemical convection and dynamo action can account for all these effects by producing a large-scale, long-term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle. The main feature of this thermochemical 'wind' is a cyclonic circulation below Asia, which concentrates magnetic field on the core-mantle boundary at the observed location and locally agrees with core flow images. This wind also causes anomalously high rates of light element release in the eastern hemisphere of the inner core boundary, suggesting that lateral seismic anomalies at the top of the inner core result from mantle-induced variations in its freezing rate.

  13. Earth's core-mantle boundary - Results of experiments at high pressures and temperatures

    Science.gov (United States)

    Knittle, Elise; Jeanloz, Raymond

    1991-01-01

    Laboratory experiments document that liquid iron reacts chemically with silicates at high pressures (above 2.4 x 10 to the 10th Pa) and temperatures. In particular, (Mg,Fe)SiO3 perovskite, the most abundant mineral of earth's lower mantle, is expected to react with liquid iron to produce metallic alloys (FeO and FeSi) and nonmetallic silicates (SiO2 stishovite and MgSiO3 perovskite) at the pressures of the core-mantle boundary, 14 x 10 to the 10th Pa. The experimental observations, in conjunction with seismological data, suggest that the lowermost 200 to 300 km of earth's mantle, the D-double-prime layer, may be an extremely heterogeneous region as a result of chemical reactions between the silicate mantle and the liquid iron alloy of earth's core. The combined thermal-chemical-electrical boundary layer resulting from such reactions offers a plausible explanation for the complex behavior of seismic waves near the core-mantle boundary and could influence earth's magnetic field observed at the surface.

  14. Variation of thermal conductivity and heat flux at the Earth's core mantle boundary

    Science.gov (United States)

    Ammann, Michael W.; Walker, Andrew M.; Stackhouse, Stephen; Wookey, James; Forte, Alessandro M.; Brodholt, John P.; Dobson, David P.

    2014-03-01

    The two convective systems that dominate Earth's internal dynamics meet at the boundary between the rocky mantle and metallic liquid core. Energy transfer between processes driving plate tectonics and the geodynamo is controlled by thermal conduction in the lowermost mantle (D″). We use atomic scale simulations to determine the thermal conductivity of MgSiO3 perovskite and post-perovskite under D″ conditions and probe how these two convective systems interact. We show that the thermal conductivity of post-perovskite (∼12 W/mK) is 50% larger than that of perovskite under the same conditions (∼8.5 W/mK) and is anisotropic, with conductivity along the a-axis being 40% higher than conductivity along the c-axis. This enhances the high heat flux into cold regions of D″ where post-perovskite is stable, strengthening the feedback between convection in the core and mantle. Reminiscent of the situation in the lithosphere, there is potential for deformation induced texturing associated with mantle convection to modify how the mantle is heated from below. We test this by coupling our atomic scale results to models of texture in D″ and suggest that anisotropic thermal conductivity may help to stabilise the roots of mantle plumes over their protracted lifetime.

  15. Assessing the feasibility and consequences of nuclear georeactors in the Earths core mantle boundary

    CERN Document Server

    De Meijer, R J

    2008-01-01

    We assess the likelihood and geochemical consequences of the presence of nuclear georeactors in the core mantle boundary region (CMB) between Earths silicate mantle and metallic core. Current geochemical models for the Earths interior predict that U and Th in the CMB are concentrated exclusively in the mineral calcium silicate perovskite (CaPv), leading to predicted concentration levels of approximately 12 ppm combined U and Th, 4.5 Ga ago if CaPv is distributed evenly throughout the CMB. Assuming a similar behaviour for primordial 244Pu provides a considerable flux of neutrons from spontaneous fission. We show that an additional concentration factor of only an order of magnitude is required to both ignite and maintain self sustaining georeactors based on fast fission. Continuously operating georeactors with a power of 5 TW can explain the observed isotopic compositions of helium and xenon in the Earths mantle. Our hypothesis requires the presence of elevated concentrations of U and Th in the CMB, and is amen...

  16. Partitioning of Phosphorus and Molybdenum between the Earth's Mantle and Core and the Conditions of Core Formation

    Science.gov (United States)

    Acuff, K. M.; Danielson, L.; Righter, K.; Lee, C. T.

    2008-01-01

    There are several hypotheses on the specific processes that might have occurred during the formation of the Earth. One hypothesis that has been proposed is that early in the Earth's formation, there was a magma ocean present, and within this body, siderophile elements separated out of the silicate liquid to form the metal core. This study addresses this hypothesis. P and Mo are moderately siderophile elements that are present in both the mantle and the core. The concentrations of P and Mo in silicate vs. metal can be measured and in turn used to determine the temperatures, pressures, oxygen fugacity and melt composition required to achieve the same concentrations as observed in the mantle. The data here include eight experiments examining the partitioning of P and Mo between metallic liquid and silicate liquid. The purpose of the experiments has been to gain a greater understanding of core-mantle separation during the Earth formation process and examines temperature effect on P and Mo, which has not been systematically studied before.

  17. Investigation of geomagnetic field forecasting and fluid dynamics of the core. [determination of the bundary between the core and mantle of the Earth

    Science.gov (United States)

    Benton, E. R. (Principal Investigator)

    1981-01-01

    Progress in the use of MAGSAT data to confirm that the radius of the Earth's core-mantle boundary can be accurately determined magnetically is reported. The MAGSAT data was used in conjunction with a high quality manfield model for epoch 1965. The unsigned flux linking the core and mantle of the Earth is considered to be a legitimate invariant for a span of time. The value from MAGSAT of this constant is 16.056 GWb (gigawebers).

  18. A thermodynamic recipe for baking the Earth's lower mantle and core as a whole

    Science.gov (United States)

    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

  19. Thermal evolution of Earth's mantle and core: Influence of reference viscosity and concentration of radioactive elements in the mantle

    Science.gov (United States)

    Nakagawa, T.; Tackley, P. J.

    2010-12-01

    In a series of studies on the thermal evolution of Earth’s mantle and core [Nakagawa and Tackley, 2004; 2005; 2010], we have assumed a reference viscosity (at T=1600 K and P=0) of 1022 Pa.s and a concentration of radioactive elements based on the surface heat flux of the Earth’s mantle (6x10-12 W/kg). In addition, the initial mantle temperature in these studies was also based on the mantle adiabat estimated from present potential temperature (1600 K). Problems with these models are that (1) the average mantle temperature increases in the initial phase of the calculation and (2) the final (present-day) surface heat flux is a factor of two lower than expected from observational constraints (46 TW [Jaupart et al., 2007]), which means the Urey ratio is higher than the expected value (~0.3) [Jaupert et al., 2007; Korenaga, 2007]. Here we present results of a coupled model of thermo-chemical mantle convection in a 2-D spherical annulus and parameterized core heat balance, in which we vary (i) the reference viscosity down to 1020 Pa.s, giving a "surface" Rayleigh number of 109, (ii) the concentration of radioactive heat-producing elements in the mantle are tried (either a theoretical estimate [Schubert et al., 2001; 25 TW], geochemical estimate [McDonough and Sun, 1995; 20 TW] and modified geochemical estimate [Lyubetskaya and Korenaga, 2006; 16 TW]) and (iii) the initial mantle adiabat (up to 2500 K at the surface). Preliminary results indicate a preference for an initial mantle adiabat of more than 2500 K and the modified geochemical estimate of radioactive element concentration, in order to understand the current thermal state of Earth’s mantle when the reference viscosity is 1022 Pa s. Results with lower reference viscosity will be presented.

  20. Core-Mantle Partitioning of Volatile Elements and the Origin of Volatile Elements in Earth and Moon

    Science.gov (United States)

    Righter, K.; Pando, K.; Danielson, L.; Nickodem, K.

    2014-01-01

    Depletions of siderophile elements in mantles have placed constraints on the conditions on core segregation and differentiation in bodies such as Earth, Earth's Moon, Mars, and asteroid 4 Vesta. Among the siderophile elements there are a sub-set that are also volatile (volatile siderophile elements or VSE; Ga, Ge, In, As, Sb, Sn, Bi, Zn, Cu, Cd), and thus can help to constrain the origin of volatile elements in these bodies, and in particular the Earth and Moon. One of the fundamental observations of the geochemistry of the Moon is the overall depletion of volatile elements relative to the Earth, but a satisfactory explanation has remained elusive. Hypotheses for Earth include addition during accretion and core formation and mobilized into the metallic core, multiple stage origin, or addition after the core formed. Any explanation for volatile elements in the Earth's mantle must also be linked to an explanation of these elements in the lunar mantle. New metal-silicate partitioning data will be applied to the origin of volatile elements in both the Earth and Moon, and will evaluate theories for exogenous versus endogenous origin of volatile elements.

  1. Core-Mantle Partitioning of Volatile Siderophile Elements and the Origin of Volatile Elements in the Earth

    Science.gov (United States)

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

    2012-01-01

    There are currently several hypotheses on the origin of volatile siderophile elements in the Earth. One hypothesis is that they were added during Earth s accretion and core formation and mobilized into the metallic core [1], others claim multiple stage origin [2], while some hypothesize that volatiles were added after the core already formed [3]. Several volatile siderophile elements are depleted in Earth s mantle relative to the chondrites, something which continues to puzzle many scientists. This depletion is likely due to a combination of volatility and core formation. The Earth s core is composed of Fe and some lighter constituents, although the abundances of these lighter elements are unknown [4]. Si is one of these potential light elements [5] although few studies have analyzed the effect of Si on metal-silicate partitioning, in particular the volatile elements. As, In, Ge, and Sb are trace volatile siderophile elements which are depleted in the mantle but have yet to be extensively studied. The metal-silicate partition coefficients of these elements will be measured to determine the effect of Si. Partition coefficients depend on temperature, pressure, oxygen fugacity, and metal and silicate composition and can constrain the concentrations of volatile, siderophile elements found in the mantle. Reported here are the results from 13 experiments examining the partitioning of As, In, Ge, and Sb between metallic and silicate liquid. These experiments will examine the effect of temperature, and metal-composition (i.e., Si content) on these elements in or-der to gain a greater understanding of the core-mantle separation which occurred during the Earth s early stages. The data can then be applied to the origin of volatile elements in the Earth.

  2. Theoretical prediction of new mineral phases in Earth's mantle and core (Invited)

    Science.gov (United States)

    Oganov, A. R.

    2010-12-01

    After theoretical-experimental discovery of MgSiO3 post-perovskite [1,2], many other important mineral phases have been proposed in the deep Earth’s interior. We have developed [3] and further enhanced [4] an evolutionary method for predicting the most stable crystal structure at given thermodynamic conditions. Here, I will illustrate several examples from our recent works. For example, we have predicted new phases of CaCO3, MgCO3 and CO2 at Earth’s mantle pressures, and many of these phases have already found experimental support [5-7]. These results shed new light on the behavior of carbon in the Earth’s mantle [7]. More recently, we have studied the behavior of methane at high pressures and temperatures [8], and we confirm that indeed CH4 should break down under pressure - first, into hydrocarbons (ethane, butane) and hydrogen, and then into diamond and hydrogen. Crucial role here is played by lattice vibrations (zero-point vibrations and entropic factor). These vibrational effects are frequently neglected, but we have demonstrated that without them the decomposition into diamond and hydrogen would not be possible. Considering variable-composition systems, we have demonstrated [9] that FeSi with the CsCl-type structure is the only iron silicide stable at pressures of the Earth’s inner core. Similar studies can be performed also for Fe-O, Fe-S, Fe-O and Fe-H systems, addressing the common assumptions on their behavior at ultrahigh pressures of the inner core. REFERENCES: [1] Murakami M., et al., Science 304, 855-858 (2004). [2] Oganov A.R., Ono S., Nature 430, 445-448 (2004). [3] Oganov A.R., Glass C.W., J. Chem. Phys. 124, 244704 (2006). [4] Lyakhov A.O., Oganov A.R., Valle M. Comp. Phys. Comm. 181, 1623-1632 (2010). [5] Oganov A.R., Glass C.W., Ono S., Earth Planet. Sci. Lett. 241, 95-103 (2006). [6] Ono S., Kikegawa T., Ohishi Y. Am. Mineral. 92, 1246-1249 (2007). [7] Oganov A.R., et al., Earth Planet. Sci. Lett. 273, 38-47 (2008). [8] Gao G., Oganov A

  3. A Mercury-like component of early Earth yields uranium in the core and high mantle (142)Nd.

    Science.gov (United States)

    Wohlers, Anke; Wood, Bernard J

    2015-04-16

    Recent (142)Nd isotope data indicate that the silicate Earth (its crust plus the mantle) has a samarium to neodymium elemental ratio (Sm/Nd) that is greater than that of the supposed chondritic building blocks of the planet. This elevated Sm/Nd has been ascribed either to a 'hidden' reservoir in the Earth or to loss of an early-formed terrestrial crust by impact ablation. Since removal of crust by ablation would also remove the heat-producing elements--potassium, uranium and thorium--such removal would make it extremely difficult to balance terrestrial heat production with the observed heat flow. In the 'hidden' reservoir alternative, a complementary low-Sm/Nd layer is usually considered to reside unobserved in the silicate lower mantle. We have previously shown, however, that the core is a likely reservoir for some lithophile elements such as niobium. We therefore address the question of whether core formation could have fractionated Nd from Sm and also acted as a sink for heat-producing elements. We show here that addition of a reduced Mercury-like body (or, alternatively, an enstatite-chondrite-like body) rich in sulfur to the early Earth would generate a superchondritic Sm/Nd in the mantle and an (142)Nd/(144)Nd anomaly of approximately +14 parts per million relative to chondrite. In addition, the sulfur-rich core would partition uranium strongly and thorium slightly, supplying a substantial part of the 'missing' heat source for the geodynamo.

  4. The tungsten isotopic composition of Eoarchean rocks: Implications for early silicate differentiation and core-mantle interaction on Earth

    Science.gov (United States)

    Iizuka, Tsuyoshi; Nakai, Shun'ichi; Sahoo, Yu Vin; Takamasa, Asako; Hirata, Takafumi; Maruyama, Shigenori

    2010-03-01

    We have measured 182W/ 184W for Eoarchean rocks from the Itsaq Gneiss Complex (3.8-3.7 Ga pillow meta-basalts, a meta-tonalite, and meta-sediments) and Acasta Gneiss Complex (4.0-3.6 Ga felsic orthogneisses) to assess possible W isotopic heterogeneity within the silicate Earth and to constrain W isotopic evolution of the mantle. The data reveal that 182W/ 184W values in the Eoarchean samples are uniform within the analytical error and indistinguishable from the modern accessible mantle signature, suggesting that the W isotopic composition of the upper mantle has not changed significantly since the Eoarchean era. The results imply either that chemical communication between the mantle and core has been insignificant in post-Hadean times, or that a lowermost mantle with a distinctive W isotope signature has been isolated from mantle convective cycling. Most terrestrial rock samples have a 0.2 ɛ142Nd/ 144Nd higher than the chondrite average. This requires either the presence of a hidden enriched reservoir formed within the first 30 Ma of the Solar System, or the bulk Earth having a ˜ 5% higher Sm/Nd than the chondrite average. We explored the relevance of the 182Hf- 182W isotope system to the 146Sm- 142Nd isotope system during early silicate differentiation events on Earth. In this context, we demonstrate that the lack of resolvable 182W excesses in the Itsaq rocks, despite 142Nd excesses compared to the modern accessible mantle, is more consistent with the view that the bulk Earth has a non-chondritic Sm/Nd. In the non-chondritic Sm/Nd Earth model, the 182W- 142Nd chronometry constrains the age of the source mantle depletion for the Itsaq samples to more than ˜ 40 Ma after the Solar System origin. Our results cannot confirm the previous report of 182W anomalies in the Eoarchean Itsaq meta-sediments, which were interpreted as reflecting an impact-derived meteoritic component.

  5. Waves in the core and mechanical core-mantle interactions

    DEFF Research Database (Denmark)

    Jault, D.; Finlay, Chris

    2015-01-01

    the motions in the direction parallel to the Earth'srotation axis. This property accounts for the signicance of the core-mantle topography.In addition, the stiening of the uid in the direction parallel to the rotation axis gives riseto a magnetic diusion layer attached to the core-mantle boundary, which would...

  6. Complete synthetic seismograms based on a spherical self-gravitating Earth model with an atmosphere-ocean-mantle-core structure

    Science.gov (United States)

    Wang, Rongjiang; Heimann, Sebastian; Zhang, Yong; Wang, Hansheng; Dahm, Torsten

    2017-09-01

    A hybrid method is proposed to calculate complete synthetic seismograms based on a spherically symmetric and self-gravitating Earth with a multilayered structure of atmosphere, ocean, mantle, liquid core and solid core. For large wavelengths, a numerical scheme is used to solve the geodynamic boundary-value problem without any approximation on the deformation and gravity coupling. With decreasing wavelength, the gravity effect on the deformation becomes negligible and the analytical propagator scheme can be used. Many useful approaches are used to overcome the numerical problems that may arise in both analytical and numerical schemes. Some of these approaches have been established in the seismological community and the others are developed for the first time. Based on the stable and efficient hybrid algorithm, an all-in-one code QSSP is implemented to cover the complete spectrum of seismological interests. The performance of the code is demonstrated by various tests including the curvature effect on teleseismic body and surface waves, the appearance of multiple reflected, teleseismic core phases, the gravity effect on long period surface waves and free oscillations, the simulation of near-field displacement seismograms with the static offset, the coupling of tsunami and infrasound waves, and free oscillations of the solid Earth, the atmosphere and the ocean. QSSP is open source software that can be used as a stand-alone FORTRAN code or may be applied in combination with a Python toolbox to calculate and handle Green's function databases for efficient coding of source inversion problems.

  7. Seismic anisotropy; a window on how the Earth works: multiple mechanisms and sites, from shallow mantle to inner core

    Science.gov (United States)

    Osmaston, Miles

    2013-04-01

    Since the seismic anisotropy (SA) in the uppermost oceanic mantle was discovered [1] and attributed to the shearing of olivine by an MOR-divergent flow velocity gradient, rheological mobility interpretations of this type have dominated studies of SA there and elsewhere in the Earth. Here I describe two other SA-generating mechanisms. I will reason that one of these, the anisotropic crystallization from melt, bids fair largely to replace the shearing one and be present in even larger volumes of the Earth, both within its outer 100km and in the Inner Core. The other, the layered deposition of disparate substances, offers to explain the ULVZs and SA in D''. We start with the Upper Mantle. New constraints on its rheological properties and dynamical behaviour have come from two directions. Firstly, contrary to the seismologists' rule-book, the oceanic LVZ is no longer to be thought of as mobile because the presence of interstitial melt strips out the water-weakening of the mineral structure [2, 3]. So we require a substitute for the divergent-flow model for MORs. In fact it also has three other, apparently unrecognized, dynamical inconsistencies. One of these [4] is that there are in the record many rapid changes of spreading rate and direction, and ridge jumps. This cannot happen with a process driven by slow-to-change body forces. Secondly, during the past decade, my work on the global dynamics for the past 150Ma (I will show examples) has shown [4 - 7] that the tectospheres of cratons must extend to very close to the bottom of the upper mantle. And that East Antarctica's 'keel' must actually reach it, because its CW rotation [7] suggests it has been picking up an electromagnetic torque from the CMB via the lower mantle. Xenoliths suggest that the reason for this downwards extent of 'keels' is the same as [3]. To meet these two sets of constraints I will demonstrate my now not-so-new MOR model, which has a narrow, wall-accreting subaxial crack. Among its many features

  8. Geodynamo Modeling of Core-Mantle Interactions

    Science.gov (United States)

    Kuang, Wei-Jia; Chao, Benjamin F.; Smith, David E. (Technical Monitor)

    2001-01-01

    Angular momentum exchange between the Earth's mantle and core influences the Earth's rotation on time scales of decades and longer, in particular in the length of day (LOD) which have been measured with progressively increasing accuracy for the last two centuries. There are four possible coupling mechanisms for transferring the axial angular momentum across the core-mantle boundary (CMB): viscous, magnetic, topography, and gravitational torques. Here we use our scalable, modularized, fully dynamic geodynamo model for the core to assess the importance of these torques. This numerical model, as an extension of the Kuang-Bloxham model that has successfully simulated the generation of the Earth's magnetic field, is used to obtain numerical results in various physical conditions in terms of specific parameterization consistent with the dynamical processes in the fluid outer core. The results show that depending on the electrical conductivity of the lower mantle and the amplitude of the boundary topography at CMB, both magnetic and topographic couplings can contribute significantly to the angular momentum exchange. This implies that the core-mantle interactions are far more complex than has been assumed and that there is unlikely a single dominant coupling mechanism for the observed decadal LOD variation.

  9. Melting of subducted basalt at the core-mantle boundary.

    Science.gov (United States)

    Andrault, Denis; Pesce, Giacomo; Bouhifd, Mohamed Ali; Bolfan-Casanova, Nathalie; Hénot, Jean-Marc; Mezouar, Mohamed

    2014-05-23

    The geological materials in Earth's lowermost mantle control the characteristics and interpretation of seismic ultra-low velocity zones at the base of the core-mantle boundary. Partial melting of the bulk lower mantle is often advocated as the cause, but this does not explain the nonubiquitous character of these regional seismic features. We explored the melting properties of mid-oceanic ridge basalt (MORB), which can reach the lowermost mantle after subduction of oceanic crust. At a pressure representative of the core-mantle boundary (135 gigapascals), the onset of melting occurs at ~3800 kelvin, which is ~350 kelvin below the mantle solidus. The SiO2-rich liquid generated either remains trapped in the MORB material or solidifies after reacting with the surrounding MgO-rich mantle, remixing subducted MORB with the lowermost mantle.

  10. Can the mantle control the core?: Energetics and dynamics

    Science.gov (United States)

    Nakagawa, T.

    2011-12-01

    The sustainability of magnetic field generation is discussed from a coupled model of numerical mantle convection simulation and core energetics theory. The pattern of geomagnetic field could be also controlled as a consequence of mantle convection [e.g. Amit and Choblet, 2009]. Our previous studies have suggested that the best-fit scenario for explaining both sustainability of magnetic field generation caused by dynamo actions and the size of inner core would be strongly controlled by the heat transfer of mantle convection with strongly compositional heterogeneities [Nakagawa and Tackley, 2004; Nakagawa and Tackley, 2010]. Here we investigate effects of initial mantle temperature and radioactive heat source in a convecting mantle with extremely high initial temperature at the core-mantle boundary that has been suggested from the hypothesis of early Earth [Labrosse et al., 2007] for checking how the mantle can control the thermal evolution of the core. Main consequence is that the amount of heat production rate and initial mantle temperature are not very sensitive to the thermal evolution of Earth's core but the convective vigor seems to be sensitive to the results. For the mantle side, the Urey ratio is not very good constraint for understanding thermal evolution of the whole Earth. In addition, we also show an example of numerical dynamo simulations with both a stably stratified layer and lateral variation of heat flux across the core-mantle boundary (CMB), which expands a paper by Nakagawa [2011], evaluated from numerical mantle convection simulations for checking how the mantle can control the dynamics of the core, which checks dead or alive for the magnetic field generated by dynamo actions with strongly lateral variation of CMB heat flux.

  11. Models of the earth's core

    Science.gov (United States)

    Stevenson, D. J.

    1981-01-01

    Combined inferences from seismology, high-pressure experiment and theory, geomagnetism, fluid dynamics, and current views of terrestrial planetary evolution lead to models of the earth's core with five basic properties. These are that core formation was contemporaneous with earth accretion; the core is not in chemical equilibrium with the mantle; the outer core is a fluid iron alloy containing significant quantities of lighter elements and is probably almost adiabatic and compositionally uniform; the more iron-rich inner solid core is a consequence of partial freezing of the outer core, and the energy release from this process sustains the earth's magnetic field; and the thermodynamic properties of the core are well constrained by the application of liquid-state theory to seismic and labroatory data.

  12. Geophysical and geochemical constraints on geoneutrino fluxes from Earth's mantle

    CERN Document Server

    Šrámek, Ondřej; Kite, Edwin S; Lekić, Vedran; Dye, Steve; Zhong, Shijie

    2012-01-01

    Knowledge of the amount and distribution of radiogenic heating in the mantle is crucial for understanding the dynamics of the Earth, including its thermal evolution, the style and planform of mantle convection, and the energetics of the core. Although the flux of heat from the surface of the planet is robustly estimated, the contributions of radiogenic heating and secular cooling remain poorly defined. Constraining the amount of heat-producing elements in the Earth will provide clues to understanding nebula condensation and planetary formation processes in early Solar System. Mantle radioactivity supplies power for mantle convection and plate tectonics, but estimates of mantle radiogenic heat production vary by a factor of up to 30. Recent experimental results demonstrate the potential for direct assessment of mantle radioactivity through observations of geoneutrinos, which are emitted by naturally occurring radionuclides. Predictions of the geoneutrino signal from the mantle exist for several established est...

  13. Rotation and Magnetism of Earth's Inner Core

    Science.gov (United States)

    Glatzmaier; Roberts

    1996-12-13

    Three-dimensional numerical simulations of the geodynamo suggest that a super- rotation of Earth's solid inner core relative to the mantle is maintained by magnetic coupling between the inner core and an eastward thermal wind in the fluid outer core. This mechanism, which is analogous to a synchronous motor, also plays a fundamental role in the generation of Earth's magnetic field.

  14. Rotation and magnetism of Earth`s inner core

    Energy Technology Data Exchange (ETDEWEB)

    Glatzmaier, G.A. [Los Alamos National Lab., NM (United States); Roberts, P.H. [Univ. of California, Los Angeles, CA (United States)

    1996-12-13

    Three-dimensional numerical simulations of the geodynamo suggest that a super-rotation of Earth`s solid inner core relative to the mantle is maintained by magnetic coupling between the inner core and an eastward thermal wind in the fluid outer core. This mechanism, which is analogous to a synchronous motor, also plays a fundamental role in the generation of Earth`s magnetic field. 18 refs., 6 figs.

  15. Strong, Multi-Scale Heterogeneity in Earth's Lowermost Mantle.

    Science.gov (United States)

    Tkalčić, Hrvoje; Young, Mallory; Muir, Jack B; Davies, D Rhodri; Mattesini, Maurizio

    2015-12-17

    The core mantle boundary (CMB) separates Earth's liquid iron outer core from the solid but slowly convecting mantle. The detailed structure and dynamics of the mantle within ~300 km of this interface remain enigmatic: it is a complex region, which exhibits thermal, compositional and phase-related heterogeneity, isolated pockets of partial melt and strong variations in seismic velocity and anisotropy. Nonetheless, characterising the structure of this region is crucial to a better understanding of the mantle's thermo-chemical evolution and the nature of core-mantle interactions. In this study, we examine the heterogeneity spectrum from a recent P-wave tomographic model, which is based upon trans-dimensional and hierarchical Bayesian imaging. Our tomographic technique avoids explicit model parameterization, smoothing and damping. Spectral analyses reveal a multi-scale wavelength content and a power of heterogeneity that is three times larger than previous estimates. Inter alia, the resulting heterogeneity spectrum gives a more complete picture of the lowermost mantle and provides a bridge between the long-wavelength features obtained in global S-wave models and the short-scale dimensions of seismic scatterers. The evidence that we present for strong, multi-scale lowermost mantle heterogeneity has important implications for the nature of lower mantle dynamics and prescribes complex boundary conditions for Earth's geodynamo.

  16. Application of Core Dynamics Modeling to Core-Mantle Interactions

    Science.gov (United States)

    Kuang, Weijia

    2003-01-01

    Observations have demonstrated that length of day (LOD) variation on decadal time scales results from exchange of axial angular momentum between the solid mantle and the core. There are in general four core-mantle interaction mechanisms that couple the core and the mantle. Of which, three have been suggested likely the dominant coupling mechanism for the decadal core-mantle angular momentum exchange, namely, gravitational core-mantle coupling arising from density anomalies in the mantle and in the core (including the inner core), the electromagnetic coupling arising from Lorentz force in the electrically conducting lower mantle (e.g. D-layer), and the topographic coupling arising from non-hydrostatic pressure acting on the core-mantle boundary (CMB) topography. In the past decades, most effort has been on estimating the coupling torques from surface geomagnetic observations (kinematic approach), which has provided insights on the core dynamical processes. In the meantime, it also creates questions and concerns on approximations in the studies that may invalidate the corresponding conclusions. The most serious problem is perhaps the approximations that are inconsistent with dynamical processes in the core, such as inconsistencies between the core surface flow beneath the CMB and the CMB topography, and that between the D-layer electric conductivity and the approximations on toroidal field at the CMB. These inconsistencies can only be addressed with numerical core dynamics modeling. In the past few years, we applied our MoSST (Modular, Scalable, Self-consistent and Three-dimensional) core dynamics model to study core-mantle interactions together with geodynamo simulation, aiming at assessing the effect of the dynamical inconsistencies in the kinematic studies on core-mantle coupling torques. We focus on topographic and electromagnetic core-mantle couplings and find that, for the topographic coupling, the consistency between the core flow and the CMB topography is

  17. Sediments at the top of Earth's core.

    Science.gov (United States)

    Buffett, B A; Garnero, E J; Jeanloz, R

    2000-11-17

    Unusual physical properties at the core-mantle boundary have been inferred from seismic and geodetic observations in recent years. We show how both types of observations can be explained by a layer of silicate sediments, which accumulate at the top of the core as Earth cools. Compaction of the sediments expels most of the liquid iron but leaves behind a small amount of core material, which is entrained in mantle convection and may account for the isotopic signatures of core material in some hot spot plumes. Extraction of light elements from the liquid core also enhances the vigor of convection in the core and may increase the power available to the geodynamo.

  18. Viscosity jump in Earth's mid-mantle.

    Science.gov (United States)

    Rudolph, Maxwell L; Lekić, Vedran; Lithgow-Bertelloni, Carolina

    2015-12-11

    The viscosity structure of Earth's deep mantle affects the thermal evolution of Earth, the ascent of mantle plumes, settling of subducted oceanic lithosphere, and the mixing of compositional heterogeneities in the mantle. Based on a reanalysis of the long-wavelength nonhydrostatic geoid, we infer viscous layering of the mantle using a method that allows us to avoid a priori assumptions about its variation with depth. We detect an increase in viscosity at 800- to 1200-kilometers depth, far greater than the depth of the mineral phase transformations that define the mantle transition zone. The viscosity increase is coincident in depth with regions where seismic tomography has imaged slab stagnation, plume deflection, and changes in large-scale structure and offers a simple explanation of these phenomena.

  19. The nature of the earth's core

    Science.gov (United States)

    Jeanloz, Raymond

    1990-01-01

    The properties of the earth's core are overviewed with emphasis on seismologically determined regions and pressures and seismologically measured density, elastic wave velocities, and gravitational acceleration. Attention is given to solid-state convection of the inner core, and it is noted that though seismological results do not conclusively prove that the inner core is convective, the occurrence and magnitude of seismic anisotropy are explained by the effects of solid-state convection. Igneous petrology and geochemistry of the inner core, a layer at the base of the mantle and contact metasomatism at the core-mantle boundary, and evolution of the core-mantle system are discussed. It is pointed out that high-pressure melting experiments indicate that the temperature of the core is ranging from 4500 to 6500 K, and a major implication of such high temperature is that the tectonics and convection of the mantle, as well as the resulting geological processes observed at the surface, are powered by heat from the core. As a result of the high temperatures, along with the compositional contrast between silicates and iron alloy, the core-mantle boundary is considered to be most chemically active region of the earth.

  20. Helium in Earth's early core

    Science.gov (United States)

    Bouhifd, M. A.; Jephcoat, Andrew P.; Heber, Veronika S.; Kelley, Simon P.

    2013-11-01

    The observed escape of the primordial helium isotope, 3He, from the Earth's interior indicates that primordial helium survived the energetic process of planetary accretion and has been trapped within the Earth to the present day. Two distinct reservoirs in the Earth's interior have been invoked to account for variations in the 3He/4He ratio observed at the surface in ocean basalts: a conventional depleted mantle source and a deep, still enigmatic, source that must have been isolated from processing throughout Earth history. The Earth's iron-based core has not been considered a potential helium source because partitioning of helium into metal liquid has been assumed to be negligible. Here we determine helium partitioning in experiments between molten silicates and iron-rich metal liquids at conditions up to 16GPa and 3,000K. Analyses of the samples by ultraviolet laser ablation mass spectrometry yield metal-silicate helium partition coefficients that range between 4.7×10-3 and 1.7×10-2 and suggest that significant quantities of helium may reside in the core. Based on estimated concentrations of primordial helium, we conclude that the early core could have incorporated enough helium to supply deep-rooted plumes enriched in 3He throughout the age of the Earth.

  1. Cascaded Evolution of Mantle Plumes and Metallogenesis of Core- and Mantle-derived Elements

    Institute of Scientific and Technical Information of China (English)

    NIU Shuyin; HOU Quanlin; HOU Zengqian; SUN Aiqun; WANG Baode; LI Hongyang; XU Chuanshi

    2003-01-01

    Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation andevolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion,lighter elements, such as radioactive, halogen-family, rare and rare earth elements and alkali metals. migrated upwards;whereas heavier elements, such as iron-family and platinum-family elements, base metals and noble metals, had atendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in theEarth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressureand viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly bycascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth wereinterdependent and constituted the motive force of the mantle-core movement. The cascaded evolution of mantle plumesopens the passageways for the migration of deep-seated ore-forming material, and thus elements such as gold and silverconcentrated in the core and on the core-mantle boundary migrate as the gaseous state together with the hot material flowof mantle plumes against the gravitational force through the passageways to the lithosphere, then migrate as the mixed gas-liquid state to the near-surface level and finally are concentrated in favorable structural expansion zones, forming mineraldeposits. This is possibly the important metallogenic mechanism for gold, silver, lead, zinc, copper and other manyelements. Take for example the NE-plunging crown of the Fuping mantle-branch structure, the paper analyzes ductile-brittle shear zone-type gold fields (Weijiayu) at the core of the magmatic-metamorphic complex, principal detachment-type gold fields (Shangmingyu) and hanging-wall cover fissure-vein-type lead-zinc polymetallic ore fields

  2. Thermoconvective waves in the earth's mantle

    Science.gov (United States)

    Birger, B. I.

    1980-06-01

    The thermoconvective instability of the Earth's mantle is analysed. The mantle is modelled as an infinite horizontal layer with a free upper surface, heated from below. The creep in the mantle is supposed to be transient when strains are small. This transient creep is described by Lomnitz's law modified by Jeffreys (1958a). It is shown that disturbances, in the form of thermoconvective waves with a period of 10 8 - 10 9y and wavelength of the order 10 3 km, can propagate through the mantle without attenuation. These waves induce oscillations of the Earth's surface. The pattern of flows differs greatly from that suggested by plate tectonics. An attempt is made to give a new explanation for the linear magnetic anomalies over oceanic ridges.

  3. Was core formation violent enough to homogenize the early mantle?

    Science.gov (United States)

    Cooperman, S. A.; Kaula, W. M.

    1985-01-01

    The dynamics of iron, its thermal state and its phase in the accreting Earth probably played a major role in the Earth's early thermal evolution. Plausible impact thermal histories make it possible that pure iron was molten in the accreting Earth after it was about 10% grown. Hence, iron eutectic alloys (FeS, FeO) certainly were. Additionally, the initial temperature of the core is an important constraint on the secular cooling of the early Earth and on the strength of the early geodynamo. Whether iron is solid or molten would influence geochemical equilibria in the upper and lower mantle; the mode of core formation, by spherical or near-spherical blobs, stalk-like instabilities, or something more catastrophic would influence the partitioning of siderophiles between silicate and iron phases. Early descent of iron (during accretion) favors partitioning according to low-pressure phase equilibria, whereas late descent favors higher pressure. The later core formation occurs, the greater the heat pulse, due to the strong dependence of gravitational potential energy on planetary radius. The heat may homogenize the mantle if core formation is global; otherwise, heterogeneity of iron differentiation may leave some of the pre-archean mantle unaffected. The larger the chunks of proto-core (and hence smaller surface/volume ratios) the greater the heterogeneity.

  4. The Earth's Core.

    Science.gov (United States)

    Jeanloz, Raymond

    1983-01-01

    The nature of the earth's core is described. Indirect evidence (such as that determined from seismological data) indicates that it is an iron alloy, solid toward its center but otherwise liquid. Evidence also suggests that it is the turbulent flow of the liquid that generates the earth's magnetic field. (JN)

  5. Earth rotation and core topography

    Science.gov (United States)

    Hager, Bradford H.; Clayton, Robert W.; Spieth, Mary Ann

    1988-01-01

    The NASA Geodynamics program has as one of its missions highly accurate monitoring of polar motion, including changes in length of day (LOD). These observations place fundamental constraints on processes occurring in the atmosphere, in the mantle, and in the core of the planet. Short-timescale (t less than or approx 1 yr) variations in LOD are mainly the result of interaction between the atmosphere and the solid earth, while variations in LOD on decade timescales result from the exchange of angular momentum between the mantle and the fluid core. One mechanism for this exchange of angular momentum is through topographic coupling between pressure variations associated with flow in the core interacting with topography at the core-mantel boundary (CMB). Work done under another NASA grant addressing the origin of long-wavelength geoid anomalies as well as evidence from seismology, resulted in several models of CMB topography. The purpose of work supported by NAG5-819 was to study further the problem of CMB topography, using geodesy, fluid mechanics, geomagnetics, and seismology. This is a final report.

  6. The core-mantle boundary region under the Gulf of Alaska : no ULVZ for shear waves

    NARCIS (Netherlands)

    Castle, John C.; Hilst, R.D. van der

    2000-01-01

    The Earth's core-mantle boundary (CMB) marks the boundary between the hot, molten iron core and the silicate mantle and is a thermal, chemical, and flow boundary. Previous observations of very slow compressional wavespeeds suggest that thin ultra-low-velocity zones (ULVZs), possibly composed of a mi

  7. Melting of the Earth's inner core.

    Science.gov (United States)

    Gubbins, David; Sreenivasan, Binod; Mound, Jon; Rost, Sebastian

    2011-05-19

    The Earth's magnetic field is generated by a dynamo in the liquid iron core, which convects in response to cooling of the overlying rocky mantle. The core freezes from the innermost surface outward, growing the solid inner core and releasing light elements that drive compositional convection. Mantle convection extracts heat from the core at a rate that has enormous lateral variations. Here we use geodynamo simulations to show that these variations are transferred to the inner-core boundary and can be large enough to cause heat to flow into the inner core. If this were to occur in the Earth, it would cause localized melting. Melting releases heavy liquid that could form the variable-composition layer suggested by an anomaly in seismic velocity in the 150 kilometres immediately above the inner-core boundary. This provides a very simple explanation of the existence of this layer, which otherwise requires additional assumptions such as locking of the inner core to the mantle, translation from its geopotential centre or convection with temperature equal to the solidus but with composition varying from the outer to the inner core. The predominantly narrow downwellings associated with freezing and broad upwellings associated with melting mean that the area of melting could be quite large despite the average dominance of freezing necessary to keep the dynamo going. Localized melting and freezing also provides a strong mechanism for creating seismic anomalies in the inner core itself, much stronger than the effects of variations in heat flow so far considered.

  8. Melting and Crystallization at Core Mantle Boundary

    Science.gov (United States)

    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

  9. Geomagnetism of earth's core

    Science.gov (United States)

    Benton, E. R.

    1983-01-01

    Instrumentation, analytical methods, and research goals for understanding the behavior and source of geophysical magnetism are reviewed. Magsat, launched in 1979, collected global magnetometer data and identified the main terrestrial magnetic fields. The data has been treated by representing the curl-free field in terms of a scalar potential which is decomposed into a truncated series of spherical harmonics. Solutions to the Laplace equation then extend the field upward or downward from the measurement level through intervening spaces with no source. Further research is necessary on the interaction between harmonics of various spatial scales. Attempts are also being made to analytically model the main field and its secular variation at the core-mantle boundary. Work is also being done on characterizing the core structure, composition, thermodynamics, energetics, and formation, as well as designing a new Magsat or a tethered satellite to be flown on the Shuttle.

  10. Geomagnetism of earth's core

    Science.gov (United States)

    Benton, E. R.

    1983-01-01

    Instrumentation, analytical methods, and research goals for understanding the behavior and source of geophysical magnetism are reviewed. Magsat, launched in 1979, collected global magnetometer data and identified the main terrestrial magnetic fields. The data has been treated by representing the curl-free field in terms of a scalar potential which is decomposed into a truncated series of spherical harmonics. Solutions to the Laplace equation then extend the field upward or downward from the measurement level through intervening spaces with no source. Further research is necessary on the interaction between harmonics of various spatial scales. Attempts are also being made to analytically model the main field and its secular variation at the core-mantle boundary. Work is also being done on characterizing the core structure, composition, thermodynamics, energetics, and formation, as well as designing a new Magsat or a tethered satellite to be flown on the Shuttle.

  11. Iron carbonates in the Earth's lower mantle: reality or imagination?

    Science.gov (United States)

    Cerantola, V.; McCammon, C. A.; Merlini, M.; Bykova, E.; Kupenko, I.; Ismailova, L.; Chumakov, A. I.; Kantor, I.; Dubrovinsky, L. S.; Prescher, C.

    2015-12-01

    Carbonates play a fundamental role in the recycling of carbon inside our planet due to their presence in oceanic slabs that sink through the Earth's interior. Through this process, iron carbonates are potential stable carbon-bearing minerals in the deep mantle in part due to spin crossover of ferrous iron. Our goal is to identify which minerals may be the dominant carriers of carbon into the deep mantle at the relevant conditions of fO2, P and T. All experiments were performed using synthetic FeCO3 and MgFeCO3 single crystals in laser heated diamond anvil cells up to 100 GPa and 3000 K in order to simulate the conditions prevailing in the Earth's lower mantle. Transformation and decomposition products of the original carbonates were characterized at different synchrotron facilities by means of single-crystal XRD, synchrotron Mössbauer source spectroscopy and XANES techniques. At deep lower mantle conditions, we observed the transformation of FeCO3 to two new HP-carbonate structures, monoclinic Fe22+Fe23+C4O13 and trigonal Fe43+(CO4)3, both characterized by the presence of CO4 tetrahedra with different degrees of polymerization. At shallower depths in the lower mantle where temperatures are lower following the geotherm, Fe-carbonates decompose to different Fe-oxides instead of new HP-carbonates. However, at slab temperatures several hundred degrees lower than the surrounding mantle, carbonates could be stabilized until reaching conditions that trigger their transformation to HP-structures. We postulate that Fe-rich carbonates could exist in regions down to the core-mantle boundary in the proximity of subducting slabs, i.e., a "cold" environment with relatively high fO2.

  12. Subduction History and the Evolution of Earth's Lower Mantle

    Science.gov (United States)

    Bull, Abigail; Shephard, Grace; Torsvik, Trond

    2016-04-01

    Understanding the complex structure, dynamics and evolution of the deep mantle is a fundamental goal in solid Earth geophysics. Close to the core-mantle boundary, seismic images reveal a mantle characterised by (1) higher than average shear wave speeds beneath Asia and encircling the Pacific, consistent with sub ducting lithosphere beneath regions of ancient subduction, and (2) large regions of anomalously low seismic wavespeeds beneath Africa and the Central Pacific. The anomalously slow areas are often referred to as Large Low Shear Velocity Provinces (LLSVPs) due to the reduced velocity of seismic waves passing through them. The origin, composition and long-term evolution of the LLSVPs remain enigmatic. Geochemical inferences of multiple chemical reservoirs at depth, strong seismic contrasts, increased density, and an anticorrelation of shear wave velocity to bulk sound velocity in the anomalous regions imply that heterogeneities in both temperature and composition may be required to explain the seismic observations. Consequently, heterogeneous mantle models place the anomalies into the context of thermochemical piles, characterised by an anomalous component whose intrinsic density is a few percent higher relative to that of the surrounding mantle. Several hypotheses have arisen to explain the LLSVPs in the context of large-scale mantle convection. One end member scenario suggests that the LLSVPs are relatively mobile features over short timescales and thus are strongly affected by supercontinent cycles and Earth's plate motion history. In this scenario, the African LLSVP formed as a result of return flow in the mantle due to circum-Pangean subduction (~240 Ma), contrasting a much older Pacific LLSVP, which may be linked to the Rodinia supercontinent and is implied to have remained largely unchanged since Rodinian breakup (~750-700 Ma). This propounds that Earth's plate motion history plays a controlling role in LLSVP development, suggesting that the location

  13. Volcanism, Earth Degassing and Replenished Lithosphere Mantle

    Science.gov (United States)

    Bailey, D. K.

    1980-07-01

    Volcanism that pierces plate interiors is characteristically rich in alkalis and volatiles, and its cause and persistence are essentially expressions of the Earth's outgassing. The general balance of mobile elements (such as H, C, F and Cl) rules out recycling of sea floor, hydrosphere, sediments or atmosphere: furthermore, it is not in accord with accepted planet degassing budgets. The typical eruptive mode of volatile-rich magmatism means that the observed regional chemical variations, and even differences between adjacent volcanoes, must largely reflect source heterogeneity. In a broader context, this magmatism is also at odds with a concept of continental crust underlain by strongly depleted (refractory) mantle. Repetition of activity along crustal zones of weakness shows that the lithosphere mantle (a) is structurally complex and (b) still holds continuing (or continual) rich reserves of mobile elements. Unbroken lithosphere muffles the evolutionary escape of volatiles from the deep mantle: any lesion that appears then offers easy escape channels, whereby volatiles are drained from a large mantle region and funnelled through the plate. Horizontal movement of thick continental lithosphere releases volatiles from deep sources, imparting some of the special chemical characteristics of the stable continental magmatism. Present evidence requires consideration of the continental lithosphere as a site of primordial heterogeneity that has been accentuated rather than diminished by geological processes.

  14. Constitution and structure of earth's mantle

    DEFF Research Database (Denmark)

    Zunino, Andrea; Khan, Amir; Cupillard, Paul

    2016-01-01

    This chapter describes a quantitative approach that integrates data and results from mineral physics, petrological analyses, and geophysical inverse calculations to map geophysical data directly for mantle composition and thermal state. Seismic tomography has proved an important tool to image...... the inaccessible parts of the Earth. Computation of physical properties using thermodynamic models is described and discussed, and an application of the joint inverse methodology is illustrated in a case study where mantle composition and thermal state beneath continental Australia is determined directly from...... seismic data. There is a growing consensus that the cause of the imaged wavespeed anomalies not only relates to variations in temperature, but also bears a strong compositional component. However, separation of thermal and chemical effects from seismic wave speeds alone is difficult and is further...

  15. Fe-FeO and Fe-Fe3C melting relations at Earth's core-mantle boundary conditions: Implications for a volatile-rich or oxygen-rich core

    Science.gov (United States)

    Morard, G.; Andrault, D.; Antonangeli, D.; Nakajima, Y.; Auzende, A. L.; Boulard, E.; Cervera, S.; Clark, A.; Lord, O. T.; Siebert, J.; Svitlyk, V.; Garbarino, G.; Mezouar, M.

    2017-09-01

    Eutectic melting temperatures in the Fe-FeO and Fe-Fe3C systems have been determined up to 150 GPa. Melting criteria include observation of a diffuse scattering signal by in situ X-Ray diffraction, and textural characterisation of recovered samples. In addition, compositions of eutectic liquids have been established by combining in situ Rietveld analyses with ex situ chemical analyses. Gathering these new results together with previous reports on Fe-S and Fe-Si systems allow us to discuss the specific effect of each light element (Si, S, O, C) on the melting properties of the outer core. Crystallization temperatures of Si-rich core compositional models are too high to be compatible with the absence of extensive mantle melting at the core-mantle boundary (CMB) and significant amounts of volatile elements such as S and/or C (>5 at%, corresponding to >2 wt%), or a large amount of O (>15 at% corresponding to ∼5 wt%) are required to reduce the crystallisation temperature of the core material below that of a peridotitic lower mantle.

  16. Electrical conductivity of the lowermost mantle explains absorption of core torsional waves at the equator

    CERN Document Server

    Schaeffer, Nathanaël

    2016-01-01

    Torsional Alfv{\\'e}n waves propagating in the Earth's core have been inferred by inversion techniques applied to geomagnetic models. They appear to propagate across the core but vanish at the equator, exchanging angular momentum between core and mantle. Assuming axial symmetry, we find that an electrically conducting layer at the bottom of the mantle can lead to total absorption of torsional waves that reach the equator. We show that the reflection coefficient depends on G Br , where Br is the strength of the radial magnetic field at the equator, and G the conductance of the lower mantle there. With Br = 7e-4 T., torsional waves are completely absorbed when they hit the equator if G = 1.3e8 S. For larger or smaller G, reflection occurs. As G is increased above this critical value, there is less attenuation and more angular momentum exchange. Our finding dissociates efficient core-mantle coupling from strong ohmic dissipation in the mantle.

  17. Geomagnetic spikes on the core-mantle boundary

    Science.gov (United States)

    Davies, Christopher; Constable, Catherine

    2017-05-01

    Extreme variations of Earth's magnetic field occurred in the Levant region around 1000 BC, when the field intensity rapidly rose and fell by a factor of 2. No coherent link currently exists between this intensity spike and the global field produced by the core geodynamo. Here we show that the Levantine spike must span >60° longitude at Earth's surface if it originates from the core-mantle boundary (CMB). Several low intensity data are incompatible with this geometric bound, though age uncertainties suggest these data could have sampled the field before the spike emerged. Models that best satisfy energetic and geometric constraints produce CMB spikes 8-22° wide, peaking at O(100) mT. We suggest that the Levantine spike reflects an intense CMB flux patch that grew in place before migrating northwest, contributing to growth of the dipole field. Estimates of Ohmic heating suggest that diffusive processes likely govern the ultimate decay of geomagnetic spikes.

  18. A sharp and flat section of the core-mantle boundary

    Science.gov (United States)

    Vidale, J.E.; Benz, H.M.

    1992-01-01

    THE transition zone between the Earth's core and mantle plays an important role as a boundary layer for mantle and core convection1. This zone conducts a large amount of heat from the core to the mantle, and contains at least one thermal boundary layer2,3; the proximity of reactive silicates and molten iron leads to the possibility of zones of intermediate composition4. Here we investigate one region of the core-mantle boundary using seismic waves that are converted from shear to compressional waves by reflection at the boundary. The use of this phase (known as ScP), the large number of receiving stations, and the large aperture of our array all provide higher resolution than has previously been possible5-7. For the 350-km-long section of the core-mantle boundary under the northeast Pacific sampled by the reflections, the local boundary topography has an amplitude of less than 500 m, no sharp radial gradients exist in the 400 km above the boundary, and the mantle-lo-core transition occurs over less than 1 km. The simplicity of the structure near and above the core-mantle boundary argues against chemical heterogeneity at the base of the mantle in this location.

  19. Initial Feasibility Study to Drill and Core the Ocean Mantle

    Directory of Open Access Journals (Sweden)

    Nicolas Pilisi

    2011-09-01

    Full Text Available An initial feasibility study (Pilisi and Whitney, 2011 of drilling through the Mohorovičić discontinuity (Moho into the oceanic mantle specifically focused on future requirements for planning, drilling and coring a hole 500 m into the oceanic mantle from three candidate locations in the Pacific Ocean (Cocos Plate, Baja California, and offshore Hawaii. The study points out some of the critical issues that need to be resolved before embarking upon such a challengingproject. It was conducted on the basis of data provided by the Integrated Ocean Drilling Program–Management International (IODP-MI, the Center for Deep Earth Exploration (CDEX operating the drilling vessel Chikyu within IODP, public domain information, and past experience that Blade Energy Partners (hereafter mentioned as “Blade”; http://www.blade-energy.com/ has had with frontier projects in the offshore deepwater oil and gas and geothermal industries.

  20. The Earth's heterogeneous mantle a geophysical, geodynamical, and geochemical perspective

    CERN Document Server

    Khan, Amir

    2015-01-01

    This book highlights and discusses recent developments that have contributed to an improved understanding of observed mantle heterogeneities and their relation to the thermo-chemical state of Earth's mantle, which ultimately holds the key to unlocking the secrets of the evolution of our planet. This series of topical reviews and original contributions address 4 themes. Theme 1 covers topics in geophysics, including global and regional seismic tomography, electrical conductivity and seismic imaging of mantle discontinuities and heterogeneities in the upper mantle, transition zone and lower mantle. Theme 2 addresses geochemical views of the mantle including lithospheric evolution from analysis of mantle xenoliths, composition of the deep Earth and the effect of water on subduction-zone processes. Theme 3 discusses geodynamical perspectives on the global thermo-chemical structure of the deep mantle. Theme 4 covers application of mineral physics data and phase equilibrium computations to infer the regional-scale ...

  1. Does the thermal wind exist near the Earth's core boundary?

    Science.gov (United States)

    Dolginov, A. Z.

    1993-01-01

    Temperature distribution in the Earth core determines many important processes such as the following: convective motion, magnetic field generation, matter exchange between the core and the mantle, and the thermal flux. This distribution depends on conditions in the core-mantle boundary and on the distribution of the thermal conductivity in the mantle. Seismic tomography shows that large horizontal temperature and compositional gradients exists at the core-mantle boundary. The simple assumption that these inhomogeneities are extended into the top of the core contradicts the common opinion that the horizontal temperature gradient (the thermal wind) wipes them out in a short time. However, this conclusion has been obtained without taking into account that the core volume is closed and the motion, if it is started, can lead to a small redistribution of composition that stops this motion.

  2. Melting curve of the deep mantle applied to properties of early magma ocean and actual core-mantle boundary

    Science.gov (United States)

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

    2010-05-01

    Our planet experienced partial melting early in its history as a consequence of energy release due to accretion. Partial mantle melting could still happen today in the lowermost mantle. Occurrence of melting is primordial for the chemical segregation between the different Earth's reservoirs and for the dynamics of the whole planet. Melting of iron-alloys is relatively easy to achieve, but the silicated mantle happens to be more refractory. We investigated experimentally melting properties of two starting material, forsterite and chondritic-mantle, at pressures ranging from 25 to 140 GPa, using laser-heated diamond anvil cell coupled with synchrotron radiation. We show that partial melting in the lowermost mantle, as suggested by seismology on the basis of the ultra-low velocity zones (ULVZ), requires temperatures above 4200 K at the core-mantle boundary. At low pressures, our curve plots significantly lower than previous reports. Compared to recent estimates of mantle geotherm, while this temperature remains possible if the Earth's core is very hot, it is more likely that ULVZs correspond to high concentration of incompatible elements driven down to the D"-layer by subducting slabs or extracted out from the outer core. When our chondritic melting curve is coupled with recent isentropic temperature profiles for a magma ocean, we obtain a correlation between magma ocean depth and the potential temperature (Tp) at its surface; an ocean depth of 1000 km (equivalent to ~40 GPa) corresponds to Tp=2000 K, which happens to be significantly hotter than the estimated surface temperature of a sustained magma ocean. It emphasizes the importance of a lid at the magma ocean surface at an epoch as early as that of core-mantle segregation.

  3. Dynamo tests for stratification below the core-mantle boundary

    Science.gov (United States)

    Olson, Peter; Landeau, Maylis; Reynolds, Evan

    2017-10-01

    Evidence from seismology, mineral physics, and core dynamics suggests a layer with an overall stable stratification in the Earth's outer core, possibly thermal in origin, extending below the core-mantle boundary (CMB) for several hundred kilometers. Yet vigorous deep mantle convection with locally elevated heat flux implies locally unstable thermal stratification below the CMB, consistent with interpretations of non-dipole geomagnetic field behavior that favor upwelling flows in places below the CMB. To resolve this apparent inconsistency, we investigate the structure of convection and magnetic fields in the core using numerical dynamos with laterally heterogeneous boundary heat flux. Strongly heterogeneous boundary heat flux generates localized convection beneath the CMB that coexists with an overall stable stratification there. Our partially stratified dynamos are distinguished by their time average magnetic field structures. Without stratification or with stratification confined to a thin layer, the octupole component is small and the CMB magnetic field structure includes polar intensity minima. With more extensive stratification, the octupole component is large and the magnetic field structure includes intense patches or high intensity lobes in the polar regions. Comparisons with the time-averaged geomagnetic field are generally favorable for partial stratification in a thin (<400 km) layer but unfavorable for stratification in a thick (∼1000 km) layer beneath the CMB.

  4. Core Forensics: Earth's Accretion and Differentiation

    Science.gov (United States)

    Badro, J.; Brodholt, J. P.; Siebert, J.; Piet, H.; Ryerson, F. J.

    2013-12-01

    Earth's accretion and its primitive differentiation are intimately interlinked processes. One way to constrain accretionary processes is by looking at the major differentiation event that took place during accretion: core formation. Understanding core formation and core composition can certainly shed a new light on early and late accretionary processes. On the other hand, testing certain accretionary models and hypothesis (fluxes, chemistries, timing) allows -short of validating them- at the very least to unambiguously refute them, through the 'filter'' of core formation and composition. Earth's core formed during accretion as a result of melting, phase-separation, and segregation of accretionary building blocks (from meteorites to planetesimals). The bulk composition of the core and mantle depends on the evolution (pressure, temperature, composition) of core extraction during accretion. The entire process left a compositional imprint on both reservoirs: (1) in the silicate Earth, in terms of siderophile trace-element (Ni, Co, V, Cr, among others) concentrations and isotopic fractionation (Si, Cu, among others), a record that is observed in present-day mantle rocks; and (2) on the core, in terms of major element composition and light elements dissolved in the metal, a record that is observed by seismology through the core density-deficit. This imprint constitutes actually a fairly impressive set of evidence (siderophile element concentration and fractionation, volatile and siderophile element isotopic fractionation), can be used today to trace back the primordial processes that occurred 4.5 billion years ago. We are seeking to provide an overhaul of the standard core formation/composition models, by using a new rationale that bridges geophysics and geochemistry. The new ingredients are (1) new laser-heated diamond anvil cell partitioning data, dramatically extending the previous P-T conditions for experimental work, (2) ab initio molecular dynamics calculations to

  5. The composition of mantle plumes and the deep Earth

    Science.gov (United States)

    Hastie, Alan R.; Fitton, J. Godfrey; Kerr, Andrew C.; McDonald, Iain; Schwindrofska, Antje; Hoernle, Kaj

    2016-06-01

    Determining the composition and geochemical diversity of Earth's deep mantle and subsequent ascending mantle plumes is vital so that we can better understand how the Earth's primitive mantle reservoirs initially formed and how they have evolved over the last 4.6 billion years. Further data on the composition of mantle plumes, which generate voluminous eruptions on the planet's surface, are also essential to fully understand the evolution of the Earth's hydrosphere and atmosphere with links to surface environmental changes that may have led to mass extinction events. Here we present new major and trace element and Sr-Nd-Pb-Hf isotope data on basalts from Curacao, part of the Caribbean large igneous province. From these and literature data, we calculate combined major and trace element compositions for the mantle plumes that generated the Caribbean and Ontong Java large igneous provinces and use mass balance to determine the composition of the Earth's lower mantle. Incompatible element and isotope results indicate that mantle plumes have broadly distinctive depleted and enriched compositions that, in addition to the numerous mantle reservoirs already proposed in the literature, represent large planetary-scale geochemical heterogeneity in the Earth's deep mantle that are similar to non-chondritic Bulk Silicate Earth compositions.

  6. A model for core formation in the early Earth

    Science.gov (United States)

    Jones, J. H.; Drake, M. J.

    1985-01-01

    Two basic types exogenous models were proposed to account for siderophile and chalcophile element abundances in the Earth's upper mantle. The first model requires that the Earth be depleted in volatiles and that, after a core formation event which extracted the most siderophile elements into the core, additional noble siderophile elements (Pt, Ir, Au) were added as a late veneer and mixed into the mantle. The second model postulates a reduced Earth with approximately CI elemental abundances in which a primary core forming event depleted all siderophile elements in the mantle. The plausibility of models which require fine scale mixing of chondritic material into the upper mantle is analyzed. Mixing in liquids is more efficient, but large degrees of silicate partial melting will facilitate the separation of magma from residual solids. Any external events affecting the upper mantle of the Earth should also be evident in the Moon; but siderophile and chalcophile element abundance patterns inferred for the mantles of the Earth and Moon differ. There appear to be significant physical difficulties associated with chondritic veneer models.

  7. When the Earth's Inner Core Shuffles

    Science.gov (United States)

    Tkalcic, H.; Young, M. K.; Bodin, T.; Ngo, S.; Sambridge, M.

    2011-12-01

    Shuffling is a tribal dance recently adapted by teenagers as a street dance. In one of the most popular moves, the so-called "Running Man", a stomp forward on one foot, shifted without being lifted from the ground, is followed by a change of position backwards on the same foot. Here, we present strong observational evidence from a newly observed collection of earthquake doublets that the Earth's inner core "shuffles" exhibiting both prograde and retrograde rotation in the reference frame of the mantle. This discovery is significant on several levels. First, the observed pattern consists of intermittent intervals of quasi-locked and differentially rotating inner core with respect to the Earth's mantle. This means that the angular alignment of the inner core and mantle oscillates in time over the past five decades. Jolting temporal changes are revealed, indicating that during the excursions from the quasi-locked state, the Earth's inner core can rotate both faster and slower than the rest of the planet, thus exhibiting both eastward and westward rotation. According to our results, a short time interval (on the order of one to two years) is needed for the inner core to accelerate to a differential rotation rate of several degrees per year, and typically a slightly longer time is needed to decelerate down to a negligibly small differential rotation rate. These time scales are in agreement with experimental spin-up times obtained when the magnetic torque alone is used to accelerate the inner core. Second, when we integrate the rotation rate over different time intervals, it is possible to explain discrepancies between the body wave and normal modes results for the rate of the inner core differential rotation found by previous authors. We show that the integrated shift in angular alignment and average rotation rates (previously determined to be constant) in normal mode studies are much smaller that those for the body waves. The repeating earthquakes from the South

  8. Isotopic evidence for internal oxidation of the Earth's mantle during accretion

    Science.gov (United States)

    Williams, Helen M.; Wood, Bernard J.; Wade, Jon; Frost, Daniel J.; Tuff, James

    2012-03-01

    The Earth's mantle is currently oxidised and out of chemical equilibrium with the core. The reasons for this and for the relatively oxidised state of Earth's mantle relative to the mantles of other terrestrial planets are unclear. It has been proposed that the oxidised nature and high ferric iron (Fe3 +) content of Earth's mantle was produced internally by disproportionation of ferrous iron (Fe2 +) into Fe3 + and metallic iron by perovskite crystallisation during accretion. Here we show that there is substantial Fe isotope fractionation between experimentally equilibrated metal and Fe3 +-bearing perovskite (≥ 0.45‰/amu), which can account for the heavy Fe isotope compositions of terrestrial basalts relative to equivalent samples derived from Mars and Vesta as the latter bodies are too small to stabilise significant perovskite. Mass balance calculations indicate that all of the mantle's Fe3 + could readily have been generated from a single disproportionation event, consistent with dissolution of perovskite in the lower mantle during a process such as the Moon-forming giant impact. The similar Fe isotope compositions of primitive terrestrial and low-titanium lunar basalts is consistent with models of equilibration between the mantles of the Earth and Moon in the aftermath of the giant impact and suggests that the heavy Fe isotope composition of the Earth's mantle was established prior to, or during the giant impact. The oxidation state and ferric iron content of the Earth's mantle was therefore plausibly set by the end of accretion, and may be decoupled from later volatile additions and the rise of oxygen in the Earth's atmosphere at 2.45 Ga.

  9. Continent-sized anomalous zones with low seismic velocity at the base of Earth's mantle

    Science.gov (United States)

    Garnero, Edward J.; McNamara, Allen K.; Shim, Sang-Heon

    2016-07-01

    Seismic images of Earth's interior reveal two massive anomalous zones at the base of the mantle, above the core, where seismic waves travel slowly. The mantle materials that surround these anomalous regions are thought to be composed of cooler rocks associated with downward advection of former oceanic tectonic plates. However, the origin and composition of the anomalous provinces is uncertain. These zones have long been depicted as warmer-than-average mantle materials related to convective upwelling. Yet, they may also be chemically distinct from the surrounding mantle, and potentially partly composed of subducted or primordial material, and have therefore been termed thermochemical piles. From seismic, geochemical and mineral physics data, the emerging view is that these thermochemical piles appear denser than the surrounding mantle materials, are dynamically stable and long-lived, and are shaped by larger-scale mantle flow. Whether remnants of a primordial layer or later accumulations of more-dense materials, the composition of the piles is modified over time by stirring and by chemical reactions with material from the surrounding mantle, underlying core and potentially from volatile elements transported into the deep Earth by subducted plates. Upwelling mantle plumes may originate from the thermochemical piles, so the unusual chemical composition of the piles could be the source of distinct trace-element signatures observed in hotspot lavas.

  10. Terrestrial magma ocean and core segregation in the earth

    Science.gov (United States)

    Ohtani, Eiji; Yurimoto, Naoyoshi

    1992-01-01

    According to the recent theories of formation of the earth, the outer layer of the proto-earth was molten and the terrestrial magma ocean was formed when its radius exceeded 3000 km. Core formation should have started in this magma ocean stage, since segregation of metallic iron occurs effectively by melting of the proto-earth. Therefore, interactions between magma, mantle minerals, and metallic iron in the magma ocean stage controlled the geochemistry of the mantle and core. We have studied the partitioning behaviors of elements into the silicate melt, high pressure minerals, and metallic iron under the deep upper mantle and lower mantle conditions. We employed the multi-anvil apparatus for preparing the equilibrating samples in the ranges from 16 to 27 GPa and 1700-2400 C. Both the electron probe microanalyzer (EPMA) and the Secondary Ion Mass spectrometer (SIMS) were used for analyzing the run products. We obtained the partition coefficients of various trace elements between majorite, Mg-perovskite, and liquid, and magnesiowustite, Mg-perovskite, and metallic iron. The examples of the partition coefficients of some key elements are summarized in figures, together with the previous data. We may be able to assess the origin of the mantle abundances of the elements such as transition metals by using the partitioning data obtained above. The mantle abundances of some transition metals expected by the core-mantle equilibrium under the lower mantle conditions cannot explain the observed abundance of some elements such as Mn and Ge in the mantle. Estimations of the densities of the ultrabasic magma Mg-perovskite at high pressure suggest existence of a density crossover in the deep lower mantle; flotation of Mg-perovskite occurs in the deep magma ocean under the lower mantle conditions. The observed depletion of some transition metals such as V, Cr, Mn, Fe, Co, and Ni in the mantle may be explained by the two stage process, the core-mantle equilibrium under the lower

  11. Timing And Processes Of Earth's Core Differentiation.

    Science.gov (United States)

    Allegre, C. J.; Manhes, G.; Gopel, C.

    2004-12-01

    Small 182W abundance excess of terrestrial W relative to W in bulk chondrites has been recently established (Yin et al. 2002, Kleine et al. 2002, Schoenberg et al. 2002). Rapid terrestrial accretion and early core formation, with completion of the bulk metal-silicate separation within less than 30 Myr have been proposed on this basis. These studies underline how much this 182W/182Hf time scale agrees with dynamic accretion models (Wetherill, 1986) that predict a ˜10 Myr interval for the main growth stage of Earth's formation. This W model time scale for terrestrial accretion is shorter than current estimates based on Pb isotope systematics of mantle-derived basalts and terrestrial Xe isotope systematics. The end of metal-silicate differentiation and large scale mantle degassing has been defined ˜100 My after beginning of the accretion. These studies also indicate agreement of this time scale with dynamic accretion models that predict 100 My for the end of Earth's accretion. The Hf-W time scale for accretion and core formation assumes total equilibration of incoming metal and silicate of impactors with the bulk silicate Earth (BSE) during planet's growth. Recently, the assumption of incomplete equilibration of metal and silicate components with BSE has been investigated (Halliday, 2004). It is proposed that impacting core material has not always efficiently mixed with the silicate portions of the Earth before being added to the Earth's core Our approach also considers that equilibration between metal and silicate has not been complete in BSE during Earth's growth, and we argue that early part of the Earth's core has segregated through unmelted silicate material. When the baby Earth was large enough, the increase of the temperature induced Fe-FeS eutectic melting. The liquid metal segregated through the crystalline silicate matrix and formed the early part of the Earth's core. Experimental study (Yoshino et al. 2003) indicates the percolation threshold for molten

  12. Highly siderophile elements were stripped from Earth's mantle by iron sulfide segregation

    CERN Document Server

    Rubie, David C; Jacobson, Seth A; Morbidelli, Alessandro; Palme, Herbert; Vogel, Antje K; Frost, Daniel J

    2016-01-01

    Highly siderophile elements (HSEs) are strongly depleted in the bulk silicate Earth (BSE) but are present in near-chondritic relative abundances. The conventional explanation is that the HSEs were stripped from the mantle by the segregation of metal during core formation but were added back in near-chondritic proportions by late accretion, after core formation had ceased. Here we show that metal-silicate equilibration and segregation during Earth's core formation actually increased HSE mantle concentrations because HSE partition coefficients are relatively low at the high pressures of core formation within Earth. The pervasive exsolution and segregation of iron sulfide liquid from silicate liquid (the "Hadean matte") stripped magma oceans of HSEs during cooling and crystallization, before late accretion, and resulted in slightly suprachondritic palladium/iridium and ruthenium/iridium ratios.

  13. Thermochemical structure of the Earth's mantle and continental crust

    DEFF Research Database (Denmark)

    Guerri, Mattia

    A detailed knowledge of the Earth's thermal structure and chemical composition is fundamental in order to understand the processes driving the planet ormation and evolution. The inaccessibility of most of the Earth's interior makes the determination of its thermo-chemical conditions a challenging...... in determining crustal seismic discontinuities. In the second chapter, I deal about the possibility to disentangle the dynamic and isostatic contribution in shaping the Earth's surface topography. Dynamic topography is directly linked to mantle convection driven by mantle thermo-chemical anomalies, and can...... argue therefore that our understandings of the lithosphere density structure, needed to determine the isostatic topography, and of the mantle density and viscosity, required to compute the dynamic topography, are still too limited to allow a robust determination of mantle convection effects on the Earth...

  14. Global-scale water circulation in the Earth's mantle: Implications for the mantle water budget in the early Earth

    Science.gov (United States)

    Nakagawa, Takashi; Spiegelman, Marc W.

    2017-04-01

    We investigate the influence of the mantle water content in the early Earth on that in the present mantle using numerical convection simulations that include three processes for redistribution of water: dehydration, partitioning of water into partially molten mantle, and regassing assuming an infinite water reservoir at the surface. These models suggest that the water content of the present mantle is insensitive to that of the early Earth. The initial water stored during planetary formation is regulated up to 1.2 OMs (OM = Ocean Mass; 1.4 ×1021 kg), which is reasonable for early Earth. However, the mantle water content is sensitive to the rheological dependence on the water content and can range from 1.2 to 3 OMs at the present day. To explain the evolution of mantle water content, we computed water fluxes due to subducting plates (regassing), degassing and dehydration. For weakly water dependent viscosity, the net water flux is almost balanced with those three fluxes but, for strongly water dependent viscosity, the regassing dominates the water cycle system because the surface plate activity is more vigorous. The increased convection is due to enhanced lubrication of the plates caused by a weak hydrous crust for strongly water dependent viscosity. The degassing history is insensitive to the initial water content of the early Earth as well as rheological strength. The degassing flux from Earth's surface is calculated to be approximately O (1013) kg /yr, consistent with a coupled model of climate evolution and mantle thermal evolution.

  15. Mantle convection and plate tectonics on Earth-like exoplanets

    Science.gov (United States)

    Sotin, C.; Schubert, G.

    2009-12-01

    The likelihood of plate tectonics on exoplanets larger than Earth can be assessed using either scaling laws or numerical models describing mantle thermal convection. We investigate the parameters which control the ratio of convective driving forces to lithosphere resisting forces. Two papers, Valencia et al. (AstroPhys. J., 670, L45-L48, 2007) and O’Neill and Lenardic (Geophys. Res. Lett., 34, L19204, 2007), came to opposite conclusions based on scaling laws and numerical calculations, respectively. The different assumptions and parameters used in each study are compared. The definition of thermal boundary layer and lithosphere and the use of their characteristics in the scaling laws are clarified. We show that Valencia et al. (2007) overestimate the ratio of driving forces to resistive forces because they infer too large values for both the thickness of the thermal boundary layer and the length of the plate and too small a value for the yield strength. We show that this ratio is so weakly dependent on the size of an Earth-like planet that other parameters such as presence of water, heating per unit mass, upper mantle thickness, etc., may actually determine the occurrence or not of plate tectonics. The numerical calculations of O’Neill and Lenardic (2007) show the importance of 2D simulations for determining the values of the velocity below the lithosphere, the convective stresses, and the plate dimensions. It demonstrates the need for 3D spherical numerical simulations. Their conclusion that super-Earths would not have plate tectonics depends on a number of assumptions including the constancy of heat-flux as a function of planetary size. We present a 3D spherical scaling including the increase of heat flux with the size of a planet showing that larger Earth-like planets would be marginally in the mobile lid convection regime reinforcing our caution that other factors may tip the balance. The present study points out the importance of the distance between

  16. ON THE VIGOR OF MANTLE CONVECTION IN SUPER-EARTHS

    Energy Technology Data Exchange (ETDEWEB)

    Miyagoshi, Takehiro [Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001 (Japan); Tachinami, Chihiro [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan); Kameyama, Masanori [Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577 (Japan); Ogawa, Masaki, E-mail: miyagoshi@jamstec.go.jp, E-mail: ctchnm.geo@gmail.com, E-mail: kameyama@sci.ehime-u.ac.jp, E-mail: cmaogawa@mail.ecc.u-tokyo.ac.jp [Department of Earth Sciences and Astronomy, University of Tokyo at Komaba, 3-8-1 Komaba, Meguro, Tokyo 153-8902 (Japan)

    2014-01-01

    Numerical models are presented to clarify how adiabatic compression affects thermal convection in the mantle of super-Earths ten times the Earth's mass. The viscosity strongly depends on temperature, and the Rayleigh number is much higher than that of the Earth's mantle. The strong effect of adiabatic compression reduces the activity of mantle convection; hot plumes ascending from the bottom of the mantle lose their thermal buoyancy in the middle of the mantle owing to adiabatic decompression, and do not reach the surface. A thick lithosphere, as thick as 0.1 times the depth of the mantle, develops along the surface boundary, and the efficiency of convective heat transport measured by the Nusselt number is reduced by a factor of about four compared with the Nusselt number for thermal convection of incompressible fluid. The strong effect of adiabatic decompression is likely to inhibit hot spot volcanism on the surface and is also likely to affect the thermal history of the mantle, and hence, the generation of magnetic field in super-Earths.

  17. Inner Core Rotation from Geomagnetic Westward Drift and a Stationary Spherical Vortex in Earth's Core

    Science.gov (United States)

    Voorhies, C. V.

    1999-01-01

    The idea that geomagnetic westward drift indicates convective leveling of the planetary momentum gradient within Earth's core is pursued in search of a differentially rotating mean state, upon which various oscillations and secular effects might be superimposed. The desired state conforms to roughly spherical boundary conditions, minimizes dissipative interference with convective cooling in the bulk of the core, yet may aide core cooling by depositing heat in the uppermost core and lower mantle. The variational calculus of stationary dissipation applied to a spherical vortex within the core yields an interesting differential rotation profile akin to spherical Couette flow bounded by thin Hartmann layers. Four boundary conditions are required. To concentrate shear induced dissipation near the core-mantle boundary, these are taken to be: (i) no-slip at the core-mantle interface; (ii) geomagnetically estimated bulk westward flow at the base of the core-mantle boundary layer; (iii) no-slip at the inner-outer core interface; and, to describe magnetic locking of the inner core to the deep outer core, (iv) hydrodynamically stress-free at the inner-outer core boundary. By boldly assuming the axial core angular momentum anomaly to be zero, the super-rotation of the inner core is calculated to be at most 1.5 degrees per year.

  18. Motion of the Mantle in the Translational Modes of the Earth and Mercury

    Science.gov (United States)

    Grinfeld, Pavel; Wisdom, Jack

    2005-01-01

    Slichter modes refer to the translational motion of the inner core with respect to the outer core and the mantle. The polar Slichter mode is the motion of the inner core along the axis of rotation. Busse presented an analysis of the polar mode which yielded an expression for its period. Busse's analysis included the assumption that the mantle was stationary. This approximation is valid for planets with small inner cores, such as the Earth whose inner core is about 1/60 of the total planet mass. On the other hand, many believe that Mercury's core may be enormous. If so, the motion of the mantle should be expected to produce a significant effect. We present a formal framework for including the motion of the mantle in the analysis of the translational motion of the inner core. We analyze the effect of the motion of the mantle on the Slichter modes for a non-rotating planet with an inner core of arbitrary size. We omit the effects of viscosity in the outer core, magnetic effects, and solid tides. Our approach is perturbative and is based on a linearization of Euler's equations for the motion of the fluid and Newton's second law for the motion of the inner core. We find an analytical expression for the period of the Slichter mode. Our result agrees with Busse's in the limiting case of small inner core. We present the unexpected result that even for Mercury the motion of the mantle does not significantly change the period of oscillation.

  19. Subduction and volatile recycling in Earth's mantle

    Science.gov (United States)

    King, S. D.; Ita, J. J.; Staudigel, H.

    1994-01-01

    The subduction of water and other volatiles into the mantle from oceanic sediments and altered oceanic crust is the major source of volatile recycling in the mantle. Until now, the geotherms that have been used to estimate the amount of volatiles that are recycled at subduction zones have been produced using the hypothesis that the slab is rigid and undergoes no internal deformation. On the other hand, most fluid dynamical mantle flow calculations assume that the slab has no greater strength than the surrounding mantle. Both of these views are inconsistent with laboratory work on the deformation of mantle minerals at high pressures. We consider the effects of the strength of the slab using two-dimensional calculations of a slab-like thermal downwelling with an endothermic phase change. Because the rheology and composition of subducting slabs are uncertain, we consider a range of Clapeyron slopes which bound current laboratory estimates of the spinel to perovskite plus magnesiowustite phase transition and simple temperature-dependent rheologies based on an Arrhenius law diffusion mechanism. In uniform viscosity convection models, subducted material piles up above the phase change until the pile becomes gravitationally unstable and sinks into the lower mantle (the avalanche). Strong slabs moderate the 'catastrophic' effects of the instabilities seen in many constant-viscosity convection calculations; however, even in the strongest slabs we consider, there is some retardation of the slab descent due to the presence of the phase change.

  20. The Origin of Non-chondritic HSE Ratios in the Earth's Mantle

    Science.gov (United States)

    Laurenz, V.; Rubie, D. C.; Frost, D. J.; Jacobson, S. A.; Morbidelli, A.; Palme, H.; Vogel, A. K.

    2015-12-01

    It is generally thought that Earth's mantle abundances of highly siderophile elements (HSE) were established by the addition of a chondritic late veneer to a mantle that was stripped of HSEs by core formation. A long-standing problem with this hypothesis is that the mantle's suprachondritic Pd/Ir and Ru/Ir ratios cannot be reconciled with any known meteorite group. To address this issue, we modelled the effect of metal-silicate segregation on abundances of the HSE and S in the Earth's mantle by including these elements in a combined accretion/core-formation model. Because in our model only a small fraction of the mantle equilibrates with core-forming metal, the bulk mantle HSE abundances are too large by the end of accretion. Sulfur abundances also greatly exceed S-saturation levels at magma ocean crystallisation temperatures, leading to the formation of a global immiscible sulfide melt that segregated to the core, thus removing HSEs from the mantle [1]. To better constrain the role of sulfide segregation on the HSE budget of the mantle, we experimentally determined the sulfide-silicate partitioning of Pt, Pd, Ru and Ir under high P-T conditions. Results show that Pd and Ru are less chalcophile at pressures above ~20 GPa compared to Pt and Ir, as opposed to the metal-silicate system where Ru is more siderophile than Pt [2]. These results are included in our model, which now involves localized segregation of core-forming metal followed by widespread exsolution and segregation of immiscible sulfide liquids. Platinum and Ir are efficiently extracted from the mantle whereas significant concentrations of Ru and Pd remain. Late veneer addition occurs after sulfide segregation has ceased due to magma ocean solidification. This model reproduces perfectly the non-chondritic Ru/Ir and Pd/Ir ratios of the mantle, reflecting incomplete removal of Ru and Pd from the mantle with core-forming sulfide melts. [1] O'Neill (1991) GCA 55, 1159-1172. [2] Mann et al. (2012) GCA 84, 593-613.

  1. Tomography of core-mantle boundary and lowermost mantle coupled by geodynamics: joint models of shear and compressional velocity

    Directory of Open Access Journals (Sweden)

    Gaia Soldati

    2015-03-01

    Full Text Available We conduct joint tomographic inversions of P and S travel time observations to obtain models of delta v_P  and delta v_S in the entire mantle. We adopt a recently published method which takes into account the geodynamic coupling between mantle heterogeneity and core-mantle boundary (CMB topography by viscous flow, where sensitivity of the seismic travel times to the CMB is accounted for implicitly in the inversion (i.e. the CMB topography is not explicitly inverted for. The seismic maps of the Earth's mantle and CMB topography that we derive can explain the inverted seismic data while being physically consistent with each other. The approach involved scaling P-wave velocity (more sensitive to the CMB to density anomalies, in the assumption that mantle heterogeneity has a purely thermal origin, so that velocity and density heterogeneity are proportional to one another. On the other hand, it has sometimes been suggested that S-wave velocity might be more directly sensitive to temperature, while P heterogeneity is more strongly influenced by chemical composition. In the present study, we use only S-, and not P-velocity, to estimate density heterogeneity through linear scaling, and hence the sensitivity of core-reflected P phases to mantle structure. Regardless of whether density is more closely related to P- or S-velocity, we think it is worthwhile to explore both scaling approaches in our efforts to explain seismic data. The similarity of the results presented in this study to those obtained by scaling P-velocity to density suggests that compositional anomaly has a limited impact on viscous flow in the deep mantle.

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

    Science.gov (United States)

    Badro, James; Siebert, Julien; Nimmo, Francis

    2016-08-01

    Recent palaeomagnetic observations report the existence of a magnetic field on Earth that is at least 3.45 billion years old. Compositional buoyancy caused by inner-core growth is the primary driver of Earth’s present-day geodynamo, but the inner core is too young to explain the existence of a magnetic field before about one billion years ago. Theoretical models propose that the exsolution of magnesium oxide—the major constituent of Earth’s mantle—from the core provided a major source of the energy required to drive an early dynamo, but experimental evidence for the incorporation of mantle components into the core has been lacking. Indeed, terrestrial core formation occurred in the early molten Earth by gravitational segregation of immiscible metal and silicate melts, transporting iron-loving (siderophile) elements from the silicate mantle to the metallic core and leaving rock-loving (lithophile) mantle components behind. Here we present experiments showing that magnesium oxide dissolves in core-forming iron melt at very high temperatures. Using core-formation models, we show that extreme events during Earth’s accretion (such as the Moon-forming giant impact) could have contributed large amounts of magnesium to the early core. As the core subsequently cooled, exsolution of buoyant magnesium oxide would have taken place at the core-mantle boundary, generating a substantial amount of gravitational energy as a result of compositional buoyancy. This amount of energy is comparable to, if not more than, that produced by inner-core growth, resolving the conundrum posed by the existence of an ancient magnetic field prior to the formation of the inner core.

  3. Alkali elements in the Earth's core: Evidence from enstatite meteorites

    Science.gov (United States)

    Lodders, K.

    1995-01-01

    The abundances of alkali elements in the Earth's core are predicted by assuming that accretion of the Earth started from material similar in composition to enstatite chondrites and that enstatite achondrites (aubrites) provide a natural laboratory to study core-mantle differentiation under extremely reducing conditions. If core formation on the aubrite parent body is comparable with core formation on the early Earth, it is found that 2600 (+/- 1000) ppm Na, 550 (+/- 260) ppm K, 3.4 (+/- 2.1) ppm Rb, and 0.31 (+/- 0.24) ppm Cs can reside in the Earth's core. The alkali-element abundances are consistent with those predicted by independent estimates based on nebula condensation calculations and heat flow data.

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

    Science.gov (United States)

    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

    , 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.

  5. Density structure of Earth's lowermost mantle from Stoneley mode splitting observations

    Science.gov (United States)

    Koelemeijer, Paula; Deuss, Arwen; Ritsema, Jeroen

    2017-05-01

    Advances in our understanding of Earth's thermal evolution and the style of mantle convection rely on robust seismological constraints on lateral variations of density. The large-low-shear-wave velocity provinces (LLSVPs) atop the core-mantle boundary beneath Africa and the Pacific are the largest structures in the lower mantle, and hence severely affect the convective flow. Here, we show that anomalous splitting of Stoneley modes, a unique class of free oscillations that are perturbed primarily by velocity and density variations at the core-mantle boundary, is explained best when the overall density of the LLSVPs is lower than the surrounding mantle. The resolved density variations can be explained by the presence of post-perovskite, chemical heterogeneity or a combination of the two. Although we cannot rule out the presence of a ~100-km-thick denser-than-average basal structure, our results support the hypothesis that LLSVPs signify large-scale mantle upwelling in two antipodal regions of the mantle.

  6. Predicting lower mantle heterogeneity from 4-D Earth models

    Science.gov (United States)

    Flament, Nicolas; Williams, Simon; Müller, Dietmar; Gurnis, Michael; Bower, Dan J.

    2016-04-01

    The Earth's lower mantle is characterized by two large-low-shear velocity provinces (LLSVPs), approximately ˜15000 km in diameter and 500-1000 km high, located under Africa and the Pacific Ocean. The spatial stability and chemical nature of these LLSVPs are debated. Here, we compare the lower mantle structure predicted by forward global mantle flow models constrained by tectonic reconstructions (Bower et al., 2015) to an analysis of five global tomography models. In the dynamic models, spanning 230 million years, slabs subducting deep into the mantle deform an initially uniform basal layer containing 2% of the volume of the mantle. Basal density, convective vigour (Rayleigh number Ra), mantle viscosity, absolute plate motions, and relative plate motions are varied in a series of model cases. We use cluster analysis to classify a set of equally-spaced points (average separation ˜0.45°) on the Earth's surface into two groups of points with similar variations in present-day temperature between 1000-2800 km depth, for each model case. Below ˜2400 km depth, this procedure reveals a high-temperature cluster in which mantle temperature is significantly larger than ambient and a low-temperature cluster in which mantle temperature is lower than ambient. The spatial extent of the high-temperature cluster is in first-order agreement with the outlines of the African and Pacific LLSVPs revealed by a similar cluster analysis of five tomography models (Lekic et al., 2012). Model success is quantified by computing the accuracy and sensitivity of the predicted temperature clusters in predicting the low-velocity cluster obtained from tomography (Lekic et al., 2012). In these cases, the accuracy varies between 0.61-0.80, where a value of 0.5 represents the random case, and the sensitivity ranges between 0.18-0.83. The largest accuracies and sensitivities are obtained for models with Ra ≈ 5 x 107, no asthenosphere (or an asthenosphere restricted to the oceanic domain), and a

  7. Chondritic Xenon in the Earth's mantle: new constrains on a mantle plume below central Europe

    Science.gov (United States)

    Caracausi, Antonio; Avice, Guillaume; Bernard, Peter; Furi, Evelin; Marty, Bernard

    2016-04-01

    Due to their inertness, their low abundances, and the presence of several different radiochronometers in their isotope systematics, the noble gases are excellent tracers of mantle dynamics, heterogeneity and differentiation with respect to the atmosphere. Xenon deserves particular attention because its isotope systematic can be related to specific processes during terrestrial accretion (e.g., Marty, 1989; Mukhopadhyay, 2012). The origin of heavy noble gases in the Earth's mantle is still debated, and might not be solar (Holland et al., 2009). Mantle-derived CO2-rich gases are particularly powerful resources for investigating mantle-derived noble gases as large quantities of these elements are available and permit high precision isotope analysis. Here, we report high precision xenon isotopic measurements in gases from a CO2 well in the Eifel volcanic region (Germany), where volcanic activity occurred between 700 ka and 11 ka years ago. Our Xe isotope data (normalized to 130Xe) show deviations at all masses compared to the Xe isotope composition of the modern atmosphere. The improved analytical precision of the present study, and the nature of the sample, constrains the primordial Xe end-member as being "chondritic", and not solar, in the Eifel mantle source. This is consistent with an asteroidal origin for the volatile elements in Earth's mantle and it implies that volatiles in the atmosphere and in the mantle originated from distinct cosmochemical sources. Despite a significant fraction of recycled atmospheric xenon in the mantle, primordial Xe signatures still survive in the mantle. This is also a demonstration of a primordial component in a plume reservoir. Our data also show that the reservoir below the Eifel region contains heavy-radiogenic/fissiogenic xenon isotopes, whose ratios are typical of plume-derived reservoirs. The fissiogenic Pu-Xe contribution is 2.26±0.28 %, the UXe contribution is negligible, the remainder being atmospheric plus primordial. Our

  8. Geochemical Constraints on Core Formation in the Earth

    Science.gov (United States)

    Jones, John H.; Drake, Michael J.

    1986-01-01

    New experimental data on the partitioning of siderophile and chalcophile elements among metallic and silicate phases may be used to constrain hypotheses of core formation in the Earth. Three current hypotheses can explain gross features of mantle geochemistry, but none predicts siderophile and chalcophile element abundances to within a factor of two of observed values. Either our understanding of metal-silicate interactions and/or our understanding of the early Earth requires revision.

  9. Thermal evolution of Earth with magnesium precipitation in the core

    Science.gov (United States)

    O'Rourke, Joseph G.; Korenaga, Jun; Stevenson, David J.

    2017-01-01

    Vigorous convection in Earth's core powers our global magnetic field, which has survived for over three billion years. In this study, we calculate the rate of entropy production available to drive the dynamo throughout geologic time using one-dimensional parameterizations of the evolution of Earth's core and mantle. To prevent a thermal catastrophe in models with realistic Urey ratios, we avoid the conventional scaling for plate tectonics in favor of one featuring reduced convective vigor for hotter mantle. We present multiple simulations that capture the effects of uncertainties in key parameters like the rheology of the lower mantle and the overall thermal budget. Simple scaling laws imply that the heat flow across the core/mantle boundary was elevated by less than a factor of two in the past relative to the present. Another process like the precipitation of magnesium-bearing minerals is therefore required to sustain convection prior to the nucleation of the inner core roughly one billion years ago, especially given the recent, upward revision to the thermal conductivity of the core. Simulations that include precipitation lack a dramatic increase in entropy production associated with the formation of the inner core, complicating attempts to determine its age using paleomagnetic measurements of field intensity. Because mantle dynamics impose strict limits on the amount of heat extracted from the core, we find that the addition of radioactive isotopes like potassium-40 implies less entropy production today and in the past. On terrestrial planets like Venus with more sluggish mantle convection, even precipitation of elements like magnesium may not sustain a dynamo if cooling rates are too slow.

  10. Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

    Science.gov (United States)

    Foley, Bradford J.; Driscoll, Peter E.

    2016-05-01

    Earth's climate, mantle, and core interact over geologic time scales. Climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. Plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. Plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles from the solar wind. Coupling between climate, mantle, and core can potentially explain the divergent evolution of Earth and Venus. As Venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. Therefore, plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. On planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. Many of these evolutionary trajectories would render the planet uninhabitable. However, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. Future work is needed to constrain potential evolutionary scenarios and the likelihood of an Earth-like evolution.

  11. The origin of volatiles in the Earth's mantle

    Science.gov (United States)

    Hier-Majumder, Saswata; Hirschmann, Marc M.

    2017-08-01

    The Earth's deep interior contains significant reservoirs of volatiles such as H, C, and N. Due to the incompatible nature of these volatile species, it has been difficult to reconcile their storage in the residual mantle immediately following crystallization of the terrestrial magma ocean (MO). As the magma ocean freezes, it is commonly assumed that very small amounts of melt are retained in the residual mantle, limiting the trapped volatile concentration in the primordial mantle. In this article, we show that inefficient melt drainage out of the freezing front can retain large amounts of volatiles hosted in the trapped melt in the residual mantle while creating a thick early atmosphere. Using a two-phase flow model, we demonstrate that compaction within the moving freezing front is inefficient over time scales characteristic of magma ocean solidification. We employ a scaling relation between the trapped melt fraction, the rate of compaction, and the rate of freezing in our magma ocean evolution model. For cosmochemically plausible fractions of volatiles delivered during the later stages of accretion, our calculations suggest that up to 77% of total H2O and 12% of CO2 could have been trapped in the mantle during magma ocean crystallization. The assumption of a constant trapped melt fraction underestimates the mass of volatiles in the residual mantle by more than an order of magnitude.Plain Language SummaryThe Earth's deep interior contains substantial amounts of volatile elements like C, H, and N. How these elements got sequestered in the Earth's interior has long been a topic of debate. It is generally assumed that most of these elements escaped the interior of the Earth during the first few hundred thousand years to create a primitive atmosphere, leaving the mantle reservoir nearly empty. In this work, we show that the key to this paradox involves the very early stages of crystallization of the mantle from a global magma ocean. Using numerical models, we show

  12. Magnetodynamo Lifetimes for Rocky, Earth-Mass Exoplanets with Contrasting Mantle Convection Regimes

    CERN Document Server

    van Summeren, Joost; Conrad, Clinton P

    2013-01-01

    We used a thermal model of an iron core to calculate magnetodynamo evolution in Earth-mass rocky planets to determine the sensitivity of dynamo lifetime and intensity to planets with different mantle tectonic regimes, surface temperatures, and core properties. The heat flow at the core-mantle boundary (CMB) is derived from numerical models of mantle convection with a viscous/pseudo-plastic rheology that captures the phenomenology of plate-like tectonics. Our thermal evolution models predict a long-lived (~8 Gyr) field for Earth and similar dynamo evolution for Earth-mass exoplanets with plate tectonics. Both elevated surface temperature and pressure-dependent mantle viscosity reduce the CMB heat flow but produce only slightly longer-lived dynamos (~8-9.5 Gyr). Single-plate ("stagnant lid") planets with relatively low CMB heat flow produce long-lived (~10.5 Gyr) dynamos. These weaker dynamos can cease for several billions of years and subsequently reactivate due to the additional entropy production associated ...

  13. Seismic evidence for slab graveyards atop the Core Mantle Boundary beneath the Indian Ocean Geoid Low

    Science.gov (United States)

    Padma Rao, B.; Ravi Kumar, M.

    2014-11-01

    The Indian Ocean Geoid Low (IOGL) that spans a vast areal extent south of the Indian subcontinent is a spectacular feature on the Earth, whose origin still remains ambiguous. In this study, we investigate the seismic character of the lower mantle below this geoid low utilizing the travel time and amplitude residuals of high quality S and ScS phases from 207 earthquakes recorded at 276 stations in the epicentral distance range of 36°-90°. For comparison, we also perform a similar exercise for a region of geoid high in the vicinity. Results reveal large variations in the ScS travel times indicating that the lowermost mantle beneath the IOGL region is heterogeneous. The ScS-S differential travel times are ∼3 s slower than those predicted by the IASP91 model, primarily due to velocity increase in the lowermost mantle beneath the IOGL region and ∼2 s higher than the IASP91 beneath the geoid high region, due to velocity decrease in the lowermost mantle. The largest negative residuals from manual method (-7.72 s) are concentrated below the IOGL. Iterative matching of differential travel time residuals reveals that the maximum positive and negative residuals can be explained in terms of a reduction in shear velocity of 0.9% and an increase of 1.6% respectively in a ∼1000 km thick layer above the Core Mantle Boundary. Further, the ScS/S amplitude residuals beneath the IOGL are positive, implying high impedance contrast at the Core Mantle Boundary, owing to the presence of high velocity material. We attribute these high velocities to the presence of dehydrated high density slab graveyards atop the Core Mantle Boundary beneath the Indian Ocean. Release of water at the mid-to-upper mantle depths due to the dehydration of subducted slabs causing a reduction in density and velocity of the ambient mantle, could be responsible for the geoid low.

  14. A crystallizing dense magma ocean at the base of the Earth's mantle.

    Science.gov (United States)

    Labrosse, S; Hernlund, J W; Coltice, N

    2007-12-06

    The distribution of geochemical species in the Earth's interior is largely controlled by fractional melting and crystallization processes that are intimately linked to the thermal state and evolution of the mantle. The existence of patches of dense partial melt at the base of the Earth's mantle, together with estimates of melting temperatures for deep mantle phases and the amount of cooling of the underlying core required to maintain a geodynamo throughout much of the Earth's history, suggest that more extensive deep melting occurred in the past. Here we show that a stable layer of dense melt formed at the base of the mantle early in the Earth's history would have undergone slow fractional crystallization, and would be an ideal candidate for an unsampled geochemical reservoir hosting a variety of incompatible species (most notably the missing budget of heat-producing elements) for an initial basal magma ocean thickness of about 1,000 km. Differences in 142Nd/144Nd ratios between chondrites and terrestrial rocks can be explained by fractional crystallization with a decay timescale of the order of 1 Gyr. These combined constraints yield thermal evolution models in which radiogenic heat production and latent heat exchange prevent early cooling of the core and possibly delay the onset of the geodynamo to 3.4-4 Gyr ago.

  15. Initial Feasibility Study to Drill and Core the Ocean Mantle

    OpenAIRE

    2011-01-01

    An initial feasibility study (Pilisi and Whitney, 2011) of drilling through the Mohorovičić discontinuity (Moho) into the oceanic mantle specifically focused on future requirements for planning, drilling and coring a hole 500 m into the oceanic mantle from three candidate locations in the Pacific Ocean (Cocos Plate, Baja California, and offshore Hawaii). The study points out some of the critical issues that need to be resolved before embarking upon such a challengingproject. It was conducted ...

  16. Magnesium stable isotope composition of Earth's upper mantle

    Science.gov (United States)

    Handler, Monica R.; Baker, Joel A.; Schiller, Martin; Bennett, Vickie C.; Yaxley, Gregory M.

    2009-05-01

    The mantle is Earth's largest reservoir of Mg containing > 99% of Earth's Mg inventory. However, no consensus exists on the stable Mg isotope composition of the Earth's mantle or how variable it is and, in particular, whether the mantle has the same stable Mg isotope composition as chondrite meteorites. We have determined the Mg isotope composition of olivine from 22 mantle peridotites from eastern Australia, west Antarctica, Jordan, Yemen and southwest Greenland by pseudo-high-resolution MC-ICP-MS on Mg purified to > 99%. The samples include fertile lherzolites, depleted harzburgites and dunites, cryptically metasomatised ('dry') peridotites and modally metasomatised apatite ± amphibole-bearing harzburgites and wehrlites. Olivine from these samples of early Archaean through to Permian lithospheric mantle have δ25Mg DSM-3 = - 0.22 to - 0.08‰. These data indicate the bulk upper mantle as represented by peridotite olivine is homogeneous within current analytical uncertainties (external reproducibility ≤ ± 0.07‰ [2 sd]). We find no systematic δ25Mg variations with location, lithospheric age, peridotite fertility, or degree or nature of mantle metasomatism. Although pyroxene may have slightly heavier δ25Mg than coexisting olivine, any fractionation between mantle pyroxene and olivine is also within current analytical uncertainties with a mean Δ25Mg pyr-ol = +0.06 ± 0.10‰ (2 sd; n = 5). Our average mantle olivine δ25Mg DSM-3 = - 0.14 ± 0.07‰ and δ26Mg DSM-3 = - 0.27 ± 0.14‰ (2 sd) are indistinguishable from the average of data previously reported for terrestrial basalts, confirming that basalts have stable Mg isotope compositions representative of the mantle. Olivine from five pallasite meteorites have δ25Mg DSM-3 = - 0.16 to - 0.11‰ that are identical to terrestrial olivine and indistinguishable from the average δ25Mg previously reported for chondrites. These data provide no evidence for measurable heterogeneity in the stable Mg isotope

  17. On the importance of lowermost mantle melt in the long term evolution of the Earth

    Science.gov (United States)

    Labrosse, S.; Hernlund, J. W.; Coltice, N.

    2011-12-01

    The thermal evolution of the Earth is usually modeled using its global energy balance and a scaling law for the heat transfer by mantle convection where the heat flow q depends on the mantle potential temperature T and its viscosity η as q=AT1+βη-β, with typical fluid dynamics models giving β≈1/3. The present small ratio of heat production to heat loss (Urey ratio) implies a large secular cooling rate and, because of the feedback from temperature dependent viscosity, backward calculations from the present time lead to a completely molten Earth about 1 Gyr ago. Starting with Christensen (1985), values of β smaller than 1/3 have been proposed to solve this problem by reducing the strength of the feedback loop between core temperature and surface heat flow. However, a self-consistent theory of mantle convection is still lacking to justify unconventional β values. We propose an entirely different approach recognizing that the lowermost mantle, which presently shows evidence of partial melting (ULVZs), was likely largely molten in its hotter past. Coupling a parameterized model of mantle convection using standard scalings for the solid upper part to a crystallizing basal magma ocean (BMO) enriched in radioactive elements and the core cuts the feedback loop very efficiently by introducing two independent potential temperatures. Backward integration of the model makes the core and the BMO hotter in the past while keeping the solid mantle temperature reasonable. A thermal catastrophe may in fact have happened, but only deep in the Earth!

  18. Pressure regimes and core formation in the accreting earth

    Science.gov (United States)

    Newsom, H. E.

    1992-01-01

    Recent work suggests that a large degree of melting is required to segregate metal from silicates, suggesting a connection with the formation of magma oceans. At low pressures metallic liquids do not wet silicate minerals, preventing the metal from aggregating into large masses that can sink. At high pressures, above 25 GPa, the dihedral angles of grains in contact with oxygen-rich metallic liquids may be reduced enough to allow percolation of metal, but this has not been confirmed. Physical models of core formation and accretion may therefore involve the formation of magma oceans and the segregation of metal at both high and low pressures. Models of core formation involving different pressure regimes are discussed as well as chemical evidence bearing on the models. Available geophysical data is ambiguous. The nature of the 670 km boundary (chemical difference or strictly phase change) between the upper and lower mantle is in doubt. There is some evidence that plumes are derived from the lower mantle, and seismic tomography strongly indicates that penetration of subducting oceanic crust into the lower mantle, but the tomography data also indicates that the 670 km discontinuity is a significant barrier to general mantle convection. The presence of the D' layer at the base of the lower mantle could be a reaction zone between the mantle and core indicating core-mantle disequilibrium, or D' layer could be subducted material. The abundance of the siderophile elements in the mantle could provide clues to the importance of high pressure processes in Earth, but partition coefficients at high pressures are only beginning to be measured.

  19. Planetary Lithosphere-Outer Core-Inner Core-Mantle Coupled Evolution Over the Entire Age of the Solar System

    Science.gov (United States)

    Tackley, P. J.; Nakagawa, T.; Louro Lourenço, D. J.; Rozel, A.

    2016-12-01

    Core evolution is determined by the heat flux extracted by the mantle as a function of time, which is itself dependent on the tectonic mode of the lithosphere and its evolution with time (Nakagawa & Tackley, 2015), as well as other factors. Thus, lithosphere, mantle and core must be treated as a coupled system in order to understand long-term core evolution. We have performed coupled modelling of mantle and core using a 2D or 3D mantle convection code with parameterized core. By plastic yielding the lithosphere may develop plate tectonics, stagnant lid, or episodic lid modes of tectonics, and the mode can change with time. Our recent models demonstrate that crustal production arising from partial melting plays a major role in facilitating plate tectonics; when this is included plate tectonics or episodic lithospheric overturn can occur even when purely thermal models predict a stagnant lithosphere (Lourenco et al, 2016). These models also demonstrate transitions between tectonic models as the planet cools. Considering Earth's core evolution, there is only a limited parameter range in which the heat extracted from the core is large enough at all times for a geodynamo to exist, but small enough that the core did not cool more than observed, a balance that becomes even more difficult if the core thermal conductivity is as high as recently thought (Nakagawa & Tackley, 2013). Models typically predict too much core cooling, which can be reduced by dense layering above the CMB: in particular such a dense, compositionally-distinct layer existing from early times is important for avoiding early too-rapid core cooling (Nakagawa & Tackley, 2014). Our latest models treat Earth evolution from the magma ocean phase to the present day (Lourenco et al., presented at this meeting). In these models an initially very hot core cools extremely rapidly until it reaches the rheological transition of mantle rock ( 40% melt fraction). Therefore, it is difficult for the core temperature at

  20. Properties of the Plasma Mantle in the Earth's Magnetotail

    Science.gov (United States)

    Shodhan-Shah, Sheela

    1998-04-01

    The plasma mantle is the site where the solar wind enters the Earth's magnetosphere. As yet, the mantle in the magnetotail (downstream part of the magnetosphere) has remained an enigma, for this region is remote and inaccessible. However, new results from the GEOTAIL spacecraft have yielded data on the mantle, making its study possible. The research reported in this dissertation uses the measurements made by the GEOTAIL spacecraft when it was beyond 100 Re (1 Re = Earth radius) in the magnetotail to determine the global geometrical and dynamical properties of the mantle. The model and the data together provide a cross-sectional picture of the mantle, as well as its extent into the tail and along the circumference of the tail. The model assesses the mass and momentum flux flowing through the mantle and merging with the plasma sheet (a relatively dense region that separates the oppositely directed fields of the tail lobes). In this way, the thesis examines the importance of the mantle as a source that replenishes and moves the plasma sheet. Moreover, it addresses the relative importance of the global dynamical modes of the tail. The analysis finds that the tail's 'breathing' mode, of shape change, occurs on a timescale of tens of minutes while a windsock-type motion, responding to changes in the solar wind direction, occurs on a scale of hours. The mantle extends about 140o around the circumference of the tail rather than 90o as previously thought and is about 20 ± 9 Re thick. It is capable of feeding the plasma sheet with sufficient particles to make up for those lost and can drag it away with a force that compares with the Earthward force on it. The rate at which the energy flows through the tail at 100 Re is about 10% of that in the solar wind and is a factor of 10 higher than the energy dissipated.

  1. Earth's core and the geodynamo

    Science.gov (United States)

    Buffett

    2000-06-16

    Earth's magnetic field is generated by fluid motion in the liquid iron core. Details of how this occurs are now emerging from numerical simulations that achieve a self-sustaining magnetic field. Early results predict a dominant dipole field outside the core, and some models even reproduce magnetic reversals. The simulations also show how different patterns of flow can produce similar external fields. Efforts to distinguish between the various possibilities appeal to observations of the time-dependent behavior of the field. Important constraints will come from geological records of the magnetic field in the past.

  2. Large gem diamonds from metallic liquid in Earth's deep mantle.

    Science.gov (United States)

    Smith, Evan M; Shirey, Steven B; Nestola, Fabrizio; Bullock, Emma S; Wang, Jianhua; Richardson, Stephen H; Wang, Wuyi

    2016-12-16

    The redox state of Earth's convecting mantle, masked by the lithospheric plates and basaltic magmatism of plate tectonics, is a key unknown in the evolutionary history of our planet. Here we report that large, exceptional gem diamonds like the Cullinan, Constellation, and Koh-i-Noor carry direct evidence of crystallization from a redox-sensitive metallic liquid phase in the deep mantle. These sublithospheric diamonds contain inclusions of solidified iron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane ± hydrogen, and sometimes majoritic garnet or former calcium silicate perovskite. The metal-dominated mineral assemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions. We verify previous predictions that Earth has highly reducing deep mantle regions capable of precipitating a metallic iron phase that contains dissolved carbon and hydrogen.

  3. Thermal, dynamic and compositional aspects of the core-forming Earth

    Science.gov (United States)

    Stevenson, D. J.

    1985-01-01

    Core formation is the most important and singular differentiation event in the history of a terrestrial planet. It almost certainly involved the downward migration of a partially or wholly molten iron alloy through a silicate and oxide mantle, and was contemporaneous with accretion. Several important, unresolved issues which have implications for mantle and core geochemistry, the thermal history of the Earth, and the origin of geomagnetism are addressed: whether the early Earth was molten; whether core formation involved low or high pressure geochemistry, or both; early Earth mantle homogenization; whether equilibration established between core forming material and the mantle through which it migrated; and how much iron is stranded and unable to reach the core.

  4. Dynamics of axial torsional libration under the mantle-inner core gravitational interaction

    Science.gov (United States)

    Chao, B. F.

    2017-01-01

    The aims of this paper are (i) formulating the dynamics of the mantle-inner core gravitational (MICG) interaction in terms of the spherical-harmonic multipoles of mass density. The modeled MICG system is composed of two concentric rigid bodies (mantle and inner core) of near-spherical but otherwise heterogeneous configuration, with a fluid outer core in between playing a passive role. We derive the general equation of motion for the vector rotation but only focus on the polar component that describes the MICG axial torsional libration. The torsion constant and hence the square of the natural frequency of the libration is proportional to the product of the equatorial ellipticities of the mantle and inner-core geoid embodied in their multipoles (of two different types) of degree 2 and order 2 (such as the Large Low-Shear-Velocity Provinces above the core-mantle boundary) and (ii) studying the geophysical implications upon equating the said MICG libration to the steady 6 year oscillation that are observed in the Earth's spin rate or the length-of-day variation (ΔLOD). In particular, the MICG torsion constant is found to be Γ>˜z = CIC σz2 ≈ 6.5 × 1019 N m, while the inner core's (BIC - AIC) ≈ 1.08 × 1031 kg m2 gives the inner core triaxiality (BIC - AIC)/CIC ≈ 1.8 × 10-4, about 8 times the whole-Earth value. It is also asserted that the required inner-core ellipticity amounts to no more than 140 m in geoid height, much smaller than the sensitivity required for the seismic wave travel time to resolve the variation of the inner core.

  5. Evolution of the Oxidation State of the Earth's Mantle

    Science.gov (United States)

    Danielson, L. R.; Righter, K.; Keller, L.; Christoffersen, E.; Rahman, Z.

    2015-01-01

    The oxidation state of the Earth's mantle during formation remains an unresolved question, whether it was constant throughout planetary accretion, transitioned from reduced to oxidized, or from oxidized to reduced. We investigate the stability of Fe3(+) at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the Earth's mantle. In our previous experiments on shergottite compositions, variable fO2, T, and P less than 4 GPa, Fe3(+)/sigma Fe decreased slightly with increasing P, similar to terrestrial basalt. For oxidizing experiments less than 7GPa, Fe3(+)/sigma Fe decreased as well, but it's unclear from previous modelling whether the deeper mantle could retain significant Fe3(+). Our current experiments expand our pressure range deeper into the Earth's mantle and focus on compositions and conditions relevant to the early Earth. Preliminary multi-anvil experiments with Knippa basalt as the starting composition were conducted at 5-7 GPa and 1800 C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal to Fe3(+)/2(+). Experiments are underway to produce glassy samples that can be measured by EELS and XANES, and are conducted at higher pressures.

  6. The Earth's Inner Core: a Black Box

    Science.gov (United States)

    Tkalčić, Hrvoje

    2016-04-01

    The Earth's inner core continues to provoke interest and interaction among various disciplines within the deep Earth scientific community for many reasons, including the following: i) The phase diagram of iron and its alloys at high pressures and temperatures is still in a state of investigation, and several crystalographic phases of iron and/or their aggregates have been proposed to be stable at inner core conditions. Seismological datasets have increased in size, but there is a serious trade-off between isotropic and anisotropic velocity structure. This is further exacerbated by the non-uniqueness of the inverse problem in which travel time data are modeled by volumetric changes in isotropic/anisotropic structure. These datasets are nevertheless invaluable, and their further growth through receiver installations in remote regions will further constrain this problem. ii) Radial and lateral variations in inner core structure have been intensively studied and confirmed, both in terms of velocity and attenuation. Studying the latter is complicated since another trade-off exists - that between the viscoelastic and scattering origin of attenuation. There is an ongoing debate about the existence of the innermost inner core and the geodynamical mechanism responsible for the seismologically observed east-west dichotomy in isotropic velocity. The growing travel time and waveform datasets, both from individual stations and arrays, hold the key to solving these problems. iii) The growth mechanism of the inner core is in dispute; its age is still unknown, and it is not completely understood how its growing front crystallizes. The seismological datasets are arguably less potent in providing direct answers to this question. Nonetheless, there is some potential in studying the texture present in the outermost inner core, the velocity gradient at the bottom of the outer core, and the nature of the inner core boundary using waveform simulations and the coda of the seismic phases

  7. Early stages of core segregation recorded by Fe isotopes in an asteroidal mantle

    OpenAIRE

    Barrat, Jean-Alix; Rouxel, O; Wang, K; Moynier, F; Yamaguchi, A; Bischoff, A; Langlade, J

    2015-01-01

    International audience; Ureilites displays  56 Fe values higher than average chondrite. 29-Segregation of Fe-sulfide melts explains the high  56 Fe values in ureilites. 30-Formation of a core can begin at very low degrees of melting through the circulation of a Fe-S melt 31 through a silicate mantle. 32 33 Earth and Planetary Science Letters, in press (11/3/15). 34 2 35 Abstract 36 37 Ureilite meteorites are achondrites that are debris of the mantle of a now disrupted 38 differentiated aste...

  8. Modelling of Equilibrium Between Mantle and Core: Refractory, Volatile, and Highly Siderophile Elements

    Science.gov (United States)

    Righter, K.; Danielson, L.; Pando, K.; Shofner, G.; Lee, C. -T.

    2013-01-01

    Siderophile elements have been used to constrain conditions of core formation and differentiation for the Earth, Mars and other differentiated bodies [1]. Recent models for the Earth have concluded that the mantle and core did not fully equilibrate and the siderophile element contents of the mantle can only be explained under conditions where the oxygen fugacity changes from low to high during accretion and the mantle and core do not fully equilibrate [2,3]. However these conclusions go against several physical and chemical constraints. First, calculations suggest that even with the composition of accreting material changing from reduced to oxidized over time, the fO2 defined by metal-silicate equilibrium does not change substantially, only by approximately 1 logfO2 unit [4]. An increase of more than 2 logfO2 units in mantle oxidation are required in models of [2,3]. Secondly, calculations also show that metallic impacting material will become deformed and sheared during accretion to a large body, such that it becomes emulsified to a fine scale that allows equilibrium at nearly all conditions except for possibly the length scale for giant impacts [5] (contrary to conclusions of [6]). Using new data for D(Mo) metal/silicate at high pressures, together with updated partitioning expressions for many other elements, we will show that metal-silicate equilibrium across a long span of Earth s accretion history may explain the concentrations of many siderophile elements in Earth's mantle. The modeling includes refractory elements Ni, Co, Mo, and W, as well as highly siderophile elements Au, Pd and Pt, and volatile elements Cd, In, Bi, Sb, Ge and As.

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

    Science.gov (United States)

    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.

  10. Between a rock and a hot place: the core-mantle boundary.

    Science.gov (United States)

    Wookey, James; Dobson, David P

    2008-12-28

    The boundary between the rocky mantle and iron core, almost 2900 km below the surface, is physically the most significant in the Earth's interior. It may be the terminus for subducted surface material, the source of mantle plumes and a control on the Earth's magnetic field. Its properties also have profound significance for the thermochemical and dynamic evolution of the solid Earth. Evidence from seismology shows that D'' (the lowermost few hundred kilometres of the mantle) has a variety of anomalous features. Understanding the origin of these observations requires an understanding of the elastic and deformation properties of the deep Earth minerals. Core-mantle boundary pressures and temperatures are achievable in the laboratory using diamond anvil cell (DAC) apparatus. Such experiments have led to the recent discovery of a new phase, 'post-perovskite', which may explain many hitherto poorly understood properties of D''. Experimental work is also done using analogue minerals at lower pressures and temperatures; these circumvent some of the limits imposed by the small sample size allowed by the DAC. A considerable contribution also comes from theoretical methods that provide a wealth of otherwise unavailable information, as well as verification and refinement of experimental results. The future of the study of the lowermost mantle will involve the linking of the ever-improving seismic observations with predictions of material properties from theoretical and experimental mineral physics in a quantitative fashion, including simulations of the dynamics of the deep Earth. This has the potential to dispel much of the mystery that still surrounds this remote but important region.

  11. Isotopic evidence of Cr partitioning into Earth's core.

    Science.gov (United States)

    Moynier, Frederic; Yin, Qing-Zhu; Schauble, Edwin

    2011-03-18

    The distribution of chemical elements in primitive meteorites (chondrites), as building blocks of terrestrial planets, provides insight into the formation and early differentiation of Earth. The processes that resulted in the depletion of some elements [such as chromium (Cr)] in the bulk silicate Earth relative to chondrites, however, remain debated between leading candidate causes: volatility versus core partitioning. We show through high-precision measurements of Cr stable isotopes in a range of meteorites, which deviate by up to ~0.4 per mil from those of the bulk silicate Earth, that Cr depletion resulted from its partitioning into Earth's core, with a preferential enrichment in light isotopes. Ab initio calculations suggest that the isotopic signature was established at mid-mantle magma ocean depth as Earth accreted planetary embryos and progressively became more oxidized.

  12. Thermal and electrical conductivity of iron at Earth's core conditions.

    Science.gov (United States)

    Pozzo, Monica; Davies, Chris; Gubbins, David; Alfè, Dario

    2012-04-11

    The Earth acts as a gigantic heat engine driven by the decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing (as the solid inner core grows), and on chemical convection (due to light elements expelled from the liquid on freezing). The power supplied to the geodynamo, measured by the heat flux across the core-mantle boundary (CMB), places constraints on Earth's evolution. Estimates of CMB heat flux depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent experimental and theoretical difficulties. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles--unlike previous estimates, which relied on extrapolations. The mixtures of iron, oxygen, sulphur and silicon are taken from earlier work and fit the seismologically determined core density and inner-core boundary density jump. We find both conductivities to be two to three times higher than estimates in current use. The changes are so large that core thermal histories and power requirements need to be reassessed. New estimates indicate that the adiabatic heat flux is 15 to 16 terawatts at the CMB, higher than present estimates of CMB heat flux based on mantle convection; the top of the core must be thermally stratified and any convection in the upper core must be driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted, and future models of mantle evolution will need to incorporate a high CMB heat flux and explain the recent formation of the inner core.

  13. Thermal and electrical conductivity of iron at Earth's core conditions

    CERN Document Server

    Pozzo, Monica; Gubbins, David; Alfè, Dario

    2012-01-01

    The Earth acts as a gigantic heat engine driven by decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes, and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing to grow the solid inner core, and on chemical convection due to light elements expelled from the liquid on freezing. The power supplied to the geodynamo, measured by the heat-flux across the core-mantle boundary (CMB), places constraints on Earth's evolution. Estimates of CMB heat-flux depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent difficulties in experimentation and theory. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles- the first directly comp...

  14. A seismologically consistent compositional model of Earth's core.

    Science.gov (United States)

    Badro, James; Côté, Alexander S; Brodholt, John P

    2014-05-27

    Earth's core is less dense than iron, and therefore it must contain "light elements," such as S, Si, O, or C. We use ab initio molecular dynamics to calculate the density and bulk sound velocity in liquid metal alloys at the pressure and temperature conditions of Earth's outer core. We compare the velocity and density for any composition in the (Fe-Ni, C, O, Si, S) system to radial seismological models and find a range of compositional models that fit the seismological data. We find no oxygen-free composition that fits the seismological data, and therefore our results indicate that oxygen is always required in the outer core. An oxygen-rich core is a strong indication of high-pressure and high-temperature conditions of core differentiation in a deep magma ocean with an FeO concentration (oxygen fugacity) higher than that of the present-day mantle.

  15. Earth's inner core: Innermost inner core or hemispherical variations?

    NARCIS (Netherlands)

    Lythgoe, K. H.; Deuss, A.; Rudge, J. F.; Neufeld, J. A.

    2014-01-01

    The structure of Earth's deep inner core has important implications for core evolution, since it is thought to be related to the early stages of core formation. Previous studies have suggested that there exists an innermost inner core with distinct anisotropy relative to the rest of the inner core.

  16. Earth's inner core: Innermost inner core or hemispherical variations?

    NARCIS (Netherlands)

    Lythgoe, K. H.; Deuss, A.; Rudge, J. F.; Neufeld, J. A.

    2014-01-01

    The structure of Earth's deep inner core has important implications for core evolution, since it is thought to be related to the early stages of core formation. Previous studies have suggested that there exists an innermost inner core with distinct anisotropy relative to the rest of the inner core.

  17. Core Formation in the Earth: Constraints from Ni and Co

    Science.gov (United States)

    Chabot, N. L.; Draper, D. S.; Agee, C. B.

    2004-01-01

    Due to their metal-loving nature, Ni and Co were strongly partitioned into the metallic core and were left depleted in the silicate mantle during core formation in the Earth. Based on experimental liquid metal- liquid silicate partition coefficients (D), studies have suggested that core formation in an early magma Ocean can explain the observed mantle depletions of Ni and Co [l-51. However, the conditions proposed by the magma ocean models have ranged from pressures of 24 to 59 GPa and temperatures of 2200 to < 4000 K. Furthermore, the proposed magma Ocean oxygen fugacities have differed by nearly two orders of magnitude.Chabot and Agee noted that the different models predicted contradictory behaviors for D(Ni) and D(Co) as a function of temperature. With the hope of resolving the discrepancies between the magma ocean models, we conducted a systematic experimental study to constrain the effects of temperature on D(Ni) and D(Co).

  18. Core formation in the earth and shergottite parent body (SPB) - Chemical evidence from basalts

    Science.gov (United States)

    Treiman, A. H.; Drake, M. J.; Janssens, M.-J.; Wolf, R.; Ebihara, M.

    1986-01-01

    Abundances of siderophile and chalcophile elements in the shergottite parental body (SPB) have been compared with those of the earth. To this end, new INAA and RNAA analyses of non-Antarctic meteorites have been performed, and the composition of the shergottite SPB mantle has been inferred from the compositions of the SNC meteorites. The composition of the earth's mantle has been inferred from the compositions of terrestrial basalt. Finally, the effects of volatile depletion, core formation, and mineral/melt fractionation on the abundances of siderophile and chalcophile elements in the SPB and the earth have been taken into consideration. Compared to the earth, the SPB mantle is richer in moderately siderophile elements and more depleted with respect to chalcophile elements. The observed relative abundances of siderophile and chalcophile elements in the SPB and the earth mantles indicate that the SPB underwent accretion and/or differentiation processes which differ from those in the earth.

  19. A New Carbonate Chemistry in the Earth's Lower Mantle

    Science.gov (United States)

    Boulard, E.; Gloter, A.; Corgne, A.; Antonangeli, D.; Auzende, A.; Perrillat, J.; Guyot, F. J.; Fiquet, G.

    2010-12-01

    explanation for the coexistence of oxidized and reduced C species observed on natural samples [4, 5], but also a new diamond formation mechanism at lower mantle conditions. [1] Sleep, N. H., and K. Zahnle (2001) J. Geophys. Res.-Planets 106(E1), 1373-1399. [2] Javoy, M. (1997) Geophys. Res. Lett. 24(2), 177-180. [3] Lecuyer et al. (2000) Earth Planet. Sci. Lett. 181(1-2), 33-40. [4] Brenker et al. (2007) Earth Planet. Sci. Lett. 260(1-2), 1-9. [5] Stachel et al. (2000) Contrib. Mineral. Petrol. 140(1), 16-27.

  20. Iron-silica interaction at extreme conditions and the electrically conducting layer at the base of Earth's mantle.

    Science.gov (United States)

    Dubrovinsky, L; Dubrovinskaia, N; Langenhorst, F; Dobson, D; Rubie, D; Gessmann, C; Abrikosov, I A; Johansson, B; Baykov, V I; Vitos, L; Le Bihan, T; Crichton, W A; Dmitriev, V; Weber, H-P

    2003-03-01

    The boundary between the Earth's metallic core and its silicate mantle is characterized by strong lateral heterogeneity and sharp changes in density, seismic wave velocities, electrical conductivity and chemical composition. To investigate the composition and properties of the lowermost mantle, an understanding of the chemical reactions that take place between liquid iron and the complex Mg-Fe-Si-Al-oxides of the Earth's lower mantle is first required. Here we present a study of the interaction between iron and silica (SiO2) in electrically and laser-heated diamond anvil cells. In a multianvil apparatus at pressures up to 140 GPa and temperatures over 3,800 K we simulate conditions down to the core-mantle boundary. At high temperature and pressures below 40 GPa, iron and silica react to form iron oxide and an iron-silicon alloy, with up to 5 wt% silicon. At pressures of 85-140 GPa, however, iron and SiO2 do not react and iron-silicon alloys dissociate into almost pure iron and a CsCl-structured (B2) FeSi compound. Our experiments suggest that a metallic silicon-rich B2 phase, produced at the core-mantle boundary (owing to reactions between iron and silicate), could accumulate at the boundary between the mantle and core and explain the anomalously high electrical conductivity of this region.

  1. Powering Earth's dynamo with magnesium precipitation from the core.

    Science.gov (United States)

    O'Rourke, Joseph G; Stevenson, David J

    2016-01-21

    Earth's global magnetic field arises from vigorous convection within the liquid outer core. Palaeomagnetic evidence reveals that the geodynamo has operated for at least 3.4 billion years, which places constraints on Earth's formation and evolution. Available power sources in standard models include compositional convection (driven by the solidifying inner core's expulsion of light elements), thermal convection (from slow cooling), and perhaps heat from the decay of radioactive isotopes. However, recent first-principles calculations and diamond-anvil cell experiments indicate that the thermal conductivity of iron is two or three times larger than typically assumed in these models. This presents a problem: a large increase in the conductive heat flux along the adiabat (due to the higher conductivity of iron) implies that the inner core is young (less than one billion years old), but thermal convection and radiogenic heating alone may not have been able to sustain the geodynamo during earlier epochs. Here we show that the precipitation of magnesium-bearing minerals from the core could have served as an alternative power source. Equilibration at high temperatures in the aftermath of giant impacts allows a small amount of magnesium (one or two weight per cent) to partition into the core while still producing the observed abundances of siderophile elements in the mantle and avoiding an excess of silicon and oxygen in the core. The transport of magnesium as oxide or silicate from the cooling core to underneath the mantle is an order of magnitude more efficient per unit mass as a source of buoyancy than inner-core growth. We therefore conclude that Earth's dynamo would survive throughout geologic time (from at least 3.4 billion years ago to the present) even if core radiogenic heating were minimal and core cooling were slow.

  2. Thermochemical Evolution of Earth's Core with Magnesium Precipitation

    Science.gov (United States)

    O'Rourke, J. G.; Stevenson, D. J.

    2014-12-01

    Vigorous convection within Earth's outer core drives a dynamo that has sustained a global magnetic field for at least 3.5 Gyr. Traditionally, people invoke three energy sources for the dynamo: thermal convection from cooling and freezing, compositional convection from light elements expelled by the growing inner core, and, perhaps, radiogenic heating from potassium-40. New theoretical and experimental work, however, indicates that the thermal and electrical conductivities of the outer core may be as much as three times higher than previously assumed. The implied increase in the adiabatic heat flux casts doubt on the ability of the usual mechanisms to explain the dynamo's longevity. Here, we present a quantitative model of the crystallization of magnesium-bearing minerals from the cooling core—a plausible candidate for the missing power source. Recent diamond-anvil cell experiments suggest that magnesium can partition into core material if thermodynamic equilibrium is achieved at high temperatures (>5000 K). We develop a model for core/mantle differentiation in which most of the core forms from material equilibrated at the base of a magma ocean as Earth slowly grows, but a small portion (~10%) equilibrated at extreme conditions in the aftermath of a giant impact. We calculate the posterior probability distribution for the original concentrations of magnesium and other light elements (chiefly oxygen and silicon) in the core, constrained by partitioning experiments and the observed depletion of siderophile elements in Earth's mantle. We then simulate the thermochemical evolution of cores with plausible compositions and thermal structures from the end of accretion to the present, focusing on the crystallization of a few percent of the initial core as ferropericlase and bridgmanite. Finally, we compute the associated energy release and verify that our final core compositions are consistent with the available seismological data.

  3. Past Plate Motions and The Evolution of Earth's Lower Mantle: Relating LLSVPs and Plume Distribution

    Science.gov (United States)

    Bull, A. L.; Torsvik, T. H.; Shephard, G. E.

    2015-12-01

    Seismic tomography elucidates broad, low shear-wave velocity structures in the lower mantle beneath Africa and the central Pacific with uncertain physical and compositional origins. The anomalously slow areas, which cover nearly 50% of the core-mantle boundary, are often referred to as Large Low Shear Velocity Provinces (LLSVPs) due to the reduced velocity of seismic waves passing through them. Several hypotheses have arisen to explain the LLSVPs in the context of large-scale mantle convection. One end-member scenario infers a spatial correlation between LLSVP margins at depth and the reconstructed surface eruption sites of hotspots, kimberlites, and Large Igneous Provinces. Such a correlation has been explained by the preferential triggering of plumes at LLSVP margins by impingement of the subducting lithosphere upon the lower thermal boundary layer at the interface between ambient mantle and the higher density structures. This scenario propounds that Earth's plate motion history plays a controlling role in plume development, and that the location, geometry and morphology of plumes may be influenced by the movement of subducting slabs. Here, we investigate what is necessary to create such a pattern of plume distribution in relation to LLSVPs. We consider what effect past plate motions may have had on the evolution of Earth's lower mantle, and discuss the development of mantle plumes in terms of subduction dynamics. We integrate plate tectonic histories and numerical models of mantle convection to investigate the role that subduction history plays in the development and evolution of plumes in the presence of LLSVPs. To test whether an interaction exists between the surface location of subduction and plume eruption sites, and if so, to what degree over time, we apply varying shifts to the absolute reference frame of the plate reconstruction. With this method, we are able to change the location of subduction at the surface and thus the global flow field. This in turn

  4. Melting of MORB at core-mantle boundary

    Science.gov (United States)

    Pradhan, Gopal K.; Fiquet, Guillaume; Siebert, Julien; Auzende, Anne-Line; Morard, Guillaume; Antonangeli, Daniele; Garbarino, Gaston

    2015-12-01

    We investigated the melting properties of natural mid-ocean ridge basalt (MORB) up to core-mantle boundary (CMB) pressures using laser-heated diamond anvil cell. Textural and chemical characterizations of quenched samples were performed by analytical transmission electron microscopy. We used in situ X-ray diffraction primarily for phase identification whereas our melting criterion based on laser power versus temperature plateau combined with textural analysis of recovered solidus and subsolidus samples is accurate and unambiguous. At CMB pressure (135 GPa), the MORB solidus temperature is 3970 (± 150) K. Quenched melt textures observed in recovered samples indicate that CaSiO3 perovskite (CaPv) is the liquidus phase in the entire pressure range up to CMB. The partial melt composition derived from the central melt pool is enriched in FeO, which suggests that such melt pockets may be gravitationally stable at the core mantle boundary.

  5. Olivine crystals align during diffusion creep of Earth's upper mantle.

    Science.gov (United States)

    Miyazaki, Tomonori; Sueyoshi, Kenta; Hiraga, Takehiko

    2013-10-17

    The crystallographic preferred orientation (CPO) of olivine produced during dislocation creep is considered to be the primary cause of elastic anisotropy in Earth's upper mantle and is often used to determine the direction of mantle flow. A fundamental question remains, however, as to whether the alignment of olivine crystals is uniquely produced by dislocation creep. Here we report the development of CPO in iron-free olivine (that is, forsterite) during diffusion creep; the intensity and pattern of CPO depend on temperature and the presence of melt, which control the appearance of crystallographic planes on grain boundaries. Grain boundary sliding on these crystallography-controlled boundaries accommodated by diffusion contributes to grain rotation, resulting in a CPO. We show that strong radial anisotropy is anticipated at temperatures corresponding to depths where melting initiates to depths where strongly anisotropic and low seismic velocities are detected. Conversely, weak anisotropy is anticipated at temperatures corresponding to depths where almost isotropic mantle is found. We propose diffusion creep to be the primary means of mantle flow.

  6. Sensitivity of the geomagnetic axial dipole to thermal core-mantle interactions

    Science.gov (United States)

    Bloxham

    2000-05-04

    Since the work of William Gilbert in 1600 (ref. 1), it has been widely believed that the Earth's magnetic field, when suitably time-averaged, is that of a magnetic dipole positioned at the Earth's centre and aligned with the rotational axis. This 'geocentric axial dipole' (GAD) hypothesis has been the central model for the study of the Earth's magnetic field--it underpins almost all interpretations of palaeomagnetic data, whether for studies of palaeomagnetic secular variation, for plate tectonic reconstructions, or for studies of palaeoclimate. Although the GAD hypothesis appears to provide a good description of the Earth's magnetic field over at least the past 100 Myr (ref. 2), it is difficult to test the hypothesis for earlier periods, and there is some evidence that a more complicated model is required for the period before 250 Myr ago. Kent and Smethurst suggested that this additional complexity might be because the inner core would have been smaller at that time. Here I use a numerical geodynamo model and find that reducing the size of the inner core does not significantly change the character of the magnetic field. I also consider an alternative process that could lead to the breakdown of the GAD hypothesis on this timescale, the evolution of heat-flux variations at the core-mantle boundary, induced by mantle convection. I find that a simple pattern of heat-flux variations at the core-mantle boundary, which is plausible for times before the Mesozoic era, results in a strong octupolar contribution to the field, consistent with previous findings.

  7. Intermediate-spin ferrous iron in the Earth's lower mantle?

    Science.gov (United States)

    Hsu, H.; Wentzcovitch, R. M.

    2013-12-01

    Intermediate-spin (IS) ferrous iron (Fe2+) has been a controversy in mineral physics. Its existence can change the detailed spin map of the Earth interior and may significantly affect mantle properties. IS Fe2+ is also a topic of interdisciplinary interest. Its existence in coordination complexes enables potential molecular devices to process more information; its connection with the superconductivity of iron chalcogenides has also been discussed. Here, we use the density functional theory + self-consistent Hubbard U (DFT+Usc) method to investigate IS Fe2+ in lower-mantle minerals. In ferropericlase, we found two different types of IS (t2g5eg1) states. Their distinct orbital occupancies lead to distinct Jahn-Teller (J-T) distortions, nuclear quadrupole splittings (QS), and on-site Coulomb interactions. Consequently, one IS state is much more favorable than the other, making it the most possible IS state in ferropericlase. In light of these new findings, we re-examine the previously reported IS Fe2+ in magnesium silicate (MgSiO3) perovskite [Hsu et al., Earth Planet. Sci. Lett. 294, 19 (2010)] and post-perovskite [Yu et al., Earth Planet. Sci. Lett. 331-332, 1 (2011)]. While these two minerals are much more complicated, the reported IS states are highly similar to the most favorable IS state in ferropericlase, suggesting that they are indeed the most possible IS states in these two minerals. However, these most possible IS Fe2+ are still not energetically favorable. Therefore, IS Fe2+ is highly unlikely in the Earth's lower mantle. *This project is supported by NSC Grant 102-2112-M-008-001-MY3 (H.H.) and NSF Awards EAR-1319361, -1019853, and -0810272 (R.M.W).

  8. The origin and chemical composition of the earth's core

    Science.gov (United States)

    Murthy, V. R.; Hall, T.

    1972-01-01

    The process of core formation in the earth is subject to the constraints that it be nearly simultaneous with accretion and yet occur in a manner that the mantle retains radiogenic Xe-129 produced from the extinct radioactivity of I-129 with a half life of 17.6 million y. From these constraints, it appears that the only feasible mechanism is the segregation of an Fe-FeS melt. Trace element abundances in major classes of meteorites and the silicate fractions of the earth show that not only there is a high depletion of sulphur in the crust and the mantle, but that it is even more highly depleted than the rare gases, water and the halogens. From the nature of this depletion pattern and the fact that any model of accretion of the earth will necessarily produce an Fe-FeS melt, it is concluded that the light element in the core is largely sulphur with minor amounts of carbon. A consequence of this mode of core formation is found to be the availability of K-40 radioactive heat production in the liquid core, estimated at about 10 to the 19th power erg/s at the present time.

  9. The origin and chemical composition of the earth's core

    Science.gov (United States)

    Murthy, V. R.; Hall, T.

    1972-01-01

    The process of core formation in the earth is subject to the constraints that it be nearly simultaneous with accretion and yet occur in a manner that the mantle retains radiogenic Xe-129 produced from the extinct radioactivity of I-129 with a half life of 17.6 million y. From these constraints, it appears that the only feasible mechanism is the segregation of an Fe-FeS melt. Trace element abundances in major classes of meteorites and the silicate fractions of the earth show that not only there is a high depletion of sulphur in the crust and the mantle, but that it is even more highly depleted than the rare gases, water and the halogens. From the nature of this depletion pattern and the fact that any model of accretion of the earth will necessarily produce an Fe-FeS melt, it is concluded that the light element in the core is largely sulphur with minor amounts of carbon. A consequence of this mode of core formation is found to be the availability of K-40 radioactive heat production in the liquid core, estimated at about 10 to the 19th power erg/s at the present time.

  10. Planet Within a Planet: Rotation of the Inner Core of Earth

    Science.gov (United States)

    Su; Dziewonski; Jeanloz

    1996-12-13

    The time dependence of the orientation of Earth's inner core relative to the mantle was determined using a recently discovered 10-degree tilt in the axis of symmetry of the inner core's seismic-velocity anisotropy. Two methods of analyzing travel-time variations for rays traversing the inner core, on the basis of 29 years of data from the International Seismological Centre (1964-1992), reveal that the inner core appears to rotate about 3 degrees per year faster than the mantle. An anomalous variation in inner-core orientation from 1969 to 1973 coincides in time with a sudden change ("jerk") in the geomagnetic field.

  11. Fate of MgSiO3 melts at core-mantle boundary conditions.

    Science.gov (United States)

    Petitgirard, Sylvain; Malfait, Wim J; Sinmyo, Ryosuke; Kupenko, Ilya; Hennet, Louis; Harries, Dennis; Dane, Thomas; Burghammer, Manfred; Rubie, Dave C

    2015-11-17

    One key for understanding the stratification in the deep mantle lies in the determination of the density and structure of matter at high pressures, as well as the density contrast between solid and liquid silicate phases. Indeed, the density contrast is the main control on the entrainment or settlement of matter and is of fundamental importance for understanding the past and present dynamic behavior of the deepest part of the Earth's mantle. Here, we adapted the X-ray absorption method to the small dimensions of the diamond anvil cell, enabling density measurements of amorphous materials to unprecedented conditions of pressure. Our density data for MgSiO3 glass up to 127 GPa are considerably higher than those previously derived from Brillouin spectroscopy but validate recent ab initio molecular dynamics simulations. A fourth-order Birch-Murnaghan equation of state reproduces our experimental data over the entire pressure regime of the mantle. At the core-mantle boundary (CMB) pressure, the density of MgSiO3 glass is 5.48 ± 0.18 g/cm(3), which is only 1.6% lower than that of MgSiO3 bridgmanite at 5.57 g/cm(3), i.e., they are the same within the uncertainty. Taking into account the partitioning of iron into the melt, we conclude that melts are denser than the surrounding solid phases in the lowermost mantle and that melts will be trapped above the CMB.

  12. Highly siderophile elements in Earth's mantle as a clock for the Moon-forming impact.

    Science.gov (United States)

    Jacobson, Seth A; Morbidelli, Alessandro; Raymond, Sean N; O'Brien, David P; Walsh, Kevin J; Rubie, David C

    2014-04-01

    According to the generally accepted scenario, the last giant impact on Earth formed the Moon and initiated the final phase of core formation by melting Earth's mantle. A key goal of geochemistry is to date this event, but different ages have been proposed. Some argue for an early Moon-forming event, approximately 30 million years (Myr) after the condensation of the first solids in the Solar System, whereas others claim a date later than 50 Myr (and possibly as late as around 100 Myr) after condensation. Here we show that a Moon-forming event at 40 Myr after condensation, or earlier, is ruled out at a 99.9 per cent confidence level. We use a large number of N-body simulations to demonstrate a relationship between the time of the last giant impact on an Earth-like planet and the amount of mass subsequently added during the era known as Late Accretion. As the last giant impact is delayed, the late-accreted mass decreases in a predictable fashion. This relationship exists within both the classical scenario and the Grand Tack scenario of terrestrial planet formation, and holds across a wide range of disk conditions. The concentration of highly siderophile elements (HSEs) in Earth's mantle constrains the mass of chondritic material added to Earth during Late Accretion. Using HSE abundance measurements, we determine a Moon-formation age of 95 ± 32 Myr after condensation. The possibility exists that some late projectiles were differentiated and left an incomplete HSE record in Earth's mantle. Even in this case, various isotopic constraints strongly suggest that the late-accreted mass did not exceed 1 per cent of Earth's mass, and so the HSE clock still robustly limits the timing of the Moon-forming event to significantly later than 40 Myr after condensation.

  13. Electronic Spin Crossover of Iron in Ferroperclase in Earth?s Lower Mantle

    Energy Technology Data Exchange (ETDEWEB)

    Lin, J F; Vanko, G; Jacobsen, S D; Iota, V; Struzhkin, V V; Prakapenka, V B; Kuznetsov, A; Yoo, C S

    2007-01-25

    Pressure-induced electronic spin-pairing transitions of iron and associated effects on the physical properties have been reported to occur in the lower-mantle ferropericlase, silicate perosvkite, and perhaps in post silicate perovskite at high pressures and room temperature. These recent results are motivating geophysicists and geodynamicists to reevaluate the implications of spin transitions on the seismic heterogeneity, composition, as well as the stability of the thermal upwellings of the Earth's lower mantle. Here we have measured the spin states of iron in ferropericlase and its crystal structure up to 95 GPa and 2000 K using a newly constructed X-ray emission spectroscopy and diffraction with the laser-heated diamond cell. Our results show that an isosymmetric spin crossover occurs over a pressure-temperature range extending from the upper part to the lower part of the lower mantle, and low-spin ferropericlase likely exists in the lowermost mantle. Although continuous changes in physical and chemical properties are expected to occur across the spin crossover, the spin crossover results in peculiar behavior in the thermal compression and sound velocities. Therefore, knowledge of the fraction of the spin states in the lower-mantle phases is thus essential to correctly evaluate the composition, geophysics, and dynamics of the Earth's lower mantle.

  14. Effect of core--mantle and tidal torques on Mercury's spin axis orientation

    CERN Document Server

    Peale, Stanton J; Hauck,, Steven A; Solomon, Sean C

    2014-01-01

    The rotational evolution of Mercury's mantle and its core under conservative and dissipative torques is important for understanding the planet's spin state. Dissipation results from tides and viscous, magnetic and topographic core--mantle interactions. The dissipative core--mantle torques take the system to an equilibrium state wherein both spins are fixed in the frame precessing with the orbit, and in which the mantle and core are differentially rotating. This equilibrium exhibits a mantle spin axis that is offset from the Cassini state by larger amounts for weaker core--mantle coupling for all three dissipative core--mantle coupling mechanisms, and the spin axis of the core is separated farther from that of the mantle, leading to larger differential rotation. The relatively strong core--mantle coupling necessary to bring the mantle spin axis to its observed position close to the Cassini state is not obtained by any of the three dissipative core--mantle coupling mechanisms. For a hydrostatic ellipsoidal core...

  15. Asteroids and meteorites - Origin of stony-iron meteorites at mantle-core boundaries

    Science.gov (United States)

    Greenberg, R.; Chapman, C. R.

    1984-01-01

    Stony-iron meteorites formed at the core/mantle interfaces of small asteroidal parents. The mesosiderites formed when the thick crust of a largely molten parent body (100-200 km in diameter) foundered and sank through the mantle to the core. Pallasites formed in smaller parent bodies (50-100 km) in which olivine crystals from the partially molten mantle sank to the core/mantle interface and rafted there. Subsequent collisions stripped away the rocky mantles of both kinds of parent bodies, exposing the stony-iron surfaces of their cores to direct impacts, which continue to knock off meteorite fragments.

  16. Imaging earth`s interior: Tomographic inversions for mantle P-wave velocity structure

    Energy Technology Data Exchange (ETDEWEB)

    Pulliam, R.J.

    1991-07-01

    A formalism is developed for the tomographic inversion of seismic travel time residuals. The travel time equations are solved both simultaneously, for velocity model terms and corrections to the source locations, and progressively, for each set of terms in succession. The methods differ primarily in their treatment of source mislocation terms. Additionally, the system of equations is solved directly, neglecting source terms. The efficacy of the algorithms is explored with synthetic data as we perform simulations of the general procedure used to produce tomographic images of Earth`s mantle from global earthquake data. The patterns of seismic heterogeneity in the mantle that would be returned reliably by a tomographic inversion are investigated. We construct synthetic data sets based on real ray sampling of the mantle by introducing spherical harmonic patterns of velocity heterogeneity and perform inversions of the synthetic data.

  17. Metal-silicate partitioning during core formation on super-Earths

    Science.gov (United States)

    Schaefer, L. K.; Jacobsen, S. B.; Petaev, M. I.; Sasselov, D. D.; Remo, J. L.

    2015-12-01

    Separation of the Earth into a rocky mantle and metallic Fe core is a problem long studied in the planetary science community (e.g. [1]). The timing of core formation influences the abundances of the siderophile elements found in the Earth's mantle, and the mechanism of core formation influences the degree of chemical equilibration between the rocky mantle and the core at the time of metal separation. However, limited work has been done on formation of metallic cores and its effects on mantle chemistry in rocky planets larger than the Earth. Super-Earths, exoplanets with masses up to ~ 5 Earth masses and radii up to ~1.6-1.7 Earth radii, have significantly larger internal pressures and consequently higher internal temperatures than the Earth, therefore conclusions from Earth-centric studies of core formation may be erroneous. Partitioning coefficients for many of the relevant elements (e.g. Fe, Ni, Si, O, etc.) are available in the literature, but only to relatively low pressures. The relevant pressures for super-Earths are significantly larger. However, data on Fe-O-Ni-Si partitioning at pressures (200-500 GPa) and temperatures relevant to super-Earths have been measured by laser-induced shocks with the ZBL laser at Sandia National Laboratory with a method described in [2]. We will present a model which integrates this data with lower pressure partition coefficients from the literature (e.g. [3],[4],[5]), with special emphasis on Fe and O, to describe partitioning behavior at high pressures and discuss its implications for core size and composition on rocky super-Earths. [1] Ringwood, A.E. (1977) Geochem. J. 11, 111-135. [2] Remo, J.L., Petaev, M.I., Jacobsen, S. B. (2008) LPSC abstract, 1420. [3] Frost, D.J. et al. (2010) JGR, B02202. [4] Kombayashi, T. (2014) JGR, 4164-4177. [5] Rubie, D.C. et al. (2011) EPSL, 301, 31-42. [5

  18. Heterogeneity and anisotropy of Earth's inner core

    NARCIS (Netherlands)

    Deuss, Arwen

    2014-01-01

    Seismic observations provide strong evidence that Earth's inner core is anisotropic, with larger velocity in the polar than in the equatorial direction. The top 60-80 km of the inner core is isotropic; evidence for an innermost inner core is less compelling. The anisotropy is most likely due to alig

  19. Heterogeneity and anisotropy of Earth's inner core

    NARCIS (Netherlands)

    Deuss, Arwen

    2014-01-01

    Seismic observations provide strong evidence that Earth's inner core is anisotropic, with larger velocity in the polar than in the equatorial direction. The top 60-80 km of the inner core is isotropic; evidence for an innermost inner core is less compelling. The anisotropy is most likely due to

  20. A conceptual model for kimberlite emplacement by solitary interfacial mega-waves on the core mantle boundary

    Science.gov (United States)

    Sim, B. L.; Agterberg, F. P.

    2006-07-01

    If convection in the Earth's liquid outer core is disrupted, degrades to turbulence and begins to behave in a chaotic manner, it will destabilize the Earth's magnetic field and provide the seeds for kimberlite melts via turbulent jets of silicate rich core material which invade the lower mantle. These (proto-) melts may then be captured by extreme amplitude solitary nonlinear waves generated through interaction of the outer core surface with the base of the mantle. A pressure differential behind the wave front then provides a mechanism for the captured melt to ascend to the upper mantle and crust so quickly that emplacement may indirectly promote a type of impact fracture cone within the relatively brittle crust. These waves are very rare but of finite probability. The assumption of turbulence transmission between layers is justified using a simple three-layer liquid model. The core derived melts eventually become frozen in place as localised topographic highs in the Mohorovicic discontinuity (Moho), or as deep rooted intrusive events. The intrusion's final composition is a function of melt contamination by two separate sources: the core contaminated mantle base and subducted Archean crust. The mega-wave hypothesis offers a plausible vehicle for early stage emplacement of kimberlite pipes and explains the age association of diamondiferous kimberlites with magnetic reversals and tectonic plate rearrangements.

  1. Lattice thermal conductivity of MgSiO3 perovskite and post-perovskite at the core-mantle boundary

    Science.gov (United States)

    Ohta, K.; Yagi, T.; Taketoshi, N.; Hirose, K.; Komabayashi, T.; Baba, T.; Ohishi, Y.; Hernlund, J. W.

    2011-12-01

    Heat in the Earth's interior is transported dominantly by convection in the mantle and core, and by conduction at thermal boundary layers. The thermal conductivity of the bottom thermal boundary layer of the mantle determines the magnitude of heat flux from the core, and is intimately related to the formation of mantle plumes, the long-term thermal evolution of both mantle and core, and the driving force for generation of the geomagnetic field (Lay et al. 2008). However, the thermal conductivity and diffusivity have been poorly constrained at the high pressures of Earth's lowermost mantle. Previous estimates of the thermal conductivity in this region ranged widely between 5 and 30 W/m/K, and it has been often assumed to be 10 W/m/K (Lay et al. 2006). The lattice thermal diffusivity of MgSiO3 perovskite, a primary mineral in the Earth's lower mantle, has only been measured at 1 bar (Osako and Ito 1991). And the thermal diffusivity of post-perovskite has not been investigated so far. We measured the lattice component of thermal diffusivities of both MgSiO3 perovskite and post-perovskite to 144 GPa using a light pulse thermoreflectance technique in a diamond anvil cell (Yagi et al. 2011). The estimated lattice thermal conductivity of perovskite-dominant lowermost mantle is about 9 W/m/K, while post-perovskite-dominant one exhibits ~50% higher diffusivity than perovskite at equivalent pressure. Since many previous calculations assumed a lowermost mantle conductivity of 10 W/m/K, compatible with values obtained in this study, the present findings do not significantly alter the magnitude of heat flow from the core estimated using the post-perovskite double-crossing model (e.g., Lay et al. 2006). Indeed, the present results continue to support the notion of high core-mantle boundary heat flow along with a large degree of secular cooling necessary to sustain a geodynamo even in the absence of an inner core.

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

    Science.gov (United States)

    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.

  3. Slow differential rotation of the Earth's inner core indicated by temporal changes in scattering

    Science.gov (United States)

    Vidale; Dodge; Earle

    2000-05-25

    The finding that the Earth's inner core might be rotating faster than the mantle has important implications for our understanding of core processes, including the generation of the Earth's magnetic field. But the reported signal is subtle--a change of about 0.01 s per year in the separation of two seismic waves with differing paths through the core. Subsequent studies of such data have generally supported the conclusion that differential rotation exists, but the difficulty of accurately locating historic earthquakes and possible biases induced by strong lateral variations in structure near the core-mantle boundary have raised doubt regarding the proposed inner-core motion. Also, a study of free oscillations constrained the motion to be relatively small compared to previous estimates and it has been proposed that the interaction of inner-core boundary topography and mantle heterogeneity might lock the inner core to the mantle. The recent detection of seismic waves scattered in the inner core suggests a simple test of inner-core motion. Here we compare scattered waves recorded in Montana, USA, from two closely located nuclear tests at Novaya Zemlya, USSR, in 1971 and 1974. The data show small but coherent changes in scattering which point toward an inner-core differential rotation rate of 0.15 degrees per year--consistent with constraints imposed by the free-oscillation data.

  4. Ultra-low velocity zone heterogeneities at the core-mantle boundary from diffracted PKKPab waves

    Science.gov (United States)

    Ma, Xiaolong; Sun, Xinlei

    2017-08-01

    Diffracted waves around Earth's core could provide important information of the lowermost mantle that other seismic waves may not. We examined PKKPab diffraction waves from 52 earthquakes occurring at the western Pacific region and recorded by USArray to probe the velocity structure along the core-mantle boundary (CMB). These diffracted waves emerge at distances up to 10° past the theoretical cutoff epicentral distance and show comparable amplitudes. We measured the ray parameters of PKKPab diffraction waves by Radon transform analysis that is suitable for large-aperture arrays. These ray parameters show a wide range of values from 4.250 to 4.840 s/deg, suggesting strong lateral heterogeneities in sampling regions at the base of the mantle. We further estimated the P-wave velocity variations by converting these ray parameters and found the CMB regions beneath the northwestern edge of African Anomaly (Ritsma et al. in Science 286:1925-1928, 1999) and southern Sumatra Islands exhibit velocity reductions up to 8.5% relative to PREM. We suggest that these low velocity regions are Ultra-low velocity zones, which may be related to partial melt or iron-enriched solids.[Figure not available: see fulltext.

  5. High-pressure phase of brucite stable at Earth's mantle transition zone and lower mantle conditions

    Science.gov (United States)

    Hermann, Andreas; Mookherjee, Mainak

    2016-12-01

    We investigate the high-pressure phase diagram of the hydrous mineral brucite, Mg(OH)2, using structure search algorithms and ab initio simulations. We predict a high-pressure phase stable at pressure and temperature conditions found in cold subducting slabs in Earth’s mantle transition zone and lower mantle. This prediction implies that brucite can play a much more important role in water transport and storage in Earth’s interior than hitherto thought. The predicted high-pressure phase, stable in calculations between 20 and 35 GPa and up to 800 K, features MgO6 octahedral units arranged in the anatase–TiO2 structure. Our findings suggest that brucite will transform from a layered to a compact 3D network structure before eventual decomposition into periclase and ice. We show that the high-pressure phase has unique spectroscopic fingerprints that should allow for straightforward detection in experiments. The phase also has distinct elastic properties that might make its direct detection in the deep Earth possible with geophysical methods.

  6. Archimedean Proof of the Physical Impossibility of Earth Mantle Convection

    CERN Document Server

    Herndon, J Marvin

    2010-01-01

    Eight decades ago, Arthur Holmes introducted the idea of mantle convection as a mechanism for continental drift. Five decades ago, continental drift was modified to become plate tectonics theory, which included mantle convection as an absolutely critical component. Using the submarine design and operation concept of "neutral buoyancy", which follows from Archimedes' discoveries, the concept of mantle convection is proven to be incorrect, concomitantly refuting plate tectonics, refuting all mantle convection models, and refuting all models that depend upon mantle convection.

  7. The geochemical constraints on Earth's accretion and core formation (Invited)

    Science.gov (United States)

    Rudge, J. F.; Kleine, T.; Bourdon, B.

    2010-12-01

    There are now a wide range of geochemical observations that can be used to place constraints on Earth's first hundred million years. During this time the Earth accreted through collisions between numerous planetary embryos, and these collisions are thought to have caused significant melting and segregation of metal, forming the Earth's core. Information on the pressure, temperature, and oxygen fugacity conditions of core formation can be obtained from the abundances of siderophile elements in Earth's mantle and high pressure partitioning experiments. Timing information can be obtained from isotopic measurements, notably Hf-W and U-Pb. Here we present a simple geochemical box model that can be used to provide constraints on Earth's accretion and core formation. A key parameter in the model is the degree of equilibration during metal-silicate segregation. Existing models have shown that the siderophile element abundances are consistent with full equilibration in a deep magma ocean, with an increase in oxygen fugacity during accretion. Here we show that the siderophile element abundances are equally consistent with scenarios involving partial equilibration. The Hf-W isotopic observations constrain the degree of equilibration to be at least 36%. The timing constraints depend strongly on the degree of equilibration, but nevertheless bounds can be placed on the timing of Earth's accretion. With full equilibration, the Hf-W observations imply a rapid early accretion stage (at least 80% of Earth accreting within 35 Myr), but with partial equilibration accretion may be much more protracted. If Pb partitions into Earth’s core, the U-Pb observations can be used to constrain the late stages of accretion, and are consistent with the final 10% of Earth’s accretion occurring during the Moon-forming giant impact at ~4.45Ga.

  8. Earth Inner Core Periodic Motion due to Pressure Difference Induced by Tidal Acceleration

    CERN Document Server

    Wolf, M

    2013-01-01

    The inner structure of the earth is still a topic of discussion. Seismic measurements showed a structure of solid, liquid, solid which describes the mantle, outer core and inner core with the inner core in the center. The analysis of waveform doublets suggests now that the inner core is out of center and even of faster rotation than the mantel and crust. From the sum of Buoyancy and Gravity on the earth inner core, the position energy is plotted and together with the tangential tidal acceleration, it is derived that Earth Inner Core cannot be in a center position without additional force. The Earth Core System is explained as Hydrodynamic Bearing. The Eccentricities out of nutation due to the effects from the sun and moon are calculated as an approximation.

  9. Correction and update to 'The earth's C21 and S21 gravity coefficients and the rotation of the core'

    Science.gov (United States)

    Wahr, John

    1990-01-01

    Wahr (1987) used satellite constraints on C21 and S21 (the spherical harmonic coefficients of the earth's external gravitational potential) to infer certain properties of the core and core/mantle boundary. It is shown here, contrary to the claim by Wahr, that it is not possible to use C21 and S21 to placed bounds on the core's products of inertia. As a result, Wahr's constraints on the l = 2, m = 1 components of the core/mantle boundary topography and on the angular orientation of the inner core with respect to the earth's rotation vector are not justified. On the other hand, Wahr's conclusions about the time-averaged torque between the core and mantle and the resulting implications for the l = 2, m = 1 components of fluid pressure at the top of the core can be strengthened. Wahr's conclusions about the mean rotational flow in the core are unaltered.

  10. Mantle Dynamics in Super-Earths: Post-Perovskite Rheology and Self-Regulation of Viscosity

    CERN Document Server

    Tackley, Paul J; Brodholt, John P; Dobson, David P; Valencia, Diana

    2012-01-01

    Simple scalings suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigor in the deep mantle. According to conventional thinking, this might result in no convection in a super-Earth's deep mantle. Here we evaluate this. First, we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of to a pressure of 1 TPa. The activation volume for diffusion creep becomes very low at very high pressure, but nevertheless for the largest super-Earths the viscosity along an adiabat may approach 1030 Pa s in the deep mantle. Second, we use these calculated values in numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induce...

  11. Viscosity of the earth's core.

    Science.gov (United States)

    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.

  12. Rapidly changing flows in the Earth's core

    DEFF Research Database (Denmark)

    Olsen, Nils; Mandea, M.

    2008-01-01

    A large part of the Earth's magnetic field is generated by fluid motion in the molten outer core(1). As a result of continuous satellite measurements since 1999, the core magnetic field and its recent variations can now be described with a high resolution in space and time(2). These data have rec...... of future numerical models of the geodynamo....

  13. Effect of width, amplitude, and position of a core mantle boundary hot spot on core convection and dynamo action

    CERN Document Server

    Dietrich, Wieland; Hori, Kumiko

    2015-01-01

    Within the fluid iron cores of terrestrial planets, convection and the resulting generation of global magnetic fields are controlled by the overlying rocky mantle. The thermal structure of the lower mantle determines how much heat is allowed to escape the core. Hot lower mantle features, such as the thermal footprint of a giant impact or hot mantle plumes, will locally reduce the heat flux through the core mantle boundary (CMB), thereby weakening core convection and affecting the magnetic field generation process. In this study, we numerically investigate how parametrised hot spots at the CMB with arbitrary sizes, amplitudes, and positions affect core convection and hence the dynamo. The effect of the heat flux anomaly is quantified by changes in global flow symmetry properties, such as the emergence of equatorial antisymmetric, axisymmetric (EAA) zonal flows. For purely hydrodynamic models, the EAA symmetry scales almost linearly with the CMB amplitude and size, whereas self-consistent dynamo simulations typ...

  14. Mantle convection and the distribution of geochemical reservoirs in the silicate shell of the Earth

    Science.gov (United States)

    Walzer, Uwe; Hendel, Roland

    2010-05-01

    . Independently of the varying individual runs, our model shows that the total mass of the present-day continents is not generated in a single process at the beginning of the thermal evolution of the Earth but in episodically distributed processes in the course of geological time. This is in accord with observation. Finally, we present results regarding the numerical method, implementation, scalability and performance. References [1] Condie, K. C., Episodie continental growth models: Afterthoughts and extensions, Tectonophysics, 322 (2000), 153-162. [2] Davidson, J. P. and Arculus, R. J., The significance of Phanerozoic arc magmatism in generating continental crust, in Evolution and Differentiation of the Continental Crust, edited by M. Brown and T. Rushmer (2006), 135-172, Cambridge Univ. Press, Cambridge, UK. [3] Hofmann, A. W., Sampling mantle heterogeneity through oceanic basalts: Isotopes and trace elements, in Treatise on Geochemistry, Vol. 2: The Mantle and the Core, edited by R. W. Carlson (2003), 61-101, Elsevier, Amsterdam. [4] Rollinson, H., Crustal generation in the Archean, in Evolution and Differentiation of the Continental Crust, edited by M. Brown and T. Rushmer (2006), 173-230, Cambridge Univ. Press, Cambridge, UK: [5] Taylor, S. R. and McLennan, S. M., Planetary Crusts. Their Composition, Origin and Evolution. (2009), 1-378, Cambridge Univ. Press, Cambridge, UK. [6] Walzer, U. and Hendel, R., Mantle convection and evolution with growing continents. J. Geophys. Res. 113 (2008), B09405, doi: 10.1029/2007JB005459 [7] http://www.igw.uni-jena.de/geodyn

  15. Viscosity of Earth's Outer Core

    CERN Document Server

    Smylie, D E

    2007-01-01

    A viscosity profile across the entire fluid outer core is found by interpolating between measured boundary values, using a differential form of the Arrhenius law governing pressure and temperature dependence. The discovery that both the retrograde and prograde free core nutations are in free decay (Palmer and Smylie, 2005) allows direct measures of viscosity at the top of the outer core, while the reduction in the rotational splitting of the two equatorial translational modes of the inner core allows it to be measured at the bottom. We find 2,371 plus/minus 1,530 Pa.s at the top and 1.247 plus/minus 0.035 x 10^11 Pa.s at the bottom. Following Brazhkin (1998) and Brazhkin and Lyapin (2000) who get 10^2 Pa.s at the top, 10^11 Pa.s at the bottom, by an Arrhenius extrapolation of laboratory experiments, we use a differential form of the Arrhenius law to interpolate along the melting temperature curve to find a viscosity profile across the outer core. We find the variation to be closely log-linear between the meas...

  16. On effect of precession-induced flows in the liquid core for early Earth's history

    Directory of Open Access Journals (Sweden)

    S. L. Shalimov

    2006-01-01

    Full Text Available Secondary and tertiary flow patterns seen in experiments simulating flow in the Earth's liquid core induced by luni-solar precession of the solid mantle (Vanyo et al., 1995 hint at the development of non-axisymmetric columnar periodic structures. A simple interpretation of the structure formation is presented in a hydrodynamic approach. It is suggested that if similar flow patterns can occur in the Earth's liquid core enclosed into precessing and rotating mantle then kinematic of the flows may be regarded as a possible geodynamo mechanism for early Earth's history (before the solid core formation.

  17. How Irreversible Heat Transport Processes Drive Earth's Interdependent Thermal, Structural, and Chemical Evolution Providing a Strongly Heterogeneous, Layered Mantle

    Science.gov (United States)

    Hofmeister, A.; Criss, R. E.

    2013-12-01

    Because magmatism conveys radioactive isotopes plus latent heat rapidly upwards while advecting heat, this process links and controls the thermal and chemical evolution of Earth. We present evidence that the lower mantle-upper mantle boundary is a profound chemical discontinuity, leading to observed heterogeneities in the outermost layers that can be directly sampled, and construct an alternative view of Earth's internal workings. Earth's beginning involved cooling via explosive outgassing of substantial ice (mainly CO) buried with dust during accretion. High carbon content is expected from Solar abundances and ice in comets. Reaction of CO with metal provided a carbide-rich core while converting MgSiO3 to olivine via oxidizing reactions. Because thermodynamic law (and buoyancy of hot particles) indicates that primordial heat from gravitational segregation is neither large nor carried downwards, whereas differentiation forced radioactive elements upwards, formation of the core and lower mantle greatly cooled the Earth. Reference conductive geotherms, calculated using accurate and new thermal diffusivity data, require that heat-producing elements are sequestered above 670 km which limits convection to the upper mantle. These irreversible beginnings limit secular cooling to radioactive wind-down, permiting deduction of Earth's inventory of heat-producing elements from today's heat flux. Coupling our estimate for heat producing elements with meteoritic data indicates that Earth's oxide content has been underestimated. Density sorting segregated a Si-rich, peridotitic upper mantle from a refractory, oxide lower mantle with high Ca, Al and Ti contents, consistent with diamond inclusion mineralogy. Early and rapid differentiation means that internal temperatures have long been buffered by freezing of the inner core, allowing survival of crust as old as ca.4 Ga. Magmatism remains important. Melt escaping though stress-induced fractures in the rigid lithosphere imparts a

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

    Science.gov (United States)

    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

  19. Investigating the translation of Earth's inner core

    DEFF Research Database (Denmark)

    Day, Elizabeth A; Cormier, Vernon F; Geballe, Zachary M;

    2012-01-01

    The Earth’s inner core provides unique insights into processes that are occurring deep within our Earth today, as well as processes that occurred in the past. The seismic structure of the inner core is complex, and is dominated by anisotropic and isotropic differences between the Eastern...... and Western ‘hemispheres’ of the inner core. Recent geodynamical models suggest that this hemispherical dichotomy can be explained by a fast translation of the inner core. In these models one side of the inner core is freezing, while the other side is melting, leading to the development of different seismic...... properties on either side of the inner core. A simple translating model of the inner core, however, does not seem to easily explain all of the seismically observed features, including the innermost inner core; the observed sharp lateral gradient in seismic properties between the two hemispheres...

  20. Mixing properties of thermal convection in the earth's mantle

    NARCIS (Netherlands)

    Schmalzl, J.T.

    1996-01-01

    The structure of mantle convection will greatly influence the generation and the survival of compositional heterogeneities. Conversely, geochemical observations can be used to obtain information about heterogeneities in the mantle and then, with certain model assumptions, information about the patte

  1. Heat Loss of the Earth and Energy Budget of the Mantle

    Science.gov (United States)

    Mareschal, J.; Jaupart, C.

    2009-05-01

    average value is independent of the size of the sampling window. Estimates of Moho heat flux beneath stable cratons obtained by several independent methods are within a range of 12-18 mW m-2. We estimate the continental heat loss to be 14±1 TW. Therefore, we obtain that the total heat loss of the Earth is 46±3 TW. Because continental heat production accounts for about half of the continental heat loss, i.e. 7 TW, the total heat loss from the mantle is 39±3 TW. It must be accounted for by radio-active heat production in the mantle, heat flux from the core, and secular cooling of the mantle. All these components are poorly constrained. The bulk silicate earth model suggests that the mantle heat production is 13±4 TW, and it is estimated that the core must lose 8±4 TW to maintain the geodynamo. The resulting estimates for the mantle Urey number are in the range 0.2-0.5.

  2. Differentiation and delivery of an enriched deep mantle reservoir during iron descent to the core.

    Science.gov (United States)

    Weeraratne, D. S.; Fleck, J.; Rains, C.; McGeehee, J.; Klein, S. M.; Rincon, J. M.; Olson, P.

    2015-12-01

    Planetary interior differentiation from a bulk silicate chondrite composition is shown by geochemical studies to occur early in planetary evolution producing separated enriched and depleted mantle reservoirs with important implications for the mantle and crustal compositions that we observe today. The absence of an enriched component at the Earth's surface, however, and has lead to implications of a reservoir at the base of the mantle, but the mechanism of differentiation or downward transport of this enriched material is unknown. Here we present results from laboratory fluid dynamic experiments using liquid metal to show that metal-silicate segregation from a metal pond which forms in a magma ocean following meteorite impacts will entrain magma ocean silicate material to the base of the mantle during metal descent to the core. We model liquid iron and silicate magma using emulsified liquid metal gallium in high viscosity glucose solutions which provide the buoyancy ratios and Stokes flow regimes expected for planetary interiors. Preliminary results indicate that emulsion metal droplets sink together as a Rayleigh-Taylor instability and forms a trailing conduit of buoyant solution. Metal droplets form a pile at the base of the box where the low density solution collects, grows, and initially rises back to the surface as a thermo-chemical plume. The remaining buoyant material, which surrounds each droplet, slowly migrates upwards and rises out of the metal pile. These physical experiments scaled to planetary interiors provide important tests of purely theoretical or numerical approximations and indicate that metal-silicate segregation is consistent with rapid core formation times and contributes simultaneously to complex mantle differentiation at all depths. Our observation of entrainment of a silicate-metal conduit provides a model for differentiation and sequestration of an enriched reservoir from a magma ocean to the base of the mantle. The composition and

  3. Partitioning of oxygen during core formation on the Earth and Mars.

    Science.gov (United States)

    Rubie, David C; Gessmann, Christine K; Frost, Daniel J

    2004-05-01

    Core formation on the Earth and Mars involved the physical separation of metal and silicate, most probably in deep magma oceans. Although core-formation models explain many aspects of mantle geochemistry, they have not accounted for the large differences observed between the compositions of the mantles of the Earth (approximately 8 wt% FeO) and Mars (approximately 18 wt% FeO) or the smaller mass fraction of the martian core. Here we explain these differences as a consequence of the solubility of oxygen in liquid iron-alloy increasing with increasing temperature. We assume that the Earth and Mars both accreted from oxidized chondritic material. In a terrestrial magma ocean, 1,200-2,000 km deep, high temperatures resulted in the extraction of FeO from the silicate magma ocean owing to high solubility of oxygen in the metal. Lower temperatures of a martian magma ocean resulted in little or no extraction of FeO from the mantle, which thus remains FeO-rich. The FeO extracted from the Earth's magma ocean may have contributed to chemical heterogeneities in the lowermost mantle, a FeO-rich D" layer and the light element budget of the core.

  4. Melting and Mixing States of the Earth's Mantle after the Moon-Forming Impact

    CERN Document Server

    Nakajima, Miki

    2015-01-01

    The Earth's Moon is thought to have formed by an impact between the Earth and an impactor around 4.5 billion years ago. This impact could have been so energetic that it could have mixed and homogenized the Earth's mantle. However, this view appears to be inconsistent with geochemical studies that suggest that the Earth's mantle was not mixed by the impact. Another plausible outcome is that this energetic impact melted the whole mantle, but the extent of mantle melting is not well understood even though it must have had a significant effect on the subsequent evolution of the Earth's interior and atmosphere. To understand the initial state of the Earth's mantle, we perform giant impact simulations using smoothed particle hydrodynamics (SPH) for three different models: (a) standard: a Mars-sized impactor hits the proto-Earth, (b) fast-spinning Earth: a small impactor hits a rapidly rotating proto-Earth, and (c) sub-Earths: two half Earth-sized planets collide. We use two types of equations of state (MgSiO3 liqui...

  5. A new model for early differentiation and chemical stratification of the Earth's mantle

    Science.gov (United States)

    Rubie, D. C.; Gessmann, C. K.; Frost, D. J.

    2003-04-01

    New experimental data on the solubility of oxygen in liquid Fe-rich alloy enable the geochemical consequences of core formation and the early geochemical evolution of the Earth's mantle to be better constrained. We have studied oxygen solubility in liquid Fe-alloy at 5-23 GPa, 2100--2700 K and variable oxygen fugacities using a multianvil apparatus. At constant oxygen fugacity, O solubility increases with increasing temperature but decreases with increasing pressure. Thus, along a high temperature adiabat (e.g. after formation of a deep magma ocean), oxygen solubility is high at relatively shallow depths (e.g. 3000 K) in a magma ocean result in significant Si being dissolved in liquid Fe-alloy whereas at depths >800--1000 km the solubility starts to decrease again and becomes close to zero at the CMB (Gessmann et al. 2001, EPSL 184, 367). Thus migration of liquid metal during core formation provides a mechanism for enriching the lower part of the mantle in the FeO component, and possibly also in SiO_2, relative to the upper part.

  6. Elastic anisotropy of Earth's inner core.

    Science.gov (United States)

    Belonoshko, Anatoly B; Skorodumova, Natalia V; Rosengren, Anders; Johansson, Börje

    2008-02-08

    Earth's solid-iron inner core is elastically anisotropic. Sound waves propagate faster along Earth's spin axis than in the equatorial plane. This anisotropy has previously been explained by a preferred orientation of the iron alloy hexagonal crystals. However, hexagonal iron becomes increasingly isotropic on increasing temperature at pressures of the inner core and is therefore unlikely to cause the anisotropy. An alternative explanation, supported by diamond anvil cell experiments, is that iron adopts a body-centered cubic form in the inner core. We show, by molecular dynamics simulations, that the body-centered cubic iron phase is extremely anisotropic to sound waves despite its high symmetry. Direct simulations of seismic wave propagation reveal an anisotropy of 12%, a value adequate to explain the anisotropy of the inner core.

  7. Archimedean Proof of the Physical Impossibility of Earth Mantle Convection

    OpenAIRE

    Herndon, J. Marvin

    2010-01-01

    Eight decades ago, Arthur Holmes introducted the idea of mantle convection as a mechanism for continental drift. Five decades ago, continental drift was modified to become plate tectonics theory, which included mantle convection as an absolutely critical component. Using the submarine design and operation concept of "neutral buoyancy", which follows from Archimedes' discoveries, the concept of mantle convection is proven to be incorrect, concomitantly refuting plate tectonics, refuting all ma...

  8. Mixing in mantle convection models with self-consistent plate tectonics and melting and crustal production: Application to mixing in the early Earth

    Science.gov (United States)

    Tackley, Paul

    2016-04-01

    It is generally thought that the early Earth's mantle was hotter than today, which using conventional convective scalings should have led to vigorous convection and mixing. Geochemical observations, however, suggest that mixing was not as rapid as would be expected, leading to the suggestion that early Earth had stagnant lid convection (Debaille et al., EPSL 2013). Additionally, the mantle's thermal evolution is difficult to explain using conventional scalings because early heat loss would have been too rapid, which has led to the hypothesis that plate tectonics convection does not follow the conventional convective scalings (Korenaga, GRL 2003). One physical process that could be important in this context is partial melting leading to crustal production, which has been shown to have the major effects of buffering mantle temperature and carrying a significant fraction of the heat from hot mantle (Nakagawa and Tackley, EPSL 2012), making plate tectonics easier (Lourenco et al., submitted), and causing compositional differentiation of the mantle that can buffer core heat loss (Nakagawa and Tackley, GCubed 2010). Here, the influence of this process on mantle mixing is examined, using secular thermo-chemical models that simulate Earth's evolution over 4.5 billion years. Mixing is quantified both in terms of how rapidly stretching occurs, and in terms of dispersion: how rapidly initially close heterogeneities are dispersed horizontally and vertically through the mantle. These measures are quantified as a function of time through Earth's evolution. The results will then be related to geochemically-inferred mixing rates.

  9. Mantle rock exposures at oceanic core complexes along mid-ocean ridges

    Directory of Open Access Journals (Sweden)

    Ciazela Jakub

    2015-12-01

    Full Text Available The mantle is the most voluminous part of the Earth. However, mantle petrologists usually have to rely on indirect geophysical methods or on material found ex situ. In this review paper, we point out the in-situ existence of oceanic core complexes (OCCs, which provide large exposures of mantle and lower crustal rocks on the seafloor on detachment fault footwalls at slow-spreading ridges. OCCs are a common structure in oceanic crust architecture of slow-spreading ridges. At least 172 OCCs have been identified so far and we can expect to discover hundreds of new OCCs as more detailed mapping takes place. Thirty-two of the thirty-nine OCCs that have been sampled to date contain peridotites. Moreover, peridotites dominate in the plutonic footwall of 77% of OCCs. Massive OCC peridotites come from the very top of the melting column beneath ocean ridges. They are typically spinel harzburgites and show 11.3–18.3% partial melting, generally representing a maximum degree of melting along a segment. Another key feature is the lower frequency of plagioclase-bearing peridotites in the mantle rocks and the lower abundance of plagioclase in the plagioclase-bearing peridotites in comparison to transform peridotites. The presence of plagioclase is usually linked to impregnation with late-stage melt. Based on the above, OCC peridotites away from segment ends and transforms can be treated as a new class of abyssal peridotites that differ from transform peridotites by a higher degree of partial melting and lower interaction with subsequent transient melt.

  10. Core Formation in the Earth and Moon: New Constraints From V, Cr, and Mn Partitioning Experiments

    Science.gov (United States)

    Chabot, N. L.; Agee, C. B.

    2002-05-01

    The mantles of the Earth and Moon are similarly depleted in V, Cr, and Mn relative to the concentrations of these elements in chondritic meteorites [1,2]. The similar depletions have been suggested to be due to a common genesis of the Earth and Moon, with the Moon inheriting its mantle, complete with V, Cr, and Mn depletions, from the Earth during the impact-induced formation of the Moon. We have conducted multi-anvil experiments that systematically examined the effects of pressure, temperature, and silicate and metallic compositions on liquid metal-liquid silicate partitioning of V, Cr, and Mn. Increasing temperature is found to significantly increase the metal-silicate partition coefficients for all three elements. Increasing the S or C content of the metallic liquid also causes the partition coefficients to increase. Silicate composition has an effect consistent with Cr and Mn being divalent and V being trivalent. Over our experimental range of 3-14 GPa, the partitioning behavior of V, Cr, and Mn did not vary with pressure. With the effects of oxygen fugacity, metallic and silicate compositions, temperature and pressure understood, the partition coefficient for each element was expressed as a function of these thermodynamic variables and applied to different core formation scenarios. Our new metal-silicate experimental partitioning data can explain the mantle depletions of V, Cr, and Mn by core formation in a high temperature magma ocean under oxygen fugacity conditions two log units below the iron-wuestite buffer, conditions similar to those proposed by [3] from their metal-magnesiowuestite study. In contrast, more oxidizing conditions proposed in recent core formation models [4] cannot account for the V, Cr, and Mn depletions. Additionally, because we observe little or no pressure effect on V, Cr, and Mn partitioning in our experiments, we conclude that the mantle depletions of these elements during core formation are not dependent on planet size. Accordingly

  11. Simultaneous inversion for the Earth's mantle viscosity and ice mass imbalance in Antarctica and Greenland

    NARCIS (Netherlands)

    Tosi, N.; Sabadini, R.; Marotta, A.M.; Vermeersen, L.L.A.

    2005-01-01

    Redistribution of mass in the Earth due to Pleistocene deglaciation and to present-day glacial melting induces secular changes in the Earth's gravitational field. The Earth is affected today by the former mechanism because of the viscous memory of the mantle and by the latter because of ongoing surf

  12. Global-scale modelling of melting and isotopic evolution of Earth's mantle: Melting modules for TERRA

    NARCIS (Netherlands)

    Van Heck, H.J.; Huw Davies, J.; Elliott, T.; Porcelli, D.

    2016-01-01

    Many outstanding problems in solid-Earth science relate to the geodynamical explanation of geochemical observations. Currently, extensive geochemical databases of surface observations exist, but satisfying explanations of underlying mantle processes are lacking. One way to address these problems is

  13. Zonal flow formation in the Earth's core.

    Science.gov (United States)

    Miyagoshi, Takehiro; Kageyama, Akira; Sato, Tetsuya

    2010-02-11

    Zonal jets are very common in nature. Well-known examples are those in the atmospheres of giant planets and the alternating jet streams found in the Earth's world ocean. Zonal flow formation in nuclear fusion devices is also well studied. A common feature of these zonal flows is that they are spontaneously generated in turbulent systems. Because the Earth's outer core is believed to be in a turbulent state, it is possible that there is zonal flow in the liquid iron of the outer core. Here we report an investigation at the current low-viscosity limit of numerical simulations of the geodynamo. We find a previously unknown convection regime of the outer core that has a dual structure comprising inner, sheet-like radial plumes and an outer, westward cylindrical zonal flow. We numerically confirm that the dual-convection structure with such a zonal flow is stable under a strong, self-generated dipole magnetic field.

  14. The iron alloys of the Earth's core

    Science.gov (United States)

    Caracas, R.; Verstraete, M. J.; Vargas Calderon, A.; Labrosse, S.; Hernlund, J. W.; Gomi, H.; Ohta, K.; Hirose, K.

    2012-12-01

    We estimate the necessary amount of several light elements - C, S, P, O, Si - as major alloying components to match the observed seismic properties of the Earth's inner core. For this we compute the elastic constants tensors and determine the seismic properties of Fe3X compounds, with X = C, S, P, O and Si, using first-principles calculations. Assuming linear relations and similar temperature corrections of velocities, we obtain as most reasonable silicon and oxygen. We perform the same exercise on Fe-Ni alloys and see a minor effect of Ni on the seismic properties of iron. We compute the electrical conductivity of iron and iron alloys at Earth's core conditions from electron-phonon coupling in the ABINIT implementation. We find an excellent agreement with experimental results for pure hcp iron below 1 mbars. We confidently use our results up to core pressure conditions. We show that the conductivity exhibits saturation at high pressures. We treat in detail the effect of Si on hcp iron and show a marked saturation effect, an increase in anisotropy and a strong dependence with the substitution pattern. The computed values suggest that the outer core should have conductivities in excess of 90 W/K/m, which is considerably larger than current estimates. This implies an inner core younger than 1 bil. years and stratification of the outer core.

  15. Metal-silicate Partitioning and Its Role in Core Formation and Composition on Super-Earths

    Science.gov (United States)

    Schaefer, Laura; Jacobsen, Stein B.; Remo, John L.; Petaev, M. I.; Sasselov, Dimitar D.

    2017-02-01

    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 the 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.

  16. Identifying regions of strong scattering at the core-mantle boundary from analysis of PKKP precursor energy

    Science.gov (United States)

    Rost, S.; Earle, P.S.

    2010-01-01

    We detect seismic scattering from the core-mantle boundary related to the phase PKKP (PK. KP) in data from small aperture seismic arrays in India and Canada. The detection of these scattered waves in data from small aperture arrays is new and allows a better characterization of the fine-scale structure of the deep Earth especially in the southern hemisphere. Their slowness vector is determined from array processing allowing location of the heterogeneities at the core-mantle boundary using back-projection techniques through 1D Earth models. We identify strong scattering at the core-mantle boundary (CMB) beneath the Caribbean, Patagonia and the Antarctic Peninsula as well as beneath southern Africa. An analysis of the scattering regions relative to sources and receivers indicates that these regions represent areas of increased scattering likely due to increased heterogeneities close to the CMB. The 1. Hz array data used in this study is most sensitive to heterogeneity with scale lengths of about 10. km. Given the small size of the scatterers, a chemical origin of the heterogeneities is likely. By comparing the location of the fine-scale heterogeneity to geodynamical models and tomographic images, we identify different scattering mechanisms in regions related to subduction (Caribbean and Patagonia) and dense thermo chemical piles (Southern Africa). ?? 2010 Elsevier B.V.

  17. Mapping the mass distribution of Earth's mantle using satellite-derived gravity gradients

    Science.gov (United States)

    Panet, Isabelle; Pajot-Métivier, Gwendoline; Greff-Lefftz, Marianne; Métivier, Laurent; Diament, Michel; Mandea, Mioara

    2014-02-01

    The dynamics of Earth's mantle are not well known. Deciphering mantle flow patterns requires an understanding of the global distribution of mantle density. Seismic tomography has been used to derive mantle density distributions, but converting seismic velocities into densities is not straightforward. Here we show that data from the GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission can be used to probe our planet's deep mass structure. We construct global anomaly maps of the Earth's gravitational gradients at satellite altitude and use a sensitivity analysis to show that these gravitational gradients image the geometry of mantle mass down to mid-mantle depths. Our maps highlight north-south-elongated gravity gradient anomalies over Asia and America that follow a belt of ancient subduction boundaries, as well as gravity gradient anomalies over the central Pacific Ocean and south of Africa that coincide with the locations of deep mantle plumes. We interpret these anomalies as sinking tectonic plates and convective instabilities between 1,000 and 2,500km depth, consistent with seismic tomography results. Along the former Tethyan Margin, our data also identify an east-west-oriented mass anomaly likely in the upper mantle. We suggest that by combining gravity gradients with seismic and geodynamic data, an integrated dynamic model for Earth can be achieved.

  18. Implications for Core Formation of the Earth from High Pressure-Temperature Au Partitioning Experiments

    Science.gov (United States)

    Danielson, L. R.; Sharp, T. G.; Hervig, R. L.

    2005-01-01

    Siderophile elements in the Earth.s mantle are depleted relative to chondrites. This is most pronounced for the highly siderophile elements (HSEs), which are approximately 400x lower than chondrites. Also remarkable is the relative chondritic abundances of the HSEs. This signature has been interpreted as representing their sequestration into an iron-rich core during the separation of metal from silicate liquids early in the Earth's history, followed by a late addition of chondritic material. Alternative efforts to explain this trace element signature have centered on element partitioning experiments at varying pressures, temperatures, and compositions (P-T-X). However, first results from experiments conducted at 1 bar did not match the observed mantle abundances, which motivated the model described above, a "late veneer" of chondritic material deposited on the earth and mixed into the upper mantle. Alternatively, the mantle trace element signature could be the result of equilibrium partitioning between metal and silicate in the deep mantle, under P-T-X conditions which are not yet completely identified. An earlier model determined that equilibrium between metal and silicate liquids could occur at a depth of approximately 700 km, 27(plus or minus 6) GPa and approximately 2000 (plus or minus 200) C, based on an extrapolation of partitioning data for a variety of moderately siderophile elements obtained at lower pressures and temperatures. Based on Ni-Co partitioning, the magma ocean may have been as deep as 1450 km. At present, only a small range of possible P-T-X trace element partitioning conditions has been explored, necessitating large extrapolations from experimental to mantle conditions for tests of equilibrium models. Our primary objective was to reduce or remove the additional uncertainty introduced by extrapolation by testing the equilibrium core formation hypothesis at P-T-X conditions appropriate to the mantle.

  19. Rare earth elements in CO2-fluid inclusions in mantle lherzolite

    Institute of Scientific and Technical Information of China (English)

    Jiuhua Xu; Yuling Xie; Lijun Wang; Heping Zhu; Liquan Wang

    2003-01-01

    Trace elements including REE (Rare Earth Elements) in fluid inclusions in lherzolite, olivine, orthopyroxene, and clinopy-roxene have been determined by heating-decrepitation and ICP-MS (Element Type Inductively Coupled Plasma-Mass Spectrometry)method. Normalized CO2 fluid/chondrite data show that mantle fluids are rich in REEs, especially LREEs (Light Rare Earth Ele-ments), several times or dozen times higher than mantle rocks and mantle mininerals. There are close relationships among the REEdata of olivine, orthopyroxene, clinopyroxene and lherzolite. Compared to the data of chemical dissolution method, it is believed thatREE data obtained from heating-decrepitation and ICP-MS technique are contributed by CO2 fluid inclusions. About 60% (massfraction) of tiny inclusions are observed not to be decrepitated above 1000℃, so REE data obtained are only contributed by decrepi-tated inclusions. Mantle fluids rich in LREE play an important role in mantle metasomatism, partial melting and mineralization.

  20. RHUM-RUM investigates La Réunion mantle plume from crust to core

    Science.gov (United States)

    Sigloch, Karin; Barruol, Guilhem

    2013-04-01

    RHUM-RUM (Réunion Hotspot and Upper Mantle - Réunions Unterer Mantel) is a French-German passive seismic experiment designed to image an oceanic mantle plume - or lack of plume - from crust to core beneath La Réunion Island, and to understand these results in terms of material, heat flow and plume dynamics. La Réunion hotspot is one of the most active volcanoes in the world, and its hotspot track leads unambiguously to the Deccan Traps of India, one of the largest flood basalt provinces on Earth, which erupted 65 Ma ago. The genesis and the origin at depth of the mantle upwelling and of the hotspot are still very controversial. In the RHUM-RUM project, 57 German and French ocean-bottom seismometers (OBS) are deployed over an area of 2000 km x 2000 km2 centered on La Réunion Island, using the "Marion Dufresne" and "Meteor" vessels. The one-year OBS deployment (Oct. 2012 - Oct. 2013) will be augmented by terrestrial deployments in the Iles Eparses in the Mozambique Channel, in Madagascar, Seychelles, Mauritius, Rodrigues and La Réunion islands. A significant number of OBS will be also distributed along the Central and South West Indian Ridges to image the lower-mantle beneath the hotspot, but also to provide independent opportunity for the study of these slow to ultra-slow ridges and of possible plume-ridge interactions. RHUM-RUM aims to characterize the vertically ascending flow in the plume conduit, as well as any lateral flow spreading into the asthenosphere beneath the western Indian Ocean. We want to establish the origin of the heat source that has been fueling this powerful hotspot, by answering the following questions: Is there a direct, isolated conduit into the deepest mantle, which sources its heat and material from the core-mantle boundary? Is there a plume connection to the African superswell at mid-mantle depths? Might the volcanism reflect merely an upper mantle instability? RHUM-RUM also aims at studying the hotspot's interaction with the

  1. Numerical modelling of the plasticity of Ringwoodite under transition zone conditions in the Earth's mantle

    Science.gov (United States)

    Ritterbex, S.; Carrez, P.; Gouriet, K.; Cordier, P.

    2013-12-01

    (Mg,Fe)2SiO4 ringwoodite spinel, a high-pressure polymorph of the main upper mantle constituent olivine, is considered to be the weakest phase in the lower half of the transition zone, generally a confined region between 410-660 km depth in the Earth's mantle which couples the upper and lower mantle. It is therefore believed to be an important phase in subducting slabs from 510-660 km depth. Knowledge of ductile deformation mechanisms of ringwoodite may therefore provide a framework for a better understanding of solid-state flow within the transition zone over which the viscosity is thought to increase rapidly. The glide of linear defects or dislocations in a crystal is one of the effective mechanisms responsible for creep of mantle minerals such as ringwoodite. A description of the core structures of the active dislocations is essentiel to obtain information about the dislocation mobility and hence the rate of deformation controlled by glide. Computer simulations at the atomic-scale are used to investigate the structure and properties of dislocation cores of Mg2SiO4 ringwoodite at a pressure of 20 GPa1. This approach is a good alternative to study intracrystalline plasticity since experimental study is more than challanging at the pressure and temperature conditions of the Earth's transition zone. The Peierls2-Nabarro3-Galerkin approach is used to understand and predict the plastic properties of Mg2SiO4 ringwoodite at 20 GPa4. In this semi-continuum model, the dislocation is described as a distribution of infinitesimal mismatches across the assumed glide planes. Ballancing the elastic forces within the crystal with the non-elastic interaction forces across the glide plane provide information about the localization of the planar core. The non-elastic forces across the glide plane can be deduced from atomic scale density functional theory based calculations of generalized stacking fault surfaces, which are energy landscapes due to the general stacking of one half of

  2. The earth's C21 and S21 gravity coefficients and the rotation of the core

    Science.gov (United States)

    Wahr, John M.

    1987-01-01

    Observational results for the earth's C21 and S21 gravity coefficients can be used to constrain the mean equatorial rotation of the core with respect to the mantle. Current satellite gravity solutions suggest the equatorial rotation rate is no larger than 1 x 10 to the -7th times the earth's diurnal spin rate, a limit more than one order of magnitude smaller than the polar rotation rate inferred from the westward drift of the earth's magnetic field. The next generation gravity solutions should improve this constraint by more than one order of magnitude. Implications for the fluid pressure at the core-mantle boundary and for the shape of that boundary are discussed.

  3. Seismological mapping of fine structure near the base of the Earth's mantle

    Science.gov (United States)

    Vidale, J.E.; Benz, H.M.

    1993-01-01

    THE Earth's core-mantle boundary (CMB) juxtaposes liquid iron and crystalline silicates, and is a region of large vertical thermal gradients. The D??? region, which extends up to 200-300 km above the CMB, often has elevated shear-wave velocity and suggestions of lateral variations in structure1. Recent improvements in our ability to assemble and analyse records from regional seismic networks have allowed us to examine long profiles of travel times, amplitudes and waveforms from more than a thousand short-period seismometers2. We observe, across Canada and the United States, P waves that have grazed the CMB from the powerful nuclear test in Lop Nor, China, on 21 May 1992. First-arrival travel times and large secondary arrivals are consistent with a 1.5% compressional velocity increase with depth ???130 km above the CMB - about half the thickness of D??? in this locality3. Our observations, together with evidence for the absence of such a thin, fast layer in neighbouring regions, suggest the presence of lateral heterogeneity in composition or phase at the base of the mantle.

  4. Highly Siderophile Elements in the Earth's Mantle as a Clock for the Moon-forming Impact

    CERN Document Server

    Jacobson, Seth A; Raymond, Sean N; O'Brien, David P; Walsh, Kevin J; Rubie, David C

    2015-01-01

    According to the generally accepted scenario, the last giant impact on the Earth formed the Moon and initiated the final phase of core formation by melting the Earth's mantle. A key goal of geochemistry is to date this event, but different ages have been proposed. Some argue for an early Moon-forming event, approximately 30 million years (Myr) after the condensation of the first solids in the Solar System, whereas others claim a date later than 50 Myr (and possibly as late as around 100 My) after condensation. Here we show that a Moon-forming event at 40 Myr after condensation, or earlier, is ruled out at a 99.9 per cent confidence level. We use a large number of N-body simulations to demonstrate a relationship between the time of the last giant impact on an Earth-like planet and the amount of mass subsequently added during the era known as Late Accretion. As the last giant impact is delayed, the late-accreted mass decreases in a predictable fashion. This relationship exists within both the classical scenario...

  5. Investigation on the stability of FeCO3 down to the core mantle boundary

    Science.gov (United States)

    Cerantola, Valerio; Bykova, Elena; McCammon, Catherine; Merlini, Marco; Dubrovinsky, Leonid

    2015-04-01

    In the last century, the high intensification of CO2 amount in the atmosphere together with the observed climate change have increasingly focused scientists' attention on the carbon cycle and its evolution at the Earth's surface. However, carbon is continuously transported from the surface into the deep Earth via subduction, mainly by means of carbonates. Fe-bearing carbonates (i.e. FeCO3) in particular are potential carbon carrier down to the deep lower mantle, indeed the presence of iron influences the stability of this phase at high pressures and high temperatures (HPHT), partly due to the spin-pairing of Fe-d electrons. In this study we perform HPHT experiments on FeCO3 in order to study its stability and eventually determine its decomposition products at the relative P and T conditions. Experiments were performed using synthetic FeCO3 crystals in a laser-heated diamond anvil cell (DAC) at 100 GPa an T > 1500 K in order to generate the conditions prevailing in the Earth's lower mantle. X-Ray Single Crystal Diffraction (XRSD) and Synchrotron Mössbauer Source (SMS) analyses were carried out at ESRF and APS synchrotron facilities. All samples were enriched in 57Fe to ensure a strong signal for Mössbauer spectroscopy. At 100 GPa we observed the complete transformation of FeCO3 into two new hp-carbonates, with Fe in different oxidation states depending on the heating temperatures and C in four-fold coordination with O. Laser heating at T > 2000 K generates a new phase with only Fe3+ in the structure: Fe4(CO4)3. Laser heating at 1600 K< T < 2000 K triggers a different redox reaction, where half of the Fe atoms are in 2+ and half in 3+ valence states: Fe(2)2+Fe(2)3+C4O13. Mössbauer spectra confirm the XRSD results by providing the exact amount of Fe-atoms in two different valence states. We assert Fe-rich carbonates can exist in regions down to the core mantle boundary, provided however the presence of an environment with relatively high fO2 e.g. in the proximity

  6. The abundance of potassium in the Earth's core

    Science.gov (United States)

    Watanabe, K.; Ohtani, E.; Kamada, S.; Miyahara, M.

    2013-12-01

    Potassium (K) has a radioactive isotope (40K), and it has been proposed that potassium might exist in the Earth's core (e.g., Wasserburg et al., 1964). If a large amount of potassium is in the core, it has a large impact on total heat budget and thermal history of the Earth. To reveal the amount of potassium in the core, many previous studies have been reported on potassium partitioning between metallic melts and silicate melts (e.g., Gessmann and Wood, 2002; Murthy et al., 2003; Hirao et al., 2006; Bouhifd et al., 2007; Corgne et al., 2007). Since there are considerable contradictions on temperature, pressure, and metal compositional dependencies, the potassium abundance in the core is not yet constrained well. In order to reveal the abundance accurately, we studied partitioning of potassium between aluminosilicate (adularia, KAlSi3O8) and metal (pure iron, iron-oxygen alloy, and iron-silicon alloy) up to 50 GPa and 3500 K using a double sided laser-heated diamond anvil cell. Our results revealed following pressure, temperature, and compositional dependencies on the partitioning coefficient of potassium DK (= the potassium contents in metal [wt%] / the potassium contents in silicate [wt%]); the pressure effect is a very weak but positive when the results by Hirao et al. (2006) are included, and the temperature effect is a positive but weaker than those reported previously. Oxygen fugacity has a positive effect, and oxygen in the metallic phase increases the K contents in the metallic phase, whereas silicon in the metallic phase has a negative effect. Based on these results, we estimated that the amount of the potassium in the core was less than 10 ppm and that the amount of 40K was about 1.0 ppb resulting generation of about 0.01 TW heat in the core. This amount of heat is relatively small compared to the heat flux at the core-mantle boundary (5 ~ 15 TW, Lay et al., 2008), therefore the radiogenic energy of potassium is not the major heat source of Earth's core.

  7. Plumes and Earth's Dynamic History : from Core to Biosphere

    Science.gov (United States)

    Courtillot, V. E.

    2002-12-01

    The last half century has been dominated by the general acceptance of plate tectonics. Although the plume concept emerged early in this story, its role has remained ambiguous. Because plumes are singularities, both in space and time, they tend to lie dangerously close to catastrophism, as opposed to the calm uniformitarian view of plate tectonics. Yet, it has become apparent that singular events and transient phenomena are of great importance, even if by definition they cover only a small fraction of geological time, in diverse observational and theoretical fields such as 1) magnetic reversals and the geodynamo, 2) tomography and mantle convection, 3) continental rifting and collision, and 4) evolution of the fluid envelopes (atmospheric and oceanic "climate"; evolution of species in the biosphere). I will emphasize recent work on different types of plumes and on the correlation between flood basalts and mass extinctions. The origin of mantle plumes remains a controversial topic. We suggest that three types of plumes exist, which originate at the three main discontinuities in the Earth's mantle (base of lithosphere, transition zone and core-mantle boundary). Most of the hotspots are short lived (~ 10Ma) and seem to come from the transition zone or above. Important concentrations occur above the Pacific and African superswells. Less than 10 hotspots have been long lived (~ 100Ma) and may have a very deep origin. In the last 50 Ma, these deep-seated plumes in the Pacific and Indo-Atlantic hemispheres have moved slowly, but motion was much faster prior to that. This change correlates with major episodes of true polar wander. The deeper ("primary") plumes are thought to trace global shifts in quadrupolar convection in the lower mantle. These are the plumes that were born as major flood basalts or oceanic plateaus (designated as large igneous provinces or LIPs). Most have an original volume on the order or in excess of 2.5 Mkm3. In most provinces, volcanism lasted on

  8. Viscosity near Earth's solid inner core

    Science.gov (United States)

    Smylie

    1999-04-16

    Anomalous splitting of the two equatorial translational modes of oscillation of Earth's solid inner core is used to estimate the effective viscosity just outside its boundary. Superconducting gravimeter observations give periods of 3.5822 +/- 0.0012 (retrograde) and 4.0150 +/- 0.0010 (prograde) hours. With the use of Ekman layer theory to estimate viscous drag forces, an inferred single viscosity of 1.22 x 10(11) Pascal seconds gives calculated periods of 3.5839 and 4.0167 hours for the two modes, close to the observed values. The large effective viscosity is consistent with a fluid, solid-liquid mixture surrounding the inner core associated with the "compositional convection" that drives Earth's geodynamo.

  9. Numerical simulations of thermal-chemical instabilities at the core-mantle boundary

    Science.gov (United States)

    Hansen, Ulrich; Yuen, David A.

    1988-01-01

    Numerical simulations of thermal-chemical instabilities in the D-double-prime layer at the core-mantle boundary are presented which show that strong lateral heterogeneities in the composition and density fields can be initiated and maintained dynamically if there is continuous replenishment of material from subduced slabs coming from the upper mantle. These chemical instabilities have a tendency to migrate laterally and may help to support core-mantle boundary topography with short and long wavelengths. The thermal-chemical flows produce a relatively stagnant D-double-prime layer with strong lateral and temporal variations in basal heat flux, which gives rise to thermal core-mantle interactions influencing the geodynamo.

  10. Exploratory models of the earth's thermal regime during segregation of the core

    Science.gov (United States)

    Davies, G. F.

    1980-01-01

    Some simple exploratory theoretical models of the thermal effects of core segregation have been investigated, assuming an initially homogeneous earth and including convective heat transport through a 'parameterized convection' approximation. The results indicate that either (1) mantle temperatures 30% or more above present values may have resulted from the gravitational energy released during core segregation, (2) the earth retained very little of its accretional energy, (3) core segregation lasted for one billion years or more, or (4) the earth accreted heterogeneously. Option 3 seems to be precluded by terrestrial lead isotope data, and the alternatives each raise substantial questions concerning the mechanics, chemistry, and petrology of the earth's early history. There is no recognized evidence for the early hot phase of option 1, and option 4 implies, among other things, an analogous early hot phase. Although it has not been favored, option 2 may be viable.

  11. Crystallization in Earth's Core after High-Temperature Core Formation

    Science.gov (United States)

    Hirose, K.; Morard, G.; Hernlund, J. W.; Helffrich, G. R.; Ozawa, H.

    2015-12-01

    Recent core formation models based on the metal-silicate partitioning of siderophile elements suggest that the Earth's core was formed by metal segregation at high pressure and high temperature in a deep magma ocean. It is also thought that the simultaneous solubility of silicon and oxygen in liquid iron are strongly enhanced at high pressure and high temperature, such that at the end of accretion the core was rich in both silicon and oxygen. Here we performed crystallization experiments on the Fe-Si binary and Fe-Si-O ternary systems up to core pressure in a laser-heated diamond-anvil cell. The starting material for the latter was a homogeneous mixture of fine-grain Fe-Si and SiO2 (sustain without extreme degrees of secular cooling. However, even for modest degrees of joint Si-O incorporation into the early core, the buoyancy released by crystallization of SiO2 is sufficient to overcome thermal stratification and sustain the geodynamo.

  12. How Inge Lehmann Discovered the Inner Core of the Earth

    Science.gov (United States)

    Rousseau, Christiane

    2013-01-01

    The mathematics behind Inge Lehmann's discovery that the inner core of the Earth is solid is explained using data collected around the Earth on seismic waves and their travel time through the Earth.

  13. The survival of early Earth mantle reservoirs: Evidence from flood basalts

    Science.gov (United States)

    Jackson, M. G.

    2011-12-01

    Over geologic time, large quantities of oceanic crust and sediment have been injected into the mantle at subduction zones, thereby generating heterogeneities in the mantle. The mantle has been further modified by melt extraction at mid-ocean ridges, a process that has generated large depleted reservoirs throughout the mantle. Owing to the fact that the Earth's mantle mixes and stirs chaotically on geologic timescales, it has long been thought that any evidence of an early terrestrial primitive mantle reservoir has either been erased by melt extraction, or has been overprinted by mixing with recycled materials. This hypothesis was supported by a lack of evidence for chondritic primitive mantle material in the mantle sources of oceanic hotspots, which are thought to yield material from the Earth's deep mantle. Instead, ocean island basalts (OIB) exhibit median 143Nd/144Nd isotopic ratios near 0.5130, suggesting that plume fed hotspots sample a largely-depleted mantle. However, the discovery of Boyet and Carlson (2005, Science) presented evidence that the Earth's primitive mantle may not be chondritic in composition. Boyet and Carlson (2005) found that modern terrestrial lavas have 142Nd/144Nd ratios ~18 ppm higher than chondrites. This result implies that all modern crustal and mantle reservoirs derive from a reservoir with Sm/Nd ratios ~5% higher than chondritic. Today, the 143Nd/144Nd of the primitive (albeit non-chondritic) reservoir would be ~0.5130. Critically, this value is similar to the median 143Nd/144Nd ratio identified in OIB lavas, suggesting that the OIB mantle may in fact be a largely primitive reservoir. However, most OIB lavas fail to exhibit the elevated 3He/4He ratios associated with primitive mantle reservoirs. Similarly, OIB lavas generally lack primitive Pb-isotopic compositions that plot on the geochron, a requirement for all early-Earth reservoirs. To date, no terrestrial OIB lavas have been found that exhibit the required He, Nd and Pb

  14. Mixing in the Earth's Mantle after the Moon-forming Impact

    Science.gov (United States)

    Korycansky, Donald

    2016-10-01

    The giant-impact hypothesis has provided a satisfactory explanation for the most salient characteristics of the Earth-Moon system. Recently, however, the discovery that many isotope patterns of the Earth and Moon are nearly identical have cast serious doubt on the most-accepted scenario of the Moon-forming impact and have forced the consideration of significantly different kinds of impacts.The original scenario pictured the grazing impact of a Mars-mass body on the proto-Earth. However, in this scenario the Moon is formed largely from impactor material which is extremely unlikely to share the isotopic patterning of the proto-Earth. Hence, two other ideas have been put forth: in one, the proto-Earth is extremely rapidly rotating, and the impactor is small: the Moon-forming disk is largely Earth material "spun-out" by the impact. In the other picture, the proto-Earth and impactor are roughly the same mass and both Earth and Moon are amalgams of the combined proto-Earth and the impactor.As found by Nakajima and Stevenson (2015) in their calculations of all three scenarios, each idea has significantly different consequences for the degree of mixing of the mantle. I will focus in detail on the stability and mixing of a stratified and shearing mantle. The approach will be from a fluid-dynamic standpoint, for which the starting point is the well-known Kelvin-Helmholtz instability, and from shear instabilities in general. The situations will be systematically investigated for relevant profiles of shear and entropy, with the aim of producing a more rigorous assessment of mixing in a post-Moon-forming terrestrial mantle. I will present results from CTH hydrocode simulations of calculations of the mantle under various conditions and velocity profiles to help determine which if any of the competing hypotheses for lunar formation are consistent with inferences of the state of the Earth's mantle in this early period.

  15. Changes in Earth's core-generated magnetic field, as observed by Swarm

    DEFF Research Database (Denmark)

    Finlay, Chris; Olsen, Nils; Gillet, Nicolas

    By far the largest part of the Earth's magnetic field is generated by motions taking place within our planet's liquid metal outer core. Variations of this core-generated field thus provide us with a unique means of probing the dynamics taking place in the deepest reaches of the Earth....... In this contribution, we will present the core-generated magnetic field, and its recent time changes, as seen by ESA's Earth explorer mission Swarm. We will present a new time-dependent geomagnetic field model, called CHAOS-6, derived from satellite data collected by the Swarm constellation, as well as data from...... of the source region, the core-mantle boundary, we present maps of the detailed structure of the geodynamo, and how this is presently evolving. Both the trend (secular variation) and accelerations in the field changes since the launch of the Swarm mission will be presented. Assuming that field changes...

  16. Zinc isotope fractionation during mantle melting and constraints on the Zn isotope composition of Earth's upper mantle

    Science.gov (United States)

    Wang, Ze-Zhou; Liu, Sheng-Ao; Liu, Jingao; Huang, Jian; Xiao, Yan; Chu, Zhu-Yin; Zhao, Xin-Miao; Tang, Limei

    2017-02-01

    The zinc (Zn) stable isotope system has great potential for tracing planetary formation and differentiation processes due to its chalcophile, lithophile and moderately volatile character. As an initial approach, the terrestrial mantle, and by inference, the bulk silicate Earth (BSE), have previously been suggested to have an average δ66Zn value of ∼+0.28‰ (relative to JMC 3-0749L) primarily based on oceanic basalts. Nevertheless, data for mantle peridotites are relatively scarce and it remains unclear whether Zn isotopes are fractionated during mantle melting. To address this issue, we report high-precision (±0.04‰; 2SD) Zn isotope data for well-characterized peridotites (n = 47) from cratonic and orogenic settings, as well as their mineral separates. Basalts including mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) were also measured to avoid inter-laboratory bias. The MORB analyzed have homogeneous δ66Zn values of +0.28 ± 0.03‰ (here and throughout the text, errors are given as 2SD), similar to those of OIB obtained in this study and in the literature (+0.31 ± 0.09‰). Excluding the metasomatized peridotites that exhibit a wide δ66Zn range of -0.44‰ to +0.42‰, the non-metasomatized peridotites have relatively uniform δ66Zn value of +0.18 ± 0.06‰, which is lighter than both MORB and OIB. This difference suggests a small but detectable Zn isotope fractionation (∼0.1‰) during mantle partial melting. The magnitude of inter-mineral fractionation between olivine and pyroxene is, on average, close to zero, but spinels are always isotopically heavier than coexisting olivines (Δ66ZnSpl-Ol = +0.12 ± 0.07‰) due to the stiffer Zn-O bonds in spinel than silicate minerals (Ol, Opx and Cpx). Zinc concentrations in spinels are 11-88 times higher than those in silicate minerals, and our modelling suggests that spinel consumption during mantle melting plays a key role in generating high Zn concentrations and heavy Zn isotopic

  17. Revealing the Earth's mantle from the tallest mountains using the Jinping Neutrino Experiment.

    Science.gov (United States)

    Šrámek, Ondřej; Roskovec, Bedřich; Wipperfurth, Scott A; Xi, Yufei; McDonough, William F

    2016-09-09

    The Earth's engine is driven by unknown proportions of primordial energy and heat produced in radioactive decay. Unfortunately, competing models of Earth's composition reveal an order of magnitude uncertainty in the amount of radiogenic power driving mantle dynamics. Recent measurements of the Earth's flux of geoneutrinos, electron antineutrinos from terrestrial natural radioactivity, reveal the amount of uranium and thorium in the Earth and set limits on the residual proportion of primordial energy. Comparison of the flux measured at large underground neutrino experiments with geologically informed predictions of geoneutrino emission from the crust provide the critical test needed to define the mantle's radiogenic power. Measurement at an oceanic location, distant from nuclear reactors and continental crust, would best reveal the mantle flux, however, no such experiment is anticipated. We predict the geoneutrino flux at the site of the Jinping Neutrino Experiment (Sichuan, China). Within 8 years, the combination of existing data and measurements from soon to come experiments, including Jinping, will exclude end-member models at the 1σ level, define the mantle's radiogenic contribution to the surface heat loss, set limits on the composition of the silicate Earth, and provide significant parameter bounds for models defining the mode of mantle convection.

  18. Carbon isotope heterogeneities in deep Earth: Recycling of surface carbon or from core?

    Science.gov (United States)

    Satish-Kumar, Madhusoodhan

    2017-04-01

    Subduction of crustal materials, mantle melting and upwelling of deep mantle, in addition to a potential source from the core, largely controls the Earth's deep carbon cycle. Large variations in carbon isotopic composition between different reservoirs have been used widely to differentiate the source of carbon and to understand the carbon inventories and its recycling processes. However, how far high-temperature and hign-pressure conditions can affect the carbon isotope distribution, is a question still unanswered to clearly address the deep carbon cycle. I present here a review on carbon isotope fractionation processes in deep Earth and critically evaluate whether we can easily differentiate between surface carbon and deep carbon based on isotope characteristics. Recent experimental carbon isotope fractionation studies in the Fe-C system suggests that light carbon is selectively partition into metallic core during early magma ocean environment (Satish-Kumar et al., 2011). Furthermore, carbonate melts can be a medium for efficient crystallisation of diamonds in Earth's mantle (Palyanov et al., 2013). Rayleigh fractionation modelling based on fractionation suggests that core can be a reservoir of 12C enriched carbon and can itself form a reservoir which can cause heterogeneity in mantle carbon (Wood et al., 2013). In addition, high pressure experiments in the carbon-saturated model harzburgite system (Enstatite-Magnesite-Olivine-Graphite), carbonated silicate melting resulted in 13C enrichment in the carbon dissolved in the silicate melt relative to elemental graphite (Mizutani et al., 2014). 13C enrichment in carbonate melt were further confirmed in experiments where redox melting between olivine and graphite produced a carbonate melt as well as carbonate reduction experiments to form graphite. A third factor, still unconquered is the effect of pressure on isotope fractionation process. Theoretical studies as well as preliminary experimental studies have suggested

  19. Partitioning experiments in the laser-heated diamond anvil cell: volatile content in the Earth's core.

    Science.gov (United States)

    Jephcoat, Andrew P; Bouhifd, M Ali; Porcelli, Don

    2008-11-28

    The present state of the Earth evolved from energetic events that were determined early in the history of the Solar System. A key process in reconciling this state and the observable mantle composition with models of the original formation relies on understanding the planetary processing that has taken place over the past 4.5Ga. Planetary size plays a key role and ultimately determines the pressure and temperature conditions at which the materials of the early solar nebular segregated. We summarize recent developments with the laser-heated diamond anvil cell that have made possible extension of the conventional pressure limit for partitioning experiments as well as the study of volatile trace elements. In particular, we discuss liquid-liquid, metal-silicate (M-Sil) partitioning results for several elements in a synthetic chondritic mixture, spanning a wide range of atomic number-helium to iodine. We examine the role of the core as a possible host of both siderophile and trace elements and the implications that early segregation processes at deep magma ocean conditions have for current mantle signatures, both compositional and isotopic. The results provide some of the first experimental evidence that the core is the obvious replacement for the long-sought, deep mantle reservoir. If so, they also indicate the need to understand the detailed nature and scale of core-mantle exchange processes, from atomic to macroscopic, throughout the age of the Earth to the present day.

  20. Magma redox and structural controls on iron isotope variations in Earth's mantle and crust

    Science.gov (United States)

    Dauphas, N.; Roskosz, M.; Alp, E. E.; Neuville, D. R.; Hu, M. Y.; Sio, C. K.; Tissot, F. L. H.; Zhao, J.; Tissandier, L.; Médard, E.; Cordier, C.

    2014-07-01

    The heavy iron isotopic composition of Earth's crust relative to chondrites has been explained by vaporization during the Moon-forming impact, equilibrium partitioning between metal and silicate at core-mantle-boundary conditions, or partial melting and magma differentiation. The latter view is supported by the observed difference in the iron isotopic compositions of MORBS and peridotites. However, the precise controls on iron isotope variations in igneous rocks remain unknown. Here, we show that equilibrium iron isotope fractionation is mainly controlled by redox (Fe3+/Fetot ratio) and structural (e.g., polymerization) conditions in magmas. We measured, for the first time, the mean force constants of iron bonds in silicate glasses by synchrotron Nuclear Resonant Inelastic X-ray Scattering (NRIXS, also known as Nuclear Resonance Vibrational Spectroscopy - NRVS, or Nuclear Inelastic Scattering - NIS). The same samples were studied by conventional Mössbauer and X-ray Absorption Near Edge Structure (XANES) spectroscopy. The NRIXS results reveal a +0.2 to +0.4‰ equilibrium fractionation on 56Fe/54Fe ratio between Fe2+ and Fe3+ end-members in basalt, andesite, and dacite glasses at magmatic temperatures. These first measurements can already explain ∼1/3 of the iron isotopic shift measured in MORBs relative to their source. Further work will be required to investigate how pressure, temperature, and structural differences between melts and glasses affect equilibrium fractionation factors. In addition, large fractionation is also found between rhyolitic glass and commonly occurring oxide and silicate minerals. This fractionation reflects mainly changes in the coordination environment of Fe2+ in rhyolites relative to less silicic magmas and mantle minerals, as also seen by XANES. We provide a new calibration of XANES features vs. Fe3+/Fetot ratio determinations by Mössbauer to estimate Fe3+/Fetot ratio in situ in glasses of basaltic, andesitic, dacitic, and rhyolitic

  1. Modeling Continental Growth and Mantle Hydration in Earth's Evolution and the Impact of Life

    Science.gov (United States)

    Höning, Dennis; Spohn, Tilman

    2016-04-01

    The evolution of planets with plate tectonics is significantly affected by several intertwined feedback cycles. On Earth, interactions between atmosphere, hydrosphere, biosphere, crust, and interior determine its present day state. We here focus on the feedback cycles including the evolutions of mantle water budget and continental crust, and investigate possible effects of the Earth's biosphere. The first feedback loop includes cycling of water into the mantle at subduction zones and outgassing at volcanic chains and mid-ocean ridges. Water is known to reduce the viscosity of mantle rock, and therefore the speed of mantle convection and plate subduction will increase with the water concentration, eventually enhancing the rates of mantle water regassing and outgassing. A second feedback loop includes the production and erosion of continental crust. Continents are formed above subduction zones, whose total length is determined by the total size of the continents. Furthermore, the total surface area of continental crust determines the amount of eroded sediments per unit time. Subducted sediments affect processes in subduction zones, eventually enhancing the production rate of new continental crust. Both feedback loops affect each other: As a wet mantle increases the speed of subduction, continental production also speeds up. On the other hand, the total length of subduction zones and the rate at which sediments are subducted (both being functions of continental coverage) affect the rate of mantle water regassing. We here present a model that includes both cycles and show how the system develops stable and unstable fixed points in a plane defined by mantle water concentration and surface of continents. We couple these feedback cycles to a parameterized thermal evolution model that reproduces present day observations. We show how Earth has been affected by these feedback cycles during its evolution, and argue that Earth's present day state regarding its mantle water

  2. Excitation of travelling torsional normal modes in an Earth's core model

    Science.gov (United States)

    Gillet, N.; Jault, D.; Canet, E.

    2017-09-01

    The proximity between the 6 yr recurrence time of the torsional Alfvén waves that have been inferred in the Earth's outer core over 1940-2010 and their 4 yr traveltime across the fluid core is nicely explained if these travelling waves are to be considered as normal modes. We discuss to what extent the emergence of free torsional modes from a stochastic forcing in the fluid core is compatible with some dissipation, specifically with an electromagnetic torque strong enough to account for the observed length of day variations of 6 yr period. In a spherical cavity enclosed by an insulating mantle, torsional normal modes consist of standing waves. In the presence of a conducting mantle, they transform into outward travelling waves very similar to the torsional waves that have been detected in the Earth's outer core. With such a resonant response a periodic forcing is not required to explain the regular recurrence of torsional waves; neither is the search for a source of motions in the vicinity of the cylindrical surface tangent to the inner core, where travelling waves seem to emerge. We discuss these results in the light of the reflection properties of torsional waves at the equator. We are able to reproduce the properties found for geophysical time-series of geostrophic flows (detection of a normal mode, almost total absorption at the equator) if the conductance of the lowermost mantle is 3 × 107 to 108 S.

  3. High-pressure metallization of FeO and implications for the earth's core

    Science.gov (United States)

    Knittle, Elise; Jeanloz, Raymond

    1986-01-01

    The phase diagram of FeO has been experimentally determined to pressures of 155 GPa and temperatures of 4000 K using shock-wave and diamond-cell techniques. A metallic phase of FeO is observed at pressures greater than 70 GPa and temperatures exceeding 1000 K. The metallization of FeO at high pressures implies that oxygen can be present as the light alloying element of the earth's outer core, in accord with the geochemical predictions of Ringwood (1977 and 1979). The high pressures necessary for this metallization suggest that the core has acquired its composition well after the initial stages of the earth's accretion. Direct experimental observations at elevated pressures and temperatures indicate that core-forming alloy can react chemically with oxides such as those forming the mantle. The core and mantle may never have reached complete chemical equilibrium, however. If this is the case, the core-mantle boundary is likely to be a zone of active chemical reactions.

  4. FeO2 and FeOOH under deep lower-mantle conditions and Earth's oxygen-hydrogen cycles.

    Science.gov (United States)

    Hu, Qingyang; Kim, Duck Young; Yang, Wenge; Yang, Liuxiang; Meng, Yue; Zhang, Li; Mao, Ho-Kwang

    2016-06-08

    The distribution, accumulation and circulation of oxygen and hydrogen in Earth's interior dictate the geochemical evolution of the hydrosphere, atmosphere and biosphere. The oxygen-rich atmosphere and iron-rich core represent two end-members of the oxygen-iron (O-Fe) system, overlapping with the entire pressure-temperature-composition range of the planet. The extreme pressure and temperature conditions of the deep interior alter the oxidation states, spin states and phase stabilities of iron oxides, creating new stoichiometries, such as Fe4O5 (ref. 5) and Fe5O6 (ref. 6). Such interactions between O and Fe dictate Earth's formation, the separation of the core and mantle, and the evolution of the atmosphere. Iron, in its multiple oxidation states, controls the oxygen fugacity and oxygen budget, with hydrogen having a key role in the reaction of Fe and O (causing iron to rust in humid air). Here we use first-principles calculations and experiments to identify a highly stable, pyrite-structured iron oxide (FeO2) at 76 gigapascals and 1,800 kelvin that holds an excessive amount of oxygen. We show that the mineral goethite, FeOOH, which exists ubiquitously as 'rust' and is concentrated in bog iron ore, decomposes under the deep lower-mantle conditions to form FeO2 and release H2. The reaction could cause accumulation of the heavy FeO2-bearing patches in the deep lower mantle, upward migration of hydrogen, and separation of the oxygen and hydrogen cycles. This process provides an alternative interpretation for the origin of seismic and geochemical anomalies in the deep lower mantle, as well as a sporadic O2 source for the Great Oxidation Event over two billion years ago that created the present oxygen-rich atmosphere.

  5. Mass Redistribution in the Core and Time-varying Gravity at the Earth's Surface

    Science.gov (United States)

    Kuang, Wei-Jia; Chao, Benjamin F.; Fang, Ming

    2003-01-01

    The Earth's liquid outer core is in convection, as suggested by the existence of the geomagnetic field in much of the Earth's history. One consequence of the convection is the redistribution of mass resulting from relative motion among fluid parcels with slightly different densities. This time dependent mass redistribution inside the core produces a small perturbation on the gravity field of the Earth. With our numerical dynamo solutions, we find that the mass redistribution (and the resultant gravity field) symmetric about the equator is much stronger than that anti-symmetric about the equator. In particular, J(sub 2) component is the strongest. In addition, the gravity field variation increases with the Rayleigh number that measures the driving force for the geodynamo in the core. With reasonable scaling from the current dynamo solutions, we could expect that at the surface of the Earth, the J(sub 2) variation from the core is on the order of l0(exp -16)/year relative to the mean (i.e. spherically symmetric) gravity field of the Earth. The possible shielding effect due to core-mantle boundary pressure variation loading is likely much smaller and is therefore negligible. Our results suggest that time-varying gravity field perturbation due to core mass redistribution may be measured with modem space geodetic observations, which will result a new means of detecting dynamical processes in the Earth's deep interior.

  6. Mass Redistribution in the Core and Time-varying Gravity at the Earth's Surface

    Science.gov (United States)

    Kuang, Wei-Jia; Chao, Benjamin F.; Fang, Ming

    2003-01-01

    The Earth's liquid outer core is in convection, as suggested by the existence of the geomagnetic field in much of the Earth's history. One consequence of the convection is the redistribution of mass resulting from relative motion among fluid parcels with slightly different densities. This time dependent mass redistribution inside the core produces a small perturbation on the gravity field of the Earth. With our numerical dynamo solutions, we find that the mass redistribution (and the resultant gravity field) symmetric about the equator is much stronger than that anti-symmetric about the equator. In particular, J(sub 2) component is the strongest. In addition, the gravity field variation increases with the Rayleigh number that measures the driving force for the geodynamo in the core. With reasonable scaling from the current dynamo solutions, we could expect that at the surface of the Earth, the J(sub 2) variation from the core is on the order of l0(exp -16)/year relative to the mean (i.e. spherically symmetric) gravity field of the Earth. The possible shielding effect due to core-mantle boundary pressure variation loading is likely much smaller and is therefore negligible. Our results suggest that time-varying gravity field perturbation due to core mass redistribution may be measured with modem space geodetic observations, which will result a new means of detecting dynamical processes in the Earth's deep interior.

  7. Siderophile and chalcophile element abundances in oceanic basalts, Pb isotope evolution and growth of the earth's core

    Science.gov (United States)

    Newsom, H. E.; White, W. M.; Jochum, K. P.; Hofmann, A. W.

    1986-01-01

    The hypothesis that the mantle Pb isotope ratios reflect continued extraction of Pb into the earth's core over geologic time is evaluated by studying the depeletion of chalcophile and siderophile elements in the mantle. Oceanic basalt samples are analyzed in order to determine the Pb, Sr, and Nd isotropic compositions and the abundances of siderophile and chalcophile elements and incompatible lithophile elements. The data reveal that there is no systematic variation of siderophile or chalcophile element abundances relative to abundances of lithophile elements and the Pb/Ce ratio of the mantle is constant. It is suggested that the crust formation involves nonmagmatic and magmatic processes.

  8. Bottom-up control of geomagnetic secular variation by the Earth's inner core.

    Science.gov (United States)

    Aubert, Julien; Finlay, Christopher C; Fournier, Alexandre

    2013-10-10

    Temporal changes in the Earth's magnetic field, known as geomagnetic secular variation, occur most prominently at low latitudes in the Atlantic hemisphere (that is, from -90 degrees east to 90 degrees east), whereas in the Pacific hemisphere there is comparatively little activity. This is a consequence of the geographical localization of intense, westward drifting, equatorial magnetic flux patches at the core surface. Despite successes in explaining the morphology of the geomagnetic field, numerical models of the geodynamo have so far failed to account systematically for this striking pattern of geomagnetic secular variation. Here we show that it can be reproduced provided that two mechanisms relying on the inner core are jointly considered. First, gravitational coupling aligns the inner core with the mantle, forcing the flow of liquid metal in the outer core into a giant, westward drifting, sheet-like gyre. The resulting shear concentrates azimuthal magnetic flux at low latitudes close to the core-mantle boundary, where it is expelled by core convection and subsequently transported westward. Second, differential inner-core growth, fastest below Indonesia, causes an asymmetric buoyancy release in the outer core which in turn distorts the gyre, forcing it to become eccentric, in agreement with recent core flow inversions. This bottom-up heterogeneous driving of core convection dominates top-down driving from mantle thermal heterogeneities, and localizes magnetic variations in a longitudinal sector centred beneath the Atlantic, where the eccentric gyre reaches the core surface. To match the observed pattern of geomagnetic secular variation, the solid material forming the inner core must now be in a state of differential growth rather than one of growth and melting induced by convective translation.

  9. Tracking Silica in the Earth's Subduction Zone and Upper Mantle

    Science.gov (United States)

    Chen, T.; Wang, X.; Zou, Y.; Gwanmesia, G. D.; Liebermann, R. C.; Li, B.

    2014-12-01

    The X-discontinuity (~300 km) in the upper mantle has been revealed under some continental or oceanic region by a number of seismic studies, at which depth the P and S wave velocities increase by about 2%. One possible cause for this discontinuity is the coesite-stishovite phase transition. In this study, we conducted ultrasonic interferometry measurements on polycrystalline coesite and stishovite up to 12.6 GPa at ambient temperature and 14GPa 1073K, respectively. While the P wave velocities of coesite continuously increase with pressure, the S wave velocities exhibit a monotonic decrease to the peak pressure of the current experiment followed by a reversible recovery upon release of pressure. As a result, within the pressure range of 8-12 GPa (corresponding to ~250-350 km depths), the velocity contrasts between coesite and stishovite reach as high as ~38% for P wave and 48%-50% for S wave together with impedance contrasts of 71-69% and ~78% for P and S waves, respectively, the highest among all known phase transitions in mantle minerals. With such extreme contrasts, the coesite-stishovite phase transition in the MORB composition with 4-10wt% of SiO2 is sufficient to generate velocity and impedance contrasts comparable to those reported for the X-discontinuity. The current data, together with the seismic X-discontinuity, may provide a geophysical approach to track the ancient subducted oceanic slabs, and place constraints on the amount of silica in the upper mantle.

  10. Storage and recycling of water in the Earth's mantle

    Science.gov (United States)

    Bolfan-Casanova, N.

    2015-12-01

    Most natural samples originating from the mantle contain traces of water. It can be observed that water content varies laterally as a function of the geodynamic context, but also with depth in cratons. Basalts from mid-ocean ridges, which sample the convecting upper mantle, contain generally below 0.6 wt% H2O leading to 50-330 parts per million by weight in the source. Oceanic Islands Basalts are more hydrated with contents ranging from 0.6 to 1.1 wt%, leading to 350-1100 ppm wt H2O in the source. Arc basalts are even more hydrated with water contents ranging from 0.2 to 5-6 wt% H2O testifying of the recycling of water by subduction. Kimberlite magmas are also the proof that local saturation in volatiles is possible. Among xenoliths, the samples from cratons are very interesting because they may provide a depth profile of water. However, the variation of water content in olivine with depth differs from craton to craton, and is the result of a complex geological history. Also, olivine inclusions in diamond and olivine from peridotite xenoliths do not give the same message regarding to water activity. The water storage capacity of the mantle is defined as the maximum water or hydroxyl that can be incorporated in its constitutive minerals before a free fluid phase appears. It can be determined experimentally and confronted to geophysical observations, such as low seismic velocities, and electrical conductivity. In this talk we will review our current knowledge of water incorporation in NAMs as determined experimentally and compare it with available observations. New data concerning clinopyroxenes will be shown. The aim being to understand the deep water cycle.

  11. Rutile is holding Nb and Ta in the mantle, negligible Nb and Ta in the core

    Science.gov (United States)

    McDonough, W. F.; Rudnick, R. L.

    2008-12-01

    Continental Crust has a significant depletion in Nb and Ta relative to La that has been attributed to convergent margin (arc) magmatism and greater retention of Nb and Ta in the mantle source. This depleted pattern is a consequence of the plotting order of elements, which has been established by the relative partitioning behavior of elements during MORB-OIB genesis. It is our hypothesis that rutile in subducting slabs or delaminated lower continental crust is the important phase causing Nb(Ta)-depletion in the continental crust, as well as lowering its Nb/Ta. Experimental studies reveal a range of Nb/Ta fractionation responses in residual rutile depending on temperature and phase relations(melting vs dehydration). Examples of rutile-bearing, refractory eclogites have been identified that serve as analog materials for residues of the continental crust. These rutiles have radiogenic Hf isotopes (Vervoort, unpubl. data), and thus are not recent precipitates from metasomatic melts, as has been recently suggested. What remains is to understand the total silicate Earth's mass balance. In this regard, it is worth noting that early Archean Barbarton komatiites possess chondritic La/Nb ratios, and Nb/Ta ~15, a value comparable to Allende CV3 chondrite. This observation is not consistent with the storage of Nb (or Ta) in the core and suggests that the silicate Earth controls the planetary budget of Nb and Ta. Constraints on the amount of Nb in the core must be evaluated by multi-element approaches, using ratios of refractory lithophile elements. Chondritic ratios for La/Nb and Nb/Ta are not defined simply as a single value with a restricted range and are not always constant, with examples of both negligible and distinct differences between groups of chondrites. The database for chondrites is still small for Nb and Ta.

  12. Alkali element depletion by core formation and vaporization on the early Earth

    Science.gov (United States)

    Lodders, K.; Fegley, B., Jr.

    1994-01-01

    The depletion of Na, K, Rb, and Cs in the Earth's upper mantle and crust relative to their abundances in chondrites is a long standing problem in geochemistry. Here we consider two commonly invoked mechanisms, namely core formation, and vaporization, for producing the observed depletions. Our models predict that a significant percentage of the Earth's bulk alkali element inventory is in the core (30 percent for Na, 52 percent for K, 74 percent for Rb, and 92 percent for Cs). These predictions agree with independent estimates from nebular volatility trends and (for K) from terrestrial heat flow data. Our models also predict that vaporization and thermal escape during planetary accretion are unlikely to produce the observed alkali element depletion pattern. However, loss during the putative giant impact which formed the Moon cannot be ruled out. Experimental, observational, and theoretical tests of our predictions are also described. Alkali element partitioning into the Earth's core was modeled by assuming that alkali element partitioning during core formation on the aubrite parent body (APB) is analogous to that on the early Earth. The analogy is reasonable for three reasons. First, the enstatite meteorites are the only known meteorites with the same oxygen isotope systematics as the Earth-Moon system. Second, the large core size of the Earth and the V depletion in the mantle requires accretion from planetesimals as reduced as the enstatite chondrites. Third, experimental studies of K partitioning between silicate and metal plus sulfide show that more K goes into the metal plus sulfide at higher pressures than at one atmosphere pressure. Thus partitioning in the relatively low pressure natural laboratory of the APB is a good guide to alkali elemental partitioning during the growth of the Earth.

  13. Mantle formation, coagulation and the origin of cloud/core-shine: II. Comparison with observations

    CERN Document Server

    Ysard, N; Jones, A P; Dartois, E; Godard, M; Gavilan, L

    2016-01-01

    Many dense interstellar clouds are observable in emission in the near-IR, commonly referred to as "Cloudshine", and in the mid-IR, the so-called "Coreshine". These C-shine observations have usually been explained with grain growth but no model has yet been able to self-consistently explain the dust spectral energy distribution from the near-IR to the submm. We want to demonstrate the ability of our new core/mantle evolutionary dust model THEMIS (The Heterogeneous dust Evolution Model at the IaS), which has been shown to be valid in the far-IR and submm, to reproduce the C-shine observations. Our starting point is a physically motivated core/mantle dust model. It consists of 3 dust populations: small aromatic-rich carbon grains; bigger core/mantle grains with mantles of aromatic-rich carbon and cores either made of amorphous aliphatic-rich carbon or amorphous silicate. We assume an evolutionary path where these grains, when entering denser regions, may first form a second aliphatic-rich carbon mantle (coagulat...

  14. Spin Transition of Iron in the Earth's Lower Mantle

    Energy Technology Data Exchange (ETDEWEB)

    Lin, J; Tsuchiya, T

    2007-05-23

    Electronic spin-pairing transitions of iron and associated effects on the physical properties of host phases have been reported in lower-mantle minerals including ferropericlase, silicate perovskite, and possibly in post-perovskite at lower-mantle pressures. Here we evaluate current understanding of the spin and valence states of iron in the lower-mantle phases, emphasizing the effects of the spin transitions on the density, sound velocities, chemical behavior, and transport properties of the lower-mantle phases. The spin transition of iron in ferropericlase occurs at approximately 50 GPa but likely turns into a wide spin crossover under lower-mantle temperatures. Current experimental results indicate a continuous nature of the spin crossover in silicate perovskite at high pressures, but which valence state of iron undergoes the spin crossover and what is its associated crystallographic site remain uncertain. The spin transition of iron results in enhanced density, incompressibility, and sound velocities, and reduced radiative thermal conductivity in the low-spin ferropericlase, which should be considered in future geophysical and geodynamic modeling of the Earth's lower mantle. Our evaluation of the experimental and theoretical pressure-volume results shows that the spin crossover of iron results in a density increase of 3-4% in ferropericlase containing 17-19% FeO. Here we have modeled the density and bulk modulus profiles of ferropericlase across the spin crossover under lower-mantle pressure-temperature conditions and showed how the ratio of the spin states of iron affects our understanding of the state of the Earth's lower mantle.

  15. Convection Destroys the Core/Mantle Structure in Hybrid C/O/Ne White Dwarfs

    CERN Document Server

    Brooks, Jared; Bildsten, Lars; Quataert, Eliot; Paxton, Bill

    2016-01-01

    A hybrid C/O/Ne white dwarf (WD) -- an unburned C/O core surrounded by an O/Ne/Na mantle -- can be formed if the carbon flame is quenched in a super-AGB (SAGB) star or white dwarf merger remnant. We show that this segregated hybrid structure becomes unstable to rapid mixing within 2,000 years of the onset of WD cooling. Carbon burning includes a weak reaction that removes electrons, resulting in a lower electron-to-baryon ratio ($Y_{\\rm e}$) in the regions processed by carbon burning compared to the unburned C/O core, making the O/Ne mantle denser than the C/O core as the WD cools. This is unstable to efficient mixing. We use the results of $\\texttt{MESA}$ models with different size C/O cores to quantify the rate at which the cores mix with the mantle as they cool. In all cases, we find that the WDs undergo significant core/mantle mixing on timescales shorter than the time available to grow the WD to the Chandrasekhar mass ($M_{\\rm Ch}$) by accretion. As a result, hybrid WDs that reach $M_{\\rm Ch}$ due to lat...

  16. Earth's deformation due to the dynamical perturbations of the fluid outer core

    Institute of Scientific and Technical Information of China (English)

    徐建桥; 孙和平

    2002-01-01

    The elasto-gravitational deformation response of the Earth's solid parts to the perturbations of the pressure and gravity on the core-mantle boundary (CMB) and the solid inner core boundary (ICB), due to the dynamical behaviors of the fluid outer core (FOC), is discussed. The internal load Love numbers, which are formulized in a general form in this study, are employed to describe the Earth's deformation. The preliminary reference Earth model (PREM) is used as an example to calculate the internal load Love numbers on the Earth's surface, CMB and ICB, respectively. The characteristics of the Earth's deformation variation with the depth and the perturbation periods on the boundaries of the FOC are also investigated. The numerical results indicate that the internal load Love numbers decrease quickly with the increasing degree of the spherical harmonics of the displacement and depend strongly on the perturbation frequencies, especially on the high frequencies. The results, obtained in this work, can be used to construct the boundary conditions for the core dynamics of the long-period oscillations of the Earth's fluid outer core.

  17. Core-mantle boundary deformations and J2 variations resulting from the 2004 Sumatra earthquake

    CERN Document Server

    Cannelli, V; De Michelis, P; Piersanti, A; Florindo, F

    2007-01-01

    The deformation at the core-mantle boundary produced by the 2004 Sumatra earthquake is investigated by means of a semi-analytic theoretical model of global coseismic and postseismic deformation, predicting a millimetric coseismic perturbation over a large portion of the core-mantle boundary. Spectral features of such deformations are analysed and discussed. The time-dependent postseismic evolution of the elliptical part of the gravity field (J2) is also computed for different asthenosphere viscosity models. Our results show that, for asthenospheric viscosities smaller than 10^18 Pa s, the postseismic J2 variation in the next years is expected to leave a detectable signal in geodetic observations.

  18. The earth's geoid and the large-scale structure of mantle convection

    Science.gov (United States)

    Richards, Mark A.; Hager, Bradford H.

    1988-01-01

    It is shown that most of the earth's low-degree geoid power is derived from density heterogeneity in the lower mantle. Much of the remaining geoid power is due to high-density slabs in active subduction zones. The compensated topography and lithospheric or crustal thickness variations contribute significantly to the observed geoid only for harmonic degrees greater than or equal to 6.

  19. Role of the Earth degassing (the core emission) for the global tectonics

    Science.gov (United States)

    Pavlenkova, Ninel

    2014-05-01

    source of the deep fluids advection and the resulting Earth degassing is the Earth's core with the high content of hydrogen and helium. The regular system of rifts and of the global rings of the earthquake epicenters may be a result of the Earth expansion generated by strong core emission. This system is traced now as zones of the higher hydrogen degassing. The data on the movement of paleomagnetic poles was explained in the fluids-rotation model by rotation of the whole mantle around the liquid core. Such interpretation, however, is too problematic. It is more reliable to propose that there were no any large movements of the continents or of the whole mantle and the mobile magnetic fields were created by the irregular convection in the core.

  20. Runaway Growth of Mars and Implications for Core Formation Relative to Earth

    Science.gov (United States)

    Halliday, A. N.; Wood, B. J.; Kleine, T.

    2005-12-01

    Martian meteorites are relatively young objects widely considered to reflect melting of the mantle of Mars over the past 1.4 Gyr. As such, their trace element compositions partly reflect the complex history of melting in the martian mantle. Hafnium (Hf) and tungsten (W) having different bulk distribution coefficients during mantle melting and thus may be fractionated by such processes. This explains why Hf/W, as measured in martian meteorites, is decoupled from W isotopic compositions, which would have been produced by 182Hf decay during the first 50 Myrs of the solar system. In contrast, little fractionation is expected among Ba, Th, and W, all of which have a similar incompatibility during melting in Earth's mantle. Assuming this is also true for the martian mantle, Ba/W and Th/W may be used as a proxy for the degree of metal segregation. The W isotopic compositions indeed show some relationship with the degree of mantle W depletion predicted to have been caused by core formation, as deduced from measured Ba/W or Th/W. These indices, as well as the W isotopic variations themselves, provide evidence of heterogeneity probably caused by early core formation, which can be compared with the effects generated by early partial melting as recorded by the 146Sm-142Nd system. Shergottites such as Zagami with no Nd isotopic effect and hence no indication of Hf/W fractionation from partial melting appear to define rapid timescales for accretion and core formation of about one million years, implying a runaway growth mechanism of accretion for Mars. This is consistent with certain dynamical models and argues against early migration of Jupiter-sized objects through the inner solar system. Melting and core formation on Mars appears to have continued for at least 10 Myrs as recorded in the W and Nd isotopic compositions of some other martian meteorites. This accretion and core formation history is strikingly different from that of the Earth. The last major stage of Earth

  1. Simulating earth core using high energy lasers

    Science.gov (United States)

    Koenig, M.; Benuzzi-Mounaix, A.; Brambrink, E.; Nourou, A.; Ravasio, A.; Wei, H. G.; Vinci, T.; Mazevet, S.; Occelli, F.; Morard, G.; Guyot, F.; De Resseguier, T.; Lescoute, E.

    2010-06-01

    The melting curve and equation of state of iron and iron alloys at the inner core boundary (330 GPa, about 5000 K) are still unknown. This severally limits current modelling of earth constitution and dynamics. In this paper, recent numerical and experimental studies performed using laser generated isentropic ramp compression on iron and aluminium samples are presented. On the experimental side, direct laser ramp compression was achieved on iron. Time-resolved measurements were compared to hydrodynamic computations accounting for the polymorphic phase transformations. Before studying iron that presents a solid-solid phase transition along the isentropic path, we studied the time evolution of the atomic structure of aluminium using molecular dynamics simulations at the same length and time scales as the experiment. Like many metals, aluminium presents an elasto-plastic phase transition and we studied, using this microscopic approach, the effect of plasticity on the backward integration technique used to extract equation of state information from the experimental VISAR signal.

  2. Using geoneutrinos to constrain the radiogenic power in the Earth's mantle

    Science.gov (United States)

    Šrámek, Ondřej; Roskovec, Bedřich; Wipperfurth, Scott A.; Xi, Yufei; McDonough, William F.

    2017-04-01

    The Earth's engine is driven by unknown proportions of primordial energy and heat produced in radioactive decay. Unfortunately, competing models of Earth's composition reveal an order of magnitude uncertainty in the amount of radiogenic power driving mantle dynamics. Together with established geoscientific disciplines (seismology, geodynamics, petrology, mineral physics), experimental particle physics now brings additional constraints to our understanding of mantle energetics. Measurements of the Earth's flux of geoneutrinos, electron antineutrinos emitted in β- decays of naturally occurring radionuclides, reveal the amount of uranium and thorium in the Earth and set limits on the amount of radiogenic power in the planet. Comparison of the flux measured at large underground neutrino experiments with geologically informed predictions of geoneutrino emission from the crust provide the critical test needed to define the mantle's radiogenic power. Measuring geoneutrinos at oceanic locations, distant from nuclear reactors and continental crust, would best reveal the mantle flux and by performing a coarse scale geoneutrino tomography could even test the hypothesis of large heterogeneous structures in deep mantle enriched in heat-producing elements. The current geoneutrino detecting experiments, KamLAND in Japan and Borexino in Italy, will by year ˜ 2020 be supplemented with three more experiments: SNO+ in Canada, and JUNO and Jinping in China. We predict the geoneutrino flux at all experimental sites. Within ˜ 8 years from today, the combination of data from all experiments will exclude end-member compositional models of the silicate Earth at the 1σ level, reveal the radiogenic contribution to the global surface heat loss, and provide tight limits on radiogenic power in the Earth's mantle. Additionally, we discuss how the geoneutrino measurements at the three relatively near-lying (≤ 3000 km) detectors KamLAND, JUNO, and Jinping may be harnessed to improve the

  3. Continental growth and mantle hydration as intertwined feedback cycles in the thermal evolution of Earth

    Science.gov (United States)

    Höning, Dennis; Spohn, Tilman

    2016-06-01

    A model of Earth's continental coverage and mantle water budget is discussed along with its thermal evolution. The model links a thermal evolution model based on parameterized mantle convection with a model of a generic subduction zone that includes the oceanic crust and a sedimentary layer as carriers of water. Part of the subducted water is used to produce continental crust while the remainder is subducted into the mantle. The total length of the subduction zones is calculated from the total surface area of continental crust assuming randomly distributed continents. The mantle viscosity is dependent of temperature and the water concentration. Sediments are generated by continental crust erosion, and water outgassing at mid-oceanic ridges closes the water cycle. We discuss the strongly coupled, non-linear model using a phase plane defined by the continental coverage and mantle water concentration. Fixed points are found in the phase plane at which the rates of change of both variables are zero. These fixed points evolve with time, but in many cases, three fixed points emerge of which two are stable and an intermediate point is unstable with respect to continental coverage. With initial conditions from a Monte-Carlo scheme we calculate evolution paths in the phase plane and find a large spread of final states that all have a mostly balanced water budget. The present day observed 40% continental surface coverage is found near the unstable fixed point. Our evolution model suggests that Earth's continental coverage formed early and has been stable for at least 1.5 Gyr. The effect of mantle water regassing (and mantle viscosity depending on water concentration) is found to lower the present day mantle temperature by about 120 K, but the present day mantle viscosity is affected little. The water cycle thus complements the well-known thermostat effect of viscosity and mantle temperature. Our results further suggest that the biosphere could impact the feedback cycles by

  4. Effect of Rheology on Mantle Dynamics and Plate Tectonics in Super-Earths

    Science.gov (United States)

    Tackley, P. J.; Ammann, M. W.; Brodholt, J. P.; Dobson, D. P.; Valencia, D. C.

    2011-12-01

    The discovery of extra-solar "super-Earth" planets with sizes up to twice that of Earth has prompted interest in their possible lithosphere and mantle dynamics and evolution. Simple scalings [1,2] suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigor in the deep mantle, which, if extralopated to the largest super-Earths might, according to conventional thinking, result a very low effective Rayleigh number in their deep mantles and possibly no convection there. Here we evaluate this. (i) As the mantle of a super-Earth is made mostly of post-perovskite we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of [3] to a pressure of 1 TPa. The activation volume for diffusion creep becomes very low at very high pressure, but nevertheless for the largest super-Earths the viscosity along an adiabat may approach 10^30 Pa s in the deep mantle, which would be too high for convection. (ii) We use these DFT-calculated values in numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induced plate-like lithospheric behavior, solved using StagYY [4]. Results confirm the likelihood of plate tectonics and show a novel self-regulation of deep mantle temperature. The deep mantle is not adiabatic; instead internal heating raises the temperature until the viscosity is low enough to facilitate convective loss of the radiogenic heat, which results in a super-adiabatic temperature profile and a viscosity increase with depth of no more than ~3 orders of magnitude, regardless of what is calculated for an adiabat. It has recently been argued [5] that at very high pressures, deformation

  5. The Ramsey phase-change hypothesis. [for development of earth core

    Science.gov (United States)

    Lyttleton, R. A.

    1978-01-01

    Ramsey's (1948, 1949, 1950, 1954) arguments for the phase-change interpretation of the nature of the terrestrial core are summarized. Some of the successes of the phase-change theory in accounting for hitherto unexplained properties of earth's interior are discussed. Evidence in favor of the phase-change theory is reviewed, and calculations are examined which indicate that the liquid-core material is far more compressible at any relevant pressure than is the mantle material. Implications of the phase-change theory for Venus, Mars, Mercury, and the moon are considered.

  6. Mantle dynamics in super-Earths: Post-perovskite rheology and self-regulation of viscosity

    Science.gov (United States)

    Tackley, P. J.; Ammann, M.; Brodholt, J. P.; Dobson, D. P.; Valencia, D.

    2013-07-01

    The discovery of extra-solar "super-Earth" planets with sizes up to twice that of Earth has prompted interest in their possible lithosphere and mantle dynamics and evolution. Simple scalings suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigour in the deep mantle, which, if extralopated to the largest super-Earths might, according to conventional thinking, result in no convection in their deep mantles due to the very low effective Rayleigh number. Here we evaluate this. First, as the mantle of a super-Earth is made mostly of post-perovskite we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of to a pressure of 1 TPa, for both slowest diffusion (upper-bound rheology) and fastest diffusion (lower-bound rheology) directions. Along a 1600 K adiabat the upper-bound rheology would lead to a post-perovskite layer of a very high (˜1030 Pa s) but relatively uniform viscosity, whereas the lower-bound rheology leads to a post-perovskite viscosity increase of ˜7 orders of magnitude with depth; in both cases the deep mantle viscosity would be too high for convection. Second, we use these DFT-calculated values in statistically steady-state numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induced plate-like lithospheric behaviour. Results confirm the likelihood of plate tectonics for planets with Earth-like surface conditions (temperature and water) and show a self-regulation of deep mantle temperature. The deep mantle is not adiabatic; instead feedback between internal heating, temperature and viscosity regulates the temperature such that the viscosity has the

  7. Influence of mantle anelasticity on the phase and amplitude of earth tides

    Science.gov (United States)

    Bodri, B.; Pedersen, G. P. H.

    1980-05-01

    The effect of the anelasticity of the mantle on the phase and amplitude of earth tides is calculated for recent models of the internal structure of the earth and its rheological characteristics. The anelastic properties of the mantle are modeled by the Maxwell and Knopoff-Lomnitz rheological bodies. For numerical calculations two different methods of solution are used. Results indicate that the effect of mantle anelasticity on tidal amplitudes is practically zero. For both types of rheological models the phase shifts of the functions characterizing solid tides are small, none of them exceeding values of some minutes of arc. These phase shifts have a very weak dependence on the variation of attenuation and viscosity within the mantle. The present study is closely related to an important problem: what proportion of the observed tidal friction arises not in the ocean but is due to the anelasticity of the mantle. The results suggest that dissipation by solid friction at present is an insignificant, almost negligible component of tidal energy sink.

  8. Atmospheric Ar and Ne returned from mantle depths to the Earth's surface by forearc recycling.

    Science.gov (United States)

    Baldwin, Suzanne L; Das, J P

    2015-11-17

    In subduction zones, sediments, hydrothermally altered lithosphere, fluids, and atmospheric gases are transported into the mantle, where ultrahigh-pressure (UHP) metamorphism takes place. However, the extent to which atmospheric noble gases are trapped in minerals crystallized during UHP metamorphism is unknown. We measured Ar and Ne trapped in phengite and omphacite from the youngest known UHP terrane on Earth to determine the composition of Ar and Ne returned from mantle depths to the surface by forearc recycling. An (40)Ar/(39)Ar age [7.93 ± 0.10 My (1σ)] for phengite is interpreted as the timing of crystallization at mantle depths and indicates that (40)Ar/(39)Ar phengite ages reliably record the timing of UHP metamorphism. Both phengite and omphacite yielded atmospheric (38)Ar/(36)Ar and (20)Ne/(22)Ne. Our study provides the first documentation, to our knowledge, of entrapment of atmospheric Ar and Ne in phengite and omphacite. Results indicate that a subduction barrier for atmospheric-derived noble gases does not exist at mantle depths associated with UHP metamorphism. We show that the crystallization age together with the isotopic composition of nonradiogenic noble gases trapped in minerals formed during subsolidus crystallization at mantle depths can be used to unambiguously assess forearc recycling of atmospheric noble gases. The flux of atmospheric noble gas entering the deep Earth through subduction and returning to the surface cannot be fully realized until the abundances of atmospheric noble gases trapped in exhumed UHP rocks are known.

  9. Seismic evidence for a chemically distinct thermochemical reservoir in Earth's deep mantle beneath Hawaii

    Science.gov (United States)

    Zhao, Chunpeng; Garnero, Edward J.; McNamara, Allen K.; Schmerr, Nicholas; Carlson, Richard W.

    2015-09-01

    Nearly antipodal continent-sized zones of reduced seismic shear wave velocities exist at the base of Earth's mantle, one beneath the Pacific Ocean, the other beneath the South Atlantic Ocean and Africa. Geophysicists have attributed the low velocity zones to elevated temperatures associated with large-scale mantle convection processes, specifically, hot mantle upwelling in response to cooler subduction-related downwelling currents. Hypotheses have included superplumes, isochemical heterogeneity, and stable as well as metastable basal thermochemical piles. Here we analyze waveform broadening and travel times of S waves from 11 deep focus earthquakes in the southwest Pacific recorded in North America, resulting in 8500 seismograms studied that sample the deep mantle beneath the Pacific. Waveform broadening is referenced to a mean S-wave shape constructed for each event, to define a relative "misfit". Large misfits are consistent with multipathing that can broaden wave pulses. Misfits of deep mantle sampling S-waves infer that the structure in the northeast part of the low velocity province beneath the Pacific has a sharp side as well as a sloping sharp top to the feature. This sharp boundary morphology is consistent with geodynamic predictions for a stable thermochemical reservoir. The peak of the imaged pile is below Hawaii, supporting the hypothesis of a whole mantle plume beneath the hotspot.

  10. Pole-strength of the earth from Magsat and magnetic determination of the core radius

    Science.gov (United States)

    Voorhies, G. V.; Benton, E. R.

    1982-01-01

    A model based on two days of Magsat data is used to numerically evaluate the unsigned magnetic flux linking the earth's surface, and a comparison of the 16.054 GWb value calculated with values from earlier geomagnetic field models reveals a smooth, monotonic, and recently-accelerating decrease in the earth's pole strength at a 50-year average rate of 8.3 MWb, or 0.052%/year. Hide's (1978) magnetic technique for determining the radius of the earth's electrically-conducting core is tested by (1) extrapolating main field models for 1960 and 1965 downward through the nearly-insulating mantle, and then separately comparing them to equivalent, extrapolated models of Magsat data. The two unsigned fluxes are found to equal the Magsat values at a radius which is within 2% of the core radius; and (2) the 1960 main field and secular variation and acceleration coefficients are used to derive models of 1930, 1940 and 1950. The same core magnetic radius value, within 2% of the seismic value, is obtained. It is concluded that the mantle is a nearly-perfect insulator, while the core is a perfect conductor, on the decade time scale.

  11. Mapping geomagnetic secular variation at the core-mantle boundary

    DEFF Research Database (Denmark)

    Holme, R.; Olsen, Nils; Bairstow, F. L.

    2011-01-01

    , the coherence of the maps up to harmonic degree 13 suggests that it is possible to obtain useful insight from their examination. Low SV is confirmed under the Pacific, but also revealed under the North Atlantic and Antarctica. These features are more readily explained in terms of dynamo control through thermal......-fit by functions proportional to l(l + 1) where l is the spherical harmonic degree. The ratio of the two spectra defines a timescale for geomagnetic variations of approximately 10 yrs for all resolvable harmonic degrees. The blue spectra should prevent meaningful maps of the SV being generated; nevertheless...... core–mantle coupling than by electromagnetic screening. Comparison with maps from measurements prior to the recent satellites, using the ‘Comprehensive Model’, suggests that models back to at least 1970 are sufficiently good to enable direct comparison of the SV....

  12. The effect of iron and aluminum incorporation on lattice thermal conductivity of bridgmanite at the Earth's lower mantle

    Science.gov (United States)

    Okuda, Yoshiyuki; Ohta, Kenji; Yagi, Takashi; Sinmyo, Ryosuke; Wakamatsu, Tatsuya; Hirose, Kei; Ohishi, Yasuo

    2017-09-01

    Bridgmanite (Bdg), iron (Fe)- and aluminum (Al)-bearing magnesium silicate perovskite is the most abundant mineral in the Earth's lower mantle. Thus, its thermal conductivity governs the lower mantle thermal conductivity that critically controls the thermo-chemical evolution of both the core and the lower mantle. While there is extensive research for the lattice thermal conductivity of MgSiO3 Bdg, the effects of Fe and Al incorporation on its lattice thermal conduction are still controversial. Here we report the lattice thermal conductivity of Mg0.832Fe0.209Al0.060Si0.916O3 Bdg measured up to 142 GPa at 300 K using the pulsed light heating thermoreflectance technique in a diamond anvil cell. The results show that the lattice thermal conductivity of Bdg is 25.5 ± 2.2 W/m/K at 135 GPa and 300 K, which is 19% lower than that of Fe and Al-free Bdg at identical conditions. Considering the temperature effect on the lattice conductivity and the contribution of radiative thermal conductivity, the total thermal conductivity of Fe and Al-bearing Bdg does not change very much with temperature at 135 GPa, and could be higher than that of post-perovskite with identical chemical composition.

  13. Composition and Structure of Earth's Lower Mantle from Elasticity and Rheology Measurements

    Science.gov (United States)

    Marquardt, Hauke; Kurnosov, Alexander; Frost, Daniel; Boffa Ballaran, Tiziana; Ziberna, Luca; Miyagi, Lowell; Liermann, Hanns-Peter; Speziale, Sergio; Immoor, Julia

    2016-04-01

    In this contribution, we present results of two novel experimental data sets on the elasticity and rheology of lower mantle minerals and discuss how the results contribute to our understanding of the composition, structure and dynamics of the shallow lower mantle. (1) We report first high-pressure single-crystal elasticity data on Al-Fe-bearing bridgmanite (Mg0.88Fe0.12Si0.89Al0.11)O3, the dominant phase in Earth's lower mantle, using high-pressure Brillouin spectroscopy and x-ray diffraction on focused ion beam (FIB) cut samples in a novel self-consistent approach. We combine our elasticity data with previous experimental measurements of the phase assemblages and element partitioning in a pyrolitic mantle and present a mineral-physics based seismic profile of the uppermost lower mantle. Within the resolution of our model, we find excellent agreement of our mineral physics prediction with the seismic Preliminary Reference Earth Model up to at least 1000 km depth, indicating chemical homogeneity of upper and shallow lower mantle. (2) We present results from synchrotron radial x-ray diffraction measurements on the deformation behavior of (Mg0.8Fe0.2)O ferropericlase, the second most abundant mineral in the lower mantle, at high-pressures and temperatures of up to 1400 K. From our data, we calculate the flow strength of ferropericlase, which we find to increase at pressures >20 GPa. Modelling based on our experimental data indicates a strong increase of viscosity around subducting slabs in the upper 900 km of a lower mantle with a pyrolitic composition. This viscosity increase takes place in the shallow lower mantle without the need for a compositional change with depth or a phase transition. It can therefore provide a plausible mechanism to explain the stagnation of sinking slabs in the shallow lower mantle as observed by seismic tomography that is consistent with the compositional constraints from our elasticity measurements on bridgmanite.

  14. Early Stage of Origin of Earth (interval after Emergence of Sun, Formation of Liquid Core, Formation of Solid Core)

    Science.gov (United States)

    Pechernikova, G. V.; Sergeev, V. N.

    2017-05-01

    Gravitational collapse of interstellar molecular cloud fragment has led to the formation of the Sun and its surrounding protoplanetary disk, consisting of 5 × 10^5 dust and gas. The collapse continued (1 years. Age of solar system (about 4.57×10^9 years) determine by age calcium-aluminum inclusions (CAI) which are present at samples of some meteorites (chondrites). Subsidence of dust to the central plane of a protoplanetary disk has led to formation of a dust subdisk which as a result of gravitational instability has broken up to condensations. In the process of collisional evolution they turned into dense planetesimals from which the planets formed. The accounting of a role of large bodies in evolution of a protoplanetary swarm in the field of terrestrial planets has allowed to define times of formation of the massive bodies permitting their early differentiation at the expense of short-lived isotopes heating and impacts to the melting temperature of the depths. The total time of Earth's growth is estimated about 10^8 years. Hf geochronometer showed that the core of the Earth has existed for Using W about 3×10^7 Hf geohronometer years since the formation of the CAI. Thus data W point to the formation of the Earth's core during its accretion. The paleomagnetic data indicate the existence of Earth's magnetic field past 3.5×10^9 years. But the age of the solid core, estimated by heat flow at the core-mantle boundary is 1.7×10^9 (0.5 years). Measurements of the thermal conductivity of liquid iron under the conditions that exist in the Earth's core, indicate the absence of the need for a solid core of existence to support the work geodynamo, although electrical resistivity measurements yield the opposite result.

  15. Geodynamo and mantle convection simulations on the Earth Simulator using the Yin-Yang grid

    Energy Technology Data Exchange (ETDEWEB)

    Kageyama, Akira; Yoshida, Masaki [Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology, Showa-machi 3173-25, Yokohama (Japan)

    2005-01-01

    We have developed finite difference codes based on the Yin-Yang grid for the geodynamo simulation and the mantle convection simulation. The Yin-Yang grid is a kind of spherical overset grid that is composed of two identical component grids. The intrinsic simplicity of the mesh configuration of the Yin-Yang grid enables us to develop highly optimized simulation codes on massively parallel supercomputers. The Yin-Yang geodynamo code has achieved 15.2 Tflops with 4096 processors on the Earth Simulator. This represents 46% of the theoretical peak performance. The Yin-Yang mantle code has enabled us to carry out mantle convection simulations in realistic regimes with a Rayleigh number of 10{sup 7} including strongly temperature dependent viscosity with spatial contrast up to 10{sup 6}.

  16. Mantle Convection, Plate Tectonics, and Volcanism on Hot Exo-Earths

    CERN Document Server

    van Summeren, Joost; Gaidos, Eric

    2011-01-01

    Recently discovered exoplanets on close-in orbits should have surface temperatures of 100's to 1000's of K. They are likely tidally locked and synchronously rotating around their parent stars and, if an atmosphere is absent, have surface temperature contrasts of many 100's to 1000's K between permanent day and night sides. We investigated the effect of elevated surface temperature and strong surface temperature contrasts for Earth-mass planets on the (i) pattern of mantle convection, (ii) tectonic regime, and (iii) rate and distribution of partial melting, using numerical simulations of mantle convection with a composite viscous/pseudo-plastic rheology. Our simulations indicate that, if a close-in rocky exoplanet lacks an atmosphere to redistribute heat, a >~ 400 K surface temperature contrast can maintain an asymmetric degree 1 pattern of mantle convection in which the surface of the planet moves preferentially toward subduction zones on the cold night side. The planetary surface features a hemispheric dicho...

  17. Imaging earth's interior: Tomographic inversions for mantle P-wave velocity structure

    Energy Technology Data Exchange (ETDEWEB)

    Pulliam, R.J.

    1991-07-01

    A formalism is developed for the tomographic inversion of seismic travel time residuals. The travel time equations are solved both simultaneously, for velocity model terms and corrections to the source locations, and progressively, for each set of terms in succession. The methods differ primarily in their treatment of source mislocation terms. Additionally, the system of equations is solved directly, neglecting source terms. The efficacy of the algorithms is explored with synthetic data as we perform simulations of the general procedure used to produce tomographic images of Earth's mantle from global earthquake data. The patterns of seismic heterogeneity in the mantle that would be returned reliably by a tomographic inversion are investigated. We construct synthetic data sets based on real ray sampling of the mantle by introducing spherical harmonic patterns of velocity heterogeneity and perform inversions of the synthetic data.

  18. A model for the evolution of the Earth's mantle structure since the Early Paleozoic

    Science.gov (United States)

    Zhang, Nan; Zhong, Shijie; Leng, Wei; Li, Zheng-Xiang

    2010-06-01

    Seismic tomography studies indicate that the Earth's mantle structure is characterized by African and Pacific seismically slow velocity anomalies (i.e., superplumes) and circum-Pacific seismically fast anomalies (i.e., a globally spherical harmonic degree 2 structure). However, the cause for and time evolution of the African and Pacific superplumes and the degree 2 mantle structure remain poorly understood with two competing proposals. First, the African and Pacific superplumes have remained largely unchanged for at least the last 300 Myr and possibly much longer. Second, the African superplume is formed sometime after the formation of Pangea (i.e., at 330 Ma) and the mantle in the African hemisphere is predominated by cold downwelling structures before and during the assembly of Pangea, while the Pacific superplume has been stable for the Pangea supercontinent cycle (i.e., globally a degree 1 structure before the Pangea formation). Here, we construct a proxy model of plate motions for the African hemisphere for the last 450 Myr since the Early Paleozoic using the paleogeographic reconstruction of continents constrained by paleomagnetic and geological observations. Coupled with assumed oceanic plate motions for the Pacific hemisphere, this proxy model for the plate motion history is used as time-dependent surface boundary condition in three-dimensional spherical models of thermochemical mantle convection to study the evolution of mantle structure, particularly the African mantle structure, since the Early Paleozoic. Our model calculations reproduce well the present-day mantle structure including the African and Pacific superplumes and generally support the second proposal with a dynamic cause for the superplume structure. Our results suggest that while the mantle in the African hemisphere before the assembly of Pangea is predominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of

  19. On the consequences of strong stable stratification at the top of earth's outer core

    Science.gov (United States)

    Bloxham, Jeremy

    1990-01-01

    The consequences of strong stable stratification at the top of the earth's fluid outer core are considered, concentrating on the generation of the geomagnetic secular variation. It is assumed that the core near the core-mantle boundary is both strongly stably stratified and free of Lorentz forces: it is found that this set of assumptions severely limits the class of possible motions, none of which is compatible with the geomagnetic secular variation. Relaxing either assumption is adequate: tangentially geostrophic flows are consistent with the secular variation if the assumption that the core is strongly stably stratified is relaxed (while retaining the assumption that Lorentz forces are negligible); purely toroidal flows may explain the secular variation if Lorentz forces are included.

  20. Reduced lattice thermal conductivity of Fe-bearing bridgmanite in Earth's deep mantle: Reduced Conductivity of Fe-Bridgmanite

    Energy Technology Data Exchange (ETDEWEB)

    Hsieh, Wen-Pin [Institute of Earth Sciences, Academia Sinica, Taipei Taiwan; Deschamps, Frédéric [Institute of Earth Sciences, Academia Sinica, Taipei Taiwan; Okuchi, Takuo [Institute for Planetary Materials, Okayama University, Misasa Japan; Lin, Jung-Fu [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin Texas USA

    2017-07-01

    Complex seismic, thermal, and chemical features have been reported in Earth's lowermost mantle. In particular, possible iron enrichments in the large low shear-wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, altering the lower mantle dynamics and heat flux across core-mantle boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of Earth's lower mantle. Importantly, the pressure-induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity, but these effects remain largely unknown. Here we precisely measured the lattice thermal conductivity of Fe-bearing bridgmanite to 120 GPa using optical pump-probe spectroscopy. The conductivity of Fe-bearing bridgmanite increases monotonically with pressure but drops significantly around 45 GPa due to pressure-induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid-lower mantle and below would promote mantle flow against a potential viscosity barrier, facilitating slabs crossing over the 1000 km depth. Modeling of our results applied to LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. The CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.

  1. Evolution of the Oxidation State of the Earth's Mantle: Challenges of High Pressure Quenching

    Science.gov (United States)

    Danielson, L. R.; Righter, K.; Keller, L.; Christoffersen, R.; Rahman, Z.

    2015-01-01

    The oxidation state of the Earth's mantle during formation remains an unresolved question, whether it was constant throughout planetary accretion, transitioned from reduced to oxidized, or from oxidized to reduced. We investigate the stability of Fe3+ at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the Earth's mantle. Experiments of more mafic compositions and at higher pressures commonly form a polyphase quench intergrowth composed primarily of pyroxenes, with interstitial glass which hosts nearly all of the more volatile minor elements. In our previous experiments on shergottite compositions, variable fO2, T, and P is less than 4 GPa, Fe3+/TotFe decreased slightly with increasing P, similar to terrestrial basalt. For oxidizing experiments less than 7GPa, Fe3+/TotFe decreased as well, but it's unclear from previous modelling whether the deeper mantle could retain significant Fe3+. Our current experiments expand our pressure range deeper into the Earth's mantle and focus on compositions and conditions relevant to the early Earth. Experiments with Knippa basalt as the starting composition were conducted at 1-8 GPa and 1800 C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products from 7-8 GPa quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal Fe3+/2+. A number of different approaches have been employed to produce glassy samples that can be measured by EELS and XANES. A more intermediate andesite was used in one experiment, and decompression during quenching was attempted after, but both resulted in a finer grained polyphase texture. Experiments are currently underway to test different capsule materials may affect quench texture. A preliminary experiment using liquid nitrogen to greatly enhance the rate of cooling of the assembly has also been attempted and this technique will be

  2. Quasi-geostrophic modes in the Earth's fluid core with an outer stably stratified layer

    CERN Document Server

    Vidal, Jérémie

    2015-01-01

    Seismic waves sensitive to the outermost part of the Earth's liquid core seem to be affected by a stably stratified layer at the core-mantle boundary. Such a layer could have an observable signature in both long-term and short-term variations of the magnetic field of the Earth, which are used to probe the flow at the top of the core. Indeed, with the recent SWARM mission, it seems reasonable to be able to identify waves propagating in the core with period of several months, which may play an important role in the large-scale dynamics. In this paper, we characterize the influence of a stratified layer at the top of the core on deep quasi-geostrophic (Rossby) waves. We compute numerically the quasi-geostrophic eigenmodes of a rapidly rotating spherical shell, with a stably stratified layer near the outer boundary. Two simple models of stratification are taken into account, which are scaled with commonly accepted values of the Brunt-V{\\"a}is{\\"a}l{\\"a} frequency in the Earth's core. In the absence of magnetic fi...

  3. Equation of State of Fe3S and Limits on the Sulfur Content of Earth's Core

    Science.gov (United States)

    Campbell, A.; Mattillion, A.; Bausch, H.; Tecklenburg, S.; Fischer, R. A.; Chidester, B.; Prakapenka, V.

    2016-12-01

    Sulfur is a common component of protoplanetary cores, as represented by iron meteorites, and it is likely to be a significant alloying component with iron in Earth's core as well, along with silicon, oxygen, and perhaps other light elements. Cosmochemical limits on the sulfur content of Earth's core, based on the relative volatilities of sulfur and other elements, are weakened by the observation that this approach fails to accurately predict the sulfur content in iron meteorite parent bodies. To better understand the geophysical consequences of sulfur addition to Earth's core, we report equation of state measurements of Fe3S to pressures and temperatures exceeding 140 GPa and 2000 K, using synchrotron X-ray diffraction in a laser heated diamond anvil cell. New room temperature measurements are also reported, improved by the use of a neon pressure medium. With this P-V-T equation of state for Fe3S, along with an assumed 2% density change upon melting and a 4000 K core-mantle boundary temperature, the PREM density in the outer core can be matched with 14 wt% sulfur, which should be considered an upper bound because of the likely additional presence of other light elements.

  4. Investigating the effect of lateral viscosity variations in the Earth's mantle

    Science.gov (United States)

    O'Farrell, K. A.; Lithgow-Bertelloni, C. R.

    2015-12-01

    Seismic tomography can be used to investigate radial viscosity variations on instantaneous flow models by predicting the global geoid and comparing with the observed geoid. This method is one of many that has been used to constrain viscosity structure in the Earth's mantle in the last few decades. Using the 3D mantle convection model, Stag-YY (e.g., Hernlund and Tackley, 2008), we are further able to explore the effect of lateral variations in viscosity in addition to the radial variations. Examining over 50 tomographic models we found notable differences by comparing a synthetically produced geoid with the observed geoid. Comparing S- and P-wave tomographic models, the S-wave models provided a better fit to the observed geoid. Using this large suite of 50 tomographic models, we have been able to constrain the radial viscosity structure of the Earth. We found that two types of viscosity profiles yielded equally good fits. A viscosity profile with a low transition zone viscosity and a lower mantle viscosity equal to the upper mantle, or a profile with a large lower mantle viscosity and a transition zone viscosity similar to the upper mantle. Using the set of radial viscosity profiles that gave the best fit to the observed geoid, we can explore a range of lateral viscosity variations and see how they affect the different types of tomographic models. Improving on previous studies of lateral viscosity variations (e.g. Ghosh, Becker and Zhong, 2010), we systematically explore a large range of tomographic models and density-velocity conversion factors. We explore which type of tomographic model (S- or P- wave) is more strongly affected by lateral viscosity variations, as well as the effect on isotropic and anisotropic models. We constrain the strength of lateral viscosity variations necessary to produce a high correlation between observed and predicted geoid anomalies. We will discuss the wavelength of flow that is most affected by the lateral viscosity variations

  5. Water in the Earth's Mantle: Mineral-specific IR Absorption Coefficients and Radiative Thermal Conductivities

    Science.gov (United States)

    Thomas, S. M.

    2015-12-01

    Minor and trace element chemistry, phase relations, rheology, thermal structure and the role of volatiles and their abundance in the deep Earth mantle are still far from fully explored, but fundamental to understanding the processes involved in Earth formation and evolution. Theory and high pressure experiments imply a significant water storage capacity of nominally anhydrous minerals, such as majoritic garnet, olivine, wadsleyite and ringwoodite, composing the Earth's upper mantle and transition zone to a depth of 660 km. Studying the effect of water incorporation on chemical and physical mineral properties is of importance, because the presence of trace amounts of water, incorporated as OH through charge-coupled chemical substitutions into such nominally anhydrous high-pressure silicates, notably influences phase relations, melting behavior, conductivity, elasticity, viscosity and rheology. Knowledge of absolute water contents in nominally anhydrous minerals is essential for modeling the Earth's interior water cycle. One of the most common and sensitive tools for water quantification is IR spectroscopy for which mineral-specific absorption coefficients are required. Such calibration constants can be derived from hydrogen concentrations determined by independent techniques, such as secondary ion mass spectrometry, Raman spectroscopy or proton-proton(pp)-scattering. Here, analytical advances and mineral-specific IR absorption coefficients for the quantification of H2O in major phases of the Earth's mantle will be discussed. Furthermore, new data from optical absorption measurements in resistively heated diamond-anvil cells at high pressures and temperatures up to 1000 K will be presented. Experiments were performed on synthetic single-crystals of olivine, ringwoodite, majoritic garnet, and Al-bearing phase D with varying iron, aluminum and OH contents to calculate radiative thermal conductivities and study their contribution to heat transfer in the Earth's interior

  6. Water cycling between ocean and mantle: Super-earths need not be waterworlds

    Energy Technology Data Exchange (ETDEWEB)

    Cowan, Nicolas B. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Department of Earth and Planetary Sciences, Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Abbot, Dorian S., E-mail: n-cowan@northwestern.edu [Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637 (United States)

    2014-01-20

    Large terrestrial planets are expected to have muted topography and deep oceans, implying that most super-Earths should be entirely covered in water, so-called waterworlds. This is important because waterworlds lack a silicate weathering thermostat so their climate is predicted to be less stable than that of planets with exposed continents. In other words, the continuously habitable zone for waterworlds is much narrower than for Earth-like planets. A planet's water is partitioned, however, between a surface reservoir, the ocean, and an interior reservoir, the mantle. Plate tectonics transports water between these reservoirs on geological timescales. Degassing of melt at mid-ocean ridges and serpentinization of oceanic crust depend negatively and positively on seafloor pressure, respectively, providing a stabilizing feedback on long-term ocean volume. Motivated by Earth's approximately steady-state deep water cycle, we develop a two-box model of the hydrosphere and derive steady-state solutions to the water partitioning on terrestrial planets. Critically, hydrostatic seafloor pressure is proportional to surface gravity, so super-Earths with a deep water cycle will tend to store more water in the mantle. We conclude that a tectonically active terrestrial planet of any mass can maintain exposed continents if its water mass fraction is less than ∼0.2%, dramatically increasing the odds that super-Earths are habitable. The greatest source of uncertainty in our study is Earth's current mantle water inventory: the greater its value, the more robust planets are to inundation. Lastly, we discuss how future missions can test our hypothesis by mapping the oceans and continents of massive terrestrial planets.

  7. On the Modes of Mantle Convection in Super-Earths (Invited)

    Science.gov (United States)

    Bercovici, D.

    2010-12-01

    The relatively recent discovery of larger-than-Earth extra-solar terrestrial planets has opened up many possibilities for different modes of interior dynamics, including mantle convection. A great deal of basic mineral physics is still needed to understand the state of matter and rheology of these super terrestrials, even assuming similar compositions to Earth (which is itself unlikely given the effect of singular events such as giant impacts and lunar formation). There has been speculation and debate as to whether the larger Rayleigh numbers of super-Earth's would promote plate tectonic style recycling, which is considered a crucial negative feedback for buffering atmospheric CO2 and stabilizing climate through weathering and mineral carbonation. However, models of plate generation through grainsize-reducing damage (see Foley & Bercovici this session) show that the effect of larger Rayleigh numbers is offset by an increase in the lithosphere-mantle viscosity contrast (due to a hotter mantle). Super-Earth's are therefore probably no more (or less) prone to plate tectonics than "normal" Earths; other conditions like surface temperature (and thus orbital position) are more important than size for facilitating plate tectonic cycling, which is of course more in keeping with observations in our own solar system (i.e., the disparity between Earth and Venus). Regardless, two major questions remain. First, what are the other modes of convective recycling that would possibly buffer CO2 and allow for a negative feedback that stabilizes climate? For example, subarial basaltic volcanism associated with plume or diapiric convection could potentially draw down CO2 because of the reactibility of mafic minerals; this mechanism possibly helped trigger Snow Ball events in the Proterozoic Earth during break-up of near-equatorial super-continents. Second, what observations of exo-planets provide tests for theories of tectonics or convective cycling? Spectroscopic techniques are most

  8. The Earth's core formation and development: evidence from evolution of tectonomagmatic processes and paleomagnetic data

    Science.gov (United States)

    Sharkov, E. V.

    2011-12-01

    Many geologists confident that the core provides modern tectonic and magmatic activity on the Earth, which explains our interest in this topic, and vice versa we can use evolution of tectonomagmatic processes throughout the Earth's (and other terrestrial planetary bodies) history for reconstruction of the core formation and evolution. Most researchers, follow to V. Safronov (1972) and A. Ringwood (1979), confident that the Earth has occurred due to accumulation of hypothetical chemically homogeneous planetesimals, composed by chondrite material, ie, as a result of homogeneous accretion. However, this single-stage chondrite model of accretion is inconsistent with fact of cardinal change of tectonomagmatic processes on the terrestrial planets in the middle stages of their development. For example, the critical irreversible change of the Earth's tectonomagmatic evolution occurred in range 2.35-2.0 Ga, when geochemical-enriched Fe-Ti picrites and basalts firstly appeared in large quantities and first geological evidence of plate tectonics showed up (Sharkov, Bogatikov, 2010). We suggest that these changes were linked with ascending of mantle superplumes of the second generation (thermochemical), originated at the the boundary of liquid iron core and silicate mantle, in similar way as the modern plumes. All terrestrial planetary bodies (Earth, Venus, Mars, Mercury, and the Moon) have a similar structure, consist of iron core and silicate envelope, and developed at the same scenario, which provide for drastic irreversible change in character of tectonomagmatic processes at the middle stages of their evolution (Sharkov, Bogatikov, 2009). Such a situation can be realized only in case: (1) the terrestrial planetary bodies originally had heterogeneous structure, and (2) their heating occurred from the top down accompanied by cooling of outer shells. As a result, material of the primordial cores, where enriched material survived, were remained a long time untouched. It

  9. Core Processes: Earth's eccentric magnetic field

    DEFF Research Database (Denmark)

    Finlay, Chris

    2012-01-01

    Earth’s magnetic field is characterized by a puzzling hemispheric asymmetry. Calculations of core dynamo processes suggest that lopsided growth of the planet’s inner core may be part of the cause.......Earth’s magnetic field is characterized by a puzzling hemispheric asymmetry. Calculations of core dynamo processes suggest that lopsided growth of the planet’s inner core may be part of the cause....

  10. The EarthChem Deep Lithosphere Dataset: Digital Access to Mantle Xenolith Petrological Data

    Science.gov (United States)

    Block, K. A.; Lehnert, K. A.; Walker, J. D.; Fishman, A.; McDonough, W. F.

    2006-12-01

    Establishment of a geologic framework for the USArray mission of EarthScope largely depends on community efforts that facilitate the integration of seismic data with petrologic, gravity, structural, and other geologic data. The EarthChem federation of interoperable databases (www.earthchem.org) provides cyberinfrastructure in which large geochemical data collections are assembled and curated to maximize data usability and accessibility. In an effort to address the needs of the GeoFrame/USArray community, EarthChem is developing the Deep Lithosphere Petrological Dataset to provide easy access to an integrated, comprehensive, global set of petrological data from upper mantle and lower crustal rocks. The initial focus for EarthChem's Deep Lithosphere dataset is xenolith data from geographic locations identified by GeoFrame as relevant to the USArray mission. Data are compiled in a relational database that complements the data collections of NAVDAT, GEOROC, and PetDB, and which together can be accessed and downloaded through the EarthChem Portal. The web interface permits the user to query by sample location, rock type, mineral, inclusion, author, major oxide, trace element and isotopic composition to build customized datasets. Additionally, radiometric age, host rock information, and model data such as pressure and temperature, including information about the geobarometer/geothermometer used by authors in their calculations, are included in the dataset to provide the perspective of geochemical modeling on the nature of the sub-continental mantle and lower crust for correlation with seismic imaging and geodynamic modeling.

  11. Mars Thermal History: Core, Atmosphere, Mantle, Phobos and Surface (MaTH CAMPS)

    Science.gov (United States)

    Wicks, J. K.; Weller, M. B.; Towles, N. J.; Thissen, C.; Knezek, N. R.; Johnston, S.; Hongsresawat, S.; Duncan, M. S.; Black, B. A.; Schmerr, N. C.; Panning, M. P.; Montesi, L.; Manga, M.; Lognonne, P. H.

    2014-12-01

    The death of the Martian dynamo ~4.1 Ga and sustained volcanism throughout Martian history place fundamental constraints on the thermal history of the planet. To explore the implications for mantle structure, we constructed holistic models of Mars that include the core, mantle, lithosphere/surface, atmosphere, and an atmospheric capture of Phobos in a collaborative effort begun at the CIDER 2014 summer program. For our thermal model of the core, we employ an iterative solver and parameterized phase diagram to compute pressure, density, and temperature in the core for a variety of initial accretion temperatures and bulk compositions. We use this model to constrain core-mantle boundary (CMB) temperature and heat flow. We couple this model for the evolution of the core with a one-dimensional parameterized convection model for the mantle. The upper boundary condition is set by the state of the Martian atmosphere. We consider the effect of a distinct compositional layer at the base of the mantle that may represent dense magma ocean crystallization products or a primitive layer untouched by magma ocean processes. We find successful models that allow sufficient CMB heat flow to power an early dynamo and the potential of melt generation through extended periods of Mars' history. In addition to dynamo and magmatism timing, other diagnostics allow us to compare model outputs to modern observables. The mass, moment of inertia, and tidal Love number of our model planet are compared directly to measured values. Additionally, deformation and stress on the lithosphere due to internal volume changes and changes in surface loading predicted by our thermal evolution models could be recorded in the Martian crust. Finally, coupling temperature-dependent tidal dissipation affects Phobos' orbital secular evolution and gives constraint on mantle temperatures. These constraints are discussed for the different scenarios of Phobos capture. We present a suite of models that satisfy the

  12. Magnetohydrodynamics and the earth's core selected works by Paul Roberts

    CERN Document Server

    Soward, Andrew M

    2003-01-01

    Paul Roberts'' research contributions are remarkable in their diversity, depth and international appeal. Papers from the Paul Roberts'' Anniversary meeting at the University of Exeter are presented in this volume. Topics include geomagnetism and dynamos, fluid mechanics and MHD, superfluidity, mixed phase regions, mean field electrodynamics and the Earth''s inner core. An incisive commentary of the papers puts the work of Paul Roberts into historical context. Magnetohydrodynamics and the Earth''s Core provides a valuable source of reference for graduates and researchers working in this area of geoscience.

  13. Sulfide Composition and Melt Stability Field in the Earth's Upper Mantle

    Science.gov (United States)

    Zhang, Z.; Hirschmann, M. M.

    2015-12-01

    In the Earth's upper mantle, sulfur occurs chiefly as (Fe, Ni)xS minerals and melts with near-monosulfide stoichiometries. These could have substantial influence on geochemical and geophysical properties of the Earth's interior. For example, sulfide mineral and melts are the major carriers of chalcophile and platinum group elements (PGEs) and sulfide melts are potentially responsible for mantle geophysical anomalies, as their physical properties (higher density, surface tension, electrical conductivity and lower melting points) differ greatly from those of silicates. Sulfide melts are a potential sink for reduced mantle carbon and perhaps be associated with carbon transport, including diamond precipitation. Sulfides may be molten in large parts of the mantle, but this is determined in part by sulfide composition, which is in turn a product of Fe-Ni exchange with olivine and of the effect of sulfur, oxygen, and carbon fugacities on metal/anion ratios of melts. Melting experiments define the monosulfide (Fe0.35Ni0.12Cu0.01S0.52) solidus from 1-8 GPa at carbon-free and graphite saturated conditions. The resulting carbon-free solidus is below the mantle adiabat to depths of at least 300 km, but does not indicate sulfide melting in continental lithosphere. In contrast, the graphite saturated solidus indicates melting in the lithosphere at 6-7 GPa (~200 km), close to the source conditions typical of diamond formation. To determine the composition of sulfide equilibrated with olivine, we performed experiments on monosulfide-olivine (crushed powders from San Carlos single crystal) under 2 GPa, 1400 ◦C. Our preliminary results suggests that Fe-Ni distribution coefficients KD, defined by (Ni/Fe)sulfide/(Ni/Fe)olivine, have significantly lower values than those determined previously at one atmosphere (Doyle and Naldrett 1987; Fleet and MacRae 1987; Gaetani and Grove 1997). This indicates that sulfide equilibrated with olivine in the mantle is richer in Fe than former

  14. Volatile-rich Melts in the Earth's Upper Mantle (AGU Kuno Medal)

    Science.gov (United States)

    Dasgupta, Rajdeep

    2013-04-01

    The onset of silicate magma generation in the Earth's upper mantle influences the thermal evolution of the planet, fluxes of key volatiles to the exosphere, and geochemical and geophysical properties of the mantle. Although carbonatitic fluid with variable water content could be stable ≤250 km beneath mid oceanic ridges [1-3], owing to the small fraction (oxygen fugacity of the mantle in the garnet peridotite field [2, 3], we suggest that on a global scale, carbonated silicate melt generation at ~250-180 km deep redox solidus, with destabilization of metal and majorite in the upwelling mantle, explains oceanic low-velocity zone and electrical conductivity structure of the mantle. In locally oxidized domains (i.e., higher than average Fe3+/Fetotal), deeper carbonated silicate melt may contribute to the X-discontinuity. Furthermore, the new experimental results along with the electrical conductivity of molten carbonated peridotite [8] and that of the oceanic upper mantle [6] suggest that if CO2-rich melt is the only possible agent to explain the high electrical conductivity of the asthenospheric mantle then the mantle at depth is CO2-rich but H2O-poor; higher H2O content in the mantle enhances melting, lowers the CO2 content and likely the conductivity of such melts. Finally, carbonated silicate melts restrict the stability of carbonatite in the Earth's deep oceanic upper mantle and the inventory of carbon, water, and other highly incompatible elements at ridges becomes controlled by flux of the former [7]. Although the stability of carbonatitic melt may be eliminated beneath oceanic ridges at all depths, beneath continents stability of carbonatitic melt is expected. Archean cratonic mantle (geotherms corresponding to surface heat flux of 40-50 mW m-2) crosses the carbonated peridotite solidus, at a depth of ~100-220 km [9]; thus considering the oxygen fugacity profile for cratons [3], carbonatitic melt is expected to be stable at 100-180 km depths, at a narrow

  15. Time-dependent heat transfer in the spherical Earth: Implications on the power and thermal evolution of the core

    Science.gov (United States)

    Hofmeister, A. M.; Criss, R. E.

    2015-12-01

    We quantitatively investigate the time-dependence of heat conduction for a post-core, spherical Earth that is not convecting, due to compositional layering, based on hundreds of measurements of thermal diffusivity (D) for insulators and metals. Consistency of our solutions for widely ranging input parameters indicates how additional heat transfer mechanisms (mantle magmatism and convection) affect thermal evolution of the core. We consider 1) interior starting temperatures (T) of 273-5000 K, which represent variations in primordial heat, 2) different distributions and decay of long-lived radioactive isotopes, 3) additional heat sources in the core (primordial or latent heat), and 4) variable depth-T dependence of D. Our new analytical solution for cooling of a constant D sphere validates our numerical results. The bottom line is that the thermally insulating nature of minerals, combined with constraints of spherical geometry, limits steep thermal gradients to the upper mantle, consistent with the short length scale (x ~700 km) of cooling over t = 4.5 Ga indicated by dimensional analysis [x2 ~ 4Dt], and with plate tectonics. Consequently, interior temperatures vary little so the core has remained hot and is possibly warming. Findings include: 1) Constant vs. variable D affects thermal profiles only in detail, with D for the metallic core being inconsequential. 2) The hottest zone in Earth may lie in the uppermost lower mantle; 3) Most radiogenic heat is released in Earth's outermost 1000 km thereby driving an active outer shell; 4) Earth's core is essentially isothermal and is thus best described by the liquid-solid phase boundary; 5) Deeply sequestered radioactivity or other heat will melt the core rather than by run the dynamo (note that the heat needed to have melted the outer core is 10% of radiogenic heat generated over Earth's history); 6) Inefficient cooling of an Earth-sized mass means that heat essentially remains where it is generated, until it is removed

  16. HSE Abundances in Angrites and HEDs: Core-Mantle Equilibration or Late Accretion Addition of a Chondritic Component

    Science.gov (United States)

    Rai, N.; Downes, H.; Smith, C. L.

    2016-08-01

    Using metal-silicate partitioning of HSEs together with their mantle abundances in Vesta and the APB respectively, we test whether formation of a metallic core could have led to the observed abundances of the HSEs, in the mantles of these bodies.

  17. Lunisolar tidal and tidal load elastic stress tensor components within the Earth's mantle and their influence on earthquake occurrences

    Science.gov (United States)

    Varga, Peter; Grafarend, Erik

    2016-04-01

    The relationship of earthquakes with the tidal phenomenon since long is a subject of scientific debates and it cannot be regarded as clarified even today. For the purpose of theoretical investigation of this problem a set of second order spheroidal Love-Shida numbers (h(r), k(r), l(r)) and their radial derivatives were determined for the case of a symmetric, non-rotating, elastic, isotropic (SNREI) Earth with a liquid core. By these means, the stress tensor components from the surface to the core-mantle boundary (CMB) were calculated for the case of zonal, tesseral and sectorial tides. Since the tidal potential and its derivatives are coordinate dependent and the zonal, tesseral and sectorial tides have different distributions on and within the Earth, the lunisolar stress cannot influence the break-out of every seismological event in the same degree. A correlation between earthquake energy release and the lunisolar effect can exist in some cases where the seismic area is well determined and has either one seismic source or severe similar ones. Particularly in volcanic areas, where the seismic activity is connected to the volcano's activity, or in the case of some aftershock swarms, significant correlation was found by different authors.

  18. Thermal conductivity of MgO, MgSiO3 perovskite and post-perovskite in the Earth's deep mantle

    CERN Document Server

    Haigis, Volker; Jahn, Sandro; 10.1016/j.epsl.2012.09.002

    2012-01-01

    We report lattice thermal conductivities of MgO and MgSiO3 in the perovskite and post-perovskite structures at conditions of the Earth's lower mantle, obtained from equilibrium molecular dynamics simulations. Using an advanced ionic interaction potential, the full conductivity tensor was calculated by means of the Green-Kubo method, and the conductivity of MgSiO3 post-perovskite was found to be significantly anisotropic. The thermal conductivities of all three phases were parameterized as a function of density and temperature. Assuming a Fe-free lower-mantle composition with mole fractions xMgSiO3 = 0.66 and xMgO = 0.34, the conductivity of the two-phase aggregate was calculated along a model geotherm. It was found to vary considerably with depth, rising from 9.5 W/(mK) at the top of the lower mantle to 20.5 W/(mK) at the top of the thermal boundary layer above the core-mantle boundary. Extrapolation of experimental data suggests that at deep-mantle conditions, the presence of a realistic amount of iron impur...

  19. Extraction of weak PcP phases using the slant-stacklet transform - II: constraints on lateral variations of structure near the core-mantle boundary

    Science.gov (United States)

    Ventosa, Sergi; Romanowicz, Barbara

    2015-11-01

    Resolving the topography of the core-mantle boundary (CMB) and the structure and composition of the D″ region is key to improving our understanding of the interaction between the Earth's mantle and core. Observations of traveltimes and amplitudes of short-period teleseismic body waves sensitive to lowermost mantle provide essential constraints on the properties of this region. Major challenges are low signal-to-noise ratio of the target phases and interference with other mantle phases. In a previous paper (Part I), we introduced the slant-stacklet transform to enhance the signal of the core-reflected (PcP) phase and to isolate it from stronger signals in the coda of the P wave. Then we minimized a linear misfit between P and PcP waveforms to improve the quality of PcP-P traveltime difference measurements as compared to standard cross-correlation methods. This method significantly increases the quantity and the quality of PcP-P traveltime observations available for the modelling of structure near the CMB. Here we illustrate our approach in a series of regional studies of the CMB and D″ using PcP-P observations with unprecedented resolution from high-quality dense arrays located in North America and Japan for events with magnitude Mw>5.4 and distances up to 80°. In this process, we carefully analyse various sources of errors and show that mantle heterogeneity is the most significant. We find and correct bias due to mantle heterogeneities that is as large as 1 s in traveltime, comparable to the largest lateral PcP-P traveltime variations observed. We illustrate the importance of accurate mantle corrections and the need for higher resolution mantle models for future studies. After optimal mantle corrections, the main signal left is relatively long wavelength in the regions sampled, except at the border of the Pacific large-low shear velocity province (LLSVP). We detect the northwest border of the Pacific LLSVP in the western Pacific from array observations in

  20. Early history of Earth's crust-mantle system inferred from hafnium isotopes in chondrites

    DEFF Research Database (Denmark)

    Bizzarro, Martin; Haack, Henning; Rosing, M.;

    2003-01-01

    depleted mantle reservoir. Here we report Lu-Hf isotope measurements of different Solar System objects including chondrites and basaltic eucrites. The chondrites define a Lu-Hf isochron with an initial Hf/Hf ratio of 0.279628 ± 0.000047, corresponding to ¿176 = 1.983 ± 0.033 x 10yr using an age of 4.56 Gyr...... for the chondrite-forming event. This ¿176 value indicates that Earth's oldest minerals were derived from melts of a mantle source with a time-integrated history of depletion rather than enrichment. The depletion event must have occurred no later than 320 Myr after planetary accretion, consistent with timing...

  1. Water Cycling Between Ocean and Mantle: Super-Earths Need Not be Waterworlds

    CERN Document Server

    Cowan, Nicolas B

    2014-01-01

    Large terrestrial planets are expected to have muted topography and deep oceans, implying that most super-Earths should be entirely covered in water, so-called waterworlds. This is important because waterworlds lack a silicate weathering thermostat so their climate is predicted to be less stable than that of planets with exposed continents. In other words, the continuously habitable zone for waterworlds is much narrower than for Earth-like planets. A planet's water is partitioned, however, between a surface reservoir, the ocean, and an interior reservoir, the mantle. Plate tectonics transports water between these reservoirs on geological timescales. Degassing of melt at mid-ocean ridges and serpentinization of oceanic crust depend negatively and positively on seafloor pressure, respectively, providing a stabilizing feedback on long-term ocean volume. Motivated by Earth's approximately steady-state deep water cycle, we develop a two-box model of the hydrosphere and derive steady-state solutions to the water pa...

  2. Towards magnetic sounding of the Earth's core by an adjoint method

    Science.gov (United States)

    Li, K.; Jackson, A.; Livermore, P. W.

    2013-12-01

    Earth's magnetic field is generated and sustained by the so called geodynamo system in the core. Measurements of the geomagnetic field taken at the surface, downwards continued through the electrically insulating mantle to the core-mantle boundary (CMB), provide important constraints on the time evolution of the velocity, magnetic field and temperature anomaly in the fluid outer core. The aim of any study in data assimilation applied to the Earth's core is to produce a time-dependent model consistent with these observations [1]. Snapshots of these ``tuned" models provide a window through which the inner workings of the Earth's core, usually hidden from view, can be probed. We apply a variational data assimilation framework to an inertia-free magnetohydrodynamic system (MHD) [2]. Such a model is close to magnetostrophic balance [3], to which we have added viscosity to the dominant forces of Coriolis, pressure, Lorentz and buoyancy, believed to be a good approximation of the Earth's dynamo in the convective time scale. We chose to study the MHD system driven by a static temperature anomaly to mimic the actual inner working of Earth's dynamo system, avoiding at this stage the further complication of solving for the time dependent temperature field. At the heart of the models is a time-dependent magnetic field to which the core-flow is enslaved. In previous work we laid the foundation of the adjoint methodology, applied to a subset of the full equations [4]. As an intermediate step towards our ultimate vision of applying the techniques to a fully dynamic mode of the Earth's core tuned to geomagnetic observations, we present the intermediate step of applying the adjoint technique to the inertia-free Navier-Stokes equation in continuous form. We use synthetic observations derived from evolving a geophysically-reasonable magnetic field profile as the initial condition of our MHD system. Based on our study, we also propose several different strategies for accurately

  3. The post-stishovite phase transition in hydrous alumina-bearing SiO2 in the lower mantle of the earth.

    Science.gov (United States)

    Lakshtanov, Dmitry L; Sinogeikin, Stanislav V; Litasov, Konstantin D; Prakapenka, Vitali B; Hellwig, Holger; Wang, Jingyun; Sanches-Valle, Carmen; Perrillat, Jean-Philippe; Chen, Bin; Somayazulu, Maddury; Li, Jie; Ohtani, Eiji; Bass, Jay D

    2007-08-21

    Silica is the most abundant oxide component in the Earth mantle by weight, and stishovite, the rutile-structured (P4(2)/mnm) high-pressure phase with silica in six coordination by oxygen, is one of the main constituents of the basaltic layer of subducting slabs. It may also be present as a free phase in the lower mantle and at the core-mantle boundary. Pure stishovite undergoes a displacive phase transition to the CaCl(2) structure (Pnnm) at approximately 55 GPa. Theory suggests that this transition is associated with softening of the shear modulus that could provide a significant seismic signature, but none has ever been observed in the Earth. However, stishovite in natural rocks is expected to contain up to 5 wt % Al(2)O(3) and possibly water. Here we report the acoustic velocities, densities, and Raman frequencies of aluminum- and hydrogen-bearing stishovite with a composition close to that expected in the Earth mantle at pressures up to 43.8(3) GPa [where (3) indicates an uncertainty of 0.3 GPa]. The post-stishovite phase transition occurs at 24.3(5) GPa (at 298 K), far lower than for pure silica at 50-60 GPa. Our results suggest that the rutile-CaCl(2) transition in natural stishovite (with 5 wt % Al(2)O(3)) should occur at approximately 30 GPa or approximately 1,000-km depth at mantle temperatures. The major changes in elastic properties across this transition could make it visible in seismic profiles and may be responsible for seismic reflectors observed at 1,000- to 1,400-km depth.

  4. Evolution of the Oxidation State of the Earth's Mantle: Challenges of High Pressure Quenching

    Science.gov (United States)

    Danielson, L. R.; Righter, K.; Keller, L. P.; Rahman, Z.

    2015-12-01

    The oxidation state of the Earth's mantle during formation remains an unresolved question, whether it was constant throughout planetary accretion [1], transitioned from reduced to oxidized [2,3,4], or from oxidized to reduced [1,5]. We investigate the stability of Fe3+ at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the Earth's mantle. Experiments of more mafic compositions and at higher pressures commonly form a polyphase quench intergrowth composed primarily of pyroxenes, with interstitial glass which hosts nearly all of the more volatile minor elements. In our previous experiments on shergottite compositions, variable fO2, T, and P <4 GPa, Fe3+/ΣFe decreased slightly with increasing P, similar to terrestrial basalt [6,7,8]. For oxidizing experiments < 7GPa, Fe3+/ΣFe decreased as well [9], but it's unclear from previous modelling whether the deeper mantle could retain significant Fe3+ [1,10]. Our current experiments expand our pressure range deeper into the Earth's mantle and focus on compositions and conditions relevant to the early Earth. Experiments with Knippa basalt as the starting composition were conducted at 1-8 GPa and 1800 °C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products from 7-8 GPa quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal Fe3+/2+. A number of different approaches have been employed to produce glassy samples that can be measured by EELS and XANES. A more intermediate andesite was used in one experiment, and decompression during quenching was attempted after [11], but both resulted in a finer grained polyphase texture. Experiments are currently underway to test how different capsule materials may affect quench texture. A preliminary experiment using liquid nitrogen to greatly enhance the rate of cooling of the assembly has also been attempted and

  5. Deep-focus earthquakes and recycling of water into the earth's mantle

    Science.gov (United States)

    Meade, Charles; Jeanloz, Raymond

    1991-01-01

    For more than 50 years, observations of earthquakes to depths of 100 to 650 kilometers inside earth have been enigmatic: at these depths, rocks are expected to deform by ductile flow rather than brittle fracturing or frictional sliding on fault surfaces. Laboratory experiments and detailed calculations of the pressures and temperatures in seismically active subduction zones indicate that this deep-focus seismicity could originate from dehydration and high-pressure structural instabilities occurring in the hydrated part of the lithosphere that sinks into the upper mantle. Thus, seismologists may be mapping the recirculation of water from the oceans back into the deep interior of the planet.

  6. Springtide-induced magnification of Earth mantle resonance causes tectonics and conceals universality of physics at all scales

    CERN Document Server

    Omerbashich, M

    2006-01-01

    I demonstrate two fundamental contributions. First, the Earth tectonics is generally a consequence of the springtide-induced magnification of mechanical resonance in the Earth mantle. The same mechanism that causes bridges to collapse under the soldiers step-marching makes also the Earth lithosphere fail under the springtide-induced magnification of the mantle resonance resulting in strong earthquakes. Secondly, by generalizing the above finding onto any body anywhere in all the Universes and at all times, I find that there is no distinction between physics at intergalactic, Newtonian, quantum, and smaller scales. Thus, the so-called constant of proportionality of physics, G, is not a constant but a parameter of a most general form: G = s e^2, nonlinearly varying amongst different scales s. Any scale-related variations of physics, erroneously recognized as such by Einstein and Planck, are only apparent and arise as a consequence of the Earth mantle springtide-induced extreme resonance, which is also criticall...

  7. A Model for Earth's Mantle Dynamic History for The Last 500 Ma and Its Implications for Continental Vertical Motions and Geomagnetism

    Science.gov (United States)

    Zhong, S.; Olson, P.; Zhang, N.

    2012-12-01

    Seismic tomography studies indicate that the Earth's mantle structure is characterized by African and Pacific seismically slow velocity anomalies (i.e., thermochemical piles) and circum Pacific seismically fast anomalies (i.e., degree 2) in the lower mantle. Mantle convection calculations including plate motion history for the last 120 Ma suggest that these degree 2 thermochemical structures result from plate subduction history (e.g., McNamara and Zhong, 2005). Given the important controls of mantle structure and dynamics on surface tectonics and volcanism and geodynamo in the core, an important question is the long-term evolution of mantle structures, for example, was the mantle structure in the past similar to the present-day's degree 2 structure, or significantly different from the present day? To address this question, we constructed a proxy model of plate motions for the African hemisphere for the last 450 Ma using the paleogeographic reconstruction of continents constrained by paleomagnetic and geological observations (e.g., Pangea assembly and breakup). Coupled with assumed oceanic plate motions for the Pacific hemisphere before 120 Ma, this proxy model for the plate motion history is used in three dimensional spherical models of mantle convection to study the evolution of mantle structure since the Early Paleozoic. Our model calculations reproduce well the present day degree 2 mantle structure including the African and Pacific thermochemical piles, and present-day surface heat flux, bathymetry and dynamic topography. Our results suggest that while the mantle in the African hemisphere before the assembly of Pangea is dominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of the African superplume structure can be formed before ˜230 Ma. Particularly, the last 120 Ma plate motion plays an important role in generating the African thermochemical pile. We reconstruct temporal

  8. Metal-silicate partitioning of U: Implications for the heat budget of the core and evidence for reduced U in the mantle

    Science.gov (United States)

    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.

  9. The Earth's Mantle Is Solid: Teachers' Misconceptions About the Earth and Plate Tectonics.

    Science.gov (United States)

    King, Chris

    2000-01-01

    Discusses the misconceptions revealed by the teachers' answers and outlines more accurate answers and explanations based on established evidence and uses these to provide a more complete understanding of plate tectonic process and the structure of Earth. (Author/YDS)

  10. The Earth's Mantle Is Solid: Teachers' Misconceptions About the Earth and Plate Tectonics.

    Science.gov (United States)

    King, Chris

    2000-01-01

    Discusses the misconceptions revealed by the teachers' answers and outlines more accurate answers and explanations based on established evidence and uses these to provide a more complete understanding of plate tectonic process and the structure of Earth. (Author/YDS)

  11. Light matter in the core of the Earth: its identity, quantity and temperature using tricritical phenomena

    CERN Document Server

    Aitta, A

    2008-01-01

    Light elements in the iron-rich core of the Earth are important indicators for the evolution of our planet. Their amount and distribution, and the temperature in the core, are essential for understanding how the core and the mantle interact and for modelling the geodynamo which generates the planetary magnetic field. However, there is a longstanding controversy surrounding the identity and quantity of the light elements. Here, the theory of tricritical phenomena is employed as a precise theoretical framework to study solidification at the high pressures and temperatures where both experimental and numerical methods are complicated to implement and have large uncertainties in their results. Combining the theory with the most reliable iron melting data and the Preliminary Reference Earth Model (PREM) seismic data, one obtains the solidification temperature at the inner core boundary (ICB) for both pure iron and for the alloy of iron and light elements in the actual core melt. One also finds a value of about 2.5...

  12. Differentiation of crusts and cores of the terrestrial planets - Lessons for the early earth

    Science.gov (United States)

    Solomon, S. C.

    1980-01-01

    The extent and mechanisms of global differentiation and the early thermal and tectonic histories of the terrestrial planets are surveyed in order to provide constraints on the first billion years of earth history. Indirect and direct seismic evidence for crusts on the moon, Mars and Venus is presented, and it is pointed out that substantial portions of these crusts have been in place since the cessation of heavy bombardment of the inner solar system four billion years ago. Evidence for sizable cores on Mars and Mercury and a small core on the moon is also discussed, and the heat involved in core formation is pointed out. Examination of the volcanic and tectonic histories of planets lacking plate tectonics indicates that core formation was not closely linked to crust formation on the moon or Mars, with chemical differentiation restricted to shallow regions, and was much more extensive on Mercury. Extension of these considerations to the earth results in a model of a hot and vigorously convecting mantle with an easily deformable crust immediately following core formation, and the gradual development of a lithosphere and plates.

  13. Hot Spots and Mantle Plumes: A Window Into the Deep Earth and a Lesson on How Science Really Works

    Science.gov (United States)

    Caplan-Auerbach, J.

    2010-12-01

    Despite years of discussion, debate and controversy over the causes of ocean island volcanism, most students simply learn that such features form from fixed plumes of hot material rising from the core mantle boundary. Although we know that the Hawaiian plume exhibited substantial southward motion, most introductory geology textbooks still report that hot spots are fixed and that the Hawaiian-Emperor bend reflects a change in plate motion. That mantle plumes are the focus of significant controversy within the scientific community is rarely, if ever, discussed, and alternative models for the formation of intraplate volcanoes are ignored. Students may thus complete their studies without learning about the dynamic debate focused on the existence and formation of mantle plumes. This issue represents an opportunity for students to see how science really works, how new models are constructed, and what distinguishes a hypothesis from a theory. The culminating project in Western Washington University’s Introduction to Geophysics class, a course required for the BS degree in geology, focuses on the hot spot and mantle plume debate. For the first nine weeks of the quarter students learn about general topics in geophysics including plate tectonics, magnetism, seismology, gravity and heat flow. At the end of the course, students break into small research groups with the goal of investigating how geophysics may be used to address three questions: (1) Do ocean island volcanoes form from mantle plumes? (2) Are “hot spots” actually hot? (3) Are hot spots stationary? Each group examines how these questions may be addressed using a specific geophysical tool. In addition to the five topics described above, a sixth group investigates the question of “if not hot spots/mantle plumes, how do ocean island volcanoes form?” Students read the current literature on the topic and present their results to their classmates. Presentations focus on topics such as the use of seismic

  14. Mapping the Earth's mantle in 4D using the proton microprobe

    Science.gov (United States)

    Griffin, W. L.; Ryan, C. G.; Win, T. T.

    1995-09-01

    The CSIRO proton microprobe is used to study the trace element chemistry of garnet and chromite grains recovered from kimberlites and other volcanic rocks, both to develop new diamond exploration methods and to further understanding of the makeup and evolution of the earth's upper mantle. Analysis of the partitioning of trace and major elements between garnet and chromite and their coexisting phases in mantle rocks has led to the development of two single-mineral thermometers and a barometer. Trace Ni in Cr-pyrope garnet is used to determine the equilibration temperature ( TNi) of each garnet grain. This is the temperature of the garnet in its source rock before it was entrained in the erupting magma. Similarly, trace Zn in chromite yields an estimate ( TZn) of its equilibration temperature. To relate these temperature to depth in the lithosphere a measure of pressure ( PCr) has been developed that estimates pressure directly from Cr-pyrope garnet composition and TNi. This breakthrough enables the information on rock composition and metasomatic processes held in the trace and major element chemistry of each garnet to be located in P and T and thus placed in its stratigraphic context. Y, Ga and Cr provide information on mantle depletion by partial melting. Zr, Y and Ti provide clues to metasomatic processes such as infiltration of asthenospheric melts. Together the result is both an improved diamond exploration tool and a method of mapping the 3D structure, lithology and metasomatic processes in the lithosphere. With the added knowledge of the date of each intrusion, these methods permit the construction of 4D maps of the lithosphere, charting variation in mantle composition both laterally, with depth and through time.

  15. Redox-freezing and nucleation of diamond via magnetite formation in the Earth's mantle.

    Science.gov (United States)

    Jacob, Dorrit E; Piazolo, Sandra; Schreiber, Anja; Trimby, Patrick

    2016-06-21

    Diamonds and their inclusions are unique probes into the deep Earth, tracking the deep carbon cycle to >800 km. Understanding the mechanisms of carbon mobilization and freezing is a prerequisite for quantifying the fluxes of carbon in the deep Earth. Here we show direct evidence for the formation of diamond by redox reactions involving FeNi sulfides. Transmission Kikuchi Diffraction identifies an arrested redox reaction from pyrrhotite to magnetite included in diamond. The magnetite corona shows coherent epitaxy with relict pyrrhotite and diamond, indicating that diamond nucleated on magnetite. Furthermore, structures inherited from h-Fe3O4 define a phase transformation at depths of 320-330 km, the base of the Kaapvaal lithosphere. The oxidation of pyrrhotite to magnetite is an important trigger of diamond precipitation in the upper mantle, explaining the presence of these phases in diamonds.

  16. Redox-freezing and nucleation of diamond via magnetite formation in the Earth's mantle

    Science.gov (United States)

    Jacob, Dorrit E.; Piazolo, Sandra; Schreiber, Anja; Trimby, Patrick

    2016-06-01

    Diamonds and their inclusions are unique probes into the deep Earth, tracking the deep carbon cycle to >800 km. Understanding the mechanisms of carbon mobilization and freezing is a prerequisite for quantifying the fluxes of carbon in the deep Earth. Here we show direct evidence for the formation of diamond by redox reactions involving FeNi sulfides. Transmission Kikuchi Diffraction identifies an arrested redox reaction from pyrrhotite to magnetite included in diamond. The magnetite corona shows coherent epitaxy with relict pyrrhotite and diamond, indicating that diamond nucleated on magnetite. Furthermore, structures inherited from h-Fe3O4 define a phase transformation at depths of 320-330 km, the base of the Kaapvaal lithosphere. The oxidation of pyrrhotite to magnetite is an important trigger of diamond precipitation in the upper mantle, explaining the presence of these phases in diamonds.

  17. The relation of mantle heterogeneity to the bulk composition and origin of the earth

    Science.gov (United States)

    Smith, J. V.

    1980-01-01

    The heterogeneity of the mantle can be viewed in the context of models for accretion of the terrestrial planets from the solar nebula. Oxygen isotope ratios and mineralogy indicate the existence of hot planetesimals of diverse compositions. Assuming that nebular condensates range from a reduced state near the sun to an oxidized state near Jupiter, a new model is proposed for heterogeneous accretion of the earth beginning with hot, reduced condensates and ending with cool, oxidized condensates. The Ganapathy-Anders cosmochemical model for the bulk composition of the earth was tested by summing measured compositions for the three outer zones and likely compositions for the inner zones. Revisions are suggested, including reduction of the content of the early condensate from that suggested by taking the U concentration as 30 ng/g, as suggested by the naive interpretation of the heat flow.

  18. Constraining the Composition of the Earth from Long-period Electromagnetic Sounding of the Lower Mantle

    DEFF Research Database (Denmark)

    Khan, A.; Connolly, J.; Olsen, Nils

    2O3-SiO2, rather than subsurface electrical conductivity structure, which is only an indirect means of estimating the former parameters. Using minimisation of Gibbs free energy, we calculate the stable mineral phases, their modes and densities. The mineral modes are combined with recent laboratory......We reexamine the problem of inverting global transfer functions to constrain the internal structure of the Earth. We go beyond the conventional approach of inverting electromagnetic induction data by inverting directly for chemical composition and thermal state, using the model system CaO-FeO-MgO-Al...... and experimental mineral electrical conductivity data are consistent with a silicate earth, with a composition close to the pyrolite model and additionally seem to require a low temperature mantle geotherm....

  19. Evolution of planetary cores and the Earth-Moon system from Nb/Ta systematics.

    Science.gov (United States)

    Münker, Carsten; Pfänder, Jörg A; Weyer, Stefan; Büchl, Anette; Kleine, Thorsten; Mezger, Klaus

    2003-07-04

    It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 +/- 0.3) and the Moon (17.0 +/- 0.8) are below the chondritic ratio of 19.9 +/- 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago.

  20. Fluid flow near the surface of earth's outer core

    Science.gov (United States)

    Bloxham, Jeremy; Jackson, Andrew

    1991-01-01

    This review examines the recent attempts at extracting information on the pattern of fluid flow near the surface of the outer core from the geomagnetic secular variation. Maps of the fluid flow at the core surface are important as they may provide some insight into the process of the geodynamo and may place useful constraints on geodynamo models. In contrast to the case of mantle convection, only very small lateral variations in core density are necessary to drive the flow; these density variations are, by several orders of magnitude, too small to be imaged seismically; therefore, the geomagnetic secular variation is utilized to infer the flow. As substantial differences exist between maps developed by different researchers, the possible underlying reasons for these differences are examined with particular attention given to the inherent problems of nonuniqueness.

  1. Fluid flow near the surface of earth's outer core

    Science.gov (United States)

    Bloxham, Jeremy; Jackson, Andrew

    1991-01-01

    This review examines the recent attempts at extracting information on the pattern of fluid flow near the surface of the outer core from the geomagnetic secular variation. Maps of the fluid flow at the core surface are important as they may provide some insight into the process of the geodynamo and may place useful constraints on geodynamo models. In contrast to the case of mantle convection, only very small lateral variations in core density are necessary to drive the flow; these density variations are, by several orders of magnitude, too small to be imaged seismically; therefore, the geomagnetic secular variation is utilized to infer the flow. As substantial differences exist between maps developed by different researchers, the possible underlying reasons for these differences are examined with particular attention given to the inherent problems of nonuniqueness.

  2. Inner-Most Inner Core: Distinct Region at the Center of the Earth

    Science.gov (United States)

    Ishii, M.; Dziewoński, A. M.

    2002-12-01

    Although the presence of anisotropy in the inner core is widely accepted, inferences of its strength and depth dependence vary considerably from model to model. We have recently shown that a significant fraction of inner-core sensitive (normal-mode and absolute/differential travel-time) data is reconciled by a model in which anisotropy does not vary with radius. This model predicts an almost linear dependence of travel-time residuals on cos2 ξ , where ξ is the angle between the ray path and the symmetry axis. The simple anisotropy model fits the absolute travel-time data well at all distance ranges except between 173° and 180°, where a strong dependence on (cos2 ξ )2 is observed. This distance range corresponds to the innermost 300~km of the Earth, where mode constraints are weak (because eigenfunctions must vanish at the center of the Earth), and where constraints from differential travel times ({ {PKP}} {AB}}-{ {PKP}}{ {DF}) are likely contaminated due to unmodelled mantle structure. We refer to this new region as the inner-most inner core. The (cos2 ξ )2 signal that indicates the existence of a distinct inner-most inner core is even more evident when effects due to anisotropy in the upper 920~km of the inner core are removed. Furthermore, division of the data into various subsets consistently reveals the anomalous dependence on (cos2 ξ )2, suggesting that it is a robust feature unique to this distance range. When the travel times are inverted for anisotropic parameters, we obtain a model with a slow direction orientered ~45° from the equator, in contrast to the bulk inner core where the slowest wave propagation occurs when the rays are parallel to the equatorial plane. The existence of the inner-most inner core has significant consequences in our understanding of the Earth's evolution. This region may represent fossil evidence of two episodes of inner core development or changes in the pattern of convection in the outer core. Furthermore, if the inner

  3. Crustal decoupling and mantle dynamics on Venus: implications for Earth-like planets

    Science.gov (United States)

    Ghail, Richard

    2013-04-01

    Venus is physically similar to Earth but with a hot dense atmosphere and no oceans; four-fifths of its surface is apparently volcanic in origin and likely basaltic in composition. Erosion and sedimentary processes are largely absent, preserving a near-random distribution of impact craters that led to the hypothesis of episodic global resurfacing, which proposes that the entire lithosphere was recycled in a short period (~50 Ma) about 750 Ma ago, and is currently in a stagnant-lid state, in which the crust and lithosphere are strongly coupled to a sluggishly convecting mantle. This hypothesis is at odds with the complex and diverse range of geological features on Venus that imply a continuum of activity, at a level at least similar to Earth's continental interiors, with little evidence for a sudden change in past rates of activity. An alternative hypothesis is presented here based on geological interpretation, topographic and gravitational data, and geomechanical inferences. The elevated surface temperature results in a weak lower crust, similar to certain terrestrial continental crust strength profiles, that is effectively decoupled from the mantle. The subcrustal lithosphere is therefore able to behave in a plate-like way, with boundary conditions defined by the base of the crust. Hypsographic data are used to infer the average plate thickness (100 ± 6 km), subcrustal plate creation rate (3·8 to 4·6 km² a-¹) and mean half-spreading rate (29 to 35 mm a-¹). The observed 55,000 to 65,000 km long network of rift systems observed on Venus are predicted to correspond to subcrustal spreading ridges; fits to their topography demonstrate that they are consistent with the model but with a range of subcrustal spreading rates from 11 to 97 mm a-¹. Geoid lows correspond well with predicted sites of subcrustal subduction. Since stress transmission is restricted by the weak lower crust, the surface is tectonically modified at only a modest rate, similar to terrestrial

  4. Electrical resistivity and thermal conductivity of liquid Fe alloys at high P and T, and heat flux in Earth's core.

    Science.gov (United States)

    de Koker, Nico; Steinle-Neumann, Gerd; Vlcek, Vojtech

    2012-03-13

    Earth's magnetic field is sustained by magnetohydrodynamic convection within the metallic liquid core. In a thermally advecting core, the fraction of heat available to drive the geodynamo is reduced by heat conducted along the core geotherm, which depends sensitively on the thermal conductivity of liquid iron and its alloys with candidate light elements. The thermal conductivity for Earth's core is very poorly constrained, with current estimates based on a set of scaling relations that were not previously tested at high pressures. We perform first-principles electronic structure computations to determine the thermal conductivity and electrical resistivity for Fe, Fe-Si, and Fe-O liquid alloys. Computed resistivity agrees very well with existing shock compression measurements and shows strong dependence on light element concentration and type. Thermal conductivity at pressure and temperature conditions characteristic of Earth's core is higher than previous extrapolations. Conductive heat flux near the core-mantle boundary is comparable to estimates of the total heat flux from the core but decreases with depth, so that thermally driven flow would be constrained to greater depths in the absence of an inner core.

  5. Temperature Dependent Mössbauer Spectra of Aluminous Perovskite and Implications for the Earth's Lower Mantle

    Science.gov (United States)

    Liu, J.; Mysen, B. O.; Fei, Y.; Mao, H.; Hemley, R. J.; Li, J.

    2011-12-01

    Perovskite in the Earth's lower mantle contains 4.0~5.3 weight % Al (Wood and Rubie, Science. 1996). To date Mössbauer data on Al-PV under cryogenic conditions have not been reported. In this study, we measured Mössbauer spectra of an Al-PV sample at 65 to 300 K and 1 bar. The temperature dependence of the center shift, fitted by Debye model, gives recoil-free fractions of fFe2+ and fFe3+, which are critical for calculating Fe3+/⊙Fe ratio. The high relative concentration of Fe3+ of our Al-PV sample is consistent with previous studies on Al-PV samples containing a similar amount of aluminum (Lauterbach et al., Contrib Mineral Petrol. 2000). However, it cannot be attributed to disproportionation of Fe2+ (Frost et al., Nature. 2004), because neither metallic iron nor wüstite was observed in the Mössbauer spectra or electron probe analysis. In comparison to other capsule materials used in previous studies, such as graphite, iron, or rhenium, the gold capsule used in our synthesis is chemically inert, and does not influence the oxidation environment. A likely candidate to oxidize Fe2+ into Fe3+ in PV structure is H2O trapped as moisture. Earth's lower mantle may contain 2.5~5 times H2O of the present ocean's mass (Murakami et al., Science. 2002; Litasov et al., Earth Planet. Sci. Lett. 2003), a high Fe3+/⊙Fe ratio in lower mantle Al-PV can be achieved without disproportionation of Fe2+. Recent studies (McCammon et al., Nature Geosci. 2008; Lin et al., Nature Geosci. 2008) found a high quadrupole splitting (QS) (~4 mm s-1) component in Al-free PV at pressures above 30 GPa, and assigned it to intermediate-spin ferrous iron. The high QS component in our Al-PV sample has similar hyperfine parameters. Its relative concentration changes with temperature, possibly due to a temperature-induced change in the degree of lattice distortion (Bengtson et al., Geophys. Res. Lett. 2009).

  6. Regionalized temperature variations in the upper 400 km of the Earth's mantle

    Science.gov (United States)

    Tralli, David M.; Ita, Joel J.

    Tectonically regionalized variations in the temperature of the upper 400 km of the Earth's mantle are estimated from analysis of global seismic travel-time data cataloged by the International Seismological Centre (ISC). Seismic parameter profiles are determined from estimates of P and S velocities obtained by tau inversion. Summary phase diagrams for the olivine and pyroxene-garnet subsystems are constructed in conjunction with a thermodynamic potential formulation that allows self-consistent determination of density, bulk modulus and adiabats throughout the pressure and temperature regimes of the mantle. Perturbations in estimated seismic parameters are expressed in terms of variations in temperature using the model temperature derivatives of the bulk modulus and density at a given temperature and pressure. Confidence bounds on the velocity estimates are used to place corresponding bounds on the constructed seismic parameters. A simple differential relationship is solved iteratively to obtain a temperature variation for a given variation in seismic parameter. This approach allows the estimation of a range of seismically determined temperature variations by employing a given compositional model. Results indicate that whereas the P and S velocity variations in the upper mantle are consistent with the tectonic regionalization, variations in V p/V s ratios are irregular. This leads to unstable estimates of the seismic parameters and thus estimates of mean temperature anomalies, typically within 600°C of the weighted mean, that are inconsistent with the regionalized seismic data. A comparison of two compositional models is used to show the trade-off with estimated temperature variations. A refined regionalization and analysis of a larger ISC data set are suggested to stabilize the S velocity inversion, reduce statistical uncertainties on the seismic parameters, and thus improve constraints on estimated temperature variations.

  7. Heterogeneous Earth Accretion and Incomplete Metal-Silicate Reequilibration at High Pressure During Core Formation

    Science.gov (United States)

    Rubie, D. C.; Mann, U.; Frost, D. J.; Kegler, P.; Holzheid, A.; Palme, H.

    2007-12-01

    We present a new model of core formation, based on the partitioning of siderophile elements, that involves accreting the Earth through a series of collisions with smaller bodies that had already differentiated at low pressure. Each impact results in a magma ocean in which the core of the impactor reequilibrates with silicate liquid at high pressure before merging with the Earth's protocore. The oxygen contents of the chondritic compositions of the proto-Earth and impactors can be varied. The compositions of coexisting metal and silicate are determined through mass balance combined with partitioning equations for Ni, FeO, Si and other siderophile elements. The oxygen fugacity is fixed by the partitioning of FeO and is a function of P, T and bulk oxygen content. An important constraint for core formation is that core-mantle partition coefficients for Ni and Co must both converge to values of 23-28. Based on a recent study of the partitioning of Ni and Co over a wide P-T range (Kegler et al., EPSL, submitted) together with other published data, this constraint is not satisfied by a single- stage core formation model at any conditions because the partition coefficients converge at values that are much too low. In the present multi-stage model, the correct values can be reached if only part of each impactor core reequilibrates with silicate liquid in the magma ocean (as proposed by previous models based on Hf-W isotope studies). Physically, this would mean that impactor cores fail to emulsify completely as they sink through the magma ocean. Incorporating other elements (e.g. V and Cr) in the model requires, in addition, that the bulk composition of the impactors changes during accretion from reduced (FeO-poor) to oxidised FeO-rich). Then, with the resulting increase in fO2, incomplete reequilibration of the cores during the final 20-30% of Earth accretion is required to satisfy the Ni-Co constraint. In addition, this model enables the concentrations of O and Si in the

  8. Super-Earths as Failed Cores in Orbital Migration Traps

    Science.gov (United States)

    Hasegawa, Yasuhiro

    2016-11-01

    I explore whether close-in super-Earths were formed as rocky bodies that failed to grow fast enough to become the cores of gas giants before the natal protostellar disk dispersed. I model the failed cores’ inward orbital migration in the low-mass or type I regime to stopping points at distances where the tidal interaction with the protostellar disk applies zero net torque. The three kinds of migration traps considered are those due to the dead zone's outer edge, the ice line, and the transition from accretion to starlight as the disk's main heat source. As the disk disperses, the traps move toward final positions near or just outside 1 au. Planets at this location exceeding about 3 M ⊕ open a gap, decouple from their host traps, and migrate inward in the high-mass or type II regime to reach the vicinity of the star. I synthesize the population of planets that formed in this scenario, finding that a fraction of the observed super-Earths could have been failed cores. Most super-Earths that formed this way have more than 4 M ⊕, so their orbits when the disks dispersed were governed by type II migration. These planets have solid cores surrounded by gaseous envelopes. Their subsequent photoevaporative mass loss is most effective for masses originally below about 6 M ⊕. The failed core scenario suggests a division of the observed super-Earth mass-radius diagram into five zones according to the inferred formation history.

  9. Interaction of mantle plume heads with the earth's surface and onset of small-scale convection

    Science.gov (United States)

    Griffiths, R. W.; Campbell, I. H.

    1991-10-01

    The interaction of a mantle plume head with the earth's surface was examined by studying the behavior of a spherical blob of a buoyant fluid under the effect of gravity which forces it toward either a rigid horizontal boundary or a free surface. In the experiments, buoyant spheres of diapir fluid having no surface tension and extremely small Reynolds numbers but diameters as large as are practical in the laboratory were injected into wide cylindrical tanks filled with viscous (nu = 149 sq cm/sec) glucose syrup. Experimental results are presented for the thinning and lateral spreading of the bouyant fluid and for the thinning of the squeeze layer for both the case of a rigid, nonslip boundary (a rigid Perspex lid) and that of a free surface. These are compared with similarity scaling laws based on a balance between the buoyancy of the diapir and the viscous stresses in the diapir's surroundings.

  10. Precessional states in a laboratory model of the Earth's core

    Science.gov (United States)

    Triana, S. A.; Zimmerman, D. S.; Lathrop, D. P.

    2012-04-01

    A water-filled three-meter diameter spherical shell, geometrically similar to the Earth's core, shows precessionally forced flows. The precessional torque is supplied by the daily rotation of the laboratory by the Earth. We identify the precessionally forced flow to be primarily the spin-over inertial mode, i.e., a uniform vorticity flow whose rotation axis is not aligned with the sphere's rotation axis. A systematic study of the spin-over mode is carried out, showing that the amplitude depends on the ratio of precession to rotation rates (the Poincaré number), in marginal qualitative agreement with Busse's (1968) laminar theory. We find its phase differs significantly though, likely due to topographic effects. At high rotation rates, free shear layers are observed. Comparison with previous computational studies and implications for the Earth's core are discussed.

  11. Little Earth Experiment: an instrument to model planetary cores

    CERN Document Server

    Aujogue, Kelig; Bates, Ian; Debray, François; Sreenivasan, Binod

    2016-01-01

    In this paper, we present a new experimental facility, Little Earth Experiment, designed to study the hydrodynamics of liquid planetary cores. The main novelty of this apparatus is that a transparent electrically conducting electrolyte is subject to extremely high magnetic fields (up to 10T) to produce electromagnetic effects comparable to those produced by moderate magnetic fields in planetary cores. This technique makes it possible to visualise for the first time the coupling between the principal forces in a convection-driven dynamo by means of Particle Image Velocimetry (PIV) in a geometry relevant to planets. We first present the technology that enables us to generate these forces and implement PIV in a high magnetic field environment. We then show that the magnetic field drastically changes the structure of convective plumes in a configuration relevant to the tangent cylinder region of the Earth's core.

  12. Little Earth Experiment: An instrument to model planetary cores

    Science.gov (United States)

    Aujogue, Kélig; Pothérat, Alban; Bates, Ian; Debray, François; Sreenivasan, Binod

    2016-08-01

    In this paper, we present a new experimental facility, Little Earth Experiment, designed to study the hydrodynamics of liquid planetary cores. The main novelty of this apparatus is that a transparent electrically conducting electrolyte is subject to extremely high magnetic fields (up to 10 T) to produce electromagnetic effects comparable to those produced by moderate magnetic fields in planetary cores. This technique makes it possible to visualise for the first time the coupling between the principal forces in a convection-driven dynamo by means of Particle Image Velocimetry (PIV) in a geometry relevant to planets. We first present the technology that enables us to generate these forces and implement PIV in a high magnetic field environment. We then show that the magnetic field drastically changes the structure of convective plumes in a configuration relevant to the tangent cylinder region of the Earth's core.

  13. Global variations in azimuthal anisotropy of the Earth's upper mantle and crust

    Science.gov (United States)

    Schaeffer, A. J.; Lebedev, S.

    2013-12-01

    Deformation within the Earth's crust and mantle often results in crystallographic preferred orientations that produce measurable seismic anisotropy. Shear wave splitting measurements have the benefit of excellent lateral resolution and are an unambiguous indicator of the presence of seismic anisotropy; however, they suffer from poor depth resolution (integrated measurement from CMB to surface), in addition to being geographically limited (measurements only made at seismometer locations). The analysis of surface wave propagation also provides insight into the azimuthal variations in wave-speed, but with significantly better depth resolution. Thanks to the rapid increase in the number of seismic stations around the world, increasingly accurate, high-resolution 3D models of azimuthal anisotropy can be calculated using surface-wave tomography. We present our new global, azimuthally anisotropic model of the upper mantle and the crust. Compared to its recent predecessor, SL2013sv (Schaeffer and Lebedev, 2013), it is constrained by an even larger waveform fit dataset (>900,000 versus 712,000 vertical-component seismograms, respectively) and was computed using a more precise regularization of anisotropy, tuned to honour the amplitude and orientation of the anisotropic terms uniformly, including near the poles. Automated, multimode waveform inversion was used to extract structural information from surface and S wave forms, yielding resolving power from the crust down to the transition zone. Our unprecedentedly large waveform dataset, with complementary high-resolution regional arrays (including USArray) and global network sub-sets within it, produces improved resolution of global azimuthal anisotropy patterns. The model also reveals smaller scale patterns of 3D anisotropy variations related to regional lithospheric deformation and mantle flow, in particular in densely sampled regions. In oceanic regions, we examine the strength of azimuthal anisotropy, as a function of

  14. Melting of iron close to Earth's inner core boundary conditions and beyond

    CERN Document Server

    Harmand, M; Mazevet, S; Bouchet, J; Denoeud, A; Dorchies, F; Feng, Y; Fourment, C; Galtier, E; Gaudin, J; Guyot, F; Kodama, R; Koenig, M; Lee, H J; Miyanishi, K; Morard, G; Musella, R; Nagler, B; Nakatsutsumi, M; Ozaki, N; Recoules, V; Toleikis, S; Vinci, T; Zastrau, U; Zhu, D; Benuzzi-Mounaix, A

    2014-01-01

    Several important geophysical features such as heat flux at the Core-Mantle Boundary or geodynamo production are intimately related with the temperature profile in the Earth's core. However, measuring the melting curve of iron at conditions corresponding to the Earth inner core boundary under pressure of 330 GPa has eluded scientists for several decades. Significant discrepancies in previously reported iron melting temperatures at high pressure have called into question the validity of dynamic measurements. We report measurements made with a novel approach using X-ray absorption spectroscopy using an X-ray free electron laser source coupled to a laser shock experiment. We determine the state of iron along the shock Hugoniot up to 420 GPa (+/- 50) and 10800 K (+/- 1390) and find an upper boundary for the melting curve of iron by detecting solid iron at 130 GPa and molten at 260, 380 and 420 GPa along the shock Hugoniot. Our result establishes unambiguous agreement between dynamic measurement and recent extrapo...

  15. Fast torsional waves and strong magnetic field within the Earth's core.

    Science.gov (United States)

    Gillet, Nicolas; Jault, Dominique; Canet, Elisabeth; Fournier, Alexandre

    2010-05-06

    The magnetic field inside the Earth's fluid and electrically conducting outer core cannot be directly probed. The root-mean-squared (r.m.s.) intensity for the resolved part of the radial magnetic field at the core-mantle boundary is 0.3 mT, but further assumptions are needed to infer the strength of the field inside the core. Recent diagnostics obtained from numerical geodynamo models indicate that the magnitude of the dipole field at the surface of a fluid dynamo is about ten times weaker than the r.m.s. field strength in its interior, which would yield an intensity of the order of several millitesla within the Earth's core. However, a 60-year signal found in the variation in the length of day has long been associated with magneto-hydrodynamic torsional waves carried by a much weaker internal field. According to these studies, the r.m.s. strength of the field in the cylindrical radial direction (calculated for all length scales) is only 0.2 mT, a figure even smaller than the r.m.s. strength of the large-scale (spherical harmonic degree n geodynamo models with studies of geostrophic motions in the Earth's core that rely on geomagnetic data. From an ensemble inversion of core flow models, we find a torsional wave recurring every six years, the angular momentum of which accounts well for both the phase and the amplitude of the six-year signal for change in length of day detected over the second half of the twentieth century. It takes about four years for the wave to propagate throughout the fluid outer core, and this travel time translates into a slowness for Alfvén waves that corresponds to a r.m.s. field strength in the cylindrical radial direction of approximately 2 mT. Assuming isotropy, this yields a r.m.s. field strength of 4 mT inside the Earth's core.

  16. Evidence for back scattering of near-podal seismic P'P' waves from the 150-220 km zone in Earth's upper mantle

    Energy Technology Data Exchange (ETDEWEB)

    Tkalcic, H; Flanagan, M P; Cormier, V F

    2005-07-15

    The deepest and most inaccessible parts of Earth's interior--the core and core-mantle boundary regions can be studied from compressional waves that turn in the core and are routinely observed following large earthquakes at epicentral distances between 145{sup o} and 180{sup o} (also called P', PKIKP or PKP waves). P'P' (PKPPKP) are P' waves that travel from a hypocenter through the Earth's core, reflect from the free surface and travel back through the core to a recording station on the surface. P'P' waves are sometimes accompanied by precursors, which were reported first in the 1960s as small-amplitude arrivals on seismograms at epicentral distances of about 50{sup o}-70{sup o}. Most prominent of these observed precursors were explained by P'P' waves generated by earthquakes or explosions that did not reach the Earth's surface but were reflected from the underside of first order velocity discontinuities at 410 and 660 km in the upper mantle mantle. Here we report the discovery of hitherto unobserved near-podal P'P' waves (at epicentral distance less than 10{sup o}) and very prominent precursors preceding the main energy by as much as 55 seconds. We interpret these precursors as a back scattered energy from undocumented structure in the upper mantle, in a zone between 150 and 220 km depth beneath Earth's surface. From these observations, we identify a frequency dependence of Q (attenuation quality factor) in the lithosphere that can be modeled by a flat relaxation spectrum below about 0.05-0.1 Hz and increasing with as the first power of frequency above this value, confirming pioneering work by B. Gutenberg.

  17. Evidence for back scattering of near-podal seismic P'P' waves from the 150-220 km zone in Earth's upper mantle

    Energy Technology Data Exchange (ETDEWEB)

    Tkalcic, H; Flanagan, M P; Cormier, V F

    2005-07-15

    The deepest and most inaccessible parts of Earth's interior--the core and core-mantle boundary regions can be studied from compressional waves that turn in the core and are routinely observed following large earthquakes at epicentral distances between 145{sup o} and 180{sup o} (also called P', PKIKP or PKP waves). P'P' (PKPPKP) are P' waves that travel from a hypocenter through the Earth's core, reflect from the free surface and travel back through the core to a recording station on the surface. P'P' waves are sometimes accompanied by precursors, which were reported first in the 1960s as small-amplitude arrivals on seismograms at epicentral distances of about 50{sup o}-70{sup o}. Most prominent of these observed precursors were explained by P'P' waves generated by earthquakes or explosions that did not reach the Earth's surface but were reflected from the underside of first order velocity discontinuities at 410 and 660 km in the upper mantle mantle. Here we report the discovery of hitherto unobserved near-podal P'P' waves (at epicentral distance less than 10{sup o}) and very prominent precursors preceding the main energy by as much as 55 seconds. We interpret these precursors as a back scattered energy from undocumented structure in the upper mantle, in a zone between 150 and 220 km depth beneath Earth's surface. From these observations, we identify a frequency dependence of Q (attenuation quality factor) in the lithosphere that can be modeled by a flat relaxation spectrum below about 0.05-0.1 Hz and increasing with as the first power of frequency above this value, confirming pioneering work by B. Gutenberg.

  18. What does Earth's electromagnetic field from ground and space measurements tell us about conductivity of the mantle?

    Science.gov (United States)

    Grayver, Alexander; Morschhauser, Achim; Kuvshinov, Alexey

    2017-04-01

    This contribution presents an overview of new models of Earth's mantle conductivity that have been derived using new methodologies and data from magnetic observatories and satellite missions such as CHAMP and Swarm. The electrical conductivity of the mantle provides a wealth of information on composition and temperature of the mantle material at depths. Lateral and vertical variations of this physical property allow us to constrain rheological and dynamic states of the tectonic processes in the subsurface. Electromagnetic (EM) induction methods is the only tool that can be used to study electrical conductivity at depth. They exploit natural electromagnetic field variations to derive frequency-dependent responses that are used to conduct Earth sounding. These variations originate from electric current systems in magnetosphere, ionosphere and even oceans. Over the last 17 years, almost continuous operation of low-orbit satellites measuring Earth's magnetic field, installation of new magnetic observatories in remote locations as well as substantial improvements in processing and modeling have enabled us to study mantle electrical conductivity using a variety of EM methods either globally or/and at different locations on Earth.

  19. The ab initio simulation of the Earth's core.

    Science.gov (United States)

    Alfè, D; Gillan, M J; Vocadlo, L; Brodholt, J; Price, G D

    2002-06-15

    The Earth has a liquid outer and solid inner core. It is predominantly composed of Fe, alloyed with small amounts of light elements, such as S, O and Si. The detailed chemical and thermal structure of the core is poorly constrained, and it is difficult to perform experiments to establish the properties of core-forming phases at the pressures (ca. 300 GPa) and temperatures (ca. 5000-6000 K) to be found in the core. Here we present some major advances that have been made in using quantum mechanical methods to simulate the high-P/T properties of Fe alloys, which have been made possible by recent developments in high-performance computing. Specifically, we outline how we have calculated the Gibbs free energies of the crystalline and liquid forms of Fe alloys, and so conclude that the inner core of the Earth is composed of hexagonal close packed Fe containing ca. 8.5% S (or Si) and 0.2% O in equilibrium at 5600 K at the boundary between the inner and outer cores with a liquid Fe containing ca. 10% S (or Si) and 8% O.

  20. Distribution of Sb, As, Ge, and In between metal and silicate during accretion and core formation in the Earth

    Science.gov (United States)

    Righter, K.; Nickodem, K.; Pando, K.; Danielson, L.; Boujibar, A.; Righter, M.; Lapen, T. J.

    2017-02-01

    A large number of siderophile (iron-loving) elements are also volatile, thus offering constraints on the origin of volatile elements in differentiated bodies such as Earth, Moon, Mars and Vesta. Metal-silicate partitioning data for many of these elements is lacking, making their overall mantle concentrations in these bodies difficult to model and origin difficult to distinguish between core formation and volatile depletion. To address this gap in understanding, we have undertaken systematic studies of four volatile siderophile elements - Sb, As, Ge and In - at variable temperature and variable Si content of metal. Several series were carried out at 1 GPa, and between 1500 and 1900 °C, for both C saturated and C-free conditions. The results show that temperature causes a decrease in the metal/silicate partition coefficient for all four elements. In addition, activity coefficients for each element have been determined and show a very strong dependence on Si content of Fe alloy. Si dissolved in metal significantly decreases the metal/silicate partition coefficients, at both 1600 and 1800 °C. The combination of temperature and Si content of the metal causes reduction of the metal-silicate partition coefficient to values that are close to those required for an origin of mantle As, Sb, Ge, and In concentrations by metal-silicate equilibrium processes. Combining these new results with previous studies on As, Sb, Ge, and In, allowed derivation of predictive expressions for metal/silicate partition coefficients for these elements which can then be applied to Earth. The expressions are applied to two scenarios for continuous accretion of Earth; specifically for constant and increasing fO2 during accretion. The results indicate that mantle concentrations of As, Sb, Ge, and In can be explained by metal-silicate equilibrium during an accretion scenario. The modeling is not especially sensitive to either scenario, although all element concentrations are explained better by a

  1. The Earth's Core: How Does It Work? Perspectives in Science. Number 1.

    Science.gov (United States)

    Carnegie Institution of Washington, Washington, DC.

    Various research studies designed to enhance knowledge about the earth's core are discussed. Areas addressed include: (1) the discovery of the earth's core; (2) experimental approaches used in studying the earth's core (including shock-wave experiments and experiments at high static pressures), the search for the core's light elements, the…

  2. Is Missing Xenon in the Earth's Inner Core

    CERN Document Server

    Zhu, Li; Zou, Guangtian; Ma, Yanming

    2013-01-01

    Atmospheric studies of Earth have shown that more than 90% of xenon (Xe) is depleted if compared to the abundance of chondritic meteorites1,2. This missing Xe paradox remains a long-standing mystery and has become an extensive debate2-18. Earlier high pressure experimental and theoretical studies3-5 that were unable to find the reaction of Xe with iron (Fe), the main constituent of the Earth's inner core, seemingly excluded the Earth's inner core from the Xe reservoir. Here we report the first evidence on the chemical reaction of Xe with Fe at conditions of Earth's inner core predicted through our developed first-principles structure searching technique unbiased by any known structural knowledge. We find that Xe and Fe form stable inter-metallic compound of XeFe3 stoichiometry by adopting a Cu3Au-type cubic structure. By virtue of an unusual Xe -> Fe charge transfer, Xe loses its chemical inertness by opening up the completed filled 5p electron shell and thereby functions as a 5p-like element, while Fe is neg...

  3. 3-D electromagnetic induction studies using the Swarm constellation: Mapping conductivity anomalies in the Earth's mantle

    DEFF Research Database (Denmark)

    Kuvshinov, A.; Sabaka, T.; Olsen, Nils

    2006-01-01

    satellite data that contain contributions from the core and lithosphere, from the rnagnetosphere and ionosphere (and their Earth-induced counterparts), as well as payload noise has been investigated. The model Studies have shown that C-responses obtained oil a regular grid might be used to map regional deep......An approach is presented to detect deep-seated regional conductivity anomalies by analysis of magnetic observations taken by low-Earth-orbiting satellites. The approach deals with recovery of C-responses on a regular grid and starts with a determination of time series of external and internal....... For validation of the approach, 3 years of realistic synthetic data at Simulated orbits of the forthcoming Swarm constellation of 3 satellites have been used. To obtain the synthetic data for a given 3-D conductivity Earth's model a time-domain scheme has been applied which relies oil a Fourier transformation...

  4. Earth's Inner Core dynamics induced by the Lorentz force

    CERN Document Server

    Lasbleis, M; Cardin, P; Labrosse, S

    2015-01-01

    Seismic studies indicate that the Earth's inner core has a complex structure and exhibits a strong elastic anisotropy with a cylindrical symmetry. Among the various models which have been proposed to explain this anisotropy, one class of models considers the effect of the Lorentz force associated with the magnetic field diffused within the inner core. In this paper we extend previous studies and use analytical calculations and numerical simulations to predict the geometry and strength of the flow induced by the poloidal component of the Lorentz force in a neutrally or stably stratified growing inner core, exploring also the effect of different types of boundary conditions at the inner core boundary (ICB). Unlike previous studies, we show that the boundary condition that is most likely to produce a significant deformation and seismic anisotropy is impermeable, with negligible radial flow through the boundary. Exact analytical solutions are found in the case of a negligible effect of buoyancy forces in the inne...

  5. Modelling the core magnetic field of the earth

    Science.gov (United States)

    Harrison, C. G. A.; Carle, H. M.

    1982-01-01

    It is suggested that radial off-center dipoles located within the core of the earth be used instead of spherical harmonics of the magnetic potential in modeling the core magnetic field. The off-center dipoles, in addition to more realistically modeling the physical current systems within the core, are if located deep within the core more effective at removing long wavelength signals of either potential or field. Their disadvantage is that their positions and strengths are more difficult to compute, and such effects as upward and downward continuation are more difficult to manipulate. It is nevertheless agreed with Cox (1975) and Alldredge and Hurwitz (1964) that physical realism in models is more important than mathematical convenience. A radial dipole model is presented which agrees with observations of secular variation and excursions.

  6. Duration of the hydrocarbon fluid formation under thermobaric conditions of the Earth's upper mantle

    Science.gov (United States)

    Mukhina, Elena; Kolesnikov, Anton; Kutcherov, Vladimir

    2016-04-01

    Deep abiogenic formation of hydrocarbons is an inherent part of the Earth's global carbon cycle. It was experimentally confirmed that natural gas could be formed from inorganic carbon and hydrogen containing minerals at pressure and temperature corresponding to the Earth's upper mantle conditions. Reaction between calcite, wustite and water in the large volume device was studied in several works. It was previously proposed that reaction is possible only after 40 minutes of exposure at high pressure and temperature. In this work similar experiment at P = 60 kbar and T = 1200 K were carried out in "Toroid" type chamber with the 5 seconds duration of thermobaric exposure. Gas chromatographic analysis of the reaction products has shown the presence of hydrocarbon mixture comparable to 5 minutes and 6 hours exposure experiments. Based on this fact it is possible to conclude that the reaction of natural gas formation is instant at least at given thermobaric conditions. This experiment will help to better understand the process of deep hydrocarbon generation, particularly its kinetics.

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

    Science.gov (United States)

    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.

  8. Effects of post-perovskite phase transition properties on the stability and structure of primordial reservoirs in the lower mantle of the Earth

    Science.gov (United States)

    Tackley, P.; Li, Y.; Deschamps, F.; Manatschal, G.

    2015-12-01

    Two key features of the lowermost Earth's mantle are the presence of the large low shear-wave velocity provinces (LLSVPs), which may be reservoirs of primordial, chemically distinct material, and the phase change from perovskite (pv) to post-perovskite (ppv), which may occur at lowermost mantle conditions. However, the influence of this phase change on the shape, dynamics, and stability of chemically distinct reservoirs are not well constrained. Here we performed numerical experiments of thermo-chemical convection in 2-D spherical annulus geometry to investigate the effects on thermo-chemical structure in the lower mantle of three parameters affecting the pPv phase change: the core-mantle (CMB) temperature, the viscosity ratio between pv and pPv, and the Clapeyron slope of the pPv phase transition. Our results indicate that increasing CMB temperature increases the wavelength of the primordial reservoirs by preventing the phase transition from pv to pPv to occur. Furthermore, a high CMB temperature promotes the development of plumes outside the reservoirs of primordial material. High CMB temperature and large Clapeyron slope both favor the formation of pPv patches and of a double-crossing of the phase boundary, thus preventing the formation of continuous layer of pPv above the CMB. Combined with a low CMB temperature and/or a low Clapeyron slope of the pPv phase transition, a full layer of weak pPv above CMB strongly enhances the mixing efficiency of primordial material with ambient regular mantle material, which may not allow the generation of large reservoirs. Based on our experiments, we conclude that the models of convection best describing the Earth's mantle dynamics include a large pPv Clapeyron slope (typically in the range of 13-16 MPa/K), and a moderate CMB temperature (around 3750 K). We also find that the phase change from pv to pPv may occur within the large reservoirs in the form of small discontinuous patches at the base when using critical values of

  9. Element Partitioning Constraints on Formation and Composition of the Earth's Core

    Science.gov (United States)

    Li, J.; Agee, C. B.; Fei, Y.

    1998-01-01

    Element partitioning study provides a number of constraints on the formation and composition of the core. First, partitioning of siderophile elements between the core and mantle should explain the "excess" siderophile elements in the mantle. Second, partitioning of light element(s) between the core and mantle should supply the core with the right amount of light element(s) to account for the density deficit in the core. Third, partitioning of light element(s) between the inner and outer core should be consistent with the observed difference in density deficits (relative to pure Fe) between these two reservoirs. In this study, high-pressure and high-temperature experiments have been conducted to investigate the pressure, temperature, and composition effects on partitioning of siderophile elements Ni and Co between core-forming Fe alloy and mantle silicate melt and minerals, partitioning of light elements S, O, and Si between core-forming Fe alloy and mantle silicate melt and minerals, and partitioning of light elements S and C between solid and liquid Fe. The implications of these results for mechanism of core formation and the composition of the core are discussed.

  10. Azimuthal seismic anisotropy in the Earth's upper mantle and the thickness of tectonic plates

    Science.gov (United States)

    Schaeffer, A. J.; Lebedev, S.; Becker, T. W.

    2016-11-01

    Azimuthal seismic anisotropy, the dependence of seismic wave speeds on propagation azimuth, is largely due to fabrics within the Earth's crust and mantle, produced by deformation. It thus provides constraints on the distribution and evolution of deformation within the upper mantle. Here, we present a new global, azimuthally anisotropic model of the crust, upper mantle and transition zone. Two versions of this new model are computed: the rough SL2016svAr and the smooth SL2016svA. Both are constrained by a very large data set of waveform fits (˜750 000 vertical component seismogram fits). Automated, multimode waveform inversion was used to extract structural information from surface and S wave forms in broad period ranges (dominantly from 11 to 450 s, with the best global sampling in the 20-350 s range), yielding resolving power from the crust down to the transition zone. In our global tomographic inversion, regularization of anisotropy is implemented to more uniformly recover the amplitude and orientation of anisotropy, including near the poles. Our massive waveform data set, with complementary large global networks and high-density regional array data, produces improved resolution of global azimuthal anisotropy patterns. We show that regional scale variations, related to regional lithospheric deformation and mantle flow, can now be resolved by the global models, in particular in densely sampled regions. For oceanic regions, we compare quantitatively the directions of past and present plate motions and the fast-propagation orientations of anisotropy. By doing so, we infer the depth of the boundary between the rigid, high-viscosity lithosphere (preserving ancient, frozen fabric) and the rheologically weak asthenosphere (characterized by fabric developed recently). The average depth of thus inferred rheological lithosphere-asthenosphere boundary (LAB) beneath the world's oceans is ˜115 km. The LAB depth displays a clear dependence on the age of the oceanic

  11. Fine-scale heterogeneity in the Earth's inner core

    Science.gov (United States)

    Vidale; Earle

    2000-03-16

    The seismological properties of the Earth's inner core have become of particular interest as we understand more about its composition and thermal state. Observations of anisotropy and velocity heterogeneity in the inner core are beginning to reveal how it has grown and whether it convects. The attenuation of seismic waves in the inner core is strong, and studies of seismic body waves have found that this high attenuation is consistent with either scattering or intrinsic attenuation. The outermost portion of the inner core has been inferred to possess layering and to be less anisotropic than at greater depths. Here we present observations of seismic waves scattered in the inner core which follow the expected arrival time of the body-wave reflection from the inner-core boundary. The amplitude of these scattered waves can be explained by stiffness variations of 1.2% with a scale length of 2 kilometres across the outermost 300 km of the inner core. These variations might be caused by variations in composition, by pods of partial melt in a mostly solid matrix or by variations in the orientation or strength of seismic anisotropy.

  12. New interpretation of data of the Earth's solid core

    Science.gov (United States)

    Guliyev, H. H.

    2017-06-01

    The commonly accepted scientific opinions on the inner core as the deformable solid globe are based on the solution of the problem on the distribution of elastic parameters in the inner structures of the Earth. The given solution is obtained within the necessary integral conditions on its self-weight, moment of inertia concerning the axes of rotation and periods of free oscillations of the Earth. It is shown that this solution does not satisfy the mechanics of the deformable solid body with sufficient local conditions following from basic principles concerning the strength, stability and actuality of velocities of propagation of elastic waves. The violation of local conditions shows that the inner core cannot exist in the form of the deformable solid body within the commonly accepted elastic parameters.

  13. Electromagnetically driven westward drift and inner-core superrotation in Earth's core.

    Science.gov (United States)

    Livermore, Philip W; Hollerbach, Rainer; Jackson, Andrew

    2013-10-01

    A 3D numerical model of the earth's core with a viscosity two orders of magnitude lower than the state of the art suggests a link between the observed westward drift of the magnetic field and superrotation of the inner core. In our model, the axial electromagnetic torque has a dominant influence only at the surface and in the deepest reaches of the core, where it respectively drives a broad westward flow rising to an axisymmetric equatorial jet and imparts an eastward-directed torque on the solid inner core. Subtle changes in the structure of the internal magnetic field may alter not just the magnitude but the direction of these torques. This not only suggests that the quasi-oscillatory nature of inner-core superrotation [Tkalčić H, Young M, Bodin T, Ngo S, Sambridge M (2013) The shuffling rotation of the earth's inner core revealed by earthquake doublets. Nat Geosci 6:497-502.] may be driven by decadal changes in the magnetic field, but further that historical periods in which the field exhibited eastward drift were contemporaneous with a westward inner-core rotation. The model further indicates a strong internal shear layer on the tangent cylinder that may be a source of torsional waves inside the core.

  14. Assessment of the effect of three-dimensional mantle density heterogeneity on Earth rotation in tidal frequencies

    Directory of Open Access Journals (Sweden)

    Lanbo Liu

    2016-11-01

    Full Text Available In this paper, we report the assessment of the effect of the three-dimensional (3D density heterogeneity in the mantle on Earth orientation parameters (EOP (i.e., the polar motion, or PM, and the length of day, or LOD in the tidal frequencies. The 3D mantle density model is estimated based upon a global S-wave velocity tomography model (S16U6L8 and the mineralogical knowledge derived from laboratory experiment. The lateral density variation is referenced against the preliminary reference earth model (PREM. Using this approach the effects of the heterogeneous mantle density variation in all three tidal frequencies (zonal long periods, tesseral diurnal, and sectorial semidiurnal are estimated in both PM and LOD. When compared with mass or density perturbations originated on the Earth's surface such as the oceanic and barometric changes, the heterogeneous mantle contributes less than 10% of the total variation in PM and LOD in tidal frequencies. However, this is the gap that has not been explained to close the gap of the observation and modeling in PM and LOD. By computing the PM and LOD caused by 3D heterogeneity of the mantle during the period of continuous space geodetic measurement campaigns (e.g., CONT94 and the contribution from ocean tides as predicted by tide models derived from satellite altimetry observations (e.g., TOPEX/Poseidon in the same period, we got the lump-sum values of PM and LOD. The computed total effects and the observed PM and LOD are generally agree with each other. In another word, the difference of the observed PM and LOD and the model only considering ocean tides, at all tidal frequencies (long periods, diurnals, and semidiurnals contains the contributions of the lateral density heterogeneity of the mantle. Study of the effect of mantle density heterogeneity effect on torque-free Earth rotation may provide useful constraints to construct the reference earth model (REM, which is the next major objective in global

  15. Open system models of isotopic evolution in Earth's silicate reservoirs: Implications for crustal growth and mantle heterogeneity

    Science.gov (United States)

    Kumari, Seema; Paul, Debajyoti; Stracke, Andreas

    2016-12-01

    An open system evolutionary model of the Earth, comprising continental crust (CC), upper and lower mantle (UM, LM), and an additional isolated reservoir (IR) has been developed to study the isotopic evolution of the silicate Earth. The model is solved numerically at 1 Myr time steps over 4.55 Gyr of Earth history to reproduce both the present-day concentrations and isotope ratios of key radioactive decay systems (Rb-Sr, Sm-Nd, and U-Th-Pb) in these terrestrial reservoirs. Various crustal growth scenarios - continuous versus episodic and early versus late crustal growth - and their effect on the evolution of Sr-Nd-Pb isotope systematics in the silicate reservoirs have been evaluated. Modeling results where the present-day UM is ∼60% of the total mantle mass and a lower mantle that is non-primitive reproduce the estimated geochemical composition and isotope ratios in Earth's silicate reservoirs. The isotopic evolution of the silicate Earth is strongly affected by the mode of crustal growth; only an exponential crustal growth pattern with crustal growth since the early Archean satisfactorily explains the chemical and isotopic evolution of the crust-mantle system and accounts for the so-called Pb paradoxes. Assuming that the OIB source is located in the deeper mantle, our model could, however, not reproduce its target ɛNd of +4.6 for the UM, which has been estimated from the average isotope ratios of 32 individual ocean island localities. Hence, either mantle plumes sample the LM in a non-representative way, or the simplified model set-up does not capture the full complexity of Earth's lower mantle (Nd isotope) evolution. Compared to the results obtained for a 4.55 Ga Earth, a model assuming a protracted U-Pb evolution of silicate Earth by ca. 100 Myr reproduces a slightly better fit for the Pb isotope ratios in Earth's silicate reservoirs. One notable feature of successful models is the early depletion of incompatible elements (as well as rapid decrease in Th/U) in

  16. Super-Earths as Failed Cores in Orbital Migration Traps

    CERN Document Server

    Hasegawa, Yasuhiro

    2016-01-01

    We explore whether close-in super-Earths were formed as rocky bodies that failed to grow fast enough to become the cores of gas giants before the natal protostellar disk dispersed. We model the failed cores' inward orbital migration in the low-mass or type I regime, to stopping points at distances where the tidal interaction with the protostellar disk applies zero net torque. The three kinds of migration traps considered are those due to the dead zone's outer edge, the ice line, and the transition from accretion to starlight as the disk's main heat source. As the disk disperses, the traps move toward final positions near or just outside 1~au. Planets at this location exceeding about 3~M$_\\oplus$ open a gap, decouple from their host trap, and migrate inward in the high-mass or type II regime to reach the vicinity of the star. We synthesize the population of planets formed in this scenario, finding that some fraction of the observed super-Earths can be failed cores. Most super-Earths formed this way have more t...

  17. The Earth's palaeorotation, postglacial rebound and lower mantle viscosity from analysis of ancient Chinese eclipse records

    Science.gov (United States)

    Pang, Kevin D.; Yau, Kevin; Chou, Hung-Hsiang

    1995-09-01

    160,000 oracle bones unearthed from the Shang dynasty capital Anyang (36.1°N, 114.3°E). Four of the 12th-century-B.C. inscriptions have cyclic days of 18, 42, 17 and 25. The chinese 60-day cycle is like our week in design, and has been in continuous use from time immemorial. These records have been uniquely matched to the sunrise eclipses of June 7, 1172 B.C. and October 31, 1161 B.C., and sunset eclipses of October 21, 1198 B.C. and June 27, 1163 B.C., respectively. Using visibility constraints on the rising and setting eclipsed Sun from Anyang we have derived upper or lower limits on Δ T. Three of them cluster around 7 hr 10 min, consistent with a Δ T of 7 hr 20 min, from the analysis of a record of the June 5, 1302 B.C. total solar eclipse, which states that “three flames ate the Sun, big stars were seen”. Analysis of our data gave an equation of best-fit of Δ T=(30±2.5) t 2, for the secular lunar acceleration ratedot n_{moon} = - 26''/cen^2 ( Williams et al., 1992). From this we derived andot ω /ω of -(19±1.6)×10-11/yr, where ω is the angular velocity of the Earth's rotation. Subtracting a tidaldot ω /ω of -27.8×10-11/yr ( Lambeck, 1980) gave a nontidaldot ω /ω of (9±1.6)×10-11/yr, which is equivalent to adot J_2 of -(4.5±0.8)×10-11/yr. The averagedot J_2 for the past 3,300 yr is larger than the presentdot J_2 from satellite laser ranging, -3×10-11/yr ( Cheng et al., 1989), as expected. Bothdot J_2 values are consistent with postglacial rebound from an upper mantle of viscosity 1021 Pa s, and a lower mantle of viscosity (2 4)×1021 Pa s, deformed by Pleistocene ice sheet loading ( Peltier, 1985). Our mantle viscosity values are consistent with those from the analyses of free air gravity anomalies and relative sea-level variations ( Mitrovica and Peltier, 1991, 1992). Accurate values of the mantle viscosity are critical to our understanding of thermal convection patterns, that are responsible for plate tectonics ( Peltier, 1986). Finally

  18. Chemical bonding and the incorporation of potassium into the Earth's core

    Energy Technology Data Exchange (ETDEWEB)

    Sherman, D.M. (Geological Survey, Denver, CO (USA))

    1990-05-01

    It has been argued that most of the Earth's potassium was segregated into the outer core and that the radioactive decay of {sup 40}K provided the heat source for the geodynamo. This idea rests on the assumption that the affinity of potassium for sulfur or metallic iron is enhanced at high pressure. In this paper, the high pressure electronic structures of K in sulfide, iron sulfide and metallic iron coordination environments were determined from molecular orbital (SCF-X{alpha}-SW) calculations on (KS{sub 8}){sup 15{minus}}, (KS{sub 8}Fe{sub 6}){sup 3{minus}} and KFe{sub 14} clusters. It is shown that, even at high pressure, potassium cannot alloy with metallic iron. Although a high-pressure electronic transition may enhance the potassium-sulfur chemical bond, the electronic structure of the KS{sub 8}Fe{sub 6} cluster shows that this electronic transition cannot happen in an iron sulfide melt. Consequently, potassium will not have an enhanced affinity for sulfur in planetary interiors. If the lower mantle were more reducing, potassium might be excluded from the silicate phases by more strongly lithophile elements and segregated into a metal sulfide phase in the outer core (cf. the phase assemblages in enstatite chondrites). Given the oxidation state of the Earth, however, it is unlikely that significant quantities of potassium have been incorporated into the outer core. The Earth, like the moon and the eucrite parent body, is depleted in potassium. An alternative heat source (e.g., the radioactive decay of U and Th) must be invoked to explain the geodynamo.

  19. Combining nutation and surface gravity observations to estimate the Earth's core and inner core resonant frequencies

    Science.gov (United States)

    Ziegler, Yann; Lambert, Sébastien; Rosat, Séverine; Nurul Huda, Ibnu; Bizouard, Christian

    2017-04-01

    Nutation time series derived from very long baseline interferometry (VLBI) and time varying surface gravity data recorded by superconducting gravimeters (SG) have long been used separately to assess the Earth's interior via the estimation of the free core and inner core resonance effects on nutation or tidal gravity. The results obtained from these two techniques have been shown recently to be consistent, making relevant the combination of VLBI and SG observables and the estimation of Earth's interior parameters in a single inversion. We present here the intermediate results of the ongoing project of combining nutation and surface gravity time series to improve estimates of the Earth's core and inner core resonant frequencies. We use VLBI nutation time series spanning 1984-2016 derived by the International VLBI Service for geodesy and astrometry (IVS) as the result of a combination of inputs from various IVS analysis centers, and surface gravity data from about 15 SG stations. We address here the resonance model used for describing the Earth's interior response to tidal excitation, the data preparation consisting of the error recalibration and amplitude fitting for nutation data, and processing of SG time-varying gravity to remove any gaps, spikes, steps and other disturbances, followed by the tidal analysis with the ETERNA 3.4 software package, the preliminary estimates of the resonant periods, and the correlations between parameters.

  20. Earth's core and inner-core resonances from analysis of VLBI nutation and superconducting gravimeter data

    Science.gov (United States)

    Rosat, S.; Lambert, S. B.; Gattano, C.; Calvo, M.

    2017-01-01

    Geophysical parameters of the deep Earth's interior can be evaluated through the resonance effects associated with the core and inner-core wobbles on the forced nutations of the Earth's figure axis, as observed by very long baseline interferometry (VLBI), or on the diurnal tidal waves, retrieved from the time-varying surface gravity recorded by superconducting gravimeters (SGs). In this paper, we inverse for the rotational mode parameters from both techniques to retrieve geophysical parameters of the deep Earth. We analyse surface gravity data from 15 SG stations and VLBI delays accumulated over the last 35 yr. We show existing correlations between several basic Earth parameters and then decide to inverse for the rotational modes parameters. We employ a Bayesian inversion based on the Metropolis-Hastings algorithm with a Markov-chain Monte Carlo method. We obtain estimates of the free core nutation resonant period and quality factor that are consistent for both techniques. We also attempt an inversion for the free inner-core nutation (FICN) resonant period from gravity data. The most probable solution gives a period close to the annual prograde term (or S1 tide). However the 95 per cent confidence interval extends the possible values between roughly 28 and 725 d for gravity, and from 362 to 414 d from nutation data, depending on the prior bounds. The precisions of the estimated long-period nutation and respective small diurnal tidal constituents are hence not accurate enough for a correct determination of the FICN complex frequency.

  1. Zoned mantle convection.

    Science.gov (United States)

    Albarède, Francis; Van Der Hilst, Rob D

    2002-11-15

    We review the present state of our understanding of mantle convection with respect to geochemical and geophysical evidence and we suggest a model for mantle convection and its evolution over the Earth's history that can reconcile this evidence. Whole-mantle convection, even with material segregated within the D" region just above the core-mantle boundary, is incompatible with the budget of argon and helium and with the inventory of heat sources required by the thermal evolution of the Earth. We show that the deep-mantle composition in lithophilic incompatible elements is inconsistent with the storage of old plates of ordinary oceanic lithosphere, i.e. with the concept of a plate graveyard. Isotopic inventories indicate that the deep-mantle composition is not correctly accounted for by continental debris, primitive material or subducted slabs containing normal oceanic crust. Seismological observations have begun to hint at compositional heterogeneity in the bottom 1000 km or so of the mantle, but there is no compelling evidence in support of an interface between deep and shallow mantle at mid-depth. We suggest that in a system of thermochemical convection, lithospheric plates subduct to a depth that depends - in a complicated fashion - on their composition and thermal structure. The thermal structure of the sinking plates is primarily determined by the direction and rate of convergence, the age of the lithosphere at the trench, the sinking rate and the variation of these parameters over time (i.e. plate-tectonic history) and is not the same for all subduction systems. The sinking rate in the mantle is determined by a combination of thermal (negative) and compositional buoyancy and as regards the latter we consider in particular the effect of the loading of plates with basaltic plateaux produced by plume heads. Barren oceanic plates are relatively buoyant and may be recycled preferentially in the shallow mantle. Oceanic plateau-laden plates have a more pronounced

  2. Dislocation-accommodated grain boundary sliding as the major deformation mechanism of olivine in the Earth's upper mantle.

    Science.gov (United States)

    Ohuchi, Tomohiro; Kawazoe, Takaaki; Higo, Yuji; Funakoshi, Ken-Ichi; Suzuki, Akio; Kikegawa, Takumi; Irifune, Tetsuo

    2015-10-01

    Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in Earth's upper mantle. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper mantle conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, ~200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper mantle. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 10(19.6) to 10(20.7) Pa·s throughout the asthenospheric upper mantle with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain size-sensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper mantle.

  3. Reduced radiative conductivity of high and low spin FeO6 octahedra in the Earth's lower mantle

    CERN Document Server

    Lobanov, Sergey S; Goncharov, Alexander F

    2016-01-01

    The ability of Earths mantle to conduct heat by radiation is determined by optical properties of mantle phases. Optical properties of mantle minerals at high pressure are accessible through diamond anvil cell experiments, but because of the extensive thermal radiation at T above 1000 K such studies are limited to lower temperatures. Particularly uncertain is the temperature-dependence of optical properties of lower mantle minerals across the spin transition as the spin state itself is a strong function of temperature. Here we use laser-heated DACs combined with a pulsed bright supercontinuum laser probe and a synchronized time-gated detector to examine optical properties of high and low spin ferrous iron at 45-73 GPa and to 1600 K in FeO6, one of the most abundant building blocks in the mantle. Siderite (FeCO3) is used as a model for FeO6-octahedra as it contains no ferric iron and exhibits a sharp optically apparent spin transition at 44 GPa, simplifying data interpretation. We find that the optical absorban...

  4. Geomagnetic secular variation as a window on the dynamics of Earth's core (Invited)

    Science.gov (United States)

    Jackson, A.

    2010-12-01

    One of the forefront questions of planetary geophysics is to understand how magnetic fields can be spontaneously created by so-called dynamo action. Giant strides have been taken in recent years in understanding the theory of convectively driven dynamos; yet equally important is the marriage between theory and observation. I will argue that we are on the cusp of a new level of understanding brought about by new methods for incorporating observations and theory. In 1950 Sir Edward Bullard wrote an influential paper entitled "The westward drift of the Earth's magnetic field", with coauthors C Freedman, H Gellman and J Nixon. A comprehensive study of observations was tied together with the then nascent dynamo theory to infer properties of the dynamics of the core. Sixty years on, we have a much enriched understanding of the theory of convectively driven dynamos, and an even more comprehensive database of observations stretching back several centuries. Equally important are the new satellite observations that provide global coverage with unprecedented accuracy over the last decade. In this talk I will try to show how the interplay between theory and observation can lead to understanding of force balances in the core, and interactions between the core and the overlying mantle.

  5. Correlation between the Earth's Magnetic Field and the Gravitational Mass of the Outer Core

    OpenAIRE

    De Aquino, Fran

    2013-01-01

    The theory accepted today for the origin of the Earth's magnetic field is based on convection currents created in the Earth's outer core due to the rotational motion of the planet Earth around its own axis. In this work, we show that the origin of the Earth's magnetic field is related to the gravitational mass of the outer core.

  6. Where is mantle's carbon?

    Science.gov (United States)

    Oganov, A. R.; Ono, S.; Ma, Y.

    2008-12-01

    Petrology: Field Observations and High Pressure Experimentation: A Tribute to Francis R. (Joe) Boyd. Geochemical Soc., Special Publication No. 6. Eds: Y. Fei, C.M. Bertka, B.O. Mysen. 4.Oganov A.R., Ono S., Ma Y., Glass C.W., Garcia A. (2008). Novel high-pressure structures of MgCO3, CaCO3 and CO2 and their role in the Earth's lower mantle. Earth Planet. Sci. Lett. 273, 38-47 5.Scott H.P.,, Williams Q., Knittle E. (2001). Stability and equation of state of Fe3C to 73 GPa: Implications for carbon in the Earth's core. Geoph. Res. Lett. 28, 1875-1878. 6.Oganov A.R., Glass C.W., Ono S. (2006). High-pressure phases of CaCO3: crystal structure prediction and experiment. Earth Planet. Sci. Lett. 241, 95-103. 7.Isshiki M., Irifune T., Hirose K., Ono S., Ohishi Y., Watanuki T., Nishibori E., Takadda M., and Sakata M. (2004). Stability of Magnesite and its high-pressure form in the lowermost mantle. Nature 427, 60-63. 8.Skorodumova N.V., Belonoshko A.B., Huang L., Ahuja R., Johansson B. (2005) Stability of the MgCO3 structures under lower mantle conditions. Am. Mineral. 90, 1008-1011. 9.Panero W.R., Kabbes J.E. (2008). Mantle-wide sequestration of carbon in silicates and the structure of magnesite II. Geophys. Res. Lett. 35, L14307. 10.Oganov A.R., Glass C.W. (2006). Crystal structure prediction using ab initio evolutionary algorithms: principles and applications. J. Chem. Phys. 124, art. 244704.

  7. Viscoplastic behavior of multiphase Earth mantle polycrystals inferred from micromechanical modeling

    Science.gov (United States)

    Castelnau, O.; Detrez, F.; Bollinger, C.; Cordier, P.; Hilairet, N.; Merkel, S.; Raterron, P. C.

    2012-12-01

    The strongly anisotropic rheology of olivine and pyroxene single grains, associated to polycrystal microstructures, constitutes a key feature affecting the dynamics of the Earth's upper mantle. High pressure deformation experiments carried out on olivine single crystals under synchrotron radiation, together with estimations of lattice friction based on first-principle calculations, show a transition from easy [100] to easy [001] slips in olivine as pressure and temperature (thus depth) increases. Besides dislocation glide, diffusion related deformation mechanisms such as dislocation climb, diffusion creep, and grain boundary sliding cannot be completely ruled out. Since their behavior is poorly known, they are grouped into a single isotropic viscous component. We input these elementary deformation mechanisms into a mean-field homogenization scheme (second-order self-consistent scheme of Ponte-Castaneda). This model presents the advantage of accurately predicting the mechanical interaction between deforming grains, as attested by many comparisons with full-field modeling on various polycrystals and 2-phases composites. The model has been adapted for predicting the viscoplastic behavior of olivine and olivine-pyroxene polycrystalline aggregates. Results illustrating the respective activation of elementary deformation mechanisms, but also the effect on texture evolution along several flow paths representative for in situ conditions, will be presented. It is shown that results strongly depart from intuitive models sometimes used in the literature. In particular, the polycrystal rheology is highly influenced by the poorly known hard slip systems and/or diffusion related processes.

  8. Micromechanical modeling of the viscoplastic behavior of multiphase Earth mantle polycrystals

    Science.gov (United States)

    Detrez, F.; Castelnau, O.; Bollinger, C.; Cordier, P.; Hilairet, N.; Merkel, S.; Raterron, P. C.

    2011-12-01

    The strongly anisotropic rheology of olivine and pyroxene single grains, associated to polycrystal microstructures, constitutes a key feature affecting the dynamics of the Earth's upper mantle. High pressure deformation experiments carried out on olivine single crystals under synchrotron radiation, together with estimations of lattice friction based on first-principle calculations, show a transition from easy [100] to easy [001] slips in olivine as pressure and temperature (thus depth) increases. Besides dislocation glide, diffusion related deformation mechanisms such as dislocation climb, diffusional creep, and grain boundary sliding cannot be completely ruled out. Since their behavior is poorly known, they are grouped into a single isotropic viscous component. We input these elementary deformation mechanisms into a mean-field homogenization scheme (second-order self-consistent scheme of Ponte-Castaneda). This model presents the advantage of accurately predicting the mechanical interaction between deforming grains, as attested by many comparisons with full-field modeling on various polycrystals and 2-phases composites. The model has been adapted for predicting the viscoplastic behavior of olivine and olivine-pyroxene polycrystalline aggregates. Results illustrating the respective activation of elementary deformation mechanisms, but also the effect on texture evolution along several flow paths representative for in situ conditions, will be presented. It is shown that results strongly depart from intuitive models sometimes used in the literature. In particular, the polycrystal rheology is highly influenced by the poorly known hard slip systems and/or diffusion related processes.

  9. Stability of earth dam with a vertical core

    Directory of Open Access Journals (Sweden)

    Orekhov Vyacheslav Valentinovich

    2016-01-01

    Full Text Available Earth dam with impervious element in the form of asphaltic concrete core is currently the most promising type of earth dams (due to simple construction technology and universal service properties of asphaltic concrete and is widely used in the world. However, experience in the construction and operation of high dams (above 160 m is not available, and their work is scarcely explored. In this regard, the paper discusses the results of computational prediction of the stress-strain state and stability of a high earth dam (256 m high with the core. The authors considered asphaltic concrete containing 7 % of bitumen as the material of the core. Gravel was considered as the material of resistant prisms. Design characteristics of the rolled asphaltic concrete and gravel were obtained from the processing of the results of triaxial tests. The calculations were performed using finite element method in elastoplastic formulation and basing on the phased construction of the dam and reservoir filling. The research shows, that the work of embankment dam with vertical core during filling of the reservoir is characterized by horizontal displacement of the lower resistant prism in the tailrace and the formation of a hard wedge prism descending along the core in the upper resistant prism. The key issue of the safety assessment is to determine the safety factor of the overall stability of the dam, for calculation of which the destruction of the earth dam is necessary, which can be done by reducing the strength properties of the dam materials. As a results of the calculations, the destruction of the dam occurs with a decrease in the strength characteristics of the materials of the dam by 2.5 times. The dam stability depends on the stability of the lower resistant prism. The destruction of its slope occurs on the classical circular-cylindrical surface. The presence of a potential collapse surface in the upper resistant prism (on the edges of the descending wedge does

  10. Oxygen in the Earth's core a first principles study

    CERN Document Server

    Alfè, D; Gillan, M J; Alfe`, Dario; Gillan, Michael J.

    1998-01-01

    First principles electronic structure calculations based on density functional theory have been used to study the thermodynamic, structural and transport properties of solid solutions and liquid alloys of iron and oxygen at Earth's core conditions. Aims of the work are to determine the oxygen concentration needed to account for the inferred density in the outer core, to probe the stability of the liquid against phase separation, to interpret the bonding in the liquid, and to find out whether the viscosity differs significantly from that of pure liquid iron at the same conditions. It is shown that the required concentration of oxygen is in the region 25-30 mol percent, and evidence is presented for phase stability at these conditions. The Fe-O bonding is partly ionic, but with a strong covalent component. The viscosity is lower than that of pure liquid iron at Earth's core conditions. It is shown that earlier first-principles calculations indicating very large enthalpies of formation of solid solutions may nee...

  11. Seismic evidence for the depression of the D″ discontinuity beneath the Caribbean: Implication for slab heating from the Earth's core

    Science.gov (United States)

    Ko, Justin Yen-Ting; Hung, Shu-Huei; Kuo, Ban-Yuan; Zhao, Li

    2017-06-01

    The lowermost 100-300 km of the Earth's mantle commonly regarded as the thermal boundary layer (TBL) of mantle circulation is characterized by its complex physical properties. Beneath the Caribbean this so-called D″ layer features relatively high velocities and abrupt impedance increase at the top (designated as the D″ discontinuity). These seismic characteristics have been attributed to the accumulation of ancient subducted slab material and the phase transition in the major lower mantle mineral of pervoskite. Geodynamic models predict that the blanketing cold slabs may trap enough heat from core to be buoyantly destabilized, and eventually broken apart and entrained into the bottom of the convection cell. Here we explore the D″ structure with unprecedented resolution through modeling traveltimes, amplitudes, and waveform shapes from the USArray. We find an east-to-west asymmetrical undulation of the D″ discontinuity with a V-shaped depression of ∼70-160 km over a lateral distance of 600 km beneath northern South America. The shear velocity perturbations vary in the same trend showing the most pronounced reduction of ∼3-4% below the thinnest D″ layer in close proximity to an intermittently undetected discontinuity. The strong correlation between the D″ topography and velocity variations indicates the phase transition boundary has been perturbed or even disrupted by the large lateral temperature gradient of slab material which has been reheated from the core over extended periods of time.

  12. Probing iron at Super-Earth core conditions

    Energy Technology Data Exchange (ETDEWEB)

    Amadou, N., E-mail: nourou.amadou@polytechnique.edu [LULI, UMR7605 CNRS, CEA, Ecole Polytechnique, Université Pierre et Marie Curie, Palaiseau (France); Département de physique, Université Abdou Moumouni de Niamey, B.P 10662 Niamey (Niger); Brambrink, E.; Vinci, T. [LULI, UMR7605 CNRS, CEA, Ecole Polytechnique, Université Pierre et Marie Curie, Palaiseau (France); Benuzzi-Mounaix, A. [LULI, UMR7605 CNRS, CEA, Ecole Polytechnique, Université Pierre et Marie Curie, Palaiseau (France); LUTH, UMR 8102 Observatoire de Paris, CNRS Université Paris Diderot, Meudon (France); Huser, G.; Brygoo, S. [CEA, DAM, DIF, F-91297 Arpajon (France); Morard, G.; Guyot, F. [Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC) Sorbonne Universités - UPMC Univ. Paris 06, UMR CNRS 7590, Muséum National d' Histoire Naturelle, IRD UMR 206, 4 Place Jussieu, F-75005 Paris (France); Resseguier, T. de [Institut PPrime, CNRS, ENSMA, Université de Poitiers, Poitiers (France); Mazevet, S. [LUTH, UMR 8102 Observatoire de Paris, CNRS Université Paris Diderot, Meudon (France); Miyanishi, K. [Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Ozaki, N.; Kodama, R. [Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Photon Pioneers Center, Osaka University, Suita, Osaka 565-0871 (Japan); Henry, O.; Raffestin, D. [CEA, DAM, CESTA, F-33114 Le Barp (France); Boehly, T. [Laboratory for Laser Energetics, University of Rochester, 250 East River Rd., Rochester, New York 14623 (United States); and others

    2015-02-15

    In this paper, we report on the quasi-isentropic compression of an iron sample using ramp shaped laser irradiation. This technique allows us to quasi-isentropically compress iron up to 700 GPa and 8500 K. To our knowledge, these data are the highest pressures reached on iron in off-Hugoniot conditions and the closest to the thermodynamic states thought to exist in Earth-like planetary cores. The experiment was performed on the Ligne d'Intégration laser facility at CESTA, Bordeaux, France.

  13. Rare Earth core/shell nanobarcodes for multiplexed trace biodetection.

    Science.gov (United States)

    Chen, Lei; Li, Xiaomin; Shen, Dengke; Zhou, Lei; Zhu, Dan; Fan, Chunhai; Zhang, Fan

    2015-06-02

    Multiplexed detection technology has been attractive for its simultaneous assay of several analytes, which play significant roles in applications such as screening for combinatorial chemistry, genetic analysis, and clinical diagnostics. This work reports a novel and potentially powerful encoding system based upon dispersible suspension arrays of multilayer rare earth core/shell nanoparticles that are capable of multiplexed, high-sensitivity reporting for biomolecule detection by the Z-contrast imaging. These nanobarcode arrays are encoded by nanostructure design based on different atomic numbers. With the well-resolved high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) decoding technique, many thousands of unique nanobarcodes can be identified by multilayer core/shell nanostructure. Their applications to multiplexed biodetection of DNA demonstrated the highly sensitive (picomole) features of this novel nanobarcode system.

  14. Applications of liquid state physics to the earth's core

    Science.gov (United States)

    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.

  15. Strong seismic scatterers near the core-mantle boundary north of the Pacific Anomaly

    Science.gov (United States)

    Ma, Xiaolong; Sun, Xinlei; Wiens, Douglas A.; Wen, Lianxing; Nyblade, Andrew; Anandakrishnan, Sridhar; Aster, Rick; Huerta, Audrey; Wilson, Terry

    2016-04-01

    Tomographic images have shown that there are clear high-velocity heterogeneities to the north of the Pacific Anomaly near the core-mantle boundary (CMB), but the detailed structure and origin of these heterogeneities are poorly known. In this study, we analyze PKP precursors from earthquakes in the Aleutian Islands and Kamchatka Peninsula recorded by seismic arrays in Antarctica, and find that these heterogeneities extend ∼400 km above the CMB and are distributed between 30° and 45°N in latitude. The scatterers show the largest P-wave velocity perturbation of 1.0-1.2% in the center (160-180°E) and ∼0.5% to the west and east (140-160°E, 180-200°E). ScS-S differential travel-time residuals reveal similar features. We suggest that these seismic scatterers are the remnants of ancient subducted slab material. The lateral variations may be caused either by different slabs, or by variations in slab composition resulting from their segregation process.

  16. Nitrogen and carbon fractionation during core-mantle differentiation at shallow depth

    Science.gov (United States)

    Dalou, Celia; Hirschmann, Marc M.; von der Handt, Anette; Mosenfelder, Jed; Armstrong, Lora S.

    2017-01-01

    One of the most remarkable observations regarding volatile elements in the solar system is the depletion of N in the bulk silicate Earth (BSE) relative to chondrites, leading to a particularly high and non-chondritic C:N ratio. The N depletion may reflect large-scale differentiation events such as sequestration in Earth's core or massive blow off of Earth's early atmosphere, or alternatively the characteristics of a late-added volatile-rich veneer. As the behavior of N during early planetary differentiation processes is poorly constrained, we determined together the partitioning of N and C between Fe-N-C metal alloy and two different silicate melts (a terrestrial and a martian basalt). Conditions spanned a range of fO2 from ΔIW-0.4 to ΔIW-3.5 at 1.2 to 3 GPa, and 1400 °C or 1600 °C, where ΔIW is the logarithmic difference between experimental fO2 and that imposed by the coexistence of crystalline Fe and wüstite.

  17. The problem of the Earth's CO2 content and the iron core

    Science.gov (United States)

    Devore, G. W.

    1985-01-01

    The near absence of metallic iron and the presence of magnetite and FeS in the C-1 chondrites imply that metallic iron was a minor phase present during the accretion process that formed the C-1 chondrites. If the C-1 chondrites provided the bulk of the initial planetary growth materials, the carbon reduction model is favored. The above estimates suggest that some 1240 to 227 times as much CO2 may have been produced during the formation of the core than can be accounted for in the crust and mantle. This discrepancy taken to the extreme suggests either that: (1) the Earth has lost more than 99 percent of its initial CO2 during early differentiation (this is highly unlikely) or: (2) the Earth has acquired some 90 percent of its present mass by the accretion of debris from previously reduced and differentiated but subsequently disrupted planetary bodies whereby the associated CO2 would not be captured, or: (3) the C-1 chondrites represent only a trivial fraction of the initial accretion materials present in the nebular cloud or: (4) condensed iron and anhydrous silicate phases were preferentially accreted during the initial formation of the planetary bodies.

  18. Experimental earth tidal models in considering nearly diurnal free wobble of the Earth's liquid core

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Based on the 28 series of the high precision and high minute sampling tidal gravity observations at 20 stations in Global Geodynamics Project (GGP) network, the resonant parameters of the Earth's nearly diurnal free wobble (including the eigenperiods, resonant strengths and quality factots) are precisely determined. The discrepancy of the eigenperiod between observed and theoretical values is studied, the important conclusion that the real dynamic ellipticity of the liquid core is about 5% larger than the one under the static equilibrium assumption is approved by using our gravity technique. The experimental Earth's tidal gravity models with considering the nearly diurnal free wobble of the Earth's liquid core are constructed in this study. The numerical results show that the difference among three experimental models is less than 0.1%, and the largest discrepancy compared to those widely used nowdays given by Dehant (1999) and Mathews (2001) is only about 0.4%. It can provide with the most recent real experimental tidal gravity models for the global study of the Earth's tides, geodesy and space techniques and so on.

  19. Irregular topography at the Earth's inner core boundary.

    Science.gov (United States)

    Dai, Zhiyang; Wang, Wei; Wen, Lianxing

    2012-05-15

    Compressional seismic wave reflected off the Earth's inner core boundary (ICB) from earthquakes occurring in the Banda Sea and recorded at the Hi-net stations in Japan exhibits significant variations in travel time (from -2 to 2.5 s) and amplitude (with a factor of more than 4) across the seismic array. Such variations indicate that Earth's ICB is irregular, with a combination of at least two scales of topography: a height variation of 14 km changing within a lateral distance of no more than 6 km, and a height variation of 4-8 km with a lateral length scale of 2-4 km. The characteristics of the ICB topography indicate that small-scale variations of temperature and/or core composition exist near the ICB, and/or the ICB topographic surface is being deformed by small-scale forces out of its thermocompositional equilibrium position and is metastable.

  20. Novel Techniques for High Pressure Falling Sphere Viscosimetry under Simulated Earth's Mantle Conditions

    Science.gov (United States)

    Mueller, H. J.; Beckmann, F.; Dobson, D. P.; Hunt, S. A.; Secco, R.; Lauterjung, J.; Lathe, C.

    2014-12-01

    Viscosity data of melts measured under in situ high pressure conditions are crucial for the understanding of Earth's lower mantle and the interior of terrestrial and extrasolar Super-Earth planets. We report recent technical advances and techniques enabling falling sphere viscosity measurements in single- and double-stage DIA-type multi-anvil apparatus. For the experiments we used presses with a maximum load of 250 tons and 1750 tons. We anticipate that our system will enable viscosity measurements up to the maximum pressure for non-diamond anvils, i.e. pressures up to some 30 GPa. For the development of the new set ups the deformation of the cell assemblies were analyzed by X-ray absorption tomography at beamline W II at DESY/HASYLAB after the high pressure runs. These analysis gave considerable insights into strategies for improving the cell assembly with the result that the optimized assemblies could be used at much higher pressures without blow-outs. We think this approach is much faster and more beneficial than the classical way of trial and error. Additionally to prevent high pressure blow outs the task was to make the whole melting chamber accessible for the high pressure X-radiography system up to the maximum pressures. This way the accuracy and reliability of the measurements can be improved. For this goal we used X-ray transparent cBN-anvils at the single-stage DIA large volume press. Because this material is recently not available for the cube size of 32 mm this aproach did not work for the double-stage DIA. As a very useful and economical alternative we used slotted carbide anvils filled with fired pyrophyllite bars. To improve the frame quality of the platinum spheres taken by the CCD-camera the energy of the monochromatic X-rays had to be increased to 100 keV. The resulting ascent of scattered radiation required a new design of the X-radiography unit. Our results are demonstrated with viscosity measurements following Stokes law by evaluation of X

  1. Reversal Frequency, Core-Mantle Conditions, and the SCOR-field Hypothesis

    Science.gov (United States)

    Hoffman, K. A.

    2009-12-01

    One of the most intriguing results from paleomagnetic data spanning the past 108 yr comes from the work of McFadden et al. (1991) who found that the variation in the rate of polarity reversal is apparently tied to the temporal variation in the harmonic content of the full-polarity field. Their finding indicates that it is the relative importance of the two dynamo families--i.e. the Primary Family (PF), the field antisymmetric about the equator, and the Secondary Family (SF), the field symmetric about the equator--that largely determines reversal frequency. More specifically, McFadden et al. found that as the relative significance of the SF increases, as is observed during the Cenozoic, so too does reversal rate. Such a finding is reminiscent of the seminal work of Allan Cox who some forty years ago proposed that interactions with the non-dipole field may provide the trigger for reversal of the axial dipole (AD) field. Hence, new questions arise: Do the two dynamo family fields interact in this manner, and, if so, how can such an interaction physically occur in the fluid core? Gaussian coefficient terms comprising the PF and SF have degree and order (n + m) that sum to an odd and even number, respectively. The most significant field term in the PF is by far that of the axial dipole (g10). The entire SF, starting with the equatorial dipole terms (g11 and h11) and the axial quadrupole (g20), are constituents of the non-axial dipole (NAD) field. By way of both paleomagnetic transition and geomagnetic data Hoffman and Singer (2008) recently proposed (1) that field sources exist within the shallow core (SCOR-field) associated with fluid motions affected by long-lived core-mantle boundary conditions; (2) that these SCOR-field sources are largely separated from, i.e. in “poor communication” with, deep field convection roll-generated sources; and (3) that the deep sources are largely responsible for the AD field, leaving the SCOR-field to be the primary source for the

  2. Evidence from Sardinian basalt geochemistry for recycling of plume heads into the Earth's mantle.

    Science.gov (United States)

    Gasperini, D; Blichert-Toft, J; Bosch, D; Del Moro, A; Macera, P; Télouk, P; Albarède, F

    2000-12-07

    Up to 10 per cent of the ocean floor consists of plateaux--regions of unusually thick oceanic crust thought to be formed by the heads of mantle plumes. Given the ubiquitous presence of recycled oceanic crust in the mantle source of hotspot basalts, it follows that plateau material should also be an important mantle constituent. Here we show that the geochemistry of the Pleistocene basalts from Logudoro, Sardinia, is compatible with the remelting of ancient ocean plateau material that has been recycled into the mantle. The Sr, Nd and Hf isotope compositions of these basalts do not show the signature of pelagic sediments. The basalts' low CaO/Al2O3 and Ce/Pb ratios, their unradiogenic 206Pb and 208Pb, and their Sr, Ba, Eu and Pb excesses indicate that their mantle source contains ancient gabbros formed initially by plagioclase accumulation, typical of plateau material. Also, the high Th/U ratios of the mantle source resemble those of plume magmas. Geochemically, the Logudoro basalts resemble those from Pitcairn Island, which contain the controversial EM-1 component that has been interpreted as arising from a mantle source sprinkled with remains of pelagic sediments. We argue, instead, that the EM-1 source from these two localities is essentially free of sedimentary material, the geochemical characteristics of these lavas being better explained by the presence of recycled oceanic plateaux. The storage of plume heads in the deep mantle through time offers a convenient explanation for the persistence of chemical and mineralogical layering in the mantle.

  3. Geodynamic models of plumes from the margins of large thermo-chemical piles in the Earth's lowermost mantle

    Science.gov (United States)

    Steinberger, B. M.; Gassmoeller, R.; Mulyukova, E.

    2012-12-01

    We present geodynamic models featuring mantle plumes that are almost exclusively created at the margins of large thermo-chemical piles in the lowermost mantle. The models are based on global plate reconstructions since 300 Ma. Sinking subducted slabs not only push a heavy chemical layer ahead, such that dome-shaped structures form, but also push the thermal boundary layer (TBL) toward the chemical domes. At the steep edges it is forced upwards and begins to rise — in the lower part of the mantle as sheets, which then split into individual plumes higher in the mantle. The models explain why Large Igneous Provinces - commonly assumed to be caused by plumes forming in the TBL above the core-mantle boundary (CMB) - and kimberlites during the last few hundred Myr erupted mostly above the margins of the African and Pacific Large Low Shear Velocity Provinces (LLSVPs) of the lowermost mantle, which are probably chemically distinct from and heavier than the overlying mantle. Computations are done with two different codes, one based on spherical harmonic expansion, and CITCOM-S. The latter is combined with a self-consistent thermodynamic material model for basalt, harzburgite, and peridotite, which is used to derive a temperature- and presssure dependent database for parameters like density, thermal expansivity and specific heat. In terms of number and distribution of plumes, results are similar in both cases, but in the latter model, plume conduits are narrower, due to consideration of realistic lateral - in addition to radial - viscosity variations. For the latter case, we quantitatively compare the computed plume locations with actual hotspots and find that the good agreement is very unlikely (probability geometry, we also show results obtained with a 2-D finite element code. These results allow us to assess how much the computed long-term stability of the piles is affected by numerical diffusion. We have also conducted a systematic investigation, which configurations

  4. Fine scale heterogeneity in the Earth's upper mantle - observation and interpretation

    DEFF Research Database (Denmark)

    Thybo, Hans

    2014-01-01

    can be correlated to main plate tectonic features, such as oceanic spreading centres, continental rift zones and subducting slabs. Much seismological mantle research is now concentrated on imaging fine scale heterogeneity, which may be detected and imaged with high-resolution seismic data with dense......High resolution seismic data has over the last decade provided significant evidence for pronounced fine scale heterogeneity in the Earth’s mantle at an unprecedented detail. Seismic tomography developed tremendously during the last 20-30 years. The results show overall structure in the mantle which...... station spacing and at high frequency, e.g. from the Russian Peaceful Nuclear Explosion (PNE) data set and array recordings of waves from natural seismic sources. Mantle body waves indicate pronounced heterogeneity at three depth levels whereas other depth intervals appear transparent, at least...

  5. The Topographic Torque on a Bounding Surface of a Rotating Gravitating Fluid and the Excitation by Core Motions of Decadal Fluctuations in the Earth's Rotation

    Science.gov (United States)

    Hide, Raymond

    1995-01-01

    General expressions (with potential applications in several areas of geophysical fluid dynamics) are derived for all three components of the contribution made by the geostrophic part of the pressure field associated with flow in a rotating gravitating fluid to the topographic torque exerted by the fluid on a rigid impermeable bounding surface of any shape. When applied to the Earth's liquid metallic core, which is bounded by nearly spherical surfaces and can be divided into two main regions, the "torosphere" and "polosphere," the expressions reduce to formulae given previously by the author, thereby providing further support for his work and that of others on the role of topographic coupling at the core-mantle boundary in the excitation by core motions of Earth rotation fluctuations on decadal time scales. They also show that recent criticisms of that work are vitiated by mathematical and physical errors. Contrary to these criticisms, the author's scheme for exploiting Earth rotation and other geophysical data (either real or simulated in computer models) in quantitative studies of the topography of the core-mantle boundary (CMB) by intercomparing various models of (a) motions in the core based on geomagnetic secular variation data and (b) CMB topography based on seismological and gravity data has a sound theoretical basis. The practical scope of the scheme is of course limited by the accuracy of real data, but this is a matter for investigation, not a priori assessment.

  6. Elasticity of ferropericlase and seismic heterogeneity in the Earth's lower mantle: Ferropericlase High Pressure-Temperature Elasticity

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Jing [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin Texas USA; Lin, Jung-Fu [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin Texas USA; Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai China; Jacobsen, Steven D. [Department of Earth and Planetary Sciences, Northwestern University, Evanston Illinois USA; Seymour, Nikki M. [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin Texas USA; Tkachev, Sergey N. [Center for Advanced Radiation Sources, University of Chicago, Chicago Illinois USA; Prakapenka, Vitali B. [Center for Advanced Radiation Sources, University of Chicago, Chicago Illinois USA

    2016-12-16

    Deciphering the origin of seismic heterogeneity has been one of the major challenges in understanding the geochemistry and geodynamics of the deep mantle. Fully anisotropic elastic properties of constituent minerals at relevant pressure-temperature conditions of the lower mantle can be used to calculate seismic heterogeneity parameters in order to better understand chemically and thermally induced seismic heterogeneities. In this study, the single-crystal elastic properties of ferropericlase (Mg0.94Fe0.06)O were measured using Brillouin spectroscopy and X-ray diffraction at conditions up to 50 GPa and 900 K. The velocity-density results were modeled using third-order finite-strain theory and thermoelastic equations along a representative geotherm to investigate high pressure-temperature and compositional effects on the seismic heterogeneity parameters. Our results demonstrate that from 660 to 2000 km, compressional wave anisotropy of ferropericlase increased from 4% to 9.7%, while shear wave anisotropy increased from 9% to as high as 22.5%. The thermally induced lateral heterogeneity ratio (RS/P = ∂lnVS/∂lnVP) of ferropericlase was calculated to be 1.48 at ambient pressure but decreased to 1.43 at 40 GPa along a representative geotherm. The RS/P of a simplified pyrolite model consisting of 80% bridgmanite and 20% ferropericlase was approximately 1.5, consistent with seismic models at depths from 670 to 1500 km, but showed an increased mismatch at lower mantle depths below ~1500 km. This discrepancy below mid-lower mantle could be due to either a contribution from chemically induced heterogeneity or the effects of the Fe spin transition in the deeper parts of the Earth's lower mantle.

  7. Origin of Ultra-Deep Diamonds: Chemical Interaction of Ca-CARBONATE and the Earth's Lower Mantle Minerals

    Science.gov (United States)

    Spivak, A. V.; Dubrovinsky, L. S.; Litvin, Yu. A.

    2012-04-01

    The main goal of the work is experimental study of physicochemical conditions of origin of ultra-deep diamonds in the substance of the Earth's lower mantle (LM) based on the experimental criterium of syngenesis of diamond and primary inclusions of LM mineral. Magnesiowustite (Mg,Fe)O, Mg-Fe perovskite (Mg,Fe)(Si,Al)O3 and Ca-perovskite CaSiO3 mainly present the LM substance and are frequently disclosed as primary inclusions in ultra-deep diamonds together with Ca-, (Ca, Mg, Fe)-, Na-Ca-carbonates. For the upper mantle conditions, the mantle-carbonatite conception of diamond genesis was developed based on the effects of congruent melting of carbonates and complete liquid miscibility of carbonate-silicate melts. Melting of Ca-carbonate and CaCO3 - (Mg,Fe)O, CaCO3 - (Mg,Fe)(Si,Al)O3 systems, stability of the melts and their decomposition were studied in static high pressure experiments at pressures of 16 to 55 GPa and temperatures of 1600 to 3900 K using diamond anvil cell technique with laser heating. It was determined that melting of Ca-carbonate is congruent at the PT-conditions of the lower mantle and characterized by an expanded field of liquid Ca-carbonate phase. We observed formation of graphite (below 16 GPa) and diamond (between 16 and 43 GPa) on decomposition of the CaCO3 melt at temperatures above 3400 K. At temperatures below 3400 K congruent melting of calcium carbonate was confirmed. Also it was shown that CaCO3 - (Mg,Fe)O - (Mg,Fe)(Si,Al)O3 system is capable to form diamonds together with Ca-carbonate, magnesiowustite and perovskite as syngenesis minerals at PT-conditions of the lower mantle. We observed formation diamond (between 40 and 55 GPa) on decomposition of the CaCO3 from CaCO3 - (Mg,Fe)(Si,Al)O3 melt at temperatures above 2000 K. The experimental data on phase relations at the melting and decomposition of CaCO3 and CaCO3-(Mg,Fe)O-(Mg,Fe)(Si,Al)O3 system as well as diamond crystallization are applied to the problem of formation of natural ultra

  8. Investigations of Eurasian Seismic Sources and Upper Mantle Structure

    Science.gov (United States)

    1989-05-25

    in classical Earth models include the free surface, the Mohorovicic (M) discontinuity, the core-mantle boundary (CMB), and the inner core-outer core...rather to the superposition of first- and higher-order reverberations generated at the Mohorovicic (M) discontinuity. Figure 3.1 depicts the effect of

  9. Oxidation state of the Earth's upper mantle during the last 3800 million years: Implications for the origin of life

    Science.gov (United States)

    Delano, J. W.

    1993-01-01

    A popular, as well as scientifically rigorous, scenario for the origin of life on Earth involves the production of organic molecules by interaction of lightning (or other forms of energy) with a chemically reducing atmosphere in the early history of Earth. Experiments since the 1950's have convincingly demonstrated that the yield of organic molecules is high when the atmosphere contains molecular hydrogen, methane, ammonia, and water vapor. Additional work has also shown that such a highly reducing atmosphere might not, however, have been sufficiently long-lived in the presence of intense solar ultraviolet radiation for life to have formed from it. One way of maintaining such an atmosphere would be to have a continual replenishment of the reduced gases by prolonged volcanic outgassing from a reducing of Earth's interior. The length of time that this replenishment might need to continue is in part constrained by the flux of asteroids onto the Earth's surface containing sufficient energy to destroy most, if not all, life that had developed up to that point in time. If a reducing atmosphere is a key ingredient for the origin of life on Earth, the time of the last environmental sterilization due to large impacts would be an important constraint. In a deep marine setting (e.g., hydrothermal vent), the last global sterilization might have occurred at 4200-4000 Ma. On the Earth's surface, the last global sterilization event might have occurred at 4000-3700 Ma. If these are meaningful constraints, how likely is it that a reducing atmosphere could have survived on the Earth until about 3800 Ma ago? Due to the importance of replenishing this atmosphere with reducing components by volcanic outgassing from the mantle, geochemical information on the history of the mantle's oxidation state would be useful for addressing this question. Geochemical and experimental data discussed in this abstract suggest that extrusive mafic volcanics derived from the upper mantle have had

  10. On the correlation between air temperature and the core Earth processes: Further investigations using a continuous wavelet analysis

    CERN Document Server

    Sello, Stefano

    2011-01-01

    In a recent article by Dickey, J. O., Marcus, S.L. and O. de Viron, 2011, the authors show evidences for correlations in the multi-decadal variability of Earth's rotation rate [i.e., length of day (LOD)], the angular momentum of the core (CAM), and natural surface air temperature (SAT). Previous investigators have already found that the LOD fluctuations are largely attributed to core-mantle interactions and that the SAT appears strongly anti-correlated with the decadal LOD. As the above authors note, the cause of this common variability needs to be further investigated and studied. In fact, "since temperature cannot affect the CAM or LOD to a sufficient extent, the results favor either a direct effect of Earth's core-generated magnetic field (e.g., through the modulation of charged-particle fluxes, which may impact cloud formation) or a more indirect effect of some other core process on the climate-or yet another process that affects both". The main aim of the present research note is to further support the a...

  11. Radiative conductivity and abundance of post-perovskite in the lowermost mantle

    CERN Document Server

    Lobanov, Sergey S; Lin, Jung-Fu; Goncharov, Alexander F

    2016-01-01

    Thermal conductivity of the lowermost mantle governs the heat flow out of the core energizing planetary-scale geological processes. Yet, there are no direct experimental measurements of thermal conductivity at relevant pressure-temperature conditions of Earth's core-mantle boundary. Here we determine the radiative conductivity of post-perovskite at near core-mantle boundary conditions by optical absorption measurements in a laser-heated diamond anvil cell. Our results show that the radiative conductivity of Mg0.9Fe0.1SiO3 post-perovskite (< 1.2 W/m/K) is ~ 40% smaller than bridgmanite at the base of the mantle. By combining this result with the present-day core-mantle heat flow and available estimations on the lattice thermal conductivity we conclude that post-perovskite is as abundant as bridgmanite in the lowermost mantle which has profound implications for the dynamics of the deep Earth.

  12. Lu Hf systematics of the ultra-high temperature Napier Metamorphic Complex in Antarctica: Evidence for the early Archean differentiation of Earth's mantle

    Science.gov (United States)

    Choi, Sung Hi; Mukasa, Samuel B.; Andronikov, Alexandre V.; Osanai, Yasuhito; Harley, Simon L.; Kelly, Nigel M.

    2006-06-01

    The Napier Complex of the East Antarctic Craton comprises some of the oldest rocks on Earth (˜ 3.8 billion years old), overprinted by an ultra-high temperature (UHT) metamorphic event near the Archean-Proterozoic boundary. Garnet, orthopyroxene, sapphirine, osumilite, rutile and a whole rock representing a fully equilibrated assemblage from this UHT granulite belt have yielded a Lu-Hf isochron age of 2403 ± 43 Ma, the first ever determined on a UHT mineral assemblage. Preservation of the UHT mineral assemblage in the rock analyzed, without any significant retrogression, suggests rapid cooling with closure likely to have occurred for the Lu-Hf system at post-peak UHT conditions near a temperature of ˜ 800 °C. This mineral-whole rock isochron yields an initial 176Hf/ 177Hf ratio corresponding to an ɛHf value of - 14 ± 1, acquired during UHT metamorphism. Such a low value demonstrates that overall UHT granulites evolved in a low Lu/Hf environment, probably formed when the rocks were first extracted from a highly depleted mantle. Zircon ɛHf values we have measured "see through" the UHT metamorphism and show that the source materials for the magmas that formed the Napier Complex were extremely depleted (> + 5.6 ɛHf at 3.85 Ga) relative to the chondritic uniform reservoir (CHUR). These results also suggest significant depletion of the early Archean mantle, in agreement with the early differentiation of the Earth that the latest core formation models require.

  13. Earth's Climate History from Glaciers and Ice Cores

    Science.gov (United States)

    Thompson, Lonnie

    2013-03-01

    Glaciers serve both as recorders and early indicators of climate change. Over the past 35 years our research team has recovered climatic and environmental histories from ice cores drilled in both Polar Regions and from low to mid-latitude, high-elevation ice fields. Those ice core -derived proxy records extending back 25,000 years have made it possible to compare glacial stage conditions in the Tropics with those in the Polar Regions. High-resolution records of δ18O (in part a temperature proxy) demonstrate that the current warming at high elevations in the mid- to lower latitudes is unprecedented for the last two millennia, although at many sites the early Holocene was warmer than today. Remarkable similarities between changes in the highland and coastal cultures of Peru and regional climate variability, especially precipitation, imply a strong connection between prehistoric human activities and regional climate. Ice cores retrieved from shrinking glaciers around the world confirm their continuous existence for periods ranging from hundreds to thousands of years, suggesting that current climatological conditions in those regions today are different from those under which these ice fields originated and have been sustained. The ongoing widespread melting of high-elevation glaciers and ice caps, particularly in low to middle latitudes, provides strong evidence that a large-scale, pervasive and, in some cases, rapid change in Earth's climate system is underway. Observations of glacier shrinkage during the 20th and 21st century girdle the globe from the South American Andes, the Himalayas, Kilimanjaro (Tanzania, Africa) and glaciers near Puncak Jaya, Indonesia (New Guinea). The history and fate of these ice caps, told through the adventure, beauty and the scientific evidence from some of world's most remote mountain tops, provide a global perspective for contemporary climate. NSF Paleoclimate Program

  14. Generation of MAC waves by convection in Earth's core

    Science.gov (United States)

    Jaupart, Etienne; Buffett, Bruce

    2017-05-01

    Convection in Earth's core is a viable mechanism for generating MAC waves when the top of the core is stably stratified. We quantify the generation mechanism by extending the physical description of MAC waves to include a source term due to buoyancy forces in the convecting part of the core. Solutions for the forced motion are obtained using a Green's function, which is constructed from the eigenfunctions for the unforced motion. When the source term is evaluated using the output of a numerical geodynamo model, the largest excitation occurs at even spherical harmonic degrees, corresponding to waves with symmetric azimuthal flow about the equator. We also find that the magnitude of the source term decreases at periods shorter than about 60 yr. As a result most of the wave generation is confined to waves with periods of 60 yr or longer. Quantitative predictions for the wave amplitudes depend on the projection of the source term into the eigenfunction of the waves. Strong stratification limits the penetration of density anomalies into the stratified layer, which means that the source term is confined to the lowermost part of the layer. Overtones of MAC waves with large amplitudes in the lower part of the stratified layer are more effectively generated by convection, even though these waves are heavily damped by magnetic diffusion. Generation of MAC waves by convection establishes a physical link between observable wave motion and deeper convective processes. Detection of changes in the amplitude and phase of MAC waves would constrain the generation processes and offer insights into the nature of the convection.

  15. Turbulent geodynamo simulations: a leap towards Earth's core

    Science.gov (United States)

    Schaeffer, N.; Jault, D.; Nataf, H.-C.; Fournier, A.

    2017-10-01

    We present an attempt to reach realistic turbulent regime in direct numerical simulations of the geodynamo. We rely on a sequence of three convection-driven simulations in a rapidly rotating spherical shell. The most extreme case reaches towards the Earth's core regime by lowering viscosity (magnetic Prandtl number Pm = 0.1) while maintaining vigorous convection (magnetic Reynolds number Rm > 500) and rapid rotation (Ekman number E = 10-7) at the limit of what is feasible on today's supercomputers. A detailed and comprehensive analysis highlights several key features matching geomagnetic observations or dynamo theory predictions—all present together in the same simulation—but it also unveils interesting insights relevant for Earth's core dynamics. In this strong-field, dipole-dominated dynamo simulation, the magnetic energy is one order of magnitude larger than the kinetic energy. The spatial distribution of magnetic intensity is highly heterogeneous, and a stark dynamical contrast exists between the interior and the exterior of the tangent cylinder (the cylinder parallel to the axis of rotation that circumscribes the inner core). In the interior, the magnetic field is strongest, and is associated with a vigorous twisted polar vortex, whose dynamics may occasionally lead to the formation of a reverse polar flux patch at the surface of the shell. Furthermore, the strong magnetic field also allows accumulation of light material within the tangent cylinder, leading to stable stratification there. Torsional Alfvén waves are frequently triggered in the vicinity of the tangent cylinder and propagate towards the equator. Outside the tangent cylinder, the magnetic field inhibits the growth of zonal winds and the kinetic energy is mostly non-zonal. Spatio-temporal analysis indicates that the low-frequency, non-zonal flow is quite geostrophic (columnar) and predominantly large-scale: an m = 1 eddy spontaneously emerges in our most extreme simulations, without any

  16. Attenuation of seismic waves and the universal rheological model of the Earth's mantle

    Science.gov (United States)

    Birger, B. I.

    2007-08-01

    Analysis of results of laboratory studies on creep of mantle rocks, data on seismic wave attenuation in the mantle, and rheological micromechanisms shows that the universal, i.e., relevant to all time scales, rheological model of the mantle can be represented as four rheological elements connected in series. These elements account for elasticity, diffusion rheology, high temperature dislocation rheology, and low temperature dislocation rheology. The diffusion rheology element is described in terms of a Newtonian viscous fluid. The high temperature dislocation rheology element is described by the rheological model previously proposed by the author. This model is a combination of a power-law non-Newtonian fluid model for stationary flows and the linear hereditary Andrade model for flows associated with small strains. The low temperature dislocation rheology element is described by the linear hereditary Lomnitz model.

  17. Seismic Anisotropy from the Core-Mantle Boundary to the Surface

    Science.gov (United States)

    Lynner, Colton Lee

    Subduction systems are vitally important to plate tectonics and mantle convection, but questions remain about many aspects of subduction dynamics, particularly the nature of sub-slab mantle flow. Observations of seismic anisotropy can shed light on the pattern of mantle flow in subduction systems. Understanding the sub-slab mantle is the focus of my first three chapters as well as my last chapter. In Chapters 1 and 2, I examine the sub-slab anisotropy beneath the Caribbean, Scotia, Central America, Alaska-Aleutians, Sumatra, Ryukyu, and IzuBonin-Japan-Kurile subduction systems. I find that measured fast splitting directions in these regions generally fall into two broad categories, aligning either with the strike of the trench or with the motion of the subducting slab relative to the overriding plate. In theses systems, there is a correlation between fast direction and age of the subducting lithosphere; older lithosphere (> 95 Ma) is associated with trench parallel splitting while younger lithosphere (studies of source-side splitting studies to test the predictions of a number of recently proposed conceptual models for the dynamics of the sub-slab mantle. I find that a model in which fast splitting directions are determined by slab age matches the observations better than either the 3D-return flow or radial anisotropic models. Based on this observation, I propose that the sub-slab mantle is characterized by two distinct anisotropic and mantle flow regimes. Beneath younger lithosphere ( 95 Ma), the entrained layer is thin and effectively serves as decoupling layer; the dynamics of the sub-slab region beneath old lithosphere is therefore dominated by three-dimensional return flow. In Chapters 4 and 5, I focus on the dynamics of lowermost mantle. Shear wave splitting of SK(K)S phases is often used to examine upper mantle anisotropy. In specific cases, however, splitting of these phases may reflect anisotropy in the lowermost mantle. In both Chapters 4 and 5, I present

  18. Compositional Evolution of the Mantle

    Science.gov (United States)

    Bennett, V. C.

    2003-12-01

    The mantle is the Earth's largest chemical reservoir comprising 82% of its total volume and 65% of its mass. The mantle constitutes almost all of the silicate Earth, extending from the base of the crust (which comprises only 0.6% of the silicate mass) to the top of the metallic core at 2,900 km depth. The chemical compositions of direct mantle samples such as abyssal peridotites (Chapter 2.04) and peridotite xenoliths (Chapter 2.05), and of indirect probes of the mantle such as basalts from mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) (Chapter 2.03), and some types of primitive granites, tell us about the compositional state of the modern mantle, with ever increasingly detailed information providing strong evidence for chemical complexity and heterogeneity at all scales (Chapter 2.03). This chemical heterogeneity must reflect the complex physical interplay of a number of distinct long-lived geochemical reservoirs that are identified primarily by their radiogenic isotopic compositions.Many of the chapters in this volume provide detailed images of the current chemical and physical state of the Earth's mantle, whereas other contributions examine the starting composition for the Earth (Chapter 2.01). This chapter attempts to link these two areas by tracking the composition of the mantle through time. The first part of this chapter is a summary of the empirical evidence for secular change in the chemical composition of the mantle from the formation of the Earth at 4.56 Ga throughto the present day. The emphasis is on results from the long-lived radiogenic isotopic systems, in particular 147Sm-143Nd, 176Lu-176Hf, 87Rb-87Sr, and 187Re-187Os systems as these isotopic data provide some of the best constraints on the composition of the mantle in the first half of Earth history, and the timing and extent of chemical differentiation that has affected the mantle over geologic time. Selected trace element data and the "short-lived" 146Sm-142Nd isotopic systems

  19. Ultrahigh-pressure structure of GeO2 glass with coordination number >6: implications for structure of magma at the core-mantle boundary

    Science.gov (United States)

    Kono, Y.; Kenney-Benson, C.; Ikuta, D.; Shibazaki, Y.; Wang, Y.; Shen, G.

    2016-12-01

    Silicate magma at the core-mantle boundary is one of the most important components in understanding nature and evolution of the Earth's deep interior. However, structure and properties of silicate magmas at the pressure condition of the core-mantle boundary remain poorly understood, because of experimental challenges. Pioneering work by Murakami and Bass (2010) showed a kink in the pressure dependence of shear-wave velocity in SiO2 glass around 140 GPa, which was interpreted as evidence of ultrahigh pressure structural transition. However, no structural information is available under such high pressures. Here we show new experimental evidence of ultrahigh pressure structural transition in GeO2 glass with Ge-O coordination number (CN) significantly greater than 6, investigated using a newly developed double-stage large volume cell combined with multi-angle energy dispersive X-ray diffraction technique for in situ amorphous structure measurement (Kono et al., 2016). The Ge-O coordination number (CN) is found to remain constant at 6 between 22.6 and 37.9 GPa. At higher pressures, CN begins to increase rapidly to 6.4 at 49.4 GPa and reaches 7.4 at 91.7 GPa. The structural change to CN higher than 6 is closely associated with the change in oxygen packing fraction (OPF). This transformation begins when the OPF in GeO2 glass is close to the maximal dense packing state (the Kepler conjecture= 0.74), which provides new insights into structural changes in network-forming glasses and liquids with CN higher than 6 at ultrahigh pressure conditions. For example, extrapolation of OPF-pressure trend in SiO2 glass shows that OPF of SiO2glass reaches to 0.74 around 108 GPa, where structural change to CN higher than 6 is expected. The data imply that silicate magma at the core-mantle boundary may possess ultrahigh-pressure structure with CN higher than 6. References Kono, Y., Kenney-Benson, C., Ikuta, D., Shibazaki, Y., Wang, Y., & Shen, G. (2016). Ultrahigh-pressure polyamorphism in

  20. The CaCO3-Fe interaction: Kinetic approach for carbonate subduction to the deep Earth's mantle

    Science.gov (United States)

    Martirosyan, N. S.; Yoshino, T.; Shatskiy, A.; Chanyshev, A. D.; Litasov, K. D.

    2016-10-01

    The CaCO3-Fe0 system, as a model for redox reactions between carbonates and reduced lithologies at the slab-mantle interface during subduction or at core-mantle boundary, was investigated systematically at temperatures from 650 to 1400 °C and pressures from 4 to 16 GPa using multianvil apparatus. CaCO3 reduction via reaction: 3 CaCO3 (aragonite) + 13 Fe0 (metal) = Fe7C3 (carbide) + 3 CaFe2O3 (Ca-wüstite) was observed. The thickness of the reaction-product layer (Δx) increases linearly with the square root of time in the time-series experiments (t), indicating diffusion-controlled process. The reaction rate constant (k = Δx2/2t) is log-linear relative to 1/T. Its temperature dependences was determined to be k [m2/s] = 2.1 × 10-7exp(-162[kJ/mol]/RT) at 4-6 GPa and k [m2/s] = 2.6 × 10-11exp(-65[kJ/mol]/RT) at 16 GPa. The sluggish kinetics of established CaCO3-Fe0 interaction suggests that significant amount of carbonates could survive during subduction from metal saturation boundary near 250 km depth down to the transition zone and presumably to the lower mantle if melting of carbonates is not involved.

  1. Two-Body Convection in the Mantle of the Earth: E/W Asymmetry, Under Astronomically Determined Tilt in g

    Science.gov (United States)

    Bostrom, R. C.

    2002-12-01

    Under purely geocentric gravity, over time displacement under mantle convection is globally symmetrical, resulting in zero net lithosphere rotation. The effect is here explored of substituting the asymmetric Earth-Moon field, gconv, prevalent in actuality. The gravity responsible for mantle convection is defined as the vector sum of a vertical component and the day-averaged attraction of masses lagging tidal equilibrium. The increasingly accurately measured lunar recession may then be used to delimit the internal field in terms of the secular luni-tidal interval of the Earth as a whole, some 600 seconds [1], without having to identify tidal components i.e. separate marine from body tides. In context the astronomic phase-lag may be viewed as a global isostatic anomaly, in which the longitude circles marking Earth's gravimetric figure are located east of those describing its perpetually unattained equilibrium figure by some 89 km at the Equator. Reference the hydrostatic ellipsoid gconv is tilted by the astronomically delimited amount, albeit that the phase lag is attributable in part to the convection itself. As with the convection, the tectonic significance of its asymmetry is determinable geodetically. Using present art-state a strategically located GPS grid [2] would provide continuously more precise separation of the asymmetric component of surface displacement. In developing plate-motion models including members of the Nuvel series, it would be logical to follow up rather than discard the set permitting minor asymmetrical convection sans net torque, such as an element of net-lithosphere-rotation relative to plumes. To conserve system angular-momentum, this may be the only valid set. Characteristics of the convection to be expected accord with 'paradoxical' features of plate tectonics under purely radial gravity, including: difficulty in closing plate-motion circuits; net-lithosphere-rotation refce. hot-spots, sans net torque; geotectonic maps ranging from

  2. Mantle Convection, Plate Tectonics, and the Asthenosphere: A Bootstrap Model of the Earth's Internal Dynamics

    Science.gov (United States)

    Lenardic, A.; Hoink, T.

    2008-12-01

    Several studies have highlighted the role of a low viscosity asthenosphere in promoting plate-like behavior in mantle convection models. It has also been argued that the asthenosphere is fed by mantle plumes (Phipps- Morgan et al. 1993; Deffeyes 1972) and that the existence of the specific plume types required for this depends on plate subduction (Lenardic and Kaula 1995; Jellinek et al. 2002). Independent of plumes, plate subduction can generate a non-adiabatic temperature gradient which, together with temperature dependent mantle viscosity, leads to a low viscosity near surface region. The above suggests a conceptual model in which the asthenosphere can not be defined solely in terms of material properties but must also be defined in terms of an active process, plate tectonics, which both maintains it and is maintained by it. The bootstrap aspect of the model is its circular causality between plates and the asthenosphere, neither being more fundamental than the other and the existence of each depending on the other. Several of the feedbacks key to the conceptual model will be quantified. The implications for modeling mantle convection in a plate-tectonic mode will also be discussed: 1) A key is to get numerical simulations into the bootstrap mode of operation and this is dependent on assumed initial conditions; 2) The model implies potentially strong hysteresis effects (e.g., transition between convection states, associated with variable yield stress, will occur at different values depending on whether the yield stress is systematically lowered or raised between successive models).

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

    Energy Technology Data Exchange (ETDEWEB)

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

    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 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.

  4. The effect of a rough core-mantle boundary on PKKP

    NARCIS (Netherlands)

    Doornbos, D.J.

    Scattering by a slightly-rough core—mantle boundary (CMB) with small-scale radial variations of up to a few hundred metres, has been an attractive (though non-unique) interpretation of at least part of the precursors to PKLKP. Here it is shown that a slightly-rough CMB has an observable effect on

  5. Seismic Structures in the Earth's Inner Core Below Southeastern Asia

    Science.gov (United States)

    Krasnoshchekov, Dmitry; Kaazik, Petr; Kozlovskaya, Elena; Ovtchinnikov, Vladimir

    2016-05-01

    Documenting seismic heterogeneities in the Earth's inner core (IC) is important in terms of getting an insight into its history and dynamics. A valuable means for studying properties and spatial structure of such heterogeneities is provided by measurements of body waves refracted in the vicinity of the inner core boundary (ICB). Here, we investigate eastern hemisphere of the solid core by means of PKPBC-PKPDF differential travel times that sample depths from 140 to 360 km below its boundary. We study 292 polar and 133 equatorial residuals measured over the traces that probe roughly the same volume of the IC in both planes. Equatorial residuals show slight spatial variations in the sampled IC volume mostly below the level of 0.5 %, whereas polar residuals are up to three times as big, direction dependent and can exhibit higher local variations. The measurements reveal fast changes in seismic velocity within a restricted volume of the IC. We interpret the observations in terms of anisotropy and check against several anisotropy models few of which have been found capable of fitting the residuals scatter. We particularly quantify the model where a dipping discontinuity separates fully isotropic roof of the IC from its anisotropic body, whereas the depth of isotropy-anisotropy transition increases in southeast direction from 190 km below Southeastern Asia (off the coast of China) to 350 km beneath Australia. Another acceptable model cast in terms of localized anisotropic heterogeneities is valid if 33 largest polar measurements over the rays sampling a small volume below Southeastern Asia and the rest of polar data are treated separately. This model envisages almost isotropic eastern hemisphere of the IC at least down to the depth of 360 km below the ICB and constrains the anisotropic volume only to the ranges of North latitudes from 18° to 23°, East longitudes from 125° to 135° and depths exceeding 170 km. The anisotropy strength in either model is about 2

  6. Alkaline Earth Core Level Photoemission Spectroscopy of High-Temperature Superconductors

    Science.gov (United States)

    Vasquez, R.

    1993-01-01

    This paper examines photoemission measurements of the alkaline Earth core levels of high-temperature superconductors and related materials, models that seek to explain the large negative shifts observed relative to the corresponding alkaline Earth metals, and the effect of lattice site disorder on the core level spectra and the presence or absence of intrinsic surface peaks.

  7. Alkaline Earth Core Level Photoemission Spectroscopy of High-Temperature Superconductors

    Science.gov (United States)

    Vasquez, R.

    1993-01-01

    This paper examines photoemission measurements of the alkaline Earth core levels of high-temperature superconductors and related materials, models that seek to explain the large negative shifts observed relative to the corresponding alkaline Earth metals, and the effect of lattice site disorder on the core level spectra and the presence or absence of intrinsic surface peaks.

  8. Inertial waves in a laboratory model of the Earth's core

    Science.gov (United States)

    Triana, Santiago Andres

    2011-12-01

    A water-filled three-meter diameter spherical shell built as a model of the Earth's core shows evidence of precessionally forced flows and, when spinning the inner sphere differentially, inertial modes are excited. We identified the precessionally forced flow to be primarily the spin-over inertial mode, i.e., a uniform vorticity flow whose rotation axis is not aligned with the container's rotation axis. A systematic study of the spin-over mode is carried out, showing that the amplitude dependence on the Poincare number is in qualitative agreement with Busse's laminar theory while its phase differs significantly, likely due to topographic effects. At high rotation rates free shear layers concentrating most of the kinetic energy of the spin-over mode have been observed. When spinning the inner sphere differentially, a total of 12 inertial modes have been identified, reproducing and extending previous experimental results. The inertial modes excited appear ordered according to their azimuthal drift speed as the Rossby number is varied.

  9. Evidence for an oxygen-depleted liquid outer core of the Earth.

    Science.gov (United States)

    Huang, Haijun; Fei, Yingwei; Cai, Lingcang; Jing, Fuqian; Hu, Xiaojun; Xie, Hongsen; Zhang, Lianmeng; Gong, Zizheng

    2011-11-23

    On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth's liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of light elements. Although the concentrations of the light elements are small, they nevertheless affect the Earth's core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo. Several light elements-including sulphur, oxygen, silicon, carbon and hydrogen-have been suggested, but the precise identity of the light elements in the Earth's core is still unclear. Oxygen has been proposed as a major light element in the core on the basis of cosmochemical arguments and chemical reactions during accretion. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe-S-O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major light element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.

  10. A generalized equation of state with an application to the Earth's mantle

    OpenAIRE

    J. A. Robles-Gutiérrez; J. M. A. Robles-Domínguez; C. Lomnitz

    2010-01-01

    This study analizes the pertinency of including in the state equation of Kamerlingh-Onnes, non additive, potentials of multiple-interactiions of particles. These forces are indeed real and of a electrodinamic character. From the state equation no gerenalized, we obtained the isotherms in the vecinity of the critical point, and of the triple point for polar (or no polar) systems. We developed the example of water. We generalized the state equation for the mantle developed by Birch, and in part...

  11. The effects of the solid inner core and nonhydrostatic structure on the earth's forced nutations and earth tides

    Science.gov (United States)

    De Vries, Dan; Wahr, John M.

    1991-01-01

    This paper computes the effects of the solid inner core (IC) on the forced nutations and earth tides, and on certain of the earth's rotational normal modes. The theoretical results are extended to include the effects of a solid IC and of nonhydrostatic structure. The presence of the IC is responsible for a new, almost diurnal, prograde normal mode which involves a relative rotation between the IC and fluid outer core about an equatorial axis. It is shown that the small size of the IC's effects on both nutations and tides is a consequence of the fact that the IC's moments of inertia are less than 1/1000 of the entire earth's.

  12. Semantic Network Analysis on Terms related Mantle in Earth Science 2 Textbooks of Korea

    Science.gov (United States)

    Chung, Duk Ho; reum Cho, Ah; Park, Seon Ok

    2016-04-01

    The purpose of this study is to demonstrate if freshmen's cognitive frame about 'Crisis of the Earth' upon taking the Earth science 1 in high school reflects the school curriculum. The data was collected from 67 freshmen who'd graduated high school in formal education. They expressed 'Crisis of the Earth' as a painting with explanation and then we extracted units of meaning from paintings, respectively. We analyzed the words and frame using the Semantic Network Analysis. The result is as follows; First, as every participant forms the cognitive frame for the crisis of the Earth, it is shown that they connect each part which that composes the global environment and realize it as the changing relation with interaction. Secondly, forming a cognitive frame regarding crisis of the Earth, both groups connect it with human endeavor. Especially, it seems that the group of participants who finished Earth Science I fully reflects the course of the formal education. It is necessary to make the students recognize it from a universal point of view, not only from the Earth. Also, much effort is required in order to enlighten about the appropriateness regarding problem-solving of the Earth and expand their mind as time changes. Keywords : Earth ScienceⅠ, cognitive frame, crisis of the earth, semantic network analysis

  13. Mars' core and magnetism.

    Science.gov (United States)

    Stevenson, D J

    2001-07-12

    The detection of strongly magnetized ancient crust on Mars is one of the most surprising outcomes of recent Mars exploration, and provides important insight about the history and nature of the martian core. The iron-rich core probably formed during the hot accretion of Mars approximately 4.5 billion years ago and subsequently cooled at a rate dictated by the overlying mantle. A core dynamo operated much like Earth's current dynamo, but was probably limited in duration to several hundred million years. The early demise of the dynamo could have arisen through a change in the cooling rate of the mantle, or even a switch in convective style that led to mantle heating. Presently, Mars probably has a liquid, conductive outer core and might have a solid inner core like Earth.

  14. The Evolution of the Earth's Magnetic Field.

    Science.gov (United States)

    Bloxham, Jeremy; Gubbins, David

    1989-01-01

    Describes the change of earth's magnetic field at the boundary between the outer core and the mantle. Measurement techniques used during the last 300 years are considered. Discusses the theories and research for explaining the field change. (YP)

  15. Short scale variation in presence and structure of complex core-mantle boundary regions beneath northern Mexico

    Science.gov (United States)

    Jasbinsek, J. J.

    2016-12-01

    A set of nine intermediate depth earthquakes with closely spaced epicenters in Central America recorded at a small aperture array in the western United States contain clear core-mantle boundary (CMB) reflections. Cross-correlation of [0.5,2] Hz bandpass filtered seismograms at the 11 station array results in well-constrained stacked PcP and ScP waveforms. Most events contain both PcP and ScP waveforms, providing two distinct areas of core-mantle boundary sampling. In approximately half of the stacked waveforms, additional pre- and/or post-cursory arrivals are observed with both PcP and ScP suggesting the presence of complicated CMB structures. Commonly the extra arrivals have the visual appearance of reverberations. Two primary observations are made: (1) One-dimensional forward modeling indicates that simple one-layer ultra-low velocity zone (ULVZ) models do not accurately reproduce the PcP and ScP waveforms, instead multi-layer ULVZ models provide a better fit to the waveforms, (2) Spatially the pattern of CMB regions requiring extra structure is contiguous, but change to a simple CMB structure over short distance scales. The simple one-dimensional modeling explored here cannot uniquely constrain the three-dimensional CMB structure, but provides insight into potential CMB structure that may be resolvable with higher accuracy and more computationally intensive forward seismogram modeling.

  16. Dust evolution, a global view: III. Core/mantle grains, organic nano-globules, comets and surface chemistry

    Science.gov (United States)

    Jones, A. P.

    2016-12-01

    Within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), this work explores the surface processes and chemistry relating to core/mantle interstellar and cometary grain structures and their influence on the nature of these fascinating particles. It appears that a realistic consideration of the nature and chemical reactivity of interstellar grain surfaces could self-consistently and within a coherent framework explain: the anomalous oxygen depletion, the nature of the CO dark gas, the formation of `polar ice' mantles, the red wing on the 3 μm water ice band, the basis for the O-rich chemistry observed in hot cores, the origin of organic nano-globules and the 3.2 μm `carbonyl' absorption band observed in comet reflectance spectra. It is proposed that the reaction of gas phase species with carbonaceous a-C(:H) grain surfaces in the interstellar medium, in particular the incorporation of atomic oxygen into grain surfaces in epoxide functional groups, is the key to explaining these observations. Thus, the chemistry of cosmic dust is much more intimately related with that of the interstellar gas than has previously been considered. The current models for interstellar gas and dust chemistry will therefore most likely need to be fundamentally modified to include these new grain surface processes.

  17. Core Angular Momentum and the IERS Sub-Centers Activity for Monitoring Global Geophysical Fluids. Part 1; Core Angular Momentum and Earth Rotation

    Science.gov (United States)

    Song, Xia-Dong; Chao, Benjamin (Technical Monitor)

    1999-01-01

    The part of the grant was to use recordings of seismic waves travelling through the earth's core (PKP waves) to study the inner core rotation and constraints on possible density anomalies in the fluid core. The shapes and relative arrival times of such waves associated with a common source were used to reduce the uncertainties in source location and excitation and the effect of unknown mantle structure. The major effort of the project is to assemble historical seismograms with long observing base lines. We have found original paper records of SSI earthquakes at COL between 1951 and 1966 in a warehouse of the U.S. Geological Survey office in Golden, Colorado, extending the previous measurements at COL by Song and Richards [1996] further back 15 years. Also in Alaska, the University of Alaska, Fairbanks Geophysical Institute (UAFGI) has been operating the Alaskan Seismic Network with over 100 stations since the late 1960s. Virtually complete archives of seismograms are still available at UAFGI. Unfortunately, most of the archives are in microchip form (develocorders), for which the use of waveforms is impossible. Paper seismograms (helicorders) are available for a limited number of stations, and digital recordings of analog signals started around 1989. Of the paper records obtained, stations at Gilmore Dome (GLM, very close to COL), Yukon (FYU), McKinley (MCK), and Sheep Creek Mountain (SCM) have the most complete continuous recordings.

  18. Deep Mantle Seismic Modeling and Imaging

    Science.gov (United States)

    Lay, Thorne; Garnero, Edward J.

    2011-05-01

    Detailed seismic modeling and imaging of Earth's deep interior is providing key information about lower-mantle structures and processes, including heat flow across the core-mantle boundary, the configuration of mantle upwellings and downwellings, phase equilibria and transport properties of deep mantle materials, and mechanisms of core-mantle coupling. Multichannel seismic wave analysis methods that provide the highest-resolution deep mantle structural information include network waveform modeling and stacking, array processing, and 3D migrations of P- and S-wave seismograms. These methods detect and identify weak signals from structures that cannot be resolved by global seismic tomography. Some methods are adapted from oil exploration seismology, but all are constrained by the source and receiver distributions, long travel paths, and strong attenuation experienced by seismic waves that penetrate to the deep mantle. Large- and small-scale structures, with velocity variations ranging from a fraction of a percent to tens of percent, have been detected and are guiding geophysicists to new perspectives of thermochemical mantle convection and evolution.

  19. Time variability in Cenozoic reconstructions of mantle heat flow: plate tectonic cycles and implications for Earth's thermal evolution.

    Science.gov (United States)

    Loyd, S J; Becker, T W; Conrad, C P; Lithgow-Bertelloni, C; Corsetti, F A

    2007-09-04

    The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by approximately 0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past.

  20. Shock Compression and Phase Transitions of Magnesiowüstite (Mg,Fe)O up to Earth's Lowermost Mantle Conditions

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li; GONG Zi-Zheng

    2006-01-01

    @@ We report new shock-compression data for polycrystalline (Mg, Fe)O up to 130 Gpa shock pressures corresponding to Earth's lowermost mantle conditions. Our data together with the existing shock-wave data of (Mg,Fe)O and its end-members MgO and FeO reveal that the Hugoniot curves of (Mg, Fe)O does not change with varying FeO content for their B1 phase (NaCl-structure) in the pressure-relative-volume plane. The evidence of the volume change within 3% at around 120 Gpa along the Hugoniot of (Mg0.6, Fe0.4)O is consistent with a structural transition from B1 phase (NaCl cubic) to B8 phase (NiAs-type hexagonal). Such a structural transition of (Mg, Fe)O, if indeed occurs, may in part contribute to the scattering of seismic waves and change in velocity gradient found in the lowermost mantle.

  1. Seismological evidence for a localized mushy zone at the Earth's inner core boundary.

    Science.gov (United States)

    Tian, Dongdong; Wen, Lianxing

    2017-08-01

    Although existence of a mushy zone in the Earth's inner core has been hypothesized several decades ago, no seismic evidence has ever been reported. Based on waveform modeling of seismic compressional waves that are reflected off the Earth's inner core boundary, here we present seismic evidence for a localized 4-8 km thick zone across the inner core boundary beneath southwest Okhotsk Sea with seismic properties intermediate between those of the inner and outer core and of a mushy zone. Such a localized mushy zone is found to be surrounded by a sharp inner core boundary nearby. These seismic results suggest that, in the current thermo-compositional state of the Earth's core, the outer core composition is close to eutectic in most regions resulting in a sharp inner core boundary, but deviation from the eutectic composition exists in some localized regions resulting in a mushy zone with a thickness of 4-8 km.The existence of a mushy zone in the Earth's inner core has been suggested, but has remained unproven. Here, the authors have discovered a 4-8 km thick mushy zone at the inner core boundary beneath the Okhotsk Sea, indicating that there may be more localized mushy zones at the inner core boundary.

  2. From mantle to critical zone: A review of large and giant sized deposits of the rare earth elements

    Directory of Open Access Journals (Sweden)

    M.P. Smith

    2016-05-01

    Full Text Available The rare earth elements are unusual when defining giant-sized ore deposits, as resources are often quoted as total rare earth oxide, but the importance of a deposit may be related to the grade for individual, or a limited group of the elements. Taking the total REE resource, only one currently known deposit (Bayan Obo would class as giant (>1.7 × 107 tonnes contained metal, but a range of others classify as large (>1.7 × 106 tonnes. With the exception of unclassified resource estimates from the Olympic Dam IOCG deposit, all of these deposits are related to alkaline igneous activity – either carbonatites or agpaitic nepheline syenites. The total resource in these deposits must relate to the scale of the primary igneous source, but the grade is a complex function of igneous source, magmatic crystallisation, hydrothermal modification and supergene enrichment during weathering. Isotopic data suggest that the sources conducive to the formation of large REE deposits are developed in subcontinental lithospheric mantle, enriched in trace elements either by plume activity, or by previous subduction. The reactivation of such enriched mantle domains in relatively restricted geographical areas may have played a role in the formation of some of the largest deposits (e.g. Bayan Obo. Hydrothermal activity involving fluids from magmatic to meteoric sources may result in the redistribution of the REE and increases in grade, depending on primary mineralogy and the availability of ligands. Weathering and supergene enrichment of carbonatite has played a role in the formation of the highest grade deposits at Mount Weld (Australia and Tomtor (Russia. For the individual REE with the current highest economic value (Nd and the HREE, the boundaries for the large and giant size classes are two orders of magnitude lower, and deposits enriched in these metals (agpaitic systems, ion absorption deposits may have significant economic impact in the near future.

  3. From mantle to critical zone:A review of large and giant sized deposits of the rare earth elements

    Institute of Scientific and Technical Information of China (English)

    M.P. Smith; K. Moore; D. Kavecsánszki; A.A. Finch; J. Kynicky; F. Wall

    2016-01-01

    The rare earth elements are unusual when defining giant-sized ore deposits, as resources are often quoted as total rare earth oxide, but the importance of a deposit may be related to the grade for indi-vidual, or a limited group of the elements. Taking the total REE resource, only one currently known deposit (Bayan Obo) would class as giant (>1.7 ? 107 tonnes contained metal), but a range of others classify as large (>1.7 ? 106 tonnes). With the exception of unclassified resource estimates from the Olympic Dam IOCG deposit, all of these deposits are related to alkaline igneous activity e either car-bonatites or agpaitic nepheline syenites. The total resource in these deposits must relate to the scale of the primary igneous source, but the grade is a complex function of igneous source, magmatic crystal-lisation, hydrothermal modification and supergene enrichment during weathering. Isotopic data suggest that the sources conducive to the formation of large REE deposits are developed in subcontinental lithospheric mantle, enriched in trace elements either by plume activity, or by previous subduction. The reactivation of such enriched mantle domains in relatively restricted geographical areas may have played a role in the formation of some of the largest deposits (e.g. Bayan Obo). Hydrothermal activity involving fluids from magmatic to meteoric sources may result in the redistribution of the REE and increases in grade, depending on primary mineralogy and the availability of ligands. Weathering and supergene enrichment of carbonatite has played a role in the formation of the highest grade deposits at Mount Weld (Australia) and Tomtor (Russia). For the individual REE with the current highest economic value (Nd and the HREE), the boundaries for the large and giant size classes are two orders of magnitude lower, and deposits enriched in these metals (agpaitic systems, ion absorption deposits) may have significant economic impact in the near future.

  4. On the admissible range of the radial temperature gradient and Brünt-Väisäla frequency in the mantle and core: I. Main relations

    Science.gov (United States)

    Molodenskii, S. M.

    2017-03-01

    The question of ambiguity in the solution of the inverse problem for determining the Brünt-Väisäla frequency in the Earth's mantle from the entire set of the up-to-date data on seismicity, free oscillations, and forced nutations of the Earth, as well as the data on the Earth's total mass and total moment of inertia, is considered. Based on the results of a series of numerical experiments, the band of admissible distributions of the Brünt-Väisäla frequency and mantle density with depth is calculated. This estimate is used for investigating the convective and gravitational stability of the different regions of the mantle against relatively small adiabatic and nonadiabatic perturbations. The generalization of the known Rayleigh criterion of convective stability of homogeneous and a nonself-gravitating incompressible viscous fluid for the case of a compressible self-gravitating fluid is given. A system of the ordinary eight-order differential equations with complex coefficients and homogeneous boundary conditions, whose eigenvalues determine the transition from the stable state to instability, is obtained. Examples of the numerical determination of these eignevalues are presented. For interpreting the data about the band of the admissible distributions of the Brünt-Väisäla frequency with depth, the notion of the effective bulk modulus of the medium at different depths is introduced. This quantity governs the depth changes in temperature in a convecting mantle and allows us to make a conclusion about the role of heat conduction and the radial heterogeneity of the mantle composition without imposing any constraints on the convection mechanism. It is shown that within the present-day observation errors in the frequencies of the Earth's free oscillations, the simplest reasonable model is that in which the ratio of the effective bulk modulus to its adiabatic value in the lower and middle mantle is 1.043 ± 0.05. The closeness of this value to unity indicates that

  5. Changes in Earth's core-generated magnetic field, as observed by Swarm

    DEFF Research Database (Denmark)

    Finlay, Chris; Olsen, Nils; Gillet, Nicolas

    By far the largest part of the Earth's magnetic field is generated by motions taking place within our planet's liquid metal outer core. Variations of this core-generated field thus provide us with a unique means of probing the dynamics taking place in the deepest reaches of the Earth....... In this contribution, we will present the core-generated magnetic field, and its recent time changes, as seen by ESA's Earth explorer mission Swarm. We will present a new time-dependent geomagnetic field model, called CHAOS-6, derived from satellite data collected by the Swarm constellation, as well as data from...

  6. Earth's evolving subcontinental lithospheric mantle: inferences from LIP continental flood basalt geochemistry

    Science.gov (United States)

    Greenough, John D.; McDivitt, Jordan A.

    2017-06-01

    Archean and Proterozoic subcontinental lithospheric mantle (SLM) is compared using 83 similarly incompatible element ratios (SIER; minimally affected by % melting or differentiation, e.g., Rb/Ba, Nb/Pb, Ti/Y) for >3700 basalts from ten continental flood basalt (CFB) provinces representing nine large igneous provinces (LIPs). Nine transition metals (TM; Fe, Mn, Sc, V, Cr, Co, Ni, Cu, Zn) in 102 primitive basalts (Mg# = 0.69-0.72) from nine provinces yield additional SLM information. An iterative evaluation of SIER values indicates that, regardless of age, CFB transecting Archean lithosphere are enriched in Rb, K, Pb, Th and heavy REE(?); whereas P, Ti, Nb, Ta and light REE(?) are higher in Proterozoic-and-younger SLM sources. This suggests efficient transfer of alkali metals and Pb to the continental lithosphere perhaps in association with melting of subducted ocean floor to form Archean tonalite-trondhjemite-granodiorite terranes. Titanium, Nb and Ta were not efficiently transferred, perhaps due to the stabilization of oxide phases (e.g., rutile or ilmenite) in down-going Archean slabs. CFB transecting Archean lithosphere have EM1-like SIER that are more extreme than seen in oceanic island basalts (OIB) suggesting an Archean SLM origin for OIB-enriched mantle 1 (EM1). In contrast, OIB high U/Pb (HIMU) sources have more extreme SIER than seen in CFB provinces. HIMU may represent subduction-processed ocean floor recycled directly to the convecting mantle, but to avoid convective homogenization and produce its unique Pb isotopic signature may require long-term isolation and incubation in SLM. Based on all TM, CFB transecting Proterozoic lithosphere are distinct from those cutting Archean lithosphere. There is a tendency for lower Sc, Cr, Ni and Cu, and higher Zn, in the sources for Archean-cutting CFB and EM1 OIB, than Proterozoic-cutting CFB and HIMU OIB. All CFB have SiO2 (pressure proxy)-Nb/Y (% melting proxy) relationships supporting low pressure, high % melting

  7. Iron geochemistry of the mantle

    Science.gov (United States)

    Humayun, M.; Campbell, T. J.; Brandon, A. D.; Davis, F. A.; Hirschmann, M. M.

    2011-12-01

    The Fe/Mg ratio is an important constraint on the compositionally controlled density of the mantle. However, this ratio cannot be inferred from erupted lavas from OIB or MORB sources, but must be determined directly from mantle peridotites. Recently, the Fe/Mn ratio of erupted lavas has been used as an indicator of potential Fe variability in the mantle driven by core-mantle interaction, recycled oceanic crust, or even variations in the temperature of mantle melting. The classic compilation of McDonough & Sun (1995) provided the currently accepted Fe/Mn ratio of the upper mantle, 60±10. The uncertainty on this ratio allows for 15-30% variability in mantle iron abundances, which is equivalent to a density variation larger than observed by seismic tomography in the mantle. To better understand the relationship between mantle peridotites and erupted lavas, and to search for real variability in the Fe/Mn ratio of mantle peridotites, we report precise new ICP-MS measurements of the transition element geochemistry of suites of mantle xenoliths that have known Fe/Mg ratios. For 12 Kilbourne Hole xenoliths, we observe a clear correlation between Fe/Mn and MgO (or Fe/Mg) over an Fe/Mn range of 59-72. Extrapolation of this trend to a Primitive Mantle (PM) MgO content of 37.8 yields an Fe/Mn of 59±1 for the PM. Our new analyses of KLB-1 powder and fused glass beads yield an Fe/Mn of 61.4 for both samples, which plots on the Kilbourne Hole Fe/Mn vs. MgO trend. A set of ten xenoliths from San Carlos yield a wide range of Fe/Mn (56-65) not correlated with MgO content. The San Carlos xenoliths may have experienced a metasomatic effect that imprinted variable Fe/Mn. A clinopyroxene-rich lithology from San Carlos yields an Fe/Mn of 38, which plots on an extension of the Kilbourne Hole Fe/Mn vs. MgO trend. These new results, and those from other xenolith localities being measured in our lab, provide new constraints on the compositional variability of the Earth's upper mantle. Mc

  8. Earth materials and earth dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Bennett, K; Shankland, T. [and others

    2000-11-01

    In the project ''Earth Materials and Earth Dynamics'' we linked fundamental and exploratory, experimental, theoretical, and computational research programs to shed light on the current and past states of the dynamic Earth. Our objective was to combine different geological, geochemical, geophysical, and materials science analyses with numerical techniques to illuminate active processes in the Earth. These processes include fluid-rock interactions that form and modify the lithosphere, non-linear wave attenuations in rocks that drive plate tectonics and perturb the earth's surface, dynamic recrystallization of olivine that deforms the upper mantle, development of texture in high-pressure olivine polymorphs that create anisotropic velocity regions in the convecting upper mantle and transition zone, and the intense chemical reactions between the mantle and core. We measured physical properties such as texture and nonlinear elasticity, equation of states at simultaneous pressures and temperatures, magnetic spins and bonding, chemical permeability, and thermal-chemical feedback to better characterize earth materials. We artificially generated seismic waves, numerically modeled fluid flow and transport in rock systems and modified polycrystal plasticity theory to interpret measured physical properties and integrate them into our understanding of the Earth. This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL).

  9. Highly siderophile element (HSE) abundances in the mantle of Mars are due to core formation at high pressure and temperature

    Science.gov (United States)

    Righter, K.; Danielson, L. R.; Pando, K. M.; Williams, J.; Humayun, M.; Hervig, R. L.; Sharp, T. G.

    2015-04-01

    Highly siderophile elements (HSEs) can be used to understand accretion and core formation in differentiated bodies, due to their strong affinity for FeNi metal and sulfides. Coupling experimental studies of metal-silicate partitioning with analyses of HSE contents of Martian meteorites can thus offer important constraints on the early history of Mars. Here, we report new metal-silicate partitioning data for the PGEs and Au and Re across a wide range of pressure and temperature space, with three series designed to complement existing experimental data sets for HSE. The first series examines temperature effects for D(HSE) in two metallic liquid compositions—C-bearing and C-free. The second series examines temperature effects for D(Re) in FeO-bearing silicate melts and FeNi-rich alloys. The third series presents the first systematic study of high pressure and temperature effects for D(Au). We then combine our data with previously published partitioning data to derive predictive expressions for metal-silicate partitioning of the HSE, which are subsequently used to calculate HSE concentrations of the Martian mantle during continuous accretion of Mars. Our results show that at midmantle depths in an early magma ocean (equivalent to approximately 14 GPa, 2100 °C), the HSE contents of the silicate fraction are similar to those observed in the Martian meteorite suite. This is in concert with previous studies on moderately siderophile elements. We then consider model calculations that examine the role of melting, fractional crystallization, and sulfide saturation/undersaturation in establishing the range of HSE contents in Martian meteorites derived from melting of the postcore formation mantle. The core formation modeling indicates that the HSE contents can be established by metal-silicate equilibrium early in the history of Mars, thus obviating the need for a late veneer for HSE, and by extension volatile siderophile elements, or volatiles in general.

  10. Importance of the Small-Scale Processes Melting, Plate Boundary Formation and Mineralogy on the Large-Scale, Long-Term Thermo-Chemical Evolution of Earth's Mantle-Plate System

    Science.gov (United States)

    Tackley, P.

    2015-12-01

    Seismic observations of the deep Earth reveal the presence of two large low shear velocity provinces (LLSVPs) that are typically inferred to be dense chemically-distinct material, as well as discontinuities that are typically linked to the post-perovskite (pPv) phase transition. Several possible origins of chemically-dense material have been proposed, including recycling of mid-ocean ridge basalt (MORB), primordial differentiation events, crystallisation of a basal magma ocean, or some combination of these creating a basal melange (BAM; Tackley 2012 Earth Sci. Rev.). Each of these possibilities would result in a different composition hence different mineralogy. In order to constrain this we have been running calculations of thermo-chemical mantle evolution over 4.5 billion years that include melting-induced differentiation, plate tectonics induced by strongly temperature-dependent viscosity and plastic yielding, core cooling and compressibility with reasonable assumptions about the pressure-dependence of other material properties. Some of our simulations start from a magma ocean state so initial layering is developed self-consistently. Already-published results (Nakagawa et al., 2009 GCubed, 2010 PEPI, 2012 GCubed) already indicate the importance of exact MORB composition on the amount of MORB segregating above the CMB, which in turn influences mantle thermal structure and the evolution of the core and geodynamo. In more recent results we have been additionally including primordial material. We find that melting-induced differentiation has several first-order effects on the dynamics, including (i) making plate tectonics easier (through stresses associated with lateral variations in crustal thickness) and (ii) reducing heat flux through the CMB (due to the build-up of dense material above the CMB); also (iii) tectonic mode (continuous plate tectonics, episodic lid or stagnant lid) also makes a first-order difference to mantle structure and dynamics. This emphasises

  11. Diagenetic remobilization of rare earth elements in a sediment core from the central Indian Basin

    Digital Repository Service at National Institute of Oceanography (India)

    Pattan, J.N.; Banakar, V.K.

    Rare earth elements (REE) distribution in a 36 cm long sediment box core from the Central Indian Basin is studied. REE concentration is generally higher in the upper oxic zone than in intermediate suboxic zone suggesting REE diffusion upwards...

  12. The Earth's mantle in a microwave oven: thermal convection driven by a heterogeneous distribution of heat sources

    Science.gov (United States)

    Fourel, Loïc; Limare, Angela; Jaupart, Claude; Surducan, Emanoil; Farnetani, Cinzia G.; Kaminski, Edouard C.; Neamtu, Camelia; Surducan, Vasile

    2017-08-01

    Convective motions in silicate planets are largely driven by internal heat sources and secular cooling. The exact amount and distribution of heat sources in the Earth are poorly constrained and the latter is likely to change with time due to mixing and to the deformation of boundaries that separate different reservoirs. To improve our understanding of planetary-scale convection in these conditions, we have designed a new laboratory setup allowing a large range of heat source distributions. We illustrate the potential of our new technique with a study of an initially stratified fluid involving two layers with different physical properties and internal heat production rates. A modified microwave oven is used to generate a uniform radiation propagating through the fluids. Experimental fluids are solutions of hydroxyethyl cellulose and salt in water, such that salt increases both the density and the volumetric heating rate. We determine temperature and composition fields in 3D with non-invasive techniques. Two fluorescent dyes are used to determine temperature. A Nd:YAG planar laser beam excites fluorescence, and an optical system, involving a beam splitter and a set of colour filters, captures the fluorescence intensity distribution on two separate spectral bands. The ratio between the two intensities provides an instantaneous determination of temperature with an uncertainty of 5% (typically 1K). We quantify mixing processes by precisely tracking the interfaces separating the two fluids. These novel techniques allow new insights on the generation, morphology and evolution of large-scale heterogeneities in the Earth's lower mantle.

  13. Redox-induced lower mantle density contrast and effect on mantle structure and primitive oxygen

    Science.gov (United States)

    Gu, Tingting; Li, Mingming; McCammon, Catherine; Lee, Kanani K. M.

    2016-09-01

    The mantle comprises nearly three-quarters of Earth's volume and through convection connects the deep interior with the lithosphere and atmosphere. The composition of the mantle determines volcanic emissions, which are intimately linked to evolution of the primitive atmosphere. Fundamental questions remain on how and when the proto-Earth mantle became oxidized, and whether redox state is homogeneous or developed large-scale structures. Here we present experiments in which we subjected two synthetic samples of nearly identical composition that are representative of the lower mantle (enstatite chondrite), but synthesized under different oxygen fugacities, to pressures and temperatures up to 90 GPa and 2,400 K. In addition to the mineral bridgmanite, compression of the more reduced material also produced Al2O3 as a separate phase, and the resulting assemblage is about 1 to 1.5% denser than in experiments with the more oxidized material. Our geodynamic simulations suggest that such a density difference can cause a rapid ascent and accumulation of oxidized material in the upper mantle, with descent of the denser reduced material to the core-mantle boundary. We suggest that the resulting heterogeneous redox conditions in Earth's interior can contribute to the large low-shear velocity provinces in the lower mantle and the evolution of atmospheric oxygen.

  14. Vertical velocity of mantle flow of East Asia and adjacent areas

    Institute of Scientific and Technical Information of China (English)

    CHENG Xianqiong; ZHU Jieshou; CAI Xuelin

    2007-01-01

    Based on the high-resolution body wave tomo- graphic image and relevant geophysical data, we calculated the form and the vertical and tangential velocities of mantle flow. We obtained the pattern of mantle convection for East Asia and the West Pacific. Some important results and under- standings are gained from the images of the vertical velocity of mantle flow for East Asia and the West Pacific. There is an upwelling plume beneath East Asia and West Pacific, which is the earth's deep origin for the huge rift valley there. We have especially outlined the tectonic features of the South China Sea, which is of the "工" type in the upper mantle shield type in the middle and divergent in the lower; the Siberian clod downwelling dives from the surface to near Core and mantle bounary (CMB), which is convergent in the upper mantle and divergent in the lower mantle; the Tethyan subduction region, centered in the Qinghai-Tibet plateau, is visible from 300 to 2 000 km, which is also convergent in the upper mantle and divergent in the lower mantle. The three regions of mantle convection beneath East Asia and the West Pacific are in accordance with the West Pacific, Ancient Asia and the Tethyan structure regions. The mantle upwelling orig- inates from the core-mantle boundary and mostly occurs in the middle mantle and the lower part of the upper mantle. The velocities of the vertical mantle flow are about 1-4 cm per year and the tangential velocities are 1-10 cm per year. The mantle flow has an effect on controlling the movement of plates and the distributions of ocean ridges, subduction zones and collision zones. The mantle upwelling regions are clearly related with the locations ofhotspots on the earth's surface.

  15. Widespread tungsten isotope anomalies and W mobility in crustal and mantle rocks of the Eoarchean Saglek Block, northern Labrador, Canada: Implications for early Earth processes and W recycling

    Science.gov (United States)

    Liu, Jingao; Touboul, Mathieu; Ishikawa, Akira; Walker, Richard J.; Graham Pearson, D.

    2016-08-01

    Well-resolved 182W isotope anomalies, relative to the present mantle, in Hadean-Archean terrestrial rocks have been interpreted to reflect the effects of variable late accretion and early mantle differentiation processes. To further explore these early Earth processes, we have carried out W concentration and isotopic measurements of Eoarchean ultramafic rocks, including lithospheric mantle rocks, meta-komatiites, a layered ultramafic body and associated crustal gneisses and amphibolites from the Uivak gneiss terrane of the Saglek Block, northern Labrador, Canada. These analyses are augmented by in situ W concentration measurements of individual phases in order to examine the major hosts of W in these rocks. Although the W budget in some rocks can be largely explained by a combination of their major phases, W in other rocks is hosted mainly in secondary grain-boundary assemblages, as well as in cryptic, unidentified W-bearing 'nugget' minerals. Whole rock W concentrations in the ultramafic rocks show unexpected enrichments relative, to elements with similar incompatibilities. By contrast, W concentrations are low in the Uivak gneisses. These data, along with the in situ W concentration data, suggest metamorphic transport/re-distribution of W from the regional felsic rocks, the Uivak gneiss precursors, to the spatially associated ultramafic rocks. All but one sample from the lithologically varied Eoarchean Saglek suite is characterized by generally uniform ∼ + 11 ppm enrichments in 182W relative to Earth's modern mantle. Modeling shows that the W isotopic enrichments in the ultramafic rocks were primarily inherited from the surrounding 182W-rich felsic precursor rocks, and that the W isotopic composition of the original ultramafic rocks cannot be determined. The observed W isotopic composition of mafic to ultramafic rocks in intimate contact with ancient crust should be viewed with caution in order to plate constraints on the early Hf-W isotopic evolution of the

  16. Magnetohydrodynamic Convection in the Outer Core and its Geodynamic Consequences

    Science.gov (United States)

    Kuang, Weijia; Chao, Benjamin F.; Fang, Ming

    2004-01-01

    The Earth's fluid outer core is in vigorous convection through much of the Earth's history. In addition to generating and maintaining Earth s time-varying magnetic field (geodynamo), the core convection also generates mass redistribution in the core and a dynamical pressure field on the core-mantle boundary (CMB). All these shall result in various core-mantle interactions, and contribute to surface geodynamic observables. For example, electromagnetic core-mantle coupling arises from finite electrically conducting lower mantle; gravitational interaction occurs between the cores and the heterogeneous mantle; mechanical coupling may also occur when the CMB topography is aspherical. Besides changing the mantle rotation via the coupling torques, the mass-redistribution in the core shall produce a spatial-temporal gravity anomaly. Numerical modeling of the core dynamical processes contributes in several geophysical disciplines. It helps explain the physical causes of surface geodynamic observables via space geodetic techniques and other means, e.g. Earth's rotation variation on decadal time scales, and secular time-variable gravity. Conversely, identification of the sources of the observables can provide additional insights on the dynamics of the fluid core, leading to better constraints on the physics in the numerical modeling. In the past few years, our core dynamics modeling efforts, with respect to our MoSST model, have made significant progress in understanding individual geophysical consequences. However, integrated studies are desirable, not only because of more mature numerical core dynamics models, but also because of inter-correlation among the geophysical phenomena, e.g. mass redistribution in the outer core produces not only time-variable gravity, but also gravitational core-mantle coupling and thus the Earth's rotation variation. They are expected to further facilitate multidisciplinary studies of core dynamics and interactions of the core with other

  17. Titanium-hydroxyl defect-controlled rheology of the Earth's upper mantle

    Science.gov (United States)

    Faul, Ulrich H.; Cline, Christopher J.; David, Emmanuel C.; Berry, Andrew J.; Jackson, Ian

    2016-10-01

    Experiments were conducted with hydrous olivine to investigate the defect responsible for the influence of water (hydrogen structurally incorporated as hydroxyl) on the olivine rheology. Solution-gelation derived Fo90 olivine doped with nominally 0.04-0.1 wt.% TiO2 was first hot-pressed and then deformed in platinum capsules at 300 MPa confining pressure and temperatures from 1200- 1350°C. The water content was not buffered so that deformation occurred at water-undersaturated conditions. Due to the enhanced grain growth under hydrous conditions, the samples were at least a factor of three more coarse-grained than their dry counterparts and deformed in powerlaw creep at differential stresses as low as a few tens of MPa. Since all experiments were conducted at the same confining pressure, the essentially linear relationship between strain rate and water content was for the first time determined independently of an activation volume. Infrared spectra are dominated by absorption bands at 3572 and 3525 cm-1. These bands also predominate in infrared spectra of natural olivine, and can only be reproduced experimentally in the presence of titanium. In contrast to the previous interpretation of the hydrous rheology in terms of intrinsic point defects, the experiments show that extrinsic defects (impurities) in natural olivine play the dominant role for water weakening at the water contents expected for most of the upper mantle.

  18. The capacity of hydrous fluids to transport and fractionate incompatible elements and metals within the Earth's mantle

    Science.gov (United States)

    Adam, John; Locmelis, Marek; Afonso, Juan Carlos; Rushmer, Tracy; Fiorentini, Marco L.

    2014-06-01

    silicate melts and aqueous fluids are thought to play critical roles in the chemical differentiation of the Earth's crust and mantle. Yet their relative effects are poorly constrained. We have addressed this issue by measuring partition coefficients for 50 trace and minor elements in experimentally produced aqueous fluids, coexisting basanite melts, and peridotite minerals. The experiments were conducted at 1.0-4.0 GPa and 950-1200°C in single capsules containing (either 40 or 50 wt %) H2O and trace element-enriched basanite glass. This allowed run products to be easily identified and analyzed by a combination of electron microprobe and LAM-ICP-MS. Fluid and melt compositions were reconstructed from mass balances and published solubility data for H2O in silicate melts. Relative to the basanite melt, the solutes from H2O-fluids are enriched in SiO2, alkalis, Ba, and Pb, but depleted in FeO, MgO, CaO, and REE. With increasing pressure, the mutual solubility of fluids and melts increases rapidly with complete miscibility between H2O and basanitic melts occurring between 3.0 and 4.0 GPa at 1100°C. Although LREE are favored over HREE in the fluid phase, they are less soluble than the HFSE (Nb, Ta, Zr, Hf, and Ti). Thus, the relative depletions of HFSE that are characteristic of arc magmas must be due to a residual phase that concentrates HFSE (e.g., rutile). Otherwise, H2O-fluids have the capacity to impart many of the geochemical characteristics that distinguish some rocks and melts from the deep mantle lithosphere (e.g., MARID and lamproites).

  19. Observation of magnetic diffusion in the Earth's outer core from Magsat, Orsted, and CHAMP data

    DEFF Research Database (Denmark)

    Chulliat, A.; Olsen, Nils

    2010-01-01

    , Orsted, and CHAMP satellites. A detectable change of magnetic fluxes through patches delimited by curves of zero radial magnetic field at the core-mantle boundary is associated with a failure of the frozen flux assumption. For each epoch (1980 and 2005), we calculate spatially regularized models...... increase of the global misfit. However, applying the constraint leads to a detectable increase of the scalar residuals at satellite altitude in the region of St. Helena, strongly suggesting a local failure of the frozen flux assumption. The observed flux expulsion within the St. Helena patch could result...... from the formation of a pair of "core spots," as predicted by numerical simulations of the geodynamo....

  20. Shear softening of Earth's inner core indicated by its high Poisson's ratio and elastic anisotropy

    CERN Document Server

    Wu, Zhongqing

    2016-01-01

    Earth's inner core exhibits an unusually high Poisson's ratio and noticeable elastic anisotropy. The mechanisms responsible for these features are critical for understanding the evolution of the Earth but remain unclear. This study indicates that once the correct formula for the shear modulus is used, shear softening can simultaneously explain the high Poisson's ratio and strong anisotropy of the inner core. Body-centred-cubic (bcc) iron shows shear instability at the pressures found in the inner-core and can be dynamically stabilized by temperature and light elements. It is very likely that some combinations of light elements stabilize the bcc iron alloy under inner-core conditions. Such a bcc phase would exhibit significant shear softening and match the geophysical constraints of the inner core. Identifying which light elements and what concentrations of these elements stabilize the bcc phase will provide critical information on the light elements of the inner core.

  1. Compressibility and planetary interiors. [solid core theory applicable to Earth and Venus

    Science.gov (United States)

    Bullen, K. E.

    1972-01-01

    Important confirmations that the Earth's inner core is solid have recently come from analyses of records of free Earth oscillations and from the apparent detection of the seismic phase PKJKP. Corresponding support is given to the theory which supplied the primary evidence for rigidity in the inner core. This theory requires the incompressibility and its gradient with respect to the pressure p to vary fairly smoothly with p inside planets, and supplies a potent restriction on the allowable variations of particular physical properties inside parts of planetary interiors. The theory is at present principally applicable to the Earth and Venus. The paper reviews some of the principal implications.

  2. Mercury's capture into the 3/2 spin-orbit resonance including the effect of core-mantle friction

    CERN Document Server

    Correia, Alexandre C M; 10.1016/j.icarus.2008.12.034

    2009-01-01

    The rotation of Mercury is presently captured in a 3/2 spin-orbit resonance with the orbital mean motion. The capture mechanism is well understood as the result of tidal interactions with the Sun combined with planetary perturbations. However, it is now almost certain that Mercury has a liquid core, which should induce a contribution of viscous friction at the core-mantle boundary to the spin evolution. This last effect greatly increases the chances of capture in all spin-orbit resonances, being 100% for the 2/1 resonance, and thus preventing the planet from evolving to the presently observed configuration. Here we show that for a given resonance, as the chaotic evolution of Mercury's orbit can drive its eccentricity to very low values during the planet's history, any previous capture can be destabilized whenever the eccentricity becomes lower than a critical value. In our numerical integrations of 1000 orbits of Mercury over 4 Gyr, the spin ends 99.8% of the time captured in a spin-orbit resonance, in partic...

  3. The lead isotopic age of the Earth can be explained by core formation alone.

    Science.gov (United States)

    Wood, Bernard J; Halliday, Alex N

    2010-06-10

    The meaning of the age of the Earth defined by lead isotopes has long been unclear. Recently it has been proposed that the age of the Earth deduced from lead isotopes reflects volatile loss to space at the time of the Moon-forming giant impact rather than partitioning into metallic liquids during protracted core formation. Here we show that lead partitioning into liquid iron depends strongly on carbon content and that, given a content of approximately 0.2% carbon, experimental and isotopic data both provide evidence of strong partitioning of lead into the core throughout the Earth's accretion. Earlier conclusions that lead is weakly partitioned into iron arose from the use of carbon-saturated (about 5% C) iron alloys. The lead isotopic age of the Earth is therefore consistent with partitioning into the core and with no significant late losses of moderately volatile elements to space during the giant impact.

  4. Stability of body-centered cubic iron-magnesium alloys in the Earth's inner core.

    Science.gov (United States)

    Kádas, Krisztina; Vitos, Levente; Johansson, Börje; Ahuja, Rajeev

    2009-09-15

    The composition and the structure of the Earth's solid inner core are still unknown. Iron is accepted to be the main component of the core. Lately, the body-centered cubic (bcc) phase of iron was suggested to be present in the inner core, although its stability at core conditions is still in discussion. The higher density of pure iron compared with that of the Earth's core indicates the presence of light element(s) in this region, which could be responsible for the stability of the bcc phase. However, so far, none of the proposed composition models were in full agreement with seismic observations. The solubility of magnesium in hexagonal Fe has been found to increase significantly with increasing pressure, suggesting that Mg can also be an important element in the core. Here, we report a first-principles density functional study of bcc Fe-Mg alloys at core pressures and temperatures. We show that at core conditions, 5-10 atomic percent Mg stabilizes the bcc Fe both dynamically and thermodynamically. Our calculated density, elastic moduli, and sound velocities of bcc Fe-Mg alloys are consistent with those obtained from seismology, indicating that the bcc-structured Fe-Mg alloy is a possible model for the Earth's inner core.

  5. Advanced Pressure Coring System for Deep Earth Sampling (APRECOS)

    Science.gov (United States)

    Anders, E.; Rothfuss, M.; Müller, W. H.

    2009-04-01

    Nowadays the recovery of cores from boreholes is a standard operation. However, during that process the mechanical, physical, and chemical properties as well as living conditions for microorganisms are significantly altered. In-situ sampling is one approach to overcome the severe scientific limitations of conventional, depressurized core investigations by recovering, processing, and conducting experiments in the laboratory, while maintaining unchanged environmental parameters. The most successful equipment today is the suite of tools developed within the EU funded projects HYACE (Hydrate Autoclave Coring Equipment) and HYACINTH (Deployment of HYACE tools In New Tests on Hydrates) between 1997 and 2005. Within several DFG (German Research Foundation) projects the Technical University Berlin currently works on concepts to increase the present working pressure of 250 bar as well as to reduce logistical and financial expenses by merging redundant and analogous procedures and scaling down the considerable size of key components. It is also proposed to extend the range of applications for the wireline rotary pressure corer and the sub-sampling and transfer system to all types of soil conditions (soft to highly-consolidated). New modifications enable the tools to be used in other pressure related fields of research, such as unconventional gas exploration (coal-bed methane, tight gas, gas hydrate), CO2 sequestration, and microbiology of the deep biosphere. Expedient enhancement of an overall solution for pressure core retrieval, process and investigation will open the way for a complete on-site, all-purpose, in-situ equipment. The advanced assembly would allow for executing the whole operation sequences of coring, non-destructive measurement, sub-sampling and transfer into storage, measurement and transportation chambers, all in sterile, anaerobic conditions, and without depressurisation in quick succession. Extensive post-cruise handling and interim storage would be

  6. Lower mantle heterogeneity, dynamic topography and the geoid

    Science.gov (United States)

    Hager, B. H.; Clayton, R. W.; Richards, M. A.; Comer, R. P.; Dziewonski, A. M.

    1985-01-01

    Density contrasts in the lower mantle, recently imaged using seismic tomography, drive convective flow which results in kilometers of dynamically maintained topography at the core-mantle boundary and at the earth's surface. The total gravity field due to interior density constrasts and boundary topography predicts the largest wavelength components of the geoid remarkably well. Neglecting dynamic surface deformation leads to geoid anomalies of opposite sign than are observed.

  7. The Gassmann-Burgers Model to Simulate Seismic Waves at the Earth Crust And Mantle

    Science.gov (United States)

    Carcione, José M.; Poletto, Flavio; Farina, Biancamaria; Craglietto, Aronne

    2016-12-01

    The upper part of the crust shows generally brittle behaviour while deeper zones, including the mantle, may present ductile behaviour, depending on the pressure-temperature conditions; moreover, some parts are melted. Seismic waves can be used to detect these conditions on the basis of reflection and transmission events. Basically, from the elastic-plastic point of view the seismic properties (seismic velocity and density) depend on effective pressure and temperature. Confining and pore pressures have opposite effects on these properties, such that very small effective pressures (the presence of overpressured fluids) may substantially decrease the P- and S-wave velocities, mainly the latter, by opening of cracks and weakening of grain contacts. Similarly, high temperatures induce the same effect by partial melting. To model these effects, we consider a poro-viscoelastic model based on Gassmann equations and Burgers mechanical model to represent the properties of the rock frame and describe ductility in which deformation takes place by shear plastic flow. The Burgers elements allow us to model the effects of seismic attenuation, velocity dispersion and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. Effective pressure effects are taken into account in the dry-rock moduli using exponential functions whose parameters are obtained by fitting experimental data as a function of confining pressure. Since fluid effects are important, the density and bulk modulus of the saturating fluids (water and steam) are modeled using the equations provided by the NIST website, including supercritical behaviour. The theory allows us to obtain the phase velocity and quality factor as a function of depth and geological pressure and temperature as well as time frequency. We then obtain the PS and SH

  8. The Gassmann-Burgers Model to Simulate Seismic Waves at the Earth Crust And Mantle

    Science.gov (United States)

    Carcione, José M.; Poletto, Flavio; Farina, Biancamaria; Craglietto, Aronne

    2017-03-01

    The upper part of the crust shows generally brittle behaviour while deeper zones, including the mantle, may present ductile behaviour, depending on the pressure-temperature conditions; moreover, some parts are melted. Seismic waves can be used to detect these conditions on the basis of reflection and transmission events. Basically, from the elastic-plastic point of view the seismic properties (seismic velocity and density) depend on effective pressure and temperature. Confining and pore pressures have opposite effects on these properties, such that very small effective pressures (the presence of overpressured fluids) may substantially decrease the P- and S-wave velocities, mainly the latter, by opening of cracks and weakening of grain contacts. Similarly, high temperatures induce the same effect by partial melting. To model these effects, we consider a poro-viscoelastic model based on Gassmann equations and Burgers mechanical model to represent the properties of the rock frame and describe ductility in which deformation takes place by shear plastic flow. The Burgers elements allow us to model the effects of seismic attenuation, velocity dispersion and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. Effective pressure effects are taken into account in the dry-rock moduli using exponential functions whose parameters are obtained by fitting experimental data as a function of confining pressure. Since fluid effects are important, the density and bulk modulus of the saturating fluids (water and steam) are modeled using the equations provided by the NIST website, including supercritical behaviour. The theory allows us to obtain the phase velocity and quality factor as a function of depth and geological pressure and temperature as well as time frequency. We then obtain the PS and SH

  9. Siderophile elements in the upper mantle of the Earth: New clues from metal-silicate partition coefficients

    Science.gov (United States)

    Holzheid, A.; Borisov, A.; Palme, H.

    1993-01-01

    New, precise data on the solubilities of Ni, Co, and Mo in silicate melts at 1400 C and fO2 from IW to IW-2 are presented. The results suggest NiO, CoO as stable species in the melt. No evidence for metallic Ni or Co was found. Equilibrium was ensured by reversals with initially high Ni and Co in the glass. Mo appears to change oxidation state at IW-1, from MoO3 to MoO2. Metal-silicate partition coefficients calculated from these data and recent data on Pd indicate similar partition coefficients for Pd and Mo at the conditions of core formation. This unexpected result constrains models of core formation in the Earth.

  10. Seismic wave velocities of rare gas solids through elastic properties in Earth's lower mantle

    Institute of Scientific and Technical Information of China (English)

    Seema GUPTA; Suresh C. GOYAL

    2009-01-01

    The expressions for second (SOE) and third order elastic (TOE) constants for rare gas solids are de-rived for comparative study of elastic behavior within the framework of many body potentials including the effect of pressure. The derived expressions are used to obtain the relations for pressure derivatives of bulk and shear moduli of RGS solids. The values of SOE, TOE constants and pressure derivative of bulk and shear modulus for Ne up to 100 GPa, Ar up to 75 GPa, for Kr up to 136 GPa and Xe up to 53.4 GPa pressure are computed. The results are in agreement with available experimental results. The computed results are then used to analyze the pressure up to high compression and the elastic and seismic wave velocities (P & S) in Earth's deep interior.

  11. Hollandite II phase in KAlSi 3O 8 as a potential host mineral of potassium in the Earth's lower mantle

    Science.gov (United States)

    Hirao, Naohisa; Ohtani, Eiji; Kondo, Tadashi; Sakai, Takeshi; Kikegawa, Takumi

    2008-01-01

    High-pressure and high-temperature experiments on the KAlSi 3O 8 composition were conducted in a laser-heated diamond-anvil cell at pressures up to 128 GPa, which correspond to the lowermost mantle conditions. In situ synchrotron X-ray diffraction measurements revealed that the hollandite II phase in KAlSi 3O 8 with a monoclinic symmetry of I2/ m was stable over the entire range of mantle conditions, and the tunnel structure formed by the double chains of edge-sharing (Si,Al)O 6 octahedra, which could accommodate a larger cation such as potassium, was sustained. The (Si,Al)O 6 octahedra in the KAlSi 3O 8 hollandite II phase showed a similar compression behavior to those in high-pressure silicate structures, such as rutile-type and perovskite-type phases, and were found to be less compressible than the KO 8 polyhedra. The KAlSi 3O 8 hollandite II phase is a potential host mineral for potassium under lower mantle conditions and, therefore, may have a significant influence on geochemistry if potassium feldspar KAlSi 3O 8 in the Earth's crust is transported into the Earth's mantle through subduction.

  12. Partitioning of potassium between silicates and sulphide melts - Experiments relevant to the earth's core.

    Science.gov (United States)

    Goettel, K. A.

    1972-01-01

    The partitioning of potassium between roedderite, K2Mg5Si12O30 and an Fe-FeS melt was investigated at temperatures about 40 C above the Fe-FeS eutectic. Roedderite was considered a prime candidate for one of the potassium-bearing phases in the primitive earth because roedderite and merrihueite are the only two silicates containing essential potassium which have been identified in stony meteorites. Application of the results to a primitive chondritic earth is discussed, and it is concluded that extraction of most of the earth's potassium into the Fe-FeS core would occur under the conditions in the early earth.-

  13. The South India Precambrian crust and shallow lithospheric mantle: Initial results from the India Deep Earth Imaging Experiment (INDEX)

    Indian Academy of Sciences (India)

    S S Rai; Kajaljyoti Borah; Ritima Das; Sandeep Gupta; Shalivahan Srivastava; K S Prakasam; K Sivaram; Sudesh Kumar; Rishikesh Meena

    2013-12-01

    We present here the most comprehensive study of the thickness and composition (/ ratio) of the South India Precambrian crust and the nature of shallower mantle inferred from analysis of teleseismic receiver functions from 70 broad-band seismic stations operated as a part of the India Deep Earth Imaging Experiment (INDEX). South India could be broadly divided into regions with thin crust (32–38 km) and thick crust (38–54 km). Thin crust domains include the East Dharwar Craton (EDC), Cuddapah basin and Madurai/Kerala Khondalite Block. The thicker crust domain includes the Western Dharwar Craton (WDC) and northern part of Southern Granulite Terrain. The WDC shows progressive increase in thickness from 38 km in north to 46–54 km in south, compared to an almost flat Moho beneath the EDC. Compositionally, most of the crustal domains are felsic to intermediate (/ ∼ 1.69–1.75) except the mid Archean block in the southern WDC where it is mafic (/ < 1.81). Considering erosion depth in the WDC, we argue for Himalaya like ∼70 km thick crust beneath it during the Archean. Variation in crustal thickness does not have a first-order influence on regional topography in South India and suggests significant role for the crustal composition. We also present evidence of mid-lithospheric low velocity at ∼85–100 km beneath South India.

  14. Formation of a solid inner core during the accretion of Earth

    Science.gov (United States)

    Arkani-Hamed, Jafar

    2017-05-01

    The formation of an inner core during the accretion of Earth is investigated by using self-gravitating and compressible Earth models formed by accreting a total of 25 or 50 Moon to Mars-sized planetary embryos. The impact of an embryo heats the proto-Earth's interior differentially, more below the impact site than elsewhere. The rotating core dynamically overturns and stratifies shortly after each impact, creating a spherically symmetric and radially increasing temperature distribution relative to an adiabatic profile. Merging of an embryo to the proto-Earth increases the lithostatic pressure that results in compressional temperature increase while further enhances the melting temperature of the core causing solidification. A total of 36 thermal evolution models of the growing proto-Earth's core are calculated to investigate effects of major physical parameters. No solidification is considered in the first 21 models where modified two-body escape velocities are used as the impact velocities of the embryos. At the end of accretion, temperatures in the upper part of the core are significantly different among these models, whereas temperatures in the deeper parts are similar. The core solidification considered in the remaining 15 models, where impact velocities higher than the modified two-body escape velocities are adopted, drastically changes the temperature distribution in the deeper parts of the core. All of the models produce partially solidified stiff inner cores, 1000-2100 km in radius, at the end of accretion, where the solid fraction is larger than 50%. The innermost of the stiff inner cores is completely solidified to radii 250-1500 km.

  15. Immiscible silicate liquids and phosphoran olivine in Netschaëvo IIE silicate: Analogue for planetesimal core-mantle boundaries

    Science.gov (United States)

    Van Roosbroek, Nadia; Hamann, Christopher; McKibbin, Seann; Greshake, Ansgar; Wirth, Richard; Pittarello, Lidia; Hecht, Lutz; Claeys, Philippe; Debaille, Vinciane

    2017-01-01

    We have investigated a piece of the Netschaëvo IIE iron meteorite containing a silicate inclusion by means of electron microprobe analysis (EMPA) and transmission electron microscopy (TEM). Netschaëvo contains chondrule-bearing clasts and impact melt rock clasts were also recently found. The examined inclusion belongs to the latter and is characterized by a porphyritic texture dominated by clusters of coarse-grained olivine and pyroxene, set in a fine-grained groundmass that consists of new crystals of olivine and a hyaline matrix. This matrix material has a quasi-basaltic composition in the inner part of the inclusion, whereas the edge of the inclusion has a lower SiO2 concentration and is enriched in MgO, P2O5, CaO, and FeO. Close to the metal host, the inclusion also contains euhedral Mg-chromite crystals and small (olivine crystallites containing up to 14 wt% P2O5, amorphous material, and interstitial Cl-apatite crystals. The Si-rich silicate glass globules show a second population of Fe-rich silicate glass droplets, indicating they formed by silicate liquid immiscibility. Together with the presence of phosphoran olivine and quenched Cl-apatite, these textures suggest rapid cooling and quenching as a consequence of an impact event. Moreover, the enrichment of phosphorus in the silicate inclusion close to the metal host (phosphoran olivine and Cl-apatite) indicates that phosphorus re-partitioned from the metal into the silicate phase upon cooling. This probably also took place in pallasite meteorites that contain late-crystallizing phases rich in phosphorus. Accordingly, our findings suggest that oxidation of phosphorus might be a general process in core-mantle environments, bearing on our understanding of planetesimal evolution. Thus, the Netschaëvo sample serves as a natural planetesimal core-mantle boundary experiment and based on our temperature estimates, the following sequence of events takes place: (i) precipitation of olivine (1400-1360 °C), (ii) re

  16. Constructing a core framework of visual engine for Digital Earth system

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A visual engine is the core of a Digital Earth system.There is a wide variety of functional requirements in Digital Earth system and different requirements correspond to different operations.Based on the development of the visual engine for ChinaStar,a 3D Digital China prototype software platform,and analysis of 3D Digital Earth platforms such as Google Earth,Virtual Earth,Skyline,etc,are discussed.A common core framework for a visual engine is proposed in this paper to construct a visual engine and then with this framework various Digital Earth application systems can be developed efficient.The parametric model of the Earth,scheduling and optimization in visual field,choice of 3D graphics library,and designing component-based visual engine framework of Digital Earth are discussed in detail.In addition,the relationships among these four basic components and the construction of visualization applications of Digital Earth by this method are also discussed.

  17. Possible detection of the earth's free-core nutation

    Science.gov (United States)

    Robertson, D. S.; Carter, W. E.; Wahr, J. M.

    1986-01-01

    The 5.5 years of VLBI observations primarily collected under project IRIS are used to search for evidence of the free-core nutation (FCN). The observations are consistent with an irregular excitation process, and a model which assumes a step excitation in the FCN amplitude to about 2.0 milliseconds of arc in late 1985 fits the data well. Theoretical analysis appears to rule out the strong Mexican earthquake of September 19, 1985, as a cause of the excitation.

  18. Saturation of electrical resistivity of solid iron at Earth's core conditions.

    Science.gov (United States)

    Pozzo, Monica; Alfè, Dario

    2016-01-01

    We report on the temperature dependence of the electrical resistivity of solid iron at high pressure, up to and including conditions likely to be found at the centre of the Earth. We have extended some of the calculations of the resistivities of pure solid iron we recently performed at Earth's core conditions (Pozzo et al. in Earth Planet Sci Lett 393:159-164, 2014) to lower temperature. We show that at low temperature the resistivity increases linearly with temperature, and saturates at high temperature. This saturation effect is well known as the Mott-Ioffe-Regel limit in metals, but has been largely ignored to estimate the resistivity of iron at Earth's core conditions. Recent experiments (Gomi et al. in Phys Earth Planet Int 224:88-103, 2013) coupled new high pressure data and saturation to predict the resitivity of iron and iron alloys at Earth's core conditions, and reported values up to three times lower than previous estimates, confirming recent first principles calculations (de Koker et al. in Proc Natl Acad Sci 109:4070-4073, 2012; Pozzo et al. in Nature 485:355-358, 2012, Phys Rev B 87:014110-10, 2013, Earth Planet Sci Lett 393:159-164, 2014; Davies et al. in Nat Geosci 8:678-685, 2015). The present results support the saturation effect idea.

  19. [Signs of the Impact of the Earth's core on the Planet's Population].

    Science.gov (United States)

    Malyshkov, Yu P; Malyshkov, S Yu

    2015-01-01

    When investigating the rhythms of the Earth's electromagnetic noise and seismicity, as well as numerous calls for ambulance, cases of baby births and people death, the authors have found that such rhythms have diurnal, seasonal and annual variations and they are principal for human being's life. The analysis of both main regularities and single peculiarities of diurnal and annual rhythms in the living and non-living nature has led us to assumption that the deep-seated processes relating. to the eccentric rotation of the Earth's core and shell could be a powerful conductor of the life and the death on the Earth. The results obtained in our study not only confirm the existence of deep-seated waves generated by the Earth's core but also make us sure that such constantly circulating waves produce a certain impact on a human being's health, birth and death and even "orchestrate" suicides.

  20. Radial profiles of temperature and viscosity in the Earth's mantle inferred from the geoid and lateral seismic structure

    NARCIS (Netherlands)

    Cadek, O.; Berg, A.P. van den

    1998-01-01

    In the framework of dynamical modelling of the geoid, we have estimated basic features of the radial profile of temperature in the mantle. The applied parameterization of the geotherm directly characterizes thermal boundary layers and values of the thermal gradient in the upper and lower mantle.

  1. Distribution of U and Th and Their Nuclear Fission in the Outer Core of the Earth and Their effects on the Geodynamics

    CERN Document Server

    Bao, Xuezhao

    2009-01-01

    Here we propose that there is a lot of heat producing elements U and Th in the outer core of the Earth. The heat released from them is the major energy source for driving the material movement within the interior of Earth, including plate motion. According to seismic tomography, the hottest area is the mantle under the central Pacific Ocean. Combined with geomagnetic data, it is derived that the magnetic and heat convection centers deviate from the geographic center to the Pacific direction for 400 km. Therefore, U and Th are more concentrated in a position close to the equator in the lower outer core under the central Pacific Ocean, and have formed a large U, Th-rich center there. Another small U, Th-rich center is located in a position close to the equator in the lower outer core under Africa, which is directly opposite of the large U, Th-rich center past the solid inner core. The two U, Th-rich centers may have led to the formation of the Pacific and Africa super-plumes and are offering energy to run the p...

  2. Sulfur Earth

    Science.gov (United States)

    de Jong, B. H.

    2007-12-01

    Variations in surface tension affect the buoyancy of objects floating in a liquid. Thus an object floating in water will sink deeper in the presence of dishwater fluid. This is a very minor but measurable effect. It causes for instance ducks to drown in aqueous solutions with added surfactant. The surface tension of liquid iron is very strongly affected by the presence of sulfur which acts as a surfactant in this system varying between 1.9 and 0.4 N/m at 10 mass percent Sulfur (Lee & Morita (2002), This last value is inferred to be the maximum value for Sulfur inferred to be present in the liquid outer core. Venting of Sulfur from the liquid core manifests itself on the Earth surface by the 105 to 106 ton of sulfur vented into the atmosphere annually (Wedepohl, 1984). Inspection of surface Sulfur emission indicates that venting is non-homogeneously distributed over the Earth's surface. The implication of such large variation in surface tension in the liquid outer core are that at locally low Sulfur concentration, the liquid outer core does not wet the predominantly MgSiO3 matrix with which it is in contact. However at a local high in Sulfur, the liquid outer core wets this matrix which in the fluid state has a surface tension of 0.4 N/m (Bansal & Doremus, 1986), couples with it, and causes it to sink. This differential and diapiric movement is transmitted through the essentially brittle mantle (1024 Pa.s, Lambeck & Johnson, 1998; the maximum value for ice being about 1030 Pa.s at 0 K, in all likely hood representing an upper bound of viscosity for all materials) and manifests itself on the surface by the roughly 20 km differentiation, about 0.1 % of the total mantle thickness, between topographical heights and lows with concomitant lateral movement in the crust and upper mantle resulting in thin skin tectonics. The brittle nature of the medium though which this movement is transmitted suggests that the extremes in topography of the D" layer are similar in range to

  3. Reactions of xenon with iron and nickel are predicted in the Earth's inner core.

    Science.gov (United States)

    Zhu, Li; Liu, Hanyu; Pickard, Chris J; Zou, Guangtian; Ma, Yanming

    2014-07-01

    Studies of the Earth's atmosphere have shown that more than 90% of the expected amount of Xe is depleted, a finding often referred to as the 'missing Xe paradox'. Although several models for a Xe reservoir have been proposed, whether the missing Xe could be contained in the Earth's inner core has not yet been answered. The key to addressing this issue lies in the reactivity of Xe with Fe/Ni, the main constituents of the Earth's core. Here, we predict, through first-principles calculations and unbiased structure searching techniques, a chemical reaction of Xe with Fe/Ni at the temperatures and pressures found in the Earth's core. We find that, under these conditions, Xe and Fe/Ni can form intermetallic compounds, of which XeFe3 and XeNi3 are energetically the most stable. This shows that the Earth's inner core is a natural reservoir for Xe storage and provides a solution to the missing Xe paradox.

  4. Implication of the lopsided growth for the viscosity of Earth's inner core

    OpenAIRE

    Mizzon, Hugau; Monnereau, Marc

    2012-01-01

    Two main seismic features characterize the Earth's inner core: a North-South polar anisotropy and an East-West asymmetry of P-wave velocity and attenuation. Anisotropy is expected if shear deformation is induced by convective motions. Translation has recently been put forward as an important mode of convection of the inner core. Combined with a simple diffusive grain growth model, this mechanism is able to explain the observed seismic asymmetry, but not the bulk anisotropy. The source of anis...

  5. On the likelihood of post-perovskite near the core-mantle boundary: A statistical interpretation of seismic observations

    NARCIS (Netherlands)

    Cobden, L.; Mosca, I.; Trampert, J.; Ritsema, J.

    2012-01-01

    Recent experimental studies indicate that perovskite, the dominant lower mantle mineral, undergoes a phase change to post-perovskite at high pressures. However, it has been unclear whether this transition occurs within the Earth’s mantle, due to uncertainties in both the thermochemical state of the

  6. Dynamic Responses of the Earth's Outer Core to Assimilation of Observed Geomagnetic Secular Variation

    Science.gov (United States)

    Kuang, Weijia; Tangborn, Andrew

    2014-01-01

    Assimilation of surface geomagnetic observations and geodynamo models has advanced very quickly in recent years. However, compared to advanced data assimilation systems in meteorology, geomagnetic data assimilation (GDAS) is still in an early stage. Among many challenges ranging from data to models is the disparity between the short observation records and the long time scales of the core dynamics. To better utilize available observational information, we have made an effort in this study to directly assimilate the Gauss coefficients of both the core field and its secular variation (SV) obtained via global geomagnetic field modeling, aiming at understanding the dynamical responses of the core fluid to these additional observational constraints. Our studies show that the SV assimilation helps significantly to shorten the dynamo model spin-up process. The flow beneath the core-mantle boundary (CMB) responds significantly to the observed field and its SV. The strongest responses occur in the relatively small scale flow (of the degrees L is approx. 30 in spherical harmonic expansions). This part of the flow includes the axisymmetric toroidal flow (of order m = 0) and non-axisymmetric poloidal flow with m (is) greater than 5. These responses can be used to better understand the core flow and, in particular, to improve accuracies of predicting geomagnetic variability in future.

  7. Anisotropy of Earth's inner core intrinsic attenuation from seismic normal mode models

    NARCIS (Netherlands)

    Mäkinen, Anna M.; Deuss, Arwen; Redfern, Simon A T

    2014-01-01

    The Earth's inner core, the slowly growing sphere of solid iron alloy at the centre of our planet, is known to exhibit seismic anisotropy. Both normal mode and body wave studies have established that, when the global average is taken, compressional waves propagate faster in the North-South direction

  8. Anisotropy of Earth's inner core intrinsic attenuation from seismic normal mode models

    NARCIS (Netherlands)

    Mäkinen, Anna M.; Deuss, Arwen; Redfern, Simon A T

    2014-01-01

    The Earth's inner core, the slowly growing sphere of solid iron alloy at the centre of our planet, is known to exhibit seismic anisotropy. Both normal mode and body wave studies have established that, when the global average is taken, compressional waves propagate faster in the North-South direction

  9. 186Os and 187Os enrichments and high-3He/4He sources in the Earth's mantle

    DEFF Research Database (Denmark)

    Brandon, A.D.; Graham, D.W.; Waight, Tod Earle

    2007-01-01

    . These Os isotope systematics are best explained by ancient recycled crust or melt enrichment in the mantle source region. If so, then the coupled enrichments displayed in 186Os/188Os and 187Os/188Os from lavas of other plume systems must result from an independent process, the most viable candidate...... picrites is best modeled as mixtures of 1 Ga or older ancient recycled crust mixed with primitive mantle or incompletely degassed depleted mantle isolated since 1-1.5 Ga, which preserves the high 3He/4He of the depleted mantle at the time. These mixtures create a hybrid source region that subsequently...... be interpreted as an increase in the proportion of ancient recycled crust in the upwelling plume over this time period. The positive correlation between 187Os/188Os and 3He/4He demonstrates that the Iceland lava He isotopic compositions do not result from simple melt depletion histories and consequent removal...

  10. Implication of the lopsided growth for the viscosity of Earth's inner core

    CERN Document Server

    Mizzon, Hugau

    2012-01-01

    Two main seismic features characterize the Earth's inner core: a North-South polar anisotropy and an East-West asymmetry of P-wave velocity and attenuation. Anisotropy is expected if shear deformation is induced by convective motions. Translation has recently been put forward as an important mode of convection of the inner core. Combined with a simple diffusive grain growth model, this mechanism is able to explain the observed seismic asymmetry, but not the bulk anisotropy. The source of anisotropy has therefore to be sought in the shear motions caused by higher modes of convection. 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 at the inner core boundary. Three parameters act independently: viscosity, internal heating and convection velocity in the outer core. Our numerical simulations show the dominance of pure translation for viscosities of the inner core hi...

  11. Development of Dynamic Ellipsometry for Measurements or Iron Conductivity at Earth's Core Conditions.

    Energy Technology Data Exchange (ETDEWEB)

    Grant, Sean Campbell [Univ. of Texas, Austin, TX (United States); Ao, Tommy [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Davis, Jean-Paul [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Dolan, Daniel H. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Seagle, Christopher T. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Lin, Jung-Fu [Univ. of Texas, Austin, TX (United States); Bernstein, Aaron [Univ. of Texas, Austin, TX (United States)

    2017-03-01

    The CHEDS researchers are engaged in a collaborative research project to study the properties of iron and iron alloys under Earth’s core conditions. The Earth’s core, inner and outer, is composed primarily of iron, thus studying iron and iron alloys at high pressure and temperature conditions will give the best estimate of its properties. Also, comparing studies of iron alloys with known properties of the core can constrain the potential light element compositions found within the core, such as fitting sound speeds and densities of iron alloys to established inner- Earth models. One of the lesser established properties of the core is the thermal conductivity, where current estimates vary by a factor of three. Therefore, one of the primary goals of this collaboration is to make relevant measurements to elucidate this conductivity.

  12. Formation, stratification, and mixing of the cores of Earth and Venus

    Science.gov (United States)

    Jacobson, Seth A.; Rubie, David C.; Hernlund, John; Morbidelli, Alessandro; Nakajima, Miki

    2017-09-01

    Earth possesses a persistent, internally-generated magnetic field, whereas no trace of a dynamo has been detected on Venus, at present or in the past, although a high surface temperature and recent resurfacing events may have removed paleomagnetic evidence. Whether or not a terrestrial body can sustain an internally generated magnetic field by convection inside its metallic fluid core is determined in part by its initial thermodynamic state and its compositional structure, both of which are in turn set by the processes of accretion and differentiation. Here we show that the cores of Earth- and Venus-like planets should grow with stable compositional stratification unless disturbed by late energetic impacts. They do so because higher abundances of light elements are incorporated into the liquid metal that sinks to form the core as the temperatures and pressures of metal-silicate equilibration increase during accretion. We model this process and determine that this establishes a stable stratification that resists convection and inhibits the onset of a geodynamo. However, if a late energetic impact occurs, it could mechanically stir the core creating a single homogenous region within which a long-lasting geodynamo would operate. While Earth's accretion has been punctuated by a late giant impact with likely enough energy to mix the core (e.g. the impact that formed the Moon), we hypothesize that the accretion of Venus is characterized by the absence of such energetic giant impacts and the preservation of its primordial stratifications.

  13. Probing the core-mantle boundary beneath Europe and Western Eurasia: A detailed study using PcP

    Science.gov (United States)

    Gassner, Alexandra; Thomas, Christine; Krüger, Frank; Weber, Michael

    2015-09-01

    We use PcP (the core reflected P phase) recordings of deep earthquakes and nuclear explosions from the Gräfenberg (Germany) and NORSAR (Norway) arrays to investigate the core-mantle boundary region beneath Europe and western Eurasia. We find evidence for a previously unknown ultra-low velocity zone 600 km south-east of Moscow, located at the edge of a middle-size low shear- velocity region imaged in seismic tomography that is located beneath the Volga river region. The observed amplitude variations of PcP can be modelled by velocity reductions of P and S-waves of -5% and -15%, respectively, with a density increase of +15%. Travel time delays of pre-and postcursors are indicating a thickness of about 13 km for this ultra-low velocity region (ULVZ). However, our modelling also reveals highly ambiguous amplitude variations of PcP and a reflection off the top of the anomaly for various ULVZs and topography models. Accordingly, large velocity contrasts of up to -10% in VP and -20% in VS cannot be excluded. In general, the whole Volga river region shows a complex pattern of PcP amplitudes caused most likely by CMB undulations. Further PcP probes beneath Paris, Kiev and northern Italy indicate likely normal CMB conditions, whereas the samples below Finland and the Hungary-Slovakia border yield strongly amplified PcP signals suggesting strong CMB topography effects. We evaluate the amplitude behaviour of PcP as a function of distance and several ULVZ models using the 1D reflectivity and the 2D Gauss beam method. The influence of the velocity and density perturbations is analysed as well as the anomaly thickness, the dominant period of the source wavelet and interface topographies. Strong variation of the PcP amplitude are obtained as a function of distance and of the impedance contrast. We also consider two types of topographies: undulations atop the CMB in the presence of flat ULVZs and vice versa. Where a broad range of CMB topography dimensions lead to large Pc

  14. A uranium core for the Earth; Un coeur d'uranium pour la terre

    Energy Technology Data Exchange (ETDEWEB)

    Rouat, S

    2003-06-01

    According to the theory of M. Herndon, a US independent geophysicist, the center of the Earth's core should be made of a uranium sphere of about 8 km of diameter. This natural reactor, or 'geo-reactor', should be at the origin of the internal heat and of the magnetic field of the Earth. M. Herndon has extended his theory to the other planets of the solar system. This theory contradicts the one adopted since the 1940's by the community of geophysicists and which involves a crystallized iron and nickel internal core inside a liquid iron external core. Herndon's theory can explain also the geomagnetic field reversals. (J.S.)

  15. On the tidal oscillations of the liquid core of the earth

    Science.gov (United States)

    Musen, P.

    1978-01-01

    An important goal of a tidal theory is the improvement of nutational amplitude and of the parameters of the earth's elastic response. A theory of tidal oscillations inside a rotating elliptical earth was developed, with special emphasis on tides in the liquid core. The Molodensky and Kramer theory of the resonance effect, as caused by the proximity of the frequency of the free diurnal wobble of the liquid core to the frequency of K sub 1 astronomical tide, was amended to include the effect of the possible deviation of the liquid core from the state of neutral stability. Coupling effects between the toroidal and spheroidal oscillations, as caused by the Coriolis force, were taken into consideration.

  16. Crystallization of silicon dioxide and compositional evolution of the Earth's core.

    Science.gov (United States)

    Hirose, Kei; Morard, Guillaume; Sinmyo, Ryosuke; Umemoto, Koichio; Hernlund, John; Helffrich, George; Labrosse, Stéphane

    2017-03-02

    The Earth's core is about ten per cent less dense than pure iron (Fe), suggesting that it contains light elements as well as iron. Modelling of core formation at high pressure (around 40-60 gigapascals) and high temperature (about 3,500 kelvin) in a deep magma ocean predicts that both silicon (Si) and oxygen (O) are among the impurities in the liquid outer core. However, only the binary systems Fe-Si and Fe-O have been studied in detail at high pressures, and little is known about the compositional evolution of the Fe-Si-O ternary alloy under core conditions. Here we performed melting experiments on liquid Fe-Si-O alloy at core pressures in a laser-heated diamond-anvil cell. Our results demonstrate that the liquidus field of silicon dioxide (SiO2) is unexpectedly wide at the iron-rich portion of the Fe-Si-O ternary, such that an initial Fe-Si-O core crystallizes SiO2 as it cools. If crystallization proceeds on top of the core, the buoyancy released should have been more than sufficient to power core convection and a dynamo, in spite of high thermal conductivity, from as early on as the Hadean eon. SiO2 saturation also sets limits on silicon and oxygen concentrations in the present-day outer core.

  17. Secular variations in zonal harmonics of Earth's geopotential and their implications for mantle viscosity and Antarctic melting history due to the last deglaciation

    Science.gov (United States)

    Nakada, Masao; Okuno, Jun'ichi

    2017-06-01

    Secular variations in zonal harmonics of Earth's geopotential based on the satellite laser ranging observations, {\\dot{J}_n}, contain important information about the Earth's deformation due to the glacial isostatic adjustment (GIA) and recent melting of glaciers and the Greenland and Antarctic ice sheets. Here, we examine the GIA-induced {\\dot{J}_n}, \\dot{J}_n^{{{GIA}}} (2 ≤ n ≤ 6), derived from the available geopotential zonal secular rate and recent melting taken from the IPCC 2013 Report (AR5) to explore the possibility of additional information on the depth-dependent lower-mantle viscosity and GIA ice model inferred from the analyses of the \\dot{J}_2^{{{GIA}}} and relative sea level changes. The sensitivities of the \\dot{J}_n^{{{GIA}}} to lower-mantle viscosity and GIA ice model with a global averaged eustatic sea level (ESL) of ∼130 m indicate that the secular rates for n = 3 and 4 are mainly caused by the viscous response of the lower mantle to the melting of the Antarctic ice sheet regardless of GIA ice models adopted in this study. Also, the analyses of the \\dot{J}_n^{{{GIA}}} based on the available geopotential zonal secular rates indicate that permissible lower-mantle viscosity structure satisfying even zonal secular rates of n = 2, 4 and 6 is obtained for the GIA ice model with an Antarctic ESL component of ∼20 or ∼30 m, but there is no viscosity solution satisfying \\dot{J}_3^{{{GIA}}} and \\dot{J}_5^{{{GIA}}} values. Moreover, the inference model for the lower-mantle viscosity and GIA ice model from each odd zonal secular rate is distinctly different from that satisfying GIA-induced even zonal secular rate. The discrepancy between the inference models for the even and odd zonal secular rates may partly be attributed to uncertainties of the geopotential zonal secular rates for n > 2 and particularly those for odd zonal secular rates due to weakness in the orbital geometry. If this problem is overcome at least for the secular rates of n

  18. Multiscale seismic tomography and mantle dynamics

    Science.gov (United States)

    Zhao, Dapeng

    2010-05-01

    Multiscale (local, regional and global) tomographic studies are made to determine the 3-D structure of the Earth, particularly for imaging mantle plumes and subducting slabs. Plume-like slow anomalies are clearly visible under the major hotspot regions in most parts of the mantle, in particular, under Hawaii, Iceland, Kerguelen, South Pacific and Africa (Zhao, 2001, 2004, 2009). The slow anomalies under South Pacific and Africa have lateral extensions of over 1000 km and exist in the entire mantle, representing two superplumes. The Pacific superplume has a larger spatial extent and stronger slow anomalies than that of the Africa superplume. The Hawaiian plume is not part of the Pacific superplume but an independent whole-mantle plume (Zhao, 2004, 2009). The slow anomalies under hotspots usually do not show a straight pillar shape, but exhibit winding images, suggesting that plumes are not fixed in the mantle but can be deflected by the mantle flow. As a consequence, hotspots are not really fixed but can wander on the Earth's surface, as evidenced by the recent paleomagnetic and numeric modeling studies. Wider and more prominent slow anomalies are visible at the core-mantle boundary (CMB) than most of the lower mantle, and there is a good correlation between the distribution of slow anomalies at the CMB and that of hotspots on the surface, suggesting that most of the strong mantle plumes under the hotspots originate from the CMB. However, there are some small-scaled, weak plumes originating from the transition zone or mid mantle depths (Zhao et al., 2006; Zhao, 2009; Lei et al., 2009; Gupta et al., 2009). Clear images of subducting slabs and magma chambers in the upper-mantle wedge beneath active arc volcanoes are obtained, indicating that geodynamic systems associated with arc magmatism and back-arc spreading are related to deep processes, such as convective circulation in the mantle wedge and dehydration reactions of the subducting slab (Zhao et al., 2002, 2007

  19. Possible links between long-term geomagnetic variations and whole-mantle convection processes

    NARCIS (Netherlands)

    Biggin, A.J.; Steinberger, B.; Aubert, J.; Suttie, N.; Holme, R.; Torsvik, T.H.; van der Meer, D.G.; van Hinsbergen, D.J.J.

    2012-01-01

    The Earth's internal magnetic field varies on timescales of months to billions of years. The field is generated by convection in the liquid outer core, which in turn is influenced by the heat flowing from the core into the base of the overlying mantle. Much of the magnetic field's variation is thoug

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

    Science.gov (United States)

    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.

  1. The ruthenium isotopic composition of the oceanic mantle

    Science.gov (United States)

    Bermingham, K. R.; Walker, R. J.

    2017-09-01

    The approximately chondritic relative, and comparatively high absolute mantle abundances of the highly siderophile elements (HSE), suggest that their concentrations in the bulk silicate Earth were primarily established during a final ∼0.5 to 1% of ;late accretion; to the mantle, following the cessation of core segregation. Consequently, the isotopic composition of the HSE Ru in the mantle reflects an amalgamation of the isotopic compositions of late accretionary contributions to the silicate portion of the Earth. Among cosmochemical materials, Ru is characterized by considerable mass-independent isotopic variability, making it a powerful genetic tracer of Earth's late accretionary building blocks. To define the Ru isotopic composition of the oceanic mantle, the largest portion of the accessible mantle, we report Ru isotopic data for materials from one Archean and seven Phanerozoic oceanic mantle domains. A sample from a continental lithospheric mantle domain is also examined. All samples have identical Ru isotopic compositions, within analytical uncertainties, indicating that Ru isotopes are well mixed in the oceanic mantle, defining a μ100Ru value of 1.2 ± 7.2 (2SD). The only known meteorites with the same Ru isotopic composition are enstatite chondrites and, when corrected for the effects of cosmic ray exposure, members of the Main Group and sLL subgroup of the IAB iron meteorite complex which have a collective CRE corrected μ100Ru value of 0.9 ± 3.0. This suggests that materials from the region(s) of the solar nebula sampled by these meteorites likely contributed the dominant portion of late accreted materials to Earth's mantle.

  2. Diffusion of hydrogen in olivine grain boundaries and implications for the survival of water-rich zones in the Earth's mantle

    Science.gov (United States)

    Demouchy, Sylvie

    2010-06-01

    Nominally anhydrous minerals (NAMs) of Earth's mantle can contain hydrogen as atomic impurity in their crystal structures. This hydrogen substantially modifies many physical properties of Earth's mantle rocks. Also, the Earth's deep interior is made of rocks where minerals are separated by nanometer-scale interfaces call grain boundaries and interphase boundaries. These grain boundaries should carefully be considered as a potential hydrogen reservoir as well. I report here an experimental investigation of hydrogen diffusion through grain boundaries in olivine polycrystalline aggregates. Hot-press and diffusion experiments were performed using a gas-medium high-pressure vessel at a confining pressure of 300 MPa, over a temperature range of 1000-1200 °C. The diffusion assembly consisted of a dense polycrystalline cylinder of natural olivine from San Carlos (Arizona) mixed with olivine singles crystals of millimeter size. This mixture was couple with a talc cylinder. Ni capsule were used to buffer the oxygen fugacity at Ni-NiO level. Experiment durations varied from 3 min to 4 h. The presence of hydrogen in the sample was quantified using Fourier transform infrared spectroscopy. The calculation of the diffusion coefficients was based on the estimation of the length of polycrystalline solid affected by the diffusion of hydrogen. The absence or presence of hydrogen was recorded by the large olivines behaving here as “hydrogen sensor”, which are implanted in the aggregate. The results indicate that effective hydrogen diffusivity which includes grain boundaries effect in olivine aggregate is barely one order of magnitude faster than hydrogen diffusion in an olivine single crystal with a diffusivity ∼ 8.5 × 10- 10 m2 s- 1 at 1000 °C and only twice faster ∼ 2.1 × 10- 9 m2 s- 1 at 1200 °C. Calculations of the diffusion data in relation to the Arrhenius Law, yield an activation energy of ∼ 70 ± 10 kJ mol- 1. From these effective diffusivities and combined with

  3. Phase transition of FeO and stratification in Earth's outer core.

    Science.gov (United States)

    Ozawa, Haruka; Takahashi, Futoshi; Hirose, Kei; Ohishi, Yasuo; Hirao, Naohisa

    2011-11-11

    Light elements such as oxygen in Earth's core influence the physical properties of the iron alloys that exist in this region. Describing the high-pressure behavior of these materials at core conditions constrains models of core structure and dynamics. From x-ray diffraction measurements of iron monoxide (FeO) at high pressure and temperature, we show that sodium chloride (NaCl)-type (B1) FeO transforms to a cesium chloride (CsCl)-type (B2) phase above 240 gigapascals at 4000 kelvin with 2% density increase. The oxygen-bearing liquid in the middle of the outer core therefore has a modified Fe-O bonding environment that, according to our numerical simulations, suppresses convection. The phase-induced stratification is seismologically invisible but strongly affects the geodynamo.

  4. Metal enhanced fluorescence in rare earth doped plasmonic core-shell nanoparticles.

    Science.gov (United States)

    Derom, S; Berthelot, A; Pillonnet, A; Benamara, O; Jurdyc, A M; Girard, C; Colas des Francs, G

    2013-12-13

    We theoretically and numerically investigate metal enhanced fluorescence of plasmonic core-shell nanoparticles doped with rare earth (RE) ions. Particle shape and size are engineered to maximize the average enhancement factor (AEF) of the overall doped shell. We show that the highest enhancement (11 in the visible and 7 in the near-infrared) is achieved by tuning either the dipolar or the quadrupolar particle resonance to the rare earth ion's excitation wavelength. Additionally, the calculated AEFs are compared to experimental data reported in the literature, obtained in similar conditions (plasmon mediated enhancement) or when a metal-RE energy transfer mechanism is involved.

  5. Magnesite formation from MgO and CO2 at the pressures and temperatures of Earth's mantle

    Energy Technology Data Exchange (ETDEWEB)

    Scott, Henry P.; Doczy, Vincent M.; Frank, Mark R.; Hasan, Maggie; Lin, Jung-Fu; Yang, Jing [NIU; (Indiana); (Texas)

    2013-08-02

    Magnesite (MgCO3) is an important phase for the carbon cycle in and out of the Earth’s mantle. Its comparably large P-T stability has been inferred for several years based on the absence of its decomposition in experiments. Here we report the first experimental evidence for synthesis of magnesite out of its oxide components (MgO and CO2) at P-T conditions relevant to the Earth’s mantle. Magnesite formation was observed in situ using synchrotron X-ray diffraction, coupled with laser-heated diamond-anvil cells (DACs), at pressures and temperatures of Earth’s mantle. Despite the existence of multiple high-pressure CO2 polymorphs, the magnesite-forming reaction was observed to proceed at pressures ranging from 5 to 40 GPa and temperatures between 1400 and 1800 K. No other pressure-quenchable materials were observed to form via the MgO + CO2 = MgCO3 reaction. This work further strengthens the notion that magnesite may indeed be the primary host phase for oxidized carbon in the deep Earth.

  6. Potassium-bearing Iron-Nickel Sulfides in Nature and High-Pressure Experiments: Geochemical Consequences of Potassium in the Earth's Core

    Science.gov (United States)

    Keshav, S.; Corgne, A.; McDonough, W. F.; Fei, Y.

    2005-01-01

    Introduction: Potassium (K) as a large ion lithophile element has dominantly been concentrated in the Earth s crust and the mantle through differentiation, and in the form of K-40 contributes to the planet s heat budget. However, whether or not K also enters core-forming phases, has been debated for over three decades. Arguments favoring entry of K in the core are based on: (1) K-sulfide (with Fe, Ni, Cu, Na, and Cl; djerfisherite) found in highly reduced enstatite chondrites (or aubrites, enstatite achondrites); (2) demonstration that K, owing to an s-d electronic switch at high-pressure, exhibits transition- element like character, (3) solubility of measurable K in Fe-Ni-S liquids at high pressure, temperature conditions, and (4) models of cooling of the core that seem to require, besides convection, some form of radioactivity, and thus lending support to the experimental work. In this contribution, we assess the effect of sequestering K in the core, as it is perhaps an element that is a key to reconciling geochemistry, paleomagnetism, accretion, and thermal evolution models for the planet.

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

    OpenAIRE

    Alboussiere, Thierry; Deguen, Renaud; Melzani, Mickael

    2010-01-01

    International audience; In addition to its global North-South anisotropy(1), there are two other enigmatic seismological observations related to the Earth's inner core: asymmetry between its eastern and western hemispheres(2-6) and the presence of a layer of reduced seismic velocity at the base of the outer core(6-12). This 250-km-thick layer has been interpreted as a stably stratified region of reduced composition in light elements(13). Here we show that this layer can be generated by simult...

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

    Science.gov (United States)

    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.

  9. Investigating the presence of post-perovskite and large-scale chemical variations in Earth's lower mantle using tomographic-geodynamic model comparisons.

    Science.gov (United States)

    Koelemeijer, Paula; Ritsema, Jeroen; Deuss, Arwen; Davies, Rhodri; Schuberth, Bernhard

    2016-04-01

    Tomographic models of the Earth's mantle consistently image two large provinces of low shear-wave velocities (LLSVPs) in the lowermost mantle beneath Africa and the Pacific. Seismic studies also find an increase in the ratio of shear-wave velocity (Vs) to compressional-wave velocity (Vp) variations, accompanied by a significant negative correlation between shear-wave and bulk-sound velocity (Vc) variations, both of which are also observed in the recent SP12RTS model. The LLSVPs have consequently been suggested to represent intrinsically dense piles of thermochemical material. Alternatively, they have been interpreted as poorly imaged clusters of thermal plumes, with the deep mantle post-perovskite (pPv) phase invoked as explanation for the high Vs/Vp ratios and Vs-Vc anti-correlation. Geodynamical calculations of thermal plumes and thermochemical piles predict a fundamentally different style of mantle convection, interface topographies and CMB heat flow. However, to interpret tomographic images using these high-resolution models, the limited resolving power of seismic tomography has to be accounted for. Here, we interpret the observed seismic characteristics of SP12RTS by comparing the velocity structures to synthetic tomography images derived from 3D mantle convection models. As in previous studies, geodynamic models are converted to seismic velocities using mineral physics constraints and subsequently convolved with the tomographic resolution operator. In contrast to these studies, where generally only the shear-wave velocity structure has been compared, we use both the Vs and Vp resolution operator of SP12RTS to allow direct comparisons of the resulting velocity ratios and correlations. We use geodynamic models with and without pPv and/or chemical variations to investigate the cause of the high Vs/Vp ratio and Vs-Vs anti-correlation. Although the tomographic filtering significantly affects the synthetic tomography images, we demonstrate that the patterns

  10. Constraints on geomagnetic secular variation modeling from electromagnetism and fluid dynamics of the Earth's core

    Science.gov (United States)

    Benton, E. R.

    1986-01-01

    A spherical harmonic representation of the geomagnetic field and its secular variation for epoch 1980, designated GSFC(9/84), is derived and evaluated. At three epochs (1977.5, 1980.0, 1982.5) this model incorporates conservation of magnetic flux through five selected patches of area on the core/mantle boundary bounded by the zero contours of vertical magnetic field. These fifteen nonlinear constraints are included like data in an iterative least squares parameter estimation procedure that starts with the recently derived unconstrained field model GSFC (12/83). Convergence is approached within three iterations. The constrained model is evaluated by comparing its predictive capability outside the time span of its data, in terms of residuals at magnetic observatories, with that for the unconstrained model.

  11. Bottom-up control of geomagnetic secular variation by the Earth's inner core

    DEFF Research Database (Denmark)

    Aubert, Julien; Finlay, Chris; Fournier, Alexandre

    2013-01-01

    Temporal changes in the Earth’s magnetic field, known as geomagnetic secular variation, occur most prominently at low latitudes in the Atlantic hemisphere1, 2 (that is, from −90 degrees east to 90 degrees east), whereas in the Pacific hemisphere there is comparatively little activity. This is a c......Temporal changes in the Earth’s magnetic field, known as geomagnetic secular variation, occur most prominently at low latitudes in the Atlantic hemisphere1, 2 (that is, from −90 degrees east to 90 degrees east), whereas in the Pacific hemisphere there is comparatively little activity....... This is a consequence of the geographical localization of intense, westward drifting, equatorial magnetic flux patches at the core surface3. Despite successes in explaining the morphology of the geomagnetic field4, numerical models of the geodynamo have so far failed to account systematically for this striking pattern......-like gyre6. The resulting shear concentrates azimuthal magnetic flux at low latitudes close to the core–mantle boundary, where it is expelled by core convection and subsequently transported westward. Second, differential inner-core growth7, 8, fastest below Indonesia6, 9, causes an asymmetric buoyancy...

  12. Body-centered cubic iron-nickel alloy in Earth's core.

    Science.gov (United States)

    Dubrovinsky, L; Dubrovinskaia, N; Narygina, O; Kantor, I; Kuznetzov, A; Prakapenka, V B; Vitos, L; Johansson, B; Mikhaylushkin, A S; Simak, S I; Abrikosov, I A

    2007-06-29

    Cosmochemical, geochemical, and geophysical studies provide evidence that Earth's core contains iron with substantial (5 to 15%) amounts of nickel. The iron-nickel alloy Fe(0.9)Ni(0.1) has been studied in situ by means of angle-dispersive x-ray diffraction in internally heated diamond anvil cells (DACs), and its resistance has been measured as a function of pressure and temperature. At pressures above 225 gigapascals and temperatures over 3400 kelvin, Fe(0.9)Ni(0.1) adopts a body-centered cubic structure. Our experimental and theoretical results not only support the interpretation of shockwave data on pure iron as showing a solid-solid phase transition above about 200 gigapascals, but also suggest that iron alloys with geochemically reasonable compositions (that is, with substantial nickel, sulfur, or silicon content) adopt the bcc structure in Earth's inner core.

  13. Resonant tidal excitation of internal waves in the Earth's fluid core

    Science.gov (United States)

    Tyler, Robert H.; Kuang, Weijia

    2014-07-01

    It has long been speculated that there is a stably stratified layer below the core-mantle boundary, and two recent studies have improved the constraints on the parameters describing this stratification. Here we consider the dynamical implications of this layer using a simplified model. We first show that the stratification in this surface layer has sensitive control over the rate at which tidal energy is transferred to the core. We then show that when the stratification parameters from the recent studies are used in this model, a resonant configuration arrives whereby tidal forces perform elevated rates of work in exciting core flow. Specifically, the internal wave speed derived from the two independent studies (150 and 155 m/s) are in remarkable agreement with the speed (152 m/s) required for excitation of the primary normal mode of oscillation as calculated from full solutions of the Laplace Tidal Equations applied to a reduced-gravity idealized model representing the stratified layer. In evaluating this agreement it is noteworthy that the idealized model assumed may be regarded as the most reduced representation of the stratified dynamics of the layer, in that there are no non-essential dynamical terms in the governing equations assumed. While it is certainly possible that a more realistic treatment may require additional dynamical terms or coupling, it is also clear that this reduced representation includes no freedom for coercing the correlation described. This suggests that one must accept either (1) that tidal forces resonantly excite core flow and this is predicted by a simple model or (2) that either the independent estimates or the dynamical model does not accurately portray the core surface layer and there has simply been an unlikely coincidence between three estimates of a stratification parameter which would otherwise have a broad plausible range.

  14. Resonant Tidal Excitation of Internal Waves in the Earth's Fluid Core

    Science.gov (United States)

    Tyler, Robert H.; Kuang, Weijia

    2014-01-01

    It has long been speculated that there is a stably stratified layer below the core-mantle boundary, and two recent studies have improved the constraints on the parameters describing this stratification. Here we consider the dynamical implications of this layer using a simplified model. We first show that the stratification in this surface layer has sensitive control over the rate at which tidal energy is transferred to the core. We then show that when the stratification parameters from the recent studies are used in this model, a resonant configuration arrives whereby tidal forces perform elevated rates of work in exciting core flow. Specifically, the internal wave speed derived from the two independent studies (150 and 155 m/s) are in remarkable agreement with the speed (152 m/s) required for excitation of the primary normal mode of oscillation as calculated from full solutions of the Laplace Tidal Equations applied to a reduced-gravity idealized model representing the stratified layer. In evaluating this agreement it is noteworthy that the idealized model assumed may be regarded as the most reduced representation of the stratified dynamics of the layer, in that there are no non-essential dynamical terms in the governing equations assumed. While it is certainly possible that a more realistic treatment may require additional dynamical terms or coupling, it is also clear that this reduced representation includes no freedom for coercing the correlation described. This suggests that one must accept either (1) that tidal forces resonantly excite core flow and this is predicted by a simple model or (2) that either the independent estimates or the dynamical model does not accurately portray the core surface layer and there has simply been an unlikely coincidence between three estimates of a stratification parameter which would otherwise have a broad plausible range.

  15. Resonant Tidal Excitation of Internal Waves in the Earth's Fluid Core

    Science.gov (United States)

    Tyler, Robert H.; Kuang, Weijia

    2014-01-01

    It has long been speculated that there is a stably stratified layer below the core-mantle boundary, and two recent studies have improved the constraints on the parameters describing this stratification. Here we consider the dynamical implications of this layer using a simplified model. We first show that the stratification in this surface layer has sensitive control over the rate at which tidal energy is transferred to the core. We then show that when the stratification parameters from the recent studies are used in this model, a resonant configuration arrives whereby tidal forces perform elevated rates of work in exciting core flow. Specifically, the internal wave speed derived from the two independent studies (150 and 155 m/s) are in remarkable agreement with the speed (152 m/s) required for excitation of the primary normal mode of oscillation as calculated from full solutions of the Laplace Tidal Equations applied to a reduced-gravity idealized model representing the stratified layer. In evaluating this agreement it is noteworthy that the idealized model assumed may be regarded as the most reduced representation of the stratified dynamics of the layer, in that there are no non-essential dynamical terms in the governing equations assumed. While it is certainly possible that a more realistic treatment may require additional dynamical terms or coupling, it is also clear that this reduced representation includes no freedom for coercing the correlation described. This suggests that one must accept either (1) that tidal forces resonantly excite core flow and this is predicted by a simple model or (2) that either the independent estimates or the dynamical model does not accurately portray the core surface layer and there has simply been an unlikely coincidence between three estimates of a stratification parameter which would otherwise have a broad plausible range.

  16. Rare earth element characteristics of pyrope garnets from the Kaavi-Kuopio kimberlites – implications for ma