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DEEP EARTH Core–mantle boundary landscapes The molten-iron alloy of the core meets the mantle’s silicate rock at Earth’s core–mantle boundary. Seismological images reveal hummocks of iron-enriched material above the boundary, highlighting the heterogeneous nature of the mantle. Thermal structure at the bottom of the mantle T Upper mantle Thermal and chemical structure at the bottom of the lower mantle n LLSVP e nuity le skit conti rov Small-sca D”-dis t-pe Material terogeneities Supporting Online Pos he ULVZ www.sciencemag.org/cgi/content/full/329/5998/1513/DC1 re Co Materials and Methods SOM Text Fig. S1 Tables S1 to S6 References and Notes Post-perov skite Sharp sides LVZ Rost, 2013 Nature Geoscience ΔVP: -5% ΔVS: -8% Δρ: ~1.5-2% H: <100 km mantle solidus -> upper bound for geotherm 19 April 2010; accepted 28 June 2010 10.1126/science.1191056 Core 2 ΔVP: ~5-10% ΔVS: 20-30% Δρ: ~10% H: <20 km Downloaded from www.sciencemag.org on February 12, 2011 pressure high-temperature melting experiments is Figure 1 | Schematic of the mantle. a, Cold, dense oceanic plates subduct downwards, and plumes of a natural KLB-1 peridotite (14). To ensure chemwarm material rise upwards in the mantle. The lowermost mantle contains large-scale heterogeneities, ical homogeneity atvelocity the smallest and Fe as dominated by the material postsuch as large low shear provincesscale (red, LLSVP) and regions pervoskite (grey by phase of mantle rocks at extremely high pressures. mostly Fe2+ , adashed glasslines), wascreated prepared bytransitions using an The lowermost levitation mantle also contains heterogeneities, aerodynamic devicesmaller-scale coupled with CO2 such as ultra-low velocity zones (orange, ULVZ). The D"-discontinuity may represent the boundary to the post-perovskite phase. Sun et al.2 laser heating under slightly reducing conditions identify a previously undocumented type of low-velocity zone (dark brown, LVZ) at the core–mantle ofboundary oxygenbeneath fugacity (17). At interpret high temperature, the USA that they as small-scale ridges of iron-enriched mantle. b, The newly documented LVZsfrom exhibitcell distinct characteristics pressures were measured parameters of compared to the ULVZs (ΔVP, decrease in P-wave seismic velocity; ΔVS, decrease in S-wave seismic velocity; Δρ, increase in density compared to the magnesium perovskite (Mg,Fe)SiO3 by using surrounding, typical mantle; H, height of feature). a thermal equation of state reported for Previous studies byrecently x-ray diffraction methods the same KLB-1 peridotitic starting material as Solidus temperature of the lower mantle G uctio Subd Melting of Peridotite to 140 Gigapascals Lower mantle Subduction he border between the core and mantle is the most significant internal boundary of our planet. The transfer of heat across this boundary plays an important role in controlling both the dynamics of Earth’s outer core and the convection of the mantle. Seismological studies1 of the lowermost few hundred kilometres of the mantle above the boundary have revealed a multitude of three-dimensional (3D) structures on scales ranging from thousands to just a few tens of kilometres. Writing in Earth REPORTS and Planetary Science Letters, Sun et al.2 use high-resolution seismic images of the Ryuichi Nomura mantle 21. O. Möhler, P. J. DeMott, G. Vali, Z. Levin, Biogeosciences 28. J. Merikanto,lowermost D. V. Spracklen, G. to W.identify Mann, S.aJ.previously Pickering, Tokyo Institute Technology undocumented chemical heterogeneity, 4, 1059of(2007). K. S. Carslaw, Atmos. Chem. Phys. 9, 8601 (2009). interpreted as local iron5,enrichment, 22. B. C. Christner, C. E. Morris, C. M. Foreman, R. M. Cai, 29. R. Krejci et al., Atmos. Chem. Phys. 1527 (2005). at the boundary beneath D. C. Sands, Science 319, 1214 (2008). 30. A. M. L. Ekman et core–mantle al., Geophys. Res. Lett. 35, L17810 North America. 23. R. M. Bowers et al., Appl. Environ. Microbiol. 75, 5121 (2008). structure of the7,lowermost mantle (2009). 31. U. Kuhn et al., The Atmos. Chem. Phys. 2855 (2007). is complex Seismic waves travel 24. K. A. Pratt et al., Nat. Geosci. 2, 398 (2009). 32. J. Lelieveld et al., Nature(Fig. 1). 452, 737 (2008). slowly of through two large regions 25. M. O. Andreae et al., Science 303, 1337 (2004). 33. Support fromunusually a large number colleagues, agencies, of the lower mantle located beneath Africa 26. P. Reutter et al., Atmos. Chem. Phys. 9, 7067 (2009). and institutions is gratefully acknowledged as detailed and the Pacific Ocean. Each region is about 27. M. Kulmala et al., J. Aerosol Sci. 35, 143 (2004). in the supporting online material. 1 15,000 km across and rises 500–1000 km above the core-mantle boundary 1. These regions, commonly termed large low shear velocity provinces (LLSVPs), have sharp peripheral boundaries and are thought to alter the speed of passing seismic waves because they have a different composition and their temperature and density is higher than that of the surrounding mantle1,3. An undulating discontinuity (D"discontinuity, Fig. 1) is also observed several 1 5 G. Fiquet,1* A. L. Auzende,1 J. Siebert,1 A. Corgne,2,3 H. Bureau, H.kilometres Ozawa,1,4 G.the Garbarino hundred above core–mantle boundary 4. This discontinuity probably Interrogating physical processes that occur within the lowermostmarks mantle is atransition key to understanding a phase in the mantle rocks, induced by the high pressures at depth that Earth’s evolution and present-day inner composition. Among such processes, partial melting has create a material known as post-perovskite5. been proposed to explain mantle regions with ultralow seismic velocities near the core-mantle Furthermore, at the edges of the LLSVPs, boundary, but experimental validation at the appropriate temperature and pressure regimesof mantle thin intermittent layers of 5–40 km have been identified that greatly remains challenging. Using laser-heated diamond anvil cells, werocks constructed the solidus curvereduce of 6–8 CMB the speed of passing waves . These smaller a natural fertile peridotite between 36 and 140 gigapascals. Melting at core-mantle boundary Lower mantle ◀ ▶︎ Outer core anomalies are known as ultra-low velocity pressures occurs at 4180 T 150 kelvin, which is a value that matches estimated mantle geotherms. zones (ULVZs). Scattered seismic waves Molten regions may therefore exist at the base of the present-day Melting phase maymantle. identify heterogeneities on relations even smaller 9 scales, about 10 km in size . Those and element partitioning data also show that these liquids could host many incompatible could be created by partial melting or chemical elements at the base of thepyrolite mantle. heterogeneities, possibly linked to subducted Lower mantle plume? Sebastian Rost oceanic plates. However, little is known about scale structure at depth by analysing details of the fine-scale structure of the deep Earth. the waveforms6 of seismic waves generated by Sun et al.2 use seismic data from deep earthquakes in the Philippines recorded 10 Earthscope’s USArray — a dense grid of in the mid-western USA. 100 3750 KThe authors identify several ridges of more thanXRD 400 seismometers112 deployed across the United States — to analyse the detailed mantle rocks at the core–mantle boundary 210 structure that cause passing seismic waves to slow 80 of the core–mantle boundary beneath North America. They image the fine- considerably. The ridges are present in some gasket 004 020 200 NATURE GEOSCIENCE | VOL 6 | FEBRUARY 2013 | www.nature.com/naturegeoscience 89 60 zones may be partially molten (5). X-ray Intensity (counts) is that these © 2013 Macmillan Publishers Limited. All rights reserved Recent high-resolution waveform studies also 002 200 find evidence the ULVZ material is denser 110 40 Multi-anvilthat press! than the + surrounding above solidus! mantle (11). These partially Melting criteria! 103 below solidus! molten+ regions have not been detected to be lat! -CaPv/Fp melting! 20 ! 111 erally continuous and have a thickness ranging ! Diamond anvil cell! from a■ few kilometers up to about 50 km. Fiquet+, 2010 Science! ! -diffuse scattering 0 It is linkEPSL these observations with ■ attractive Andrault+,to 2011 250 an episode of extensive melting that probably Fiquet+, 2010 Science 2715 K affected the primitive Earth, leading to the formation of a deep magma ocean. If the evolution 200 of a terrestrial magma ocean resulted in the Difficulty for detecting the initiation of melting formation of a layer of melt at the base of the 4 150 mantle early in Earth history, its survival depends on whether it was (and maybe still is) gravitationally and chemically stable (12). If this is the 100 case, such a layer would be an ideal candidate for an unsampled geochemical reservoir hosting a 50 variety of incompatible species, notably the planet’s missing budget of heat-producing elements 0 (13). The presence of high-pressure melts would 6 10 12 14 8 also have consequences for chemical reactions Diffraction angle (2-θ) between the mantle and core, the dynamics of REPORTS the lowermost mantle, and the heat flow across The lower abundance of ~10- to 100-mm paranalyzed here. mass GPa of each mineral (table Fig. 1. Diffraction patterns collected atThe61 1 S1) was obtained from the modal abundances, ticles in the smooth terrain can potentially be the CMB. Institut de Minéralogie et de Physique des Milieux Condensés, and the density calculated from its mean chem- explained by (i) smaller grains having higher after normalized reference background subtracical compositions (3). The total mass of our ex- ejection velocity and therefore higher loss rates To constrain the existence of melt at the base Institut de Physique du Globe de Paris, Université Pierre et X-ray micro-CT methods Results amined particles mg. From the mineral from Itokawa after impacts (13), (ii) selective tion: subsolidus at 2715 K (bottom) andis 14.5 above Marie Curie, UMR CNRS 7590, Université Paris Diderot, 140 mass and the porosity, we obtained an average electrostatic levitation of smaller grains (13), and/or of the mantle, we performed melting experiments solidus at 3750 K (top). The diffuse scattering density of 3.4 g/cm . liquid This corresponds to grain (iii) size-dependent segregation by vibration [the rue de Lourmel, 75015 Paris, France. 2Institut de Physique du density and is comparable to the measured grain Brazil-nut effect (14)]. on a fertile peridotite composition over a range of contribution is outlined by the shaded area (3.54 as Ta0.13 g/cm ) (10). Globe de Paris, Equipe de Minéralogie à l’Institut de Minéralogie density of LL chondrites BL47XU@SPring8 the collected sample is representative of Itokawa lower-mantle pressures between 36 and 140 GPa guide; it does not correspond to a Ifphysical et de Physique des Milieux Condensés, 140 rue de Lourmel, structural has the average porosity of LL chondrites, its (B) subsolidus (A) above solidus GPa/3690 K and 151 GPa/3680 K bulk density would be 3.1 T 0.2 g/cm . The using a laser-heated diamond-anvil cell (DAC) model of142 75015 Paris, France. 3Observatoire Midi-Pyrénées, UMR CNRS the liquid. HKL indexes are ofgiven forthen be 39 T 6% macroporosity Itokawa would keV 7 keV 5562, 14 rue Edouard Belin, 31400 Toulouse, France. 4Department on the basis of the bulk density of Itokawa (1.9 T coupled with in situ synchrotron measurements 7 remaining diffraction peaks that0.13can assigned g/cm be ) (1). This is consistent with a rubbleof Earth and Planetary Sciences, Tokyo Institute of Technology asteroid model of Itokawa (1). (14). Our study thus extends the pressure range of to magnesium silicate perovskite,pileobserved above The sphere-equivalent diameters of tapping 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan. 5Eurosample particles calculated from their volumes previous measurements (15, 16) of the solidus the solidus temperature at this pressure (top). Stars pean Synchrotron Radiation Facility, BP220, 38043 Grenoble range from 14 to 114 mm (median 36.8 mm), whereas the diameters of spatula and liquidus temperatures of a mantle-like com- denote diffraction peaks of Ca-perovskite and fer-sample particles cedex, France. range from 0.5 to 32 mm (median 3.5 mm). These are smaller the size-sorted, mm- to position to depths exceeding those of the CMB at ropericlase affected by partial particles melting atthanthese *To whom correspondence should be addressed. E-mail: cm-sized particles observed in close-up images of MUSES-C Regio (2). The mm- to cm-sized parti2900 km. The starting material used for the high- conditions [email protected] 8bykeV 8 keV (bottom). cles were not comminuted the pressure of the eophysical and geochemical observations favor the presence of chemical heterogeneities in the lowermost chondritemantle. These are thought to be either primitive mantle residues (1), dense subducted slab components (2), products of chemical interactions between the core and mantle (3, 4), or dense melts perhaps as old as the Earth itself (5). The core-mantle boundary is a complex region that has been the focus of numerous geophysical studies. Seismologic studies suggest the presence of two large low-shear velocity provinces (LLSVPs) under the African continent and in the pacific basin (6, 7). 3 The consensus view is that these slow regions (which are possibly up to 1000 km thick) exhibit an anomalously low shear velocity and increased bulk modulus but are not usually thought to be partially molten (8). Additionally, extensively documented ultralow-velocity zones (ULVZs) correspond to localized features at the core mantle boundary (CMB), with strong reductions in seismic velocities (in the range of 10 to 30%) for both P and S waves (9, 10); the interpretation * * * * 3 3 Figure 3A shows the shape distri tapping samples. The mean b/a an 0.71 T 0.13 and 0.43 T 0.14, resp and c are longest, middle, and diameters, respectively, of a best-fi The distribution among polyminer mineralic particles does not have difference based on the Kolmog 3 3 1516 17 SEPTEMBER 2010 Spatial resolution! ~70nm (for <100um sample)! ~200nm(for >100um sample)! X-ray energy! 7, 8 keV (Fe K edge: 7.11 keV) VOL 329 SCIENCE www.sciencemag.org 5um melt spacecraft during touchdown [~0.02 MPa (7)] if they are coherent (11), and the collected small particles should be original regolith particles from the smooth terrain. Three sampling mechanisms are possible (7): (i) impact by the sampler horn, (ii) electrostatic interaction between charged particles and possibly charged sampler horn, and (iii) levitation by thruster jets from the ascending spacecraft. Some mechanisms may have caused some size sorting. However, because details concerning the touchdown conditions are not known, we cannot specify the mechanism(s) and such effect. The cumulative size distribution of the tapping samples has a log slope of about –2 in the range of 30 to 100 mm (Fig. 2). Large particles might have been selectively picked up from the tapping samples. The spatula samples have a log slope of –2.8 in the range of 5 to 20 mm (Fig. 2). However, sweeping by the spatula would have pulverized some of the particles, and the slope is an upper limit to the original slope. Thus, the slope for the fine particles (~5 6 to 100 mm) in the smooth terrain should be shallower than –2.8 and probably around –2. This slope is shallower than that of Itokawa boulders of 5 to 30 m (–3.1 T 0.1) (12). If transition of the slope from about –3 to –2 occurs at the mm- to cm-sized region, then we can explain the observation of abundant mm- to cm-sized regolith (2). The lack of mm-sized particle in the Hayabusa samples might be explained by a small probability of collecting these small particles. However, the possibility of size selection biases during sampling from Itokawa or agglomerations of small particles (11) cannot be excluded. In contrast, abundant sub-mm regolith powder was observed on the Moon, and the size distribution from lunar sam- heated region Nomura+, 2014 Science 0 642 LAC (cm-1) Fig. 1. Slice images of Itokawa particles obtained by microtomography with a gray sca linear attenuation coefficient (LAC) of objects (from 0 to X cm−1), where X is the maximum L CT images. (A) Sample RA-QD02-0063 (7 keV, X = 431 cm−1). (B) RA-QD02-0014 (7 keV, Some voids define a 3D plane (arrows). (C) RA-QD02-0042 (7 keV, X = 575 cm−1). (D) R (7 keV, X = 431 cm−1). Concentric structure is a ring artifact. Bright edges of particles artifacts resulting from refraction contrast. Ol indicates olivine; LPx, low-Ca pyroxene pyroxene; Pl, plagioclase; CP, Ca phosphate; Tr, troilite; and Meso, mesostasis. Iron-rich region in the hottest part 5 Fig. 2. Cumulative size distribution of Itokawa particles. Sphereequivalent diameters of the tapping samples and diameters of the spatula samples are shown. Solidus temperature of the pyrolitic mantle Thermal structure at the bottom of the mantle CMB Lower mantle ◀ ▶︎ Outer core CMB Lower mantle ◀ ▶︎ Outer core Solidus Nomura+, 2014 Science Nomura+, 2014 Science Solidus temperature: 3570(200) K @CMB Mantle solidus: upper bound for geotherm 7 8 news & views –mantle boundary landscapes lloy of the core meets the mantle’s silicate rock at Earth’s core–mantle boundary. Seismological mmocks of iron-enriched material above the boundary, highlighting the heterogeneous nature of Chemical structure at the bottom of the mantle letters to nature le Small-sca es neiti heteroge ULVZ re Co Sharp sides 600 700 800 4,500 4.2 4,000 4.0 MORB 3.8 Post-perov PYROLITE 3.6 skite 3.4 14 16 LVZ 18 660 km depth 20 22 24 26 Pressure (GPa) 28 S Core adiabat 120 140 3,000 Mantle adiabat 2,000 0 20 40 60 80 100 solid circles represent melting temperatures of MORB and MgSiO3, respectively, Δρ: ~1.5-2% to perovskitite lithology, but once MORB transbecause of the transformation H: <100 forms to perovskitite at 720km km depth, it is no longer buoyant in the deep mantle. determined in a laser-heated diamond cell. Open squares represent melting temperatures of MORB, determined in the multi-anvil apparatus. Melting curves of St14, Ca-pv14,15 and Mg-pv13,14 are substantially higher than that of 10 MORB. The melting curves of Mg-pv from refs 13 and 14 (labelled as Mg-pv13 and Mg-pv14, respectively) are plotted for comparison. The mantle adiabats are from Boehler23. shallower than that expected1,2,8,9. The transition boundary has a positive pressure±temperature Figure 1 | Schematic of the mantle. a, Cold, dense oceanic plates subduct downwards, and plumes of slope, whereas the transition boundary inlarge-scale the underlying harzburgite has a negative slope10. Within a warm material rise upwards in the mantle. The lowermost mantle contains heterogeneities, cool slabby (for such as large low shear velocity provinces (red, LLSVP) and regions dominated theexample material1,000 post-8C at the 660 km depth), the transforperovskite lithology in the basaltic crust and the underpervoskite (grey dashed lines), created by phase transitions of mantle mation rocks at to extremely high pressures. lying harzburgite layer would occur at a similar depth, implying that The lowermost mantle also contains smaller-scale heterogeneities, such as ultra-low velocity zones the delamination of the basaltic crust from the slab is unlikely at the 2 (orange, ULVZ). The D"-discontinuity may represent the boundary to the post-perovskite phase. Sun et al. 660 km discontinuity. identify a previously undocumented type of low-velocity zone (dark brown, LVZ) atexperiments the core–mantle Melting were carried out using a multi-anvil 3 boundary beneath the USA that they interpret as small-scale ridges of apparatus iron-enriched mantle. and laser-heated diamond cell11 in a pressure range between and(ΔV 64 PGPa (Fig. in 3). The solidus temperatures are b, The newly documented LVZs exhibit distinct characteristics compared to the 16 ULVZs , decrease 2,400 K and 2,700 at 22 GPa P-wave seismic velocity; ΔVS, decrease in S-wave seismic velocity; Δρ, increase in densityKcompared to and 27 GPa, respectively, based on the multi-anvil experiments. The solidus phase assemblage at surrounding, typical mantle; H, height of feature). 27 GPa is Al-bearing Mg±perovskite and Ca±perovskite, stishovite, Al-phase and trace majorite (,3%). No important phase transformations have been reported at higher pressures up to 100 GPa oceanic plates. However, little is known about scale structure(ref. at depth by analysing details of 9), suggesting that this assemblage remains in the deep mantle, 6 the fine-scale structure of the deep Earth. the waveformsexcept of seismic waves would generated by that majorite be completely transformed to perovskite 2 Sun et al. use seismic data from deep earthquakes in the Philippines recorded at pressures slightly above 27 GPa. Analysis of run products above Earthscope’s USArray 10 — a dense grid of in the mid-western USA.temperature at 27 GPa showed that Ca±perovskite is the the solidus phase, followed more than 400 seismometers deployed across The authorsliquidus identify several ridgesbyofstishovite, Al-Ca-phase and Al-bearing Mg±perovskite. Theboundary partial melt composition is enriched in MgO the United States — to analyse the detailed mantle rocks at the core–mantle and FeO andwaves depleted in SiO2 and Al2O3, reØecting that Mg± structure of the core–mantle boundary that cause passing seismic to slow perovskite is eliminated near the solidus temperature. The beneath North America. They image the fine- considerably. The ridges are present inÆrst some partial melt is probably denser than the solid residue in MORB composition at lower mantle pressures because of its higher iron 6 | FEBRUARY 2013 | www.nature.com/naturegeoscience 89 content. The melting curve of MORB determined in the laserheated diamond cell is consistent with that determined by multi© 2013 Macmillan Publishers Limited. All rights reserved anvil experiments for the same starting material between 22 and 27 GPa (Fig. 3), and also with previous results at low pressures12. It is substantially lower than that of each constituent mineral: Mg± perovskite13,14, Ca±perovskite14,15 and stishovite14. The present measurements of the melting temperature of MgSiO3 are consistent with previous studies13,14,16 at 12±28 GPa. The melting temperature of basalt is about 250 K lower than that of mantle peridotite17 at a depth of 1,500 km (corresponding to a pressure of 64 GPa). Extrapolation to 135 GPa yields a melting temperature of MORB of about 4,000 K at the core±mantle bound- Future work: melting temperature measurement ancient crust, BIF, MORB, and BMO residues… Multi-anvil press NATURE | VOL 397 | 7 JANUARY 1999 | www.nature.com 3600(100) K Temperature uncertainty Melting criteria! ! -Temperature jump with increasing laser power the melting relationships of Simon22 (S) and Kraut and Kennedy23 (KK). Open and 27 GPa from X-rayΔV diffraction P: -5% and microprobe data. The density proÆle of pyrolite ancient crust, BIF, MORB, BMO residues… Laser-heated diamond anvil cell! (LH-DAC) Figure 3 Melting curve of MORB extrapolated to the core±mantle boundary using pyrolite (dashed line). Solid circles represent the calculated densities at 24, 26 and is from a previousΔV study . Pyrolite becomes denser than MORB at 660 km depth S: -8% 9 ary, which is substantially lower than that of single-phase MgSiO3 ± perovskite (Fig. 3). If the temperature locally reaches 4,000 K in the D0 region, which may be a graveyard for subducted lithosphere, the former basaltic crust could partially melt. This may provide an explanation for the recent seismic observations of the seismic anisotropy18,19 and anomalously slow P-wave velocities20,21 at the base of the mantle. Under such a scenario, the temperature of the outer core must be higher than the 4,000 K required for melting of MORB perovskitite (Fig. 3). The temperature difference over the thermal boundary between core and mantle may reach 1,500 K, and hot mantle plumes, including partially molten slab materials, are likely to arise from this depth. M ......................................................................................................................... Conclusions and future works Methods We have determined the phase relations and the melting temperatures of MORB over a wide pressure range by using two complementary high-pressure techniques, the multi-anvil apparatus and the diamond-anvil cell. The multianvil experiments provide detailed chemical composition information of the individual minerals in the high-pressure assemblages through the electron ! microprobe and structure data through X-ray diffraction. The phase identiÆcation was also conÆrmed by micro-Raman spectroscopy. The temperatures in the multi-anvil experiments were measured with a W5Re-W26Re ther! mocouple, whereas pressures were determined based on Æxed pressure calibration points, including the ilmenite±perovskite transition in MgSiO3 CMB (ref. 3). Pressure calibration at high temperature was based on the Al2O3 solubility in the MgSiO3 ±perovskite structure at pressures above 23 GPa (ref. 6). Combining accurate temperature measurements with a self-consistent pressure calibration, the present multi-anvil experiments provide a reliable determination of the dP/dT slope of the majorite±perovskite transformation in MORB and relatively accurate measurements of melting temperature up to 27 GPa, the maximum attainable pressure in the multi-anvil apparatus. ! To extend the melting-temperature measurements for MORB to pressures higher than 27 GPa, we conducted experiments in a laser-heated diamondanvil cell. In the present diamond cell experiments, a double-sided heating system with a multimode Nd:YAG laser was used to minimize both axial and radical temperature gradients in the heated sample11. The MORB glass sample was sandwiched between two Re foils with Al2O3 layers, as thermal insulators, on the top and bottom of the sandwich assemblage. The interface between the Thermal structure! -Solidus temperature of pyrolite 3570(200) K @CMB! ! -> upper bound for T Nomura+, 2014 Science ! Chemical heterogeneities! ! ! <- melting temperature of ancient crust, BIF, MORB and BMO ! ! residues © 1999 Macmillan Magazines Ltd 55 Zhang+Fei, 2008 GRL 11 160 Hirose+, 1999 Nature Pressure (GPa) Figure 2 Comparison of zero-pressure density changes in MORB (solid line) and ΔVP: ~5-10% ΔVS: 20-30% Δρ: ~10% H: <20 km Upper bound for TCMB 3,500 1,500 10 Core KK MORB 2,500 30 Rost, 2013 Nature Geoscience LLSVP: iron-rich?! ULVZ: partially molten? Mg -pv 1 3 Mg -pv 1 4 500 4.4 Temperature (K) Zero-Pressure Sub Density (g cm–3) duction Lower mantle plume? n LLSVP e nuity skit conti rov D”-dis t-pe Pos 5,000 Depth (km) Lower mantle uctio e lowermost mantle ismic waves travel ugh two large regions cated beneath Africa Each region is about rises 500–1000 km boundary 1. These rmed large low shear SVPs), have sharp and are thought to ing seismic waves fferent composition and density is higher unding mantle1,3. ontinuity (D"also observed several ove the core–mantle ntinuity probably on in the mantle rocks, essures at depth that n as post-perovskite5. ges of the LLSVPs, s of 5–40 km of mantle fied that greatly reduce aves6–8. These smaller as ultra-low velocity red seismic waves neities on even smaller size9. Those could elting or chemical ly linked to subducted Melting temperature: MORB Upper mantle Subd en the core and ost significant ry of our planet. ross this boundary e in controlling both ’s outer core and the tle. Seismological ost few hundred tle above the ed a multitude of D) structures on ousands to just a . Writing in Earth Letters, Sun et al.2 ismic images of the dentify a previously cal heterogeneity, on enrichment, undary beneath 12 CMB Lower mantle ◀ ▶︎ Outer core pure iron Anzellini+, 2013 Science Fe-O-S liquidus Terasaki+, 2012 EPSL FeH Sakamaki+, 2009 PEPI Nomura+, 2014 Science 0.6wt% hydrogen to make the “liquid” outer core 13 14 Temperature gradient in LH-DAC Conclusions and future works Thermal structure! 3800 Radia 3300 ! l (mea sured -Solidus temperature of pyrolite 3570(200) K @CMB! ) Temperature (K) Nomura+, 2014 Science ! ! 2800 Thermal conductivity (κ∝)! 1/T (lattice)! const.! T3 (radiation) 2300 1800 1300 -lower bound for core geotherm -> FeHx Tm only up to 20 GPa Sakamaki+, 2009 PEPI Calculation after! Manga+Jeanloz, 1996 GRL 800 -> upper bound for TCMB! -> Tm in Fe-H-X system over 135 GPa is necessary Chemical heterogeneities! 300 0 1 2 3 4 Axial distance from hotspot (µm) 5 ! ! ! <- melting temperature of ancient crust, BIF, MORB and BMO ! ! residues 15 16 17 18