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Sample records for subarc mantle source

  1. Sources and timing of pyroxenite formation in the sub-arc mantle: Case study of the Cabo Ortegal Complex, Spain

    Science.gov (United States)

    Tilhac, Romain; Grégoire, Michel; O'Reilly, Suzanne Y.; Griffin, William L.; Henry, Hadrien; Ceuleneer, Georges

    2017-09-01

    on the sources of the metasomatic agents involved (and potentially the parental melts) and notably indicate the contributions from enriched mantle components (EM I and/or II). This suggests the involvement of an old crustal component, which is consistent with the derivation of the pyroxenites and granulites from an ensialic island arc, potentially built on the northern margin of either Gondwana or a pre-Gondwanan continental block. This case study thus documents the role of melt-rock reactions as major pyroxenite-forming processes in the sub-arc mantle, providing further constraints on their sources and timing in the Cabo Ortegal Complex.

  2. Origin of the Luobusa diamond-bearing peridotites from the sub-arc mantle

    Science.gov (United States)

    Liu, Chuanzhou; Zhang, Chang; Wu, Fuyuang; Chung, Sunlin

    2016-04-01

    accreted through a plume activity (Yang et al., 2014) up to the lithospheric mantle beneath the Lhasa terrane, where they have been metasomatized by Neo-Tethyan subduction processes. This sub-arc lithospheric mantle was exhumed at seafloor during the Early Cretaceous, in response to the fore-arc hyperextension (Maffione et al., 2015), and intruded by mafic dykes resulting from decompression melting of the ascended asthenosphere (Zhang et al., 2015). Reference Maffione, M. et al. Forearc hyperextension dismembered the south Tibetan ophiolites. Geology 46, 475-478 (2015). Robinson, P. T. et al. The origin and significance of crustal minerals in ophiolitic chromitites and peridotites. Gond. Res., 486-506 (2015). Yang, J. S. et al. Diamond- and coesite-bearing chromitites from the Luobusa ophiolite, Tibet. Geology 35, 875-878 (2007). Yang, J. S., Robinson, P. T. & Dilek, Y. Diamonds in ophiolites. Elements 10, 127-130 (2014). Zhang, C., Liu, C. Z., Wu, F. Y., Zhang, L. L. & Ji, W. Q. Geochemistry and geochronology of maifc rocks from the Luobusa ophiolite, South Tibet. Lithos, 10.1016/j.lithos.2015.1006.1031 (2015). Zhou, M. F., Robinson, P. T., Malpas, J. & Li, Z. J. Podiform chromitites in the Luobusa Ophiolite (Southern Tibet): Implications for melt-rock interaction and chromite segregation in the upper mantle. J. Petrol. 37, 3-21 (1996).

  3. Chlorine and fluorine partition coefficients and abundances in sub-arc mantle xenoliths (Kamchatka, Russia): Implications for melt generation and volatile recycling processes in subduction zones

    Science.gov (United States)

    Bénard, A.; Koga, K. T.; Shimizu, N.; Kendrick, M. A.; Ionov, D. A.; Nebel, O.; Arculus, R. J.

    2017-02-01

    We report chlorine (Cl) and fluorine (F) abundances in minerals, interstitial glasses, and melt inclusions in 12 andesite-hosted, spinel harzburgite xenoliths and crosscutting pyroxenite veins exhumed from the sub-arc lithospheric mantle beneath Avacha volcano in the Kamchatka Arc (NE Russia). The data are used to calculate equilibrium mineral-melt partition coefficients (D mineral / melt) for Cl and F relevant to subduction-zone processes and unravel the history of volatile depletion and enrichment mechanisms in an arc setting. Chlorine is ∼100 times more incompatible in pyroxenes (DClmineral/melt = 0.005-0.008 [±0.002-0.003]) than F (DFmineral/melt = 0.50-0.57 [±0.21-0.24]), which indicates that partial melting of mantle sources leads to strong depletions in Cl relative to F in the residues. The data set in this study suggests a strong control of melt composition on DCl,Fpyroxene/melt, in particular H2O contents and Al/(Al + Si), which is in line with recent experiments. Fluorine is compatible in Ca-amphibole in the 'wet' sub-arc mantle (DFamphibole/melt = 3.5-3.7 [±1.5]) but not Cl (DClamphibole/melt = 0.03-0.05 [±0.01-0.03]), indicating that amphibole may fractionate F from Cl in the mantle wedge. The inter-mineral partition coefficients for Cl and F in this study are consistent amongst different harzburgite samples, whether they contain glass or not. In particular, disseminated amphibole hosts much of the Cl and F bulk rock budgets of spinel harzburgites (DClamphibole/pyroxene up to 14 and DFamphibole/pyroxene up to 40). Chlorine and fluorine are variably enriched (up to 1500 ppm Cl and 750 ppm F) in the parental arc picrite and boninite melts of primitive pyroxenite veins (and related melt inclusions) crosscutting spinel harzburgites. Based on the data in this study, the main inferences on the behaviour of Cl and F during melting and metasomatic processes in the sub-arc mantle are as follow: (i) Melting models show that most depleted mantle protoliths

  4. Modelling Mt. Etna mantle sources

    Science.gov (United States)

    Casetta, Federico; Giacomoni, Pier Paolo; Coltorti, Massimo; Ferlito, Carmelo; Bonadiman, Costanza

    2017-04-01

    The mantle source beneath Mt. Etna is matter of a longstanding and controversial debate, due to the absence of mantle xenoliths, the evolved nature of the erupted magmas and their geochemical variations. This study is focused on the modelling of the petrogenetic processes responsible for the production of Mt. Etna magmas and their variation through time, by means of a comparison with the Hyblean lavas (Southern Sicily), their evolution and mantle source(s). Samples from all Mt. Etna eruptive events, from the tholeiites to the nowadays K-rich eruptions, were used to a backward reconstruction of the primitive magma compositions, taking into account the fO2 of the magmatic system and its effect on mineral-melt Fe partitioning. The eutectic melting proportions and the modal composition of the Mt. Etna mantle source, obtained by a mass balance melting model, allowed to: i) compare the etnean inferred primary magmas with the Ol-hosted melt inclusions (MI) composition and with the Hyblean real primary magmas; ii) define some petrologic and geodynamic constraints on the Hyblean-Mt. Etna area taking also in account the compositions of the Hyblean xenoliths. A 2% to 17% addition of dunitic to wehrlitic assemblages (Ol + Cpx in progressive equilibrium) to Mt. Etna less evolved lavas allowed to equilibrate the Mt. Etna primitive magmas (mg# = 68) compositions for Timpe, AAV, Ellittico, Mongibello and Post-1971 stages to mantle conditions; Ol with Fo=88). The calculated Lh source is constituted by Ol + Opx + Cpx + Cr-Sp, with addition of small amounts (4.3%) of Amph and Phlog. Decreasing partial melting degrees (from 19% to 13-10%) and a change in Amph and Phlog eutectic melting proportions can explain the entire Mt. Etna compositional range, from the tholeiitic event to the Post-1971 LILE-enriched episodes, leading to the production of primary magmas characterized by a 0.6 to 1.2 wt% H2O content. Some speculation between geodynamic and magmatic evolution of the articulated and

  5. The source location of mantle plumes from 3D spherical models of mantle convection

    Science.gov (United States)

    Li, Mingming; Zhong, Shijie

    2017-11-01

    Mantle plumes are thought to originate from thermal boundary layers such as Earth's core-mantle boundary (CMB), and may cause intraplate volcanism such as large igneous provinces (LIPs) on the Earth's surface. Previous studies showed that the original eruption sites of deep-sourced LIPs for the last 200 Myrs occur mostly above the margins of the seismically-observed large low shear velocity provinces (LLSVPs) in the lowermost mantle. However, the mechanism that leads to the distribution of the LIPs is not clear. The location of the LIPs is largely determined by the source location of mantle plumes, but the question is under what conditions mantle plumes form outside, at the edges, or above the middle of LLSVPs. Here, we perform 3D geodynamic calculations and theoretical analyses to study the plume source location in the lowermost mantle. We find that a factor of five decrease of thermal expansivity and a factor of two increase of thermal diffusivity from the surface to the CMB, which are consistent with mineral physics studies, significantly reduce the number of mantle plumes forming far outside of thermochemical piles (i.e., LLSVPs). An increase of mantle viscosity in the lowermost mantle also reduces number of plumes far outside of piles. In addition, we find that strong plumes preferentially form at/near the edges of piles and are generally hotter than that forming on top of piles, which may explain the observations that most LIPs occur above LLSVP margins. However, some plumes originated at pile edges can later appear above the middle of piles due to lateral movement of the plumes and piles and morphologic changes of the piles. ∼65-70% strong plumes are found within 10 degrees from pile edges in our models. Although plate motion exerts significant controls over the large-scale mantle convection in the lower mantle, mantle plume formation at the CMB remains largely controlled by thermal boundary layer instability which makes it difficult to predict geographic

  6. Do mantle plumes preserve the heterogeneous structure of their deep-mantle source?

    Science.gov (United States)

    Jones, T. D.; Davies, D. R.; Campbell, I. H.; Wilson, C. R.; Kramer, S. C.

    2016-01-01

    It has been proposed that the spatial variations recorded in the geochemistry of hotspot lavas, such as the bilateral asymmetry recorded at Hawaii, can be directly mapped as the heterogeneous structure and composition of their deep-mantle source. This would imply that source-region heterogeneities are transported into, and preserved within, a plume conduit, as the plume rises from the deep-mantle to Earth's surface. Previous laboratory and numerical studies, which neglect density and rheological variations between different chemical components, support this view. However, in this paper, we demonstrate that this interpretation cannot be extended to distinct chemical domains that differ from surrounding mantle in their density and viscosity. By numerically simulating thermo-chemical mantle plumes across a broad parameter space, in 2-D and 3-D, we identify two conduit structures: (i) bilaterally asymmetric conduits, which occur exclusively for cases where the chemical effect on buoyancy is negligible, in which the spatial distribution of deep-mantle heterogeneities is preserved during plume ascent; and (ii) concentric conduits, which occur for all other cases, with dense material preferentially sampled within the conduit's centre. In the latter regime, the spatial distribution of geochemical domains in the lowermost mantle is not preserved during plume ascent. Our results imply that the heterogeneous structure and composition of Earth's lowermost mantle can only be mapped from geochemical observations at Earth's surface if chemical heterogeneity is a passive component of lowermost mantle dynamics (i.e. its effect on density is outweighed by, or is secondary to, the effect of temperature). The implications of our results for: (i) why oceanic crust should be the prevalent component of ocean island basalts; and (ii) how we interpret the geochemical evolution of Earth's deep-mantle are also discussed.

  7. Mantle source characterization of Sylhet Traps, northeastern India: A ...

    Indian Academy of Sciences (India)

    Mantle source characterization of Sylhet Traps, northeastern India: A petrological and geochemical study. Md Shofiqul Islam. 1,2,∗. , Daniel Meshesha1,3 and Ryuichi Shinjo1. 1Department of Physics and Earth Sciences, University of the Ryukyus, Senbaru 1, Nishihara,. Okinawa 903-0213, Japan. 2Department of ...

  8. An Olivine-free mantle source of Hawaiian shield basalts

    NARCIS (Netherlands)

    Sobolev, A.V.; Hofmann, A.W.; Sobolev, S.V.; Nikogosian, I.

    2005-01-01

    More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent

  9. Mantle flow, melting, and the thermochemical evolution of the mantle wedge due to back-arc spreading

    Science.gov (United States)

    Hall, P. S.

    2012-12-01

    The Lau Basin - Tonga Arc system provides a unique window on the evolution of the mantle in arc - back-arc spreading center (BASC) systems. In particular, the southward propagation of rifting in the Lau Basin allows north-south (i.e., along-strike) variations in the characteristics of both the arc and the BASC to be mapped to temporal variations associated with migration of the BASC away from the arc. Systematic along-strike variations in both geophysical (e.g., crustal thickness, axial depth, gravity) and petrological observations at BASCs in the Lau Basin have accordingly been taken to reflect changes in the composition of the mantle source beneath the BASC as spreading progresses [Martinez and Taylor, 2002]. Similarly, along-strike variations in geochemistry (e.g., Ti6.0, Si6.0) within the active Tonga Arc have been attributed to changes in the composition of the mantle source beneath the arc with time as mantle that is depleted by decompression melting at the BASC is advected beneath the arc by slab-induced corner flow [Cooper et al., 2010]. Here I present the results of a series of computational geodynamic experiments undertaken to test these hypotheses by characterizing the thermal and compositional evolution of the mantle wedge in an arc-back-arc spreading center system. Mantle flow in an arc-BASC system is modeled within a 2-D model domain (600 km x 600 km) oriented perpendicular the strike of the arc and BASC using the COMSOL Multiphysics finite element package. Flow is driven kinematically by prescribing a constant velocity along an internal boundary corresponding to the surface of the subducting plate, and a time-varying divergent velocity along the upper boundary of the model, corresponding to the migrating BASC. A temperature-dependent diffusion creep rheology is employed, and melting and the resulting depletion of the mantle source within the model domain are calculated and tracked over time using Lagrangian particles. Experiments consider a range of

  10. A tomographic glimpse of the upper mantle source of magmas of the Jemez lineament, New Mexico

    Science.gov (United States)

    Spence, W.; Gross, R.S.

    1990-01-01

    To infer spatial distributions of partial melt in the upper mantle source zones for the Rio Grande rift and the Jemez lineament, the lateral variations of P wave velocity in the upper mantle beneath these features has been investigated. Teleseismic P wave delays recorded at a 22-station network were used to perform a damped least squares, three-dimensional inversion for these lateral variations. Results infer that a large magmatic source zone exists beneath the Jemez lineament but not beneath the Rio Grande rift. This implies that the volcanic potential of the Jemez lineaments continues to greatly exceed that of the Rio Grande rift. The magmatic source zones of the Jemez lineament are modeled as due to clockwise rotation of the Colorado Plateau about a pole in northeastern Colorado. This rotation caused extension of the lithosphere beneath the Jemez lineament, permitting concentration there of partially melted rock in the upper mantle. -from Authors

  11. Mantle cloaks for elliptical cylinders excited by an electric line source

    DEFF Research Database (Denmark)

    Kaminski, Piotr Marek; Yakovlev, Alexander B.; Arslanagic, Samel

    2016-01-01

    We investigate the ability of surface impedance mantle cloaks for cloaking of elliptical cylinders excited by an electric line source. The exact analytical solution of the problem utilizing Mathieu functions is obtained and is used to derive optimal surface impedances to cloak a number of configu......We investigate the ability of surface impedance mantle cloaks for cloaking of elliptical cylinders excited by an electric line source. The exact analytical solution of the problem utilizing Mathieu functions is obtained and is used to derive optimal surface impedances to cloak a number...

  12. Tracking the evolution of mantle sources with incompatible element ratios in stagnant-lid and plate-tectonic planets

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    Condie, Kent C.; Shearer, Charles K.

    2017-09-01

    The distribution of high field strength incompatible element ratios Zr/Nb, Nb/Th, Th/Yb and Nb/Yb in terrestrial oceanic basalts prior to 2.7 Ga suggests the absence or near-absence of an enriched mantle reservoir. Instead, most oceanic basalts reflect a variably depleted mantle source similar in composition to primitive mantle. In contrast, basalts from hydrated mantle sources (like those associated with subduction) exist from 4 Ga onwards. The gradual appearance of enriched mantle between 2 and 3 Ga may reflect the onset and propagation of plate tectonics around the globe. Prior to 3 Ga, Earth may have been in a stagnant-lid regime with most basaltic magmas coming from a rather uniform, variably depleted mantle source or from a non-subduction hydrated mantle source. It was not until the extraction of continental crust and accompanying propagation of plate tectonics that ;modern type; enriched and depleted mantle reservoirs developed. Consistent with the absence of plate tectonics on the Moon is the near absence of basalts derived from depleted (DM) and enriched (EM) mantle reservoirs as defined by the four incompatible element ratios of this study. An exception are Apollo 17 basalts, which may come from a mixed source with a composition similar to primitive mantle as one end member and a high-Nb component as the other end member. With exception of Th, which requires selective enrichment in at least parts of the martian mantle, most martian meteorites can be derived from sources similar to terrestrial primitive mantle or by mixing of enriched and depleted mantle end members produced during magma ocean crystallization. Earth, Mars and the Moon exhibit three very different planetary evolution paths. The mantle source regions for Mars and the Moon are ancient and have HFS element signatures of magma ocean crystallization well-preserved, and differences in these signatures reflect magma ocean crystallization under two distinct pressure regimes. In contrast, plate

  13. The roles of pyroxenite and peridotite in the mantle sources of oceanic basalts

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    Matzen, Andrew K.; Wood, Bernard J.; Baker, Michael B.; Stolper, Edward M.

    2017-07-01

    Subduction of oceanic crust generates chemical and lithological heterogeneities in the mantle. An outstanding question is the extent to which these heterogeneities contribute to subsequent magmas generated by mantle melting, but the answer differs depending on the geochemical behaviour of the elements under investigation: analyses of incompatible elements (those that preferentially concentrate into silicate melts) suggest that recycled oceanic crust is an important contributor, whereas analyses of compatible elements (those that concentrate in crystalline residues) generally suggest it is not. Recently, however, the concentrations of Mn and Ni--two elements of varying compatibility--in early-crystallizing olivines, have been used to infer that erupted magmas are mixtures of partial melts of olivine-rich mantle rocks (that is, peridotite) and of metasomatic pyroxene-rich mantle rocks (that is, pyroxenite) formed by interaction between partial melts of recycled oceanic crust and peridotite. Here, we test whether melting of peridotite alone can explain the observed trend in olivine compositions by combining new experimental data on the partitioning of Mn between olivine and silicate melt under conditions relevant to basalt petrogenesis with earlier results on Ni partitioning. We show that the observed olivine compositions are consistent with melts of fertile peridotite at various pressures--importantly, melts from metasomatic pyroxenites are not required. Thus, although recycled materials may well be present in the mantle source regions of some basalts, the Mn and Ni data can be explained without such a contribution. Furthermore, the success of modelling the Mn-Ni contents of olivine phenocrysts as low-pressure crystallization products of partial melts of peridotite over a range of pressures implies a simple new approach for constraining depths of mantle melting.

  14. Evidence for two upper mantle sources driving volcanism in Central Kamchatka

    Science.gov (United States)

    Nikulin, Alex; Levin, Vadim; Carr, Michael; Herzberg, Claude; West, Michael

    2012-03-01

    Volcanoes of the Central Kamchatka Depression (CKD) form the most active arc volcano system in the world. Volcanoes of the CKD are positioned ~ 170 km above the subducting Pacific Plate, in excess of the typical global value of ~ 100 km for arc volcanism. We present results of a combined geophysical and petrological study of the main volcanic center in the CKD, and argue for the presence of a second contributing melt source within the mantle wedge. This region of melt generation is separate from the fluid fluxed region above the subducting Pacific Plate; it may explain the presence of the active CKD arc in its current location. Results of receiver function imaging of the upper mantle beneath CKD reveal a distinct area of low velocities at approximately 110 km depth that is clearly distinct from the crust of the subducting Pacific Plate. Results of petrological modeling suggest presence of pyroxenite source melt contribution to CKD lavas, alongside previously described peridotite source melts. We contend that our results advance the notion that melting at two separate sources, rather than the simple flux-induced melting within the mantle wedge, drives volcanoes of the CKD.

  15. Helium-oxygen-osmium isotopic and elemental constraints on the mantle sources of the Deccan Traps

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    Peters, Bradley J.; Day, James M. D.; Greenwood, Richard C.; Hilton, David R.; Gibson, Jennifer; Franchi, Ian A.

    2017-11-01

    The Deccan Traps, a 65 million-year-old continental flood basalt province located in western India, is the result of one of the largest short-lived magmatic events to have occurred on Earth. The nature and composition of its mantle source(s), however, have been difficult to resolve due to extensive assimilation of continental crust into the ascending Traps magmas. To circumvent this issue, using high-precision electron microprobe analysis, we have analyzed olivine grains from MgO-rich (up to 15.7 wt.%) lavas that likely erupted before substantial crustal assimilation occurred. We compare olivine, pyroxene and plagioclase mineral chemistry and He-O-Os isotope compositions with bulk rock major- and trace-element abundances and 187Os/188Os for both bulk-rocks and mineral separates. Helium isotope compositions for the olivine grains generally show strong influence from crustal assimilation (rocks. Despite significant He-Os isotopic variations, Δ17O is relatively invariant (- 0.008 ± 0.014 ‰) and indistinguishable from the bulk mantle, consistent with high-3He/4He hotspots measured to-date. Compositions of olivine grains indicate the presence of up to 25% of a pyroxenite source for Deccan parental magmas, in good agreement with ∼20% predicted from isotopic data for the same samples. Modeled pyroxenite signatures are similar to geochemical signatures expected to arise due to other types of mantle differentiation or due to assimilation of continental crust; however, we show that crustal assimilation cannot account for all of the compositional features of the olivine. Weak correlations exist between a global compilation of Xpx (Deccan: 0.2-0.7) and 3He/4He, δ18O (Deccan olivine: 4.9-5.2‰) and 187Os/188Os. Robust relationships between these parameters may be precluded due to a lack of two-reservoir source mixing, instead involving multiple mantle domains with distinct compositions, or because Xpx may reflect both source features and crustal assimilation

  16. Olivine-hornblende-lamprophyre dikes from Quebrada los Sapos, El Teniente, Central Chile (34°S: implications for the temporal geochemical evolution of the Andean subarc mantle Diques lamprofídicos de olivino-hornblenda de la quebrada los Sapos, El Teniente, Chile central (34°S: implicancias para la evolución temporal de la geoquímica del manto subarco Andino

    Directory of Open Access Journals (Sweden)

    Charles R Stern

    2011-01-01

    their mantle source region. Significantly Sr, Nd and Pb isotopic compositions are independent of SiO2 content for rocks in each age group, which precludes contamination by isotopically heterogeneous Paleozoic and Mesozoic continental crust during evolution of intermediate and silicic rocks from mantle-derived mafic magmas. The Oligocene to Pliocene isotopic evolution of the mantle source of the mafic magmas may be explained by an increase from 1% to 6% in the extent of mantle source region contamination by subducted components, including continental crust tectonically eroded off the continental margin. We attribute this to both decreasing subduction angle and increasing rates of subduction erosión associated with the southward migration of the locus of subduction of the Juan Fernández Ridge. The lamprophyres also imply increased hydration of the mantle below this portion of the are by the Pliocene, which may have played an important role in producing oxidized volatile-rich magmas and mineralization at El Teniente.Diques de lamprófidos mancos, con fenocristales de olivino magnésicos (Fo884-hornblendas y contenidos de Ni -190 ppm y Cr 390 ppm, cortan lavas miocénicas superior en la quebrada los Sapos a escasos kilómetros al oeste del depósito de Cu-Mo El Teniente. Estos diques tienen afinidades petroquímicas con otros diques lamprófidos del Plioceno (2,9-3,9Ma, menos primitivos y sin fenocristales de divinos, los cuales han sido descritos tanto dentro como alrededor de El Teniente. Estos diques de lamprófidos mancos en la quebrada los Sapos, derivados del manto, tienen razones de La/Yb entre 10-13, más altas que la de los más antiguos basaltos de olivino (La/Yb entre 4 y 9 del Complejo Mañeo El Teniente (CMET, sugerente de un decrecimiento temporal de la fusión parcial del manto, y esto es consistente con el volumen decreciente observado de las rocas ígneas en este período de tiempo, como también con el término del magmatismo y la migración hacia >40 km

  17. A primitive mantle source for the Neoarchean mafic rocks from the Tanzania Craton

    Directory of Open Access Journals (Sweden)

    Y.A. Cook

    2016-11-01

    Full Text Available Mafic rocks comprising tholeiitic pillow basalt, dolerite and minor gabbro form the basal stratigraphic unit in the ca. 2.8 to 2.6 Ga Geita Greenstone Belt situated in the NW Tanzania Craton. They outcrop mainly along the southern margin of the belt, and are at least 50 million years older than the supracrustal assemblages against which they have been juxtaposed. Geochemical analyses indicate that parts of the assemblage approach high Mg-tholeiite (more than 8 wt.% MgO. This suite of samples has a restricted compositional range suggesting derivation from a chemically homogenous reservoir. Trace element modeling suggests that the mafic rocks were derived by partial melting within the spinel peridotite field from a source rock with a primitive mantle composition. That is, trace elements maintain primitive mantle ratios (Zr/Hf = 32–35, Ti/Zr = 107–147, producing flat REE and HFSE profiles [(La/Ybpm = 0.9–1.3], with abundances of 3–10 times primitive mantle and with minor negative anomalies of Nb [(Nb/Lapm = 0.6–0.8] and Th [(Th/Lapm = 0.6–0.9]. Initial isotope compositions (ɛNd range from 1.6 to 2.9 at 2.8 Ga and plot below the depleted mantle line suggesting derivation from a more enriched source compared to present day MORB mantle. The trace element composition and Nd isotopic ratios are similar to the mafic rocks outcropping ∼50 km south. The mafic rocks outcropping in the Geita area were erupted through oceanic crust over a short time period, between ∼2830 and ∼2820 Ma; are compositionally homogenous, contain little to no associated terrigenous sediments, and their trace element composition and short emplacement time resemble oceanic plateau basalts. They have been interpreted to be derived from a plume head with a primitive mantle composition.

  18. An olivine-free mantle lithology as a source for mantle-derived magmas: the role of metasomes in the Ethiopian-Arabian large igneous province.

    Science.gov (United States)

    Rooney, T. O.; Nelson, W. R.; Ayalew, D.; Yirgu, G.; Herzberg, C. T.; Hanan, B. B.

    2014-12-01

    Peridotite constitutes most of the Earth's upper mantle, and it is therefore unsurprising that most mantle-derived magmas exhibit evidence of past equilibrium with olivine-dominated source. There is mounting evidence, however, for the role of pyroxenite in magma generation within upwelling mantle plumes; a less documented non-peridotite source of melts are metasomatic veins (metasomes) within the lithospheric mantle. Melts derived from metasomes may exhibit extreme enrichment or depletion in major and trace elements. We hypothesize that phenocrysts such as olivine, which are commonly used to probe basalt source lithology, will reflect these unusual geochemical signals. Here we present preliminary major and trace element analyses of 60 lavas erupted from a small Miocene shield volcano located within the Ethiopian flood basalt province. Erupted lavas are intercalated with lahars and pyroclastic horizons that are overlain by a later stage of activity manifested in small cinder cones and flows. The lavas form two distinctive petrographic and geochemical groups: (A) an olivine-phyric, low Ti group (1.7-2.7 wt. % TiO2; 4.0-13.6 wt. % MgO), which geochemically resembles most of the basalts in the region. These low Ti lavas are the only geochemical unit identified in the later cinder cones and associated lava flows. (B) a clinopyroxene-phyric high Ti group (1-6.7 wt. % TiO2; 1.0-9.5 wt. % MgO), which resembles the Oligocene HT-2 flood basalts. This unit is found intercalated with low Ti lavas within the Miocene shield. In comparison to the low Ti group, the high Ti lavas exhibit a profound depletion in Ni, Cr, Al, and Si, and significant enrichment in Ca, Fe, V, and the most incompatible trace elements. When combined with a diagnostic negative K anomaly in primitive-mantle normalized diagrams and Na2O>K2O, the geochemical data point towards a source which is rich in amphibole, devoid of olivine, and perhaps containing some carbonate. Our preliminary results have identified

  19. Sr, Nd, Pb and Hf isotopic constraints on mantle sources and crustal contaminants in the Payenia volcanic province, Argentina

    DEFF Research Database (Denmark)

    Søager, Nina; Holm, Paul Martin; Thirlwall, Matthew F.

    2015-01-01

    The presented Sr, Nd, Hf and double-spike Pb-isotopic analyses of Quaternary basalts from the Payenia volcanic province in southern Mendoza, Argentina, confirm the presence of two distinct mantle types feeding the Payenia volcanism. The southern Payenia mantle source feeding the intraplate-type Río...... material to the mantle source of the Nevado basalts and the transitional SVZ arc and retroarc rocks and similar degrees of melting throughout this arc segment. A gradual depletion of the pre-metasomatic mantle source going from the backarc over the retroarc to the arc is indicated. The depletion...... is suggested to be caused by step-wise melt extraction due to repeated injections of subduction zone fluids and melts. The lower crustal contamination trends found in the trace element variations of basalt groups from all parts of the Payenia province are also recognized in isotopic space and the dominant...

  20. Evidence for a deep mantle source for EM and HIMU domains from integrated geochemical and geophysical constraints

    Science.gov (United States)

    Jackson, M. G.; Becker, T. W.; Konter, J. G.

    2018-02-01

    Subduction of oceanic and continental crust (and associated sediments) into the mantle over geologic time generates mantle domains with geochemically distinct signatures, referred to as HIMU (high "μ", where μ =238 U/204 Pb) and EM (enriched mantle) domains. Identification of EM and HIMU geochemical signatures in hotspot lavas provides evidence that subducted crustal materials are recycled into the source of hotspots. It remains uncertain where these materials are located in the mantle, and a key question is whether upwelling mantle plumes are required to transport mantle domains with EM and HIMU signatures to the shallow mantle beneath hotspots. Therefore, this study evaluates relationships between extreme EM and HIMU compositions at oceanic hotspots and the presence (or absence) of seismically-constrained mantle plumes beneath the hotspots. We draw on three existing plume catalogs based on global seismic shear-wave velocity models, and these plume catalogs indicate the presence or absence of a plume beneath each of 42 oceanic hotspots. From each hotspot, we select a lava with the highest 206Pb/204Pb composition and one with the lowest 143Nd/144Nd composition. We show that hotspots associated with seismically defined plumes show a greater likelihood of hosting lavas with either extreme EM (143Nd/144Nd ≤ 0.512630) or extreme HIMU (206Pb/204Pb ≥ 20.0) compositions than hotspots not associated with plumes, but HIMU hotspots show a stronger association with plumes than EM hotspots. The significance of the relationship between plumes and extreme geochemical signatures at hotspots improves if extreme EM and HIMU compositions are considered together instead of separately: hotspots sourced by mantle plumes are even more likely to exhibit extreme EM or extreme HIMU signatures than hotspots not sourced by plumes. The significance tests also show that hotspots with extreme EM or HIMU compositions are more likely to be associated with mantle plumes than hotspots that

  1. Effect of Mantle Wedge Hybridization by Sediment Melt on Geochemistry of Arc Magma and Arc Mantle Source - Insights from Laboratory Experiments at High Pressures and Temperatures

    Science.gov (United States)

    Mallik, A.; Dasgupta, R.; Tsuno, K.; Nelson, J. M.

    2015-12-01

    Generation of arc magmas involves metasomatism of the mantle wedge by slab-derived H2O-rich fluids and/or melts and subsequent melting of the modified source. The chemistry of arc magmas and the residual mantle wedge are not only regulated by the chemistry of the slab input, but also by the phase relations of metasomatism or hybridization process in the wedge. The sediment-derived silica-rich fluids and hydrous partial melts create orthopyroxene-rich zones in the mantle wedge, due to reaction of mantle olivine with silica in the fluid/melt [1,2]. Geochemical evidence for such a reaction comes from pyroxenitic lithologies coexisting with peridotite in supra-subduction zones. In this study, we have simulated the partial melting of a parcel of mantle wedge modified by bulk addition of sediment-derived melt with variable H2O contents to investigate the major and trace element chemistry of the magmas and the residues formed by this process. Experiments at 2-3 GPa and 1150-1300 °C were conducted on mixtures of 25% sediment-derived melt and 75% lherzolite, with bulk H2O contents varying from 2 to 6 wt.%. Partial reactive crystallization of the rhyolitic slab-derived melt and partial melting of the mixed source produced a range of melt compositions from ultra-K basanites to basaltic andesites, in equilibrium with an orthopyroxene ± phlogopite ± clinopyroxene ± garnet bearing residue, depending on P and bulk H2O content. Model calculations using partition coefficients (from literature) of trace elements between experimental minerals and silicate melt suggest that the geochemical signatures of the slab-derived melt, such as low Ce/Pb and depletion in Nb and Ta (characteristic slab signatures) are not erased from the resulting melt owing to reactive crystallization. The residual mineral assemblage is also found to be similar to the supra-subduction zone lithologies, such as those found in Dabie Shan (China) and Sanbagawa Belt (Japan). In this presentation, we will also

  2. Iron isotope tracing of mantle heterogeneity within the source regions of oceanic basalts

    OpenAIRE

    Williams, Helen M.; Bizimis, Michael

    2014-01-01

    Mineralogical variations in the Earth's mantle and the relative proportions of peridotitic versus enriched and potentially crustally-derived pyroxenitic domains within the mantle have important implications for mantle dynamics, magma generation, and the recycling of surface material back into the mantle. Here we present iron (Fe) stable isotope data (δ 57Fe, deviation in 57Fe/54Fe from the IRMM-014 standard in parts per thousand) for peridotite and garnet–pyroxenite xenoliths from Oahu, Hawa...

  3. Lead Isotopes in Olivine-Phyric Shergottite Tissint: Implications for the Geochemical Evolution of the Shergottite Source Mantle

    Science.gov (United States)

    Moriwaki, R.; Usui, T.; Simon, J. I.; Jones, J. H.; Yokoyama, T.

    2015-01-01

    Geochemically-depleted shergottites are basaltic rocks derived from a martian mantle source reservoir. Geochemical evolution of the martian mantle has been investigated mainly based on the Rb-Sr, Sm-Nd, and Lu-Hf isotope systematics of the shergottites [1]. Although potentially informative, U-Th- Pb isotope systematics have been limited because of difficulties in interpreting the analyses of depleted meteorite samples that are more susceptible to the effects of near-surface processes and terrestrial contamination. This study conducts a 5-step sequential acid leaching experiment of the first witnessed fall of the geochemically-depleted olivinephyric shergottite Tissint to minimize the effect of low temperature distrubence. Trace element analyses of the Tissint acid residue (mostly pyroxene) indicate that Pb isotope compositions of the residue do not contain either a martian surface or terrestrial component, but represent the Tissint magma source [2]. The residue has relatively unradiogenic initial Pb isotopic compositions (e.g., 206Pb/204Pb = 10.8136) that fall within the Pb isotope space of other geochemically-depleted shergottites. An initial µ-value (238U/204Pb = 1.5) of Tissint at the time of crystallization (472 Ma [3]) is similar to a time-integrated mu- value (1.72 at 472 Ma) of the Tissint source mantle calculated based on the two-stage mantle evolution model [1]. On the other hand, the other geochemically-depleted shergottites (e.g., QUE 94201 [4]) have initial µ-values of their parental magmas distinctly lower than those of their modeled source mantle. These results suggest that only Tissint potentially reflects the geochemical signature of the shergottite mantle source that originated from cumulates of the martian magma ocean

  4. Olivine compositions from the Hawaii Scientific Drilling Project, Phase 2: Evidence for a peridotite mantle source region

    Energy Technology Data Exchange (ETDEWEB)

    Putirka, K D; Ryerson, F J

    2008-10-27

    To the extent that mantle plumes reflect whole mantle convection, Hawaii may provide the clearest window into Earth's lower mantle. Samples from the Hawaii Scientific Drilling Project (HSDP) thus provide valuable tests for models of mantle mineralogy and composition. In this vein, it has been argued recently that Hawaiian olivines, especially those from the shield-building phase as sampled by HSDP, are so high in Ni (Sobolev et al., 2005, 2007), and that Hawaiian whole rocks are so low in CaO (Herzberg, 2006) and high in SiO{sub 2} (Hauri, 1996) that a peridotite mantle source cannot generate such compositions. The Hawaiian plume, so the argument goes, is thus supposedly rich in pyroxenite, and possibly olivine-free. However, comparisons of HSDP olivines to lherzolites, and HSDP whole rocks to lherzolites and partial melting experiments belie these premises. Testable predictions of the pyroxenite model also fail. New comparisons instead show that Hawaiian lavas can be produced from a peridotite source. First, it is unclear that the Hawaiian source is enriched in NiO. The NiO contents of olivines hosted by lherzolites (GEOROC) have the same range as olivines from the HSDP; indeed, the maximum NiO for olivines from lherzolites (0.6 wt.%) is as high as that reported for olivines from any oceanic volcano locality. There is a compositional separation between lherzolite- and HSDP-hosted olivines. But HSDP olivines are not NiO enriched so much as lherzolite olivines are higher in Fo at a given NiO. Lower Fo contents at Hawaii (at a given NiO) ensue because olivine compositions there follow a liquid line of descent, where both Ni and Mg decrease with differentiation. In contrast, subsolidus equilibria involving orthopyroxene enforce a higher and less variable Fo content for lherzolite-derived olivines. Moreover, the pyroxenite mantle model predicts that whole rocks with low CaO and high SiO{sub 2} should host olivines with high NiO. But in HSDP samples, neither

  5. The Upper Mantle Shear Boundary Layer Is The Source Of Midplate Volcanoes

    Science.gov (United States)

    Anderson, D. L.

    2011-12-01

    The lithosphere, lid, low-velocity layer (LVL) and the shallow part of the asthenosphere are all part of the upper boundary layer (BL) of the mantle, which generally overlies the canonical "convecting" upper mantle source (DMM) of ridge basalts. This global BL, Gutenberg's Region B (=BL), extends to ~200-250 km depth under cratons, which is well known, and to comparable depths under oceans, which is not generally appreciated because lid, plate, lithosphere and BL are often (erroneously) equated. A new BL is superposed on top of the pre-existing older one in oceans. The region above 220±20 km depth supports a high thermal gradient and is the most anisotropic and heterogeneous part of the mantle, indicators of thermal and shear BLs. The magnitude of the anisotropy and the velocity drop into the LVL, plus internal reflections, imply a laminated structure probably with refractory harzburgite lamellae coexisting with melt-rich sills, both normally less dense than DMM. This structure is sheared by plate motions causing shear-driven melt segregation into parallel fine-grained shear-bands, shear-driven upwellings, and decoupling and long-term isolation from DMM. The BL is twice as thick and is hotter at the base than canonical petrological and geochemical models based on McKenzie-Bickle-Steins thin-plate assumptions. The lower part of the shear layer (>150 km depth) is almost stationary with respect to plate motions and is ~200 K hotter than plate boundary magmas, features that are often attributed to mantle plumes. The refractory lamellae preserve ancient isotope signatures such as high 3He/4He ala Albarede; the melt-rich lamellae explain the volumes, compositions and locations of midplate volcanoes. BL is the largest (4x larger than D") and most accessible of all proposed geochemical reservoirs and has the required chemical, spatial, scale and thermal attributes. It resolves the Hart-Hanan conundrum concerning the Common Component FOZO; this resides in the shallowest

  6. Calculation of water-bearing primary basalt and estimation of source mantle conditions beneath arcs: PRIMACALC2 model for WINDOWS

    Science.gov (United States)

    Kimura, Jun-Ichi; Ariskin, Alexey A.

    2014-04-01

    We present a new method for estimating the composition of water-bearing primary arc basalt and its source mantle conditions. The PRIMACALC2 model uses a thermodynamic fractional crystallization model COMAGMAT3.72 and runs with an Excel macro to examine the mantle equilibrium and trace element calculations of a primary basalt. COMAGMAT3.72 calculates magma fractionation in 0-10 kb at various compositions, pressure, oxygen fugacity, and water content, but is only applicable for forward calculations. PRIMACALC2 first calculates the provisional composition of a primary basalt from an observed magma. The basalt composition is then calculated by COMAGMAT3.72 for crystallization. Differences in elemental concentrations between observed and the closest-match calculated magmas are then adjusted in the primary basalt. Further iteration continues until the calculated magma composition converges with the observed magma, resulting in the primary basalt composition. Once the fitting is satisfied, back calculations of trace elements are made using stepwise addition of fractionated minerals. Mantle equilibrium of the primary basalt is tested using the Fo-NiO relationship of olivine in equilibrium with the primary basalt, and thus with the source mantle. Source mantle pressure, temperature, and degree of melting are estimated using petrogenetic grids based on experimental data obtained in anhydrous systems. Mantle melting temperature in a hydrous system is computed by adjusting T with a parameterization for a water-bearing system. PRIMACALC2 can be used either in dry or water-bearing arc magmas and is also applicable to mid-ocean ridge basalts and nonalkalic ocean island basalts.

  7. Mantle Source of Cretaceous Seafloor in the Nova-Canton Trough

    Science.gov (United States)

    Pyle, D. G.; Mahoney, J. J.

    2006-12-01

    The Nova-Canton Trough (NCT) is an 8-km-deep abyss that merges with the far western trace of the Clipperton Fracture Zone north-northwest of the Manihiki Plateau. Ocean crust in this region formed during Cretaceous long magnetic normal Chron 34. Larson (Geology, 25, 779) argued that the NCT is part of an aborted rift system that formed between the Ontong Java and Manihiki plume heads, and terminated plateau construction around 120 Ma via drain-off of plume mantle to the region of rifting. Taylor (EPSL, 241, 372) instead proposed the two plateaus formed as one short-lived mega-plateau that broke apart, and that the NCT is part of the post-breakup transform system that separated a series of short spreading segments. Recently, the R.V. Kilo Moana dredged four sites along the prominent north-facing escarpment of the NCT between 168° 06' W and 168° 42' W at ~1° 24' S, and retrieved basalt, diabase, gabbro, pyroxenite, peridotite, serpentinite, breccias and sedimentary rocks. The diversity of rock types recovered demonstrates that a large cross-section through Cretaceous seafloor is exposed. The MgO content of the basalt and diabase samples varies from 8.9-4.3 wt.%. Incompatible element patterns display relative depletions in alteration- resistant large-ion lithophile elements, and most samples have a distinctive hump-shaped REE pattern, with chondrite-normalized (Sm/Yb)n >1.3 and (La/Sm)n values between +8.2 and +7.5. In contrast, data for the Ontong Java and Manihiki plateaus fall well below the Pacific MORB field at lower 206Pb/204Pb and ɛNd < +6.6. Thus, our data provide no evidence for Ontong Java or Manihiki mantle components in the NCT source.

  8. A novel method for sub-arc VMAT dose delivery verification based on portal dosimetry with an EPID.

    Science.gov (United States)

    Cools, Ruud A M; Dirkx, Maarten L P; Heijmen, Ben J M

    2017-11-01

    The EPID-based sub-arc verification of VMAT dose delivery requires synchronization of the acquired electronic portal images (EPIs) with the VMAT delivery, that is, establishment of the start- and stop-MU of the acquired images. To realize this, published synchronization methods propose the use of logging features of the linac or dedicated hardware solutions. In this study, we developed a novel, software-based synchronization method that only uses information inherently available in the acquired images. The EPIs are continuously acquired during pretreatment VMAT delivery and converted into Portal Dose Images (PDIs). Sub-arcs of approximately 10 MU are then defined by combining groups of sequentially acquired PDIs. The start- and stop-MUs of measured sub-arcs are established in a synchronization procedure, using only dosimetric information in measured and predicted PDIs. Sub-arc verification of a VMAT dose delivery is based on comparison of measured sub-arc PDIs with synchronized, predicted sub-arc PDIs, using γ-analyses. To assess the accuracy of this new method, measured and predicted PDIs were compared for 20 clinically applied VMAT prostate cancer plans. The sensitivity of the method for detection of delivery errors was investigated using VMAT deliveries with intentionally inserted, small perturbations (25 error scenarios; leaf gap deviations ≤ 1.5 mm, leaf motion stops during ≤ 15 MU, linac output error ≤ 2%). For the 20 plans, the average failed pixel rates (FPR) for full-arc and sub-arc dose QA were 0.36% ± 0.26% (1 SD) and 0.64% ± 0.88%, based on 2%/2 mm and 3%/3 mm γ-analyses, respectively. Small systematic perturbations of up to 1% output error and 1 mm leaf offset were detected using full-arc QA. Sub-arc QA was able to detect positioning errors in three leaves only during approximately 20 MU and small dose delivery errors during approximately 40 MU. In an ROC analysis, the area under the curve (AUC) for the combined full-arc/sub-arc approach was

  9. Louisville Seamount Chain: Petrogenetic processes and geochemical evolution of the mantle source

    Science.gov (United States)

    Vanderkluysen, Loÿc.; Mahoney, John J.; Koppers, Anthony A. P.; Beier, Christoph; Regelous, Marcel; Gee, Jeffrey S.; Lonsdale, Peter F.

    2014-06-01

    The Louisville Seamount Chain is a ˜4300 km long chain of submarine volcanoes in the southwestern Pacific that spans an age range comparable to that of the Hawaiian-Emperor chain and is commonly thought to represent a hot spot track. Dredging in 2006 recovered igneous rocks from 33 stations on 22 seamounts covering some 49 Myr of the chain's history. All samples are alkalic, similar to previous dredge and drill samples, providing no evidence for a Hawaiian-type tholeiitic shield-volcano stage. Major and trace element variations appear to be predominantly controlled by small but variable extents of fractional crystallization and by partial melting. Isotopic values define only a narrow range, in agreement with a surprising long-term source homogeneity—relative to the length scale of melting—and overlap with proposed fields for the "C" and "FOZO" mantle end-members. Trace element and isotope geochemistry is uncorrelated with either seamount age or lithospheric thickness at the time of volcanism, except for a small number of lavas from the westernmost Louisville Seamounts built on young (Java Plateau, but the Louisville isotopic signature cannot have evolved from a source with isotopic ratios like those measured for Ontong Java Plateau basalts. On the other hand, this signature can be correlated with that of samples dredged from the Danger Islands Troughs of the Manihiki Plateau, which has been interpreted as a rifted fragment of the "Greater" Ontong Java Plateau.

  10. Mixing and Progressive Melting of Deep and Shallow Mantle Sources in the NE Atlantic and Arctic

    DEFF Research Database (Denmark)

    Trønnes, Reidar; Debaille, Vincianne; Erambert, M.

    2013-01-01

    NE Atlantic and Arctic MORB and primitive off-rift basalts in Iceland, Jan Mayen and Spitsbergen (late Quaternary alkaline basalts) record variable geochemical interaction between the asthenospheric mantle (AM), material supplied by the Iceland plume and subcontinental lithospheric mantle (SCLM)....

  11. Re-Os isotope and platinum group elements of a FOcal ZOne mantle source, Louisville Seamounts Chain, Pacific ocean

    Science.gov (United States)

    Tejada, Maria Luisa G.; Hanyu, Takeshi; Ishikawa, Akira; Senda, Ryoko; Suzuki, Katsuhiko; Fitton, Godfrey; Williams, Rebecca

    2015-02-01

    The Louisville Seamount Chain (LSC) is, besides the Hawaiian-Emperor Chain, one of the longest-lived hotspot traces. We report here the first Re-Os isotope and platinum group element (PGE) data for Canopus, Rigil, and Burton Guyots along the chain, which were drilled during IODP Expedition 330. The LSC basalts possess (187Os/188Os)i = 0.1245-0.1314 that are remarkably homogeneous and do not vary with age. A Re-Os isochron age of 64.9 ± 3.2 Ma was obtained for Burton seamount (the youngest of the three seamounts drilled), consistent with 40Ar-39Ar data. Isochron-derived initial 187Os/188Os ratio of 0.1272 ± 0.0008, together with data for olivines (0.1271-0.1275), are within the estimated primitive mantle values. This (187Os/188Os)i range is similar to those of Rarotonga (0.124-0.139) and Samoan shield (0.1276-0.1313) basalts and lower than those of Cook-Austral (0.136-0.155) and Hawaiian shield (0.1283-0.1578) basalts, suggesting little or no recycled component in the LSC mantle source. The PGE data of LSC basalts are distinct from those of oceanic lower crust. Variation in PGE patterns can be largely explained by different low degrees of melting under sulfide-saturated conditions of the same relatively fertile mantle source, consistent with their primitive mantle-like Os and primordial Ne isotope signatures. The PGE patterns and the low 187Os/188Os composition of LSC basalts contrast with those of Ontong Java Plateau (OJP) tholeiites. We conclude that the Re-Os isotope and PGE composition of LSC basalts reflect a relatively pure deep-sourced common mantle sampled by some ocean island basalts but is not discernible in the composition of OJP tholeiites.

  12. A five million year record of compositional variations in mantle sources to magmatism on Santiago, southern Cape Verde archipelago

    DEFF Research Database (Denmark)

    Barker, Abigail K.; Holm, Paul Martin; Peate, David W.

    2010-01-01

    High-precision Pb isotope data and Sr-Nd-Hf isotope data are presented together with major and trace element data for samples spanning the 4.6 Ma history of volcanism at Santiago, in the southern Cape Verde islands. Pb isotope data confirm the positive ¿8/4 signature of the southern islands....... The temporal variations in 208Pb/204Pb reflect minor lateral variations in Th/U of this recycled ocean crust package entering the melting zone beneath the islands. The location of the EM1-like component is more equivocal. A shallow lithospheric location is possible, but this would require a coincidence between...... spatial compositional variations in the lithosphere (EM1 is spatially restricted to the southern islands) and flow lines in the upwelling mantle revealed by seismic anisotropy. Therefore, we favour a deeper asthenospheric mantle source for the EM1-like source...

  13. Continental basalts record the crust-mantle interaction in oceanic subduction channel: A geochemical case study from eastern China

    Science.gov (United States)

    Xu, Zheng; Zheng, Yong-Fei

    2017-09-01

    Continental basalts, erupted in either flood or rift mode, usually show oceanic island basalts (OIB)-like geochemical compositions. Although their depletion in Sr-Nd isotope compositions is normally ascribed to contributions from the asthenospheric mantle, their enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) is generally associated with variable enrichments in the Sr-Nd isotope compositions. This indicates significant contributions from crustal components such as igneous oceanic crust, lower continental crust and seafloor sediment. Nevertheless, these crustal components were not incorporated into the mantle sources of continental basalts in the form of solidus rocks. Instead they were processed into metasomatic agents through low-degree partial melting in order to have the geochemical fractionation of the largest extent to achieve the enrichment of LILE and LREE in the metasomatic agents. Therefore, the mantle sources of continental basalts were generated by metasomatic reaction of the depleted mid-ocean ridge basalts (MORB) mantle with hydrous felsic melts. Nevertheless, mass balance considerations indicate differential contributions from the mantle and crustal components to the basalts. While the depleted MORB mantle predominates the budget of major elements, the crustal components predominate the budget of melt-mobile incompatible trace elements and their pertinent radiogenic isotopes. These considerations are verified by model calculations that are composed of four steps in an ancient oceanic subduction channel: (1) dehydration of the subducting crustal rocks at subarc depths, (2) anataxis of the dehydrated rocks at postarc depths, (3) metasomatic reaction of the depleted MORB mantle peridotite with the felsic melts to generate ultramafic metasomatites in the lower part of the mantle wedge, and (4) partial melting of the metasomatites for basaltic magmatism. The composition of metasomatites is quantitatively dictated by

  14. A high 87Sr 86Sr mantle source for low alkali tholeiite, northern Great Basin

    Science.gov (United States)

    Mark, R.K.; Lee, Hu C.; Bowman, H.R.; Asaro, F.; McKee, E.H.; Coats, R.R.

    1975-01-01

    Olivine tholeiites, the youngest Tertiary units (about 8-11 m.y. old) at five widely spaced localities in northeastern Nevada, are geologically related to the basalts of the Snake River Plain, Idaho, to the north and are similar in major element and alkali chemistry to mid-ocean ridge basalts (MORB) and island arc tholeiites. The measured K (1250-3350 ppm), Rb (1??9-6??2 ppm) and Sr (140-240 ppm) concentrations overlap the range reported for MORB. Three of the five samples have low, unfractionated rare earth element (REE) patterns, the other two show moderate light-REE enrichment. Barium concentration is high and variable (100-780 ppm) and does not correlate with the other LIL elements. The rocks have 87Sr/86Sr = 0??7052-0??7076, considerably higher than MORB (~0??702-0??703). These samples are chemically distinct (i.e. less alkalic) from the olivine tholeiites from the adjacent Snake River Plain, but their Sr isotopic compositions are similar. They contain Sr that is distinctly more radiogenic than the basalts from the adjacent Great Basin. About 10 b.y. would be required for the mean measured Rb/Sr (~ 0??02) of these samples to generate, in a closed system, the radiogenic Sr they contain. The low alkali content of these basalts makes crustal contamination an unlikely mechanism. If the magma is uncontaminated, the time-averaged Rb/Sr of the source material must have been ~0??04. A significant decrease in Rb/Sr of the source material (a factor 2??) thus most probably occurred in the relatively recent (1??09 yr) past. Such a decrease of Rb/Sr in the mantle could accompany alkali depletion produced by an episode of partial melting and magma extraction. In contrast, low 87Sr 86Sr ratios indicate that the source material of the mid-ocean ridge basalts may have been depleted early in the Earth's history. ?? 1975.

  15. The fate of sulfide during decompression melting of peridotite - implications for sulfur inventory of the MORB-source depleted upper mantle

    Science.gov (United States)

    Ding, Shuo; Dasgupta, Rajdeep

    2017-02-01

    mantle can all affect the Cu concentration of primitive MORBs, 100-200 ppm S in the MORB source mantle can satisfy both S and Cu geochemistry of partial melts parental to ocean floor basalts.

  16. The experimental study on the emanation power of a flow-through thoron source made from incandescent gas mantles.

    Science.gov (United States)

    Wang, Yunxiang; Zhang, Lei; Guo, Qiuju

    2017-12-18

    To improve the quality of the calibration of thoron concentration activity measurement, an experimental study on the emanation power of a flow-through thoron source based on incandescent gas mantles was carried out in this paper. The thoron activity concentrations of the outflowed air from the flow-through source were measured using RAD7, and the quantitative relationship between thoron concentrations and flowrates was studied through theoretical analysis, and the thoron emanation powers were obtained from the fitting of the relationship above. Results show that the thoron concentration decreased with the increasing flowrate in the gas path, and the thoron emanation powers of three batches of gas mantles obtained by fitting were 1.33% ± 0.17%, 0.77% ± 0.10% and 0.57% ± 0.07% respectively in low humidity condition. Those results were checked using the gamma spectroscopy method, and were consistent within the error range.

  17. Iron carbide as a source of carbon for graphite and diamond formation under lithospheric mantle P-T parameters

    Science.gov (United States)

    Bataleva, Yuliya V.; Palyanov, Yuri N.; Borzdov, Yuri M.; Bayukov, Oleg A.; Zdrokov, Evgeniy V.

    2017-08-01

    Experimental modeling of natural carbide-involving reactions, implicated in the graphite and diamond formation and estimation of the iron carbide stability in the presence of S-bearing fluids, sulfide melts as well as mantle silicates and oxides, was performed using a multi-anvil high-pressure split-sphere apparatus. Experiments were carried out in the carbide-sulfur (Fe3C-S), carbide-sulfur-oxide (Fe3C-S-SiO2-MgO) and carbide-sulfide (Fe3C-FeS2) systems, at pressure of 6.3 GPa, temperatures in the range of 900-1600 °C and run time of 18-40 h. During the interaction of cohenite with S-rich reduced fluid or pyrite at 900-1100 °C, extraction of carbon from carbide was realized, resulting in the formation of graphite in assemblage with pyrrhotite and cohenite. At higher temperatures complete reaction of cohenite with newly-formed sulfide melt was found to produce metal-sulfide melt with dissolved carbon (Fe64S27C9 (1200 °C)-Fe54S40C6 (1500 °C), at.%), which acted as a crystallization medium for graphite (1200-1600 °C) and diamond growth on seeds (1300-1600 °C). Reactions of cohenite and oxides with S-rich reduced fluid resulted in the formation of graphite in assemblage with highly ferrous orthopyroxene and pyrrhotite (900-1100 °C) or in hypersthene formation, as well as graphite crystallization and diamond growth on seeds in the Fe-S-C melt (1200-1600 °C). We show that the main processes of carbide interaction with S-rich fluid or sulfide melt are recrystallization of cohenite (900-1100 °C), extraction of carbon and iron in the sulfide melt, and graphite formation and diamond growth in the metal-sulfide melt with dissolved carbon. Our results evidence that iron carbide can act as carbon source in the processes of natural graphite and diamond formation under reduced mantle conditions. We experimentally demonstrate that cohenite in natural environments can be partially consumed in the reactions with mantle silicates and oxides, and is absolutely unstable in

  18. A source-sink model of the generation of plate tectonics from non-Newtonian mantle flow

    Science.gov (United States)

    Bercovici, David

    1995-01-01

    A model of mantle convection which generates plate tectonics requires strain rate- or stress-dependent rheology in order to produce strong platelike flows with weak margins as well as strike-slip deformation and plate spin (i.e., toroidal motion). Here, we employ a simple model of source-sink driven surface flow to determine the form of such a rheology that is appropriate for Earth's present-day plate motions. In this model, lithospheric motion is treated as shallow layer flow driven by sources and sinks which correspond to spreading centers and subduction zones, respectively. Two plate motion models are used to derive the source sink field. As originally implied in the simpler Cartesian version of this model, the classical power law rheologies do not generate platelike flows as well as the hypothetical Whitehead-Gans stick-slip rheology (which incorporates a simple self-lubrication mechanism). None of the fluid rheologies examined, however, produce more than approximately 60% of the original maximum shear. For either plate model, the viscosity fields produced by the power law rheologies are diffuse, and the viscosity lows over strike-slip shear zones or pseudo-margins are not as small as over the prescribed convergent-divergent margins. In contrast, the stick-slip rheology generates very platelike viscosity fields, with sharp gradients at the plate boundaries, and margins with almost uniformly low viscosity. Power law rheologies with high viscosity contrasts, however, lead to almost equally favorable comparisons, though these also yield the least platelike viscosity fields. This implies that the magnitude of toroidal flow and platelike strength distributions are not necessarily related and thus may present independent constraints on the determination of a self-consistent plate-mantle rheology.

  19. An assessment of the record in compositional variations from mantle source to magmatism at East Island, Crozet archipelago

    Science.gov (United States)

    Meyzen, C. M.; Marzoli, A.; Bellieni, G.

    2013-12-01

    The Crozet archipelago, located midway between Madagascar and Antarctica, constitutes the emerged part of the easternmost bank of the Crozet plateau, which lies upon upper Cretaceous oceanic seafloor derived from the Southeast Indian Ridge. It forms an elongated chain of five islands and islets, divided into two groups: an older eastern island group (islands) and a younger western one (islands. The whole region exhibits some of the most typical gravimetric, seismic and bathymetric characteristics associated with upwelling hotter than average mantle including: a geoid high, a topographic swell, a deep low-velocity zone (up to 2350 km), an anomalous heat flow and a thickened crust (10-16.5 km). Most of these features are exacerbated by the near stationary absolute motion of the Antarctic plate. However, since thirty years, the chemical composition of Crozet archipelago magmas has beneficiated from little interest compared to that of other Earth's hotspots. Because of the occurrence of both a thick and old lithosphere and of a near stagnant absolute plate motion, new data from the Crozet archipelago magmatic record will provide new critical perspective on oceanic island building processes. The data presented here are based on a basaltic suite of ~ 25 samples collected by a 'Terres Australes et Antarctiques Francaises' expedition in 1969 from the northern part of East Island. Our alkali basalts from the Crozet archipelago are distinct from other oceanic within-plate magmatic rocks in showing ubiquitous large depletions in LILE with respect to other incompatible elements, although these rocks constitute one of the most incompatible-element-enriched suites among Earth's oceanic island basalts (OIB). The similarity of their trace element ratios and parallelism of their rare earth element patterns indicate: (1) a mantle source homogeneity over at least 1 Ma; (2) an uniformity of the melting conditions (i.e. degree of melting and residual mineralogy) during most of the sub

  20. 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.

  1. Mafic dikes at Kahel Tabelbala (Daoura, Ougarta Range, south-western Algeria): New insights into the petrology, geochemistry and mantle source characteristics

    Science.gov (United States)

    Mekkaoui, Abderrahmane; Remaci-Bénaouda, Nacéra; Graïne-Tazerout, Khadidja

    2017-09-01

    New petrological, geochemical and Sr-Nd isotopic data of the Late Triassic and Early Jurassic Kahel Tabelbala (KT) mafic dikes (south-western Algeria) offer a unique opportunity to examine the nature of their mantle sources and their geodynamic significance. An alkaline potassic Group 1 of basaltic dikes displaying relatively high MgO, TiO2, Cr and Ni, La/YbN ∼ 15, coupled with low 87Sr/86Sri ∼ 0.7037 and relatively high ɛNd(t) ∼ +3, indicates minor olivine and clinopyroxene fractionation and the existence of a depleted mantle OIB source. Their parental magma was generated from partial melting in the garnet-lherzolite stability field. A tholeiitic Group 2 of doleritic dikes displaying low MgO, Cr and Ni contents, La/YbN ∼ 5, positive Ba, Sr and Pb anomalies, the absence of a negative Nb anomaly coupled with moderate 87Sr/86Sri ∼ 0.7044 and low ɛNd(t) ∼ 0 (BSE-like), indicates a contamination of a mantle-derived magma that experienced crystal fractionation of plagioclase and clinopyroxene. This second group, similar to the low-Ti tholeiitic basalts of the Central Atlantic Magmatic Province (CAMP), was derived from partial melting in the peridotite source within the spinel stability field. Lower Mesozoic continental rifting could have been initiated by a heterogeneous mantle plume that supplied source components beneath Daoura, in the Ougarta Range.

  2. Insights into mantle heterogeneities: mid-ocean ridge basalt tapping an ocean island magma source in the North Fiji Basin

    Science.gov (United States)

    Brens, R., Jr.; Jenner, F. E.; Bullock, E. S.; Hauri, E. H.; Turner, S.; Rushmer, T. A.

    2015-12-01

    stability field of garnet and/or spinel lherzolite, suggesting that the source of these lavas may stem from MORB mixing with an enriched plume (OIB) source. The discovery of these magmatic signatures beneath the North Fiji Basin is important in understanding the heterogeneities of volatiles in the mantle, in addition to linking deeper mantle and subsurface crustal processes.

  3. Enrichments of the mantle sources beneath the Southern Volcanic Zone (Andes) by fluids and melts derived from abraded upper continental crust

    DEFF Research Database (Denmark)

    Holm, Paul Martin; Søager, Nina; Dyhr, Charlotte Thorup

    2014-01-01

    mantle by means of subduction erosion in response to the northward increasingly strong coupling of the converging plates. Both types of enrichment had the same Pb isotope composition in the TSVZ with no significant component derived from the subducting oceanic crust. Pb–Sr–Nd isotopes indicate a major......, was dominated by fluids which enriched a pre-metasomatic South Atlantic depleted MORB mantle type asthenosphere. The second enrichment was by melts having the characteristics of upper continental crust (UCC), distinctly different from Chile trench sediments. We suggest that granitic rocks entered the source...

  4. Elemental and Sr-Nd-Pb isotope geochemistry of the Cenozoic basalts in Southeast China: Insights into their mantle sources and melting processes

    Science.gov (United States)

    Sun, Pu; Niu, Yaoling; Guo, Pengyuan; Ye, Lei; Liu, Jinju; Feng, Yuexing

    2017-02-01

    We analyzed whole-rock major and trace elements and Sr-Nd-Pb isotopes of the Cenozoic basalts in Southeast China to investigate their mantle source characteristics and melting process. These basalts are spatially associated with three extensional fault systems parallel to the coast line. After correction for the effect of olivine microlites on bulk-rock compositions and the effect of crystal fractionation, we obtained primitive melt compositions for these samples. These primitive melts show increasing SiO2, Al2O3 but decreasing FeO, MgO, TiO2, P2O5, CaO and CaO/Al2O3 from the interior to the coast. Such spatial variations of major element abundances and ratios are consistent with a combined effect of fertile source compositional variation and increasing extent and decreasing pressure of decompression melting from beneath the thick lithosphere in the interior to beneath the thin lithosphere in the coast. These basalts are characterized by incompatible element enrichment but varying extent of isotopic depletion. This element-isotope decoupling is most consistent with recent mantle source enrichment by means of low-degree melt metasomatism that elevated incompatible element abundances without yet having adequate time for isotopic ingrowth in the mantle source regions. Furthermore, Sr and Nd isotope ratios show significant correlations with Nb/Th, Nb/La, Sr/Sr* and Eu/Eu*, which substantiates the presence of recycled upper continental crustal material in the mantle sources of these basalts. Pb isotope ratios also exhibit spatial variation, increasing from the interior to the coastal area. The significant correlations of major element abundances with Pb isotope ratios indicate that the Pb isotope variations also result from varied extent and pressure of decompression melting. We conclude that the elevated Pb isotope ratios from the interior to coast are consistent with increasing extent of decompression melting of the incompatible element depleted mantle matrix, which

  5. Petrogenesis of nephelinites from the Tarim Large Igneous Province, NW China: Implications for mantle source characteristics and plume-lithosphere interaction

    Science.gov (United States)

    Cheng, Zhiguo; Zhang, Zhaochong; Hou, Tong; Santosh, M.; Zhang, Dongyang; Ke, Shan

    2015-04-01

    The nephelinite exposed in the Wajilitage area in the northwestern margin of the Tarim large igneous province (TLIP), Xinjiang, NW China display porphyritic textures with clinopyroxene, nepheline and olivine as the major phenocryst phases, together with minor apatite, sodalite and alkali feldspar. The groundmass typically has cryptocrystalline texture and is composed of crystallites of clinopyroxene, nepheline, Fe-Ti oxides, sodalite, apatite, rutile, biotite, amphibole and alkali feldspar. We report rutile SIMS U-Pb age of 268 ± 30 Ma suggesting that the nephelinite may represent the last phase of the TLIP magmatism, which is also confirmed by the field relation. The nephelinite shows depleted Sr-Nd isotopic compositions with age-corrected 87Sr/86Sr and εNd(t) values of 0.70348-0.70371 and + 3.28 to + 3.88 respectively indicating asthenospheric mantle source. Based on the reconstructed primary melt composition, the depth of magma generation is estimated as 115-140 km and the temperatures of mantle melting as 1540-1575 °C. The hotter than normal asthenospheric mantle temperature suggests the involvement of mantle thermal plume. The Mg isotope values display a limited range of δ26Mg from - 0.35 to - 0.55‰, which are lower than the mantle values (- 0.25‰). The Mg isotopic compositions, combined with the Sr-Nd isotopes and major and trace element data suggest that the Wajilitage nephelinite was most likely generated by low-degree partial melting of the hybridized carbonated peridotite/eclogite source, which we correlate with metasomatism by subducted carbonates within the early-middle Paleozoic convergent regime. A plume-lithosphere model is proposed with slight thinning of the lithosphere and variable depth and degree of melting of the carbonated mantle during the plume-lithosphere interaction. This model also accounts for the variation in lithology of the TLIP.

  6. Lithium isotope evidence for subduction-enriched mantle in the source of mid-ocean-ridge basalts.

    Science.gov (United States)

    Elliott, Tim; Thomas, Alex; Jeffcoate, Alistair; Niu, Yaoling

    2006-10-05

    'Recycled' crustal materials, returned from the Earth's surface to the mantle by subduction, have long been invoked to explain compositional heterogeneity in the upper mantle. Yet increasingly, problems have been noted with this model. The debate can be definitively addressed using stable isotope ratios, which should only significantly vary in primitive, mantle-derived materials as a consequence of recycling. Here we present data showing a notable range in lithium isotope ratios in basalts from the East Pacific Rise, which correlate with traditional indices of mantle heterogeneity (for example, 143Nd/144Nd ratios). Such co-variations of stable and radiogenic isotopes in melts from a normal ridge segment provide critical evidence for the importance of recycled material in generating chemical heterogeneity in the upper mantle. Contrary to many models, however, the elevated lithium isotope ratios of the 'enriched' East Pacific Rise lavas imply that subducted ocean crust is not the agent of enrichment. Instead, we suggest that fluid-modified mantle, which is enriched during residency in a subduction zone, is mixed back into the upper mantle to cause compositional variability.

  7. Noble gas data from Goldfield and Tonopah epithermal Au-Ag deposits, ancestral Cascades Arc, USA: Evidence for a primitive mantle volatile source

    Science.gov (United States)

    Manning, Andrew H.; Hofstra, Albert H.

    2017-01-01

    The He, Ne, and Ar isotopic composition of fluid inclusions in ore and gangue minerals were analyzed to determine the source of volatiles in the high-grade Goldfield and Tonopah epithermal Au-Ag deposits in southwestern Nevada, USA. Ar and Ne are mainly atmospheric, whereas He has only a minor atmospheric component. Corrected 3He/4He ratios (with atmospheric He removed) range widely from 0.05 to 35.8 times the air 3He/4He ratio (RA), with a median of 1.43 RA. Forty-one percent of measured 3He/4He ratios are ≥4 RA, corresponding to ≥50% mantle He assuming a mantle ratio of 8 RA. These results suggest that mafic magmas were part of the magmatic-hydrothermal system underlying Goldfield and Tonopah, and that associated mantle-sourced volatiles may have played a role in ore formation. The three highest corrected 3He/4He ratios of 17.0, 23.7, and 35.8 RAindicate a primitive mantle He source and are the highest yet reported for any epithermal-porphyry system and for the Cascades arc region. Compiled 3He/4He measurements from epithermal-porphyry systems in subduction-related magmatic arcs around the world (n = 209) display a statistically significant correlation between 3He/4He and Au-Ag grade. The correlation suggests that conditions which promote higher fluid inclusion 3He/4He ratios (abundance of mantle volatiles and focused upward volatile transport) have some relation to conditions that promote higher Au-Ag grades (focused flow of metal-bearing fluids and efficient chemical traps). Results of this and previous investigations of He isotopes in epithermal-porphyry systems are consistent with the hypothesis posed in recent studies that mafic magmas serve an important function in the formation of these deposits.

  8. Mantle and Crustal Sources of Carbon, Nitrogen, and Noble gases in Cascade-Range and Aleutian-Arc Volcanic gases

    Science.gov (United States)

    Symonds, Robert B.; Poreda, Robert J.; Evans, William C.; Janik, Cathy J.; Ritchie, Beatrice E.

    2003-01-01

    Here we report anhydrous chemical (CO2, H2S, N2, H2, CH4, O2, Ar, He, Ne) and isotopic (3He/4He, 40Ar/36Ar, δ13C of CO2, δ13C of CH4, δ15N) compositions of virtually airfree gas samples collected between 1994 and 1998 from 12 quiescent but potentially restless volcanoes in the Cascade Range and Aleutian Arc (CRAA). Sample sites include ≤173°C fumaroles and springs at Mount Shasta, Mount Hood, Mount St. Helens, Mount Rainier, Mount Baker, Augustine Volcano, Mount Griggs, Trident, Mount Mageik, Aniakchak Crater, Akutan, and Makushin. The chemical and isotopic data generally point to magmatic (CO2, Ar, He), shallow crustal sedimentary (hereafter, SCS) (CO2, N2, CH4), crustal (He), and meteoric (N2, Ar) sources of volatiles. CH4 clearly comes from SCS rocks in the subvolcanic systems because CH4 cannot survive the higher temperatures of deeper potential sources. Further evidence for a SCS source for CH4 as well as for non-mantle CO2 and non-meteoric N2 comes from isotopic data that show wide variations between volcanoes that are spatially very close and similar isotopic signatures from volcanoes from very disparate areas. Our results are in direct opposition to many recent studies on other volcanic arcs (Kita and others, 1993; Sano and Marty, 1995; Fischer and others, 1998), in that they point to a dearth of subducted components of CO2 and N2 in the CRAA discharges. Either the CRAA volcanoes are fundamentally different from volcanoes in other arcs or we need to reevaluate the significance of subducted C and N recycling in convergent-plate volcanoes.

  9. New age (ca. 2970 Ma), mantle source composition and geodynamic constraints on the Archean Fiskenæsset anorthosite complex, SW Greenland

    DEFF Research Database (Denmark)

    Polat, A; Frei, Robert; Scherstén, Anders

    2010-01-01

    rocks collectively yield an Sm–Nd errorchron age of 2973 ± 28 Ma (MSWD = 33), with an average initial eNd = + 3.3 ± 0.7, consistent with a long-term depleted mantle source. Regression of Pb isotope data define an age of 2945 ± 36 Ma (MSWD = 44); and the regression line intersects the average growth...... is proposed to explain the evolution of the Fiskenæsset Complex. Stage 1 represents the formation of depleted shallow mantle source > 3000 Ma (eNd = + 3.3 ± 0.7) for the complex. Stage 2 corresponds to the development of an intra-oceanic island arc between 3000–2950 Ma. Stage 3 is characterized...

  10. Seismic tomography model reveals mantle magma sources of recent volcanic activity at El Hierro Island (Canary Islands, Spain)

    Science.gov (United States)

    García-Yeguas, Araceli; Ibáñez, Jesús M.; Koulakov, Ivan; Jakovlev, Andrey; Romero-Ruiz, M. Carmen; Prudencio, Janire

    2014-12-01

    We present a 3-D model of P and S velocities beneath El Hierro Island, constructed using the traveltime data of more than 13 000 local earthquakes recorded by the Instituto Geográfico Nacional (IGN, Spain) in the period from 2011 July to 2012 September. The velocity models were performed using the LOTOS code for iterative passive source tomography. The results of inversion were thoroughly verified using different resolution and robustness tests. The results reveal that the majority of the onshore area of El Hierro is associated with a high-velocity anomaly observed down to 10-12-km depth. This anomaly is interpreted as the accumulation of solid igneous rocks erupted during the last 1 Myr and intrusive magmatic bodies. Below this high-velocity pattern, we observe a low-velocity anomaly, interpreted as a batch of magma coming from the mantle located beneath El Hierro. The boundary between the low- and high-velocity anomalies is marked by a prominent seismicity cluster, thought to represent anomalous stresses due to the interaction of the batch of magma with crust material. The areas of recent eruptions, Orchilla and La Restinga, are associated with low-velocity anomalies surrounding the main high-velocity block. These eruptions took place around the island where the crust is much weaker than the onshore area and where the melted material cannot penetrate. These results put constraints on the geological model that could explain the origin of the volcanism in oceanic islands, such as in the Canaries, which is not yet clearly understood.

  11. Petrologic evaluation of Pliocene basaltic volcanism in Eastern Anatolian region, Turkey: Evidence for mixing of melts derived from both shallow and deep mantle sources

    Science.gov (United States)

    Oyan, Vural; Özdemir, Yavuz; Keskin, Mehmet; Güleç, Nilgün

    2017-04-01

    Collision-related Neogene volcanism in the Eastern Anatolia region (EAR) began after the continent-continent collision between the Arabia and the Eurasia plates, and spreads in a wide zone from the Erzurum-Kars Plateau in the northeast to the Karacadaǧ in the south. Volcanic activity in the EAR started 15 Ma ago (Middle Miocene) in the south of the region. Voluminous basaltic lavas from local eruption centers formed basaltic lava plateaus and volcanic cones as a result of high production level of volcanism during the Pliocene time interval. Our dating results (Ar-Ar and K-Ar) indicate that age of this Late Miocene-Pliocene magmatic activity range between 6 and 3.5 Ma. Volcanic products contain alkaline and subalkaline lavas, ranging in composition from basalts to andesites and trachyandesites. Our EC-AFC and AFC modeling, based on trace element and Sr, Nd, Pb isotopic compositions, suggests about 2-7 % crustal contamination in the evolved andesites and trachyandesites. MORB and primitive mantle normalized patterns of the lavas and isotopic compositions imply that alkaline and subalkaline basalts erupted in Pliocene time interval in the EAR could have been derived from a mantle source that had previously been enriched by a clear subduction component. A partial melting model was conducted to evaluate partial melting processes in the mantle source of the Pliocene basalts. Our melting model calculations suggest that basaltic melts in the EAR could have been produced by melting of mantle sources containing spinel, garnet and amphibole with melting degree in the range of 0.7-7%. The products of mixing of these derivative melts are the Pliocene basaltic lavas of the Eastern Anatolian Region.

  12. Geochemistry of Woranso-Mille Pliocene basalts from west-central Afar, Ethiopia: Implications for mantle source characteristics and rift evolution

    Science.gov (United States)

    Alene, Mulugeta; Hart, William K.; Saylor, Beverly Z.; Deino, Alan; Mertzman, Stanley; Haile-Selassie, Yohannes; Gibert, Luis B.

    2017-06-01

    The Woranso-Mille (WORMIL) area in the west-central Afar, Ethiopia, contains several Pliocene basalt flows, tuffs, and fossiliferous volcaniclastic beds. We present whole-rock major- and trace-element data including REE, and Sr-Nd-Pb isotope ratios from these basalts to characterize the geochemistry, constrain petrogenetic processes, and infer mantle sources. Six basalt groups are distinguished stratigraphically and geochemically within the interval from 3.8 to 3 Ma. The elemental and isotopic data show intra- and inter-group variations derived primarily from source heterogeneity and polybaric crystallization ± crustal inputs. The combined Sr-Nd-Pb isotope data indicate the involvement of three main reservoirs: the Afar plume, depleted mantle, and enriched continental lithosphere (mantle ± crust). Trace element patterns and ratios further indicate the basalts were generated from spinel-dominated shallow melting, consistent with significantly thinned Pliocene lithosphere in western Afar. The on-land continuation of the Aden rift into western Afar during the Pliocene is reexamined in the context of the new geochemistry and age constraints of the WORMIL basalts. The new data reinforce previous interpretations that progressive rifting and transformation of the continental lithosphere to oceanic lithosphere allows for increasing asthenospheric inputs through time as the continental lithosphere is thinned.

  13. Amphiboles as indicators of mantle source contamination: Combined evaluation of stable H and O isotope compositions and trace element ratios

    NARCIS (Netherlands)

    Demény, A.; Harangi, S.; Vennemann, T.W.; Casillas, R.; Horváth, P.; Milton, A.J.; Mason, P.R.D.; Ulianov, A.

    2012-01-01

    Stable isotope and trace element compositions of igneous amphiboles from different tectonic settings (ocean island basalts, intraplate alkaline basalts, subduction-related andesitic complexes) were compiled to help understand the role of fluids and melts in subduction-related mantle metasomatism

  14. Scales of mantle heterogeneity

    Science.gov (United States)

    Moore, J. C.; Akber-Knutson, S.; Konter, J.; Kellogg, J.; Hart, S.; Kellogg, L. H.; Romanowicz, B.

    2004-12-01

    and Pb), we correlated isotopic data from oceanic islands and seamounts with geophysical measurements and observations in order to determine whether the mantle source component end-members are related to geophysical structure. For this, data obtained from the GeoROC database and other sources were first carefully examined for consistency and then correlated with recent global upper mantle tomographic models of seismic attenuation and velocity structure. Complementing this approach is a fractal analysis of dynamical models of mantle mixing. A variety of published numerical mixing models show a fractal distribution of heterogeneities, consistent with a marble-cake mantle.

  15. Louisville seamount subduction and its implication on mantle flow beneath the central Tonga-Kermadec arc.

    Science.gov (United States)

    Timm, Christian; Bassett, Daniel; Graham, Ian J; Leybourne, Matthew I; de Ronde, Cornel E J; Woodhead, Jon; Layton-Matthews, Daniel; Watts, Anthony B

    2013-01-01

    Subduction of intraplate seamounts beneath a geochemically depleted mantle wedge provides a seldom opportunity to trace element recycling and mantle flow in subduction zones. Here we present trace element and Sr, Nd and Pb isotopic compositions of lavas from the central Tonga-Kermadec arc, west of the contemporary Louisville-Tonga trench intersection, to provide new insights into the effects of Louisville seamount subduction. Elevated (206)Pb/(204)Pb, (208)Pb/(204)Pb, (86)Sr/(87)Sr in lavas from the central Tonga-Kermadec arc front are consistent with localized input of subducted alkaline Louisville material (lavas and volcaniclastics) into sub-arc partial melts. Furthermore, absolute Pacific Plate motion models indicate an anticlockwise rotation in the subducted Louisville seamount chain that, combined with estimates of the timing of fluid release from the subducting slab, suggests primarily trench-normal mantle flow beneath the central Tonga-Kermadec arc system.

  16. Geochemistry of olivine-hosted melt inclusions in the Baekdusan (Changbaishan) basalts: Implications for recycling of oceanic crustal materials into the mantle source

    Science.gov (United States)

    Choi, Hyun-Ok; Choi, Sung Hi; Schiano, Pierre; Cho, Moonsup; Cluzel, Nicolas; Devidal, Jean-Luc; Ha, Kyoochul

    2017-07-01

    We determined the major and trace element concentrations of olivine-hosted melt inclusions in basalts from the active Baekdusan volcano situated on the border between China and North Korea in order to understand better the nature of the mantle source and the geodynamic processes that gave rise to volcanism at this site. Rehomogenized melt inclusions (after 'Fe-loss' correction) can be divided into three groups: a low-Si alkaline group, a high-Si alkaline group, and a high-Si sub-alkaline group. The low-Si group is composed of picrobasalt to basanite, and the high-Si group consists of (trachy)basalt to basaltic (trachy)andesite. The low-Si group has generally higher TiO2, CaO, and P2O5, but lower Al2O3, Na2O, and K2O contents at a given MgO concentration compared with those in the high-Si group. The CaO and P2O5 contents are positively correlated, indicating the presence of a calcium phosphate, probably tuite [γ-Ca3(PO4)2], in the source. The melt inclusions are enriched in light rare earth elements [(La/Yb)N = 7.8-30.4]. On a primitive-mantle-normalized incompatible element plot, the low-Si group has positive anomalies in Ba and P compared with typical oceanic island basalt (OIB). On the other hand, the high-Si group exhibits remarkable positive anomalies in Eu, Ba, Rb, K, Pb, P, and Ti, implying that K-hollandite and tuite are essential phases in the source. The high-Si subalkaline group has lower abundances of incompatible elements than the high-Si alkaline group, reflecting different degrees of partial melting from the same source. In contrast to OIB, Baekdusan magmatism is characterized by positively fractionated (Zr/Hf)N ratios, and is best approximated by admixture of partial melts derived from both clinopyroxene-rich eclogite and garnet peridotite. Intraplate volcanism in northeastern Asia is closely associated with deep subduction of the Pacific plate. The subducting Pacific slab flattens and stagnates in the mantle transition zone under northeastern Asia

  17. Correlated Os-Pb-Nd-Sr isotopes in the Austral-Cook chain basalts: the nature of mantle components in plume sources

    Science.gov (United States)

    Schiano, P.; Burton, K. W.; Dupré, B.; Birck, J.-L.; Guille, G.; Allègre, C. J.

    2001-04-01

    Osmium (Os), strontium (Sr), neodymium (Nd) and lead (Pb) isotopes have been measured on a suite of aphyric basalts from 12 islands of the Austral-Cook island archipelago, an area which exhibits a range in Pb isotope compositions that encompasses almost the entire range displayed by ocean island basalts (OIB). Although the samples have Os concentrations (1.69-34.80 ppt) at the lower end of the range measured for OIB, they display a range of initial 187Os/188Os ratios (between 0.1279 and 0.1594) similar to that defined by olivine-phyric, Os-rich OIB. Positive Os-Nd, Os-Pb and negative Os-Sr isotope correlations are documented, indicating that the isotopic arrays represent various proportions of mixing between a HIMU-type end-member represented by Mangaia and Tubuai islands and characterized by radiogenic Os and Pb isotopic compositions, and an end-member represented by Rarotonga island which is characterized by unradiogenic Os and intermediate Sr, Nd and Pb isotopic compositions. The HIMU signature of the mantle component involved in Tubuai-Mangaia mantle sources requires long-term enrichments of U and Th relative to Pb and Re relative to Os, without associated increase in Rb/Sr, that are consistent with recycled oceanic crust. The end-member represented by Rarotonga basalts shows Os, Sr, Nd, and Pb isotopic signatures similar to those presumed for the 'bulk silicate earth' (BSE), which cannot be obtained by mixing the four mantle components (DMM, HIMU and EM1 and 2) generally used to circumscribe the Sr-Nd-Pb isotopic data of OIB. The primitive-like isotopic characters of this end-member might be ascribed to the presence of undepleted material from a lower segment of the mantle in the source of the Austral-Cook island basalts (and more specifically Rarotonga basalts); however, such a hypothesis is challenged by both the absence of a primordial 3He signature and the non-primitive Ce/Pb and Nb/U values for the Austral-Cook island basalts. Alternatively, assuming that

  18. Different degrees of partial melting of the enriched mantle source for Plio-Quaternary basic volcanism, Toprakkale (Osmaniye) Region, Southern Turkey

    DEFF Research Database (Denmark)

    Bagci, U; Alpaslan, M; Frei, Robert

    2011-01-01

    ) Ba, Th and U, and show light rare earth element (LREE) enrichment relative to heavy rare earth element (HREE) on primitive mantle trace and rare earth element patterns that indicate different partial melting of the same source. The isotopic 87Sr/86Sr ratio is relatively low (0.703534 –0......The Toprakkale (Osmaniye) region, located in the Yumurtalik fault zone in southern Turkey, contains Quaternary volcanic rocks, shown by their mineralogical and petrographical features to be alkali basaltic and basanitic. These alkaline rocks are enriched in the large ion lithophile elements (LILE...

  19. Variation in the mantle sources of the northern Izu arc with time and space — Constraints from high-precision Pb isotopes

    Science.gov (United States)

    Ishizuka, Osamu; Taylor, Rex N.; Milton, J. Andy; Nesbitt, Robert W.; Yuasa, Makoto; Sakamoto, Izumi

    2006-09-01

    We present new ages and geochemical data for back-arc lavas from the northern Izu Bonin arc 33 35° N including high-precision double-spike Pb isotope measurements. The northern part of the Izu Bonin arc is distinct from the rest of the arc as it lacks active rifting behind the volcanic front but it does have Quaternary volcanoes (e.g. Niijima). However, in common with the rest of the arc the northern section has back-arc seamount chains and NE SW volcanic ridges. 40Ar/39Ar dating of volcanic rocks has revealed that Quaternary volcanism is limited to within 40 km of the volcanic front. Miocene and Pliocene volcanism extended as far as 120 km west of the current volcanic front along the back-arc seamounts and ridges. The chemical characteristics of back-arc volcanism are significantly different in the Pliocene Quaternary compared to the Miocene. Opx cpx andesite and hornblende andesite are dominant in Miocene volcanic centres, while Pliocene and Quaternary centres are characterized by basalt and rhyolite. Miocene volcanic centres show a marked correlation between Th/Ce and Pb and Nd isotopes. Generally, these lavas have higher Δ7/4 and lower 143Nd/144Nd with increasing Th/Ce. In contrast, the Pliocene and Quaternary lavas show little, if any, Th enrichment relative to potential mantle sources and no correlation with isotopes. These correlations suggest that partial melt of sediment from the subducting slab was an important component in the Miocene, whereas, the Pliocene Quaternary volcanic centres show little evidence of sediment melt and are restricted to a contribution of fluid from altered oceanic crust and fluid from sediment. Quaternary volcanoes at similar distances from the volcanic front are calculated to have similar compositions and amounts of slab-derived fluid in their sources. However, on Pb Pb isotope plots, they lie closer to the NHRL towards south (i.e., Δ8/4 decreases towards south). Almost parallel but distinct trends on Pb Pb plots imply

  20. Dynamical geochemistry of the mantle

    Directory of Open Access Journals (Sweden)

    G. F. Davies

    2011-09-01

    Full Text Available The reconciliation of mantle chemistry with the structure of the mantle inferred from geophysics and dynamical modelling has been a long-standing problem. This paper reviews three main aspects. First, extensions and refinements of dynamical modelling and theory of mantle processing over the past decade. Second, a recent reconsideration of the implications of mantle heterogeneity for melting, melt migration, mantle differentiation and mantle segregation. Third, a recent proposed shift in the primitive chemical baseline of the mantle inferred from observations of non-chondritic 142Nd in the Earth. It seems most issues can now be resolved, except the level of heating required to maintain the mantle's thermal evolution.

    A reconciliation of refractory trace elements and their isotopes with the dynamical mantle, proposed and given preliminary quantification by Hofmann, White and Christensen, has been strengthened by work over the past decade. The apparent age of lead isotopes and the broad refractory-element differences among and between ocean island basalts (OIBs and mid-ocean ridge basalts (MORBs can now be quantitatively accounted for with some assurance.

    The association of the least radiogenic helium with relatively depleted sources and their location in the mantle have been enigmatic. The least radiogenic helium samples have recently been recognised as matching the proposed non-chondritic primitive mantle. It has also been proposed recently that noble gases reside in a so-called hybrid pyroxenite assemblage that is the result of melt from fusible pods reacting with surrounding refractory peridotite and refreezing. Hybrid pyroxenite that is off-axis may not remelt and erupt at MORs, so its volatile constituents would recirculate within the mantle. Hybrid pyroxenite is likely to be denser than average mantle, and thus some would tend to settle in the D" zone at the base of the mantle, along with some old subducted

  1. A common Pan-African Lithospheric Mantle (PALM) source for HIMU-like Pb-isotope signatures in circum-Mediterranean magmas

    Science.gov (United States)

    Young, H. P.; Wang, Z.; Brandon, M. T.

    2013-12-01

    conjugate margin of the Atlantic. Its distribution completely overlaps with the distribution of EAR rocks. We therefore propose that the previously termed European Asthenospheric Reservoir (EAR) is actually the Pan-African Lithospheric Mantle (PALM), which is a direct source of alkalic-basaltic melts. A mechanism for the generation of melts from an ancient, veined sub-continental lithospheric mantle is the advection of heat by melts generated in the asthenosphere as a result of extensional decompression which infiltrate or underplate the lithosphere, or alternatively heating by advection of hotter mantle such as by a plume. Cebria, J., and Wilson, M., 1995, Cenozoic mafic magmatism in Western/Central Europe: a common European asthenospheric reservoir: Terra Nova, v. 7, p. 162. Médard, E., Schmidt, M. W., Schiano, P., and Ottolini, L., 2006, Melting of Amphibole-bearing Wehrlites: an Experimental Study on the Origin of Ultra-calcic Nepheline-normative Melts: Journal of Petrology, v. 47, no. 3, p. 481-504. Pilet, S., Baker, M. B., Müntener, O., and Stolper, E. M., 2011, Monte Carlo simulations of metasomatic enrichment in the lithosphere and implications for the source of alkaline basalts: Journal of Petrology, v. 52, no. 7-8, p. 1415-1442. Zindler, A., and Hart, S., 1986, Chemical geodynamics: Annual review of earth and planetary sciences, v. 14, p. 493-571.

  2. Genesis of Ultra-High Pressure Garnet Pyroxenite in Orogenic Peridotites and its bearing on the Isotopic Chemical Heterogeneity in the Mantle Source of Oceanic Basalts

    Science.gov (United States)

    Varas Reus, María Isabel; Garrido, Carlos J.; Marchesi, Claudio; Bosch, Delphine; Hidas, Károly

    2017-04-01

    The genesis of ultra-high pressure (UHP) garnet pyroxenites in orogenic peridotite massifs and its implications on the formation of chemical heterogeneities in the mantle and on basalt petrogenesis are still not fully understood. Some UHP (diamond-bearing) garnet pyroxenites have isotopic, and major and trace element compositions similar to the recycled oceanic crustal component observed in oceanic basalts [1-6]. These pyroxenites hence provide an exceptional opportunity to investigate in situ the nature and scale of the Earth's mantle chemical heterogeneities. Here, we present an integrated geochemical study of UHP garnet pyroxenites from the Ronda (Betic Belt, S. Spain) and Beni Bousera (Rif Belt, N. Morocco) peridotite massifs. This investigation encompasses, in the same sample, bulk rock major and trace elements, as well as Sr-Nd-Pb-Hf isotopic analyses. According to their Al2O3 content, we classify UHP garnet pyroxenites into three groups that have distinct trace elements and Sr-Nd-Pb-Hf isotopic signatures. Group A pyroxenites (Al2O3: 15 - 17.5 wt. %) are characterized by low initial 87Sr/86Sr, relatively high 143Nd/144Nd, 206Pb/204Pb and 176Hf/177Hf ratios, and highly variable 207Pb/204Pb and 208Pb/204Pb ratios. Group B pyroxenites (Al2O3 element, and isotopic compositions of the studied Ronda and Beni Bousera UHP garnet pyroxenites lend support to the "Marble Cake Mantle" model [7] for the genesis of these pyroxenites. This model envisions the mantle source of oceanic basalts as a mélange of subducted, ancient oceanic crust —-represented by garnet pyroxenites in orogenic peridotites—- intimately mixed with peridotites by mantle convection. The present study reveals, however, that besides this exotic component of ancient recycled oceanic crust, the genesis of these pyroxenites requires a previously unnoticed component of recycled lower continental crust akin to the lower crustal section of the lithosphere where these UHP garnet pyroxenites now reside in

  3. Evolution of the mantle source in an evolving arc-backarc system (Torres del Paine, Patagonia): Evidence from Hf isotopes in zircon

    Science.gov (United States)

    Ewing, T. A.; Muntener, O.; Leuthold, J.; Baumgartner, L. P.; Putlitz, B.; d'Abzac, F. X.; Chiaradia, M.

    2015-12-01

    The Miocene Torres del Paine intrusive complex (TPIC) in Patagonia is a transitional alkaline backarc intrusion1 emplaced on short timescales of 162 ± 11 ka2. It is subdivided into two units with distinct ages of ~12.6 Ma and ~12.45 Ma1. Smaller intrusive bodies in the area record a change in chemistry from calc-alkaline at ~16 Ma, to transitional alkaline at ~12.5 Ma. Zircons from ~16 Ma intrusives and the 12.6 Ma part of the TPIC have remarkably consistent, slightly enriched Hf isotope compositions with ɛHf(i) of -1 to +2. An abrupt shift towards more juvenile Hf isotope compositions is observed in the ~12.45 Ma part of the TPIC, with ɛHf(i) of +3 to +6. Bulk rock Nd and Sr isotopes for the TPIC show the same shift towards more juvenile compositions at this time1. The long-term consistency of ɛHf(i) from 16 to 12.6 Ma is surprising, given that in the same period the bulk rock chemistry changes from calc-alkaline to transitional alkaline. Conversely, the major shift in ɛHf(i) is not correlated with any change in bulk rock chemistry, which remains transitional alkaline from 12.6 to 12.45 Ma. The decoupling of major element chemical evolution and Hf isotope signatures suggests that the subsequent rapid influx of juvenile material recorded by our Hf isotope data must have occurred by renewed mantle melting. Subduction of the Chile ridge at ~12.5 Ma in this area caused arc magmatism to move westwards and back-arc extension to initiate. We propose that the first TPIC magmas (12.6 Ma) came from a mantle wedge with a residual subduction signature. Subsequent melting of more juvenile mantle, less contaminated by a subduction component, generated the 12.45 Ma TPIC magmas. These results demonstrate that magmatic complexes such as the TPIC may tap distinct mantle sources even on very short timescales, fingerprinting arc-backarc transition processes. 1Leuthold et al., 2013, JPET, 54: 273-303 2Leuthold et al., 2012, EPSL, 325: 85-92

  4. Longevity of Yellowstone hotspot volcanism: Isotopic evidence linking the Siletzia LIP (56 Ma) and early Columbia River Basalt Group (17 Ma) mantle sources

    Science.gov (United States)

    Pyle, D. G.; Duncan, R. A.; Wells, R. E.; Graham, D. W.; Hanan, B. B.; Harrison, B. K.; Haileab, B.

    2015-12-01

    Siletzia is a Paleocene-Eocene accreted terrane of submarine and subaerially erupted mafic lavas exposed in the Cascadia forearc. This large igneous province [LIP] is exposed in multiple volcanic sections from Vancouver Island, B.C., to southern Oregon [~700 km]. We estimate Siletzia magmatism at ~2.3 x 106 km3 west of the Cascades and may reach 4.6 x 106 km3 if correlative with Alaskan Yakutat terrane and significant portions of the LIP filled the Oregon Embayment. 40Ar-39Ar ages show the bulk of Siletzia erupted over a 6-7 Myr interval beginning at 56 Ma, implying eruption rates of 0.3-0.7 km3/yr. In Oregon, Siletz River volcanism began in the south [56-53 Ma] and migrated northward [54-50 Ma]. Concurrent eruptions of Metchosin and Crescent basalts do not show a southerly age progression. Therefore, Siletzia likely erupted south of the Kula-Farallon spreading center with ridge collision at or north of the Metchosin igneous complex. Isotopic data for 29 Siletzia lavas have initial 7/6Sr 0.7030-0.7037, ΕNd +4.9 - +7.7, 6/4Pb 18.70-19.94, 7/4Pb 15.49-15.63 and 8/4Pb 38.27-39.53. Olivine yield 3He/4He from 9.4 to 13.7 (R/Ra) and high MgO lavas display a narrow 187Os/188Os range (0.131-0.134) when age corrected. Both He and Os tracers are elevated above typical depleted MORB mantle and indicate plume involvement. Pb-Pb and Pb-Nd arrays suggest 3 mantle components for Siletzia volcanism: a depleted source with isotopic and trace element characteristics expected for spreading center lavas (i.e., Ku-Fa) influenced by a plume, a HIMU contaminant (i.e., high 6/4Pb; low 7/6Sr) confined to southern Siletzia, and a plume source (6/4Pb 19.00; 7/4Pb 15.55; 8/4Pb 38.60; 7/6Sr; 0.7033; ΕNd +6.4; γOs +5.0). Siletzia plume mantle is a close match to recent Yellowstone plume estimates based on early CRBG lavas. Mounting geophysical and geochemical evidence supports the contention that Siletzia is an early product of the Yellowstone hot spot in a sub-oceanic setting.

  5. Ultra-Refractory Domains in the Oceanic Lithosphere: Evidence from Major Element and Modal Relationships in Mantle Xenoliths from Ocean Islands

    Science.gov (United States)

    Neumann, E.; Simon, N. S.; Bonadiman, C.; Coltorti, M.; Delpech, G.; Gregoire, M.

    2007-12-01

    We have compiled a database for major element and modal data of mantle harzburgite and lherzolite xenoliths from different ocean islands. The xenoliths fall in two main categories. Xenoliths showing no petrographic evidence of metasomatism (OI1) from the Canary Islands, Kerguelen, Cape Verde and Samoa are ultra-depleted spinel harzburgites. These xenoliths formed by high degrees of partial melting leading to total exhaustion of cpx. Small amounts of cpx observed in these rocks (mainly fertilization). Unradiogenic Os isotopes and high Re-Os model ages suggest that OI1 and OI1cpx rocks from some islands are much older than the abyssal lithosphere in which they are found. P-T estimates of 0.7-1.3 GPa and 850- 1200°C indicate that the OI1 xenoliths last equilibrated at depths corresponding to >80 Ma old oceanic lithospheric mantle. We interpret the ultra-depleted xenoliths as fragments of material trapped in the oceanic mantle lithosphere. Major element similarities to some series of oceanic sub-arc mantle, and significant differences from continental xenolith series, makes it most likely that the ultra-refractory OI1 peridotites represent recycled abyssal mantle. The large proportion of ultra-refractory peridotite xenoliths in ocean islands, and the presence of such rocks also along some mid-ocean ridges and in sub-arc mantle, suggest that ultra-refractory material may be important ingredients in the convecting mantle. Because of their ultra-depleted chemistry the OI1 type harzburgites will have relatively low densities and are therefore buoyant relative to less refractory mantle rock types. Their high solidus temperatures make the OI1 xenoliths immune to further partial melting (sterile).

  6. Petrogenesis of postcollisional magmatism at Scheelite Dome, Yukon, Canada: Evidence for a lithospheric mantle source for magmas associated with intrusion-related gold systems

    Science.gov (United States)

    Mair, John L.; Farmer, G. Lang; Groves, David I.; Hart, Craig J.R.; Goldfarb, Richard J.

    2011-01-01

    The type examples for the class of deposits termed intrusion-related gold systems occur in the Tombstone-Tungsten belt of Alaska and Yukon, on the eastern side of the Tintina gold province. In this part of the northern Cordillera, extensive mid-Cretaceous postcollisional plutonism took place following the accretion of exotic terranes to the continental margin. The most cratonward of the resulting plutonic belts comprises small isolated intrusive centers, with compositionally diverse, dominantly potassic rocks, as exemplified at Scheelite Dome, located in central Yukon. Similar to other spatially and temporally related intrusive centers, the Scheelite Dome intrusions are genetically associated with intrusion-related gold deposits. Intrusions have exceptional variability, ranging from volumetrically dominant clinopyroxene-bearing monzogranites, to calc-alkaline minettes and spessartites, with an intervening range of intermediate to felsic stocks and dikes, including leucominettes, quartz monzonites, quartz monzodiorites, and granodiorites. All rock types are potassic, are strongly enriched in LILEs and LREEs, and feature high LILE/HFSE ratios. Clinopyroxene is common to all rock types and ranges from salite in felsic rocks to high Mg augite and Cr-rich diopside in lamprophyres. Less common, calcic amphibole ranges from actinolitic hornblende to pargasite. The rocks have strongly radiogenic Sr (initial 87Sr/86Sr from 0.711-0.714) and Pb isotope ratios (206Pb/204Pb from 19.2-19.7), and negative initial εNd values (-8.06 to -11.26). Whole-rock major and trace element, radiogenic isotope, and mineralogical data suggest that the felsic to intermediate rocks were derived from mafic potassic magmas sourced from the lithospheric mantle via fractional crystallization and minor assimilation of metasedimentary crust. Mainly unmodified minettes and spessartites represent the most primitive and final phases emplaced. Metasomatic enrichments in the underlying lithospheric mantle

  7. Zircon Hf isotopic constraints on the mantle source of felsic magmatic rocks in the Phan Si Pan uplift and Tu Le basin, northern Vietnam

    Science.gov (United States)

    Usuki, T.; Lan, C.; Tran, T.; Pham, T.; Wang, K.

    2013-12-01

    Permian plume-related rocks, such as picrites, flood basalts and silicic volcanic rocks occur in northern Vietnam. This area was displaced 600 km southeastward along the Ailao Shan-Red River fault during mid-Tertiary in response to the India-Eurasia collision. The original location of the area was situated at the central Emeishan Large Igneous Province (ELIP) in SW China before Tertiary. The picrites and flood basalts in northern Vietnam have been investigated by many authors and are comparable with the ELIP. While, felsic magmatisms in northern Vietnam has been poorly studied. Zircon U-Pb age and Hf isotopic data are useful to compare the felsic magmatism in northern Vietnam with that in the ELIP, because the magmatisms of the ELIP had a characteristic time period (260-250 Ma) and the Hf isotopes show a remarkable mantle signature. Therefore, this study carried out in-situ U-Pb ages and Hf isotopic compositions for 300 zircon grains in eighteen granitoids and rhyolites in Phan Si Pan uplift and Tu Le basin in northern Vietnam. Zircons from the granitoids and rhyolites occasionally show development of {101} pyramid and {100} prism crystal facies, suggesting typical zircons crystallized from high temperature alkaline granite. 206Pb/238U ages of granitoid and rhyolite yield consistently in a narrow range of 260 to 250 Ma, which coincides with those from peralkaline to metaluminous granites in the ELIP. ɛHf(t) values of zircons in rhyolites and granites of this study dominate in the range of +5 to +10, which is consistent with those from the ELIP. U-Pb ages and Hf isotopic compositions of zircons indicate that felsic magmatic rocks in the Phan Si Pan uplift and Tu La basin have been derived from the same mantle source with the ELIP.

  8. An integrated chemical and oxygen isotopic study of primitive olivine grains in picrites from the Emeishan Large Igneous Province, SW China: Evidence for oxygen isotope heterogeneity in mantle sources

    Science.gov (United States)

    Yu, Song-Yue; Shen, Neng-Ping; Song, Xie-Yan; Ripley, Edward M.; Li, Chusi; Chen, Lie-Meng

    2017-10-01

    Recognition of the nature of potential mantle sources of continental flood basalts is complicated by possible overprinting related to crustal contamination as magmas migrate to the surface (Arndt and Christensen, 1992). However, in picritic lava flows primitive olivine phenocrysts that formed early in the crystallization sequence can potentially provide unperturbed information of their mantle source. We have carried out an integrated chemical and oxygen isotopic (in situ SIMS) study of primitive olivine grains (Fo ranging from 88 to 92.6 mol%) in the Emeishan picrites at different locations (Wulongba, Wuguijing, Tanglanghe and Maoniuping). We use these data to evaluate the geochemical nature of mantle sources for magmas from which the primitive olivine crystallized. The primitive olivine grains in the samples from Maoniuping, Wuguijing and Tanglanghe are characterized by mantle-like δ18O values (mean values are 5.1 ± 0.3‰ (2σ, n = 53), 5.2 ± 0.3‰ (2σ, n = 122) and 5.3 ± 0.3‰ (n = 25), respectively) coupled with generally low Fo contents (mean values are 88.7 ± 1.4 mol% (2σ, n = 53), 89.8 ± 1.8 mol% (2σ, n = 122) and 89.4 ± 1.8 mol% (2σ, n = 25), respectively). In contrast, the olivine grains in the samples from Wulongba are characterized by elevated δ18O values (mean = 5.6 ± 0.3‰ (2σ, n = 58)) coupled with generally higher Fo contents (mean = 91 ± 2.8 mol% (2σ, n = 58)) than primitive olivine in the samples from the other locations. Based on olivine compositions, primitive olivine in picrites from Maoniuping, Tanglanghe and Wuguijing are consistent with derivation from hybrid mantle sources containing similar proportions of peridotite and pyroxenite/eclogite components. The δ18O values of these primitive olivine grains are consistent with melting of plume source materials. The chemical composition of the primitive olivine from Wulongba are also consistent with derivation from a hybrid peridotite/pyroxenite source, but the high δ18O values

  9. Preserving noble gases in a convecting mantle.

    Science.gov (United States)

    Gonnermann, Helge M; Mukhopadhyay, Sujoy

    2009-05-28

    High (3)He/(4)He ratios sampled at many ocean islands are usually attributed to an essentially undegassed lower-mantle reservoir with high (3)He concentrations. A large and mostly undegassed mantle reservoir is also required to balance the Earth's (40)Ar budget, because only half of the (40)Ar produced from the radioactive decay of (40)K is accounted for by the atmosphere and upper mantle. However, geophysical and geochemical observations suggest slab subduction into the lower mantle, implying that most or all of Earth's mantle should have been processed by partial melting beneath mid-ocean ridges and hotspot volcanoes. This should have left noble gases in both the upper and the lower mantle extensively outgassed, contrary to expectations from (3)He/(4)He ratios and the Earth's (40)Ar budget. Here we suggest a simple solution: recycling and mixing of noble-gas-depleted slabs dilutes the concentrations of noble gases in the mantle, thereby decreasing the rate of mantle degassing and leaving significant amounts of noble gases in the processed mantle. As a result, even when the mass flux across the 660-km seismic discontinuity is equivalent to approximately one lower-mantle mass over the Earth's history, high (3)He contents, high (3)He/(4)He ratios and (40)Ar concentrations high enough to satisfy the (40)Ar mass balance of the Earth can be preserved in the lower mantle. The differences in (3)He/(4)He ratios between mid-ocean-ridge basalts and ocean island basalts, as well as high concentrations of (3)He and (40)Ar in the mantle source of ocean island basalts, can be explained within the framework of different processing rates for the upper and the lower mantle. Hence, to preserve primitive noble gas signatures, we find no need for hidden reservoirs or convective isolation of the lower mantle for any length of time.

  10. Mantle-derived sources of syenites from the A-type igneous suites - New approach to the provenance of alkaline silicic magmas

    Science.gov (United States)

    Litvinovsky, B. A.; Jahn, B. M.; Eyal, M.

    2015-09-01

    Granite is generally dominant in A-type igneous suites but these frequently include also alkali feldspar- and peralkaline- syenite and quartz syenite. Such syenites can provide essential information about magma sources and mode of generation of A-type silicic magma. This paper addresses the petrogenesis of syenites based on comparisons between the Mongolian-Transbaikalian Belt, Russia (MTB), and the northern Arabian-Nubian Shield (ANS) as exposed in the Sinai Peninsula, Egypt and adjacent areas of southern Israel. The syenitic rocks from MTB and ANS are characterized by high alkali content (Na2O + K2O = 10.5 to 12.5 wt.%) and are assigned to alkaline metaluminous and peralkaline granitoids. Peralkaline syenites are generally richer in Na and contain slightly less K and Ba than are metaluminous granitoids. REE abundances are similar in all types of syenites. The Eu/Eu* ratios range commonly from 0.35 to 0.65, although higher values, up to 1.15, attributed to presence of accumulated Afs and minor Pl, also occur in some plutons. The geochemical and Sr-Nd isotope characteristics of associated syenite, granite and monzogabbro from five igneous suites ( 80 samples) suggest that the main rock types, silicic and mafic, are cogenetic in each suite. Syenite magmas were produced from mantle-derived source with little, if any silicic crustal component. The generation of abundant A-type granite and syenite magmas in the young juvenile crust (ANS) argues that old continental crust is not required for generation of highly alkaline silicic magmas, as commonly advocated. The most probable source of both syenite and granite was mantle-derived K-rich shoshonitic monzogabbro. The bimodal character of the A-type suites suggests that partial melting of monzogabbro, rather than fractional crystallization of basic magma, accompanied with enrichment of a cumulate phase in the mafic units, was the dominant mode of granitoid magma formation. Granite magmas were produced in the lower crust at

  11. Source contamination and tectonomagmatic signals of overlapping Early to Middle Miocene orogenic magmas associated with shallow continental subduction and asthenospheric mantle flows in Western Anatolia: A record from Simav (Kütahya) region

    Science.gov (United States)

    Çoban, Hakan; Karacık, Zekiye; Ece, Ömer Işık

    2012-05-01

    The disappearances of mafic shoshonitic and ultrapotassic magma prior to Late Oligocene in Western Anatolia post-collisional tectonic settings, and the sudden appearance of Early-Middle Miocene potassic lavas with orogenic geochemical signatures, indicate a striking change of mantle sources during the Early-Middle Miocene period, and require a special explanation. In this regard, the Simav (Kütahya) region of Western Anatolia represents a critical area, where the Early-Middle Miocene mafic potassic (shoshonite, absarokite, ultrapotassic) and high-K calc-alkaline (andesite, dacite-rhyolite, granite) series rocks overlap in the extensional geotectonic setting in a back-arc position. The appraisal of petrological data obtained from Simav igneous complex indicates that there is a remarkable geochemical and isotopic similarity (e.g., negative Eu anomalies; Nb-Ta depletions; high Sr, low Nd and variable Pb isotope compositions) between coevally generated mafic potassic and high-K calc-alkaline magma series. The near primitive mafic potassic (MHKS) lavas with high Sr isotope compositions require a heterogeneous mantle source contaminated with crustal materials. Dragged and delaminated crustal components, caused by shallow continental subduction and the late arrived subducted terrigenous sediments from the Aegean trench are likely candidate sources of continental materials incorporated into the mantle source of the Simav mafic potassic (MHKS) magmas. The nature of these components also played a significant role in the compositional variations of Simav mafic series rocks. The Simav mafic potassic (MHKS) magmas were derived from a crust-contaminated, subduction-modified (metasomatized) EM-II type mantle source, interacting with influxed asthenosphere in a back-arc mantle wedge, whereas mixing of lower crustal silicic melts with underplated potassic mafic magmas resulted in coeval high-K calc-alkaline rocks, matched by the extent of crustal contamination observed in the more

  12. Multiple carbon and nitrogen sources associated with the parental mantle fluids of fibrous diamonds from Diavik, Canada, revealed by SIMS microanalysis

    Science.gov (United States)

    Petts, D. C.; Stachel, T.; Stern, R. A.; Hunt, L.; Fomradas, G.

    2016-02-01

    Fibrous diamonds are often interpreted as direct precipitates of primary carbonate-bearing fluids in the lithospheric mantle, sourced directly from common reservoirs of "mantle" carbon and nitrogen. Here we have examined fibrous growth layers in five diamonds (as three rims or "coats" and two whole-crystal cuboids) from the Diavik Diamond Mine, Canada, using in situ C- and N-isotope and N-abundance measurements to investigate the origin and evolution of their parental fluids, and in particular, to test for isotopic variability within a suite of fibrous diamonds. High-resolution growth structure information was gleaned from cathodoluminescence (CL) imaging and, in combination with the isotopic data, was used to assess the nature of the transition from gem to fibrous growth in the coated diamonds. The two cuboids are characterized by fine concentric bands of fibrous and/or milky opaque diamond, with one sample (S1719) having intermittent gem-like growth layers that are transparent and colourless. The three coated diamonds comprise octahedral gem cores mantled by massive or weakly zoned fibrous rims, with sharp and well-defined gem-fibrous boundaries. For the two cuboid samples, δ 13C and δ 15N values were -7.7 to -3.2 ‰ (mean -6.3 ± 1.3 ‰; 1 SD; n = 84) and -5.6 to -2.1 ‰ (mean -4.0 ± 0.8 ‰; 1 SD; n = 48), respectively. The three fibrous rims have combined δ 13C values of -8.3 to -4.8 ‰ (mean -6.9 ± 0.7 ‰; 1 SD; n = 113) and δ 15N values of -3.8 to -1.9 ‰ (mean -2.7 ± 0.4 ‰; 1 SD; n = 43). N-abundances of the combined cuboid-fibrous rim dataset range from 339 to 1714 at. ppm. The gem cores have δ 13C and δ 15N values of -5.4 to -3.5 ‰ and -17.7 to +4.5 ‰, respectively, and N-abundances of 480 to 1699 at. ppm. Broadly uniform C- and N-isotope compositions were observed in each of the gem cores (variations of ~<1 ‰ for carbon and ~<3 ‰ for nitrogen). This limited C- and N- isotope variability implies that the gem cores formed from

  13. Nitrogen evolution within the Earth's atmosphere-mantle system assessed by recycling in subduction zones

    Science.gov (United States)

    Mallik, Ananya; Li, Yuan; Wiedenbeck, Michael

    2018-01-01

    Understanding the evolution of nitrogen (N) across Earth's history requires a comprehensive understanding of N's behaviour in the Earth's mantle - a massive reservoir of this volatile element. Investigation of terrestrial N systematics also requires assessment of its evolution in the Earth's atmosphere, especially to constrain the N content of the Archaean atmosphere, which potentially impacted water retention on the post-accretion Earth, potentially causing enough warming of surface temperatures for liquid water to exist. We estimated the proportion of recycled N in the Earth's mantle today, the isotopic composition of the primitive mantle, and the N content of the Archaean atmosphere based on the recycling rates of N in modern-day subduction zones. We have constrained recycling rates in modern-day subduction zones by focusing on the mechanism and efficiency of N transfer from the subducting slab to the sub-arc mantle by both aqueous fluids and slab partial melts. We also address the transfer of N by aqueous fluids as per the model of Li and Keppler (2014). For slab partial melts, we constrained the transfer of N in two ways - firstly, by an experimental study of the solubility limit of N in melt (which provides an upper estimate of N uptake by slab partial melts) and, secondly, by the partitioning of N between the slab and its partial melt. Globally, 45-74% of N introduced into the mantle by subduction enters the deep mantle past the arc magmatism filter, after taking into account the loss of N from the mantle by degassing at mid-ocean ridges, ocean islands and back-arcs. Although the majority of the N in the present-day mantle remains of primordial origin, our results point to a significant, albeit minor proportion of mantle N that is of recycled origin (17 ± 8% or 12 ± 5% of N in the present-day mantle has undergone recycling assuming that modern-style subduction was initiated 4 or 3 billion years ago, respectively). This proportion of recycled N is enough to

  14. Lead isotope constraints on the mantle sources involved in the genesis of Mesozoic high-Ti tholeiite dykes (Urubici type from the São Francisco Craton (Southern Espinhaço, Brazil

    Directory of Open Access Journals (Sweden)

    Leila Soares Marques

    Full Text Available ABSTRACT: The first results of Pb isotope compositions of the high-Ti Mesozoic dykes of the Southern Espinhaço are presented. The results do not show large variations and are significantly more radiogenic than the Pb isotope compositions of the high-Ti tholeiites from the Paraná Continental Flood Basalts. The data combined with published geochemical and Sr-Nd isotope results rule out crustal contamination processes in the genesis of the dykes, requiring magma generation in metasomatized subcontinental lithospheric mantle with the involvement of HIMU-type and carbonatite components. The magmas may have been also derived from a mantle source containing ~4 - 5% of pyroxenite and ~1% of carbonatite melts, agreeing with published Os isotope compositions of high-Ti rocks from the Paraná Continental Flood Basalts. These metasomatizing agents could be responsible for mantle source refertilization, as was also proposed in the literature to explain the characteristics of xenoliths of the Goiás Alkaline Province, which also occurs in the border of the São Francisco Craton. Additionally, to evaluate the risks of Pb contamination during sample preparation for analysis, several experimental tests were accomplished, which indicate the need of sawed surface removal and a careful washing of small-sized rock fragments before powdering, especially for rocks with [Pb] < 7 µg/g.

  15. Pb, Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, Yoichi; Tatsumoto, Mitsunobu (Geological Survey, Denver, CO (USA))

    1988-12-01

    Sr, Nd, and Pb isotopic compositions were measured in alkane volcanic rocks from the South Cook Islands and the Austral Islands. The results show that the Cook-Austral rocks have an extremely wide range in isotopic compositions of Pb: {sup 206}Pb/{sup 204}Pb from 18.25 to 21.76, {sup 207}Pb/{sup 204}Pb from 15.48 to 15.83, and {sup 208}Pb/{sup 204}Pb from 38.37 to 40.62, whereas isotopic compositions of Sr and Nd are less variable. Isotopically, Mangaia, Rimatara, and Rurutu form one group, which shows extremely ratiogenic Pb isotopic compositions but near-MORB (mid-ocean ridge basalts) values for Sr and Nd isotopic ratios. In contrast, samples from Aitutaki, Rarotonga, Mauke, and Atiu (Aitutaki group) have high {sup 207}Pb/{sup 204}Pb and {sup 208}Pb/{sup 204}Pb and moderately high {sup 87}Sr/{sup 86}Sr (Dupal anomaly). The Aitutaki group could have been derived from heterogeneous mantle plumes, which rose from the enriched deep mantle (the almost primitive lower mantle or recycled continental and oceanic slabs). On the other hand, the Mangaia component could have been derived from the depleted upper mantle which may have been metasomatized with a Co{sub 2}-rich fluid, as indicated by the near-MORB values of Sr and Nd isotopes. Although Pb isotopic data of the two groups cannot be distinguished from each other statistically, the end components of the Pb-Pb system do not match with those of the Nd-Sr system. Thus, the data must be explained by a multi-, at least three, component mixing model: the mantle plumes, metasomatized upper mantle, and lithosphere. The K-Ar ages and isotopic characteristics of the Cook-Austral rocks indicate that if one mantle plume rises from the deep mantle in this region, it has separated into at least two segments on the way to the surface.

  16. Pb, Nd, and Sr isotopic evidence for a multicomponent source for rocks of Cook-Austral Islands and heterogeneities of mantle plumes

    Science.gov (United States)

    Nakamura, Y.; Tatsumoto, M.

    1988-01-01

    Sr, Nd, and Pb isotopic compositions were measured in alkaline volcanic rocks (alkali basalt, ankaramite, nephelinite, phonolite, and trachyte) from the South Cook Islands (Aitutaki, Mauke, Rarotonga, Atiu, and Mangaia) and the Austral Islands (Rimatara and Rurutu). The results show that the Cook-Austral rocks have an extremely wide range in isotopic compositions of Pb: 206Pb 204Pb from 18.25 to 21.76, 207pb 204pb from 15.48 to 15.83, and sol208pb 204Pb from 38.37 to 40.62, whereas isotopic compositions of Sr and Nd are less variable. Isotopically, Mangaia, Rimatara, and Rurutu form one group (Mangaia group), which shows extremely radiogenic Pb isotopic compositions but near-MORB (mid-oceanic ridge basalts) values for Sr and Nd isotopic ratios. In contrast, samples from Aitutaki, Rarotonga, Mauke, and Atiu (Aitutaki group) have high 207Pb 204Pb and 208Pb 204Pb and moderately high 87Sr 86Sr (Dupal anomaly). The Aitutaki group could have been derived from heterogeneous mantle plumes, which rose from the enriched deep mantle (the almost primitive lower mantle or recycled continental and oceanic slabs). On the other hand, the Mangaia component could have been derived from the depleted upper mantle which may have been metasomatized with a CO2-rich fluid, as indicated by the near-MORB values of Sr and Nd isotopes. Although Pb isotopic data of the two groups cannot be distinguished from each other statistically, the end components of the Pb-Pb system do not match with those of the Nd-Sr system. Thus, the data must be explained by a multi-, at least three, component mixing model: the mantle plumes (Dupal component and a recycled oceanic slab), metasomatized upper mantle, and lithosphere. The K-Ar ages and isotopic characteristics of the Cook-Austral rocks indicate that if one mantle plume rises from the deep mantle in this region, it has separated into at least two segments on the way to the surface. ?? 1988.

  17. Coupled Hf-Nd-Pb isotope co-variations of HIMU oceanic island basalts suggest an Archean source component in the mantle transition zone

    NARCIS (Netherlands)

    Nebel, O.; Arculus, R.J.; van Westrenen, W.; Woodhead, J.D.; Jenner, F.E.; Nebel-Jacobsen, Y.J.; Wille, M.; Eggins, S.M.

    2013-01-01

    Although it is widely accepted that oceanic island basalts (OIB) sample geochemically distinct mantle reservoirs including recycled oceanic crust, the composition, age, and locus of these reservoirs remain uncertain. OIB with highly radiogenic Pb isotope signatures are grouped as HIMU (high-μ, with

  18. Electrical conductivity of the deep mantle: Joint inversion approach based on EM induction by external sources and rapid changes of secular variation

    Science.gov (United States)

    Velímský, Jakub

    2010-05-01

    The basic idea of this study is to combine two different, previously established techniques to study the electrical conductivity of the Earth's deep mantle, into one joint inversion scheme. Both methods are based on time-domain integration of electromagnetic induction equation in the Earth's mantle with one-dimensional, depth-dependent electrical conductivity. In the first forward problem, external excitation by intense geomagnetic storms is assumed, while in the second forward problem, induction by rapid changes of secular variation of the main field at the core-mantle boundary (the geomagnetic jerks) is studied. Different time scales of both approaches lead to use of two distinct datasets. Seven years of CHAMP satellite data is processed into time series of spherical harmonic coefficients with 1 hr sampling rate and used in the external induction problem. Annual means provided by Intermagnet observatories for selected 20th century jerks, are used in the modelling of secular variation. The joint inversion aims to recover both the radial profile of mantle conductivity, and the unknown spatial structure of the secular acceleration at the CMB for each jerk. Limited-memory quasi-Newton technique is used to minimize the misfit, complemented by effective evaluation of data sensitivities based on solutions of adjoint problems. First results of the inversion suggest only small increase of electrical conductivity to values about 10 S/m in D".

  19. Timing, mantle source and origin of mafic dykes within the gravity anomaly belt of the Taihang-Da Hinggan gravity lineament, central North China Craton

    Science.gov (United States)

    Liu, Shen; Feng, Caixia; Feng, Guangying; Xu, Mengjing; Coulson, Ian M.; Guo, Xiaolei; Guo, Zhuang; Peng, Hao; Feng, Qiang

    2017-09-01

    Six mafic dyke swarms crop out in Hebei Province within the Taihang-Da Hinggan gravity lineament magmatic belt, China, and were sampled. Here, we present new zircon laser ablation-inductively coupled plasma-mass spectrometry U-Pb age, whole rock geochemical, and Sr-Nd-Pb-Hf isotopic data for the six areas where these mafic dykes occur. The mafic (dolerite) dykes formed between 131.6 ± 1.6 and 121.6 ± 1.1 Ma, and are enriched in the light rare earth elements (LREE), some of the large ion lithophile elements (LILE; e.g., Rb, Ba, and Sr) and Pb, and are depleted in Th, U, Nb and Ta; some samples are also depleted in Eu. The dykes have high initial 87Sr/86Sr ratios (0.7055-0.7057), negative εNd (t) values (-12.5 to -11.9), relatively constant Pb isotopic ratios ((206Pb/204Pb)i = 16.45-16.51, (207Pb/204Pb)i = 15.44-15.51, (208Pb/204Pb)i = 36.49-36.53), negative εHf (t) values (-18.2 to -15.1), and old Nd (TNdDM2; 2.17-2.47 Ga) and Hf (THfDM2; 2.28-2.33 Ga) model ages. These geochronological, geochemical, and isotopic data indicate that the dykes were derived from magmas generated by low to moderate degree partial melting (1.0%-10%) of an EM1-like garnet lherzolite mantle source; these magmas fractionated olivine, clinopyroxene, and hornblende prior to emplacement, and assimilated minimal amounts of crustal material. Several possible models have previously been proposed to explain the origin of Mesozoic magmatism in this region. However, here we propose a foundering model for these studied mafic dykes, involving the foundering of eclogite from thickened lower crust due to the collision between the Siberian Craton and the North China Craon.

  20. Long and short wavelengths of Indian Ocean geoid and gravity lows: Mid-to-upper mantle sources, rapid drift and seismicity of Kachchh and Shillong plateau, India

    Science.gov (United States)

    Mishra, D. C.; Ravi Kumar, M.

    2012-10-01

    Spectral analysis of the Indian Ocean geoid low provides depth to the large wavelength sources as ˜1300, ˜700 and 340 km that are supported from the spectral analysis and the modeling of the corresponding large wavelength regional gravity anomaly with negative density contrasts at these levels. The three levels coincide with the sharp changes in the gradient of the seismic velocities related to the olivine-spinel transformation of successively increasing Fe/Mg ratio as depth increases, known as transition zones. The first two segments are supported from continuous wavelet transform analysis of the large wavelength component of the corresponding gravity field. The low density rocks in this section appear to be related to the subducted Indian/Tethyan lithosphere that roll back and drifted southwards after subduction as inferred from tomography experiments. The relatively short wavelength sources of the spectrum of the geoid data at depths of 162 and 85 km suggest sources along the lithosphere - asthenosphere boundary (LAB) under the Indian continent and surrounding oceans, respectively. A low viscosity zone has been envisaged below 660 km discontinuity that may correspond to the low density rocks in this section which is popularly referred to as graveyards of the subducted rocks under geoid lows. The subducted slab is hydrated due to dehydration from metamorphism that causes upwelling in the mid-to-upper mantle which is likely to set in baby plumes. Presence of fluid may transform part of olivine to serpentine further reducing the bulk density of rocks in this section. They would make this region buoyant that appears to be responsible for the Central Indian Ocean Deformation Zone with large scale folding, faulting, seismicity, and high heat flow. The same also appear to be responsible for the rapid drift of the Indian plate. Short wavelength component of the Indian Ocean geoid low reflects most of the surface/shallow tectonics of the region similar to the gravity

  1. Mantle Calcium Dominates Continental Magmas

    Science.gov (United States)

    Simon, J. I.; Depaolo, D. J.; Bachmann, O.

    2009-12-01

    Trace element and isotopic compositions of continental igneous rocks are often used to model the generation and evolution of crustal magmas. Here we report new Ca isotopic measurements of crystal-poor (35%) rhyolites from the Oligocene San Juan Volcanic Field (SJVF) and Pliocene to Pleistocene tuffs from Yellowstone Caldera. Because both volcanic fields are located within the North American craton the extruded magmas could have assimilated old crustal source components with radiogenic Ca that would be clearly distinguishable from that of the mantle. New Ca data are also reported for two crustal xenoliths found within the 28.2 Ma Fish Canyon Tuff (FCT) of the SJVF that yield ɛCa values of 3.8±0.6 (2 σ, n=3) and 7.5±0.4 (2 σ, n=3), respectively. The 40Ca excesses of these possible source rocks are due to long-term in situ 40K decay and suggest that they are Precambrian in age. In contrast to the excess radiogenic Ca signatures, most Cenozoic basalts and many silicic igneous rocks from Earth yield initial ɛCa values close to zero, which indicates that the 40Ca/44Ca ratio of the Earth’s mantle is well defined and virtually invariant at the resolution of our measurements. The crystal-rich FCT, inferred to result from batholith-scale remobilization of a shallow subvolcanic magma chamber, exhibits an ɛCai value of 0.32±0.02 (2 σ, n=5) that is indistinguishable from Ca in clinopyroxene from an ultramafic xenolith that has a mantle-like ɛCai value of -0.35±0.62 (2 σ, n=2). Simple mass balance calculations indicate that Ca in the FCT is greater than ~75% mantle derived. Similar mixing models based on published Nd data for the FCT that consider the range of possible crustal source components can deviate substantially from the Ca models. At face value the Nd data indicate that the FCT magma underwent significant crustal assimilation (i.e., at least ~10% and possibly ~75% of the Nd appears to have come from an enriched source component). So even in cases where a

  2. Hf isotope evidence for a hidden mantle reservoir

    DEFF Research Database (Denmark)

    Bizzarro, Martin; Simonetti, A.; Stevenson, R.K.

    2002-01-01

    High-precision Hf isotopic analyses and U-Pb ages of carbonatites and kimberlites from Greenland and eastern North America, including Earth's oldest known carbonatite (3 Ga), indicate derivation from an enriched mantle source. This previously unidentified mantle reservoir-marked by an unradiogenic...... Hf isotopic composition and preserved in the deep mantle for at least 3 b.y.-may account for the mass imbalance in Earth's Hf-Nd budget. The Hf isotopic data presented here support a common mantle source region and genetic link between carbonatite and some oceanic-island basalt volcanoes....

  3. Deep Mantle Fluids Bottled Up in Diamonds

    Science.gov (United States)

    Weiss, Y.; Pearson, D. G.

    2015-12-01

    Many mantle xenoliths and mineral inclusions in diamonds reflect refertilisation and enrichment by mantle metasomatism, a key mechanism for controlling abrupt changes in the chemical and physical properties of the continental lithospheric mantle (CLM) globally. However, the nature of the fluids involved can normally only be constrained indirectly from geochemical proxies or calculated using mineral/melt partition coefficients. Direct samples of mantle metasomatic fluids, shielded from any late stage alteration, are encased as microinclusions in fast-growing diamonds - "fibrous diamonds". These trapped high-density fluids (HDFs) provide a unique chemical and physical record for tracing the sources of deep mantle fluids and constraining the processes that shape their nature.Diamond HDFs vary between four major compositional types: saline, silicic and high-Mg plus low-Mg carbonatitic. A strong connection has been established between high-Mg carbonatitic HDFs and a carbonated peridotite source. In addition, the silicic and low-Mg carbonatitic HDFs have been related to hydrous eclogite (±carbonate). However, the compositionally extreme saline fluid endmember remained enigmatic and its source in the deep lithosphere has remained ambiguous. Our new data on fluid-rich diamonds show the geochemical fingerprints of a subducting slab as the source of deep mantle fluids of saline composition. In addition, for the first time, we show that these deep saline fluids are parental, via fluid rock interaction, to in-situ forming carbonatitic and silicic melts in the lithosphere. This model provides a strong platform for resolving the effects of the compositional spectrum of mantle fluids, which alter the deep lithosphere globally and play key roles in diamond formation.

  4. Primary magmas and mantle temperatures through time

    Science.gov (United States)

    Ganne, Jérôme; Feng, Xiaojun

    2017-03-01

    Chemical composition of mafic magmas is a critical indicator of physicochemical conditions, such as pressure, temperature, and fluid availability, accompanying melt production in the mantle and its evolution in the continental or oceanic lithosphere. Recovering this information has fundamental implications in constraining the thermal state of the mantle and the physics of mantle convection throughout the Earth's history. Here a statistical approach is applied to a geochemical database of about 22,000 samples from the mafic magma record. Potential temperatures (Tps) of the mantle derived from this database, assuming melting by adiabatic decompression and a Ti-dependent (Fe2O3/TiO2 = 0.5) or constant redox condition (Fe2+/∑Fe = 0.9 or 0.8) in the magmatic source, are thought to be representative of different thermal "horizons" (or thermal heterogeneities) in the ambient mantle, ranging in depth from a shallow sublithospheric mantle (Tp minima) to a lower thermal boundary layer (Tp maxima). The difference of temperature (ΔTp) observed between Tp maxima and minima did not change significantly with time (˜170°C). Conversely, a progressive but limited cooling of ˜150°C is proposed since ˜2.5 Gyr for the Earth's ambient mantle, which falls in the lower limit proposed by Herzberg et al. [2010] (˜150-250°C hotter than today). Cooling of the ambient mantle after 2.5 Ga is preceded by a high-temperature plateau evolution and a transition from dominant plumes to a plate tectonics geodynamic regime, suggesting that subductions stabilized temperatures in the Archaean mantle that was in warming mode at that time.Plain Language SummaryThe Earth's upper mantle constitutes a major interface between inner and outer envelops of the planet. We explore at high resolution its thermal state evolution (potential temperature of the ambient mantle, Tp) in depth and time using a multi-dimensional database of mafic lavas chemistry (>22,000 samples formed in the last 4 billion years

  5. Polybaric melting of a single mantle source during the Neogene Siverek phase of the Karacadaǧ Volcanic Complex, SE Turkey

    Science.gov (United States)

    Ekici, Taner; Macpherson, Colin G.; Otlu, Nazmi

    2012-08-01

    Siverek plateau basalts represent the Neogene activity of the Karacadağ Volcanic Complex in southeast Turkey and can be divided into two groups based on incompatible element concentrations. Group 1 is largely basaltic, containing some alkali basalts, while Group 2 consists of alkali basalts, trachybasalts and tephrites. The lavas display a range in major element concentrations that are consistent with restricted amounts of differentiation in the crust. Melts from both groups have experienced variable, small amounts of interaction with crustal rocks, which is responsible for most of the isotopic heterogeneity and caused significant Ba-enrichment. Neither fractional crystallisation nor crustal contamination can account for the differences in trace element enrichment observed between the two groups. Group 1 is derived mainly from the spinel lherzolite field by > 1% partial melting. Group 2 lavas were derived from very similar mantle but by smaller degrees of melting and contain a larger relative contribution from garnet-lherzolite. The Siverek plateau lavas are indistinguishable from contemporaneous magmatism in the Karasu Valley of southern Turkey and in northernmost Syria. Together, these plateau basalt fields represent mantle upwelling and melting beneath the thinned and/or weakened Arabian Plate as it migrated northwards during the Neogene.

  6. 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.

  7. Carbon sources and biogeochemical processes in Monticchio maar lakes, Mt Vulture volcano (southern Italy): New geochemical constrains of active degassing of mantle derived fluids

    Science.gov (United States)

    Caracausi, A.; Nuccio, P. M.; Favara, R.; Grassa, F.

    2012-04-01

    Since the catastrophic releases of carbon dioxide from the African volcanic lakes Nyos and Monoun in the 1980s, the scientific community draw attention towards all those crater lakes able to accumulate massive amount of CO2, which could be catastrophically released following overturn of their deep waters. This implies a quantification of the gas accumulation rate into the lakes and the knowledge of recharge processes and their evolution in time. In fact the gaseous recharge in a lake occurs at alarming rates, when an active degassing of hazardous nature volatiles occurs into the lakes and the structure and dynamic of the lake permit the accumulation of gases into the water. The Monticchio lakes, LPM and LGM, occupies two maar craters formed during the last volcanic activity of Mt. Vulture occurred ˜ 140 000 years ago. LPM is a permanently stratified lake, with a thick deep volume of stagnant water and a shallower layer affected by seasonal overturn. On the contrary LGM is a monomittic lake with a complete overturn of the water during winter time. The major dissolved volatiles are methane and CO2. Dissolved helium is in trace amounts and its isotopic signature ranges between 6.1 and 5.3 Ra (Ra is the atmospheric 3He/4He isotopic ratio). These values are within the range of those measured in the olivine fluid inclusions (both of mantle xenoliths and dispersed in the pyroclastics) of LPM maar ejecta. During three years of investigations we observed that dissolved methane in the deep waters of LGM drastically decreases in wintertime as consequence of the complete overturn of the water. The isotopic signature of methane in the deepest portions of LGM (both sediment and water) is quite stable with time and highlights a biogenic origin, being produced both by acetate fermentation and by CO2-reduction in variable proportions. In contrast, a higher contribution of methane produced via CO2 reduction characterizes sediments at shallower depths. At LPM, there is a great

  8. Mineralogy of subducted clay and clay restite in the lower mantle

    Science.gov (United States)

    Armstrong, L.; Skora, S. E.; Walter, M. J.

    2012-12-01

    Seismic tomography indicates that subducting oceanic lithosphere often penetrates the transition zone and eventually the lower mantle [e.g. 1, 2]. While mineralogical changes in the mafic and ultramafic portions of slabs have been well documented experimentally, the phase relations of overlying sediments at pressures above 25 GPa remain poorly studied. This is in part because sediments are expected to partially melt at sub-arc depth (P~2.5-4.5 GPa), and contribute to the genesis of arc magmas. Sediment restites left behind after the extraction of low pressure melts undergo major chemical changes, according to the melting reaction: Coe+Phen+Cpx+H2O = Grt+Ky+Melt [3]. However, sediments may not always melt depending on the thermal regime and volatile availability and composition [3]. Hence, chemically unmodified sediments as well as restites may be entrained to greater depths and contribute to compositional heterogeneity in the deep mantle. Indeed, mineral inclusions with compositions indicative of subducted sedimentary protoliths (CAS-phase; K-hollandite; stishovite) have been reported in 'ultradeep' diamonds and suggest that deep subduction and survival of sediments occurs to at least transition zone depths [4]. With this in mind, we have performed laser heated diamond anvil cell experiments at pressures of 8-80 GPa on two anhydrous glass starting materials: a marine clay and the restite that is left after 50% melt extraction of this clay at 3 GPa and 800 °C [3]. We chose to work with an anhydrous version of the marine clay given that the investigated pressure range exceeds that of phengite stability [5], and phengite is the only hydrous phase in subducted sediments at UHP conditions. The clay was heated along a P-T path representative of a cold subduction geotherm, whereas the clay restite was heated along a hotter subduction geotherm consistent with low pressure melting. Phases were identified by synchrotron X-ray micro-diffraction at beamline I15 of the Diamond

  9. Heating in the Solar Mantle

    Science.gov (United States)

    Chiuderi, C.

    1985-01-01

    In the case of the solar chromosphere and corona (the solar mantle) the primary energy source is the mechanical energy from photospheric motions. Plenty of energy is available; the problem is to transfer the needed amount of energy to the proper place to account for the observations. The global problem is reviewed from the point of view of the generation and transmission of energy, the intermediate storage of energy, and the release of energy in such a way that the observed features are generated.

  10. Where is mantle's carbon?

    Science.gov (United States)

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

    2008-12-01

    Due to the strongly reducing conditions (the presence of metallic iron was suggested both by experiments [1] and theory [2]), diamond was believed to be the main host of carbon through most of the lower mantle [3]. We showed [4] that cementite Fe3C is another good candidate to be the main host of "reduced" carbon in the mantle, reinforcing an earlier hypothesis [5]. The fate of "oxidised" carbon (in subducted slabs) is of particular importance - if carbonates decompose producing fluid CO2, this would have important implications for the chemistry and rheology of the mantle. Knowledge of crystal structures and phase diagrams of carbonates is crucial here. The high-pressure structures of CaCO3 were predicted [6] and subsequently verified by experiments. For MgCO3, Isshiki et al. [7] found a new phase above 110 GPa, and several attempts were made to solve it [8,9]. Here [4], using an evolutionary algorithm for crystal structure prediction [10], we show that there are two post-magnesite phases at mantle-relevant pressure range, one stable at 82-138 GPa, and the other from 138 GPa to ~160 GPa. Both are based on threefold rings of CO4-tetrahedra and are more favourable than all previously proposed structures. We show that through most of the P-T conditions of the mantle, MgCO3 is the major host of oxidized carbon in the Earth. We predict the possibility of CO2 release at the very bottom of the mantle (in SiO2-rich basaltic part of subducted slabs), which could enhance partial melting of rocks and be related to the geodynamical differences between the Earth and Venus. 1.Frost D.J., Liebske C., Langenhorst F., McCammon C.A., Tronnes R.G., Rubie D.C. (2004). Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle. Nature 428, 409-412. 2.Zhang F., Oganov A.R. (2006). Valence and spin states of iron impurities in mantle-forming silicates. Earth Planet. Sci. Lett. 249, 436-443. 3.Luth R.W. (1999). Carbon and carbonates in the mantle. In: Mantle

  11. Crust and upper-mantle structure of Wanganui Basin and southern Hikurangi margin, North Island, New Zealand as revealed by active source seismic data

    Science.gov (United States)

    Tozer, B.; Stern, T. A.; Lamb, S. L.; Henrys, S. A.

    2017-11-01

    Wide-angle reflection and refraction data recorded during the Seismic Array HiKurangi Experiment (SAHKE) are used to constrain the crustal P-wave velocity (Vp) structure along two profiles spanning the length and width of Wanganui Basin, located landwards of the southern Hikurangi subduction margin, New Zealand. These models provide high-resolution constraints on the structure and crustal thickness of the overlying Australian and subducted Pacific plates and plate interface geometry. Wide-angle reflections are modelled to show that the subducted oceanic Pacific plate crust is anomalously thick (∼10 km) below southern North Island and is overlain by a ∼1.5-4.0 km thick, low Vp (4.8-5.4 km s-1) layer, interpreted as a channel of sedimentary material, that persists landwards at least as far as Kapiti Island. Distinct near vertical reflections from onshore shots identify a ∼4 km high mound of low-velocity sedimentary material that appears to underplate the overlying Australian plate crust and is likely to contribute to local rock uplift along the Axial ranges. The overriding Australian plate Moho beneath Wanganui Basin is imaged as deepening southwards and reaches a depth of at least 36.4 km. The Moho shape approximately mirrors the thickening of the basin sediments, suggestive of crustal downwarping. However, the observed crustal thickness variation is insufficient to explain the large negative Bouguer gravity anomaly (-160 mGal) centred over the basin. Partial serpentinization within the upper mantle with a concomitant density decrease is one possible way of reconciling this anomaly.

  12. Crust and upper-mantle structure of Wanganui Basin and southern Hikurangi margin, North Island, New Zealand as revealed by active source seismic data

    Science.gov (United States)

    Tozer, B.; Stern, T. A.; Lamb, S. L.; Henrys, S. A.

    2017-11-01

    Wide-angle reflection and refraction data recorded during the Seismic Array HiKurangi Experiment (SAHKE) are used to constrain the crustal P-wave velocity (Vp) structure along two profiles spanning the length and width of Wanganui Basin, located landwards of the southern Hikurangi subduction margin, New Zealand. These models provide high-resolution constraints on the structure and crustal thickness of the overlying Australian and subducted Pacific plates and plate interface geometry. Wide-angle reflections are modelled to show that the subducted oceanic Pacific plate crust is anomalously thick (˜10 km) below southern North Island and is overlain by a ˜1.5-4.0 km thick, low Vp (4.8-5.4 km s-1) layer, interpreted as a channel of sedimentary material, that persists landwards at least as far as Kapiti Island. Distinct near vertical reflections from onshore shots identify a ˜4 km high mound of low-velocity sedimentary material that appears to underplate the overlying Australian plate crust and is likely to contribute to local rock uplift along the Axial ranges. The overriding Australian plate Moho beneath Wanganui Basin is imaged as deepening southwards and reaches a depth of at least 36.4 km. The Moho shape approximately mirrors the thickening of the basin sediments, suggestive of crustal downwarping. However, the observed crustal thickness variation is insufficient to explain the large negative Bouguer gravity anomaly (-160 mGal) centred over the basin. Partial serpentinization within the upper mantle with a concomitant density decrease is one possible way of reconciling this anomaly.

  13. Abundant carbon in the mantle beneath Hawai`i

    Science.gov (United States)

    Anderson, Kyle R.; Poland, Michael

    2017-01-01

    Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2content of mantle-derived magma supplying Hawai‘i’s active volcanoes is 0.97−0.19+0.25 wt%—roughly 40% higher than previously believed—and is supplied from a mantle source region with a carbon concentration of 263−62+81 ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.

  14. Abundant carbon in the mantle beneath Hawai`i

    Science.gov (United States)

    Anderson, Kyle R.; Poland, Michael P.

    2017-09-01

    Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2 content of mantle-derived magma supplying Hawai`i’s active volcanoes is 0.97-0.19+0.25 wt%--roughly 40% higher than previously believed--and is supplied from a mantle source region with a carbon concentration of 263-62+81 ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.

  15. Smoldering mantle cell lymphoma.

    Science.gov (United States)

    Ye, Haige; Desai, Aakash; Zeng, Dongfeng; Nomie, Krystle; Romaguera, Jorge; Ahmed, Makhdum; Wang, Michael L

    2017-12-15

    Mantle cell lymphoma (MCL) is an aggressive disease, with poor prognosis and a limited survival. However, some patients with indolent MCL can survive beyond 7~10 years. These patients remain largely asymptomatic and can be in observation for a long time without any treatment. The process of "wait and watch" leaves these patients with the potential risk of evolution to classic, aggressive MCL. On the other hand, early treatment for these patients may not impact overall survival but rather affects the quality of life. Therefore, it is essential to clearly identify this type of indolent MCL at the time of diagnosis. Reported findings of indolent presentation of MCL include: lack of B symptoms, normal serum lactic dehydrogenase (LDH) and β2-microglobulin levels (β2M), low MCL-International Prognostic Index (MIPI) score, maximum tumor diameter less than 3 cm, spleen size Smoldering Mantle Cell Lymphoma".

  16. Pillars of the Mantle

    KAUST Repository

    Pugmire, David

    2017-07-05

    In this work, we investigate global seismic tomographic models obtained by spectral-element simulations of seismic wave propagation and adjoint methods. Global crustal and mantle models are obtained based on an iterative conjugate-gradient type of optimization scheme. Forward and adjoint seismic wave propagation simulations, which result in synthetic seismic data to make measurements and data sensitivity kernels to compute gradient for model updates, respectively, are performed by the SPECFEM3D-GLOBE package [1] [2] at the Oak Ridge Leadership Computing Facility (OLCF) to study the structure of the Earth at unprecedented levels. Using advances in solver techniques that run on the GPUs on Titan at the OLCF, scientists are able to perform large-scale seismic inverse modeling and imaging. Using seismic data from global and regional networks from global CMT earthquakes, scientists are using SPECFEM3D-GLOBE to understand the structure of the mantle layer of the Earth. Visualization of the generated data sets provide an effective way to understand the computed wave perturbations which define the structure of mantle in the Earth.

  17. A >100 Ma Mantle Geochemical Record: Retiring Mantle Plumes may be Premature

    Science.gov (United States)

    Konter, J. G.; Hanan, B. B.; Blichert-Toft, J.; Koppers, A. A.; Plank, T.; Staudigel, H.

    2006-12-01

    Hotspot volcanism has long been attributed to mantle plumes, but in recent years suggestions have been made that plate tectonic processes, such as extension, can account for all hotspot tracks. This explanation involves a profoundly less dynamic lower mantle, which justifies a critical evaluation before the plume model is dismissed. Such an evaluation has to involve a wide range of geochemical, geological, and geophysical techniques, broadly investigating the products of volcanism as well as the underlying lithosphere and mantle. We argue here that the combined geological record and geochemistry of intraplate volcanoes holds some important clues that help us decide between models of plume-like upwelling versus passive upwelling with lithospheric extension. The best of these integrated datasets can be obtained from the long seamount chains in the Pacific Ocean. A new combined dataset of trace element and isotopic compositions, along with modern 40Ar/39Ar ages from seamounts in the Gilbert Ridge, Tokelau chain, and West Pacific Seamount Province (WPSP) provides a record of current to Cretaceous volcanism in the South Pacific. We have reconstructed the eruptive locations of the seamounts using a range of absolute plate motion models, including some models with hotspot motion and others that use the Indo-Atlantic hotspot reference frame. Our results show that the backtracked locations consistently form clusters (300km radius) around the active ends of the Macdonald, Rurutu and Rarotonga hotspot chains, while closely matching their distinct C-HIMU and C-EM1 signatures. The oldest WPSP seamounts (older than 100 Ma) form the only exception and backtrack, with larger uncertainty, to north of Rarotonga. Therefore, the mantle currently underlying the Cook-Austral islands has produced volcanoes in three geochemically distinct areas for at least 100 m.y. Furthermore, we find the shortest mantle residence time, 0.6 Ga, for a source of mixed recycled DMM and an EM1-like

  18. Kinematics and flow patterns in deep mantle and upper mantle subduction models : Influence of the mantle depth and slab to mantle viscosity ratio

    NARCIS (Netherlands)

    Schellart, W. P.

    Three-dimensional fluid dynamic laboratory simulations are presented that investigate the subduction process in two mantle models, an upper mantle model and a deep mantle model, and for various subducting plate/mantle viscosity ratios (ηSP/ηM = 59-1375). The models investigate the mantle flow field,

  19. Seismic anisotropy and mantle flow below subducting slabs

    Science.gov (United States)

    Walpole, Jack; Wookey, James; Kendall, J.-Michael; Masters, T.-Guy

    2017-05-01

    Subduction is integral to mantle convection and plate tectonics, yet the role of the subslab mantle in this process is poorly understood. Some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle, although the geodynamical feasibility of this has been questioned. Here, we use the source-side shear wave splitting technique to probe anisotropy beneath subducting slabs, enabling us to test petrofabric models and constrain the geometry of mantle fow. Our global dataset contains 6369 high quality measurements - spanning ∼ 40 , 000 km of subduction zone trenches - over the complete range of available source depths (4 to 687 km) - and a large range of angles in the slab reference frame. We find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow-symmetry-axis pointing normal to the plane of the slab. This appears incompatible with purely trench-parallel flow models. On the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction. Trench parallel measurements are most commonly associated with shallow events (source depth < 50 km) - suggesting a separate region of anisotropy in the lithospheric slab. This may correspond to the shape preferred orientation of cracks, fractures, and faults opened by slab bending. Meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite.

  20. Tracing recycled volatiles in a heterogeneous mantle with boron isotopes

    Science.gov (United States)

    Walowski, Kristina; Kirstein, Linda; de Hoog, Cees-Jan; Elliot, Tim; Savov, Ivan; Devey, Colin

    2016-04-01

    Recycling of oceanic lithosphere drives the chemical evolution of the Earth's mantle supplying both solids and volatiles to the Earth's interior. Yet, how subducted material influences mantle composition remains unclear. A perfect tracer for slab recycling should be only fractionated at the Earth's surface, have a strong influence on mantle compositions but be resistant to perturbations en route back to the surface. Current understanding suggests that boron concentrations linked to B isotope determinations fulfil all these requirements and should be an excellent tracer of heterogeneity in the deep mantle. Here, we present the trace element, volatile and the B isotope composition of basaltic glasses and melt inclusions in olivine from distinct end-member ocean island basalts (OIB) to track the fate of recycled lithosphere and ultimately document how recycling contributes to mantle heterogeneity. The chosen samples represent the different end member OIB compositions and include: EMI (Pitcairn), EMII (MacDonald), HIMU (St. Helena), and FOZO (Cape Verde & Reunion). The data is derived from both submarine and subaerial deposits, with B isotope determination of both basaltic glass and melt inclusions from each locality. Preliminary results suggest OIB have B isotopic compositions that overlap the MORB array (-7.5‰±0.7; Marschall et al., 2015) but extend to both lighter and heavier values. These results suggest that B isotopes will be useful for resolving mantle source heterogeneity at different ocean islands and contribute to our understanding of the volatile budget of the deep mantle.

  1. Geoneutrino perspective on Earth's heat budget and mantle structure

    Science.gov (United States)

    Sramek, O.; McDonough, W. F.; Kite, E. S.; Lekic, V.; Dye, S.; Zhong, S.

    2012-12-01

    Neutrino geophysics is an emerging interdisciplinary field with the potential to map the abundances and distribution of radiogenic heat sources in the continental crust and deep Earth. To date, data from two different experiments quantify the amount of Th and U in the Earth, and begin to put constraints on radiogenic power in the Earth available for driving mantle convection and plate tectonics. New improved detectors are under construction or in planning stages. Critical testing of compositional models of the Earth requires integrating geoneutrino and geological observations. Such tests will lead to significant constraints on the absolute and relative abundances of Th and U in the continents. High radioactivity in continental crust puts limits on land-based observatories' capacity to resolve mantle models with current detection methods. However, the quantification of deep-seated radioactivity is crucial for understanding the composition and dynamics of the Earth, including its thermal evolution, the style and planform of mantle convection, and the energetics of the core. Estimates of mantle radiogenic heat production vary significantly between some models. Th and U budget of Earth's compositional models based on enstatite chondrite chemistry, as well as models that employ an early loss of crustal material by a collisional erosion mechanism are consistent with a uniform mantle composition. Typically, these models end up with negligible amount of radiogenic power in the mantle after accounting for that in the crust. On the other hand, models constrained by composition of available Earth rock samples and C1 chondritic ratios of refractory lithophile elements require a mantle reservoir enriched in heat producing elements relative to the source of mid-oceanic ridge basalts. Such a reservoir is likely to show strong variation in thickness in the convecting mantle; it is usually identified with the seismically seen low shear wave velocity provinces (LLSVPs) in the deep

  2. Modeling Mantle Heterogeneity Development in Earth's Mantle Using Multidisciplinary Approaches

    Science.gov (United States)

    de Silva, S. M. S.; Finlayson, V.; Gu, T.; Li, M.; Lithgow-Bertelloni, C. R.; Cormier, V. F.

    2014-12-01

    The process of subduction provides continuous chemical and thermal heterogeneity to Earth's mantle. How heterogeneity is stirred, stretched and distributed depends on the detail of mantle convection as well as chemical and physical properties of mantle materials. Seismic observations have revealed heterogeneities in Earth's mantle at varying scales. Seismic velocities are controlled by physical parameters such as density, bulk modulus and shear modulus, which are a function of temperature, pressure and composition. Thus, understanding the origin of seismic heterogeneities play an important role in understanding the thermal and chemical state of the present Earth's mantle. Originating from the CIDER 2014 workshop, our goal is to take a multidisciplinary approach to tackle a variety of questions, foremost what length scales of heterogeneity might we expect from the convecting process and how do they manifest themselves in seismic imaging. This touches upon fundamental issues such as the composition of the mantle, the nature of stirring and mixing, and the nature of large-scale mantle upwellings (LLSVPs). We will investigate the development of heterogeneity in response to various compositions and redox states using existing and new thermochemical mantle convection simulations, and test the sensitivity of seismic measurements to different length scales of chemical heterogeneity. We try to reconcile large differences in length scales of heterogeneity as well as fractional perturbations of seismic velocity and density predicted by tomography and scattering seismic experiments. Preliminary results from the CIDER workshop initiate with conversion of geodynamic models to profiles of seismic velocity and density which are then taken as input models to predict multiply scattered, high frequency, P wave coda envelopes synthesized by a radiative transport technique. The predicted sensitivity of P coda envelopes to varying chemical compositions and heterogeneity length scales

  3. Stagnant lids and mantle overturns: Implications for Archaean tectonics, magmagenesis, crustal growth, mantle evolution, and the start of plate tectonics

    Directory of Open Access Journals (Sweden)

    Jean H. Bédard

    2018-01-01

    Full Text Available The lower plate is the dominant agent in modern convergent margins characterized by active subduction, as negatively buoyant oceanic lithosphere sinks into the asthenosphere under its own weight. This is a strong plate-driving force because the slab-pull force is transmitted through the stiff sub-oceanic lithospheric mantle. As geological and geochemical data seem inconsistent with the existence of modern-style ridges and arcs in the Archaean, a periodically-destabilized stagnant-lid crust system is proposed instead. Stagnant-lid intervals may correspond to periods of layered mantle convection where efficient cooling was restricted to the upper mantle, perturbing Earth's heat generation/loss balance, eventually triggering mantle overturns. Archaean basalts were derived from fertile mantle in overturn upwelling zones (OUZOs, which were larger and longer-lived than post-Archaean plumes. Early cratons/continents probably formed above OUZOs as large volumes of basalt and komatiite were delivered for protracted periods, allowing basal crustal cannibalism, garnetiferous crustal restite delamination, and coupled development of continental crust and sub-continental lithospheric mantle. Periodic mixing and rehomogenization during overturns retarded development of isotopically depleted MORB (mid-ocean ridge basalt mantle. Only after the start of true subduction did sequestration of subducted slabs at the core-mantle boundary lead to the development of the depleted MORB mantle source. During Archaean mantle overturns, pre-existing continents located above OUZOs would be strongly reworked; whereas OUZO-distal continents would drift in response to mantle currents. The leading edge of drifting Archaean continents would be convergent margins characterized by terrane accretion, imbrication, subcretion and anatexis of unsubductable oceanic lithosphere. As Earth cooled and the background oceanic lithosphere became denser and stiffer, there would be an increasing

  4. Understanding slab-mantle interaction by 3D seismic imaging of reflectivity in the mantle wedge

    Science.gov (United States)

    Li, L.; Hu, H.; Li, X.; Zheng, Y.

    2016-12-01

    Fluids released from the downgoing slab can flush the overlying mantle over time and generate seismic reflectivity in the mantle. By mapping the depth, lateral spatial extent, and the strength of the reflector, we can achieve better understanding of the pervasive metasomatic process and dynamics of the mineral phase changes. We use seismic waves radiated by deep subduction-zone earthquakes to image possible reflectors shallower than the earthquakes. To mitigate the uncertainties of the source depth determination and velocity heterogeneities along the ray path, we first pick the energetic pP (or sP and sSH; lowercase, upgoing wave; upper case, downgoing after being reflected by the surface) phase as a reference phase. pP represents a ray geometry that an upgoing P wave leaving from the source is reflected by the Earth surface and emerges at the station. Any underside reflection by a reflector above the source should produce a precursory phase to the reference phase. We use our 3D elastic Kirchhoff migration to migrate these precursory phases to image possible reflectors in the mantle wedge. To do this, we have collected 3-component broadband seismic data from IRIS generated by earthquakes (magnitude >5) occurring in the time window spanning from 2006 to 2015 recorded by global seismographs to produce 3D images of the mantle wedge. We first validate our imaging algorithm in Tonga subduction zone. We examined 530373 P-waves from 567 earthquakes visually and picked 18928 high signal-to-noise traces in the imaging. In the image, discontinuities such as the Gutenberg and the `410 km' phase boundary are clearly seen. Localized reflectors due to impedance changes around 210km depth and around 330km depth are also imaged. The results agree with those in previous works. We will show results in other subduction zones, which include Java, Mariana, Japan, Kurile, and South America to systematically understand slab mantle interactions in various subduction environments.

  5. Deep mantle forces and the uplift of the Colorado Plateau

    Energy Technology Data Exchange (ETDEWEB)

    Moucha, R; Forte, A M; Rowley, D B; Mitrovica, J X; Simmons, N A; Grand, S P

    2009-06-23

    Since the advent of plate tectonics, it has been speculated that the northern extension of the East Pacific Rise, specifically its mantle source, has been over-ridden by the North American Plate in the last 30 Myrs. Consequently, it has also been postulated that the opening of the Gulf of California, the extension in the Basin and Range province, and the uplift of the Colorado Plateau are the resulting continental expressions of the over-ridden mantle source of the East Pacific Rise. However, only qualitative models based solely on surface observations and heuristic, simplified conceptions of mantle convection have been used in support or against this hypothesis. We introduce a quantitative model of mantle convection that reconstructs the detailed motion of a warm mantle upwelling over the last 30 Myrs and its relative advance towards the interior of the southwestern USA. The onset and evolution of the crustal uplift in the central Basin and Range province and the Colorado Plateau is determined by tracking the topographic swell due to this mantle upwelling through time. We show that (1) the extension and magmatism in the central Basin and Range province between 25 and 10 Ma coincides with the reconstructed past position of this focused upwelling, and (2) the southwestern portion of the Colorado Plateau experienced significant uplift between 10 Ma and 5 Ma that progressed towards the northeastern portion of the plateau. These uplift estimates are consistent with a young, ca. 6 Ma, Grand Canyon model and the recent commencement of mafic magmatism.

  6. The Elephants' Graveyard: Constraints from Mantle Plumes on the Fate of Subducted Slabs and Implications for the Style of Mantle Convection

    Science.gov (United States)

    Lassiter, J. C.

    2007-12-01

    The style of mantle convection (e.g., layered- vs. whole-mantle convection) is one of the most hotly contested questions in the Geological Sciences. Geochemical arguments for and against mantle layering have largely focused on mass-balance evidence for the existence of "hidden" geochemical reservoirs. However, the size and location of such reservoirs are largely unconstrained, and most geochemical arguments for mantle layering are consistent with a depleted mantle comprising most of the mantle mass and a comparatively small volume of enriched, hidden material either within D" or within seismically anomalous "piles" beneath southern Africa and the South Pacific. The mass flux associated with subduction of oceanic lithosphere is large and plate subduction is an efficient driver of convective mixing in the mantle. Therefore, the depth to which oceanic lithosphere descends into the mantle is effectively the depth of the upper mantle in any layered mantle model. Numerous geochemical studies provide convincing evidence that many mantle plumes contain material which at one point resided close to the Earth's surface (e.g., recycled oceanic crust ± sediments, possibly subduction-modified mantle wedge material). Fluid dynamic models further reveal that only the central cores of mantle plumes are involved in melt generation. The presence of recycled material in the sources of many ocean island basalts therefore cannot be explained by entrainment of this material during plume ascent, but requires that recycled material resides within or immediately above the thermo-chemical boundary layer(s) that generates mantle plumes. More recent Os- isotope studies of mantle xenoliths from OIB settings reveal the presence not only of recycled crust in mantle plumes, but also ancient melt-depleted harzburgite interpreted to represent ancient recycled oceanic lithosphere [1]. Thus, there is increasing evidence that subducted slabs accumulate in the boundary layer(s) that provide the source

  7. A Consensus on Mantle Potential Temperatures? (Invited)

    Science.gov (United States)

    Putirka, K. D.

    2009-12-01

    Recent publications may indicate a mounting consensus regarding mantle temperatures - an agreement that can be crucial for improving our understanding of mantle dynamics. To compare temperatures at various localities, McKenzie & Bickle (1988) proposed the concept of a mantle potential temperature (Tp) as a reference; Tp is the temperature the mantle would have at the surface, if it ascended along an adiabat without undergoing melting. Perhaps the most precise method to estimate Tp involves estimating the conditions of partial melting, and then correcting for the heat of fusion. The several sources of error include estimation of: a parental liquid, an equilibrium mantle olivine, the degree of partial melting (F), and the depth at which the parental melt is generated. There is also model error inherent to any thermometer. And when correcting for the heat of fusion we assume that we are correcting up to the convective adiabat, but if the parental melt was generated within the conductive lithosphere, Tp will be low. In any case, if we accept that the highest Tp estimates at Hawaii are of most interest (since magmas generated away from a plume centerline will not reflect the full heat content of a high T source), then in spite of these sources of error, recent estimates, published over a span of 10 months by three independent research groups, indicate considerable convergence. At Hawaii maximum Tp values are: 1600 deg. C by Herzberg & Asimow (2008), ca. 1630 deg. C by Lee et al. (2009; their Fig. 2B), and using two slightly different equation sets, 1687 deg. C by Putirka (2008; Geology) and 1660 deg. C by Putirka (2008; RiMG volume 69), yielding an average of 1644±38oC. Similarly, there is convergence for mean Tp at MORs (accepting that MORs are not isothermal; Klein and Langmuir, 1987): Herzberg & Asimow (2008) and Lee et al. (2009) estimate that Tp is ca. 1350 deg. C, and Putirka (2008; Geology) estimates a Tp of 1396 deg. C; these estimates average to 1365±26o

  8. The East African Mantle: Warm but not Hot

    Science.gov (United States)

    Rooney, T. O.; Herzberg, C. T.; Bastow, I. D.

    2011-12-01

    East Africa is underlain by one of the most conspicuous features of global tomographic models: the African Super-plume. Magmatism during the African-Arabian flood basalt event and ongoing development of the East African rift have long been linked to the super-plume, with high temperatures usually cited as evidence for its existence. However, our work shows that seismic wave-speeds in the East African mantle are too low to be accounted for by only thermal effects. Other factors such as composition must also play a role. To address these issues we present mantle potential temperature estimates (TP) and preliminary high-precision compositional data from olivine crystals for East African lavas with the goal of constraining the thermo-chemical conditions of the East African upper mantle. Our estimates of mantle TP show that the East African mantle has remained warmer than ambient mantle conditions over the past 40 Myr, peaking during the Oligocene African-Arabian flood basalt episode (1520°C). These TP values, while clearly elevated, fall toward the lower end of the global temperature range of large igneous provinces, and are inconsistent with a solely thermal origin for the profound mantle seismic velocity anomalies beneath East Africa. Evidence of compositional heterogeneity in the East African upper mantle is preserved in the Fe, Mn, Ca, and Ni content of olivine crystals in lavas. We have found that Fe/Mn (42-95) within this preliminary dataset extend to the most extreme values yet recorded in the global LIP and oceanic island database, plotting well-outside fields accepted for olivine derived from peridotite-sourced melt. These data are strong evidence of a significant role for non-peridotite lithologies such as pyroxenite in the East African upper mantle. Such pyroxenites may reside in the metasomatized lithospheric mantle, or be derived from the reaction of recycled oceanic slabs upwelling in the African Superplume. Such recycled materials likely contain

  9. Understanding the nature of mantle upwelling beneath East-Africa

    Science.gov (United States)

    Civiero, Chiara; Hammond, James; Goes, Saskia; Ahmed, Abdulhakim; Ayele, Atalay; Doubre, Cecile; Goitom, Berhe; Keir, Derek; Kendall, Mike; Leroy, Sylvie; Ogubazghi, Ghebrebrhan; Rumpker, Georg; Stuart, Graham

    2014-05-01

    The concept of hot upwelling material - otherwise known as mantle plumes - has long been accepted as a possible mechanism to explain hotspots occurring at Earth's surface and it is recognized as a way of removing heat from the deep Earth. Nevertheless, this theory remains controversial since no one has definitively imaged a plume and over the last decades several other potential mechanisms that do not require a deep mantle source have been invoked to explain this phenomenon, for example small-scale convection at rifted margins, meteorite impacts or lithospheric delamination. One of the best locations to study the potential connection between hotspot volcanism at the surface and deep mantle plumes on land is the East African Rift (EAR). We image seismic velocity structure of the mantle below EAR with higher resolution than has been available to date by including seismic data recorded by stations from many regional networks ranging from Saudi Arabia to Tanzania. We use relative travel-time tomography to produce P- velocity models from the surface down into the lower mantle incorporating 9250 ray-paths in our model from 495 events and 402 stations. We add smaller earthquakes (4.5 image structures of ~ 100-km length scales to ~ 1000 km depth beneath the northern East-Africa rift (Ethiopia, Eritrea, Djibouti, Yemen) with good resolution also in the transition zone and uppermost lower mantle. Our observations provide evidence that the shallow mantle slow seismic velocities continue trough the transition zone and into the lower mantle. In particular, the relatively slow velocity anomaly beneath the Afar Depression extends up to depths of at least 1000 km depth while another low-velocity anomaly beneath the Main Ethiopian Rift seems to be present in the upper mantle only. These features in the lower mantle are isolated with a diameter of about 400 km indicating deep multiple sources of upwelling that converge in broader low-velocity bodies along the rift axis at shallow

  10. Mineralogy and composition of the oceanic mantle

    Science.gov (United States)

    Putirka, Keith; Ryerson, F.J.; Perfit, Michael; Ridley, W. Ian

    2011-01-01

    The mineralogy of the oceanic basalt source region is examined by testing whether a peridotite mineralogy can yield observed whole-rock and olivine compositions from (1) the Hawaiian Islands, our type example of a mantle plume, and (2) the Siqueiros Transform, which provides primitive samples of normal mid-ocean ridge basalt. New olivine compositional data from phase 2 of the Hawaii Scientific Drilling Project (HSDP2) show that higher Ni-in-olivine at the Hawaiian Islands is due to higher temperatures (T) of melt generation and processing (by c. 300°C) related to the Hawaiian mantle plume. DNi is low at high T, so parental Hawaiian basalts are enriched in NiO. When Hawaiian (picritic) parental magmas are transported to shallow depths, olivine precipitation occurs at lower temperatures, where DNi is high, leading to high Ni-in-olivine. Similarly, variations in Mn and Fe/Mn ratios in olivines are explained by contrasts in the temperatures of magma processing. Using the most mafic rocks to delimit Siqueiros and Hawaiian Co and Ni contents in parental magmas and mantle source compositions also shows that both suites can be derived from natural peridotites, but are inconsistent with partial melting of natural pyroxenites. Whole-rock compositions at Hawaii and Siqueiros are also matched by partial melting experiments conducted on peridotite bulk compositions. Hawaiian whole-rocks have elevated FeO contents compared with Siqueiros, which can be explained if Hawaiian parental magmas are generated from peridotite at 4-5 GPa, in contrast to pressures of slightly greater than 1 GPa for melt generation at Siqueiros; these pressures are consistent with olivine thermometry, as described in an earlier paper. SiO2-enriched Koolau compositions are reproduced if high-Fe Hawaiian parental magmas re-equilibrate at 1-1·5 GPa. Peridotite partial melts from experimental studies also reproduce the CaO and Al2O3 contents of Hawaiian (and Siqueiros) whole-rocks. Hawaiian magmas have TiO2

  11. Serpentinization and fluids in the forearc mantle

    Science.gov (United States)

    Reynard, B.

    2016-12-01

    with the source rocks of the volcanic arc and explain geochemical signatures of primitive magma inclusions. Signature of deep high-Cl fluids was also identified in forearc hot springs. Potential fluid circulations between the forearc mantle and the hot spring hydrothermal system or the volcanic arc are discussed.

  12. Pb evolution in the Martian mantle

    Science.gov (United States)

    Bellucci, J. J.; Nemchin, A. A.; Whitehouse, M. J.; Snape, J. F.; Bland, P.; Benedix, G. K.; Roszjar, J.

    2018-03-01

    The initial Pb compositions of one enriched shergottite, one intermediate shergottite, two depleted shergottites, and Nakhla have been measured by Secondary Ion Mass Spectrometry (SIMS). These values, in addition to data from previous studies using an identical analytical method performed on three enriched shergottites, ALH 84001, and Chassigny, are used to construct a unified and internally consistent model for the differentiation history of the Martian mantle and crystallization ages for Martian meteorites. The differentiation history of the shergottites and Nakhla/Chassigny are fundamentally different, which is in agreement with short-lived radiogenic isotope systematics. The initial Pb compositions of Nakhla/Chassigny are best explained by the late addition of a Pb-enriched component with a primitive, non-radiogenic composition. In contrast, the Pb isotopic compositions of the shergottite group indicate a relatively simple evolutionary history of the Martian mantle that can be modeled based on recent results from the Sm-Nd system. The shergottites have been linked to a single mantle differentiation event at 4504 Ma. Thus, the shergottite Pb isotopic model here reflects a two-stage history 1) pre-silicate differentiation (4504 Ma) and 2) post-silicate differentiation to the age of eruption (as determined by concordant radiogenic isochron ages). The μ-values (238U/204Pb) obtained for these two different stages of Pb growth are μ1 of 1.8 and a range of μ2 from 1.4-4.7, respectively. The μ1-value of 1.8 is in broad agreement with enstatite and ordinary chondrites and that proposed for proto Earth, suggesting this is the initial μ-value for inner Solar System bodies. When plotted against other source radiogenic isotopic variables (Sri, γ187Os, ε143Nd, and ε176Hf), the second stage mantle evolution range in observed mantle μ-values display excellent linear correlations (r2 > 0.85) and represent a spectrum of Martian mantle mixing-end members (depleted

  13. Heterogeneously hydrated mantle beneath the late Archean Yilgarn Craton

    Science.gov (United States)

    Ivanic, T. J.; Nebel, O.; Jourdan, F.; Faure, K.; Kirkland, C. L.; Belousova, E. A.

    2015-12-01

    Archean mafic-ultramafic melts, crystallized as layered intrusions in the upper crust and extruded as komatiitic flows, are primary probes of upper mantle chemistry. However, the message from their primary chemical composition can be compromised by different modes of contamination. Contaminants are typically cryptic in terms of their geochemical and isotopic signals but may be related to metasomatised mantle sources, ambient crustal assimilation or subduction-related inputs. In this work we present critical evidence for both dry and wet Archean mantle sources for two juxtaposed layered intrusions in the Australian Yilgarn Craton. The ca. 2813 Ma Windimurra and ca. 2800 Ma Narndee Igneous Complexes in Western Australia are two adjacent layered intrusions and would be expected to derive via similar mantle sections. A key difference in their chemistry is the presence of crystal-bound water in the Narndee Igneous Complex, represented primarily by abundant hornblende. Such a primary hydrous phase is notably absent in the Windimurra Igneous Complex. New 40Ar/39Ar plateau ages for fresh Narndee hornblende (weighted mean: 2805 ± 14 Ma, MSWD = 1.8, probability = 0.18) agrees with the published U-Pb age of 2800 ± 6 Ma for the complex and is consistent with a magmatic origin for this phase. Zircon Hf and whole-rock Hf and Nd isotopes for the Narndee Igneous Complex indicate only minor crustal contamination, in agreement with H and O isotope values in amphibole and O isotope values in rare zircon crystals, plagioclase and pyroxene within both complexes. These findings illustrate a fast temporal transition, in proximal bodies, from anhydrous to hydrous mantle sources with very minor crustal contamination. These large layered mafic-ultramafic intrusions are igneous bodies with a primitive chemical bulk composition that requires large degrees of mantle melting. This has been attributed by many workers to mantle plume activity, yet not without dispute, as subduction-related flux

  14. Lithology and temperature: How key mantle variables control rift volcanism

    Science.gov (United States)

    Shorttle, O.; Hoggard, M.; Matthews, S.; Maclennan, J.

    2015-12-01

    Continental rifting is often associated with extensive magmatic activity, emplacing millions of cubic kilometres of basalt and triggering environmental change. The lasting geological record of this volcanic catastrophism are the large igneous provinces found at the margins of many continents and abrupt extinctions in the fossil record, most strikingly that found at the Permo-Triassic boundary. Rather than being considered purely a passive plate tectonic phenomenon, these episodes are frequently explained by the involvement of mantle plumes, upwellings of mantle rock made buoyant by their high temperatures. However, there has been debate over the relative role of the mantle's temperature and composition in generating the large volumes of magma involved in rift and intra-plate volcanism, and even when the mantle is inferred to be hot, this has been variously attributed to mantle plumes or continental insulation effects. To help resolve these uncertainties we have combined geochemical, geophysical and modelling results in a two stage approach: Firstly, we have investigated how mantle composition and temperature contribute to melting beneath Iceland, the present day manifestation of the mantle plume implicated in the 54Ma break up of the North Atlantic. By considering both the igneous crustal production on Iceland and the chemistry of its basalts we have been able to place stringent constraints on the viable temperature and lithology of the Icelandic mantle. Although a >100°C excess temperature is required to generate Iceland's thick igneous crust, geochemistry also indicates that pyroxenite comprises 10% of its source. Therefore, the dynamics of rifting on Iceland are modulated both by thermal and compositional mantle anomalies. Secondly, we have performed a global assessment of the mantle's post break-up thermal history to determine the amplitude and longevity of continental insulation in driving excess volcanism. Using seismically constrained igneous crustal

  15. Mantle hydration and the role of water in the generation of large igneous provinces.

    Science.gov (United States)

    Liu, Jia; Xia, Qun-Ke; Kuritani, Takeshi; Hanski, Eero; Yu, Hao-Ran

    2017-11-28

    The genesis of large igneous provinces (LIP) is controlled by multiple factors including anomalous mantle temperatures, the presence of fusible fertile components and volatiles in the mantle source, and the extent of decompression. The lack of a comprehensive examination of all these factors in one specific LIP makes the mantle plume model debatable. Here, we report estimates of the water content in picrites from the Emeishan LIP in southwestern China. Although these picrites display an island arc-like H 2 O content (up to 3.4 by weight percent), the trace element characteristics do not support a subduction zone setting but point to a hydrous reservoir in the deep mantle. Combining with previous studies, we propose that hydrous and hot plumes occasionally appeared in the Phanerozoic era to produce continental LIPs (e.g., Tarim, Siberian Trap, Karoo). The wide sampling of hydrous reservoirs in the deep mantle by mantle plumes thus indicates that the Earth's interior is largely hydrated.

  16. A great thermal divergence in the mantle beginning 2.5 Ga: Geochemical constraints from greenstone basalts and komatiites

    Directory of Open Access Journals (Sweden)

    Kent C. Condie

    2016-07-01

    Full Text Available Greenstone basalts and komatiites provide a means to track both mantle composition and magma generation temperature with time. Four types of mantle are characterized from incompatible element distributions in basalts and komatiites: depleted, hydrated, enriched and mantle from which komatiites are derived. Our most important observation is the recognition for the first time of what we refer to as a Great Thermal Divergence within the mantle beginning near the end of the Archean, which we ascribe to thermal and convective evolution. Prior to 2.5 Ga, depleted and enriched mantle have indistinguishable thermal histories, whereas at 2.5–2.0 Ga a divergence in mantle magma generation temperature begins between these two types of mantle. Major and incompatible element distributions and calculated magma generation temperatures suggest that Archean enriched mantle did not come from mantle plumes, but was part of an undifferentiated or well-mixed mantle similar in composition to calculated primitive mantle. During this time, however, high-temperature mantle plumes from dominantly depleted sources gave rise to komatiites and associated basalts. Recycling of oceanic crust into the deep mantle after the Archean may have contributed to enrichment of Ti, Al, Ca and Na in basalts derived from enriched mantle sources. After 2.5 Ga, increases in Mg# in basalts from depleted mantle and decreases in Fe and Mn reflect some combination of growing depletion and cooling of depleted mantle with time. A delay in cooling of depleted mantle until after the Archean probably reflects a combination of greater radiogenic heat sources in the Archean mantle and the propagation of plate tectonics after 3 Ga.

  17. Decarbonation and carbonation processes in the slab and mantle wedge - insights from thermomechanical modeling

    Science.gov (United States)

    Gonzalez, C. M.; Gorczyk, W.; Connolly, J. A.; Gerya, T.; Hobbs, B. E.; Ord, A.

    2013-12-01

    understanding the fate of carbonates beyond the subarc and consequent subduction into the deeper mantle within a fully coupled model framework. A case study where CO2 fluids are intimately connected to subduction and metasomatism of the mantle is in the Western Mediterranean in Italy. There, carbonate melts metasomatized the asthenosphere leading to a seismic low velocity zone associated with large scale mantle degassing in the region of approximately 70 Mt/year of CO2 [1]. This natural laboratory provides us with a present day example to help constrain the benchmarking process in order to refine our numerical techniques. [1] Frezzotti, Peccerillo, & Panza, 2009. Chemical Geology, 262(1-2), 108-120. doi: DOI 10.1016/j.chemgeo.2009.02.015

  18. Sublithospheric flows in the mantle

    Science.gov (United States)

    Trifonov, V. G.; Sokolov, S. Yu.

    2017-11-01

    The estimated rates of upper mantle sublithospheric flows in the Hawaii-Emperor Range and Ethiopia-Arabia-Caucasus systems are reported. In the Hawaii-Emperor Range system, calculation is based on motion of the asthenospheric flow and the plate moved by it over the branch of the Central Pacific plume. The travel rate has been determined based on the position of variably aged volcanoes (up to 76 Ma) with respect to the active Kilauea Volcano. As for the Ethiopia-Arabia-Caucasus system, the age of volcanic eruptions (55-2.8 Ma) has been used to estimate the asthenospheric flow from the Ethiopian-Afar superplume in the northern bearing lines. Both systems are characterized by variations in a rate of the upper mantle flows in different epochs from 4 to 12 cm/yr, about 8 cm/yr on average. Analysis of the global seismic tomographic data has made it possible to reveal rock volumes with higher seismic wave velocities under ancient cratons; rocks reach a depth of more than 2000 km and are interpreted as detached fragments of the thickened continental lithosphere. Such volumes on both sides of the Atlantic Ocean were submerged at an average velocity of 0.9-1.0 cm/yr along with its opening. The estimated rates of the mantle flows clarify the deformation properties of the mantle and regulate the numerical models of mantle convection.

  19. Density heterogeneity of the North American upper mantle from satellite gravity and a regional crustal model

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2014-01-01

    We present a regional model for the density structure of the North American upper mantle. The residual mantle gravity anomalies are based on gravity data derived from the GOCE geopotential models with crustal correction to the gravity field being calculated from a regional crustal model. We analyze...... how uncertainties and errors in the crustal model propagate from crustal densities to mantle residual gravity anomalies and the density model of the upper mantle. Uncertainties in the residual upper (lithospheric) mantle gravity anomalies result from several sources: (i) uncertainties in the velocity......-density conversion and (ii) uncertainties in knowledge of the crustal structure (thickness and average Vp velocities of individual crustal layers, including the sedimentary cover). In this study, we address both sources of possible uncertainties by applying different conversions from velocity to density...

  20. Recycled crust and the secular cooling of mantle plumes

    Science.gov (United States)

    Gazel Dondi, E.; Herzberg, C. T.; Vidito, C. A.

    2012-12-01

    Current models suggest that the massive basaltic production responsible for the emplacement of Large Igneous Provinces (LIPS) during the Permian-Paleocene may represent the initial phases of some of the mantle plumes that feed the current ocean island basalts (OIB). In some cases this magmatism was so voluminous that it produced global environmental impacts. Recent petrological, geochemical and geophysical studies of some of these localities like Samoa, Hawaii, Galapagos provide evidence that melting is related to a true mantle plume that originates from a boundary layer beneath the upper mantle. Thus, plume-related magmas produced in OIB and LIPS and their connecting plume tracks provide evidence on mantle temperature, size and composition of heterogeneities, and deep geochemical cycles. Although a lot of work has been done on LIPS and OIB, no complete record of the evolution of a mantle plume is available to this point. Galapagos-related lavas provide a complete record of the evolution of a mantle plume since the plume's initial stages in the Cretaceous. In the case of the Galapagos, our work suggests a decrease from TP(max) of 1650 °C in the Cretaceous to 1500 °C in the present day. Our recent work on the Galapagos Islands and the preliminary work on older Galapagos-related terranes suggest that this secular cooling is related with increasing amounts of recycled crust in the plume. Detailed olivine chemistry shows that although peridotite is the dominant source lithology of the Galapagos Plume, a recycled pyroxenite component is also significant in both isotopically enriched and depleted domains of the archipelago. We suggest that this possibly represents two separate bodies of recycled crust within the Galapagos mantle plume.

  1. Fluorine and chlorine in mantle minerals and the halogen budget of the Earth's mantle

    Science.gov (United States)

    Urann, B. M.; Le Roux, V.; Hammond, K.; Marschall, H. R.; Lee, C.-T. A.; Monteleone, B. D.

    2017-07-01

    The fluorine (F) and chlorine (Cl) contents of arc magmas have been used to track the composition of subducted components, and the F and Cl contents of MORB have been used to estimate the halogen content of depleted MORB mantle (DMM). Yet, the F and Cl budget of the Earth's upper mantle and their distribution in peridotite minerals remain to be constrained. Here, we developed a method to measure low concentrations of halogens (≥0.4 µg/g F and ≥0.3 µg/g Cl) in minerals by secondary ion mass spectroscopy. We present a comprehensive study of F and Cl in co-existing natural olivine, orthopyroxene, clinopyroxene, and amphibole in seventeen samples from different tectonic settings. We support the hypothesis that F in olivine is controlled by melt polymerization, and that F in pyroxene is controlled by their Na and Al contents, with some effect of melt polymerization. We infer that Cl compatibility ranks as follows: amphibole > clinopyroxene > olivine orthopyroxene, while F compatibility ranks as follows: amphibole > clinopyroxene > orthopyroxene ≥ olivine, depending on the tectonic context. In addition, we show that F, Cl, Be and B are correlated in pyroxenes and amphibole. F and Cl variations suggest that interaction with slab melts and fluids can significantly alter the halogen content of mantle minerals. In particular, F in oceanic peridotites is mostly hosted in pyroxenes, and proportionally increases in olivine in subduction-related peridotites. The mantle wedge is likely enriched in F compared to un-metasomatized mantle, while Cl is always low (<1 µg/g) in all tectonic settings studied here. The bulk anhydrous peridotite mantle contains 1.4-31 µg/g F and 0.14-0.38 µg/g Cl. The bulk F content of oceanic-like peridotites (2.1-9.4 µg/g) is lower than DMM estimates, consistent with F-rich eclogite in the source of MORB. Furthermore, the bulk Cl budget of all anhydrous peridotites studied here is lower than previous DMM estimates. Our results indicate that

  2. Intraplate mantle oxidation by volatile-rich silicic magmas

    Energy Technology Data Exchange (ETDEWEB)

    Martin, Audrey M.; Médard, Etienne; Righter, Kevin; Lanzirotti, Antonio

    2017-11-01

    The upper subcontinental lithospheric mantle below the French Massif Central is more oxidized than the average continental lithosphere, although the origin of this anomaly remains unknown. Using iron oxidation analysis in clinopyroxene, oxybarometry, and melt inclusions in mantle xenoliths, we show that widespread infiltration of volatile (HCSO)-rich silicic melts played a major role in this oxidation. We propose the first comprehensive model of magmatism and mantle oxidation at an intraplate setting. Two oxidizing events occurred: (1) a 365–286 Ma old magmatic episode that produced alkaline vaugnerites, potassic lamprophyres, and K-rich calc-alkaline granitoids, related to the N–S Rhenohercynian subduction, and (2) < 30 Ma old magmatism related to W–E extension, producing carbonatites and hydrous potassic trachytes. These melts were capable of locally increasing the subcontinental lithospheric mantle fO2 to FMQ + 2.4. Both events originate from the melting of a metasomatized lithosphere containing carbonate + phlogopite ± amphibole. The persistence of this volatile-rich lithospheric source implies the potential for new episodes of volatile-rich magmatism. Similarities with worldwide magmatism also show that the importance of volatiles and the oxidation of the mantle in intraplate regions is underestimated.

  3. Two-phase deformation of lower mantle mineral analogs

    Science.gov (United States)

    Kaercher, P.; Miyagi, L.; Kanitpanyacharoen, W.; Zepeda-Alarcon, E.; Wang, Y.; Parkinson, D.; Lebensohn, R. A.; De Carlo, F.; Wenk, H. R.

    2016-12-01

    The lower mantle is estimated to be composed of mostly bridgmanite and a smaller percentage of ferropericlase, yet very little information exists for two-phase deformation of these minerals. To better understand the rheology and active deformation mechanisms of these lower mantle minerals, especially dislocation slip and the development of crystallographic preferred orientation (CPO), we deformed mineral analogs neighborite (NaMgF3, iso-structural with bridgmanite) and halite (NaCl, iso-structural with ferropericlase) together in the deformation-DIA at the Advanced Photon Source up to 51% axial shortening. Development of CPO was recorded in situ with X-ray diffraction, and information on microstructural evolution was collected using X-ray microtomography. Results show that when present in as little as 15% volume, the weak phase (NaCl) controls the deformation. Compared to single phase NaMgF3 samples, samples with just 15% volume NaCl show a reduction of CPO in NaMgF3 and weakening of the aggregate. Microtomography shows both NaMgF3 and NaCl form highly interconnected networks of grains. Polycrystal plasticity simulations were carried out to gain insight into slip activity, CPO evolution, and strain and stress partitioning between phases for different synthetic two-phase microstructures. The results suggest that ferropericlase may control deformation in the lower mantle and reduce CPO in bridgmanite, which implies a less viscous lower mantle and helps to explain why the lower mantle is fairly isotropic.

  4. Heat transfer correlations in mantle tanks

    DEFF Research Database (Denmark)

    Furbo, Simon; Knudsen, Søren

    2005-01-01

    Small solar domestic hot water systems are best designed as low flow systems based on vertical mantle tanks. Theoretical investigations of the heat transfer in differently designed vertical mantle tanks during different operation conditions have been carried out. The investigations are based...... on calculations with a CFD-model, which has earlier been validated by means of experiments. The CFD-model is used to determine the heat transfer between the solar collector fluid in the mantle and the walls surrounding the mantle in all levels of the mantle as well as the heat transfer between the wall...... of the inner hot water tank and the domestic water in all levels of the tank. The heat transfer analysis showed that the heat transfer near the mantle inlet port between the solar collector fluid in the mantle and the walls surrounding the mantle is in the mixed convection regime, and as the distance from...

  5. 182W evidence from flood basalt lavas for the long-term survival of primordial mantle

    Science.gov (United States)

    Rizo Garza, H. L.; Walker, R. J.; Carlson, R.; Horan, M. F.; Mukhopadhyay, S.; Francis, D.; Jackson, M. G.

    2016-12-01

    How much of the chemical heterogeneity present in mantle today dates to processes that occurred during Earth's planetary formation stage remains an unanswered question. Geochemical observations obtained from short-lived radiogenic isotope systems, however, provide important insights. Tungsten isotope data for flood basalt lavas from two large igneous provinces, the North Atlantic Igneous Province ( 60 Ma) and the Ontong Java Plateau ( 120 Ma), show well resolved 182W excesses, compared with terrestrial standards that are presumed to be representative of the present bulk mantle. These W isotope results, thus, indicate that one or more mantle domains formed very early in Earth history and have been preserved well into the Phanerozoic eon. The flood basalts from Baffin Bay contain among the highest 3He/4He ratios ever measured, as well as Pb and 143Nd isotopic compositions, and D/H ratios consistent with a chemically primitive, un-degassed mantle source. Ontong Java is the Earth's largest known volcanic province and shares chemical and isotopic similarities with the Baffin Bay lavas, indicative of a similarly primitive mantle source. The 182W-enriched nature of the mantle sources of rocks from both locations indicates that their primitive characteristics were likely isolated in a deep mantle reservoir within the first 50 Ma of Solar System history. The correlation between large low seismic shear velocity provinces (LLSVPs) and the distribution of reconstructed eruption sites of these large igneous provinces makes the LLSVPs possible candidate domains for the required primitive and un-degassed reservoirs.

  6. Oceanic Domains - Observed Relationship With Tomographic Features and Inferred Mantle Structure

    Science.gov (United States)

    Loubet, M.

    A persistent contradiction exists between the current views of mantle stratification derived from geochemistry and number of geophysical and simulations which sug- gest the existence of a significant material exchange throughout the entire mantle and favor mixing processes. In this presentation, we will show that the common interpre- tation of oceanic basalt heterogeneities can be contested and that a new interpretation of these heterogeneities can be done which leads to interesting relationships between geochemical and geophysical (tomographic) features. The new approach is based on (a) identification of mantle heterogeneities at the scale of oceanic domains recovering in some cases MORB and OIB basalt types and (b) use of incompatible element ratios in (Cx/Cz,Cy/Cz) representations as in particular the (Th/La,Nb/La) representation. This last representation is very interesting for identification of magmatic processes and for estimating magma sources compositions. Analysis of oceanic basalts compo- sitions based on a large set of literature data leads to identify 4 (eventually 5) large scale oceanic domains: Atlantic East Pacific (AEP), Indian ocean (IO), South Central Pacific (SCP), Kerguelen South Atlantic (KSA) (and eventually Hawaï (H)). The two first ones which include MORB sources extend at upper mantle levels. The good geo- graphical recovery of the SCP and KSA domains with tomographic features assigned to take place within the mantle at the D" level in the Central Pacific and South Africa (Masters et al., 2000) leads to interpret the basalts from the KSA and SCP domains as issued from D" layer source. Two different mantle structures (general ones before discussing more complex ones), both comprising a D" layer (composed of recycled oceanic crust enriched materials) at the CMB, can be inferred from these oceanic basalt source interpretations: (a) a layered mantle with an upper and a lower mantle with primitive mantle material composing a significant part of

  7. West Antarctic Mantle Plume Hypothesis and Basal Water Generation

    Science.gov (United States)

    Ivins, Erik; Seroussi, Helene; Wiens, Doug; Bondzio, Johannes

    2017-04-01

    The hypothesis of a deep mantle plume that manifests Pliocene and Quaternary volcanism and present-day seismicity in West Antarctica has been speculated for more than 30 years. Recent seismic images support the plume hypothesis as the cause of Marie Byrd Land (MBL) volcanism and geophysical structure [ Lloyd et al., 2015; Ramirez et al., 2016]. Mantle plumes can more that double the geothermal heat flux, qGHF, above nominal continental values at their axial peak position and raise qGHF in the surrounding plume head to 60 mW/m2 or higher. Unfortunately, there is a dearth of in-situ basal ice sheet data that sample the heat flux. Consequently, we examine a realistic distribution of heat flux associated with a late-Cenozoic mantle plume in West Antarctica and explore its impact on thermal and melt conditions near the ice sheet base. The solid Earth model assumes a parameterized deep mantle plume and head. The 3-D ice flow model includes an enthalpy framework and full-Stokes stress balance. Both the putative plume location and extent are uncertain. Therefore, we perform broadly scoped experiments to characterize plume related basal conditions. The experiments show that mantle plumes have an important local impact on the ice sheet, with basal melting rates reaching several centimeters per year directly above the hotspot. The downstream active lake system of Whillans Ice Stream suggests a rift-related source of anomalous mantle heat. However, the lack of lake and stream activity in MBL suggests a relatively weak plume: one that delivers less flux by 35% below the heat flux to the crustal surface at the site of the Yellowstone hotspot [e.g., DeNosaquo et al., 2009], with peak value no higher than about 145 mW/m2.

  8. Iron speciation and redox state of mantle eclogites: Implications for ancient volatile cycles during mantle melting and oceanic crust subduction

    Science.gov (United States)

    Aulbach, Sonja; Woodand, Alan; Vasilyev, Prokopiy; Viljoen, Fanus

    2017-04-01

    Kimberlite-borne mantle eclogite xenoliths of Archaean and Palaeoproterozoic age are commonly interpreted as representing former oceanic crust. As such, they may retain a memory of the redox state of the ancient convecting mantle sources that gave rise to their magmatic protoliths and which controls the speciation of volatiles in planetary interiors. Mantle eclogite suites commonly include both cumulate and variably evolved extrusive varieties [1], which may be characterised by initial differences in Fe3+/Fetotal. Recent Fe-based oxybarometry shows mantle eclogites to have fO2 relative to the fayalite-magnetite-quartz buffer (ΔFMQ) of -3 to 0, whereby low fO2 relative to modern MORB may relate to subduction of more reducing Archaean oceanic crust or loss of ferric Fe during partial melt loss [2]. Indeed, using V/Sc as a redox proxy, it was recently shown that Archaean mantle eclogites are more reduced than modern MORB (ΔFMQ-1.3 vs. ΔFMQ -0.4) [3]. However, in the warmer ancient mantle, they were also subject to modification due to partial melt loss upon recycling and, after capture in the cratonic mantle lithosphere, may be overprinted by interaction with metasomatic melts and fluids. In order to help further constrain the redox state of mantle eclogites and unravel the effect of primary and secondary processes, we measured Fe3+/Fetotal by Mössbauer in garnet from mantle eclogites from the Lace kimberlite (Kaapvaal craton), comprising samples with melt- and cumulate-like oceanic crustal protoliths as well as metasomatised samples. Fe3+/ΣFe in garnet shows a strong negative correlation with jadeite content and bulk-rock Li and Cu abundances, suggesting increased partitioning of Fe3+ into jadeite in the presence of monovalent cations with which it can form coupled substitutions. Broad negative correlation with whole-rock Al2O3/TiO2 and positive correlation with ΣREE are interpreted as incompatible behaviour of Fe3+ during olivine-plagioclase accumulation

  9. Martian rocks, minerals, and mantles

    OpenAIRE

    Albee, Arden

    2002-01-01

    The variable nature of Mars was first observed almost 400 years ago and modern observations began almost 40 years ago, culminating with the flotilla of spacecraft now at or heading for Mars. We now know that the atmosphere, which produced the visible variation of Mars, has also covered it with a mantle that makes difficult any detailed investigation of the rocks and minerals of Mars.

  10. Evolution of the martian mantle as recorded by igneous rocks

    Science.gov (United States)

    Balta, J. B.; McSween, H. Y.

    2013-12-01

    Martian igneous rocks provide our best window into the current state of the martian mantle and its evolution after accretion and differentiation. Currently, those rocks have been examined in situ by rovers, characterized in general from orbiting spacecraft, and analyzed in terrestrial laboratories when found as meteorites. However, these data have the potential to bias our understanding of martian magmatism, as most of the available meteorites and rover-analyzed rocks come from the Amazonian (3.8 Ga) have only been examined by orbiters and as the unique meteorite ALH 84001. After initial differentiation, the main planetary-scale changes in the structure of Mars which impact igneous compositions are cooling of the planet and thickening of the crust with time. As the shergottite meteorites give ages Ma1, they might be expected to represent thick-crust, recent volcanism. Using spacecraft measurements of volcanic compositions and whole rock compositions of meteorites, we demonstrate that the shergottite meteorites do not match the composition of the igneous rocks composing the young volcanoes on Mars, particularly in their silica content, and no crystallization or crustal contamination trend reproduces the volcanoes from a shergottite-like parent magma. However, we show that the shergottite magmas do resemble older martian rocks in composition and mineralogy. The Noachian-aged meteorite ALH 84001 has similar radiogenic-element signatures to the shergottites and may derive from a similar mantle source despite the age difference2. Thus, shergottite-like magmas may represent melting of mantle sources that were much more abundant early in martian history. We propose that the shergottites represent the melting products of an originally-hydrous martian mantle, containing at least several hundred ppm H2O. Dissolved water can increase the silica content of magmas and thus plausibly explains the high silica content of the shergottites. A dehydrating martian mantle with time can

  11. Search for seismic discontinuities in the lower mantle

    Science.gov (United States)

    Vinnik, Lev; Kato, Mamoru; Kawakatsu, Hitoshi

    2001-09-01

    Indications of lower mantle discontinuities have been debated for decades, but still little is known about their properties, and their origins are enigmatic. In our study broad-band recordings of deep events are examined for the presence of signals from the lower-mantle discontinuities with a novel technique. We deconvolve vertical component of the P-wave coda in the period range around 10s by the S waveform and stack many deconvolved traces with moveout time corrections. In synthetic seismograms for an earth model without lower mantle discontinuities, the strongest signal thus detected in the time window of interest is often s`410'P phase (generated as S and reflected as P from the `410km' discontinuity above the source). In actual seismograms there are other phases that can be interpreted as converted from S to P at discontinuities in the lower mantle beneath the seismic source. We summarize the results of processing the seismograms (1) of deep events in Sunda arc at seismograph stations in east Asia, (2) deep Kermadec-Fiji-Tonga events at the J-array and FREESIA networks in Japan and stations in east Asia, and (3) deep events in the northwest Pacific region (Mariana, Izu-Bonin and the Japan arc) recorded at stations in north America. In our data there are indications of discontinuities near 860-880, 1010-1120, 1170-1250 and 1670-1800km depths. The clearest signals are obtained from the discontinuity at a depth of 1200km. We argue that the `900', `1200' and `1700km' discontinuities are global, but laterally variable in both depth and strength. Seismic stratification of the lower mantle may have bearings on the patterns of subduction, as revealed by tomographic models.

  12. Helium isotope signature of the Permo-Carboniferous magmatic province in Scotland - no role for a mantle Plume

    NARCIS (Netherlands)

    Kirstein, L.A.; Dunai, T.J.; Davies, G.R.; Upton, B.G.J.

    2004-01-01

    Noble gas studies of well-characterized spinel-peridotite-facies lithospheric mantle xenoliths and garnet megacrysts from Scottish Permo-Carboniferous dykes, sills and vents demonstrate that the mantle beneath Scotland during the late Palaeozoic was more radiogenic than the source of mid-ocean ridge

  13. Earth's CMB topography and mantle convection

    Science.gov (United States)

    Lassak, T. M.; McNamara, A. K.; Zhong, S.; Garnero, E.

    2008-12-01

    Better understanding topography on Earth's core-mantle boundary (CMB) may provide important constraints on mantle dynamics, specifically the style of mantle convection, and on lower mantle heterogeneity. For example, the origin of large, lowermost mantle low shear wave velocity provinces beneath the central Pacific and Africa is not well constrained, but are likely related to both mantle dynamics and CMB topography. Two competing hypotheses for these anomalies are: thermal upwellings (e.g., plume clusters) or large intrinsically dense piles of primitive mantle material (e.g., thermochemical piles). Here we discuss the results from our current 3D investigation of CMB topography in two styles of mantle convection: 1) an isochemical mantle with plume clusters, and 2) a thermochemical mantle with large, intrinsically dense piles. In this study, we numerically investigate 3D spherical models of mantle convection and calculate maps of topography (CMB and surface, with self-gravitation included) and geoid (CMB and surface). Maps of CMB topography and geoid (CMB and surface) are produced, and compared to observed CMB topography (e.g., Morelli and Dziewonski, 1987; Boschi and Dziewonski, 2000; Sze and van der Hilst, 2003) and surface geoid (e.g., Earth Geopotential Model, 1996). Our predicted surface geoid maps provide a key image of how CMB topography, for any given model, will affect the geoid. The results of this work emphasize the importance in using a suite of observables (in this case, topography and geoid maps for CMB and surface) to constrain whole mantle dynamics and lower mantle structure.

  14. Mantle wedge serpentinization effects on slab dips

    Directory of Open Access Journals (Sweden)

    Eh Tan

    2017-01-01

    Full Text Available The mechanical coupling between a subducting slab and the overlying mantle wedge is an important factor in controlling the subduction dip angle and the flow in mantel wedge. This paper investigates the role of the amount of mantle serpentinization on the subduction zone evolution. With numerical thermos-mechanical models with elasto-visco-plastic rheology, we vary the thickness and depth extent of mantle serpentinization in the mantle wedge to control the degree of coupling between the slab and mantle wedge. A thin serpentinized mantle layer is required for stable subduction. For models with stable subduction, we find that the slab dip is affected by the down-dip extent and the mantle serpentinization thickness. A critical down-dip extent exists in mantle serpentinization, determined by the thickness of the overriding lithosphere. If the down-dip extent does not exceed the critical depth, the slab is partially coupled to the overriding lithosphere and has a constant dip angle regardless of the mantle serpentinization thickness. However, if the down-dip extent exceeds the critical depth, the slab and the base of the overriding lithosphere would be separated and decoupled by a thick layer of serpentinized peridotite. This allows further slab bending and results in steeper slab dip. Increasing mantle serpentinization thickness will also result in larger slab dip. We also find that with weak mantle wedge, there is no material flowing from the asthenosphere into the serpentinized mantle wedge. All of these results indicate that serpentinization is an important ingredient when studying the subduction dynamics in the mantle wedge.

  15. Upper mantle structure at Walvis Ridge from Pn tomography

    Science.gov (United States)

    Ryberg, Trond; Braeuer, Benjamin; Weber, Michael

    2017-10-01

    Passive continental margins offer the unique opportunity to study the processes involved in continental extension and break-up. Within the LISPWAL (LIthospheric Structure of the Namibian continental Passive margin at the intersection with the Walvis Ridge from amphibious seismic investigations) project, combined on- and offshore seismic experiments were designed to characterize the Southern African passive margin at the Walvis Ridge in northern Namibia. In addition to extensive analysis of the crustal structures, we carried out seismic investigations targeting the velocity structure of the upper mantle in the landfall region of the Walvis Ridge with the Namibian coast. Upper mantle Pn travel time tomography from controlled source, amphibious seismic data was used to investigate the sub-Moho upper mantle seismic velocity. We succeeded in imaging upper mantle structures potentially associated with continental break-up and/or the Tristan da Cunha hotspot track. We found mostly coast-parallel sub-Moho velocity anomalies, interpreted as structures which were created during Gondwana break-up.

  16. Viscosity undulations in the lower mantle: The dynamical role of iron spin transition

    Science.gov (United States)

    Justo, J. F.; Morra, G.; Yuen, D. A.

    2015-07-01

    A proper determination of the lower-mantle viscosity profile is fundamental to understanding Earth geodynamics. Based on results coming from different sources, several models have been proposed to constrain the variations of viscosity as a function of pressure, stress and temperature. While some models have proposed a relatively modest viscosity variation across the lower mantle, others have proposed variations of several orders of magnitude. Here, we have determined the viscosity of ferropericlase, a major mantle mineral, and explored the role of the iron high-to-low spin transition. Viscosity was described within the elastic strain energy model, in which the activation parameters are obtained from the bulk and shear wave velocities. Those velocities were computed combining first principles total energy calculations and the quasi-harmonic approximation. As a result of a strong elasticity softening across the spin transition, there is a large reduction in the activation free energies of the materials creep properties, leading to viscosity undulations. These results suggest that the variations of the viscosity across the lower mantle, resulting from geoid inversion and postglacial rebound studies, may be caused by the iron spin transition in mantle minerals. Implications of the undulated lower mantle viscosity profile exist for both, down- and up-wellings in the mantle. We find that a viscosity profile characterized by an activation free energy of G* (z0) ˜ 300- 400 kJ /mol based on diffusion creep and dilation factor δ = 0.5 better fits the observed high velocity layer at mid mantle depths, which can be explained by the stagnation and mixing of mantle material. Our model also accounts for the growth of mantle plume heads up to the size necessary to explain the Large Igneous Provinces that characterize the start of most plume tracks.

  17. Sampling Mantle Heterogeneity through Oceanic Basalts: Isotopes and Trace Elements

    Science.gov (United States)

    Hofmann, A. W.

    2003-12-01

    Early History of Mantle GeochemistryUntil the arrival of the theories of plate tectonics and seafloor spreading in the 1960s, the Earth's mantle was generally believed to consist of peridotites of uniform composition. This view was shared by geophysicists, petrologists, and geochemists alike, and it served to characterize the compositions and physical properties of mantle and crust as "Sial" (silica-alumina) of low density and "Sima" (silica-magnesia) of greater density. Thus, Hurley and his collaborators were able to distinguish crustal magma sources from those located in the mantle on the basis of their initial strontium-isotopic compositions (Hurley et al., 1962; and Hurley's lectures and popular articles not recorded in the formal scientific literature). In a general way, as of early 2000s, this view is still considered valid, but literally thousands of papers have since been published on the isotopic and trace-elemental composition of oceanic basalts because they come from the mantle and they are rich sources of information about the composition of the mantle, its differentiation history and its internal structure. Through the study of oceanic basalts, it was found that the mantle is compositionally just as heterogeneous as the crust. Thus, geochemistry became a major tool to decipher the geology of the mantle, a term that seems more appropriate than the more popular "chemical geodynamics."The pioneers of this effort were Gast, Tilton, Hedge, Tatsumoto, and Hart (Hedge and Walthall, 1963; Gast et al., 1964; Tatsumoto, et al., 1965; Hart, 1971). They discovered from isotope analyses of strontium and lead in young (effectively zero age) ocean island basalts (OIBs) and mid-ocean ridge basalts (MORBs) that these basalts are isotopically not uniform. The isotope ratios 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb increase as a function of time and the respective radioactive-parent/nonradiogenic daughter ratios, 87Rb/86Sr, 238U/204Pb, 235U/204Pb, and 232Th

  18. sources

    Directory of Open Access Journals (Sweden)

    Shu-Yin Chiang

    2002-01-01

    Full Text Available In this paper, we study the simplified models of the ATM (Asynchronous Transfer Mode multiplexer network with Bernoulli random traffic sources. Based on the model, the performance measures are analyzed by the different output service schemes.

  19. Thermal Stratification in Vertical Mantle Tanks

    DEFF Research Database (Denmark)

    Knudsen, Søren; Furbo, Simon

    2001-01-01

    are carried out to investigate how the thermal stratification is affected by different placements of the mantle inlet. The heat transfer between the solar collector fluid in the mantle and the domestic water in the inner tank is analysed by CFD-simulations. Furthermore, the flow pattern in the vertical mantle......It is well known that it is important to have a high degree of thermal stratification in the hot water storage tank to achieve a high thermal performance of SDHW systems. This study is concentrated on thermal stratification in vertical mantle tanks. Experiments based on typical operation conditions...

  20. Mineralogy and petrology of leucite ankaratrites with affinities to kamafugites and carbonatites from the Kayıköy area, Isparta, SW Anatolia, Turkey: Implications for the influences of carbonatite metasomatism into the parental mantle sources of silica-undersaturated potassic magmas

    Science.gov (United States)

    Caran, Şemsettin

    2016-07-01

    In the Kayıköy area of Isparta-Gölcük district, Inner Isparta Angle, SW Anatolia, Turkey, a small volume of newly discovered K-rich mafic potassic magma was emplaced in the form of dome in the vicinity of graben structures under Pliocene (3.68 ± 0.5 Ma) extensional tectonics. Kayıköy leucite ankaratrites are made up of abundant diopside, barian phlogopite and leucite, and lesser olivine, that rarely contains Cr-spinel, nepheline and haüyne, with abundant magnetite. They have low SiO2 (44.00-46.04 wt.%) and Al2O3 (12.10-12.64 wt.%) with high K2O (4.00-4.42 wt.%), CaO (13.50-14.40 wt.%) and MgO (8.52-9.36 wt.%), with high Cr (397-547 ppm) and moderate Ni (57-74 ppm) contents. They represent the less evolved silica-undersaturated mafic potassic magmas within the Isparta-Gölcük volcanic province, and may be considered another parental source to the wide spectrum of the K-rich rocks. They are highly enriched in most of the incompatible elements (e.g., Ba, 2761 to > 10,000 ppm; Sr, 3700-4074 ppm; Th, 33.60-36.99 ppm; Zr, 274-321 ppm) with high LREEs, low HREEs and elevated LREEs/HREEs ratios [(La/Yb)N, 73-80] and are comparable with kamafugite and carbonatites. Trace element patterns have negative P, Ti and Nb-Ta anomalies in common with the Italian kamafugite province and lack of a Eu anomaly, in contrast to the negative Eu anomaly of the Italian province. Their Sr87/86-Nd143/144 (0.703877-0.512765) isotopic compositions, together with those of other potassic volcanics from the Inner Isparta Angle, coincide with the West Quinling (China) kamafugites with highly depleted mantle signatures, and young East African carbonatites. Olivine-Cr-spinel pairs, high Mg# (0.69-0.73) numbers and Cr values, and high incompatible and LREE contents in Kayıköy leucite ankaratritic magma are consistent with near-primary magmas equilibrated with enriched and heterogeneous (peridotitic/pyroxenitic) mantle sources. On the basis of (i) their geochemical signatures [low Ti

  1. BurnMan: A lower mantle mineral physics toolkit

    KAUST Repository

    Cottaar, Sanne

    2014-04-01

    We present BurnMan, an open-source mineral physics toolbox to determine elastic properties for specified compositions in the lower mantle by solving an Equation of State (EoS). The toolbox, written in Python, can be used to evaluate seismic velocities of new mineral physics data or geodynamic models, and as the forward model in inversions for mantle composition. The user can define the composition from a list of minerals provided for the lower mantle or easily include their own. BurnMan provides choices in methodology, both for the EoS and for the multiphase averaging scheme. The results can be visually or quantitatively compared to observed seismic models. Example user scripts show how to go through these steps. This paper includes several examples realized with BurnMan: First, we benchmark the computations to check for correctness. Second, we exemplify two pitfalls in EoS modeling: using a different EoS than the one used to derive the mineral physical parameters or using an incorrect averaging scheme. Both pitfalls have led to incorrect conclusions on lower mantle composition and temperature in the literature. We further illustrate that fitting elastic velocities separately or jointly leads to different Mg/Si ratios for the lower mantle. However, we find that, within mineral physical uncertainties, a pyrolitic composition can match PREM very well. Finally, we find that uncertainties on specific input parameters result in a considerable amount of variation in both magnitude and gradient of the seismic velocities. © 2014. American Geophysical Union. All Rights Reserved.

  2. Seawater subduction controls the heavy noble gas composition of the mantle.

    Science.gov (United States)

    Holland, Greg; Ballentine, Chris J

    2006-05-11

    The relationship between solar volatiles and those now in the Earth's atmosphere and mantle reservoirs provides insight into the processes controlling the acquisition of volatiles during planetary accretion and their subsequent evolution. Whereas the light noble gases (helium and neon) in the Earth's mantle preserve a solar-like isotopic composition, heavy noble gases (argon, krypton and xenon) have an isotopic composition very similar to that of the modern atmosphere, with radiogenic and (in the case of xenon) solar contributions. Mantle noble gases in a magmatic CO2 natural gas field have been previously corrected for shallow atmosphere/groundwater and crustal additions. Here we analyse new data from this field and show that the elemental composition of non-radiogenic heavy noble gases in the mantle is remarkably similar to that of sea water. We challenge the popular concept of a noble gas 'subduction barrier'--the convecting mantle noble gas isotopic and elemental composition is explained by subduction of sediment and seawater-dominated pore fluids. This accounts for approximately 100% of the non-radiogenic argon and krypton and 80% of the xenon. Approximately 50% of the convecting mantle water concentration can then be explained by this mechanism. Enhanced recycling of subducted material to the mantle plume source region then accounts for the lower ratio of radiogenic to non-radiogenic heavy noble gas isotopes and higher water content of plume-derived basalts.

  3. Textural and compositional characteristics of mantle xenoliths from southeastern Libya: Evidence of mantle refertilization processes

    Science.gov (United States)

    Radivojević, Maša; Erić, Suzana; Turki, Salah M.; Toljić, Marinko; Cvetković, Vladica

    2014-05-01

    The study presents the very first data on mantle xenoliths of the Wādi Eghei area, southeastern Libya. These dm- to cm-sized xenoliths are found in a small volcanic cone of Pliocene basalts, which is situated on the northeastern slopes of the Tibesti Mountains. The host basalts originated from near primary magmas derived by melting of an enriched and garnet-bearing mantle source in within-plate geotectonic settings. Generally, the Wādi Eghei xenoliths can be divided into two texturally different groups: i) well-equilibrated, undeformed protogranular xenoliths, and ii) moderately/strongly sheared, porphyroclastic/equigranular types. Despite their textural diversity, all xenoliths are anhydrous clinopyroxene (cpx)-rich lherzolites, except one protogranular sample (V-5) that can be classified as cpx-poor lherzolite or harzburgite (≡5% of modal cpx). In terms of mineral chemistry, the protogranular xenoliths display only slightly more depleted compositions compared to sheared xenoliths, with sample V-5 as always the most depleted of the whole suite. Fo contents in olivine from protogranular and sheared xenoliths range 90.5-91.0 (V-5~91.5). Orthopyroxene (opx) from protogranular samples has higher Mg#(Mg#=100*Mg/[Mg+Fetot]mol%) from 90.5 to 91.2 (91.8 for V-5 opx), than those from deformed xenoliths (Mg#=89.5-90.5). The composition of spinel also correlates with the texture of the xenoliths. Spinel from the undeformed samples has Cr#s(Cr#=100*Cr/[Cr+Al]mol%) mostly ranging 12-14 (V-5~16), whereas Cr# in spinel occurring in sheared xenoliths is always <10. The variations in cpx composition do not show discernible textural dependences. They display a wide compositional range: En=45.5-50.2; Fs=3.7-5.7; Wo=42.0-50.1. The contents of Al2O3, Na2O and TiO2 range from 2.32-7.75 wt.%, 0.96-1.79 wt.%, and 0.2-0.84 wt.%, respectively. Calculated temperatures indicate that the undeformed types of xenoliths equilibrated at slightly higher temperatures (with minimal and maximal

  4. Mineralogical Processes in the Lower Mantle and their Implications for Seismic Heterogeneities

    Science.gov (United States)

    Shim, S.; Catalli, K.; Grocholski, B.

    2009-12-01

    It has been proposed that the large-scale lateral variations in seismic velocities detected at the lower mantle may be related to compositional changes. Yet the source and origin of the heterogeneities are unknown. Some major changes in mantle phases have been recently discovered, such as the charge disproportionation reaction of iron in mantle silicates, spin transitions of iron in mantle silicates and oxides, and the perovskite-to-postperovskite phase transition. These processes may profoundly alter the properties of the lowermost mantle. However, implications of these mineralogical changes to the lower-mantle heterogeneities are not well established. We have conducted systematic experimental investigations on the effects of Fe2+, Fe3+, and Al on the density, compressibility, and phase relations of Mg-silicates (perovskite and postperovskite) in the laser-heated diamond-anvil cell. The most important advance in our large dataset is in the use of the same pressure scale and quasi-hydrostatic pressure medium for all the subsets, which makes the dataset internally consistent therefore enables us to extract compositional effects accurately. Fe2+ in perovskite appears to be in mixed spin state in the lower mantle and its spin state does not impact the density and compressibility of perovskite. However, Fe3+ in the octahedral sites of perovskite undergoes a gradual spin transition, resulting in an increase in the compressibility of perovskite at the mid mantle when Al is absent. When Al is present in perovskite, Fe3+ undergoes a relatively sharp high-spin to low-spin transition, resulting in a volume collapse at the mid lower mantle. This difference in compressional behavior between Fe2+ and Fe3+ in perovskite makes Fe3+ thermodynamically stable in the lowermost mantle, supporting the occurrence of the charge disproportionation reaction and gravitationally stabilizing Al-rich mantle heterogeneities (such as basaltic materials). We also found that the depth of the

  5. Sources

    OpenAIRE

    2015-01-01

    Sources Fondation Pablo Iglesias. Alcala de Henares. Sections : Archives privées de Manuel ArijaArchives extérieuresArchives FNJS de EspañaPrensa Archives Générales de l’Administration. Alcala de Henares. Sections : Opposition au franquismeSig. 653 Sig TOP 82/68.103-68.602.Índice de las cartas colectivas, Relaciones, Cartas al Ministro de Información de Marzo de 1965. c.662. Sources cinématographiques Filmothèque Nationale d’Espagne.NO.DO. N° 1157C. 08/03/1965.aguirre Javier, Blanco vertical....

  6. Development of the Central-Afar volcanic margin, mantle upwelling and break-up processes

    Science.gov (United States)

    Pik, Raphaël; Bellahsen, Nicolas; Leroy, Sylvie; Stab, Martin; Ayalew, Dereje; Yirgu, Gezahegn

    2017-04-01

    Whereas the present day mantle dynamics is now well imaged by geophysical investigations, the long-term expression of mantle dynamics below rifted lithosphere is not directly recorded at the surface of the earth. Such information must therefore be extracted from non-direct manifestations of mantle upwelling, which are principally (i) the uplift of the upperlying lithosphere and (ii) the melts produced when the solidus of mantle mineral assemblages is crossed. These first order and unique evidences should therefore represent corner stones output of any geodynamic models used to deduce the interplay between mantle dynamics and surface deformations. For magmatism produced during extension of lithosphere, the dynamics of mantle upwelling can be recognized in the volumes of magmas and also in their geochremistry, which allow tracking the various types of mantle sources and the various types of mantle melting regime (P, T and intensity of partial melting). Volcanism has been closely associated with extension in the East African rift system. It is yet (and logically) heterogeneously distributed along the western, eastern and northern volcanic provinces. We have concentrated the efforts of a multidisciplinary team these last years in the northern Ethiopian volcanic province where the most important volumes of volcanism have been emplaced since 30 Ma, from Continental Flood Basalts episode to active extension along the Central Afar magmatic segment. These structural and geochemical data point out new constraints on the interplay between the upwelling of the Afar mantle plume and the style and mechanisms of extension, and imply to update and revise our understanding of the development of this volcanic margin.

  7. BurnMan: A Lower Mantle Mineral Physics Toolkit

    Science.gov (United States)

    Unterborn, C. T.; Rose, I.; Heister, T.; Cottaar, S.

    2013-12-01

    We present BurnMan (www.burnman.org), a python based, open-source toolbox to determine seismic velocities for specified compositions in the lower mantle. BurnMan calculates the isotropic thermoelastic moduli by solving the Equations-of-State (EoS) for a mixture of minerals defined by the user. BurnMan includes various libraries of lower mantle minerals or users can easily define their own. Tools to calculate the pressure and temperature dependent iron exchange between minerals, moduli variation across spin transitions, and more are integrated into the BurnMan infrastructure and easily adaptable to the user's specific needs. Example user scripts provide the user a guide to quickly and easily calculate seismic velocities and compare with observed values. Other scripts exemplify the many choices that can be made to customize BurnMan, for example in the choice of EoS, the averaging scheme, or the geotherm. BurnMan is easily scriptable and can be directly used to produce publication quality figures. BurnMan is currently focused on the lower mantle, but as it is offered open-source, it has the potential to expand to other planetary applications. Applications of BurnMan include forward modeling seismic velocities for a geodynamical model with a given composition, comparing models of different bulk Earth composition, and fitting experimental values with an EoS. An advantage of BurnMan is that experimental values can be fit by mineral physical constants, and subsequently these constants can be used with consistent methods and assumptions in the forward problem. Future work includes applying the BurnMan code as the forward model for a Bayesian inversion of seismic velocity models in the lower mantle, applying the latest results from mineral physics, and reasoning that the lower mantle cannot be represented by an average 1D radial seismic model. This collaboration was initiated at the CIDER 2012 summer meeting. Cottaar, S., Heister, T., Rose, I., and Unterborn, C.: Burn

  8. Tracing Proterozoic arc mantle Hf isotope depletion of southern Fennoscandia through coupled zircon U-Pb and Lu-Hf isotopes

    Science.gov (United States)

    Petersson, Andreas; Bjärnborg, Karolina; Scherstén, Anders; Gerdes, Axel; Næraa, Tomas

    2017-07-01

    Constraints on the composition of the depleted mantle Sm-Nd and Lu-Hf crust formation ages have a long history of scientific debate. When calculating mantle extraction ages, and constructing crustal growth models, a linear evolution of incompatible trace elements in a depleted mantle since > 4 Ga is routinely used. Mantle depletion however varies regionally and over time and subduction of sediments and oceanic crust renders a mantle-wedge variously enriched relative to a modelled depleted mantle. Here we show that primitive mantle-derived subduction related gabbroic intrusions from southern Fennoscandia have Hf isotope compositions that are enriched relative to a MORB-like linear depleted mantle evolution curve. Extrapolation of primitive Paleoproterozoic gabbro suites enables the construction of a regional mantle evolution curve, providing improved constraints on model ages, crustal residence times and the fraction of juvenile versus reworked continental crust. Convergent margins are assumed to be one of the main sites of continental crust growth, and using an overly depleted mantle source yield model ages that are too old, and hence cumulative crustal growth models show too much crust generation early in the Earth's history. The approach of using the Hf isotope composition of zircon from primitive subduction related gabbroic intrusions as a proxy for mantle Hf isotope composition, piloted in this study, can be applied to other convergent margins.

  9. A colossal impact enriched Mars' mantle with noble metals

    Science.gov (United States)

    Brasser, R.; Mojzsis, S. J.

    2017-06-01

    Once the terrestrial planets had mostly completed their assembly, bombardment continued by planetesimals left over from accretion. Highly siderophile element (HSE) abundances in Mars' mantle imply that its late accretion supplement was 0.8 wt %; Earth and the Moon obtained an additional 0.7 wt % and 0.02 wt %, respectively. The disproportionately high Earth/Moon accretion ratio is explicable by stochastic addition of a few remaining Ceres-sized bodies that preferentially targeted Earth. Here we show that Mars' late accretion budget also requires a colossal impact, a plausible visible remnant of which is the emispheric dichotomy. The addition of sufficient HSEs to the Martian mantle entails an impactor of at least 1200 km in diameter to have struck Mars before 4430 Ma, by which time crust formation was well underway. Thus, the dichotomy could be one of the oldest geophysical features of the Martian crust. Ejected debris could be the source material for its satellites.

  10. Old continental roots in young mantle plumes - the HIMU-diamond connection

    Science.gov (United States)

    Weiss, Y.; Class, C.; Goldstein, S. L.; Hanyu, T.

    2016-12-01

    Mantle melting leading to oceanic and continental crust formation, and crust recycling through plate tectonics, are primary processes driving the chemical differentiation of Earth. Present-day mantle, as sampled by MORB and OIB, shows large chemical and isotopic variability bounded by a few end-member compositions: the `depleted MORB mantle' or `DMM', sampled by most MORB, and three distinct trace-element `enriched mantle flavors' in OIBs called EM1, EM2 and HIMU. Among these, HIMU basalts stand out with the highest Pb isotope ratios, high Os isotope ratios, low Sr isotope ratios slightly higher than depleted MORB, and Nd-Sr isotopes plotting `below' the so-called `Nd-Sr mantle array'. Its mantle source is generally considered as recycled basaltic oceanic crust. However, recent analyses of olivine phenocrysts in HIMU lavas indicate derivation from peridotite partial melting, rather than pyroxenitic remnants of recycled basalt. We report high-precision trace element analyses of olivine phenocrysts from HIMU basalts (Mangaia and Tubuai, Cook Austral Islands), showing exceptionally high Ca/Al ratios that are far outside the range previously reported for olivines from MORB and OIB. These high Ca/Al ratios in olivines indicate an old metasomatic enrichment process involving carbonatitic fluid of the HIMU source. Moreover, a key piece to the HIMU puzzle is the similarities in trace element patterns between carbonatitic melt inclusions in diamonds, formed in the subcontinental lithospheric mantle (SCLM), and HIMU lavas. This "HIMU-diamond connection" indicates that carbonatite-metasomatized SCLM plays a major role in forming the HIMU source-mantle. Taking into account evidence from sulfur isotopes for Archean surface material in the deep HIMU source (Cabral et al., Nature 2013), we conclude the following multi-stage evolution for the HIMU end-member. Prior to entrainment in the convecting mantle, storage in a boundary layer, upwelling as a mantle plume, and partially

  11. Modelling the interplate domain in thermo-mechanical simulations of subduction: Critical effects of resolution and rheology, and consequences on wet mantle melting

    Science.gov (United States)

    Arcay, Diane

    2017-08-01

    surface temperature inferred from geothermometry, and 10-40 kJ/mol to reproduce the shallow hot mantle wedge core inferred from conditions of last equilibration of near-primary arc magmas and seismic tomographies. Therefore, an extra process controlling mantle wedge dynamics is needed to satisfy simultaneously the aforementioned observations. A mantle viscosity reduction, by a factor 4-20, caused by metasomatism in the mantle wedge is proposed. From these results, I conclude that the subduction channel down-dip extent, zcoup , should depend on the subduction setting, to be consistent with the observed variability of sub-arc depths of the subducting plate surface.

  12. Rhenium-osmium isotopes and highly siderophile elements in ultramafic rocks from the Eoarchean Saglek Block, northern Labrador, Canada: implications for Archean mantle evolution

    Science.gov (United States)

    Ishikawa, Akira; Suzuki, Katsuhiko; Collerson, Kenneth D.; Liu, Jingao; Pearson, D. Graham; Komiya, Tsuyoshi

    2017-11-01

    We determined highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) concentrations and 187Os/188Os ratios for ultramafic rocks distributed over the Eoarchean gneiss complex of the Saglek-Hebron area in northern Labrador, Canada in order to constrain to what extent variations in HSE abundances are recorded in Early Archean mantle that have well-resolved 182W isotope anomalies relative to the present-day mantle (∼+11 ppm: Liu et al., 2016). The samples analysed here have been previously classified into two suites: mantle-derived peridotites occurring as tectonically-emplaced slivers of lithospheric mantle, and metakomatiites comprising mostly pyroxenitic layers in supracrustal units dominated by amphibolites. Although previous Sm-Nd and Pb-Pb isotope studies provided whole-rock isochrons indicative of ∼3.8 Ga protolith formation for both suites, our whole-rock Re-Os isotope data on a similar set of samples yield considerably younger errorchrons with ages of 3612 ± 130 Ma (MSWD = 40) and 3096 ± 170 Ma (MSWD = 10.2) for the metakomatiite and lithospheric mantle suites, respectively. The respective initial 187Os/188Os = 0.10200 ± 18 for metakomatiites and 0.1041 ± 18 for lithospheric mantle rocks are within the range of chondrites. Re-depletion Os model ages for unradiogenic samples from the two suites are consistent with the respective Re-Os errorchrons (metakomatiite TRD = 3.4-3.6 Ga; lithospheric mantle TRD = 2.8-3.3 Ga). These observations suggest that the two ultramafic suites are not coeval. However, the estimated mantle sources for the two ultramafics suites are similar in terms of their broadly chondritic evolution of 187Os/188Os and their relative HSE patterns. In detail, both mantle sources show a small excess of Ru/Ir similar to that in modern primitive mantle, but a ∼20% deficit in absolute HSE abundances relative to that in modern primitive mantle (metakomatiite 74 ± 18% of PUM; lithospheric mantle 82 ± 10% of PUM), consistent with the

  13. A Dynamical Context for Small-scale Heterogeneity Throughout the Mantle Beneath Subduction

    Science.gov (United States)

    Frost, D. A.; Rost, S.; Garnero, E.

    2014-12-01

    Subduction zones are a source for mantle heterogeneity within the convection system and there is mounting evidence that seismic signatures can be used to track slabs down from the surface throughout the mantle. Seismic studies of the mantle beneath Central America demonstrate that subducted slab material reaches the Core-Mantle Boundary (CMB). The lowermost mantle beneath this convergent margin shows strong seismic evidence for heterogeneity. Tomographic models characterise subduction zones to be underlain by increased seismic velocities over 100s-1000s km laterally, in association with D'´ discontinuities 100-300 km above the CMB, consistent with phase transitions in the Bridgmanite system. Recent analyses have found evidence for isolated Ultra Low Velocity Zones in addition to prevalent fine-scale heterogeneity, on the order of 1-10 km, scattering high frequency waves. These techniques indicate thermal and/or chemical anomalies within the mantle on a range of scales. Numerical geodynamical simulations suggest small-scale mechanical mixing of initially coherent compositionally anomalous subducted material separating into entities of various sizes consistent with the range of heterogeneity sizes observed in the lower mantle.Investigating seismic scattering, the re-radiation of a wavefront due to interaction with a sharply contrasting volumetric anomaly, is an effective method for studying small-scale elastic heterogeneities in the Earth's mantle. Studies commonly record structure with scale lengths of about 10 km. Here we analyse scattered energy related to PKPPKP — PKP•PKP (the • indicates the scattering location along the raypath) — sampling a large volume of the mantle beneath Central America. We reveal the character of heterogeneity in various frequency bands within the whole mantle using both broadband and short-period data. These observations will be placed in context with other studies in this region illustrating the large-scale background structure

  14. The importance of mantle wedge heterogeneity to subduction zone magmatism and the origin of EM1

    Science.gov (United States)

    Turner, Stephen J.; Langmuir, Charles H.; Dungan, Michael A.; Escrig, Stephane

    2017-08-01

    -member found in continental arcs is produced by low-degree melt-metasomatism of the sub-continental lithospheric mantle may be more plausible. The 143Nd/144Nd maximum along the SVZ may be a consequence of either rifting and collision of two ancient lithospheric domains or a slab tear. The correspondence of mantle wedge variations with EM1 suggests a potential role for metasomatized sub-continental lithosphere in creating EM1 sources globally.

  15. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Pulliam, Robert Jay [Univ. of California, Berkeley, CA (United States)

    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. Sources

    OpenAIRE

    2014-01-01

    Archives Archivo Histórico del Estado de Jalisco Fondo Gobernación, Asunto Pasaportes y Salvoconductos : G-8-877/9773-9775 G-8-878/9774, 9776, 9777 et 9781 G-8-879/9782-9788 G-8-880/9789-9798 G-8-881-882/9803 G-8-882/9804-9805 G-8-883/9806-9811 G-8-884/9813 G-8-885/9817-9820 G-8-886/9822-9825 G-8-887/9826-9830 G-8-888/9835 G-8-889-890/9837 G-8-889/9839 Sources imprimées Livres et chroniques O’Farrill Romulo, (2004) Reseña histórica estadística y comercial de México y sus estados, directorio g...

  18. Tomography images of the Alpine roots and surrounding upper mantle

    Science.gov (United States)

    Plomerova, Jaroslava; Babuska, Vladislav

    2017-04-01

    -processed, mostly the ISC-bulletin data (Babuska et al., Tectonophysics 1990). Calculated relative travel-time residuals have been assigned to source clusters and filtered relative to the residual mean of each cluster of events. We expect that future 3D studies of the mantle velocities and mantle fabrics with the use of body-wave anisotropic parameters from the AlpArray data will shed a new light on tectonic development of the complex Alpine region and its surroundings.

  19. Radiative conductivity in the Earth's lower mantle.

    Science.gov (United States)

    Goncharov, Alexander F; Haugen, Benjamin D; Struzhkin, Viktor V; Beck, Pierre; Jacobsen, Steven D

    2008-11-13

    Iron in crustal and mantle minerals adopts several possible oxidation states: this has implications for biogeochemical processes, oxygenation of the atmosphere and the oxidation state of the mantle. In the deep Earth, iron in silicate perovskite, (Mg(0.9)Fe(0.1))SiO(3), and ferropericlase, (Mg(0.85)Fe(0.15))O, influences the thermal conductivity of the lower mantle and therefore heat flux from the core. Little is known, however, about the effect of iron oxidation states on transport properties. Here we show that the radiative component of thermal conductivity in the dominant silicate perovskite material of Earth's lower mantle is controlled by the amount of ferric iron, Fe(3+). We obtained the optical absorption spectra of silicate perovskite and ferropericlase at pressures up to 133 GPa, corresponding to pressures at the core-mantle boundary. Absorption spectra of ferropericlase up to 800 K and 60 GPa exhibit minimal temperature dependence. The results on silicate perovskite show that optical absorption in the visible and near-infrared spectral range is dominated by O-Fe(3+) charge transfer and Fe(3+)-Fe(2+) intervalence transitions, whereas a contribution from the Fe(2+) crystal-field transitions is substantially smaller. The estimated pressure-dependent radiative conductivity, k(rad), from these data is 2-5 times lower than previously inferred from model extrapolations, with implications for the evolution of the mantle, such as generation and stability of thermo-chemical plumes in the lower mantle.

  20. Early mantle dynamics inferred from 142Nd variations in Archean rocks from southwest Greenland

    DEFF Research Database (Denmark)

    Rizo, Hanika; Boyet, Maud; Blichert-Toft, Janne

    2013-01-01

    of the Greenland samples from a source formed in the Hadean. This mantle source is the oldest yet identified on Earth and therefore provides key information about the nature and evolution of early-differentiated reservoirs. In contrast, modern mantle-derived rocks from around the world do not have Nd-142 anomalies......, suggesting that the primordial heterogeneities detected in Earth's early mantle have been erased over time. In order to better constrain the rate at which early mantle heterogeneities have been re-homogenized, we produced new Sm-146-Nd-142 data for both 3.8 and 3.3 Ga old mafic rocks from different tectonic...... domains of the ISB, accompanied by their corresponding Sm-147-Nd-143 and Lu-176-Hf-176 systematics. The 3.8 Ga suite yields Nd-142 excesses comparable to those detected previously in 3.7 Ga old ISB amphibolites, indicating that Eoarchean mafic ISB Iavas originated from sources with similar differentiation...

  1. Consequences of an unstable chemical stratification on mantle dynamics

    Science.gov (United States)

    Plesa, Ana-Catalina; Tosi, Nicola; Breuer, Doris

    2013-04-01

    phase transition between lower and upper mantle and assumed all radiogenic heat sources to be enriched during the freezing-phase of the magma ocean in the uppermost 50 km [4]. A stagnant lid forms rapidly because of the strong temperature dependence of the viscosity. This prevents the uppermost dense cumulates to sink, even when allowing for a plastic yielding mechanism. Below this dense stagnant lid, the mantle chemical gradient settles to a stable configuration. The convection pattern is dominated by small-scale structures, which are difficult to reconcile with the large-scale volcanic features observed over Mars' surface. Assuming that the stagnant lid will break, a stable density gradient is obtained, with the densest material and the entire amount of heat sources lying above the core-mantle-boundary. This leads to a strong overheating of the lowermost mantle, whose temperature increases to values that exceed the liquidus. Therefore a fractionated global and deep magma ocean is difficult to reconcile with observations. Different scenarios assuming, for instance, a hemispherical or shallow magma ocean will have to be considered. References [1] N. Tosi, D.A. Yuen and O. Dadek; EPSL (2010) (Yet Another Convection Code, https://code.google.com/p/yacc-convection/) [2] C. Huettig and K. Stemmer; PEPI (2008) [3] L.T. Elkins-Tanton, E.M. Parmentier and P.C. Hess; Meteoritic and Planetary Science (2003) [4] L.T. Elkins-Tanton, S.E. Zaranek, E.M. Parmentier and P.C. Hess; EPSL (2005)

  2. What Comes Around Goes Around: Mantle Convection and the Meaning of Mantle Isochrons

    Science.gov (United States)

    Hauri, E. H.; Brandenburg, J.; Vankeken, P.; Ballentine, C.

    2007-12-01

    The perceived significance of isotopic data arrays for oceanic basalts has long occupied a middle ground between the endmember interpretations of mixing and age. Brooks et al. [1] were the first to attach age significance to the correlations between parent-daughter ratios and daughter isotope ratios that are a regular feature of the geochemistry of OIB and MORB [e.g. 2,3]. Pseudo-isochrons derived from mixed mantle can still have age significance if the various packets of source material have been physically juxtaposed for long periods of time, yet the current paradigm has generally been to focus on daughter ratios alone, and to interpret their variations in terms of multi-component mixing. Numerous high-quality geochemical data sets now exist, and continute to be generated, for specific regions of OIB and MORB volcanism. In order to take the next step in a more accurate interpretation of this data, a forward model is needed that delimits the bounds of chemical variability and isotopic correlations expected to arise from the major processes operative during terrestrial mantle convection. In this talk, we will present the results of cylindrical 2D convection models with force-balanced plates [4] and examine specifically the roles of subduction and convective mixing of oceanic crust, with extraction of continental crust superimposed. In these models, melting occurs at divergent plate boundaries and geochemical evolution is recorded by millions of passive (harzburgite) and active (basalt) tracers that record the times, extents of melting, and extents of degassing and continent extraction at every melting event, allowing the geochemical evolution of any isotope system to be easily calculated (and recalculated) in a post-processing algorithm that operates on the tracer data independently from the dynamic calculations. We will explore the range of isotopic variability in these models as functions of partition coefficients, chemical density of basalt tracers, convective

  3. Solubility of Nitrogen in Stishovite: A Possible Storage Mechanism for Nitrogen in Earth's Deep Mantle

    Science.gov (United States)

    Noble, S. M.; Shim, S. H. D.; Hervig, R. L.; Prakapenka, V.

    2016-12-01

    Although studies have suggested the flux of nitrogen from the mantle as well as the subduction of nitrogen back into the mantle, it is unknown how much nitrogen can be stored in the deep mantle. Some key questions remain unknown: Does nitrogen exist in major mantle minerals or in minor phases? Or does nitrogen form nitrides or oxynitrides in the mantle? We have synthesized stishovite under nitrogen saturated conditions in laser-heated diamond-anvil cells at pressures between 16 and 44 GPa and temperatures centered at 1800 K. Experimental products were recovered and analyzed for nitrogen content via SIMS, SEM and EDX analysis at Arizona State University, while unit cell parameters were measured through synchrotron x-ray diffraction at the GSECARS sector of the Advanced Photon Source. Our SIMS data show that nitrogen solubility in stishovite is 1.54 wt %. The existence of nitrogen was also confirmed through energy-dispersive X-ray spectroscopy in SEM. Diffraction data indicates a slightly higher unit cell volume of stishovite synthesized under a nitrogen saturated environment than pure stishovite at pressures above 28 GPa. Because stishovite is expected to be a major phase in subducting oceanic crust in the mantle (more than 15%), according to our new experiments, stishovite can serve as a host for nitrogen in the mantle. With similar atomic radii, slightly smaller-sized nitrogen may substitute for oxygen atoms in the crystal structure of stishovite. At a storage capacity of 1.54 wt % for N in stishovite, this study indicates a potentially large nitrogen reservoir within the Earth's mantle.

  4. Teaching the Mantle Plumes Debate

    Science.gov (United States)

    Foulger, G. R.

    2010-12-01

    There is an ongoing debate regarding whether or not mantle plumes exist. This debate has highlighted a number of issues regarding how Earth science is currently practised, and how this feeds into approaches toward teaching students. The plume model is an hypothesis, not a proven fact. And yet many researchers assume a priori that plumes exist. This assumption feeds into teaching. That the plume model is unproven, and that many practising researchers are skeptical, may be at best only mentioned in passing to students, with most teachers assuming that plumes are proven to exist. There is typically little emphasis, in particular in undergraduate teaching, that the origin of melting anomalies is currently uncertain and that scientists do not know all the answers. Little encouragement is given to students to become involved in the debate and to consider the pros and cons for themselves. Typically teachers take the approach that “an answer” (or even “the answer”) must be taught to students. Such a pedagogic approach misses an excellent opportunity to allow students to participate in an important ongoing debate in Earth sciences. It also misses the opportunity to illustrate to students several critical aspects regarding correct application of the scientific method. The scientific method involves attempting to disprove hypotheses, not to prove them. A priori assumptions should be kept uppermost in mind and reconsidered at all stages. Multiple working hypotheses should be entertained. The predictions of a hypothesis should be tested, and unpredicted observations taken as weakening the original hypothesis. Hypotheses should not be endlessly adapted to fit unexpected observations. The difficulty with pedagogic treatment of the mantle plumes debate highlights a general uncertainty about how to teach issues in Earth science that are not yet resolved with certainty. It also represents a missed opportunity to let students experience how scientific theories evolve, warts

  5. Elastic Properties of Mantle Minerals

    Science.gov (United States)

    Duffy, T. S.; Stan, C. V.

    2012-12-01

    The most direct information about the interior structure of the Earth comes from seismic wave velocities. Interpretation of seismic data requires an understanding of how sound velocities and elastic properties of minerals vary with pressure, temperature, crystal structure, and composition as well as the role of anelasticity, melts, etc. More generally, elastic moduli are important for understanding many solid-state phenomena including mechanical stability, interatomic interactions, material strength, compressibility, and phase transition mechanisms. The database of mineral elasticity measurements has been growing rapidly in recent years. In this work, we report initial results of an ongoing survey of our current knowledge of mineral elasticity at both ambient conditions and high pressures and temperatures. The analysis is selective, emphasizing single crystal measurements but also incorporating polycrystalline measurements and volume compression data as appropriate. The goal is to synthesize our current understanding of mineral elasticity in terms of structure and composition, and to identify the major remaining needs for experimental and theoretical work. Clinopyroxenes (Cpx) provide an example of our approach. A wide range of clinopyroxene compositions are found geologically and Mg-, Ca-, and Na-rich clinopyroxenes are expected to be important components in the upper mantle. The single-crystal elastic properties of a number of endmember Cpx compositions have been measured and these exhibit a range of ~25% in shear velocity. Those with monovalent cations (spodumene, jadeite) in the M2 site exhibit the highest velocities while Fe-rich (hendenbergit, acmite) compositions have the lowest velocities. The effects on velocity due to a wide range of chemical substitutions can be defined, but there are important discrepancies and omissions in the database. New measurements of omphacites, intermediate diopside-hedenbergite compositions, aegerine/acmite, augite, etc. are

  6. Characteristics of Vertical Mantle Heat Exchangers for Solar Water Heaters

    DEFF Research Database (Denmark)

    Shah, Louise Jivan; Morrison, G.L.; Behnia, M.

    1999-01-01

    - The flow structure in vertical mantle heat exchangers was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the mantle were measured using a particle Image Velocimetry (PIV) system. A CFD simulation model of vertical mantle heat...... exchangers was also developed for detailed evaluation of the heat flux distribution over the mantle surface. Both the experimental and simulation results indicate that distribution of the flow around the mantle gap is governed by buoyancy driven recirculation in the mantle. The operation of the mantle...

  7. How mantle slabs drive plate tectonics.

    Science.gov (United States)

    Conrad, Clinton P; Lithgow-Bertelloni, Carolina

    2002-10-04

    The gravitational pull of subducted slabs is thought to drive the motions of Earth's tectonic plates, but the coupling between slabs and plates is not well established. If a slab is mechanically attached to a subducting plate, it can exert a direct pull on the plate. Alternatively, a detached slab may drive a plate by exciting flow in the mantle that exerts a shear traction on the base of the plate. From the geologic history of subduction, we estimated the relative importance of "pull" versus "suction" for the present-day plates. Observed plate motions are best predicted if slabs in the upper mantle are attached to plates and generate slab pull forces that account for about half of the total driving force on plates. Slabs in the lower mantle are supported by viscous mantle forces and drive plates through slab suction.

  8. The lithospheric mantle below southern West Greenland

    DEFF Research Database (Denmark)

    Sand, Karina Krarup; Waight, Tod Earle; Pearson, D. Graham

    2009-01-01

    Geothermobarometry of primarily garnet lherzolitic xenoliths from several localities in southern West Greenland is applied to address the diamond potential, pressure and temperature distribution and the stratigraphy of the subcontinental lithospheric mantle ~600 Ma ago. The samples are from...

  9. Fine-scale structure of the mid-mantle characterised by global stacks of PP precursors

    Science.gov (United States)

    Bentham, H. L. M.; Rost, S.; Thorne, M. S.

    2017-08-01

    Subduction zones are likely a major source of compositional heterogeneities in the mantle, which may preserve a record of the subduction history and mantle convection processes. The fine-scale structure associated with mantle heterogeneities can be studied using the scattered seismic wavefield that arrives as coda to or as energy preceding many body wave arrivals. In this study we analyse precursors to PP by creating stacks recorded at globally distributed stations. We create stacks aligned on the PP arrival in 5° distance bins (with range 70-120°) from 600 earthquakes recorded at 193 stations stacking a total of 7320 seismic records. As the energy trailing the direct P arrival, the P coda, interferes with the PP precursors, we suppress the P coda by subtracting a best fitting exponential curve to this energy. The resultant stacks show that PP precursors related to scattering from heterogeneities in the mantle are present for all distances. Lateral variations are explored by producing two regional stacks across the Atlantic and Pacific hemispheres, but we find only negligible differences in the precursory signature between these two regions. The similarity of these two regions suggests that well mixed subducted material can survive at upper and mid-mantle depth. To describe the scattered wavefield in the mantle, we compare the global stacks to synthetic seismograms generated using a Monte Carlo phonon scattering technique. We propose a best-fitting layered heterogeneity model, BRT2017, characterised by a three layer mantle with a background heterogeneity strength (ɛ = 0.8%) and a depth-interval of increased heterogeneity strength (ɛ = 1%) between 1000 km and 1800 km. The scalelength of heterogeneity is found to be 8 km throughout the mantle. Since mantle heterogeneity of 8 km scale may be linked to subducted oceanic crust, the detection of increased heterogeneity at mid-mantle depths could be associated with stalled slabs due to increases in viscosity

  10. Mantle heterogeneity and the D" discontinuity

    Science.gov (United States)

    Grocholski, B.; Catalli, K.; Shim, S.

    2011-12-01

    The observation of the D'' discontinuity, especially in regions of high shear-wave velocity, has been attributed to the thermal response of the perovskite (Pv) to post-perovskite (PPv) transition. This interpretation requires a large and positive Clapeyron slope in addition to a narrow two-phase region to be seismically detectable. Mineral physics experiments of this system have been evolving to investigate both chemical and mineralogical variations possible for the D'' region of the mantle. This has come with some surprises, including two-phase regions that would span hundreds of km depth in aluminum (Tateno et al., 2005), iron (Catalli et al., 2009), and mantle-relevant aluminum-iron bearing systems (Catalli et al., 2009, Andrault et al., 2010). Our most recent experimental results suggest that other minerals play an important role in partitioning iron and aluminum to decrease the thickness of the mixed phase region such that the transition will be seismically detectable. In particular, aluminum stabilizing Pv makes it challenging for the PPv transition to be detectable in a homogeneous (pyrolitic) mantle. However, subduction of oceanic lithosphere injects heterogeneous rock types (basaltic, harzburgitic) that are more likely to have seismically detectable transitions. Therefore, the mantle heterogeneities originated from recycled oceanic lithosphere may be responsible for the D'' discontinuity. Enriched, basalt-like compositions would be expected to have a discontinuity ˜400 km above the core-mantle boundary (CMB) possibly controlled by the appearance of a PbO2-like structured silica capable of dissolving large amounts of aluminum. Depleted, harzburgite-like mantle compositions are likely to have a transition ˜100 km above the CMB, which is sharp due to iron partitioning into ferropericlase combined with a low aluminum content. This picture of heterogeneity in the lowermost mantle not only helps explains the seismic results on the D'' discontinuity itself, but

  11. Noble Gases as Mantle Tracers

    Science.gov (United States)

    Hilton, D. R.; Porcelli, D.

    2003-12-01

    The study of the noble gases has been associated with some of the most illustrious names in experimental science, and some of the most profound discoveries. Fundamental advances in nuclear chemistry and physics - including the discovery of isotopes - have resulted from their study, earning Nobel Prizes for a number of early practitioners (Rutherford in 1908; Soddy in 1921; Aston in 1922) as well as for their discoverers (Ramsay and Rayleigh in 1904). Within the Earth Sciences, the noble gases found application soon after discovery - helium was used as a chronometer to estimate formation ages of various minerals (Strutt, 1908). In more recent times, the emphasis of noble gas research has shifted to include their exploitation as inert tracers of geochemical processes. In large part, this shift stems from the realization that primordial volatiles have been stored within the Earth since the time of planetary accretion and are still leaking to the surface today. In this introduction, we give a brief overview of the discovery of the noble gases and their continuing utility in the Earth Sciences, prior to setting into perspective the present contribution, which focuses on noble gases in the Earth's mantle.

  12. Fine scale heterogeneity in the Earth's upper mantle - observation and interpretation

    DEFF Research Database (Denmark)

    Thybo, Hans

    2014-01-01

    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...... in the frequency band of 0.5-15 Hz: (1) The Mantle Low-Velocity Zone (LVZ) is a global feature which has been detected in more than 50 long-range seismic profiles (Thybo and Perchuc, Science, 1997). Since then numerous studies based on receiver functions, surface waves, and controlled source seismology have......) Heterogeneity arising from subducted slabs that have equilibrated around the Transition Zone. We model characteristic scale lengths and velocity contrasts of the mantle heterogeneity by application of 2D Finite Difference simulation of seismic wave propagation. Unfortunately the seismic data does not allow...

  13. Dehydration melting of nominally anhydrous mantle: The primacy of partitioning

    Science.gov (United States)

    Hirschmann, Marc M.; Tenner, Travis; Aubaud, Cyril; Withers, A. C.

    2009-09-01

    melting at 110 km requires 300 ppm H 2O and generation of small finite (≥0.1%) melt fractions across the entire LVZ from 90 to 200 km requires 600 ppm H 2O. The minimum concentration, 300 ppm H 2O, is 2-3 times that of typical convecting oceanic (MORB-source) mantle, so it is not likely that pervasive hydrous partial melting is responsible for the seismic properties of the LVZ. Extrapolation of low pressure partition coefficients to the base of the upper mantle indicates that at least 500 ppm H 2O is required to induce partial melting at depths of 300-400 km along a normal mantle geotherm. This argues that typical upper mantle with ˜100 ppm H 2O is not produced by partial melting above the 410 km discontinuity. Furthermore, the 500 ppm H 2O concentration is likely to be an underestimate, as it does not take into account probable enhancement in DHmin/liq at high pressure.

  14. Vapor Undersaturation in Primitive MORBs and the Volatile Content of the Earth's Upper Mantle

    Science.gov (United States)

    Saal, A. E.; Hauri, E. H.; Langmuir, C. H.; Perfit, M. R.

    2002-12-01

    We present the first report of undersaturated pre-eruptive volatile content for a suite of MORBs from the Siqueiros intra-transform spreading center. The undersaturation leads to correlations between volatiles and refractory trace elements that provide new constraints on the volatile abundances in the depleted upper mantle and their behavior during melting. The constant CO2/Nb ratio of the samples show that CO2 is a higly incompatible element during MORB generation and constrains the abundance of CO2 in the MORB mantle source to (72+/-19) values substantially lower than most previous estimates. This result is supported by the excellent correlation between Cl and CO2 in the Siqueiros melt inclusions. Thus, the CO2-Nb, CO2-Cl correlations permit primitive CO2 and Cl estimates to be made for degassed and Cl contaminated MORBs. The volatile-rich popping rocks that have led to previous high CO2 estimates for the upper mantle have very high volatile contents in large part because of their incompatible element enrichment (e.g. very high Nb contents). Our results and the relatively constant CO2/3He ratio for MORBs allow constraints on the extent of 3He degassing, its flux at ridges and its content in the upper mantle. The constant ratios of H2O/Ce, F/P, S/Dy and Cl/K in Siqueiros glasses and melt inclusions together with previous estimates of the refractory trace element content in the MORB mantle constrain the abundances of H2O (142+/-85), F (16+/-3), S (146+/-35) and Cl (1+/-0.5) in the Earth's upper mantle. These abundances are much lower than estimates for the source regions of hotspots, indicating the presence of volatile heterogeneity in the Earth's mantle.

  15. Tectonic plates, D (double prime) thermal structure, and the nature of mantle plumes

    Science.gov (United States)

    Lenardic, A.; Kaula, W. M.

    1994-01-01

    It is proposed that subducting tectonic plates can affect the nature of thermal mantle plumes by determining the temperature drop across a plume source layer. The temperature drop affects source layer stability and the morphology of plumes emitted from it. Numerical models are presented to demonstrate how introduction of platelike behavior in a convecting temperature dependent medium, driven by a combination of internal and basal heating, can increase the temperature drop across the lower boundary layer. The temperature drop increases dramatically following introduction of platelike behavior due to formation of a cold temperature inversion above the lower boundary layer. This thermal inversion, induced by deposition of upper boundary layer material to the system base, decays in time, but the temperature drop across the lower boundary layer always remains considerably higher than in models lacking platelike behavior. On the basis of model-inferred boundary layer temperature drops and previous studies of plume dynamics, we argue that generally accepted notions as to the nature of mantle plumes on Earth may hinge on the presence of plates. The implication for Mars and Venus, planets apparently lacking plate tectonics, is that mantle plumes of these planets may differ morphologically from those of Earth. A corollary model-based argument is that as a result of slab-induced thermal inversions above the core mantle boundary the lower most mantle may be subadiabatic, on average (in space and time), if major plate reorganization timescales are less than those acquired to diffuse newly deposited slab material.

  16. Evolution of continental crust and mantle heterogeneity: Evidence from Hf isotopes

    Science.gov (United States)

    Jonathan, Patchett P.; Kouvo, O.; Hedge, C.E.; Tatsumoto, M.

    1982-01-01

    We present initial 176Hf/177 Hf ratios for many samples of continental crust 3.7-0.3 Gy old. Results are based chiefly on zircons (1% Hf) and whole rocks: zircons are shown to be reliable carriers of essentially the initial Hf itself when properly chosen on the basis of U-Pb studies. Pre-3.0 Gy gneisses were apparently derived from an unfractionated mantle, but both depleted and undepleted mantle are evident as magma sources from 2.9 Gy to present. This mantle was sampled mainly from major crustal growth episodes 2.8, 1.8 and 0.7 Gy ago, all of which show gross heterogeneity of 176Hf/177Hf in magma sources from ??Hf=0 to +14, or about 60% of the variability of the present mantle. The approximate ??Hf=2??Nd relationship in ancient and modern igneous rocks shows that 176Lu/177Hf fractionates in general twice as much as 147Sm/144Nd in mantle melting processes. This allows an estimation of the relative value of the unknown bulk solid/liquid distribution coefficient for Hf. DLu/DHf=??? 2.3 holds for most mantle source regions. For garnet to be an important residual mantle phase, it must hold Hf strongly in order to preserve Hf-Nd isotopic relationships. The ancient Hf initials are consistent with only a small proportion of recycled older cratons in new continental crust, and with quasi-continuous, episodic growth of the continental crust with time. However, recycling of crust less than 150 My old cannot realistically be detected using Hf initials. The mantle shows clearly the general positive ??Hf resulting from a residual geochemical state at least back to 2.9 Gy ago, and seems to have repeatedly possessed a similar degree of heterogeneity, rather than a continuously-developing depletion. This is consistent with a complex dynamic disequilibrium model for the creation, maintenance and destruction of heterogeneity in the mantle. ?? 1981 Springer-Verlag.

  17. Extreme incompatibility of helium during mantle melting: Evidence from undegassed mid-ocean ridge basalts

    Science.gov (United States)

    Graham, David W.; Michael, Peter J.; Shea, Thomas

    2016-11-01

    We report total helium concentrations (vesicles + glass) for a suite of thirteen ultradepleted mid-ocean ridge basalts (UD-MORBs) that were previously studied for volatile contents (CO2, H2O) plus major and trace elements. The selected basalts are undersaturated in CO2 + H2O at their depths of eruption and represent rare cases of undegassed MORBs. Sample localities from the Atlantic (2), Indian (1) and Pacific (7) Oceans collectively show excellent linear correlations (r2 = 0.75- 0.92) between the concentrations of helium and the highly incompatible elements C, K, Rb, Ba, Nb, Th and U. Three basalts from Gakkel Ridge in the Arctic were also studied but show anomalous behavior marked by excess lithophile trace element abundances. In the Atlantic-Pacific-Indian suite, incompatible element concentrations vary by factors of 3-4.3, while helium concentration varies by a factor of 13. The strong correlations between the concentrations of helium and incompatible elements are explained by helium behavior as the most incompatible element during mantle melting. Partial melting of an ultradepleted mantle source, formed as a residue of earlier melt extraction, accounts for the observed concentrations. The earlier melting event involved removal of a small degree melt (∼1%) at low but non-zero porosity (0.01-0.5%), leading to a small amount of melt retention that strongly leveraged the incompatible element budget of the ultradepleted mantle source. Equilibrium melting models that produce the range of trace element and helium concentrations from this source require a bulk solid/melt distribution coefficient for helium that is lower than that for other incompatible elements by about a factor of ten. Alternatively, the bulk solid/melt distribution coefficient for helium could be similar to or even larger than that for other incompatible elements, but the much larger diffusivity of helium in peridotite leads to its more effective incompatibility and efficient extraction from a

  18. Seismic anisotropy in the Hellenic subduction zone: Effects of slab segmentation and subslab mantle flow

    Science.gov (United States)

    Evangelidis, C. P.

    2017-12-01

    The segmentation and differentiation of subducting slabs have considerable effects on mantle convection and tectonics. The Hellenic subduction zone is a complex convergent margin with strong curvature and fast slab rollback. The upper mantle seismic anisotropy in the region is studied focusing at its western and eastern edges in order to explore the effects of possible slab segmentation on mantle flow and fabrics. Complementary to new SKS shear-wave splitting measurements in regions not adequately sampled so far, the source-side splitting technique is applied to constrain the depth of anisotropy and to densify measurements. In the western Hellenic arc, a trench-normal subslab anisotropy is observed near the trench. In the forearc domain, source-side and SKS measurements reveal a trench-parallel pattern. This indicates subslab trench-parallel mantle flow, associated with return flow due to the fast slab rollback. The passage from continental to oceanic subduction in the western Hellenic zone is illustrated by a forearc transitional anisotropy pattern. This indicates subslab mantle flow parallel to a NE-SW smooth ramp that possibly connects the two subducted slabs. A young tear fault initiated at the Kefalonia Transform Fault is likely not entirely developed, as this trench-parallel anisotropy pattern is observed along the entire western Hellenic subduction system, even following this horizontal offset between the two slabs. At the eastern side of the Hellenic subduction zone, subslab source-side anisotropy measurements show a general trench-normal pattern. These are associated with mantle flow through a possible ongoing tearing of the oceanic lithosphere in the area. Although the exact geometry of this slab tear is relatively unknown, SKS trench-parallel measurements imply that the tear has not reached the surface yet. Further exploration of the Hellenic subduction system is necessary; denser seismic networks should be deployed at both its edges in order to achieve

  19. Horizontal mantle flow controls subduction dynamics.

    Science.gov (United States)

    Ficini, E; Dal Zilio, L; Doglioni, C; Gerya, T V

    2017-08-08

    It is generally accepted that subduction is driven by downgoing-plate negative buoyancy. Yet plate age -the main control on buoyancy- exhibits little correlation with most of the present-day subduction velocities and slab dips. "West"-directed subduction zones are on average steeper (~65°) than "East"-directed (~27°). Also, a "westerly"-directed net rotation of the lithosphere relative to the mantle has been detected in the hotspot reference frame. Thus, the existence of an "easterly"-directed horizontal mantle wind could explain this subduction asymmetry, favouring steepening or lifting of slab dip angles. Here we test this hypothesis using high-resolution two-dimensional numerical thermomechanical models of oceanic plate subduction interacting with a mantle flow. Results show that when subduction polarity is opposite to that of the mantle flow, the descending slab dips subvertically and the hinge retreats, thus leading to the development of a back-arc basin. In contrast, concordance between mantle flow and subduction polarity results in shallow dipping subduction, hinge advance and pronounced topography of the overriding plate, regardless of their age-dependent negative buoyancy. Our results are consistent with seismicity data and tomographic images of subduction zones. Thus, our models may explain why subduction asymmetry is a common feature of convergent margins on Earth.

  20. Upper mantle structure of the Tonga-Lau-Fiji region from Rayleigh wave tomography

    Science.gov (United States)

    Wei, S. Shawn; Zha, Yang; Shen, Weisen; Wiens, Douglas A.; Conder, James A.; Webb, Spahr C.

    2016-11-01

    We investigate the upper mantle seismic structure in the Tonga-Lau-Fiji region by jointly fitting the phase velocities of Rayleigh waves from ambient-noise and two-plane-wave tomography. The results suggest a wide low-velocity zone beneath the Lau Basin, with a minimum SV-velocity of about 3.7 ± 0.1 km/s, indicating upwelling hot asthenosphere with extensive partial melting. The variations of velocity anomalies along the Central and Eastern Lau Spreading Centers suggest varying mantle porosity filled with melt. In the north where the spreading centers are distant from the Tonga slab, the inferred melting commences at about 70 km depth, and forms an inclined zone in the mantle, dipping to the west away from the arc. This pattern suggests a passive decompression melting process supplied by the Australian plate mantle from the west. In the south, as the supply from the Australian mantle is impeded by the Lau Ridge lithosphere, flux melting controlled by water from the nearby slab dominates in the back-arc. This source change results in the rapid transition in geochemistry and axial morphology along the spreading centers. The remnant Lau Ridge and the Fiji Plateau are characterized by a 60-80 km thick lithosphere underlain by a low-velocity asthenosphere. Our results suggest the removal of the lithosphere of the northeastern Fiji Plateau-Lau Ridge beneath the active Taveuni Volcano. Azimuthal anisotropy shows that the mantle flow direction rotates from trench-perpendicular beneath Fiji to spreading-perpendicular beneath the Lau Basin, which provides evidence for the southward flow of the mantle wedge and the Samoan plume.

  1. Compositions and processes of lithospheric mantle beneath the west Cathaysia block, southeast China

    Science.gov (United States)

    Zhang, Hui; Zheng, Jianping; Pan, Shaokui; Lu, Jianggu; Li, Yihe; Xiang, Lu; Lin, Abing

    2017-08-01

    Knowledge about the nature and history of the lithospheric mantle beneath the west Cathaysia block (South China) is still sparse. The major- and trace-element compositions and H2O contents of minerals from peridotite xenoliths entrained in the Cenozoic lamprophyres of the Anyuan area (SE China), were conducted to investigate the nature and evolution of the lithospheric mantle, as well as the factors controlling the distribution of water. The xenoliths including spinel harzburgites and lherzolites are moderately refractory (Mg# Olivine = 90.2-91.2) with minor fertile lherzolites (Mg# Olivine = 89.1-89.9). Clinopyroxenes in lherzolites show variable REE patterns from LREE-depleted to LREE-enriched patterns, and commonly exhibit negative anomalies of U, Pb and Ti. The mantle represented by the xenoliths mostly experienced 1-10% partial melting and obvious subsequent silicate metasomatism. H2O contents of clinopyroxene, orthopyroxene, and olivine in the peridotites are 320-404 ppm, 138-200 ppm, and 11-33 ppm, respectively. The whole-rock H2O contents range from 63 to 120 ppm, similar to that estimated for the MORB source. The negative correlations of H2O contents with Mg# in olivine and lack of correlation correlations with (La/Yb)N in clinopyroxene suggest that the H2O contents are mainly controlled by the partial melting process rather than mantle metasomatism. The fertile and moderately refractory peridotite xenoliths have similar equilibrium temperatures, implying that the lithospheric mantle is not compositionally stratified. Integrated with published data, we suggest that the widespread fertile and moderately refractory lithospheric mantle beneath the studied area (west Cathaysia), even the whole South China, might be eroded or melt-rock reacted by upwelling asthenospheric materials. Finally, the cooling of the upwelled asthenospheric materials resulted in the formation of the accreted lithospheric mantle mixed with pre-existing moderately refractory volumes.

  2. OPTIMISATION OF MANTLE TANKS FOR LOW FLOW SOLAR HEATING SYSTEMS

    DEFF Research Database (Denmark)

    Shah, Louise Jivan; Furbo, Simon

    1996-01-01

    A model, describing the heat transfer coefficients in the mantle of a mantle tank has been developed. The model is validated by means of measurements with varying operational conditions for different designed mantle tanks. The model has been implemented in an existing detailed mathematical...... with the programme and by means of tests of three SDHW systems with different designed mantle tanks. Based on the investigations design rules for mantle tanks are proposed. The model, describing the heat transfer coefficients in the mantle is approximate. In addition, the measurements have revealed...

  3. Iron isotopes may reveal the redox conditions of mantle melting from Archean to Present

    OpenAIRE

    Dauphas, Nicolas; Craddock, Paul R.; Bennett, Vickie C.; Nutman, Allen P.; Ohnenstetter, Daniel; Asimow, Paul D.

    2009-01-01

    High-precision Fe isotopic data for 104 samples, including modern and ancient (≥ 3.7 Ga) subduction-related magmas and mantle peridotites, are presented. These data demonstrate that mid-ocean ridge and oceanic-island basalts (MORBs and OIBs) have on average small, but distinctly (~+ 0.06‰) higher ^(56)Fe/^(54)Fe ratios than both modern and Eoarchean boninites and many island arc basalts (IABs) that are interpreted to form by large degrees of flux melting of depleted mantle sources. Additional...

  4. Variable Azimuthal Anisotropy in Earth's Lowermost Mantle

    Science.gov (United States)

    Garnero, Edward J.; Maupin, Valérie; Lay, Thorne; Fouch, Matthew J.

    2004-10-01

    A persistent reversal in the expected polarity of the initiation of vertically polarized shear waves that graze the D'' layer (the layer at the boundary between the outer core and the lower mantle of Earth) in some regions starts at the arrival time of horizontally polarized shear waves. Full waveform modeling of the split shear waves for paths beneath the Caribbean requires azimuthal anisotropy at the base of the mantle. Models with laterally coherent patterns of transverse isotropy with the hexagonal symmetry axis of the mineral phases tilted from the vertical by as much as 20° are consistent with the data. Small-scale convection cells within the mantle above the D'' layer may cause the observed variations by inducing laterally variable crystallographic or shape-preferred orientation in minerals in the D'' layer.

  5. Magnesium and calcium isotopic characteristics of Tengchong volcanics: Recycling of marine carbonates into the SE Tibetan mantle

    Science.gov (United States)

    Liu, F.; Zhang, Z.; Liu, Y.; Zhu, H.; Kang, J.; Zhang, C.; Sun, W.; Wang, G. Q.

    2015-12-01

    Post-collisional high-K calc-alkaline volcanic rocks are widely distributed in Tengchong in the southeastern margin of Tibetan Plateau. Previous considerable petrological and Sr-Nd-Pb isotopic researches undoubtedly indicate that the mantle beneath Tengchong is heterogeneous and enriched. However, the genesis of such a kind of mantle is still poor understood and needs more constrains. One of the key points lead to the answer to this question is that, is there any recycled carbonate involved? Therefore, Magnesium and calcium isotopic compositions of mantle-derived volcanics should be investigated because they are good candidates to be potentially used to trace recycling of ancient marine carbonates into the mantle. In this study, we report high-precision Mg and Ca isotopic compositions for calc-alkaline volcanic rocks in Tengchong. These volcanic rocks show significantly lighter δ26Mg values (-0.44 to -0.36‰) than the mantle value (-0.25±0.07‰). Similarly, they display lighter δ44Ca values (0.65-0.80‰) than the mantle value (1.05±0.04‰). Because neither δ26Mg nor δ44Ca are correlated with SiO2 (50.8-61.6 wt.%) contents, and there is no relationships between δ26Mg or δ44Ca and typical trace element abundance ratios (e.g. Sm/Yb, Ba/Y), we conclude that magma differentiation or partial melting would lead to limited Mg and Ca isotopes fractionation. Thus, low δ26Mg and δ44Ca signatures of Tengchong volcanic rocks probably reflect that the δ26Mg and δ44Ca characteristics of the underneath mantle source, and are resulted from adding ancient marine carbonates into the primitive mantle which has low Mg and Ca isotopic compositions. Our model simulation using a two end-member mixing between Mg-Ca isotopic compositions of primitive mantle and ancient marine carbonate indicates that carbonates involved in the mantle source is mainly dolostone with minor limestone. Combined with the geotectonic evolution history in Tengchong, we propose that the enriched

  6. The effects of mantle and anelasticity on nutations, earth tides, and tidal variations in rotation rate

    Science.gov (United States)

    Wahr, John; Bergen, Zachary

    1986-01-01

    The paper models the effects of mantle anelasticity on luni-solar nutations, on tidal deformation, on tidal variations in rotation rate, and on the eigenfrequency of the free core nutation. The results can be used to invert observations to solve for the anelastic contributions to the shear and bulk moduli of the upper and lower mantle. Specific anelastic models are used to numerically estimate the effects of anelasticity on these geodetic observables. The nutation estimates are compared with observational results. Among the conclusions: (1) mantle anelasticity is likely to be the most important source of damping for the free core nutation; (2) present VLBI nutation results are, in principle, accurate enough to usefully bound anelasticity at diurnal periods. But the discrepancy between the VLBI observed nutations and the 1984 IAU nutation model cannot be explained by anelasticity and is not yet well enough understood to allow anelasticity to be determined from the data.

  7. A rapid burst in hotspot motion through the interaction of tectonics and deep mantle flow.

    Science.gov (United States)

    Hassan, Rakib; Müller, R Dietmar; Gurnis, Michael; Williams, Simon E; Flament, Nicolas

    2016-05-12

    Volcanic hotspot tracks featuring linear progressions in the age of volcanism are typical surface expressions of plate tectonic movement on top of narrow plumes of hot material within Earth's mantle. Seismic imaging reveals that these plumes can be of deep origin--probably rooted on thermochemical structures in the lower mantle. Although palaeomagnetic and radiometric age data suggest that mantle flow can advect plume conduits laterally, the flow dynamics underlying the formation of the sharp bend occurring only in the Hawaiian-Emperor hotspot track in the Pacific Ocean remains enigmatic. Here we present palaeogeographically constrained numerical models of thermochemical convection and demonstrate that flow in the deep lower mantle under the north Pacific was anomalously vigorous between 100 million years ago and 50 million years ago as a consequence of long-lasting subduction systems, unlike those in the south Pacific. These models show a sharp bend in the Hawaiian-Emperor hotspot track arising from the interplay of plume tilt and the lateral advection of plume sources. The different trajectories of the Hawaiian and Louisville hotspot tracks arise from asymmetric deformation of thermochemical structures under the Pacific between 100 million years ago and 50 million years ago. This asymmetric deformation waned just before the Hawaiian-Emperor bend developed, owing to flow in the deepest lower mantle associated with slab descent in the north and south Pacific.

  8. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

    Science.gov (United States)

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-12-04

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins.

  9. The Role of Deep Mantle Flow in Shaping the Hawaiian-Emperor Bend

    Science.gov (United States)

    Hassan, R.; Müller, D.; Gurnis, M.; Williams, S.; Flament, N. E.

    2016-12-01

    Age-progressive volcanic hotspot tracks are typical surface expressions of plate tectonic movement on top of narrow plumes of hot material within Earth's mantle. Seismic imaging reveals that these plumes can be of deep origin, potentially rooted on thermochemical structures in the lower mantle. Although palaeomagnetic and radiometric age data suggest that mantle flow can advect plume conduits laterally, the flow dynamics underlying the formation of the sharp bend occurring only in the Hawaiian-Emperor hotspot track in the Pacific Ocean remains enigmatic. The north Pacific features long-lasting subduction systems, unlike those in the south Pacific. We present palaeogeographically-constrained numerical models of thermochemical convection demonstrating that flow in the deep lower mantle under the north Pacific was anomalously vigorous between 100 Ma and 50 Ma. These models show a sharp bend in the Hawaiian-Emperor hotspot track arising from the interplay of plume tilt and the lateral advection of plume sources. We show that the different trajectories of the Hawaiian and Louisville hotspot tracks arise from asymmetric deformation of thermochemical structures under the Pacific between 100 Ma and 50 Ma. This asymmetric deformation waned just before the Hawaiian-Emperor bend developed, owing to flow in the deepest lower mantle associated with slab descent in the north and south Pacific.

  10. A rapid burst in hotspot motion through the interaction of tectonics and deep mantle flow

    Science.gov (United States)

    Hassan, Rakib; Müller, R. Dietmar; Gurnis, Michael; Williams, Simon E.; Flament, Nicolas

    2016-05-01

    Volcanic hotspot tracks featuring linear progressions in the age of volcanism are typical surface expressions of plate tectonic movement on top of narrow plumes of hot material within Earth’s mantle. Seismic imaging reveals that these plumes can be of deep origin—probably rooted on thermochemical structures in the lower mantle. Although palaeomagnetic and radiometric age data suggest that mantle flow can advect plume conduits laterally, the flow dynamics underlying the formation of the sharp bend occurring only in the Hawaiian-Emperor hotspot track in the Pacific Ocean remains enigmatic. Here we present palaeogeographically constrained numerical models of thermochemical convection and demonstrate that flow in the deep lower mantle under the north Pacific was anomalously vigorous between 100 million years ago and 50 million years ago as a consequence of long-lasting subduction systems, unlike those in the south Pacific. These models show a sharp bend in the Hawaiian-Emperor hotspot track arising from the interplay of plume tilt and the lateral advection of plume sources. The different trajectories of the Hawaiian and Louisville hotspot tracks arise from asymmetric deformation of thermochemical structures under the Pacific between 100 million years ago and 50 million years ago. This asymmetric deformation waned just before the Hawaiian-Emperor bend developed, owing to flow in the deepest lower mantle associated with slab descent in the north and south Pacific.

  11. The Moho as a magnetic boundary. [Earth crust-mantle boundary

    Science.gov (United States)

    Wasilewski, P. J.; Thomas, H. H.; Mayhew, M. A.

    1979-01-01

    Magnetism in the crust and the upper mantle and magnetic results indicating that the seismic Moho is a magnetic boundary are considered. Mantle derived rocks - peridotites from St. Pauls rocks, dunite xenoliths from the Kaupulehu flow, and peridotite, dunite, and eclogite xenoliths from Roberts Victor and San Carlos diatremes - are weakly magnetic with saturation magnetization values from 0.013 emu/gm to less than 0.001 emu/gm which is equivalent to 0.01 to 0.001 wt% Fe304. Literature on the minerals in mantle xenoliths shows that metals and primary Fe304 are absent, and that complex Cr, Mg, Al, and Fe spinels are dominant. These spinels are non-magnetic at mantle temperatures, and the crust/mantle boundary can be specified as a magnetic mineralogy discontinuity. The new magnetic results indicate that the seismic Moho is a magnetic boundary, the source of magnetization is in the crust, and the maximum Curie isotherm depends on magnetic mineralogy and is located at depths which vary with the regional geothermal gradient.

  12. A reconnaissance view of tungsten reservoirs in some crustal and mantle rocks: Implications for interpreting W isotopic compositions and crust-mantle W cycling

    Science.gov (United States)

    Liu, Jingao; Pearson, D. Graham; Chacko, Thomas; Luo, Yan

    2018-02-01

    High-precision measurements of W isotopic ratios have enabled increased exploration of early Earth processes. However, when applying W isotopic data to understand the geological processes, it is critical to recognize the potential mobility of W and hence evaluate whether measured W contents and isotopic compositions reflect the primary petrogenetic processes or instead are influenced by the effects of secondary inputs/mobility. Furthermore, if we are to better understand how W is partitioned between different minerals during melting and metasomatic processes it is important to document the likely sinks for W during these processes. In addition, an understanding of the main hosts for W in the crust and mantle is critically important to constrain how W is cycled and stored in the crust-mantle geochemical cycle. As a first step to investigate these issues, we have carried out in situ concentration measurements of W and other HFSEs in mineral phases within a broad spectrum of crustal and mantle rocks, along with whole-rock concentration measurements. Mass balance shows that for tonalitic gneiss and amphibolite, the major rock-forming minerals can adequately account for the bulk W budget, and for the pristine ultramafic rocks, olivine and orthopyroxene are the major controlling phases for W whereas for metasomatized ultramafic rocks, significant W is hosted in Ti-bearing trace phases (e.g., rutile, lindsleyite) along grain boundaries or is inferred to reside in cryptic W-bearing trace phases. Formation or decomposition of these phases during secondary processes could cause fractionation of W from other HFSEs, and also dramatically modify bulk W concentrations in rocks. For rocks that experienced subsequent W enrichment/alteration, their W isotopic compositions may not necessarily represent their mantle sources, but could reflect later inputs. The relatively small suite of rocks analyzed here serves as a reconnaissance study but allows some preliminary speculations on

  13. Are Melt Migration Rates Through the Mantle Universally Rapid?

    Science.gov (United States)

    Reagan, M. K.; Sims, K. W.

    2001-12-01

    Significant enrichments in 226Ra over 230Th have been observed in basalts erupted in nearly all tectonic settings. These enrichments generally are greatest in lavas with low concentrations of U, Th and other incompatible elements, including those from mid-ocean ridges and "depleted" volcanic arcs. Excesses of 226Ra over 230Th in mid-ocean ridge settings are commonly attributed to smaller bulk partition coefficients for Ra with respect to Th during mantle melting, and extraction of ingrown Ra into melts slowly migrating through interconnected pore space. In contrast, 226Ra excesses in basalts from volcanic arcs have been attributed to fluid additions from subducting slabs to the sources of the basalt and rapid (102 - 103y) melt migration to the surface (e.g. Turner et al., 2001). Such rapid melt velocities imply channeled flow rather than diffuse porous flow, and suggest that basalts from other tectonic settings migrate similarly rapidly. Here, we show that the compositions of basalts from both arc and mid-ocean ridge settings indeed can be explained by melting models involving rapid transit times to the surface. Simple fluxed melting models and rapid transfer of melt to the surface explain the U-Th-Ra systematics and incompatible trace element compositions of arc basalts. The U-Th-Ra and trace element data for young MORB from the East Pacific Rise (Sims et al. 2001) and the Siqueiros transform (Lundstrom et al. 1999) are modeled using simple 2-d polybaric melting based on Braun et al. (2000) and rapid melt migration rates. Successful models mix small-degree fractional melts derived from a broad cross-sectional area of mantle at depth with high-degree melts derived from a small cross-sectional area of shallow mantle that is the aged residue of the small degree melt.

  14. Role of the transition zone and 660 km discontinuity in mantle dynamics

    Science.gov (United States)

    Ringwood, A. E.

    1994-10-01

    Recent seismic evidence suggests that subducted slabs experience resistance to further descent when they encounter the 660 km seismic discontinuity. Several possible causes of this resistance are evaluated. It is concluded that the chemical composition of the lower mantle is similar to that of the upper mantle, and that compositional change is therefore unlikely to be the cause of resistance to slab penetration. The proposal that a large increase of viscosity at the 660 km discontinuity impedes descending slabs is also rejected. However, three other factors are identified, each of which is capable of causing substantial resistance to descending slabs: (1) the negative slope of the transformation of silicate spinel to Mg-perovskite+magnesiowuestite; (2) differentiation of oceanic lithosphere into basaltic and depleted peridotitic layers, causing the slab to be buoyant compared with surrounding mantle pyrolite between depths of 660-800 km; (3) the accumulation of former oceanic crust to produce a gravitationally stable layer of garnetite (about 50 km thick) on top of the 660 km discontinuity. The combined effects of these sources of resistance provide a filter for subducted slabs. Those slabs with seismic zones extending below 600 km may possess sufficient negative buoyancy and strength to overcome the barriers and penetrate into the lower mantle. However, the resistance causes strong buckling and plastic thickening of these slabs, which accumulate to form huge blobs or 'megaliths' underneath the 660 km discontinuity. In contrast, slabs with seismic zones extending no deeper than 300 km possess much smaller degrees of negative buoyancy and strength and hence are unable to penetrate the 660 km discontinuity. Slabs of this type are recycled within the transition zone and upper mantle. Mixing and petrological homogenization processes are less efficient in the transition zone than in the upper mantle (above 400 km). The transition zone is composed mainly of ancient slabs

  15. 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 ...

  16. Phantom Archean crust in Mangaia hotspot lavas and the meaning of heterogeneous mantle

    Science.gov (United States)

    Herzberg, C.; Cabral, R. A.; Jackson, M. G.; Vidito, C.; Day, J. M. D.; Hauri, E. H.

    2014-06-01

    Lavas from Mangaia in the Cook-Austral island chain, Polynesia, define an HIMU (or high μ, where μ=U238/Pb204) global isotopic end-member among ocean island basalts (OIB) with the highest 206,207,208Pb/204Pb. This geochemical signature is interpreted to reflect a recycled oceanic crust component in the mantle source. Mass independently fractionated (MIF) sulfur isotopes indicate that Mangaia lavas sampled recycled Archean material that was once at the Earth's surface, likely hydrothermally-modified oceanic crust. Recent models have proposed that crust that is subducted and then returned to the surface in a mantle plume is expected to transform to pyroxenite/eclogite during transit through the mantle. Here we examine this hypothesis for Mangaia using high-precision electron microprobe analysis on olivine phenocrysts. Contrary to expectations of a crustal component and, hence pyroxenite, results show a mixed peridotite and pyroxenite source, with peridotite dominating. If the isotopic compositions were inherited from subduction of recycled oceanic crust, our work shows that this source has phantom-like properties in that it can have its lithological identity destroyed while its isotope ratios are preserved. This may occur by partial melting of the pyroxenite and injection of its silicic melts into the surrounding mantle peridotite, yielding a refertilized peridotite. Evidence from one sample reveals that not all pyroxenite in the melting region was destroyed. Identification of source lithology using olivine phenocryst chemistry can be further compromised by magma chamber fractional crystallization, recharge, and mixing. We conclude that the commonly used terms mantle “heterogeneities” and “streaks” are ambiguous, and distinction should be made of its lithological and isotopic properties.

  17. Compositional stratification in the deep mantle

    NARCIS (Netherlands)

    Kellogg, louise H.; Hager, Bradford H.; Hilst, R.D. van der

    1999-01-01

    A boundary between compositionally distinct regions at a depth of about 1600 kilometers may explain the seismological observations pertaining to Earth's lower mantle, produce the isotopic signatures of mid-ocean ridge basalts and oceanic island basalts, and reconcile the discrepancy between the

  18. Steady-state creep in the mantle

    Directory of Open Access Journals (Sweden)

    G. RANALLI

    1977-06-01

    Full Text Available SUMMARY - The creep equations for steady-state flow of olivine at high
    pressure and temperature are compared in an attempt to elucidate the rheological
    behaviour of the mantle. Results are presented in terms of applied deformation
    maps and curves of effective viscosity v depth.
    In the upper mantle, the transition stress between dislocation and diffusion
    creep is between 10 to 102 bar (as orders of magnitude for grain sizes from
    0.01 to 1 cm. The asthenosphere under continents is deeper, and has higher
    viscosity, than under oceans. Predominance of one creep mechanism above the
    others depends on grain size, strain rate, and volume fraction of melt; the
    rheological response can be different for different geodynamic processes.
    In the lower mantle, on the other hand, dislocation creep is predominant
    at all realistic grain sizes and strain rates. If the effective viscosity has to be only
    slightly higher than in the upper mantle, as some interpretations of glacioisostatic
    rebound suggest, then the activation volume cannot be larger than
    11 cm3 mole^1.

  19. 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...

  20. Executive Summary: “Mantle Frontier” Workshop

    Directory of Open Access Journals (Sweden)

    Workshop Report Writing Group

    2011-03-01

    Full Text Available The workshop on “Reaching the Mantle Frontier: Moho and Beyond” was held at the Broad Branch Road Campus of the Carnegie Institution of Washington on 9–11 September 2010. The workshop attracted seventy-four scientists and engineers from academia and industry in North America, Asia, and Europe.Reaching and sampling the mantle through penetration of the entire oceanic crust and the Mohorovičić discontinuity (Moho has been a longstanding goal of the Earth science community. The Moho is a seismic transition, often sharp, from a region with compressional wave velocities (Vp less than 7.5 km s-1 to velocities ~8 km s-1. It is interpreted in many tectonic settings, and particularly in tectonic exposures of oceanic lower crust, as the transition from igneous crust to mantle rocks that are the residues of melt extraction. Revealing the in situ geological meaning of the Moho is the heart of the Mohole project. Documenting ocean-crust exchanges and the nature and extent of the subseafloor biosphere have also become integral components of the endeavor. The purpose of the “Mantle Frontier” workshop was to identify key scientific objectives associated with innovative technology solutions along with associated timelines and costs for developments and implementation of this grandchallenge.

  1. Early-stage mantle cell lymphoma

    DEFF Research Database (Denmark)

    Dabaja, B S; Zelenetz, A D; Ng, A K

    2017-01-01

    Background: Mantle cell lymphoma (MCL) rarely presents as early-stage disease, but clinical observations suggest that patients who present with early-stage disease may have better outcomes than those with advanced-stage disease. Patients and methods: In this 13-institution study, we examined...

  2. Imaging mantle plumes with instantaneous phase measurements of diffracted waves

    NARCIS (Netherlands)

    Rickers, F.; Fichtner, A.; Trampert, J.

    2012-01-01

    In a synthetic tomographic experiment, we succeeded to recover an idealized narrow mantle plume reaching deep into the lower mantle by using a misfit based on the instantaneous phase difference. A misfit based on simple cross-correlation traveltime shifts leaves the lower mantle part of the plume

  3. MODELLING MANTLE TANKS FOR SDHW SYSTEMS USING PIV AND CFD

    DEFF Research Database (Denmark)

    Shah, Louise Jivan; Morrison, G.L.; Behnia, Masud

    1999-01-01

    Characteristics of vertical mantle heat exchanger tanks for SDHW systems have been investigated experimentally and theoretically using particle image velocimetry (PIV) and CFD modelling. A glass model of a mantle heat exchanger tank was constructed so that the flow distribution in the mantle coul...

  4. Mantle source characterization of Sylhet Traps, northeastern India: A ...

    Indian Academy of Sciences (India)

    ... Meshesha1 3 Ryuichi Shinjo1. Department of Physics and Earth Sciences, University of the Ryukyus, Senbaru 1, Nishihara, Okinawa 903-0213, Japan. Department of Petroleum and Mining Engineering, Shahjalal University of Science and Technology, Sylhet 3114, Bangladesh. EL MINING PLC, Addis Ababa, Ethiopia.

  5. Investigations of Eurasian Seismic Sources and Upper Mantle Structure.

    Science.gov (United States)

    1987-03-06

    possibility is Ringwood’s (19821 " megalith " hypothesis, illustrated in Figure 3.3b, where the buckling of former oceanic crust and the harzburgite...enure depth of the oceanic lithosphere, in, Geodynainics of the Western Pacific- Indonesian Region. Geodynamics Series. Vol. 11, ed. by T. W. C. Hilde... Indonesian Archipelago: a geophysical study, Geol. Soc. Am. Bull.. 65, 143-164, 1954. Vink, G. E., W. J. Morgan, and W.-L. Zhao, Preferential rifting

  6. Investigating Late Cenozoic Mantle Dynamics beneath Yellowstone

    Science.gov (United States)

    Zhou, Q.; Liu, L.

    2015-12-01

    Recent tomography models (Sigloch, 2011; Schmandt & Lin, 2014) reveal unprecedented details of the mantle structure beneath the United States (U.S.). Prominent slow seismic anomalies below Yellowstone, traditionally interpreted as due to a mantle plume, are restricted to depths either shallower than 200 km or between 500 and 1000 km, but a continuation to greater depth is missing. Compared to fast seismic anomalies, which are usually interpreted as slabs or delaminated lithosphere, origin of deep slow seismic anomalies, especially those in the vicinity of subduction zones, is more enigmatic. As a consequence, both the dynamics and evolution of these slow anomalies remain poorly understood. To investigate the origin and evolution of the Yellowstone slow anomaly during the past 20 Myr, we construct a 4D inverse mantle convection model with a hybrid data assimilation scheme. On the one hand, we use the adjoint method to recover the past evolution of mantle seismic structures beyond the subduction zones. On the other hand, we use a high-resolution forward model to simulate the subduction of the oceanic (i.e., Farallon) plate. During the adjoint iterations, features from these two approaches are blended together at a depth of ~200 km below the subduction zone. In practice, we convert fast and slow seismic anomalies to effective positive and negative density heterogeneities. Our preliminary results indicate that at 20 Ma, the present-day shallow slow anomalies beneath the western U.S. were located inside the oceanic asthenosphere, which subsequently entered the mantle wedge, through the segmented Farallon slab. The eastward encroachment of the slow anomaly largely followed the Yellowstone hotspot track migration. The present deep mantle Yellowstone slow anomaly originated at shallower depths (i.e. transition zone), and was then translated down to the lower mantle accompanying the sinking fast anomalies. The temporal evolution of the slow anomalies suggests that the deep

  7. Water in the Cratonic Mantle Lithosphere

    Science.gov (United States)

    Peslier, A. H.

    2016-01-01

    The fact that Archean and Proterozoic cratons are underlain by the thickest (>200 km) lithosphere on Earth has always puzzled scientists because the dynamic convection of the surrounding asthenosphere would be expected to delaminate and erode these mantle lithospheric "keels" over time. Although density and temperature of the cratonic lithosphere certainly play a role in its strength and longevity, the role of water has only been recently addressed with data on actual mantle samples. Water in mantle lithologies (primarily peridotites and pyroxenites) is mainly stored in nominally anhydrous minerals (olivine, pyroxene, garnet) where it is incorporated as hydrogen bonded to structural oxygen in lattice defects. The property of hydrolytic weakening of olivine [4] has generated the hypothesis that olivine, the main mineral of the upper mantle, may be dehydrated in cratonic mantle lithospheres, contributing to its strength. This presentation will review the distribution of water concentrations in four cratonic lithospheres. The distribution of water contents in olivine from peridotite xenoliths found in kimberlites is different in each craton (Figure 1). The range of water contents of olivine, pyroxene and garnet at each xenolith location appears linked to local metasomatic events, some of which occurred later then the Archean and Proterozoic when these peridotites initially formed via melting. Although the low olivine water contents ( 6 GPa at the base of the Kaapvaal cratonic lithosphere may contribute to its strength, and prevent its delamination, the wide range of those from Siberian xenoliths is not compatible with providing a high enough viscosity contrast with the asthenophere. The water content in olivine inclusions from Siberian diamonds, on the other hand, have systematically low water contents (water contents. The olivine inclusions, however, may have been protected from metasomatism by their host diamond and record the overall low olivine water content of

  8. Nickel isotopic composition of the mantle

    Science.gov (United States)

    Gall, Louise; Williams, Helen M.; Halliday, Alex N.; Kerr, Andrew C.

    2017-02-01

    This paper presents a detailed high-precision study of Ni isotope variations in mantle peridotites and their minerals, komatiites as well as chondritic and iron meteorites. Ultramafic rocks display a relatively large range in δ60 Ni (permil deviation in 60 Ni /58 Ni relative to the NIST SRM 986 Ni isotope standard) for this environment, from 0.15 ± 0.07‰ to 0.36 ± 0.08‰, with olivine-rich rocks such as dunite and olivine cumulates showing lighter isotope compositions than komatiite, lherzolite and pyroxenite samples. The data for the mineral separates shed light on the origin of these variations. Olivine and orthopyroxene display light δ60 Ni whereas clinopyroxene and garnet are isotopically heavy. This indicates that peridotite whole-rock δ60 Ni may be controlled by variations in modal mineralogy, with the prediction that mantle melts will display variable δ60 Ni values due to variations in residual mantle and cumulate mineralogy. Based on fertile peridotite xenoliths and Phanerozoic komatiite samples it is concluded that the upper mantle has a relatively homogeneous Ni isotope composition, with the best estimate of δ60Nimantle being 0.23 ± 0.06‰ (2 s.d.). Given that >99% of the Ni in the silicate Earth is located in the mantle, this also defines the Ni isotope composition of the Bulk Silicate Earth (BSE). This value is nearly identical to the results obtained for a suite of chondrites and iron meteorites (mean δ60 Ni 0.26 ± 0.12‰ and 0.29 ± 0.10‰, respectively) showing that the BSE is chondritic with respect to its Ni isotope composition, with little to no Ni mass-dependent isotope fractionation resulting from core formation.

  9. High accuracy mantle convection simulation through modern numerical methods

    KAUST Repository

    Kronbichler, Martin

    2012-08-21

    Numerical simulation of the processes in the Earth\\'s mantle is a key piece in understanding its dynamics, composition, history and interaction with the lithosphere and the Earth\\'s core. However, doing so presents many practical difficulties related to the numerical methods that can accurately represent these processes at relevant scales. This paper presents an overview of the state of the art in algorithms for high-Rayleigh number flows such as those in the Earth\\'s mantle, and discusses their implementation in the Open Source code Aspect (Advanced Solver for Problems in Earth\\'s ConvecTion). Specifically, we show how an interconnected set of methods for adaptive mesh refinement (AMR), higher order spatial and temporal discretizations, advection stabilization and efficient linear solvers can provide high accuracy at a numerical cost unachievable with traditional methods, and how these methods can be designed in a way so that they scale to large numbers of processors on compute clusters. Aspect relies on the numerical software packages deal.II and Trilinos, enabling us to focus on high level code and keeping our implementation compact. We present results from validation tests using widely used benchmarks for our code, as well as scaling results from parallel runs. © 2012 The Authors Geophysical Journal International © 2012 RAS.

  10. Episodic entrainment of primordial material in plumes from isolated lower mantle reservoirs

    Science.gov (United States)

    Williams, C. D.; McNamara, A. K.; Garnero, E. J.; Van Soest, M. C.

    2012-12-01

    The noble gas systematics observed in ocean island basalts (OIBs) relative to mid-ocean ridge basalts (MORBs), suggests OIBs preferentially sample a primordial reservoir located somewhere within Earth's mantle. The lower mantle has been favored as a candidate reservoir, either in its entirety or discrete reservoirs located within it. Thermal plumes originating from the lower mantle could potentially sample these reservoirs, which may have remained isolated from the MORB source region over much of Earth's history. Recently, seismic observations of two, nearly anti-podal large, low-shear velocity provinces (LLSVPs) in the lowermost mantle have been hypothesized as being chemically distinct, and thus, may be long-lived reservoirs that have retained primordial noble gas signatures from earlier in Earth's history. Geodynamic models predict that thermal plumes are likely to be associated with LLSVPs and could potentially entrain a small amount of these chemically distinct reservoirs, which may ultimately reach the surface of the Earth in the form of OIBs. However, isotopic variability within OIBs challenges the notion of multiple plumes tapping the same reservoir. Here, we perform geodynamic calculations that investigate the time-dependent rate of material entrained into thermal plumes from these primordial reservoirs. In particular, we examine how the rate of entrainment varies within a single, long-lived thermal plume with a relatively steady buoyancy flux. Using phase relations for mantle peridotite, the amount of entrained material comprising the melt is estimated. We find that time-dependent dynamical processes at the interface between a deep, primordial reservoir and the base of a mantle plume strongly influences the entrainment rate, causing the amount of entrainment to vary episodically with time. Thus, melts rising to the surface (e.g., OIBs) are predicted to contain variable proportions of material entrained from these primordial reservoirs. This time

  11. Average Potential Temperature of the Upper Mantle and Excess Temperatures Beneath Regions of Active Upwelling

    Science.gov (United States)

    Putirka, K. D.

    2006-05-01

    The question as to whether any particular oceanic island is the result of a thermal mantle plume, is a question of whether volcanism is the result of passive upwelling, as at mid-ocean ridges, or active upwelling, driven by thermally buoyant material. When upwelling is passive, mantle temperatures reflect average or ambient upper mantle values. In contrast, sites of thermally driven active upwellings will have elevated (or excess) mantle temperatures, driven by some source of excess heat. Skeptics of the plume hypothesis suggest that the maximum temperatures at ocean islands are similar to maximum temperatures at mid-ocean ridges (Anderson, 2000; Green et al., 2001). Olivine-liquid thermometry, when applied to Hawaii, Iceland, and global MORB, belie this hypothesis. Olivine-liquid equilibria provide the most accurate means of estimating mantle temperatures, which are highly sensitive to the forsterite (Fo) contents of olivines, and the FeO content of coexisting liquids. Their application shows that mantle temperatures in the MORB source region are less than temperatures at both Hawaii and Iceland. The Siqueiros Transform may provide the most precise estimate of TpMORB because high MgO glass compositions there have been affected only by olivine fractionation, so primitive FeOliq is known; olivine thermometry yields TpSiqueiros = 1430 ±59°C. A global database of 22,000 MORB show that most MORB have slightly higher FeOliq than at Siqueiros, which translates to higher calculated mantle potential temperatures. If the values for Fomax (= 91.5) and KD (Fe-Mg)ol-liq (= 0.29) at Siqueiros apply globally, then upper mantle Tp is closer to 1485 ± 59°C. Averaging this global estimate with that recovered at Siqueiros yields TpMORB = 1458 ± 78°C, which is used to calculate plume excess temperatures, Te. The estimate for TpMORB defines the convective mantle geotherm, and is consistent with estimates from sea floor bathymetry and heat flow (Stein and Stein, 1992), and

  12. Integrating Geochemical and Geodynamic Numerical Models of Mantle Evolution and Plate Tectonics

    Science.gov (United States)

    Tackley, P. J.; Xie, S.

    2001-12-01

    The thermal and chemical evolution of Earth's mantle and plates are inextricably coupled by the plate tectonic - mantle convective system. Convection causes chemical differentiation, recycling and mixing, while chemical variations affect the convection through physical properties such as density and viscosity which depend on composition. It is now possible to construct numerical mantle convection models that track the thermo-chemical evolution of major and minor elements, and which can be used to test prospective models and hypotheses regarding Earth's chemical and thermal evolution. Model thermal and chemical structures can be compared to results from seismic tomography, while geochemical signatures (e.g., trace element ratios) can be compared to geochemical observations. The presented, two-dimensional model combines a simplified 2-component major element model with tracking of the most important trace elements, using a tracer method. Melting is self-consistently treated using a solidus, with melt placed on the surface as crust. Partitioning of trace elements occurs between melt and residue. Decaying heat-producing elements and secular cooling of the mantle and core provide the driving heat sources. Pseudo-plastic yielding of the lithosphere gives a first-order approximation of plate tectonics, and also allows planets with a rigid lid or intermittent plate tectonics to be modeled simply by increasing the yield strength. Preliminary models with an initially homogeneous mantle show that regions with a HIMU-like signature can be generated by crustal recycling, and regions with high 3He/4He ratios can be generated by residuum recycling. Outgassing of Argon is within the observed range. Models with initially layered mantles will also be investigated. In future it will be important to include a more realistic bulk compositional model that allows continental crust as well as oceanic crust to form, and to extend the model to three dimensions since toroidal flow may alter

  13. Influence of a West Antarctic mantle plume on ice sheet basal conditions

    Science.gov (United States)

    Seroussi, Helene; Ivins, Erik R.; Wiens, Douglas A.; Bondzio, Johannes

    2017-09-01

    The possibility that a deep mantle plume manifests Pliocene and Quaternary volcanism and potential elevated heat flux in West Antarctica has been studied for more than 30 years. Recent seismic images support the plume hypothesis as the cause of Marie Byrd Land (MBL) volcanism and geophysical structure. Mantle plumes may more than double the geothermal heat flux above nominal continental values. A dearth of in situ ice sheet basal data exists that samples the heat flux. Consequently, we examine a realistic distribution of heat flux associated with a possible late Cenozoic mantle plume in West Antarctica and explore its impact on thermal and melt conditions at the ice sheet base. We use a simple analytical mantle plume parameterization to produce geothermal heat flux at the base of the ice sheet. The three-dimensional ice flow model includes an enthalpy framework and full-Stokes stress balance. As both the putative plume location and extent are uncertain, we perform broadly scoped experiments to characterize the impact of the plume on geothermal heat flux and ice sheet basal conditions. The experiments show that mantle plumes have an important local impact on the ice sheet, with basal melting rates reaching several centimeters per year directly above the hotspot. In order to be consistent with observations of basal hydrology in MBL, the upper bound on the plume-derived geothermal heat flux is 150 mW/m2. In contrast, the active lake system of the lower part of Whillans Ice Stream suggests a widespread anomalous mantle heat flux, linked to a rift source.

  14. Age-Orientation Relationships of Northern Hemisphere Martian Gullies and "Pasted-on" Mantling Unit: Implications for Near-Surface Water Migration in Mars' Recent History

    Science.gov (United States)

    Bridges, N. T.; Lackner, C. N.

    2005-01-01

    The finding of abundant, apparently young, Martian gullies with morphologies indicative of formation by flowing fluid was surprising in that volumes of near-surface liquid water in sufficient quantities to modify the surface geology were not thought possible under current conditions. Original hypotheses on origin of gullies were mostly centered on groundwater seepage and surface runoff and melting of near-surface ground ice. More recently, melting of snow deposited in periods of higher obliquity has been proposed as a possible origin of the gullies. Tied to this hypothesis is the supposition that the "pasted-on" mantling unit observed in association with many gullies is composed of remnant snowpack. The mantling unit has distinct rounded edge on its upper boundary and exhibits features suggestive of flow noted that the uppermost part of the mantle marks where gullies begin, suggesting that the source of water for the gullies was within the mantle. The mantle is found preferentially on cold, pole-facing slopes and, where mantled and non-mantled slopes are found together, gullies are observed incised into the latter. In other cases, the mantling material lacks gullies.

  15. Life Cycle of Mantle Plumes: A perspective from the Galapagos Plume (Invited)

    Science.gov (United States)

    Gazel, E.; Herzberg, C. T.

    2009-12-01

    Hotspots are localized sources of heat and magmatism considered as modern-day evidence of mantle plumes. Some hotspots are related to massive magmatic production that generated Large Igneous Provinces (LIPS), an initial-peak phase of plume activity with a mantle source hotter and more magmatically productive than present-day hotspots. Geological mapping and geochronological studies have shown much lower eruption rates for OIB compared to lavas from Large Igneous Provinces LIPS such as oceanic plateaus and continental flood provinces. Our study is the first quantitative petrological comparison of mantle source temperatures and extent of melting for OIB and LIP sources. The wide range of primary magma compositions and inferred mantle potential temperatures for each LIP and OIB occurrence suggest that this rocks originated form a hotspot, a spatially localized source of heat and magmatism restricted in time. Extensive outcrops of basalt, picrite, and sometimes komatiite with circa 65-95 Ma ages occupy portions of the pacific shore of Central and South America included in the Caribbean Large Igneous Province (CLIP). There is general consensus of a Pacific-origin of CLIP and most studies suggest that it was produced by melting in the Galapagos mantle plume. The Galapagos connection is consistent with isotopic and geochemical similarities with lavas from the present-day Galapagos hotspot. A Galapagos link for rocks in South American oceanic complexes (eg. the island of Gorgona) is more controversial and requires future work. The MgO and FeO contents of lavas from the Galapagos related lavas and their primary magmas have decreased since the Cretaceous. From petrological modeling we infer that these changes reflect a cooling of the Galapagos mantle plume from a potential temperature of 1560-1620 C in the Cretaceous to 1500 C at the present time. These temperatures are higher than 1350 C for ambient mantle associated with oceanic ridges, and provide support for the mantle

  16. Viscous Fingering in the Mantle Asthenosphere

    Science.gov (United States)

    Nissanka, U. S.; Weeraratne, D. S.; Parmentier, E. M.; Rincon, J. M.

    2015-12-01

    Regional seismic tomography studies in the Pacific ocean and continental western U.S show linear bands of low velocity anomalies that are aligned with absolute plate motion and coincident with volcanic lineaments located within the interior of plates far from plate boundaries. Small-scale convection provides one possible explanation for these lineations but does not predict age progressive seafloor volcanism that opposes plate motion. We propose a new hypothesis where viscous fingering instabilities form due to hot and wet mantle plumes which rise and discharge into the upper mantle asthenosphere and displace higher viscosity depleted mantle. We perform laboratory fluid experiments scaled to the Earth's mantle, with stationary and moving surface plates that use fluids with viscosities (μ) from 1 to 300 Pas and viscosity ratios (μ1/μ2) from 3 to 400. Viscous fingers are observed to form for all viscosity ratios we consider and after an initial growth period, exhibit a constant wavelength that depends on several parameters. Fingering wavelength is strongly dependent on plate spacing (and therefore asthenospheric layer thickness) but shows weak or no dependence on viscosity ratio and injection rate. The radius, Ro, at which fingers first form varies inversely with increasing viscosity ratio. This indicates that low viscosity mantle may flow long distances before fingers develop if viscosity ratios are small. For mobile plates, a ratio Γ of plume flux to plate velocity is defined where Γ is varied from 3.6x10-4 to 3.6x105 which considers the range expected in the Earth (6.3x10-3 to 1.5x10-2). Results indicate that fingers align with plate motion both upstream and downstream, with longer wavelengths in the downstream direction. Particle imaging successfully resolves particle motion vectors and also indicates the presence of a thin film layer above and below each finger. This new geodynamic model for viscous fingering in the asthenosphere links off-axis and rising

  17. Primordial metallic melt in the deep mantle

    Science.gov (United States)

    Zhang, Zhou; Dorfman, Susannah M.; Labidi, Jabrane; Zhang, Shuai; Li, Mingming; Manga, Michael; Stixrude, Lars; McDonough, William F.; Williams, Quentin

    2016-04-01

    Seismic tomography models reveal two large low shear velocity provinces (LLSVPs) that identify large-scale variations in temperature and composition in the deep mantle. Other characteristics include elevated density, elevated bulk sound speed, and sharp boundaries. We show that properties of LLSVPs can be explained by the presence of small quantities (0.3-3%) of suspended, dense Fe-Ni-S liquid. Trapping of metallic liquid is demonstrated to be likely during the crystallization of a dense basal magma ocean, and retention of such melts is consistent with currently available experimental constraints. Calculated seismic velocities and densities of lower mantle material containing low-abundance metallic liquids match the observed LLSVP properties. Small quantities of metallic liquids trapped at depth provide a natural explanation for primitive noble gas signatures in plume-related magmas. Our model hence provides a mechanism for generating large-scale chemical heterogeneities in Earth's early history and makes clear predictions for future tests of our hypothesis.

  18. High-pressure behavior of djerfisherite: Implication for its origin in diamonds and mantle xenoliths

    Science.gov (United States)

    Minin, D.; Sharygin, I.; Litasov, K.; Sharygin, V.; Shatskiy, A.; Ohtani, E.

    2016-12-01

    Djerfisherite K6(Fe,Cu,Ni)25S26Cl is a widespread mineral in kimberlite-hosted mantle xenoliths and diamonds. It usually occurs as rims around primary Fe-Ni-Cu sulfides. It is assumed that metasomatic origin of djerfisherite is related to interaction of primary sulfides with the hypothetical K-Cl-rich fluid or melt. However, source and composition of metasomatic agent as well as PT-conditions of the interaction is unclear. There are two basic hypothesis of djerfisherite origin in diamonds and mantle xenoliths: (1) in-situ mantle metasomatism; (2) infiltration of kimberlite melt into mantle nodules during magma ascent. To date, djerfisherite was synthesized only at 1 atm and 350-650 oC (Clarke, 1979) and at 0.1 GPa and 470 oC (Gorbachev and Nekrasov, 1980). We performed first experimental study on the stability of this sulfide at high pressures. The experiments were performed at 3 GPa nd 800-1200 oC. Also we have planned to perform experiments at 6 GPa, however, it was not necessary due to instability of djerfisherite at lower pressures. As starting materials we used natural Cu-rich djerfisherite from peralkaline pegmatites of Khibina massif (Kola peninsula, Russia) and synthetic mixtures with the following compositions (in mol.%) (Fe18Cu2Ni5)25S26 + 5KCl + 3.5K2CO3 and (Fe18Cu2Ni5)25S26 + 6KCl + K2CO3 + 3.5Na2CO3 + 8Mg2SiO4. Potassium content was in excess by an addition of K2CO3. Sulfide portion of synthetic mixtures compositionally corresponds to djerfisherite in diamonds and mantle xenoliths. The results of experiments showed that djerfisherite is unstable at 3 GPa, or higher pressures. This indicates that djerfisherite in diamond, diamond-bearing garnet peridotite could not be crystallized in cratonic lithosphere mantle in-situ. Consequently, djerfisherite formation in mantle nodules is a result of their interaction with kimberlite melt during ascent of magma at the subsurface conditions. Instead of djerfisherite we synthesized two new potassium sulfides: K0

  19. The interaction of plume heads with compositional discontinuities in the Earth's mantle

    Science.gov (United States)

    Manga, Michael; Stone, Howard A.; O'Connell, Richard J.

    1993-01-01

    The effects of compositional discontinuities of density and viscosity in the Earth's mantle on the ascent of mantle plume heads is studied using a boundary integral numerical technique. Three specific problems are considered: (1) a plume head rising away from a deformable interface, (2) a plume head passing through an interface, and (3) a plume head approaching the surface of the Earth. For the case of a plume attached to a free-surface, the calculated time-dependent plume shapesare compared with experimental results. Two principle modes of plume head deformation are observed: plume head elingation or the formation of a cavity inside the plume head. The inferred structure of mantle plumes, namely, a large plume head with a long tail, is characteristic of plumes attached to their source region, and also of buoyant material moving away from an interface and of buoyant material moving through an interface from a high- to low-viscosity region. As a rising plume head approaches the upper mantle, most of the lower mantle will quickly drain from the gap between the plume head and the upper mantle if the plume head enters the upper mantle. If the plume head moves from a high- to low-viscosity region, the plume head becomes significantly elongated and, for the viscosity contrasts thought to exist in the Earth, could extend from the 670 km discontinuity to the surface. Plume heads that are extended owing to a viscosity decrease in the upper mantle have a cylindrical geometry. The dynamic surface topography induced by plume heads is bell-shaped when the top of the plume head is at depths greater than about 0.1 plume head radii. As the plume head approaches the surface and spreads, the dynamic topography becomes plateau-shaped. The largest stresses are produced in the early stages of plume spreading when the plume head is still nearly spherical, and the surface expression of these stresses is likely to be dominated by radial extension. As the plume spreads, compressional

  20. Incipient boninitic arc crust built on denudated mantle: the Khantaishir ophiolite (western Mongolia)

    Science.gov (United States)

    Gianola, Omar; Schmidt, Max W.; Jagoutz, Oliver; Sambuu, Oyungerel

    2017-12-01

    The 570 Ma old Khantaishir ophiolite is built by up to 4 km harzburgitic mantle with abundant pyroxenites and dunites followed by 2 km of hornblende-gabbros and gabbronorites and by a 2.5 km thick volcanic unit composed of a dyke + sill complex capped by pillow lavas and some volcanoclastics. The volcanics are mainly basaltic andesites and andesites (or boninites) with an average of 58.2 ± 1.0 wt% SiO2, X Mg = 0.61 ± 0.03 ( X Mg = molar MgO/(MgO + FeOtot), TiO2 = 0.4 ± 0.1 wt% and CaO = 7.5 ± 0.6 wt% (errors as 2 σ). Normalized trace element patterns show positive anomalies for Pb and Sr, a negative Nb-anomaly, large ion lithophile elements (LILE) concentrations between N- and E-MORB and distinctly depleted HREE. These characteristics indicate that the Khantaishir volcanics were derived from a refractory mantle source modified by a moderate slab-component, similar to boninites erupted along the Izu-Bonin-Mariana subduction system and to the Troodos and Betts Cove ophiolites. Most strikingly and despite almost complete outcrops over 260 km2, there is no remnant of any pre-existing MORB crust, suggesting that the magmatic suite of this ophiolite formed on completely denudated mantle, most likely upon subduction initiation. The architecture of this 4-5 km thick early arc crust resembles oceanic crust formed at mid ocean ridges, but lacks a sheeted dyke complex; volcanic edifices are not observed. Nevertheless, low melting pressures combined with moderate H2O-contents resulted in high-Si primitive melts, in abundant hornblende-gabbros and in a fast enrichment in bulk SiO2. Fractional crystallization modeling starting from the observed primitive melts (56.6 wt% SiO2) suggests that 25 wt% pyroxene + plagioclase fractionation is sufficient to form the average Khantaishir volcanic crust. Most of the fractionation happened in the mantle, the observed pyroxenite lenses and layers in and at the top of the harzburgites account for the required cumulate volumes. Finally

  1. 26 million years of mantle upwelling below a segment of the Mid Atlantic Ridge: The Vema Lithospheric Section revisited

    Science.gov (United States)

    Cipriani, Anna; Bonatti, Enrico; Brunelli, Daniele; Ligi, Marco

    2009-07-01

    Temporal variations of temperature and composition of the mantle upwelling below a 80-km long segment of the Mid Atlantic Ridge were reconstructed from 20 to 4 Ma ago from peridotites sampled along a > 300-km long section of oceanic lithosphere (Vema Lithospheric Section or VLS) exposed south of the Vema transform at 11° N [Bonatti, E., Ligi, M., Brunelli, D., Cipriani, A., Fabretti, P., Ferrante, V., Gasperini, L., Ottolini, L., 2003. Mantle thermal pulses below the Mid-Atlantic Ridge and temporal variation in the formation of oceanic lithosphere, Nature, 423, 499-505]. We extended this time interval from 26 to 2 Ma by sampling mantle ultramafics at 18 new sites along the VLS. Peridotite orthopyroxene, clinopyroxene and spinel chemistry suggest a weak trend of decreasing extent of melting of the mantle from 26 to 18.5 Ma ago with superimposed short-wavelength (~ 4 Ma) oscillations followed by a steady increase of degree of melting from 18.5 to 2 Ma ago, with superimposed 3-4 Ma oscillations. Temporal variations of crustal thickness inferred from the Residual Mantle Bouguer Anomaly calculated from gravity data reveal similar trends. The older (26 to 18.5 Ma) and the younger (18.5 to 2 Ma) mantle suites differ in cpx Na 2O content and CaO/Al 2O 3 ratio, suggesting that not only the thermal regime, but also the composition of the mantle source might have been different in the two suites. The two trends are separated by a ~ 1.4 Ma-long stretch (from 18.2 to 16.8 Ma) where deformed ultramafic mylonites prevail, indicating probably an interval of nearly a-magmatic lithospheric emplacement at ridge axis, corresponding to a thermal minimum. Spatially offset correlation along the VLS of crustal thickness (i.e., quantity of basaltic melt released by the mantle) and mantle peridotite degree of melting led to an estimate of ~ 16.1 mm/a for the solid mantle average velocity of upwelling, a value close to the average half spreading rate for the 26 Ma interval covered by the

  2. Os and HSE of the hot upper mantle beneath southern Tibet: Indian mantle affinity?

    Science.gov (United States)

    Zhao, Z.; Dale, C. W.; Pearson, D. G.; Niu, Y.; Zhu, D.; Mo, X.

    2011-12-01

    The subduction of the Indian plate (including cratonic continental crust and/or upper mantle) beneath southern Tibet is widely accepted from both geological and geophysical studies. Mantle-derived xenoliths from this region provide a means of directly investigating the mantle underlying the southern part of the plateau. Studies of xenoliths hosted in the Sailipu ultrapotassic volcanic rocks, erupted at ~17 Ma, have indicated that the subcontinental mantle of southern Tibetan Plateau is hot and strongly influenced by metasomatism (Zhao et al., 2008a, b; Liu et al., 2011). Here we report comprehensive EPMA and LA-ICP-MS major and trace element data for the Sailipu xenoliths and also whole rock Os isotope and HSE data in order to constrain the depletion history of the mantle and to identify the presence of any potential Indian cratonic mantle. The xenoliths, ranging in size from 0.5cm to 1.5cm in diameter, are mostly peridotites. The calculated temperatures are 1010-1230°C at the given pressures of ~1.6-2.0 GPa (n=47). These P-T conditions are similar to rift-related upper mantle regimes (e.g. Kenya), indicating the influence of regional extension beneath southern Tibet in the Miocene. A series of compositional discriminations for minerals (Cpx, Opx, Ol, and Phl), e.g. Fo ~91), with a clear metasomatic signature We obtained Os isotope data and abundances of highly siderophile elements (HSE, including Os, Ir, Ru, Pt, Pd and Re) on a set of six olivine-dominated peridotite samples from Sailipu volcanics, less than 1 cm in dimension. They allow us to further constrain the nature and state of the upper mantle beneath the southern Tibet. Sailipu samples display low total HSE abundances (Os+Ir+Ru+Pt+Pd+Re) ranging from 8.7 to 25 ppb, with nearly constant Os, Ir , and Ru, but rather varied Pt (2-13), Pd (0.4-5.2), and Re (0.01-0.5). Chondrite-normalised Pd/Ir ratios range from 0.2 to 2.4 reflecting significant metasomatism of some samples. The xenoliths exhibit 187Os/188Os

  3. Diamond Formation in Dehydration Zones in the deep Upper Mantle and Lower Mantle

    Science.gov (United States)

    Harte, Ben

    2010-05-01

    Introduction. During the last 25 years a series of publications have documented the occurrence of inclusions in diamonds that show mineral compositions and mineral associations predicted for mantle rocks at deeper levels than the mantle lithosphere (e.g Harte et al., 1999; Harte & Cayzer, 2007). Although the diamonds bearing deep mantle inclusions are not abundant in absolute terms they are widespread and have been reported from cratonic blocks on all major continents. As with natural diamonds in general these deep diamonds appear to have grown in fluids/melts. Depth Zones indicated by inclusion suites. The silicate inclusions and their mineral associations form a series showing good correlation with mineral assemblages expected in basic and ultrabasic rock compositions at depth. However, there is a strong bias towards assemblages from two principal zones: (1)uppermost Transition zone and Asthenosphere (upper TZ group)) (2)lowermost Transition Zone and uppermost Lower Mantle (UM/LM group) In the case of (1) the assemblages are predominantly of majorite garnet, and majorite garnet + cpx with an affinity to eclogitic bulk compositions. In many of these inclusions the cpx appears to have exsolved from the majoritic garnet and the depth of origin of the initial inclusions may often be near the top of the Transition Zone. The assemblages from (2) are predominantly of peridotic affinity and involve fPer as well as silicates. They indicate material from three depth zones near the upper mantle to lower mantle boundary (UM/LM boundary). 2a) Upper/Lower Mantle Boundary association - inclusions of: Mg2SiO4, fPer, maj/tapp, mpv, cpv 2b) uppermost Lower Mantle association with: Mpv(Al-poor) with fPer and cpv,maj/tapp 2c)lower Mantle association with: Mpv(Al-rich) with fPer, and crn [fPer:ferropericlase; maj:majorite; tapp:tetragonal-almandine-pyrope phase; mpv:MgSiperovskite; cpv:CaSiperovskite] Discussion. The above features show that the formation of deep mantle diamonds is

  4. Resolving the Mantle Plume Heat Transfer Discrepancy

    Science.gov (United States)

    Hoggard, M.; Parnell-Turner, R. E.; White, N.

    2016-12-01

    Estimates of the buoyancy and heat flux of upwelling mantle plumes are important for understanding many aspects of convection within the Earth. These fluxes influence melt productivity and geochemistry at mid-oceanic spreading centres and hotspots, dynamic topography, mantle mixing timescales and Earth's bulk heat budget. The majority of existing plume flux estimates are calculated from the cross-sectional area of swells multiplied by either plate velocities or spreading rates. Hawaii and the other Pacific hotspots dominate these estimates, which indicate a total heat flux carried by plumes to the base of plates at ˜ 2 TW. Here, we use an alternative approach that calculates buoyancy flux using the swell volume constrained from a new map of dynamic topography, scaled by a characteristic swell decay time. This method avoids the assumption that plume material moves at or below the velocity of the overriding plate. Our results indicate that the Icelandic plume has a buoyancy flux of ˜ 27 ± 4 Mg/s , which is significantly larger than the Hawaiian plume and an order of magnitude greater than some previous estimates. These new values match independent geophysical constraints from Hawaii and the North Atlantic Ocean. All magmatic and amagmatic swells have been included in our global analysis, which reveals a total heat flux carried to the base of the plates of ˜ 10 ± 2 TW. This increased global heat flux is consistent with recent global seismic tomographic images of large upwelling plumes in the mid-mantle and predictions of heat flux through the core-mantle boundary.

  5. 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.

  6. The role of thermodynamics in mantle convection: is mantle-layering intermittent?

    Science.gov (United States)

    Stixrude, L. P.; Cagney, N.; Lithgow-Bertelloni, C. R.

    2016-12-01

    We examine the thermal evolution of the Earth using a 1D model in which mixing length theory is used to characterise the role of thermal convection. Unlike previous work, our model accounts for the complex role of thermodynamics and phase changes through the use of HeFESTo (Stixrude & Lithgow-Bertelloni, Geophys. J. Int. 184, 2011), a comprehensive thermodynamic model that enables self-consistent computation of phase equilibria, physical properties (e.g. density, thermal expansivity etc.) and mantle isentropes. Our model also accounts for the freezing of the inner core, radiogenic heating and Arrhenius rheology, and is validated by comparing our results to observations, including the present-day size of the inner core and the heat flux at the surface.If phase changes and the various thermodynamic effects on mantle properties are neglected, the results are weakly dependent on the initial conditions, as has been observed in several previous studies. However, when these effects are accounted for, the initial temperature profile has a strong influence on the thermal evolution of the mantle, because small changes in the temperature and phase-assemblage can lead to large changes in the local physical properties and the adiabatic gradient.The inclusion of thermodynamic effects leads to some new and interesting insights. We demonstrate that the Clapeyron slope and the thermal gradient at the transition zone both vary significantly with time; this causes the mantle to switch between a layered state, in which convection across the transition zone is weak or negligible, and an un-layered state, in which there is no resistance to mass transfer between the upper and lower mantles.Various plume models describe plumes either rising directly from the CMB to the lithosphere, or stalling at the transition zone before spawning new plumes in the upper mantle. The observance of switching behaviour indicates that both models may be applicable depending on the state of the mantle: plumes

  7. Thermodynamic constraints on Fe and Si carbide stabilities in the Earth's mantle

    Science.gov (United States)

    Golubkova, A.; Schmidt, M. W.; Connolly, J. A.

    2013-12-01

    -Fe-Cr alloy at lower fO2 than IW, but is, nonetheless, stable at conditions that are ~ 4 log units more oxidizing than SiC. Based on these phase relations, the variety of Fe-, Si- and C-bearing phases in mantle-derived inclusions can only be explained by extraordinary mantle heterogeneity in terms of redox conditions. Subducted organic sediments are a possible source for such ultra-reducing environments, a hypothesis that is consistent with the light C isotopic composition of moissanite [Trumbull et al., 2009]. The temperature of interaction between mantle minerals and recycled material must be low (chromite and SiC do not stably coexist. Therefore, we attribute natural SiC + chromite assemblages to kinetic inhibition. The involvement of recycled components transported by fluids into the source region of deeply generated magmas has been proposed based on isotopic and trace-element chemistry. Evidently, the interaction between mantle peridotites and subducted material at different P-T-fO2 results in the formation of mantle regions with highly contrasting redox environments. The change of Fe and C redox states in such regions is one of important mechanisms initiating melting or freezing within the mantle [Rohrbach & Schmidt 2011, Nature].

  8. Mantle updrafts and mechanisms of oceanic volcanism

    Science.gov (United States)

    Anderson, Don L.; Natland, James H.

    2014-10-01

    Convection in an isolated planet is characterized by narrow downwellings and broad updrafts-consequences of Archimedes' principle, the cooling required by the second law of thermodynamics, and the effect of compression on material properties. A mature cooling planet with a conductive low-viscosity core develops a thick insulating surface boundary layer with a thermal maximum, a subadiabatic interior, and a cooling highly conductive but thin boundary layer above the core. Parts of the surface layer sink into the interior, displacing older, colder material, which is entrained by spreading ridges. Magma characteristics of intraplate volcanoes are derived from within the upper boundary layer. Upper mantle features revealed by seismic tomography and that are apparently related to surface volcanoes are intrinsically broad and are not due to unresolved narrow jets. Their morphology, aspect ratio, inferred ascent rate, and temperature show that they are passively responding to downward fluxes, as appropriate for a cooling planet that is losing more heat through its surface than is being provided from its core or from radioactive heating. Response to doward flux is the inverse of the heat-pipe/mantle-plume mode of planetary cooling. Shear-driven melt extraction from the surface boundary layer explains volcanic provinces such as Yellowstone, Hawaii, and Samoa. Passive upwellings from deeper in the upper mantle feed ridges and near-ridge hotspots, and others interact with the sheared and metasomatized surface layer. Normal plate tectonic processes are responsible both for plate boundary and intraplate swells and volcanism.

  9. Earth's oldest mantle fabrics indicate Eoarchaean subduction.

    Science.gov (United States)

    Kaczmarek, Mary-Alix; Reddy, Steven M; Nutman, Allen P; Friend, Clark R L; Bennett, Vickie C

    2016-02-16

    The extension of subduction processes into the Eoarchaean era (4.0-3.6 Ga) is controversial. The oldest reported terrestrial olivine, from two dunite lenses within the ∼3,720 Ma Isua supracrustal belt in Greenland, record a shape-preferred orientation of olivine crystals defining a weak foliation and a well-defined lattice-preferred orientation (LPO). [001] parallel to the maximum finite elongation direction and (010) perpendicular to the foliation plane define a B-type LPO. In the modern Earth such fabrics are associated with deformation of mantle rocks in the hanging wall of subduction systems; an interpretation supported by experiments. Here we show that the presence of B-type fabrics in the studied Isua dunites is consistent with a mantle origin and a supra-subduction mantle wedge setting, the latter supported by compositional data from nearby mafic rocks. Our results provide independent microstructural data consistent with the operation of Eoarchaean subduction and indicate that microstructural analyses of ancient ultramafic rocks provide a valuable record of Archaean geodynamics.

  10. Resetting of Re-Os ages in mantle rocks

    Science.gov (United States)

    Becker, H.; Gawronski, T.; Wang, Z.

    2011-12-01

    Among long-lived geochronometers, the Re-Os decay system is unique in that it permits to obtain direct age information on past melt extraction events in the mantle. Some studies have discovered ancient melting residues in oceanic peridotites emplaced on young seafloor [1-3]. Other work indicates that melt transport and reactive infiltration may affect the Re-Os systematics of both depleted and fertile peridotites to variable extent [4-6]. Open system polybaric melting of depleted lherzolites and harzburgites should lead to removal of basaltic components and at the same time partial or complete equilibration with infiltrating magma. If such magma carries radiogenic Os, it will lead to partial or complete resetting of the Re-Os clock. This is what may have occurred in many abyssal peridotites [e.g. 2, 7], although, the parameters that control isotopic resetting, the timing, extent and controls on equilibration with melts carrying radiogenic Os are still incompletely understood. Studies of well-characterized Phanerozoic peridotite massifs that represent former ocean-continent transitions and analogues of modern slow spreading environments do offer some additional insight. Re-Os data on the Ligurian peridotite massifs [8,9], the Lanzo peridotite [9], and peridotites from the Ivrea zone [10,11] suggest addition of radiogenic Os to some, but not all, harzburgites and depleted lherzolites. The source of the radiogenic Os may have been either local (melting of pyroxenites) or external. Fertile lherzolites in these massifs often display petrological and geochemical evidence for refertilization, but the timing of magmatic processes is not always clear. In the Ivrea zone, Sm-Nd dates obtained on clinopyroxenes from peridotites are Paleozoic [12], as are some Os model ages of peridotites [10, 11], however, the spectrum of Re-Os (primitive mantle) model ages ranges between 0.2 and 1.6 Ga (median 0.5 Ga). Hence, it is likely that extensive magmatic re-equilibration occurred in

  11. A view into crustal evolution at mantle depths

    Science.gov (United States)

    Kooijman, Ellen; Smit, Matthijs A.; Ratschbacher, Lothar; Kylander-Clark, Andrew R. C.

    2017-05-01

    melted, densified, and buried to 80-90 km depth - 20 km deeper than the present-day Moho - at 930 ± 35°C. The material descended rapidly, accelerating from 0.9-1.7 mm yr-1 to 4.7-5.8 mm yr-1 within 10-12 Myr, and continued descending after reaching mantle depth at 14-13 Ma. The data reflect the foundering of differentiated deep-crustal fragments (2.9-3.5 g cm-3) into a metasomatized and less dense mantle wedge. Through our new approach in constraining the burial history of rocks, we provided the first time-resolved record of this crustal-recycling process. Foundering introduced vestiges of old evolved crust into the mantle wedge over a relatively short period (c. 10 Myr). The recycling process could explain the variability in the degree of crustal contamination of mantle-derived magmatic rocks in the Pamir and neighboring Tibet during the Cenozoic without requiring a change in plate dynamics or source region.

  12. Chromium isotope heterogeneity in the mantle

    Science.gov (United States)

    Xia, Jiuxing; Qin, Liping; Shen, Ji; Carlson, Richard W.; Ionov, Dmitri A.; Mock, Timothy D.

    2017-04-01

    To better constrain the Cr isotopic composition of the silicate Earth and to investigate potential Cr isotopic fractionation during high temperature geological processes, we analyzed the Cr isotopic composition of different types of mantle xenoliths from diverse geologic settings: fertile to refractory off-craton spinel and garnet peridotites, pyroxenite veins, metasomatised spinel lherzolites and associated basalts from central Mongolia, spinel lherzolites and harzburgites from North China, as well as cratonic spinel and garnet peridotites from Siberia and southern Africa. The δ53CrNIST 979 values of the peridotites range from - 0.51 ± 0.04 ‰ (2SD) to + 0.75 ± 0.05 ‰ (2SD). The results show a slight negative correlation between δ53Cr and Al2O3 and CaO contents for most mantle peridotites, which may imply Cr isotopic fractionation during partial melting of mantle peridotites. However, highly variable Cr isotopic compositions measured in Mongolian peridotites cannot be caused by partial melting alone. Instead, the wide range in Cr isotopic composition of these samples most likely reflects kinetic fractionation during melt percolation. Chemical diffusion during melt percolation resulted in light Cr isotopes preferably entering into the melt. Two spinel websterite veins from Mongolia have extremely light δ53Cr values of - 1.36 ± 0.04 ‰ and - 0.77 ± 0.06 ‰, respectively, which are the most negative Cr isotopic compositions yet reported for mantle-derived rocks. These two websterite veins may represent crystallization products from the isotopically light melt that may also metasomatize some peridotites in the area. The δ53Cr values of highly altered garnet peridotites from southern Africa vary from - 0.35 ± 0.04 ‰ (2SD) to + 0.12 ± 0.04 ‰ (2SD) and increase with increasing LOI (Loss on Ignition), reflecting a shift of δ53Cr to more positive values by secondary alteration. The Cr isotopic composition of the pristine, fertile upper mantle is

  13. Electrical conductivity of mantle peridotite at the uppermost lower mantle condition

    Energy Technology Data Exchange (ETDEWEB)

    Yoshino, T; Katsura, T; Yamazaki, D; Ito, E, E-mail: tyoshino@misasa.okayama-u.ac.j [Institute for Study of the Earth' s Interior, Okayama University, 827 Yamada, Misasa, Tottori 682-1093 (Japan)

    2010-03-01

    Electrical conductivity of mantle peridotite was measured at 25 GPa and temperature up to 1800 K in a Kawai-type multi-anvil apparatus. The starting material was gel with a composition of fertile spinel lherzolite (KLB1). After the conductivity measurement, mineral phases of run products are composed of magnesium silicate perovskite, ferro-periclase and Ca perovskite. The conductivity value of the peridotite is distinctly higher than those of post-spinel and magnesian silicate perovskite with a composition of (Mg{sub 0.9},Fe{sub 0.1})SiO{sub 3}, but lower than that of ferro-periclase. Both absolute values and change in activation enthalpy for the conductivity of the mantle peridotite are similar to those for the silicate perovskite. A presence of aluminous perovskite with substantial amount of ferric iron in crystal structure would enhance bulk conductivity of the lower mantle.

  14. Volcanic Infillings of Large Basins on Mercury as Indicators of Mantle Thermal State and Composition

    Science.gov (United States)

    Padovan, Sebastiano; Tosi, Nicola; Plesa, Ana-Catalina; Ruedas, Thomas

    2017-04-01

    The crust of Mercury is mostly the cumulative result of partial melting in the mantle associated with solid-state convection [1]. The details of how the surface composition represents the result of dynamical processes in the interior are difficult to elucidate. Explanations for the observed geochemically varied surface include a heterogeneous mantle, the effects of ancient giant impacts, an evolving mantle composition, or a combination of these processes [e.g., 2]. Here we explore the effects of large impacts on mantle dynamics and associated melt production. With the convection code GAIA we compute thermal evolution histories of Mercury compatible with the expected amount of heat producing elements in the mantle and with the crustal thickness inferred from gravity and topography data. We estimate the thermal anomalies in the mantle generated by large impacts using scaling laws [3]. Impactors have a velocity of 42 km/s and an impact angle of 45°, as appropriate for Mercury [4]. Their size is varied in order to produce basins with diameters in the range from 715 km (Rembrandt) to 1550 km (Caloris). Depending on the timing of the impact, the melt erupting in the basin interior is a combination of convective melt generated at depth and shallow melt resulting from shallow impact-induced convective currents. The volcanic infillings following an impact happening early in the evolution of the planet, when convection is still vigorous, are dominated by convective melt. Later in the evolution, the erupted melt shows the signature of the impact-induced shallow melt. We show that the properties of melt sheets within the young large basins Caloris and Rembrandt depend on the mantle thermal state and composition. In particular, we predict the source depth of the volcanic plains within large young basins to be different from the source depth of older surface units, a result that can help explaining the peculiar composition of the volcanic plains inside Caloris [2, 5]. [1] Tosi

  15. Inferring global Upper-Mantle Shear Attenuation structure by waveform tomography using the Spectral Element Method

    Science.gov (United States)

    Karaoǧlu, Haydar; Romanowicz, Barbara

    2018-01-01

    We present a global upper-mantle shear wave attenuation model that is built through a hybrid full-waveform inversion algorithm applied to long-period waveforms, using the Spectral Element Method for wavefield computations. Our inversion strategy is based on an iterative approach that involves the inversion for successive updates in the attenuation parameter (δ Q^{-1}_μ) and elastic parameters (isotropic velocity VS, and radial anisotropy parameter ξ) through a Gauss-Newton type optimization scheme that employs envelope- and waveform-type misfit functionals for the two steps, respectively. We also include source and receiver terms in the inversion steps for attenuation structure. We conducted a total of 8 iterations (6 for attenuation and 2 for elastic structure), and one inversion for updates to source parameters. The starting model included the elastic part of the relatively high resolution 3-D whole mantle seismic velocity model, SEMUCB-WM1, which served to account for elastic focusing effects. The data set is a subset of the three component surface waveform data set, filtered between 400 and 60 s, that contributed to the construction of the whole-mantle tomographic model SEMUCB-WM1. We applied strict selection criteria to this data set for the attenuation iteration steps, and investigated the effect of attenuation crustal structure on the retrieved mantle attenuation structure. While a constant 1-D Qμ model with a constant value of 165 throughout the upper-mantle was used as starting model for attenuation inversion, we were able to recover, in depth extent and strength, the high attenuation zone present in the depth range 80-200 km. The final three-dimensional model, SEMUCB-UMQ, shows strong correlation with tectonic features down to 200˜250 km depth, with low attenuation beneath the cratons, stable parts of continents and regions of old oceanic crust, and high attenuation along mid-ocean ridges and back-arcs. Below 250 km, we observe strong attenuation in

  16. The Atlas of the Underworld: a catalogue of slab remnants in the mantle imaged by seismic tomography, and their geological interpretation

    Science.gov (United States)

    van der Meer, Douwe; van Hinsbergen, Douwe; Spakman, Wim

    2017-04-01

    Seismic tomography has provided a breakthrough in the analysis of plate tectonic history by allowing to trace now-subducted, ancient lithosphere in the Earth's mantle, where they appear as large positive seismic wave-speed anomalies. Subduction also leaves a geological record that allows for dating the geological period of active subduction. By combining these sources of information, we previously compiled 28 lower-mantle slab remnants and estimated for the timing of onset and end of subduction of these slabs, from which we derived a first-order sinking rate of slabs through the mantle (van der Meer et al., 2010). This constraint on lower mantle slab sinking rates allowed for the development of the first slab mantle reference frame, and was used to constrain of mantle viscosity. Since that first compilation, the plate tectonic and seismological community has made major progress on linking geological history to mantle structure. Slabs were linked to plate tectonic models at regional scale, contributed to understanding of orogenies at local level, and was recently even used as a novel basis for plate kinematic restorations. When analyses were expanded into the Pacific realm it improved our understanding of the presence of seismic scatterers in the sub-Pacific mantle and Pacific LLSVP topography. Expanding the tomographic analysis to a global, whole-mantle scale has led to the calculation of total lateral slab lengths, which was used to calculated corresponding subduction zone lengths through time that provided constraints for plate tectonic activity over the past 235 Myr impacting atmospheric CO2 and providing insights in the link between strontium isotope curves and global sea level. Encouraged by the direct and indirect results of our previous work, we have expanded our analysis to nearly 100 mantle images throughout the upper and lower mantle, which we correlate to 94 subduction systems active in the past 300 Myr. We provide our geological interpretation of these

  17. Tottori earthquakes and Daisen volcano: Effects of fluids, slab melting and hot mantle upwelling

    Science.gov (United States)

    Zhao, Dapeng; Liu, Xin; Hua, Yuanyuan

    2018-03-01

    We investigate the 3-D seismic structure of source areas of the 6 October 2000 Western Tottori earthquake (M 7.3) and the 21 October 2016 Central Tottori earthquake (M 6.6) which occurred near the Daisen volcano in SW Japan. The two large events took place in a high-velocity zone in the upper crust, whereas low-velocity (low-V) and high Poisson's ratio (high-σ) anomalies are revealed in the lower crust and upper mantle. Low-frequency micro-earthquakes (M 0.0-2.1) occur in or around the low-V and high-σ zones, which reflect upward migration of magmatic fluids from the upper mantle to the crust under the Daisen volcano. The nucleation of the Tottori earthquakes may be affected by the ascending fluids. The flat subducting Philippine Sea (PHS) slab has a younger lithosphere age and so a higher temperature beneath the Daisen and Tottori area, facilitating the PHS slab melting. It is also possible that a PHS slab window has formed along the extinct Shikoku Basin spreading ridge beneath SW Japan, and mantle materials below the PHS slab may ascend to the shallow area through the slab window. These results suggest that the Daisen adakite magma was affected by the PHS slab melting and upwelling flow in the upper mantle above the subducting Pacific slab.

  18. 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.

  19. Determining resolvability of mantle plumes with synthetic seismic modeling

    Science.gov (United States)

    Maguire, R.; Van Keken, P. E.; Ritsema, J.; Fichtner, A.; Goes, S. D. B.

    2014-12-01

    Hotspot volcanism in locations such as Hawaii and Iceland is commonly thought to be associated with plumes rising from the deep mantle. In theory these dynamic upwellings should be visible in seismic data due to their reduced seismic velocity and their effect on mantle transition zone thickness. Numerous studies have attempted to image plumes [1,2,3], but their deep mantle origin remains unclear. In addition, a debate continues as to whether lower mantle plumes are visible in the form of body wave travel time delays, or whether such delays will be erased due to wavefront healing. Here we combine geodynamic modeling of mantle plumes with synthetic seismic waveform modeling in order to quantitatively determine under what conditions mantle plumes should be seismically visible. We model compressible plumes with phase changes at 410 km and 670 km, and a viscosity reduction in the upper mantle. These plumes thin from greater than 600 km in diameter in the lower mantle, to 200 - 400 km in the upper mantle. Plume excess potential temperature is 375 K, which maps to seismic velocity reductions of 4 - 12 % in the upper mantle, and 2 - 4 % in the lower mantle. Previous work that was limited to an axisymmetric spherical geometry suggested that these plumes would not be visible in the lower mantle [4]. Here we extend this approach to full 3D spherical wave propagation modeling. Initial results using a simplified cylindrical plume conduit suggest that mantle plumes with a diameter of 1000 km or greater will retain a deep mantle seismic signature. References[1] Wolfe, Cecily J., et al. "Seismic structure of the Iceland mantle plume." Nature 385.6613 (1997): 245-247. [2] Montelli, Raffaella, et al. "Finite-frequency tomography reveals a variety of plumes in the mantle." Science 303.5656 (2004): 338-343. [3] Schmandt, Brandon, et al. "Hot mantle upwelling across the 660 beneath Yellowstone." Earth and Planetary Science Letters 331 (2012): 224-236. [4] Hwang, Yong Keun, et al

  20. Lenalidomide-bendamustine-rituximab in untreated mantle cell lymphoma > 65 years with untreated mantle cell lymphoma

    DEFF Research Database (Denmark)

    Albertsson-Lindblad, Alexandra; Kolstad, Arne; Laurell, Anna

    2016-01-01

    For elderly patients with mantle cell lymphoma (MCL), there is no defined standard therapy. In this multicenter open-label phase I/II trial we evaluated the addition of lenalidomide (LEN) to rituximab-bendamustine (R-B) as first-line treatment to elderly MCL patients. Patients >65 years with untr......For elderly patients with mantle cell lymphoma (MCL), there is no defined standard therapy. In this multicenter open-label phase I/II trial we evaluated the addition of lenalidomide (LEN) to rituximab-bendamustine (R-B) as first-line treatment to elderly MCL patients. Patients >65 years...

  1. Seismic images of the upper mantle velocities and structure of European mantle lithosphere

    Science.gov (United States)

    Plomerova, Jaroslava; Munzarova, Helena; Vecsey, Ludek; Babuska, Vladislav

    2014-05-01

    Tomography images of seismic velocities in the Earth mantle represent significant tool for recovering first order structural features. Regional studies, based on dense networks of temporary stations allow us to focus on structure of the continental upper mantle and to study variations of body-wave velocities in greater detail. However, the standard tomography exhibits only isotropic view of the Earth, whose structure is anisotropic in general, as shown by results of various studies exploiting a broad range of methods, types of waves and scales. We present results of our studies of seismic anisotropy in tectonically different provinces that clearly demonstrate the continental mantle lithosphere consists of domains with different fossil fabrics. We detect anisotropic signal both in teleseismic P-wave travel-time deviations and shear-wave splitting and show changes of the anisotropic parameters across seismic arrays, in which stations with similar characteristics form groups. The geographical variations of seismic-wave anisotropy delimit individual, often sharply bounded domains of the mantle lithosphere, each of them having a consistent fabric. The domains can be modelled in 3D by peridotite aggregates with dipping lineation a or foliation (a,c). These findings allow us to interpret the domains as micro-plate fragments retaining fossil fabrics in the mantle lithosphere, reflecting thus an olivine LPO created before the micro-plates assembled. Modelling anisotropic structure of individual domains of the continental mantle lithosphere helps to decipher boundaries of individual blocks building the continental lithosphere and hypothesize on processes of its formation (Plomerova and Babuska, Lithos 2010). Exploiting the long memory of the deep continental lithosphere fabric, we present the lithosphere-asthenosphere boundary (LAB) as a transition between a fossil anisotropy in the mantle lithosphere and an underlying seismic anisotropy related to the present-day flow in

  2. Mantle compositional layering revealed by slab stagnation in the uppermost lower mantle

    Science.gov (United States)

    Ballmer, Maxim; Ritsema, Jeroen; Schmerr, Nicholas; Motoki, Matthew

    2015-04-01

    Seismic tomography reveals three different modes of slab sinking behavior. Some slabs segments (1) descend through the upper mantle to stagnate in the transition zone (e.g., Japan slab), others (2) sink into the deep mantle (e.g., Tethys slab), and yet others (3) sink through the upper mantle and transition zone to stagnate at ~1000 km depth (e.g., Peru, Kermadec, Sunda and Nicaragua slabs) [Fukao and Obayashi, 2013]. Whereas stagnation in the transition zone is well explained by the supporting effect of the spinel-to-perovskite phase transition at ~660 km depth ("the 660"), a scenario for equilibrium stagnation in the uppermost lower mantle, where no endothermic phase transitions occur, remains to be proposed. Here, we explore slab sinking behavior using two-dimensional numerical models. We show that slabs stagnate at 900~1000 km depth if the lower mantle be intrinsically dense, for example due to enrichment in Si and/or Fe relative to Mg. A gradual and moderate compositional contrast across the 660 in a heterogeneous mantle is (at least locally) able to provide sufficient support for long-term slab stagnation. While such a contrast is expected to result from early-Earth processes (e.g., differential crystallization of the magma ocean), its maintenance over 4.5 Gyrs of mantle convection and stirring requires ongoing geodynamic mechanism(s) to sustain it. One such mechanism is stagnant slab disintegration, in which a superplastic slab that stagnates above or below the 660 undergoes convective instability to separate into its (enriched) basaltic and (depleted) harzburgitic components. As dense basaltic material and buoyant harzburgite tend to sink and rise, respectively, this mechanism sets up an efficient compositional filter across the transition zone. Thus, the fate of subducted slabs can sustain (disintegration) - as well as provide evidence for (stagnation at ~1000 km depth) - relative enrichment of the lower compared to the upper mantle. Such an enrichment is

  3. A sulfide-saturated lunar mantle?

    Science.gov (United States)

    Brenan, James M.; Mungall, James E.

    2017-04-01

    lunar source regions could be saturated in a low sulfur, sulfide melt. Additional sulfide-silicate partitioning experiments for the PGE and Re have also been done at Fe-metal saturation at 1400oC, 0.1 MPa using chromite capsules sealed in silica ampoules. Results confirm that the highly siderophile elements (HSE) will be strongly sequestered by residual sulfide, and that the concentrations of these elements will be strongly depleted in lunar basalts. Hence, estimates of the HSE content of the lunar mantle from basalt compositions must take into account the fractionation imposed by sulfide-silicate partitioning at reduced conditions.

  4. Mantle mixing and thermal evolution during Pangaea assembly and breakup

    Science.gov (United States)

    Rudolph, M. L.; Li, M.; Zhong, S.; Manga, M.

    2016-12-01

    Continents insulate the underlying mantle, and it has been suggested that the arrangement of the continents can have a significant effect on sub-continental mantle temperatures. Additionally, the dispersal or agglomeration of continents may affect the efficacy of continental insulation, with some studies suggesting warming of 100K beneath supercontinents. During the most recent supercontinent cycle, Pangaea was encircled by subduction, potentially creating a `curtain' of subducted material that may have prevented mixing of the sub-Pangaea mantle with the sub-Panthalassa mantle. Using 3D spherical shell geometry mantle convection simulations, we quantify the effect of insulation by continents and supercontinents. We explore the differences in model predictions for purely thermal vs. thermochemical convection, and we use tracers to quantify the exchange of material between the sub-oceanic to the sub-continental mantle.

  5. Iron isotope fractionation and the oxygen fugacity of the mantle.

    Science.gov (United States)

    Williams, Helen M; McCammon, Catherine A; Peslier, Anne H; Halliday, Alex N; Teutsch, Nadya; Levasseur, Sylvain; Burg, Jean-Pierre

    2004-06-11

    The oxygen fugacity of the mantle exerts a fundamental influence on mantle melting, volatile speciation, and the development of the atmosphere. However, its evolution through time is poorly understood. Changes in mantle oxidation state should be reflected in the Fe3+/Fe2+ of mantle minerals, and hence in stable iron isotope fractionation. Here it is shown that there are substantial (1.7 per mil) systematic variations in the iron isotope compositions (delta57/54Fe) of mantle spinels. Spinel delta57/54Fe values correlate with relative oxygen fugacity, Fe3+/sigmaFe, and chromium number, and provide a proxy of changes in mantle oxidation state, melting, and volatile recycling.

  6. Five years of the Normal Oceanic Mantle (NOMan) Project

    Science.gov (United States)

    Utada, Hisashi; Kawakatsu, Hitoshi; Shiobara, Hajime; Baba, Kiyoshi; Isse, Takehi; Suetsugu, Daisuke; NOMan Project Team

    2016-04-01

    The Normal Oceanic Mantle (NOMan) project was carried out for 5 years from 2010, aiming to solve two fundamental questions on the 'normal' oceanic mantle from observational approach, which are: (a) Cause of asthenosphere lubrication, and (b) Amount of water in the mantle transition zone. We selected two study areas (A and B) of similar seafloor age (about 130 and 140 Ma, respectively) in the northwestern Pacific Ocean where the mantle below is supposed to be normal. This presentation will give an overview of five years of the NOMan project, especially of its observational activities and a summary of preliminary results so far obtained. In June 2010, we deployed a small array consisting of 5 (both seismic and EM) sites and started data acquisition from area A, which we call the NOMan pilot experiment. The main observation by long-term seafloor arrays in areas A and B was started by two installation cruises carried out in November 2011 and in August 2012, deploying state-of-the-art ocean bottom seismic and electromagnetic instruments (BBOBS-NXs and EFOSs) in area A that are handled by ROV for installation and recovery. Conventional instruments (BBOBS and OBEM of free-fall/self-pop-up type) were also deployed both in areas A and B. Most of instruments of the pilot experiment were recovered by the cruise in August 2012. So-called advanced instruments (BBOBS-NXs and EFOSs) were equipped with batteries sufficient for 2 years of deployment, but conventional instruments (BBOBSs and OBEMs) only for one year or so. Therefore, we conducted a cruise by W/V Kaiyu in August 2013 to maintain the observation array by retrieving and re-deploying respective instruments. In June 2014, we conducted another W/V Kaiyu cruise, in which we recovered most of conventional instruments in area A after conducting a controlled source seismic experiment by using explosive sources. In September 2014, we completed a recovery cruise by R/V Kairei with ROV Kaiko-7000II. By these two cruises

  7. Structure of the mantle lithosphere beneath the Siberian kimberlite pipes reconstructed by monomineral thermobarometry

    Science.gov (United States)

    Ashchepkov, I. V.

    2009-04-01

    columns (10-13) is reconstructed by the stepped TPX trends formed at first by the combinations of subduction and superplume events coinciding with the Re/Os ages (Spetsius, 2007), overprinted by the reactions with the plume and other percolating melts The Fe# increase near the 60 kbar refer to the last superplume events the previous leave similar rhythmic Fe- dunite horizons at 11-12 levels. The comparison of the compositions of minerals and reconstruction of mantle roots for several phases for Yubileinay, Udachnaya and Nyurbinskaya pipes allow to reveal the evolution of the magmatic sources and their interaction with the mantle lithosphere. Reconstruction of the mantle columns beneath 60 pipes allow to make the transsects of the kimberlite fields and the 3D model of the mantle beneath the dense kimberlite clusters with many close located diatrems Mesozoic mantle columns beneath the Anabar, Olenek, Aldan show the HT -Fe# alteration in 60-40 kbar due to interaction with the PT superplume, but relic and LT and low Fe# associations occurs to 60 kbar also. RBRF 05-05-74718, 06-05-65021, 06-05-64416.

  8. Is Earth coming out of the recent ice house age in the long-term? - constraints from probable mantle CO2-degassing reconstructions

    Science.gov (United States)

    Hartmann, Jens; Li, Gaojun; West, A. Joshua

    2017-04-01

    Enhanced partial melting of mantle material probably started when the subduction motor started around 3.2 Ga ago as evidenced by the formation history of the continental crust. Carbon is degassing due partial melting as it is an incompatible element. Therefore, mantle carbon degassing rates would change with time proportionally to the reservoir mantle concentration evolution and the ocean crust production rate, causing a distinct CO2-degassing rate change with time. The evolution of the mantle degassing rate has some implications for the reconstruction of the carbon cycle and therefore climate and Earth surface processes rates, as CO2-degassing rates are used to constrain or to balance the atmosphere-ocean-crust carbon cycle system. It will be shown that compilations of CO2-degassing from relevant geological sources are probably exceeding the established CO2-sink terrestrial weathering, which is often used to constrain long-term mantle degassing rates to close the carbon cycle on geological time scales. In addition, the scenarios for the degassing dynamics from the mantle sources suggest that the mantle is depleting its carbon content since 3 Ga. This has further implications for the long-term CO2-sink weathering. Results will be compared with geochemical proxies for weathering and weathering intensity dynamics, and will be set in context with snow ball Earth events and long-term emplacement dynamics of mafic areas as Large Igneous Provinces. Decreasing mantle degassing rates since about 2 Ga suggest a constraint for the evolution of the carbon cycle and recycling potential of the amount of subducted carbon. If the given scenarios hold further investigation, the contribution of mantle degassing to climate forcing (directly and via recycling) will decrease further.

  9. Tracking Long-lived Hotspots to Constrain Temporal Mantle Compositional Evolution

    Science.gov (United States)

    Konter, J. G.; Jackson, M. G.; Koppers, A. A.

    2011-12-01

    Linear chains of intraplate volcanoes provide a record of the geochemical composition of the mantle through geologic time. Their geochemical compositions characterize the mantle source material that melted and place constraints on the geodynamic origin of the source, and thereby the dynamic character of the mantle. In particular, long-lived volcanic chains provide strong constraints, since they require large volumes of mantle source material and provide the best way to evaluate hotspot source stability. Some of the longest-lived volcanic chains are anchored by the current Cook-Austral Islands continuing into the Western Pacific, where their tracks are complicated by cross-cutting volcanic chains and isolated seamounts. The connection between recent volcanism in the Cook-Austral Islands and Cretaceous volcanism in the Western Pacific is revealed by a combination of ages and isotopic compositions, suggesting three simultaneously erupting hotspot locations. The ages of the Western Pacific volcanoes fit with three predicted hotspot tracks, while the isotopic compositions along each track have a limited range and are largely distinct from each other. However, until recently no data existed on volcanoes in the 30-60 Ma age range for these hotspot chains. New data collected on samples from volcanoes in Samoa and Tuvalu are now starting to provide a more complete geochemical record through time. In the Tuvalu Islands very limited dredging only provided a small number of samples. Isotopic compositions for these volcanoes correspond very well to the range in compositions observed for the Rurutu hotspot in the Cook-Austral Islands, and the Tuvalu Islands lie along the predicted hotspot track for the Rurutu hotspot. Similarly, a number of volcanoes with similar composition are found along the Samoan chain of volcanoes. Since plate motion models predicts that the Pacific Plate around Samoa passed over the Rurutu hotspot, the Samoan region represents a complex area of

  10. Mantle to surface degassing of alkalic magmas at Erebus volcano, Antarctica

    Science.gov (United States)

    Oppenheimer, C.; Moretti, R.; Kyle, P.R.; Eschenbacher, A.; Lowenstern, J. B.; Hervig, R.L.; Dunbar, N.W.

    2011-01-01

    Continental intraplate volcanoes, such as Erebus volcano, Antarctica, are associated with extensional tectonics, mantle upwelling and high heat flow. Typically, erupted magmas are alkaline and rich in volatiles (especially CO2), inherited from low degrees of partial melting of mantle sources. We examine the degassing of the magmatic system at Erebus volcano using melt inclusion data and high temporal resolution open-path Fourier transform infrared (FTIR) spectroscopic measurements of gas emissions from the active lava lake. Remarkably different gas signatures are associated with passive and explosive gas emissions, representative of volatile contents and redox conditions that reveal contrasting shallow and deep degassing sources. We show that this unexpected degassing signature provides a unique probe for magma differentiation and transfer of CO2-rich oxidised fluids from the mantle to the surface, and evaluate how these processes operate in time and space. Extensive crystallisation driven by CO2 fluxing is responsible for isobaric fractionation of parental basanite magmas close to their source depth. Magma deeper than 4kbar equilibrates under vapour-buffered conditions. At shallower depths, CO2-rich fluids accumulate and are then released either via convection-driven, open-system gas loss or as closed-system slugs that ascend and result in Strombolian eruptions in the lava lake. The open-system gases have a reduced state (below the QFM buffer) whereas the closed-system gases preserve their deep oxidised signatures (close to the NNO buffer). ?? 2011 Elsevier B.V.

  11. The Importance of Upper Mantle Heterogeneity in Generating the Indian Ocean Geoid Low

    Science.gov (United States)

    Ghosh, Attreyee; Thyagarajulu, G.; Steinberger, Bernhard

    2017-10-01

    One of the most pronounced geoid lows on Earth lies in the Indian Ocean just south of the Indian peninsula. Several theories have been proposed to explain this geoid low, most of which invoke past subduction. Some recent studies have also argued that high-velocity anomalies in the lower mantle coupled with low-velocity anomalies in the upper mantle are responsible for these negative geoid anomalies. However, there is no general consensus regarding the source of this particular anomaly. We investigate the source of this geoid low by using models of density-driven mantle convection. Our study is the first to successfully explain the occurrence of this anomaly using a global convection model driven by present-day density anomalies derived from tomography. We test various tomography models in our flow calculations with different radial and lateral viscosity variations. Some of them produce a fairly high correlation to the global geoid, but only a few (SMEAN2, GyPSuM, SEMUCB, and LLNL-JPS) could match the precise location and pattern of the geoid low in the Indian Ocean. The source of this low stems from a low-density anomaly stretching from a depth of 300 km down to ˜900 km in the northern Indian Ocean region. This density anomaly potentially originates from material rising along the edge of the African Large Low Shear Velocity Province and moving toward the northeast, facilitated by the movement of the Indian plate in the same direction.

  12. Carbon in MOR basalts, mantle and global C cycling

    Science.gov (United States)

    Holloway, J. R.

    2003-04-01

    The carbon content of mid-ocean ridge (MOR) erupted magmas is well known from analysis of glassy rims on pillow basalts (1), is dissolved exclusively in the form of carbonate ion, and provides a measure of the minimum CO_2 content of pre-eruption MORB magmas. The solubility of CO_2 in MORB liquids is also well known (2) and shows that most MORB magmas were oversaturated in CO_2 at seafloor pressures (3) so the CO_2 content of MORB magma could be much greater than observed in MORB glasses. Possible hosts for C in MORB magma source regions are dolomite/magnesite or graphite/diamond depending on oxygen fugacity (4). Oxygen fugacities measured from MORB glasses (5) and mantle nodules (6) require that graphite/diamond is the C source (4). Assuming graphite as the source I constructed a model to calculate the CO_2 content of primary MORB magma and arrived at a probable value of 1800 ppm (7). That model predicts that le80 ppm of graphite/diamond in the MORB source mantle is consumed. That is a surprisingly low value; however simple mass balance shows that if the integrated melt fraction is 15 wt.% the amount of graphite required to generate 1800 ppm CO_2 in primary MORB magma is 74 ppm. A new equation of state (8) yields CO_2 fugacities up to 50% greater than used in (7) but this results in only minor differences with the previous model calculations, e.g. a 0.2 log unit increase in calculated oxygen fugacity. The 1800 ppm value for the CO_2 content of primary MORB magma erupted at present-day rates for the last 3.3 AE equals estimates of the Earth's global crustal, oceanic and atmospheric carbon content (7,9). (1) e.g. Dixon et al. 1988; (2) Pan, et al. (1991), Jendrzejewski, et al. 1997; (3) Dixon et al. 1995, Jendrzejewski, et al. 1997; (4) Eggler & Baker, 1982; (5) Christi, et al., 1986; (6) Wood et al., 1990; (7) Holloway, 1998; (8) Frost &Wood, 1997; Holloway &O'Day, 2000.

  13. Water distribution in the lower mantle: Implications for hydrolytic weakening

    Science.gov (United States)

    Muir, Joshua M. R.; Brodholt, John P.

    2018-02-01

    The presence of water in lower mantle minerals is thought to have substantial effects on the rheological properties of the Earth's lower mantle in what is generally known as "hydrolytic weakening". This weakening will have profound effects on global convection, but hydrolytic weakening in lower mantle minerals has not been observed experimentally and thus the effect of water on global dynamics remains speculative. In order to constrain the likelihood of hydrolytic weakening being important in the lower mantle, we use first principles methods to calculate the partitioning of water (strictly protons) between mineral phases of the lower mantle under lower mantle conditions. We show that throughout the lower mantle water is primarily found either in the minor Ca-perovskite phase or in bridgmanite as an Al3+-H+ pair. Ferropericlase remains dry. However, neither of these methods of water absorption creates additional vacancies in bridgmanite and thus the effect of hydrolytic weakening is likely to be small. We find that water creates significant number of vacancies in bridgmanite only at the deepest part of the lower mantle and only for very high water contents (>1000 ppm). We conclude that water is thus likely to have only a limited effect on the rheological properties of the lower mantle.

  14. Mantle plume or slab window?: Physical and geochemical constraints on the origin of the Caribbean oceanic plateau (Invited)

    Science.gov (United States)

    Kerr, A. C.; Hastie, A.

    2009-12-01

    The Caribbean oceanic plateau formed in the Pacific realm when it erupted onto the Farallon plate due to melting of (possibly) the Galapagos hotspot at ~93 Ma. The plateau was subsequently transported to the northeast and collided with the Great Arc of the Caribbean thus initiating subduction polarity reversal and the consequent tectonic emplacement of the Caribbean plate between the North and South American continents. The plateau represents a large outpouring of mafic volcanism, which has been interpreted as having formed by melting of a hot mantle plume. Conversely, some have suggested that a slab window could be involved in forming the plateau. However, the source regions of oceanic plateaus are distinct from N-MORB (the likely source composition for slab window mafic rocks). Furthermore, melt modelling using primitive (high-MgO) Caribbean oceanic plateau lavas from Curaçao, shows that the primary magmas of the plateau contained ~20 wt.% MgO and were derived from 30-32 % partial melting of a fertile peridotite source region which had a potential temperature (Tp) of 1564-1614 °C. Thus, the Caribbean oceanic plateau lavas are derived from decompression melting of a hot upwelling mantle plume with excess heat relative to ambient upper mantle. Extensional decompression partial melting of sub-slab asthenosphere in a slab window with an ambient mantle Tp cannot produce enough melt to form a plateau. The formation of the Caribbean oceanic plateau by melting of ambient upper mantle in, or close to, a slab window setting, is therefore, highly improbable. Reference Hastie, A.R., Kerr, A.C. 2010. Mantle plume or slab window?: Physical and geochemical constraints on the origin of the Caribbean oceanic plateau. Earth Science Reviews, in press.

  15. MicroRNAs in mantle cell lymphoma

    DEFF Research Database (Denmark)

    Husby, Simon; Geisler, Christian; Grønbæk, Kirsten

    2013-01-01

    Mantle cell lymphoma (MCL) is a rare and aggressive subtype of non-Hodgkin lymphoma. New treatment modalities, including intensive induction regimens with immunochemotherapy and autologous stem cell transplant, have improved survival. However, many patients still relapse, and there is a need...... for novel therapeutic strategies. Recent progress has been made in the understanding of the role of microRNAs (miRNAs) in MCL. Comparisons of tumor samples from patients with MCL with their normal counterparts (naive B-cells) have identified differentially expressed miRNAs with roles in cellular growth...

  16. The role of mantle-derived magmas in the isotopic evolution of Yellowstone's magmatic system

    Science.gov (United States)

    Stelten, Mark E.; Cooper, Kari M.; Wimpenny, Josh B.; Vazquez, Jorge A.; Yin, Qing-Zhu

    2017-04-01

    Injection of mantle-derived magmas into the Earth's crust provides the heat necessary to develop and maintain large silicic magmatic systems. However, the role of mantle-derived magmas in controlling the compositional evolution of large silicic systems remains poorly understood. Here we examine the role of mantle-derived magmas in the postcaldera magmatic system at Yellowstone Plateau, the youngest magmatism associated with the Yellowstone hotspot. Using microbeam techniques, we characterize the age and Hf isotope composition of single zircon crystals hosted in rhyolites from the most recent eruptive episode at Yellowstone Plateau, which produced the Central Plateau Member rhyolites. We place these zircon data into context by comparing them to new solution Hf isotope data for the Central Plateau Member glasses, Yellowstone basalts, and potential local crustal sources. Zircons in the Central Plateau Member rhyolites record a wide range of Hf isotope compositions relative to their host melts and extend from values similar to previously erupted Yellowstone rhyolites to values similar to Yellowstone basalts. Most zircons (˜90%) are in isotopic equilibrium with their host melt, but a significant proportion show ɛHf values higher than their host melt, thus providing the direct evidence that silicic derivatives of mantle-derived basalts have recharged Yellowstone's magmatic system. Mixing models confirm that the isotopic characteristics of the youngest Yellowstone rhyolites can be explained by recharge of Yellowstone's magma reservoir with silicic derivatives of underplating, mantle-derived basalts (˜5-10% material added by mass). This process helps drive the long-term isotopic evolution of Yellowstone's magmatic system.

  17. Potassic-ultrapotassic mafic rocks delineate two lithospheric mantle blocks beneath the southern Peruvian Altiplano

    Science.gov (United States)

    Carlier, G.; Lorand, J. P.; Liégeois, J. P.; Fornari, M.; Soler, P.; Carlotto, V.; Cárdenas, J.

    2005-07-01

    The Altiplano of southern Peru displays a large spectrum of Cenozoic potassic (K) and ultrapotassic (UK) mafic rocks that delineate two deep lithospheric mantle blocks that have undergone different depletion and enrichment events. Phlogopite lamproites indicate that the eastern Altiplano block is underlain by a metasomatized harzburgitic mantle of Paleoproterozoic to Archean age (depleted mantle age, TDM = 1130 2485 Ma; ɛNd = -5.0 to -11.4; 87Sr/86Sri = 0.7100 0.7159). Beneath the western Altiplano block, the presence of a younger (TDM = 837 1259 Ma; ɛNd = +0.6 to -6.3; 87Sr/86Sri = 0.7048 0.7069) metasomatized lherzolitic mantle is deduced from multiple occurrences of diopside-rich K-UK lavas (leucitites, leucite-bearing tephrites, olivine, and diopside trachybasalts). A third suite of young (Cusco Vilcanota fault system separating the western and eastern Altiplano blocks; this third suite, composed of diopside-phlogopite lamproites and augite kersantites, minettes, and trachybasalts, sampled a composite mantle source that probably included an asthenospheric component (TDM = 612 864 Ma; ɛNd = -1.1 to -3.5; 87Sr/86Sri = 0.7051 0.7062), in addition to lithospheric components inherited from the eastern and western Altiplano blocks. The spatial distribution of the south Peruvian K-UK magmatism suggests that K-UK melts reached the surface through reuse of older translithospheric weakness zones extending at least to the depth of magma generation. These latter were reactivated by a dextral transpressional regime imposed on the two rigid lithospheric blocks by the Andean orogen.

  18. Using osmium isotopes to explore the link between alkaline lavas and metasomatized mantle in the Western Branch, Uganda

    Science.gov (United States)

    Nelson, W. R.; Furman, T.; Pitcavage, E.

    2016-12-01

    The subcontinental lithospheric mantle (SCLM) is foundational to understanding the construction, destruction, and division of tectonic plates. Tectonic processes both directly and indirectly influence the lithosphere's thermal, physical and mineralogical properties. Mantle melting and melt/fluid percolation cause fundamental changes to the lithosphere that affect its composition and stability. Specifically, metasomatism by silicate melts and hydrous/carbonated fluids can create lithologies (i.e. pyroxenites) that are denser, more fusible, and less viscous than adjacent peridotite. The resulting density instabilities may lead to lithospheric erosion, topographic uplift and even continental rifting. We explore the link between metasomatized SCLM and mafic volcanism in the Ugandan portion of the Western Branch of the East African Rift System using Re-Os isotopes from both alkaline mafic lavas and pyroxenite mantle xenoliths. The lavas record age-corrected 187Os/188Os that range from 0.1421 to 0.2105, which is more radiogenic than primitive mantle. These data demonstrate that many of the lavas were derived from a metasomatized mantle source though a few have experienced crustal contamination. Mantle xenoliths also record a wide range of 187Os abundances. One peridotite xenolith has a mildly radiogenic signature (187Os/188Os = 0.1342) whereas the pyroxenites span a wide range of 187Os/188Os ratios (0.1270-0.5052). Based on these data, we conclude that the lavas were derived from metasomatized SCLM. Some of the SCLM was sampled by mantle xenoliths but, as a whole, the SCLM is more heterogeneous than the lavas suggest. The widespread, metasomatized SCLM readily contributed to melt generation both in situ as well as during foundering via lithospheric drip (Furman et al., 2016). The SCLM-derived volcanism occurred prior to and during Western Rift extension, suggesting that the metasomatized SCLM played a vital role in rift development

  19. Plume-subduction interaction in southern Central America: Mantle upwelling and slab melting

    Science.gov (United States)

    Gazel, Esteban; Hoernle, Kaj; Carr, Michael J.; Herzberg, Claude; Saginor, Ian; den Bogaard, Paul van; Hauff, Folkmar; Feigenson, Mark; Swisher, Carl

    2011-01-01

    The volcanic front in southern Central America is well known for its Galapagos OIB-like geochemical signature. A comprehensive set of geochemical, isotopic and geochronological data collected on volumetrically minor alkaline basalts and adakites were used to better constrain the mantle and subduction magma components and to test the different models that explain this OIB signature in an arc setting. We report a migration of back-arc alkaline volcanism towards the northwest, consistent with arc-parallel mantle flow models, and a migration towards the southeast in the adakites possibly tracking the eastward movement of the triple junction where the Panama Fracture Zone intersects the Middle America Trench. The adakites major and trace element compositions are consistent with magmas produced by melting a mantle-wedge source metasomatized by slab derived melts. The alkaline magmas are restricted to areas that have no seismic evidence of a subducting slab. The geochemical signature of the alkaline magmas is mostly controlled by upwelling asthenosphere with minor contributions from subduction components. Mantle potential temperatures calculated from the alkaline basalt primary magmas increased from close to ambient mantle (~ 1380-1410 °C) in the Pliocene to ~ 1450 °C in the younger units. The calculated initial melting pressures for these primary magmas are in the garnet stability field (3.0-2.7 GPa). The average final melting pressures range between 2.7 and 2.5 GPa, which is interpreted as the lithosphere-asthenosphere boundary at ~ 85-90 km. We provide a geotectonic model that integrates the diverse observations presented here. The slab detached after the collision of the Galapagos tracks with the arc (~ 10-8 Ma). The detachment allowed hotter asthenosphere to flow into the mantle wedge. This influx of hotter asthenosphere explains the increase in mantle potential temperatures, the northwest migration in the back-arc alkaline lavas that tracks the passage of the

  20. Long-lived but Discontinuous Hotspot Volcanism of the South Pacific Mantle

    Science.gov (United States)

    Koppers, A.; Staudigel, H.; Wijbrans, J.; Pringle, M.

    2001-12-01

    Hotspots of the South Pacific have been operating since the Early Cretaceous. We present evidence that their heterogeneous geochemical character and, hence, their respective HIMU-EMI-EMII mantle sources, can be traced back into the West Pacific Seamount Province (WPSP) using plate tectonic reconstructions. This implies that the HIMU, EMI and EMII mantle components are enduring features within the Earth's mantle, at least, for the last 140 Myr. These correlations are eminent on the scale of the WPSP and the South Pacific Thermal and Isotopic Anomaly (SOPITA) although the evolution of individual hotspots emerges notably more complicated. Hotspots in the WPSP and SOPITA mantle regions typically display intermittent volcanic activity, longevities shorter than 70 Myr, superposition of hotspot volcanism, and indirectly the motion of their mantle plumes through time. In our plate tectonic reconstructions, we use 40Ar/39Ar seamount ages and Sr-Nd-Pb isotopic signatures to map out Cretaceous hotspot volcanism in the WPSP and to characterize its evolution with respect to the currently active hotspots in the SOPITA region. EM-type Magellan, Anewetak, Ralik and Ratak seamount trails can be traced back to the magmatic activity of the Macdonald, Rurutu and Rarotonga hotspots during the Cretaceous; the HIMU-type seamounts within the Southern Wake seamount trail (97-120 Ma) most likely originated from the Mangaia-Rurutu "hot-line" in the Cook-Austral Islands. The Typhoon and Japanese guyots terminated their volcanism during the Early Cretaceous and have no presently active hot spot. However, the currently active Samoan, Society, Pitcairn and Marquesas hotspots may be traced back only to about 30-70 Myr and lack long-lived counterparts in the WPSP. These hotspots may have become active over the last 30-70 Myr only. All in all hotspot volcanism in the South Pacific seems to be controlled by a "superplume" type of mantle convection giving rise to multiple weak mantle plumes, each

  1. Mantle transition zone beneath the central Tien Shan: Lithospheric delamination and mantle plumes

    Science.gov (United States)

    Kosarev, Grigoriy; Oreshin, Sergey; Vinnik, Lev; Makeyeva, Larissa

    2018-01-01

    We investigate structure of the mantle transition zone (MTZ) under the central Tien Shan in central Asia by using recordings of seismograph stations in Kyrgyzstan, Kazakhstan and adjacent northern China. We apply P-wave receiver functions techniques and evaluate the differential time between the arrivals of seismic phases that are formed by P to SV mode conversion at the 410-km and 660-km seismic boundaries. The differential time is sensitive to the thickness of the MTZ and insensitive to volumetric velocity anomalies above the 410-km boundary. Under part of the southern central Tien Shan with the lowest S wave velocity in the uppermost mantle and the largest thickness of the crust, the thickness of the MTZ increases by 15-20 km relative to the ambient mantle and the reference model IASP91. The increased thickness is a likely effect of low (about - 150 K) temperature. This anomaly is indicative of delamination and sinking of the mantle lithosphere. The low temperature in the MTZ might also be a relic of subduction of the oceanic lithosphere in the Paleozoic, but this scenario requires strong coupling and coherence between structures in the MTZ and in the lithosphere during plate motions in the last 300 Myr. Our data reveal a reduction of thickness of the MTZ of 10-15 km under the Fergana basin, in the neighborhood of the region of small-scale basaltic volcanism at the time near the Cretaceous-Paleogene boundary. The reduced thickness of the MTZ is the effect of a depressed 410-km discontinuity, similar to that found in many hotspots. This depression suggests a positive temperature anomaly of about 100-150 K, consistent with the presence of a thermal mantle plume. A similar depression on the 410-km discontinuity is found underneath the Tarim basin.

  2. Deuterium enrichment of the interstellar grain mantle

    Science.gov (United States)

    Das, Ankan; Sahu, Dipen; Majumdar, Liton; Chakrabarti, Sandip K.

    2016-01-01

    We carry out Monte Carlo simulation to study deuterium enrichments of interstellar grain mantles under various physical conditions. Based on the physical properties, various types of clouds are considered. We find that in diffuse cloud regions, very strong radiation fields persists and hardly a few layers of surface species are formed. In translucent cloud regions with a moderate radiation field, significant number of layers would be produced and surface coverage is mainly dominated by photo-dissociation products such as, C, CH3, CH2D, OH and OD. In the intermediate dense cloud regions (having number density of total hydrogen nuclei in all forms ˜2 × 104 cm-3), water and methanol along with their deuterated derivatives are efficiently formed. For much higher density regions (˜106 cm-3), water and methanol productions are suppressed but surface coverages of CO, CO2, O2 and O3 are dramatically increased. We find a very high degree of fractionation of water and methanol. Observational results support a high fractionation of methanol but surprisingly water fractionation is found to be low. This is in contradiction with our model results indicating alternative routes for de-fractionation of water. Effects of various types of energy barriers are also studied. Moreover, we allow grain mantles to interact with various charged particles (such as H+, Fe+, S+ and C+) to study the stopping power and projected range of these charged particles on various target ices.

  3. Vapor Undersaturation in Primitive Mid-Ocean Ridge Basalt and the Volatile Content of the Earth's Upper Mantle

    Science.gov (United States)

    Saal, A. E.; Hauri, E. H.; Langmuir, C. H.; Perfit, M. R.

    2002-05-01

    We present the first report of undersaturated pre-eruptive volatile content for one of the most primitive sample suites of mid-ocean ridge basalts (MORB) from the Siqueiros intra-transform spreading center. Our results clearly show that carbon dioxide and sulfur are incompatible elements during mantle melting, and behave similarly to niobium and dysprosium respectively. These results can be used to constrain the amount of carbon dioxide and helium degassing during magma transport and eruption, and suggest that carbonate, rather than graphite, is the phase controlling the carbon budget in the mantle during MORB generation. The undersaturation of volatiles, constant ratios of CO2/Nb, F/P, S/Dy and Cl/K in glasses and melt inclusions, and previous estimates of the trace element content in the MORB mantle generate precise new constraints on the abundances of H2O (160ñ40 ppm), CO2 (100ñ40 ppm), F (16ñ3 ppm), S (150ñ20 ppm) and Cl (2.0ñ0.5 ppm) in the Earth's upper mantle. These abundances are much lower than similar estimates for the source regions of hotspots, indicating the presence of volatile heterogeneity in the Earth's mantle.

  4. 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.

  5. Structure of the Crust and the Lithosperic Mantle in Siberia

    DEFF Research Database (Denmark)

    Cherepanova, Yulia

    in the lithospheric mantle density, are interpreted in terms of regional tectonic evolution, namely the mechanism by which the Paleozoic intracontinental basin has been formed and the tectono-magmatic processes by which the Archean-Proterozoic craton has been modified as reflected in the composition of its mantle....

  6. Geophysical evidence for chemical variations in the Australian continental mantle

    NARCIS (Netherlands)

    Gerven, van L.P.A.; Deschamps, F.; Hilst, R.D.

    2004-01-01

    The relative density-to-shear velocity scaling (¿) provides a diagnostic for the presence of compositional variations in the mantle. We invert shear-wave velocity from a recent 3-D model and gravity anomalies for radial profiles of ¿ of the uppermost mantle beneath Australia. We performed

  7. Geophysical evidence for chemical variations in the Australian Continental Mantle

    NARCIS (Netherlands)

    Gerven, Luuk van; Deschamps, Frédéric; Hilst, R.D. van der

    2004-01-01

    The relative density-to-shear velocity scaling (ζ) provides a diagnostic for the presence of compositional variations in the mantle. We invert shear-wave velocity from a recent 3-D model and gravity anomalies for radial profiles of ζ of the uppermost mantle beneath Australia. We performed

  8. Magmatic plumbing system from lower mantle of Hainan plume

    Science.gov (United States)

    Xia, Shaohong; Sun, Jinlong; Xu, Huilong; Huang, Haibo; Cao, Jinghe

    2017-04-01

    Intraplate volcanism during Late Cenozoic in the Leiqiong area of southernmost South China, with basaltic lava flows covering a total of more than 7000 km2, has been attributed to an underlying Hainan plume. However, detailed features of Hainan plume, such as morphology of magmatic conduits, depth of magmatic pool in the upper mantle and pattern of mantle upwelling, are still enigmatic. Here we present seismic tomographic images of the upper 1100 km of the mantle beneath the southern South China. Our results show a mushroom-like continuous low-velocity anomaly characterized by a columnar tail with diameter of about 200-300 km that tilts downward to lower mantle beneath north of Hainan hotspot and a head that spreads laterally near the mantle transition zone, indicating a magmatic pool in the upper mantle. Further upward, this head is decomposed into small patches, but when encountering the base of the lithosphere, a pancake-like anomaly is shaped again to feed the Hainan volcanism. Our results challenge the classical model of a fixed thermal plume that rises vertically to the surface, and propose the new layering-style pattern of magmatic upwelling of Hainan plume. This work indicates the spatial complexities and differences of global mantle plumes probably due to heterogeneous compositions and changefully thermochemical structures of deep mantle.

  9. Behaviour of the Sm-Nd and Rb-Sr systems of the mafic-ultramafic layered sequence from Ribeirao dos Motas (Archaean), meridional craton Sao Francisco: evidences of mantle source enrichment and isotopic fractionation; Comportamento dos sistemas Sm-Nd e Rb-Sr da sequencia acamadada mafico-ultramafico Ribeirao dos Motas (Arqueano), craton Sao Francisco Meridional: evidencias de enriquecimento mantelico e fracionamento isotopico

    Energy Technology Data Exchange (ETDEWEB)

    Carneiro, Mauricio Antonio; Carvalho Junior, Irneu Mendes de; Oliveira, Arildo Henrique de [Ouro Preto Univ., (UFOP), MG (Brazil). Dept. de Geologia]. E-mail: mauricio@degeo.ufop.br; Teixeira, Wilson [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Pimentel, Marcio Martins [Brasilia Univ., DF (Brazil). Inst. de Geociencias. Lab. de Geocronologia

    2004-10-15

    The Ribeirao dos Motas layered sequence (SARM) crops out in the southern part of the Sao Francisco Craton, Brazil. This sequence comprises phaneritic meta ultramafic and metamafic rocks, which, although slightly deformed and metamorphosed, retain primary igneous layers. Porphyritic rocks with idiomorphic pyroxene crystals and heteradcumulate and adcumulate textures are also present. Eighteen isotopic analyses were performed in the SARM, comprising rocks with primary (relict) textures, as well as rocks in amphibolite facies and retro-metamorphosed to green-schist facies. Seven samples yield a Sm/Nd isochron age of 2.79 +- 0.30 Ga (MSWD=1.2 e epsilon {sub Ndt}=+0.48), constraining the accretion time of the SARM rocks. The positive epsilon {sub Ndt} value coupled with the Rb/Sr evidence is consistent with mantle source relatively enriched in Nd and Sr isotopes. Nevertheless, some SARM samples display isotopic fractionation and disturbance, which can be ascribed to the following processes or their combinations: a) mobilization of the incompatible elements due to regional high grade metamorphism; b) isotopic changes during upper amphibolite facies overprint; c) isotopic resetting by low-grade fluids associated to the Claudio Shear zone, which is located nearby the SARM. (author)

  10. Deep permeable fault-controlled helium transport and limited mantle flux in two extensional geothermal systems in the Great Basin, United States

    Science.gov (United States)

    Banerjee, Amlan; Person, Mark; Hofstra, Albert; Sweetkind, Donald S.; Cohen, Denis; Sabin, Andrew; Unruh, Jeff; Zyvoloski, George; Gable, Carl W.; Crossey, Laura; Karlstrom, Karl

    2011-01-01

    This study assesses the relative importance of deeply circulating meteoric water and direct mantle fluid inputs on near-surface 3He/4He anomalies reported at the Coso and Beowawe geothermal fields of the western United States. The depth of meteoric fluid circulation is a critical factor that controls the temperature, extent of fluid-rock isotope exchange, and mixing with deeply sourced fluids containing mantle volatiles. The influence of mantle fluid flux on the reported helium anomalies appears to be negligible in both systems. This study illustrates the importance of deeply penetrating permeable fault zones (10-12 to 10-15 m2) in focusing groundwater and mantle volatiles with high 3He/4He ratios to shallow crustal levels. These continental geothermal systems are driven by free convection.

  11. The Earth's mantle and geoneutrinos

    Energy Technology Data Exchange (ETDEWEB)

    Fiorentini, Giovanni, E-mail: fiorentini@fe.infi1.it [Dipartimento di Fisica, Università di Ferrara, Via Saragat 1, 44100 Ferrara (Italy); Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Via del/' Università 2 -35020 Legnaro, Padova (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara, Via Saragat 1, 44100 Ferrara (Italy); Fogli, Gian Luigi [Dipartimento Interateneo di Fisica “Michelangelo Merlin”, Via Amendola 173, 70126 Bari (Italy); lstituto Nazionale di Fisica Nucleare, Sezione di Bari, Via Orabona 4, 70126, Bari (Italy); Lisi, Eligio [lstituto Nazionale di Fisica Nucleare, Sezione di Bari, Via Orabona 4, 70126, Bari (Italy); Mantovani, Fabio [Dipartimento di Fisica, Università di Ferrara, Via Saragat 1, 44100 Ferrara (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara, Via Saragat 1, 44100 Ferrara (Italy); Rotunno, Anna Maria [Dipartimento Interateneo di Fisica “Michelangelo Merlin”, Via Amendola 173, 70126 Bari (Italy); Xhixha, Gerti [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Via del/' Università 2 -35020 Legnaro, Padova (Italy)

    2013-04-15

    The KamLAND and Borexino experiments have observed, each at ∼4σ level, signals of electron antineutrinos produced in the decay chains of thorium and uranium in the Earth's crust and mantle (Th and U geoneutrinos). Various pieces of geochemical and geophysical information allow an estimation of the crustal geoneutrino flux components with relatively small uncertainties. The mantle component may then be inferred by subtracting the estimated crustal flux from the measured total flux. We find that crust-subtracted signals show hints of a residual mantle component, emerging at ∼2.4σ level by combining the KamLAND and Borexino data. The inferred mantle flux, slightly favoring scenarios with relatively high Th and U abundances, within ∼1σ uncertainties is comparable to the predictions from recent mantle models.

  12. Molybdenum isotope fractionation in the mantle

    Science.gov (United States)

    Liang, Yu-Hsuan; Halliday, Alex N.; Siebert, Chris; Fitton, J. Godfrey; Burton, Kevin W.; Wang, Kuo-Lung; Harvey, Jason

    2017-02-01

    We report double-spike molybdenum (Mo) isotope data for forty-two mafic and fifteen ultramafic rocks from diverse locations and compare these with results for five chondrites. The δ98/95Mo values (normalized to NIST SRM 3134) range from -0.59 ± 0.04 to +0.10 ± 0.08‰. The compositions of one carbonaceous (CI) and four ordinary chondrites are relatively uniform (-0.14 ± 0.01‰, 95% ci (confidence interval)) in excellent agreement with previous data. These values are just resolvable from the mean of 10 mid-ocean ridge basalts (MORBs) (0.00 ± 0.02‰, 95% ci). The compositions of 13 mantle-derived ultramafic xenoliths from Kilbourne Hole, Tariat and Vitim are more diverse (-0.39 to -0.07‰) with a mean of -0.22 ± 0.06‰ (95% ci). On this basis, the isotopic composition of the bulk silicate Earth (BSE or Primitive Mantle) is within error identical to chondrites. The mean Mo concentration of the ultramafic xenoliths (0.19 ± 0.07 ppm, 95% ci) is similar in magnitude to that of MORB (0.48 ± 0.13 ppm, 95% ci), providing evidence, either for a more compatible behaviour than previously thought or for selective Mo enrichment of the subcontinental lithospheric mantle. Intraplate and ocean island basalts (OIBs) display significant isotopic variability within a single locality from MORB-like to strongly negative (-0.59 ± 0.04‰). The most extreme values measured are for nephelinites from the Cameroon Line and Trinidade, which also have anomalously high Ce/Pb and low Mo/Ce relative to normal oceanic basalts. δ98/95Mo correlates negatively with Ce/Pb and U/Pb, and positively with Mo/Ce, explicable if a phase such as an oxide or a sulphide liquid selectively retains isotopically heavy Mo in the mantle and fractionates its isotopic composition in low degree partial melts. If residual phases retain Mo during partial melting, it is possible that the [Mo] for the BSE may be misrepresented by values estimated from basalts. This would be consistent with the high Mo

  13. Whole-mantle convection with tectonic plates preserves long-term global patterns of upper mantle geochemistry.

    Science.gov (United States)

    Barry, T L; Davies, J H; Wolstencroft, M; Millar, I L; Zhao, Z; Jian, P; Safonova, I; Price, M

    2017-05-12

    The evolution of the planetary interior during plate tectonics is controlled by slow convection within the mantle. Global-scale geochemical differences across the upper mantle are known, but how they are preserved during convection has not been adequately explained. We demonstrate that the geographic patterns of chemical variations around the Earth's mantle endure as a direct result of whole-mantle convection within largely isolated cells defined by subducting plates. New 3D spherical numerical models embedded with the latest geological paleo-tectonic reconstructions and ground-truthed with new Hf-Nd isotope data, suggest that uppermost mantle at one location (e.g. under Indian Ocean) circulates down to the core-mantle boundary (CMB), but returns within ≥100 Myrs via large-scale convection to its approximate starting location. Modelled tracers pool at the CMB but do not disperse ubiquitously around it. Similarly, mantle beneath the Pacific does not spread to surrounding regions of the planet. The models fit global patterns of isotope data and may explain features such as the DUPAL anomaly and long-standing differences between Indian and Pacific Ocean crust. Indeed, the geochemical data suggests this mode of convection could have influenced the evolution of mantle composition since 550 Ma and potentially since the onset of plate tectonics.

  14. The North American upper mantle: density, composition, and evolution

    Science.gov (United States)

    Mooney, Walter D.; Kaban, Mikhail K.

    2010-01-01

    The upper mantle of North America has been well studied using various seismic methods. Here we investigate the density structure of the North American (NA) upper mantle based on the integrative use of the gravity field and seismic data. The basis of our study is the removal of the gravitational effect of the crust to determine the mantle gravity anomalies. The effect of the crust is removed in three steps by subtracting the gravitational contributions of (1) topography and bathymetry, (2) low-density sedimentary accumulations, and (3) the three-dimensional density structure of the crystalline crust as determined by seismic observations. Information regarding sedimentary accumulations, including thickness and density, are taken from published maps and summaries of borehole measurements of densities; the seismic structure of the crust is based on a recent compilation, with layer densities estimated from P-wave velocities. The resultant mantle gravity anomaly map shows a pronounced negative anomaly (−50 to −400 mGal) beneath western North America and the adjacent oceanic region and positive anomalies (+50 to +350 mGal) east of the NA Cordillera. This pattern reflects the well-known division of North America into the stable eastern region and the tectonically active western region. The close correlation of large-scale features of the mantle anomaly map with those of the topographic map indicates that a significant amount of the topographic uplift in western NA is due to buoyancy in the hot upper mantle, a conclusion supported by previous investigations. To separate the contributions of mantle temperature anomalies from mantle compositional anomalies, we apply an additional correction to the mantle anomaly map for the thermal structure of the uppermost mantle. The thermal model is based on the conversion of seismic shear-wave velocities to temperature and is consistent with mantle temperatures that are independently estimated from heat flow and heat production data

  15. Molecular pathogenesis of mantle cell lymphoma

    Science.gov (United States)

    Jares, Pedro; Colomer, Dolors; Campo, Elias

    2012-01-01

    Mantle cell lymphoma is a B cell malignancy in which constitutive dysregulation of cyclin D1 and the cell cycle, disruption of DNA damage response pathways, and activation of cell survival mechanisms contribute to oncogenesis. A small number of tumors lack cyclin D1 overexpression, suggesting that its dysregulation is always not required for tumor initiation. Some cases have hypermutated IGHV and stable karyotypes, a predominant nonnodal disease, and an indolent clinical evolution, which suggests that they may correspond to distinct subtypes of the disease. In this review, we discuss the molecular pathways that contribute to pathogenesis, and how improved understanding of these molecular mechanisms offers new perspectives for the treatment of patients. PMID:23023712

  16. Mantle temperature under drifting deformable continents during the supercontinent cycle

    Science.gov (United States)

    Yoshida, Masaki

    2013-04-01

    The thermal heterogeneity of the Earth's mantle under the drifting continents during a supercontinent cycle is a controversial issue in earth science. Here, a series of numerical simulations of mantle convection are performed in 3D spherical-shell geometry, incorporating drifting deformable continents and self-consistent plate tectonics, to evaluate the subcontinental mantle temperature during a supercontinent cycle. Results show that the laterally averaged temperature anomaly of the subcontinental mantle remains within several tens of degrees (±50 °C) throughout the simulation time. Even after the formation of the supercontinent and the development of subcontinental plumes due to the subduction of the oceanic plates, the laterally averaged temperature anomaly of the deep mantle under the continent is within +10 °C. This implies that there is no substantial temperature difference between the subcontinental and suboceanic mantles during a supercontinent cycle. The temperature anomaly immediately beneath the supercontinent is generally positive owing to the thermal insulation effect and the active upwelling plumes from the core-mantle boundary. In the present simulation, the formation of a supercontinent causes the laterally averaged subcontinental temperature to increase by a maximum of 50 °C, which would produce sufficient tensional force to break up the supercontinent. The periodic assembly and dispersal of continental fragments, referred to as the supercontinent cycle, bear close relation to the evolution of mantle convection and plate tectonics. Supercontinent formation involves complex processes of introversion, extroversion or a combination of these in uniting dispersed continental fragments, as against the simple opening and closing of individual oceans envisaged in Wilson cycle. In the present study, I evaluate supercontinent processes in a realistic mantle convection regime. Results show that the assembly of supercontinents is accompanied by a

  17. Formation and modification of chromitites in the mantle

    Science.gov (United States)

    Arai, Shoji; Miura, Makoto

    2016-11-01

    Podiform chromitites have long supplied us with unrivaled information on various mantle processes, including the peridotite-magma reaction, deep-seated magmatic evolution, and mantle dynamics. The recent discovery of ultrahigh-pressure (UHP) chromitites not only sheds light on a different aspect of podiform chromitites, but also changes our understanding of the whole picture of podiform chromitite genesis. In addition, new evidence was recently presented for hydrothermal modification/formation chromite/chromitite in the mantle, which is a classical but innovative issue. In this context, we present here an urgently needed comprehensive review of podiform chromitites in the upper mantle. Wall-rock control on podiform chromitite genesis demonstrates that the peridotite-magma reaction at the upper mantle condition is an indispensable process. We may need a large system in the mantle, far larger than the size of outcrops or mining areas, to fulfill the Cr budget requirement for podiform chromitite genesis. The peridotite-magma reaction over a large area may form a melt enriched with Na and other incompatible elements, which mixes with a less evolved magma supplied from the depth to create chromite-oversaturated magma. The incompatible-element-rich magma trapped by the chromite mainly precipitates pargasite and aspidolite (Na analogue of phlogopite), which are stable under upper mantle conditions. Moderately depleted harzburgites, which contain chromite with a moderate Cr# (0.4-0.6) and a small amount of clinopyroxene, are the best reactants for the chromitite-forming reaction, and are the best hosts for podiform chromitites. Arc-type chromitites are dominant in ophiolites, but some are of the mid-ocean ridge type; chromitites may be common beneath the ocean floor, although it has not yet been explored for chromitite. The low-pressure (upper mantle) igneous chromitites were conveyed through mantle convection or subduction down to the mantle transition zone to form

  18. The boron and lithium isotopic composition of mid-ocean ridge basalts and the mantle

    Science.gov (United States)

    Marschall, Horst R.; Wanless, V. Dorsey; Shimizu, Nobumichi; Pogge von Strandmann, Philip A. E.; Elliott, Tim; Monteleone, Brian D.

    2017-06-01

    variation is unrelated to differentiation, assimilation or mantle source indicators, such as radiogenic isotopes or trace elements. It, therefore, seems likely that kinetic fractionation of Li isotopes during magma extraction, transport and storage may generate δ7 Li excursions in MORB. No mantle heterogeneities, such as those generated by deeply recycled subducted materials, are invoked in the interpretation of the Li and B isotope data presented here, in contrast to previous work on smaller data sets. Lithium and boron budgets for the silicate Earth are presented that are based on isotope and element mass balance. A refined estimate for the B isotopic composition of the bulk continental crust is given as δ11 B = - 9.1 ± 2.4 ‰ . Mass balance allows the existence of recycled B reservoirs in the deep mantle, but these are not required. However, mass balance among the crust, sediments and seawater shows enrichment of 6 Li in the surface reservoirs, which requires the existence of 7 Li -enriched material in the mantle. This may have formed by the subduction of altered oceanic crust since the Archaean.

  19. Mantle hydration and Cl-rich fluids in the subduction forearc

    Science.gov (United States)

    Reynard, Bruno

    2016-12-01

    a given thermal state through variations of fluid salinity. High-Cl fluids produced by serpentinization can mix with the source rocks of the volcanic arc and explain geochemical signatures of primitive magma inclusions. Signature of deep high-Cl fluids was also identified in forearc hot springs. These observations suggest the existence of fluid circulations between the forearc mantle and the hot spring hydrothermal system or the volcanic arc. Such circulations are also evidenced by recent magnetotelluric profiles.

  20. Mantle-derived trace element variability in olivines and their melt inclusions

    Science.gov (United States)

    Neave, David A.; Shorttle, Oliver; Oeser, Martin; Weyer, Stefan; Kobayashi, Katsura

    2018-02-01

    inclusion suites, and confirm that the Stapafell eruption was fed by lower degree melts from greater depths within the melting region than the Háleyjabunga eruption. Although olivine macrocrysts from Stapafell are slightly richer in Ni than those from Háleyjabunga, their overall CTE systematics (e.g., Ni/(Mg/Fe), Fe/Mn and Zn/Fe) are inconsistent with being derived from olivine-free pyroxenites. However, the major element systematics of Icelandic basalts require lithological heterogeneity in their mantle source in the form of Fe-rich and hence fusible domains. We thus conclude that enriched heterogeneities in the Icelandic mantle are composed of modally enriched, yet nonetheless olivine-bearing, lithologies and that olivine CTE contents provide an incomplete record of lithological heterogeneity in the mantle. Modally enriched peridotites may therefore play a more important role in oceanic magma genesis than previously inferred.

  1. Mantles of terrestrial planets immediately following magma ocean solidification

    Science.gov (United States)

    Scheinberg, A. L.; Elkins-Tanton, L. T.; Zhong, S.; Parmentier, E.

    2010-12-01

    Energy of accretion in terrestrial planets is expected to create liquid silicate magma oceans. Their solidification processes create silicate differentiation and set the initial mantle structure for the planet. Solidification results in a compositionally unstable density profile, leading to cumulate Rayleigh-Taylor overturn in the early stages of planetary history. The pattern and timescale of overturn, in which cold, dense surface material sinks to the core mantle boundary, has implications for core dynamo production, volatile escape and fundamental differences between differently-sized bodies. Our fully spherical mantle models reaffirm previous work suggesting harmonic degree of overturn is dependent on viscosity contrast and layer thickness. We then explore the dependence of overturn morphology in the early mantles of Mars, Earth, Mercury and the Moon on these parameters and on the respective planets’ characteristics using a composition- and temperature-dependent viscosity model. Initial results indicate that fractional solidification and overturn in terrestrial planets always creates some radius range in which the mantle is azimuthally compositionally heterogeneous. After overturn, compositional stability in the mantle suppresses the onset of thermal convection; the broad conclusions of this work indicate that the earliest solid mantle of terrestrial planets is compositionally differentiated and stable.

  2. Lithospheric mantle evolution in the Afro-Arabian domain: Insights from Bir Ali mantle xenoliths (Yemen)

    Science.gov (United States)

    Sgualdo, P.; Aviado, K.; Beccaluva, L.; Bianchini, G.; Blichert-Toft, J.; Bryce, J. G.; Graham, D. W.; Natali, C.; Siena, F.

    2015-05-01

    Detailed petrological and geochemical investigations of an extensive sampling of mantle xenoliths from the Neogene-Quaternary Bir Ali diatreme (southern Yemen) indicate that the underlying lithospheric mantle consists predominantly of medium- to fine-grained (often foliated) spinel-peridotites (85-90%) and spinel-pyroxenites (10-15%) showing thermobarometric estimates in the P-T range of 0.9-2.0 GPa and 900-1150 °C. Peridotites, including lherzolites, harzburgites and dunites delineate continuous chemical, modal and mineralogical variations compatible with large extractions of basic melts occurring since the late Proterozoic (~ 2 Ga, according to Lu-Hf model ages). Pyroxenites may represent intrusions of subalkaline basic melts interacting and equilibrated with the host peridotite. Subsequent metasomatism has led to modal changes, with evidence of reaction patches and clinopyroxene and spinel destabilization, as well as formation of new phases (glass, amphibole and feldspar). These changes are accompanied by enrichment of the most incompatible elements and isotopic compositions. 143Nd/144Nd ranges from 0.51419 to 0.51209 (εNd from + 30.3 to - 10.5), 176Hf/177Hf from 0.28459 to 0.28239 (εHf from + 64.4 to - 13.6), and 208Pb/204Pb from 36.85 to 41.56, thus extending from the depleted mantle (DM) towards the enriched OIB mantle (EM and HIMU) components. 3He/4He (R/RA) ratios vary from 7.2 to 7.9 with He concentrations co-varying with the most incompatible element enrichment, in parallel with metasomatic effects. These metasomatic events, particularly effective in harzburgites and dunites, are attributable to the variable interaction with alkaline basic melts related to the general extensional and rifting regime affecting the East Africa-Arabian domain during the Cenozoic. In this respect, Bir Ali mantle xenoliths resemble those occurring along the Arabian margins and the East Africa Rift system, similarly affected by alkaline metasomatism, whereas they are

  3. 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.

  4. Solar combi system based on a mantle tank

    DEFF Research Database (Denmark)

    Yazdanshenas, Eshagh; Furbo, Simon

    2007-01-01

    A solar combisystem based on a mantle tank is investigated numerically and experimentally. Three different houses with four different radiator systems are considered for the simulations. The needed temperature for the auxiliary heater is determined for different houses and radiator systems....... The thermal performance of the solar combisystem is compared to the thermal performance of a solar domestic hot water system based on a mantle tank. In the experimental study, tank temperatures and the heat transfer coefficient for the top mantle for a discharge test is determined. The investigations showed...

  5. Mantle structure and tectonic history of SE Asia

    Science.gov (United States)

    Hall, Robert; Spakman, Wim

    2015-09-01

    Seismic travel-time tomography of the mantle under SE Asia reveals patterns of subduction-related seismic P-wave velocity anomalies that are of great value in helping to understand the region's tectonic development. We discuss tomography and tectonic interpretations of an area centred on Indonesia and including Malaysia, parts of the Philippines, New Guinea and northern Australia. We begin with an explanation of seismic tomography and causes of velocity anomalies in the mantle, and discuss assessment of model quality for tomographic models created from P-wave travel times. We then introduce the global P-wave velocity anomaly model UU-P07 and the tectonic model used in this paper and give an overview of previous interpretations of mantle structure. The slab-related velocity anomalies we identify in the upper and lower mantle based on the UU-P07 model are interpreted in terms of the tectonic model and illustrated with figures and movies. Finally, we discuss where tomographic and tectonic models for SE Asia converge or diverge, and identify the most important conclusions concerning the history of the region. The tomographic images of the mantle record subduction beneath the SE Asian region to depths of approximately 1600 km. In the upper mantle anomalies mainly record subduction during the last 10 to 25 Ma, depending on the region considered. We interpret a vertical slab tear crossing the entire upper mantle north of west Sumatra where there is a strong lateral kink in slab morphology, slab holes between c.200-400 km below East Java and Sumbawa, and offer a new three-slab explanation for subduction in the North Sulawesi region. There is a different structure in the lower mantle compared to the upper mantle and the deep structure changes from west to east. What was imaged in earlier models as a broad and deep anomaly below SE Asia has a clear internal structure and we argue that many features can be identified as older subduction zones. We identify remnants of slabs

  6. Diamond exploration and mantle structure imaging using PIXE microanalysis

    Energy Technology Data Exchange (ETDEWEB)

    Ryan, C.G.; Griffin, W.L.; Win, T.T. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), North Ryde, NSW (Australia). Div. of Exploration Geoscience

    1996-12-31

    Geochemical methods of diamond exploration rely on recognizing indicator minerals that formed in the earth`s upper mantle, within the diamond stability field, and were entrained in rapidly rising volatile-rich magmas and emplaced in or on the crust. Diamond is only stable at high pressure. Therefore, diamond exploration commonly targets prospects containing high pressure minerals, such as low-Ca, high-Cr (`G10`) garnets and high-Cr chromites, similar to inclusions in diamonds. However, this procedure can be ambiguous; some barren pipes contain abundant `G10` garnets. while such garnets are extremely rare in the Argyle pipe, the world`s largest diamond producer. Similarly, high-Cr chromites are shed by a wide variety of barren rock types. PIXE microanalysis of trace elements in concentrate garnets and chromites from kimberlites and other volcanic rocks helps to remove the ambiguities by pinning down the source temperature (T), pressure (P) and local (paleo)geotherm (P-T relation), which permits the rich store of trace element information in these minerals, reflecting rock chemistry and metasomatic processes, to be placed in a stratigraphic context. 11 refs., 4 figs.

  7. Mantle fluid evolution—a tale of one diamond

    Science.gov (United States)

    Klein-BenDavid, Ofra; Izraeli, Elad S.; Hauri, Erik; Navon, Oded

    2004-09-01

    Microinclusions analyzed in a coated diamond from the Diavik mine in Canada comprise peridotitic minerals and fluids. The fluids span a wide compositional range between a carbonatitic melt and brine. The diamond is concentrically zoned. The brine microinclusions reside in an inner growth zone and their endmember composition is K 19Na 25Ca 5Mg 8Fe 3Ba 2Si 4Cl 32 (mol%). The carbonatitic melt is found in an outer layer and its endmember composition is K 11Na 21Ca 11Mg 26Fe 7Ba 2Si 10Al 3P 2Cl 5. The transition in inclusion chemistry is accompanied by a change in the carbon isotopic composition of the diamond from -8.5‰ in the inner zone to -12.1‰ in the outer zone. We suggest that this transition reflects mixing between already evolved brine and a freshly introduced carbonatitic melt of different isotopic composition. The compositional range found in diamond ON-DVK-294 is the widest ever recorded in a single diamond. It closes the gap between brine found in cloudy octahedral diamonds from South Africa and carbonatitic melt analyzed in cubic diamonds from Zaire and Botswana. Thus, all microinclusions analyzed to date fall along two arrays connecting the carbonatitic melt composition to either a hydrous-silicic endmember or to a brine endmember. This connection suggests that many diamonds are formed from fluids derived form a mantle source not significantly influenced by local heterogeneities.

  8. Multiple subduction imprints in the mantle below Italy detected in a single lava flow

    Science.gov (United States)

    Nikogosian, Igor; Ersoy, Özlem; Whitehouse, Martin; Mason, Paul R. D.; de Hoog, Jan C. M.; Wortel, Rinus; van Bergen, Manfred J.

    2016-09-01

    Post-collisional magmatism reflects the regional subduction history prior to collision but the link between the two is complex and often poorly understood. The collision of continents along a convergent plate boundary commonly marks the onset of a variety of transitional geodynamic processes. Typical responses include delamination of subducting lithosphere, crustal thickening in the overriding plate, slab detachment and asthenospheric upwelling, or the complete termination of convergence. A prominent example is the Western-Central Mediterranean, where the ongoing slow convergence of Africa and Europe (Eurasia) has been accommodated by a variety of spreading and subduction systems that dispersed remnants of subducted lithosphere into the mantle, creating a compositionally wide spectrum of magmatism. Using lead isotope compositions of a set of melt inclusions in magmatic olivine crystals we detect exceptional heterogeneity in the mantle domain below Central Italy, which we attribute to the presence of continental material, introduced initially by Alpine and subsequently by Apennine subduction. We show that superimposed subduction imprints of a mantle source can be tapped during a melting episode millions of years later, and are recorded in a single lava flow.

  9. Rheology of Materials of Earth's Mantle: High-end Computational/Visualization Research and Education

    Science.gov (United States)

    Karki, B. B.

    2011-12-01

    This NSF Career grant has supported our effort to systematically apply ideas and techniques of computer and materials sciences to challenging problems in the theoretical investigation of fundamental issues of Earth materials. One such issue is to understand the rheological properties of the component materials of Earth's mantle at geophysically relevant pressure and temperature conditions that are still experimentally inaccessible. Rheology is a key factor, which has strong influence on the complicated mantle dynamics implied by seismological observations and other sources. Towards this goal, we have studied point defects in major mantle minerals including MgO, SiO2, MgSiO3 and Mg2SiO4 polymorphs, and grain boundaries in MgO. In addition to ionic vacancies, we have also studied interstitials and proton defects. Our results have shown that the defect energetics (formation and migration), geometries (core structures), and electronic structures are strongly dependent on pressure and vary abruptly across the phase transitions. Similarly, the boundary structure is highly sensitive to pressure. Besides performing simulations for predicting defect (bulk) properties, we have contributed to the development/application of visualization methods for gaining insight (at microscopic scale) into the simulation data. Also developed is the molecular dynamics simulation program to study grain boundary and polycrystalline systems. Through this project, we have trained few graduate and undergraduate (minority) students in the aforementioned interdisciplinary research activities.

  10. Thermal Coupling Between the Ocean and Mantle of Europa: Implications for Ocean Convection

    Science.gov (United States)

    Soderlund, Krista M.; Schmidt, Britney E.; Wicht, Johannes; Blankenship, Donald D.

    2015-11-01

    Magnetic induction signatures at Europa indicate the presence of a subsurface ocean beneath the cold icy crust. The underlying mantle is heated by radioactive decay and tidal dissipation, leading to a thermal contrast sufficient to drive convection and active dynamics within the ocean. Radiogenic heat sources may be distributed uniformly in the interior, while tidal heating varies spatially with a pattern that depends on whether eccentricity or obliquity tides are dominant. The distribution of mantle heat flow along the seafloor may therefore be heterogeneous and impact the regional vigor of ocean convection. Here, we use numerical simulations of thermal convection in a global, Europa-like ocean to test the sensitivity of ocean dynamics to variations in mantle heat flow patterns. Towards this end, three end-member cases are considered: an isothermal seafloor associated with dominant radiogenic heating, enhanced seafloor temperatures at high latitudes associated with eccentricity tides, and enhanced equatorial seafloor temperatures associated with obliquity tides. Our analyses will focus on convective heat transfer since the heat flux pattern along the ice-ocean interface can directly impact the ice shell and the potential for geologic activity within it.

  11. 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

    The Lu to Hf decay series has been widely used to understand the nature of Earth's early crust-mantle system. The interpretation, however, of Lu-Hf isotope data requires accurate knowledge of the radioactive decay constant of Lu (¿176), as well as bulk-Earth reference parameters. A recent...... calibration of the ¿176 value calls for the presence of highly unradiogenic hafnium in terrestrial zircons with ages greater than 3.9 Gyr, implying widespread continental crust extraction from an isotopically enriched mantle source more than 4.3 Gyr ago, but does not provide evidence for a complementary...... 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...

  12. Glucocorticoid levels in free ranging resident mantled howlers: a study of coping strategies.

    Science.gov (United States)

    Cristóbal-Azkarate, Jurgi; Chavira, Roberto; Boeck, Lourdes; Rodríguez-Luna, Ernesto; Veà, Joaquím J

    2007-08-01

    A growing amount of data shows that a preference for passive-nonaggressive over active-aggressive problem solving is associated with higher levels of glucocorticoids (GC). For mantled howlers, the arrival of an adult male in a new group is a potential source of psychological stress for both resident males and females. Resident mantled howler males take an active stand and aggressively repel the entrance of solitary males, while females take a passive-nonaggressive stand. In order to study whether the relationship between coping strategies and the activation of the hypothalamic-pituitary-adrenal (HPA) axis observed in other species applies to the response of resident mantled howlers to the presence of solitary males, we examine the relationship between different group and subpopulation variables and the GC levels measured in feces collected from 10 groups living in six forest fragments, in Los Tuxtlas, Mexico. The results of our study suggest that the resident mantled howler females' passive response to the presence of solitary males is accompanied by the activation of the HPA axis, whereas resident males' aggressive response is not accompanied by any changes in the HPA axis. In contrast, a previous study suggests that resident male howlers respond by increasing their testosterone levels to the presence of solitary males (Cristobal-Azkarate et al., Hormones and Behavior 2006;49 261-267). These different behavioral and hormonal responses coincide with the active and passive coping styles described for other species. The conditions in which howlers live in our study area may be favoring the interaction between solitary and resident howlers, and inducing chronically high GC levels, which in turn could negatively affect the fitness of these subpopulations.

  13. Quantifying global melt flux and degassing rate from global mantle convection models with plate motion history

    Science.gov (United States)

    Li, M.; Black, B. A.; Zhong, S.; Manga, M.; Rudolph, M. L.; Olson, P.

    2015-12-01

    How does the Earth's deep mantle convection affect surface climate change? Volcanism in various geological settings, including mid-ocean ridges, volcanic arcs, rift zones and sites with intraplate volcanism, releases volatiles to Earth's surface. The amount and composition of these volatiles influence the evolution Earth's ocean, crust and atmosphere, which in turn control the evolution of the biosphere. While there are constraints of Earth's degassing from the geochemistry of samples in some localized regions, a quantification of the time evolution of degassing on a global scale remains largely unknown.In this study, we run geodynamical calculations with a full 3D spherical geometry to explore the amount of partial melting in the shallow part of Earth's mantle and implied degassing at a global scale. The plate motion history for the last 200 Ma or longer is employed as time-dependent velocity boundary condition for mantle flow. Using the temperature, pressure and composition in mantle convection models, we calculate the degree of partial melting in different geological settings. We show that the melt flux at mid-ocean ridges generally increases linearly with the speed of plates, with some perturbations due to changes of length of mid-ocean ridges. Generally, this melt flux is about 2-3 times in the past 200 million years than that of the present-day Earth. The present-day melt flux is ~20 km3/year, but this value reaches ~40 km3/year at about 80Ma, and ~60 km3/year at about 120-160Ma. Given estimates of volatile content in the source regions where partial melting occurs and the melt flux we calculate, we quantify the evolution of degassing rate (of CO2) at mid-ocean ridges, hotspots, large igneous provinces, and subduction zones.

  14. Compressible magma/mantle dynamics: 3-D, adaptive simulations in ASPECT

    Science.gov (United States)

    Dannberg, Juliane; Heister, Timo

    2016-12-01

    Melt generation and migration are an important link between surface processes and the thermal and chemical evolution of the Earth's interior. However, their vastly different timescales make it difficult to study mantle convection and melt migration in a unified framework, especially for 3-D global models. And although experiments suggest an increase in melt volume of up to 20 per cent from the depth of melt generation to the surface, previous computations have neglected the individual compressibilities of the solid and the fluid phase. Here, we describe our extension of the finite element mantle convection code ASPECT that adds melt generation and migration. We use the original compressible formulation of the McKenzie equations, augmented by an equation for the conservation of energy. Applying adaptive mesh refinement to this type of problems is particularly advantageous, as the resolution can be increased in areas where melt is present and viscosity gradients are high, whereas a lower resolution is sufficient in regions without melt. Together with a high-performance, massively parallel implementation, this allows for high-resolution, 3-D, compressible, global mantle convection simulations coupled with melt migration. We evaluate the functionality and potential of this method using a series of benchmarks and model setups, compare results of the compressible and incompressible formulation, and show the effectiveness of adaptive mesh refinement when applied to melt migration. Our model of magma dynamics provides a framework for modelling processes on different scales and investigating links between processes occurring in the deep mantle and melt generation and migration. This approach could prove particularly useful applied to modelling the generation of komatiites or other melts originating in greater depths. The implementation is available in the Open Source ASPECT repository.

  15. Dehydration of chlorite explains anomalously high electrical conductivity in the mantle wedges.

    Science.gov (United States)

    Manthilake, Geeth; Bolfan-Casanova, Nathalie; Novella, Davide; Mookherjee, Mainak; Andrault, Denis

    2016-05-01

    Mantle wedge regions in subduction zone settings show anomalously high electrical conductivity (~1 S/m) that has often been attributed to the presence of aqueous fluids released by slab dehydration. Laboratory-based measurements of the electrical conductivity of hydrous phases and aqueous fluids are significantly lower and cannot readily explain the geophysically observed anomalously high electrical conductivity. The released aqueous fluid also rehydrates the mantle wedge and stabilizes a suite of hydrous phases, including serpentine and chlorite. In this present study, we have measured the electrical conductivity of a natural chlorite at pressures and temperatures relevant for the subduction zone setting. In our experiment, we observe two distinct conductivity enhancements when chlorite is heated to temperatures beyond its thermodynamic stability field. The initial increase in electrical conductivity to ~3 × 10(-3) S/m can be attributed to chlorite dehydration and the release of aqueous fluids. This is followed by a unique, subsequent enhancement of electrical conductivity of up to 7 × 10(-1) S/m. This is related to the growth of an interconnected network of a highly conductive and chemically impure magnetite mineral phase. Thus, the dehydration of chlorite and associated processes are likely to be crucial in explaining the anomalously high electrical conductivity observed in mantle wedges. Chlorite dehydration in the mantle wedge provides an additional source of aqueous fluid above the slab and could also be responsible for the fixed depth (120 ± 40 km) of melting at the top of the subducting slab beneath the subduction-related volcanic arc front.

  16. Mix or un-mix? Trace element segregation from a heterogeneous mantle, simulated.

    Science.gov (United States)

    Katz, R. F.; Keller, T.; Warren, J. M.; Manley, G.

    2016-12-01

    Incompatible trace-element concentrations vary in mid-ocean ridge lavas and melt inclusions by an order of magnitude or more, even in samples from the same location. This variability has been attributed to channelised melt flow [Spiegelman & Kelemen, 2003], which brings enriched, low-degree melts to the surface in relative isolation from depleted inter-channel melts. We re-examine this hypothesis using a new melting-column model that incorporates mantle volatiles [Keller & Katz 2016]. Volatiles cause a deeper onset of channelisation: their corrosivity is maximum at the base of the silicate melting regime. We consider how source heterogeneity and melt transport shape trace-element concentrations in basaltic lavas. We use both equilibrium and non-equilibrium formulations [Spiegelman 1996]. In particular, we evaluate the effect of melt transport on probability distributions of trace element concentration, comparing the inflow distribution in the mantle with the outflow distribution in the magma. Which features of melt transport preserve, erase or overprint input correlations between elements? To address this we consider various hypotheses about mantle heterogeneity, allowing for spatial structure in major components, volatiles and trace elements. Of interest are the roles of wavelength, amplitude, and correlation of heterogeneity fields. To investigate how different modes of melt transport affect input distributions, we compare melting models that produce either shallow or deep channelisation, or none at all.References:Keller & Katz (2016). The Role of Volatiles in Reactive Melt Transport in the Asthenosphere. Journal of Petrology, http://doi.org/10.1093/petrology/egw030. Spiegelman (1996). Geochemical consequences of melt transport in 2-D: The sensitivity of trace elements to mantle dynamics. Earth and Planetary Science Letters, 139, 115-132. Spiegelman & Kelemen (2003). Extreme chemical variability as a consequence of channelized melt transport. Geochemistry

  17. Spin Transition in the Lower Mantle: Deep Learning and Pattern Recognition of Superplumes from the Mid-mantle and Mid-mantle Slab Stagnation

    Science.gov (United States)

    Yuen, D. A.; Shahnas, M. H.; De Hoop, M. V.; Pysklywec, R.

    2016-12-01

    The broad, slow seismic anomalies under Africa and Pacific cannot be explained without ambiguity. There is no well-established theory to explain the fast structures prevalent globally in seismic tomographic images that are commonly accepted to be the remnants of fossil slabs at different depths in the mantle. The spin transition from high spin to low spin in iron in ferropericlase and perovskite, two major constituents of the lower mantle can significantly impact their physical properties. We employ high resolution 2D-axisymmetric and 3D-spherical control volume models to reconcile the influence of the spin transition-induced anomalies in density, thermal expansivity, and bulk modulus in ferropericlase and perovskite on mantle dynamics. The model results reveal that the spin transition effects increase the mixing in the lower regions of mantle. Depending on the changes of bulk modulus associated with the spin transition, these effects may also cause both stagnation of slabs and rising plumes at mid-mantle depths ( 1600 km). The stagnation may be followed by downward or upward penetration of cold or hot mantle material, respectively, through an avalanche process. The size of these mid-mantle plumes reaches 1500 km across with a radial velocity reaching 20 cm/yr near the seismic transition zone and plume heads exceeding 2500 km across. We will employ a deep-learning algorithm to formulate this challenge as a classification problem where modelling/computation aids in the learning stage for detecting the particular patterns.The parameters based on which the convection models are developed are poorly constrained. There are uncertainties in initial conditions, heterogeneities and boundary conditions in the simulations, which are nonlinear. Thus it is difficult to reconstruct the past configuration over long time scales. In order to extract information and better understand the parameters in mantle convection, we employ deep learning algorithm to search for different

  18. The viscosity of Earth's lower mantle inferred from sinking speed of subducted lithosphere

    NARCIS (Netherlands)

    Čížková, H.; van den Berg, A.P.; Spakman, W.; Matyska, C.

    2012-01-01

    The viscosity of the mantle is indispensable for predicting Earth's mechanical behavior at scales ranging from deep mantle material flow to local stress accumulation in earthquakes zones. But, mantle viscosity is not well determined. For the lower mantle, particularly, only few constraints result

  19. Upper Mantle of the Central Part of the Russian Platform by Receiver Function Data.

    Science.gov (United States)

    Goev, Andrey; Kosarev, Grigoriy; Sanina, Irina; Riznichenko, Oksana

    2017-04-01

    The study of the upper mantle of the Russian Platform (RP) with seismic methods remains limited due to the lack of broadband seismic stations. Existing velocity models have been obtained by using the P-wave travel-times from seismic events interpreted as explosions recorded at the NORSAR array in 1974-75 years. Another source of information is deep seismic sounding data from long-range profiles (exceeding 3000 km) such as QUARTZ, RUBIN-1 and GLOBUS and peaceful nuclear explosions (PNE) as sources. However, the data with the maximum distances larger than 1500 km have been acquired on the RP and only in the northern part. Being useful, these velocity models have low spatial resolution. This study analyzes and integrates all the existing RP upper mantle velocity models with the main focus on the central region. We discuss the completeness of the RP area of the LITHO 1.0 model. Based on results of our analysis, we conclude that it is necessary to get up-to-date velocity models of the upper mantle using broadband stations located at the central part of the RP using Vp/Vs ratio data and anisotropy parameters for robust estimation of the mantle boundaries. By applying the joint inversion of receiver-function (RF) data, travel-time residuals and dispersion curves of surface waves we get new models reaching 300 km depth at the locations of broadband seismic stations at the central part of the RP. We used IRIS stations OBN, ARU along with MHV and mobile array NOV. For each station we attempt to determine thickness of the lithosphere and to locate LVL, LAB, Lehman and Hales boundaries as well as the discontinuities in the transition zones at the depth of 410 and 660 km. Also we investigate the necessity of using short-period and broadband RF separately for more robust estimation of the velocity model of the upper mantle. This publication is based on work supported by the Russian Foundation for Basic Research (RFBR), project 15-05-04938 and by the leading scientific school NS

  20. Pure climb creep mechanism drives flow in Earth's lower mantle.

    Science.gov (United States)

    Boioli, Francesca; Carrez, Philippe; Cordier, Patrick; Devincre, Benoit; Gouriet, Karine; Hirel, Pierre; Kraych, Antoine; Ritterbex, Sebastian

    2017-03-01

    At high pressure prevailing in the lower mantle, lattice friction opposed to dislocation glide becomes very high, as reported in recent experimental and theoretical studies. We examine the consequences of this high resistance to plastic shear exhibited by ringwoodite and bridgmanite on creep mechanisms under mantle conditions. To evaluate the consequences of this effect, we model dislocation creep by dislocation dynamics. The calculation yields to an original dominant creep behavior for lower mantle silicates where strain is produced by dislocation climb, which is very different from what can be activated under high stresses under laboratory conditions. This mechanism, named pure climb creep, is grain-size-insensitive and produces no crystal preferred orientation. In comparison to the previous considered diffusion creep mechanism, it is also a more efficient strain-producing mechanism for grain sizes larger than ca. 0.1 mm. The specificities of pure climb creep well match the seismic anisotropy observed of Earth's lower mantle.

  1. Continental flood basalts derived from the hydrous mantle transition zone.

    Science.gov (United States)

    Wang, Xuan-Ce; Wilde, Simon A; Li, Qiu-Li; Yang, Ya-Nan

    2015-07-14

    It has previously been postulated that the Earth's hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported. Here we demonstrate that hydrothermally altered subducted oceanic crust was involved in generating the late Cenozoic Chifeng continental flood basalts of East Asia. This study combines oxygen isotopes with conventional geochemistry to provide evidence for an origin in the hydrous mantle transition zone. These observations lead us to propose an alternative thermochemical model, whereby slab-triggered wet upwelling produces large volumes of melt that may rise from the hydrous mantle transition zone. This model explains the lack of pre-magmatic lithospheric extension or a hotspot track and also the arc-like signatures observed in some large-scale intracontinental magmas. Deep-Earth water cycling, linked to cold subduction, slab stagnation, wet mantle upwelling and assembly/breakup of supercontinents, can potentially account for the chemical diversity of many continental flood basalts.

  2. The effect of plumes and a free surface on mantle dynamics with continents and self-consistent plate tectonics

    Science.gov (United States)

    Jain, Charitra; Rozel, Antoine; Tackley, Paul

    2014-05-01

    Rolf et al. (EPSL, 2012) and Coltice et al. (Science, 2012) investigated the thermal and dynamical influences of continents on plate tectonics and the thermal state of Earth's mantle, but they did not explicitly consider the influence of mantle plumes. When present, strong mantle plumes arising from the deep mantle can impose additional stresses on the continents, thereby facilitating continental rifting (Storey, Nature 1995; Santosh et al., Gondwana Research 2009) and disrupting the supercontinent cycle (Philips and Bunge, Geology 2007). In recent years, several studies have characterized the relation between the location of the plumes and the continents, but with contradicting observations. While Heron and Lowman (GRL, 2010; Tectonophysics, 2011) propose regions where downwelling has ceased (irrespective of overlying plate) as the preferred location for plumes, O'Neill et al. (Gondwana Research, 2009) show an anti-correlation between the average positions of subducting slabs at continental margins, and mantle plumes at continental/oceanic interiors. Continental motion is attributed to the viscous stresses imparted by the convecting mantle and the extent of this motion depends on the heat budget of the mantle. Core-mantle boundary (CMB) heat flux, internal heating from decay of radioactive elements, and mantle cooling contribute to this heat budget. Out of these sources, CMB heat flux is not well defined; however, the recent determination that the core's thermal conductivity is much higher than previously thought requires a CMB heat flow of at least 12 TW (de Koker et al., PNAS 2012; Pozzo et al., Nature 2012; Gomi et al., PEPI 2013), much higher than early estimates of 3-4 TW (Lay et al., Nature 2008). Thus, it is necessary to characterize the effect of increased CMB heat flux on mantle dynamics. In almost all mantle convection simulations, the top boundary is treated as a free-slip surface whereas Earth's surface is a deformable free surface. With a free

  3. 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

  4. An application of GOCE satellite gravity to resolve mantle heterogeneity in Europe

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2015-01-01

    The aim of this study is to obtain new information on the density structure of the European upper mantle by incorporating the state-of-the-art global gravity data derived from the GOCE satellite gravity mission and recently released seismic model for the crustal structure, EUNAseis. The residual...... mantle gravity anomalies are derived from the GOCE data, from which gravitational effects of the deep mantle and the crust are removed. Our model of mantle density structure has lateral resolution of ca. 100 km, which allows to distinguish small-scale mantle anomalies and to link them to regional......, examine the propagation of crustal model uncertainties into determinations of lithospheric mantle density. To understand better geodynamic causes of mantle density heterogeneity, we compare mantle residual gravity anomalies for the European upper mantle with upper mantle velocity structure constrained...

  5. [Mantle dentin as biomodel of materials for structural teeth restoration].

    Science.gov (United States)

    Starodubova, A V; Vinnichenko, Yu A; Pourovskaya, I Ya; Rusanov, F S

    The article describes a structural element of natural teeth - mantle dentin. It has been shown that the presence of this element in the structure of a natural tooth largely ensures its strength under the influence of repeated loads in a functional oral environment and arrests crack growth at the enamel/dentine interface. This later effect is explained by the influence of a thin layer of mantle dentine, which has physical and mechanical characteristics different from that of the main dentin.

  6. Execution of mantle field with multileaf collimator: A simple approach

    Directory of Open Access Journals (Sweden)

    Prabhakar Ramachandran

    2008-01-01

    Full Text Available Background: Until very recently mantle field radiotherapy remained the gold standard for the treatment of favorable early-stage Hodgkin′s lymphoma. The classic mantle includes all the major lymph nodes above the diaphragm and extends from the inferior portion of the mandible to the level of the insertion of the diaphragm. Aims: To describe a simple technique that has been devised to treat the mantle field with the help of multileaf collimator and using computed tomography (CT-based treatment planning. Materials and Methods: CT scan was performed with the patient in the supine position and the datasets were transferred to the Eclipse™ treatment planning system. Elekta Precise™ linear accelerator equipped with 40 pairs of multileaf collimator (MLC was used for the execution of the mantle field. The MLC′s shapes were designed to take the shape of the conventional customized blocks used for treatment of mantle field. The anterior mantle field was divided into three separate MLC segments with the collimator kept at 0°. The first MLC segment was shaped to cover the neck, clavicular regions, and mediastinum. The second and the third MLC segments covered the right and left axilla, respectively. The posterior fields were opposed to the anterior subfields in a similar fashion. The dose was prescribed at the midplane, using reference points. Results and Conclusion: The technique described in this study is very simple, easy to implement, and avoids unnecessary delay in the execution of the mantle field. The mantle field can be easily shaped with the multileaf collimators, without any collimator rotation.

  7. [Mantle cell lymphoma with multiple extranodal involvement].

    Science.gov (United States)

    Orii, K; Kobayashi, H; Ueno, M; Ishida, F; Saito, H; Hata, S; Aoki, K; Narita, A; Shimodaira, S; Kitano, K; Uchimaru, K; Motokura, T

    1997-06-01

    A 79-year-old male was admitted to our hospital because of general fatigue and night sweat. Physical examination showed generalized superficial lymphadenopathy, marked splenomegaly, and tumors in the conjunctiva and the abdomen. Chest X-ray and computed tomography (CT) revealed pleural effusion and intrathoracic lymphadenopathy. Abdominal ultrasonography and CT showed hepatosplenomegaly and intraperitoneal tumors. Upper gastrointestinal fiberscopy revealed multiple polypoid lesions and ulcers in the duodenum and the stomach. Involvement of relatively small-sized lymphocytes with cleaved nuclei was identified in each biopsied specimen from a cervical lymph node, a tumor in the conjunctiva, gastrointestinal polypoid lesions, and the bone marrow. Surface marker analysis of abnormal lymphocytes in the bone marrow revealed that CD5, CD19, and CD20 were strongly positive, but CD23 was weakly positive. Although (11:14)(q13:q32) translocation was not identified by chromosome analysis of bone marrow cells, Northern blot analysis of bone marrow cells revealed overexpression of the PRAD1 oncogene. Diagnosis of mantle cell lymphoma (MCL) was made. Combination chemotherapy by cyclophosphamide and vincristine was not effective, but etoposide perorally given at a dose of 50 mg per day was effective. In MCL, extranodal involvement of a digestive tract and bone marrow is well known. This case suggests that involvement of multiple organs including lacrimal glands and pleura could be characteristic of MCL cells.

  8. Structure of the Upper Mantle and Mantle Transition Zone in Central Mongolia

    Science.gov (United States)

    Cui, Z.; Meltzer, A.; Stachnik, J.; Fischer, K. M.; Russo, R. M.; Munkhuu, U.; Baasanbat, T.

    2016-12-01

    Located between two major Archean cratons, the Siberian Craton to the north and the Tarim and Sino-Korean Cratons to the south, the lithosphere of Central Mongolia was constructed over an extended period of orogenesis associated with the Central Asian Orogenic Belt. Archean to Early Proterozoic basement was modified by accreted subduction complexes during the Paleozoic and early Mesozoic and basalt magmatism in the Cenozoic. Central and western Mongolia constitute a significant portion of the greater Mongolian plateau, an approximately 2.6 million km2area of Central Asia with an average elevation of 1500 meters. The high topography of the Mongolian Plateau has been attributed to far-field effects of India-Asia convergence, Pacific plate subduction, mantle plume activity, convective mantle flow, and magmatic underplating. The origin and persistence of continental plateaus through time provides insight into the evolution of continents and interactions between mantle dynamics and surface processes. As part of a larger interdisciplinary project to understand the origin of high topography in continental interiors we deployed 112 seismic broadband stations in central Mongolia as three separate subarrays in two separate mobilizations over a four year period (2012-2016). The stations extend from the Hovsgol rift in northern Mongolia, through the Hangay Dome, and into the Gobi Altai in southern Mongolia. We use S wave Receiver functions (SRF) to examine the lithosphere asthenosphere boundary and P wave Receiver functions (PRF) to investigate the mantle transition zone (MTZ). Preliminary SRF results from the subarray in the Hangay show lithospheric thinning and E-W variation. The LAB beneath the Hangay is 100km. It gradually thins to 90 km at the western end of the central Hangay and thins more abruptly to 80km at the eastern end of the central Hangay. These results are in agreement with results from joint inversion of receiver functions and surface waves and teleseismic

  9. Trace Elements in Olivine in Italian Potassic Volcanic Rocks Distinguish Between Mantle Metasomatism by Carbonatitic and Silicate Melts

    Science.gov (United States)

    Foley, S. F.; Ammannati, E.; Jacob, D. E.; Avanzinelli, R.; Conticelli, S.

    2014-12-01

    The Italian Peninsula is the site of intense subduction-related potassic magmatism with bimodal character in terms of silica activity: Ca-poor silica-saturated lamproitic rocks and Ca-enriched silica-undersaturated leucitites. Lamproitic magmas formed in the early phases of magmatic activity and were followed by leucititic magmas. The primary magmas are generated in the sub-continental lithospheric mantle at the destructive plate margin, and both series have olivine as the first crystallizing phenocrysts. Trace elements in olivine phenocrysts are important in recognizing metasomatic effects on the mineralogy of the mantle source. Since Ni is the most compatible trace element in olivine, particularly in alkaline melts, modal changes of olivine in the source strongly affect its bulk partition coefficient, and therefore its content in primary melts and in olivine that crystallizes from them.The concentration of other compatible trace elements (e.g. Mn, Co) in olivine phenocrysts also depends on the abundance of olivine in the magma source. Ni contents in olivine of the Italian rocks show a clear bimodal distribution. Olivine from lamproitic samples has systematically higher Fo and Ni contents, whereas olivine from leucititic rocks never exceeds Fo92 and has markedly lower Ni, reaching among the lowest levels ever observed in olivine phenocrysts in primitive melts. The Mn/Fe ratio of olivine is also sensitive to changes of the modal abundance of olivine in the source, 100*Mn/Fe of olivine from lamproitic rocks never exceeds 2, while it is always >1.8 in leucititic rocks, meaning that the leucitite source regions are much richer in olivine. Lithium is generally enriched in the crust and in sediments compared to the lithospheric mantle and to mantle-derived melts,so that Li in olivine above 10 ppm is suggested to indicate recycled sediments. Li contents are up to 35 ppm in leucititic olivines and up to >50 ppm in lamproitic olivines, confirming the recycling of crustal

  10. An inverted continental Moho and serpentinization of the forearc mantle.

    Science.gov (United States)

    Bostock, M G; Hyndman, R D; Rondenay, S; Peacock, S M

    2002-05-30

    Volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge, resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere. Asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back-arc region, but the forearc mantle (in the corner of the wedge) is thought to be significantly cooler. Here we explore the structure of the mantle wedge in the southern Cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers. We find very low shear-wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an 'inverted' continental Moho, which reverts to normal polarity seaward of the Cascade arc. This observation provides compelling evidence for a highly hydrated and serpentinized forearc region, consistent with thermal and petrological models of the forearc mantle wedge. This serpentinized material is thought to have low strength and may therefore control the down-dip rupture limit of great thrust earthquakes, as well as the nature of large-scale flow in the mantle wedge.

  11. Tracking the Martian Mantle Signature in Olivine-Hosted Melt Inclusions of Basaltic Shergottites Yamato 980459 and Tissint

    Science.gov (United States)

    Peters, T. J.; Simon, J. I.; Jones, J. H.; Usui, T.; Moriwaki, R.; Economos, R.; Schmitt, A.; McKeegan, K.

    2014-01-01

    The Martian shergottite meteorites are basaltic to lherzolitic igneous rocks that represent a period of relatively young mantle melting and volcanism, approximately 600-150 Ma (e.g. [1,2]). Their isotopic and elemental composition has provided important constraints on the accretion, evolution, structure and bulk composition of Mars. Measurements of the radiogenic isotope and trace element concentrations of the shergottite meteorite suite have identified two end-members; (1) incompatible trace element enriched, with radiogenic Sr and negative epsilon Nd-143, and (2) incompatible traceelement depleted, with non-radiogenic Sr and positive epsilon 143-Nd(e.g. [3-5]). The depleted component represents the shergottite martian mantle. The identity of the enriched component is subject to debate, and has been proposed to be either assimilated ancient martian crust [3] or from enriched domains in the martian mantle that may represent a late-stage magma ocean crystallization residue [4,5]. Olivine-phyric shergottites typically have the highest Mg# of the shergottite group and represent near-primitive melts having experienced minimal fractional crystallization or crystal accumulation [6]. Olivine-hosted melt inclusions (MI) in these shergottites represent the most chemically primitive components available to understand the nature of their source(s), melting processes in the martian mantle, and origin of enriched components. We present trace element compositions of olivine hosted melt inclusions in two depleted olivinephyric shergottites, Yamato 980459 (Y98) and Tissint (Fig. 1), and the mesostasis glass of Y98, using Secondary Ionization Mass Spectrometry (SIMS). We discuss our data in the context of understanding the nature and origin of the depleted martian mantle and the emergence of the enriched component.

  12. Mantle Flow Beneath the Juan de Fuca and East Pacific Rise Spreading Centers and Adjacent Plates

    Science.gov (United States)

    Toomey, D. R.; Hooft, E. E.; Wilcock, W. S.

    2010-12-01

    Observations of seismic anisotropy are a principal means of inferring the direction of mantle flow beneath tectonic plates. Azimuthal anisotropy of mantle head waves (Pn) observed in mid-plate settings, for example, has been used to infer that beneath oceanic crust the mantle flow that is frozen in is parallel to the paleospreading direction. While the agreement between historical measurements of azimuthal anisotropy and paleospreading direction is good, the combined uncertainties in experimental results (many of which date back 30 to 50 years) and in inferring the paleospreading direction are often 10-15°. In contrast to historical results from mid-plate settings, recent studies of Pn anisotropy beneath the East Pacific Rise (EPR) and the Mid-Atlantic Ridge reveal that the fast-direction of seismic anisotropy - and by inference the direction of mantle flow - is skewed with respect to the current spreading direction. This result indicates that sub-ridge mantle flow is not an entirely passive response to plate spreading. Here we use data from recent active-source seismic experiments to investigate azimuthal anisotropy of Pn arrivals in two near-ridge settings. These modern experiments, which use dense arrays of ocean-bottom seismometers (OBSs) and well-navigated seismic shooting lines, can constrain azimuthal anisotropy to within ±1°. One data set is from the multi-scale Endeavour seismic tomography experiment (ETOMO) that took place in September 2009. Seismic data were collected using 68 four-component OBSs at 64 sites and the 6600 in3 airgun array of the R/V Marcus G. Langseth. The study includes 5567 shots covering 90 km along-axis and 50 km across. The second data set is from the UNDERSHOOT experiment, which was conducted at the EPR between the Siqueiros and Clipperton transforms, a section of ridge that is sub-divided by the 9°03'N overlapping spreading center (OSC). Seismic data were collected using a combination of four-component OBSs and single

  13. Highly CO2-supersaturated melts in the Pannonian lithospheric mantle - A transient carbon reservoir?

    Science.gov (United States)

    Créon, Laura; Rouchon, Virgile; Youssef, Souhail; Rosenberg, Elisabeth; Delpech, Guillaume; Szabó, Csaba; Remusat, Laurent; Mostefaoui, Smail; Asimow, Paul D.; Antoshechkina, Paula M.; Ghiorso, Mark S.; Boller, Elodie; Guyot, François

    2017-08-01

    Subduction of carbonated crust is widely believed to generate a flux of carbon into the base of the continental lithospheric mantle, which in turn is the likely source of widespread volcanic and non-volcanic CO2 degassing in active tectonic intracontinental settings such as rifts, continental margin arcs and back-arc domains. However, the magnitude of the carbon flux through the lithosphere and the budget of stored carbon held within the lithospheric reservoir are both poorly known. We provide new constraints on the CO2 budget of the lithospheric mantle below the Pannonian Basin (Central Europe) through the study of a suite of xenoliths from the Bakony-Balaton Highland Volcanic Field. Trails of secondary fluid inclusions, silicate melt inclusions, networks of melt veins, and melt pockets with large and abundant vesicles provide numerous lines of evidence that mantle metasomatism affected the lithosphere beneath this region. We obtain a quantitative estimate of the CO2 budget of the mantle below the Pannonian Basin using a combination of innovative analytical and modeling approaches: (1) synchrotron X-ray microtomography, (2) NanoSIMS, Raman spectroscopy and microthermometry, and (3) thermodynamic models (Rhyolite-MELTS). The three-dimensional volumes reconstructed from synchrotron X-ray microtomography allow us to quantify the proportions of all petrographic phases in the samples and to visualize their textural relationships. The concentration of CO2 in glass veins and pockets ranges from 0.27 to 0.96 wt.%, higher than in typical arc magmas (0-0.25 wt.% CO2), whereas the H2O concentration ranges from 0.54 to 4.25 wt.%, on the low end for estimated primitive arc magmas (1.9-6.3 wt.% H2O). Trapping pressures for vesicles were determined by comparing CO2 concentrations in glass to CO2 saturation as a function of pressure in silicate melts, suggesting pressures between 0.69 to 1.78 GPa. These values are generally higher than trapping pressures for fluid inclusions

  14. Platinum Concentrations and Tungsten Isotope Ratios of Earth's Mantle as Tracers for Late Veneer Mixing into the Early Mantle

    Science.gov (United States)

    Zeng, L.; Jacobsen, S. B.; Sasselov, D. D.

    2014-12-01

    Platinum (Pt) and tungsten (W) are both depleted in Earth's mantle. Due to their siderophile nature, they were both strongly partitioned into the Earth's core during its formation. However, in particular the Pt concentration in the Earth's mantle is much higher than expected from experimental data on metal-silicate partitioning appropriate for the conditions of core formation. A plausible explanation for this high Pt concentration is the late veneer hypothesis, where volatile-rich chondritic type material was delivered to Earth's surface after core formation. This can in principle explain both the volatiles in the Earth's ocean-atmosphere as well as the high Pt concentrations in the Earth's mantle. There are tungsten isotopic heterogeneities (182W/183W variations) in the early Earth that have been explained as being due to late veneer addition, as this material would have lower 182W/183W than the post-core formation mantle. There is also the gradual increase of Pt abundance through history in mantle as measured in mantle-derived rocks of various old ages. Both observations are thought to be caused by gradual mixing of late veneer material into Earth's mantle through plate subduction and mantle convection through geologic time. This would increase the Pt concentration and decrease the 182W/183W ratio in the mantle with time, as observed. Here we model the late veneer material as a thin sheet which is subducted into the mantle, and get stretched and mixed with the mantle material gradually. The stretching is assumed to follow a simple exponential law of decrease of the characteristic size of heterogeneity regions. The melting events that produce the rock samples of various ages measured on the surface are modeled as random geometric sampling of a sampling box with a certain length-scale. We are testing various scenarios of this mathematical model to see if both the variations in W isotopic ratio and the Pt concentration in Earth's history can be made consistent with

  15. Slab-mantle interactions in simulations of self-consistent mantle convection with single-sided subduction

    Science.gov (United States)

    Crameri, F.; Tackley, P. J.; Meilick, I.; Gerya, T. V.; Kaus, B. J. P.

    2012-04-01

    Subduction zones on present-day Earth are strongly asymmetric features (Zhao 2004) composed of an overriding plate above a subducting plate that sinks into the mantle. Our recent advances in numerical modelling allow global mantle convection models to produce single-sided subduction self-consistently by allowing for free surface topography on and lubrication between the converging plates (Crameri et al., 2012). Thereby, they are indicating important mantle-slab interactions. The increase of viscosity with depth is an important mantle property affecting the dynamics of subduction: a large viscosity increase on the one hand favours an immediate stagnant lid because the slab cannot sink fast enough, while a small increase on the other hand does not provide enough resistance for the sinking slab and therefore facilitates an immediate slab break-off. While in the mobile lid (plate tectonic like) regime, our model also shows that single-sided subduction in turn has strong implications on Earth's interior such as its rms. velocity or its stress distribution. The arcuate trench curvature is such a feature that is caused by single-sided subduction in 3-D geometry. The pressure difference between the mantle region below the inclined sinking slab and the region above it causes a toroidal mantle flow around the slab edges. This flow of mantle material is responsible for forming the slabs and subsequently also the subduction trenches above it towards an arcuate shape. For this study we perform experiments in 2-D and global spherical 3-D, fully dynamic mantle convection models with self-consistent plate tectonics. These are calculated using the finite volume multi-grid code StagYY (Tackley 2008) with strongly temperature and pressure-dependent viscosity, ductile and/or brittle plastic yielding, and non-diffusive tracers tracking compositional variations (the 'air' and the weak crustal layer in this case).

  16. A failure to reject: Testing the correlation between large igneous provinces and deep mantle structures with EDF statistics

    Science.gov (United States)

    Doubrovine, Pavel V.; Steinberger, Bernhard; Torsvik, Trond H.

    2016-03-01

    Absolute reconstructions of large igneous provinces (LIPs) for the past 300 Ma reveal a remarkable spatial pattern suggesting that almost all LIPs have erupted over the margins of the two large-scale structures in the Earth's lower mantle commonly referred to as the Large Low Shear-wave Velocity Provinces (LLSVPs). This correlation suggests that mantle plumes that have triggered LIP eruptions rose from the margins of LLSVPs, implying long-term stability of these structures and suggesting that they may be chemically distinct from the bulk of the mantle. Yet, some researchers consider the LLSVPs to be purely thermal upwellings, arguing that the observed distribution of LIPs can be explained by plumes randomly forming over the entire areas of LLSVPs. Here we examine the correlation between the LIPs and LLSVPs using nonparametric statistical tests, updated plate reconstructions, and a large number of alternative definitions of LLSVPs based on seismic tomography. We show that probability models assuming plume sources originating at the margins of LLSVPs adequately explain the observed distribution of reconstructed LIPs. In contrast, we find strong evidence against the models seeking to link LIPs with plumes randomly forming over the entire LLSVP areas. However, the hypothesis proposing that the correlation can be explained by plumes randomly forming over a larger area of slower-than-average shear wave velocities in the lowermost mantle cannot be ruled out formally. Our analysis suggests that there is no statistically sound reason for questioning the hypothesis that the LIPs correlate with the margins of LLSVP globally.

  17. Universal single grain amphibole thermobarometer for mantle rocks - preliminary calibration.

    Science.gov (United States)

    Ashchepkov, Igor

    2017-04-01

    Calibration of S-Al- K-Na-Ca distribution in the structure of the mantle amphiboles (Cr- hornblende, pargasite, kaersutite) using experimental data (Niida, Green, 1999; Wallace Green, 1991, Conceicao, Green, 2004; Medard et al, 2006; Safonov, Butvina, 2013; 2016; Pirard, Hermann, 2015 etc) allows to obtain an equation for pressure estimates in 0.5 - 4.5 GPa interval. Regression calculated pressures with experimental values (R 0.82) and precision 5 kbar allow to use barometer for a wide range of mantle rocks from peridotite to pyroxenites and megacrystals. For the higher pressures (Cr- pargasite richterite) calibration is carried by the cross- correlations with the estimates calculated for the natural associations obtained using clino- and orthopyroxene. IT was used KD =Si/(8-Al-2.2*Ti)*(Na+K))/Ca for the following equation: P(GPa)=0.0035*(4+K/(Na+K))*2*Mg)/Fe+3.75*(K+Na)/Ca))*KD*ToK**0.75/ (1+3.32*Fe)-ln(1273/ToK*5*(8*Mg-Al*2 +3*Ti+8*Cr+3*K)/10 Th advantage of this barometer comparing with the previous (Ridolfi, Renzulli, 2012) is that is working with all mantle amphibole types. For the calculations of the PT parameters of the natural xenocrysts it was used monomineral version of Gar-Amph termometer (Ravna et al., 2000) in combination with the received barometer. Contents of Ca- Mg and Fe in associated garnets were calculated usinf the regressions obtained from natural and experimental associations. Aplication of the mantle amphibole thermobarometry for the reconstruction of sections of the cratonic mantle lithosphere of Yakutia show that amphibloles are distributed in various parts of mantle sections in deifferent mantle terranes of Yakutia. The most abundant amphoboles from Alakite region are distributed within all mantle section. In the SCLM beneat Yubileyaya pipe thehalf of them belong to the spinel garnet facie refering to the upper pyroxenitic suit and Cr- hornblende - mica viens. The second group reffer to the eclogite pyroxenite layer in the middle part of

  18. The significance of seismic wavespeed minima and thermal maxima in the mantle and the role of dynamic melting

    OpenAIRE

    Sammis, Charles G.; Anderson, Don L.

    2015-01-01

    It is widely assumed that the boundary layer above the core is the source of intraplate volcanoes such as Hawaii, Samoa, and Yellowstone, and that the sub-plate boundary layer at the top of the mantle is thin and entirely subsolidus. In fact, this upper layer is thicker and has higher expansivity, buoyancy, and insulating power than the lower one, and may have higher potential temperatures. The observed seismic structure of the low-velocity zone (LVZ) including attenuation, anisotropy, sharp ...

  19. Geochemical and Fluid Dynamic Investigations into the Nature of Chemical Heterogeneity in the Earth’s Mantle

    Science.gov (United States)

    1992-09-01

    samples are from the islands of Savaii (Western Samoa), Rarotonga and Mangaia ( Cook Islands ), Rurutu and Tubuai (Austral Islands ) and Tahaa (Society...crustal materials. The Re-Os isotope systematics of oceanic island basalts from Rarotonga . S .,ail. Tahaa, Rurutu, Tubuai, and Mangaia are examined...source for rocks of Cook -Austral Islands and heterogeneities of mantle l plumes. Geochim. Cosmochim. Acta, 52, 2909-2924. Navon, 0. and E. Stolper

  20. The Oxidation State of Fe in MORB Glasses and the Oxygen Fugacity of the Upper Mantle

    Energy Technology Data Exchange (ETDEWEB)

    E Cottrell; K Kelley

    2011-12-31

    Micro-analytical determination of Fe{sup 3+}/{Sigma}Fe ratios in mid-ocean ridge basalt (MORB) glasses using micro X-ray absorption near edge structure ({mu}-XANES) spectroscopy reveals a substantially more oxidized upper mantle than determined by previous studies. Here, we show that global MORBs yield average Fe{sup 3+}/{Sigma}Fe ratios of 0.16 {+-} 0.01 (n = 103), which trace back to primary MORB melts equilibrated at the conditions of the quartz-fayalite-magnetite (QFM) buffer. Our results necessitate an upward revision of the Fe{sup 3+}/{Sigma}Fe ratios of MORBs, mantle oxygen fugacity, and the ferric iron content of the mantle relative to previous wet chemical determinations. We show that only 0.01 (absolute, or < 10%) of the difference between Fe{sup 3+}/{Sigma}Fe ratios determined by micro-colorimety and XANES can be attributed to the Moessbauer-based XANES calibration. The difference must instead derive from a bias between micro-colorimetry performed on experimental vs. natural basalts. Co-variations of Fe{sup 3+}/{Sigma}Fe ratios in global MORB with indices of low-pressure fractional crystallization are consistent with Fe{sup 3+} behaving incompatibly in shallow MORB magma chambers. MORB Fe{sup 3+}/{Sigma}Fe ratios do not, however, vary with indices of the extent of mantle melting (e.g., Na{sub 2}O(8)) or water concentration. We offer two hypotheses to explain these observations: The bulk partition coefficient of Fe{sup 3+} may be higher during peridotite melting than previously thought, and may vary with temperature, or redox exchange between sulfide and sulfate species could buffer mantle melting at {approx} QFM. Both explanations, in combination with the measured MORB Fe{sup 3+}/{Sigma}Fe ratios, point to a fertile MORB source with greater than 0.3 wt.% Fe{sub 2}O{sub 3}.

  1. Rayleigh wave group velocity tomography of Gujarat region, Western India and its implications to mantle dynamics

    Science.gov (United States)

    Dixit, Mayank; Singh, A. P.; Mishra, O. P.

    2017-07-01

    In the present study, fundamental Rayleigh waves with varying period from 10 to 80 s are used to obtain group velocity maps in the northwest Deccan Volcanic Province of India. About 350 paths are obtained using 53 earthquakes (4.8 ≤ M ≥ 7.9) recorded by the SeisNetG (Seismic Network of Gujarat). Individual dispersion curves of group velocity of Rayleigh wave for each source-station path are estimated using multiple filter technique. These curves are used to determine lateral distribution of Rayleigh wave group velocity by tomographic inversion method. Our estimated Rayleigh group velocity at varying depths showed conspicuous corroboration with three tectonic blocks [Kachchh Rift Basin (KRB), Saurashtra Horst (SH), and Mainland Gujarat (MG)] in the region. The seismically active KRB with a thicker crust is characterized as a low velocity zone at a period varying from 10 to 30 s as indicative of mantle downwarping or sagging of the mantle beneath the KRB, while the SH and MG are found to be associated with higher group velocities, indicating the existence of the reduced crustal thickness. The trend of higher group velocity was found prevailed adjacent to the Narmada and Cambay rift basins that also correspond to the reduced crust, suggesting the processes of mantle upwarping or uplifting due to mantle upwelling. The low velocities at periods longer than 40 s beneath the KRB indicate thicker lithosphere. The known Moho depth correlates well with the observed velocities at a period of about 30 s in the Gujarat region. Our estimates of relatively lower group velocities at periods varying from 70 to 80 s may correspond to the asthenospheric flow beneath the region. It is interesting to image higher group velocity for the thinner crust beneath the Arabian Sea adjacent to the west coast of Gujarat at the period of 40 s that may correspond to the upwarped or upwelled mantle beneath the Arabian Sea. Our results have better resolution estimated by a radius of equivalent

  2. Modeling Crustal Thickness Variations Beneath the East Pacific Rise: Mantle Diapirs or Plate Kinematics?

    Science.gov (United States)

    George, S. A.; Toomey, D. R.

    2003-12-01

    Geophysical studies along the East Pacific Rise between the Siqueiros and Clipperton fracture zones reveal along- and cross-axis variations in crustal thickness whose origins are poorly understood. By one view, variations in crustal thickness are the result of three-dimensional upwelling of the mantle associated with a melt-rich diapir centered at 9° 50'N. Alternatively, it has been proposed that the migration of the 9° 03'N overlapping spreading center (OSC) alters the thickness of crust by increasing the amount of time that a crustal unit resides near the spreading axis. In this case, crustal thickness variations arise from plate kinematics, and not from three-dimensional variations in mantle upwelling. We report on a modeling study designed to explore how the evolution of OSCs may alter the thickness of newly-formed crust. OSC propagation is modeled using the kinematic algorithm developed by Wilson [1990], modified to track parcels of crust through time. Given an OSC's kinematic history and two-dimensional descriptions of the melt flux out of the mantle (i.e. invariant along the rise), we predict relative variations in crustal thickness. Our modeling assumes that underplating increases the thickness of the crust and/or Moho transition zone as long as a crustal unit resides over the source of mantle-derived melt. Results suggest two general kinematic mechanisms whereby variations in crustal thickness can occur: those due to an offset between the mantle-level magmatic system and the spreading axis, and those due to any relative reduction in the velocity of a crustal unit as it moves off axis. Offset-induced crustal thickness variations are manifest as long-wavelength ( ˜50 km), low-amplitude cross-axis asymmetries. Local slowing of crustal units as they move off axis -- in direct association with the OSC and its overlap basins -- results in relatively short-wavelength ( ˜10 km), high-amplitude variations in crustal thickness. Using a kinematic history

  3. The Thermal Evolution of the Galapagos Mantle Plume: Insights from Al-in-Olivine Thermometry

    Science.gov (United States)

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

    2016-12-01

    The mantle plume hypothesis is widely accepted for the formation of large igneous provinces (LIP) and many ocean island basalts (OIB). Petrologic models support a mantle plume origin by indicating high mantle temperatures (>1500 °C) for some plume-melts relative to melts generated at ambient mid ocean ridge conditions (1350 °C). Mantle plumes forming LIPs and OIBs provide our primary source of information on the geochemical and lithological heterogeneity of the lower mantle. The Galapagos hotspot represents one of the most thermally and geochemically heterogeneous plumes on the planet, sustaining long-lived isotopic and lithological heterogeneity over its 90 Ma evolution. Previous petrologic studies showed that the Galapagos plume secularly cooled over time and that the decrease in the plume's temperature correlates with an increase in a recycled (pyroxenite) component. We used Al-in-olivine thermometry to show that maximum olivine crystallization temperatures confirm secular cooling of the Galapagos plume. Olivines from the early melting stages of the plume at 90 Ma (Caribbean LIP) record the highest crystallization temperatures (1600 °C). Olivines from the current archipelago record the lowest temperatures of only 1300 °C. The largest decrease in temperature occurred between 90 and 70 Ma ( 200 °C decrease) and coincides with the plume head-tail transition. Olivines from the 60-90 Ma-old accreted Galapagos-tracks in Costa Rica and Panama record higher Ni, Fe/Mn, and lower Ca contents than those from the present-day archipelago, indicating a higher abundance of pyroxenite (recycled oceanic crust) entrained in parts of the plume head that melted to form the Caribbean LIP. However, the Galapagos plume was pyroxenite-rich for 40 Ma thus pyroxenite-entrainment goes beyond the plume-tail transition. Our results suggest that hotter regions of the Galapagos plume entrained larger amounts of dense, recycled components due to their greater buoyancy; however, this

  4. Modeling mantle circulation and density distributions in subduction zones: Implications for seismic studies

    Science.gov (United States)

    Kincaid, C. R.; Druken, K. A.; Griffiths, R. W.; Long, M. D.; Behn, M. D.; Hirth, G.

    2009-12-01

    highlight how strongly subduction-driven circulation modifies buoyancy-driven flows, effectively converting these features into passive, small scale features within the mantle wedge. Plume-like features are efficiently disconnected from their deep buoyancy source and drawn into small scale (relative to plate motions. The melt production history of these features is calculated and combined with measured temperature anomalies to estimate spatial patterns in seismic velocity anomaly.

  5. Receiver Function Imaging of Upper Mantle Discontinuities Beneath the Oregon High Lava Plains and Surrounding Regions

    Science.gov (United States)

    Eagar, K. C.; Fouch, M. J.

    2007-12-01

    The Pacific Northwestern United States has experienced wide-spread tectonomagmatism from the late Cenozoic to present-day, the reasons for which are likely linked to complex interactions between subduction zone processes near the edge of a Precambrian craton, possible hotspot effects, and mantle flow within the asthenosphere. The goal of this study is to examine upper mantle seismic velocity discontinuities beneath this region to investigate the connection between these geodynamic processes. We present results from analysis of Ps receiver functions using stations from the High Lava Plains temporary broadband seismic experiment, the USArray Transportable Array (TA), and other regional broadband stations for a total of over 108 stations in the region. We compute receiver functions at individual stations using an iterative deconvolution approach, and generate common conversion point (CCP) stacks using moveout corrections defined by the Tectonic North America (TNA) shear wave velocity model. Results from our imaging show that conversions from the 410 km discontinuity have narrow, high amplitude peaks across most of the region, with local complexity in peaks for some areas. Conversely, most conversions near the 660 km discontinuity exhibit peaks that are broad and less well-defined. Estimates in transition zone thickness show local variability, with notable areas of thickening in northeastern Oregon into Idaho and thinning under the coastal regions. The complexity in upper mantle discontinuity structure in this region is likely due to a combination of strong variations in isotropic and anisotropic seismic wavespeeds. The local complexities of the 410 km discontinuity correlate well with seismic wavespeed anomalies imaged by regional P-wave tomography. The source of the variations in the 660 km discontinuity are less apparent, but we note that seismic anisotropy is strong and regionally homogenous across much of the region, perhaps producing backazimuthal variations in

  6. Ensemble data assimilation for the reconstruction of mantle circulation

    Science.gov (United States)

    Bocher, Marie; Coltice, Nicolas; Fournier, Alexandre; Tackley, Paul

    2016-04-01

    The surface tectonics of the Earth is the result of mantle dynamics. This link between internal and surface dynamics can be used to reconstruct the evolution of mantle circulation. This is classically done by imposing plate tectonics reconstructions as boundary conditions on numerical models of mantle convection. However, this technique does not account for uncertainties in plate tectonics reconstructions and does not allow any dynamical feedback of mantle dynamics on surface tectonics to develop. Mantle convection models are now able to produce surface tectonics comparable to that of the Earth to first order. We capitalize on these convection models to propose a more consistent integration of plate tectonics reconstructions into mantle convection models. For this purpose, we use the ensemble Kalman filter. This method has been developed and successfully applied to meteorology, oceanography and even more recently outer core dynamics. It consists in integrating sequentially a time series of data into a numerical model, starting from an ensemble of possible initial states. The initial ensemble of states is designed to represent an approximation of the probability density function (pdf) of the a priori state of the system. Whenever new observations are available, each member of the ensemble states is corrected considering both the approximated pdf of the state, and the pdf of the new data. Between two observation times, each ensemble member evolution is computed independently, using the convection model. This technique provides at each time an approximation of the pdf of the state of the system, in the form of a finite ensemble of states. We perform synthetic experiments to assess the efficiency of this method for the reconstruction of mantle circulation.

  7. Mantle Convection in a Microwave Oven: New Perspectives for the Internally Heated Convection

    Science.gov (United States)

    Limare, A.; Fourel, L.; Surducan, E.; Neamtu, C.; Surducan, V.; Vilella, K.; Farnetani, C. G.; Kaminski, E. C.; Jaupart, C. P.

    2015-12-01

    The thermal evolution of silicate planets is primarily controlled by the balance between internal heating - due to radioactive decay - and heat transport by mantle convection. In the Earth, the problem is particularly complex due to the heterogeneous distribution of heat sources in the mantle and the non-linear coupling between this distribution and convective mixing. To investigate the behaviour of such systems, we have developed a new technology based on microwave absorption to study internally-heated convection in the laboratory. This prototype offers the ability to reach the high Rayleigh-Roberts and Prandtl numbers that are relevant for planetary convection. Our experimental results obtained for a uniform distribution of heat sources were compared to numerical calculations reproducing exactly experimental conditions (3D Cartesian geometry and temperature-dependent physical properties), thereby providing the first cross validation of experimental and numerical studies of convection in internally-heated systems. We find that the thermal boundary layer thickness and interior temperature scale with RaH-1/4, where RaH is the Rayleigh-Roberts number, as theoretically predicted by scaling arguments on the dissipation of kinetic energy. Our microwave-based method offers new perspectives for the study of internally-heated convection in heterogeneous systems which have been out of experimental reach until now. We are able to selectively heat specific regions in the convecting layer, through the careful control of the absorption properties of different miscible fluids. This is analogous to convection in the presence of chemical reservoirs with different concentration of long-lived radioactive isotopes. We shall show results for two different cases: the stability of continental lithosphere over a convective fluid and the evolution of a hidden enriched reservoir in the lowermost mantle.

  8. The LIP-OIB transitional phase in the Galapagos mantle plume

    Science.gov (United States)

    Trela, J.; Gazel, E.; Vidito, C. A.; Class, C.; Jicha, B. R.; Bizimis, M.; Herzberg, C. T.; Alvarado-Induni, G.

    2014-12-01

    Although significant work has been done on LIPS and OIB, no complete record of the evolution of a mantle plume is available at this point. Galapagos-related lavas provide a complete record of the evolution of a mantle plume since the plume's initial stages in the Cretaceous. Our petrological models (PRIMELT2) suggest that the Galapagos plume head that formed the Caribbean Large Igneous Province (CLIP) at ~95 Ma melted at hotter temperatures than the ocean island basalt (OIB) equivalents of the modern archipelago. While this work suggests a significant decrease in mantle potential temperatures (Tp) over time, the exact mechanism responsible for secular cooling of the Galapagos plume remains unclear. One viable explanation is that plumes entraining recycled oceanic crust (pyroxenite) will be cooler than purely peridotite plumes, due to the effect of dense pyroxenite on the plume's buoyancy. High-precision electron microprobe analyses on olivine cores from the ~70 Ma Galapagos-related Quepos terrane in Costa Rica indicate a mixed peridotite-pyroxenite source lithology, not evident during the LIP stage. The appearance of this pyroxenitic component correlates with the first record of an EMII isotopic signature (Northern Galapagos Domain), and significant high-field strength enrichments in the Galapagos plume related lavas. This dense pyroxenite component may explain the marked decrease in Tp observed at ~70 Ma due to its effect on the plume's buoyancy. Otherwise, the pyroxenite component may have been diluted during voluminous basalt production of the CLIP by high peridotite melt fractions. Future research will incorporate further petrological modeling, olivine chemistry, and radiogenic isotope work of accreted Galapagos terranes in Central America to test whether or not a decrease in Tp correlates with increasing pyroxenite content in source melts.

  9. Mantle layering from ScS reverberations: 3. The upper mantle

    Science.gov (United States)

    Revenaugh, Justin; Jordan, Thomas H.

    1991-11-01

    This is the third paper in a four-part sequence that examines the nature of mantle layering using the multiple-ScS phases and internal reflections observed within the reverberative interval of SH-polarized seismograms. In this paper, migration techniques are applied to ScS reverberations to image discontinuities in shear impedance beneath a tectonically diverse study area that includes the western Pacific, Japan, the Philippine Sea, and Australasia. Between the M and 410-km discontinuities (Bullen's region B), the analysis reveals four reflectors, designated H, G, L, and X. The H (Hales) reflector is a positive impedance increase occurring at an average depth of about 60 km with a mean reflection coefficient of about 3.5%. It can be seen on all profiles except those where its signature is overwhelmed by the G discontinuity and is best explained as the seismic expression of the spinel → garnet facies boundary. The G (Gutenberg) reflector, marking the lid-to-low-velocity zone (LVZ) interface, is the only negative impedance contrast identified from ScS reverberations anywhere in the mantle. It is observed along most of the oceanic paths sampled in our study, where its depth generally correlates with QScS but it is not found on any of the profiles from predominantly continental corridors, consistent with the notion that the LVZ is absent or only weakly expressed beneath the cratons. G occurs at a depth of ˜60 km beneath the western Pacific, shallower than most estimates of thermal boundary layer (plate) thickness; the data are consistent with a sharp drop in shear velocity owing to the breakdown of hydrous phases such as amphibole along a steeply rising portion of the geotherm within the thermal boundary layer. The G contrasts with the largest magnitude (up to 10%) occur on profiles for back arc regions, where upper mantle melting may be accentuated by volatiles fluxing from subducted oceanic lithosphere. None of the eight profiles having a G discontinuity show an L

  10. Analysis of the flow structure and heat transfer in a vertical mantle heat exchanger

    DEFF Research Database (Denmark)

    Knudsen, Søren; Morrison, GL; Behnia, M

    2005-01-01

    The flow structure inside the inner tank and inside the mantle of a vertical mantle heat exchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image...... Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heat exchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both...... initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level. (C...

  11. Improved design of mantle tanks for small low flow SDHW systems

    DEFF Research Database (Denmark)

    Furbo, Simon; Knudsen, Søren

    2006-01-01

    of the mantle and the other mantle tank has the mantle inlet port moved 0.175 m down from the top of the mantle. The thermal performance is almost the same for the two systems in the measuring period of 252 days. The solar fractions were 0.66 and 0.68 for the two systems. The tests showed also that the system......Side-by-side tests of two small low flow SDHW systems based on mantle tanks have been carried out under the same test conditions in a laboratory test facility. The systems are identical with exception of the mantle tanks. One of the mantle tanks has the mantle inlet port located at the top...... improved by relatively simple design changes: increasing the height/diameter ratio, reducing the mantle height and increasing the insulation thickness on the sides of t he tank....

  12. Project Hotspot - The Snake River Scientific Drilling Project - Investigating the Interactions of Mantle Plumes and Continental Lithosphere

    Science.gov (United States)

    Shervais, J. W.

    2008-12-01

    The Yellowstone-Snake River Plain (YSRP) volcanic province is the world's best modern example of a time- transgressive hotspot track beneath continental crust. Recently, a 100 km wide thermal anomaly has been imaged by seismic tomography to depths of over 500 km beneath the Yellowstone Plateau. The Yellowstone Plateau volcanic field consists largely of rhyolite lavas and ignimbrites, with few mantle-derived basalts. In contrast, the Snake River Plain (SRP), which represents the track of the Yellowstone hotspot, consists of rhyolite caldera complexes that herald the onset of plume-related volcanism and basalts that are compositionally similar to ocean island basalts like Hawaii. The SRP preserves a record of volcanic activity that spans over 16 Ma and is still active today, with basalts as young as 200 ka in the west and 2 ka in the east. The SRP is unique because it is young and relatively undisturbed tectonically, and because it contains a complete record of volcanic activity associated with passage of the hotspot. This complete volcanic record can only be sampled by drilling. In addition, the western SRP rift basin preserves an unparalleled deep-water lacustrine archive of paleoclimate evolution in western North America during the late Neogene. The central question addressed by the Snake River Scientific Drilling Project is how do mantle hotspots interact with continental lithosphere, and how does this interaction affect the geochemical evolution of mantle-derived magmas and the continental lithosphere? Our hypothesis is that continental mantle lithosphere is constructed in part from the base up by the underplating of mantle plumes, which are compositionally distinct from cratonic lithosphere, and that plumes modify the impacted lithosphere by thermally and mechanically eroding cratonic mantle lithosphere, and by underplating depleted plume-source mantle. Addition of mafic magma to the crust represents a significant contribution to crustal growth, and densifies

  13. Diamond Formation in association with Deep Mantle Dehydration Zones

    Science.gov (United States)

    Harte, B.

    2009-12-01

    INTRODUCTION. During the last 25 years a series of publications have documented the occurrence of inclusions in diamonds that show mineral compositions and mineral associations predicted for mantle rocks at deeper levels than the mantle lithosphere (e.g Harte et al., 1999; Harte & Cayzer, 2007). Although the diamonds bearing deep mantle inclusions are not abundant in absolute terms they are widespread and have been reported from cratonic blocks on all major continents. DEPTH ZONES OF INCLUSION SUITES. The silicate inclusions and their mineral associations form a series showing good correlation with mineral assemblages expected in basic and ultrabasic rock compositions at depth. However, there is a strong bias towards assemblages from two principal zones: (1)uppermost Transition zone and Asthenosphere. (2)lowermost Transition Zone and uppermost Lower Mantle. In the case of (1) the assemblages are predominantly of majorite garnet, and majorite garnet + cpx with an affinity to eclogitic bulk compositions. In many of these inclusions the cpx appears to have exsolved from the majoritic garnet and the depth of origin of the initial inclusions may be near the top of the Transition Zone. The assemblages from (2) are predominantly of peridotic affinity and involve fPer as well as silicates. They indicate material from three depth zones near the upper mantle to lower mantle boundary (UM/LM boundary). 2a) Upper/Lower Mantle Boundary association - inclusions of: Mg2SiO4, fPer, majorite/TAPP, MgSi-perovskite(mpv), CaSi-perovskite (cpv). 2b) uppermost Lower Mantle association with: Mpv(Al-poor), fPer and cpv, majorite/tapp 2c)lower Mantle association with: Mpv(Al-rich) with fPer, and corundum. DISCUSSION. The above features show that the formation of deep mantle diamonds is concentrated in a zone around the top of the Transition Zone (ca 400-500 kms deep), and a zone at 600-800 kms embracing the bottom of the Transition Zone and the top of Lower Mantle. Associations including Mg

  14. 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.

  15. The depth of sub-lithospheric diamond formation and the redistribution of carbon in the deep mantle

    Science.gov (United States)

    Beyer, Christopher; Frost, Daniel J.

    2017-03-01

    Most diamonds form in the Earth's lithosphere but a small proportion contain Si-rich majoritic garnet inclusions that indicate formation in the deeper mantle. The compositions of syngenetic garnet inclusions can potential yield information on both the depth and mantle lithology in which the diamonds formed. Pressure dependent changes in garnet compositions have been calibrated using the results of experiments conducted in a multi-anvil apparatus at pressures between 6 and 16 GPa and temperatures of 1000 to 1400 °C. Using the results of these experiments a barometer was formulated based on an empirical parameterisation of the two major majoritic substitutions, referred to as majorite (Maj; Al3+ =Mg2+ +Si4+), and Na-majorite (Na-Maj; Mg2+ +Al3+ =Na+ +Si4+). Moreover, previously published experimental garnet compositions from basaltic, kimberlite, komatiite and peridotite bulk compositions were included in the calibration, which consequently covers pressures from 6 to 20 GPa and temperatures from 900 to 2100 °C. Experimental pressures are reproduced over these conditions with a standard deviation of 0.86 GPa. The barometer is used to determine equilibration pressures of approximately 500 reported garnet inclusions in diamonds from a range of localities. As the majority of these inclusions are proposed to be syngenetic this allows a detailed picture of diamond formation depths and associated source rocks to be established using inclusion chemistry. Geographic differences in diamond source rocks are mapped within the sub-lithospheric mantle to over 500 km depth. Continuous diamond formation occurs over this depth range within lithologies with eclogitic affinities but also in lithologies that appear transitional between eclogitic and peridotitic bulk compositions, with an affinity to pyroxenites. The geographic differences between eclogitic and pyroxenitic diamond source rocks are rationalised in terms of diamond formation within downwelling and upwelling regimes

  16. Thermally-Driven Mantle Plumes Reconcile Hot-spot Observations

    Science.gov (United States)

    Davies, D.; Davies, J.

    2008-12-01

    Hot-spots are anomalous regions of magmatism that cannot be directly associated with plate tectonic processes (e.g. Morgan, 1972). They are widely regarded as the surface expression of upwelling mantle plumes. Hot-spots exhibit variable life-spans, magmatic productivity and fixity (e.g. Ito and van Keken, 2007). This suggests that a wide-range of upwelling structures coexist within Earth's mantle, a view supported by geochemical and seismic evidence, but, thus far, not reproduced by numerical models. Here, results from a new, global, 3-D spherical, mantle convection model are presented, which better reconcile hot-spot observations, the key modification from previous models being increased convective vigor. Model upwellings show broad-ranging dynamics; some drift slowly, while others are more mobile, displaying variable life-spans, intensities and migration velocities. Such behavior is consistent with hot-spot observations, indicating that the mantle must be simulated at the correct vigor and in the appropriate geometry to reproduce Earth-like dynamics. Thermally-driven mantle plumes can explain the principal features of hot-spot volcanism on Earth.

  17. Centrifugal librations due to lunar core-mantle couplings

    Science.gov (United States)

    Bois, Eric

    2005-01-01

    We present a study of the dynamical behavior of a molten core inside the Moon related to the mantle by inertial coupling. In order to integrate the lunar core-mantle interaction in a realistic model of the Moon's rotation we have used our SONYR (acronym of Spin-Orbit N-bodY Relativistic) model of the solar System including the Moon's spin-orbit motion. This model was previously built in accordance with the requirements of the Lunar Laser Ranging observational accuracy. We have extended this model to the spin-orbit couplings of the terrestrial planets in order to compare different dynamical behaviors of core-mantle interactions in these planets (Mercury Venus Earth and Mars). Our core-mantle mechanism prove to be adequate to excite the two resonant frequencies of the lunar physical librations namely 2.9 and 80.1 years. Signature of such a core with for instance a 1/10 homothetic ratio appears clearly on the proper rotation angle; the amplitude is then around 12 milliarcseconds and its period 2.9 years. Besides we present the results obtained for various lunar nucleus radii and various initial nutations of the core relatively to the mantle. Other computations and comparisons are in progress involving Mercury the Earth and Mars.

  18. Tidal tomography constrains Earth’s deep-mantle buoyancy

    Science.gov (United States)

    Lau, Harriet C. P.; Mitrovica, Jerry X.; Davis, James L.; Tromp, Jeroen; Yang, Hsin-Ying; Al-Attar, David

    2017-11-01

    Earth’s body tide—also known as the solid Earth tide, the displacement of the solid Earth’s surface caused by gravitational forces from the Moon and the Sun—is sensitive to the density of the two Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific. These massive regions extend approximately 1,000 kilometres upward from the base of the mantle and their buoyancy remains actively debated within the geophysical community. Here we use tidal tomography to constrain Earth’s deep-mantle buoyancy derived from Global Positioning System (GPS)-based measurements of semi-diurnal body tide deformation. Using a probabilistic approach, we show that across the bottom two-thirds of the two LLSVPs the mean density is about 0.5 per cent higher than the average mantle density across this depth range (that is, its mean buoyancy is minus 0.5 per cent), although this anomaly may be concentrated towards the very base of the mantle. We conclude that the buoyancy of these structures is dominated by the enrichment of high-density chemical components, probably related to subducted oceanic plates or primordial material associated with Earth’s formation. Because the dynamics of the mantle is driven by density variations, our result has important dynamical implications for the stability of the LLSVPs and the long-term evolution of the Earth system.

  19. Modeling of Seismic Anisotropy Near the Hawaiian Mantle Plume

    Science.gov (United States)

    Shen, Chenghao

    Seismic anisotropy, the dependence of velocity on direction, is often induced by mantle flow. Here, I studied the influence of a proposed mantle plume beneath Hawaii on the azimuth dependence of Rayleigh wave phase velocity. I used a two-layer forward modeling code to explore how the orientation of a transversely isotropic Pyrolite mantle model controls the fast direction and strength of azimuthal anisotropy. Two layers are assumed because plate motion of the Pacific plate rearranged about 45 Million years ago. It is thought that the fossil spreading direction was 'frozen' into parts of the lithosphere while the asthenosphere below carries the signature of current mantle flow. Depending on how different the horizontal orientation of Pyrolite is in both layers, the strength of anisotropy can vanish for some frequencies but not others. This can ultimately be used to estimate the thickness of the anisotropic layers and the orientation of Pyrolite. In the second part, I forward-modeled data collected for the Hawaiian PLUME project. At high frequencies, the overall pattern of azimuthal anisotropy follows the fossil spreading direction while this coherency breaks down at low frequencies. I find that anisotropy in the upper lithosphere is largely intact, but the pattern is incoherent in the lower lithosphere and asthenosphere. These results provide strong evidence for the presence of a mantle plume beneath Hawaii.

  20. The lithospheric stress field from joint modeling of lithosphere and mantle circulation using constraints from the latest global tomography models

    Science.gov (United States)

    Wang, X.; Holt, W. E.; Ghosh, A.

    2013-12-01

    An understanding of the lithospheric stress field is important because these stresses are one indication of processes within the Earth's interior. In order to calculate the lithosphere stress field it is necessary to take into account the effects of lithosphere structure and topography along with coupling with 3-D mantle flow. We separate these effects into two parts: (1) contributions from topography and lithosphere structure are calculated by computing the stresses associated with gravitational potential energy (GPE) differences, and (2) stresses associated with mantle tractions are computed using the latest tomography models. The contributions from GPE and tractions are then combined to obtain model estimates of the lithospheric stress field, strain rate field, and surface velocity field. We simultaneously use the World Stress Map, the Global Strain Rate Model, and the No-Net-Rotation (NNR) surface velocity vectors to constrain models. We systematically test the latest global tomography models (SEMum [Lekic and Romanowicz, 2011], S40RTS [Ritsema et al., 2011], and S362ANI_PREM [Kustowski et al., 2008]) and the composite tomography model (SMEAN [Becker and Boschi, 2002]), along with the influence of different mantle radial viscosity models. We find that a coupled model with a weak viscosity channel, sandwiched between a strong lithosphere and strong lower mantle is best able to match the observational constraints, although there is a slight difference in stress field among the different tomography models. There is considerable evidence that the contributions from shallow versus deeper sources vary dramatically over the surface of the globe. We quantify these relative contributions as a function of position on the globe and systematically compare the results of different tomography models. Subduction zones are dominated by the effects of GPE differences, whereas within many of the plate interiors the contributions from mantle flow dominate.

  1. The Taurus-Littrow dark mantle, light mantle, crater cluster, and scarp

    Science.gov (United States)

    Lucchitta, Baerbel K.

    1992-12-01

    The Taurus-Littrow landing site is on the floor of a grabenlike valley that is radial to the Serenitatis Basin; the valley is gently inclined to the east. It is bordered by steep-sided massifs that rise 2 km above the valley floor and form part of the Serenitatis Basin rim. The valley floor is exceptionally dark, and in one place it is overlain by a light-colored mantle apparently derived from the massif to the south. The floor is also peppered by overlapping craters. A scarp, up on the west, transects the valley floor and enters the highlands to the north. Pre- and post-mission analyses of this geological formation are presented.

  2. Seeking the mantle contribution for the formation of giant ore deposits: Contemporaneous alkaline lamproites and carbonatites in the Kalmakyr and Muruntau ore districts, Tienshan, Uzbekistan

    Science.gov (United States)

    Seltmann, Reimar; Choulet, Flavien

    2014-05-01

    The decline in discoveries of ore deposits contrasted by the rising demand for e-tech metals requires the global mining industry to continuously seek innovation in exploration. Unravelling the source of metals is among the crucial questions in exploration targeting and geologists have often had to recourse to indirect determinations based on the nature of the magma conveying the metals. The relative contributions of mantle and crust in metallogenic processes and the origin of the magmas from either shallow or deep mantle are not fully understood in the current models of ore genesis. To help to resolve this dilemma, research must establish the link between anorogenic (within-plate) and orogenic processes by using a holistic approach featuring crustal processes, mantle dynamics and crust-mantle interactions that may contribute to the magma fertilization. To achieve this, our study focuses on indicators for the involvement of deep-mantle intrusions (lamproites, lamprophyres, etc.), which have the potential to encapsulate pristine samples of the mantle (xenoliths) during magma ascent [1,2]. The Tienshan belt hosting many giant ore deposits is quite exemplary for understanding mantle-crust interactions and identifying the nature of mantle contribution to ore systems. Sr-Nd-Hf-Pb isotope systematics on granitoids [3] showed a variation of crustal to mixed signatures, indicating involvement of both older crustal sources and mantle-derived material, but the mantle source is not clearly assessed. As objects for our case study in Uzbekistan we choose the Kalmakyr Cu-Au porphyry deposit (~ 315 Ma; Chatkal-Kurama continental arc of Middle Tienshan) and the Muruntau orogenic Au deposit (~290 Ma, Turkestan-Alai / Kyzylkum accretionary complex of South Tienshan) to investigate the impact of associated alkaline magmas on the ore-bearing intrusions and mineralization. Field observations and geochronological data shed light on the spatial and temporal relationships between the

  3. Time Variations In The Geomagnetic Secular Changes and The Electrical Conductivity of The Lower Mantle

    Science.gov (United States)

    Rotanova, N. M.; Bondar, T. N.; Ivanov, V. V.

    The time series of the geomagnetic field at European observatories and the time series of spherical harmonic coefficients are analyzed for studying the spatial- temporal structure, its features and nature of the 1969-70 and 1989 -90 jerks. The autoregression model of describing SV time series and not V-shaped model is proposed. In this case the jerk is interpreted by the field's additional perturbation against the background of its regular changes. Torsional oscillations and local sources are used for explaining the nature of jerks. The spatial field distribution charts during the jerk are mapped out. Comparison with charts of other variations of long duration is made and the conclusion is drawn about their generation by the same sources. The wavelet-transform of the time series has been done. It allowed to single out the peculiarities coinciding with the jerk epochs. The scalelograms calculated from wavelet-analysis gave the possibility to estimate the jerk duration, the characteris tic time of screening the mantle and the electrical conductivity of the lower mantle.

  4. Mantle ingredients for making the fingerprint of Etna alkaline magmas: implications for shallow partial melting within the complex geodynamic framework of Eastern Sicily

    Science.gov (United States)

    Viccaro, Marco; Zuccarello, Francesco

    2017-09-01

    Mantle ingredients responsible for the signature of Etnean Na- and K-alkaline magmas and their relationships with short-term geochemical changes of the erupted volcanic rocks have been constrained through a partial melting model that considers major, trace elements and water contents in the produced liquids. Characteristics of the Etnean source for alkaline magmas have been supposed similar to those of the mantle accessible at a regional scale, namely below the Hyblean Plateau. The assumption that the Etnean mantle resembles the one beneath the Hyblean Plateau is justified by the large geochemical affinities of the Etnean hawaiites/K-trachybasalts and the Hyblean hawaiites/alkali basalts for what concerns both trace elements and isotope systematics. We have modeled partial melting of a composite source constituted by two rock types, inferred by lithological and geochemical features of the Hyblean xenoliths: 1) a spinel lherzolite bearing metasomatic, hydrous phases and 2) a garnet pyroxenite in form of veins intruded into the spinel lherzolite. The partial melting modeling has been applied to each rock type and the resulting primary liquids have been then mixed in various proportions. These compositions have been compared with some Etnean alkaline magmas of the post ∼60 ka activity, which were firstly re-equilibrated to mantle conditions through mass balance calculations. Our results put into evidence that concentrations of major and trace elements along with the water obtained from the modeling are remarkably comparable with those of Etnean melts re-equilibrated at primary conditions. Different proportions of the spinel lherzolite with variable modal contents of metasomatic phases and of the garnet pyroxenite can therefore account for the signature of a large spectrum of Etnean alkaline magmas and for their geochemical variability through time, emphasizing the crucial role played by compositional small-scale heterogeneity of the source. These heterogeneities are

  5. Grain mantles: The impact on grain evolution and selective extinction

    Science.gov (United States)

    Joseph, Charles L.

    1989-01-01

    Depletion studies are used to infer the presence of mantles and to constrain grain evolutionary models in the diffuse interstellar medium. The presence of these mantles appears to be important in the evolution of the grains inside diffuse as well as dense clouds. In dense clouds where the element-to-element abundances sometimes differ from those found in diffuse clouds, empirical relationships are starting to emerge between gas abundances and various types of peculiar selective extinction. These peculiar extinction curves may be the results of nonvolatile mantle formation on grain cores or may reflect chemical differences due to variations in the intrinsic metalicity from one cloud to another. A simple model of the time evolution of a parcel of gas and dust as observed by the depletion of two elements is presented. Different studies of grain evolution and selective extinction are discussed and compared.

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

    DEFF Research Database (Denmark)

    Guerri, Mattia

    elastic properties and chemical composition taking into account the thermal and pressure effects. I found that even small amounts of H2O have an extremely high impact on the elastic properties of crustal rock. In addition, I show the potential that modifications in the stable mineralogical assemblage have...... be therefore used as a constraint regarding the mantle thermo-chemical structure. In the thesis I highlight the fact that the modelling of the isostatic component of topography is affected by uncertainties large enough to hamper a clear detection of the dynamic effects. Furthermore, residual topography maps...... (obtained as the difference between observed topography and computed isostatic component) and dynamic topography maps (computed through mantle flow modelling), that theoretically should both represent the effect of mantle convection on surface topography, present instead a low correlation coefficient. I...

  7. Mantle Attenuation Estimated from Regional and Teleseismic P-waves of Deep Earthquakes and Surface Explosions

    Science.gov (United States)

    Ichinose, G.; Woods, M.; Dwyer, J.

    2014-03-01

    We estimated the network-averaged mantle attenuation t*(total) of 0.5 s beneath the North Korea test site (NKTS) by use of P-wave spectra and normalized spectral stacks from the 25 May 2009 declared nuclear test (mb 4.5; IDC). This value was checked using P-waves from seven deep (580-600 km) earthquakes (4.8 North Korea. These earthquakes are 200-300 km from the NKTS, within 200 km of the Global Seismic Network seismic station in Mudanjiang, China (MDJ) and the International Monitoring System primary arrays at Ussuriysk, Russia (USRK) and Wonju, Republic of Korea (KSRS). With the deep earthquakes, we split the t*(total) ray path into two segments: a t*(u), that represents the attenuation of the up-going ray from the deep hypocenters to the local-regional receivers, and t*(d), that represents the attenuation along the down-going ray to teleseismic receivers. The sum of t*(u) and t*(d) should be equal to t*(total), because they both share coincident ray paths. We estimated the upper-mantle attenuation t*(u) of 0.1 s at stations MDJ, USRK, and KSRS from individual and stacks of normalized P-wave spectra. We then estimated the average lower-mantle attenuation t*(d) of 0.4 s using stacked teleseismic P-wave spectra. We finally estimated a network average t*(total) of 0.5 s from the stacked teleseismic P-wave spectra from the 2009 nuclear test, which confirms the equality with the sum of t*(u) and t*(d). We included constraints on seismic moment, depth, and radiation pattern by using results from a moment tensor analysis and corner frequencies from modeling of P-wave spectra recorded at local distances. We also avoided finite-faulting effects by excluding earthquakes with complex source time functions. We assumed ω2 source models for earthquakes and explosions. The mantle attenuation beneath the NKTS is clearly different when compared with the network-averaged t* of 0.75 s for the western US and is similar to values of approximately 0.5 s for the Semipalatinsk test site

  8. Mantle flow and dynamic topography associated with slab window opening

    Science.gov (United States)

    Guillaume, Benjamin; Moroni, Monica; Funiciello, Francesca; Martinod, Joseph; Faccenna, Claudio

    2010-05-01

    A slab window is defined as an 'hole' in the subducting lithosphere. In the classical view, slab windows develop where a spreading ridge intersects a subduction zone. The main consequences of this phenomenon are the modifications of the physical, chemical and thermal conditions in the backarc mantle that in turn affect the tectonic and magmatic evolution of the overriding plate. In this work, we perform dynamically self-consistent mantle-scale laboratory models, to evaluate how the opening of a window in the subducting panel influences the geometry and the kinematics of the slab, the mantle circulation pattern and, finally, the overriding plate dynamic topography. The adopted setup consists in a two-layer linearly viscous system simulating the roll-back of a fixed subducting plate (simulated using silicone putty) into the upper mantle (simulated using glucose syrup). Our experimental setting is also characterized by a constant-width rectangular window located at the center of a laterally confined slab, modeling the case of the interaction of a trench-parallel spreading ridge with a wide subduction zone. We find that the geometry and the kinematics of the slab are only minorly affected by the opening of a slab window. On the contrary, slab induced mantle circulation, quantified using Feature Tracking image analysis technique, is strongly modified and produces a peculiar non-isostatic topographic signal on the overriding plate. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compare them to the Patagonian subduction zone finding that anomalous backarc volcanism that developed since middle Miocene could result from the lateral flowage of subslab mantle, and that part of the Patagonian uplift could be dynamically supported.

  9. Understanding the Earth's Mantle Through Advanced Elasticity Measurements

    Science.gov (United States)

    Marquardt, Hauke; Schulze, Kirsten; Kurnosov, Alexander; Buchen, Johannes; Frost, Daniel; Boffa Ballaran, Tiziana; Marquardt, Katharina; Kawazoe, Takaaki

    2017-04-01

    Constraints on the inner structure, chemical and mineralogical composition as well as dynamics of Earth's mantle can be derived through comparison of laboratory elasticity data to seismological observables. A quantitative knowledge of the elastic properties of mantle minerals, and their variations with chemical composition, at pressure and temperature conditions of Earth's mantle is key to construct reliable synthetic mineral physics-based seismic velocity models to be compared to seismic observables. We will discuss results of single-crystal elasticity measurements on Earth mantle minerals that have been conducted using the combined Brillouin scattering and x-ray diffraction (XRD) system at BGI Bayreuth in combination with advanced sample preparation using the focused ion beam (FIB) technique [1] that allows for tailoring sizes and shapes of tiny single-crystals. In our experiments, multiple FIB-prepared single-crystals were loaded in a single sample chamber of a resistively-heated diamond-anvil cell (DAC). The possiblity to measure simultaneously acoustic wave velocities and density (unit-cell parameters) in the DAC in combination with the multi-sample approach facilitates direct quantification of the effects of chemical substitution on the elasticity and seismic wave velocities at non-ambient conditions. Our experimental approach eliminates uncertainties arising from the combination of data collected under (potentially) different conditions in several DAC runs, in different laboratories and/or from using different pressure-temperature sensors. We will present our recent experiments on the elasticity of single-crystal Fe-Al-bearing bridgmanite in the lower mantle and discuss implications for the composition and oxidation state of Earth's lower mantle. We will further discuss our laboratory data on the effects of 'water' and iron on the seismic wave velocities of ringwoodite in Earth's transition zone and outline implications for mapping 'water' in the transition

  10. Nd-Sr-Hf-Pb Isotopic Evidence for a Mantle Plume Origin for the Mafic Rocks from the Palaeotethyan Karakaya Complex, Turkey

    Science.gov (United States)

    Sayit, K.; Hanan, B. B.; Göncüoglu, M.; Furman, T.

    2010-12-01

    The Karakaya Subduction/Accretion Complex consists of various pre-Liassic melange units that record the closing of the Palaeotethys ocean basin. One of these melange units, the Nilufer Unit, is composed of variably metamorphosed (dominantly prehnite-pumpellyite to greenschist facies), mafic rock assemblages that are primarily associated with neritic/pelagic limestones, mudstones and chert. The metabasic rocks are thought to represent oceanic islands/seamounts formed on the Palaeotethyan oceanic crust, fed by a mantle plume. The mafic rocks within the Nilufer Unit have mainly alkaline OIB-type geochemical signature, with marked enrichment in the most incompatible elements, relative to N-MORB. A subset of the mafic rocks are characterized by tholeiitic E-MORB-type signatures. Trace element modelling of elements least effected by metamorphism shows that the mafic rocks have been generated across a source region where garnet- and spinel-facies melts were variably mixed. The Sr isotopic values of the Nilufer mafic rocks are highly variable, indicative of post-magmatic redistribution of Sr and/or Rb. In contrast, the Nd-Hf-Pb systematics provide consistent isotope variations and source affinities in multi-isotope plots. The variations in these rocks cannot be explained solely by a single end-member or binary mixing. Instead, a multi-component mixing between three enriched sources, C-, EM II- and HIMU is required. The modelling suggests an ordered sequence of mixing initially between EM II and HIMU, followed by mixing between the C-like mantle source and the hybrid mantle. In terms of a physical model, the plume may have derived from a heterogeneous deep mantle source, or alternatively, result from the interaction of C-like plume material, upwelling from the margins of the African superplume, with continental lithosphere mantle adjacent to Palaeotethys ocean basin.

  11. Deep long-period earthquakes west of the volcanic arc in Oregon: evidence of serpentine dehydration in the fore-arc mantle wedge

    Science.gov (United States)

    Vidale, John E.; Schmidt, David A.; Malone, Stephen D.; Hotovec-Ellis, Alicia J.; Moran, Seth C.; Creager, Kenneth C.; Houston, Heidi

    2014-01-01

    Here we report on deep long-period earthquakes (DLPs) newly observed in four places in western Oregon. The DLPs are noteworthy for their location within the subduction fore arc: 40–80 km west of the volcanic arc, well above the slab, and near the Moho. These “offset DLPs” occur near the top of the inferred stagnant mantle wedge, which is likely to be serpentinized and cold. The lack of fore-arc DLPs elsewhere along the arc suggests that localized heating may be dehydrating the serpentinized mantle wedge at these latitudes and causing DLPs by dehydration embrittlement. Higher heat flow in this region could be introduced by anomalously hot mantle, associated with the western migration of volcanism across the High Lava Plains of eastern Oregon, entrained in the corner flow proximal to the mantle wedge. Alternatively, fluids rising from the subducting slab through the mantle wedge may be the source of offset DLPs. As far as we know, these are among the first DLPs to be observed in the fore arc of a subduction-zone system.

  12. Iron-rich Oxides at the Core-mantle Boundary

    Science.gov (United States)

    Wicks, J. K.; Jackson, J. M.; Sturhahn, W.; Bower, D. J.; Zhuravlev, K. K.; Prakapenka, V.

    2013-12-01

    Seismic observations near the base of the core-mantle boundary (CMB) have detected 5-20 km thick patches in which the seismic wave velocities are reduced by up to 30%. These ultra-low velocity zones (ULVZs) have been interpreted as aggregates of partially molten material (e.g. Williams and Garnero 1996, Hernlund and Jellinek, 2010) or as solid, iron-enriched residues (e.g. Knittle and Jeanloz, 1991; Mao et al., 2006; Wicks et al., 2010), typically based on proposed sources of velocity reduction. The stabilities of these structure types have been explored through dynamic models that have assembled a relationship between ULVZ stability and density (Hernlund and Tackley, 2007; Bower et al., 2010). Now, to constrain the chemistry and mineralogy of ULVZs, more information is needed on the relationship between density and sound velocity of candidate phases. We present the pressure-volume-temperature equation of state of (Mg0.06 57Fe0.94)O determined up to pressures of 120 GPa and temperatures of 2000 K. Volume was measured with X-ray diffraction at beamline 13-ID-D of the Advanced Photon Source (APS), where high pressures and temperatures are achieved in a diamond anvil cell with in-situ laser heating. Sample assemblies were prepared using dehydrated NaCl as an insulator and neon as a pressure transmitting medium. We present results with and without iron as a buffer and thermal pressure gauge. We have also determined the room temperature Debye velocity (VD) of (Mg0.06 57Fe0.94)O using nuclear resonant inelastic x-ray scattering and in-situ X-ray diffraction, up to 80 GPa at 3-ID-B of the APS. The effect of the electronic environment of the iron sites on the velocities was tracked in-situ using synchrotron Moessbauer spectroscopy. Using our measured equation of state, the seismically relevant compressional (VP) and shear (VS) wave velocities were calculated from the Debye velocities. We combine these studies with a simple mixing model to predict the properties of a solid

  13. Temperature fluctuation of the Iceland mantle plume through time

    OpenAIRE

    Spice, Holly E.; Fitton, John; Kirstein, Linda

    2016-01-01

    The newly developed Al-in-olivine geothermometer was used to find the olivine-Cr-spinel crystallization temperatures of a suite of picrites spanning the spatial and temporal extent of the North Atlantic Igneous Province (NAIP), which is widely considered to be the result of a deep-seated mantle plume. Our data confirm that start-up plumes are associated with a pulse of anomalously hot mantle over a large spatial area before becoming focused into a narrow upwelling. We find that the thermal an...

  14. Crustal Signatures in Mantle Peridotites From Yakutian Kimberlites

    Science.gov (United States)

    Taylor, L. A.; Spetsius, Z.; Wiesli, R.; Anand, M.; Valley, J.

    2002-12-01

    Peridotites and eclogites are considered as the original hosts for diamonds in the mantle. However, it is now generally agreed that these "mantle" eclogites from kimberlites had their origin in the subduction of oceanic crust beneath the major cratons of the world. One of the first indications for such crustal protoliths was from studies of oxygen and carbon isotopes (e.g., Peter Deines and colleagues, Ian McGregor, as well as our group). Indeed, subsequent studies of such rocks have revealed several additional crustal signatures. A possible scenario involves the subduction of an ophiolite sequence, whereby the basaltic and lower mafic components were metamorphosed, devolatilized/partially melted, and otherwise transformed into eclogites. Being within the diamond-stability field, they later experience metasomatic diamond formation. Surprisingly, the closely associated diamondiferous peridotites are considered to be of original mantle origin. We pose the query: What became of the ultramafic portion at the bottom of the crustal sequence? Could this be the origin of at least some of the mantle peridotites? The restricted δ13C values for P-type (peridotitic) diamonds is commonly used as evidence for the mantle origin of peridotites. However, a compilation of δ13C data, published by Peter Deines and our group, for P-type diamonds, mainly from numerous south African pipes, also shows a significant number of values that are well below the mantle field (to -20 \\permil). Fresh, clean garnets were carefully selected from over a hundred peridotites collected from several Yakutian kimberlites. These were subjected to oxygen-isotope analyses by laser-fluorination at the University of Wisconsin. The majority of the δ18O values plot within the accepted mantle value of 5.5+/-0.4 \\permil (Mattey et al., 1994). However, a significant number (~20%) lies outside this window, both above and below. These values are interpreted to represent the effects of both high- and low

  15. Slab Stagnation in the Lower Mantle: A Multidisciplinary Investigation

    Science.gov (United States)

    Waszek, L.; Arredondo, K.; Finkelstein, G. J.; Kellogg, L. H.; Lekic, V.; Li, M.; Lithgow-Bertelloni, C. R.; Romanowicz, B. A.; Schmerr, N. C.; Rudolph, M. L.; Townsend, J. P.; Xing, Z.; Yang, F.

    2014-12-01

    Recent tomographic models show that while many slabs seem to deflect or stagnate at the 660 km discontinuity, some slabs continue to subduct deeper and pond at 1000 km below the earth's surface (Fukao and Obayashi, 2013). Only one slab is observed to penetrate significantly deeper into the mantle. Furthermore, some mantle upwellings also appear to be deflected at 1000 km in depth. The radial correlation functions for the low-order spherical harmonics of most tomographic inversions show that while seismic wave velocities are correlated for all depths below ~1000 km, velocities at depths between 400-1000 km are uncorrelated with velocities at any other depth. This implies that there are large scale velocity features coherent from 1000 km to the core-mantle boundary, but no large scale features coherent from the top of the transition zone down to 1000 km. Seismic studies using precursors and receiver functions find evidence for numerous reflectors in the mid-mantle, ranging from 900 km in depth beneath the southern Pacific and southeast Asia to 1200 km beneath Europe and Japan. This range of depths could indicate topography along a single laterally continuous discontinuity or result from multiple unconnected features. Some reflectors are geographically near, and therefore may be associated with, subducted slabs, however the origin of the others is unclear. The 1000 km 'discontinuity' could potentially be explained by an increase in viscosity or density, such as a compositional difference in the mantle below this depth. We use an interdisciplinary approach to investigate the diversity in apparent slab stagnation behavior and which geophysical mechanisms prevent subduction into the lower mantle. The controlling factor may be a function of the slab itself, including subduction rate, trench rollback, composition, or temperature. Alternatively, bulk mantle properties may control slab penetration. We perform 2D and 3D numerical simulations to determine the influence of

  16. Serpentine and the chemical evolution of the earth's mantle

    Science.gov (United States)

    Ruepke, L.; Phipps Morgan, J.; Hort, M.; Connolly, J.; Ranero, C.

    2003-04-01

    Hydration and dehydration of oceanic lithosphere play an important role in element recycling at convergent margins. Most studies agree that subduction related recycling is necessary to explain some aspects of the mantle's chemical evolution. However, some of these recycling processes are not yet well understood, for example (1) OIB type lavas sometimes show a radiogenic 206Pb/204Pb component commonly termed HIMU whose origin is yet to be exactly determined. (2) What is the fate of rare gases during subduction? Does a previously proposed 'subduction barrier' exist and prevent deep recycling of all rare gases, so that todays atmosphere's content reflects the total of degassed rare gases? Here we explore the potential impact of slab serpentinization and deserpentinization processes on arc-melting and on water, U, Pb, and noble gas recycling into the deep mantle. We examine the consequences of a scenario in which bend-faulting between the outer rise and trench axis creates the conduits for seawater to reach and react with cold lithospheric mantle to serpentinize it. If this process occurs, then the incoming lithosphere will typically contain ˜500m of altered sediments, ˜6km of partially hydrated oceanic crust, and ˜20-55km of partially serpentinized slab mantle. Our thermomechanical modelling implies strong deep recycling (30-90%) of the slab's chemical water, depending upon slab age and subduction rate. Possible global geochemical consequences of this scenario are: 1) At current subduction rates, 0.5-1.5 oceans of water would be recycled past the arc-melting region into the deeper mantle during the past Ga. ) Since 0.3%, 1%, and 3% of the exosphere's Ne, Ar, and Xe are dissolved in the oceans, this implies that at present rates ˜0.02, ˜0.06, and ˜0.2 'atmospheres' of Ne, Ar, and Xe, respectively, would have been recycled into the mantle during the past 4 Ga. These numbers imply that dissolved rare gases were transported at bulk-seawater concentrations during

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

    DEFF Research Database (Denmark)

    Jault, D.; Finlay, Chris

    2015-01-01

    This Chapter focuses on time-dependent uid motions in the core interior, which can beconstrained by observations of the Earth's magnetic eld, on timescales which are shortcompared to the magnetic diusion time. This dynamics is strongly inuenced by the Earth's rapid rotation, which rigidies...... 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...

  18. Penetrative convective flows induced by internal heating and mantle compressibility

    Science.gov (United States)

    Machetel, Philippe; Yuen, David A.

    1989-01-01

    Penetrative convective flows induced in a spherical shell by combined effects of internal heating and mantle compressibility are investigated using mathematical and numerical formulations for compressible spherical shell convection. Isothermal stress-free boundary conditions applied at the top and the bottom of the shell are solved using a time-dependent finite difference code in a temperature, vorticity, stream function formulation for Rayleigh numbers ranging from the critical Rc up to 2000 Rc. Results indicate that compressibility, together with internal heating, could be a mechanism capable of generating spontaneously layered convection and local melting in the mantle and that non-Boussinesq effects must be considered in interpretations of geophysical phenomena.

  19. Sensitivity on Earth core and mantle densities using atmospheric neutrinos

    Energy Technology Data Exchange (ETDEWEB)

    Adrega de Moura, Celio [INFN - Sezione di Napoli, Complesso Universitario di Monte S.Angelo, Via Cinthia, 80126, Napoli (Italy); Pisanti, Ofelia, E-mail: pisanti@na.infn.i [Dipartimento di Scienze Fisiche - Universita di Napoli ' Federico II' , Complesso Universitario di Monte S.Angelo, Via Cinthia, 80126, Napoli (Italy)

    2010-01-01

    Neutrino radiography may provide a tool, alternative to conventional seismic studies, to study the very deep structures of the Earth. The aim of this paper is to assess how well the core and mantle averaged densities can be reconstructed through atmospheric neutrino radiography. We find that about a 2% sensitivity for the mantle and 5% for the core could be achieved for a ten year data taking at an underwater km{sup 3} Neutrino Telescope. This result does not take into account systematics related to the details of the experimental apparatus.

  20. Olivine Crystallization and Mantle Potential Temperatures Beneath Yellowstone

    Science.gov (United States)

    Wonderly, A.; Putirka, K. D.; Atosa, A.; Hurwitz, S.

    2007-12-01

    New basalt samples from the Yellowstone Plateau volcanic field provide evidence for some of the most primitive liquids yet recovered for the region, and yield clues regarding mantle processes. The sample distribution covers a large area and an extended period, and one sample in particular (basalt of Warm River) contains 11% MgO, with olivines that are in equilibrium with the host whole rock. Using olivine thermometry, we calculate both olivine crystallization and mantle potential temperatures (Tp, the temperature a parcel of mantle would have if it rose adiabatically to Earth's surface without melting) to test whether the alleged Yellowstone hot spot is truly hot. These tests make use of thermometers from (1) and (2), and we compare temperatures at Yellowstone with estimates from the Hawaii Scientific Drilling Project, HSDP-2 (2, 3) and the Siqueiros Transform, near the East Pacific Rise (4). Assessment of olivine-liquid equilibrium is based on the Fe-Mg exchange coefficient between olivine and liquid, which is assumed to be 0.30+/-0.03 (5). In total, the Yellowstone lavas have mean crystallization temperatures of 1251+/-41°C (n=79) with a maximum of 1327°C. The mean temperature is similar to crystallization temperatures of basalts from Siqueiros (1264+/-21°C), but lower than the mean temperature for HDSP samples (1343+/-50°C). Mantle potential temperatures appear to approach an olivine-control line, which if valid, yields a mantle potential temperature of 1610°C, slightly higher than most Snake River Plain (SRP) lavas (Tp =1540°C). Applying the same model to lavas from the Siqueiros Transform yields a Tp of 1400°C, and so excess temperatures (relative to MORB) along the SRP are in the range of 140-209°C, consistent with a mantle plume interpretation for the Yellowstone hot spot track. These calculations presume that primitive melts have equilibrated with mantle olivine of Fo90 in composition; given the FeO contents of SRP lavas, parental liquids should

  1. Subduction recycling of continental sediments and the origin of geochemically enriched reservoirs in the deep mantle

    Energy Technology Data Exchange (ETDEWEB)

    Rapp, R.P.; Irifune, T.; Shimizu, N.; Nishiyama, N.; Norman, M.D.; Inoue, T. (Ehime U); (WHOI); (UC); (ANU)

    2008-10-08

    Isotopic and trace element geochemical studies of ocean island basalts (OIBs) have for many years been used to infer the presence of long-lived ({approx} 1-2 Ga old) compositional heterogeneities in the deep mantle related to recycling of crustal lithologies and marine and terrigenous sediments via subduction [e.g., Zindler, A., Hart, S.R., 1986. Chemical geodynamics. Annu. Rev. Earth Planet. Sci. 14, 493-571; Weaver, B.L., 1991. The origin of ocean island basalt end-member compositions: trace element and isotopic constraints. Earth Planet. Sci. Lett. 104, 381-397; Chauvel, C., Hofmann, A.W., Vidal, P., 1992. HIMU-EM: the French Polynesian connection. Earth Planet. Sci. Lett. 110, 99-119; Hofmann, A.W., 1997. Mantle geochemistry: the message from oceanic volcanism. Nature 385, 219-229; Willbold, M., Stracke, A., 2006. Trace element composition of mantle end-members: Implications for recycling of oceanic and upper and lower continental crust. Geochem. Geophys. Geosyst. Q04004. 7, doi:10.1029/2005GC001005]. In particular, models for the EM-1 type ('enriched mantle') OIB reservoir have invoked the presence of subducted, continental-derived sediment to explain high {sup 87}Sr/{sup 86}Sr ratios, low {sup 143}Nd/{sup 144}Nd and {sup 206}Pb/{sup 204}Pb ratios, and extreme enrichments in incompatible elements observed in OIB lavas from, for example, the Pitcairn Island group in the South Pacific [Woodhead, J.D., McCulloch, M.T., 1989; Woodhead, J.D., Devey, C.W., 1993. Geochemistry of the Pitcairn seamounts, I: source character and temporal trends. Earth Planet. Sci. Lett. 116, 81-99; Eisele, J., Sharma, M., Galer, S.J.G., Blichert-Toft, J., Devey, C.W., Hofmann, A.W., 2002. The role of sediment recycling in EM-1 inferred from Os, Pb, Hf, Nd, Sr isotope and trace element systematics of the Pitcairn hotspot. Earth Planet. Sci. Lett. 196, 197-212]. More recently, ultrapotassic, mantle-derived lavas (lamproites) from Gaussberg, Antarctica have been interpreted as

  2. Water, lithium and trace element compositions of olivine from Lanzo South replacive mantle dunites (Western Alps): New constraints into melt migration processes at cold thermal regimes

    Science.gov (United States)

    Sanfilippo, Alessio; Tribuzio, Riccardo; Ottolini, Luisa; Hamada, Morihisa

    2017-10-01

    Replacive mantle dunites are considered to be shallow pathways for extraction of mantle melts from their source region. Dunites offer a unique possibility to unravel the compositional variability of the melts produced in the upper mantle, before mixing and crystal fractionation modify their original signature. This study includes a quantification of H2O, Li and trace elements (Ni, Mn, Co, Sc, V, Ti, Zr, Y and HREE) in olivine from large replacive dunite bodies (>20 m) within a mantle section exposed in the Western Italian Alps (Lanzo South ophiolite). On the basis of olivine, clinopyroxene and spinel compositions, these dunites were previously interpreted to be formed by melts with a MORB signature. Variations in Ni, Mn, Co and Ca contents in olivine from different dunite bodies suggested formation by different melt batches. The variable H2O and Li contents of these olivines agree with this idea. Compared to olivine from residual peridotites and olivine phenocrysts in MORB (both having H2O 1 ppm), the Lanzo South dunite olivine has high H2O (18-40 ppm) and low Li (0.35-0.83 ppm) contents. Geochemical modelling suggests that the dunite-forming melts were produced by low melting degrees of a mixed garnet-pyroxenite-peridotite mantle source, with a contribution of a garnet pyroxenite component variable from 20 to 80%. The Lanzo dunites experienced migration of melts geochemically enriched and mainly produced in the lowermost part of the melting region. Extraction of enriched melts through dunite channels are probably characteristic of cold thermal regimes, where low temperatures and a thick mantle lithosphere inhibit mixing with melts produced at shallower depths.

  3. 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.

  4. Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: role of crystal fractionation and mantle heterogeneity.

    Science.gov (United States)

    Clague, D.A.; Frey, F.A.; Thompson, G.; Rindge, S.

    1981-01-01

    A wide range of rock types (abyssal tholeiite, Fe-Ti-rich basalt, andesite, and rhyodacite) were dredged from near 95oW and 85oW on the Galapagos spreading center. Computer modeling of major element compositions has shown that these rocks could be derived from common parental magmas by successive degrees of fractional crystallization. However, the P2O5/K2O ratio implies distinct mantle source compositions for the two areas. These source regions also have different rare earth element (REE) abundance patterns. The sequence of fractionated lavas differs for the two areas and indicates earlier fractionation of apatite and titanomagnetite in the lavas from 95oW. The mantle source regions for these two areas are interpreted to be depleted in incompatible (and volatile?) elements, although the source region beneath 95oW is less severely depleted in La and K. -Authors

  5. Mapping the mantle transition zone beneath Hawaii from Ps receiver functions: Evidence for a hot plume and cold mantle downwellings

    Science.gov (United States)

    Agius, Matthew R.; Rychert, Catherine A.; Harmon, Nicholas; Laske, Gabi

    2017-09-01

    Hawaii is the archetypal example of hotspot volcanism. Classic plume theory suggests a vertical plume ascent from the core-mantle boundary to the surface. However, recently it has been suggested that the plume path may be more complex. Determining the exact trajectory of the Hawaiian plume seismic anomaly in the mantle has proven challenging. We determine P-to-S (Ps) receiver functions to illuminate the 410- and 660-km depth mantle discontinuities beneath the Hawaiian Islands using waveforms recorded on land and ocean-bottom seismometers, applying new corrections for tilt and coherence to the ocean bottom data. Our 3-D depth-migrated maps provide enhanced lateral resolution of the mantle transition zone discontinuities. The 410 discontinuity is characterised by a deepened area beneath central Hawaii, surrounded by an elevated shoulder. At the 660 discontinuity, shallow topography is located to the north and far south of the islands, and a deep topographic anomaly is located far west and east. The transition zone thickness varies laterally by ±13 km depth: thin beneath north-central Hawaii and thick farther away in a horseshoe-like feature. We infer that at 660-km depth a broad or possibly a double region of upwelling converges into a single plume beneath central Hawaii at 410-km depth. As the plume rises farther, uppermost mantle melting and flow results in the downwelling of cold material, down to at least 410 km surrounding the plume stem. This result in the context of others supports complex plume dynamics including a possible non-vertical plume path and adjacent mantle downwellings.

  6. Long-Term Stability of Plate-Like Behavior Caused by Hydrous Mantle Convection and Water Absorption in the Deep Mantle

    Science.gov (United States)

    Nakagawa, Takashi; Iwamori, Hikaru

    2017-10-01

    We investigate the cycling of water (regassing, dehydration, and degassing) in mantle convection simulations as a function of the strength of the oceanic lithosphere and its influence on the evolution of mantle water content. We also consider pseudo-plastic yielding with a friction coefficient for simulating brittle behavior of the plates and the water-weakening effect of mantle materials. This model can generate long-term plate-like behavior as a consequence of the water-weakening effect of mantle minerals. This finding indicates that water cycling plays an essential role in generating tectonic plates. In vigorous plate motion, the mantle water content rapidly increases by up to approximately 4-5 ocean masses, which we define as the "burst" effect. A burst is related to the mantle temperature and water solubility in the mantle transition zone. When the mantle is efficiently cooled down, the mantle transition zone can store water transported by the subducted slabs that can pass through the "choke point" of water solubility. The onset of the burst effect is strongly dependent on the friction coefficient. The burst effect of the mantle water content could have significantly influenced the evolution of the surface water if the burst started early, in which case the Earth's surface cannot preserve the surface water over the age of the Earth.

  7. Enriched continental flood basalts from depleted mantle melts: modeling the lithospheric contamination of Karoo lavas from Antarctica

    Science.gov (United States)

    Heinonen, Jussi S.; Luttinen, Arto V.; Bohrson, Wendy A.

    2016-01-01

    Continental flood basalts (CFBs) represent large-scale melting events in the Earth's upper mantle and show considerable geochemical heterogeneity that is typically linked to substantial contribution from underlying continental lithosphere. Large-scale partial melting of the cold subcontinental lithospheric mantle and the large amounts of crustal contamination suggested by traditional binary mixing or assimilation-fractional crystallization models are difficult to reconcile with the thermal and compositional characteristics of continental lithosphere, however. The well-exposed CFBs of Vestfjella, western Dronning Maud Land, Antarctica, belong to the Jurassic Karoo large igneous province and provide a prime locality to quantify mass contributions of lithospheric and sublithospheric sources for two reasons: (1) recently discovered CFB dikes show isotopic characteristics akin to mid-ocean ridge basalts, and thus help to constrain asthenospheric parental melt compositions and (2) the well-exposed basaltic lavas have been divided into four different geochemical magma types that exhibit considerable trace element and radiogenic isotope heterogeneity (e.g., initial ɛ Nd from -16 to +2 at 180 Ma). We simulate the geochemical evolution of Vestfjella CFBs using (1) energy-constrained assimilation-fractional crystallization equations that account for heating and partial melting of crustal wall rock and (2) assimilation-fractional crystallization equations for lithospheric mantle contamination by using highly alkaline continental volcanic rocks (i.e., partial melts of mantle lithosphere) as contaminants. Calculations indicate that the different magma types can be produced by just minor (1-15 wt%) contamination of asthenospheric parental magmas by melts from variable lithospheric reservoirs. Our models imply that the role of continental lithosphere as a CFB source component or contaminant may have been overestimated in many cases. Thus, CFBs may represent major juvenile crustal

  8. Profiling the robustness, efficiency and limits of the forward-adjoint method for 3-D mantle convection modelling

    Science.gov (United States)

    Price, M. G.; Davies, J. H.

    2018-02-01

    Knowledge of Earth's past mantle structure is inherently unknown. This lack of knowledge presents problems in many areas of Earth science, including in mantle circulation modelling (MCM). As a mathematical model of mantle convection, MCMs require boundary and initial conditions. While boundary conditions are readily available from sources such as plate reconstructions for the upper surface, and as free slip at the core-mantle boundary, the initial condition is not known. MCMs have historically `created' an initial condition using long `spin up' processes using the oldest available plate reconstruction period available. While these do yield good results when models are run to present day, it is difficult to infer with confidence results from early in a model's history. Techniques to overcome this problem are now being studied in geodynamics, such as by assimilating the known internal structure (e.g. from seismic tomography) of Earth at present day backwards in time. One such method is to use an iterative process known as the forward-adjoint method. While this is an efficient means of solving this inverse problem, it still strains all but the most cutting edge computational systems. In this study we endeavour to profile the effectiveness of this method using synthetic test cases as our known data source. We conclude that savings in terms of computational expense for forward-adjoint models can be achieved by streamlining the time-stepping of the calculation, as well as determining the most efficient method of updating initial conditions in the iterative scheme. Furthermore, we observe that in the models presented, there exists an upper limit on the time interval over which solutions will practically converge, although this limit is likely to be linked to Rayleigh number.

  9. Mantle Wedge formation during Subduction Initiation: evidence from the refertilized base of the Oman ophiolitic mantle

    Science.gov (United States)

    Prigent, C.; Guillot, S.; Agard, P.; Godard, M.; Lemarchand, D.; Ulrich, M.

    2015-12-01

    Although the Oman ophiolite is classically regarded as being the direct analog of oceanic lithosphere created at fast spreading ridges, the geodynamic context of its formation is still highly debated. The other alternative end-member model suggests that this ophiolite entirely formed in a supra-subduction zone setting. The latter one is supported by studies on volcanic sequences whereas studies dealing on the mantle section do not involve a significant influence of subduction processes on its structure and composition. We herein focus on basal peridotites from all along the ophiolite strike in order to decipher and characterize potential fluid/melt transfers relate to subduction processes. Samples were taken across the basal banded unit directly overlying the amphibolitic/granulitic metamorphic sole which represents an accreted part of the lower plate. We carried out a petrological, structural and geochemical study on these rocks and their constitutive minerals. Our results show that basal peridotites range from lherzolites to highly depleted harzburgites in composition. Clinopyroxenes (cpx) display melt impregnation textures and co-crystallized with HT/HP amphiboles (amph), spinels and sulfurs. Major and trace elements of the constitutive minerals indicate that these minerals represent trapped incremental partial melt after hydrous melting. Different cpx-bearing lithologies then result from varying degrees of partial melting and melt extraction. Combined with Boron isotopic data, we demonstrate that fluids responsible for hydrous melting of these ophiolitic basal peridotites are subduction-related, most likely derived from dehydration of the metamorphic sole during its formation in subduction initiation. From these observations and thermal constraints, we interpret the occurrence of these basal lherzolites as representing a freezing front developed by thermal re-equilibration (cooling) during subduction processes: subduction-related hydrous partial melts were

  10. Geochemistry of the mantle beneath the Rodriguez Triple Junction and the South-East Indian Ridge

    Science.gov (United States)

    Michard, A.; Montigny, R.; Schlich, R.

    1986-05-01

    Rare earth element abundances and Sr, Nd. Pb isotope compositions have been measured on zero-age dredge samples from the Rodriguez Triple Junction (RTJ) and the South-East Indian Ridge (SEIR), Along the SEIR. the geochemical "halo" of the St. Paul hot spot has a half-width of about 400 km and the data may be fairly well accounted for by a binary mixing between an Indian MORB-type component ( 87Sr/ 86Sr = 0.7028. 143Nd/ 144Nd = 0.51304. 206Pb/ 204Pb = 17.8) and the plume-type St. Paul component (0.7036, 0.5129, and 18.7 respectively). The alignment of the lead isotope data is particularly good with an apparent age of 1.95 ± 0.13 Ga and Th/U source value of 3.94. One sample dredged on the ridge 60 km southeast of St. Paul bears a definite Kerguelen isotopic signature. The RTJ has distinctive geochemical properties which contrast with those of the adjacent ridge segments. Low 206Pb/ 204Pb ratios which plots to the left of the geochron, rather high 208Pb/ 204Pb and 87Sr/ 87Sr ratios (17.4. 37.4, and 0.7031 respectively), a striking isotopic homogeneity, and variable LREE/HREE fractionation with (La/Sm) N, = 0.3-0.8 make this triple junction an anomalous site. The geochemical properties of the Indian Ocean basats have been examined using a three-component mantle model involving (a) a normal MORB-type source though to represent the depleted upper mantle matrix, (b) an OIB-type source of uncertain parentage (recycled oceanic crust?), and (c) a component with low μ. low Sm/Nd. high Rb/Sr (time-averaged value) which is tentatively assigned to ancient hydrothermal and abyssal sediments recycled in the mantle. The high 208Pb/ 204Pb and 87Sr/ 86Sr ratios typical of the Dupal anomaly are likely due to the widespread distribution of this latter component in the basalt source from this area. including that for MORBs.

  11. Mantle dentine in man--a quantitative microradiographic study.

    Science.gov (United States)

    Herr, P; Holz, J; Baume, L J

    1986-06-01

    50 microradiographs taken in a standardized manner of midsagittal ground sections of teeth of individuals aged 18 to 56 years were densitometrically evaluated along a track passing through enamel, dentine and an aluminium stepwedge. Semi-quantitative analysis of mineral density uniformly showed an irregular platform representing circumpulpal dentine and a peripheral down slope in the region of the amelodentinal junction, representing mantle dentine. The width of this less mineralized peripheral zone measured on densitometric recordings averaged 150 microns (+/- 50). Quantitative analysis of the two dentinal regions permitted the calculation of the mineral content in terms of volume percentage using both a graphic method and an electronic computer method. The sections were also examined by polarized light microscopy which clearly visualized the presence of peripheral mantle dentine. The mean mineral density of circumpulpal dentine was 46% according to both the graphic and the computer methods; mantle dentine yielded means close to 42% according by both methods. The 4% difference in density between circumpulpal dentine and mantle dentine proved to be statistically significant; there was no significant difference between the means obtained graphically and those obtained electronically. The need for further investigation of this region of the amelodentinal junction was stressed.

  12. Upper mantle viscosity and lithospheric thickness under Iceland

    NARCIS (Netherlands)

    Barnhoorn, A.; Wal, W. van der; Drury, M.R.

    2011-01-01

    Deglaciation during the Holocene on Iceland caused uplift due to glacial isostatic adjustment. Relatively low estimates for the upper mantle viscosity and lithospheric thickness result in rapid uplift responses to the deglaciation cycles on Iceland. The relatively high temperatures of the upper

  13. Late Archaean mantle metasomatism below eastern Indian craton ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 113; Issue 4. Late Archaean mantle metasomatism below eastern Indian craton: Evidence from trace elements, REE geochemistry and Sr-Nd-O isotope systematics of ultramafic dykes. Abhijit Roy A Sarkar S Jeyakumar S K Aggrawal M Ebihara H Satoh. Volume ...

  14. Seismic structure of the mantle ; from subduction zone to craton

    NARCIS (Netherlands)

    Kennett, B.L.N.; Hilst, R.D. van der

    1998-01-01

    Seismological techniques have provided much of the currently available information on the internal structure of the Earth, and in particular on the mantle. Early studies revealed the need for an increase in seismic velocity with depth in the Earth, and by 1915 Gutenberg was able to make a good

  15. Project Skippy explores the lithosphere and mantle beneath Australia

    NARCIS (Netherlands)

    Hilst, R.D. van der; Kennett, Brian; Christie, Doug; Grant, John

    1994-01-01

    A new project is probing the seismic structure of the lithosphere and mantle beneath Australia. The Skippy Project, named after the bush kangaroo, exploits Australia's regional seismicity and makes use of recent advances in digital recording technology to collect three-component broadband

  16. Mantle transition zone structure beneath the Canadian Shield

    Science.gov (United States)

    Thompson, D. A.; Helffrich, G. R.; Bastow, I. D.; Kendall, J. M.; Wookey, J.; Eaton, D. W.; Snyder, D. B.

    2010-12-01

    The Canadian Shield is underlain by one of the deepest and most laterally extensive continental roots on the planet. Seismological constraints on the mantle structure beneath the region are presently lacking due to the paucity of stations in this remote area. Presented here is a receiver function study on transition zone structure using data from recently deployed seismic networks from the Hudson Bay region. High resolution images based on high signal-to-noise ratio data show clear arrivals from the 410 km and 660 km discontinuities, revealing remarkably little variation in transition zone structure. Transition zone thickness is close to the global average (averaging 245 km across the study area), and any deviations in Pds arrival time from reference Earth models can be readily explained by upper-mantle velocity structure. The 520 km discontinuity is not a ubiquitous feature, and is only weakly observed in localised areas. These results imply that the Laurentian root is likely confined to the upper-mantle and if any mantle downwelling exists, possibly explaining the existence of Hudson Bay, it is also confined to the upper 400 km. Any thermal perturbations at transition zone depths associated with the existence of the root, whether they be cold downwellings or elevated temperatures due to the insulating effect of the root, are thus either non-existent or below the resolution of the study.

  17. Treatment of older patients with mantle-cell lymphoma

    DEFF Research Database (Denmark)

    Kluin-Nelemans, H C; Hoster, E; Hermine, O

    2012-01-01

    The long-term prognosis for older patients with mantle-cell lymphoma is poor. Chemoimmunotherapy results in low rates of complete remission, and most patients have a relapse. We investigated whether a fludarabine-containing induction regimen improved the complete-remission rate and whether...

  18. Consequences and Resolution of Lunar Lower Mantle Partial Melt

    Science.gov (United States)

    Fuqua, H.; Bremner, P. M.; Diamond, M. R.; Garapic, G.; Lock, S. J.; Mallik, A.; Nishikawa, Y.; Panovska, S.; Shahar, A.; Lognonne, P. H.; Panero, W. R.; Faul, U.; Panning, M. P.; Jimenez-Perez, H.; Schmerr, N. C.; Williams, Q. C.

    2014-12-01

    Existence of a partially molten layer at depth has been proposed to explain the lack of observed farside deep moonquakes, the observation of reflected phases from deep moonquakes, and the dissipation of tidal energy within the lunar interior. However, subsequent models explore the possibility that dissipation due to elevated temperatures alone can explain the observed dissipation factor (Q) and tidal love numbers. We have explored the hypothesis that high titanium melt compositions associated with lunar mantle overturn may sink to the base of the mantle, locally or regionally. We have performed forward calculations varying composition and thickness of layers to evaluate if a partially molten layer at the base of the mantle is well constrained by the observational data. Self-consistent physical parameters are calculated for each compositional model that are then compared against the observed data to determine a subset of permissible models. The data constraints considered by this study include bulk density, moment of inertia, real and imaginary parts of the Love numbers, seismic travel times, and electrical conductivity. Dynamic calculations using ASPECT have also been considered to determine the implications of early lunar mantle convection for the survivability of the partially molten layer. Finally, and as a perspective for a future NASA New Frontiers Geophysical Network, we present 1D synthetic seismograms calculated for each proposed structure of the Moon to investigate the future seismological resolution of these deep lunar structure features. This work was initiated at the CIDER 2014 program.

  19. Mantle transition zone discontinuities beneath the Tien Shan

    Science.gov (United States)

    Yu, Youqiang; Zhao, Dapeng; Lei, Jianshe

    2017-10-01

    To better understand geodynamic processes of intracontinental mountain building, we conduct a systematic investigation of the mantle transition zone (MTZ) beneath the Tien Shan and its surrounding areas using a receiver function method under non-plane wave front assumption. The resulting apparent depths of the 410 km (d410) and 660 km (d660) discontinuities and the MTZ thickness display significant lateral variations. Both the central Tien Shan and the Pamir Plateau are characterized by a thick MTZ, which can be well explained by the existence of lithospheric segments resulted from possible break-off of the subducted slab or lithosphere delamination. A thin MTZ and an obviously depressed d410, which may be induced by asthenosphere upwelling associated with the dropping lithospheric segment, are revealed beneath the Kazakh Shield. Seismic evidence is obtained for the potential existence of lower mantle upwelling beneath the Tarim Basin based on the observed thin MTZ and relatively significant uplift of d660. The subduction of the Kazakh Shield and Tarim lithosphere driven by the India-Eurasia collision possibly plays an essential role in the formation and evolution of the Tien Shan orogenic belt, and the lower mantle upwelling revealed beneath the Tarim Basin may promote the uplift of the Tien Shan by softening the upper mantle.

  20. Treatment of older patients with mantle-cell lymphoma

    NARCIS (Netherlands)

    J.C. Kluin-Nelemans (Hanneke); E. Hoster (Eva); O. Hermine (Olivier); J. Walewski (Jan); M. Trneny (Marek); C.H. Geisler (Christian); S. Stilgenbauer (S.); C. Thieblemont (C.); U. Vehling-Kaiser (U.); J.K. Doorduijn (Jeanette); B. Coiffier (Bertrand); R. Forstpointner (R.); H. Tilly (Herve); L. Kanz (Lothar); P. Feugier (Pierre); M. Szymczyk (M.); M. Hallek (M.); S. Kremers (Stef); G. Lepeu (G.); L. Sanhes (L.); J. Zijlstra (Jose); R. Bouabdallah (Reda); P.J. Lugtenburg (Pieternella); M. Macro; M. Pfreundschuh (Michael); V. Procházka (V.); F. Di Raimondo (F.); V. Ribrag (Vincent); M. Uppenkamp (M.); J.-L. André (Jean-Luc); W. Klapper (Wolfram); W. Hiddemann (Wolfgang); M. Unterhalt (Michael); M. Dreyling (Martin)

    2012-01-01

    textabstractBACKGROUND: The long-term prognosis for older patients with mantle-cell lymphoma is poor. Chemoimmunotherapy results in low rates of complete remission, and most patients have a relapse. We investigated whether a fludarabine-containing induction regimen improved the complete-remission

  1. Treatment of Older Patients with Mantle-Cell Lymphoma

    NARCIS (Netherlands)

    Kluin-Nelemans, H. C.; Hoster, E.; Hermine, O.; Walewski, J.; Trneny, M.; Geisler, C. H.; Stilgenbauer, S.; Thieblemont, C.; Vehling-Kaiser, U.; Doorduijn, J. K.; Coiffier, B.; Forstpointner, R.; Tilly, H.; Kanz, L.; Feugier, P.; Szymczyk, M.; Hallek, M.; Kremers, S.; Lepeu, G.; Sanhes, L.; Zijlstra, J. M.; Bouabdallah, R.; Lugtenburg, P. J.; Macro, M.; Pfreundschuh, M.; Prochazka, V.; Di Raimondo, F.; Ribrag, V.; Uppenkamp, M.; Andre, M.; Klapper, W.; Hiddemann, W.; Unterhalt, M.; Dreyling, M. H.

    2012-01-01

    BACKGROUND The long-term prognosis for older patients with mantle-cell lymphoma is poor. Chemoimmunotherapy results in low rates of complete remission, and most patients have a relapse. We investigated whether a fludarabine-containing induction regimen improved the complete-remission rate and

  2. Mantle structure and tectonic history of SE Asia

    NARCIS (Netherlands)

    Hall, Robert; Spakman, Wim|info:eu-repo/dai/nl/074103164

    2015-01-01

    Seismic travel-time tomography of the mantle under SE Asia reveals patterns of subduction-related seismic P-wave velocity anomalies that are of great value in helping to understand the region's tectonic development. We discuss tomography and tectonic interpretations of an area centred on Indonesia

  3. determination of upper mantle conductivity using quiet day ...

    African Journals Online (AJOL)

    2008-01-18

    Jan 18, 2008 ... produces large lateral variation in electrical conductivity. Keywords: Sq, spherical harmonic analysis, conductivity, ionospheric curtent. And upper mantle. 1 . Introduction. The systematic flow of varying electric current in the part of the earth's upper atmosphere, the ionosphere, give rise to a magnetic field ...

  4. 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.

  5. Mantle electrical conductivity profile of Niger delta region

    Indian Academy of Sciences (India)

    The mantle electrical conductivity-depth profile of the Niger delta region in Nigeria has been determined using solar quiet day ionospheric current (Sq).The magnetometer data obtained in 2010 from geomagnetic stations installed in Lagos by magnetic dataset (MAGDAS) in 2008 and data from magnetometers installed in ...

  6. Dehydrogenation of goethite in Earth’s deep lower mantle

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Qingyang; Kim, Duck Young; Liu, Jin; Meng, Yue; Yang, Liuxiang; Zhang, Dongzhou; Mao, Wendy L.; Mao, Ho-kwang

    2017-01-31

    The cycling of hydrogen influences the structure, composition, and stratification of Earth’s interior. Our recent discovery of pyrite-structured iron peroxide (designated as the P phase) and the formation of the P phase from dehydrogenation of goethite FeO2H implies the separation of the oxygen and hydrogen cycles in the deep lower mantle beneath 1,800 km. Here we further characterize the residual hydrogen, x, in the P-phase FeO2Hx. Using a combination of theoretical simulations and high-pressure–temperature experiments, we calibrated the x dependence of molar volume of the P phase. Within the current range of experimental conditions, we observed a compositional range of P phase of 0.39 < x < 0.81, corresponding to 19–61% dehydrogenation. Increasing temperature and heating time will help release hydrogen and lower x, suggesting that dehydrogenation could be approaching completion at the high-temperature conditions of the lower mantle over extended geological time. Our observations indicate a fundamental change in the mode of hydrogen release from dehydration in the upper mantle to dehydrogenation in the deep lower mantle, thus differentiating the deep hydrogen and hydrous cycles.

  7. Experimental Constraints on the Chemical Differentiation of Mercurys Mantle

    Science.gov (United States)

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

    2015-01-01

    Mercury is known as being the most reduced terrestrial planet with the highest core/mantle ratio. Results from MESSENGER spacecraft have shown that its surface is FeO-poor (2-4 wt%) and S-rich (up to 6-7 wt%), which confirms the reducing nature of its silicate mantle. In addition several features suggest important melting stages of the Mercurian mantle: widespread volcanic deposits on its surface, a high crustal thickness (approximately 10% of the planet's volume) and chemical compositions of its surface suggesting several stages of differentiation and remelting processes. Therefore it is likely that igneous processes like magma ocean crystallization and continuous melting have induced chemical and mineralogical heterogeneities in the Mercurian mantle. The extent and nature of compositional variations produced by partial melting remains poorly constrained for the particular compositions of Mercury (very reducing conditions, low FeO-contents and high sulfur-contents). Melting experiments with bulk Mercury-analogue compositions are scarce and with poorly con-trolled starting compositions. Therefore additional experimental data are needed to better understand the differentiation processes that lead to the observed chemical compositions of Mercury's surface.

  8. Page 1 Crust and mantle studies using magnetic Surveys 583 ...

    Indian Academy of Sciences (India)

    Cosmos 49, the OGO –2, —4, and —6 satellites (for Orbiting Geophysical Observatory,. OGO – 2, — 4 and – 6 are also called POGO, for Polar Orbiting Geophysical. Observatory), and the Magsat satellite were truly useful for studies of the Earth's crust and mantle. Each of these has been used to study the internal field of the ...

  9. Influencing parameters on performance of a mantle heat exchanger ...

    African Journals Online (AJOL)

    Thermal performance of a solar water heater mainly depends on the thermal stratification. Thermal stratification in solar water tanks is essential for a better performance of energy storage systems where these tanks are integrated. In this research work, the performance of a solar water heater with a mantle heat exchanger is ...

  10. 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

  11. Compositional mantle layering revealed by slab stagnation at ~1000-km depth.

    Science.gov (United States)

    Ballmer, Maxim D; Schmerr, Nicholas C; Nakagawa, Takashi; Ritsema, Jeroen

    2015-12-01

    Improved constraints on lower-mantle composition are fundamental to understand the accretion, differentiation, and thermochemical evolution of our planet. Cosmochemical arguments indicate that lower-mantle rocks may be enriched in Si relative to upper-mantle pyrolite, whereas seismic tomography images suggest whole-mantle convection and hence appear to imply efficient mantle mixing. This study reconciles cosmochemical and geophysical constraints using the stagnation of some slab segments at ~1000-km depth as the key observation. Through numerical modeling of subduction, we show that lower-mantle enrichment in intrinsically dense basaltic lithologies can render slabs neutrally buoyant in the uppermost lower mantle. Slab stagnation (at depths of ~660 and ~1000 km) and unimpeded slab sinking to great depths can coexist if the basalt fraction is ~8% higher in the lower mantle than in the upper mantle, equivalent to a lower-mantle Mg/Si of ~1.18. Global-scale geodynamic models demonstrate that such a moderate compositional gradient across the mantle can persist can in the presence of whole-mantle convection.

  12. Robust constraints on average radial lower mantle anisotropy and consequences for composition and texture

    NARCIS (Netherlands)

    de Wit, R. W L; Trampert, J.

    2015-01-01

    Seismic anisotropy has been observed in the upper mantle (<660 km depth) and the lowermost ~150-250 km of the mantle (the D″ region), while the remainder of the lower mantle is believed to be isotropic. Here, we used centre frequencies for spheroidal and toroidal normal modes together with a

  13. Mantle Dynamics Studied with Parameterized Prescription From Mineral Physics Database

    Science.gov (United States)

    Tosi, N.; Yuen, D.; Wentzcovich, R.; deKoker, N.

    2012-04-01

    The incorporation of important thermodynamic and transport properties into mantle convection models has taken a long time for the community to appreciate, even though it was first spurred by the high-pressure experimental work at Mainz a quarter of a century ago and the experimental work at Bayreuth and St. Louis. The two quantities whose effects have yet to be widely appreciated are thermal expansivity α and thermal conductivity k, which are shown to impact mantle dynamics and thermal history in more ways than geoscientists have previously imagined. We have constructed simple parameterization schemes, which are cast analytically for describing α and k over a wide range of temperatures and pressures corresponding to the Earth's mantle. This approach employs the thermodynamics data set drawn from the VLAB at the University of Minnesota based on first-principles density functional theory [1] and also recent laboratory data from the Bayreuth group [2]. Using analytical formulae to determine α and k increases the computational speed of the convection code with respect to employing pre-calculated look-up tables and allows us to sweep out a wide parameter space. Our results, which also incorporate temperature and pressure dependent viscosity show the following prominent features: 1) The temperature-dependence of α is important in the upper mantle. It enhances strongly the rising hot plumes and inhibits the cold downwellings, thus making subduction more difficult for young slabs. 2) The pressure dependence of α is dominant in the lower mantle. It focuses upwellings and speeds them up during their upward rise. 3) The temperature-dependence of the thermal conductivity helps to homogenize the lateral thermal anomalies in cold downwellings and helps to maintain the heat in the upwellings, thus, in concert with alpha, helps to encourage fast hot plumes. 4) The lattice thermal conductivity of post-perovskite plays an important role in heat-transfer in the lower mantle and

  14. The electronic spin state of iron in Earth's mantle

    Science.gov (United States)

    Catalli, K.; Grocholski, B.; Shim, S.

    2011-12-01

    Mg-silicate perovskite and ferropericlase are thought to be the dominant minerals existing in the Earth's lower mantle, making understanding their properties integral for interpretations of seismic and geodynamic models of the mantle. Of specific interest over the past decade is the electronic spin state of iron in these minerals and the effect of spin crossovers on elasticity and transport properties (Badro et al., 2003, 2004, Science). Ferropericlase, the structurally simpler of the two minerals with only one valence state of iron (Fe2+) entering only one crystallographic site, has been shown to undergo a high-spin to low-spin crossover over an extended pressure-temperature range in the mantle. This spin crossover has been found to have a substantial effect on the elasticity of the mineral during the spin transition (e.g., Fei et al., 2007, GRL; Crowhurst et al., 2008, Science; Marquardt et al., 2009, Science). The spin behavior of Mg-silicate, on the other hand, is complicated by the existence of two potential crystallographic sites and two valence states for iron and affected by other chemical variability such as the presence of aluminum. Although controversial, recent studies found Fe2+ remains high-spin in perovskite (e.g., Grocholski et al., 2009, GRL; Bengtson, 2009, GRL), and the presence of Fe2+ has not been found to have any effect on the compressibility of perovskite (Lundin et al., 2008, PEPI). However, Fe3+ in the B site of perovskite has been found to become low spin at mid-lower mantle pressures (Catalli et al., 2010, EPSL), though the nature of the spin transition is likely affected by the presence of aluminum, and at least when in large concentrations, has been found to have a strong effect on compressibility. Here we summarize some of the findings of the last decade on the spin state of iron in Mg-silicate perovskite and ferropericlase under lower mantle conditions and their effects on the mineral properties that are of likely interest to mantle

  15. Global Correlations of Mantle Structure with Crustal Tectonic Regions

    Science.gov (United States)

    Paulson, E.; Jordan, T. H.

    2011-12-01

    Tomographic models of Earth's mantle depend on a priori estimates of crustal elastic structure, but the model prior is usually independent of other structural information about the crust, such as geochronological age and tectonic history. Therefore, the correlation of mantle models with crustal structure can provide powerful insights about the relationship of mantle heterogeneity to lithospheric dynamics and continental evolution. In a meta-analysis of more than 20 whole-mantle tomographic models published by various research groups, we estimate the correlation between upper-mantle seismic structure and crustal tectonic structure by projecting the tomographic models onto the GTR1 global tectonic regionalization. The 5 x 5 degree GTR1 map comprises three continental regions based on generalized tectonic behavior during the Phanerozoic: S (Precambrian shields and platforms), P (Phanerozoic platforms), Q (Phanerozoic orogenic zones); as well as three oceanic regions based on crustal age: A (0-25 Ma), B (25-100 Ma), and C (>100 Ma). We computed shear-velocity perturbation profiles by averaging a tomographic model over each of the six tectonic regions. For each model, we assessed the statistical significance of the inter-regional variations at a fixed depth by computing the intra-regional variance and correlation length. The regionalized velocity profiles of the upper mantle are similar among all of the tomographic models that we analyzed. Within the oceanic regions, the models display a consistent increase of shear velocity with crustal age that remains statistically significant to a depth of 200 km. The oceanic shear-velocity variations are consistent with high-resolution models derived from anisotropic inversions of multi-phase waveform data in localized regions. The profiles for regions S and P show consistent and statistically significant cratonic signatures extending below 300 km depth. In particular, the shear velocity gradients of both regions are distinctly

  16. Global Upper Mantle Azimuthal Anisotropy From Probabilistic Tomography

    Science.gov (United States)

    Beghein, C.; Yuan, K.

    2014-12-01

    The new model of Yuan and Beghein (2013), hereafter YBaniSV13, is the first global model to constrain 3-D azimuthal anisotropy in the deep upper mantle. It is compatible with previous models in the uppermost 200km of the mantle, but also displays 1% anisotropy above, inside, and below the Mantle Transition Zone (MTZ). Another interesting characteristic of this model is the change in fast seismic direction detected, on average, at ~250km depth and at the MTZ boundaries. These results have important consequences for our understanding of mantle deformation and convection patterns in the mantle. It is therefore important to assess the robustness if these features. We already tested that the model does not strongly depend on the reference 1-D mantle model, on the presence of discontinuities in this reference model, or on the crustal model and Moho depth used to calculate the laterally varying partial derivatives. In this work, we apply a model space approach, the Neighborhood Algorithm (NA) of Sambridge (1999), to determine quantitative model uncertainties and parameter trade-offs. First, the NA generates an ensemble of models with a sampling density that increases toward the best fitting regions of the model space, and then performs a Bayesian appraisal of the models obtained that allows us to determine the likelihood of azimuthal anisotropy in different region of Earth's interior. Such approaches have the advantage of sampling the model null-space, and therefore provide more reliable model uncertainties than traditional inverse techniques. We use YBaniSV13 as initial model, and search the model space around it, allowing for large enough deviations to test the robustness of the anisotropy amplitude. We compare results from a model space search based on the chi-square misfit and from a model space search based on the variance reduction, which is another useful measure of data fit that is independent of data uncertainties. Preliminary results for the chi-square driven

  17. Mineralogical constraints on seismic heterogeneities in the mid-mantle

    Science.gov (United States)

    Sanchez-Valle, C.; Bolfan-Casanova, N.; Merkel, S.

    2013-12-01

    Seismic observations show extensive evidence for negative shear wave anomalies of 2 to 6% in the shallow to middle parts of the lower mantle ( 800 to 1850 km depths) in the vicinity of subduction zones [e.g., 1-4]. Although the origin of these anomalies is still under debate, shear softening related to the stishovite (rutile structure) to post-stishovite (CaCl2 structure) in subducted MORB may be a plausible explanation for these features [5], suggesting the presence of unmixed slab remnants in the mid-lower mantle. The broad range of depths over which the heterogeneities span may be related to compositional effects on the phase transition pressure [5,6]. To better deciphering the observed seismic heterogeneities in terms of mineralogy and chemistry, a more detailed evaluation of the seismic properties of deformed stishovite due to mantle flow is required. In this contribution, we present and discuss recent investigations of the effect of texture development on the shear wave velocities of Al-bearing stishovite containing 5wt% of Al2O3, a plausible composition for subducted slabs. Experiments were conducted using synchrotron radial x-ray diffraction and a panoramic diamond anvil cell as deformation apparatus at pressures above 50 GPa. Upon compression, changes in the texture and the strength on Al-Stishovite are observed across the stishovite to post-stishovite transition that strongly modify the mechanical properties of the sample at lower mantle pressures. The results from the deformation experiments were combined with available elasticity data for similar samples [5] to model the effect of texture on the shear wave anisotropy of stishovite at lower mantle conditions. The implications of these mineral physics results for the interpretation of seismic heterogeneities in the mid-mantle and the link with chemical heterogeneities derived for unmixing in the mantle will be discussed. [1] Stunff et al., (1995); [2]Kaneshima and Helffrich (1999); [3] Vinnik et al

  18. Numerical Modeling of Deep Mantle Flow: Thermochemical Convection and Entrainment

    Science.gov (United States)

    Mulyukova, Elvira; Steinberger, Bernhard; Dabrowski, Marcin; Sobolev, Stephan

    2013-04-01

    One of the most robust results from tomographic studies is the existence of two antipodally located Large Low Shear Velocity Provinces (LLSVPs) at the base of the mantle, which appear to be chemically denser than the ambient mantle. Results from reconstruction studies (Torsvik et al., 2006) infer that the LLSVPs are stable, long-lived, and are sampled by deep mantle plumes that rise predominantly from their margins. The origin of the dense material is debated, but generally falls within three categories: (i) a primitive layer that formed during magma ocean crystallization, (ii) accumulation of a dense eclogitic component from the recycled oceanic crust, and (iii) outer core material leaking into the lower mantle. A dense layer underlying a less dense ambient mantle is gravitationally stable. However, the flow due to thermal density variations, i.e. hot rising plumes and cold downwelling slabs, may deform the layer into piles with higher topography. Further deformation may lead to entrainment of the dense layer, its mixing with the ambient material, and even complete homogenisation with the rest of the mantle. The amount of the anomalous LLSVP-material that gets entrained into the rising plumes poses a constraint on the survival time of the LLSVPs, as well as on the plume buoyancy, on the lithospheric uplift associated with plume interaction and geochemical signature of the erupted lavas observed at the Earth's surface. Recent estimates for the plume responsible for the formation of the Siberian Flood Basalts give about 15% of entrained dense recycled oceanic crust, which made the hot mantle plume almost neutrally buoyant (Sobolev et al., 2011). In this numerical study we investigate the mechanics of entrainment of a dense basal layer by convective mantle flow. We observe that the types of flow that promote entrainment of the dense layer are (i) upwelling of the dense layer when it gets heated enough to overcome its stabilizing chemical density anomaly, (ii

  19. Mantle hydrous-fluid interaction with Archaean granite.

    Science.gov (United States)

    Słaby, E.; Martin, H.; Hamada, M.; Śmigielski, M.; Domonik, A.; Götze, J.; Hoefs, J.; Hałas, S.; Simon, K.; Devidal, J.-L.; Moyen, J.-F.; Jayananda, M.

    2012-04-01

    Water content/species in alkali feldspars from late Archaean Closepet igneous bodies as well as growth and re-growth textures, trace element and oxygen isotope composition have been studied (Słaby et al., 2011). Both processes growth and re-growth are deterministic, however they differ showing increasing persistency in element behaviour during interaction with fluids. The re-growth process fertilized domains and didn't change their oxygen-isotope signature. Water speciation showed persistent behaviour during heating at least up to 600oC. Carbonate crystals with mantle isotope signature are associated with the recrystallized feldspar domains. Fluid-affected domains in apatite provide evidence of halide exchange. The data testify that the observed recrystallization was a high-temperature reaction with fertilized, halide-rich H2O-CO2 mantle-derived fluids of high water activity. A wet mantle being able to generate hydrous plumes, which appear to be hotter during the Archean in comparison to the present time is supposed by Shimizu et al. (2001). Usually hot fluids, which can be strongly carbonic, precede asthenospheric mantle upwelling. They are supposed to be parental to most recognized compositions, which can be derived by their immiscible separation into saline aqueous-silicic and carbonatitic members (Klein-BenDavid et al., 2007). The aqueous fractions are halogen-rich with a significant proportion of CO2. Both admixed fractions are supposed to be fertile. The Closepet granite emplaced in a major shear zone that delimitates two different terrains. Generally such shear zones, at many places, are supposed to be rooted deep into the mantle. The drain, that favoured and controlled magma ascent and emplacement, seemed to remain efficient after granite crystallization. In the southern part of the Closepet batholiths an evidence of intensive interaction of a lower crust fluid (of high CO2 activity) is provided by the extensive charnockitization of amphibolite facies (St

  20. Memories of Earth Formation in the Modern Mantle: W Isotopic Composition of Flood Basalt Lavas

    Science.gov (United States)

    Rizo Garza, H. L.; Walker, R. J.; Carlson, R.; Horan, M. F.; Mukhopadhyay, S.; Francis, D.; Jackson, M. G.

    2015-12-01

    Four and a half billion years of geologic activity has overprinted much of the direct evidence for processes involved in Earth's formation and its initial chemical differentiation. Xenon isotopic ratios [1] and 3He/22Ne ratios [2] suggest that heterogeneities formed during Earth's accretion have been preserved to the present time. New opportunities to learn about early Earth history have opened up with the development of analytical techniques that allow high precision analysis of short-lived isotopic systems. The Hf-W system (t½ = 8.9 Ma) is particularly valuable for studying events that occurred during the first ~50 Ma of Solar System history. Here we report new data for ~ 60 Ma Baffin Bay and ~ 120 Ma Ontong Java Plateau lava samples. Both are large igneous provinces that may have sampled a primitive, less degassed deep mantle reservoir that has remained isolated since shortly after Earth formation [3,4]. Three samples analyzed have 182W/184W ratios that are 10 to 48 ppm higher than our terrestrial standard. These excesses in 182W are the highest ever measured in terrestrial rocks, and may reflect 182W ingrowth in an early-formed high Hf/W mantle domain that was produced by magma ocean differentiation [5]. Long and short-lived Sm-Nd systematics in these samples, however, are inconsistent with this hypothesis. The 182W excessses could rather reflect the derivation of these lavas from a mantle reservoir that was isolated from late accretionary additions [6]. The chondritic initial Os isotopic compositions and highly siderophile element abundances of these samples, however, are inconsistent with this interpretation. Tungsten concentrations for the Baffin Bay and Ontong Java Plateau samples range from 23 ppb to 62 ppb, and are negatively correlated with their 182W/184W ratios. We propose that the source reservoirs for these flood basalts likely formed through Hf/W fractionation caused by core-forming events occuring over a protacted time interval during Earth

  1. Investigation of mantle kinematics beneath the Hellenic-subduction zone with teleseismic direct shear waves

    Science.gov (United States)

    Confal, Judith M.; Eken, Tuna; Tilmann, Frederik; Yolsal-Çevikbilen, Seda; Çubuk-Sabuncu, Yeşim; Saygin, Erdinc; Taymaz, Tuncay

    2016-12-01

    The subduction and roll-back of the African plate beneath the Eurasian plate along the arcuate Hellenic trench is the dominant geodynamic process in the Aegean and western Anatolia. Mantle flow and lithospheric kinematics in this region can potentially be understood better by mapping seismic anisotropy. This study uses direct shear-wave splitting measurements based on the Reference Station Technique in the southern Aegean Sea to reveal seismic anisotropy in the mantle. The technique overcomes possible contamination from source-side anisotropy on direct S-wave signals recorded at a station pair by maximizing the correlation between the seismic traces at reference and target stations after correcting the reference stations for known receiver-side anisotropy and the target stations for arbitrary splitting parameters probed via a grid search. We obtained splitting parameters at 35 stations with good-quality S-wave signals extracted from 81 teleseismic events. Employing direct S-waves enabled more stable and reliable splitting measurements than previously possible, based on sparse SKS data at temporary stations, with one to five events for local SKS studies, compared with an average of 12 events for each station in this study. The fast polarization directions mostly show NNE-SSW orientation with splitting time delays between 1.15 s and 1.62 s. Two stations in the west close to the Hellenic Trench and one in the east show N-S oriented fast polarizations. In the back-arc region three stations exhibit NE-SW orientation. The overall fast polarization variations tend to be similar to those obtained from previous SKS splitting studies in the region but indicate a more consistent pattern, most likely due to the usage of a larger number of individual observations in direct S-wave derived splitting measurements. Splitting analysis on direct shear waves typically resulted in larger split time delays compared to previous studies, possibly because S-waves travel along a longer path

  2. Sustaining a global magnetic field on Earth but not Venus with mantle dynamics

    Science.gov (United States)

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

    2016-12-01

    Global magnetic fields strongly affect the atmospheric properties and surface habitability of terrestrial planets. Paleomagnetic evidence indicates that Earth's dynamo has survived for at least 3.5 billion years, whereas spacecraft have failed to detect an internally generated magnetic field at Venus today. Vigorous convection and thus a dynamo may exist if the heat flow across the core/mantle boundary exceeds a critical value that is determined by the available sources and sinks of entropy and whether the core is isentropic and compositionally uniform. Less heat flow is necessary, for example, while Earth's growing inner core provides gravitational energy from the exclusion of light elements. Giant impacts during Earth's violent birth probably homogenized the core and mixed in some lithophile elements like magnesium. Subsequent precipitation of magnesium-bearing minerals perhaps powered the dynamo for billions of years before the nucleation of the inner core. Finding direct evidence that Venus suffered or avoided similar giant impacts would provide a major constraint on the formation of our Solar System. Here we discuss whether mantle dynamics alone explain the lack of a magnetic field at Venus. First, we compute the minimum heat flow required to sustain a dynamo considering all plausible values for uncertain parameters: thermal conductivity of the core, radius of the inner core, and precipitation of lithophile elements. We use a fourth-order, analytic model that was developed for Earth, slightly modified for Venus. Next, we consider the actual cooling rate permitted by different scenarios for mantle dynamics such as catastrophic resurfacing versus continuous evolution in the stagnant-lid regime. We find that the stagnant lid usually suppresses convection even if the core initially contains some lithophile elements and is close to an adiabatic state. Given the large uncertainties, however, we might expect an Earth-like core to generate a magnetic field at Venus if

  3. Persistence of Strong Silica-Enriched Domains in the Earth's Lower Mantle

    Science.gov (United States)

    Ballmer, M.; Houser, C. T.; Hernlund, J. W.; Wentzcovitch, R. M.; Hirose, K.

    2016-12-01

    The composition of the Earth's lower mantle is poorly constrained. Among the major elements, the lower-mantle Mg/Si ratio remains controversial, ranging from upper-mantle "pyrolite" composition (Mg/Si 1.2 1.3) to a "perovskititic" composition similar to primitive chondrites and the Sun's photosphere (Mg/Si 0.9 1.1). Geophysical evidence for deep subduction of lithospheric slabs into the lower mantle implies that whole-mantle convection and mixing may have homogenized the entire mantle. However, previous models did not consider the effect of variable Mg/Si upon the viscosity of lower-mantle rocks. Here we use geodynamical models to show that rocks with Mg/Si smaller than pyrolite can avoid efficient mixing throughout Earth's history owing to an intrinsically high viscosity. We find a new style of whole-mantle convection that consists of viscous cores of "bridgmanite-enriched ancient mantle structures" (BEAMS) in the lower mantle (at 1000 2200 km depth), separated by conduits of relatively weak pyrolitic rocks that circulate between the shallow and deep mantle. The resultant pattern of convection is stable over time-scales longer than the age of the Earth, and sustains significant differences in Mg/Si between the lower and upper mantles. The BEAMS model provides a physical mechanism to explain the hypothesized long-term stability of deep-mantle convection patterns and the geographical fixity of upwelling centers. It can also account for the deflection of upwelling plumes in the uppermost lower mantle, since mantle "wind" is predicted to circulate around BEAMS. Analogously, the BEAMS model can explain why some (but not all) slabs stagnate at 1000 km depth due to large-scale lateral heterogeneity in the lower mantle. The presence of BEAMS in the lower mantle can further account for the inferred "viscosity hill" in the mid mantle, as well as differences in the long-wavelength seismic structure between the shallow and deep mantle. Possibly, organization of mantle wind

  4. The life cycle of continental rifts: Numerical models of plate tectonics and mantle convection.

    Science.gov (United States)

    Ulvrova, Martina; Brune, Sascha; Williams, Simon

    2017-04-01

    Plate tectonic processes and mantle convection form a self-organized system whose surface expression is characterized by repeated Wilson cycles. Conventional numerical models often capture only specific aspects of plate-mantle interaction, due to imposed lateral boundary conditions or simplified rheologies. Here we study continental rift evolution using a 2D spherical annulus geometry that does not require lateral boundary conditions. Instead, continental extension is driven self-consistently by slab pull, basal drag and trench suction forces. We use the numerical code StagYY to solve equations of conservation of mass, momentum and energy and transport of material properties. This code is capable of computing mantle convection with self-consistently generated Earth-like plate tectonics using a pseudo-plastic rheology. Our models involve an incompressible mantle under the Boussinesq approximation with internal heat sources and basal heating. Due to the 2D setup, our models allow for a comparably high resolution of 10 km at the mantle surface and 15 km at the core mantle boundary. Viscosity variations range over 7 orders of magnitude. We find that the causes for rift initiation are often related to subduction dynamics. Some rifts initiate due to increasing slab pull, others because of developing trench suction force, for instance by closure of an intra-oceanic back-arc basin. In agreement with natural settings, our models reproduce rifts forming in both young and old collision zones. Our experiments show that rift dynamics follow a characteristic evolution, which is independent of the specific setting: (1) continental rifts initiate during tens of million of years at low extension rates (few millimetres per year) (2) the extension velocity increases during less than 10 million years up to several tens of millimetres per year. This speed-up takes place before lithospheric break-up and affects the structural architecture of rifted margins. (3) high divergence rates

  5. Reaction between lherzolite and eclogite-derived melts in the upper mantle

    Science.gov (United States)

    Lo Cascio, M.; Liang, Y.

    2007-12-01

    rates, and the time-scale of equilibration. Depending on the style of melt-rock reaction taking place in the mantle, the trace element and isotopic contribution of pyroxenite-derived melts will vary dramatically. During the highP/lowT regime, dissolution of lherzolite will be extremely slow and the pyroxenite-derived melt will react very little with the surrounding mantle, keeping most of its original geochemical signature. As melting of the pyroxenite proceeds, the lack of reaction and infiltration into the peridotite will cause the melt fraction to increase, which could lead to local brittle failure. In order for the pyroxenite-derived melt to reach the base of the lithosphere unaffected by the transport process, a combination of fracturing at highP and flow through pre-existing high-porosity conduits is necessary. Alternatively, extensive re-equilibration will take place, as expected by the lowP/highT regime, and the melt composition will inherit a hybrid signature of both the lherzolite and pyroxenite-derived melts. Using two-phase flow theory applied to a 1\\-D mantle column, we calculated the chromatographic effect that an enriched pyroxenite-derived melt would undergo by reacting with a porous mantle. The model shows that the melt composition leaving the porous column evolves from an initial DMM-derived composition towards a variable U- shape trace element pattern in a spider diagram, depending on depth. Although the exact melt compositions produced by this melting model depends on the source composition, transport properties, and P-T path, we believe these initial results show some of the essential features of melt-rock reaction in the mantle.

  6. Lunar librations due to core-mantle couplings

    Science.gov (United States)

    Rambaux, N.; Bois, E.

    2003-04-01

    We present a study of the dynamical behavior of a molten core inside the Moon related to the mantle by inertial coupling. In order to integrate the lunar core-mantle interaction in a realistic model of the Moon's rotation, we have used our SONYR (acronym of Spin-Orbit N-bodY Relativistic) model of the solar System including the Moon's spin-orbit motion. This model was previously built in accordance with the requirements of the Lunar Laser Ranging observational accuracy. We have extended this model to the spin-orbit couplings of the terrestrial planets in order to compare different dynamical behaviors of core-mantle interactions in these planets (Mercury, Venus, Earth and Mars). Presence of a liquid or melted core inside the Moon has been alleged since a long time and this possibility has been discussed in several papers. In our first model, the lunar core being simply related to the mantle by inertial coupling, it is sufficient to assume a slight differential rotation of the core. Our core-mantle mechanism prove to be adequate to excite the two resonant frequencies of the lunar physical librations, namely 2.9 and 80.1 years. Signature of such a core whith a 1/10 homothetic ratio appears clearly on the proper rotation angle; the amplitude is around 12 mas (milliarcseconds) and its period 2.9 years. According to the chosen value of the lunar nucleus radius R, the resulting amplitudes L for the libration vary as follows~: 10 mas Mercury, the Earth and Mars.

  7. Superweak asthenosphere in light of upper mantle seismic anisotropy

    Science.gov (United States)

    Becker, Thorsten W.

    2017-05-01

    Earth's upper mantle includes a ˜200 km thick asthenosphere underneath the plates where viscosity and seismic velocities are reduced compared to the background. This zone of weakness matters for plate dynamics and may be required for the generation of plate tectonics itself. However, recent seismological and electromagnetic studies indicate strong heterogeneity in thinner layers underneath the plates which, if related to more extreme, global viscosity reductions, may require a revision of our understanding of mantle convection. Here, I use dynamically consistent mantle flow modeling and the constraints provided by azimuthal seismic anisotropy as well as plate motions to explore the effect of a range of global and local viscosity reductions. The fit between mantle flow model predictions and observations of seismic anisotropy is highly sensitive to radial and lateral viscosity variations. I show that moderate suboceanic viscosity reductions, to ˜0.01-0.1 times the upper mantle viscosity, are preferred by the fit to anisotropy and global plate motions, depending on layer thickness. Lower viscosities degrade the fit to azimuthal anisotropy. Localized patches of viscosity reduction, or layers of subducted asthenosphere, however, have only limited additional effects on anisotropy or plate velocities. This indicates that it is unlikely that regional observations of subplate anomalies are both continuous and indicative of dramatic viscosity reduction. Locally, such weak patches may exist and would be detectable by regional anisotropy analysis, for example. However, large-scale plate dynamics are most likely governed by broad continent-ocean asthenospheric viscosity contrasts rather than a thin, possibly high melt fraction layer.

  8. Numerical modelling of volatiles in the deep mantle

    Science.gov (United States)

    Eichheimer, Philipp; Thielmann, Marcel; Golabek, Gregor J.

    2017-04-01

    The transport and storage of water in the mantle significantly affects several material properties of mantle rocks and thus water plays a key role in a variety of geodynamical processes (tectonics, magmatism etc.). The processes driving transport and circulation of H2O in subduction zones remain a debated topic. Geological and seismological observations suggest different inflow mechanisms of water e.g. slab bending, thermal cracking and serpentinization (Faccenda et al., 2009; Korenaga, 2017), followed by dehydration of the slab. On Earth both shallow and steep subduction can be observed (Li et al., 2011). However most previous models (van Keken et al., 2008; Wilson et al., 2014) did not take different dip angles and subduction velocities of slabs into account. To which extent these parameters and processes influence the inflow of water still remains unclear. We present 2D numerical models simulating the influence of the various water inflow mechanisms on the mantle with changing dip angle and subduction velocity of the slab over time. The results are used to make predictions regarding the rheological behavior of the mantle wedge, dehydration regimes and volcanism at the surface. References: van Keken, P. E., et al. A community benchmark for subduction zone modeling. Phys. Earth Planet. Int. 171, 187-197 (2008). Faccenda, M., T.V. Gerya, and L. Burlini. Deep slab hydration induced by bending-related variations in tectonic pressure. Nat. Geosci. 2, 790-793 (2009). Korenaga, J. On the extent of mantle hydration caused by plate bending. Earth Planet. Sci. Lett. 457, 1-9 (2017). Wilson, C. R., et al. Fluid flow in subduction zones: The role of solid rheology and compaction pressure. Earth Planet. Sci. Lett. 401, 261-274 (2014). Li, Z. H., Z. Q. Xu, and T. V. Gerya. Flat versus steep subduction: Contrasting modes for the formation and exhumation of high- to ultrahigh-pressure rocks in continental collision zones. Earth Planet. Sci. Lett. 301, 65-77 (2011).

  9. Mantle cell leukemia as a cause of leukostasis

    Directory of Open Access Journals (Sweden)

    Rappaport E

    2011-04-01

    Full Text Available Daniel Smith1, Christian Cable2, Cary Chisholm1, Walter Linz1, William Koss1, Sheila Dobin1, Edward Rappaport11Department of Pathology, 2Internal Medicine, Scott and White Healthcare/Texas A & M Health Science Center College of Medicine, Temple, TX, USAAbstract: A 72-year-old man was admitted with hypoxemic respiratory distress. Given a white blood cell count of 600 × 109/L and symptoms of leukostasis, emergency leukapheresis was initiated. The white blood cell count immediately after the first leukapheresis was paradoxically increased to over 700 × 109/L. Peripheral blood smear findings showed morphologically immature mononuclear cells and numerous circulating mitotic figures. Initial flow cytometry results showed a lambda light chain-restricted B lymphoid population positive for CD20, CD19, CD5, and FMC-7, and negative for TdT, CD10, CD23, CD34, CD117, and myeloid markers, suggesting classification as a blastoid variant of mantle cell lymphoma in a leukemic phase. Subsequent testing using DNA fluorescence in situ hybridization was positive for t(11;14, confirming the diagnosis of mantle cell leukemia. Although mantle cell lymphoma occasionally transforms or can even present as leukemia (leukocytes >40 × 109/L, it is rare for it to present with such profound leukocytosis and an overwhelming number of pleomorphic/blastoid forms. Although morphology suggested acute lymphoblastic leukemia, a more specific diagnosis of blastoid variant mantle cell lymphoma was obtained in 12 hours by applying complementary techniques of flow cytometry and rapid cytogenetics.Keywords: mantle cell lymphoma, chemotherapy, leukapheresis, lymphocytic leukemia

  10. Deep Mantle Structure As a Reference Frame for Absolute Plate Motions

    Science.gov (United States)

    Torsvik, T. H.; Van Der Voo, R.; Doubrovine, P. V.; Burke, K. C.; Steinberger, B. M.; Domeier, M.

    2014-12-01

    Since the Pangea supercontinent formed some 320 million years ago, the majority of large igneous provinces and diamond-bearing rocks (kimberlites) near Earth's surface can be sourced to plumes erupting from the margins of two large thermochemical reservoirs at the core-mantle boundary. Using this surface to core-mantle boundary correlation to locate continents in longitude and a new iterative approach for defining a paleomagnetic reference frame corrected for true polar wander, we present a model for plate motion back to earliest Paleozoic time (540 Ma). We have identified six phases of slow, oscillatory true polar wander during the Paleozoic. True polar wander rates (<1 Degree/Myr) are compatible to those in the Mesozoic but plate velocities are on average twice as high. We show that a geologically reasonable model that reconstructs continents in longitude in such a way that large igneous provinces and kimberlites are positioned above the plume generation zones at the times of their formation can be successfully applied to the entire Phanerozoic. Our model is a kinematic model for only the continents. The next step in improving it will be developing a model for the entire lithosphere, including synthetic oceanic lithosphere. This is challenging, but we will demonstrate a full-plate model back to the Late Paleozoic (410 Ma).

  11. Mantle flow and oceanic crust formation during the opening of the Tyrrhenian back-arc basin

    Science.gov (United States)

    Magni, Valentina

    2017-04-01

    The formation of the Tyrrhenian back-arc basin occurred through short-lived episodes of fast spreading alternated with periods of slow rifting. I present results from three-dimensional numerical models of laterally varying subduction to explain the mechanism of back-arc basin opening and its episodic spreading behaviour. Moreover, I explore the consequences of this alternation between fast and slow episodes of extension on the production of new oceanic crust in the back-arc basin. Results show that the presence of continental plates (i.e. Africa and Adria) nearby the oceanic subduction of the Ionian slab produces localised deformation within the overriding plate and it is, thus, crucial for the opening of the back-arc basin. Moreover, the occurrence of collision results in the formation of two slab windows at the ocean-continent boundaries, which is in very good agreement with what is observed in the Central Mediterranean, nearby the Calabrian slab. During the evolution of the system the trench velocity shows pulses of fast trench retreat that last a few millions of years. This is associated with episodes of more intense melting of the asthenosphere rising at the back-arc basin. Finally, these three-dimensional models are used to track the mantle flow throughout the model evolution and the source of the mantle melting at the spreading centre.

  12. Upper mantle seismic anisotropy in the intra-continental Kachchh rift zone, Gujarat, India

    Science.gov (United States)

    Mandal, Prantik

    2011-08-01

    Shear wave splitting study of 411 SKS/SKKS phases covering backazimuth range of 13 ° to 305 ° recorded by 12 broadband stations in the Kachchh rift has led to estimates of fast axis orientations and splitting times for 118 good measurements. The average vector mean of fast axis orientation (86 ± 14 °) corresponds to the E-W axis of the Kachchh rift and the delay time (~ 1.6 s) is attributed to the ~ 184 km-thick upper mantle layer with 4% anisotropy. The anisotropic character observed for the Kachchh rift (KR) is comparable to other continental rifts and these are related to the high-temperature, lattice-preferred orientation fabric of olivine, inherited from the mantle flows. The source of the rift-axis parallel anisotropy is traced to the rift-parallel flows within the 76 ± 6 km-thick lithosphere. Additionally, the rift-parallel pockets of partial melts also induce anisotropy within the asthenosphere. Both these are inherited from the plume-lithosphere interaction during the Deccan/Reunion plume episode (~ 65 Ma).

  13. Secular Cooling Rates of the Mantle : Various Influences

    Science.gov (United States)

    Rainey, E.; van den Berg, A. P.; Yuen, D. A.

    2002-12-01

    The history of secular cooling of the mantle is an old important issue, which has been attacked for many years using temperature-dependent viscosity as the primary agent (Tozer, 1972. Phys. Earth Planet. Int., 6, 182-197). In this work we have ventured to look at the impact of variable thermal conductivity on the secular cooling rates predicted by models using just temperature-dependent viscosity. We have found the following salient results. (1) A delayed secular cooling is found as in the constant viscosity models (van den Berg and Yuen, 2002, Earth Planet. Sci. Lett., 199, 403-413, van den Berg et al., 2002, Phys. Earth Planet. Inter., 129, 359-375). We have applied an exponential temperature and pressure dependent viscosity model, using thermal viscosity contrast up to 3000 and fixed presssure viscosity contrast of 100 for this verification. (2) A purely depth-dependent thermal conductivity k(P) cannot catch the destructive effect of temperature dependent conductivity on the negative thermal buoynacy of cold downwellings, driving the convective circulation. These k(P) models also lack feedback physics between time-dependent internal heating and variable thermal conductivity k(T,P), thus stressing the need to use k(T,P) whenever there is a strong source of heat present. (3) Large-differences occur between predictions from 2-D numerical models based on Partial Differential Equations (PDE) and averaged parameterized convection models, formulated using an Ordinary Differential Equation (ODE), within the framework of integrating the nonlinear ODE for the volume average temperature. The ODE results for this comparison are computed using the time series of volume average quantities (viscosity, conductivity) obtained from the 2-D PDE results. The comparison shows that the 1-2 Gyr delay in secular cooling, characteristic for full convection PDE models, is not reproduced in the ODE results from parameterized convection models. The temperature dependence of the ice thermal

  14. Petrogenesis of 3.15 Ga old Banasandra komatiites from the Dharwar craton, India: Implications for early mantle heterogeneity

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    J.M. Maya

    2017-05-01

    Full Text Available Spinifex-textured, magnesian (MgO >25 wt.% komatiites from Mesoarchean Banasandra greenstone belt of the Sargur Group in the Dharwar craton, India were analysed for major and trace elements and 147,146Sm-143,142Nd systematics to constrain age, petrogenesis and to understand the evolution of Archean mantle. Major and trace element ratios such as CaO/Al2O3, Al2O3/TiO2, Gd/Yb, La/Nb and Nb/Y suggest aluminium undepleted to enriched compositional range for these komatiites. The depth of melting is estimated to be varying from 120 to 240 km and trace-element modelling indicates that the mantle source would have undergone multiple episodes of melting prior to the generation of magmas parental to these komatiites. Ten samples of these komatiites together with the published results of four samples from the same belt yield 147Sm-143Nd isochron age of ca. 3.14 Ga with an initial ɛNd(t value of +3.5. High precision measurements of 142Nd/144Nd ratios were carried out for six komatiite samples along with standards AMES and La Jolla. All results are within uncertainties of the terrestrial samples. The absence of 142Nd/144Nd anomaly indicates that the source of these komatiites formed after the extinction of 146Sm, i.e. 4.3 Ga ago. In order to evolve to the high ɛNd(t value of +3.5 by 3.14 Ga the time-integrated ratio of 147Sm/144Nd should be 0.2178 at the minimum. This is higher than the ratios estimated, so far, for mantle during that time. These results indicate at least two events of mantle differentiation starting with the chondritic composition of the mantle. The first event occurred very early at ∼4.53 Ga to create a global early depleted reservoir with superchondritic Sm/Nd ratio. The source of Isua greenstone rocks with positive 142Nd anomaly was depleted during a second differentiation within the life time of 146Sm, i.e. prior to 4.46 Ga. The source mantle of the Banasandra komatiite was a result of a differentiation event that occurred

  15. Mantle inputs to Himalayan anatexis: Insights from petrogenesis of the Miocene Langkazi leucogranite and its dioritic enclaves

    Science.gov (United States)

    Zheng, Yuan-chuan; Hou, Zeng-qian; Fu, Qiang; Zhu, Di-Cheng; Liang, Wei; Xu, Peiyan

    2016-11-01

    Oligocene and Miocene Himalayan anatexis is generally thought to have been induced by intracrustal heating or processes without the involvement of mantle-derived heat and materials, suggesting that the Himalayan leucogranites are typical examples of purely crustal melts. This study focuses on a Miocene leucogranite at Langkazi within the Himalayan orogen, an intrusion that contains a large number of dioritic enclaves. These enclaves have typical igneous textures, contain acicular apatites, and have back-veining structures, quenched margins, and crystallization ages identical to the hosting two-mica granites, indicating that these enclaves are magmatic. Although the enclaves are evolved, the most primitive samples contain high concentrations of MgO (up to 4.3 wt.%), Cr (up to 159 ppm), and Ni (up to 102 ppm), are strongly enriched in large-ion lithophile elements, are depleted in high-field-strength elements, have negative εNd(t) values (-8.6 to -6.1), and have relatively high 87Sr/86Sr(i) values (0.7085-0.7137), suggesting that they were derived from a relatively enriched region of the lithospheric mantle source. Whole-rock geochemical data indicate that the hosting Langkazi leucogranite formed from magmas generated by the partial melting of metapelite material within the High Himalaya crystalline sequence, and these magmas subsequently mixed with mantle-derived melts that are now represented by the Langkazi dioritic enclaves. This indicates that mantle-derived material played an important role in the generation of the Langkazi intrusions. The whole-rock geochemical compositions of samples from the study area also indicate that the primary melts that formed the Langkazi enclaves were significantly contaminated by the relatively juvenile Himalayan lower crustal material, suggesting in turn that these mantle-derived magmas underwent MASH (crustal melting, melt assimilation, magma storage, and homogenization) processes at the base of crust, introducing heat to the

  16. MORB Composition in Intra-transform Spreading Centers: A Key Test of Models of Mantle Flow and Melt Transport

    Science.gov (United States)

    Saal, A. E.; Forsyth, D. W.

    2004-12-01

    Models of mantle flow, melt generation and melt transport predict the composition and volume of melts delivered to the base of the crust in a mid-ocean ridge system. Many models can be tuned to match normal crustal thickness and composition, but they differ in predicting how the system behaves when it is perturbed by a transform fault offset. However, this "transform edge effect" or the pattern of along-axis delivery of melt to the crust within a ridge segment can be obscured by along-axis transport of magma within the crust in dikes or long-lived, continuous magma chambers. The advantage of sampling intra-transform spreading centers is that they provide well-defined locations of upwelling and crustal formation in a perturbed part of the system that does not allow along-axis transport of melt in the crust from other parts of the system. The composition of basalts from these settings can thus provide a critical test of mantle flow and melting models. Basalts from both the Garrett and Siqueiros intra-transform settings on the East Pacific Rise (EPR) have primitive composition with very depleted trace element contents, low ratios of very incompatible to moderately incompatible elements, and (230Th/238U) activity ratios ranging from slightly higher to lower than 1 suggesting that the first incompatible-element-rich melts are missing and only the magma from subsequent, shallower melting of an already depleted mantle reaches the intra-transform spreading centers. We have constructed 3-D models of passive mantle flow and melt driven by dynamic pressure gradients and buoyancy using the specific geometry of these two transform settings to predict the resulting composition. We compare the measured trace element and isotopic composition of both the intra-transform and normal segment lavas to those calculated using our model. To minimize the influence of a heterogeneous source, we chose samples from the 9-10 N EPR and Siqueiros with very similar isotopic composition. In

  17. Does the Spin Transition in Mantle Silicate Perovskite Change the Seismic Properties of the Lower Mantle? (Invited)

    Science.gov (United States)

    Shim, S.; Grocholski, B.; Catalli, K.; Sturhahn, W.; Prakapenka, V.

    2010-12-01

    Recent studies have shown that iron in perovskite and ferropericlase undergoes a spin transition at mantle-related pressures, but it has been unclear if the spin transition can change the seismic properties of the lower mantle. One of the difficulties in experimental studies has been the complex crystal chemistry of perovskite, i.e., Fe2+, Fe3+, and Al in two different cation sites. We have conducted X-ray diffraction and spectroscopy in the laser-heated diamond-anvil cell under quasi-hydrostatic conditions and controlled redox state to measure the properties of perovskite in six different compositions: pure MgSiO3 and MgSiO3 with Fe2+ only (Lundin et al., 2008; Grocholski et al., 2009), Fe3+ only (Catalli et al., 2010), Al only, Fe3+ and Al, and Fe2+, Fe3+, and Al. Because the different compositions were measured using the same experimental setup, our dataset provides an accurate measure of the effects of composition on density (dlnρ/dX) and bulk sound speed (dlnVΦ/dX) through comparison within an internally consistent dataset. Fe2+ remains high spin at least up to 70 GPa and does not change the equation of state of perovskite. Therefore, dlnρ/dX(Fe2+) and dlnVΦ/dX(Fe2+) remain nearly constant throughout the lower mantle. Fe3+ undergoes a gradual spin transition between 0 and 55 GPa in Al-free perovskite and a sharp spin transition at 70 GPa in aluminous perovskite. The spin transition of Fe3+ results in a change in the bulk modulus of perovskite. In aluminous perovskite, Fe3+ induces a volume collapse, similar to ferropericlase, resulting in an increase in density at ~1800 km depth. The spin transition of Fe3+ unlikely results in a seismic discontinuity in the lower mantle, due to its gradual nature and thermal effects. However, Fe3+ makes dlnVΦ more negative by a factor of 3 compared with Fe2+ before its spin transition and makes dlnVΦ comparable to Fe2+ or even positive after the spin transition. Therefore, Fe3+-rich heterogeneities (e.g., basalt) may

  18. Post-orogenic shoshonitic magmas of the Yzerfontein pluton, South Africa: the `smoking gun' of mantle melting and crustal growth during Cape granite genesis?

    Science.gov (United States)

    Clemens, J. D.; Buick, I. S.; Frei, D.; Lana, C.; Villaros, A.

    2017-09-01

    The post-orogenic Yzerfontein pluton, in the Saldania Belt of South Africa was constructed through numerous injections of shoshonitic magmas. Most magma compositions are adequately modelled as products of fractionation, but the monzogranites and syenogranites may have a separate origin. A separate high-Mg mafic series has a less radiogenic mantle source. Fine-grained magmatic enclaves in the intermediate shoshonitic rocks are autoliths. The pluton was emplaced between 533 ± 3 and 537 ± 3 Ma (LA-SF-ICP-MS U-Pb zircon), essentially synchronously with many granitic magmas of the Cape Granite Suite (CGS). Yzerfontein may represent a high-level expression of the mantle heat source that initiated partial melting of the local crust and produced the CGS granitic magmas, late in the Saldanian Orogeny. However, magma mixing is not evident at emplacement level and there are no magmatic kinships with the I-type granitic rocks of the CGS. The mantle wedge is inferred to have been enriched during subduction along the active continental margin. In the late- to post-orogenic phase, the enriched mantle partially melted to produce heterogeneous magma batches, exemplified by those that formed the Yzerfontein pluton, which was further hybridised through minor assimilation of crustal materials. Like Yzerfontein, the small volumes of mafic rocks associated with many batholiths, worldwide, are probably also low-volume, high-level expressions of crustal growth through the emplacement of major amounts of mafic magma into the deep crust.

  19. Signals and noise in magnetic observatory annual means - Mantle conductivity and jerks

    Science.gov (United States)

    McLeod, Malcolm G.

    1992-11-01

    Geomagnetic temporal variations can yield valuable information on the electrical conductivity of earth's mantle and on motion of core fluid. The external-source signal in first differences of magnetic observatory annual means is primarily due to a degree-one spherical harmonic closely aligned with earth's magnetic dipole axis. The transfer function between the electromagnetically induced degree-one internal Gauss coefficient (Schmidt seminormalized) and the inducing degree-one external Gauss coefficient is 0.089 +/- 0.020 with a phase shift of +/- 45 deg for a 2-year period. This transfer function is consistent with a nearly insulating mantle and a highly conducting core for which the theoretical transfer function is 0.082 with no phase shift. The temporal power spectrum for noise in first differences of magnetic observatory annual means is approximately white. Third differences of annual means are primarily noise and degree-one external-source signal; thus, when the degree-one external-source signal is removed from annual means third differences, the rms residuals for a given field component and time interval at a given observatory are a good indicator of noise for the relevant component, observatory, and time interval. These rms residuals were used as weights for construction of spherical harmonic models of geomagnetic secular variation. European secular variation graphs for the 1962-1983 time interval exhibit prominent changes of slope (geomagnetic jerks) in the geomagnetic east component at approximately 1970 and 1978. The jerk of 1970 (but not 1978) is evident on the geomagnetic north and vertical components. The vertical component exhibits additional slope changes at approximately 1966 and 1975.

  20. 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

  1. Secondary Hotspots in the South Pacific as a Result of Mantle Plumelets and Lithospheric Extension?

    Science.gov (United States)

    Koppers, A.; Staudigel, H.; Wijbrans, J.; Pringle, M.

    2003-12-01

    By far the largest number of secondary hotspots (cf. Courtillet et al., 2003) can be found in the "South Pacific Thermal and Isotopic Anomaly" (SOPITA) or "Superswell" region. Its Cretaceous counterpart is preserved in a large range of seamounts and guyots found in the "West Pacific Seamount Province" (WPSP). The seamounts in these regions display very distinct and long-lived isotopic signatures (Staudigel et al., 1991; Koppers et al., 2003) that can be used to combine source region chemistry and seamount geochronology to map out mantle melting anomalies over geological time. These mappings may resolve many important questions regarding the stationary character, continuity and longevity of the melting anomalies in the South Pacific mantle - and its secondary hotspots. Of all secondary hotspots that are currently active in the SOPITA we could identify only two hotspots that appear to be long-lived and that have Cretaceous counterparts in the WPSP. Plate reconstructions show that the "HIMU-type" Southern Wake seamounts may have originated from the Mangaia-Rurutu "hotline" in the Cook-Austral Islands, whereas the "EMI-type" Magellan seamounts may have originated from the Rarotonga hotspot. All other hotspots in the SOPITA and WPSP are short-lived (or intermittently active) as evidenced by the presence of numerous seamount trail "segments" representing no more than 10-40 Myr of volcanism. Our observations violate one or more assumptions of the classical Wilson-Morgan hotspot hypothesis: (1) none of the South Pacific hotspots are continuously active, (2) most are short-lived, (3) some show evidence of hotspot motion, and (4) most of them have poor linear age progressions, if any at all. On top of this we have evidence for volcanism along "hotlines" and the "superposition" of hotspots. The simple and elegant "hotspot" model, therefore, seems insufficient to explain the age distribution and source region characteristics of intra-plate volcanoes in the South Pacific. This

  2. Mantle convection and plate tectonics: toward an integrated physical and chemical theory

    Science.gov (United States)

    Tackley

    2000-06-16

    Plate tectonics and convection of the solid, rocky mantle are responsible for transporting heat out of Earth. However, the physics of plate tectonics is poorly understood; other planets do not exhibit it. Recent seismic evidence for convection and mixing throughout the mantle seems at odds with the chemical composition of erupted magmas requiring the presence of several chemically distinct reservoirs within the mantle. There has been rapid progress on these two problems, with the emergence of the first self-consistent models of plate tectonics and mantle convection, along with new geochemical models that may be consistent with seismic and dynamical constraints on mantle structure.

  3. Petrogenesis of fertile mantle peridotites from the Monte del Estado massif (southwest Puerto Rico): a preserved section of Proto-Caribbean oceanic lithospheric mantle?

    Science.gov (United States)

    Marchesi, Claudio; Jolly, Wayne T.; Lewis, John F.; Garrido, Carlos J.; Proenza, Joaquín. A.; Lidiak, Edward G.

    2010-05-01

    The Monte del Estado massif is the largest and northernmost serpentinized peridotite belt in southwest Puerto Rico. It is mainly composed of spinel lherzolite and minor harzburgite with variable clinopyroxene modal abundances. Mineral and whole rock major and trace element compositions of peridotites coincide with those of fertile abyssal peridotites from mid ocean ridges. Peridotites lost 2-14 wt% of relative MgO and variable amounts of CaO by serpentinization and seafloor weathering. HREE contents in whole rock indicate that the Monte del Estado peridotites are residues after low to moderate degrees (2-15%) of fractional partial melting in the spinel stability field. However, very low LREE/HREE and MREE/HREE in clinopyroxene cannot be explained by melting models of a spinel lherzolite source and support that the Monte del Estado peridotites experienced initial low fractional melting degrees (~ 4%) in the garnet stability field. The relative enrichment of LREE in whole rock is not due to secondary processes but probably reflects the capture of percolating melt fractions along grain boundaries or as microinclusions in minerals, or the presence of exotic micro-phases in the mineral assemblage. We propose that the Monte del Estado peridotite belt represents a section of ancient Proto-Caribbean (Atlantic) lithospheric mantle originated by seafloor spreading between North and South America in the Late Jurassic-Early Cretaceous. This portion of oceanic lithospheric mantle was subsequently trapped in the forearc region of the Greater Antilles paleo-island arc generated by the northward subduction of the Caribbean plate beneath the Proto-Caribbean ocean. Finally, the Monte del Estado peridotites belt was emplaced in the Early Cretaceous probably as result of the change in subduction polarity of the Greater Antilles paleo-island arc without having been significantly modified by subduction processes.

  4. 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.

  5. Crust and upper-mantle seismic anisotropy variations from the coast to inland in central and Southern Mexico

    Science.gov (United States)

    Castellanos, Jorge; Pérez-Campos, Xyoli; Valenzuela, Raúl; Husker, Allen; Ferrari, Luca

    2017-07-01

    Subduction zones are among the most dynamic tectonic environments on Earth. Deformation mechanisms of various scales produce networks of oriented structures and faulting systems that result in a highly anisotropic medium for seismic wave propagation. In this study, we combine shear wave splitting inferred from receiver functions and the results from a previous SKS-wave study to quantify and constrain the vertically averaged shear wave splitting at different depths along the 100-station MesoAmerican Subduction Experiment array. This produces a transect that runs perpendicular to the trench across the flat slab portion of the subduction zone below central and southern Mexico. Strong anisotropy in the continental crust is found below the Trans-Mexican Volcanic Belt (TMVB) and above the source region of slow-slip events. We interpret this as the result of fluid/melt ascent. The upper oceanic crust and the overlying low-velocity zone exhibit highly complex anisotropy, while the oceanic lower crust is relatively homogeneous. Regions of strong oceanic crust anisotropy correlate with previously found low Vp/Vs regions, indicating that the relatively high Vs is an anisotropic effect. Upper-mantle anisotropy in the southern part of the array is in trench-perpendicular direction, consistent with the alignment of type-A olivine and with entrained subslab flow. The fast polarization direction of mantle anisotropy changes to N-S in the north, likely reflecting mantle wedge corner flow perpendicular to the TMVB.

  6. Anisotropy of S wave velocity in the lowermost mantle using broad-band data recorded at Syowa in Antarctica

    Science.gov (United States)

    Usui, Y.; Hiramatsu, Y.; Furumoto, M.; Kanao, M.

    2003-12-01

    We investigate the velocity structure of the lowermost mantle (D") beneath the Antarctic Ocean. We analyze seismograms from 16 deep earthquakes in south Pacific subduction zones from 1990 to 2001 recorded by STS-1 broad-band seismographs at Syowa station in Antarctica. The source-receiver combinations span distances range 85\\deg-95\\deg with associated S waves passing through D" beneath the Antarctic ocean. Differential travel times of split S waves are estimated to be up to 2s, showing that longitudinal components (SV) energy arrives earlier than transverse components (SH) energy. The absence of significant splitting for S waves with turning points more than four hundred kilometers above the core-mantle boundary (CMB) indicates that anisotropy is localized within the D" region. Differential travel times among S, ScS and SKS phases and waveform modeling are used to construct the velocity structure in D". We calculate synthetic waveforms by the Direct Solution Method (DSM: Geller and Ohminato, 1994; Geller and Takeuchi, 1995). SH shows a double arrival at the epicentral distance near 89\\deg. However SV in this range remains a single arrival. Isotropic model_@can not explain these observation. We find that synthetics for transverse isotropic models with SH velocity discontinuity (SYYM model) explain well the observed differential travel times and waveforms. The thickness of the anisotropic zone, where SH wave is faster up to 2.0% than SV wave, estimated to be about 350 km. This study region corresponds to the high velocity region at the lowermost mantle by tomographic studies (Kuo et al., 2000; Masters et al., 2000). This kind of transverse anisotropy correlates with high velocity regions where paleo-slabs may descend into the lower mantle (Kendall and Silver, 1996; Garnero and Lay, 1997). We conclude that these observations may be explained by an anisotropic D" layer and D" layer anisotropy is attributed to the paleo-slab material subducted during 120Myr-180Myr.

  7. Sensitivity analysis of crustal correction and its error propagation to upper mantle residual gravity and density anomalies

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2013-01-01

    mantle gravity anomalies are mainly caused by a heterogeneous density distribution in the uppermost mantle. Additionally, separation of the temperature effects from the residual upper mantle gravity anomalies provides constraints of the density changes due to variations in mantle composition. Given...

  8. Can We Probe the Conductivity of the Lithosphere and Upper Mantle Using Satellite Tidal Magnetic Signals?

    Science.gov (United States)

    Schnepf, N. R.; Kuvshinov, A.; Sabaka, T.

    2015-01-01

    A few studies convincingly demonstrated that the magnetic fields induced by the lunar semidiurnal (M2) ocean flow can be identified in satellite observations. This result encourages using M2 satellite magnetic data to constrain subsurface electrical conductivity in oceanic regions. Traditional satellite-based induction studies using signals of magnetospheric origin are mostly sensitive to conducting structures because of the inductive coupling between primary and induced sources. In contrast, galvanic coupling from the oceanic tidal signal allows for studying less conductive, shallower structures. We perform global 3-D electromagnetic numerical simulations to investigate the sensitivity of M2 signals to conductivity distributions at different depths. The results of our sensitivity analysis suggest it will be promising to use M2 oceanic signals detected at satellite altitude for probing lithospheric and upper mantle conductivity. Our simulations also suggest that M2 seafloor electric and magnetic field data may provide complementary details to better constrain lithospheric conductivity.

  9. The role of eclogite in the mantle heterogeneity at Cape Verde

    DEFF Research Database (Denmark)

    Barker, Abigail Katrine; Holm, Paul Martin; Troll, Valentin R.

    2014-01-01

    The Cape Verde hotspot, like many other Ocean Island Basalt provinces, demonstrates isotopic heterogeneity on a 100–200 km scale. The heterogeneity is represented by the appearance of an EM1-like component at several of the southern islands and with a HIMU-like component present throughout...... have been limited. We apply the minor elements in olivine approach (Sobolev et al. in Nature 434:590–597, 2005; Science, doi:10.1126/science.1138113, 2007), to determine and quantify the contributions of peridotite, pyroxenite and eclogite melts to the mantle heterogeneity observed at Cape Verde. Cores...... of olivine phenocrysts of the Cape Verde volcanics have low Mn/FeO and low Ni*FeO/MgO that deviate from the negative trend of the global array. The global array is defined by mixing between peridotite and pyroxenite, whereas the Cape Verde volcanics indicate contribution of an additional eclogite source...

  10. Lasting mantle scars lead to perennial plate tectonics.

    Science.gov (United States)

    Heron, Philip J; Pysklywec, Russell N; Stephenson, Randell

    2016-06-10

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a 'perennial' phenomenon.

  11. Geoelectromagnetic investigation of the earth’s crust and mantle

    CERN Document Server

    Rokityansky, Igor I

    1982-01-01

    Electrical conductivity is a parameter which characterizes composition and physical state of the Earth's interior. Studies of the state equations of solids at high temperature and pressure indicate that there is a close relation be­ tween the electrical conductivity of rocks and temperature. Therefore, measurements of deep conductivity can provide knowledge of the present state and temperature of the Earth's crust and upper mantle matter. Infor­ mation about the temperature of the Earth's interior in the remote past is derived from heat flow data. Experimental investigation of water-containing rocks has revealed a pronounced increase of electrical conductivity in the temperature range D from 500 to 700 DC which may be attributed to the beginning of fractional melting. Hence, anomalies of electrical conductivity may be helpful in identitying zones of melting and dehydration. The studies of these zones are perspective in the scientific research of the mobile areas of the Earth's crust and upper mantle where t...

  12. Lasting mantle scars lead to perennial plate tectonics

    Science.gov (United States)

    Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

    2016-01-01

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a ‘perennial' phenomenon. PMID:27282541

  13. 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.

  14. Sinking of spherical slablets through a non-Newtonian mantle

    Science.gov (United States)

    Crameri, Fabio; Stegman, Dave; Petersen, Robert; Tackley, Paul

    2014-05-01

    The dominant driving force for plate tectonics is slab pull, in which sinking slabs pull the trailing plate. Forward plate velocities are typically similar in magnitude (7 cm/yr) as estimates for sinking velocities of slabs through the upper mantle. However, these estimates are based on data for slabs that are coherent into the transition zone as well as models that considered the upper mantle to be entirely Newtonian. Dislocation creep in the upper mantle can strongly influence mantle flow, and is likely activated for flow around vertically sinking slabs in the uppermost mantle. Thus, it is possible that in some scenarios, a non-Newtonian mantle will have an influence on plate motions but it is unclear to what degree. To address this question, we investigate how the non-Newtonian rheology modifies the sinking velocities of slablets (spherical, negatively buoyant and highly viscous blobs). The model set-up is similar to a Stokes sphere sinking, but is in 2-D cartesian with temperature-and stress-dependent rheology. For these numerical models, we use the Stag-YY code (e.g., Tackley 2008) and apply a pseudo-free surface using the 'sticky-air' approach (Matsumoto and Tomoda 1983; Schmeling et al, 2008, Crameri et al., 2012). The sinking blob is both highly viscous and compositionally dense, but is the same temperature as the background fluid which eliminates thermal diffusion and associated variations in thermal buoyancy. The model domain is 2x1 or 4x1 and allows enough distance to the sidewalls so that sinking velocities are not influenced by the boundary conditions. We compare our results with those previously obtained for salt diapirs rising through a power-law rheology mantle/crust (Weinberg, 1993; Weinberg and Podladchikov, 1994), which provided both numerical and analytic results. Previous results indicate a speed-up of an order of magnitude is possible. Finally, we then extend the models and analysis to mantle convection systems that include for single

  15. Directions of seismic anisotropy in laboratory models of mantle plumes

    Science.gov (United States)

    Druken, K. A.; Kincaid, C.; Griffiths, R. W.

    2013-07-01

    recent expansion in global seismic anisotropy data provides important new insights about the style of mantle convection. Interpretations of these geophysical measurements rely on complex relationships between mineral physics, seismology, and mantle dynamics. We report on 3-D laboratory experiments using finite strain markers evolving in time-dependent, viscous flow fields to quantify the range in expected anisotropy patterns within buoyant plumes surfacing in a variety of tectonic settings. A surprising result is that laboratory proxies for the olivine fast axis overwhelmingly align tangential to radial outflow in plumes well before reaching the surface. These remarkably robust, and ancient, anisotropy patterns evolve differently in stagnant, translational, and divergent plate tectonic settings and are essentially orthogonal to patterns typically referenced when prospecting for plume signals in seismic data. Results suggest a fundamental change in the mineral physics-seismology-circulation relationship used in accepting or rejecting a plume model.

  16. Hydromagnetic scaling and core-mantle evolution of the Earth, Mars and Moon

    Science.gov (United States)

    Starchenko, Sergey; Pushkarev, Yuriy

    2013-04-01

    For fast rotating planet/moon, we derive hydrodynamic and electromagnetic scaling laws in the limit of negligible molecular diffusivity, viscosity and magnetic diffusivity effects. In the Earth, ancient Mars and Moon magnetic energy dominate over kinetic one and typical magnetic field is proportional to the third root of the buoyancy flux power driving the convection as it was obtained recently via numerical simulations. Besides, here we present new scaling laws for estimation of the long-time magnetic consequences due to different evolution scenarios of core-mantle system. The currently accepted scenario with the inner solid core of the Earth crystallizing from the liquid core provides us with too small value of geomagnetic field during more than 3 billions years after formation of the liquid core. Since this is inconsistent with the available paleomagnetic records we are suggesting another scenario with a solid protocore which occupied almost all the core of just formatted Earth. This protocore is slowly melted under the surface influence of the overheated liquid core. It grows up to its modern size when the solid core is small relic of the protocore. Such protocore concept resolves the problem of the energy source for geodynamo and for plume activity in the mantle. In case of validity of this concept the mantle should be supplemented by silicate material from the protocore with primitive isotope composition of the lead but which can't be the result of the liquid core crystallization. Additional argument to the validity of this concept could be the primitive isotope composition of lead in combination with the primary helium enriched by isotope He-3. Following the currently accepted crystallization concept Martian dynamo should be stopped only when the central solid core occupies almost all the volume of Martian core. So, nowadays the liquid core should be sufficiently smaller than the solid one. That contradicts to all the available models of the Martian interior

  17. The formation of glycine and other complex organic molecules in exploding ice mantles.

    Science.gov (United States)

    Rawlings, J M C; Williams, D A; Viti, S; Cecchi-Pestellini, C; Duley, W W

    2014-01-01

    Complex Organic Molecules (COMs), such as propylene (CH3CHCH2) and the isomers of C2H4O2 are detected in cold molecular clouds (such as TMC-1) with high fractional abundances (Marcelino et al., Astrophys. J., 2007, 665, L127). The formation mechanism for these species is the subject of intense speculation, as is the possibility of the formation of simple amino acids such as glycine (NH2CH2COOH). At typical dark cloud densities, normal interstellar gas-phase chemistries are inefficient, whilst surface chemistry is at best ill defined and does not easily reproduce the abundance ratios observed in the gas phase. Whatever mechanism(s) is/are operating, it/they must be both efficient at converting a significant fraction of the available carbon budget into COMs, and capable of efficiently returning the COMs to the gas phase. In our previous studies we proposed a complementary, alternative mechanism, in which medium- and large-sized molecules are formed by three-body gas kinetic reactions in the warm high density gas phase. This environment exists, for a very short period of time, after the total sublimation of grain ice mantles in transient co-desorption events. In order to drive the process, rapid and efficient mantle sublimation is required and we have proposed that ice mantle 'explosions' can be driven by the catastrophic recombination of trapped hydrogen atoms, and other radicals, in the ice. Repeated cycles of freeze-out and explosion can thus lead to a cumulative molecular enrichment of the interstellar medium. Using existing studies we based our chemical network on simple radical addition, subject to enthalpy and valency restrictions. In this work we have extended the chemistry to include the formation pathways of glycine and other large molecular species that are detected in molecular clouds. We find that the mechanism is capable of explaining the observed molecular abundances and complexity in these sources. We find that the proposed mechanism is easily capable