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Sample records for previously depleted mantle

  1. Mantle depletion and metasomatism recorded in orthopyroxene in highly depleted peridotites

    DEFF Research Database (Denmark)

    Scott, James; Liu, Jingao; Pearson, D. Graham

    2016-01-01

    Although trace element concentrations in clinopyroxene serve as a useful tool for assessing the depletion and enrichment history of mantle peridotites, this is not applicable for peridotites in which the clinopyroxene component has been consumed (~ 25% partial melting). Orthopyroxene persists...

  2. Rapid fish stock depletion in previously unexploited seamounts: the ...

    African Journals Online (AJOL)

    Rapid fish stock depletion in previously unexploited seamounts: the case of Beryx splendens from the Sierra Leone Rise (Gulf of Guinea) ... A spectral analysis and red-noise spectra procedure (REDFIT) algorithm was used to identify the red-noise spectrum from the gaps in the observed time-series of catch per unit effort by ...

  3. Chemical and isotopic evidence for mixing between depleted and enriched mantle, northwestern U.S.A.

    Science.gov (United States)

    Hart, William K.

    1985-01-01

    Combined elemental and Sr, Nd, Pb and O isotopic data for late Cenozoic olivine tholeiite lavas from the northwestern Great Basin indicate derivation from at least two chemically and isotopically distinct mantle source regions with no significant modification by interaction with continental crust. The lack of crustal involvement is a direct reflection of the extensional tectonic environment which favors rapid ascent of magmas, minimal residence time in crustal magma chambers and scattered fissure eruptions. The observed chemical and isotopic variations in the tholeiite suite are attributed to mixing between depleted oceanic type mantle ( 87Sr /86Sr ~ 0.7030 and 143Nd /144Nd ~ 0.51305 ) and old, chemically heterogeneous, isotopically enriched subcontinental mantle ( 87Sr /86Sr ~ 0.7078 and 143Nd /144Nd ~ 0.51233 ). Model incompatible element concentrations suggest strong similarities between the depleted mantle and the mantles beneath normal oceanic ridge segments and back-arc basins and between the enriched mantle and the mantle beneath enriched oceanic ridge segments such as the Azores. Superimposed upon the characteristics derived from the two component mixing model may be the effects of a third mantle source which is identifiable only by its apparent radiogenic 206Pb /204Pb ratios. If present, this third source may reflect a component derived from the downgoing slab of an ancient subduction zone.

  4. Ancient melt depletion overprinted by young carbonatitic metasomatism in the New Zealand lithospheric mantle

    Science.gov (United States)

    Scott, J. M.; Hodgkinson, A.; Palin, J. M.; Waight, T. E.; Van der Meer, Q. H. A.; Cooper, A. F.

    2014-01-01

    Spinel facies dunite, harzburgite, lherzolite and wehrlite mantle xenoliths from a cluster of Miocene volcanoes in southern New Zealand preserve evidence of the complex evolution of the underlying continental mantle lithosphere. Spinel Cr# records melt extraction with some values indicative of near complete removal of clinopyroxene. LREE-enriched, low Ti/Eu and low Al2O3 clinopyroxene and rare F-, LREE-rich apatite indicates subsequent interaction between peridotite and a metasomatising carbonatitic melt. The clearest metasomatic signature occurs in the formerly highly depleted samples because there was little or no pre-existing clinopyroxene to dilute the carbonatite signature. For the same reason, the isotopic character of the metasomatising agent is best observed in the formerly highly depleted peridotites (87Sr/86Sr = 0.7028-0.7031; 143Nd/144Nd = 0.5129; 206Pb/204Pb = 20.2-20.3). These isotope ratios are very close to, but slightly less radiogenic than, the HIMU end-member mantle reservoir. Nd isotope data imply carbonatite metasomatism occurred within the last several hundred million years, with ubiquitous pyroxene core-to-rim Al diffusion zoning indicating that it must pre-date cooling of the lithospheric mantle following Late Cretaceous-Eocene rifting of Zealandia from Gondwana. Metasomatism was significantly younger than ancient Re-depletion ages of ~2 Ga and shows that decoupling of peridotite isotope systems has occurred.

  5. Ultra Depleted Mantle at the Gakkel Ridge Based on Hafnium and Neodymium Isotopes

    Science.gov (United States)

    Salters, V. J.; Dick, H. J.

    2011-12-01

    The Gakkel Ridge is one of the slowest spreading ridge segments in the global ridge system and with some of the thinnest oceanic crust. In some locations there is little or no evidence for volcanic activity and oceanic mantle is directly exposed on the ocean floor. This provides an excellent opportunity to investigate the heterogeneity of the oceanic mantle in situ. We have analyzed a number of peridotites from the western end of the Sparsely Magmatic Zone (3o to 28oE and found highly radiogenic Hf and Nd isotopic composition. All but two samples are more radiogenic in either Nd or Hf than MORB. Four samples lie in the extension of the OIB MORB array with ɛNd up to 23.7 and ɛHf up to 54.6. The remainder of the data falls above the OIB-MORB array and its extension with ɛNd values up to 27.4 and ɛHf values up to 291! These values are the most extreme values measured for oceanic mantle. This data confirms the ultra depleted nature of the Gakkel Ridge mantle proposed by Stracke et al. (2011) and its highly heterogeneous nature as proposed by Liu et al. (2008). Preliminary model ages using the measured trace element concentrations in the clinopyroxene range from 40-700Ma for the Nd isotope system and from 100Ma to 3Ga for the Hf isotope system. These are minimum ages as it assumes no melting during ascent under the Gakkel Ridge. If 2% melting is assumed then the model ages approach the age of the Earth. The Hf and Nd isotopes are best correlated with Sm/Yb whereby high Sm/Yb samples have unradiogenic Hf and Nd. The Cr# of the spinel is relatively low for all the samples (<30), although all samples have a LREE depleted character with YbN between 8 and 3 and LaN between 0.8 and 0.1 (Subscript N stands for C1 normalized). The Gakkel Ridge basalts form the radiogenic Hf-end of the MORB field (S. Goldstein pers.comm.), and although the peridotites are far out of isotopic equilibrium with the basalts Hf-Nd systematics indicates that the peridotites have contributed to the

  6. Inherited Depletion in the Oceanic Mantle: Peridotite Composition and Distribution Along Gakkel Ridge

    Science.gov (United States)

    Hellebrand, E.; Snow, J. E.; Dick, H. J.; von der Handt, A.

    2006-12-01

    depleted on the ocean floor, and not consistent with a spreading-rate dependent F. Most cpx REE patterns are LREE-enriched, one dunite is LREE-depleted, two hzb have hump-shaped cpx REE patterns. The distribution of breccia-hosted spinels (n=113) from Domain D show a similar range (0.50-0.65), confirming that there is no fertile peridotite relict preserved in the locally exposed mantle. These results suggest that low degrees of regional partial melting occurred in domains A, B and parts of C. From A to C, the amount of reactive melt transport seems to increase. The extreme depletion of domain D may be the result of a large-scale reaction with percolating melts. However, this is not consistent with scarcity of axial or off-axis basalts, unless there was highly asymmetrical along-axis melt focussing. The LREE enrichment in the interstitial cpx of the depleted hzb is best explained by diffuse and pervasive percolation of low-F melts from a garnet-pyroxenite source. Importantly, this signature can only be preserved at low F, suggesting that a strong depletion prior to upwelling underneath Gakkel Ridge is required. Depleted 'blobs' in the upper mantle may be present 'everywhere' with different scales and extents of pre- upwelling depletion. Their identification is the combination of ultra-slow spreading, dense sampling and detailed petrologic and geochemical investigations. One consequence is that quantitative partial melting models based on the measured peridotite compositions yield a F relative to DMM, which may not have been the appropriate source.

  7. An Ultra-Depleted Mantle Component in the Ontong Java Plateau Revealed by Major, Trace and Volatile Element Abundances in Olivine-Hosted Melt Inclusions

    Science.gov (United States)

    Jackson, M. G.; Cabral, R. A.; Rose-Koga, E. F.; Koga, K. T.; Price, A. A.; Hauri, E. H.; Michael, P. J.

    2014-12-01

    The Ontong Java Plateau (OJP) represents the most voluminous large igneous province (LIP) preserved in the geologic record. The most voluminous volcanic stages of the OJP—the Kroenke and Kwaimbaita stages, which dominate the accessible portions of the plateau—have relatively flat primitive mantle normalized rare earth element (REE) patterns, or spidergrams. With the exception of relatively small volumes of late-stage melts—referred to as the Singgalo stage—that are characterized by slightly enriched REE spidergrams, the volcanic stages that dominated the eruptive history of the OJP exhibit remarkably homogeneous, flat REE patterns. Here we isolate, for the first time, olivine-hosted melt inclusions from OJP. We show that the melt inclusions have two clear populations defined by having distinct trace element characteristics. The first population has relatively flat trace element patterns that are similar to that observed in whole rock lavas from the most voluminous volcanic stages (Kroenke and Kwaimbaita stages) recorded in the OJP. In contrast, a second group of melt inclusions, referred to as UDM (ultra-depleted melt) inclusions, exhibit strikingly depleted REE spidergrams; these trace element patterns are far more depleted than any previously reported lava from OJP. The UDM have unique trace element signatures that preclude an origin by assimilation of hydrothermally-altered oceanic crust or re-melting the depleted mantle source left over after melt extraction during construction of the OJP. We interpret the new UDM compositions to be the result of melting of a previously unrecognized ultra-depleted component hosted in the OJP mantle source.

  8. Ancient melt depletion overprinted by young carbonatitic metasomatism in the New Zealand lithospheric mantle

    DEFF Research Database (Denmark)

    Scott, James M.; Hodgkinson, A.; Palin, J.M.

    2014-01-01

    Spinel facies dunite, harzburgite, lherzolite and wehrlite mantle xenoliths from a cluster of Miocene volcanoes in southern New Zealand record evidence for the complex evolution of the underlying mantle lithosphere. Spinel Cr# records melt extraction with some values indicative of near complete r...

  9. 186Os/188Os Isotopic Compositions of Peridotites: Constraints on Melt Depletion and Pt/Os Evolution of the Upper Mantle

    Science.gov (United States)

    Chatterjee, R. N.; Lassiter, J. C.

    2014-12-01

    Global correlations between Al2O3 and Pt/Os in mantle peridotites suggest that Pt behaves incompatibly relative to Os during partial melting [c.f., 1]. Because 190Pt decays to 186Os (t1/2 = 468 Ga), correlations between 186Os/188Os and peridotite fertility can be used to constrain the long-term Pt/Os evolution of the depleted mantle and the initial Pt/Os ratio of the primitive upper mantle (PUM). We examined 186Os/188Os in mantle peridotites from continental (Rio Grande Rift/Colorado Plateau) and oceanic (Lena Trough, Hawaiian Islands) settings that span a wide range in fertility (Al2O3 ~0.67-4.42 %) and 187Os/188Os ratios (0.1138-0.1305). The new data define a narrow range in 186Os/188Os (0.1198338 to 0.1198393, 2 SD~24 ppm), placing constraints on long-term Pt/Os variability in the DMM. 186Os/188Os is broadly correlated with indices of melt depletion including spinel Cr#, clinopyroxene Cr#, and clinopyroxene Yb content, consistent with the inferred relative compatibility of Pt and Os during partial melting. Extrapolation of the alumina-186Os/188Os trend to PUM alumina content (~4.5 wt% Al2O3; [2]) suggests a PUM 186Os/188Os of ~0.1198380±15, similar to the 186Os/188Os of H chondrites (~0.1198398±16; [3]). This 186Os/188Os value is consistent with a PUM Pt/Os of 1.8±0.3, similar to Pt/Os values measured in several classes of chondrites (Carbonaceous ~1.9±0.2, Ordinary ~2.0±0.3 and Enstatite ~1.9±0.2; [3]). Whereas ~84% of peridotites worldwide [excluding low-[Os] samples (age). This suggests that much of the observed Pt/Os variability in mantle peridotites is relatively recent. Close agreement between our inferred Pt/OsPUM with previous estimates inferred from chondrites [3] is consistent with the addition of a chondritic late veneer to explain the HSE abundances in the upper mantle. [1] Becker et al., GCA 2006; [2] McDonough et al., Chem Geo 1995; [3] Brandon et al., GCA 2006

  10. Tracking the Depleted Mantle Signature in Melt Inclusions and Residual Glass of Basaltic Martian Shergottites using Secondary Ionization Mass Spectrometry

    Science.gov (United States)

    Peters, Timothy J.; Simon, Justin I.; Jones, John H.; Usui, Tomohiro; Economos, Rita C.; Schmitt, Axel K.; McKeegan, Kevin D.

    2013-01-01

    Trace element abundances of depleted shergottite magmas recorded by olivine-hosted melt inclusions (MI) and interstitial mesostasis glass were measured using the Cameca ims-1270 ion microprobe. Two meteorites: Tissint, an olivine-­phyric basaltic shergottite which fell over Morocco July 18th 2001; and the Antarctic meteorite Yamato 980459 (Y98), an olivine-phyric basaltic shergottite with abundant glassy mesostasis have been studied. Chondrite-­normalized REE patterns for MI in Tissint and Y98 are characteristically LREE depleted and, within analytical uncertainty, parallel those of their respective whole rock composition; supporting each meteorite to represent a melt composition that has experienced closed-­system crystallization. REE profiles for mesostasis glass in Y98 lie about an order of magnitude higher than those from the MI; with REE profiles for Tissint MI falling in between. Y98 MI have the highest average Sm/Nd and Y/Ce ratios, reflecting their LREE depletion and further supporting Y98 as one of our best samples to probe the depleted shergotitte mantle. In general, Zr/Nb ratios overlap between Y98 and Tissint MI, Ce/Nb ratios overlap between Y98 MI and mesostasis glass, and Sm/Nd ratios overlap between Y98 mesostasis glass and Tissint MI. These features support similar sources for both, but with subtle geochemical differences that may reflect different melting conditions or fractionation paths during ascent from the mantle. Interestingly, the REE patterns for both Y98 bulk and MI analyses display a flattening of the LREE that suggests a crustal contribution to the Y98 parent melt. This observation has important implications for the origins of depleted and enriched shergottites.

  11. Synchronous development of breast cancer and chest wall fibrosarcoma after previous mantle radiation for Hodgkin's disease

    International Nuclear Information System (INIS)

    Patlas, Michael; McCready, David; Kulkarni, Supriya; Dill-Macky, Marcus J.

    2005-01-01

    Survivors of Hodgkin's disease are at increased risk of developing a second malignant neoplasm, including breast carcinoma and sarcoma. We report the first case of synchronous development of chest wall fibrosarcoma and breast carcinoma after mantle radiotherapy for Hodgkin's disease. Mammographic, sonographic and MR features are demonstrated. (orig.)

  12. Behaviour of Platinum-group elements in the subcontinental mantle of eastern Australia during variable metasomatism and melt depletion

    Science.gov (United States)

    Handler, Monica R.; Bennett, Victoria C.

    1999-11-01

    Increasing recognition of complexities in the Platinum-group element (PGE) and Re concentration patterns in mantle samples are challenging the view of chondritic relative abundances in the upper mantle. To investigate the possible causes of PGE abundance variations, a suite of east Australian, mantle-derived, spinel peridotite xenoliths, ranging from fertile lherzolites to depleted harzburgites, and including apatite ± phlogopite ± amphibole bearing samples, have been analysed for their whole rock PGE and Re abundances. Whole rock abundances for 21 samples, combined with mineral separate analyses of 2 xenoliths, are presented to constrain the distribution of the PGEs and Re, their inherent heterogeneity at difference scales, and their behaviour during both melt extraction and metasomatism. Fertile (>2.9 wt% Al 2O 3) xenoliths have broadly chondritic relative PGE abundances, with the significant exception of positive Rh anomalies and variable negative Os anomalies. The high Rh abundances cannot be attributed to melt extraction or metasomatism. Bulk mineral separate PGE-Re analyses of 2 fertile xenoliths indicate less than 6% of the whole rock PGE budget resides in either silicate or oxide (spinel) phases. The remainder of the PGEs, and at least 80% of the whole rock Re budget, are sited in acid-leachable sulfides and less soluble trace phases such as PGE-sulfides or alloys. Individual PGEs partition into different trace phases resulting in small scale heterogeneity of both PGE ratios and concentrations on the order of 8%-20%. Although these trace phases may be present within the mantle, it is more likely at least some exsolved from monosulfide solid solutions at low temperatures. Ir and Rh abundances are consistent with compatible behaviour during melt extraction, whereas Ru, Pt and Pd abundances are consistent with slightly incompatible behaviour and can be modeled by assuming all reside in sulfides within the mantle, with D sulfRu ˜ D sulfPt > D sulf

  13. Synchronous development of breast cancer and chest wall fibrosarcoma after previous mantle radiation for Hodgkin's disease

    Energy Technology Data Exchange (ETDEWEB)

    Patlas, Michael [Hamilton General Hospital, Department of Radiology, Hamilton, ON (Canada); McCready, David [University Health Network and Mount Sinai Hospital, Department of Surgery, Toronto, ON (Canada); Kulkarni, Supriya; Dill-Macky, Marcus J. [University Health Network and Mount Sinai Hospital, Department of Medical Imaging, Toronto, ON (Canada)

    2005-09-01

    Survivors of Hodgkin's disease are at increased risk of developing a second malignant neoplasm, including breast carcinoma and sarcoma. We report the first case of synchronous development of chest wall fibrosarcoma and breast carcinoma after mantle radiotherapy for Hodgkin's disease. Mammographic, sonographic and MR features are demonstrated. (orig.)

  14. Dynamical geochemistry of the mantle

    Directory of Open Access Journals (Sweden)

    G. F. Davies

    2011-09-01

    oceanic crust. Residence times in D" are longer, so the hybrid pyroxenite there would be less degassed. Plumes would sample both the degassed, enriched old oceanic crust and the gassy, less enriched hybrid pyroxenite and deliver them to OIBs. These findings can account quantitatively for the main He, Ne and Ar isotopic observations.

    It has been commonly inferred that the MORB source is strongly depleted of incompatible elements. However it has recently been argued that conventional estimates of the MORB source composition fail to take full account of mantle heterogeneity, and in particular focus on an ill-defined "depleted" mantle component while neglecting less common enriched components. Previous estimates have also been tied to the composition of peridotites, but these probably do not reflect the full complement of incompatible elements in the heterogeneous mantle. New estimates that account for enriched mantle components suggest the MORB source complement of incompatibles could be as much as 50–100 % larger than previous estimates.

    A major difficulty has been the inference that mass balances of incompatible trace elements could only be satisfied if there is a deep enriched layer in the mantle, but the Earth's topography precludes such a layer. The difficulty might be resolved if either the Earth is depleted relative to chondritic or the MORB source is less depleted than previous estimates. Together these factors can certainly resolve the mass balance difficulties.

  15. Depleted subcontinental lithospheric mantle and its tholeiitic melt metasomatism beneath NE termination of the Eger Rift (Europe): the case study of the Steinberg (Upper Lusatia, SE Germany) xenoliths

    Science.gov (United States)

    Kukuła, Anna; Puziewicz, Jacek; Matusiak-Małek, Magdalena; Ntaflos, Theodoros; Büchner, Jörg; Tietz, Olaf

    2015-12-01

    The ca. 30 Ma Steinberg basanite occurs at the NE termination of the Eger (Ohře) Rift in the NW Bohemian Massif, Central Europe, and belongs to the Cenozoic alkaline Central European Volcanic Province. The basanite hosts a suite of mantle xenoliths, most of which are harzburgites containing relatively magnesian olivine (Fo 90.5-91.6) and Al-poor (0.04-0.13 a pfu) orthopyroxene (mg# 0.90-0.92). Some of these harzburgites also contain volumetrically minor clinopyroxene (mg# 0.92-0.95, Al 0.03-0.13 a pfu) and have U-shaped LREE-enriched REE patterns. The Steinberg harzburgites are typical for the Lower Silesian - Upper Lusatian domain of the European subcontinental lithospheric mantle. They represent residual mantle that has undergone extensive partial melting and was subsequently affected by mantle metasomatism by mixed carbonatite-silicate melts. The Steinberg xenolith suite comprises also dunitic xenoliths affected by metasomatism by melt similar to the host basanite, which lowered the Fo content in olivine to 87.6 %. This metasomatism happened shortly before xenolith entrainment in the erupting lava. One of the xenoliths is a wehrlite (olivine Fo 73 %, clinopyroxene mg# 0.83-0.85, subordinate orthopyroxene mg# 0.76-0.77). Its clinopyroxene REE pattern is flat and slightly LREE-depleted. This wehrlite is considered to be a tholeiitic cumulate. One of the studied harzburgites contains clinopyroxene with similar trace element contents to those in wehrlite. This type of clinopyroxene records percolation of tholeiitic melt through harzburgite. The tholeiitic melt might be similar to Cenozoic continental tholeiites occurring in the Central European Volcanic Province (e.g., Vogelsberg, Germany).

  16. Depletion, cryptic metasomatism, and modal metasomatism of central European lithospheric mantle: evidence from elemental and Li isotope compositions of spinel peridotite xenoliths, Kozákov volcano, Czech Republic

    Science.gov (United States)

    Medaris, L. Gordon; Ackerman, Lukáš; Jelínek, Emil; Magna, Tomáš

    2015-11-01

    Spinel peridotite xenoliths in 4.1 Ma basanite lava at Kozákov volcano vary in equilibration temperature from 675 to 1,135 °C and provide a continuous sample of lithospheric mantle from the Moho to a depth of ~82 km. The sub-Kozákov mantle is layered, consisting of an upper equigranular layer (UEL) from 32 to 45 km, an intermediate protogranular layer (PGL) from 45 to 66 km, and a lower equigranular layer (LEL) below 66 km. Relative to primitive mantle, all three layers are depleted in major incompatible elements and heavy rare earth elements, with the UEL being most depleted among the three layers, consisting of harzburgite and having experienced >15 % fractional melting. In contrast, the PGL and LEL experienced -3.5 ‰ in the UEL and LEL. The layered structure and geochemical characteristics of sub-Kozákov lithospheric mantle are the product of Variscan or pre-Variscan melting, Variscan tectonics, and Neogene volcanism and metasomatism.

  17. Vorinostat, Rituximab, Ifosfamide, Carboplatin, and Etoposide in Treating Patients With Relapsed or Refractory Lymphoma or Previously Untreated T-Cell Non-Hodgkin Lymphoma or Mantle Cell Lymphoma

    Science.gov (United States)

    2017-04-17

    Adult Nasal Type Extranodal NK/T-cell Lymphoma; Anaplastic Large Cell Lymphoma; Angioimmunoblastic T-cell Lymphoma; Contiguous Stage II Mantle Cell Lymphoma; Cutaneous B-cell Non-Hodgkin Lymphoma; Extranodal Marginal Zone B-cell Lymphoma of Mucosa-associated Lymphoid Tissue; Nodal Marginal Zone B-cell Lymphoma; Noncontiguous Stage II Mantle Cell Lymphoma; Recurrent Adult Burkitt Lymphoma; Recurrent Adult Diffuse Large Cell Lymphoma; Recurrent Adult Diffuse Mixed Cell Lymphoma; Recurrent Adult Diffuse Small Cleaved Cell Lymphoma; Recurrent Adult Grade III Lymphomatoid Granulomatosis; Recurrent Adult Hodgkin Lymphoma; Recurrent Adult Immunoblastic Large Cell Lymphoma; Recurrent Adult Lymphoblastic Lymphoma; Recurrent Cutaneous T-cell Non-Hodgkin Lymphoma; Recurrent Grade 1 Follicular Lymphoma; Recurrent Grade 2 Follicular Lymphoma; Recurrent Grade 3 Follicular Lymphoma; Recurrent Mantle Cell Lymphoma; Recurrent Marginal Zone Lymphoma; Recurrent Mycosis Fungoides/Sezary Syndrome; Recurrent Small Lymphocytic Lymphoma; Splenic Marginal Zone Lymphoma; Stage I Cutaneous T-cell Non-Hodgkin Lymphoma; Stage I Mantle Cell Lymphoma; Stage I Mycosis Fungoides/Sezary Syndrome; Stage II Cutaneous T-cell Non-Hodgkin Lymphoma; Stage II Mycosis Fungoides/Sezary Syndrome; Stage III Cutaneous T-cell Non-Hodgkin Lymphoma; Stage III Mantle Cell Lymphoma; Stage III Mycosis Fungoides/Sezary Syndrome; Stage IV Cutaneous T-cell Non-Hodgkin Lymphoma; Stage IV Mantle Cell Lymphoma; Stage IV Mycosis Fungoides/Sezary Syndrome; Waldenström Macroglobulinemia

  18. Petrogenesis of orogenic lamproites of the Bohemian Massif: Sr-Nd-Pb-Li isotope constraints for Variscan enrichment of ultra-depleted mantle domains

    Czech Academy of Sciences Publication Activity Database

    Krmíček, Lukáš; Romer, R. L.; Ulrych, Jaromír; Glodny, J.; Prelevič, D.

    2016-01-01

    Roč. 35, 1 July (2016), s. 198-216 ISSN 1342-937X Institutional support: RVO:67985831 Keywords : Silica-rich lamproites * Sr-Nb-Pb-Li isotopes * mantle metasomatism * Variscides Subject RIV: DB - Geology ; Mineralogy Impact factor: 6.959, year: 2016

  19. Depletion, cryptic metasomatism, and modal metasomatism (refertilization) of Variscan lithospheric mantle: Evidence from major elements, trace elements, and Sr-Nd-Os isotopes in a Saxothuringian garnet peridotite

    Czech Academy of Sciences Publication Activity Database

    Medaris Jr., L. G.; Ackerman, Lukáš; Jelínek, E.; Michels, Z. D.; Erban, V.; Kotková, J.

    2015-01-01

    Roč. 226, SI (2015), s. 81-97 ISSN 0024-4937 Institutional support: RVO:67985831 Keywords : garnet peridotite * Variscan * Bohemian Massif * Sr-Nd-Os isotopes * depletion cryptic metasomatism and refertilization * P-T conditions Subject RIV: DD - Geochemistry Impact factor: 3.723, year: 2015

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

    OpenAIRE

    Marschall, H.R.; Wanless, V.D.; Shimizu, N.; Pogge von Strandmann, Philip A.E.; Elliott, T.; Monteleone, B.D.

    2017-01-01

    A global selection of 56 mid-ocean ridge basalt (MORB) glasses were analysed for Li and B abundances and isotopic compositions. Analytical accuracy and precision of analyses constitute an improvement over previously published MORB data and allow a more detailed discussion of the Li and B systematics of the crust-mantle system. Refined estimates for primitive mantle abundances ([Li]=1.39±0.10[Li]=1.39±0.10 μg/g and [B]=0.19±0.02[B]=0.19±0.02 μg/g) and depleted mantle abundances ([Li]=1.20±0.10...

  1. Ancient, highly heterogeneous mantle beneath Gakkel ridge, Arctic Ocean.

    Science.gov (United States)

    Liu, Chuan-Zhou; Snow, Jonathan E; Hellebrand, Eric; Brügmann, Gerhard; von der Handt, Anette; Büchl, Anette; Hofmann, Albrecht W

    2008-03-20

    The Earth's mantle beneath ocean ridges is widely thought to be depleted by previous melt extraction, but well homogenized by convective stirring. This inference of homogeneity has been complicated by the occurrence of portions enriched in incompatible elements. Here we show that some refractory abyssal peridotites from the ultraslow-spreading Gakkel ridge (Arctic Ocean) have very depleted 187Os/188Os ratios with model ages up to 2 billion years, implying the long-term preservation of refractory domains in the asthenospheric mantle rather than their erasure by mantle convection. The refractory domains would not be sampled by mid-ocean-ridge basalts because they contribute little to the genesis of magmas. We thus suggest that the upwelling mantle beneath mid-ocean ridges is highly heterogeneous, which makes it difficult to constrain its composition by mid-ocean-ridge basalts alone. Furthermore, the existence of ancient domains in oceanic mantle suggests that using osmium model ages to constrain the evolution of continental lithosphere should be approached with caution.

  2. Solid-liquid iron partitioning in Earth's deep mantle.

    Science.gov (United States)

    Andrault, Denis; Petitgirard, Sylvain; Lo Nigro, Giacomo; Devidal, Jean-Luc; Veronesi, Giulia; Garbarino, Gaston; Mezouar, Mohamed

    2012-07-18

    Melting processes in the deep mantle have important implications for the origin of the deep-derived plumes believed to feed hotspot volcanoes such as those in Hawaii. They also provide insight into how the mantle has evolved, geochemically and dynamically, since the formation of Earth. Melt production in the shallow mantle is quite well understood, but deeper melting near the core-mantle boundary remains controversial. Modelling the dynamic behaviour of deep, partially molten mantle requires knowledge of the density contrast between solid and melt fractions. Although both positive and negative melt buoyancies can produce major chemical segregation between different geochemical reservoirs, each type of buoyancy yields drastically different geodynamical models. Ascent or descent of liquids in a partially molten deep mantle should contribute to surface volcanism or production of a deep magma ocean, respectively. We investigated phase relations in a partially molten chondritic-type material under deep-mantle conditions. Here we show that the iron partition coefficient between aluminium-bearing (Mg,Fe)SiO(3) perovskite and liquid is between 0.45 and 0.6, so iron is not as incompatible with deep-mantle minerals as has been reported previously. Calculated solid and melt density contrasts suggest that melt generated at the core-mantle boundary should be buoyant, and hence should segregate upwards. In the framework of the magma oceans induced by large meteoritic impacts on early Earth, our results imply that the magma crystallization should push the liquids towards the surface and form a deep solid residue depleted in incompatible elements.

  3. Depleted uranium

    International Nuclear Information System (INIS)

    Huffer, E.; Nifenecker, H.

    2001-02-01

    This document deals with the physical, chemical and radiological properties of the depleted uranium. What is the depleted uranium? Why do the military use depleted uranium and what are the risk for the health? (A.L.B.)

  4. Petrogenesis of ultramafic rocks from the eastern Orhaneli ophiolite, NW Turkey: Hints on the initiation and evolution of melt-peridotite interaction processes within a heterogeneously depleted mantle section

    Science.gov (United States)

    Uysal, Ibrahim; Dokuz, Abdurrahman; Kapsiotis, Argyrios; Saka, Samet; Karslı, Orhan; Kaliwoda, Melanie; Müller, Dirk

    2017-10-01

    The eastern Orhaneli ophiolite in NW Anatolia (Turkey) consists of voluminous dunite and minor harzburgite intruded by clinopyroxenite veins. Harzburgite contains spinel of low Cr# [100 × Cr/(Cr + Al) = 40-45] and diopside of low Al2O3 and TiO2 contents, whereas dunite contains spinel of higher Cr# (62-82) and diopside (blebs) (even more) depleted in Al2O3 and TiO2 (than harzburgite). The concentrations of Heavy Rare Earth Elements (HREE) in harzburgite are consistent with derivation of this type of peridotite from 19% dry melting of a fertile mantle protolith at a MOR regime. Dunites have lower concentrations of HREE than harzburgite implying that dunites were generated by higher degrees (>30%) of (cumulative) melting of the same protolith. Furthermore, the characteristic U-shapes of the chondrite-normalized REE-patterns of dunites indicate the involvement of hydrous melt-peridotite interaction processes in their genesis. Nevertheless, a set of mosaic-in-texture dunite samples contain olivine that has lower Fo# [100 × Mg/(Mg + Fe2+)] and NiO contents than olivine in harzburgite. These dunites are probably of cumulate origin as it is also indicated by their enrichment in Pt and Pd (≤17.92 ppb). Micro-textural and Re-Os isotopic data support that clinopyroxenite intrusions do not have a pure magmatic origin and their formation was partly controlled by metasomatic processes. Overall data indicate that the eastern Orhaneli ultramafic rocks have a complex petrological history including various stages of partial melting, metasomatism and magmatism in an evolving from MOR to SSZ geotectonic setting.

  5. 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

  6. The longevity of Archean mantle residues in the convecting upper mantle and their role in young continent formation

    Science.gov (United States)

    Liu, Jingao; Scott, James M.; Martin, Candace E.; Pearson, D. Graham

    2015-08-01

    The role played by ancient melt-depleted lithospheric mantle in preserving continental crust through time is critical in understanding how continents are built, disrupted and recycled. While it has become clear that much of the extant Archean crust is underpinned by Archean mantle roots, reports of Proterozoic melt depletion ages for peridotites erupted through Phanerozoic terranes raise the possibility that ancient buoyant lithospheric mantle acts as a "life-raft" for much of the Earth's continental crust. Here we report the largest crust-lithospheric mantle age decoupling (∼2.4 Ga) so far observed on Earth and examine the potential cause for such extreme age decoupling. The Phanerozoic (Zealandia continent explains the decoupled age relationship that we observe today. Hence, the newly formed lithospheric root incorporates a mixture of ancient and modern mantle derived from the convecting mantle, cooled and accreted in recent times. We argue that in this case, the ancient components played no earlier role in continent stabilization, but their highly depleted nature along with that of their younger counterparts now represents a highly viscous, stable continental keel. This model could account for the large spectrum of ages observed in fertile to moderately depleted peridotites sampled from lithospheric mantle beneath SE Australia, W Antarctica and other locations in Zealandia, as well as the oceanic mantle. Our data confirm the longevity and dispersal of ancient depleted mantle domains in the convecting mantle and their re-appearance beneath young continents.

  7. 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

  8. Depletion, cryptic metasomatism, and modal metasomatism of central European lithospheric mantle: evidence from elemental and Li isotope compositions of spinel peridotite xenoliths, Kozákov volcano, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Medaris Jr., L. G.; Ackerman, Lukáš; Jelínek, E.; Magna, T.

    2015-01-01

    Roč. 104, č. 8 (2015), s. 1925-1956 ISSN 1437-3254 Institutional support: RVO:67985831 Keywords : Central European lithospheric mantle * geochemistry * geothermometry * Li isotopes * spinel peridotite xenoliths Subject RIV: DD - Geochemistry Impact factor: 2.133, year: 2015

  9. 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

  10. 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

  11. 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...... transfer correlations are suitable as input for a detailed simulation model for mantle tanks. The heat transfer correlations determined in this study are somewhat different from previous reported heat transfer correlations. The reason is that this study includes more mantle tank designs and operation...... 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...

  12. Mantle dynamics following supercontinent formation

    Science.gov (United States)

    Heron, Philip J.

    This thesis presents mantle convection numerical simulations of supercontinent formation. Approximately 300 million years ago, through the large-scale subduction of oceanic sea floor, continental material amalgamated to form the supercontinent Pangea. For 100 million years after its formation, Pangea remained relatively stationary, and subduction of oceanic material featured on its margins. The present-day location of the continents is due to the rifting apart of Pangea, with supercontinent dispersal being characterized by increased volcanic activity linked to the generation of deep mantle plumes. The work presented here investigates the thermal evolution of mantle dynamics (e.g., mantle temperatures and sub-continental plumes) following the formation of a supercontinent. Specifically, continental insulation and continental margin subduction are analyzed. Continental material, as compared to oceanic material, inhibits heat flow from the mantle. Previous numerical simulations have shown that the formation of a stationary supercontinent would elevate sub-continental mantle temperatures due to the effect of continental insulation, leading to the break-up of the continent. By modelling a vigorously convecting mantle that features thermally and mechanically distinct continental and oceanic plates, this study shows the effect of continental insulation on the mantle to be minimal. However, the formation of a supercontinent results in sub-continental plume formation due to the re-positioning of subduction zones to the margins of the continent. Accordingly, it is demonstrated that continental insulation is not a significant factor in producing sub-supercontinent plumes but that subduction patterns control the location and timing of upwelling formation. A theme throughout the thesis is an inquiry into why geodynamic studies would produce different results. Mantle viscosity, Rayleigh number, continental size, continental insulation, and oceanic plate boundary evolution are

  13. Mantle dynamics and basalt petrogenesis

    Science.gov (United States)

    Ringwood, A. E.

    1985-03-01

    Differentiation at mid-ocean ridges generates a layered lithosphere consisting of a basaltic crust, immediately underlain by harzburgite and further underlain by pyrolite which has experienced depletion only of highly incompatible elements. The body forces driving subduction are concentrated mainly in the upper half of the lithosphere which is relatively cool and brittle. During subduction, the lower layer of relatively ductile, slightly depleted pyrolite is stripped off and resorbed into the upper mantle, thereby providing a future source region for MORB magmas. The slab which sinks to ~ 600 km is comprised mainly of differentiated former basalt and harzburgite which undergo a different series of phase transformations to those experienced by mantle pyrolite. In consequence, the former basaltic crust remains denser than surrounding mantle whereas former harzburgite becomes relatively buoyant below the 650 km seismic discontinuity. The resulting non-uniformity in stress distribution causes the slab to buckle at this depth and accrete to form a large, relatively cool ovoid "megalith" of mixed former harzburgite and basaltic crust. Heating of the megalith occurs over 1-2 b.y., leading to partial melting of the former basaltic crust. The resultant liquids contaminate regions of former harzburgite, rendering them fertile in the sense of future capacity to produce basaltic magmas. After thermal equilibration, the newly fertile, former harzburgite becomes buoyant, leading to the separation of diapirs which rise into the upper mantle. Such diapirs rising beneath sub-oceanic lithosphere experience small degrees of partial melting to produce ocean island basalts, mainly of the alkaline suite. Diapirs of fertile former harzburgite rising beneath continents become incorporated into the sub-continental lithosphere. This is a cumulative process and is ultimately responsible for the development of the chemical, physical and isotopic characteristics of the sub

  14. The role and conditions of second-stage mantle melting in the generation of low-Ti tholeiites and boninites: the case of the Manihiki Plateau and the Troodos ophiolite

    Science.gov (United States)

    Golowin, Roman; Portnyagin, Maxim; Hoernle, Kaj; Sobolev, Alexander; Kuzmin, Dimitry; Werner, Reinhard

    2017-12-01

    High-Mg, low-Ti volcanic rocks from the Manihiki Plateau in the Western Pacific share many geochemical characteristics with subduction-related boninites such as high-Ca boninites from the Troodos ophiolite on Cyprus, which are believed to originate by hydrous re-melting of previously depleted mantle. In this paper we compare the Manihiki rocks and Troodos boninites using a new dataset on the major and trace element composition of whole rocks and glasses from these locations, and new high-precision, electron microprobe analyses of olivine and Cr-spinel in these rocks. Our results show that both low-Ti Manihiki rocks and Troodos boninites could originate by re-melting of a previously depleted lherzolite mantle source (20-25% of total melting with 8-10% melting during the first stage), as indicated by strong depletion of magmas in more to less incompatible elements (Sm/Yb Y 0.5). In comparison with Troodos boninites, the low-Ti Manihiki magmas had distinctively lower H2O contents ( 2 wt% in boninites), 100 °C higher liquidus temperatures at a given olivine Fo-number, lower fO2 (ΔQFM + 0.2) and originated from deeper and hotter mantle (1.4-1.7 GPa, 1440 °C vs. 0.8-1.0 GPa, 1300 °C for Troodos boninites). The data provide new evidence that re-melting of residual upper mantle is not only restricted to subduction zones, where it occurs under hydrous conditions, but can also take place due to interaction of previously depleted upper mantle with mantle plumes from the deep and hotter Earth interior.

  15. Investigating melting induced mantle heterogeneities in plate driven mantle convection models

    Science.gov (United States)

    Price, M.; Davies, H.; Panton, J.

    2017-12-01

    Observations from geochemistry and seismology continue to suggest a range of complex heterogeneity in Earth's mantle. In the deep mantle, two large low velocity provinces (LLVPs) have been regularly observed in seismic studies, with their longevity, composition and density compared to the surrounding mantle debated. The cause of these observed LLVPs is equally uncertain, with previous studies advocating either thermal or thermo-chemical causes. There is also evidence that these structures could provide chemically distinct reservoirs within the mantle, with recent studies also suggesting there may be additional reservoirs in the mantle, such as bridgmanite-enriched ancient mantle structures (BEAMS). One way to test these hypotheses is using computational models of the mantle, with models that capture the full 3D system being both complex and computationally expensive. Here we present results from our global mantle model TERRA. Using our model, we can track compositional variations in the convecting mantle that are generated by self-consistent, evolving melting zones. Alongside the melting, we track trace elements and other volatiles which can be partitioned during melting events, and expelled and recycled at the surface. Utilising plate reconstruction models as a boundary condition, the models generate the tectonic features observed at Earth's surface, while also organising the lower mantle into recognisable degree-two structures. This results in our models generating basaltic `oceanic' crusts which are then brought into the mantle at tectonic boundaries, providing additional chemical heterogeneity in the mantle volume. Finally, by utilising thermodynamic lookup tables to convert the final outputs from the model to seismic structures, together with resolution filters for global tomography models, we are able to make direct comparisons between our results and observations. By varying the parameters of the model, we investigate a range of current hypotheses for

  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. 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

    concentrations of all the ultramafic xenoliths of 40-400 ppb, similar to or, significantly higher than, current estimates for the BSE (39 ppb). On this basis a revised best estimate of the Mo content in the BSE based on these concentrations would be in the range 113-180 ppb, significantly higher than previously assumed. These values are similar to the levels of depletion in the other refractory moderately siderophile elements W, Ni and Co. A simpler explanation may be that the subcontinental lithospheric mantle has been selectively enriched in Mo leading to the higher concentrations observed. Cryptic melt metasomatism would be difficult to reconcile with the high Mo/Ce of the most LREE depleted xenoliths. Ancient Mo-enriched subducted components would be expected to have heavy δ98/95Mo, which is not observed. The Mo isotope composition of the BSE, cannot be reliably resolved from that of chondrites at this time despite experimental evidence for metal-silicate fractionation. An identical isotopic composition might result from core-mantle differentiation under very high temperatures such as were associated with the Moon-forming Giant Impact, or from the BSE inventory reflecting addition of moderately siderophile elements from an oxidised Moon-forming impactor (O'Neill, 1991). However, the latter would be inconsistent with the non-chondritic radiogenic W isotopic composition of the BSE. Based on mantle fertility arguments, Mo in the BSE could even be lighter (lower 98/95Mo) than that in chondrites, which might be explained by loss of S rich liquids from the BSE during core formation (Wade et al., 2012). Such a late removal model is no longer required to explain the Mo concentration of the BSE if its abundance is in fact much higher, and similar to the values for ultramafic xenoliths.

  18. Effect of H2O on Upper Mantle Phase Transitions in MgSiO3: is the Seismic X-discontinuity an Indicator of Mantle Water Content

    Energy Technology Data Exchange (ETDEWEB)

    S Jacobsen; Z Liu; T Boffa Ballaran; E Littlefield; L Ehm; R Hemley

    2011-12-31

    The mantle X-discontinuity, usually assigned to positive seismic velocity reflectors in the 260-330 km depth range, has proved difficult to explain in terms of a single mineralogical phase transformation in part because of its depth variability. The coesite to stishovite transition of SiO{sub 2} matches deeper X-discontinuity depths but requires 5-10% free silica in the mantle to match observed impedance contrast. The orthoenstatite (OEn) to high-pressure clinoenstatite (HPCen) transformation of MgSiO{sub 3} also broadly coincides with depths of the X but requires chemically depleted and orthoenstatite-rich lithology at 300 km depth in order to match observed seismic impedance contrast. On the basis of high-pressure infrared spectroscopy, X-ray diffraction, and Raman spectroscopy, we show that 1300 ppm variation of H{sub 2}O content in MgSiO{sub 3} can displace the transition of low-pressure clinoenstatite (LPCen) to HPCen by up to 2 GPa, similar to previous quench experiments on the OEn to HPCen phase transition, where about 30-45 km (1.0-1.5 GPa) of deflection could occur per 0.1 wt% H{sub 2}O. If the mantle X-discontinuity results from pyroxene transitions in a depleted harzburgite layer, because of the strong influence of minor amounts of water on the transformation boundary, the depth of the mantle X-discontinuity could serve as a potentially sensitive indicator of water content in the uppermantle.

  19. Na, Rb and Cs partitioning between metal, silicate and sulfide: Implications for volatile depletion in terrestrial planets

    Science.gov (United States)

    Boujibar, A.; Fei, Y.; Du, Z.; Righter, K.; Bullock, E. S.

    2017-12-01

    Inner Solar System materials are known for their depletion in volatile elements, including the moderately volatile alkalis: Na, K, Rb, and Cs. The origin of this depletion is still uncertain, as several processes could have been involved, during the nebular condensation or planetary accretion. Volatile depletion is commonly estimated through comparison of alkali concentrations relatively to those of chondrites, assuming they remain in planetary mantles during core segregation. However, experimental studies show that substantial K can partition into metals that are enriched in sulfur and oxygen. Several models have also suggested that sulfides may have played an important role during episodes of sulfide segregation from a crystallizing magma ocean (sulfide matte) or accretion of S-rich planetary embryos. For Mercury, a sulfide layer could be present between core and mantle, due to immiscibility between Si-rich and S-rich metals. Therefore, here we investigate whether alkali elements (Na, Cs and Rb) could be partly sequestered in planetary cores during their differentiation. We conducted experiments at high pressure and temperature (1 to 5 GPa and up to 1900 °C) to determine partition coefficients of Na, Rb and Cs between metal and silicate. Our results show that pressure, temperature, sulfur and oxygen in metals enhance the partitioning of Na, Rb and Cs into metals, as previously found for K. For all three investigated alkalis (Na, Rb and Cs), we found a maximum partition coefficient of 1 between sulfides containing 13 wt% O and silicate melt. Therefore, S-rich cores or sulfide layers formed due to immiscibility in Fe-S-O systems could have acted as important geochemical reservoirs for alkali elements. Using our experimental data and different assumptions on initial bulk abundances, we evaluate volatile depletion in terrestrial planets, by comparing resulting mantle alkali concentrations after core segregation, with actual concentrations in the Earth's mantle.

  20. Core formation and mantle differentiation on Mars

    OpenAIRE

    Mezger Klaus; Debaille Vinciane; Kleine Thorsten

    2012-01-01

    Geochemical investigation of Martian meteorites (SNC meteorites) yields important constraints on the chemical and geodynamical evolution of Mars. These samples may not be representative of the whole of Mars; however they provide constraints on the early differentiation processes on Mars. The bulk composition of Martian samples implies the presence of a metallic core that formed concurrently as the planet accreted. The strong depletion of highly siderophile elements in the Martian mantle is on...

  1. Upper mantle fluids evolution, diamond formation, and mantle metasomatism

    Science.gov (United States)

    Huang, F.; Sverjensky, D. A.

    2017-12-01

    During mantle metasomatism, fluid-rock interactions in the mantle modify wall-rock compositions. Previous studies usually either investigated mineral compositions in xenoliths and xenocrysts brought up by magmas, or examined fluid compositions preserved in fluid inclusions in diamonds. However, a key study of Panda diamonds analysed both mineral and fluid inclusions in the diamonds [1] which we used to develop a quantitative characterization of mantle metasomatic processes. In the present study, we used an extended Deep Earth Water model [2] to simulate fluid-rock interactions at upper mantle conditions, and examine the fluids and mineral assemblages together simultaneously. Three types of end-member fluids in the Panda diamond fluid inclusions include saline, rich in Na+K+Cl; silicic, rich in Si+Al; and carbonatitic, rich in Ca+Mg+Fe [1, 3]. We used the carbonatitic end-member to represent fluid from a subducting slab reacting with an excess of peridotite + some saline fluid in the host environment. During simultaneous fluid mixing and reaction with the host rock, the logfO2 increased by about 1.6 units, and the pH increased by 0.7 units. The final minerals were olivine, garnet and diamond. The Mg# of olivine decreased from 0.92 to 0.85. Garnet precipitated at an early stage, and its Mg# also decreased with reaction progress, in agreement with the solid inclusions in the Panda diamonds. Phlogopite precipitated as an intermediate mineral and then disappeared. The aqueous Ca, Mg, Fe, Si and Al concentrations all increased, while Na, K, and Cl concentrations decreased during the reaction, consistent with trends in the fluid inclusion compositions. Our study demonstrates that fluids coming from subducting slabs could trigger mantle metasomatism, influence the compositions of sub-lithospherc cratonic mantle, precipitate diamonds, and change the oxygen fugacity and pH of the upper mantle fluids. [1] Tomlinson et al. EPSL (2006); [2] Sverjensky, DA et al., GCA (2014

  2. 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

    A global selection of 56 mid-ocean ridge basalt (MORB) glasses were analysed for Li and B abundances and isotopic compositions. Analytical accuracy and precision of analyses constitute an improvement over previously published MORB data and allow a more detailed discussion of the Li and B systematics of the crust-mantle system. Refined estimates for primitive mantle abundances ([ Li ] = 1.39 ± 0.10 μg/g and [ B ] = 0.19 ± 0.02 μg/g) and depleted mantle abundances ([ Li ] = 1.20 ± 0.10 μg/g and [ B ] = 0.077 ± 0.010 μg/g) are presented based on mass balance and on partial melting models that utilise observed element ratios in MORB. Assimilation of seawater (or brine) or seawater-altered material beneath the ridge, identified by high Cl / K , causes significant elevation of MORB δ11 B and variable elevation in δ7 Li . The B isotope ratio is, hence, identified as a reliable indicator of assimilation in MORB and values higher than -6‰ are strongly indicative of shallow contamination of the magma. The global set of samples investigated here were produced at various degrees of partial melting and include depleted and enriched MORB from slow and fast-spreading ridge segments with a range of radiogenic isotope signatures and trace element compositions. Uncontaminated (low- Cl / K) MORB show no significant boron isotope variation at the current level of analytical precision, and hence a homogenous B isotopic composition of δ11 B = - 7.1 ± 0.9 ‰ (mean of six ridge segments; 2SD). Boron isotope fractionation during mantle melting and basalt fractionation likely is small, and this δ11 B value reflects the B isotopic composition of the depleted mantle and the bulk silicate Earth, probably within ±0.4‰. Our sample set shows a mean δ7 Li = + 3.5 ± 1.0 ‰ (mean of five ridge segments; 2SD), excluding high- Cl / K samples. A significant variation of 1.0-1.5‰ exists among various ridge segments and among samples within individual ridge segments, but this

  3. Highly Siderophile Elements as Tracers for the Subcontinental Mantle Evolution Beneath the Southwestern USA: The San Carlos and Kilbourne Hole Peridotite Xenoliths Revisited

    Science.gov (United States)

    vanAcken, D.; Brandon, A. D.; Peslier, A. H.; Lee, C.-T. A.

    2010-01-01

    factors of up to 4 for Pt, 6 for Pd, and 20 for Re, compared to primitive mantle estimates. This is in agreement with previous studies from the same locales, which demonstrated the presence of different populations of mantle xenoliths having undergone various degrees of melt extraction. The depletion of the more incompatible elements (Re, Pd, and Pt) also suggests that the HSE budgets of the SW USA peridotites were primarily established by extraction of basaltic melt, and reflect only minor influence from later episodes of metasomatism. Model Re-Os ages obtained from San Carlos and Kilbourne Hole xenoliths may thus reflect ages of crustal formation and mantle depletion in the SW USA region.

  4. Pristine MORB mantle from Gakkel Ridge

    Science.gov (United States)

    Snow, J. E.; Hellebrand, E.

    2010-12-01

    Fresh mantle rocks (Total ~300Kg) have been recovered from three dredge hauls on Gakkel Ridge. Most of the fresh material (~275 Kg) is from a single dredge haul (PS66-238) from PFS POLARSTERN ARK XX/2 in 2004 (not from the AMORE expedition). The samples from this group comprise extremely fresh protogranular lherzolites that have clearly defined 1-2 cm orange weathering rinds. The weathered material seems to be mostly discoloration along grain boundaries, as bulk weathering (e.g. Snow and Dick, 1995) cannot be detected in bulk analyses. The fresh cores are largely devoid of serpentine that can be identified in hand sample or SEM. The samples show a bimodal grain size distribution and abundant polygonization of olivine, but little stretching of pyroxene grains, suggesting that they have not been subject to intense deformation that has been seen in many mid-ocean ridge peridotites. Currently, 14 of the 208 discrete samples have been studied. The major element compositions of these samples range from relatively fertile spinel lherzolites to moderately depleted cpx-bearing harzburgites, both in their bulk chemistry and in the compositions of major minerals. The average Cr# (Dick and Bullen, 1984) of spinel ranges from 0.15 to 0.28, suggesting 5-12% melt extraction (Hellebrand et al. 2001). Trace elements measured by SIMS and LA-ICPMS reveal metasomatism and refertilization of the LREE. Os isotopes vary from 187Os/188Os of 0.128 to 0.114, revealing an ancient component that can be interpreted either as a fertile ambient mantle with a highly depleted ancient exotic block or as a single mantle domain variably depleted in an ancient melting event (Liu et al., 2008). Bulk Li isotopic data correspond to estimates of the MORB mantle, however mineral separates show significant isotopic heterogeneity that appears to be caused by diffusion caused by Li redistribution during uplift and cooling (Gao et al., accepted). The altered samples have radically different textures. These

  5. Low-Ti basalts from the Faroe Islands constrain the early Iceland depleted plume component

    DEFF Research Database (Denmark)

    Søager, Nina; Holm, Paul Martin

    -Toft, J, Kingsley, R., Schilling, J.G., 2000: Depleted Iceland mantle plume geochemical signature: Artifact of multicomponent mixing? Geochemistry, Geophysics, Geosystems vol.1. Thirlwall, M.F., Gee, M.A.M., Taylor, R.N., Murton, B.J., 2004: Mantle components in Iceland and adjecent ridges investigated...

  6. Geochemical make-up of oceanic peridotites from NW Turkey and the multi-stage melting history of the Tethyan upper mantle

    Science.gov (United States)

    Uysal, İbrahim; Şen, A. Dündar; Ersoy, E. Yalçın; Dilek, Yildirim; Saka, Samet; Zaccarini, Federica; Escayola, Monica; Karslı, Orhan

    2014-02-01

    We present the whole-rock and the mineral chemical data for upper mantle peridotites from the Harmancık region in NW Turkey and discuss their petrogenetic-tectonic origin. These peridotites are part of a Tethyan ophiolite belt occurring along the İzmir-Ankara-Ercincan suture zone in northern Turkey, and include depleted lherzolites and refractory harzburgites. The Al2O3 contents in orthopyroxene and clinopyroxene from the depleted lherzolite are high, and the Cr-number in the coexisting spinel is low falling within the abyssal field. However, the orthopyroxene and clinopyroxene in the harzburgites have lower Al2O3 contents for a given Cr-number of spinel, and plot within the lower end of the abyssal field. The whole-rock geochemical and the mineral chemistry data imply that the Harmancık peridotites formed by different degrees of partial melting (~%10-27) of the mantle. The depleted lherzolite samples have higher MREE and HREE abundances than the harzburgitic peridotites, showing convex-downward patterns. These peridotites represent up to ~16 % melting residue that formed during the initial seafloor spreading stage of the Northern Neotethys. On the other hand, the more refractory harzburgites represent residues after ~4-11 % hydrous partial melting of the previously depleted MOR mantle, which was metasomatized by slab-derived fluids during the early stages of subduction. The Harmancık peridotites, hence, represent the fragments of upper mantle rocks that formed during different stages of the tectonic evolution of the Tethyan oceanic lithosphere in Northern Neotethys. We infer that the multi-stage melting history of the Harmancık peridotites reflect the geochemically heterogeneous character of the Tethyan oceanic lithosphere currently exposed along the İzmir-Ankara-Erzincan suture zone.

  7. Length-scales of chemical and isotopic heterogeneity in the mantle section of the Shetland Ophiolite Complex, Scotland

    Science.gov (United States)

    O'Driscoll, B.; Walker, R. J.; Clay, P. L.; Day, J. M. D.; Ash, R. D.; Daly, J. S.

    2018-04-01

    Kilometre to sub-metre scale heterogeneities have been inferred in the oceanic mantle based on sampling of both ophiolites and abyssal peridotites. The ∼492 Ma Shetland Ophiolite Complex (SOC) contains a well-preserved mantle section that is dominated by harzburgite (∼70 vol.%) previously reported to have variable major and trace element compositions, yet dominantly chondritic initial 187Os/188Os compositions. To assess the preservation of compositional heterogeneities at sub-metre length-scales in the oceanic mantle, a ∼45 m2 area of the SOC mantle section was mapped and sampled in detail. Harzburgites, dunites and a pyroxenite from this area were analysed for lithophile and highly-siderophile element (HSE) abundances, as well as for 187Os/188Os ratios. Lithophile element data for most rocks are characteristic of supra-subduction zone (SSZ) metasomatic processes. Two dunites have moderately fractionated HSE patterns and suprachondritic γOs(492 Ma) values (+5.1 and +7.5) that are also typical of ophiolitic dunites generated by SSZ melt-rock interactions. By contrast, six harzburgites and four dunites have approximately chondritic-relative abundances of Os, Ir and Ru, and γOs(492 Ma) values ranging only from -0.6 to +2.7; characteristics that imply no significant influence during SSZ processes. Two harzburgites are also characterised by significantly less radiogenic γOs(492 Ma) values (-3.5 and -4), and yield Mesoproterozoic time of Re depletion (TRD) model ages. The range of Os isotope compositions in the studied area is comparable to the range reported for a suite of samples representative of the entire SOC mantle section, and approaches the total isotopic variation of the oceanic mantle, as observed in abyssal peridotites. Mechanisms by which this heterogeneity can be formed and preserved involve inefficient and temporally distinct melt extraction events and strong localised channelling of these melts.

  8. 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

  9. Density structure of the cratonic mantle in southern Africa

    DEFF Research Database (Denmark)

    Artemieva, Irina; Vinnik, Lev P.

    2016-01-01

    . An unusually high topography may be caused by a low density (high depletion) of the cratonic lithospheric mantle and/or by the dynamic support of the mantle with origin below the depth of isostatic compensation (assumed here to be at the lithosphere base). We use free-board constraints to examine the relative...... contributions of the both factors to surface topography in the cratons of southern Africa. Our analysis takes advantage of the SASE seismic experiment which provided high resolution regional models of the crustal thickness.We calculate the model of density structure of the lithospheric mantle in southern Africa...... and show that it has an overall agreement with xenolith-based data for lithospheric terranes of different ages. Density of lithospheric mantle has significant short-wavelength variations in all tectonic blocks of southern Africa and has typical SPT values of ca. 3.37-3.41g/cm3 in the Cape Fold and Namaqua...

  10. 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...

  11. Early mantle differentiation: constraint from 146Sm-142Nd systematics

    International Nuclear Information System (INIS)

    Caro, G.

    2005-07-01

    We present new ultra-high precision 142 Nd/ 144 Nd measurements of early Archaean rocks using the new generation thermal ionization mass spectrometer TRITON. Repeated measurements of the Ames Nd standard demonstrate that the 142 Nd/ 144 Nd ratio can be determined with external precision of 2 ppm (2s), allowing confident resolution of anomalies as small as 5 ppm. A major analytical improvement lies in the elimination of the double normalization procedure required to correct our former measurements from a secondary mass fractionation effect. Our new results indicate that metasediments, meta-basalts and orthogneisses from the 3.6 - 3.8 Ga West Greenland craton display positive 142 Nd anomalies ranging from 8 to 15 ppm. Using a simple two-stage model with initial e 143 Nd value of 1.9 ± 0.6 e-units, coupled 147 Sm- 143 Nd and 146 Sm- 142 Nd chronometry constrains mantle differentiation to 50 to 200 Ma after formation of the solar system. This chronological constraint is consistent with differentiation of the Earth's mantle during the late stage of crystallization of a magma ocean. We have developed a two-box model describing 142 Nd and 143 Nd isotopic evolution of depleted mantle during the subsequent evolution of the crust-mantle system. Our results indicate that early terrestrial proto-crust had a lifetime of ca. 500 Ma in order to produce the observed Nd isotope signature of Archaean rocks. In the context of this two box mantle-crust system, we model the evolution of isotopic and chemical heterogeneity of depleted mantle as a function of the mantle stirring time. Using the dispersion of 142 Nd/ 144 Nd and 143 Nd/ 144 Nd ratios observed in early Archaean rocks, we constrain the stirring time of early Earth's mantle to 100 - 150 Ma, a factor of 5 to 10 shorter than stirring time inferred from modern oceanic basalts. (author)

  12. 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

    for the chondrite-forming event. This ¿176 value indicates that Earth's oldest minerals were derived from melts of a mantle source with a time-integrated history of depletion rather than enrichment. The depletion event must have occurred no later than 320 Myr after planetary accretion, consistent with timing...

  13. 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

  14. Geochemical Consequence of Extraction of Incipient CO2-rich melts from Earth's Deep Upper Mantle

    Science.gov (United States)

    Dasgupta, R.; Withers, A. C.; McDonough, W. F.; Hirschmann, M. M.

    2007-12-01

    The initiation of partial melting beneath mid-oceanic ridges and ocean islands likely produces incipient carbonatitic melts. These highly mobile melts generated at great depth may not only affect geophysical properties of deep upper mantle but can also influence Earth's geochemical evolution by releasing incompatible parent and/or daughter elements, heat producing elements, and volatiles. But constraints on the fractionation of the key trace elements between the peridotitic residue and carbonatitic melts are lacking at conditions of initiation of partial melting beneath ridges.Experiments at 6.6-8.6 GPa and 1265-1470 °C on carbonated peridotite doped with a blend of trace elements produced cpx + garnet + magnesite ± opx ± olivine + carbonatitic melt (cbL) similar in composition to that expected at the solidus of carbonated peridotite (Ca# = 0.52 at 6.6 GPa and 0.45 at 8.6 GPa; Na2O = ~4 wt.% at 6.6 GPa and ~2.5 wt.% at 8.6 GPa). Compared to previous studies at lower pressures (2.0-4.6 GPa), Dcpx/cbL from the present study are smaller for elements substituting into the cpx M2 site, especially trivalent cations ( DLu = 0.17, DLa = 0.006). Dcpx/cbL for U (0.001) and Th (0.002) are also noticeably lower than the previous estimates. In contrast, Dgarnet/cbL values are higher for REEs ( DLu = 4.6, DLa = 0.039) and HFSEs, U (0.023) and Th (0.017).Our estimate of Dperidotite/cbL indicates that incipient carbonatite extraction from the deep upper mantle will produce a residue with a more depleted Rb/Sr, U/Pb, Th/U, and enriched Sm/Nd, which may evolve to produce the most common of the mantle end member components, PREMA. Metasomatic implantation of deep carbonatitic melt into the lithosphere can generate a high-μ (238U/204Pb) signature, whereas mixing of carbonatite with elevated Th/U can contribute to the observed 230Th-excesses in MORBs. However, carbonatites derived by incipient melting of depleted (DMM) mantle have limited trace element enrichments, ~10-100

  15. High-voltage-compatible, fully depleted CCDs

    Energy Technology Data Exchange (ETDEWEB)

    Holland, Stephen E.; Bebek, Chris J.; Dawson, Kyle S.; Emes, JohnE.; Fabricius, Max H.; Fairfield, Jessaym A.; Groom, Don E.; Karcher, A.; Kolbe, William F.; Palaio, Nick P.; Roe, Natalie A.; Wang, Guobin

    2006-05-15

    We describe charge-coupled device (CCD) developmentactivities at the Lawrence Berkeley National Laboratory (LBNL).Back-illuminated CCDs fabricated on 200-300 mu m thick, fully depleted,high-resistivity silicon substrates are produced in partnership with acommercial CCD foundry.The CCDs are fully depleted by the application ofa substrate bias voltage. Spatial resolution considerations requireoperation of thick, fully depleted CCDs at high substrate bias voltages.We have developed CCDs that are compatible with substrate bias voltagesof at least 200V. This improves spatial resolution for a given thickness,and allows for full depletion of thicker CCDs than previously considered.We have demonstrated full depletion of 650-675 mu m thick CCDs, withpotential applications in direct x-ray detection. In this work we discussthe issues related to high-voltage operation of fully depleted CCDs, aswell as experimental results on high-voltage-compatible CCDs.

  16. 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

  17. Density structure of the cratonic mantle in Southern Africa. 2. Correlations with kimberlite distribution, seismic velocities, and Moho sharpness

    DEFF Research Database (Denmark)

    Artemieva, Irina; Vinnik, Lev

    2016-01-01

    belts.Wedemonstrate that in southern Africa, the lithosphericmantle has a general trend in mantle density increase from Archean to younger lithospheric terranes. Density of the Kaapvaal mantle is typically cratonic, with a subtle difference between the eastern, more depleted, (3.31– 3.33 g/cm3...

  18. Prolonged Mantle Melting Revealed in the Curaçao Lava Formation: Implications for the Origin of the Caribbean Plateau

    Science.gov (United States)

    Krawl, K.; Duncan, R. A.; Kent, A. J.; Loewen, M.

    2013-12-01

    The Curaçao Lava Formation (CLF), a ~5 km thick section of submarine-erupted lava flows, hyaloclastites, dikes and sills, provides a ~30 Ma record of the magmatic processes involved in the formation of the Caribbean Large Igneous Province (CLIP). The CLF presents ol-tholeiitic and picritic compositions, exposed along the southern transform margin of the CLIP, that are typical of other in situ and tectonized pieces of this ocean plateau. The wide range of recently acquired 40Ar-39Ar ages (62 to 93 Ma) obtained for the Curaçao lavas contradicts previous proposals that the CLF formed over a relatively short period (1-2 million years), but is similar to extended volcanic histories recorded in Haiti (Dumisseau Fm) and at the Beata Ridge. Petrochemical modeling using MELTS indicates that the CLF rock compositions could have formed by fractional crystallization of high-MgO parental magmas with broadly similar major element contents, generated during multiple melting events over this prolonged period. The persistently flat rare earth element patterns in rocks spanning the full age range of the CLF can be reproduced by 10-30% partial melting of a predominantly depleted mantle source with a minor enriched component. The geochemical and age data and modeling results are consistent with a mantle dynamic model for the CLIP in which lateral displacement of mantle plume head material beneath the Caribbean plateau results from subduction-driven mantle flow, which allows for the generation of magmas from a continuously replenished mantle source over approximately 30 million years. While no subduction influence is seen in CLF compositions, the island does record intrusive, arc-related rocks.

  19. Mineralogy and composition of the oceanic mantle

    Science.gov (United States)

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

    2011-01-01

    contents, however, that are enriched compared with melts from natural peridotites and magmas derived from the Siqueiros depleted mantle, and consequently may require an enriched source. TiO2 is not the only element that is enriched relative to melts of natural peridotites. Moderately incompatible elements, such as Ti, Zr, Hf, Y, and Eu, and compatible elements, such as Yb and Lu, are all enriched at the Hawaiian Islands. Such enrichments can be explained by adding 5-10% mid-ocean ridge basalt (crust) to depleted mantle; when the major element composition of such a mixture is recast into mineral components, the result is a fertile peridotite mineralogy.

  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

    Trace element variability in oceanic basalts is commonly used to constrain the physics of mantle melting and the chemistry of Earth's deep interior. However, the geochemical properties of mantle melts are often overprinted by mixing and crystallisation processes during ascent and storage. Studying primitive melt inclusions offers one solution to this problem, but the fidelity of the melt-inclusion archive to bulk magma chemistry has been repeatedly questioned. To provide a novel check of the melt inclusion record, we present new major and trace element analyses from olivine macrocrysts in the products of two geographically proximal, yet compositionally distinct, primitive eruptions from the Reykjanes Peninsula of Iceland. By combining these macrocryst analyses with new and published melt inclusion analyses we demonstrate that olivines have similar patterns of incompatible trace element (ITE) variability to the inclusions they host, capturing chemical systematics on intra- and inter-eruption scales. ITE variability (element concentrations, ratios, variances and variance ratios) in olivines from the ITE-enriched Stapafell eruption is best accounted for by olivine-dominated fractional crystallisation. In contrast, ITE variability in olivines and inclusions from the ITE-depleted Háleyjabunga eruption cannot be explained by crystallisation alone, and must have originated in the mantle. Compatible trace element (CTE) variability is best described by crystallisation processes in both eruptions. Modest correlations between host and inclusion ITE contents in samples from Háleyjabunga suggest that melt inclusions can be faithful archives of melting and magmatic processes. It also indicates that degrees of ITE enrichment can be estimated from olivines directly when melt inclusion and matrix glass records of geochemical variability are poor or absent. Inter-eruption differences in olivine ITE systematics between Stapafell and Háleyjabunga mirror differences in melt

  1. A Re-Os Study of Depleted Trench Peridotites from Northern Mariana

    Science.gov (United States)

    Ghosh, T.; Snow, J. E.; Heri, A. R.; Brandon, A. D.; Ishizuka, O.

    2017-12-01

    Trench peridotites provide information about the influence of subduction initiation on the extent of mantle wedge melting. They preserve melting records throughout subduction history, and as a result, likely experience multiple melt extraction events leading to successive depletion of melt/fluid mobile major and trace elements. To track melting histories of trench peridotites, Re-Os and PGEs can be used as reliable tracers to constrain early melt extraction or re-fertilization events. The Izu-Bonin-Mariana arc, being the largest intra-oceanic subduction system, provides an excellent area to study the formation of supra-subduction zone mantle and crust. Residual peridotite (harzburgite and dunite) samples were collected by dredging from the landward slope of the northern Mariana Trench. The samples are serpentinized to various extents (typical of abyssal peridotites), leaving behind relict grains of spinel, enstatite and olivine embedded within a serpentine matrix along with occasional interstitial diopside. Major element analyses of primary minerals reveal a wide range of variations in Cr# of spinels from 0.31-0.85 indicating 16-20% of melt fraction with dunites apparently experiencing the highest amount of partial melting. For Re-Os and PGE geochemistry, samples with high amounts of spinel (>4 vol %) and variable Cr# were chosen. Initial results show that bulk rock 187Os/188Os ratios range from 0.1113 to 0.1272. All of the samples are sub-chondritic, but in some cases, they are more radiogenic than average abyssal peridotites. Os abundances vary from 1-9 ppb. Sub-chondritic values can be attributed to the samples having evolved from a Re-depleted mantle source indicating a previous melt-extraction event. The cpx-harzburgites, having lower Cr# ( 0.4) are more radiogenic than ultra depleted dunites (Cr# 0.8), which might indicate preferential removal of Os during an apparent higher degree of partial melting experienced by dunites. The higher 187Os/188Os ratios of

  2. Oxygen Fugacity of the Upper Mantle of Mars. Evidence from the Partitioning Behavior of Vanadium in Y980459 (Y98) and other Olivine-Phyric Shergottites

    Science.gov (United States)

    Shearer, C. K.; McKay, G. A.; Papike, J. J.; Karner, J.

    2006-01-01

    Using partitioning behavior of V between olivine and basaltic liquid precisely calibrated for martian basalts, we determined the redox state of primitive (olivine-rich, high Mg#) martian basalts near their liquidus. The combination of oxidation state and incompatible element characteristics determined from early olivine indicates that correlations between fO2 and other geochemical characteristics observed in many martian basalts is also a fundamental characteristic of these primitive magmas. However, our data does not exhibit the range of fO2 observed in these previous studies.. We conclude that the fO2 for the martian upper mantle is approximately IW+1 and is incompatible-element depleted. It seems most likely (although clearly open to interpretation) that these mantle-derived magmas assimilated a more oxidizing (>IW+3), incompatible-element enriched, lower crustal component as they ponded at the base of the martian crust.

  3. Long-Lived Mantle Plumes Sample Multiple Deep Mantle Geochemical Domains: The Example of the Hawaiian-Emperor Chain

    Science.gov (United States)

    Harrison, L.; Weis, D.

    2017-12-01

    Oceanic island basalts provide the opportunity for the geochemist to study the deep mantle source removed from continental sources of contamination and, for long-lived systems, the evolution of mantle sources with time. In the case of the Hawaiian-Emperor (HE) chain, formation by a long-lived (>81 Myr), deeply-sourced mantle plume allows for insight into plume dynamics and deep mantle geochemistry. The geochemical record of the entire chain is now complete with analysis of Pb-Hf-Nd-Sr isotopes and elemental compositions of the Northwest Hawaiian Ridge (NWHR), which consists of 51 volcanoes spanning 42 Ma between the bend in the chain and the Hawaiian Islands. This segment of the chain previously represented a significant data gap where Hawaiian plume geochemistry changed markedly, along with magmatic flux: only Kea compositions have been observed on Emperor seamounts (>50 Ma), whereas the Hawaiian Islands (drift through different lower mantle geohemical domains.

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

    Science.gov (United States)

    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

  5. 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.

  6. Volatile element content of the heterogeneous upper mantle

    Science.gov (United States)

    Shimizu, K.; Saal, A. E.; Hauri, E. H.; Forsyth, D. W.; Kamenetsky, V. S.; Niu, Y.

    2014-12-01

    The physical properties of the asthenosphere (e.g., seismic velocity, viscosity, electrical conductivity) have been attributed to either mineral properties at relevant temperature, pressure, and water content or to the presence of a low melt fraction. We resort to the geochemical studies of MORB to unravel the composition of the asthenosphere. It is important to determine to what extent the geochemical variations in axial MORB do represent a homogeneous mantle composition and variations in the physical conditions of magma generation and transport; or alternatively, they represent mixing of melts from a heterogeneous upper mantle. Lavas from intra-transform faults and off-axis seamounts share a common mantle source with axial MORB, but experience less differentiation and homogenization. Therefore they provide better estimates for the end-member volatile budget of the heterogeneous upper mantle. We present major, trace, and volatile element data (H2O, CO2, Cl, F, S) as well as Sr, Nd, and Pb isotopic compositions [1, 2] of basaltic glasses (MgO > 6.0 wt%) from the NEPR seamounts, Quebrada-Discovery-Gofar transform fault system, and Macquarie Island. The samples range from incompatible trace element (ITE) depleted (DMORB: Th/La0.07) spanning the entire range of EPR MORB. The isotopic composition of the samples correlates with the degree of trace element enrichment indicating long-lived mantle heterogeneity. Once shallow-level processes (degassing, crystallization, and crustal assimilation) have been considered, we conducted a two-component (DMORB- and EMORB-) mantle melting-mixing model. Our model reproduces the major, trace and volatile element contents and isotopic composition of our samples and suggests that (1) 90% of the upper mantle is highly depleted in ITE (DMORB source) with only 10% of an enriched component (EMORB source), (2) the EMORB source is peridotitic rather than pyroxenitic, and (3) NMORB do not represent an actual mantle source, but the product of

  7. 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

  8. Long-term cycling of mantle Pb: A trace element study of the major mantle mineral phases in abyssal peridotites

    Science.gov (United States)

    D'Errico, M. E.; Warren, J. M.; Godard, M.; Ildefonse, B.

    2012-12-01

    Peridotites from ultraslow-spreading ridges preserve signatures of the depleted mantle, while also reflecting the fine scale compositional variability present in the mantle. Traditional analyses of these depleted rocks have focused on clinopyroxene, the main trace element host in spinel peridotites. However, key isotopic systems, such as lead and osmium, are hosted in other phases at low but significant concentration levels. The amount of lead contained within mantle mineral phases is of critical importance to understanding the long-term evolution of the Earth, because the radiogenic isotopes of lead are sensitive to past material cycling and melt-rock interaction. Sulfides have long been suggested as the main host for lead (Pb) in the mantle, but recent studies have demonstrated that Pb is not exclusively hosted in this trace phase. Therefore, the Pb contents of the major peridotite mineral phases (olivine, orthopyroxene, and clinopyroxene) need to be reassessed. Lead concentration data is available for orogenic and xenolith peridotite samples, which are typically more enriched than abyssal peridotites, but these do not provide direct information on the oceanic upper mantle. Direct measurement of Pb in abyssal peridotites has so far been limited because of its extremely low concentration (often spreading Gakkel and Southwest Indian Ridges (SWIR), with samples coming from segments with full spreading rates Gakkel and SWIR samples are relatively unaltered (Gakkel. A total of five Gakkel and six SWIR peridotites were analyzed by LA-ICP-MS, with a subset of samples also analyzed for bulk rock trace elements by solution ICP-MS. Combined with mineral modal data, this study provides a direct comparison of measured and calculated bulk rock Pb concentrations to determine a comprehensive assessment of the distribution of Pb among upper mantle phases Results indicate that all three of the main mantle mineral phases have similar Pb concentrations, ranging from 2-20 ppb, which

  9. Lithosphere erosion atop mantle plumes

    Science.gov (United States)

    Agrusta, R.; Arcay, D.; Tommasi, A.

    2012-12-01

    Mantle plumes are traditionally proposed to play an important role in lithosphere erosion. Seismic images beneath Hawaii and Cape Verde show a lithosphere-asthenosphere-boundary (LAB) up to 50 km shallower than the surroundings. However, numerical models show that unless the plate is stationary the thermo-mechanical erosion of the lithosphere does not exceed 30 km. We use 2D petrological-thermo-mechanical numerical models based on a finite-difference method on a staggered grid and marker in cell method to study the role of partial melting on the plume-lithosphere interaction. A homogeneous peridotite composition with a Newtonian temperature- and pressure-dependent viscosity is used to simulate both the plate and the convective mantle. A constant velocity, ranging from 5 to 12.5 cm/yr, is imposed at the top of the plate. Plumes are created by imposing a thermal anomaly of 150 to 350 K on a 50 km wide domain at the base of the model (700 km depth); the plate right above the thermal anomaly is 40 Myr old. Partial melting is modeled using batch-melting solidus and liquidus in anhydrous conditions. We model the progressive depletion of peridotite and its effect on partial melting by assuming that the melting degree only strictly increases through time. Melt is accumulated until a porosity threshold is reached and the melt in excess is then extracted. The rheology of the partially molten peridotite is determined using viscous constitutive relationship based on a contiguity model, which enables to take into account the effects of grain-scale melt distribution. Above a threshold of 1%, melt is instantaneously extracted. The density varies as a function of partial melting degree and extraction. Besides, we analyze the kinematics of the plume as it impacts a moving plate, the dynamics of time-dependent small-scale convection (SSC) instabilities developing in the low-viscosity layer formed by spreading of hot plume material at the lithosphere base, and the resulting thermal

  10. Uplift and seismicity driven by groundwater depletion in central California.

    Science.gov (United States)

    Amos, Colin B; Audet, Pascal; Hammond, William C; Bürgmann, Roland; Johanson, Ingrid A; Blewitt, Geoffrey

    2014-05-22

    Groundwater use in California's San Joaquin Valley exceeds replenishment of the aquifer, leading to substantial diminution of this resource and rapid subsidence of the valley floor. The volume of groundwater lost over the past century and a half also represents a substantial reduction in mass and a large-scale unburdening of the lithosphere, with significant but unexplored potential impacts on crustal deformation and seismicity. Here we use vertical global positioning system measurements to show that a broad zone of rock uplift of up to 1-3 mm per year surrounds the southern San Joaquin Valley. The observed uplift matches well with predicted flexure from a simple elastic model of current rates of water-storage loss, most of which is caused by groundwater depletion. The height of the adjacent central Coast Ranges and the Sierra Nevada is strongly seasonal and peaks during the dry late summer and autumn, out of phase with uplift of the valley floor during wetter months. Our results suggest that long-term and late-summer flexural uplift of the Coast Ranges reduce the effective normal stress resolved on the San Andreas Fault. This process brings the fault closer to failure, thereby providing a viable mechanism for observed seasonality in microseismicity at Parkfield and potentially affecting long-term seismicity rates for fault systems adjacent to the valley. We also infer that the observed contemporary uplift of the southern Sierra Nevada previously attributed to tectonic or mantle-derived forces is partly a consequence of human-caused groundwater depletion.

  11. Addressing Ozone Layer Depletion

    Science.gov (United States)

    Access information on EPA's efforts to address ozone layer depletion through regulations, collaborations with stakeholders, international treaties, partnerships with the private sector, and enforcement actions under Title VI of the Clean Air Act.

  12. Convective upwelling in the mantle beneath the Gulf of California.

    Science.gov (United States)

    Wang, Yun; Forsyth, Donald W; Savage, Brian

    2009-11-26

    In the past six million years, Baja California has rifted obliquely apart from North America, opening up the Gulf of California. Between transform faults, seafloor spreading and rifting is well established in several basins. Other than hotspot-dominated Iceland, the Gulf of California is the only part of the world's seafloor-spreading system that has been surrounded by enough seismometers to provide horizontal resolution of upper-mantle structure at a scale of 100 kilometres over a distance great enough to include several spreading segments. Such resolution is needed to address the long-standing debate about the relative importance of dynamic and passive upwelling in the shallow mantle beneath spreading centres. Here we use Rayleigh-wave tomography to image the shear velocity in the upper 200 kilometres or so of the mantle. Low shear velocities similar to those beneath the East Pacific Rise oceanic spreading centre underlie the entire length of the Gulf, but there are three concentrated locations of anomalously low velocities spaced about 250 kilometres apart. These anomalies are 40 to 90 kilometres beneath the surface, at which depths petrological studies indicate that extensive melting of passively upwelling mantle should begin. We interpret these seismic velocity anomalies as indicating that partial melting triggers dynamic upwelling driven by either the buoyancy of retained melt or by the reduced density of depleted mantle.

  13. Diamond growth in mantle fluids

    OpenAIRE

    Bureau, Hélène; Frost, Daniel J.; Bolfan-casanova, Nathalie; Leroy, Clémence; Esteve, Imène; Cordier, Patrick

    2016-01-01

    International audience; In the upper mantle, diamonds can potentially grow from various forms of media (solid, gas, fluid) with a range of compositions (e.g. graphite, C–O–H fluids, silicate or carbonate melts). Inclusions trapped in diamonds are one of the few diagnostic tools that can constrain diamond growth conditions in the Earth's mantle. In this study, inclusion-bearing diamonds have been synthesized to understand the growth conditions of natural diamonds in the upper mantle. Diamonds ...

  14. Interaction between Edge-Driven Convection and Mantle Plumes

    Science.gov (United States)

    Manjón-Cabeza Córdoba, A.; Ballmer, M.

    2017-12-01

    Intraplate volcanism can occur in a variety of geodynamic settings. Its characteristics can inform about the underlying mantle dynamics. A non-negligible number of intraplate oceanic volcanoes are located close to continental shelves (e.g. Bermuda, Canary Islands, Cape Verde…). In these regions, any putative plumes would interact with Edge-Driven Convection (EDC), a mode of Small-Scale Convection that is triggered along steps of lithospheric thickness. We have systematically explored 2-D geodynamic models of EDC, varying e.g. the viscosity of the mantle, geometry of the edge, potential temperature, etc. In addition, we study the influence of a mantle plume with variable excess temperature and buoyancy flux at a given distance to the edge. The mantle-convection code is coupled with a new melting parameterization that considers the depletion effect on productivity. We apply this parameterization not only to predict the extent of melting for a given lithology, but also the major-element composition of extracted melts for comparison with geochemical data. Results show that the first EDC upwellings are always localized in the oceanic domain at a distance from the continental margin that depends on mantle viscosity. The initial geometry of the edge does not have a significant influence on the "steady-state" shape of EDC. Depending on the distance of the plume from the edge and plume vigor, the plume is either deflected or enhanced by EDC. The mix of materials that melts in the mantle, as well as the amount of melting, is controlled by the interaction of the plume with EDC (e.g., with melting restricted to fertile heterogeneities in the end-member EDC case). Because several model parameters affect this interaction and related melting, a joint analysis of major-element and trace-element composition of hotspot lavas is required to constrain mantle processes.

  15. 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,

  16. Nd-isotopes in selected mantle-derived rocks and minerals and their implications for mantle evolution

    Science.gov (United States)

    Basu, A.R.; Tatsumoto, M.

    1980-01-01

    The Sm-Nd systematics in a variety of mantle-derived samples including kimberlites, alnoite, carbonatite, pyroxene and amphibole inclusions in alkali basalts and xenolithic eclogites, granulites and a pyroxene megacryst in kimberlites are reported. The additional data on kimberlites strengthen our earlier conclusion that kimberlites are derived from a relatively undifferentiated chondritic mantle source. This conclusion is based on the observation that the e{open}Nd values of most of the kimberlites are near zero. In contrast with the kimberlites, their garnet lherzolite inclusions show both time-averaged Nd enrichment and depletion with respect to Sm. Separated clinopyroxenes in eclogite xenoliths from the Roberts Victor kimberlite pipe show both positive and negative e{open}Nd values suggesting different genetic history. A whole rock lower crustal scapolite granulite xenolith from the Matsoku kimberlite pipe shows a negative e{open}Nd value of -4.2, possibly representative of the base of the crust in Lesotho. It appears that all inclusions, mafic and ultramafic, in kimberlites are unrelated to their kimberlite host. The above data and additional Sm-Nd data on xenoliths in alkali basalts, alpine peridotite and alnoite-carbonatites are used to construct a model for the upper 200 km of the earth's mantle - both oceanic and continental. The essential feature of this model is the increasing degree of fertility of the mantle with depth. The kimberlite's source at depths below 200 km in the subcontinental mantle is the most primitive in this model, and this primitive layer is also extended to the suboceanic mantle. However, it is clear from the Nd-isotopic data in the xenoliths of the continental kimberlites that above 200 km the continental mantle is distinctly different from their suboceanic counterpart. ?? 1980 Springer-Verlag.

  17. Dynamics of mantle rock metasomatic transformation in permeable lithospheric zones beneath Siberian craton

    Science.gov (United States)

    Sharapov, Victor; Sorokin, Konstantin; Perepechko, Yury

    2015-04-01

    inevitably causes the formation of the faults in ultrabasic lithospheric mantle and creation of zonal metasomatic columns, 2) input of the major silicate components to the depleted ultrabasic lithospheric mantle transform them to substrates, which can be attributed to deep seated analogs rodingites, or developing of granatites within the original matrix 3) input of any carbon bearing combinations of fluid follows to the deep carbonation of metasomatic substrate 4 above the marked zones the regenerated pyroxenite zone appears, followed by phlogopitzation and amphibolization, 5) evaluation of heat-mass transfer according to the two-velocity hydrodynamics showed that Darcy approximation Apparently brings to the overestimation of the the rate of thermal wave development during the convective warming up underestimation of the pressure in the fluid stream. It is shown that grospidity, previously considered to be eclogites are the legitimate metasomatic rock associations appearing in permeable zones of lithospheric mantle above the magmatic chambers

  18. Dihedral angle of carbonatite melts in mantle residue near the upper mantle and transition zone

    Science.gov (United States)

    Ghosh, S. K.; Rohrbach, A.; Schmidt, M. W.

    2015-12-01

    Carbonate melts are thought to be ideal metasomatic agents in the deep upper mantle (Green & Wallace, 1988) and these melts are low in viscosities (10-1-10-3 Pa·s) compared to primitive basalt (101-102 Pa·s), furthermore the ability to form an interconnected grain-edge melt network at low melt fractions (3 GPa (Dasgupta et al. 2006, Ghosh et al., 2009), dissolve a number of geochemically incompatible elements much better than silicate melts (Blundy and Dalton, 2000). Previous studies of carbonate melt dihedral angles in olivine-dominated matrices yielded 25-30oat 1-3 GPa, relatively independent of melt composition (Watson et al., 1990) and temperature (Hunter and McKenzie, 1989). Dihedral angles of carbonate melts in contact with deep mantle silicate phases (e.g. garnet, wadsleyite, and ringwoodite) which constitute more than 70 % of the deep upper mantle and transition zone have not been studied yet. We have performed multi-anvil experiments on carbonate-bearing peridotites with 5.0 wt% CO2 from 13.5 to 20 GPa 1550 oC to investigate the dihedral angle of magnesio-carbonatite melts in equilibrium with garnet, olivine (and its high-pressure polymorphs), and clinoenstatite. The dihedral angle of carbonate melts in the deep upper mantle and transition zone is ~30° for majorite garnet and olivine (and its polymorphs) dominated matrices. It does not change with increasing pressure in the range 13.5-20 GPa. Our results suggest that very low melt fractions of carbonatite melt forming in the deep upper mantle and transition zone are interconnected at melt fractions less than 0.01. Consistent with geophysical observations, this could possibly explain low velocity regions in the deep mantle and transition zone.

  19. 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.

  20. 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...... kimberlitic and ultramafic lamprophyre (senso lato) dikes and sills emplaced into three tectonically distinct crustal areas in the North Atlantic Craton. Several geothermobarometry formulations have been applied and a thorough assessment of which P-T combinations are most applicable to this sample suite has...... and the Kirkland Lake locality within the Superior craton. In supporting previous studies we find that the continental lithospheric mantle is layered and increases in fertility with depth. Twenty-five of 32 investigated samples are estimated to be derived from the diamond stability field that extends...

  1. Plasmonic Nanoprobes for Stimulated Emission Depletion Nanoscopy.

    Science.gov (United States)

    Cortés, Emiliano; Huidobro, Paloma A; Sinclair, Hugo G; Guldbrand, Stina; Peveler, William J; Davies, Timothy; Parrinello, Simona; Görlitz, Frederik; Dunsby, Chris; Neil, Mark A A; Sivan, Yonatan; Parkin, Ivan P; French, Paul M W; Maier, Stefan A

    2016-11-22

    Plasmonic nanoparticles influence the absorption and emission processes of nearby emitters due to local enhancements of the illuminating radiation and the photonic density of states. Here, we use the plasmon resonance of metal nanoparticles in order to enhance the stimulated depletion of excited molecules for super-resolved nanoscopy. We demonstrate stimulated emission depletion (STED) nanoscopy with gold nanorods with a long axis of only 26 nm and a width of 8 nm. These particles provide an enhancement of up to 50% of the resolution compared to fluorescent-only probes without plasmonic components irradiated with the same depletion power. The nanoparticle-assisted STED probes reported here represent a ∼2 × 10 3 reduction in probe volume compared to previously used nanoparticles. Finally, we demonstrate their application toward plasmon-assisted STED cellular imaging at low-depletion powers, and we also discuss their current limitations.

  2. Early episodes of high-pressure core formation preserved in plume mantle

    Science.gov (United States)

    Jackson, Colin R. M.; Bennett, Neil R.; Du, Zhixue; Cottrell, Elizabeth; Fei, Yingwei

    2018-01-01

    The decay of short-lived iodine (I) and plutonium (Pu) results in xenon (Xe) isotopic anomalies in the mantle that record Earth’s earliest stages of formation. Xe isotopic anomalies have been linked to degassing during accretion, but degassing alone cannot account for the co-occurrence of Xe and tungsten (W) isotopic heterogeneity in plume-derived basalts and their long-term preservation in the mantle. Here we describe measurements of I partitioning between liquid Fe alloys and liquid silicates at high pressure and temperature and propose that Xe isotopic anomalies found in modern plume rocks (that is, rocks with elevated 3He/4He ratios) result from I/Pu fractionations during early, high-pressure episodes of core formation. Our measurements demonstrate that I becomes progressively more siderophile as pressure increases, so that portions of mantle that experienced high-pressure core formation will have large I/Pu depletions not related to volatility. These portions of mantle could be the source of Xe and W anomalies observed in modern plume-derived basalts. Portions of mantle involved in early high-pressure core formation would also be rich in FeO, and hence denser than ambient mantle. This would aid the long-term preservation of these mantle portions, and potentially points to their modern manifestation within seismically slow, deep mantle reservoirs with high 3He/4He ratios.

  3. 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

    The composition of the convecting asthenospheric mantle that feeds the mantle wedge can be investigated via rear-arc lavas that have minimal slab influence. This "ambient mantle wedge" composition (the composition of the wedge prior to the addition of a slab component) varies substantially both worldwide and within individual arcs. 143Nd/144Nd measurements of rear-arc samples that have minimal slab influence are similar to 143Nd/144Nd in the stratovolcanoes of the adjacent volcanic fronts, suggesting that 143Nd/144Nd of arc-front volcanics are largely inherited from the ambient mantle composition. 143Nd/144Nd correlates with ratios such as Th/U, Zr/Nb, and La/Sm, indicating that these ratios also are strongly influenced by ambient wedge heterogeneity. The same phenomenon is observed among individual volcanoes from the Chilean Southern Volcanic Zone (SVZ), where along-strike variability of the volcanic front tracks that of rear-arc monogenetic volcanics. Depleted mantle wedges are more strongly influenced by slab-derived components than are enriched wedges. This leads to surprising trace element correlations in the global dataset, such as between Pb/Nb and Zr/Nb, which are not explicable by variable compositions or fluxes of slab components. Depleted ambient mantle is present beneath arcs with back-arc spreading; relatively enriched mantle is present adjacent to continents. Ambient mantle wedge heterogeneity both globally and regionally forms isotope mixing trajectories for Sr, Nd and Hf between depleted mantle and EM1-type enriched compositions as represented by Gough Island basalts. Making use of this relationship permits a quantitative match with the SVZ data. It has been suggested that EM1-type mantle reservoirs are the result of recycled lower continental crust, though such models do not account for certain trace element ratios such as Ce/Pb and Nb/U or the surprisingly homogeneous trace element compositions of EM1 volcanics. A model in which the EM1 end

  4. Linking lowermost mantle structure, core-mantle boundary heat flux and mantle plume formation

    Science.gov (United States)

    Li, Mingming; Zhong, Shijie; Olson, Peter

    2018-04-01

    The dynamics of Earth's lowermost mantle exert significant control on the formation of mantle plumes and the core-mantle boundary (CMB) heat flux. However, it is not clear if and how the variation of CMB heat flux and mantle plume activity are related. Here, we perform geodynamic model experiments that show how temporal variations in CMB heat flux and pulses of mantle plumes are related to morphologic changes of the thermochemical piles of large-scale compositional heterogeneities in Earth's lowermost mantle, represented by the large low shear velocity provinces (LLSVPs). We find good correlation between the morphologic changes of the thermochemical piles and the time variation of CMB heat flux. The morphology of the thermochemical piles is significantly altered during the initiation and ascent of strong mantle plumes, and the changes in pile morphology cause variations in the local and the total CMB heat flux. Our modeling results indicate that plume-induced episodic variations of CMB heat flux link geomagnetic superchrons to pulses of surface volcanism, although the relative timing of these two phenomena remains problematic. We also find that the density distribution in thermochemical piles is heterogeneous, and that the piles are denser on average than the surrounding mantle when both thermal and chemical effects are included.

  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. Experimental investigation of mantle melting in the presence of carbonates

    Science.gov (United States)

    Dasgupta, Rajdeep

    High pressure-temperature experiments are performed at pressures of 2 to 10 GPa and temperatures of 900 to 1600 °C to constrain partial melting of carbonate bearing mantle eclogite and peridotite. Eclogite and peridotite in the presence of CO2 is observed to produce carbonatitic melts at their respective solidi for most parts of Earth's upper mantle. The solidus of carbonated eclogite at 3 GPa is observed to vary significantly with bulk Ca/Mg and Na2O content. But the appropriate solidus of carbonated ocean crust remains hotter than the subduction geotherms up to 260 km, indicating subduction of carbon, in the form of magnesite-eclogite, deep into the mantle. Upwelling mantle eclogite, on the other hand, must release carbonatite at depths >350 km. From experiments at 3 GPa, it is found that carbonated eclogite can generate silicate partial melts that can give rise to silica-undersaturated ocean island lavas. Solidus of carbonated peridotite from 3 to 10 GPa indicates that along an oceanic geotherm, the onset of partial melting happens shallower than that of carbonated eclogite, but still as deep as 300-330 km beneath ridges. Extraction of incipient carbonatite from deep mantle implies efficient removal of highly incompatible trace elements, including carbon, from the mantle. This deep melting likely creates a vast mantle residue that is depleted and fractionated in important trace elements and also might explain many geophysical features of Earth's deep upper mantle. Experiments with peridotite of variable carbonate concentrations also indicate that increasing CO2, unlike H2O, does not cause the isobaric solidus of carbonated peridotite to decrease. Using a new method of iterative sandwich experiments, the detailed composition of near-solidus melt from carbonated peridotite is determined at 6.6 GPa. Near-solidus melt of peridotite + CO2 at a depth of ˜200 km is Fe-Na bearing magnesio-dolomitic carbonatite. Transition from near-solidus carbonatite to carbonated

  7. Revisiting The Depleted Self.

    Science.gov (United States)

    Abraham, Reggie

    2018-04-01

    This article revisits Donald Capps's book The Depleted Self (The depleted self: sin in a narcissistic age. Fortress Press, Minneapolis, 1993), which grew out of his 1990 Schaff Lectures at Pittsburgh Theological Seminary. In these lectures Capps proposed that the theology of guilt had dominated much of post-Reformation discourse. But with the growing prevalence of the narcissistic personality in the late twentieth century, the theology of guilt no longer adequately expressed humanity's sense of "wrongness" before God. Late twentieth-century persons sense this disjunction between God and self through shame dynamics. Narcissists are not "full" of themselves, as popular perspectives might indicate. Instead, they are empty, depleted selves. Psychologists suggest this stems from lack of emotional stimulation and the absence of mirroring in the early stages of life. The narcissist's search for attention and affirmation takes craving, paranoid, manipulative, or phallic forms and is essentially a desperate attempt to fill the internal emptiness. Capps suggests that two narratives from the Gospels are helpful here: the story of the woman with the alabaster jar and the story of Jesus's dialogue with Mary and John at Calvary. These stories provide us with clues as to how depleted selves experienced mirroring and the potential for internal peace in community with Jesus.

  8. Ozone depletion update.

    Science.gov (United States)

    Coldiron, B M

    1996-03-01

    Stratospheric ozone depletion due to chlorofluorocarbons an d increased ultraviolet radiation penetration has long been predicted. To determine if predictions of ozone depletion are correct and, if so, the significance of this depletion. Review of the English literature regarding ozone depletion and solar ultraviolet radiation. The ozone layer is showing definite thinning. Recently, significantly increased ultraviolet radiation transmission has been detected at ground level at several metering stations. It appears that man-made aerosols (air pollution) block increased UVB transmission in urban areas. Recent satellite measurements of stratospheric fluorine levels more directly implicate chlorofluorocarbons as a major source of catalytic stratospheric chlorine, although natural sources may account for up to 40% of stratospheric chlorine. Stratospheric chlorine concentrations, and resultant increased ozone destruction, will be enhanced for at least the next 70 years. The potential for increased transmission of ultraviolet radiation will exist for the next several hundred years. While little damage due to increased ultraviolet radiation has occurred so far, the potential for long-term problems is great.

  9. Is composition a critical dynamical element of mantle convection?

    Science.gov (United States)

    Davies, J. H.; Davies, D. R.; Wolstencroft, M. W.

    2009-04-01

    It is clear from observations of differentiation producing oceanic crust and depleted residue, and its ultimate subduction that compositional heterogeneity does exist in the mantle. An important question for mantle dynamics however, is how important is this composition? Compositional variations have been attributed to be critical for explaining many dynamical aspects of mantle upwellings as evidenced in hot-spots, such as their relative fixity (Jellinek and Manga, 2004) and non-steady upwelling velocity (Lin and van Keken, 2005). They have also been attributed to causing peaks in magma production. Our modeling work in spherical geometry shows that a wide variety of upwelling behaviour can be produced in models that have NO compositional variations and are only driven by thermal anomalies. The critical component of this family of models is a high, Earth-like Rayleigh number. Our models have also reproduced time varying magma production on a long time-scale in thermal convection models. The critical element is again a very high Rayleigh number, but this time combined with a realistic Clapeyron slope at the 660km discontinuity. Schuberth et al., 2009, have also shown that composition is not required to explain some of the seismic signatures of mantle convection models either, including at the base of the mantle. While, as stated initially, composition must play a role, we would argue that given that much of the supposedly ‘non-thermal' behaviour can be explained by thermal models that the simplest current paradigm is to assume thermally driven convection. A further advantage of this class of model is that there are fewer degrees of freedom in comparing the geodynamics models with seismology, and therefore tighter tests will be possible. While there are other arguments for compositional variations close to the core-mantle boundary and in the upper boundary / lithosphere; tests from simpler models could help to refine and bound the degree of compositional variation

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

    Science.gov (United States)

    Hier-Majumder, Saswata; Hirschmann, Marc M.

    2017-08-01

    that the mantle stored substantially higher amounts of volatiles than previously thought, thanks to large quantities of melt trapped in the mantle due to rapid freezing of the magma ocean. Our models show that up to 77% of the total planetary budget of water and 12% of CO2 can be stored in the mantle due to this previously unaccounted process.

  11. Evidence for trench-parallel mantle flow in the northern Cascade Arc from basalt geochemistry

    Science.gov (United States)

    Mullen, Emily K.; Weis, Dominique

    2015-03-01

    Geochemical data for basalts from the Garibaldi Volcanic Belt (northern segment of the Cascade Arc) define arc-parallel gradients in trace elements and isotope ratios that extend at least 150 km into the arc from the northern margin of the subducting Juan de Fuca plate. Southerly increases in Zr/Nb, Ba/Nb, Th/La, Pb/Ce, 208Pb/204Pb and 176Hf/177Hf indicate greater mantle depletion and higher slab-derived contributions with distance from the slab edge. Temperatures and pressures of mantle melt segregation also decrease to the south. The gradients are most plausibly explained as a consequence of slab rollback-induced toroidal flow at the northern slab edge (Nootka fault zone), whereby enriched (OIB-type) NE Pacific asthenospheric mantle from beneath the slab is drawn into the mantle wedge in a trench-parallel southerly flow pattern. Melts of the enriched asthenosphere are progressively diluted to the south by melts of the slab-modified, depleted mantle wedge. Arc-parallel changes in slab thermal conditions cannot account for these gradients. Trench parallel geochemical gradients in the northern Cascade Arc are consistent with shear wave splitting data, numerical modeling, and experimental studies showing that trench-parallel mantle flow may be a common phenomenon near slab edges and slab gaps.

  12. A Nd and Sr isotopic study of the Trinity peridotite Implications for mantle evolution

    Science.gov (United States)

    Jacobsen, S. B.; Quick, J. E.; Wasserburg, G. J.

    1984-01-01

    Field evidence is reported which indicates that the Trinity peridotite in Northern California was partially melted during its rise as part of the upwelling convecting mantle at a spreading center. A Sm-Nd mineral isochron for a plagioclase Iherzolite yielded an age of about 427 Ma which is significantly higher than that expected for depleted mantle during this period. The age is interpreted as the time of crystallization of trapped melt in the plagioclase Iherzolite P-T field, and probably represents the time when the massif was incorporated as a part of the oceanic lithosphere. The Sm-Nd model age of the plagioclase Iherzolite total rock is 3.4 AE. This suggests that the peridotite was derived from a mantle that was depleted early in earth history. Although most available data indicate that the depleted upper mantle has been relatively well stirred through time, the Trinity data suggest that very ancient Nd isotropic values are preserved and chemical and physical heterogeneities are sometimes preserved in the depleted source of midocean ridge basalts as well as the oceanic lithosphere which they intrude.

  13. Isotopic characterisation of the sub-continental lithospheric mantle beneath Zealandia, a rifted fragment of Gondwana

    DEFF Research Database (Denmark)

    Waight, Tod Earle; Scott, James M.; van der Meer, Quinten Har Adriaan

    2013-01-01

    and that contained a HIMU component. The volcanics have tapped two adjacent but chemically contrasting upper mantle domains: a fertile eastern domain and an extremely depleted western domain. Both domains underlie Mesozoic metasedimentary crust. Radiogenic isotope compositions of the clinopyroxene have 87Sr/86Sr...

  14. Mantle plumes and hotspot geochemistry

    Science.gov (United States)

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

    2017-12-01

    Ever improving global seismic models, together with expanding databases of mantle derived hotspot lavas, herald advances that relate the geochemistry of hotspots with low seismic shear-wave velocity conduits (plumes) in the mantle. Early efforts linked hotspot geochemistry with deep mantle large low velocity provinces (LLVPs) [1]. More recently, Konter and Becker (2012) [2] observed that the proportion of the C mantle component (inferred from Sr-Nd-Pb isotopes) in hotspot lavas shows an inverse relationship with seismic S-wave velocity anomalies in the shallow mantle (200 km) beneath each hotspot. They proposed that these correlations should also be made based on 3He/4He. Thus, we compare 3He/4He versus seismic S-wave velocity anomalies at 200 km depth. We find that plume-fed hotspots with the highest maximum 3He/4He (i.e., which host more of the C component) have higher hotspot buoyancy fluxes and overlie regions of lower seismic S-wave velocity (interpreted to relate to hotter mantle temperatures) at 200 km depth than hotspots that have only low 3He/4He [3]. This result complements recent work that shows an inverse relationship between maximum 3He/4He and seismic S-wave velocity anomalies in the mantle beneath the western USA [4]. The relationship between 3He/4He, shallow mantle seismic S-wave velocity anomalies, and buoyancy flux is most easily explained by a model where hotter plumes are more buoyant and entrain more of a deep, dense high 3He/4He reservoir than cooler plumes that underlie low 3He/4He hotspots. If the high 3He/4He domain is denser than other mantle components, it will be entrained only by the hottest, most buoyant plumes [3]. Such a deep, dense reservoir is ideally suited to preserving early-formed Hadean domains sampled in modern plume-fed hotspots. An important question is whether, like 3He/4He, seismic S-wave velocity anomalies in the mantle are associated with distinct heavy radiogenic isotopic compositions. C signatures are related to hot

  15. Release of Nitrogen during Planetary Accretion Explains Missing Nitrogen in Earth's Mantle

    Science.gov (United States)

    Liu, J.; Dorfman, S.; Lv, M.; Li, J.; Kono, Y.

    2017-12-01

    Nitrogen and carbon are essential elements for life on Earth, and their relative abundances in planetary bodies (C/N ratios) are important for understanding planetary evolution and habitability1,2. However, the high C/N ratio in the bulk silicate Earth relative to CI chondrites and other volatile-rich chondrites is difficult to explain with partitioning behavior between silicate and metallic liquid or solubility in silicate melt, and has thus been a major unsolved problem in geochemistry1-5. Because core formation does not explain nitrogen depletion in the mantle, another process is required to match the observed BSE C/N ratio, such as devolatilization of metallic liquid. Previous studies have examined the Fe-C phase diagram extensively (e.g. ref. 6), but very limited melting data is available for the Fe-N system7. Here we examine melting relations for four Fe-N-C compositions with 1-7 wt% nitrogen up to 7 GPa and 2200 K in the Paris-Edinburgh press by a combination of in-situ X-ray radiography, X-ray diffraction and ex-situ electron microprobe techniques. In striking contrast to the Fe-C system, near-surface melting in all compositions in the Fe-N-C system entails release of nitrogen fluid and depletion of nitrogen from the liquid alloy. This could provide a pathway for nitrogen to escape the magma ocean in the accretion stage while carbon is retained. On the basis of our experimental results, we propose a new quantitative model of mantle nitrogen evolution during the core formation stage to explain the high BSE C/N ratios and resolve the paradox of missing mantle nitrogen1-5. Although nitrogen itself is not a greenhouse gas, the nitrogen released to the atmosphere from metallic melt early in Earth's history could amplify the greenhouse effect through collision-enhanced absorption8,9, which may help to explain warm surface temperatures during the Hadean and Archean eras on Earth when the solar luminosity was 25-30% lower than the present10. References1. Bergin et

  16. Depleted uranium: A DOE management guide

    International Nuclear Information System (INIS)

    1995-10-01

    The U.S. Department of Energy (DOE) has a management challenge and financial liability in the form of 50,000 cylinders containing 555,000 metric tons of depleted uranium hexafluoride (UF 6 ) that are stored at the gaseous diffusion plants. The annual storage and maintenance cost is approximately $10 million. This report summarizes several studies undertaken by the DOE Office of Technology Development (OTD) to evaluate options for long-term depleted uranium management. Based on studies conducted to date, the most likely use of the depleted uranium is for shielding of spent nuclear fuel (SNF) or vitrified high-level waste (HLW) containers. The alternative to finding a use for the depleted uranium is disposal as a radioactive waste. Estimated disposal costs, utilizing existing technologies, range between $3.8 and $11.3 billion, depending on factors such as applicability of the Resource Conservation and Recovery Act (RCRA) and the location of the disposal site. The cost of recycling the depleted uranium in a concrete based shielding in SNF/HLW containers, although substantial, is comparable to or less than the cost of disposal. Consequently, the case can be made that if DOE invests in developing depleted uranium shielded containers instead of disposal, a long-term solution to the UF 6 problem is attained at comparable or lower cost than disposal as a waste. Two concepts for depleted uranium storage casks were considered in these studies. The first is based on standard fabrication concepts previously developed for depleted uranium metal. The second converts the UF 6 to an oxide aggregate that is used in concrete to make dry storage casks

  17. 186Os and 187Os enrichments and high-3He/4He sources in the Earth's mantle

    DEFF Research Database (Denmark)

    Brandon, A.D.; Graham, D.W.; Waight, Tod Earle

    2007-01-01

    picrites is best modeled as mixtures of 1 Ga or older ancient recycled crust mixed with primitive mantle or incompletely degassed depleted mantle isolated since 1-1.5 Ga, which preserves the high 3He/4He of the depleted mantle at the time. These mixtures create a hybrid source region that subsequently...... be interpreted as an increase in the proportion of ancient recycled crust in the upwelling plume over this time period. The positive correlation between 187Os/188Os and 3He/4He demonstrates that the Iceland lava He isotopic compositions do not result from simple melt depletion histories and consequent removal...

  18. 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

  19. Intrinsic Depletion or Not

    DEFF Research Database (Denmark)

    Klösgen, Beate; Bruun, Sara; Hansen, Søren

      The presence of a depletion layer of water along extended hydrophobic interfaces, and a possibly related formation of nanobubbles, is an ongoing discussion. The phenomenon was initially reported when we, years ago, chose thick films (~300-400Å) of polystyrene as cushions between a crystalline...... carrier and biomimetic membranes deposited thereupon and exposed to bulk water. While monitoring the sequential build-up of the sandwiched composite structure by continuous neutron reflectivity experiments the formation of an unexpected additional layer was detected (1). Located at the polystyrene surface...... in between he polymer cushion and bulk water the layer was attributed to water of reduced density and was called "depletion layer".  Impurities or preparative artefacts were excluded as its origin. Later on, the formation of nanobubbles from this vapour-like water phase was initiated by tipping the surface...

  20. Deep mantle seismic heterogeneities in Western Pacific subduction zones

    Science.gov (United States)

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

    2012-04-01

    In recent years array seismology has been used extensively to image the small scale (~10 km) structure of the Earth. In the mantle, small scale structure likely represents chemical heterogeneity and is essential in our understanding of mantle convection and especially mantle mixing. As subduction is the main source of introducing crustal material into the Earth's mantle, it is of particular interest to track the transport of subducted crust through the mantle to resolve details of composition and deformation of the crust during the subduction process. Improved knowledge of subduction can help provide constraints on the mechanical mixing process of crustal material into the ambient mantle, as well as constraining mantle composition and convection. This study uses seismic array techniques to map seismic heterogeneities associated with Western Pacific subduction zones, where a variety of slab geometries have been previously observed. We use seismic energy arriving prior to PP, a P-wave underside reflection off the Earth's surface halfway between source and receiver, to probe the mantle for small-scale heterogeneities. PP precursors were analysed at Eielson Array (ILAR), Alaska using the recently developed Toolkit for Out-of-Plane Coherent Arrival Tracking (TOPCAT) algorithm. The approach combines the calculated optimal beampower and an independent semblance (coherency) measure, to improve the signal-to-noise ratio of coherent arrivals. 94 earthquakes with sufficient coherent precursory energy were selected and directivity information of the arrivals (i.e. slowness and backazimuth) was extracted from the data. The scattering locations for 311 out-of-plane precursors were determined by ray-tracing and minimising the slowness, backazimuth and differential travel time misfit. Initial analyses show that deep scattering (>1000 km) occurs beneath the Izu-Bonin subduction zone, suggesting that subducted crust does continue into the lower mantle in this location. Other

  1. Capital expenditure and depletion

    International Nuclear Information System (INIS)

    Rech, O.; Saniere, A.

    2003-01-01

    In the future, the increase in oil demand will be covered for the most part by non conventional oils, but conventional sources will continue to represent a preponderant share of the world oil supply. Their depletion represents a complex challenge involving technological, economic and political factors. At the same time, there is reason for concern about the decrease in exploration budgets at the major oil companies. (author)

  2. Seismic Imaging of Mantle Plumes

    Science.gov (United States)

    Nataf, Henri-Claude

    The mantle plume hypothesis was proposed thirty years ago by Jason Morgan to explain hotspot volcanoes such as Hawaii. A thermal diapir (or plume) rises from the thermal boundary layer at the base of the mantle and produces a chain of volcanoes as a plate moves on top of it. The idea is very attractive, but direct evidence for actual plumes is weak, and many questions remain unanswered. With the great improvement of seismic imagery in the past ten years, new prospects have arisen. Mantle plumes are expected to be rather narrow, and their detection by seismic techniques requires specific developments as well as dedicated field experiments. Regional travel-time tomography has provided good evidence for plumes in the upper mantle beneath a few hotspots (Yellowstone, Massif Central, Iceland). Beneath Hawaii and Iceland, the plume can be detected in the transition zone because it deflects the seismic discontinuities at 410 and 660 km depths. In the lower mantle, plumes are very difficult to detect, so specific methods have been worked out for this purpose. There are hints of a plume beneath the weak Bowie hotspot, as well as intriguing observations for Hawaii. Beneath Iceland, high-resolution tomography has just revealed a wide and meandering plume-like structure extending from the core-mantle boundary up to the surface. Among the many phenomena that seem to take place in the lowermost mantle (or D''), there are also signs there of the presence of plumes. In this article I review the main results obtained so far from these studies and discuss their implications for plume dynamics. Seismic imaging of mantle plumes is still in its infancy but should soon become a turbulent teenager.

  3. The Preservation of Meso- Archean Refractory Lithospheric Mantle Underneath the Eastern Margin of the Tanzania Craton

    Science.gov (United States)

    Shu, Q.; Liu, J.; Pearson, G. D.; Gibson, S. A.

    2014-12-01

    Numerous studies on the petrology and geochemistry of peridotite xenoliths from the Tanzanian Craton and its rifted margins have investigated the origin, chemical change and thermal state of the cratonic roots from its core area (Nzega and Mwadui), its Northern (Marsabit) and Eastern margin Labait and Lashaine area (e.g. Dawson, 1964; Henjes-Kunst and Altherr, 1991; Lee & Rudnick, 1999; Chesley et al., 1999; Gibson et al., 2013). These studies suggest that the Tanzanian cratonic mantle formed via high degrees of melt extraction in the Archean (oldest Re-depletion age TRD = 3.4 Ga, Burton et al., 2000) and sev­eral episodes of refertilization. In order to gain further temporal and chemical understanding on the effects of tectonic processes on cratonic roots, we carried out a Re-Os isotopic study on peridotites (n = 11) from Lashaine, which will be followed by Lu-Hf, Sm-Nd and Sr isotope investigations of the constituent minerals of the same samples. The preliminary whole-rock Os isotope data from Lashaine peridotites show a large range of 187Os/188Os (0.1061 - 0.1261), with TRD ages from Meso-Archean to very young (3.1 Ga to 0.3 Ga). There is a negative correlation between TRD and bulk alumina contents. One sample with the lowest Al2O3 yields the oldest age of 3.1 Ga. Five samples range from 2.5 to 2.8 Ga, three give ages close to 2 Ga, and one sample with a high Al2O3 has a TRD at 0.3 Ga. The positive Al2O3-187Os/188Os correlation trend passes above the PM composition may reflect ancient metasomatism by high Re/Os melts or recent metasomatism by very radiogenic Os plume-derived melts. These processes could be related to the evolution of the peripheral Proterozoic mobile belts, or Cenozoic rifting on the Eastern margin. Collectively, our new Os isotope data demonstrate that Meso-Archean (at least 3.1 Ga old) mantle portions are still retained underneath the rifted Eastern margin of the Craton. This is in line with previous results indicating that Archean cratonic

  4. Geochemical heterogeneity in the Arctic mantle at Gakkel Ridge

    Science.gov (United States)

    D'Errico, M. E.; Warren, J. M.; Godard, M.

    2014-12-01

    Conductive cooling due to ultraslow spreading has been suggested to limit partial melting of the mantle and crustal production at Gakkel Ridge. In addition, the thick lithosphere induced by cooling should significantly control melt migration and extraction. To explore these effects at ultraslow spreading rates, major and trace element concentrations in pyroxene minerals are presented for 14 dredged Gakkel abyssal peridotites. Samples from the same dredge and among dredges reveal wide compositional variation. Trace element compositions of lherzolites reflect 4-6% non-modal fractional mantle melting. However, these high degrees of melting without a corresponding amount of oceanic crust suggest the occurrence of infertile mantle due to ancient melting event(s). In addition, high degrees of melt depletion at short length-scales (<60 km) cannot be thermally driven and must instead reflect inherited small length-scale variability. Harzburgite samples exhibit low concentrations in heavy rare earth elements that can be fit by 6 to ≥13% non-modal melting, but this results in modeled light rare earth element contents that are too low relative to observed concentrations. Instead, harzburgite trace element patterns require open-system melting involving interaction with a percolating melt. Extreme enrichments in highly incompatible elements also suggest the occurrence of late-stage refertilization and melt entrapment. Modeling of several different source melt compositions indicates that the trapped melt was generated from garnet field-equilibrated peridotite. Overall, the compositional variability in Gakkel peridotite samples reflects a heterogeneous mantle resulting from inherited depletion and recent melt percolation and entrapment.

  5. Seismic structure of the lithosphere beneath NW Namibia: Impact of the Tristan da Cunha mantle plume

    Science.gov (United States)

    Yuan, Xiaohui; Heit, Benjamin; Brune, Sascha; Steinberger, Bernhard; Geissler, Wolfram H.; Jokat, Wilfried; Weber, Michael

    2017-01-01

    Northwestern Namibia, at the landfall of the Walvis Ridge, was affected by the Tristan da Cunha mantle plume during continental rupture between Africa and South America, as evidenced by the presence of the Etendeka continental flood basalts. Here we use data from a passive-source seismological network to investigate the upper mantle structure and to elucidate the Cretaceous mantle plume-lithosphere interaction. Receiver functions reveal an interface associated with a negative velocity contrast within the lithosphere at an average depth of 80 km. We interpret this interface as the relic of the lithosphere-asthenosphere boundary (LAB) formed during the Mesozoic by interaction of the Tristan da Cunha plume head with the pre-existing lithosphere. The velocity contrast might be explained by stagnated and "frozen" melts beneath an intensively depleted and dehydrated peridotitic mantle. The present-day LAB is poorly visible with converted waves, indicating a gradual impedance contrast. Beneath much of the study area, converted phases of the 410 and 660 km mantle transition zone discontinuities arrive 1.5 s earlier than in the landward plume-unaffected continental interior, suggesting high velocities in the upper mantle caused by a thick lithosphere. This indicates that after lithospheric thinning during continental breakup, the lithosphere has increased in thickness during the last 132 Myr. Thermal cooling of the continental lithosphere alone cannot produce the lithospheric thickness required here. We propose that the remnant plume material, which has a higher seismic velocity than the ambient mantle due to melt depletion and dehydration, significantly contributed to the thickening of the mantle lithosphere.

  6. Ozone-depleting Substances (ODS)

    Data.gov (United States)

    U.S. Environmental Protection Agency — This site includes all of the ozone-depleting substances (ODS) recognized by the Montreal Protocol. The data include ozone depletion potentials (ODP), global warming...

  7. Deep and persistent melt layer in the Archaean mantle

    Science.gov (United States)

    Andrault, Denis; Pesce, Giacomo; Manthilake, Geeth; Monteux, Julien; Bolfan-Casanova, Nathalie; Chantel, Julien; Novella, Davide; Guignot, Nicolas; King, Andrew; Itié, Jean-Paul; Hennet, Louis

    2018-02-01

    The transition from the Archaean to the Proterozoic eon ended a period of great instability at the Earth's surface. The origin of this transition could be a change in the dynamic regime of the Earth's interior. Here we use laboratory experiments to investigate the solidus of samples representative of the Archaean upper mantle. Our two complementary in situ measurements of the melting curve reveal a solidus that is 200-250 K lower than previously reported at depths higher than about 100 km. Such a lower solidus temperature makes partial melting today easier than previously thought, particularly in the presence of volatiles (H2O and CO2). A lower solidus could also account for the early high production of melts such as komatiites. For an Archaean mantle that was 200-300 K hotter than today, significant melting is expected at depths from 100-150 km to more than 400 km. Thus, a persistent layer of melt may have existed in the Archaean upper mantle. This shell of molten material may have progressively disappeared because of secular cooling of the mantle. Crystallization would have increased the upper mantle viscosity and could have enhanced mechanical coupling between the lithosphere and the asthenosphere. Such a change might explain the transition from surface dynamics dominated by a stagnant lid on the early Earth to modern-like plate tectonics with deep slab subduction.

  8. Picrite "Intelligence" from the Middle-Late Triassic Stikine arc: Composition of mantle wedge asthenosphere

    Science.gov (United States)

    Milidragovic, D.; Zagorevski, A.; Weis, D.; Joyce, N.; Chapman, J. B.

    2018-05-01

    Primitive, near-primary arc magmas occur as a volumetrically minor ≤100 m thick unit in the Canadian Cordillera of northwestern British Columbia, Canada. These primitive magmas formed an olivine-phyric, picritic tuff near the base of the Middle-Late Triassic Stuhini Group of the Stikine Terrane (Stikinia). A new 40Ar/39Ar age on hornblende from a cross-cutting basaltic dyke constrains the tuff to be older than 221 ± 2 Ma. An 87Sr/86Sr isochron of texturally-unmodified tuff samples yields 212 ± 25 Ma age, which is interpreted to represent syn-depositional equilibration with sea-water. Parental trace element magma composition of the picritic tuff is strongly depleted in most incompatible trace elements relative to MORB and implies a highly depleted ambient arc mantle. High-precision trace element and Hf-Nd-Pb isotopic analyses indicate an origin by mixing of a melt of depleted ambient asthenosphere with ≤2% of subducted sediment melt. Metasomatic addition of non-conservative incompatible elements through melting of subducted Panthalassa Ocean floor sediments accounts for the arc signature of the Stuhini Group picritic tuff, enrichment of light rare earth elements (LREE) relative to heavy rare earth elements (HREE) and high field strength elements (HFSE), and anomalous enrichment in Pb. The inferred Panthalassan sediments are similar in composition to the Neogene-Quaternary sediments of the modern northern Cascadia Basin. The initial Hf isotopic composition of the picritic tuff closely approximates that of the ambient Middle-Late Triassic asthenosphere beneath Stikinia and is notably less radiogenic than the age-corrected Hf isotopic composition of the Depleted (MORB) Mantle reservoir (DM or DMM). This suggests that the ambient asthenospheric mantle end-member experienced melt depletion (F ≤ 0.05) a short time before picrite petrogenesis. The mantle end-member in the source of the Stuhini Group picritic tuff is isotopically similar to the mantle source of

  9. 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

  10. PREVIOUS SECOND TRIMESTER ABORTION

    African Journals Online (AJOL)

    PNLC

    PREVIOUS SECOND TRIMESTER ABORTION: A risk factor for third trimester uterine rupture in three ... for accurate diagnosis of uterine rupture. KEY WORDS: Induced second trimester abortion - Previous uterine surgery - Uterine rupture. ..... scarred uterus during second trimester misoprostol- induced labour for a missed ...

  11. How inheritance, geochemical and geophysical properties of the lithospheric mantle influence rift development and subsequent collision

    Science.gov (United States)

    Picazo, Suzanne; Chenin, Pauline; Müntener, Othmar; Manatschal, Gianreto; Karner, Garry; Johnson, Christopher

    2017-04-01

    In magma-poor rifted margins, the rift structures, width of necking zones and overall geometry are controlled by the heterogeneities of geochemical and geophysical properties of the crust and mantle. In this presentation we focus on the mantle heterogeneities and their major implications on the closure of a hyper-extended rifted system. In our study, we review the clinopyroxene and spinel major element composition from the Liguria-Piemonte domain, the Pyrenean domain, the Dinarides and Hellenides ophiolites and the Iberia-Newfoundland rifted margins (Picazo et al, 2016). It would seem that during an extensional cycle i.e., from post-orogenic collapse to polyphase rifting to seafloor spreading, the mineral compositions of mantle peridotites are systematically modified. The initially heterogeneous subcontinental mantle cpx (inherited mantle type 1) equilibrated in the spinel peridotite field and is too enriched in Na2O and Al2O3 to be a residue of syn-rift melting. The heterogeneous inherited subcontinental mantle becomes progressively homogenized due to impregnation by MORB-type melts (refertilized mantle-type 2) during extensional thinning of the lithosphere. At this stage, cpx equilibrate with plagioclase and display lower Na2O and Al2O3 and high Cr2O3 contents. The system might evolve into breakup and oceanization (mantle type 3) i.e., self-sustained steady-state seafloor spreading. The different mantle-types are present in various reconstructed sections of magma-poor margins and display a systematic spatial distribution from mantle type 1 to 3 going oceanwards in Western and Central Europe. We estimated the density of the three identified mantle types using idealized modal peridotite compositions using the algorithm by Hacker et al, (2003). The density of the refertilized plagioclase peridotite is predicted to be lower than that of inherited subcontinental and depleted oceanic mantle. This has some interesting consequences on the reactivation of rifted margins

  12. Mantle Melting as a Function of Water Content in Arcs

    Science.gov (United States)

    Kelley, K. A.; Plank, T.; Newman, S.; Stolper, E.; Grove, T. L.; Parman, S.; Hauri, E.

    2003-12-01

    Subduction zone magmas are characterized by high concentrations of dissolved H2O, presumably derived from the subducted plate and ultimately responsible for melt generation in this tectonic setting. Almost ten years ago, Stolper and Newman (EPSL, 1994) illustrated a linear relationship between the concentration of water (H2Oo) and the fraction of melting (F) in the mantle beneath the Mariana back-arc. Here we report new major element and volatile data for olivine-hosted melt inclusions from the Mariana Islands to test this relationship for melting beneath an arc. Basaltic melt inclusions from the Mariana arc have water contents (2.3-6.1 wt% H2O) significantly higher than all basaltic glasses or melt inclusions from the Mariana back-arc (0.2-2.2 wt% H2O). We use TiO2 as a proxy for F, after correcting for crystal fractionation, and evaluate the Ti source composition with a model based on Ti/Y variations in mid-ocean ridge basalts (MORBs). Each calculated F thus represents the amount of mantle melting for a single melting episode. Even after accounting for mantle depletion, the TiO2 concentrations in Mariana arc magmas record higher extents of mantle melting (F = 10-30%) than recorded in back-arc magmas (F = 5-24%). As a whole, the Mariana arc broadly extends the linear H2Oo-F array defined by the back-arc, although in detail the islands show important differences. Two islands from the Mariana arc (Guguan and Pagan) define a H2Oo-F slope similar to the Mariana back-arc, suggesting similar mantle potential temperature beneath the arc and back-arc ( ˜1360 +/- 20° C). Melts from Agrigan island, however, indicate a steeper slope suggestive both of cooler mantle beneath Agrigan and of along-strike thermal variations beneath the Mariana Islands. Both the arc and back-arc arrays project to finite F at zero water in the mantle, providing evidence for decompression melting in both settings. These relationships may be extended globally to other back-arc and arc systems

  13. Lithospheric Mantle Contribution to High Topography in Central Mongolia

    Science.gov (United States)

    Carlson, R. W.; Ionov, D. A.

    2014-12-01

    Over 110 spinel peridotite xenoliths collected from four localities in the Tariat region, central Mongolia, show a predominance (over 90%) of fertile lherzolites with subordinant harzburgite and peridotites veined with pyroxenite. Equilibration temperatures are high (~900°C at 1.5 GPa [1]). Major element compositions of the fertile samples are consistent with them being the residues of 0-6% partial melt removal at shallow depths [2]. The clinopyroxenes in the lherzolites are moderately LREE depleted (average chondrite normalized La/Sm = 0.45) and most whole rocks show small, if any, depletions in Re and Pd compared to the other HSE. These data point to minimal metasomatic overprinting of these fertile lherzolites. 187Os/188Os for samples with more than 3.2% Al2O3 range only from 0.126 to 0.131, within the range of modern fertile asthenospheric mantle. In contrast to the indicators of fertility in most samples, Sr, Nd and Hf isotopic composition of acid-leached clinopyroxene separates from the lherzolites plot within the range of modern MORB with 87Sr/86Sr from 0.7021 to 0.7026, eNd from +7.7 to +9.8 and eHf from +13.3 to +18.5. The lherzolites thus appear to sample a section of mantle that has compositional and isotope characteristics consistent with modern fertile asthenosphere. The isotopic composition of the Tariat lherzolites are distinct from that of Cenozoic Mongolian basaltic volcanism pointing to limited involvement of the lithospheric mantle in magma generation in this area. The implied asthenospheric provenance of the mantle lithosphere suggests that it either could be the replacement for recently delaminated lithosphere or, more likely, a section of fertile mantle accreted to the base of the crust earlier, e.g. during construction of the Central Asian Orogenic Belt in the Mesozoic/Paleozoic. Although fertile, and hence compositionally dense, the high temperatures of the shallow lithospheric mantle under this section of Mongolia likely contribute to the

  14. Consequences of biome depletion

    International Nuclear Information System (INIS)

    Salvucci, Emiliano

    2013-01-01

    The human microbiome is an integral part of the superorganism together with their host and they have co-evolved since the early days of the existence of the human species. The modification of the microbiome as a result changes in food and social habits of human beings throughout their life history has led to the emergence of many diseases. In contrast with the Darwinian view of nature of selfishness and competence, new holistic approaches are rising. Under these views, the reconstitution of the microbiome comes out as a fundamental therapy for emerging diseases related to biome depletion.

  15. Depleted uranium management alternatives

    Energy Technology Data Exchange (ETDEWEB)

    Hertzler, T.J.; Nishimoto, D.D.

    1994-08-01

    This report evaluates two management alternatives for Department of Energy depleted uranium: continued storage as uranium hexafluoride, and conversion to uranium metal and fabrication to shielding for spent nuclear fuel containers. The results will be used to compare the costs with other alternatives, such as disposal. Cost estimates for the continued storage alternative are based on a life-cycle of 27 years through the year 2020. Cost estimates for the recycle alternative are based on existing conversion process costs and Capital costs for fabricating the containers. Additionally, the recycle alternative accounts for costs associated with intermediate product resale and secondary waste disposal for materials generated during the conversion process.

  16. The new MCNP6 depletion capability

    International Nuclear Information System (INIS)

    Fensin, M. L.; James, M. R.; Hendricks, J. S.; Goorley, J. T.

    2012-01-01

    The first MCNP based in-line Monte Carlo depletion capability was officially released from the Radiation Safety Information and Computational Center as MCNPX 2.6.0. Both the MCNP5 and MCNPX codes have historically provided a successful combinatorial geometry based, continuous energy, Monte Carlo radiation transport solution for advanced reactor modeling and simulation. However, due to separate development pathways, useful simulation capabilities were dispersed between both codes and not unified in a single technology. MCNP6, the next evolution in the MCNP suite of codes, now combines the capability of both simulation tools, as well as providing new advanced technology, in a single radiation transport code. We describe here the new capabilities of the MCNP6 depletion code dating from the official RSICC release MCNPX 2.6.0, reported previously, to the now current state of MCNP6. NEA/OECD benchmark results are also reported. The MCNP6 depletion capability enhancements beyond MCNPX 2.6.0 reported here include: (1) new performance enhancing parallel architecture that implements both shared and distributed memory constructs; (2) enhanced memory management that maximizes calculation fidelity; and (3) improved burnup physics for better nuclide prediction. MCNP6 depletion enables complete, relatively easy-to-use depletion calculations in a single Monte Carlo code. The enhancements described here help provide a powerful capability as well as dictate a path forward for future development to improve the usefulness of the technology. (authors)

  17. The New MCNP6 Depletion Capability

    International Nuclear Information System (INIS)

    Fensin, Michael Lorne; James, Michael R.; Hendricks, John S.; Goorley, John T.

    2012-01-01

    The first MCNP based inline Monte Carlo depletion capability was officially released from the Radiation Safety Information and Computational Center as MCNPX 2.6.0. Both the MCNP5 and MCNPX codes have historically provided a successful combinatorial geometry based, continuous energy, Monte Carlo radiation transport solution for advanced reactor modeling and simulation. However, due to separate development pathways, useful simulation capabilities were dispersed between both codes and not unified in a single technology. MCNP6, the next evolution in the MCNP suite of codes, now combines the capability of both simulation tools, as well as providing new advanced technology, in a single radiation transport code. We describe here the new capabilities of the MCNP6 depletion code dating from the official RSICC release MCNPX 2.6.0, reported previously, to the now current state of MCNP6. NEA/OECD benchmark results are also reported. The MCNP6 depletion capability enhancements beyond MCNPX 2.6.0 reported here include: (1) new performance enhancing parallel architecture that implements both shared and distributed memory constructs; (2) enhanced memory management that maximizes calculation fidelity; and (3) improved burnup physics for better nuclide prediction. MCNP6 depletion enables complete, relatively easy-to-use depletion calculations in a single Monte Carlo code. The enhancements described here help provide a powerful capability as well as dictate a path forward for future development to improve the usefulness of the technology.

  18. Dust evolution, a global view: III. Core/mantle grains, organic nano-globules, comets and surface chemistry.

    Science.gov (United States)

    Jones, A P

    2016-12-01

    Within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), this work explores the surface processes and chemistry relating to core/mantle interstellar and cometary grain structures and their influence on the nature of these fascinating particles. It appears that a realistic consideration of the nature and chemical reactivity of interstellar grain surfaces could self-consistently and within a coherent framework explain: the anomalous oxygen depletion, the nature of the CO dark gas, the formation of 'polar ice' mantles, the red wing on the 3 μm water ice band, the basis for the O-rich chemistry observed in hot cores, the origin of organic nano-globules and the 3.2 μm 'carbonyl' absorption band observed in comet reflectance spectra. It is proposed that the reaction of gas phase species with carbonaceous a-C(:H) grain surfaces in the interstellar medium, in particular the incorporation of atomic oxygen into grain surfaces in epoxide functional groups, is the key to explaining these observations. Thus, the chemistry of cosmic dust is much more intimately related with that of the interstellar gas than has previously been considered. The current models for interstellar gas and dust chemistry will therefore most likely need to be fundamentally modified to include these new grain surface processes.

  19. Boron isotope variations in Tonga-Kermadec-New Zealand arc lavas: Implications for the origin of subduction components and mantle influences

    Science.gov (United States)

    Leeman, William P.; Tonarini, Sonia; Turner, Simon

    2017-03-01

    The Tonga-Kermadec-New Zealand volcanic arc is an end-member of arc systems with fast subduction suggesting that the Tonga sector should have the coolest modern slab thermal structure on Earth. New data for boron concentration and isotopic composition are used to evaluate the contrasting roles of postulated subduction components (sediments and oceanic slab lithologies) in magma genesis. Major observations include: (a) Tonga-Kermadec volcanic front lavas are enriched in B (as recorded by B/Nb and similar ratios) and most have relatively high δ11B (>+4‰), whereas basaltic lavas from New Zealand have relatively low B/Nb and δ11B (enrichments in the arc magma sources are likely dominated by serpentinite domains deeper within the subducting slab (±altered oceanic crust), and B systematics are consistent with dominant transport by slab-derived aqueous fluids. Effects of this process are amplified by mantle wedge source depletion due to prior melt extraction.Plain Language SummaryBoron isotope and other geochemical data are used to evaluate contributions from subducted materials to magma sources for volcanoes of the Tonga-Kermadec-New Zealand volcanic arc. The data are used to estimate the composition of modified mantle sources for the arc magmas as well as the extent of melting to produce them. It is shown that the mantle was previously depleted in melt components, and then overprinted by B and other components from the subducting slab, predominantly by aqueous fluids produced by dehydration of the slab. Some elements (e.g., Th, Be, La) considered to be relatively immobile in aqueous fluids, show strong correlation with B-enrichment, suggesting that they too can be mobilized in this manner. This result is important for understanding the origin of arc magmas from other localities. In addition our data imply that slab inputs to arc magma sources are cumulative over time.

  20. Transition region of the earth's upper mantle

    Science.gov (United States)

    Anderson, D. L.; Bass, J. D.

    1986-01-01

    The chemistry of the earth's mantle is discussed using data from cosmochemistry, geochemistry, petrology, seismology, and mineral physics. The chondritic earth, the upper mantle and the 400-km discontinuity, the transition region, lower mantle mineralogy, and surface wave tomography are examined. Three main issues are addressed: (1) whether the mantle is homogeneous in composition or chemically stratified, (2) whether the major element chemistry of the mantle is more similar to upper mantle peridotites or to chondrites, and (3) the nature of the composition of the source region of basalts erupted at midocean ridges.

  1. Crustal and upper mantle structure of the Slave craton from P- and S- Receiver Functions

    Science.gov (United States)

    Barantseva, Olga; Vinnik, Lev; Artemieva, Irina

    2017-04-01

    Teleseismic events recorded by POLARIS array in NW Canada (Slave craton) and Yellowknife station were used to calculate a sufficient number of receiver functions for P (PRF) and S (SRF) waves. Velocity (Vp and Vs) and Vp/Vs profiles from the Earth's surface down to 300 km are obtained through the simultaneous inversion of PRF and SRF with teleseismic travel time residuals for the crust and upper mantle. We observe highly heterogeneous structure of the cratonic upper mantle. The Lehman discontinuity (the bottom of the low velocity zone) is found in the western Slave craton, whereas it is not observed in the eastern part of the Slave craton. At stations located in the southern part of the craton, we observe an increase of S-wave velocities (as compared to IASP91 values) at the depths 45-150 km which is typical for depleted cratonic mantle. Low Vp/Vs ratio, obtained for the uppermost mantle (1.65-1.70) can be explained by a high fraction of Opx. A comparison of our results with available xenoliths data shows a good agreement between seismic velocity change at a depth of ca. 160 km and a decrease in mantle depletion at about the same depth.

  2. Coupled petrological-geodynamical modeling of a compositionally heterogeneous mantle plume

    Science.gov (United States)

    Rummel, Lisa; Kaus, Boris J. P.; White, Richard W.; Mertz, Dieter F.; Yang, Jianfeng; Baumann, Tobias S.

    2018-01-01

    Self-consistent geodynamic modeling that includes melting is challenging as the chemistry of the source rocks continuously changes as a result of melt extraction. Here, we describe a new method to study the interaction between physical and chemical processes in an uprising heterogeneous mantle plume by combining a geodynamic code with a thermodynamic modeling approach for magma generation and evolution. We pre-computed hundreds of phase diagrams, each of them for a different chemical system. After melt is extracted, the phase diagram with the closest bulk rock chemistry to the depleted source rock is updated locally. The petrological evolution of rocks is tracked via evolving chemical compositions of source rocks and extracted melts using twelve oxide compositional parameters. As a result, a wide variety of newly generated magmatic rocks can in principle be produced from mantle rocks with different degrees of depletion. The results show that a variable geothermal gradient, the amount of extracted melt and plume excess temperature affect the magma production and chemistry by influencing decompression melting and the depletion of rocks. Decompression melting is facilitated by a shallower lithosphere-asthenosphere boundary and an increase in the amount of extracted magma is induced by a lower critical melt fraction for melt extraction and/or higher plume temperatures. Increasing critical melt fractions activates the extraction of melts triggered by decompression at a later stage and slows down the depletion process from the metasomatized mantle. Melt compositional trends are used to determine melting related processes by focusing on K2O/Na2O ratio as indicator for the rock type that has been molten. Thus, a step-like-profile in K2O/Na2O might be explained by a transition between melting metasomatized and pyrolitic mantle components reproducible through numerical modeling of a heterogeneous asthenospheric mantle source. A potential application of the developed method

  3. 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.

  4. 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.

  5. Riddle of depleted uranium

    International Nuclear Information System (INIS)

    Hussein, A.S.

    2005-01-01

    Depleted Uranium (DU) is the waste product of uranium enrichment from the manufacturing of fuel rods for nuclear reactors in nuclear power plants and nuclear power ships. DU may also results from the reprocessing of spent nuclear reactor fuel. Potentially DU has both chemical and radiological toxicity with two important targets organs being the kidney and the lungs. DU is made into a metal and, due to its availability, low price, high specific weight, density and melting point as well as its pyrophoricity; it has a wide range of civilian and military applications. Due to the use of DU over the recent years, there appeared in some press on health hazards that are alleged to be due to DU. In these paper properties, applications, potential environmental and health effects of DU are briefly reviewed

  6. 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

  7. 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...

  8. Laparoscopy After Previous Laparotomy

    Directory of Open Access Journals (Sweden)

    Zulfo Godinjak

    2006-11-01

    Full Text Available Following the abdominal surgery, extensive adhesions often occur and they can cause difficulties during laparoscopic operations. However, previous laparotomy is not considered to be a contraindication for laparoscopy. The aim of this study is to present that an insertion of Veres needle in the region of umbilicus is a safe method for creating a pneumoperitoneum for laparoscopic operations after previous laparotomy. In the last three years, we have performed 144 laparoscopic operations in patients that previously underwent one or two laparotomies. Pathology of digestive system, genital organs, Cesarean Section or abdominal war injuries were the most common causes of previouslaparotomy. During those operations or during entering into abdominal cavity we have not experienced any complications, while in 7 patients we performed conversion to laparotomy following the diagnostic laparoscopy. In all patients an insertion of Veres needle and trocar insertion in the umbilical region was performed, namely a technique of closed laparoscopy. Not even in one patient adhesions in the region of umbilicus were found, and no abdominal organs were injured.

  9. The Toxicity of Depleted Uranium

    OpenAIRE

    Briner, Wayne

    2010-01-01

    Depleted uranium (DU) is an emerging environmental pollutant that is introduced into the environment primarily by military activity. While depleted uranium is less radioactive than natural uranium, it still retains all the chemical toxicity associated with the original element. In large doses the kidney is the target organ for the acute chemical toxicity of this metal, producing potentially lethal tubular necrosis. In contrast, chronic low dose exposure to depleted uranium may not produce a c...

  10. AND THEIR IMPLICATIONS TO MANTLE DYNAMICS

    African Journals Online (AJOL)

    ... the southwest Indian ridge appears to be tapping the same portion of mantle as did the Central Indian ridge. These results have important thermo-chemical implications, such as variations in the extent of melting and mineralogicalcomposition of the mantle beneath diflerent ridges, which may influence mantle dynamics.

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

    Science.gov (United States)

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

    2017-04-01

    Knowledge of melting properties is critical to predict the nature and the fate of melts produced in the deep mantle. Early in the Earth's history, melting properties controlled the magma ocean crystallization, which potentially induced chemical segregation in distinct reservoirs. Today, partial melting most probably occurs in the lowermost mantle as well as at mid upper-mantle depths, which control important aspects of mantle dynamics, including some types of volcanism. Unfortunately, despite major experimental and theoretical efforts, major controversies remain about several aspects of mantle melting. For example, the liquidus of the mantle was reported (for peridotitic or chondritic-type composition) with a temperature difference of ∼1000 K at high mantle depths. Also, the Fe partitioning coefficient (DFeBg/melt) between bridgmanite (Bg, the major lower mantle mineral) and a melt was reported between ∼0.1 and ∼0.5, for a mantle depth of ∼2000 km. Until now, these uncertainties had prevented the construction of a coherent picture of the melting behavior of the deep mantle. In this article, we perform a critical review of previous works and develop a coherent, semi-quantitative, model. We first address the melting curve of Bg with the help of original experimental measurements, which yields a constraint on the volume change upon melting (ΔVm). Secondly, we apply a basic thermodynamical approach to discuss the melting behavior of mineralogical assemblages made of fractions of Bg, CaSiO3-perovskite and (Mg,Fe)O-ferropericlase. Our analysis yields quantitative constraints on the SiO2-content in the pseudo-eutectic melt and the degree of partial melting (F) as a function of pressure, temperature and mantle composition; For examples, we find that F could be more than 40% at the solidus temperature, except if the presence of volatile elements induces incipient melting. We then discuss the melt buoyancy in a partial molten lower mantle as a function of pressure

  12. Physical and petrologic evidence for a two component mantle MORB source

    Science.gov (United States)

    Dick, H.; Standish, J.; Snow, J.; Michael, P.; Salters, V.

    2003-04-01

    Study of ultra-slow spreading sections of the Southwest Indian and Gakkel Ridges support a two-component (veined?) mantle source for MORB. At both the Southwest Indian and Gakkel Ridges, mantle upwelling slows continuously over long sections of the ridge system due to changing ridge geometry and position with respect to the pole of rotation. For a simple peridotitic mantle this predicts steadily decreasing crustal production due to conductive heat loss depressing the top of the mantle-melting column. Instead, at 16 degrees E on the Southwest Indian Ridge and at 3 degrees E on the Gakkel, seafloor spreading abruptly goes from magmatic to amagmatic, with peridotite instead of basalt emplaced to the sea floor for long distances. As the mantle upwelling rate continues to decrease, however, volcanism reappears on both ridges at point source volcanoes and at large long-lived cross-axis volcanic highs, with intervening amagmatic segments. Such low levels of crustal production show that mantle melting is limited, and that abyssal peridotites there must have compositions close to unmelted mantle. However, significant areas of the amagmatic sections of the SW Indian and Gakkel Ridges appear to be floored dominantly by harzburgite, while other regions predominantly expose lherzolite. This poses a problem for modeling the MORB source as simply peridotite; as harzburgite is too depleted too generate MORB. The limited melt production during ultra-slow spreading also makes it difficult to produce the harzburgite during the axial mantle-melting event from lherzolite. In this case there is likely another mantle component contributing to MORB generation. Basalts over the transition from slow to ultra-slow spreading show a regular compositional gradient over 1000 km. Helium isotopes range from only 7.3 RA to 6.3 RA across this region, suggesting that while there is a chemical gradient in the mantle, there is not an abrupt change in the mantle source at the 16 degree E discontinuity

  13. The Interaction Between Supercontinent Cycles and Compositional Variations in the Deep Mantle

    Science.gov (United States)

    Lowman, J. P.; Trim, S. J.

    2015-12-01

    Earth is the only planet known to currently feature active plate tectonics. Two features that may influence the Earth's ability to sustain plate-like surface motion are the presence of continents and the inferred chemical piles lying on the core mantle boundary. In our previous study that modelled thermochemical convection in the mantle with evolving plates, it was shown that upwellings that form on top of chemical piles are relatively weak and make a diminished contribution to lithospheric stress. Yet, surface yielding is required in order to maintain plate tectonics and form new plate boundaries. Consequently an intrinsically dense layer in the lower mantle can decrease the vigour of convection and the likelihood of surface failure. In contrast to the mantle upwellings that form above the chemically dense provinces in our models, particularly vigorous plumes form where the ambient mantle lies adjacent to the core mantle boundary and at the edges of the chemically dense piles. Continents also affect surface mobility, due to their inherent buoyancy and their distinct yield strength. In this study we employ numerical models of mantle convection featuring both tectonic plates and compositional variation in the mantle and lithosphere. Plate-like surface motion is dynamically modelled using a force-balance method that determines plate velocities based upon lithospheric stresses. Oceanic and continental margins evolve in response to the plate velocities and specified lithospheric yield stresses. Compositional variations in the deep mantle are tracked using the tracer ratio method. For a range of ratios of the ambient mantle density to the density of the compositionally enriched material, we examine the the impact of mantle compositional variation on plate evolution, the effect of continents on planetary surface mobility and the frequency of supercontinent assembly versus the mobility of compositional provinces.

  14. 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.

  15. 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

  16. Evidence for chemically heterogeneous Arctic mantle beneath the Gakkel Ridge

    Science.gov (United States)

    D'Errico, Megan E.; Warren, Jessica M.; Godard, Marguerite

    2016-02-01

    Ultraslow spreading at mid-ocean ridges limits melting due to on-axis conductive cooling, leading to the prediction that peridotites from these ridges are relatively fertile. To test this, we examined abyssal peridotites from the Gakkel Ridge, the slowest spreading ridge in the global ocean ridge system. Major and trace element concentrations in pyroxene and olivine minerals are reported for 14 dredged abyssal peridotite samples from the Sparsely Magmatic (SMZ) and Eastern Volcanic (EVZ) Zones. We observe large compositional variations among peridotites from the same dredge and among dredges in close proximity to each other. Modeling of lherzolite trace element compositions indicates varying degrees of non-modal fractional mantle melting, whereas most harzburgite samples require open-system melting involving interaction with a percolating melt. All peridotite chemistry suggests significant melting that would generate a thick crust, which is inconsistent with geophysical observations at Gakkel Ridge. The refractory harzburgites and thin overlying oceanic crust are best explained by low present-day melting of a previously melted heterogeneous mantle. Observed peridotite compositional variations and evidence for melt infiltration demonstrates that fertile mantle components are present and co-existing with infertile mantle components. Melt generated in the Gakkel mantle becomes trapped on short length-scales, which produces selective enrichments in very incompatible rare earth elements. Melt migration and extraction may be significantly controlled by the thick lithosphere induced by cooling at such slow spreading rates. We propose the heterogeneous mantle that exists beneath Gakkel Ridge is the consequence of ancient melting, combined with subsequent melt percolation and entrapment.

  17. Depletable resources and the economy

    NARCIS (Netherlands)

    Heijman, W.J.M.

    1991-01-01

    The subject of this thesis is the depletion of scarce resources. The main question to be answered is how to avoid future resource crises. After dealing with the complex relation between nature and economics, three important concepts in relation with resource depletion are discussed: steady state,

  18. The Toxicity of Depleted Uranium

    Directory of Open Access Journals (Sweden)

    Wayne Briner

    2010-01-01

    Full Text Available Depleted uranium (DU is an emerging environmental pollutant that is introduced into the environment primarily by military activity. While depleted uranium is less radioactive than natural uranium, it still retains all the chemical toxicity associated with the original element. In large doses the kidney is the target organ for the acute chemical toxicity of this metal, producing potentially lethal tubular necrosis. In contrast, chronic low dose exposure to depleted uranium may not produce a clear and defined set of symptoms. Chronic low-dose, or subacute, exposure to depleted uranium alters the appearance of milestones in developing organisms. Adult animals that were exposed to depleted uranium during development display persistent alterations in behavior, even after cessation of depleted uranium exposure. Adult animals exposed to depleted uranium demonstrate altered behaviors and a variety of alterations to brain chemistry. Despite its reduced level of radioactivity evidence continues to accumulate that depleted uranium, if ingested, may pose a radiologic hazard. The current state of knowledge concerning DU is discussed.

  19. Contrasting thermal and melting histories for segments of mantle lithosphere in the Nahlin ophiolite, British Columbia, Canada

    Science.gov (United States)

    McGoldrick, Siobhan; Canil, Dante; Zagorevski, Alex

    2018-03-01

    The Permo-Triassic Nahlin ophiolite is the largest and best-preserved ophiolite in the Canadian Cordillera of British Columbia and Yukon, Canada. The ophiolite is well-exposed along its 150 km length with mantle segments divisible into the Hardluck and Menatatuline massifs. Both massifs comprise mostly depleted spinel harzburgite (exchange temperatures in the mantle of the ophiolite also change systematically along strike with the degree of partial melt depletion. The temperatures recorded by REE and Ca-Mg exchange between coexisting pyroxenes require markedly higher peak temperatures and cooling rates for the Menatatuline massif (1250 °C, 0.1-0.01 °C/year) compared to the Hardluck massif (rates controlled by presence or absence of a crustal section above the mantle lithosphere, or by rapid exhumation along a detachment.

  20. Isotopic characterisation of the sub-continental lithospheric mantle beneath Zealandia, a rifted fragment of Gondwana

    DEFF Research Database (Denmark)

    Waight, Tod Earle; Scott, James M.; van der Meer, Quinten Har Adriaan

    2013-01-01

    and that contained a HIMU component. The volcanics have tapped two adjacent but chemically contrasting upper mantle domains: a fertile eastern domain and an extremely depleted western domain. Both domains underlie Mesozoic metasedimentary crust. Radiogenic isotope compositions of the clinopyroxene have 87Sr/86Sr...... between 0.7023 to 0.7035, 143Nd/144Nd between 0.5128 and 0.5132 (corresponding to eNd between +3 and +13) with a few samples extending to even more depleted compositions, 206Pb/204 Pb between ca. 19.5 to 21.5 and 208Pb/204Pb between ca. 38.5 to 40.5. No correlations are observed between isotopic......-like, strongly LREE-depleted, through to patterns displaying evidence for depletion and subsequent re-enrichment. These variations occur throughout the region and also between different xenoliths from a single eruption site. There are no clear correlations between REE characteristics and isotopic composition...

  1. Mantle heterogeneity in the source region of mid-ocean ridge basalts along the northern Central Indian Ridge (8°S-17°S)

    Science.gov (United States)

    Kim, Jonguk; Pak, Sang-Joon; Moon, Jai-Woon; Lee, Sang-Mook; Oh, Jihye; Stuart, Finlay M.

    2017-04-01

    The northern Central Indian Ridge (CIR) between 8°S and 17°S is composed of seven segments whose spreading rates increase southward from ˜35 to ˜40 mm/yr. During expeditions of R/V Onnuri to study hydrothermal activity on the northern CIR in 2009-2011, high-resolution multibeam mapping was conducted and ridge axis basalts were dredged. The major and trace element and Sr-Nd-Pb-He isotopic compositions of basaltic glasses dredged from the spreading axis require three mantle sources: depleted mantle and two distinct enriched mantle sources. The southern segments have Sr, Nd, and Pb that are a mix of depleted mantle and an enriched component as recorded in southern CIR MORB. This enrichment is indistinguishable from Rèunion plume mantle, except for He isotopes. This suggests that the southern segments have incorporated a contribution of the fossil Rèunion plume mantle, as the CIR migrated over hot-spot-modified mantle. The low 3He/4He (7.5-9.2 RA) of this enriched component may result from radiogenic 4He ingrowth in the fossil Rèunion mantle component. Basalts from the northern segments have high 206Pb/204Pb (18.53-19.15) and low 87Sr/86Sr (0.70286-0.70296) that are distinct from the Rèunion plume but consistent with derivation from mantle with FOZO signature, albeit with 3He/4He (9.2-11.8 RA) that are higher than typical. The FOZO-like enriched mantle cannot be attributed to the track of a nearby mantle plume. Instead, this enrichment may have resulted from recycling oceanic crust, possibly accompanied by small plume activity.

  2. First Row Transition Metals in Olivine - Petrogenetic Tracers for the Evolution of Mantle-Derived Magmas

    Science.gov (United States)

    Locmelis, M.; Arevalo, R. D., Jr.; Puchtel, I. S.; Barnes, S. J.; Fiorentini, M. L.

    2015-12-01

    Olivine is the most abundant mineral in the upper mantle and a major constituent of most mantle-derived rocks. However, despite its abundance, studies on the trace element chemistry of olivine are underrepresented in the literature. We present the results of a comprehensive study on the contents of first-row transition metals (FRTM: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn), Ga and Ge in olivines from 2.7-3.5 Ga old Munro- and Barberton-type komatiites from the Kapvaal and Zimbabwe Cratons in southern Africa, the Yilgarn Craton in Australia, and the Superior Craton in Canada. Komatiitic olivines are compared to olivines from a Devonian-Carboniferous mantle peridotite (Finero, Italy) and contemporary ocean Island basalts (OIB, from St. Helena, South Atlantic Ocean). The olivine major element chemistry was determined using a JEOL JXA-8900 Superprobe at the University of Maryland. Trace element contents were determined using a Photon Machines Analyte G2 193 nm Excimer laser ablation system coupled to a Nu Instruments AttoM single collector ICP-MS at NASA Goddard Space Flight Center. Medium resolution mass discrimination (m/Δm = 2500, at 5% peak intensity) was leveraged to separate isobaric interferences and support accurate quantitation of elemental abundances. The results show that olivines from komatiites are largely depleted in FRTM, Ga and Ge relative to the composition of the primitive mantle (FRTMPM-norm = ~0.01 - 1). All komatiitic olivines have similar mantle-normalized trace element patterns, regardless of age and/or locality. Olivines from the Finero mantle peridotite and the St. Helena OIB are similarly depleted. However, compared to komatiites, grains from Finero are enriched in Ge and distinctly depleted in Ti, V, Cr, and Ga, whereas olivines from St. Helena have overall flatter normalized trace element patterns. The distinct patterns show that olivine chemistry can be used to identify and understand the source and evolution of mantle-derived rocks

  3. [Acute tryptophan depletion in eating disorders].

    Science.gov (United States)

    Díaz-Marsa, M; Lozano, C; Herranz, A S; Asensio-Vegas, M J; Martín, O; Revert, L; Saiz-Ruiz, J; Carrasco, J L

    2006-01-01

    This work describes the rational bases justifying the use of acute tryptophan depletion technique in eating disorders (ED) and the methods and design used in our studies. Tryptophan depletion technique has been described and used in previous studies safely and makes it possible to evaluate the brain serotonin activity. Therefore it is used in the investigation of hypotheses on serotonergic deficiency in eating disorders. Furthermore, and given the relationship of the dysfunctions of serotonin activity with impulsive symptoms, the technique may be useful in biological differentiation of different subtypes, that is restrictive and bulimic, of ED. 57 female patients with DSM-IV eating disorders and 20 female controls were investigated with the tryptophan depletion test. A tryptophan-free amino acid solution was administered orally after a two-day low tryptophan diet to patients and controls. Free plasma tryptophan was measured at two and five hours following administration of the drink. Eating and emotional responses were measured with specific scales for five hours following the depletion. A study of the basic characteristics of the personality and impulsivity traits was also done. Relationship of the response to the test with the different clinical subtypes and with the temperamental and impulsive characteristics of the patients was studied. The test was effective in considerably reducing plasma tryptophan in five hours from baseline levels (76%) in the global sample. The test was well tolerated and no severe adverse effects were reported. Two patients withdrew from the test due to gastric intolerance. The tryptophan depletion test could be of value to study involvement of serotonin deficits in the symptomatology and pathophysiology of eating disorders.

  4. Diamonds in an upper mantle peridotite nodule from kimberlite in southern wyoming.

    Science.gov (United States)

    McCallum, M E; Eggler, D H

    1976-04-16

    Diamonds in a serpentinized garnet peridotite nodule from a diatreme in southern Wyoming are the first known occurrence in an upper mantle peridotite xenolith from a kimberlite intrusion in North America as well as the second authenticated occurrence of diamonds from kimberlite pipes in North America. The nodule is believed to have come from a section of depleted (partially melted) lherzolite at a depth of 130 to 180 kilometers.

  5. Composition and spatial evolution of mantle and fluids released beneath the active Southeast Mariana Forearc Rift: do they have arc or backarc basin signatures?

    Science.gov (United States)

    Ribeiro, J. M.; Stern, R. J.; Kelley, K. A.; Ishizuka, O.; Anthony, E. Y.; Ren, M.; Manton, W. I.; Ohara, Y.; Reagan, M. K.; Bloomer, S. H.

    2010-12-01

    -shallow subduction component. Compositional variations suggest that mantle depletion and the ultra-shallow subduction component increase from the south Mariana BAB to SEMFR; while the deep subduction component is similar in both SEMFR and BAB, suggesting that BAB mantle source (previously depleted by BAB melt extraction) or BAB melt is enriched in deep subduction component beneath the BAB before flowing towards SEMFR. The mantle source or BAB melt progressively interacted with the ultra-shallow, metasomatic agent and/or mixed with hydrous melts produced beneath the forearc to generate SEMFR lavas. Better understanding of rift magmatic evolution is likely to follow recovery and study of more samples from the SEMFR, scheduled for Sept. 2010 using R/V Yokosuka and Shinkai 6500.

  6. Composition of uppermost mantle beneath the Northern Fennoscandia - numerical modeling and petrological interpretation

    Science.gov (United States)

    Virshylo, Ivan; Kozlovskaya, Elena; Prodaivoda, George; Silvennoinen, Hanna

    2013-04-01

    -forming oxides using stoichiometric formulas. The results indicate significant variation of Fe and Mg oxides concentration in the uppermost mantle. The Mg/Fe ratio could be different from the results of previous studies (Griffin et al., 2003; Svetov & Smolkin, 2003), but it is in agreement with the geophysical models considered in our study. At the same time the SiO2 concentration is close to the chemical composition of xenoliths from the Fennoscandia, including Kola Peninsula and Central Finland (Beard, Downes, Mason, & Vetrin, 2007; Kukkonen et al., 2008; Lehtonen et al., 2004). Brief conclusions from our study could be formulated as follows: 1) Modelling confirms potential significant lateral inhomogeneity of mineral composition of the uppermost mantle of northern Fennoscandian Shield. 2) Lherzolitic composition of the mantle lithosphere generally explains seismic velocities obtained by teleseismic tomography in northern Fennoscandian Shield. It could be used as a primary a priori model for interpretation. But potential presence of eclogites cannot be rejected, at least for some parts of studied area. 3) The future study needs to include more precise evaluation of temperature and density in the upper mantle using gravity and heat flow data. Afonso, J. C., Fernàndez, M., Ranalli, G., Griffin, W. L., & Connolly, J. a. D. (2008). Integrated geophysical-petrological modeling of the lithosphere and sublithospheric upper mantle: Methodology and applications. Geochemistry Geophysics Geosystems, 9(5). doi:10.1029/2007GC001834 Beard, a. D., Downes, H., Mason, P. R. D., & Vetrin, V. R. (2007). Depletion and enrichment processes in the lithospheric mantle beneath the Kola Peninsula (Russia): Evidence from spinel lherzolite and wehrlite xenoliths. Lithos, 94(1-4), 1-24. doi:10.1016/j.lithos.2006.02.002 Dziewonski, A.M., A.L. Hales, & E.R. Lapwood. (1975) Parametrically simple earth models consistent with geophysical data Phys. Earth Plan. Int. 10:12. Fullea, J., Afonso, J. C., Connolly

  7. 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.

  8. Mantle viscosity structure constrained by joint inversions of seismic velocities and density

    Science.gov (United States)

    Rudolph, M. L.; Moulik, P.; Lekic, V.

    2017-12-01

    The viscosity structure of Earth's deep mantle affects the thermal evolution of Earth, the ascent of mantle upwellings, sinking of subducted oceanic lithosphere, and the mixing of compositional heterogeneities in the mantle. Modeling the long-wavelength dynamic geoid allows us to constrain the radial viscosity profile of the mantle. Typically, in inversions for the mantle viscosity structure, wavespeed variations are mapped into density variations using a constant- or depth-dependent scaling factor. Here, we use a newly developed joint model of anisotropic Vs, Vp, density and transition zone topographies to generate a suite of solutions for the mantle viscosity structure directly from the seismologically constrained density structure. The density structure used to drive our forward models includes contributions from both thermal and compositional variations, including important contributions from compositionally dense material in the Large Low Velocity Provinces at the base of the mantle. These compositional variations have been neglected in the forward models used in most previous inversions and have the potential to significantly affect large-scale flow and thus the inferred viscosity structure. We use a transdimensional, hierarchical, Bayesian approach to solve the inverse problem, and our solutions for viscosity structure include an increase in viscosity below the base of the transition zone, in the shallow lower mantle. Using geoid dynamic response functions and an analysis of the correlation between the observed geoid and mantle structure, we demonstrate the underlying reason for this inference. Finally, we present a new family of solutions in which the data uncertainty is accounted for using covariance matrices associated with the mantle structure models.

  9. Ancient lead and osmium in the oceanic mantle

    Science.gov (United States)

    Burton, K. W.; Cenki-Tok, B.; Mokadem, F.; Harvey, J.; Gannoun, A.; Parkinson, I. J.

    2011-12-01

    The isotope composition of lead (Pb) in the silicate Earth appears to be far too radiogenic for evolution from chondritic (primitive solar system) material over 4.57 billion years, the so-called 'Pb paradox' [1]. Loss of Pb to the core [2], storage in the lower continental crust [3], or arrival in a late veneer [4], have all been proposed as mechanisms to account for this imbalance. Recently is has been suggested that orogenic peridotites, and by implication the upper mantle itself, could serve as a complementary reservoir of the unradiogenic Pb [5]. However, orogenic peridotites may not be representative of the asthenopshere underlying present-day mid-ocean ridges, furthermore, it is unclear why such material is not sampled by oceanic basalts. This study presents high-precision double-spike Pb isotope data for sulphides trapped as inclusions in silicate minerals in abyssal peridotites from the North Atlantic ocean (ODP Leg 209; Site 1274A). These sulphides preserve extremely unradiogenic Pb isotope compositions, some corresponding to an age of 1.83±0.23 billion years. These ages are indistinguishable from those preserved by Os isotopes in sulphides from the same samples [6], and demonstrate that both Pb and Os isotopes preserve an unequivocal record of ancient melt depletion in the sub-oceanic mantle. from abyssal peridotites exposed on the sea-floor the North Atlantic ocean.That these sulphides contribute little of their Pb to the isotope composition of oceanic basalts may be, in part, due to their entrapment in host silicate phases but also because they are present in refractory domains in the mantle that are little sampled by later melting events. If MORB do not sample these refractory domains then neither do they constrain the overall chemistry of the asthensophere, and will tend to underestimate the actual extent of depletion of the upper mantle. [1] Allègre, C.J. Earth Planet. Sci. lett. 5, 261-269 (1969). [2] Vollmer, R. Nature 270, 144-147 (1977). [3] O

  10. Rock species formation due to deep-mantle melting

    Science.gov (United States)

    Fomin, Ilya; Tackley, Paul

    2017-04-01

    Melting and melting migration are processes leading to chemically distinct rock species from a homogeneous substrate in the Earth mantle. Iron-rich melts and corresponding rock species are proposed to result from magma ocean progressive crystallization [Labrosse et al., 2007], and modern geophysical models of ULVZ (e.g. [Beuchert & Schmeling, 2013]) discuss their presence at around the CMB today. We perform long-term (tens of millions of years) numerical simulations of the Earth's mantle for a plausible range of CMB temperatures to understands the possibility of melting and it's consequences. Our model of melting is based on experimental data and ab initio simulations. Physical properties (liquid-solid density differences) are adjusted with data of [de Koker et al., 2013; Mosenfelder et al., 2007; Stixrude & Lithgow-Bertelloni, 2011; Thomas & Asimow, 2013]. This model is included in StagYY numerical code (e.g. [Tackley, 2008]) to simulate mass and thermal fluxes within the Earth mantle. Melt segregation (rocks' permeability and velocities) is considered using equations listed in [Abe, 1995; Solomatov, Stevenson, 1993; Martin & Nokes, 1989]. Thermal effects (adiabatic heating and viscous dissipation) are considered. Viscous dissipation term includes Darcy flux term, but omits highly non-linear Brinkman contribution [Nield, 2007]. Modeling predicts formation of melt if temperature at CMB exceeds 4000-4050K. It's segregation and reequilibration results in sufficient volumes of slightly iron-enriched melt lighter than solid counterpart and moving upward. However, it's propagation is strongly controlled by temperature. Partial melting atop the molten layer results in formation of refractory iron-poor restite which delaminates and sink down, so that a layer of iron-depleted material forms underneath the molten layer. Our model applied to homogeneous pyrolitic mantle results in formation of layers of iron-depleted material with average FeO around 4.6 mol.% and iron

  11. Mantle xenoliths from South Auckland Volcanic Provinces (New Zealand)

    Science.gov (United States)

    Faccini, B.; Bonadiman, C.; Coltorti, M.; Briggs, R.

    2012-04-01

    and cumulitic lithotypes. Two kind of reaction textures are found. The first one consists of a complete recrystallization of previous unrecognizable phases into a mingling of small secondary iso-oriented minerals in an altered glassy matrix. The second mainly involves opx, which is partially destabilized and forms thick, interconnected areas made up of secondary phases and glass. Ol in NG samples have mg# [MgO/(MgO+FeO) mol%] in the range of 0.84-0.90 sensibly lower than those of OK peridotites (mg# = 0.89-0.92). The highest NiO content is recorded in the OK lherzolites (NiO up to 0.44 wt%). Major element compositions of opx are clearly distinct in the two xenolith suites. In NG dunites, opx have lower mg# and extremely low aluminum contents, whereas OK harzburgites and lherzolites have opx with mg# and Al2O3 typical of mantle enstatites (NG opx: mg# = 0.88-0.90; Al2O3 = 0.56-1.23 wt%; OK opx: mg# = 0.89-0.93; Al2O3 = 3.42-5.03 wt%). The opx in the vein of sample NG6 has variable mg values (mg# = 0.86-0.90), but Al2O3 and TiO2 almost absent (< 0.19 wt% and < 0.04 wt% respectively). In both populations cpx show similar mg# (NG = 0.88-0.93; OK= 0.89-0.92). Al2O3 content range from 8.33 wt% in cpx from OK6 lherzolite to <0.89 wt% in cpx from NG4 dunite, close to the diopside end-member ideal composition. Spinels in NG dunites are very restitic in composition with cr# up to 0.80, whereas those from the OK peridotites have lower cr#, clustering around 0.20, except for spinels in dunite OK11 (average cr# = 48). The extreme heterogeneity in the chemical composition of these peridotitic assemblages point toward a complex petrological evolution of the lithospheric mantle beneath the north-western part of the North Island characterized by various depletion events, followed by enrichment process/es also related SiO2-saturated magmas.

  12. Hsp90 depletion goes wild

    OpenAIRE

    Siegal, Mark L; Masel, Joanna

    2012-01-01

    Abstract Hsp90 reveals phenotypic variation in the laboratory, but is Hsp90 depletion important in the wild? Recent work from Chen and Wagner in BMC Evolutionary Biology has discovered a naturally occurring Drosophila allele that downregulates Hsp90, creating sensitivity to cryptic genetic variation. Laboratory studies suggest that the exact magnitude of Hsp90 downregulation is important. Extreme Hsp90 depletion might reactivate transposable elements and/or induce aneuploidy, in addition to r...

  13. Eutectic melting temperature of the lowermost Earth's mantle

    Science.gov (United States)

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

    2009-12-01

    Partial melting of the Earth's deep mantle probably occurred at different stages of its formation as a consequence of meteoritic impacts and seismology suggests that it even continues today at the core-mantle boundary. Melts are important because they dominate the chemical evolution of the different Earth's reservoirs and more generally the dynamics of the whole planet. Unfortunately, the most critical parameter, that is the temperature profile inside the deep Earth, remains poorly constrained accross the planet history. Experimental investigations of the melting properties of materials representative of the deep Earth at relevant P-T conditions can provide anchor points to refine past and present temperature profiles and consequently determine the degree of melting at the different geological periods. Previous works report melting relations in the uppermost lower mantle region, using the multi-anvil press [1,2]. On the other hand, the pyrolite solidus was determined up to 65 GPa using optical observations in the laser-heated diamond anvil cell (LH-DAC) [3]. Finally, the melting temperature of (Mg,Fe)2SiO4 olivine is documented at core-mantle boundary (CMB) conditions by shock wave experiments [4]. Solely based on these reports, experimental data remain too sparse to draw a definite melting curve for the lower mantle in the relevant 25-135 GPa pressure range. We reinvestigated melting properties of lower mantle materials by means of in-situ angle dispersive X-ray diffraction measurements in the LH-DAC at the ESRF [5]. Experiments were performed in an extended P-T range for two starting materials: forsterite and a glass with chondrite composition. In both cases, the aim was to determine the onset of melting, and thus the eutectic melting temperatures as a function of pressure. Melting was evidenced from drastic changes of diffraction peak shape on the image plate, major changes in diffraction intensities in the integrated pattern, disappearance of diffraction rings

  14. Increased mantle heat flow with on-going rifting of the West Antarctic rift system inferred from characterisation of plagioclase peridotite in the shallow Antarctic mantle

    Science.gov (United States)

    Martin, A. P.; Cooper, A. F.; Price, R. C.

    2014-03-01

    The lithospheric, and shallow asthenospheric, mantle in Southern Victoria Land are known to record anomalously high heat flow but the cause remains imperfectly understood. To address this issue plagioclase peridotite xenoliths have been collected from Cenozoic alkalic igneous rocks at three localities along a 150 km transect across the western shoulder of the West Antarctic rift system in Southern Victoria Land, Antarctica. There is a geochemical, thermal and chronological progression across this section of the rift shoulder from relatively hot, young and thick lithosphere in the west to cooler, older and thinner lithosphere in the east. Overprinting this progression are relatively more recent mantle refertilising events. Melt depletion and refertilisation was relatively limited in the lithospheric mantle to the west but has been more extensive in the east. Thermometry obtained from orthopyroxene in these plagioclase peridotites indicates that those samples most recently affected by refertilising melts have attained the highest temperatures, above those predicted from idealised dynamic rift or Northern Victoria Land geotherms and higher than those prevailing in the equivalent East Antarctic mantle. Anomalously high heat flow can thus be attributed to entrapment of syn-rift melts in the lithosphere, probably since regional magmatism commenced at least 24 Myr ago. The chemistry and mineralogy of shallow plagioclase peridotite mantle can be explained by up to 8% melt extraction and a series of refertilisation events. These include: (a) up to 8% refertilisation by a N-MORB melt; (b) metasomatism involving up to 1% addition of a subduction-related component; and (c) addition of ~ 1.5% average calcio-carbonatite. A high MgO group of clinopyroxenes can be modelled by the addition of up to 1% alkalic melt. Melt extraction and refertilisation mainly occurred in the spinel stability field prior to decompression and uplift. In this region mantle plagioclase originates by a

  15. Mantle Noble Gas Contents Controlled by Subduction of Serpentinite

    Science.gov (United States)

    Krantz, J. A.; Parman, S. W.; Kelley, S. P.; Smye, A.; Jackson, C.

    2017-12-01

    Geochemical analyses of exhumed subduction zone material1, well gases2, MORB, and OIBs3 indicate that noble gases are being recycled from the surface of the earth into the mantle. However, the path taken by these noble gases is unclear. To estimate the distribution and quantity of Ar, Kr, and Xe in subducting slabs, a model consisting of layers of sediments, altered oceanic crust (AOC), and serpentinite (hydrously altered mantle) has been developed. The noble gas contents of sediments and AOC were calculated using the least air-like and most gas-rich analyses from natural systems4,5, while serpentinite was modelled using both data from natural systems1 and experimentally determined solubilities. Layer thicknesses were assessed over a range of values: 1 to 12 km of sediments, 5 to 9 km of AOC, and 1 to 30 km of serpentinite. In all cases, the serpentinite layer contains at least an order of magnitude more Ar and Kr than the other layers. For realistic layer thicknesses (1 km of sediments, 6 km of AOC, and 3 km of serpentinite), Xe is distributed roughly equally between the three layers. By incorporating global subduction rates6, fluxes of the heavy noble gases into the mantle have been calculated as 4 · 1012 mol/Ma for 36Ar, 6 · 1011 mol/Ma for 84Kr, and 8 · 109 mol/Ma for 130Xe. These fluxes are equivalent to the total 84Kr and 130Xe contents of the depleted and bulk mantle over 1 and 10 Ma7. Similarly, the flux of 36Ar is equivalent over 1 and 100 Ma. Since the Kr and Xe have not been completely overprinted by recycling, the large majority of subducted noble gases must escape in the subduction zone. However, even the small amounts that are subducted deeper have affected the mantle as measured in both MORB and OIBs. 1. Kendrick, M.A. et al., Nature Geoscience, 4, 807-812, 2011 2. Holland, G. and Ballentine, C.J., Nature, 441, 186-191, 2006 3. Parai, R. and Mukhopadhyay, S., G3, 16, 719-735, 2015 4. Matsuda, J. and Nagao, K., Geochemical Journal, 20, 71-80, 1986

  16. 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...

  17. The peculiar case of Marosticano xenoliths: a cratonic mantle fragment affected by carbonatite metasomatism in the Veneto Volcanic Province (Northern Italy)

    Science.gov (United States)

    Brombin, Valentina; Bonadiman, Costanza; Coltorti, Massimo; Florencia Fahnestock, M.; Bryce, Julia G.; Marzoli, Andrea

    2017-04-01

    The Tertiary Magmatic Province of Veneto, known as Veneto Volcanic Province (VVP), in the Northern Italy, represents one of the most important volcanic provinces of the Adria Plate. It is composed by five volcanic districts: Val d'Adige, Marosticano, Mts. Lessini, Berici Hills and Euganean Hills. Most of the volcanic products are relatively undifferentiated lavas, from nephelinites to tholeiites in composition. Commonly VVP nephelinites and basanites carry mantle xenoliths. This study presents a petrological characterization of the new xenolith occurrence of Marosticano and comparison with previously studied VVP xenolith populations (i.e. from the Lessinean and Val d'Adige areas), which represent off-craton lithospheric mantle fragment affected by Na-alkaline silicate metasomatism (Siena & Coltorti 1989; Beccaluva et al., 2001; Gasperini et al., 2006). Marosticano (MA) peridotites are anhydrous spinel-bearing lherzolites and harzburgites, which are geochemically well distinguishible from the other VVP mantle xenoliths. Primary minerals record the "most restitic" composition of the VVP sampled mantle, even calling the geochemical features of a sub-cratonic mantle. Olivines in both lherzolites and harzburgites show high Ni contents compared with the Fo values (Ni→ lherzolite: 2600-3620 ppm; harzburgite: 2600-3540 ppm; Fo → lh: 91-92; hz: 90-93) that follow the trend of olivine from a cratonic area (Kelemen, 1998). Orthopyroxenes have mg# values with 1:1 ratio with coexisting olivines and Al2O3 contents always 0.5 wt%) contents are also the chemical characteristics of the clinopyroxenes. On the whole both MA pyroxenes show major element contents that recall the characteristics of those from cratonic (sp-bearing) peridotites (e.g. from Greenland, South Africa and Tanzania; Downes et al., 2004). In addition, the relationship between the high Fo content of olivine and the high chromium contents (cr#=(Cr/(Cr+Al)X100); lh: 30-53; hz: 38-67) in coexisting spinel, out of

  18. 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.

  19. 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).

  20. Komatiites constrain molybdenum isotope composition of the Earth's mantle

    Science.gov (United States)

    Greber, Nicolas D.; Puchtel, Igor S.; Nägler, Thomas F.; Mezger, Klaus

    2015-07-01

    In order to estimate the Mo isotope composition and Mo abundance in the Bulk Silicate Earth (BSE), a total of thirty komatiite samples from five localities on three continents were analyzed using an isotope dilution double spike technique. Calculated Mo concentrations of the emplaced komatiite lavas range from 25 ± 3 to 66 ± 22 ng /g, and the inferred Mo concentrations in the deep mantle sources of the komatiites range between 17 ± 4 and 30 ± 12 ng /g, with an average value of 23 ± 7 ng /g (2SE). This average value represents our best estimate for the Mo concentration in the BSE; it is identical, within the uncertainty, to published previous estimates of 39 ± 16 ng /g, but is at least a factor of 2 more precise. The Mo isotope compositions of the komatiite mantle sources overlap within uncertainty and range from δ98Mo = - 0.04 ± 0.28 to 0.11 ± 0.10 ‰, with an average of 0.04 ± 0.06 ‰ (2SE). This value is analytically indistinguishable from published Mo isotope compositions of ordinary and enstatite chondrites and represents the best estimate for the Mo isotope composition of the BSE. The inferred δ98Mo for the BSE is therefore lighter than the suggested average of the upper continental crust (0.3 to 0.4‰). Thus, from the mass balance standpoint, a reservoir with lighter Mo isotope composition should exist in the Earth's mantle; this reservoir can potentially be found in subducted oceanic crust. The similarity of δ98Mo between chondritic meteorites and estimates for the BSE from this study indicates that during the last major equilibration between Earth's core and mantle, i.e., the one that occurred during the giant impact that produced the Moon, chemical and isotopic equilibrium of Mo between Fe metal of the core and the silicate mantle was largely achieved.

  1. Crust and mantle structure under Botswana - the new key-player in African geodynamics?

    Science.gov (United States)

    van der Meijde, M.; Fadel, I.; Paulssen, H.

    2016-12-01

    The 3D crustal and upper mantle structure of Botswana is a major gap in our knowledge about the tectonic evolution of Africa. We will present a new model for crust and upper mantle structure. Our model is based on data from the NARS Botswana and AfricaArray networks, broadband temporary networks in southern Africa (Botswana, Namibia, South Africa and Zambia). The NARS-Botswana seismic network was established to provide broadband recordings in Botswana, covering one of the least studied regions in the world. It is an area that is for a large part covered by the Kalahari sands but also covers the southwestern most branch of the African Rift under the Okavango delta. The goal is to understand how the rifting process and cratonic provinces influence crustal thickness and couple to the underlying mantle. Crust and upper mantle structure, down to the bottom of the mantle transition zone, will be based on receiver function analysis. We observe crustal thicknesses between 35 and 46 km, strongly linked to basins and cratons in the region. The central Kalahari part, which has been previously unstudied, showed some anomalous structure, possibly suggesting melt in the lower crust. The deeper mantle structure shows a discontinuity between 100-150 km depth for a large number of the stations. The mantle transition zone varies in thickness and sharpness of the bounding discontinuities suggesting active dynamical processes underneath Botswana.

  2. Analysis of PKP scattering using mantle mixing simulations and axisymmetric 3D waveforms

    Science.gov (United States)

    Haugland, Samuel M.; Ritsema, Jeroen; van Keken, Peter E.; Nissen-Meyer, Tarje

    2018-03-01

    The scattering of PKP waves in the lower mantle produces isolated signals before the PKIKP phase. We explore whether these so-called PKIKP precursors can be related to wave scattering off mid ocean ridge basalt (MORB) fragments that have been advected in the deep mantle throughout geologic time. We construct seismic models of small-scale (>20 km) heterogeneity in the lower mantle informed by mantle mixing simulations from Brandenburg et al. (2008) and generate PKIKP precursors using 3D, axisymmetric waveform simulations up to 0.75 Hz. We consider two end-member geodynamic models with fundamentally different distributions of MORB in the lower mantle. Our results suggest that the accumulation of MORB at the base of the mantle is a viable hypothesis for the origin of PKP scattering. We find that the strength of the PKIKP precursor amplitudes is consistent with P wave speed heterogeneity of 0.1-0.2%, as reported previously. The radial distribution of MORB has a profound effect on the strength of PKIKP precursors. Simulation of PKIKP precursors for models with an increasing MORB concentration in the lowermost 500 km of the mantle appears to reproduce most accurately the strength of PKIKP precursors in Global Seismic Network waveforms. These models assume that MORB has an excess density of at least 7%. Additional simulations of more complex geodynamic models will better constrain the geodynamic conditions to explain the significant variability of PKP scattering strength.

  3. Nature gives us strength: exposure to nature counteracts ego-depletion.

    Science.gov (United States)

    Chow, Jason T; Lau, Shun

    2015-01-01

    Previous research rarely investigated the role of physical environment in counteracting ego-depletion. In the present research, we hypothesized that exposure to natural environment counteracts ego-depletion. Three experiments were conducted to test this hypothesis. In Experiment 1, initially depleted participants who viewed pictures of nature scenes showed greater persistence on a subsequent anagram task than those who were given a rest period. Experiment 2 expanded upon this finding by showing that natural environment enhanced logical reasoning performance after ego-depleting task. Experiment 3 adopted a two- (depletion vs. no-depletion) -by-two (nature exposure vs. urban exposure) factorial design. We found that nature exposure moderated the effect of depletion on anagram task performance. Taken together, the present studies offer a viable and novel strategy to mitigate the negative impacts of ego-depletion.

  4. 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.

  5. Isotopic characterisation of the sub-continental lithospheric mantle beneath Zealandia, a rifted fragment of Gondwana

    Science.gov (United States)

    Waight, Tod E.; Scott, James M.; van der Meer, Quinten H. A.

    2013-04-01

    The greater New Zealand region, known as Zealandia, represents an amalgamation of crustal fragments accreted to the paleo-Pacific Gondwana margin and which underwent significant thinning during the subsequent split from Australia and Antarctica in the mid-Cretaceous following opening of the Tasman Sea and the Southern Ocean. We present Sr, Nd and Pb isotopes and laser ablation trace element data for a comprehensive suite of clinopyroxene separates from spinel peridotite xenoliths (lherzolite to harzburgite) from the sub-continental lithospheric mantle across southern New Zealand. These xenoliths were transported to the surface in intra-plate alkaline volcanics that erupted across the region in the Eocene and Miocene (33-10 m.y.a.). Most of the volcanic suites have similar geochemical and isotopic properties that indicate melting of an OIB-like mantle source in the garnet stability zone and that contained a HIMU component. The volcanics have tapped two adjacent but chemically contrasting upper mantle domains: a fertile eastern domain and an extremely depleted western domain. Both domains underlie Mesozoic metasedimentary crust. Radiogenic isotope compositions of the clinopyroxene have 87Sr/86Sr between 0.7023 to 0.7035, 143Nd/144Nd between 0.5128 and 0.5132 (corresponding to ?Nd between +3 and +13) with a few samples extending to even more depleted compositions, 206Pb/204 Pb between ca. 19.5 to 21.5 and 208Pb/204 Pb between ca. 38.5 to 40.5. No correlations are observed between isotopic composition, age or geographical separation. These isotopic compositions indicate that the sub-continental lithospheric mantle under southern New Zealand has a regionally distinct and pervasive FOZO to HIMU - like signature. The isotopic signatures are also similar to those of the alkaline magmas that transported the xenoliths and suggest that most of the HIMU signature observed in the volcanics could be derived from a major source component in the sub-continental lithospheric mantle

  6. Interaction between protokimberlite melts and mantle lithosphere: Evidence from mantle xenoliths from the Dalnyaya kimberlite pipe, Yakutia (Russia

    Directory of Open Access Journals (Sweden)

    I.V. Ashchepkov

    2017-07-01

    Full Text Available The Dalnyaya kimberlite pipe (Yakutia, Russia contains mantle peridotite xenoliths (mostly lherzolites and harzburgites that show both sheared porphyroclastic (deformed and coarse granular textures, together with ilmenite and clinopyroxene megacrysts. Deformed peridotites contain high-temperature Fe-rich clinopyroxenes, sometimes associated with picroilmenites, which are products of interaction of the lithospheric mantle with protokimberlite related melts. The orthopyroxene-derived geotherm for the lithospheric mantle beneath Dalnyaya is stepped similar to that beneath the Udachnaya pipe. Coarse granular xenoliths fall on a geotherm of 35 mWm−2 whereas deformed varieties yield a 45 mWm−2 geotherm in the 2–7.5 GPa pressure interval. The chemistry of the constituent minerals including garnet, olivine and clinopyroxene shows trends of increasing Fe# (=Fe/(Fe + Mg with decreasing pressure. This may suggest that the interaction with fractionating protokimberlite melts occurred at different levels. Two major mantle lithologies are distinguished by the trace element patterns of their constituent minerals, determined by LA-ICP-MS. Orthopyroxenes, some clinopyroxenes and rare garnets are depleted in Ba, Sr, HFSE and MREE and represent relic lithospheric mantle. Re-fertilized garnet and clinopyroxene are more enriched. The distribution of trace elements between garnet and clinopyroxene shows that the garnets dissolved primary orthopyroxene and clinopyroxene. Later high temperature clinopyroxenes related to the protokimberlite melts partially dissolved these garnets. Olivines show decreases in Ni and increases in Al, Ca and Ti from Mg-rich varieties to the more Fe-rich, deformed and refertilized ones. Minerals showing higher Fe# (0.11–0.15 are found within intergrowths of low-Cr ilmenite-clinopyroxene-garnet related to the crystallization of protokimberlite melts in feeder channels. In P-f(O2 diagrams, garnets and Cr-rich clinopyroxenes

  7. Seismic-geodynamic constraints on three-dimensional structure, vertical flow, and heat transfer in the mantle

    Science.gov (United States)

    Forte, A.M.; Woodward, R.L.

    1997-01-01

    Joint inversions of seismic and geodynamic data are carried out in which we simultaneously constrain global-scale seismic heterogeneity in the mantle as well as the amplitude of vertical mantle flow across the 670 km seismic discontinuity. These inversions reveal the existence of a family of three-dimensional (3-D) mantle models that satisfy the data while at the same time yielding predictions of layered mantle flow. The new 3-D mantle models we obtain demonstrate that the buoyancy forces due to the undulations of the 670 km phase-change boundary strongly inhibit the vertical flow between the upper and lower mantle. The strong stabilizing effect of the 670 km topography also has an important impact on the predicted dynamic topography of the Earth's solid surface and on the surface gravity anomalies. The new 3-D models that predict strongly or partially layered mantle flow provide essentially identical fits to the global seismic data as previous models that have, until now, predicted only whole-mantle flow. The convective vertical transport of heat across the mantle predicted on the basis of the new 3-D models shows that the heat flow is a minimum at 1000 km depth. This suggests the presence at this depth of a globally defined horizon across which the pattern of lateral heterogeneity changes rapidly. Copyright 1997 by the American Geophysical Union.

  8. Dynamical links between small- and large-scale mantle heterogeneity: Seismological evidence

    Science.gov (United States)

    Frost, Daniel A.; Garnero, Edward J.; Rost, Sebastian

    2018-01-01

    We identify PKP • PKP scattered waves (also known as P‧ •P‧) from earthquakes recorded at small-aperture seismic arrays at distances less than 65°. P‧ •P‧ energy travels as a PKP wave through the core, up into the mantle, then scatters back down through the core to the receiver as a second PKP. P‧ •P‧ waves are unique in that they allow scattering heterogeneities throughout the mantle to be imaged. We use array-processing methods to amplify low amplitude, coherent scattered energy signals and resolve their incoming direction. We deterministically map scattering heterogeneity locations from the core-mantle boundary to the surface. We use an extensive dataset with sensitivity to a large volume of the mantle and a location method allowing us to resolve and map more heterogeneities than have previously been possible, representing a significant increase in our understanding of small-scale structure within the mantle. Our results demonstrate that the distribution of scattering heterogeneities varies both radially and laterally. Scattering is most abundant in the uppermost and lowermost mantle, and a minimum in the mid-mantle, resembling the radial distribution of tomographically derived whole-mantle velocity heterogeneity. We investigate the spatial correlation of scattering heterogeneities with large-scale tomographic velocities, lateral velocity gradients, the locations of deep-seated hotspots and subducted slabs. In the lowermost 1500 km of the mantle, small-scale heterogeneities correlate with regions of low seismic velocity, high lateral seismic gradient, and proximity to hotspots. In the upper 1000 km of the mantle there is no significant correlation between scattering heterogeneity location and subducted slabs. Between 600 and 900 km depth, scattering heterogeneities are more common in the regions most remote from slabs, and close to hotspots. Scattering heterogeneities show an affinity for regions close to slabs within the upper 200 km of the

  9. Diamond morphology as a key to understanding metasomatic processes in subcratonic mantle

    Science.gov (United States)

    Fedortchouk, Yana; Perritt, Samantha; Chinn, Ingrid

    2016-04-01

    Metasomatism in the subcratonic mantle is responsible for growth as well as dissolution of diamond. The morphology of resorption features developed on diamond during its residence in the mantle provides an important record of the nature of the metasomatic media and conditions of diamond destructive metasomatic events, while the diversity of these features indicates different metasomatic processes occurring in the mantle. The objective of this study was to shed more light on the nature of metasomatic processes in the subcratonic mantle by examining the conditions of mantle-derived diamond resorption. Towards this end, we conducted a study of 800 diamonds from two kimberlite pipes in the Orapa kimberlite field, Botswana, and examined the relationship between the conditions of diamond growth, as recorded in their nitrogen defects, and subsequent dissolution recorded in their resorption features. Using a set of morphological criteria we identified preservation of mantle-derived resorption features on 55% of diamonds from one pipe and 25-75% of diamonds from the second pipe. We identified at least twelve distinct morphological types developed during mantle residence of the diamond, and examined the possible effect of diamond internal features vs. the effect of the conditions of the mantle metasomatism. The mantle resorption types are the same for diamonds from both of the Orapa kimberlites studied, and compare well to the types previously described on diamonds from Ekati Mine (Canada), implying similarity of metasomatic history beneath the Slave and Zimbabwe cratons. A comparison of the mantle-derived diamond morphologies to the products of diamond dissolution experiments allows assessment of the importance of metasomatism caused by carbonatitic melts vs. aqueous silicate melts in the mantle underlying the kimberlites. The nitrogen content and nitrogen aggregation state of the diamonds from the different morphological groups provides insights into the relationship

  10. Ozone depletion: implications for the veterinarian.

    Science.gov (United States)

    Kopecky, K E

    1978-09-15

    Man has inadvertently modified the stratosphere. There is a good possibility that the ozone layer is being depleted by the use of jet aircraft (SST), chlorofluoromethane propellants, and nitrogen fertilizers. Under unpolluted conditions, the production of ozone equals its destruction. By man's intervention, however, the destruction may exceed the production. The potential outcome is increased intensity of solar ultraviolet (280-400 nm) radiation and penetration to the earth's surface of previously absorbed wavelengths below about 280 nm. The increased ultraviolet radiation would increase the likelihood of skin cancer in man and ocular squamous cell carcinoma in cattle. The climate also might be modified, possibly in an undesirable way.

  11. Late-stage magmatic outgassing from a volatile-depleted Moon.

    Science.gov (United States)

    Day, James M D; Moynier, Frédéric; Shearer, Charles K

    2017-09-05

    The abundance of volatile elements and compounds, such as zinc, potassium, chlorine, and water, provide key evidence for how Earth and the Moon formed and evolved. Currently, evidence exists for a Moon depleted in volatile elements, as well as reservoirs within the Moon with volatile abundances like Earth's depleted upper mantle. Volatile depletion is consistent with catastrophic formation, such as a giant impact, whereas a Moon with Earth-like volatile abundances suggests preservation of these volatiles, or addition through late accretion. We show, using the "Rusty Rock" impact melt breccia, 66095, that volatile enrichment on the lunar surface occurred through vapor condensation. Isotopically light Zn (δ 66 Zn = -13.7‰), heavy Cl (δ 37 Cl = +15‰), and high U/Pb supports the origin of condensates from a volatile-poor internal source formed during thermomagmatic evolution of the Moon, with long-term depletion in incompatible Cl and Pb, and lesser depletion of more-compatible Zn. Leaching experiments on mare basalt 14053 demonstrate that isotopically light Zn condensates also occur on some mare basalts after their crystallization, confirming a volatile-depleted lunar interior source with homogeneous δ 66 Zn ≈ +1.4‰. Our results show that much of the lunar interior must be significantly depleted in volatile elements and compounds and that volatile-rich rocks on the lunar surface formed through vapor condensation. Volatiles detected by remote sensing on the surface of the Moon likely have a partially condensate origin from its interior.

  12. Facilitating atmosphere oxidation through mantle convection

    Science.gov (United States)

    Lee, K. K. M.; Gu, T.; Creasy, N.; Li, M.; McCammon, C. A.; Girard, J.

    2017-12-01

    Earth's mantle connects the surface with the deep interior through convection, and the evolution of its redox state will affect the distribution of siderophile elements, recycling of refractory isotopes, and the oxidation state of the atmosphere through volcanic outgassing. While the rise of oxygen in the atmosphere, i.e., the Great Oxidation Event (GOE) occurred 2.4 billion years ago (Ga), multiple lines of evidence point to oxygen production in the atmosphere well before 2.4 Ga. In contrast to the fluctuations of atmospheric oxygen, vanadium in Archean mantle lithosphere suggests that the mantle redox state has been constant for 3.5 Ga. Indeed, the connection between the redox state of the deep Earth and the atmosphere is enigmatic as is the effect of redox state on mantle dynamics. Here we show a redox-induced density contrast affects mantle convection and may potentially cause the oxidation of the upper mantle. We compressed two synthetic enstatite chondritic samples with identical bulk compositions but formed under different oxygen fugacities (fO2) to lower mantle pressures and temperatures and find Al2O3 forms its own phase separate from the dominant bridgmanite phase in the more reduced composition, in contrast to a more Al-rich, bridgmanite-dominated assemblage for a more oxidized starting composition. As a result, the reduced material is 1-1.5% denser than the oxidized material. Subsequent experiments on other plausible mantle compositions, which differ only in redox state of the starting glass materials, show similar results: distinct mineral assemblages and density contrasts up to 4%. Our geodynamic simulations suggest that such a density contrast causes a rapid ascent and accumulation of oxidized material in the upper mantle, with descent of the denser reduced material to the core-mantle boundary. The resulting heterogeneous redox conditions in Earth's interior may have contributed to the large low-shear velocity provinces in the lower mantle and the

  13. 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.

  14. Multiscale, finite-frequency P and S tomography of the upper mantle in the southwestern Fennoscandian Shield

    Science.gov (United States)

    Kolstrup, Marianne L.; Hung, Shu-Huei; Maupin, Valerie

    2015-07-01

    We image the P- and S-wave structure of the upper mantle in southwestern Scandinavia using a wavelet-based, multiscale parametrization and finite-frequency theory to model wave propagation. Relative traveltime residuals of direct P and S waves are measured in a high- and low-frequency band and are corrected for crustal structure using a detailed model for the study area. A range of resolution tests are used to find optimal damping values not only for variations in VP and VS separately, but also for perturbations in their ratio VP/VS. The tests show that features down to a size of 100 (150) km can be well resolved in the P (S) tomography. To ease comparison with previous studies we also perform ray-theoretical multiscale tomographies, and to test the degree of vertical smearing we evaluate different parametrizations in the vertical direction (wavelet-based multiscale and convolutional quelling). Our finite-frequency, multiscale images of variations in VP and VS confirm the existence of low velocities below southern Norway and Denmark and high velocities beneath the shield proper in Sweden, as seen in previous studies, but add more details to this simplified picture. The low velocities below southern Norway and Denmark are confined to a channel-like structure at about 100-200 km depth, and the lateral transition from low to high velocities follows zones of Carboniferous-Permian extension and magmatism very closely. A deeper low-velocity anomaly below central southern Norway emerges from the channel at 150 km depth and extends to a depth of 350 km. In the Swedish area we infer high-velocity anomalies in VP and VS, and negative anomalies in VP/VS that indicate a strongly depleted mantle. We propose that the episodic erosion and convective removal of an originally thick mantle lithosphere below southern Norway to its current thickness of about 100 km could have been a trigger for episodic uplift in the Mesozoic and Cenozoic.

  15. Hsp90 depletion goes wild

    Directory of Open Access Journals (Sweden)

    Siegal Mark L

    2012-02-01

    Full Text Available Abstract Hsp90 reveals phenotypic variation in the laboratory, but is Hsp90 depletion important in the wild? Recent work from Chen and Wagner in BMC Evolutionary Biology has discovered a naturally occurring Drosophila allele that downregulates Hsp90, creating sensitivity to cryptic genetic variation. Laboratory studies suggest that the exact magnitude of Hsp90 downregulation is important. Extreme Hsp90 depletion might reactivate transposable elements and/or induce aneuploidy, in addition to revealing cryptic genetic variation. See research article http://wwww.biomedcentral.com/1471-2148/12/25

  16. A Viscosity Model for the Mantle Based on Diffusion in Minerals and Constrained by the Thermal History and Melting of the Mantle

    Science.gov (United States)

    Tirone, M.; Ganguly, J.

    2011-12-01

    and a viscosity drop by ~ an order of magnitude from the transition zone to the top of the lower mantle. The latter result is in contrast to the viscosity jump inferred from geophysical observations. This conclusion applies for the present day most relevant thermal conditions retrieved from the thermal history model. However it is possible that using a multiphase model for the rock assemblage in the transition zone the mineralogical and geophysical models may be in better agreement. As it would be shown here, the viscosity model (and the thermal state of the CMB) combined with a thermodynamic formulation allows us to study the geodynamics of mantle plumes with a considerably smaller number of assumptions than in previous studies. The thermal evolution of the plume in the upper mantle is then applied to model the petrological evolution of melting in hot spots using a coupled thermodynamic and two phase flow model (session DI03, contribution entitled: Present Day Hot Spot Melting Inferred from Geodynamics and Thermodynamics Modeling and the Thermal History of the Mantle).

  17. Metasomatized ancient lithospheric mantle beneath the young Zealandia microcontinent and its role in HIMU-like intraplate magmatism

    Science.gov (United States)

    Scott, J. M.; Waight, T. E.; van der Meer, Q. H. A.; Palin, J. M.; Cooper, A. F.; Münker, C.

    2014-09-01

    There has been long debate on the asthenospheric versus lithospheric source for numerous intraplate basalts with ocean island basalt (OIB) and high time-integrated U/Pb (HIMU)-like source signatures that have erupted through the Zealandia continental crust. Analysis of 157 spinel facies peridotitic mantle xenoliths from 25 localities across Zealandia permits the first comprehensive regional description of the subcontinental lithospheric mantle (SCLM) and insights into whether it could be a source to the intraplate basalts. Contrary to previous assumptions, the Oligocene-Miocene Zealandia SCLM is highly heterogeneous. It is composed of a refractory craton-like domain (West Otago) adjacent to several moderately fertile domains (East Otago, North Otago, Auckland Islands). Each domain has an early history decoupled from the overlying Carboniferous and younger continental crust, and each domain has undergone varying degrees of depletion followed by enrichment. Clinopyroxene grains reveal trace element characteristics (low Ti/Eu, high Th/U) consistent with enrichment through reaction with carbonatite. This metasomatic overprint has a composition that closely matches HIMU in Sr, Pb ± Nd isotopes. However, clinopyroxene Hf isotopes are in part highly radiogenic and decoupled from the other isotope systems, and also mostly more radiogenic than the intraplate basalts. If the studied spinel facies xenoliths are representative of the thin Zealandia SCLM, the melting of garnet facies lithosphere could only be the intraplate basalt source if it had a less radiogenic Hf-Nd isotope composition than the investigated spinel facies, or was mixed with asthenosphere-derived melts containing less radiogenic Hf.

  18. Adakite Induced Metasomatism of the Mantle Wedge: a Systematic Experimental Study at 1.6 GPa

    Science.gov (United States)

    Rapp, R. P.; Laporte, D.; Martin, H.

    2005-12-01

    In order to better understand the origin and nature of the slab-derived agent in subduction zones, and how the arc geochemical signature is imparted to the mantle wedge, it is necessary to have specific geochemical parameters to differentiate between fluids and partial melts generated by dehydration of the crustal component (MORB) of the downgoing oceanic lithosphere. ``Adakite'' magmatism in subduction zones is generally attributed to partial melting of basaltic oceanic crust during prograde metamorphism and dehydration of the subducting slab. In this study, we focus on adakites or ``slab melts'' as the agent of metasomatism of the overlying mantle wedge, armed beforehand with relatively comprehensive major- and trace-element constraints on the geochemical nature of these melts from our previous work. We have conducted a series of melt-rock reaction experiments in the piston-cylinder apparatus at 1.6 GPa and temperatures of 1000-1250°C in which we systematically vary the proportion of adakite melt relative to mantle peridotite. Our starting materials consist of mechanical mixtures of an adakite glass containing ~8 wt% H2O (pre-hydrated in an internally-heated pressure vessel at 900°C and 2.5 kbar for 3-4 hours), and a natural depleted peridotite powder made from a xenolith from the Kamchatkan sub-arc mantle. Experiments were conducted in thick-walled, pressure-welded gold capsules at temperatures below 1100°C, and in Ag-Pd capsules at higher temeperatures; the adakite melt:peridotite rock ratio has been varied from 2:1 to 1:4, with the mixtures allowed to equilibrate over the course of 5-10 days, depending on run temperature. Our results indicate that the reaction between adakite melt and peridotite is dominated by the consumption of olivine and crystallization of orthopyroxene and amphibole, and takes the general form: melts1 (pristine adakite) + olivine 0 melt2 (hybridized adakite) + orthopyroxene + amphibole. The chemical characteristics of metasomatic

  19. Impact of mineral resource depletion

    CSIR Research Space (South Africa)

    Brent, AC

    2006-09-01

    Full Text Available In a letter to the editor, the authors comment on BA Steen's article on "Abiotic Resource Depletion: different perceptions of the problem with mineral deposits" published in the special issue of the International Journal of Life Cycle Assessment...

  20. Rapid Cenozoic ingrowth of isotopic signatures simulating "HIMU" in ancient lithospheric mantle: Distinguishing source from process

    Science.gov (United States)

    McCoy-West, Alex J.; Bennett, Vickie C.; Amelin, Yuri

    2016-08-01

    Chemical and isotopic heterogeneities in the lithospheric mantle are increasingly being recognised on all scales of examination, although the mechanisms responsible for generating this variability are still poorly understood. To investigate the relative behaviour of different isotopic systems in off-cratonic mantle, and specifically the origin of the regional southwest Pacific "HIMU" (high time integrated 238U/204Pb) Pb isotopic signature, we present the first U-Th-Pb, Rb-Sr, Sm-Nd and Re-Os isotopic dataset for spinel peridotite xenoliths sampling the subcontinental lithospheric mantle (SCLM) beneath Zealandia. Strongly metasomatised xenoliths converge to a restricted range of Sr and Nd isotopic compositions (87Sr/86Sr = 0.7028-0.7033; εNd ≈ +3-+6) reflecting pervasive overprinting of their original melt depletion signatures by carbonatite-rich melts. In contrast, rare, weakly metasomatised samples possess radiogenic Nd isotopic compositions (εNd > +15) and unradiogenic Sr isotopic compositions (87Sr/86Sr Zealandia argues for preservation of a significant mantle keel (⩾2 million km3) associated with a large-scale Paleoproterozoic melting event. Lead isotopic compositions are highly variable with 206Pb/204Pb = 17.3-21.3 (n = 34) and two further samples with more extreme compositions of 22.4 and 25.4, but are not correlated with other isotopic data or U/Pb and Th/Pb ratios in either strongly or weakly metasomatised xenoliths; this signature is thus a recent addition to the lithospheric mantle. Lead model ages suggest that this metasomatism occurred in the last 200 m.y., with errorchrons from individual localities providing ages younger than 116 Ma. When considered in the regional tectonic context the Pb isotopic signatures are best explained through interaction of the lithospheric mantle with a weak upwelling mantle plume that contained carbonatitic domains at ca. 110-115 Ma. Projection of the measured high U/Pb and Th/Pb signatures into the future predicts

  1. Rogue Mantle Helium and Neon

    Science.gov (United States)

    Albarede, F.

    2007-12-01

    The canonical view of He isotope geochemistry holds that high 3He/4He ratios in basalts fingerprints undegassed mantle sources. Hawaiian basalts with unradiogenic He with 3He/4He up to 30 RA are therefore seen as originating from parts of the mantle that is still primordial, at least much more so than MORB mantle (3He/4He ~ 8 RA). This view was strongly reinforced by the discovery of solar and even planetary Ne components in oceanic basalts and gas wells. The canonical view, however, conflicts with multiple observations on ocean islands, notably Hawaiian basalts: the correlation of {187}Os/{186}Os with δ 18O combined with the presence of unusually radiogenic Hf isotope compositions for a given Nd isotope composition and the correlation between Hf and Pb isotopes are all features strongly reminiscent of ancient subducted oceanic crust and pelagic sediments in the source of the Hawaiian plume. These conflicting observations beg the question of how Hawaiian basalts, which carry the embodiment of a primordial gas signature, at the same time can provide such strong evidence of surface material recycling. I here suggest and alternative model that uses the marble cake paradigm and Shuster et al.'s data on olivine. A solution to this conundrum lies in an analogy with oil genesis: 3He and Ne do not reside in the low-melting point peridotites in which they were originally hosted but rather migrated since early in Earth history into refractory 'reservoir' rocks. Since there can be no free gas phase percolating at pressures in excess of olivine carbonation at ~3 GPa, He must be largely redistributed by diffusion. The time scale of diffusion is the defining parameter: although over billions of years 3He diffuses across large distances, melting events are too short to efficiently strip residual refractory rocks from their high-3He/4He component. Assuming that melts begin forming over the uppermost 100 km with an upwelling rate of 10 m y-1 in plume conduits and 10 cm y-1 under

  2. Noble gas composition of subcontinental lithospheric mantle: An extensively degassed reservoir beneath Southern Patagonia

    Science.gov (United States)

    Jalowitzki, Tiago; Sumino, Hirochika; Conceição, Rommulo V.; Orihashi, Yuji; Nagao, Keisuke; Bertotto, Gustavo W.; Balbinot, Eduardo; Schilling, Manuel E.; Gervasoni, Fernanda

    2016-09-01

    Patagonia, in the Southern Andes, is one of the few locations where interactions between the oceanic and continental lithosphere can be studied due to subduction of an active spreading ridge beneath the continent. In order to characterize the noble gas composition of Patagonian subcontinental lithospheric mantle (SCLM), we present the first noble gas data alongside new lithophile (Sr-Nd-Pb) isotopic data for mantle xenoliths from Pali-Aike Volcanic Field and Gobernador Gregores, Southern Patagonia. Based on noble gas isotopic compositions, Pali-Aike mantle xenoliths represent intrinsic SCLM with higher (U + Th + K)/(3He, 22Ne, 36Ar) ratios than the mid-ocean ridge basalt (MORB) source. This reservoir shows slightly radiogenic helium (3He/4He = 6.84-6.90 RA), coupled with a strongly nucleogenic neon signature (mantle source 21Ne/22Ne = 0.085-0.094). The 40Ar/36Ar ratios vary from a near-atmospheric ratio of 510 up to 17700, with mantle source 40Ar/36Ar between 31100-6800+9400 and 54000-9600+14200. In addition, the 3He/22Ne ratios for the local SCLM endmember, at 12.03 ± 0.15 to 13.66 ± 0.37, are higher than depleted MORBs, at 3He/22Ne = 8.31-9.75. Although asthenospheric mantle upwelling through the Patagonian slab window would result in a MORB-like metasomatism after collision of the South Chile Ridge with the Chile trench ca. 14 Ma, this mantle reservoir could have remained unhomogenized after rapid passage and northward migration of the Chile Triple Junction. The mantle endmember xenon isotopic ratios of Pali-Aike mantle xenoliths, which is first defined for any SCLM-derived samples, show values indistinguishable from the MORB source (129Xe/132Xe =1.0833-0.0053+0.0216 and 136Xe/132Xe =0.3761-0.0034+0.0246). The noble gas component observed in Gobernador Gregores mantle xenoliths is characterized by isotopic compositions in the MORB range in terms of helium (3He/4He = 7.17-7.37 RA), but with slightly nucleogenic neon (mantle source 21Ne/22Ne = 0.065-0.079). We

  3. Early Mantle Evolution and the Late Veneer - New Perspectives from Highly Siderophile Elements

    Science.gov (United States)

    Coggon, J. A.; Luguet, A.; Lorand, J. P.; Fonseca, R.; Appel, P.; Mondal, S. K.; Peters, S.; Nowell, G. M.; Hoffmann, J. E.

    2015-12-01

    Numerous studies show that core - mantle differentiation should have fractionated the highly siderophile elements (HSE) into Earth's core during its formation, leaving them almost entirely depleted in the mantle. It is widely held that later addition of chondritic material (a.k.a. the "late veneer") can account for the disparity between modelled and observed HSE concentrations in the upper mantle. Recent experimental data (Médard et al., 2015) indicate that addition of ~0.6 % of the mass of the Earth could re-enrich the mantle HSE budget sufficiently to satisfy these observations. However, debate remains strong regarding the absolute timing, duration and nature of the re-enrichment. Chondrite-normalised HSE patterns (Coggon et al., 2015) of massive chromitites from the >3.811 Ga Ujaragssuit nunât layered ultramafic body, Greenland, are strikingly similar in both shape and abundance to the patterns of Phanerozoic chromitites from ultramafic layered intrusions. These data suggest that late veneer re-enrichment had already occurred prior to 3.811 Ga (Bennett et al., 2002; Coggon et al., 2013). Furthermore, Pt-Os model ages for these samples indicate that a late veneer component may have been present in Earth's mantle as early as 4.1 - 4.3 Ga (Coggon et al., 2013). HSE inter-element ratios demonstrate distinct differences between this chromitite sample suite and younger chromitites from analogous tectonic settings. It remains unclear whether late veneer addition was already complete at 3.82 Ga and how long it took for this material to be accreted and homogenised within the upper mantle. We will address these issues using HSE and Os isotope data from Ujaragssuit nunât, Greenland, and the Singhbum Craton, India.

  4. Silicate melt metasomatism in the lithospheric mantle beneath SW Poland

    Science.gov (United States)

    Puziewicz, Jacek; Matusiak-Małek, Magdalena; Ntaflos, Theodoros; Grégoire, Michel; Kukuła, Anna

    2014-05-01

    The xenoliths of peridotites representing the subcontinental lithospheric mantle (SCLM) beneath SW Poland and adjacent parts of Germany occur in the Cenozoic alkaline volcanic rocks. Our study is based on detailed characterization of xenoliths occurring in 7 locations (Steinberg in Upper Lusatia, Księginki, Pilchowice, Krzeniów, Wilcza Góra, Winna Góra and Lutynia in Lower Silesia). One of the two major lithologies occurring in the xenoliths, which we call the "B" lithology, comprises peridotites (typically harzburgites) with olivine containing from 90.5 to 84.0 mole % of forsterite. The harzburgites contain no clinopyroxene or are poor in that mineral (eg. in Krzeniów the group "B" harzburgites contain pfu in ortho-, and pfu in clinopyroxene). The exception are xenoliths from Księginki, which contain pyroxenes characterised by negative correlation between mg# and Al. The REE patterns of both ortho- and clinopyroxene in the group "B" peridotites suggest equilibration with silicate melt. The rocks of "B" lithology were formed due to alkaline silicate melt percolation in the depleted peridotitic protolith. The basaltic melts formed at high pressure are usually undersaturated in both ortho- and clinopyroxene at lower pressures (Kelemen et al. 1992). Because of cooling and dissolution of ortho- and clinopyroxene the melts change their composition and become saturated in one or both of those phases. Experimental results (e.g. Tursack & Liang 2012 and references therein) show that the same refers to alkaline basaltic silicate melts and that its reactive percolation in the peridotitic host leads to decrease of Mg/(Mg+Fe) ratios of olivine and pyroxenes. Thus, the variation of relative volumes of olivine and orthopyroxene as well as the decrease of mg# of rock-forming silicates is well explained by reactive melt percolation in the peridotitic protolith consisting of high mg# olivine and pyroxenes (in the area studied by us that protolith was characterised by olivine

  5. A Global Upper-Mantle Tomographic Model of Shear Attenuation

    Science.gov (United States)

    Karaoglu, H.; Romanowicz, B. A.

    2016-12-01

    Mapping anelastic 3D structure within the earth's mantle is key to understanding present day mantle dynamics, as it provides complementary constraints to those obtained from elastic structure, with the potential to distinguish between thermal and compositional heterogeneity. For this, we need to measure seismic wave amplitudes, which are sensitive to both elastic (through focusing and scattering) and anelastic structure. The elastic effects are less pronounced at long periods, so previous global upper-mantle attenuation models are based on teleseismic surface wave data, sometimes including overtones. In these studies, elastic effects are considered either indirectly, by eliminating data strongly contaminated by them (e.g. Romanowicz, 1995; Gung and Romanowicz, 2004), or by correcting for elastic focusing effects using an approximate linear approach (Dalton et al., 2008). Additionally, in these studies, the elastic structure is held fixed when inverting for intrinsic attenuation . The importance of (1) having a good starting elastic model, (2) accurate modeling of the seismic wavefield and (3) joint inversion for elastic and anelastic structure, becomes more evident as the targeted resolution level increases. Also, velocity dispersion effects due to anelasticity need to be taken into account. Here, we employ a hybrid full waveform inversion method, inverting jointly for global elastic and anelastic upper mantle structure, starting from the latest global 3D shear velocity model built by our group (French and Romanowicz, 2014), using the spectral element method for the forward waveform modeling (Capdeville et al., 2003), and normal-mode perturbation theory (NACT - Li and Romanowicz, 1995) for kernel computations. We present a 3D upper-mantle anelastic model built by using three component fundamental and overtone surface waveforms down to 60 s as well as long period body waveforms down to 30 s. We also include source and site effects to first order as frequency

  6. Rhenium-osmium isotopes in pervasively metasomatized mantle xenoliths from the Bohemian Massif and implications for the reliability of Os model ages

    Czech Academy of Sciences Publication Activity Database

    Kochergina, Y. V.; Ackerman, Lukáš; Erban, V.; Matusiak-Malek, M.; Puziewicz, J.; Halodová, P.; Špaček, P.; Trubač, J.; Magna, T.

    2016-01-01

    Roč. 430, July 15 (2016), s. 90-107 ISSN 0009-2541 Institutional support: RVO:67985831 Keywords : Bohemian Massif * depletion age * Ohře/Eger rift * Os isotopes * peridotite xenolith * Re-Os * sub-continental lithospheric mantle Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.347, year: 2016

  7. Inositol depletion restores vesicle transport in yeast phospholipid flippase mutants.

    Science.gov (United States)

    Yamagami, Kanako; Yamamoto, Takaharu; Sakai, Shota; Mioka, Tetsuo; Sano, Takamitsu; Igarashi, Yasuyuki; Tanaka, Kazuma

    2015-01-01

    In eukaryotic cells, type 4 P-type ATPases function as phospholipid flippases, which translocate phospholipids from the exoplasmic leaflet to the cytoplasmic leaflet of the lipid bilayer. Flippases function in the formation of transport vesicles, but the mechanism remains unknown. Here, we isolate an arrestin-related trafficking adaptor, ART5, as a multicopy suppressor of the growth and endocytic recycling defects of flippase mutants in budding yeast. Consistent with a previous report that Art5p downregulates the inositol transporter Itr1p by endocytosis, we found that flippase mutations were also suppressed by the disruption of ITR1, as well as by depletion of inositol from the culture medium. Interestingly, inositol depletion suppressed the defects in all five flippase mutants. Inositol depletion also partially restored the formation of secretory vesicles in a flippase mutant. Inositol depletion caused changes in lipid composition, including a decrease in phosphatidylinositol and an increase in phosphatidylserine. A reduction in phosphatidylinositol levels caused by partially depleting the phosphatidylinositol synthase Pis1p also suppressed a flippase mutation. These results suggest that inositol depletion changes the lipid composition of the endosomal/TGN membranes, which results in vesicle formation from these membranes in the absence of flippases.

  8. Long-term preservation of early formed mantle heterogeneity by mobile lid convection: Importance of grainsize evolution

    Science.gov (United States)

    Foley, Bradford J.; Rizo, Hanika

    2017-10-01

    The style of tectonics on the Hadean and Archean Earth, particularly whether plate tectonics was in operation or not, is debated. One important, albeit indirect, constraint on early Earth tectonics comes from observations of early-formed geochemical heterogeneities: 142Nd and 182W anomalies recorded in Hadean to Phanerozoic rocks from different localities indicate that chemically heterogeneous reservoirs, formed during the first ∼500 Myrs of Earth's history, survived their remixing into the mantle for over 1 Gyrs. Such a long mixing time is difficult to explain because hotter mantle temperatures, expected for the early Earth, act to lower mantle viscosity and increase convective vigor. Previous studies found that mobile lid convection typically erases heterogeneity within ∼100 Myrs under such conditions, leading to the hypothesis that stagnant lid convection on the early Earth was responsible for the observed long mixing times. However, using two-dimensional Cartesian convection models that include grainsize evolution, we find that mobile lid convection can preserve heterogeneity at high mantle temperature conditions for much longer than previously thought, because higher mantle temperatures lead to larger grainsizes in the lithosphere. These larger grainsizes result in stronger plate boundaries that act to slow down surface and interior convective motions, in competition with the direct effect temperature has on mantle viscosity. Our models indicate that mobile lid convection can preserve heterogeneity for ≈0.4-1 Gyrs at early Earth mantle temperatures when the initial heterogeneity has the same viscosity as the background mantle, and ≈1-4 Gyrs when the heterogeneity is ten times more viscous than the background mantle. Thus, stagnant lid convection is not required to explain long-term survival of early formed geochemical heterogeneities, though these heterogeneities having an elevated viscosity compared to the surrounding mantle may be essential for their

  9. Duration of a Magma Ocean and Subsequent Mantle Overturn in Mars: Evidence from Nakhlites

    Science.gov (United States)

    Debaille, V.; Brandon, A. D.; Yin, Q.-Z.; Jacobsen, B.

    2008-01-01

    It is now generally accepted that the heat produced by accretion, short-lived radioactive elements such as Al-26, and gravitational energy from core formation was sufficient to at least partially melt the silicate portions of terrestrial planets resulting in a global-scale magma ocean. More particularly, in Mars, the geochemical signatures displayed by shergottites, are likely inherited from the crystallization of this magma ocean. Using the short-lived chronometer Sm-146 - Nd-142 (t(sup 1/2) = 103 Myr), the duration of the Martian magma ocean (MMO) has been evaluated to being less than 40 Myr, while recent and more precise ND-142/ND-144 data were used to evaluate the longevity of the MMO to approximately 100 Myr after the solar system formation. In addition, it has been proposed that the end of the crystallization of the MMO may have triggered a mantle overturn, as a result of a density gradient in the cumulate layers crystallized at different levels. Dating the mantle overturn could hence provide additional constraint on the duration of the MMO. Among SNC meteorites, nakhlites are characterized by high epsilon W-182 of approximately +3 and an epsilon Nd-142 similar to depleted shergottites of +0.6-0.9. It has hence been proposed that the source of nakhlites was established very early in Mars history (approximately 8-10 Myr). However, the times recorded in HF-182-W-182 isotope system, i.e. when 182Hf became effectively extinct (approximately 50 Myr after solar system formation) are less than closure times recorded in the Sm-146-Nd-142 isotope system (with a full coverage of approximately 500 Myr after solar system formation). This could result in decoupling between the present-day measured epsilon W-182 and epsilon Nd-142 as the SM-146 may have recorded later differentiation events in epsilon ND-142 not observed in epsilon W-182 values. With these potential complexities in short-lived chronological data for SNC's in mind, new Hf-176/Hf-177, Nd-143/Nd-144 and Nd

  10. Stability of a radiative mantle in ITER

    International Nuclear Information System (INIS)

    Mahdavi, M.A.; Staebler, G.M.; Wood, R.D.; Whyte, D.G.; West, W.P.

    1996-12-01

    We report results of a study to evaluate the efficacy of various impurities for heat dispersal by a radiative mantle and radiative divertor(including SOL). We have derived a stability criterion for the mantle radiation which favors low Z impurities and low ratios of edge to core thermal conductivities. Since on the other hand the relative strength of boundary line radiation to core bremsstrahlung favors high Z impurities, we find that for the ITER physics phase argon is the best gaseous impurity for mantle radiation. For the engineering phase of ITER, more detailed analysis is needed to select between krypton and argon

  11. Hainan mantle plume produced late Cenozoic basaltic rocks in Thailand, Southeast Asia.

    Science.gov (United States)

    Yan, Quanshu; Shi, Xuefa; Metcalfe, Ian; Liu, Shengfa; Xu, Taoyu; Kornkanitnan, Narumol; Sirichaiseth, Thanyapat; Yuan, Long; Zhang, Ying; Zhang, Hui

    2018-02-08

    Intraplate volcanism initiated shortly after the cessation of Cenozoic seafloor spreading in the South China Sea (SCS) region, but the full extent of its influence on the Indochina block has not been well constrained. Here we present major and trace element data and Sr-Nd-Pb-Hf isotope ratios of late Cenozoic basaltic lavas from the Khorat plateau and some volcanic centers in the Paleozoic Sukhothai arc terrane in Thailand. These volcanic rocks are mainly trachybasalts and basaltic trachyandesites. Trace element patterns and Sr-Nd-Pb-Hf isotopic compositions show that these alkaline volcanic lavas exhibit oceanic island basalt (OIB)-like characteristics with enrichments in both large-ion lithophile elements (LILE) and high field strength elements (HFSEs). Their mantle source is a mixture between a depleted Indian MORB-type mantle and an enriched mantle type 2 (EMII). We suggest that the post-spreading intraplate volcanism in the SCS region was induced by a Hainan mantle plume which spread westwards to the Paleozoic Sukhothai arc terrane.

  12. Stagnation and Storage of Strongly Depleted Melts in Slow-Ultraslow Spreading Oceans: Evidence from the Ligurian Tethys

    Science.gov (United States)

    Piccardo, Giovanni; Guarnieri, Luisa; Padovano, Matteo

    2013-04-01

    Our studies of Alpine-Apennine ophiolite massifs (i.e., Lanzo, Voltri, Ligurides, Corsica) show that the Jurassic Ligurian Tethys oceanic basin was a slow-ultraslow spreading basin, characterized by the exposures on the seafloor of mantle peridotites with extreme compositional variability. The large majority of these peridotites are made of depleted spinel harzburgites and plagioclase peridotites. The former are interpreted as reactive peridotites formed by the reactive percolation of under-saturated, strongly trace element depleted asthenospheric melts migrated by porous flow through the mantle lithosphere. The latter are considered as refertilized peridotites formed by peridotite impregnation by percolated silica-saturated, strongly trace element depleted melts. Strongly depleted melts were produced as low-degrees, single melt increments by near fractional melting of the passively upwelling asthenosphere during the rifting stage of the basin. They escaped single melt increment aggregation, migrated isolated through the mantle lithosphere by reactive porous or channeled flow before oceanic opening, and were transformed into silica-saturated derivative liquids that underwent entrapment and stagnation in the shallow mantle lithosphere forming plagioclase-enriched peridotites. Widespread small bodies of strongly depleted gabbro-norites testify for the local coalescence of these derivative liquids. These melts never reached the surface (i.e., the hidden magmatism), since lavas with their composition have never been found in the basin. Subsequently, aggregated MORB melts upwelled within replacive dunite channels (as evidenced by composition of magmatic clinopyroxenes in dunites), intruded at shallow levels as olivine gabbro bodies and extruded as basaltic lavas, to form the crustal rocks of the oceanic lithosphere (i.e., the oceanic magmatism). Km-scale bodies of MORB olivine gabbros were intruded into the plagioclase-enriched peridotites, which were formed in the

  13. The mantle source of island arc magmatism during early subduction: Evidence from Hf isotopes in rutile from the Jijal Complex (Kohistan arc, Pakistan)

    Science.gov (United States)

    Ewing, Tanya A.; Müntener, Othmar

    2018-05-01

    The Cretaceous-Paleogene Kohistan arc complex, northern Pakistan, is renowned as one of the most complete sections through a preserved paleo-island arc. The Jijal Complex represents a fragment of the plutonic roots of the Kohistan arc, formed during its early intraoceanic history. We present the first Hf isotope determinations for the Jijal Complex, made on rutile from garnet gabbros. These lithologies are zircon-free, but contain rutile that formed as an early phase. Recent developments in analytical capabilities coupled with a careful analytical and data reduction protocol allow the accurate determination of Hf isotope composition for rutile with <30 ppm Hf for the first time. Rutile from the analysed samples contains 5-35 ppm Hf, with sample averages of 13-17 ppm. Rutile from five samples from the Jijal Complex mafic section, sampling 2 km of former crustal thickness, gave indistinguishable Hf isotope compositions with εHf(i) ranging from 11.4 ± 3.2 to 20.1 ± 5.7. These values are within error of or only slightly more enriched than modern depleted mantle. The analysed samples record variable degrees of interaction with late-stage melt segregations, which produced symplectitic overprints on the main mineral assemblage as well as pegmatitic segregations of hydrous minerals. The indistinguishable εHf(i) across this range of lithologies demonstrates the robust preservation of the Hf isotope composition of rutile. The Hf isotope data, combined with previously published Nd isotope data for the Jijal Complex garnet gabbros, favour derivation from an inherently enriched, Indian Ocean type mantle. This implies a smaller contribution from subducted sediments than if the source was a normal (Pacific-type) depleted mantle. The Jijal Complex thus had only a limited recycled continental crustal component in its source, and represents a largely juvenile addition of new continental crust during the early phases of intraoceanic magmatism. The ability to determine the Hf

  14. Structure and evolution of the lithospheric mantle beneath Siberian craton, thermobarometric study

    Science.gov (United States)

    Ashchepkov, Igor V.; Pokhilenko, Nikolai P.; Vladykin, Nikolai V.; Logvinova, Alla M.; Afanasiev, Valentin P.; Pokhilenko, Lyudmila N.; Kuligin, Sergei S.; Malygina, Elena V.; Alymova, Natalia A.; Kostrovitsky, Sergey I.; Rotman, Anatolii Y.; Mityukhin, Sergey I.; Karpenko, Mikhail A.; Stegnitsky, Yuri B.; Khemelnikova, Olga S.

    2010-04-01

    70 kbar. Sub-continental lithospheric mantle (SCLM) beneath the Alakite field has been subjected to pervasive multistage metasomatism, as indicated by Fe-enriched Cr-diopsides and Ti-rich low-Ca garnets. Ilmenite PT trends were formed by rising protokimberlites that underwent AFC. In the Upper Muna field the mantle is similar in structure to that of the Alakite region. Fe-rich clinopyroxene-bearing rocks (60-55 kbar) are located between the ilmenite-forming systems (70-60 and 55-40 kbar), sub-Ca garnets start from 40 kbar and become more abundant downward. Beneath the Nakyn field, rhythmic layering is found for peridotites in the lower part ( P > 40 kbar), fertilization by Fe-Cpx (40-50 kbar) follow the Ilm-forming system ˜ 55-60 kbar correlating with the occurrence of depleted (low-Ca) peridotites. Beneath the Anabar fields highly depleted mantle at depth > 40 kbar has been subjected to Fe-metasomatism and pervasive metasomatism that accompanied protokimberlite feeders marked by low Cr-ilmenites accompanied by fertilization. In the upper section abundant garnet- and clinopyroxene-rich peridotites are typical. Comparison of mantle sections reconstructed from monomineral PT estimates from Paleozoic and Mesozoic kimberlites show differences in entrainment levels which were elevated after the Permian-Triassic superplume to > 55-40 kbar without delamination.

  15. Crust and Mantle Structure Beneath the Samoan Islands

    Science.gov (United States)

    Browning, J. M.; Courtier, A. M.; Jackson, M. G.; Lekic, V.; Hart, S. R.; Collins, J. A.

    2013-12-01

    We used teleseismic receiver functions to map the seismic structure under the Samoan Islands in the southern Pacific Ocean. We acquired seismograms for the permanent seismic station, AFI, and for five temporary stations located across the island chain from the Samoan Lithospheric Integrated Seismic Experiment (SLISE). We used multiple-taper correlation and Markov chain Monte Carlo algorithms to calculate receiver functions for events with epicentral distance of 30° to 95° and examined the results in a frequency range of 1.0 - 5.0 Hz for crustal structure and 0.1 - 2.0 Hz for mantle structure. We identify complex crustal layering, including the interface between volcanic rocks and the ocean crust and a substantial underplated layer beneath the normal ocean crust. We find that the crust thins with decreasing age across the Samoan Islands and correlates with previous observations from gravity data (Workman, 2005). We additionally identify a velocity increase in the range of 50-100 km depth, potentially the Hales discontinuity. Deeper in the mantle, we observe transition zone thickness of 245-250 km across the island chain, which is within the margin of error for globally observed transition zone thickness. When migrated with IASP, transition zone discontinuity depths do appear deeper beneath the youngest island, indicating slower velocities and/or deeper discontinuity depths relative to the older islands in the system. We will provide improved constraints on transition zone discontinuity depths from ScS reverberations for all stations, and will place the crust and mantle results into a multi-disciplinary context, with comparisons to geochemical and surface observations. Workman, R., 2005. Geochemical characterization of endmember mantle components, Doctoral dissertation, Massachusetts Institute of Technology, http://dspace.mit/edu/handle/1721.1/33721.

  16. FAST TRACK PAPER: Inference of mantle viscosity from GRACE and relative sea level data

    Science.gov (United States)

    Paulson, Archie; Zhong, Shijie; Wahr, John

    2007-11-01

    Gravity Recovery And Climate Experiment (GRACE) satellite observations of secular changes in gravity near Hudson Bay, and geological measurements of relative sea level (RSL) changes over the last 10000 yr in the same region, are used in a Monte Carlo inversion to infer-mantle viscosity structure. The GRACE secular change in gravity shows a significant positive anomaly over a broad region (>3000 km) near Hudson Bay with a maximum of ~2.5 μGalyr-1 slightly west of Hudson Bay. The pattern of this anomaly is remarkably consistent with that predicted for postglacial rebound using the ICE-5G deglaciation history, strongly suggesting a postglacial rebound origin for the gravity change. We find that the GRACE and RSL data are insensitive to mantle viscosity below 1800 km depth, a conclusion similar to that from previous studies that used only RSL data. For a mantle with homogeneous viscosity, the GRACE and RSL data require a viscosity between 1.4 × 1021 and 2.3 × 1021 Pas. An inversion for two mantle viscosity layers separated at a depth of 670km, shows an ensemble of viscosity structures compatible with the data. While the lowest misfit occurs for upper- and lower-mantle viscosities of 5.3 × 1020 and 2.3 × 1021 Pas, respectively, a weaker upper mantle may be compensated by a stronger lower mantle, such that there exist other models that also provide a reasonable fit to the data. We find that the GRACE and RSL data used in this study cannot resolve more than two layers in the upper 1800 km of the mantle.

  17. The mantle-plume model, its feasibility and consequences

    NARCIS (Netherlands)

    Calsteren, van P.W.C.

    1981-01-01

    High beat-flow foci on the Earth have been named ‘hot-spots’ and are commonly correlated with ‘mantle-plumes’ in the deep. A mantle plume may be described as a portion of mantle material with a higher heat content than its surroundings. The intrusion of a mantle-plume is inferred to be similar to

  18. 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

  19. 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...

  20. 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 could...... be studied using the PIV test facility. Two transient three-dimensional CFD-models of the glass model mantle tank were developed using the CFD-programmes CFX and FLUENT.The experimental results illustrate that the mantle flow structure in the mantle is complicated and the distribution of flow in the mantle...

  1. Thermoconvective waves in the earth's mantle

    Science.gov (United States)

    Birger, B. I.

    1980-06-01

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

  2. Comparative Analysis of VERA Depletion Problems

    International Nuclear Information System (INIS)

    Park, Jinsu; Kim, Wonkyeong; Choi, Sooyoung; Lee, Hyunsuk; Lee, Deokjung

    2016-01-01

    Each code has its own solver for depletion, which can produce different depletion calculation results. In order to produce reference solutions for depletion calculation comparison, sensitivity studies should be preceded for each depletion solver. The sensitivity tests for burnup interval, number of depletion zones, and recoverable energy per fission (Q-value) were performed in this paper. For the comparison of depletion calculation results, usually the multiplication factors are compared as a function of burnup. In this study, new comparison methods have been introduced by using the number density of isotope or element, and a cumulative flux instead of burnup. In this paper, optimum depletion calculation options are determined through the sensitivity study of the burnup intervals and the number of depletion intrazones. Because the depletion using CRAM solver performs well for large burnup intervals, smaller number of burnup steps can be used to produce converged solutions. It was noted that the depletion intra-zone sensitivity is only pin-type dependent. The 1 and 10 depletion intra-zones for the normal UO2 pin and gadolinia rod, respectively, are required to obtain the reference solutions. When the optimized depletion calculation options are used, the differences of Q-values are found to be a main cause of the differences of solutions. In this paper, new comparison methods were introduced for consistent code-to-code comparisons even when different kappa libraries were used in the depletion calculations

  3. Comparative Analysis of VERA Depletion Problems

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jinsu; Kim, Wonkyeong; Choi, Sooyoung; Lee, Hyunsuk; Lee, Deokjung [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)

    2016-10-15

    Each code has its own solver for depletion, which can produce different depletion calculation results. In order to produce reference solutions for depletion calculation comparison, sensitivity studies should be preceded for each depletion solver. The sensitivity tests for burnup interval, number of depletion zones, and recoverable energy per fission (Q-value) were performed in this paper. For the comparison of depletion calculation results, usually the multiplication factors are compared as a function of burnup. In this study, new comparison methods have been introduced by using the number density of isotope or element, and a cumulative flux instead of burnup. In this paper, optimum depletion calculation options are determined through the sensitivity study of the burnup intervals and the number of depletion intrazones. Because the depletion using CRAM solver performs well for large burnup intervals, smaller number of burnup steps can be used to produce converged solutions. It was noted that the depletion intra-zone sensitivity is only pin-type dependent. The 1 and 10 depletion intra-zones for the normal UO2 pin and gadolinia rod, respectively, are required to obtain the reference solutions. When the optimized depletion calculation options are used, the differences of Q-values are found to be a main cause of the differences of solutions. In this paper, new comparison methods were introduced for consistent code-to-code comparisons even when different kappa libraries were used in the depletion calculations.

  4. Upper-mantle velocities below the Scandinavian Mountains from P- and S- wave traveltime tomography

    DEFF Research Database (Denmark)

    Hejrani, Babak; Balling, N.; Jacobsen, B. H.

    2017-01-01

    condition: High relative VP, even higher relative VS and hence low VP/VS, consistent with thick dry depleted lithosphere, similar to what is found in most of the Baltic Shield. This shows that upper-mantle velocity anomalies are very poor predictors of topography in this region. An important deviation from...... is more uneven. A pronounced upper-mantle velocity boundary (UMVB), transecting the study region is defined. It runs from SE Norway (east of the Oslo Graben) across the mountains to the Norwegian coast near Trondheim (around the Møre-Trøndelag Fault Complex), from where it follows the coast and runs...... between Lofoten and the crest of the Northern Scandes Mountains and stays off the coast further north. Seismic velocities in the depth interval 100-300 km change across the UMVB from low relative VP and even lower relative VS on the western side to high relative VP and even higher relative VS to the east...

  5. Phosphates in pallasite meteorites as probes of mantle processes in small planetary bodies

    Science.gov (United States)

    Davis, Andrew M.; Olsen, Edward J.

    1991-01-01

    Trace element analyses of the phosphates minerals in stony-iron pallasite meteorites are used here to investigate the magmatic history of the silicate portions of pallasites. In Eagle Station and seven other pallasites, the phosphates have relatively low concentrations of REEs and are strongly enriched in heavy relative to light REE. These patterns are consistent with formation of phosphate by subsolidus reactions between metal and silicate, in which phosphate inherits the REE pattern of olivine. In Springwater and Santa Rosalia, calcium-rich phosphates have higher concentrations of REE, are enriched in light relative to heavy REE, and have negative europium anomalies. These patterns are consistent with crystallization of phosphate from a europium-depleted chondritic liquid. This is unlikely to have happened near the base of the differentiating parent-body mantle; it suggests that some pallasites may come from regions of their parent bodies much nearer the surface than the core-mantle boundary.

  6. Mantle flow influence on subduction evolution

    Science.gov (United States)

    Chertova, Maria V.; Spakman, Wim; Steinberger, Bernhard

    2018-05-01

    The impact of remotely forced mantle flow on regional subduction evolution is largely unexplored. Here we investigate this by means of 3D thermo-mechanical numerical modeling using a regional modeling domain. We start with simplified models consisting of a 600 km (or 1400 km) wide subducting plate surrounded by other plates. Mantle inflow of ∼3 cm/yr is prescribed during 25 Myr of slab evolution on a subset of the domain boundaries while the other side boundaries are open. Our experiments show that the influence of imposed mantle flow on subduction evolution is the least for trench-perpendicular mantle inflow from either the back or front of the slab leading to 10-50 km changes in slab morphology and trench position while no strong slab dip changes were observed, as compared to a reference model with no imposed mantle inflow. In experiments with trench-oblique mantle inflow we notice larger effects of slab bending and slab translation of the order of 100-200 km. Lastly, we investigate how subduction in the western Mediterranean region is influenced by remotely excited mantle flow that is computed by back-advection of a temperature and density model scaled from a global seismic tomography model. After 35 Myr of subduction evolution we find 10-50 km changes in slab position and slab morphology and a slight change in overall slab tilt. Our study shows that remotely forced mantle flow leads to secondary effects on slab evolution as compared to slab buoyancy and plate motion. Still these secondary effects occur on scales, 10-50 km, typical for the large-scale deformation of the overlying crust and thus may still be of large importance for understanding geological evolution.

  7. Rare earth element characteristics of pyrope garnets from the Kaavi-Kuopio kimberlites – implications for mantle metasomatism

    Directory of Open Access Journals (Sweden)

    Marjaleena Lehtonen

    2005-01-01

    Full Text Available Peridotitic garnet xenocrysts from five kimberlite pipes in the Kaavi-Kuopio area of eastern Finland have been studied using major and trace element geochemistry to obtain information on the stratigraphy, compositional variability and evolutionary history of the underlyinglithospheric mantle. Ni thermometry on garnet xenocrysts gives 650–1350°C and, when extrapolated to the geotherm determined using mantle xenoliths, indicates a sampling interval of c. 80–230 km. Three distinct mantle layers are recognized based on the xenolith/xenocryst record: (1 A shallow, 180 km, composed largely of fertile material. The chondrite-normalized REE profiles of subcalcic harzburgitic garnet xenocrysts originating from layer 2 bear evidence of an extensive ancient melt extraction event, similar to that observed in lithosphere underlying Archean cratons elsewhere. Memory of this eventhas possibly also been preserved in the REEN signatures of rare depleted garnets from layer 3 and in the CCGE pyropes from layer 1 despite their saturation in Ca. The lherzolitic and megacryst garnet varieties exhibit LREEN depletion relative to MREEN and HREEN, withthe steady enrichment from SmN to YbN typical of Ca-saturated mantle garnets. The enrichment of MREE and HREE probably derives from a metasomatic event caused by silicate melts close in composition to megacryst magma, which also imprinted a Ti-metasomatic overprint on many pyrope garnets. Harzburgitic and rare lherzolitic garnets, however, appear to have escaped this metasomatism.

  8. A comparison of peridotites from the Molloy Deep and the Gakkel Ridge with mantle xenolites from Spitsbergen

    Science.gov (United States)

    Hansen, H. E.; Amundsen, H. E. F.; Snow, J. E.; Pedersen, R. B.

    2003-04-01

    Along the Arctic ridges, mantle peridotites are tectonically exposed in the Molloy Deep and along the Gakkel Ridge. In the Arctic region, mantel peridotites are also present as xenolites in Quaternary volcanoes in the Bockfjord area on Spitsbergen -- approximately 150 km east of the Molloy Deep. These volcanic centres contain up to 15--20% of xenolites that comprise: Cr-diopside lherzolites, wehrlites, meta-pyroksenites and granulites. The Sr and Nd isotopic composition of clinopyroxenes from lherzolite xenolites have been analysed and compared with the isotopic composition of clinopyroxenes extracted from mantle peridotites from the Molloy Deep and the Gakkel Ridge, as well as with the isotopic compositions of basalts dredged from the Mohns and the Knipovich Ridges. Preliminary results show that a group of lherzolite xenolites from Spitsbergen have Sr-Nd isotopic compositions similar to the enriched end member of the Mohns-Knipovich trend. Other xenolites show much more depleted Nd-isotopic compositions. These xenolites have Sm-Nd model ages ranging from 900 Ma to 1700 Ma suggesting that parts of the sub-continental mantle in the region experienced Precambrian melt extraction. The peridotites from the Molloy Deep have similar Nd-isotopic compositions as the least depleted mantle xenolites from Spitsbergen, and plot also at the enriched end of the Mohns-Knipovich trend. The peridotites analysed from the Gakkel Ridge show, however, significantly higher 143Nd/144Nd ratios than the peridotites from the Molloy Deep.

  9. The Earth’s mantle before convection: Effects of magma oceans and the Moon (Invited)

    Science.gov (United States)

    Elkins-Tanton, L. T.; Smrekar, S. E.; Tobie, G.

    2009-12-01

    Studies of magma oceans indicate that planets obtain a gravitationally stable, compositionally differentiated mantle following solidification. This stable mantle results primarily from iron-magnesium partitioning during solidification, producing progressively iron-enriched mantle phases as solidification proceeds. Near the end of solidification, the dense solids will overturn to a stable configuration. The resulting differentiated mantle is stable from compositional density gradients that are significant enough to suppress thermal convection for up to hundreds of millions of years or longer, a scenario that proceeds self-consistently from physical and chemical principals, but is in contradiction with a previous image of a hot, turbulently convecting earliest terrestrial mantle. The isotopic range found in Martian meteorites indicates that its mantle differentiated in the first tens of millions of years of the solar system and has not been thoroughly remixed since. The specific isotopic range found on Mars is consistent with formation in a magma ocean. Based on the isotopic compositions of magmas, the Earth’s mantle is well mixed in comparison with the mantle of Mars. If the terrestrial planets experienced partial or whole magma oceans and thus began with stable mantles, resisting the onset of thermal convection and subsequent remixing, then why is Earth’s mantle well mixed? Two processes predicted to occur on the Earth, but not on the smaller Mars, may explain the divergent evolutions of these bodies. Here we will present model calculations for these two processes. First, we hypothesize that in the brief period that the Moon was very close to the Earth, it may have tidally heated Earth’s interior sufficiently to overcome its initial compositionally stable mantle, initiate active convection, and set the stage for the well-mixed mantle sampled today. Mars, conversely, may have cooled significantly before thermal convection began, allowing the formation of a

  10. Global P-wave tomography of mantle plumes and subducting slabs

    Science.gov (United States)

    Yamamoto, Y.; Zhao, D.

    2008-12-01

    There are many volcanoes on the Earth which can be generally classified into 3 categories: island arc volcanoes, mid-ocean ridge volcanoes, and hotspot volcanoes. Hotspot volcanoes denote intraplate volcanoes like Hawaii, or anomalously large mid-ocean ridge volcanoes like Iceland. So far many researchers have studied the origin of hotspot volcanoes and have used mantle plume hypothesis to explain them. However, we still have little knowledge about mantle plumes yet. In this study, we determined a new model of whole mantle P-wave tomography to understand the origin of hotspot volcanoes. We used the global tomography method of Zhao (2001, 2004). A 3-D grid net was set up in the mantle, and velocity perturbations at every grid nodes were taken as unknown parameters. The iasp91 velocity model (Kennett and Engdahl, 1991) was taken as the 1-D initial model. We selected 9106 earthquakes from the events occurred in the last forty years from the ISC catalog. About 1.6 million arrival-time data of five-type P phases (P, pP, PP, PcP, and Pdiff) were used to conduct the tomographic inversion. In our previous model (Zhao, 2004), the grid interval in the E-W direction is too small in the polar regions. In this study, in order to remedy this problem, we use a flexible-grid approach to make the lateral grid intervals in the polar regions nearly the same as the other portions of the mantle. As a result, the tomographic images in the polar regions are remarkably improved. Our new tomographic model shows huge low-velocity (low-V) zones in the entire mantle under Tahiti and Lake Victoria, which reflect the Pacific and African superplumes, being consistent with the previous studies. A clear low-V zone is revealed under Mt. Erebus volcano in Antarctica. Other major hotspots also exhibit significant low-V zones in the mantle under their surface locations. Beneath Bering Sea, we found that the Pacific slab is subducting from the Aleutian trench and it is stagnant in the mantle transition

  11. Ibrutinib, lenalidomide, and rituximab in relapsed or refractory mantle cell lymphoma (PHILEMON)

    DEFF Research Database (Denmark)

    Jerkeman, Mats; Eskelund, Christian Winther; Hutchings, Martin

    2018-01-01

    on either regimen alone. METHODS: In this multicentre, open-label, single-arm, phase 2 trial, we enrolled patients aged 18 years or older with relapsed or refractory mantle cell lymphoma who had previously been treated with at least one rituximab-containing regimen, an Eastern Cooperative Oncology Group......BACKGROUND: Regimens based on ibrutinib alone and lenalidomide and rituximab in combination show high activity in patients with relapsed or refractory mantle cell lymphoma. We hypothesised that the combination of all three drugs would improve efficacy compared with previously published data....... The trial is ongoing, but is no longer accruing patients, and is registered with ClinicalTrials.gov, number NCT02460276. FINDINGS: Between April 30, 2015, and June 1, 2016, we enrolled 50 patients with relapsed or refractory mantle cell lymphoma at ten centres in Sweden, Finland, Norway, and Denmark...

  12. Melting and refertilization of the Arctic mantle from the ultra-slow spreading Gakkel Ridge

    Science.gov (United States)

    Cai, Y.; Goldstein, S. L.; Langmuir, C. H.; Michael, P. J.

    2011-12-01

    Mid-Ocean Ridge basalts (MORB) from the slowest spreading zone of the ultra-slow spreading Gakkel Ridge (the eastern volcanic zone or EVZ), comprise ~100 km long segments showing coherent geochemical and isotopic affinities, created by melt depletion and refertilization of the sub-ridge mantle. The EVZ lies to the east of a "sparsely magmatic zone" where peridotite outcrops in the ridge axis. Basalts just to the east of the sparsely magmatic zone (at 29°E - 40°E, segment EVZ1) show some of the highest MORB Hf and Nd isotope ratios on Earth (with ɛHf values up to nearly +26). They plot significantly above the Nd-Hf mantle-crust array. Basalts further to the east (segments EVZ2 and EVZ3), where spreading rate is even lower, show lower ɛNd and ɛHf values and plot closer to the mantle-crust array. Basalts from EVZ1 also show higher Lu/Hf and lower Dy/Yb ratios than basalts from EVZ2 and EVZ3. Comparing the differences in Hf-Nd isotope ratios for these segments, and accounting for the Lu/Hf-Sm/Nd ratios, the "depletion age" for the EVZ1 segment can be estimated, and the data are consistent with significant ancient melt removal (~9%) in the garnet stability field from the EVZ1 mantle source ca. 200Ma ago. In contrast to their high Hf-Nd isotope ratios (indicating severe incompatible element depletion), basalts from EVZ1 segment show strong enrichments in highly incompatible elements (for example, K2O/TiO2 up to 0.37 and (La/Sm)N up to 1.4). These geochemical signatures are consistent with recent melt refertilization of the sub-ridge mantle. In contrast to basalts from segment EVZ1, with enriched trace elements but Hf-Nd isotopes indicating long-term incompatible depletion, a group of samples from segment EVZ2, further to the east, show the opposite characteristics, that is, depleted incompatible element signatures (K2O/TiO2 down to 0.05 and low Dy/Yb), but long-term trace element enrichment (low ɛNd and ɛHf). These basalts may represent a second-round of melting

  13. Mantle xenoliths from Szentbékálla, Balaton: Geochemical and petrological constraints on the evolution of the lithospheric mantle underneath Pannonian Basin, Hungary

    Science.gov (United States)

    Ntaflos, Theo; Bizimis, Michael; Abart, Rainer

    2017-04-01

    Pliocene alkali basalts from the Bakony-Balaton Highland Volcanic Field (BBHVF) in the western Pannonian Basin carry mantle xenoliths comprising hydrous and anhydrous spinel peridotites. The studied mantle xenoliths from Szentbékálla, near Lake Balaton, Hungary, are fine- and coarse-grained fertile to depleted spinel lherzolites, spinel harzburgites and dunites, with protogranular, porphyroclastic, and secondary protogranular and mosaic equigranular textures. Melt pockets, with shapes resembling amphibole, are common in a number of samples, whereas other samples have thin films of intergranular glass. Bulk-rock major element abundances show that the mantle lithosphere beneath this area experienced variable degrees (up to 20%) of partial melting. The clinopyroxene trace elements systematics retain a record of melt depletion and metasomatic processes attributed to subduction-related melt/fluids or to the infiltration of percolating undersaturated melts in the Pannonian lithospheric mantle. The radiogenic isotopes of Sr, Nd and Hf in clinopyroxene suggest that this metasomatism was a relatively recent event. Textural evidence suggests that the calcite filling up the vesicles in the melt pockets and in veinlets cross-cutting the constituent minerals is of epigenetic nature and not due to carbonatite metasomatism. The non-metasomatized primitive mantle normalized clinopyroxene REE abundances mimic those, but at higher values, of their bulk-rock REE patterns. Bulk-rock and clinopyroxene REE with upward and downward LREE respectively, indicate up to 2.4% host basalt infiltration. The calculated bulk composition of the melt pockets is identical to small amphibole relics found as inclusions in second generation clinopyroxene within the melt pockets, suggesting incongruent melting of amphibole, without the need for additional metasomatic melt/fluids to initiate the amphibole breakdown. The heat for the temperature increase necessary for amphibole breakdown was derived from

  14. Teaching machines to find mantle composition

    Science.gov (United States)

    Atkins, Suzanne; Tackley, Paul; Trampert, Jeannot; Valentine, Andrew

    2017-04-01

    The composition of the mantle affects many geodynamical processes by altering factors such as the density, the location of phase changes, and melting temperature. The inferences we make about mantle composition also determine how we interpret the changes in velocity, reflections, attenuation and scattering seen by seismologists. However, the bulk composition of the mantle is very poorly constrained. Inferences are made from meteorite samples, rock samples from the Earth and inferences made from geophysical data. All of these approaches require significant assumptions and the inferences made are subject to large uncertainties. Here we present a new method for inferring mantle composition, based on pattern recognition machine learning, which uses large scale in situ observations of the mantle to make fully probabilistic inferences of composition for convection simulations. Our method has an advantage over other petrological approaches because we use large scale geophysical observations. This means that we average over much greater length scales and do not need to rely on extrapolating from localised samples of the mantle or planetary disk. Another major advantage of our method is that it is fully probabilistic. This allows us to include all of the uncertainties inherent in the inference process, giving us far more information about the reliability of the result than other methods. Finally our method includes the impact of composition on mantle convection. This allows us to make much more precise inferences from geophysical data than other geophysical approaches, which attempt to invert one observation with no consideration of the relationship between convection and composition. We use a sampling based inversion method, using hundreds of convection simulations run using StagYY with self consistent mineral physics properties calculated using the PerpleX package. The observations from these simulations are used to train a neural network to make a probabilistic inference

  15. Boron isotopes reveal multiple metasomatic events in the mantle beneath the eastern North China Craton

    Science.gov (United States)

    Li, Hong-Yan; Zhou, Zhou; Ryan, Jeffrey G.; Wei, Gang-Jian; Xu, Yi-Gang

    2016-12-01

    Linkages inferred between the geochemical heterogeneity of the mantle beneath eastern Eurasia and the stagnant Pacific slab documented geophysically in its mantle transition zone are as yet not clearly characterized. In this paper we report new elemental and isotopic data for boron (B) on a suite of well-characterized Cenozoic basalts (alkali basalts, basanites and nephelinites), with ocean island basalt (OIB)-like trace element signatures from western Shandong of the eastern North China Craton (NCC). Correlations between major elements (e.g., FeOT versus SiO2), trace elements (e.g., CeN/PbN versus BaN/ThN) and radiogenic isotopes (e.g., 206Pb/204Pb versus 87Sr/86Sr) suggest these basalts are derived via the mixing of melts from two mantle components: a fluid mobile element (FME; such as Ba, K, Pb and Sr) enriched component, which is most evident in the alkali basalts, and a FME depleted mantle component that is more evident in the basanites and nephelinites. The alkali basalts in this study have lower B concentrations (1.4-2.2 μg/g) but higher δ11B (-4.9 to -1.4) values than the basanites and nephelinites (B = 2.1-5.0 μg/g; δ11B = -6.9 to -3.9), and all the samples have nearly constant B/Nb ratios between 0.03 and 0.07, similar to the observed range in B/Nb for intraplate lavas. Our high-SiO2 samples have higher δ11B than that of our low SiO2 samples, indicating that the B isotopic differences among our samples do not result from the addition of a continental crustal component in the mantle source, or direct crustal assimilation during the eruption process. The positive B versus Nb correlation suggests the B isotopic compositions of the western Shandong basalts primarily reflect the pre-eruptive compositions of their mantle sources. Correlations among B, Nd and Sr isotope signatures of the western Shandong basalts differ from those among basalts from plume settings (e.g., Azores and Hawaii), and are inconsistent with models suggesting single-step metasomatic

  16. Geochemical insights into the lithology of mantle sources for Cenozoic alkali basalts in West Qinling, China

    Science.gov (United States)

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

    2018-03-01

    Although alkali basalts are common in oceanic islands and continental rifts, the lithology of their mantle sources is still controversial. While the peridotite is usually viewed as a common source lithology, there are increasing studies suggesting significant contributions from ultramafic metasomatites such as carbonated peridotite, pyroxenite and hornblendite to the origin of alkali basalts. The present study indicates that carbonated peridotite plus hornblendite would have served as the mantle sources of Cenozoic alkali basalts from the West Qinling orogen in China. The target basalts show low SiO2 contents of 36.9 to 40.8 wt% and highly variable Na2O + K2O contents from 0.86 to 4.77 wt%, but high CaO contents of 12.5 to 16.3 wt% and CaO/Al2O3 ratios of 1.42 to 2.19. They are highly enriched in the majority of incompatible trace elements, but depleted in Rb, K, Pb, Zr, Hf, and Ti. Furthermore, they exhibit high (La/Yb)N, Zr/Hf, Ce/Pb and Nb/Ta ratios, but low Ti/Eu and Hf/Sm ratios. Generally, with increasing (La/Yb)N and CaO/Al2O3 ratios, their Ti/Eu and Hf/Sm ratios decrease whereas their Zr/Hf, Ce/Pb and Nb/Ta ratios increase. These major and trace element features are similar to those of carbonatites and hornblendite-derived melts to some extent, but significantly different from those of mid-ocean ridge basalts (MORB). This suggests that the alkali basalts would be originated from metasomatic mantle sources. A comparison of the major-trace elements in the alkali basalts with those of some representative mantle-derived melts indicates that the source lithology of alkali basalts is a kind of ultramafic metasomatites that are composed of carbonated peridotite and hornblendite. Such metasomatites would be generated by reaction of the depleted MORB mantle peridotite with hydrous, carbonate-bearing felsic melts derived from partial melting of the subducted Paleotethyan oceanic crust. Therefore, the melt-peridotite reaction at the slab-mantle interface in the

  17. Uranium, depleted uranium, biological effects

    International Nuclear Information System (INIS)

    2001-01-01

    Physicists, chemists and biologists at the CEA are developing scientific programs on the properties and uses of ionizing radiation. Since the CEA was created in 1945, a great deal of research has been carried out on the properties of natural, enriched and depleted uranium in cooperation with university laboratories and CNRS. There is a great deal of available data about uranium; thousands of analyses have been published in international reviews over more than 40 years. This presentation on uranium is a very brief summary of all these studies. (author)

  18. Global storm time depletion of the outer electron belt.

    Science.gov (United States)

    Ukhorskiy, A Y; Sitnov, M I; Millan, R M; Kress, B T; Fennell, J F; Claudepierre, S G; Barnes, R J

    2015-04-01

    The outer radiation belt consists of relativistic (>0.5 MeV) electrons trapped on closed trajectories around Earth where the magnetic field is nearly dipolar. During increased geomagnetic activity, electron intensities in the belt can vary by orders of magnitude at different spatial and temporal scales. The main phase of geomagnetic storms often produces deep depletions of electron intensities over broad regions of the outer belt. Previous studies identified three possible processes that can contribute to the main-phase depletions: adiabatic inflation of electron drift orbits caused by the ring current growth, electron loss into the atmosphere, and electron escape through the magnetopause boundary. In this paper we investigate the relative importance of the adiabatic effect and magnetopause loss to the rapid depletion of the outer belt observed at the Van Allen Probes spacecraft during the main phase of 17 March 2013 storm. The intensities of >1 MeV electrons were depleted by more than an order of magnitude over the entire radial extent of the belt in less than 6 h after the sudden storm commencement. For the analysis we used three-dimensional test particle simulations of global evolution of the outer belt in the Tsyganenko-Sitnov (TS07D) magnetic field model with an inductive electric field. Comparison of the simulation results with electron measurements from the Magnetic Electron Ion Spectrometer experiment shows that magnetopause loss accounts for most of the observed depletion at L >5, while at lower L shells the depletion is adiabatic. Both magnetopause loss and the adiabatic effect are controlled by the change in global configuration of the magnetic field due to storm time development of the ring current; a simulation of electron evolution without a ring current produces a much weaker depletion.

  19. DOUBLE-SHELL TANK (DST) HYDROXIDE DEPLETION MODEL FOR CARBON DIOXIDE ABSORPTION

    International Nuclear Information System (INIS)

    OGDEN DM; KIRCH NW

    2007-01-01

    This document generates a supernatant hydroxide ion depletion model based on mechanistic principles. The carbon dioxide absorption mechanistic model is developed in this report. The report also benchmarks the model against historical tank supernatant hydroxide data and vapor space carbon dioxide data. A comparison of the newly generated mechanistic model with previously applied empirical hydroxide depletion equations is also performed

  20. DOUBLE SHELL TANK (DST) HYDROXIDE DEPLETION MODEL FOR CARBON DIOXIDE ABSORPTION

    Energy Technology Data Exchange (ETDEWEB)

    OGDEN DM; KIRCH NW

    2007-10-31

    This document generates a supernatant hydroxide ion depletion model based on mechanistic principles. The carbon dioxide absorption mechanistic model is developed in this report. The report also benchmarks the model against historical tank supernatant hydroxide data and vapor space carbon dioxide data. A comparison of the newly generated mechanistic model with previously applied empirical hydroxide depletion equations is also performed.

  1. Mantle strength of the San Andreas fault system and the role of mantle-crust feedbacks

    NARCIS (Netherlands)

    Chatzaras, V.; Tikoff, B.; Newman, J.; Withers, A.C.; Drury, M.R.

    2015-01-01

    In lithospheric-scale strike-slip fault zones, upper crustal strength is well constrained from borehole observations and fault rock deformation experiments, but mantle strength is less well known. Using peridotite xenoliths, we show that the upper mantle below the San Andreas fault system

  2. Heterogeneous hydrogen distribution in orthopyroxene from veined mantle peridotite (San Carlos, Arizona): Impact of melt-rock interactions

    Science.gov (United States)

    Denis, Carole M. M.; Demouchy, Sylvie; Alard, Olivier

    2018-03-01

    Experimental studies have shown that hydrogen embedded as a trace element in mantle mineral structures affects the physical properties of mantle minerals and rocks. Nevertheless, hydrogen concentrations in mantle minerals are much lower than predicted by hydrogen solubilities obtained experimentally at high pressure and temperature. Here, we report textural analyses and major and trace element concentrations (including hydrogen) in upper mantle minerals from a spinel-bearing composite xenolith (dunite and pyroxenite) transported by silica-undersaturated mafic alkaline lavas from the San Carlos volcanic field (Arizona, USA). Our results suggest that the composite xenolith results from the percolation-reaction of a basaltic liquid within dunite channels, and is equilibrated with respect to trace elements. Equilibrium temperatures range between 1011 and 1023 °C. Hydrogen concentrations (expressed in ppm H2O by weight) obtained from unpolarized and polarized Fourier transform infrared spectroscopy are low, with average values infrared profile measurements across single-crystals of orthopyroxene reveal hydrogen-depleted rims, which are interpreted as the result of dehydration by ionic diffusion, possibly triggered by melt-rock interactions. We conclude that pyroxenes, like olivine, are unreliable hydrogen proxies, and that the remaining hydrogen concentrations observed in peridotites might only represent the 'tip of the iceberg' of the water stored in the Earth's upper mantle.

  3. Mantle peridotite in newly discovered far-inland subduction complex, southwest Arizona: Initial report

    Science.gov (United States)

    Haxel, Gordon B.; Jacobson, Carl E.; Wittke, James H.

    2015-01-01

    The latest Cretaceous to early Palaeogene Orocopia Schist and related units are generally considered a low-angle subduction complex that underlies much of southern California and Arizona. A recently discovered exposure of Orocopia Schist at Cemetery Ridge west of Phoenix, Arizona, lies exceptionally far inland from the continental margin. Unexpectedly, this body of Orocopia Schist contains numerous blocks, as large as ~300 m, of variably serpentinized mantle peridotite. These are unique; elsewhere in the Orocopia and related schists, peridotite is rare and completely serpentinized. Peridotite and metaperidotite at Cemetery Ridge are of three principal types: (1) serpentinite and tremolite serpentinite, derived from dunite; (2) partially serpentinized harzburgite and olivine orthopyroxenite (collectively, harzburgite); and (3) granoblastic or schistose metasomatic rocks, derived from serpentinite, made largely of actinolite, calcic plagioclase, hercynite, and chlorite. In the serpentinite, paucity of relict olivine, relatively abundant magnetite (5%), and elevated Fe3+/Fe indicate advanced serpentinization. Harzburgite contains abundant orthopyroxene, only slightly serpentinized, and minor to moderate (1–15%) relict olivine. Mantle tectonite fabric is locally preserved. Several petrographic and geochemical characteristics of the peridotite at Cemetery Ridge are ambiguously similar to either abyssal or mantle-wedge (suprasubduction) peridotites and serpentinites. Least ambiguous are orthopyroxene compositions. Orthopyroxene is distinctively depleted in Al2O3, Cr2O3, and CaO, indicating mantle-wedge affinities. Initial interpretation of field and petrologic data suggests that the peridotite blocks in the Orocopia Schist subduction complex at Cemetery Ridge may be derived from the leading corner or edge of a mantle wedge, presumably in (pre-San Andreas fault) southwest California. However, derivation from a subducting plate is not precluded.

  4. Towards modelling of water inflow into the mantle

    Science.gov (United States)

    Thielmann, M.; Eichheimer, P.; Golabek, G.

    2017-12-01

    The transport and storage of water in the mantle significantly affects various material properties of mantle rocks and thus water plays a key role in a variety of geodynamical processes (tectonics, magmatism etc.) Geological and seismological observations suggest different inflow mechanisms of water via the subducting slab like slab bending, thermal cracking and serpentinization (Faccenda et al., 2009; Korenaga, 2017). Most of the previous numerical models do not take different dip angles of the subduction slab and subduction velocities into account, while nature provides two different types of subduction regimes i.e. shallow and deep subduction (Li et al., 2011). To which extent both parameters influence the inflow and outflow of water in the mantle still remains unclear. For the investigation of the inflow and outflow of fluids e.g. water in the mantle, we use high resolution 2D finite element simulations, which allow us to resolve subducted sediments and crustal layers. For this purpose the finite element code MVEP2 (Kaus, 2010), is tested against benchmark results (van Keken et al., 2008). In a first step we reproduced the analytical cornerflow model (Batchelor, 1967) used in the benchmark of van Keken et al.(2008) as well as the steady state temperature field. Further steps consist of successively increasing model complexity, such as the incorporation of hydrogen diffusion, water transport and dehydration reactions. ReferencesBatchelor, G. K. An Introduction to Fluid Dynamics. Cambridge University Press, Cambridge, UK (1967) 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). Li, Z. H., Xu, Z. Q., and T.V. Gerya. Flat versus

  5. Persistence of fertile and hydrous lithospheric mantle beneath the northwestern Ethiopian plateau: Evidence from modal, trace element and Sr-Nd-Hf isotopic compositions of amphibole-bearing mantle xenoliths

    Science.gov (United States)

    Alemayehu, Melesse; Zhang, Hong-Fu; Aulbach, Sonja

    2017-07-01

    We present new trace element compositions of amphiboles, Sr-Nd-Hf isotope compositions of clinopyroxenes and mineral modes for spinel peridotite xenoliths that were entrained in a Miocene alkali basalt (Gundeweyn, northwestern Ethiopian plateau), in order to understand the geochemical evolution and variation occurring within the continental lithospheric mantle (CLM) in close proximity to the East African Rift system, and its dynamic implications. With the exception of a single amphibole-bearing sample that is depleted in LREE (La/YbN = 0.45 × Cl), amphiboles in lherzolites and in one harzburgite show variable degrees of LREE enrichment (La/YbN = 2.5-12.1 × Cl) with flat HREE (Dy/YbN = 1.5-2.1 × Cl). Lherzolitic clinoyroxenes have 87Sr/86Sr (0.70227 to 0.70357), 143Nd/144Nd (0.51285 to 0.51346), and 176Hf/177Hf (0.28297 to 0.28360) ranging between depleted lithosphere and enriched mantle. LREE-enriched clinopyroxenes generally have more enriched isotope compositions than depleted ones. While lherzolites with isotope compositions similar to those of the Afar plume result from the most recent metasomatic overprint, isotope compositions more depleted than present-day MORB can be explained by an older melt extraction and/or isotopic rehomogenisation event, possibly related to the Pan-African orogeny. Several generations of amphibole are recognized in accord with this multi-stage evolution. Texturally unequilibrated amphibole occurring within the peridotite matrix and in melt pockets attest to continued hydration and refertilization of the lithospheric mantle subsequent to Oligocene flood basalt magmatism, during which an earlier-emplaced inventory of amphibole was likely largely consumed. However, a single harzburgite contains amphibole with the highest Mg# and lowest TiO2 content, which is interpreted as sampling a volumetrically subordinate mantle region beneath the Ethiopian plateau that was not tapped during flood basalt magmatism. Strikingly, both trace

  6. Alternate Histories of the Core-Mantle Boundary Region: Discrimination by Heat Flow

    Science.gov (United States)

    Hernlund, J. W.

    2017-12-01

    Interactions between material that would become Earth's core and mantle began prior to accretion. For example, during and just after the supernova event that is thought to have produced the matter that comprises our solar system, a substantial amount of its iron and other heavy elements were forged in nucleosynthetic processes, establishing a pattern of elemental and isotopic abundances that is reflected in the composition of our planet today, and sets the relative size of the core and mantle. As Earth accreted, metals and silicates were delivered together in mostly small increments, and formation of the core required separation and gravitational settling of the metal to the center, probably facilitated by extensive melting. This process over-printed previous metal-silicate interactions, owing to chemical interactions and re-equilibration at higher pressures and temperatures. The heat of core formation was dissipated largely in the mantle if metal descended as diapirs, or was retained in the metal if it was able to crack the mantle and sink by rapid turbulent injection into the core. These processes established the first temperature contrast between the core and the mantle, controlling the extent to which the core could become a giant heat capacitor and supply thermal energy heat to the mantle. Beginning from this very early stage we are able to correlate different hypothesized processes with their variable implications for core-mantle boundary (CMB) heat flow through time. In fact, CMB heat flow is a thread that runs through almost every important question regarding the evolution of the core and mantle. Whole mantle convection vs. layered convection, the abundance of radioactive isotopes, age of the inner core, sustenance of the ancient geodynamo, the possibility of basal magma oceans, core-mantle chemical interactions, etc., all have close connections to CMB heat flow. Here I will attempt to discriminate hypotheses for many processes into high vs. low CMB heat

  7. Detailed microstructure of two-phase lower mantle mineral analogs from SEM and EBSD

    Science.gov (United States)

    Kaercher, Pamela; Mariani, Elisabetta; Dawson, Karl

    2016-04-01

    The rheology and viscosity of the lower mantle influence convection, heat transport through the mantle, slab subduction, and many surface processes. Plastic flow in the lower mantle depends on the deformation mechanics of its constituent mineral phases - mostly bridgmanite, (Mg,Fe)SiO3, with a smaller percent of the rheologically weaker ferropericlase, (Mg,Fe)O. For deformation in a (mostly) two-phase system with large strength contrast, such as in the lower mantle, microstructure greatly influences deformation and rheology. We examined microstructures of an analog two-phase system of the lower mantle before and after deformation using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Halite (NaCl) and neighborite (NaMgF3) were used as analogs to lower mantle minerals ferropericlase (Mg,Fe)O and bridgmanite MgSiO3, respectively, and deformed up to 50% strain at 4 GPa confining pressure and average strain rates of 2×10-3 s-1in the D-DIA. One goal of our microstructural analysis is to help determine whether deformation in the bulk of the lower mantle occurs by diffusion creep or by dislocation creep, which has been long debated. Previous X-ray diffraction and microtomography studies of these samples (Kaercher et al. submitted) show the weaker NaCl is likely interconnected at just 15 percent volume and greatly reduces crystallographic preferred orientation (CPO) in NaMgF3, while NaCl itself develops either very little or heterogeneous CPO. New SEM and EBSD results show that NaCl deforms primarily by subgrain rotation recrystallization (a recrystallization mechanism active during dislocation creep) at 200° C, resulting in drastically reduced grain sizes. While we have less information for the NaMgF3 due to difficulties polishing soft, hydrophilic NaCl and harder NaMgF3 together, it appears that NaMgF3 grains remain the same size. This suggests that periclase may control deformation in the lower mantle resulting in a weaker, more viscous

  8. Seismic Structure of the Shallow Mantle Beneath the Endeavor Segment of the Juan de Fuca Ridge

    Science.gov (United States)

    VanderBeek, B. P.; Toomey, D. R.; Hooft, E. E.; Wilcock, W. S.; Weekly, R. T.; Soule, D. C.

    2013-12-01

    We present tomographic images of the seismic structure of the shallow mantle beneath the intermediate-spreading Endeavor segment of the Juan de Fuca ridge. Our results provide insight into the relationship between magma supply from the mantle and overlying ridge crest processes. We use seismic energy refracted below the Moho (Pn), as recorded by the Endeavor tomography (ETOMO) experiment, to image the anisotropic and isotropic P wave velocity structure. The ETOMO experiment was an active source seismic study conducted in August 2009 as part of the RIDGE2000 science program. The experimental area extends 100 km along- and 60 km across-axis and encompasses active hydrothermal vent fields near the segment center, the eastern end of the Heck seamount chain, and two overlapping spreading centers (OSCs) at either end of the segment. Previous tomographic analyses of seismic arrivals refracted through the crust (Pg), and reflected off the Moho (PmP), constrain a three-dimensional starting model of crustal velocity and thickness. These Pg and PmP arrivals are incorporated in our inversion of Pn travel-time data to further constrain the isotropic and anisotropic mantle velocity structure. Preliminary results reveal three distinct mantle low-velocity zones, inferred as regions of mantle melt delivery to the base of the crust, that are located: (i) off-axis near the segment center, (ii) beneath the Endeavor-West Valley OSC, and (iii) beneath the Cobb OSC near Split Seamount. The mantle anomalies are located at intervals of ~30 to 40 km along-axis and the low velocity anomalies beneath the OSCs are comparable in magnitude to the one located near the segment center. The direction of shallow mantle flow is inferred from azimuthal variations in Pn travel-time residuals relative to a homogeneous isotropic mantle. Continuing analysis will focus on constraining spatial variations in the orientation of azimuthal anisotropy. On the basis of our results, we will discuss the transport of

  9. Health behaviours and their facilitation under depletion conditions: the case of snacking.

    Science.gov (United States)

    Sellahewa, Dilan A; Mullan, Barbara

    2015-07-01

    Previous research suggests that depletion (the state ensuing from self-control exertion) engenders lapses in health behaviours. The present study tested for that effect in relation to the health behaviour of limiting snacking, and investigated whether health goal-priming might facilitate such health behaviours even under depletion conditions. A laboratory study was conducted involving an analytic sample of 85 undergraduates (mean age = 20.08, SD = 3.96; female: n= 63). Depletion was manipulated by having participants watch a humorous video while suppressing their responses (depletion condition) or remaining natural (non-depletion condition). The activation of participants' health goals was then manipulated by subtly exposing (goal-priming condition) or not exposing (non-priming condition) participants to health-related words in a Scrambled Sentence Task. Finally, snacking was measured using a bogus taste-test. Controlling for initial hunger, snacking was higher among depleted compared to non-depleted participants. Snacking was lower among primed compared to non-primed participants. The interaction between depletion and goal-priming was not significant. These findings suggest that depletion should be recognised as a risk factor for lapses in health behaviours, and that health goal-priming may be a useful technique for facilitating such behaviours even when individuals are depleted. Copyright © 2015 Elsevier Ltd. All rights reserved.

  10. The mantle cells lymphoma: a proposed treatment

    International Nuclear Information System (INIS)

    Chavez Martinez, Marlene Elizabeth

    2012-01-01

    A literature review was performed on mantle cells lymphoma in the therapeutic schemes. The literature that has been used is published in journals of medicine specializing in hematology, oncology, radiation therapy, molecular biology and internal medicine. The literature review was performed to propose a scheme of treatment according to Costa Rica. Epigenetic alterations have been revealed in patients with mantle lymphoma on current researches. The mantle lymphoma pathology has been described in various forms of clinical and histological presentation, stressing the importance of detailing the different methods and diagnostic reports. Working groups have proposed and developed various chemotherapy regimens and concluded that CHOP alone is without effect in mantle cell lymphoma unlike R-hyper-CVAD, CHOP / DHAP, high-dose Ara-C. Researchers have tried to develop new treatments based vaccines, use of modified viruses, specific monoclonal antibodies. The classic treatment has been triple intrathecal therapy. The central nervous system has been one of the most momentous sites of mantle cell lymphoma infiltration because poorer patient prognosis [es

  11. Radiation doses from radioactivity in incandescent mantles

    International Nuclear Information System (INIS)

    1985-01-01

    Thorium nitrate is used in the production of incandescent mantles for gas lanterns. In this report dose estimates are given for internal and external exposure that result from the use of the incandescent mantles for gas lanterns. The collective, effective dose equivalent for all users of gas mantles is estimated to be about 100 Sv per annum in the Netherlands. For the population involved (ca. 700,000 persons) this is roughly equivalent to 5% to 10% of the collective dose equivalent associated with exposure to radiation from natural sources. The major contribution to dose estimates comes from inhalation of radium during burning of the mantles. A pessimistic approach results in individual dose estimates for inhalation of up to 0.2 mSv. Consideration of dose consequences in case of a fire in a storage department learns that it is necessary for emergency personnel to wear respirators. It is concluded that the uncontrolled removal of used gas mantles to the environment (soil) does not result in a significant contribution to environmental radiation exposure. (Auth.)

  12. Driving forces: Slab subduction and mantle convection

    Science.gov (United States)

    Hager, Bradford H.

    1988-01-01

    Mantle convection is the mechanism ultimately responsible for most geological activity at Earth's surface. To zeroth order, the lithosphere is the cold outer thermal boundary layer of the convecting mantle. Subduction of cold dense lithosphere provides tha major source of negative buoyancy driving mantle convection and, hence, surface tectonics. There are, however, importnat differences between plate tectonics and the more familiar convecting systems observed in the laboratory. Most important, the temperature dependence of the effective viscosity of mantle rocks makes the thermal boundary layer mechanically strong, leading to nearly rigid plates. This strength stabilizes the cold boundary layer against small amplitude perturbations and allows it to store substantial gravitational potential energy. Paradoxically, through going faults at subduction zones make the lithosphere there locally weak, allowing rapid convergence, unlike what is observed in laboratory experiments using fluids with temperature dependent viscosities. This bimodal strength distribution of the lithosphere distinguishes plate tectonics from simple convection experiments. In addition, Earth has a buoyant, relatively weak layer (the crust) occupying the upper part of the thermal boundary layer. Phase changes lead to extra sources of heat and bouyancy. These phenomena lead to observed richness of behavior of the plate tectonic style of mantle convection.

  13. Seismic Investigations of the Crust and Upper Mantle Structure in Antarctica and Madagascar

    Science.gov (United States)

    Ramirez, Cristo

    In the three studies that form this dissertation, seismic data from Antarctica and Madagascar have been analyzed to obtain new insights into crustal structure and mantle flow. Until recently, there have been little seismic data available from these areas for interrogating Earth structure and processes. In Antarctica, I analyzed datasets from temporary deployments of broadband seismic stations in both East and West Antarctica. In Madagascar, I analyzed data from a temporary network of broadband stations, along with data from three permanent stations. The seismic data have been processed and modeled using a wide range of techniques to characterize crust and mantle structure. Crustal structure in the East Antarctic Craton resembles Precambrian terrains around the world in its thickness and shear wave velocities. The West Antarctic Rift System has thinner crust, consistent with crustal thickness beneath other Cretaceous rifts. The Transantarctic Mountains show thickening of the crust from the costal regions towards the interior of the mountain range, and high velocities in the lower crust at several locations, possibly resulting from the Ferrar magmatic event. Ross Island and Marie Byrd Land Dome have elevated crustal Vp/Vs ratios, suggesting the presence of partial melt and/or volcaniclastic material within the crust. The pattern of seismic anisotropy in Madagascar is complex and cannot arise solely due to mantle flow from the African superplume, as previously proposed. To explain the complex pattern of anisotropy, a combination of mechanisms needs to be invoked, including mantle flow from the African superplume, mantle flow from the Comoros hotspot, small scale upwelling in the mantle induced by lithospheric delamination, and fossil anisotropy in the lithospheric mantle along Precambrian shear zones.

  14. Constraining Lower Mantle Heterogeneity With Differential Dispersion of Core-Diffracted Waves

    Science.gov (United States)

    Euler, G. G.; Wysession, M. E.; Aleqabi, G. I.

    2006-12-01

    We investigate global differential travel-time dispersion of core-diffracted phases from large, deep earthquakes. This technique aids in constraining radial velocity structure at the core-mantle interface in a manner analogous to surface waves constraining upper mantle structure. We show that there is noticeable differential dispersion, that the cause is likely associated with the diffraction process and that the dispersion varies with geographic location. Variations in differential dispersion between Pdiff and Sdiff along the same azimuth are also observed. We attempt to utilize dispersion characteristics to put bounds on the magnitude and distribution of large-scale velocity perturbations in the lowermost mantle region and draw comparisons to variations found in several 3D whole-mantle models. We have included in our study all broadband recordings available from the IRIS DMC. Preprocessing of the records includes deconvolution of the instrument response, conversion to displacement, rotation of horizontals to the backazimuth, filtering using a set of bandpass filters, and sample-rate decimation (20 sps). Relative arrival times are found by computing cross correlegrams in the frequency domain, automatically detecting and removing poor recordings with cluster analysis, weighted least-squares inversion, and robust regression techniques to remedy misidentification in noisy signals. Raypath-approximated corrections for ellipticity, mantle, and crustal differences are applied to the relative times for the derivation of apparent slowness as a function of azimuth and frequency. Following previous studies of diffracted signals, we limit our analysis to stations located in narrow azimuthal windows spread over a considerable distance. This method has the advantage of removing source-side effects, averaging out minor timing errors, and, for our analysis, averaging out receiver-side upper mantle and crustal differential dispersion. Comparison with differential dispersion

  15. Mantle plumes on Venus revisited

    Science.gov (United States)

    Kiefer, Walter S.

    1992-01-01

    The Equatorial Highlands of Venus consist of a series of quasicircular regions of high topography, rising up to about 5 km above the mean planetary radius. These highlands are strongly correlated with positive geoid anomalies, with a peak amplitude of 120 m at Atla Regio. Shield volcanism is observed at Beta, Eistla, Bell, and Atla Regiones and in the Hathor Mons-Innini Mons-Ushas Mons region of the southern hemisphere. Volcanos have also been mapped in Phoebe Regio and flood volcanism is observed in Ovda and Thetis Regiones. Extensional tectonism is also observed in Ovda and Thetis Regiones. Extensional tectonism is also observed in many of these regions. It is now widely accepted that at least Beta, Atla, Eistla, and Bell Regiones are the surface expressions of hot, rising mantel plumes. Upwelling plumes are consistent with both the volcanism and the extensional tectonism observed in these regions. The geoid anomalies and topography of these four regions show considerable variation. Peak geoid anomalies exceed 90 m at Beta and Atla, but are only 40 m at Eistla and 24 m at Bell. Similarly, the peak topography is greater at Beta and Atla than at Eistla and Bell. Such a range of values is not surprising because terrestrial hotspot swells also have a side range of geoid anomalies and topographic uplifts. Kiefer and Hager used cylindrical axisymmetric, steady-state convection calculations to show that mantle plumes can quantitatively account for both the amplitude and the shape of the long-wavelength geoid and topography at Beta and Atla. In these models, most of the topography of these highlands is due to uplift by the vertical normal stress associated with the rising plume. Additional topography may also be present due to crustal thickening by volcanism and crustal thinning by rifting. Smrekar and Phillips have also considered the geoid and topography of plumes on Venus, but they restricted themselves to considering only the geoid-topography ratio and did not

  16. Thermal Conductivity of Lower Mantle Minerals and Heat Flux Across the Core-Mantle Boundary

    Science.gov (United States)

    Bennett, C.; Rainey, E.; Kavner, A.

    2014-12-01

    The thermal conductivity properties of the minerals comprising the Earth's lowermost mantle control the core-mantle boundary heat flux, and are therefore critical properties for determining the thermal state and evolution of the Earth's interior. Here we present measurements of the thermal conductivity of lower mantle oxides and silicates as a function of pressure, temperature, and iron content determined in the laser-heated diamond anvil cell using a combination of measurements and 3-D modeling. Our models and measurements demonstrate that the measured steady-state temperature and its increase with increasing laser power depend on the sample thermal conductivity as well as the experimental geometry, enabling measurements of the pressure- and temperature- dependence of lattice thermal conductivity in the laser-heated diamond anvil cell. We applied this technique to iron-bearing silicate perovskites and MgO at lower mantle pressure and temperature conditions. For MgO, we determine the increase in thermal conductivity k with density ρ to be ∂lnk/∂lnρ=4.7±0.6, which is in agreement with results obtained using other experimental and computational techniques. For (Mg0.8,Fe0.2)SiO3 perovskite, we find ∂lnk/∂lnρ=2.9±0.6. We use these values in combination with independent computational and experimental results to determine thermal conductivity of lower mantle minerals up to core-mantle boundary conditions. We combine the mineralogical thermal conductivity estimates in a composite model and include an estimate for the radiative contribution to thermal conductivity. Our new value of the thermal conductivity of the lowermost mantle is ~5-6 W/m/K and is sensitive to the details of the lower mantle assemblage, but is relatively insensitive to pressure and temperature. We combine our mantle thermal conductivity with models for the lower mantle boundary layer to generate a series of two-dimensional maps of core-mantle boundary heat flux, which emphasize the

  17. Depletion analysis of the UMLRR reactor core using MCNP6

    Science.gov (United States)

    Odera, Dim Udochukwu

    Accurate knowledge of the neutron flux and temporal nuclide inventory in reactor physics calculations is necessary for a variety of application in nuclear engineering such as criticality safety, safeguards, and spent fuel storage. The Monte Carlo N- Particle (MCNP6) code with integrated buildup depletion code (CINDER90) provides a high-fidelity tool that can be used to perform 3D, full core simulation to evaluate fissile material utilization, and nuclide inventory calculations as a function of burnup. The University of Massachusetts Lowell Research Reactor (UMLRR) reactor has been modeled with the deterministic based code, VENTURE and with an older version of MCNP (MCNP5). The MIT developed MCODE (MCNP ORIGEN DEPLETION CODE) was used previously to perform some limited depletion calculations. This work chronicles the use of MCNP6, released in June 2013, to perform coupled neutronics and depletion calculation. The results are compared to previously benchmarked results. Furthermore, the code is used to determine the ratio of fission products 134Cs and 137Cs (burnup indicators), and the resultant ratio is compared to the burnup of the UMLRR.

  18. Metasomatic Control of Water in Garnet and Pyroxene from Kaapvaal Craton Mantle Xenoliths

    Science.gov (United States)

    Peslier, Anne H.; Woodland, Alan B.; Bell, David R.; Lazarov, Marina; Lapen, Thomas J.

    2012-01-01

    Fourier transform infrared spectrometry (FTIR) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) were used to determine water, rare earth (REE), lithophile (LILE), and high field strength (HFSE) element contents in garnet and pyroxene from mantle xenoliths, Kaapvaal craton, southern Africa. Water enters these nominally anhydrous minerals as protons bonded to structural oxygen in lattice defects. Pyroxene water contents (150-400 ppm in clinopyroxene; 40-250 ppm in orthopyroxene) correlate with their Al, Fe, Ca and Na and are homogeneous within a mineral grains and a xenolith. Garnets from Jagersfontein are chemically zoned for Cr, Ca, Ti and water contents. Garnets contain 0 to 20 ppm H2 Despite the fast diffusion rate of H in mantle m inerals, the observations above indicate that the water contents of mantle xenolith minerals were not disturbed during kimberlite entrainment and that the measured water data represent mantle values. Trace elements in all minerals show various degrees of light REE and LILE enrichments indicative of minimal to strong metasomatism. Water contents of peridotite minerals from the Kaapvaal lithosphere are not related to the degree of depletion of the peridotites. Instead, metasomatism exerts a clear control on the amount of water of mantle minerals. Xenoliths from each location record specific types of metasomatism with different outcomes for the water contents of mantle minerals. At pressures . 5.5 GPa, highly alkaline melts metasomatized Liqhobong and Kimberley peridotites, and increased the water contents of their olivine, pyroxenes and garnet. At higher pressures, the circulation of ultramafic melts reacting with peridotite resulted in co-variation of Ca, Ti and water at the edge of garnets at Jagersfontein, overall decreasing their water content, and lowered the water content of olivines at Finsch Mine. The calculated water content of these melts varies depending on whether the water content of the peridotite

  19. 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.

  20. Peridotite xenoliths from Ethiopia: inferences on mantle processes from Plume to Rift settings

    Science.gov (United States)

    Beccaluva, Luigi; Bianchini, Gianluca; Ellam, Robert Mark; Natali, Claudio; Santato, Alessandro; Siena, Franca; Stuart, Finlay

    2010-05-01

    A comprehensive petrological study has been carried out on Ethiopian mantle xenoliths entrained in Neogene-Quaternary alkaline lavas both overlying the Continental Flood Basalt area (Dedessa River - Wollega Region, Injibara - Gojam Region) and from southern Main Ethiopian Rift (MER - Mega, Sidamo Region) in order to investigate the mantle evolution from plume to rift settings. Mantle xenoliths from the plateau area (Injibara, Dedessa River) range in composition from spinel lherzolite to harzburgite and olivine websterite, showing P-T equilibration conditions in the range of 1-2 GPa/950-1050 °C. These xenoliths show flat chondrite-normalized bulk-rock REE patterns, with only few LREE-enriched samples (LaN/YbN up to 5). Clinopyroxene (cpx) REE patterns are generally flat or LREE depleted (LaN/YbN down to 0.6). Sr-Nd isotopes on separated cpx mainly show compositions (87Sr/86Sr 0.5132) approaching the Depleted Mantle end-member, or displaced (87Sr/86Sr 0.7033-0.7034; 143Nd/144Nd 0.5129-0.5128) toward the Enriched Mantle components which also characterize the Ethiopian Oligocene plateau basalts. These characteristics indicate that most xenoliths reflect complex asthenosphere/lithosphere interactions due to plume-related refertilization processes, whose agents may be envisaged as mafic subalkaline melts that infiltrated and reacted with the pristine parageneses ultimately leading to the formation of olivine-websterite domains. On the other hand, mantle xenoliths from southern MER (Mega) consist of spinel lherzolite to harzburgites showing various degree of deformation and recrystallization coupled with an extremely wide incompatible element distribution. Bulk rock Rare Earth Element (REE) patterns show generally flat HREE ranging from 0.1 x chondrite (ch) in harzburgites up to 2 x ch in fertile lherzolites, and are variably enriched in LREE, with LaN/YbN up to 41.5. The constituent clinopyroxenes have flat HREE distribution and LaN/YbN between 0.1 and 55, in general

  1. Depleted uranium disposal options evaluation

    Energy Technology Data Exchange (ETDEWEB)

    Hertzler, T.J.; Nishimoto, D.D.; Otis, M.D. [Science Applications International Corp., Idaho Falls, ID (United States). Waste Management Technology Div.

    1994-05-01

    The Department of Energy (DOE), Office of Environmental Restoration and Waste Management, has chartered a study to evaluate alternative management strategies for depleted uranium (DU) currently stored throughout the DOE complex. Historically, DU has been maintained as a strategic resource because of uses for DU metal and potential uses for further enrichment or for uranium oxide as breeder reactor blanket fuel. This study has focused on evaluating the disposal options for DU if it were considered a waste. This report is in no way declaring these DU reserves a ``waste,`` but is intended to provide baseline data for comparison with other management options for use of DU. To PICS considered in this report include: Retrievable disposal; permanent disposal; health hazards; radiation toxicity and chemical toxicity.

  2. Depleted uranium disposal options evaluation

    International Nuclear Information System (INIS)

    Hertzler, T.J.; Nishimoto, D.D.; Otis, M.D.

    1994-05-01

    The Department of Energy (DOE), Office of Environmental Restoration and Waste Management, has chartered a study to evaluate alternative management strategies for depleted uranium (DU) currently stored throughout the DOE complex. Historically, DU has been maintained as a strategic resource because of uses for DU metal and potential uses for further enrichment or for uranium oxide as breeder reactor blanket fuel. This study has focused on evaluating the disposal options for DU if it were considered a waste. This report is in no way declaring these DU reserves a ''waste,'' but is intended to provide baseline data for comparison with other management options for use of DU. To PICS considered in this report include: Retrievable disposal; permanent disposal; health hazards; radiation toxicity and chemical toxicity

  3. One hundred million years of mantle geochemical history suggest the retiring of mantle plumes is premature

    Science.gov (United States)

    Konter, Jasper G.; Hanan, Barry B.; Blichert-Toft, Janne; Koppers, Anthony A. P.; Plank, Terry; Staudigel, Hubert

    2008-11-01

    Linear chains of intraplate volcanoes and their geochemistry provide a record of mantle melting through geological time. The isotopic compositions of their lavas characterize their mantle sources, and their ages help backtrack these volcanoes to their original, eruptive source regions. Such data may shed light on a much-debated issue in Earth Sciences: the origin of intraplate volcanism and its underlying mantle and lithosphere dynamics. We show here that three major Western Pacific Seamount groups, ˜ 50-100 million years in age, display distinct Sr, Nd, Hf, and Pb isotopic signatures that can be traced back in time, both geographically and geochemically, to three separate, recently-active intraplate volcanoes in the South Pacific Cook-Austral Islands. Their unique 100 million year history, which shows a persistent geochemical fingerprint, suggests formation from large volumes of laterally fixed, long-lived source regions. Such longevity is unlikely to be attained in the relatively dynamic upper mantle. Therefore, these sources are likely anchored deep in the mantle, isolated from homogenization by mantle convection, and imply a primary origin from deep mantle plumes rather than resulting from lithosphere extension.

  4. Experimental constraints on the damp peridotite solidus and oceanic mantle potential temperature.

    Science.gov (United States)

    Sarafian, Emily; Gaetani, Glenn A; Hauri, Erik H; Sarafian, Adam R

    2017-03-03

    Decompression of hot mantle rock upwelling beneath oceanic spreading centers causes it to exceed the melting point (solidus), producing magmas that ascend to form basaltic crust ~6 to 7 kilometers thick. The oceanic upper mantle contains ~50 to 200 micrograms per gram of water (H 2 O) dissolved in nominally anhydrous minerals, which-relative to its low concentration-has a disproportionate effect on the solidus that has not been quantified experimentally. Here, we present results from an experimental determination of the peridotite solidus containing known amounts of dissolved hydrogen. Our data reveal that the H 2 O-undersaturated peridotite solidus is hotter than previously thought. Reconciling geophysical observations of the melting regime beneath the East Pacific Rise with our experimental results requires that existing estimates for the oceanic upper mantle potential temperature be adjusted upward by about 60°C. Copyright © 2017, American Association for the Advancement of Science.

  5. The role of a mantle plume in the formation of Yellowstone volcanism

    Science.gov (United States)

    Leonard, Tiffany; Liu, Lijun

    2016-02-01

    The origin of the Yellowstone volcanic province remains debated. Proposed hypotheses involve either a mantle plume or not. Recent tomographic images allow a quantitative evaluation of the plume hypothesis and its interaction with the Farallon slabs. Using 4-D geodynamic models with data assimilation, we find that the slab is always in the way of the initially rising plume and that the plume could reach the surface only through the broken slab hinge at ~15 Ma. For most of the time, the sinking slabs dominate the mantle flow and prohibit upwelling. We find that a plume that satisfies the present mantle image beneath Yellowstone fails to predict both voluminous hot materials at shallow depths beneath the western U.S. and the age migration of the hot spot tracks. We suggest that a plume is likely to have much less influence on the Yellowstone volcanism than previously thought.

  6. Attenuation of seismic waves and the universal rheological model of the Earth's mantle

    Science.gov (United States)

    Birger, B. I.

    2007-08-01

    Analysis of results of laboratory studies on creep of mantle rocks, data on seismic wave attenuation in the mantle, and rheological micromechanisms shows that the universal, i.e., relevant to all time scales, rheological model of the mantle can be represented as four rheological elements connected in series. These elements account for elasticity, diffusion rheology, high temperature dislocation rheology, and low temperature dislocation rheology. The diffusion rheology element is described in terms of a Newtonian viscous fluid. The high temperature dislocation rheology element is described by the rheological model previously proposed by the author. This model is a combination of a power-law non-Newtonian fluid model for stationary flows and the linear hereditary Andrade model for flows associated with small strains. The low temperature dislocation rheology element is described by the linear hereditary Lomnitz model.

  7. Phase transitions in MgSiO3 post-perovskite in super-Earth mantles

    Science.gov (United States)

    Umemoto, Koichiro; Wentzcovitch, Renata M.; Wu, Shunqing; Ji, Min; Wang, Cai-Zhuang; Ho, Kai-Ming

    2017-11-01

    The highest pressure form of the major Earth-forming mantle silicate is MgSiO3 post-perovskite (PPv). Understanding the fate of PPv at TPa pressures is the first step for understanding the mineralogy of super-Earths-type exoplanets, arguably the most interesting for their similarities with Earth. Modeling their internal structure requires knowledge of stable mineral phases, their properties under compression, and major element abundances. Several studies of PPv under extreme pressures support the notion that a sequence of pressure induced dissociation transitions produce the elementary oxides SiO2 and MgO as the ultimate aggregation form at ∼3 TPa. However, none of these studies have addressed the problem of mantle composition, particularly major element abundances usually expressed in terms of three main variables, the Mg/Si and Fe/Si ratios and the Mg#, as in the Earth. Here we show that the critical compositional parameter, the Mg/Si ratio, whose value in the Earth's mantle is still debated, is a vital ingredient for modeling phase transitions and internal structure of super-Earth mantles. Specifically, we have identified new sequences of phase transformations, including new recombination reactions that depend decisively on this ratio. This is a new level of complexity that has not been previously addressed, but proves essential for modeling the nature and number of internal layers in these rocky mantles.

  8. Supercritical fluid in the mantle transition zone deduced from H-D interdiffusion of wadsleyite

    Science.gov (United States)

    Sun, Wei; Yoshino, Takashi; Sakamoto, Naoya; Yurimoto, Hisayoshi

    2018-02-01

    Knowledge of the distribution of water in the Earth's mantle is key to understanding the mantle convection and geochemical evolution of the Earth. As wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures, proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge, where descending slab stagnates at the transition zone. However, there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies, because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite. Here we report the hydrogen self-diffusion coefficient obtained from H-D interdiffusion experiments in wadsleyite single-crystal couples. Our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone. In contrast, the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle, probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales. This phenomenon provides an alternative explanation for both the high-conductivity and seismic-velocity anomalies observed in the mantle wedge at the transition-zone depth.

  9. Mantle transition zone, stagnant slab and intraplate volcanism in Northeast Asia

    Science.gov (United States)

    Chen, Chuanxu; Zhao, Dapeng; Tian, You; Wu, Shiguo; Hasegawa, Akira; Lei, Jianshe; Park, Jung-Ho; Kang, Ik-Bum

    2017-04-01

    3-D P- and S-wave velocity structures of the mantle down to a depth of 800 km beneath NE Asia are investigated using ∼981 000 high-quality arrival-time data of local earthquakes and teleseismic events recorded at 2388 stations of permanent and portable seismic networks deployed in NE China, Japan and South Korea. Our results do not support the existence of a gap (or a hole) in the stagnant slab under the Changbai volcano, which was proposed by a previous study of teleseismic tomography. In this work we conducted joint inversions of both local-earthquake arrival times and teleseismic relative traveltime residuals, leading to a robust tomography of the upper mantle and the mantle transition zone (MTZ) beneath NE Asia. Our joint inversion results reveal clearly the subducting Pacific slab beneath the Japan Islands and the Japan Sea, as well as the stagnant slab in the MTZ beneath the Korean Peninsula and NE China. A big mantle wedge (BMW) has formed in the upper mantle and the upper part of the MTZ above the stagnant slab. Localized low-velocity anomalies are revealed clearly in the crust and the BMW directly beneath the active Changbai and Ulleung volcanoes, indicating that the intraplate volcanism is caused by hot and wet upwelling in the BMW associated with corner flows in the BMW and deep slab dehydration as well.

  10. Thermally-driven mantle plumes reconcile multiple hot-spot observations

    Science.gov (United States)

    Davies, D. R.; Davies, J. H.

    2009-02-01

    Hot-spots are anomalous regions of magmatism that cannot be directly associated with plate tectonic processes. They are widely-regarded as the surface expression of upwelling mantle plumes. Hot-spots exhibit variable life-spans, magmatic productivity and fixity. 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 fully-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.

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

    Science.gov (United States)

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

    2015-11-17

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

  12. Acute tryptophan depletion dose dependently impairs object memory in serotonin transporter knockout rats

    NARCIS (Netherlands)

    Olivier, J D A; Jans, L A W; Korte-Bouws, G A H; Korte, S M; Deen, P M T; Cools, A R; Ellenbroek, B A; Blokland, A

    2008-01-01

    RATIONALE: Acute tryptophan depletion (ATD) transiently lowers central serotonin levels and can induce depressive mood states and cognitive defects. Previous studies have shown that ATD impairs object recognition in rats. OBJECTIVES: As individual differences exist in central serotonin

  13. Supercontinents, mantle dynamics and plate tectonics: A perspective based on conceptual vs. numerical models

    Science.gov (United States)

    Yoshida, Masaki; Santosh, M.

    2011-03-01

    assembly which erodes the continental crust. Ongoing subduction erosion also occurs at the leading edges of dispersing plates, which also contributes to crustal destruction, although this is only a temporary process. The previous numerical studies of mantle convection suggested that there is a significant feedback between mantle convection and continental drift. The process of assembly of supercontinents induces a temperature increase beneath the supercontinent due to the thermal insulating effect. Such thermal insulation leads to a planetary-scale reorganization of mantle flow and results in longest-wavelength thermal heterogeneity in the mantle, i.e., degree-one convection in three-dimensional spherical geometry. The formation of degree-one convection seems to be integral to the emergence of periodic supercontinent cycles. The rifting and breakup of supercontinental assemblies may be caused by either tensional stress due to the thermal insulating effect, or large-scale partial melting resulting from the flow reorganization and consequent temperature increase beneath the supercontinent. Supercontinent breakup has also been correlated with the temperature increase due to upwelling plumes originating from the deeper lower mantle or CMB as a return flow of plate subduction occurring at supercontinental margins. The active mantle plumes from the CMB may disrupt the regularity of supercontinent cycles. Two end-member scenarios can be envisaged for the mantle convection cycle. One is that mantle convection with dispersing continental blocks has a short-wavelength structure, or close to degree-two structure as the present Earth, and when a supercontinent forms, mantle convection evolves into degree-one structure. Another is that mantle convection with dispersing continental blocks has a degree-one structure, and when a supercontinent forms, mantle convection evolves into degree-two structure. In the case of the former model, it would take longer time to form a supercontinent

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

    Science.gov (United States)

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

    2012-01-01

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

  15. Redox state of the Archean mantle: Evidence from V partitioning in 3.5-2.4 Ga komatiites

    Science.gov (United States)

    Nicklas, Robert W.; Puchtel, Igor S.; Ash, Richard D.

    2018-02-01

    Oxygen fugacity of the mantle is a crucial thermodynamic parameter that controls such fundamental processes as planetary differentiation, mantle melting, and possible core-mantle exchange. Constraining the evolution of the redox state of the mantle is of paramount importance for understanding the chemical evolution of major terrestrial reservoirs, including the core, mantle, and atmosphere. In order to evaluate the secular evolution of the redox state of the mantle, oxygen fugacities of six komatiite systems, ranging in age from 3.48 to 2.41 Ga, were determined using high-precision partitioning data of the redox-sensitive element vanadium between liquidus olivine, chromite and komatiitic melt. The calculated oxygen fugacities range from -0.11 ± 0.30 ΔFMQ log units in the 3.48 Ga Komati system to +0.43 ± 0.26 ΔFMQ log units in the 2.41 Ga Vetreny system. Although there is a slight hint in the data for an increase in the oxygen fugacity of the mantle between 3.48 and 2.41 Ga, these values generally overlap within their respective uncertainties; they are also largely within the range of oxygen fugacity estimates for modern MORB lavas of +0.60 ± 0.30 ΔFMQ log units that we obtained using the same technique. Our results are consistent with the previous findings that argued for little change in the mantle oxygen fugacity since the early Archean and indicate that the mantle had reached its nearly-present day redox state by at least 3.48 Ga.

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

    NARCIS (Netherlands)

    Schmalzl, J.T.

    1996-01-01

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

  17. 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 ...

  18. 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...... programme that simulates the thermal behaviour of low flow SDHW systems. The yearly thermal performance of low flow SDHW systems with different designed mantle tanks has been calculated. The influence of the mantle tank design on the thermal performance is investigated by means of the calculations...... 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...

  19. Is gas in the Orion nebula depleted

    International Nuclear Information System (INIS)

    Aiello, S.; Guidi, I.

    1978-01-01

    Depletion of heavy elements has been recognized to be important in the understanding of the chemical composition of the interstellar medium. This problem is also relevant to the study of H II regions. In this paper the gaseous depletion in the physical conditions of the Orion nebula is investigated. The authors reach the conclusion that very probably no depletion of heavy elements, due to sticking on dust grains, took place during the lifetime of the Orion nebula. (Auth.)

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

    Science.gov (United States)

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

    1994-01-01

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

  1. [Nutritional depletion in chronic obstructive pulmonary disease].

    Science.gov (United States)

    Chen, Yan; Yao, Wan-zhen

    2004-10-01

    Chronic obstructive pulmonary disease (COPD) is one of the major diseases worldwide. Nutritional depletion is a common problem in COPD patients and also an independant predictor of survival in these patients. Many data are helpful for determining nutritional depletion, including anthropometric measurement, laboratory markers, body composition analysis (fat-free mass and lean mass), and body weight. The mechanism of nutritional depletion in patients with COPD is still uncertain. It may be associated with energy/metabolism imbalance, tissue hypoxia, systemic inflammation, and leptin/orexin disorders. In patients with nutritional depletion, growth hormone and testosterone can be used for nutritional therapy in addition to nutrition supplementation.

  2. Preliminary data on the Bramberg (Hassberge, Bavaria, Germany) mantle xenoliths

    Science.gov (United States)

    Kukuła, Anna; Puziewicz, Jacek; Ntaflos, Theodoros; Matusiak-Małek, Magdalena

    2015-04-01

    Bramberg hill is a well preserved basaltic volcanic cone (494 m asl), situated 2 km north-west of Bramberg village (Hassberge, Bavaria, Germany). Bramberg basalt belongs to Heldburger Ganschar subset of the Central European Volcanic Province and contains 5 - 8 cm peridotitic xenoliths, which are the aim of our study, based on characterization of 7 xenoliths. Two groups of spinel peridotite xenoliths occur in the Bramberg basalt. Group A spinel peridotite (6 xenoliths) is characterized by protogranular texture with typical grain size of 2 - 3 mm (max 8 mm). It consists of olivine (89.9 - 91.1 % Fo, 0.32 - 0.44 wt. % NiO), orthopyroxene (mg# 0.90 - 0.92, Al 0.10 - 0.18 a. pfu), clinopyroxene (mg# 0.90 - 0.92, Al 0.13 - 0.26 a pfu) and spinel (cr# 0.13 - 0.39, mg# 0.58 - 0.75). LA-ICP-MS trace element analyses (xenolith 3150) show that orthopyroxene is depleted relative to primitive mantle. Rare earth element patterns exhibit two trends. The first (U-shaped, LaN/YbN = 0.1) probably reflects orthopyroxene with thin clinopyroxene lamellae, while pure orthopyroxene is characterized by constant depletion from Lu to La (LaN/YbN = 1.1). In the primitive mantle normalized trace element diagram negative Ti, Hf, Sr anomalies occur. Clinopyroxene is enriched in trace elements relative primitive mantle. REE normalized diagram is characterized by constant enrichment from Lu to La (LaN/YbN = 10.7). Strong negative Ti, Hf, Nd and Pb anomalies occur in the trace element pattern. The group B (1 xenolith) contains olivine of forsterite content 87.3 - 88.2 mole % and containing 0.35 - 0.39 wt. % NiO. Orthopyroxene is characterized by mg# 0.88 - 0.89 and variable content of Al 0.07 - 0.14 atoms pfu. Clinopyroxene (mg# 0.88 - 0.90) contains 0.10 - 0.26 atoms Al pfu. Spinel is characterized by low mg# (0.50 - 0.52) and high cr# (0.49) relative to group A xenoliths. The group B xenolith is characterized by presence of carbonates. Carbonates (up to 0.5 mm grains) are located in interstices

  3. Implications of terrestrial 40Ar/36Ar for atmospheric and mantle evolutionary models

    International Nuclear Information System (INIS)

    Fisher, D.E.

    1982-01-01

    The terrestrial 40 Ar/ 36 Ar ratio is a function of the degassing history of the earth because 40 Ar is the volatile daughter produced by continuing decay of the non-volatile parent 40 K. The value of the ratio for the solid earth needs to be known and whether there is a single value, or a range of values, depending on the extent of depletion in volatiles. Measurement of 40 Ar/ 36 Ar for the interior is obtained from diamonds (a), which gives low values for the ratio ( 4 He/ 136 Xe. If the amount of contamination varies in a suite of samples, 40 Ar/ 36 Ar gives a straight line when plotted against ( 36 Ar) -1 . Again, the data suggests low values (approx. equal to 295) relative to the oceanic basalts but will need to be checked for contamination. From oceanic glasses (c) where there are enough data for the 40 Ar/ 36 Ar v. ( 36 Ar) -1 test to be significant. A good straight line is obtained for the results from seamount P-50, leading to a ratio approx. equal to 10 4 for the mantle region feeding the oceanic seamounts and ridge system. Further checks on atmospheric contamination, using the straight line test, should enable depleted and undepleted regions of the mantle to be mapped, and thus provide more definite data for models of atmospheric evolution. (orig.)

  4. Alkaline and carbonatite metasomatism of lithospheric mantle beneath SW Poland- Pilchowice case

    Science.gov (United States)

    Ćwiek, Mateusz; Matusiak-Małek, Magdalena; Puziewicz, Jacek; Ntaflos, Theodoros

    2014-05-01

    The Cenozoic basanites from Pilchowice (SW Poland) form volcanic plug located exactly at Intra- Sudetic Fault. These basanites belong to the Polish part of the Central European Volcanic Province and contain numerous, usually small (pfu and mg# from 0.915- 0.920 . One xenolith contains clinopyroxene with abundant spongy rims. Primary clinopyroxene is very rare and Al-enriched (mg# 0.92, 0.17 atoms of Al pfu). The spinel is Cr enriched (cr# 0.46-0.68) and is usually associated with clinopyroxene. Orthopyroxene is depleted in REE compared to primitive mantle. Orthopyroxene from majority of xenoliths are strongly LREE depleted ((La/Lu)N = 0.03-0.21). All studied peridotites contain clinopyroxene which is enriched (2 to 70 times) in REE compared to primitive mantle. Clinopyroxene patterns show relative low HREE concentration ((La/Lu)N = 4.75- 19.99), moreover patterns from three samples are convex- upward shaped with inflection point on Nd ((La/Nd)N = 0.36-0.96). Clinopyroxene- poor lithology, high cr# in spinel and LREE- depleted nature of orthopyroxene suggest that upper mantle sampled by Pilchowice basanite is a restite after partial melting. The LREE enriched composition of clinopyroxene suggest that peridotites were metasomatised. Clinopyroxene convex- upward shaped REE plots with inflection point on Nd is typical for metasomatism related with alkaline melt. On the other hand very low ratios of Ti/ Eu (24.8- 738.9) and high (La/ Yb)N (3.5- 17) ratio (Coltorti, 1999) suggest that the metasomatic agent was either a mixture of alkaline silicate melt with carbonatite or peridotite reaction with two independent agents is recorded. This study is a part of MSc thesis of the first author and was possible thanks to the project NCN 2011/03/B/ST10/06248 of Polish National Centre for Science. Coltorti, M., Bonadiman, C., Hinton, R. W., Siena, F. & Upton, B. G. J. (1999). Carbonatite metasomatism of the oceanic upper mantle: Evidence from clinopyroxenes and glasses in

  5. Impact of Mantle Wind on Subducting Plate Geometry and Interplate Pressure: Insights From Physical Modelling.

    Science.gov (United States)

    Boutelier, D.; Cruden, A. R.

    2005-12-01

    New physical models of subduction investigate the impact of large-scale mantle flow on the structure of the subducted slab and deformation of the downgoing and overriding plates. The experiments comprise two lithospheric plates made of highly filled silicone polymer resting on a model asthenosphere of low viscosity transparent silicone polymer. Subduction is driven by a piston that pushes the subducting plate at constant rate, a slab-pull force due to the relative density of the slab, and a basal drag force exerted by flow in the model asthenosphere. Large-scale mantle flow is imposed by a second piston moving at constant rate in a tunnel at the bottom of the experiment tank. Passive markers in the mantle track the evolution of flow during the experiment. Slab structure is recorded by side pictures of the experiment while horizontal deformation is studied via passive marker grids on top of both plates. The initial mantle flow direction beneath the overriding plate can be sub-horizontal or sub-vertical. In both cases, as the slab penetrates the mantle, the mantle flow pattern changes to accommodate the subducting high viscosity lithosphere. As the slab continues to descend, the imposed flow produces either over- or under-pressure on the lower surface of the slab depending on the initial mantle flow pattern (sub-horizontal or sub-vertical respectively). Over-pressure imposed on the slab lower surface promotes shallow dip subduction while under-pressure tends to steepen the slab. These effects resemble those observed in previous experiments when the overriding plate moves horizontally with respect to a static asthenosphere. Our experiments also demonstrate that a strong vertical drag force (due to relatively fast downward mantle flow) exerted on the slab results in a decrease in strain rate in both the downgoing and overriding plates, suggesting a decrease in interplate pressure. Furthermore, with an increase in drag force deformation in the downgoing plate can switch

  6. Imaging Lower Mantle Heterogeniety With Differential Dispersion and Attenuation of Core- Diffracted Waves

    Science.gov (United States)

    Euler, G. G.; Wysession, M. E.; Huhmann, B.

    2007-12-01

    We investigate global differential travel-time dispersion and attenuation of core-diffracted phases from large, deep earthquakes. This technique aids in constraining radial velocity structure at the core-mantle interface in a manner analogous to surface wave observables constraining upper mantle structure. We confirm that there is noticeable differential dispersion and attenuation caused by diffraction on a global basis for both Pdiff and Sdiff. Variations in differential dispersion and attenuation are observed with both geographic location and between Pdiff and Sdiff along the same azimuth suggesting lateral variations in Vp, Vs and Vp/Vs ratio in the lowermost mantle. We attempt to utilize dispersion and attenuation characteristics to put bounds on the magnitude and distribution of large-scale velocity perturbations in the lowermost mantle and draw comparisons to variations found in several 3D whole-mantle models. Our dataset consists of broadband records available from the IRIS DMC for deep (>180 km), large (>5.6 mb) teleseismic events. Preprocessing of the records includes deconvolution of the instrument response, rotation of horizontal components, filtering using a set of bandpass filters, and sample-rate decimation (5 sps). Relative arrival times and amplitudes are found by computing cross correlegrams in the frequency domain, detecting and removing poor recordings with cluster analysis, and iteratively converging on a stable low-variance solution with a weighted least-squares inversion while automatically remediating phase-skips utilizing a database of potential relative arrivals. Raypath-approximated corrections for reciever-side differences in ellipticity, mantle, and crust are applied for the derivation of phase velocites in the lowermost mantle as a function of azimuth and frequency. Following previous studies of diffracted signals, we limit our analysis to station pairs located in narrow azimuthal windows spread over a considerable distance while

  7. Subduction to the lower mantle – a comparison between geodynamic and tomographic models

    Directory of Open Access Journals (Sweden)

    T. W. Becker

    2012-11-01

    Full Text Available It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000 s of km scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ~1020 Pas, and viscosity increases to ~1023 Pas in the lower mantle above D". Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved, presumably because of advances in both plate reconstructions and mantle flow computations. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation – in particular at spherical harmonic degree two – is a basal chemical layer. Subduction shapes this layer into two rather stable hot but chemically dense "piles

  8. Primitive magmas at five Cascade volcanic fields: Melts from hot, heterogeneous sub-arc mantle

    Science.gov (United States)

    Bacon, C.R.; Bruggman, P.E.; Christiansen, R.L.; Clynne, M.A.; Donnelly-Nolan, J. M.; Hildreth, W.

    1997-01-01

    Major and trace element concentrations, including REE by isotope dilution, and Sr, Nd, Pb, and O isotope ratios have been determined for 38 mafic lavas from the Mount Adams, Crater Lake, Mount Shasta, Medicine Lake, and Lassen volcanic fields, in the Cascade arc, northwestern part of the United States. Many of the samples have a high Mg# [100Mg/(Mg + FeT) > 60] and Ni content (>140 ppm) such that we consider them to be primitive. We recognize three end-member primitive magma groups in the Cascades, characterized mainly by their trace-element and alkali-metal abundances: (1) High-alumina olivine tholeiite (HAOT) has trace element abundances similar to N-MORB, except for slightly elevated LILE, and has Eu/Eu* > 1. (2) Arc basalt and basaltic andesite have notably higher LILE contents, generally have higher SiO2 contents, are more oxidized, and have higher Cr for a given Ni abundance than HAOT. These lavas show relative depletion in HFSE, have lower HREE and higher LREE than HAOT, and have smaller Eu/Eu* (0.94-1.06). (3) Alkali basalt from the Simcoe volcanic field east of Mount Adams represents the third end-member, which contributes an intraplate geochemical signature to magma compositions. Notable geochemical features among the volcanic fields are: (1) Mount Adams rocks are richest in Fe and most incompatible elements including HFSE; (2) the most incompatible-element depleted lavas occur at Medicine Lake; (3) all centers have relatively primitive lavas with high LILE/HFSE ratios but only the Mount Adams, Lassen, and Medicine Lake volcanic fields also have relatively primitive rocks with an intraplate geochemical signature; (4) there is a tendency for increasing 87Sr/86Sr, 207Pb/204Pb, and ??18O and decreasing 206Pb/204Pb and 143Nd/144Nd from north to south. The three end-member Cascade magma types reflect contributions from three mantle components: depleted sub-arc mantle modestly enriched in LILE during ancient subduction; a modern, hydrous subduction component

  9. 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...

  10. Inferences on melting and mantle heterogeneity through analyses of olivine-hosted melt inclusions from the Eastern Volcanic Zone, Gakkel Ridge

    Science.gov (United States)

    Wanless, V.; Shaw, A. M.; Behn, M. D.

    2012-12-01

    Here we combine volatile (CO2, H2O, Cl, Fl, and S), major, and trace element concentrations from 66 olivine-hosted melt inclusions with petrologic models of mantle melting to explore mantle source heterogeneity and melting dynamics beneath the Eastern Volcanic Zone (EVZ) of the ultraslow-spreading Gakkel Ridge. The EVZ is the easternmost segment of the Gakkel Ridge and it is volcanically active compared to the adjacent Sparsely Magmatic Zone. Naturally glassy melt inclusions hosted in olivine phenocrysts from lavas erupted at four locations along the length of the EVZ (31°E, 39°E, 57°E and 72°E) were analyzed. Melt inclusion analyses suggest that there are systematic variations in the mantle composition from the eastern end (at 72°E) to the western end (31°E, near the Sparsely Magmatic Zone) of the EVZ. Water contents increase from an average of 0.16 ± 0.01 wt % at 72°E to an average of 0.40 ± 0.03 wt % at 31°E. Highly incompatible trace elements (e.g., Ba, U, and Nb) increase from east to west, while the middle and heavy rare earth elements remain constant or decrease along the ridge axis. Ratios of light to heavy rare earth elements in the easternmost melt inclusions are relatively constant (at 72°E La/Yb ratios range from 1.41 to 1.68) compared to compositions observed at 31°E (La/Yb from 1.80 to 3.14). To determine the source of the geochemical variability observed along the EVZ, we model mantle melting in one and two component systems, where melting occurs in either the spinel field only or the garnet and spinel fields. Possible mantle sources that were investigated include depleted MORB mantle, depleted mantle peridotite, metasomatised mantle, and/or pyroxenite veins. Melt inclusion compositions from all four locations are depleted in heavy rare earth elements (e.g., Dy, Y, and Yb) compared to normal MORB, consistent with mantle melting beginning in the garnet stability field. However, variable degrees of melting of a single mantle composition

  11. 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

  12. 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...

  13. Mapping mantle-melting anomalies in Baja California: a combined subaereal-submarine noble gas geochemistry new data set.

    Science.gov (United States)

    Spelz, R. M.; Negrete-Aranda, R.; Hilton, D. R.; Virrueta, C.; Tellez, M.; Lupton, J. E.; Evans, L. J.; Clague, D. A.; Zierenberg, R. A.; Neumann, F.

    2017-12-01

    In active tectonic settings, the presence of helium in aqueous fluids with 3He/4He ratios greater than in-situ production values ( 0.05 RA where RA = air He or 1.4 x 10-6) indicates the contribution of mantle-derived volatiles to the total volatile inventory. This is an indicative of the presence of mantle-derived melts, which act to transfer volatiles from the solid Earth towards the surface. Thus, He has the potential to map regions of the underlying mantle which are undergoing partial melting - a phenomenon which should also be evident in the seismic record. Reports of high 3He/4He in hot springs in Baja California (BC) has prompted us to initiate a survey of the region to assess relationship(s) between He isotopes and geophysical images of the underlying mantle. Previous studies report 3He/4He ratios of 0.54 RA for submarine hot springs (Punta Banda 108oC) and 1.3 RA for spring waters (81oC) at Bahia Concepcion. Our new survey of hot springs in northern BC has revealed that all 12 localities sampled to date, show the presence of mantle He with the highest ratio being 1.74RA (21% mantle-derived) at Puertecitos on the Gulf coast. He ratios are generally lower on the Pacific coast with the minimum mantle He contribution being 5% at Santa Minerva (0.11RA). Thus, preliminary trends are of a west-to-east increase in the mantle He signal across the peninsula. In the Gulf of California, recent He analyses from the newly discovered Meyibo (350 °C) and Auka (250-290 °C) hydrothermal fields at Alarcon rise and Pescadero basin, respectively, show high 3He/4He ratios ( 8RA), typical of MORB's. These ratios are higher than the ones reported for Guaymas Basin (6.95 RA), suggesting that primordial He signal from the mantle increases following a North-South direction along the Gulf axis. He results presented in this study correlate well with high resolution Rayleigh wave tomography images by DiLuccio et al (2014). Shear velocity variations in the BC crust and upper mantle

  14. 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

  15. The influence of mantle refertilisation on the formation of TTGs in a plume-lid tectonics setting

    Science.gov (United States)

    Fischer, R.; Gerya, T.

    2017-12-01

    Higher amounts of radiogenic elements and leftover primordial heat in the early Earth both contribute to the increased temperature in the Earth's interior and it is mainly this increased mantle potential temperature that controls the dynamics of the crust and upper mantle and the predominant style of tectonics in the Early Earth. The increased upper mantle temperature precludes the modern plate tectonics regime and stabilizes another type of global tectonics often called plume-lid tectonics (Fischer and Gerya, 2016) or 'plutonic squishy lid' tectonics(Rozel et al., 2017). Plume-lid tectonics is dominated by intrusive mantle-derived magmatism which results in a thickening of the overlaying crust. The overthickened basaltic crust is transformed into eclogite and episodically recycled back into the mantle. Melt extraction from hydrated partially molten basaltic crust leads to the production of primordial tonalite-trondhjemite-granodiorite (TTG) continental crust. TTGs make up over half of the Archean crust and can be classied into low-, medium- and high-pressure types (Moyen, 2011). Field studies show that the three different types (low-, medium- and high-pressure) appear in a ratio of 20%, 60% and 20% (Moyen, 2011). Numerical models of plume-lid tectonics generally agree very well with these values (Rozel et al., 2017) but also show that the ratio between the three different TTG types varies greatly during the two phases of the plume-lid tectonics cycle: growth phase and overturn phase. Melt productivity of the mantle decreases rapidly after removal of the garnet and clinopyroxene components. Addition of new garnet and clinopyroxene-rich material into the harzburgitic residue should lead to a refertilised lherzolite which could potentially yield new melt (Bédard, 2006). Mixing of eclogite drips back into the mantle can lead to the geochemical refertilisation of already depleted mantle and allow for further extraction of melt (Bédard, 2006). We will explore this

  16. Plutonium in depleted uranium penetrators

    International Nuclear Information System (INIS)

    McLaughlin, J.P.; Leon-Vintro, L.; Smith, K.; Mitchell, P.I.; Zunic, Z.S.

    2002-01-01

    Depleted Uranium (DU) penetrators used in the recent Balkan conflicts have been found to be contaminated with trace amounts of transuranic materials such as plutonium. This contamination is usually a consequence of DU fabrication being carried out in facilities also using uranium recycled from spent military and civilian nuclear reactor fuel. Specific activities of 239+240 Plutonium generally in the range 1 to 12 Bq/kg have been found to be present in DU penetrators recovered from the attack sites of the 1999 NATO bombardment of Kosovo. A DU penetrator recovered from a May 1999 attack site at Bratoselce in southern Serbia and analysed by University College Dublin was found to contain 43.7 +/- 1.9 Bq/kg of 239+240 Plutonium. This analysis is described. An account is also given of the general population radiation dose implications arising from both the DU itself and from the presence of plutonium in the penetrators. According to current dosimetric models, in all scenarios considered likely ,the dose from the plutonium is estimated to be much smaller than that due to the uranium isotopes present in the penetrators. (author)

  17. 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

  18. Upper mantle anisotropic attenuation of the Sierra Nevada and surroundings

    Science.gov (United States)

    Bernardino, M. J.; Jones, C. H.; Monsalve, G.

    2016-12-01

    We investigate the contribution of anelasticity in the generation of seismic velocity variations within the upper mantle of the Sierra Nevada and surrounding regions through teleseismic shear-wave attenuation. Given that anelastic effects are most sensitive to temperature and hydration and less to composition and small degrees of partial melt, we aim constrain the thermal structure beneath this region and identify locations where elevated upper mantle temperatures dominate. We also investigate the dependence of shear-wave attenuation on direction by accounting for seismic anisotropy in our measurements. S-wave t* values are determined from teleseismic S- and SKS- phases recorded on permanent and temporary deployments within the California region with particular focus on the Sierra Nevada Earthscope Project (SNEP) and the Sierran Paradox Experiment (SPE) stations. S-waveforms are rotated into the Sierran SFast, N75°E, and SSlow, N15°W, components. Following the method of Stachnik et al., (2004), S-wave spectra for each event are jointly inverted for a single seismic moment, M0k, and corner frequency, fck, for each event, and separate t* for each ray path. The resulting t*Fast and t*Slow measurements are then inverted for three-dimensional variations in (1/QFast) and (1/QSlow). Results are compared with previous magnetotelluric, surface heat flow, and body-wave velocity inversion studies.

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

    Science.gov (United States)

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

    2014-01-01

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

  20. Partitioning of Pd Between Fe-S-C and Mantle Liquids at High Pressure and Temperature: Implications for Core Formation

    Science.gov (United States)

    Righter, K.; Humayun, M.; Danielson, L.

    2007-01-01

    One of the most elusive geochemical aspects of the early Earth has been explaining the near chondritic relative abundances of the highly siderophile elements (HSE; Au, Re and the platinum group elements) in Earth's primitive upper mantle (PUM). Perhaps they were delivered to the Earth after core formation, by late addition of carbonaceous chondrite material. However, the recognition that many moderately siderophile elements can be explained by high pressure and temperature (PT) metal-silicate equilibrium, leads to the question whether high PT equilibrium can also explain the HSE concentrations. Answers to this question have been slowed by experimental difficulties (nugget effect and very low solubilities). But two different perspectives have emerged from recent studies. One perspective is that D(M/S) for HSE at high PT are not low enough to explain terrestrial mantle depletions of these elements (for Pd and Pt). A second perspective is D(M/S) are reduced substantially at high PT and even low enough to explain terrestrial mantle depletions (for Au and Pt). Issues complicating interpretation of all experiments include use of MgO- and FeO-free silicate melts, and S-free and FeNi metal-free systems. In addition, conclusions for Pt rest on an interpretation that the tiny metallic nuggets plaguing many such experiments, were formed upon quench. There is not agreement on this issue, and the general question of HSE solubility at high PT remains unresolved

  1. From crustal protoliths to mantle garnet pyroxenites: a highly siderophile elements and Os isotope perspective from the Ligurian mantle section (N. Apennine, Italy)

    Science.gov (United States)

    Montanini, A.; Luguet, A.; van Acken, D.; Tribuzio, R.

    2017-12-01

    Pyroxenites are a major form of mantle heterogeneity and may originate through migration of melts or recycling of mafic crustal lithologies. Here, we present HSE (Os, Ir, Pt, Pd, Re) and 187Os/188Os isotopic systematics of "aged" pyroxenites (Mg-rich, Al-poor garnet websterites and Al-rich garnet clinopyroxenites) enclosed in fertile mantle sequences of the Jurassic Alpine-Apennine ophiolites. The garnet clinopyroxenites have heterogeneous mafic crustal precursors that experienced a long-lived evolution of recycling into the mantle (1.5-1.0 Ga) as inferred from Lu-Hf isotope systematics. They originated as melt-dominated systems by crystallization of eclogite-derived melts. The websterites were interpreted as hybrid lithologies with a crustal geochemical fingerprint and a larger peridotite wall rock contribution. The host lherzolites show flat CI-chondrite-normalized HSE patterns. All the pyroxenites are variably depleted in Os and Ir and enriched in the incompatible HSE (Pt, Pd and Re) with respect to host peridotites and have flat to negatively sloping Pd-Re segments. Centimetre- to metre-scale 187Os isotopic heterogeneity is observed in the investigated mantle sequence. The initial 187Os/188Os ratios recalculated for the age of the Mesozoic partial melting event inferred from Nd-Hf isotope systematics are unradiogenic to slightly radiogenic in the peridotites (0.124-0.134) and vary from moderately to highly radiogenic in the pyroxenites (0.149-2.190). Bulk rock HSE compositions of the pyroxenites do not match gabbroic eclogites nor residua after eclogite partial melting, in agreement with lithophile element geochemistry. The HSE patterns of the garnet clinopyroxenites are related to sulphur saturation and sulfide crystallization from partial melts of gabbro-derived eclogites. Decoupling between Re/Os (TMa = 2.0-2.8 Ga) and Lu-Hf isotope systematics of the pyroxenites may be due to fractionation of Re/Os ratios with no Os isotopic homogenization of the sulfide

  2. The Chemistry and Toxicology of Depleted Uranium

    Directory of Open Access Journals (Sweden)

    Sidney A. Katz

    2014-03-01

    Full Text Available Natural uranium is comprised of three radioactive isotopes: 238U, 235U, and 234U. Depleted uranium (DU is a byproduct of the processes for the enrichment of the naturally occurring 235U isotope. The world wide stock pile contains some 1½ million tons of depleted uranium. Some of it has been used to dilute weapons grade uranium (~90% 235U down to reactor grade uranium (~5% 235U, and some of it has been used for heavy tank armor and for the fabrication of armor-piercing bullets and missiles. Such weapons were used by the military in the Persian Gulf, the Balkans and elsewhere. The testing of depleted uranium weapons and their use in combat has resulted in environmental contamination and human exposure. Although the chemical and the toxicological behaviors of depleted uranium are essentially the same as those of natural uranium, the respective chemical forms and isotopic compositions in which they usually occur are different. The chemical and radiological toxicity of depleted uranium can injure biological systems. Normal functioning of the kidney, liver, lung, and heart can be adversely affected by depleted uranium intoxication. The focus of this review is on the chemical and toxicological properties of depleted and natural uranium and some of the possible consequences from long term, low dose exposure to depleted uranium in the environment.

  3. Refertilized mantle keel below the Southern Alps domain (North-East Italy): Evidence from Marosticano refractory mantle peridotites

    Science.gov (United States)

    Brombin, Valentina; Bonadiman, Costanza; Coltorti, Massimo; Fahnestock, M. Florencia; Bryce, Julia G.; Marzoli, Andrea

    2018-02-01

    The Veneto Volcanic Province (VVP), a Cenozoic magmatic province in northeastern Italy, is one of the widest volcanic areas of the Adria plate. It consists of five main magmatic districts, and its most primitive products commonly host mantle xenoliths. In this study, we present a newly discovered xenolith suite from the Marosticano district that contains peridotites with compositional characteristics of mineral assemblages that provide insight into an unexpected nature of the sub-continental lithospheric mantle (SCLM) of the Adria plate. In contrast to xenoliths from other VVP sites previously studied (i.e., Val d'Adige and Lessini Mts.), Marosticano xenoliths exhibit highly refractory compositions typical of on-craton peridotites. High olivine forsteritic contents (Fo: 91-93) indicate high degrees of partial melting (> 25%) that should have been associated with the complete consumption of clinopyroxene. Major and trace element compositions further link these peridotite fragments to early Proterozoic cratonic mantle. The occurrence of clinopyroxene within such rocks suggests Marosticano clinopyroxene testify to a metasomatic legacy. The i) LREE-enrichments of Marosticano clinopyroxene and ii) the dissolved CO2 mole fractions (up to 1.0) for the inferred clinopyroxene-forming melt are consistent with carbonatite/CO2-rich silicatic melts as metasomatic agents. The latter could be responsible for the equilibrium temperatures (1033-1117 °C) and oxidizing conditions [ΔlogfO2 (FMQ) = - 0.6 - + 1.1], anomalously high for a cratonic environment but similar to the off-craton VVP xenoliths. The cratonic signature and carbonatite/CO2-rich silicate metasomatism found together in the Marosticano mantle xenoliths reveal that ancient features can be preserved in SCLM in a young, active geodynamic setting such as the Adria plate boundary. In this framework Lessini Mts. and Val d'Adige xenoliths could be interpreted as circumcratonic reminiscent domains affected by

  4. Progressive enrichment of island arc mantle by melt-peridotite interaction inferred from Kamchatka xenoliths

    Science.gov (United States)

    Kepezhinskas, Pavel; Defant, Marc J.; Drummond, Mark S.

    1996-04-01

    The Pliocene (7 Ma) Nb-enriched arc basalts of the Valovayam Volcanic Field (VVF) in the northern segment of Kamchatka arc (Russia) host abundant xenoliths of spinel peridotites and pyroxenites. Textural and microstructural evidence for the high-temperature, multistage creep-related deformations in spinel peridotites supports a sub-arc mantle derivation. Pyroxenites show re-equilibrated mosaic textures, indicating recrystallization during cooling under the ambient thermal conditions. Three textural groups of clinopyroxenes exhibit progressive enrichment in Na, Al, Sr, La, and Ce accompanied by increase in Sr/Y, La/Yb, and Zr/Sm. Trace elements in various mineral phases and from felsic veins obtained through ion microprobe analysis suggest that the xenoliths have interacted with a siliceous (dacitic) melt completely unlike the host basalt. The suite of xenoliths grade from examples that display little evidence of metasomatic reaction to those containing an assemblage of minerals that have been reproduced experimentally from the reaction of a felsic melt with ultramafic rock, e.g., pargasitic amphibole, albite-rich plagioclase, Al-rich augite, and garnet. The dacitic veins within spinel lherzolite display a strong enrichment in Sr and depletion in Y and the heavy rare earth elements (e.g., Yb). The dacites are comparable to adakites (melts derived from subducted metabasalt), and not typical arc melts. We believe that these potential slab melts were introduced into the mantle beneath this portion of Kamchatka subsequent to partial melting of a relatively young (and hot) subducted crust. Island arc metasomatism by peridotite-slab melt interaction is an important mantle hybridization process responsible for arc-related alkaline magma generation from a veined sub-arc mantle.

  5. 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

  6. Cosmochemical Estimates of Mantle Composition

    Science.gov (United States)

    Palme, H.; O'Neill, H. St. C.

    2003-12-01

    In 1794 the German physicist Chladni published a small book in which he suggested the extraterrestrial origin of meteorites. The response was skepticism and disbelief. Only after additional witnessed falls of meteorites did scientists begin to consider Chladni's hypothesis seriously. The first chemical analyses of meteorites were published by the English chemist Howard in 1802, and shortly afterwards by Klaproth, a professor of chemistry in Berlin. These early investigations led to the important conclusion that meteorites contained the same elements that were known from analyses of terrestrial rocks. By the year 1850, 18 elements had been identified in meteorites: carbon, oxygen, sodium, magnesium, aluminum, silicon, phosphorous, sulfur, potassium, calcium, titanium, chromium, manganese, iron, cobalt, nickel, copper, and tin (Burke, 1986). A popular hypothesis, which arose after the discovery of the first asteroid Ceres on January 1, 1801 by Piazzi, held that meteorites came from a single disrupted planet between Mars and Jupiter. In 1847 the French geologist Boisse (1810-1896) proposed an elaborate model that attempted to account for all known types of meteorites from a single planet. He envisioned a planet with layers in sequence of decreasing densities from the center to the surface. The core of the planet consisted of metallic iron surrounded by a mixed iron-olivine zone. The region overlying the core contained material similar to stony meteorites with ferromagnesian silicates and disseminated grains of metal gradually extending into shallower layers with aluminous silicates and less iron. The uppermost layer consisted of metal-free stony meteorites, i.e., eucrites or meteoritic basalts. About 20 years later, Daubrée (1814-1896) carried out experiments by melting and cooling meteorites. On the basis of his results, he came to similar conclusions as Boisse, namely that meteorites come from a single, differentiated planet with a metal core, a silicate mantle

  7. 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.

  8. 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

  9. Evolution of the earliest mantle caused by the magmatism-mantle upwelling feedback: Implications for the Moon and the Earth

    Science.gov (United States)

    Ogawa, M.

    2017-12-01

    The two most important agents that cause mantle evolution are magmatism and mantle convection. My earlier 2D numerical models of a coupled magmatism-mantle convection system show that these two agents strongly couple each other, when the Rayleigh number Ra is sufficiently high: magmatism induced by a mantle upwelling flow boosts the upwelling flow itself. The mantle convection enhanced by this positive feedback (the magmatism-mantle upwelling, or MMU, feedback) causes vigorous magmatism and, at the same time, strongly stirs the mantle. I explored how the MMU feedback influences the evolution of the earliest mantle that contains the magma ocean, based on a numerical model where the mantle is hot and its topmost 1/3 is partially molten at the beginning of the calculation: The evolution drastically changes its style, as Ra exceeds the threshold for onset of the MMU feedback, around 107. At Ra 107, however, the mantle remains compositionally more homogeneous in spite of the widespread magmatism, and the deep mantle remains hotter than the shallow mantle, because of the strong convective stirring caused by the feedback. The threshold value suggests that the mantle of a planet larger than Mars evolves in a way substantially different from that in the Moon does. Indeed, in my earlier models, magmatism makes the early mantle compositionally stratified in the Moon, but the effects of strong convective stirring overwhelms that of magmatism to keep the mantle compositionally rather homogeneous in Venus and the Earth. The MMU feedback is likely to be a key to understanding why vestiges of the magma ocean are so scarce in the Earth.

  10. Slab-derived components in the subcontinental lithospheric mantle beneath Chilean Patagonia: Geochemistry and Sr-Nd-Pb isotopes of mantle xenoliths and host basalt

    Science.gov (United States)

    Jalowitzki, Tiago; Gervasoni, Fernanda; Conceição, Rommulo V.; Orihashi, Yuji; Bertotto, Gustavo W.; Sumino, Hirochika; Schilling, Manuel E.; Nagao, Keisuke; Morata, Diego; Sylvester, Paul

    2017-11-01

    In subduction zones, ultramafic xenoliths hosted in alkaline basalts can yield significant information about the role of potential slab-derived components in the subcontinental lithospheric mantle (SCLM). Chemical and isotopic heterogeneities in such xenoliths are usually interpreted to reflect melt extraction followed by metasomatic re-enrichment. Here we report new whole-rock major, trace element and isotopic (Sr-Nd-Pb) data for a Proterozoic suite of 17 anhydrous spinel-lherzolites and Eocene (new K-Ar data) host alkaline basalt found near Coyhaique ( 46°S), Aysén Region, Chile. These Patagonian nodules are located in a current back-arc position, 100 km east of the present day volcanic arc and 320 km from the Chile Trench. The mantle xenoliths consist of coarse- to medium-grained spinel-lherzolites with trace element compositions characteristic of a subduction zone setting, such as pronounced negative Nb, Ta and Ti anomalies coupled with significant enrichment of LILEs (e.g., U) and chalcophile elements (W, Pb and Sn). Most of them are characterized by flat to depleted light-rare earth element (LREE) patterns (Ce/YbN = 0.6-1.1) coupled with less radiogenic Sr-Pb (87Sr/86Sr = 0.702422-0.703479; 206Pb/204Pb = 18.212-18.539) and more radiogenic Nd isotopic compositions (143Nd/144Nd = 0.512994-0.513242), similar to the depleted mantle component (DMM or PREMA). In contrast, samples with slight LREE enrichment (Ce/YbN = 1.3-1.8) show more radiogenic Sr-Pb (87Sr/86Sr = 0.703791-0.704239; 206Pb/204Pb = 18.572-18.703) and less radiogenic Nd isotopic compositions (143Nd/144Nd = 0.512859-0.512934), similar to the EM-2 reservoir. These new geochemical and isotope data suggest that the Coyhaique spinel-lherzolites are derived from a heterogeneous SCLM resulting from mixing between a depleted mantle component and up to 10% of slab-derived components. The enriched component added to the SCLM represents variable extents of melts of both subducted Chile Trench sediments and

  11. Continuous eclogite melting and variable refertilisation in upwelling heterogeneous mantle.

    Science.gov (United States)

    Rosenthal, Anja; Yaxley, Gregory M; Green, David H; Hermann, Joerg; Kovács, István; Spandler, Carl

    2014-08-18

    Large-scale tectonic processes introduce a range of crustal lithologies into the Earth's mantle. These lithologies have been implicated as sources of compositional heterogeneity in mantle-derived magmas. The model being explored here assumes the presence of widely dispersed fragments of residual eclogite (derived from recycled oceanic crust), stretched and stirred by convection in the mantle. Here we show with an experimental study that these residual eclogites continuously melt during upwelling of such heterogeneous mantle and we characterize the melting reactions and compositional changes in the residue minerals. The chemical exchange between these partial melts and more refractory peridotite leads to a variably metasomatised mantle. Re-melting of these metasomatised peridotite lithologies at given pressures and temperatures results in diverse melt compositions, which may contribute to the observed heterogeneity of oceanic basalt suites. We also show that heterogeneous upwelling mantle is subject to diverse local freezing, hybridization and carbonate-carbon-silicate redox reactions along a mantle adiabat.

  12. Tectonic predictions with mantle convection models

    Science.gov (United States)

    Coltice, Nicolas; Shephard, Grace E.

    2018-04-01

    Over the past 15 yr, numerical models of convection in Earth's mantle have made a leap forward: they can now produce self-consistent plate-like behaviour at the surface together with deep mantle circulation. These digital tools provide a new window into the intimate connections between plate tectonics and mantle dynamics, and can therefore be used for tectonic predictions, in principle. This contribution explores this assumption. First, initial conditions at 30, 20, 10 and 0 Ma are generated by driving a convective flow with imposed plate velocities at the surface. We then compute instantaneous mantle flows in response to the guessed temperature fields without imposing any boundary conditions. Plate boundaries self-consistently emerge at correct locations with respect to reconstructions, except for small plates close to subduction zones. As already observed for other types of instantaneous flow calculations, the structure of the top boundary layer and upper-mantle slab is the dominant character that leads to accurate predictions of surface velocities. Perturbations of the rheological parameters have little impact on the resulting surface velocities. We then compute fully dynamic model evolution from 30 and 10 to 0 Ma, without imposing plate boundaries or plate velocities. Contrary to instantaneous calculations, errors in kinematic predictions are substantial, although the plate layout and kinematics in several areas remain consistent with the expectations for the Earth. For these calculations, varying the rheological parameters makes a difference for plate boundary evolution. Also, identified errors in initial conditions contribute to first-order kinematic errors. This experiment shows that the tectonic predictions of dynamic models over 10 My are highly sensitive to uncertainties of rheological parameters and initial temperature field in comparison to instantaneous flow calculations. Indeed, the initial conditions and the rheological parameters can be good enough

  13. Nature of the uppermost mantle below the Porcupine Basin, offshore Ireland: new insights from seismic refraction and gravity data modeling

    Science.gov (United States)

    Prada, M.; Watremez, L.; Chen, C.; O'Reilly, B.; Minshull, T. A.; Reston, T. J.; Wagner, G.; Gaw, V.; Klaeschen, D.; Shannon, P.

    2015-12-01

    The Porcupine Basin is a tongue-shaped basin SW of Ireland formed during the opening of the North Atlantic Ocean. Its history of sedimentation reveals several rifting and subsidence phases during the Late Paleozoic and Cenozoic, with a particular major rift phase occurring in Late Jurassic-Early Cretaceous times. Previous work, focused on seismic and gravity data, suggest the presence of major crustal faulting and uppermost mantle serpentinization in the basin. Serpentinization is a key factor in lithospheric extension since it reduces the strength of mantle rocks, and hence, influences the tectonics of the lithosphere. Besides reducing the seismic velocity of the rock, serpentinization decreases mantle rock density favoring isostatic rebound and basin uplift, thus affecting the tectonic and thermal evolution of the basin. Here we characterize the deep structure of the Porcupine Basin from wide-angle seismic (WAS) and gravity data, with especial emphasis on the nature of the underlying mantle. The WAS data used were acquired along a 300 km long transect across the northern region of the basin. We used a travel time inversion method to model the data and obtain a P-wave velocity (Vp) model of the crust and uppermost mantle, together with the geometry of the main geological interfaces. The crustal structure along the model reveals a maximum stretching factor of ~5-6. These values are well within the range of crustal extension at which the crust becomes entirely brittle allowing the formation of major crustal faulting and serpentinization of the mantle. To further constrain the seismic structure and hence the nature of the mantle we assess the Vp uncertainty of the model by means of a Monte Carlo analysis and perform gravity modeling to test different interpretations regarding mantle rock nature. This project is funded by the Irish Shelf Petroleum Studies Group (ISPSG) of the Irish Petroleum Infrastructure Programme Group 4.

  14. 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

  15. Mathematical analysis of a mouse experiment suggests little role for resource depletion in controlling influenza infection within host

    OpenAIRE

    Ahmed, Hasan; Moore, James; Manicassamy, Balaji; Garcia-Sastre, Adolfo; Handel, Andreas; Antia, Rustom

    2017-01-01

    How important is resource depletion (e.g. depletion of target cells) in controlling infection within a host? And how can we distinguish between resource depletion and other mechanisms that may contribute to decline of pathogen load or lead to pathogen clearance? In this paper we examine data from a previously published experiment. In this experiment, mice were infected with influenza virus carrying a green fluorescent protein reporter gene, and the proportion of lung epithelial cells that wer...

  16. Mantle amphibole control on arc and within-plate chemical signatures: Quaternary lavas from Kurdistan Province, Iran

    Science.gov (United States)

    Kheirkhah, M.; Allen, M. B.; Neill, I.; Emami, M. H.; McLeod, C.

    2012-04-01

    New analyses of Quaternary lavas from Kurdistan Province in west Iran shed light on the nature of collision zone magmatism. The rocks are from the Turkish-Iranian plateau within the Arabia-Eurasia collision. Compositions are typically basanite, hawaiite and alkali basalt. Sr-Nd isotope values are close to BSE, which is similar to Quaternary alkali basalts of NW Iran, but distinct from a depleted source melting under Mount Ararat. The chemical signatures suggests variable melting of two distinct sources. One inferred source produced melts with La/Nb from~3.5 to~1.2, which we model as the result of depletion of amphibole during ≤1% melting in the garnet stability field. We infer phlogopite in the source of potassic lavas from Takab. Lithosphere delamination or slab break-off mechanisms for triggering melting are problematic, as the lithosphere is~150-200km thick. It is possible that the negative dT/dP section of the amphibole peridotite solidus was crossed as a result of lithospheric thickening in the collision zone. This explanation is conditional upon the mantle source being weakly hydrated and so only containing a small proportion of amphibole, which can be exhausted during small degrees of partial melting. Our model maybe viable for other magmatic areas within orogenic plateaux, e.g. northern Tibet. Depletion of mantle amphibole may also help explain larger scale transitions from arc to within-plate chemistry in orogens, such as the Palaeogene Arabia-Eurasia system.

  17. Petrogenesis of siliceous high-Mg series rocks as exemplified by the Early Paleoproterozoic mafic volcanic rocks of the Eastern Baltic Shield: enriched mantle versus crustal contamination

    Science.gov (United States)

    Bogina, Maria; Zlobin, Valeriy; Sharkov, Evgenii; Chistyakov, Alexeii

    2015-04-01

    The Early Paleoproterozoic stage in the Earth's evolution was marked by the initiation of global rift systems, the tectonic nature of which was determined by plume geodynamics. These processes caused the voluminous emplacement of mantle melts with the formation of dike swarms, mafic-ultramafic layered intrusions, and volcanic rocks. All these rocks are usually considered as derivatives of SHMS (siliceous high-magnesian series). Within the Eastern Baltic Shield, the SHMS volcanic rocks are localized in the domains with different crustal history: in the Vodlozero block of the Karelian craton with the oldest (Middle Archean) crust, in the Central Block of the same craton with the Neoarchean crust, and in the Kola Craton with a heterogeneous crust. At the same time, these rocks are characterized by sufficiently close geochemical characteristics: high REE fractionation ((La/Yb)N = 4.9-11.7, (La/Sm)N=2.3-3.6, (Gd/Yb)N =1.66-2.74)), LILE enrichment, negative Nb anomaly, low to moderate Ti content, and sufficiently narrow variations in Nd isotope composition from -2.0 to -0.4 epsilon units. The tectonomagmatic interpretation of these rocks was ambiguous, because such characteristics may be produced by both crustal contamination of depleted mantle melts, and by generation from a mantle source metasomatized during previous subduction event. Similar REE patterns and overlapping Nd isotope compositions indicate that the studied basaltic rocks were formed from similar sources. If crustal contamination en route to the surface would play a significant role in the formation of the studied basalts, then almost equal amounts of contaminant of similar composition are required to produce the mafic rocks with similar geochemical signatures and close Nd isotopic compositions, which is hardly possible for the rocks spaced far apart in a heterogeneous crust. This conclusion is consistent with analysis of some relations between incompatible elements and their ratios. In particular, the

  18. Orbital mantle cell lymphoma presenting as myasthenia gravis.

    Science.gov (United States)

    Karlin, Justin; Peck, Travis; Prenshaw, Karyn; Portell, Craig A; Kirzhner, Maria

    2017-12-01

    A 69-year-old man, previously treated with pyridostigmine for myasthenia gravis (manifesting as ptosis and diplopia) was evaluated for several concomitant bilateral anterior orbital masses. Imaging revealed 3 discrete, solid masses within and around the orbits. An incisional biopsy demonstrated atypical lymphocytes positive for CD20 and Cyclin-D1, consistent with mantle cell lymphoma. The patient received induction chemotherapy with a rituximab-based regimen. He experienced resolution of his diplopia and ptosis after one cycle of chemotherapy and achieved complete remission of the orbital masses and myasthenia symptoms after 6 cycles. Myasthenia gravis is most commonly associated with thymoma, but may also be observed with other malignancies. Recognition that orbital lymphoma may coexist with myasthenia gravis will help in expediting the diagnosis of future cases and in guiding treatment decisions.

  19. Upper mantle flow in the western Mediterranean

    International Nuclear Information System (INIS)

    Panza, G.F.; Raykova, R.; Carminati, E.; Doglioni, C.

    2006-07-01

    Two cross-sections of the western Mediterranean Neogene-to-present backarc basin are presented, in which geological and geophysical data of the Transmed project are tied to a new shear-wave tomography. Major results are i) the presence of a well stratified upper mantle beneath the older African continent, with a marked low-velocity layer between 130-200 km of depth; ii) the dilution of this layer within the younger western Mediterranean backarc basin to the north, and iii) the easterly raising of a shallower low-velocity layer from about 140 km to about 30 km in the Tyrrhenian active part of the backarc basin. These findings suggest upper mantle circulation in the western Mediterranean backarc basin, mostly easterly-directed and affecting the boundary between upper asthenosphere (LVZ) and lower asthenosphere, which undulates between about 180 km and 280 km. (author)

  20. Mantle Partial Melting Beneath Gakkel Ridge Reflected in the Petrography of Spinel Lherzolites

    Science.gov (United States)

    Snow, J. E.; Dick, H.; Buechl, A.; Michael, P.; Hellebrand, E.; Ship Sc Parties HEALY 102-POLARSTERN 59,; Ship Sc Parties HEALY 102-POLARSTERN 59,; Ship Sc Parties HEALY 102-POLARSTERN 59,

    2001-12-01

    One of the main aims of the AMORE expedition to Gakkel Ridge was to investigate the nature of mantle residues of low-degree partial melting. Previous results from a single sample of highly serpentinized Gakkel peridotite were unable to conclusively resolve many of the issues of mantle melting and mantle veining involved (1). We have made a preliminary examination of 46 thin sections and hundreds of hand samples of mantle peridotites made on board PFS POLARSTERN and HEALY in the course of the expedition. Most of these peridotites are altered 60-90%, like most abyssal peridotites. Some however are stunningly fresh, containing no detectable serpentine in thin section. The distribution of mantle rock types is similar to that from other mid-ocean ridges. Dunites are present but rare, in contrast to the SW Indian Ridge oblique spreading center at 12° E, as are plagioclase peridotites, in contrast to their abundance at Molloy Ridge further south on the arctic ridge system. There are two differences between this sample set and those commonly observed on mid-ocean ridges that are of particular note. First is the relative abundance of clinopyroxene. The mean clinopyroxene content and size observed in thin section are both qualitatively greater than is commonly observed in abyssal peridotites. Second, the spinels are more nearly euhedral, more abundant and commonly very pale in color. The pale color is well known to be a sign of low Cr content (and thus high activity of Al) in the residual system. All of these observations suggest a low degree of partial melting in the Gakkel Ridge mantle, in accordance with theoretical predictions. What has not been observed to date in even the largest and freshest samples is any evidence of significant mantle veining. It may be that mantle veins have sufficiently low solidi that they melt out completely without a trace even at the lowest degrees of partial melting. The petrographic evidence however suggests that there never was significant

  1. Resolving the Mantle Heat Transfer Discrepancy by Reassessing Buoyancy Flux Estimates of Upwelling Plumes

    Science.gov (United States)

    Hoggard, Mark; Parnell-Turner, Ross; White, Nicky

    2017-04-01

    The size and relative importance of mantle plumes is a controversial topic within the geodynamics community. Numerical experiments of mantle convection suggest a wide range of possible behaviours, from minor plumelets through to large scale, whole-mantle upwellings. In terms of observations, recent seismic tomographic models have identified many large, broad plume-like features within the lower mantle. In contrast, existing estimates of buoyancy flux calculated from plume swells have suggested that these upwellings transfer a relatively minor amount of material and heat into the uppermost mantle. Here, we revisit these calculations of buoyancy flux using a global map of plume swells based upon new observations of dynamic topography. Usually, plume flux is calculated from the cross-sectional area of a swell multiplied by either plate velocity or spreading rate. A key assumption is that plume head material flows laterally at or below the velocity of the overriding plate. Published results are dominated by contributions from the Pacific Ocean and suggest that a total of ˜ 2 TW of heat is carried by plumes into the uppermost mantle. An alternative approach exploits swell volume scaled by a characteristic decay time, which removes the reliance on plate velocities. The main assumption of this method is that plumes are in quasi-steady state. In this study, we have applied this volumetric approach in a new global analysis. Our results indicate that the Icelandic plume has a buoyancy flux of ˜ 27 ± 4 Mg s-1 and the Hawaiian plume is ˜ 2.9 ± 0.6 Mg s-1. These revised values are consistent with independent geophysical constraints from the North Atlantic Ocean and Hawaii. All magmatic and amagmatic swells have been included, suggesting that the total heat flux carried to the base of the plates is ˜ 10 ± 2 TW. This revised value is a five-fold increase compared with previous estimates and provides an improved match to published predictions of basal heat flux across the

  2. Operation of heavily irradiated silicon detectors in non-depletion mode

    International Nuclear Information System (INIS)

    Verbitskaya, E.; Eremin, V.; Ilyashenko, I.; Li, Z.; Haerkoenen, J.; Tuovinen, E.; Luukka, P.

    2006-01-01

    The non-depletion detector operation mode has generally been disregarded as an option in high-energy physics experiments. In this paper, the non-depletion operation is examined by detailed analysis of the electric field distribution and the current pulse response of heavily irradiated silicon (Si) detectors. The previously reported model of double junction in heavily irradiated Si detector is further developed and a simulation of the current pulse response has been performed. It is shown that detectors can operate in a non-depletion mode due to the fact that the value of the electric field in a non-depleted region is high enough for efficient carrier drift. This electric field originates from the current flow through the detector and a consequent drop of the potential across high-resistivity bulk of a non-depleted region. It is anticipated that the electric field in a non-depleted region, which is still electrically neutral, increases with fluence that improves the non-depleted detector operation. Consideration of the electric field in a non-depleted region allows the explanation of the recorded double-peak current pulse shape of heavily irradiated Si detectors and definition of the requirements for the detector operational conditions. Detailed reconstruction of the electric field distribution gives new information on radiation effects in Si detectors

  3. 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

    .703575 for the alkali basalts and 0.703120–0.703130 for the basanites) and the 143Nd/144Nd ratio is high (0.512868–0.512877 for the alkali basalts and 0.512885–0.512913 for the basanites), suggesting that both units originated from an isotopically depleted mantle source. The degree of partial melting of the Toprakkale...

  4. High pressure elasticity and thermal properties of depleted uranium

    International Nuclear Information System (INIS)

    Jacobsen, M. K.; Velisavljevic, N.

    2016-01-01

    Studies of the phase diagram of uranium have revealed a wealth of high pressure and temperature phases. Under ambient conditions the crystal structure is well defined up to 100 gigapascals (GPa), but very little information on thermal conduction or elasticity is available over this same range. This work has applied ultrasonic interferometry to determine the elasticity, mechanical, and thermal properties of depleted uranium to 4.5 GPa. Results show general strengthening with applied load, including an overall increase in acoustic thermal conductivity. Further implications are discussed within. This work presents the first high pressure studies of the elasticity and thermal properties of depleted uranium metal and the first real-world application of a previously developed containment system for making such measurements.

  5. Fully Depleted Charge-Coupled Devices

    Energy Technology Data Exchange (ETDEWEB)

    Holland, Stephen E.

    2006-05-15

    We have developed fully depleted, back-illuminated CCDs thatbuild upon earlier research and development efforts directed towardstechnology development of silicon-strip detectors used inhigh-energy-physics experiments. The CCDs are fabricated on the same typeof high-resistivity, float-zone-refined silicon that is used for stripdetectors. The use of high-resistivity substrates allows for thickdepletion regions, on the order of 200-300 um, with corresponding highdetection efficiency for near-infrared andsoft x-ray photons. We comparethe fully depleted CCD to thep-i-n diode upon which it is based, anddescribe the use of fully depleted CCDs in astronomical and x-ray imagingapplications.

  6. Water in Earth's mantle: Hydrogen analysis of mantle olivine, pyroxenes and garnet using the SIMS

    Science.gov (United States)

    Kurosawa, Masanori; Yurimoto, Hisayoshi; Sueno, Shigeho

    1993-01-01

    Hydrogen (or water) in the Earth's interior plays a key role in the evolution and dynamics of the planet. However, the abundance and the existence form of the hydrogen have scarcely been clear in practice. Hydrogen in the mantle was incorporated in the interior during the formation of the Earth. The incorporated hydrogen was hardly possible to concentrate locally inside the Earth considering its high mobility and high reactivity. The hydrogen, preferably, could be distributed homogeneously over the mantle and the core by the subsequent physical and chemical processes. Therefore, hydrogen in the mantle could be present in the form of trace hydrogen in nominally anhydrous mantle minerals. The hydrogen and the other trace elements in mantle olivines, orthopyroxenes, clinopyroxenes, and garnets were determined using secondary ion mass spectrometry (SIMS) for elucidating (1) the exact hydrogen contents, (2) the correlation between the hydrogen and the other trace elements, (3) the dependence of the hydrogen contents on the depth, and (4) the dependence of the whole rock water contents on the depth.

  7. 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.

  8. Mantle updrafts and mechanisms of oceanic volcanism.

    Science.gov (United States)

    Anderson, Don L; Natland, James H

    2014-10-14

    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. Os-186 and Os-187 Enrichments and High-He-3/He-4 sources in the Earth's Mantle: Evidence from Icelandic Picrites

    Science.gov (United States)

    Brandon, Alan D.; Graham, David W.; Waight, Tod; Gautason, Bjarni

    2007-01-01

    Picrites from the neovolcanic zones in Iceland display a range in Os-187/Os-188O from 0.1297 to 0.1381 ((gamma)Os = 0.0 to 6.5) and uniform Os-186/Os-188 of 0.1198375+/-32 (2 (sigma)). The value for Os-186/Os-188 is within uncertainty of the present-day value for the primitive upper mantle of 0.1198398+/-16. These Os isotope systematics are best explained by ancient recycled crust or melt enrichment in the mantle source region. If so, then the coupled enrichments displayed in Os-186/Os-188 and Os-187/Os-188 from lavas of other plume systems must result from an independent process, the most viable candidate at present remains core-mantle interaction. While some plumes with high He-3/He-4, such as Hawaii, appear to have been subjected to detectable addition of Os (and possibly He) from the outer core, others such as Iceland do not. A positive correlation between Os-187/Os-188 and He-3/He-4 from 9.6 to 19 RA in Iceland picrites is best modeled as mixtures of 500 Ma or older ancient recycled crust mixed with primitive mantle, creating a hybrid source region that subsequently mixes with the convecting MORB mantle during ascent and melting. This multistage mechanism to explain these isotope systematics is consistent with ancient recycled crust juxtaposed with more primitive, relatively He-rich mantle, in convective isolation from the upper mantle, most likely in the lowermost mantle. This is inconsistent with models that propose random mixing between heterogeneities in the convecting upper mantle as a mechanism to explain the observed isotopic variation in oceanic lavas or models that produce a high He-3/He-4 signature in melt depleted and strongly outgassed, He-poor mantle. Instead these systematics require a deep mantle source to explain the 3He/4He signature in Iceland lavas. The He-3/He-4 of lavas derived from the Iceland plume changed over time, from a maximum of 50 RA at 60 Ma, to approximately 25-27 RA at present. The changes are coupled with distinct

  10. Water Contents of the Mantle Beneath the Rio Grande Rift: FTIR Analysis of Kilbourne Hole Peridotite Xenoliths

    Science.gov (United States)

    Schaffer, Lillian A.; Peslier, Anne; Brandon, Alan

    2013-01-01

    Although nominally anhydrous mantle minerals contain only trace amounts of water, they are the main reservoir of water in the mantle. Added up at the scale of the Earth's mantle, these trace amounts of water represent oceans worth in mass]. Mantle xenoliths from Kilbourne Hole in southern New Mexico are ideal to study mantle water distribution in a rift tectonic setting as they come from a recently-erupted maar in the middle of the Rio Grande Rift. Eleven lherzolites, one harzburgite, and one dunite are being analyzed for water contents by FTIR. The xenoliths will also be analyzed for major and trace element composition, Fe3+/Summation (Fe) ratios, and characterized petrologically. Olivines exhibit variable water contents with less water at the rims compared to the cores. This is probably due to H loss during decompression and xenolith transport by the host magma. Mantle water contents appear to have been primarily preserved in the core of the olivines, based on diffusion modeling of the typically plateau-shaped water content profiles across these grains. Water concentrations are in equilibrium between clino- and orthopyroxene, but olivine concentrations are typically not in equilibrium with those of either pyroxene. Lherzolites analyzed so far have water contents of 2-12 ppm H2O in olivines, 125-165 ppm H2O in orthopyroxenes, and 328-447 ppm H2O in clinopyroxenes. These water contents are similar to, but with a narrower range, than those for the respective minerals in other continental peridotite xenoliths. The lherzolites have bulk-rock (BR) Al2O3 contents that range between 3.17 and 3.78 wt%, indicating similar degrees of partial melting, which could explain the narrow range of their pyroxene water contents. Primitive mantle normalized rare earth element (REE) profiles of the bulk lherzolites vary from light REE depleted to flat, with no significant differences between, nor relation to, their mineral water contents. Consequently, the metasomatic agents that

  11. Reconstructing mantle flow and long-wavelength dynamic topography since the Jurassic Period (GD Division Outstanding ECS Award Lecture)

    Science.gov (United States)

    Flament, Nicolas

    2017-04-01

    Global tectonic reconstructions can be used as boundary conditions of forward mantle convection models to simulate past mantle flow and long-wavelength dynamic topography. The predictions of such models can be compared to seismic tomography, to estimates of residual topography and to geological indicators of past vertical motions. Here we present models that reproduce the present-day structure of the lower mantle, including two large structures that resemble the Pacific and African Large Low Shear Velocity Provinces (LLSVPs, ˜15,000 km in diameter) and a smaller structure that resembles the recently discovered Perm Anomaly (˜1,000 km in diameter). The match between predicted and seismically inferred lower mantle structure is quantified across a series of mantle flow and tomography models. In the models, the Perm-like anomaly forms in isolation within a closed and long-lived subduction network (East Asia, Northern Tethys and Mongol-Okhotsk) ˜22,000 km in circumference before migrating ˜1,500 km westward at an average rate of 1 cm yr-1 since 150 million years ago. These results indicate a greater mobility of deep mantle structures than previously recognized, and illustrate that the predictive power of mantle flow models has significantly increased over the last thirty years. We suggest that the mobile Perm Anomaly could be linked to the ˜258 Ma Emeishan volcanics, in contrast to the previously proposed ˜251 Ma Siberian Traps. We also compare the present-day dynamic topography predicted by forward mantle flow models to residual topography models, and show that radial and lateral viscosity variations significantly influence the distribution of power of predicted dynamic topography as a function of spherical harmonic degree. We finally show how past vertical motions preserved in the geological record and the present-day position of slabs in the mantle inferred from seismic tomography may be used to constrain tectonic reconstructions and mantle rheology, including

  12. Progressive Muscle Atrophy and Weakness After Treatment by Mantle Field Radiotherapy in Hodgkin Lymphoma Survivors

    Energy Technology Data Exchange (ETDEWEB)

    Leeuwen-Segarceanu, Elena M. van, E-mail: e.segarceanu@antoniusziekenhuis.nl [Department of Internal Medicine, St. Antonius Hospital, Nieuwegein (Netherlands); Dorresteijn, Lucille D.A. [Department of Neurology, Medisch Spectrum Twente, Enschede (Netherlands); Pillen, Sigrid [Department of Neurology and Clinical Neurophysiology, Donders Center for Neuroscience, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Biesma, Douwe H. [Department of Internal Medicine, University Medical Center Utrecht (Netherlands); Vogels, Oscar J.M. [Department of Neurology and Clinical Neurophysiology, St. Antonius Hospital, Nieuwegein (Netherlands); Alfen, Nens van [Department of Neurology and Clinical Neurophysiology, Donders Center for Neuroscience, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands)

    2012-02-01

    Purpose: To describe the damage to the muscles and propose a pathophysiologic mechanism for muscle atrophy and weakness after mantle field radiotherapy in Hodgkin lymphoma (HL) survivors. Methods and Materials: We examined 12 patients treated by mantle field radiotherapy between 1969 and 1998. Besides evaluation of their symptoms, the following tests were performed: dynamometry; ultrasound of the sternocleidomastoid, biceps, and antebrachial flexor muscles; and needle electromyography of the neck, deltoid, and ultrasonographically affected arm muscles. Results: Ten patients (83%) experienced neck complaints, mostly pain and muscle weakness. On clinical examination, neck flexors were more often affected than neck extensors. On ultrasound, the sternocleidomastoid was severely atrophic in 8 patients, but abnormal echo intensity was seen in only 3 patients. Electromyography of the neck muscles showed mostly myogenic changes, whereas the deltoid, biceps, and antebrachial flexor muscles seemed to have mostly neurogenic damage. Conclusions: Many patients previously treated by mantle field radiotherapy develop severe atrophy and weakness of the neck muscles. Neck muscles within the radiation field show mostly myogenic damage, and muscles outside the mantle field show mostly neurogenic damage. The discrepancy between echo intensity and atrophy suggests that muscle damage is most likely caused by an extrinsic factor such as progressive microvascular fibrosis. This is also presumed to cause damage to nerves within the radiated field, resulting in neurogenic damage of the deltoid and arm muscles.

  13. Differential motion between upper crust and lithospheric mantle in the central Basin and Range

    Science.gov (United States)

    Schulte-Pelkum, Vera; Biasi, Glenn; Sheehan, Anne; Jones, Craig

    2011-09-01

    Stretching of the continental crust in the Basin and Range, western USA, has more than doubled the surface area of the central province. But it is unknown whether stretching affects the entire column of lithosphere down to the convecting mantle, if deep extension occurs offset to the side, or if deeper layers are entirely decoupled from the upper crust. The central Basin and Range province is unusual, compared with its northern and southern counterparts: extension began later; volcanism was far less voluminous; and the unique geochemistry of erupted basalts suggests a long-preserved mantle source. Here we use seismic data and isostatic calculations to map lithospheric thickness in the central Basin and Range. We identify an isolated root of ancient mantle lithosphere that is ~125km thick, providing geophysical confirmation of a strong, cold mantle previously inferred from geochemistry. We suggest that the root caused the later onset of extension and prevented the eruption of voluminous volcanism at the surface. We infer that the root initially pulled away from the Colorado Plateau along with the crust, but then was left behind intact during extension across Death Valley to the Sierra Nevada. We conclude that the upper crust is now decoupled from and moving relative to the root.

  14. Progressive muscle atrophy and weakness after treatment by mantle field radiotherapy in Hodgkin lymphoma survivors.

    Science.gov (United States)

    van Leeuwen-Segarceanu, Elena M; Dorresteijn, Lucille D A; Pillen, Sigrid; Biesma, Douwe H; Vogels, Oscar J M; van Alfen, Nens

    2012-02-01

    To describe the damage to the muscles and propose a pathophysiologic mechanism for muscle atrophy and weakness after mantle field radiotherapy in Hodgkin lymphoma (HL) survivors. We examined 12 patients treated by mantle field radiotherapy between 1969 and 1998. Besides evaluation of their symptoms, the following tests were performed: dynamometry; ultrasound of the sternocleidomastoid, biceps, and antebrachial flexor muscles; and needle electromyography of the neck, deltoid, and ultrasonographically affected arm muscles. Ten patients (83%) experienced neck complaints, mostly pain and muscle weakness. On clinical examination, neck flexors were more often affected than neck extensors. On ultrasound, the sternocleidomastoid was severely atrophic in 8 patients, but abnormal echo intensity was seen in only 3 patients. Electromyography of the neck muscles showed mostly myogenic changes, whereas the deltoid, biceps, and antebrachial flexor muscles seemed to have mostly neurogenic damage. Many patients previously treated by mantle field radiotherapy develop severe atrophy and weakness of the neck muscles. Neck muscles within the radiation field show mostly myogenic damage, and muscles outside the mantle field show mostly neurogenic damage. The discrepancy between echo intensity and atrophy suggests that muscle damage is most likely caused by an extrinsic factor such as progressive microvascular fibrosis. This is also presumed to cause damage to nerves within the radiated field, resulting in neurogenic damage of the deltoid and arm muscles. Copyright © 2012 Elsevier Inc. All rights reserved.

  15. Progressive Muscle Atrophy and Weakness After Treatment by Mantle Field Radiotherapy in Hodgkin Lymphoma Survivors

    International Nuclear Information System (INIS)

    Leeuwen-Segarceanu, Elena M. van; Dorresteijn, Lucille D.A.; Pillen, Sigrid; Biesma, Douwe H.; Vogels, Oscar J.M.; Alfen, Nens van

    2012-01-01

    Purpose: To describe the damage to the muscles and propose a pathophysiologic mechanism for muscle atrophy and weakness after mantle field radiotherapy in Hodgkin lymphoma (HL) survivors. Methods and Materials: We examined 12 patients treated by mantle field radiotherapy between 1969 and 1998. Besides evaluation of their symptoms, the following tests were performed: dynamometry; ultrasound of the sternocleidomastoid, biceps, and antebrachial flexor muscles; and needle electromyography of the neck, deltoid, and ultrasonographically affected arm muscles. Results: Ten patients (83%) experienced neck complaints, mostly pain and muscle weakness. On clinical examination, neck flexors were more often affected than neck extensors. On ultrasound, the sternocleidomastoid was severely atrophic in 8 patients, but abnormal echo intensity was seen in only 3 patients. Electromyography of the neck muscles showed mostly myogenic changes, whereas the deltoid, biceps, and antebrachial flexor muscles seemed to have mostly neurogenic damage. Conclusions: Many patients previously treated by mantle field radiotherapy develop severe atrophy and weakness of the neck muscles. Neck muscles within the radiation field show mostly myogenic damage, and muscles outside the mantle field show mostly neurogenic damage. The discrepancy between echo intensity and atrophy suggests that muscle damage is most likely caused by an extrinsic factor such as progressive microvascular fibrosis. This is also presumed to cause damage to nerves within the radiated field, resulting in neurogenic damage of the deltoid and arm muscles.

  16. Ensemble Kalman filter for the reconstruction of the Earth's mantle circulation

    Science.gov (United States)

    Bocher, Marie; Fournier, Alexandre; Coltice, Nicolas

    2018-02-01

    Recent advances in mantle convection modeling led to the release of a new generation of convection codes, able to self-consistently generate plate-like tectonics at their surface. Those models physically link mantle dynamics to surface tectonics. Combined with plate tectonic reconstructions, they have the potential to produce a new generation of mantle circulation models that use data assimilation methods and where uncertainties in plate tectonic reconstructions are taken into account. We provided a proof of this concept by applying a suboptimal Kalman filter to the reconstruction of mantle circulation (Bocher et al., 2016). Here, we propose to go one step further and apply the ensemble Kalman filter (EnKF) to this problem. The EnKF is a sequential Monte Carlo method particularly adapted to solve high-dimensional data assimilation problems with nonlinear dynamics. We tested the EnKF using synthetic observations consisting of surface velocity and heat flow measurements on a 2-D-spherical annulus model and compared it with the method developed previously. The EnKF performs on average better and is more stable than the former method. Less than 300 ensemble members are sufficient to reconstruct an evolution. We use covariance adaptive inflation and localization to correct for sampling errors. We show that the EnKF results are robust over a wide range of covariance localization parameters. The reconstruction is associated with an estimation of the error, and provides valuable information on where the reconstruction is to be trusted or not.

  17. Sn-wave velocity structure of the uppermost mantle beneath the Australian continent

    Science.gov (United States)

    Wei, Zhi; Kennett, Brian L. N.; Sun, Weijia

    2018-03-01

    We have extracted a dataset of more than 5000 Sn traveltimes for source-station pairs within continental Australia, with 3-D source relocation using Pn arrivals to improve data consistency. We conduct tomographic inversion for S-wavespeed structure down to 100 km using the FMTOMO method for the whole Australian continent. We obtain a 3-D model with potential resolution of 3.0° 3.0°. The new S wavespeed model provides strong constraints on structure in a zone that was previously poorly characterised. The S velocities in the uppermost mantle are rather fast, with patterns of variation generally corresponding to those for Pn. We find strong heterogeneities of S wavespeed in the uppermost mantle across the entire continent of Australia with a close relation to crustal geological features. For instance, the cratons in the western Australia usually have high S velocities (> 4.70 km/s), while the volcanic regions on the eastern margin of Australia are characterised by low S velocities (continent. We find most of the uppermost mantle has Vp/Vs between 1.65 and 1.85, but with patches in central Australia and in the east with much higher Vp/Vs ratios. Distinctive local anomalies on the eastern margin may indicate the positions of remnants of mantle plumes.

  18. Depleted UF6 programmatic environmental impact statement

    International Nuclear Information System (INIS)

    1997-01-01

    The US Department of Energy has developed a program for long-term management and use of depleted uranium hexafluoride, a product of the uranium enrichment process. As part of this effort, DOE is preparing a Programmatic Environmental Impact Statement (PEIS) for the depleted UF 6 management program. This report duplicates the information available at the web site (http://www.ead.anl.gov/web/newduf6) set up as a repository for the PEIS. Options for the web site include: reviewing recent additions or changes to the web site; learning more about depleted UF 6 and the PEIS; browsing the PEIS and related documents, or submitting official comments on the PEIS; downloading all or part of the PEIS documents; and adding or deleting one's name from the depleted UF 6 mailing list

  19. A definition of depletion of fish stocks

    Science.gov (United States)

    Van Oosten, John

    1949-01-01

    Attention was focused on the need of a common and better understanding of the term depletion as applied to the fisheries in order to eliminate if possible the existing inexactness of thought on the subject. Depletion has been confused at various times with at least ten different ideas associated with it but which, as has has heen pointed out, are not synonymous at all. In defining depletion we must recognize that the term represents a condition and must not he confounded with the cause (overfishing) that leads to this condition or with the symptoms that identify it. Depletion was defined as a reduction, through overfishing, in the level of abundance of the exploitable segment of a stock that prevents the realization of the maximum productive capacity.

  20. Real depletion in nodal diffusion codes

    International Nuclear Information System (INIS)

    Petkov, P.T.

    2002-01-01

    The fuel depletion is described by more than one hundred fuel isotopes in the advanced lattice codes like HELIOS, but only a few fuel isotopes are accounted for even in the advanced steady-state diffusion codes. The general assumption that the number densities of the majority of the fuel isotopes depend only on the fuel burnup is seriously in error if high burnup is considered. The real depletion conditions in the reactor core differ from the asymptotic ones at the stage of lattice depletion calculations. This study reveals which fuel isotopes should be explicitly accounted for in the diffusion codes in order to predict adequately the real depletion effects in the core. A somewhat strange conclusion is that if the real number densities of the main fissionable isotopes are not explicitly accounted for in the diffusion code, then Sm-149 should not be accounted for either, because the net error in k-inf is smaller (Authors)

  1. Fully Depleted Charge-Coupled Devices

    International Nuclear Information System (INIS)

    Holland, Stephen E.

    2006-01-01

    We have developed fully depleted, back-illuminated CCDs that build upon earlier research and development efforts directed towards technology development of silicon-strip detectors used in high-energy-physics experiments. The CCDs are fabricated on the same type of high-resistivity, float-zone-refined silicon that is used for strip detectors. The use of high-resistivity substrates allows for thick depletion regions, on the order of 200-300 um, with corresponding high detection efficiency for near-infrared and soft x-ray photons. We compare the fully depleted CCD to the p-i-n diode upon which it is based, and describe the use of fully depleted CCDs in astronomical and x-ray imaging applications

  2. Ecological considerations of natural and depleted uranium

    International Nuclear Information System (INIS)

    Hanson, W.C.

    1980-01-01

    Depleted 238 U is a major by-product of the nuclear fuel cycle for which increasing use is being made in counterweights, radiation shielding, and ordnance applications. This paper (1) summarizes the pertinent literature on natural and depleted uranium in the environment, (2) integrates results of a series of ecological studies conducted at Los Alamos Scientific Laboratory (LASL) in New Mexico where 70,000 kg of depleted and natural uranium has been expended to the environment over the past 34 years, and (3) synthesizes the information into an assessment of the ecological consequences of natural and depleted uranium released to the environment by various means. Results of studies of soil, plant, and animal communities exposed to this radiation and chemical environment over a third of a century provide a means of evaluating the behavior and effects of uranium in many contexts

  3. Seasonal total methane depletion in limestone caves

    OpenAIRE

    Waring Chris L; Hankin Stuart I; Griffith David W T; Kertesz Michael A; Kobylski Victoria; Wilson Neil L; Coleman Nicholas V; Kettlewell Graham; Zlot Robert; Bosse Michael; Bell Graham

    2017-01-01

    Methane concentration in caves is commonly much lower than the external atmosphere, yet the cave CH4 depletion causal mechanism is contested and dynamic links to external diurnal and seasonal temperature cycles unknown. Here, we report a continuous 3-year record of cave methane and other trace gases in Jenolan Caves, Australia which shows a seasonal cycle of extreme CH4 depletion, from ambient ~1,775?ppb to near zero during summer and to ~800?ppb in winter. Methanotrophic bacteria, some newly...

  4. Depleted Bulk Heterojunction Colloidal Quantum Dot Photovoltaics

    KAUST Repository

    Barkhouse, D. Aaron R.

    2011-05-26

    The first solution-processed depleted bulk heterojunction colloidal quantum dot solar cells are presented. The architecture allows for high absorption with full depletion, thereby breaking the photon absorption/carrier extraction compromise inherent in planar devices. A record power conversion of 5.5% under simulated AM 1.5 illumination conditions is reported. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Noble Gases And Changing Models Of Mantle Evolution

    Science.gov (United States)

    Ballentine, C. J.; van Keken, P. E.; Porcelli, D.; Hauri, E. H.

    2003-04-01

    The noble gas isotopes recorded in Ocean Island Basalts (OIB) and Mid Ocean Ridge Basalts (MORB) combined with an estimate of ^3He concentration in the upper mantle have played a defining role in the development of models describing the geochemical evolution of the mantle. The three most cited noble gas constraints on a layered mantle system are the Heat/He discrepancy, 40Ar mass balance, and low ^3He concentration (relative to U+Th) in the upper mantle. These are all equally dependant on the validity of integrating the mantle ^3He flux into the oceans (t_frac{1}{2} ˜ 10^3 years) with the record of ocean floor generation (t_frac{1}{2} ˜ 5x10^6 years) to obtain the mantle ^3He concentration. A ^3He concentration 3.5 times higher in the mantle than currently accepted removes these noble gas constraints. A deep reservoir would then no longer be required to: i) trap ^4He produced by U+Th decay but let the associated heat escape; ii) provide a reservoir for the 'missing' 40Ar generated by K decay; and iii) provide a flux of ^3He to balance the ^3He/^4He ratio and U+Th content of the upper mantle. Numerical models simulating whole mantle convection show that natural fluctuations in the Heat/He ratio due to different extraction methods can accommodate the difference between predicted and observed values, while these same models illustrate that the efficiency of mantle 40Ar degassing is low enough to account for the 'missing' 40Ar within the context of whole mantle convection. The simple observation that ^3He/^4He ratios in OIB are higher than MORB nevertheless demands that there is a high ^3He reservoir in the mantle and that the model 'zero paradox' concentration remains the upper limit reference value. While higher upper mantle ^3He concentrations remove the need for a layer at the 670km boundary, mantle models satisfying the noble gases must still provide a system that separates radiogenic Heat from Helium production, preserves a region of the mantle with higher 40Ar

  6. 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

  7. 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.

  8. A Bayesian Method to Quantify Azimuthal Anisotropy Model Uncertainties: Application to Global Azimuthal Anisotropy in the Upper Mantle and Transition Zone

    Science.gov (United States)

    Yuan, K.; Beghein, C.

    2018-01-01

    Seismic anisotropy is a powerful tool to constrain mantle deformation, but its existence in the deep upper mantle and topmost lower mantle is still uncertain. Recent results from higher mode Rayleigh waves have, however, revealed the presence of 1 % azimuthal anisotropy between 300 km and 800 km depth, and changes in azimuthal anisotropy across the mantle transition zone boundaries. This has important consequences for our understanding of mantle convection patterns and deformation of deep mantle material. Here, we propose a Bayesian method to model depth variations in azimuthal anisotropy and to obtain quantitative uncertainties on the fast seismic direction and anisotropy amplitude from phase velocity dispersion maps. We applied this new method to existing global fundamental and higher mode Rayleigh wave phase velocity maps to assess the likelihood of azimuthal anisotropy in the deep upper mantle and to determine whether previously detected changes in anisotropy at the transition zone boundaries are robustly constrained by those data. Our results confirm that deep upper mantle azimuthal anisotropy is favored and well-constrained by the higher mode data employed. The fast seismic directions are in agreement with our previously published model. The data favor a model characterized, on average, by changes in azimuthal anisotropy at the top and bottom of the transition zone. However, this change in fast axes is not a global feature as there are regions of the model where the azimuthal anisotropy direction is unlikely to change across depths in the deep upper mantle. We were, however, unable to detect any clear pattern or connection with surface tectonics. Future studies will be needed to further improve the lateral resolution of this type of model at transition zone depths.

  9. Simulating the Seismic Signal of Phase Transitions in the Deepest Mantle (Invited)

    Science.gov (United States)

    Walker, A.; Dobson, D. P.; Nowacki, A.; Wookey, J. M.; Forte, A. M.; Kendall, J. M.

    2013-12-01

    The discovery of the perovskite to post-perovskite phase transition in (Mg,Fe)SiO3 explains many of the seismic observations of the lowermost mantle including the presence of multiple seismic discontinuities and significant seismic anisotropy. However, the explanations of many detailed features remain elusive. The recent discovery of a topotactic relationship between the orientation of perovskite and post-perovskite crystals in a partially transformed analogue opens the possibility of texture inheritance through the phase transition [1]. This must be captured in simulations designed to explain the anisotropy of the lowermost mantle, especially those which link mantle dynamics with seismic observations. We have extended our previous work linking models of flow in the lowermost mantle with simulations of texture development and predictions of seismic anisotropy [2] to account for the topotaxy between perovskite and post-perovskite. In particular, we compare four cases: (1) As in [2], anisotropy is only generated in post-perovskite by dislocation mediated deformation dominated by one of a number of slip systems, phase transitions destroy texture and ferropericlase and perovskite dominated rocks are isotropic. (2) Although phase transitions destroy texture, ferropericlase and/or perovskite deform by dislocation motion permitting the generation of seismic anisotropy in warmer regions of the mantle where post-perovskite is unstable. We account for the possibility of the inversion of slip-system activities in ferropericlase at high pressure as suggested by models of dislocation motion based on atomic scale simulations [3]. (3) Allow texture development by dislocation motion in perovskite and post-perovskite and texture inheritance through phase transitions by the mechanism described in [1]. However, we assume that the bulk of the lower mantle deforms by a mechanism that does not lead to the development of texture and so begin the simulation from a random distribution of

  10. Water in the Cratonic Mantle: Insights from FTIR Data on Lac De Gras Xenoliths (Slave Craton, Canada)

    Science.gov (United States)

    Peslier, Anne H.; Brandon, Alan D.; Schaffer, Lillian Aurora; O'Reilly, Suzanne Yvette; Griffin, William L.; Morris, Richard V.; Graff, Trevor G.; Agresti, David G.

    2014-01-01

    The mantle lithosphere beneath the cratonic part of continents is the deepest (> 200 km) and oldest (>2-3 Ga) on Earth, remaining a conundrum as to how these cratonic roots could have resisted delamination by asthenospheric convection over time. Water, or trace H incorporated in mineral defects, could be a key player in the evolution of continental lithosphere because it influences melting and rheology of the mantle. Mantle xenoliths from the Lac de Gras kimberlite in the Slave craton were analyzed by FTIR. The cratonic mantle beneath Lac de Gras is stratified with shallow (<145 km) oxidized ultradepleted peridotites and pyroxenites with evidence for carbonatitic metasomatism, underlain by reduced and less depleted peridotites metasomatized by kimberlite melts. Peridotites analyzed so far have H O contents in ppm weight of 7-100 in their olivines, 58 to 255 in their orthopyroxenes (opx), 11 to 84 in their garnet, and 139 in one clinopyroxene. A pyroxenite contains 58 ppm H2O in opx and 5 ppm H2O in its olivine and garnet. Olivine and garnet from the deep peridotites have a range of water contents extending to higher values than those from the shallow ones. The FTIR spectra of olivines from the shallow samples have more prominent Group II OH bands compared to the olivines from the deep samples, consistent with a more oxidized mantle environment. The range of olivine water content is similar to that observed in Kaapvaal craton peridotites at the same depths (129-184 km) but does not extend to as high values as those from Udachnaya (Siberian craton). The Slave, Kaapvaal and Siberian cratons will be compared in terms of water content distribution, controls and role in cratonic root longevity.

  11. Super-Si garnet exsolution kinetics denotes multistage mantle exhumation

    Science.gov (United States)

    Spengler, Dirk; Nishihara, Yu; Fujino, Kiyoshi

    2013-04-01

    Previous decompression experiments have shown that super-Si garnet decomposes to normal garnet + pyroxene, which supports that natural analogues (found in mantle xenoliths, diamond inclusions, peridotite massifs) record up to several hundreds of kilometre exhumation, all proposed to apply to contrasting geological scenarios including mantle convection, kimberlite magmatism and plate tectonics. To verify this proposition we used glass powder with a 'pyrolite minus olivine' composition for polycrystalline dry super-Si garnet synthesis (18 GPa, 1600 °C, 2 1/3 h) and subsequent decompression (10 GPa, 1450 °C, 0-12 h). All samples recovered after decompression share a coronitic texture of new grains of garnet + pyroxene that surround relic super-Si garnet. Quantified XRD spectra show transformed volumes are similar, ~40 %, that mark a rapid decrease of the transformation rate within the first minutes of the decompression runs. Fitted kinetic data does not fulfil conditions for steady nucleation and growth. The Tschermak's component of corona clinopyroxene is four times higher than that of equilibrium clinopyroxene synthesised along with each decompression experiment. Element concentration profiles (TEM EDS) and element mapping (FE-SEM EDS) across the corona microstructure show steep but discontinuous Al concentration gradients at both relic and corona garnet grain margins. Transformation rate and mineral chemistry suggest that volume diffusion (1) exceeds decompression induced initial partial breakdown of super-Si garnet and (2) will be rate limiting for exsolution to reach equilibrium. Modelled Si-Al and Si-Al-Mg interdiffusion in garnet at different water contents in combination with geological cooling rates suggests that diffusion distances exceed metamorphic garnet grain sizes of ≤1 cm within the amphibolit facies, unless dry conditions apply. In contrast, mantle garnet of 1-2 cm in size may allow for up to two types of pyroxene precipitiation, depending on the

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

    OpenAIRE

    Herndon, J. Marvin

    2010-01-01

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

  13. Chemical equilibration of the Earth's core and upper mantle

    Science.gov (United States)

    Brett, R.

    1984-01-01

    The oxygen fugacity (fO2) of the Earth's upper mantle appears to lie somewhat above that of the iron-wu??stite buffer, its fO2 is assumed to have been similar to the present value at the time of core formation. In the upper mantle, the Fe-rich liquid protocore that would form under such conditions of fO2 at elevated temperatures would lie predominantly in the system Fe-S-O. Distribution coefficients for Co, Cu, Ni, Ir, Au, Ir, W, Re, Mo, Ag and Ga between such liquids and basalt are known and minimum values are known for Ge. From these coefficients, upper mantle abundances for the above elements can be calculated by assuming cosmic abundances for the whole Earth and equilibrium between the Fe-S-O protocore and upper mantle. These calculated abundances are surprisingly close to presently known upper mantle abundances; agreements are within a factor of 5, except for Cu, W, and Mo. Therefore, siderophile element abundances in the upper mantle based on known distribution coefficients do not demand a late-stage meteoritic bombardment, and a protocore formed from the upper mantle containing S and O seems likely. As upper mantle abundances fit a local equilibrium model, then either the upper mantle has not been mixed with the rest of the mantle since core formation, or else partition coefficients between protocore and mantle were similar for the whole mantle regardless of P, T, and fO2. The latter possibility seems unlikely over such a P-T range. ?? 1984.

  14. Variations in melting dynamics and mantle compositions along the Eastern Volcanic Zone of the Gakkel Ridge: insights from olivine-hosted melt inclusions

    Science.gov (United States)

    Wanless, V. D.; Behn, M. D.; Shaw, A. M.; Plank, T.

    2014-05-01

    We present major element, trace element, and volatile concentrations from 66 naturally glassy, olivine-hosted melt inclusions erupted along the Eastern Volcanic Zone (EVZ) of the ultraslow-spreading Gakkel Ridge. Melt inclusion compositions suggest that there are systematic variations in the mantle source composition and melting dynamics from the eastern to the western end of the EVZ. This includes increasing water contents and highly incompatible trace element concentrations (e.g., Ba and Nb) and decreasing light and middle rare earth element concentrations. Ratios of light to heavy rare earth elements in the easternmost melt inclusions are relatively homogeneous, but become more variable to the west. To determine the source of the geochemical variability observed along the EVZ, we model trace elements associated with mantle melting in one- and two-component systems. We consider four possible mantle sources and a range of melting regime shapes, from a full melting triangle to a vertical melting column centered beneath the ridge axes. The observed geochemical variations can be explained by melting of a heterogeneous mantle source composed of depleted MORB mantle plus a metasomatized mantle, where the proportion of the metasomatized component and the extent of melting increases toward the west. Lower rare earth element concentrations and trace element ratios in the westernmost sites also suggest inefficient melt focusing from the outer edges of the melting region. Our results indicate that despite variations in the size of the melting zone and the composition of the mantle source along the ridge axis, the region over which the melts are pooled back to the ridge axis is relatively constant (~10-20 km), suggesting that there is a limit to the distance melts can be transported from off-axis in ultraslow-spreading environments.

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

    Science.gov (United States)

    Walzer, Uwe; Hendel, Roland

    2010-05-01

    We present a dynamic 3-D spherical-shell model of mantle convection and the evolution of the chemical reservoirs of the Earth`s silicate shell. Chemical differentiation, convection, stirring and thermal evolution constitute an inseparable dynamic system. Our model is based on the solution of the balance equations of mass, momentum, energy, angular momentum, and four sums of the number of atoms of the pairs 238U-206Pb, 235U-207Pb, 232Th-208Pb, and 40K-40Ar. Similar to the present model, the continental crust of the real Earth was not produced entirely at the start of the evolution but developed episodically in batches [1-7]. The details of the continental distribution of the model are largely stochastic, but the spectral properties are quite similar to the present real Earth. The calculated Figures reveal that the modeled present-day mantle has no chemical stratification but we find a marble-cake structure. If we compare the observational results of the present-day proportion of depleted MORB mantle with the model then we find a similar order of magnitude. The MORB source dominates under the lithosphere. In our model, there are nowhere pure unblended reservoirs in the mantle. It is, however, remarkable that, in spite of 4500 Ma of solid-state mantle convection, certain strong concentrations of distributed chemical reservoirs continue to persist in certain volumes, although without sharp abundance boundaries. We deal with the question of predictable and stochastic portions of the phenomena. Although the convective flow patterns and the chemical differentiation of oceanic plateaus are coupled, the evolution of time-dependent Rayleigh number, Rat , is relatively well predictable and the stochastic parts of the Rat(t)-curves are small. Regarding the juvenile growth rates of the total mass of the continents, predictions are possible only in the first epoch of the evolution. Later on, the distribution of the continental-growth episodes is increasingly stochastic

  16. COMPOSITIONAL AND THERMAL DIFFERENCES BETWEEN LITHOSPHERIC AND ASTHENOSPHERIC MANTLE AND THEIR INFLUENCE ON CONTINENTAL DELAMINATION

    Directory of Open Access Journals (Sweden)

    A. I. Kiselev

    2015-01-01

    . Density inversion occurs if one assumes the presence of the asthenosphereic material in the composition similar to that of the primitive mantle or lherzolite KH in amounts no less than 1.40 and 0.83 wt. %, respectively, of the conventionally neutral fluid. This amount of the fluid seems to be overestimated and thus does not fully correlate with the current estimates of the fluid content in the mantle. Therefore, the most appropriate material for delamination of the thickened lithosphere is only the fluid-bearing asthenosphere which composition corresponds to that of the depleted mantle of middle-ocean ridges (DMM being the reservoir existing from the Precambrian. In our model, abyssal peridotite is most similar to DMM as compared with other more fertile compositions of the lithosphere. Heat advection due to uplift of fluid-bearing plumes that occurred much time after collisional events may initiate repeated delamination of gravitationally instable parts of the orogenic and cratonic lithosphere. 

  17. 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.

  18. Low-Ti basalts from the Faroe Islands constrain the early Iceland depleted plume component

    DEFF Research Database (Denmark)

    Søager, Nina; Holm, Paul Martin

    New Sr, Nd, Hf and high precision Pb isotope analyses of 46 Faroese low-Ti lavas erupted at the rifting of the proto-North Atlantic ~56-55 Ma ago are presented. The low-Ti lavas are depleted, MORB-like basalts erupted close to the riftzone at the same time as enriched high-Ti basalts were erupted...... of the magmas. However, 5 of the samples show signs of mixing with high-Ti melts. Although highly sensitive to crustal contamination, only little is detected in the low-Ti basalts. Isotopically the low-Ti basalts can be explained by mixing of the two end-members DM (the local depleted mantle as defined...... by the sample array) and NAEM (North Atlantic End-Member) (Ellam & Stuart 2000). The NAEM component is very similar to the Icelandic depleted plume component ID1 (Thirlwall et al. 2004) and both have negative ¿207Pb, low 206Pb/204Pb and eNd and high 87Sr/86Sr compared to MORB. Therefore the NAEM component could...

  19. Global rates of mantle serpentinization and H2 release at oceanic transform faults

    Science.gov (United States)

    Ruepke, Lars; Hasenclever, Joerg

    2017-04-01

    The cycling of seawater through the ocean floor is the dominant mechanism of biogeochemical exchange between the solid earth and the global ocean. Crustal fluid flow appears to be typically associated with major seafloor structures, and oceanic transform faults (OTF) are one of the most striking yet poorly understood features of the global mid-ocean ridge systems. Fracture zones and transform faults have long been hypothesized to be sites of substantial biogeochemical exchange between the solid Earth and the global ocean. This is particularly interesting with regard to the ocean biome. Deep ocean ecosystems constitute 60% of it but their role in global ocean biogeochemical cycles is much overlooked. There is growing evidence that life is supported by chemosynthesis at hydrothermal vents but also in the crust, and therefore this may be a more abundant process than previously thought. In this context, the serpentine forming interaction between seawater and cold lithospheric mantle rocks is particularly interesting as it is also a mechanism of abiotic hydrogen and methane formation. Interestingly, a quantitative global assessment of mantle serpentinization at oceanic transform faults in the context of the biogeochemical exchange between the seafloor and the global ocean is still largely missing. Here we present the results of a set of 3-D thermo-mechanical model calculations that investigate mantle serpentinization at OTFs for the entire range of globally observed slip rates and fault lengths. These visco-plastic models predict the OTF thermal structure and the location of crustal-scale brittle deformation, which is a prerequisite for mantle serpentinization to occur. The results of these simulations are integrated with information on the global distribution of OTF lengths and slip rates yielding global estimates on mantle serpentinization and associated H2 release. We find that OTFs are potentially sites of intense crustal fluid flow and are in terms of H2 release

  20. Enriched mantle source for the Central Atlantic magmatic province: New supporting evidence from southwestern Europe

    Science.gov (United States)

    Callegaro, Sara; Rapaille, Cedric; Marzoli, Andrea; Bertrand, Hervé; Chiaradia, Massimo; Reisberg, Laurie; Bellieni, Giuliano; Martins, Línia; Madeira, José; Mata, João; Youbi, Nasrrddine; De Min, Angelo; Azevedo, Maria Rosário; Bensalah, Mohamed Khalil

    2014-02-01

    Remnants of the Central Atlantic magmatic province (CAMP), emplaced ca. 201 Ma during the rifting phases leading to Pangaea breakup, are still preserved in southwestern Europe (SWE) in the form of sills, dykes and lava flows. Low-Ti (TiO2 0.48-1.46 wt.%) tholeiitic basalts and basaltic andesites crop out as sills only in the Pyrenean area, as dykes (especially the Messejana-Plasencia dyke) from central Spain to the Atlantic coast, and as lava flows within sedimentary basins in Southern Portugal. Here we present new geochemical data (major and trace elements, mineral chemistry and combined Sr-Nd-Pb-Os analyses) on 132 samples, aiming to investigate the mantle source of these rocks and correlate them with magmatism from other areas of the CAMP. Crustal-like signatures in incompatible element patterns (Nb-Ta troughs, Pb peaks, generally shared by most CAMP rocks) and the enriched Sr-Nd-Pb isotopic characters (87Sr/86Sr200 Ma 0.70529-0.70657; 143Nd/144Nd200 Ma 0.51238-0.51225; 206Pb/204Pb200 Ma 18.15-18.48; 207Pb/204Pb200 Ma 15.57-15.68; 208Pb/204Pb200 Ma 37.99-38.52) apparently argue in favor of crustal assimilation playing an important role in the evolution of these magmas. However, the low initial 187Os/188Os values (0.1298 ± 0.0056) as well as the restricted geochemical variations shown by SWE-CAMP rocks over such a large area limit the crustal assimilation of various Iberian lithologies to small amounts. We thus locate this enrichment in the mantle source, in the form of upper and lower crustal material recycled during earlier subduction-related events. This process, while imparting crustal signatures to incompatible elements and Sr-Nd-Pb isotopes, would not alter the Os isotopic signature, dominated by the peridotite. The mixed contribution of 3-7% of local upper (pelitic) and lower (felsic granulitic) crust is sufficient to enrich a depleted mantle source, which can be either the sub-SWE lithosphere or the upper depleted asthenosphere. Similar processes of

  1. Crust-mantle coupling mechanism in Cameroon, West Africa, revealed by 3D S-wave velocity and azimuthal anisotropy

    Science.gov (United States)

    Ojo, Adebayo Oluwaseun; Ni, Sidao; Chen, Haopeng; Xie, Jun

    2018-01-01

    To understand the depth variation of deformation beneath Cameroon, West Africa, we developed a new 3D model of S-wave isotropic velocity and azimuthal anisotropy from joint analysis of ambient seismic noise and earthquake surface wave dispersion. We found that the Cameroon Volcanic Line (CVL) is well delineated by slow phase velocities in contrast with the neighboring Congo Craton, in agreement with previous studies. Apart from the Congo Craton and the Oubanguides Belt, the uppermost mantle revealed a relatively slow velocity indicating a thinned or thermally altered lithosphere. The direction of fast axis in the upper crust is mostly NE-SW, but trending approximately N-S around Mt. Oku and the southern CVL. The observed crustal azimuthal anisotropy is attributed to alignment of cracks and crustal deformation related to magmatic activities. A widespread zone of weak-to-zero azimuthal anisotropy in the mid-lower crust shows evidence for vertical mantle flow or isotropic mid-lower crust. In the uppermost mantle, the fast axis direction changed from NE-SW to NW-SE around Mt. Oku and northern Cameroon. This suggests a layered mechanism of deformation and revealed that the mantle lithosphere has been deformed. NE-SW fast azimuths are observed beneath the Congo Craton and are consistent with the absolute motion of the African plate, suggesting a mantle origin for the observed azimuthal anisotropy. Our tomographically derived fast directions are consistent with the local SKS splitting results in some locations and depths, enabling us to constrain the origin of the observed splitting. The different feature of azimuthal anisotropy in the upper crust and the uppermost mantle implies decoupling between deformation of crust and mantle in Cameroon.

  2. Nonlinear 1D and 2D waveform inversions of SS precursors and their applications in mantle seismic imaging

    Science.gov (United States)

    Dokht, R.; Gu, Y. J.; Sacchi, M. D.

    2016-12-01

    Seismic velocities and the topography of mantle discontinuities are crucial for the understanding of mantle structure, dynamics and mineralogy. While these two observables are closely linked, the vast majority of high-resolution seismic images are retrieved under the assumption of horizontally stratified mantle interfaces. This conventional correction-based process could lead to considerable errors due to the inherent trade-off between velocity and discontinuity depth. In this study, we introduce a nonlinear joint waveform inversion method that simultaneously recovers discontinuity depths and seismic velocities using the waveforms of SS precursors. Our target region is the upper mantle and transition zone beneath Northeast Asia. In this region, the inversion outcomes clearly delineate a westward dipping high-velocity structure in association with the subducting Pacific plate. Above the flat part of the slab west of the Japan sea, our results show a shear wave velocity reduction of 1.5% in the upper mantle and 10-15 km depression of the 410 km discontinuity beneath the Changbaishan volcanic field. We also identify the maximum correlation between shear velocity and transition zone thickness at an approximate slab dip of 30 degrees, which is consistent with previously reported values in this region.To validate the results of the 1D waveform inversion of SS precursors, we discretize the mantle beneath the study region and conduct a 2D waveform tomographic survey using the same nonlinear approach. The problem is simplified by adopting the discontinuity depths from the 1D inversion and solving only for perturbations in shear velocities. The resulting models obtained from the 1D and 2D approaches are self-consistent. Low-velocities beneath the Changbai intraplate volcano likely persist to a depth of 500 km. Collectively, our seismic observations suggest that the active volcanoes in eastern China may be fueled by a hot thermal anomaly originating from the mantle transition

  3. 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...... seismic data. There is a growing consensus that the cause of the imaged wavespeed anomalies not only relates to variations in temperature, but also bears a strong compositional component. However, separation of thermal and chemical effects from seismic wave speeds alone is difficult and is further...

  4. 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...

  5. Multiple mantle upwellings through the transition zone beneath the Afar Depression?

    Science.gov (United States)

    Hammond, J. O.; Kendall, J. M.; Stuart, G. W.; Thompson, D. A.; Ebinger, C. J.; Keir, D.; Ayele, A.; Goitom, B.; Ogubazghi, G.

    2012-12-01

    Previous seismic studies using regional deployments of sensors in East-Africa show that low seismic velocities underlie Africa, but their resolution is limited to the top 200-300km of the Earth. Thus, the connection between the low velocities in the uppermost mantle and those imaged in global studies in the lower mantle is unclear. We have combined new data from Afar, Ethiopia with 7 other regional experiments and global network stations across Kenya, Ethiopia, Eritrea, Djibouti and Yemen, to produce high-resolution models of upper mantle P- and S-wave velocities to the base of the transition zone. Relative travel time tomographic inversions show that within the transition zone two focussed sharp-sided low velocity regions exist: one beneath the Western Ethiopian plateau outside the rift valley, and the other beneath the Afar depression. Estimates of transition zone thickness suggest that this is unlikely to be an artefact of mantle discontinuity topography as a transition zone of normal thickness underlies the majority of Afar and surrounding regions. However, a low velocity layer is evident directly above the 410 discontinuity, co-incident with some of the lowest seismic velocities suggesting that smearing of a strong low velocity layer of limited depth extent may contribute to the tomographic models in north-east Afar. The combination of seismic constraints suggests that small low temperature (<50K) upwellings may rise from a broader low velocity plume-like feature in the lower mantle. This interpretation is supported by numerical and analogue experiments that suggest the 660km phase change and viscosity jump may impede flow from the lower to upper mantle creating a thermal boundary layer at the base of the transition zone. This allows smaller, secondary upwellings to initiate and rise to the surface. These, combined with possible evidence of melt above the 410 discontinuity can explain the seismic velocity models. Our images of secondary upwellings suggest that

  6. Xenoliths from Bunyaruguru volcanic field: Some insights into lithology of East African Rift upper mantle

    Science.gov (United States)

    Muravyeva, N. S.; Senin, V. G.

    2018-01-01

    The mineral composition of mantle xenoliths from kamafugites of the Bunyaruguru volcanic field has been determined. The major and some trace elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, Cr, Ni, Ba, Sr, La, Ce, Nd, Nb) has been analyzed in olivine, clinopyroxene, phlogopite, Cr-spinel, titanomagnetite, perovskite and carbonates of xenoliths and their host lavas. Bunyaruguru is one of three (Katwe-Kikorongo, Fort Portal and Bunyaruguru) volcanic fields included in the Toro-Ankole province located on the North end of the West Branch of the East African Rift. The xenoliths from three craters within the Bunyaruguru volcanic field revealed the different character of metasomatic alteration, reflecting the heterogeneity of the mantle on the kilometer scale. The most unusual finding was composite glimmerite-wehrlite xenolith from the crater Kazimiro, which contains the fresh primary high-Mg olivine with inclusions of Cr-spinel that had not been previously identified in this area. The different composition of phenocryst and xenolith minerals indicates that the studied xenoliths are not сumulus of enclosing magma, but the composition of xenoliths characterizes the lithology of the upper mantle of the area. The carbonate melt inclusions in olivine Fo90 demonstrate the existence of primary carbonatitic magmas in Bunyaruguru upper mantle. The results of texture and chemical investigation of the xenolith minerals indicate the time sequence of metasomatic alteration of Bunyaruguru upper mantle: MARID metasomatism at the first stage followed by carbonate metasomatism. The abundances of REE in perovskites from kamafugite are 2-4 times higher than similar values for xenolith. Therefore the kamafugite magma was been generated from a more enriched mantle source than the source of the xenoliths. The evaluation of P-T conditions formation of clinopyroxene xenolith revealed the range of pressure 20-65 kbar and the temperatures range 830-1040 °C. The pressure of clinopyroxene phenocryst

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

    Science.gov (United States)

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

    2015-12-01

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

  8. Large-scale global convection in the mantle beneath Australia from 55 Ma to now

    International Nuclear Information System (INIS)

    Zhang, M.

    1999-01-01

    Full text: The global-scale mantle convection cells in the asthenosphere are not geochemically homogeneous. The heterogeneity is most prominently reflected in the isotopic compositions (Pb-Sr-Nd) of the mid-ocean ridge basalts (MORB) that are direct partial melts from the underlying asthenosphere. Of particular relevance to Australia's geodynamic evolution from about 100 million years, are the distinctive geochemical signatures of the asthenosphere beneath the Pacific Ocean (Pacific MORB) and Indian Ocean (Indian MORB). Therefore, delineation of the boundary between the two distinct mantle reservoirs and any change in that boundary with time provide information about the patterns of global-scale asthenospheric mantle convection. This information has also allowed us to track large-scale mantle chemical reservoirs such as the distinctive Gondwana lithospheric mantle, and hence better understand the geodynamic evolution of the Australian continent from the time of Gondwana dispersal. Pb-Sr-Nd isotope data for Cenozoic basalts in eastern Australia (Zhang et al, 1999) indicate that Pacific-MORB type isotopic signatures characterise the lava-field basalts (55-14 Ma) in southeastern Australia, whereas Indian-MORB type isotopic signatures characterise younger basalts (6-0 Ma) from northeastern Australia. This discovery helps to constrain the changing locus of the major asthenospheric mantle convection cells represented by the Pacific and Indian MORB sources during and following the breakup of the eastern part of Gondwana, and locates, for the first time, the boundary of these convection cells beneath the Australian continent. This extends previous work in the SW Pacific back-arc basins (eg Hickey-Vargas et al., 1995) and the Southern Ocean (Lanyon et al., 1995) that indicates that the 1- and P-MORB mantle convection cells have been moving in opposite directions since the early Tertiary. These new data also indicate that the Indian-MORB source is a long-term asthenospheric

  9. Mantle Serpentinization near the Central Mariana Trench Constrained by Ocean Bottom Surface Wave Observations

    Science.gov (United States)

    Cai, C.; Wiens, D. A.; Lizarralde, D.; Eimer, M. O.; Shen, W.

    2017-12-01

    . Assuming the velocity anomaly remaining in the subducting plate mantle is caused by serpentinization, calculations suggest the top 20 km of the slab mantle retains 10-15% serpentinization beyond the outer forearc. The amount of water carried into the deep mantle by this layer ( 54 Tg/Myr/m) is two to three times greater than previous estimates for the entire slab.

  10. Core-mantle differentiation in Mars

    NARCIS (Netherlands)

    Rai, N.; van Westrenen, W.

    2013-01-01

    The physical and chemical conditions under which Martian core formation took place are not well constrained. We modeled the pressure, temperature, and oxygen fugacity conditions under which it would be possible to match the inferred depletions of moderately siderophile elements Ni, Co, W, Mo, Ga, P,

  11. Operation of heavily irradiated silicon detectors in non-depletion mode

    CERN Document Server

    Verbitskaya, E; Ilyashenko, Yu S; Li, Z; Härkönen, J; Tuovinen, E; Luukka, Panja

    2006-01-01

    The non-depletion detector operation mode has generally been disregarded as an option in high-energy physics experiments. In this paper, the non-depletion operation is examined by detailed analysis of the electric field distribution and the current pulse response of heavily irradiated silicon (Si) detectors. The previously reported model of double junction in heavily irradiated Si detector is further developed and a simulation of the current pulse response has been performed. It is shown that detectors can operate in a non-depletion mode due to the fact that the value of the electric field in a non-depleted region is high enough for efficient carrier drift. This electric field originates from the current flow through the detector and a consequent drop of the potential across high-resistivity bulk of a non-depleted region. It is anticipated that the electric field in a non-depleted region, which is still electrically neutral, increases with fluence that improves the non-depleted detector operation. Considerati...

  12. 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

    conducted in 2014, we have recovered instruments from all sites except only one site (NM03) where a few EM instruments were left and are to be retrieved in September, 2015. The seafloor age difference between study areas A and B is only about 10 Ma, which was thought small enough for the temperature difference between two areas to be ignored at the first order approximation. So we originally expected that corresponding results in area B show close similarity to those in are A. However, a result of 1-D array analysis of the surface waves indicated substantial difference in the lithosphere-asthenosphere structure between areas A and B. 1-D inversion results of multi-station seafloor magnetotelluric (MT) data also show a certain difference between these two areas. Furthermore, MT results in surrounding areas obtained by previous projects imply the presence of further significant heterogeneity in the old oceanic mantle in the northwestern Pacific toward the subduction zone. For the moment, we are trying to invert each of NOMan geophysical dataset as accurately as possible so as to characterize the mantle structure and its lateral variation. Later we try to clarify the cause for these lateral variabilities, as it can be one of the key issues to understand the lithosphere-asthenosphere system in the old oceanic mantle. For the key question (b), high-quality data obtained by the long-term seafloor observations are used to investigate the MTZ structure. In particular, electric field data obtained by EFOS (with 2 km electrode separation) provide longer period MT responses sensitive to the MTZ. Resulting MT and GDS (Geomagnetic Deep sounding) responses are almost consistent with the NW Pacific semi-global 1-D model (Shimizu et al., 2010). This indicates that the MTZ conductivity below the study region has weak lateral variation (well approximated by a 1-D model) and is also consistent with the conductivity of MTZ minerals containing at most 0.1-0.5 wt.% water.

  13. Depletion sensitivity predicts unhealthy snack purchases.

    Science.gov (United States)

    Salmon, Stefanie J; Adriaanse, Marieke A; Fennis, Bob M; De Vet, Emely; De Ridder, Denise T D

    2016-01-01

    The aim of the present research is to examine the relation between depletion sensitivity - a novel construct referring to the speed or ease by which one's self-control resources are drained - and snack purchase behavior. In addition, interactions between depletion sensitivity and the goal to lose weight on snack purchase behavior were explored. Participants included in the study were instructed to report every snack they bought over the course of one week. The dependent variables were the number of healthy and unhealthy snacks purchased. The results of the present study demonstrate that depletion sensitivity predicts the amount of unhealthy (but not healthy) snacks bought. The more sensitive people are to depletion, the more unhealthy snacks they buy. Moreover, there was some tentative evidence that this relation is more pronounced for people with a weak as opposed to a strong goal to lose weight, suggesting that a strong goal to lose weight may function as a motivational buffer against self-control failures. All in all, these findings provide evidence for the external validity of depletion sensitivity and the relevance of this construct in the domain of eating behavior. Copyright © 2015 Elsevier Ltd. All rights reserved.

  14. Taurine depletion alters vascular reactivity in rats.

    Science.gov (United States)

    Abebe, Worku; Mozaffari, Mahmood S

    2003-09-01

    We recently showed that chronic taurine supplementation is associated with attenuation of contractile responses of rat aorta to norepinephrine and potassium chloride. However, the potential involvement of endogenous taurine in modulation of vascular reactivity is not known. Therefore, we examined the effect of beta-alanine-induced taurine depletion on the in vitro reactivity of rat aorta to selected vasoactive agents. The data indicate that both norepinephrine- and potassium-chloride-induced maximum contractile responses of endothelium-denuded aortae were enhanced in taurine-depleted rats compared with control animals. However, taurine depletion did not affect tissue sensitivity to either norepinephrine or potassium chloride. By contrast, sensitivity of the endothelium-denuded aortae to sodium nitroprusside was attenuated by taurine depletion. Similarly, taurine deficiency reduced the relaxant responses of endothelium-intact aortic rings elicited by submaximal concentrations of acetylcholine, and this effect was associated with decreased nitric oxide production. Taken together, the data suggest that taurine depletion augments contractility but attenuates relaxation of vascular smooth muscle in a nonspecific manner. Impairment of endothelium-dependent responses, which is at least in part associated with reduced nitric oxide generation, may contribute to the attenuation of the vasorelaxant responses. These vascular alterations could be of potential consequence in pathological conditions associated with taurine deficiency.

  15. Groundwater depletion embedded in international food trade

    Science.gov (United States)

    Dalin, Carole; Wada, Yoshihide; Kastner, Thomas; Puma, Michael J.

    2017-03-01

    Recent hydrological modelling and Earth observations have located and quantified alarming rates of groundwater depletion worldwide. This depletion is primarily due to water withdrawals for irrigation, but its connection with the main driver of irrigation, global food consumption, has not yet been explored. Here we show that approximately eleven per cent of non-renewable groundwater use for irrigation is embedded in international food trade, of which two-thirds are exported by Pakistan, the USA and India alone. Our quantification of groundwater depletion embedded in the world’s food trade is based on a combination of global, crop-specific estimates of non-renewable groundwater abstraction and international food trade data. A vast majority of the world’s population lives in countries sourcing nearly all their staple crop imports from partners who deplete groundwater to produce these crops, highlighting risks for global food and water security. Some countries, such as the USA, Mexico, Iran and China, are particularly exposed to these risks because they both produce and import food irrigated from rapidly depleting aquifers. Our results could help to improve the sustainability of global food production and groundwater resource management by identifying priority regions and agricultural products at risk as well as the end consumers of these products.

  16. Early mantle differentiation: constraint from {sup 146}Sm-{sup 142}Nd systematics; Radioactivite eteinte du {sup 146}Sm et differenciation precoce du manteau terrestre

    Energy Technology Data Exchange (ETDEWEB)

    Caro, G

    2005-07-15

    We present new ultra-high precision {sup 142}Nd/{sup 144}Nd measurements of early Archaean rocks using the new generation thermal ionization mass spectrometer TRITON. Repeated measurements of the Ames Nd standard demonstrate that the {sup 142}Nd/{sup 144}Nd ratio can be determined with external precision of 2 ppm (2s), allowing confident resolution of anomalies as small as 5 ppm. A major analytical improvement lies in the elimination of the double normalization procedure required to correct our former measurements from a secondary mass fractionation effect. Our new results indicate that metasediments, meta-basalts and orthogneisses from the 3.6 - 3.8 Ga West Greenland craton display positive {sup 142}Nd anomalies ranging from 8 to 15 ppm. Using a simple two-stage model with initial e{sup 143}Nd value of 1.9 {+-} 0.6 e-units, coupled {sup 147}Sm-{sup 143}Nd and {sup 146}Sm-{sup 142}Nd chronometry constrains mantle differentiation to 50 to 200 Ma after formation of the solar system. This chronological constraint is consistent with differentiation of the Earth's mantle during the late stage of crystallization of a magma ocean. We have developed a two-box model describing {sup 142}Nd and {sup 143}Nd isotopic evolution of depleted mantle during the subsequent evolution of the crust-mantle system. Our results indicate that early terrestrial proto-crust had a lifetime of ca. 500 Ma in order to produce the observed Nd isotope signature of Archaean rocks. In the context of this two box mantle-crust system, we model the evolution of isotopic and chemical heterogeneity of depleted mantle as a function of the mantle stirring time. Using the dispersion of {sup 142}Nd/{sup 144}Nd and {sup 143}Nd/{sup 144}Nd ratios observed in early Archaean rocks, we constrain the stirring time of early Earth's mantle to 100 - 150 Ma, a factor of 5 to 10 shorter than stirring time inferred from modern oceanic basalts. (author)

  17. 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.

  18. A two-component mantle source feeding Mt. Etna magmatism: Insights from the geochemistry of primitive magmas

    Science.gov (United States)

    Correale, Alessandra; Paonita, Antonio; Martelli, Mauro; Rizzo, Andrea; Rotolo, Silvio G.; Corsaro, Rosa Anna; Di Renzo, Valeria

    2014-01-01

    The major elements, trace elements and Sr and Nd isotopes of selected Etnean primitive rocks (Y versus La/Yb), can be attributed to varying degrees of melting of a common mantle source. Numerical simulations performed with the MELTS program allowed the melting percentages associated with each product to be estimated. This led us to recalculate the hypothetical parental trace-element content of the Etnean mantle source, which was common to all of the investigated rocks. The characteristics of the Sr, Nd and He isotopes confirmed the primitive nature of the rocks, with the most-depleted and primitive lava being that of Mt. Spagnolo (SPA; 143Nd/144Nd = 0.512908 87Sr/86Sr = 0.703317-0.703325 and 3He/4He = 7.6 Ra), and highlighted the similarity of the mantle sources feeding the volcanic activity of Mt. Etna and the Hyblean Plateau (a region to the south of Mt. Etna and characterized by older magmatism than Mt. Etna). The coupling of noble gases and trace elements suggests an origin for the investigated Etnean lavas from melting of a Hyblean-like mantle, consisting of a two-component source where a peridotitic matrix is veined by 10% pyroxenite. A variable degree of mantle contamination by crustal-like fluids, probably related to subduction, is proposed to explain the higher Sr-isotope and lower Nd-isotope values in some rocks (143Nd/144Nd up to 0.512865 and 87Sr/86Sr up to 0.703707). This process probably occurred in the source prior to magma generation, refertilizing some portions of the mantle. Accordingly, the estimated degree of melting responsible for each magma appears to be related to its 87Sr/86Sr enrichment. In contrast, the decoupling between 3He/4He and 87Sr/86Sr ratios requires the occurrence in the crustal reservoirs of further processes capable of shifting the He isotope ratio towards slightly more radiogenic values, such as magma aging or a contribution of shallow fluid. Therefore, different residence times in the Etnean reservoir and/or various rates of

  19. Sensibility analysis of fuel depletion using different nuclear fuel depletion codes

    Energy Technology Data Exchange (ETDEWEB)

    Martins, F.; Velasquez, C.E.; Castro, V.F.; Pereira, C.; Silva, C. A. Mello da, E-mail: felipmartins94@gmail.com, E-mail: carlosvelcab@hotmail.com, E-mail: victorfariascastro@gmail.com, E-mail: claubia@nuclear.ufmg.br, E-mail: clarysson@nuclear.ufmg.br [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Departamento de Engenharia Nuclear

    2017-07-01

    Nowadays, the utilization of different nuclear codes to perform the depletion and criticality calculations has been used to simulated nuclear reactors problems. Therefore, the goal is to analyze the sensibility of the fuel depletion of a PWR assembly using three different nuclear fuel depletion codes. The burnup calculations are performed using the codes MCNP5/ORIGEN2.1 (MONTEBURNS), KENO-VI/ORIGEN-S (TRITONSCALE6.0) and MCNPX (MCNPX/CINDER90). Each nuclear code performs the burnup using different depletion codes. Each depletion code works with collapsed energies from a master library in 1, 3 and 63 groups, respectively. Besides, each code uses different ways to obtain neutron flux that influences the depletions calculation. The results present a comparison of the neutronic parameters and isotopes composition such as criticality and nuclides build-up, the deviation in results are going to be assigned to features of the depletion code in use, such as the different radioactive decay internal libraries and the numerical method involved in solving the coupled differential depletion equations. It is also seen that the longer the period is and the more time steps are chosen, the larger the deviation become. (author)

  20. Ozone depletion and chlorine loading potentials

    Science.gov (United States)

    Pyle, John A.; Wuebbles, Donald J.; Solomon, Susan; Zvenigorodsky, Sergei; Connell, Peter; Ko, Malcolm K. W.; Fisher, Donald A.; Stordal, Frode; Weisenstein, Debra

    1991-01-01

    The recognition of the roles of chlorine and bromine compounds in ozone depletion has led to the regulation or their source gases. Some source gases are expected to be more damaging to the ozone layer than others, so that scientific guidance regarding their relative impacts is needed for regulatory purposes. Parameters used for this purpose include the steady-state and time-dependent chlorine loading potential (CLP) and the ozone depletion potential (ODP). Chlorine loading potentials depend upon the estimated value and accuracy of atmospheric lifetimes and are subject to significant (approximately 20-50 percent) uncertainties for many gases. Ozone depletion potentials depend on the same factors, as well as the evaluation of the release of reactive chlorine and bromine from each source gas and corresponding ozone destruction within the stratosphere.

  1. Self-regulation, ego depletion, and inhibition.

    Science.gov (United States)

    Baumeister, Roy F

    2014-12-01

    Inhibition is a major form of self-regulation. As such, it depends on self-awareness and comparing oneself to standards and is also susceptible to fluctuations in willpower resources. Ego depletion is the state of reduced willpower caused by prior exertion of self-control. Ego depletion undermines inhibition both because restraints are weaker and because urges are felt more intensely than usual. Conscious inhibition of desires is a pervasive feature of everyday life and may be a requirement of life in civilized, cultural society, and in that sense it goes to the evolved core of human nature. Intentional inhibition not only restrains antisocial impulses but can also facilitate optimal performance, such as during test taking. Self-regulation and ego depletion- may also affect less intentional forms of inhibition, even chronic tendencies to inhibit. Broadly stated, inhibition is necessary for human social life and nearly all societies encourage and enforce it. Copyright © 2014 Elsevier Ltd. All rights reserved.

  2. Acute tryptophan depletion in humans: a review of theoretical, practical and ethical aspects

    Science.gov (United States)

    Young, Simon N.

    2013-01-01

    The acute tryptophan depletion (ATD) technique has been used extensively to study the effect of low serotonin in the human brain. This review assesses the validity of a number of published criticisms of the technique and a number of previously unpublished potential criticisms. The conclusion is that ATD can provide useful information when results are assessed in conjunction with results obtained using other techniques. The best-established conclusion is that low serotonin function after tryptophan depletion lowers mood in some people. However, this does not mean that other variables, altered after tryptophan depletion, are necessarily related to low serotonin. Each aspect of brain function has to be assessed separately. Furthermore, a negative tryptophan depletion study does not mean that low serotonin cannot influence the variable studied. This review suggests gaps in knowledge that need to be filled and guidelines for carrying out ATD studies. PMID:23428157

  3. Sweetened blood sweetens behavior. Ego depletion, glucose, guilt, and prosocial behavior.

    Science.gov (United States)

    Xu, Hanyi; Bègue, Laurent; Sauve, Laure; Bushman, Brad J

    2014-10-01

    Although guilt feels bad to the individual, it is good for society because guilty feelings can prompt people to perform good deeds. Previous research shows that fatigue decreases guilty feelings and helpful behavior. This present research tests whether glucose restores guilty feelings and increases helpful behavior. Depleted participants watched a movie about butchering animals for their meat or skin and were told to express no emotions, whereas non-depleted participants watched the same movie, but could express their emotions. Afterwards they drank a glucose or placebo beverage. Having participants play a game in which another person was punished for their errors induced guilt. Finally, participants played a dictator game in which they could leave lottery tickets for the next participant. Depleted participants felt less guilty and helped less than non-depleted participants, and those who consumed a placebo beverage felt less guilt and helped less than those who consumed a glucose beverage. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. Electromagnetic exploration of the oceanic mantle.

    Science.gov (United States)

    Utada, Hisashi

    2015-01-01

    Electromagnetic exploration is a geophysical method for examining the Earth's interior through observations of natural or artificial electromagnetic field fluctuations. The method has been in practice for more than 70 years, and 40 years ago it was first applied to ocean areas. During the past few decades, there has been noticeable progress in the methods of instrumentation, data acquisition (observation), data processing and inversion. Due to this progress, applications of this method to oceanic regions have revealed electrical features of the oceanic upper mantle down to depths of several hundred kilometers for different geologic and tectonic environments such as areas around mid-oceanic ridges, areas around hot-spot volcanoes, subduction zones, and normal ocean areas between mid-oceanic ridges and subduction zones. All these results estimate the distribution of the electrical conductivity in the oceanic mantle, which is key for understanding the dynamics and evolution of the Earth together with different physical properties obtained through other geophysical methods such as seismological techniques.

  5. Volcanism on Mercury (dikes, lava flows, pyroclastics): Crust/mantle density contrasts, the evolution of compressive stress and the presence of mantle volatiles

    Science.gov (United States)

    Wilson, L.; Head, J. W., III

    2008-09-01

    have assumed a series of permutations of crustal density, crustal thickness, mantle density, magma density, source depth in mantle of melt generation, and crustal compressive stress, and investigated which permutations will allow the transfer of magma from source to surface. With so many variables it is easiest to illustrate the results by choosing one set of densities and varying the depths and stresses. We begin with crustal density of 2700 kg m-3, a mantle density of 3400 kg m-3 and a melt density of 3000 kg m-3. Table 1 then shows, as a function of the thickness of the crust (Hc), the minimum depth below the surface (Hm) from which mantle melts must be derived if their positive buoyancy in the mantle is to just compensate for their negative buoyancy in the crust and so enable them to reach the surface and erupt. For the values of Hm in Table 1 to be valid, the stress conditions in the crust must be such that a dike can remain open at all depths. However, this may not be possible in the presence of a horizontal compressive stress. The third and fourth columns of the table show the maximum horizontal compressive stress allowed if a dike is to remain open when the compressive stress is either uniform, i.e. the same at all depths in the crust (Su), or variable, specifically decreasing from the value given (Sv) at the surface to zero at the base of the crust. We now increase the crustal density slightly to 2800 kg m-3 but keep the mantle and melt densities the same. The results in Table 2 show, as expected, that the reduced amount of negative buoyancy of magma in the crust means that mantle melt sources need not be quite as deep as before. However, if a pathway is to remain open at all depths, significantly smaller compressive stresses are needed than in the previous case. Implications: This comparison demonstrates the major trend that we find: as the crust becomes denser it is easier, in terms of magma buoyancy alone, to erupt magma from a given depth in the mantle

  6. The Mineralogical Record of Oxygen Fugacity Variation and Alteration in Northwest Africa 8159: Evidence for Interaction Between a Mantle Derived Martian Basalt and a Crustal Component(s)

    Science.gov (United States)

    Shearer, Charles K.; Burger, Paul V.; Bell, Aaron S.; McCubbin, Francis M.; Agee, Carl; Simon, Justin I.; Papike, James J.

    2015-01-01

    A prominent geochemical feature of basaltic magmatism on Mars is the large range in initial Sr isotopic ratios (approx. 0.702 - 0.724) and initial epsilon-Nd values (approx. -10 to greater than +50). Within this range, the shergottites fall into three discreet subgroups. These subgroups have distinct bulk rock REE patterns, mineral chemistries (i.e. phosphate REE patterns, Ni, Co, V in olivine), oxygen fugacity of crystallization, and stable isotopes, such as O. In contrast, nakhlites and chassignites have depleted epsilon-Nd values (greater than or equal to +15), have REE patterns that are light REE enriched, and appear to have crystallized near the FMQ buffer. The characteristics of these various martian basalts have been linked to different reservoirs in the martian crust and mantle, and their interactions during the petrogenesis of these magmas. These observations pose interesting interpretive challenges to our understanding of the conditions of the martian mantle (e.g. oxygen fugacity) and the interaction of mantle derived magmas with the martian crust and surface. Martian meteorite NWA 8159 is a unique fine-grained augite basalt derived from a highly depleted mantle source as reflected in its initial epsilon-Nd value, contains a pronounced light REE depleted pattern, and crystallized presumably under very oxidizing conditions. Although considerably older than both shergottites and nahklites, it has been petrogenetically linked to both styles of martian magmatism. These unique characteristics of NWA 8159 may provide an additional perspective for deciphering the petrogenesis of martian basalts and the nature of the crust of Mars.

  7. Depleted uranium hexafluoride: Waste or resource?

    International Nuclear Information System (INIS)

    Schwertz, N.; Zoller, J.; Rosen, R.; Patton, S.; Bradley, C.; Murray, A.

    1995-07-01

    The US Department of Energy is evaluating technologies for the storage, disposal, or re-use of depleted uranium hexafluoride (UF 6 ). This paper discusses the following options, and provides a technology assessment for each one: (1) conversion to UO 2 for use as mixed oxide duel, (2) conversion to UO 2 to make DUCRETE for a multi-purpose storage container, (3) conversion to depleted uranium metal for use as shielding, (4) conversion to uranium carbide for use as high-temperature gas-cooled reactor (HTGR) fuel. In addition, conversion to U 3 O 8 as an option for long-term storage is discussed

  8. Elasticity and clustering in concentrated depletion gels.

    Science.gov (United States)

    Ramakrishnan, S; Chen, Y-L; Schweizer, K S; Zukoski, C F

    2004-10-01

    X-ray scattering and rheology are employed to study the volume fraction dependence of the collective structure and elastic moduli of concentrated nanoparticle-polymer depletion gels. The nonequilibrium gel structure consists of locally densified nonfractal clusters and narrow random interfaces. The elastic moduli display a power law dependence on volume fraction with effective exponents that decrease with increasing depletion attraction strength. A microscopic theory that combines local structural information with a dynamic treatment of gelation is in good agreement with the observations.

  9. Depletion of selenium in blood, liver and muscle from beef heifers previously fed forages containing high levels of selenium.

    Science.gov (United States)

    Benes, Sharon E; Robinson, Peter H; Cun, Grace S

    2015-12-01

    Beef heifers which had grazed 'Jose' tall wheatgrass (TWG; Thinopyrum ponticum var. 'Jose'; 10 heifers) and creeping wildrye (CWR; Leymus triticoides var. 'Rio'; 10 heifers) with high levels of Se (>2 mg/kg DM) due to growth in saline soils, accumulated high Se levels in blood, liver and muscle (Juchem et al., 2012). We determined the decrease in Se levels in blood, liver and muscle from these heifers, particularly the decrease of Se in muscle, in order to determine the maximum feeding length of a low Se diet (LSeD) required sustaining Se-enriched beef. Immediately after grazing, all heifers were fed a LSeD containing forages with high Se levels can result in Se-enriched beef, but a LSeD feeding period of <82 d is required to maintain enrichment. Copyright © 2015. Published by Elsevier B.V.

  10. Crust and Upper Mantle Structure of Antarctica from Rayleigh Wave Tomography

    Science.gov (United States)

    Wiens, D. A.; Heeszel, D. S.; Sun, X.; Chaput, J. A.; Aster, R. C.; Nyblade, A.; Anandakrishnan, S.; Wilson, T. J.; Huerta, A. D.

    2012-12-01

    We combine data from three temporary arrays of seismometers (AGAP/GAMSEIS 2007-2010, ANET/POLENET 2007-2012, TAMSEIS 2001-2003) deployed across Antarctica, along with permanent stations in the region, to produce a large scale shear velocity model of the continent extending from the Gamburtsev Subglacial Mountains (GSM) in East Antarctica, across the Transantarctic Mountains (TAM) and West Antarctic Rift System (WARS) to Marie Byrd Land (MBL) in West Antarctica. Our combined dataset consists of Rayleigh wave phase and amplitude measurements from 112 stations across the study region. We first invert for 2-D Rayleigh wave phase velocities using the two-plane wave method. These results are then inverted for shear velocity structure using crustal thicknesses derived from ambient noise tomography and teleseismic receiver functions. We refine our shear velocity model by performing a Monte Carlo simulation that explores the tradeoff between crustal thickness and upper mantle seismic velocities. The resulting model is higher resolution than previous studies (~150 km resolution length) and highlights significant differences in crustal and uppermost mantle structure between East and West Antarctica in greater detail than previously possible. East Antarctica is underlain by thick crust (reaching ~55 km beneath the GSM) and fast, cratonic lithosphere. West Antarctica is defined by thinner crust and slow upper mantle velocities indicative of its more recent tectonic activity. The observed boundary in crustal thickness closely follows the TAM front. MBL is underlain by a thicker lithosphere than that observed beneath the WARS, but slow mantle velocities persist to depths greater than 200 km, indicating a 'deep seated' (i.e. deeper than the deepest resolvable features of our model) thermal source for volcanism in the region. The slowest seismic velocities at shallow depths are observed in the Terror Rift region of the Ross Sea along an arc following the TAM front, where the most

  11. The behaviour of platelets in natural diamonds and the development of a new mantle thermometer

    Science.gov (United States)

    Speich, L.; Kohn, S. C.; Bulanova, G. P.; Smith, C. B.

    2018-05-01

    Platelets are one of the most common defects occurring in natural diamonds but their behaviour has not previously been well understood. Recent technical advances, and a much improved understanding of the correct interpretation of the main infrared (IR) feature associated with platelets (Speich et al. 2017), facilitated a systematic study of platelets in 40 natural diamonds. Three different types of platelet behaviour were identified here. Regular diamonds show linear correlations between both B-centre concentrations and platelet density and also between platelet size and platelet density. Irregular diamonds display reduced platelet density due to platelet breakdown, anomalously large or small platelets and a larger platelet size distribution. These features are indicative of high mantle storage temperatures. Finally, a previously unreported category of subregular diamonds is defined. These diamonds experienced low mantle residence temperatures and show smaller than expected platelets. Combining the systematic variation in platelet density with temperatures of mantle storage, determined by nitrogen aggregation, we can demonstrate that platelet degradation proceeds at a predictable rate. Thus, in platelet-bearing diamonds where N aggregation is complete, an estimate of annealing temperature can now be made for the first time.

  12. Reversible stress softening of collagen based networks from the jumbo squid mantle (Dosidicus gigas)

    International Nuclear Information System (INIS)

    Torres, F.G.; Troncoso, O.P.; Rivas, E.R.; Gomez, C.G.; Lopez, D.

    2014-01-01

    Dosidicus gigas is the largest and one of the most abundant jumbo squids in the eastern Pacific Ocean. In this paper we have studied the muscle of the mantle of D. gigas (DGM). Morphological, thermal and rheological properties were assessed by means of atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, thermogravimetry and oscillatory rheometry. This study allowed us to assess the morphological and rheological properties of a collagen based network occurring in nature. The results showed that the DGM network displays a nonlinear effect called reversible stress softening (RSS) that has been previously described for other types of biological structures such as naturally occurring cellulose networks and actin networks. We propose that the RSS could play a key role on the way jumbo squids withstand hydrostatic pressure. The results presented here confirm that this phenomenon occurs in a wider number of materials than previously thought, all of them exhibiting different size scales as well as physical conformation. - Highlights: • We studied the structure property relationships of the jumbo squid mantle. • Rheological tests showed that such a mantle exhibits reversible stress softening (RSS). • RSS could also play a role on the way jumbo squids withstand hydrostatic pressure

  13. Reversible stress softening of collagen based networks from the jumbo squid mantle (Dosidicus gigas)

    Energy Technology Data Exchange (ETDEWEB)

    Torres, F.G., E-mail: fgtorres@pucp.edu.pe [Department of Mechanical Engineering, Catholic University of Peru, Lima 32 (Peru); Troncoso, O.P.; Rivas, E.R. [Department of Mechanical Engineering, Catholic University of Peru, Lima 32 (Peru); Gomez, C.G. [Departament de Química Física and Institut de Ciencia dels Materials, Universitat de València, Dr. Moliner 50, Burjassot, E-46100 Valencia (Spain); Lopez, D. [Instituto de Ciencia y Tecnología de Polímeros, C.S.I.C., Calle Juan de la Cierva 3, 28006 Madrid (Spain)

    2014-04-01

    Dosidicus gigas is the largest and one of the most abundant jumbo squids in the eastern Pacific Ocean. In this paper we have studied the muscle of the mantle of D. gigas (DGM). Morphological, thermal and rheological properties were assessed by means of atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, thermogravimetry and oscillatory rheometry. This study allowed us to assess the morphological and rheological properties of a collagen based network occurring in nature. The results showed that the DGM network displays a nonlinear effect called reversible stress softening (RSS) that has been previously described for other types of biological structures such as naturally occurring cellulose networks and actin networks. We propose that the RSS could play a key role on the way jumbo squids withstand hydrostatic pressure. The results presented here confirm that this phenomenon occurs in a wider number of materials than previously thought, all of them exhibiting different size scales as well as physical conformation. - Highlights: • We studied the structure property relationships of the jumbo squid mantle. • Rheological tests showed that such a mantle exhibits reversible stress softening (RSS). • RSS could also play a role on the way jumbo squids withstand hydrostatic pressure.

  14. Continental smokers couple mantle degassing and distinctive microbiology within continents

    Science.gov (United States)

    Crossey, Laura J.; Karlstrom, Karl E.; Schmandt, Brandon; Crow, Ryan R.; Colman, Daniel R.; Cron, Brandi; Takacs-Vesbach, Cristina D.; Dahm, Clifford N.; Northup, Diana E.; Hilton, David R.; Ricketts, Jason W.; Lowry, Anthony R.

    2016-02-01

    The discovery of oceanic black (and white) smokers revolutionized our understanding of mid-ocean ridges and led to the recognition of new organisms and ecosystems. Continental smokers, defined here to include a broad range of carbonic springs, hot springs, and fumaroles that vent mantle-derived fluids in continental settings, exhibit many of the same processes of heat and mass transfer and ecosystem niche differentiation. Helium isotope (3He/4He) analyses indicate that widespread mantle degassing is taking place in the western U.S.A., and that variations in mantle helium values correlate best with low seismic-velocity domains in the mantle and lateral contrasts in mantle velocity rather than crustal parameters such as GPS, proximity to volcanoes, crustal velocity, or composition. Microbial community analyses indicate that these springs can host novel microorganisms. A targeted analysis of four springs in New Mexico yield the first published occurrence of chemolithoautotrophic Zetaproteobacteria in a continental setting. These observations lead to two linked hypotheses: that mantle-derived volatiles transit through conduits in extending continental lithosphere preferentially above and at the edges of mantle low velocity domains. High CO2 and other constituents ultimately derived from mantle volatiles drive water-rock interactions and heterogeneous fluid mixing that help structure diverse and distinctive microbial communities.

  15. 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

  16. 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

  17. Influencing parameters on performance of a mantle heat exchanger ...

    African Journals Online (AJOL)

    The experiments arte simulated and validated by using CFD tool ANSYS-CFX and a good agreement is obtained between experiments and simulations. The objective of this paper is to investigate the influence of location of hot fluid inlet, mass flow rate of mantle fluid and type of hot fluid on the performance of the mantle ...

  18. Upper-mantle P- and S- wave velocities across the Northern Tornquist Zone from traveltime tomography

    DEFF Research Database (Denmark)

    Hejrani, Babak; Balling, N.; Jacobsen, B. H.

    2015-01-01

    This study presents P- and S-wave velocity variations for the upper mantle in southern Scandinavia and northern Germany based on teleseismic traveltime tomography. Tectonically, this region includes the entire northern part of the prominent Tornquist Zone which follows along the transition from old...... wave and ±2 s for S wave, with early arrivals in shield areas of southern Sweden and later arrivals in the Danish and North German Basins, as well as in most of southern Norway. In good accordance with previous, mainly P-velocity models, a marked upper-mantle velocity boundary (UMVB) is accurately...... pronounced in our new S-velocity model, with velocity contrasts of up to ±2–3 per cent. It is also clearly reflected in the VP/VS ratio. Differences in this ratio of up to about ±2 per cent are observed across the boundary, with generally low values in shield areas to the east and relatively higher values...

  19. Asymmetric three-dimensional topography over mantle plumes.

    Science.gov (United States)

    Burov, Evgueni; Gerya, Taras

    2014-09-04

    The role of mantle-lithosphere interactions in shaping surface topography has long been debated. In general, it is supposed that mantle plumes and vertical mantle flows result in axisymmetric, long-wavelength topography, which strongly differs from the generally asymmetric short-wavelength topography created by intraplate tectonic forces. However, identification of mantle-induced topography is difficult, especially in the continents. It can be argued therefore that complex brittle-ductile rheology and stratification of the continental lithosphere result in short-wavelength modulation and localization of deformation induced by mantle flow. This deformation should also be affected by far-field stresses and, hence, interplay with the 'tectonic' topography (for example, in the 'active/passive' rifting scenario). Testing these ideas requires fully coupled three-dimensional numerical modelling of mantle-lithosphere interactions, which so far has not been possible owing to the conceptual and technical limitations of earlier approaches. Here we present new, ultra-high-resolution, three-dimensional numerical experiments on topography over mantle plumes, incorporating a weakly pre-stressed (ultra-slow spreading), rheologically realistic lithosphere. The results show complex surface evolution, which is very different from the smooth, radially symmetric patterns usually assumed as the canonical surface signature of mantle upwellings. In particular, the topography exhibits strongly asymmetric, small-scale, three-dimensional features, which include narrow and wide rifts, flexural flank uplifts and fault structures. This suggests a dominant role for continental rheological structure and intra-plate stresses in controlling dynamic topography, mantle-lithosphere interactions, and continental break-up processes above mantle plumes.

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

    Science.gov (United States)

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

    2015-01-01

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

  1. Mercury's Solar Wind Interaction as Characterized by Magnetospheric Plasma Mantle Observations With MESSENGER

    Science.gov (United States)

    Jasinski, Jamie M.; Slavin, James A.; Raines, Jim M.; DiBraccio, Gina A.

    2017-12-01

    We analyze 94 traversals of Mercury's southern magnetospheric plasma mantle using data from the MESSENGER spacecraft. The mean and median proton number densities in the mantle are 1.5 and 1.3 cm-3, respectively. For sodium number density these values are 0.004 and 0.002 cm-3. Moderately higher densities are observed on the magnetospheric dusk side. The mantle supplies up to 1.5 × 108 cm-2 s-1 and 0.8 × 108 cm-2 s-1 of proton and sodium flux to the plasma sheet, respectively. We estimate the cross-electric magnetospheric potential from each observation and find a mean of 19 kV (standard deviation of 16 kV) and a median of 13 kV. This is an important result as it is lower than previous estimations and shows that Mercury's magnetosphere is at times not as highly driven by the solar wind as previously thought. Our values are comparable to the estimations for the ice giant planets, Uranus and Neptune, but lower than Earth. The estimated potentials do have a very large range of values (1-74 kV), showing that Mercury's magnetosphere is highly dynamic. A correlation of the potential is found to the interplanetary magnetic field (IMF) magnitude, supporting evidence that dayside magnetic reconnection can occur at all shear angles at Mercury. But we also see that Mercury has an Earth-like magnetospheric response, favoring -BZ IMF orientation. We find evidence that -BX orientations in the IMF favor the southern cusp and southern mantle. This is in agreement with telescopic observations of exospheric emission, but in disagreement with modeling.

  2. 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.

  3. Serial reversal learning and acute tryptophan depletion

    NARCIS (Netherlands)

    van der Plasse, G.; Feenstra, M.G.P.

    2008-01-01

    Cognitive flexibility (i.e. the ability to adapt goal-directed behaviour in response to changed environmental demands) has repeatedly been shown to depend on the prefrontal cortex (PFC). Recent data from primate studies moreover show that depletion of prefrontal 5-HT impairs reversal learning of

  4. Global Warming: Lessons from Ozone Depletion

    Science.gov (United States)

    Hobson, Art

    2010-01-01

    My teaching and textbook have always covered many physics-related social issues, including stratospheric ozone depletion and global warming. The ozone saga is an inspiring good-news story that's instructive for solving the similar but bigger problem of global warming. Thus, as soon as students in my physics literacy course at the University of…

  5. Seasonal total methane depletion in limestone caves.

    Science.gov (United States)

    Waring, Chris L; Hankin, Stuart I; Griffith, David W T; Kertesz, Michael A; Kobylski, Victoria; Wilson, Neil L; Coleman, Nicholas V; Kettlewell, Graham; Zlot, Robert; Bosse, Michael; Bell, Graham

    2017-08-16

    Methane concentration in caves is commonly much lower than the external atmosphere, yet the cave CH 4 depletion causal mechanism is contested and dynamic links to external diurnal and seasonal temperature cycles unknown. Here, we report a continuous 3-year record of cave methane and other trace gases in Jenolan Caves, Australia which shows a seasonal cycle of extreme CH 4 depletion, from ambient ~1,775 ppb to near zero during summer and to ~800 ppb in winter. Methanotrophic bacteria, some newly-discovered, rapidly consume methane on cave surfaces and in external karst soils with lifetimes in the cave of a few hours. Extreme bacterial selection due to the absence of alternate carbon sources for growth in the cave environment has resulted in an extremely high proportion 2-12% of methanotrophs in the total bacteria present. Unexpected seasonal bias in our cave CH 4 depletion record is explained by a three-step process involving methanotrophy in aerobic karst soil above the cave, summer transport of soil-gas into the cave through epikarst, followed by further cave CH 4 depletion. Disentangling cause and effect of cave gas variations by tracing sources and sinks has identified seasonal speleothem growth bias, with implied palaeo-climate record bias.

  6. Ozone depleting substances management inventory system

    Directory of Open Access Journals (Sweden)

    Felix Ivan Romero Rodríguez

    2018-02-01

    Full Text Available Context: The care of the ozone layer is an activity that contributes to the planet's environmental stability. For this reason, the Montreal Protocol is created to control the emission of substances that deplete the ozone layer and reduce its production from an organizational point of view. However, it is also necessary to have control of those that are already circulating and those present in the equipment that cannot be replaced yet because of the context of the companies that keep it. Generally, the control mechanisms for classifying the type of substances, equipment and companies that own them, are carried in physical files, spreadsheets and text documents, which makes it difficult to control and manage the data stored in them. Method: The objective of this research is to computerize the process of control of substances that deplete the ozone layer. An evaluation and description of all process to manage Ozone-Depleting Substances (ODS, and its alternatives, is done. For computerization, the agile development methodology SCRUM is used, and for the technological solution tools and free open source technologies are used. Result: As a result of the research, a computer tool was developed that automates the process of control and management of substances that exhaust the ozone layer and its alternatives. Conclusions: The developed computer tool allows to control and manage the ozone-depleting substances and the equipment that use them. It also manages the substances that arise as alternatives to be used for the protection of the ozone layer.

  7. Nitrogen depletion in field red giants

    DEFF Research Database (Denmark)

    Masseron, T.; Lagarde, N.; Miglio, A.

    2017-01-01

    , the behaviour of nitrogen data along the evolution confirms the existence of non-canonical extramixing on the red giant branch (RGB) for all low-mass stars in the field. But more surprisingly, the data indicate that nitrogen has been depleted between the RGB tip and the red clump. This may suggest that some...

  8. Calcium isotopic composition of mantle peridotites

    Science.gov (United States)

    Huang, F.; Kang, J.; Zhang, Z.

    2015-12-01

    Ca isotopes are useful to decipher mantle evolution and the genetic relationship between the Earth and chondrites. It has been observed that Ca isotopes can be fractionated at high temperature [1-2]. However, Ca isotopic composition of the mantle peridotites and fractionation mechanism are still poorly constrained. Here, we report Ca isotope composition of 12 co-existing pyroxene pairs in 10 lherzolites, 1 harzburgite, and 1 wehrlite xenoliths collected from Hainan Island (South Eastern China). Ca isotope data were measured on a Triton-TIMS using the double spike method at the Guangzhou Institute of Geochemistry, CAS. The long-term external error is 0.12‰ (2SD) based on repeated analyses of NIST SRM 915a and geostandards. δ44Ca of clinopyroxenes except that from the wehrlite ranges from 0.85‰ to 1.14‰, while opx yields a wide range from 0.98‰ up to 2.16‰. Co-existing pyroxene pairs show large Δ44Caopx-cpx (defined as δ44Caopx-δ44Cacpx) ranging from 0 to 1.23‰, reflecting equilibrium fractionation controlled by variable Ca contents in the opx. Notably, clinopyroxene of wehrlite shows extremely high δ44Ca (3.22‰). δ44Ca of the bulk lherzolites and harzburgites range from 0.86‰ to 1.14‰. This can be explained by extracting melts with slightly light Ca isotopic compositions. Finally, the high δ44Ca of the wehrlite (3.22‰) may reflect metasomatism by melt which has preferentially lost light Ca isotopes due to chemical diffusion during upwelling through the melt channel. [1] Amini et al (2009) GGR 33; [2] Huang et al (2010) EPSL 292.

  9. Geochemical constraints on komatiite volcanism from Sargur Group Nagamangala greenstone belt, western Dharwar craton, southern India: Implications for Mesoarchean mantle evolution and continental growth

    Directory of Open Access Journals (Sweden)

    Tushipokla

    2013-05-01

    Full Text Available We present field, petrographic, major and trace element data for komatiites and komatiite basalts from Sargur Group Nagamangala greenstone belt, western Dharwar craton. Field evidences such as crude pillow structure indicate their eruption in a marine environment whilst spinifex texture reveals their komatiite nature. Petrographic data suggest that the primary mineralogy has been completely altered during post-magmatic processes associated with metamorphism corresponding to greenschist to lower amphibolite facies conditions. The studied komatiites contain serpentine, talc, tremolite, actinolite and chlorite whilst tremolite, actinolite with minor plagioclase in komatiitic basalts. Based on the published Sm-Nd whole rock isochron ages of adjoining Banasandra komatiites (northern extension of Nagamangala belt and further northwest in Nuggihalli belt and Kalyadi belt we speculate ca. 3.2–3.15 Ga for komatiite eruption in Nagamangala belt. Trace element characteristics particularly HFSE and REE patterns suggest that most of the primary geochemical characteristics are preserved with minor influence of post-magmatic alteration and/or contamination. About 1/3 of studied komatiites show Al-depletion whilst remaining komatiites and komatiite basalts are Al-undepleted. Several samples despite high MgO, (Gd/YbN ratios show low CaO/Al2O3 ratios. Such anomalous values could be related to removal of CaO from komatiites during fluid-driven hydrothermal alteration, thus lowering CaO/Al2O3 ratios. The elemental characteristics of Al-depleted komatiites such as higher (Gd/YbN (>1.0, CaO/Al2O3 (>1.0, Al2O3/TiO2 (18 together with higher HREE, Y, Zr suggest their derivation from shallower upper mantle without garnet involvement in residue. The observed chemical characteristics (CaO/Al2O3, Al2O3/TiO2, MgO, Ni, Cr, Nb, Zr, Y, Hf, and REE indicate derivation of the komatiite and komatiite basalt magmas from heterogeneous mantle (depleted to primitive mantle at

  10. Amphibole incongruent melting under Lithospheric Mantle conditions in spinel peridotites from Balaton area, Hungary

    Science.gov (United States)

    Ntaflos, Theodoros; Abart, Rainer; Bizimis, Michel

    2017-04-01

    Pliocene alkali basalts from the western Pannonian Basin carry mantle xenoliths comprising hydrous and anhydrous spinel peridotites. We studied coarse and fine grained fertile to depleted spinel lherzolites, spinel harzubrgites and dunites from Szentbékálla, Balaton, in detail, using XRF, EPMA and LA-ICP-MS and MC-ICP-MS techniques. Pliocene alkali basalts containing mantle xenoliths with three major types of textures are widespread in the studied area: fine-grained primary and secondary equigranular, coarse-grained protogranular and transitional between equigranular and protogranular textures. Melt pockets, are common in the studied xenoliths. The shape of several melt pockets resembles euhedral amphibole. Other samples have thin films of intergranular glass attributed to the host basalt infiltration. Calculations have shown that such xenoliths experienced an up to 2.4% host basalt infiltration. The bulk rock Al2O3 and CaO concentrations vary from 0.75 to 4.1 and from 0.9 to 3.6 wt% respectively, and represent residues after variable degrees of partial melting. Using bulk rock major element abundances, the estimated degree of partial melting ranges from 4 to 20%.. The Primitive Mantle normalized clinopyroxene trace element abundances reveal a complicated evolution of the Lithospheric mantle underneath Balaton, which range from partial melting to modal and cryptic metasomatism. Subduction-related melt/fluids and/or infiltration of percolating undersaturated melts could be account for the metasomatic processes. The radiogenic isotopes of Sr, Nd and Hf in clinopyroxene suggest that this metasomatism was a relatively recent event. Textural evidence suggests that the calcite filling up the vesicles in the melt pockets and in veinlets cross-cutting the constituent minerals is of epigenetic nature and not due to carbonatite metasomatism. Mass balance calculations have shown that the bulk composition of the melt pockets is identical to small amphibole relics found as

  11. Nitrogen solubility in the deep mantle and the origin of Earth's primordial nitrogen budget

    Science.gov (United States)

    Yoshioka, Takahiro; Wiedenbeck, Michael; Shcheka, Svyatoslav; Keppler, Hans

    2018-04-01

    be modeled. Such models show that if the magma ocean coexisted with a primordial atmosphere having a nitrogen partial pressure of just a few bars, several times the current atmospheric mass of nitrogen must have been trapped in the deep mantle. It is therefore plausible that the apparent depletion of nitrogen relative to other volatiles in the near-surface reservoirs reflects the storage of a larger reservoir of nitrogen in the solid Earth. Dynamic exchange between these reservoirs may have induced major fluctuations of bulk atmospheric pressure over Earth's history.

  12. Geochemistry of oceanic carbonatites compared with continental carbonatites: mantle recycling of oceanic crustal carbonate

    Science.gov (United States)

    Hoernle, Kaj; Tilton, George; Le Bas, Mike; Duggen, Svend; Garbe-Schönberg, Dieter

    Major and trace element and Sr-Nd-Pb-O-C isotopic compositions are presented for carbonatites from the Cape Verde (Brava, Fogo, Sáo Tiago, Maio and Sáo Vicente) and Canary (Fuerteventura) Islands. Carbonatites show pronounced enrichment in Ba, Th, REE, Sr and Pb in comparison to most silicate volcanic rocks and relative depletion in Ti, Zr, Hf, K and Rb. Calcio (calcitic)-carbonatites have primary (mantle-like) stable isotopic compositions and radiogenic isotopic compositions similar to HIMU-type ocean island basalts. Cape Verde carbonatites, however, have more radiogenic Pb isotope ratios (e.g. 206Pb/204Pb=19.3-20.4) than reported for silicate volcanic rocks from these islands (18.7-19.9 Gerlach et al. 1988; Kokfelt 1998). We interpret calcio-carbonatites to be derived from the melting of recycled carbonated oceanic crust (eclogite) with a recycling age of 1.6 Ga. Because of the degree of recrystallization, replacement of calcite by secondary dolomite and elevated ∂13C and ∂18O, the major and trace element compositions of the magnesio (dolomitic)-carbonatites are likely to reflect secondary processes. Compared with Cape Verde calcio-carbonatites, the less radiogenic Nd and Pb isotopic ratios and the negative Δ7/4 of the magnesio-carbonatites (also observed in silicate volcanic rocks from the Canary and Cape Verde Islands) cannot be explained through secondary processes or through the assimilation of Cape Verde crust. These isotopic characteristics require the involvement of a mantle component that has thus far only been found in the Smoky Butte lamproites from Montana, which are believed to be derived from subcontinental lithospheric sources. Continental carbonatites show much greater variation in radiogenic isotopic composition than oceanic carbonatites, requiring a HIMU-like component similar to that observed in the oceanic carbonatites and enriched components. We interpret the enriched components to be Phanerozoic through Proterozoic marine carbonate (e

  13. Health and environmental impact of depleted uranium

    International Nuclear Information System (INIS)

    Furitsu, Katsumi

    2010-01-01

    Depleted Uranium (DU) is 'nuclear waste' produced from the enrichment process and is mostly made up of 238 U and is depleted in the fissionable isotope 235 U compared to natural uranium (NU). Depleted uranium has about 60% of the radioactivity of natural uranium. Depleted uranium and natural uranium are identical in terms of the chemical toxicity. Uranium's high density gives depleted uranium shells increased range and penetrative power. This density, combined with uranium's pyrophoric nature, results in a high-energy kinetic weapon that can punch and burn through armour plating. Striking a hard target, depleted uranium munitions create extremely high temperatures. The uranium immediately burns and vaporizes into an aerosol, which is easily diffused in the environment. People can inhale the micro-particles of uranium oxide in an aerosol and absorb them mainly from lung. Depleted uranium has both aspects of radiological toxicity and chemical toxicity. The possible synergistic effect of both kinds of toxicities is also pointed out. Animal and cellular studies have been reported the carcinogenic, neurotoxic, immuno-toxic and some other effects of depleted uranium including the damage on reproductive system and foetus. In addition, the health effects of micro/ nano-particles, similar in size of depleted uranium aerosols produced by uranium weapons, have been reported. Aerosolized DU dust can easily spread over the battlefield spreading over civilian areas, sometimes even crossing international borders. Therefore, not only the military personnel but also the civilians can be exposed. The contamination continues after the cessation of hostilities. Taking these aspects into account, DU weapon is illegal under international humanitarian laws and is considered as one of the inhumane weapons of 'indiscriminate destruction'. The international society is now discussing the prohibition of DU weapons based on 'precautionary principle'. The 1991 Gulf War is reportedly the first

  14. The Sensitivity of Joint Inversions of Seismic and Geodynamic Data to Mantle Viscosity

    Science.gov (United States)

    Lu, C.; Grand, S. P.; Forte, A. M.; Simmons, N. A.

    2017-12-01

    Seismic tomography has mapped the existence of large scale mantle heterogeneities in recent years. However, the origin of these velocity anomalies in terms of chemical and thermal variations is still under debate due to the limitations of tomography. Joint inversion of seismic, geodynamic, and mineral physics observations has proven to be a powerful tool to decouple thermal and chemical effects in the deep mantle (Simmons et al. 2010). The approach initially attempts to find a model that can be explained assuming temperature controls lateral variations in mantle properties and then to consider more complicated lateral variations that account for the presence of chemical heterogeneity to further fit data. The geodynamic observations include Earth's free air gravity field, tectonic plate motions, dynamic topography and the excess ellipticity of the core. The sensitivity of the geodynamic observables to density anomalies, however, depends on an assumed radial mantle viscosity profile. Here we perform joint inversions of seismic and geodynamic data using a number of published viscosity profiles. The goal is to test the sensitivity of joint inversion results to mantle viscosity. For each viscosity model, geodynamic sensitivity kernels are calculated and used to jointly invert the geodynamic observations as well as a new shear wave data set for a model of density and seismic velocity. Also, compared with previous joint inversion studies, two major improvements have been made in our inversion. First, we use a nonlinear inversion to account for anelastic effects. Applying the very fast simulate annealing (VFSA) method, we let the elastic scaling factor and anelastic parameters from mineral physics measurements vary within their possible ranges and find the best fitting model assuming thermal variations are the cause of the heterogeneity. We also include an a priori subducting slab model into the starting model. Thus the geodynamic and seismic signatures of short wavelength

  15. Multidimensional Mantle Convection Models in Eastern Anatolia, the North Arabian Platform, and Caucasus Region

    Science.gov (United States)

    Sengul Uluocak, E.; Shahnas, H.; Pysklywec, R.; Gogus, O.; Eken, T.

    2017-12-01

    Eastern Anatolia, the North Arabian Platform, and Caucasus regions show many features of collisional tectonics with different convergence rates and shortening from south to north. The volcanism, sediment provenience, and thermochronological data suggest that the shortening and exhumation in the Greater Caucasus started during the Eocene-Oligocene synchronously with the collision between Arabia-Bitlis-Pötürge Massif in the south. Previous works indicate that the uplift (up to 2 km) in Eastern Anatolia related to upwelling mantle following the deformation of the Arabian oceanic lithosphere ( 11 Ma) during the ongoing Greater Caucasus closure is the dominant tectonic processes in the center of the region. However, there is no integrated geodynamic model that explains the deformation mechanisms of the region -and their possible interactions with each other -under the dynamic forces. In this study, we use multidimensional mantle-lithosphere convection/deformation models to quantify the geodynamic processes as constrained by the geological/geophysical observations in the region. For the models, seismic studies provide the high-resolution images of the upwelling mantle beneath Eastern Anatolia and the presence -and the locations- of the seismically fast structures associated with the relic/subducted slabs at varying depths such as the Bitlis slab in the south, and the Pontide and Kura slabs in the north. Fast polarization directions observed from splitting analyses exhibit an overall NE-SW oriented mantle anisotropy and a comparison between Pn and SKS derived fast wave azimuths indicates a crust-mantle coupling most likely implying vertically coherent deformation to the north of the study area. For the geodynamic models, we modify the mantle and lithosphere rheology as well as the thermal state. We interpret the estimated uplift and subsidence anomalies related to lithospheric variations (ranging from 54 km to 211 km) and subducting slab behavior with observed

  16. Computational and experimental studies of iron-bearing carbonates and silicate glasses at lower mantle pressures

    Science.gov (United States)

    Solomatova, N. V.; Jackson, J. M.; Asimow, P. D.; Sturhahn, W.; Rossman, G. R.; Roskosz, M.

    2017-12-01

    Decomposition of carbonates may be responsible for creating silicate melts within the lower mantle by lowering the melting temperature of surrounding rock. Identifying and characterizing the stability of carbonates is therefore a necessary step towards understanding the transport of carbon in Earth's interior. Dolomite is one of the major mineral forms in which carbon is subducted into the Earth's mantle. Although iron-free dolomite is expected to break down upon compression, high-pressure polymorphs of iron-bearing dolomite may resist decomposition. Using a genetic algorithm that predicts crystal structures, we found a monoclinic phase with space group C2/c that has a lower energy than all previously reported dolomite structures at pressures above 15 GPa, where the substitution of iron for magnesium stabilizes monoclinic dolomite at certain pressures of the lower mantle. Thus, an iron-bearing dolomite polymorph may be an important carbon carrier in regions of Earth's lower mantle. The depth at which carbonates will decompose is dependent on the age, temperature and density of subducting slabs. Decarbonation reactions may lower the melting temperature of surrounding rocks to produce silicate melts. In regions of the mantle where silicate melts may exist, it is important to understand the physical properties and dynamic behavior of the melts because they affect the chemical and thermal evolution of its interior. Composition, degree of polymerization, and iron's spin state affect such properties. The behavior of iron in silicate melts is poorly understood but, in some cases, may be approximated by iron-bearing glasses. We measured the hyperfine parameters of iron-bearing rhyolitic and basaltic glasses up to 120 GPa and 100 GPa, respectively, in a neon pressure medium using time-domain synchrotron Mössbauer spectroscopy. The spectra for rhyolitic and basaltic glasses are well explained by three high-spin Fe2+-like sites with distinct quadrupole splittings, reflecting

  17. Seismic scatterers in the mid-lower mantle beneath Tonga-Fiji

    Science.gov (United States)

    Kaneshima, Satoshi

    2018-01-01

    We analyze deep and intermediate-depth earthquakes at the Tonga-Fiji region in order to reveal the distribution of scattering objects in the mid-lower mantle. By array processing waveform data recorded at regional seismograph stations in the US, Alaska, and Japan, we investigate S-to-P scattering waves in the P coda, which arise from kilometer-scale chemically distinct objects in the mid-lower mantle beneath Tonga-Fiji. With ten scatterers previously reported by the author included, twenty-three mid-lower mantle scatterers have been detected below 900 km depth, while scatterers deeper than 1900 km have not been identified. Strong mid-lower mantle S-to-P scattering most frequently occurs at the scatterers located within a depth range between 1400 km and 1600 km. The number of scatterers decreases below 1600 km depth, and the deeper objects tend to be weaker. The scatterer distribution may reflect diminishing elastic anomalies of basaltic rocks with depth relative to the surrounding mantle rocks, which mineral physics has predicted to occur. The predominant occurrence of strong S-to-P scattering waves within a narrow depth range may reflect significant reduction of rigidity due to the ferro-elastic transformation of stishovite in basaltic rocks. Very large signals associated with mid-mantle scatterers are observed only for a small portion of the entire earthquake-array pairs. Such infrequent observations of large scattering signals, combined with quite large event-to-event differences in the scattering intensity for each scatterer, suggest both that the strong arrivals approximately represent ray theoretical S-to-P converted waves at objects with a plane geometry. The plane portions of the strong scatterers may often dip steeply, with the size exceeding 100 km. For a few strong scatterers, the range of receivers showing clear scattered waves varies substantially from earthquake-array pair to pair. Some of the scatterers are also observed at different arrays that have

  18. 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}.

  19. Perturbation of the Vacuolar ATPase: A NOVEL CONSEQUENCE OF INOSITOL DEPLETION.

    Science.gov (United States)

    Deranieh, Rania M; Shi, Yihui; Tarsio, Maureen; Chen, Yan; McCaffery, J Michael; Kane, Patricia M; Greenberg, Miriam L

    2015-11-13

    Depletion of inositol has profound effects on cell function and has been implicated in the therapeutic effects of drugs used to treat epilepsy and bipolar disorder. We have previously shown that the anticonvulsant drug valproate (VPA) depletes inositol by inhibiting myo-inositol-3-phosphate synthase, the enzyme that catalyzes the first and rate-limiting step of inositol biosynthesis. To elucidate the cellular consequences of inositol depletion, we screened the yeast deletion collection for VPA-sensitive mutants and identified mutants in vacuolar sorting and the vacuolar ATPase (V-ATPase). Inositol depletion caused by starvation of ino1Δ cells perturbed the vacuolar structure and decreased V-ATPase activity and proton pumping in isolated vacuolar vesicles. VPA compromised the dynamics of phosphatidylinositol 3,5-bisphosphate (PI3,5P2) and greatly reduced V-ATPase proton transport in inositol-deprived wild-type cells. Osmotic stress, known to increase PI3,5P2 levels, did not restore PI3,5P2 homeostasis nor did it induce vacuolar fragmentation in VPA-treated cells, suggesting that perturbation of the V-ATPase is a consequence of altered PI3,5P2 homeostasis under inositol-limiting conditions. This study is the first to demonstrate that inositol depletion caused by starvation of an inositol synthesis mutant or by the inositol-depleting drug VPA leads to perturbation of the V-ATPase. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  20. Water Distribution in the Continental and Oceanic Upper Mantle

    Science.gov (United States)

    Peslier, Anne H.

    2015-01-01

    Nominally anhydrous minerals such as olivine, pyroxene and garnet can accommodate tens to hundreds of ppm H2O in the form of hydrogen bonded to structural oxygen in lattice defects. Although in seemingly small amounts, this water can significantly alter chemical and physical properties of the minerals and rocks. Water in particular can modify their rheological properties and its distribution in the mantle derives from melting and metasomatic processes and lithology repartition (pyroxenite vs peridotite). These effects will be examined here using Fourier transform infrared spectrometry (FTIR) water analyses on minerals from mantle xenoliths from cratons, plume-influenced cratons and oceanic settings. In particular, our results on xenoliths from three different cratons will be compared. Each craton has a different water distribution and only the mantle root of Kaapvaal has evidence for dry olivine at its base. This challenges the link between olivine water content and survival of Archean cratonic mantle, and questions whether xenoliths are representative of the whole cratonic mantle. We will also present our latest data on Hawaii and Tanzanian craton xenoliths which both suggest the intriguing result that mantle lithosphere is not enriched in water when it interacts with melts from deep mantle upwellings (plumes).

  1. 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.

  2. Petrogenesis of 3.15 Ga old Banasandra komatiites from the Dharwar craton, India: Implications for early mantle heterogeneity

    Directory of Open Access Journals (Sweden)

    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

  3. Seismic Evidence for Lower Mantle Plume Under the Yellowstone Hotspot

    Science.gov (United States)

    Nelson, P.; Grand, S.

    2017-12-01

    The mantle plume hypothesis for the origin of intraplate volcanism has been controversial since its inception in the 1970s. The hypothesis proposes hot narrow upwelling of rock rooted at the core mantle boundary (CMB) rise through the mantle and interact with the base of the lithosphere forming linear volcanic systems such as Hawaii and Yellowstone. Recently, broad lower mantle (>500 km in diameter) slow velocity conduits, most likely thermochemical in origin, have been associated with some intraplate volcanic provinces (French and Romanowicz, 2015). However, the direct detection of a classical thin thermal plume in the lower mantle using travel time tomography has remained elusive (Anderson and Natland, 2014). Here we present a new shear wave tomography model for the mantle beneath the western United States that is optimized to find short wavelength, sub-vertical structures in the lower mantle. Our approach uses carefully measured SKS and SKKS travel times recorded by dense North American seismic networks in conjunction with finite frequency kernels to build on existing tomography models. We find the presence of a narrow ( 300 km diameter) well isolated cylindrically shaped slow anomaly in the lower most mantle which we associate with the Yellowstone Hotspot. The conduit has a 2% reduction in shear velocity and is rooted at the CMB near the California/Arizona/Nevada border. A cross sectional view through the anomaly shows that it is slightly tilted toward the north until about 1300 km depth where it appears to weaken and deflect toward the surficial positon of the hotspot. Given the anomaly's strength, proximity to the Yellowstone Hotspot, and morphology we argue that a thermal plume interpretation is the most reasonable. Our results provide strong support for a lower mantle plume origin of the Yellowstone hotspot and more importantly the existence of deep thermal plumes.

  4. 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.

  5. Moho vs crust-mantle boundary: Evolution of an idea

    Science.gov (United States)

    O'Reilly, Suzanne Y.; Griffin, W. L.

    2013-12-01

    The concept that the Mohorovicic Discontinuity (Moho) does not necessarily coincide with the base of the continental crust as defined by rock-type compositions was introduced in the early 1980s. This had an important impact on understanding the nature of the crust-mantle boundary using information from seismology and from deep-seated samples brought to the surface as xenoliths in magmas, or as tectonic terranes. The use of empirically-constrained P-T estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment. The xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere, and revealed that the crust-mantle boundary in off-craton regions commonly is transitional over a depth range of about 5-20 km. Early seismic-reflection data showed common layering near the Moho, correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust-mantle boundary. Developments in seismology, petrophysics and experimental petrology have refined interpretation of lithospheric domains. The expansion of in situ geochronology (especially zircon U-Pb ages and Hf-isotopes; Os isotopes of mantle sulfides) has defined tectonic events that affected whole crust-mantle sections, and revealed that the crust-mantle boundary can change in depth through time. However, the nature of the crust-mantle boundary in cratonic regions remains enigmatic, mainly due to lack of key xenoliths or exposed sections. The observation that the Moho may lie significantly deeper than the crust-mantle boundary has important implications for modeling the volume of the crust. Mapping the crust using seismic techniques alone, without consideration of the petrological problems, may lead to an overestimation of crustal thickness by 15-30%. This will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust-formation processes

  6. Non-chondritic HSE budget in Earth's upper mantle evidenced by abyssal peridotites from Gakkel ridge (Arctic Ocean)

    Science.gov (United States)

    Liu, Chuan-Zhou; Snow, Jonathan E.; Brügmann, Gerhard; Hellebrand, Eric; Hofmann, Albrecht W.

    2009-06-01

    Constraints on the highly siderophile element (HSE: including Os, Ir, Ru, Pt, Pd and Re) budget of the upper mantle upwelling beneath mid-ocean ridges have until now been based on samples that have experienced varying degrees of alteration, partial melting and secondary igneous processes. Here we present results from a set of abyssal peridotites that have been relatively unaffected by these phenomena. Eighteen abyssal peridotites from two localities along the ultra-slow spreading Gakkel Ridge (Arctic Ocean) were selected for this study. Samples from one locality (PS66-238) are extremely fresh, while those from HLY0102-D70 are typical abyssal serpentinites. Comparison of HSE data between fresh peridotites and weathering products supports the contention that HSE are stable during serpentinization, but that Pd and Re are mobile during subsequent weathering. HSE budgets of spinel lherzolites suggest that all platinum group elements (PGEs: including Os, Ir, Ru, Pt and Pd) are compatible during very low degree of partial melting (5-8%), whereas Re behaves as an incompatible element. Harzburgites from each locality were subjected to ~ 12% fractional partial melting, which is lower than that expected for total consumption of sulfides in mantle peridotites (ca. 16%). The harzburgites are depleted in PPGE (Pt, Pd) and Re relative to IPGE (Os, Ir, Ru), which reflects the extraction of sulfide melt along with the silicate melt. Low bulk-rock contents of both Na 2O and TiO 2 in the fresh PS66-238 lherzolites indicate that they were not transformed from harzburgites through melt refertilization, but represent pristine fertile mantle rocks. Their systematic suprachondritic Ru/Ir and Pd/Ir ratios, but chondritic Pt/Ir ratios, cannot be ascribed to partial melting or secondary igneous processes. This signature may reflect the primary HSE signature of the Earth's upper mantle. Non-chondritic HSE patterns discovered in PS66-238 lherzolites are consistent with the primitive upper

  7. Rheological structure of a lithosphere-asthenosphere boundary zone, decoded from EBSD analysis of mantle xenoliths from Ichinomegata, NE Japan

    Science.gov (United States)

    Sato, Y.; Ozawa, K.

    2017-12-01

    Mantle xenoliths are fragments of mantle materials entrapped in alkali basalts or kimberlites and transported to the surface (Nixon, 1987). They provide information on rheological, thermal, chemical, petrological structures of the upper mantle (e.g. Green et al., 2010; McKenzie and Bickle, 1988; O'Reilly and Griffin, 1996). They potentially represent materials from a boundary zone of lithosphere and asthenosphere (LABZ), where the heat transportation mechanism changes from convection to conduction (Sleep, 2005, 2006). However, difficulties in geobarometry for spinel peridotite (e.g. O'Reilly et al., 1997) have hampered our understanding of shallow LABZ. Ichinomegata located in the back-arc side of NE Japan is a latest Pleistocene andesitic-dacitic volcano yielding spinel peridotite xenoliths (Katsui et al., 1979). Through our works (Sato and Ozawa, 2016, 2017a, 2017b), we have overcome difficulties in geobarometry of spinel peridotites and gained accurate thermal structure (0.74-1.60 GPa, 832-1084 °C) from eight of the nine examined xenoliths. The rheological and chemical features suggest drastic changes: undeformed (granular), depleted, subsolidus mantle representing lithospheric mantle (ca. 28-35 km) and deformed (porphyroclastic), fertile, hydrous supersolidus mantle representing rheological LABZ (ca. 35-54 km). We investigate depth dependent variation of crystallographic preferred orientation (CPO) of constituent minerals of the xenoliths by electron back-scattered diffraction analysis (using JSM-7000F with a CCD detector and the CHANNEL5 software at the University of Tokyo). A shallower (ca. 32 km) sample with tabulargranular texture and coarse olivine size (0.92 mm) has A-type olivine CPO with [100] maximum as reported by Satsukawa and Michibayashi (2014) (hereafter SM14), whereas a deep (ca. 51 km) sample with porphyroclastic texture and finer olivine size (0.46 mm) has CPO with weaker fabric intensity characterized by a [100] girdle similar to AG-type and

  8. Cenozoic mantle composition evolution of southern Tibet indicated by Paleocene ( 64 Ma) pseudoleucite phonolitic rocks in central Lhasa terrane

    Science.gov (United States)

    Qi, Yue; Gou, Guo-Ning; Wang, Qiang; Wyman, Derek A.; Jiang, Zi-Qi; Li, Qiu-Li; Zhang, Le

    2018-03-01

    The question of whether continental subduction processes in collisional orogenic belts can trigger wide-spread mantle metesomatism and crustal material recycling remains unresolved. Miocene (25-8 Ma) ultrapotassic rocks in southern Tibet are the only mantle-derived magmatic rocks emplaced after the collision between India and Asia and they have been linked to the onset of east-west extensional stresses as the surface uplift of the Tibetan Plateau reached near-maximum elevation. However, their petrogenesis remains highly controversial, particularly the issue of whether their extremely enriched Sr-Nd isotopic characteristics were related to metasomatism derived from subducted Indian continental materials during the Cenozoic. Here we report on a Paleocene silicate-unsaturated, pseudoleucite phonolitic dike, in the Rongniduo area of central Lhasa terrane. In-situ SIMS (secondary ion mass spectrometry) apatite U-Pb age indicates the dike was generated at 64.1 ± 4.2 Ma, which slightly predates the age of initial India and Asia collision (about 55-50 Ma). This is the oldest age yet reported for ultrapotassic rocks in southern Tibet. Samples from this dike have distinctly more depleted Sr-Nd (whole rock: (87Sr/86Sr)i = 0.7064 to 0.7062, εNd(t) = - 1.5 to 0.4; in situ apitite: (87Sr/86Sr)i = 0.7059 to 0.7060, εNd(t) = - 2.0 to 0.4) isotopic compositions, than those of Miocene (25-8 Ma) ultrapotassic rocks in the central Lhasa terrane ((87Sr/86Sr)i = 0.7106 to 0.7399, εNd(t) = - 10.6 to - 18.5). Our new data provides important constraints on pre-collisional mantle characteristics beneath the Lhasa terrane. We suggest that these 64 Ma pseudoleucite phonolitic rocks were derived from the enriched lithospheric mantle metasomatized by subducted Tethyan oceanic materials in response to Neo-Tethyan slab roll-back. As a consequence, the younger Miocene ultrapotassic rocks, which display different geochemical compositions from the pre-collisional ultrapotassic rocks, were most

  9. PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma.

    Science.gov (United States)

    Restall, Ian J; Parolin, Doris A E; Daneshmand, Manijeh; Hanson, Jennifer E L; Simard, Manon A; Fitzpatrick, Megan E; Kumar, Ritesh; Lavictoire, Sylvie J; Lorimer, Ian A J

    2015-01-01

    Cellular senescence is a tumor suppressor mechanism where cells enter a permanent growth arrest following cellular stress. Oncogene-induced senescence (OIS) is induced in non-malignant cells following the expression of an oncogene or inactivation of a tumor suppressor. Previously, we have shown that protein kinase C iota (PKCι) depletion induces cellular senescence in glioblastoma cells in the absence of a detectable DNA damage response. Here we demonstrate that senescent glioblastoma cells exhibit an aberrant centrosome morphology. This was observed in basal levels of senescence, in p21-induced senescence, and in PKCι depletion-induced senescence. In addition, senescent glioblastoma cells are polyploid, Ki-67 negative and arrest at the G1/S checkpoint, as determined by expression of cell cycle regulatory proteins. These markers are all consistent with cells that have undergone mitotic slippage. Failure of the spindle assembly checkpoint to function properly can lead to mitotic slippage, resulting in the premature exit of mitotic cells into the G1 phase of the cell cycle. Although in G1, these cells have the replicated DNA and centrosomal phenotype of a cell that has entered mitosis and failed to divide. Overall, we demonstrate that PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma cells. To our knowledge, this is the first evidence of markers of mitotic slippage directly in senescent cells by co-staining for senescence-associated β-galactosidase and immunofluorescence markers in the same cell population. We suggest that markers of mitotic slippage be assessed in future studies of senescence to determine the extent of mitotic slippage in the induction of cellular senescence.

  10. Early Cretaceous gabbroic rocks from the Taihang Mountains: Implications for a paleosubduction-related lithospheric mantle beneath the central North China Craton

    Science.gov (United States)

    Wang, Yuejun; Fan, Weiming; Zhang, Hongfu; Peng, Touping

    2006-02-01

    SHRIMP zircon U-Pb ages and geochemical and Sr-Nd-Pb isotopic data are presented for the gabbroic intrusive from the southern Taihang Mountains to characterize the nature of the Mesozoic lithospheric mantle beneath the central North China Craton (NCC). The gabbroic rocks emplaced at 125 Ma and are composed of plagioclase (40-50%), amphibole (20-30%), clinopyroxene (10-15%), olivine (5-10%) and biotite (5-7%). Olivines have high MgO (Fo = 78-85) and NiO content. Clinopyroxenes are high in MgO and CaO with the dominant ones having the formula of En 42-46Wo 41-50Fs 8-13. Plagioclases are dominantly andesine-labradorite (An = 46-78%) and have normal zonation from bytownite in the core to andesine in the rim. Amphiboles are mainly magnesio and actinolitic hornblende, distinct from those in the Precambrian high-pressure granulites of the NCC. These gabbroic rocks are characterized by high MgO (9.0-11.04%) and SiO 2 (52.66-55.52%), and low Al 2O 3, FeOt and TiO 2, and could be classified as high-mg basaltic andesites. They are enriched in LILEs and LREEs, depleted in HFSEs and HREEs, and exhibit ( 87Sr/ 86Sr) i = 0.70492-0.70539, ɛNd( t) = - 12.47-15.07, ( 206Pb/ 204Pb) i = 16.63-17.10, Δ8/4 = 70.1-107.2 and Δ7/4 = - 2.1 to - 9.4, i.e., an EMI-like isotopic signatures. Such geochemical features indicate that these early Cretaceous gabbroic rocks were originated from a refractory pyroxenitic veined-plus-peridotite source previously modified by an SiO 2-rich melt that may have been derived from Paleoproterozoic subducted crustal materials. Late Mesozoic lithospheric extension might have induced the melting of the metasomatised lithospheric mantle in response to the upwelling of the asthenosphere to generate these gabbroic rocks in the southern Taihang Mountains.

  11. 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...

  12. Upper mantle seismic velocity anomaly beneath southern Taiwan as revealed by teleseismic relative arrival times

    Science.gov (United States)

    Chen, Po-Fei; Huang, Bor-Shouh; Chiao, Ling-Yun

    2011-01-01

    Probing the lateral heterogeneity of the upper mantle seismic velocity structure beneath southern and central Taiwan is critical to understanding the local tectonics and orogeny. A linear broadband array that transects southern Taiwan, together with carefully selected teleseismic sources with the right azimuth provides useful constraints. They are capable of differentiating the lateral heterogeneity along the profile with systematic coverage of ray paths. We implement a scheme based on the genetic algorithm to simultaneously determine the relative delayed times of the teleseismic first arrivals of array data. The resulting patterns of the delayed times systematically vary as a function of the incident angle. Ray tracing attributes the observed variations to a high velocity anomaly dipping east in the mantle beneath the southeast of Taiwan. Combining the ray tracing analysis and a pseudo-spectral method to solve the 2-D wave propagations, we determine the extent of the anomaly that best fits the observations via the forward grid search. The east-dipping fast anomaly in the upper mantle beneath the southeast of Taiwan agrees with the results from several previous studies and indicates that the nature of the local ongoing arc-continent collision is likely characterized by the thin-skinned style.

  13. Mantle rare gas relative abundances in a steady-state mass transport model

    Science.gov (United States)

    Porcelli, D.; Wasserburg, G. J.

    1994-01-01

    A model for He and Xe was presented previously which incorporates mass transfer of rare gases from an undegassed lower mantle (P) and the atmosphere into a degassed upper mantle (D). We extend the model to include Ne and Ar. Model constraints on rare gas relative abundances within P are derived. Discussions of terrestrial volatile acquisition have focused on the rare gas abundance pattern of the atmosphere relative to meteoritic components, and the pattern of rare gases still trapped in the Ear,th is important in identifying volatile capture and loss processes operating during Earth formation. The assumptions and principles of the model are discussed in Wasserburg and Porcelli (this volume). For P, the concentrations in P of the decay/nuclear products 4 He, 21 Ne, 40 Ar, and 136 Xe can be calculated from the concentrations of the parent elements U, Th, K, and Pu. The total concentration of the daughter element in P is proportional to the isotopic shifts in P. For Ar, ((40)Ar/(36)Ar)p - ((40)Ar/(36)Ar)o =Delta (exp 40) p= 40 Cp/(exp 36)C where(i)C(sub j) the concentration of isotope i in j. In D, isotope compositions are the result of mixing rare gases from P, decay/nuclear products generated in the upper mantle, and subducted rare gases (for Ar and Xe).

  14. Mantle cell lymphoma relapsing at the lymphedematous arm.

    Directory of Open Access Journals (Sweden)

    Giuseppina Massini

    2013-02-01

    Full Text Available Lymphedema (LE is a chronic medical condition characterized by lymphatic fluid retention, resulting in tissue swelling. Cancer treatments involving lymph nodes can damage lymph drainage routes, causing accumulation of lymph fluid in the interstitial tissue of related limbs and body areas and secondary LE.  Basically, the LE has a negative impact on physical and mental quality of life. Moreover, 0.07-0.04% of long term survivors (most patients undergone mastectomy can develop the Stewart-Treves syndrome,  a rare and aggressive multifocal lymphangiosarcoma arising within the LE region. Here we describe a   45-year-old woman  with a massive LE of the left arm,  as a consequence of previous breast cancer,  who  was diagnosed after 4 years  of stage IV mantle cell lymphoma (MCL . The patient after obtaining complete remission with chemotherapy and ABMT  relapsed of MCL in lymphedema site.

  15. Reactor fuel depletion benchmark of TINDER

    International Nuclear Information System (INIS)

    Martin, W.J.; Oliveira, C.R.E. de; Hecht, A.A.

    2014-01-01

    Highlights: • A reactor burnup benchmark of TINDER, coupling MCNP6 to CINDER2008, was performed. • TINDER is a poor candidate for fuel depletion calculations using its current libraries. • Data library modification is necessary if fuel depletion is desired from TINDER. - Abstract: Accurate burnup calculations are key to proper nuclear reactor design, fuel cycle modeling, and disposal estimations. The TINDER code, originally designed for activation analyses, has been modified to handle full burnup calculations, including the widely used predictor–corrector feature. In order to properly characterize the performance of TINDER for this application, a benchmark calculation was performed. Although the results followed the trends of past benchmarked codes for a UO 2 PWR fuel sample from the Takahama-3 reactor, there were obvious deficiencies in the final result, likely in the nuclear data library that was used. Isotopic comparisons versus experiment and past code benchmarks are given, as well as hypothesized areas of deficiency and future work

  16. Depleted uranium hexafluoride: Waste or resource?

    Energy Technology Data Exchange (ETDEWEB)

    Schwertz, N.; Zoller, J.; Rosen, R.; Patton, S. [Lawrence Livermore National Lab., CA (United States); Bradley, C. [USDOE Office of Nuclear Energy, Science, Technology, Washington, DC (United States); Murray, A. [SAIC (United States)

    1995-07-01

    the US Department of Energy is evaluating technologies for the storage, disposal, or re-use of depleted uranium hexafluoride (UF{sub 6}). This paper discusses the following options, and provides a technology assessment for each one: (1) conversion to UO{sub 2} for use as mixed oxide duel, (2) conversion to UO{sub 2} to make DUCRETE for a multi-purpose storage container, (3) conversion to depleted uranium metal for use as shielding, (4) conversion to uranium carbide for use as high-temperature gas-cooled reactor (HTGR) fuel. In addition, conversion to U{sub 3}O{sub 8} as an option for long-term storage is discussed.

  17. The depletion of the stratospheric ozone layer

    International Nuclear Information System (INIS)

    Sabogal Nelson

    2000-01-01

    The protection of the Earth's ozone layer is of the highest importance to mankind. The dangers of its destruction are by now well known. The depletion of that layer has reached record levels. The Antarctic ozone hole covered this year a record area. The ozone layer is predicted to begin recovery in the next one or two decades and should be restored to pre-1980 levels by 2050. This is the achievement of the regime established by the 1985 Vienna Convention for the Protection of the Ozone Layer and the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. The regime established by these two agreements has been revised, and made more effective in London (1990), Copenhagen (1992), Vienna (1995), and Beijing (1999)

  18. Depleted uranium plasma reduction system study

    International Nuclear Information System (INIS)

    Rekemeyer, P.; Feizollahi, F.; Quapp, W.J.; Brown, B.W.

    1994-12-01

    A system life-cycle cost study was conducted of a preliminary design concept for a plasma reduction process for converting depleted uranium to uranium metal and anhydrous HF. The plasma-based process is expected to offer significant economic and environmental advantages over present technology. Depleted Uranium is currently stored in the form of solid UF 6 , of which approximately 575,000 metric tons is stored at three locations in the U.S. The proposed system is preconceptual in nature, but includes all necessary processing equipment and facilities to perform the process. The study has identified total processing cost of approximately $3.00/kg of UF 6 processed. Based on the results of this study, the development of a laboratory-scale system (1 kg/h throughput of UF6) is warranted. Further scaling of the process to pilot scale will be determined after laboratory testing is complete

  19. Improvements in EBR-2 core depletion calculations

    International Nuclear Information System (INIS)

    Finck, P.J.; Hill, R.N.; Sakamoto, S.

    1991-01-01

    The need for accurate core depletion calculations in Experimental Breeder Reactor No. 2 (EBR-2) is discussed. Because of the unique physics characteristics of EBR-2, it is difficult to obtain accurate and computationally efficient multigroup flux predictions. This paper describes the effect of various conventional and higher order schemes for group constant generation and for flux computations; results indicate that higher-order methods are required, particularly in the outer regions (i.e. the radial blanket). A methodology based on Nodal Equivalence Theory (N.E.T.) is developed which allows retention of the accuracy of a higher order solution with the computational efficiency of a few group nodal diffusion solution. The application of this methodology to three-dimensional EBR-2 flux predictions is demonstrated; this improved methodology allows accurate core depletion calculations at reasonable cost. 13 refs., 4 figs., 3 tabs

  20. Depletion zones and crystallography on pinched spheres

    Science.gov (United States)

    Chen, Jingyuan; Xing, Xiangjun; Yao, Zhenwei

    2018-03-01

    Understanding the interplay between ordered structures and substrate curvature is an interesting problem with versatile applications, including functionalization of charged supramolecular surfaces and modern microfluidic technologies. In this work, we investigate the two-dimensional packing structures of charged particles confined on a pinched sphere. By continuously pinching the sphere, we observe cleavage of elongated scars into pleats, proliferation of disclinations, and subsequently, emergence of a depletion zone at the negatively curved waist that is completely void of particles. We systematically study the geometrics and energetics of the depletion zone, and reveal its physical origin as a finite size effect, due to the interplay between Coulomb repulsion and concave geometry of the pinched sphere. These results further our understanding of crystallography on curved surfaces, and have implications in design and manipulation of charged, deformable interfaces in various applications.

  1. Geochemical and Sr-Nd isotopic characteristics of mantle xenoliths from NE Spain

    Science.gov (United States)

    Galán, G.; Oliveras, V.

    2012-04-01

    Mantle xenoliths in alkaline mafic lavas and pyroclasts from the Neogene-Quaternary volcanism in NE Spain are studied using major, trace element geochemistry and Sr-Nd isotopes, to compare the lithospheric mantle of this area with that of other European zones, and to assess the different processes that conditioned its evolution. The xenoliths mostly come from two volcanoes and are mainly formed of anhydrous spinel lherzolites and harzburgites, in approximately equal proportion. Accessory amphibole and phlogopite are occasional, as it happens with plagioclase, which appears in corona textures around lherzolite spinel. Much subordinated cumulate pyroxenite xenoliths (olivine wbsterite, clinopyroxenite types) are also found. Textures are mostly protogranular, but there are also porphyroclastic, transitional between protogranular and porphyroclastic, and equigranular forms among lherzolites. Pyrometamorphic textures are observed in a few xenoliths. Co-variation diagrams for basaltic components and MgO concentrations in whole rock analyses show gradation from lherzolites to harzburgites. This is also the case for compatible and mildly incompatible trace elements, but not for the most incompatible ones. This gradual variation is also confirmed by mineral compositions, most of which correspond to off-craton xenoliths. REE patterns for lherzolites and for their clinopyroxene are LREE and MREE depleted, whereas for harzburgites are LREE and MREE enriched. U-shaped REE patterns are rarely observed in lherzolite clinopyroxene that also shows more significant negative anomalies at Zr and Ti. Clinopyroxene from harzburgites is also remarked by more significant negative anomalies at Nb, Ti and Zr, and by higher Th and U abundances, than lherzolite clinopyroxene . Sr and Nd isotopic compositions for clinopyroxene define a continuous and inverse trend from DMM lherzolites to enriched harzburgites (87Sr/86Sr: 0.702486-0.709772; 143Nd/144Nd: 0.513359-0.512411). Harzburgite

  2. The Whitish Inner Mantle of the Giant Clam, Tridacna squamosa, Expresses an Apical Plasma Membrane Ca2+-ATPase (PMCA Which Displays Light-Dependent Gene and Protein Expressions

    Directory of Open Access Journals (Sweden)

    Yuen K. Ip

    2017-10-01

    Full Text Available Giant clams live in symbiosis with extracellular zooxanthellae and display high rates of growth and shell formation (calcification in light. Light-enhanced calcification requires an increase in the supply of Ca2+ to, and simultaneously an augmented removal of H+ from, the extrapallial fluid where shell formation occurs. We have obtained the complete coding cDNA sequence of Plasma Membrane Ca2+-ATPase (PMCA from the thin and whitish inner mantle, which is in touch with the extrapallial fluid, of the giant clam Tridacna squamosa. The deduced PMCA sequence consisted of an apical targeting element. Immunofluorescence microscopy confirmed that PMCA had an apical localization in the shell-facing epithelium of the inner mantle, whereby it can actively secrete Ca2+ in exchange for H+. More importantly, the apical PMCA-immunofluorescence of the shell-facing epithelium of the inner mantle increased significantly after 12 h of exposure to light. The transcript and protein levels of PMCA/PMCA also increased significantly in the inner mantle after 6 or 12 h of light exposure. These results offer insights into a light-dependable mechanism of shell formation in T. squamosa and a novel explanation of light-enhanced calcification in general. As the inner mantle normally lacks light sensitive pigments, our results support a previous proposition that symbiotic zooxanthellae, particularly those in the colorful and extensible outer mantle, may act as light-sensing elements for the host clam.

  3. Elastic Properties of Orthoenstatite at Simultaneous High Pressure-Temperature Conditions and the Implication for the Origin of Low VP/VS Zones in the Mantle Wedge

    Science.gov (United States)

    Qian, W.; Wang, W.; Zou, F.; Wu, Z.

    2017-12-01

    The compositions of the Earth's interiors are critical in understanding the origin and evolution of the Earth and its geodynamics. Orthopyroxene is an important component for the upper mantle both in pyrolite model and in piclogite model. Furthermore, many evidences suggest the local enrichment of opx in the upper mantle. Therefore, its thermodynamic and elastic properties are fundamental for understanding of chemical compositions and dynamics of the upper mantle. We obtain the elastic properties of orthoenstatite (MgSiO3), Mg end-member orthopyroxene with space group Pbca, up to 20 GPa and 2000 K using first principles calculations with local density approximation (LDA). The calculated results are in good agreement with previous available experimental measurements and theoretical results. Both bulk and shear modulus show noticeable nonlinear pressure dependence, and the softening of shear wave velocities is prominent at high pressure. Meanwhile, orthoenstatite exhibits a negative temperature derivate of VP/VS ratios. This is different from other upper mantle minerals, such as olivine, ringwoodite and garnet, whose VP/VS increase with the increasing of the temperature. Compared to other major minerals in the upper mantle, orthoenstatite shows the lowest compressional velocities, shear velocities, and VP/VS (account for the observed low VP/VS in the mantle wedge.

  4. An experimental study of Fe-Ni exchange between sulfide melt and olivine at upper mantle conditions: implications for mantle sulfide compositions and phase equilibria

    Science.gov (United States)

    Zhang, Zhou; von der Handt, Anette; Hirschmann, Marc M.

    2018-03-01

    The behavior of nickel in the Earth's mantle is controlled by sulfide melt-olivine reaction. Prior to this study, experiments were carried out at low pressures with narrow range of Ni/Fe in sulfide melt. As the mantle becomes more reduced with depth, experiments at comparable conditions provide an assessment of the effect of pressure at low-oxygen fugacity conditions. In this study, we constrain the Fe-Ni composition of molten sulfide in the Earth's upper mantle via sulfide melt-olivine reaction experiments at 2 GPa, 1200 and 1400 °C, with sulfide melt X_{{{Ni}}}^{{{Sulfide}}}={{Ni}}/{{Ni+{Fe}}} (atomic ratio) ranging from 0 to 0.94. To verify the approach to equilibrium and to explore the effect of {f_{{{O}2}}} on Fe-Ni exchange between phases, four different suites of experiments were conducted, varying in their experimental geometry and initial composition. Effects of Ni secondary fluorescence on olivine analyses were corrected using the PENELOPE algorithm (Baró et al., Nucl Instrum Methods Phys Res B 100:31-46, 1995), "zero time" experiments, and measurements before and after dissolution of surrounding sulfides. Oxygen fugacities in the experiments, estimated from the measured O contents of sulfide melts and from the compositions of coexisting olivines, were 3.0 ± 1.0 log units more reduced than the fayalite-magnetite-quartz (FMQ) buffer (suite 1, 2 and 3), and FMQ - 1 or more oxidized (suite 4). For the reduced (suites 1-3) experiments, Fe-Ni distribution coefficients K_{{D}}{}={(X_{{{Ni}}}^{{{sulfide}}}/X_{{{Fe}}}^{{{sulfide}}})}/{(X_{{{Ni}}^{{{olivine}}}/X_{{{Fe}}}^{{{olivine}}})}} are small, averaging 10.0 ± 5.7, with little variation as a function of total Ni content. More oxidized experiments (suite 4) give larger values of K D (21.1-25.2). Compared to previous determinations at 100 kPa, values of K D from this study are chiefly lower, in large part owing to the more reduced conditions of the experiments. The observed difference does not seem

  5. Molten-Salt Depleted-Uranium Reactor

    OpenAIRE

    Dong, Bao-Guo; Dong, Pei; Gu, Ji-Yuan

    2015-01-01

    The supercritical, reactor core melting and nuclear fuel leaking accidents have troubled fission reactors for decades, and greatly limit their extensive applications. Now these troubles are still open. Here we first show a possible perfect reactor, Molten-Salt Depleted-Uranium Reactor which is no above accident trouble. We found this reactor could be realized in practical applications in terms of all of the scientific principle, principle of operation, technology, and engineering. Our results...

  6. The ultimate disposition of depleted uranium

    Energy Technology Data Exchange (ETDEWEB)

    Lemons, T.R. [Uranium Enrichment Organization, Oak Ridge, TN (United States)

    1991-12-31

    Depleted uranium (DU) is produced as a by-product of the uranium enrichment process. Over 340,000 MTU of DU in the form of UF{sub 6} have been accumulated at the US government gaseous diffusion plants and the stockpile continues to grow. An overview of issues and objectives associated with the inventory management and the ultimate disposition of this material is presented.

  7. Optical assessment of phytoplankton nutrient depletion

    DEFF Research Database (Denmark)

    Heath, M.R.; Richardson, Katherine; Kiørboe, Thomas

    1990-01-01

    The ratio of light absorption at 480 and 665 nm by 90% acetone extracts of marine phytoplankton pigments has been examined as a potential indicator of phytoplankton nutritional status in both laboratory and field studies. The laboratory studies demonstrated a clear relationship between nutritiona......-replete and nutrient-depleted cells. The field data suggest that the absorption ratio may be a useful indicator of nutritional status of natural phytoplankton populations, and can be used to augment the interpretation of other data....

  8. Heatstroke Pathophysiology: The Energy Depletion Model

    Science.gov (United States)

    1989-06-12

    metabolic acidosis suggested preexisting whole body K* deficiency. In Kt-depleted dogs (49), muscle weakness occurred when animals had lost...and A.C. Issekutz. Lactate metabolism in resting and exercising dogs . J. ADDI. Physiol. 40:312-319, 1976. 43. Jacobs, I. Brod lactate: Implications...31 50. Kreisberg, R.A., L.F. Pennington, and B.R. Boshell. Lactate turnover and gluconeogenesis in normal and obese humans. Diabetes 19:53-63, 1970

  9. Carbon sequestration in depleted oil shale deposits

    Science.gov (United States)

    Burnham, Alan K; Carroll, Susan A

    2014-12-02

    A method and apparatus are described for sequestering carbon dioxide underground by mineralizing the carbon dioxide with coinjected fluids and minerals remaining from the extraction shale oil. In one embodiment, the oil shale of an illite-rich oil shale is heated to pyrolyze the shale underground, and carbon dioxide is provided to the remaining depleted oil shale while at an elevated temperature. Conditions are sufficient to mineralize the carbon dioxide.

  10. A technical study of TLD beta calibration factor for exposures to depleted uranium

    International Nuclear Information System (INIS)

    Ashley, J.C.; Turner, J.E.; McMahan, K.L.; Souleyrette, M.L.; Bogard, R.S.

    1995-06-01

    The beta calibration factor for converting light output (on reading a thermoluminescent dosimeter) to shallow dose equivalent has been reexamined through theoretical calculations and experimental measurements. The results support the previously determined value for contact with a depleted uranium slab but indicate that for many actual workplace situations, the contact value may be overly conservative

  11. Constraints on melt migration in the Earth's upper mantle

    Science.gov (United States)

    Garapic, Gordana

    Melting and melt segregation are key processes in the geochemical evolution of the Earth. However, mechanism and time scale of melt transport from the source to the surface are still not well understood and are dependent on the grain-scale distribution of melt. A related question is the retention of melt in partially molten regions of the Earth's upper mantle. Seismic observations from mid-ocean ridges (MOR) and subduction zones are interpreted to show in-situ melt contents up to 3%, while geochemical observations from MOR basalts are inferred to indicate very efficient extraction of melt (porosities of order of 0.1%). Earlier theoretical models of the melt distribution were based on the balance of surface tension between melt and uniform crystalline grains, predicting a simple network of melt along three-grain edges. Analyses of experimentally produced samples of olivine and basaltic melt show that the melt geometry is much more complex, and includes wetted two-grain boundaries. I reconstructed the 3-D model of melt geometry of two experimentally produced samples by serial sectioning and rendering of the pore space which demonstrates for the first time that melt exists in thin layers on two-grain boundaries. This confirms the inferences from previous 2-D observations and has significant implications for physical properties of partially molten regions, for example seismic velocities and attenuation. The wetted two-grain boundaries are inferred to be a consequence of continuous grain growth. Due to the complexity of the 3-D melt geometry the permeability of partially molten rocks can not be predicted from simple models. I therefore investigated the permeability as a function of porosity for both synthetic and experimentally determined pore geometries using a lattice-Boltzmann method. The calculated permeability is not a simple function of porosity, but increases rapidly at a critical fraction of wetted two-grain boundaries. To extrapolate the experimentally based

  12. A Subsolidus Olivine Water Solubility Equation for the Earth's Upper Mantle

    Science.gov (United States)

    Padrón-Navarta, J. A.; Hermann, J.

    2017-12-01

    The pressure and temperature sensitivity of the two most important point hydrous defects in mantle olivine involving Si vacancies (associated to trace amounts of titanium [TiChu-PD] or exclusively to Si vacancies [Si]) was investigated at subsolidus conditions in a fluid-saturated natural peridotite from 0.5 to 6 GPa (approximately 20-200 km depth) at 750 to 1050°C. Water contents in olivine were monitored in sandwich experiments with a fertile serpentine layer in the middle and olivine and pyroxene sensor layers at the border. Textures and mineral compositions provide evidence that olivine completely recrystallized during the weeklong experiments, whereas pyroxenes displayed only partial equilibration. A site-specific water solubility law for olivine has been formulated based on the experiments reconciling previous contradictory results from low- and high-pressure experiments. The site-specific solubility laws permit to constrain water incorporation into olivine in the subducting slab and the mantle wedge, as these are rare locations on Earth where fluid-present conditions exist. Chlorite dehydration in the hydrated slab is roughly parallel to the isopleth of 50 ± 20 ppm wt H2O in olivine, a value which is independent of the pressure and temperature trajectory followed by the slab. Hydrous defects are dominated by [Si] under the relevant conditions for the mantle wedge affected by fluids coming from the slab dehydration (slab-adjacent low viscosity/seismic low-velocity channel, P > 3 GPa). In cold subduction zones at 5.5 km from the slab surface the storage capacity of the mantle wedge at depths of 100-250 km ranges from 400 to 2,000 ppm wt H2O.

  13. Ensemble Kalman filter for the reconstruction of the Earth's mantle circulation

    Directory of Open Access Journals (Sweden)

    M. Bocher

    2018-02-01

    Full Text Available Recent advances in mantle convection modeling led to the release of a new generation of convection codes, able to self-consistently generate plate-like tectonics at their surface. Those models physically link mantle dynamics to surface tectonics. Combined with plate tectonic reconstructions, they have the potential to produce a new generation of mantle circulation models that use data assimilation methods and where uncertainties in plate tectonic reconstructions are taken into account. We provided a proof of this concept by applying a suboptimal Kalman filter to the reconstruction of mantle circulation (Bocher et al., 2016. Here, we propose to go one step further and apply the ensemble Kalman filter (EnKF to this problem. The EnKF is a sequential Monte Carlo method particularly adapted to solve high-dimensional data assimilation problems with nonlinear dynamics. We tested the EnKF using synthetic observations consisting of surface velocity and heat flow measurements on a 2-D-spherical annulus model and compared it with the method developed previously. The EnKF performs on average better and is more stable than the former method. Less than 300 ensemble members are sufficient to reconstruct an evolution. We use covariance adaptive inflation and localization to correct for sampling errors. We show that the EnKF results are robust over a wide range of covariance localization parameters. The reconstruction is associated with an estimation of the error, and provides valuable information on where the reconstruction is to be trusted or not.

  14. Active and fossil mantle flows in the western Alpine region unravelled by seismic anisotropy analysis and high-resolution P wave tomography

    Science.gov (United States)

    Salimbeni, Simone; Malusà, Marco G.; Zhao, Liang; Guillot, Stéphane; Pondrelli, Silvia; Margheriti, Lucia; Paul, Anne; Solarino, Stefano; Aubert, Coralie; Dumont, Thierry; Schwartz, Stéphane; Wang, Qingchen; Xu, Xiaobing; Zheng, Tianyu; Zhu, Rixiang

    2018-04-01

    The anisotropy of seismic velocities in the mantle, when integrated with high-resolution tomographic models and geologic information, can be used to detect active mantle flows in complex plate boundary areas, providing new insights on the impact of mantle processes on the topography of mountain belts. Here we use a densely spaced array of temporary broadband seismic stations to analyze the seismic anisotropy pattern of the western Alpine region, at the boundary between the Alpine and Apenninic slabs. Our results are supportive of a polyphase development of anisotropic mantle fabrics, possibly starting from the Jurassic to present. Geophysical data presented in this work, and geologic evidence taken from the literature, indicate that: (i) fossil fabrics formed during Tethyan rifting may be still preserved within the Alpine and Apenninic slabs; (ii) mantle deformation during Apenninic slab rollback is not compensated by a complete toroidal flow around the northern tip of the retreating slab; (iii) the previously observed continuous trend of anisotropy fast axes near-parallel to the western Alpine arc is confirmed. We observe that this arc-parallel trend of fast axes is located in correspondence to a low velocity anomaly in the European upper mantle, beneath regions of the Western and Ligurian Alps showing the highest uplift rates. We propose that the progressive rollback of the Apenninic slab, in the absence of a counterclockwise toroidal flow at its northern tip, induced a suction effect at the scale of the supraslab mantle. The resulting mantle flow pattern was characterized by an asthenospheric counterflow at the rear of the unbroken Western Alps slab and around its southern tip, and by an asthenospheric upwelling, mirrored by low P wave velocities, that would have favored the topographic uplift of the Alpine belt from the Mont Blanc to the Mediterranean sea.

  15. 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

  16. Carbon isotope fractionation during diamond growth in depleted peridotite: Counterintuitive insights from modelling water-maximum CHO fluids as multi-component systems

    Science.gov (United States)

    Stachel, T.; Chacko, T.; Luth, R. W.

    2017-09-01

    Because of the inability of depleted cratonic peridotites to effectively buffer oxygen fugacities when infiltrated by CHO or carbonatitic fluids, it has been proposed recently (Luth and Stachel, 2014) that diamond formation in peridotites typically does not occur by rock-buffered redox reactions as previously thought but by an oxygen-conserving reaction in which minor coexisting CH4 and CO2 components in a water-rich fluid react to form diamond (CO2 + CH4 = 2C + 2H2O). In such fluid-buffered systems, carbon isotope fractionation during diamond precipitation occurs in the presence of two dominant fluid carbon species. Carbon isotope modelling of diamond precipitation from mixed CH4- and CO2-bearing fluids reveals unexpected fundamental differences relative to diamond crystallization from a single carbon fluid species: (1) irrespective of which carbon fluid species (CH4 or CO2) is dominant in the initial fluid, diamond formation is invariably associated with progressive minor (units), the carbon isotope composition of the first-precipitated diamond decreases by 3.7‰. The tight mode in δ13C of - 5 ± 1 ‰ for diamonds worldwide places strict constraints on the dominant range of XCO2 in water-rich fluids responsible for diamond formation. Specifically, precipitation of diamonds with δ13C values in the range -4 to -6‰ from mantle-derived fluids with an average δ13C value of -5‰ (derived from evidence not related to diamonds) requires that diamond-forming fluids were relatively reduced and had methane as the dominant carbon species (XCO2 = 0.1-0.5). Application of our model to a recently published set of in-situ carbon isotope analyses for peridotitic diamonds from Marange, Zimbabwe (Smit et al., 2016), which contain CH4 fluid inclusions, allows us to perfectly match the observed co-variations in δ13 C, δ15 N and N content and at the same time explain the previously counter-intuitive observation of progressive 13C enrichment in diamonds that appear to have

  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. Gamma spectrometric determination of depleted Uranium in Yugoslavia

    International Nuclear Information System (INIS)

    Pantelic, G.; Eremic Savkovic, M.; Javorina, L.; Tanaskovic, I.; Vuletic, V.; Milacic, S.

    2002-01-01

    The radiation protection is very important interdisciplinary research field due to the presence of the radiation in daily life. The systematic examination of radioactive contamination of various environmental samples was established forty years ago in the Institute of Occupational and Radiological Health Dr Dragomir Karajovic for the sake of preventive protection of population and environment from the harmful effect of ionizing radiation. The global sources of radionuclide contamination in our country are the fallout due to previous nuclear testing and the deposition of radionuclides from the region of Chernobyl accident. The contents of radionuclides were determined in aerosol, soil, fallout (wet and dry deposition), rivers, lakes, drinking water, human and animal food. The samples were collected in several locations of the Republic of Serbia and in regular time intervals, according to methods determined by the regulation. The regulations and the monitoring programs were updated after the Chernobyl accident. In the recent time, after the NATO aggression, we analyzed depleted uranium content in the environmental samples. We used high-resolution gamma spectrometry measurements, because of their simplicity and accuracy. Aims of the control were to asses the increase of radioactivity above the natural levels in the immediate and near vicinity of the bomb craters, to asses the corresponding effect of changed natural radioactivity on the health of the population living in these places and finding unexploded depleted uranium bullets

  19. Characterization of Prochlorococcus clades from iron-depleted oceanic regions.

    Science.gov (United States)

    Rusch, Douglas B; Martiny, Adam C; Dupont, Christopher L; Halpern, Aaron L; Venter, J Craig

    2010-09-14

    Prochlorococcus describes a diverse and abundant genus of marine photosynthetic microbes. It is primarily found in oligotrophic waters across the globe and plays a crucial role in energy and nutrient cycling in the ocean ecosystem. The abundance, global distribution, and availability of isolates make Prochlorococcus a model system for understanding marine microbial diversity and biogeochemical cycling. Analysis of 73 metagenomic samples from the Global Ocean Sampling expedition acquired in the Atlantic, Pacific, and Indian Oceans revealed the presence of two uncharacterized Prochlorococcus clades. A phylogenetic analysis using six different genetic markers places the clades close to known lineages adapted to high-light environments. The two uncharacterized clades consistently cooccur and dominate the surface waters of high-temperature, macronutrient-replete, and low-iron regions of the Eastern Equatorial Pacific upwelling and the tropical Indian Ocean. They are genetically distinct from each other and other high-light Prochlorococcus isolates and likely define a previously unrecognized ecotype. Our detailed genomic analysis indicates that these clades comprise organisms that are adapted to iron-depleted environments by reducing their iron quota through the loss of several iron-containing proteins that likely function as electron sinks in the photosynthetic pathway in other Prochlorococcus clades from high-light environments. The presence and inferred physiology of these clades may explain why Prochlorococcus populations from iron-depleted regions do not respond to iron fertilization experiments and further expand our understanding of how phytoplankton adapt to variations in nutrient availability in the ocean.

  20. Interstellar depletions and the filling factor of the hot interstellar medium

    International Nuclear Information System (INIS)

    Dwek, E.; Scalo, J.M.

    1979-01-01

    We have examined theoretically the evolution of refractory interstellar grain abundances and corresponding metal deplections in the solar neighborhood. The calculations include a self-consistent treatment of red-giant winds, planetary nebulae, protostellar nebulae, and suprnovae as sources of grains and star formation, and of encounters with supernova blast waves as sinks. We find that in the standard two-phase model for the interstellar medium (ISM), grain destruction is very efficient, and the abundance of refractory grains should be negligible, contrary to observations. In a cloudy three-phase ISM most grains reside in the warm and cold phases of the medium. Supernova blast waves expand predominantly in the hot and tenuous phase of the medium and are showed down as they propagate through a cloud. In order to obtain significant (approx.3) depletions of metals presubably locked up in refractory grain cores, the destruction of grains that reside in the clouds must be minimal. This requires that (a) the density contrast between the cloud and intercloud medium be sufficiently high, and (b) the filling factor of the hot and tenuous gas of the interstellar medium, which presumably gives rise to the O VI absorption and soft X-ray emission, be nearly unity. Much larger depletions (> or approx. =10) must reflect accretion of mantles within interstellar clouds

  1. European upper mantle tomography: adaptively parameterized models

    Science.gov (United States)

    Schäfer, J.; Boschi, L.

    2009-04-01

    We have devised a new algorithm for upper-mantle surface-wave tomography based on adaptive parameterization: i.e. the size of each parameterization pixel depends on the local density of seismic data coverage. The advantage in using this kind of parameterization is that a high resolution can be achieved in regions with dense data coverage while a lower (and cheaper) resolution is kept in regions with low coverage. This way, parameterization is everywhere optimal, both in terms of its computational cost, and of model resolution. This is especially important for data sets with inhomogenous data coverage, as it is usually the case for global seismic databases. The data set we use has an especially good coverage around Switzerland and over central Europe. We focus on periods from 35s to 150s. The final goal of the project is to determine a new model of seismic velocities for the upper mantle underlying Europe and the Mediterranean Basin, of resolution higher than what is currently found in the literature. Our inversions involve regularization via norm and roughness minimization, and this in turn requires that discrete norm and roughness operators associated with our adaptive grid be precisely defined. The discretization of the roughness damping operator in the case of adaptive parameterizations is not as trivial as it is for the uniform ones; important complications arise from the significant lateral variations in the size of pixels. We chose to first define the roughness operator in a spherical harmonic framework, and subsequently translate it to discrete pixels via a linear transformation. Since the smallest pixels we allow in our parameterization have a size of 0.625 °, the spherical-harmonic roughness operator has to be defined up to harmonic degree 899, corresponding to 810.000 harmonic coefficients. This results in considerable computational costs: we conduct the harmonic-pixel transformations on a small Beowulf cluster. We validate our implementation of adaptive

  2. Highly siderophile element depletion in the Moon

    Science.gov (United States)

    Day, James M. D.; Walker, Richard J.

    2015-08-01

    Coupled 187Os/188Os and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance data are reported for Apollo 12 (12005, 12009, 12019, 12022, 12038, 12039, 12040), Apollo 15 (15555) and Apollo 17 (70135) mare basalts, along with mare basalt meteorites La Paz icefield (LAP) 04841 and Miller Range (MIL) 05035. These mare basalts have consistently low HSE abundances, at ∼ 2 ×10-5 to 2 ×10-7 the chondritic abundance. The most magnesian samples have broadly chondrite-relative HSE abundances and chondritic measured and calculated initial 187Os/188Os. The lower abundances and fractionated HSE compositions of more evolved mare basalts can be reproduced by modeling crystal-liquid fractionation using rock/melt bulk-partition coefficients of ∼2 for Os, Ir, Ru, Pt and Pd and ∼1.5 for Re. Lunar mare basalt bulk-partition coefficients are probably higher than for terrestrial melts as a result of more reducing conditions, leading to increased HSE compatibility. The chondritic-relative abundances and chondritic 187Os/188Os of the most primitive high-MgO mare basalts cannot readily be explained through regolith contamination during emplacement at the lunar surface. Mare basalt compositions are best modeled as representing ∼5-11% partial melting of metal-free sources with low Os, Ir, Ru, Pd (∼0.1 ng g-1), Pt (∼0.2 ng g-1), Re (∼0.01 ng g-1) and S (∼75 μg g-1), with sulphide-melt partitioning between 1000 and 10,000. Apollo 12 olivine-, pigeonite- and ilmenite normative mare basalts define an imprecise 187Re-187Os age of 3.0 ± 0.9 Ga with an initial 187Os/188Os of 0.107 ± 0.010. This age is within uncertainty of 147Sm-143Nd ages for the samples. The initial Os isotopic composition of Apollo 12 samples indicates that the source of these rocks evolved with Re/Os within ∼10% of chondrite meteorites, from the time that the mantle source became a system closed to siderophile additions, to the time that the basalts erupted. Similarity in absolute HSE

  3. Magnitude corrections for attenuation in the upper mantle

    International Nuclear Information System (INIS)

    Anon.

    1978-01-01

    Since 1969, a consistent discrepancy in seismic magnitudes of nuclear detonations at NTS compared with magnitudes of detonations elsewhere in the world has been observed. This discrepancy can be explained in terms of a relatively high seismic attenuation for compressional waves in the upper mantle beneath the NTS and in certain other locations. A correction has been developed for this attenuation based on a relationship between the velocity of compressional waves at the top of the earth's mantle (just beneath the Mohorovicic discontinuity) and the seismic attenuation further down in the upper mantle. Our new definition of body-wave magnitude includes corrections for attenuation in the upper mantle at both ends of the teleseismic body-wave path. These corrections bring the NTS oservations into line with measurements of foreign events, and enable one to make more reliable estimates of yields of underground nuclear explosions, wherever the explosion occurs

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

    DEFF Research Database (Denmark)

    Cherepanova, Yulia

    the development of a new regional crustal model, SibCrust, that is a digital crustal model for both the Siberian Craton and the West Siberian Basin. The SibCrust model, constrained by digitizing of all available seismic profiles and crustal velocity models across the Siberia, also includes a critical quality...... assessment of regional seismic data and crustal regionalization based on seismic structure of the crust. The second part of the study included the development of the SibDensity model that is the density model of the lithospheric mantle calculated by the mass balance method. Mantle density modeling involved...... 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....

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

    DEFF Research Database (Denmark)

    Guerri, Mattia

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

  6. Circulation of carbon dioxide in the mantle: multiscale modeling

    Science.gov (United States)

    Morra, G.; Yuen, D. A.; Lee, S.

    2012-12-01

    Much speculation has been put forward on the quantity and nature of carbon reservoirs in the deep Earth, because of its involvement in the evolution of life at the surface and inside planetary interiors. Carbon penetrates into the Earth's mantle mostly during subduction of oceanic crust, which contains carbonate deposits [1], however the form that it assumes at lower mantle depths is scarcely understood [2], hampering our ability to estimate the amount of carbon in the entire mantle by orders of magnitude. We present simulations of spontaneous degassing of supercritical CO2 using in-house developed novel implementations of the Fast-Multipole Boundary Element Method suitable for modeling two-phase flow (here mantle mineral and free CO2 fluid) through disordered materials such as porous rocks. Because the mutual interaction of droplets immersed either in a fluid or a solid matrix and their weakening effect to the host rock alters the strength of the mantle rocks, at the large scale the fluid phases in the mantle may control the creeping of mantle rocks [3]. In particular our study focuses on the percolation of supercritical CO2, estimated through the solution of the Laplace equation in a porous system, stochastically generated through a series of random Karhunen-Loeve decomposition. The model outcome is employed to extract the transmissivity of supercritical fluids in the mantle from the lowest scale up to the mantle scale and in combination with the creeping flow of the convecting mantle. The emerging scenarios on the global carbon cycle are finally discussed. [1] Boulard, E., et al., New host for carbon in the deep Earth. Proceedings of the National Academy of Sciences, 2011. 108(13): p. 5184-5187. [2] Walter, M.J., et al., Deep Mantle Cycling of Oceanic Crust: Evidence from Diamonds and Their Mineral Inclusions. Science, 2011. 334(6052): p. 54-57. [3] Morra, G., et al., Ascent of Bubbles in Magma Conduits Using Boundary Elements and Particles. Procedia Computer

  7. 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

  8. 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.

  9. Radiological safety assessment of gas mantle industries in India

    International Nuclear Information System (INIS)

    Sadagopan, G.; Venkataraman, G.

    1994-01-01

    Thorium, a radioactive element of actinide family was discovered by Berzelius in 1828 and named by him in honor of the Scandinavian God open-quote Thor close-quote. Following its discovery the earliest known use of thorium was in the making of gas mantles. The other use as an X-ray contrast medium open-quote Thorotrast close-quote has since long been discontinued, where as even today its use in gas mantles is continued. Gas lights have been used as a source of light since 1800's. In India, although electric bulbs have replaced most of the gas lights, even today in villages and in urban areas where there is no continuous power supply and in outdoor lightings gas lamps are used. The mantle which is used in these lamps is called the Welsbach mantle and is a netted hose that is impregnated with thorium nitrate and other metals. The function of a gas mantle is to produce a bright light during operation of the lighting device (gas or kerosene lamp) in which the mantle is placed. When placed in a lighting device and heated to 1300-1800 degree Celcius thorium in the mantle incandesces and gives off bright light. In India presently there are about 70 manufacturing units handling 150 metric tons of thorium nitrate annually. There are about four hundred persons involved in manufacturing 200 million mantles per year. Thorium is chosen because of its property of incadescence, however since it is radioactive, radiation safety of the workplace, handling personnel and safe environmental condition for members of public have to be maintained

  10. Sr-Nd evidence of paleoproterozoic mantle metasomatism in the lithospheric mantle beneath northeastern Brazil

    International Nuclear Information System (INIS)

    Hollanda, M.H.B.M.; Pimentel, M.M.; Jardim de Sa, E.F

    2001-01-01

    discuss about mantle metasomatism against crustal contamination. The difficulty in commenting about this question taking into consideration Proterozoic mantle-derived plutonic rocks is related to non-uniqueness in interpreting the common enriched signatures, since that are similar to geochemical signature of crustal rocks. In this study, the data were carefully treated for filtering out the effects of crustal contamination to recognise the nature of their mantle source and obtain a picture of the lithospheric mantle chemical at Proterozoic time (au)

  11. Late-orogenic mantle garnet pyroxenites evidence mantle refertilization during exhumation of orogenic belt

    Science.gov (United States)

    Chazot, G.; France, L.;