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Sample records for underlying upper mantle

  1. Upper mantle viscosity and lithospheric thickness under Iceland

    NARCIS (Netherlands)

    Barnhoorn, A.; Wal, W. van der; Drury, M.R.

    2011-01-01

    Deglaciation during the Holocene on Iceland caused uplift due to glacial isostatic adjustment. Relatively low estimates for the upper mantle viscosity and lithospheric thickness result in rapid uplift responses to the deglaciation cycles on Iceland. The relatively high temperatures of the upper

  2. Lateral, radial and temporal variations in upper mantle viscosity and rheology under Scandinavia

    NARCIS (Netherlands)

    Barnhoorn, A.; Wal, W. van der; Vermeersen, L.L.A.; Drury, M.R.

    2011-01-01

    The viscosity of the upper mantle has a large control on the dynamics of plate tectonic processes or the response of the Earth's crust after a period of glaciation. Temperature variations within the upper mantle, time-dependent stress changes due to glaciations, and/or variations in the

  3. Three-dimensional P velocity structure of the crust and upper mantle under Beijing region

    Energy Technology Data Exchange (ETDEWEB)

    Quan, A.; Liu, F.; Sun, Y.

    1980-04-01

    By use of the teleseismic P arrival times at 15 stations of the Beijing network for 120 events distributed over various azimuths, we studied the three-dimensional P velocity structure under the Beijing region. In calculating the theoretic travel time, we adopted the source parameters given in BISC, and used the J-B model as the standard model of earth. On inversion, we adopted singular value decomposition as a generalized inversion package, which can be used for solving very large over-determined systems of equations Gm = t without resorting to normal equations G/sup T/Gm = G/sup T/t. The results are that within the crust and upper mantle under the Beijing region there are clear lateral differences. In the results obtained by use of data from 1972 to 1975, it can be seen that there are three different zones of P-velocity. In the southeast Beijing region, P velocity is lower than that of the normal model by 10 to 14% within the crust, and by 8 to 9% within the upper mantle. The northwest Beijing region is a higher-velocity zone, within which the average P-velocity is faster than that of the normal model by about 9%. It disappears after entering into the upper mantle. The central part of this region is a normal zone. On the surface, the distribution of these P velocity variations corresponds approximately to the distribution of the over-burden. But in the deeper region, the distribution of velocity variation agrees with the distribution of seismicity. It is interesting to note that the hypocenters of several major earthquakes in this region, e.g., the Sanhe-Pinggu earthquake (1679, M = 8), the Shacheng earthquake (1730, M = 6-3/4) and the Tangshan earthquake (1976, M = 7.8), are all located very close to this boundary of these P-velocity variation zones.

  4. New Constraints on Upper Mantle Structure Underlying the Diamondiferous Central Slave Craton, Canada, from Teleseismic Body Wave Tomography

    Science.gov (United States)

    Esteve, C.; Schaeffer, A. J.; Audet, P.

    2017-12-01

    Over the past number of decades, the Slave Craton (Canada) has been extensively studied for its diamondiferous kimberlites. Not only are diamonds a valuable resource, but their kimberlitic host rocks provide an otherwise unique direct source of information on the deep upper mantle (and potentially transition zone). Many of the Canadian Diamond mines are located within the Slave Craton. As a result of the propensity for diamondiferous kimberlites, it is imperative to probe the deep mantle structure beneath the Slave Craton. This work is further motivated by the increase in high-quality broadband seismic data across the Northern Canadian Cordillera over the past decade. To this end we have generated a P and S body wave tomography model of the Slave Craton and its surroundings. Furthermore, tomographic inversion techniques are growing ever more capable of producing high resolution Earth models which capture detailed structure and dynamics across a range of scale lengths. Here, we present preliminary results on the structure of the upper mantle underlying the Slave Craton. These results are generated using data from eight different seismic networks such as the Canadian National Seismic Network (CNSN), Yukon Northwest Seismic Network (YNSN), older Portable Observatories for Lithospheric Analysis and Reseach Investigating Seismicity (POLARIS), Regional Alberta Observatory for Earthquake Studies Network (RV), USArray Transportable Array (TA), older Canadian Northwest Experiment (CANOE), Batholith Broadband (XY) and the Yukon Observatory (YO). This regional model brings new insights about the upper mantle structure beneath the Slave Craton, Canada.

  5. 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.

  6. 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.

  7. Deep global cycling of carbon constrained by the solidus of anhydrous, carbonated eclogite under upper mantle conditions

    Science.gov (United States)

    Dasgupta, Rajdeep; Hirschmann, Marc M.; Withers, Anthony C.

    2004-10-01

    eclogite solidus is likely to intersect the oceanic geotherm at a depth close to 400 km. Carbonated eclogite bodies entering the convecting upper mantle will thus release carbonate melt near the top of the mantle transition zone and may account for anomalously slow seismic velocities at depths of 280-400 km. Upon release, this small volume, highly reactive melt could be an effective agent of deep mantle metasomatism. Comparison of the carbonated eclogite solidus with that of peridotite-CO 2 shows a shallower solidus-geotherm intersection for the latter. This implies that carbonated peridotite is a more likely proximal source of magmatic carbon in oceanic provinces. However, carbonated eclogite is a potential source of continental carbonatites, as its solidus crosses the continental shield geotherm at ca. 4 GPa. Transfer of eclogite-derived carbonate melt to peridotite may account for the geochemical characteristics of some oceanic island basalts (OIBs) and their association with high CaO and CO 2.

  8. 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

  9. 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)

  10. 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

  11. 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,

  12. Magnetotellurics with geomagnetic observatory data influenced by the ocean effect: upper mantle conductivity under the islands of Gan and Tristan da Cunha

    Science.gov (United States)

    Morschhauser, A.; Grayver, A.; Kuvshinov, A. V.; Samrock, F.; Matzka, J.

    2017-12-01

    The electric conductivity of the oceanic lithosphere and upper mantle is not well constrained, mainly due to logistical challenges in oceanic surveys. However, electric field measurements can easily be added to geomagnetic observatories on islands.Currently, such measurements are available for Tristan da Cunha in the Atlantic Ocean and Gan on the Maldives in the Indian Ocean, and we derive tippers, impedances, and phase tensors for those observatories. The main challenge is that these transfer functions are severely affected by the conductivity contrast between seawater and land, which results in a three-dimensional (3-D) behaviour of the responses. We use an adaptive finite-element MT forward solver in order to properly account for this 3-D effect by including the available bathymetry and topography data into the model. Then, different transfer functions are individually inverted for upper mantle conductivities using a stochastic approach. We observe that tippers are mostly sensitive down to depths of approx. 100 km, and that additional electric field measurements improve the resolution for 100 to 200 km depth. The obtained 1-D conductivity profiles indicate a normal oceanic mantle below GAN and an anomalously conductive mantle below TDC, which may be related to the presence of melt below the island.

  13. Redox-influenced seismic properties of upper-mantle olivine

    Science.gov (United States)

    Cline, C. J., II; Faul, U. H.; David, E. C.; Berry, A. J.; Jackson, I.

    2018-03-01

    Lateral variations of seismic wave speeds and attenuation (dissipation of strain energy) in the Earth’s upper mantle have the potential to map key characteristics such as temperature, major-element composition, melt fraction and water content. The inversion of these data into meaningful representations of physical properties requires a robust understanding of the micromechanical processes that affect the propagation of seismic waves. Structurally bound water (hydroxyl) is believed to affect seismic properties but this has yet to be experimentally quantified. Here we present a comprehensive low-frequency forced-oscillation assessment of the seismic properties of olivine as a function of water content within the under-saturated regime that is relevant to the Earth’s interior. Our results demonstrate that wave speeds and attenuation are in fact strikingly insensitive to water content. Rather, the redox conditions imposed by the choice of metal sleeving, and the associated defect chemistry, appear to have a substantial influence on the seismic properties. These findings suggest that elevated water contents are not responsible for low-velocity or high-attenuation structures in the upper mantle. Instead, the high attenuation observed in hydrous and oxidized regions of the upper mantle (such as above subduction zones) may reflect the prevailing oxygen fugacity. In addition, these data provide no support for the hypothesis whereby a sharp lithosphere–asthenosphere boundary is explained by enhanced grain boundary sliding in the presence of water.

  14. Redox-influenced seismic properties of upper-mantle olivine.

    Science.gov (United States)

    Cline Ii, C J; Faul, U H; David, E C; Berry, A J; Jackson, I

    2018-03-14

    Lateral variations of seismic wave speeds and attenuation (dissipation of strain energy) in the Earth's upper mantle have the potential to map key characteristics such as temperature, major-element composition, melt fraction and water content. The inversion of these data into meaningful representations of physical properties requires a robust understanding of the micromechanical processes that affect the propagation of seismic waves. Structurally bound water (hydroxyl) is believed to affect seismic properties but this has yet to be experimentally quantified. Here we present a comprehensive low-frequency forced-oscillation assessment of the seismic properties of olivine as a function of water content within the under-saturated regime that is relevant to the Earth's interior. Our results demonstrate that wave speeds and attenuation are in fact strikingly insensitive to water content. Rather, the redox conditions imposed by the choice of metal sleeving, and the associated defect chemistry, appear to have a substantial influence on the seismic properties. These findings suggest that elevated water contents are not responsible for low-velocity or high-attenuation structures in the upper mantle. Instead, the high attenuation observed in hydrous and oxidized regions of the upper mantle (such as above subduction zones) may reflect the prevailing oxygen fugacity. In addition, these data provide no support for the hypothesis whereby a sharp lithosphere-asthenosphere boundary is explained by enhanced grain boundary sliding in the presence of water.

  15. 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.

  16. The upper-mantle transition zone beneath the Chile-Argentina flat subduction zone

    Science.gov (United States)

    Bagdo, Paula; Bonatto, Luciana; Badi, Gabriela; Piromallo, Claudia

    2016-04-01

    The main objective of the present work is the study of the upper mantle structure of the western margin of South America (between 26°S and 36°S) within an area known as the Chile-Argentina flat subduction zone. For this purpose, we use teleseismic records from temporary broad band seismic stations that resulted from different seismic experiments carried out in South America. This area is characterized by on-going orogenic processes and complex subduction history that have profoundly affected the underlying mantle structure. The detection and characterization of the upper mantle seismic discontinuities are useful to understand subduction processes and the dynamics of mantle convection; this is due to the fact that they mark changes in mantle composition or phase changes in mantle minerals that respond differently to the disturbances caused by mantle convection. The discontinuities at a depth of 410 km and 660 km, generally associated to phase changes in olivine, vary in width and depth as a result of compositional and temperature anomalies. As a consequence, these discontinuities are an essential tool to study the thermal and compositional structure of the mantle. Here, we analyze the upper-mantle transition zone discontinuities at a depth of 410 km and 660 km as seen from Pds seismic phases beneath the Argentina-Chile flat subduction.

  17. 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

  18. Upper Mantle Responses to India-Eurasia Collision in Indochina, Malaysia, and the South China Sea

    Science.gov (United States)

    Hongsresawat, S.; Russo, R. M.

    2016-12-01

    We present new shear wave splitting and splitting intensity measurements from SK(K)S phases recorded at seismic stations of the Malaysian National Seismic Network. These results, in conjunction with results from Tibet and Yunnan provide a basis for testing the degree to which Indochina and South China Sea upper mantle fabrics are responses to India-Eurasia collision. Upper mantle fabrics derived from shear wave splitting measurements in Yunnan and eastern Tibet parallel geodetic surface motions north of 26°N, requiring transmission of tractions from upper mantle depths to surface, or consistent deformation boundary conditions throughout the upper 200 km of crust and mantle. Shear wave splitting fast trends and surface velocities diverge in eastern Yunnan and south of 26°N, indicating development of an asthenospheric layer that decouples crust and upper mantle, or corner flow above the subducted Indo-Burma slab. E-W fast shear wave splitting trends southwest of 26°N/104°E indicate strong gradients in any asthenospheric infiltration. Possible upper mantle flow regimes beneath Indochina include development of olivine b-axis anisotropic symmetry due to high strain and hydrous conditions in the syntaxis/Indo-Burma mantle wedge (i.e., southward flow), development of strong upper mantle corner flow in the Indo-Burma wedge with olivine a-axis anisotropic symmetry (i.e., westward flow), and simple asthenospheric flow due to eastward motion of Sundaland shearing underlying asthenosphere. Further south, shear-wave splitting delay times at Malaysian stations vary from 0.5 seconds on the Malay Peninsula to over 2 seconds at stations on Borneo. Splitting fast trends at Borneo stations and Singapore trend NE-SW, but in northern Peninsular Malaysia, the splitting fast polarization direction is NW-SE, parallel to the trend of the Peninsula. Thus, there is a sharp transition from low delay time and NW-SE fast polarization to high delay times and fast polarization directions that

  19. Upper mantle structure at Walvis Ridge from Pn tomography

    Science.gov (United States)

    Ryberg, Trond; Braeuer, Benjamin; Weber, Michael

    2017-10-01

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

  20. The upper mantle beneath the Philippine Sea from waveform inversions

    NARCIS (Netherlands)

    Lebedev, Sergei; Nolet, Guust; Hilst, R.D. van der

    1997-01-01

    We present a three‐dimensional S‐velocity model for the upper mantle beneath the Philippine Sea region. It was derived from inversions of 281 broad band vertical‐component seismograms recorded in the area at the Global Seismological Network (GSN) and SKIPPY portable array stations. We have been able

  1. 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

  2. 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.

  3. TranSCorBe Project: A high-resolution seismic-passive profile to study the variation of the crustal and upper mantle structures under the Betic mountain ranges

    Science.gov (United States)

    Morales, José; Martín, Rosa; Stich, Daniel; Heit, Benjamín; Yuan, Xiaohui; Mancilla, Flor; Benito, José; Carrion, Francisco; Serrano, Inmaculada; López-Comino, Jose Angel; Abreu, Rafael; Alguacil, Gerardo; Almendros, Javier; Carmona, Enrique; Ontiveros, Alfonso; García-Quiroga, Daniel; García-Jerez, Antonio

    2014-05-01

    The goal of this project is to study the crustal and upper mantle structures under the Betic mountain ranges and their variations between the different geological domains. We deployed 50 broadband and short period seismic stations during 18 months following two profiles. We collect teleseismic events to perform a high-resolution P-to-S and S-to-P receiver function analysis. The main profile (TranSCorBe), of 160 km length, starts near the coast in Mazarrón (Murcia) and follows a NW-SE direction, crossing the Cazorla mountain range. It probes, from south to north, the Alboran domain (metamorphic rocks), the External zones (sedimentary rocks) and the Variscan terrains of the Iberian Massif. The spacing between stations is around 3-4 km. This inter-station distance allows us mapping with high accuracy the variations of the crust and upper mantle discontinuities in the Betic Range and their transition to the Iberian Massif. A second profile (HiRe II) with a larger spacing between seismic stations, is a continuation of a previously installed HiRe I profile, a NS profile starting near the Mediterranean coast in Adra (Almería) through Sierra Nevada Mountains. HiRe II profile prolongs HiRe I profile until the Variscan intersecting with TranSCorBe profile near Cazorla.

  4. Measurements of upper mantle shear wave anisotropy from a permanent network in southern Mexico

    NARCIS (Netherlands)

    van Benthem, S.A.C.; Valenzuela, R.W.; Ponce, G.J.

    2013-01-01

    Upper mantle shear wave anisotropy under stations in southern Mexico was measured using records of SKS phases. Fast polarization directions where the Cocos plate subducts subhorizontally are oriented in the direction of the relative motion between the Cocos and North American plates, and are

  5. Upper-mantle velocity structure and its relation to topography across the Caledonides in Greenland and Norway

    DEFF Research Database (Denmark)

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

    2015-01-01

    This study investigates the upper-mantle P- and S-wave velocity structure as well as structure in the VP/VS ratio across the high topography areas of north Atlantic Caledonides, integrating data from a new East Greenland Caledonide Central Fjord Array (EGCFA) with results of recent studies...... strong upper-mantle velocity boundary under the East Greenland Caledonides. However, the contrast in the VP/VS ratio is not as clear at this location. A correlation study of topography versus upper-mantle velocity revealed positive correlation in southern Norway but negative or absent correlation...

  6. The European Continent : Surface Expression of Upper Mantle Dynamics

    Science.gov (United States)

    Tondi, M. R.; Schivardi, R.; Molinari, I.; Morelli, A.

    2012-12-01

    images of the European upper mantle isotropic shear-wave speeds and mass densities, recently recovered by combined inversion of surface-wave information and GRACE satellite gravity data (Tondi et al., 2012) are used to select the regions where the residual topography and the residual mantle gravity anomalies are strongly correlated (correlation coefficient is equal to 1). We assume surface uplift processes with negative density anomalies and downward pull with positive anomalies. Our work shows a strong correlation among the areas where, on the basis of our assumptions, the mantle dynamics have surface expression and the areas of low values of radial anisotropy: (1) the southern margins of the East European Craton, (2) the North-Eastern edges of the Arabian Plateau, (3) the northern edge of the CEVP (Central European Volcanic Province), (4) the North-Eastern part of the Atlantic Ocean, between Greenland and Iceland.

  7. Upper mantle and crustal structure of the East Greenland Caledonides

    DEFF Research Database (Denmark)

    Schiffer, Christian; Balling, N.; Jacobsen, B. H.

    of the North Atlantic passive margins, including the gravitational collapse, extension, rifting and a possible influence by volcanism related to the Iceland hot spot. The landscape and topography were finally shaped by extensive erosion, finding its peak in the quaternary glaciations. Seismological data were...... present selected results from on-going detailed studies of the crustal and upper mantle, including a Receiver Function inversion, seismic P-wave travel time tomography and gravity modelling....

  8. Superweak asthenosphere in light of upper mantle seismic anisotropy

    Science.gov (United States)

    Becker, Thorsten W.

    2017-05-01

    Earth's upper mantle includes a ˜200 km thick asthenosphere underneath the plates where viscosity and seismic velocities are reduced compared to the background. This zone of weakness matters for plate dynamics and may be required for the generation of plate tectonics itself. However, recent seismological and electromagnetic studies indicate strong heterogeneity in thinner layers underneath the plates which, if related to more extreme, global viscosity reductions, may require a revision of our understanding of mantle convection. Here, I use dynamically consistent mantle flow modeling and the constraints provided by azimuthal seismic anisotropy as well as plate motions to explore the effect of a range of global and local viscosity reductions. The fit between mantle flow model predictions and observations of seismic anisotropy is highly sensitive to radial and lateral viscosity variations. I show that moderate suboceanic viscosity reductions, to ˜0.01-0.1 times the upper mantle viscosity, are preferred by the fit to anisotropy and global plate motions, depending on layer thickness. Lower viscosities degrade the fit to azimuthal anisotropy. Localized patches of viscosity reduction, or layers of subducted asthenosphere, however, have only limited additional effects on anisotropy or plate velocities. This indicates that it is unlikely that regional observations of subplate anomalies are both continuous and indicative of dramatic viscosity reduction. Locally, such weak patches may exist and would be detectable by regional anisotropy analysis, for example. However, large-scale plate dynamics are most likely governed by broad continent-ocean asthenospheric viscosity contrasts rather than a thin, possibly high melt fraction layer.

  9. 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

  10. Seismic imaging of the upper mantle beneath the northern Central Andean Plateau: Implications for surface topography

    Science.gov (United States)

    Ward, K. M.; Zandt, G.; Beck, S. L.; Wagner, L. S.

    2015-12-01

    Extending over 1,800 km along the active South American Cordilleran margin, the Central Andean Plateau (CAP) as defined by the 3 km elevation contour is second only to the Tibetan Plateau in geographic extent. The uplift history of the 4 km high Plateau remains uncertain with paleoelevation studies along the CAP suggesting a complex, non-uniform uplift history. As part of the Central Andean Uplift and the Geodynamics of High Topography (CAUGHT) project, we use surface waves measured from ambient noise and two-plane wave tomography to image the S-wave velocity structure of the crust and upper mantle to investigate the upper mantle component of plateau uplift. We observe three main features in our S-wave velocity model including (1), a high velocity slab (2), a low velocity anomaly above the slab where the slab changes dip from near horizontal to a normal dip, and (3), a high-velocity feature in the mantle above the slab that extends along the length of the Altiplano from the base of the Moho to a depth of ~120 km with the highest velocities observed under Lake Titicaca. A strong spatial correlation exists between the lateral extent of this high-velocity feature beneath the Altiplano and the lower elevations of the Altiplano basin suggesting a potential relationship. Non-uniqueness in our seismic models preclude uniquely constraining this feature as an uppermost mantle feature bellow the Moho or as a connected eastward dipping feature extending up to 300 km in the mantle as seen in deeper mantle tomography studies. Determining if the high velocity feature represents a small lithospheric root or a delaminating lithospheric root extending ~300 km into the mantle requires more integration of observations, but either interpretation shows a strong geodynamic connection with the uppermost mantle and the current topography of the northern CAP.

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

    Science.gov (United States)

    Plomerova, Jaroslava; Babuska, Vladislav

    2017-04-01

    Teleseismic body-wave tomography represents powerful tool to study regional velocity structure of the upper mantle and to image velocity anomalies, such as subducted lithosphere plates in collisional zones. In this contribution, we recapitulate 3D models of the upper mantle beneath the Alps, which developed at a collision zone of the Eurasian and African plates. Seismic tomography studies indicate a leading role of the rigid mantle lithosphere that functioned as a major stress guide during the plate collisions. Interactions of the European lithosphere with several micro-plates in the south resulted in an arcuate shape of this mountain range on the surface and in a complicated geometry of the Alpine subductions in the mantle. Early models with one bended lithosphere root have been replaced with more advanced models showing two separate lithosphere roots beneath the Western and Eastern Alps (Babuska et al., Tectonophysics 1990; Lippitsch et al., JGR 2003). The standard isotropic velocity tomography, based on pre-AlpArray data (the currently performed passive seismic experiment in the Alps and surroundings) images the south-eastward dipping curved slab of the Eurasian lithosphere in the Western Alps. On the contrary, beneath the Eastern Alps the results indicate a very steep northward dipping root that resulted from the collision of the European plate with the Adriatic microplate. Dando et al. (2011) interpret high-velocity heterogeneities at the bottom of their regional tomographic model as a graveyard of old subducted lithospheres. High density of stations, large amount of rays and dense ray-coverage of the volume studied are not the only essential pre-requisites for reliable tomography results. A compromise between the amount of pre-processed data and the high-quality of the tomography input (travel-time residuals) is of the high importance as well. For the first time, the existence of two separate roots beneath the Alps has been revealed from carefully pre

  12. Upper Mantle Discontinuities Underneath Central and Southern Mexico

    Science.gov (United States)

    Perez-Campos, X.; Clayton, R. W.

    2011-12-01

    Central and southern Mexico are affected by the subduction of Cocos plate beneath North American plate. The MesoAmerican Subduction Experiment (MASE) and the Veracruz-Oaxaca (VEOX) project have mapped the geometry of the Cocos slab. It is characterized in central Mexico by a shallow horizontal geometry up to ~300 km from the trench, then it dives steeply (70°) into the mantle, to its apparent end at 500 km depth. In contrast, some 400 km to the south, the slab subducts smoothly, with a dip angle of ~26° to a depth of 150 km. We use receiver functions from teleseismic events, recorded at stations from MASE, VEOX, and the Servicio Sismológico Nacional (SSN, Mexican National Seismological Service) to map the upper mantle discontinuities and properties of the transition zone in central and southern Mexico. We also use data from the Mapping the Rivera Subduction Zone (MARS) Experiment to get a complete picture of the subduction regime in central Mexico and compare the mantle transition zone in a slab tear regime. The 410 discontinuity shows significant variation in topography in central Mexico, particularly where the slab is expected to reach such depth. The 660 discontinuity shows a smoother topography, indicating that the slab does not penetrate this far down. The results will be compared with a ridge regime in the Gulf of California.

  13. Origin of a 'Southern Hemisphere' geochemical signature in the Arctic upper mantle.

    Science.gov (United States)

    Goldstein, Steven L; Soffer, Gad; Langmuir, Charles H; Lehnert, Kerstin A; Graham, David W; Michael, Peter J

    2008-05-01

    The Gakkel ridge, which extends under the Arctic ice cap for approximately 1,800 km, is the slowest spreading ocean ridge on Earth. Its spreading created the Eurasian basin, which is isolated from the rest of the oceanic mantle by North America, Eurasia and the Lomonosov ridge. The Gakkel ridge thus provides unique opportunities to investigate the composition of the sub-Arctic mantle and mantle heterogeneity and melting at the lower limits of seafloor spreading. The first results of the 2001 Arctic Mid-Ocean Ridge Expedition (ref. 1) divided the Gakkel ridge into three tectonic segments, composed of robust western and eastern volcanic zones separated by a 'sparsely magmatic zone'. On the basis of Sr-Nd-Pb isotope ratios and trace elements in basalts from the spreading axis, we show that the sparsely magmatic zone contains an abrupt mantle compositional boundary. Basalts to the west of the boundary display affinities to the Southern Hemisphere 'Dupal' isotopic province, whereas those to the east-closest to the Eurasian continent and where the spreading rate is slowest-display affinities to 'Northern Hemisphere' ridges. The western zone is the only known spreading ridge outside the Southern Hemisphere that samples a significant upper-mantle region with Dupal-like characteristics. Although the cause of Dupal mantle has been long debated, we show that the source of this signature beneath the western Gakkel ridge was subcontinental lithospheric mantle that delaminated and became integrated into the convecting Arctic asthenosphere. This occurred as North Atlantic mantle propagated north into the Arctic during the separation of Svalbard and Greenland.

  14. 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.

  15. Experimental investigation of flow-induced fabrics in rocks at upper-mantle pressures. Application to understanding mantle dynamics and seismic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Durham, William B. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

    2016-05-02

    The goal of this collaborative research effort between W.B. Durham at the Massachusetts Institute of Technology (MIT) and D.L. Kohlstedt and S. Mei at the University of Minnesota (UMN) was to exploit a newly developed technology for high-pressure, high-temperature deformation experimentation, namely, the deformation DIA (D-DIA), to determine the deformation behavior of a number of important upper mantle rock types including olivine, garnet, enstatite, and periclase. Experiments were carried out under both hydrous and anhydrous conditions and at both lithospheric and asthenospheric stress and temperature conditions. The result was a group of flow laws for Earth’s upper mantle that quantitatively describe the viscosity of mantle rocks from shallow depths (the lithosphere) to great depths (the asthenosphere). These flow laws are fundamental for modeling the geodynamic behavior and heat transport from depth to Earth’s surface.-

  16. Experimental investigation of flow-induced fabrics in rocks at upper-mantle pressures: Application to understanding mantle dynamics and seismic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Kohlstedt, David L. [Univ. of Minnesota, Minneapolis, MN (United States)

    2016-04-26

    The goal of this collaborative research effort between W.B. Durham at the Massachusetts Institute of Technology (MIT) and D.L. Kohlstedt and S. Mei at the University of Minnesota (UMN) was to exploit a newly developed technology for high-pressure, high-temperature deformation experimentation, namely, the deformation DIA (D-DIA) to determine the deformation behavior of a number of important upper mantle rock types including olivine, garnet, enstatite, and periclase. Experiments were carried out under both hydrous and anhydrous conditions and at both lithospheric and asthenospheric stress and temperature conditions. The result was a group of flow laws for Earth’s upper mantle that quantitatively describe the viscosity of mantle rocks from shallow depths (the lithosphere) to great depths (the asthenosphere). These flow laws are fundamental for modeling the geodynamic behavior and heat transport from depth to Earth’s surface.

  17. Kinematics of subduction and subduction-induced flow in the upper mantle

    NARCIS (Netherlands)

    Schellart, W. P.

    2004-01-01

    Results of fluid dynamical experiments are presented to model the kinematics of lithospheric subduction in the upper mantle. The experiments model a dense highviscosity plate (subducting lithosphere) overlying a less dense low-viscosity layer (upper mantle). The overriding lithosphere is not

  18. The upper mantle beneath the Gulf of California from surface wave dispersion. Geologica Ultraiectina (299)

    NARCIS (Netherlands)

    Zhang, X.

    2009-01-01

    This thesis is a study on upper mantle shear velocity structure beneath the Gulf of California. Surface wave interstation dispersion data were measured in the Gulf of California area and vicinity to obtain a 3-D shear velocity structure of the upper mantle. This work has particular significance for

  19. 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.

  20. Upper-mantle structure in southern Norway from beamforming of Rayleigh wave data presenting multipathing

    Science.gov (United States)

    Maupin, Valérie

    2011-05-01

    A model for the upper mantle SV-wave velocity under southern Norway is obtained by depth inversion of the average phase velocity of the Rayleigh wave fundamental mode in the area. The average dispersion curve is obtained in the period range 22-200 s by beamforming of 190 Rayleigh waves recorded by the MAGNUS network, a temporary regional network of 41 broad-band stations. Resolution of the beamforming procedure is increased by deconvolving the original beams from the array response function using the Lucy-Richardson algorithm. In addition to an average phase velocity, beamforming gives us some information concerning the nature of the incoming wavefield. We detect deviations of the wave propagation direction from the great-circle paths which commonly reach 10° at a period of 25 s for the teleseismic events. The amplitude of the deviations decreases with increasing period and with decreasing epicentral distance, as expected. The phase velocity measured by beamforming does not show any correlation with the deviation from great circle path, suggesting that deviation does not bias phase velocity measurements. We detect also significant multipathing with characteristics that vary rapidly with frequency. The obtained SV-wave velocity profile clearly shows that southern Norway is underlain by a low-velocity zone in the upper mantle and does not have shield-like characteristics, despite its location in the Baltic shield. These findings support the hypothesis that the high topography of southern Norway is sustained by anomalous upper-mantle material.

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

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2014-01-01

    and by introducing variations into the crustal structure which corresponds to the uncertainty of its resolution by highquality and low-quality seismic models. We examine the propagation of these uncertainties into determinations of lithospheric mantle density. Given a relatively small range of expected density......We present a regional model for the density structure of the North American upper mantle. The residual mantle gravity anomalies are based on gravity data derived from the GOCE geopotential models with crustal correction to the gravity field being calculated from a regional crustal model. We analyze...... how uncertainties and errors in the crustal model propagate from crustal densities to mantle residual gravity anomalies and the density model of the upper mantle. Uncertainties in the residual upper (lithospheric) mantle gravity anomalies result from several sources: (i) uncertainties in the velocity-density...

  2. Slow upper mantle beneath Southern Norway from surface waves

    Science.gov (United States)

    Weidle, C.; Maupin, V.

    2009-04-01

    A recent regional surface wave tomography for Northern Europe revealed unprecedented images of the upper mantle beneath the (Tertiary) North Atlantic and the bordering Fennoscandian craton of Archean-Proterozoic age. With respect to the circum-Atlantic regions of uplift, no common mantle pattern supporting the uplift of these regions is observed. The western boundary of the thick cratonic lithosphere follows the trend of the continental margin offshore northern Norway (i.e. the northern Scandes are underlain by thick lithosphere) whereas further south the boundary of the craton is located further east beneath southwestern Sweden. SV shear wave velocities beneath southern Norway are 10% slower than ak135 (at 70-115 km depth) and these low-velocities are clearly connected to the North Atlantic low-velocity regime through a ~ 400 km wide "channel". The low-velocity anomaly beneath Southern Norway coincides in geometry roughly with the dome-like high topography of the southern Scandes and may thus have a non-negligible contribution to the isostatic balance of the region. The amplitude and depth-distribution of this anomaly are due to be further constrained by new data that were acquired during the MAGNUS experiment in 2006-2008. The temporary seismic network, consisting of 40 broadband seismometers covers to a large extent the location of the anomaly as imaged by the regional tomography. This enables us to get unique control on the tomographic model at improved lateral and vertical resolution. Preliminary analysis of surface wave phase velocities yields an average 1-D shear wave velocity profile for southern Norway as a first step to constrain the presence and depth extent of this low-velocity anomaly.

  3. 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

  4. Combined teleseismic surface wave and receiver function analysis of the crust and upper mantle of Madagascar

    Science.gov (United States)

    Pratt, M. J.; Aleqabi, G. I.; Wysession, M. E.; Wiens, D. A.; Nyblade, A.; Shore, P.; Rambolamanana, G.; Tsiriandrimanana, R.; Andriampenomanana Ny Ony, F. S. T.

    2014-12-01

    The continental crust and upper mantle velocity structure beneath Madagascar remained poorly constrained until recent deployments of broadband seismic instrumentation across the island. The MACOMO (MAdagascar, COmoros and MOzambique), RHUM-RUM (Réunion Hotspot and Upper Mantle - Réunions Unterer Mantel) and the Madagascar Seismic Profile experiments have opened up this region to be studied in detail for the first time. The island is an amalgamation of an Archean craton, associated with the Western Dhawar craton of southern India, and a series of Proterozoic terranes that comprise the backbone of the island (Tucker et al., 2010). A receiver-function analysis has provided both the first Moho depth measurements and spatially discrete 1-D shear velocity results that matched well with known tectonic regions. To provide a more continuous 2-D and 3-D velocity structure map, teleseismic surface wave analysis is employed. Using Helmholtz tomography as implemented by the ASWMS package (Ge, Gaherty and Hutko; 2014), we are able to map phase velocities from the cross-correlation of station pairs at periods 20-100 s. At periods 20-40 s our results compare well with ambient noise analysis results (see poster by Wysession et al. (this meeting)). The prominent features of these results are a distinct low phase-velocity sector beneath the central Itasy region, with a secondary low phase-velocity region to the north of the island. Both the central part of the island and the northern region have experienced geothermal activity in recent times as well as volcanic activity within the last 10,000 years. This may suggest that the crust and underlying mantle in these regions remains at relatively higher temperatures than the surrounding rock. Combining this information with receiver-function analysis, we jointly invert our data for the shear velocity structure. These analyses will constrain the upper mantle seismic velocities in the region, allowing further analysis from body waves to

  5. 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).

  6. Multiple-frequency tomography of the upper mantle beneath the African/Iberian collision zone

    Science.gov (United States)

    Bonnin, Mickaël; Nolet, Guust; Villaseñor, Antonio; Gallart, Josep; Thomas, Christine

    2014-09-01

    During the Cenozoic, the geodynamics of the western Mediterranean domain has been characterized by a complex history of subduction of Mesozoic oceanic lithosphere. The final stage of these processes is proposed to have led to the development of the Calabria and Gibraltar arcs, whose formation is still under debate. In this study, we take advantage of the dense broad-band station networks now available in the Alborán Sea region, to develop a high-resolution 3-D tomographic P velocity model of the upper mantle beneath the African/Iberian collision zone that will better constraint the past dynamics of this zone. The model is based on 13200 teleseismic arrival times recorded between 2008 and 2012 at 279 stations for which cross-correlation delays are measured with a new technique in different frequency bands centred between 0.03 and 1.0 Hz, and for the first time interpreted using multiple frequency tomography. Our model shows, beneath the Alborán Sea, a strong (4 per cent) fast vertically dipping anomaly observed to at least 650 km depth. The arched shape of this anomaly, and its extent at depth, are coherent with a lithospheric slab, thus favouring the hypothesis of a westward consumption of the Ligurian ocean slab by roll-back during Cenozoic. In addition to this fast anomaly in the deep upper mantle, high intensity slow anomalies are widespread in the lithosphere and asthenosphere beneath Morocco and southern Spain. These anomalies are correlated at the surface with the position of the Rif and Atlas orogens and with Cenozoic volcanic fields. We thus confirm the presence, beneath Morocco, of an anomalous (hot?) upper mantle, but without clear indication for a lateral spreading of the Canary plume to the east.

  7. Tomography of the upper mantle beneath the African/Iberian collision zone

    Science.gov (United States)

    Mickael, B.; Nolet, G.; Villasenor, A.; Josep, G.; Thomas, C.

    2013-12-01

    During Cenozoic, geodynamics of the western Mediterranean domain has been characterized by a complex history of subduction of Mesozoic oceanic lithosphere. The final stage of these processes is proposed to have led to the development of the Calabria and Gibraltar arcs, whose formation is still under debate. In this study we take advantage of the dense broadband-station networks now available in Alborán Sea region, to develop a high-resolution 3D tomographic P velocity model of the upper mantle beneath the African/Iberian collision zone that will bring new constraints on the past dynamics of this zone. The model is based on 13200 teleseismic arrival times recorded between 2008 and 2012 at 279 stations for which cross-correlation delays are measured with a new technique in different frequency bands centered between 0.03 and 1.0 Hz, and interpreted using multiple frequency tomography. Our model shows, beneath Alborán Sea, a strong (~ 4%) fast vertically dipping anomaly observed to at least 650 km depth. The arched shape of this anomaly and its extent at depth are coherent with a lithospheric slab, thus favoring the hypothesis of a westward consumption of the Ligurian ocean slab by roll-back during Cenozoic. In addition to this fast anomaly in the deep upper-mantle, several high intensity slow anomalies are widely observed in the lithosphere and asthenosphere beneath Morocco and southern Spain. These anomalies are correlated at surface with the position of the orogens (Rif and Atlas) and with Cenozoic volcanic fields. We thus confirm the presence, beneath Morocco, of an anomalous (hot) upper mantle, with piece of evidence for a lateral connection with the Canary volcanic islands, likely indicating a lateral spreading of the Canary plume to the east.

  8. High pressure and temperature deformation experiments on San Carlos olivine and implications for upper mantle anisotropy

    Science.gov (United States)

    Shekhar, Sushant; Frost, Daniel J.; Walte, Nicolas; Miyajima, Nobuyoshi; Heidelbach, Florian

    2010-05-01

    Crystallographic preferred orientation developed in olivine due to shearing in the mantle is thought to be the prominent reason behind seismic anisotropy in the upper mantle. Seismic anisotropy in upper mantle can be observed up to a depth of 350 km with a marked drop in the strength of anisotropy seen around 250 km. Studies on natural rock samples from the mantle and deformation experiments performed on olivine have revealed that olivine deforms mainly through dislocation creep with Burgers vectors parallel to the [100] crystallographic axis under low pressure conditions (up to 3 GPa). Under similar pressures, evidence of [001] slip has been reported due to the presence of water. In order to understand the deformation mechanism in olivine at pressures greater than 3 GPa, we have performed experiments using the deformation DIA multi-anvil apparatus. The DIA consist of 6 square faceted anvils that compress a cubic high-pressure assembly. The deformation DIA possesses two vertically acting opposing inner rams, which can be operated independently of the main compressive force to deform the sample assembly. The experimental setup consists of a hot-pressed sample of polycrystalline dry San Carlos olivine 0.2 mm cut from a 1.2 mm diameter core at 45° . This slice is sandwiched between alumina pistons also cut at 45° in simple shear geometry. Experiments have been performed at 3, 5 and 8 GPa at a deformation anvil strain rate of 1.0x10-4 s-1and temperatures between 1200-1400° C. Deformed samples were cut normal to the shear plane and parallel to the shear direction. Then the sample was polished and analyzed using electron back scattered diffraction (EBSD) to identify the crystallographic preferred orientation (CPO). The fabric that developed in olivine deformed at 3 GPa mainly resulted from the [100] slip on the (010) plane. Samples deformed at 5 GPa showed both [100] and [001] slip. On the other hand, samples deformed at 8 GPa and 1200° C, show deformation mainly

  9. H2O solubility in basalt at upper mantle conditions

    Science.gov (United States)

    Mitchell, Alexandra L.; Gaetani, Glenn A.; O'Leary, Julie A.; Hauri, Erik H.

    2017-10-01

    This study presents a new experimental approach for determining H2O solubility in basaltic melt at upper mantle conditions. Traditional solubility experiments are limited to pressures of 600 MPa or less because it is difficult to reliably quench silicate melts containing greater than 10 wt% dissolved H2O. To overcome this limitation, our approach relies on the use of secondary ion mass spectrometry to measure the concentration of H dissolved in olivine and on using the measured H in olivine as a proxy for the concentration of H2O in the co-existing basaltic melt. The solubility of H2O in the melt is determined by performing a series of experiments at a single pressure and temperature with increasing amounts of liquid H2O added to each charge. The point at which the concentration of H in the olivine first becomes independent of the amount of initial H2O content of the charge (added + adsorbed H2O) indicates its solubility in the melt. Experiments were conducted by packing basalt powder into a capsule fabricated from San Carlos olivine, which was then pressure-sealed inside a Ni outer capsule. Our experimental results indicate that at 1000 MPa and 1200 °C, the solubility of H2O in basaltic melt is 20.6 ± 0.9 wt% (2 × standard deviation). This concentration is considerably higher than predicted by most solubility models but defines a linear relationship between H2O fugacity and the square of molar H2O solubility when combined with solubility data from lower pressure experiments. Further, our solubility determination agrees with melting point depression determined experimentally by Grove et al. (2006) for the H2O-saturated peridotite solidus at 1000 MPa. Melting point depression calculations were used to estimate H2O solubility in basalt along the experimentally determined H2O-saturated peridotite solidus. The results suggest that a linear relationship between H2O fugacity and the square of molar solubility exists up to 1300 MPa, where there is an inflection point

  10. Helium Isotope Variations in Basalts Along Gakkel Ridge and Heterogeneity of the Arctic Upper Mantle

    Science.gov (United States)

    Graham, D. W.; Lupton, J. E.; Goldstein, S. L.; Langmuir, C. H.; Michael, P. J.

    2009-12-01

    We report helium isotope compositions, determined by crushing in vacuum to release the gas trapped in vesicles, for 57 basalt glasses from the ultra-slow spreading Gakkel Ridge. Other geochemical data, especially radiogenic isotopes (Pb, Nd, Sr) reveal the presence of an isotopic boundary in the mid-section of this ridge that separates basalts in the west (west of 14°E longitude) having “Indian Ocean” (Dupal) isotopic signatures, from basalts in the east which resemble the North Atlantic/Pacific domain (Goldstein et al. 2008). This boundary reflects heterogeneity in the underlying mantle related to the tectonic history of continental land masses surrounding the Arctic Ocean. In the west there is a narrow range of 3He/4He with lower values (7.0-7.9 RA), while in the east there is a wider range of 3He/4He with higher values (7.9-9.3 RA) and effectively no overlap with the western group. Off-axis lavas do not fit this simple picture however, revealing some systematic temporal variability, perhaps associated with mantle flow beneath the ridge. All Gakkel Ridge basalts are deeply erupted and most have high helium contents, in some cases at the upper end of the MORB range (>50 μccSTP/g). The few exceptions, having He contents below 0.1 μccSTP/g, have the highest 3He/4He (>8.8 RA). This effect appears to reflect earlier (recent) melting of isotopically heterogeneous mantle, during which the initial melt fractions were slightly enriched in 4He, perhaps due to a larger modal contribution of clinopyroxene and/or garnet to those melts. The temporal variability and the melting effects, while significant, do not account for the large 3He/4He signal observed along the ridge axis. Overall, 3He/4He shows systematic covariation with other isotopic indicators of mantle heterogeneity (Pb, Nd, Sr and Hf), indicating that the helium isotope variations are a long-lived feature of the Arctic upper mantle. The 3He/4He ratio is as effective a discriminant of eastern and western

  11. Evidence for upper mantle intrusion in the west African coastal ...

    African Journals Online (AJOL)

    The Bouguer gravity profiles obtained across the gravity anomaly contour lines in the region have been interpreted using 2D1/2 gravity modelling. The results reveal that in the southern part of the Douala Sedimentary Basin, two major structures exist: a half-dome of mantle material explained by isostatic compensation and a ...

  12. Seismic structure of the crust and upper mantle in central-eastern Greenland

    DEFF Research Database (Denmark)

    Kraft, Helene Anja

    thinned with up to 25 km thinner than standard. The delay times of P410s and P660s furthermore imply that the average upper mantle velocities are below IASP91-velocities. These two observations together indicate a significant heating of the region that probably cannot be explained by the passage...... of the Iceland hotspot alone, but requires an additional process. Analysis of the shape of the P410s signal suggests a low velocity layer below the 410-km discontinuity inside the mantle transition zone. Plans for further work include proceeding with closing the gap between the crust and the mantle transition...... zone and constructing seismic models for the entire upper mantle....

  13. The upper mantle low resistivity layer's relationship with endogenous metallic ore and petroleum reservoir

    Science.gov (United States)

    Qing, Z.; Hui, F.; Piyuan, Y.; Li, L.; Fagen, P.; Yongzhen, Y.

    2013-12-01

    Based on the 1°x1° depth map of the low resistivity layers in upper mantle in China(1996), with the addition of magnetotelluric data from 1995 to 2010, we created the new map of the upper mantle low resistivity layers in China. The distribution of upper mantle low resistivity layers in China appears north-south zonation and west-east block, overall performance for the shallow in the east, deep in the west, shallow in the north and deep in the south. The depth of the upper mantle low resistivity layers can vary widely in China, the shallowest place which located in the northeast of Songliao basin is about 50 ~ 60 km; The deepest place is located in Changsha -Guilin area at where the deepest depth can be 230 km and the average depth can be 100 ~ 120 km. According to the distribution form of the the upper mantle low resistivity layers in China, 27 uplift zones have been divided. The extensional faults generated by the uplift of the upper mantle low resistivity layers is the main passageway of earth interior material and energy migrating to the upper crust, not only produce the hydrothermal deposit in petroliferous basin surrounding orogenic belt , but also brought oil and gas to the basins. Comparing the distribution of metallic ore with oil and gas fields in China, we have found that there are good correlations between the distribution of Mesozoic endogenous metallic ore deposit and the upper mantle low resistivity layers uplift and depression pattern in China, by about 70% of the metallic ore deposit are located in the the upper mantle low resistivity layers uplift areas, 20% of the metallic ore deposit are located in the gradient areas. In eastern China, most of the petroliferous basins are located in the upper mantle low resistivity layers areas, and most of the oil and gas field are above the uplift area or on the transitional zones of the edge; In Western China, most of the petroliferous basins are located in the mantle depression areas, the main oil and gas

  14. Stability of Carbonated Eclogite in the Upper Mantle: Experimental Solidus from 2 to 9 GPa

    Science.gov (United States)

    Dasgupta, R.; Withers, A. C.; Hirschmann, M. M.

    2003-12-01

    Carbonates are pervasive alteration products of the oceanic crust and likely survive subduction-related dehydration and/or melting. Thus, significant quantities of carbonated refractory eclogite are probably delivered to the deeper mantle. The melting behavior of such recycled carbonate influences the fate of recycled carbon, determines the possible sources and depths of carbonated metasomatic melts in the mantle, and delimits the conditions under which carbonated eclogite may act as a source of carbonatite and other types of magmatic CO2. We present partial melting experiments of carbonated eclogite that constrain the solidus and near solidus phase relations from 2 to 9 GPa. To simulate the near-isochemical nature of ocean floor carbonation, the starting material was prepared by adding 5 wt.% CO2 in the form of a mixture of Fe-Mg-Ca-Na-K carbonates to a bimineralic eclogite from Salt Lake crater, Oahu, Hawaii. The starting composition is a reasonable approximation of carbonated oceanic crust from which siliceous hydrous fluid has been extracted by subduction. We find that melt-present versus melt-absent conditions can be distinguished based on textural criteria. Garnet and cpx appear in all the experiments. Between 2 and 3 GPa, the subsolidus assemblage also includes calcite-dolomitess + ilmenite, whereas above the solidus (950-975 ° C at 2 GPa and 1050-1075 ° C at 3 GPa) calcio-dolomitic liquid appears. From 3 to 4.5 GPa, dolomitess becomes stable at the solidus and the near solidus melt becomes increasingly dolomitic. Appearance of dolomite above 3 GPa is accompanied by a negative Clapeyron slope of the solidus, with the cusp located between 995 and 1025 ° C at ca. 4 GPa. Above 4-4.5 GPa, the solidus again rises with increasing pressure to ca. 1245 ° C at 9 GPa and magnesite becomes the subsolidus carbonate. Dolomitic melt coexists with magnesite + garnet + cpx + rutile between 5 and 9 GPa. If extrapolated to higher pressures, the carbonated eclogite solidus

  15. The African upper mantle and its relationship to tectonics and surface geology

    Science.gov (United States)

    Priestley, Keith; McKenzie, Dan; Debayle, Eric; Pilidou, Sylvana

    2008-12-01

    This paper focuses on the upper-mantle velocity structure of the African continent and its relationship to the surface geology. The distribution of seismographs and earthquakes providing seismograms for this study results in good fundamental and higher mode path coverage by a large number of relatively short propagation paths, allowing us to image the SV-wave speed structure, with a horizontal resolution of several hundred kilometres and a vertical resolution of ~50 km, to a depth of about 400 km. The difference in mantle structure between the Archean and Pan-African terranes is apparent in our African upper-mantle shear wave model. High-velocity (4-7 per cent) roots exist beneath the cratons. Below the West African, Congo and Tanzanian Cratons, these extend to 225-250 km depth, but beneath the Kalahari Craton, the high wave speed root extends to only ~170 km. With the exception of the Damara Belt that separates the Congo and Kalahari Cratons, any high-speed upper-mantle lid below the Pan-African terranes is too thin to be resolved by our long-period surface wave technique. The Damara Belt is underlain by higher wave speeds, similar to those observed beneath the Kalahari Craton. Extremely low SV-wave speeds occur to the bottom of our model beneath the Afar region. The temperature of the African upper mantle is determined from the SV-wave speed model. Large temperature variations occur at 125 km depth with low temperatures beneath west Africa and all of southern Africa and warm mantle beneath the Pan-African terrane of northern Africa. At 175 km depth, cool upper mantle occurs below the West African, Congo, Tanzanian and Kalahari Cratons and anomalously warm mantle occurs below a zone in northcentral Africa and beneath the region surrounding the Red Sea. All of the African volcanic centres are located above regions of warm upper mantle. The temperature profiles were fit to a geotherm to determine the thickness of the African lithosphere. Thick lithosphere exists

  16. Carbonatite melt in oceanic upper mantle beneath the Kerguelen Archipelago

    Science.gov (United States)

    Moine, B. N.; Grégoire, M.; O'Reilly, Suzanne Y.; Delpech, G.; Sheppard, S. M. F.; Lorand, J. P.; Renac, C.; Giret, A.; Cottin, J. Y.

    2004-07-01

    Some mantle-derived Kerguelen harzburgite and dunite xenoliths have bulk-rock and mineral trace element compositions that provide evidence of carbonatitic metasomatism similar to that described in some continental and other oceanic settings. Rare xenoliths contain carbonates that are highly enriched in rare earth elements (REE), interpreted to be quenched, evolved carbonatitic melts. One amphibole-bearing dunite mantle wall-rock containing carbonates in small interstitial pockets (100-500 μm across) has been studied in detail. Mg-bearing calcite (MgO: magnesio-wüstite concentrated near the boundaries of the carbonate pockets. The unusual metasomatic mineral assemblage, together with the microstructural features and chemical composition of carbonates (with trace element contents similar to those of common carbonatite magmas), suggests that the pockets of Mg-bearing calcite represent quenched carbonate melts rather than crystal cumulates from carbonate-rich melts. The associated mafic silicate glass could represent the immiscible silicate fraction of an evolved fluid produced by the dissolution-percolation of the original carbonate melt in the dunitic matrix and subsequent unmixing as the xenoliths ascended to the surface. Clinopyroxene formed during the percolation event and is therefore inferred to be in chemical equilibrium with the carbonate melt. This allowed calculation of clinopyroxene/carbonate melt partition coefficients for a large set of trace elements at relatively low pressure (1 GPa). As a result, a significant pressure control on REE partitioning between carbonate melt and silicate minerals was observed. This study provides further evidence for the occurrence of carbonate melts and demonstrates that these melts can be preserved in hot oceanic uppermost mantle.

  17. Evolution of the continental upper mantle : numerical modelling of thermo-chemical convection including partial melting

    NARCIS (Netherlands)

    de Smet, J.H.

    1999-01-01

    This thesis elaborates on the evolution of the continental upper mantle based on numerical modelling results. The descriptive and explanatory basis is formed by a numerical thermo-chemical convection model. The model evolution starts in the early Archaean about 4 billion years ago. The model follows

  18. Evolution of the continental upper mantle : numerical modelling of thermo-chemical convection including partial melting

    NARCIS (Netherlands)

    Smet, J.H. de

    1999-01-01

    This thesis elaborates on the evolution of the continental upper mantle based on numerical modelling results. The descriptive and explanatory basis is formed by a numerical thermo-chemical convection model. The model evolution starts in the early Archaean about 4 billion years ago. The model

  19. Upper-mantle fabrics beneath the Northern Apennines revealed by seismic anisotropy

    Czech Academy of Sciences Publication Activity Database

    Munzarová, Helena; Plomerová, Jaroslava; Babuška, Vladislav; Vecsey, Luděk

    2013-01-01

    Roč. 14, č. 4 (2013), s. 1156-1181 ISSN 1525-2027 R&D Projects: GA AV ČR IAA300120709; GA ČR GAP210/12/2381 Institutional support: RVO:67985530 Keywords : body-wave anisotropy * Northern Apennines * upper mantle Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 3.054, year: 2013

  20. Bridging the connection between effective viscosity and electrical conductivity through water content in the upper mantle.

    Science.gov (United States)

    Xu, Yixian; Zhang, Anqi; Yang, Bo; Bao, Xuewei; Wang, Qinyan; Xia, Jianghai; Yang, Wencai

    2018-01-29

    Upper mantle viscosity plays a key role in understanding plate tectonics and is usually extrapolated from laboratory-based creep measurements of upper mantle conditions or constrained by modeling geodetic and post-seismic observations. At present, an effective method to obtain a high-resolution viscosity structure is still lacking. Recently, a promising estimation of effective viscosity was obtained from a transform derived from the results of magnetotelluric imaging. Here, we build a relationship between effective viscosity and electrical conductivity in the upper mantle using water content. The contribution of water content to the effective viscosity is isolated in a flow law with reference to relatively dry conditions in the upper mantle. The proposed transform is robust and has been verified by application to data synthesized from an intraoceanic subduction zone model. We then apply the method to transform an electrical conductivity cross-section across the Yangtze block and the North China Craton. The results show that the effective viscosity structure coincides well with that estimated from other independent datasets at depths of 40 to 80 km but differs slightly at depths of 100 to 200 km. We briefly discussed the potentials and associated problems for application.

  1. THE VELOCITY STRUCTURE OF THE UPPER MANTLE AND REGIONAL DEEP THERMODYNAMICS OF THE BAIKAL RIFT ZONE

    Directory of Open Access Journals (Sweden)

    Alexander V. Pospeev

    2012-01-01

    Full Text Available The article is aimed at discussion of geological and geophysical aspects of the ‘asthenospheric’ interpretation of the ‘anomalous’ mantle layer that is revealed in the Baikal rift zone by deep seismic sounding (DSS methods. Based on the analysis of the geoelectrical model, estimations of rheological properties, regional geothermal and deep petrological data, it is concluded that the ‘anomalous’ mantle phenomenon should be interpreted within the framework of solid-phase models. It is shown that the actual minimum depth to the top of the asthenosphere is about 60–70 km in the region under study, and temperatures at the surface of the Earth’s mantle varies from 600 to 900 °С. It is most probable that velocities are reduced in the ‘anomalous’ mantle layer due to the presence of hightemperature spinel-pyroxene facies of the mantle rocks.

  2. Carbon-dioxide-rich silicate melt in the Earth's upper mantle.

    Science.gov (United States)

    Dasgupta, Rajdeep; Mallik, Ananya; Tsuno, Kyusei; Withers, Anthony C; Hirth, Greg; Hirschmann, Marc M

    2013-01-10

    The onset of melting in the Earth's upper mantle influences the thermal evolution of the planet, fluxes of key volatiles to the exosphere, and geochemical and geophysical properties of the mantle. Although carbonatitic melt could be stable 250 km or less beneath mid-oceanic ridges, owing to the small fraction (∼0.03 wt%) its effects on the mantle properties are unclear. Geophysical measurements, however, suggest that melts of greater volume may be present at ∼200 km (refs 3-5) but large melt fractions are thought to be restricted to shallower depths. Here we present experiments on carbonated peridotites over 2-5 GPa that constrain the location and the slope of the onset of silicate melting in the mantle. We find that the pressure-temperature slope of carbonated silicate melting is steeper than the solidus of volatile-free peridotite and that silicate melting of dry peridotite + CO(2) beneath ridges commences at ∼180 km. Accounting for the effect of 50-200 p.p.m. H(2)O on freezing point depression, the onset of silicate melting for a sub-ridge mantle with ∼100 p.p.m. CO(2) becomes as deep as ∼220-300 km. We suggest that, on a global scale, carbonated silicate melt generation at a redox front ∼250-200 km deep, with destabilization of metal and majorite in the upwelling mantle, explains the oceanic low-velocity zone and the electrical conductivity structure of the mantle. In locally oxidized domains, deeper carbonated silicate melt may contribute to the seismic X-discontinuity. Furthermore, our results, along with the electrical conductivity of molten carbonated peridotite and that of the oceanic upper mantle, suggest that mantle at depth is CO(2)-rich but H(2)O-poor. Finally, carbonated silicate melts restrict the stability of carbonatite in the Earth's deep upper mantle, and the inventory of carbon, H(2)O and other highly incompatible elements at ridges becomes controlled by the flux of the former.

  3. 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.

  4. Petrology of lower crustal and upper mantle xenoliths from the Cima Volcanic Field, California

    Science.gov (United States)

    Wilshire, H.G.; McGuire, A.V.; Noller, J.S.; Turrin, B.D.

    1991-01-01

    Basaltic rocks of the Cima Volcanic Field in the southern Basin and Range province contain abundant gabbro, pyroxenite, and peridotite xenoliths. Composite xenoliths containing two or more rock types show that upper-mantle spinel peridotite was enriched by multiple dike intrusions in at least three episodes; the mantle was further enriched by intergranular and shear-zone melt infiltration in at least two episodes. Because of their high densities, the gabbros and pyroxenites can occupy the zone immediately above the present Moho (modeled on seismic data as 10-13 km thick, with Vp 6.8 km/s) only if their seismic velocities are reduced by the joints, partial melts, and fluid inclusions that occur in them. Alternatively, these xenoliths may have been derived entirely from beneath the Moho, in which case the Moho is not the local crust-mantle boundary. -from Authors

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

    Science.gov (United States)

    Karaoǧlu, Haydar; Romanowicz, Barbara

    2018-01-01

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

  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. Upper-mantle water stratification inferred from observations of the 2012 Indian Ocean earthquake.

    Science.gov (United States)

    Masuti, Sagar; Barbot, Sylvain D; Karato, Shun-Ichiro; Feng, Lujia; Banerjee, Paramesh

    2016-10-20

    Water, the most abundant volatile in Earth's interior, preserves the young surface of our planet by catalysing mantle convection, lubricating plate tectonics and feeding arc volcanism. Since planetary accretion, water has been exchanged between the hydrosphere and the geosphere, but its depth distribution in the mantle remains elusive. Water drastically reduces the strength of olivine and this effect can be exploited to estimate the water content of olivine from the mechanical response of the asthenosphere to stress perturbations such as the ones following large earthquakes. Here, we exploit the sensitivity to water of the strength of olivine, the weakest and most abundant mineral in the upper mantle, and observations of the exceptionally large (moment magnitude 8.6) 2012 Indian Ocean earthquake to constrain the stratification of water content in the upper mantle. Taking into account a wide range of temperature conditions and the transient creep of olivine, we explain the transient deformation in the aftermath of the earthquake that was recorded by continuous geodetic stations along Sumatra as the result of water- and stress-activated creep of olivine. This implies a minimum water content of about 0.01 per cent by weight-or 1,600 H atoms per million Si atoms-in the asthenosphere (the part of the upper mantle below the lithosphere). The earthquake ruptured conjugate faults down to great depths, compatible with dry olivine in the oceanic lithosphere. We attribute the steep rheological contrast to dehydration across the lithosphere-asthenosphere boundary, presumably by buoyant melt migration to form the oceanic crust.

  8. 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.

  9. Upper Mantle Dynamics of Bangladesh by Splitting Analyzes of Core Refracted SKS and SKKS Waves

    Science.gov (United States)

    Tiwari, A. K.; Bhushan, K.; Eken, T.; Singh, A.

    2017-12-01

    New shear wave splitting measurements are obtained from hitherto less studied Bengal Basin using core refracted SKS and SKKS phases. Splitting parameters, time delays (δt) and fast polarization directions (Φ) were estimated through analysis of 64 high-quality waveforms (≥ 2.5 signal to noise ratio) from 29 earthquakes with magnitude ≥5.5 recorded at eight seismic stations deployed over Bangladesh. We found no evidence of splitting which indicates azimuthal isotropy beneath the region. Null measurements can be explained by near vertical axis of anisotropy or by the presence of multiple anisotropic layers with different fast polarization directions, where combined effect results in null. We consider that the presence of partial melts within the upper mantle due to Kerguelen mantle plume activities may be the potential geodynamic cause for observed null measurements. It locally perturbed mantle convection flow beneath the region and reoriented the lattice preferred orientation of the upper mantle mineral mainly olivine as this disabled the core refracted SKS and SKKS phases to scan the anisotropic characteristics of the region, and hence null measurements are obtained.

  10. 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...

  11. 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...

  12. The Indian Ocean gravity low - Evidence for an isostatically uncompensated depression in the upper mantle

    Science.gov (United States)

    Ihnen, S. M.; Whitcomb, J. H.

    1983-01-01

    The broad gravity low in the equatorial Indian Ocean south of Sri Lanka is the largest and most striking feature in the gravitational field of the earth. The most negative long-wavelength free-air gravity anomalies are found there and the sea surface (geoid) lies more than 100 meters below the best fitting ellipsoid. A model of the lithosphere and upper mantle is proposed which accurately predicts the observed free-air gravity and geoid elevation. This model is consistent with bathymetry and sediment thickness data and suggests that the crust south of India currently floats as much as 600 meters lower than would be expected if the region were isostatically compensated. This residual depression of the crust is apparently confirmed by observations of ocean depth. An uncompensated depression is consistent with the presence of a mechanical wake left in the upper mantle behind India as it traveled toward Asia.

  13. Finite-Frequency Seismic Imaging of Upper-Mantle Velocity Structures Beneath the South China Continent

    Science.gov (United States)

    Qu, P.; Chen, Y. J.; Yu, Y.

    2017-12-01

    South China Continent is major formed from the Paleo-South China plate. The continent has experienced complicated tectonic history after Neoproterozoic. Previous studies suggested some possible model for the collision between South China Continent and North China Continent. Body wave tomography and surface wave tomography are widely used to inverse upper mantle velocity structure. In our study, finite frequency tomography were carried on to get explanation more correctly. We gathered nearly 60000 pieces of teleseismic event records by 166 broad band seismic stations with Mw > 5.5. Here sensitive kernel of ak135 velocity structure was calculated, which is based on Born approximation, and then we applied multi-channel cross-correlation to pick arrival time difference under 3 frequency band. Combining with crust thickness correct from receiver function, we solve the inversion matrix by LSQR method, and get accurate upper mantle structure of P, S velocity. For more accurate results, we apply a method to calculate Vp/Vs ratio, to help to verify the velocity anomaly. The result in this research shows: 1. A strong velocity anomaly exists in the northern of South China Continent, in an area 31°N between 112°-118°E. The anomaly is about . We suggest that, this anomaly is related to the collision from North China Continent. It implies the collision underthrusted to southward. 2. A clearly slow velocity anomaly exists in the northern of Cathaysia block. This low velocity anomaly exist on the boundary of Yangtz block and Cathysian block, it is related to the left over of block collision in early phanerozoic. 3. We recognized some little velocity anomaly exit in the research area. Comparing these velocity anomaly with U-Pb zircon ages, we suggest complicated orogenesis in Phanerozoic is the cause of the formation of these little anomaly. The result in our study support the collision model, which shows the underthrust direction is southward, on the south of Qinling

  14. 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.

  15. Crust and upper mantle structure in the Caribbean region by group velocity tomography and regionalization

    International Nuclear Information System (INIS)

    O'Leary, Gonzalez; Alvarez, L.; Chimera, G.; Panza, G.F.

    2004-04-01

    An overview of the crust and upper mantle structure of the Central America and Caribbean region is presented as a result of the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. By FTAN analysis of the fundamental mode of the Rayleigh waves, group velocity dispersion curves are obtained in the period range from 10 s to 40 s; the error of these measurements varies from 0.06 and 0.10 km/s. From the dispersion curves, seven tomographic maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region are extended to 150 s by adding data from the tomographic study of and inverted using a non-linear procedure. As a result of the inversion process, a set of models of the S-wave velocity vs. depth in the crust and upper mantle are found. In six regions, we identify a typically oceanic crust and upper mantle structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth. (author)

  16. Structure and Evolution of the North American Upper Mantle: Insight from Integrative Modeling of Gravity, Topography and Seismic Tomography Data

    Science.gov (United States)

    Mooney, W. D.; Kaban, M. K.; Tesauro, M.

    2014-12-01

    A limitation on the application of geophysical methods for the study of the upper mantle is the effect of lateral variations in the structure of the overlying crust that obscure the signal from the mantle. However, the North American upper mantle is particularly well-suited for geophysical study because crustal corrections can be made based on the results from numerous active- and passive-source seismic investigations that have determined lateral variations in crustal properties, including crustal thickness, P- and S-wave velocities, and crustal density estimated from empirical velocity-density relations. We exploit this knowledge of the crust of North America to construct an integrated 3D model of variations in density, temperature and composition within the upper mantle to a depth of 250 km. Our model is based on a joint analysis of topography, gravity, and seismic tomography data, coupled with mineral physics constraints. In the first step we remove the effect of the laterally-varying crust from the observed gravity field and topography (assuming Airy isostasy) using our crustal model NACr2014 (Tesauro et al., submitted). In the second step the residual mantle gravity field and residual topography (obtained in the first step) are inverted to obtain a 3D density model of the upper mantle. Thermal effects dominate this initial density model. To compensate for the thermal effects we invert for mantle temperatures based on the S-wave velocities determined by two seismic tomography models (S40RTS and NA2007). After removing the thermal effect from the mantle gravity anomalies we are left with the upper mantle density variations that are due to compositional variations. We recover two long-wavelength (5°-10°) features in the upper mantle compositional density model that are not evident in seismic tomography models: (1) a strong (+200 mgal) positive compositional anomaly beneath the Gulf of Mexico, perhaps due to eclogite in the uppermost mantle, and (2) a NE

  17. Constraints on upper mantle Vp/Vs ratio variations beneath eastern North China from receiver function tomography

    Science.gov (United States)

    Si, Shaokun; Tian, Xiaobo; Gao, Rui

    2017-05-01

    To detect the thinning, modification, and replacement of the basement of the lithosphere is a key step in understanding the destruction mechanism of the North China lithosphere. The difference of the basement of the lithosphere is mainly displayed by the variation of the peridotite composition and its physical state. Vp/Vs ratio (hereafter referred to as velocity ratio) is more sensitive to this change than Vp or Vs alone. By means of the strong dependence of the travel-time of the wave converted at the 410-km discontinuity (P410s) observed in the receiver function (RF) on the velocity ratio in the upper mantle, we developed a new mapping method to constrain the velocity ratio between the Moho and 410-km discontinuity. Using the RFs extracted from 246 broadband stations beneath the North China Craton (NCC), we obtained a high-resolution velocity ratio image of the upper mantle. The abnormal velocity ratio indicates a strong lateral variation of the mineral composition in the upper mantle beneath North China. Two low-velocity-ratio patches are imaged at the top of the upper mantle and the 410 km depth, respectively. The former may be related to the orthopyroxene enrichment in the lithospheric mantle, and the latter may reflect the stagnant Pacific slab in the mantle transition zone (MTZ). A prominent high-velocity-ratio anomaly is also imaged in the upper mantle beneath the Shaanxi-Shanxi rift system in the central NCC, with the highest anomaly reaching 10%. We speculate that the high velocity ratio of upper mantle is related to convective flow due to slab dehydration in the MTZ. The dehydration of the retained slab in the MTZ results in partial melting and upwelling of upper mantle materials. Such convective flow and their melting are closely related to the Cenozoic basalt eruption in the northern section of the Shaanxi-Shanxi rift system.

  18. Probability density functions for radial anisotropy: implications for the upper 1200 km of the mantle

    Science.gov (United States)

    Beghein, Caroline; Trampert, Jeannot

    2004-01-01

    The presence of radial anisotropy in the upper mantle, transition zone and top of the lower mantle is investigated by applying a model space search technique to Rayleigh and Love wave phase velocity models. Probability density functions are obtained independently for S-wave anisotropy, P-wave anisotropy, intermediate parameter η, Vp, Vs and density anomalies. The likelihoods for P-wave and S-wave anisotropy beneath continents cannot be explained by a dry olivine-rich upper mantle at depths larger than 220 km. Indeed, while shear-wave anisotropy tends to disappear below 220 km depth in continental areas, P-wave anisotropy is still present but its sign changes compared to the uppermost mantle. This could be due to an increase with depth of the amount of pyroxene relative to olivine in these regions, although the presence of water, partial melt or a change in the deformation mechanism cannot be ruled out as yet. A similar observation is made for old oceans, but not for young ones where VSH> VSV appears likely down to 670 km depth and VPH> VPV down to 400 km depth. The change of sign in P-wave anisotropy seems to be qualitatively correlated with the presence of the Lehmann discontinuity, generally observed beneath continents and some oceans but not beneath ridges. Parameter η shows a similar age-related depth pattern as shear-wave anisotropy in the uppermost mantle and it undergoes the same change of sign as P-wave anisotropy at 220 km depth. The ratio between dln Vs and dln Vp suggests that a chemical component is needed to explain the anomalies in most places at depths greater than 220 km. More tests are needed to infer the robustness of the results for density, but they do not affect the results for anisotropy.

  19. The electrical conductivity of the upper mantle and lithosphere from satellite magnetic signal due to ocean tidal flow

    Science.gov (United States)

    Schnepf, N. R.; Kuvshinov, A. V.; Grayver, A.; Sabaka, T. J.; Olsen, N.

    2015-12-01

    Global electromagnetic (EM) studies provide information on mantle electrical conductivity with the ultimate aim of understanding the composition, structure, and dynamics of Earth's interior. There is great much interest in mapping the global conductivity of the lithosphere and upper mantle (i.e., depths of 10-400 km) because recent laboratory experiments demonstrate that the electrical conductivity of minerals in these regions are greatly affected by small amounts of water or by partial melt. For decades, studies of lithospheric/mantle conductivity were based on interpretation of magnetic data from a global network of observatories. The recent expansion in magnetic data from low-Earth orbiting satellite missions (Ørsted, CHAMP, SAC-C, and Swarm) has led to a rising interest in probing Earth from space. The largest benefit of using satellite data is much improved spatial coverage. Additionally, and in contrast to ground-based data, satellite data are overall uniform and very high quality. Probing the conductivity of the lithosphere and upper mantle requires EM variations with periods of a few hours. This is a challenging period range for global EM studies since the ionospheric (Sq) source dominates these periods and has a much more complex spatial structure compared to the magnetospheric ring current. Moreover, satellite-based EM induction studies in principle cannot use Sq data since the satellites fly above the Sq source causing the signals to be seen by the satellite as a purely internal source, thus precluding the separation of satellite Sq signals into internal and external parts. Lastly, magnetospheric and ionospheric sources interact inductively with Earth's conducting interior. Fortunately, there exists an alternative EM source in the Sq period range: electric currents generated by oceanic tides. Tides instead interact galvanically with the lithosphere (i.e. by direct coupling of the source currents in the ocean with the underlying substrate), enabling

  20. 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

  1. Structure of Lithospheric and Upper Mantle Discontinuities beneath Central Mongolia from Receiver Functions

    Science.gov (United States)

    Cui, Z.; Meltzer, A.; Fischer, K. M.; Stachnik, J. C.; Munkhuu, U.; Tsagaan, B.; Russo, R. M.

    2017-12-01

    The origin and preservation of high-elevation low-relief surfaces in continental interiors remains an open questions. Central Mongolia constitutes a major portion of the Mongolian Plateau and is an excellent place to link deep earth and surface processes. The lithosphere of Mongolia was constructed through accretionary orogenesis associated with the Central Asian Orogenic Belt (CAOB) from the late Paleozoic to the early Triassic. Alkaline volcanic basalt derived from sublithospheric sources has erupted sporadically in Mongolia since 30 Ma. Constraining the depth variation of lithospheric and upper mantle discontinuities is crucial for understanding the interaction between upper mantle structure and surface topography. We conducted receiver functions (RF) analyses suitable data recorded at112 seismic broadband stations in central Mongolia to image the LAB and mantle transition zone beneath Central Mongolia. A modified H-κ stacking was performed to determine crustal average thickness (H) and Vp/Vs ratio (κ). Central Mongolia is characterized by thick crust (43-57 km) enabling use of both P wave RF and to S wave RF to image the LAB. The PRF traces in the depth domain are stacked based on piercing point locations for the 410 and 660 discontinuities using 0.6 ° × 0.6 ° bins in a grid. From south to north, the average lithospheric thickness is 85km in Gobi Altai gradually thinning northeastward to 78km in the southern Hangay Dome, 72 km in the northern Hangay Dome then increases to 75km in Hovsgol area. While there is overall thinning of the lithosphere from SW to NE, beneath the Hangay, there is a slight increase beneath the highest topography. The thickness of the mantle transition zone (MTZ) beneath central Mongolia is similar to global averages. This evidence argues against the hypothesis that a mantle plume exists beneath Central Mongolia causing low velocity anomalies in the upper mantle. To the east of the Hovsgol area in northern Mongolia, the MTZ thickens

  2. Water sensitivity of the seismic properties of upper-mantle olivine

    Science.gov (United States)

    Cline, Christopher; David, Emmanuel; Faul, Ulrich; Berry, Andrew; Jackson, Ian

    2017-04-01

    The wave speeds and attenuation of seismic waves in the upper mantle are expected to be strongly influenced by the defect chemistry of olivine grain interiors and the associated chemical complexity of grain-boundary regions. Changes in chemical environment (oxygen fugacity and/or water fugacity) can impose different defect chemistries, including the creation and retention of hydrous defects, and therefore can directly influence anelastic relaxation involving stress-induced migration of lattice defects and/or grain-boundary sliding. Here we report the first low-frequency experimental study of the seismic properties of olivine under water-undersaturated conditions. Three synthetic sol-gel derived olivine (Fo90) specimens were fabricated by hot-pressing in welded Pt capsules with various concentrations of hydroxyl, chemically bound as doubly protonated Si vacancies, charge balanced by substitution of Ti on a neighboring M-site (i.e., the Ti-clinohumite-like defect). Hydroxyl contents, determined following the subsequent mechanical testing within Pt sleeves, increased systematically with the amount of added Ti-dopant. Added Ti concentrations ranged between 176 and 802 atom ppm Ti/Si, resulting in concentrations of bound hydrogen in the three samples ranging between 330 and 1150 atom ppm H/Si. Each hot-pressed specimen was precision ground and then sleeved in Pt for mechanical testing in forced torsional oscillation under water-undersaturated conditions. Forced-oscillation tests were conducted at seismic periods of 1 - 1000 s and 200 MPa confining pressure during slow staged cooling from 1200 to 25°C. Each Ti-doped specimen showed mechanical behavior of the high-temperature background type involving monotonically increasing dissipation and decreasing shear modulus with increasing oscillation period and increasing temperature. Comparison of the mechanical data acquired in these water-undersaturated conditions with a similarly tested, but dry, Ti-bearing specimen

  3. An internally consistent pressure calibration of geobarometers applicable to the Earth's upper mantle using in situ XRD

    Science.gov (United States)

    Beyer, Christopher; Rosenthal, Anja; Myhill, Robert; Crichton, Wilson A.; Yu, Tony; Wang, Yanbin; Frost, Daniel J.

    2018-02-01

    We have performed an experimental cross calibration of a suite of mineral equilibria within mantle rock bulk compositions that are commonly used in geobarometry to determine the equilibration depths of upper mantle assemblages. Multiple barometers were compared simultaneously in experimental runs, where the pressure was determined using in-situ measurements of the unit cell volumes of MgO, NaCl, Re and h-BN between 3.6 and 10.4 GPa, and 1250 and 1500 °C. The experiments were performed in a large volume press (LVPs) in combination with synchrotron X-ray diffraction. Noble metal capsules drilled with multiple sample chambers were loaded with a range of bulk compositions representative of peridotite, eclogite and pyroxenite lithologies. By this approach, we simultaneously calibrated the geobarometers applicable to different mantle lithologies under identical and well determined pressure and temperature conditions. We identified discrepancies between the calculated and experimental pressures for which we propose simple linear or constant correction factors to some of the previously published barometric equations. As a result, we establish internally-consistent cross-calibrations for a number of garnet-orthopyroxene, garnet-clinopyroxene, Ca-Tschermaks-in-clinopyroxene and majorite geobarometers.

  4. An internally consistent pressure calibration of geobarometers applicable to the Earth’s upper mantle using in situ XRD

    Energy Technology Data Exchange (ETDEWEB)

    Beyer, Christopher; Rosenthal, Anja; Myhill, Robert; Crichton, Wilson A.; Yu, Tony; Wang, Yanbin; Frost, Daniel J.

    2018-02-01

    We have performed an experimental cross calibration of a suite of mineral equilibria within mantle rock bulk compositions that are commonly used in geobarometry to determine the equilibration depths of upper mantle assemblages. Multiple barometers were compared simultaneously in experimental runs, where the pressure was determined using in-situ measurements of the unit cell volumes of MgO, NaCl, Re and h-BN between 3.6 and 10.4 GPa, and 1250 and 1500 °C. The experiments were performed in a large volume press (LVPs) in combination with synchrotron X-ray diffraction. Noble metal capsules drilled with multiple sample chambers were loaded with a range of bulk compositions representative of peridotite, eclogite and pyroxenite lithologies. By this approach, we simultaneously calibrated the geobarometers applicable to different mantle lithologies under identical and well determined pressure and temperature conditions. We identified discrepancies between the calculated and experimental pressures for which we propose simple linear or constant correction factors to some of the previously published barometric equations. As a result, we establish internally-consistent cross-calibrations for a number of garnet-orthopyroxene, garnet-clinopyroxene, Ca-Tschermaks-in-clinopyroxene and majorite geobarometers.

  5. An adaptive Bayesian inversion for upper mantle structure using surface waves and scattered body waves

    Science.gov (United States)

    Eilon, Zachary; Fischer, Karen M.; Dalton, Colleen A.

    2018-04-01

    We present a methodology for 1-D imaging of upper mantle structure using a Bayesian approach that incorporates a novel combination of seismic data types and an adaptive parameterisation based on piecewise discontinuous splines. Our inversion algorithm lays the groundwork for improved seismic velocity models of the lithosphere and asthenosphere by harnessing the recent expansion of large seismic arrays and computational power alongside sophisticated data analysis. Careful processing of P- and S-wave arrivals isolates converted phases generated at velocity gradients between the mid-crust and 300 km depth. This data is allied with ambient noise and earthquake Rayleigh wave phase velocities to obtain detailed VS and VP velocity models. Synthetic tests demonstrate that converted phases are necessary to accurately constrain velocity gradients, and S-p phases are particularly important for resolving mantle structure, while surface waves are necessary for capturing absolute velocities. We apply the method to several stations in the northwest and north-central United States, finding that the imaged structure improves upon existing models by sharpening the vertical resolution of absolute velocity profiles, offering robust uncertainty estimates, and revealing mid-lithospheric velocity gradients indicative of thermochemical cratonic layering. This flexible method holds promise for increasingly detailed understanding of the upper mantle.

  6. 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.

  7. 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.

  8. Seismic and petrological properties of the upper mantle between 300 and 400 km depth

    Science.gov (United States)

    Perchuc, E.; Malinowski, M.; Nita, B.

    2008-12-01

    We compare the traveltime data from the long range seismic profiles and from the earthquakes recorded to the offset of 3000 km with theoretical traveltimes predicted by standard seismological models: PREM, IASP- 91, AK-135 and especially from seismo-petrological model PREF (Cammarano and Romanowicz - 2007). We try to compare our models to earlier studies by Thybo and Perchuc (1997a). Our data suggests that for several events in the distance range 2000-2800 km, the first-arrivals are characterized by a relatively high velocity of 8.7-8.9 km/s. It is about 2.5% higher than P-wave velocity of the Lehmann phases, observed in the nearest offset and about 3% smaller than velocity below 410 km discontinuity. We suggest that this is a new first-order seismological boundary which can be interpreted as a top of the mantle transition zone. Seismological arguments for the existence of such a boundary are as follows: refracted waves with velocity 8.7-8.9 km/s and reflected waves find by Warren at al. (1967) and by Thybo and Perchuc (1997b). Also the interpretation of the SS precursor phases (Deuss and Woodhouse 2002) suggested a reflection boundary around 300 km (our interpretation). Depth of this boundary strongly depends on the thermal state of the mantle in particular regions. In conclusion we can say that the mantle transition zone starts much earlier and the lower part of the upper mantle is much faster than predicted by purely pyrolitic mantle model. Several petrological studies suggest influences of fluids (especialy H2O) on the character of the 410 km discontinuity and of the transition zone. All the differences in experimental data can be explained by the effect of temperature on the phase transformations within the olivine-wadsleyite system.

  9. Upper-mantle P- and S-wave velocities below Scandinavia and East Greenland from teleseismic traveltime tomography

    DEFF Research Database (Denmark)

    Hejrani, Babak

    2014-01-01

    with permanent station data from the North Atlantic and Greenland, and a dense temporary profile, the East Greenland Caledonian Central Fjord Array (EGCFA). EGCFA resolves low upper-mantle velocities close to the east coast of Greenland and high mantle velocities below the high topography inland. High and low......This dissertation deals with the resolution of P- and S-velocity variations in the upper mantle (down to 600 km) using teleseismic P- and S-wave arrival times. The natural laboratory is the land areas bordering the North Atlantic; the Scandinavian and East Greenland Caledonides and the Northern......-correlation and arrival-time picking, involving about 50% rewriting and 50% code extension, now also interfacing with the SAC-system and GMT. Ellipticity correction was built in, following the Kennett and Gudmundsson (1996). With these improved methods, I studied the upper-mantle velocity structure in three regions...

  10. Seismic characteristics of central Brazil crust and upper mantle: A deep seismic refraction study

    Science.gov (United States)

    Soares, J.E.; Berrocal, J.; Fuck, R.A.; Mooney, W.D.; Ventura, D.B.R.

    2006-01-01

    A two-dimensional model of the Brazilian central crust and upper mantle was obtained from the traveltime interpretation of deep seismic refraction data from the Porangatu and Cavalcante lines, each approximately 300 km long. When the lines were deployed, they overlapped by 50 km, forming an E-W transect approximately 530 km long across the Tocantins Province and western Sa??o Francisco Craton. The Tocantins Province formed during the Neoproterozoic when the Sa??o Francisco, the Paranapanema, and the Amazon cratons collided, following the subduction of the former Goia??s ocean basin. Average crustal VP and VP/VS ratios, Moho topography, and lateral discontinuities within crustal layers suggest that the crust beneath central Brazil can be associated with major geological domains recognized at the surface. The Moho is an irregular interface, between 36 and 44 km deep, that shows evidences of first-order tectonic structures. The 8.05 and 8.23 km s-1 P wave velocities identify the upper mantle beneath the Porangatu and Cavalcante lines, respectively. The observed seismic features allow for the identification of (1) the crust has largely felsic composition in the studied region, (2) the absence of the mafic-ultramafic root beneath the Goia??s magmatic arc, and (3) block tectonics in the foreland fold-and-thrust belt of the northern Brasi??lia Belt during the Neoproterozoic. Seismic data also suggested that the Bouguer gravimetric discontinuities are mainly compensated by differences in mass distribution within the lithospheric mantle. Finally, the Goia??s-Tocantins seismic belt can be interpreted as a natural seismic alignment related to the Neoproterozoic mantle domain. Copyright 2006 by the American Geophysical Union.

  11. 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

  12. Crustal and Upper Mantle Structure of the Ultra-slow Spreading Gakkel Ridge

    Science.gov (United States)

    Schmidt-Aursch, M.; Jokat, W.

    2003-12-01

    The 1800 km long Gakkel Ridge (Arctic Ocean) shows full spreading rates between 13 mm/yr north of Greenland and 6 mm/yr near its termination in the Laptev Sea. It is the slowest-spreading mid-oceanic ridge worldwide, and therefor plays a key role in understanding melt generation and crustal accretion processes. The joint AMORE expedition investigated the rigde in summer 2001 with the two research icebreakers RV Polarstern and USCGC Healy. Several geophysical and petrological experiments have been conducted including refraction seismic profiling along the rift valley and detailed sampling of the sea floor. Analysis of the rock samples and forward modelling of the wide-angle seismic data resulted in a clear division of the ridge in three parts with completely different structural characteristics. First results of a helicopter-based magnetic survey gave evidence for long-term focused magmatism along some parts of the ridge. The seismic data yielded also an exceptional thin oceanic crust with thicknesses not higher than 3 km and seismic velocities well below 6.4 km/s. Seismic velocities in the upper mantle are with values around 7.8 km/s also very low. The velocity models gave direct constraints for a 3D forward modelling of gravity data based on the 5-minute-grid of the Arctic Gravity Project. The crustal thickness shows only little variations along the rift valley, but perpendicular to the ridge the thickness varies between vanishingly thin and about 6 km. The density models off-axis strongly depend on the assumed temperature structure of the upper mantle. We will present several 3D density models of the oceanic crust and upper mantle to discuss different melt generation processes along the ridge.

  13. Flow behavior and microstructures of hydrous olivine aggregates at upper mantle pressures and temperatures

    Science.gov (United States)

    Ohuchi, Tomohiro; Kawazoe, Takaaki; Higo, Yuji; Suzuki, Akio

    2017-08-01

    Deformation experiments on olivine aggregates were performed under hydrous conditions using a deformation-DIA apparatus combined with synchrotron in situ X-ray observations at pressures of 1.5-9.8 GPa, temperatures of 1223-1800 K, and strain rates ranging from 0.8 × 10-5 to 7.5 × 10-5 s-1. The pressure and strain rate dependencies of the plasticity of hydrous olivine may be described by an activation volume of 17 ± 6 cm3 mol-1 and a stress exponent of 3.2 ± 0.6 at temperatures of 1323-1423 K. A comparison between previous data sets and our results at a normalized temperature and a strain rate showed that the creep strength of hydrous olivine deformed at 1323-1423 K is much weaker than that for the dislocation creep of water-saturated olivine and is similar to that for diffusional creep and dislocation-accommodated grain boundary sliding, while dislocation microstructures showing the [001] slip or the [001](100) slip system were developed. At temperatures of 1633-1800 K, a much stronger pressure effect on creep strength was observed for olivine with an activation volume of 27 ± 7 cm3 mol-1 assuming a stress exponent of 3.5, water fugacity exponent of 1.2, and activation energy of 520 kJ mol-1 (i.e., power-law dislocation creep of hydrous olivine). Because of the weak pressure dependence of the rheology of hydrous olivine at lower temperatures, water weakening of olivine could be effective in the deeper and colder part of Earth's upper mantle.

  14. Trans-Dimensional Bayesian Imaging of 3-D Crustal and Upper Mantle Structure in Northeast Asia

    Science.gov (United States)

    Kim, S.; Tkalcic, H.; Rhie, J.; Chen, Y.

    2016-12-01

    Imaging 3-D structures using stepwise inversions of ambient noise and receiver function data is now a routine work. Here, we carry out the inversion in the trans-dimensional and hierarchical extension of the Bayesian framework to obtain rigorous estimates of uncertainty and high-resolution images of crustal and upper mantle structures beneath Northeast (NE) Asia. The methods inherently account for data sensitivities by means of using adaptive parameterizations and treating data noise as free parameters. Therefore, parsimonious results from the methods are balanced out between model complexity and data fitting. This allows fully exploiting data information, preventing from over- or under-estimation of the data fit, and increases model resolution. In addition, the reliability of results is more rigorously checked through the use of Bayesian uncertainties. It is shown by various synthetic recovery tests that complex and spatially variable features are well resolved in our resulting images of NE Asia. Rayleigh wave phase and group velocity tomograms (8-70 s), a 3-D shear-wave velocity model from depth inversions of the estimated dispersion maps, and regional 3-D models (NE China, the Korean Peninsula, and the Japanese islands) from joint inversions with receiver function data of dense networks are presented. High-resolution models are characterized by a number of tectonically meaningful features. We focus our interpretation on complex patterns of sub-lithospheric low velocity structures that extend from back-arc regions to continental margins. We interpret the anomalies in conjunction with distal and distributed intraplate volcanoes in NE Asia. Further discussion on other imaged features will be presented.

  15. Upper-Mantle Shear Velocities beneath Southern California Determined from Long-Period Surface Waves

    OpenAIRE

    Polet, J.; Kanamori, H.

    1997-01-01

    We used long-period surface waves from teleseismic earthquakes recorded by the TERRAscope network to determine phase velocity dispersion of Rayleigh waves up to periods of about 170 sec and of Love waves up to about 150 sec. This enabled us to investigate the upper-mantle velocity structure beneath southern California to a depth of about 250 km. Ten and five earthquakes were used for Rayleigh and Love waves, respectively. The observed surface-wave dispersion shows a clear Love/Rayleigh-wave d...

  16. Experimental evidence supporting a global melt layer at the base of the Earth's upper mantle.

    Science.gov (United States)

    Freitas, D; Manthilake, G; Schiavi, F; Chantel, J; Bolfan-Casanova, N; Bouhifd, M A; Andrault, D

    2017-12-19

    The low-velocity layer (LVL) atop the 410-km discontinuity has been widely attributed to dehydration melting. In this study, we experimentally reproduced the wadsleyite-to-olivine phase transformation in the upwelling mantle across the 410-km discontinuity and investigated in situ the sound wave velocity during partial melting of hydrous peridotite. Our seismic velocity model indicates that the globally observed negative Vs anomaly (-4%) can be explained by a 0.7% melt fraction in peridotite at the base of the upper mantle. The produced melt is richer in FeO (~33 wt.%) and H 2 O (~16.5 wt.%) and its density is determined to be 3.56-3.74 g cm -3 . The water content of this gravitationally stable melt in the LVL corresponds to a total water content in the mantle transition zone of 0.22 ± 0.02 wt.%. Such values agree with estimations based on magneto-telluric observations.

  17. USArray Enables Improved Resolution Studies of Earth's Upper and Lower Mantle

    Science.gov (United States)

    Garnero, E. J.; Lay, T.

    2007-12-01

    The first full deployment of EarthScope's USArray has now been completed, with over 400 high-quality broadband stations distributed over a 70-km grid covering the western U.S. The openly-available USArray data can be obtained in near real-time using convenient IRIS-hosted data retrieval tools (e.g., SOD, JWeed). The dramatic increase in number of seismograms for each event, along with the unusual combination of large aperture and dense wave field sampling, are enabling improved resolution of deep Earth structure in diverse applications. Automation is now important for most initial data processing steps, in order to handle the large numbers of records that quickly accumulate. We highlight several applications of USArray data to Earth structure investigations in locations remote from North American lithosphere where the bulk of applications are focused. Earthquake source distributions relative to the USArray define several target study regions. For example, deep focus South American and Fiji-Tonga earthquakes allow high-resolution analyses of lower mantle structure beneath the Cocos Plate and the central Pacific, respectively. The increasingly detailed models that are inferred have many thermal, compositional and dynamical implications. Fiji-Tonga events recorded by USArray are enabling detailed mapping of upper mantle discontinuity structures in the vicinity of the Tonga slab. Images of upper mantle discontinuities beneath South America and Hawaii are brought into sharper focus using teleseismic data recorded by USArray. Various data processing approaches, such as stacking, migration, and source wavelet deconvolution are now stabilized by the dense USArray data sets. The increasingly detailed characterization of deep structure is motivating both advances in 3D wave propagation methods and collaborative interdisciplinary efforts to provide viable interpretations.

  18. Structural Heterogeneities in Southeast Tibet: Implications for Regional Flow in the Lower Crust and Upper Mantle

    Directory of Open Access Journals (Sweden)

    Zhi Wang

    2012-01-01

    Full Text Available Our seismic study together with the MT analysis reveal a “R-shape” flow existing in both the lower crust and uppermost mantle, which suggests the crustal deformation along the deep, large sutures (such as the Longmen Shan fault and the Anninghe Fault under the southeastern Tibetan Plateau is maintained by dynamic pressure from the regional flow intermingled with the hot upwelling asthenosphere. The material in the lower crust and uppermost mantle flowing outward from the center of the plateau is buttressed by the old, strong lithosphere that underlies the Sichuan basin, pushing up on the crust above and maintaining steep orogenic belt through dynamic pressure. We therefore consider that the “R-shape” regional flow played a key role in the crustal deformation along the deep suture zones of the Bangong-Nujiang, the Longmen-Shan faults, and other local heavily faulted zones beneath the southeastern Tibetan Plateau.

  19. 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}.

  20. New upper mantle model for North America: no longer a pyrolite composition?

    Science.gov (United States)

    Perchuc, E.; Malinowski, M.

    2009-04-01

    We compare the traveltimes data for P and S waves from the long range seismic profiles and from the earthquakes recorded to the offset of 3000 km with theoretical traveltimes predicted by standard seismological models: PREM, IASP- 91, AK-135 and especially by seismo-petrological model PREF (Cammarano and Romanowicz - 2007). For our analysis we are used data from north American array also. Our analysis suggests that for several events in the distance range 2000-3000 km, the first-arrivals are characterized by a relatively high velocity of 8.7-8.9 km/s. It is about 2.5% higher than P-wave velocity of the Lehmann phases, observed in the nearest offset and about 3% smaller than velocity below 410 km discontinuity. S waves model suggested significant differences in Vp/Vs ratio. We suggest that this is a new first-order seismological boundary which can be interpreted as a top of the mantle transition zone. Seismological arguments for the existence of such a boundary are as follows: refracted waves with velocity 8.7-8.9 km/s and reflected waves find by Warren at al. (1967) and by Thybo and Perchuc (1997b). Several new publications suggested existence of a low velocity zone above the 410-km discontinuity. We also see this feature in our studies. Important suggestion is existence of 300 km discontinuity below cold areas and it is also difficult to exclude this boundary below "cold" areas however phases from this boundary are in secondary impulses. Depth of this boundary strongly depends on the thermal state of the mantle in particular regions. In conclusion we can say that the mantle transition zone starts much earlier and the lower part of the upper mantle is much faster than predicted by purely pyrolitic mantle model. Several petrological studies suggest influences of fluids (especially H2O) on the character of the 410 km discontinuity and of the transition zone. All the differences in experimental data can be explained by the effect of temperature on the phase

  1. 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.

  2. 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.

  3. Spectral-element global waveform tomography: A second-generation upper-mantle model

    Science.gov (United States)

    French, S. W.; Lekic, V.; Romanowicz, B. A.

    2012-12-01

    The SEMum model of Lekic and Romanowicz (2011a) was the first global upper-mantle VS model obtained using whole-waveform inversion with spectral element (SEM: Komatitsch and Vilotte, 1998) forward modeling of time domain three component waveforms. SEMum exhibits stronger amplitudes of heterogeneity in the upper 200km of the mantle compared to previous global models - particularly with respect to low-velocity anomalies. To make SEM-based waveform inversion tractable at global scales, SEMum was developed using: (1) a version of SEM coupled to 1D mode computation in the earth's core (C-SEM, Capdeville et al., 2003); (2) asymptotic normal-mode sensitivity kernels, incorporating multiple forward scattering and finite-frequency effects in the great-circle plane (NACT: Li and Romanowicz, 1995); and (3) a smooth anisotropic crustal layer of uniform 60km thickness, designed to match global surface-wave dispersion while reducing the cost of time integration in the SEM. The use of asymptotic kernels reduced the number of SEM computations considerably (≥ 3x) relative to purely numerical approaches (e.g. Tarantola, 1984), while remaining sufficiently accurate at the periods of interest (down to 60s). However, while the choice of a 60km crustal-layer thickness is justifiable in the continents, it can complicate interpretation of shallow oceanic upper-mantle structure. We here present an update to the SEMum model, designed primarily to address these concerns. The resulting model, SEMum2, was derived using a crustal layer that again fits global surface-wave dispersion, but with a more geologically consistent laterally varying thickness: approximately honoring Crust2.0 (Bassin, et al., 2000) Moho depth in the continents, while saturating at 30km in the oceans. We demonstrate that this approach does not bias our upper mantle model, which is constrained not only by fundamental mode surface waves, but also by overtone waveforms. We have also improved our data-selection and

  4. Can We Probe the Conductivity of the Lithosphere and Upper Mantle Using Satellite Tidal Magnetic Signals?

    Science.gov (United States)

    Schnepf, N. R.; Kuvshinov, A.; Sabaka, T.

    2015-01-01

    A few studies convincingly demonstrated that the magnetic fields induced by the lunar semidiurnal (M2) ocean flow can be identified in satellite observations. This result encourages using M2 satellite magnetic data to constrain subsurface electrical conductivity in oceanic regions. Traditional satellite-based induction studies using signals of magnetospheric origin are mostly sensitive to conducting structures because of the inductive coupling between primary and induced sources. In contrast, galvanic coupling from the oceanic tidal signal allows for studying less conductive, shallower structures. We perform global 3-D electromagnetic numerical simulations to investigate the sensitivity of M2 signals to conductivity distributions at different depths. The results of our sensitivity analysis suggest it will be promising to use M2 oceanic signals detected at satellite altitude for probing lithospheric and upper mantle conductivity. Our simulations also suggest that M2 seafloor electric and magnetic field data may provide complementary details to better constrain lithospheric conductivity.

  5. Shear wave anisotropy beneath the Sierra Nevada range: Implications for lithospheric foundering and upper mantle flow

    Science.gov (United States)

    Badger, N. B.; Bastow, I. D.; Owens, T. J.; Zandt, G.; Jones, C. H.; Gilbert, H.

    2007-12-01

    Recent work asserts that the garnet-rich Sierra Nevada batholith root has undergone foundering since the early Cenozoic. The Sierra Nevada EarthScope Project (SNEP), undertaken to gain a better understanding of this phenomena, consists of a network of ~80 broadband seismometers spaced at ~25 km from ~37.0N to 40.5N. We use the Silver and Chan method to determine shear wave splitting parameters (dt and φ) for teleseismic SKS phases recorded at SNEP and US Array Transportable Array stations in the region. We find dt>1.1s and φ approximately in the E-NE direction over most of the batholith. Splitting of this magnitude cannot be accounted for solely in the crust, and our results, therefore, have significant implications for upper mantle flow beneath the region. At latitude ~39N to 40N, from the western Sierra Nevada range across our study area to central Nevada, we observe dtGorda-Juan de Fuca Plate. Such a flow pattern is also consistent with the circular pattern of splitting measurements that exist in the broader California and Western Nevada region. We observe subtle variations in splitting parameters as a function of backazimuth primarily at stations situated on the western foothills of the Sierra Nevada. These complexities may be indicative of either a two-layer or dipping layer structure beneath the batholith that may be associated with on- going lithospheric foundering beneath the Sierran range. Additionally, in the southern part of our study area, we note a reduction in dt for arrivals that sample the high Vp Isabella anomaly - an upper mantle downwelling thought to be a result of recent lithospheric foundering.

  6. Modeling the Crust and Upper Mantle in Northern Beata Ridge (CARIBE NORTE Project)

    Science.gov (United States)

    Núñez, Diana; Córdoba, Diego; Cotilla, Mario Octavio; Pazos, Antonio

    2016-05-01

    The complex tectonic region of NE Caribbean, where Hispaniola and Puerto Rico are located, is bordered by subduction zone with oblique convergence in the north and by incipient subduction zone associated to Muertos Trough in the south. Central Caribbean basin is characterized by the presence of a prominent topographic structure known as Beata Ridge, whose oceanic crustal thickness is unusual. The northern part of Beata Ridge is colliding with the central part of Hispaniola along a transverse NE alignment, which constitutes a morphostructural limit, thus producing the interruption of the Cibao Valley and the divergence of the rivers and basins in opposite directions. The direction of this alignment coincides with the discontinuity that could explain the extreme difference between west and east seismicity of the island. Different studies have provided information about Beata Ridge, mainly about the shallow structure from MCS data. In this work, CARIBE NORTE (2009) wide-angle seismic data are analyzed along a WNW-ESE trending line in the northern flank of Beata Ridge, providing a complete tectonic view about shallow, middle and deep structures. The results show clear tectonic differences between west and east separated by Beata Island. In the Haiti Basin area, sedimentary cover is strongly influenced by the bathymetry and its thickness decreases toward to the island. In this area, the Upper Mantle reaches 20 km deep increasing up to 24 km below the island where the sedimentary cover disappears. To the east, the three seamounts of Beata Ridge provoke the appearance of a structure completely different where sedimentary cover reaches thicknesses of 4 km between seamounts and Moho rises up to 13 km deep. This study has allowed to determine the Moho topography and to characterize seismically the first upper mantle layers along the northern Beata Ridge, which had not been possible with previous MCS data.

  7. Isotopic and trace element compositions of upper mantle and lower crustal xenoliths, Cima volcanic field, California: Implications for evolution of the subcontinental lithospheric mantle

    Science.gov (United States)

    Mukasa, S.B.; Wilshire, H.G.

    1997-01-01

    Ultramafic and mafic xenoliths from the Cima volcanic field, southern California, provide evidence of episodic modification of the upper mantle and underplating of the crust beneath a portion of the southern Basin and Range province. The upper mantle xenoliths include spinel peridotite and anhydrous and hydrous pyroxenite, some cut by igneous-textured pyroxenite-gabbro veins and dikes and some by veins of amphibole ?? plagioclase. Igneous-textured pyroxenites and gabbros like the dike rocks also occur abundantly as isolated xenoliths inferred to represent underplated crust. Mineral and whole rock trace element compositions among and within the different groups of xenoliths are highly variable, reflecting multiple processes that include magma-mantle wall rock reactions, episodic intrusion and it filtration of basaltic melts of varied sources into the mantle wall rock, and fractionation. Nd, Sr, and Pb isotopic compositions mostly of clinopyroxene and plagioclase mineral separates show distinct differences between mantle xenoliths (??Nd = -5.7 to +3.4; 87Sr/86Sr = 0.7051 - 0.7073; 206Pb/204Pb = 19.045 - 19.195) and the igneous-textured xenoliths (??Nd = +7.7 to +11.7; 87Sr/86Sr = 0.7027 - 0.7036 with one carbonate-affected outlier at 0.7054; and 206Pb/204Pb = 18.751 - 19.068), so that they cannot be related. The igneous-textured pyroxenites and gabbros are similar in their isotopic compositions to the host basaltic rocks, which have ??Nd of+5.1 to +9.3; 87Sr/86Sr of 0.7028 - 0.7050, and 206Pb/204Pb of 18.685 - 21.050. The igneous-textured pyroxenites and gabbros are therefore inferred to be related to the host rocks as earlier cogenetic intrusions in the mantle and in the lower crust. Two samples of peridotite, one modally metasomatized by amphibole and the other by plagioclase, have isotopic compositions intermediate between the igneous-textured xenoliths and the mantle rock, suggesting mixing, but also derivation of the metasomatizing magmas from two separate and

  8. Evolution of the slab bending radius and the bending dissipation in three-dimensional subduction models with a variable slab to upper mantle viscosity ratio

    NARCIS (Netherlands)

    Schellart, W. P.

    2009-01-01

    Three-dimensional laboratory subduction models are presented investigating the influence of the slab/upper mantle viscosity ratio (ηSP/ηUM) on the slab bending radius (RB), with ηSP/ηUM = 66-1375. Here, RB is non-dimensionalized by dividing it by the upper mantle thickness (TUM). The results show

  9. A database of crystal preferred orientation of olivine in upper mantle rocks

    Science.gov (United States)

    Mainprice, D.

    2012-12-01

    Olivine is the most volumetrically abundant mineral in the Earth's upper mantle, as such it dominates the mechanical and physical properties and has a controlling influence of the geodynamics of plate tectonics. Since the pioneering work of Hess and others we know that seismic anisotropy of the shallow mantle is related to olivine and it's crystal preferred orientation (CPO). With advent of plate tectonics the understanding of the key role of peridotite rocks became a major scientific objective and the measurement CPO of olivine in upper mantle samples became an important tool for studying the kinematics of these rocks. Our group originally lead by Adolphe Nicolas introduced the systematic use of CPO measured by U-stage for field studies all over the world for over 30 years, this tradition was extended in last 15 years by the use of electron back-scattered diffraction (EBSD) to study of CPO and the associated digital microstructure. It is an appropriate time to analysis this significant database of olivine CPO, which represents the work of our group, both present and former members, as well as collaborating colleagues. It is also interesting to compare the natural record as illustrated by our database in the light of recent experimental results stimulated by the extended ranges in temperature, pressure and finite strain, as well as intrinsic olivine variables such as hydrogen content. To analysis the database, which is heterogeneous because it is constructed from the individual work of many people over a 45 year period containing U-stage data and EBSD measurements (manual indexing point per grain, automatic indexing one point per grain, automatic indexing gridded mapping data) of various formats, we need a flexible software tool that can handle large volumes of data in consistent way. We have used the state-of-art open source MTEX toolbox for quantitative texture analysis. MTEX is a scriptable MATLAB toolbox, which permits all aspects of quantitative texture

  10. Deep Sources: New constraints on the tectonic origin of the Klyuchevskoy Group upper mantle anomaly

    Science.gov (United States)

    Bourke, J. R.; Nikulin, A.; Levin, V. L.

    2017-12-01

    Volcanoes of the Klyuchevskoy Group (KG) form one of the most active volcanic clusters on the planet, yet its position relative to the subducting Pacific Plate seems to be in violation of the understood principles of the flux-induced arc volcanism. Positioned at 170km above the accepted subduction contact, the KG is seemingly outside the maximum fluid flux release zone of 100km, as observed across global subduction zone environments. Past geophysical studies indicate presence of a planar seismic anomaly 110km below the KG, and it has been noted that the KG lavas exhibit anomalous geochemical signatures, possibly associated with two separate melt generation regions. This interpretation was largely based on receiver function analysis of seismic data recorded by 3 stations of the Partnership in International Research and Education (PIRE) network, done prior to this data becoming publically available. We present results of receiver function and a teleseismic, regional, and local source shear wave splitting study, focused on datasets obtained by the full PIRE network of 12 stations, as well as a hybrid summation of all stations. We present our findings in the form of depth migrated receiver function images convolved with a three-dimensional model of the subduction zone and shear-wave splitting measurements. Our results vastly increase the resolution of the previously identified upper mantle anomaly, further constraining its geometry both vertically and laterally. We complement our observations with a forward modeling effort aimed at assessing the geological nature of the anomaly. Specifically, we test three scenarios that were previously invoked to explain the presence of the low-velocity anomaly in the upper mantle below the KG: a 3D flow of mantle material around the corner of the subducting Pacific Plate, a sinking paleoslab left behind as a result of subduction rollback, and a plume of sediments from the subducting plate. We show that presence of remnant paleoslab

  11. The crustal and upper mantle structure around the Gulf of California, inferred from surface wave data and receiver functions

    NARCIS (Netherlands)

    de Vos, D.

    2016-01-01

    This thesis reports on studies that have been carried out to better image the crustal and upper mantle shear velocity structure around the Gulf of California, Mexico. The Gulf of California forms a part of the plate boundary between the Pacific and North-American plates, where transform motion in

  12. Geothermal Heat Flux and Upper Mantle Viscosity across West Antarctica: Insights from the UKANET and POLENET Seismic Networks

    Science.gov (United States)

    O'Donnell, J. P.; Dunham, C.; Stuart, G. W.; Brisbourne, A.; Nield, G. A.; Whitehouse, P. L.; Hooper, A. J.; Nyblade, A.; Wiens, D.; Aster, R. C.; Anandakrishnan, S.; Huerta, A. D.; Wilson, T. J.; Winberry, J. P.

    2017-12-01

    Quantifying the geothermal heat flux at the base of ice sheets is necessary to understand their dynamics and evolution. The heat flux is a composite function of concentration of upper crustal radiogenic elements and flow of heat from the mantle into the crust. Radiogenic element concentration varies with tectonothermal age, while heat flow across the crust-mantle boundary depends on crustal and lithospheric thicknesses. Meanwhile, accurately monitoring current ice mass loss via satellite gravimetry or altimetry hinges on knowing the upper mantle viscosity structure needed to account for the superimposed glacial isostatic adjustment (GIA) signal in the satellite data. In early 2016 the UK Antarctic Network (UKANET) of 10 broadband seismometers was deployed for two years across the southern Antarctic Peninsula and Ellsworth Land. Using UKANET data in conjunction with seismic records from our partner US Polar Earth Observing Network (POLENET) and the Antarctic Seismographic Argentinian Italian Network (ASAIN), we have developed a 3D shear wave velocity model of the West Antarctic crust and uppermost mantle based on Rayleigh and Love wave phase velocity dispersion curves extracted from ambient noise cross-correlograms. We combine seismic receiver functions with the shear wave model to help constrain the depth to the crust-mantle boundary across West Antarctica and delineate tectonic domains. The shear wave model is subsequently converted to temperature using a database of densities and elastic properties of minerals common in crustal and mantle rocks, while the various tectonic domains are assigned upper crustal radiogenic element concentrations based on their inferred tectonothermal ages. We combine this information to map the basal geothermal heat flux variation across West Antarctica. Mantle viscosity depends on factors including temperature, grain size, the hydrogen content of olivine and the presence of melt. Using published mantle xenolith and magnetotelluric

  13. An upper-mantle S-wave velocity model for Northern Europe from Love and Rayleigh group velocities

    Science.gov (United States)

    Weidle, Christian; Maupin, Valérie

    2008-12-01

    A model of upper-mantle S-wave velocity and transverse anisotropy beneath northwestern Europe is presented, based on regional surface wave observations. Group velocities for both Love and Rayleigh surface waves are measured on waveform data from international and regional data archives (including temporary deployments) and then inverted for group velocity maps, using a method accounting for Fresnel zone sensitivity. The group velocity variations are larger than in global reference maps, and we are able to resolve unprecedented details. We then apply a linear inversion scheme to invert for local 1-D shear wave velocity profiles which are consequently assembled to a 3-D model. By choosing conservative regularization parameters in the 2-D inversion, we ensure the smoothness of the group velocity maps and hence of the resulting 3-D shear wave speed model. To account for the different tectonic regimes in the study region and investigate the sensitivity of the 1-D inversions to inaccuracies in crustal parameters, we analyse inversions with different reference models of increasing complexity (pure 1-D, 3-D crust/1-D mantle and pure 3-D). We find that all inverted models are very consistent at depths below 70 km. At shallower depths, the constraints put by the reference models, primarily Moho depth which we do not invert for, remain the main cause for uncertainty in our inversion. The final 3-D model shows large variations in S-wave velocity of up to +/-12 per cent. We image an intriguing low-velocity anomaly in the depth range 70-150 km that extends from the Iceland plume beneath the North Atlantic and in a more than 400 km wide channel under Southern Scandinavia. Beneath Southern Norway, the negative perturbations are around 10 per cent with respect to ak135, and a shallowing of the anomaly is indicated which could be related to the sustained uplift of Southern Scandinavia in Neogene times. Furthermore, our upper-mantle model reveals good alignment to ancient plate

  14. The Mono Arch, eastern Sierra region, California: Dynamic topography associated with upper-mantle upwelling?

    Science.gov (United States)

    Jayko, A.S.

    2009-01-01

    A broad, topographic flexure localized east of and over the central and southern Sierra Nevada, herein named the Mono Arch, apparently represents crustal response to lithospheric and/or upper-mantle processes, probably dominated by mantle upwelling within the continental interior associated Pacific-North American plate-boundary deformation. This zone of flexure is identified through comparison between the topographic characteristics of the active Cascade volcanic arc and backarc regions with the analogous former arc and backarc in the Sierra Nevada and eastern Sierra Nevada. Serial topographic profiles measured normal to the modern Cascade backarc reveal an accordance of topographic lows defined by valley floors with an average minimum elevation of ???1400-1500m for over 175km to the southeast. Although the accordance drops in elevation slightly to the south, the modern Cascade backarc region is remarkably level, and is characterized by relief up to ???750m above this baseline elevation. By contrast, serial topographic profiles over the former arc and backarc transitions of the eastern Sierra region exhibit a regional anticlinal warping defined by accordant valley floors and by a late Miocene-early Pliocene erosion surface and associated deposits. The amplitude of this flexure above regionally flat baseline elevations to the east varies spatially along the length of the former Sierran arc, with a maximum of ???1000m centred over the Bridgeport Basin. The total zone of flexure is approximately 350km long N-S and 100km wide E-W, and extends from Indian Wells Valley in the south to the Sonora Pass region in the north. Previous geophysical, petrologic, and geodetic studies suggest that the Mono Arch overlies a zone of active mantle upwelling. This region also represents a zone crustal weakness formerly exploited by the middle-to-late Miocene arc and is presently the locus of seismic and volcanic activities. This seismic zone, which lies east of the Sierra Nevada block

  15. Tracking silica in Earth's upper mantle using new sound velocity data for coesite to 5.8 GPa and 1073 K: Tracking Silica in Earth's Upper Mantle

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Ting [Department of Geosciences, Stony Brook University, Stony Brook New York USA; Liebermann, Robert C. [Department of Geosciences, Stony Brook University, Stony Brook New York USA; Mineral Physics Institute, Stony Brook University, Stony Brook New York USA; Zou, Yongtao [Mineral Physics Institute, Stony Brook University, Stony Brook New York USA; State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun China; Li, Ying [Mineral Physics Institute, Stony Brook University, Stony Brook New York USA; Key Laboratory of Earthquake Prediction, Institute of Earthquake Science, China Earthquake Administration, Beijing China; Qi, Xintong [Department of Geosciences, Stony Brook University, Stony Brook New York USA; Li, Baosheng [Department of Geosciences, Stony Brook University, Stony Brook New York USA; Mineral Physics Institute, Stony Brook University, Stony Brook New York USA

    2017-08-12

    The compressional and shear wave velocities for coesite have been measured simultaneously up to 5.8 GPa and 1073 K by ultrasonic interferometry for the first time. The shear wave velocity decreases with pressure along all isotherms. The resulting contrasts between coesite and stishovite reach ~34% and ~45% for P and S wave velocities, respectively, and ~64% and ~75% for their impedance at mantle conditions. The large velocity and impedance contrasts across coesite-stishovite transition imply that to generate the velocity and impedance contrasts observed at the X-discontinuity, only a small amount of silica would be required. The velocity jump dependences on silica, d(lnVP)/d(SiO2) = 0.38 (wt %)-1 and d(lnVS)/d(SiO2) = 0.52 (wt %)-1, are utilized to place constraints on the amount of silica in the upper mantle and provide a geophysical approach to track mantle eclogite materials and ancient subducted oceanic slabs.

  16. Crustal and upper mantle investigations of the Caribbean-South American plate boundary

    Science.gov (United States)

    Bezada, Maximiliano J.

    The evolution of the Caribbean --- South America plate boundary has been a matter of vigorous debate for decades and many questions remain unresolved. In this work, and in the framework of the BOLIVAR project, we shed light on some aspects of the present state and the tectonic history of the margin by using different types of geophysical data sets and techniques. An analysis of controlled-source traveltime data collected along a boundary-normal profile at ˜65°W was used to build a 2D P-wave velocity model. The model shows that the Caribbean Large Igenous Province is present offshore eastern Venezuela and confirms the uniformity of the velocity structure along the Leeward Antilles volcanic belt. In contrast with neighboring profiles, at this longitude we see no change in velocity structure or crustal thickness across the San Sebastian - El Pilar fault system. A 2D gravity modeling methodology that uses seismically derived initial density models was developed as part of this research. The application of this new method to four of the BOLIVAR boundary-normal profiles suggests that the uppermost mantle is denser under the South American continental crust and the island arc terranes than under the Caribbean oceanic crust. Crustal rocks of the island arc and extended island arc terranes of the Leeward Antilles have a relatively low density, given their P-wave velocity. This may be caused by low iron content, relative to average magmatic arc rocks. Finally, an analysis of teleseismic traveltimes with frequency-dependent kernels produced a 3D P-wave velocity perturbation model. The model shows the structure of the mantle lithosphere under the study area and clearly images the subduction of the Atlantic slab and associated partial removal of the lower lithosphere under northern South America. We also image the subduction of a section of the Caribbean plate under South America with an east-southeast direction. Both the Atlantic and Caribbean subducting slabs penetrate the

  17. Anisotropy of the upper mantle beneath the equatorial part of the Mid-Atlantic Ridge

    Science.gov (United States)

    Kendall, J. M.; Rychert, C.; Harmon, N.; Tharimena, S.; Agius, M. R.

    2017-12-01

    It has been long-known that the mantle beneath ocean spreading centres is anisotropic, holding the signature of the formation of new oceanic lithosphere and its coupling with the underlying convecting asthenosphere. Numerical studies have suggested that there should be significant differences between the anisotropy at slow versus fast spreading centres, but there is little observational evidence to calibrate these simulations, especially at slow spreading centres. Near the ridge axis, the anisotropic effects of melt versus the lattice preferred orientation of minerals is not well understood. Finally, the mantle flow near ridge-transform interactions is also poorly understood. Here we present observations of SKS splitting in a region of the Mid-Atlantic Ridge near the equator and offset by the Romanche and Chain Fracture Zones. An array of 37 ocean-bottom seismometers were deployed for a year in depths of up to nearly 6000m, with the aim of studying the nature of the lithosphere-asthenosphere boundary as it forms (the PiLAB - Passive Imaging of the lithosphere-asthenosphere boundary - experiment). Stations were deployed on crust that varies from newly formed to 80 My old. We analyse 40 teleseismic events of magnitude greater than 5.8 and with epicentral distances between 88 and 130 degrees. The ocean-bottom is a noisy environment and a range of filters are used to isolate the SKS, SKKS, and related signals. Furthermore, stacking splitting error envelopes is used to improve confidence in the splitting parameters. Many of the splitting measurements show an orientation parallel to the direction of plate spreading, as expected, but variability in the orientation of the anisotropy increases towards the ridge axis. The magnitude of the anisotropy is also quite variable and suggests larger delay times near the ridge axis. Off-axis anisotropy is interpreted in terms of deformation of peridotite due to mantle flow. Near the ridge axis, the effect of ridge-parallel melt

  18. GRAVITY ANOMALIES OF THE CRUST AND UPPER MANTLE FOR CENTRAL AND SOUTH ASIA

    Directory of Open Access Journals (Sweden)

    V. N. Senachin

    2016-01-01

    Full Text Available Studying the density of both the crust and mantle is one of the topical problems in modern geophysics. Gravity modeling in combination with seismic tomography is an important tool for detecting density inhomogeneities in the crust and mantle, which can cause stresses and thus significantly impact the regional tectonics [Pogorelov, Baranov, 2010], especially in zones wherein continental margins actively interact with subducting oceanic plates and the entire depth of the tectonosphere is subject to stresses. Associated processes lead to considerable horizontal and vertical stresses that often cause catastrophic events on a global scale. The challenge of studying the global tectonic processes in the Earth’s tectonosphere can be addressed by gravity modeling in combination with seismic surveying.Data from previous studies. I.L. Nersesov et al. [1975] pioneered in calculating the spatial pattern of mantle density inhomogeneities in Central Asia. Although the accuracy of their estimations was not high due to the limited database, their study yielded significant results considering the structure of the crust. Numerous subsequent geophysical projects have researched the crust to a level sufficient to develop regional models, that can give quite adequate information on the depths of external and internal boundaries of the crust and suggest the distribution patterns of seismic velocities and density values. With reference to such data, mantle density inhomogeneities can be studied with higher accuracy.This paper reports on the estimations of gravity anomalies in the crust and upper mantle in Central and South Asia. The study region represents the full range of crust thicknesses and ages, as well a variety of crust formation types [Christensen, Mooney, 1995]. We used the 3D gravity modeling software package 3SGravity developed by Senachin [2015a, 2015b] that considers the spherical shape of the Earth's surface, and estimated gravitional anomalies using

  19. Modeling 3-D density distribution in the upper mantle beneath the Yellowstone from inversion of geoid anomaly data

    Science.gov (United States)

    Moreno Chaves, C. M.; Ussami, N.

    2011-12-01

    We developed a simple three-dimensional scheme to invert geoid anomalies, aiming to map density variations in the lower crust and the upper mantle. Using a flat-Earth approximation, the model space is represented by a finite set of rectangular prisms. The linear inversion algorithm is based on Tikhonov regularization and the convergence of the solution is controlled by the Levenberg-Marquardt method. Our linear inversion algorithm does not require an initial density model, allowing it to be used where geological constraints on density are not available. To analyze the quality of the model density obtained by the inversion algorithm, we used the resolution and the covariance matrices. In order to study the thermal and the composition state beneath the Yellowstone and to test our algorithm inversion, geoid anomalies were inverted and modeled. Yellowstone exhibits a high geoid anomaly (~13 m), with a topographic swell of about 500 km wide. Residual geoid anomalies were obtained using the EGM2008 [Pavlis et al., 2008] geopotential model expanded up to degree 2160 after removing the long-wavelength component (degree 10). Lower crust and mantle-related geoid anomalies with -80 m amplitude were obtained after removing crustal effects (topographic masses, sediments and crustal thickness variations). The center of the negative geoid anomaly coincides geographically with the low velocity body (Yuan and Dueker [2005] and Waite et al. [2006]) in the upper mantle and with a depression of 12 km of the 410 km discontinuity detected by Fee and Dueker [2004]. Our results show that the lower crust and the upper mantle of the Yellowstone have a predominantly negative density contrast (-10 to -75 kg/m3) relative to the surrounding mantle. The mass deficiency mapped beneath the Yellowstone suggests the mantle to be hotter (-200 to -300 °C) and buoyant to isostatically sustain the high topography of this province (> 3000 m above sea level). The density model shows that the negative

  20. NoMelt Experiment: High-resolution constraints on Pacific upper mantle fabric inferred from radial and azimuthal anisotropy

    Science.gov (United States)

    Russell, J. B.; Gaherty, J. B.; Lin, P. P.; Lizarralde, D.; Collins, J. A.; Hirth, G.; Evans, R. L.

    2017-12-01

    Observations of seismic anisotropy in the ocean basins are important for constraining deformation and melting processes in the upper mantle. The NoMelt OBS array was deployed on relatively pristine, 70 Ma seafloor in the central Pacific with the aim of constraining upper mantle circulation and the evolution of the lithosphere-asthenosphere system. Surface-waves traversing the array provide a unique opportunity to estimate a comprehensive set of anisotropic parameters. Azimuthal variations in Rayleigh-wave velocity over a period band of 15-180 s suggest strong anisotropic fabric both in the lithosphere and deep in the asthenosphere. High-frequency ambient noise (4-10 s) provides constraints on average VSV and VSH as well as azimuthal variations in both VS and VP in the upper ˜10 km of the mantle. Our best fitting models require radial anisotropy in the uppermost mantle with VSH > VSV by 3 - 7% and as much as 2% radial anisotropy in the crust. Additionally, we find a strong azimuthal dependence for Rayleigh- and Love-wave velocities, with Rayleigh 2θ fast direction parallel to the fossil spreading direction (FSD) and Love 2θ and 4θ fast directions shifted 90º and 45º from the FSD, respectively. These are some of the first direct observations of the Love 2θ and 4θ azimuthal signal, which allows us to directly invert for anisotropic terms G, B, and E in the uppermost Pacific lithosphere, for the first time. Together, these observations of radial and azimuthal anisotropy provide a comprehensive picture of oceanic mantle fabric and are consistent with horizontal alignment of olivine with the a-axis parallel to fossil spreading and having an orthorhombic or hexagonal symmetry.

  1. Crust and upper mantle structure associated with extension in the Woodlark Rift, Papua New Guinea from Rayleigh-wave tomography

    Science.gov (United States)

    Jin, Ge; Gaherty, James B.; Abers, Geoffery A.; Kim, Younghee; Eilon, Zachary; Buck, W. Roger

    2015-11-01

    The Woodlark seafloor spreading center is propagating westward into the Australian plate near the D'Entrecasteaux Islands (DI), Papua New Guinea, generating an active transition zone from continental rifting to seafloor spreading. From March 2010 to July 2011, we deployed 31 on-shore and 8 offshore broadband seismic stations around the DI region, to explore the dynamic processes of the lithosphere extension and the exhumation of the high-pressure terranes exposed on those islands. We measure the multiband (10-60 s) Rayleigh-wave phase velocities from both ambient noise and earthquake signals. These measurements are then inverted for a three-dimensional shear-velocity model for the crust and upper mantle. The results indicate that the lithosphere extension is localized near the rift axis beneath the DI, with a shear-velocity structure in the upper mantle that is similar to mid-ocean ridges. Beneath the Kiribisi Basin west of DI, an ultraslow shear-velocity anomaly (˜4.0 km/s) is observed at shallow mantle depth (30-60 km), which can be interpreted either by the presence of excess partial melt due to slow melt extraction, or by the existence of felsic crustal material buried to mantle depth and not yet exhumed.

  2. Upper mantle seismic structure beneath southwest Africa from finite-frequency P- and S-wave tomography

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Yuan, Xiaohui; Tilmann, Frederik

    2015-01-01

    are related to the impact of asthenosphere-lithosphere interaction, (plume-related features), on the continental areas and the evolution of the continent-ocean transition that followed the break-up of Gondwana. This process is supposed to leave its imprint as distinct seismic signature in the upper mantle....... Utilizing 3D sensitivity kernels, we invert traveltime residuals to image velocity perturbations in the upper mantle down to 1000 km depth. To test the robustness of our tomographic image we employed various resolution tests which allow us to evaluate the extent of smearing effects and help defining...... structures. We present detailed tomographic images of the oceanic and continental lithosphere beneath the study area. The fast lithospheric keel of the Congo Craton reaches a depth of ∼250 km. Relatively low velocity perturbations have been imaged within the orogenic Damara Belt down to a depth of ∼150 km...

  3. Ferric iron partitioning between pyroxene and melt during partial melting of the Earth's upper mantle

    Science.gov (United States)

    Rudra, A.; Hirschmann, M. M.

    2017-12-01

    The oxidation state of the Earth's mantle influences melt production, volatile behavior, partitioning of key trace elements and possible saturation of alloy at depth. Average Fe3+/FeT ratios in MORBs indicate oxygen fugacitiy of the source regions is close to QFM, in contrast to a 3 log unit variation of fO2 recorded by abyssal peridotites. Quantification of the relationship between basalt and source Fe3+/FeT, oxygen fugacity, and melting requires constraints on Fe3+ partitioning between melt and mantle minerals and in particular the principal Fe3+ host, pyroxene. McCanta et al. (2004) investigated valence dependent partitioning of Fe between Martian ferroan pigeonites and melt, but behavior in terrestrial pyroxene compositions relevant to MORB petrogenesis has not been investigated. We are conducting 1 atm controlled fO2 experiments over 4 log unit variation of fO2 between ΔQFM = 2.5 to -1.5 to grow pyroxenes of variable tetrahedral and octahedral cationic population from andesitic melts of varying Mg#, alumina and alkali content. Dynamic crystallization technique facilitates growth of pyroxene crystals (100-200 um) that EPMA analyses show to be compositionally homogeneous and in equilibrium with the melt. Fe3+/FeT ratio of the synthetic pyroxenes have been analyzed by XAFS spectroscopy at the APS (GSECARS) synchrotron. To quantify the x-ray anisotropy in pyroxenes, we collected Fe K-edge XAFS spectra of oriented natural single crystals for a wide range compositions whose Fe3+/FeT ratios we determined by Mossbauer spectroscopy. We have collected both XANES and EXAFS spectral regions spanning from 7020-7220 eV to explore predictive capabilities of different spectral regions about ferric iron concentration and site occupancy. Our results will document the Fe3+ compatibility in pyroxenes of different compositions under a variety of fO2 conditions, which in turn will better constrain the interrelationship between mantle redox and melting.

  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. Neutron activation analysis of the rare earth elements in rocks from the earth's upper mantle and deep crust

    International Nuclear Information System (INIS)

    Stosch, H.-G.; Koetz, J.; Herpers, U.

    1986-01-01

    Three techniques for analyzing rare earth elements (REE) in geological materials are described, i.e. instrumental neutron activation analysis (INAA), neutron activation analysis with pre-irradiation chemical REE separation (PCS-NAA) and radiochemical neutron activation analysis (RNAA). The knowledge of REE concentrationd in eclogites, peridotites and minerals from the earth's lower crust and upper mantle is very useful in constraining their petrogenetic history. (author)

  6. An upper bound on the electrical conductivity of hydrated oceanic mantle at the onset of dehydration melting

    Science.gov (United States)

    Naif, Samer

    2018-01-01

    Electrical conductivity soundings provide important constraints on the thermal and hydration state of the mantle. Recent seafloor magnetotelluric surveys have imaged the electrical conductivity structure of the oceanic upper mantle over a variety of plate ages. All regions show high conductivity (0.02 to 0.2 S/m) at 50 to 150 km depths that cannot be explained with a sub-solidus dry mantle regime without unrealistic temperature gradients. Instead, the conductivity observations require either a small amount of water stored in nominally anhydrous minerals or the presence of interconnected partial melts. This ambiguity leads to dramatically different interpretations on the origin of the asthenosphere. Here, I apply the damp peridotite solidus together with plate cooling models to determine the amount of H2O needed to induce dehydration melting as a function of depth and plate age. Then, I use the temperature and water content estimates to calculate the electrical conductivity of the oceanic mantle with a two-phase mixture of olivine and pyroxene from several competing empirical conductivity models. This represents the maximum potential conductivity of sub-solidus oceanic mantle at the limit of hydration. The results show that partial melt is required to explain the subset of the high conductivity observations beneath young seafloor, irrespective of which empirical model is applied. In contrast, the end-member empirical models predict either nearly dry (<20 wt ppm H2O) or slightly damp (<200 wt ppm H2O) asthenosphere for observations of mature seafloor. Since the former estimate is too dry compared with geochemical constraints from mid-ocean ridge basalts, this suggests the effect of water on mantle conductivity is less pronounced than currently predicted by the conductive end-member empirical model.

  7. Fluids of the lower crust and upper mantle: deep is different

    Science.gov (United States)

    Manning, C. E.

    2017-12-01

    Deep fluids are important for the evolution and properties of the lower crust and upper mantle in tectonically active settings. Uncertainty about their chemistry has led past workers to use upper crustal fluids as analogues. However, recent results show that fluids at >15 km differ fundamentally from shallow fluids and help explain high-pressure metasomatism and resistivity patterns. Deep fluids are comprised of four components: H2O, non-polar gases (chiefly CO2), salts (mostly alkali chlorides), and rock-derived solutes (dominated by aluminosilicates and related components). The first three generally define the solvent properties of the fluid, and models must account for observations that H2O activity may be quite low. The contrasting behavior of H2O-gas and H2O-salt mixtures yields immiscibility in the ternary system, which can lead to separation of two phases with fundamentally different chemical and transport properties. Thermodynamic modeling of equilibrium between rocks and H2O using simple ionic species known from shallow-crustal systems yields solutions possessing total dissolved solids and ionic strength that are too low to be consistent with experiments and resistivity surveys. Addition of CO2 further lowers bulk solubility and conductivity. Therefore, additional species must be present in H2O, and H2O-salt solutions likely explain much of the evidence for fluid action in high-P settings. At low salinity, H2O-rich fluids are powerful solvents for aluminosilicate rock components that are dissolved as previously unrecognized polymerized clusters. Experiments show that, near H2O-saturated melting, Al-Si polymers comprise >80% of solutes. The stability of these species facilitates critical critical mixing in rock-H2O systems. Addition of salt (e.g., NaCl) changes solubility patterns, but aluminosilicate contents remain high. Thermodynamic models indicate that the ionic strength of fluids with Xsalt = 0.05 to 0.4 and equilibrated with model crustal rocks have

  8. P and SH velocity structure in the upper mantle beneath Northeast China: Evidence for a stagnant slab in hydrous mantle transition zone

    Science.gov (United States)

    Li, Juan; Wang, Xin; Wang, Xiujiao; Yuen, David A.

    2013-04-01

    Using high-dense regional body waves for three deep earthquakes that occurred around Russia-China border, we investigate both S and P wave velocity structures in the mantle transition zone beneath Northeast China and northern part of North China Craton, where the northwestern Pacific plate is imaged to subhorizontally lie above the 660-km discontinuity. We observe an increasing trend of S-P travel time residuals along the epicentral distance within a distance range of 11-16.5°, indicating a velocity anomaly in MTZ. We seek the simplest model that explains the observed broadband waveforms and relative travel times of triplication for a confined azimuth sector. Both SH and P data suggest a ˜140±20 km high velocity layer lying above a slightly depressed and broad 660-km discontinuity. Shear velocity reduction of ˜2.5% in the deeper part of the transition zone is required to compensate for the significantly large relative time between AB and CD triplicate branches and the increased trending of S-P travel time residuals as well. The MTZ, as a whole, is featured by low shear velocity and high Vp/Vs ratio. A water-rich mantle transition zone with 0.2-0.4 wt% of H2O may account for the discrepancy between the observed Vp and Vs velocity structures. Our result supports the scenario of a viscosity-dominated stagnant slab with an increased thickness of ˜140 km, which was caused by the large viscosity contrast between the lower and upper mantles. The addition of water and eastward trench retreat might facilitate stagnation of the subducting Pacific slab beneath Northeast China.

  9. 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

  10. Crust and upper-mantle seismic anisotropy variations from the coast to inland in central and Southern Mexico

    Science.gov (United States)

    Castellanos, Jorge; Pérez-Campos, Xyoli; Valenzuela, Raúl; Husker, Allen; Ferrari, Luca

    2017-07-01

    Subduction zones are among the most dynamic tectonic environments on Earth. Deformation mechanisms of various scales produce networks of oriented structures and faulting systems that result in a highly anisotropic medium for seismic wave propagation. In this study, we combine shear wave splitting inferred from receiver functions and the results from a previous SKS-wave study to quantify and constrain the vertically averaged shear wave splitting at different depths along the 100-station MesoAmerican Subduction Experiment array. This produces a transect that runs perpendicular to the trench across the flat slab portion of the subduction zone below central and southern Mexico. Strong anisotropy in the continental crust is found below the Trans-Mexican Volcanic Belt (TMVB) and above the source region of slow-slip events. We interpret this as the result of fluid/melt ascent. The upper oceanic crust and the overlying low-velocity zone exhibit highly complex anisotropy, while the oceanic lower crust is relatively homogeneous. Regions of strong oceanic crust anisotropy correlate with previously found low Vp/Vs regions, indicating that the relatively high Vs is an anisotropic effect. Upper-mantle anisotropy in the southern part of the array is in trench-perpendicular direction, consistent with the alignment of type-A olivine and with entrained subslab flow. The fast polarization direction of mantle anisotropy changes to N-S in the north, likely reflecting mantle wedge corner flow perpendicular to the TMVB.

  11. Active thrusting and folding in the Qilian Shan, and decoupling between upper crust and mantle in northeastern Tibet

    Science.gov (United States)

    Tapponnier, P.; Meyer, B.; Avouac, J. P.; Peltzer, G.; Gaudemer, Y.; Guo, Shunmin; Xiang, Hongfa; Yin, Kelun; Chen, Zhitai; Cai, Shuahua; Dai, Huagang

    1990-03-01

    Fieldwork south of the city of Gaotai (Gansu province, China) shows that active shortening of surface sediments in the foothills of the Yumu Shan, a large fore-mountain of the Qilian Shan, at the northeastern edge of Tibet, involves both overthrusting and flexural-slip folding. North of this mountain, we found and mapped a prominent north-facing thrust scarp that offsets a Holocene fan sloping gently (3.4°) to the north. Part of this scarp appears to be related to the M ≈ 7.5, 180 A.D. earthquake that may have led to the demise of the Han Dynasty city of Luo Tuo Chen, in the Hexi corridor. A set of 10, 100-150 m long profiles measured across this scarp, 3.2 m high on the average, can be made to fit the diffusion-degraded morphology of a surface break related to the 180 A.D. event using a value of about 3.3 m 2/10 3 yr for the mass diffusivity ϰ of fanglomerates in this part of Gansu province. Smaller mountain-facing scarps on a terrace-capped foothill result from bedding slip concurrent with active folding of underlying, steeply northdipping, Plioquaternary sandstone and conglomerate beds. Holocene uplift rates along the Yumu Shan, which is only one of the Qilian Shan ranges, are estimated to be between 0.4 and 1.9 mm/yr, which implies that much of the mountain formed in the Quaternary. The periclinal structure of the Plioquaternary envelope under which the Paleozoic core of the Yumu Shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline. Mountains striking parallel to the Yumu Shan, with similar structure and comparable or greater sizes north and south of the Hexi corridor probably also correspond to recent, crustal ramp anticlines. This implies that the wide, mountainous upper crustal wedge making the northeastern edge of the Tibet-Qinghai plateau is detached from the underlying lower crust and upper mantle.

  12. 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.

  13. Seismic structure of the central US crust and upper mantle: Uniqueness of the Reelfoot Rift

    Science.gov (United States)

    Pollitz, Fred; Mooney, Walter D.

    2014-01-01

    Using seismic surface waves recorded with Earthscope's Transportable Array, we apply surface wave imaging to determine 3D seismic velocity in the crust and uppermost mantle. Our images span several Proterozoic and early Cambrian rift zones (Mid-Continent Rift, Rough Creek Graben—Rome trough, Birmingham trough, Southern Oklahoma Aulacogen, and Reelfoot Rift). While ancient rifts are generally associated with low crustal velocity because of the presence of thick sedimentary sequences, the Reelfoot Rift is unique in its association with low mantle seismic velocity. Its mantle low-velocity zone (LVZ) is exceptionally pronounced and extends down to at least 200 km depth. This LVZ is of variable width, being relatively narrow (∼50km">∼50km wide) within the northern Reelfoot Rift, which hosts the New Madrid Seismic Zone (NMSZ). We hypothesize that this mantle volume is weaker than its surroundings and that the Reelfoot Rift consequently has relatively low elastic plate thickness, which would tend to concentrate tectonic stress within this zone. No other intraplate ancient rift zone is known to be associated with such a deep mantle low-velocity anomaly, which suggests that the NMSZ is more susceptible to external stress perturbations than other ancient rift zones.

  14. 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.

  15. Hydration-reduced lattice thermal conductivity of olivine in Earth’s upper mantle

    Science.gov (United States)

    Chang, Yun-Yuan; Hsieh, Wen-Pin; Tan, Eh; Chen, Jiuhua

    2017-01-01

    Earth’s water cycle enables the incorporation of water (hydration) in mantle minerals that can influence the physical properties of the mantle. Lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs. However, the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible. Here we have precisely measured the lattice thermal conductivity of hydrous San Carlos olivine (Mg0.9Fe0.1)2SiO4 (Fo90) up to 15 gigapascals using an ultrafast optical pump−probe technique. The thermal conductivity of hydrous Fo90 with ∼7,000 wt ppm water is significantly suppressed at pressures above ∼5 gigapascals, and is approximately 2 times smaller than the nominally anhydrous Fo90 at mantle transition zone pressures, demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region. Modeling the thermal structure of a subducting slab with our results shows that the hydration-reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold, dry center of the subducting slab. Therefore, the olivine−wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone. PMID:28377520

  16. Hydration-reduced lattice thermal conductivity of olivine in Earth's upper mantle.

    Science.gov (United States)

    Chang, Yun-Yuan; Hsieh, Wen-Pin; Tan, Eh; Chen, Jiuhua

    2017-04-18

    Earth's water cycle enables the incorporation of water (hydration) in mantle minerals that can influence the physical properties of the mantle. Lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs. However, the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible. Here we have precisely measured the lattice thermal conductivity of hydrous San Carlos olivine (Mg 0.9 Fe 0.1 ) 2 SiO 4 (Fo90) up to 15 gigapascals using an ultrafast optical pump-probe technique. The thermal conductivity of hydrous Fo90 with ∼7,000 wt ppm water is significantly suppressed at pressures above ∼5 gigapascals, and is approximately 2 times smaller than the nominally anhydrous Fo90 at mantle transition zone pressures, demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region. Modeling the thermal structure of a subducting slab with our results shows that the hydration-reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold, dry center of the subducting slab. Therefore, the olivine-wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone.

  17. Sensitivity analysis of crustal correction and its error propagation to upper mantle residual gravity and density anomalies

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2013-01-01

    We investigate the effect of the crustal structure heterogeneity and uncertainty in its determination on stripped gravity field. The analysis is based on interpretation of residual upper mantle gravity anomalies which are calculated by subtracting (stripping) the gravitational effect of the crust...... a relatively small range of expected density variations in the lithospheric mantle, knowledge on the uncertainties associated with incomplete knowledge of density structure of the crust is of utmost importance for further progress in such studies......) uncertainties in the velocity-density conversion and (ii) uncertainties in knowledge of the crustal structure (thickness and average Vp velocities of individual crustal layers, including the sedimentary cover). In this study, we address both sources of possible uncertainties by applying different conversions...... from velocity to density and by introducing variations into the crustal structure which corresponds to the uncertainty of its resolution by high-quality and low-quality seismic models. We examine the propagation of these uncertainties into determinations of lithospheric mantle density. The residual...

  18. Raman Spectroscopy of Orthopyroxene and Clinopyroxene at Simultaneous High Pressures and Temperatures: Implications for the Upper Mantle

    Science.gov (United States)

    Chopelas, A.; Kavner, A.

    2011-12-01

    The upper mantle has a complicated structure which is controlled by the subduction of crust and the upwelling of the hot mantle. The pyroxene (ortho and clino) minerals comprise 30% of the upper mantle. Previous studies of pyroxenes show them to have atypical elastic properties compared to other silicates and are complex in structure, transforming to several different structures in a narrow range of pressure and temperature. The goal of this study is to use Raman spectroscopy to monitor lattice vibrational properties of pyroxenes at temperatures and pressures corresponding to the Earth's crust and mantle. Specifically, we will determine the phase stability of a variety of different pyroxenes, and pressure- and temperature- dependence of the Raman-active spectral peaks. The former helps us to plot out the phase diagram of these complicated minerals; the latter provides information on the thermodynamic behavior of the pyroxenes as they are subjected to extreme conditions. Raman spectroscopy measurements versus temperatures to 470 K on a natural enstatite (Mg90) and diopside (deKalb) isobarically to 20 kbar have been performed in an externally heated membrane diamond cell. The figure shows typical results on enstatite at 11 kbar (1.1 GPa) to 468 K. The pressure derivatives the Raman modes at room temperature match those from our previous studies. For example, the 687 cm^(-1) line in enstatite has a (∂lnν/∂lnV)_T of 0.6±0.3 versus pressure while the temperature shift at 1.8 GPa (∂lnν/∂lnV)_p is 0.7±0.1 versus temperature. Similar results were found for the other modes in both enstatite and diopside. Thus, intrinsic anharmonicity was substantially reduced from high values at ambient temperatures as shown by the reduced volume dependence of the Raman modes versus temperature, meaning at mantle conditions, the vibrational properties scale with volume and are unaffected by temperatures. Higher pressures and temperatures are anticipated and will be further

  19. Crustal and upper mantle structure of Siberia from teleseismic receiver functions

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Thybo, Hans; Artemieva, Irina

    2015-01-01

    . The current results of RF analysis of the crustal and mantle structure will help to build a model for tectonic and geodynamic evolution of different provinces of Siberia. We compare our results to the recent detailed models of crustal structure in the area and with seismic models for similar geodynamic...

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

    DEFF Research Database (Denmark)

    Thybo, Hans

    2014-01-01

    can be correlated to main plate tectonic features, such as oceanic spreading centres, continental rift zones and subducting slabs. Much seismological mantle research is now concentrated on imaging fine scale heterogeneity, which may be detected and imaged with high-resolution seismic data with dense...

  1. Tomographic image of crust and upper mantle off the Boso Peninsula using data from an ocean-bottom seismograph array

    Science.gov (United States)

    Ito, Aki; Yamamoto, Yojiro; Hino, Ryota; Suetsugu, Daisuke; Sugioka, Hiroko; Nakano, Masaru; Obana, Koichiro; Nakahigashi, Kazuo; Shinohara, Masanao

    2017-08-01

    We determined the three-dimensional structure of the crust and upper mantle off the Boso Peninsula, Japan, by analyzing seismograms recorded by ocean-bottom seismometers and land stations between 2011 and 2013. We employed seismic tomography to determine the P- and S-wave velocity structures and earthquake locations simultaneously. The tomographic image shows that the mantle parts of the Pacific and the Philippine Sea plates have high-velocity anomalies. The upper boundary of the Philippine Sea plate is delineated as approximately 2-6 km shallower than that previously estimated from land-based data for the area 140.5°E-141.5°E and 35°N-35.5°N. A pronounced low-velocity anomaly in P- and S-waves with low- V p/ V s ratio (1.5-1.6) was observed at depths shallower than 20 km in the overriding North American plate. This anomaly may be caused by the presence of rocks with a low- V p/ V s ratio, such as quartzite, and the water expelled from the subducted Pacific and Philippine Sea plates.[Figure not available: see fulltext.

  2. Model of the Arctic evolution since the Cretaceous to present, based on upper mantle convection linked with Pacific lithosphere subduction

    Science.gov (United States)

    Lobkovsky, Leopold

    2015-04-01

    The present paper comprises a model of Arctic basin evolution since early-mid Cretaceous to present. The model is based on the mechanism of upper mantle substance circulation beneath the Arctic lithosphere linked with Pacific lithosphere subduction. Seismic tomography data obtained for the Pacific-Eurasia-Arctic joint area indicate that Pacific lithosphere slab sinking to the mantle in subduction zone transforms into the horizontal layer upon reaching the upper mantle foot, this layer extending for two or more thousands km beneath the Eurasian continent. This pattern of seismic tomography indicates the presence of a horizontal convective cell where a flow of substance moving along the upper mantle foot from a subduction zone into the continent is compensated by a return flow moving along the lithosphere foot towards the subduction zone. The return mantle flow makes continental lithosphere extension, giving rise to processes of rifting, magmatism and spreading. The convective cell being continuously supplied with new substance which is transported through the subduction zone it is sure to expand horizontally. The above cell expansion occurs first, due to ocean ward movement of subduction zone (roll back) and secondly, due to the cell front propagation into the continent. The given model allows to understand main features for the Arctic evolution since early-mid Cretaceous to present. Numerous seismic profiling data obtained for shelf and deep water sedimentary basins in the Arctic Ocean as well as on land geological investigation reveal that since Aptian up to present the Arctic region has been characterized by sublatitudinal lithosphere extension. This extension is explained by the effect the return mantle flow related to the subduction of the Northern part of the Pacific plate acts on the Arctic lithosphere foot. The model shows the phenomenon of Arctic plume to be caused by the convective cell uprising flow. In fact lower horizontal flow of convective cell moving

  3. Records of upper mantle oxygen fugacity gleaned from high-density sampling of basalts and peridotites at ultraslow ridges

    Science.gov (United States)

    Birner, S.; Cottrell, E.; Warren, J. M.; Kelley, K. A.; Davis, F. A.

    2016-12-01

    Mantle oxygen fugacity (fO2) controls volatile speciation, phase stability, and the depth of the peridotite solidus, and is thus critical to our understanding of melt production at mid-ocean ridges. Both basalts [1] and peridotites [2] have been used as proxies for calculating upper mantle fO2 beneath ridges. Though the global peridotite dataset for fO2 is limited and does not overlap geographically with samples from the more comprehensive global basalt dataset, the average fO2 recorded by peridotites is lower than that recorded by basalts. Ultraslow spreading ridges such as the Southwest Indian Ridge (SWIR) and Gakkel Ridge have limited magma production due to thick conductive cooling lids at the ridge axis, and thus offer a unique opportunity to compare geographically overlapping suites of basalt and peridotite. In this study, we determined the oxygen fugacity of 41 peridotite samples from the Oblique Segment of SWIR and 10 peridotite samples from Gakkel - more than doubling the number of fO2 estimates for ridge peridotites globally. Our results for SWIR show that peridotite fO2 is highly variable on the dredge to sub-segment scale, ranging from 1.7 log units below the quartz-fayalite-magnetite buffer (QFM) to 1 log unit above QFM, with an average of QFM+0.2 (±0.6). We also calculated fO2 for 25 basalt glasses from the Oblique Segment, which have an average fO2 of QFM+0.3 (±0.1). Importantly, on average, we find no offset between mantle fO2 as recorded by basalts versus peridotites. However, fO2 recorded by basalts is significantly more homogenous than by peridotites, consistent with the idea of aggregate melts recording homogenization of a heterogeneous mantle. The most reduced peridotites at both ridges are generally highly refractory samples at high spinel Cr# (Cr# = Cr/(Cr+Al)) and low modal cpx. This suggests that the process of melt extraction may leave behind a reduced residue. Alternatively, if these highly refractory lithologies are residues from

  4. Mission Moho: Rationale for drilling deep through the ocean crust into the upper mantle

    Science.gov (United States)

    Ildefonse, B.; Abe, N.; Kelemen, P. B.; Kumagai, H.; Teagle, D. A. H.; Wilson, D. S.; Moho Proponents, Mission

    2009-04-01

    Sampling a complete section of the ocean crust to the Moho was the original inspiration for scientific ocean drilling, and remains the main goal of the 21st Century Mohole Initiative in the IODP Science Plan. Fundamental questions about the composition, structure, and geophysical characteristics of the ocean lithosphere, and about the magnitude of chemical exchanges between the mantle, crust and oceans remain unresolved due to the absence of in-situ samples and measurements. The geological nature of the Mohorovičić discontinuity itself remains poorly constrained. "Mission Moho" is a proposal that was submitted to IODP in April 2007, with the ambition to drill completely through intact oceanic crust formed at a fast spreading rate, across the Moho and into the uppermost mantle. Although, eventually, no long-term mission was approved by IODP, the scientific objectives related to deep drilling in the ocean crust remain essential to our understanding of the Earth. These objectives are to : - Determine the geological meaning of the Moho in different oceanic settings, determine the in situ composition, structure and physical properties of the uppermost mantle, and understand mantle melt migration, - Determine the bulk composition of the oceanic crust to establish the chemical links between erupted lavas and primary mantle melts, understand the extent and intensity of seawater hydrothermal exchange with the lithosphere, and estimate the chemical fluxes returned to the mantle by subduction, - Test competing hypotheses of the ocean crust accretion at fast spreading mid-ocean ridges, and quantify the linkages and feedbacks between magma intrusion, hydrothermal circulation and tectonic activity, - Calibrate regional seismic measurements against recovered cores and borehole measurements, and understand the origin of marine magnetic anomalies, - Establish the limits of life in the ocean lithosphere. The "MoHole" was planned as the final stage of Mission Moho, which requires

  5. Resolution Analysis and Jointly Inverted P- and S-Wave Models of Japan's Crust and Upper Mantle.

    Science.gov (United States)

    Bogiatzis, P.; Ishii, M.

    2014-12-01

    Seismic tomography is the most powerful tool for imaging the internal structure of the Earth, and the deployment of dense arrays over the last decade provides opportunities for investigating the interior with exceptionally high resolution. We use travel-time data from regional earthquakes recorded by the Hi-net array in Japan to constrain the elastic properties of the crust and the upper mantle. The large number of high-quality recordings allows refined resolution through the increase of the number of model parameters. However, large amount of data also gives rise to significant challenges. It makes manual picking and reviewing impractical, and these picks are neither errorless nor objective. We address this problem by developing and applying a wavelet-based automatic algorithm to pick the arrival time of both compressional and shear waves and to obtain estimates of the picking uncertainty. Additionally, both forward and inverse calculations require significant computational resources. We use parallel computing implemented in a distributed memory cluster. Forward problem is solved under the high-frequency approximation of wave equation by calculating P and S wave ray paths using a combination of graph theory and pseudo-bending method. We incorporate finite frequency effects by calculating the first Fresnel volume of each travel-time measurement based upon its dominant frequency that is also provided by the automatic picking algorithm. The inverse problem similarly presents difficulties as the number of model parameters increases. Among the most prominent issues is the computational difficulty of explicitly calculating the model and data resolution matrices. These matrices are of great importance in quantifying the spatial resolution of the method and in designing the inverse problem, but they are computational expensive, if not almost impossible, to determine. We attempt to remedy these problems by taking advantage of recent computational developments and

  6. Layering of Structure in the North American Upper Mantle: Combining Short Period Constraints and Full Waveform Tomography

    Science.gov (United States)

    Roy, C.; Calo, M.; Bodin, T.; Romanowicz, B. A.

    2016-12-01

    long period information. We present here the first images of the North American upper mantle obtained with this approach. Further adjustments to the depths of discontinuities can then be obtained by recomputing 1D models under individual stations using constraints from the smooth 3D model obtained in the second step of our procedure.

  7. Coexisting contraction-extension consistent with buoyancy of the crust and upper mantle in North-Central Italy

    CERN Document Server

    Aoudia, A; Ismail-Zadeh, A T; Panza, G F; Pontevivo, A

    2002-01-01

    The juxtaposed contraction and extension observed in the crust of the Italian Apennines and elsewhere has, for a long time, attracted the attention of geoscientists and is a long-standing enigmatic feature. Several models, invoking mainly external forces, have been put forward to explain the close association of these two end-member deformation mechanisms clearly observed by geophysical and geological investigations. These models appeal to interactions along plate margins or at the base of the lithosphere such as back-arc extension or shear tractions from mantle flow or to subduction processes such as slab roll back, retreat or pull and detachment. We present here a revisited crust and upper mantle model that supports delamination processes beneath North-Central Italy and provides a new background for the genesis and age of the recent magmatism in Tuscany. Although external forces must have been important in the building up of the Apennines, we show that internal buoyancy forces solely can explain the coexist...

  8. Magmatic infiltration and melting in the lower crust and upper mantle beneath the Cima volcanic field, California

    Science.gov (United States)

    Wilshire, H.G.; McGuire, A.V.

    1996-01-01

    Xenoliths of lower crustal and upper mantle rocks from the Cima volcanic field (CVF) commonly contain glass pockets, veins, and planar trains of glass and/or fluid inclusions in primary minerals. Glass pockets occupy spaces formerly occupied by primary minerals of the host rocks, but there is a general lack of correspondence between the composition of the glass and that of the replaced primary minerals. The melting is considered to have been induced by infiltration of basaltic magma and differentiates of basaltic magma from complex conduits formed by hydraulic fracturing of the mantle and crustal rocks, and to have occurred during the episode of CVF magmatism between ???7.5 Ma and present. Variable compositions of quenched melts resulted from mixing of introduced melts and products of melting of primary minerals, reaction with primary minerals, partial crystallization, and fractionation resulting from melt and volatile expulsion upon entrainment of the xenoliths. High silica melts (> ??? 60% SiO2) may result by mixing introduced melts with siliceous melts produced by reaction of orthopyroxene. Other quenched melt compositions range from those comparable to the host basalts to those with intermediate Si compositions and elevated Al, alkalis, Ti, P, and S; groundmass compositions of CVF basalts are consistent with infiltration of fractionates of those basalts, but near-solidus melting may also contribute to formation of glass with intermediate silica contents with infiltration only of volatile constituents.

  9. Metal-silicate thermochemistry at high temperature - Magma oceans and the 'excess siderophile element' problem of the earth's upper mantle

    Science.gov (United States)

    Capobianco, Christopher J.; Jones, John H.; Drake, Michael J.

    1993-01-01

    Low-temperature metal-silicate partition coefficients are extrapolated to magma ocean temperatures. If the low-temperature chemistry data is found to be applicable at high temperatures, an important assumption, then the results indicate that high temperature alone cannot account for the excess siderophile element problem of the upper mantle. For most elements, a rise in temperature will result in a modest increase in siderophile behavior if an iron-wuestite redox buffer is paralleled. However, long-range extrapolation of experimental data is hazardous when the data contains even modest experimental errors. For a given element, extrapolated high-temperature partition coefficients can differ by orders of magnitude, even when data from independent studies is consistent within quoted errors. In order to accurately assess siderophile element behavior in a magma ocean, it will be necessary to obtain direct experimental measurements for at least some of the siderophile elements.

  10. Upper mantle diapers, lower crustal magmatic underplating, and lithospheric dismemberment of the Great Basin and Colorado Plateau regions, Nevada and Utah; implications from deep MT resistivity surveying

    Science.gov (United States)

    Wannamaker, P. E.; Doerner, W. M.; Hasterok, D. P.

    2005-12-01

    In the rifted Basin and Range province of the southwestern U.S., a common faulting model for extensional basins based e.g. on reflection seismology data shows dominant displacement along master faults roughly coincident with the main topographic scarp. On the other hand, complementary data such as drilling, earthquake focal mechanisms, volcanic occurrences, and trace indicators such as helium isotopes suggest that there are alternative geometries of crustal scale faulting and material transport from the deep crust and upper mantle in this province. Recent magnetotelluric (MT) profiling results reveal families of structures commonly dominated by high-angle conductors interpreted to reflect crustal scale fault zones. Based mainly on cross cutting relationships, these faults appear to be late Cenozoic in age and are of low resistivity due to fluids or alteration (including possible graphitization). In the Ruby Mtns area of north-central Nevada, high angle faults along the margins of the core complex connect from near surface to a regional lower crustal conductor interpreted to contain high-temperature fluids and perhaps melts. Such faults may exemplify the high angle normal faults upon which the major earthquakes of the Great Basin appear to nucleate. A larger-scale transect centered on Dixie Valley shows major conductive crustal-scale structures connecting to conductive lower crust below Dixie Valley, the Black Rock desert in NW Nevada, and in east-central Nevada in the Monitor-Diamond Valley area. In the Great Basin-Colorado Plateau transition of Utah, the main structures revealed are a series of nested low-angle detachment structures underlying the incipient development of several rift grabens. All these major fault zones appear to overlie regions of particularly conductive lower crust interpreted to be caused by recent basaltic underplating. In the GB-CP transition, long period data show two, low-resistivity upper mantle diapirs underlying the concentrated

  11. Upper mantle low velocity heterogeneities beneath NE China revealed by source- and receiver-side converted waves

    Science.gov (United States)

    Guan, Z.; Niu, F.

    2017-12-01

    Common-conversion-point (CCP) stacking of receiver function is a powerful tool in mapping upper mantle heterogeneities. However, reverberations from shallow boundaries with large velocity contrast could contaminate the imaging profiles severely. Applying the refined Slowness Weighted CCP (SWCCP) stacking technique (Guan and Niu, 2017) on NECESSArray data, we eliminated the multiple effects and systematically imaged the upper mantle low velocity heterogeneities in NE China where there exist rich unconsolidated sediments. The SWCCP profiles reveal a 350 km low velocity heterogeneity which is possibly associated with the Changbai Mountain volcanism and interpreted as a negatively buoyant silicate melt lying atop of the 410 km discontinuity. Besides, the imaging results are also suggestive of a sporadic 580-620 km low velocity heterogeneity locating in the easternmost part of NE China with a velocity contrast comparable with the 660-km discontinuity. In addition, between 42º N and 45º N, we also found a double 660-km discontinuity at the two sides of the localized depression in the longitudinal range of 128º E to 131º E. On the other hand, we gathered USArray and Alaska regional array seismic data of deep earthquakes occurring beneath NE China and the surrounding areas and employed stacking technique to study the source side S-to-P conversions. The source-side stacking also showed a strong S-to-P conversion at 600 km deep, consistent with the SWCCP stacks. Meanwhile, we also confirmed the double 660-km discontinuity feature from the source-side conversions. The receiver- and source-side observations provide strong constraints on these low velocity anomalies that may offer insights on the subduction dynamics of the Pacific plate.

  12. Upper Mantle Seismic Anisotropy Beneath the Northern Transantarctic Mountains, Antarctica from PKS, SKS, and SKKS Splitting Analysis

    Science.gov (United States)

    Graw, J. H.; Hansen, S. E.

    2016-12-01

    Stretching 3500 km across Antarctica, the Transantarctic Mountains (TAMs) separate the stable East Antarctic craton from the West Antarctic Rift System. Using data from a new, 15-station seismic array, known as the Transantarctic Mountains Northern Network, this study aims to constrain azimuthal anisotropy beneath a previously unexplored portion of the TAMs to assess both past and present deformational processes occurring in this region. Shear wave splitting parameters, including fast anisotropic axis directions and delay times, have been calculated for PKS, SKS, and SKKS phases using both the rotation-correlation and eigenvalue methods within the MATLAB-based SplitLab software package. Results show a relatively consistent average fast direction across the study area of 43 degrees, with an average delay time of 1.0 second. However, stations closer to the Ross Sea coastline show larger delay times compared to those behind the TAMs front, averaging 1.62 seconds. Our findings are similar to those from previous shear wave splitting investigations in regions neighboring our study area. Behind the TAMs front, East Antarctica is underlain by cold, thick continental lithosphere, and we suggest that anisotropy in this area is primarily localized in the upper mantle, associated with relict tectonic fabric from deformation events early in Antarctica's tectonic history. In contrast, the larger delay times near the coast may reflect anisotropy associated with a recently identified upper mantle velocity anomaly. This feature has been interpreted as the signature of rift-related decompression melting and Cenozoic extension; hence, the anisotropic signature may be associated with current tectonic processes beneath the TAMs front.

  13. Waveform anomaly caused by strong attenuation in the crust and upper mantle in the Okinawa Trough region

    Science.gov (United States)

    Padhy, S.; Furumura, T.; Maeda, T.

    2017-12-01

    region. It is expected that simulation results help to resolve rift-induced crust and upper mantle anomalies in the trough showing maximum waveform distortion as we observed in broadband records, and will enhance understanding of tectonic processes related to back-arc rifting in the region.

  14. Effects of crystal preferred orientation on upper-mantle flow near plate boundaries: rheologic feedbacks and seismic anisotropy

    Science.gov (United States)

    Blackman, D. K.; Boyce, D. E.; Castelnau, O.; Dawson, P. R.; Laske, G.

    2017-09-01

    Insight into upper-mantle processes can be gained by linking flow-induced mineral alignment to regional deformation and seismic anisotropy patterns. Through a series of linked micro-macro scale numerical experiments, we explore the rheologic effects of crystal preferred orientation (CPO) and evaluate the magnitude of possible impacts on the pattern of flow and associated seismic signals for mantle that includes a cooling, thickening young oceanic lithosphere. The CPO and associated anisotropic rheology, computed by a micromechanical polycrystal model, are coupled with a large scale flow model (Eulerian Finite Element method) via a local viscosity tensor field, which quantifies the stress:strain rate response of a textured polycrystal. CPO is computed along streamlines throughout the model space and the corresponding viscosity tensor field at each element defines the local properties for the next iteration of the flow field. Stable flow and CPO distributions were obtained after several iterations for the two dislocation glide cases tested: linear and nonlinear stress:strain rate polycrystal behaviour. The textured olivine polycrystals are found to have anisotropic viscosity tensors in a significant portion of the model space. This directional dependence in strength impacts the pattern of upper-mantle flow. For background asthenosphere viscosity of ∼1020 Pa s and a rigid lithosphere, the modification of the corner flow pattern is not drastic but the change could have geologic implications. Feedback in the development of CPO occurs, particularly in the region immediately below the base of the lithosphere. Stronger fabric is predicted below the flanks of a spreading centre for fully coupled, power-law polycrystals than was determined using prior linear, intermediate coupling polycrystal models. The predicted SKS splitting is modestly different (∼0.5 s) between the intermediate and fully coupled cases for oceanic plates less than 20 Myr old. The magnitude of

  15. Receiver function analysis of the crust and upper mantle in Fennoscandia - isostatic implications

    DEFF Research Database (Denmark)

    Frassetto, Andrew; Thybo, Hans

    2013-01-01

    The mountains across southern Norway and other margins of the North Atlantic Ocean appear conspicuously high in the absence of recent convergent tectonics. We investigate this phenomenon with receiver functions calculated for seismometers deployed across southern Fennoscandia. These are used...... to constrain the structure and seismic properties of the lithosphere and primarily to measure the thickness and infer the bulk composition of the crust. Such parameters are key to understanding crustal isostasy and assessing its role, or lack thereof, in supporting the observed elevations. Our study focuses...... on the southern Scandes mountain range that has an average elevation >1.0 km above mean sea level. The crust-mantle boundary (Moho) is ubiquitously imaged, and we occasionally observe structures that may represent the base of the continental lithosphere or other thermal, chemical, or viscous boundaries...

  16. Velocity gradients in the Earth's upper mantle: insights from higher mode surface waves

    Science.gov (United States)

    Fishwick, Stewart; Maupin, Valerie; Afonso, Juan Carlos

    2016-04-01

    The majority of seismic tomographic models of the uppermost mantle beneath Precambrian regions show a positive velocity gradient from the Moho to depths of around 100 km. It is becoming increasingly well recognised that this gradient is not readily compatible with simple models of a craton with constant composition and a steady-state geotherm and more complex compositional variations are invoked to explain this feature. At these depths most of the models are dominated by data from fundamental mode surface waves, and the combination of the sensitivity kernels alongside the choice of model parameterisation means that the velocity gradient could be an artefact of the particular inversion. Indeed, recent work using thermodynamically consistent velocity models suggests that in some cases there is not a requirement of this style of gradient. We investigate this aspect of the mantle structure further by returning to the Sa phase. This phase can be considered as the build up of a wave packet due to the overlapping group velocities of higher modes at periods of around 8 - 30 s. Using the Australian shield as a test-case we compare waveforms built from three different styles of velocity model. Firstly, the 1D model AU3 (Gaherty & Jordan, 1995) which did incorporate the Sa phase as part of the waveform in their modelling. Secondly, recent tomographic models of the Australian continent are used, which include no a priori information from the phase. Thirdly, a thermodynamically consistent velocity model that fits the broad dispersion characteristics of the tomography is tested. Finally, these synthetic waveforms are compared to real data crossing the Australian shield. The results illustrate small, but clear, variations in waveform dependent on the velocity structure. Complicating factors in any analysis involve the importance of having good knowledge of the crustal structure and a very accurate source depth (particularly if this is similar to the average crustal thickness).

  17. Bayesian inversion of surface wave data for discontinuities and velocity structure in the upper mantle using Neural Networks. Geologica Ultraiectina (287)

    NARCIS (Netherlands)

    Meier, U.

    2008-01-01

    We present a neural network approach to invert surface wave data for discontinuities and velocity structure in the upper mantle. We show how such a neural network can be trained on a set of random samples to give a continuous approximation to the inverse relation in a compact and computationally

  18. Microstructural and seismic properties of the upper mantle underneath a rifted continental terrane (Baja California): An example of sub-crustal mechanical asthenosphere?

    NARCIS (Netherlands)

    Palasse, L.N.; Vissers, R.L.M.; Paulssen, H.; Basu, A.R.; Drury, M.R.

    2012-01-01

    The Gulf of California rift is a young and active plate boundary that links the San Andreas strike-slip fault system in California to the oceanic spreading system of the East Pacific Rise. The xenolith bearing lavas of the San Quintin volcanic area provide lower crust and upper mantle samples from

  19. Composition of the earth's upper mantle-I. Siderophile trace elements in ultramafic nodules

    Science.gov (United States)

    Morgan, J.W.; Wandless, G.A.; Petrie, R.K.; Irving, A.J.

    1981-01-01

    Seven siderophile elements (Au, Ge, Ir, Ni, Pd, Os, Re) were determined by radiochemical neutron activation analysis in 19 ultramafic rocks, which are spinel lherzollites-xenoliths from North and Central America, Hawaii and Australia, and garnet Iherzolitexenoliths from Lesotho. Abundances of the platinum metals are very uniform in spinel lherzolites averaging 3.4 ?? 1.2 ppb Os, 3.7 ?? 1.1 ppb Ir, and 4.6 ?? 2.0 ppb Pd. Sheared garnet lherzolite PHN 1611 has similar abundances of these elements, but in 4 granulated garnet lherzolites, abundances are more variable. In all samples, the Pt metals retain cosmic ( Cl-chondrite) ratios. Abundances of Au and Re vary more than those of Pt metals, but the Au/Re ratio remains close to the cosmic value. The fact that higher values of Au and Re approach cosmic proportions with respect to the Pt metals, suggests that Au and Re have been depleted in some ultramafic rocks from an initially chondrite-like pattern equivalent to about 0.01 of Cl chondrite abundances. The relative enrichment of Au and Re in crustal rocks is apparently the result of crust-mantle fractionation and does not require a special circumstance of core-mantle partitioning. Abundances of moderately volatile elements Ni, Co and Ge are very uniform in all rocks, and are much higher than those of the highly siderophile elements Au, Ir, Pd, Os and Re. When normalized to Cl chondrites, abundances of Ni and Co are nearly identical, averaging 0.20 ?? 0.02 and 0.22 ?? 0.02, respectively; but Ge is only 0.027 ?? 0.004. The low abundance of Ge relative to Ni and Co is apparently a reflection of the general depletion of volatile elements in the Earth. The moderately siderophile elements cannot be derived from the same source as the highly siderophile elements because of the marked difference in Cl chondrite-normalized abundances and patterns. We suggest that most of the Ni, Co and Ge were enriched in the silicate by the partial oxidation of pre-existing volatile-poor Fe

  20. Constraints on the mantle and lithosphere dynamics from the observed geoid with the effect of visco-elasto-plastic rheology in the upper 300 km

    Science.gov (United States)

    Osei Tutu, Anthony; Steinberger, Bernhard; Rogozhina, Irina; Sobolev, Stephan

    2015-04-01

    Over the past decades rheological properties of the Earth's mantle and lithosphere have been extensively studied using numerical models calibrated versus a range of surface observations (e.g., free-air-gravity anomaly/geoid, dynamic topography, plate velocity, etc.).The quality of model predictions however strongly depends on the simplifying assumptions, spatial resolution and parameterizations adopted by numerical models. The geoid is largely (Hager & Richards, 1989) determined by both the density anomalies driving the mantle flow and the dynamic topography at the Earth surface and the core-mantle boundary. This is the effect of the convective processes within the Earth's mantle. The remainder is mostly due to strong heterogeneities in the lithospheric mantle and the crust, which also need to be taken into account. The surface topography caused by density anomalies both in the sub-lithospheric mantle and within the lithosphere also depends on the lithosphere rheology. Here we investigate the effects of complex lithosphere rheology on the modelled dynamic topography, geoid and plate motion using a spectral mantle flow code (Hager & O'Connell, 1981) considering radial viscosity distribution and a fully coupled code of the lithosphere and mantle accounting for strong heterogeneities in the upper mantle rheology in the 300 km depths (Popov & Sobolev, 2008). This study is the first step towards linking global mantle dynamics with lithosphere dynamics using the observed geoid as a major constraint. Here we present the results from both codes and compare them with the observed geoid, dynamic topography and plate velocities from GPS measurements. This method allows us to evaluate the effects of plate rheology (e.g., strong plate interiors and weak plate margins) and stiff subducted lithosphere on these observables (i.e. geoid, topography, plate boundary stresses) as well as on plate motion. This effort will also serve as a benchmark of the two existing numerical methods

  1. Garnet Yield Strength at High Pressures and Implications for Upper Mantle and Transition Zone Rheology

    International Nuclear Information System (INIS)

    Kavner, A.

    2008-01-01

    Garnet helps control the mechanical behavior of the Earth's crust, mantle, and transition zone. Here, measurements are presented suggesting that garnet, long considered to be a high-viscosity phase, is actually weaker than the other dominant components in the transition zone. The mechanical behavior of garnet at high pressures was examined using radial diffraction techniques in the diamond anvil cell. The yield strength of grossular garnet was inferred from synchrotron X-ray measurements of differential lattice strains. The differential stress was found to increase from 1.3 (±0.6) GPa at a hydrostatic pressure 5.8 (±1.1) GPa to 4.1 (±0.4) GPa at 15.7 (±1.0) GPa, where it was level to 19 GPa. The strength results are consistent with inferred strength values for majorite garnet from measurements in the diamond cell normal geometry, bolstering the idea that garnet-structured materials may all have similar strengths. In this low-temperature, high differential stress regime, garnet is shown to be significantly weaker than anhydrous ringwoodite and to have a strength similar to hydrous ringwoodite. This result suggests that the presence of water in the transition zone may not be required to explain a weak rheology, and therefore models of transition zone behavior built assuming that garnet is the high-strength phase may need to be revised.

  2. Nd and Sr isotopic variations in acidic rocks from Japan: significance of upper-mantle heterogeneity

    Science.gov (United States)

    Terakado, Yasutaka; Nakamura, Noboru

    1984-10-01

    Initial Nd and Sr isotopic ratios have been measured for Cretaceous acidic and related intermediate rocks (24 volcanic and two plutonic rocks) from the Inner Zone of Southwest Japan (IZSWJ) to investigate the genesis of acidic magmas. The initial Nd and Sr isotopic ratios for these rocks show three interesting features: (1) ɛ Nd values for acidic rocks (+2 to -9) are negatively correlated with ɛ Sr values (+10 to +90) together with those for intermediate rocks ( ɛ Nd=+3 to -8; ɛ Sr=0 to +65). (2) The ɛ Nd values for silica rich rocks (>60% SiO2) correlate with the longitude of the sample locality, decreasing from west to east in a stepwise fashion: Four areas characterized by uniform ɛ Nd values are discriminated. (3) Low silica rocks (high silica rocks in the same area. These results as well as those deduced from the additional samples collected, for comparison, from other provinces in Japan suggest that the acidic rocks can be formed neither by fractional crystallization processes from more basic magmas nor by crustal assimilation processes. The isotopic variations of the acidic rocks may reflect regional isotopic heterogeneity in the lower crust, and this heterogeneity may ultimately be attributed to the regional heterogeneity of the uppermost-mantle beneath the Japanese Islands.

  3. Crustal and upper mantle S-wave velocity structures across the Taiwan Strait from ambient seismic noise and teleseismic Rayleigh wave analyses

    Science.gov (United States)

    Huang, Y.; Yao, H.; Wu, F. T.; Liang, W.; Huang, B.; Lin, C.; Wen, K.

    2013-12-01

    Although orogeny seems to have stopped in western Taiwan large and small earthquakes do occur in the Taiwan Strait. Limited studies have focused on this region before and were barely within reach for comprehensive projects like TAICRUST and TAIGER for logistical reasons; thus, the overall crustal structures of the Taiwan Strait remain unknown. Time domain empirical Green's function (TDEGF) from ambient seismic noise to determine crustal velocity structure allows us to study an area using station pairs on its periphery. This research aims to resolve 1-D average crustal and upper mantle S-wave velocity (Vs) structures alone paths of several broadband station-pairs across the Taiwan Strait; 5-120 s Rayleigh wave phase velocity dispersion data derived by combining TDEGF and traditional surface wave two-station method (TS). The average Vs structures show significant differences in the upper 15 km as expected. In general, the highest Vs are observed in the coastal area of Mainland China and the lowest Vs appear along the southwest offshore of the Taiwan Island; they differ by about 0.6-1.1 km/s. For different parts of the Strait, the Vs are lower in the middle by about 0.1-0.2 km/s relative to those in the northern and southern parts. The overall crustal thickness is approximately 30 km, much thinner and less variable than under the Taiwan Island.

  4. P and S velocity structure of the crust and the upper mantle beneath central Java from local tomography inversion

    Science.gov (United States)

    Koulakov, I.; Bohm, M.; Asch, G.; Lühr, B.-G.; Manzanares, A.; Brotopuspito, K. S.; Fauzi, Pak; Purbawinata, M. A.; Puspito, N. T.; Ratdomopurbo, A.; Kopp, H.; Rabbel, W.; Shevkunova, E.

    2007-08-01

    Here we present the results of local source tomographic inversion beneath central Java. The data set was collected by a temporary seismic network. More than 100 stations were operated for almost half a year. About 13,000 P and S arrival times from 292 events were used to obtain three-dimensional (3-D) Vp, Vs, and Vp/Vs models of the crust and the mantle wedge beneath central Java. Source location and determination of the 3-D velocity models were performed simultaneously based on a new iterative tomographic algorithm, LOTOS-06. Final event locations clearly image the shape of the subduction zone beneath central Java. The dipping angle of the slab increases gradually from almost horizontal to about 70°. A double seismic zone is observed in the slab between 80 and 150 km depth. The most striking feature of the resulting P and S models is a pronounced low-velocity anomaly in the crust, just north of the volcanic arc (Merapi-Lawu anomaly (MLA)). An algorithm for estimation of the amplitude value, which is presented in the paper, shows that the difference between the fore arc and MLA velocities at a depth of 10 km reaches 30% and 36% in P and S models, respectively. The value of the Vp/Vs ratio inside the MLA is more than 1.9. This shows a probable high content of fluids and partial melts within the crust. In the upper mantle we observe an inclined low-velocity anomaly which links the cluster of seismicity at 100 km depth with MLA. This anomaly might reflect ascending paths of fluids released from the slab. The reliability of all these patterns was tested thoroughly.

  5. 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.

  6. Oxidation state of the Earth's upper mantle during the last 3800 million years: Implications for the origin of life

    Science.gov (United States)

    Delano, J. W.

    1993-01-01

    A popular, as well as scientifically rigorous, scenario for the origin of life on Earth involves the production of organic molecules by interaction of lightning (or other forms of energy) with a chemically reducing atmosphere in the early history of Earth. Experiments since the 1950's have convincingly demonstrated that the yield of organic molecules is high when the atmosphere contains molecular hydrogen, methane, ammonia, and water vapor. Additional work has also shown that such a highly reducing atmosphere might not, however, have been sufficiently long-lived in the presence of intense solar ultraviolet radiation for life to have formed from it. One way of maintaining such an atmosphere would be to have a continual replenishment of the reduced gases by prolonged volcanic outgassing from a reducing of Earth's interior. The length of time that this replenishment might need to continue is in part constrained by the flux of asteroids onto the Earth's surface containing sufficient energy to destroy most, if not all, life that had developed up to that point in time. If a reducing atmosphere is a key ingredient for the origin of life on Earth, the time of the last environmental sterilization due to large impacts would be an important constraint. In a deep marine setting (e.g., hydrothermal vent), the last global sterilization might have occurred at 4200-4000 Ma. On the Earth's surface, the last global sterilization event might have occurred at 4000-3700 Ma. If these are meaningful constraints, how likely is it that a reducing atmosphere could have survived on the Earth until about 3800 Ma ago? Due to the importance of replenishing this atmosphere with reducing components by volcanic outgassing from the mantle, geochemical information on the history of the mantle's oxidation state would be useful for addressing this question. Geochemical and experimental data discussed in this abstract suggest that extrusive mafic volcanics derived from the upper mantle have had

  7. Joint inversion of satellite-detected tidal and magnetospheric signals constrains electrical conductivity and water content of the upper mantle and transition zone

    DEFF Research Database (Denmark)

    Grayver, Alexander V.; Munch, F. D.; Kuvshinov, Alexey V.

    2017-01-01

    signals results in a model with much improved resolution. Comparison with laboratory-based conductivity profiles shows that obtained models are compatible with a pyrolytic composition and a water content of 0.01 wt% and 0.1 wt% in the upper mantle and transition zone, respectively.......We present a new global electrical conductivity model of Earth's mantle. The model was derived by using a novel methodology, which is based on inverting satellite magnetic field measurements from different sources simultaneously. Specifically, we estimated responses of magnetospheric origin...

  8. Mapping the upper mantle beneath North American continent with joint inversion of surface-wave phase and amplitude

    Science.gov (United States)

    Yoshizawa, K.; Hamada, K.

    2017-12-01

    A new 3-D S-wave model of the North American upper mantle is constructed from a large number of inter-station phase and amplitude measurements of surface waves. A fully nonlinear waveform fitting method by Hamada and Yoshizawa (2015, GJI) is applied to USArray for measuring inter-station phase speeds and amplitude ratios of the fundamental-mode Rayleigh and Love waves. We employed the seismic events from 2007 - 2014 with Mw 6.0 or greater, and collected a large-number of inter-station phase speed data (about 130,000 for Rayleigh and 85,000 for Love waves) and amplitude ratio data (about 75,000 for Rayleigh waves) in a period range from 30 to 130 s for fundamental-mode surface waves. Typical inter-station distances are mostly in a range between 300 and 800 km, which can be of help in enhancing the lateral resolution of a regional tomography model. We first invert Rayleigh-wave phase speeds and amplitudes simultaneously for phase speed maps as well as local amplification factors at receiver locations. The isotropic 3-D S-wave model constructed from these phase speed maps incorporating both phase and amplitude data exhibits better recovery of the strength of velocity perturbations. In particular, local tectonic features characterized by strong velocity gradients, such as Rio Grande Rift, Colorado Plateau and New Madrid Seismic Zone, are more enhanced than conventional models derived from phase information only. The results indicate that surface-wave amplitude, which is sensitive to the second derivative of phase speeds, can be of great help in retrieving small-scale heterogeneity in the upper mantle. We also obtain a radial anisotropy model from the simultaneous inversions of Rayleigh and Love waves (without amplitude information). The model has shown faster SH wave speed anomalies than SV above the depth of 100 km, particularly in tectonically active regions in the western and central U.S., representing the effects of current and former tectonic processes on

  9. Tracking silica in Earth's upper mantle using new sound velocity data for coesite to 5.8 GPa and 1073 K

    Science.gov (United States)

    Chen, Ting; Liebermann, Robert C.; Zou, Yongtao; Li, Ying; Qi, Xintong; Li, Baosheng

    2017-08-01

    The compressional and shear wave velocities for coesite have been measured simultaneously up to 5.8 GPa and 1073 K by ultrasonic interferometry for the first time. The shear wave velocity decreases with pressure along all isotherms. The resulting contrasts between coesite and stishovite reach 34% and 45% for P and S wave velocities, respectively, and 64% and 75% for their impedance at mantle conditions. The large velocity and impedance contrasts across coesite-stishovite transition imply that to generate the velocity and impedance contrasts observed at the X-discontinuity, only a small amount of silica would be required. The velocity jump dependences on silica, d(lnVP)/d(SiO2) = 0.38 (wt %)-1 and d(lnVS)/d(SiO2) = 0.52 (wt %)-1, are utilized to place constraints on the amount of silica in the upper mantle and provide a geophysical approach to track mantle eclogite materials and ancient subducted oceanic slabs.

  10. The upper mantle structure of the central Rio Grande rift region from teleseismic P and S wave travel time delays and attenuation

    Science.gov (United States)

    Slack, P.D.; Davis, P.M.; Baldridge, W.S.; Olsen, K.H.; Glahn, A.; Achauer, U.; Spence, W.

    1996-01-01

    The lithosphere beneath a continental rift should be significantly modified due to extension. To image the lithosphere beneath the Rio Grande rift (RGR), we analyzed teleseismic travel time delays of both P and S wave arrivals and solved for the attenuation of P and S waves for four seismic experiments spanning the Rio Grande rift. Two tomographic inversions of the P wave travel time data are given: an Aki-Christofferson-Husebye (ACH) block model inversion and a downward projection inversion. The tomographic inversions reveal a NE-SW to NNE-SSW trending feature at depths of 35 to 145 km with a velocity reduction of 7 to 8% relative to mantle velocities beneath the Great Plains. This region correlates with the transition zone between the Colorado Plateau and the Rio Grande rift and is bounded on the NW by the Jemez lineament, a N52??E trending zone of late Miocene to Holocene volcanism. S wave delays plotted against P wave delays are fit with a straight line giving a slope of 3.0??0.4. This correlation and the absolute velocity reduction imply that temperatures in the lithosphere are close to the solidus, consistent with, but not requiring, the presence of partial melt in the mantle beneath the Rio Grande rift. The attenuation data could imply the presence of partial melt. We compare our results with other geophysical and geologic data. We propose that any north-south trending thermal (velocity) anomaly that may have existed in the upper mantle during earlier (Oligocene to late Miocene) phases of rifting and that may have correlated with the axis of the rift has diminished with time and has been overprinted with more recent structure. The anomalously low-velocity body presently underlying the transition zone between the core of the Colorado Plateau and the rift may reflect processes resulting from the modern (Pliocene to present) regional stress field (oriented WNW-ESE), possibly heralding future extension across the Jemez lineament and transition zone.

  11. Upper mantle deformation in the western US determined from seismic anisotropy; 2: Western North American plate boundary

    Energy Technology Data Exchange (ETDEWEB)

    Ozalaybey, S.; Savage, M.K. (Univ. of Nevada, Reno, NV (United States). Seismological Lab.); Silver, P.G. (Carnegie Inst., Washington, DC (United States))

    1993-04-01

    The western margin of the North American plate includes subduction, transform faulting and a migrating triple junction. The authors have measured polarization azimuths ([phi]) and delay-times ([delta]t) of split shear waves. Stations located close to the northern end of the San Andreas fault, near the San Francisco Bay area yielded well-constrained but azimuthally varying splitting parameters. These can be explained by a model consisting of two anisotropic layers: an upper layer with fast direction parallel to the strike of the San Andreas fault and a lower layer with E-W fast direction. Both layers have average delay-times of 1[+-]0.3 s. The authors have found that an east-west fast feature is also present beneath stations in the Sierra-Nevada, the Mojave Desert and the Los Angeles area. These latter measurements do not require more than one layer. The E-W fast layer diminishes near the southern edge of the Gorda plate. The authors interpret their measurements as caused by single or double layers of homogeneously, transversely anisotropic material with horizontal symmetry axes due to strain-induced preferred orientation of olivine in the upper mantle. They suggest that the fault-parallel fast layer is the result of finite strain associated with the transform plate motion between the North American and Pacific plates. The deeper layer with E-W fast direction can not be associated with known surface tectonic features. One possible mechanisms for this E-W fast feature is that it may be related to the passage of the trailing edge of the Farallon plate as the slab migrated northward beneath central California. The shear associated with the different motion between the slab and the asthenosphere may cause mineral alignment leading to shear-wave splitting.

  12. Subduction and volcanism in the Iberia-North Africa collision zone from tomographic images of the upper mantle

    Science.gov (United States)

    Villaseñor, Antonio; Chevrot, Sébastien; Harnafi, Mimoun; Gallart, Josep; Pazos, Antonio; Serrano, Inmaculada; Córdoba, Diego; Pulgar, Javier A.; Ibarra, Pedro

    2015-11-01

    New tomographic images of the upper mantle beneath the westernmost Mediterranean suggest that the evolution of the region experienced two subduction-related episodes. First subduction of oceanic and/or extended continental lithosphere, now located mainly beneath the Betics at depths greater than 400 km, took place on a NW-SE oriented subduction zone. This was followed by a slab-tear process that initiated in the east and propagated to the west, leading to westward slab rollback and possibly lower crustal delamination. The current position of the slab tear is located approximately at 4°W, and to the west of this location the subducted lithosphere is still attached to the surface along the Gibraltar Arc. Our new P-wave velocity model is able to image the attached subducted lithosphere as a narrow high-velocity body extending to shallow depths, coinciding with the region of maximum curvature of the Gibraltar Arc, the occurrence of intermediate-depth earthquakes, and anomalously thick crust. This thick crust has a large influence in the measured teleseismic travel time residuals and therefore in the obtained P-wave tomographic model. We show that removing the effects of the thick crust significantly improves the shallow images of the slab and therefore the interpretations based on the seismic structure.

  13. Differences in the Upper Mantle Structure between 'Hot' and 'Cold' Areas in North America based on USArray Seismic Data along California - Virginia Profile

    Science.gov (United States)

    Dec, M.; Sroda, P.; Tesauro, M.; Kaban, M. K.; Perchuc, E.

    2013-12-01

    Nowadays, United States is an area extensively studied by seismic research due to the fact that the EarthScope USArray project provides an unique opportunity to verify previous seismological models and improve our understanding of the upper mantle structure. The data from this experiment are fundamental to study the upper mantle structure because they allow us to present much more detailed analysis. In this study we use the data recorded by the Transportable Array of the USArray and data from the ISC bulletin. We refer also to data from longitudinal Early Rise project while analysing New Madrid Seismic Zone. We use the travel time data from the earthquakes recorded at a distance up to 3500 km in order to image the upper mantle down to about 600 km depth. We present P- and S-wave velocity models for the tectonically stable central part of US and for the active western part. The 1D models are constructed based on the forward modelling of traveltimes from the events located along the California - Virginia profile, for e.g. in California, Colorado or Virginia. This provides a possibility to update the previous MP-1 model (Malinowski et al., 2010). The models were corrected for the crustal effect using the crustal model of Tesauro et al. (2013). All the models have been verified by synthetic seismograms calculated using the reflectivity method. The models show significant differences in the first-arrivals observed at the 800-1800 km epicentral distance range. In the Western, tectonically active region, the 300-km discontinuity is observed. It is interpreted based on the refracted phases with the apparent velocity of 8.9-9.0 km/s and clearly observed reflections. In this area, a low-velocity zone at the bottom of the upper mantle significantly deepens the 410-km discontinuity. The stable North American Craton is characterized by blurred arrivals from the 300-km discontinuity. These 1D models of the upper mantle structure in North America served as a starting point for

  14. Cumulate xenoliths from St. Vincent, Lesser Antilles Island Arc: a window into upper crustal differentiation of mantle-derived basalts

    Science.gov (United States)

    Tollan, P. M. E.; Bindeman, I.; Blundy, J. D.

    2012-02-01

    In order to shed light on upper crustal differentiation of mantle-derived basaltic magmas in a subduction zone setting, we have determined the mineral chemistry and oxygen and hydrogen isotope composition of individual cumulus minerals in plutonic blocks from St. Vincent, Lesser Antilles. Plutonic rock types display great variation in mineralogy, from olivine-gabbros to troctolites and hornblendites, with a corresponding variety of cumulate textures. Mineral compositions differ from those in erupted basaltic lavas from St. Vincent and in published high-pressure (4-10 kb) experimental run products of a St. Vincent high-Mg basalt in having higher An plagioclase coexisting with lower Fo olivine. The oxygen isotope compositions (δ18O) of cumulus olivine (4.89-5.18‰), plagioclase (5.84-6.28‰), clinopyroxene (5.17-5.47‰) and hornblende (5.48-5.61‰) and hydrogen isotope composition of hornblende (δD = -35.5 to -49.9‰) are all consistent with closed system magmatic differentiation of a mantle-derived basaltic melt. We employed a number of modelling exercises to constrain the origin of the chemical and isotopic compositions reported. δ18OOlivine is up to 0.2‰ higher than modelled values for closed system fractional crystallisation of a primary melt. We attribute this to isotopic disequilibria between cumulus minerals crystallising at different temperatures, with equilibration retarded by slow oxygen diffusion in olivine during prolonged crustal storage. We used melt inclusion and plagioclase compositions to determine parental magmatic water contents (water saturated, 4.6 ± 0.5 wt% H2O) and crystallisation pressures (173 ± 50 MPa). Applying these values to previously reported basaltic and basaltic andesite lava compositions, we can reproduce the cumulus plagioclase and olivine compositions and their associated trend. We conclude that differentiation of primitive hydrous basalts on St. Vincent involves crystallisation of olivine and Cr-rich spinel at depth

  15. Cenozoic volcanism in the Bohemian Massif in the context of P- and S-velocity high-resolution teleseismic tomography of the upper mantle

    Czech Academy of Sciences Publication Activity Database

    Plomerová, Jaroslava; Munzarová, Helena; Vecsey, Luděk; Kissling, E.; Achauer, U.; Babuška, Vladislav

    2016-01-01

    Roč. 17, č. 8 (2016), s. 3326-3349 ISSN 1525-2027 R&D Projects: GA ČR GAP210/12/2381; GA ČR GA205/01/1154; GA MŠk LM2010008; GA MŠk(CZ) LM2015079 Institutional support: RVO:67985530 Keywords : seismic tomography * upper mantle * body waves Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 3.201, year: 2016

  16. Highly siderophile element geochemistry of peridotites and pyroxenites from Horní Bory, Bohemian Massif: Implications for HSE behaviour in subduction-related upper mantle

    Czech Academy of Sciences Publication Activity Database

    Ackerman, Lukáš; Pitcher, L.; Strnad, L.; Puchtel, I. S.; Jelínek, E.; Walker, R. J.; Rohovec, Jan

    2013-01-01

    Roč. 100, č. 1 (2013), s. 158-175 ISSN 0016-7037 R&D Projects: GA AV ČR KJB300130902 Institutional research plan: CEZ:AV0Z30130516 Institutional support: RVO:67985831 Keywords : alloy * high pressure * high temperature * igneous geochemistry * isotopic composition * mass balance * nappe * osmium isotope * peridotite * petrography * platinum group element * precipitation (chemistry) * pyroxenite * siderophile element * subduction * sulfide * upper mantle Subject RIV: DD - Geochemistry Impact factor: 4.250, year: 2013

  17. Crust and upper mantle velocity structure of the northwestern Indian Peninsular Shield from inter-station phase velocities of Rayleigh and Love waves

    Directory of Open Access Journals (Sweden)

    Gaddale Suresh

    2015-06-01

    Full Text Available We measure the inter-station Rayleigh and Love wave phase velocities across the northwestern Indian Peninsular shield (NW-IP through cross-correlation and invert these velocities to evaluate the underneath crust and upper mantle velocity structure down to 400 km. We consider a cluster of three stations in the northern tip of the Peninsula and another cluster of eight stations in the south. We measure phase velocities along 28 paths for Rayleigh waves and 17 paths for Love waves joining two stations with one from each cluster and using broadband records of earthquakes which lie nearly on the great circle joining the pair of stations. The phase velocities are in the period range of 10 to 275 s for Rayleigh waves and of 10 to 120 s for Love waves. The isotropic model obtained through inversion of the phase velocities indicates 199.1 km thick lithosphere with 3-layered crust of thickness 36.3 km; the top two layers have nearly same velocities and both constitute the upper crust with thickness of 12.6 km. The upper crust is mafic, whereas the lower crust is felsic. In the mantle lid, velocities increase with depth. The velocities of mantle lid beneath NW-IP is lower than those beneath south Indian Peninsula showing the former is hotter than the later perhaps due to large Phanerozoic impact on NW-IP. The significant upper mantle low velocity zone beneath NW-IP indicates high temperature which could be attributed to the past existence of a broad plume head at the west-central part of the Peninsula.

  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. a Global Shear Velocity Model of the Upper Mantle from New Fundamental and Higher Rayleigh Mode Measurements

    Science.gov (United States)

    Debayle, E.; Ricard, Y. R.

    2011-12-01

    We present a global SV-wave tomographic model of the upper mantle, built from a new dataset of fundamental and higher mode Rayleigh waveforms. We use an extension of the automated waveform inversion approach of Debayle (1999) designed to improve the extraction of fundamental and higher mode information from a single surface wave seismogram. The improvement is shown to be significant in the transition zone structure which is constrained by the higher modes. The new approach is fully automated and can be run on a Beowulf computer to process massive surface wave dataset. It has been used to match successfully over 350 000 fundamental and higher mode Rayleigh waveforms, corresponding to about 20 millions of new measurements extracted from the seismograms. For each seismogram, we obtain a path average shear velocity and quality factor model, and a set of fundamental and higher mode dispersion and attenuation curves compatible with the recorded waveform. The set of dispersion curves provides a global database for future finite frequency inversion. Our new 3D SV-wave tomographic model takes into account the effect of azimuthal anisotropy and is constrained with a lateral resolution of several hundred kilometers and a vertical resolution of a few tens of kilometers. In the uppermost 200 km, our model shows a very strong correlation with surface tectonics. The slow velocity signature of mid-oceanic ridges extend down to ~100 km depth while the high velocity signature of cratons vanishes below 200 km depth. At depth greater than 400 km, the pattern of seismic velocities appear relatively homogeneous at large scale, except for high velocity slabs which produce broad high velocity regions within the transition zone. Although resolution is still good, the region between 200 and 400 km is associated with a complex pattern of seismic heterogeneities showing no simple correlation with the shallower or deeper structure.

  20. Anisotropic full waveform ambient noise and earthquake tomography of the Ontong Java Plateau and surrounding Pacific upper mantle

    Science.gov (United States)

    Hirsch, A. C.; Savage, B.; Shen, Y.

    2017-12-01

    The Ontong Java (OJP) and Manihiki plateau (MP) large igneous provinces (LIP) of the Southwest Pacific took shape from a complicated, but poorly understood geological history. Unraveling the formation and deformation of these Pacific LIPs is not straightforward due to limited available data, remote location, and atypical geology. Origin hypotheses include melting of a plume or a fast-spreading triple junction, but distinguishing between these requires a further understanding of 120 Ma of deformation of each LIP. A previous tomographic model of OJP observed highly abnormal Rayleigh shear wave speeds, >4.75km/s, and attributed these to an unusual composition, garnet and clinopyroxene residual from melting pyroxenite entrained within a rising plume. Unfortunately, this model lacks constraints on the horizontally polarized shear wave speeds, SH or Love waves, anisotropy, and attenuation. We therefore perform a transverse-isotropic, scattering-integral, full-waveform tomography between periods of 25 and 200 seconds utilizing both ambient noise empirical Green's functions and seismic data from regional earthquakes. Our tomographic model improves upon previous work using permanent and temporary seismic stations, increased model space, and utilizing three components of seismic data (vertical, radial, and tangential). Included is also an assessment of the anelastic attenuation in the western Pacific using both surface waves and multiple core reflections. Our results will improve the tomographic resolution around OJP and the Pacific upper mantle between 35 and 300 km depth. This improved model will enhance our understanding of the tectonic history of the OJP and MP regions, and the Pacific Indo-Australian plate boundary.

  1. High frequency local reflections and conversions from upper mantle discontinuities in the Fiji-Tonga subduction zone

    Science.gov (United States)

    Tibi, R.; Wiens, D. A.

    2003-12-01

    Recordings of deep Fiji-Tonga earthquakes from an array of 15 broadband seismographs in Fiji are stacked and searched for reflections and conversions from upper mantle discontinuities near the Fiji-Tonga slab. The Fiji array operated as part of the SAFT (Seismic Arrays in Fiji and Tonga) experiment from July 2001 to August 2002. In comparison with the commonly used teleseismic approaches, the short path lengths for the local data provide smaller Fresnel zones and high frequency content for precise mapping of discontinuity topography and sharpness. This is particularly important for a subduction zone, where variations in temperature and water content may be expected which should cause changes in the elevation and sharpness of the discontinuities. We study the phases s410p, P660p and S660p where they arrive at least 10 seconds after the direct P wave and prior to the S wave accross the array. To anhance low-amplitude reflections/conversions, deconvolved seismograms from each event are aligned on the maximum amplitude of the direct P wave and slant stacked. Preliminary results indicate that for the northern part of the Fiji-Tonga subduction zone, the 660-km discontinuity varies between 660 and 670 km in depth. In the central part we observe converted phases consistent with a ``410'' depth of 380 km, indicating the effect of the cold subducting plate. The reflections/conversions show only a slight frequency shift relative to the direct P waveforms, suggesting the discontinuities are relatively sharp. The thickness for the 660-km discontinuity is estimated as between 2 and 6 km.

  2. 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

  3. Crust and Upper Mantle Structure beneath Isparta Angle in SW Turkey from P and S Receiver Functions

    Science.gov (United States)

    Kahraman, M.; Turkelli, N.; Özacar, A.; Sandvol, E. A.; Teoman, U.

    2015-12-01

    Isparta Angle (IA) constitutes a triangular shape elevated tectonic domain in SW Turkey which contains units stacked with opposing thrust vergences during Late Cretaceous to Miocene. The region which is located at the junction between Aegean and Cyprus arcs separated by a slab tear is now bounded by Fethiye-Burdur Fault Zone (FBFZ) in the west and Akşehir-Afyon Fault Zones (AAFZ) in the east. In the area, seismicity displays ongoing extension along active grabens oriented at different directions. In the past, many competing geodynamic scenarios had been proposed to explain the complex tectonic evolution of the area. In this study, we used both P and S receiver functions (RFs) to present high resolution crustal and upper mantle images down to 200 km. Moho and upper crustal discontinuities were well resolved by P Rfs; however S RFs were utilized to image lithospheric-asthenospheric boundaries having the benefit of being free of multiple conversions. RFs were calculated from 916 teleseismic earthquakes (Mw ≥ 5.5) recorded by 42 permanent and temporary broadband stations BU-KOERI/NEMC, DEMP/ERD and Isparta Angle Seismic Experiment deployed by collaboration of BU-KOERI and University of Missouri. Totally, 4501 P and 946 S RFs with the cut-off frequencies of ~1.0 Hz and ~0.5 Hz, respectively, were obtained by applying iterative-time domain deconvolution. Crustal thickness and Vp/Vs ratios were calculated by grid search of maximum amplitude of P RFs(Ps,PpPs and PsPs+PpSs) in depth and Vp/Vs domain. Then, we created 2-D P and S migrated cross-sections to observe crustal and lithospheric-asthenospheric discontinuities beneath the region. P RFs indicates that, average crustal thickness and Vp/Vs ratio is ~36 km and 1.78 in the region with small changing values close to the edges. Migrated P RFs cross-sections revealed a sharp change in Moho (Moho offset) on the western boundary that spatially correlates with the FBFZ. We also found a relatively flat Moho in the center and

  4. The Diamondiferous Lithospheric Mantle Underlying the Eastern Superior Craton: Evidence From Mantle Xenoliths From the Renard Kimberlites, Quebec

    Science.gov (United States)

    Hunt, L.; Stachel, T.; Armstrong, J. P.; Simonetti, A.

    2009-05-01

    The Renard kimberlite cluster consists of nine pipes located within a 2km2 area in the northern Otish Mountains of Quebec. The pipes are named Renards 1 to 10, with subsequent investigation revealing Renards 5 and 6 to join at depth (now Renard 65). The pipes are located within the eastern portion of the Superior craton, emplaced into Archean granitic and gneissic host rocks of the Opinica Subprovince (Percival, 2007). Amphibolite grade metamorphism, locally passing into the granulite facies (Percival et al., 1994) occurred in late Archean time (Moorhead et al., 2003). Radiometric dating of the hypabyssal Renard 1 kimberlite indicates Neoproterozoic emplacement, with a 206Pb/238U model age of 631.6±3.5 Ma (2σ) (Birkett et al., 2004). A later study on the main phases in Renard 2 and 3 gave a similar emplacement, with a 206Pb/238U model age of 640.5±2.8Ma (Fitzgerald et al., 2008). This makes this kimberlite district one of the oldest in Canada, similar in eruption age to the Wemindji kimberlites (629±29Ma: Letendre et al., 2003). These events are broadly coeval with the conversion from subduction magmatism to rifting in northern Laurentia (Birkett et al., 2004). The bodies are part of a late Neoproterozoic to Cambrian kimberlite field in eastern Canada (Girard, 2001; Moorhead et al, 2002; Letendre et al., 2003) and fit into the north-east of the Eocambrian/Cambrian Labrador Sea Province of Heaman et al. (2004). To better understand the diamondiferous lithospheric mantle beneath the Renard kimberlites, 116 microxenoliths and xenocrysts were analysed. The samples were dominantly peridotitic, composed primarily of purple garnet, emerald green clinopyroxene and olivine, with a few pink and red garnets. A minor eclogitic component comprises predominantly orange garnets and lesser amounts of clinopyroxene. A detailed study on the major, minor and trace element composition of xenolith minerals is currently underway. All but three of the clinopyroxenes analysed to date

  5. Joint inversion of satellite-detected tidal and magnetospheric signals constrains electrical conductivity and water content of the upper mantle and transition zone

    Science.gov (United States)

    Grayver, A. V.; Munch, F. D.; Kuvshinov, A. V.; Khan, A.; Sabaka, T. J.; Tøffner-Clausen, L.

    2017-06-01

    We present a new global electrical conductivity model of Earth's mantle. The model was derived by using a novel methodology, which is based on inverting satellite magnetic field measurements from different sources simultaneously. Specifically, we estimated responses of magnetospheric origin and ocean tidal magnetic signals from the most recent Swarm and CHAMP data. The challenging task of properly accounting for the ocean effect in the data was addressed through full three-dimensional solution of Maxwell's equations. We show that simultaneous inversion of magnetospheric and tidal magnetic signals results in a model with much improved resolution. Comparison with laboratory-based conductivity profiles shows that obtained models are compatible with a pyrolytic composition and a water content of 0.01 wt % and 0.1 wt % in the upper mantle and transition zone, respectively.

  6. 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.

  7. 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.

  8. 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

  9. Seismic model of the upper mantle beneath the Alpine-Himalayan orogenic belt from tomographic inversion of the ISC data

    Science.gov (United States)

    Koulakov, Ivan

    2010-05-01

    A new seismic model of P and S anomalies in the upper mantle beneath the Alpine-Himalayan orogenic belt is presented. Travel-time data from the ISC catalogue have been inverted using a linearized approach. A large amount of global data for more than 40 years enables good ray coverage which ensures high quality of synthetic tests (e.g. checkerboard tests). At the same time, these data are very noisy, and the noise seems often to be biased. The data quality varies in different parts of the study area that makes adequate simulating of real situation in synthetic modeling almost impossible. To validate our results, we present the result of independent inversion of two data subsets (with odd and even events) that allows us revealing robust features which are not affected by random factors. The presented seismic model reveals some important features which can be attributed to geodynamical processes controlling the collision process. In the Mediterranean part we observe complex shapes of the subducting African lithosphere. In particular, the Calabrian slab looks as an elongated (~700 km long and ~100 km thick) "sausage" which penetrates to the depth of 300-400 km. In Asia we observe a few high velocity patterns which can be attributed to the process of the lithosphere recycling in the collision belts. Beneath Zagros (Iran) a slab-shaped anomaly coincides with active seismicity down to 100 km depth and probably marks the final stage of the Tethyan subduction. A trace of suspended old slab is observed beneath Tien Shan. We observe an almost isometrical bright high-velocity anomaly beneath Pamir - Hindukush. We interpret this pattern as a drop of delaminating material triggered by eclogitization of the lower part of thickened crust, and not as a subducting lithosphere as often proposed. Based on our tomographic models, we claim that the delamination is the major mechanism of the lithosphere recycling in the continent-continent collision areas. Today we have a chance to

  10. Detailed Structure and Thickness of Upper Mantle Discontinuities in the Tonga Subduction Zone From Regional Broadband Arrays

    Science.gov (United States)

    Tibi, R.; Wiens, D. A.

    2004-12-01

    Recordings of deep Tonga earthquakes from two arrays of 12 broadband seismographs each in the Fiji and Tonga islands are stacked and searched for reflections and conversions from upper mantle discontinuities in the Tonga subduction zone. The arrays operated as part of the Seismic Arrays in Fiji and Tonga (SAFT) experiment from July 2001 to August 2002. In comparison with the commonly used teleseismic approaches, the short path lengths for the regional data provide smaller Fresnel zones and high frequency content for precise mapping of discontinuity topography and sharpness. This is particularly important for a subduction zone, where variations in temperature and water content may be expected which should cause changes in the elevation and sharpness of the discontinuities. We studied the phases s410p, P660p and S660p. To enhance these low-amplitude phases, deconvolved seismograms from each event/array pair are aligned on the maximum amplitude of the direct P wave and subsequently slant-stacked. For the 410-km discontinuity, the results show no systematic variations in depth with distance to the cold slab. The 660-km discontinuity varies between 656 and 714 km in depth. For the southern and central parts of the subduction zone, the largest depths occur in the core of the Tonga slab. For the northern part, two separate depressions of the 660 are observed. These anomalies are interpreted as being induced by the active, steeply subducting Tonga deep zone and a subhorizontally lying remnant of subducted lithosphere from the fossil Vityaz trench, respectively. Interpreting the deflections of the 660 in terms of local temperatures implies a thermal anomaly at 660 km depth of -800 to -1200oK for the Tonga slab, and -600 to -950oK for the piece of the Vityaz lithosphere. Except for the southern region where it thickens, the Tonga slab seems to penetrate the 660 with little deformation. Waveform modeling susggests that both the 410 and 660 discontinuities are sharp. The 410

  11. Detailed structure and sharpness of upper mantle discontinuities in the Tonga subduction zone from regional broadband arrays

    Science.gov (United States)

    Tibi, Rigobert; Wiens, Douglas A.

    2005-06-01

    Recordings of deep Tonga earthquakes from two arrays of 12 broadband seismographs each in the Fiji and Tonga islands are stacked and searched for reflections and conversions from upper mantle discontinuities in the Tonga subduction zone. The arrays operated as part of the Seismic Arrays in Fiji and Tonga (SAFT) experiment from July 2001 to August 2002. In comparison with the commonly used teleseismic approaches, the short path lengths for the local data provide smaller Fresnel zones and high-frequency content for precise mapping of discontinuity topography and sharpness. To enhance the low-amplitude discontinuity phases s410p, P660p and S660p, deconvolved seismograms from each event/array pair are aligned on the maximum amplitude of the direct P wave and subsequently slant stacked. For the 410-km discontinuity, the results show no systematic variations in depth with distance to the cold slab. The 660-km discontinuity varies between 656 and 714 km in depth. For the southern and central parts of the subduction zone, the largest depths occur in the core of the Tonga slab. For the northern part, two separate depressions of the 660-km discontinuity are observed. These anomalies are interpreted as being induced by the active, steeply subducting Tonga deep zone and a subhorizontally lying remnant of subducted lithosphere from the fossil Vityaz trench, respectively. Interpreting the deflections of the 660-km discontinuity in terms of local temperatures implies a thermal anomaly of -800°K to -1200°K at 660 km depth. Except for the southern region where it may thicken, the width of the depressed 660-km discontinuity region implies that the Tonga slab seems to penetrate the 660-km discontinuity with little deformation. Waveform modeling suggests that both the 410- and 660-km discontinuities are sharp. The 660-km discontinuity is at most 2 km thick in many parts of the region, and a first-order discontinuity cannot be precluded. The 410-km discontinuity thickness shows

  12. Elasticity of Orthoenstatite at High Pressure and Temperature: Implications for the Origin of Low VP/VS Zones in the Mantle Wedge

    Science.gov (United States)

    Qian, Wangsheng; Wang, Wenzhong; Zou, Fan; Wu, Zhongqing

    2018-01-01

    Orthopyroxene (opx) is an important mineral in petrologic models for the upper mantle. Its elastic properties are fundamental for understanding the chemical composition and geodynamics of the upper mantle. Here we calculate the elastic properties of orthoenstatite (MgSiO3), the Mg end-member orthopyroxene under upper mantle pressure and temperature conditions using first principle calculations with local density approximation. Bulk and shear moduli increase nonlinearly with pressure at mantle temperatures, but the shear modulus and VS show very weak pressure dependence in comparison with VP. Compared to other major minerals in the upper mantle, orthoenstatite has the lowest compressional velocities (VP), shear velocities (VS), and VP/VS ratio down to the depth of approximately 300 km. The enrichment of opx in the upper mantle can cause the unusually low VP/VS observed in the mantle wedge.

  13. Lithosphere and upper-mantle structure of the southern Baltic Sea estimated from modelling relative sea-level data with glacial isostatic adjustment

    Science.gov (United States)

    Steffen, H.; Kaufmann, G.; Lampe, R.

    2014-06-01

    During the last glacial maximum, a large ice sheet covered Scandinavia, which depressed the earth's surface by several 100 m. In northern central Europe, mass redistribution in the upper mantle led to the development of a peripheral bulge. It has been subsiding since the begin of deglaciation due to the viscoelastic behaviour of the mantle. We analyse relative sea-level (RSL) data of southern Sweden, Denmark, Germany, Poland and Lithuania to determine the lithospheric thickness and radial mantle viscosity structure for distinct regional RSL subsets. We load a 1-D Maxwell-viscoelastic earth model with a global ice-load history model of the last glaciation. We test two commonly used ice histories, RSES from the Australian National University and ICE-5G from the University of Toronto. Our results indicate that the lithospheric thickness varies, depending on the ice model used, between 60 and 160 km. The lowest values are found in the Oslo Graben area and the western German Baltic Sea coast. In between, thickness increases by at least 30 km tracing the Ringkøbing-Fyn High. In Poland and Lithuania, lithospheric thickness reaches up to 160 km. However, the latter values are not well constrained as the confidence regions are large. Upper-mantle viscosity is found to bracket [2-7] × 1020 Pa s when using ICE-5G. Employing RSES much higher values of 2 × 1021 Pa s are obtained for the southern Baltic Sea. Further investigations should evaluate whether this ice-model version and/or the RSL data need revision. We confirm that the lower-mantle viscosity in Fennoscandia can only be poorly resolved. The lithospheric structure inferred from RSES partly supports structural features of regional and global lithosphere models based on thermal or seismological data. While there is agreement in eastern Europe and southwest Sweden, the structure in an area from south of Norway to northern Germany shows large discrepancies for two of the tested lithosphere models. The lithospheric

  14. 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).

  15. Loss of Karma transposon methylation underlies the mantled somaclonal variant of oil palm

    Science.gov (United States)

    Ong-Abdullah, Meilina; Ordway, Jared M.; Jiang, Nan; Ooi, Siew–Eng; Kok, Sau-Yee; Sarpan, Norashikin; Azimi, Nuraziyan; Hashim, Ahmad Tarmizi; Ishak, Zamzuri; Rosli, Samsul Kamal; Malike, Fadila Ahmad; Bakar, Nor Azwani Abu; Marjuni, Marhalil; Abdullah, Norziha; Yaakub, Zulkifli; Amiruddin, Mohd Din; Nookiah, Rajanaidu; Singh, Rajinder; Low, Eng-Ti Leslie; Chan, Kuang-Lim; Azizi, Norazah; Smith, Steven W.; Bacher, Blaire; Budiman, Muhammad A.; Van Brunt, Andrew; Wischmeyer, Corey; Beil, Melissa; Hogan, Michael; Lakey, Nathan; Lim, Chin-Ching; Arulandoo, Xaviar; Wong, Choo-Kien; Choo, Chin-Nee; Wong, Wei-Chee; Kwan, Yen-Yen; Alwee, Sharifah Shahrul Rabiah Syed; Sambanthamurthi, Ravigadevi; Martienssen, Robert A.

    2015-01-01

    Somaclonal variation arises in plants and animals when differentiated somatic cells are induced into a pluripotent state, but the resulting clones differ from each other and from their parents. In agriculture, somaclonal variation has hindered micropropagation of elite hybrids and genetically modified crops, but the mechanism remains a mystery1. The oil palm fruit abnormality, mantled, is a somaclonal variant arising from tissue culture that drastically reduces yield, and has largely halted efforts to clone elite hybrids for oil production2–4. Widely regarded as epigenetic5, mantling has defied explanation, but here we identify the MANTLED gene using Epigenome Wide Association Studies. DNA hypomethylation of a LINE retrotransposon related to rice Karma, in the intron of the homeotic gene DEFICIENS, is common to all mantled clones and is associated with alternative splicing and premature termination. Dense methylation near the Karma splice site (the Good Karma epiallele) predicts normal fruit set, while hypomethylation (the Bad Karma epiallele) predicts homeotic transformation, parthenocarpy and dramatic loss of yield. Loss of Karma methylation and small RNA in tissue culture contributes to the origin of mantled, while restoration in spontaneous revertants accounts for non-Mendelian inheritance. The ability to predict and cull mantling at the plantlet stage will facilitate the introduction of higher performing clones and optimize environmentally sensitive land resources. PMID:26352475

  16. Crustal and upper mantle shear velocities of Iberia, the Alboran Sea, and North Africa from ambient noise and ballistic finite-frequency Rayleigh wave tomography

    Science.gov (United States)

    Palomeras, I.; Villasenor, A.; Thurner, S.; Levander, A.; Gallart, J.; mimoun, H.

    2013-12-01

    The complex Mesozoic-Cenozoic Alpine deformation in the western Mediterranean extends from the Pyrenees in northern Spain to the Atlas Mountains in southern Morocco. The Iberian plate was accreted to the European plate in late Cretaceous, resulting in the formation of the Pyrenees. Cenozoic African-European convergence resulted in subduction of the Tethys oceanic plate beneath Europe. Rapid Oligocene slab rollback from eastern Iberia spread eastward and southward, with the trench breaking into three segments by the time it reached the African coast. One trench segment moved southwestward and westward creating the Alboran Sea, floored by highly extended continental crust, and building the encircling Betics Rif mountains comprising the Gibraltar arc, and the Atlas mountains, which formed as the inversion of a Jurassic rift. A number of recent experiments have instrumented this region with broad-band arrays (the US PICASSO array, Spanish IberArray and Siberia arrays, the University of Munster array), which, including the Spanish, Portuguese, and Moroccan permanent networks, provide a combined array of 350 stations having an average interstation spacing of ~60 km. Taking advantage of this dense deployment, we have calculated the Rayleigh waves phase velocities from ambient noise for short periods (4 s to 40 s) and teleseismic events for longer periods (20 s to 167 s). Approximately 50,000 stations pairs were used to measure the phase velocity from ambient noise and more than 160 teleseismic events to measure phase velocity for longer periods. The inversion of the phase velocity dispersion curves provides a 3D shear velocity for the crust and uppermost mantle. Our results show differences between the various tectonic regions that extend to upper mantle depths (~200 km). In Iberia we obtain, on average, higher upper mantle shear velocities in the western Variscan region than in the younger eastern part. We map high upper mantle velocities (>4.6 km/s) beneath the

  17. 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

  18. Joint inversion of shear wave travel time residuals and geoid and depth anomalies for long-wavelength variations in upper mantle temperature and composition along the Mid-Atlantic Ridge

    Science.gov (United States)

    Sheehan, Anne F.; Solomon, Sean C.

    1991-01-01

    Measurements were carried out for SS-S differential travel time residuals for nearly 500 paths crossing the northern Mid-Atlantic Ridge, assuming that the residuals are dominated by contributions from the upper mantle near the surface bounce point of the reflected phase SS. Results indicate that the SS-S travel time residuals decrease linearly with square root of age, to an age of 80-100 Ma, in general agreement with the plate cooling model. A joint inversion was formulated of travel time residuals and geoid and bathymetric anomalies for lateral variation in the upper mantle temperature and composition. The preferred inversion solutions were found to have variations in upper mantle temperature along the Mid-Atlantic Ridge of about 100 K. It was calculated that, for a constant bulk composition, such a temperature variation would produce about a 7-km variation in crustal thickness, larger than is generally observed.

  19. Physical properties of the crust and upper mantle in Eurasia through the analysis of waveforms from the Soviet analog seismic network

    Science.gov (United States)

    Dricker, Ilya G.

    Seismic networks in the Commonwealth of Independent States (CIS) consist of more than a hundred broadband analog stations and have been in operation for more than 30 years. The longevity of the network, the number and distribution of stations, and the large number of earthquakes recorded has made the seismic data collected by the networks a valuable source of information about the structure of the Earth. The analog recording format and a lack of access to adequate computing facilities has resulted in most of these data undergoing only rudimentary analysis in the past. For this thesis I have collected and digitized several thousands analog records from the archives of more than 30 stations. I found that the quality of the digitized seismograms from the CIS analog stations is good enough to be useful in such types of analysis as the receiver functions, SKS splitting and SS-S differential travel times analysis. Studies of SKS phases recorded by stations in Eastern Europe suggest the existence of a present or recent large-scale mantle flow in central and eastern Europe, parallel to the Alpine belt, which is consistent with the hypothesis of flow proposed previously for the mantle beneath Western Europe. Application of SKS technique to the data recorded in the Altai and Sayan mountains of Central Asia show strain in the mantle beneath the Altai-Sayan region is similar, both in style and scale, to strain in the crust. The receiver functions technique was used to investigate the uppermost layers in the Khibina plutonic region of northern Russia. The results suggest that short (50 km) wavelength lateral variations in the depth of crust-mantle transition persist in this region, despite the cessation of rifting activity in the Kola peninsula in Devonian times. Finally, mapping the upper mantle velocity structure of the Tibetan Plateau and its surroundings with SS-S travel time residuals suggest that while the lithospere beneath southern Tibet is thickened by the India

  20. In-situ observation of the lower crust and upper mantle lithology in Atlantis Bank, SWIR - results from ABCDE Cruise

    Science.gov (United States)

    Matsumoto, T.; Dick, H. J.; Abcde Cruise, O.

    2002-12-01

    The ABCDE Cruise (Cruise ID = YK01-14) was carried out in the Southwest Indian Ridge by R/V YOKOSKA from December 2001 until January 2002. The main purpose of the cruise was to test the ophiolite model, lithology and development processes of the oceanic crust by observing crust-mantle boundary and distribution of dike intrusion into the gabbroic massifs in the Atlantis Bank core-complex by SHINKAI6500 dives and precise geophysical surveys. The cruise was based on the past three ODP legs and three submersible cruises. Dive area was limited to Atlantis bank surrounded by 33-00'S, 32-30'S, 57-05'E, and 57-30'E lines. Finally 13 dives were completed during the one-month cruise. Unaltered lower crust and uppermost mantle rocks were observed in a limited site on the southwestern slope of Atlantis Bank. It was proved that the lower crust of SWIR is essentially the same as the ophiolite which exposes ashore as a result. On the other hand, a large number of sites of dike intrusion into gabbroic massifs were observed on the eastern wall and on the southern slope of the bank. This is corresponding to dike-gabbro transition in the ophiolite model. However, dike intrusion was also observed in the mantle peridotite domains. This suggests that mantle peridotite was dragged out just after the construction of the bank near the spreading axis along the detachment faults then the remaining magma intruded into the bank. The segment west of the Atlantis-II Fracture Zone was mapped intensively for regional geophysical survey at night and on the submersible maintenance days. The northern RTI of the Atlantis-II active transform presents an L-shaped nodal basin while the southern RTI a V-shaped one. The difference in these RTI types suggest the difference in the structure and basement rock types. Mantle Bouguer anomaly shows intense bull's eye above the spreading segment west of the Atlantis-II FZ while a slight bull_fs eye is located above the axis east of the FZ, suggesting that the

  1. Synchrotron in-situ deformation experiments of perovskite + (Mg,Fe)O aggregates under shallow lower mantle conditions (Invited)

    Science.gov (United States)

    Girard, J.; Amulele, G.; Farla, R. J.; Liu, Z.; Mohiuddin, A.; Karato, S.

    2013-12-01

    Experimental studies on rheological properties of mantle's minerals are crucial to understand the dynamics of Earth's interior, but direct experimental studies under the relevant lower mantle conditions are challenging. Most of the earlier studies were performed at lower mantle pressures but low temperatures using DAC (diamond anvil cell) (e.g., Merkel et al., 2003)), and in DAC experiments strain-rate and stress are unknown. Some previous studies were carried out under high pressures and high temperatures (e.g, Cordier et al., 2004) , but quantitative results on rheological behaviour of said minerals were not obtained. Here we present the results of the first in-situ deformation experiments of perovskite + (Mg,Fe)O (Pv + fp) aggregates using RDA (rotational Drickamer apparatus). The RDA has a better support for the anvils at high pressure than the more commonly used D-DIA apparatus and hence we can reach higher pressures and temperatures than the D-DIA. We have recently made new modifications to the cell assembly to reach the lower mantle conditions with less interference in X-ray diffraction patterns by the surrounding materials. The starting material was ringwoodite synthesized using a multi-anvil. In-situ deformation experiments were then carried at pressure up to 28 GPa (calculated from thermal EOS of Pt) and estimated temperatures up to 2200 K using RDA. Under these conditions, ringwoodite transformed to Pv + fp. We subsequently deformed the sample between strain rates of 10-4 to 10-5 s-1. Stress and strain were measured in-situ using X-ray synchrotron beam. The recovered sample analyses show evidence of perovskite+(Mg,Fe)O microstructure (Fig. 1). The radial X-ray diffraction data are being analysed to determine the stress levels of two minerals. Also microstructures of deformed specimens are studied to understand the deformation mechanisms and strain partitioning. The results will contribute towards our understanding of the rheological properties of the

  2. 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 ...

  3. Shear wave splitting as a diagnostic of variable anisotropic structure of the upper mantle beneath central Fennoscandia

    Czech Academy of Sciences Publication Activity Database

    Vecsey, Luděk; Plomerová, Jaroslava; Kozlovskaya, E.; Babuška, Vladislav

    2007-01-01

    Roč. 438, č. 1-4 (2007), s. 57-77 ISSN 0040-1951 R&D Projects: GA AV ČR IAA3012405; GA AV ČR(CZ) KJB300120605 Grant - others:Academy of Finland(FI) 208068; Academy of Finland(FI) 107991 Institutional research plan: CEZ:AV0Z30120515 Source of funding: V - iné verejné zdroje ; V - iné verejné zdroje Keywords : shear wave splitting * joint inversion of body wave anisotropic parameters * 3D anisotropic model of mantle lithosphere Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.729, year: 2007

  4. Shear wave velocities in the Pampean flat-slab region from Rayleigh wave tomography: Implications for slab and upper mantle hydration

    Science.gov (United States)

    Porter, Ryan; Gilbert, Hersh; Zandt, George; Beck, Susan; Warren, Linda; Calkins, Josh; Alvarado, Patricia; Anderson, Megan

    2012-11-01

    The Pampean flat-slab region, located in central Argentina and Chile between 29° and 34°S, is considered a modern analog for Laramide flat-slab subduction within western North America. Regionally, flat-slab subduction is characterized by the Nazca slab descending to ˜100 km depth, flattening out for ˜300 km laterally before resuming a more "normal" angle of subduction. Flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of deformation and the cessation of volcanism within the region. To better understand flat-slab subduction we combine ambient-noise tomography and earthquake-generated surface wave measurements to calculate a regional 3D shear velocity model for the region. Shear wave velocity variations largely relate to changes in lithology within the crust, with basins and bedrock exposures clearly defined as low- and high-velocity regions, respectively. We argue that subduction-related hydration plays a significant role in controlling shear wave velocities within the upper mantle. In the southern part of the study area, where normal-angle subduction is occurring, the slab is visible as a high-velocity body with a low-velocity mantle wedge above it, extending eastward from the active arc. Where flat-slab subduction is occurring, slab velocities increase to the east while velocities in the overlying lithosphere decrease, consistent with the slab dewatering and gradually hydrating the overlying mantle. The hydration of the slab may be contributing to the excess buoyancy of the subducting oceanic lithosphere, helping to drive flat-slab subduction.

  5. Single-crystal elasticity of MgAl2O4-spinel up to 10.9 GPa and 1000 K: Implication for the velocity structure of the top upper mantle

    Science.gov (United States)

    Duan, Yunfei; Li, Xinyang; Sun, Ningyu; Ni, Huaiwei; Tkachev, Sergey N.; Mao, Zhu

    2018-01-01

    The combined effect of pressure and temperature on the single-crystal elasticity of MgAl2O4-spinel has been studied using Brillouin scattering and X-ray diffraction up to 10.9 GPa and 1000 K in externally-heated diamond anvil cells. The obtained single-crystal elastic moduli of MgAl2O4-spinel at ambient conditions are consistent with literature values and follow a linear increase with pressure at high temperatures. More importantly, the pressure dependence of the elastic moduli at high temperatures is much smaller than that at 300 K, indicating a stronger temperature effect on the elastic moduli of MgAl2O4-spinel at high pressures. Our new results were applied to model the sound velocity of MgAl2O4-spinel at relevant pressure and temperature conditions of the top upper mantle, showing that MgAl2O4-spinel has the greatest velocity and the VP /VS ratio among major mantle minerals. We further modeled the velocity of spinel-peridotite at the top upper mantle. Varying the composition of spinel-peridotite can lead to up to 2.1% variation in VP and 1.3% in VS. The top upper mantle with greater VP and VS should contain more olivine and spinel but less orthopyroxene. The velocity of the top upper mantle is thus strongly correlated with the composition of the region. Our results are thus important in understanding the composition and velocity of the top upper mantle.

  6. A Simultaneous Multi-phase Approach to Determine P-wave and S-wave Attenuation of the Crust and Upper Mantle

    Energy Technology Data Exchange (ETDEWEB)

    Pasyanos, M E; Walter, W R; Matzel, E M

    2009-02-26

    We have generalized the methodology of our regional amplitude tomography from the Lg phase to the four primary regional phases (Pn, Pg, Sn, Lg). Differences in the geometrical spreading, source term, site term, and travel paths are accounted for, while event source parameters such as seismic moment are consistent among phases. In the process, we have developed the first regional attenuation model that uses the amplitudes of four regional phases to determine a comprehensive P-wave and S-wave attenuation model of the crust and upper mantle. When applied to an area encompassing the Middle East, eastern Europe, western Asia, south Asia, and northeast Africa for the 1-2 Hz passband, we find large differences in the attenuation of the lithosphere across the region. The tectonic Tethys collision zone has high attenuation, while stable outlying regions have low attenuation. While crust and mantle Q variations are often consistent, we do find several notable areas where they differ considerably, but are appropriate given the region's tectonic history. Lastly, the relative values of Qp and Qs indicate that scattering Q is likely the dominant source of attenuation in the crust at these frequencies.

  7. Copper isotope fractionation during partial melting and melt percolation in the upper mantle: Evidence from massif peridotites in Ivrea-Verbano Zone, Italian Alps

    Science.gov (United States)

    Huang, Jian; Huang, Fang; Wang, Zaicong; Zhang, Xingchao; Yu, Huimin

    2017-08-01

    To investigate the behavior of Cu isotopes during partial melting and melt percolation in the mantle, we have analyzed Cu isotopic compositions of a suite of well-characterized Paleozoic peridotites from the Balmuccia and Baldissero massifs in the Ivrea-Verbano Zone (IVZ, Northern Italy). Our results show that fresh lherzolites and harzburgites have a large variation of δ65Cu ranging from -0.133 to 0.379‰, which are negatively correlated with Al2O3 contents as well as incompatible platinum-group (e.g., Pd) and chalcophile element (e.g., Cu, S, Se, and Te) contents. The high δ65Cu can be explained by Cu isotope fractionation during partial melting of a sulfide-bearing peridotite source, with the light isotope (63Cu) preferentially entering the melts. The low δ65Cu can be attributed to precipitation of sulfides enriched in 63Cu during sulfur-saturated melt percolation. Replacive dunites from the Balmuccia massif display high δ65Cu from 0.544 to 0.610‰ with lower Re, Pd, S, Se, and Te contents and lower Pd/Ir ratios relative to lherzolites, which may result from dissolution of sulfides during interactions between S-undersaturated melts and lherzolites at high melt/rock ratios. Thus, our results suggest that partial melting and melt percolation largely account for the Cu isotopic heterogeneity of the upper mantle. The correlation between δ65Cu and Cu contents of the lherzolites and harzburgites was used to model Cu isotope fractionation during partial melting of a sulfide-bearing peridotite, because Cu is predominantly hosted in sulfide. The modelling results indicate an isotope fractionation factor of αmelt-peridotite = 0.99980-0.99965 (i.e., 103lnαmelt-peridotite = -0.20 to -0.35‰). In order to explain the Cu isotopic systematics of komatiites and mid-ocean ridge basalts reported previously, the estimated αmelt-peridotite was used to simulate Cu isotopic variations in melts generated by variable degrees of mantle melting. The results suggest that high

  8. Evidence for small-scale convection in the Pacific and Atlantic upper mantle from joint analysis of surface wave phase velocity and seafloor bathymetry

    Science.gov (United States)

    Ma, Z.; Dalton, C. A.

    2017-12-01

    It has been long observed that the rate of seafloor subsidence in the Pacific Ocean is lower than predicted by half-space cooling at ages older than 70 Myr. The magnitude, geographical distribution, onset time, and physical origin of the flattening are fundamental to our understanding of the evolution of oceanic lithosphere, and give important constraints on the Earth's heat budget and ocean volume throughout its history. However, none of these quantities is well established even after a long history of debates. Here, we present evidence from bathymetry and seismic tomography for the wide-scale operation of small-scale convection in the Pacific and Atlantic upper mantle. We track the temporal evolution of surface wave phase velocity and seafloor topography along age trajectories, which connect each piece of seafloor with the ridge segment that created it. The half-space cooling model (HSCM) and plate cooling model are used to predict the age dependence of phase velocity and bathymetry and to identify, for each age trajectory, the age at which the HSCM fails to explain the observations. The phase velocity and bathymetry are analyzed independently and yet yield identical results for more than 80% of points. We observe a wide range of ages at which the HSCM fails in the Atlantic and a much narrower range in the Pacific. We find that the age at which the HSCM fails is anti-correlated with the present-day depth of the ridge axis, with younger failure ages corresponding to deeper ridge axes and therefore colder mantle beneath the ridge.Such dependence is best explained by the small-scale convection model in which the effective viscosity of the lithosphere is regulated by the dehydration process that happens at the mid-ocean ridges. Decompression melting at a ridge removes water from the mantle and generates a depleted, dehydrated, and viscous layer. Since high mantle potential temperatures cause decompression melting to begin at greater depths, the thickness of the

  9. SPECIFIC VELOCITY STRUCTURE OF THE UPPER MANTLE IN THE TRANSBAIKALIA SEGMENT OF THE MONGOLIA-OKHOTSK OROGENIC BELT

    Directory of Open Access Journals (Sweden)

    V. M. Soloviev

    2017-01-01

    Full Text Available The paper presents the results of deep seismic studies on Geophysical Reference Profile 1-SB (Sredneargunsk – Ust-Karenga – Taksimo – Vitim in East Transbaikalia,Russia. The1200 kmlong profile crosses the major tectonic structures of the Central Asian fold belt: the Argun median massif, the Selenga-Stanovoy and Transbaikalia folded regions, and the Baikal rift zone. Its northwestern fragment extends into the Angara-Lena monocline of the Siberian platform. The southeastern (Transbaikalia and northwestern (Baikal-Patom fragments of the profile are based on the spot (differential seismic sounding technique using explosions and 40-tonne vibrators. The south­eastern (Transbaikalia fragment shows small crustal thickness values (~40 km, an almost horizontal position of the Moho, and high velocities of longitudinal waves (~8.4 km/sec beneath the Moho. The analysis of parallelism graphs and the dynamic expression of the wave refracted from the Moho suggests a less than 5–10 km thick layer of high velocities and low gradients below Moho. The database on theterritoryofTransbaikaliaincludes ~200 wave arrival times from large earthquakes, which were refracted at the Moho at distances of ~200–1400 km. As part of the tomographic interpretation, using additional DSS data on the Moho, theterritoryofTransbaikaliahas been mapped to show the patterns of the threshold velocity values at the Moho. The seismic data was used to contour an area with high velocity values in the mantle in the central part of the Mongolia-Okhotsk orogenic belt and the neighboring fold structures of Transbaikalia. According to the analysis of the seismic and geologic data on the study area, the mantle layer with high velocity values in the Mongolian-Okhotsk orogenic belt may be represented by the eclogitic rock plates.

  10. 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.

  11. Upper mantle structure of shear-waves velocities and stratification of anisotropy in the Afar Hotspot region

    Science.gov (United States)

    Sicilia, D.; Montagner, J.-P.; Cara, M.; Stutzmann, E.; Debayle, E.; Lépine, J.-C.; Lévêque, J.-J.; Beucler, E.; Sebai, A.; Roult, G.; Ayele, A.; Sholan, J. M.

    2008-12-01

    The Afar area is one of the biggest continental hotspots active since about 30 Ma. It may be the surface expression of a mantle "plume" related to the African Superswell. Central Africa is also characterized by extensive intraplate volcanism. Around the same time (30 Ma), volcanic activity re-started in several regions of the African plate and hotspots such as Darfur, Tibesti, Hoggar and Mount Cameroon, characterized by a significant though modest volcanic production. The interactions of mantle upwelling with asthenosphere, lithosphere and crust remain unclear and seismic anisotropy might help in investigating these complex interactions. We used data from the global seismological permanent FDSN networks (GEOSCOPE, IRIS, MedNet, GEO- FON, etc.), from the temporary PASSCAL experiments in Tanzania and Saudi Arabia and a French deployment of 5 portable broadband stations surrounding the Afar Hotspot. A classical two-step tomographic inversion from surface waves performed in the Horn of Africa with selected Rayleigh wave and Love wave seismograms leads to a 3D-model of both S V velocities and azimuthal anisotropy, as well as radial SH/ SV anisotropy, with a lateral resolution of 500 km. The region is characterized by low shear-wave velocities beneath the Afar Hotspot, the Red Sea, the Gulf of Aden and East of the Tanzania Craton to 400 km depth. High velocities are present in the Eastern Arabia and the Tanzania Craton. The results of this study enable us to rule out a possible feeding of the Central Africa hotspots from the "Afar plume" above 150-200 km. The azimuthal anisotropy displays a complex pattern near the Afar Hotspot. Radial anisotropy, although poorly resolved laterally, exhibits S H slower than S V waves down to about 150 km depth, and a reverse pattern below. Both azimuthal and radial anisotropies show a stratification of anisotropy at depth, corresponding to different physical processes. These results suggest that the Afar hotspot has a different and

  12. 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

  13. Lateral displacement of crustal units relative to underlying mantle lithosphere: Example from the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Babuška, Vladislav; Plomerová, Jaroslava

    2017-01-01

    Roč. 48, December (2017), s. 125-138 ISSN 1342-937X R&D Projects: GA ČR GAP210/12/2381; GA MŠk(CZ) LD15029; GA MŠk LM2010008; GA MŠk(CZ) LM2015079 Institutional support: RVO:67985530 Keywords : Bohemian Massif * Teplá-Barrandian mantle lithosphere * Zone Erbendorf-Vohenstrauss * Jáchymov Fault Zone Subject RIV: DC - Siesmology, Volcanology, Earth Structure OBOR OECD: Volcanology Impact factor: 6.959, year: 2016

  14. 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

  15. Mantle Evolution under the Bouvet Triple Junction (SMAR) from the aspect of Tectonic and Geochemistry

    Science.gov (United States)

    Migdisova, Natalia; Sobolev, Alexander; Sushchevskaya, Nadejda; Belyatsky, Boris; Kuzmin, Dmitrii

    2010-05-01

    Three main structures of the oceanic floor - Mid Atlantic Ridge (MAR), American Antarctic Ridge (AAR) and Southwest Indian Ridge (SWIR) - constitute the Bouvet Triple Junction (BTJ). These constituents have changed their position relatively each other a lot of times during the evolution (Ligi et al., 1999). The unstable character of their interaction was the main cause of the complicated structure of BTJ. The segment of BTJ is characterized by the tholeiitic type of magmatism. However those magmas have different conditions of generation and eruption. Nevertheless basaltic rocks of the studying segment of the rift valley SWIR are determined as moderately enriched tholeiites on the basis of trace and major element variations. Normalized patterns of incompatible elements of BTJ basalts are characterized by relative maxima of Nb, Ta, and La and minima of Pb and less pronounced minima of Th and U. There is a clear Sr minimum in the most fractionated basalts from the Spiess Ridge. Apparent "garnet signature" expressed in the elevated values of (Gd/Yb)N ratio (up to 2.5) present in some basalt compositions. This indicates the presence of garnet in the source of basaltic melts of the BTJ. Ni excess over Mg and Mn deficiency over Fe in olivine phenocrysts suggest the presence of olivine-free pyroxenite lithologies in the sources of primary melts (Sobolev et al., 2007). The lowest amounts of pyroxenite component (X PX Mn/Fe = 0-10%) were recorded for the samples from the station S18-63, located in the MAR valley. The greatest range (X PX Mn/Fe = 0-90% in the single rock) was observed in samples from the station G96-10 situated on the western slope of the Spiess Ridge. Obtained results suggest the participation of recycled crustal component in the generation of primary melts. That component was involved in the rising mantle in the form of silica oversaturated eclogite as previously subducted oceanic crust or as fragments of ancient continental lithosphere. Melts generated

  16. Upper mantle seismic anisotropy beneath the Northern Transantarctic Mountains, Antarctica from PKS, SKS, and SKKS splitting analysis

    Science.gov (United States)

    Graw, Jordan H.; Hansen, Samantha E.

    2017-02-01

    Using data from the new Transantarctic Mountains Northern Network, this study aims to constrain azimuthal anisotropy beneath a previously unexplored portion of the Transantarctic Mountains (TAMs) to assess both past and present deformational processes occurring in this region. Shear-wave splitting parameters have been measured for PKS, SKS, and SKKS phases using the eigenvalue method within the SplitLab software package. Results show two distinct geographic regions of anisotropy within our study area: one behind the TAMs front, with an average fast axis direction of 42 ± 3° and an average delay time of 0.9 ± 0.04 s, and the other within the TAMs near the Ross Sea coastline, with an average fast axis oriented at 51 ± 5° and an average delay time of 1.5 ± 0.08 s. Behind the TAMs front, our results are best explained by a single anisotropic layer that is estimated to be 81-135 km thick, thereby constraining the anisotropic signature within the East Antarctic lithosphere. We interpret the anisotropy behind the TAMs front as relict fabric associated with tectonic episodes occurring early in Antarctica's geologic history. For the coastal stations, our results are best explained by a single anisotropic layer estimated to be 135-225 km thick. This places the anisotropic source within the viscous asthenosphere, which correlates with low seismic velocities along the edge of the West Antarctic Rift System. We interpret the coastal anisotropic signature as resulting from active mantle flow associated with rift-related decompression melting and Cenozoic extension.

  17. Upper tropospheric humidity changes under constant relative humidity

    OpenAIRE

    K. Gierens; K. Eleftheratos

    2016-01-01

    Theoretical derivations are given on the change of upper tropospheric humidity (UTH) in a warming climate. The considered view is that the atmosphere, which is getting moister with increasing temperatures, will retain a constant relative humidity. In the present study, we show that the upper tropospheric humidity, a weighted mean over a relative humidity profile, will change in spite of constant relative humidity. The simple reason for this is that the weighting function ...

  18. Teleseismic P and S wave attenuation constraints on temperature and melt of the upper mantle in the Alaska Subduction Zone.

    Science.gov (United States)

    Soto Castaneda, R. A.; Abers, G. A.; Eilon, Z.; Christensen, D. H.

    2017-12-01

    Recent broadband deployments in Alaska provide an excellent opportunity to advance our understanding of the Alaska-Aleutians subduction system, with implications for subduction processes worldwide. Seismic attenuation, measured from teleseismic body waves, provides a strong constraint on thermal structure as well as an indirect indication of ground shaking expected from large intermediate-depth earthquakes. We measure P and S wave attenuation from pairwise amplitude and phase spectral ratios for teleseisms recorded at 204 Transportable Array, Alaska Regional, and Alaska Volcano Observatory, SALMON (Southern Alaska Lithosphere & Mantle Observation Network) and WVLF (Wrangell Volcanics & subducting Lithosphere Fate) stations in central Alaska. The spectral ratios are inverted in a least squares sense for differential t* (path-averaged attenuation operator) and travel time anomalies at every station. Our preliminary results indicate a zone of low attenuation across the forearc and strong attenuation beneath arc and backarc in the Cook Inlet-Kenai region where the Aleutian-Yakutat slab subducts, similar to other subduction zones. This attenuation differential is observed in both the volcanic Cook Inlet segment and amagmatic Denali segments of the Aleutian subduction zone. By comparison, preliminary results for the Wrangell-St. Elias region past the eastern edge of the Aleutian slab show strong attenuation beneath the Wrangell Volcanic Field, as well as much further south than in the Cook Inlet-Kenai region. This pattern of attenuation seems to indicate a short slab fragment in the east of the subduction zone, though the picture is complex. Results also suggest the slab may focus or transmit energy with minimal attenuation, adding to the complexity. To image the critical transition between the Alaska-Aleutian slab and the region to its east, we plan to incorporate new broadband data from the WVLF array, an ongoing deployment of 37 PASSCAL instruments installed in 2016

  19. Mesozoic high-Mg andesites from the Daohugou area, Inner Mongolia: Upper-crustal fractional crystallization of parental melt derived from metasomatized lithospheric mantle wedge

    Science.gov (United States)

    Meng, Fanxue; Gao, Shan; Song, Zhaojun; Niu, Yaoling; Li, Xuping

    2018-03-01

    Mineral chemistry, major- and trace-element data, zircon U-Pb ages, and Sr-Nd isotopic data are presented for a suite of volcanic rocks from the Daohugou area, Ningcheng City, Inner Mongolia, on the northern margin of the North China Craton. Samples from the suite are of basaltic andesite to rhyolite in composition, with the rocks containing low εNd (t) values, moderate (87Sr/86Sr) i ratios, enrichment in LREEs relative to LILEs, and depletion in HFSEs (e.g., Nb, Ta, Ti), indicating formation through protracted fractional crystallization of a common parental magma. The unusually low CaO contents and CaO/FeO ratios of olivine phenocrysts in the HMAs suggest that the parental melt was subduction-related. The results of Rhyolite-MELTS modelling indicates that HMAs may form through upper-crustal fractional crystallization from arc basalts. Therefore, the Daohugou HMAs were most likely formed through fractional crystallization of a parental melt derived from metasomatized lithospheric mantle at crustal depths. The addition of "water" to the cratonic keel may have played a key role in the destruction of the North China Craton.

  20. Seismic velocity model of the crust and upper mantle along profile PANCAKE across the Carpathians between the Pannonian Basin and the East European Craton

    DEFF Research Database (Denmark)

    Starostenko, V.; Janik, T.; Kolomiyets, K.

    2013-01-01

    Results are presented of a seismic wide-angle reflection/refraction survey along a profile between the Pannonian Basin (PB) and the East European Craton (EEC) called PANCAKE. The P- and S-wave velocity model derived can be divided into three sectors: the PB; the Carpathians, including the Transca......Results are presented of a seismic wide-angle reflection/refraction survey along a profile between the Pannonian Basin (PB) and the East European Craton (EEC) called PANCAKE. The P- and S-wave velocity model derived can be divided into three sectors: the PB; the Carpathians, including...... the Transcarpathian Depression and the Carpathian Foredeep; and the south-western part of the EEC, including the Trans European Suture Zone (TESZ). Seismic data support a robust model of the Vp velocity structure of the crust. In the PB, the 22-23km thick crust consists of a 2-5km thick sedimentary layer (Vp=2...... of the lower crust towards the Ukrainian Shield, where a high velocity lower crust (Vp>7.2km/s) is observed. Two low-velocity lenses in the upper crust of the EEC are interpreted beneath major sedimentary troughs (Lviv and Volyn-Podolsk). Mantle reflectors are observed at depths of ~45km and ~75km below the PB...

  1. Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

    Science.gov (United States)

    Syracuse, E. M.; Zhang, H.; Maceira, M.

    2017-10-01

    We present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body wave first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region. Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. Without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.

  2. Major element composition of the lithospheric mantle under the North Atlantic craton

    DEFF Research Database (Denmark)

    Bizzarro, Martin; Stevenson, R.K.

    2003-01-01

    is compositionally layered as follows: (1) an internally stratified upper layer (70 to 180 km) consisting of coarse, un-deformed, refractory garnet-bearing and garnet-free peridotites and, (2) a lower layer (180 to 225 km) characterized by fertile, CPX-bearing, porphyroclastic garnet lherzolites. The stratification...

  3. Imaging the lithosphere and underlying mantle of the South Atlantic, South America and Africa using waveform tomography with massive datasets

    Science.gov (United States)

    Celli, N. L.; Lebedev, S.; Schaeffer, A. J.; Ravenna, M.; Gaina, C.

    2017-12-01

    Recent growth in global seismic station coverage has created dense data sampling of the previously poorly constrained lithosphere and underlying mantle beneath the South Atlantic, South America and Africa. The new data enable us to image the vast region at a new level of detail and address important open questions regarding its lithospheric architecture and mantle dynamics. In order to fully exploit the data sampling, we use an efficient, multimode waveform tomography scheme that enables the extraction of structural information from millions of seismograms and use the inherent data redundancy to minimize effects of errors in the data. Our tomographic model is constrained by waveform fits of over 1.2 million vertical-component seismograms, computed using the Automated Multimode Inversion of surface, S- and multiple S-waves. Each successful seismogram fit provides a set of linear equations describing 1D average velocity perturbations within approximate sensitivity volumes, with respect to a 3D reference model. We then combine all equations into a large linear system and invert jointly for a model of S- and P-wave speeds and azimuthal anisotropy within the lithosphere and underlying mantle. We are now able to image the detailed structure of various African shields. For example, in West Africa, two clearly separate high-velocity units underlay the Reguibat and Man-Léo Shields; in the Congo area, a single high-velocity body, formed by three main units correspond to the Gabon-Cameroon, Bomu-Kibali and Kasai Shields. Strong low-velocity anomalies underlay the Afar Hotspot and the East African Rift; pronounced low velocities are also seen beneath parts of the Sahara Desert. We discuss the shape of the deep Afar anomaly and its possible relationships with the Saharan volcanism and the neighboring Tanzania Craton. In the South Atlantic, we retrieve fine-scale velocity structure along the Mid-Atlantic Ridge (MAR), indicative of hotspot-ridge interactions. Major hotspots show

  4. Natural impacts on the Moon and Mars: seismic constrains on the impact shock wave and perspectives in term of crustal and upper mantle imaging.

    Science.gov (United States)

    Lognonne, P.; Gudkova, T.; Le Feuvre, M.; Garcia, R. F.; Kawamura, T.; Banerdt, B.; Kobayashi, N.

    2011-12-01

    Natural Impacts occurring on the surface of telluric planets are important seismic sources for constraining the crustal and upper mantle structure, especially when their impact location and impacting time can be determined by other complementing experiments, such as Earth based flash detection for the Moon or differential orbital imaging of the surface for Mars. When these complementary data are not available, which was the case of Apollo with the exception of artificial impacts, the location of impact as compared to quake is easier, as only their geographical location must be determined from seismic data. We present recent results of the analysis of impact related seismic data gathered by the Apollo Lunar seismic network during the 70th. By using the artificial impact, we first develop a calibrated analysis for extracting the impulse (i.e. mass time impact velocity) from the amplitude of seismic waves, and point out the effect of the generation of ejecta in the seismic impulse. This approach not only allows to constrain the mass of the impacts, but also to constrain the impact frequency-impactor mass relation. By combining both the Apollo long period and short period data, further analysis can be made on the dynamic of the seismic source. The combination of these date provides indeed broadband seismic analysis have been made allowing to constraint the seismic cut-off frequency and source spectrum associated with both natural and artificial impacts. We show that the source cut-off is, as compared to moonquakes, relatively low and around a few Hz for remotely detected impacts. It is also depending not only on the impact size, but also on the impact location, as the seismic radiation of the shock wave depends on the most-upper regolith layers. We finally use our results and forward modeling to prepare the GEMS seismic mission to Mars, considered by NASA for a launch in 2016. In order to have a robust estimation of the rates of seismic detection of impacts, we analyze

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

    Science.gov (United States)

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

    2017-11-01

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

  6. Crust and Mantle Deformation Revealed from High-Resolution Radially Anisotropic Velocity Models

    Science.gov (United States)

    Li, A.; Dave, R.; Yao, Y.

    2017-12-01

    Love wave tomography, which can achieve a similar model resolution as Rayleigh wave, so far has limited applications to the USArray data. Recently, we have developed high-resolution Love wave phase velocity maps in the Wyoming craton and Texas using data at the Transportable Array stations. 3-D, radially anisotropic velocity models are obtained by jointly inverting Love and Rayleigh wave phase velocities. A high-velocity anomaly extending to about 200 km depth beneath central Wyoming correlates with negative radial anisotropy (Vsv>Vsh), suggesting that mantle downwelling develops under the cratonic lithosphere. Surprisingly, the significantly low velocity beneath the Yellowstone hotspot, which has been interpreted as partial melting and asthenospheric upwelling, is associated with the largest radial anisotropy (Vsh>Vsv) in the area. This observation does not support mantle upwelling. Instead, it indicates that the upper mantle beneath the hotspot has experienced strong shear deformation probably by the plate motion and large-scale mantle flow. In Texas, positive radial anisotropy in the lower crust extends from the coast to the Ouachita belt, which is characterized by high velocity and negative radial anisotropy. In the upper mantle, large variations of velocity and anisotropy exit under the coastal plain. A common feature in these anisotropic models is that high-velocity anomalies in the upper mantle often correlate with negative anisotropy (Vsv>Vsh) while low-velocity anomalies are associated with positive anisotropy (Vsh>Vsv). The manifestation of mantle downweling as negative radial anisotropy is largely due to the relatively high viscosity of the high-velocity mantle block, which is less affected by the surrounding large-scale horizontal flow. However, mantle upwelling, which is often associated with low-velocity anomalies, presumably low-viscosity mantle blocks, is invisible in radial anisotropy models. Such upwelling may happen too quickly to make last

  7. 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

  8. Combined Determination of Elastic Properties and Structure of Coesite under Simulated Mantle Conditions

    Science.gov (United States)

    Mueller, H. J.; Schilling, F. R.; Lauterjung, J.; Lathe, C.

    2001-12-01

    The high pressure SiO2-polymorph coesite seems to be an important mineral in the subduction process including crustal material (Chopin, 1984; Schreyer, 1995). The quartz to coesite transition is thus of fundamental importance to understand the processes within a subducting crust. Furthermore, the nature of the quartz to coesite transition is discussed controversially, because high pressure XRD-studies suggest an intermediate phase during the transformation process (Zinn et al., 1997). For the combined determination of elastic properties and structure a cubic multi-anvil high pressure apparatus (MAX80) was used. For the maximum sample volume of 20 mm3 the pressure limit is about 7GPa. The pressure is measured by use of NaCl as an internal pressure marker with calibrated PVT-data. The maximum temperature of about 2,000K is generated by an internal graphite heater and controlled by a thermocouple. The synchrotron beam (100x100 microns) is guided by a collimator through the sample between the anvils. For energy-dispersive X-ray diffraction, a Ge-solid state detector analyses the diffracted white beam at a fixed angle. The compressional and shear wave velocities were determined simultaneously by ultrasonic interferometry inside MAX80. Two of the six anvils are equipped with overtone polished lithium niobate transducers at their rear side, outside the volume under pressure, for generation and detection of ultrasonic waves between 10 and 60 MHz. Different buffer - reflector combinations and transducer arrangements were used to optimize the critical interference between both sample echoes. Therefore MAX80 is equipped for asymmetrical and symmetrical interferometric set-ups, i.e. compressional and shear waves are generated from the same or from two anvils, opposite to each other. We used for our transient measurements 3 natural fine-grained quartzites from Turkey and Germany. As a first step the pressure was increased gradually up to 4GPa at ambient temperature. At each

  9. 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

  10. Key role of Upper Mantle rocks in Alpine type orogens: some speculations derived from extensional settings for subduction zone processes and mountain roots

    Science.gov (United States)

    Müntener, Othmar

    2016-04-01

    Orogenic architecture and mountain roots are intrinsically related. Understanding mountain roots largely depends on geophysical methods and exhumed high pressure and high temperature rocks that might record snapshots of the temporal evolution at elevated pressure, temperatures and/or fluid pulses. If such high pressure rocks represent ophiolitic material they are commonly interpreted as exhumed remnants of some sort of 'mid-ocean ridge' processes. Mantle peridotites and their serpentinized counterparts thus play a key role in understanding orogenic architecture as they are often considered to track suture zones or ancient plate boundaries. The recognition that some mantle peridotites and their serpentinized counterparts are derived from ocean-continent transition zones (OCT's) or non-steady state (ultra-)slow plate separation systems question a series of 'common beliefs' that have been applied to understand Alpine-type collisional orogens in the framework of the ophiolite concept. Among these are: (i) the commonly held assumption of a simple genetic link between mantle melting and mafic (MORB-type) magmatism, (ii) the commonly held assumption that mélange zones represent deep subduction zone processes at the plate interface, (iii) that pre-collisional continental crust and oceanic crust can easily be reconstructed to their original thickness and used for reconstructions of the size of small subducted oceanic basins as geophysical data from rifted margins increasingly indicate that continental crust is thinned to much less than the average 30-35 kilometers over a large area that might be called the 'zone of hyperextension', and (iv) the lack of a continuous sheet of mafic oceanic crust and the extremely short time interval of formation results in a lack of 'eclogitization potential' during convergence and hence a lack of potential for subsequent slab pull and, perhaps, a lack of potential for 'slab-breakoff'. Here we provide a synopsis of mantle rocks from the

  11. From the Bay of Biscay to the High Atlas: Completing the anisotropic characterization of the upper mantle beneath the westernmost Mediterranean region

    Science.gov (United States)

    Díaz, J.; Gallart, J.; Morais, I.; Silveira, G.; Pedreira, D.; Pulgar, J. A.; Dias, N. A.; Ruiz, M.; González-Cortina, J. M.

    2015-11-01

    The knowledge of the anisotropic properties beneath the Iberian Peninsula and Northern Morocco has been dramatically improved since late 2007 with the analysis of the data provided by the dense TopoIberia broad-band seismic network, the increasing number of permanent stations operating in Morocco, Portugal and Spain, and the contribution of smaller scale/higher resolution experiments. Results from the two first TopoIberia deployments have evidenced a spectacular rotation of the fast polarization direction (FPD) along the Gibraltar Arc, interpreted as an evidence of mantle flow deflected around the high velocity slab beneath the Alboran Sea, and a rather uniform N100°E FPD beneath the central Iberian Variscan Massif, consistent with global mantle flow models taking into account contributions of surface plate motion, density variations and net lithosphere rotation. The results from the last Iberarray deployment presented here, covering the northern part of the Iberian Peninsula, also show a rather uniform FPD orientation close to N100°E, thus confirming the previous interpretation globally relating the anisotropic parameters to the LPO of mantle minerals generated by mantle flow at asthenospheric depths. However, the degree of anisotropy varies significantly, from delay time values of around 0.5 s beneath NW Iberia to values reaching 2.0 s in its NE corner. The anisotropic parameters retrieved from single events providing high quality data also show significant differences for stations located in the Variscan units of NW Iberia, suggesting that the region includes multiple anisotropic layers or complex anisotropy systems. These results allow to complete the map of the anisotropic properties of the westernmost Mediterranean region, which can now be considered as one of best constrained regions worldwide, with more than 300 sites investigated over an area extending from the Bay of Biscay to the Sahara platform.

  12. Where is mantle's carbon?

    Science.gov (United States)

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

    2008-12-01

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

  13. 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

  14. Heterogeneously hydrated mantle beneath the late Archean Yilgarn Craton

    Science.gov (United States)

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

    2015-12-01

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

  15. Determining Crust and Upper Mantle Structure by Bayesian Joint Inversion of Receiver Functions and Surface Wave Dispersion at a Single Station: Preparation for Data from the InSight Mission

    Science.gov (United States)

    Jia, M.; Panning, M. P.; Lekic, V.; Gao, C.

    2017-12-01

    The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission will deploy a geophysical station on Mars in 2018. Using seismology to explore the interior structure of the Mars is one of the main targets, and as part of the mission, we will use 3-component seismic data to constrain the crust and upper mantle structure including P and S wave velocities and densities underneath the station. We will apply a reversible jump Markov chain Monte Carlo algorithm in the transdimensional hierarchical Bayesian inversion framework, in which the number of parameters in the model space and the noise level of the observed data are also treated as unknowns in the inversion process. Bayesian based methods produce an ensemble of models which can be analyzed to quantify uncertainties and trade-offs of the model parameters. In order to get better resolution, we will simultaneously invert three different types of seismic data: receiver functions, surface wave dispersion (SWD), and ZH ratios. Because the InSight mission will only deliver a single seismic station to Mars, and both the source location and the interior structure will be unknown, we will jointly invert the ray parameter in our approach. In preparation for this work, we first verify our approach by using a set of synthetic data. We find that SWD can constrain the absolute value of velocities while receiver functions constrain the discontinuities. By joint inversion, the velocity structure in the crust and upper mantle is well recovered. Then, we apply our approach to real data from an earth-based seismic station BFO located in Black Forest Observatory in Germany, as already used in a demonstration study for single station location methods. From the comparison of the results, our hierarchical treatment shows its advantage over the conventional method in which the noise level of observed data is fixed as a prior.

  16. Trace-element perovskite-melt partitioning at the top of the upper mantle or the bottom of the magma ocean

    Science.gov (United States)

    Minarik, W. G.

    2002-05-01

    The 25 years since the Sedona conference have brought considerable advancement in our knowledge of melt-mineral partition coefficients. High-pressure, high temperature experimental environments are better characterized, with lower thermal gradients and longer run times. Microbeam analytical techniques allow concentrations to be determined in situ on the several micron scale at near natural abundance levels. Crystal chemical modeling and atomistic simulations allow results to be generalized to other compositions and more extreme conditions. Mineral-melt partitioning data have been determined for a suite of major and trace elements using peridotite and basalt starting materials. Temperature gradients within the experiment were reduced by using diamond capsules. The capsules were placed in an 8/3mm TEL multianvil assembly at 24-27 GPa, 2200-2600° C for 8 to 45 minutes. Pressures were referenced to the Al solubility in MgSiO3 Pv pressure scale, tied to the EOS of Au. SIMS was used to determine the partitioning between 15-25 micron diameter crystals of silicate perovskite (Pv), magnesiow\\x81stite (Mw) and melt for REE, LIL and HFSE doped to 10-100 ppm concentrations. Compositional reversals were used to evaluate the approach to equilibrium and for tests of Henry's law. LREE are incompatible, HREE less so, and Yb and Lu are compatible in Pv. The HFSE are compatible in Pv, with Hf slightly more compatible than Lu. U, Th, Pb are all incompatible, but the Kd for U/Th equals 2. These elements are excluded from Mw. The partitioning data on parent/daughter ratios of the radiogenic isotope systems (Sm/Nd, Lu/Hf, U+Th/Pb, and Hf/W) are particularly useful, as isotope systems, through the action of time, magnify small variations in these trace element ratios. The mild compatibility of Hf in Pv relaxes the constraints imposed by the Lu-Hf system on the extent of a preserved lower mantle magma ocean cumulate. Even so, at most several percent perovskite crystallized from a magma

  17. Interaction of peridotite with Ca-rich carbonatite melt at 3.1 and 6.5 GPa: Implication for merwinite formation in upper mantle, and for the metasomatic origin of sublithospheric diamonds with Ca-rich suite of inclusions

    Science.gov (United States)

    Sharygin, Igor S.; Shatskiy, Anton; Litasov, Konstantin D.; Golovin, Alexander V.; Ohtani, Eiji; Pokhilenko, Nikolay P.

    2018-03-01

    We performed an experimental study, designed to reproduce the formation of an unusual merwinite + olivine-bearing mantle assemblage recently described as a part of a Ca-rich suite of inclusions in sublithospheric diamonds, through the interaction of peridotite with an alkali-rich Ca-carbonatite melt, derived from deeply subducted oceanic crust. In the first set of experiments, we studied the reaction between powdered Mg-silicates, olivine and orthopyroxene, and a model Ca-carbonate melt (molar Na:K:Ca = 1:1:2), in a homogeneous mixture, at 3.1 and 6.5 GPa. In these equilibration experiments, we observed the formation of a merwinite + olivine-bearing assemblage at 3.1 GPa and 1200 °C and at 6.5 GPa and 1300-1400 °C. The melts coexisting with this assemblage have a low Si and high Ca content (Ca# = molar 100 × Ca/(Ca + Mg) > 0.57). In the second set of experiments, we investigated reaction rims produced by interaction of the same Ca-carbonate melt (molar Na:K:Ca = 1:1:2) with Mg-silicate, olivine and orthopyroxene, single crystals at 3.1 GPa and 1300 °C and at 6.5 GPa and 1400 °C. The interaction of the Ca-carbonate melt with olivine leads to merwinite formation through the expected reaction: 2Mg2SiO4 (olivine) + 6CaCO3 (liquid) = Ca3MgSi2O8 (merwinite) + 3CaMg(CO3)2 (liquid). Thus, our experiments confirm the idea that merwinite in the upper mantle may originate via interaction of peridotite with Ca-rich carbonatite melt, and that diamonds hosting merwinite may have a metasomatic origin. It is remarkable that the interaction of the Ca-carbonate melt with orthopyroxene crystals does not produce merwinite both at 3.1 and 6.5 GPa. This indicates that olivine grain boundaries are preferable for merwinite formation in the upper mantle.

  18. Melting phase relations in the systems Mg2SiO4-H2O and MgSiO3-H2O and the formation of hydrous melts in the upper mantle

    Science.gov (United States)

    Novella, Davide; Dolejš, David; Myhill, Robert; Pamato, Martha G.; Manthilake, Geeth; Frost, Daniel J.

    2017-05-01

    High-pressure and high-temperature melting experiments were conducted in the systems Mg2SiO4-H2O and MgSiO3-H2O at 6 and 13 GPa and between 1150 and 1900 °C in order to investigate the effect of H2O on melting relations of forsterite and enstatite. The liquidus curves in both binary systems were constrained and the experimental results were interpreted using a thermodynamic model based on the homogeneous melt speciation equilibrium, H2O + O2- = 2OH-, where water in the melt is present as both molecular H2O and OH- groups bonded to silicate polyhedra. The liquidus depression as a function of melt H2O concentration is predicted using a cryoscopic equation with the experimental data being reproduced by adjusting the water speciation equilibrium constant. Application of this model reveals that in hydrous MgSiO3 melts at 6 and 13 GPa and in hydrous Mg2SiO4 melts at 6 GPa, water mainly dissociates into OH- groups in the melt structure. A temperature dependent equilibrium constant is necessary to reproduce the data, however, implying that molecular H2O becomes more important in the melt with decreasing temperature. The data for hydrous forsterite melting at 13 GPa are inconclusive due to uncertainties in the anhydrous melting temperature at these conditions. When applied to results on natural peridotite melt systems at similar conditions, the same model infers the presence mainly of molecular H2O, implying a significant difference in physicochemical behaviour between simple and complex hydrous melt systems. As pressures increase along a typical adiabat towards the base of the upper mantle, both simple and complex melting results imply that a hydrous melt fraction would decrease, given a fixed mantle H2O content. Consequently, the effect of pressure on the depression of melting due to H2O could not cause an increase in the proportion, and hence seismic visibility, of melts towards the base of the upper mantle.

  19. 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.

  20. 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.

  1. Electric resistivity distribution in the Earth's crust and upper mantle for the southern East European Platform and Crimea from area-wide 2D models

    Science.gov (United States)

    Logvinov, Igor M.; Tarasov, Viktor N.

    2018-03-01

    Previously obtained magnetotelluric 2D models for 30 profiles made it possible to create an overview model of electric resistivity for the territory between 28°E and 36°E and between 44.5°N and 52.5°N. It allows us to distinguish a number of low resistivity objects (LRO) with resistivities lower than 100 Ω m the Earth's crust and mantle. Two regional conductivity anomalies are traced. The Kirovograd conductivity anomaly extends south to the Crimea mountains. A new regional conductivity anomaly (Konkskaya) can be distinguished along the southern slope of the Ukrainian Shield from 29° to 34°E. In addition, many local LROs have been identified. According to the modeling results, the local low resistivity objects on the East European Platform appear along fault zones activated during last 5-7 M years and the model suggests their relation to known zones of graphitization and polymetallic ore deposits. Local LROs in the Dnieper-Donets Basin correlate with the main oil and natural gas fields in this area. The depth of the anomalous objects amounts to 5-22 km. This is consistent with the hypotheses that hydrocarbon deposits are related to generation and transport zones of carbon-bearing fluids.

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

    Science.gov (United States)

    Zhao, Dapeng; Liu, Xin; Hua, Yuanyuan

    2018-03-01

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

  3. Self-Organized Mantle Layering After the Magma-Ocean Period

    Science.gov (United States)

    Hansen, U.; Dude, S.

    2017-12-01

    The thermal history of the Earth, it's chemical differentiation and also the reaction of the interior with the atmosphere is largely determined by convective processes within the Earth's mantle. A simple physical model, resembling the situation, shortly after core formation, consists of a compositionally stable stratified mantle, as resulting from fractional crystallization of the magma ocean. The early mantle is subject to heating from below by the Earth's core and cooling from the top through the atmosphere. Additionally internal heat sources will serve to power the mantle dynamics. Under such circumstances double diffusive convection will eventually lead to self -organized layer formation, even without the preexisting jumps is material properties. We have conducted 2D and 3D numerical experiments in Cartesian and spherical geometry, taking into account mantle realistic values, especially a strong temperature dependent viscosity and a pressure dependent thermal expansivity . The experiments show that in a wide parameter range. distinct convective layers evolve in this scenario. The layering strongly controls the heat loss from the core and decouples the dynamics in the lower mantle from the upper part. With time, individual layers grow on the expense of others and merging of layers does occur. We observe several events of intermittent breakdown of individual layers. Altogether an evolution emerges, characterized by continuous but also spontaneous changes in the mantle structure, ranging from multiple to single layer flow. Such an evolutionary path of mantle convection allows to interpret phenomena ranging from stagnation of slabs at various depth to variations in the chemical signature of mantle upwellings in a new framework.

  4. 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 ...

  5. Crustal and upper mantle structure of the Anatolian plate: Imaging the effects of subduction termination and continental collision with seismic techniques

    Science.gov (United States)

    Delph, Jonathan R.

    The neotectonic evolution of the eastern Mediterranean is intimately tied to interactions between the underthrusting/subducting slab along the southern margin of Anatolia and the overriding plate. The lateral variations in the subduction zone can be viewed as a temporal analogue of the transition between continuous subduction and subduction termination by continent-continent collision. By investigating the lateral variations along this subduction zone in the overriding plate, we can gain insight into the processes that precede continent collision. This dissertation summarizes the results of three studies that focus on different parts of the subduction margin: 1) In the west, where the development of a slab tear represents the transition between continuous and enigmatic subduction, 2) In the east, where continent-continent collision between the Arabian and Eurasian Plate is leading to the development of the third largest orogenic plateau on earth after complete slab detachment, and 3) In central Anatolia, where the subducting slab is thought to be in the processes of breaking up, which is affecting the flow of mantle material leading to volcanism and uplift along the margin. In the first study, we interpret that variations in the composition of material in the downgoing plate (i.e. a change from the subduction of oceanic material to continental material) may have led to the development of a slab tear in the eastern Aegean. This underthrusting, buoyant continental fragment is controlling overriding plate deformation, separating the highly extensional strains of western Anatolia from the much lower extensional strains of central Anatolia. Based on intermediate depth seismicity, it appears that the oceanic portion of the slab is still attached to this underthrusting continental fragment. In the second study, we interpret that the introduction of continental lithosphere into the north-dipping subduction zone at the Arabian-Eurasian margin led to the rollback and

  6. Surface-wave amplitude analysis for array data with non-linear waveform fitting: Toward high-resolution attenuation models of the upper mantle

    Science.gov (United States)

    Hamada, K.; Yoshizawa, K.

    2013-12-01

    Anelastic attenuation of seismic waves provides us with valuable information on temperature and water content in the Earth's mantle. While seismic velocity models have been investigated by many researchers, anelastic attenuation (or Q) models have yet to be investigated in detail mainly due to the intrinsic difficulties and uncertainties in the amplitude analysis of observed seismic waveforms. To increase the horizontal resolution of surface wave attenuation models on a regional scale, we have developed a new method of fully non-linear waveform fitting to measure inter-station phase velocities and amplitude ratios simultaneously, using the Neighborhood Algorithm (NA) as a global optimizer. Model parameter space (perturbations of phase speed and amplitude ratio) is explored to fit two observed waveforms on a common great-circle path by perturbing both phase and amplitude of the fundamental-mode surface waves. This method has been applied to observed waveform data of the USArray from 2007 to 2008, and a large-number of inter-station amplitude and phase speed data are corrected in a period range from 20 to 200 seconds. We have constructed preliminary phase speed and attenuation models using the observed phase and amplitude data, with careful considerations of the effects of elastic focusing and station correction factors for amplitude data. The phase velocity models indicate good correlation with the conventional tomographic results in North America on a large-scale; e.g., significant slow velocity anomaly in volcanic regions in the western United States. The preliminary results of surface-wave attenuation achieved a better variance reduction when the amplitude data are inverted for attenuation models in conjunction with corrections for receiver factors. We have also taken into account the amplitude correction for elastic focusing based on a geometrical ray theory, but its effects on the final model is somewhat limited and our attenuation model show anti

  7. Behavioral Effects of Upper Respiratory Tract Illnesses: A Consideration of Possible Underlying Cognitive Mechanisms

    Directory of Open Access Journals (Sweden)

    Andrew P. Smith

    2012-03-01

    Full Text Available Previous research has shown that both experimentally induced upper respiratory tract illnesses (URTIs and naturally occurring URTIs influence mood and performance. The present study investigated possible cognitive mechanisms underlying the URTI-performance changes. Those who developed a cold (N = 47 had significantly faster, but less accurate, performance than those who remained healthy (N = 54. Illness had no effect on manipulations designed to influence encoding, response organisation (stimulus-response compatilibility or response preparation. Similarly, there was no evidence that different components of working memory were impaired. Overall, the present research confirms that URTIs can have an effect on performance efficiency. Further research is required to identify the physiological and behavioral mechanisms underlying these effects.

  8. Bases of the Mantle-Carbonatite Conception of Diamond Genesis

    Science.gov (United States)

    Litvin, Yuriy; Spivak, Anna; Kuzyura, Anastasia

    2016-04-01

    In the mantle-carbonatite conception of diamond genesis, the results of physic-chemical experiments are coordinated with the data of analytic mineralogy of primary inclusions in natural diamonds. Generalization of the solutions of principal genetic problems constitutes the bases of the conception. The solutions are following: (1) it is grounded that diamond-parental melts of the upper mantle have peridotite/eclogite - carbonatite - carbon compositions, of the transition zone - (wadsleite↔ringwoodite) - majorite - stishovite - carbonatite - carbon compositions, and of the lower mantle - periclase/wustite - bridgmanite - Ca-perovskite -stishovite - carbonatite - carbon compositions; (2) a construction of generalized diagrams for the diamond-parental media, which reveal changeable compositions of the growth melts of diamonds and associated phases, their genetic relations to the mantle substance, and classification connections of the primary inclusions in natural diamonds; (3) experimental equilibrium phase diagrams of syngenesis of diamonds and primary inclusions, which characterize the nucleation and growth conditions of diamonds and a capture of paragenetic and xenogenetic minerals by the growing diamonds; (4) a determination of the phase diagrams of diamonds and inclusions syngenesis under the regime of fractional crystallization, which discover the regularities of ultrabasic-basic evolution and paragenesis transitions in the diamond-forming systems of the upper and lower mantle. The evidence of the physic-chemically united mode of diamond genesis at the mantle depths with different mineralogy is obtained. References. Litvin Yu.A. (2007). High-pressure mineralogy of diamond genesis. In: Advances in High-Pressure Mineralogy (edited by Eiji Ohtani), Geological Society of America Special paper 421, 83-103. Litvin Yu.A. (2012). Experimental study of physic-chemical conditions of natural diamond formation on an example of the eclogite

  9. Future Water Availability from Hindukush-Karakoram-Himalaya upper Indus Basin under Conflicting Climate Change Scenarios

    Directory of Open Access Journals (Sweden)

    Shabeh ul Hasson

    2016-08-01

    Full Text Available Future of the crucial Himalayan water supplies has generally been assessed under the anthropogenic warming, typically consistent amid observations and climate model projections. However, conflicting mid-to-late melt-season cooling within the upper Indus basin (UIB suggests that the future of its melt-dominated hydrological regime and the subsequent water availability under changing climate has yet been understood only indistinctly. Here, the future water availability from the UIB is presented under both observed and projected—though likely but contrasting—climate change scenarios. Continuation of prevailing climatic changes suggests decreased and delayed glacier melt but increased and early snowmelt, leading to reduction in the overall water availability and profound changes in the overall seasonality of the hydrological regime. Hence, initial increases in the water availability due to enhanced glacier melt under typically projected warmer climates, and then abrupt decrease upon vanishing of the glaciers, as reported earlier, is only true given the UIB starts following uniformly the global warming signal. Such discordant future water availability findings caution the impact assessment communities to consider the relevance of likely (near-future climate change scenarios—consistent to prevalent climatic change patterns—in order to adequately support the water resource planning in Pakistan.

  10. Dissonance and harmony between global and regional-scale seismic anisotropy and mantle dynamics

    Science.gov (United States)

    Becker, T. W.

    2017-12-01

    Huge numbers of SKS splitting observations and improved surface-wave based models of azimuthal anisotropy have advanced our understanding of how convection is recorded in mantle fabrics in the upper mantle. However, we are still debating the relative importance of frozen to actively forming olivine fabrics, subduction zone anisotropy lacks a clear reference model, and regional marine studies yield conflicting evidence as to what exactly is going on at the base of the plates and below. Here, I review the degree of agreement between regional and global observations of seismic anisotropy and how well those may be matched by first-order mantle convection models. Updated bean counting can help contextualize the spatial scales of alignment, and I discuss several examples of the relative roles of plate shear to mantle density anomalies and frozen-in structure for oceanic and continental plates. Resolution of seismological models is globally uneven, but there are some locales where such exercises may yield information on the relative strength of asthenosphere and mantle. Another long-standing question is how olivine fabrics record flow under different stress and volatile conditions. I illustrate how different petrological assumptions might be used to reconcile observations of azimuthal dependency of wave speeds for both Love and Rayleigh waves, and how this could improve our models of the upper mantle, much in the spirit of Montagner's vectorial tomography. This is but one approach to improve the regional realism of global geodynamic background models to understand where in space and time dissonance arises, and if a harmonious model may yet be constructed given our assumptions about the workings of the mantle.

  11. Thermo-mechanical Properties of Upper Jurassic (Malm) Carbonate Rock Under Drained Conditions

    Science.gov (United States)

    Pei, Liang; Blöcher, Guido; Milsch, Harald; Zimmermann, Günter; Sass, Ingo; Huenges, Ernst

    2018-01-01

    The present study aims to quantify the thermo-mechanical properties of Neuburger Bankkalk limestone, an outcrop analog of the Upper Jurassic carbonate formation (Germany), and to provide a reference for reservoir rock deformation within future enhanced geothermal systems located in the Southern German Molasse Basin. Experiments deriving the drained bulk compressibility C were performed by cycling confining pressure p c between 2 and 50 MPa at a constant pore pressure p p of 0.5 MPa after heating the samples to defined temperatures between 30 and 90 °C. Creep strain was then measured after each loading and unloading stage, and permeability k was obtained after each creep strain measurement. The drained bulk compressibility increased with increasing temperature and decreased with increasing differential pressure p d = p c - p p showing hysteresis between the loading and unloading stages above 30 °C. The apparent values of the indirectly calculated Biot coefficient α ind containing contributions from inelastic deformation displayed the same temperature and pressure dependencies. The permeability k increased immediately after heating and the creep rates were also temperature dependent. It is inferred that the alteration of the void space caused by temperature changes leads to the variation of rock properties measured under isothermal conditions while the load cycles applied under isothermal conditions yield additional changes in pore space microstructure. The experimental results were applied to a geothermal fluid production scenario to constrain drawdown and time-dependent effects on the reservoir, overall, to provide a reference for the hydromechanical behavior of geothermal systems in carbonate, and more specifically, in Upper Jurassic lithologies.

  12. Removal of coin from upper esophageal tract in children with Magill's forceps under propofol sedation.

    Science.gov (United States)

    Baral, B K; Joshi, R R; Bhattarai, B K; Sewal, R B

    2010-03-01

    Foreign body ingestion is a common emergency problem in children. Coins are the most common foreign bodies lodged in the esophagus. This is a retrospective study where we reviewed 21 consecutive paediatric cases of coins impacted in the upper esophagus. These children were attended at the BP Koirala Institute of Health Sciences, Dharan, from March 2007 to March 2008. In this study, Mc-Intosh laryngoscopes were inserted into the pharynx to elevate the larynx and to expose the esophageal entrance. Then Magill's forceps were advanced into the esophagus and opened in order to see and extract the coin from the esophagus under propofol sedation. Coins were successfully removed by Magill forceps without any complications from all 21 children. Amongst these children, 14 (66.7%) were male and 7 (33.3%) were female. The mean age of the children was 3.79 (+/- 3.02) years. The coin was grasped and extracted on the first attempt in all 21 patients. The mean time for the removal of the coin (i.e. initiation of laryngoscope to removal of coin) was 51.48 (+/- 24.17) seconds. During direct laryngoscopy, 15 (71.4%) coins were visualized clearly, whereas 6 (28.6%) were not. However all coins were successfully removed. The most commonly ingested coin is a one rupee Nepali coin (42.9%) followed by a two rupee coin (19.0%) and an Indian one rupee coin. Thus it can be seen that the coin impacted at the cricopharynx and upper oesophagus can be safely, easily and quickly removed by direct laryngoscopy and Magill's forceps under propofol sedation.

  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. Modeled intermittency risk for small streams in the Upper Colorado River Basin under climate change

    Science.gov (United States)

    Reynolds, Lindsay V.; Shafroth, Patrick B.; Poff, N. LeRoy

    2015-01-01

    Longer, drier summers projected for arid and semi-arid regions of western North America under climate change are likely to have enormous consequences for water resources and river-dependent ecosystems. Many climate change scenarios for this region involve decreases in mean annual streamflow, late summer precipitation and late-summer streamflow in the coming decades. Intermittent streams are already common in this region, and it is likely that minimum flows will decrease and some perennial streams will shift to intermittent flow under climate-driven changes in timing and magnitude of precipitation and runoff, combined with increases in temperature. To understand current intermittency among streams and analyze the potential for streams to shift from perennial to intermittent under a warmer climate, we analyzed historic flow records from streams in the Upper Colorado River Basin (UCRB). Approximately two-thirds of 115 gaged stream reaches included in our analysis are currently perennial and the rest have some degree of intermittency. Dry years with combinations of high temperatures and low precipitation were associated with more zero-flow days. Mean annual flow was positively related to minimum flows, suggesting that potential future declines in mean annual flows will correspond with declines in minimum flows. The most important landscape variables for predicting low flow metrics were precipitation, percent snow, potential evapotranspiration, soils, and drainage area. Perennial streams in the UCRB that have high minimum-flow variability and low mean flows are likely to be most susceptible to increasing streamflow intermittency in the future.

  15. 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

  16. Episodic kinematics in continental rifts modulated by changes in mantle melt fraction

    Science.gov (United States)

    Lamb, Simon; Moore, James D. P.; Smith, Euan; Stern, Tim

    2017-07-01

    Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor ‘spreading centres’ found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres, but direct observation of this process is difficult beneath the oceans. Continental rifts, however—which are also associated with mantle melt production—are amenable to detailed measurements of their short-term kinematics using geodetic techniques. Here we show that such data can provide evidence for an upwelling mantle flow, as well as information on the dimensions and timescale of mantle melting. For North Island, New Zealand, around ten years of campaign and continuous GPS measurements in the continental rift system known as the Taupo volcanic zone reveal that it is extending at a rate of 6-15 millimetres per year. However, a roughly 70-kilometre-long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence, and is flanked by regions of extension and uplift. These features fit a simple model that involves flexure of an elastic upper crust, which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15 kilometres. We propose that flexure is caused by melt-induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis, triggering a transient lower-crustal flow. A drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence, whereas melt accumulation reduces viscosity and allows uplift—processes that are also likely to occur in oceanic spreading centres.

  17. 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.

  18. The latest geodynamics in Asia: Synthesis of data on volcanic evolution, lithosphere motion, and mantle velocities in the Baikal-Mongolian region

    Directory of Open Access Journals (Sweden)

    Sergei Rasskazov

    2017-07-01

    Full Text Available From a synthesis of data on volcanic evolution, movement of the lithosphere, and mantle velocities in the Baikal-Mongolian region, we propose a comprehensive model for deep dynamics of Asia that assumes an important role of the Gobi, Baikal, and North Transbaikal transition-layer melting anomalies. This layer was distorted by lower-mantle fluxes at the beginning of the latest geodynamic stage (i.e. in the early late Cretaceous due to avalanches of slab material that were stagnated beneath the closed fragments of the Solonker, Ural-Mongolian paleoceans and Mongol-Okhotsk Gulf of Paleo-Pacific. At the latest geodynamic stage, Asia was involved in east–southeast movement, and the Pacific plate moved in the opposite direction with subduction under Asia. The weakened upper mantle region of the Gobi melting anomaly provided a counterflow connected with rollback in the Japan Sea area. These dynamics resulted in the formation of the Honshu-Korea flexure of the Pacific slab. A similar weakened upper mantle region of the North Transbaikal melting anomaly was associated with the formation of the Hokkaido-Amur flexure of the Pacific slab, formed due to progressive pull-down of the slab material into the transition layer in the direction of the Pacific plate and Asia convergence. The early–middle Miocene structural reorganization of the mantle processes in Asia resulted in the development of upper mantle low-velocity domains associated with the development of rifts and orogens. We propose that extension at the Baikal Rift was caused by deviator flowing mantle material, initiated under the moving lithosphere in the Baikal melting anomaly. Contraction at the Hangay orogen was created by facilitation of the tectonic stress transfer from the Indo-Asian interaction zone due to the low-viscosity mantle in the Gobi melting anomaly.

  19. Mantle wedge exhumation beneath the Dora-Maira (U)HP dome unravelled by local earthquake tomography (Western Alps)

    Science.gov (United States)

    Solarino, Stefano; Malusà, Marco G.; Eva, Elena; Guillot, Stéphane; Paul, Anne; Schwartz, Stéphane; Zhao, Liang; Aubert, Coralie; Dumont, Thierry; Pondrelli, Silvia; Salimbeni, Simone; Wang, Qingchen; Xu, Xiaobing; Zheng, Tianyu; Zhu, Rixiang

    2018-01-01

    In continental subduction zones, the behaviour of the mantle wedge during exhumation of (ultra)high-pressure [(U)HP] rocks provides a key to distinguish among competing exhumation mechanisms. However, in spite of the relevant implications for understanding orogenic evolution, a high-resolution image of the mantle wedge beneath the Western Alps is still lacking. In order to fill this gap, we perform a detailed analysis of the velocity structure of the Alpine belt beneath the Dora-Maira (U)HP dome, based on local earthquake tomography independently validated by receiver function analysis. Our results point to a composite structure of the mantle wedge above the subducted European lithosphere. We found that the Dora-Maira (U)HP dome lays directly above partly serpentinized peridotites (Vp 7.5 km/s; Vp/Vs = 1.70-1.72), documented from 10 km depth down to the top of the eclogitized lower crust of the European plate. These serpentinized peridotites, possibly formed by fluid release from the subducting European slab to the Alpine mantle wedge, are juxtaposed against dry mantle peridotites of the Adriatic upper plate along an active fault rooted in the lithospheric mantle. We propose that serpentinized mantle-wedge peridotites were exhumed at shallow crustal levels during late Eocene transtensional tectonics, also triggering the rapid exhumation of (U)HP rocks, and were subsequently indented under the Alpine metamorphic wedge in the early Oligocene. Our findings suggest that mantle-wedge exhumation may represent a major feature of the deep structure of exhumed continental subduction zones. The deep orogenic levels here imaged by seismic tomography may be exposed today in older (U)HP belts, where mantle-wedge serpentinites are commonly associated with coesite-bearing continental metamorphic rocks.

  20. Evaluating BMP effectiveness in improving freshwater provisioning under changing climate in the upper Mississippi river basin

    Science.gov (United States)

    Li, Ping; Logsdon Muenich, Rebecca; Chaubey, Indrajeet; Wei, Xiaomei

    2017-04-01

    Freshwater provisioning (FWP) is one of the critical ecosystem services that is sensitive to climate change and variability and agricultural management strategies. Best management practices (BMPs) are widely used to relieve the adverse impacts of agricultural production on hydrology and water quality. However, climate change may alter the BMP effectiveness in protecting hydrology and water quality. A relatively large number of studies have evaluated BMP effectiveness in improving water quality and attenuating peak flow, however the impact of climate change on BMPs effectiveness in improving FWP service is poorly understood. In this study, five BMP scenarios (no tillage, filter strips, cover crops, grassed waterways and combination of all BMPs) were simulated using Soil and Water Assessment Tool (SWAT). Then an index-based ecosystem service approach was adopted to quantify annual FWP services by using model outputs for each BMP scenario, in order to evaluate the BMP effectiveness in improving FWP service for 13 studied watersheds in the Upper Mississippi River Basin (UMRB) in the US. The effectiveness of each BMP was evaluated both for baseline climate (1975-2004) and projected near future climate (2021-2050) from three regional climate models (CCCma-CanESM2 RCA4, ICHEC-EC-EARTH RCA4 and ICHEC-EC-EARTH HIRHAM5) under two Representative Concentration Pathway scenarios (RCP4.5 and RCP8.5), with an objective to assess the impacts of future climate changes on BMP effectiveness. Results suggest that the annual FWP could be improved by implementing BMPs. The future climate change may reduce the BMP effectiveness due to altered runoff conditions under projected increased precipitation and temperature resulting in increased losses of pollutants from crop fields to streams and reduced freshwater availability. Results from this study may provide an insight for water resource managers to implement effective BMPs in responding to future climate change, in order to protect and

  1. A micro-scale investigation of melt production and extraction in the upper mantle based on silicate melt pockets in ultramafic xenoliths from the Bakony-Balaton Highland Volcanic Field (Western Hungary)

    DEFF Research Database (Denmark)

    Bali, Eniko; Zanetti, A.; Szabo, C.

    2008-01-01

    Mantle xenoliths in Neogene alkali basalts of the Bakony-Balaton Highland Volcanic Field (Western Hungary) frequently have melt pockets that contain silicate minerals, glass, and often carbonate globules. Textural, geochemical and thermobarometric data indicate that the melt pockets formed...

  2. 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

  3. Socio-demographic factors related to under-diagnosis of childhood asthma in Upper Silesia, Poland.

    Science.gov (United States)

    Zejda, Jan E; Farnik, Małgorzata; Smółka, Irena; Lawson, Joshua; Brożek, Grzegorz M

    2017-06-07

    Introduction. The presented study of 4,535 children aged 7-17 years in the Upper Silesian region of Poland yielded 186 cases of previously known asthma, and 44 children with newly diagnosed asthma. The aim of the presented study was to identify non-medical factors that could explain why children with a newly established diagnosis ('undiagnosed asthma') had not been diagnosed in the past. Materials and method. The study was performed according to a case-control design. Parents of the children answered questionnaires on socio-economic status and family-related factors. Statistical determinants of undiagnosed asthma were explored using raw (OR) and logistic odds ratios with their 95% confidence intervals (logOR, 95%CI). Results. Children with undiagnosed asthma were younger compared to the group with previously known asthma (11.3±2.1 vs. 12.6±2.5 years; p=0.0008). Newly diagnosed cases were more frequent in children who had less parental attention (less than 1 hour/day spent by parent with child - OR=4.36; 95%CI: 1.76-10.81) and who were not registered with specialized health care (OR=2.20; 95%CI: 0.95-5.06). Results of logistic regression analysis suggest that under-diagnosis of asthma is related to age below 12 years - logOR = 3.59 (95%CI: 1.28-10.36), distance to a health centre > 5 km - logOR = 3.45 (95%CI: 1.05-11.36), time spent with child Conclusion. Among non-medical determinants of undiagnosed asthma the age of a child plays a major role. Another factors of importance is the large distance between residence and health centre, and low parental attention at home.

  4. P-wave anisotropy, mantle wedge flow and olivine fabrics beneath Japan

    Science.gov (United States)

    Liu, Xin; Zhao, Dapeng

    2017-09-01

    We present a new 3-D anisotropic P-wave velocity (Vp) model for the crust and upper mantle of the Japan subduction zone obtained by inverting a large number of high-quality P-wave traveltime data of local earthquakes and teleseismic events. By assuming orthorhombic anisotropy with a vertical symmetry axis existing in the modeling space, isotropic Vp tomography and 3-D Vp azimuthal and radial anisotropies are determined simultaneously. According to a simple flow field and the obtained Vp anisotropic tomography, we estimate the distribution of olivine fabrics in the mantle wedge. Our results show that the forearc mantle wedge above the subducting Pacific slab beneath NE Japan exhibits an azimuthal anisotropy with trench-parallel fast velocity directions (FVDs) and Vhf > Vv > Vhs (here Vv is Vp in the vertical direction, Vhf and Vhs are P-wave velocities in the fast and slow directions in the horizontal plane), where B-type olivine fabric with vertical trench-parallel flow may dominate. Such an anisotropic feature is not obvious in the forearc mantle wedge above the Philippine Sea (PHS) slab under SW Japan, probably due to higher temperatures and more fluids there associated with the young and warm PHS slab subduction. Trench-normal FVDs and Vhf > Vv > Vhs are generally revealed in the mantle wedge beneath the arc and backarc in Japan, where E-type olivine fabric with FVD-parallel horizontal flow may dominate. Beneath western Honshu, however, the mantle wedge exhibits an anisotropy of Vv > Vhf > Vhs and so C-type olivine fabric may dominate, suggesting that the water content is the highest there, because both the PHS and Pacific slabs exist there and their dehydration reactions release abundant fluids to the overlying mantle wedge.

  5. 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

  6. Deep Mantle Layering by Post-Perovskite Dissociation at 0.9 TPa in GJ876d Super Earth

    Science.gov (United States)

    Shahnas, H.; Pysklywec, R.; Yuen, D. A.

    2017-12-01

    The processes in the interior of the exoplanets are poorly known. This is due to the uncertainties in the pressure- and temperature-dependence of the mantle properties, as well as the circumstances under which the mantle processes such as phase and spin transitions and structural changes in the mantle minerals occur. Recent advances in high pressure mineral physics as well as some recent theoretical studies have yielded new insights into our understanding of mantle dynamics. MgSiO3 post-perovskite (pPv) dissociates into MgO and MgSi2O5 at 0.9 TPa, and MgSi2O5 dissociates into MgO and SiO2 at 2.1 TPa. Both dissociations are endothermic and the first dislocation with a large Clapeyron slope of -12 MPa/K is expected to occur close to the bottom of the mantle in GJ876d super-Earth which is 7.5 times more massive than the Earth. Employing 3D-spherical control volume compressible models we perform a systematic investigation on the combined impact of the deep mantle dissociation of post-perovskite and the mantle conductivity and the viscosity, on the mixing, cooling and the style of the convection in GJ876d super Earth. Our model results reveal that in the presence of deep mantle dissociation of post-perovskite into MgO and MgSi2O5 at 0.9 TP, the mean mantle temperature decreases which is associated with the viscosity increase. However, while this deep mantle endothermic process for high viscosities ( 1023 Pa.s) does not cause layering in the bottom of mantle, for viscosities 1022 Pa.s and below, a layering of thickness 500 km develops above the CMB. The mean temperature and heat flow decrease in the presence of pPv dissociation-induced layering and the impact of the viscosity on mean mantle temperature is enhanced. In the layered models while the upper layer is cooling mainly by conduction; there may exist a vigorous convection in the lower layer above the CMB depending on the strength of the viscosity.

  7. Magmatic and Seismic Evidence for the Neogene Evolution of the Subducting Slab and Crustal and Mantle Lithosphere under the Central Andes

    Science.gov (United States)

    Kay, S. M.; Sandvol, E. A.

    2017-12-01

    Geophysical models coupled with the distribution, chemistry and age of magmatic rocks provide powerful tools for reconstructing the thermal and material balance and deformational history of the Central Andean crust and lithosphere in time and space. Two examples are given. In the first, a model for changing slab geometry, delamination (foundering) of the crust and mantle and forearc subduction erosion beneath the southern Puna plateau comes from studies of Miocene to Recent magmatic rocks linked with seismic studies. The distribution and chemistry (e.g., Sm/Yb, La/Ta, Ba/La, isotopes) of the volcanic rocks support an 18-7 Ma period of slab shallowing, followed by slab steepening and forearc subduction erosion linked with backarc crustal and lithospheric delamination and eruption of large ignimbrites. Support for delamination comes from seismic attenuation and Vs tomographic images that reveal an 100 km wide high velocity anomaly associated with an irregular shear wave splitting pattern, which is interpreted as a delaminated block above a nearly aseismic segment of the subducting slab at a depth of 150-200 km (Calixto et al., 2013, 2014; Liang et al. 2014). This block underlies the 1350°C at 2 Gpa followed by fractionation and mixing with melts of garnet-pyroxene-amphibole bearing crust (Risse et al., 2013). In accord, the lavas are over a region where receiver functions indicate a lithosphere-asthenosphere boundary at 60-80 km and a regionally thin 45-55 km thick crust with a low Vp/Vs (< 1.70) ratio (Heit et al., 2014). Calculations of crustal loss and gain allow up to 10% of the southern Puna lower crust to have been lost in the last 10 Ma. A second region where the characteristics of the magmatic rocks provide clues to the timing of slab shallowing and proposed slab tears (e.g., Lynner et al, 2017) is over and on the margins of the Chilean flat-slab). In this case, shallowing of the slab as the trench normal portion of the Juan Fernandez Ridge began to subduct

  8. Numerical Analysis of Flood modeling of upper Citarum River under Extreme Flood Condition

    Science.gov (United States)

    Siregar, R. I.

    2018-02-01

    This paper focuses on how to approach the numerical method and computation to analyse flood parameters. Water level and flood discharge are the flood parameters solved by numerical methods approach. Numerical method performed on this paper for unsteady flow conditions have strengths and weaknesses, among others easily applied to the following cases in which the boundary irregular flow. The study area is in upper Citarum Watershed, Bandung, West Java. This paper uses computation approach with Force2 programming and HEC-RAS to solve the flow problem in upper Citarum River, to investigate and forecast extreme flood condition. Numerical analysis based on extreme flood events that have occurred in the upper Citarum watershed. The result of water level parameter modeling and extreme flood discharge compared with measurement data to analyse validation. The inundation area about flood that happened in 2010 is about 75.26 square kilometres. Comparing two-method show that the FEM analysis with Force2 programs has the best approach to validation data with Nash Index is 0.84 and HEC-RAS that is 0.76 for water level. For discharge data Nash Index obtained the result analysis use Force2 is 0.80 and with use HEC-RAS is 0.79.

  9. Vector movement underlies avian malaria at upper elevation in Hawaii: implications for transmission of human malaria.

    Science.gov (United States)

    Freed, Leonard A; Cann, Rebecca L

    2013-11-01

    With climate warming, malaria in humans and birds at upper elevations is an emerging infectious disease because development of the parasite in the mosquito vector and vector life history are both temperature dependent. An enhanced-mosquito-movement model from climate warming predicts increased transmission of malaria at upper elevation sites that are too cool for parasite development in the mosquito vector. We evaluate this model with avian malaria (Plasmodium relictum) at 1,900-m elevation on the Island of Hawaii, with air temperatures too low for sporogony in the vector (Culex quinquefasciatus). On a well-defined site over a 14-year period, 10 of 14 species of native and introduced birds became infected, several epizootics occurred, and the increase in prevalence was driven more by resident species than by mobile species that could have acquired their infections at lower elevations. Greater movement of infectious mosquitoes from lower elevations now permits avian malaria to spread at 1,900 m in Hawaii, in advance of climate warming at that elevation. The increase in malaria at upper elevations due to dispersal of infectious mosquitoes is a real alternative to temperature for the increased incidence of human malaria in tropical highlands.

  10. 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

  11. 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.

  12. Sensitivity analysis of crustal correction for calculation of lithospheric mantle density from gravity data

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2016-01-01

    of the crust from the observed satellite gravity field data (GOCE Direct release 3). Thus calculated residual mantle gravity anomalies are caused mainly by a heterogeneous density distribution in the upper mantle. Given a relatively small range of expected compositional density variations in the lithospheric......We investigate how uncertainties in seismic and density structure of the crust propagate to uncertainties in mantle density structure. The analysis is based on interpretation of residual upper-mantle gravity anomalies which are calculated by subtracting (stripping) the gravitational effect...... mantle, knowledge on uncertainties associated with incomplete information on crustal structure is of utmost importance for progress in gravity modelling. Uncertainties in the residual upper-mantle gravity anomalies result chiefly from uncertainties in (i) seismic VP velocity-density conversion...

  13. Compositional mantle layering revealed by slab stagnation at ~1000-km depth.

    Science.gov (United States)

    Ballmer, Maxim D; Schmerr, Nicholas C; Nakagawa, Takashi; Ritsema, Jeroen

    2015-12-01

    Improved constraints on lower-mantle composition are fundamental to understand the accretion, differentiation, and thermochemical evolution of our planet. Cosmochemical arguments indicate that lower-mantle rocks may be enriched in Si relative to upper-mantle pyrolite, whereas seismic tomography images suggest whole-mantle convection and hence appear to imply efficient mantle mixing. This study reconciles cosmochemical and geophysical constraints using the stagnation of some slab segments at ~1000-km depth as the key observation. Through numerical modeling of subduction, we show that lower-mantle enrichment in intrinsically dense basaltic lithologies can render slabs neutrally buoyant in the uppermost lower mantle. Slab stagnation (at depths of ~660 and ~1000 km) and unimpeded slab sinking to great depths can coexist if the basalt fraction is ~8% higher in the lower mantle than in the upper mantle, equivalent to a lower-mantle Mg/Si of ~1.18. Global-scale geodynamic models demonstrate that such a moderate compositional gradient across the mantle can persist can in the presence of whole-mantle convection.

  14. [Research on safe implantation of upper-middle thoracic pedicle screws under the X-ray perspective].

    Science.gov (United States)

    Xu, Wei-Xing; Chen, Qi-Xin; Li, Fang-Cai

    2008-02-01

    To explore the method of implanting upper-middle thoracic pedicle screws under monitoring by X-ray and evaluate accuracy and safety. (1) Six normal adult thoracic spine samples (T1-T8) were selected, from which single spine units were separated. A surgical probe went in along the pedicle axis. By C-shaped arm X-ray, the four probe positions were recorded: at the entering point, the front end of the probe in the middle of the pedicle, at the pack of the spine, and under the cortex of the front of the spine. The position of the front end of the probe at the entering point, and the front end of the probe at different depth at central-side perspective position were analyzed. The related positions and their corresponding changing rules were also analyzed. (2) Based on the changing rules mentioned above, different steps were adopted under the guidance of the C-shaped arm X-ray, to safely implant upper-middle thoracic pedicle screws. First, six T1-T8 spine samples were used, and under the guidance of the C-shaped arm device, 96 pedicle screws were implanted. After the operation,the sping samples were scanned through CT, and the positions of the screws were determined. According to the result of the CT scanning, the result were excellent (the screw was safely inside the pedicle) in 90 screws; Medium (the screw penetrated a little of the inside or outside bone cortex, within 2 mm) in 6; No one was had (the screw penetrated a lot, more than 2 mm). The implantation of upper-middle thoracic pedicle screw under the guidance of the C-shaped arm X-ray perspective is a simple and feasible method, and improve the accuracy and safety.

  15. Numerical investigation of transient transport and deposition of microparticles under unsteady inspiratory flow in human upper airways.

    Science.gov (United States)

    Naseri, Arash; Shaghaghian, Sana; Abouali, Omid; Ahmadi, Goodarz

    2017-10-01

    In the present study, unsteady airflow patterns and particle deposition in healthy human upper airways were simulated. A realistic 3-D computational model of the upper airways including the vestibule to the end of the trachea was developed using a series of CT scan images of a healthy human. Unsteady simulations of the inhaled and exhaled airflow fields in the upper airway passages were performed by solving the Navier-Stokes and continuity equations for low breathing rates corresponding to low and moderate activities. The Lagrangian trajectory analysis approach was utilized to investigate the transient particle transport and deposition under cyclic breathing condition. Particles were released uniformly at the nostrils' entrance during the inhalation phase, and the total and regional depositions for various micro-particle sizes were evaluated. The transient particle deposition fractions for various regions of the human upper airways were compared with those obtained from the equivalent steady flow condition. The presented results revealed that the equivalent constant airflow simulation can approximately predict the total particle deposition during cyclic breathing in human upper airways. While the trends of steady and unsteady model predictions for local deposition were similar, there were noticeable differences in the predicted amount of deposition. In addition, it was shown that a steady simulation cannot properly predict some critical parameters, such as the penetration fraction. Finally, the presented results showed that using a detached nasal cavity (commonly used in earlier studies) for evaluation of total deposition fraction of particles in the nasal cavity was reasonably accurate for the steady flow simulations. However, in transient simulation for predicting the deposition fraction in a specific region, such as the nasal cavity, using the full airway system geometry becomes necessary. Copyright © 2017 Elsevier B.V. All rights reserved.

  16. Measurement of two-phase flow at the core upper plenum interface under simulated reflood conditions

    International Nuclear Information System (INIS)

    Thomas, D.G.; Combs, S.K.; Bagwell, M.E.

    1980-01-01

    Objectives of the Instrument Development Loop program were to simulate flows at the core/upper plenum interface during the reflood phase of a LOCA and to develop instruments for measuring mass-flows at this interface. A tie plate drag body was developed and tested successfully, and the data obtained were shown to be equivalent to pressure drops. The tie-plate drag body gave useful measurements in pure downflow, and the drag/turbine combination correlates with mass flow for high upflow

  17. Changes in groundwater recharge under projected climate in the upper Colorado River basin

    Science.gov (United States)

    Tillman, Fred; Gangopadhyay, Subhrendu; Pruitt, Tom

    2016-01-01

    Understanding groundwater-budget components, particularly groundwater recharge, is important to sustainably manage both groundwater and surface water supplies in the Colorado River basin now and in the future. This study quantifies projected changes in upper Colorado River basin (UCRB) groundwater recharge from recent historical (1950–2015) through future (2016–2099) time periods, using a distributed-parameter groundwater recharge model with downscaled climate data from 97 Coupled Model Intercomparison Project Phase 5 climate projections. Simulated future groundwater recharge in the UCRB is generally expected to be greater than the historical average in most decades. Increases in groundwater recharge in the UCRB are a consequence of projected increases in precipitation, offsetting reductions in recharge that would result from projected increased temperatures.

  18. P and S Wave Velocity Structure of the Crust and Upper Mantle Under China and Surrounding Areas From Body and Surface Wave Tomography

    Science.gov (United States)

    2008-03-31

    and H. Hartse, 2005, Pn tomography and location in Eurasia, 2005 IASPEI Meeting, Santiago, Chile . Shapiro, N. M., and M. H. Ritzwoller, 2002, Monte...con- sistent with the distribution of Cenozoic volcanoes and magmatic rocks [Ma, 1989; Liu, 1999]. There are 29 large Cenozoic volcanoes (or...Yunnan-Guizhou Plateau. In this area, we may be seeing the effect of pure shear deformation, although Figure 12. Distribution of Cenozoic volcanoes

  19. Management of post-traumatic stiffness of the shoulder following upper limb trauma with manipulation under anaesthetic.

    Science.gov (United States)

    Lancaster, Sarah T; Grove, Thomas N; Woods, David A

    2017-10-01

    A proportion of patients who sustain upper limb fractures develop post-traumatic stiffness (PTS), which may progress in a similar way to primary frozen shoulder (PFS). We have had success in treating PFS with manipulation under anaesthetic (MUA) and therefore treated PTS using MUA. Oxford Shoulder Scores (OSS), range of motion (ROM) data pre- and post-MUA, and the need for repeat procedure were compared. Sixty-four patients with PTS following an upper limb fracture, unresponsive to conservative measures, were seen between 1 January 1999 and 1 November 2015. Thirty-two patients had sustained a proximal humeral fracture, six of whom had a concurrent shoulder dislocation. MUA was performed using a standard technique. The results were compared with 487 PFS patients undergoing the same procedure. There was no significant difference in ROM change between the groups. Improvement in OSS was slightly greater in the PFS group (17 versus 14, p  = 0.005) but, upon subgroup analysis of the PTS group, no significant difference was found for patients presenting with humeral fractures alone. MUA results for PTS following upper limb fracture are comparable to MUA for PFS. We therefore recommend MUA in PTS cases where conservative methods have failed.

  20. 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.

  1. 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.

  2. 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

  3. 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

    containing 90.5 - 92.0 mole % forsterite). The rocks which were subjected to significant decrease of mg# of silicates (down to 84) may be difficult to distinguish from cumulates. However, since the alkaline basaltic melts do not precipitate orthopyroxene under lithospheric pressures, their mineral composition is different than that of mantle harzburgites. Kelemen PB, Dick HJB, Quick JE (1992) Formation of harzburgite by pervasive melt/rock reaction in the upper mantle. Nature 358: 635-641. Tursack E, Liang Y (2012) A comparative study of melt-rock reactions in the mantle: laboratory dissolution experiments and geological field observations. Contributions to Mineralogy and Petrology 163: 861-876

  4. Delayed antibiotic prescription for upper respiratory tract infections in children under primary care: Physicians' views.

    Science.gov (United States)

    Raft, Camilla Flintholm; Bjerrum, Lars; Arpi, Magnus; Jarløv, Jens Otto; Jensen, Jette Nygaard

    2017-12-01

    Overprescribing antibiotics for common or inaccurately diagnosed childhood infections is a frequent problem in primary healthcare in most countries. Delayed antibiotic prescriptions have been shown to reduce the use of antibiotics in primary healthcare. The aim was to examine primary care physicians' views on delayed antibiotic prescriptions to preschool children with symptoms of upper respiratory tract infections (URTIs). A questionnaire was sent to 1180 physicians working in general practice in the Capital Region of Denmark, between January and March 2015. The questions focused on physicians' attitude and use of delayed antibiotic prescriptions to children with URTIs. The response rate was 49% (n = 574). Seven per cent of the physicians often used delayed prescriptions to children with symptoms of URTI, but 46% believed that delayed prescription could reduce antibiotic use. The physicians' views on delayed antibiotic prescription were significantly associated with their number of years working in general practice. Parents' willingness to wait-and-see, need for reassurance, and knowledge about antibiotics influenced the physicians' views. Also, clinical symptoms and signs, parents' willingness to shoulder the responsibility, the capability of observation without antibiotic treatment, and structural factors like out-of-hour services were relevant factors in the decision. Most physicians, especially those with fewer years of practice, had a positive attitude towards delayed antibiotic prescription. Several factors influence the views of the physicians-from perceptions of parents to larger structural elements and years of experience.

  5. Phase relations in the Fe-Fe3C-Fe3N system at 7.8 GPa and 1350 °C: Implications for carbon and nitrogen hosts in Fe0-saturated upper mantle

    Science.gov (United States)

    Sokol, Alexander G.; Kruk, Alexey N.; Seryotkin, Yurii V.; Korablin, Alexander A.; Palyanov, Yury N.

    2017-04-01

    Phase relations in the Fe-Fe3C-Fe3N system are studied in high-pressure experiments at 7.8 GPa and 1350 °C using a split-sphere multi-anvil apparatus. The starting mixtures consisting of Fe, Fe3C and Fe3N are loaded into ceramic or graphite capsules. Contamination with trace amounts of oxygen leads to the appearance of wüstite in the system retaining oxygen fugacity (fO2) near the iron-wüstite (IW) buffer. The metal melt rich in carbon and nitrogen has a large stability field in the central part of the phase diagram, and this field at 1350 °C is tangent to the Fe-Fe3C side of the Fe-Fe3C-Fe3N triangle at the point of the Fe-Fe3C eutectics. Iron nitride ε-Fe3N (space group P6322 or P63/mmc) contains variable amounts of C and N: up to 2.0-2.5 wt% C and 6.0-7.3 wt% N in equilibrium with a C- and N-rich melt and as little as 1.0 wt% C and 3.2 wt% N in equilibrium with γ- Fe. The limit C and N contents in γ-Fe equilibrated with the C- and N-rich melt is about 1.0 wt%, while the N solubility in cementite (Fe3C) does not exceed 0.5 wt%. The obtained data make basis for the isothermal section of the Fe-Fe3C-Fe3N system. The metal melt phase is inferred to be the main host of carbon and nitrogen in the Fe0-saturated (0.1 wt%) mantle at a depth of ∼250 km. In particular, C- and N-bearing austenite (γ-Fe) and metal melts host carbon and nitrogen in the mantle depleted in volatiles (20 ppm C and 1 ppm N), whereas carbon and nitrogen in the mantle with high concentrations of volatiles (250 ppm C and 100 ppm N) reside in C- and N-rich melts with a minor amount of iron carbide (Fe3C). The presence of nickel and sulphur in metal are expected to inhibit the formation of iron carbide and increases the melt phase stability. Redox freezing of N-rich carbonate melts from subduction slabs in Fe0-saturated mantle may produce iron melts supersaturated with nitrogen and stable ε-Fe3N.

  6. Warm-up with weighted bat and adjustment of upper limb muscle activity in bat swinging under movement correction conditions.

    Science.gov (United States)

    Ohta, Yoichi; Ishii, Yasumitsu; Ikudome, Sachi; Nakamoto, Hiroki

    2014-02-01

    The effects of weighted bat warm-up on adjustment of upper limb muscle activity were investigated during baseball bat swinging under dynamic conditions that require a spatial and temporal adjustment of the swinging to hit a moving target. Seven male college baseball players participated in this study. Using a batting simulator, the task was to swing the standard bat coincident with the arrival timing and position of a moving target after three warm-up swings using a standard or weighted bat. There was no significant effect of weighted bat warm-up on muscle activity before impact associated with temporal or spatial movement corrections. However, lower inhibition of the extensor carpi ulnaris muscle activity was observed in a velocity-changed condition in the weighted bat warm-up, as compared to a standard bat warm-up. It is suggested that weighted bat warm-up decreases the adjustment ability associated with inhibition of muscle activation under movement correction conditions.

  7. Mountains Under Pressure: Evaluating Ecosystem Services and Livelihoods in the Upper Himalayan Region of Nepal

    NARCIS (Netherlands)

    Bhusal, Jagat K.; Chapagain, Prem Sagar; Regmi, Santosh; Gurung, Praju; Zulkafli, Zed; Karpouzoglou, T.D.; Pandeya, Bhopal; Buytaert, Wouter; Clark, Julian

    2016-01-01

    Natural resource-based livelihoods in mountainous regions are subject to new types of development as well as climate related pressures and vulnerabilities. On one hand, the integrity of the mountainous landscape is under pressure from the melting of glaciers, changes in water availability, rainfall

  8. determinants of under-five mortality in builsa district, upper east

    African Journals Online (AJOL)

    DEPT OF AGRICULTURAL ENGINEERING

    equipped to pay special attention to mothers with previous child deaths in order to assist them to prevent further deaths. Keywords: Under-five ... children worldwide die before their fifth birth- day, with almost all of such deaths .... odds ratio worth detecting at a 95% confidence level with a power of 80% and allowing for a.

  9. 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.

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

    DEFF Research Database (Denmark)

    Furbo, Simon; Knudsen, Søren

    2006-01-01

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

  11. Crustal and Mantle Structure Beneath the Iles Eparses (Mozambique Channel, Indian Ocean)

    Science.gov (United States)

    Barruol, G.; Fontaine, F. R.; Davy, C.; Schlindwein, V. S. N.; Sigloch, K.

    2014-12-01

    In order to investigate the lithospheric structure of the Mozambique channel (Indian Ocean), we deployed 5 broadband three-components seismic stations between April 2011 and January 2014 on the Islands of Europa (EURO), Juan de Nova (JNOV), Mayotte (MAYO), and Glorieuses (GLOR) in the Mozambique channel and on Tromelin Island (TROM) located ca. 450 km east of Madagascar. We performed measurements of teleseismic shear wave splitting using SKS and SKKS phases and receiver function analyses to characterize the nature and thickness of the crust and the underlying upper mantle structure. Seismic anisotropy is observed at all seismic stations and display a rather homogeneous pattern: average values of the splitting parameters show fast polarization trending between N112°E (EURO) and N120°E (JNOV) to N81°E (MAYO). Observed delay times vary between 0.8 (JNOV) and 1.0 s (MAYO). In Mayotte, analysis of individual backazimuthal variation of splitting parameters suggests an upper mantle more complex than a single anisotropic layer. Station TROM located on Tromelin Island shows similar fast polarization azimuth of N123°E but slightly higher delay time (1.4 s). Fast polarization directions are compared with values predicted by drag-induced anisotropy and absolute plate motion direction and with lithospheric fossil spreading directions. Results are also compared to orientation predicted by large-scale mantle convection models. Receiver functions observations and modelling of P-to-S conversions at the Mohorovičić (Moho) discontinuity have been employed to investigate the variations in the Moho depth, the nature of the crust and of the crust-mantle transition. Preliminary results suggest a Moho depth of 16 km beneath Europa Island.

  12. Axial‐type olivine crystallographic preferred orientations: the effect of strain geometry on mantle texture

    NARCIS (Netherlands)

    Chatzaras, V.; Kruckenberg, Seth C.; Cohen, Shaina M.; Medaris Jr., L. Gordon; Withers, Anthony C.; Bagley, Brian

    The effect of finite strain geometry on crystallographic preferred orientation (CPO) is poorly constrained in the upper mantle. Specifically, the relationship between shape preferred orientation (SPO) and CPO in the mantle rocks remains unclear. We analyzed a suite of 40 spinel peridotite xenoliths

  13. 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.

  14. 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

  15. A diffusion mechanism for core-mantle interaction.

    Science.gov (United States)

    Hayden, Leslie A; Watson, E Bruce

    2007-11-29

    Understanding the geochemical behaviour of the siderophile elements--those tending to form alloys with iron in natural environments--is important in the search for a deep-mantle chemical 'fingerprint' in upper mantle rocks, and also in the evaluation of models of large-scale differentiation of the Earth and terrestrial planets. These elements are highly concentrated in the core relative to the silicate mantle, but their concentrations in upper mantle rocks are higher than predicted by most core-formation models. It has been suggested that mixing of outer-core material back into the mantle following core formation may be responsible for the siderophile element ratios observed in upper mantle rocks. Such re-mixing has been attributed to an unspecified metal-silicate interaction in the reactive D'' layer just above the core-mantle boundary. The siderophile elements are excellent candidates as indicators of an outer-core contribution to the mantle, but the nature and existence of possible core-mantle interactions is controversial. In light of the recent findings that grain-boundary diffusion of oxygen through a dry intergranular medium may be effective over geologically significant length scales and that grain boundaries can be primary storage sites for incompatible lithophile elements, the question arises as to whether siderophile elements might exhibit similar (or greater) grain-boundary mobility. Here we report experimental results from a study of grain-boundary diffusion of siderophile elements through polycrystalline MgO that were obtained by quantifying the extent of alloy formation between initially pure metals separated by approximately 1 mm of polycrystalline MgO. Grain-boundary diffusion resulted in significant alloying of sink and source particles, enabling calculation of grain-boundary fluxes. Our computed diffusivities were high enough to allow transport of a number of siderophile elements over geologically significant length scales (tens of kilometres

  16. Deep mantle seismic heterogeneities in Western Pacific subduction zones

    Science.gov (United States)

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

    2012-04-01

    findings suggest that upper mantle scattering in the vicinity of many other subduction zones can be correlated to past subduction in the last 20 Myr, indicating the presence and possible storage of crustal material in the upper mantle, for some subduction regions.

  17. 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

  18. 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.

  19. Origin and Distribution of Water Contents in Continental and Oceanic Lithospheric Mantle

    Science.gov (United States)

    Peslier, Anne H.

    2013-01-01

    The water content distribution of the upper mantle will be reviewed as based on the peridotite record. The amount of water in cratonic xenoliths appears controlled by metasomatism while that of the oceanic mantle retains in part the signature of melting events. In both cases, the water distribution is heterogeneous both with depth and laterally, depending on localized water re-enrichments next to melt/fluid channels. The consequence of the water distribution on the rheology of the upper mantle and the location of the lithosphere-asthenosphere boundary will also be discussed.

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

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2015-01-01

    The aim of this study is to obtain new information on the density structure of the European upper mantle by incorporating the state-of-the-art global gravity data derived from the GOCE satellite gravity mission and recently released seismic model for the crustal structure, EUNAseis. The residual...... mantle gravity anomalies are derived from the GOCE data, from which gravitational effects of the deep mantle and the crust are removed. Our model of mantle density structure has lateral resolution of ca. 100 km, which allows to distinguish small-scale mantle anomalies and to link them to regional...... geodynamic processes. Given a relatively small range of expected density variations in the lithospheric mantle, knowledge on the uncertainties associated with incomplete knowledge of density structure of the crust is of utmost importance for further progress in density heterogeneity studies. Therefore...

  1. 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.

  2. Seismic anisotropy and mantle flow below subducting slabs

    Science.gov (United States)

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

    2017-05-01

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

  3. Isotopic evidence for a large-scale plume-derived mantle domain between the Indian and Pacific mantles beneath the Southern Ocean.

    Science.gov (United States)

    Park, S. H.; Langmuir, C. H.; Scott, S. R.; Sims, K. W. W.; Lin, J.; Kim, S. S.; Blichert-Toft, J.; Choi, H.; Yang, Y. S.; Michael, P. J.

    2017-12-01

    Earth's upper mantle is characterized by Indian- and Pacific-type domains with distinctive isotope characteristics. The boundary between these two mantle regions has been hypothesized to be located at the Australian-Antarctic-Discordance (AAD), where regions west and east of the AAD are Indian- and Pacific-type, respectively. It was further posited that the Pacific mantle feeds into the Indian mantle as the boundary is moving westward. These scenarios have important implications for the dynamics of mantle convection in the area. In the present model, regions east of the AAD are assumed to be entirely Pacific-type mantle, but our recent recovery of basalts from a 2,000-km sampling gap along the Australian-Antarctic Ridge (AAR), located east of the AAD on the Pacific side, challenges this picture. Here we show that the Hf, Nd, Pb, and Sr isotopic compositions of AAR MORB are distinct from those of Pacific and Indian MORB. Rather, the AAR lavas show mixing relationships with volcanoes from the Hikurangi seamounts, the Balleney and Scott Islands, the West Antarctic Rift System, New Zealand, and east Australia. According to tectonic reconstruction models, these volcanoes are related to super-plume activity that caused Gondwana to break up at 90 Ma. These results imply that a large-scale plume-derived mantle domain exists between the Indian and Pacific mantle domains, and that mantle dynamics along the AAD should be reinterpreted in light of interaction with a super-plume.

  4. Redox freezing and melting in the Earth's deep mantle resulting from carbon-iron redox coupling.

    Science.gov (United States)

    Rohrbach, Arno; Schmidt, Max W

    2011-04-14

    Very low seismic velocity anomalies in the Earth's mantle may reflect small amounts of melt present in the peridotite matrix, and the onset of melting in the Earth's upper mantle is likely to be triggered by the presence of small amounts of carbonate. Such carbonates stem from subducted oceanic lithosphere in part buried to depths below the 660-kilometre discontinuity and remixed into the mantle. Here we demonstrate that carbonate-induced melting may occur in deeply subducted lithosphere at near-adiabatic temperatures in the Earth's transition zone and lower mantle. We show experimentally that these carbonatite melts are unstable when infiltrating ambient mantle and are reduced to immobile diamond when recycled at depths greater than ∼250 kilometres, where mantle redox conditions are determined by the presence of an (Fe,Ni) metal phase. This 'redox freezing' process leads to diamond-enriched mantle domains in which the Fe(0), resulting from Fe(2+) disproportionation in perovskites and garnet, is consumed but the Fe(3+) preserved. When such carbon-enriched mantle heterogeneities become part of the upwelling mantle, diamond will inevitably react with the Fe(3+) leading to true carbonatite redox melting at ∼660 and ∼250 kilometres depth to form deep-seated melts in the Earth's mantle.

  5. 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

  6. Atlas of the underworld: Slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity

    Science.gov (United States)

    van der Meer, Douwe G.; van Hinsbergen, Douwe J. J.; Spakman, Wim

    2018-01-01

    Across the entire mantle we interpret 94 positive seismic wave-speed anomalies as subducted lithosphere and associate these slabs with their geological record. We document this as the Atlas of the Underworld, also accessible online at www.atlas-of-the-underworld.org, a compilation comprising subduction systems active in the past 300 Myr. Deeper slabs are correlated to older geological records, assuming no relative horizontal motions between adjacent slabs following break-off, using knowledge of global plate circuits, but without assuming a mantle reference frame. The longest actively subducting slabs identified reach the depth of 2500 km and some slabs have impinged on Large Low Shear Velocity Provinces in the deepest mantle. Anomously fast sinking of some slabs occurs in regions affected by long-term plume rising. We conclude that slab remnants eventually sink from the upper mantle to the core-mantle boundary. The range in subduction-age versus - depth in the lower mantle is largely inherited from the upper mantle history of subduction. We find a significant depth variation in average sinking speed of slabs. At the top of the lower mantle average slab sinking speeds are between 10 and 40 mm/yr, followed by a deceleration to 10-15 mm/yr down to depths around 1600-1700 km. In this interval, in situ time-stationary sinking rates suggest deceleration from 20 to 30 mm/yr to 4-8 mm/yr, increasing to 12-15 mm/yr below 2000 km. This corroborates the existence of a slab deceleration zone but we do not observe long-term (> 60 My) slab stagnation, excluding long-term stagnation due to compositional effects. Conversion of slab sinking profiles to viscosity profiles shows the general trend that mantle viscosity increases in the slab deceleration zone below which viscosity slowly decreases in the deep mantle. This is at variance with most published viscosity profiles that are derived from different observations, but agrees qualitatively with recent viscosity profiles suggested

  7. Tracing Mantle Plumes: Quantifying their Morphology and Behavior from Seismic Tomography

    Science.gov (United States)

    O'Farrell, K. A.; Eakin, C. M.; Jones, T. D.; Garcia, E.; Robson, A.; Mittal, T.; Lithgow-Bertelloni, C. R.; Jackson, M. G.; Lekic, V.; Rudolph, M. L.

    2016-12-01

    Hotspot volcanism provides a direct link between the deep mantle and the surface, but the location, depth and source of the mantle plumes that feed hotspots are highly controversial. In order to address this issue it is important to understand the journey along which plumes have travelled through the mantle. The general behavior of plumes in the mantle also has the potential to tell us about the vigor of mantle convection, net rotation of the mantle, the role of thermal versus chemical anomalies, and important bulk physical properties of the mantle such as the viscosity profile. To address these questions we developed an algorithm to trace plume-like features in shear-wave (Vs) seismic tomographic models based on picking local minima in velocity and searching for continuous features with depth. We apply this method to several of the latest tomographic models and can recover 30 or more continuous plume conduits that are >750 km long. Around half of these can be associated with a known hotspot at the surface. We study the morphology of these plume chains and find that the largest lateral deflections occur near the base of the lower mantle and in the upper mantle. We analyze the preferred orientation of the plume deflections and their gradient to infer large scale mantle flow patterns and the depth of viscosity contrasts in the mantle respectively. We also retrieve Vs profiles for our traced plumes and compare with velocity profiles predicted for different mantle adiabat temperatures. We use this to constrain the thermal anomaly associated with these plumes. This thermal anomaly is then converted to a density anomaly and an upwelling velocity is derived. We compare this to buoyancy fluxes calculated at the surface and use this in conjunction with our measured plume tilts/deflections to estimate the strength of the "mantle wind".

  8. 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

  9. 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

  10. 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

  11. 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.

  12. Characteristics of the Human Upper Gastrointestinal Contents in the Fasted State Under Hypo- and A-chlorhydric Gastric Conditions Under Conditions of Typical Drug - Drug Interaction Studies.

    Science.gov (United States)

    Litou, Chara; Vertzoni, Maria; Goumas, Constantinos; Vasdekis, Vassilis; Xu, Wei; Kesisoglou, Filippos; Reppas, Christos

    2016-06-01

    Evaluate the impact of reduced gastric acid secretion after administration of two acid-reducing agents on the physicochemical characteristics of contents of upper gastrointestinal lumen of fasted adults. Eight healthy male adults, fasted from food for 12 h, participated in a three-phase crossover study. Phase 1: No drug treatment prior to aspirations. Phase 2: Oral administration of 40 mg pantoprazole at ~9 am the last 3 days prior to aspirations and at ~7 am on aspiration day. Phase 3: Oral administration of 20 mg famotidine at ~7 pm prior to aspirations and at ~7 am on aspiration day. Samples from the contents of upper gastrointestinal lumen were aspirated for 50 min, after administration of 240 ml table water at ~9 am. Reduction of gastric acid secretion was accompanied by reduced buffer capacity, chloride ion concentration, osmolality and surface tension in stomach and by increased pH (up to ~0.7 units) in upper small intestine during the first 50 min post-water administration. The mechanism of reduction of acid secretion seems to be important for the buffer capacity in stomach and for the surface tension in upper gastrointestinal lumen. Apart from gastric pH, reduced acid secretion affects physicochemical characteristics of contents of upper gastrointestinal lumen which may be important for the performance of certain drugs/products in the fasted state.

  13. Dynamical geochemistry of the mantle

    Directory of Open Access Journals (Sweden)

    G. F. Davies

    2011-09-01

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

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

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

  14. 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.

  15. Reconstructing mantle heterogeneity with data assimilation based on the back-and-forth nudging method: Implications for mantle-dynamic fitting of past plate motions

    Science.gov (United States)

    Glišović, Petar; Forte, Alessandro

    2016-04-01

    The paleo-distribution of density variations throughout the mantle is unknown. To address this question, we reconstruct 3-D mantle structure over the Cenozoic era using a data assimilation method that implements a new back-and-forth nudging algorithm. For this purpose, we employ convection models for a compressible and self-gravitating mantle that employ 3-D mantle structure derived from joint seismic-geodynamic tomography as a starting condition. These convection models are then integrated backwards in time and are required to match geologic estimates of past plate motions derived from marine magnetic data. Our implementation of the nudging algorithm limits the difference between a reconstruction (backward-in-time solution) and a prediction (forward-in-time solution) on over a sequence of 5-million-year time windows that span the Cenozoic. We find that forward integration of reconstructed mantle heterogeneity that is constrained to match past plate motions delivers relatively poor fits to the seismic-tomographic inference of present-day mantle heterogeneity in the upper mantle. We suggest that uncertainties in the past plate motions, related for example to plate reorganization episodes, could partly contribute to the poor match between predicted and observed present-day heterogeneity. We propose that convection models that allow tectonic plates to evolve freely in accord with the buoyancy forces and rheological structure in the mantle could provide additional constraints on geologic estimates of paleo-configurations of the major tectonic plates.

  16. Reconciling laboratory and observational models of mantle rheology in geodynamic modelling

    Science.gov (United States)

    King, Scott D.

    2016-10-01

    Experimental and geophysical observations constraining mantle rheology are reviewed with an emphasis on their impact on mantle geodynamic modelling. For olivine, the most studied and best-constrained mantle mineral, the tradeoffs associated with the uncertainties in the activation energy, activation volume, grain-size and water content allow the construction of upper mantle rheology models ranging from nearly uniform with depth to linearly increasing from the base of the lithosphere to the top of the transition zone. Radial rheology models derived from geophysical observations allow for either a weak upper mantle or a weak transition zone. Experimental constraints show that wadsleyite and ringwoodite are stronger than olivine at the top of the transition zone; however the uncertainty in the concentration of water in the transition zone precludes ruling out a weak transition zone. Both observational and experimental constraints allow for strong or weak slabs and the most promising constraints on slab rheology may come from comparing inferred slab geometry from seismic tomography with systematic studies of slab morphology from dynamic models. Experimental constraints on perovskite and ferropericlase strength are consistent with general feature of rheology models derived from geophysical observations and suggest that the increase in viscosity through the top of the upper mantle could be due to the increase in the strength of ferropericlase from 20-65 GPa. The decrease in viscosity in the bottom half of the lower mantle could be the result of approaching the melting temperature of perovskite. Both lines of research are consistent with a high-viscosity lithosphere, a low viscosity either in the upper mantle or transition zone, and high viscosity in the lower mantle, increasing through the upper half of the lower mantle and decreasing in the bottom half of the lower mantle, with a low viscosity above the core. Significant regions of the mantle, including high

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

    Science.gov (United States)

    Ashchepkov, Igor

    2017-04-01

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

  18. 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

  19. [The mantle zone in lymphatic follicles and its stratification].

    Science.gov (United States)

    Bednár, B

    1993-04-01

    Ten inguinal lymph nodes and spleens from autopsies were chosen according to age decades in order to get an idea about usual appearance of follicular structures. The group was complemented by 4 palatine tonsils from routine biopsies. Phenotype was ascertained by using about 30 standard markers and results were compared with a basic histocytological picture. The appearance of lymphatic tissue was quite different according to location and age categories, nevertheless, there were common immunophenotypic and structural features of follicular mantle in younger persons. It mostly comprised four cellular layers, more conspicuous at the upper pole of the follicle. An innermost layer was small-celled blastic, MB 2 and IgD positive, the next B monocytoid layer had medium sized cells of a similar phenotype but more alc, phosphatase positive. An inconstant plasmacytoid layer and a clarocellular layer used to be incomplete. It was cytostructurally characteristic but immunohistologically non-standard (faint CD 19 et CD 20 positivity). T 4 lymphocytes and perhaps some other elements leaving germinal centres were admixed into the inner mantle layer. Various small lymphoid cells, especially T 8 lymphocytes and sometimes litoral cells, were admixed into mantle periphery. Mutual exchange of lymphatic cells between the germinal and mantle zones was very scant. The mantle zone is presumed therefore to be independent from the structural and functional point of view as well.

  20. Intraplate mantle oxidation by volatile-rich silicic magmas

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-11-01

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

  1. Inference of viscosity jump at 670 km depth and lower mantle viscosity structure from GIA observations

    Science.gov (United States)

    Nakada, Masao; Okuno, Jun'ichi; Irie, Yoshiya

    2018-03-01

    A viscosity model with an exponential profile described by temperature (T) and pressure (P) distributions and constant activation energy (E_{{{um}}}^{{*}} for the upper mantle and E_{{{lm}}}^* for the lower mantle) and volume (V_{{{um}}}^{{*}} and V_{{{lm}}}^*) is employed in inferring the viscosity structure of the Earth's mantle from observations of glacial isostatic adjustment (GIA). We first construct standard viscosity models with an average upper-mantle viscosity ({\\bar{η }_{{{um}}}}) of 2 × 1020 Pa s, a typical value for the oceanic upper-mantle viscosity, satisfying the observationally derived three GIA-related observables, GIA-induced rate of change of the degree-two zonal harmonic of the geopotential, {\\dot{J}_2}, and differential relative sea level (RSL) changes for the Last Glacial Maximum sea levels at Barbados and Bonaparte Gulf in Australia and for RSL changes at 6 kyr BP for Karumba and Halifax Bay in Australia. Standard viscosity models inferred from three GIA-related observables are characterized by a viscosity of ˜1023 Pa s in the deep mantle for an assumed viscosity at 670 km depth, ηlm(670), of (1 - 50) × 1021 Pa s. Postglacial RSL changes at Southport, Bermuda and Everglades in the intermediate region of the North American ice sheet, largely dependent on its gross melting history, have a crucial potential for inference of a viscosity jump at 670 km depth. The analyses of these RSL changes based on the viscosity models with {\\bar{η }_{{{um}}}} ≥ 2 × 1020 Pa s and lower-mantle viscosity structures for the standard models yield permissible {\\bar{η }_{{{um}}}} and ηlm (670) values, although there is a trade-off between the viscosity and ice history models. Our preferred {\\bar{η }_{{{um}}}} and ηlm (670) values are ˜(7 - 9) × 1020 and ˜1022 Pa s, respectively, and the {\\bar{η }_{{{um}}}} is higher than that for the typical value of oceanic upper mantle, which may reflect a moderate laterally heterogeneous upper-mantle

  2. 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.

  3. Initiation of the Andean orogeny by lower mantle subduction

    Science.gov (United States)

    Faccenna, C.; Oncken, O.; Holt, A.; Becker, T. W.

    2017-12-01

    The Cordillera of the Andes is a double-vergent orogenic belt built up by thickening of South American plate crust. Several models provide plausible explanations for the evolution of the Andes, but the reason why shortening started at 50 Ma is still unclear. We explore the evolution of the subduction zone through time by restoring the position of the Nazca trench in an absolute reference frame, comparing its position with seismic tomography models and balancing the evolution of the subducting slab. Reconstructions show that the slab enters into the lower mantle at 50+10 Ma, and then progressed, moving horizontally at shallow lower mantle depth while thickening and folding in the transition zone. We test this evolutionary scenario by numerical models, which illustrate that compression in the upper plate emerges once the slab is anchored in the lower mantle. We conclude that onset of significant shortening and crustal thickening in the Andes and its sustained action over tens of million years is related to the penetration of the slab into the lower mantle, producing a slowdown of lateral slab migration, and dragging the upper plate against the subduction zone by large-scale return flow.

  4. 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

  5. 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

  6. Ambient Noise Tomography of Southern California Images Dipping San Andreas-Parallel Structure and Low-Velocity Salton Trough Mantle

    Science.gov (United States)

    Barak, S.; Klemperer, S. L.; Lawrence, J. F.

    2014-12-01

    Ambient noise tomography (ANT) images the entire crust but does not depend on the spatial and temporal distribution of events. Our ANT high-resolution 3D velocity model of southern California uses 849 broadband stations, vastly more than previous studies, and four years of data, 1997-1998, 2007, and 2011, chosen to include our own broadband Salton Seismic Imaging Project, a 40-station transect across the Salton Trough, as well as other campaign stations in both Mexico and the U.S.A., and permanent stations. Our shear-wave model has 0.05° x 0.05° lateral and 1 km vertical blocks. We used the Harvard Community Velocity Model (CVM-H) as the initial model for the inversion. We show significant differences relative to the CVM-H model, especially in the lower crust and upper mantle. We observe prominent low-velocity anomalies in the upper mantle under the Salton Buttes and Cerro Prieto geothermal fields, indicating high-temperatures and possibly partial-melt. Similar low-velocity zones have been previously observed along the Gulf of California. We also observe vertical to gradually dipping lateral velocity contrasts in the lower crust under the southern part of the San Andreas Fault. The east to northeast dip may represent crustal fabric sheared by movement of the Pacific plate under the North American plate prior to the initiation of transform motion.

  7. 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.

  8. CO2, carbonate-rich melts, and brines in the mantle

    Directory of Open Access Journals (Sweden)

    Maria-Luce Frezzotti

    2014-09-01

    Full Text Available This paper reviews the origin and evolution of fluid inclusions in ultramafic xenoliths, providing a framework for interpreting the chemistry of mantle fluids in the different geodynamic settings. Fluid inclusion data show that in the shallow mantle, at depths below about 100 km, the dominant fluid phase is CO2 ± brines, changing to alkali-, carbonate-rich (silicate melts at higher pressures. Major solutes in aqueous fluids are chlorides, silica and alkalis (saline brines; 5–50 wt.% NaCl eq.. Fluid inclusions in peridotites record CO2 fluxing from reacting metasomatic carbonate-rich melts at high pressures, and suggest significant upper-mantle carbon outgassing over time. Mantle-derived CO2 (±brines may eventually reach upper-crustal levels, including the atmosphere, independently from, and additionally to magma degassing in active volcanoes.

  9. Geoelectromagnetic investigation of the earth’s crust and mantle

    CERN Document Server

    Rokityansky, Igor I

    1982-01-01

    Electrical conductivity is a parameter which characterizes composition and physical state of the Earth's interior. Studies of the state equations of solids at high temperature and pressure indicate that there is a close relation be­ tween the electrical conductivity of rocks and temperature. Therefore, measurements of deep conductivity can provide knowledge of the present state and temperature of the Earth's crust and upper mantle matter. Infor­ mation about the temperature of the Earth's interior in the remote past is derived from heat flow data. Experimental investigation of water-containing rocks has revealed a pronounced increase of electrical conductivity in the temperature range D from 500 to 700 DC which may be attributed to the beginning of fractional melting. Hence, anomalies of electrical conductivity may be helpful in identitying zones of melting and dehydration. The studies of these zones are perspective in the scientific research of the mobile areas of the Earth's crust and upper mantle where t...

  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. Joint Inversion Of Local And Teleseismic Data For The Crust And Mantle Structure Of The Chinese Capital Region

    Science.gov (United States)

    Huang, J.; Zhao, D.

    2004-12-01

    . Our tomographic images of the deep crust and upper mantle layers also show different velocity features under different tectonic units. In the Yanshan uplift, a high-V patch is visible from the crust to about 300 km depth, which may reflect that the Yanshan uplift is a stable block without strong earthquakes. In the North China Basin, especially around Beijing, Tianjin and Tangshan,broad low-V anomalies are visible in the lower crust and at depths of 50¡«100 km. Beneath the Bohai Bay, low-V anomalies exist and extend down to about 120 km depth. These results suggest that the lithosphere becomes thinner in this region. From the Taihangshan uplift to the Shanxi rift low-V anomalies exist from the uppermost mantle to about 300 km depth. In this region, lava rocks are distributed broadly and the Datong volcano is located. In addition, most of the large earthquakes, such as the 1976 Tangshan earthquake and the 1679 Sanhe earthquake (M 8.0), generally occurred in high-V areas in the upper to middle crust. However, in the lower crust and uppermost mantle under the source zones of the large earthquakes, low-V and high-conductivity anomalies exist. This result suggests the occurrence of strong earthquakes is related to the deep structure and processes in the deep crust and upper mantle.

  12. Shallow mantle melt stagnation under Gakkel Ridge

    Science.gov (United States)

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

    2003-04-01

    Few studies have been devoted to abyssal plagioclase peridotites, despite their relatively high abundance (30% of AP). Their origin is still unresolved, probably because intense alteration sets limits to spatially controlled geochemical analysis and obliterates textural relationships. Impregnation by a melt is the most widely accepted theory whereas other studies propose an origin by retrogression from spinel to plagioclase facies conditions. During the AMORE cruise along Gakkel Ridge in summer 2001, a dredge haul recovered spinel and plagioclase lherzolites in the axial valley of the amagmatic area. Their exceptional freshness has allowed to analyse all mineral phases. Plagioclase-bearing and -free samples are coarse-grained cpx-rich lherzolites. The plagioclase lherzolites show a wide range of modal plagioclase-contents and often showes textures related to impregnation. Noticeable are the common symplectite textures in the plagioclase peridotites, mostly opx-plag around cpx grains but also one ol-plag around cpx, suggesting a breakdown origin. The spinel lherzolites are characterised by low spinel-Cr# (˜16) and homogeneous flat cpx REE-patterns (~6 x CI). The plagioclase peridotites display strong compositional heterogeneities with pronounced core-rim variations in major and trace elements. Trace element variations in cpx show consistent correlations with textures as contact with plagioclase or symplectite formation. The An-contents of plagioclase range from 76 to 94, spinel Cr# from 10 to 48. Plagioclase trace element data reveal low concentrations for the LREE and no positive Sr-anomaly. Therefore it suggests an impregnation origin for most of the plagioclase by an already fractionated and depleted melt. Yet a minor breakdown component can be observed which was probably triggered by the impregnation. The inferred composition of this melt cannot be correlated with the nearest basalts in this region nor with a melt produced by melting of the spinel lherzolites.

  13. 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.

  14. 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.

  15. Partial melting of stagnant oceanic lithosphere in the mantle transition zone and its geophysical implications

    Science.gov (United States)

    Zhang, Yanfei; Wang, Chao; Jin, Zhenmin; Zhu, Lüyun

    2017-11-01

    Widespread low velocity anomalies have been observed in the upper mantle around many oceanic subduction zones. Fluid or melt released from a stagnant slab may have contributed to the formation of these anomalies. Furthermore, slab partial melting or dehydration is also thought to be closely related to the origin of intraplate volcanoes (i.e., Changbaishan). However, experimental evidence on the process of slab partial melting is very limited. Here, our experimental results show that partial melting of stagnant oceanic lithosphere may occurs for temperatures above 1300-1400 °C, with residual phases composed of wadsleyite/ringwoodite + garnet + clinopyroxene/stishovite/akimotite. The density of melt was approximately 1.0-1.5 g/cm3 less dense than the surrounding mantle, which provided a buoyancy force for ascent to the upper mantle across the 410-km seismic discontinuity. The ascending melt may react with mantle peridotite, leading to the formation of a variably metasomatized mantle, which may contribute to the formation of the observed low velocity anomalies above stagnant slab. Re-melting of the metasomatized mantle may have contributed to the origin of the intraplate volcanoes, e.g., Changbaishan volcanoes. We suggest that partial melting of stagnant oceanic lithosphere in the MTZ may have close relations with the origin of the big mantle wedge beneath eastern China.

  16. The upper to uppermost Cenomanian oceanic anoxic event: a review and an interpretation involving a seawater stratification by the CO{sub 2} of mantle origin; L`evenement oceanique anoxique du Cenomanien superieur-terminal: une revue et une interpretation mettant en jeu une stratification des eaux marines par le CO{sub 2} mantellique

    Energy Technology Data Exchange (ETDEWEB)

    Busson, G.; Cornee, A. [Laboratoire de Geologie du Museum, 75 - Paris (France)

    1996-12-31

    Oil exploration data have revealed the exceptional richness of the middle Cretaceous in source rocks worldwide. Oceanic drillings have shown the existence of oceanic anoxic events (OAE) well defined in time. This study analyzes the OAE 2 event dated from the upper Cenomanian-lower Turonian. This event has been recognized in numerous sites from the northern, central and southern Atlantic and punctually in the Pacific and Indian oceans. It occurs in both numerous deep oceanic sites and orogenic zones, and stable platforms covered by epeiric seas. It coincides with a sea level rise which is one of the most sudden and highest in Phanerozoic times and it stands out as a remarkable episode of massive faunal extinction which led to the deposition of organic matter of marine planktonic dominant nature. The first part of the study recalls the previous interpretations of this event (oceanic stratification, euxinic conditions, spreading of an oxygen minimum zone, greenhouse climate effect, sluggish atmospheric and oceanic circulations, high planktonic production, great oceanic overturns, marginal or general upwellings, marine transgressions on epeiric areas etc..). The second part gives the basis of the new hypothesis: connection between separated seas due to the transgression, retreat of evaporite facies, high sea-floor spreading rates, intense volcanic activity and high mantle outgassing with huge CO{sub 2} influxes. The last part describes the proposed interpretation: CO{sub 2} accumulation in deep and intermediate waters and sea overflows on marginal and continental areas which led to a rise of the CO{sub 2}-rich hypolimnion. (J.S.) 236 refs.

  17. Traveltime Dispersion in an Isotropic Elastic Mantle: Dominance of the Lower Mantle Signal in Differential-frequency Time Residuals

    Science.gov (United States)

    Schuberth, B. S. A.; Zaroli, C.; Nolet, G.

    2014-12-01

    We study wavefield effects in elastic isotropic 3-D seismic structures derived from the temperature field of a high resolution mantle circulation model. More specifically, we quantify the structural dispersion of traveltime residuals of direct P- and S-waves in a model with realistic length-scales and magnitudes of the variations in seismic velocities and density. 3-D global wave propagation is simulated using a spectral element method, and traveltime residuals are measured in four different frequency bands by cross-correlation of 3-D and 1-D synthetic waveforms. Intrinsic (dissipative) attenuation is deliberately neglected, so that any variation of traveltimes with frequency can be attributed to structural effects. Additional simulations are performed for a model in which 3-D structure is removed in the upper 800 km to isolate the dispersion signal of the lower mantle. One question that we address is whether the structural length-scales inherent to a vigorously convecting mantle give rise to significant body-wave dispersion. In our synthetic dataset, the difference between long-period and short-period traveltime residuals generally increases with increasing short-period residual. However, we do not find an exact linear dependence, and in case of P-waves even non-monotonic behaviour. At largest short-period residuals, average dispersion is on the order of 2 s for both P- and S-waves and even larger when structure is confined to the lower mantle. Dispersion also appears to be asymmetric; that is, larger for negative than for positive residuals. The standard deviations of both P- and S-wave residuals also increase with increasing period and we discuss possible explanations for this behaviour. Overall, wavefield effects in both models are generally stronger for P-waves than for S-waves at the same frequencies. We also find that for certain combinations of periods, the difference between the respective residuals is very similar between the "whole mantle" and the "lower

  18. 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

  19. The importance of grain size to mantle dynamics and seismological observations

    Science.gov (United States)

    Gassmoeller, R.; Dannberg, J.; Eilon, Z.; Faul, U.; Moulik, P.; Myhill, R.

    2017-12-01

    Grain size plays a key role in controlling the mechanical properties of the Earth's mantle, affecting both long-timescale flow patterns and anelasticity on the timescales of seismic wave propagation. However, dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity, and a limited treatment of changes in mineral assemblage. We study grain size evolution, its interplay with stress and strain rate in the convecting mantle, and its influence on seismic velocities and attenuation. Our geodynamic models include the simultaneous and competing effects of dynamic recrystallization resulting from dislocation creep, grain growth in multiphase assemblages, and recrystallization at phase transitions. They show that grain size evolution drastically affects the dynamics of mantle convection and the rheology of the mantle, leading to lateral viscosity variations of six orders of magnitude due to grain size alone, and controlling the shape of upwellings and downwellings. Using laboratory-derived scaling relationships, we convert model output to seismologically-observable parameters (velocity, attenuation) facilitating comparison to Earth structure. Reproducing the fundamental features of the Earth's attenuation profile requires reduced activation volume and relaxed shear moduli in the lower mantle compared to the upper mantle, in agreement with geodynamic constraints. Faster lower mantle grain growth yields best fit to seismic observations, consistent with our re-examination of high pressure grain growth parameters. We also show that ignoring grain size in interpretations of seismic anomalies may underestimate the Earth's true temperature variations.

  20. Young planets under extreme UV irradiation. I. Upper atmosphere modelling of the young exoplanet K2-33b

    Science.gov (United States)

    Kubyshkina, D.; Lendl, M.; Fossati, L.; Cubillos, P. E.; Lammer, H.; Erkaev, N. V.; Johnstone, C. P.

    2018-04-01

    The K2-33 planetary system hosts one transiting 5 R⊕ planet orbiting the young M-type host star. The planet's mass is still unknown, with an estimated upper limit of 5.4 MJ. The extreme youth of the system (stage when the planet is exposed to an extremely high level of high-energy radiation emitted by the host star. We perform a series of 1D hydrodynamic simulations of the planet's upper atmosphere considering a range of possible planetary masses, from 2 to 40 M⊕, and equilibrium temperatures, from 850 to 1300 K, to account for internal heating as a result of contraction. We obtain temperature profiles mostly controlled by the planet's mass, while the equilibrium temperature has a secondary effect. For planetary masses below 7-10 M⊕, the atmosphere is subject to extremely high escape rates, driven by the planet's weak gravity and high thermal energy, which increase with decreasing mass and/or increasing temperature. For higher masses, the escape is instead driven by the absorption of the high-energy stellar radiation. A rough comparison of the timescales for complete atmospheric escape and age of the system indicates that the planet is more massive than 10 M⊕.

  1. Improvement in upper leg muscle strength underlies beneficial effects of exercise therapy in knee osteoarthritis: secondary analysis from a randomised controlled trial.

    Science.gov (United States)

    Knoop, J; Steultjens, M P M; Roorda, L D; Lems, W F; van der Esch, M; Thorstensson, C A; Twisk, J W R; Bierma-Zeinstra, S M A; van der Leeden, M; Dekker, J

    2015-06-01

    Although exercise therapy is effective for reducing pain and activity limitations in patients with knee osteoarthritis (OA), the underlying mechanisms are unclear. This study aimed to evaluate if improvements in neuromuscular factors (i.e. upper leg muscle strength and knee proprioception) underlie the beneficial effects of exercise therapy in patients with knee OA. Secondary analyses from a randomised controlled trial, with measurements at baseline, 6 weeks, 12 weeks and 38 weeks. Rehabilitation centre. One hundred and fifty-nine patients diagnosed with knee OA. Exercise therapy. Changes in pain [numeric rating scale (NRS)] and activity limitations [Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) physical function subscale and get-up-and-go test] during the study period. Independent variables were changes in upper leg muscle strength and knee joint proprioception (i.e. motion sense) during the study period. Longitudinal regression analyses (generalised estimating equation) were performed to analyse associations between changes in upper leg muscle strength and knee proprioception with changes in pain and activity limitations. Improved muscle strength was significantly associated with reductions in NRS pain {B coefficient -2.5 [95% confidence interval (CI) -3.7 to -1.4], meaning that every change of 1 unit of strength was linked to a change of -2.5 units of pain}, WOMAC physical function (-8.8, 95% CI -13.4 to -4.2) and get-up-and-go test (-1.7, 95% CI -2.4 to -1.0). Improved proprioception was not significantly associated with better outcomes of exercise therapy (P>0.05). Upper leg muscle strengthening is one of the mechanisms underlying the beneficial effects of exercise therapy in patients with knee OA. Copyright © 2014 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved.

  2. 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

    restricted volume in the multi-dimensional parameter space. In order to constrain concentration of minerals we used equilibrium of mineral associations for selected P-T condition obtained by free Gibbs energy minimization (c.f. Stixrude & Lithgow-Bertelloni, 2005). We also considered the mineralogical composition of upper mantle xenoliths, although the representativeness of xenoliths in Precambrian rocks could be treated with care, if one tries to describe the modern mantle. As a first step, we estimated 1D model of mineralogical composition in the depth range of 35-350 km using the IASP91 reference model (Kennett & Engdahl, 1991). Both the P- and S- wave velocities were used for inversion, in order to improve the reliability of the model. More comprehensive result could be obtained if density distribution is involved. In our study we used the 1D PEMC density model (Dziewonski, Hales & Lapwood, 1975) as it is the most adequate for the continental lithosphere. The 1D modeling showed that the garnet lherzolite model (forsterite, fayalite, enstatite, ferrosilite, diopside, jadeite, pyrope) can be considered as a basic one. The end-members of olivine and orthopyroxene solutions were included with the aim of Fe/Mg ratio estimation. Testing with modified models including hedenbergite, harzburgite spinel, etc. showed that these minerals have no significant influence on bulk elastic properties. Selected set of minerals allows modelling the most species of peridote-pyroxenite associations known from xenoliths investigations (Kukkonen, Kuusisto, Lehtonen, & Peltonen, 2008; Lehtonen, O'Brien, Peltonen, Johanson, & Pakkanen, 2004). However, there exist also a number of evidences for mantle eclogite xenoliths from the region under study and its surrounding (Lehtonen et al., 2004; Peltonen, Kinnunen, & Huhma, 2002). That is why we also made modelling for garnet-clinopyroxene model of eclogite. The volumetric mineral compositions obtained were transformed into weight concentration of rock

  3. 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

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

    Science.gov (United States)

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

    2017-04-01

    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

  5. Constraining the Composition of the Subcontinental Lithospheric Mantle Beneath the East African Rift: FTIR Analysis of Water in Spinel Peridotite Mantle Xenoliths

    Science.gov (United States)

    Erickson, Stephanie Gwen; Nelson, Wendy R.; Peslier, Anne H.; Snow, Jonathan E.

    2014-01-01

    The East African Rift System was initiated by the impingement of the Afar mantle plume on the base of the non-cratonic continental lithosphere (assembled during the Pan-African Orogeny), producing over 300,000 kmof continental flood basalts approx.30 Ma ago. The contribution of the subcontinental lithospheric mantle (SCLM) to this voluminous period of volcanism is implied based on basaltic geochemical and isotopic data. However, the role of percolating melts on the SCLM composition is less clear. Metasomatism is capable of hybridizing or overprinting the geochemical signature of the SCLM. In addition, models suggest that adding fluids to lithospheric mantle affects its stability. We investigated the nature of the SCLM using Fourier transform infrared spectrometry (FTIR) to measure water content in mantle xenoliths entrained in young (1 Ma) basaltic lavas from the Ethiopian volcanic province. The mantle xenoliths consist dominantly of spinel lherzolites and are composed of nominally anhydrous minerals, which can contain trace water as H in mineral defects. Eleven mantle xenoliths come from the Injibara-Gojam region and two from the Mega-Sidamo region. Water abundances of olivines in six samples are 1-5ppm H2O while the rest are below the limit of detection (<0.5 ppm H2O); orthopyroxene and clinopyroxene contain 80-238 and 111-340 ppm wt H2O, respectively. Two xenoliths have higher water contents - a websterite (470 ppm) and dunite (229 ppm), consistent with involvement of ascending melts. The low water content of the upper SCLM beneath Ethiopia is as dry as the oceanic mantle except for small domains represented by percolating melts. Consequently, rifting of the East African lithosphere may not have been facilitated by a hydrated upper mantle.

  6. Constraining the Composition of the Subcontinental Lithospheric Mantle Beneath the East African Rift: FTIR Analysis of Water in Spinel Peridotite Mantle Xenoliths

    Science.gov (United States)

    Erickson, S. G.; Nelson, W. R.; Peslier, A. H.; Snow, J. E.

    2014-12-01

    The East African Rift System was initiated by the impingement of the Afar mantle plume on the base of the non-cratonic continental lithosphere (assembled during the Pan-African Orogeny), producing over 300,000 km3 [1] of continental flood basalts ~30 Ma ago. The contribution of the subcontinental lithospheric mantle (SCLM) to this voluminous period of volcanism is implied based on basaltic geochemical and isotopic data. However, the role of percolating melts on the SCLM composition is less clear. Metasomatism is capable of hybridizing or overprinting the geochemical signature of the SCLM. In addition, models suggest that adding fluids to lithospheric mantle affects its stability [e.g. 2, 3]. We investigated the nature of the SCLM using Fourier transform infrared spectrometry (FTIR) to measure water content in mantle xenoliths entrained in young (1 Ma) basaltic lavas from the Ethiopian volcanic province. The mantle xenoliths consist dominantly of spinel lherzolites and are composed of nominally anhydrous minerals, which can contain trace water as H in mineral defects. Eleven mantle xenoliths come from the Injibara-Gojam region and two from the Mega-Sidamo region. Water abundances of olivines in six samples are 1-5ppm H2O while the rest are below the limit of detection (<0.5 ppm H2O); orthopyroxene and clinopyroxene contain 80-238 and 111-340 ppm wt H2O, respectively. Two xenoliths have higher water contents - a websterite (470 ppm) and dunite (229 ppm), consistent with involvement of ascending melts. The low water content of the upper SCLM beneath Ethiopia is as dry as the oceanic mantle [2] except for small domains represented by percolating melts. Consequently, rifting of the East African lithosphere may not have been facilitated by a hydrated upper mantle. [1] Hoffman et al., 1997 Nature 389, 838-841. [2] Peslier et al., 2010 Nature 467, 78-81. [3] Lee et al., 2011 AREPS 39, 59-90.

  7. Toward Near Real-Time Tomography of the Upper Mantle

    Science.gov (United States)

    Debayle, E.; Dubuffet, F.

    2014-12-01

    We added a layer of automation to the Debayle and Ricard (2012)'s waveform modeling scheme for fundamental and higher mode surface waves in the period range 50-160s. We processed all the Rayleigh waveforms recorded on the LHZ channel by the virtual networks GSN_broadband, FDSN_all, and US_backbone between January 1996 and December 2013. Six millions of waveforms were obtained from IRIS DMC. We check that all the necessary information (instrument response, global CMT determination) is available and that each record includes a velocity window which encompasses the surface wave. Selected data must also have a signal-to-noise ratio greater than 3 in a range covering at least the periods between 50 and 100 s. About 3 millions of waveforms are selected (92% of the rejections are due to the signal to noise ratio criterion) and processed using Debayle and Ricard (2012)'s scheme, which allows the successful modeling of about 1.5 millions of waveforms. We complete this database with 60,000 waveforms recorded between 1976 and 1996 or after 1996 during various temporary experiments and with 161,730 Rayleigh waveforms analyzed at longer period, between 120 and 360 s. The whole data set is inverted using Debayle and Sambridge (2004)'s scheme to produce a 3D shear velocity model. A simple shell command "update_tomo" can then update our seismic model in an entirely automated way. Currently, this command checks from the CMT catalog what are the potential data available at the GSN_broadband, FDSN_all, and US_backbone virtual networks, uses web services to request these data from IRIS DMC and applies the processing chain described above to update our seismic model. We plan to update our seismic model on a regular basis in a near future, and to make it available on the web. Our most recent seismic model includes azimuthal anisotropy, achieves a lateral resolution of few hundred kilometers and a vertical resolution of a few tens of kilometers. The correlation with surface tectonics is very strong in the uppermost 200 km. Regions deeper than 400 km show no velocity contrasts larger than 1%, except for high velocity slabs which produce broad high velocity regions within the transition zone. The use of higher modes and long period surface waves allows us to extract the shear velocity structure down to about 1000 km depth.

  8. 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.

  9. 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

  10. 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

  11. 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...

  12. Lithosphere-mantle coupling and the dynamics of the Eurasian Plate

    NARCIS (Netherlands)

    Warners-Ruckstuhl, K.N.; Govers, R.; Wortel, R.

    2012-01-01

    Mechanical equilibrium of tectonic plates implies that lithospheric edge and body forces are balanced by forces arising from interaction with the underlying mantle. We use this quantitative physical relation to integrate existing modelling approaches of lithosphere dynamics and mantle flow into a

  13. Simultaneous Inversion of Mantle Mode Splitting Coefficients for Vs, Vp and ρ Using the Neighbourhood Algorithm.

    Science.gov (United States)

    Rousset, S. C.; Romanowicz, B.

    2003-12-01

    Unlike travel times or waveform data, normal mode data are directly sensitive to the density of the Earth. However, the sensitivity kernels for density are much smaller than those for velocities, so the controversy about the possibility of resolution of the mantle's density is vivid, especially since the publication of model SPRD6 (Ishii and Tromp, 1999) whose high density structures corresponding with the "plumes" under Pacific and Africa would have important consequences on deep mantle dynamics. Using least squares inversion, several authors (e.g. Resovsky and Ritzwoller, 1999, Kuo and Romanowicz, 2002) pointed out significant trade-offs between velocity and density structure. Using a stochastic method may end the controversy about the resolution of density by estimating the posterior probability density of the parameter space. Such an approach was used by Resovsky and Ritzwoller (2002) who concluded in the non resolution of the density but did not investigate further. Here we investigate the effect of other parameterizations and of an extended dataset (Widmer, 2002). In particular, we look at the possibility of resolving a spline-based shear velocity model and the scaling relations d(ln Vp)/d(ln Vs) and d(ln ρ )/d(ln Vs). We search for 3 scaling parameters (lowermost, middle and upper mantle) and allow spatial variations of these parameters as each degree 2 spherical harmonic coefficient is considered separately. We present the results of the sampling of the parameter space and of the appraising of the ensemble generated in the form of marginal probabilities for the different parameters.

  14. Investigating the Mantle Source of the Lunar Crater Volcanic Field, Nevada: Evidence of a Thermal Plume?

    Science.gov (United States)

    Lee, J. W.; Roden, M.

    2016-12-01

    The Easy Chair Crater (ECC), located within the Lunar Crater Volcanic Field (LCVF) in central Nevada is particularly interesting because of the unusually high equilibrium temperatures and strain recorded by the mantle-derived xenoliths at LCVF1. In addition, a gravity and elevation anomaly suggests the possibility of an underlying thermal plume in the region2. In order to determine if the rocks at ECC are geochemically similar to rocks from other plume-related regions, we analyzed melt inclusions and olivine phenocrysts collected from basalts near the crater. Chlorine amounts in melt inclusions were normalized to the highly incompatible K to produce a ratio that is insensitive to crystallization within or along the walls of the inclusion3. Because Cl is implicated in lithosphere recycling, the Cl/K ratio can be used to differentiate magmatic source components. Initial results (Fig. 1) indicate that basalts from ECC are geochemically more similar to ocean island basalts than to MORB or arc basalts. Elemental ratios in olivine phenocrysts from basaltic magmas can be used to determine the petrology of the source rock for particular silicate melts. In turn, petrology of mantle sources is thought to correlate with source nature (e.g., plume versus upper mantle)4. Specifically, Ni and Mn amounts were evaluated in order to determine if magma sources were pyroxenite-rich. Preliminary calculations of the wt. fraction of pyroxenite in the source of ECC basalts ranged from 0.13 to 0.68 indicating the possibility of a significant amount of pyroxenite in the magmatic source which would be expected if a plume was present beneath LCVF. References:1Smith, D. (2000) JGR 105: 16769; 2Saltus, R.W. & Thompson, G.A. (1995) Tectonics 14:1235; 3Patiño Douce, A.E. & Roden, M.F. (2006) Geochim Cosmochim Acta 70: 3173; 4Gurenko et al. (2010) Contrib Mineral Petrol 159: 689

  15. Time Dependent Geoid Constraints Upon Mantle Viscosity Stratification

    Science.gov (United States)

    Harlow, C.; Peltier, W. R.

    2004-12-01

    The global measurement of the time dependence of geoid height that is being provided by the GRACE satellite system that is now in space will eventually provide the basis for considerably more accurate inversions for mantle viscosity structure than are now possible. However, existing data on the time dependence of geoid height based upon the results of satellite laser ranging already provide very strong constraints upon the effective viscosity of the of the deepest mantle, especially when these are conbined with observations of the spectrum of relaxation times that characterize the process of glacial isostatic adjustment (GIA). Such data, by themselves, very tightly constrain the viscosity structure in the upper mantle and transition zone. We will describe a series of new analyses of the expected global pattern of geoid height time dependence based upon the recently published refined model of the GIA process denoted ICE-5G(VM2), a model based upon a significant refinement of the ICE-4G(VM2) precursor ( see W.R. Peltier, Ann. Rev. Earth and Planet. Sci., 32, 111-149, 2004). The impact of the new model of surface loading upon the mantle viscosity inverse problem turns out to be both interesting and significant.

  16. Dehydrogenation of goethite in Earth's deep lower mantle

    Science.gov (United States)

    Hu, Qingyang; Kim, Duck Young; Liu, Jin; Meng, Yue; Yang, Liuxiang; Zhang, Dongzhou; Mao, Wendy L.; Mao, Ho-kwang

    2017-02-01

    The cycling of hydrogen influences the structure, composition, and stratification of Earth’s interior. Our recent discovery of pyrite-structured iron peroxide (designated as the P phase) and the formation of the P phase from dehydrogenation of goethite FeO2H implies the separation of the oxygen and hydrogen cycles in the deep lower mantle beneath 1,800 km. Here we further characterize the residual hydrogen, x, in the P-phase FeO2Hx. Using a combination of theoretical simulations and high-pressure-temperature experiments, we calibrated the x dependence of molar volume of the P phase. Within the current range of experimental conditions, we observed a compositional range of P phase of 0.39 hydrogen and lower x, suggesting that dehydrogenation could be approaching completion at the high-temperature conditions of the lower mantle over extended geological time. Our observations indicate a fundamental change in the mode of hydrogen release from dehydration in the upper mantle to dehydrogenation in the deep lower mantle, thus differentiating the deep hydrogen and hydrous cycles.

  17. 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

    Viscosity of the mantle is traditionally inferred from geophysical data. However the geophysical approach provides only a spatially averaged information. At high temperature, viscosity is mainly controlled by the diffusivity of the slowest species in the minerals forming the rock assemblage (diffusion creep regime). Therefore to characterize the viscosity of the mantle, one can take a direct approach using the available experimental diffusion data in the most common mantle minerals. In this way the viscosity is expressed as a function of pressure, temperature and mineralogical assemblage. One problem with this method is that the uncertainty (experimental error) can have a significant effect on the characterization of the viscosity model. Here we present our simplified model for the viscosity of the mantle based on the diffusion data in olivine (alpha, beta, gamma) magnesio-wüstite and perovskite. In the upper mantle viscosity is assumed to be controlled by the most abundant mineral (olivine) and by the fastest diffusion process between grain boundary and volume diffusion of silicon, which is considered to be the slowest diffusing species. In the lower mantle the viscosity of the mantle assemblage is determined by a weighted average of the properties in magnesio-wüstite and perovskite. The initial model has been applied to study the thermal history of the mantle and the CMB temperature using a parametrized mantle convection model combined with a thermodynamic formulation, and then refined based on the results of the thermal model. In particular the thermal evolution model must satisfy certain criteria that define the melting temperature requirement in the upper mantle in the past (Archean) and more recent times. Some diffusion parameters have been adjusted within the experimental uncertainty and we have opted for the homogeneous stress model to construct the viscosity of the lower mantle. Our results show a steady increase of viscosity vs depth in the lower mantle

  18. Traveltime dispersion in an isotropic elastic mantle: strong lower-mantle signal in differential-frequency residuals

    Science.gov (United States)

    Schuberth, Bernhard S. A.; Zaroli, Christophe; Nolet, Guust

    2015-12-01

    We study wavefield effects of direct P- and S-waves in elastic and isotropic 3-D seismic structures derived from the temperature field of a high-resolution mantle circulation model. More specifically, we quantify the dispersion of traveltime residuals caused by diffraction in structures with dynamically constrained length scales and magnitudes of the lateral variations in seismic velocities and density. 3-D global wave propagation is simulated using a spectral element method. Intrinsic attenuation (i.e. dissipation of seismic energy) is deliberately neglected, so that any variation of traveltimes with frequency can be attributed to structural effects. Traveltime residuals are measured at 15, 22.5, 34 and 51 s dominant periods by cross-correlation of 3-D and 1-D synthetic waveforms. Additional simulations are performed for a model in which 3-D structure is removed in the upper 800 km to isolate the dispersion signal of the lower mantle. We find that the structural length scales inherent to a vigorously convecting mantle give rise to significant diffraction-induced body-wave traveltime dispersion. For both P- and S-waves, the difference between long-period and short-period residuals for a given source-receiver pair can reach up to several seconds for the period bands considered here. In general, these `differential-frequency' residuals tend to increase in magnitude with increasing short-period delay. Furthermore, the long-period signal typically is smaller in magnitude than the short-period one; that is, wave-front healing is efficient independent of the sign of the residuals. Unlike the single-frequency residuals, the differential-frequency residuals are surprisingly similar between the `lower-mantle' and the `whole-mantle' model for corresponding source-receiver pairs. The similarity is more pronounced in case of S-waves and varies between different combinations of period bands. The traveltime delay acquired in the upper mantle seems to cancel in these differential

  19. Simple Method for Assessing Spread of Flood Prone Areas under Historical and Future Rainfall in the Upper Citarum Watershed

    Directory of Open Access Journals (Sweden)

    Bambang Dwi Dasanto

    2014-06-01

    Full Text Available From 1931 to 2010 the flood frequency in Upper Citarum Watershed had increased sharply indicating the decline of the wateshed quality. With the change of climate, risk of the flood may get worse. This study aims to determine effective rainfall that caused flooding and to evaluate the impact of future rainfall changes on the flood prone areas. Effective rainfall which contributes to direct runoff (DRO and leads to flooding was determined using regression equation relating the DRO and cumulative rainfall of a number of consecutive days. Mapping the flood prone areas was developed using the GIS techniques. Results showed that the effective rainfall which caused flooding was the rainfall accumulation for four consecutive days before occurrence of peak of DRO. The percentage of accuracy between estimated and actual flood maps was about 76.9%. According to historical rainfall, the flood prone areas spreaded at right and left directions of the Upstream Citarum River. If this area experiences the climate change, the frequency and flood extents will increase. This study can only identify locations and possibility of flood occurrence but it cannot demonstrate widespread of flood inundation precisely. However, this simple approach can evaluate the flood frequency and intensity quite well.

  20. 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.

  1. 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...

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

    Science.gov (United States)

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

    2006-10-05

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

  3. Quantifying mantle structure and dynamics using plume tracing in seismic tomography

    Science.gov (United States)

    O'Farrell, K. A.; Eakin, C. M.; Jackson, M. G.; Jones, T. D.; Lekic, V.; Lithgow-Bertelloni, C. R.

    2017-12-01

    Directly linking deep mantle processes with surface features and dynamics is a complex problem. Hotspot volcanism gives us surface observables of mantle signatures, but the depth and source of the mantle plumes feeding these hotspots are highly debated. To address these issues, it is necessary to consider the entire journey of a plume through the mantle. By analyzing the behavior of mantle plumes we can constrain the vigor of mantle convection, the net rotation of the mantle and the role of thermal versus chemical anomalies as well as the bulk physical properties such as the viscosity profile. To do this, we developed a new algorithm to trace plume-like features in shear-wave (Vs) seismic tomography models based on picking local minima in the velocity and searching for continuous features with depth. We applied this method to recent tomographic models and find 60+ continuous plume conduits that are > 750 km long. Approximately a third of these can be associated with known hotspots at the surface. We analyze the morphology of these continuous conduits and infer large scale mantle flow patterns and properties. We find the largest lateral deflections in the conduits occur near the base of the lower mantle and in the upper mantle (near the thermal boundary layers). The preferred orientation of the plume deflections show large variability at all depths and indicate no net mantle rotation. Plate by plate analysis shows little agreement in deflection below particular plates, indicating these deflected features might be long lived and not caused by plate shearing. Changes in the gradient of plume deflection are inferred to correspond with viscosity contrasts in the mantle and found below the transition zone as well as at 1000 km depth. From this inferred viscosity structure, we explore the dynamics of a plume through these viscosity jumps. We also retrieve the Vs profiles for the conduits and compare with the velocity profiles predicted for different mantle adiabat

  4. Thymus-directed immunotoxicity of airborne dust particles from Upper Silesia (Poland) under acute extrapulmonary studies in mice

    Energy Technology Data Exchange (ETDEWEB)

    Kozlowska, E. [Warsaw Univ. (Poland); Krzystniak, K. [Universite du Quebec a Montreal, Quebec (Canada); Drela, N. [Warsaw Univ. (Poland)] [and others

    1996-12-27

    Industrial air pollutants from Upper Silesia, Poland, contain over 250 polycyclic and heterocyclic aromatic hydrocarbons and heavy metals, including mutagenic and carcinogenic chemicals that have been shown to from DNA adducts. Over 4 million habitants of Silesia are permanently exposed to the industrial pollution by pulmonary and dermal routes and by contaminated food and water. These chemicals, when examined separately in animals models, were proven immunotoxic. We studied the extrapulmonary immunotoxic potential of a typical mixture of Silesian filter-suspended matter from a selected area, over a specific season and time period. Early changes in the immune system were analyzed in BALB/c mice exposed ip to acute doses of 20-330 mg dust mixture/kg body weight (0.06-1.0 LD50). No major changes were noted for weight and the cellularity of spleen, liver and kidneys. However, dramatic decrease in thymus weight index and thymocyte cell count were noted as early as 24-72 h postexposure, which correlated with almost complete depletion of immature, double-positive CD4{sup +}CD8{sup +} thymocytes. Changes in spleen were less profound; however, increased depletion of B cells over T cells was noted at high doses of the suspended matter. Exposure to the airborne dust also decreased cytokine production by spleen cells, such as interferon-{gamma} (IFN-{gamma}) and tumor necrosis factor-{alpha} (TNF-{alpha}). Overall, a single exposure to Silesian dust, even at the relatively low 0.06 LD50 dose, affected lymphokine production, suppressed B-cell proliferative response, and depleted thymuses of immature, double-positive CD4{sup +}CD8{sup +} cells. A chemical synergism is suspected. To our knowledge, none of the known components of Silesian suspended matter, when examined as a single chemical, was shown to exert such a profound biological effect. 32 refs., 5 figs.

  5. The 2016 Case for Mantle Plumes and a Plume-Fed Asthenosphere (Augustus Love Medal Lecture)

    Science.gov (United States)

    Morgan, Jason P.

    2016-04-01

    discrepancies between idealized plume/hotspot models and geochronological observations will also be briefly discussed. A further consequence of the existence of strong deep mantle plumes is that hot plume material should preferentially pond at the base of the lithosphere, draining towards and concentrating beneath the regions where the lithosphere is thinnest, and asthenosphere is being actively consumed to make new tectonic plates - mid-ocean ridges. This plume-fed asthenosphere hypothesis makes predictions for the structure of asthenosphere flow and anisotropy, patterns of continental edge-volcanism linked to lateral plume drainage at continental margins, patterns of cratonic uplift and subsidence linked to passage from hotter plume-influenced to cooler non-plume-influenced regions of the upper mantle, and variable non-volcanic versus volcanic modes of continental extension linked to rifting above '~1425K cool normal mantle' versus 'warm plume-fed asthenosphere' regions of upper mantle. These will be briefly discussed. My take-home message is that "Mantle Plumes are almost certainly real". You can safely bet they will be part of any successful paradigm for the structure of mantle convection. While more risky, I would also recommend betting on the potential reality of the paradigm of a plume-fed asthenosphere. This is still a largely unexplored subfield of mantle convection. Current observations remain very imperfect, but seem more consistent with a plume-fed asthenosphere than with alternatives, and computational and geochemical advances are making good, falsifiable tests increasingly feasible. Make one!

  6. 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.

  7. Pulses of earthquake activity in the mantle wedge track the route of slab fluid ascent

    Science.gov (United States)

    White, Lloyd; Rawlinson, Nicholas; Lister, Gordon; Tanner, Dominique; Macpherson, Colin; Morgan, Jason

    2016-04-01

    Earthquakes typically record the brittle failure of part of the Earth at a point in space and time. These almost invariably occur within the crust or where the upper surface of subducting lithosphere interacts with the overriding mantle. However, there are also reports of rare, enigmatic earthquakes beneath rifts, above mantle plumes or very deep in the mantle. Here we report another type of mantle earthquake and present three locations where earthquake clusters occur in the mantle wedge overlying active subduction zones. These earthquake clusters define broadly circular to ellipsoidal columns that are 50 km or greater in diameter from depths between ~150 km and the surface. We interpret these rare pulses of earthquakes as evidence of near vertical transport of fluids (and associated flux-melts) from the subducted lithosphere through the mantle wedge. Detailed temporal analysis shows that most of these earthquakes occur over two-year periods, with the majority of events occurring in discrete month-long flurries of activity. As the time and location of each earthquake is recorded, pulses of seismic activity may provide information about the rate of magma ascent from the dehydrated subducted slab to sub-arc/backarc crust. This work indicates that fluids are not transported through the mantle wedge by diapirism, but through sub-vertical pathways facilitated by fracture networks and dykes on monthly to yearly time scales. These rare features move us toward solving what has until now represented a missing component of the subduction factory.

  8. 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.

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

    Science.gov (United States)

    Arcay, Diane

    2017-08-01

    The present study aims at better deciphering the different mechanisms involved in the functioning of the subduction interplate. A 2D thermo-mechanical model is used to simulate a subduction channel, made of oceanic crust, free to evolve. Convergence at constant rate is imposed under a 100 km thick upper plate. Pseudo-brittle and non-Newtonian behaviours are modelled. The influence of the subduction channel strength, parameterized by the difference in activation energy between crust and mantle (ΔEa) is investigated to examine in detail the variations in depth of the subduction plane down-dip extent, zcoup . First, simulations show that numerical resolution may be responsible for an artificial and significant shallowing of zcoup if the weak crustal layer is not correctly resolved. Second, if the age of the subducting plate is 100 Myr, subduction occurs for any ΔEa . The stiffer the crust is, that is, the lower ΔEa is, the shallower zcoup is (60 km depth if ΔEa = 20 kJ/mol) and the hotter the fore-arc base is. Conversely, imposing a very weak subduction channel (ΔEa > 135 J/mol) leads there to an extreme mantle wedge cooling and inhibits mantle melting in wet conditions. Partial kinematic coupling at the fore-arc base occurs if ΔEa = 145 kJ/mol. If the incoming plate is 20 Myr old, subduction can occur under the conditions that the crust is either stiff and denser than the mantle, or weak and buoyant. In the latter condition, cold crust plumes rise from the subduction channel and ascend through the upper lithosphere, triggering (1) partial kinematic coupling under the fore-arc, (2) fore-arc lithosphere cooling, and (3) partial or complete hindrance of wet mantle melting. zcoup then ranges from 50 to more than 250 km depth and is time-dependent if crust plumes form. Finally, subduction plane dynamics is intimately linked to the regime of subduction-induced corner flow. Two different intervals of ΔEa are underlined: 80-120 kJ/mol to reproduce the range of slab

  10. 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.

  11. 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.

  12. 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.

  13. A Plastic Flow and Rheomorfic Differentiation of the Mantle Ultramafic Rocks

    Directory of Open Access Journals (Sweden)

    D. E. Saveliev

    2014-12-01

    Full Text Available In this paper, the general characteristics of morphological features of the ophiolitic ultramafic rock formations are discussed. The ultramafic rocks are the fragments of upper mantle, which were exposed on the surface due to tectonic events. It is shown that their main chemical and structural characteristic is a stratification accompanied by separation of the rheologically weakest dunite bodies usually containing the economic amount of chromite ore. Based on results of conducted analysis, we propose a new hypothesis of petro- and ore genesis in the upper mantle. Using the thermodynamic approach, we developed the rheomorfic model of the differentiation of the mantle matter. This model solves many problems inherent to currently used magmatic or metasomatic models.

  14. The influence of bubble populations generated under windy conditions on the blue-green light transmission in the upper ocean: An exploratory approach

    Science.gov (United States)

    Wang, Chengan; Tan, Jianyu; Lai, Qingzhi

    2016-12-01

    The “blue-green window” in the ocean plays an important role in functions such as communication between vessels, underwater target identification, and remote sensing. In this study, the transmission process of blue-green light in the upper ocean is analyzed numerically using the Monte Carlo method. First, the effect of total number of photons on the numerical results is evaluated, and the most favorable number is chosen to ensure accuracy without excessive costs for calculation. Then, the physical and mathematical models are constructed. The rough sea surface is generated under windy conditions and the transmission signals are measured in the far field. Therefore, it can be conceptualized as a 1D slab with a rough boundary surface. Under windy conditions, these bubbles form layers that are horizontally homogeneous and decay exponentially with depth under the influence of gravity. The effects of bubble populations on the process of blue-green light transmission at different wind speeds, wavelengths, angle of incidence and chlorophyll-a concentrations are studied for both air-incident and water-incident cases. The results of this study indicate that the transmission process of blue-green light is significantly influenced by bubbles under high wind-speed conditions.

  15. 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...

  16. MHD mixed convection and entropy generation of nanofluid filled lid driven cavity under the influence of inclined magnetic fields imposed to its upper and lower diagonal triangular domains

    Energy Technology Data Exchange (ETDEWEB)

    Selimefendigil, Fatih, E-mail: fatih.selimefendigil@cbu.edu.tr [Department of Mechanical Engineering, Celal Bayar University, 45140 Manisa (Turkey); Öztop, Hakan F., E-mail: hfoztop1@gmail.com [Department of Mechanical Engineering, Technology Faculty, Fırat University, 23119 Elazığ (Turkey); Chamkha, Ali J., E-mail: achamkha@pmu.edu.sa [Mechanical Engineering Department, Prince Mohammad Bin Fahd University, Al-Khobar 31952 (Saudi Arabia)

    2016-05-15

    In this study, mixed convection of CuO–water nanofluid filled lid driven cavity having its upper and lower triangular domains under the influence of inclined magnetic fields is numerically investigated. The top horizontal wall of the cavity is moving with constant speed of u{sub w} with +x direction while no-slip boundary conditions are imposed on the other walls of the cavity. The top wall of the cavity is maintained at constant cold temperature of T{sub c} while the bottom wall is at hot temperature of T{sub h} and on the other walls of the cavity are assumed to be adiabatic. The governing equations are solved by using Galerkin weighted residual finite element formulation. Entropy generation is produced by using formulation and integrated with calculated velocities and temperatures. The numerical investigation is performed for a range of parameters: Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of magnetic field (between 0° and 90°) and solid volume fraction of the nanofluid (between 0 and 0.05). Different combinations of Hartmann numbers and inclination angles of the magnetic fields are imposed in the upper and lower triangular domains of the square cavity. It is observed that the local and averaged heat transfer deteriorates when the Richardson number, Hartmann number of the triangular domains increase. When the Hartmann number and magnetic angle of the upper triangle are increased, more deterioration of the averaged transfer is obtained when compared to lower triangular domain. Local and averaged heat transfer increase as the solid volume fraction of the nanoparticles increases and adding nanoparticles is more effective for the local enhancement of the heat transfer when the heat transfer rate is high and convection is not damped with lowering the Hartmann number. Second law analysis of the system for different combinations of flow parameters is also performed. - Highlights: • MHD mixed convection of

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

    Science.gov (United States)

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

    2017-04-01

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

  18. Attenuation of short-period P, PcP, ScP, and pP waves in the earth's mantle

    International Nuclear Information System (INIS)

    Bock, G.; Clements, J.R.

    1982-01-01

    The parameter t* (ratio of body wave travel time to the average quality factor Q) was estimated under various assumptions of the nature of the earthquake sources for short-period P, PcP, and ScP phases originating from earthquakes in the Fiji-Tonga region and recorded at the Warramunga Seismic Array at Tennant Creek (Northern Territory, Australia). Spectral ratios were calculated for the amplitudes of PcP to P and of pP to P. The data reveal a laterally varying Q structure in the Fiji-Tonga region. The high-Q lithosphere descending beneath the Tonga Island arc is overlain above 350 km depth by a wedgelike zone of high attenuation with an average Q/sub α/ between 120 and 200 at short periods. The upper mantle farther to the west of the Tonga island arc is less attenuating, with Q/sub α/, between 370 and 560. Q/sub α/ is about 500 in the upper mantle on the oceanic side of the subduction zone. The t* estimates of this study are much smaller than estimates from the free oscillation model SL8. This can be partly explained by regional variations of Q in the upper mantle. If no lateral Q variations occur in the lower mantle, a frequency-dependent Q can make the PcP and ScP observations consistent with model SL8. Adopting the absorption band model to describe the frequency dependence of Q, the parameter tau 2 , the cut-off period of the high-frequency end of the absorption band, was determined. For different source models with finite corner frequencies, the average tau 2 for the mantle is between 0.01 and 0.10 s (corresponding to frequencies between 16 and 1.6 Hz) as derived from the PcP data, and between 0.06 and 0.12 s (2.7 and 1.3 Hz), as derived from the ScP data

  19. Deformation processes in mantle peridotites : with emphasis on the Ronda peridotite of SW Spain

    NARCIS (Netherlands)

    Wal, D. van der

    1993-01-01

    This thesis aims to study upper mantle deformation processes in a case study of the Ronda peridotite in the Alpine Betic Cordilleras of SW Spain. The choice for this massif is motivated by its following characteristics: (i) pioneering geochemical and geological studies have shown that the W

  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...

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

    NARCIS (Netherlands)

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

    2016-01-01

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

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

    Science.gov (United States)

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

    2015-05-01

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

  3. Crust and mantle of the gulf of Mexico

    Science.gov (United States)

    Moore, G.W.

    1972-01-01

    A SEEMING paradox has puzzled investigators of the crustal structure of the Gulf of Mexico since Ewing et al.1 calculated that a unit area of the rather thick crust in the gulf contains less mass than does a combination of the crust and enough of the upper mantle to make a comparable thickness in the Atlantic Ocean. They also noted that the free-air gravity of the gulf is essentially normal and fails by a large factor to be low enough to reflect the mass difference that they calculated. We propose a solution to this problem. ?? 1972 Nature Publishing Group.

  4. 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.

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

    Science.gov (United States)

    Mallik, Ananya; Li, Yuan; Wiedenbeck, Michael

    2018-01-01

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

  6. Active carbon sequestration in the Alpine mantle wedge and implications for long-term climate trends.

    Science.gov (United States)

    Malusà, Marco Giovanni; Frezzotti, Maria Luce; Ferrando, Simona; Brandmayr, Enrico; Romanelli, Fabio; Panza, Giuliano Francesco

    2018-03-16

    The long-term carbon budget has major implications for Earth's climate and biosphere, but the balance between carbon sequestration during subduction, and outgassing by volcanism is still poorly known. Although carbon-rich fluid inclusions and minerals are described in exhumed mantle rocks and xenoliths, compelling geophysical evidence of large-scale carbon storage in the upper mantle is still lacking. Here, we use a geophysical surface-wave seismic tomography model of the mantle wedge above the subducted European slab to document a prominent shear-wave low-velocity anomaly at depths greater than 180 km. We propose that this anomaly is generated by extraction of carbonate-rich melts from the asthenosphere, favoured by the breakdown of slab carbonates and hydrous minerals after cold subduction. The resulting transient network of carbon-rich melts is frozen in the mantle wedge without producing volcanism. Our results provide the first in-situ observational evidence of ongoing carbon sequestration in the upper mantle at a plate-tectonic scale. We infer that carbon sequestered during cold subduction may partly counterbalance carbon outgassed from ridges and oceanic islands. However, subducted carbon may be rapidly released during continental rifting, with global effects on long-term climate trends and the habitability of planet Earth.

  7. The effect of fluorine on the stability of wadsleyite: Implications for the nature and depths of the transition zone in the Earth's mantle

    Science.gov (United States)

    Grützner, Tobias; Klemme, Stephan; Rohrbach, Arno; Gervasoni, Fernanda; Berndt, Jasper

    2018-01-01

    The Earth's mantle contains significant amounts of volatile elements, such as hydrogen (H), carbon (C) and the halogens fluorine (F), chlorine (Cl) and bromine (Br) and iodine (I). There is a wealth of knowledge about the global cycling of H and C, but there is only scant data on the concentrations of halogens in different Earth reservoirs and on the behavior of halogens during recycling in subduction zones. Here we focus on the storage potential of F in deeper parts of the Earth's mantle. The transition zone is a region in the Earth's mantle (410-660 km) known for its high water storage capacity, as the high pressure polymorphs of olivine, wadsleyite and ringwoodite are known to be able to incorporate several per-cent of water. In order to assess potential fractionation between water and F in the transition zone of the Earth's mantle, we set out to investigate the storage capacity of the halogen F in wadsleyite and olivine at transition zone conditions. Experiments were performed in a simplified mantle composition at temperatures from 1400 °C to 1900 °C and pressures from 17 up to 21 GPa in a multi anvil apparatus. The results show that F can shift the olivine-wadsleyite transition towards higher pressure. We find that F has an opposing effect to water, the latter of which extends the transition zone towards lower pressure. Moreover, the F storage capacity of wadsleyite is significantly lower than previously anticipated. F concentrations in wadsleyite range from 1470 ± 60 μg/g to 2110 ± 600 μg/g independent of temperature or pressure. The F storage capacity in wadsleyite is even lower than the F storage capacity of forsterite under transition zone conditions, and the latter can incorporate 3930 ± 140 μg/g F under these conditions. Based on our data we find that the transition zone cannot be a reservoir for F as it is assumed to be for water. Furthermore, we argue that during subduction of a volatile-bearing slab, fractionation of water from F will occur

  8. Effects of mantle rheologies on viscous heating induced by Glacial Isostatic Adjustment

    Science.gov (United States)

    Huang, PingPing; Wu, Patrick; van der Wal, Wouter

    2018-04-01

    It has been argued that viscous dissipation from mantle flow in response to surface loading during glacial cycles can result in short-term heating and thus trigger transient volcanism or changes in mantle properties, which may in turn affect mantle dynamics. Furthermore, heating near the Earth's surface can also affect the stability of ice sheets. We have studied the magnitude and spatial-temporal distribution of viscous heating induced in the mantle by the realistic ice model ICE-6G and gravitationally consistent ocean loads. Three types of mantle rheologies, including linear, non-linear and composite rheologies are considered to see if non-linear creep can induce larger viscous heating than linear rheology. We used the Coupled-Laplace-Finite-Element model of Glacial Isostatic Adjustment (GIA) to compute the strain, stress and shear heating during a glacial cycle. We also investigated the upper bound of temperature change and surface heat flux change due to viscous heating. We found that maximum viscous heating occurs near the end of deglaciation near the edge of the ice sheet with amplitude as high as 120 times larger than that of the chondritic radioactive heating. The maximum heat flux due to viscous heating can reach 30 mW m-2, but the area with large heat flux is small and the timescale of heating is short. As a result, the upper bound of temperature change due to viscous heating is small. Even if 30 glacial cycles are included, the largest temperature change can be of the order of 0.3 °C. Thus, viscous heating induced by GIA cannot induce volcanism and cannot significantly affect mantle material properties, mantle dynamics nor ice-sheet stability.

  9. 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

  10. Core-exsolved SiO2 Dispersal in the Earth's Mantle

    Science.gov (United States)

    Helffrich, G. R.; Ballmer, M.; Hirose, K.

    2017-12-01

    SiO2 may have been expelled from the core following its formation in the early stages of Earth's accretion and onwards through the present day. On account of SiO2's low density with respect to both the core and the lowermost mantle, we examine the process of SiO2 accumulation at the core-mantle boundary (CMB) and its incorporation into the mantle by buoyant rise. Today, the if SiO2 is 100-10000 times more viscous than lower mantle material, the dimensions of SiO2 diapirs formed by the viscous Rayleigh-Taylor instability at the CMB would cause them to be swept into the mantle as inclusions of 100 m - 10 km diameter. Under early Earth conditions of rapid heat loss after core formation, SiO2 diapirs of 5-80 km diameter could have risen independently of mantle flow to their level of neutral buoyancy in the mantle, trapping them there due to a combination of high viscosity and neutral buoyancy. We examine the SiO2 yield by assuming Si+O saturation at the conditions found at the base of a magma ocean and find that for a range of conditions, dispersed bodies could reach as high as 2 volume percent in shallow parts of the lower mantle, with their abundance decreasing with depth. At such low concentrations, their effect on aggregate seismic wavespeeds would be within the uncertainty of the radial Earth model PREM. However, their presence would be revealed by small-scale scattering in the lower mantle due to the bodies' large velocity contrast. We conclude that the shallow lower mantle (700-1500 km depth) could harbor SiO2 released in early Earth times.

  11. 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.

  12. 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...

  13. 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.

  14. 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.

  15. Crack-arrest behavior in SEN wide plates of low-upper-shelf base metal tested under nonisothermal conditions: WP-2 series

    International Nuclear Information System (INIS)

    Naus, D.J.; Keeney-Walker, J.; Bass, B.R.; Robinson, G.C. Jr.; Iskander, S.K.; Alexander, D.J.; Fields, R.J.; deWit, R.; Low, S.R.; Schwartz, C.W.

    1990-08-01

    The Heavy-Section Steel Technology (HSST) Program at the Oak Ridge National Laboratory under the sponsorship of the Nuclear Regulatory Commission is conducting analytical and experimental studies aimed at understanding the circumstances that would initiate the growth of an existing crack in a reactor pressure vessel (RPV) and the conditions leading to arrest of a propagating crack. Objectives of these studies are to determine (1) if the material will exhibit crack-arrest behavior when the driving force on a crack exceeds the ASME limit, (2) the relationship between K Ia and temperature, and (3) the interaction of fracture modes (arrest, stable crack growth, unstable crack growth, and tensile instability) when arrest occurs at high temperatures. In meeting these objectives, crack-arrest data are being developed over an expanded temperature range through tests involving large thermally shocked cylinders, pressurized thermally shocked vessels, and wide-plate specimens. The wide-plate specimens provide the opportunity for a significant number of data points to be obtained at relatively affordable costs. These tests are designed to provide fracture-toughness measurements approaching or above the onset of the Charpy upper-shelf regime in a rising toughness region and with an increasing driving force. This document discusses test methodology and results. 23 refs., 92 figs., 25 tabs

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

    Science.gov (United States)

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

    2017-08-01

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

  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. Plate tectonics, mantle convection and D'' seismic structures

    Science.gov (United States)

    Wen, Lianxing

    This thesis adopts multidisciplinary (geodynamical and seismological) approaches toward understanding dynamics of the Earth's mantle. My geodynamical approach is directed at understanding the relationship between large-scale surface observables (geoid, topography, plate motions) and mantle rheology and convection of the present-day Earth. In chapter 2, I remove shallow mantle structure of various tectonic features to generate "residual tomography." In chapter 3, I show that the pattern, spectrum and amplitude of the "residual topography" are consistent with shallow origin of the "Earth surface dynamic topography;" the long wavelength geoid and topography (l = 2-3) are successfully explained by density models inferred from the "residual tomography," assuming layered mantle convection stratified at the "920 km seismic discontinuity." In chapter 4, I develop a new method to calculate mantle flow with lateral variation of viscosity. The viscosity contrast between continental and oceanic regions is identified to have dominating effects on both the observed poloidal/toroidal ratio and pattern of toroidal motions at long wavelengths. My seismological approach is focused on exploring fine structures near the core-mantle boundary (CMB) and developing new seismic techniques. I discuss the method development and strategies to explore fine structures in the following chapters. In chapter 5, I develop a hybrid method, a combination of analytical and numerical methods, with numerical methods applied in heterogeneous regions only. In chapter 6, I constrain the general structures of the ultra low velocity zones (ULVZ) near the CMB under the south-east Pacific and Iceland. The SKS-SPdKS data are explained by ULVZ with P-velocity reduction of 10%, horizontal length-scales of about 250 km and height of about 40 km. S-velocity reduction of 30% is consistent with the data. In chapter 7, I constrain the detailed structures of the ULVZ near the CMB from observed broadband PKP precursors

  19. 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

  20. Geomechanical characterization of the Upper Carboniferous under thermal stress for the evaluation of a High Temperature - Mine Thermal Energy Storage (HT-MTES)

    Science.gov (United States)

    Hahn, Florian; Brüggemann, Nina; Bracke, Rolf; Alber, Michael

    2017-04-01

    The goal of this R&D project is to create a technically and economically feasible conceptual model for a High Temperature - Mine Thermal Energy Storage (HT-MTES) for the energetic reuse of a mine on the example of the Prosper-Haniel coal mine in Bottrop, Germany. This project is funded by the "Initiative Energy Storage" program of the German Federal Ministries BMWi, BMU and BMBF. At the end of 2018, the last operative coal mine in North Rhine-Westphalia, Germany (Prosper-Haniel), is going to be closed down, plugged and abandoned. Large amounts of subsurface infrastructures, resembled mainly by open parts of former galleries and mining faces are going to be flooded, after the mine is closed down and therefore have the potential to become an enormous geothermal reservoir for a seasonal heat storage. During the summer non-used (waste) heat from solar thermal power plants, garbage incineration, combined heat and power plants (CHP) or industrial production processes can be stored within dedicated drifts of the mine. During the winter season, this surplus heat can be extracted and directly utilized in commercial and/or residential areas. For the evaluation of such a HT-MTES within a former coal mine, the corresponding geomechanical parameters of the Upper Carboniferous under thermal stress needs to be evaluated. Therefore the main rock types of the Upper Carboniferous (claystone, siltstone and sandstone) are subject to a geomechanical characterization before and after thermal cyclic loadings of temperatures up to 200 °C. The samples have been collected directly from the coal mine Prosper-Haniel within a depth range of 1000 - 1200 m. Unconfined compressive and tensile strengths, as well as triaxial tests were performed at room temperature. Furthermore, a range of petrophysical properties like density, thin-section analysis and P-wave velocities were determined. First results show an indication that the overall strength properties of the samples are not effected by

  1. Nanodiamond Finding in the Hyblean Shallow Mantle Xenoliths

    OpenAIRE

    Simakov, S. K.; Kouchi, A.; Mel?nik, N.N.; Scribano, V.; Kimura, Y.; Hama, T.; Suzuki, N.; Saito, H.; Yoshizawa, T.

    2015-01-01

    Most of Earth?s diamonds are connected with deep-seated mantle rocks; however, in recent years, ?m-sized diamonds have been found in shallower metamorphic rocks, and the process of shallow-seated diamond formation has become a hotly debated topic. Nanodiamonds occur mainly in chondrite meteorites associated with organic matter and water. They can be synthesized in the stability field of graphite from organic compounds under hydrothermal conditions. Similar physicochemical conditions occur in ...

  2. Numerical Modeling of Deep Mantle Flow: Thermochemical Convection and Entrainment

    Science.gov (United States)

    Mulyukova, Elvira; Steinberger, Bernhard; Dabrowski, Marcin; Sobolev, Stephan

    2013-04-01

    One of the most robust results from tomographic studies is the existence of two antipodally located Large Low Shear Velocity Provinces (LLSVPs) at the base of the mantle, which appear to be chemically denser than the ambient mantle. Results from reconstruction studies (Torsvik et al., 2006) infer that the LLSVPs are stable, long-lived, and are sampled by deep mantle plumes that rise predominantly from their margins. The origin of the dense material is debated, but generally falls within three categories: (i) a primitive layer that formed during magma ocean crystallization, (ii) accumulation of a dense eclogitic component from the recycled oceanic crust, and (iii) outer core material leaking into the lower mantle. A dense layer underlying a less dense ambient mantle is gravitationally stable. However, the flow due to thermal density variations, i.e. hot rising plumes and cold downwelling slabs, may deform the layer into piles with higher topography. Further deformation may lead to entrainment of the dense layer, its mixing with the ambient material, and even complete homogenisation with the rest of the mantle. The amount of the anomalous LLSVP-material that gets entrained into the rising plumes poses a constraint on the survival time of the LLSVPs, as well as on the plume buoyancy, on the lithospheric uplift associated with plume interaction and geochemical signature of the erupted lavas observed at the Earth's surface. Recent estimates for the plume responsible for the formation of the Siberian Flood Basalts give about 15% of entrained dense recycled oceanic crust, which made the hot mantle plume almost neutrally buoyant (Sobolev et al., 2011). In this numerical study we investigate the mechanics of entrainment of a dense basal layer by convective mantle flow. We observe that the types of flow that promote entrainment of the dense layer are (i) upwelling of the dense layer when it gets heated enough to overcome its stabilizing chemical density anomaly, (ii

  3. 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

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

    Science.gov (United States)

    Wahr, John; Bergen, Zachary

    1986-01-01

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

  5. 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

    thick solid lid and diminished the likelihood of mantle remixing. Second, on an Earth-sized planet a magma ocean would solidify to produce very dense near-surface solids that also contain the bulk of the water held in the solid state, and the bulk of the incompatible elements. During gravitationally-driven overturn shallow, dense, damp solids carry their water as they sink into the perovskite stability zone and transform the bulk of their mineralogy into perovskite. The last solids that form near the surface exceed the likely water saturation levels of perovskite and will be forced to dewater as they cross the boundary into the lower mantle, leaving water behind in a rapid flux as the dense material sinks. This event will form a kind of “water catastrophe,” and would have the potential to partially melt the upper mantle, to produce a damp asthensosphere, and indeed to encourage convection. These results imply that planets in which perovskite is stable, that is, planets that are larger than Mars, are perhaps more likely to have an early initiation of plate tectonics, and that larger planets may have more violent and near-surface mantle volatile releases during any overturn event.

  6. Magnetic Properties of Mantle Xenoliths and Evidence of Localized Modification of the Mantle Beneath the Rio Puerco Volcanic Field, New Mexico

    Science.gov (United States)

    Callahan, C. N.; Geissman, J. W.; Selverstone, J.; Brearley, A. J.

    2005-12-01

    Little is known about the magnetic petrology and processes that affect the magnetization of the upper mantle. Petrologic and geochemical studies of a suite of xenoliths from the Rio Puerco volcanic necks (RPVN), west-central New Mexico, show that pyroxenites (PYX) have a metasomatic origin, as a result of interaction between spinel lherzolites (SL) and basaltic and carbonatitic melt or fluid. This study demonstrates that magnetic properties of these mantle xenoliths can characterize localized mantle modification events and heterogeneity in mantle oxidation states. In situ, oriented PYXs carry a well-defined post-emplacement, cooling-related remanence (typical NRM of 0.23 A/m) defined by progressive thermal and AF demagnetization. Thermal demagnetization of SL and PYX remove >90% of the magnetization by 580°C and IRM acquisition curves reach saturation by 0.3T, indicating a dominance by magnetite in both rock types. SL and PYX have relatively small concentrations (~0.01%) of magnetite (bulk susceptibility of 10-4 to 10-5 SI vol). SLs generally contain multi-domain magnetite (mean destructive fields of NRM between 20 to 40 mT), whereas PYXs are dominated by single domain magnetite (MDFs between 20 to 70 mT). The magnetic properties of SLs and PYXs are a reflection of phases formed in the mantle and not from basalt-xenolith interaction en route to the surface. In addition, the differences in magnetic properties give insight into how melt infiltration modifies the magnetization of mantle xenoliths. In comparison to other SLs, red-colored SLs found only at Cerro de Santa Rosa, one of the RPVN, contain hematite and relatively low-coercivity magnetite. Complete thermal unblocking of a high coercivity phase occurs at 680°C and a medium to low-coercivity fraction at 580°C. Textural evidence suggests that alteration involved oxidation in the mantle, prior to transport of these xenoliths to the surface in the host basalt. TEM analyses reveal micron-sized needles of

  7. 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

  8. 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

  9. 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.

  10. Hydrogen self-diffusion in single crystal olivine and electrical conductivity of the Earth's mantle.

    Science.gov (United States)

    Novella, Davide; Jacobsen, Benjamin; Weber, Peter K; Tyburczy, James A; Ryerson, Frederick J; Du Frane, Wyatt L

    2017-07-13

    Nominally anhydrous minerals formed deep in the mantle and transported to the Earth's surface contain tens to hundreds of ppm wt H 2 O, providing evidence for the presence of dissolved water in the Earth's interior. Even at these low concentrations, H 2 O greatly affects the physico-chemical properties of mantle materials, governing planetary dynamics and evolution. The diffusion of hydrogen (H) controls the transport of H 2 O in the Earth's upper mantle, but is not fully understood for olivine ((Mg, Fe) 2 SiO 4 ) the most abundant mineral in this region. Here we present new hydrogen self-diffusion coefficients in natural olivine single crystals that were determined at upper mantle conditions (2 GPa and 750-900 °C). Hydrogen self-diffusion is highly anisotropic, with values at 900 °C of 10 -10.9 , 10 -12.8 and 10 -11.9 m 2 /s along [100], [010] and [001] directions, respectively. Combined with the Nernst-Einstein relation, these diffusion results constrain the contribution of H to the electrical conductivity of olivine to be σ H  = 10 2.12 S/m·C H2O ·exp -187kJ/mol/(RT) . Comparisons between the model presented in this study and magnetotelluric measurements suggest that plausible H 2 O concentrations in the upper mantle (≤250 ppm wt) can account for high electrical conductivity values (10 -2 -10 -1  S/m) observed in the asthenosphere.

  11. Uppermost mantle and crustal structure at Tristan da Cunha derived from ambient seismic noise

    Science.gov (United States)

    Ryberg, T.; Geissler, W. H.; Jokat, W.; Pandey, S.

    2017-08-01

    According to classical plume theory, the Tristan da Cunha hotspot, located ∼400 km east off the Mid-Atlantic Ridge, is thought to have played a major role in the rifting while creating an aseismic Walvis Ridge during and after the breakup of the South Atlantic margins. Volcanic activity on the Tristan da Cunha Island shows that the hotspot might still be there influencing the upper mantle and crustal structure. In this study we present ambient noise data from 24 broadband OBS around Tristan da Cunha and a seismic station on Nightingale Island, which provide first constraints on the crustal and uppermost mantle structure around the island. By combining ambient noise techniques, dispersion curve analysis of Rayleigh waves, 2D tomographic inversion of travel times and 3D depth inversion of dispersion data we derived a 3D VS velocity model around the archipelago of Tristan da Cunha. The model shows an isolated, vertically sharp bounded thickened and modified crust beneath the islands surrounded by thin oceanic crust (feeding system/magmatic underplating, respectively. The observed simple and localized volcanic structure, embedded in a rather homogeneous crust and upper mantle indicates only minor and very localized magmatic overprinting of the existing lithosphere by the Tristan da Cunha hotspot. The uppermost mantle S wave velocity beneath nearby seamounts and to the SW of the islands is also slow and could indicate a thermal influence from a deeper source, whereas the Tristan da Cunha Fracture Zone shows no signs of modification.

  12. 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Lin, J; Tsuchiya, T

    2007-05-23

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

  14. Mantle convection patterns reveal the enigma of the Red Sea rifting

    Science.gov (United States)

    Petrunin, Alexey; Kaban, Mikhail; El Khrepy, Sami; Al-Arifi, Nassir

    2017-04-01

    Initiation and further development of the Red Sea rift (RSR) is usually associated with the Afar plume at the Oligocene-Miocene separating the Arabian plate from the rest of the continent. Usually, the RSR is divided into three parts with different geological, tectonic and geophysical characteristics, but the nature of this partitioning is still debatable. To understand origin and driving forces responsible for the tectonic partitioning of the RSR, we have developed a global mantle convection model based on the refined density model and viscosity distribution derived from tectonic, rheological and seismic data. The global density model of the upper mantle is refined for the Middle East based on the high-resolution 3D model (Kaban et al., 2016). This model based on a joint inversion of the residual gravity and residual topography provides much better constraints on the 3D density structure compared to the global model based on seismic tomography. The refined density model and the viscosity distribution based on a homologous temperature approach provide an initial setup for further numerical calculations. The present-day snapshot of the mantle convection is calculated by using the code ProSpher 3D that allows for strong lateral variations of viscosity (Petrunin et al., 2013). The setup includes weak plate boundaries, while the measured GPS velocities are used to constrain the solution. The resulting mantle flow patterns show clear distinctions among the mantle flow patterns below the three parts of the RSR. According to the modeling results, tectonics of the southern part of the Red Sea is mainly determined by the Afar plume and the Ethiopian rift opening. It is characterized by a divergent mantle flow, which is connected to the East African Rift activity. The rising mantle flow is traced down to the transition zone and continues in the lower mantle for a few thousand kilometers south-west of Afar. The hot mantle anomaly below the central part of the RSR can be

  15. A 4D ultrasound real-time tracking system for external beam radiotherapy of upper abdominal lesions under breath-hold

    Energy Technology Data Exchange (ETDEWEB)

    Sihono, Dwi Seno Kuncoro; Vogel, Lena; Thoelking, Johannes; Wenz, Frederik; Boda-Heggemann, Judit; Wertz, Hansjoerg [University of Heidelberg, Department of Radiation Oncology, University Medical Center Mannheim, Mannheim (Germany); Weiss, Christel [University of Heidelberg, Department of Biomathematics and Medical Statistics, University Medical Center Mannheim, Mannheim (Germany); Lohr, Frank [University of Heidelberg, Department of Radiation Oncology, University Medical Center Mannheim, Mannheim (Germany); Az. Ospedaliero-Universitaria di Modena, Struttura Complessa di Radioterapia, Dipartimento di Oncologia, Modena (Italy)

    2017-03-15

    To evaluate a novel four-dimensional (4D) ultrasound (US) tracking system for external beam radiotherapy of upper abdominal lesions under computer-controlled deep-inspiration breath-hold (DIBH). The tracking accuracy of the research 4D US system was evaluated using two motion phantoms programmed with sinusoidal and breathing patterns to simulate free breathing and DIBH. Clinical performance was evaluated with five healthy volunteers. US datasets were acquired in computer-controlled DIBH with varying angular scanning angles. Tracked structures were renal pelvis (spherical structure) and portal/liver vein branches (non-spherical structure). An external marker was attached to the surface of both phantoms and volunteers as a secondary object to be tracked by an infrared camera for comparison. Phantom measurements showed increased accuracy of US tracking with decreasing scanning range/increasing scanning frequency. The probability of lost tracking was higher for small scanning ranges (43.09% for 10 and 13.54% for 20 ).The tracking success rates in healthy volunteers during DIBH were 93.24 and 89.86% for renal pelvis and portal vein branches, respectively. There was a strong correlation between marker motion and US tracking for the majority of analyzed breath-holds: 84.06 and 88.41% of renal pelvis target results and 82.26 and 91.94% of liver vein target results in anteroposterior and superoinferior directions, respectively; Pearson's correlation coefficient was between 0.71 and 0.99. The US system showed a good tracking performance in 4D motion phantoms. The tracking capability of surrogate structures for upper abdominal lesions in DIBH fulfills clinical requirements. Further investigation in a larger cohort of patients is underway. (orig.) [German] Evaluation eines neuen vierdimensionalen (4D) Ultraschall(US)-Tracking-Systems fuer die externe Strahlentherapie von Oberbauchlaesionen unter computergesteuertem tiefem Atemanhalt (DIBH). Die Tracking-Genauigkeit des 4D

  16. Seismic and thermal structure of the crust and uppermost mantle beneath Antarctica from inversion of multiple seismic datasets

    Science.gov (United States)

    Wiens, D.; Shen, W.; Anandakrishnan, S.; Aster, R. C.; Gerstoft, P.; Bromirski, P. D.; Dalziel, I.; Hansen, S. E.; Heeszel, D.; Huerta, A. D.; Nyblade, A.; Stephen, R. A.; Wilson, T. J.; Winberry, J. P.; Stern, T. A.

    2017-12-01

    Since the last decade of the 20th century, over 200 broadband seismic stations have been deployed across Antarctica (e.g., temporary networks such as TAMSEIS, AGAP/GAMSEIS, POLENET/ANET, TAMNNET and RIS/DRIS by U.S. geoscientists as well as stations deployed by Japan, Britain, China, Norway, and other countries). In this presentation, we discuss our recent efforts to build reference crustal and uppermost mantle shear velocity (Vs) and thermal models for continental Antarctica based on those seismic arrays. By combing the high resolution Rayleigh wave dispersion maps derived from both ambient noise and teleseismic earthquakes, together with P receiver function waveforms, we develop a 3-D Vs model for the crust and uppermost mantle beneath Central and West Antarctica to a depth of 200 km. Additionally, using this 3-D seismic model to constrain the crustal structure, we re-invert for the upper mantle thermal structure using the surface wave data within a thermodynamic framework and construct a 3-D thermal model for the Antarctic lithosphere. The final product, a high resolution thermal model together with associated uncertainty estimates from the Monte Carlo inversion, allows us to derive lithospheric thickness and surface heat flux maps for much of the continent. West Antarctica shows a much thinner lithosphere ( 50-90 km) than East Antarctica ( 130-230 km), with a sharp transition along the Transantarctic Mountains (TAM). A variety of geological features, including a slower/hotter but highly heterogeneous West Antarctica and a much faster/colder East Antarctic craton, are present in the 3-D seismic/thermal models. Notably, slow seismic velocities observed in the uppermost mantle beneath the southern TAM are interpreted as a signature of lithospheric foundering and replacement with hot asthenosphere. The high resolution image of these features from the 3-D models helps further investigation of the dynamic state of Antarctica's lithosphere and underlying asthenosphere

  17. 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

  18. 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

  19. Power law olivine crystal size distributions in lithospheric mantle xenoliths

    Science.gov (United States)

    Armienti, P.; Tarquini, S.

    2002-12-01

    Olivine crystal size distributions (CSDs) have been measured in three suites of spinel- and garnet-bearing harzburgites and lherzolites found as xenoliths in alkaline basalts from Canary Islands, Africa; Victoria Land, Antarctica; and Pali Aike, South America. The xenoliths derive from lithospheric mantle, from depths ranging from 80 to 20 km. Their textures vary from coarse to porphyroclastic and mosaic-porphyroclastic up to cataclastic. Data have been collected by processing digital images acquired optically from standard petrographic thin sections. The acquisition method is based on a high-resolution colour scanner that allows image capturing of a whole thin section. Image processing was performed using the VISILOG 5.2 package, resolving crystals larger than about 150 μm and applying stereological corrections based on the Schwartz-Saltykov algorithm. Taking account of truncation effects due to resolution limits and thin section size, all samples show scale invariance of crystal size distributions over almost three orders of magnitude (0.2-25 mm). Power law relations show fractal dimensions varying between 2.4 and 3.8, a range of values observed for distributions of fragment sizes in a variety of other geological contexts. A fragmentation model can reproduce the fractal dimensions around 2.6, which correspond to well-equilibrated granoblastic textures. Fractal dimensions >3 are typical of porphyroclastic and cataclastic samples. Slight bends in some linear arrays suggest selective tectonic crushing of crystals with size larger than 1 mm. The scale invariance shown by lithospheric mantle xenoliths in a variety of tectonic settings forms distant geographic regions, which indicate that this is a common characteristic of the upper mantle and should be taken into account in rheological models and evaluation of metasomatic models.

  20. The crust and mantle beneath the Siberian provinces: a preliminary model based on new receiver function analysis

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Artemieva, Irina; Thybo, Hans

    2012-01-01

    The new receiver function (RF) study complements the existing seismic data on the crustal and upper mantle structure at the margins of the Siberian craton and the West Siberian Basin. So far, RF studies of Siberia have been largely restricted to the Baikal rift zone (Gao et al., 2004; Liu and Gao...

  1. 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

  2. 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...

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

    DEFF Research Database (Denmark)

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

    1999-01-01

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

  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. Abnormal high surface heat flow caused by the Emeishan mantle plume

    Science.gov (United States)

    Jiang, Qiang; Qiu, Nansheng; Zhu, Chuanqing

    2016-04-01

    It is commonly believed that increase of heat flow caused by a mantle plume is small and transient. Seafloor heat flow data near the Hawaiian hotspot and the Iceland are comparable to that for oceanic lithosphere elsewhere. Numerical modeling of the thermal effect of the Parana large igneous province shows that the added heat flow at the surface caused by the magmatic underplating is less than 5mW/m2. However, the thermal effect of Emeishan mantle plume (EMP) may cause the surface hear-flow abnormally high. The Middle-Late Emeishan mantle plume is located in the western Yangtze Craton. The Sichuan basin, to the northeast of the EMP, is a superimposed basin composed of Paleozoic marine carbonate rocks and Mesozoic-Cenozoic terrestrial clastic rocks. The vitrinite reflectance (Ro) data as a paleogeothermal indicator records an apparent change of thermal regime of the Sichuan basin. The Ro profiles from boreholes and outcrops which are close to the center of the basalt province exhibit a 'dog-leg' style at the unconformity between the Middle and Upper Permian, and they show significantly higher gradients in the lower subsection (pre-Middle Permian) than the Upper subsection (Upper Permian to Mesozoic). Thermal history inversion based on these Ro data shows that the lower subsection experienced a heat flow peak much higher than that of the upper subsection. The abnormal heat flow in the Sichuan basin is consistent with the EMP in temporal and spatial distribution. The high-temperature magmas from deep mantle brought heat to the base of the lithosphere, and then large amount of heat was conducted upwards, resulting in the abnormal high surface heat flow.

  6. Global Scale Exploration Seismics: Mapping Mantle Discontinuities with Inverse Scattering Methods and Millions of Seismograms

    Science.gov (United States)

    van der Hilst, R. D.; de Hoop, M. V.; Shim, S. H.; Shang, X.; Wang, P.; Cao, Q.

    2012-04-01

    Over the past three decades, tremendous progress has been made with the mapping of mantle heterogeneity and with the understanding of these structures in terms of, for instance, the evolution of Earth's crust, continental lithosphere, and thermo-chemical mantle convection. Converted wave imaging (e.g., receiver functions) and reflection seismology (e.g. SS stacks) have helped constrain interfaces in crust and mantle; surface wave dispersion (from earthquake or ambient noise signals) characterizes wavespeed variations in continental and oceanic lithosphere, and body wave and multi-mode surface wave data have been used to map trajectories of mantle convection and delineate mantle regions of anomalous elastic properties. Collectively, these studies have revealed substantial ocean-continent differences and suggest that convective flow is strongly influenced by but permitted to cross the upper mantle transition zone. Many questions have remained unanswered, however, and further advances in understanding require more accurate depictions of Earth's heterogeneity at a wider range of length scales. To meet this challenge we need new observations—more, better, and different types of data—and methods that help us extract and interpret more information from the rapidly growing volumes of broadband data. The huge data volumes and the desire to extract more signal from them means that we have to go beyond 'business as usual' (that is, simplified theory, manual inspection of seismograms, …). Indeed, it inspires the development of automated full wave methods, both for tomographic delineation of smooth wavespeed variations and the imaging (for instance through inverse scattering) of medium contrasts. Adjoint tomography and reverse time migration, which are closely related wave equation methods, have begun to revolutionize seismic inversion of global and regional waveform data. In this presentation we will illustrate this development - and its promise - drawing from our work

  7. 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.

  8. Waveform inversion of mantle Love waves - The Born seismogram approach

    Science.gov (United States)

    Tanimoto, T.

    1984-01-01

    Normal mode theory, extended to the slightly laterally heterogeneous earth by the first-order Born approximation, is applied to the waveform inversion of mantle Love waves (200-500 sec) for the earth's lateral heterogeneity at l = 2 and a spherically symmetric anelasticity (Q sub mu) structure. The data are from the Global Digital Seismograph Network (GDSN). The l = 2 pattern is very similar to the results of other studies that used either different methods, such as phase velocity measurements and multiplet location measurements, or a different data set, such as mantle Rayleigh waves from different instruments. The results are carefully analyzed for variance reduction and are most naturally explained by heterogeneity in the upper 420 km. Because of the poor resolution of the data set for the deep interior, however, a fairly large heterogeneity in the transition zones, of the order of up to 3.5 percent in shear wave velocity, is allowed. It is noteworthy that Love waves of this period range can not constrain the structure below 420 km and thus any model presented by similar studies below this depth are likely to be constrained by Rayleigh waves (spheroidal modes) only.

  9. Waveform inversion of mantle Love waves: The born se