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Sample records for active mantle upwelling

  1. Stability of active mantle upwelling revealed by net characteristics of plate tectonics.

    PubMed

    Conrad, Clinton P; Steinberger, Bernhard; Torsvik, Trond H

    2013-06-27

    Viscous convection within the mantle is linked to tectonic plate motions and deforms Earth's surface across wide areas. Such close links between surface geology and deep mantle dynamics presumably operated throughout Earth's history, but are difficult to investigate for past times because the history of mantle flow is poorly known. Here we show that the time dependence of global-scale mantle flow can be deduced from the net behaviour of surface plate motions. In particular, we tracked the geographic locations of net convergence and divergence for harmonic degrees 1 and 2 by computing the dipole and quadrupole moments of plate motions from tectonic reconstructions extended back to the early Mesozoic era. For present-day plate motions, we find dipole convergence in eastern Asia and quadrupole divergence in both central Africa and the central Pacific. These orientations are nearly identical to the dipole and quadrupole orientations of underlying mantle flow, which indicates that these 'net characteristics' of plate motions reveal deeper flow patterns. The positions of quadrupole divergence have not moved significantly during the past 250 million years, which suggests long-term stability of mantle upwelling beneath Africa and the Pacific Ocean. These upwelling locations are positioned above two compositionally and seismologically distinct regions of the lowermost mantle, which may organize global mantle flow as they remain stationary over geologic time. PMID:23803848

  2. Stability of active mantle upwelling revealed by net characteristics of plate tectonics.

    PubMed

    Conrad, Clinton P; Steinberger, Bernhard; Torsvik, Trond H

    2013-06-27

    Viscous convection within the mantle is linked to tectonic plate motions and deforms Earth's surface across wide areas. Such close links between surface geology and deep mantle dynamics presumably operated throughout Earth's history, but are difficult to investigate for past times because the history of mantle flow is poorly known. Here we show that the time dependence of global-scale mantle flow can be deduced from the net behaviour of surface plate motions. In particular, we tracked the geographic locations of net convergence and divergence for harmonic degrees 1 and 2 by computing the dipole and quadrupole moments of plate motions from tectonic reconstructions extended back to the early Mesozoic era. For present-day plate motions, we find dipole convergence in eastern Asia and quadrupole divergence in both central Africa and the central Pacific. These orientations are nearly identical to the dipole and quadrupole orientations of underlying mantle flow, which indicates that these 'net characteristics' of plate motions reveal deeper flow patterns. The positions of quadrupole divergence have not moved significantly during the past 250 million years, which suggests long-term stability of mantle upwelling beneath Africa and the Pacific Ocean. These upwelling locations are positioned above two compositionally and seismologically distinct regions of the lowermost mantle, which may organize global mantle flow as they remain stationary over geologic time.

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

    PubMed

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

    2014-01-01

    Large-scale tectonic processes introduce a range of crustal lithologies into the Earth's mantle. These lithologies have been implicated as sources of compositional heterogeneity in mantle-derived magmas. The model being explored here assumes the presence of widely dispersed fragments of residual eclogite (derived from recycled oceanic crust), stretched and stirred by convection in the mantle. Here we show with an experimental study that these residual eclogites continuously melt during upwelling of such heterogeneous mantle and we characterize the melting reactions and compositional changes in the residue minerals. The chemical exchange between these partial melts and more refractory peridotite leads to a variably metasomatised mantle. Re-melting of these metasomatised peridotite lithologies at given pressures and temperatures results in diverse melt compositions, which may contribute to the observed heterogeneity of oceanic basalt suites. We also show that heterogeneous upwelling mantle is subject to diverse local freezing, hybridization and carbonate-carbon-silicate redox reactions along a mantle adiabat. PMID:25130275

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

    PubMed

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

    2014-08-18

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

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

    PubMed Central

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

    2014-01-01

    Large-scale tectonic processes introduce a range of crustal lithologies into the Earth's mantle. These lithologies have been implicated as sources of compositional heterogeneity in mantle-derived magmas. The model being explored here assumes the presence of widely dispersed fragments of residual eclogite (derived from recycled oceanic crust), stretched and stirred by convection in the mantle. Here we show with an experimental study that these residual eclogites continuously melt during upwelling of such heterogeneous mantle and we characterize the melting reactions and compositional changes in the residue minerals. The chemical exchange between these partial melts and more refractory peridotite leads to a variably metasomatised mantle. Re-melting of these metasomatised peridotite lithologies at given pressures and temperatures results in diverse melt compositions, which may contribute to the observed heterogeneity of oceanic basalt suites. We also show that heterogeneous upwelling mantle is subject to diverse local freezing, hybridization and carbonate-carbon-silicate redox reactions along a mantle adiabat. PMID:25130275

  6. Electrical image of passive mantle upwelling beneath the northern East Pacific Rise.

    PubMed

    Key, Kerry; Constable, Steven; Liu, Lijun; Pommier, Anne

    2013-03-28

    Melt generated by mantle upwelling is fundamental to the production of new oceanic crust at mid-ocean ridges, yet the forces controlling this process are debated. Passive-flow models predict symmetric upwelling due to viscous drag from the diverging tectonic plates, but have been challenged by geophysical observations of asymmetric upwelling that suggest anomalous mantle pressure and temperature gradients, and by observations of concentrated upwelling centres consistent with active models where buoyancy forces give rise to focused convective flow. Here we use sea-floor magnetotelluric soundings at the fast-spreading northern East Pacific Rise to image mantle electrical structure to a depth of about 160 kilometres. Our data reveal a symmetric, high-conductivity region at depths of 20-90 kilometres that is consistent with partial melting of passively upwelling mantle. The triangular region of conductive partial melt matches passive-flow predictions, suggesting that melt focusing to the ridge occurs in the porous melting region rather than along the shallower base of the thermal lithosphere. A deeper conductor observed east of the ridge at a depth of more than 100 kilometres is explained by asymmetric upwelling due to viscous coupling across two nearby transform faults. Significant electrical anisotropy occurs only in the shallowest mantle east of the ridge axis, where high vertical conductivity at depths of 10-20 kilometres indicates localized porous conduits. This suggests that a coincident seismic-velocity anomaly is evidence of shallow magma transport channels rather than deeper off-axis upwelling. We interpret the mantle electrical structure as evidence that plate-driven passive upwelling dominates this ridge segment, with dynamic forces being negligible. PMID:23538832

  7. Electrical image of passive mantle upwelling beneath the northern East Pacific Rise.

    PubMed

    Key, Kerry; Constable, Steven; Liu, Lijun; Pommier, Anne

    2013-03-28

    Melt generated by mantle upwelling is fundamental to the production of new oceanic crust at mid-ocean ridges, yet the forces controlling this process are debated. Passive-flow models predict symmetric upwelling due to viscous drag from the diverging tectonic plates, but have been challenged by geophysical observations of asymmetric upwelling that suggest anomalous mantle pressure and temperature gradients, and by observations of concentrated upwelling centres consistent with active models where buoyancy forces give rise to focused convective flow. Here we use sea-floor magnetotelluric soundings at the fast-spreading northern East Pacific Rise to image mantle electrical structure to a depth of about 160 kilometres. Our data reveal a symmetric, high-conductivity region at depths of 20-90 kilometres that is consistent with partial melting of passively upwelling mantle. The triangular region of conductive partial melt matches passive-flow predictions, suggesting that melt focusing to the ridge occurs in the porous melting region rather than along the shallower base of the thermal lithosphere. A deeper conductor observed east of the ridge at a depth of more than 100 kilometres is explained by asymmetric upwelling due to viscous coupling across two nearby transform faults. Significant electrical anisotropy occurs only in the shallowest mantle east of the ridge axis, where high vertical conductivity at depths of 10-20 kilometres indicates localized porous conduits. This suggests that a coincident seismic-velocity anomaly is evidence of shallow magma transport channels rather than deeper off-axis upwelling. We interpret the mantle electrical structure as evidence that plate-driven passive upwelling dominates this ridge segment, with dynamic forces being negligible.

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

    PubMed

    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.

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

    PubMed

    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. PMID:19940924

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

    NASA Astrophysics Data System (ADS)

    Rosenthal, A.; Yaxley, G. M.; Green, D. H.; Frost, D. J.; Kovacs, I.; Spandler, C.; Hermann, J.

    2015-12-01

    Subduction and recycling of oceanic crust entrained in adiabatic upwelling mantle causes complex heterogeneities, chemically and physically [1-3]. Yet, the creation of such heterogeneites, and their impact on magmatism remain poorly constrained. The model presented here assumes the presence of widely dispersed bodies of residual eclogites with varying bulk CaO/Na2O ratios, stirred by convection in the mantle. We examine the effects of such heterogeneities in eclogites on melting and phase relations, and on density and seismic velocity relations in mantle adiabatically upwelling from ~160 to ~90 km depth. Res2 [1] is the melting residue of a model altered MORB GA2 [2] at 5 GPa, following loss of a siliceous melt fraction during upwelling. Res3 is similar to Res2 (CaO/Na2O=4) but has a higher CaO/Na2O ratio (12). The subsolidus phases are garnet, clinopyroxene and minor quartz/coesite. The Res2 solidus is at 1210±15°C at 3 GPa, 1375±25°C at 4 GPa, and 1410±15°C at 5 GPa [1]. The Res3 solidus is similar, but slightly higher in temperature than that of Res2 at 3 GPa, 1260±15°C. Along a near-adiabatic path of Tp≈1360°C, the eclogites start to melt at higher pressure than ambient 'dry' mantle owing to the lower solidus of the former. The relative slopes of the adiabat and eclogitic solidus ensure self-fluxing continuous melting, caused by continuous exsolution of SiO2 out of clinopyroxene during adiabatic ascent. At 5 GPa, near-solidus andesitic Res3 melts (~10%) are much less siliceous and sodic, more calcic and have higher Mg# than Res2 incipient dacitic melts (<5%). During further upwelling to 3 GPa, as eclogitic melt fractions increase, they become basaltic, and cotectics control melt compositions. Siliceous eclogitic melts formed will react out of existence with peridotitic mantle, effectively refertilising it and producing hybrid, pyroxene and garnet-rich rocks [3]. As eclogitic melts differ, a variety of refertilisied, hybrid mantle rocks are formed

  11. Skew of mantle upwelling beneath the East Pacific Rise governs segmentation.

    PubMed

    Toomey, Douglas R; Jousselin, David; Dunn, Robert A; Wilcock, William S D; Detrick, R S

    2007-03-22

    Mantle upwelling is essential to the generation of new oceanic crust at mid-ocean ridges, and it is generally assumed that such upwelling is symmetric beneath active ridges. Here, however, we use seismic imaging to show that the isotropic and anisotropic structure of the mantle is rotated beneath the East Pacific Rise. The isotropic structure defines the pattern of magma delivery from the mantle to the crust. We find that the segmentation of the rise crest between transform faults correlates well with the distribution of mantle melt. The azimuth of seismic anisotropy constrains the direction of mantle flow, which is rotated nearly 10 degrees anticlockwise from the plate-spreading direction. The mismatch between the locus of mantle melt delivery and the morphologic ridge axis results in systematic differences between areas of on-axis and off-axis melt supply. We conclude that the skew of asthenospheric upwelling and transport governs segmentation of the East Pacific Rise and variations in the intensity of ridge crest processes. PMID:17377578

  12. Skew of mantle upwelling beneath the East Pacific Rise governs segmentation.

    PubMed

    Toomey, Douglas R; Jousselin, David; Dunn, Robert A; Wilcock, William S D; Detrick, R S

    2007-03-22

    Mantle upwelling is essential to the generation of new oceanic crust at mid-ocean ridges, and it is generally assumed that such upwelling is symmetric beneath active ridges. Here, however, we use seismic imaging to show that the isotropic and anisotropic structure of the mantle is rotated beneath the East Pacific Rise. The isotropic structure defines the pattern of magma delivery from the mantle to the crust. We find that the segmentation of the rise crest between transform faults correlates well with the distribution of mantle melt. The azimuth of seismic anisotropy constrains the direction of mantle flow, which is rotated nearly 10 degrees anticlockwise from the plate-spreading direction. The mismatch between the locus of mantle melt delivery and the morphologic ridge axis results in systematic differences between areas of on-axis and off-axis melt supply. We conclude that the skew of asthenospheric upwelling and transport governs segmentation of the East Pacific Rise and variations in the intensity of ridge crest processes.

  13. Seismic tomographic evidence for upwelling mantle plume in NE China

    NASA Astrophysics Data System (ADS)

    He, Chuansong; Santosh, M.

    2016-05-01

    In this study, we collected teleseismic data recorded by permanent and mobile seismic stations and carried out a teleseismic P-wave tomographic study. The results reveal low velocity perturbation regions at the central part of NE China and specifically in the Songliao basin at different depths, which correspond to the location of a proposed upwelling mantle plume identified by receiver function in a recent study. Receiver function data show a predominantly mafic/ultra-mafic lower crust in the Songliao basin, in contrast to the predominantly felsic lower crust in the other regions. The vestige of upwelling mantle plume is well defined at the mantle transition region. Based on the above results, we suggest that the volcanism in NE China and the Songliao basin formation might be related to Mesozoic mantle plume beneath NE China. We also evaluate alternate models on lower crustal delamination contributing to the volcanism in NE China following collision and amalgamation between the Siberia craton and the North China-Mongolian block during late Jurassic and early Cretaceous.

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

    NASA Astrophysics Data System (ADS)

    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 < mb < 5.5) from poorly sampled regions in order to have a more uniform data coverage. The tomographic results allow us to 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

  15. Large Topographic Rises on Venus: Implications for Mantle Upwelling

    NASA Technical Reports Server (NTRS)

    Stofan, Ellen R.; Smrekar, Suzanne E.; Bindschandler, Duane L.; Senske, David A.

    1995-01-01

    Topographic rises on Venus have been identified that are interpreted to be the surface manifestation of mantle upwellings. These features are classified into groups based on their dominant morphology. Atla and Beta Regiones are classified as rift-dominated, Dione, western Eistla, Bell, and Imdr Regiones as volcano-dominated, and Themis, eastern Eistla, and central Eistla Regiones as corona-dominated. At several topographic rises, geologic indicators were identified that may provide evidence of uplifted topography (e.g., volcanic flow features trending upslope). We assessed the minimum contribution of volcanic construction to the topography of each rise, which in general represents less than 5% of the volume of the rise, similar to the volumes of edifices at terrestrial hotspot swells. The total melt volume at each rise is approximated to be 10(exp 4) - 10(exp 6) cu km. The variations in morphology, topography, and gravity signatures at topographic rises are not interpreted to indicate variations in stage of evolution of a mantle upwelling. Instead, the morphologic variations between the three classes of topographic rises are interpreted to indicate the varying influences of lithospheric structure, plume characteristics, and regional tectonic environment. Within each class, variations in topography, gravity, and amount of volcanism may be indicative of differing stages of evolution. The similarity between swell and volcanic volumes for terrestrial and Venusian hotspots implies comparable time-integrated plume strengths for individual upwellings on the two planets.

  16. Linking mantle upwelling with the lithosphere descent [corrected] and the Japan Sea evolution: a hypothesis.

    PubMed

    Ismail-Zadeh, Alik; Honda, Satoru; Tsepelev, Igor

    2013-01-01

    Recent seismic tomography studies image a low velocity zone (interpreted as a high temperature anomaly) in the mantle beneath the subducting Pacific plate near the Japanese islands at the depth of about 400 km. This thermal feature is rather peculiar in terms of the conventional view of mantle convection and subduction zones. Here we present a dynamic restoration of the thermal state of the mantle beneath this region assimilating geophysical, geodetic, and geological data up to 40 million years. We hypothesise that the hot mantle upwelling beneath the Pacific plate partly penetrated through the subducting plate into the mantle wedge and generated two smaller hot upwellings, which contributed to the rapid subsidence in the basins of the Japan Sea and to back-arc spreading. Another part of the hot mantle migrated upward beneath the Pacific lithosphere, and the presently observed hot anomaly is a remnant part of this mantle upwelling.

  17. Linking mantle upwelling with the lithosphere decent and the Japan Sea evolution: a hypothesis

    PubMed Central

    Ismail-Zadeh, Alik; Honda, Satoru; Tsepelev, Igor

    2013-01-01

    Recent seismic tomography studies image a low velocity zone (interpreted as a high temperature anomaly) in the mantle beneath the subducting Pacific plate near the Japanese islands at the depth of about 400 km. This thermal feature is rather peculiar in terms of the conventional view of mantle convection and subduction zones. Here we present a dynamic restoration of the thermal state of the mantle beneath this region assimilating geophysical, geodetic, and geological data up to 40 million years. We hypothesise that the hot mantle upwelling beneath the Pacific plate partly penetrated through the subducting plate into the mantle wedge and generated two smaller hot upwellings, which contributed to the rapid subsidence in the basins of the Japan Sea and to back-arc spreading. Another part of the hot mantle migrated upward beneath the Pacific lithosphere, and the presently observed hot anomaly is a remnant part of this mantle upwelling. PMID:23355951

  18. Simultaneous Quantification of Temperature, Pyroxenite Abundance, and Upwelling Rates in the Iceland Mantle Source

    NASA Astrophysics Data System (ADS)

    Brown, E.; Lesher, C. E.

    2014-12-01

    The compositions and volumes of basalts erupted at the earth's surface are a function of mantle temperature, mantle composition, and the rate at which the mantle upwells through the melting zone. Thus, basaltic magmatism has long been used to probe the thermal and physiochemical state of the earth's mantle. Great insight has been gained into the mantle beneath the global spreading ridge system, where the mantle source is assumed to be homogeneous peridotite that upwells passively [1]. However, it is now recognized that many basalt source regions are lithologically heterogeneous (i.e. containing recycled lithospheric material ranging from harzburgite to pyroxenite) and upwell at rates in excess of those governed by plate separation. To account for these complexities, we have developed a forward melting model for lithologically heterogeneous mantle that incorporates thermodynamically and experimentally constrained melting functions for a range of peridotite and pyroxenite lithologies. The model is unique because it quantifies mantle upwelling rates based on the net buoyancy of the source, thus providing a means for linking basalt compositions/volumes to mantle flow while accounting for source heterogeneity. We apply the model to investigate the mantle properties governing magmatism along different rift segments in Iceland, where lithologic heterogeneity and variable upwelling rates have been inferred through geochemical means [2,3]. Using constraints from seismically determined crustal thicknesses and recent estimates of the proportion of pyroxenite-derived melt contributing to Icelandic basalt compositions [4,5], we show that mantle sources beneath Iceland have excess potential temperatures >85 °C, contain <7% pyroxenite, and maximum upwelling rates ~14 times the passive rate. Our modeling highlights the dominant role of elevated mantle temperature and enhanced upwelling for high productivity magmatism in Iceland, and a subordinate role for mantle heterogeneity

  19. 26 million years of mantle upwelling below a segment of the Mid Atlantic Ridge: The Vema Lithospheric Section revisited

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

    VLS. However, peridotite clinopyroxene geothermometry shows oscillations superimposed on a decreasing trend of calculated equilibration temperature from 26 to 18.5 Ma ago, followed by a steady increase from 16 to 4 Ma ago, suggesting that the solid mantle upwelling velocity varied through time. These results hint at the existence of ~ 10-20 Ma cycles in the activity of the northern Mid Atlantic Ridge.

  20. Mantle Plume Upwelling Rates: Evidence from U-Series in Young Ocean Island Basalts

    NASA Astrophysics Data System (ADS)

    Bourdon, B.; Turner, S. P.; Stracke, A.; Saal, A. E.

    2004-12-01

    U-series disequilibria measured in recent lavas at intraplate volcanoes provide a powerful probe to examine the validity of the plume model. U-Th and U-Pa fractionation produced during melting is a function of the melting rate. In turn, this parameter should scale with mantle upwelling velocities. Simply stated, a larger melting rate (larger mantle upwelling velocity) yields smaller Th and Pa excess relative to their parent nuclides. A number of observations supports this approach: (1) there is a negative correlation between 230Th excess and buoyancy fluxes (2) based on new measurements of 231Pa in the Azores, Iceland and the Galapagos and literature data, we show here that there is also a well defined correlation between 231Pa excess and buoyancy flux (3) For Hawaii, Iceland and the Azores, 230Th excess (or 231Pa excess) increases as a function of the distance from the centre of the `hotspot'. These observations suggests that `hotspot' buoyancy fluxes are associated with a greater melt production per unit of time and that the centre of `hotspot' corresponds to a faster mantle upwelling velocity than its periphery. This is therefore in strong support of a model where ocean islands are associated with faster upwelling at depth. However, there is in fact not a simple relationship between melt productivity and upwelling velocities. Notably, the presence of volatiles, of mafic lithologies or of variably enriched peridotitic source could all affect melting rate and hence U-Th-Pa fractionation. We have considered these issues in great detail using a large data base for the Azores islands. While there are clear variations in mantle source composition, they cannot explain the observations of increasing 231Pa/235U ratio with distance from the centre of the Azores hotspot . If we take into account the effect of water in the source of the Azores, it clearly affects the scaling between U-series fractionation and upwelling velocity but not the overall conclusions.

  1. Investigating Transition Zone Thickness Variation under the Arabian Plate: Evidence Lacking for Deep Mantle Upwellings

    NASA Astrophysics Data System (ADS)

    Juliá, J.; Tang, Z.; Mai, P. M.; Zahran, H.

    2014-12-01

    Cenozoic volcanic outcrops in Arabia - locally known as harrats - span more than 2000 km along the western half of the Arabian plate, from eastern Yemen to southern Syria. The magmatism is bimodal in character, with older volcanics (30 to 20 My) being tholeiitic-to-transitional and paralleling the Red Sea margin, and younger volcanics (12 Ma to Recent) being transitional-to-strongly-alkalic and aligning in a more north-south direction. The bimodal character has been attributed to a two-stage rifting process along the Red Sea, where the old volcanics would have produced from shallow sources related to an initial passive rifting stage, and young volcanics would have originated from one or more deep-seated mantle plumes driving present active rifting. Early models suggested the harrats would have resulted from either lateral flow from the Afar plume in Ethiopia, or more locally from a separate mantle plume directly located under the shield. Most recently, tomographic images of the Arabian mantle have suggested the northern harrats could be resulting from flow originating at a deep plume under Jordan. In this work, we investigate the location of deep mantle plumes under the Arabian plate by mapping transition zone thickness with teleseismic receiver functions. The transition zone is bounded by seismic discontinuities, nominally at 410 and 660 km depth, originating from phase transitions in the olivine-normative component of the mantle. The precise depth of the discontinuities is strongly dependent on temperature and, due to the opposing signs of the corresponding Clapeyron slopes, positive temperature anomalies are expected to result in thinning of the transition zone. Our dataset consists of ~5000 low-frequency (fc < 0.25 Hz) receiver function waveforms obtained at ~110 broadband stations belonging to a number of permanent and temporary seismic networks in the region. The receiver functions were migrated to depth and stacked along a ~2000 km long record section

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

    USGS Publications Warehouse

    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

  3. Localisation of Mantle Upwelling Beneath Recent Intra-Plate Volcanism in Australia

    NASA Astrophysics Data System (ADS)

    Davies, R.; Rawlinson, N.

    2014-12-01

    The widespread occurrence of intraplate volcanism is difficult to explain using the primary features of plate tectonics, such as subduction at convergent boundaries or upwelling at rifted margins, which are responsible for most volcanism on Earth. Instead, other mechanisms are invoked, foremost of which is the mantle plume model, typically characterised by a localised thermal upwelling that brings material from the deep mantle up to the base of the lithosphere to form a volcanic hotspot at Earth's surface. However, it is becoming increasingly apparent that many instances of intraplate volcanism do not adhere to this model, which has lead to a variety of other causes being postulated, including edge driven convection (EDC), shear driven upwelling (SDU) of the asthenosphere, lithospheric cracking, ductile removal of lithosphere via gravitational instability, glacial rebound and slab tear. Here, we use a combination of seismic tomography and geodynamic modelling to show that the source of the most recent volcanism within the Australian continent is restricted to the upper mentle and is unlikely to be plume-fed. Moreover, we demonstrate, for the first time, that mantle upwelling induced by EDC can be localised and intensified as a result of 3-D variations in lithospheric thickness and SDU caused by plate motion. In this case, geodynamic modelling constrained by seismic imaging results predicts a localised zone of mantle upwelling beneath the Quaternary Newer Volcanics Province (NVP) in southeast Australia. This helps to solve the puzzle of why EDC - which occurs at step changes in lithospheric thickness - only manifests at isolated locations along craton edges and passive margins.

  4. Mantle convection in the Middle East: Reconciling Afar upwelling, Arabia indentation and Aegean trench rollback

    NASA Astrophysics Data System (ADS)

    Faccenna, Claudio; Becker, Thorsten W.; Jolivet, Laurent; Keskin, Mehmet

    2013-08-01

    The Middle East region represents a key site within the Tethyan domain where continental break-up, collision, backarc extension and escape tectonics are kinematically linked together. We perform global mantle circulation computations to test the role of slab pull and mantle upwellings as driving forces for the kinematics of the Arabia-Anatolia-Aegean (AAA) system, evaluating different boundary conditions and mantle density distributions as inferred from seismic tomography or slab models. Model results are compared with geodetically inferred crustal motions, residual topography, and shear wave splitting measurements. The AAA velocity field with respect to Eurasia shows an anti-clockwise toroidal pattern, with increasing velocities toward the Aegean trench. The best match to these crustal motions can be obtained by combining the effect of slab pull exerted in the Aegean with a mantle upwelling underneath Afar and, more generally, with the large-scale flow associated with a whole mantle, Tethyan convection cell. Neogene volcanism for AAA is widespread, not only in the extensional or subduction settings, but also within plates, such as in Syria-Jordan-Israel and in Turkey, with geochemical fingerprints similar of those of the Afar lava. In addition, morphological features show large uplifting domains far from plate boundaries. We speculate that the tectonic evolution of AAA is related to the progressive northward entrainment of upwelling mantle material, which is itself associated with the establishment of the downwelling part of a convection cell through the segmented Tethyan slab below the northern Zagros and Bitlis collision zone. The recently established westward flow dragged Anatolia and pushed the Aegean slab south-westward, thus accelerating backarc extension. Our model reconciles Afar plume volcanism, the collision in the Bitlis mountains and northern Zagros, and the rapid increase of Aegean trench rollback in a single coherent frame of large scale mantle

  5. Response of the topography and gravity field on Venus to mantle upwelling beneath a chemical boundary layer

    NASA Technical Reports Server (NTRS)

    Smrekar, Suzanne E.; Parmentier, E. Marc

    1993-01-01

    The long wavelength correlation of the gravity and topography and the large apparent depths of compensation (approximately 150-300 km) for large highland regions on Venus require significant differences between the interior structure of Earth and Venus. The morphology, geologic history, and large apparent depths of compensation for many highlands have been interpreted to indicate areas of mantle upwelling. A large apparent depth of compensation at a mantle upwelling is generally interpreted to indicate the base of the thermal boundary layer of convection. A boundary layer thickness of 150-300 km implies that the interior of Venus is presently much colder than Earth and thus tectonically less active. The recent Magellan mission has provided contradictory evidence regarding the present level of tectonic activity on Venus, prompting considerable debate. In this study, we investigate the possibility that a chemical boundary layer acts together with a thermal boundary layer to produce large apparent depths of compensation, or equivalently, large geoid-to-topography-ratios (GTR's). The crust of a planet forms through partial melting of mantle materials. Both the melt and the residuum are lower in density than unmelted (or undepleted) mantle. In the absence of vigorous plate tectonics, a thick layer of buoyant residuum, or depleted mantle, may collect beneath the lithosphere. In this scenario, the thermal lithosphere does not need to be thick and cold to match the GTR's. Cooling of the depleted layer may lead to overturn of the upper mantle and episodic resurfacing with time scales on the order of 300-500 MY, consistent with the resurfacing age of Venus.

  6. Mantle upwelling and trench-parallel mantle flow in the northern Cascade arc indicated by basalt geochemistry

    NASA Astrophysics Data System (ADS)

    Mullen, E.; Weis, D.

    2013-12-01

    Cascadia offers a unique perspective on arc magma genesis as an end-member ';hot' subduction zone in which relatively little water may be available to promote mantle melting. The youngest and hottest subducting crust (~5 Myr at the trench) occurs in the Garibaldi Volcanic Belt, at the northern edge of the subducting Juan de Fuca plate [1]. Geochemical data from GVB primitive basalts provide insights on mantle melting where a slab edge coincides with high slab temperatures. In subduction zones worldwide, including the Cascades, basalts are typically calc-alkaline and produced from a depleted mantle wedge modified by slab input. However, basalts from volcanic centers overlying the northern slab edge (Salal Glacier and Bridge River Cones) are alkalic [2] and lack a trace element subduction signature [3]. The mantle source of the alkalic basalts is significantly more enriched in incompatible elements than the slab-modified depleted mantle wedge that produces calc-alkaline basalts in the southern GVB (Mt. Baker and Glacier Peak) [3]. The alkalic basalts are also generated at temperatures and pressures of up to 175°C and 1.5 GPa higher than those of the calc-alkaline basalts [3], consistent with decompression melting of fertile, hot mantle ascending through a gap in the Nootka fault, the boundary between the subducting Juan de Fuca plate and the nearly stagnant Explorer microplate. Mantle upwelling may be related to toroidal mantle flow around the slab edge, which has been identified in southern Cascadia [4]. In the GVB, the upwelling fertile mantle is not confined to the immediate area around the slab edge but has spread southward along the arc axis, its extent gradually diminishing as the slab-modified depleted mantle wedge becomes dominant. Between Salal Glacier/Bridge River and Glacier Peak ~350 km to the south, there are increases in isotopic ratios (ɛHf = 8.3 to13.0, ɛNd = 7.3 to 8.5, and 208Pb*/206*Pb* = 0.914 to 0.928) and trace element indicators of slab

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

    NASA Astrophysics Data System (ADS)

    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

  8. Joint seismic and geodynamic evidence for a long-lived, stable mantle upwelling under the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Forte, A. M.; Glisovic, P.; Rowley, D. B.; Simmons, N. A.; Grand, S. P.

    2013-12-01

    Global seismic tomography has consistently imaged large-scale structures in the lower mantle under the Pacific Ocean and under Africa that are characterised by strongly reduced seismic shear velocities. These so-called "low shear-velocity provinces" (LVSP) have been variously interpreted as hot, stagnant thermochemical "piles" that are compositionally dense, or as deeply rooted expressions of positively buoyant, active upwellings. To distinguish which of these two end-member models is relevant to the actual dynamics in the deep mantle requires robust constraints on the density structure of these LVSP. Recent global tomography models reveal what appear to be three distinct 'lobes' of the Pacific LVSP: one located in the Western-Pacific mantle under the Caroline Islands, another in the South-Central-Pacific mantle under French Polynesia, and another below the East Pacific Rise (EPR), centred under Easter Island. To understand the dynamics and time-dependent evolution of these structures we employ recent tomography models derived from the joint inversion of global seismic and geodynamic data sets, which also include constraints from mineral physics (Simmons et al., GJI 2009, JGR 2010). A critically important feature of these joint tomography models is the inclusion of a laterally variable scaling between density and seismic shear velocity, thereby accounting for the spatially localized effect of compositional heterogeneity in the lower mantle. These lower-mantle compositional contributions to density are directly constrained by long-wavelength gravity anomaly data and the excess ellipticity of the CMB. We show that it is not possible to properly account for this compositional heterogeneity using a constant, or simple depth-dependent density-velocity scaling. We have carried out very-long-time mantle convection simulations employing as a starting condition the joint seismic-geodynamic inferences of mantle density structure (Glisovic et al., GJI 2012). We demonstrate

  9. Receiver Function Study of the Upper Mantle Discontinuities beneath Northeast China: Evidence for Local Mantle Upwelling Beneath the Songliao Basin

    NASA Astrophysics Data System (ADS)

    Tao, K.; Chen, Y. J.; Liu, H.; Niu, F.; Ning, J.; Grand, S. P.; Kawakatsu, H.; Tanaka, S.; Necessarray Project Team

    2011-12-01

    We employ receiver function technique and pseudo-station stacking method to study the crust and upper mantle discontinuities beneath Northeast China. Receiver functions are calculated from waveforms recorded by the NorthEast China Extended SeiSmic Array (NECESSArray). NECESSArray is a large deployment of 120 high quality broadband seismographs operated by a multi-national collaboration of China, United States and Japan. The operation of this array began in September 2009 and lasted for two years. This seismic experiment was designed to study the behavior of the Pacific subducting slab in the mantle transition zone, the cause of intraplate continental magmatism and tectonics in Northeast China, and the evolution of ancient Archean lithosphere. Preliminary results show strong velocity heterogeneity beneath the Songliao basin. In this region, there is a negative pulse before the Ps conversion of the Moho in most receiver functions and this may indicate the existence of a low velocity zone in the crust of the Songliao basin. There exists a negative pulse at about 37 s which might stand for the signature of a low velocity zone above the 410-km discontinuity. The most important finding is that both of the 410-km and the 660-km discontinuities are depressed. This observation suggests that a local mantle upwelling probably exists in the upper mantle above, including the upper part of, the transition zone, while the remnant subducted Pacific slab is remained in the lower part of the transition zone.

  10. Seismic tomography shows that upwelling beneath Iceland is confined to the upper mantle

    USGS Publications Warehouse

    Foulger, G.R.; Pritchard, M.J.; Julian, B.R.; Evans, J.R.; Allen, R.M.; Nolet, G.; Morgan, W.J.; Bergsson, B.H.; Erlendsson, P.; Jakobsdottir, S.; Ragnarsson, S.; Stefansson, R.; Vogfjord, K.

    2001-01-01

    range ??? 100-300 km beneath east-central Iceland. The anomalous body is approximately cylindrical in the top 250 km but tabular in shape at greater depth, elongated north-south and generally underlying the spreading plate boundary. Such a morphological change and its relationship to surface rift zones are predicted to occur in convective upwellings driven by basal heating, passive upwelling in response to plate separation and lateral temperature gradients. Although we cannot resolve structure deeper than ??? 450 km, and do not detect a bottom to the anomaly, these models suggest that it extends no deeper than the mantle transition zone. Such models thus suggest a shallow origin for the Iceland hotspot rather than a deep mantle plume, and imply that the hotspot has been located on the spreading ridge in the centre of the north Atlantic for its entire history, and is not fixed relative to other Atlantic hotspots. The results are consistent with recent, regional full-thickness mantle tomography and whole-mantle tomography images that show a strong, low-wave-speed anomaly beneath the Iceland region that is confined to the upper mantle and thus do not require a plume in the lower mantle. Seismic and geochemical observations that are interpreted as indicating a lower mantle, or core-mantle boundary origin for the North Atlantic Igneous Province and the Iceland hotspot should be re-examined to consider whether they are consistent with upper mantle processes.

  11. The mantle transition zone beneath Antarctica: Evidence for thermal upwellings and hydration

    NASA Astrophysics Data System (ADS)

    Nyblade, Andrew; Emry, Erica; Hansen, Samantha; Julia, Jordi; Anandakrishnan, Sridhar; Aster, Richard; Wiens, Douglas; Huerta, Audrey; Wilson, Terry

    2015-04-01

    West Antarctica has experienced abundant Cenozoic volcanism, and it is suspected that the region is influenced by upwelling thermal plumes from the lower mantle; however this has not yet been verified, because seismic tomography results are not well resolved at mantle transition zone (MTZ) depths. We use P-wave receiver functions (PRFs) from temporary and permanent arrays throughout Antarctica, including the Antarctic POLENET, TAMNET, TAMSEIS, and GAMSEIS arrays, to explore the characteristics of the MTZ beneath the continent. We obtained PRFs for earthquakes occurring at 30-90° with Mb>5.5 using a time-domain iterative deconvolution method filtered with a Gaussian-width of 0.5 and 1.0, corresponding to frequencies less than ~0.24 Hz and ~0.48 Hz, respectively. We combine P receiver functions as single-station and as common conversion point stacks and migrate them to depth using the ak135 1-d velocity model. Results from West Antarctica suggest that the thickness of the MTZ varies throughout the region with thinning beneath the Ruppert Coast of Marie Byrd Land and beneath the Bentley Subglacial Trench and Whitmore Mountains. Also, prominent negative peaks are detected above the transition zone beneath much of West Antarctica and may be evidence for water-induced partial melt above the MTZ. Preliminary results from single-station stacks for the mantle transition zone beneath East Antarctica suggests that one section of East Antarctica, off of the South Pole may have slightly thinned transition zone. Results are forthcoming from the mantle transition zone beneath Victoria Land and the Northern Transantarctics. We propose that the MTZ beneath parts of West Antarctica and possibly also beneath one region of East Antarctica, is hotter than average, possibly due to material upwelling from the lower mantle. Furthermore, we propose that the transition zone beneath much of West Antarctica is water-rich and that upward migration of hydrated material results in formation of

  12. Imaging of Mantle Upwelling and Downwelling by Broadband Ocean Bottom Seismograms

    NASA Astrophysics Data System (ADS)

    Fukao, Y.; Kanazawa, T.; Suetsugu, D.; Shiobara, H.; Sugioka, H.

    2008-12-01

    Uniform coverage of the oceanic part of the globe by permanently operated broadband ocean bottom seismographs (BBOBS) is one of major observational goals in global seismology. Our effort in this direction is to deploy large-scale, long-term BBOBS arrays to fill spatial gaps of land-based broadband networks. Our main targets are the regions of mantle upwelling in the south Pacific (7 stations, 2003-2005) and downwelling in the northwestern Pacific (16 stations, 2005-2008). The background spectra based on one-year long records at 28 stations at depths ranging from 1200 to 5800 m represent the most comprehensive dataset of the Pacific seafloor noise. Noise in the tidal band synchronizes almost exactly with the tilt component of theoretical solid Earth tide. Vertical noise at 5 to 20 mHz is dominated by infragravity wave signal, with its peak shifting to the lower frequency side with increasing seafloor depth, a behavior explainable by the hydrodynamic filtering effect. Noise well below the NLNM model occurs at 30 to 100 mHz around the primary frequency of microseisms. Noise as high the NHNM model is ubiquitous in a band of the secondary frequency of microseisms. The BBOBS data have been incorporated into travel time tomography for mantle structure, receiver function analyses for topography of the 410- and 660-km discontinuities and surface wave dispersion studies for uppermost mantle structure. The large-scale Pacific superplume extends from the lowermost mantle to a depth of 1000 km, above which only narrow plumes appear to exist and continue up to the Earth"fs surface near the hotspots. The Pacific plate subducted along the Izu-Bonin-Mariana trenches accompanies a low velocity zone at its top down to depths of more than 200 km under the Philippine Sea. The stagnant slab beneath Mariana is an isolated body, well confined in a depth range from 800 to 1000 km. We lastly touch on a future direction of BBOBS seismology.

  13. Control of slab width on subduction-induced upper mantle flow and associated upwellings: Insights from analog models

    NASA Astrophysics Data System (ADS)

    Strak, Vincent; Schellart, Wouter P.

    2016-06-01

    The impact of slab width W (i.e., trench-parallel extent) on subduction-induced upper mantle flow remains uncertain. We present a series of free subduction analog models where W was systematically varied to upscaled values of 250-3600 km to investigate its effect on subducting plate kinematics and upper mantle return flow around the lateral slab edges. We particularly focused on the upwelling component of mantle flow, which might promote decompression melting and could thereby produce intraplate volcanism. The models show that W has a strong control on trench curvature and on the trench retreat, subducting plate, and subduction velocities, generally in good agreement with previous modeling studies. Upper mantle flow velocity maps produced by means of a stereoscopic particle image velocimetry technique indicate that the magnitude of the subduction-induced mantle flow around the lateral slab edges correlates positively with the product of W and trench retreat velocity. For all models an important upwelling component is always produced close to the lateral slab edges, with higher magnitudes for wider slabs. The trench-parallel lateral extent of this upwelling component is the same irrespective of W, but its maximum magnitude gets located closer to the subducting plate in the trench-normal direction and it is more focused when W increases. For W ≤ 2000 km the upwelling occurs laterally (in the trench-parallel direction) next to the subslab domain and the mantle wedge domain, while for W ≥ 2000 km it is located only next to the subslab domain and focuses closer to the trench tip, because of stronger poloidal flow in the mantle wedge extending laterally.

  14. A high-order numerical study of reactive dissolution in an upwelling heterogeneous mantle: 2. Effect of shear deformation

    NASA Astrophysics Data System (ADS)

    Baltzell, Conroy; Parmentier, E. M.; Liang, Yan; Tirupathi, Seshu

    2015-11-01

    High-porosity dunite channels produced by orthopyroxene dissolution may provide pathways for orthopyroxene-undersaturated melt generated in the deep mantle to reach shallower depth without extensive chemical reequilibration with surrounding mantle. Previous studies have considered these high-porosity channels and melt localization in the presence of a uniform upwelling mantle flow through the process of melt-rock reaction as well as shear deformation, but not both simultaneously. In this Part 2 of a numerical study of high-porosity melt and dunite channel formation during reactive dissolution, we considered the effect of shear deformation on channel distribution and channel geometry in an upwelling and viscously compacting mantle column. We formulated a high-order numerical experiment using conditions similar to those in Part 1, but with an additional prescribed horizontal shearing component in the solid matrix, as could be present in flowing mantle beneath spreading centers. Our focus was to examine orthopyroxene dissolution to determine the behavior of dunite formation and its interaction with melt flow field, by varying the upwelling and shear rate, orthopyroxene solubility gradient, and domain height. Introduction of shearing tilts the developing dunite, causing asymmetry in the orthopyroxene gradient between the dunite channels and the surrounding harzburgite. The downwind gradient is sharp, nearly discontinuous, whereas the upwind gradient is more gradual. For higher shear rates, a wave-like pattern of alternating high and low-porosity bands form on the downwind side of the channel. The band spacing increases with increasing shear rate, relative melt flow rate, and orthopyroxene solubility gradient, whereas the band angle is independent of solubility gradient and increases with increasing shear rate and decreasing relative melt flow rate. Such features could be observable in the field and provide evidence for mantle shearing. Standing wave-like patterns of

  15. Multiple mantle upwellings beneath the Northern East-African Rift System from relative P- and S-wave traveltime tomography

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Mantle plumes have been invoked as the likely cause of East African Rift volcanism and extension. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume, the African Superplume, connected to the LLSVP beneath Southern Africa, to one or more distinct lower-mantle sources along the rift. We present a new relative travel-time tomography model that images detailed P- and S- wave velocities from P,S and SKS phases below the northern East-African, Red Sea and Gulf of Aden rift. Data comes from stations that cover the area from Tanzania to Saudi Arabia. The aperture of the integrated dataset allows us to image for the first time structures of ~100 km length scale down to depths of 900 km beneath this region. Our images provide evidence of at least two low-velocity structures with a diameter of ~200 km that continue through the transition zone and into the lower mantle: the first extends to at least 900 km beneath Afar, and a second reaching at least 750 km depth just west of the Main Ethiopian Rift, a region with off-rift volcanism. Taking into account seismic sensitivity to temperature and thermally controlled phase boundary topography, we interpret these features as multiple focused upwellings from below the transition zone with excess temperatures of 100±50 K. The scale of the upwellings is smaller than any of the previously proposed lower mantle plume sources. This suggests the ponding or flow of deep-plume material below the transition zone may be spawning smaller upper-mantle upwellings.

  16. Electrical properties of the mantle upwelling zone beneath a mid-ocean ridge: An application of vertical gradient sounding

    NASA Astrophysics Data System (ADS)

    Jegen, Marion Dorothea

    On mid-ocean ridges, as adjacent plates move apart, the mantle material rises to fill the void created. During its ascent the solidus of the material is crossed and melting occurs. The melt itself is eventually emplaced at the ridge axis producing new oceanic crust. The understanding of the flow of the solid and molten material is hampered by the lack of knowledge of vital model parameters such as the connectivity of the partial melt. Connectivity is related to the permeability in the upwelling region. It therefore controls the migration pattern of the buoyant melt, the flow of the solid phase material, and the mantle upwelling mechanism. Changes in the geometry of the distribution of melt in the solid material have a large impact on the electrical conductivity. I have measured the conductivity of the upwelling region to constrain possible partial melt geometries. I present results of vertical gradient sounding (VGS) experiments on the Endeavour and Explorer ridge, which are part of the Juan de Fuca and its northern extension, the Explorer ridge, respectively. The VGS method is a natural source EM method based entirely on measurements of the magnetic fields. Electrical responses of the 1D layered normal seafloor combined with a 2D region representing the mantle upwelling zone and proposed upwelling mechanisms are derived. A comparison of the synthetic response of a range of models with data measured on the Endeavour segment shows that the conductivity in the upwelling region is very high (in the order of 1 to 5 ohm m depending on the shape of the upwelling region). The results of this experiment suggest that the pore space containing the conductive melt is well connected. The melt must be able to move freely through the upwelling region. The experiments support so called melt migration models. The data measured on the Explorer segment yielded a different conductivity model. The data do not require the presence of a pronounced 2D conductivity anomaly at depth and

  17. Tag team tectonics: mantle upwelling and lithospheric heterogeneity ally to rift continents (Invited)

    NASA Astrophysics Data System (ADS)

    Nelson, W. R.; Furman, T.

    2013-12-01

    The configuration of continents we know today is the result of several billion years of active Wilson Cycle tectonics. The rifting of continents and subsequent development of ocean basins is an integral part of long-term planetary-scale recycling processes. The products of this process can be seen globally, and the East African Rift System (EARS) provides a unique view of extensional processes that actively divide a continent. Taken together with the adjoining Red Sea and Gulf of Aden, the EARS has experienced over 40 Ma of volcanism and ~30 Ma of extension. While early (pre-rift) volcanism in the region is attributed to mantle plume activity, much of the subsequent volcanism occurs synchronously with continental rifting. Numerous studies indicate that extension and magmatism are correlated: extension leads to decompression melting while magmatism accommodates further extension (e.g. Stein et al., 1997; Buck 2004; Corti 2012). Evaluation of the entire EARS reveals significant geochemical patterns - both spatial and temporal - in the volcanic products. Compositional variations are tied directly to the melt source(s), which changes over time. These variations can be characterized broadly by region: the Ethiopian plateau and Turkana Depression, the Kenya Rift, and the Western Rift. In the Ethiopian plateau, early flood basalt volcanism is dominated by mantle plume contributions with variable input from lherzolitic mantle lithosphere. Subsequent alkaline shield volcanism flanking the juvenile Main Ethiopian Rift records the same plume component as well as contributions from a hydrous peridotitic lithosphere. The hydrous lithosphere does not contribute indefinitely. Instead, young (< 2 Ma) volcanism taps a combination of the mantle plume and anhydrous depleted lithospheric mantle. In contrast, volcanism in the Kenya Rift and the Western Rift are derived dominantly from metasomatized lithospheric mantle rather than mantle plume material. These rifts lie in the mobile

  18. Geodynamic constraints on deep-mantle buoyancy: Implications for thermochemical structure of LLSVP and large-scale upwellings under the Pacific Ocean.

    NASA Astrophysics Data System (ADS)

    Forte, A. M.; Glisovic, P.; Grand, S. P.; Lu, C.; Simmons, N. A.; Rowley, D. B.

    2015-12-01

    Convection-related data constrain lower-mantle density anomalies that contribute to mantle convective flow. These include global gravity and topography anomalies, plate motions and excess ellipticity of the core-mantle boundary (CMB). Each datum possesses differing wavelength and depth dependent resolution of heterogeneity and thus the strongest constraints on density anomalies are obtained by jointly inverting all data in combination. The joint-inversions employ viscous response functions (i.e. geodynamic kernels) for a flowing mantle. Non-uniqueness is greatly reduced by including seismic and mineral physics data into the joint inversions. We present the results of inversions where seismic and geodynamic data are singly and jointly inverted to map density anomalies. Employing mineral physical data we estimate thermal and compositional contributions to density anomalies. We evaluate the extent to which "Large Low Shear Velocity Provinces" (LLSVP) are anomalous and we determine their impact on the global pattern of convective flow. The inversions yield consistent maps of lower-mantle flow (see figure) that are dominated by two large upwellings, under the Western Pacific (next to the Caroline microplate) and Eastern Pacific (under the East Pacific Rise). These hot upwellings effectively delimit the margins of the Pacific LLSVP, suggesting intrinsic negative buoyancy within this structure impedes large-scale upwellings in the mantle above. These two upwellings do not resemble classical mantle "plumes" found in simple isoviscous and isochemical convection models but their contribution to mass and heat transport across the lower mantle is significant and thus behave similarly to plumes. The large scale of these upwellings may be understood in terms of the high viscosity in the lower mantle, inferred from geodynamic constraints on mantle rheology. Very-long time convection simulations initiated with present-day structure inferred from these inversions show the two

  19. Thermo-mechanical modeling of continental rift evolution over mantle upwelling in presence of far-field stresses

    NASA Astrophysics Data System (ADS)

    Koptev, Alexander; Burov, Evgueni; Calais, Eric; Leroy, Sylvie; Gerya, Taras

    2016-04-01

    We conducted fully-coupled high resolution rheologically consistent 3D thermo-mechanical numerical models to investigate the processes of mantle-lithosphere interaction (MLI) in presence of preexisting far-field tectonic stresses. MLI-induced topography exhibits strongly asymmetric small-scale 3D features, such as rifts, flexural flank uplifts and complex faults structures. This suggests a dominant role of continental rheological structure and intra-plate stresses in controlling continental rifting and break-up processes above mantle upwelling while reconciling the passive (far-field tectonic stresses) versus active (plume-activated) rift concepts as our experiments show both processes in action. We tested different experiments by varying two principal controlling parameters: 1) horizontal extension velocity and 2) Moho temperature used as simplified indicator of the thermal and rheological lithosphere layering. An increase in the applied extension expectedly gives less localized deformation at lithospheric scale: the growth of external velocity from 1.5 mm/years to 6 mm/years leads to enlargement of the rift zones from 75-175 km to 150-425 km width. On the contrary, increasing of the lithospheric geotherm has an opposite effect leading to narrowing of the rift zone: the change of the Moho isotherm from 600°C to 800°C causes diminution of the rift width from 175-425 km to 75-150 km. Some of these finding are contra-intuitive in terms of usual assumptions. The models refer to strongly non-linear impact of far-field extension rates on timing of break-up processes. Experiments with relatively fast far-field extension (6 mm/years) show intensive normal fault localization in crust and uppermost mantle above the plume head at 15-20 Myrs after the onset of the experiment. When plume head material reaches the bottom of the continental crust (at 25 Myrs), the latter is rapidly ruptured (<1 Myrs) and several steady oceanic floor spreading centers develop. Slower (3 mm

  20. The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity

    NASA Astrophysics Data System (ADS)

    Dobson, D. P.; Mariani, E.

    2014-12-01

    We have measured the kinetics of reaction between MgO and majoritic garnet at 20 GPa and 1773-2123 K as a proxy for the reaction between perovskite and ferropericlase during mantle upwelling across the 660 km seismic discontinuity. Ringwoodite forms a layer between MgO and garnet and, in the case of aluminous garnets the interface between ringwoodite and garnet develops a fingering instability resulting in a complex intergrowth at this interface. By contrast, the MgO-ringwoodite interface is always planar for an initial planar MgO-garnet interface. Two thicknesses are therefore defined; (1) a layer thickness, X1, which is the maximum thickness of ringwoodite which forms a plane-parallel bounded layer next to the MgO, and (2) an interface thickness, X2, which is the maximum extent of the intergrowth region away from the ringwoodite layer. The growth of both of these regions can be described by apparent rate constants, ki, which are Arrhenius with ln ⁡ (k10) = - 6.36 ± 0.25m2 /s and E1 = 456 ± 40 kJ /mol for the ringwoodite layer, and ln ⁡ (k20) = - 9.2 ± 3.3m2 /s and E2 = 371 ± 53 kJ /mol for the intergrowth region. The fingering instability is caused by the incompatibility of aluminium in ringwoodite and its low chemical diffusivity in garnet which results in an increase of surface area at the ringwoodite-garnet interface to minimise the aluminium concentration at the interface. The intergrowth region contains a fine-grained mixture of ringwoodite and garnet which coarsens very slowly with time. This might result in a transient weakening of upwelling regions of mantle just above the 660 km seismic discontinuity allowing some viscous decoupling between the upper and lower mantle.

  1. High Pressure Experimental Investigation of the Interaction between Partial Melts of Eclogite and Mantle Peridotite during Upwelling

    NASA Astrophysics Data System (ADS)

    Pinter, Z.; Rosenthal, A.; Frost, D. J.; McCammon, C. A.; Höfer, H. E.; Yaxley, G. M.; Berry, A.; Woodland, A. B.; Vasilyev, P.; Pearson, G. D.

    2015-12-01

    Many mantle-derived magmas may originate through partial melting of complex, mixed mantle rocks including not only peridotite, but also oceanic crust recycled into the mantle [1,2]. There is, however, little detailed knowledge concerning how such material is produced, how it melts, the types of liquids produced and how they are extracted from the mantle. We have conducted a series of peridotite/basalt layered experiments using an average altered mid-ocean ridge basalt GA2 [3] and fertile peridotite HZ1 [4] doped with Ir to act as a redox sensor [5,6]. Experiments were performed at 3-10 GPa, 1235-1660°C, using a multi anvil apparatus. The compositions of minerals and melts were analysed using an electron microprobe. Fourier-transform infrared and Mössbauer spectroscopy were also employed to determine the concentrations of small amounts of volatiles and the Fe3+/ΣFe ratio, respectively. Experiments yielded well-crystallised heterogeneous mantle assemblages. Similar to previous studies [3,7], 'dry' eclogite starts to melt at higher depths than ambient 'dry' mantle along adiabatic paths. Highly siliceous melts produced through near-adiabatic ascent freeze into ambient peridotite, forming distinct orthopyroxene-rich reaction zones [8]. We demonstrate that impregnating partial melts of eclogite in an upwelling mantle differ in their metasomatic effects depending on the particular adiabatic path, as suggested previously [7]. Thus, melt compositions formed by subsequent re-melting of such metasomatic assemblages strongly depend on potential temperature of the adiabat [7]. [1] Hofmann et al. Treatise Geochem 2, 2.03, 61-101 (2003) [2] Sobolev et al. Science 316, 412-417 (2007) [3] Spandler et al. J Petrol 49, 771-795 (2008) [4] Green et al. Nature 467, 448-451 (2010) [5] Stagno et al. Nature 493, 84-88 (2013) [6] Stagno et al. Contrib Mineral Petrol 169:16 (2015) [7] Rosenthal et al. Sci Rep 4, 6099 (2014) [8] Yaxley & Green Schweiz Mineral Petrogr Mitt 78, 243-255 (1998)

  2. Mantle transition zone structure beneath the Changbai volcano: Insight into deep slab dehydration and hot upwelling near the 410 km discontinuity

    NASA Astrophysics Data System (ADS)

    Tian, You; Zhu, Hongxiang; Zhao, Dapeng; Liu, Cai; Feng, Xuan; Liu, Ting; Ma, Jincheng

    2016-08-01

    We study the detailed mantle transition zone structure beneath the active Changbai intraplate volcano in Northeast China by using a receiver-function method. A total of 3005 teleseismic receiver functions recorded by 70 broadband stations are obtained by using a common-conversion-point stacking method. For conducting the time-to-depth conversion, we use a three-dimensional velocity model of the study region so as to take into account the influence of structural heterogeneities. Our results reveal significant depth variations of the 410, 520, and 660 km discontinuities. A broad depression of the 410 km discontinuity and a low-velocity anomaly are revealed beneath the Changbai volcano, which may reflect a large-scale hot mantle upwelling around the 410 km discontinuity with a positive Clapeyron slope. The 520 km discontinuity is identified clearly, and its uplift occurs above the stagnant Pacific slab. We also find a prominent depression of the 660 km discontinuity, which is elongated along the trend of deep earthquake clusters in a range of 39°N-44°N latitude, and the depression area has a lateral extent of about 400 km. Because the 520 and 660 km discontinuities correspond to positive and negative Clapeyron slopes, respectively, we think that the 520 uplift and the 660 depression are caused by the cold subducting Pacific slab. A part of the Pacific slab may have penetrated into the lower mantle and so caused the large-scale 660 depression in front of the deep earthquake clusters. Our results also reveal a part of the upper boundary of the subducting Pacific slab in the mantle transition zone.

  3. Simulation of active tectonic processes for a convecting mantle with moving continents

    USGS Publications Warehouse

    Trubitsyn, V.; Kaban, M.; Mooney, W.; Reigber, C.; Schwintzer, P.

    2006-01-01

    Numerical models are presented that simulate several active tectonic processes. These models include a continent that is thermally and mechanically coupled with viscous mantle flow. The assumption of rigid continents allows use of solid body equations to describe the continents' motion and to calculate their velocities. The starting point is a quasi-steady state model of mantle convection with temperature/ pressure-dependent viscosity. After placing a continent on top of the mantle, the convection pattern changes. The mantle flow subsequently passes through several stages, eventually resembling the mantle structure under present-day continents: (a) Extension tectonics and marginal basins form on boundary of a continent approaching to subduction zone, roll back of subduction takes place in front of moving continent; (b) The continent reaches the subduction zone, the extension regime at the continental edge is replaced by strong compression. The roll back of the subduction zone still continues after closure of the marginal basin and the continent moves towards the upwelling. As a result the ocean becomes non-symmetric and (c) The continent overrides the upwelling and subduction in its classical form stops. The third stage appears only in the upper mantle model with localized upwellings. ?? 2006 The Authors Journal compilation ?? 2006 RAS.

  4. Heterogeneous mantle anisotropy and fluid upwelling: implication for generation of the 1891 Nobi earthquake

    NASA Astrophysics Data System (ADS)

    Iidaka, Takashi; Hiramatsu, Yoshihiro

    2016-10-01

    The 1891 Nobi earthquake was the largest historic intraplate earthquake in Japan. The rupture origin corresponds to a zone of high strain rate inferred from geodetic data. To understand the geologic setting of this event, we deployed temporary seismic stations in the area. Shear-wave splitting analysis was performed using data from temporary and permanent seismic stations, revealing significant lateral variations in polarization directions. Polarization directions of NE-SW, ESE-WNW, and ENE-WSW were observed in the northeastern, central, and southwestern parts of the study area, respectively. The NE-SW- and ENE-WSW-aligned polarizations are consistent with the subduction directions of the Philippine Sea plate and Pacific plate, respectively; thus, shear-wave splitting in the northeastern and southwestern regions of the study area is likely caused by mantle wedge anisotropy, a consequence of mantle flow caused by the subducting oceanic slabs. However, the ESE-WNW orientations observed in the central Chubu Region are inconsistent with the subduction direction of either slab. Regions of low seismic velocity and low resistivity have been reported in the inferred position of the mantle wedge; these heterogeneities are thought to be caused by fluid rising from the dehydrated oceanic slabs. Thus, the ESE-WNW polarization in central Chubu could be a consequence of structural heterogeneities created by fluid to the crust from the mantle. The presence of crustal fluid is closely related to weakening, and the faults responsible for the 1891 Nobi earthquake are located just above the anisotropic region. Because fluids in the crust weaken the surrounding rock, this could explain the occurrence of the 1891 Nobi earthquake.[Figure not available: see fulltext.

  5. Multiple mantle upwellings in the transition zone beneath the northern East-African Rift system from relative P-wave travel-time tomography

    NASA Astrophysics Data System (ADS)

    Civiero, Chiara; Hammond, James O. S.; Goes, Saskia; Fishwick, Stewart; Ahmed, Abdulhakim; Ayele, Atalay; Doubre, Cecile; Goitom, Berhe; Keir, Derek; Kendall, J.-Michael; Leroy, Sylvie; Ogubazghi, Ghebrebrhan; Rümpker, Georg; Stuart, Graham W.

    2015-09-01

    Mantle plumes and consequent plate extension have been invoked as the likely cause of East African Rift volcanism. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume connected to the large low-shear-velocity province beneath Southern Africa, the so-called African Superplume, to multiple lower-mantle sources along the rift. We present a new P-wave travel-time tomography model below the northern East-African, Red Sea, and Gulf of Aden rifts and surrounding areas. Data are from stations that span an area from Madagascar to Saudi Arabia. The aperture of the integrated data set allows us to image structures of ˜100 km length-scale down to depths of 700-800 km beneath the study region. Our images provide evidence of two clusters of low-velocity structures consisting of features with diameter of 100-200 km that extend through the transition zone, the first beneath Afar and a second just west of the Main Ethiopian Rift, a region with off-rift volcanism. Considering seismic sensitivity to temperature, we interpret these features as upwellings with excess temperatures of 100 ± 50 K. The scale of the upwellings is smaller than expected for lower mantle plume sources. This, together with the change in pattern of the low-velocity anomalies across the base of the transition zone, suggests that ponding or flow of deep-plume material below the transition zone may be spawning these upper mantle upwellings. This article was corrected on 28 SEP 2015. See the end of the full text for details.

  6. Toroidal, Counter-Toroidal, and Upwelling Flow in the Mantle Wedge of the Rivera and Cocos Plates: Implications for IOB Geochemistry in the Trans-Mexican Volcanic Belt

    NASA Astrophysics Data System (ADS)

    Neumann, Florian; Vásquez-Serrano, Alberto; Tolson, Gustavo; Negrete-Aranda, Raquel; Contreras, Juan

    2016-10-01

    We carried out analog laboratory modeling at a scale 1:4,000,000 and computer rendering of the flow patterns in a simulated western Middle American subduction zone. The scaled model consists of a transparent tank filled with corn syrup and housing two conveyor belts made of polyethylene strips. One of the strips dips 60° and moves at a velocity of 30 mm/min simulating the Rivera plate. The other one dips 45°, moves at 90 mm/min simulating the subduction of the Cocos plate. Our scaled subduction zone also includes a gap between the simulated slabs analogous to a tear recently observed in shear wave tomography studies. An acrylic plate 3 mm thick floats on the syrup in grazing contact with the polyethylene strips and simulates the overriding North America plate. Our experiments reveal a deep toroidal flow of asthenospheric mantle through the Cocos-Rivera separation. The flow is driven by a pressure gradient associated with the down-dip differential-motion of the slabs. Similarly, low pressure generated by the fast-moving Cocos plate creates a shallow counter-toroidal flow in the uppermost 100 km of the mantle wedge. The flow draws mantle beneath the western Trans-Mexican Volcanic Belt to the Jalisco block, then plunges into the deep mantle by the descending poloidal cell of the Cocos slab. Moreover, our model suggests a hydraulic jump causes an ~250 km asthenosphere upwelling around the area where intra-arc extensional systems converge in western Mexico. The upwelling eventually merges with the shallow counter-toroidal flow describing a motion in 3D space similar to an Archimedes' screw. Our results indicate the differential motion between subducting slabs drives mixing in the mantle wedge of the Rivera plate and allows the slab to steepen and retreat. Model results are in good agreement with seismic anisotropy studies and the geochemistry of lavas erupted in the Jalisco block. The model can explain the eruption of OIB lavas in the vicinity of the City of

  7. Toroidal, Counter-Toroidal, and Upwelling Flow in the Mantle Wedge of the Rivera and Cocos Plates: Implications for IOB Geochemistry in the Trans-Mexican Volcanic Belt

    NASA Astrophysics Data System (ADS)

    Neumann, Florian; Vásquez-Serrano, Alberto; Tolson, Gustavo; Negrete-Aranda, Raquel; Contreras, Juan

    2015-12-01

    We carried out analog laboratory modeling at a scale 1:4,000,000 and computer rendering of the flow patterns in a simulated western Middle American subduction zone. The scaled model consists of a transparent tank filled with corn syrup and housing two conveyor belts made of polyethylene strips. One of the strips dips 60° and moves at a velocity of 30 mm/min simulating the Rivera plate. The other one dips 45°, moves at 90 mm/min simulating the subduction of the Cocos plate. Our scaled subduction zone also includes a gap between the simulated slabs analogous to a tear recently observed in shear wave tomography studies. An acrylic plate 3 mm thick floats on the syrup in grazing contact with the polyethylene strips and simulates the overriding North America plate. Our experiments reveal a deep toroidal flow of asthenospheric mantle through the Cocos-Rivera separation. The flow is driven by a pressure gradient associated with the down-dip differential-motion of the slabs. Similarly, low pressure generated by the fast-moving Cocos plate creates a shallow counter-toroidal flow in the uppermost 100 km of the mantle wedge. The flow draws mantle beneath the western Trans-Mexican Volcanic Belt to the Jalisco block, then plunges into the deep mantle by the descending poloidal cell of the Cocos slab. Moreover, our model suggests a hydraulic jump causes an ~250 km asthenosphere upwelling around the area where intra-arc extensional systems converge in western Mexico. The upwelling eventually merges with the shallow counter-toroidal flow describing a motion in 3D space similar to an Archimedes' screw. Our results indicate the differential motion between subducting slabs drives mixing in the mantle wedge of the Rivera plate and allows the slab to steepen and retreat. Model results are in good agreement with seismic anisotropy studies and the geochemistry of lavas erupted in the Jalisco block. The model can explain the eruption of OIB lavas in the vicinity of the City of

  8. Lunar maria - result of mantle plume activity?

    NASA Astrophysics Data System (ADS)

    Sharkov, E.

    It is generally accepted that lunar maria are the result of catastrophic impact events. However, comparative studying of the Earth's and the Moon's tectonomagmatic evolution could evidence about another way of these specific structures origin. Such studies showed that the both planetary bodies evolved on the close scenario: their geological development began after solidification of global magmatic oceans which led to appearance of their primordial crusts: granitic on the Earth and anorthositic - on the Moon. The further evolution of the both bodies occurred in two stages. For their first stages, lasted ˜2.5 mlrd. years on the Earth and ˜1.5 mlrd. years on the Moon, were typical melts, generated in depleted mantle (Bogatikov et al., 2000). However, at the boundary 2.2-2.0 Ga ago on the Earth and 3.9-3.8 Ga on the Moon another type of magmas appeared: geochemical enriched Fe-Ti picrites and basalts, characteristic for the terrestrial Phanerozoic plume-related situations, and basaltic mare magmatism with high-Ti varieties on the Moon. It suggests that evolution of the Earth's magmatism was linked with ascending of mantle plumes (superplumes) of two generation: (1) generated in the mantle, depleted during solidification of magmatic ocean and Archean magmatic activity, and (2) generated at the core-mantle boundary (CMB). The latter were enriched in the mantle fluid components (Fe, Ti, alkalies, etc); this lighter material could ascend to shallower depths, leading to change of tectonic processes, in particular, to appearance of plate tectonics as the major type of tectonomagmatic activity till now (Bogatikov et al., 2000). By analogy to the Earth, magmatism of the Moon was also linked with ascending of mantle plumes: (1) generated in the depleted mantle (magnesian suite) and (2) generated at the lunar CMB with liquid at that time metallic core (mare basalt and picrites with high-Ti varieties). Like on the Earth, these plumes were lighter than the older plumes, and

  9. The use of circulation weather types to predict upwelling activity along the Western Iberian Peninsula coast

    NASA Astrophysics Data System (ADS)

    Ramos, Alexandre M.; Cordeiro Pires, Ana; Sousa, Pedro M.; Trigo, Ricardo M.

    2013-04-01

    Coastal upwelling is a phenomenon that occurs in most western oceanic coasts due to the presence of mid-latitude high-pressure systems that generate equatorward winds along the coast and consequent offshore displacement of surface waters that in turn cause deeper, colder, nutrient-rich waters to arise. In western Iberian Peninsula (IP) the high-pressure system associated to northerly winds occurs mainly during spring and summer. Upwelling systems are economically relevant, being the most productive regions of the world ocean and crucial for fisheries. In this work, we evaluate the intra- and inter-annual variability of the Upwelling Index (UI) off the western coast of the IP considering four locations at various latitudes: Rias Baixas, Aveiro, Figueira da Foz and Cabo da Roca. In addition, the relationship between the variability of the occurrence of several circulation weather types (Ramos et al., 2011) and the UI variability along this coast was assessed in detail, allowing to discriminate which types are frequently associated with strong and weak upwelling activity. It is shown that upwelling activity is mostly driven by wind flow from the northern quadrant, for which the obtained correlation coefficients (for the N and NE types) are higher than 0.5 for the four considered test locations. Taking into account these significant relationships, we then developed statistical multi-linear regression models to hindcast upwelling series (April to September) at the four referred locations, using monthly frequencies of circulation weather types as predictors. Modelled monthly series reproduce quite accurately observational data, with correlation coefficients above 0.7 for all locations, and relatively small absolute errors. Ramos AM, Ramos R, Sousa P, Trigo RM, Janeira M, Prior V (2011) Cloud to ground lightning activity over Portugal and its association with Circulation Weather Types. Atmospheric Research 101:84-101. doi: 10.1016/j.atmosres.2011.01

  10. Petrology and geochemistry of mantle xenoliths from the Kapsiki Plateau (Cameroon Volcanic Line): Implications for lithospheric upwelling

    NASA Astrophysics Data System (ADS)

    Tamen, Jules; Nkoumbou, Charles; Reusser, Eric; Tchoua, Felix

    2015-01-01

    Mantle xenoliths hosted by Oligocene alkaline basalts of the Kapsiki Plateau, northern end of the Cameroon Volcanic Line consist of group I spinel and plagioclase peridotites, mainly protogranular and accessorily porphyroclastic. The sub-continental lithospheric mantle here is heterogeneous and encloses both depleted and fertile components. Minerals exhibit wide range major element compositions compared to Nyos and Kumba grabens equivalent rocks. Spinel occurs as homogeneous brown crystals or as composite (brown-core-dark-rim) crystals when in contact with diopside or swatted in melt pools. Clinopyroxene crystals are either spinel exsolution-bearing or exsolution-free, the latter being often skeletal or frameworked and riddled with intracrystalline melt pools. Intraxenolith melt pockets and veinlets are always associated to plagioclase-bearing samples. Feldspars depict two distinctive compositions (An37-66Ab57-32Or6-2 and An3-7Ab52-62Or31-48) partly attributed to host xenolith type and to the involvement in the spinel and/or diopside melting reaction of an infiltrating alkali and carbonate-rich liquid. Petrographic and geochemical data discriminate melt pockets from their host basalts, excluding thus infiltration of basaltic melt as prospective origin. Thermo-barometric estimates reveal that prior to their entrainment the Kapsiki mantle xenoliths experienced two P-T equilibrium stages resulting in subsolidus re-equilibration from spinel- to plagioclase-facies conditions. Furthermore mineral textural relations show that the occurrence of plagioclase and melts inclusions is linked to spinel and/or diopside breakdown, likely subsequent to decompression and/or metasomatic induced melting events predating Oligo-Miocene volcanism.

  11. Seismic wave propagation in the MELT Experiment area: Probing the nature of intraplate earthquakes, lithospheric anisotropy and mantle upwelling in the vicinity of the southern East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Hung, Shu-Huei

    This thesis conducts comprehensive investigations of on-going tectonic processes from observations and modeling of seismic waves propagating through the MELT Experiment area across the southern East Pacific Rise (EPR). In Chapter One, a moment-tensor inversion procedure is developed to derive the source mechanism of a sequence of teleseismic earthquakes about 300 km west of the 18sp°S EPR. All the determined events are nearly pure normal faults striking in a variety of directions with significant non-double-couple components, which are likely due to simultaneously slip on randomly-oriented fault planes. The summed moment tensor indicates no preferred orientation of horizontal extension with maximum vertical compression, consistent with the release of thermal stresses in the cooling oceanic seafloor. In Chapter Two, a parallel multi-domain pseudospectral method is developed for simulation of seismic wave propagation in generalized inhomogeneous and anisotropic media. We illustrate the variabilities in wavefront geometry and waveform complexity for different anisotropic symmetries present in the Earth. In Chapter Three, we measure shear wave splitting parameters to constrain lithospheric anisotropy in the vicinity of the earthquake swarm. Most of the resolving fast polarization directions are subparallel to the plate motion vector, attributable to crystal fabrics formed by shearing mantle flow. Some of them are scattered nearly orthogonal to the spreading direction, associated with crack-induced crustal anisotropy. Waveform modeling is employed to test the hypothesis of double-layered anisotropy. The models reconstruct the observed splitting pattern and demonstrate that shear waves split in nonuniform anisotropic layers display frequency-dependent behavior. In Chapter Four, we combine observed and synthetic waveforms and travel-time delays recorded in the MELT seismometer array to characterize the nature of mantle upwelling beneath the EPR. The similar waveforms and

  12. Studies of Coronae and Large Volcanoes on Venus: Constraining the Diverse Outcomes of Small-Scale Mantle Upwellings on Venus

    NASA Technical Reports Server (NTRS)

    Stofan, Ellen R.

    2005-01-01

    Proxemy Research had a grant from NASA to perform science research on upwelling and volcanism on Venus. This was a 3 year Planetary Geology and Geophysics grant to E. Stofan, entitled Coronae and Large volcanoes on Venus. This grant closes on 12/31/05. Here we summarize the scientific progress and accomplishments of this grant. Scientific publications and abstracts of presentations are indicated in the final section. This was a very productive grant and the progress that was made is summarized. Attention is drawn to the publications and abstracts published in each year. The proposal consisted of two tasks, one examining coronae and one studying large volcanoes. The corona task (Task 1) consisted of three parts: 1) a statistical study of the updated corona population, with Sue Smrekar, Lori Glaze, Paula Martin and Steve Baloga; 2) geologic analysis of several specific groups of coronae, with Sue Smrekar and others; and 3) determining the histories and significance of a number of coronae with extreme amounts of volcanism, with Sue Smrekar. Task 2, studies of large volcanoes, consisted of two subtasks. In the first, we studied the geologic history of several volcanoes, with John Guest, Peter Grindrod, Antony Brian and Steve Anderson. In the second subtask, I analyzed a number of Venusian volcanoes with evidence of summit diking along with Peter Grindrod and Francis Nimmo.

  13. Porosity of the melting zone and variations in the solid mantle upwelling rate beneath Hawaii: Inferences from {sup 238}U-{sup 230}Th-{sup 226}Ra and {sup 235}U-{sup 231}Pa disequilibria

    SciTech Connect

    Sims, K.W.W.; DePaolo, D.J.; Murrell, M.T.; Baldridge, W.S.; Goldstein, S.; Clague, D.; Jull, M.

    1999-12-01

    Measurements of {sup 238}U-{sup 230}Th-{sup 226}Ra and {sup 235}U-{sup 231}Pa disequilibria in a suite of tholeiitic-to-basanitic lavas provide estimates of porosity, solid mantle upwelling rate and melt transport times beneath Hawaii. The observation that ({sup 230}Th/{sup 238}U) {gt} 1 indicates that garnet is required as a residual phase in the magma sources for all of the lavas. Both chromatographic porous flow and dynamic melting of a garnet peridotite source can adequately explain the combined U-Th-Ra and U-Pa data for these Hawaiian basalts. For chromatographic porous flow, the calculated maximum porosity in the melting zone ranges from 0.3--3% for tholeiites and 0.1--1% for alkali basalts and basanites, and solid mantle upwelling rates range from 40 to 100 cm/yr for tholeiites and from 1 to 3 cm/yr for basanites. For dynamic melting, the escape or threshold porosity is 0.5--2% for tholeiites and 0.1--0.8% for alkali basalts and basanites, and solid mantle upwelling rates range from 10 to 30 cm/yr for tholeiites and from 0.1 to 1 cm/yr for basanites. Assuming a constant melt productivity, calculated total melt fractions range from 15% for the tholeiitic basalts to 3% for alkali basalts and basanites.

  14. Observed impact of upwelling events on water properties and biological activity off the southwest coast of New Caledonia.

    PubMed

    Ganachaud, Alexandre; Vega, Andrés; Rodier, Martine; Dupouy, Cécile; Maes, Christophe; Marchesiello, Patrick; Eldin, Gerard; Ridgway, Ken; Le Borgne, Robert

    2010-01-01

    The upwelling events that follow strong trade wind episodes have been described in terms of their remarkable signature in the sea surface temperature southwest off New Caledonia. Upwelling brings deeper, and colder waters to the surface, causing 2-4 degrees C drops in temperature in a few hours, followed by a slower relaxation over several days. Upwelling may sporadically bring nutrients to the surface under certain conditions, and increase the biological productivity. Two multidisciplinary hydrographic cruises allow the impact of upwelling on the chemical and biological properties of the water to be documented. Both cruises took place in austral summer (December 2004 and December 2005), but the first cruise occurred during a strong upwelling event, while the second cruise occurred in calm conditions. The water properties and planktonic composition show important contrasts, with a strong southeastward current (the "ALIS current of New Caledonia") competing with the upwelling system. Our analysis suggests that, while observed productivities are far less than those of typical upwelling systems, some wind events in New Caledonia may contribute to biological activity. A currentmeter mooring, deployed during the second cruise, documents the ocean response to a changing wind field and the local impact of upwelling on currents and temperatures on the water column. The results are discussed, with the help of climatology, Argo float profiler data, satellite data and of a high-resolution numerical simulation. PMID:20723944

  15. Three-dimensional spherical models of convection in the earth's mantle

    SciTech Connect

    Bercovici, D.; Schubert, G. ); Glatzmaier, G.A. )

    1989-05-26

    Three-dimensional, spherical models of mantle convection in the earth reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of mantle circulation. Thus, subduction zones and descending sheetlike slabs in the mantle are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs, which are cooler than the surrounding mantle. Cylindrical mantle plumes that cause hotspots such as Hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large-scale mantle circulation. Active sheetlike upwellings that could be associated with mid-ocean ridges did not develop in the model simulations, a result that is in agreement with evidence suggesting that ridges are passive phenomena resulting from the tearing of surface plates by the pull of descending slabs. 36 refs., 3 figs.

  16. Which mantle below the active rift segments in Afar?

    NASA Astrophysics Data System (ADS)

    Pik, Raphael; Stab, Martin; Ancellin, Marie-Anne; Sarah, Medynski; Cloquet, Christophe; Vye-Brown, Charlotte; Ayalew, Dereje; Chazot, Gilles; Bellahsen, Nicolas; Leroy, Sylvie

    2014-05-01

    The evolution of mantle sources beneath the Ethiopian volcanic province has long been discussed and debated with a long-lived controversy in identifying mantle reservoirs and locating them in the mantle. One interpretation of the isotopic composition of erupted lavas considers that the Afar mantle plume composition is best expressed by recent lavas from Afar and Gulf of Aden (e.g. Erta Ale, Manda Inakir and the 45°E torus anomaly on the Gulf of Aden) implying that all other volcanics (including other active segments and the initial flood basalt province) result from mixing of this plume component with additional lithospheric and asthenospheric components. A completely opposite view considers that the initial Oligocene continental flood basalts best represent the isotopic composition of the Afar mantle plume, which is subsequently mixed in various proportions with continental lithospheric mantle for generating some of the specific signature of Miocene and Quaternary volcanics. The precise and correct identification of mantle components involved in the generation of magmas is of particular importance because this is the only way to document the participation of mantle during extension and its potential role in break-up processes. In this contribution we provide new isotopic data for central Afar and we revisit the whole data set of the Ethiopian volcanic province in order to: (i) precisely identify the distinct mantle components implicated and (ii) discuss their location and evolution not only considering geochemical mixings, but also taking into account additional characteristics of erupted magmatic suites (volumes, location and relationships with amount of extension and segmentation). This new interpretation of geochemical data allows reconsidering the evolution of mantle in the course of rift evolution. In terms of mantle sources, two populations of active segments are frontally opposed in the volcanic province: those that share exactly the same composition with

  17. Plate boundary processes as alternatives to mantle plume effects on the Reykjanes Ridge

    NASA Astrophysics Data System (ADS)

    Martinez, F.; Hey, R. N.; Eason, D. E.

    2015-12-01

    The North Atlantic basin displays clear regional anomalies in depth and other features centered near Iceland. A current paradigm holds that these anomalies are due to a mantle plume and that the Reykjanes Ridge, located over this plume, is a sensitive recorder of its activity in the crust it accretes. Thus, many seafloor spreading features of the Reykjanes Ridge including axial reconfigurations from orthogonal to oblique spreading, elimination of segment offsets and transform faults, and formation of V-shaped ridges and troughs flanking the axis have been attributed to mantle plume thermal effects radiating outward from beneath Iceland. Based on new geophysical data from a R/V Marcus G Langseth cruise to the southern Reykjanes Ridge we propose an alternate hypothesis: that plate boundary processes superimposed on the larger regional anomalies can account for these seafloor spreading features. A key plate boundary process is sub-axial buoyant mantle upwelling because it can increase melt production and crustal thickness relative to passive mantle advection without changes in mantle temperature. We hypothesize that on a long and linear slow spreading ridge underlain by a regional gradient in mantle temperature and water content, buoyant mantle upwelling can propagate along axis and create many of the seafloor spreading effects currently attributed to radiating mantle plume thermal pulses. However, propagating buoyant mantle upwelling is fundamentally a wave-like phenomenon wherein only the form of upwelling propagates along axis, not actual mantle material. This has profoundly different implications for the formation of crustal structures than in mantle plume models, which require actual rapid radial mantle flow. This property of the sub-axial propagating buoyant mantle upwelling model, if correct, invalidates interpretation of prominent Reykjanes Ridge seafloor spreading features as indicators of regional mantle plume flow and requires reevaluation of geodynamic

  18. Isotopic and enzymatic analyses of planktonic nitrogen utilisation in the vicinity of Cape Sines (Portugal) during weak upwelling activity

    NASA Astrophysics Data System (ADS)

    Slawyk, Gerd; Coste, Bernard; Collos, Yves; Rodier, Martine

    1997-01-01

    Using measurements of 15N uptake and activities of nitrate reductase and glutamine synthetase, the utilization of nitrogenous nutrients by microplankton in the Portuguese upwelling area was investigated. During this cruise the euphotic zone of coastal waters was in most cases bisected by a nitracline forming two layers. Total inorganic nitrogen uptake rates (NH 4+ + NO 3-) in the upper mixed and nitrate-impoverished layer ranged from 0.1 to 0.8 nM h -1 and were primarily supported by regenerated (ammonium) nitrogen (62-97%), whereas they varied between 0.9 and 10.4 nM h -1 in the deep nitrate-rich layer and were mainly driven by new (nitrate) nitrogen (52-82%). Depth profiles of Chl a-specific uptake rates for ammonium and nitrate paralleled those of absolute uptake rates, i.e. values of VNH 4+Chl were highest (up to 16.1 nmol μg -1 h -1) in nitrate-poor surface waters while values of VNO 3-Chl were maximum (up to 8.4 nmol μg -1 h -1)within the nitracline. This latter vertical ordering of planktonic nitrogen nutrition was consistent with an aged upwelling situation. However, applying several indices of cell metabolism and nutritional status, such as 15N uptake/enzyme activity, surge uptake internally controlled uptake, and V maxChl/K t ratios, we were able to demonstrate that the phytoplankton assemblages inhabiting the nutrient-impoverished upper layer still bore the signature of physically mediated nitrogen (nitrate) supply generated by active upwelling that had occurred during the week before our visit to the area. This signature was the most evident in samples from the station furthest inshore and faded with distance from shore as a result of the deepening of the nitrate isopleths (weakening of upwelling activity), which showed the same offshore trend. The appearance of nitrate-rich waters at the surface, after a strong pulse of upwelling favourable winds just before the end of the cruise, led to a five-fold increase in average (over the euphotic zone

  19. Active mantle flow and crustal dynamics in southern California

    NASA Astrophysics Data System (ADS)

    Fay, N.; Bennett, R.; Spinler, J.

    2007-12-01

    We present numerical modeling analysis of active upper mantle flow and its role in driving crustal deformation in southern California. The forces driving lithospheric deformation at tectonic plate boundaries can be thought of as the sum from two sources: (1) forces transmitted from the far-field by rigid tectonic plates, and (2) forces created locally at the plate boundary by heterogeneous density distribution. Here we quantify the latter by estimating the stresses acting on the base of the crust caused by density-driven flow of the upper mantle. Anomalous density structure is derived from shear wave velocity models (Yang & Forsyth, 2006) and is used to drive instantaneous incompressible viscous upper mantle flow relative to a fixed crust; this allows isolation of stresses acting on the crust. Comparison of results with the finite element codes Abaqus (commercial) and GALE (community- developed) is good. We find that horizontal tractions range from 0 to ~3 MPa and vertical tractions range between approximately -15 to 15 MPa (negative indicating downward, positive upward); Absolute magnitudes depend on the assumed velocity-density scaling relationship but the overall patterns of flow are more robust. Anomalous density beneath the Transverse Ranges, in particular beneath the San Bernardino Mountains and offshore beneath the Channel Islands, drives convergent horizontal tractions and negative vertical tractions on the base of the crust there. Anomalous buoyancy beneath the southern Walker Lane Belt and anomalous density beneath the southern Great Valley create a small convective cell (the Sierra Nevada "drip"), which promotes extension on the eastern edge of the Sierra Nevada block and subsidence of the Great Valley. Favorable comparison with contemporary crustal thickness, heat flow, and surface strain rate indicates that upper mantle flow plays a very important role in active crustal deformation in southern California and much of the non-ideal behavior of this

  20. Distribution of zooplankton biomass and potential metabolic activities across the northern Benguela upwelling system

    NASA Astrophysics Data System (ADS)

    Fernández-Urruzola, I.; Osma, N.; Packard, T. T.; Gómez, M.; Postel, L.

    2014-11-01

    The distribution of zooplankton biomass and potential metabolic rates, in terms of electron transport system (ETS) and glutamate dehydrogenase (GDH), were analyzed along a cross-shelf transect in waters off Namibia. The highly variable dynamics of upwelling filaments promoted short-term fluctuations in the zooplankton biomass and metabolism. Maximum values were characteristically found over the shelf-break, where zooplankton biomass as dry mass (DM) reached peaks of 64.5 mg m- 3 within the upper 200 m in late August. Two weeks later, the zooplankton-DM decreased by more than a third (19 mg DM m- 3). Zooplankton potential respiration and NH4+ excretion averaged 234 μmol O2 m- 3 d- 1 and 169 μmol NH4+ m- 3 d- 1 in the Namibian shelf, respectively. High protein-specific ETS activities even in the low-chlorophyll waters outside the filament suggested a shift into greater omnivory seaward. In this light, zooplankton elemental and isotopic compositions were used to investigate the pelagic food web interactions. They evidenced spatial changes in the carbon resource for zooplankton as well as changes in the form of nitrogen that fueled the biological production in aging advected waters. Overall, both aspects of zooplankton metabolism impacted the primary productivity at a level less than 10% under all the different oceanographic conditions.

  1. Alkaline phosphatase activity at the southwest coast of India: A comparison of locations differently affected by upwelling

    NASA Astrophysics Data System (ADS)

    Mamatha, S. S.; Malik, Ashish; Varik, Sandesh; Parvathi, V.; Jineesh, V. K.; Gauns, Mangesh U.; LokaBharathi, P. A.

    2015-01-01

    The realization of the potential importance of phosphorus (P) as a limiting nutrient in marine ecosystem is increasing globally. Hence, the contribution of biotic variables in mobilizing this nutrient would be relevant especially in productive coastal waters. As alkaline phosphatase activity (APA) indicates the status of P for primary production in aquatic environments, we asked the following question: is the level of APA indicative of P sufficiency or deficiency in coastal waters, especially, where upwelling is a regular phenomenon? Therefore, we have examined the total APA, chlorophyll a along with phosphatase producing bacteria (PPB) and related environmental parameters from nearshore to offshore in coastal waters off Trivandrum and Kochi regions differently affected by upwelling during the onset of monsoon. Off Trivandrum, APA in the offshore waters of 5-m layer at 2.23 μM P h- 1 was > 4 times higher than nearshore. Thus, low APA could be indicative of P sufficiency in coastal waters and higher activity suggestive of deficiency in offshore waters off Trivandrum. In contrast, there was less difference in APA between near and offshore surface waters off Kochi. Our results show that the regions differently affected by upwelling respond differently according to ambient P concentration, distance from shore or depth of water. These observations could apparently be applicable to other coastal systems as well, where gradients in upwelling and phosphate runoff have been noticed. Further studies on other transects would throw more light on the extent and direction of the relationship between APA and ambient P concentration. Such studies would help in understanding the level of control of this nutrient on the productivity of coastal waters.

  2. Mantle geodynamics and implications for Earth's mantle

    NASA Astrophysics Data System (ADS)

    Lassak, Teresa Mae

    Seismic evidence suggests the presence of two large, low shear wave velocity provinces in Earth's lowermost mantle beneath Africa and the central Pacific. The origin and evolution of these provinces is not constrained but is thought to be linked to Earth's large-scale mantle dynamics. The focus of this work is to determine if seismic models of core-mantle boundary (CMB) topography can be useful in characterizing Earth's mantle dynamics. The dynamic motions in Earth's mantle exert stress on the boundaries of Earth's mantle, which results in topography at the Earth's CMB. Better understanding topography on Earth's CMB could provide important constraints on mantle dynamics and on lower mantle heterogeneity. The work in this dissertation investigates two proposed dynamical hypotheses for Earth's mantle: thermal upwellings (plume clusters) and large intrinsically dense yet thermally buoyant piles of primitive mantle material (thermochemical piles). CMB topography is calculated for each model in order to identify topography patterns that are unique to each model. CMB topographic relief beneath thermochemical piles is relatively flat and upwarped compared to downwarping CMB topography beneath downwelling regions. In plume cluster models, there is a direct correlation between upwarping relief on the CMB and upwellings while downwarping relief occurs exclusively beneath downwelling regions. The results show that both thermochemical pile and plume cluster models produce unique CMB topography signatures; thus as seismic studies better resolve the global topography of Earth's CMB, there is potential to constrain the chemical and dynamic nature of Earth's lower mantle.

  3. Activation volume for creep in the upper mantle.

    PubMed

    Ross, J V; Ave'lallemant, H G; Carter, N L

    1979-01-19

    The activation volume for creep, V*, of olivine-rich rocks has been determined in pressure-differential creep experiments on dunite at temperatures from 1100 degrees to 1350 degrees C and confining pressures from 5 to 15 kilobars. Values of V* range from 10.6 to 15.4 cubic centimeters per mole with a mean value of 13.4 cubic centimeters per mole, near that expected for oxygen ion self-diffusion. The quantity V* is incorporated into existing flow equations; in combination with observations on naturally deformed mantle xenoliths, estimates are given of the variation with depth of stress, strain rate, and viscosity. PMID:17738997

  4. Kolumbo active seamount (Greece): A window into the Aegean mantle

    NASA Astrophysics Data System (ADS)

    Rizzo, A. L.; Caracausi, A.; Chavagnac, V.; Nomikou, P.; Polymenakou, P.; Magoulas, A.; Mandalakis, M.; Kotoulas, G.

    2015-12-01

    Submarine volcanism is ubiquitous in active tectonic settings of the earth, but due to depth and hazardousness of these environments the study is a challenge. In May 2014, we performed a cruise in the Aegean Sea aimed to investigate the high-temperature (>200°C) hydrothermal system of Kolumbo active underwater volcano, 7 km northeast off Santorini. Last explosive eruption occurred in 1650 A.D. and killed ~70 people, so plainly the eruptive potential is real. We sampled gases discharged from seven chimneys located at ~500 m b.s.l. and we investigated their composition. The chemistry indicates that these consist of almost pure CO2 with a small atmospheric contamination. The δ13C-CO2 varies from 0 to 1.5‰ and shows a positive correlation with the concentration of He, H2, CO and CH4 as the result of chemical and isotope fractionation due to variable extents of gas-water interaction. The 3He/4He varies from 7.0 to 7.1 Ra, coherently with the fact that this ratio does not suffer any fractionation due to gas-water interaction. These values are surprisingly higher (more than 3 units Ra) than the measurements performed in gases and rocks from Santorini (Rizzo et al., 2015). They are in the typical range of arc volcanoes worldwide (7-9 Ra; Hilton et al., 2002; Di Piazza et al., 2015), indicating that the 3He/4He ratios measured at Kolumbo are likely the result of direct mantle degassing in a general extensive regime. More importantly, these ratios are the highest in all the South Aegean volcanism, which leads to consider homogeneous (and MORB-like) the He isotope composition of the mantle below the central part of the Hellenic Volcanic Arc and eastward up to Nisyros, which until this study showed the highest ratios (6.2Ra; Shimizu et al., 2005). Our results strongly emphasize the role of tectonics in the transfer of fluids from the mantle toward the surface. The complicated geodynamics status of the Aegean-Anatolian region, plays a key role in generating crustal

  5. Groundwater Sustainability in the Michigan Lowlands - Understanding the Complex Interplay of Natural Brine Upwelling, Human Activity, and Climate Change

    NASA Astrophysics Data System (ADS)

    Curtis, Z. K.; Li, S. G.; Sampath, P. V.; Liao, H. S.

    2015-12-01

    /analysis to simulate the complex interplay of human activity, natural upwelling, and climate change. Insight from the modeling effort will be used to inform resource planners and policy makers of various groundwater management options available to vulnerable communities across the Lower Peninsula of Michigan in years to come.

  6. Mantle dynamics following supercontinent formation

    NASA Astrophysics Data System (ADS)

    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

  7. Intense submesoscale upwelling in anticyclonic eddies

    NASA Astrophysics Data System (ADS)

    Brannigan, L.

    2016-04-01

    Observations from around the global ocean show that enhanced biological activity can be found in anticyclonic eddies. This may mean that upwelling of nutrient-rich water occurs within the eddy, but such upwelling is not captured by models that resolve mesoscale processes. High-resolution simulations presented here show intense submesoscale upwelling from the thermocline to the mixed layer in anticyclonic eddies. The properties of the upwelling are consistent with a process known as symmetric instability. A simple limiting nutrient experiment shows that this upwelling can drive much higher biological activity in anticyclonic eddies when there is a high nutrient concentration in the thermocline. An estimate for the magnitude of upwelling associated with symmetric instability in anticyclonic eddies in the Sargasso Sea shows that it may be of comparable magnitude to other processes, though further work is required to understand the full implications for basin-scale nutrient budgets.

  8. Relationship between observed upper mantle structures and recent tectonic activity across the Southeastern United States

    NASA Astrophysics Data System (ADS)

    Biryol, C. Berk; Wagner, Lara S.; Fischer, Karen M.; Hawman, Robert B.

    2016-05-01

    The lithospheric structure of the Southeastern United States is a product of earlier episodes of continental collision and breakup. The region is located in the interior of the North American Plate, away from active plate margins. However, there is ongoing tectonism in the region with multiple zones of seismicity, uplifting arches, and Cenozoic intraplate volcanism. The mechanisms controlling this activity and the state of stress remain enigmatic. Two important factors are plate strength and preexisting, inherited structures. Here we present new tomographic images of the upper mantle beneath the Southeastern United States, revealing large-scale structural variations in the upper mantle. Examples include the relatively thick lithospheric mantle of stable North America that abruptly thins beneath the Paleozoic Appalachian orogeny, and the slow upper mantle of the Proterozoic Reelfoot rift. Our results also indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering. This provides a viable explanation for seismicity, uplifting, and young intraplate volcanism. We postulate that not only tectonic inheritance but also continuing lithospheric foundering may control the ongoing activity of the region long after it became a passive margin. Based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere, we propose that piecemeal delamination has occurred beneath the region throughout the Cenozoic, removing a significant amount of reworked/deformed mantle lithosphere. Ongoing lithospheric foundering beneath the eastern margin of stable North America explains significant variations in thickness of lithospheric mantle across the former Grenville deformation front.

  9. Widespread distribution of ascending fluids transporting mantle helium in the fore-arc region and their upwelling processes: Noble gas and major element composition of deep groundwater in the Kii Peninsula, southwest Japan

    NASA Astrophysics Data System (ADS)

    Morikawa, Noritoshi; Kazahaya, Kohei; Takahashi, Masaaki; Inamura, Akihiko; Takahashi, Hiroshi A.; Yasuhara, Masaya; Ohwada, Michiko; Sato, Tsutomu; Nakama, Atsuko; Handa, Hiroko; Sumino, Hirochika; Nagao, Keisuke

    2016-06-01

    Chemical and isotopic studies including analyses of noble gases were comprehensively conducted on the groundwater of the entire Kii Peninsula, which is located in the fore-arc region of southwest Japan. Groundwater of Na-Cl-HCO3, Na-HCO3-Cl, and Na-Cl types was shown to be distributed across the whole area. Groundwater in the inland central part of the peninsula shows relatively low salinity, whereas groundwater from the area along the ENE-trending Median Tectonic Line (MTL), on the north side of the peninsula, shows high salinity (up to 18,800 mg/L of Cl-) and the presence of unusual heavy oxygen isotopes. This trend is similar to that documented in saline waters from the Arima region (the so-called "Arima-type thermal water"). High 3He/4He ratios relative to the atmospheric value (up to 6.7 Ra) were recorded throughout the Kii Peninsula, covering a wider area than documented previously. The saline groundwater is also strongly depleted in 20Ne and heavy noble gases. From the wide distribution of high 3He/4He values and the associated 20Ne and Cl- concentrations, we infer that aqueous fluids derived from dehydration of the subducting slab are present at depth beneath almost the entire Kii Peninsula. These aqueous fluids may ascend along the major north-dipping boundary faults. The isotopic composition of groundwater from the southern part of the peninsula suggests that the contribution from these dehydration-derived fluids is relatively small in this region. However, volatile components (e.g., noble gases and CO2) in the groundwater of this area may originate from the dehydration-derived fluids. Upwelling of Arima-type thermal water of the Na-Cl-HCO3 type is expected to undergo a phase separation of volatile species due to decompression as the fluid ascends. The variety of water types documented may be due to this water-gas separation and the subsequent incorporation of gaseous species into shallow meteoric groundwater. The observed high 3He/4He ratios in the

  10. Intermittent upwelling of asthenosphere beneath the Gregory Rift, Kenya

    SciTech Connect

    Tatsumi, Yoshiyuki Kyoto Univ. ); Kimura, Nobukazu ); Itaya, Tetsumaru ); Koyaguchi, Takehiro ); Suwa, Kanenori )

    1991-06-01

    K-Ar dates and chemical compositions of basalts in the Gregory Rift, Kenya, demonstrate marked secular variation of lava chemistry. Two magmatic cycles characterized by incompatible element relative depletion are recognized; both occurring immediately after the peak of basaltic volcanism and coeval with both trachyte/phonolite volcanism and domal uplift of the region. These cycles may be attributed to increasing degree of partial melting of mantle source material in association with thinning of the lithosphere by thermal erosion through contact with hot upwelling asthenospheric mantle. Cyclic variation in asthenosphere upwelling may be considered an important controlling process in the evolution of the Gregory Rift.

  11. Melt extraction in the Earth's mantle: Constraints from U Th Pa Ra studies in oceanic basalts

    NASA Astrophysics Data System (ADS)

    Stracke, Andreas; Bourdon, Bernard; McKenzie, Dan

    2006-04-01

    U-series studies in oceanic basalts are critical for understanding melting and melt extraction in the Earth's mantle. The combined results of a detailed geochemical study of melting and melt extraction at Theistareykir, northern Iceland, provide a strong case for melt extraction via channeled melt flow at an active spreading ridge. It has often been argued, however, that widely used melting and melt extraction models, which simulate channeled melt extraction (i.e. fractional and/or dynamic melting), can only partially explain the global U-series systematics in oceanic basalts. As a consequence, more complicated models have been invoked, which suggest different styles of melt extraction at different depths/pressures in the mantle, so-called "two-porosity models". Alternatively, diffusion-controlled mechanisms have been proposed. Here we show that U-Th-Pa-Ra systematics in oceanic basalts can indeed be explained by models where melt transport occurs without chemical equilibrium between melt and solid when variations in all three critical melting parameters (residual porosity, upwelling rate of the solid mantle and melt velocity) are taken into account. Melting at ridges requires systematic variation of at least two critical melting parameters, most likely upwelling and melt extraction rate. Melts generated with increasing lateral distance to the ridge axis are generated with slower upwelling rates and are extracted with lower velocities than melts created closer to the ridge axis. Melting at ocean islands, on the other hand, can successfully be explained by variations in upwelling rate only. Global U-series systematics in OIB originate from superimposed global variations in upwelling velocity due to different buoyancy fluxes and from local variation in upwelling velocity as a function of radial distance to the plume center. The model proposed here is consistent with other geochemical data for oceanic basalts and strongly supports melt extraction via high

  12. Dynamics of the Active Altiplano Puna Magmatic Body: Large-Scale Melt Transport and Buoyant Upwelling

    NASA Astrophysics Data System (ADS)

    Diez, M.; Del Potro, R.

    2014-12-01

    A wide range of geophysical observations suggest that an active partially molten region (Altiplano Puna Magmatic Body or APMB) lies in the mid-upper crust of the Altiplano Puna Plateau, in the Central Andes, with its upper contact at around 20 km depth. In particular, gravity, magnetotellurics and seismics have helped delineating the overall geometry of this intrusive body, which is approximately 200 km in diameter and could be many kilometers thick. The average melt fraction is poorly constrained, although it has been suggested that it could be rather high, around ~15% or higher. In addition to constraining the general shape of the APMB, its dynamics can in principle be partially accessed through geodetic measurements at the surface. In fact, recent InSAR-related studies have shown a ground deformation rate in the order of centimeter per year, with a central uplifting region, centered roughly around a lava-dome complex type of system, Uturuncu volcano, surrounded by an extensive peripheral zone of subsidence. This wealth of observations has leaded us to propose two different hypotheses to partially explain the inner workings of the APMB: (i) the dynamic deformation of the uplift-subsidence of the surface is explained by the impingement of a buoyant melt-rich blob on the more brittle upper levels of the crust, and; (ii) such surface deformation could be associated to the poroviscous compaction induced by lateral melt transport toward a central region of ascent. Both scenarios are modeled numerically. In principle the two hypotheses could explain the rate and geometry of subsidence under some simplifications. We discuss the consequences of both hypotheses, and entertain the possibility of both processes operating together.

  13. SEASONAL EFFECTS ON COMET NUCLEI EVOLUTION: ACTIVITY, INTERNAL STRUCTURE, AND DUST MANTLE FORMATION

    SciTech Connect

    De Sanctis, M. C.; Capria, M. T.; Lasue, J.

    2010-07-15

    Rotational properties can strongly influence a comet's evolution in terms of activity, dust mantling, and internal structure. In this paper, we investigate the effects of various rotation axis directions on the activity, internal structure, and dust mantling of cometary nuclei. The numerical code developed is able to reproduce different shapes and spin axis inclinations, taking into account both the latitudinal and the longitudinal variations of illumination, using a quasi-three-dimensional approach. The results obtained show that local variations in the dust and gas fluxes can be induced by the different spin axis directions and completely different behaviors of the comet evolution can result in the same cometary shape by using different obliquities of the models. The internal structures of cometary nuclei are also influenced by comet obliquity, as well as dust mantling. Gas and dust production rates show diversities related to the comet seasons.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  15. Mantle compensation of active metamorphic core complexes at Woodlark rift in Papua New Guinea.

    PubMed

    Abers, Geoffrey A; Ferris, Aaron; Craig, Mitchell; Davies, Hugh; Lerner-Lam, Arthur L; Mutter, John C; Taylor, Brian

    2002-08-22

    In many highly extended rifts on the Earth, tectonic removal of the upper crust exhumes mid-crustal rocks, producing metamorphic core complexes. These structures allow the upper continental crust to accommodate tens of kilometres of extension, but it is not clear how the lower crust and underlying mantle respond. Also, despite removal of the upper crust, such core complexes remain both topographically high and in isostatic equilibrium. Because many core complexes in the western United States are underlain by a flat Moho discontinuity, it has been widely assumed that their elevation is supported by flow in the lower crust or by magmatic underplating. These processes should decouple upper-crust extension from that in the mantle. In contrast, here we present seismic observations of metamorphic core complexes of the western Woodlark rift that show the overall crust to be thinned beneath regions of greatest surface extension. These core complexes are actively being exhumed at a rate of 5-10 km Myr(-1), and the thinning of the underlying crust appears to be compensated by mantle rocks of anomalously low density, as indicated by low seismic velocities. We conclude that, at least in this case, the development of metamorphic core complexes and the accommodation of high extension is not purely a crustal phenomenon, but must involve mantle extension.

  16. Asymmetric three-dimensional topography over mantle plumes.

    PubMed

    Burov, Evgueni; Gerya, Taras

    2014-09-01

    The role of mantle-lithosphere interactions in shaping surface topography has long been debated. In general, it is supposed that mantle plumes and vertical mantle flows result in axisymmetric, long-wavelength topography, which strongly differs from the generally asymmetric short-wavelength topography created by intraplate tectonic forces. However, identification of mantle-induced topography is difficult, especially in the continents. It can be argued therefore that complex brittle-ductile rheology and stratification of the continental lithosphere result in short-wavelength modulation and localization of deformation induced by mantle flow. This deformation should also be affected by far-field stresses and, hence, interplay with the 'tectonic' topography (for example, in the 'active/passive' rifting scenario). Testing these ideas requires fully coupled three-dimensional numerical modelling of mantle-lithosphere interactions, which so far has not been possible owing to the conceptual and technical limitations of earlier approaches. Here we present new, ultra-high-resolution, three-dimensional numerical experiments on topography over mantle plumes, incorporating a weakly pre-stressed (ultra-slow spreading), rheologically realistic lithosphere. The results show complex surface evolution, which is very different from the smooth, radially symmetric patterns usually assumed as the canonical surface signature of mantle upwellings. In particular, the topography exhibits strongly asymmetric, small-scale, three-dimensional features, which include narrow and wide rifts, flexural flank uplifts and fault structures. This suggests a dominant role for continental rheological structure and intra-plate stresses in controlling dynamic topography, mantle-lithosphere interactions, and continental break-up processes above mantle plumes. PMID:25186903

  17. Asymmetric three-dimensional topography over mantle plumes.

    PubMed

    Burov, Evgueni; Gerya, Taras

    2014-09-01

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

  18. Geology of the Crust and Mantle, Western United States: Geophysical data reveal a thin crust and anomalous upper mantle characteristic of active regions.

    PubMed

    Thompson, G A; Talwani, M

    1964-12-18

    compressional and transverse waves in the upper mantle may be related to this problem. Whatever its origin and composition, an anomalous upper mantle characterizes many regions of present or recent tectonic activity, such as Japan and the Mid-Atlantic Ridge (39). The anomalous mantle of western North America might form a continuous belt to the south, with anomalous mantle beneath the crest of the East Pacific Rise (40). The anomalous upper mantle may thus be an essential part of the heat engine driving the tectonic activity of these regions. The Basin and Range region was broken into blocks and laterally extended during the Cenozoic uplift, so that some blocks lagged behind, or sank. Some of the intricate disruption of the upper crust may be related to shallow Cenozoic volcanism. The relatively large and rigid Sierra Nevada block may have been tilted westward during Basin-Range deformation because of the high density of greenstones on the west side and the lower density of granitic rocks to the east. Man's environment, in the longer view of geologic time, is strongly influenced by mountain-building processes originating in the earth's crust and mantle. In the scale of a few lifetimes, climate, sea level, and the shape of the land are appreciably altered. How this comes about, and whether man can hope to influence the processes, are challenging, unsolved problems. But enough has now been learned about the crust and mantle to suggest precisely what questions must be answered and what critical experiments performed. Note added in proof: Osborne (42) has directed our attention to the possibility that the granitic rocks and also the andesites and dacites were formed by fractional crystallization of basaltic magma under conditions of high oxygen pressure. This possibility in no way conflicts with the geophysical data. In fact, such direct additions to the silicic upper crust from the mantle or lower crust would simplify the perplexing problem of how the crust is replenished in areas

  19. Geology of the Crust and Mantle, Western United States: Geophysical data reveal a thin crust and anomalous upper mantle characteristic of active regions.

    PubMed

    Thompson, G A; Talwani, M

    1964-12-18

    compressional and transverse waves in the upper mantle may be related to this problem. Whatever its origin and composition, an anomalous upper mantle characterizes many regions of present or recent tectonic activity, such as Japan and the Mid-Atlantic Ridge (39). The anomalous mantle of western North America might form a continuous belt to the south, with anomalous mantle beneath the crest of the East Pacific Rise (40). The anomalous upper mantle may thus be an essential part of the heat engine driving the tectonic activity of these regions. The Basin and Range region was broken into blocks and laterally extended during the Cenozoic uplift, so that some blocks lagged behind, or sank. Some of the intricate disruption of the upper crust may be related to shallow Cenozoic volcanism. The relatively large and rigid Sierra Nevada block may have been tilted westward during Basin-Range deformation because of the high density of greenstones on the west side and the lower density of granitic rocks to the east. Man's environment, in the longer view of geologic time, is strongly influenced by mountain-building processes originating in the earth's crust and mantle. In the scale of a few lifetimes, climate, sea level, and the shape of the land are appreciably altered. How this comes about, and whether man can hope to influence the processes, are challenging, unsolved problems. But enough has now been learned about the crust and mantle to suggest precisely what questions must be answered and what critical experiments performed. Note added in proof: Osborne (42) has directed our attention to the possibility that the granitic rocks and also the andesites and dacites were formed by fractional crystallization of basaltic magma under conditions of high oxygen pressure. This possibility in no way conflicts with the geophysical data. In fact, such direct additions to the silicic upper crust from the mantle or lower crust would simplify the perplexing problem of how the crust is replenished in areas

  20. Seafloor doming driven by active mantle degassing offshore Naples (Italy)

    NASA Astrophysics Data System (ADS)

    Ventura, Guido; Passaro, Salvatore; Tamburrino, Stella; Vallefuoco, Mattia; Tassi, Franco; Vaselli, Orlando; Giannini, Luciano; Caliro, Stefano; Chiodini, Giovanni; Sacchi, Marco; Rizzo, Andrea

    2016-04-01

    Structures and processes associated with shallow water hydrothermal fluid discharges on continental shelves are poorly known. We report geomorphological, geophysical, and geochemical evidences of a 5.5 x 5.3 km seabed doming located 5 km offshore the Naples harbor (Italy). The dome lies between 100 and 170 m of water depth and it is 15-20 m higher than the surrounding seafloor. It is characterized by a hummocky morphology due to 280 sub-circular to elliptical mounds, about 660 cones, and 30 pockmarks. The mounds and pockmarks alignments follow those of the main structural discontinuity affecting the Gulf of Naples. The seafloor swelling and breaching require relatively low pressures (about 2-3 MPa), and the sub-seafloor structures, which consists of 'pagodas' affecting the present-day seabed, record the active upraise, pressurization, and release of magmatic fluids. The gas composition of the sampled submarine emissions is consistent with that of the emissions from the hydrothermal systems of Ischia, CampiFlegrei and Somma-Vesuvius active volcanoes, and CO2 has a magmatic/thermometamorphic origin. The 3He/4He ratios (1.66-1.96 Ra) are slightly lower than in the Somma-Vesuvius and Campi Flegrei volcanoes (~2.6-3.0 Ra) indicating the contamination of fluids originated from the same magmatic source by crustal-derived radiogenic 4He. All these evidences concur to hypothesize an extended magmatic reservoir beneath Naples and its offshore. Seabed doming, faulting, and hydrothermal discharges are manifestations of non-volcanic unrests potentially preluding submarine eruptions and/or hydrothermal explosions. We conclude that seabed deformations and hydrothermal discharge must be included in the coastal hazard studies.

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

    NASA Astrophysics Data System (ADS)

    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

  2. Mantle dynamics beneath the Pacific Northwest and the generation of voluminous back-arc volcanism

    NASA Astrophysics Data System (ADS)

    Long, Maureen D.; Till, Christy B.; Druken, Kelsey A.; Carlson, Richard W.; Wagner, Lara S.; Fouch, Matthew J.; James, David E.; Grove, Timothy L.; Schmerr, Nicholas; Kincaid, Chris

    2012-08-01

    The Pacific Northwest (PNW) has a complex tectonic history and over the past ˜17 Ma has played host to several major episodes of intraplate volcanism. These events include the Steens/Columbia River flood basalts (CRB) and the striking spatiotemporal trends of the Yellowstone/Snake River Plain (Y/SRP) and High Lava Plains (HLP) regions. Several different models have been proposed to explain these features, which variously invoke the putative Yellowstone plume, rollback and steepening of the Cascadia slab, extensional processes in the lithosphere, or a combination of these. Here we integrate seismologic, geodynamic, geochemical, and petrologic results from the multidisciplinary HLP project and associated analyses of EarthScope USArray seismic data to propose a conceptual model for post-20 Ma mantle dynamics beneath the PNW and the relationships between mantle flow and surface tectonomagmatic activity. This model invokes rollback subduction as the main driver for mantle flow beneath the PNW beginning at ˜20 Ma. A major pulse of upwelling due to slab rollback and upper plate extension and consequent melting produced the Steens/CRB volcanism, and continuing trench migration enabled mantle upwelling and hot, shallow melting beneath the HLP. An additional buoyant mantle upwelling is required to explain the Y/SRP volcanism, but subduction-related processes may well have played a primary role in controlling its timing and location, and this upwelling likely continues today in some form. This conceptual model makes predictions that are broadly consistent with seismic observations, geodynamic modeling experiments, and petrologic and geochemical constraints.

  3. New Insights into the Basin and Swell Dynamics of Africa Driven by Whole-Mantle Convection (Invited)

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Over the past decade, a number of geodynamic studies have attempted to relate different surface manifestations of mantle convection under the African plate, such as plate velocity, gravity and topography anomalies, to the underlying mantle flow. To date, these studies have not been successful in simultaneously reconciling the ensemble of these geodynamic data with the 3-D pattern of convection below Africa. This difficulty has hampered efforts to elucidate the detailed relationship between mantle convection and surface dynamics, in particular the unique basin and swell physiography of the African continent. We present a recent tomography-based mantle convection model derived from the joint inversion of seismic, geodynamic and mineral physical data sets that successfully reproduces the totality of the convection-related data outlined above [Forte et al., EPSL 2010]. The resolution of 3-D mantle structure provided by this new convection model also yields detailed regional maps of shallow mantle flow which clearly connect late-Cenozoic volcanic structures and adjacent basins to asthenospheric upwellings and downwellings, respectively. We find strong asthenospheric upwellings under the African swells such as the Hoggar massif, Main Ethiopian Rift, Kenya domes, Cameroon volcanic line, Canary and Cape Verde Islands. These upwellings of hot mantle material are driven by active, positive buoyancy forces that extend deep into the mantle. The convection model also reveals a distinct pattern of downwellings below the main African basins, in particular the Congo in central Africa and the offshore Somali basin. The subcontinental downwellings below these basins appear to provide a heretofore unrecognised mechanism for accommodating the opening of the East African Rift system. Such 'rift-accommodating' downwellings are similar to that predicted under the eastern margin of the Arabian plate, in the Persian Gulf, in response to the opening of the Red Sea.

  4. Uppermost mantle (Pn) velocity model for the Afar region, Ethiopia: an insight into rifting processes

    NASA Astrophysics Data System (ADS)

    Stork, A. L.; Stuart, G. W.; Henderson, C. M.; Keir, D.; Hammond, J. O. S.

    2013-04-01

    The Afar Depression, Ethiopia, offers unique opportunities to study the transition from continental rifting to oceanic spreading because the process is occurring onland. Using traveltime tomography and data from a temporary seismic deployment, we describe the first regional study of uppermost mantle P-wave velocities (VPn). We find two separate low VPn zones (as low as 7.2 km s-1) beneath regions of localized thinned crust in northern Afar, indicating the existence of high temperatures and, potentially, partial melt. The zones are beneath and off-axis from, contemporary crustal magma intrusions in active magmatic segments, the Dabbahu-Manda-Hararo and Erta'Ale segments. This suggests that these intrusions can be fed by off-axis delivery of melt in the uppermost mantle and that discrete areas of mantle upwelling and partial melting, thought to characterize segmentation of the uppermost mantle at seafloor spreading centres, are initiated during the final stages of break-up.

  5. Mantle Plumes and Geologically Recent Volcanism on Mars

    NASA Astrophysics Data System (ADS)

    Kiefer, W. S.

    2013-12-01

    Despite its small size, Mars has remained volcanically active until the geologically recent past. Crater retention ages on the volcanos Arsia Mon, Olympus Mons, and Pavonis Mons indicate significant volcanic activity in the last 100-200 million years. The radiometric ages of many shergottites, a type of igneous martian meteorite, indicate igneous activity at about 180 million years ago. These ages correspond to the most recent 2-4% of the age of the Solar System. The most likely explanation for this young martian volcanism is adiabatic decompression melting in upwelling mantle plumes. Multiple plumes may be active at any time, with each of the major volcanos in the Tharsis region being formed by a separate plume. Like at least some terrestrial mantle plumes, mantle plumes on Mars likely form via an instability of the thermal boundary layer at the base of the mantle. Because Mars operates in the stagnant lid convection regime, the temperature difference between mantle and core is lower than on Earth. This reduces the temperature contrast between mantle and core, resulting in mantle plumes on Mars that are about 100 K hotter than the average mantle. The chemical composition of the martian meteorites indicates that the martian mantle is enriched in both iron and sodium relative to Earth's mantle. This lowers the dry solidus on early Mars by 30-40 K relative to Earth. Migration of sodium to the crust over time decreases this difference in solidus temperature to about 15 K at present, but that is sufficient to increase the current plume magma production rate by a factor of about 2. Hydrous phases in the martian meteorites indicate the presence of a few hundred ppm water in the mantle source region, roughly the same as Earth. Finite element simulations of martian plumes using temperature-dependent viscosity and realistic Rayleigh numbers can reproduce the geologically recent magma production rate that is inferred from geologic mapping and the melt fraction inferred from

  6. Seismic activity response as observed in mantled howlers (Alouatta palliata), Cuero y Salado Wildlife Refuge, Honduras.

    PubMed

    Snarr, Kymberley Anne

    2005-10-01

    This report documents the response of wild mantled howlers (Alouatta palliata) to coseismic activity (seismic activity at the time of an earthquake). During field work on the north coast of Honduras, data were collected on a habituated troop of mantled howlers as they responded to coseismic activity. The seismic event occurred on 13 February 2001 at 0822 hours local time with a magnitude of Richter scale 6.6, focus depth of approximately 15 km at a distance of 341 km from the epicentre to the field site, Cuero y Salado. At the field site, based upon Jeffreys and Bullen (1988), body waves, noted as P and S waves, arrived at 60 and 87 s, respectively, with surface waves arriving approximately 103 s post-origin time of the seismic event. While there are three reports on non-human primate response to coseismic activity in the literature, they report on captive non-human primates. This is the first documented response on a non-captive troop. In addition, this report compares the intensity measure encountered by a wild troop of howlers and one captive group of orangutans as set out by the Modified Mercalli Intensity scale. The Modified Mercalli measure of intensity is one of two standard measures of seismic activity and rates what a person sees and feels at their location (Wood and Neumann 1931; Richter 1958). Thus, arboreal nonhuman primates are found to respond to coseismic activity ranging from Level IV to Level VI as based upon the modified Mercalli intensity scale.

  7. North Atlantic magmatism controlled by temperature, mantle composition and buoyancy

    NASA Astrophysics Data System (ADS)

    Brown, Eric L.; Lesher, Charles E.

    2014-11-01

    Large igneous provinces are characterized by anomalously high rates of magma production. Such voluminous magmatism is commonly attributed to partial melting of hot, buoyantly upwelling mantle plume material. However, compositional heterogeneity in the mantle, caused by the subduction of oceanic crust, can also enhance magma production, diminishing the need for elevated temperatures associated with upwelling plumes. A plume origin for the North Atlantic large igneous province has been questioned because lava compositions correlate with crustal thickness, implying a link between magma productivity and mantle source composition. Here we use a numerical model that simulates upwelling and melting of compositionally heterogeneous mantle material to constrain the conditions that gave rise to magmatism in the North Atlantic. Using observations of lava compositions and volumes from the North Atlantic, we show that subducted crustal material represented less than 10% of the mantle source. We further show that mantle temperatures have remained elevated by 85-210 °C and increased mantle upwelling up to 14 times the rate of plate separation has occurred over the past 56 Myr. The enhanced temperatures and upwelling rates extended along more than 1,000 km of the Palaeogene rift, but are substantially more restricted along the modern Mid-Atlantic Ridge. These findings reflect the long-term manifestation of a mantle plume.

  8. Actively heated high-resolution fiber-optic-distributed temperature sensing to quantify streambed flow dynamics in zones of strong groundwater upwelling

    NASA Astrophysics Data System (ADS)

    Briggs, Martin A.; Buckley, Sean F.; Bagtzoglou, Amvrossios C.; Werkema, Dale D.; Lane, John W.

    2016-07-01

    Zones of strong groundwater upwelling to streams enhance thermal stability and moderate thermal extremes, which is particularly important to aquatic ecosystems in a warming climate. Passive thermal tracer methods used to quantify vertical upwelling rates rely on downward conduction of surface temperature signals. However, moderate to high groundwater flux rates (>-1.5 m d-1) restrict downward propagation of diurnal temperature signals, and therefore the applicability of several passive thermal methods. Active streambed heating from within high-resolution fiber-optic temperature sensors (A-HRTS) has the potential to define multidimensional fluid-flux patterns below the extinction depth of surface thermal signals, allowing better quantification and separation of local and regional groundwater discharge. To demonstrate this concept, nine A-HRTS were emplaced vertically into the streambed in a grid with ˜0.40 m lateral spacing at a stream with strong upward vertical flux in Mashpee, Massachusetts, USA. Long-term (8-9 h) heating events were performed to confirm the dominance of vertical flow to the 0.6 m depth, well below the extinction of ambient diurnal signals. To quantify vertical flux, short-term heating events (28 min) were performed at each A-HRTS, and heat-pulse decay over vertical profiles was numerically modeled in radial two dimension (2-D) using SUTRA. Modeled flux values are similar to those obtained with seepage meters, Darcy methods, and analytical modeling of shallow diurnal signals. We also observed repeatable differential heating patterns along the length of vertically oriented sensors that may indicate sediment layering and hyporheic exchange superimposed on regional groundwater discharge.

  9. Upwelling relaxation and estuarine plumes

    NASA Astrophysics Data System (ADS)

    Rao, Shivanesh; Pringle, James; Austin, Jay

    2011-09-01

    After coastal upwelling, the water properties in the nearshore coastal region close to estuaries is determined by the race between the new estuarine plume traveling along the coast and the upwelled front (a marker for the old upwelled plume and the coastal pycnocline) returning to the coast under downwelling winds. Away from an estuary, downwelling winds can return the upwelled front to the coast bringing less dense water nearshore. Near the estuary, the estuarine plume can arrive along the coast and return less dense water to the nearshore region before the upwelled front returns to the coast. Where the plume brings less dense water to the coast first, the plume keeps the upwelled front from returning to the coast. In this region, only the plume and the anthropogenic input and larvae associated with the plume waters influence the nearshore after upwelling. We quantify the extent of the region where the plume is responsible for bringing less dense water to the nearshore and keeping the upwelled front from returning to the coast after upwelling. We successfully tested our predictions against numerical experiments and field observations of the Chesapeake plume near Duck, North Carolina. We argue that this alongshore region exists for other estuaries where the time-integrated upwelling and downwelling wind stresses are comparable.

  10. Thermal and chemical convection in planetary mantles

    NASA Technical Reports Server (NTRS)

    Dupeyrat, L.; Sotin, C.; Parmentier, E. M.

    1995-01-01

    Melting of the upper mantle and extraction of melt result in the formation of a less dense depleted mantle. This paper describes series of two-dimensional models that investigate the effects of chemical buoyancy induced by these density variations. A tracer particles method has been set up to follow as closely as possible the chemical state of the mantle and to model the chemical buoyant force at each grid point. Each series of models provides the evolution with time of magma production, crustal thickness, surface heat flux, and thermal and chemical state of the mantle. First, models that do not take into account the displacement of plates at the surface of Earth demonstrate that chemical buoyancy has an important effect on the geometry of convection. Then models include horizontal motion of plates 5000 km wide. Recycling of crust is taken into account. For a sufficiently high plate velocity which depends on the thermal Rayleigh number, the cell's size is strongly coupled with the plate's size. Plate motion forces chemically buoyant material to sink into the mantle. Then the positive chemical buoyancy yields upwelling as depleted mantle reaches the interface between the upper and the lower mantle. This process is very efficient in mixing the depleted and undepleted mantle at the scale of the grid spacing since these zones of upwelling disrupt the large convective flow. At low spreading rates, zones of upwelling develop quickly, melting occurs, and the model predicts intraplate volcanism by melting of subducted crust. At fast spreading rates, depleted mantle also favors the formation of these zones of upwelling, but they are not strong enough to yield partial melting. Their rapid displacement toward the ridge contributes to faster large-scale homogenization.

  11. Superplumes and the Viscosity Structure of the Mantle

    NASA Astrophysics Data System (ADS)

    Hansen, U.; Yuen, D.

    2004-05-01

    Seismological studies indicate the existence of large upwelling regions of complex structures in the lower mantle. A mantle flow model with only a few strong upwellings is an alternative to conventional convection models with respect not only to pattern of the flow but also to heat transport and mixing properties. By two- and three-dimensional numerical models we demonstrate that a significant increase of the viscosity with pressure in the lower mantle leads to a focusing of buoyancy into strong upwellings from the core-mantle boundary.This phenomenon is further enhanced by a thermal expansion coefficient which decreases with pressure. Besides pressure, the viscosity of the mantle material will strongly depend on temperature. Combining the effects of temperature and pressure-dependent viscosity, generates a significant viscosity maximum in the lower mantle. Pressure dependence let the viscosity increase from the upper to the lower mantle, temperature dependence, however, compensates this effect at greater depth. The spatiotemporal evolution of plumes is likewise influenced: While a purely pressure-dependent viscosity creates single plumes, additional temperature dependence leads to plume-clusters, characterized by instabilities at the core-mantle boundary, which are centered around a strong upwelling flow. These plumes generate a complex flow pattern at the base of the mantle.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  13. Why productive upwelling areas are often sources rather than sinks of CO2? - A comparative study on eddy upwellings in the South China Sea

    NASA Astrophysics Data System (ADS)

    Jiao, N.; Zhang, Y.; Zhou, K.; Li, Q.; Dai, M.; liu, J.; Guo, J.; Huang, B.

    2013-12-01

    Marine upwelling regions are known to be productive in carbon fixation and thus thought to be sinks of CO2, whereas many upwelling areas in the ocean are actually sources rather than sinks of CO2. To address this paradox, multiple biogeochemical parameters were investigated at two cyclonic-eddy-induced upwelling sites CE1 and CE2 in the western South China Sea. The results showed that upwelling can exert significant influences on biological activities in the euphotic zone and can either increase or decrease particulate organic carbon (POC) export flux depending on upwelling conditions such as the magnitude, timing, and duration of nutrient input and consequent microbial activities. At CE2 the increase of phytoplankton biomass caused by the upwelled nutrients resulted in increase of POC export flux compared to non-eddy reference sites, while at CE1 the microbial respiration of organic carbon stimulated by the upwelled nutrients significantly contributed to the attenuation of POC export flux, aggravating outgassing of CO2. These results suggest that on top of upwelled dissolved inorganic carbon release, microbial activities stimulated by upwelled nutrients and phytoplankton labile organic carbon can play a critical role for a marine upwelling area to be a source rather than a sink of CO2. Meanwhile, we point out that even though an upwelling region is outgassing, carbon sequestration still takes place through the POC-based biological pump as well as the refractory dissolved organic carbon (RDOC)-based microbial carbon pump.

  14. Tharsis: Consequence of Mars' Dichotomy and Layered Mantle

    NASA Astrophysics Data System (ADS)

    Wenzel, M. J.; Manga, M.; Jellinek, A. M.

    2003-12-01

    The two largest and most striking features on Mars are the crustal dichotomy, the nearly hemispheric division in topography, gravity, crustal thickness, and age, and Tharsis, a volcanic center active from the Noachian to the present. Tharsis' long-term persistence of localized volcanism is, to the best of our knowledge, unique in the solar system. Explaining the timing of Tharsis volcanism, from initiation early in martian history to recent activity, has been an enduring challenge. Here we present an model of the martian mantle that can explain early and persistent volcanism at Tharsis by incorporating the effects of the crustal dichotomy and a compositionally layered mantle. As the crust is expected to be enriched in heat-producing elements, this dichotomy in thickness leads to a dichotomous heat flux boundary condition on the mantle, which affects the internal dynamics. The evidence for layering includes the ability of a layered mantle to simultaneously meet a chondritic bulk composition and the moment-of-inertia factor (Elkins-Tanton et al., in revision), which can not be done with a one-layered mantle. In addition, studies of the martian meteorites suggest that the martian mantle is heterogeneous, a constraint that can be met with layering. We perform analog laboratory experiments with corn syrup to simulate Mars' thermal evolution. We vary the presence of a partial insulating lid, to simulate the effect of the dichotomy, and layering in the convecting fluid. We show that in the case of a layered mantle and an insulating lid, a large swell, which acts to localize upwelling plumes under the lid, forms early and endures for the scaled equivalent of billions of years. Linda T. Elkins-Tanton, E. M. Parmentier, and P. C. Hess, "Magma ocean fractional crystallization and cumulate overturn in terrestrial planets: implications for Mars," in revision for Meteoritics and Planetary Science.

  15. Pevonedistat, a NEDD8-activating enzyme inhibitor, is active in mantle cell lymphoma and enhances rituximab activity in vivo.

    PubMed

    Czuczman, Natalie M; Barth, Matthew J; Gu, Juan; Neppalli, Vishala; Mavis, Cory; Frys, Sarah E; Hu, Qiang; Liu, Song; Klener, Pavel; Vockova, Petra; Czuczman, Myron S; Hernandez-Ilizaliturri, Francisco J

    2016-03-01

    Mantle cell lymphoma (MCL) is characterized by an aggressive clinical course and inevitable development of refractory disease, stressing the need to develop alternative therapeutic strategies. To this end, we evaluated pevonedistat (MLN4924), a novel potent and selective NEDD8-activating enzyme inhibitor in a panel of MCL cell lines, primary MCL tumor cells, and 2 distinct murine models of human MCL. Pevonedistat exposure resulted in a dose-, time-, and caspase-dependent cell death in the majority of the MCL cell lines and primary tumor cells tested. Of interest, in the MCL cell lines with lower half-maximal inhibitory concentration (0.1-0.5 μM), pevonedistat induced G1-phase cell cycle arrest, downregulation of Bcl-xL levels, decreased nuclear factor (NF)-κB activity, and apoptosis. In addition, pevonedistat exhibited additive/synergistic effects when combined with cytarabine, bendamustine, or rituximab. In vivo, as a single agent, pevonedistat prolonged the survival of 2 MCL-bearing mouse models when compared with controls. Pevonedistat in combination with rituximab led to improved survival compared with rituximab or pevonedistat monotherapy. Our data suggest that pevonedistat has significant activity in MCL preclinical models, possibly related to effects on NF-κB activity, Bcl-xL downregulation, and G1 cell cycle arrest. Our findings support further investigation of pevonedistat with or without rituximab in the treatment of MCL. PMID:26675347

  16. Small-scale convective instability and upper mantle viscosity under California

    SciTech Connect

    Zandt, G.; Carrigan, C.R. )

    1993-07-23

    Thermal calculations and convection analysis, constrained by seismic tomography results, suggest that a small-scale convective instability developed in the upper 200 kilometers of the mantle under California after the upwelling and cooling of asthenosphere into the slab window associated with the formation of the San Andreas transform boundary. The upper bound for the upper mantle viscosity in the slab window, 5 [times] 10[sup 19] pascal seconds, is similar to independent estimates for the asthenosphere beneath young oceanic and tectonically active continental regions. These model calculations suggest that many tectonically active continental regions characterized by low upper mantle seismic velocities may be affected by time-dependent small-scale convection that can generate localized areas of uplift and subsidence.

  17. Small-scale convective instability and upper mantle viscosity under california.

    PubMed

    Zandt, G; Carrigan, C R

    1993-07-23

    Thermal calculations and convection analysis, constrained by seismic tomography results, suggest that a small-scale convective instability developed in the upper 200 kilometers of the mantle under California after the upwelling and cooling of asthenosphere into the slab window associated with the formation of the San Andreas transform boundary. The upper bound for the upper mantle viscosity in the slab window, 5 x 10(19) pascal seconds, is similar to independent estimates for the asthenosphere beneath young oceanic and tectonically active continental regions. These model calculations suggest that many tectonically active continental regions characterized by low upper mantle seismic velocities may be affected by time-dependent small-scale convection that can generate localized areas of uplift and subsidence. PMID:17770025

  18. Small-scale convective instability and upper mantle viscosity Under California

    NASA Astrophysics Data System (ADS)

    Zandt, George; Carrigan, Charles R.

    1993-07-01

    Thermal calculations and convection analysis, constrained by seismic tomography results, suggest that a small-scale convective instability developed in the upper 200 kilometers of the mantle under California after the upwelling and cooling of asthenosphere into the slab window associated with the formation of the San Andreas transform boundary. The upper bound for the upper mantle viscosity in the slab window, 5 x 1019 pascal seconds, is similar to independent estimates for the asthenosphere beneath young oceanic and tectonically active continental regions. These model calculations suggest that many tectonically active continental regions characterized by low upper mantle seismic velocities may be affected by time-dependent small-scale convection that can generate localized areas of uplift and subsidence.

  19. Superplumes and Plume-Clustering: Dynamical Influences from Mantle Rheology

    NASA Astrophysics Data System (ADS)

    Hansen, U.; Yuen, D. A.

    2003-04-01

    Seismological studies indicate the existence of large upwelling regions of complex structures in the lower mantle. A mantle flow model with only a few strong upwellings is an alternative to conventional convection models with respect not only to pattern of the flow but also to heat transport and mixing properties. By two- and three-dimensional numerical models we demonstrate that a significant increase of the viscosity with pressure in the lower mantle leads to a focusing of buoyancy into strong upwellings from the core-mantle boundary. Taking into account a realistically decreasing coefficient of thermal expansion further facilitates the generation of superplumes. Besides pressure, the viscosity of the mantle material will strongly depend on temperature. Combining the effects of temperature and pressure-dependent viscosity, generates a significant viscosity maximum in the lower mantle. Pressure dependence let the viscosity increase from the upper to the lower mantle, temperature dependence, however, compensates this effect at greater depth. The spatiotemporal evolution of plumes is likewise influenced: While a purely pressure-dependent viscosity creates single plumes, additional temperature dependence leads to plume-clusters, characterized by instabilities at the core-mantle boundary, which are centered around a strong upwelling flow.

  20. The p-wave upper mantle structure beneath an active spreading centre - The Gulf of California

    NASA Technical Reports Server (NTRS)

    Walck, M. C.

    1984-01-01

    Over 1400 seismograms of earthquakes in Mexico are analyzed and data sets for the travel time, apparent phase velocity, and relative amplitude information are utilized to produce a tightly constrained, detailed model for depths to 900 km beneath an active oceanic ridge region, the Gulf of California. The data are combined by first inverting the travel times, perturbing that model to fit the p-delta data, and then performing trial and error synthetic seismogram modelling to fit the short-period waveforms. The final model satisfies all three data sets. The ridge model is similar to existing upper mantle models for shield, tectonic-continental, and arc-trench regimes below 400 km, but differs significantly in the upper 350 km. Ridge model velocities are very low in this depth range; the model 'catches up' with the others with a very large velocity gradient from 225 to 390 km.

  1. Salinity driven oceanographic upwelling

    DOEpatents

    Johnson, David H.

    1986-01-01

    The salinity driven oceanographic upwelling is maintained in a mariculture device that includes a long main duct in the general shape of a cylinder having perforated cover plates at each end. The mariculture device is suspended vertically in the ocean such that one end of the main duct is in surface water and the other end in relatively deep water that is cold, nutrient rich and relatively fresh in comparison to the surface water which is relatively warm, relatively nutrient deficient and relatively saline. A plurality of elongated flow segregating tubes are disposed in the main duct and extend from the upper cover plate beyond the lower cover plate into a lower manifold plate. The lower manifold plate is spaced from the lower cover plate to define a deep water fluid flow path to the interior space of the main duct. Spacer tubes extend from the upper cover plate and communicate with the interior space of the main duct. The spacer tubes are received in an upper manifold plate spaced from the upper cover plate to define a surface water fluid flow path into the flow segregating tubes. A surface water-deep water counterflow is thus established with deep water flowing upwardly through the main duct interior for discharge beyond the upper manifold plate while surface water flows downwardly through the flow segregating tubes for discharge below the lower manifold plate. During such counterflow heat is transferred from the downflowing warm water to the upflowing cold water. The flow is maintained by the difference in density between the deep water and the surface water due to their differences in salinity. The upwelling of nutrient rich deep water is used for marifarming by fertilizing the nutrient deficient surface water.

  2. Salinity driven oceanographic upwelling

    DOEpatents

    Johnson, D.H.

    1984-08-30

    The salinity driven oceanographic upwelling is maintained in a mariculture device that includes a long main duct in the general shape of a cylinder having perforated cover plates at each end. The mariculture device is suspended vertically in the ocean such that one end of the main duct is in surface water and the other end in relatively deep water that is cold, nutrient rich and relatively fresh in comparison to the surface water which is relatively warm, relatively nutrient deficient and relatively saline. A plurality of elongated flow segregating tubes are disposed in the main duct and extend from the upper cover plate beyond the lower cover plate into a lower manifold plate. The lower manifold plate is spaced from the lower cover plate to define a deep water fluid flow path to the interior space of the main duct. Spacer tubes extend from the upper cover plate and communicate with the interior space of the main duct. The spacer tubes are received in an upper manifold plate spaced from the upper cover plate to define a surface water fluid flow path into the flow segregating tubes. A surface water-deep water counterflow is thus established with deep water flowing upwardly through the main duct interior for discharge beyond the upper manifold plate while surface water flows downwardly through the flow segregating tubes for discharge below the lower manifold plate. During such counterflow heat is transferred from the downflowing warm water to the upflowing cold water. The flow is maintained by the difference in density between the deep water and the surface water due to their differences in salinity. The upwelling of nutrient rich deep water is used for marifarming by fertilizing the nutrient deficient surface water. 1 fig.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  5. Mantle dynamics beneath the Pacific Northwest and the generation of post-20 Ma volcanism

    NASA Astrophysics Data System (ADS)

    Long, M. D.; Till, C. B.; Druken, K. A.; Fouch, M. J.; James, D. E.; Grove, T. L.; Wagner, L. S.; Kincaid, C. R.; Carlson, R. W.

    2011-12-01

    The Pacific Northwest (PNW) has a complex recent tectonic history and over the past ~17 Ma has played host to several major episodes of intraplate volcanism. These include the Steens/Columbia River flood basalts (CRB) and the striking spatiotemporal trends of the Yellowstone/Snake River Plain (Y/SRP) and High Lava Plains (HLP) regions. Several different models have been proposed to explain these features, which variously invoke the putative Yellowstone plume, the rollback and steepening of the Cascadia slab, extensional processes in the lithosphere, or a combination of these. Here we integrate seismological, geodynamical, petrological, and geochemical results from the multidisciplinary HLP project and associated efforts related to EarthScope data to propose a conceptual model for mantle dynamics beneath the PNW and the relationships between mantle flow and surface tectonomagmatic activity. The model invokes rollback subduction as the main driver for mantle flow beneath the PNW; a major pulse of upwelling due to the initiation of rollback drove melting associated with the Steens/CRB volcanism and continuing trench migration enabled hot, shallow melting beneath the HLP. A buoyant mantle upwelling is required to explain the Y/SRP volcanism, but subduction-related processes likely played a role in controlling its timing and location. This conceptual model makes predictions that are broadly consistent with seismic anisotropy measurements, tomographic velocity models, geodynamical modeling experiments, petrological constraints, and geochemical observations.

  6. Intraplate volcanism and mantle dynamics in East Asia: Big mantle wedge (BMW) model (Invited)

    NASA Astrophysics Data System (ADS)

    Zhao, D.

    2009-12-01

    In the East Asia continent there are many Cenozoic volcanoes, but only a few are still active now, such as the Changbai, Wudalianchi, and Tengchong volcanoes which have erupted several times in the past 1000 years. Although many studies have been made by using various approaches, the origin of the intraplate volcanoes in East Asia is still not very clear. Recently we used regional and global seismic tomography to determine high-resolution 3-D mantle structure under Western Pacific to East Asia (Zhao, 2004; Huang and Zhao, 2006; Zhao et al., 2009). Our results show prominent low-velocity anomalies from the surface down to 410 km depth beneath the intraplate volcanoes and a broad high-velocity anomaly in the mantle transition zone under East Asia. Focal-mechanism solutions of deep earthquakes indicate that the subducting Pacific slab under the Japan Sea and the East Asia margin is subject to compressive stress regime. These results suggest that the Pacific slab meets strong resistance at the 660-km discontinuity and so it becomes stagnant in the mantle transition zone under East Asia. The Philippine Sea slab has also subducted down to the mantle transition zone under western Japan and the Ryukyu back-arc region. The western edge of the stagnant slab is generally parallel with the Japan trench and the Ryukyu trench and roughly coincides with a prominent surface topography and gravity boundary in East China, which is located approximately 1800 km west of the trenches. The upper mantle under East Asia has formed a big mantle wedge (BMW) above the stagnant slab. The BMW exhibits low seismic-velocity and high electrical-conductivity, which is hot and wet because of the deep dehydration reactions of the stagnant slab and the convective circulation process in the BMW. These processes lead to the upwelling of hot and wet asthenospheric materials and thinning and fracturing of the continental lithosphere, leading to the formation of the active intraplate volcanoes in East

  7. Is there any mantle plume beneath Tristan da Cunha?

    NASA Astrophysics Data System (ADS)

    Schloemer, A.; Geissler, W. H.; Jegen, M. D.; Jokat, W.

    2015-12-01

    Tristan da Cunha is a volcanic island in the South Atlantic located very close to the Mid-Atlantic Ridge. Generally, it is accepted to be the location of a mantle plume, which has been active at least since the breakup of Gondwana at 130 Ma, the time when the Paraná/Etendeka flood basalts were emplaced. Furthermore, it is associated with the formation of the Walvis Ridge and the Rio Grande Rise, and therefore it's one of the key examples of a hot spot track linking a flood basalt province to an active ocean island volcano. However, global tomography models are contradicting about the origin of Tristan da Cunha: Whether it is a deep mantle plume or caused by shallow plate tectonics. To gain a better understanding, we deployed 24 broadband ocean-bottom seismometers, 26 ocean-bottom electromagnetic stations and 2 seismological land stations in January 2012 with the German research vessel Maria S. Merian. We acquired continuous seismological data for one year and recovered the instruments in January 2013.We use cross-correlated travel time residuals of teleseismic earthquakes to perform a finite-frequency tomography to resolve the P wave velocity upper mantle structure beneath the island. Here we show our preliminary results of the 3-D velocity perturbations in the upper mantle: We do not image a plume-like structure directly beneath the island. Instead we observe a low velocity region in the southwest of our array that might be related to a local mantle upwelling (mantle plume). Additionally we show the local seismicity in the Tristan da Cunha region.Chen et al. and Baba et al. will present the first results on the magnetotelluric experiment and Ryberg et al. will present the crustal structure around the Tristan da Cunha hotspot.

  8. Adaptation strategy of bivalve Modiolus modiolus from upwelling regions of the Kuril Islands shelf (Sea of Okhotsk) to heavy metal effects

    NASA Astrophysics Data System (ADS)

    Kavun, Victor Ya.; Podgurskaya, Olga V.

    2009-06-01

    Cd, Cu, Fe, Mn, Ni, Pb, Zn concentration in the organs (muscle, gonads, mantle, gills, digestive gland, kidney) of mussel Modiolus modiolus was studied. Mussels were collected from shelf upwelling sites of Kuril Is. Sea of Okhotsk (104 and 85 m) and, for comparison, coastal high contaminated and clean sites (Peter the Great Bay, Sea of Japan). It was found that mussels from shelf upwelling regions accumulated unusually high Cd concentration in studied organs, excepting digestive gland. Shelf mussels have evolved passive adaptation to elevated level of ambient heavy metals (distribution of heavy metal load between all organs, especially, muscle). In contrast, mussels from high contaminated sites have evolved active adaptation (strong regulation of metal concentration in the organs at the maximal permissible concentration due to increased kidney function). We supported that under natural condition, passive adaptation of aquatic organisms to increased ambient metal level have been evolved only under constant low-water temperature.

  9. Measles Virus Entry Through the Signaling Lymphocyte Activation Molecule Governs Efficacy of Mantle Cell Lymphoma Radiovirotherapy

    PubMed Central

    Miest, Tanner S; Frenzke, Marie; Cattaneo, Roberto

    2013-01-01

    We developed here a vaccine-identical measles virus (MV) as an oncolytic agent against mantle cell lymphoma (MCL), an aggressive B-cell non-Hodgkin's lymphoma that is difficult to cure but radiosensitive. We armed the virus with the sodium-iodide symporter, which concentrates iodide within infected cells enabling noninvasive imaging and combination radiovirotherapy. Through high-resolution in vivo and ex vivo imaging, we visualized the spread of infections in primary and metastatic tumors for over 2 weeks after therapy, documenting homogeneous virus seeding and spread restricted to perfused tissue. Infection of metastases was more rapid and intense than primary tumors, achieving isotope uptake within about threefold the efficiency of the thyroid. Virotherapy combined with systemic 131I resulted in more rapid disease regression than either therapy alone. In addition to ubiquitous CD46, vaccine MV retains cell entry through its immune cell-specific receptor signaling lymphocytic activation molecule (SLAM). We asked whether both receptors could sustain effective oncolysis of MCL. Strikingly, only SLAM-dependent entry sustained efficient viral spread, tumor regression, and prolonged survival. These observations shift the focus of future clinical trials to SLAM-expressing hematologic malignancies and suggest that oncolytic vectors may depend on tissue-specific receptors for both cell entry and activation of responses assisting their replication. PMID:23913184

  10. Measles virus entry through the signaling lymphocyte activation molecule governs efficacy of mantle cell lymphoma radiovirotherapy.

    PubMed

    Miest, Tanner S; Frenzke, Marie; Cattaneo, Roberto

    2013-11-01

    We developed here a vaccine-identical measles virus (MV) as an oncolytic agent against mantle cell lymphoma (MCL), an aggressive B-cell non-Hodgkin's lymphoma that is difficult to cure but radiosensitive. We armed the virus with the sodium-iodide symporter, which concentrates iodide within infected cells enabling noninvasive imaging and combination radiovirotherapy. Through high-resolution in vivo and ex vivo imaging, we visualized the spread of infections in primary and metastatic tumors for over 2 weeks after therapy, documenting homogeneous virus seeding and spread restricted to perfused tissue. Infection of metastases was more rapid and intense than primary tumors, achieving isotope uptake within about threefold the efficiency of the thyroid. Virotherapy combined with systemic (131)I resulted in more rapid disease regression than either therapy alone. In addition to ubiquitous CD46, vaccine MV retains cell entry through its immune cell-specific receptor signaling lymphocytic activation molecule (SLAM). We asked whether both receptors could sustain effective oncolysis of MCL. Strikingly, only SLAM-dependent entry sustained efficient viral spread, tumor regression, and prolonged survival. These observations shift the focus of future clinical trials to SLAM-expressing hematologic malignancies and suggest that oncolytic vectors may depend on tissue-specific receptors for both cell entry and activation of responses assisting their replication.

  11. Birch's Mantle

    NASA Astrophysics Data System (ADS)

    Anderson, D. L.

    2002-12-01

    Francis Birch's 1952 paper started the sciences of mineral physics and physics of the Earth's interior. Birch stressed the importance of pressure, compressive strain and volume in mantle physics. Although this may seem to be an obvious lesson many modern paradoxes in the internal constitution of the Earth and mantle dynamics can be traced to a lack of appreciation for the role of compression. The effect of pressure on thermal properties such as expansivity can gravitational stratify the Earth irreversibly during accretion and can keep it chemically stratified. The widespread use of the Boussinesq approximation in mantle geodynamics is the antithesis of Birchian physics. Birch pointed out that eclogite was likely to be an important component of the upper mantle. Plate tectonic recycling and the bouyancy of oceanic crust at midmantle depths gives credence to this suggestion. Although peridotite dominates the upper mantle, variations in eclogite-content may be responsible for melting- or fertility-spots. Birch called attention to the Repetti Discontinuity near 900 km depth as an important geodynamic boundary. This may be the chemical interface between the upper and lower mantles. Recent work in geodynamics and seismology has confirmed the importance of this region of the mantle as a possible barrier. Birch regarded the transition region (TR ; 400 to 1000 km ) as the key to many problems in Earth sciences. The TR contains two major discontinuities ( near 410 and 650 km ) and their depths are a good mantle thermometer which is now being exploited to suggest that much of plate tectonics is confined to the upper mantle ( in Birch's terminology, the mantle above 1000 km depth ). The lower mantle is homogeneous and different from the upper mantle. Density and seismic velocity are very insensitive to temperature there, consistent with tomography. A final key to the operation of the mantle is Birch's suggestion that radioactivities were stripped out of the deeper parts of

  12. Not so hot "hot spots" in the oceanic mantle.

    PubMed

    Bonath, E

    1990-10-01

    Excess volcanism and crustal swelling associated with hot spots are generally attributed to thermal plumes upwelling from the mantle. This concept has been tested in the portion of the Mid-Atlantic Ridge between 34 degrees and 45 degrees (Azores hot spot). Peridotite and basalt data indicate that the upper mantle in the hot spot has undergone a high degree of melting relative to the mantle elsewhere in the North Atlantic. However, application of various geothermometers suggests that the temperature of equilibration of peridotites in the mantle was lower, or at least not higher, in the hot spot than elsewhere. The presence of H(2)O-rich metasomatized mantle domains, inferred from peridotite and basalt data, would lower the melting temperature of the hot spot mantle and thereby reconcile its high degree ofmelting with the lack of a mantle temperature anomaly. Thus, some so-called hot spots might be melting anomalies unrelated to abnormally high mantle temperature or thermal plumes.

  13. Three-Dimensional Geophysical Structure of the Yellowstone / Snake River Plain Hotspot System: Is a Deep Mantle Plume Required?

    NASA Astrophysics Data System (ADS)

    Fouch, M. J.; James, D. E.; Kelbert, A.; Egbert, G. D.; Wagner, L. S.; Carlson, R. W.; Roth, J. B.

    2011-12-01

    Providing new constraints on the origin of the Yellowstone / Snake River Plain (YSRP) hotspot system is an important contribution enabled the EarthScope program. This age-progressive track of rhyolitic volcanism has long been hypothesized as resulting from a deep mantle plume. Here we present an integrated view of new results from EarthScope seismic and magnetotelluric (MT) data that shed new light on the deep structure and dynamics of the YSRP system. Nearly all new body wave tomographic models utilizing EarthScope data show a distinct swath of strongly reduced seismic wavespeeds extending laterally from the central SRP to Yellowstone, extending to depths of no greater than ~200 km. There is no evidence for a singular, concentrated conduit of reduced velocities below 200 km, as expected from a focused mantle plume upwelling. Surface wave tomography shows similar patterns for the YSRP region, with shear wavespeeds consistent with partial melt zones within the YSRP crust and uppermost mantle extending to depths of ~125 km, and aligned with the widespread distribution of Quaternary basaltic volcanism all along the SRP. Results from regional 3D MT models show focused zones of highly conductive crust and upper mantle, with the strongest conductivities in the uppermost mantle residing beneath the central Snake River Plain and the largest contrasts extending to ~100km depth. Given the paucity of evidence for a present-day plume, we explore geophysical proxies in the mantle flow field for past plume-related dynamics, appealing to proxies for mantle flow. Data from several seismic anisotropy studies confirm that the Yellowstone region exhibits little evidence for vertical mantle flow across the region. Further, the downgoing Juan de Fuca plate, imaged clearly in the tomographic studies, would provide a barrier to an upwelling mantle plume. An alternative to the plume model involves mantle flow around a stranded fragment of the Farallon plate whose northern edge parallels

  14. Mantle metasomatism

    SciTech Connect

    Menzies, M.; Hawkesworth, C.

    1986-01-01

    The concept of metasomatism and its role in the geochemical enrichment and depletion processes in upper mantle rocks remains contentious. This volume makes a comprehensive contribution to the study of metasomatic and enrichment processes: origin and importance in determining trace element and isotopic heterogeneity in the lithospheric mantle. It begins with a theoretical thermodynamic and experimental justification for metasomatism and proceeds to present evidence for this process from the study of mantle xenoliths. Finally the importance of metasomatism in relation to basaltic volcanism is assessed. The contents are as follows: Dynamics of Translithospheric Migration of Metasomatic Fluid and Alkaline Magma. Solubility of Major and Trace Elements in Mantle Metasomatic Fluids: Experimental Constraints. Mineralogic and Geochemical Evidence for Differing Styles of Metasomatism in Spinel Lherzolite Xenoliths: Enriched Mantle Source Regions of Basalts. Characterization of Mantle Metasomatic Fluids in Spinel Lherzolites and Alkali Clinophyroyxenites from the West Eifel and South-West Uganda. Metasomatised Harzburgites in Kimberlite and Alkaline Magmas: Enriched Resites and ''Flushed'' Lherzolites. Metasomatic and Enrichment Phenomena in Garnet-Peridotite Facies Mantle Xenoliths from the Matsoku Kimberlite Pipe Lesotho. Evidence for Mantle Metasomatism in Periodite Nodules from the Kimberley Pipes South Africa. Metasomatic and Enrichment Processes in Lithospheric Peridotites, an Effective of Asthenosphere-Lithosphere Interaction. Isotope Variations in Recent Volcanics: A Trace Element Perspective. Source Regions of Mid-Ocean Ridge Basalts: Evidence for Enrichment Processes. The Mantle Source for the Hawaiian Islands: Constraints from the Lavas and Ultramafic Inclusions.

  15. Mantle convection-driven variable uplift of the eastern US: A mechanism for late-Cenozoic rejuvenation of topography.

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Topographic uplift driven by hot, buoyant upwelling flow in the mantle is a natural consequence of convection with sufficiently strong bottom heating across the core-mantle boundary (CMB). An adequate CMB heat flux is needed to maintain an active, unstable lower thermal boundary layer that gives rise to hot upwellings that can generate surface topography in a mantle-wide convective flow. This dynamic topography provides a global mechanism for uplifting and rejuvenating landscapes, in particular ancient decaying orogens, in intraplate environments far from plate boundaries. We have recently carried out a new series of time-dependent mantle convection simulations that feature substantial CMB heat flux and numerous buoyant, hot mantle upwellings under several continents, in particular Africa and North America. These convection calculations incorporate a wide suite of data from seismology, geodynamics and mineral physics and they are capable of successfully reconciling all the data constraints we have employed. This work has yielded models of the 3-D thermo-chemical structure of the mantle [Simmons et al. 2007,2009,2010] that have been employed to successfully predict the present-day mantle convective flow and surface dynamics [Forte et al. 2009,2010] as well as providing detailed reconstructions of time-dependent mantle convection in the geologic past [Moucha et al. 2008, Moucha & Forte 2011]. Here we employ these high-resolution global convection models to elucidate the role of hot buoyant mantle, entering under the eastern US from the mid-Atlantic, in generating topographic uplift. While previous tomography-based convection models have predicted monotonic subsidence of the eastern half of the US [e.g. Spasojevic et al. 2008] due to the sole effect of the descending Farallon slab, we instead predict a time-dependent topography that includes variable uplift of the eastern margin of the US. This pattern of uplift extends inland, away from the coast, and suggests a new

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

    NASA Astrophysics Data System (ADS)

    Plomerová, Jaroslava; Munzarová, Helena; Vecsey, Luděk.; Kissling, Eduard; Achauer, Ulrich; Babuška, Vladislav

    2016-08-01

    New high-resolution tomographic models of P- and S-wave isotropic-velocity perturbations for the Bohemian upper mantle are estimated from carefully preprocessed travel-time residuals of teleseismic P, PKP and S waves recorded during the BOHEMA passive seismic experiment. The new data resolve anomalies with scale lengths 30-50 km. The models address whether a small mantle plume in the western Bohemian Massif is responsible for this geodynamically active region in central Europe, as expressed in recurrent earthquake swarms. Velocity-perturbations of the P- and S-wave models show similar features, though their resolutions are different. No model resolves a narrow subvertical low-velocity anomaly, which would validate the "baby-plume" concept. The new tomographic inferences complement previous studies of the upper mantle beneath the Bohemian Massif, in a broader context of the European Cenozoic Rift System (ECRIS) and of other Variscan Massifs in Europe. The low-velocity perturbations beneath the Eger Rift, observed in about 200km-broad zone, agree with shear-velocity models from full-waveform inversion, which also did not identify a mantle plume beneath the ECRIS. Boundaries between mantle domains of three tectonic units that comprise the region, determined from studies of seismic anisotropy, represent weak zones in the otherwise rigid continental mantle lithosphere. In the past, such zones could have channeled upwelling of hot mantle material, which on its way could have modified the mantle domain boundaries and locally thinned the lithosphere.

  17. Rocket Experiment For Neutral Upwelling

    NASA Astrophysics Data System (ADS)

    Kenward, D. R.; Lessard, M.

    2015-12-01

    Observations from the CHAMP satellite from 2004 show relatively small scale heating in the thermosphere. Several different mechanisms have been proposed to explain this phenomenon. The RENU 2 rocket mission includes a suite of 14 instruments which will acquire data to help understand processes involved in neutral upwelling in the cusp. Neutral, ion, and electron measurements will be made to provide an assessment of the upwelling process. SUPERDarn measurements of large- scale Joule heating in the cusp during overflight will also be acquired. Small-scale data which could possibly be associated with Alfvén waves, will be acquired using onboard electric field measurements. In-situ measurement of precipitating electrons and all other measurements will be used in thermodynamic and electrodynamic models for comparison to the observed upwelling.

  18. the P-wave upper mantle structure beneath an active spreading center: The Gulf of California

    NASA Technical Reports Server (NTRS)

    Walck, M. C.

    1983-01-01

    Detailed analysis of short period travel time, and waveform data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km. More than 1400 digital seismograms from earthquakes in Mexico and central America recorded at SCARLET yield 1753 travel times and 58 direct measurements of short period travel time as well as high quality, stable waveforms. The 29 events combine to form a continuous record section from 9 deg to 40 deg with an average station spacing of less than 5 km. First the travel times are inverted. Further constraints arise from the observed relative amplitudes of mantle phases, which are modeled by trial and error.

  19. Mantle volatiles in spring gases in the Basin and Range Province on the west of Beijing, China: Constraints from helium and carbon isotopes

    NASA Astrophysics Data System (ADS)

    Zhang, Weibin; Du, Jianguo; Zhou, Xiaocheng; Wang, Fei

    2016-01-01

    The mantle degassing observed at the Earth surface demonstrates both a provenance of fluids in the mantle and a pathway to the surface. Quantities of this process are discovered on the plate boundaries, where there are plenty of active volcanoes and active faults, releasing plenty of mantle volatiles. However, in intraplate tectonic settings without obvious mantle plume, the work for mantle degassing observed in spring gasses seems comparatively limited. We selected the Basin and Range Province on the west of Beijing, an area in the inner part of North China Craton, to discuss the mantle degassing based on the helium and carbon isotopes of spring gasses, and the previous works on seismic tomography and fault slip rate. The spring gas helium and carbon (CO2) isotopes indicate the mixture of crustal and mantle materials. The helium ratios (reported as RC/RA, air-corrected 3He/4He ratio, RA = 1.4 × 10- 6; RA is the air ratio) vary in the range of 0.33-2.08. The calculated mantle helium contributes 4% ~ 26% of helium in spring gasses, and the remaining is generated in the crust by radiogenic decay of U-Th series with tiny air mixture. CO2 acquires analytical δ13CV-PDB values in the range from - 20.3‰ to - 10.2‰, affected by carbonate precipitation. The unaffected values are calculated to be - 8.5 ~ 5.1 ‰ by temperature-dependent isotope fractionation, indicating the mixture of mantle and crustal (limestone) materials. The mantle volatiles are possibly generated in the upwelling asthenosphere, in that, the 3He/4He ratio corresponds well with the negative anomaly of P-wave velocity at the depth of 70 km imaged by seismic tomography. The 3He/4He ratio also correlates with time-averaged fault slip rate, suggesting higher slip rate renders more permeable mantle vent. These consequences help to construct a conceptual model for intraplate mantle degassing, that the mantle volatiles generate in the upwelling asthenosphere and uprise through faults and fractures whose

  20. Retrodicting the Cenozoic evolution of the mantle: Implications for dynamic surface topography

    NASA Astrophysics Data System (ADS)

    Glišović, Petar; Forte, Alessandro; Rowley, David; Simmons, Nathan; Grand, Stephen

    2014-05-01

    Seismic tomography is the essential starting ingredient for constructing realistic models of the mantle convective flow and for successfully predicting a wide range of convection-related surface observables. However, the lack of knowledge of the initial thermal state of the mantle in the geological past is still an outstanding problem in mantle convection. The resolution of this problem requires models of 3-D mantle evolution that yield maximum consistency with a wide suite of geophysical constraints. Quantifying the robustness of the reconstructed thermal evolution is another major concern. We have carried out mantle dynamic simulations (Glišović & Forte, EPSL 2014) using a pseudo-spectral solution for compressible-flow thermal convection in 3-D spectral geometry that directly incorporate: 1) joint seismic-geodynamic inversions of mantle density structure with constraints provided by mineral physics data (Simmons et al., GJI 2009); and 2) constraints on mantle viscosity inferred by inversion of a suite of convection-related and glacial isostatic adjustment data sets (Mitrovica & Forte, EPSL 2004) characterised by Earth-like Rayleigh numbers. These time-reversed convection simulations reveal how the buoyancy associated with hot, active upwellings is a major driver of the mantle-wide convective circulation and the changes in dynamic topography at the Earth's surface. These simulations reveal, for example, a stable and long-lived superplume under the East Pacific Rise (centred under the Easter and Pitcairn hotspots) that was previously identified by Rowley et al. (AGU 2011, Nature in review) on the basis of plate kinematic data. We also present 65 Myr reconstructions of the Reunion plume that gave rise to the Deccan Traps.

  1. Mantle-driven geodynamo features - accounting for non-thermal lower mantle features

    NASA Astrophysics Data System (ADS)

    Choblet, G.; Amit, H.

    2011-12-01

    Lower mantle heterogeneity responsible for spatial variations of the CMB heat flux could control long term geodynamo properties such as deviations from axial symmetry in the magnetic field and the core flow, frequency of geomagnetic reversals and anisotropic growth of the inner core. In this context, a classical interpretation of tomographic mapping of the lowermost mantle is to correlate linearly seismic velocities to heat flux anomalies. This implicitly assumes that temperature alone controls the tomographic anomalies. In addition, the limited spatial resolution of tomographic images precludes modeling sharp CMB heat flux structures.. There has been growing evidence however that non-thermal origins are also be expected for seismic velocity anomalies: the three main additional control parameters are (i) compositional anomalies possibly associated to the existence of a deep denser layer, (ii) the phase transition in magnesium perovskite believed to occur in the lowermost mantle and (iii) the possible presence of partial melts. Numerical models of mantle dynamics have illustrated how the first two parameters could distort the linear relationship between shear wave velocity anomalies and CMB heat flux (Nakagawa and Tackley, 2008). In this presentation we will consider the effect of such alternative interpretations of seismic velocity anomalies in order to prescribe CMB heat flux as an outer boundary for dynamo simulations. We first focus on the influence of post-perovskite. Taking into account this complexity could result in an improved agreement between the long term average properties of simulated dynamos and geophysical observations, including the Atlantic/Pacific hemispherical dichotomy in core flow activity, the single intense paleomagnetic field structure in the southern hemisphere, and possibly degree 1 dominant mode of inner-core seismic heterogeneity. We then account for sharp anomalies that are not resolved by the global tomographic probe. For instance

  2. Insight into the upper mantle beneath an active extensional zone: the spinel-peridotite xenoliths from San Quintin (Baja California, Mexico)

    NASA Astrophysics Data System (ADS)

    Cabanes, N.; Mercier, J.-C. C.

    1988-11-01

    fracturing in the coarse-grained lherzolites. At shallower depth, the magma cross-cut an active shear zone, sampling prophyroclastic and mosaic samples of the strained peridotites. Our model is consistent with the regional tectonic context: upwelling of the mantle by isostatic re-equilibration after the end of the subduction processes and subsequent opening of the California Gulf. The only questionable parameter of the model remains the geometry of the shearzone, high or low angle orientation.

  3. Weak Intraplate Volcanism Caused by Shear-Driven Upwelling

    NASA Astrophysics Data System (ADS)

    Bianco, T. A.; Conrad, C. P.; Smith, E. I.; Wessel, P.

    2011-12-01

    Statistical analysis shows that there is an unusually high incidence of recent (<10 Ma), intraplate volcanism over asthenosphere that is predicted to be rapidly shearing. This result is heavily influenced by the large number of small seamounts west of the Eastern Pacific Rise, and small-volume basaltic volcanism throughout the Western United States. Here we explore one relationship that may explain why small-volume volcanism preferentially occurs above rapidly-shearing asthenosphere. Numerical models show that asthenospheric shear can be deflected upward by lateral viscosity variations within the asthenosphere, producing "shear-driven upwelling" (SDU). To constrain the rate, duration, and surface expression of intraplate volcanism caused by SDU, we simulated 2D flow and peridotite melting in the upper 200 km of the mantle. Asthenospheric shear is driven by lithospheric plates with different thicknesses moving at 3 to 9 cm/yr, and the initial low-viscosity region is a rectangular-shaped pocket with an imposed viscosity that is two orders of magnitude smaller than the surrounding asthenosphere. Melting decreases as the pocket deforms, and reaches steady state after 3 to 12 Myr. The age progression of surface volcanism is nearly stationary in the reference frame of the plate, which distinguishes SDU from hotspot volcanism. Similar steady-state behavior occurs if the viscosity heterogeneity is induced by variations in the water content of mantle peridotite. If the pocket's low viscosity is caused by excess temperature, buoyant upwelling of the entire pocket dominates volcanism, which decreases exponentially with time. Differences in the time dependence of volcanism associated with damp and warm pockets may help identify which type of mantle heterogeneity and associated dynamic process best explains weak, intermittent, intraplate volcanism with no obvious age progression. We suggest that asthenospheric shear induced by plate motions and global mantle flow, by exciting

  4. The effects of mantle compressibility on mantle dynamics, magmatism and degassing for super-Earths

    NASA Astrophysics Data System (ADS)

    Liu, X.; Zhong, S.

    2010-12-01

    The discovery of extra-solar planets, especially massive terrestrial super-Earths, prompts studies of surface and internal characteristics of super-Earths that may help characterize super-Earths and understand their surface environments and habitability. An important question is related to the formation and evolution of super-Earth’s atmosphere for which mantle degassing resulting from magmatism has important controls. Similar to terrestrial planets in our Solar system, volcanism and magmatism for super-Earths, as a form of heat release from planetary interiors, are likely controlled by the dynamics of mantle convection, and more specifically plate tectonic process and mantle upwelling plumes. However, compared with that for terrestrial planets in our Solar system, the dynamics of mantle convection for super-Earths due to their larger size and mass should be more dissipative and display larger compressibility effects. Using a radius scaling with mass for super-Earths by Valencia et al. [2007], it can be inferred that the mantle dissipation number Di for super-Earths with ~10 Earth’s mass may be 4 times larger than that for the Earth. This may lead to rapid cooling of mantle upwellings and warming of mantle downwellings for super-Earths, thus diminishing mantle buoyancy driving mantle convection. With the large dissipation number, we found that the excess temperature of mantle upwelling plumes may decrease by one order of magnitude as they ascend through the mantle, thus greatly reducing plume-related magmatism and degassing. Another important control on Super-Earth’s magmatism and degassing comes from their increased surface gravitational acceleration that for super-Earths with ~10 Earth’s mass may be three times larger than that at the Earth’s surface. This limits the melting to relatively shallow depths and within small depth ranges, thus posing additional difficulties for plume-related magmatism and degassing. This implies that degassing for super

  5. Pattern of lobate scarps on Mercury's surface reproduced by a model of mantle convection

    NASA Astrophysics Data System (ADS)

    King, Scott D.

    2008-04-01

    Mercury is the smallest and least tectonically active of the terrestrial planets. Although Mercury's ancient, cratered surface resembles the Moon, it has the largest ratio of metallic core to silicate mantle among the terrestrial planets as well as an internal magnetic field. Images from the Mariner 10 spacecraft reveal lobate scarps, so called because of their curved or scalloped edges, which have been interpreted to be high-angle thrust faults resulting from a period of global contraction. A range of mechanisms has been invoked to explain the stresses leading to global contraction, including cooling and core formation, tidal effects due to gravitational interactions with the Sun, mantle convection and the impact that formed the Caloris basin. Here I present numerical simulations of the three-dimensional nature of convection within Mercury's silicate mantle. The model yields a regularly spaced pattern of convection, in which upwelling regions of the mantle assume linear, sheet-like shapes at low latitudes and a nearly hexagonal pattern near the poles. The distribution of resultant surface stresses is consistent with the observed pattern of lobate scarps, suggesting that the compressive features record an ancient pattern of mantle convection, in addition to global contraction. The gravity and topographic data returned from the MESSENGER 11 mission will help test this hypothesis.

  6. Experimental Deformation of Olivine Single Crystal at Mantle P and T: Pressure Effect on Olivine Dislocation Slip-System Activities

    NASA Astrophysics Data System (ADS)

    Paul, R.; Girard, J.; Chen, J.; Amiguet, E.

    2008-12-01

    Seismic velocity anisotropies observed in the upper mantle are interpreted from lattice preferred orientations (LPO) produced experimentally in olivine, which depends on the dominant dislocation slip systems. At low pressure P<3 GPa, mantle temperature (T) and in dry conditions, olivine [100] dislocation slip dominates the less active [001] slip. This tends to align crystal fast velocity [100] axis with the principal shear direction. Yet recent high-pressure deformation experiments (Couvy et al., 2004, EJM, 16, 877; Raterron et al., 2007, Am. Min., 92, 1436; Raterron et al., 2008, Phys. Earth Planet. Int., doi:10.1016/j.pepi.2008.07.026) show that [001](010) slip system dominates [100](010) system in the (P,T) range of the deep upper mantle. This may promote a shear-parallel slow-velocity [001] axis and may explain the seismic-velocity attenuation observed at depth >200 km (Mainprice et al., 2005, Nature, 433, 731). In order to further constrain the effect of P on olivine slip system activities, which is classically quantified by the activation volume V* in power creep laws, deformation experiments were carried out in poor water condition, at P>5 GPa and T=1400°C, on pure forsterite (Fo100) and San Carlos olivine crystals, using the Deformation-DIA apparatus at the X17B2 beamline of the NSLS (Upton, NY). Ten crystals were oriented in order to active either [100] slip alone or [001] slip alone in (010) plane, or both [100](001) and [001](100) systems together. Constant applied stress σ <300 MPa and specimen strain rates were monitored in situ using time-resolved x-ray diffraction and radiography, respectively, for a total of 27 investigated steady state conditions. The obtained rheological data were compared with data previously obtained in comparable T and σ conditions, but at room P, by Darot and Gueguen (1981, JGR, 86, 6219) for Fo100 and by Bai et al. (1991, JGR, 96, 2441) for San Carlos olivine. This new set of data confirms previous deformation data

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

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

    PubMed

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

    2015-07-14

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

  9. Crystal chemistry of amphiboles: implications for oxygen fugacity and water activity in lithospheric mantle beneath Victoria Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Bonadiman, C.; Nazzareni, S.; Coltorti, M.; Comodi, P.; Giuli, G.; Faccini, B.

    2014-03-01

    is present in mantle peridotites, the application of oxy-amphibole equilibrium is preferred, because ol-opx-sp oxy-calibrations are not "sensitive" enough in recording the effects (if any) of amphibole in the peridotite matrix. Amphibole acts as the main H acceptor among the peridotite minerals and may prevent fluid circulation and buffer oxygen fugacity. The important conclusion of this study is that amphibole within the lithospheric mantle does not always means high water activity and oxidizing conditions.

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

    NASA Astrophysics Data System (ADS)

    Morgan, Jason P.

    2016-04-01

    The process of science always returns to weighing evidence and arguments for and against a given hypothesis. As hypotheses can only be falsified, never universally proved, doubt and skepticism remain essential elements of the scientific method. In the past decade, even the hypothesis that mantle plumes exist as upwelling currents in the convecting mantle has been subject to intense scrutiny; from geochemists and geochronologists concerned that idealized plume models could not fit many details of their observations, and from seismologists concerned that mantle plumes can sometimes not be 'seen' in their increasingly high-resolution tomographic images of the mantle. In the place of mantle plumes, various locally specific and largely non-predictive hypotheses have been proposed to explain the origins of non-plate boundary volcanism at Hawaii, Samoa, etc. In my opinion, this debate has now passed from what was initially an extremely useful restorative from simply 'believing' in the idealized conventional mantle plume/hotspot scenario to becoming an active impediment to our community's ability to better understand the dynamics of the solid Earth. Having no working hypothesis at all is usually worse for making progress than having an imperfect and incomplete but partially correct one. There continues to be strong arguments and strong emerging evidence for deep mantle plumes. Furthermore, deep thermal plumes should exist in a mantle that is heated at its base, and the existence of Earth's (convective) geodynamo clearly indicates that heat flows from the core to heat the mantle's base. Here I review recent seismic evidence by French, Romanowicz, and coworkers that I feel lends strong new observational support for the existence of deep mantle plumes. I also review recent evidence consistent with the idea that secular core cooling replenishes half the mantle's heat loss through its top surface, e.g. that the present-day mantle is strongly bottom heated. Causes for

  11. Mapping mantle-melting anomalies in Baja California: a combined helium-seismology approach

    NASA Astrophysics Data System (ADS)

    Negrete-Aranda, R.; Spelz, R. M.; Hilton, D. R.; Tellez, M.; González-Yahimovich, O.

    2015-12-01

    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; Vidal, 1982) and 1.3 RA for spring waters (81oC) at Bahia Concepcion (Forrest et al.,2005). Our new survey of hot springs in northern BC has revealed that all 6 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 Sierra Juárez (0.11RA). Thus, preliminary trends are of a west-to-east increase in the mantle He signal across the peninsula. He results presented in this study correlate well with high resolution Rayleigh wave tomography images by Forsythe et al. (2007). Shear velocity variations in the BC crust and upper mantle have been interpreted as low velocity anomalies associated with dynamic upwelling and active melt production. More extensive sampling throughout BC coupled with analysis of other geochemical indicators of mantle degassing (e.g. CO2) will allow more detailed characterization of the extent and distribution of mantle melts in the region, facilitating assessment of the region's geothermal

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

    SciTech Connect

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

    2009-06-23

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

  13. Mantle Plume Dynamics Constrained by Seismic Tomography and Geodynamics

    NASA Astrophysics Data System (ADS)

    Glisovic, P.; Forte, A. M.

    2012-12-01

    We construct a time-dependent, compressible mantle convection model in three-dimensional spherical geometry that is consistent with tomography-based instantaneous flow dynamics, using an updated and revised pseudo-spectral numerical method [Glisovic et al., Geophys. J. Int. 2012]. We explored the impact of two end-member surface boundary conditions, for a rigid and plate-like surface, along with geodynamically-inferred radial viscosity profiles. In each case we find that deep-mantle hot upwellings are durable and stable features in the mantle-wide convective circulation. These deeply-rooted mantle plumes show remarkable longevity over very long geological time spans (several hundred million years), mainly owing to the high viscosity in the lower mantle. Our very-long time convection simulations suggest that the deep-mantle plumes beneath the following hotspots: Pitcairn, Easter, Galapagos, Crozet, Kerguelen, Caroline and Cape Verde, are most reliably resolved in the present-day tomographic images.

  14. Potential temperature, upwelling rate and eclogite in the formation of the North Atlantic large igneous province

    NASA Astrophysics Data System (ADS)

    Brown, E. L.; Lesher, C. E.

    2010-12-01

    The volumes and compositions of basalts generated by adiabatic decompression melting of the Earth’s mantle depend on mantle potential temperature (T_P), upwelling rate and the fertility of the mantle source. The relative importance of these factors in generating the high productivity magmatism of the Paleogene - Recent North Atlantic large igneous province (NAIP) remains controversial. Each has been proposed as a primary factor in the region. To assess the significance of these mechanisms in NAIP magmatism, we apply our forward melting model, REEBOX PRO, which simulates the melting of a heterogeneous source comprised of peridotite and eclogite lithologies. The model accounts for the thermodynamics of adiabatic decompression melting of a heterogeneous source using constraints from laboratory melting experiments. Input values of T_P and eclogite abundance are used to calculate the buoyancy of the mantle source and maximum upwelling rates. Source buoyancy constrains the maximum amount of eclogite in the mantle source that can ascend beneath the rift axis. All melts generated within the melting regime are pooled to form magmatic crust according to the residual column method. Using the model, variations in magmatic crustal thickness (from geophysics) as a function of eclogite content (from geochemistry) can be related to T_P and upwelling rate. Models with no thermal anomaly, that call on either enhanced upwelling rates due to plate separation (edge - driven convection) or the melting of abundant (> 30%) eclogite at “ambient” T_P (1325 °C), cannot generate the observed igneous crustal thicknesses around the province. Rather, elevated mantle T_P (minimum thermal anomaly ~ 85 - 195 °C) and associated buoyancy - driven upwelling are needed to explain the volume of igneous crust in the province. Involvement of eclogite, while necessary to explain the compositions of many NAIP lavas, does not significantly enhance melt production. These factors, coupled with the long

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  16. Supercontinents, Plate Tectonics, Large Igneous Provinces and Deep Mantle Heterogeneities

    NASA Astrophysics Data System (ADS)

    Torsvik, T. H.; Steinberger, B.; Burke, K.; Smethurst, M. A.

    2008-12-01

    The formation and break-up of supercontinents is a spectacular demonstration of the Earth's dynamic nature. Pangea, the best-documented supercontinent, formed at the end of the Palaeozoic era (320 Ma) and its dispersal, starting in the Early Jurassic (190 Ma), was preceded by and associated with widespread volcanic activity, much of which produced Large Igneous Provinces (LIPs), but whether any of the heat or material involved in the generation of LIP rocks comes from greater depths has remained controversial. Two antipodal Large Low Shear wave Velocity Provinces with centre of mass somewhat south of the equator (African and Pacific LLSVPs), isolated within the faster parts of the deep mantle dominate all global shear- wave tomography models. We have tested eight global models and two D" models: They all show that deep- plume sourced hotspots and most reconstructed LIPs for the last 300 million years project radially downwards to the core-mantle-boundary near the edges of the LLSVPs showing that the plumes that made those hotspots and LIPS came only from those plume generation zones. This is a robust result because it is observed in multiple reference frames, i.e. fixed/moving hotspot and palaeomagnetic frames, and in the latter case whether the effect of True Polar Wander (TPW) is considered or not. Our observations show that the LLSVPs must have remained essentially stable in their present position for the last 300 million years. LIPs have erupted since the Archean and may all have been derived from the margins of LLSVPs but whether the African and Pacific LLSVPs have remained the same throughout Earth's history is less certain although analogous structures on Mars do indicate long-term stability on that planet. Deep mantle heterogeneities and the geoid have remained very stable for the last 300 million years, and the possibility is therefore open for speculating on links to Pangea assembly. In a numerical model, Zhong et al. (2007, EPSL) argued that Pangea

  17. East Asia: Seismotectonics, magmatism and mantle dynamics

    NASA Astrophysics Data System (ADS)

    Zhao, Dapeng; Yu, Sheng; Ohtani, Eiji

    2011-02-01

    In this article, we review the significant recent results of geophysical studies and discuss their implications on seismotectonics, magmatism, and mantle dynamics in East Asia. High-resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes, which may reflect magma and fluids that affected the rupture nucleation of large earthquakes. In subduction zone regions, the crustal fluids originate from the dehydration of the subducting slab. Magmatism in arc and back-arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab. The intraplate magmatism has different origins. The continental volcanoes in Northeast Asia (such as Changbai and Wudalianchi) seem to be caused by the corner flow in the big mantle wedge (BMW) above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well. The Tengchong volcano in Southwest China is possibly caused by a similar process in BMW above the subducting Burma microplate (or Indian plate). The Hainan volcano in southernmost China seems to be a hotspot fed by a lower-mantle plume associated with the Pacific and Philippine Sea slabs' deep subduction in the east and the Indian slab's deep subduction in the west down to the lower mantle. The occurrence of deep earthquakes under the Japan Sea and the East Asia margin may be related to a metastable olivine wedge in the subducting Pacific slab. The stagnant slab finally collapses down to the bottom of the mantle, which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and cause the slab-plume interactions. Some of these issues, such as the origin of intraplate magmatism, are still controversial, and so further detailed studies are needed from now.

  18. The bent Hawaiian-Emperor hotspot track: inheriting the mantle wind.

    PubMed

    Tarduno, John; Bunge, Hans-Peter; Sleep, Norm; Hansen, Ulrich

    2009-04-01

    Bends in volcanic hotspot lineaments, best represented by the large elbow in the Hawaiian-Emperor chain, were thought to directly record changes in plate motion. Several lines of geophysical inquiry now suggest that a change in the locus of upwelling in the mantle induced by mantle dynamics causes bends in hotspot tracks. Inverse modeling suggests that although deep flow near the core-mantle boundary may have played a role in the Hawaiian-Emperor bend, capture of a plume by a ridge, followed by changes in sub-Pacific mantle flow, can better explain the observations. Thus, hotspot tracks can reveal patterns of past mantle circulation.

  19. Activity of ibrutinib in mantle cell lymphoma patients with central nervous system relapse

    PubMed Central

    Bernard, Sophie; Goldwirt, Lauriane; Amorim, Sandy; Brice, Pauline; Brière, Josette; de Kerviler, Eric; Mourah, Samia; Sauvageon, Hélène

    2015-01-01

    The risk of central nervous system (CNS) dissemination in mantle cell lymphoma (MCL) is low and occurs late in the course of the disease. However, prognosis in such cases remains extremely poor despite high-dose antimetabolite chemotherapy. Among novel drugs used to treat relapsing MCL patients, ibrutinib, an oral inhibitor of Bruton tyrosine kinase, shows great promise. Here we report the clinical observation of 3 MCL patients with symptomatic CNS relapse treated with single-agent ibrutinib. All 3 patients had dramatic and rapid responses with almost immediate recovery from symptoms. We also confirmed that ibrutinib crosses the blood-brain barrier with parallel pharmacokinetic analyses in plasma and cerebrospinal fluid using a validated LC-MS/MS method. All responses were ongoing after 2 months to 1 year of follow-up. PMID:26239089

  20. Convective instability rising out of the underbelly of stagnant slabs in the Mantle Transition Zone

    NASA Astrophysics Data System (ADS)

    Ballmer, Maxim D.; Motoki, Matthew H.

    2016-04-01

    The study of volcanism can further our understanding of Earth's mantle processes and composition. Continental intraplate volcanism commonly occurs above subducted slabs that stagnate in the Mantle Transition Zone (MTZ), such as in Europe, eastern China, and western North America. Here, we use two-dimensional numerical models to explore the evolution of stagnant slabs in the MTZ and their potential to sustain mantle upwellings that can support volcanism. We find [1] that weak slabs may go convectively unstable within tens of Myr. Upwellings rise out of the relatively warm underbelly of the slab, are entrained by ambient-mantle flow and reach the base of the lithosphere. The first and most vigorous upwellings rise adjacent to lateral heterogeneity within the slab. Ultimately, convective instability also acts to separate the compositional components of the slab, harzburgite and eclogite, from each other with harzburgite rising into the upper mantle and eclogite sinking toward the base of the MTZ, and potentially into the lower mantle. Such a physical filtering process may sustain a long-term compositional stratification across the mantle [2]. [1] Motoki, M. H. and M. D. Ballmer (2015): Convective instability of Stagnant Slabs in the Mantle Transition Zone, Geochem. Geophys. Geosys., doi:10.1002/2014GC005608. [2] Ballmer, M. D., N. C. Schmerr, T. Nakagawa, and J. Ritsema (2015): Compositional mantle layering revealed by slab stagnation at ~1,000 km depth, Science Advances, doi:10.1126/sciadv.1500815

  1. Hunting for the Tristan plume - An upper mantle tomography around the volcanic island Tristan da Cunha

    NASA Astrophysics Data System (ADS)

    Schlömer, Antje; Geissler, Wolfram H.; Jokat, Wilfried; Jegen, Marion

    2016-04-01

    Tristan da Cunha is a volcanic island in the South Atlantic close to the Mid-Atlantic Ridge. It is part of an area consisting of widely scattered seamounts and small islands at the western and youngest end of the aseismic Walvis Ridge. Tristan da Cunha together with the Walvis Ridge represents the classical example of a mantle plume track, because of the connection to the Cretaceous Etendeka flood basalt province in NW Namibia. The genesis of the island has so far remained enigmatic. It is hotly debated, if Tristan da Cunha sits actually above a deep mantle plume or if it is only originated by upwelling material from weak (leaky) fracture zones. It also has to be clarified if there are any indications for a plume-ridge interaction. Geochemical investigations have shown complex compositions of magmatic samples from Tristan da Cunha, which could be interpreted as a mixing of plume-derived melts and depleted upper mantle sources. To improve our understanding about the origin of Tristan and to test the mantle plume hypothesis, we deployed 24 broadband ocean-bottom seismometers and 2 seismological land stations around and on the island during an expedition in January 2012 with the German research vessel Maria S. Merian. After acquiring continuous seismological data for almost one year, the seismometers were recovered in early January 2013. We cross-correlated the arrival times of teleseismic P and PKP phases to perform a finite-frequency tomography of the upper mantle beneath the study area. Here we show the 3D mantle structure in terms of velocity variations: We do not image a "classical" plume-like structure directly beneath Tristan da Cunha, but we observe regions of low velocities at the edges of our array that we relate to local mantle upwelling from potentially deeper sources. Additionally we discuss local seismicity within the Tristan da Cunha region, which show processes along the nearby mid-ocean ridge and transform faults. Furthermore, the local seismicity

  2. Evolution of North Atlantic Passive Margins Controlled by the Iceland Mantle Plume

    NASA Astrophysics Data System (ADS)

    Parnell-Turner, R. E.; White, N. J.; Henstock, T.; Murton, B. J.; Jones, S. M.

    2015-12-01

    Evolution of North Atlantic passive margins has been profoundly influenced by the Iceland mantle plume over the past 60 Ma. Residual depth anomalies of oceanic lithosphere, long wavelength gravity anomalies and seismic tomographic models show that upwelling mantle material extends from Baffin Bay to Western Norway. At fringing passive margins such as Northwest Scotland, there is evidence for present-day dynamic support of the crust. The Iceland plume is bisected by the Reykjanes Ridge ridge, which acts as a tape-recorder of the temporal variability of the plume. We present regional seismic reflection profiles that traverse the oceanic basin between northwest Europe and Greenland. A diachronous pattern of V-shaped ridges and troughs are imaged beneath marine sediments, revealing a complete record of transient periodicity that can be traced continuously back to ~55 Myrs. This periodicity increases from ~3 to ~8 Ma with clear evidence for minor, but systematic, asymmetric crustal accretion. V-shaped ridges grow with time and reflect small (5-30°C) changes in mantle temperature, consistent with episodic generation of hot solitary waves triggered by growth of thermal boundary layer instabilities within the mantle. Our continuous record of convective activity suggests that the otherwise uniform thermal subsidence of sedimentary basins, which fringe the North Atlantic Ocean, has been punctuated by periods of variable dynamic topography. This record can explain a set of diverse observations from the geologic record. Paleogene unconformities in the Faroe-Shetland Basin, the punctuated deposition of contourite drifts and variations in deep-water current strength can all be explained by transient mantle plume behavior. These signals of convective activity should lead to improved insights into the fluid dynamics of the mantle, and into the evolution of volcanic passive margins.

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

    NASA Astrophysics Data System (ADS)

    Davies, D.; Davies, J.

    2008-12-01

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

  4. Formation and Preservation of the Depleted and Enriched Shergottite Isotopic Reservoirs in a Convecting Martian Mantle

    NASA Technical Reports Server (NTRS)

    Kiefer, Walter S.; Jones, John H.

    2015-01-01

    There is compelling isotopic and crater density evidence for geologically recent volcanism on Mars, in the last 100-200 million years and possibly in the last 50 million years. This volcanism is due to adiabatic decompression melting and thus requires some type of present-day convective upwelling in the martian mantle. On the other hand, martian meteorites preserve evidence for at least 3 distinct radiogenic isotopic reservoirs. Anomalies in short-lived isotopic systems (Sm-146, Nd-142, Hf-182, W-182) require that these reservoirs must have developed in the first 50 to 100 million years of Solar System history. The long-term preservation of chemically distinct reservoirs has sometimes been interpreted as evidence for the absence of mantle convection and convective mixing on Mars for most of martian history, a conclusion which is at odds with the evidence for young volcanism. This apparent paradox can be resolved by recognizing that a variety of processes, including both inefficient mantle mixing and geographic separation of isotopic reservoirs, may preserve isotopic heterogeneity on Mars in an actively convecting mantle. Here, we focus on the formation and preservation of the depleted and enriched isotopic and trace element reservoirs in the shergottites. In particular, we explore the possible roles of processes such as chemical diffusion and metasomatism in dikes and magma chambers for creating the isotopically enriched shergottites. We also consider processes that may preserve the enriched reservoir against convective mixing for most of martian history.

  5. Cold cratonic roots and thermal blankets: How continents affect mantle convection

    USGS Publications Warehouse

    Trubitsyn, V.P.; Mooney, W.D.; Abbott, D.H.

    2003-01-01

    Two-dimensional convection models with moving continents show that continents profoundly affect the pattern of mantle convection. If the continents are wider than the wavelength of the convection cells (???3000 km, the thickness of the mantle), they cause neighboring deep mantle thermal upwellings to coalesce into a single focused upwelling. This focused upwelling zone will have a potential temperature anomaly of about 200??C, much higher than the 100??C temperature anomaly of upwelling zones generated beneath typical oceanic lithosphere. Extensive high-temperature melts (including flood basalts and late potassic granites) will be produced, and the excess temperature anomaly will induce continental uplift (as revealed in sea level changes) and the eventual breakup of the supercontinent. The mantle thermal anomaly will persist for several hundred million years after such a breakup. In contrast, small continental blocks (<1000 km diameter) do not induce focused mantle upwelling zones. Instead, small continental blocks are dragged to mantle downwelling zones, where they spend most of their time, and will migrate laterally with the downwelling. As a result of sitting over relatively cold mantle (downwellings), small continental blocks are favored to keep their cratonic roots. This may explain the long-term survival of small cratonic blocks (e.g., the Yilgarn and Pilbara cratons of western Australia, and the West African craton). The optimum size for long-term stability of a continental block is <3000 km. These results show that continents profoundly affect the pattern of mantle convection. These effects are illustrated in terms of the timing and history of supercontinent breakup, the production of high-temperature melts, and sea level changes. Such two-dimensional calculations can be further refined and tested by three-dimensional numerical simulations of mantle convection with moving continental and oceanic plates.

  6. What does hotspot-ridge interaction tell us about mantle plumes?

    NASA Astrophysics Data System (ADS)

    Murton, B. J.

    2005-05-01

    depth, increase in segment length, and multi-component geochemical mixing that varies with distance along the plate boundary. Both the Icelandic and Réunion 'plume'-ridge couplets provide compelling evidence for advection and lateral flow of 'plume' mantle away from a central source and subsequent mingling with depleted, sub-ridge mantle characteristic of MORB genesis. As such, these studies support the current paradigm for mantle 'plumes' as phenomena associated with actively upwelling material that has resided deep within the mantle and whose influence upon spreading ridges is profound.

  7. Synthetic Seismic Signature of Thermal Mantle plumes

    NASA Astrophysics Data System (ADS)

    Goes, S.; Hansen, U.

    2002-12-01

    With increasing resolution in global tomographic models and targeted regional experiments the first seismic images of mantle plumes have emerged. The low velocity anomalies interpreted as plumes are generally significantly more complex than the simple head-tail model of a mantle upwelling. Although some models show low velocities crossing the 660 km discontinuity, the significance of the lower mantle anomalies is still heavily debated. In order to obtain a better idea of the expected seismic signature of a mantle plume we perform a set of three-dimensional numerical experiments with parameters relevant to the Earth's mantle. The thermal plumes thus obtained are converted into P and S velocity structure taking into account the effect of temperature, pressure, an average mantle composition including phase transitions and anelasticity on the seismic velocities. Excess plume temperatures were constrained to be about 300oC below the lithosphere to be consistent with surface observations. Such plumes are 400-800 km wide. An abrupt lowering of the viscosity above 660 km causes additional narrowing in the upper mantle. VP (VS) anomalies range from -2.2 (-4) % above the transition zone to -0.5 (-1) % in the lower mantle. Due to the varying sensitivity of seismic velocities to temperature with depth and mineralogy, variations in amplitude and width of the seismic plume do not coincide with the variations in the thermal structure of the plume. Reduced sensitivity in the transition zone may hamper imaging continuous whole mantle plumes. Seismic anelasticity structure follows the thermal structure more closely and yields plume anomalies of up to 200% in dln(1/QS).

  8. Mantle hydrous-fluid interaction with Archaean granite.

    NASA Astrophysics Data System (ADS)

    Słaby, E.; Martin, H.; Hamada, M.; Śmigielski, M.; Domonik, A.; Götze, J.; Hoefs, J.; Hałas, S.; Simon, K.; Devidal, J.-L.; Moyen, J.-F.; Jayananda, M.

    2012-04-01

    Water content/species in alkali feldspars from late Archaean Closepet igneous bodies as well as growth and re-growth textures, trace element and oxygen isotope composition have been studied (Słaby et al., 2011). Both processes growth and re-growth are deterministic, however they differ showing increasing persistency in element behaviour during interaction with fluids. The re-growth process fertilized domains and didn't change their oxygen-isotope signature. Water speciation showed persistent behaviour during heating at least up to 600oC. Carbonate crystals with mantle isotope signature are associated with the recrystallized feldspar domains. Fluid-affected domains in apatite provide evidence of halide exchange. The data testify that the observed recrystallization was a high-temperature reaction with fertilized, halide-rich H2O-CO2 mantle-derived fluids of high water activity. A wet mantle being able to generate hydrous plumes, which appear to be hotter during the Archean in comparison to the present time is supposed by Shimizu et al. (2001). Usually hot fluids, which can be strongly carbonic, precede asthenospheric mantle upwelling. They are supposed to be parental to most recognized compositions, which can be derived by their immiscible separation into saline aqueous-silicic and carbonatitic members (Klein-BenDavid et al., 2007). The aqueous fractions are halogen-rich with a significant proportion of CO2. Both admixed fractions are supposed to be fertile. The Closepet granite emplaced in a major shear zone that delimitates two different terrains. Generally such shear zones, at many places, are supposed to be rooted deep into the mantle. The drain, that favoured and controlled magma ascent and emplacement, seemed to remain efficient after granite crystallization. In the southern part of the Closepet batholiths an evidence of intensive interaction of a lower crust fluid (of high CO2 activity) is provided by the extensive charnockitization of amphibolite facies (St

  9. Determining resolvability of mantle plumes with synthetic seismic modeling

    NASA Astrophysics Data System (ADS)

    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

  10. Mantle cryptology

    SciTech Connect

    Zindler, A.; Jagoutz, E.

    1988-02-01

    A group of anhydrous peridotites from Peridot Mesa, Arizona, document isotopic and trace element heterogeneity in the source mantle. LREE enrichments in two spinel periodotites may have occurred immediately prior to entrainment through interaction with a melt similar to the hose basanite. Detailed characterization of inclusion-free peridotite phases, and washed and unwahsed whole-rock samples, verifies the presence of a ubiquitous secondary contaminant which derives from interaction of the peridotites with local ground waters and host magma. Once the veil of this contamination is removed, coexisting phases are found to be in isotopic equilibrium. Further, a comparison of washed whole rocks and calculated clean-bulk compositions documents the occurrence of an important intragranular fluid-hosted trace element component. For the very incompatible elements (K, Rb, Cs, and Ba, and probably U, Th, Pb and gaseous components as well) this component dominates the nodule budget for two of the three samples studied in detail. Production of basaltic magmas from fertile but incompatible-element-depleted peridotite requires the action of melting processes such as those recently proposed by McKenzie (1985) and O'Hara (1985). The distinctive feature of these models is that they call on effectively larger source volumes for more incompatible elements. In this context, depletions of incompatible trace elements in MORB source mantle will be more extreme than has heretofore been suspected. This would essentially preclude the long-term total isolation of a MORB source mantle above the 670 km seismic discontinuity.

  11. Seismic evidence of the Hainan mantle plume by receiver function analysis in southern China

    NASA Astrophysics Data System (ADS)

    Wei, S. Shawn; Chen, Y. John

    2016-09-01

    The Lei-Qiong region is the largest igneous province in southern China and may be a surface expression of a mantle plume beneath the region (the Hainan mantle plume). To investigate the existence of the Hainan mantle plume, we used P-to-S receiver function to image the major seismic discontinuities beneath this region with a regional dense broadband array. We found that the Moho discontinuity beneath the Leizhou Peninsula, mostly covered by Cenozoic basaltic outcrops, is 10-15 km deeper compared to the adjacent region of Eurasian continental margin, showing a thickened local crust by upwelling mantle materials. Additionally, the imaged 410- and 660-km discontinuities suggest a thinner-than-normal mantle transition zone beneath the region, implying that hot materials penetrate through the transition zone from the lower mantle. Both seismic evidences support the existence of the mantle plume, which might be 170-200°C hotter than the surrounding mantle.

  12. Pacific Upper Mantle Seismic Anisotropy from the Active-Source Seismic Component of the NoMelt Experiment

    NASA Astrophysics Data System (ADS)

    Mark, H. F.; Lizarralde, D.; Gaherty, J. B.; Collins, J. A.; Hirth, G.; Evans, R. L.

    2014-12-01

    We will present a measurement of azimuthal seismic anisotropy of Pacific-plate upper mantle based on Pn travel times from the active-source seismic component of the NoMelt experiment. The NoMelt experiment was conducted in 2012 on ~70-m.y.-old lithosphere, in the center of the spreading segment between the Clarion and Clipperton fracture zones, with the goal of delineating the detailed seismic and electrical structure of "normal," mature oceanic lithosphere. The seismic component of the experiment consisted of a 600x400 km array of 27 broad-band (BB) ocean bottom seismometers (OBS); 31 short period (SP) OBS, spaced at 20 km, deployed along the long axis of the array (the main transect), oriented along a plate-kinematic flow line; and 3 SP OBS deployed along a line normal to the main transect, at 50 km spacing, extending to 200 km southeast of the center of the main transect. The SP OBS array was deployed to record airgun shots fired by the R/V M.G. Langseth's 36-element array. Airgun shots were fired along the two perpendicular lines and also along a semi-circular arc with a 75-km radius centered at the line intersection at the center of the main transect. Pn (upper mantle refraction) arrivals from shots fired along the semicircle and recorded by OBS within the semicircle's arc span 180 degrees of azimuth and an offset range of ~40-150 km. Preliminary analyses of these Pn arrival travel times indicate an azimuthal dependence of P-wave speeds, which range from ~8.6 km/s to ~7.6 km/s. These preliminary results suggest a pattern of azimuthal wave-speed dependence that requires depth-dependent seismic anisotropy and/or a dipping mantle fabric, with the latter being more likely given the limited range of source/receiver offsets spanned by the Pn arrivals used in this analysis. We will present results that include these observations as well as Pn arrivals from a much more comprehensive set of source/receiver pairs from the NoMelt experiment.

  13. Delineating the Exmouth Mantle Plume (NW Australia) : Implications for the Origin of Volcanic Margins

    NASA Astrophysics Data System (ADS)

    Rohrman, M. H.

    2014-12-01

    Denudation and magmatism are distinct characteristics of Large Igneous Provinces, such as the Northwest Australian volcanic margin. Unfortunately, its temporal and spatial extent is poorly defined. Here, I present a simple isostatic model relating denudation to plume induced lithospheric thinning and underplating to delineate the Late Jurassic/Early Cretaceous Exmouth mantle plume. This upwelling was centered on a highly extended and subsided continental fragment known as the subsea Sonne/Sonja Ridge area and includes the Cuvier Margin (CM) and Cape Range Fracture Zone (CRFZ). The region is characterized by ~3 km denudation and ~ 500 m tectonic uplift, with erosion products acting as provenance for the Early Cretaceous Lower Barrow delta. Partial melting of the plume generated an underplate, characterized as a high velocity body (HVB) on seismic data. Denudation analysis indicates that only ~40 % of the HVB is melt related, with the effective underplate ~ 4 km thick at the plume centre, decreasing in the outer regions. Widespread plume induced convective lithospheric thinning set the boundary conditions for subsequent extension related magmatism and breakup in the Valanginian, as recorded by subsidence analysis of exploration wells. Hot plume derived material flowed to regions under extension, initiating additional magmatism now observed as SDRs (Seaward Dipping Reflectors series), initially thick magmatic crust, followed by normal ocean spreading in the Hauterivian. After initial upwelling, the thermal plume can be traced in a western direction as a hotspot to the Quokka Rise in the mid Cretaceous, before terminating after 35 - 50 Ma of activity. These findings suggest that most volcanic margins are generated by plume upwellings that are relatively passive features, with uplift consisting of a combination of plume induced convective lithospheric thinning and underplating. Melt migration and mantle heating subsequently lower stresses and facilitate breakup.

  14. Perinucleolar relocalization and nucleolin as crucial events in the transcriptional activation of key genes in mantle cell lymphoma.

    PubMed

    Allinne, Jeanne; Pichugin, Andrei; Iarovaia, Olga; Klibi, Manel; Barat, Ana; Zlotek-Zlotkiewicz, Ewa; Markozashvili, Diana; Petrova, Natalia; Camara-Clayette, Valérie; Ioudinkova, Elena; Wiels, Joëlle; Razin, Sergey V; Ribrag, Vincent; Lipinski, Marc; Vassetzky, Yegor S

    2014-03-27

    In mantle cell lymphoma (MCL), one allele of the cyclin D1 (Ccnd1) gene is translocated from its normal localization on chromosome 11 to chromosome 14. This is considered as the crucial event in the transformation process of a normal naive B-cell; however, the actual molecular mechanism leading to Ccnd1 activation remains to be deciphered. Using a combination of three-dimensional and immuno-fluorescence in situ hybridization experiments, the radial position of the 2 Ccnd1 alleles was investigated in MCL-derived cell lines and malignant cells from affected patients. The translocated Ccnd1 allele was observed significantly more distant from the nuclear membrane than its nontranslocated counterpart, with a very high proportion of IgH-Ccnd1 chromosomal segments localized next to a nucleolus. These perinucleolar areas were found to contain active RNA polymerase II (PolII) clusters. Nucleoli are rich in nucleolin, a potent transcription factor that we found to bind sites within the Ccnd1 gene specifically in MCL cells and to activate Ccnd1 transcription. We propose that the Ccnd1 transcriptional activation in MCL cells relates to the repositioning of the rearranged IgH-Ccnd1-carrying chromosomal segment in a nuclear territory with abundant nucleolin and active PolII molecules. Similar transforming events could occur in Burkitt and other B-cell lymphomas.

  15. The Effect of Subduction Events on Rising Mantle Currents

    NASA Astrophysics Data System (ADS)

    Moeller, A.; Stein, C.; Hansen, U.

    2007-12-01

    Mantle convection systems with periodic events of subduction exhibit two different kinds of upwelling currents: plumes and thermals. Plumes are strong upwelling currents with a well-defined head and tail structure. Thermals having only little buoyancy do not develop this typical structure and are strongly influenced by the large- scale convection. In vigorous convection thermals are driven towards the locations of the plumes. In this study we numerically investigate the structure and evolution of the rising mantle currents in a 2D Rayleigh- Benard set-up. Periodic events of the subduction occur due to the application of a temperature- and stress- dependent rheology. Model calculations in a Cartesian geometry with large aspect ratios are run with variations in the Rayleigh number, the viscosity contrast (measure of the temperature dependence) and the yield stress (measure of the stress dependence). Our study indicates that a system with periodic subduction events is characterised by three phases. In the first phase the cold thick lid at the surface has no influence on the upwelling currents. Strong, stationary plumes drive the convection. In the second phase the subducted cold material suppresses upwellings. Only small transient currents rise in front of the cold slab. In the third phase the cold material at the bottom is heated up allowing for the formation of strong upwelling currents again.

  16. Influence of heating mode on three-dimensional mantle convection

    NASA Technical Reports Server (NTRS)

    Bercovici, D.; Schubert, G.; Glatzmaier, G. A.

    1989-01-01

    Numerical models of three-dimensional thermal convection in highly viscous spherical shells with different combinations of internal and basal heating consistently have upwelling concentrations in the form of cylindrical plumes and downwelling in planar sheets. As the proportion of internal heating increases, the number of upwelling plumes increases, and downwelling sheets become more vigorous and time-dependent. With any amount of basal heating, the entire convective pattern, during its evolution, is anchored to the upwelling plumes. As the proportion of internal heating increases, the heat flow carried by the upwelling plumes remains a large fraction of the basal heat flow. Downwelling sheets carry only a minor fraction (approximately 30 percent) of the basal heat flow (even when the shell is entirely heated from below), but they advect almost all of the internally generated heat. The relatively large number of plumes in the earth's mantle (inferred from hotspots), the possibility that downwelling slabs are vigorous enough to penetrate the lower mantle, and the small fraction of terrestrial surface heat flow carried by plumes all suggest that the mantle is predominantly heated from within.

  17. Olivine Slip-system Activity at High Pressure: Implications for Upper-Mantle Rheology and Seismic Anisotropy (Invited)

    NASA Astrophysics Data System (ADS)

    Raterron, P.; Castelnau, O.; Geenen, T.; Merkel, S.

    2013-12-01

    The past decade abounded in technical developments allowing the investigation of materials rheology at high pressure (P > 3 GPa) [1]. This had a significant impact on our understanding of olivine rheology in the Earth asthenosphere, where P is in the range 3 - 13 GPa. A dislocation slip-system transition induced by pressure has been documented in dry Fe-bearing olivine [2]; it induces changes in olivine aggregate lattice preferred orientation (LPO) [3,4], which may explain the seismic velocity anisotropy attenuation observed at depths > 200 km in the upper mantle [5]. Deformation experiments carried out on olivine single crystals at high pressure allowed quantifying the effect of P on individual slip system activities [6]. Integration of these data, together with data on lattice friction arising from computational models (e.g., [7]), into analytical or mean-field numerical models for aggregate plasticity gave insight on the viscosity and LPO of olivine aggregates deformed at geological conditions in the dislocation creep regime [8,9]. We will review these recent findings and their implications for upper mantle rheology and seismic anisotropy. [1] Raterron & Merkel, 2009, J. Sync. Rad., 16, 748 ; [2] Raterron et al., 2009, PEPI, 172, 74 ; [3] Jung et al., 2009, Nature Geoscience, 2, 73 ; [4] Ohuchi et al., 2011, EPSL, 304, 55 ; [5] Mainprice et al., 2005, Nature, 433, 731 ; [6] Raterron et al., 2012, PEPI, 200-201, 105 ; [7] Durinck et al., 2007, EJM, 19, 631 ; [8] Castelnau et al., 2010, C.R. Physique, 11, 304 ; [9] Raterron et al., 2011, PEPI, 188, 26

  18. Laboratory Experiments Concerning Upwellings From the Slab-Graveyard: Implications For Geochemical and Seismic Models

    NASA Astrophysics Data System (ADS)

    Harris, A. C.; Kincaid, C.; Hall, P.

    2005-12-01

    The ongoing plume debate appears to focus on upwellings characterized by large heads and smaller tails, that form from a deep or basal thermal boundary layer (BTBL), which are driven by temperature excesses in the range of 200° C. We use 3-D laboratory experiments to explore how upwellings might differ from this common plume description when BTBLs are influenced by subducted plates. An important aspect of the models is the representation of ridge chemical differentiation processes resulting in slabs with two distinct layers; a lighter, depleted upper mantle component (Harzburgite:H) and a heavier, iron-rich crustal component (Basalt/Eclogite:B/E). Laboratory experiments utilize a working fluid of glucose syrup with temperature dependent density and viscosity. Compositionally distinct mantle reservoirs are represented through isothermal density/viscosity contrasts controlled by water content. The ambient fluid (AF) is contained within a rectangular tank that is heated from below and cooled from above to produce background convection with a Rayleigh number of 10-5-10-6. Highly viscous, tabular slabs are produced by pouring compositionally distinct syrup from two slab reservoirs (B/E and H) into a mold which is chilled to -5° C. The viscous layered slab is emplaced at the fluid surface and subsequently sinks through, stalls and spreads within a BTBL roughly twice the slab thickness (1 cm). Results show that a wide variety in upwelling morphologies form when layered slabs reside within the BTBL and that plume heads/tails are largely dissimilar to those of the standard plume model. The manner in which the slab laminae vs. AF in the BTBL combine (or segregate) within upwellings depends on viscosity/density contrasts, how slabs collapse in the BTBL, and time. End-member regimes include: experiments dominated by a very light H-slab component with early, cold H-plumes and late, hot B/E-AF plumes and experiments where density differences between H, B/E and AF are small and

  19. Mesozooplankton metabolism and feeding in the NW Iberian upwelling

    NASA Astrophysics Data System (ADS)

    Isla, José Alejandro; Ceballos, Sara; Anadón, Ricardo

    2004-09-01

    Mesozooplankton size-fractionated biomass, feeding, and metabolic rates were investigated during a cruise conducted off NW Spain in August 1998. Based on different hydrographic conditions observed throughout the study area (upwelling events nearshore and stratified waters offshore), the sampling area was divided into coastal and oceanic zones. Both phytoplankton and mesozooplankton biomass were higher in the coastal upwelling than in the offshore zone. Size structure analysis shows that the small fraction (200-500 μm) of mesozooplankton was more important than the larger fractions (500-1000 μm and >1000 μm) in the open ocean in terms of both biomass and grazing activity. The relationship between copepod ingestion rate and the concentration of chlorophyll a >5 μm resembled a type II functional response. Saturation occurred at the coastal stations, where copepod gut contents were highest. The grazing impact on both phytoplankton biomass and primary production seemed to be higher offshore (5.7 and 12.9%, respectively) than in upwelled waters (5.2 and 5.2%), although the differences were not statistically significant. Phytoplankton ingestion was enough to fulfil the basal metabolism of mesozooplankton in the upwelling area (102.1% of the minimum carbon requirements met) but not in the offshore (45.9%). Feeding activity and metabolic measurements on mesozooplankton point to a herbivorous food web in the coastal upwelling zone and a multivorous food web in the stratified open oceanic waters. The amount of metabolic end products released by mesozooplankton was higher in the coastal zone, but mesozooplankton played a more important role as nutrient regenerators in the multivorous food web (30.3 and 21.7% of the nitrogen and phosphorus phytoplankton demand accounted for ammonium and phosphate excretion, respectively) than in the herbivorous one (3.8% for ammonium and 2.6% for phosphate).

  20. Mantle Redox Conditions in the North Atlantic Igneous Province

    NASA Astrophysics Data System (ADS)

    Heister, L. E.; Gras, M. A.; Lesher, C. E.

    2004-12-01

    The North Atlantic igneous province (NAIP) has long been viewed as a region of anomalous mantle upwelling related to plume activity, continental rifting, and a heterogeneous mantle source. Prior to continental rifting in the Tertiary, the northern portion of the region was the site of closure of the Iapetus ocean basin. This tectonic event may have contributed to heterogeneities within the upper mantle and altered its oxidation state relative to the ambient mantle. Vanadium has been shown to be a useful indicator of redox conditions due to its multiple valence states (e.g. [1-2]). In mantle minerals, vanadium becomes increasingly incompatible under more oxidizing conditions [3]. Because both scandium and vanadium are moderately incompatible during melting, the Sc/V ratio of primitive basalts can be used to investigate the oxidation state of the mantle [1-3]. We have examined the Sc/V ratios of primitive lavas from the mid-Atlantic ridge (MAR), Iceland, and the East Greenland margin to determine if there are spatial or temporal variations in the oxidation state of the NAIP mantle. The Sc/V ratios for MAR basalts are 0.13-0.20 (GEOROC chemical database); while Icelandic basalts range from 0.10-0.25 with an average of 0.16 (1 σ =0.05). The entire range of Sc/V ratios of the Paleogene East Greenland basalts is 0.07-0.17 with an average of 0.10 (1 σ = 0.05). The Sc/V ratios of Icelandic basalts are similar to MAR basalts, but the East Greenland lavas are distinctly lower than both the MAR and Iceland. The Sc/V ratio also can vary as a function of mean pressure of melting (i.e. spinel versus garnet lherzolite). To test the relative importance of melting systematics, source composition, and oxygen fugacity on the Sc/V systematics for NAIP basalts, we incorporated the oxygen-fugacity-dependent V mineral-melt partitioning data of [3] into the polybaric decompression melting model REEBOX [4]. The best-fit model parameters for the majority of the Iceland and MAR basalts

  1. Mid mantle seismic anisotropy around subduction zones

    NASA Astrophysics Data System (ADS)

    Faccenda, M.

    2014-02-01

    There is increasing evidence for mid mantle seismic anisotropy around subduction zones whose interpretation remains elusive. In this study I estimate the strain-induced mid mantle fabric and associated seismic anisotropy developing in 3D petrological-thermo-mechanical subduction models where the slab is either stagnating over the 660 km discontinuity or penetrating into the lower mantle. The modelling of synthetic lattice-preferred-orientation (LPO) development of wadsleyite and perovskite has been calibrated with results from deformational experiments and ab-initio atomic scale models, and the single crystal elastic tensor of the different mineral phases is scaled by local P-T conditions. The lower transition zone (ringwoodite + garnet) is assumed to be isotropic. Mid mantle fabric develops in proximity of the subducting slab where deformation and stresses are high, except at depths where upwelling or downwelling material undergoes phase transformations, yielding to LPO reset. The upper transition zone (wadsleyite + garnet) is characterized by weak transverse isotropy (2-3%) with symmetry axes oriented and fast S wave polarized dip-normal. A slightly stronger transverse isotropy develops in the lower mantle (perovskite + periclase), where the symmetry axes, the polarization of the fast S wave and the maximum Vp and dVs are parallel to the slab dip and subduction direction. For stagnating slab models this translates into negative and positive radial anisotropy in the upper transition zone and lower mantle back-arc, respectively, minimum delay times for vertically travelling shear waves and large shear wave splitting for waves propagating horizontally in the lower mantle. These results may help in reconciling the seismic anisotropy patterns observed in some subduction zones with subduction-induced deformation, such as those measured in the mid mantle between the Australian plate and the New Hebrides-Tonga-Kermadec trenches that I interpret as related to stagnating

  2. Grain size evolution in the mantle and its effect on geodynamics, seismic velocities and attenuation

    NASA Astrophysics Data System (ADS)

    Dannberg, Juliane; Eilon, Zach; Gassmoeller, Rene; Moulik, Pritwiraj; Myhill, Robert; Faul, Ulrich; Asimow, Paul

    2015-04-01

    Dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity and a limited treatment of variations associated with changes in mineral assemblage. These simplifications greatly reduce computational requirements but preclude effects such as shear localisation and transient changes in rheology associated with phase transitions, which have the potential to fundamentally change flow patterns in the mantle. Here we use the finite-element code ASPECT (Bangerth et al., 2013) to model grain size evolution and the interplay between grain size, stress and strain rate in the convecting mantle. We include the simultaneous and competing effects of dynamic recrystallisation resulting from work done by dislocation creep, grain growth in multiphase assemblages and recrystallisation at phase transitions. Grain size variations also affect seismic properties of mantle materials. We use several published formulations to relate intrinsic variables (P, T, and grain size) from our numerical models to seismic velocity (Vs) and attenuation (Q). Our calculations use thermodynamically self-consistent anharmonic elastic moduli determined for the mineral assemblages in the mantle using HeFESTo (Stixrude and Lithgow-Bertelloni, 2013). We investigate the effect of realistically heterogeneous grain sizes by computing body wave travel times, ray paths, and attenuation (t*) at different frequencies. We highlight the frequency-dependent sensitivity of seismic waves to grain size, which is important when interpreting Vs and Q observations in terms of mineral assemblage and temperature. Our models show that rapid metamorphic reactions in mantle upwellings and downwellings lead to high lateral viscosity contrasts, as a result of gradual grain size evolution. Positive feedback between grain size reduction and viscosity reduction results in shear localisation. As a result, the edges of thermal plumes have smaller grain sizes and lower

  3. 3D spherical models of Martian mantle convection constrained by melting history

    NASA Astrophysics Data System (ADS)

    Sekhar, Pavithra; King, Scott D.

    2014-02-01

    While most of Tharsis rise was in place by end of the Noachian period, at least one volcano on Tharsis swell (Arsia Mons) has been active within the last 2 Ma. This places an important constraint on mantle convection and on the thermal evolution of Mars. The existence of recent volcanism on Mars implies that adiabatic decompression melting and, hence, upwelling convective flow in the mantle remains important on Mars at present. The thermal history on Mars can be constrained by the history of melt production, specifically generating sufficient melt in the first billion years of the planets history to produce Tharsis rise as well as present day melt to explain recent volcanism. In this work, mantle convection simulations were performed using finite element code CitcomS in a 3D sphere starting from a uniformly hot mantle and integrating forward in time for the age of the solar system. We implement constant and decaying radioactive heat sources; and vary the partitioning of heat sources between the crust and mantle, and consider decreasing core-mantle boundary temperature and latent heat of melting. The constant heat source calculations produce sufficient melt to create Tharsis early in Martian history and continue to produce significant melt to the present. Calculations with decaying radioactive heat sources generate excessive melt in the past, except when all the radiogenic elements are in the crust, and none produce melt after 2 Gyr. Producing a degree-1 or degree-2 structure may not be pivotal to explain the Tharsis rise: we present multi-plume models where not every plume produces melt. The Rayleigh number controls the timing of the first peak of volcanism while late-stage volcanism is controlled more by internal mantle heating. Decreasing the Rayleigh number increases the lithosphere thickness (i.e., depth), and increasing lithosphere thickness increases the mean mantle temperature. Increasing pressure reduces melt production while increasing temperature

  4. Off-axis volcanism as fueled by shear-driven upwelling near the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Ballmer, M. D.; Conrad, C. P.; Harmon, N.; Smith, E. I.

    2012-04-01

    The study of off-axis volcanism provides an opportunity to understand the make-up and dynamics of the upper mantle beneath mid-ocean ridges (MOR). Close to the East Pacific Rise (EPR), active magmatism propagated towards the spreading center to create a series of parallel volcanic ridges on the Pacific Plate (of length ~3500 km for the Pukapuka, and ~500 km for the Sojourn, and Hotu-Matua ridges). Propagation of this volcanism at ~20 cm/a, as well as asymmetry in a variety of geophysical observables across the EPR, indicates strong lateral eastward return flow in the asthenosphere that is driven by upwelling beneath the South Pacific Superswell¹. Although this pattern of large-scale mantle flow can account for the propagation of intraplate melting towards the EPR, it does not explain decompression melting itself. Volcanism off the EPR has been attributed to various mechanisms, but each of them has trouble in reconciling its entire characteristics. First, lithospheric cracking is inconsistent with its occurrence in the lows of the apparent gravity lineations2. Second, small-scale convection is not expected to develop beneath nascent and young oceanic lithosphere. Third, return flow that is channelized into viscous fingers is likely insufficient to sustain significant volumes of volcanism. We hypothesize that shear-driven upwelling (SDU) supports off-axis volcanism. SDU is a mechanism for mantle decompression that does not require lateral density heterogeneity. For example, vertical flow emerges at the edges of viscosity anomalies if the asthenosphere is sheared horizontally3. These two ingredients are present in the SE Pacific, where (1) shear across the asthenosphere is inferred to be greatest worldwide3, and (2) lateral variability in mantle viscosity is indicated by gravity and seismic anomalies2. Channelized return flow from the South Pacific thermal anomaly may initially provide this variability in viscosity. Here we show that SDU can account for the observed

  5. Cenozoic magmatism in the South China Basin: Decompression melting and implications of an enriched mantle source

    SciTech Connect

    Flower, M.F.J.; Kan Tu; Ming Zhang ); Guanghong Xie )

    1990-06-01

    A widespread eposide of interplate volcanism followed the cessation of seafloor spreading in the South China Basin (SCB), affecting the South China Sea, and fringing areas of southern China and Indochina. Geochemical data for basalts from South China Sea islands and seamounts, Hainan Island, and Taiwan define an enriched (Dupal-like) mantle domain yielding oceanic island basalt (OIB) suites with {Delta}7/4Pb = 2-13, {Delta}8/4Pb = 45-73, {sup 87}Sr/{sup 86}Sr > {approximately}0.70325, Th/Ta > 2, and Th/Ba > 0.02. Opening of the SCB resulted from disaggregation of the South China block in response to the Indo-Eurasian collision, a process involving at least one seafloor spreading episode, terminated by collision of microcontinents with the Philippines and Borneo. The lack of precursive flood basalt suggests that active mantle upwelling was not involved and that melting was a passive effect of lithosphere stretching. However, while mantle decompression at ambient stretching factors ({approximately}1.7-2.5) appears to permit melting on the observed scale, the enriched source may preclude such a simple mantle dynamic. Three alternatives are considered: (1) passive melting of a mature metasomatised boundary layer, (2) active melting of thermally eroded subcontinental lithosphere (deep enrichment) or metasomatised boundary layer (shallow enrichment), and (3) relict diapirs of pre-SCB and/or Java trench subduction slabs (intermediate/deep enrichment). These models are evaluated in terms of chemical and isotopic mass balances associated with the generation and movement of small melt fractions in depleted, nondepleted, and enriched mantle.

  6. Pattern and evolution of the 3-D subduction-induced mantle flow in the laboratory: from generic models to case studies

    NASA Astrophysics Data System (ADS)

    Strak, Vincent; Schellart, Wouter P.

    2015-04-01

    Three-dimensional self-evolving subduction models have been quantitatively analysed in the laboratory by means of a stereoscopic Particle Image Velocimetry (sPIV) technique. The purpose is (1) to provide information on the pattern of the quasi-toroidal mantle flow induced by subduction, particularly focusing on the location and magnitude of upwellings, and (2) to study the evolution of mantle upwellings in terms of location and magnitude. These generic models simulating a narrow subduction zone of ~750 km wide indicate that 4 types of upwelling are generated by subduction in a Newtonian mantle. One of these upwellings occurs laterally away from the sub-slab domain and is of high magnitude, suggesting that it could potentially trigger decompression melting, thereby producing intraplate volcanism. Another set of experiments has been performed to investigate how slab width controls the pattern of mantle flow. Crucial points to study are (1) how the lateral extent of the slab controls the position and magnitude of mantle upwellings located laterally away from the sub-slab domain, and (2) what is the relationship between slab width and the extent of the toroidal-component cells. We tested slab widths ranging from narrow (e.g., Calabria) to wider (e.g., Tonga-Kermadec-Hikurangi) subduction zones. The models show that both the magnitude of the upwelling occurring laterally away from the sub-slab domain and the extent of the toroidal-component of mantle flow increase non-linearly with increasing slab width.

  7. Superplumes from the core-mantle boundary to the lithosphere: implications for heat flux.

    PubMed

    Romanowicz, Barbara; Gung, Yuancheng

    2002-04-19

    Three-dimensional modeling of upper-mantle anelastic structure reveals that thermal upwellings associated with the two superplumes, imaged by seismic elastic tomography at the base of the mantle, persist through the upper-mantle transition zone and are deflected horizontally beneath the lithosphere. This explains the unique transverse shear wave isotropy in the central Pacific. We infer that the two superplumes may play a major and stable role in supplying heat and horizontal flow to the low-viscosity asthenospheric channel, lubricating plate motions and feeding hot spots. We suggest that more heat may be carried through the core-mantle boundary than is accounted for by hot spot fluxes alone.

  8. Seasonality in planktic foraminifera of the central California coastal upwelling region

    NASA Astrophysics Data System (ADS)

    Davis, Catherine V.; Hill, Tessa M.; Russell, Ann D.; Gaylord, Brian; Jahncke, Jaime

    2016-09-01

    The close association between planktic foraminiferal assemblages and local hydrography make foraminifera invaluable proxies for environmental conditions. Modern foraminiferal seasonality is important for interpreting fossil distributions and shell geochemistry as paleoclimate proxies. Understanding this seasonality in an active upwelling area is also critical for anticipating which species may be vulnerable to future changes in upwelling intensity and ocean acidification. Two years (2012-2014) of plankton tows, along with conductivity-temperature-depth profiles and carbonate chemistry measurements taken along the north-central California shelf, offer new insights into the seasonal dynamics of planktic foraminifera in a seasonal coastal upwelling regime. This study finds an upwelling affinity for Neogloboquadrina pachyderma as well as a seasonal and upwelling associated alternation between dominance of N. pachyderma and Neogloboquadrina incompta, consistent with previous observations. Globigerina bulloides, however, shows a strong affinity for non-upwelled waters, in contrast to findings in Southern California where the species is often associated with upwelling. We also find an apparent lunar periodicity in the abundances of all species and document the presence of foraminifera even at very low saturation states of calcite.

  9. Testing thermochemical mantle circulation with Mantle Transition Zone velocities and topography

    NASA Astrophysics Data System (ADS)

    Houser, C. T.; Hernlund, J. W.

    2014-12-01

    trench migration above silica rich domains. The behavior of upwelling harzburgitic material will be complicated by the high temperature perovskite and (Mg,Fe)O transition to majorite garnet. Thus, the lack of correlated patterns in the 410 and 660 km discontinuity topography outside of subduction zones could be due to partial chemical layering of the mantle.

  10. Two forms of volcanism: Implications for mantle flow and off-axis crustal production on the west flank of the southern east Pacific rise

    NASA Astrophysics Data System (ADS)

    Shen, Yang; Forsyth, Donald W.; Scheirer, Daniel S.; MacDonald, Ken, C.

    1993-10-01

    SeaMarc II side-scan sonar and bathymetric data on the west flank of the East Pacific Rise (16 deg-18 deg) reveal a large number of seamounts, organized primarily in chains. The easternmost ends of the chains near the ridge axis appear to be active as indicated by fresh lava flows. In addition, areas of unusually high reflectivity representing recent lava flows were found as far as 60 to 80 km from the spreading axis. The flows are sometimes dammed by abyssal hill scarps formed near the ridge axis that have maximum relief of the order of 100 m. In other cases, the scarps appear to be buried by flows. The disappearance of scarps can be used to estimate the extent of old lava flows or volcanic debris that are not detected acoustically in the sonar image. Under this criterion, lava flows and volcanic debris surrounding the seamounts cover 40-50% of the survey area of about 18,000 sq km. With an estimated average thickness of about 100 m, the volume of lava flows and volcanic debris is about 0.8 +/- 0.3% of that of the total crust. The volume of the seamounts is estimated by isolating the seamounts from the background topography with an anisotropic, median-filtering technique. The volume of seamount edifices is 1.05 +/- 0.05% of the volume of the crust. Thus the total volume of volcanic material extruded off-axis is about 1.5 to 2.2% of the volume of the crust. The decreasing volcanic activity away from the ridge axis suggests that near-axis seamounts may be associated with the upwelling system, beneath the ridge, perhaps by preferential melting of embedded, passive heterogeneities. The existence of closely spaced linear chains and the tendency for fresh flows to be found at near-ridge ends of chains suggest that there are discrete sources in the upper mantle active for extended periods (over 1.8 m.y.). Passive heterogeneities embedded in the upwelling mantle would have to be highly elongated along streamlines to produce persistent, nearl stationary melting anomalies

  11. Plume's buoyancy and heat fluxes from the deep mantle estimated by an instantaneous mantle flow simulation based on the S40RTS global seismic tomography model

    NASA Astrophysics Data System (ADS)

    Yoshida, Masaki

    2012-11-01

    It is still an open question as to how much heat is transported from the deep mantle to the upper mantle by mantle upwelling plumes, which would impose a strong constraint on models of the thermal evolution of the earth. Here I perform numerical computations of instantaneous mantle flow based on a recent highly resolved global seismic tomography model (S40RTS), apply new simple fluid dynamics theories to the plume's radius and velocity, considering a Poiseuille flow assumption and a power-law relationship between the boundary layer thickness and Rayleigh number, and estimate the plume's buoyancy and heat fluxes from the deep lower mantle under varying plume viscosity. The results show that for some major mantle upwelling plumes with localized strong ascent velocity under the South Pacific and Africa, the buoyancy fluxes of each plume beneath the ringwoodite to perovskite + magnesiowüstite ("660-km") phase decomposition boundary are comparable to those inferred from observed hotspot swell volumes on the earth, i.e., on the order of 1 Mg s-1, when the plume viscosity is 1019-1020 Pa s. This result, together with previous numerical simulations of mantle convection and the gentle Clausius-Clapeyron slope for the 660-km phase decomposition derived from recent high-pressure measurements under dehydrated/hydrated conditions in the mantle transition zone, implies that mantle upwelling plumes in the lower mantle penetrate the 660-km phase decomposition boundary without significant loss in thermal buoyancy because of the weak thermal barrier at the 660-km boundary. The total plume heat flux under the South Pacific is estimated to be about 1 TW beneath the 660-km boundary, which is significantly smaller than the core-mantle boundary heat flux. Previously published scaling laws for the plume's radius and velocity based on a plume spacing theory, which explains well plume dynamics in three-dimensional time-dependent mantle convection, suggest that these plume fluxes depend

  12. The Mantle-Atmosphere Connection: Oxidation of the Atmosphere through Mantle Convection

    NASA Astrophysics Data System (ADS)

    Lee, K. K. M.; Gu, T.; Li, M.; McCammon, C. A.

    2015-12-01

    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 elements1, recycling of refractory isotopes2 and the oxidation state of the atmosphere through volcanic outgassing3. The rise of oxygen in atmosphere, i.e., the Great Oxidation Event (G.O.E.) occurred ~2.4 billion years ago (Ga)4. However, multiple lines of evidence point to biological oxygen production well before 2.4 Ga5; while chromium isotopes in iron formations indicates a decline of atmospheric oxygen about 1.88 Ga6. In contrast to the fluctuation of atmospheric oxygen, vanadium in Archean mantle lithosphere suggests that the mantle redox state has been constant for ~3.5 Ga7. Indeed, the redox state of the deep Earth's interior is not well constrained8 and its effect on mantle dynamics is unknown. Here we show a redox-induced density difference affects mantle convection and may potentially cause the oxidation of the upper mantle. From two synthetic enstatite chondritic samples with identical bulk compositions but formed under different oxygen fugacities (fO2) compressed to lower mantle pressures and temperatures, we find Al2O3 forms its own phase separate from the dominant Mg-silicate perovskite phase (i.e., bridgmanite9) 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. Geodynamical numerical simulations show that the redox-induced density difference could lead to an increased oxidation of Earth's upper mantle but is buffered by slow mixing with more reduced material through hot upwellings, which will potentially affect mantle redox and rise of oxygen in atmosphere.

  13. Air-sea feedback during coastal upwelling

    SciTech Connect

    Gallacher, P.C.

    1994-12-31

    The basic dynamics of coastal upwelling are well known. Consider a steady, curl-free, alongshore wind blowing down a coastline. This results in an Ekman divergence. If the resulting Ekman transport is offshore, coastal upwelling ensues. When this occurs, a front develops between the cold, upwelled water and the less dense offshore surface water. This front propagates offshore at a rate determined by the Ekman transport. The question is what effect does this front have on the atmosphere, and is there a feedback between the atmosphere and the ocean. The results of the FASINEX study have shown that the atmospheric boundary layer can respond dramatically to changes in the ocean surface temperature, and this may happen on small scales and quite rapidly. The author hypothesizes that an interaction can occur in which the atmospheric surface layer becomes more stable on the upwelling side of the front due the colder sea surface temperature.

  14. Iron Meteorites and Upwelling in Antarctica

    NASA Astrophysics Data System (ADS)

    Gourlay, B. S.; Behr, E.; Mardon, A.; Behr, E.

    2016-09-01

    In Antarctica, a meteorite stranding zone, stone meteorites are more common than iron. Dr. Evatt's team suggests that the heat conductivity of iron may be opposing the upwelling effects so iron meteorites sink under the ice unlike the stone ones.

  15. Upper mantle structure beneath the Hangay dome, central Mongolia and implications for high topography and magmatism

    NASA Astrophysics Data System (ADS)

    Souza, Stephanie

    Origin and support of high topography in an intracontinental setting is not fully understood. The Hangay Dome in central Mongolia spans an area of ˜200,000 km2 and reaches elevations of ˜4,000 m. It has a complex accretionary history associated with the Central Asian Orogenic Belt and is bound to the north, south, and west by active strike-slip faults. The extent to which the accretionary history or present day deformation contributes to current topography remain open questions. Geodynamic models that have been proposed to account for current topography include far-field effects of Pacific Plate subduction or the India-Asia collision, rifting stemming from the Lake Baikal region, mantle-plume activity, upwelling of the asthenospheric mantle, lithospheric delamination, and/or the underplating of magmatic rocks at the base of the crust. In order to determine which whether upper mantle structure might contribute to the origin of high topography in the Hangay, two years of teleseismic P and S body wave data are inverted for 3D velocity variations in Vp and Vs in the upper mantle beneath the Hangay. Velocity perturbations range between +/-3% for the P wave model and +/-7% for the S wave model. Changes in velocity are a function of temperature, density, composition, and presence of melt or fluid. Thermal anomalies are the primary causes for velocity perturbations in the upper mantle. The Hangay is underlain by non-uniform low velocity zones that correlate well with areas of the Hangay that have experienced volcanism in the past ˜30 Ma. High velocity zones are located off the edges of the dome to the west, east, and south. One low velocity anomaly in particular, is located near the headwaters of the Orkhon River beneath a region that had experienced magmatism ˜15-20 million years ago. Interestingly, this region sits between two areas ˜50 km away on either side that have experienced magmatism in the last 3 million years. This low velocity anomaly has a DeltaVp of -4

  16. Joint seismic-geodynamic-mineral physical modelling of African geodynamics: A reconciliation of deep-mantle convection with surface geophysical constraints

    SciTech Connect

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

    2008-08-22

    Recent progress in seismic tomography provides the first complete 3-D images of the combined thermal and chemical anomalies that characterise the unique deep mantle structure below the African continent. With these latest tomography results we predict flow patterns under Africa that reveal a large-scale, active hot upwelling, or superplume, below the western margin of Africa under the Cape Verde Islands. The scale and dynamical intensity of this West African superplume (WASP) is comparable to that of the south African superplume (SASP) that has long been assumed to dominate the flow dynamics under Africa. On the basis of this new tomography model, we find the dynamics of the SASP is strongly controlled by chemical contributions to deep mantle buoyancy that significantly compensate its thermal buoyancy. In contrast, the WASP appears to be entirely dominated by thermal buoyancy. New calculations of mantle convection incorporating these two superplumes reveal that the plate-driving forces due to the flow generated by the WASP is as strong as that due to the SASP. We find that the chemical buoyancy of the SASP exerts a strong stabilising control on the pattern and amplitude of shallow mantle flow in the asthenosphere below the southern half of the African plate. The asthenospheric flow predictions provide the first high resolution maps of focussed upwellings that lie below the major centres of Late Cenozoic volcanism, including the Kenya domes and Hoggar massif that lies above a remnant plume head in the upper mantle. Inferences of sublithospheric deformation from seismic anisotropy data are shown to be sensitive to the contributions of chemical buoyancy in the SASP.

  17. Aurora inhibitor MLN8237 in combination with docetaxel enhances apoptosis and anti-tumor activity in mantle cell lymphoma.

    PubMed

    Qi, Wenqing; Cooke, Laurence S; Liu, Xiaobing; Rimsza, Lisa; Roe, Denise J; Manziolli, Ann; Persky, Daniel O; Miller, Thomas P; Mahadevan, Daruka

    2011-04-01

    Auroras (A and B) are oncogenic serine/threonine kinases that play key roles in the mitotic phase of the eukaryotic cell cycle. Analysis of the leukemia lymphoma molecular profiling project (LLMPP) database indicates Aurora over-expression correlates with poor prognosis. A tissue microarray (TMA) composed of 20 paired mantle cell lymphoma (MCL) patients demonstrated >75% of patients had high levels Aurora expression. Aurora A and B were also found elevated in 13 aggressive B-NHL cell lines. MLN8237, an Aurora inhibitor induced G2/M arrest with polyploidy and abrogated Aurora A and histone-H3 phosphorylation. MLN8237 inhibited aggressive B-NHL cell proliferation at an IC(50) of 10-50 nM and induced apoptosis in a dose- and time-dependent manner. Low dose combinations of MLN8237+docetaxel enhanced apoptosis by ~3-4-fold in cell culture compared to single agents respectively. A mouse xenograft model of MCL demonstrated that MLN8237 (10 or 30 mg/kg) or docetaxel (10mg/kg) alone had modest anti-tumor activity. However, MLN8237 plus docetaxel demonstrated a statistically significant tumor growth inhibition and enhanced survival compared to single agent therapy. Together, our results suggest that MLN8237 plus docetaxel may represent a novel therapeutic strategy that could be evaluated in early phase trials in relapsed/refractory aggressive B-cell NHL. PMID:21291867

  18. Aurora inhibitor MLN8237 in combination with docetaxel enhances apoptosis and anti-tumor activity in mantle cell lymphoma.

    PubMed

    Qi, Wenqing; Cooke, Laurence S; Liu, Xiaobing; Rimsza, Lisa; Roe, Denise J; Manziolli, Ann; Persky, Daniel O; Miller, Thomas P; Mahadevan, Daruka

    2011-04-01

    Auroras (A and B) are oncogenic serine/threonine kinases that play key roles in the mitotic phase of the eukaryotic cell cycle. Analysis of the leukemia lymphoma molecular profiling project (LLMPP) database indicates Aurora over-expression correlates with poor prognosis. A tissue microarray (TMA) composed of 20 paired mantle cell lymphoma (MCL) patients demonstrated >75% of patients had high levels Aurora expression. Aurora A and B were also found elevated in 13 aggressive B-NHL cell lines. MLN8237, an Aurora inhibitor induced G2/M arrest with polyploidy and abrogated Aurora A and histone-H3 phosphorylation. MLN8237 inhibited aggressive B-NHL cell proliferation at an IC(50) of 10-50 nM and induced apoptosis in a dose- and time-dependent manner. Low dose combinations of MLN8237+docetaxel enhanced apoptosis by ~3-4-fold in cell culture compared to single agents respectively. A mouse xenograft model of MCL demonstrated that MLN8237 (10 or 30 mg/kg) or docetaxel (10mg/kg) alone had modest anti-tumor activity. However, MLN8237 plus docetaxel demonstrated a statistically significant tumor growth inhibition and enhanced survival compared to single agent therapy. Together, our results suggest that MLN8237 plus docetaxel may represent a novel therapeutic strategy that could be evaluated in early phase trials in relapsed/refractory aggressive B-cell NHL.

  19. The oxidation state of the mantle and the extraction of carbon from Earth's interior.

    PubMed

    Stagno, Vincenzo; Ojwang, Dickson O; McCammon, Catherine A; Frost, Daniel J

    2013-01-01

    Determining the oxygen fugacity of Earth's silicate mantle is of prime importance because it affects the speciation and mobility of volatile elements in the interior and has controlled the character of degassing species from the Earth since the planet's formation. Oxygen fugacities recorded by garnet-bearing peridotite xenoliths from Archaean lithosphere are of particular interest, because they provide constraints on the nature of volatile-bearing metasomatic fluids and melts active in the oldest mantle samples, including those in which diamonds are found. Here we report the results of experiments to test garnet oxythermobarometry equilibria under high-pressure conditions relevant to the deepest mantle xenoliths. We present a formulation for the most successful equilibrium and use it to determine an accurate picture of the oxygen fugacity through cratonic lithosphere. The oxygen fugacity of the deepest rocks is found to be at least one order of magnitude more oxidized than previously estimated. At depths where diamonds can form, the oxygen fugacity is not compatible with the stability of either carbonate- or methane-rich liquid but is instead compatible with a metasomatic liquid poor in carbonate and dominated by either water or silicate melt. The equilibrium also indicates that the relative oxygen fugacity of garnet-bearing rocks will increase with decreasing depth during adiabatic decompression. This implies that carbon in the asthenospheric mantle will be hosted as graphite or diamond but will be oxidized to produce carbonate melt through the reduction of Fe(3+) in silicate minerals during upwelling. The depth of carbonate melt formation will depend on the ratio of Fe(3+) to total iron in the bulk rock. This 'redox melting' relationship has important implications for the onset of geophysically detectable incipient melting and for the extraction of carbon dioxide from the mantle through decompressive melting. PMID:23282365

  20. Complex interactions between diapirs and 4-D subduction driven mantle wedge circulation.

    NASA Astrophysics Data System (ADS)

    Sylvia, R. T.; Kincaid, C. R.

    2015-12-01

    Analogue laboratory experiments generate 4-D flow of mantle wedge fluid and capture the evolution of buoyant mesoscale diapirs. The mantle is modeled with viscous glucose syrup with an Arrhenius type temperature dependent viscosity. To characterize diapir evolution we experiment with a variety of fluids injected from multiple point sources. Diapirs interact with kinematically induced flow fields forced by subducting plate motions replicating a range of styles observed in dynamic subduction models (e.g., rollback, steepening, gaps). Data is collected using high definition timelapse photography and quantified using image velocimetry techniques. While many studies assume direct vertical connections between the volcanic arc and the deeper mantle source region, our experiments demonstrate the difficulty of creating near vertical conduits. Results highlight extreme curvature of diapir rise paths. Trench-normal deflection occurs as diapirs are advected downward away from the trench before ascending into wedge apex directed return flow. Trench parallel deflections up to 75% of trench length are seen in all cases, exacerbated by complex geometry and rollback motion. Interdiapir interaction is also important; upwellings with similar trajectory coalesce and rapidly accelerate. Moreover, we observe a new mode of interaction whereby recycled diapir material is drawn down along the slab surface and then initiates rapid fluid migration updip along the slab-wedge interface. Variability in trajectory and residence time leads to complex petrologic inferences. Material from disparate source regions can surface at the same location, mix in the wedge, or become fully entrained in creeping flow adding heterogeneity to the mantle. Active diapirism or any other vertical fluid flux mechanism employing rheological weakening lowers viscosity in the recycling mantle wedge affecting both solid and fluid flow characteristics. Many interesting and insightful results have been presented based

  1. The oxidation state of the mantle and the extraction of carbon from Earth's interior.

    PubMed

    Stagno, Vincenzo; Ojwang, Dickson O; McCammon, Catherine A; Frost, Daniel J

    2013-01-01

    Determining the oxygen fugacity of Earth's silicate mantle is of prime importance because it affects the speciation and mobility of volatile elements in the interior and has controlled the character of degassing species from the Earth since the planet's formation. Oxygen fugacities recorded by garnet-bearing peridotite xenoliths from Archaean lithosphere are of particular interest, because they provide constraints on the nature of volatile-bearing metasomatic fluids and melts active in the oldest mantle samples, including those in which diamonds are found. Here we report the results of experiments to test garnet oxythermobarometry equilibria under high-pressure conditions relevant to the deepest mantle xenoliths. We present a formulation for the most successful equilibrium and use it to determine an accurate picture of the oxygen fugacity through cratonic lithosphere. The oxygen fugacity of the deepest rocks is found to be at least one order of magnitude more oxidized than previously estimated. At depths where diamonds can form, the oxygen fugacity is not compatible with the stability of either carbonate- or methane-rich liquid but is instead compatible with a metasomatic liquid poor in carbonate and dominated by either water or silicate melt. The equilibrium also indicates that the relative oxygen fugacity of garnet-bearing rocks will increase with decreasing depth during adiabatic decompression. This implies that carbon in the asthenospheric mantle will be hosted as graphite or diamond but will be oxidized to produce carbonate melt through the reduction of Fe(3+) in silicate minerals during upwelling. The depth of carbonate melt formation will depend on the ratio of Fe(3+) to total iron in the bulk rock. This 'redox melting' relationship has important implications for the onset of geophysically detectable incipient melting and for the extraction of carbon dioxide from the mantle through decompressive melting.

  2. Seismic tomography of the Colorado Rocky Mountains upper mantle from CREST: Lithosphere-asthenosphere interactions and mantle support of topography

    NASA Astrophysics Data System (ADS)

    MacCarthy, J. K.; Aster, R. C.; Dueker, K.; Hansen, S.; Schmandt, B.; Karlstrom, K.

    2014-09-01

    currently being, replaced and modified by upwelling asthenosphere. Low velocity features resolved here indicate that this process may be sourced as deeply as the top of the mantle transition zone at 410 km. One driving mechanism for this is upper mantle interaction between upwelling hydration-induced partial melt and destabilized downwelling lithosphere in the deeper upper mantle. Tomographic imaging of mantle seismic velocity and crustal thickness results and modeling from the CREST experiment indicate that the highest elevations of the Colorado Rocky Mountains are substantially supported by the mantle, and strong correlations between low velocity mantle and thin crust/high topography are noted across the region. This, along with rich upper mantle seismic heterogeneity, suggests that mantle buoyancy and dynamics are central to present day topographic support and recent geomorphic evolution of the region.

  3. Coupling surface and mantle dynamics: A novel experimental approach

    NASA Astrophysics Data System (ADS)

    Kiraly, Agnes; Faccenna, Claudio; Funiciello, Francesca; Sembroni, Andrea

    2015-05-01

    Recent modeling shows that surface processes, such as erosion and deposition, may drive the deformation of the Earth's surface, interfering with deeper crustal and mantle signals. To investigate the coupling between the surface and deep process, we designed a three-dimensional laboratory apparatus, to analyze the role of erosion and sedimentation, triggered by deep mantle instability. The setup is constituted and scaled down to natural gravity field using a thin viscous sheet model, with mantle and lithosphere simulated by Newtonian viscous glucose syrup and silicon putty, respectively. The surface process is simulated assuming a simple erosion law producing the downhill flow of a thin viscous material away from high topography. The deep mantle upwelling is triggered by the rise of a buoyant sphere. The results of these models along with the parametric analysis show how surface processes influence uplift velocity and topography signals.

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

    USGS Publications Warehouse

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

    2011-01-01

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

  5. Post-Eocene Subduction Dynamics and Mantle Flow beneath Western U.S.

    NASA Astrophysics Data System (ADS)

    Liu, L.; Zhou, Q.; Leonard, T.

    2015-12-01

    Both surface geology and mantle seismic images suggest a complex late Cenozoic history of mantle dynamics over western U.S. We try to understand this history by simulating the Farallon subduction since 40 Ma. Forward subduction models assimilating time dependent seafloor ages, plate kinematics and evolving plate boundaries suggest that the present-day 3D distribution of fast seismic anomalies below western U.S. mostly represent late Cenozoic slabs, which experienced multiple phases of segmentation during subduction because of their young age and small mechanical strength (Liu & Stegman, 2011). A major slab segmentation event occurred around mid-Miocene, with the resulting slab tear and induced asthenosphere upwelling correlating with the Steens-Columbia River flood basalts (SCRB) eruption both in space and in time (Liu & Stegman, 2012). This suggests that a mantle plume is not required for the formation of the SCRB. Segmentation of the Farallon slab generates rapid toroidal flows around the newly formed slab edges beneath the Cascadia arc. These mantle flows may affect both the pattern and composition of arc volcanism through transportation of oceanic asthenosphere material into the mantle wedge. Based on the forward model, we further test the influence of slow seismic anomalies on mantle dynamics. On the one hand, we explicitly input a deep hot anomaly to represent the putative Yellowstone plume. On the other hand, we develop a hybrid scheme that combines the adjoint inverse method with the high-resolution forward simulation approach, so that the present-day mantle seismic structure is entirely consistent with the convection model. Our preliminary results suggest that a hot plume could actively rise up only when it is several hundreds of kilometers away from the slabs, as is the case prior to 20 Ma. Subsequently, the plume is dominated by the surrounding slabs, resulting in an overall downwelling mantle flow. This suggests that a plume might have contributed to

  6. Dehumidification of Iberia by enhanced summer upwelling

    NASA Astrophysics Data System (ADS)

    Miranda, P. M.; Costa, V.; Nogueira, M.; Semedo, A.

    2015-12-01

    Dehumidification of Iberia by enhanced summer upwelling Miranda PMA, Costa V, Semedo AIDL, Faculdade de Ciências, University of LisbonA 24-year simulation of the recent Iberian climate, using the WRF model at 9km resolution forced by ERA-Interim reanalysis (1989-2012), is analysed for the decadal evolution of the upwelling forcing coastal wind and for column integrated Precipitable water vapour (PWV). Results indicate that, unlike what was found by Bakun et al. (2009) for the Peruvian region, a statistically significant trend in the upwelling favourable (northerly) wind has been accompanied by a corresponding decrease in PWV, not only inland but also over the coastal waters. Such increase is consistent with a reinforced northerly coastal jet in the maritime boundary layer contributing to atmospheric Ekman pumping of dry continental air into the coastal region. Diagnostics of the prevalence of the Iberian thermal low following Hoinka and Castro (2003) also show a positive trend in its frequency during an extended summer period (April to September). These results are consistent with recent studies indicating an upward trend in the frequency of upwelling in SW Iberia (Alves and Miranda 2013), and may be relevant for climate change applications as an increase in coastal upwelling (Miranda et al 2013) may lead to substantial regional impacts in the subtropics. Aknowledgements: Study supported by FCT Grant RECI/GEO-MET/0380/2012Alves JMR, Miranda PMA (2013) Variability of Iberian upwelling implied by ERA-40 and ERA-Interim reanalyses, Tellus A 2013, http://dx.doi.org/10.3402/tellusa.v65i0.19245.Bakun et al (2010) Greenhouse gas, upwelling-favorable winds, and the future of coastal ocean upwelling ecosystems, Global Change Biology, doi: 10.1111/j.1365-2486.2009.02094.xHoinka KP, Castro M (2003) The Iberian Peninsula thermal low. QJRMS, 129, 1491- 1511, doi: 10.1256/qj.01.189.Miranda et al (2013) Climate change and upwelling: response of Iberian upwelling to atmospheric

  7. Assessing sinkhole activity in the Ebro Valley mantled evaporite karst using advanced DInSAR

    NASA Astrophysics Data System (ADS)

    Galve, Jorge Pedro; Castañeda, Carmen; Gutiérrez, Francisco; Herrera, Gerardo

    2015-01-01

    Sinkholes in karst areas may cause subsidence damage in transportation infrastructures, demolition of buildings and even the loss of human lives when they occur in a catastrophic way. Differential Interferometry (DInSAR) is a promising technology for detecting and characterizing sinkholes, as well as for reducing the associated risk when combined with other sources of data such as a sinkhole inventory. In this work, the usefulness of InSAR techniques and data for sinkhole risk management has been analyzed through the comparison of three DInSAR-derived velocity maps with a comprehensive sinkhole inventory in the Ebro Valley, NE Spain. The DInSAR maps have contributed to improve the sinkhole inventory in different ways: (1) detection of non-inventoried sinkholes; (2) revision of sinkhole areas previously classified as inactive as active; and (3) refinement of underestimated sinkhole boundaries. The obtained results suggest that DInSAR products are suitable for analyzing active dissolution-induced subsidence. The application of these techniques may help in recognizing and better characterizing previously unknown karst subsidence problems and in preventing personal and property losses. However, the analysis reveals that the available DInSAR maps combined overlook about 70% of the previously mapped active sinkholes mainly due to decorrelation.

  8. Not so hot "hot spots" in the oceanic mantle.

    PubMed

    Bonath, E

    1990-10-01

    Excess volcanism and crustal swelling associated with hot spots are generally attributed to thermal plumes upwelling from the mantle. This concept has been tested in the portion of the Mid-Atlantic Ridge between 34 degrees and 45 degrees (Azores hot spot). Peridotite and basalt data indicate that the upper mantle in the hot spot has undergone a high degree of melting relative to the mantle elsewhere in the North Atlantic. However, application of various geothermometers suggests that the temperature of equilibration of peridotites in the mantle was lower, or at least not higher, in the hot spot than elsewhere. The presence of H(2)O-rich metasomatized mantle domains, inferred from peridotite and basalt data, would lower the melting temperature of the hot spot mantle and thereby reconcile its high degree ofmelting with the lack of a mantle temperature anomaly. Thus, some so-called hot spots might be melting anomalies unrelated to abnormally high mantle temperature or thermal plumes. PMID:17808242

  9. Evolution of helium isotopes in the Earth's mantle.

    PubMed

    Class, Cornelia; Goldstein, Steven L

    2005-08-25

    Degassing of the Earth's mantle through magmatism results in the irreversible loss of helium to space, and high (3)He/(4)He ratios observed in oceanic basalts have been considered the main evidence for a 'primordial' undegassed deep mantle reservoir. Here we present a new global data compilation of ocean island basalts, representing upwelling 'plumes' from the deep mantle, and show that island groups with the highest primordial signal (high (3)He/(4)He ratios) have striking chemical and isotopic similarities to mid-ocean-ridge basalts. We interpret this as indicating a common history of mantle trace element depletion through magmatism. The high (3)He/(4)He in plumes may thus reflect incomplete degassing of the deep Earth during continent and ocean crust formation. We infer that differences between plumes and the upper-mantle source of ocean-ridge basalts reflect isolation of plume sources from the convecting mantle for approximately 1-2 Gyr. An undegassed, primordial reservoir in the mantle would therefore not be required, thus reconciling a long-standing contradiction in mantle dynamics.

  10. Local Discontinuous Galerkin (LDG) Method for Advection of Active Compositional Fields with Discontinuous Boundaries: Demonstration and Comparison with Other Methods in the Mantle Convection Code ASPECT

    NASA Astrophysics Data System (ADS)

    He, Y.; Billen, M. I.; Puckett, E. G.

    2015-12-01

    Flow in the Earth's mantle is driven by thermo-chemical convection in which the properties and geochemical signatures of rocks vary depending on their origin and composition. For example, tectonic plates are composed of compositionally-distinct layers of crust, residual lithosphere and fertile mantle, while in the lower-most mantle there are large compositionally distinct "piles" with thinner lenses of different material. Therefore, tracking of active or passive fields with distinct compositional, geochemical or rheologic properties is important for incorporating physical realism into mantle convection simulations, and for investigating the long term mixing properties of the mantle. The difficulty in numerically advecting fields arises because they are non-diffusive and have sharp boundaries, and therefore require different methods than usually used for temperature. Previous methods for tracking fields include the marker-chain, tracer particle, and field-correction (e.g., the Lenardic Filter) methods: each of these has different advantages or disadvantages, trading off computational speed with accuracy in tracking feature boundaries. Here we present a method for modeling active fields in mantle dynamics simulations using a new solver implemented in the deal.II package that underlies the ASPECT software. The new solver for the advection-diffusion equation uses a Local Discontinuous Galerkin (LDG) algorithm, which combines features of both finite element and finite volume methods, and is particularly suitable for problems with a dominant first-order term and discontinuities. Furthermore, we have applied a post-processing technique to insure that the solution satisfies a global maximum/minimum. One potential drawback for the LDG method is that the total number of degrees of freedom is larger than the finite element method. To demonstrate the capabilities of this new method we present results for two benchmarks used previously: a falling cube with distinct buoyancy and

  11. Local Discontinuous Galerkin (LDG) Method for Advection of Active Compositional Fields with Discontinuous Boundaries: Demonstration and Comparison with Other Methods in the Mantle Convection Code ASPECT

    NASA Astrophysics Data System (ADS)

    Hsu, S. K.; Armada, L. T.; Yeh, Y. C.; Bacolcol, T. C.; Dimalanta, C. B.; Doo, W. B.; Liang, C. W.

    2014-12-01

    Flow in the Earth's mantle is driven by thermo-chemical convection in which the properties and geochemical signatures of rocks vary depending on their origin and composition. For example, tectonic plates are composed of compositionally-distinct layers of crust, residual lithosphere and fertile mantle, while in the lower-most mantle there are large compositionally distinct "piles" with thinner lenses of different material. Therefore, tracking of active or passive fields with distinct compositional, geochemical or rheologic properties is important for incorporating physical realism into mantle convection simulations, and for investigating the long term mixing properties of the mantle. The difficulty in numerically advecting fields arises because they are non-diffusive and have sharp boundaries, and therefore require different methods than usually used for temperature. Previous methods for tracking fields include the marker-chain, tracer particle, and field-correction (e.g., the Lenardic Filter) methods: each of these has different advantages or disadvantages, trading off computational speed with accuracy in tracking feature boundaries. Here we present a method for modeling active fields in mantle dynamics simulations using a new solver implemented in the deal.II package that underlies the ASPECT software. The new solver for the advection-diffusion equation uses a Local Discontinuous Galerkin (LDG) algorithm, which combines features of both finite element and finite volume methods, and is particularly suitable for problems with a dominant first-order term and discontinuities. Furthermore, we have applied a post-processing technique to insure that the solution satisfies a global maximum/minimum. One potential drawback for the LDG method is that the total number of degrees of freedom is larger than the finite element method. To demonstrate the capabilities of this new method we present results for two benchmarks used previously: a falling cube with distinct buoyancy and

  12. Synergistic activity of BET protein antagonist-based combinations in mantle cell lymphoma cells sensitive or resistant to ibrutinib

    PubMed Central

    Sun, Baohua; Shah, Bhavin; Fiskus, Warren; Qi, Jun; Rajapakshe, Kimal; Coarfa, Cristian; Li, Li; Devaraj, Santhana G. T.; Sharma, Sunil; Zhang, Liang; Wang, Michael L.; Saenz, Dyana T.; Krieger, Stephanie; Bradner, James E.

    2015-01-01

    Mantle cell lymphoma (MCL) cells exhibit increased B-cell receptor and nuclear factor (NF)-κB activities. The bromodomain and extra-terminal (BET) protein bromodomain 4 is essential for the transcriptional activity of NF-κB. Here, we demonstrate that treatment with the BET protein bromodomain antagonist (BA) JQ1 attenuates MYC and cyclin-dependent kinase (CDK)4/6, inhibits the nuclear RelA levels and the expression of NF-κB target genes, including Bruton tyrosine kinase (BTK) in MCL cells. Although lowering the levels of the antiapoptotic B-cell lymphoma (BCL)2 family proteins, BA treatment induces the proapoptotic protein BIM and exerts dose-dependent lethality against cultured and primary MCL cells. Cotreatment with BA and the BTK inhibitor ibrutinib synergistically induces apoptosis of MCL cells. Compared with each agent alone, cotreatment with BA and ibrutinib markedly improved the median survival of mice engrafted with the MCL cells. BA treatment also induced apoptosis of the in vitro isolated, ibrutinib-resistant MCL cells, which overexpress CDK6, BCL2, Bcl-xL, XIAP, and AKT, but lack ibrutinib resistance-conferring BTK mutation. Cotreatment with BA and panobinostat (pan-histone deacetylase inhibitor) or palbociclib (CDK4/6 inhibitor) or ABT-199 (BCL2 antagonist) synergistically induced apoptosis of the ibrutinib-resistant MCL cells. These findings highlight and support further in vivo evaluation of the efficacy of the BA-based combinations with these agents against MCL, including ibrutinib-resistant MCL. PMID:26254443

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  14. Two-stage melting and the geochemical evolution of the mantle: a recipe for mantle plum-pudding

    NASA Astrophysics Data System (ADS)

    Phipps Morgan, Jason; Morgan, W. Jason

    1999-07-01

    We explore a geochemical model for mantle evolution where a sequence of hotspot and ridge upwelling has melted the mantle to make hotspot and mid-ocean ridge basalts and their residues, and plate subduction has re-cycled and stirred all of these differentiation products back into the mantle. After billions of years this process has mixed various `plums' of incompatible-element rich veins within a matrix made from the residues of melting that have been depleted in incompatible elements. We propose that the mantle flows upward and melts in a two-stage process. During the first stage, plume upwelling and melting creates an enriched ocean island basalt by extracting a low degree melt (˜1-4%) from the rising mantle mixture. The plums are easier to melt, so proportionally more of the incompatible elements are extracted from these components. After melt extraction, the mixture of leftovers is depleted in composition, even though it still contains ˜96-99% of the mass of the original plume upwelling. These depleted leftovers are hot and buoyant so they pond beneath the lithosphere as an asthenosphere layer. When they rise and melt a second time beneath a mid-ocean ridge, a depleted mid-ocean ridge basalt is extracted. The now extremely depleted leftovers, ˜85% of the mass of the original plume upwelling, accrete to oceanic lithosphere which eventually subducts to recycle leftovers, eroded continental crust, and basaltic plums back into the mantle. Observed trace element, rare gas, and isotopic contrasts between oceanic island and mid-ocean ridge basalts can be produced by a recipe which assumes that throughout Earth history these two sequential stages of deep plume and shallower ridge melting have both created and reprocessed the plums and residues that make up the present-day mantle. In this recipe the two-stage melting process does not change through time, but the rate of mantle overturn slows over time in proportion to the decrease in radioactive heat production.

  15. Bathymetric Constraints on Dynamic Topography and Mantle Flow from Asymmetric Subsidence Across the Mid-Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Watkins, C. E.; Conrad, C. P.

    2015-12-01

    topography of this magnitude and pattern is best explained as being supported by active downwelling associated with subducted slabs in the lower mantle beneath eastern Asia and the Americas, without significant contribution from active upwelling driven by the seismically slow regions beneath Africa and the central Pacific.

  16. Upper mantle discontinuity structure from underside reflections

    NASA Astrophysics Data System (ADS)

    Schmerr, Nicholas C.

    This research investigates Earth structure in the mantle transition zone, a range of depths bounded by two major solid-state phase transformations of the mineral olivine: the conversion of olivine to wadsleyite near 410 km depth, and the dissociation of ringwoodite into Mg-silicate perovskite plus magnesiowuestite near 660 km depth. The phase transformations are dependent upon the thermal and chemical state of the mantle; lateral heterogeneity in mantle temperature and composition will change the transformation depth. The denser, more compact structures of olivine possess higher seismic wave speeds and densities, thus giving rise to seismic discontinuities at the phase transitions. The depth and sharpness of the 410 and 660 km discontinuities are mapped using seismic energy that reflects from the underside of these boundaries to investigate the thermal and chemical state of the mantle. Underside reflections of shear and compressional seismic waves arrive as precursory energy several hundred seconds before the seismic phases SS and PP, which form as underside reflections off the crust. Using broadband datasets of precursors to SS and PP, topographic variation maps of the 410 km and 660 km boundaries are produced for study regions beneath the Pacific Ocean and South American continent. Beneath most of the Pacific, the discontinuities are found close to the global average, suggesting that the mantle in this region is not significantly perturbed in temperature and chemistry. However, within 1000 km of several Pacific hotspots, including Hawaii, there is evidence for hot upwelling material rising through the transition zone that correlates with the edges of extremely hot (i.e., seismically low velocity) regions of the lowermost mantle, supporting whole mantle convection. Beneath the South American continent there is evidence for both thermal and chemical variation near the subducting Nazca plate, consistent with cold, and hydrated materials sinking into the mantle

  17. Upper mantle structure beneath the Galápagos Archipelago from joint inversion of body and surface waves (Invited)

    NASA Astrophysics Data System (ADS)

    Villagomez, D. R.; Toomey, D. R.; Hooft, E. E.; Solomon, S. C.

    2010-12-01

    resulting from melt extraction. The viscosity increase associated with such dehydration may decrease or stall mantle upwelling, resulting in lateral spreading of the plume. Between 50 and 100 km depth, the low-velocity anomaly is located beneath the northeastern part of the archipelago, a pattern we attribute to melting produced as upwelling mantle spreads toward a region with a thinner lid. There is a pronounced low-velocity anomaly (maximum VS anomaly of -3%) at depths shallower than 50 km beneath the southwestern part of the archipelago that we attribute to another stage of melting of mantle driven upward by plume flow and residuum buoyancy. This anomaly lies beneath Fernandina and Isabela, sites of the most active volcanoes in the archipelago. Our results support the interpretation that the Galápagos Islands are the product of an upwelling thermal plume that is continuous from at least 300 km depth to the base of a high-velocity lid and also suggest that mantle flow and melting beneath the Galápagos are influenced by the formation of residuum. In support of the last inference, the thickness of the high-velocity lid correlates well with regional variations in lava geochemistry.

  18. Peru-Chile upwelling dynamics under climate change

    NASA Astrophysics Data System (ADS)

    Oerder, Véra; Colas, Francois; Echevin, Vincent; Codron, Francis; Tam, Jorge; Belmadani, Ali

    2015-02-01

    The consequences of global warming on the Peru-Chile Current System (PCCS) ocean circulation are examined with a high-resolution, eddy-resolving regional oceanic model. We performed a dynamical downscaling of climate scenarios from the IPSL-CM4 Coupled General Circulation Model (CGCM), corresponding to various levels of CO2 concentrations in the atmosphere. High-resolution atmospheric forcing for the regional ocean model are obtained from the IPSL atmospheric model run on a stretched grid with increased horizontal resolution in the PCCS region. When comparing future scenarios to preindustrial (PI) conditions, the circulation along the Peru and Chile coasts is strongly modified by changes in surface winds and increased stratification caused by the regional warming. While the coastal poleward undercurrent is intensified, the surface equatorial coastal jet shoals and the nearshore mesoscale activity are reinforced. Reduction in alongshore wind stress and nearshore wind stress curl drive a year-round reduction in upwelling intensity off Peru. Modifications in geostrophic circulation mitigate this upwelling decrease in late austral summer. The depth of the upwelling source waters becomes shallower in warmer conditions, which may have a major impact on the system's biological productivity.

  19. Petrological constraints on evolution of continental lithospheric mantle beneath the northwestern Ethiopian plateau: Insight from mantle xenoliths from the Gundeweyn area, East Gojam, Ethiopia

    NASA Astrophysics Data System (ADS)

    Alemayehu, Melesse; Zhang, Hong-Fu; Zhu, Bin; Fentie, Birhanu; Abraham, Samuel; Haji, Muhammed

    2016-01-01

    Detailed petrographical observations and in-situ major- and trace-element data for minerals from ten spinel peridotite xenoliths from a new locality in Gundeweyn area, East Gojam, have been examined in order to understand the composition, equilibrium temperature and pressure conditions as well as depletion and enrichment processes of continental lithospheric mantle beneath the Ethiopian plateau. The peridotite samples are very fresh and, with the exception of one spinel harzburgite, are all spinel lherzolites. Texturally, the xenoliths can be divided into two groups as primary and secondary textures. Primary textures are protogranular and porphyroclastic while secondary ones include reaction, spongy and lamellae textures. The Fo content of olivine and Cr# of spinel ranges from 86.5 to 90.5 and 7.7 to 14.1 in the lherzolites, respectively and are 89.8 and 49.8, respectively, in the harzburgite. All of the lherzolites fall into the lower Cr# and Fo region in the olivine-spinel mantle array than the harzburgite, which indicates that they are fertile peridotites that experienced low degrees of partial melting and melt extraction. Orthopyroxene and clinopyroxene show variable Cr2O3 and Al2O3 contents regardless of their lithology. The Mg# of orthopyroxene and clinopyroxene are 87.3 to 90.1 and 85.8 to 90.5 for lherzolite and 90.4 and 91.2 for harzburgite, respectively. The peridotites have been equilibrated at a temperature and pressure ranging from 850 to 1100 °C and 10.2 to 30 kbar, respectively, with the highest pressure record from the harzburgite. They record high mantle heat flow between 60 and 150 mW/m2, which is not typical for continental environments (40 mW/m2). Such a high geotherm in continental area shows the presence of active mantle upwelling beneath the Ethiopian plateau, which is consistent with the tectonic setting of nearby area of the Afar plume. Clinopyroxene of five lherzolites and one harzburgite samples have a LREE enriched pattern and the rest

  20. Active degassing of mantle-derived fluid: A geochemical study along the Vulture line, southern Apennines (Italy)

    NASA Astrophysics Data System (ADS)

    Caracausi, A.; Martelli, M.; Nuccio, P. M.; Paternoster, M.; Stuart, F. M.

    2013-03-01

    We report the results of a geochemical study of gas emissions along a NE-SW transect in southern Italy in order to test the hypothesis that the region around Monte Vulture is affected by degassing of mantle-derived fluids through a lithospheric discontinuity. We also investigated lavas from the Monte Vulture volcano displaying 3He/4He (up to ~ 6.0 Ra) and Sr isotopes that are consistent with an origin in mantle that has had minimal pollution from subducted Adriatic slab. Similar 3He/4He in fluids from around Mt. Vulture indicate that the deep volcanic system is still degassing. Mantle-derived He occurs in fluids along the length of the Vulture line, reinforcing the hypothesis that it is a deep tectonic discontinuity along which mantle fluids and/or melts advect to the surface. The CO2/3He ratios are highly variable (2.7 × 108-2.15 × 1011) in response to processes such as gas dissolution into aquifers, addition of crustal gases and degassing fractionation.

  1. Spatial dynamics of coccolithophore communities during an upwelling event in the Southern Benguela system

    NASA Astrophysics Data System (ADS)

    Giraudeau, Jacques; Bailey, Geoffrey W.

    1995-12-01

    The spatial dynamics of coccolithophore communities were investigated in the top 100 m of a longitudinal transect off Hondeklip Bay, Southern Benguela region, during a period of active upwelling in late June 1993. This transect crossed five hydrological domains that were identified from the vertical sections of temperature and salinity, namely the upwelling zone, the upwelling front, the intermediate domain, the offshore divergence, and the oceanic region. Total coccolithophore standing crops ranged from less than 10 × 10 3 cells 1 -1 to a maximum of 278 × 103 cells 1-1. Highest values were recorded in the top 25 m in the upwelling zone and at the offshore edge of the upwelling front. Fifty different taxa were identified with Emiliania huxleyi and Syracosphaera epigrosa being the dominant forms in the standing stock. The offshore divergence and upwelling front effectively isolated assemblages with distinct species compositions and diversity trends. The most successful assemblage in terms of both species diversity and standing crop was found in the intermediate domain where oceanic and upwelled water mix. Equally important was the control of the water-masses motion on the vertical distribution of coccolithophore communities. Shallow-dwelling communities thrived in the inshore upwelling and offshore divergence areas, whereas deep-dwelling communities were found in the intermediate domain, where surface waters downwell. No clear relationship was found between the concentrations in major nutrients, and the species diversity and total standing crop values. S. epigrosa was the only recorded species whose absolute abundance showed a positive relationship with the nitrate and phosphate surface-water concentrations.

  2. Observations of nonlinear internal waves at a persistent coastal upwelling front

    NASA Astrophysics Data System (ADS)

    Walter, Ryan K.; Stastna, Marek; Woodson, C. Brock; Monismith, Stephen G.

    2016-04-01

    We collected high-resolution observations of nonlinear internal waves (NLIWs) at a persistent upwelling front in the shallow coastal environment (~20 m) of northern Monterey Bay, CA. The coastal upwelling front forms between recently upwelled waters and warmer stratified waters that are trapped in the bay (upwelling shadow). The front propagates up and down the coast in the along-shore direction as a buoyant plume front due to modulation by strong diurnal wind forcing. The evolution of the coastal upwelling front, and the subsequent modulation of background environmental conditions, is examined using both individual events and composite day averages. We demonstrate that regional-scale upwelling and local diurnal wind forcing are key components controlling local stratification and the formation of internal wave guides that allow for high-frequency internal wave activity. Finally, we discuss the ability of theoretical models to describe particularly large-amplitude internal waves that exist in the presence of a strong background shear and test a fully nonlinear model (i.e., the Dubreil-Jacotin-Long equation).

  3. Superplume Metasomatism: Evidence from Siberian mantle xenoliths

    NASA Astrophysics Data System (ADS)

    Taylor, L. A.; Howarth, G. H.; Barry, P. H.; Pernet-Fisher, J. F.; Baziotis, I. P.; Pokhilenko, L. N.; Bodnar, R. J.; Pokhilenko, N. P.

    2013-12-01

    within the SCLM during Siberian flood basalt (SFB) emplacement. Based on peridotite xenolith analyses from the Udachnaya (pre-SFB) and Obnazhennaya (post-SFB) kimberlites, we present a model for the temporal evolution of the SCLM during the development of the Siberian Superplume. Four main stages of metasomatism are identified: 1) Metasomatism from circulating low-T fluids in the SCLM, resulting in harzburgite to lherzolite re-fertilization of the SCLM, prior to the onset of Superplume-induced partial melting of the SCLM; 2) Kimberlitic metasomatism, caused by small-degree, partial melting of SCLM, induced by the onset of Superplume, as it continues to upwell through the mantle; 3) Syn-SFB basaltic metasomatism, as the result of extensive percolation of basaltic fluids derived from the main stages of Superplume activity; and 4) Post-SFB local kimberlitic metasomatism related to the diminishing Superplume activity. Herein, Superplume activity is witnessed for over 180 Ma. This documentation of the life of the Siberian Superplume as evidenced in peridotite xenoliths from temporally related kimberlites, relative to the climax of plume activity with the Siberian flood basalts, is manifest in major-trace- and isotopic-element concentrations [1,2]. [1] J.F. Pernet-Fisher et al., AGU 2013 Abstract. [2] P. Barry et al., AGU 2013 Abstract.

  4. Linking mantle dynamics, plate tectonics and surface processes in the active plate boundary zones of eastern New Guinea (Invited)

    NASA Astrophysics Data System (ADS)

    Baldwin, S.; Moucha, R.; Fitzgerald, P. G.; Hoke, G. D.; Bermudez, M. A.; Webb, L. E.; Braun, J.; Rowley, D. B.; Insel, N.; Abers, G. A.; Wallace, L. M.; Vervoort, J. D.

    2013-12-01

    Eastern New Guinea lies within the rapidly obliquely converging Australian (AUS)- Pacific (PAC) plate boundary zone and is characterized by transient plate boundaries, rapidly rotating microplates and a globally significant geoid high. As the AUS plate moved northward in the Cenozoic, its leading edge has been a zone of subduction and arc accretion. The variety of tectonic settings in this region permits assessment of the complex interplay among mantle dynamics, plate tectonics, and surface processes. Importantly, the timescale of tectonic events (e.g., subduction, (U)HP exhumation, seafloor spreading) are within the valid bounds of mantle convection models. A record of changes in bathymetry and topography are preserved in high standing mountain belts, exhumed extensional gneiss domes and core complexes, uplifted coral terraces, and marine sedimentary basins. Global seismic tomography models indicate accumulation of subducted slabs beneath eastern New Guinea at the bottom of the upper mantle (i.e., <660km depth). Some of the deeply subducted material may indeed be buoyant subducted AUS continental margin (to depths of ~250-300 km), as well as subducted continental material that has reached the point of no return (i.e., > 250-300 km). Preliminary global-scale backward advected mantle convection models, driven by density inferred from joint seismic-geodynamic tomography models, exhibit large-scale flow associated with these subducted slab remnants and predict the timing and magnitude (up to 1500 m) of dynamic topography change (both subsidence and uplift) since the Oligocene. In this talk we will explore the effects of large-scale background mantle flow and plate tectonics on the evolution of topography and bathymetry in eastern New Guinea, and discuss possible mechanisms to explain basin subsidence and surface uplift in the region.

  5. Mantle segmentation along the Oman ophiolite fossil mid-ocean ridge.

    PubMed

    Le Mée, Laurent; Girardeau, Jacques; Monnier, Christophe

    2004-11-11

    It has been difficult to relate the segmentation of mid-ocean ridges to processes occurring in the Earth's underlying mantle, as the mantle is rarely sampled directly and chemical variations observed in lavas at the surface are heavily influenced by details of their production as melt extracted from the mantle. Our understanding of such mantle processes has therefore relied on the analysis of pieces of fossil oceanic lithosphere now exposed at the Earth's surface, known as ophiolites. Here we present the phase chemistry and whole-rock major- and trace-element contents of 174 samples of the mantle collected along over 400 km of the Oman Sultanate ophiolite. We show that, when analysed along the fossil ridge, variations of elemental ratios sensitive to the melting process define a three-dimensional geometry of mantle upwellings, which can be related to the segmentation observed in modern mid-ocean ridge environments.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  7. Adiabaticity and viscosity in deep mantle convection

    NASA Technical Reports Server (NTRS)

    Quareni, F.; Yuen, D. A.; Saari, M. R.

    1986-01-01

    A study has been conducted of steady convection with adiabatic and viscous heating for variable viscosity in the Boussinesq limit using the mean-field theory. A strong nonlinear coupling is found between the thermodynamic constants governing adiabatic heating and the rheological parameters. The range of rheological values for which adiabaticity would occur throughout the mantle has been established. Too large an activation volume, greater than 6 cu cm/mol for the cases examined, would produce unreasonably high temperature at the bottom of the mantle (greater than 6000 K) and superadiabatic gradients, especially in the lower mantle. Radiogenic heating plays a profound role in controlling dynamically mantle temperatures. Present values for the averaged mantle heat production would yield objectionably high temperatures in the lower mantle.

  8. Dynamics of plankton populations in upwelling areas

    NASA Technical Reports Server (NTRS)

    Szekielda, K. H. (Principal Investigator)

    1975-01-01

    The author has identified the following significant results. Spectral properties of the upwelled waters off the NW coast of Africa were studied with observations derived from aircraft and Skylab. Results indicate that the two-channel, ratio approach is ineffective in determining surface chlorophyll concentrations. Ocean color boundaries and temperature gradients were found to be directly correlated with each other and also with fishing effort in the upwelling region. Photographic and scanner data derived from Skylab were effective in locating ocean boundaries and mapping temperature distributions.

  9. Water Distribution in the Continental and Oceanic Upper Mantle

    NASA Technical Reports Server (NTRS)

    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).

  10. Progress on upwelling studies in the China seas

    NASA Astrophysics Data System (ADS)

    Hu, Jianyu; Wang, Xiao Hua

    2016-09-01

    East Asian marginal seas surrounding China exhibit rich ocean upwelling, mostly in response to the southwesterly summer monsoon. Upwelling in the China seas, namely, the South China Sea, the Taiwan Strait, the East China Sea, the Yellow Sea, and the Bohai Sea, has become increasingly important because the potential changes in the upwelling may have dramatic ecosystem, socioeconomic, and climate impacts. This paper reviews the progress of upwelling studies in the China seas since the year 2000, by presenting the principal characteristics and new understanding of 12 major upwelling regions in the China seas. Upwelling exhibits long-term variability at intraseasonal to multidecadal scales as well as short-term variability frequently caused by tropical cyclones. It is also associated with the El Niño-Southern Oscillation, local environmental variation, and biogeochemical factors. The coastal upwelling around Hainan Island and the upwelling or cold dome northeast of Taiwan Island are specifically highlighted because they have attracted great interest for decades. This paper summarizes upwelling mechanisms in terms of wind, topography, tide, stratification, and background flow, with applications mostly to the China seas. Finally, we propose some topics for future upwelling research, i.e., potential intensification of coastal upwelling under global climate change, downwelling, intrusion of upwelling into coastal embayments, and the influence of upwelling on fishery and biogeochemical processes.

  11. Pn anisotropic tomography and mantle dynamics beneath China

    NASA Astrophysics Data System (ADS)

    Zhou, Zhigang; Lei, Jianshe

    2016-08-01

    We present a new high-resolution Pn anisotropic tomographic model of the uppermost mantle beneath China inferred from 52,061 Pn arrival-time data manually picked from seismograms recorded at provincial seismic stations in China and temporary stations in Tibet and the Tienshan orogenic belt. Significant features well correlated with surface geology are revealed and provide new insights into the deep dynamics beneath China. Prominent high Pn velocities are visible under the stable cratonic blocks (e.g., the Tarim, Junngar, and Sichuan basins, and the Ordos block), whereas remarkable low Pn velocities are observed in the tectonically active areas (e.g., Pamir, the Tienshan orogenic belt, central Tibet and the Qilian fold belt). A distinct N-S trending low Pn velocity zone around 86°E is revealed under the rift running from the Himalayan block through the Lhasa block to the Qiangtang block, which indicates the hot material upwelling due to the breaking-off of the subducting Indian slab. Two N-S trending low Pn velocity belts with an approximate N-S Pn fast direction along the faults around the Chuan-Dian diamond block suggest that these faults may serve as channels of mantle flow from Tibet. The fast Pn direction changes from N-S in the north across 27°N to E-W in the south, which may reflect different types of mantle deformation. The anisotropy in the south could be caused by the asthenospheric flow resulted from the eastward subduction of the Indian plate down to the mantle transition zone beneath the Burma arc. Across the Talas-Fergana fault in the Tienshan orogenic belt, an obvious difference in velocity and anisotropy is revealed. To the west, high Pn velocities and an arc-shaped fast Pn direction are observed, implying the Indo-Asian collision, whereas to the east low Pn velocities and a range-parallel Pn fast direction are imaged, reflecting the northward underthrusting of the Tarim lithosphere and the southward underthrusting of the Kazakh lithosphere. In

  12. Deep structure and origin of active volcanoes in China

    NASA Astrophysics Data System (ADS)

    Zhao, D.

    2010-12-01

    Recent geophysical studies have provided important constraints on the deep structure and origin of the active intraplate volcanoes in Mainland China. Magmatism in the western Pacific arc and back-arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab (e.g., Zhao et al., 2009a), while the intraplate magmatism in China has different origins. The active volcanoes in Northeast China (such as the Changbai and Wudalianchi) are caused by hot upwelling in the big mantle wedge (BMW) above the stagnant slab in the mantle transition zone and deep slab dehydration as well (Zhao et al., 2009b). The Tengchong volcano in Southwest China is caused by a similar process in the BMW above the subducting Burma microplate (or Indian plate) (Lei et al., 2009a). The Hainan volcano in southernmost China is a hotspot fed by a lower-mantle plume which may be associated with the Pacific and Philippine Sea slabs' deep subduction in the east and Indian slab's deep subduction in the west down to the lower mantle (Lei et al., 2009b; Zhao, 2009). The stagnant slab finally collapses down to the bottom of the mantle, which can trigger the upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and may cause the slab-plume interactions (Zhao, 2009). References Lei, J., D. Zhao, Y. Su, 2009a. Insight into the origin of the Tengchong intraplate volcano and seismotectonics in southwest China from local and teleseismic data. J. Geophys. Res. 114, B05302. Lei, J., D. Zhao, B. Steinberger et al., 2009b. New seismic constraints on the upper mantle structure of the Hainan plume. Phys. Earth Planet. Inter. 173, 33-50. Zhao, D., 2009. Multiscale seismic tomography and mantle dynamics. Gondwana Res. 15, 297-323. Zhao, D., Z. Wang, N. Umino, A. Hasegawa, 2009a. Mapping the mantle wedge and interplate thrust zone of the northeast Japan arc. Tectonophysics 467, 89-106. Zhao, D., Y. Tian, J. Lei, L. Liu, 2009b. Seismic

  13. Shallow Mantle Discontinuities Beneath the North Anatolian Fault

    NASA Astrophysics Data System (ADS)

    Friedman, D. P.; Fischer, K. M.; Hopper, E.

    2015-12-01

    The goal of this study is to better understand deformation in the mantle lithosphere beneath continental strike-slip plate boundaries through Sp receiver function analysis of mantle discontinuities beneath the North Anatolian Fault (NAF). This fault zone marks the boundary between the Anatolian and Eurasian plates. Sp receiver functions were calculated using waveforms filtered with a variety of bandpasses, and 33 s to 4 s was found to produce coherent images while reducing interference between phases from the Moho and shallow mantle discontinuities. Using common conversion point stacking, we calculated 3D images of scattering beneath the region for two different cases: migration with the S-wave and P-wave velocities from the waveform tomography model of Fichtner et al. (2013) and with the AK135 velocity model. In both cases, a clear Moho is observed and Moho depth does not systematically vary between sides of the NAF. In contrast, shallow mantle discontinuities show pronounced changes in depth that correlate with strong lateral variations in mantle velocity observed in the Fichtner et al. tomography model, and some of these discontinuity depth variations occur within 50 km horizontally of the surface expression of the NAF. Where the tomography contains a clear high velocity lithospheric mantle layer, the Sp stack contains a negative velocity gradient at depths comparable to the base of the high velocity layer that can be interpreted as the seismological LAB. Where the tomography shows low mantle velocities that persist to the crust, a feature that may represent either anomalously low velocity lithosphere or upwelling asthenosphere beneath thin lithosphere, mantle discontinuities differ significantly from surrounding regions. Mantle discontinuity depth variations beneath the NAF also occur when the data are migrated with the AK135 model. Hence, the presence of the discontinuity depth variations is not an artifact of the assumed velocity model, although depths differ

  14. West Florida shelf upwelling: Origins and pathways

    NASA Astrophysics Data System (ADS)

    Weisberg, Robert H.; Zheng, Lianyuan; Liu, Yonggang

    2016-08-01

    Often described as oligotrophic, the west Florida continental shelf supports abundant fisheries, experiences blooms of the harmful alga, Karenia brevis, and exhibits subsurface chlorophyll maxima evident in shipboard and glider surveys. Renewal of inorganic nutrients by the upwelling of deeper ocean water onto the shelf may account for this, but what are the origins and pathways by which such new water may broach the shelf break and advance toward the shoreline? We address these questions via numerical model simulations of pseudo-Lagrangian, isopycnic water parcel trajectories. Focus is on 2010, when the west Florida shelf was subjected to an anomalously protracted period of upwelling caused by Gulf of Mexico Loop Current interactions with the shelf slope. Origins and pathways are determined by integrating trajectories over successive 45 day intervals, beginning from different locations along the shelf break and at various locations and depths along the shelf slope. Waters upwelling across the shelf break are found to originate from relatively shallow depths along the shelf slope. Even for the anomalous 2010 year, much of this upwelling occurs from about 150 m and above, although waters may broach the shelf break from 300 m depth, particularly in the Florida Panhandle. Such interannual renewal of west Florida shelf waters appears to have profound effects on west Florida shelf ecology.

  15. Mantle convection pattern and subcrustal stress field under South America

    NASA Technical Reports Server (NTRS)

    Liu, H.-S.

    1980-01-01

    The tectonic, igneous and metallogenic features of South America are discussed in terms of the crustal deformation associated with stresses due to mantle convection as inferred from the high degree harmonics in the geopotential field. The application of Runcorn's model for the laminar viscous flows in the upper mantle to satellite and gravity data results in a convection pattern which reveals the ascending flows between the descending Nazca plate and the overlying South American plate as well as segments of the descending Nazca plate beneath South America. The arc volcanism in South America is shown apparently to be related to the upwelling of high-temperature material induced by the subduction of the Nazca plate, with the South American basin systems associated with downwelling mantle flows. The resulting tensional stress fields are shown to be regions of structural kinship characterized by major concentrations of ore deposits and related to the cordillera, shield and igneous systems and the upward Andean movements. It is suggested that the upwelling convection flows in the upper mantle, coupled with crustal tension, have provided an uplift mechanism which has forced the hydrothermal systems in the basement rocks to the surface.

  16. Incipient mantle delamination, active tectonics and crustal thickening in Northern Morocco: Insights from gravity data and numerical modeling

    NASA Astrophysics Data System (ADS)

    Baratin, Laura-May; Mazzotti, Stéphane; Chéry, Jean; Vernant, Philippe; Tahayt, Abdelilah; Mourabit, Taoufik

    2016-11-01

    The Betic-Rif orocline surrounding the Alboran Sea, the westernmost tip of the Mediterranean Sea, accommodates the NW-SE convergence between the Nubia and Eurasia plates. Recent GPS observations indicate a ∼4 mm/yr SW motion of the Rif Mountains, relative to stable Nubia, incompatible with a simple two-plate model. New gravity data acquired in this study define a pronounced negative Bouguer anomaly south of the Rif, interpreted as a ∼40 km-thick crust in a state of non-isostatic equilibrium. We study the correlation between these present-day kinematic and geodynamic processes using a finite-element code to model in 2-D the first-order behavior of a lithosphere affected by a downward normal traction (representing the pull of a high-density body in the upper mantle). We show that intermediate viscosities for the lower crust and uppermost mantle (1021-1022Pas) allow an efficient coupling between the mantle and the base of the brittle crust, thus enabling (1) the conversion of vertical movement, resulting from the downward traction, to horizontal movement and (2) shortening in the brittle upper crust. Our results show that incipient delamination of the Nubian continental lithosphere, linked to slab pull, can explain the present-day abnormal tectonics, contribute to the gravity anomaly observed in northern Morocco, and give insight into recent tectonics in the Western Mediterranean region.

  17. A thermal scanning study of coastal upwelling in Lake Superior

    NASA Technical Reports Server (NTRS)

    Scarpace, F. L.; Green, T., III; Madding, R. P.

    1979-01-01

    The use of a thermal scanner to monitor the time evolution of the thermal structure of the coastal waters in Lake Superior during an upwelling event is described. Mosaics of thermal imagery from ten different times are described. Qualitative descriptions of the imagery give insight into the upwelling event. Recommendations for future use of a thermal scanner to monitor an upwelling event are discussed.

  18. Impact of far-field stress distributions and thermo-rheological structure of continental lithosphere on mantle-lithosphere interactions.

    NASA Astrophysics Data System (ADS)

    Burov, E. B.; Koptev, A.; Gerya, T.; Calais, E.; Leroy, S. D.

    2015-12-01

    We implement fully-coupled high resolution 3D thermo-mechanical numerical models to investigate the impact of the laterally heterogeneous structure and rheological stratification of the continental lithosphere on the plume-activated rifting and continental break-up processes in presence of preexisting far-field tectonic stresses. In our experiments, "mantle plumes" represent short-lived diapiric upwellings that have no continuous feeding at depth. Such upwellings may be associated with "true" plumes but also with various instabilities in the convective mantle. Numerical models demonstrate strong dependence of crustal strain distributions and surface topography on the rheological composition of the lower crust and the initial thermal structure of the lithosphere. In contrast to the usual inferences from passive rifting models, distributed wide rifting takes place in case of cold (500 °C at Moho depth) initial isotherm and mafic composition of the lower crust, whereas hotter geotherms and weaker (wet quartzite) lower crustal rheology lead to strong localization of rifting. Moreover, it appears that the prerequisite of strongly anisotropic strain localization during plume-lithosphere interaction (linear rift structures instead of axisymmetric radial faulting) refers to simultaneous presence of a mantle upwelling and of (even extremely weak) directional stress field produced by far-field tectonic forces (i.e. ultra-slow far field extension at < 3 mm/y). Higher (than 1.5-3 mm/y) velocities of far-field extension lead to enlargement of the active fault zone for the same lapse of time. Yet, simultaneous rise of the lithospheric geotherm associated with active rifting has an opposite effect leading to the narrowing of the rift zone. Presence of heterogeneities (cratonic blocks) leads to splitting of the plume head onto initially nearly symmetrical parts, each of which flows towards beneath the craton borders. This craton-controlled distribution of plume material causes

  19. Potential Dynamical Mechanisms Behind Global Mantle Events

    NASA Astrophysics Data System (ADS)

    Hansen, U.; Loddoch, A.; Stein, C.

    2007-05-01

    By numerical models we have investigated three potential mechanisms behind global mantle events. Plumes, originating in the thermal boundary layers of the mantle convection system can exhibit a significant episodicity, once a strong temperature-dependence of the viscosity of the mantle material is taken into account. An increase of the viscosity with pressure, as sometimes believed to suppress plumes, acts in fact to focus buoyancy into a few strong upwellings, which are potentially able to generate events on global scale. Plumes originating self- consistently from a thermal boundary layer, transport mostly material from their source region, while they entrain only little material during ascent. Compositionally dense material at the Core-mantle boundary has been proposed to explain seismological observed anomalies. The stability of such heterogeneities against entrainment by the overlying mantle-flow is determined by a complex set of properties, rather than by the density difference alone. Model calculations, taking into account a combined dependence of viscosity on temperature, pressure and , as mostly neglected; on composition, demonstrate, that under such conditions the D", can function as an isolated reservoir form some time, that however the destruction of the compositionally distinct layer, shielding the Earth'core can take place rapidly., with a profound effect also on the surface heat flow.. Finally we observe that episodic mobilization events of the surface are dynamically plausible for appropriate rheologies. A combination of temperature- and stress-dependent viscosity leads to an intermittent type of temporal behavior, where periods showing no surface motion (stagnant lid) are interrupted by phases with strong plate motions at the top. It seems at least possible that plate motion is not a continuously operating process.

  20. The anti-histaminic cyproheptadine synergizes the antineoplastic activity of bortezomib in mantle cell lymphoma through its effects as a histone deacetylase inhibitor.

    PubMed

    Paoluzzi, Luca; Scotto, Luigi; Marchi, Enrica; Seshan, Venkatraman E; O'Connor, Owen A

    2009-09-01

    Cyproheptadine, an inhibitor of the H1 histamine receptors, has recently shown activity in models of leukaemia and myeloma, presumably through inhibition of cyclin-D expression. Mantle cell lymphoma (MCL) is an aggressive subtype of non-Hodgkin lymphoma characterized by overexpression of cyclin-D1. We investigated the effect of cyproheptadine alone and in combination with the proteasome inhibitor bortezomib in models of MCL. The combination of these drugs was mathematically synergistic, producing significant reductions in the mitochondrial membrane potential leading to apoptosis. In a severe combined immunodeficient beige mouse model, cyproheptadine plus bortezomib demonstrated a statistically significant advantage compared to either agent alone.

  1. Record of the Pacific Large Low Shear Velocity Province Upwellings Preserved in the Cretaceous Large Igneous Provinces

    NASA Astrophysics Data System (ADS)

    Madrigal, P.; Gazel, E.; Flores, K. E.; Bizimis, M.; Jicha, B. R.

    2015-12-01

    As the surface expression of deep mantle dynamics, Large Igneous Provinces (LIPs) are associated with the edges of large low shear velocity provinces (LLSVP) rooted at the core-mantle boundary. Instabilities in the LLSVP can cause periodic upwellings of material in the form of mantle plumes, which impact the lithosphere forming LIPs. However, the time frames of these massive lava outpourings are still uncertain. While continental LIPs are more readily accessible, oceanic LIPs have only been studied through drilling and sampling of fragments accreted to continental margins or island arcs, hence, they are relatively less understood. The impact of oceanic LIPs on oceanic biota is conspicuously recorded in global occurrences of black shale deposits that evidence episodes of anoxia and mass extinctions shortly after the formation of LIPs that ultimately can affect life on the entire planet. Our new geochemical and geochronological data of accreted Pacific LIPs found in the coasts of Nicoya Peninsula in Costa Rica record three LIP pulses possibly reflecting upwelling periods of the LLSVP at 140, 120 and 90 Ma. In order to test different models of origin of these LIPS, we created a complete reconstruction of the Pacific Plate configuration from the Mid-Jurassic to Upper-Cretaceous to show the existing correlation between upwelling pulses at edges of the Pacific LLSVP, oceanic anoxic events and the age from Pacific LIPs. We propose that since the formation of the Pacific plate at circa 175-180 Ma, a series of upwellings that interacted with mid-ocean ridge systems separated by 10-20 Ma have affected the planet periodically forming oceanic LIPs that still can be found today on the Pacific seafloor and accreted along the plate margins.

  2. Mantle CO2 degassing at Mt. Vulture volcano (Italy): Relationship between CO2 outgassing of volcanoes and the time of their last eruption

    NASA Astrophysics Data System (ADS)

    Caracausi, Antonio; Paternoster, Michele; Nuccio, Pasquale Mario

    2015-02-01

    tectonic discontinuities that controlled the magma upwelling during the most recent volcanic activity are still the main active degassing structures. The new estimate of CO2 budget in the Mt. Vulture area, together with literature data on CO2 budget from historically active and inactive Italian volcanoes, suggests a power-law functional relationship between the age of the most recent volcanic eruption and both total discharged CO2 (R2 = 0.73) and volcano size-normalized CO2 flux (R2 = 0.66). This relation is also valid by using data from worldwide volcanoes highlighting that deep degassing can occur over very long time too. In turn, the highlighted relation provides also an important tool to better evaluate the state of activity of a volcano, whose last activity occurred far in time. Finally, our study highlights that in the southern Apennines, an active degassing of mantle-derived volatiles (i.e., He, CO2) occurs indiscriminately from west to east. This is in contrast to the central-northern Apennine, which is characterized by a crustal radiogenic volatile contribution, which increases eastward, coupled to a decrease in deep CO2 flux. This difference between the two regions is probably due to lithospheric tears which control the upwelling of mantle melts, their degassing and the transport of volatiles through the crust.

  3. Does mesoscale matters in decadal changes observed in the northern Canary upwelling system?

    NASA Astrophysics Data System (ADS)

    Relvas, P.; Luís, J.; Santos, A. M. P.

    2009-04-01

    The Western Iberia constitutes the northern limb of the Canary Current Upwelling System, one of the four Eastern Boundary Upwelling Systems of the world ocean. The strong dynamic link between the atmosphere and the ocean makes these systems highly sensitive to global change, ideal to monitor and investigate its effects. In order to investigate decadal changes of the mesoscale patterns in the Northern Canary upwelling system (off Western Iberia), the field of the satellite-derived sea surface temperature (SST) trends was built at the pixel scale (4x4 km) for the period 1985-2007, based on the monthly mean data from the Advanced Very High Resolution Radiometer (AVHRR) on board NOAA series satellites, provided by the NASA Physical Oceanography Distributed Active Archive Center (PO.DAAC) at the Jet Propulsion Laboratory. The time series were limited to the nighttime passes to avoid the solar heating effect and a suite of procedures were followed to guarantee that the temperature trends were not biased towards the seasonally more abundant summer data, when the sky is considerably clear. A robust linear fit was applied to each individual pixel, crossing along the time the same pixel in all the processed monthly mean AVHRR SST images from 1985 until 2007. The field of the SST trends was created upon the slopes of the linear fits applied to each pixel. Monthly mean SST time series from the one degree enhanced International Comprehensive Ocean-Atmosphere Data Set (ICOADS) and from near-shore measurements collected on a daily basis by the Portuguese Meteorological Office (IM) are also used to compare the results and extend the analysis back until 1960. A generalized warming trend is detected in the coastal waters off Western Iberia during the last decades, no matter which data set we analyse. However, significant spatial differences in the warming rates are observed in the satellite-derived SST trends. Remarkably, off the southern part of the Western Iberia the known

  4. Structure of axisymmetric mantle plumes

    NASA Technical Reports Server (NTRS)

    Olson, Peter; Schubert, Gerald; Anderson, Charles

    1993-01-01

    The structure of axisymmetric subsolidus thermal plumes in the earth's lower mantle is inferred from calculations of axisymmetric thermal plumes in an infinite Prandtl number fluid with thermally activated viscosity. The velocity and temperature distribution is determined for axisymmetric convection above a heated disk in an incompressible fluid cylinder 2,400 km in height and 1,200 km in diameter. Several calculations of plumes with heat transport in the range 100-400 GW, similar to the advective heat transport at the Hawaiian hotspot, are presented. Hotspot formation by plumes originating at the base of the mantle requires both large viscosity variations and a minimum heat transport.

  5. Canary current upwelling: More or less?

    NASA Astrophysics Data System (ADS)

    Barton, E. D.; Field, D. B.; Roy, C.

    2013-09-01

    It has been hypothesized that coastal upwelling in the four major eastern boundary current systems might be intensified as global warming could result in a greater land-sea temperature gradient and hence strengthen alongshore winds. Recent research has suggested a substantial increase of upwelling intensity off Northwest Africa. Evidence there is based on the derivation of a proxy for upper ocean temperatures from the alkenone unsaturation index (U37K) derived from two sediment cores recovered off Cape Ghir, Morocco. An accelerating decrease of over 1 °C during the last century was concluded for near surface temperature near the Cape. Support for this conclusion was found in an increase in Bakun’s upwelling index for the same area. The evidence for a general intensification of upwelling within the whole Canary current upwelling system is examined here. Using available estimates of wind from PFEL, NCAR/NCEP, ECMWF, ICOADS and WASWind plus measured wind data from coastal meteorological stations, no evidence of a coherent intensification in winds at the regional scale off Northwest Africa is found. Moreover, sea surface temperature records from ships-of-opportunity (ICOADS data set) and also from the Pathfinder satellite AVHRR data set show a significant and correlated increase at all latitudes in the region, including in the area around Cape Ghir. It is concluded that there is no evidence for a general increase in upwelling intensity off Northwest Africa or Iberia. The apparent lowering of SST off Cape Ghir indicated by the alkenone unsaturation index can be explained by coccolithophorids (phytoplankton from which the U37K signal is derived) living deeper in the water column. The distribution of most phytoplankton (including coccolithophorids) will deepen and have less overlap with mixed layer temperatures as the ocean warms, resulting in a near surface temperature estimate that is increasingly biased by subsurface temperatures and lower than the actual SST. sea

  6. A numerical study of the upwelling circulation off Central Chile

    NASA Astrophysics Data System (ADS)

    Mesias, Jorge M.

    The summer upwelling circulation off Central Chile between 34°--40°S is studied using the Princeton Ocean Circulation numerical model, implemented with realistic atmospheric forcings and bottom topography. The simulations are made for summers of years 1992, 1993, and 1994. Sea surface temperature (SST) from the model results and satellite sensors (derived from NASA/NOAA Pathfinder Project datasets) are compared to determine regions where the numerical simulations more realistically represent the oceanic fields. The summer local winds are predominantly equatorward and fluctuate affected by the seasonal displacement of the Subtropical Anticyclone of the Southeast Pacific. The model ocean circulation shows the presence of a surface coastal equatorward jet flowing over a poleward undercurrent that spreads over the continental shelf and slope break. These currents resemble those historically observed off Central Chile, following a classical Ekman-geostrophy dynamics. The oceanic variability is strongly related to the variability of the local wind forcing, bottom relief, and coastline geometry. Strong wind fluctuations induce the formation of cyclonic/anticyclonic mesoscale eddies, favored by the separation of the equatorward jet from the coast, downstream of a prominent mid-domain cape. The flow variability between regions depends on the spatial variability of the wind forcing. The wind relaxation is larger in the southern regions, where the upwelling tends to disappear. In the northern areas, the separation of the jet and the formation of eddies induce a strong cross-shelf transport activity. Comparisons among SST fields for all years indicate that the model and satellite fields vary in similar patterns, especially in the northern coastal areas, and suggest that oceanic fields are largely affected by changes in local winds during El Nino events. During El Nino periods, the upwelling activity weakens due to a rapid decrease of the equatorward winds, and the passage of

  7. What controls biological productivity in coastal upwelling systems? Insights from a comparative modeling study

    NASA Astrophysics Data System (ADS)

    Lachkar, Z.; Gruber, N.

    2011-06-01

    The magnitude of the biological productivity in Eastern Boundary Upwelling Systems (EBUS) is traditionally viewed as directly reflecting the upwelling intensity. Yet, different EBUS show different sensitivities of productivity to upwelling-favorable winds (Carr and Kearns, 2003). Here, using a comparative modeling study of the California Current System (California CS) and Canary Current System (Canary CS), we show how physical and environmental factors, such as light, temperature and cross-shore circulation modulate the response of biological productivity to upwelling strength. To this end, we made a series of eddy-resolving simulations of the California CS and Canary CS using the Regional Ocean Modeling System (ROMS), coupled to a nitrogen based Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD) ecosystem model. We find the nutrient content of the euphotic zone to be 20 % smaller in the Canary CS relative to the California CS. Yet, the biological productivity is 50 % smaller in the latter. This is due to: (1) a faster nutrient-replete growth in the Canary CS relative to the California CS, related to a more favorable light and temperature conditions in the Canary CS, and (2) the longer nearshore water residence times in the Canary CS which lead to larger buildup of biomass in the upwelling zone, thereby enhancing the productivity. The longer residence times in the Canary CS appear to be associated with the wider continental shelves and the lower eddy activity characterizing this upwelling system. This results in a weaker offshore export of nutrients and organic matter, thereby increasing local nutrient recycling and enhancing the coupling between new and export production in the Northwest African system. Our results suggest that climate change induced perturbations such as upwelling favorable wind intensification might lead to contrasting biological responses in the California CS and the Canary CS, with major implications for the biogeochemical cycles and fisheries

  8. Mantle updrafts and mechanisms of oceanic volcanism.

    PubMed

    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. PMID:25201992

  9. Mantle updrafts and mechanisms of oceanic volcanism.

    PubMed

    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.

  10. Mantle updrafts and mechanisms of oceanic volcanism

    PubMed Central

    Anderson, Don L.; Natland, James H.

    2014-01-01

    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. PMID:25201992

  11. Mantle updrafts and mechanisms of oceanic volcanism

    NASA Astrophysics Data System (ADS)

    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.

  12. Deep crust and mantle structure linked to subduction of the Pacific plate at a continental margin from an active seismic source study

    NASA Astrophysics Data System (ADS)

    Stern, T. A.; Okaya, D. A.; Henrys, S. A.; Savage, M. K.; Sato, H.; Iwasaki, T.

    2013-12-01

    We present new results that bear on mantle structure in a subduction zone of both the down going and over-riding plates. Wellington region, New Zealand, sits on the Australian plate a mere ~ 15-25 km above the subducted Pacific plate. This is rare: most active continental margins have at least 30-50 km of free board above subduction zones (cf, Pacific NW, Honshu). Such a shallow setting offers unusually good conditions for making terrestrial observations of the subduction process. In 2010-11 an active source seismic experiment (SAHKE) was carried out across the Wellington region. Both active and passive seismic methods were used to establish a model of the crustal structure and upper mantle structure beneath SAHKE (Henrys et al , 2013). We recorded 12 x 500 kg dynamite shots on ~ 1000 recorders place at 100 m spacing from coast to coast. These data contain excellent returns from the subduction zone at two-way travel times of 7-15 s, but we also recorded coherent reflection energy down to 30 s two-way-travel-time on vertical recorders and 47 s on horizontal recorders. We performed a low-fold stack of these deep reflections and see two zones. The deepest reflections define a westward 17 degree-dipping zone at ~ 100 km deep that is possibly the base of the subducted Pacific plate. The westward dip on this 100 km deep reflector matches that for the top of the plate. Moreover, the total plate thickness implied is ~ 80 km, which matches that predicted for 100 my old oceanic lithosphere. The other deep reflection zone dips eastward across the shot gathers and is typically seen at two-way travel times of 18-25 s on the vertical phones. We also see the same event as a Vs arrival on horizontal phones at two-way travel times of 34-47s. When migrated these reflections define an east dipping reflector that is within the mantle of the overriding Australian plate, and the surface projection of the reflector is ~ 80 km west of SAHKE line. This finding raises the question of what

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

    PubMed

    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. PMID:21441908

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

    PubMed

    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.

  15. Upwelling in Cretaceous western interior seaway

    SciTech Connect

    Parrish, J.T.; Gautier, D.L.

    1988-01-01

    The Sharon Springs Member of the Pierre Shale, usually described as a stagnant-basin deposit, shares more features in common with upwelling zones than with stratified stagnant basins. Specifically, the overall facies distribution of the Sharon Springs includes a basin-ward zone of laminated, highly organic-rich strata bounded on the west by phosphate, which is, in turn, bounded at the western shoreline by glauconitic sandstone. The same facies distribution might be expected on the eastern shoreline, but the Sharon Springs is truncated there by erosion. The organic matter in the Sharon Springs is almost entirely contained in fecal pellets and is predominantly marine in origin. Organic carbon accumulation rates are comparable to those of upwelling zones. Finally, the Sharon Springs is noted for high concentrations of bones of marine reptiles. These bones occur in a band that may mark the zone of highest biologic productivity.

  16. VOCALS-CUpEx: the Chilean Upwelling Experiment

    NASA Astrophysics Data System (ADS)

    Garreaud, R. D.; Rutllant, J. A.; Muñoz, R. C.; Rahn, D. A.; Ramos, M.; Figueroa, D.

    2010-11-01

    The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) was a major field experiment conducted in spring of 2008 off southern Peru and northern Chile, aimed at better understanding the coupled climate systems of the southeast Pacific. Because of logistical constrains, the coastal area around 30° S was not sampled during VOCALS-REx. This area not only marks the poleward edge of the subtropical stratocumulus cloud regime (thus acting as a source of transient disturbances) but is also one of the most active upwelling centers and source of surface ocean kinetic energy along the Chilean coast. To fill such an observational gap, a small, brief, but highly focused field experiment was conducted in late spring 2009 in the near-shore region around 30° S. The Chilean Upwelling Experiment (CUpEx) was endorsed by VOCALS as a regional component. CUpEx included long-term monitoring, an intensive two-week field campaign and off-shore research flights. Our goal was to obtain an atmospheric/oceanic dataset with enough temporal and spatial coverage to be able to document (a) the mean diurnal cycles of the lower-troposphere and upper-ocean in a region of complex topography and coastline geometry, and (b) the ocean-atmosphere response to the rapid changes in coastal winds from strong, upwelling-favorable southerly winds to relaxed southerlies or even downwelling-favorable northerlies. In this paper we describe the measurement platforms and sampling strategy, and provide an observational overview, highlighting some key mean and transient features.

  17. VOCALS-CUpEx: the Chilean Upwelling Experiment

    NASA Astrophysics Data System (ADS)

    Garreaud, R. D.; Rutllant, J. A.; Muñoz, R. C.; Rahn, D. A.; Ramos, M.; Figueroa, D.

    2011-03-01

    The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) was a major field experiment conducted in spring of 2008 off southern Peru and northern Chile, aimed at better understanding the coupled climate systems of the southeast Pacific. Because of logistical constrains, the coastal area around 30° S was not sampled during VOCALS-REx. This area not only marks the poleward edge of the subtropical stratocumulus cloud regime (thus acting as a source of transient disturbances) but is also one of the most active upwelling centers and source of surface ocean kinetic energy along the Chilean coast. To fill such an observational gap, a small, brief, but highly focused field experiment was conducted in late spring 2009 in the near-shore region around 30° S. The Chilean Upwelling Experiment (CUpEx) was endorsed by VOCALS as a regional component. CUpEx included long-term monitoring, an intensive two-week field campaign and off-shore research flights. Our goal was to obtain an atmospheric/oceanic dataset with enough temporal and spatial coverage to be able to document (a) the mean diurnal cycles of the lower-troposphere and upper-ocean in a region of complex topography and coastline geometry, and (b) the ocean-atmosphere response to the rapid changes in coastal winds from strong, upwelling-favorable equatorward flow (southerly winds) to downwelling-favorable poleward flow (northerly winds). In this paper we describe the measurement platforms and sampling strategy, and provide an observational overview, highlighting some key mean-state and transient features.

  18. Domoic acid production near California coastal upwelling zones, June 1998

    SciTech Connect

    Trainer, V L.; Adams, Nicolaus G.; Bill, Brian D.; Stehr, Carla M.; Wekell, John C.; Moeller, Peter; Busman, Mark; Woodruff, Dana L. )

    2000-01-01

    Sea lion mortalities in central California during May and June 1998 were traced to their ingestion of sardines and anchovies that had accumulated the neurotoxin domoic acid. The detection of toxin in urine, feces, and stomach contents of several sea lions represents the first proven occurrence of domoic acid transfer through the food chain to a marine mammal. The pennate diatoms, Pseudo-nitzschia multiseries and P. australis, were the dominant, toxin-producing phytoplankton constituting algal blooms near Monterey Bay, Half Moon Bay, and Oceano Dunes, areas where sea lions with neurological symptoms stranded. Toxic Pseudo-nitzschia were also found near Morrow Bay, Point Conception, Point Arguello, and Santa Barbara, demonstrating that these species were widespread along the central California coast in June 1998. Measurements of domoic acid during three cruises in early June showed the highest cellular toxin levels in P. multiseries near Point A?o Nuevo and in P. australis from Morro w Bay. Maximum cellular domoic acid levels were observed within 20 km of the coast between 0 and 5 m depth, although toxin was also measured to depths of 40 m. Hydrographic data indicated that the highest toxin levels and greatest numbers of toxic cells were positioned in water masses associated with upwelling zones near coastal headlands. Nutrient levels at these sites were less than those typically measured during periods of active upwelling, due to the 1998 El Ni?o event. The flow of cells and/or nutrients from coastal headlands into embayments where cells can multiply in a stratified environment is a possible mechanism of bloom development along the central California coast. This coupling of toxic Pseudo-nitzschia growth near upwelling zones with physical processes involved in cell transport will be understood only when long-term measurements are made at several key coastal locations, aiding in our capability to predict domoic-acid producing algal blooms.

  19. A kinematic model for the late Cenozoic development of southern California crust and upper mantle

    NASA Technical Reports Server (NTRS)

    Humphreys, Eugene D.; Hager, Bradford H.

    1990-01-01

    A model is developed for the young and ongoing kinematic deformation of the southern California crust and upper mantle. The kinematic model qualitatively explains both the overall seismic structure of the upper mantle and much of the known geological history of the late Cenozoic as consequences of ongoing convection beneath southern California. In this model, the high-velocity upper-mantle anomaly of the Transverse ranges is created through the convergence and sinking of the entire thickness of subcrustal lihtosphere, and the low-velocity upper-mantle anomaly beneath the Salton Trough region is attributed to high temperatures and 1-4 percent partial melt related to adiabatic decompression during mantle upwelling.

  20. Effects of depth-variations in creep laws on the formation of plates in mantle dynamics

    NASA Technical Reports Server (NTRS)

    Van Den Berg, Arie P.; Van Keken, Peter E.; Yuen, David A.

    1991-01-01

    The influences of depth-varying rheologies on the structure of mantle convection and the near surface flow fields are studied. Upwelling flows crossing the upper-lower mantle boundary become considerably thinner and faster. Streamlines are concentrated near the surface and other platelike characteristics are enhanced by this type of rheological stratification in which the averaged effective viscosity of the upper mantle is about two orders of magnitude lower than that of the lower mantle. The presence of a lithosphere with a higher nonlinear dependence in the flow law further promotes platelike behavior. Platelike character of the top boundary-layer is encouraged by a decreasing depth-dependent viscosity in the non-Newtonian upper-mantle and by greater convective vigor.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Fluids of progressively changing composition are released from the subducting slab. Whereas the composition and effects of deep fluids are understood from studying arcs and backarc basin (BAB) lavas, those released at shallower depths beneath forearcs are less well known. Forearc rifts give us a unique opportunity to study the composition of ultra-shallow subduction-related fluids. At the southern end of the Mariana arc, the S.E. Mariana Forearc Rift (SEMFR), was discovered by HMR-1 sonar swath mapping (Martinez et al. 2000, JGR), and investigated in July 2008 by the manned submersible Shinkai 6500. The rift extends from the trench to the BAB spreading axis, where a magma chamber was recently documented (Becker et al., 2010, G-cubed). SEMFR is opening due to continued widening of the Mariana Trough BAB. Two suites of tholeiitic pillow lavas were recovered from the N.E. flank of the rift (dive 1096; slab depth ~ 30 ± 5 km), indicating recent magmatic activity. Dive 1096 lavas consist of upper primitive basalts (Mg# ≥ 60) and lower fractionated, basaltic andesites (Mg# < 60), separated by a thin sediment layer. Geochemical and isotopic studies show that these lavas were produced by extensive hydrous melting (≥ 15%) of a common depleted MORB-like mantle (Nb/Yb ~ 1, ɛNd ~ 9.3), likely S. Mariana BAB mantle, that interacted with < 3% metasomatic fluids. Thermobarometry constraints (Lee et al., 2009, EPSL) suggest that the primary melts equilibrated with the mantle at ~ 28 km, just above the slab, with a mean temperature ~1230°C. The fluid was enriched in fluid-mobile elements (Rb, Ba, K, U, Sr, Pb, Cs), mobilized from the ultra-shallow slab at low temperature, as well as melt-mobile elements (e.g. Th, LREE), released deeper and hotter. These fluids contribute 100% Cs, 97% Rb, 99% Ba, 69% Th, 74% U, 80% K, 83% Pb, 71% Sr, 45% La, 33% Ce, 20% Nd and 11% Sm to the magma. SEMFR lavas acquired BAB-like deep subduction component as well as arc-like ultra

  2. Detection of Chemical Interactions Between the Core and Mantle

    NASA Astrophysics Data System (ADS)

    Walker, R. J.

    2002-05-01

    Unambiguous detection of chemical interaction between Earth's outer core and lower mantle would be a major breakthrough in understanding mass transport within the mantle. Although most geophysicists and geochemists accept the possibilities of both slab penetration into the lower mantle, and upwelling of hot plumes from the lower mantle into the upper mantle, as yet, no unambiguous geochemical signal can be tied directly to the lower mantle or outer core. Demonstration of an outer core component in mantle-derived materials would prove that at least some matter traverses the distance between the core and mantle. Detection of chemical interaction between the core and mantle is potentially possible via the study of a rather limited suite of elements. There are at least two qualifying criteria for such elements: 1) contrast in concentration between core and mantle such that modest chemical interaction between the metallic core and silicate mantle would be detectible in the "contaminated" or "altered" silicate, 2) the relative abundances of two or more associated elements must record a uniquely core signature. Elements that may meet these requirements include the highly siderophile elements (Re, Au, Pt, Pd, Ir, Rh, Ru, Os) and some moderately siderophile elements (e.g. Au and W). Isotopic systems are of greatest interest in prosecuting this task because characteristic isotopic signals may be immune to subsequent processing in the mantle or crust. Pros and cons in application, and overviews of existing data will be presented for three isotopic systems. Inner core-outer core fractionation may have led to Pt/Os and Re/Os ratios in the outer core that can be generated only by liquid metal-solid metal interaction. Depending on the age of the inner core and the partitioning characteristics of Pt-Re-Os, an outer core signature may be recorded by the long-lived 190Pt-186Os and 187Re-187Os systems. 2 and 3) Core-mantle segregation likely fractionated Hf from W and Pd from Ag

  3. Mantle thermal pulses below the Mid-Atlantic Ridge and temporal variations in the formation of oceanic lithosphere.

    PubMed

    Bonatti, Enrico; Ligi, Marco; Brunelli, Daniele; Cipriani, Anna; Fabretti, Paola; Ferrante, Valentina; Gasperini, Luca; Ottolini, Luisa

    2003-05-29

    A 20-Myr record of creation of oceanic lithosphere is exposed along a segment of the central Mid-Atlantic Ridge on an uplifted sliver of lithosphere. The degree of melting of the mantle that is upwelling below the ridge, estimated from the chemistry of the exposed mantle rocks, as well as crustal thickness inferred from gravity measurements, show oscillations of approximately 3-4 Myr superimposed on a longer-term steady increase with time. The time lag between oscillations of mantle melting and crustal thickness indicates that the mantle is upwelling at an average rate of approximately 25 mm x yr(-1), but this appears to vary through time. Slow-spreading lithosphere seems to form through dynamic pulses of mantle upwelling and melting, leading not only to along-axis segmentation but also to across-axis structural variability. Also, the central Mid-Atlantic Ridge appears to have become steadily hotter over the past 20 Myr, possibly owing to north-south mantle flow.

  4. Global distribution of MORB isotopic variability and mantle convection

    NASA Astrophysics Data System (ADS)

    Albarede, F.; Meyzen, C.; Blichert-Toft, J.

    2006-12-01

    In order to assess the potential of mantle isochrons as parameters relevant to mantle convection, we compiled the isotopic variations of Sr, Nd, Hf, and Pb in MORB along most of the mid-ocean ridge system from the North Atlantic to the North Pacific. The data were extracted from the PetDB database. We calculated the variance of isotope distributions as a function of the distance along the ridge axis over a moving window of 5 degrees. Most of the variance is carried by a small number of regularly spaced peaks (~45°) which correspond to the locations of triple junctions at the time of continental breakup and to well-identified hot spots (Iceland, Azores, Ascension, Bouvet, St Paul, and Sala y Gomez). Overall, large hotspots, such as Iceland, contribute to less peak variance than smaller ones such as Bouvet and St Paul. These peaks also show some decoupling of the different isotopic systems, notably between Hf and the other isotopes, and between the source Th/U and 87Sr/86Sr. On a global scale, the variance is mainly localized along the Atlantic and Indian ridge segments (the Pangea domain), where near-ridge hotspots are much more abundant and spreading velocities much slower than in the Pacific domain. This large-scale pattern reflects different modes of lower mantle injection into the upper mantle. The upper mantle in the Pangea domain is only slowly filled by multiple narrow upwellings and the drag exerted by the deep roots of the Archean cratons strongly perturbs its velocity field. This mode is particularly well expressed along the Southwest Indian Ridge, which is very slowly pulling apart Africa from Antarctica, two continents with Archean cratons underlain by thick lithospheric roots. In contrast, upper mantle material from the Pacific domain is quickly replaced by broad lower mantle upwellings with no significant continental hindrance. The geochemical contrast between the Pangea and Pacific domains demonstrates therefore the long-term influence of

  5. Slab pull, mantle convection, and Pangaean assembly and dispersal

    NASA Astrophysics Data System (ADS)

    Collins, W. J.

    2003-01-01

    Two global-scale mantle convection cells presently exist on Earth, centred on upwelling zones in the South Pacific Ocean and northeast Africa: one cell (Panthalassan) contains only oceanic plates, the other (Pangaean) contains all the continental plates. They have remained fixed relative to one another for >400 Ma. A transverse (Rheic-Tethyian) subduction system splits the Pangaean cell. Poloidal plate motion in the oceanic cell reflects circumferential pull of Panthalassan slabs, but toroidal flow in the Pangaean cell, reflected by vortex-type motion of continents toward the Altaids of central-east Asia throughout the Phanerozoic, has resulted from the competing slab-pull forces of both cells. The combined slab-pull effects from both cells also controlled Pangaean assembly and dispersal. Assembly occurred during Palaeozoic clockwise toroidal motion in the Pangaean cell, when Gondwana was pulled into Pangaea by the NE-trending Rheic subduction zone, forming the Appalachian-Variscide-Altaid chain. Pangaean dispersal occurred when the Rheic trench re-aligned in the Jurassic to form the NW-trending Tethyside subduction system, which pulled east Gondwanan fragments in the opposite direction to form the Cimmerian-Himalayan-Alpine chain. This re-alignment also generated a new set of (Indian) mid-ocean ridge systems which dissected east Gondwana and facilitated breakup. 100-200-Myr-long Phanerozoic Wilson cycles reflect rifting and northerly migration of Gondwanan fragments across the Pangaean cell into the Rheic-Tethyian trench. Pangaean dispersal was amplified by retreat of the Panthalassan slab away from Europe and Africa, which generated mantle counterflow currents capable of pulling the Americas westward to create the Atlantic Ocean. Thermal blanketing beneath Pangaea and related hotspot activity were part of a complex feedback mechanism that established the breakup pattern, but slab retreat is considered to have been the main driving force. The size and longevity of

  6. How will Somali coastal upwelling evolve under future warming scenarios?

    NASA Astrophysics Data System (ADS)

    Decastro, M.; Sousa, M. C.; Santos, F.; Dias, J. M.; Gómez-Gesteira, M.

    2016-07-01

    Somali upwelling system, the fifth in the world, presents some unique features compared with the other major upwelling systems: 1) it is a Western Boundary Upwelling System located near the Equator and 2) upwelling affects the moisture responsible for monsoon rainfall. The intensity of Somali coastal upwelling during summer was projected for the twenty first century by means of an ensemble of Global Climate Models and Regional Climate Models within the framework of CMIP5 and CORDEX projects, respectively. Regardless global or regional circulation models and the chosen greenhouse warming scenario, the strengthening of Somali coastal upwelling, which increases with latitude, is even higher than observed for the Eastern Boundary Upwelling System. In addition, coastal upwelling strengthening is mainly due to Ekman transport since Ekman pumping shows no clear trend for most of the latitudes. Projected land-sea air temperature and pressure show a clear intensification of land-sea thermal and pressure gradient as a consequence of the global warming, which is likely to affect the strengthening of Somali upwelling verifying the hypothesis of Bakun. As a consequence, projected sea surface temperature warming is less intense nearshore than at oceanic locations, especially at latitudes where upwelling strengthening is more intense.

  7. How will Somali coastal upwelling evolve under future warming scenarios?

    PubMed Central

    deCastro, M.; Sousa, M. C.; Santos, F.; Dias, J. M.; Gómez-Gesteira, M.

    2016-01-01

    Somali upwelling system, the fifth in the world, presents some unique features compared with the other major upwelling systems: 1) it is a Western Boundary Upwelling System located near the Equator and 2) upwelling affects the moisture responsible for monsoon rainfall. The intensity of Somali coastal upwelling during summer was projected for the twenty first century by means of an ensemble of Global Climate Models and Regional Climate Models within the framework of CMIP5 and CORDEX projects, respectively. Regardless global or regional circulation models and the chosen greenhouse warming scenario, the strengthening of Somali coastal upwelling, which increases with latitude, is even higher than observed for the Eastern Boundary Upwelling System. In addition, coastal upwelling strengthening is mainly due to Ekman transport since Ekman pumping shows no clear trend for most of the latitudes. Projected land-sea air temperature and pressure show a clear intensification of land-sea thermal and pressure gradient as a consequence of the global warming, which is likely to affect the strengthening of Somali upwelling verifying the hypothesis of Bakun. As a consequence, projected sea surface temperature warming is less intense nearshore than at oceanic locations, especially at latitudes where upwelling strengthening is more intense. PMID:27440455

  8. Characterization of upwelling phenomenon along the Italian coasts

    NASA Astrophysics Data System (ADS)

    Orasi, Arianna; Morucci, Sara; Rinaldi, Eleonora; Bignami, Francesco; Inghilesi, Roberto; Santoleri, Rosalia

    2013-04-01

    In order to investigate wind-driven upwelling along the Italian coasts, preliminary wind data provided by the ISPRA Italian Tide Gauge Measurement Network (RMN) have been analyzed. In a further step, MyOcean Sea Surface Temperature (SST) data have been analyzed in order to define an SST index for wind-driven coastal upwelling assessment. At first, hourly wind data for the period 2009 - 2011 have been used in order to provide the statistical distribution and the wind rose plots at each RMN station. In particular, wind direction and speed have been selected in order to find upwelling-favorable areas and periods of time. E.g. wind directions in the sector between North and West in the Tyrrhenian Sea and between South and East in the Adriatic Sea have been defined as upwelling favorable, the wind sector being defined as the ± 30° arc around the direction parallel to the coast. Moreover only wind speeds greater than 3.0 m/s have been considered as significant for upwelling. For each location, the number of selected data has been divided by the total number of recorded wind data, thus obtaining a sort of upwelling frequency, which allows to define areas mostly exposed to upwelling. Once these areas were defined, satellite SST data have been used as a proxy to study the changes in upwelling intensity, since upwelling waters are colder than surrounding waters. So, in a given satellite SST image the upwelling event is identifiable through SST minima along the coasts. Finally, the SST upwelling index has been defined; also, this index has been "weighted" with wind intensity and direction indicating upwelling conditions obtained from the RMN wind dataset, to better distinguish between upwelling-favorable and downwelling-favorable conditions at each RMN site.

  9. Gondwana subduction-modified mantle domain prevents magmatic seafloor generation in the Central Indian Ridge

    NASA Astrophysics Data System (ADS)

    Morishita, T.; Nakamura, K.; Senda, R.; Suzuki, K.; Kumagai, H.; Sato, H.; Sato, T.; Shibuya, T.; Minoguchi, K.; Okino, K.

    2013-12-01

    The creation of oceanic crust at mid-ocean ridges is essential to understanding the genesis of oceanic plate and the evolution of the Earth. Detailed bathymetric measurements coupled with dense sample recovery at mid-ocean ridge revealed a wide range of variations in the ridge and seafloor morphologies, which cannot be simply explained by a spreading rate, but also by ridge geometry, mantle compositions and thermal structure (Dick et al., 2003 Nature; Cannat et al. 2006 Geology). It is now widely accepted that very limited magmatic activity with tectonic stretching generates oceanic core complex and/or smooth seafloor surface in the slow to ultraslow-spreading ridges, where serpentinized peridotite and gabbros are expected to be exposed associated with detachment faults (Cann et al., 1997 Nature; Cannat et al., 2006), although magmatism might be an essential role for the formation of oceanic core complexes (Buck et al., 2005 Nature; Tucholke et al 2008 JGR). A rising question is why magmatic activity is sometimes prevented during the oceanic plate formation. Ancient melting domain, that are too refractory to melt even in adiabatically upwelling to the shallow upper mantle, might cause the amagmatic spreading ridges (Harvey et al., 2006 EPSL, Liu et al.,2008 Nature). Its origin and effect on seafloor generations are, however, not well understood yet. We report an oceanic hill as an example of an ancient subduction-modified mantle domain, probably formed at continental margin of the Gondwanaland~Pangea supercontinent, existing beneath the Central Indian Ridge. This domain is the most likely to have prevented magmatic seafloor generation, resulting in creation of very deep oceanic valley and serpentine diaper (now the studied oceanic hill) at the present Central Indian ridge.

  10. Viscosity distribution in the mantle convection models

    NASA Astrophysics Data System (ADS)

    Trubitsyn, V. P.

    2016-09-01

    Viscosity is a fundamental property of the mantle which determines the global geodynamical processes. According to the microscopic theory of defects and laboratory experiments, viscosity exponentially depends on temperature and pressure, with activation energy and activation volume being the parameters. The existing laboratory measurements are conducted with much higher strain rates than in the mantle and have significant uncertainty. The data on postglacial rebound only allow the depth distributions of viscosity to be reconstructed. Therefore, spatial distributions (along the depth and lateral) are as of now determined from the models of mantle convection which are calculated by the numerical solution of the convection equations, together with the viscosity dependences on pressure and temperature ( PT-dependences). The PT-dependences of viscosity which are presently used in the numerical modeling of convection give a large scatter in the estimates for the lower mantle, which reaches several orders of magnitude. In this paper, it is shown that it is possible to achieve agreement between the calculated depth distributions of viscosity throughout the entire mantle and the postglacial rebound data. For this purpose, the values of the volume and energy of activation for the upper mantle can be taken from the laboratory experiments, and for the lower mantle, the activation volume should be reduced twice at the 660-km phase transition boundary. Next, the reduction in viscosity by an order of magnitude revealed at the depths below 2000 km by the postglacial rebound data can be accounted for by the presence of heavy hot material at the mantle bottom in the LLSVP zones. The models of viscosity spatial distribution throughout the entire mantle with the lithospheric plates are presented.

  11. Mesozoic-Cenozoic thermal evolution of lithospheric mantle beneath the North China Craton: evidence from REE-in-two-pyroxene temperatures of mantle xenoliths

    NASA Astrophysics Data System (ADS)

    Wang, C.; Xu, W.; Liang, Y.

    2014-12-01

    Thermal state is an important property for us to understand the nature of the lithospheric mantle beneath the North China Craton (NCC). Traditionally, it was obtained by calculating equilibrium temperatures for the mantle xenoliths using thermometers based on major element compositions of coexisting minerals. A REE-in-two-pyroxene thermometer developed by Liang et al. (2013) is able to extract near-solidus temperatures,which can deduce the thermal histories of mantle rocks in combination with major-element-in-two-pyroxene temperatures (Tmaj). We calculated REE temperatures (TREE) for mantle samples from the NCC including ancient refractory peridotites entrained by Early Cretaceous high-Mg diorites from the central NCC (Fushan), Mantle pyroxenites entrained by Early Cretaceous basalts from the eastern NCC (Feixian and Fangcheng), and fertile/moderately depleted peridotites entrained by <100 Ma basalts from the central and eastern NCC. The Fushan peridotites have low Tmaj (<880°C) and mismatched high TREE (780-1150°C), indicating that the ancient mantle was subjected to melt-rock reactions. The Feixian and Fangcheng pyroxenites have both high Tmaj (>890°C) and high TREE - Tmaj values (80-220°C), suggestive of a hot and fast-cooled mantle in Early Cretaceous. The peridotites in <100 Ma basalts have similar TREE and Tmaj, characteristics of well-equilibrated mantle. Based on the thermometric data, we suggest that the transition of nature of the NCC lithospheric mantle is marked by the interaction between ancient lithospheric mantle and hot melt derived from recycling lower crust in Early Cretaceous. After that a fertile mantle was accreted from upwelling asthenosphere, which accomplished the replacement of the NCC lithsospheric mantle. Reference: Liang et al., 2013, A REE-in-two-pyroxene thermometer for mafic and ultramafic rocks. Geochimica et Cosmochimia Acta 102, 246-260.

  12. Modulation of mantle plumes and heat flow at the core mantle boundary by plate-scale flow: results from laboratory experiments

    NASA Astrophysics Data System (ADS)

    Gonnermann, Helge M.; Jellinek, A. Mark; Richards, Mark A.; Manga, Michael

    2004-09-01

    We report results from analog laboratory experiments, in which a large-scale flow is imposed upon natural convection from a hot boundary layer at the base of a large tank of corn syrup. The experiments show that the subdivision of the convective flow into four regions provides a reasonable conceptual framework for interpreting the effects of large-scale flow on plumes. Region I includes the area of the hot thermal boundary layer (TBL) that is thinned by the large-scale flow, thereby suppressing plumes. Region II encompasses the critically unstable boundary layer where plumes form. Region III is the area above the boundary layer that is devoid of plumes. Region IV comprises the area of hot upwelling and plume conduits. Quantitative analysis of our experiments results in a scaling law for heat flux from the hot boundary and for the spatial extent of plume suppression. When applied to the Earth's core-mantle boundary (CMB), our results suggest that large-scale mantle flow, due to sinking lithospheric plates, can locally thin the TBL and suppress plume formation over large fractions of the CMB. Approximately 30% of heat flow from the core may be due to increased heat flux from plate-scale flow. Furthermore, CMB heat flux is non-uniformly distributed along the CMB, with large areas where heat flux is increased on average by a factor of 2. As a consequence, the convective flow pattern in the outer core may be affected by CMB heat-flux heterogeneity and sensitive to changes in plate-scale mantle flow. Because of plume suppression and 'focusing' of hot mantle from the CMB into zones of upwelling flow, plume conduits (hotspots) are expected to be spatially associated with lower-mantle regions of low seismic velocities, inferred as hot upwelling mantle flow.

  13. Estimates of upwelling rates in the Arabian Sea and the equatorial Indian Ocean based on bomb radiocarbon.

    PubMed

    Bhushan, R; Dutta, K; Somayajulu, B L K

    2008-10-01

    Radiocarbon measurements were made in the water column of the Arabian Sea and the equatorial Indian Ocean during 1994, 1995 and 1997 to assess the temporal variations in bomb 14C distribution and its inventory in the region with respect to GEOSECS measurements made during 1977-1978. Four GEOSECS stations were reoccupied (three in the Arabian Sea and one in the equatorial Indian Ocean) during this study, with all of them showing increased penetration of bomb 14C along with decrease in its surface water activity. The upwelling rates derived by model simulation of bomb 14C depth profile using the calculated exchange rates ranged from 3 to 9 m a(-1). The western region of the Arabian Sea experiencing high wind-induced upwelling has higher estimated upwelling rates. However, lower upwelling rates obtained for the stations occupied during this study could be due to reduced 14C gradient compared to that during GEOSECS.

  14. Water circulation and global mantle dynamics: Insight from numerical modeling

    NASA Astrophysics Data System (ADS)

    Nakagawa, Takashi; Nakakuki, Tomoeki; Iwamori, Hikaru

    2015-05-01

    We investigate water circulation and its dynamical effects on global-scale mantle dynamics in numerical thermochemical mantle convection simulations. Both dehydration-hydration processes and dehydration melting are included. We also assume the rheological properties of hydrous minerals and density reduction caused by hydrous minerals. Heat transfer due to mantle convection seems to be enhanced more effectively than water cycling in the mantle convection system when reasonable water dependence of viscosity is assumed, due to effective slab dehydration at shallow depths. Water still affects significantly the global dynamics by weakening the near-surface oceanic crust and lithosphere, enhancing the activity of surface plate motion compared to dry mantle case. As a result, including hydrous minerals, the more viscous mantle is expected with several orders of magnitude compared to the dry mantle. The average water content in the whole mantle is regulated by the dehydration-hydration process. The large-scale thermochemical anomalies, as is observed in the deep mantle, is found when a large density contrast between basaltic material and ambient mantle is assumed (4-5%), comparable to mineral physics measurements. Through this study, the effects of hydrous minerals in mantle dynamics are very important for interpreting the observational constraints on mantle convection.

  15. Functional morphology of the mantle of Nautilus pompilius (Mollusca, Cephalopoda).

    PubMed

    Westermann, Bettina; Schmidtberg, Henrike; Beuerlein, Knut

    2005-06-01

    This study presents histological and cytological findings on the structural differentiation of the mantle of Nautilus pompilius in order to characterize the cells that are responsible for shell formation. The lateral and front mantle edges split distally into three folds: an outer, middle, and inner fold. Within the upper part of the mantle the mantle edge is divided into two folds only; the inner fold disappears where the hood is attached to the mantle. At the base of the outer fold of the lateral and front mantle edge an endo-epithelial gland, the mantle edge gland, is localized. The gland cells are distinguished by a distinct rough endoplasmic reticulum and by numerous secretory vesicles. Furthermore, they show a strong accumulation of calcium compounds, indicating that the formation of the shell takes place in this region of the mantle. Numerous synaptic contacts between the gland cells and the axons of the nerve fibers reveal that the secretion in the area of the mantle edge gland is under nervous control. The whole mantle tissue is covered with a columnar epithelium having a microvillar border. The analyses of the outer epithelium show ultrastructural characteristics of a transport active epithelium, indicating that this region of the mantle is involved in the sclerotization of the shell. Ultrastructural findings concerning the epithelium between the outer and middle fold suggest that the periostracum is formed in this area of the mantle, as it is in other conchiferan molluscs.

  16. Oxygen fugacity profile of the oceanic upper mantle and the depth of redox melting beneath ridges

    NASA Astrophysics Data System (ADS)

    Davis, F. A.; Cottrell, E.

    2014-12-01

    Oxygen fugacity (fO2) of a mantle mineral assemblage, controlled primarily by Fe redox chemistry, sets the depth of the diamond to carbonated melt reaction (DCO3). Near-surface fO2 recorded by primitive MORB glasses and abyssal peridotites anchor the fO2 profile of the mantle at depth. If the fO2-depth relationship of the mantle is known, then the depth of the DCO3 can be predicted. Alternatively, if the DCO3 can be detected geophysically, then its depth can be used to infer physical and chemical characteristics of upwelling mantle. We present an expanded version of a model of the fO2-depth profile of adiabatically upwelling mantle first presented by Stagno et al. (2013), kindly provided by D. Frost. The model uses a chemical mass balance and empirical fits to experimental data to calculate compositions and modes of mantle minerals at specified P, T, and bulk Fe3+/ƩFe. We added P and T dependences to the partitioning of Al and Ca to better simulate the mineralogical changes in peridotite at depth and included majorite component in garnet to increase the depth range of the model. We calculate fO2 from the mineral assemblages using the grt-ol-opx oxybarometer (Stagno et al., 2013). The onset of carbonated melting occurs at the intersection of a Fe3+/ƩFe isopleth with the DCO3. Upwelling mantle is tied to the DCO3 until all native C is oxidized to form carbonated melts by reduction of Fe3+ to Fe2+. The depth of intersection of a parcel of mantle with the DCO3 is a function of bulk Fe3+/ƩFe, potential temperature, and bulk composition. We predict that fertile mantle (PUM) along a 1400 °C adiabat, with 50 ppm bulk C, and Fe3+/ƩFe = 0.05 after C oxidation begins redox melting at a depth of 250 km. The model contextualizes observations of MORB redox chemistry. Because fertile peridotite is richer in Al2O3, the Fe2O3-bearing components of garnet are diluted leading to lower fO2 at a given depth compared to refractory mantle under the same conditions. This may indicate

  17. Consequences of natural upwelling in oligotrophic marine ecosystems

    SciTech Connect

    Walsh, J J

    1980-03-01

    One of the major environmental consequences of Ocean Thermal Energy Conversion (OTEC) plans may be the artificial upwelling of nutrients to the surface waters of oligotrophic ecosystems. Within a 10 km/sup 2/ area, OTEC plants of 1000 MWe total capacity could upwell the same amount of nutrients as occurs naturally off Peru each day. The biological response to possible eutrophication by OTEC plants may not be similar to that within coastal upwelling ecosystems, however. Upwelling in offshore oceanic systems does not lead to increased primary production despite high nutrient content of the euphotic zone. Continuous grazing may not allow phytoplankton blooms to develop in oceanic upwelling systems to the proposed OTEC sites. At present this is a hypothesis to be tested before full evaluation of OTEC induced upwelling can be made.

  18. Has upwelling strengthened along worldwide coasts over 1982-2010?

    PubMed

    Varela, R; Álvarez, I; Santos, F; deCastro, M; Gómez-Gesteira, M

    2015-01-01

    Changes in coastal upwelling strength have been widely studied since 1990 when Bakun proposed that global warming can induce the intensification of upwelling in coastal areas. Whether present wind trends support this hypothesis remains controversial, as results of previous studies seem to depend on the study area, the length of the time series, the season, and even the database used. In this study, temporal and spatial trends in the coastal upwelling regime worldwide were investigated during upwelling seasons from 1982 to 2010 using a single wind database (Climate Forecast System Reanalysis) with high spatial resolution (0.3°). Of the major upwelling systems, increasing trends were only observed in the coastal areas of Benguela, Peru, Canary, and northern California. A tendency for an increase in upwelling-favourable winds was also identified along several less studied regions, such as the western Australian and southern Caribbean coasts. PMID:25952477

  19. Has upwelling strengthened along worldwide coasts over 1982-2010?

    NASA Astrophysics Data System (ADS)

    Varela, R.; Álvarez, I.; Santos, F.; Decastro, M.; Gómez-Gesteira, M.

    2015-05-01

    Changes in coastal upwelling strength have been widely studied since 1990 when Bakun proposed that global warming can induce the intensification of upwelling in coastal areas. Whether present wind trends support this hypothesis remains controversial, as results of previous studies seem to depend on the study area, the length of the time series, the season, and even the database used. In this study, temporal and spatial trends in the coastal upwelling regime worldwide were investigated during upwelling seasons from 1982 to 2010 using a single wind database (Climate Forecast System Reanalysis) with high spatial resolution (0.3°). Of the major upwelling systems, increasing trends were only observed in the coastal areas of Benguela, Peru, Canary, and northern California. A tendency for an increase in upwelling-favourable winds was also identified along several less studied regions, such as the western Australian and southern Caribbean coasts.

  20. Stable intermediate-spin ferrous iron in lower-mantle perovskite

    SciTech Connect

    McCammon, C.; Kantor, I.; Narygina, O.; Rouquette, J.; Ponkratz, U.; Sergueev, I.; Mezouar, M.; Prakapenka, V.; Dubrovinsky, L.

    2008-11-10

    The lower mantle is dominated by a magnesium- and iron-bearing mineral with the perovskite structure. Iron has the ability to adopt different electronic configurations, and transitions in its spin state in the lower mantle can significantly influence mantle properties and dynamics. However, previous studies aimed at understanding these transitions have provided conflicting results. Here we report the results of high-pressure (up to 110 GPa) and high-temperature (up to 1,000 K) experiments aimed at understanding spin transitions of iron in perovskite at lower-mantle conditions. Our Moessbauer and nuclear forward scattering data for two lower-mantle perovskite compositions demonstrate that the transition of ferrous iron from the high-spin to the intermediate-spin state occurs at approximately 30 GPa, and that high temperatures favour the stability of the intermediate-spin state. We therefore infer that ferrous iron adopts the intermediate-spin state throughout the bulk of the lower mantle. Our X-ray data show significant anisotropic compression of lower-mantle perovskite containing intermediate-spin ferrous iron, which correlates strongly with the spin transition. We predict spin-state heterogeneities in the uppermost part of the lower mantle associated with sinking slabs and regions of upwelling. These may affect local properties, including thermal and electrical conductivity, deformation (viscosity) and chemical behaviour, and thereby affect mantle dynamics.

  1. Formation of Australian continental margin highlands driven by plate-mantle interaction

    NASA Astrophysics Data System (ADS)

    Müller, R. Dietmar; Flament, Nicolas; Matthews, Kara J.; Williams, Simon E.; Gurnis, Michael

    2016-05-01

    Passive margin highlands occur on most continents on Earth and play a critical role in the cycle of weathering, erosion, and atmospheric circulation. Yet, in contrast to the well-developed understanding of collisional mountain belts, such as the Alps and Himalayas, the origin of less elevated (1-2 km) passive margin highlands is still unknown. The eastern Australian highlands are a prime example of these plateaus, but compared to others they have a well-documented episodic uplift history spanning 120 million years. We use a series of mantle convection models to show that the time-dependent interaction of plate motion with mantle downwellings and upwellings accounts for the broad pattern of margin uplift phases. Initial dynamic uplift of 400-600 m from 120-80 Ma was driven by the eastward motion of eastern Australia's margin away from the sinking eastern Gondwana slab, followed by tectonic quiescence to about 60 Ma in the south (Snowy Mountains). Renewed uplift of ∼700 m in the Snowy Mountains is propelled by the gradual motion of the margin over the edge of the large Pacific mantle upwelling. In contrast the northernmost portion of the highlands records continuous uplift from 120 Ma to present-day totalling about 800 m. The northern highlands experienced a continuous history of dynamic uplift, first due to the end of subduction to the east of Australia, then due to moving over a large passive mantle upwelling. In contrast, the southern highlands started interacting with the edge of the large Pacific mantle upwelling ∼ 40- 50 million years later, resulting in a two-phase uplift history. Our results are in agreement with published uplift models derived from river profiles and the Cretaceous sediment influx into the Ceduna sub-basin offshore southeast Australia, reflecting the fundamental link between dynamic uplift, fluvial erosion and depositional pulses in basins distal to passive margin highlands.

  2. The Earth's Mantle.

    ERIC Educational Resources Information Center

    McKenzie, D. P.

    1983-01-01

    The nature and dynamics of the earth's mantle is discussed. Research indicates that the silicate mantle is heated by the decay of radioactive isotopes and that the heat energizes massive convention currents in the upper 700 kilometers of the ductile rock. These currents and their consequences are considered. (JN)

  3. Analysis of coastal upwelling and the production of a biomass

    NASA Technical Reports Server (NTRS)

    Howe, J. T.

    1979-01-01

    The coastal upwelling index derived from weather data is input to a set of coupled differential equations that describe the production of a biomass. The curl of the wind stress vector is discussed in the context of the physical extent of the upwelling structure. An analogy between temperature and biomass concentration in the upwelled coastal water is derived and the relationship is quantified. The use of remote satellite or airborne sensing to obtain biomass rate production coefficients is considered.

  4. Intensification and spatial homogenization of coastal upwelling under climate change.

    PubMed

    Wang, Daiwei; Gouhier, Tarik C; Menge, Bruce A; Ganguly, Auroop R

    2015-02-19

    The timing and strength of wind-driven coastal upwelling along the eastern margins of major ocean basins regulate the productivity of critical fisheries and marine ecosystems by bringing deep and nutrient-rich waters to the sunlit surface, where photosynthesis can occur. How coastal upwelling regimes might change in a warming climate is therefore a question of vital importance. Although enhanced land-ocean differential heating due to greenhouse warming has been proposed to intensify coastal upwelling by strengthening alongshore winds, analyses of observations and previous climate models have provided little consensus on historical and projected trends in coastal upwelling. Here we show that there are strong and consistent changes in the timing, intensity and spatial heterogeneity of coastal upwelling in response to future warming in most Eastern Boundary Upwelling Systems (EBUSs). An ensemble of climate models shows that by the end of the twenty-first century the upwelling season will start earlier, end later and become more intense at high but not low latitudes. This projected increase in upwelling intensity and duration at high latitudes will result in a substantial reduction of the existing latitudinal variation in coastal upwelling. These patterns are consistent across three of the four EBUSs (Canary, Benguela and Humboldt, but not California). The lack of upwelling intensification and greater uncertainty associated with the California EBUS may reflect regional controls associated with the atmospheric response to climate change. Given the strong linkages between upwelling and marine ecosystems, the projected changes in the intensity, timing and spatial structure of coastal upwelling may influence the geographical distribution of marine biodiversity.

  5. Viscosity profile of the lower mantle

    NASA Technical Reports Server (NTRS)

    Ellsworth, K.; Schubert, G.; Sammis, C. G.

    1985-01-01

    The viscosity of the earth's mantle is an important factor in studies of mantle convection and other problems in geodynamics. The present investigation is concerned with a determination of the variation of effective viscosity across the lower mantle from models of the Gibb's free energy of activation G(asterisk) and the adiabatic temperature profile. The variation of G(asterisk) with depth is calculated using both an elastic strain energy model, in which G(asterisk) is related to the seismic velocities, and a model which assumes G(asterisk) is proportional to the melting temperature.

  6. The Active Solid Earth

    NASA Astrophysics Data System (ADS)

    Ebinger, Cynthia

    2016-04-01

    Dynamic processes in Earth's crust, mantle and core shape Earth's surface and magnetic field over time scales of seconds to millennia, and even longer time scales as recorded in the ca. 4 Ga rock record. Our focus is the earthquake-volcano deformation cycles that occur over human time scales, and their comparison with time-averaged deformation studies, with emphasis on mantle plume provinces where magma and volatile release and vertical tectonics are readily detectable. Active deformation processes at continental and oceanic rift and back arc zones provide critical constraints on mantle dynamics, the role of fluids (volatiles, magma, water), and plate rheology. For example, recent studies of the East African rift zone, which formed above one of Earth's largest mantle upwellings reveal that magma production and volatile release rates are comparable to those of magmatic arcs, the archetypal zones of continental crustal creation. Finite-length faults achieve some plate deformation, but magma intrusion in the form of dikes accommodates extension in continental, back-arc, and oceanic rifts, and intrusion as sills causes permanent uplift that modulates the local time-space scales of earthquakes and volcanoes. Volatile release from magma intrusion may reduce fault friction and permeability, facilitating aseismic slip and creating magma pathways. We explore the implications of active deformation studies to models of the time-averaged structure of plume and extensional provinces in continental and oceanic plate settings.

  7. Water partitioning between bridgmanite and postperovskite in the lowermost mantle

    NASA Astrophysics Data System (ADS)

    Townsend, Joshua P.; Tsuchiya, Jun; Bina, Craig R.; Jacobsen, Steven D.

    2016-11-01

    The lowermost mantle appears to contain geochemically primitive reservoirs of volatile components including water, as evidenced by certain ocean island basalts (Hallis et al., 2015). We used ab initio lattice dynamics to calculate the water partition coefficient between bridgmanite and postperovskite using quasi-harmonic free energies to determine how water is distributed between nominally anhydrous minerals in the D″ region. In the absence of aluminum, hydrogen was incorporated into both phases by a simple substitution of Mg2+ ⇔ 2H+, and we found that water favors bridgmanite over postperovskite by a factor of about 5:1 at conditions where an average mantle geotherm intersects the phase boundary. In the Al-bearing system, hydrogen and aluminum were coupled as Si4+ ⇔Al3+ +H+ defects into both phases, and we found that water favors postperovskite over bridgmanite in the Al-bearing system by a factor of about 3:1 at ambient mantle conditions, and by about 8:1 at colder slab conditions. Our results indicate that aluminum controls the partitioning of water between bridgmanite and postperovskite, and that aluminous postperovskite may be a potential host for primordial water in the lowermost region of the mantle. The strong partitioning of water into aluminous postperovskite over bridgmanite provides a potential mechanism for dehydration melting in the lowermost mantle that could be a source for ocean island basalts in regions of upwelling.

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

    PubMed

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

    2008-03-20

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

  9. Gradients in microbial methanol uptake: productive coastal upwelling waters to oligotrophic gyres in the Atlantic Ocean.

    PubMed

    Dixon, Joanna L; Sargeant, Stephanie; Nightingale, Philip D; Colin Murrell, J

    2013-03-01

    Methanol biogeochemistry and its importance as a carbon source in seawater is relatively unexplored. We report the first microbial methanol carbon assimilation rates (k) in productive coastal upwelling waters of up to 0.117±0.002 d(-1) (~10 nmol l(-1 )d(-1)). On average, coastal upwelling waters were 11 times greater than open ocean northern temperate (NT) waters, eight times greater than gyre waters and four times greater than equatorial upwelling (EU) waters; suggesting that all upwelling waters upon reaching the surface (≤20 m), contain a microbial population that uses a relatively high amount of carbon (0.3-10 nmol l(-1 )d(-1)), derived from methanol, to support their growth. In open ocean Atlantic regions, microbial uptake of methanol into biomass was significantly lower, ranging between 0.04-0.68 nmol l(-1 )d(-1). Microbes in the Mauritanian coastal upwelling used up to 57% of the total methanol for assimilation of the carbon into cells, compared with an average of 12% in the EU, and 1% in NT and gyre waters. Several methylotrophic bacterial species were identified from open ocean Atlantic waters using PCR amplification of mxaF encoding methanol dehydrogenase, the key enzyme in bacterial methanol oxidation. These included Methylophaga sp., Burkholderiales sp., Methylococcaceae sp., Ancylobacter aquaticus, Paracoccus denitrificans, Methylophilus methylotrophus, Methylobacterium oryzae, Hyphomicrobium sp. and Methylosulfonomonas methylovora. Statistically significant correlations for upwelling waters between methanol uptake into cells and both chlorophyll a concentrations and methanol oxidation rates suggest that remotely sensed chlorophyll a images, in these productive areas, could be used to derive total methanol biological loss rates, a useful tool for atmospheric and marine climatically active gas modellers, and air-sea exchange scientists. PMID:23178665

  10. Gradients in microbial methanol uptake: productive coastal upwelling waters to oligotrophic gyres in the Atlantic Ocean.

    PubMed

    Dixon, Joanna L; Sargeant, Stephanie; Nightingale, Philip D; Colin Murrell, J

    2013-03-01

    Methanol biogeochemistry and its importance as a carbon source in seawater is relatively unexplored. We report the first microbial methanol carbon assimilation rates (k) in productive coastal upwelling waters of up to 0.117±0.002 d(-1) (~10 nmol l(-1 )d(-1)). On average, coastal upwelling waters were 11 times greater than open ocean northern temperate (NT) waters, eight times greater than gyre waters and four times greater than equatorial upwelling (EU) waters; suggesting that all upwelling waters upon reaching the surface (≤20 m), contain a microbial population that uses a relatively high amount of carbon (0.3-10 nmol l(-1 )d(-1)), derived from methanol, to support their growth. In open ocean Atlantic regions, microbial uptake of methanol into biomass was significantly lower, ranging between 0.04-0.68 nmol l(-1 )d(-1). Microbes in the Mauritanian coastal upwelling used up to 57% of the total methanol for assimilation of the carbon into cells, compared with an average of 12% in the EU, and 1% in NT and gyre waters. Several methylotrophic bacterial species were identified from open ocean Atlantic waters using PCR amplification of mxaF encoding methanol dehydrogenase, the key enzyme in bacterial methanol oxidation. These included Methylophaga sp., Burkholderiales sp., Methylococcaceae sp., Ancylobacter aquaticus, Paracoccus denitrificans, Methylophilus methylotrophus, Methylobacterium oryzae, Hyphomicrobium sp. and Methylosulfonomonas methylovora. Statistically significant correlations for upwelling waters between methanol uptake into cells and both chlorophyll a concentrations and methanol oxidation rates suggest that remotely sensed chlorophyll a images, in these productive areas, could be used to derive total methanol biological loss rates, a useful tool for atmospheric and marine climatically active gas modellers, and air-sea exchange scientists.

  11. Equatorial upwelling enhances nitrogen fixation in the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Subramaniam, Ajit; Mahaffey, Claire; Johns, William; Mahowald, Natalie

    2013-05-01

    Surface waters in upwelling regions are thought to be nutrient rich and hence inhibit nitrogen fixation (diazotrophy) because diazotrophs can preferentially assimilate nitrate and ammonia instead of expending energy to fix dinitrogen. We found average nitrogen fixation rates to be two to seven times higher in the surface waters of the upwelling region of the eastern equatorial Atlantic than typically measured here during non-upwelling periods. We posit that in this region, low nitrate-phosphate ratio waters are upwelled, and an initial bloom of non-diazotrophic phytoplankton removes recently upwelled nitrate. Thereby, diazotrophy is fuelled by residual phosphate and by a combination of aeolian and upwelled sources of iron. Annually, we estimate that approximately 47 Gmol of new nitrogen is introduced by diazotrophy in upwelled waters alone and 195 Gmol N is fixed in the equatorial Atlantic region. Our findings challenge the paradigm that the highest nitrogen fixation rates occur in oligotrophic gyres and instead provide evidence of its importance in upwelling regimes where phosphate- and iron-rich waters rich are upwelled.

  12. Influence of upwelling on SST trends in La Guajira system

    NASA Astrophysics Data System (ADS)

    Santos, F.; Gómez-Gesteira, M.; Varela, R.; Ruiz-Ochoa, M.; Días, J. M.

    2016-04-01

    La Guajira upwelling system has shown a moderate cooling (˜-0.05°C dec-1) over the period 1982-2014 for the months with strong upwelling (JFM). This contrasts with the general warming observed for most of the Caribbean region (˜0.25°C dec-1) over the same period. Cooling is in good agreement with the upwelling increase (˜0.04 m2s-1dec-1) observed in the region during winter months, although the position of the peaks in upwelling and SST trends does not coincide exactly due to the presence of the Caribbean Coastal Undercurrent.

  13. 3-d numerical modeling for the interaction of mantle plumes with cratonic keel

    NASA Astrophysics Data System (ADS)

    Lin, S.; Kuo, B.

    2003-04-01

    The magmatism of the Ethiopian and east African plateaus is one of the largest active continental igneous provinces on Earth. Great volumes of volcanic deposits have been thought to be originated from the upwelling mantle or plumes under the African continent [e.g., Ebinger et al., 1989]. Major, trace element and radiogenic isotope ratios (Sr, Nd and Pb) and the dating data [George et al., 1998] suggest that there are at least two mantle plumes, i.e., the latter Afar plume and earlier Kenya plume, beneath the East African rift system. It was proposed [e.g., Rogers et al., 2000] that the northeastward plate motion over the Kenya plume produced the magmatism from southern Ethiopia to northern Tanzania since about 45 Ma, and that the Afar plume later generated the magma in the Ethiopia Plateau. Meanwhile, it has been found that the Tanzania Craton in central Africa has survived the thermal erosion of the mantle plumes and the extensional tectonics in this region [e.g., Ritsema and van Heijst, 2000]. Here we investigate how the plume material changes its directions when it meets the tectonically stable cratonic keel using 3-D numerical experiments. The stronger temperature dependence of viscosity as well as the hotter plumes can at times provide higher buoyancy flux and determine how far the plume material can reach. In the meantime, the cratonic keel can divert the plume material and induce the edge-driven convection. Numerical models have been designed to address the double-plume hypothesis, in which the plumes were initiated at different periods of time and interacted with the cratonic keel on a moving plate. The numerical models and a comparison between the models and geological constraints will be presented.

  14. Rogue Mantle Helium and Neon

    NASA Astrophysics Data System (ADS)

    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

  15. Oceanic contributions from tropical upwelling systems to atmospheric halogens

    NASA Astrophysics Data System (ADS)

    Ziska, Franziska; Hepach, Helmke; Stemmler, Irene; Quack, Birgit; Atlas, Elliot; Fuhlbrügge, Steffen; Bracher, Astrid; Tegtmeier, Susann; Krüger, Kirstin

    2014-05-01

    Short lived halogenated substances (halocarbons) from the oceans contribute to atmospheric halogens, where they are involved in ozone depletion and aerosol formation. Oceanic regions that are characterized by high biological activity are often associated with increased halocarbon abundance of e.g. bromoform (CHBr3) and dibromomethane (CH2Br2), representing the main contributors to atmospheric organic bromine. Apart from biological production, photochemical pathways play an important role in the formation of methyl iodide (CH3I), the most abundant organoiodine in the marine atmosphere. Recently, the contribution of biogenic diiodomethane (CH2I2) and chloroiodomethane (CH2ClI) to atmospheric organic iodine has been estimated to be similarly significant as CH3I. In the tropics, rapid uplift of surface air can transport these short-lived compounds into the upper troposphere and into the stratosphere. Oceanic upwelling systems off Mauritania, Peru and in the equatorial Atlantic might therefore potentially contribute large amounts of halocarbons to the stratosphere. Concentrations and emissions of iodo- and bromocarbons from several SOPRAN campaigns in different tropical upwelling systems, the Mauritanian and the equatorial upwelling in the Atlantic, as well as the Peruvian upwelling in the Pacific, will be presented. Processes contributing to halocarbon occurrence in the water column, as well as biological and physical factors influencing their emission into the atmosphere are investigated (Fuhlbrügge, et al. 2013; Hepach et al., 2013). We will present the relative contribution of the upwelling systems to global air-sea fluxes from different modelling studies. The data based bottom-up emissions from Ziska et al. (2013) will be compared to model simulated halocarbons. The model is a global three-dimensional ocean general circulation model with an ecosystem model and halocarbon module embedded (MPIOM/HAMOCC). It resolves CH3I and CHBr3 production, degradation, and

  16. Preclinical activity of 8-chloroadenosine with mantle cell lymphoma: Roles of energy depletion and inhibition of DNA and RNA synthesis

    PubMed Central

    Dennison, Jennifer B.; Balakrishnan, Kumudha; Gandhi, Varsha

    2009-01-01

    8-Chloroadenosine (8-Cl-Ado), an RNA-directed nucleoside analog, is currently being evaluated in phase I clinical trials for treatment of chronic lymphocytic leukemia. In the current study, the efficacy of 8-Cl-Ado was evaluated using mantle cell lymphoma (MCL) cell lines: Granta 519, JeKo, Mino, and SP-53. After continuous exposure to 10 μM 8-Cl-Ado for 24 h, loss of mitochondrial transmembrane potential and PARP cleavage were detected in 3 of 4 cell lines. Reduced ATP levels (30 to 60% reduction) and concurrent 8-Cl-ATP accumulation were highly associated with cell death (P < 0.01). The intracellular 8-Cl-ATP concentrations were also highly correlated with inhibition of global transcription (50 to 90%, r2 = 0.90, P < 0.01). However, the inhibition of transcription only accounted for 30 to 40% of cell death as determined by equivalent inhibition with actinomycin D. Likewise, short-lived mRNAs, those encoding cyclin D1 and Mcl-1, were not consistently reduced after treatment. Unique to MCL as compared to other hematological malignancies, 8-Cl-Ado inhibited the rates of DNA synthesis and selectively depleted dATP pools (50 to 80%). We conclude that the DNA and RNA directed actions of 8-Cl-Ado in combination with depleted energetics may promote cell death and inhibit growth of MCL cell lines. PMID:19709085

  17. Currents in the mantle and the geology of continents

    NASA Astrophysics Data System (ADS)

    Wilson, J. Tuzo

    1991-02-01

    This paper is the first of a series which have considered the possible effects of currents in the mantle upon continents. It mentions effects of aging in oceans upon the direction of slope of coastal peneplains. When oceans are young the coasts are cliffs from which peneplains dip downward on the inland side. As the margins separate from the ridge they cool and the slopes reverse. It suggests how Jeffreys' arguments against convection currents breaking the lithosphere can be avoided and discusses the possibility that upwelling has penetrated beneath the southwestern United States.

  18. No thermal anomalies in the mantle transition zone beneath an incipient continental rift: evidence from the first receiver function study across the Okavango Rift Zone, Botswana

    NASA Astrophysics Data System (ADS)

    Yu, Y.; Liu, K. H.; Moidaki, M.; Reed, C. A.; Gao, S. S.

    2015-08-01

    Mechanisms leading to the initiation and early-stage development of continental rifts remain enigmatic, in spite of numerous studies. Among the various rifting models, which were developed mostly based on studies of mature rifts, far-field stresses originating from plate interactions (passive rifting) and nearby active mantle upwelling (active rifting) are commonly used to explain rift dynamics. Situated atop of the hypothesized African Superplume, the incipient Okavango Rift Zone (ORZ) of northern Botswana is ideal to investigate the role of mantle plumes in rift initiation and development, as well as the interaction between the upper and lower mantle. The ORZ developed within the Neoproterozoic Damara belt between the Congo Craton to the northwest and the Kalahari Craton to the southeast. Mantle structure and thermal status beneath the ORZ are poorly known, mostly due to a complete paucity of broad-band seismic stations in the area. As a component of an interdisciplinary project funded by the United States National Science Foundation, a broad-band seismic array was deployed over a 2-yr period between mid-2012 and mid-2014 along a profile 756 km in length. Using P-to-S receiver functions (RFs) recorded by the stations, the 410 and 660 km discontinuities bordering the mantle transition zone (MTZ) are imaged for the first time. When a standard Earth model is used for the stacking of RFs, the apparent depths of both discontinuities beneath the Kalahari Craton are about 15 km shallower than those beneath the Congo Craton. Using teleseismic P- and S-wave traveltime residuals obtained by this study and lithospheric thickness estimated by previous studies, we conclude that the apparent shallowing is the result of a 100-150 km difference in the thickness of the lithosphere between the two cratons. Relative to the adjacent tectonically stable areas, no significant anomalies in the depth of the MTZ discontinuities or in teleseismic P- and S-wave traveltime residuals are

  19. Zoned mantle convection.

    PubMed

    Albarède, Francis; Van Der Hilst, Rob D

    2002-11-15

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

  20. Zoned mantle convection.

    PubMed

    Albarède, Francis; Van Der Hilst, Rob D

    2002-11-15

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

  1. Coastal upwelling and downwelling forcing of circulation in a semi-enclosed bay: Ria de Vigo

    NASA Astrophysics Data System (ADS)

    Barton, E. D.; Largier, J. L.; Torres, R.; Sheridan, M.; Trasviña, A.; Souza, A.; Pazos, Y.; Valle-Levinson, A.

    2015-05-01

    Semi-enclosed bays in upwelling regions are exposed to forcing related to winds, currents and buoyancy over the shelf. The influence of this external forcing is moderated by factors such as connectivity to the open ocean, shelter by surrounding topography, dimensions of the bay, and freshwater outflows. Such bays, preferred locations for ports, mariculture, marine industry, recreational activities and coastal settlement, present a range of characteristics, understanding of which is necessary to their rational management. Observations in such a semi-enclosed bay, the Ria de Vigo in Spain, are used to characterize the influence of upwelling and downwelling pulses on its circulation. In this location, near the northern limit of the Iberian upwelling system, upwelling events dominate during a short summer season and downwelling events the rest of the year. The ria response to the external forcing is central to nutrient supply and resultant plankton productivity that supports its high level of cultured mussel production. Intensive field studies in September 2006 and June 2007 captured a downwelling event and an upwelling event, respectively. Data from eight current profiler moorings and boat-based MiniBat/ADCP surveys provided an unprecedented quasi-synoptic view of the distribution of water masses and circulation patterns in any ria. In the outer ria, circulation was dominated by the introduction of wind-driven alongshore flow from the external continental shelf through the ria entrances and its interaction with the topography. In the middle ria, circulation was primarily related to the upwelling/downwelling cycle, with a cool, salty and dense lower layer penetrating to the inner ria during upwelling over the shelf. A warmer, lower salinity and less dense surface layer of coastal waters flowed inward during downwelling. Without external forcing, the inner ria responded primarily to tides and buoyancy changes related to land runoff. Under both upwelling and downwelling

  2. What controls biological production in coastal upwelling systems? Insights from a comparative modeling study

    NASA Astrophysics Data System (ADS)

    Lachkar, Z.; Gruber, N.

    2011-10-01

    The magnitude of net primary production (NPP) in Eastern Boundary Upwelling Systems (EBUS) is traditionally viewed as directly reflecting the wind-driven upwelling intensity. Yet, different EBUS show different sensitivities of NPP to upwelling-favorable winds (Carr and Kearns, 2003). Here, using a comparative modeling study of the California Current System (California CS) and Canary Current System (Canary CS), we show how physical and environmental factors, such as light, temperature and cross-shore circulation modulate the response of NPP to upwelling strength. To this end, we made a series of eddy-resolving simulations of the two upwelling systems using the Regional Oceanic Modeling System (ROMS), coupled to a nitrogen-based Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD) ecosystem model. Using identical ecological/biogeochemical parameters, our coupled model simulates a level of NPP in the California CS that is 50 % smaller than that in the Canary CS, in agreement with observationally based estimates. We find this much lower NPP in the California CS despite phytoplankton in this system having nearly 20 % higher nutrient concentrations available to fuel their growth. This conundrum can be explained by: (1) phytoplankton having a faster nutrient-replete growth in the Canary CS relative to the California CS; a consequence of more favorable light and temperature conditions in the Canary CS, and (2) the longer nearshore water residence times in the Canary CS, which permit a larger buildup of biomass in the upwelling zone, thereby enhancing NPP. The longer residence times in the Canary CS appear to be a result of the wider continental shelves and the lower mesoscale activity characterizing this upwelling system. This results in a weaker offshore export of nutrients and organic matter, thereby increasing local nutrient recycling and reducing the spatial decoupling between new and export production in the Canary CS. Our results suggest that climate change

  3. Seismic evidence of hyper-stretched crust and mantle exhumation offshore Vietnam

    NASA Astrophysics Data System (ADS)

    Savva, D.; Meresse, F.; Pubellier, M.; Chamot-Rooke, N.; Lavier, L.; Po, K. Wong; Franke, D.; Steuer, S.; Sapin, F.; Auxietre, J. L.; Lamy, G.

    2013-11-01

    We study the evolution of the Eocene-Recent Phu Khanh Basin opened during the rifting of the South China Sea (SCS). This sub-basin formed when continental crust ruptured along the East-Vietnam Boundary Fault (EVBF) at the western edge of the SCS. Using high quality long-streamer seismic lines we interpret structures that highlight the different phases of the SCS rifting and processes related to crustal boudinage. Extreme crustal thinning and mantle uplift that sometimes places sediments in contact with the Moho discontinuity mark the central part of the basin. The mantle is shallowest there and marks the final rupture of the continental crust during an intense phase of mantle upwelling. There, a low-angle detachment fault separates several crustal blocks from the Moho. The cylindrical axis of the Moho rise is roughly parallel to the trend of the South China Sea propagator. Above the mantle, the upper and lower crusts form large crustal boudins. The network of normal faults is dense in the upper crust and occasionally propagates into the lower crust. However, the lower crust is missing at some places. The seismic facies above the Moho rise is poorly stratified and might have been affected by a certain degree of metamorphism. At the apex of mantle uplift, there are frequent indications of fluid circulations, including volcanic edifices and gas escapes features. Three stages of extension are clearly identifiable, with ages of the two youngest constrained by well calibration: the first and oldest rift sequence is situated between the tilted pre-rift basement and the Oligocene horizons (32 Ma); the second is delimited by the Oligocene to the Mid Miocene (15.5 Ma) horizons, and the third is bound by the Mid Miocene and the Upper Miocene (before 10.5 Ma) horizons. These three rift episodes formed in at least two extension directions, the first N-S and the second NW-SE. The distinct Mid Miocene (15.5 Ma) horizon is tilted and the above layers show a diverging reflection

  4. Phosphorus cycling in the red tide incubator region of monterey bay in response to upwelling.

    PubMed

    Mackey, Katherine R M; Mioni, Cécile E; Ryan, John P; Paytan, Adina

    2012-01-01

    This study explores the cycling of phosphorus (P) in the euphotic zone following upwelling in northeastern Monterey Bay (the Red Tide Incubator region) of coastal California, with particular emphasis on how bacteria and phytoplankton that form harmful algal blooms mediate and respond to changes in P availability. In situ measurements of nutrient concentrations, phytoplankton community composition, and cell-specific alkaline phosphatase (AP) activity (determined via enzyme-labeled fluorescence assay) were measured during three cruises. Upwelling led to a 10-fold increase in dissolved inorganic (DIP) in surface waters, reaching ∼0.5 μmol L(-1). This DIP was drawn down rapidly as upwelling relaxed over a period of 1 week. Ratios of nitrate to DIP drawdown (∼5:1, calculated as the change in nitrate divided by the change in DIP) were lower than the Redfield ratio of 16:1, suggesting that luxury P uptake was occurring as phytoplankton bloomed. Dissolved organic (DOP) remained relatively constant (∼0.3 μmol L(-1)) before and immediately following upwelling, but doubled as upwelling relaxed, likely due to phytoplankton excretion and release during grazing. This transition from a relatively high DIP:DOP ratio to lower DIP:DOP ratio was accompanied by a decline in the abundance of diatoms, which had low AP activity, toward localized, spatially heterogeneous blooms of dinoflagellates in the genera Prorocentrum, Ceratium, Dinophysis, Alexandrium, and Scrippsiella that showed high AP activity regardless of ambient DIP levels. A nutrient addition incubation experiment showed that phytoplankton growth was primarily limited by nitrate, followed by DIP and DOP, suggesting that P regulates phytoplankton physiology and competition, but is not a limiting nutrient in this region. AP activity was observed in bacteria associated with lysed cell debris and aggregates of particulate organic material, where it may serve to facilitate P regeneration, as well as affixed to

  5. Comparing the nature of the western and eastern Azores mantle

    NASA Astrophysics Data System (ADS)

    Genske, Felix S.; Beier, Christoph; Stracke, Andreas; Turner, Simon P.; Pearson, Norman J.; Hauff, Folkmar; Schaefer, Bruce F.; Haase, Karsten M.

    2016-01-01

    The Azores islands in the central North-Atlantic originate from a regional melting anomaly, probably created by melting hot, unusually hydrous and geochemically enriched mantle. Here, we present Hf, Pb and Os isotopic data in geochemically well-characterised primitive lavas from the islands Flores and Corvo that are located west of the Mid-Atlantic Ridge (MAR), as well as submarine samples from a subsided island west of Flores and from Deep Sea Drilling Project (DSDP) holes drilled in the western part of the Azores platform and beyond. These are compared to existing data from the Azores islands east of the MAR. The geodynamic origin of the two islands west of the ridge axis and furthest from the inferred plume centre in the central part of the plateau is enigmatic. The new data constrain the source compositions of the Flores and Corvo lavas and show that the western and eastern Azores mantle is isotopically similar, with the exception of an enriched component found exclusively on eastern São Miguel. Trace element ratios involving high field strength elements (HFSE) are distinctly different in the western islands (e.g. twofold higher Nb/Zr) compared to any of the islands east of the MAR. A similar signature is observed in MAR basalts to the south of the Azores platform and inferred to originate from (auto-) metasomatic enrichment of the sub-ridge mantle (Gale et al., 2011, 2013). In a similar fashion, low degree melts from an enriched source component may metasomatise the ambient plume mantle underneath the western Azores islands. Melting such a modified plume mantle can explain the chemical differences between lavas from the western and eastern Azores islands without the need for additional plume components. Recent re-enrichment and intra melting column modification of the upwelling mantle can cause local to regional scale geochemical differences in mantle-derived melts.

  6. Role of the subduction filter in mantle recycling

    NASA Astrophysics Data System (ADS)

    Kimura, J. I.; Skora, S. E.; Gill, J.; Van Keken, P. E.

    2015-12-01

    Subduction modifies the descending basaltic and sedimentary oceanic crust and generates felsic arc materials and continental crust. Studies of element mass balances in the subduction zone therefore reveal the evolution of the Earth's two major geochemical reservoirs: the continent crust and mantle. We use the Arc Basalt Simulator ver.4 (ABS4) to model the geochemical mass balance during dehydration by prograde metamorphism and melting of the slab followed by subsequent flux melting of the wedge mantle caused by the addition of slab-derived liquids. The geochemistry of high-Mg andesite or adakite formed in a hot subduction zone is akin to the present-day bulk continental crust and to the Archean (>2 Ga) Tonalite-Trondjhemite-Granodiorite composition. Therefore, the residual slab and the metasomatized mantle wedge at hot subduction zones should be the most plausible sources for materials recycled back into the deep mantle. Model calculations of isotopic growth in the residual slab and mantle formed in hot subduction zones reproduce fairly well the EM1-FOZO-HIMU isotope arrays found in ocean island basalts (OIBs) of deep mantle plume origin, although FOZO with high 3He/4He is not generated by this slab recycling process. The recycled materials are bulk igneous ocean crust for HIMU and metasomatized mantle wedge peridotite for EM1. In contrast, the EM2-FOZO array can be generated in a cold subduction zone with igneous oceanic crust for FOZO and sediment for EM2 sources. Necessary residence time are ~2 Ga to form HIMU-FOZO-EM1 and ~1 Ga to form EM2-FOZO. The subducted oceanic crust (forming HIMU) and mantle wedge peridotite (forming EM1) may have travelled in the mantle together. They then melted together in an upwelling mantle plume to form the EM1-FOZO-HIMU isotopic variations found frequently in OIBs. In contrast, the less frequent EM2-FOZO array suggests a separate source and recycling path. These recycling ages are consistent with the change in the mantle potential

  7. Anti-CCR7 therapy exerts a potent anti-tumor activity in a xenograft model of human mantle cell lymphoma

    PubMed Central

    2013-01-01

    Background The chemokine receptor CCR7 mediates lymphoid dissemination of many cancers, including lymphomas and epithelial carcinomas, thus representing an attractive therapeutic target. Previous results have highlighted the potential of the anti-CCR7 monoclonal antibodies to inhibit migration in transwell assays. The present study aimed to evaluate the in vivo therapeutic efficacy of an anti-CCR7 antibody in a xenografted human mantle cell lymphoma model. Methods NOD/SCID mice were either subcutaneously or intravenously inoculated with Granta-519 cells, a human cell line derived from a leukemic mantle cell lymphoma. The anti-CCR7 mAb treatment (3 × 200 μg) was started on day 2 or 7 to target lymphoma cells in either a peri-implantation or a post-implantation stage, respectively. Results The anti-CCR7 therapy significantly delayed the tumor appearance and also reduced the volumes of tumors in the subcutaneous model. Moreover, an increased number of apoptotic tumor cells was detected in mice treated with the anti-CCR7 mAb compared to the untreated animals. In addition, significantly reduced number of Granta-519 cells migrated from subcutaneous tumors to distant lymphoid organs, such as bone marrow and spleen in the anti-CCR7 treated mice. In the intravenous models, the anti-CCR7 mAb drastically increased survival of the mice. Accordingly, dissemination and infiltration of tumor cells in lymphoid and non-lymphoid organs, including lungs and central nervous system, was almost abrogated. Conclusions The anti-CCR7 mAb exerts a potent anti-tumor activity and might represent an interesting therapeutic alternative to conventional therapies. PMID:24305507

  8. Spatio-Temporal Variation in Effects of Upwelling on the Fatty Acid Composition of Benthic Filter Feeders in the Southern Benguela Ecosystem: Not All Upwelling Is Equal.

    PubMed

    Puccinelli, Eleonora; McQuaid, Christopher David; Noyon, Margaux

    2016-01-01

    Variability in mesoscale nearshore oceanographic conditions plays an important role in the distribution of primary production and food availability for intertidal consumers. Advection of nutrient rich waters by upwelling usually allows the proliferation of diatoms, later replaced by dinoflagellates. We examined upwelling effects on the fatty acid (FA) signature of a benthic intertidal filter feeder to identify its response to pulsed variability in food availability. The study took place in two contrasting seasons and at two upwelling and two non-upwelling sites interspersed within the southern Benguela upwelling system of South Africa. We investigated the FA composition of the adductor muscles and gonads of the mussel Mytilus galloprovincialis to assess how FA are apportioned to the different tissues and whether this changes between upwelling and non-upwelling conditions. In situ temperature loggers used to identify upwelling conditions at the four sites indicated that such events occurred only at the upwelling centres and only in summer. Tissues differed strongly, with gonads presenting a higher proportion of essential FAs. This could reflect the faster turnover rate of gonad tissue or preferential retention of specific FA for reproductive purposes. FA composition did not vary as a direct function of upwelling, but there were strong dissimilarities among sites. Upwelling influenced mussel diets at one upwelling site while at the other, the expected signature of upwelling was displaced downstream of the core of upwelling. Condition Index (CI) and Gonad Index (GI) differed among sites and were not influenced by upwelling, with GI being comparable among sites. In addition, FA proportions were consistent among sites, indicating similar food quality and quantity over time and under upwelling and non-upwelling conditions. This suggests that the influence of upwelling on the west coast of South Africa is pervasive and diffuse, rather than discrete; while nearshore

  9. Spatio-Temporal Variation in Effects of Upwelling on the Fatty Acid Composition of Benthic Filter Feeders in the Southern Benguela Ecosystem: Not All Upwelling Is Equal

    PubMed Central

    McQuaid, Christopher David; Noyon, Margaux

    2016-01-01

    Variability in mesoscale nearshore oceanographic conditions plays an important role in the distribution of primary production and food availability for intertidal consumers. Advection of nutrient rich waters by upwelling usually allows the proliferation of diatoms, later replaced by dinoflagellates. We examined upwelling effects on the fatty acid (FA) signature of a benthic intertidal filter feeder to identify its response to pulsed variability in food availability. The study took place in two contrasting seasons and at two upwelling and two non-upwelling sites interspersed within the southern Benguela upwelling system of South Africa. We investigated the FA composition of the adductor muscles and gonads of the mussel Mytilus galloprovincialis to assess how FA are apportioned to the different tissues and whether this changes between upwelling and non-upwelling conditions. In situ temperature loggers used to identify upwelling conditions at the four sites indicated that such events occurred only at the upwelling centres and only in summer. Tissues differed strongly, with gonads presenting a higher proportion of essential FAs. This could reflect the faster turnover rate of gonad tissue or preferential retention of specific FA for reproductive purposes. FA composition did not vary as a direct function of upwelling, but there were strong dissimilarities among sites. Upwelling influenced mussel diets at one upwelling site while at the other, the expected signature of upwelling was displaced downstream of the core of upwelling. Condition Index (CI) and Gonad Index (GI) differed among sites and were not influenced by upwelling, with GI being comparable among sites. In addition, FA proportions were consistent among sites, indicating similar food quality and quantity over time and under upwelling and non-upwelling conditions. This suggests that the influence of upwelling on the west coast of South Africa is pervasive and diffuse, rather than discrete; while nearshore

  10. Evolution of the interior of Mercury influenced by coupled magmatism-mantle convection system and heat flux from the core

    NASA Astrophysics Data System (ADS)

    Ogawa, Masaki

    2016-02-01

    To discuss mantle evolution in Mercury, I present two-dimensional numerical models of magmatism in a convecting mantle. Thermal, compositional, and magmatic buoyancy drives convection of temperature-dependent viscosity fluid in a rectangular box placed on the top of the core that is modeled as a heat bath of uniform temperature. Magmatism occurs as a permeable flow of basaltic magma generated by decompression melting through a matrix. Widespread magmatism caused by high initial temperature of the mantle and the core makes the mantle compositionally stratified within the first several hundred million years of the 4.5 Gyr calculated history. The stratified structure persists for 4.5 Gyr, when the reference mantle viscosity at 1573 K is higher than around 1020 Pa s. The planet thermally contracts by an amount comparable to the one suggested for Mercury over the past 4 Gyr. Mantle upwelling, however, generates magma only for the first 0.1-0.3 Gyr. At lower mantle viscosity, in contrast, a positive feedback between magmatism and mantle upwelling operates to cause episodic magmatism that continues for the first 0.3-0.8 Gyr. Convective current stirs the mantle and eventually dissolves its stratified structure to enhance heat flow from the core and temporarily resurrect magmatism depending on the core size. These models, however, predict larger contraction of the planet. Coupling between magmatism and mantle convection plays key roles in mantle evolution, and the difficulty in numerically reproducing the history of magmatism of Mercury without causing too large radial contraction of the planet warrants further exploration of this coupling.

  11. Enhanced convection and fast plumes in the lower mantle induced by the spin transition in ferropericlase.

    SciTech Connect

    Bower, D. J.; Gurnis, M.; Jackson, J. M.; Sturhahn, W.; X-Ray Science Division; California Inst. of Tech.

    2009-05-28

    Using a numerical model we explore the consequences of the intrinsic density change ({Delta}{rho}/{rho} {approx} 2-4%) caused by the Fe{sup 2+} spin transition in ferropericlase on the style and vigor of mantle convection. The effective Clapeyron slope of the transition from high to low spin is strongly positive in pressure-temperature space and broadens with high temperature. This introduces a net spin-state driving density difference for both upwellings and downwellings. In 2-D cylindrical geometry spin-buoyancy dominantly enhances the positive thermal buoyancy of plumes. Although the additional buoyancy does not fundamentally alter large-scale dynamics, the Nusselt number increases by 5-10%, and vertical velocities by 10-40% in the lower mantle. Advective heat transport is more effective and temperatures in the core-mantle boundary region are reduced by up to 12%. Our findings are relevant to the stability of lowermost mantle structures.

  12. Coastal Upwelling Drives Intertidal Assemblage Structure and Trophic Ecology

    PubMed Central

    Reddin, Carl J.; Docmac, Felipe; O’Connor, Nessa E.; Bothwell, John H.; Harrod, Chris

    2015-01-01

    Similar environmental driving forces can produce similarity among geographically distant ecosystems. Coastal oceanic upwelling, for example, has been associated with elevated biomass and abundance patterns of certain functional groups, e.g., corticated macroalgae. In the upwelling system of Northern Chile, we examined measures of intertidal macrobenthic composition, structure and trophic ecology across eighteen shores varying in their proximity to two coastal upwelling centres, in a hierarchical sampling design (spatial scales of >1 and >10 km). The influence of coastal upwelling on intertidal communities was confirmed by the stable isotope values (δ13C and δ15N) of consumers, including a dominant suspension feeder, grazers, and their putative resources of POM, epilithic biofilm, and macroalgae. We highlight the utility of muscle δ15N from the suspension feeding mussel, Perumytilus purpuratus, as a proxy for upwelling, supported by satellite data and previous studies. Where possible, we used corrections for broader-scale trends, spatial autocorrelation, ontogenetic dietary shifts and spatial baseline isotopic variation prior to analysis. Our results showed macroalgal assemblage composition, and benthic consumer assemblage structure, varied significantly with the intertidal influence of coastal upwelling, especially contrasting bays and coastal headlands. Coastal topography also separated differences in consumer resource use. This suggested that coastal upwelling, itself driven by coastline topography, influences intertidal communities by advecting nearshore phytoplankton populations offshore and cooling coastal water temperatures. We recommend the isotopic values of benthic organisms, specifically long-lived suspension feeders, as in situ alternatives to offshore measurements of upwelling influence. PMID:26214806

  13. Intraplate volcanism at the edges of the Colorado Plateau sustained by shear-driven upwelling

    NASA Astrophysics Data System (ADS)

    Ballmer, M. D.; Conrad, C. P.; Smith, E. I.; Johnsen, R. L.

    2012-12-01

    While most volcanism on Earth occurs at plate boundaries, the study of intraplate basaltic volcanism provides an opportunity to examine the make-up and dynamics of the mantle. In continental settings, a range of mechanisms may sustain mantle decompression and hence feed intraplate volcanism. These include mantle plumes, fertile melting anomalies, self-sustaining buoyant decompression melting, lithospheric dripping, and edge-driven small-scale convection. Recent studies showing that basaltic continental volcanism occurs preferentially where asthenospheric shear is most vigorous (e.g., beneath the western US) indicate that shear-driven upwelling (SDU) may induce intraplate volcanism. SDU produces decompression melting without mantle density heterogeneity: viscosity heterogeneity and/or sublithospheric topography can divert a portion of asthenospheric shear into vertical flow. In particular, asthenospheric shear becomes concentrated within a low-viscosity pocket, and this amplified flow is accommodated by up- and down-welling close to the edges of the anomaly. Vertical flow is also induced if the asthenosphere is sheared across a step in lithospheric thickness (such as beneath the edge of the Colorado Plateau), and becomes invigorated if a low-viscosity pocket is entrained in such a flow. The induced upwelling may indeed be sufficient to sustain significant decompression melting, particularly for low-viscosity pockets caused by higher water contents or temperatures. Seismic observations indicate that sublithospheric topography and heterogeneity in mantle viscosity are common beneath continents in general and the western US in particular. We use three-dimensional numerical models to explore SDU in low-viscosity pockets that interact with sublithospheric topography beneath the Colorado Plateau. We find that the tips of warm and damp and/or geochemically enriched pockets undergo SDU-driven decompression melting while travelling through the asthenosphere. Melting is

  14. Reactivation and mantle dynamics of North China Craton: insight from P-wave anisotropy tomography

    NASA Astrophysics Data System (ADS)

    Tian, You; Zhao, Dapeng

    2013-12-01

    We determined the first 3-D P-wave anisotropic tomography beneath the North China Craton (NCC) using a large number of high-quality arrival-time data from local earthquakes and teleseismic events, which reveals depth-dependent azimuthal anisotropy in the crust and upper mantle down to 600 km depth. In the NCC western block, the fast velocity direction (FVD) varies from east-west in the southern part to northeast-southwest in the northern part, which may reflect either the interaction between the Yangtze block and NCC or fossil lithospheric fabrics in the craton. Under the NCC eastern block, a uniform northwest-southeast FVD is revealed in the lower part of the upper mantle (300-410 km depths) and the mantle transition zone (410-660 km depths), which may reflect horizontal and upwelling flows in the big mantle wedge (BMW) above the stagnant Pacific slab in the mantle transition zone. The NCC central block exhibits a northeast-southwest FVD, consistent with the surface tectonic orientation there, suggesting that the cold and thick (>300 km) cratonic root of the NCC western block may obstruct the northwest-southeast trending mantle flow induced by the Pacific Plate subduction, resulting in a northeast-southwest trending mantle flow under the central block. Our present results indicate that the corner flow in the BMW associated with the deep subduction of the Pacific Plate is the main cause of NCC reactivation and mantle dynamics under East China.

  15. Thermal state of northwest Kyushu mantle suggested by the petrochemistry of the Tara-dake basalts

    NASA Astrophysics Data System (ADS)

    Higo, Tomohiko; Mashima, Hidehisa

    2004-02-01

    Temperatures of northwest Kyushu mantle are estimated using petrochemical data of the relatively primitive Tara-dake basalts erupted at around 1 Ma. Model primitive melt compositions estimated by the addition of equilibrated olivines to bulk compositions indicate that melting temperatures range from 1230 to 1300°C at around 1 GPa. Moderately high melting temperatures of the Tara-dake basalts indicate that mantle upwelling in NW Kyushu is caused not by thermal plumes but by the convection at the boundary between the continent and the ocean.

  16. Effects of depth-dependent thermal expansivity on mantle circulations and lateral thermal anomalies

    NASA Technical Reports Server (NTRS)

    Hansen, Ulrich; Yuen, David A.; Kroening, Sherri E.

    1991-01-01

    The influences of depth-dependent thermal expansivity on the structure of Newtonian thermal convection and lateral thermal anomalies are studied. In an aspect-ratio ten box the effects of the depth-dependent expansivity are to produce large aspect-ratio cells with a few relatively stationary upwellings. The lateral thermal anomalies in the lower mantle are greatly diminished by depth-dependent expansivity. This together with a decrease in the temperature derivative of seismic velocities in the lower mantle would support the low level of lateral heterogeneities found in recent tomographic studies.

  17. Origin of the DUPAL anomaly in mantle xenoliths of Patagonia (Argentina) and geodynamic consequences

    NASA Astrophysics Data System (ADS)

    Mazzucchelli, Maurizio; Cipriani, Anna; Hémond, Christophe; Zanetti, Alberto; Bertotto, Gustavo Walter; Cingolani, Carlos Alberto

    2016-04-01

    The sub-continental lithospheric mantle of South America has been known for some time to carry the DUPAL isotope anomaly as seen in volcanics from the Paraná volcanic province. However, this has not allowed discriminating whether the DUPAL anomaly is a primary feature of the mantle source or acquired during the upwelling and emplacement of the primary magmas. We discovered mantle xenoliths from the Tres Lagos location in Patagonia that carry evidence of percolation by metasomatic melts that imparted the DUPAL isotope anomaly signature. We discuss a model that requires four isotope components (LCC, EM2, HIMU and DM) to account for the Sr, Nd and Pb isotope variability of our samples. We propose that upwelling of hot astenosphere during the Miocene could have triggered the melting of the LCC and EM2 components carrying the DUPAL anomaly, previously entrained in the subcontinental mantle by subduction. These ascending melts would have then metasomatised the local SCLM characterised by DMM and HIMU geochemical affinity generating the hybrid DUPAL-bearing mantle sampled by the Tres Lagos xenoliths.

  18. Mantle Dynamics Studied with Parameterized Prescription From Mineral Physics Database

    NASA Astrophysics Data System (ADS)

    Tosi, N.; Yuen, D.; Wentzcovich, R.; deKoker, N.

    2012-04-01

    The incorporation of important thermodynamic and transport properties into mantle convection models has taken a long time for the community to appreciate, even though it was first spurred by the high-pressure experimental work at Mainz a quarter of a century ago and the experimental work at Bayreuth and St. Louis. The two quantities whose effects have yet to be widely appreciated are thermal expansivity α and thermal conductivity k, which are shown to impact mantle dynamics and thermal history in more ways than geoscientists have previously imagined. We have constructed simple parameterization schemes, which are cast analytically for describing α and k over a wide range of temperatures and pressures corresponding to the Earth's mantle. This approach employs the thermodynamics data set drawn from the VLAB at the University of Minnesota based on first-principles density functional theory [1] and also recent laboratory data from the Bayreuth group [2]. Using analytical formulae to determine α and k increases the computational speed of the convection code with respect to employing pre-calculated look-up tables and allows us to sweep out a wide parameter space. Our results, which also incorporate temperature and pressure dependent viscosity show the following prominent features: 1) The temperature-dependence of α is important in the upper mantle. It enhances strongly the rising hot plumes and inhibits the cold downwellings, thus making subduction more difficult for young slabs. 2) The pressure dependence of α is dominant in the lower mantle. It focuses upwellings and speeds them up during their upward rise. 3) The temperature-dependence of the thermal conductivity helps to homogenize the lateral thermal anomalies in cold downwellings and helps to maintain the heat in the upwellings, thus, in concert with alpha, helps to encourage fast hot plumes. 4) The lattice thermal conductivity of post-perovskite plays an important role in heat-transfer in the lower mantle and

  19. Anomalous sulphur isotopes in plume lavas reveal deep mantle storage of Archaean crust.

    PubMed

    Cabral, Rita A; Jackson, Matthew G; Rose-Koga, Estelle F; Koga, Kenneth T; Whitehouse, Martin J; Antonelli, Michael A; Farquhar, James; Day, James M D; Hauri, Erik H

    2013-04-25

    Basaltic lavas erupted at some oceanic intraplate hotspot volcanoes are thought to sample ancient subducted crustal materials. However, the residence time of these subducted materials in the mantle is uncertain and model-dependent, and compelling evidence for their return to the surface in regions of mantle upwelling beneath hotspots is lacking. Here we report anomalous sulphur isotope signatures indicating mass-independent fractionation (MIF) in olivine-hosted sulphides from 20-million-year-old ocean island basalts from Mangaia, Cook Islands (Polynesia), which have been suggested to sample recycled oceanic crust. Terrestrial MIF sulphur isotope signatures (in which the amount of fractionation does not scale in proportion with the difference in the masses of the isotopes) were generated exclusively through atmospheric photochemical reactions until about 2.45 billion years ago. Therefore, the discovery of MIF sulphur in these young plume lavas suggests that sulphur--probably derived from hydrothermally altered oceanic crust--was subducted into the mantle before 2.45 billion years ago and recycled into the mantle source of Mangaia lavas. These new data provide evidence for ancient materials, with negative Δ(33)S values, in the mantle source for Mangaia lavas. Our data also complement evidence for recycling of the sulphur content of ancient sedimentary materials to the subcontinental lithospheric mantle that has been identified in diamond-hosted sulphide inclusions. This Archaean age for recycled oceanic crust also provides key constraints on the length of time that subducted crustal material can survive in the mantle, and on the timescales of mantle convection from subduction to upwelling beneath hotspots. PMID:23619695

  20. Jurassic-Cretaceous paleogeography, paleoclimate and upwelling of the northern margin of Tethys

    SciTech Connect

    Golonka, J.; Krobicki, M.

    1995-08-01

    The Jurassic and Cretaceous global paleogeographic reconstructions illustrate the changing configuration of mountains, land, shallow seas and deep ocean basins. Active plate boundaries, such as spreading centers and subduction zones, are also shown. The Pliensbachian, Toarcian, Bathonian, Oxfordian-Kimmeridgian, Tithonian-Berriasian, Valanginian, Albian, Turonian and Maastrichtian maps were generated The outlines of paleogeography are used as input for paleoclimatic modeling. The PALEOCLIMATE program models global atmospheric pressure, derive paleo-wind directions and estimate the likelihood of coastal upwelling. The program is based on the paleoclimatic methods first developed by Judith Parrish, adopted by C. R. Scotese and modified by M. I. Ross. The maps depict air pressure, wind directions, humid zones and areas favorable for upwelling conditions plotted on the paleogeographic background. Paleoclimate modeling suggests that prevailing Jurassic-Cretaceous wind directions in the northern Tethys area were from north-northeast. These winds were parallel to the axis of Czorsztyn ridge. The ridge was uplifted between Magura and Pieniny basins as the result of extension during Jurassic supercontinent breakup. The upwelling may have been induced at the southeastern margin of the ridge. The model is consistent with rock records, especially from the upper part of ammonitico rosso type Czorsztyn formation. Mass occurrence of Tithonian and Berriasian brachiopods was probably controlled by upwelling-induced trophic relationships which is resulted in the intense growth of benthic organisms on the ridge. This is additionally supported by the presence of phosphorites at localities which corresponded to the continental shelf/slope transition.

  1. The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

    NASA Astrophysics Data System (ADS)

    Clark, Darren R.; Widdicombe, Claire E.; Rees, Andrew P.; Woodward, E. Malcolm S.

    2016-05-01

    The Lagrangian progression of a biological community was followed in a filament of the Mauritanian upwelling system, north-west Africa, during offshore advection. The inert dual tracers sulfur hexafluoride and helium-3 labelled a freshly upwelled patch of water that was mapped for 8 days. Changes in biological, physical, and chemical characteristics were measured, including phytoplankton productivity, nitrogen assimilation, and regeneration. Freshly upwelled water contained high nutrient concentrations but was depleted in N compared to Redfield stoichiometry. The highest rate of primary productivity was measured on the continental shelf, associated with high rates of nitrogen assimilation and a phytoplankton community dominated by diatoms and flagellates. Indicators of phytoplankton abundance and activity decreased as the labelled water mass transited the continental shelf slope into deeper water, possibly linked to the mixed layer depth exceeding the light penetration depth. By the end of the study, the primary productivity rate decreased and was associated with lower rates of nitrogen assimilation and lower nutrient concentrations. Nitrogen regeneration and assimilation took place simultaneously. Results highlighted the importance of regenerated NH4+ in sustaining phytoplankton productivity and indicate that the upwelled NO3- pool contained an increasing fraction of regenerated NO3- as it advected offshore. By calculating this fraction and incorporating it into an f ratio formulation, we estimated that of the 12.38 Tg C of annual regional production, 4.73 Tg C was exportable.

  2. Crustal and uppermost mantle structure variation beneath La Réunion hotspot track

    NASA Astrophysics Data System (ADS)

    Fontaine, Fabrice R.; Barruol, Guilhem; Tkalčić, Hrvoje; Wölbern, Ingo; Rümpker, Georg; Bodin, Thomas; Haugmard, Méric

    2015-10-01

    The Piton de la Fournaise basaltic volcano, on La Réunion Island in the western Indian Ocean, is one of the most active volcanoes in the world. This volcano is classically considered as the surface expression of an upwelling mantle plume and its activity is continuously monitored, providing detailed information on its superficial dynamics and on the edifice structure. Deeper crustal and upper mantle structure under La Réunion Island is surprisingly poorly constrained, motivating this study. We used receiver function techniques to determine a shear wave velocity profile through the crust and uppermost mantle beneath La Réunion, but also at other seismic stations located on the hotspot track, to investigate the plume and lithosphere interaction and its evolution through time. Receiver functions (RFs) were computed at permanent broad-band seismic stations from the GEOSCOPE network (on La Réunion and Rodrigues), at IRIS stations MRIV and DGAR installed on Mauritius and Diego Garcia islands, and at the GEOFON stations KAAM and HMDM on the Maldives. We performed non-linear inversions of RFs through modelling of P-to-S conversions at various crustal and upper mantle interfaces. Joint inversion of RF and surface wave dispersion data suggests a much deeper Mohorovičić discontinuity (Moho) beneath Mauritius (˜21 km) compared to La Réunion (˜12 km). A magmatic underplated body may be present under La Réunion as a thin layer (≤3 km thick), as suggested by a previous seismic refraction study, and as a much thicker layer beneath other stations located on the hotspot track, suggesting that underplating is an important process resulting from the plume-lithosphere interaction. We find evidence for a strikingly low velocity layer starting at about 33 km depth beneath La Réunion that we interpret as a zone of partial melt beneath the active volcano. We finally observe low velocities below 70 km beneath La Réunion and below 50 km beneath Mauritius that could represent

  3. Upwelling Rates and Vertical Diffusivities Determined During the 2013 US GEOTRACES Eastern Tropical Pacific Zonal Transect: Results from 7Be Analysis

    NASA Astrophysics Data System (ADS)

    Kadko, D. C.

    2014-12-01

    Upwelling is an important physical process affecting biogeochemical cycling within the global ocean. Direct measurements are difficult because of the relatively small velocities involved, and must therefore be inferred by indirect methods such as those provided by tracer observations. Measurements of the cosmogenic radioisotope 7Be (half-life = 53.3 d) were used to derive upwelling rates and upper thermocline vertical diffusivities during the 2013 US GEOTRACES Eastern Tropical Pacific Zonal Transect. In the eastern, upwelling zone of this transect, the 7Be activity in the mixed layer varied between low values of 63 dpm/m3 in areas with the coldest sea surface temperatures (SSTs) to values of 190 dpm/m3 associated with warm SSTs. The 7Be inventory in the coldest water was only 5,150 dpm/m2 while that in the warmer water was 19,000 dpm/m2. The decrease in mixed layer 7Be with decrease in temperature occurs as 7Be ''dead'', cold water is upwelled from below. The deficit of the 7Be inventory relative to the non-upwelling stations provides a measure of the upwelling rate. For the eastern-most station with the lowest SST (17.6 deg C) an upwelling rate of 2.56 m/d was derived. Towards the west, as SST increased, derived upwelling rates decreased. At SST of 20.9 deg C, upwelling was zero. With knowledge of upwelling rates, 7Be and temperature profiles were used to constrain vertical diffusivity within the upper thermocline. Diffusivities derived from 7Be profiles were approximately twice that derived from temperature, likely reflecting the difference in vertical resolution of these measurements. Diffusivities derived from temperature were on the order of 1-4 x 10-4 m2/s. These parameters will be applied to profiles of nutrients and trace elements to derive fluxes of these species into the mixed layer.

  4. Upper mantle structure of the Yellowstone hotspot from teleseismic body-wave velocity tomography and shear-wave anisotropy

    NASA Astrophysics Data System (ADS)

    Waite, Gregory Phillip

    The question of whether the Yellowstone hotspot volcanic system is the result of a mantle plume, or shallower convection processes, is addressed by examining the upper mantle seismic isotropic and anisotropic velocity structure with data from temporary and permanent seismographs. Key features of the system can be explained by the motion of the lithosphere over a stationary mantle plume: a series of progressively older calderas that track plate motion for the last 16 million years; a parabolic pattern of high topography, seismicity, and active faulting around the axis of the Snake River Plain (SRP---the hotspot track); and high 3He/4He ratios found at Yellowstone. Alternatively, models involving upper mantle processes may explain these observations. The VP and VS tomography reveals a strong low-velocity anomaly (up to -2.3% for VP and -5.5% for VS) from ˜50 to 200 km beneath the Yellowstone caldera and SRP. A weaker, smaller-volume anomaly (-1.0% VP and -2.5% VS) is imaged from about 250 to at least 350 km depth at a position ˜100 km WNW of the caldera. A prominent high-velocity anomaly (1.2% VP and 1.9% VS) is located at ˜50 to 200 km depth to the SE of Yellowstone. The fast polarization directions measured from splitting of teleseismic shear-wave core phases are generally aligned parallel to the direction of plate motion. This suggests asthenosphere flow is primarily due to shear of the lithosphere. There is little evidence for radial flow away from Yellowstone that is expected for buoyant plume material flattening against a plate. The buoyancy flux of a Yellowstone plume, calculated from the excess temperature and radius inferred from the tomography, is an order of magnitude lower than previous estimates for Yellowstone. The tomography and anisotropy results are inconsistent with a cylindrical, vertical mantle plume. However, the seismic results could be interpreted as a weak plume dipping to the WNW. This upwelling may work in conjunction with lithosphere

  5. Mantle seismic structure beneath the MELT region of the east pacific rise from P and S wave tomography

    PubMed

    Toomey; Wilcock; Solomon; Hammond; Orcutt

    1998-05-22

    Relative travel time delays of teleseismic P and S waves, recorded during the Mantle Electromagnetic and Tomography (MELT) Experiment, have been inverted tomographically for upper-mantle structure beneath the southern East Pacific Rise. A broad zone of low seismic velocities extends beneath the rise to depths of about 200 kilometers and is centered to the west of the spreading center. The magnitudes of the P and S wave anomalies require the presence of retained mantle melt; the melt fraction near the rise exceeds the fraction 300 kilometers off axis by as little as 1%. Seismic anisotropy, induced by mantle flow, is evident in the P wave delays at near-vertical incidence and is consistent with a half-width of mantle upwelling of about 100 km.

  6. The Multifarious Martian Mantle

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2004-06-01

    Pieces of relatively young lava flows from Mars (all less than 600 million years old) preserve a record of the planet's initial segregation into core, mantle, and crust. Research by Lars Borg (University of New Mexico), his colleague David Draper, and his former colleagues at the Johnson Space Center, Chris Herd (University of Alberta, Canada), and Cyrena Goodrich (formerly at the University of Hawaii and now at Kingsborough Community College in Brooklyn, New York) shows that there are distinctive regions in the interior of Mars. These regions, or reservoirs as cosmochemists like to call them, formed early, about 4.5 billion years ago, and come in two flavors. One, dubbed "enriched," contains high concentrations of trace elements, has a high ratio of lanthanum to ytterbium (La/Yb), high strontium-87 to strontium-86 ratio, a low ratio of neodynmium-143 to neodynmium-144, and is relatively oxidized. The other, dubbed "depleted," contains lower levels of trace elements, has lower La/Yb and strontium-87 to strontium-86, higher neodynmium-143 to neodynmium-144, and is relatively reduced (much less oxidizing than the enriched reservoir). There are mixtures in between these extremes. The reservoirs may have formed in a global magma ocean. Their preservation for 4.5 billion years indicates that Mars, in contrast to Earth, did not have active plate tectonics since the reservoirs formed.

  7. Scales of mantle heterogeneity

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    A long-standing question in mantle dynamics concerns the scale of heterogeneity in the mantle. Mantle convection tends to both destroy (through stirring) and create (through melt extraction and subduction) heterogeneity in bulk and trace element composition. Over time, these competing processes create variations in geochemical composition along mid-oceanic ridges and among oceanic islands, spanning a range of scales from extremely long wavelength (for example, the DUPAL anomaly) to very small scale (for example, variations amongst melt inclusions). While geochemical data and seismic observations can be used to constrain the length scales of mantle heterogeneity, dynamical mixing calculations can illustrate the processes and timescales involved in stirring and mixing. At the Summer 2004 CIDER workshop on Relating Geochemical and Seismological Heterogeneity in the Earth's Mantle, an interdisciplinary group evaluated scales of heterogeneity in the Earth's mantle using a combined analysis of geochemical data, seismological data and results of numerical models of mixing. We mined the PetDB database for isotopic data from glass and whole rock analyses for the Mid-Atlantic Ridge (MAR) and the East Pacific Rise (EPR), projecting them along the ridge length. We examined Sr isotope variability along the East Pacific rise by looking at the difference in Sr ratio between adjacent samples as a function of distance between the samples. The East Pacific Rise exhibits an overall bowl shape of normal MORB characteristics, with higher values in the higher latitudes (there is, however, an unfortunate gap in sampling, roughly 2000 km long). These background characteristics are punctuated with spikes in values at various locations, some, but not all of which are associated with off-axis volcanism. A Lomb-Scargle periodogram for unevenly spaced data was utilized to construct a power spectrum of the scale lengths of heterogeneity along both ridges. Using the same isotopic systems (Sr, Nd

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

    NASA Astrophysics Data System (ADS)

    Sigloch, K.; Barruol, G.

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Sigloch, Karin; Barruol, Guilhem

    2013-04-01

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

  10. Mantle plume interaction with an endothermic phase change

    NASA Technical Reports Server (NTRS)

    Schubert, Gerald; Anderson, Charles; Goldman, Peggy

    1995-01-01

    High spatial resolution numerical simulations of mantle plumes impinging from below on the endothermic phase change at 660-km depth are used to investigate the effects of latent heat release on the plume-phase change interaction. Both axisymmetric and planar upflows are considered, and the strong temperature dependence of mantle viscosity is taken into account. For plume strengths considered, a Clapeyron slope of -4 MPa/K prevents plume penetration of the phase change. Plumes readily penetrate the phase change for a Clapeyron slope of -2 MPa/K and arrive in the upper mantle considerably hotter than if they had not traversed the phase change. For the same amount of thermal drive, i.e., the same excess basal temperature, axisymmetric plumes are hotter upon reaching the upper mantle than are planar upwellings. Heating of plumes by their passage through the spinel-perovskite endothermic phase change can have important consequences for the ability of the plume to thermally thin the lithosphere and cause melting and volcanism.

  11. Temperature fluctuation of the Iceland mantle plume through time

    NASA Astrophysics Data System (ADS)

    Spice, Holly E.; Fitton, J. Godfrey; Kirstein, Linda A.

    2016-02-01

    The newly developed Al-in-olivine geothermometer was used to find the olivine-Cr-spinel crystallization temperatures of a suite of picrites spanning the spatial and temporal extent of the North Atlantic Igneous Province (NAIP), which is widely considered to be the result of a deep-seated mantle plume. Our data confirm that start-up plumes are associated with a pulse of anomalously hot mantle over a large spatial area before becoming focused into a narrow upwelling. We find that the thermal anomaly on both sides of the province at Baffin Island/West Greenland and the British Isles at ˜61 Ma across an area ˜2000 km in diameter was uniform, with Al-in-olivine temperatures up to ˜300°C above that of average mid-ocean ridge basalt (MORB) primitive magma. Furthermore, by combining our results with geochemical data and existing geophysical and bathymetric observations, we present compelling evidence for long-term (>107 year) fluctuations in the temperature of the Iceland mantle plume. We show that the plume temperature fell from its initial high value during the start-up phase to a minimum at about 35 Ma, and that the mantle temperature beneath Iceland is currently increasing.

  12. The Role of Subduction and Mantle Plumes in the Supercontinent Cycle

    NASA Astrophysics Data System (ADS)

    Heron, P. J.; Lowman, J. P.; Stein, C.

    2014-12-01

    Several processes unfold during the supercontinent cycle, more than one of which might result in an elevation in subcontinental mantle temperatures through the generation of mantle plumes. Geodynamic modeling motivated by paleogeographic plate reconstructions has indicated that subcontinental mantle upwellings appear below large continents that are extensively ringed by subduction zones. Moreover, several numerical simulations of supercontinent formation and dispersal show that the genesis of subcontinental plumes follows the formation of subduction zones on the edges of the supercontinent, rather than resulting from continental thermal insulation. However, the influence of the location of mantle downwellings on the position of subcontinental plumes has received little attention. Using 2D and 3D numerical mantle convection models, featuring geotherm- and pressure- dependent viscosity profiles with thermally and mechanically distinct oceanic and continental plates, we examine the evolution of mantle dynamics after continental accretion at a subduction zone (as occurred during the formation of Pangea). In simulations of vigorous mantle convection, we consider a range of supercontinent areas and change the upper and lower mantle viscosity contrast to determine their relation to plume formation. The results presented show that the formation of subduction zones at the margins of a supercontinent has a profound effect on mantle dynamics, and may help to explain how the sites of previous (and future) large igneous provinces were (or will be) determined. Subcontinental plume locations for all viscosity profiles show varying degrees of dependence on the location of continental margin subduction post-supercontinent formation. Furthermore, we find that changing the viscosity structure for mantle convection simulations (with similar surface heat flux) can determine the position (and number) of subcontinental plumes penetrating the upper mantle post-supercontinent formation.

  13. Full seismic waveform inversion of the African crust and Mantle - Initial Results

    NASA Astrophysics Data System (ADS)

    Afanasiev, Michael; Ermert, Laura; Staring, Myrna; Trampert, Jeannot; Fichtner, Andreas

    2016-04-01

    We report on the progress of a continental-scale full-waveform inversion (FWI) of Africa. From a geodynamic perspective, Africa presents an especially interesting case. This interest stems from the presence of several anomalous features such as a triple junction in the Afar region, a broad region of high topography to the south, and several smaller surface expressions such as the Cameroon Volcanic Line and Congo Basin. The mechanisms behind these anomalies are not fully clear, and debate on their origin spans causative mechanisms from isostatic forcing, to the influence of localized asthenospheric upwelling, to the presence of deep mantle plumes. As well, the connection of these features to the African LLSVP is uncertain. Tomographic images of Africa present unique challenges due to uneven station coverage: while tectonically active areas such as the Afar rift are well sampled, much of the continent exhibits a severe dearth of seismic stations. As well, while mostly surrounded by tectonically active spreading plate boundaries (a fact which contributes to the difficulties in explaining the South's high topography), sizeable seismic events (M > 5) in the continent's interior are relatively rare. To deal with these issues, we present a combined earthquake and ambient noise full-waveform inversion of Africa. The noise component serves to boost near-surface sensitivity, and aids in mitigating issues related to the sparse source / station coverage. The earthquake component, which includes local and teleseismic sources, aims to better resolve deeper structure. This component also has the added benefit of being especially useful in the search for mantle plumes: synthetic tests have shown that the subtle scattering of elastic waves off mantle plumes makes the plumes an ideal target for FWI [1]. We hope that this new model presents a fresh high-resolution image of sub-African geodynamic structure, and helps advance the debate regarding the causative mechanisms of its surface

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  15. Upwelling: a unit of disturbance in equatorial spread F

    NASA Astrophysics Data System (ADS)

    Tsunoda, Roland T.

    2015-12-01

    Plasma structure in the nighttime equatorial F layer, often referred to as equatorial spread F (ESF), is not uniformly distributed, either in time or in space. Observations indicate that ESF in the bottomside F layer takes the form of patches; plasma structure within the F layer takes the form of localized plasma depletions, called equatorial plasma bubbles (EPBs), which tend to occur in clusters. Another observed feature is an upwelling, which has been described as a localized, upward modulation of isodensity contours in the bottomside F layer. Interestingly, zonal widths of ESF patches, EPB clusters, and upwellings are similar. Moreover, all display an east-west asymmetry. The objective of this paper is to show, for the first time, that an ESF patch is the bottomside counterpart of an EPB cluster, and that both are products of the electrodynamical process that takes place within an upwelling. The process can be described as having three phases: (1) amplification of upwelling amplitude during the post-sunset rise of the F layer, (2) launching of the first EPB of the evening, from crest of the upwelling, and (3) structuring of plasma within the upwelling. Hence, an upwelling, whose presence is responsible for the formation of ESF patches and EPB clusters, can be envisioned as a unit of disturbance that occurs in the nighttime equatorial ionosphere.

  16. Retention controls on-shelf hypoxia in coastal upwelling systems

    NASA Astrophysics Data System (ADS)

    Harrison, C. S.; Long, M. C.; Hales, B. R.; Siedlecki, S. A.; Samelson, R. M.

    2015-12-01

    A maximally simple, coupled physical-biogeochemical box model is used to examine interactions controlling seasonal hypoxia over the continental shelf in an idealized Eastern Boundary upwelling system (EBUS). On-shelf bottom oxygen drawdown is controlled by the balance between flushing with offshore source waters and the degree to which surface particulate organic carbon (POC) production and its subsequent sinking and respiration are retained over the shelf and focused on the bottom. In the model, POC production is controlled by wind-driven upwelling of a generic nutrient to the surface, balanced by respiration and sinking. The degree to which this production occurs over shelf is a balance between the net POC growth rate η, and the upwelling driven shelf flushing rate λ, equivalent to the Ekman upwelling index scaled by the shelf width and surface layer depth. Initial oxygen drawdown follows this exponential rate of surface POC accumulation over shelf (α=η-λ), and so is slower for rapid upwelling (large λ) or nutrient limited conditions (small η). Retention efficiency indicates that up to 40% or more of upwelled nutrients can be retained over the shelf and contribute to oxygen drawdown. Fluctuations in the amplitude of the upwelling forcing can systematically reduce the potential for oxygen depletion below these estimates, especially when surface sinking export is rapid or forcing is strong.

  17. Upwelling processes along a western boundary current in the Abrolhos-Campos region of Brazil

    NASA Astrophysics Data System (ADS)

    Aguiar, A. L.; Cirano, M.; Pereira, J.; Marta-Almeida, M.

    2014-08-01

    Upwelling events observed from the years 2003 to 2011 were analyzed. Our focus was on the Abrolhos-Campos region (ACR, 15°S-23°S), which is located along the Brazilian Margin and influenced by a western boundary current, the Brazil Current (BC). Satellite sea surface temperature, National Centers for Environmental Prediction (NCEP) and Global Forecast System (GFS) wind data were used to complement the results of a high-resolution regional oceanic model to investigate the occurrence of and the mechanisms responsible for intense upwelling events in this region. These events were more frequent from 20°S to 23°S. Over 90% of the identified upwelling events were influenced by favorable wind stress. Surface Ekman transport was found to be more important for the region from Prado (17°S) to Marataízes (21°S), whereas upward Ekman pumping played a more important role from 22°S to 23°S. Current-driven upwelling processes associated with the location of the BC as well as its velocity and meso-scale activity were also analyzed. The results showed that these mechanisms are highly influenced by the local topography. Topographic effects exerted via the acceleration of the BC are more obvious in the southern ACR, while in the Prado region, BC cyclonic meanders tend to be more relevant. Moreover, eddy-driven upwelling increases in the southward direction after the passage of the Vitória-Trindade Ridge (20°S), an important submarine chain, which acts to constrain and modulate the southward flow of the BC.

  18. Deep mantle subduction flux

    NASA Astrophysics Data System (ADS)

    Porter, Katherine A.; White, William M.

    2009-12-01

    We assess the flux of incompatible trace elements into the deep mantle in the Aleutian, Central America, Izu-Bonin, Kurile, Lesser Antilles, Mariana, Sunda, and Tonga subduction zones. We use a simple mass balance approach in which we assume that all of the material lost from the subducting crust and sediment (the "slab") is incorporated into the magmas erupted above the subduction zone, and we use these assumptions to calculate a residual slab composition. The calculated residual slabs are enriched in incompatible elements compared to mid-ocean ridge basalts and highly enriched compared to primitive or depleted mantle. Almost all of the subducted Nb, Ta, and intermediate and heavy rare earths survive into the deep mantle, as do most of the light rare earths. On average, 73% of Th and Pb, 74% of K, 79% of U, 80% of Rb, 80% of Sr, and 82% of Ba survive into the deep mantle. Pb/Ce ratios are systematically lower, and Nb/U ratios are systematically higher, in the deep mantle flux than they are in the flux of material into the trench. Nevertheless, most residual slabs have Pb/Ce and Nb/U ratios outside the typical mantle range. Changes to U/Pb and Th/U ratios tend to be small and are not systematic. Rb/Sr ratios significantly decrease in some subduction zones but increase in others. In contrast, Sm/Nd ratios increase by small but significant amounts in most arcs. Based on these results, we attempt to predict the Sr, Nd, and Pb composition of anciently recycled material now in the mantle. We find that such material would most resemble enriched mantle II-type oceanic island basalts (OIB). None of our calculated residual slabs would evolve to Sr-Nd-Pb isotopic compositions similar to either high 238U/204Pb or enriched mantle I. The range of Sr and Pb isotope ratios in anciently recycled material is similar to that seen in modern OIB, but Nd isotopic compositions do not range to ɛNd values as low as those in some modern OIB. Neither radiogenic nor unradiogenic Pb isotope

  19. Enhanced benthic response to upwelling of the Indonesian Throughflow onto the southern shelf of Timor-Leste, Timor Sea

    NASA Astrophysics Data System (ADS)

    Alongi, Daniel M.; Brinkman, Richard; Trott, Lindsay A.; Silva, Fernando; Pereira, Francisco; Wagey, Tonny

    2013-03-01

    Benthic microbial metabolism and bacterial diagenetic pathways were measured along the southern shelf of Timor-Leste during an upwelling event in the winter SE monsoon season. Vertical profiles of water properties and bottom water nutrient concentrations, and operational ocean modeling showed subsurface upwelling from the Indonesian Throughflow (ITF) along the southern shelf west of longitude 126°25'E and surface upwelling at the far eastern end of the shelf. Warm surface waters above the halocline had salinities of 33.6 to 33.9 overlying cooler ITF water with salinities of 34.4 to 34.6. Beneath the zone of subsurface upwelling and stratification, sediment chlorophyll a (range: 2.8-4.4 µg g-1) and phaeopigment (range: 4.5-7.0 µg g-1) concentrations were sufficient to fuel very rapid rates of benthic oxygen consumption (range: 89.9-142.3 mmol m-2 day-1) and dissolved inorganic carbon (DIC) release (range: 108.1-148.9 mmol m-2 day-1) across the sediment-water interface, and DIC (range: 94.7-142.5 mmol m-2 day-1) and NH4+ (range: 13.3-19.9 mmol m-2 day-1) production from incubated surface (0-10 cm) sediments. Molar ratios of DIC/NH4+ production were lower (range: 6.6-7.7) in fine-grained sediments under the subsurface upwelling regime than in sandy, possibly scoured sediments under surface upwelling (range: 11.9-21.2) where there was no evidence of benthic enrichment. It is proposed that subsurface upwelling along the widest portions of the shelf stimulates phytoplankton production, leading to deposition of fresh phytodetritus that is rapidly decomposed on the seafloor. These zones of high biological activity may attract and support large populations of pelagic fish and cetaceans that have been caught for centuries along the south coast.

  20. Contrasting crustal production and rapid mantle transitions beneath back-arc ridges.

    PubMed

    Dunn, Robert A; Martinez, Fernando

    2011-01-13

    The opening of back-arc basins behind subduction zones progresses from initial rifting near the volcanic arc to seafloor spreading. During this process, the spreading ridge and the volcanic arc separate and lavas erupted at the ridge are predicted to evolve away from being heavily subduction influenced (with high volatile contents derived from the subducting plate). Current models predict gradational, rather than abrupt, changes in the crust formed along the ridge as the inferred broad melting region beneath it migrates away from heavily subduction-influenced mantle. In contrast, here we show that across-strike and along-strike changes in crustal properties at the Eastern Lau spreading centre are large and abrupt, implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes. With incremental separation of the ridge axis from the volcanic front of as little as 5 km, seafloor morphology changes from shallower complex volcanic landforms to deeper flat sea floor dominated by linear abyssal hills, upper crustal seismic velocities abruptly increase by over 20%, and gravity anomalies and isostasy indicate crustal thinning of more than 1.9 km. We infer that the abrupt changes in crustal properties reflect rapid evolution of the mantle entrained by the ridge, such that stable, broad triangular upwelling regions, as inferred for mid-ocean ridges, cannot form near the mantle wedge corner. Instead, the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water-rich low-viscosity mantle when it is near the arc. As the ridge moves away from the arc, a tipping point is reached at which that material is rapidly released from the upwelling zone, resulting in rapid changes in the character of the crust formed at the ridge. PMID:21228874

  1. Crust and Upper Mantle Structure of the Hellenic and Cyprus Subduction Zones from Gravity Data Modelling

    NASA Astrophysics Data System (ADS)

    Alemdar, S.; Mahatsente, R.; Cemen, I.

    2015-12-01

    The neotectonics of the Anatolian and Aegean regions is the result of the African plate subduction along the Hellenic and Cyprus trenches and the Anatolian plate collision with the Eurosian plate. The African slab, as imaged by seismic tomography, penetrates the lower mantle and exhibits two major lateral tears below the Anatolian plate. The tears in the slab are related to low velocity structures in the sub-lithospheric mantle. The presence of low velocity structures in the upper mantle is a clear indication of anomalous asthenosphere (asthenospheric windows). What remains unclear is, however, how and to what extent the crust and upper mantle structure beneath the Anatolian region has been modified by the upwelling hot asthenospheric material. To determine the effects of the upwelling hot asthenospheric material in the region, we developed a 3-D gravity model of the crust and upper mantle structure of the Aegean and Anatolian regions (24°-33° E and 34°-40° N). The gravity model is based on satellite-derived gravity data from GRACE, LAGEOS and GOCE missions (EIGEN 6C2). The results of the gravity modelling, as constrained by seismic tomography, shows that the crust above the asthenospheric window, where the subducted African slab exhibits major lateral tears, is relatively thin. The crustal thickness variation within the asthenospheric window area is between 24 & 29 km. In contrast, the regions outside the asthenospheric window area exhibit by far the largest crustal thickness (30 - 42 km). We therefore conclude that the observed crustal thinning in the asthenospheric window area might be attributed to thermal erosion induced by the upwelling hot asthenospheric material and extensional tectonics related to the Southwest retreating Hellenic trench and westward movement of the Anatolian micro plate. The thinning may also be responsible for the high geothermal gradient in the Denizli graben area where two major grabens (i.e., Alaşehir and Bűyűk Menderes Grabens

  2. Contrasting crustal production and rapid mantle transitions beneath back-arc ridges.

    PubMed

    Dunn, Robert A; Martinez, Fernando

    2011-01-13

    The opening of back-arc basins behind subduction zones progresses from initial rifting near the volcanic arc to seafloor spreading. During this process, the spreading ridge and the volcanic arc separate and lavas erupted at the ridge are predicted to evolve away from being heavily subduction influenced (with high volatile contents derived from the subducting plate). Current models predict gradational, rather than abrupt, changes in the crust formed along the ridge as the inferred broad melting region beneath it migrates away from heavily subduction-influenced mantle. In contrast, here we show that across-strike and along-strike changes in crustal properties at the Eastern Lau spreading centre are large and abrupt, implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes. With incremental separation of the ridge axis from the volcanic front of as little as 5 km, seafloor morphology changes from shallower complex volcanic landforms to deeper flat sea floor dominated by linear abyssal hills, upper crustal seismic velocities abruptly increase by over 20%, and gravity anomalies and isostasy indicate crustal thinning of more than 1.9 km. We infer that the abrupt changes in crustal properties reflect rapid evolution of the mantle entrained by the ridge, such that stable, broad triangular upwelling regions, as inferred for mid-ocean ridges, cannot form near the mantle wedge corner. Instead, the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water-rich low-viscosity mantle when it is near the arc. As the ridge moves away from the arc, a tipping point is reached at which that material is rapidly released from the upwelling zone, resulting in rapid changes in the character of the crust formed at the ridge.

  3. How stratified is mantle convection?

    NASA Astrophysics Data System (ADS)

    Puster, Peter; Jordan, Thomas H.

    1997-04-01

    due to slabs alone. A stratification index, Sƒ≲0.2, is sufficient to exclude many stratified convection models still under active consideration, including most forms of chemical layering between the upper and lower mantle, as well as the more extreme versions of avalanching convection governed by a strong endothermic phase change.

  4. Broad plumes rooted at the base of the Earth's mantle beneath major hotspots.

    PubMed

    French, Scott W; Romanowicz, Barbara

    2015-09-01

    Plumes of hot upwelling rock rooted in the deep mantle have been proposed as a possible origin of hotspot volcanoes, but this idea is the subject of vigorous debate. On the basis of geodynamic computations, plumes of purely thermal origin should comprise thin tails, only several hundred kilometres wide, and be difficult to detect using standard seismic tomography techniques. Here we describe the use of a whole-mantle seismic imaging technique--combining accurate wavefield computations with information contained in whole seismic waveforms--that reveals the presence of broad (not thin), quasi-vertical conduits beneath many prominent hotspots. These conduits extend from the core-mantle boundary to about 1,000 kilometres below Earth's surface, where some are deflected horizontally, as though entrained into more vigorous upper-mantle circulation. At the base of the mantle, these conduits are rooted in patches of greatly reduced shear velocity that, in the case of Hawaii, Iceland and Samoa, correspond to the locations of known large ultralow-velocity zones. This correspondence clearly establishes a continuous connection between such zones and mantle plumes. We also show that the imaged conduits are robustly broader than classical thermal plume tails, suggesting that they are long-lived, and may have a thermochemical origin. Their vertical orientation suggests very sluggish background circulation below depths of 1,000 kilometres. Our results should provide constraints on studies of viscosity layering of Earth's mantle and guide further research into thermochemical convection. PMID:26333468

  5. Inhibition of constitutive NF-kappa B activation in mantle cell lymphoma B cells leads to induction of cell cycle arrest and apoptosis.

    PubMed

    Pham, Lan V; Tamayo, Archito T; Yoshimura, Linda C; Lo, Piao; Ford, Richard J

    2003-07-01

    Constitutive activation of the NF-kappaB has been documented to be involved in the pathogenesis of many human malignancies, including hemopoietic neoplasms. In this study, we examined the status of NF-kappaB in two non-Hodgkin's lymphoma cell lines derived from mantle cell lymphoma (MCL) samples and in patient MCL biopsy specimens by EMSA and confocal microscopic analysis. We observed that NF-kappaB is constitutively activated in both the MCL cell lines and in the MCL patient biopsy cells. Since NF-kappaB has been shown to play an important role in a variety of cellular processes, including cell cycle regulation and apoptosis, targeting the NF-kappaB pathways for therapy may represent a rational approach in this malignancy. In the MCL cell lines, inhibition of constitutive NF-kappaB by the proteasome inhibitor PS-341 or a specific pIkappaBalpha inhibitor, BAY 11-7082, led to cell cycle arrest in G(1) and rapid induction of apoptosis. Apoptosis was associated with the down-regulation of bcl-2 family members bcl-x(L) and bfl/A1, and the activation of caspase 3, that mediates bcl-2 cleavage, resulting in the release of cytochrome c from the mitochondria. PS-341or BAY 11-induced G(1) cell cycle arrest was associated with the inhibition of cyclin D1 expression, a molecular genetic marker of MCL. These studies suggest that constitutive NF-kappaB expression plays a key role in the growth and survival of MCL cells, and that PS-341 and BAY 11 may be useful therapeutic agents for MCL, a lymphoma that is refractory to most current chemotherapy regimens.

  6. Relationships between temporal-spatial distribution of monogenetic volcanoes, crustal structure, and mantle velocity anomalies: An example from the Abu Monogenetic Volcano Group, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Kiyosugi, K.; Connor, C. B.; Zhao, D.; Connor, L. J.; Tanaka, K.

    2008-12-01

    Achieving an understanding of the nature of monogenetic volcanic fields depends on identification of the spatial and temporal patterns of volcanism in these fields, and their relationships to structures mapped in the shallow crust and inferred in the deep crust and mantle through interpretation of geophysical data. We investigated the spatial and temporal distributions of volcanism in the Abu Monogenetic Volcano Group (AMVG), Southwest Japan, and compare these distributions to fault and seismic data in the brittle crust, and mantle P-wave tomographic anomalies in the upper mantle and lower crust. Late Cenozoic monogenetic volcano groups in the southwest Japan Arc are thought to originate from the upwelling of mantle diapirs. The AMVG is one such monogenetic volcano group consisting of alkaline basalt and calc-alkaline andesite-dacite lavas and pyroclastics distributed over an area of 400km2. Some of the 56 volcanoes comprised by the AMVG are located under the Sea of Japan, and are known primarily from bathymetry. Previous studies indicate that the AMVG is within a zone of predominantly E-W compressive stress. Essential characteristics of the volcano distribution are extracted by a nonparametric kernel method using an algorithm to estimate anisotropic bandwidth. Overall E-W elongate smooth modes in spatial density are identified that are consistent with upper mantle and lower crustal P-wave velocity anomalies, supporting the idea that the spatial density map of volcanic vents reflects the geometry of a mantle diaper. The maximum volcano density of this case is 4.0×10-3 event/km2. While estimated basalt productivity decreased after 0.2 Ma, andesite productivity increased and overall volume production is approximately steady-state. The estimated basalt productivity behaves as a volume-predictable model. Obvious increase in the area affected by volcanic activity did not occur at that time. This productivity also supports the idea that volcanism is related to a mantle

  7. Mantle plumes on Venus revisited

    NASA Technical Reports Server (NTRS)

    Kiefer, Walter S.

    1992-01-01

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

  8. Intensification of upwelling along Oman coast in a warming scenario

    NASA Astrophysics Data System (ADS)

    Praveen, V.; Ajayamohan, R. S.; Valsala, V.; Sandeep, S.

    2016-07-01

    The oceanic impact of poleward shift in monsoon low-level jet (MLLJ) is examined using a Regional Ocean Modeling System (ROMS). Two sets of downscaling experiments were conducted using ROMS with boundary and initial conditions from six CMIP5 models. While outputs from the historical run (1981-2000) acts as forcing for the first, the second uses RCP8.5 (2080-2099). By comparing the outputs, it is found that Oman coast will experience an increase in upwelling in tune with MLLJ shift. Consistent with the changes in upwelling and zonal Ekman transport, temperature, salinity, and productivity show significant changes near the Oman coast. The changes in MLLJ causes the coastal wind to angle against the Oman coast in such a fashion that the net upwelling increases in the next century and so does the marine productivity. This study contrasts the general view of weakening of upwelling along the Arabian coasts due to the weakening of monsoon winds.

  9. Climate science: The future of coastal ocean upwelling

    NASA Astrophysics Data System (ADS)

    di Lorenzo, Emanuele

    2015-02-01

    An ensemble of climate models predicts that winds along the world's coasts will intensify because of global warming, inducing more ocean upwelling -- a process that will affect the health of coastal marine ecosystems. See Letter p.390

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

    NASA Astrophysics Data System (ADS)

    Yoshida, Masaki; Santosh, M.

    2011-03-01

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

  11. Pliocene Warm Period Upwelling in the Southern Benguela Region

    NASA Astrophysics Data System (ADS)

    Petrick, B. F.; McClymont, E.; Felder, S.; Leng, M. J.; Rosell Mele, A.; Rueda, G.

    2014-12-01

    The mid-Pliocene has been proposed as a possible analogue for understanding future climate change and testing climate models. Previous work has shown that during the Pliocene the major upwelling systems were relatively warm, and thus either inactive, contracted, or upwelling warmer waters than present. Here we examine evidence from a core site located on the margins of the modern Benguela upwelling system, to test whether the upwelling cells had migrated or contracted relative to present during the Pliocene. We applied several organic geochemistry proxies and foraminiferal analyses to reconstruct the Pliocene history of ODP site 1087 (31º28'S, 15º19'E, 1374m water depth), including the UK37' index and TEX86 index (for reconstructing sea surface temperatures), chlorins (for estimating primary productivity) and planktonic foraminifera assemblages (for inferring water mass changes). These proxies show that between 3.5 and 3.0 Ma the southern Benguela region was significantly cooler than the northern Benguela region, the latter where the main upwelling cells are found today. Coupled with higher primary production, a shift in planktonic foraminifera assemblage, and an offset between the UK37' index and TEX86 index, we infer that more extensive upwelling was present in the southern Benguela region during the Pliocene. We infer that the main Benguela upwelling cells had shifted southward relative to today, as a result of changes in the local wind field. We find evidence for pronounced cooling and a shift in the planktonic foraminifera assemblage during the M2 and KM2 glacial stages, showing a sensitivity of Benguela upwelling to these short-lived climate events.

  12. High rates of nitrogen fixation in equatorial upwelling region

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2013-05-01

    Surface waters in upwelling regions of the ocean are generally rich in nutrients. Scientists had thought that these areas would have low rates of nitrogen fixation because diazotrophs—microbes that convert nitrogen gas from the atmosphere into usable forms, such as ammonia—could use the nutrients in the water directly instead of having to fix nitrogen gas. However, researchers recently recorded high rates of nitrogen fixation in an upwelling region in the equatorial Atlantic.

  13. Insights on slab-driven mantle flow from advances in three-dimensional modelling

    NASA Astrophysics Data System (ADS)

    Jadamec, Margarete A.

    2016-10-01

    The wealth of seismic observations collected over the past 20 years has raised intriguing questions about the three-dimensional (3D) nature of the mantle flow field close to subduction zones and provided a valuable constraint for how the plate geometry may influence mantle flow proximal to the slab. In geodynamics, there has been a new direction of subduction zone modelling that has explored the 3D nature of slab-driven mantle flow, motivated in part by the observations from shear wave splitting, but also by the observed variations in slab geometries worldwide. Advances in high-performance computing are now allowing for an unprecedented level of detail to be incorporated into numerical models of subduction. This paper summarizes recent advances from 3D geodynamic models that reveal the complex nature of slab-driven mantle flow, including trench parallel flow, toroidal flow around slab edges, mantle upwelling at lateral slab edges, and small scale convection within the mantle wedge. This implies slab-driven mantle deformation zones occur in the asthenosphere proximal to the slab, wherein the mantle may commonly flow in a different direction and rate than the surface plates, implying laterally variable plate-mantle coupling. The 3D slab-driven mantle flow can explain, in part, the lateral transport of geochemical signatures in subduction zones. In addition, high-resolution geographically referenced models can inform the interpretation of slab structure, where seismic data are lacking. The incorporation of complex plate boundaries into high-resolution, 3D numerical models opens the door to a new avenue of research in model construction, data assimilation, and modelling workflows, and gives 3D immersive visualization a new role in scientific discovery.

  14. Mantle flow and dynamic topography associated with slab window opening: Insights from laboratory models

    NASA Astrophysics Data System (ADS)

    Guillaume, Benjamin; Moroni, Monica; Funiciello, Francesca; Martinod, Joseph; Faccenna, Claudio

    2010-12-01

    We present dynamically self-consistent mantle-scale laboratory models that have been conducted to improve our understanding of the influence of slab window opening on subduction dynamics, mantle flow and associated dynamic topography over geological time scales. The adopted setup consists of a two-layer linearly viscous system simulating the subduction of a fixed plate of silicone (lithosphere) under negative buoyancy in a viscous layer of glucose syrup (mantle). Our experimental setting is also characterized by a constant-width rectangular window located at the center of a laterally confined slab, modeling the case of the interaction of a trench-parallel spreading ridge with a wide subduction zone. We found that the opening of a slab window does not produce consistent changes of the geometry and the kinematics of the slab. On the contrary, slab-induced mantle circulation, quantified both in the vertical and horizontal sections using the Feature Tracking image analysis technique, is strongly modified. In particular, rollback subduction and the opening of the slab window generate a complex mantle circulation pattern characterized by the presence of poloidal and toroidal components, with the importance of each evolving according to kinematic stages. Mantle coming from the oceanic domain floods through the slab window, indenting the supra-slab mantle zone and producing its deformation without any mixing between mantle portions. The opening of the slab window and the upwelling of sub-slab mantle produce a regional-scale non-isostatic topographic uplift of the overriding plate that would correspond to values ranging between ca. 1 and 5 km in nature. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compared them to the tectonics and volcanism of the Patagonian subduction zone. We found that the anomalous backarc volcanism that has been developing since the middle Miocene could result from the lateral flow of sub

  15. Coastal upwellings in 1941-2005 at Listvyanka settlement (Southern Baikal)

    NASA Astrophysics Data System (ADS)

    Troitskaya, Elena; Shimaraev, Mikhail; Zhdanov, Andrey; Zhdanova, Rita; Salva, Elena

    2010-05-01

    The first results of studies of coastal upwelling are presented in this paper based on long-term (1941-2005) measurements of surface water temperature in May-December at the pier of Limnological Institute (Listvyanka settlement, Southern Baikal). Listvyanka settlement is situated in Listvenichnoye Bay not far from the outlet of the Angara River. The flow of the Angara River is formed from the surface waters and ascending deep waters of Lake Baikal. Therefore, when the wind is of northwest direction, either surface waters are driven away along the northern shore or upwelling is formed if the wind blows for 2-3 days. Analyzing a temperature set, upwelling was considered in those cases when temperature dropped sharply by 2 or more degrees and it stayed for more than 3 days. Coastal upwelling developed more often in July and August in the area studied (it was recorded in 41 and 46 cases from 65 years analyzed), more rarely in September (in 36 cases from 65), seldom in October (in 16 from 65), 3 times in June (in 1948, 1972 and 1994), and once in November (1969). One-two upwellings were usually formed during a month. However, three-four upwellings were recorded in some years (July: 1949, 1974, 1976, 1994, 1996, 2003; August: 1942, 1955, 1972, 1973, 1975, 1976, 1978, 1982, 1990; and September: 1951, 2002). The duration of upwelling varied from 3 days to 3 weeks. The most long-lasting upwellings were recorded in August-September due to the intensification of wind activity above Lake Baikal in late summer. The temperature drop in the upwelling zone was 2.3-3.5°C in June, in July - 2.1-10.8 °C, in August - 2.2-11.9°C, in September - 2.5-11.2°C, in October - 2.1-7.5°C, and in November - 1.9°C. There were recorded some cases when the temperature decreased by more than 10°C (July 1949, August 1953, 1963, 1979, 1986, 1993, 2002, 2004, and September 1943, 1964, 1974). In some years, upwelling occurred every month in July-October or July-September (1974, 1984, 1987, 1988

  16. Upwelling events may cause cyanobacteria blooms in the Baltic Sea

    NASA Astrophysics Data System (ADS)

    Wasmund, Norbert; Nausch, Günther; Voss, Maren

    2012-02-01

    Cyanobacteria blooms in the Baltic Sea appear after upwelling events, which transport phosphate-rich intermediate water to the surface. The growth potential of diazotrophic cyanobacteria in upwelled water was studied in a mesocosm (tank) experiment in summer 2007. An Anabaena bloom was only induced in the tanks filled with upwelled surface water but not in those filled with surface water from outside the upwelling cell and with intermediate water. The low initial cyanobacteria biomass in the intermediate water could not grow to bloom concentrations within three weeks. It is concluded that mixing of upwelled water with surrounding surface water forms a precondition for a cyanobacteria bloom. An additional mesocosm experiment conducted in 2009 revealed that mixing of intermediate water with surface water had the same stimulating effect on nitrogen fixation and cyanobacteria growth as artificial phosphate input. Phosphate input stimulates the growth of Nodularia and Anabaena more than that of Aphanizomenon. We suggest that the upwelled phosphate-rich intermediate water has to be mixed with the surface water containing physiologically “young” cyanobacteria biomass of at least 20 mg/m3 as an inoculum in order to initiate a cyanobacteria bloom.

  17. Thermochemical differentiation and intermittent convection of the Earth's mantle

    NASA Astrophysics Data System (ADS)

    Kotelkin, Vycheslav; Lobkovsky, Leopold

    2010-05-01

    The numerical experiments are based on the thermochemical model of mantle convection. The model includes the description of the endothermic phase transition at the upper/lower mantle boundary. The aim of this work is the influence of thermochemical processes on mantle convection. As regards the thermochemical differentiation takes place near the mantle boundaries. The differentiation in the D" layer is due to melting with the rise in temperature and the descent of molten iron-bearing components of mantle material into the core. This process generates the lighter fraction, particularly produces the lower mantle plums. It takes place only if the current temperature exceeds the melting temperature. The differentiation near the outer mantle boundary is due to extracting the lighter mantle components into the crust. These thermochemical processes take place when the hot substance is lifting and the pressure falls. The growth of the continental crust on the outer surface is modeling. The oceanic crust returns into mantle throw the subducting zones. The modeling includes the "gabbro-eclogite" transition of oceanic crust. As regards the generation of heavy eclogitic material is located at the depths 80-100 km. Seismic tomography of deep mantle layers showed that the mantle really contains large inclusions of heavy, supposedly eclogitic material. The numerical experiments give a strong nonlinear interaction (either accelerating or slowing down) between the thermochemical processes and mantle convection. It leads to an impulsive character of geodynamics and promotes the formation of different cycles in the evolutionary process. Periods of gradual evolution are interrupted by the geodynamic activity outbursts. These peaks of geodynamic activity play a key role in the geological history of the Earth. Analogous oscillations of geodynamic process produce interaction heavy and light density inhomogeneities with the endothermic phase transition. When convection is layered then the

  18. Mountain building and mantle dynamics: a journey through the Tethyan belt (Stephan Mueller Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Faccenna, Claudio

    2014-05-01

    upwelling beneath Africa. This surge of mantle convection drags plates against each other, generating the necessary compressional forces to create and sustain these two orogenic belts. If this "bottom-up" tectonic model is correct, the geological records of orogeny cycle and of the topographic evolution along mobile belt can be used to decipher time-dependent mantle convection. Our main conclusion is that beneath the Tethyan belt we should imagine a multi-scale style of convection operating at different time and length scale, with a small scale convection style in the upper most part of the upper mantle embedded within a larger/slower and intermittent large scale whole mantle convection.

  19. Melt migration modeling in partially molten upper mantle

    NASA Astrophysics Data System (ADS)

    Ghods, Abdolreza

    The objective of this thesis is to investigate the importance of melt migration in shaping major characteristics of geological features associated with the partial melting of the upper mantle, such as sea-floor spreading, continental flood basalts and rifting. The partial melting produces permeable partially molten rocks and a buoyant low viscosity melt. Melt migrates through the partially molten rocks, and transfers mass and heat. Due to its much faster velocity and appreciable buoyancy, melt migration has the potential to modify dynamics of the upwelling partially molten plumes. I develop a 2-D, two-phase flow model and apply it to investigate effects of melt migration on the dynamics and melt generation of upwelling mantle plumes and focusing of melt migration beneath mid-ocean ridges. Melt migration changes distribution of the melt-retention buoyancy force and therefore affects the dynamics of the upwelling plume. This is investigated by modeling a plume with a constant initial melt of 10% where no further melting is considered. Melt migration polarizes melt-retention buoyancy force into high and low melt fraction regions at the top and bottom portions of the plume and therefore results in formation of a more slender and faster upwelling plume. Allowing the plume to melt as it ascends through the upper mantle also produces a slender and faster plume. It is shown that melt produced by decompressional melting of the plume migrates to the upper horizons of the plume, increases the upwelling velocity and thus, the volume of melt generated by the plume. Melt migration produces a plume which lacks the mushroom shape observed for the plume models without melt migration. Melt migration forms a high melt fraction layer beneath the sloping base of the impermeable oceanic lithosphere. Using realistic conditions of melting, freezing and melt extraction, I examine whether the high melt fraction layer is able to focus melt from a wide partial melting zone to a narrow region

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

    NASA Astrophysics Data System (ADS)

    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

  1. Calcium isotopic composition of mantle peridotites

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Ca isotopes are useful to decipher mantle evolution and the genetic relationship between the Earth and chondrites. It has been observed that Ca isotopes can be fractionated at high temperature [1-2]. However, Ca isotopic composition of the mantle peridotites and fractionation mechanism are still poorly constrained. Here, we report Ca isotope composition of 12 co-existing pyroxene pairs in 10 lherzolites, 1 harzburgite, and 1 wehrlite xenoliths collected from Hainan Island (South Eastern China). Ca isotope data were measured on a Triton-TIMS using the double spike method at the Guangzhou Institute of Geochemistry, CAS. The long-term external error is 0.12‰ (2SD) based on repeated analyses of NIST SRM 915a and geostandards. δ44Ca of clinopyroxenes except that from the wehrlite ranges from 0.85‰ to 1.14‰, while opx yields a wide range from 0.98‰ up to 2.16‰. Co-existing pyroxene pairs show large ∆44Caopx-cpx (defined as δ44Caopx-δ44Cacpx) ranging from 0 to 1.23‰, reflecting equilibrium fractionation controlled by variable Ca contents in the opx. Notably, clinopyroxene of wehrlite shows extremely high δ44Ca (3.22‰). δ44Ca of the bulk lherzolites and harzburgites range from 0.86‰ to 1.14‰. This can be explained by extracting melts with slightly light Ca isotopic compositions. Finally, the high δ44Ca of the wehrlite (3.22‰) may reflect metasomatism by melt which has preferentially lost light Ca isotopes due to chemical diffusion during upwelling through the melt channel. [1] Amini et al (2009) GGR 33; [2] Huang et al (2010) EPSL 292.

  2. Effect of partial melting on small scale convection atop a mantle plume

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    A lithospheric plate passing atop a mantle plume is likely to be thermally thinned or "rejuvenated". Geophysical data on the lithosphere-asthenosphere boundary (LAB) depth beneath active hotspots partly validate this prediction, but there is a large variation of the LAB upwelling estimated from different methods. Numerical simulations of plume-lithosphere interactions show that the development of small-scale convection (SSC) in the plume pancake spreading out along the base of the lithosphere is a mechanism able to rejuvenate the lithosphere, even for a fast-moving plate. The triggering of SSC has been shown to depend on the rheological behaviour of the unstable layer underlying the stagnant upper part of the thermal boundary layer (TBL), but the stability of the this layer may also be affected by partial melting.We analyze, using a 2D petrological-thermo-mechanical numerical model, the influence of partial melting on the dynamics of time-dependent SSC instabilities and the resulting rejuvenation of a lithosphere passing atop a mantle plume. These models show a complex behavior, with either an acceleration, no change or a slight decceleration of the SSC onset, due to the competing effects of the latent heat of melting, which cools the plume material, and of the buoyancy increase associated with melting, among which the dominant effect is the depletion in heavy elements of the solid fraction. The viscosity reduction, though significant (up to 2 orders of magnitude) is too localized to affect the SSC dynamics. Despite the presence of partial melting, the mechanical lithosphere erosion in not enhanced significantly relatively to melt-free models.

  3. Decadal changes in the Canary Current Upwelling Ecosystem

    NASA Astrophysics Data System (ADS)

    Santos, A. M.; Luis, J. M.; Relvas-Almeida, P.

    2013-12-01

    The Canary Current Upwelling System (CCUS) covers the latitudinal range 12-43 degrees N and has some singularities in relation to the other three major Eastern Boundary Upwelling Systems (EBUS), namely a major interruption in the continuity of the system at the Strait of Gibraltar and it is the only one with a sardine species from a different genus (Sardina vs Sardinops). Long-term trends in ocean temperature and coastal upwelling were investigated using the AVHRR Pathfinder SST (sea surface temperature) Version 5.1 dataset, in situ SST from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS), and upwelling indices from the Pacific Fisheries Environmental Laboratory (PFEL). The analysis is applied to the eastern boundary of the North Atlantic, from 10 to 45 degrees N extending until 30 degrees W, focusing mainly in the CCUS because the strong dynamic link between the atmosphere and the ocean makes upwelling regions highly sensitive to global change and ideal to monitor and investigate its effects. The detail in SST variability results in a large extent from the fine analysis and the numerical processing carefully designed to avoid trend bias in the climatological studies. The obtained fields of SST trends show a generalized warming of the entire region. However, alternate patches of significantly different warming rates are observed, ranging from large scale down to mesoscale. Known coastal upwelling features are seen to warm at a lower rate than corresponding offshore waters, pointing to an intensification of the upwelling in the last decades. Wind data are used to attempt to explain the variability of some upwelling structures. Our results evidence the main role that mesoscale processes play in the modulation of the spatial and temporal variability of SST, namely at the decadal scale. This result prevents any global conclusion about the intensification of the upwelling at the scale of the entire CCUS. The bulk of the sardine population is located

  4. Upper-Mantle Flow Driven Dynamic Topography in Eastern Anatolia

    NASA Astrophysics Data System (ADS)

    Sengul Uluocak, Ebru; Pysklywec, Russell; Eken, Tuna; Hakan Gogus, Oguz

    2016-04-01

    Eastern Anatolia is characterized by 2 km plateau uplift -in the last 10 Myrs-, high surface heat flow distribution, shallow Curie-point depth, anomalous gravity field. Seismological observations indicate relatively high Pn and Sn attenuation and significant low seismic velocity anomalies in the region. Moreover, the surface geology is associated predominantly with volcanic rocks in which melt production through mantle upwelling (following lithospheric delamination) has been suggested. It has been long known that the topographic loading in the region cannot be supported by crustal thickness (~45 km) based on the principle of Airy isostasy. Recent global geodynamic studies carried out for evaluating the post-collisional processes imply that there is an explicit dynamic uplift in Eastern Anatolia and its adjacent regions. In this study we investigate the instantaneous dynamic topography driven by 3-D upper-mantle flow in Eastern Anatolia. For this purpose we conducted numerous thermo-mechanical models using a 2-D Arbitrary Lagrangian Eulerian (ALE) finite element method. The available P-wave tomography data extracted along 10 profiles were used to obtain depth-dependent density anomalies in the region. We present resulting dynamic topography maps and estimated 3D mantle flow velocity vectors along these 2-D cross sections for each profile. The residual topography based on crustal thickness and observed topography was calculated and compared with other independent datasets concerning geological deformation and dynamic topography predictions. The results indicate an upper mantle driven dynamic uplift correlated with the under-compensated characteristic in Eastern Anatolia. We discuss our results combined with 3D mantle flow by considering seismic anisotropy studies in the region. Initial results indicate that high dynamic uplift and the localized low Pn velocities in concurrence with Pn anisotropy structures show nearly spatial coherence in Eastern Anatolia.

  5. Driving forces: Slab subduction and mantle convection

    NASA Technical Reports Server (NTRS)

    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.

  6. Ferrous iron partitioning in the lower mantle

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    We used density functional theory (DFT) to examine the partitioning of ferrous iron between periclase and bridgmanite under lower mantle conditions. To study the effects of the three major variables - pressure, temperature and concentration - these have been varied from 0 to 150 GPa, from 1000 to 4000 K and from 0 to 100% total iron content. We find that increasing temperature increases KD, increasing iron concentration decreases KD, while pressure can both increase and decrease KD. We find that KD decreases slowly from about 0.32 to 0.06 with depth under lower mantle conditions. We also find that KD increases sharply to 0.15 in the very lowermost mantle due to the strong temperature increases near the CMB. Spin transitions have a large effect on the activity of ferropericlase which causes KD to vary with pressure in a peak-like fashion. Despite the apparently large changes in KD through the mantle, this actually results in relatively small changes in total iron content in the two phases, with XFefp ranging from about 0.20 to 0.35, before decreasing again to about 0.28 at the CMB, and XFebd has a pretty constant value of about 0.04-0.07 throughout the lower mantle. For the very high Fe concentrations suggested for ULVZs, Fe partitions very strongly into ferropericlase.

  7. Evidence for Little Shallow Entrainment in Starting Mantle Plumes

    NASA Astrophysics Data System (ADS)

    Lohmann, F. C.; Phipps Morgan, J.; Hort, M.

    2005-12-01

    Basalts from intraplate or hotspot ocean islands show distinct geochemical signatures. Their diversity in composition is generally believed to result from the upwelling plume entraining shallow mantle material during ascent, while potentially also entraining other deep regions of the mantle. Here we present results from analogue laboratory experiments and numerical modelling that there is evidence for little shallow entrainment into ascending mantle plumes, i.e. most of the plume signature is inherited from the source. We conducted laboratory experiments using glucose syrup contaminated with glass beads to visualize fluid flow and origin. The plume is initiated by heating from below or by injecting hot, uncontaminated syrup. Particle movement is captured by a CCD camera. In our numerical experiments we solve the Stokes equations for a viscous fluid at infinite Prandtl number with passive tracer particles being used to track fluid flow and entrainment rates, simulating laboratory as well as mantle conditions. In both analogue experiments and numerical models we observe the classical plume structure being embedded in a `sheath' of material from the plume source region that retains little of the original temperature anomaly of the plume source. Yet, this sheath ascends in the `slipstream' of the plume at speeds close to the ascent speed of the plume head, and effectively prevents the entrainment of surrounding material into the plume head or plume tail. We find that the source region is most effectively sampled by an ascending plume and that compositional variations in the source region are preserved during plume ascent. The plume center and plume sheath combined are composed of up to 85% source material. However, there is also evidence of significant entrainment of up to 30% of surrounding material into the outer layers of the plume sheath. Entrainment rates are found to be influenced by mantle composition and structure, with the radial viscosity profile of the

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

    NASA Astrophysics Data System (ADS)

    Leonard, Tiffany; Liu, Lijun

    2016-02-01

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

  9. Single-agent lenalidomide in relapsed/refractory mantle cell lymphoma: results from a UK phase II study suggest activity and possible gender differences.

    PubMed

    Eve, Heather E; Carey, Sean; Richardson, Sarah J; Heise, Carla C; Mamidipudi, Vidya; Shi, Tao; Radford, John A; Auer, Rebecca L; Bullard, Sheila H; Rule, Simon A J

    2012-10-01

    We present data from a phase II study investigating a novel treatment strategy for relapsed/refractory mantle cell lymphoma (MCL). Twenty-six patients received lenalidomide 25 mg/d (days 1-21 of a 28-d cycle) for up to 6 cycles followed by low-dose maintenance lenalidomide (15 mg) in responding patients. Eight patients achieved complete or partial response to give an overall response rate of 31% with median response duration of 22·2 months [95% confidence interval (CI) 0·0-53·6] and median progression-free survival (PFS) of 3·9 months (95% CI 0·0-11·1). An additional six patients (23%) achieved stable disease. Eleven patients received maintenance with median PFS of 14·6 months (95% CI 7·3-21·9). Correlative studies showed that peripheral T and Natural Killer (NK) cells increased in responding patients by 40-60% over the first 6 cycles with an initial dip in NK cells suggestive of tumour infiltration. Peripheral regulatory T cells were increased in MCL patients (P = 0·001) and expanded further following lenalidomide. Sequential plasma analysis showed increased IL12 p40 and IL7 alongside decreased MMP9, IL10, and adiponectin. Finally, a significant correlation (P = 0·02) between gender and response suggested that female MCL patients were more sensitive to lenalidomide than males. In summary, we confirm the activity, safety and immunomodulatory properties of lenalidomide in MCL and highlight its potential as a low-dose maintenance agent.

  10. Chemical stratification of the mantle

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.

    1979-01-01

    A possible scenario for the chemical stratification of the earth's mantle is presented. Differentiation of the mantle by either the production of basaltic magmas or partial melting by the upper mantle is proposed to lead to a thick basalt layer, the lower part of which is converted to eclogite as the earth cools. Density estimates indicate that the eclogite formed would not be able to sink to below 670 km. The eclogite layer is thus demonstrated to be trapped as a result of whole-mantle convection and possible irreversible differentiation of the mantle into eclogite and overlying residual peridotite layers.

  11. The Chemical Surface Signature Created by Upwelling Plumes

    NASA Astrophysics Data System (ADS)

    Schmalzl, J.; Hansen, U.

    2004-12-01

    Convective flows govern much of the dynamics of the Earth. Examples of such flows are convection in the Earth's mantle, convection in magma chambers and much of the dynamics of the world oceans. Nowadays these time-dependent flows are often studied by means of three dimensional (3D) numerical models which solve the equations for the transport of heat and momentum alternatingly. These flows are often driven by a temperature difference. But for many flows there is also an active or passive chemical component that has to be considered such as entrainment of material from an underlying layer. One characteristics of these flows is that the chemical diffusivity is very small. Implementing such a chemical field with a very low diffusivity into a numerical model using a field approach is difficult due to numerical diffusion introduced by the Eulerian schemes. We have implemented a tracer-mesh method which tracks only the position of the interface between the two different components. While the thermal shape of a plume for conditions as appropriate for the Earth's mantle is cylindrical in an first order approximation the shape of the entrained chemical material also has a very strong sheet-like component. This can be important for the understanding of the observed isotopic variability of plumes.

  12. The Influence of Natural Variability on Future California Current Upwelling

    NASA Astrophysics Data System (ADS)

    Brady, R.; Rykaczewski, R. R.; Alexander, M. A.

    2015-12-01

    Upwelling in the California Current sustains a productive ecosystem and is largely mediated by the cross-shore, atmospheric pressure gradient that develops during the boreal summer. This pressure gradient may be intensified through increased warming of the continent relative to the Pacific Ocean, resulting in accelerated alongshore winds and amplified coastal upwelling (a concept known as the Bakun Hypothesis). Past attempts to investigate the Bakun Hypothesis have utilized multi-model "ensembles-of-opportunity" to examine the response of upwelling to climate change. However, attempts to distinguish anthropogenic changes relative to natural climate variability are limited, largely because model divergences present in an ensemble-of-opportunity include both natural variability and inter-model variability (i.e., the differing response of each model to identical radiative forcing). To address this concern, modeling centers are developing "large ensembles" consisting of numerous, independent model runs separated only by round-off differences in their initial atmospheric state. Differences between these runs are void of inter-model variability, allowing disparities between runs to be attributed entirely to natural variability within the system. Using output from the CESM1 Large Ensemble, we consider the influence of anthropogenic activity—relative to natural climate variability—on the future seasonality, extent, and amplitude of upwelling in the California Current. Here we show that minor perturbations in the initial atmosphere significantly alter the influence of natural variability on the system. Furthermore, we expect change to vary both seasonally and meridionally, following trends of enhanced and weakened upwelling conditions. Finally, upwelling is expected to follow a complex path, rather than increasing linearly. Our results demonstrate the importance of considering upwelling conditions over varying scales of space and time, as quite different patterns

  13. Thermal and Chemical Structures at the Core-Mantle Boundary: Implications for the Mantle Dynamics

    NASA Astrophysics Data System (ADS)

    Stein, C.; Mertens, M.; Hansen, U.

    2013-12-01

    The core-mantle boundary (CMB) represents the lower boundary layer of the actively convecting Earth's mantle and is structurally very complex. For example, large low shear wave velocity provinces (LLSVPs) but also small-scale ultra-low velocity zones (ULVZs) have been detected seismically. Thermal and chemical structures such as thermal plumes and thermochemical piles have been considered to explain the complexities. Both affect the dynamics of the Earth's mantle and its temporal evolution. But also the surface plates are an essential aspect of mantle convection that strongly influence the dynamics of the interior. Cold subducting slabs penetrating the lower boundary layer will also affect the CMB topography. To study the structure and dynamics of the lower mantle we use numerical thermochemical models of mantle convection with a complex rheological approach, including a strong temperature-, stress- and pressure-dependent viscosity. This allows for the investigation of thermal plumes and thermochemical piles in combination with plate-like surface motion and deep subduction. In thermochemical convection dense material is viscously trapped by the flow and piled beneath plumes. The presence of the dense layer reduces the mobility of the surface plates but during plate evolution we find a variety of plume classes (plumes, thermals, line-plumes) leaving a complex structure in the CMB topography.

  14. Mantle heterogeneity beneath the southern Mid-Atlantic Ridge: trace element evidence for contamination of ambient asthenospheric mantle

    NASA Astrophysics Data System (ADS)

    le Roux, P. J.; le Roex, A. P.; Schilling, J.-G.; Shimizu, N.; Perkins, W. W.; Pearce, N. J. G.

    2002-10-01

    We report new trace element data for an extensive suite of quench basalt glasses dredged from the southern Mid-Atlantic Ridge (MAR) between 40°S and 52.5°S. Ratios between highly incompatible trace elements are strongly correlated and indicate a systematic distribution of incompatible element enriched mid-ocean ridge basalt (MORB) (E-type: Zr/Nb=5.9-19, Y/Nb=0.9-8.4, (La/Sm) n=1.0-2.9) and incompatible element depleted MORB (N-type: Zr/Nb=30-69, Y/Nb=11-29, (La/Sm) n=0.48-0.79) along this section of the southern MAR. A notable feature of N-type MORB from the region is the higher than usual Ba/Nb (4-9), La/Nb (1.2-2.4) and primitive mantle normalised K/Nb ratios (>1). Ba/Nb ratios in E-type MORB samples from 47.5 to 49°S are especially elevated (>10). The occurrence and geographic distribution of E-type MORB along this section of the southern MAR can be correlated with the ridge-centred Shona and off-axis Discovery mantle plumes. In conjunction with published isotope data for a subset of the same sample suite [Douglass et al., J. Geophys. Res. 104 (1999) 2941], a model is developed whereby prior to the breakup of Gondwana and the opening of the South Atlantic Ocean, the underlying asthenospheric mantle was locally contaminated by fluids/melts rising from the major Mesozoic subduction zone along the south-southwest boundary of Gondwana, leaving a subduction zone geochemical imprint (elevated (K/Nb) n and 87Sr/ 86Sr ratios, decreased 143Nd/ 144Nd ratios). Subsequent impingement of three major mantle plume heads (Tristan/Gough, Discovery, Shona) resulted in heating and thermal erosion of the lowermost subcontinental lithosphere and dispersal into the convecting asthenospheric mantle. With the opening of the ocean basin, continued plume upwelling led to plume-ridge interactions and mixing between geochemically enriched mantle derived from the Shona and Discovery mantle plumes, material derived from delamination of the subcontinental lithosphere, and mildly subduction

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

    NASA Astrophysics Data System (ADS)

    Thybo, H.

    2012-12-01

    Mantle Transition Zone indicates the presence of highly heterogeneous depth intervals above and below the 410 km discontinuity at a characteristic scale length of 8-20 by 3-8 km. These observations may be explained by either (i) A high percentage of Fe in this part of the mantle (up to Fe# 17%) which affects the phase transformations of the olivine component; (ii) Possible phase changes from pyroxenes to the garnet phase majorite; or (iii) Heterogeneity arising from subducted slabs that have equilibrated around the Transition Zone. (3) Strong heterogeneity has also been detected in the Ultra-Low-Velocity-Zone (ULVZ)at the Core-Mantle Boundary by the same methods. High-resolution seismic data indicates that the ULVZ extends around the whole core, contrary to previous expectations that it is present at major up+wellings. We model characteristic scale lengths and velocity contrasts of the mantle heterogeneity by application of 2D Finite Difference simulation of seismic wave propagation. Unfortunately the seismic data does not allow direct detection of the structure, but the heterogeneous structure of the mantle is now well demonstrated, probably caused by different processes.

  16. Density Effects of Melt Extraction from a Mantle Plum Pudding

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, G.; Phipps Morgan, J.

    2006-12-01

    Both ocean island (plume) and mid ocean ridge melting are thought to tap a lithologically heterogeneous source with both peridotites and `eclogite' recycled basaltic material. We explore how melting of both components effect the density of the upwelling and melting assemblage. Using the thermodynamic modeling program Perplex, two potential mantle sources are put through adiabatic batch and fractional melting to determine variations in density. For fertile peridotite compositions, the results show two continuous zones of melting. At pressures greater than ~1.5 GPa(~50km) melt removal increases residue density. At pressures below ~1.5GPa the melt includes high density phases with a corresponding reduction in the density of the residue. This melting behavior conflicts with conventional wisdom - so we also examine the density consequences of `conventional' deep melting behavior of peridotite. Deep melting of an eclogite phase poses a challenge for the current parameterization used in Perplex. Therefore, we also calculate melt compositions from a non-thermodynamic formulation and use Perplex to determine the evolving density of solid residues to melt extraction. In general for a heterogeneous mantle assemblage, the average density differs from that assuming a single homogenous mantle lithology even if the average composition is the same. We will discuss the implications of these calculations for the `stability' of a plume-fed asthenosphere.

  17. Teleseismic array analysis of upper mantle compressional velocity structure. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Walck, M. C.

    1984-01-01

    Relative array analysis of upper mantle lateral velocity variations in southern California, analysis techniques for dense data profiles, the P-wave upper mantle structure beneath an active spreading center: the Gulf of California, and the upper mantle under the Cascade ranges: a comparison with the Gulf of California are presented.

  18. Vertically deflected mantle flow at the eastern edge of the African Large Low Shear Velocity Province

    NASA Astrophysics Data System (ADS)

    Ford, H. A.; Long, M. D.; He, X.; Lynner, C.

    2014-12-01

    Despite the abundantly clear evidence for the existence of two Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle, the origin, composition, and dynamics are still not well understood, nor is the relationship of the LLSVPs to the greater mantle. Observations of seismic anisotropy are often used to better understand flow in the mantle, but their utility is limited in the mostly isotropic lower mantle. An exception to this is in the lowermost mantle (D") where observations of seismic anisotropy are numerous; however, the interpretation of such measurements in terms of dynamic processes remains challenging. Here we use observations of seismic anisotropy at the eastern edge of the African LLSVP beneath the Afar hotspot to 1) test the consistency of different mechanisms for D" anisotropy with observations, and 2) constrain the geometry of mantle flow at an LLSVP edge. Our observational data set consists of measurements of differential S-ScS and discrepant SKS-SKKS splitting, totaling 22 SKS, SKKS and ScS phases, corrected for upper mantle anisotropy. By utilizing different raypath combinations, we are able to sample the edge structure of the African LLSVP from five distinct raypath orientations, an improvement over previous work. Through forward modeling using mineral physics constraints, we find that our splitting observations are best fit by a model of crystallographically aligned post-perovskite, with the [100] axis oriented either vertically, or highly oblique to the horizontal plane. Such an alignment suggests that mantle flow at the eastern edge of the African LLSVP has an upward component, consistent with either the vertical deflection of material at the LLSVP or with sheet-like upwellings. Placing our preferred flow scenario(s) in context with other recent work, we propose that the edge of the African LLSVP acts as a barrier to mantle flow, ultimately deflecting flow upwards along the margins.

  19. Seismic interferometry of the mantle transition zone beneath the western United States

    NASA Astrophysics Data System (ADS)

    Anderson, H. R.; Thorne, M. S.; Schmerr, N. C.; Brown, S. P.

    2011-12-01

    and mantle upwelling beneath Yellowstone.

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

    SciTech Connect

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

    2007-01-25

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

  1. Long-term interaction between mid-ocean ridges and mantle plumes

    NASA Astrophysics Data System (ADS)

    Whittaker, J. M.; Afonso, J. C.; Masterton, S.; Müller, R. D.; Wessel, P.; Williams, S. E.; Seton, M.

    2015-06-01

    Plate tectonic motions are commonly considered to be driven by slab pull at subduction zones and ridge push at mid-ocean ridges, with motion punctuated by plumes of hot material rising from the lower mantle. Within this model, the geometry and location of mid-ocean ridges are considered to be independent of lower-mantle dynamics, such as deeply sourced plumes that produce voluminous lava eruptions--termed large igneous provinces. Here we use a global plate model to reconstruct the locations of large igneous provinces relative to plumes and mid-ocean ridges at the time they formed. We find that large igneous provinces repeatedly formed at specific locations where mid-ocean ridges and plumes interact. We calculate how much mantle material was converted to oceanic lithosphere at the mid-ocean ridges and find that slowly migrating ridge systems that have been stabilized by upwelling plumes have extracted large volumes of material from the same part of the upper mantle over periods up to 180 million years. The geochemical signatures of mid-ocean ridge basalts and seismic tomographic data show that upper-mantle temperatures are elevated at significant distances from ridge-plume interactions, indicating a far-field, indirect influence of plume-ridge interactions on the upper-mantle structure. We conclude that strong feedbacks exist between the dynamics of slowly migrating ridges and deeply sourced plumes.

  2. Midcontinent rift volcanism in the Lake Superior region: Sr, Nd, and Pb isotopic evidence for a mantle plume origin

    USGS Publications Warehouse

    Nicholson, S.W.; Shirey, S.B.

    1990-01-01

    Between 1091 and 1098 Ma, most of a 15- to 20-km thickness of dominantly tholeiitic basalt erupted in the Midcontinent Rift System of the Lake Superior region, North America. The Portage Lake Volcanics in Michigan, which are the younget MRS flood basalts, fall into distinctly high- and low-TiO2 types having different liquid lines of descent. Incompatible trace elements in both types of tholeiites are enriched compared to depleted or primitive mantle and both basalt types are isotopically indistinguishable. The isotopic enrichment of the MRS source compared to depleted mantle is striking and must have occurred at least 700 m.y. before 1100 Ma. There are two likely sources for such magmatism: subcontinental lithospheric mantle enriched during the early Proterozoic or enriched mantle derived from an upwelling plume. Decompression melting of an upwelling enriched mantle plume in a region of lithosphere thinned by extension could have successfully generated the enormous volume (850 ?? 103 km3) of relatively homogeneous magma in a restricted time interval. -from Authors

  3. Physiological acclimation to elevated temperature in a reef-building coral from an upwelling environment

    NASA Astrophysics Data System (ADS)

    Mayfield, A. B.; Fan, T.-Y.; Chen, C.-S.

    2013-12-01

    Recent work has found that pocilloporid corals from regions characterized by unstable temperatures, such as those exposed to periodic upwelling, display a remarkable degree of phenotypic plasticity. In order to understand whether important reef builders from these upwelling reefs remain physiologically uncompromised at temperatures they will experience in the coming decades as a result of global climate change, a long-term elevated temperature experiment was conducted with Pocillopora damicornis specimens collected from Houbihu, a small embayment within Nanwan Bay, southern Taiwan that is characterized by 8-9 °C temperature changes during upwelling events. Upon nine months of exposure to nearly 30 °C, all colony (mortality and surface area), polyp ( Symbiodinium density and chlorophyll a content), tissue (total thickness), and molecular (gene expression and molecular composition)-level parameters were documented at similar levels between experimental corals and controls incubated at 26.5 °C, suggesting that this species can readily acclimate to elevated temperatures that cause significant degrees of stress, or even bleaching and mortality, in conspecifics of other regions of the Indo-Pacific. However, the gastrodermal tissue layer was relatively thicker in corals of the high temperature treatment sampled after nine months, possibly as an adaptive response to shade Symbiodinium from the higher photosynthetically active radiation levels that they were experiencing at that sampling time. Such shading may have prevented high light and high temperature-induced photoinhibition, and consequent bleaching, in these samples.

  4. Apollinaris Patera: An Early Martian Mantle Plume?

    NASA Astrophysics Data System (ADS)

    Kiefer, W. S.

    2015-12-01

    Apollinaris Patera is one of the largest volcanos on Mars outside of the Tharsis volcanic province (summit relief 5.4 km, volume 7.3x1013 m3). The mapped crater densities on Apollinaris indicate that volcanic activity ended 3.5 to 3.8 billion years ago. Apollinaris is located on the northern (lowland) side of the martian hemispheric dichotomy. Because it is an isolated, relatively point-like source of volcanism, it is plausibly interpreted as an early example of a martian mantle plume. Plume structure and conditions in the mantle can be constrained using finite element mantle convection simulations combined with a variety of petrological, geophysical, and geologic observations. (1) Basalts studied by the MER Spirit rover in nearby Gusev crater are similar in age and possibly physically connected to Apollinaris Patera. Petrologic modeling of the Gusev crater basalt compositions indicates that the thermal lithosphere was about 100 km thick with a mantle potential temperature of 1480-1530 °C. This requires a mantle thermal Rayleigh number of about 2x108 at the time of volcanism, based on the volume-averaged mantle viscosity. (2) Pyroclastic deposits at Apollinaris indicate that at least a portion of the volcanism occurred in the presence of a high concentration of water or other volatiles. This lowers the solidus temperature and increases the magma production rate but has only a limited effect on the minimum depth of melting. (3) There is a localized magnetic anomaly beneath Apollinaris that indicates that the martian core dynamo persisted until at least the earliest stage of Apollinaris volcanism, which in turn sets a lower bound on the core heat flux of 5-10 mW m-2. Preservation of the magnetic field may be the result of formation of magnetic minerals such as magnetite due to volcanically-driven hydrothermal alteration of crustal rocks beneath Apollinaris.

  5. Melt-rock reaction in the asthenospheric mantle: Perspectives from high-order accurate numerical simulations in 2D and 3D

    NASA Astrophysics Data System (ADS)

    Tirupathi, S.; Schiemenz, A. R.; Liang, Y.; Parmentier, E.; Hesthaven, J.

    2013-12-01

    The style and mode of melt migration in the mantle are important to the interpretation of basalts erupted on the surface. Both grain-scale diffuse porous flow and channelized melt migration have been proposed. To better understand the mechanisms and consequences of melt migration in a heterogeneous mantle, we have undertaken a numerical study of reactive dissolution in an upwelling and viscously deformable mantle where solubility of pyroxene increases upwards. Our setup is similar to that described in [1], except we use a larger domain size in 2D and 3D and a new numerical method. To enable efficient simulations in 3D through parallel computing, we developed a high-order accurate numerical method for the magma dynamics problem using discontinuous Galerkin methods and constructed the problem using the numerical library deal.II [2]. Linear stability analyses of the reactive dissolution problem reveal three dynamically distinct regimes [3] and the simulations reported in this study were run in the stable regime and the unstable wave regime where small perturbations in porosity grows periodically. The wave regime is more relevant to melt migration beneath the mid-ocean ridges but computationally more challenging. Extending the 2D simulations in the stable regime in [1] to 3D using various combinations of sustained perturbations in porosity at the base of the upwelling column (which may result from a viened mantle), we show the geometry and distribution of dunite channel and high-porosity melt channels are highly correlated with inflow perturbation through superposition. Strong nonlinear interactions among compaction, dissolution, and upwelling give rise to porosity waves and high-porosity melt channels in the wave regime. These compaction-dissolution waves have well organized but time-dependent structures in the lower part of the simulation domain. High-porosity melt channels nucleate along nodal lines of the porosity waves, growing downwards. The wavelength scales

  6. Surface-wave analysis and its application to determining crustal and mantle structure beneath regional arrays

    NASA Astrophysics Data System (ADS)

    Jin, Ge

    We develop several new techniques to better retrieve Earth's structure by analyzing seismic surface waves. These techniques are applied in regional studies to understand a variety of tectonic structures and geodynamic processes in Earth's crust and upper mantle. We create an automated method to retrieve surface-wave phase velocities using dense seismic arrays. The method is based on the notion of using cross-correlation to measure phase variations between nearby stations. Frequency-dependent apparent phase velocities are inverted from the phase-variation measurements via the Eikonal equation. The multi-pathing interference is corrected using amplitude measurements via the Helmholtz equation. The coherence between nearby-station waveforms, together with other data-selection criteria, helps to automate the entire process. We build up the Automated Surface-Wave Measuring System (ASWMS) that retrieves structural phase velocity directly from raw seismic waveforms for individual earthquakes without human intervention. This system is applied on the broad-band seismic data recorded by the USArray from 2006-2014, and obtain Rayleigh-wave phase-velocity maps at the periods of 20-100~s. In total around half million seismograms from 850 events are processed, generating about 4 million cross-correlation measurements. The maps correlate well with several published studies, including ambient-noise results at high frequency. At all frequencies, a significant contrast in Rayleigh-wave phase velocity between the tectonically active western US and the stable eastern US can be observed, with the phase-velocity variations in the western US being 1-2 times greater. The Love wave phase-velocity maps are also calculated. We find that overtone interference may produce systematic bias for the Love-wave phase-velocity measurements. We apply surface-wave analysis on the data collected by a temporary broad-band seismic array near the D'Entrecasteaux Island (DI), Papua New Guinea. The array

  7. An investigation of Ekman upwelling in the North Atlantic

    NASA Technical Reports Server (NTRS)

    Mcclain, Charles R.; Firestone, James

    1993-01-01

    The spatial and temporal variability of the North Atlantic Ekman upwelling fields on seasonal and interannual time scales is investigated on the basis of surface winds from the Fleet Numerical Oceanography Center for 1979-1986. A pronounced minimum in the basin-wide monthly mean vertical Ekman velocities during 1981-1982 is found. It is shown that the primary source of the interannual signal was the region off NW Africa in the vicinity of the Guinea Dome. Other sectors of the basin experienced no significant interannual trends. Hydrographic data and SST data from the NW Africa sector for 1981-1986 indicate a cooling trend beginning in late 1982, consistent with increased upwelling. The fall and winter seasons' mixed layers at the center of the Guinea Dome were deeper in 1984 and 1985 than in previous years. The potential impact of large interannual variations in Ekman upwelling on basin-wide primary productivity is discussed.

  8. Dynamics of plankton populations in upwelling areas. [by remote sensors

    NASA Technical Reports Server (NTRS)

    Szekielda, K.

    1974-01-01

    Recent investigations of the upwelling area along the NW Coast of Africa which include studies with satellites are discussed. The detection of patchiness in temperature and plankton distribution in the upwelling area is of special interest because they can be investigated from space synoptically with repeated coverage. The recent satellite missions provide recordings in the infrared region of the electromagnetic spectrum (EMR) as well as in the visible part. The information from those two parts of the EMR is useful for establishing the sea surface temperature and plankton distribution in upwelling areas. The temperature distribution as observed with infrared sensors and the patchiness in plankton patterns are discussed as observed with the most recent satellites, namely the Earth Resources Technology Satellite (ERTS) and NOAA-2.

  9. Dynamics of transient upwelling across the tropical tropopause

    NASA Astrophysics Data System (ADS)

    Randel, W. J.; Abalos, M.

    2013-12-01

    Tropical upwelling is a fundamental component of the stratospheric Brewer Dobson circulation (BDC), influencing temperatures, water vapor and chemical constituents throughout the global stratosphere. There is a substantial component of sub-seasonal variability in upwelling, with strong effects on temperatures and tracers in the tropical lower stratosphere. Upwelling diagnosed using momentum balance calculations from ERAinterim data demonstrate that transience is linked to the effects of extratropical wave forcing, with centers of action in the high latitude winter stratosphere and in the subtropical upper troposphere of both hemispheres. Zonal mean wind tendencies are an important part of communicating the remote wave forcing to the deep tropics. Dynamical patterns reflect clear differences in forcing the shallow vs. deep branches of the BDC; the shallow branch is most correlated with wave forcing in the subtropical upper troposphere, while the deep branch is mainly influenced by high latitude planetary waves.

  10. Surface circulation variability and upwelling phenomenology in the western Sardinia

    NASA Astrophysics Data System (ADS)

    Olita, Antonio; Cucco, Andrea; Fazioli, Leopoldo; Perilli, Angelo; Ribotti, Alberto; Sorgente, Roberto

    2013-04-01

    The mean and turbulent surface circulation of the Sardinan Sea (the shelf-slope region west of Sardinia, western Mediterranean sea) was studied by analyzing an interannual simulation performed with a hydrodinamic 3D numerical model. The model (an implementation of the Princeton Ocean Model) was forced with realistic atmospheric and oceanic fields (analyses) for the quadriennium 2008-2011. The model assimilates along track Sea Level Anomalies by means of a 3D-variational software. Velocities (meridional and zonal components) were decomposed in their mean and turbulent part to investigate the mean and fluctuating surface flow. EOF decomposition was used to get further insight on the simulated dataset and throw light on the variability of the main circulation features. At surface the mean circulation is characterized by a southward current field getting closer to the coast in the southern corner of the Island where if flows over the shelf edge. Eddy momentum flux field suggests that this southward stream is accelerated by a transfer of momentum from the eddy to the mean field. The accelerated stream contributes to precontidition the coastal upwelling in the southern area. The phenomenology of such a coastal upwelling along the SW Sardinia is described for the first time. The upwelling in the southern part of Sardinia constitutes the main surface temperature signal of the modeled SST anomalies, as evidenced by EOF decomposition. A significant correlation both with wind directions and current intensity was found. This, jointly with synoptic satellite observations before and during an upwelling event, suggests that both current and winds participate in creating the upwelling: alongshore current preconditions the upwelling that is finally triggered by favourable NW winds.

  11. Workshop on the Archean Mantle

    NASA Technical Reports Server (NTRS)

    Ashwal, L. D. (Editor)

    1989-01-01

    The Workshop on the Archaen mantle considers and discusses evidence for the nature of earth's Archaen mantle, including its composition, age and structure, influence on the origin and evolution of earth's crust, and relationship to mantle and crustal evolution of the other terrestrial planets. The summaries of presentations and discussions are based on recordings made during the workshop and on notes taken by those who agreed to serve as summarizers.

  12. Upwelling Response to Hurricane Isaac in Geostrophic Oceanic Vortices

    NASA Astrophysics Data System (ADS)

    Jaimes, B.; Shay, L. K.; Brewster, J. K.; Schuster, R.

    2013-05-01

    As a tropical cyclone (TC) moves over the ocean, the cyclonic curl of the wind stress produces a region of upwelling waters under the TC center that is compensated by downwelling waters at regions outside the center. Direct measurements conducted during hurricane Rita and recent numerical studies indicate that this is not necessarily the case when TCs move over geostrophic oceanic features, where its background relative vorticity impacts wind-driven horizontal current divergence and the upwelling velocity. Modulation of the upwelling response in these energetic oceanic regimes impacts vertical mixing across the oceanic mixed layer base, air-sea fluxes into the atmosphere, and ultimately storm intensity. As part of NOAA Intensity Forecasting Experiment, an experiment was conducted during the passage of TC Isaac over the energetic geostrophic eddy field in the Gulf of Mexico in August 2012. Expendable bathythermographs, current profilers, and conductivity-temperature-depth probes were deployed in Isaac from NOAA WP-3D aircraft during four in-storm flights to measure oceanic variability and its impact on TC-driven upwelling and surface fluxes of heat and momentum. During intensification to hurricane, the cyclonic curl of the wind stress of Isaac extended over a region of more than 300 km in diameter (4 to 5 times the radius of maximum winds). Isaac's center moved over a cold cyclonic feature, while its right and left sides moved over warm anticyclones. Contrasting upwelling and downwelling regimes developed inside the region of cyclonic curl of the wind stress. Both positive (upwelling) and negative (downwelling) vertical displacements of 40 and 60 m, respectively, were measured inside the region of cyclonic curl of the wind stress, which are between 3 to 4 times larger than predicted vertical displacements for a quiescent ocean based on scaling arguments. Oceanic mixed layer (OML) currents of 0.2 to 0.7 m s-1 were measured, which are about 50% smaller than the

  13. Upper Mantle Anisotropy Structures Beneath Eastern Tibet and Northeast Asia

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Wen, L.

    2015-12-01

    Tibetan plateau and eastern Asia subduction zone are tectonic active regions. Understanding the evolution and dynamics process of the two regions is important for us to understand mantle dynamics. A lot of work has been done on the velocity structures beneath the two regions, and several tectonic models are proposed to explain their dynamic process. But due to the absence of the detailed upper mantle anisotropy structures, those models are still under debate. Fine upper mantle velocity and anisotropy structures can help us understand the dynamic process of the two regions. Waveform modeling of upper mantle triplication phases can provide a good vertical resolution of upper mantle velocity structures, but present methods for calculating synthetic seismograms cannot process anisotropic media. We develop a method based on the generalized reflection and transmission method (GRTM) to calculate synthetic seismograms for wave propagating in stratified VTI media, so we can waveform model upper mantle triplications propagating in anisotropic media. In this study, we waveform model the tangential and radial seismic triplication data recorded in Chinese digital seismic stations at a epicentral distance of 10-30 degree for one event occurring in middle Tibet and one event occurring in Japan, to constrain fine upper mantle velocity and anisotropy structures beneath eastern Tibet and northeast Asia. The result shows that beneath eastern Tibet, horizontal S wave velocity is larger than vertical S wave velocity in the upper mantle; beneath northeast Asia, horizontal S wave velocity is larger than vertical S wave velocity above the depth of 190 km, and is smaller than vertical S wave velocity below the depth of 190 km. We also build a mineral physics modeling method, which can calculate upper mantle anisotropy structures based on mantle temperatures, compositions and directions of mantle flow, and use this method to explore compositional and dynamic models that would explain the

  14. Basaltic volcanism in Ethiopia: Constraints on continental rifting and mantle interactions

    SciTech Connect

    Hart, W. K.; WoldeGabriel, G.; Walter, R. C.; Mertzman, S. A.

    1989-06-10

    Middle to late Cenozoic mafic lavas from the Ethiopian volcanic province exhibit considerable chemical and isotopic diversity that is linked to eruption age and eruption location. These variations provide a geochemical framework in which continental rifting can be examined. Trace element and Sr, Nd, and Pb isotopic data are interpreted to indicate involvement of up to two depleted and two enriched mantle reservoirs throughout Cenozoic rift development in Ethiopia. Superimposed on the characteristics imparted by varying degrees of melting of these distinct reservoirs are the effects of crystal fractionation and, in some instances, crustal contamnation. Initial stages of Oligocene rifting and volcanism, as manifested by the rift-bounding plateau flood basalts, are attributed to asthenospheric upwelling and melting of a heterogeneous, enriched subcontinental lithospheric mantle. Mildly alkaline lavas were produced from an enriched source with characteristics similar to those of the inferred source of other mantle/minus/derived lavas and xenoliths from east Africa (LoNd array, EMI to HIMU). Contemporaneous tholeiitic lavas were derived from a source similar to that producing oceanic basalts from Samoa and the Society Islands (EMII). As lithospheric thinning and rifting continued into the Miocene, upwelling depleted asthenosphere (depleted OIB reservoir, PREMA) interacted with the lithospheric sources producing lavas with hybrid elemental and isotopic characteristics (11-6 Ma plateau and rift margin basalts).

  15. Mid-mantle seismic anisotropy patterns around subduction zones predicted by numerical modelling

    NASA Astrophysics Data System (ADS)

    Faccenda, Manuele

    2014-05-01

    There is increasing evidence for mid mantle seismic anisotropy around subduction zones whose interpretation remains elusive. In this study I estimate the strain-induced mid mantle fabric and associated seismic anisotropy developing in 3D petrological-thermo-mechanical subduction models where the slab is either stagnating over the 660 km discontinuity or penetrating into the lower mantle. The modeling of synthetic lattice-preferred-orientation (LPO) development of wadsleyite and perovskite has been calibrated with results from deformational experiments and ab-initio atomic scale models, and the single crystal elastic tensor of the different mineral phases is scaled by local P-T conditions. The lower transition zone (ringwoodite + garnet) is assumed to be isotropic. Mid mantle fabric develops in proximity of the subducting slab where deformation and stresses are high, except at depths where upwelling or downwelling material undergoes phase transformations, yielding to LPO reset. The upper transition zone (wadsleyite + garnet) is characterized by weak transverse isotropy (2-3%) with symmetry axes oriented and fast S wave polarized dip-normal. A slightly stronger transverse isotropy develops in the lower mantle (perovskite + periclase), where the symmetry axes, the polarization of the fast S wave and the maximum Vp and dVs are parallel to the slab dip and subduction direction. For stagnating slab models this translates into negative and positive radial anisotropy in the upper transition zone and lower mantle back-arc, respectively, minimum delay times for vertically travelling shear waves and large shear wave splitting for waves propagating horizontally in the lower mantle. These results may help in reconciling the seismic anisotropy patterns observed in some subduction zones with subduction-induced deformation, such as those measured in the mid mantle between the Australian plate and the New Hebrides-Tonga-Kermadec trenches that I interpret as related to stagnating

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    plausibly explains the high silica content of the shergottites. A dehydrating martian mantle with time can explain the decreasing silica contents measured in the young volcanoes and thus fits the measurements from the surface, and producing the high-silica shergottites through a thick crust is difficult without the presence of water. Our model requires that, after differentiation, the martian mantle retained significant water. Much of that water was released early in Mars's history as widespread volcanism allowed for initial dehydration of much of the mantle. The more recent volcanism involved in building the large surface volcanoes was then produced largely from the melting of previously-dehydrated mantle, with possible contributions from crustal rocks and fluids rich in volatiles such as Cl or CO2. Rocks such as the Gusev basalts and the nakhlite and chassignite meteorites also fit into this model and do not require unique circumstances such as a highly-oxidized early martian atmosphere or mantle. Finally, the magmas that eventually became the shergottites were produced when surviving hydrous mantle, similar to that which produced ALH 84001, was entrained in a mantle upwelling such as Tharsis. 1 Nyquist, L. E. et al.. GCA 73, 4288-4309 (2009). 2 Lapen, T. J. et al.. Science 328, 347-351, (2010).

  17. Slab Driven Mantle Deformation and Plate-Mantle Decoupling

    NASA Astrophysics Data System (ADS)

    Jadamec, M. A.; MacDougall, J.; Fischer, K. M.

    2015-12-01

    Observations of shear wave splitting derived from local sources in subduction zones suggest viscous flow in the mantle wedge is commonly non-parallel to both the subducting plate velocity vector and the motion of the overriding plate. However, far from the subduction zone trench, observations indicate the fast axis of shear wave splitting tends to align with the velocity vector of the surface plates. Similarly, previous 3D geodynamic models show the slab can drive local decoupling of the mantle and surface plates, in both direction and speed. This suggests that there is some distance from the trench over which there is significant decoupling of the mantle flow from surface plate motion, and that this decoupling zone then decays with continued distance from the trench, resulting in far-field plate-mantle coupling. Here we present results from geodynamic models of subduction coupled with calculations of olivine fabric deformation and synthetic splitting to 1) examine the influence of slab strength, slab dip, and non-Newtonian viscosity on the deformation fabric in the mantle wedge and subslab mantle and 2) quantify the spatial extent and intensity of this slab driven decoupling zone. We compare the deformation fabric in a 2D corner flow solution with varying dip to that of a 2D free subduction model with varying initial dip and slab strength. The results show that using an experimentally derived flow law to define viscosity (both diffusion creep and dislocation creep deformation mechanisms) has a first order effect on the viscosity structure and flow velocity in the upper mantle. The free subduction models using the composite viscosity formulation produce a zone of subduction induced mantle weakening that results in reduced viscous support of the slab and lateral variability in coupling of the mantle to the base of the surface plates. The maximum yield stress, which places an upper bound on the slab strength, can also have a significant impact on the viscosity

  18. Effects of Fertile Mantle Compositional Variation and Spreading Rate Variation on the Working of Global Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Niu, Y.; O'Hara, M. J.

    2014-12-01

    Mantle temperature variation, plate spreading rate variation and mantle compositional variation have been considered to be the three fundamental variables that govern the working of global ocean ridges [1]. An analysis demonstrates that mantle compositional variation exerts the primary control on ocean ridge processes; it determines (1) variation in both composition and mode of mantle mineralogy, (2) variation of mantle density, (3) variation of ridge axial depth, (4) source-inherited MORB compositional variation, (4) density-controlled variation in the amplitude of mantle upwelling, (5) apparent variation in the extent of melting, and (6) the correlated variation of MORB chemistry with ridge axial depth [2]. The above interpretations are reinforced by the updated MORB database [3]. The new database also confirms spreading rate control on the extent of melting as shown previously [4]. Mantle temperature variation could play a part, but its overstated role [3,5] results from a basic error (1) in treating ridge axial depth variation as evidence of mantle temperature variation by ignoring the intrinsic control of mantle composition, (2) in treating "mantle plume" influenced ridges (e.g., Iceland) as normal ridges of plate spreading origin, and (3) in treating low Vs at greater depths (> 300 km vs. < 200 km beneath ridges) beneath these "mantle plume" influenced ridges as evidence for hot ridge mantle. In order to understand the working of global ocean ridges, we must avoid plume-influenced ridges (e.g., in the vicinity of Iceland) and remove/average out data from such ridges. As a result, the correlations (e.g., between ridge axial depth, mantle low Vs anomaly, and some geochemical parameters) required for the interpretation of mantle temperature control all disappear. There is thus no evidence for large mantle temperature variation away from ridges influenced by "mantle plumes". References: [1] Niu et al., 2001, Earth Planet Sci. Lett., 186, 383-399; [2] Niu & O

  19. A synopsis of recent conceptual models on supercontinent tectonics in relation to mantle dynamics, life evolution and surface environment

    NASA Astrophysics Data System (ADS)

    Santosh, M.

    2010-09-01

    and energy through mantle downwelling and upwelling associated with supercontinent assembly and breakup is thought to affect the Earth's dynamo which would lead to catastrophic environmental changes, sometimes even triggering mass extinction. When a rising plume impinges the base of a supercontinent, the resultant continental rifting, formation of large igneous provinces and volcanic emissions might lead to the initiation of a plume winter, the aftermath of which would be mass extinction and long-term oceanic anoxia. Supercontinent tectonics in relation to mantle dynamics thus provides a key to evaluate the history of evolution and destruction of the continental crust, to understand the history of life, and to trace the major surface environmental changes of our planet.

  20. Mantle hydrocarbons: abiotic or biotic?

    PubMed

    Sugisaki, R; Mimura, K

    1994-06-01

    Analyses of 227 rocks from fifty localities throughout the world showed that mantle derived rocks such as tectonized peridotites in ophiolite sequences (tectonites) arid peridotite xenoliths in alkali basalts contain heavier hydrocarbons (n-alkanes), whereas igneous rocks produced by magmas such as gabbro arid granite lack them. The occurrence of hydrocarbons indicates that they were not derived either from laboratory contamination or from held contamination; these compounds found in the mantle-derived rocks are called here "mantle hydrocarbons." The existence of hydrocarbons correlates with petrogenesis. For example, peridotite cumulates produced by magmatic differentiation lack hydrocarbons whereas peridotite xenoliths derived from the mantle contain them. Gas chromatographic-mass spectrometric records of the mantle hydrocarbons resemble those of aliphatics in meteorites and in petroleum. Features of the hydrocarbons are that (a) the mantle hydrocarbons reside mainly along grain boundaries and in fluid inclusions of minerals; (b) heavier isoprenoids such as pristane and phytane are present; and (c) delta 13C of the mantle hydrocarbons is uniform (about -27%). Possible origins for the mantle hydrocarbons are as follows. (1) They were in organically synthesized by Fischer-Tropsch type reaction in the mantle. (2) They were delivered by meteorites and comets to the early Earth. (3) They were recycled by subduction. The mantle hydrocarbons in the cases of (1) and (2) are abiogenic and those in (3) are mainly biogenic. It appears that hydrocarbons may survive high pressures and temperatures in the mantle, but they are decomposed into lighter hydrocarbon gases such as CH4 at lower pressures when magmas intrude into the crust; consequently, peridotite cumulates do not contain heavier hydrocarbons but possess hydrocarbon gases up to C4H10. PMID:11541663

  1. Mantle hydrocarbons: Abiotic or biotic?

    SciTech Connect

    Sugisaki, Ryuichi; Mimura, Koichi

    1994-06-01

    Analyses of 227 rocks from fifty localities throughout the world showed that mantle derived rocks such as tectonized peridotites in ophiolite sequences (tectonites) and peridotite xenoliths in alkali basalts contain heavier hydrocarbons (n-alkanes), whereas igneous rocks produced by magmas such as gabbro and granite lack them. The occurrence of hydrocarbons indicates that they were not derived either from laboratory contamination or from field contamination; these compounds found in the mantle-derived rocks are called here {open_quotes}mantle hydrocarbons.{close_quotes} The existence of hydrocarbons correlates with petrogenesis. For example, peridotite cumulates produced by magmatic differentiation lack hydrocarbons whereas peridotite xenoliths derived from the mantle contain them. Gas chromatographic-mass spectrometric records of the mantle hydrocarbons resemble those of aliphatics in meteorites and in petroleum. Features of the hydrocarbons are that (a) the mantle hydrocarbons reside mainly along grain boundaries and in fluid inclusions of minerals; (b) heavier isoprenoids such as pristane and phytane are present; and (c) {delta}{sup 13}C of the mantle hydrocarbons is uniform (about {minus}27{per_thousand}). Possible origins for the mantle hydrocarbons are as follows. (1) They were inorganically synthesized by Fischer-Tropsch type reaction in the mantle. (2) They were delivered by meteorites and comets to the early Earth. (3) They were recycled by subduction. The mantle hydrocarbons in the cases of (1) and (2) are abiogenic and those in (3) are mainly biogenic. It appears that hydrocarbons may survive high pressures and temperatures in the mantle, but they are decomposed into lighter hydrocarbon gases such as CH{sub 4} at lower pressures when magmas intrude into the crust; consequently, peridotite cumulates do not contain heavier hydrocarbons but possess hydrocarbon gases up to C{sub 4}H{sub 10}. 76 refs., 5 figs., 3 tabs.

  2. Mantle hydrocarbons: abiotic or biotic?

    PubMed

    Sugisaki, R; Mimura, K

    1994-06-01

    Analyses of 227 rocks from fifty localities throughout the world showed that mantle derived rocks such as tectonized peridotites in ophiolite sequences (tectonites) arid peridotite xenoliths in alkali basalts contain heavier hydrocarbons (n-alkanes), whereas igneous rocks produced by magmas such as gabbro arid granite lack them. The occurrence of hydrocarbons indicates that they were not derived either from laboratory contamination or from held contamination; these compounds found in the mantle-derived rocks are called here "mantle hydrocarbons." The existence of hydrocarbons correlates with petrogenesis. For example, peridotite cumulates produced by magmatic differentiation lack hydrocarbons whereas peridotite xenoliths derived from the mantle contain them. Gas chromatographic-mass spectrometric records of the mantle hydrocarbons resemble those of aliphatics in meteorites and in petroleum. Features of the hydrocarbons are that (a) the mantle hydrocarbons reside mainly along grain boundaries and in fluid inclusions of minerals; (b) heavier isoprenoids such as pristane and phytane are present; and (c) delta 13C of the mantle hydrocarbons is uniform (about -27%). Possible origins for the mantle hydrocarbons are as follows. (1) They were in organically synthesized by Fischer-Tropsch type reaction in the mantle. (2) They were delivered by meteorites and comets to the early Earth. (3) They were recycled by subduction. The mantle hydrocarbons in the cases of (1) and (2) are abiogenic and those in (3) are mainly biogenic. It appears that hydrocarbons may survive high pressures and temperatures in the mantle, but they are decomposed into lighter hydrocarbon gases such as CH4 at lower pressures when magmas intrude into the crust; consequently, peridotite cumulates do not contain heavier hydrocarbons but possess hydrocarbon gases up to C4H10.

  3. Mantle dynamics in Mars and Venus: Influence of an immobile lithosphere on three-dimensional mantle convection

    SciTech Connect

    Schubert, G.; Bercovici ); Glatzmaier, G.A. )

    1990-08-30

    Numerical calculations of fully three-dimensional convection in constant viscosity, compressible spherical shells are interpreted in terms of possible convective motions in the mantles of Venus and Mars. The shells are heated both internally and from below to account for radiogenic heating, secular cooling, and heat flow from the core. The lower boundary of each of the shells is isothermal and shear stress free, as appropriate to the interface between a mantle and a liquid outer core. The upper boundary of each of the shells is rigid and isothermal, as appropriate to the base of a thick immobile lithosphere. Calculations with shear stress-free upper boundaries are also carried out to assess the role of the rigid surface condition. The ratio of the inner radius of each shell to its outer radius is in accordance with possible core sizes in both Venus and Mars. A calculation is also carried out for a Mars model with a small core to simulate mantle convection during early core formation. Different relative proportions of internal and bottom heating are investigated, ranging from nearly complete heating from within to almost all heating from below. The Rayleigh numbers of all the cases are approximately 100 times the critical Rayleigh numbers for the onset of convection. Cylindrical plumes are the prominent form of upwelling in the models independent of the surface boundary condition so long as sufficient heat derives from the core. Thus major volcanic centers on Mars, such as Tharsis and Elysium, and the coronae and some equatorial highlands on Venus may be the surface expressions of cylindrical mantle plumes.

  4. Mapping mantle flow during retreating subduction: Laboratory models analyzed by feature tracking

    NASA Astrophysics Data System (ADS)

    Funiciello, F.; Moroni, M.; Piromallo, C.; Faccenna, C.; Cenedese, A.; Bui, H. A.

    2006-03-01

    Three-dimensional dynamically consistent laboratory models are carried out to model the large-scale mantle circulation induced by subduction of a laterally migrating slab. A laboratory analogue of a slab-upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank. The circulation pattern is continuously monitored and quantitatively estimated using a feature tracking image analysis technique. The effects of plate width and mantle viscosity/density on mantle circulation are systematically considered. The experiments show that rollback subduction generates a complex three-dimensional time-dependent mantle circulation pattern characterized by the presence of two distinct components: the poloidal and the toroidal circulation. The poloidal component is the answer to the viscous coupling between the slab motion and the mantle, while the toroidal one is produced by lateral slab migration. Spatial and temporal features of mantle circulation are carefully analyzed. These models show that (1) poloidal and toroidal mantle circulation are both active since the beginning of the subduction process, (2) mantle circulation is intermittent, (3) plate width affects the velocity and the dimension of subduction induced mantle circulation area, and (4) mantle flow in subduction zones cannot be correctly described by models assuming a two-dimensional steady state process. We show that the intermittent toroidal component of mantle circulation, missed in those models, plays a crucial role in modifying the geometry and the efficiency of the poloidal component.

  5. Partial melting and upwelling rates beneath the Azores from a U-series isotope perspective [rapid communication

    NASA Astrophysics Data System (ADS)

    Bourdon, Bernard; Turner, Simon P.; Ribe, Neil M.

    2005-10-01

    We report U-series systematics ( 238U- 230Th- 231Pa- 226Ra) for basalts from the Azores islands and the nearby mid-Atlantic ridge with the aim of constraining melting processes in this region of plume-ridge interaction. Both 230Th and 231Pa excess show rough negative trends with indices of source enrichment (Sr, Nd and Pb isotopes) which cannot be explained by melting of a source variably enriched by mafic components (e.g. pyroxenite). However, there is evidence for a distinct source component, possibly sediment, beneath Sao Miguel which may give rise to these trends. 231Pa excess and Sm-Nd fractionation are positively and negatively correlated (respectively) with distance from the centre of the plume, while 230Th excesses show no clear trend. This suggests that mantle upwelling velocity exerts a strong control on U-Pa fractionation and that melting is initiated deeper in the centre of the plume. These observations are used to infer melting conditions beneath the mid-Atlantic ridge and Azores islands. The mantle upwelling velocity is constrained to be 3-4 cm/a which is smaller than that inferred for Hawaii or Iceland. Predicted 226Ra-excesses are similar to, or lower than those measured, suggesting high velocity melt ascent in channels and rapid differentiation prior to eruption. The effect of the presence of volatiles in the source is also investigated and we show that the presence of water could explain the 230Th and 231Pa trends as a function of distance across the plume. A 3-D model for the Azores plume can reproduce the U-series isotope observations.

  6. Nutrients, Recycling, and Biological Populations in Upwelling Ecosystems

    SciTech Connect

    Whitledge, T. E.

    1980-01-01

    Nutrient recycling has been studied in the upwelling areas of Baja California, Northwest Africa, and Peru. Regeneration by biological populations in these areas contributes significant quantities of recycled nitrogen which is utilized in productivity processes. Each area has a different combination of organisms which leads to differences in the relative contributions of zooplankton, nekton, or benthos to the nutrient cycles. Comparisons of ammonium regeneration rates of zooplankton and nekton-micronekton populations in the three upwelling areas show that zooplankton recycle relatively less nitrogen in the Baja California and Peru systems than nekton. In the Northwest Africa upwelling region, however, zooplankton, fish, and benthic inputs are all substantial. In recent years the Peruvian upwelling system has been altered with the decline of the anchoveta population and an increase in the importance of zooplankton in nutrient recycling. The distribution of recycled nitrogen (ammonium and urea) in transects across the shelf at 10°S and 15°S indicates that regeneration is relatively more important at 10°S in the region of the wide shelf. In both areas the distribution of ammonium and urea are not entirely coincident thereby indicating differences in their production and/or utilization.

  7. Meteorological constraints on oceanic halocarbons above the Peruvian Upwelling

    NASA Astrophysics Data System (ADS)

    Fuhlbrügge, S.; Quack, B.; Atlas, E.; Fiehn, A.; Hepach, H.; Krüger, K.

    2015-07-01

    Halogenated very short lived substances (VSLS) are naturally produced in the ocean and emitted to the atmosphere. Recently, oceanic upwelling regions in the tropical East Atlantic were identified as strong sources of brominated halocarbons to the atmosphere. During a cruise of R/V METEOR in December 2012 the oceanic sources and emissions of various halogenated trace gases and their mixing ratios in the marine atmospheric boundary layer (MABL) were investigated above the Peruvian Upwelling for the first time. This study presents novel observations of the three VSLS bromoform, dibromomethane and methyl iodide together with high resolution meteorological measurements and Lagrangian transport modelling. Although relatively low oceanic emissions were observed, except for methyl iodide, surface atmospheric abundances were elevated. Radiosonde launches during the cruise revealed a low, stable MABL and a distinct trade inversion above acting both as strong barriers for convection and trace gas transport in this region. Significant correlations between observed atmospheric VSLS abundances, sea surface temperature, relative humidity and MABL height were found. We used a simple source-loss estimate to identify the contribution of oceanic emissions to observed atmospheric concentrations which revealed that the observed marine VSLS abundances were dominated by horizontal advection below the trade inversion. The observed VSLS variations can be explained by the low emissions and their accumulation under different MABL and trade inversion conditions. This study confirms the importance of oceanic upwelling and trade wind systems on creating effective transport barriers in the lower atmosphere controlling the distribution of VSLS abundances above ocean upwelling regions.

  8. Role of Upwelling on Larval Dispersal and Productivity of Gooseneck Barnacle Populations in the Cantabrian Sea: Management Implications

    PubMed Central

    Rivera, Antonella; Weidberg, Nicolás; Pardiñas, Antonio F.; González-Gil, Ricardo; García-Flórez, Lucía; Acuña, J. L.

    2013-01-01

    The effect of coastal upwelling on the recruitment and connectivity of coastal marine populations has rarely been characterized to a level of detail to be included into sound fishery management strategies. The gooseneck barnacle (Pollicipes pollicipes) fishery at the Cantabrian Coast (Northern Spain) is located at the fringes of the NW Spanish Upwelling system. This fishery is being co-managed through a fine-scale, interspersed set of protected rocks where each rock receives a distinct level of protection. Such interspersion is potentially beneficial, but the extent to which such spacing is consistent with mean larval dispersal distances is as yet unknown. We have simulated the spread of gooseneck barnacle larvae in the Central Cantabrian Coast using a high-resolution time-series of current profiles measured at a nearshore location. During a year of high upwelling activity (2009), theoretical recruitment success was 94% with peak recruitment predicted 56 km west of the emission point. However, for a year of low upwelling activity (2011) theoretical recruitment success dropped to 15.4% and peak recruitment was expected 13 km east of the emission point. This is consistent with a positive correlation between catch rates and the Integrated Upwelling Index, using a 4-year lag to allow recruits to reach commercial size. Furthermore, a net long-term westward larval transport was estimated by means of mitochondrial cytochrome c oxidase subunit I (COI) sequences for five populations in the Cantabrian Sea. Our results call into question the role of long distance dispersal, driven by the mesoscale processes in the area, in gooseneck barnacle populations and point to the prevalent role of small-scale, asymmetric connectivity more consistent with the typical scale of the co-management process in this fishery. PMID:24236020

  9. Shock and Rarefaction Waves in a Heterogeneous Mantle

    NASA Astrophysics Data System (ADS)

    Jordan, J.; Hesse, M. A.

    2012-12-01

    We explore the effect of heterogeneities on partial melting and melt migration during active upwelling in the Earth's mantle. We have constructed simple, explicit nonlinear models in one dimension to examine heterogeneity and its dynamic affects on porosity, temperature and the magnesium number in a partially molten, porous medium comprised of olivine. The composition of the melt and solid are defined by a closed, binary phase diagram for a simplified, two-component olivine system. The two-component solid solution is represented by a phase loop where concentrations 0 and 1 to correspond to fayalite and forsterite, respectively. For analysis, we examine an advective system with a Riemann initial condition. Chromatographic tools and theory have primarily been used to track large, rare earth elements as tracers. In our case, we employ these theoretical tools to highlight the importance of the magnesium number, enthalpy and overall heterogeneity in the dynamics of melt migration. We calculate the eigenvectors and eigenvalues in the concentration-enthalpy space in order to glean the characteristics of the waves emerging the Riemann step. Analysis on Riemann problems of this nature shows us that the composition-enthalpy waves can be represented by self-similar solutions. The eigenvalues of the composition-enthalpy system represent the characteristic wave propagation speeds of the compositions and enthalpy through the domain. Furthermore, the corresponding eigenvectors are the directions of variation, or ``pathways," in concentration-enthalpy space that the characteristic waves follow. In the two-component system, the Riemann problem yields two waves connected by an intermediate concentration-enthalpy state determined by the intersections of the integral curves of the eigenvectors emanating from both the initial and boundary states. The first wave, ``slow path," and second wave, ``fast path," follow the aformentioned pathways set by the eigenvectors. The slow path wave

  10. Intraseasonal variability of upwelling in the equatorial Eastern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Chen, Gengxin; Han, Weiqing; Li, Yuanlong; Wang, Dongxiao; Shinoda, Toshiaki

    2015-11-01

    By analyzing satellite observations and conducting a series of ocean general circulation model experiments, this study examines the physical processes that determine intraseasonal variability (ISV) of the equatorial eastern Indian Ocean (EIO) upwelling for the 2001-2011 period. The ISV of EIO upwelling—as indicated by sea level, thermocline depth, and sea surface temperature (SST)—is predominantly forced by atmospheric intraseasonal oscillations (ISOs), and shows larger amplitudes during winter-spring season (November-April) when atmospheric ISOs are stronger than summer-fall (May-October). The chlorophyll (Chl-a) concentration, another indicator of upwelling, however reveals its largest intraseasonal variability during May-October, when the mean thermocline is shallow and seasonal upwelling occurs. For both winter-spring and summer-fall seasons, the ISV of EIO sea level and thermocline depth is dominated by remote forcing from the equatorial Indian Ocean wind stress, which drives Kelvin waves that propagate along the equator and subsequently along the Sumatra-Java coasts. Local wind forcing within the EIO plays a secondary role. The ISV of SST, however, is dominated by upwelling induced by remote equatorial wind only during summer-fall, with less contribution from surface heat fluxes for this season. During winter-spring, the ISV of SST results primarily from shortwave radiation and turbulent heat flux induced by wind speed associated with the ISOs, and local forcing dominates the SST variability. In this season, the mean thermocline is deep in the warm pool and thus thermocline variability decouples from the ISV of SST. Only in summer-fall when the mean thermocline is shallow, upwelling has important impact on SST.

  11. The thermochemical structure and evolution of Earth's mantle: constraints and numerical models.

    PubMed

    Tackley, Paul J; Xie, Shunxing

    2002-11-15

    Geochemical observations place several constraints on geophysical processes in the mantle, including a requirement to maintain several distinct reservoirs. Geophysical constraints limit plausible physical locations of these reservoirs to a thin basal layer, isolated deep 'piles' of material under large-scale mantle upwellings, high-viscosity blobs/plums or thin strips throughout the mantle, or some combination of these. A numerical model capable of simulating the thermochemical evolution of the mantle is introduced. Preliminary simulations are more differentiated than Earth but display some of the proposed thermochemical processes, including the generation of a high-mu mantle reservoir by recycling of crust, and the generation of a high-(3)He/(4)He reservoir by recycling of residuum, although the resulting high-(3)He/(4)He material tends to aggregate near the top, where mid-ocean-ridge melting should sample it. If primitive material exists as a dense basal layer, it must be much denser than subducted crust in order to retain its primitive (e.g. high-(3)He) signature. Much progress is expected in the near future.

  12. Seismological constraints on a possible plume root at the core-mantle boundary.

    PubMed

    Rost, Sebastian; Garnero, Edward J; Williams, Quentin; Manga, Michael

    2005-06-01

    Recent seismological discoveries have indicated that the Earth's core-mantle boundary is far more complex than a simple boundary between the molten outer core and the silicate mantle. Instead, its structural complexities probably rival those of the Earth's crust. Some regions of the lowermost mantle have been observed to have seismic wave speed reductions of at least 10 per cent, which appear not to be global in extent. Here we present robust evidence for an 8.5-km-thick and approximately 50-km-wide pocket of dense, partially molten material at the core-mantle boundary east of Australia. Array analyses of an anomalous precursor to the reflected seismic wave ScP reveal compressional and shear-wave velocity reductions of 8 and 25 per cent, respectively, and a 10 per cent increase in density of the partially molten aggregate. Seismological data are incompatible with a basal layer composed of pure melt, and thus require a mechanism to prevent downward percolation of dense melt within the layer. This may be possible by trapping of melt by cumulus crystal growth following melt drainage from an anomalously hot overlying region of the lowermost mantle. This magmatic evolution and the resulting cumulate structure seem to be associated with overlying thermal instabilities, and thus may mark a root zone of an upwelling plume.

  13. Mantle dynamics and seismic tomography.

    PubMed

    Tanimoto, T; Lay, T

    2000-11-01

    Three-dimensional imaging of the Earth's interior, called seismic tomography, has achieved breakthrough advances in the last two decades, revealing fundamental geodynamical processes throughout the Earth's mantle and core. Convective circulation of the entire mantle is taking place, with subducted oceanic lithosphere sinking into the lower mantle, overcoming the resistance to penetration provided by the phase boundary near 650-km depth that separates the upper and lower mantle. The boundary layer at the base of the mantle has been revealed to have complex structure, involving local stratification, extensive structural anisotropy, and massive regions of partial melt. The Earth's high Rayleigh number convective regime now is recognized to be much more interesting and complex than suggested by textbook cartoons, and continued advances in seismic tomography, geodynamical modeling, and high-pressure-high-temperature mineral physics will be needed to fully quantify the complex dynamics of our planet's interior.

  14. Mantle helium and carbon isotopes in Separation Creek Geothermal Springs, Three Sisters area, Central Oregon: Evidence for renewed volcanic activity or a long term steady state system?

    SciTech Connect

    van Soest, M.C.; Kennedy, B.M.; Evans, W.C.; Mariner, R.H.

    2002-04-30

    Cold bubbling springs in the Separation Creek area, the locus of current uplift at South Sister volcano show strong mantle signatures in helium and carbon isotopes and CO{sub 2}/{sup 3}He. This suggests the presence of fresh basaltic magma in the volcanic plumbing system. Currently there is no evidence to link this system directly to the uplift, which started in 1998. To the contrary, all geochemical evidence suggests that there is a long-lived geothermal system in the Separation Creek area, which has not significantly changed since the early 1990s. There was no archived helium and carbon data, so a definite conclusion regarding the strong mantle signature observed in these tracers cannot yet be drawn. There is a distinct discrepancy between the yearly magma supply required to explain the current uplift (0.006 km{sup 3}/yr) and that required to explain the discharge of CO{sub 2} from the system (0.0005 km{sup 3}/yr). This discrepancy may imply that the chemical signal associated with the increase in magma supply has not reached the surface yet. With respect to this the small changes observed at upper Mesa Creek require further attention, due to the recent volcanic vent in that area it may be the location were the chemical signal related to the uplift can most quickly reach the surface. Occurrence of such strong mantle signals in cold/diffuse geothermal systems suggests that these systems should not be ignored during volcano monitoring or geothermal evaluation studies. Although the surface-expression of these springs in terms of heat is minimal, the chemistry carries important information concerning the size and nature of the underlying high-temperature system and any changes taking place in it.

  15. Upwelling and surface cold patches in the Yellow Sea in summer: Effects of tidal mixing on the vertical circulation

    NASA Astrophysics Data System (ADS)

    Lü, Xingang; Qiao, Fangli; Xia, Changshui; Wang, Guansuo; Yuan, Yeli

    2010-04-01

    A three-dimensional, prognostic, wave-tide-circulation coupled numerical model is developed to study the effects of tidal mixing on the summertime vertical circulation in the Yellow Sea (YS). The distribution and mechanisms of upwelling are investigated by numerical means. Validated by historical tide gauge data, satellite sea surface temperature (SST) data, and cruise observation data, the model shows satisfactory performances in reproducing the dominant tidal system and three-dimensional sea temperature structure. Model results suggest that strong tidal mixing plays an important role in the formation of the vertical circulation in the YS. The Yellow Sea Cold Water Mass (YSCWM) is fringed by typical tidal mixing fronts (TMFs), which separate the cold, stratified water at the offshore side from the warm, well-mixed, shallow water at the other side. Considerable baroclinic gradient across the TMF makes the frontal zone the spot where the most active vertical circulation occurs; a secondary circulation is triggered with a distinct upwelling branch occurring mainly on the mixed side of the front. The numerical model produces systematic upwelling belts surrounding the YSCWM, and the upwelling is essentially induced by the TMF over sloping topography. The relative importance of tidal mixing and wind forcing for upwelling is further examined in numerical experiments. The southerly wind enhances the upwelling off the western coasts, but its overall influences in the whole YS are less important than tidal mixing. As shown by both satellite data and numerical modeling, the summertime SST field in the YS is featured by the stable existence of several site-selective surface cold patches (SCPs), most of which scatter in the waters off convex coastlines. One of the SCPs is found off Subei Bank, and the others are located off the eastern tip of Shandong Peninsula and off the three tips of Korean Peninsula. Two processes give rise to the SCP: on the one hand, TMF

  16. Lower mantle dynamics and the role of pressure-dependent thermodynamic and transport properties

    NASA Astrophysics Data System (ADS)

    Tosi, N.; Yuen, D. A.; Cadek, O.

    2010-12-01

    We have carried out numerical simulations of large aspect-ratio 2-D mantle convection that feature pressure-dependent thermal expansivity and conductivity along with the major mantle phase transitions, including the deep phase change from perovskite (pv) to post-perovskite (ppv). The rheological law is Newtonian and has both temperature- and pressure-dependences, while the extended Boussinesq approximation is assumed for the energetics. We have analyzed the combined effects of a strongly decreasing thermal expansivity, according to the diffraction experiments on pv by Katsura et al. (2009), and steeply increasing lattice thermal conductivity based on different models obtained from experiments (Ohta, 2010) and first principles (de Koker, 2010; Tang and Dong, 2010). Since ppv is expected to have a relatively weak rheology with respect to pv (Hunt et al., 2009; Ammann et al., 2010) and a large thermal conductivity (Ohta, 2010), we have also assumed that the transition from pv to ppv is accompanied by both a reduction in viscosity by 1 order of magnitude and by a 50% increase in conductivity. As long as the thermal expansivity and conductivity are constant, ppv exerts small but noticeable effects: it destabilizes the D" layer, causes focusing of the heat flux peaks and a slight increase of the average mantle temperature and of the temporal and spatial frequency of upwellings. The destabilizing character of ppv is strong enough to affect the stability of mantle plumes even in the presence of a large decrease of the thermal expansivity which otherwise, without ppv, delivers remarkably stable large upwellings. However we have found that if a sufficiently large thermal conductivity near the core-mantle is also accounted for, lower mantle plumes are stabilized for a geologically long time-span in excess of billion of years, even in the presence of the disturbances induced by the pv-ppv transition. Preliminary results confirm the validity of these findings even for thermo

  17. The North American upper mantle: Density, composition, and evolution

    NASA Astrophysics Data System (ADS)

    Mooney, Walter D.; Kaban, Mikhail K.

    2010-12-01

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

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

    USGS Publications Warehouse

    Mooney, Walter D.; Kaban, Mikhail K.

    2010-01-01

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

  19. Mantle convection and crustal tectonics in the Tethyan subduction zone

    NASA Astrophysics Data System (ADS)

    Jolivet, L.; Sternai, P.; Menant, A.; Faccenna, C.; Becker, T. W.; Burov, E. B.

    2013-12-01

    of kinematic boundary conditions (push or pull on lateral sides), and rarely account for basal stresses due to mantle flow. On the other hand, convection models often treat the lithosphere as a single-layer stagnant lid with vertically undeformable surface. There is thus a gap between convection models and lithospheric-scale geodynamic models. We test different degrees of coupling using 3-D lithospheric deformation models. Preliminary results suggest that lithosphere can be carried by asthenospheric flow, which may lead to plate fragmentation, especially if this flow is applied on a large surface and involves mantle upwelling. However, the presence of a ductile lower crust inhibits the upward transmission of stresses. A highly extended crust in a hot environment such as a backarc domain, with no lithospheric mantle and a ductile lower crust in direct contact with asthenosphere, is more prone to follow the mantle flow than a thick and stratified lithosphere.

  20. [Culture of mussel Mytiuls edulis I. mantle cells].

    PubMed

    Daugavet, M A; Blinova, M I

    2015-01-01

    To date, cell lines derived from marine invertebrates have not been available. Hence primary cell cultures serve as model systems for various experiments. In present study we established primary culture of mussel Mytilus edulis L. mantle cells. Cells were isolated by means of explant culture or enzymatic dissociation of mantle tissue. They maintained viability up to 22 months regardless of culture initiation method. In course of culturing, cells, which were transferred onto new plates, successfully attached to a new surface. Physiological activity of cultured cells was also confirmed by formation of crystals, which appeared after 4-6 months. After continuous time of culturing, mantle cells can be cryopreserved using 5 % DMSO with post-freezing survival up to 50%. These results demonstrate that M. edulis mantle cells can maintain viability and physiological activity for exceptionally long time and can be cryopreserved for further examination.

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

    SciTech Connect

    Miyagoshi, Takehiro; Tachinami, Chihiro; Kameyama, Masanori; Ogawa, Masaki E-mail: ctchnm.geo@gmail.com E-mail: cmaogawa@mail.ecc.u-tokyo.ac.jp

    2014-01-01

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

  2. Ocean-Atmosphere-Land interactions and their consequences on the biogeochemical variability in Eastern Boundary Upwelling System

    NASA Astrophysics Data System (ADS)

    Renault, L.; McWilliams, J. C.; Deutsch, C.; Molemaker, M. J.

    2015-12-01

    Coastal winds and upwelling of deep water along Eastern Boundary Upwelling System (EBUS) yield some of the ocean's most productive ecosystems, but the effect of coastal wind shape and ocean-atmosphere interactions on regional Net Primary Production (NPP) is not well known. Here, we first show how the spatial and temporal variability of nearshore winds in EBUS is affected by orography, coastline shape, and air-sea interaction. Using regional atmospheric simulations over the US West Coast, we determine monthly characteristics of the wind drop-off, and show that when the mountain orography is combined with the coastline shape of a cape, it has the biggest influence on wind drop-off. Then, using a realistic ocean model of the California Current System, we show that the slackening of the winds near the coast has little effect on near-shore phytoplankton productivity, despite a large reduction in upwelling velocity. On a regional scale, the wind drop-off leads to a substantially higher NPP, especially when it occurs over a broad swath, even when the total upwelling rate remains the same. This partial decoupling of NPP from upwelling is effected by alongshore currents and the eddies they generate. When peak winds extend all the way to the coast, alongshore current shear is stronger, and a more energetic eddy field subducts nutrients offshore and out of the photic zone, reducing overall productivity. This causal sequence is supported by satellite remote sensing. Finally, using a interanual coupled simulation over the US West Coast, we show the ocean-atmosphere interactions can also reduce the eddy activity by pumping energy out from the eddies, reducing their amplitude and rotation speed, and leading to more realistic eddies characteristics. This may also reduce the eddy quenching and therefore increase the NPP. This complex ocean-atmosphere-land interactions imply that simple wind indices are incomplete predictors of productivity in EBUS.

  3. Rapid Mantle Ascent Rates Beneath Brazil: Diamond Bullets from a Smoking Plume?

    NASA Astrophysics Data System (ADS)

    Walter, M. J.; Frost, D. J.

    2010-12-01

    The concept of upwelling plumes of mantle material is, for many, integral to plate tectonics theory. However, proving that plumes exist has been frustrating, and a growing cadre of geoscientists either deny their existence, or remain uncomfortably agnostic. To the uninitiated, seismic tomography can seem a game of now-you-see-it, now-you-don’t, and igneous petrology a malarial fever of now-it's-hot, now-it's-cold. We suggest that diamonds and their mineral inclusions from Juina, Brazil, may provide direct evidence for rapid mantle ascent caused by an upwelling plume. Cretaceous kimberlites in Juina are famous for producing diamonds with inclusions that originated at transition zone and lower mantle depths [1]. Many of these sublithospheric inclusions show evidence of un-mixing of original single-phase minerals into composite inclusions during ascent in the mantle unrelated to kimberlite eruption [2,3]. What is not known is the timeframe or causality of mantle ascent. Diamonds are notoriously hard to date, but Re/Os dates of sulfide inclusions in lithospheric diamonds are generally Early Proterozoic or older, whereas host kimberlites are typically much younger [4]. If the Brazilian diamonds were also ancient, then un-mixing could have been the result of a couple billion years of passive upward migration in the mantle, unrelated to anything so torrid as a mantle plume. Diamond J1 from the Collier4 kimberlite has a composite CaTiO3+CaSiO3 inclusion in a core growth zone (originally perovskite) and a majoritic garnet inclusion in a rim zone. On the basis of excess silica in its formula, the garnet crystallized at 6-7 GPa (about 200 km), consistent with the un-mixing pressure obtained from the perovskite [5]. Experimental phase relations show that the original single-phase perovskite must have formed deeper, between about 300 and 700 km [5]. Thus, diamond J1 exhibits polybaric growth, having ascended some 100 to 500 km during its growth history. Many other mineral

  4. Iron geochemistry of the mantle

    NASA Astrophysics Data System (ADS)

    Humayun, M.; Campbell, T. J.; Brandon, A. D.; Davis, F. A.; Hirschmann, M. M.

    2011-12-01

    The Fe/Mg ratio is an important constraint on the compositionally controlled density of the mantle. However, this ratio cannot be inferred from erupted lavas from OIB or MORB sources, but must be determined directly from mantle peridotites. Recently, the Fe/Mn ratio of erupted lavas has been used as an indicator of potential Fe variability in the mantle driven by core-mantle interaction, recycled oceanic crust, or even variations in the temperature of mantle melting. The classic compilation of McDonough & Sun (1995) provided the currently accepted Fe/Mn ratio of the upper mantle, 60±10. The uncertainty on this ratio allows for 15-30% variability in mantle iron abundances, which is equivalent to a density variation larger than observed by seismic tomography in the mantle. To better understand the relationship between mantle peridotites and erupted lavas, and to search for real variability in the Fe/Mn ratio of mantle peridotites, we report precise new ICP-MS measurements of the transition element geochemistry of suites of mantle xenoliths that have known Fe/Mg ratios. For 12 Kilbourne Hole xenoliths, we observe a clear correlation between Fe/Mn and MgO (or Fe/Mg) over an Fe/Mn range of 59-72. Extrapolation of this trend to a Primitive Mantle (PM) MgO content of 37.8 yields an Fe/Mn of 59±1 for the PM. Our new analyses of KLB-1 powder and fused glass beads yield an Fe/Mn of 61.4 for both samples, which plots on the Kilbourne Hole Fe/Mn vs. MgO trend. A set of ten xenoliths from San Carlos yield a wide range of Fe/Mn (56-65) not correlated with MgO content. The San Carlos xenoliths may have experienced a metasomatic effect that imprinted variable Fe/Mn. A clinopyroxene-rich lithology from San Carlos yields an Fe/Mn of 38, which plots on an extension of the Kilbourne Hole Fe/Mn vs. MgO trend. These new results, and those from other xenolith localities being measured in our lab, provide new constraints on the compositional variability of the Earth's upper mantle. Mc

  5. Osmium isotopes and mantle convection.

    PubMed

    Hauri, Erik H

    2002-11-15

    The decay of (187)Re to (187)Os (with a half-life of 42 billion years) provides a unique isotopic fingerprint for tracing the evolution of crustal materials and mantle residues in the convecting mantle. Ancient subcontinental mantle lithosphere has uniquely low Re/Os and (187)Os/(188)Os ratios due to large-degree melt extraction, recording ancient melt-depletion events as old as 3.2 billion years. Partial melts have Re/Os ratios that are orders of magnitude higher than their sources, and the subduction of oceanic or continental crust introduces into the mantle materials that rapidly accumulate radiogenic (187)Os. Eclogites from the subcontinental lithosphere have extremely high (187)Os/(188)Os ratios, and record ages as old as the oldest peridotites. The data show a near-perfect partitioning of Re/Os and (187)Os/(188)Os ratios between peridotites (low) and eclogites (high). The convecting mantle retains a degree of Os-isotopic heterogeneity similar to the lithospheric mantle, although its amplitude is modulated by convective mixing. Abyssal peridotites from the ocean ridges have low Os isotope ratios, indicating that the upper mantle had undergone episodes of melt depletion prior to the most recent melting events to produce mid-ocean-ridge basalt. The amount of rhenium estimated to be depleted from the upper mantle is 10 times greater than the rhenium budget of the continental crust, requiring a separate reservoir to close the mass balance. A reservoir consisting of 5-10% of the mantle with a rhenium concentration similar to mid-ocean-ridge basalt would balance the rhenium depletion of the upper mantle. This reservoir most likely consists of mafic oceanic crust recycled into the mantle over Earth's history and provides the material that melts at oceanic hotspots to produce ocean-island basalts (OIBs). The ubiquity of high Os isotope ratios in OIB, coupled with other geochemical tracers, indicates that the mantle sources of hotspots contain significant quantities

  6. Dissolved Organic Phosphorus Production during Simulated Phytoplankton Blooms in a Coastal Upwelling System

    PubMed Central

    Ruttenberg, K. C.; Dyhrman, S. T.

    2012-01-01

    Dissolved organic phosphorus (DOP) is increasingly recognized as an important phosphorus source to marine primary producers. Despite its importance, the production rate and fate of DOP is poorly understood. In this study, patterns of DOP production were evaluated by tracking the evolution of DOP during simulated phytoplankton blooms initiated with nutrient amended surface waters, relative to controls, from the Oregon (USA) coastal upwelling system. Nitrogen (N) and phosphorus (P) additions were used to decouple DOP production and hydrolysis by inducing or repressing, respectively, community alkaline phosphatase activity. In order to examine the progression of nutrient uptake and DOP production under upwelling versus relaxation conditions, two experiments were initiated with waters collected during upwelling events, and two with waters collected during relaxation events. Maximum [under (+P) conditions] and minimum [under (+N) conditions] DOP production rates were calculated and applied to in situ DOP levels to evaluate which end-member rate most closely approximates the in situ DOP production rate at the four study sites in this coastal system. Increases in DOP concentration occurred by day-5 in control treatments in all experiments. N treatments displayed increased chlorophyll a, increased alkaline phosphatase activity, and yielded lower net DOP production rates relative to controls, suggesting that DOP levels were depressed as a consequence of increased hydrolysis of bioavailable DOP substrates. Phosphorus additions resulted in a significant net production of DOP at all stations, but no increase in chlorophyll a relative to control treatments. The contrasting patterns in DOP production between treatments suggests that changes in the ambient dissolved inorganic nitrogen:dissolved inorganic phosphorus (DIN:DIP) ratio could exert profound control over DOP production rates in this system. Patterns of DOP production across the different experiments also suggest that

  7. Can upwelling signals be detected in intertidal fishes of different trophic levels?

    PubMed

    Pulgar, J; Poblete, E; Alvarez, M; Morales, J P; Aranda, B; Aldana, M; Pulgar, V M

    2013-11-01

    For intertidal fishes belonging to three species, the herbivore Scartichthys viridis (Blenniidae), the omnivore Girella laevifrons (Kyphosidae) and the carnivore Graus nigra (Kyphosidae), mass and body size relationships were higher in individuals from an upwelling zone compared with those from a non-upwelling zone. RNA:DNA were higher in the herbivores and omnivores from the upwelling zone. Higher biomass and RNA:DNA in the upwelling intertidal fishes may be a consequence of an increased exposure to higher nutrient availability, suggesting that increased physiological conditioning in vertebrates from upwelling areas can be detected and measured using intertidal fishes of different trophic levels.

  8. High-resolution Waveform Tomography of Mantle Transition Zone and Slab Structure beneath Northeast China

    NASA Astrophysics Data System (ADS)

    TAO, K.; Grand, S.; Niu, F.; Chen, M.; Zhu, H.

    2015-12-01

    Northeast China has undergone widespread extension and magmatism since Late Cretaceous. There are many Cenozoic volcanoes in this region and a few of them are still active today, such as Changbaishan and Wudalianchi. Previous tomography models show stagnant slabs within the transition zone beneath NE China, and suggest deep slab control on the regional tectonics and volcanism. Proposed mechanisms for the magmatism include: 1) a mantle plume, 2) hot upwelling above the stagnant slab by deep dehydration and 3) upwelling induced by deep slab segmentation and detachment. To date, NE China seismic images still contain enough uncertainty to allow for multiple models. Using the dense seismic data coverage in NE China and adjacent regions our goal is to make high-resolution image of the transition zone and slab structure to test the origins of intraplate volcanism. Recently Chen et al. (2015) developed a 3D model for P and S velocity structure beneath East Asia using adjoint tomography using the SPECFEM3D synthetic technique and cross-correlation time shifts as the objective function. We use their model as a starting model and further improve the resolution by fitting waveforms to a shorter period (from ~12s to ~5s) using the correlation coefficient as the objective function. The new objective function is closely related to the L2 waveform misfit but is insensitive to a constant amplitude ratio between the synthetic and data within each time window used. This feature is desirable because the absolute amplitude can be hard to model as it can be affected by many factors difficult to incorporate in simulations, such as site effects, source magnitude and mechanism error or even poor calibration of instruments. During inversion we focus specifically on the transition zone and the structure of slabs with the goal of fitting triplicated and multipath body waves. We have performed a waveform inversion experiment using data from a single deep earthquake. Excellent fits of the

  9. Mantle convection on modern supercomputers

    NASA Astrophysics Data System (ADS)

    Weismüller, Jens; Gmeiner, Björn; Mohr, Marcus; Waluga, Christian; Wohlmuth, Barbara; Rüde, Ulrich; Bunge, Hans-Peter

    2015-04-01

    Mantle convection is the cause for plate tectonics, the formation of mountains and oceans, and the main driving mechanism behind earthquakes. The convection process is modeled by a system of partial differential equations describing the conservation of mass, momentum and energy. Characteristic to mantle flow is the vast disparity of length scales from global to microscopic, turning mantle convection simulations into a challenging application for high-performance computing. As system size and technical complexity of the simulations continue to increase, design and implementation of simulation models for next generation large-scale architectures demand an interdisciplinary co-design. Here we report about recent advances of the TERRA-NEO project, which is part of the high visibility SPPEXA program, and a joint effort of four research groups in computer sciences, mathematics and geophysical application under the leadership of FAU Erlangen. TERRA-NEO develops algorithms for future HPC infrastructures, focusing on high computational efficiency and resilience in next generation mantle convection models. We present software that can resolve the Earth's mantle with up to 1012 grid points and scales efficiently to massively parallel hardware with more than 50,000 processors. We use our simulations to explore the dynamic regime of mantle convection assessing the impact of small scale processes on global mantle flow.

  10. Mantle Convection on Modern Supercomputers

    NASA Astrophysics Data System (ADS)

    Weismüller, J.; Gmeiner, B.; Huber, M.; John, L.; Mohr, M.; Rüde, U.; Wohlmuth, B.; Bunge, H. P.

    2015-12-01

    Mantle convection is the cause for plate tectonics, the formation of mountains and oceans, and the main driving mechanism behind earthquakes. The convection process is modeled by a system of partial differential equations describing the conservation of mass, momentum and energy. Characteristic to mantle flow is the vast disparity of length scales from global to microscopic, turning mantle convection simulations into a challenging application for high-performance computing. As system size and technical complexity of the simulations continue to increase, design and implementation of simulation models for next generation large-scale architectures is handled successfully only in an interdisciplinary context. A new priority program - named SPPEXA - by the German Research Foundation (DFG) addresses this issue, and brings together computer scientists, mathematicians and application scientists around grand challenges in HPC. Here we report from the TERRA-NEO project, which is part of the high visibility SPPEXA program, and a joint effort of four research groups. TERRA-NEO develops algorithms for future HPC infrastructures, focusing on high computational efficiency and resilience in next generation mantle convection models. We present software that can resolve the Earth's mantle with up to 1012 grid points and scales efficiently to massively parallel hardware with more than 50,000 processors. We use our simulations to explore the dynamic regime of mantle convection and assess the impact of small scale processes on global mantle flow.

  11. Unusual δ56Fe values in Samoan rejuvenated lavas generated in the mantle

    NASA Astrophysics Data System (ADS)

    Konter, Jasper G.; Pietruszka, Aaron J.; Hanan, Barry B.; Finlayson, Valerie A.; Craddock, Paul R.; Jackson, Matthew G.; Dauphas, Nicolas

    2016-09-01

    Several magmatic processes contribute to the Fe isotope composition of igneous rocks. Most basalts fall within a limited range of δ56Fe (+ 0.10 ± 0.05 ‰), although more differentiated lavas trend towards slightly elevated values (up to + 0.3 ‰). New data for basalts and olivine crystals from the Samoan Islands show higher δ56Fe values than have previously been reported for basalts worldwide. Common magmatic processes - from partial melting of average mantle to subsequent differentiation of melts - cannot sufficiently fractionate the Fe isotopes to explain the elevated δ56Fe values (∼ + 0.3 ‰) in rejuvenated Samoan lavas. Instead, a mantle source with an elevated δ56Fe value - in conjunction with effects due to common magmatic processes - is required. The Samoan mantle source is known to be unique in its radiogenic isotope composition and indications that melting of the Samoan mantle source can generate elevated δ56Fe values in lavas comes from: (1) High fO2 values of Samoan lavas and their likely sources affecting Fe isotope fractionation during melting; (2) Metasomatism that caused elevated δ56Fe in the Samoan mantle, as observed in xenoliths; and (3) Involvement of a pyroxenite source lithology, based on the Zn/Fe ratios and TiO2 (and other high field-strength element) abundances of the lavas, that can generate melts with elevated δ56Fe values. Two models are presented to explain the elevated δ56Fe values in Samoan lavas: a metasomatized source (∼ + 0.07 ‰) or the presence of a pyroxenite source component (∼ + 0.12 ‰). Both models subsequently elevate δ56Fe values with both partial melting (∼ + 0.14 ‰) and fractional crystallization (∼ + 0.1 ‰). These processes may be related to an upwelling mantle plume with a pyroxenite component, or melting of previously metasomatized upper mantle.

  12. Does the "mantle" helium signature provide useful information about lithospheric architecture of Tibet/Himalaya?

    NASA Astrophysics Data System (ADS)

    Klemperer, S. L.; Liu, T.; Hilton, D. R.; Karlstrom, K. E.; Crossey, L. J.; Zhao, P.

    2015-12-01

    Measurements of 3He/4He > 0.1*Ra (where Ra = 3He/4He in Earth's atmosphere) in geothermal fluids are conventionally taken to represent derivation from a mantle source. 3He/4He values < 0.1*Ra are taken to represent only radiogenic helium with no modern mantle input (the canonical 3He/4He ratio for the crust is 0.02*Ra). Upward transport rates are hard to constrain, but transit times of 3He through the crust in a CO2-rich carrier fluid may be as short as a few years, so 3He/4He measurements offer a proxy for mantle temperature on geologically short time-scales. In Tibet, enhanced 3He/4He ratios could in principle represent (1) incipient partial melt of Indian lithospheric mantle; (2) of Asian lithospheric mantle; (3) upwelling asthenosphere north of underthrust India or along tears in the subducting Indian plate; and/or (4) high-T prograde metamorphism releasing previously trapped 3He from older, voluminous mafic/ultramafic rocks in the crust. We present data from our recent field campaigns and our compilations from the western and Chinese literature. Any individual observation of 3He/4He > 0.1*Ra may still be argued to result from mantle-derived 3He previously stored in the crust. However, our growing regional database of widely spaced observations of 3He/4He > 0.1*Ra, from the Karakoram Fault in the west to the Sangri-Cona rift and Yalaxiangbo Dome in the east, and from south of the Yarlung-Zangbo suture (YZS) to north of the Banggong-Nujiang suture, makes such special pleading increasingly implausible. The observation of 3He/4He > 0.1*Ra at the YZS and even within the Tethyan Himalaya south of the YZS cannot represent melting of Indian mantle close to the Moho unless existing thermal models are grossly in error. The source of 3He close to the YZS is likely either asthenosphere accessed by faults and shear zones that cut through subducting Indian lithospheric mantle; or incipient melt of Asian lithospheric mantle at the Moho north of the northern edge of

  13. Volatile cycling and the thermal evolution of planetary mantle

    NASA Astrophysics Data System (ADS)

    Sandu, Constantin

    The thermal histories of terrestrial planets are investigated using two parameterized mantle convection models for either Earth like planets and planets with no active plate tectonics. Using parameterized models of mantle convection, we performed computer simulations of planetary cooling and volatile cycling. The models estimate the amount of volatile in mantle reservoir, and calculate the outgassing and regassing rates. A linear model of volatile concentration-dependent is assumed for the activation energy of the solid-state creep in the mantle. The kinematic viscosity of the mantle is thus dynamically affected by the activation energy through a variable concentration in volatile. Mantle temperature and heat flux is calculated using a model derived from classic thermal boundary layer theory of a single layered mantle with temperature dependent viscosity. The rate of volatile exchanged between mantle and surface is calculated by balancing the amount of volatiles degassed in the atmosphere by volcanic and spreading related processes and the amount of volatiles recycled back in the mantle by the subduction process. In the cases that lack plate tectonics, the degassing efficiency is dramatically reduced and the regassing process is absent. The degassing effect is dependent on average spreading rate of tectonic plates and on the amount of volatile in the melt extract in the transition zone between mantle and upper boundary laver. The regassing effect is dependent on the subduction rate and on the amount of volatile present on a hydrated layer on top of the subducting slab. The degassing and regassing parameters are all related to the intensity of the convection in the mantle and to the surface temperature of the planet, and they are regulated by the amount of volatiles in reservoir. Comparative study with the previous models display significant differences and improve the versatility of the model. The optimum efficiency factors found are in the range of 0.01--0.06 for

  14. Episodic Earth Evolution: a Mantle Geodynamic Model

    NASA Astrophysics Data System (ADS)

    Davaille, A.; Arndt, N.

    2008-12-01

    Three major regimes of crust-mantle evolution are recorded in U-Pb ages of zircons in granites and large rivers. Plate tectonics operated in the first stage, from ~4.4 to 2.7 Ga; huge peaks of crustal growth separated by long troughs dominated the second stage, from 2.7 to 1.8 Ga, and semi-continuous growth punctuated by large peaks characterized the last stage, from 1.8 to 0 Ga. Individual peaks in the second stage, at 2.7, 2.5, 2.1 and 1.8 Ga, open with massive mafic-ultramafic volcanism and climax 30 m.y. later with intrusion of voluminous granitoids: each peak was initiated by enhanced mantle plume activity, culminated with accelerated plate tectonics that produced large amounts of granitoid crust, and was followed by a long period of diminished tectonic activity. New fluid-mechanics experiments show that this second regime could have resulted from destabilization of a hot dense layer at the bottom of the lower mantle. Domes rising from this layer partially melt to form voluminous mafic magmas, and also trigger enhanced subduction. The first pulse of thermochemical instabilities was synchronous over the whole mantle, like the major 2.7 Ga crustal- growth peak, and later pulses were more disorganized, like the later peaks. During each peak, enhanced subduction removes quickly the upper cold thermal boundary layer: it is therefore followed by an inter-peak period of diminished activity, during which the cold boundary layer is growing again. This episodic evolution closely links continental growth and the extraction of heat from the core. In particular, the onset of the second regim could have been decisive for the timing of the inner core crystallization and the establishment of today's core dynamo regim.

  15. The statistical upper mantle assemblage

    NASA Astrophysics Data System (ADS)

    Meibom, Anders; Anderson, Don L.

    2004-01-01

    A fundamental challenge in modern mantle geochemistry is to link geochemical data with geological and geophysical observations. Most of the early geochemical models involved a layered mantle and the concept of geochemical reservoirs. Indeed, the two layer mantle model has been implicit in almost all geochemical literature and the provenance of oceanic island basalt (OIB) and mid-ocean ridge basalt (MORB) [van Keken et al., Annu. Rev. Earth Planet. Sci. 30 (2002) 493-525]. Large-scale regions in the mantle, such as the 'convective' (i.e. well-stirred, homogeneous) upper mantle, sub-continental lithosphere, and the lower mantle were treated as distinct and accessible geochemical reservoirs. Here we discuss evidence for a ubiquitous distribution of small- to moderate-scale (i.e. 10 2-10 5 m) heterogeneity in the upper mantle, which we refer to as the statistical upper mantle assemblage (SUMA). This heterogeneity forms as the result of long-term plate tectonic recycling of sedimentary and crustal components. The SUMA model does not require a convectively homogenized MORB mantle reservoir, which has become a frequently used concept in geochemistry. Recently, Kellogg et al. [Earth Planet. Sci. Lett. 204 (2002) 183-202] modeled MORB and OIB Sr and Nd isotopic compositions as local mantle averages of random distributions of depleted residues and recycled continental crustal material. In this model, homogenization of the MORB source region is achieved by convective stirring and mixing. In contrast, in the SUMA model, the isotopic compositions of MORB and OIB are the outcome of homogenization during sampling, by partial melting and magma mixing (e.g. [Helffrich and Wood, Nature 412 (2001) 501-507]), of a distribution of small- to moderate-scale upper mantle heterogeneity, as predicted by the central limit theorem. Thus, the 'SUMA' acronym also captures what we consider the primary homogenization process: sampling upon melting and averaging. SUMA does not require the

  16. The role of Equatorial Undercurrent in sustaining the Eastern Indian Ocean upwelling

    NASA Astrophysics Data System (ADS)

    Chen, Gengxin; Han, Weiqing; Shu, Yeqiang; Li, Yuanlong; Wang, Dongxiao; Xie, Qiang

    2016-06-01

    By combining volume transport and salinity analysis from 1958 to 2014, this paper investigates how the transient Equatorial Undercurrent (EUC) sustains the summer-fall equatorial eastern Indian Ocean (EIO) upwelling. On seasonal time scales, the EIO upwelling is mainly supplied by the salty water from the western basin through a buffering process: The winter-spring EUC carries the salty water from the western basin eastward, induces downwelling in the EIO, and pushes portion of the salty water below the central thermocline, which subsequently upwells to the central thermocline during summer-fall and sustains the EIO upwelling. On interannual time scales, enhanced upwelling occurs during positive Indian Ocean Dipole (+IOD) years. The strong summer-fall EUC associated with the +IOD supplies water for the intensified upwelling. This research provides new knowledge for basin-scale mass and property exchanges associated with the EIO upwelling, contributing to our understanding of three-dimensional ocean circulation and climate variability.

  17. Upper mantle P velocity structure beneath the Baikal Rift from modeling regional seismic data

    NASA Astrophysics Data System (ADS)

    Brazier, Richard A.; Nyblade, Andrew A.

    2003-02-01

    Uppermost mantle P wave velocity structure beneath the Baikal rift and southern margin of the Siberian Platform has been investigated by using a grid search method to model Pnl waveforms from two moderate earthquakes recorded by station TLY at the southwestern end of Lake Baikal. The results yielded a limited number of successful models which indicate the presence of upper mantle P wave velocities beneath the rift axis and the margin of the platform that are 2-5% lower than expected. The magnitude of the velocity anomalies and their location support the presence of a thermal anomaly that extends laterally beyond the rift proper, possibly created by small-scale convection or a plume-like, thermal upwelling.

  18. Coupled Atmosphere-Hydrosphre-Mantle Evolution: Exploring Mantle Feedbacks

    NASA Astrophysics Data System (ADS)

    Moore, W. B.

    2008-12-01

    Venus is, in bulk, nearly Earth's twin, yet the tectonic styles of the two planets are radically different. Suggested explanations for this extreme difference have invoked the lack of liquid water on Venus, the greater degree of crustal differentiation on Venus, and recently, the effect of the elevated surface temperature on convective stresses. These explanations generally involve an interaction between the state of the atmosphere/hydrosphere and the state of the mantle. Atmospheric evolution models have long considered the interaction between different reservoirs, including the mantle, but have never considered the feedback between rates of mantle processes and volatile recycling rates. Coupled atmospheric- hydrosphere-mantle dynamics models will be presented that explore the relationships between water recycling, mantle viscosities, lithospheric stresses, melt production rates and plate yielding. The models include two-dimensional solutions of mantle flow that include water-dependent viscosity and solidus behavior, volatile recycling and outgassing, and a parameterized greenhouse atmosphere with both carbon dioxide and water reservoirs. The complex system of feedbacks yields multiple equilibira and quasi-stable oscillatory states.

  19. Mantle plumes - A boundary layer approach for Newtonian and non-Newtonian temperature-dependent rheologies. [modeling for island chains and oceanic aseismic ridges

    NASA Technical Reports Server (NTRS)

    Yuen, D. A.; Schubert, G.

    1976-01-01

    Stress is placed on the temperature dependence of both a linear Newtonian rheology and a nonlinear olivine rheology in accounting for narrow mantle flow structures. The boundary-layer theory developed incorporates an arbitrary temperature-dependent power-law rheology for the medium, in order to facilitate the study of mantle plume dynamics under real conditions. Thermal, kinematic, and dynamic structures of mantle plumes are modelled by a two-dimensional natural-convection boundary layer rising in a fluid with a temperature-dependent power-law relationship between shear stress and strain rate. An analytic similarity solution is arrived at for upwelling adjacent to a vertical isothermal stress-free plane. Newtonian creep as a deformation mechanism, thermal anomalies resulting from chemical heterogeneity, the behavior of plumes in non-Newtonian (olivine) mantles, and differences in the dynamics of wet and dry olivine are discussed.

  20. Influence of the Geometry on Mantle Convection Models

    NASA Astrophysics Data System (ADS)

    Noack, L.; Tosi, N.

    2012-04-01

    Modelling of geodynamic processes like mantle or core convection has strongly improved over the last two decades thanks to the steady development of numerical codes that tend to incorporate a more and more realistic physics. High-performance parallel computations allow the simulation of complex problems, such as the self-consistent generation of tectonic plates or the formation of planetary magnetic fields. However, the need to perform broad explorations of the parameter space and the large computational demands imposed by the non-linear, multi-scale nature of convection require several simplifications, in the domain geometry as well as in the physical complexity of the problem. A straightforward approach to limit the computational complexity of the simulations is to decrease the total number of degrees of freedom of the problem by reducing either the number of dimensions or the size of the model domain. On the one hand, for a given resolution, a 3D spherical shell clearly needs a much larger number of grid points than a 2D cylindrical shell or a 2D Cartesian box. At the resolutions typically employed to solve mantle convection problems, this difference amounts to at least a factor of a few hundreds. On the other hand, for certain problems, only a relatively small part of the mantle may be of interest, as in the case of the modelling of subduction [1], mid-ocean ridges or transform faults [2]. We adapted the code GAIA [3] to solve the Stokes problem in several different geometries (Cartesian box, cylindrical, spherical and regional-spherical) and dimensions (2D and 3D) and started a benchmark along the lines of [4] to assess the loss of accuracy when using reduced domains instead of a 3D spherical shell [5]. In general, upwellings in Cartesian geometry are rather flat, whereas the spherical geometry changes their shape to more mushroom-like structures. Furthermore, the number of plumes, which is representative of the characteristic wavelength of convection, varies

  1. Vibrio diversity and dynamics in the Monterey Bay upwelling region

    PubMed Central

    Mansergh, Sarah; Zehr, Jonathan P.

    2013-01-01

    The Vibrionaceae (Vibrio) are a ubiquitous group of metabolically flexible marine bacteria that play important roles in biogeochemical cycling in the ocean. Despite this versatility, little is known about Vibrio diversity and abundances in upwelling regions. The seasonal dynamics of Vibrio populations was examined by analysis of 16S rRNA genes in Monterey Bay (MB), California from April 2006–April 2008 at two long term monitoring stations, C1 and M2. Vibrio phylotypes within MB were diverse, with subpopulations clustering with several different cultured representatives including Allivibrio spp., Vibrio penaecida, and Vibrio splendidus as well as with many unidentified marine environmental bacterial 16S rRNA gene sequences. Total Vibrio population abundances, as well as abundances of a Vibrio sp. subpopulation (MBAY Vib7) and an Allivibrio sp. subpopulation (MBAY Vib4) were examined in the context of environmental parameters from mooring station and CTD cast data. Total Vibrio populations showed some seasonal variability but greater variability was observed within the two subpopulations. MBAY Vib4 was negatively associated with MB upwelling indices and positively correlated with oceanic season conditions, when upwelling winds relax and warmer surface waters are present in MB. MBAY Vib7 was also negatively associated with upwelling indices and represented a deeper Vibrio sp. population. Correlation patterns suggest that larger oceanographic conditions affect the dynamics of the populations in MB, rather than specific environmental factors. This study is the first to target and describe the diversity and dynamics of these natural populations in MB and demonstrates that these populations shift seasonally within the region. PMID:24575086

  2. Monsoon response of the Somali Current and associated upwelling

    NASA Astrophysics Data System (ADS)

    Schott, Friedrich

    The Somali Current typically develops in different phases in response to the onset of the summer monsoon. Each of these phases exists quasistationary for some time ranging from weeks to months. These periods of rather constant circulation patterns are separated by periods of rapid transition. In the early phase of the monsoon response, during May, with weak southerly winds off Somalia, a cross equatorial inertial current develops which turns offshore a few degrees north of the equator with a coastal upwelling wedge just north of the offshore flow. North of that region, an Ekman upwelling regime exists all the way up the coast. At the onset of strong winds in June, a northern anticyclonic gyre develops north of 5°N and a second cold wedge forms north of 8°-9°N, where that current turns offshore. The most drastic change of upwelling pattern occurs in the late phase of the summer monsoon, August/September, when the southern cold wedge propagates northward, indicating a break-down of the two-gyre pattern and development of a continuous boundary current from south of the equator to about 10°N. The wedge propagation during 1976-1978 is discussed, based on satellite observations (EVANS and BROWN, 1981), moored station data during 1978, 1979 and shipboard hydrographic data during 1979. A simple relation between the decrease of local monsoon winds offshore and wedge propagation cannot be determined. The southward coastal undercurrent, which is part of the Ekman upwelling regime north of 5° during the early summer monsoon, seems to turn offshore between 3° and 5°, probably due to a zonal excursion of depth contours in that area. With the spin-up of the deep-reaching northern gyre the undercurrent is extinguished during July to August but seems to get reestablished after the coalescence of the two gyres.

  3. Determining correlation between Emerita analoga recruitment and coastal upwelling (Invited)

    NASA Astrophysics Data System (ADS)

    Wong, K.; Godoy, E.; Dean, A.; Johnson, R.

    2009-12-01

    Since 2003, Careers in Science (CiS) interns have been participating in the Farallones Marine Sanctuary Association's Long-term Monitoring Program and Experiential Training for Students (LiMPETS) program monitoring populations of Emerita analoga, the Pacific mole crab. The CiS intern program at the California Academy of Sciences is a multi-year, year-round work-based science education and youth development program for young people from groups typically under-represented in the sciences. E. analoga, an inhabitant of sandy beach swash zone, plays an essential role in marine food webs. Recent studies have suggested E. analoga to be indicators of DDT and domoic acid in the ecosystem. My peers and I collected E. analoga to determine population demographics, including size and sex. On a weekly basis during the months of June, July and August, at San Francisco’s Ocean Beach in Golden Gate National Recreational Area we systematically collect live samples and data for the population monitoring. From June to August 2009, field observations indicated the most abundant E. analoga recruit populations since 2003. After observing this change, we wanted to find possible causes for the increase in recruits. We hypothesized that there was a correlation between recruit population and coastal upwelling events because of the increased nutrient availability due to the events. We compared recruit population data from 2003 through 2009 to upwelling anomalies off the coast of San Francisco. We did not find an increased recruit population 4 to 5 months after an upwelling event, which is the time needed for E. analoga to develop from its planktonic stage to a recruit. One implication of our comparison is that upwelling events cannot be directly correlated with successful recruiting of E. analoga.

  4. Meteorological constraints on oceanic halocarbons above the Peruvian upwelling

    NASA Astrophysics Data System (ADS)

    Fuhlbrügge, Steffen; Quack, Birgit; Atlas, Elliot; Fiehn, Alina; Hepach, Helmke; Krüger, Kirstin

    2016-09-01

    During a cruise of R/V METEOR in December 2012 the oceanic sources and emissions of various halogenated trace gases and their mixing ratios in the marine atmospheric boundary layer (MABL) were investigated above the Peruvian upwelling. This study presents novel observations of the three very short lived substances (VSLSs) - bromoform, dibromomethane and methyl iodide - together with high-resolution meteorological measurements, Lagrangian transport and source-loss calculations. Oceanic emissions of bromoform and dibromomethane were relatively low compared to other upwelling regions, while those for methyl iodide were very high. Radiosonde launches during the cruise revealed a low, stable MABL and a distinct trade inversion above acting as strong barriers for convection and vertical transport of trace gases in this region. Observed atmospheric VSLS abundances, sea surface temperature, relative hu