Science.gov

Sample records for active mantle upwelling

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

    NASA Astrophysics Data System (ADS)

    Putirka, K. D.

    2006-05-01

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

  2. Mantle thermal structure and active upwelling during continental breakup in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Holbrook, W. Steven; Larsen, H. C.; Korenaga, J.; Dahl-Jensen, T.; Reid, I. D.; Kelemen, P. B.; Hopper, J. R.; Kent, G. M.; Lizarralde, D.; Bernstein, S.; Detrick, R. S.

    2001-08-01

    Seismic reflection and refraction data acquired on four transects spanning the Southeast Greenland rifted margin and Greenland-Iceland Ridge (GIR) provide new constraints on mantle thermal structure and melting processes during continental breakup in the North Atlantic. Maximum igneous crustal thickness varies along the margin from >30 km in the near-hotspot zone (<500 km from the hotspot track) to ˜18 km in the distal zone (500-1100 km). Magmatic productivity on summed conjugate margins of the North Atlantic decreases through time from 1800±300 to 600±50 km 3/km/Ma in the near-hotspot zone and from 700±200 to 300±50 km 3/km/Ma in the distal zone. Comparison of our data with the British/Faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist. Joint consideration of crustal thickness and mean crustal seismic velocity suggests that along-margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature. The thermal anomaly (Δ T) at breakup was modest (˜100-125°C), varied little along the margin, and transient. Data along the GIR indicate that the potential temperature anomaly (125±50°C) and upwelling ratio (˜4 times passive) of the Iceland hotspot have remained roughly constant since 56 Ma. Our results are consistent with a plume-impact model, in which (1) a plume of radius ˜300 km and Δ T of ˜125°C impacted the margin around 61 Ma and delivered warm material to distal portions of the margin; (2) at breakup (56 Ma), the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin; and (3) by 45 Ma, both the remaining plume head and the distal warm layer were exhausted, with excess magmatism thereafter largely confined to a narrow (<200 km radius) zone immediately above the Iceland plume stem. Alternatively, the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been

  3. 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

  4. 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

  5. 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

  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. 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

  8. 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

  9. 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.

  10. 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

  11. Upwelling process of mantle helium in northeast Japan

    NASA Astrophysics Data System (ADS)

    Horiguchi, K.; Kazahaya, K.; Tsukamoto, H.; Morikawa, N.; Ohwada, M.; Nakama, A.

    2014-12-01

    Northeast Japan has an island arc structure where the Pacific plate subducts from the east. The helium isotope ratio is a good indicator to discriminate the origin of fluid carring helium, because the ratios in the mantle and crust are clearly different from each other. We performed a detailed study of helium isotope ratios in northeast Japan, and clarified the boundaries of the higher and lower helium isotope ratio distributions. The crustal components are dominant in the fore-arc region, whereas the mantle components dominate along the volcanic front and in the back-arc region. It is suggested that the clear contrast of the helium isotope ratio between the fore-arc and back-arc regions is due to the difference in whether helium isotope ratio of the wedge mantle or radiogenic helium-4 production rate in the crust. Specifically, we found the following characteristics; 1) comparison of the distribution between helium isotope ratios and faults revealed that the area along faults shows higher helium isotope ratios, 2) distribution of the helium isotope ratios is correlated with that of Li/Cl ratios which is the indicator of slab-derived water or magmatic water, suggesting that the mantle helium is transported by the slab-derived aqueous fluid. Important constraints on mantle helium upwelling are concluded as follows; a) the slab-derived water as the carrier of mantle helium, b) the faults, tectonic lines and volcanoes as the flow paths of slab-derived water, and c) crustal helium-4 contamination during upwelling process. *This research project has been conducted as the regulatory supporting research funded by the Secretariat of Nuclear Regulation Authority (Secretariat of NRA), Japan.

  12. 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.

  13. Surface expressions of mantle upwellings: Expect the unexpected

    NASA Astrophysics Data System (ADS)

    Druken, K. A.; Kincaid, C. R.; Griffiths, R. W.

    2011-12-01

    Surface expressions of deep mantle upwellings are oftentimes complex and vary from highly simplified schematic models. We present results from a series of 3-D laboratory experiments that examine patterns of strain alignment within mantle upwellings under a variety of tectonic settings (e.g. mid-plate, spreading centers, subduction zones) and compare these to observations from seismic anisotropy studies. Laboratory experiments utilize a glucose working fluid with a temperature dependent density and viscosity. In the strain alignment cases, ~5 mm long synthetic paintbrush hairs, or "whiskers", are embedded within the fluid and used as passive markers for the local orientation of maximum finite strain. Contrary to the common expectation, results show that finite strain aligns tangent, not parallel, to the radial flow within plume heads. In cases where a plume rises under a moving plate or spreading center, strain markers are initially tangential and then evolve towards alignment with the shear flow. Within subduction settings, upwellings are so severely distorted by slab-driven flow that they appear seismically invisible in terms of anisotropy patterns.

  14. Hot mantle upwelling across the 660 beneath Yellowstone

    NASA Astrophysics Data System (ADS)

    Schmandt, Brandon; Dueker, Kenneth; Humphreys, Eugene; Hansen, Steven

    2012-05-01

    P-to-s receiver functions mapped to depth through P and S body-wave tomography models image continuous 410 and 660 km discontinuities beneath the area covered by USArray prior to the year 2011. Mean depths to the 410 and 660 km discontinuities of 410 and 656 km imply a mantle transition zone that is about 4 km thicker than the global average and hence has a slightly cooler mean temperature and/or enhanced water content. Compared to the mean 660 depth beneath this ~ 2000 km wide area, the 660 beneath the Yellowstone hotspot is deflected upward by 12-18 km over an area about 200 km wide. This is the most anomalous shallowing of the 660 imaged and its horizontal extent is similar to the area where P and S tomography image low-velocity mantle extending from the top of the transition zone to about 900 km depth. Together, these results indicate a high-temperature, plume-like upwelling extending across the 660. The depth of 410 km discontinuity beneath the Yellowstone region is within 5 km of the mean depth implying that the plume is vertically heterogeneous and possibly discontinuous. Tomography indicates a similar vertically heterogeneous thermal plume. The irregular plume structure may be intrinsic to the dynamics of upwelling through the transition zone, or distortion may be caused by subduction-induced mantle flow. Topography of the 410 and 660 confirms that subducted slabs beneath the western U.S. are highly segmented, as inferred from recent tomography studies. We find no evidence of regionally pervasive velocity discontinuities between 750 and 1400 km depth. The plume's depth of origin within the lower mantle remains uncertain.

  15. Mantle Upwelling Beneath the East Pacific Rise at 9

    NASA Astrophysics Data System (ADS)

    Key, K.; Constable, S.

    2006-12-01

    In February 2004 we carried out a combined broadband magnetotelluric (MT) and controlled source electromagnetic (CSEM) study of the mid-ocean ridge in the Pacific Ocean at 9-10° North latitude. This paper presents results from MT data collected at 9°30' on the East Pacific Rise (EPR). A 200~km aperture array of 40 sites deployed perpendicular to the ridge axis recorded data for 5-14~days duration. MT impedance responses were obtained in the period band of 20 to 4000~s, which is a higher frequency band than measured by previous ridge MT experiments and thus allows for stronger constraints on the structure of the shallow mantle. Impedance skew estimates, an indicator of 3D conductivity structure, are generally low for sites located west of the ridge axis, while skews as high as 0.7 are observed for sites east of the ridge. Two dimensional inversion of the MT data produces a model with a broad region of conductive mantle that is beneath the ridge axis. The highest conductivities are around 1 ohm-m and are observed 20-40~km east of the ridge axis and at 30-60~km depth. The conductivities constrain most of the mantle melt supply to only a few percent (1-6%) in a region about 150-200~km wide and about 40-60~km thick. However, the anomalously high conductivity region in the east lies atop the broader melting region and requires a nearly fully molten mantle and implies either a locally zone of dynamic upwelling, or else ponding of melt at a permeability barrier. While our modeling has concentrated on the mantle conductivity, the high conductivity region in the east may be related to recent seismic tomographic studies indicating the presence of off-axis crustal melt east of the ridge axis. We can explain our model with mantle melting of dry olivine if we assume a mantle temperature of 1450°C; if we assume a temperature of 1350°C then our model requires mantle hydration to get melting as deep as 80~km. We have generated a thermal model for the mantle by mapping

  16. Mantle P wave travel time tomography of Eastern and Southern Africa: New images of mantle upwellings

    NASA Astrophysics Data System (ADS)

    Benoit, M. H.; Li, C.; van der Hilst, R.

    2006-12-01

    Much of Eastern Africa, including Ethiopia, Kenya, and Tanzania, has undergone extensive tectonism, including rifting, uplift, and volcanism during the Cenozoic. The cause of this tectonism is often attributed to the presence of one or more mantle upwellings, including starting thermal plumes and superplumes. Previous regional seismic studies and global tomographic models show conflicting results regarding the spatial and thermal characteristics of these upwellings. Additionally, there are questions concerning the extent to which the Archean and Proterozoic lithosphere has been altered by possible thermal upwellings in the mantle. To further constrain the mantle structure beneath Southern and Eastern Africa and to investigate the origin of the tectonism in Eastern Africa, we present preliminary results of a large-scale P wave travel time tomographic study of the region. We invert travel time measurements from the EHB database with travel time measurements taken from regional PASSCAL datasets including the Ethiopia Broadband Seismic Experiment (2000-2002); Kenya Broadband Seismic Experiment (2000-2002); Southern Africa Seismic Experiment (1997- 1999); Tanzania Broadband Seismic Experiment (1995-1997), and the Saudi Arabia PASSCAL Experiment (1995-1997). The tomographic inversion uses 3-D sensitivity kernels to combine different datasets and is parameterized with an irregular grid so that high spatial resolution can be obtained in areas of dense data coverage. It uses an adaptive least-squares context using the LSQR method with norm and gradient damping.

  17. 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. PMID:23355951

  18. 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

  19. Three-dimensional Numerical Models of Slab Edges: Implications for Mantle Upwelling and Anomalous Volcanism

    NASA Astrophysics Data System (ADS)

    Jadamec, M.; Moresi, L. N.; Durance-Sie, P. M.; Mclean, K. A.

    2013-05-01

    Adakitic volcanics associated with slab edges have been identified in numerous localities (Defant and Drummond (1990); Yogodzinski et al. (2001); Durance et al. (2012)). However, there is a range in composition as well as hypothesized petrogenetic formation for the samples worldwide designated as adakites (e.g., Yogodzinski and Kelemen (1998); Thorkelson and Breitsprecher (2005); Castillo (2012)). Three-dimensional (3D) models investigating the solid state flow in the mantle due to subduction with a slab edge predict toroidal flow around the slab edge and an associated upward component of flow that may be important for the generation of adakites (Schellart (2004); Piromallo et al. (2006); Jadamec and Billen (2010); Schellart (2010); Jadamec and Billen (2012)). However, the position of the slab edge at depth and associated location of upwelling in the mantle relative to the location of the observed anomalous volcanics on the surface have not been studied in detail. Three-dimensional high-resolution numerical models of subduction are used to investigate slab edge associated mantle upwelling and the potential links to the formation of adakites. The numerical models are geographically referenced to specific subduction zone settings and are constructed with SlabGenerator (Jadamec and Billen, 2010, 2012). The mantle convection code CitcomCU is used to solve for the viscous flow (Moresi and Solomatov, 1995; Moresi and Gurnis, 1996; Zhong, 2006). Specific slab edges settings investigated are the Antilles subduction zone in the eastern Caribbean, the Scotia subduction zone-back arc spreading system, the eastern Alaska subduction-transform system, and the eastern New Hebrides slab edge-back arc spreading system. The models suggest upwelling associated with the return flow around the slab edge can lead to decompression melting located within several hundred kilometers outward of the slab edge, and thus contribute to melting of the slab edge and the formation of adakites. In

  20. 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

  1. 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

  2. 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

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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

  8. Evidence for anomalous mantle upwelling beneath the Arabian Platform from travel time tomography inversion

    NASA Astrophysics Data System (ADS)

    Koulakov, Ivan; Burov, Evgeniy; Cloetingh, Sierd; El Khrepy, Sami; Al-Arifi, Nassir; Bushenkova, Natalia

    2016-01-01

    We present a new model of P-velocity anomalies in the upper mantle beneath the Arabian Peninsula, Red Sea, and surrounding regions. This model was computed with the use of travel time data from the global catalogue of the International Seismological Center (ISC) for the years of 1980-2011. The reliability of the model was tested with several synthetic tests. In the resulting seismic model, the Red Sea is clearly associated with a higher P-velocity anomaly in the upper mantle at least down to 300 km depth. This anomaly might be caused by upward deviation of the main mantle interfaces caused by extension and thinning of the lithosphere due to passive rifting. Thick lithosphere of the Arabian Platform is imaged as a high-velocity anomaly down to 200-250 km depth. Below this plate, we observe a low-velocity structure that is interpreted as a hot mantle upwelling. Based on the tomography results, we propose that this upper mantle anomaly may represent hot material that migrates westward and play a major role in the formation of Cenozoic basaltic lava fields in western Arabia. On the northeastern side of the Arabian Plate, we clearly observe a dipping high-velocity zone beneath Zagros and Makran, which is interpreted as a trace of subduction or delamination of the Arabian Plate lithosphere.

  9. 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.

  10. 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

  11. 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.

  12. Zonal structure of Cenozoic basalts related to mantle upwelling in southwest Japan

    NASA Astrophysics Data System (ADS)

    Iwamori, Hikaru

    1991-04-01

    Cenozoic olivine-bearing basaltic rocks in the central Chugoku district form eight provinces, each 20 to 30 km in diameter. These provinces can be grouped into three zones almost parallel to the elongation of the SW Japan arc, based on geological and petrological characteristics. The San-yo zone (the closest to the Nankai trough) is characterized by a small amount of alkaline basalt. In the Sekiryo zone (intermediate zone), transitional basalt is dominant. The San-in zone along the Japan Sea coast is characterized by subalkaline basalt and a large amount of andesitic rocks. The eruption volume of these volcanics exponentially increases toward the back arc side (less than 1 km3 to more than 100 km3). Chemical compositions of relatively undifferentiated basalts show systematic across-arc variations. SiO2 and Al2O3increase, and FeO*, MgO and CaO decrease toward the back arc side (44 to 54, 13 to 18, 11 to 6, 13 to 7 and 12 to 8 wt % at FeO*/MgO=0.85, respectively). Melting experiments on the basalt-H2O-CO2 systems show that the pressure and temperature of magma segregation decrease toward the back arc side (17-19 kbar and 1340°-1320°C to 8 kbar and 1250°C), and the coexisting phases change from a spinel lherzolite assemblage to a harzburgite assemblage. These PT conditions define a trend which can be interpreted as a PT path for adiabatic upwelling of the mantle material. Consequently, the observed volcanism and zonation may have been caused by upwelling of a plume from a deep part of the mantle.

  13. Evidence of upwelling of mantle materials beneath the middle and lower Yangtze region by teleseismic tomography

    NASA Astrophysics Data System (ADS)

    Jiang, G.; Zhang, G.; Lu, Q.; Shi, D.; Sino-Probe-CUGB

    2011-12-01

    We have applied the teleseismic tomography method to determine a 3-D P-wave velocity structure of the mantle down to 500 km depth beneath the middle and lower Yangtze region, by using 14,740 P-wave arrival times collected from 519 teleseismic events recorded by 46 portable and 51 static seismic stations in this region (Fig. 1a-b). All the data are recorded from September 2007 to April 2011. The relative residual times were calculated by using the multi-channel cross-correlation method which increases the efficiency and the data precisions up to 0.01 second. Our tomographic results show that along the profile line of OO' the lithosphere with high velocity anomalies (blue color in Fig. 1c) is separated into two parts: one locates above the depth of 50 km and the other at the depths between 300 km and 450 km, and the asthenosphere with low velocity anomalies (red color in Fig. 1c) locates between two parts of lithosphere, which may indicate that the lithosphere is split due to the incursion of the upwelling of asthenosphere, which is consistent with other previous results. Therefore, our study provides an evidence of upwelling of mantle materials. Acknowledgment: We thank the financial support by the Ministry of Finance and Ministry of Land and Resources, P. R. China, under Grant sinoprobe-03, the financial support by National Natural Science Foundation of China under Grants 40930418. We also thank Data Management Center of China National Seismic Network at Institute of Geophysics, China Earthquake Administration for providing the waveform data.

  14. 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.

  15. Impingement of Deep Mantle-Derived Upwelling Beneath Northern, Subducted Extension of the East Pacific Rise and Palinspastically Restored Cenozoic Mafic Magmatism in Western North America

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    Reconstruction of the retrodicted whole mantle flow, based on presently imaged distribution of variations in seismic velocity and its correlation to density (Simmons et al. 2009), over the past 30 Ma, in the North American fixed frame of reference, reveals that the northern, now subducted, extension of the East Pacific Rise is coincident with mantle buoyancy arising from near the core-mantle boundary and extending to the base of the lithosphere (Moucha et al. 2009 GRL, in press). Divergence of the reconstructed flow near the surface is independent of the surface plate(s) and results in predicted geological manifestations distinct from those predicted by traditional plate driven models of flow. Most particularly the retrodicted flow-related dynamic topography results in progressive west to east sweep of surface uplift, that is now centered on the Colorado Plateau (Moucha et al. 2008, 2009 GRL, in press). In addition, and the primary focus of the current study is the relationship between this retrodicted mantle-wide flow and the history of magmatism within the western U.S. and adjacent Mexico. There is a close spatial correlation between the impingement of upwelling with palinspastic restored western North America (McQuarrie and Wernicke, 2005) and onset and distribution of magmatism, particularly of mafic compositions as revealed in the Navdat (www.navdat.org) database. Although often attributed to effects of opening of a slab window (Snyder and Dickinson, 1979, McQuarrie and Oskins, 2008) associated with continued plate-driven separation, this model predicts active mantle flow induced upwelling and divergence resulting in mantle melting that sweeps across east-northeast across southern Basin and Range to the Rio Grande Rift with time and as seen in the distribution of magmatism in this region.

  16. 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

  17. 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

  18. Testing Models of Mantle Upwelling: Microstructure, Crystallography, and Seismic Anisotropy of Peridotites From 15 Degrees N, Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Achenbach, K. L.; Faul, U.; Cheadle, M.; Swapp, S.

    2005-12-01

    Owing to the scarcity of oriented mantle peridotite samples, few microstructural and crystallographic data are currently available to constrain models of mantle upwelling and deformation beneath slow-spreading ridges. Here we present quantitative data regarding the shape- and lattice-preferred orientations (SPO and LPO) of olivine and orthopyroxene in peridotites from Hole 1274A, drilled to a depth of 156 mbsf, on the western flank of the rift valley wall at 15° 39' N on the Mid-Atlantic Ridge during ODP Leg 209. With as little as 50% alteration in places, our samples are the freshest peridotites recovered during Leg 209. The rocks are protogranular harzburgites with 75-82% olivine, 17-22% orthopyroxene, 0.8-1.4% clinopyroxene, and 0.9-2.4% spinel, and one dunite with 96.3% olivine, 0.1% opx, 1.7% clinopyroxene, and 1.9% spinel . The samples preserve evidence of melt-rock interaction and weak lithospheric deformation, but the primary asthenospheric SPO is preserved. Olivine and orthopyroxene exhibit a weak but consistently measurable foliation; no spinel lineation is readily apparent. Crystallographic data, collected using Electron Backscatter Diffraction (EBSD), are based on measurements of as many as 1100 olivine crystals and 530 orthopyroxene crystals per sample in rocks from ten sections of core (recovered from depths ranging from 20 - 150 mbsf). Olivine crystals show a strong [010] maximum subperpendicular to foliation, with a less strongly developed [100] maximum and diffuse clusters of [001] axes roughly parallel to the foliation plane. This fabric is consistent with dislocation creep operating at ~1200° C predominantly on the olivine (010)[100] slip system. The relatively weakly developed [100] and [001] maxima may be attributed to a low strain rate, or to a component of slip in another slip system. Orthopyroxene crystals show a [001] maximum parallel to the foliation plane, with a [100] maximum subperpendicular to the foliation plane, indicative of the

  19. 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.

  20. 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.

  1. 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

  2. Seismic and Geodynamic Constraints on Compositional Heterogeneity in the Lower Mantle: Implications for Deeply-Rooted Hot Upwellings Under the African and Pacific Plates

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    We present the results of a series of tests that probe the possible existence of compositionally distinct material in the central core of the LLSVPs under the African and Pacific plates using tomography-based mantle flow models that employ several independently-derived viscosity profiles (Mitrovica & Forte 2004, Behn et al. 2004, Steinberger & Calderwood 2006, Forte et al. 2010). We also consider four global tomography models derived from seismic shear velocity data alone (Grand 2002, Panning & Romanowicz 2006, Kustowski et al. 2008, Ritsema et al. 2011). The possible combinations of viscosity and tomography models yield 16 different tests for compositional heterogeneity inside the LLSVPs. In all tests we begin with a mineral physical scaling between lower-mantle shear velocity and density anomalies that assumes thermal effects are dominant everywhere, including within the LLSVPs. We find it is not possible, in any of the tests, to obtain a satisfactory fit to surface geodynamic data, especially the global, long-wavelength gravity anomalies and space-geodetic inferences of excess CMB flattening with a purely thermal interpretation of lower-mantle heterogeneity. If we introduce compositionally-distinct material in the central portions of the LLSVPs, all tests show a notable improvement in the fit to the gravity anomaly and CMB ellipticity data. An optimal reconciliation of the gravity and CMB data is obtained by extending compositional heterogeneity upwards, with maximum-amplitude in the seismic D"-layer and tapering off to negligible values in the mid-mantle. A robust assessment of the dynamical impact of this deeply-rooted compositional heterogeneity is obtained with maps of "mean" convective flow, by averaging the results of all 16 test cases. We find (see map below) dominant lower-mantle upwellings below the axis of the East Pacific Rise (EPR), and under the Caroline Islands in the Western Pacific. Under the African plate we find large-scale upwellings under the

  3. Coastal Upwelling.

    ERIC Educational Resources Information Center

    Clark, Steve

    1998-01-01

    Features a three-part activity designed to teach students about coastal upwelling, the upward movement of cooler, more nutrient-rich water along a coast. Activity includes a mapping exercise, a graphing exercise, and questions for analyzing the map and graph. (Author/WRM)

  4. Fabric characterization associated with asthenospheric upwelling in the uppermost mantle, back-arc region of the southwest Japan arc: Evidence from peridotite xenoliths, Oki-Dogo Island

    NASA Astrophysics Data System (ADS)

    Satsukawa, Takako; Michibayashi, Katsuyoshi

    2010-05-01

    supported by petrologic and geochemical studies. In particular, the decreasing of olivine Mg# is correlated with not only a decrease in crystallographic fabric strength (J-index) but also the change in olivine CPO. Thus, heat transfer from a neighboring large-scale partial melting domain (or ‘asthenospherized' mantle) results in an extremely high thermal gradient in this domain, which controls both deformation distribution and the melt migration ahead of the partial melting zone. The variation of in olivine CPO intensities implies that the presence of melt result in a higher contribution of diffusion to deformation, leading to a slower CPO evolution. Thus, peridotites in SW Japan derived from the uppermost mantle were deformed in the melting field due to asthenospheric upwelling associated with back-arc spreading. Consequently, the uppermost mantle peridotites in the back-arc region of the SW Japan were deformed on a condition that melts distributed no homogeneous field due to the asthenosphere upwelling of back-arc spreading. And now, they erupt with keeping structures formed by the back-arc spreading.

  5. Microbial Diversity of a Brazilian Coastal Region Influenced by an Upwelling System and Anthropogenic Activity

    PubMed Central

    Cury, Juliano C.; Araujo, Fabio V.; Coelho-Souza, Sergio A.; Peixoto, Raquel S.; Oliveira, Joana A. L.; Santos, Henrique F.; Dávila, Alberto M. R.; Rosado, Alexandre S.

    2011-01-01

    Background Upwelling systems are characterised by an intense primary biomass production in the surface (warmest) water after the outcrop of the bottom (coldest) water, which is rich in nutrients. Although it is known that the microbial assemblage plays an important role in the food chain of marine systems and that the upwelling systems that occur in southwest Brazil drive the complex dynamics of the food chain, little is known about the microbial composition present in this region. Methodology/Principal Findings We carried out a molecular survey based on SSU rRNA gene from the three domains of the phylogenetic tree of life present in a tropical upwelling region (Arraial do Cabo, Rio de Janeiro, Brazil). The aim was to analyse the horizontal and vertical variations of the microbial composition in two geographically close areas influenced by anthropogenic activity (sewage disposal/port activity) and upwelling phenomena, respectively. A lower estimated diversity of microorganisms of the three domains of the phylogenetic tree of life was found in the water of the area influenced by anthropogenic activity compared to the area influenced by upwelling phenomena. We observed a heterogenic distribution of the relative abundance of taxonomic groups, especially in the Archaea and Eukarya domains. The bacterial community was dominated by Proteobacteria, Cyanobacteria and Bacteroidetes phyla, whereas the microeukaryotic community was dominated by Metazoa, Fungi, Alveolata and Stramenopile. The estimated archaeal diversity was the lowest of the three domains and was dominated by uncharacterised marine Crenarchaeota that were most closely related to Marine Group I. Conclusions/Significance The variety of conditions and the presence of different microbial assemblages indicated that the area of Arraial do Cabo can be used as a model for detailed studies that contemplate the correlation between pollution-indicating parameters and the depletion of microbial diversity in areas close

  6. 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.

  7. Regional mantle upwelling on Venus: The Beta-Atla-Themis anomaly and correlation with global tectonic patterns

    NASA Technical Reports Server (NTRS)

    Crumpler, L. S.; Head, J. W.; Aubele, Jayne C.

    1993-01-01

    The morphology and global distribution of volcanic centers and their association with other geological characteristics offers significant insight into the global patterns of geology, tectonic style, thermal state, and interior dynamics of Venus. Magellan data permit the detailed geological interpretation necessary to address questions about interior dynamics of Venus particularly as they reflect relatively physical, chemical, and thermal conditions of the interior. This paper focuses on the distribution of anomalous concentrations of volcanic centers on Venus and regional patterns of tectonic deformation as it may relate to the identification of global internal anomalies, including mantle dynamic, petrological, or thermal patterns.

  8. 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.

  9. 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.

  10. Lattice-preferred orientation and microstructure of peridotites from ODP Hole 1274A (15°39‧N), Mid-Atlantic Ridge: Testing models of mantle upwelling and tectonic exhumation

    NASA Astrophysics Data System (ADS)

    Achenbach, Kay L.; Cheadle, Michael J.; Faul, Ulrich; Kelemen, Peter; Swapp, Susan

    2011-01-01

    Eleven harzburgites and one dunite from Ocean Drilling Program Leg 209 Hole 1274A preserve high-temperature mantle textures. Electron backscatter diffraction (EBSD) analysis shows moderately developed crystal lattice preferred orientations (LPOs) in olivine and orthopyroxene (M-indices ≈ 0.1) indicative of crystal-plastic deformation at ~ 1250 °C. These rocks preserve a protogranular texture with a weak olivine foliation, a very weak or absent orthopyroxene foliation that may be decoupled from the orthopyroxene LPO, and minor interstitial clinopyroxene and spinel. Olivine grain size distributions, along with melt-related microstructures in orthopyroxene, clinopyroxene and spinel suggest that high-temperature deformation textures have been overprinted by pervasive post-deformation melt-rock interaction. Paleomagnetic data constrain the olivine [100] axes to be subhorizontal and oriented at low angle (≤ 28.6° ± 10.6°) to the ridge axis at the onset of serpentinization. This orientation is consistent with either complex 3-D mantle upwelling or 2-D mantle upwelling coupled with complex 3-D tectonic emplacement to the seafloor.

  11. 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

  12. 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

  13. 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

  14. Fluid dynamics of active heterogeneities in a mantle plume conduit

    NASA Astrophysics Data System (ADS)

    Farnetani, C. G.; Limare, A.; Hofmann, A. W.

    2015-12-01

    Laboratory experiments and numerical simulations indicate that the flow of a purely thermal plume preserves the azimuthal zonation of the source region, thus providing a framework to attribute a deep origin to the isotopic zonation of Hawaiian lavas. However, previous studies were limited to passive heterogeneities not affecting the flow. We go beyond this simplification by considering active heterogeneities which are compositionally denser, or more viscous, and we address the following questions: (1) How do active heterogeneities modify the axially symmetric velocity field of the plume conduit? (2) Under which conditions is the azimuthal zonation of the source region no longer preserved in the plume stem? (3) How do active heterogeneities deform during upwelling and what is their shape once at sublithospheric depths? We conducted both laboratory experiments, using a Particle Image Velocimetry (PIV) to calculate the velocity field, and high resolution three-dimensional simulations where millions of tracers keep track of the heterogeneous fluid. For compositionally denser heterogeneities we cover a range of buoyancy ratios 0active heterogeneities, and we explore the relation between strain rates and the evolving shape of the upwelling heterogeneity.

  15. 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.

  16. 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

  17. 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.

  18. Light effects and diel variations of nitrate reductase activity in phytoplankton from the northwest Africa upwelling region

    NASA Astrophysics Data System (ADS)

    Martinez, Rosa; Packard, Theodore T.; Blasco, Dolors

    1987-06-01

    Light kinetics and diel cycles of nitrate reductase (NR) activity were studied in the upwelling ecosystem off northwest Africa. The activity of the enzyme showed a strong response to light at low intensities but became saturated at light intensities above 15-30% of the incident light intensity. At higher irradiances, NR activity showed photoinhibition. At sea surface irradiances an average inhibition of 32% in the NR activity was observed. Diel cycles of NR activity exhibited the following characteristics: a low pre-dawn value (0.03-0.009 μmol NO 3-N (μg Chl α) -1), a rapid increase with the onset of daylight, a maximum before noon (tripling the dark value), a secondary maximum in the early afternoon, and an afternoon-evening decrease that coincided with the decrease in sunlight. To simulate these characteristics a continuous polynomial function of light and time was developed.

  19. Alkaline phosphatase activity and its relationship to inorganic phosphorus in the transition zone of the North-western African upwelling system

    NASA Astrophysics Data System (ADS)

    Sebastián, Marta; Arístegui, Javier; Montero, María F.; Escanez, Jose; Xavier Niell, F.

    2004-08-01

    The enzymatic activity of alkaline phosphatase (APA) was studied in the transition zone between the African upwelling system and the open ocean waters of the Canary Islands region. This region is recurrently dominated by the presence of upwelling filaments that may transport nutrient-enriched waters out into the open ocean before nutrients become exhausted by plankton. Turnover rates by APA were generally low in the whole region, but detectable in all the measurements carried out. On average, turnover rates were higher in the upwelling stations, and APA in those waters seemed to be mainly generated by heterotrophic bacteria to supply easily assimilable organic C. APA outside the upwelling area showed an inverse hyperbolic relationship with increasing phosphate, suggesting the presence of both constitutive and Pi-inducible APA. In these offshore waters, a threshold of 0.1 μM of phosphate could be defined for the regulatory function of Pi on APA. Thus, APA in nutrient-poor waters seemed to be induced to compensate for Pi-deficiency. Turnover rates in the filaments showed basal (probably constitutive) levels, whereas they increased in the surrounding waters, where phosphate concentration presumably did not satisfy plankton P-demands. The fertilising effect of the filaments and associated cyclonic eddies extended to at least 175 km offshore, where basal alkaline phosphatase activities were still found. The magnitude of this effect depends probably on the intensity of upwelling events and the degree of recirculation of filament water back to the coastal jet.

  20. 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.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  3. 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

  4. Mantle to surface gas triggers of magmatic activity at Erebus volcano, Antarctica

    NASA Astrophysics Data System (ADS)

    Oppenheimer, C.; Moretti, R.; Kyle, P.

    2009-04-01

    Intraplate volcanoes are associated with extensional tectonics, mantle upwelling and high heat flow. Erupted magmas have an alkaline nature and are rich in volatiles, especially CO2, that are inherited from fluid-rich magmatic sources in the mantle. Localized alkaline centers emit gas fluxes that exceed what can be sustained by the rates of magma erupted. At Mount Erebus this dichotomy is evidenced by open-path Fourier transform infrared (FTIR) spectroscopy of gases released from the lava lake. Different gas signatures are associated with explosive and non-explosive gas emissions, representative of volatile contents and redox conditions that identify the overlap between shallow and deep degassing sources. We show that this multiple signature of magma degassing provides a unique probe for magma differentiation and transfer of CO2-rich oxidized fluids from lithospheric roots up to the surface, and show how these processes operate in time and space. Magma deeper than 4 km equilibrates under vapour buffered conditions, whereas shallower magmas allow deep, CO2-rich fluids to accumulate and prior to release either via open-system degassing conditions and reduced oxidation states, or as volatile-enriched, phonolitic blobs that preserve the deep oxidized signature, and ascend as a closed-system to explode at the surface during Strombolian phases.

  5. Evidence for mantle plumes?

    PubMed

    Anderson, Don L; Natland, James H

    2007-11-22

    Geophysical hotspots have been attributed to partially molten asthenosphere, fertile blobs, small-scale convection and upwellings driven by core heat. Most are short-lived or too close together to be deeply seated, and do not have anomalous heat flow or temperature; many are related to tectonic features. Bourdon et al. investigate the dynamics of mantle plumes from uranium-series geochemistry and interpret their results as evidence for thermal plumes. Here we show why alternative mechanisms of upwelling and melting should be considered. PMID:18033248

  6. 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.

  7. 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.

  8. 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.

  9. The relationship between Arabian Sea upwelling and Indian Monsoon revisited

    NASA Astrophysics Data System (ADS)

    Yi, Xing; Zorita, Eduardo; Hünicke, Birgit

    2015-04-01

    Coastal upwelling is important to marine ecosystems and human activities. It transports nutrient-rich deep water mass that supports marine biological productivity. In this study, we aim to characterize the large-scale climate forcings that drive upwelling along the western Arabian Sea coast. Studies based on ocean sediments suggest that there is a link between this coastal upwelling system and the Indian summer monsoon. However, a more direct method is needed to examine the influence of various forcings on upwelling. For this purpose, we analyse a high-resolution (about 10 km) global ocean simulation (denoted STORM), which is based on the MPI-OM model developed by the Max-Planck-Institute for Meteorology in Hamburg driven by the global meteorological reanalysis NCEP over the period 1950-2010. This very high spatial resolution allows us to identify characteristics of the coastal upwelling system. We compare the simulated upwelling velocity of STORM with two traditional upwelling indices: along-shore wind speed and sea surface temperature. The analysis reveals good consistency between these variables, with high correlations between coastal upwelling and along-shore wind speed (r=0.85) as well as coastal sea surface temperature (r=-0.77). To study the impact of the monsoon on the upwelling we analyse both temporal and spatial co-variability between upwelling velocity and the Indian summer monsoon index. The spatial analysis shows that the impact of the monsoon on the upwelling is concentrated along the coast, as expected. However, somewhat unexpectedly, the temporal correlation between the coastal upwelling and the monsoon index is rather weak (r=0.26). Also, the spatial structure of upwelling in the Arabian Sea as revealed by a Principal Component Analysis is rather rich, indicating that factors other than the Monsoon are also important drivers of upwelling. In addition, no detectable trend in our coastal upwelling is found in the simulation that would match the

  10. Revisiting the CO2 "source" problem in upwelling areas - 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.

    2014-05-01

    The causes for a productive upwelling region to be a source of CO2 are usually referred to the excess CO2 supplied via upwelling of high dissolved inorganic carbon (DIC) from deep water. Furthermore, we hypothesize that microbial activity plays a significant role on top of that. To test this hypothesis, multiple biogeochemical parameters were investigated at two cyclonic-eddy-induced upwelling sites, CE1 and CE2, in the western South China Sea. The data showed that upwelling can exert significant influences on biological activities in the euphotic zone and can also impact on 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. These results suggest that on top of upwelled DIC, microbial activities stimulated by upwelled nutrients and labile organic carbon produced by phytoplankton can play a critical role for an upwelling area to be outgassing or uptaking CO2. We point out that even though an upwelling region is outgassing CO2, carbon sequestration still takes place through the POC-based biological pump as well as the refractory dissolved organic carbon (RDOC)-based microbial carbon pump.

  11. Lena Trough (Arctic Ocean): Active mantle exhumation on a continental rifted margin

    NASA Astrophysics Data System (ADS)

    Snow, J. E.; Hellebrand, E.; von der Handt, A.; Nauret, F.

    2004-12-01

    Lena Trough is the northern continuation of the Mid-Atlantic Ridge through Fram Strait and into the Arctic Ocean. The rifting of Lena Trough began in the Miocene, and significantly, is the final and the most recent event in the separation of the North American from the Eurasian continent. Lena Trough was mapped in 1999, 2001 and 2004 by PFS Polarstern (Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany), revealing sea floor structures that are inconsistent with any normally conceived mid-ocean ridge spreading, and instead indicative of late continental rifting. Lena Trough is shown to be a deep, fault-bounded basin with depths of 3800-4200m, and irregular, steep valley sides that are oblique to the spreading direction. Basement horst structures that outcrop as sigmoidal ridges with steeply dipping sides project out of the valley floor. These basement ridges are roughly parallel along flow lines to the valley walls on either side. Ridge-orthogonal topography is simply absent (ie no segments trending parallel nor fracture zones perpendicular to Gakkel Ridge). Most faults trend approximately SSE-NNW, an obliquity with respect to Gakkel Ridge (SW-NE) of about 55°. The basement ridges are composed nearly entirely of fertile mantle peridotite, as are the valley walls. Only at the northern and southern extremities of Lena Trough do basalts appear at all. The peridotites compositions are consistent with either continental or oceanic (asthenospheric) mantle. They show evidence of low-degree mantle melting, followed by high-level stagnation in a thick lithosphere. This evidence (veining, impregnation) is more evident where little or no basaltic cover is present, while peridotites dredged in the vicinity of basalts tend to be more residual. This may indicate some degree of magmatic focusing in the absence of a basaltic crust per se. Lena Trough contains rare, highly alkaline basalts that are unlike any compositions dredged from mid-ocean ridges

  12. Lena Trough (Arctic Ocean): Active mantle exhumation on a continental rifted margin

    NASA Astrophysics Data System (ADS)

    Snow, J. E.; Hellebrand, E.; von der Handt, A.; Nauret, F.

    2007-12-01

    Lena Trough is the northern continuation of the Mid-Atlantic Ridge through Fram Strait and into the Arctic Ocean. The rifting of Lena Trough began in the Miocene, and significantly, is the final and the most recent event in the separation of the North American from the Eurasian continent. Lena Trough was mapped in 1999, 2001 and 2004 by PFS Polarstern (Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany), revealing sea floor structures that are inconsistent with any normally conceived mid-ocean ridge spreading, and instead indicative of late continental rifting. Lena Trough is shown to be a deep, fault-bounded basin with depths of 3800-4200m, and irregular, steep valley sides that are oblique to the spreading direction. Basement horst structures that outcrop as sigmoidal ridges with steeply dipping sides project out of the valley floor. These basement ridges are roughly parallel along flow lines to the valley walls on either side. Ridge-orthogonal topography is simply absent (ie no segments trending parallel nor fracture zones perpendicular to Gakkel Ridge). Most faults trend approximately SSE-NNW, an obliquity with respect to Gakkel Ridge (SW-NE) of about 55°. The basement ridges are composed nearly entirely of fertile mantle peridotite, as are the valley walls. Only at the northern and southern extremities of Lena Trough do basalts appear at all. The peridotites compositions are consistent with either continental or oceanic (asthenospheric) mantle. They show evidence of low-degree mantle melting, followed by high-level stagnation in a thick lithosphere. This evidence (veining, impregnation) is more evident where little or no basaltic cover is present, while peridotites dredged in the vicinity of basalts tend to be more residual. This may indicate some degree of magmatic focusing in the absence of a basaltic crust per se. Lena Trough contains rare, highly alkaline basalts that are unlike any compositions dredged from mid-ocean ridges

  13. 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. PMID:12192406

  14. 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

  15. High Resolution Modelling of Mantle Convective Flow Below the North American Plate.

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    Recent progress in joint seismic-geodynamic tomographic imaging of both thermal and compositional anomalies in Earth's mantle allows us to carry out new high-resolution calculations of the present-day mantle convective flow at all depths, from the lithosphere down to the core-mantle boundary. We are therefore able to delineate the detailed connections between fundamental geological and geophysical surface processes and the underlying mantle convection. We employ these convection calculations to consider North American continental dynamics, with a special focus on the detailed relationship between flow in upper mantle, especially in the asthenosphere, and the impact on present-day dynamic topography as well as its rate-of- change. The surface dynamics that we obtain show a clear and detailed connection to the mantle flow driven by the descent of the ancient Kula-Farallon plate system and a buoyant, actively ascending hot upwelling under the western US. Of particular importance is the relationship of the deep-seated upwelling under the Colorado Plateau as a driving force for current rifting in the Rio Grande River valley. This rifting and its temporal evolution bears a strong resemblance to the convection-induced rifting our convection model also predicts under the East African Rift system. The close similarity between these two rifts, in terms of asthenospheric flow dynamics, will be discussed.

  16. Upwellings in Lake Baikal

    NASA Astrophysics Data System (ADS)

    Shimaraev, M. N.; Troitskaya, E. S.; Blinov, V. V.; Ivanov, V. G.; Gnatovskii, R. Yu.

    2012-02-01

    Based on shipboard and satellite observations, the characteristics of upwelling in Lake Baikal in the period of direct temperature stratification have been determined for the first time. Coastal upwellings appear annually under the effect of run-down and alongshore winds and are traced along the coast to a distance of up to 60-100 km and up to 250 km in North Baikal. Analogous to the way it occurs in seas, water rises from the depths of 100-200 m (350 m as a maximum) at the velocity of 0.1 × 10-2-6.5 × 10-2 cm/s. Divergence in the field of intràbasin cyclonic macrovortices produces upwelling in the Baikal pelagic zone and downwelling in the vicinity of shores; this lasts from 7 to 88 days and covers the depth interval of 80-300 m in August and up to 400-800 m in early-mid November. The area of upwellings occupies up to 20-60% of the separate basins of the lake. Vertical circulation of water in the field of pelagic upwellings leads to intensification of coastal currents and to formation of the thermobar with a heat inert zone in the central part of the lake in November, and this thermobar is not observed in other lakes, at that.

  17. Mantle heterogeneities within active margins of the world oceans and their seismological characteristics

    NASA Astrophysics Data System (ADS)

    Boldyrev, S. A.

    1985-03-01

    The principal geotectonic element of active marginal areas is represented by arcuate structures characterized by two mantle volumes in contact containing materials with different properties. The rigid, high-density, and comparatively cold region with concentrated earthquake hypocentres is accompanied by an aseismic mantle where a low-velocity layer at depths from 150 to 250 km and a low-velocity zone under the present volcanoes form a specific volume. P-wave velocity of the latter is nearly 15% below the standard values and nearly 20% lower than that in the adjacent seismically active blocks. As a result of these lateral changes in the physical properties, there appears to exist a considerable gradient of lithostatic pressure whose maximum occurs in the focal zone and its resulting forces point to the arc centre, thus determining the horizontal displacement of sinking high-density matter with the focal zone. Velocity changes of the aseismic mantle block along the geostructure are determined by the geological evolution of the region and reflected in its morphostructure. In shallow parts of the northern Sea of Okhotsk and western Kamchatka with continenetal type of crust developed on the bottom of the pre-Mesozoic platform, the P-wave velocities in the upper mantle are 0.5-0.6 km/s smaller than those under the Kuril abyssal plain with suboceanic crust. Small-scale mantle inhomogeneities of the focal zone manifest themselves in a seismic anisotropy which changes both in magnitude and direction. It reflects a reaction of the medium to the shearing stresses and is controlled by strength anisotropy. Distribution of seismic parameters, velocity and attenuation of elastic waves in the mantle of active margins is represented by alternating areas of high and low strength. Weaker areas coincide both in setting and trend with deep-seated faults which cut across the arcuate geofeatures. This combination of arcuate and orthogonal tectonic systems in the northwestern Pacific

  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. Non-hotspot volcano chains produced by migration of shear-driven upwelling toward the East Pacific Rise (Invited)

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    While most oceanic volcanism is associated with the passive rise of hot mantle beneath the spreading axes of mid-ocean ridges (MOR), volcanism occurring off-axis reflects intraplate upper-mantle dynamics and composition, yet is poorly understood. 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 ( ~3500 km in length for the Pukapuka, and ~500 km for the Sojourn, and Hotu-Matua ridges). Propagation of this volcanism by ~20 cm/a, as well as asymmetry in a variety of geophysical observables across the EPR, indicates strong lateral eastward pressure-driven flow in the asthenosphere; likely driven by upwelling beneath the South Pacific Superswell [1]. Although this pattern of large-scale mantle flow can account for the propagation of intraplate magmatism towards the EPR, it does not explain decompression melting itself. We hypothesize that shear-driven upwelling sustains off-axis volcanism. Unlike e.g. mantle plumes, shear-driven upwelling is a mechanism for mantle decompression that does not require lateral density heterogeneity to drive upwelling. For example, in the presence of shear across the asthenosphere, vertical flow emerges at the edges of viscosity heterogeneity [2]. These ingredients are present in the SE Pacific, where (1) shear across the asthenosphere is inferred to be greatest worldwide [2], and (2) lateral heterogeneity in mantle viscosity is indicated by geoid lineations that are associated with anomalies in seismic tomography [3]. Eastward pressure-driven flow from the South Pacific Superswell may separate into low-viscosity fingers thus providing viscosity heterogeneity [3]. Our three-dimensional numerical models [4] show that asthenospheric shear can excite upwelling and decompression melting at the tip of low-viscosity fingers that are propelled eastward by vigorous asthenospheric flow. This shear-driven upwelling is able to sustain

  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. Measurement of activation volume for creep of anhydrous olivine at upper mantle pressures

    NASA Astrophysics Data System (ADS)

    Dixon, N. A.; Durham, W. B.; Kohlstedt, D. L.; Mei, S.; Xu, L.

    2012-12-01

    Olivine is the most abundant and likely the weakest phase in the upper mantle, and thus its rheological properties have a critical role in controlling convective flow in this region. A persistent obstacle to understanding the behavior of olivine in the mantle has been the difficulty of determining activation volume (V*), the influence of hydrostatic pressure on high-temperature creep. The bulk of previous studies examining V* were conducted at low pressure (<300 MPa) and over small pressure ranges in gas-medium deformation machines, limiting precision and raising questions about application to relevant geological conditions. For this study, we conducted numerous deformation experiments on dry polycrystalline olivine in the D-DIA apparatus to pressures 1.5 to 9 GPa at 1373 K. Stress and strain were measured in-situ with synchrotron x rays. Refinement of diffraction technique has allowed stress resolution of ±0.02 GPa. For the pressure range in this study, we have measured an average activation volume of about 11-17 cm3/mol for dry polycrystalline San Carlos olivine. This is a substantial pressure effect, representing a pressure-induced viscosity increase seven orders of magnitude from the base of the lithosphere to the bottom of the upper mantle. The diffraction technique used for stress measurement in these experiments also illuminates the relative strength of differently oriented grains in our polycrystalline sample, providing new experimental evidence for preferred dislocation slip systems in olivine at high pressure.

  3. Measurement of activation volume for creep of dry olivine at upper mantle pressure

    NASA Astrophysics Data System (ADS)

    Dixon, N. A.; Durham, W. B.; Suzuki, A. M.; Mei, S.; Kohlstedt, D. L.; Hustoft, J. W.

    2011-12-01

    Olivine is the most abundant and weakest phase in the upper mantle, and thus its rheological properties have a critical role in controlling convective flow in this region. A resilient obstacle to understanding the behavior of olivine in the mantle has been the difficulty of determining activation volume (V*), the influence of hydrostatic pressure on flow strength. The bulk of previous studies examining V* were conducted at low pressure (<300 MPa) and small pressure ranges in gas-medium deformation apparatuses, limiting precision and raising questions about application to relevant geological conditions. For this study, we conducted deformation experiments on dry polycrystalline olivine in the D-DIA apparatus. The development of a new hybrid soft-fired pyrophyllite/mullite sample assembly allowed for a broadened pressure range (2-9 GPa), while stress and strain were measured in-situ with synchrotron x rays. Refinement in diffraction technique has allowed stress resolution of ±0.01 GPa. For the pressure range in this study, we have measured an average activation volume of about 17 cm^3/mol for dry polycrystalline San Carlos olivine. This is a substantial pressure effect, representing a pressure-induced viscosity increase of nearly 7 orders of magnitude from the base of the lithosphere to the bottom of the upper mantle.

  4. Long-term cycles in Large Igneous Province (LIP) eruptions and fossil diversity may be related to periodic mantle plume activity

    NASA Astrophysics Data System (ADS)

    Rampino, M. R.; Prokoph, A.

    2013-12-01

    Wavelet analysis shows evidence for an approximately 62 Myr cycle in the eruptions of Large Igneous Provinces (LIPs) over the last 540 Myr. This agrees with a cycle of 62×3 Myr seen in fossil biodiversity over the same interval. A similar cycle (about 56-62 Myr) has been reported in data related to continental-scale fluctuations of sedimentation, most likely resulting from changes in climate, sea level and tectonics. A longer about 140 Myr cycle is also detected in the LIP eruption data, matching a similar cycle seen in fossil diversity and in global climate. Both the LIP and fossil diversity data sets show a shorter approximately 28-35 Myr period, especially during the last 135 Myr. Cross-spectral wavelet analysis of the LIP occurrences against the marine diversity record shows that almost all cross-variability in the two data sets is concentrated in the 28 to 35 Myr, 62 to 65 Myr and around 140 Myr wavelength bands, showing a sharp change from dominant 62 Myr to 32 Myr cyclicity since the Early Cretaceous. The phase differences for the cycles indicate an inverse LIP-diversity relationship at these wavebands. The LIP eruptions commonly mark the initiation of hotspots, presumably created by upwelling mantle plumes. The agreement among these periodicities suggests that long-term global cycles of biodiversity, sea level, climate and sedimentation are partly driven by periodic or quasi-periodic fluctuations in mantle plume activity. This conclusion is bolstered by the close temporal correlation of several LIPs with times of mass extinction and climatic crises indicated by ocean anoxic events.

  5. Mantle Flow beneath Arabia Offset from the Opening Red Sea

    NASA Astrophysics Data System (ADS)

    Stein, S. A.; Chang, S.; Merino, M.; van der Lee, S.; Stein, C. A.

    2010-12-01

    The rifting of continents involves a complex and poorly understood sequence of lithospheric stretching, volcanism, and mantle flow that eventually gives rise to seafloor spreading that forms a new ocean basin. The Red Sea, forming as the Arabian plate diverges from Africa, is a classic area for studying this process. Here, we present new insight from joint inversion of seismic wave travel times and waveforms to map velocity structure beneath Arabia and its surroundings. We find the low velocities expected for hot upwelling mantle material centered beneath the southern Red Sea and Gulf of Aden, consistent with the active spreading there. However, this hot material extends not below the northern Red Sea, but is instead offset to the east beneath Arabia, showing northward upper mantle flow from the Afar hotspot. The location of this low velocity channel beneath volcanic rocks erupted since rifting began 30 million years ago indicates that although the flow originates from the hotspot that is essentially fixed in the upper mantle, the channel moves with the Arabian plate. We thus propose that the absence of seafloor spreading in the northern Red Sea reflects the offset mantle flow. Because this offset has existed for millions of years, it is unclear whether it will evolve into seafloor spreading, rifting of Arabia above the channel, or both. This situation has aspects of the end-member models of rifting initiated by either mantle flow or lithospheric extension, and thus shows that the two can occur somewhat independently in different places before coalescing to seafloor spreading.

  6. 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.

  7. 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.

  8. 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.

  9. Activity and safety of combined rituximab with chlorambucil in patients with mantle cell lymphoma.

    PubMed

    Bauwens, Deborah; Maerevoet, Marie; Michaux, Lucienne; Théate, Ivan; Hagemeijer, Anne; Stul, Michel; Danse, Etienne; Costantini, Sabrina; Vannuffel, Pascal; Straetmans, Nicole; Vekemans, Marie-Christiane; Deneys, Véronique; Ferrant, Augustin; Van Den Neste, Eric

    2005-11-01

    We evaluated the combination of rituximab with chlorambucil in patients with mantle cell lymphoma (MCL) not eligible for aggressive therapy. Fourteen patients (male/female: 9/5) were included (two newly diagnosed, 12 relapsed/refractory). The toxicities were neutropenia, thrombopenia and infection. Nine (64%) patients responded; five (36%) achieved complete remission and four (29%) achieved partial remission. The median progression-free survival for responders was 26 months (95% CI, 4-48). Marrow polymerase chain reaction negativity was attained in seven responders. These results suggest that this schedule may have notable antitumour activity in patients with MCL, including patients in relapse after autologous stem cell transplantation. PMID:16225653

  10. Non-hotspot volcano chains produced by migration of shear-driven upwelling toward the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Ballmer, Maxim D.; Conrad, Clinton P.; Harmon, Nicholas; Smith, Eugene I.

    2013-04-01

    While most oceanic volcanism is associated with the passive rise of hot mantle beneath the spreading axes of mid-ocean ridges (MOR), volcanism occurring off-axis reflects intraplate upper-mantle dynamics and composition, yet is poorly understood. 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 by ~20 cm/a, as well as asymmetry in a variety of geophysical observables across the EPR, indicates strong lateral eastward pressure-driven flow in the asthenosphere that is driven by upwelling beneath the South Pacific Superswell [1]. 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. We hypothesize that shear-driven upwelling sustains off-axis volcanism. Shear-driven upwelling is a mechanism for mantle decompression that does not require lateral density heterogeneity to drive upwelling. For example, vertical flow emerges at the edges of viscosity anomalies, if the asthenosphere is sheared horizontally [2]. These two ingredients are present in the SE Pacific, where (1) shear across the asthenosphere is inferred to be greatest worldwide [2], and (2) lateral variability in mantle viscosity is indicated by geoid lineations and anomalies in seismic tomography [3]. Eastward pressure-driven flow from the South Pacific Superswell has been suggested to break up into fingers thus providing this variability in viscosity [3]. Our three-dimensional numerical models [4] show that asthenospheric shear can excite upwelling and decompression melting at the tip of low-viscosity fingers that are propelled by vigorous sublithospheric flow. This shear-driven upwelling is able to sustain intraplate volcanism that progresses towards the MOR

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  14. Numerical Simulation Analysis of Deformation Effect of The Upper Mantle Flow to Ordos and Its Surroundings

    NASA Astrophysics Data System (ADS)

    Yun, S.; Ping, L. C.; Qi, D.

    2014-12-01

    Ordos block is a typical representative of cratonic lithosphere in North China. It is stable in the block ,but around the block there are a series of faulted basins and folded mountains, the new tectonic movement around the block is intense. Some scholars propose that the upper mantle flow is an important factor to the extension activity of the fault zone around the block. But it has never been discussed in detail that how the upper mantle flow affects the movement and deformation around Ordos block? A 3D viscoelastic modeling is realized for studying the deformation effect of the upper mantle flow to Ordos and its surroundings, based on the comprehensive geological and geophysical data ,such as 3d rheological structure, the active blocks of China, thermal structure, shear wave splitting, et al. The modeling results indicate that in the vertical direction, compared with the local uplift and depression caused by the compression among the plates, the uplifting of Ordos block as a whole is mainly effected by mantle upwelling. In general the upper mantle surrounding of Ordos block is upwelling, Linfen basin goes up more faster. In the horizontal direction, The general flow direction of upper mantle in the study area is NE, basically the same as Qingzang block movement direction. But there is a bifurcation flow along the southwestern margin of Liupanshan. Generally speaking, the regional deformation is drive mainly by the movement of Qingzang block and adjacent blocks pushing into each other,the deformation effect of the upper mantle flow to Ordos and its surroundings is a superposition and partial adjustment.

  15. 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.

  16. 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.

  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. Differential river incision across active normal faults in Grand Canyon: a response to mantle-driven uplift of the western Colorado Plateau

    NASA Astrophysics Data System (ADS)

    Karlstrom, K. E.; Crow, R.

    2010-12-01

    trends in the isotopic values and geochronology of Neogene basalts from the southwestern USA that indicate that magmatism migrated towards the plateau center and became progressively more asthenospheric through time, 5) the fault dampened differential incision data, and 6) geodynamic models for active upwelling of asthenospheric mantle around the plateau that is likely driving 100-400 m-scale Neogene surface uplift. But details of uplift, for example rolling incision transients suggested by mantle flow models rather than piston uplift, are being tested via improved data on differential incision through time in different reaches. The concept of dampened measured incision rates due to relative uplift/subsidence is applicable to a range of tectonic-geomorphic interactions such as fault-dampened incision, salt-induced collapse, differential epeirogenic uplift, and isostatic response.

  19. Subduction: The Gatekeeper for Mantle Melting.

    NASA Astrophysics Data System (ADS)

    Kincaid, C. R.; Druken, K. A.; Griffiths, R. W.

    2011-12-01

    Geodynamic models are used to show the importance of subduction in controlling vertical thermal and chemical fluxes from Earth's interior to surface. In our models subduction-induced circulation produces conditions favorable to both steady-state and episodic melt production and also plays the role of gatekeeper in thwarting large scale melt production from rising plumes. We use laboratory experiments to characterize three-dimensional (3D) flow fields in convergent margins in response to a range of subduction and back-arc deformation styles, and how these flows interact with upwellings. Models utilize a glucose working fluid with a temperature dependent viscosity to represent the upper 2000 km of the mantle. Subducting lithosphere is modeled with a descending Phenolic plate and back-arc extension is produced by moving Mylar sheets. Thermal plumes are generated from a pressurized, temperature controlled source. Our results show that naturally occurring transitions from downdip- to rollback-dominated subduction produce conditions that favor both widespread decompression melting in the mantle wedge and short-lived pulses of extensive slab melting. For cases of plume-subduction interaction, 3D slab-induced flow quickly converts the active upwelling to a passive thermal anomaly that bears little to no resemblance to traditional models for plume surface expressions. Instead of rising to make LIPs with age-progressive chains, the bulk of the original plume material is trapped below depths of melt production before being re-subducted by the slab. A limited volume of this passive, former plume material is capable of surfacing. Interestingly, this is seen to occur through a range of morphologies that are consistently offset from the original rise location (e.g., conduit). Surface expressions include anything from small circular patches to long, linear features with complex age trends (e.g., progressive or regressive) resulting from the competition between plate motions and

  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. 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

  2. Peroxisome proliferator-activated receptor-gamma ligands inhibit proliferation and induce apoptosis in mantle cell lymphoma.

    PubMed

    Eucker, Jan; Sterz, Jan; Krebbel, Holger; Zavrski, Ivana; Kaiser, Martin; Zang, Chuanbing; Heider, Ulrike; Jakob, Christian; Elstner, Elena; Sezer, Orhan

    2006-08-01

    Peroxisome proliferator-activated receptor-gamma, a nuclear receptor and transcription factor, and its natural and synthetic ligands have become a focus of novel approaches to induction of apoptosis in solid tumors and hematologic malignancies, including malignant B-lineage cells. The effect on mantle cell lymphoma, a subtype with dismal prognosis, has not yet been analyzed. We investigated the effect of 15-deoxy-delta-12,14-prostaglandin J2 (15d-PGJ2), pioglitazone (PGZ) or rosiglitazone (RGZ) on human mantle cell lymphoma cell lines (GRANTA-519, Hbl-2 and JeKo-1). Mantle cell lymphoma cell lines exhibited a high expression of Peroxisome proliferator-activated receptor-gamma protein in Western blot analysis. MTT assays revealed anti-proliferative effects induced by both 15d-PGJ2, the natural activator of Peroxisome proliferator-activated receptor-gamma, and PGZ and RGZ, synthetic Peroxisome proliferator-activated receptor-gamma ligands, in a dose-dependent manner. At a dose of 50 micromol/l, 15d-PGJ2 induced growth inhibition in all cell lines. The anti-proliferative effect of PGZ and RGZ was slightly lower. Induction of apoptosis was indicated by annexin V staining. At a dose of 50 micromol/l, 15d-PGJ2 led to apoptosis in all cell lines (87-99%) after 48 h of incubation. Again, the apoptotic effect with thiazolidinediones was slightly lower at the same dose level. This is the first study evaluating Peroxisome proliferator-activated receptor-gamma expression and its therapeutic implications in human mantle cell lymphoma cells. Thiazolidinediones comprise anti-lymphoma activity in vitro and should be further explored for the treatment of mantle cell lymphoma. PMID:16926626

  3. Double layering of a thermochemical plume in the upper mantle beneath Hawaii

    NASA Astrophysics Data System (ADS)

    Ballmer, Maxim D.; Ito, Garrett; Wolfe, Cecily J.; Solomon, Sean C.

    2013-08-01

    According to classical plume theory, purely thermal upwellings rise through the mantle, pond in a thin layer beneath the lithosphere, and generate hotspot volcanism. Neglected by this theory, however, are the dynamical effects of compositional heterogeneity carried by mantle plumes even though this heterogeneity has been commonly identified in sources of hotspot magmas. Numerical models predict that a hot, compositionally heterogeneous mantle plume containing a denser eclogite component tends to pool at ∼300-410 km depth before rising to feed a shallower sublithospheric layer. This double-layered structure of a thermochemical plume is more consistent with seismic tomographic images at Hawaii than the classical plume model. The thermochemical structure as well as time dependence of plume material rising from the deeper into the shallower layer can further account for long-term fluctuations in volcanic activity and asymmetry in bathymetry, seismic structure, and magma chemistry across the hotspot track, as are observed.

  4. Upwelling studies with satellites

    NASA Technical Reports Server (NTRS)

    Szekielda, K.

    1971-01-01

    Two different ways of obtaining surface temperature structures with data from an orbiting platform are: (1) Analysis of radiometric recordings during one overpass over apparently cloud-free regions has provided the surface structures of an area. This method can be used to analyze a synoptic recording and has the further advantage of noting rapid changes in the sea surface temperatures over typical scales of a few days. (2) Mapping the sea surface temperature through use of a multispectral method which detects cloud-free conditions and uses the radiation for the determination of the sea surface temperature. This method includes data recorded from orbiting platforms over a period of 2 to 4 weeks; therefore, short-time fluctuations are smoothed out. The method is applicable to map ocean surfaces on a global scale. Both methods were used to study areas in oceans where upwelling exists.

  5. 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.

  6. 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.

  7. Mechanism of the antitumoral activity of deferasirox, an iron chelation agent, on mantle cell lymphoma.

    PubMed

    Vazana-Barad, Liat; Granot, Galit; Mor-Tzuntz, Rahav; Levi, Itai; Dreyling, Martin; Nathan, Ilana; Shpilberg, Ofer

    2013-04-01

    Mantle cell lymphoma (MCL) characterized by the t(11;14)(q13;q32) translocation, resulting in cyclin D1 overexpression, is one of the most challenging lymphomas to treat. Iron chelators, such as deferasirox, have previously been shown to exhibit anti-proliferative properties; however, their effect on MCL cells has never been investigated. We showed that deferasirox exhibited antitumoral activity against the MCL cell lines HBL-2, Granta-519 and Jeko-1, with 50% inhibitory concentration (IC(50)) values of 7.99 ± 2.46 μM, 8.93 ± 2.25 μM and 31.86 ± 7.26 μM, respectively. Deferasirox induced apoptosis mediated through caspase-3 activation and decreased cyclin D1 protein levels resulting from increased proteasomal degradation. We also demonstrated down-regulation of phosphor-RB (Ser780) expression, which resulted in increasing levels of the E2F/RB complex and G(1)/S arrest. Finally, we showed that deferasirox activity was dependent on its iron chelating ability. The present data indicate that deferasirox, by down-regulating cyclin D1 and inhibiting its related signals, may constitute a promising adjuvant therapeutic molecule in the strategy for MCL treatment. PMID:23020673

  8. 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

  9. Contourite Deposition in the North Atlantic Ocean Moderated By Mantle Plume Activity: Evidence from Seismic Reflection Images

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    It is generally accepted that the strength of Northern Component Water overflow, the ancient precursor of North Atlantic Deep Water, has varied throughout Neogene times. Variations in dynamic support of the lithosphere, due to transient behavior of the Iceland mantle plume, probably control spatial and temporal water depth variations this region. Pathways and intensities of oceanic bottom currents, together with deposition of contourite drifts, are strongly influenced by changing bathymetry. Here, we combine detailed observations of contourite drift deposits from seismic reflection profiles with a chronology of plume activity, to test the relationships between deep-water circulation, sedimentary drift accumulation and mantle convection. We present multi-channel seismic reflection profiles acquired over Bjorn, Gardar and Hatton Drifts in the Iceland Basin and over the northernmost portion of Eirik Drift, east of Greenland. Depositional hiatuses are easily identified and correlated between these high-quality images and nearby boreholes, which allows us to construct history of sedimentation across the North Atlantic Ocean over the past 5 Ma. We observe kilometer-scale westward-migration of Bjorn Drift, which can be explained by varying current strength and sediment supply, probably moderated by fluctuating dynamic support on overall subsidence. We place these observations into a new continuous 55 Ma record of Iceland mantle plume activity. There is compelling evidence to support the hypothesis that variations in mantle convection deep beneath the plates has profound consequences for deep-water flow and sediment deposition at Earth's surface.

  10. Modeling The Role of Subduction in the Production and Evolution of Thermal and Chemical Heterogeneity in the Mantle

    NASA Astrophysics Data System (ADS)

    Kincaid, C.; Harris, A.; Griffiths, R. W.

    2007-12-01

    One cornerstone of multidisciplinary chemical geodynamics is modeling. Both numerical and laboratory experiments have been employed in modeling studies of mantle dynamics. The different techniques bring different strengths to the field. There are many examples in the scientific literature where laboratory methods are used to develop empirical relationships between the response of a fluid system and simple combinations of the physical parameters that define the system. Laboratory methods are also useful in modeling fine scale thermal- chemical structures in three dimensional flow morphologies and for testing first-order features of observationally based, dynamic process models. The focus of this talk is subduction, which introduces heterogeneity deep into the mantle and acts to stir the mantle. We summarize results from laboratory experiments on the relationship between subduction and both the deep production of thermal-chemical upwellings and how mantle heterogeneity is recycled to the surface. In one set of experiments chemically laminated slabs are subducted into a deep thermal boundary layer. Different styles of buoyant upwelling evolve from the slab pile through time, which are related to the isothermal densities of the slab laminates. Observed length scales of chemical heterogeneity ranging from passive 1 km features in tendrils embedded within upwellings to active 300km wide features within plume heads have implications for melt production models. In a second set of experiments, laboratory models consider the interaction between rollback subduction and back-arc extension, three-dimensional mantle circulation and the shallow dispersion of buoyant upwellings. The models are developed to represent basic features of the Cascades subduction system. Results suggest that first order features of the Cascades system (e.g., gross spatial and temporal patterns in melt production) may be consistent with a model in which an upwelling is deformed by large scale, subduction

  11. 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

  12. A 3-D numerical study of the thermal evolution of the Moon after cumulate mantle overturn: The importance of rheology and core solidification

    NASA Astrophysics Data System (ADS)

    Zhang, Nan; Parmentier, E. M.; Liang, Yan

    2013-09-01

    in which the mantle of the Moon evolves from an initially stratified state following magma ocean solidification and overturn have been applied to address important features of long-term thermal evolution of the Moon, including convective instability of overturned ilmenite-bearing cumulates (IBC) at the lunar core-mantle boundary, generation of mare basalts, core sulfur content and inner core radius, paleomagnetism, and the present-day mantle structure. Whether a dense overturned IBC-rich layer at the bottom of the mantle can become thermally unstable to generate a single upwelling is controlled largely by the temperature-dependence of viscosity (the activation energy). Convective instability of the IBC-rich layer controls the heat flux out the core and the presence of an internally generated magnetic field. A long period of (~700 Ma) high positive core-mantle-boundary (CMB) heat flux after the instability of the IBC-rich layer is expected from our models. Present-day deep mantle temperatures inferred from seismic and gravitational inversion constrain the magnitude of mantle viscosity from 5 × 1019 to 1 × 1021 Pa s. The CMB temperature and solidified inner core radius inferred from seismic reflection constrain the core sulfur content. Our evolution models with 5-10 wt % sulfur content can produce the observed 240 km radius inner core at the present day. The asymmetrical distribution of the deep moonquakes only in the nearside mantle could be explained as the remnant structure of the single chemical upwelling generated from IBC-rich layer. Our evolution model after the overturn results in an early ~0.55 km expansion in radius for ~1000 Ma due to the radiogenic heating associated with IBC in the deep mantle and may provide a simple explanation for the early expansion inferred from the Gravity Recovery and Interior Laboratory mission.

  13. The effect of Bortezomib and Rapamycin on Telomerase Activity in Mantle Cell Lymphoma

    PubMed Central

    Uziel, Orit; Cohen, Olga; Beery, Einat; Nordenberg, Jardena; Lahav, Meir

    2014-01-01

    Mantle cell lymphoma (MCL) is a hematological malignancy with unfavorable prognosis. Novel therapeutic approaches for treating the disease are aimed at the mechanisms regulating growth signals, cellular proliferation, and survival pathways of the malignant clones. Bortezomib (Brt), a proteasome inhibitor with pleiotropic activities was shown to be active in MCL and is currently implemented in therapeutic combinations for this disease. Telomerase activity is essential for survival of malignant cells and as such is considered a valid therapeutic target. This study evaluated the effects of bortezomib on telomerase activity and its regulation in MCL cells in vitro and ex vivo. Our study shows that bortezomib exerts a cytotoxic effect in a dose dependent manner in two MCL cell lines, with differential sensitivity. While the IC50 for HBL-2 cells ranged between 2.5 ng/ml to 1.5 ng/ml during 24-72 h respectively, the IC50 for the NCEB cells was twice. Bortezomib differentially inhibited telomerase activity (TA): in HBL-2 cells there was a decline of 20%-55% during 24-72 h respectively. However in NCEB cells the decline was much smaller, and did not exceed 25%. Inhibition of telomerase activity is shown to be operated by two separate mechanisms: reduction of the hTERT mRNA expression (controlled by the binding of transcription factors) and reduction in phosphorylation of the catalytic subunit of hTERT by its kinases, AKT and PKCα. A decrease in telomerase activity was demonstrated also in mononuclear cells, isolated from three MCL patients following incubation of the cells in the presence of bortezomib for 24-72 h. In one patient the decrease in TA ranged between 17%-37% respectively, in the second patient between 63%-76% and in the third patient between 70-100% for 24-72 h respectively. The current study indicates that a combination of bortezomib and rapamycin, (an m-Tor pathway inhibitor used in MCL treatment) induced synergistic inhibition of telomerase activity. In HBL

  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. 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.

  16. 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

  17. The effect of plate stresses and shallow mantle temperatures on tectonics of northwestern Europe

    NASA Astrophysics Data System (ADS)

    Goes, S.; Loohuis, J. J. P.; Wortel, M. J. R.; Govers, R.

    2000-12-01

    Northwestern Europe is tectonically more active, in terms of seismicity, vertical motions and volcanism, than would be expected from its location far from any plate boundaries. In the context of the Netherlands Earth System Dynamics Initiative, we investigated the implications of two recent modeling efforts, of Eurasian plate forces and European mantle structure, for our understanding of the dynamics of these intraplate tectonics. We find that: (1) a simple balance between ridge push and collision forces along the southern European boundary does not seem sufficient to explain the observed direction of maximum horizontal compression in northwestern Europe. Our stress model, which imposes dynamical equilibrium on the full Eurasian plate, predicts that collision forces along the African-European boundary are relatively weak and have only a minor effect on the stress field in northwestern Europe; (2) seismic velocity anomalies in the shallow mantle imply 100-300°C variations in temperature under northwestern Europe. This regional mantle structure probably plays a significant role in the high level of intraplate tectonic activity and the regional variations in stress and tectonic style. For most tectonically active areas in Europe, observed surface heat flow anomalies coincide with anomalies in mantle velocity. Low velocity anomalies under northwestern Europe coincide with areas of recent volcanism and uplift, but are offset from the regions of maximum surface heat flow. This suggests that the thermal regime of the central European lithosphere is not in a steady state, probably due to changing mantle conditions. The effect of strong variations in lithospheric strength, predicted from the modeled thermal gradients in the shallow mantle, and of dynamic stresses induced by proposed active mantle upwellings may account for (some of) the differences between the observed and modeled stress field and will be investigated in future stress models.

  18. 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.

  19. 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

  20. 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

  1. Nimbus observation of oceanic upwelling

    NASA Technical Reports Server (NTRS)

    Szekielda, K.

    1972-01-01

    Observing the development of upwelling on the northeast coast of Africa by measuring ocean surface emission with infrared radiometers on Nimbus satellites is reported. Using the temperature of the ocean as telemetered by the satellite, the biological potential of an area is estimated, and consequently the highest potential for fisheries.

  2. The Effect of an Early Dichotomy on Mars Mantle Convection

    NASA Astrophysics Data System (ADS)

    King, S. D.

    2006-12-01

    Several attempts have been made to produce a crustal dichotomy followed by a single, stationary mantle plume, giving rise to the Tharsis volcanic province using 3D mantle convection models. If Mars evolved in such a scenario, two degree-1 (i.e., hemispherical) patterns would be required to develop at 90° to each other in the span of a few hundred million years. This has not yet been accomplished although recent numerical models (e.g. Roberts and Zhong, 2006) have made significant strides towards a solution including the use of both a lower mantle phase change and a layered viscosity mantle. Our goal is not to determine how the crustal dichotomy formed, but to assume it was already in place within the first 0.5 Ga of Mars' evolution. The presence of an early dichotomy boundary likely affected the planform of mantle convection and may have played a role in the formation of the Tharsis Rise based on the proximity of Tharsis to the dichotomy boundary. We model Martian mantle convection using the 3D finite element code CitComS (Zhong et al., 2000). Previous laboratory experiments have shown that an insulating lid overlying part of a temperature-dependent mantle will generate a large, stationary upwelling beneath the center of the lid. Thus, we incorporate a dry, Newtonian rheology with E*=300 kJ/mol and simulate a dichotomy boundary by integrating a high viscosity lid over the "southern hemisphere" of our model. Redmond and King (2004) illustrate that the effect of a strongly temperature-dependent rheology is the development of a stiff, rheological lithosphere. Thus, for small Rayleigh numbers, the initially imposed dichotomy boundary does not have an effect on the location of mantle upwellings because of the global lid that forms as a result of the temperature-dependent rheology. Our results suggest that an initially larger Rayleigh number, on the order of 107, will produce stationary upwellings beneath the imposed southern hemisphere lid before a global lid develops

  3. 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

  4. The Tyrrhenian Basin: fault activity migration, focusing of deformation, break up, magmatism and fast mantle exhumation

    NASA Astrophysics Data System (ADS)

    Ranero, Cesar R.; Sallarés, Valenti; Vendrell, Montserrat G.; Prada, Manuel; Grevemeyer, Ingo; Zitellini, Nevio

    2015-04-01

    We present a new interpretation of the creation of the geological domains and the processes forming the Tyrrhenian basin by rifting of Cratonic Variscan lithosphere. The basin is not presently extending, but its crustal structure preserves information of the temporal evolution of rifting processes. Our work is based on the tectonic structure and stratigraphy of over 3000 km of calibrated multichannel seismic data and full coverage multibeam bathymetry of the basin. From these data circa 2000 km are new and about 1000 are vintage data. The seismic data are used to understand the formation of the domains (continental, backarc magmatism, exhumed mantle) defined with our recently published, under review, or submitted 5 across-the-basin wide-angle reflection and refraction transects. The 5 transects provide the Vp distribution of the crust and upper mantle. This information has allowed defining the petrological nature and distribution of the geological domains, and to infer the importance of magmatism in the rifting process, to constrain the location of break up and the expanse of the region of mantle exhumation. The seismic reflection images have been interpreted to map in time and space the evolution of the deformation across the basin. We analyzed the tectonic structure and mapped the calibrated stratigraphy across the basin to understand the temporal evolution and styles of faulting processes. The stratigraphy provides also constraints on the rates at which the different processes of extension, magmatism, break up and mantle exhumation have occurred. The basin has opened with different extension factors from north to south. The northern region stopped opening after a relatively low extension factors. Towards the south extension increased up to full crustal separation. Here extension in some areas was coeval with abundant magmatism. Changing in the locus of faulting and rates of extension led to break up and to a surprisingly fast mantle exhumation. Subsequent

  5. Mantle peridotite xenoliths in andesite lava at El Peñon, central Mexican Volcanic Belt: Isotopic and trace element evidence for melting and metasomatism in the mantle wedge beneath an active arc

    NASA Astrophysics Data System (ADS)

    Mukasa, Samuel B.; Blatter, Dawnika L.; Andronikov, Alexandre V.

    2007-08-01

    Peridotites in the mantle wedge and components added to them from the subducting slab are thought to be the source of most arc magmas. However, direct sampling of these materials, which provides a glimpse into the upper mantle beneath an active margin, is exceedingly rare. In the few arc localities where found, peridotite xenoliths are usually brought to the surface by basaltic magmas. Remarkably, the hornblende-bearing ultramafic xenoliths and clinopyroxene megaxenocrysts from El Peñon in the central Mexican Volcanic Belt were brought to the surface by a Quaternary high-Mg siliceous andesite, a rock type usually considered too evolved to be a direct product of mantle melting. The xenoliths and megaxenocrysts from El Peñon represent lithospheric mantle affected by significant subduction of oceanic lithosphere since as early as the Permian. Trace element and radiogenic isotope data we report here on these materials suggest a history of depletion by melt extraction, metasomatism involving a fluid phase, and finally, limited reaction between the ultramafic materials and the host andesite, probably during transport. They also show that high-Mg siliceous andesite can be a direct product of 1-5% melting of H 2O-bearing spinel lherzolite.

  6. 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

  7. 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.

  8. 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

  9. 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.

  10. 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

  11. Petrology of exhumed mantle rocks at passive margins: ancient lithosphere and rejuvenation processes

    NASA Astrophysics Data System (ADS)

    Müntener, Othmar; McCarthy, Anders; Picazo, Suzanne

    2014-05-01

    Mantle peridotites from ocean-continent transition zones (OCT's) and ultraslow spreading ridges question the commonly held assumption of a simple link between mantle melting and MORB. 'Ancient' and partly refertilized mantle in rifts and ridges illustrates the distribution of the scale of chemical and isotopic upper mantle heterogeneity even on a local scale. Field data and petrology demonstrates that ancient, thermally undisturbed, pyroxenite-veined subcontinental mantle blobs formed parts of the ocean floor next to thinned continental crust. These heterogeneities might comprise an (ancient?) subduction component. Upwelling of partial melts that enter the conductive lithospheric mantle inevitably leads to freezing of the melt and refertilization of the lithosphere and this process might well be at the origin of the difference between magma-poor and volcanic margins. Similar heterogeneity might be created in the oceanic lithosphere, in particular at slow to ultra-slow spreading ridges where the thermal boundary layer (TBM) is thick and may be veined with metasomatic assemblages that might be recycled in subduction zones. In this presentation, we provide a summary of mantle compositions from the European realm to show that inherited mantle signatures from previous orogenies play a key role on the evolution of rift systems and on the chemical diversity of peridotites exposed along passive margins and ultra-slow spreading ridges. Particularly striking is the abundance of plagioclase peridotites in the Alpine ophiolites that are interpreted as recorders of refertilization processes related to thinning and exhumation of mantle lithosphere. Another important result over the last 20 years was the discovery of extremely refractory Nd-isotopic compositions with highly radiogenic 147Sm/144Nd which indicates that partial melting processes and Jurassic magmatism in the Western Thetys are decoupled. Although the isotopic variability might be explained by mantle heterogeneities

  12. 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

  13. Upwelling off Yangtze River estuary in summer

    NASA Astrophysics Data System (ADS)

    Lü, Xingang; Qiao, Fangli; Xia, Changshui; Zhu, Jianrong; Yuan, Yeli

    2006-11-01

    The mechanisms of upwelling off the Yangtze River estuary (YRE) and in the adjacent waters in boreal summer are studied using numerical modeling. First, the persistent feature of this phenomenon is confirmed using cruise observations, satellite sea surface temperature (SST), and SST climatologic data. Then, the MASNUM (Marine Science and Numerical Modeling) wave-tide-circulation coupled numerical model is employed to simulate the upwelling patterns. On the basis of the simulation, a set of numerical experiments are designed to explore the main mechanisms inducing the upwelling. The results suggest that tidal mixing plays a predominant role in inducing the upwelling. In offshore waters, strong tidal mixing results in considerable horizontal density gradient across tidal fronts. Upwelling is induced as a branch of the secondary circulation, which is stimulated by the cross-frontal density gradient. Topography also exerts profound influences on upwelling by steering bottom currents to ascend upward and regulating tidal fronts in both location and intensity. Besides the tides and topography, other dynamical factors also alter the strength of upwelling locally. The Yangtze River discharge (YRD) and Taiwan Warm Current (TWC) account partly for the upwelling off the YRE and near Zhoushan Islands, respectively. The influence of wind on upwelling is small. In the coastal waters near Zhoushan Islands, the wind forcing exerts negative influences on upwelling by weakening the encroachment of TWC onto the continental shelf, which may exceed the positive effects of Ekman pumping.

  14. 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.

  15. Rollback subduction: the great killer of mantle plumes

    NASA Astrophysics Data System (ADS)

    Druken, K. A.; Kincaid, C. R.; Griffiths, R. W.

    2010-12-01

    Subduction driven mantle flow is shown to stall and decapitate buoyant upwellings, thereby severely limiting vertical heat and mass transport. Ongoing debate tends to focus on the expected surface expression of plumes rising independently of the background circulation, however we present 3-D laboratory results that suggest rollback subduction greatly alters this classic plume model. A Phenolic sheet and temperature dependent glucose fluid, are used to model the subducting plate and upper ~2000 km of the mantle, respectively. Experiments varied style and rate of rollback subduction as well as plume temperature and position. Results show that buoyant upwellings located as far as 1500 km behind the trench fall under two regimes, (I) plate dominated or (II) plume dominated. In either regime, down-dip sinking of the slab initially stalls vertical plume motion and the combination of down-dip sinking and trench rollback redistributes material throughout the system. Plumes with as much as 400°C excess temperature behave as passive features in the subduction-induced 3-D flow (Regime I). Less than 10% of plume material in this regime is capable of reaching zones for melt generation, with rollback subduction trapping or re-subducting the majority of plume material at depth. Only plumes of 600°C excess temperature (or more) are able to overcome the dominant 3-D flow and transport heat and mass to the surface (Regime II). Regardless of plume temperature, conduit velocities (proxy for melt generation) show cycles of high and low hotspot activity also due to distortion from subduction-induced flow. As a result of both the sinking and rollback motions, the temporal hotspot trend is variable and differs from conventional plate-conduit interaction.

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. Mantle seismic structure beneath USArray: slab segmentation and deep roots of the Yellowstone hotspot (Invited)

    NASA Astrophysics Data System (ADS)

    Schmandt, B.

    2013-12-01

    The Yellowstone hotspot track is a dramatic example of how EarthScope data are helping to reveal systematic connectivity between deep Earth convection, plate tectonics, and surface geologic activity in the plate interior. Two types of seismic constraints provide evidence for buoyant ascent of a lower mantle thermal plume beneath Yellowstone. First, teleseismic body-wave tomography images of smooth 3-D velocity structure show a vertically elongated and irregular low-velocity volume extending to about 1000 km depth. Second, upward deflection of the endothermic postspinel phase transition that represents the boundary between the lower and upper mantle specifically indicates local upwelling of hot lower mantle. Beyond establishing the present day existence of the Yellowstone plume, recent seismic images afford further insight into hotspot initiation in a region where subducted slabs might be expected to block ascent of a lower mantle plume. Several body-wave tomography using EarthScope data reveal a dissected distribution of high-velocity slabs beneath the western U.S., thus providing potential pathways for plume ascent and origins for the plume's vertical irregularity. The possibility of plume ascent through such a slab gap has recently been substantiated by other workers' numerical forward modeling of Farallon subduction constrained by a global plate tectonic model, which predicts a trench-normal slab segmentation event that is spatially consistent with present day tomography and temporally consistent with Miocene initiation of the Yellowstone hotspot track near the edge of Precambrian North America lithosphere.

  2. 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.

  3. Imprint of external climate forcing on coastal upwelling in past and future climate

    NASA Astrophysics Data System (ADS)

    Tim, N.; Zorita, E.; Hünicke, B.; Yi, X.; Emeis, K.-C.

    2015-11-01

    The Eastern Boundary Upwelling Systems are the major coastal upwelling regions. The trade winds are driving these upwelling regimes located in the subtropics at the eastern boundary of the Atlantic and Pacific Ocean. Here we analyse the impact of the external climate forcing, e.g. the greenhouse gas concentration, solar activity and volcano eruptions, on these upwelling systems in simulations of ensembles of two Earth System Models. The ensembles contain three simulations for each time period which cover the past millennium (900-1850), the 20th century (1850-2005) and the near future (2006-2100). Using a set of simulations, differing only in their initial conditions, enables us to detect whether the variability is driven internally or externally. Our analysis shows that the variability of the simulated upwelling is to the most driven internally and that there are no significant trends except for the scenario with the most dramatic increase of greenhouse gas concentrations.

  4. Seismic anisotropy and mantle fabrics beneath eastern Africa and Arabia

    NASA Astrophysics Data System (ADS)

    Elsheikh, A. A.; Gao, S. S.; Liu, K. H.

    2013-12-01

    In spite of numerous studies, the mechanisms for the rifting, uplifting, and volcanism on the African plate remain enigmatic. The most popular hypotheses proposed to explain these tectonic phenomena involve edge-driven small-scale mantle convection and the thermal or dynamic effects of one or more mantle plumes. In particular, several recent models suggested that the rise of the African plateaus and western Arabia was due to the dynamic upwelling of an active mantle plume located beneath southern Africa, despite of the fact that most studies revealed that the mantle transition zone beneath southern Africa has a normal temperature. In this study we use continental scale shear-wave splitting measurements to provide additional constraints on the various models of rifting and uplifting of the African plate. The splitting of P-to-S converted phases at the core-mantle boundary on the receiver side (XKS including PKS, SKKS, and SKS) is one of the most effective approaches to image mantle flow, and to constrain convective mantle flow patterns. Most of the previous shear-wave splitting (SWS) studies in eastern Africa and Arabia assumed a single anisotropic layer as the source of the observed shear-wave splitting. Some studies attributed the observed anisotropy to Precambrian lithospheric fabric developed during compressional orogenic events, while others emphasized the role of mantle flow. Almost all of these studies focused on restricted geographic regions or used a limited number of stations, which led to results applicable to localized areas rather than a continent-wide scale. In addition, the results were presented as station-averages, which prevent the identification of complex anisotropy. This presentation reports preliminary results from an ongoing study using all the broadband XKS data available at the IRIS Data Management Center. The data set was recorded by more than 200 stations in east Africa and Arabia. We are in the process to produce a uniform SWS database

  5. Experimental petrology of peridotites, including effects of water and carbon on melting in the Earth's upper mantle

    NASA Astrophysics Data System (ADS)

    Green, David H.

    2015-02-01

    shallower depths and lower temperatures within the asthenosphere and the upwelling lherzolite is enriched in water, carbonate and incompatible elements. Magmas including olivine melilitites, olivine nephelinites, basanites, alkali picrites and tholeiitic picrites are consequences of increasing melt fraction and decreasing pressure at melt segregation. Major element, trace element and isotopic characteristics of island chain or `hot-spot' magmas show that they sample geochemically distinct components in the upper mantle, differing from MORB sources. There is no evidence for higher-temperature `hot-spot' magmas, relative to primitive MORB, but there is evidence for higher water, CO2 and incompatible element contents. The distinctive geochemical signatures of `hot-spot' magmas and their `fixed' position and long-lived activity relative to plate movement are attributed to melt components derived from melting at interfaces between old, oxidised subducted slabs (suspended beneath or within the deeper asthenosphere) and ambient, reduced mantle. In convergent margin volcanism, the inverted temperature gradients inferred for the mantle wedge above the subducting lithosphere introduce further complexity which can be explored by overlaying the phase relations of appropriate mantle and crustal lithologies. Water and carbonate derived from the subducted slab play significant roles, magmas are relatively oxidised, and distinctive primary magmas such as boninites, adakites and island arc ankaramites provide evidence for fluxing of melting in refractory harzburgite to lherzolite by slab-derived hydrous adakitic melt and by wedge-derived carbonatite.

  6. 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

  7. Model for Transition Zone Formation from Upwelling Thermo-Chemical Plumes of Intermediate Rheology

    NASA Astrophysics Data System (ADS)

    Nguyen, C. T.; Weeraratne, D. S.

    2008-12-01

    The mantle transition zone has been limited to a layer of approximately 250 km at the base of the upper mantle, identified by studies in seismology and mineral physics. However, there are many uncertainties as to the nature of formation of this mid-mantle layer, its evolution over geological time, physical properties, and its role facilitating or inhibiting whole mantle flow. Here, we conduct laboratory fluid experiments using high viscosity corn syrup fluids and liquid gallium to study mantle convection processes in the early Earth. Specifically, we consider early core formation events involving metal-silicate plumes which sink following impact events and entrain magma ocean material from the surface during descent. Preliminary studies indicate that low viscosity, buoyant material, that makes up the model magma ocean near the surface is entrained in conduits that form behind quickly descending liquid metal plumes to the base of the lower mantle. This low density material brought to the base of the model lower mantle becomes buoyant and subsequently rises back up to the top of the fluid box forming a new intermediate material that has experienced both chemical and thermal diffusion along its mantle pathway and empties at the top of the lower mantle or base of a magma ocean. Two-component fluid experiments are considered in the presence of a hot lower thermal boundary layer at Rayleigh numbers of 103 to 105 and low Reynolds number flow, and indicate that upwelling thermo-chemical plumes may form following core formation events. This new third fluid layer of intermediate rheology is considered as a model for the mantle transition zone. Shadow graph images indicate a sharp density contrast with surrounding fluids that persists for long times, consistent with seismic discontinuities observed for the Earth's transition zone. We will present quantitative estimates of material rheology, density, and flow properties for scaling with a silicate mantle, geophysical, and

  8. 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

  9. 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. PMID:24452204

  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. 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

  12. 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).

  13. 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

  14. JNK is constitutively active in mantle cell lymphoma: cell cycle deregulation and polyploidy by JNK inhibitor SP600125.

    PubMed

    Wang, Miao; Atayar, Cigdem; Rosati, Stefano; Bosga-Bouwer, Anneke; Kluin, Philip; Visser, Lydia

    2009-05-01

    Mantle cell lymphoma (MCL) is characterized by genetic instability and a poor prognosis. Many blastoid variants are (hypo)tetraploid and have an even worse prognosis. We investigated the role of signalling by mitogen-activated protein kinases (MAPKs) in MCL. As compared to normal tonsil B cells, MCL cells showed higher activation of the JNK MAPK in both an MAPK array and a sandwich ELISA assay. Immunohistochemistry showed overexpression of phospho (p)-JNK (Thr183/Tyr185) in 30 of 37 MCL cases. Inhibition of p-JNK with SP600125 resulted in growth arrest in all four MCL cell lines (Jeko-1, HBL-2, UPN-1, Granta-519), which could be partly reversed by the addition of CD40L and IL-4. Furthermore, SP600125 led to G2/M phase arrest on day 1 and a striking increase in endoreduplication on day 2 and day 3, which was confirmed by karyotype analysis. G2/M arrest was associated with down-regulation of EGR1 and p21 protein expression. SP600125-induced polyploidy could be blocked by the BCL-2 inhibitor YC137. These data suggest that constitutive JNK activity is necessary to promote proliferation and maintain diploidy in MCL. JNK inhibition leads to cell cycle deregulation and endoreduplication, mimicking the tetraploid state seen in a subset of MCL cases. Thus, our data also provide an experimental model to study polyploid MCL cells. PMID:19206150

  15. Pathogenic role of B-cell receptor signaling and canonical NF-κB activation in mantle cell lymphoma.

    PubMed

    Saba, Nakhle S; Liu, Delong; Herman, Sarah E M; Underbayev, Chingiz; Tian, Xin; Behrend, David; Weniger, Marc A; Skarzynski, Martin; Gyamfi, Jennifer; Fontan, Lorena; Melnick, Ari; Grant, Cliona; Roschewski, Mark; Navarro, Alba; Beà, Sílvia; Pittaluga, Stefania; Dunleavy, Kieron; Wilson, Wyndham H; Wiestner, Adrian

    2016-07-01

    To interrogate signaling pathways activated in mantle cell lymphoma (MCL) in vivo, we contrasted gene expression profiles of 55 tumor samples isolated from blood and lymph nodes from 43 previously untreated patients with active disease. In addition to lymph nodes, MCL often involves blood, bone marrow, and spleen and is incurable for most patients. Recently, the Bruton tyrosine kinase (BTK) inhibitor ibrutinib demonstrated important clinical activity in MCL. However, the role of specific signaling pathways in the lymphomagenesis of MCL and the biologic basis for ibrutinib sensitivity of these tumors are unknown. Here, we demonstrate activation of B-cell receptor (BCR) and canonical NF-κB signaling specifically in MCL cells in the lymph node. Quantification of BCR signaling strength, reflected in the expression of BCR regulated genes, identified a subset of patients with inferior survival after cytotoxic therapy. Tumor proliferation was highest in the lymph node and correlated with the degree of BCR activation. A subset of leukemic tumors showed active BCR and NF-κB signaling apparently independent of microenvironmental support. In one of these samples, we identified a novel somatic mutation in RELA (E39Q). This sample was resistant to ibrutinib-mediated inhibition of NF-κB and apoptosis. In addition, we identified germ line variants in genes encoding regulators of the BCR and NF-κB pathway previously implicated in lymphomagenesis. In conclusion, BCR signaling, activated in the lymph node microenvironment in vivo, appears to promote tumor proliferation and survival and may explain the sensitivity of this lymphoma to BTK inhibitors. PMID:27127301

  16. 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

  17. 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.

  18. Corona Formation and Heat Loss on Venus by Coupled Upwelling and Delamination

    NASA Technical Reports Server (NTRS)

    Smrekar, Suzanne E.; Stofan, Ellen R.

    1997-01-01

    Coronae are volcanotectonic features that are unique to Venus and are interpreted to be small-scale upwellings. A model in which upwelling causes delamination at the edge of the plume head, along with deformation of a pre-existing depleted mantel Layer, can produce the full range of topographic forms of coronae. If half of the coronae are active, delamination of the lower lithosphere could account for about 10% of venus's heat loss, with another 15% due to upwelling. Delamination may occur in other geologic enviroment and could help account for 'Venus' heat loss 'deficit'.

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. Eddies in eastern boundary subtropical upwelling systems

    NASA Astrophysics Data System (ADS)

    Capet, X.; Colas, F.; McWilliams, J. C.; Penven, P.; Marchesiello, P.

    Over the last decade, mesoscale-resolving ocean models of eastern boundary upwelling systems (EBS) have helped improve our understanding of the functioning of EBS and, in particular, assess the role of eddy activity in these systems. We review the main achievements in this regard and highlight remaining issues and challenges. In EBS, eddy activity arises from baroclinic/barotropic instability of the inshore and also offshore currents. Mesoscale eddies play a significant (although not leading) role in shaping the EBS dynamical structure, both directly and through associated submesoscale activity (i.e., primarily frontal). They do so by modifying both momentum and tracer balances in ways that cannot simply be understood in terms of diffusion. The relative degree to which these assertions about eddy activity and eddy role apply to each of the four major EBS (Canary, Benguela, Peru-Chile, and California Current Systems) remains to be established. Besides resolving the eddies, benefits from EBS high-resolution modeling include the possibility of accounting for the fine-scale structures of the nearshore wind, a better representation of the Ekman-driven coastal divergence, and (at resolution σ (1 km) or lower) inclusion of submesoscale (i.e., mainly frontal) processes. Recent numerical experiments suggest that accounting for these various processes in climate models, through resolution increase (possibly locally) or parameterization, would lead to significant basin-scale bias reduction. The mechanisms involved in upscaling from EBS toward the larger scale remain to be fully elucidated.

  4. The EMT activator ZEB1 promotes tumor growth and determines differential response to chemotherapy in mantle cell lymphoma

    PubMed Central

    Sánchez-Tilló, E; Fanlo, L; Siles, L; Montes-Moreno, S; Moros, A; Chiva-Blanch, G; Estruch, R; Martinez, A; Colomer, D; Győrffy, B; Roué, G; Postigo, A

    2014-01-01

    Mantle cell lymphoma (MCL) is a B-cell malignancy characterized by a poor response to treatment and prognosis. Constitutive activation of different signaling pathways in subsets of MCLs, through genetic and/or nongenetic alterations, endows tumor cells with enhanced proliferation and reduced apoptosis. The canonical Wnt pathway (β-catenin/TCF-LEF), implicated in the pathogenesis of numerous cancers, is constitutively active in half of MCLs. Here, we show that ZEB1, a transcription factor better known for promoting metastasis in carcinomas, is expressed in primary MCLs with active Wnt signaling. ZEB1 expression in MCL cells depends on Wnt, being downregulated by β-catenin knockdown or blocking of Wnt signaling by salinomycin. Knockdown of ZEB1 reduces in vitro cell viability and proliferation in MCL cells, and, importantly, tumor growth in mouse xenograft models. ZEB1 activates proliferation-associated (HMGB2, UHRF1, CENPF, MYC, MKI67, and CCND1) and anti-apoptotic (MCL1, BCL2, and BIRC5) genes and inhibits pro-apoptotic ones (TP53, BBC3, PMAIP1, and BAX). We show that ZEB1 expression in MCL cells determines differential resistance to chemotherapy drugs and regulates transporters involved in drug influx/efflux. Downregulation of ZEB1 by salinomycin increases the sensitivity of MCL cells to the cytotoxic effect of doxorubicin, cytarabine and gemcitabine. Lastly, salinomycin and doxorubicin display a synergistic effect in established and primary MCL cells. These results identify ZEB1 in MCL where it promotes cell proliferation, enhanced tumor growth and a differential response to chemotherapy drugs. ZEB1 could thus potentially become a predictive biomarker and therapeutic target in this lymphoma. PMID:24013721

  5. 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

  6. 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.

  7. 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

  8. 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

  9. 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

  10. Three-Dimensional Numerical Simulation on Passively Excited Flows by Distributed Local Hot Sources Settled at the D" Layer Below Hotspots and/or Large-Scale Cool Masses at Subduction Zones Within the Static Layered Mantle

    NASA Astrophysics Data System (ADS)

    Eguchi, T.; Matsubara, K.; Ishida, M.

    2001-12-01

    To unveil dynamic process associated with three-dimensional unsteady mantle convection, we carried out numerical simulation on passively exerted flows by simplified local hot sources just above the CMB and large-scale cool masses beneath smoothed subduction zones. During the study, we used our individual code developed with the finite difference method. The basic three equations are for the continuity, the motion with the Boussinesq (incompressible) approximation, and the (thermal) energy conservation. The viscosity of our model is sensitive to temperature. To get time integration with high precision, we used the Newton method. In detail, the size and thermal energy of the hot or cool sources are not uniform along the latitude, because we could not select uniform local volumes assigned for the sources within the finite difference grids throughout the mantle. Our results, thus, accompany some latitude dependence. First, we treated the case of the hotspots, neglecting the contribution of the subduction zones. The local hot sources below the currently active hotspots were settled as dynamic driving forces included in the initial condition. Before starting the calculation, we assumed that the mantle was statically layered with zero velocity component. The thermal anomalies inserted instantaneously in the initial condition do excite dynamically passive flows. The type of the initial hot sources was not 'plume' but 'thermal.' The simulation results represent that local upwelling flows which were directly excited over the initial heat sources reached the upper mantle by approximately 30 My during the calculation. Each of the direct upwellings above the hotspots has its own dynamic potential to exert concentric down- and up-welling flows, alternately, at large distances. Simultaneously, the direct upwellings interact mutually within the spherical mantle. As an interesting feature, we numerically observed secondary upwellings somewhere in a wide region covering east Eurasia

  11. A survey of upwelling ion event characteristics

    NASA Technical Reports Server (NTRS)

    Pollock, C. J.; Chandler, M. O.; Moore, T. E.; Chappell, C. R.; Waite, J. H., Jr.

    1990-01-01

    Quasi-static electric field data collected by the DE-1 spacecraft were used to study ionospheric ion upwelling events observed in the vicinity of the dayside cleft. Bulk plasma parameters such as ion-species density and field-aligned bulk velocity and flux were derived at points within several upwelling ion events for the H(+), He(+), O(+), and O(2+), and the ion-species bulk parameters near the source altitude were compared. It was found that O(+) ions comprise about 90 percent of the upwelling particle density, followed by H(+) at less than 10 percent; He(+) and O(2+) contribute about 1 percent each. The upwelling O(+) flux is also dominant, followed by upward H(+) flux, which is relatively more significant than the fractional H(+) density, due to its high upward flow velocity.

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

    NASA Astrophysics Data System (ADS)

    Oppenheimer, Clive; Moretti, Roberto; Kyle, Philip R.; Eschenbacher, Al; Lowenstern, Jacob B.; Hervig, Richard L.; Dunbar, Nelia W.

    2011-06-01

    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 CO 2), 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 CO 2-rich oxidised fluids from the mantle to the surface, and evaluate how these processes operate in time and space. Extensive crystallisation driven by CO 2 fluxing is responsible for isobaric fractionation of parental basanite magmas close to their source depth. Magma deeper than 4 kbar equilibrates under vapour-buffered conditions. At shallower depths, CO 2-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).

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. Seismic tomogram of the earth's mantle - Geodynamic implications

    NASA Astrophysics Data System (ADS)

    Fukao, Yoshio

    1992-10-01

    Seismic tomography studies of the terrestrial mantle reveal a pattern of mantle convection involving upwelling columnar plumes in the Pacific and Africa, as well as circum-Pacific downwelling planar sheets. Extensive upwelling occurs in the south Pacific, and downwelling in the west Pacific. Attention is given to a high resolution image of plate subduction gathered from dense seismic networks surrounding Japan; these networks offer unique capabilities for resolving the internal structure of a large convection system's downwelling current. Chemistry/Food Science, general Engineering, general Materials Science 60 60 12 11 11 16 2008 11 13 2008 11 2008 TMS 2008 149 10.1007/s11837-008-0149-1 11 Magnesium: Applications and advanced processing in the automotive industry Magnesium for Automotive Applications Commentary 56 56 2008 11 7 2008 11 13 TMS 2008

  19. 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

  20. 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. PMID:16121171

  1. A mantle plume model for the Equatorial Highlands of Venus

    NASA Technical Reports Server (NTRS)

    Kiefer, Walter S.; Hager, Bradford H.

    1991-01-01

    The possibility that the Equatorial Highlands are the surface expressions of hot upwelling mantle plumes is considered via a series of mantle plume models developed using a cylindrical axisymmetric finite element code and depth-dependent Newtonian rheology. The results are scaled by assuming whole mantle convection and that Venus and the earth have similar mantle heat flows. The best model fits are for Beta and Atla. The common feature of the allowed viscosity models is that they lack a pronounced low-viscosity zone in the upper mantle. The shape of Venus's long-wavelength admittance spectrum and the slope of its geoid spectrum are also consistent with the lack of a low-viscosity zone. It is argued that the lack of an asthenosphere on Venus is due to the mantle of Venus being drier than the earth's mantle. Mantle plumes may also have contributed to the formation of some smaller highland swells, such as the Bell and Eistla regions and the Hathor/Innini/Ushas region.

  2. 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

  3. Retinoic acid inhibits the proliferative response induced by CD40 activation and interleukin-4 in mantle cell lymphoma.

    PubMed

    Guidoboni, Massimo; Zancai, Paola; Cariati, Roberta; Rizzo, Silvana; Dal Col, Jessica; Pavan, Alessandro; Gloghini, Annunziata; Spina, Michele; Cuneo, Antonio; Pomponi, Fabrizio; Bononi, Antonio; Doglioni, Claudio; Maestro, Roberta; Carbone, Antonino; Boiocchi, Mauro; Dolcetti, Riccardo

    2005-01-15

    Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin's lymphoma with poor response to therapy and unfavorable prognosis. Here, we show that retinoic acid (RA) isomers significantly inhibit the proliferation of both primary MCL cultures (n = 7) and established cell lines (Granta 519 and SP-53) as shown by [(3)H]thymidine uptake and carboxyfluorescein diacetate succinimidyl ester labeling coupled with cyclin D1 staining. RA induces cell accumulation in G(0)-G(1) together with a marked up-regulation of p27(Kip1) by inhibiting ubiquitination and proteasome-dependent degradation of the protein. The p21(Cip1) inhibitor was also up-regulated by RA in Granta 519 cells, whereas the expression of cyclin D1 is unaffected. Most of RA-induced p27(Kip1) was bound to cyclin D1/cyclin-dependent kinase 4 complexes, probably contributing to the decreased cyclin-dependent kinase 4 kinase activity and pRb hypophosphorylation observed in RA-treated cells. Experiments with receptor-selective ligands indicate that RA receptor alpha cooperates with retinoid X receptors in mediating RA-dependent MCL cell growth inhibition. Notably, RA isomers, and particularly 9-cis-RA, also inhibited the growth-promoting effect induced in primary MCL cells by CD40 activation alone or in combination with interleukin-4. Immunohistochemical analysis showed that significant numbers of CD40L-expressing lymphoid cells are present in lymph node biopsies of MCL patients. These results therefore further strengthen the possibility that triggering of CD40 by infiltrating CD40L+ cells may continuously promote the growth of MCL cells in vivo. On these grounds, our findings that RA inhibits basal MCL proliferation as well as MCL growth-promoting effects exerted by microenvironmental factors make these compounds highly attractive in terms of potential clinical efficacy in this setting. PMID:15695403

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

    PubMed

    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; Bhalla, Kapil N

    2015-09-24

    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

  5. 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

  6. Fertile Lithospheric Mantle beneath Far East Russia; evidence for Lithospheric delamination

    NASA Astrophysics Data System (ADS)

    Ntaflos, T.; Koutsovitis, P.; Aschchepkov, I.; Hauzenberger, C. A.; Prikhodko, V.; Barkar, A.

    2012-12-01

    In the back-arc environment of Far East Russia, mantle xenoliths from Sikhoti-Alin( Komku area, KO) and Primorie (Sviyaginsky area, SV), Far East Russia are fertile spinel lherzolites with traces of amphibole, phlogopite and hyalophane in some of the studied samples. Though samples from both localities are fertile there is a systematic difference in their fertility. The KO samples have mg# varying from 0.891 to 0.899 and are slightly more fertile than the SV samples that have mg# ranging from 0.898 to 0.904. LA-ICP-MS analyses on clinopyroxenes confirm this trend as the (La/Yb)N in KO samples range from 1.49 to 5.4 and in SV samples from 0.15 to 1.73. The estimated equilibration temperatures for the KO suite range from 940 °C to 1035 °C and for the SV suite from 770 to 945. The differences in the estimated equilibrium temperatures between the KO and SV suites suggest that the less fertile SV suite originated in shallower depths than the more fertile KO suite. Kaersutite, and extremely Ti-rich phlogopite, up to 14 wt% TiO2, are associated with intergranular glass indicating clearly metasomatism of undersaturated alkaline melts. Pargasitic amphibole occurs as inclusion in clinopyroxene. Incompatible element abundances, besides Ba, Sr and Ti that are slightly enriched in the amphibole, are similar in both phases suggesting minor metasomatism due to percolation of small amounts of water-rich fluids. The lithospheric mantle beneath the studied area represents the residue after partial melting of up to 2 % of a primitive mantle and is comparable to that of Mongolia. Despite the fact that the studied area experienced several subducting episodes, the lithospheric mantle appears to be unaffected from the upwelling fluids/melts of the subducted slab(s). Since there is no indication for plume activity, and/or evidence for refertilization, it is likely that the lithospheric mantle has been delaminated as the result of tectonic events (lithospheric attenuation, inverse

  7. 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

  8. 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

  9. (abstract) Seasonal Variability in Coastal Upwelling: A Comparison of Four Coastal Upwelling Sites from Space

    NASA Technical Reports Server (NTRS)

    Carr, Mary-Elena

    1996-01-01

    Coastal upwelling of subsurface nutrient-rich water occurs along the eastern boundary of the ocean basins and leads to high primary production and fish catches. In this study satellite observations are used to compare the seasonal cycle in wind forcing and in the oceanic and biological response of the major coastal upwelling regions associated with the Canary, Benguela, California, and Humboldt Currents.

  10. Seismic evidence of on-going sublithosphere upper mantle convection for intra-plate volcanism in Northeast China

    NASA Astrophysics Data System (ADS)

    Guo, Zhen; Chen, Y. John; Ning, Jieyuan; Yang, Yingjie; Afonso, Juan Carlos; Tang, Youcai

    2016-01-01

    A 3-D crustal and upper mantle S-wave velocity model of NE China is constructed by inversion of phase velocity dispersion curves at 6-140 s periods from ambient noise tomography and two-plane surface wave tomography. The seismic data used in this study are collected from 120 China Earthquake Administration (CEA) permanent stations and 127 portable stations of NECESSArray. We observe strong low S-wave velocity beneath the Changbaishan volcano in the upper mantle to at least 200-km depth, which is interpreted as a mantle upwelling beneath the Changbaishan volcano that is consistent with the body wave tomographic image. The Songliao Basin is dominated by a high velocity extending to at least 200-km depth. Built upon the observed velocity anomalies, we propose a sub-lithosphere mantle convection model for NE China in which the upwelling of upper mantle materials from the mantle transition zone to the Changbaishan volcano could induce a local sub-lithosphere convection in the upper mantle and the strong high velocity of the upper mantle beneath the Songliao Basin corresponds to the downwelling limb of this convection cell. The downwelling beneath the Songliao Basin could also induce secondary local convection in the asthenosphere to the west, leading to local asthenospheric upwelling beneath the Abaga and Halaha volcanoes in the Xing'an-Mongolia Orogenic Belt.

  11. 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

  12. 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.

  13. 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.

  14. Impact of lithosphere rheology on 3D continental rift evolution in presence of mantle plumes: insights from numerical models

    NASA Astrophysics Data System (ADS)

    Koptev, Alexander; Burov, Evgueni; Gerya, Taras

    2015-04-01

    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, the "plumes" represent short-lived diapiric upwellings that have no continuous feeding from the depth. Such upwellings may be associated with "true" plumes but also with various instabilities in the convective mantle. The models demonstrate 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). Although in all experiments the new-formed spreading centers have similar orientations perpendicular to the direction of the main far-field axis, the models with homogeneous lithosphere show that their number and spatial location is different for various extension rates and thermo-rheological structures of the lithosphere: relatively slow extension (3 mm/year) and colder isotherm (600-700°C at Moho depth) at the crustal bottom lead to the development of single rifts, whereas "faster" external velocities (6 mm/year) and "hotter" crustal geotherm (800°C at Moho depth) result in dual (sometimes asymmetric) rift evolution. On the contrary, the models with heterogeneous lithosphere (thick cratonic block with cold and thick depleted mantle embedded into «normal» lithosphere) and the plume centered below the craton, systematically show similar behaviors: two symmetrical and coeval rifting zones embrace the cratonic micro-plate along its long sides. The experiments where the initial plume position has been laterally shifted with

  15. 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.

  16. 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

  17. 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).

  18. A local upwelling controls viral and microbial community structure in South Australian continental shelf waters

    NASA Astrophysics Data System (ADS)

    Paterson, James S.; Nayar, Sasi; Mitchell, James G.; Seuront, Laurent

    2012-01-01

    Despite the increasing awareness of the role of viruses and heterotrophic bacteria in microbial dynamics and biogeochemical cycles, there is still a critical lack of information on their community composition and dynamics, especially in relation to upwellings. We investigated, within surface waters and the Deep Chlorophyll Max, the community composition and dynamics of flow cytometrically defined sub-populations of heterotrophic bacteria and virus-like particles in nearby water masses that were affected and unaffected by a localised wind-driven coastal upwelling. In contrast to previous studies we uniquely identified a 4-fold increase in total viral abundance and a decrease in bacterial abundance, from upwelled to offshore waters. Individual viral sub-populations were seen to correlate significantly to both bacterial populations and chlorophyll a, suggesting the possibility of individual viral populations infecting multiple host species rather than the often assumed single host species. The percentage of HDNA bacteria was high (84.3-93.4%) within upwelled waters, in accordance with the highest recorded values within an upwelling system, and decreased down to 35.5-42.6% away from the upwelling. Additionally, changes in the community composition of individual bacterial sub-populations suggest individual populations might be better adapted to distinct environments. We suggest that each flow cytometrically defined bacterial population may possess its own environmental niche where favourable conditions for that population result in an increase in abundance, cellular activity and productivity.

  19. 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.

  20. The East Pacific Rise: An Active Not Passive Spreading System

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Traditional plate tectonic interpretations of mid-oceanic ridges regard spreading as an entirely passive phenomenon. From this one would assume that the oceanic ridges will move over the mantle in response to the geodynamics of the diverging plates, and do not remain fixed spatially over any protracted period of time. An analysis of the kinematics of ridge motions in the Indo-Atlantic hotspot frame of reference since 83 Ma generally supports this view, with the notable exception of the East Pacific Rise (EPR). The Pacific-Nazca/Farallon segment of the EPR north of Easter Island (27°S) is oriented essentially N-S, and has produced more than 9500km of E-W spreading in the past 80 Ma, making it the dominant ridge in the world's plate system over this interval of time. Yet despite the large amount of E-W divergence, the spreading center has maintained its longitudinal position to within <±250 km of the current ridge axis. Global mantle convective flow modeling indicates that the EPR, unlike any other extensive segment of the mid-oceanic ridge system, is underlain by an active upwelling system extending from the core-mantle boundary to the surface. We suggest that the lack of E-W motion of the EPR apparent from the kinematics is a consequence of these mantle dynamics; this ridge is thus not behaving as a passive plate boundary, but is actively and directly linked to, and controlled by, whole mantle upwelling. This observation overturns the notion that ridges are always entirely passive features of the plate system. Subduction of the northern EPR beneath western North America has thus resulted in the overriding of an active upwelling system that has contributed significantly to the evolution of Basin and Range kinematics and superimposed dynamics, including significant contributions from dynamic topography.

  1. 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).

  2. 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

  3. Mantle flow beneath La Réunion hotspot track from SKS splitting

    NASA Astrophysics Data System (ADS)

    Barruol, Guilhem; Fontaine, Fabrice R.

    2013-01-01

    If upper mantle anisotropy beneath fast-moving oceanic plates is expected to align the fast azimuths close to the plate motion directions, the upper mantle flow pattern beneath slow-moving oceanic plates will reflect the relative motion between the moving plate and the underlying large-scale convecting mantle. In addition to the non-correlation of the fast azimuths with the plate motion direction, the flow and anisotropy pattern may be locally perturbed by other factors such as the upwelling and the sublithospheric spreading of mantle plumes. Investigating such plume-lithosphere interaction is strongly dependent on the available seismological data, which are generally sparse in oceanic environment. In this study, we take the opportunity of recent temporary deployments of 15 seismic stations and 5 permanent stations on the Piton de la Fournaise volcano, the active locus of La Réunion hotspot and of 6 permanent stations installed along or close to its fossil track of about 3700 km in length, to analyze azimuthal anisotropy detected by SKS wave splitting and to decipher the various possible origins of anisotropy beneath the Western Indian Ocean. From about 150 good and fair splitting measurements and more than 1000 null splitting measurements, we attempt to distinguish between the influence of a local plume signature and large-scale mantle flow. The large-scale anisotropy pattern obtained at the SW-Indian Ocean island stations is well explained by plate motion relative to the deep mantle circulation. By contrast, stations on La Réunion Island show a complex signature characterized by numerous "nulls" and by fast split shear wave polarizations trending normal to the plate motion direction and obtained within a small backazimuthal window, that cannot be explained by either a single or two anisotropic layers. Despite the sparse spatial coverage which precludes a unique answer, we show that such pattern may be compatible with a simple model of sublithospheric spreading

  4. 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.

  5. Remote sensing and ichthyoplankton ecology of coastal upwelling fronts off central California

    NASA Astrophysics Data System (ADS)

    Bjorkstedt, Eric Peter

    1998-11-01

    Recruitment to many marine populations is determined by processes affecting survival and transport of planktonic larvae. Coastal upwelling poses a trade-off between larval access to high productivity supported by upwelled nutrients and increased risk of offshore transport and failure to return to coastal habitats. I used plankton surveys, remote sensing, and a simple model to investigate the role of coastal upwelling fronts and behavior in pelagic ecology and recruitment success, focussing on rockfish (Sebastes spp.) off central California. Distributions of early stage larvae suggest that coastal upwelling fronts reduce offshore transport of rockfish larvae, in contrast to distributions of taxa with life histories that minimize larval exposure to strong upwelling. Coincident distributions of larval fish, prey (i.e., small copepods and invertebrate eggs) and phytoplankton patches indicate that coastal upwelling fronts provide enhanced foraging conditions for larvae. Thus, coastal upwelling fronts may allow coastal taxa to successfully exploit high productivity during the upwelling season while reducing the risk of offshore transport. I developed a novel method for utilizing a single HF radar to resolve currents and detect fronts that matched sea surface temperature fronts generated by coastal upwelling. Fronts and currents detected with NF radar affect distributions and transport of planktonic larval fish and intertidal barnacle larvae, demonstrating that remote sensing with HF radar can support field and modelling research on ecological dynamics in coastal marine systems. I used an empirically-based model that incorporated the advection-foraging trade-off and long-distance swimming as an active settlement behavior to investigate optimal settlement strategies as a function of pelagic transport and growth. For parameters loosely describing pelagic stages of rockfish, the model predicts optimal settling strategies (ages and sizes) for pelagic juveniles that roughly

  6. Multi-stage impregnation of the lithospheric mantle at the Andrew Bain FZ (SWIR)

    NASA Astrophysics Data System (ADS)

    Paganelli, E.; Brunelli, D.; Bonatti, E.; Cipriani, A.; Ligi, M.

    2008-12-01

    The Southern ridge-transform intersection of Andrew Bain Fracture Zone (ABFZ) is interpreted as a "cold spot" in the mid-ocean ridge system being characterized by a negative thermal anomaly in the oceanic upper mantle. The negative thermal anomaly is associated to the cold-edge effect due to the great age contrast of the active ridge segments. During the oceanic expedition AB06-S23, in 2006, (organized by ISMAR-CNR, Bologna, Italy, and co-financed by PRNA, Italy) with the russian R/V N. Strakhov, several samples of abyssal peridotites have been collected. Textures and modal distribution of the samples have been investigated revealing a multistage impregnation history. Deep spinel-field impregnation assemblages (sp+cpx-ol) are followed by plagioclase-field patches and mineral trails (pl+cpx-ol) and late shallow gabbroic pockets and veins. The major elements mineral chemistry reveals compositional trends of low-P/T subsolidus partial- to-complete re-equilibration undergone by the upper mantle during the upwelling beneath the ridge. These samples have experienced variable degrees of melting and reacted with percolating melts of possible different composition. In particular, samples showing the lowest degrees of melting have interacted with MORB-like melts and pyroxenitic-derived melts in the spinel and plagioclase stability fields. The presence of these two kinds of melts might prove the presence of enriched portions scattered in a normal depleted mantle beneath ocean ridges. MELTS-based runs provide constraints to variable extents of pyroxenitic-derived melt interaction with the mantle source and crystallization at variable depth of the products of such an interaction. Supported by MIUR-PRIN Cofin project 2007

  7. Shallow-mantle Recycling and Anomalous, Voluminous Volcanism along the Northern and Northwestern African Continental Margin

    NASA Astrophysics Data System (ADS)

    Bryce, J. G.; Blichert-Toft, J.; Graham, D. W.; Miller, S. A.

    2015-12-01

    Mantle-derived volcanism on Earth's surface is generally associated with magma generation as a consequence of volatile addition to suprasubduction zone mantle or in response to decompression melting at diverging plates or in thermochemical anomalies thought to originate deep in the convecting mantle. Many of the hotspots surrounding the northern and northwestern African margin are thought to originate from decompression melting due to upwellings from deep thermochemical anomalies. Similar compositions of lavas erupted in Sicily in the Hyblean Plateau and Mount Etna, Europe's largest most active volcano, have been attributed to contributions from subduction zone enrichments. Considering high-MgO lavas from the northern to northwestern African-Mediterranean margins in the context of recent petrologic models we find the strong majority of the lavas in this region are predominantly alkaline and bear geochemical signatures consistent with derivation from fusible lithologies (volatilized peridotite and/or pyroxenite) [1]. Such results are consistent with implications from recent experimental results that suggest that the mobilization of hydrous, carbonate-rich melts commonly occurs during subduction zone processing [2]. Accordingly, we argue many products generally considered "hot spot" volcanism in this region largely result from partial melting of easily fusible pyroxene-rich and carbonated mantle domains that are relics of shallow-level recycling of volatile-rich melts and/or lithosphere shed during plate boundary processes along the African margin. Long-lived volcanism near continental margins subsequently develops as a consequence of convective anomalies associated with unique tectonic arrangements (oversteepened slabs or slab windows) [3] or, alternatively, as manifestations of convective tectonic anomalies beneath thin lithosphere juxtaposed next to thicker, more stable continental margins [4]. [1] Herzberg and Asimow, 2008; [2] Poli, 2015; [3] Schellart, 2010; [4

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

    PubMed

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

    2015-01-01

    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. PMID:26169260

  9. 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

  10. 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.

  11. 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.

  12. Mesoscale distribution of clupeoid larvae in an upwelling filament trapped by a quasi-permanent cyclonic eddy off Northwest Africa

    NASA Astrophysics Data System (ADS)

    Bécognée, P.; Moyano, M.; Almeida, C.; Rodríguez, J. M.; Fraile-Nuez, E.; Hernández-Guerra, A.; Hernández-León, S.

    2009-03-01

    The distribution of fish larvae in relation to a filament shed from the Northwest African coastal upwelling was studied in February 2001. During the cruise, the filament was located between 27°N and 28°N, extending from the African coastal upwelling zone to the south of Fuerteventura Island (Canary Islands). This filament was trapped and remained over the quasi-permanent cyclonic eddy observed in previous studies. Almost all Sardina pilchardus, Engraulis encrasicolus and Sardinella aurita larvae caught during the cruise were associated with upwelled waters and filament structures. The sampled larval fish assemblage was composed by 12.6% of clupeoid larvae. These were distributed as follows: 73.9% were S. pilchardus, 20.7% were E. encrasicolus and 5.4% were S. aurita. Their distribution suggested that the coastal upwelling filament is a mechanism of transport from the upwelling area to oceanic waters, but its junction with the generated cyclonic eddy may not always work as a retention structure for those transported larvae, as described in previous studies. Physiological studies based on gut fluorescence and ETS activity of clupeoid larvae, as proxies for grazing and respiration, respectively, denoted a switch from pigmented food near the upwelling zone to unpigmented food toward the ocean. This pattern agrees with observed mesozooplankton feeding along an upwelling filament in previous studies. Therefore, this work confirms the close relationship between clupeoids distribution and mesoscale circulation, as well as constitutes the first assessment of the metabolic activity of those larvae in the region.

  13. Melt migration through Io's convecting mantle

    NASA Astrophysics Data System (ADS)

    Elder, C. M.; Showman, A. P.

    2013-12-01

    The extensive volcanism occurring on the surface of Io suggests that its interior must contain at least some partial melt. Unlike Earth, Io cannot lose its internal heat through convection alone [1]. Instead, melt moving through the solid mantle helps remove heat from Io's interior by carrying its latent heat towards the surface as it buoyantly ascends through the mantle. We investigate this process by considering melt migration in a column of rock rising through the mantle between downwelling plumes. Convective scaling laws provide the upwelling velocity and the temperature of the rising mantle. Properties of melt migration in this rising mantle are calculated using porous flow equations and an equation for the conservation of energy which includes latent heat consumption, heat advection and heat conduction [2]. This combination of convective scaling laws and porous flow laws allows us to self-consistently determine the radial melt fraction profile in Io's interior, the average melt fraction in Io's interior and the heat flux due to advection of melt. The average melt fraction can be compared to the melt fraction constraints calculated by [3] from Galileo magnetometer measurements. The surface heat flux calculations can be compared to the value of Io's observed surface heat flux which ranges with observation from 1.5-4 W m-2 [4]. [1] Moore W. B. (2003) J. Geophys. Res., 108, E8, 15-1. [2] Hewitt I. J. and Fowler A. C. (2008) Proc. R. Soc. A., 464, 2467-2491. [3] Khurana K. K. et al. (2011) Science, 332, 1186-1189. [4] Moore, W. B. et al. (2007) In: Io After Galileo, Springer-Praxis, 89-108.

  14. 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.

  15. 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

  16. A study of Benguela upwelling system using different upwelling indices derived from remotely sensed data

    NASA Astrophysics Data System (ADS)

    Chen, Zhaoyun; Yan, Xiao-Hai; Jo, Young-Heon; Jiang, Lide; Jiang, Yuwu

    2012-08-01

    Two upwelling indices (UI) derived from remotely sensed data, which are related to offshore Ekman transport (UIw) and the Sea Surface Temperature (SST) (UISST), are evaluated to study the spatial and temporal variations of the Benguela Upwelling System (BUS). The comparisons present the advantages and disadvantages of using UISST and UIW to scale upwelling intensity using the chlorophyll-a (Chl-a) concentration as a referential upwelling enhanced relative biomass proxy. The causes for the discrepancies of temporal and spatial variations of UISST, UIW and Chl-a in the BUS area are also discussed. By examining the UISST, UIW and Absolute Dynamic Topography (ADT) at 27-28°S, we find that the extension of the upwelling band is largely impacted by the anti-cyclonic eddy there. Furthermore, we discuss the Benguela Niños in 2006, and estimate the contribution from the wind effects to the total upwelling intensity off Hondeklip and Cape Columbine based on these remote sensing results.

  17. Rogue mantle helium and neon.

    PubMed

    Albarède, Francis

    2008-02-15

    The canonical model of helium isotope geochemistry describes the lower mantle as undegassed, but this view conflicts with evidence of recycled material in the source of ocean island basalts. Because mantle helium is efficiently extracted by magmatic activity, it cannot remain in fertile mantle rocks for long periods of time. Here, I suggest that helium with high 3He/4He ratios, as well as neon rich in the solar component, diffused early in Earth's history from low-melting-point primordial material into residual refractory "reservoir" rocks, such as dunites. The difference in 3He/4He ratios of ocean-island and mid-ocean ridge basalts and the preservation of solar neon are ascribed to the reservoir rocks being stretched and tapped to different extents during melting. PMID:18202257

  18. 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

  19. 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

  20. 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

  1. 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.

  2. 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

  3. 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

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

    PubMed

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

    2002-05-30

    Volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge, resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere. Asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back-arc region, but the forearc mantle (in the corner of the wedge) is thought to be significantly cooler. Here we explore the structure of the mantle wedge in the southern Cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers. We find very low shear-wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an 'inverted' continental Moho, which reverts to normal polarity seaward of the Cascade arc. This observation provides compelling evidence for a highly hydrated and serpentinized forearc region, consistent with thermal and petrological models of the forearc mantle wedge. This serpentinized material is thought to have low strength and may therefore control the down-dip rupture limit of great thrust earthquakes, as well as the nature of large-scale flow in the mantle wedge. PMID:12037564

  5. A discontinuity in mantle composition beneath the southwest Indian ridge.

    PubMed

    Meyzen, Christine M; Toplis, Michael J; Humler, Eric; Ludden, John N; Mével, Catherine

    2003-02-13

    The composition of mid-ocean-ridge basalt is known to correlate with attributes such as ridge topography and seismic velocity in the underlying mantle, and these correlations have been interpreted to reflect variations in the average extent and mean pressures of melting during mantle upwelling. In this respect, the eastern extremity of the southwest Indian ridge is of special interest, as its mean depth of 4.7 km (ref. 4), high upper-mantle seismic wave velocities and thin oceanic crust of 4-5 km (ref. 6) suggest the presence of unusually cold mantle beneath the region. Here we show that basaltic glasses dredged in this zone, when compared to other sections of the global mid-ocean-ridge system, have higher Na(8.0), Sr and Al2O3 compositions, very low CaO/Al2O3 ratios relative to TiO2 and depleted heavy rare-earth element distributions. This signature cannot simply be ascribed to low-degree melting of a typical mid-ocean-ridge source mantle, as different geochemical indicators of the extent of melting are mutually inconsistent. Instead, we propose that the mantle beneath approximately 1,000 km of the southwest Indian ridge axis has a complex history involving extensive earlier melting events and interaction with partial melts of a more fertile source. PMID:12610622

  6. 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

  7. 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.

  8. 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.

  9. Dynamics of three-dimensional hydrous thermal-chemical plumes in the mantle wedge

    NASA Astrophysics Data System (ADS)

    Zhu, Guizhi; Gerya, Taras; Kaus, Boris; Tackley, Paul; Honda, Satoru; Yoshida, Takeyoshi; Yuen, David; Connolly, James

    2010-05-01

    As a plate subducts, fluid release from the subducting slab lowers the melting point of the surrounding mantle, which results in the configuration of more dense and viscous dry mantle overlying a thin layer of hydrated mantle with lowered density and viscosity. These processes trigger Rayleigh-Taylor (RT) type instabilities in a low-viscosity wedge with complex three-dimensional (3-D) geometries. RT-type cold plumes atop the slab were previously studied in 2-D. Here we use 3-D petrological-thermomechanical numerical simulations to investigate the dynamics of 3-D hydrous thermal-chemical plumes in the mantle wedge. The simulations were carried out with the I3ELVIS code which is based on a multigrid approach combined with marker-in-cell methods and conservative finite difference schemes. Our numerical simulations show that three types of upwelling plumes occur above the slab-mantle interface: (1) finger-like plumes forming roll/sheet-like structures parallel to the trench; (2) ridge-like structures perpendicular to the trench; and (3) flattened, wave-like instabilities propagating upward along the upper surface of the slab and forming zigzag patterns parallel to the trench. Plume-related melt productivity correlates well with volcanic activity clustering in natural intraoceanic arcs, such as in northeast Japan. Why do the above different plume patterns form atop the slab? Variation in partially molten rock viscosity notably affects plume patterns and lateral dimensions: wave-like plumes are most pronounced at higher (10^19 Pa s) viscosity, which also favors the development of larger plumes compared to models with lower (10^18 Pa s) viscosity. The "effective" density contrast between solid and molten rocks, which is closely related to melt extraction processes, is the key factor in determining plume patterns. A large to moderate density contrast of >200 kg/m3 (i.e. low to moderate degree of melt extraction) promotes the development of three distinct patterns of the

  10. 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

  11. Manganese content records seasonal upwelling in Lake Tanganyika mussels

    NASA Astrophysics Data System (ADS)

    Langlet, D.; Alleman, L. Y.; Plisnier, P.-D.; Hughes, H.; André, L.

    2007-03-01

    Biogenic productivity of Lake Tanganyika is highly dependent on seasonal upwellings of cold, oxygen-depleted, nutrient-rich deep waters. We investigated the shell of freshwater bivalve Pleiodon spekii as a geochemical archive of these periodic hydrological changes tuned by the monsoon regime. The results of a three-year-long limnological and geochemical survey of the coastal waters performed on the dissolved and particulate fractions were compared to LA-ICP-MS profiles of Mn in five aragonitic shells from the same lake location. Three shells present very similar Mn/Ca profiles dominated by a peak that matched the concomitant increase of Mn and chlorophyll a in surface waters during the 2002 upwelling, while a shell collected during 2003 dry season detect both 2002 and 2003 upwelling events. Larger shells showing an extremely reduced growth display more than 8 Mn/Ca peaks suggesting at least an 8-year-record of seasonal changes in water composition. We postulate that Mn/Ca in shells record the conjunction of an increase of biological activity with supplied of dissolved Mn and nutriments in coastal waters, resulting in an enhanced assimilation of biogenic Mn-rich particles. By combining the most recent generation of laser ablation system and the powerful High Resolution ICP-MS, the spatial resolution could be improved down to 5 to 10 µm crater size and end up in a better constrain of the relative variations of the annual Mn peaks. Such an approach on P. spekii from Lake Tanganyika has definitively a great potential to provide recent and past records on primary productivity associated with the monsoon climate system.

  12. 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.

  13. Connecting wind-driven upwelling and offshore stratification to nearshore internal bores and oxygen variability

    NASA Astrophysics Data System (ADS)

    Walter, Ryan K.; Woodson, C. Brock; Leary, Paul R.; Monismith, Stephen G.

    2014-06-01

    This study utilizes field observations in southern Monterey Bay, CA, to examine how regional-scale upwelling and changing offshore (shelf) conditions influence nearshore internal bores. We show that the low-frequency wind forcing (e.g., upwelling/relaxation time scales) modifies the offshore stratification and thermocline depth. This in turn alters the strength and structure of observed internal bores in the nearshore. An internal bore strength index is defined using the high-pass filtered potential energy density anomaly in the nearshore. During weak upwelling favorable conditions and wind relaxations, the offshore thermocline deepens. In this case, both the amplitude of the offshore internal tide and the strength of the nearshore internal bores increase. In contrast, during strong upwelling conditions, the offshore thermocline shoals toward the surface, resulting in a decrease in the offshore internal tide amplitude. As a result, cold water accumulates in the nearshore (nearshore pooling), and the internal bore strength index decreases. Empirical orthogonal functions are utilized to support the claim that the bore events contribute to the majority of the variance in cross-shelf exchange and transport in the nearshore. Observed individual bores can drive shock-like drops in dissolved oxygen (DO) with rapid onset times, while extended upwelling periods with reduced bore activity produce longer duration, low DO events.

  14. Ion energization in upwelling ion events

    NASA Technical Reports Server (NTRS)

    Waite, J. H., Jr.; Moore, T. E.; Chandler, M. O.; Lockwood, M.; Persoon, A.; Suguira, M.

    1986-01-01

    A source of H(+), He(+), O(+), and N(+) outflow from the ionosphere has been identified near the polar cusp/cleft using the Dynamics Explorer/retarding ion mass spectrometer data set. This ion outflow termed 'upwelling ions' is characterized by large outfluxes of H(+) and O(+) ions and high transverse ion temperatures. This paper reports on the associated particle and field characteristics of one such upwelling ion event on March 12, 1982. Field-aligned currents and strong E x B convection channels are associated with the event as well as strong broadband plasma wave emission. One or all of these sources may play an important role in the ion energization in this region.

  15. Interactions between trophic levels in upwelling and non-upwelling regions during summer monsoon

    NASA Astrophysics Data System (ADS)

    Malik, A.; Fernandes, C. E. G.; Gonsalves, M.-J. B. D.; Subina, N. S.; Mamatha, S. S.; Krishna, K.; Varik, S.; Kumari, R.; Gauns, M.; Cejoice, R. P.; Pandey, S. S.; Jineesh, V. K.; Kamaleson, A. S.; Vijayan, V.; Mukherjee, I.; Subramanyan, S.; Nair, S.; Ingole, B.; LokaBharathi, P. A.

    2015-01-01

    Coastal upwelling is a regular phenomenon occurring along the southwest coast of India during summer monsoon (May-September). We hypothesize that there could be a shift in environmental parameters along with changes in the network of interactions between bacteria, phytoplankton, and zooplankton in upwelling and non-upwelling regions. During cruise # 267 on FORV Sagar Sampada, water samples were analysed for environmental and biological parameters from two transects, one upwelling region off Trivandrum (TVM) (8°26‧N, 76°20‧E-8°30‧N, 76°50‧E), and the other non-upwelling region off Calicut (CLT) (11°11‧N, 75°30‧E-11°14‧N,74°54‧E), about 230 nmi to the north. Meteorological, hydrological, and nutrient profiles confirmed upwelling off TVM. Bacteria, phytoplankton and zooplankton significantly responded. Primary and bacterial productivity enhanced together with increase in the percentage of viable bacteria (TVC). Pearson's correlation analysis pointed out the differences in bacterial interactions with other trophic levels at both transects. TVC played a prominent role in trophic interactions off TVM by depending on phytoplankton for substrate (r = 0.754). This contrasted with CLT where total counts (TC) played an important role. However, most interrelationships were less pronounced. Principal component analysis (PCA) confirmed the correlation analysis and further showed that the factor loadings of the biotic and abiotic parameters differed in strength and direction in the two regions. More importantly, the processes of mineralization by bacteria and uptake by phytoplankton are obviously more coupled off TVM as evidenced by the clustering of the related parameters in the PCA biplot. Canonical correspondence analysis also complements these findings and demonstrated that the abiotic factors influenced phytoplankton and bacteria similarly at TVM but differently at CLT. The impact on the trophic interrelationships is evident by the close association

  16. 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

  17. Diatom Transfer Functions for Sea Surface Temperature and Primary Productivity in Upwelling Areas: the Cupex Project

    NASA Astrophysics Data System (ADS)

    Lopes, C.; Abrantes, F.; Mix, A. C.

    2008-12-01

    Marine productivity plays an important role in natural carbon dioxide (CO2) variations through the "biological pump". This biological pump (mainly driven by diatom activity) is focused in specific regions, like the upwelling areas (less that 1% of the world's oceans total area), which support high export production. In these areas, atmospheric CO2 can be transported into the ocean. Therefore, to understand natural variations in atmospheric CO2 and other oceanic properties, we must understand the long-term history of these regional upwelling systems. Because of the interrelation between wind-driven coastal upwelling and diatom domination in phytoplankton blooms, diatom time-series from such areas can provide important information on climate change related variability in upwelling and nutrient supply. Therefore, upwelling areas represent key regions for oceanic properties reconstructions, which can be approached by the use of diatom Transfer Functions (TFs). Since the early 80's, TFs development became a major issue due to the extreme importance of understanding past ocean properties. However, the major focus has been on open ocean and calcareous microorganisms. Besides, the existing data for sea surface properties was a problem (data was cease and irregular), as such, some properties were more investigated than others. Today, with satellite data and better instrumental technologies, more and uniformly distributed information is available. Furthermore, the modern computer technology and power enable us to apply stronger and faster statistical tools and models. The development of TFs for coastal upwelling areas is one of the main goals of the CUPEX project: Coastal Upwelling Natural Variability: the last two Climate Extremes (21,000 ± 2,000 Cal-yr BP and 8,000 ± 1,500 Cal- yr BP), so that quantitative reconstructions of the environmental conditions of the last two past climate extremes: the Last Glacial Maximum and the Holocene Optimum are possible. Our

  18. 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

  19. The geochemical geometry of mantle plumes

    NASA Astrophysics Data System (ADS)

    Jackson, Matthew

    2015-04-01

    Lavas erupted at oceanic hotspot volcanoes exhibit tremendous isotopic variability, which indicates that the mantle sources of the hotspots are highly heterogeneous geochemically. A key question is how the surface expression of hotspot lavas relates to the spatial distribution of the geochemical components within upwelling mantle plumes. Significant progress has been made in recent years relating the geographic distribution of geochemical heterogeneities in hotspot lavas to parallel volcanic lineaments that define the traces of oceanic hotspot tracks. For example, a well known geographic separation of parallel volcanic lineaments at Hawaii - the Loa and Kea trends - are also isotopically resolved. In addition to the Hawaiian example, clear patterns relating the geographic distribution of geochemical components along hotspot tracks are emerging from a suite of global hotspots, and these patterns suggest that geochemical heterogeneities are highly organized within upwelling mantle plume conduits. At the Samoan hotspot, the Pb-isotopic compositions measured in lavas reveal several geochemical groups, and each group corresponds to a different geographic lineament of volcanoes. Each group has a geochemical signature that relates to each of the canonical low 3He/4He mantle endmembers: EMII (enriched mantle 2), EMI (enriched mantle 1), HIMU (high U/Pb) and DM (depleted mantle). In Pb-isotopic space, the four geochemical groups each form an array that trends toward a common component (thus forming an "X-shape" in Pb-isotopic space). The region of isotope space where the 4 Pb-isotopic array intersect is defined by the highest 3He/4He (up to 34 Ra, or ratio to atmosphere) in the Samoan hotspot. In Pb-isotopic space, 3He/4He decreases monotonically along each of the Pb-isotopic groups away from the common region of convergence. In order to quantify the relationship between He and Pb isotopes, 3He/4He is plotted versus distance from the common component in Pb-isotopic space

  20. 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

  1. A unique lower mantle source for Southern Italy volcanics

    NASA Astrophysics Data System (ADS)

    Cadoux, Anita; Blichert-Toft, Janne; Pinti, Daniele L.; Albarède, Francis

    2007-07-01

    The Southern Italy volcanism is characterized by the unusual occurrence of volcanic rocks with ocean-island basalt (OIB)-like characteristics, in particular at Etna and Iblean Mts in Sicily. The geochemical properties of the source of the Italian magmatism are usually explained by a north-south binary mixing between a mantle- and a crustally-derived end-members. The nature of the mantle end-member is, however, not agreed upon. One type of interpretation invokes a mixture of depleted mantle (DMM) and high U/Pb (HIMU) end-members [Gasperini, D., Blichert-Toft, J., Bosch, D., Del Moro, A., Macera, P., Albarède, F., 2002. Upwelling of deep mantle material through a plate window: Evidence from the geochemistry of Italian basaltic volcanics, J. Geophys. Res. 107, 2367-2386], whereas an alternative view holds that the mantle end-member is unique and homogeneous, and similar to the FOZO- or C-type end-member identified in oceanic basalts [Bell, K., Castorina, F., Lavecchia, G., Rosatelli, G., Stoppa, F., 2004. Is there a mantle plume below Italy? EOS 85, 541-547]. Because mixing does not produce linear relationships between the isotopic compositions of different elements, we applied Principal Component Analysis (PCA) to the Pb isotope compositions of the Italian volcanics inclusive 36 of Sicily volcanoes. We demonstrate that HIMU cannot be an end-member of the Italian volcanics, but rather that the common component C (˜FOZO), which we interpret as reflecting the lower mantle, best represents the mantle source of the Italian magmatism. Our PCA calculation shows that the first principal component alone, which we take to be a mixture of two geochemical end-members, C and a crustally-derived component, explains 99.4% of the whole data variability. In contrast, the DMM end-member (the second principal component) is only present in the volcanics from the Tyrrhenian Sea floor. The C-like end-member, well represented by the Etna and Iblean Mts (Sicily), has relatively low 3He/ 4

  2. Mantle dynamics and geodesy

    NASA Technical Reports Server (NTRS)

    Albee, Arden

    1990-01-01

    Both completed work and work that is still in progress are presented. The completed work presented includes: (1) core-mantle boundary topography; (2) absolute value for mantle viscosity; (3) code development; (4) lateral heterogeneity of subduction zone rheology; and (5) planning for the Coolfront meeting. The work presented that is still in progress includes: (1) geoid anomalies for a chemically stratified mantle; and (2) geoid anomalies with lateral variations in viscosity.

  3. Disruption of the PV-PPV Phase Transition by a Dome-like Upwelling Beneath Alaska

    NASA Astrophysics Data System (ADS)

    Sun, D.; Helmberger, D. V.; Miller, M. S.

    2014-12-01

    The lowermost mantle region, D", represents one of the most dramatic thermal andcompositional layers within our planet. Global tomographic models display relatively fast patchsalong the circum-Pacific which is generally attributed to slab-debris. Such cold patches interactwith the PV-PPV phase boundary to generate particularly strong heterogeneity at their edges.Most seismic observations for the D" come from the lower mantle S wave triplication (Scd).However, the sampling regions concentrated beneath Central America, where intensive studies,including migration methods and array analysis, have been accomplished. Beneath the centralAmerica, the D" can have a step variation of ~ 100 km, which argues strong lateral temperaturevariations or possible chemical variations. However, the common used ray paths between SouthAmerican events and seismic stations in US sample such sharp boundary azimuthally, whichmake the modeling difficult. Here, we exploit the USArray waveform data to examine one ofthese sharp transitions beneath Alaska. From west to east beneath Alaska, we observed threedifferent type of D": West region with strong Scd requiring sharp δVS = 2% increase;Middle region with no clear Scd indicating lack of D"; East region with strong Scd requiring gradientδVS increase. To explain such strong lateral variation, chemical variations must be involved. Wesuggested that West region represents a normal mantle. In contrast, the east region is dominated bysubducted slab. At the Middle region, we discovered a strong upwelling structure that disrupts the phaseboundary. A distinct pattern of travel time delays, waveform distortions, and amplitude patternsreveal a circular anomaly about 5° across which can be modeled synthetically as a dome about400 km high with a shear velocity reduction of ~5%. Geodynamic modeling indicates thatthis structure could be the base of an upwelling and/or a hot Fe-rich oxide hill.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. Geochemistry of the Quaternary alkali basalts of Garrotxa (NE Volcanic Province, Spain): a case of double enrichment of the mantle lithosphere

    NASA Astrophysics Data System (ADS)

    Cebriá, J. M.; López-Ruiz, J.; Doblas, M.; Oyarzun, R.; Hertogen, J.; Benito, R.

    2000-11-01

    The area of Garrotxa (also known as the Olot area) represents the most recent (700,000-11,500 y) and better preserved area of magmatic activity in the NE Volcanic Province of Spain (NEVP). This region comprises a suite of intracontinental leucite basanites, nepheline basanites and alkali olivine basalts, which in most cases represent primary or nearly primary liquids. The geochemical characteristics of these lavas are very similar to the analogous petrologic types of other Cenozoic volcanics of Europe, which are intermediate between HIMU, DM and EM1. Quantitative trace element modeling, suggests derivation from an enriched mantle source by degrees of melting that progressively increased from the leucite basanites (˜4%) to the olivine basalts (˜16%). However, the relatively more variable Sr-Nd-Pb isotope signature of the magmas suggests the participation of at least two distinct components in the mantle source: (1) a sublithospheric one with a geochemical signature similar to the magmas of Calatrava (Central Spain) and other basalts of Europe; and (2) an enriched lithospheric component with a K-bearing phase present. The geochemical model proposed here involves the generation of a hybrid mantle lithosphere source produced by the infiltration of the sublithospheric liquids into enriched domains of the mantle lithosphere, shortly before the melting event that generated the Garrotxa lavas. The available geological data suggest that the first enrichment event of the mantle lithosphere under the NEVP could be the result of Late Variscan mantle upwelling triggered by the extensional collapse of the Variscan orogen during the Permo-Carboniferous. By Jurassic/Cretaceous time, large-scale NNE-directed sublithospheric mantle channeling of thermally and chemically anomalous plume material was placed under the Iberian Peninsula and Central Europe. However, the geodynamic conditions in the NEVP did not favor magmatism, which could not take place until the Cenozoic after

  9. 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.

  10. Geoid anomalies and dynamic topography from convection in cylindrical geometry - Applications to mantle plumes on earth and Venus

    NASA Technical Reports Server (NTRS)

    Kiefer, Walter S.; Hager, Bradford H.

    1992-01-01

    A variety of evidence suggests that at least some hotspots are formed by quasi-cylindrical mantle plumes upwelling from deep in the mantle. Such plumes are modeled in cylindrical, axisymmetric geometry with depth-dependent, Newtonian viscosity. Cylindrical and sheet-like, Cartesian upwellings have significantly different geoid and topography signatures. However, Rayleigh number-Nusselt number systematics in the two geometries are quite similar. The geoid anomaly and topographic uplift over a plume are insensitive to the viscosity of the surface layer, provided that it is at least 1000 times the interior viscosity. Increasing the Rayleigh number or including a low-viscosity asthenosphere decreases the geoid anomaly and the topographic uplift associated with an upwelling plume.

  11. Zonation of bacterioplankton communities along aging upwelled water in the northern Benguela upwelling

    PubMed Central

    Bergen, Benjamin; Herlemann, Daniel P. R.; Jürgens, Klaus

    2015-01-01

    Upwelling areas are shaped by enhanced primary production in surface waters, accompanied by a well-investigated planktonic succession. Although bacteria play an important role in biogeochemical cycles of upwelling systems, little is known about bacterial community composition and its development during upwelling events. The aim of this study was to investigate the succession of bacterial assemblages in aging upwelled water of the Benguela upwelling from coastal to offshore sites. Water from the upper mixed layer at 12 stations was sampled along two transects from the origin of the upwelling to a distance of 220 km. 16S rRNA gene amplicon sequencing was then used in a bacterial diversity analysis and major bacterial taxa were quantified by catalyzed reporter deposition-fluorescence in situ hybridization. Additionally, bacterial cell numbers and bacterial production were assessed. Community statistical analysis revealed a reproducible zonation along the two transects, with four clusters of significantly different microbial assemblages. Clustering was mainly driven by phytoplankton composition and abundance. Similar to the temporal succession that occurs during phytoplankton blooms in temperate coastal waters, operational taxonomic units (OTUs) affiliated with Bacteroidetes and Gammaproteobacteria were dominant during algal blooming whereas “Pelagibacterales” were highly abundant in regions with low algal abundance. The most dominant heterotrophic OTU (9% of all reads) was affiliated with “Pelagibacterales” and showed a strong negative correlation with phytoplankton. By contrast, the second most abundant heterotrophic OTU (6% of all reads) was affiliated with the phylum Verrucomicrobia and correlated positively with phytoplankton. Together with the close relation of bacterial production and phytoplankton abundance, our results showed that bacterial community dynamics is strongly driven by the development and composition of the phytoplankton community. PMID

  12. 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

  13. Physical state of the western U.S. upper mantle

    NASA Technical Reports Server (NTRS)

    Humphreys, Eugene D.; Dueker, Kenneth G.

    1994-01-01

    Using observed P wave images of the western U.S. upper mantle, which show lateral variations of up to 8%, and existing scaling relations, we infer that the low-velocity mantle is hot and partially molten to depths of 100-200 km, and that the high-velocity upper mantle is subsolidus. Most the high-velocity upper mantle within a few hundred kilometers of the coastline appears to be relatively dense, suggesting that it is relatively cool (i.e., a thermal lithosphere). This is expected for features associated with the subducting Juan de Fuca and Gorda slabs, and the high velocity upper mantle beneath the Transverse Ranges has been attributed to the sinking of negatively buoyant mantle lithosphere. Other high-velocity mantle structures near the continental margin are consistent with this interpretation. In contrast, the generally high elevations of the continental interior imply a buoyant upper mantle there, an inference that holds for both the high- and the low-velocity upper mantle. The only resonable way to produce the high-velocity low-density upper mantle is through basalt depletion, thereby creating mantle of increased solidus temperature and decreased density. We distinguish a marginal domain, within approximately 250 km of the Pacific coast, from an interior domain. This is based on the inferred upper mantle compositional difference and regional associations: beneath the marginal domain, upper mantle structures trend parallel to the surface physiography and young tectonic structures, whereas upper mantle structures beneath the continental interior trend northeasterly. This northeast orientation is discordant with the young tectonic structures, but aligns with young volcanic activity. The high lateral gradients in observed upper mantle seismic structure found throughout the western United States imply high lateral gradients in the associated temperature or partial melt fields. Because these fields diffuse on time scales of less than a few tens of millions of

  14. 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.

  15. 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.

  16. 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.

  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. Interconnections Between the Mantle and the Near-Surface System Above the Aspen Anomaly, Central Colorado, and Implications for Cenozoic Uplift of the Rocky Mountains

    NASA Astrophysics Data System (ADS)

    Karlstrom, K. E.; Project, C.

    2007-12-01

    anomaly in Colorado indicate onset of rapid exhumation about 6 Ma, perhaps related to Neogene rock and surface uplift in the Rockies. We postulate that this and other Cenozoic changes in lithospheric buoyancy have resulted in epeirogenic uplift such that the highest elevation region of the Rocky Mountains may be directly responding to active mantle tectonism. Lithospheric structure of continents is the time-integrated composite of structures that formed during lithosphere assembly and later modification, including active tectonism. The CD-ROM experiment interpreted some velocity variations to be associated with old lithospheric structure as shown by dipping velocity boundaries found beneath paleosutures, dipping anisotropy, and a depth-extent of mantle anomalies of >200 km. The Aspen anomaly and related (?) Four Corners anomaly may extend to depths of > 400 km and hence are at least partly in the asthenosphere and may reflect Cenozoic small scale asthenospheric convection. For Yellowstone, Aspen, and Jemez mantle anomalies, lowest mantle velocities coincide with the intersection of postulated NE-trending Proterozoic paleosutures and active Cenozoic mantle tectonism. This suggests a geodynamic process in which Cenozoic and still-active asthenospheric upwelling and uplift are influenced by Proterozoic lithospheric heterogeneity. As a new geodynamic process, we infer that reactivation of old structures can induce material and energy exchange across the base of the lithosphere and thus influence upper asthenospheric circulation.

  19. Coastal upwelling on the far eastern Agulhas Bank associated with large meanders in the Agulhas Current

    NASA Astrophysics Data System (ADS)

    Goschen, W. S.; Bornman, T. G.; Deyzel, S. H. P.; Schumann, E. H.

    2015-06-01

    Six large solitary meanders in the Agulhas Current, so-called Natal Pulses, propagated down the eastern coast of South Africa between 2009 and 2011. Their influence on the coastal waters between Port Alfred and Algoa Bay, on the far eastern Agulhas Bank, was measured by thermistor strings moored at 30-80 m bottom depths and two current metres (30 m bottom depth) located at both sides of Algoa Bay. During all events active upwelling lasting 1-3 weeks was observed over the inner shelf and in Algoa Bay. During upwelling the isotherms ascended at an average rate of 1.8 m day-1 as the cold bottom layer increased in thickness to 40-60 m, although upwelled water did not break the surface in all cases. Cold water remained in the area for a further 2-3 weeks. During three Natal Pulses the water temperatures at the outer moorings initially increased as the plume of the leading edge (crest) of the meander moved onshore. During one Natal Pulse upwelling was recorded before the warm water plume impacted the moorings. At the onset of upwelling currents switched to the southwest in the case of Bird Island and southward at the Cape Recife inner-bay site and reached a maximum speed of 80 cm s-1. During all Natal Pulses cold bottom water (10-12 °C) flooded over the 80 m bottom depth moorings as the crest of the meander moved onshore, but also around the same time the core of the Agulhas Current began to move offshore. In all cases upwelling was wide-spread.

  20. 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)

  1. 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.

  2. 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. PMID:25693571

  3. Diffusive fractionation of U-series radionuclides during mantle melting and shallow-level melt cumulate interaction

    NASA Astrophysics Data System (ADS)

    Van Orman, James A.; Saal, Alberto E.; Bourdon, Bernard; Hauri, Erik H.

    2006-09-01

    U-series radioactive disequilibria in basaltic lavas have been used to infer many important aspects of melt generation and extraction processes in Earth's mantle and crust, including the porosity of the melting zone, the solid mantle upwelling rate, and the melt transport rate. Most of these inferences have been based on simplified theoretical treatments of the fractionation process, which assume equilibrium partitioning of U-series nuclides among minerals and melt. We have developed a numerical model in which solid-state diffusion controls the exchange of U-series nuclides among multiple minerals and melt. First the initial steady-state distribution of nuclides among the phases, which represents a balance between diffusive fluxes and radioactive production and decay, is calculated. Next, partial melting begins, or a foreign melt is introduced into the system, and nuclides are again redistributed among the phases via diffusion. U-series nuclides can be separated during this stage due to differences in their diffusivity; radium in particular, and possibly protactinium as well, can be strongly fractionated from slower-diffusing thorium and uranium. We show that two distinct processes are not required for the generation of 226Ra and 230Th excesses in mid-ocean ridge basalts, as has been argued previously; instead the observed negative correlations of the ( 226Ra/ 230Th) activity ratio with ( 230Th/ 238U) and with the extent of trace element enrichment may result from diffusive fractionation of Ra from Th during partial melting of the mantle. Alternatively, the ( 226Ra/ 230Th) disequilibrium in mid-ocean ridge basalts may result from diffusive fractionation during shallow-level interaction of mantle melts with gabbroic cumulates, and we show that the results of the interaction have a weak dependence on the age of the cumulate if both plagioclase and clinopyroxene are present.

  4. Of Mantle Plumes, Their Existence, and Their Nature: Insights from Whole Mantle SEM-Based Seismic Waveform Tomography

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Many questions remain on the detailed morphology of mantle convection patterns. While high resolution P wave studies show a variety of subducted slab behaviors, some stagnating in the transition zone, others penetrating into the lower mantle (e.g. Fukao & Obayashi, 2013), low velocity structures - the upwelling part of flow - are more difficult to resolve at the same scale. Indeed, depth extent and morphology of the low velocity roots of hotspot volcanoes is still debated, along with the existence of "mantle plumes". Using spectral element waveform tomography, we previously constructed a global, radially anisotropic, upper mantle Vs model (SEMum2, French et al., 2013) and have now extended it to the whole mantle by adding shorter period waveform data (SEMUCB-WM1, French & Romanowicz, GJI, in revision). This model shows long wavelength structure in good agreement with other recent global Vs models derived under stronger approximations (Ritsema et al. 2011; Kustowski, et al. 2008), but exhibits better focused, finer scale structure throughout the mantle. SEMUCB-WM1 confirms the presence in all major ocean basins of the quasi-periodic, upper mantle low velocity anomalies, previously seen in SEMum2. At the same time, lower mantle low velocity structure is dominated by a small number (~15 globally) of quasi-vertical anomalies forming discrete "column"" rooted at the base of the mantle. Most columns are positioned near major hotspots, as defined by buoyancy flux, and are wider (~800-1000 km diameter) than expected from the thermal plume model - suggestive of thermo-chemical plumes, which may be stable for long times compared to purely thermal ones. Some columns reach the upper mantle, while others deflect horizontally near 1000 km - the same depth where many slabs appear to stagnate. As they reach the transition zone, the wide columnar structure can be lost, as these "plumes" appear to meander through the upper mantle, perhaps entrained by more vigorous, lower viscosity

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

    PubMed

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

    2009-11-01

    8-Chloroadenosine (8-Cl-Ado), an RNA-directed nucleoside analogue, is currently under evaluation in phase I clinical trials for treatment of chronic lymphocytic leukaemia. 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 mumol/l 8-Cl-Ado for 24 h, loss of mitochondrial transmembrane potential and poly [adenosine diphosphate (ADP)-ribose] polymerase (PARP) cleavage were detected in three of four cell lines. Reduced ATP levels (30-60% 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 (50-90%, r(2) = 0.90, P < 0.01). However, the inhibition of transcription only accounted for 30-40% 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 haematological malignancies, 8-Cl-Ado inhibited the rates of DNA synthesis and selectively depleted dATP pools (50-80%). 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

  6. Eddy-induced reduction of biological production in eastern boundary upwelling systems

    NASA Astrophysics Data System (ADS)

    Gruber, Nicolas; Lachkar, Zouhair; Frenzel, Hartmut; Marchesiello, Patrick; Münnich, Matthias; McWilliams, James C.; Nagai, Takeyoshi; Plattner, Gian-Kasper

    2011-11-01

    Eddies and other mesoscale oceanic processes, such as fronts, can enhance biological production in the ocean, according to several open-ocean studies. The effect is thought to be particularly pronounced in low-nutrient environments, where mesoscale processes increase the net upward flux of limiting nutrients. However, eddies have been suggested to suppress production in the highly productive eastern boundary upwelling systems. Here, we examine the relationship between satellite-derived estimates of net primary production, of upwelling strength, and of eddy-kinetic energy--a measure of the intensity of mesoscale activity--in the four most productive eastern boundary upwelling systems. We show that high levels of eddy activity tend to be associated with low levels of biological production, indicative of a suppressive effect. Simulations using eddy-resolving models of two of these upwelling systems support the suggestion that eddies suppress production, and show that the downward export of organic matter is also reduced. According to these simulations, the reduction in production and export results from an eddy-induced transport of nutrients from the nearshore environment to the open ocean. Eddies might have a similar effect on marine productivity in other oceanic systems that are characterized by intense eddy activity, such as the Southern Ocean.

  7. 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

  8. Coastal upwelling in the East China Sea in winter

    NASA Astrophysics Data System (ADS)

    Qiao, Fangli; Yang, Yongzeng; Lü, Xingang; Xia, Changshui; Chen, Xianyao; Wang, Baodong; Yuan, Yeli

    2006-11-01

    The dynamic mechanisms of the upwelling off the East China Sea (ECS) coast in wintertime are studied. First, the upwelling signals off the ECS coast are identified by the observed temperature, salinity, nutrients, and dissolved oxygen data obtained during the cruises in January 1999. The MASNUM wave-tide-circulation coupled model is then employed to simulate the hydrography of the ECS. Comparisons between the simulations and observations show that the model performance is satisfactory. On the basis of successful simulation, four numerical experiments are conducted to investigate the upwelling mechanisms. The results suggest that the density (or salinity) front, which separates the inshore Low Salinity Coastal Water and the offshore Taiwan Warm Current (TWC), is the primary inducement for the upwelling. Owing to strong density gradient, the baroclinic pressure gradient force (PGF) is quite large near the frontal zone, and this PGF elicits an upwelling branch along the topography slope. Wind, TWC, and tide affect the density front in extension and intensity, thus exerting subsidiary influences on the upwelling. According to Ekman's theory, the northerly monsoon is downwelling favorable. However, the net effects of wind on the upwelling off the ECS coast in winter are positive because it drives the Changjiang River Diluted Water (CDW) flowing southward and forms the density front. Similarly, the resultant effects of TWC on the upwelling are negative for obstructing the pathway of CDW. Tide contributes to the upwelling because tidal mixing facilitates the expansion of CDW.

  9. 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

  10. 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.

  11. 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

  12. 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

  13. Anomalous upper mantle structure around the Tyrrhenian Sea imaged from Rayleigh wave tomography

    NASA Astrophysics Data System (ADS)

    Greve, S. M.; Paulssen, H.

    2012-04-01

    We present detailed 3D shear velocity structure for the Tyrrhenian Sea and surrounding onshore areas down to about 160 km depth. The high resolution and accurate constraints of the anomalies are achieved through the use of interstation Rayleigh wave dispersion curves in a small regional setting with good station coverage. The most noticeable imaged structure is a pronounced ring-shaped low velocity region at about 80 km depth surrounding the higher velocity centre of the Tyrrhenian Sea. Its depth extend is constrained to a maximum of 40 km and it is independent of the chosen inversion parameters or the background model. Underneath southwestern Italy the lateral extend of the low velocity region is well correlated with the location of recent subduction volcanism. Two different types of subduction become apparent in the observed velocity structure. In the Adriatic region around western Apennines the velocity anomaly is located below the volcanic chain as expected for a standard subduction with undisturbed mantle corner flow. In the area underneath Sicily and Calabria the velocity anomaly is offset to the north of the volcanic chain. We relate this to the different slab geometry in this area. The Ionian slab is still attached but discontinued by a vertical tear towards the west. In this setting mantle flow around the edge could divert the corner flow and cause the observed offset of the velocity. To the north of the study area, the imaged low velocity anomaly extends under the island of Corsica. As no recent subduction volcanism is active in this area, other processes must cause the anomaly. We propose that the front of the Adriatic slab resting on the 660-km transition zone causes convective instabilities and upward mantle flow (Faccenna et al., 2010). This, in turn, then helps to trigger a melting process in the shallower mantle underneath Corsica/Sardinia. Upward push from mantle upwellings can result in observable dynamic topography. Thus, the good correlation of

  14. 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

  15. Mantle dynamics in super-Earths: Post-perovskite rheology and self-regulation of viscosity

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; Ammann, M.; Brodholt, J. P.; Dobson, D. P.; Valencia, D.

    2013-07-01

    The discovery of extra-solar "super-Earth" planets with sizes up to twice that of Earth has prompted interest in their possible lithosphere and mantle dynamics and evolution. Simple scalings suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigour in the deep mantle, which, if extralopated to the largest super-Earths might, according to conventional thinking, result in no convection in their deep mantles due to the very low effective Rayleigh number. Here we evaluate this. First, as the mantle of a super-Earth is made mostly of post-perovskite we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of to a pressure of 1 TPa, for both slowest diffusion (upper-bound rheology) and fastest diffusion (lower-bound rheology) directions. Along a 1600 K adiabat the upper-bound rheology would lead to a post-perovskite layer of a very high (˜1030 Pa s) but relatively uniform viscosity, whereas the lower-bound rheology leads to a post-perovskite viscosity increase of ˜7 orders of magnitude with depth; in both cases the deep mantle viscosity would be too high for convection. Second, we use these DFT-calculated values in statistically steady-state numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induced plate-like lithospheric behaviour. Results confirm the likelihood of plate tectonics for planets with Earth-like surface conditions (temperature and water) and show a self-regulation of deep mantle temperature. The deep mantle is not adiabatic; instead feedback between internal heating, temperature and viscosity regulates the temperature such that the viscosity has the

  16. 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

  17. 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

  18. Evolution of 3-D subduction-induced mantle flow around lateral slab edges in analogue models of free subduction analysed by stereoscopic particle image velocimetry technique

    NASA Astrophysics Data System (ADS)

    Strak, Vincent; Schellart, Wouter P.

    2014-10-01

    We present analogue models of free subduction in which we investigate the three-dimensional (3-D) subduction-induced mantle flow focusing around the slab edges. We use a stereoscopic Particle Image Velocimetry (sPIV) technique to map the 3-D mantle flow on 4 vertical cross-sections for one experiment and on 3 horizontal depth-sections for another experiment. On each section the in-plane components are mapped as well as the out-of-plane component for several experimental times. The results indicate that four types of maximum upwelling are produced by the subduction-induced mantle flow. The first two are associated with the poloidal circulation occurring in the mantle wedge and in the sub-slab domain. A third type is produced by horizontal motion and deformation of the frontal part of the slab lying on the 660 km discontinuity. The fourth type results from quasi-toroidal return flow around the lateral slab edges, which produces a maximum upwelling located slightly laterally away from the sub-slab domain and can have another maximum upwelling located laterally away from the mantle wedge. These upwellings occur during the whole subduction process. In contrast, the poloidal circulation in the mantle wedge produces a zone of upwelling that is vigorous during the free falling phase of the slab sinking but that decreases in intensity when reaching the steady-state phase. The position of the maximum upward component and horizontal components of the mantle flow velocity field has been tracked through time. Their time-evolving magnitude is well correlated to the trench retreat rate. The maximum upwelling velocity located laterally away from the subducting plate is ∼18-24% of the trench retreat rate during the steady-state subduction phase. It is observed in the mid upper mantle but upwellings are produced throughout the whole upper mantle thickness, potentially promoting decompression melting. It could thereby provide a source for intraplate volcanism, such as Mount Etna in

  19. 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.

  20. Progressive melting of a hot mantle diapir with entrainment beneath southwestern Japan

    NASA Astrophysics Data System (ADS)

    Sakuyama, T.; Yoshikawa, M.; Shibata, T.; Nakai, S.; Sumino, H.; Ozawa, K.

    2009-12-01

    In back arc regions, many geophysical and petrological studies suggest that the lithosphere is at high temperature and the upper mantle is influenced by fluid supplied from the subducting slab. The distribution of volatile components, the thermal structure, and their relationship with magmatism, together with the thermal and material transportation mechanisms, all of which are relevant to mantle dynamics in back arc regions, are, however, still open to question. We have conducted comprehensive major and trace element, and isotope analyses, as well as geochronological investigations on intra-plate back arc volcanism in the Kita-Matsuura area (8.5~6 Ma) in southwestern Japan, active over the time scale of ~2.5 Myr and horizontal scale of ~35km to address this issue. The geochemistry of the Kita-Matsuura basalts vary temporally from low- (47~50 wt%), through medium- (49~52 wt%), to high- (51~54 wt%) SiO2: these three groups exhibit separate trends, which can only be reproduced by unique fractionation of phenocryst minerals from their respective least differentiated sample. The water contents of the least differentiated magma for the low-, medium, and high-SiO2 groups are estimated to be 0~0.5, 0.25~1.0, and 1.0~2.0 wt%, respectively, which are constrained by respective fractionation path and An content of plagioclase. The average melt segregation pressures and temperatures, calculated by comparing the estimated primary melt compositions with melt compositions obtained in high pressure melting experiments on peridotite, are estimated to be 3.0~2.3, 2.7~1.8, and 2.0~1.3 GPa, and 1410~1550, 1370~1510, and 1290~1400°C, for each group respectively. The temporal decrease of melting temperature and pressure with increase of water content in the primary melt over a few Myr requires melting of actively upwelling mantle with a progressive supply of water from external source. The abundance of incompatible trace elements, Zr/Y, Nb/Th, and LREE/HREE ratios smoothly decrease from

  1. 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.

  2. 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

  3. 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

  4. 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. PMID:11964474

  5. Mantle shear-wave velocity structure beneath the Hawaiian hot spot.

    PubMed

    Wolfe, Cecily J; Solomon, Sean C; Laske, Gabi; Collins, John A; Detrick, Robert S; Orcutt, John A; Bercovici, David; Hauri, Erik H

    2009-12-01

    Defining the mantle structure that lies beneath hot spots is important for revealing their depth of origin. Three-dimensional images of shear-wave velocity beneath the Hawaiian Islands, obtained from a network of sea-floor and land seismometers, show an upper-mantle low-velocity anomaly that is elongated in the direction of the island chain and surrounded by a parabola-shaped high-velocity anomaly. Low velocities continue downward to the mantle transition zone between 410 and 660 kilometers depth, a result that is in agreement with prior observations of transition-zone thinning. The inclusion of SKS observations extends the resolution downward to a depth of 1500 kilometers and reveals a several-hundred-kilometer-wide region of low velocities beneath and southeast of Hawaii. These images suggest that the Hawaiian hot spot is the result of an upwelling high-temperature plume from the lower mantle. PMID:19965755

  6. Plume or Mantle Heterogeneity? Numerical Modeling of the Mid-Atlantic Ridge between 2°-14°S

    NASA Astrophysics Data System (ADS)

    Hasenclever, J.; Hort, M. K.; Phipps-Morgan, J.

    2009-12-01

    The ˜900 km long section of the Mid-Atlantic ridge (MAR) between 2°-14°S is a study area of the German priority program SPP 1144, and has been the site of several ship cruises since 2004. Ridge morphology, ridge axis bathymetry, and crustal thickness vary considerably along this part of the MAR, several large- and small-offset fracture zones displace the ridge axis by up to 250 km. The most prominent (and mostly unexplained) geodynamic features are the active volcanic island of Ascension, located 80 km west of the MAR, and a melting anomaly beneath the MAR at 9°30'S causing an elevated ridge axis without axial valley, with crustal thicknesses of up to 11 km, and large seamounts. Possible explanations are enhanced melting of a mantle heterogeneity or the influence of a weak mantle plume located either close to the ridge axis or beneath the Circe seamount (˜450 km east of the MAR). By numerically modeling the different scenarios we test their feasibility in terms of mantle flow and melting. We use a self-developed parallel 3D finite element MATLAB code to numerically solve for viscous flow, advection and diffusion of heat, and melting of a multi-component mantle, discretized on unstructured tetrahedra meshes. The velocity-pressure formulation is based on Maday and Patera [State of the Art Surveys in Computational Mechanics, 1989] and solved using a multigrid-preconditioned conjugate gradient algorithm. Advection of temperature and compositional fields is achieved by a semi-Lagrange Predictor-Corrector scheme combined with bi-cubic interpolation on the unstructured mesh. Diffusion of heat is solved using standard operator-splitting methods and a conjugate gradient algorithm. The melting formulation is based on Phipps Morgan [G3, 2001], to which we added the effect of source water using the parameterization of Katz et al. [G3, 2004]. We include the buoyancy effects of Fe-depletion and melt in pores, and assume a rheology that depends on depth, temperature, water

  7. 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.

  8. 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.

  9. The relationship between Arabian Sea upwelling and Indian monsoon revisited

    NASA Astrophysics Data System (ADS)

    Yi, X.; Hünicke, B.; Tim, N.; Zorita, E.

    2015-11-01

    Studies based on upwelling indices (sediment records, sea-surface temperature and wind) suggest that upwelling along the western coast of Arabian Sea is strongly affected by the Indian summer monsoon (ISM). In order to examine this relationship directly, we employ the vertical water mass transport produced by the eddy-resolving global ocean simulation STORM driven by meteorological reanalysis over the last 61 years. With its very high spatial resolution (10 km), STORM allows us to identify characteristics of the upwelling system. We analyze the co-variability between upwelling and meteorological and oceanic variables from 1950 to 2010. The analyses reveal high interannual correlations between coastal upwelling and along-shore wind-stress (r=0.73) as well as with sea-surface temperature (r0.83). However, the correlation between the upwelling and the ISM is small and other factors might contribute to the upwelling variability. In addition, no long-term trend is detected in our modeled upwelling time series.

  10. 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

  11. Coastal Upwelling Drives Intertidal Assemblage Structure and Trophic Ecology.

    PubMed

    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

  12. Dynamical consequences of mantle heterogeneity in two-phase models of mid-ocean ridges

    NASA Astrophysics Data System (ADS)

    Katz, R. F.

    2010-12-01

    The mid-ocean ridge system, over 50,000 km in length, samples the magmatic products of a large swath of the asthenosphere. It provides our best means to assess the heterogeneity structure of the upper mantle. Interpretation of the diverse array of observations of MOR petrology, geochemistry, tomography, etc requires models that can map heterogeneity structure onto predictions testable by comparison with these observations. I report on progress to this end; in particular, I describe numerical models of coupled magma/mantle dynamics at mid-ocean ridges [1,2]. These models incorporate heterogeneity in terms of a simple, two-component thermochemical system with specified amplitude and spatial distribution. They indicate that mantle heterogeneity has significant fluid-dynamical consequences for both mantle and magmatic flow. Models show that the distribution of enrichment can lead to asymmetry in the strength of upwelling across the ridge-axis and channelised magmatic transport to the axis. Furthermore, heterogeneity can cause off-axis upwelling of partially molten diapirs, trapping of enriched melts off-axis, and re-fertilization of the mantle by pooled and refrozen melts. Predicted consequences of geochemical heterogeneity may also be considered. References: [1] Katz, RF, (2008); Magma dynamics with the Enthalpy Method: Benchmark Solutions and Magmatic Focusing at Mid-ocean Ridges. Journal of Petrology, doi: 10.1093/petrology/egn058. [2] Katz RF, (2010); Porosity-driven convection and asymmetry beneath mid-ocean ridges. Submitted to G3.

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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.

  19. Mantle viscosity beneath the Galapagos 95.5 deg W propagating rift

    NASA Technical Reports Server (NTRS)

    Schubert, G.; Hey, R. N.

    1986-01-01

    Detailed geophysical surveys in the vicinity of the Galapagos 95.5 deg W propagating rift tip establish the opening history of the rift and its velocity of propagation. These data together with a theory for mantle upwelling into slowly widening lithospheric cracks constrain the viscosity of the asthenosphere beneath the propagating rift to be less than about 10 to the 17th to 10 to the 18th Pa s.

  20. 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.

  1. 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.

  2. Climate engineering by artificial ocean upwelling: Channelling the sorcerer's apprentice

    NASA Astrophysics Data System (ADS)

    Oschlies, A.; Pahlow, M.; Yool, A.; Matear, R. J.

    2010-02-01

    Recent suggestions to reduce the accumulation of anthropogenic carbon dioxide in the atmosphere have included ocean fertilization by artificial upwelling. Our coupled carbon-climate model simulations suggest that artificial upwelling may, under most optimistic assumptions, be able to sequester atmospheric CO2 at a rate of about 0.9 PgC/yr. However, the model predicts that about 80% of the carbon sequestered is stored on land, as a result of reduced respiration at lower air temperatures brought about by upwelling of cold waters. This remote and distributed carbon sequestration would make monitoring and verification particularly challenging. A second caveat predicted by our simulations is that whenever artificial upwelling is stopped, simulated surface temperatures and atmospheric CO2 concentrations rise quickly and for decades to centuries to levels even somewhat higher than experienced in a world that never engaged in artificial upwelling.

  3. 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. PMID:9596567

  4. 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

  5. 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.

  6. 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.

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

    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

  8. Interaction of the Upper-Mantle Plumes

    NASA Astrophysics Data System (ADS)

    Sharapov, V.; Perepechko, Y.

    2006-12-01

    This work deals with the problem of interaction and combined evolution of closely spaced plumes. One of activities, which initiated this problem statement, was an attempt to explain via this mechanism the formation of large igneous provinces in the form of surface manifestations of a hot spot system. Convection in the upper mantle was simulated using the expanded Boussinesq model with non-linear state equations for mantle substance and lithosphere rocks, which considered the main solid-state phase transitions and melting processes. This system consisted of the upper mantle and mantle lithosphere, including non-uniform continental crust of a given thickness. The asthenosphere and regions of partial melting in lithosphere were formed during convection of the mantle substance. Interaction between several plumes, generated by hot spots, was considered. These plumes were located at distances, characteristic for the upper mantle (of about the lithosphere or upper mantle thickness). The initial distribution of plume sources and their physical parameters were assigned. According to numerical simulation, combined evolution of two plumes provides formation of a united igneous province in the upper geospheres. An increase in the number of closely spaced hot spots leads to division of a single igneous province into several areas of a smaller scale. A horizontal size of these areas is determined by a typical size of large dissipative structures in the upper mantle and lithosphere thickness. This research was supported by the Russian Foundation for Basic Research grant 04-05-64107, by the President's grants NSh-1573.2003.5, and by the Russian Ministry Science and Education grant RNP.2.1.1.702.

  9. Where is mantle's carbon?

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  10. 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.

  11. Formation of plate boundaries: The role of mantle volatilization

    NASA Astrophysics Data System (ADS)

    Seno, Tetsuzo; Kirby, Stephen H.

    2014-02-01

    In the early Earth, convection occurred with the accumulation of thick crust over a weak boundary layer downwelling into the mantle (Davies, G.F., 1992. On the emergence of plate tectonics. Geology 20, 963-966.). This would have transitioned to stagnant-lid convection as the mantle cooled (Solomatov, V.S., Moresi, L.-N., 1997. Three regimes of mantle convection with non-Newtonian viscosity and stagnant lid convection on the terrestrial planets. Geophys. Res. Lett. 24, 1907-1910.) or back to a magma ocean as the mantle heated (Sleep, N., 2000. Evolution of the mode of convection within terrestrial planets. J. Geophys. Res. 105(E7): 17563-17578). Because plate tectonics began operating on the Earth, subduction must have been initiated, thus avoiding these shifts. Based on an analogy with the continental crust subducted beneath Hindu Kush and Burma, we propose that the lithosphere was hydrated and/or carbonated by H2O-CO2 vapors released from magmas generated in upwelling plumes and subsequently volatilized during underthrusting, resulting in lubrication of the thrust above, and subduction of the lithosphere along with the overlying thick crust. Once subduction had been initiated, serpentinized forearc mantle may have formed in a wedge-shaped body above a dehydrating slab. In relict arcs, suture zones, or rifted margins, any agent that warms and dehydrates the wedge would weaken the region surrounding it, and form various types of plate boundaries depending on the operating tectonic stress. Thus, once subduction is initiated, formation of plate boundaries might be facilitated by a major fundamental process: weakening due to the release of pressurized water from the warming serpentinized forearc mantle.

  12. The Influence of Remote Wind Forcing and Kelvin Waves on the Java Upwelling in Positive IOD Years

    NASA Astrophysics Data System (ADS)

    Delman, A. S.; Sprintall, J.; McClean, J.; Talley, L. D.

    2014-12-01

    The seasonal upwelling region just south of Java, Indonesia plays a critical role in the development and evolution of Indian Ocean Dipole (IOD) events. In this study the effects of local and remote surface wind anomalies on the interannual variability of SST south of Java are investigated using remote sensing datasets. Though upwelling-favorable winds along the Java coast are responsible for the seasonal SST cooling (June-September) in most years, the anomalously enhanced upwelling that precedes positive IOD (IOD+) events is almost entirely associated with remote wind forcing. Surface wind-SST anomaly correlations for May-July and composites of the early phases of IOD+ events both suggest that the anomalous Java upwelling is closely linked to strengthened southeasterly winds in the eastern equatorial Ocean and along the coast of Sumatra. In contrast, only minor wind anomalies are observed along coastal Java during IOD+ years. To explain the influence of remote winds on the interannual variability of Java upwelling, we also quantify oceanic Kelvin wave activity along the equator-Sumatra-Java waveguide. A sea level projection method is applied to altimetric observations, removing sea level anomaly (SLA) variations due to steric height changes and Rossby waves. The method produces a Kelvin wave amplitude that is more robustly correlated with SST cooling south of Java than gridded SLA. Extreme negative values of the Kelvin wave amplitude in May-July, corresponding to high-amplitude upwelling waves, precede all of the strong IOD+ events in the period of record. These results suggest an outsize impact from anomalous winds in the equatorial-coastal waveguide during austral late fall/early winter, and emphasize the important role of oceanic Kelvin waves in conveying remote wind forcing to the upwelling region.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. Activation of mitochondrial apoptotic pathway in mantle cell lymphoma: high sensitivity to mitoxantrone in cases with functional DNA-damage response genes.

    PubMed

    Ferrer, Ana; Marcé, Silvia; Bellosillo, Beatriz; Villamor, Neus; Bosch, Francesc; López-Guillermo, Armando; Espinet, Blanca; Solé, Francesc; Montserrat, Emili; Campo, Elias; Colomer, Dolors

    2004-11-25

    Mantle cell lymphoma (MCL) is a mature B-cell proliferation characterized by the presence of translocation t(11;14)(q13;q32), an aggressive clinical course, and poor response to chemotherapy. The majority of drugs currently used in the treatment of lymphoproliferative disorders induce cell death by triggering apoptosis, but few data concerning drug-induced apoptosis in MCL have been reported. We have analysed the mechanisms of drug-induced cell death in four cell lines with the t(11;14) and in primary cells from 10 patients with MCL. Mitoxantrone, a topoisomerase II inhibitor, induced a strong cytotoxic effect in three cell lines (JVM-2, REC-1, and Granta 519), and in primary MCL cells. This cytotoxic effect due to apoptosis induction was observed despite the presence of either p53 or ATM abnormalities. However, no cytotoxic effect was detected after incubation with DNA-damaging agents in the NCEB-1 cell line, carrying p53 and ATM alterations, despite the presence of functional mitochondrial machinery. These results support that mitoxantrone can be effective in the treatment of MCL but that this activity requires the integrity of functional DNA-damage response genes. PMID:15480431

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

    NASA Astrophysics Data System (ADS)

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

    2008-11-01

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

  19. 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

  20. Episodic Entrainment of Subducted Oceanic Crust into Primordial Reservoirs of the Lower Mantle

    NASA Astrophysics Data System (ADS)

    Li, M.; McNamara, A. K.; Garnero, E. J.

    2012-12-01

    The origin and dynamic nature of proposed large-scale compositional heterogeneity in Earth's lowermost mantle is not well understood. The preservation of primordial dense materials in the lowermost mantle has long been proposed by both geochemical and geophysical studies. As is shown in geodynamic models, primordial reservoirs can be passively swept to upwelling regions by mantle flow and form stable piles. In addition, oceanic crust can be subducted into the lowermost mantle, providing an additional source of compositional heterogeneity. We performed high resolution 2D calculations to study the interaction between primordial reservoirs and subducted oceanic crust that is compositionally different from the reservoirs, and its implications for deep mantle structure, dynamics, and chemical evolution. We find that oceanic crust subducted to the lowermost mantle is viscously dragged toward upwelling regions, where primordial reservoirs are hypothesized to exist. While most oceanic crust avoids interaction with a reservoir itself and is entrained into thermal plumes that form along the tops of reservoirs, some crust accumulates at the base of the plumes, along reservoir tops. Eventually the volume of accumulated crust at the base of a plume gains enough negative buoyancy such that it is flushed into the reservoir below, through the reservoir's top margin. Crust that is flushed into the reservoirs may explain some of the internal heterogeneity within LLSVPs observed by seismic studies. Experiments and theoretical calculations have suggested a reduction in viscosity within cold regions due to the post-perovskite phase transition. We find that this viscosity drop may act to increase the amount of crust that is entrained into primordial reservoirs. Furthermore, plumes that originate from reservoir tops will exhibit a time-dependent variation in chemistry, containing all three components (background mantle, primordial reservoir, subducted oceanic crust), perhaps explaining

  1. 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.

  2. 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

  3. 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

  4. 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

  5. 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.

  6. 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

  7. 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.

  8. 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

  9. 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.

  10. 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

  11. 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

  12. Radial and Azimuthal Anisotropic Structure of the North American Upper Mantle From Inversion of Surface Waveform Data

    NASA Astrophysics Data System (ADS)

    Marone, F.; Romanowicz, B.

    2005-12-01

    Seismic anisotropy provides insight into paleo and recent deformation processes and therefore mantle dynamics. To date, our knowledge of the North American anisotropic structure arises mainly from global tomographic models or SKS splitting studies which lack horizontal and vertical resolution respectively, and are limited to either radial or azimuthal anisotropy. Our goal is a high resolution model for the North American upper mantle incorporating both radial and azimuthal anisotropy. We hope to achieve unprecedented lateral and depth resolution by improving both current methodology and data coverage. In a first step, we inverted long period waveform data simultaneously for perturbations in the isotropic S-velocity structure and the anisotropic parameter ξ=vSH2/vSV2, in the framework of normal mode asymptotic coupling theory (NACT). The resulting 2D broad band sensitivity kernels allow us to exploit the information contained in long period seismograms for body, fundamental and higher mode surface waves at the same time. To ensure high quality of the retrieved regional upper mantle structure, accurate crustal corrections are essential. Here, we follow an approach which goes beyond the linear perturbation approximation and split the correction into a linear and non-linear part. The inverted dataset consists of more than 40,000 high quality 3 component fundamental and overtone surface waveforms, recorded at broad band seismic stations in North America from teleseismic events and provides a fairly homogeneous path and azimuthal coverage. Our 3D radial anisotropic model shares the large scale features of previous regional studies for North America. We confirm the pronounced difference in the isotropic velocity structure between the western active tectonic region and the central/eastern stable shield, as well as the presence of subducted material (Juan de Fuca and Farallon plate) at transition zone depths. Concerning the anisotropic signature, we observe a positive

  13. Crust-mantle density distribution in the eastern Qinghai-Tibet Plateau revealed by satellite-derived gravity gradients

    NASA Astrophysics Data System (ADS)

    LI, Honglei; Fang, Jian; Braitenberg, Carla; Wang, Xinsheng

    2015-04-01

    As the highest, largest and most active plateau on Earth, the Qinghai-Tibet Plateau has a complex crust-mantle structure, especially in its eastern part. In response to the subduction of the lithospheric mantle of the Indian plate, large-scale crustal motion occurs in this area. Despite the many previous studies, geodynamic processes at depth remain unclear. Knowledge of crust and upper mantle density distribution allows a better definition of the deeper geological structure and thus provides critically needed information for understanding of the underlying geodynamic processes. With an unprecedented precision of 1-2 mGal and a spatial resolution better than 100 km, GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission products can be used to constrain the crust-mantle density distribution. Here we used GOCE gravitational gradients at an altitude of 10km after reducing the effects of terrain, sediment thickness variations, and Moho undulations to image the density structures of eastern Tibet up to 200 km depths. We inverted the residual satellite gravitational gradients using a least square approach. The initial density model for the inversion is based on seismic velocities from the tomography. The model is composed of rectangular blocks, having a uniform density, with widths of about 100 km and variable thickness and depths. The thickness of the rectangular cells changes from10 to 60km in accordance with the seismic model. Our results reveal some large-scale, structurally controlled density variations at depths. The lithospheric root defined by higher-density contrast features from southwest to northeast, with shallowing in the central part: base of lithosphere reaches a depth of180 km, less than 100km, and 200 km underneath the Lhasa, Songpan-Ganzi, and Ordos crustal blocks, respectively. However, these depth values only represent a first-order parameterization because they depend on model discretization inherited from the original seismic

  14. 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.

  15. A Heated Debate: Evidence for Two Thermal Upwellings in East Africa

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    East African Cenozoic magmatism records the thermal influence of one or more long-lived mantle plumes. We present primary magma compositions, mantle potential temperatures (Tp), and mantle melt fractions using PRIMELT2 in order to examine the geographic and historical distribution of upper mantle thermal anomalies in East Africa. Regional magmatism can be divided into an early flood basalt phase in Ethiopia/Yemen (~30 Ma), a longer-lived episode of basaltic magmatism in Kenya and Southern Ethiopia (~45 to 23 Ma), and a more recent phase (~23 Ma to Present) that is coincidental with the development of the East African Rift (EAR). We have carefully selected a total of 54 samples from these time periods, excluding erroneous results derived from lavas with evidence of clinopyroxene fractionation or volatile rich and pyroxenitic sources. Our results show that elevated Tp in the Ethiopian/Yemen flood basalt province (Tp max =1520°C) and in the early Kenya/S. Ethiopia magmatism (Tp max = 1510°C) are virtually identical. Our results indicate that the existing geochemical division between high and low Ti Ethiopia/Yemen flood basalts has a thermal basis: low-Ti lavas are hotter than the high-Ti lavas. Magmatism in the region subsequent to 23 Ma exhibits only minor cooling (Tp max = 1490°C), though more substantial cooling is observed in Turkana, Kenya (60°C) and Yemen (80°C). Rift lavas from Ethiopia exhibit a clear decrease in Tp away from Afar southwestward along the EAR before progressively rising again in Southern Ethiopia towards Turkana. South of Turkana, elevated Tp is observed in the western and eastern branches of the EAR surrounding the Tanzania Craton. The modern spatial distribution of Tp in EAR magmatism indicate two distinct heat sources, one in Afar and another under the Tanzania craton. We suggest that hot mantle plume material from Afar and Turkana (which may or may not merge at depth) is channeled beneath the thinned rift lithosphere and provides a

  16. 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.

  17. 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.

  18. A flow law for ilmenite in dislocation creep: Implications for lunar cumulate mantle overturn

    NASA Astrophysics Data System (ADS)

    Dygert, Nick; Hirth, Greg; Liang, Yan

    2016-01-01

    We present results from new deformation experiments and a dislocation creep flow law for synthetic ilmenite. The flow law predicts an effective viscosity more than 3 orders of magnitude lower than dry olivine at mantle stresses and temperatures. Using the flow law, we predict that lunar ilmenite-bearing cumulates (IBC) will be weakened by the presence of low-viscosity ilmenite. Dense, low-viscosity IBC are expected to flow into the lunar interior by a process known as cumulate mantle overturn. Low-viscosity IBC that sink to the core-mantle boundary may be dynamically stable with respect to upwelling. A hot, stable layer of IBC surrounding the lunar core would suppress the development of a core dynamo. A layer of partially molten IBC can also explain the inferred zone of seismic attenuation around the lunar core, as well as a low-viscosity layer suggested by tidal dissipation.

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. Petrogenesis of Cretaceous mafic intrusive rocks in the Fosdick Mountains, Marie Byrd Land, West Antarctica: melting of metasomatized sub-continental arc mantle along the active plate margin of Gondwana

    NASA Astrophysics Data System (ADS)

    Saito, S.; Brown, M.; Korhonen, F. J.; Mcfadden, R. R.; Siddoway, C. S.

    2013-12-01

    A diorite pluton and widely distributed mafic dykes occur in the Fosdick migmatite-granite complex, which is interpreted to represent middle-to-lower crustal rocks of the paleo-Pacific active continental margin of Gondwana. The mafic dykes exhibit a variety of relationships with host rocks in the field ranging from undeformed dykes with sharp contacts with host gneisses to dismembered dykes with comingled textures and numerous back-veins of leucosome intruded from host migmatitic gneisses suggestive of significant interaction with crustal rocks. U-Pb ages for magmatic zircon in these rocks yields Cretaceous crystallization ages ranging from ca. 113 Ma to ca. 98 Ma for the mafic dykes and ca. 100 Ma for the diorite pluton. These mafic intrusive rocks, which contain abundant hydrous minerals, are medium- to high-K-series calc-alkaline rocks with basic-intermediate compositions (47-59 wt % SiO2 for mafic dykes and 52-56 wt % SiO2 for the diorite pluton). They have trace element patterns characterized by LILE enrichments and negative Nb anomalies indicating an origin from a hydrous mantle source metasomatized by slab-derived components. The samples without evidence of interaction with crustal rocks, which are likely to better reflect the mantle source composition, have positive ɛSr(100Ma) values (+8.1 to +14.5) and negative to slightly positive ɛNd(100Ma) values (-1.6 to +2.5) consistent with derivation from an enriched mantle source. These samples may be divided into two groups either characterized by higher LILE/HFSE ratios, less radiogenic ɛSr(100Ma) values and more radiogenic ɛNd(100Ma) values, or characterized by relatively lower LILE/ HFSE ratios, more radiogenic ɛSr(100Ma) values and less radiogenic ɛNd(100Ma) values suggesting differences in the mantle source. The results of this study are consistent with melting of a variably metasomatized sub-arc mantle source during a transition from a wrench to a transtensional tectonic setting, but are inconsistent

  4. 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.

  5. Topology of the postperovskite phase transition and mantle dynamics

    PubMed Central

    Monnereau, Marc; Yuen, David A.

    2007-01-01

    The postperovskite (ppv) phase transition occurs in the deep mantle close to the core–mantle boundary (CMB). For this reason, we must include in the dynamical considerations both the Clapeyron slope and the temperature intercept, Tint, which is the temperature of the phase transition at the CMB pressure. For a CMB temperature greater than Tint, there is a double crossing of the phase boundary by the geotherms associated with the descending flow. We have found a great sensitivity of the shape of the ppv surface due to the CMB from variations of various parameters such as the amount of internal heating, the Clapeyron slope, and the temperature intercept. Three-dimensional spherical models of mantle convection that can satisfy the seismological constraints depend on the Clapeyron slope. At moderate value, 8 MPa/K, the best fit is found with a core heat flow amounting for 40% of the total heat budget (≈15 TW), whereas for 10 MPa/K the agreement is for a lower core heat flow (20%, ≈7.5 TW). In all cases, these solutions correspond to a temperature intercept 200 K lower than the CMB temperature. These models have holes of perovskite adjacent to ppv in regions of hot upwellings. PMID:17483485

  6. 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.

  7. 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.

  8. Mantle exhumation and OCT architecture dependency on lithosphere deformation modes during continental breakup: Numerical experiments

    NASA Astrophysics Data System (ADS)

    Jeanniot, Ludovic; Kusznir, Nick; Manatschal, Gianreto; Cowie, Leanne

    2013-04-01

    The initiation of sea-floor spreading, during the continental breakup process, requires both the rupture of the continental crust and the initiation of decompression melting. This process results in mantle upwelling and at some point decompressional melting which creates new oceanic crust. Using numerical experiments, we investigate how the deformation mode of continental lithosphere thinning and stretching controls the rupture of continental crust and lithospheric mantle, the onset of decompression melting, their relative timing, and the circumstances under which mantle exhumation may occur. We assume that the topmost continental and ocean lithosphere, corresponding to the cooler brittle seismogenic layer, deforms by extensional faulting (pure-shear deformation) and magmatic intrusion, consistent with the observations of deformation processes occurring at slow spreading ocean ridges (Cannat, 1996). We assume that deformation beneath this topmost lithosphere layer (approximately 15-20 km thick) occurs in response to passive upwelling and thermal and melt buoyancy driven small-scale convection. We use a 2D finite element viscous flow model (FeMargin) to describe lithosphere and asthenosphere deformation. This flow field is used to advect lithosphere and asthenosphere temperature and material. The finite element model is kinematically driven by Vx for the topmost upper crust inducing passive upwelling beneath that layer. A vertical velocity Vz is defined for buoyancy enhanced upwelling as predicted by Braun et al. (2000). Melt generation is predicted by decompression melting using the parameterization and methodology of Katz et al. (2003). Numerical experiments have been used to investigate the dependency of continental crust and lithosphere rupture, decompression melt initiation, rifted margin ocean-continent transition architecture and subsidence history on the half-spreading rate Vx, buoyancy driven upwelling rate Vz, the relative contribution of these deformation

  9. The Mantle Transition-Zone Water Filter Model: Implications for Volatile Transport and Storage

    NASA Astrophysics Data System (ADS)

    Bercovici, D.; Karato, S.; Leahy, G.; Richard, G.; Jing, Z.

    2006-12-01

    The transition-zone water-filter model of mantle convection was proposed (Bercovici and Karato, Nature v425, p39, 2003) to reconcile geochemical observations of isolated chemical mantle reservoirs (evident in distinct chemical signatures of OIB and MORB) with geophysical, especially seismological evidence for whole mantle circulation and mixing. The model proposed that as the background ambient mantle upwelling (rising in response to the downward flux of subducting slabs) moves out of the high-water-solubility transition zone into the less-solubile upper mantle above 410km, it undergoes water supersaturation and partial melting that filters out incompatible elements. The remaining solid phase continues to ascend and supplies relatively dry and depleted materials to the MORB source region; however, in contrast to recent "bulk water storage capacity" arguments, the water transported up by the solid phase is less than solidus water limit which is itself considerably less than the sub-eutectic solubility limit. The residual melt is presumed denser than the surrounding solid and is thus trapped at the 410km boundary until slab entrainment recirculates the enriched material back into the deeper mantle. The filtering effect is suppressed for hotter mantle plumes because of their greater ascent rates, allowing plumes to generate more enriched OIBs. Experimental data implies that while melting is likely under a broad range of conditions, the presence of a dense melt likely requires dense volatiles, such as K2O, in addition to water. Theoretical models of a melt layer structure and the circulation of volatiles suggests a relatively thin melt-rich layer that can be efficiently entrained by reaction with ambient downgoing mantle (mantle dragged down by slabs). Moreover, circulation of entrained water is focussed in the transition zone by slabs lingering at the 660km, thereby providing a mechanism to keep the transition zone hydrated and water concentration well mixed.

  10. The uppermost mantle beneath the Kenya dome and relation to melting, rifting and uplift in East Africa

    NASA Astrophysics Data System (ADS)

    Davis, Paul M.; Slack, Philip D.

    2002-04-01

    We compare new results on S-wave delays and P wave tomography to characterize the rising limb and melt zone of an inferred mantle convection cell beneath the Kenya dome. These results are extended to the Nyiragongo and Ethiopia domes using long wavelength gravity and topography. We suggest that the east African rift results from separation of deeper mantle upwelling into three currents that impinge on and erode the base of the lithosphere. Their thermal buoyancy drives the domal uplift, whereas brittle failure of the upper lithosphere forms the rift grabens.

  11. 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.

  12. 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

  13. How does the lithosphere deformation mode during continental breakup affect mantle exhumation and subsidence history?

    NASA Astrophysics Data System (ADS)

    Jeanniot, L.; Kusznir, N.; Manatschal, G.

    2012-04-01

    Mantle exhumation at magma-poor rifted continental margin requires that continental crust ruptures prior to the onset of significant decompression melting. Both the relative timing of crustal rupture and melting, and therefore mantle exhumation, and rifted margin subsidence are dependent on the deformation mode of the continental lithosphere stretching and thinning leading to breakup. Fletcher et al. (2009) showed that for the Iberia-Newfoundland rifted margin, modelling of continental lithosphere stretching and thinning by pure-shear resulted in decompression melt initiation before continental crustal-rupture, while stretching and thinning by upwelling-divergent "corner flow" resulted in crustal-rupture before melt initiation. Observations at rifted continental margins (including Iberia-Newfoundland rifted margin) suggest a complex rifting evolution that cannot be explained by simplistic end-member pure-shear or "corner flow" deformation modes of lithosphere thinning and stretching (Péron-Pinvidic and Manatschal, 2009). By analogy with the deformation processes occurring at slow spreading ocean-ridges (Cannat, 1996), a more realistic lithosphere deformation mode for magma-poor continental breakup is extensional faulting for the colder brittle upper 12-15km above upwelling-divergent "corner flow" for the remaining lithosphere and asthenosphere. We use a kinematic numerical model of continental lithosphere thinning and stretching to examine decompression melt initiation, continental crustal rupture and subsidence for such a hybrid lithosphere deformation model represented by pure-shear deformation in the topmost brittle lithosphere above upwelling-divergent flow. We explore the relative contributions of pure-shear and upwelling-divergent "corner flow" deformation and its sensitivity to deformation rate, pure-shear half-width, the "corner flow" Vz/Vx ration and mantle potential temperature. The kinematic numerical model that we use represents lithosphere and

  14. Phosphorus Cycling in the Red Tide Incubator Region of Monterey Bay in Response to Upwelling

    PubMed Central

    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

  15. U-series isotope and geodynamic constraints on mantle melting processes beneath the Newer Volcanic Province in South Australia

    NASA Astrophysics Data System (ADS)

    Demidjuk, Zoe; Turner, Simon; Sandiford, Mike; George, Rhiannon; Foden, John; Etheridge, Mike

    2007-09-01

    Young (< 5 kyr) olivine- and clinopyroxene-phyric ne-hawaiites from Mounts Gambier and Schank in the Newer Volcanic Province in South Australia have been analysed for major and trace elements as well as for Sr and Nd isotopes and 238U- 230Th disequilibria in order to constrain the mantle melting processes responsible for their origin. The rocks are relatively primitive (6.9-9.1% MgO), incompatible trace element-enriched alkali basalts with 87Sr/ 86Sr = 0.70398-0.70415 and 143Nd/ 144Nd = 0.51280-0.51271. Trace element modelling suggests that they reflect 3-6% partial melting in the presence of 2-8% residual garnet. Trends towards low K/K * are accompanied by decreasing 87Sr/ 86Sr and provide evidence for the involvement of hydrous phases during melting. 230Th excesses of 12-57% cannot be simulated by batch melting of the lithosphere and instead require dynamic melting models. It is argued that the distinction between continental basalts bearing significant U-Th disequilibria and those in secular equilibrium reflects dynamic melting in upwelling asthenosphere, rather than static batch melting within the lithosphere or the presence or absence of residual garnet. Upwelling rates are estimated at ˜ 1.5 cm/yr. A subdued, localised topographic uplift associated with the magmatism suggests that any upwelling is more likely associated with a secondary mode localised to the upper mantle, rather than a broad zone of deeply-sourced (plume) upwelling. Upper mantle, 'edge-driven' convection is consistent with seismic tomographic and anisotropy studies that imply rapid differential motion of variable thickness Australian lithosphere and the underlying asthenosphere. In this scenario, melting is linked to a significant contribution from hydrous mantle that is envisaged as resulting either from convective entrainment of lithosphere along the trailing edge of a lithospheric keel, or inherited variability in the asthenosphere.

  16. 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.

  17. 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

  18. L' upwelling de la côte atlantique du Maroc entre 1994 et 1998

    NASA Astrophysics Data System (ADS)

    Makaoui, Ahmed; Orbi, Abdelattif; Hilmi, Karim; Zizah, Soukaina; Larissi, Jamila; Talbi, Mohammed

    2005-12-01

    The pelagic ecosystem of the Moroccan Atlantic coast is influenced by the spatiotemporal variability of upwelling. The changes in the physicochemical and biological parameters as well as their interrelationship and regrouping by the principal components analysis allowed us to subdivide the Atlantic coast in four active areas: two areas located at the north of Cape Juby (28°N), characterised by a summery activity and two areas located at the south, active permanently, with a variable intensity. To cite this article: A. Makaoui et al., C. R. Geoscience 337 (2005).

  19. Upwelling variability off southern Indonesia over the past two millennia

    NASA Astrophysics Data System (ADS)

    Steinke, Stephan; Prange, Matthias; Feist, Christin; Groeneveld, Jeroen; Mohtadi, Mahyar

    2014-11-01

    Modern variability in upwelling off southern Indonesia is strongly controlled by the Australian-Indonesian monsoon and the El Niño-Southern Oscillation, but multidecadal to centennial-scale variations are less clear. We present high-resolution records of upper water column temperature, thermal gradient, and relative abundances of mixed layer- and thermocline-dwelling planktonic foraminiferal species off southern Indonesia for the past two millennia that we use as proxies for upwelling variability. We find that upwelling was generally strong during the Little Ice Age (LIA) and weak during the Medieval Warm Period (MWP) and the Roman Warm Period (RWP). Upwelling is significantly anticorrelated to East Asian summer monsoonal rainfall and the zonal equatorial Pacific temperature gradient. We suggest that changes in the background state of the tropical Pacific may have substantially contributed to the centennial-scale upwelling trends observed in our records. Our results implicate the prevalence of an El Niño-like mean state during the LIA and a La Niña-like mean state during the MWP and the RWP.

  20. Weakened stratospheric quasibiennial oscillation driven by increased tropical mean upwelling.

    PubMed

    Kawatani, Yoshio; Hamilton, Kevin

    2013-05-23

    The zonal wind in the tropical stratosphere switches between prevailing easterlies and westerlies with a period of about 28 months. In the lowermost stratosphere, the vertical structure of this quasibiennial oscillation (QBO) is linked to the mean upwelling, which itself is a key factor in determining stratospheric composition. Evidence for changes in the QBO have until now been equivocal, raising questions as to the extent of stratospheric circulation changes in a global warming context. Here we report an analysis of near-equatorial radiosonde observations for 1953-2012, and reveal a long-term trend of weakening amplitude in the zonal wind QBO in the tropical lower stratosphere. The trend is particularly notable at the 70-hectopascal pressure level (an altitude of about 19 kilometres), where the QBO amplitudes dropped by roughly one-third over the period. This trend is also apparent in the global warming simulations of the four models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) that realistically simulate the QBO. The weakening is most reasonably explained as resulting from a trend of increased mean tropical upwelling in the lower stratosphere. Almost all comprehensive climate models have projected an intensifying tropical upwelling in global warming scenarios, but attempts to estimate changes in the upwelling by using observational data have yielded ambiguous, inconclusive or contradictory results. Our discovery of a weakening trend in the lower-stratosphere QBO amplitude provides strong support for the existence of a long-term trend of enhanced upwelling near the tropical tropopause. PMID:23698448

  1. 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

  2. Contrasting lithospheric mantle domains beneath the Massif Central (France) revealed by geochemistry of peridotite xenoliths

    NASA Astrophysics Data System (ADS)

    Lenoir, Xavier; Garrido, Carlos J.; Bodinier, Jean-Louis; Dautria, Jean-Marie

    2000-09-01

    We report major and trace element analyses for 82 coarse-grained peridotite xenoliths from 25 Cenozoic volcanic centres throughout the Massif Central (France). These data cover a region of about 150×150 km, allowing an investigation of large scale compositional variations in the subcontinental lithospheric mantle (SCLM). In agreement with textural variations, geochemical data define two contrasting lithospheric domains, situated north and south of latitude 45°30'. Peridotites of the northern domain show protogranular textures, characterised by clustered pyroxene-spinel distributions. They are rather refractory and depleted in MREE relative to HREE, but pervasively enriched in LREE and other highly incompatible elements. The samples show mantle-normalised patterns with negative anomalies of Nb, Ta, Zr and Hf, similar to enriched mantle xenoliths ascribed to carbonatitic metasomatism. In contrast, the peridotites of the southern domain are devoid of pyroxene-spinel clusters and are therefore referred to as coarse-granular. They are distinguished from the northern suite by more fertile compositions and relatively flat MREE-HREE patterns. In addition, only the harzburgites and a few lherzolites are enriched in LREE. Most southern domain lherzolites are depleted in these elements and the average composition of the southern suite is comparable to that of depleted MORB-source mantle (DMM). The main compositional differences between the two domains cannot be accounted for by a secular evolution of the Massif Central SCLM caused by Cenozoic plume upwelling. Instead, these differences record the existence of distinct lithospheric blocks assembled during the Variscan orogeny. To some degree, the northern and southern domains are reminiscent of cratonic and circumcratonic SCLM domains. Being relatively refractory and pervasively enriched in LREE, the northern domain displays similarities with cratonic SCLM. It is interpreted as a relatively ancient (pre

  3. Observations of Upwelling Filaments in the Southern North-West African Upwelling System : a Joint Effect of the Bottom Topography and the Offshore Eddy Field?

    NASA Astrophysics Data System (ADS)

    Meunier, T.; Barton, E. D.; Torres, R.; Barreiro, B.

    2010-12-01

    the upwelling front. The presence of the Cabo Verde frontal zone in the vicinity of the upwelling system is assumed to be responsible for the different behavior in the evolution of the 2 surveyed filaments : previous studies (Spall, 1992; Onken and Klein, 1991; Joyce et al., 1998) showed that the Cabo Verde front was baroclinically unstable and thus an important source of eddy activity in the region. The variability in the evolution of the offshore extension of the observed filaments are believed to be related with this external mesoscale activity. As the topographic eddies can trigger permanent meanders on the upwelling front, the resulting structures can be stretched and evolve into more complex and variable patterns by the interaction with the external eddy field.

  4. Evaluation of upwelling infrared radiance in a nonequilibrium nonhomogeneous atmosphere

    NASA Technical Reports Server (NTRS)

    Tiwari, S. N.; Subramanian, S. V.

    1982-01-01

    The influence of vibrational nonequilibrium upon upwelling infrared radiance from the earth's atmosphere is investigated. By employing the line-by-line model for spectral absorption, heating rates and upwelling radiances are calculated for equilibrium and nonequilibrium conditions in the spectral range of 4.7 micron CO and 3.3 micron CH4 bands. Heating rates are calculated also for the 15 micron CO2 band and are compared with other available results in the literature. For the spectral range of the CO fundamental band, the influence of different parameters on the upwelling radiance is investigated. It is found that for CO the assumption of local thermodynamic equilibrium (LTE) is not justified at tropospheric temperatures and pressures. If the resonance effects of CO-N2 collisions are considered, then the assumption of LTE is justified up to 60 kilometers. This information is very useful for measurement of atmospheric pollutants, earth radiation budget studies and climate modeling, and infrared signature works.

  5. 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.

  6. Evaluation of upwelling infrared radiance from earth's atmosphere

    NASA Technical Reports Server (NTRS)

    Gupta, S. K.; Tiwari, S. N.

    1975-01-01

    Basic equations for calculating the upwelling atmospheric radiation are presented which account for various sources of radiation coming out at the top of the atmosphere. The theoretical formulation of the transmittance models (line-by-line and quasi-random band model) and the computational procedures used for the evaluation of the transmittance and radiance are discussed in detail. By employing the Lorentz line-by-line and quasi-random computer programs, model calculations were made to determine the upwelling radiance and signal change in the wave number interval of CO fundamental band. These results are useful in determining the effects of different interfering molecules, water vapor profiles, ground temperatures, and ground emittances on the upwelling radiance and signal change. This information is of vital importance in establishing the feasibility of measuring the concentrations of pollutants in the atmosphere from a gas filter correlation instrument flown on an aircraft or mounted on a satellite.

  7. Virioplankton Abundance in Trophic Gradients of an Upwelling Field

    PubMed Central

    Pereira, G.C.; Granato, A.; Figueiredo, A.R.; Ebecken, N.F.F.

    2009-01-01

    This work correlates time series of biological and physical variables to the marine viruses across trophic gradients within Arraial do Cabo upwelling system, Southeast of Brazil. The objective is to investigate the major controlling factors of virioplankton dynamics among different water masses. It was used an in situ and ex situ flow cytometry for accessing the plankton community. Viruses were highly correlated to bacteria and phytoplankton, but although the lack of direct correlation with physicals, upwelling turned out to be the main contributing factor to the highest values of viral abundance and virus:bacterial ratio. Our data suggest that the lowest temperature of upwelled South Atlantic Central Waters would help to maintain a high viral abundance and higher temperatures of Coastal and Tropical Waters might be another ecological niche allowing the co-existence. PMID:24031434

  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. Mn seasonal upwellings recorded in Lake Tanganyika mussels

    NASA Astrophysics Data System (ADS)

    Langlet, D.; Alleman, L. Y.; Plisnier, P.-D.; Hughes, H.; André, L.

    2006-09-01

    Biogenic productivity of Lake Tanganyika is highly dependent on seasonal upwellings of anoxic deep waters. We investigated the shell of freshwater bivalve Pleiodon spekii as a geochemical archive of these periodic hydrological changes tuned by the monsoon regime. The results of a 2-years-long geochemical survey of the coastal waters performed on the dissolved and particulate fractions were put in perspective against laser ablation ICP-MS profiles of Mn in five aragonitic shells from the same lake location. Skeletal Mn profiles in 3 shells are very similar and dominated by episodic peaks that matched the Mn increase recorded in surface waters during the 2002 upwelling, while a shell collected during 2003 dry season detect both 2002 and 2003 upwelling events. Larger shells showing an extremely reduced growth display more than 8Mn peaks suggesting at least an 8 years record of seasonal changes in water composition.

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

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

  11. Basaltic continental intraplate volcanism as sustained by shear-driven upwelling

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    While most volcanism on Earth occurs at plate boundaries, the study of intraplate basaltic volcanism may provide an opportunity to scrutinize the make-up and dynamics of the mantle. In continental settings, a range of mechanisms were proposed to sustain mantle decompression and hence to support such volcanism. These include mantle plumes, fertile melting anomalies, self-sustaining buoyant decompression melting, lithospheric dripping, and edge-driven small-scale convection. Recently, Conrad et al. showed that basaltic continental volcanism occurs more often where shear across the asthenosphere is greatest, and hence propose shear-driven upwelling (SDU) to support such volcanism¹. SDU does not require density heterogeneity to drive convection, in contrast to other mechanisms. Rather, it develops when rapid shear across the asthenosphere meets lateral viscosity variation2. For example, in a case with a low-viscosity pocket in the mantle, asthenospheric shear is accommodated in a different manner across the pocket than across the ambient mantle. This contrast drives vertical flow close to the margins of the pocket, and may be sufficient to sustain decompression melting, particularly if the viscosity anomaly is supported by higher water contents or temperatures2. Mantle melting is also expected for situations in which asthenospheric shear flow enters a lithospheric cavity, or decompresses across a step in lithospheric thickness3 - and even more so if a low-viscosity pocket is entrained in such a flow. Seismic observations indicate that sublithospheric topography, and heterogeneity in mantle viscosity are indeed common beneath continents (regardless of whether the imaged anomalies are thermal or compositional in origin). We use three-dimensional numerical models to explore shear-driven flow, and investigate a range of cases with pockets of variable viscosity contrast and shape, lithospheric steps of variable offset and spacing, and asthenospheric flow with variable

  12. 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.

  13. 13000 cal years upwelling variation in southwestern Atlantic (Brazil): continental paleoclima implications

    NASA Astrophysics Data System (ADS)

    Albuquerque, A.

    2009-12-01

    Ana Luiza ALBUQUERQUE(1); Bruno TURCq(2); Abdel SIFEDDINE(1,2). (1) Departamento de Geoquímica, Universidade Federal Fluminense, Niterói, Brazil. (2) LOCEAN, IRD/UPMC/CNRS/MNHN, Bondy, France. The Cabo Frio region as indicated by its name is a place of low SST due to a local upwelling triggered by the Northeast trade winds, the northward flow of cool South Atlantic Central Water and vortex of the Brazilian current in the upper warm Tropical Water. Paleoceanographic conditions during the last 13000 years have been reconstructed based on two cores collected on the outer shelf. The studied proxies included mineral and heavy metal quantification, bulk organic matter characteristics and planktonic foraminifera. A first phase of sedimentation between 13000 and 7000 cal BP is characterized by high mineral content probably due to the lower sea level. SST reconstruction indicate cool and highly variable temperatures that were probably not related to upwelling events made difficult by the low sea level but to lower regional SSTs. This is in good agreement with observations of continental climate dryer in southwest Brazil with intense events of precipitation. A second phase between 7000 and 3000 cal BP shows higher SST indicating few occurrences of upwelling. Its may be due to the decrease of South Atlantic Convergence Zone (ZCAS) intensity linked to the lower summer insolation and the reduced monsoonal flux at that time. On the adjacent continent the decrease monsoon is evidenced by low lake levels and poorly developed forests. The third and last phase, post 3000 cal BP, is characterized by the onset of upwelling events that may be related to an intensification of the South American Monsoon and of the ZCAS activity leading to an increase of Northeast winds during summer which is typically the upwelling season. On the continent this period was marked by forest development. The transition at 3000 yrs BP is very late compared to other Holocene Record. Paleoclimate model

  14. 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

  15. Seismic structure of the western U.S. mantle and the origin of the Yellowstone hotspot

    NASA Astrophysics Data System (ADS)

    Schmandt, B.; Dueker, K.; Humphreys, E.; Hansen, S. M.

    2012-12-01

    As a result of EarthScope's Transportable Array and prior seismic deployments the quality of mantle imaging beneath Yellowstone is unparalleled among hotspots. P-to-s receiver functions mapped to depth through P and S body-wave tomography models image continuous 410 and 660 km discontinuities beneath the area covered by the TA prior to the middle of the year 2011. Mean depths to the 410 and 660 km discontinuities of 410 and 656 km imply a mantle transition zone that is about 4 km thicker than the global average and hence has a slightly cooler mean temperature and/or enhanced water content. Compared to the mean 660 depth beneath this ~2000 km wide area, the 660 beneath the Yellowstone hotspot is deflected upward by 12-18 km over an area about 200 km wide. This is the most anomalous shallowing of the 660 imaged and its horizontal extent is similar to the area where P and S tomography image low-velocity mantle extending from the top of the transition zone to about 900 km depth. Together, these results indicate a high-temperature, plume-like upwelling extending across the 660. The depth of 410 km discontinuity beneath the Yellowstone region is within 5 km of the mean depth implying the plume is vertically heterogeneous and possibly discontinuous. Tomography images a similar vertically heterogeneous thermal plume. The irregular plume structure may be intrinsic to the dynamics of upwelling through the transition zone, or distortion may be caused by subduction-induced mantle flow. Topography of the 410 and 660 confirm that subducted slabs beneath the western U.S. are highly segmented, as inferred from recent tomography studies. We find no evidence of regionally pervasive velocity discontinuities between 750 and 1400 km depth. The plume's depth of origin within the lower mantle remains uncertain.

  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. 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

  18. Novel Agents in Mantle Cell Lymphoma

    PubMed Central

    Noel, Marcus S.; Friedberg, Jonathan W.

    2012-01-01

    Mantle cell lymphoma is a mature B cell neoplasm constituting 5–7% of all non-Hodgkin lymphoma. Overall prognosis with current therapeutics remains poor, thus numerous novel agents are currently under investigation. In this review we focus on early phase trials that have demonstrated promise in mantle cell. Constitutive activation of signaling components downstream of the B cell receptor play an important role in the pathobiology of mantle cell lymphoma. Targeting of this signaling pathway has become a focus with specific agents under development including inhibitors of spleen tyrosine kinase, phosphoinositide-3-kinase and Bruton’s tyrosine kinase. Promsing data also supports further development of BH-3 mimetics, a crucial component of anti-apoptotic signaling. Histone deacetylase inhibitors have an established role in cutaneous T cell lymphoma and are now under investigation in mantle cell lymphoma as well. With further understanding of cellular signaling, the armamentarium of treatment options will be enhanced, with the hope of improving the prognosis of this disease. PMID:22687455

  19. Estimates of potential new production in the Java-Sumatra upwelling system

    NASA Astrophysics Data System (ADS)

    Wei, Xing; Liao, Xiaomei; Zhan, Haigang; Liu, Hailong

    2012-11-01

    The Java-Sumatra upwelling is one of the most important upwelling systems in the Indian Ocean, with maximum upwelling intensity in July through August. To estimate the nitrate supplied by upwelling, we developed a three-dimensional hydrodynamic model to calculate the mean vertical speed and determine the depth of upwelling. We used in-situ vertical nitrate profiles to assess nitrate concentration in the upwelled waters, and calculated the nitrate supply as the product of nitrate concentration and vertical transport obtained from the numerical model. The calculated result represents potential new production generated in the upwelling region. We found that on the event time scale (monthly) of Java-Sumatra upwelling, water brought to the surface originated from locations 100-m deep, giving a nitrate supply of 93.77×103 mol/s and potential new production of 1.02×1014 gC/a.

  20. 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

  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. PMID:11541663

  3. Mantle hydrocarbons: Abiotic or biotic?

    NASA Astrophysics Data System (ADS)

    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 "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 (c) δ13C of the mantle hydrocarbons is uniform (about -27%.). 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 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 4H 10.

  4. 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

  5. Is there any correlation between continents and elevated temperatures in the subcontinental mantle?

    NASA Astrophysics Data System (ADS)

    Jain, Charitra; Rozel, Antoine; Tackley, Paul

    2015-04-01

    Rolf et al. (EPSL, 2012) and Coltice et al. (Science, 2012) have previously shown that continents exert a first order influence on Earth's mantle flow by affecting convective wavelength and surface heat flow. However, how continents influence the development and location of mantle plumes (upwellings) remains a topic of considerable debate. While Heron and Lowman (GRL, 2010; Tectonophysics, 2011) propose regions where downwelling has ceased (irrespective of overlying plate) as the preferred location for plumes, O'Neill et al. (Gondwana Research, 2009) show an anti-correlation between the average positions of subducting slabs at continental margins, and mantle plumes at continental/oceanic interiors. Continental motion is attributed to the viscous stresses imparted by the convecting mantle and the extent of this motion depends on the heat budget of the mantle. Core-mantle boundary (CMB) heat flux, internal heating from decay of radioactive elements, and mantle cooling contribute to this heat budget. Out of these sources, CMB heat flux is not well defined. However, the recent determination of core's high thermal conductivity requires a CMB heat flow of at least 12 TW (de Koker et al., PNAS 2012; Pozzo et al., Nature 2012; Gomi et al., PEPI 2013). Thus it is necessary to characterize the impact of basal heating on mantle dynamics with continents and self-consistent plate tectonics. By systematically varying parameters like CMB temperature, continental size, mantle heating modes (basal and internal), and Rayleigh number; we model Boussinesq, incompressible, thermo-chemical mantle convection in 2D spherical annulus geometry using StagYY (Tackley, PEPI 2008). We observe correlation between continents and elevated temperatures in the subcontinental mantle irrespective of the variations in basal heating and continental size (except for very small continents). Moreover, we see episodicity between correlation and anti-correlation with increasing Rayleigh number. Furthermore

  6. Upwelling O(+) ion source characteristics. [in polar magnetosphere

    NASA Technical Reports Server (NTRS)

    Moore, T. E.; Lockwood, M.; Chandler, M. O.; Waite, J. H., Jr.; Chappell, C. R.; Persoon, A.; Sugiura, M.

    1986-01-01

    The characteristics of an upwelling ion source are discussed. A typical upwelling event is analyzed using Dynamic Explorer 1 satellite retarding ion mass spectrometer (RIMS) observations of the low-energy plasma, and energetic ion and local electromagnetic field observations. The RIMS spectrograms of the O(+) ion species, radial and axial head data for O(+), and spin plan O(+) distribution functions are examined. The features of the upwelling observed include: (1) transverse ion heating to temperature of 100,000 K, (2) large outward flows of O(+), (3) enhanced flow of H(+) and He (+), (4) moderately strong field-aligned current sheets, (5) an associated intense eastward convection channel, and (6) strong wave emissions in the range near and below the proton gyrofrequency. The association between the upwelling O(+) signature and auroral current is investigated. Plasma wave and electric field environments are studied and plasma flows and densities are derived. It is noted that the mechanism for ion heating which defines the source region for these polar ion outflows is related to field-aligned currents and an associated auroral convection channel or jet.

  7. Evaluation of upwelling infrared radiance from the earth's troposphere

    NASA Technical Reports Server (NTRS)

    Tiwari, S. N.; Gupta, S. K.

    1976-01-01

    Basic equations for calculating the upwelling atmospheric radiance are presented. Theoretical formulation of the transmittance models (line-by-line and quasi-random band) and computational procedures for the evaluation of transmittance and radiance are discussed. This information is useful in the interpretation of the data obtained from measuring gaseous pollutants in the troposphere.

  8. 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.

  9. Wind-driven upwelling around grounded tabular icebergs

    NASA Astrophysics Data System (ADS)

    Stern, Alon A.; Johnson, Eric; Holland, David M.; Wagner, Till J. W.; Wadhams, Peter; Bates, Richard; Abrahamsen, E. Povl; Nicholls, Keith W.; Crawford, Anna; Gagnon, Jonathan; Tremblay, Jean-Eric

    2015-08-01

    Temperature and salinity data collected around grounded tabular icebergs in Baffin Bay in 2011, 2012, and 2013 indicate wind-induced upwelling at certain locations around the icebergs. These data suggest that along one side of the iceberg, wind forcing leads to Ekman transport away from the iceberg, which causes upwelling of the cool saline water from below. The upwelling water mixes with the water above the thermocline, causing the mixed layer to become cooler and more saline. Along the opposite side of the iceberg, the surface Ekman transport moves towards the iceberg, which causes a sharpening of the thermocline as warm fresh water is trapped near the surface. This results in higher mixed layer temperatures and lower mixed layer salinities on this side of the iceberg. Based on these in situ measurements, we hypothesize that the asymmetries in water properties around the iceberg, caused by the opposing effects of upwelling and sharpening of the thermocline, lead to differential deterioration around the iceberg. Analysis of satellite imagery around iceberg PII-B-1 reveals differential decay around the iceberg, in agreement with this mechanism.

  10. 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.

  11. Thermal Structure and Mantle Dynamics of Rocky Exoplanets

    NASA Astrophysics Data System (ADS)

    Wagner, F. W.; Tosi, N.; Hussmann, H.; Sohl, F.

    2011-12-01

    The confirmed detections of CoRoT-7b and Kepler-10b reveal that rocky exoplanets exist. Moreover, recent theoretical studies suggest that small planets beyond the Solar System are indeed common and many of them will be discovered by increasingly precise observational surveys in the years ahead. The knowledge about the interior structure and thermal state of exoplanet interiors provides crucial theoretical input not only for classification and characterization of individual planetary bodies, but also to better understand the origin and evolution of the Solar System and the Earth in general. These developments and considerations have motivated us to address several questions concerning thermal structure and interior dynamics of terrestrial exoplanets. In the present study, depth-dependent structural models of solid exoplanet interiors have been constructed in conjunction with a mixing length approach to calculate self-consistently the radial distribution of temperature and heat flux. Furthermore, 2-D convection simulations using the compressible anelastic approximation have been carried through to examine the effect of thermodynamic quantities (e.g., thermal expansivity) on mantle convection pattern within rocky planets more massive than the Earth. In comparison to parameterized convection models, our calculated results predict generally hotter planetary interiors, which are mainly attributed to a viscosity-regulating feedback mechanism involving temperature and pressure. We find that density and thermal conductivity increase with depth by a factor of two to three, however, thermal expansivity decreases by more than an order of magnitude across the mantle for planets as massive as CoRoT-7b or Kepler-10b. The specific heat capacity is observed to stay almost constant over an extended region of the lower mantle. The planform of mantle convection is strongly modified in the presence of depth-dependent thermodynamic quantities with hot upwellings (plumes) rising across

  12. Atmosphere/mantle coupling and feedbacks on Venus

    NASA Astrophysics Data System (ADS)

    Gillmann, Cedric; Tackley, Paul

    2014-06-01

    We investigate the coupled evolution of the atmosphere and mantle on Venus. Here we focus on mechanisms that deplete or replenish the atmosphere: atmospheric escape to space and volcanic degassing of the mantle. These processes are linked to obtain a coupled model of mantle convection and atmospheric evolution, including feedback of the atmosphere on the mantle via the surface temperature. During early atmospheric evolution, hydrodynamic escape is dominant, while for later evolution we focus on nonthermal escape, as observed by the Analyzer of Space Plasma and Energetic Atoms instrument on the Venus Express Mission. The atmosphere is replenished by volcanic degassing from the mantle, using mantle convection simulations based on those of Armann and Tackley [2012], and include episodic lithospheric overturn. The evolving surface temperature is calculated from the amount of CO2 and water in the atmosphere using a gray radiative-convective atmosphere model. This surface temperature in turn acts as a boundary condition for the mantle convection model. We obtain a Venus-like behavior (episodic lid) for the solid planet and an atmospheric evolution leading to the present conditions. CO2 pressure is unlikely to vary much over the history of the planet, with only a 0.25-20% postmagma-ocean buildup. In contrast, atmospheric water vapor pressure is strongly sensitive to volcanic activity, leading to variations in surface temperatures of up to 200 K, which have an effect on volcanic activity and mantle convection. Low surface temperatures trigger a mobile lid regime that stops once surface temperatures rise again, making way to stagnant lid convection that insulates the mantle.

  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. PMID:11035784

  14. 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.

  15. 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

  16. 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

  17. Multidecadal to Millenial-Scale Variability of Productivity and Oxygenation in the Main Peruvian Upwelling Zone Since the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Gutierrez, D. A.; Sifeddine, A.; Skilbeck, C. G.; Salvatteci, R.

    2011-12-01

    Mud-belts containing laminated or near-laminated sedimentary sequences exist in the central Peruvian continental margin beneath the oxygen minimum zone (12 - 14°S, 150 - 400 m), an area where upwelling-favorable alongshore winds are active year-round. The sediments here are dominated by siliceous and phosphatic biogenic remains, organic matter aggregates and lithogenic particles. Sediment cores collected in these belts record past climatic and biogeochemical conditions associated to the Peruvian upwelling system, providing decadal or even sub-decadal time-resolution for the reconstruction of past variabilities. We have examined paleorecords of past productivity and oxygenation in these continental margin sediments since the Last Glacial Maximum (0 - 22Ky BP), as inferred from stratigraphy (absence of bioturbation), geochemical and isotopic proxies, the latter for the past millenium. Laminated sequences are best preserved for the LGM, the Bolling/Allerod period, the early Holocene and the last millennium. In these sequences, the Mo:Al ratio, a proxy for anoxic conditions in the sediments is higher, suggesting an intensification of the oxygen minimum zone. Here also siliceous sedimentation is dominant and carbonate preservation is enhanced. For the past millennium, multiproxy records indicate a less intense OMZ and lower productivity during the Little Ice Age. There is a correspondence between the periods of high (low) lithogenic input and low (high) siliceous productivity with global/Northern Hemisphere cool (warm) climatic conditions since the deglaciation. The main mechanism driving this behavior for the Peruvian upwelling system appears to be the southward/northward migration of the ITCZ, modulating the inland precipitation and the alongshore wind field off Peru. Nevertheless, recent studies in other eastern boundary upwelling systems suggest that local land-sea pressure gradients under hemispheric warming or cooling modulate upwelling and biological

  18. 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.

  19. 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

  20. 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.

  1. Dynamical geochemistry of the mantle

    NASA Astrophysics Data System (ADS)

    Davies, G. F.

    2011-09-01

    The reconciliation of mantle chemistry with the structure of the mantle inferred from geophysics and dynamical modelling has been a long-standing problem. This paper reviews three main aspects. First, extensions and refinements of dynamical modelling and theory of mantle processing over the past decade. Second, a recent reconsideration of the implications of mantle heterogeneity for melting, melt migration, mantle differentiation and mantle segregation. Third, a recent proposed shift in the primitive chemical baseline of the mantle inferred from observations of non-chondritic 142Nd in the Earth. It seems most issues can now be resolved, except the level of heating required to maintain the mantle's thermal evolution. A reconciliation of refractory trace elements and their isotopes with the dynamical mantle, proposed and given preliminary quantification by Hofmann, White and Christensen, has been strengthened by work over the past decade. The apparent age of lead isotopes and the broad refractory-element differences among and between ocean island basalts (OIBs) and mid-ocean ridge basalts (MORBs) can now be quantitatively accounted for with some assurance. The association of the least radiogenic helium with relatively depleted sources and their location in the mantle have been enigmatic. The least radiogenic helium samples have recently been recognised as matching the proposed non-chondritic primitive mantle. It has also been proposed recently that noble gases reside in a so-called hybrid pyroxenite assemblage that is the result of melt from fusible pods reacting with surrounding refractory peridotite and refreezing. Hybrid pyroxenite that is off-axis may not remelt and erupt at MORs, so its volatile constituents would recirculate within the mantle. Hybrid pyroxenite is likely to be denser than average mantle, and thus some would tend to settle in the D" zone at the base of the mantle, along with some old subducted oceanic crust. Residence times in D" are longer, so

  2. Outside the paradigm of upwelling rias in NW Iberian Peninsula: Biogeochemical and phytoplankton patterns of a non-upwelling ria

    NASA Astrophysics Data System (ADS)

    Ospina-Alvarez, Natalia; Varela, Manuel; Doval, María Dolores; Gómez-Gesteira, Moncho; Cervantes-Duarte, Rafael; Prego, Ricardo

    2014-02-01

    The Atlantic Galician rias show the effect of natural eutrophication during ENACW upwelling episodes when large amounts of nutrients are injected. However, the Cantabrian Galician rias do not appear to be disturbed by upwelling events and it can be hypothesized that eutrophy is not inherent to the Galician rias. This question was tackled regarding the biogeochemical and phytoplankton characteristic in the Ria of Barqueiro, located on the western boundary of the Cantabrian Sea, from January 2008 to January 2009. Thermohaline, PAR and fluorescence profiles, dissolved oxygen, nutrient salts, DOC, DON and chlorophyll concentrations, phytoplankton abundances and primary production were monthly determined in a monitoring station (43°45.509‧N-07°39.493‧W); moreover, the daily upwelling index information and fluvial contributions from Sor River were considered. Throughout the year only four annual oceanographic periods were observed: spring, summer stratification, autumn and winter, unlike the Atlantic rias, where a long upwelling period occurs with usually outstanding upwelling processes. Nutrient concentrations (a maximum of 6.2 μM of nitrate, 0.5 μM of nitrite, 2.8 μM of ammonium, 0.4 μM of phosphate and 5.7 μM of silicate), organic matter (98 μM of DOC, 14 μM of DON, 16.4 μM of POC and 2.0 μM of PON), Chl-a (1.1 μg L-1), primary production (280 gC m-2 yr-1) and phytoplankton abundance were clearly lower (about half) when compared to those reported for the other rias during upwelling. Diatoms dominated the phytoplankton assemblages especially during spring and autumn blooms. In summer, although the wind conditions were favorable, upwelling was not observed in the Ria and a mixing of diatoms and dinoflagellates co-dominated the phytoplankton community with a lower contribution of diatoms in comparison to the Atlantic rias. The paradigm of natural eutrophication reported for the Galician rias was not observed in the Ria of Barqueiro, which may be

  3. 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

  4. 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

  5. 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.

  6. Pacific slab subduction-induced carbonatite mantle metasomatism in the eastern North China Craton

    NASA Astrophysics Data System (ADS)

    Deng, L. L.; Liu, Y.; Gao, S.

    2014-12-01

    Trace element and Sr-Li isotopic compositions of pyroxene and olivine in mantle peridotite xenoliths entrained by the Cenozoic Changle basalt from the eastern block of the North China Craton (NCC) were analyzed by LA-(MC)-ICPMS. Calcite and carbonatitic melt inclusions occur in clinopyroxene and olivine. Clinopyroxene in these xenoliths generally have a relatively higher Mg# (92.3-93.0) than that of olivine (Mg# = 90.8). Clinopyroxene is characterized by enrichments in LREE and zonations of REE, Li and Sr increasing from the cores to the rims. Furthermore, they have high Ca/Al (8.4-8.7), Zr/Hf (69.9-78.4) and (La/Yb)N (21-36) ratios and low Ti/Eu (618-755) ratios, which are features of mantle peridotite metasomatized by carbonatitic melt. These observations indicate that the peridotitic mantle beneath the Changle area could have suffered a carbonatitic metasomatism. Clinopyroxene, othopyroxene and olivine in these peridotites exhibit variably low δ7Li (+3.9 to -27.2‰) and slightly high 87Sr/86Sr (0.7030-0.7036), suggesting involvement of recycled crustal material. It has been previously suggested that the Mesozoic destruction of the eastern NCC was closely related to the hydration and mantle upwelling associated with Pacific plate subduction. The Cenozoic Changle basalt locates at the eastern margin of the NCC. Thus, we suggest that the carbonatitic metasomatism of the lithopheric mantle beneath the Changle area could have been induced by the westward subduction of the Pacific plate. The subduction-related carbonatitic metasomatism can transform the depleted harzburgite/dunite mantle to clinopyroxne/orthopyroxene-rich mantle, which could have played an important role in the lithospheric thinning of the NCC.

  7. 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.

  8. 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.

  9. Coastal Upwelling off Chile: Ocean Productivity and Surface Sediments

    NASA Astrophysics Data System (ADS)

    Hebbeln, D.; Lamy, F.

    2002-12-01

    The coastal upwelling system of the Peru-Chile Current belongs to the most productive regions in the world oceans. In spite of this fact only very little is known about the sediment distribution in its southern part off the coast of Chile. To increase the knowledge about this region a multi-parameter study of the surface sediment distribution at over 100 sampling sites along the Chilean continental slope between 23°S and 45°S has been carried out. Detailed analyses of sedimentary data (TOC, carbonate, and biogenic opal contents, delta 15N) reveal a close relation to environmental conditions in the region. Coastal upwelling along the Chilean coast, centered around main upwelling centers such as off Antofagasta (23°S), off Lengua de Vaca (30°S), off Valparaiso (33°S), and off Concepci¢n (35-38°S), sustains the high productivity observed in satellite pigment data and in sediment data. However, the highest pigment concentrations are found south of 40°S where prevailing onshore winds of the Southern Westerlies generally prevent coastal upwelling. There, also highest estimated accumulation rates of organic carbon and biogenic opal at the sea floor are found. Thus, the general pattern of a southward increase of surface water productivity known from satellite data is closely reflected in the organic carbon, biogenic opal and ?15N data, although the observation of highest productivity south of the upwelling area is surprising. Probably, this high productivity in the south can be attributed to the advection of (macro-) nutrients by the Antarctic Circumpolar Current, supplying so-called high nutrient-low chlorophyll (HNLC) waters to the Chilean margin. Impinging on the Chilean margin these waters can take up micronutrients such as iron from the strong riverine input and from benthic exchange processes. The combination of macro- and micro-nutrients in this area most likely results in the high productivity of the area between 40°S and 45°S. From there these fertile

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. Mantle source volumes and the origin of the mid-Tertiary ignimbrite flare-up in the southern Rocky Mountains, western U.S.

    NASA Astrophysics Data System (ADS)

    Farmer, G. Lang; Bailley, Treasure; Elkins-Tanton, Linda T.

    2008-04-01

    to hot, upwelling sub-lithospheric mantle during mid-Tertiary slab roll back could have then triggered the mantle melting. While a plausible source for mid-Tertiary basaltic magmas in the southern Rocky Mountains, lithospheric mantle could not have been the sole source for mafic magmas generated to the south in that portion of the ignimbrite flare-up now preserved in the Sierra Madre Occidental of northern Mexico. The large mantle source volumes (> 45 M km 3) required to fuel the voluminous silicic ignimbrites deposited in this region (> 400 K km 3) are too large to have been accommodated within the lithospheric mantle alone, implying that melting in sub-lithospheric mantle must have played a significant role in generating this mid-Tertiary magmatic event.

  15. Ocean Carbon Cycling and CO2 Air-Sea Exchange in Eastern Boundary Upwelling Systems

    NASA Astrophysics Data System (ADS)

    Plattner, G.; Gruber, N.; Lachkar, Z.; Frenzel, H.; Loher, D.

    2008-12-01

    Eastern boundary current (EBC) upwelling systems are regions of intense biogeochemical transformations and transports. Strong upwelling of nutrient- and carbon-rich waters tends to lead to CO2 outgassing nearshore and biologically-driven CO2 uptake offshore. Yet, the net air-sea CO2 balance of EBCs remains unknown. High near-shore productivity coupled with filaments and other meso- and submesoscale phenomena cause a substantial lateral export of organic carbon. We investigate these coastal processes in the California Current (CalCS) and the Canary Current Systems (CanCS), on the basis of the eddy-resolving, physical-biogeochemical model ROMS. Our results confirm the onshore-offshore trends in the air-sea fluxes, with substantial spatial and temporal differences due to topography, upwelling strength, and eddy activity. The CalCS is modeled to be, on average, a very small source of CO2 to the atmosphere, consistent with a recent data-based estimate by Chavez and Takahashi, while for the CanCS this is not clear yet. Regarding offshore transport, the CalCS appears to be stronger than the CanCS. Spatio-temporal variability of all carbon fluxes is substantial, particularly nearshore, posing a tremendous challenge for observing systems targeting e.g. air-sea CO2 fluxes in these dynamic regions. Further analyses of the processes that determine the mean carbon fluxes and their spatio-temporal variability will be presented. Characteristic differences and similarities between the two EBC systems will be discussed.

  16. 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

  17. Yearly variation of bacterial production in the Arraial do Cabo protection area (Cabo Frio upwelling region): An evidence of anthropogenic pressure

    PubMed Central

    Coelho-Souza, Sérgio A.; Pereira, Gilberto C.; Coutinho, Ricardo; Guimarães, Jean R.D.

    2013-01-01

    Arraial do Cabo is where upwelling occurs more intensively on the Brazilian coast. Although it is a protection area it suffers anthropogenic pressure such as harbor activities and sporadic sewage emissions. Short-time studies showed a high variability of bacterial production (BP) in this region but none of them evaluated BP during long periods in a large spatial scale including stations under different natural (upwelling and cold fronts) and anthropogenic pressures. During 2006, we sampled surface waters 10 times (5 in upwelling and 5 in subsidence periods) in 8 stations and we measured BP, temperature as well as the concentrations of inorganic nutrients, pigments and particulate organic matter (POM). BP was up to 400 times higher when sewage emissions were observed visually and it had a positive correlation with ammonia concentrations. Therefore, in 2007, we did two samples (each during upwelling and subsidence periods) during sewage emissions in five stations under different anthropogenic pressure and we also measured particles abundance by flow cytometry. The 12 samples in the most impacted area confirmed that BP was highest when ammonia was higher than 2 μM, also reporting the highest concentrations of chlorophyll a and suspended particles. However, considering all measured variables, upwelling was the main disturbing factor but the pressure of fronts should not be neglected since it had consequences in the auto-heterotrophic coupling, increasing the concentrations of non fluorescent particles and POM. Stations clustered in function of natural and anthropogenic pressures degrees and both determined the temporal-spatial variability. PMID:24688533

  18. Inheritance and refertilization of Upper Mantle rocks in Alpine type orogens and rift systems: what and why

    NASA Astrophysics Data System (ADS)

    Muntener, O.

    2015-12-01

    Mantle peridotites and their serpentinized counterparts from ocean-continent transition zones (OCT's) and (ultra-) slow spreading ridges question a series of 'common beliefs' that have been applied to understand Alpine-type collisional orogens in the framework of the ophiolite concept. I will show that inherited mantle signatures play a key role for the interpretation of ophiolites, and similar processes are relevant for present-day passive margins. Field data and petrology demonstrates that ancient, thermally undisturbed, pyroxenite-veined subcontinental mantle formed parts of the ocean floor next to thinned continental crust. These heterogeneities might comprise an ancient subduction component. Mantle upwelling and decompression melting during rifting forms partial melts that enter a thick conductive lithospheric mantle and inevitably leads to freezing of the melt and refertilization of the lithospheric mantle. Mafic bodies (gabbros, basalts) are small and discontinous. The abundance of plagioclase peridotites in the Alpine ophiolites and elswhere along rifted margins are interpreted as recorders of refertilization processes related to thinning and exhumation of mantle lithosphere. Similar features are found (ultra-) slow spreading ridges. Another important result is the discovery of extremely refractory Nd-isotopic compositions with highly radiogenic 147Sm/144Nd, which indicates that partial melting processes and Jurassic magmatism in the Western Tethys are locally decoupled. Although the isotopic variability along ridges is generally explained by mantle heterogeneities such as pyroxenites, an alternative is that these depleted domains represent snapshots of melting processes that are related to Permian and/or even older crust forming processes, and during the most recent decompression they were unffected by (further) melting. Similarly, refractory rocks from rifted margins and (ultra-) slow spreading ridges have been interpreted to represent ancient melting

  19. Influence of combined primordial layering and recycled MORB on the coupled thermal evolution of Earth's mantle and core

    NASA Astrophysics Data System (ADS)

    Nakagawa, Takashi; Tackley, Paul

    2014-05-01

    A thermo-chemical mantle convection model with both primordial compositional layering and recycling of mid-ocean ridge basalt (MORB) coupled to a parameterized core heat balance model is used to investigate how the thermo-chemical evolution of the mantle affects the thermal history of the core including primordial material proposed by early Earth hypotheses. The viscosity formulation has been improved from our previous works. The amount of MORB that accumulates above the CMB is strongly dependent on effective Rayleigh number, such that more accumulates at higher Ra (lower viscosity), but a continuous layer of MORB is not obtained here. With initial primordial layering, large-scale thermo-chemical anomalies are found in the deep mantle, which are generated mainly by the primordial material with small amount of segregated basaltic material on top of it, localized in the hot upwelling region. A successful core evolution can only be obtained when initial primordial layering is present. In conclusion, primordial material above the CMB originated from early mantle differentiation might be needed to construct a realistic model of a coupled mantle and core evolution. Nakagawa, T. and P. J. Tackley, Influence of combined primordial layering and recycled MORB on the coupled thermal evolution of Earth's mantle and core, Geochem. Geophys. Geosyst., in press

  20. Thermal and geochemical evolution of the mantle wedge in the northeast Japan arc. 2: Contribution from geochemistry

    NASA Astrophysics Data System (ADS)

    Yamashita, Shigeru; Tatsumi, Yoshiyuki

    1994-11-01

    Compositions of primary basalt magmas were backcalculated from Miocene Mg-rich basalts in the Japan Sea back arc basin and the NE Japanese volcanic front, in order to assess the spatial variation in physicochemical conditions for magma production during opening of the back arc basin. Chemical compositions of these magmas together with available liquidus experimental data suggest that the primary basalt magmas both in the Japan Sea (BABB magma) and the NE Japanese volcanic front (VFB magma) were equilibrated with harzburgitic mantle materials at almost identical pressure and temperature conditions. The observation that the BABB magma is more depleted in Fe and some incompatible trace elements and more enriched in Al than the VFB magma then suggests that these magmas may have been derived from source mantle materials with different chemical compositions. An equilibrium melting model further demonstrates that the BABB magma was produced by a smaller degree of partial melting of a more depleted source mantle material (compositional equivalent to abyssal harzburgites) than the VFB magma. Provided that the varying degrees of depletion in the source mantle materials were manifestations of mantle upwelling efficient beneath the back arc side region, the more depleted BABB magma source may have been a plausible geochemical reservoir in the deeper portion of the mantle wedge.

  1. Shear Wave Structure in the Crust and Upper Mantle Beneath the Wyoming Craton

    NASA Astrophysics Data System (ADS)

    Dave, R.; Li, A.

    2013-12-01

    The Wyoming craton was pervasively deformed during the Laramide and has been encroached by the Yellowstone hotspot. It is therefore an ideal place to study the survival and evolution of cratonic lithosphere. We have analyzed Rayleigh wave data recorded by the USArray and applied the two-plane-wave tomography method to determine average and 2-D phase velocities in the Wyoming craton area. These phase velocities were inverted to construct 3-D shear wave structure of the crust and upper mantle. Vertical component seismograms from 82 events at 103 stations were filtered at 18 center frequencies with a narrow bandwidth of 10 mHz. The average phase velocity varies from 3.48 km/s at 20 s to 4.36 km/s at 166 s. Compared to the average global phase velocities, these values are lower at longer periods, indicating a generally slower upper mantle. 2-D variation of phase velocity shows significantly low velocities at the hotspot and relatively high velocities in the north of the stable craton. The same pattern of velocity variation is also imaged in the 3-D shear wave model. The lowest velocity tilted to north and east to the current hotspot location with depth, reflecting shearing of the hotspot material due to the relative motion of the North American plate. In addition, a low velocity anomaly is imaged at central-eastern portion of the craton at depths greater than 150 km, correlated with a thin crust. Relative high velocity anomaly is found in between this slow anomaly and the hotspot. This slow-fast-slow velocity variation in the upper mantle could be associated with small-scale mantle convection of upwelling-downwelling-upwelling trigged by the hotspot, which could thermally erode the cratonic lithosphere.

  2. Insights into