Sample records for mantle plume event

  1. Did mantle plume magmatism help trigger the Great Oxidation Event? (United States)

    Ciborowski, T. Jake. R.; Kerr, Andrew C.


    The Great Oxidation Event (GOE) represents the first sustained appearance of free oxygen in Earth's atmosphere. This fundamental event in Earth's history has been dated to approximately 2450 million years ago (Ma), that is, hundreds of millions of years after the appearance of photosynthetic cyanobacteria in the fossil record. A variety of mechanisms have been suggested to explain this time lag between the onset of photosynthesis and atmospheric oxygenation, including orogenesis, changes in the areal extent and distribution of continental shelves, the secular release of hydrogen to space, and methanogenic bacterial stress. Recently, it has been proposed that subaerial volcanism during the early Proterozoic could have provided a large pulse of sulphate to the ancient oceans, the reduction of which liberated the oxygen to drive the GOE. Here we show that the Matachewan Large Igneous Province (LIP), which is partially preserved in Scandinavia and North America, is both exactly coincident with the onset of the GOE, and of sufficient magnitude to be the source of this sulphate release. We therefore propose that the volcanism associated with the emplacement of the Matachewan LIP was a principal driver of the oxygenation of our planet.

  2. Mantle plumes and continental tectonics. (United States)

    Hill, R I; Campbell, I H; Davies, G F; Griffiths, R W


    Mantle plumes and plate tectonics, the result of two distinct modes of convection within the Earth, operate largely independently. Although plumes are secondary in terms of heat transport, they have probably played an important role in continental geology. A new plume starts with a large spherical head that can cause uplift and flood basalt volcanism, and may be responsible for regional-scale metamorphism or crustal melting and varying amounts of crustal extension. Plume heads are followed by narrow tails that give rise to the familiar hot-spot tracks. The cumulative effect of processes associated with tail volcanism may also significantly affect continental crust.

  3. A case for mantle plumes

    Institute of Scientific and Technical Information of China (English)

    Geoffrey F. Davies


    The existence of at least several plumes in the Earth's mantle can be inferred with few assumptions from well-established observations. As well, thermal mantle plumes can be predicted from well-established and quantified fluid dynamics and a plausible assumption about the Earth's early thermal state. Some additional important observations, especially of flood basalts and rift-related magmatism, have been shown to be plausibly consistent with the physical theory. Recent claims to have detected plumes using seismic tomography may comprise the most direct evidence for plumes, but plume tails are likely to be difficult to resolve definitively and the claims need to be well tested. Although significant questions remain about its viability, the plume hypothesis thus seems to be well worth continued investigation. Nevertheless there are many non-plate-related magmatic phenomena whose association with plumes is unclear or unlikely. Compositional buoyancy has recently been shown potentially to substantially complicate the dynamics of plumes, and this may lead to explanations for a wider range of phenomena, including "headless" hotspot tracks, than purely thermal plumes.

  4. Redox conditions for mantle plumes (United States)

    Heister, L. E.; Lesher, C. E.


    The vanadium to scandium ratio (V/Sc) for basalts from mid-ocean ridge (MOR) and arc environments has been proposed as a proxy for fO2 conditions during partial melting (e.g. [1] and [2]). Contrary to barometric measurements of the fO2 of primitive lavas, the V/Sc ratio of the upper mantle at mid-ocean ridges and arcs is similar, leading previous authors to propose that the upper mantle has uniform redox potential and is well-buffered. We have attempted to broaden the applicability of the V/Sc parameter to plume-influenced localities (both oceanic and continental), where mantle heterogeneities associated with recycled sediments, mafic crust, and metasomatized mantle, whether of shallow or deep origin, exist. We find that primitive basalts from the North Atlantic Igneous Province (NAIP), Hawaii (both the Loa and Kea trends), Deccan, Columbia River, and Siberian Traps show a range of V/Sc ratios that are generally higher (average ~9) than those for MOR (average ~ 6.7) or arc (average ~7) lavas. Based on forward polybaric decompression modeling, we attribute these differences to polybaric melting and melt segregation within the garnet stability field rather than the presence of a more oxidized mantle in plume-influenced settings. Like MORB, the V/Sc ratios for plume-influenced basalts can be accounted for by an oxidation state approximately one log unit below the Ni-NiO buffer (NNO-1). Our analysis suggests that source heterogeneities have little, if any, resolvable influence on mantle redox conditions, although they have significant influence on the trace element and isotopic composition of mantle-derived melts. We suggest that variations in the redox of erupted lavas is largely a function of shallow lithospheric processes rather than intrinsic to the mantle source, regardless of tectonic setting. [1] Li and Lee (2004) EPSL, [2] Lee et al. (2005) J. of Petrology

  5. Numerical modeling of mantle plume diffusion (United States)

    Krupsky, D.; Ismail-Zadeh, A.


    To clarify the influence of the heat diffusion on the mantle plume evolution, we develop a two-dimensional numerical model of the plume diffusion and relevant efficient numerical algorithm and code to compute the model. The numerical approach is based on the finite-difference method and modified splitting algorithm. We consider both von Neumann and Direchlet conditions at the model boundaries. The thermal diffusivity depends on pressure in the model. Our results show that the plume is disappearing from the bottom up - the plume tail at first and its head later - because of the mantle plume geometry (a thin tail and wide head) and higher heat conductivity in the lower mantle. We study also an effect of a lateral mantle flow associated with the plate motion on the distortion of the diffusing mantle plume. A number of mantle plumes recently identified by seismic tomography seem to disappear in the mid-mantle. We explain this disappearance as the effect of heat diffusion on the evolution of mantle plume.

  6. Lunar maria - result of mantle plume activity? (United States)

    Sharkov, E.

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

  7. The composition of mantle plumes and the deep Earth (United States)

    Hastie, Alan R.; Fitton, J. Godfrey; Kerr, Andrew C.; McDonald, Iain; Schwindrofska, Antje; Hoernle, Kaj


    Determining the composition and geochemical diversity of Earth's deep mantle and subsequent ascending mantle plumes is vital so that we can better understand how the Earth's primitive mantle reservoirs initially formed and how they have evolved over the last 4.6 billion years. Further data on the composition of mantle plumes, which generate voluminous eruptions on the planet's surface, are also essential to fully understand the evolution of the Earth's hydrosphere and atmosphere with links to surface environmental changes that may have led to mass extinction events. Here we present new major and trace element and Sr-Nd-Pb-Hf isotope data on basalts from Curacao, part of the Caribbean large igneous province. From these and literature data, we calculate combined major and trace element compositions for the mantle plumes that generated the Caribbean and Ontong Java large igneous provinces and use mass balance to determine the composition of the Earth's lower mantle. Incompatible element and isotope results indicate that mantle plumes have broadly distinctive depleted and enriched compositions that, in addition to the numerous mantle reservoirs already proposed in the literature, represent large planetary-scale geochemical heterogeneity in the Earth's deep mantle that are similar to non-chondritic Bulk Silicate Earth compositions.

  8. On predicting mantle mushroom plumes

    Directory of Open Access Journals (Sweden)

    Ka-Kheng Tan


    Top cooling may produce plunging plumes of diameter of 585 km and at least 195 Myr old. The number of cold plumes is estimated to be 569, which has not been observed by seismic tomography or as cold spots. The cold plunging plumes may overwhelm and entrap some of the hot rising plumes from CMB, so that together they may settle in the transition zone.

  9. Mantle plumes: Why the current skepticism?

    Institute of Scientific and Technical Information of China (English)

    Gillian R. Foulger


    The present reappraisal of the mantle plume hypothesis is perhaps the most exciting current debate in Earth science. Nevertheless, the fundamental reasons for why it has arisen are often not well understood. They are that 1) many observations do not agree with the predictions of the original model, 2) it is possible that convection of the sort required to generate thermal plumes in the Earth's mantle does not occur, 3) so many variants of the original model have been invoked to accommodate conflicting data that the plume hypthesis is in practice no longer testable, and 4) alternative models are viable, though these have been largely neglected by researchers. Regardless of the final outcome, the present vigorous debate is to be welcomed since it is likely to stimulate new discoveries in a way that unquestioning acceptance of the conventional plume model will not.

  10. Determining resolvability of mantle plumes with synthetic seismic modeling (United States)

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


    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

  11. Mantle plumes in the vicinity of subduction zones (United States)

    Mériaux, C. A.; Mériaux, A.-S.; Schellart, W. P.; Duarte, J. C.; Duarte, S. S.; Chen, Z.


    We present three-dimensional deep-mantle laboratory models of a compositional plume within the vicinity of a buoyancy-driven subducting plate with a fixed trailing edge. We modelled front plumes (in the mantle wedge), rear plumes (beneath the subducting plate) and side plumes with slab/plume systems of buoyancy flux ratio spanning a range from 2 to 100 that overlaps the ratios in nature of 0.2-100. This study shows that 1) rising side and front plumes can be dragged over thousands of kilometres into the mantle wedge, 2) flattening of rear plumes in the trench-normal direction can be initiated 700 km away from the trench, and a plume material layer of lesser density and viscosity can ultimately almost entirely underlay a retreating slab after slab/plume impact, 3) while side and rear plumes are not tilted until they reach ∼600 km depth, front plumes can be tilted at increasing depths as their plume buoyancy is lessened, and rise at a slower rate when subjected to a slab-induced downwelling, 4) rear plumes whose buoyancy flux is close to that of a slab, can retard subduction until the slab is 600 km long, and 5) slab-plume interaction can lead to a diversity of spatial plume material distributions into the mantle wedge. We discuss natural slab/plume systems of the Cascadia/Bowie-Cobb, and Nazca/San Felix-Juan Fernandez systems on the basis of our experiments and each geodynamic context and assess the influence of slab downwelling at depths for the starting plumes of Java, Coral Sea and East Solomon. Overall, this study shows how slab/plume interactions can result in a variety of geological, geophysical and geochemical signatures.

  12. Evidence for Little Shallow Entrainment in Starting Mantle Plumes (United States)

    Lohmann, F. C.; Phipps Morgan, J.; Hort, M.


    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

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

    Morgan, Jason P.


    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

  14. West Antarctic Mantle Plume Hypothesis and Basal Water Generation (United States)

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


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

  15. The link between Hawaiian mantle plume composition, magmatic flux, and deep mantle geodynamics (United States)

    Harrison, Lauren N.; Weis, Dominique; Garcia, Michael O.


    Oceanic island basalts sample mantle reservoirs that are isotopically and compositionally heterogeneous. The Hawaiian-Emperor chain represents ∼85 Myr of volcanism supplied by a deep mantle plume. Two geographically and geochemically delineated trends, Kea and Loa, are well documented within the Hawaiian Islands. Enriched Loa compositions originate from subduction recycled or primordial material stored in deep mantle reservoirs such as the large low shear velocity province (LLSVP) below Hawai'i. Loa compositions have not been observed along the Emperor Seamounts (>50 Ma), whereas lavas on the Hawaiian Islands (chain and the Hawaiian Islands record the geochemical evolution of the Hawaiian mantle plume over a time period when many geophysical parameters (volcanic propagation rate, magmatic flux, mantle potential temperature) increased significantly. Along the NWHR, the Loa geochemical component appears ephemerally, which we link to the sampling of different lower mantle compositional domains by the Hawaiian mantle plume. The plume initially sampled only the deep Pacific mantle (Kea component) from outside the LLSVP during the formation of the Emperor Seamounts. Southward migration and anchoring of the plume on the LLSVP led to entrainment of increasing amounts of LLSVP material (Loa component) along the NWHR as documented by an increase in 208Pb*/206Pb* with decreasing age. The correlation between 208Pb*/206Pb* and magmatic flux suggests source composition affects the magmatic flux, and explains why the Hawaiian mantle plume has dramatically strengthened through time.

  16. Laboratory-Scale Simulation of Spiral Plumes in the Mantle

    CERN Document Server

    Sharifulin, A N


    On the basis of laboratory simulation a mechanism is established for the formation of the upper mantle convection spiral plumes from a hot point in the presence of a roll-type large-scale convective flow. The observed plume has horizontal sections near the upper limit, which may lead to the formation of chains of volcanic islands.

  17. Limited latitudinal mantle plume motion for the Louisville hotspot (United States)

    Koppers, Anthony A. P.; Yamazaki, Toshitsugu; Geldmacher, Jörg; Gee, Jeffrey S.; Pressling, Nicola; Koppers, Anthony A. P.; Yamazaki, Toshitsugu; Geldmacher, Jörg; Gee, Jeffrey S.; Pressling, Nicola; Hoshi, Hiroyuki; Anderson, L.; Beier, C.; Buchs, D. M.; Chen, L.-H.; Cohen, B. E.; Deschamps, F.; Dorais, M. J.; Ebuna, D.; Ehmann, S.; Fitton, J. G.; Fulton, P. M.; Ganbat, E.; Hamelin, C.; Hanyu, T.; Kalnins, L.; Kell, J.; Machida, S.; Mahoney, J. J.; Moriya, K.; Nichols, A. R. L.; Rausch, S.; Sano, S.-I.; Sylvan, J. B.; Williams, R.


    Hotspots that form above upwelling plumes of hot material from the deep mantle typically leave narrow trails of volcanic seamounts as a tectonic plate moves over their location. These seamount trails are excellent recorders of Earth's deep processes and allow us to untangle ancient mantle plume motions. During ascent it is likely that mantle plumes are pushed away from their vertical upwelling trajectories by mantle convection forces. It has been proposed that a large-scale lateral displacement, termed the mantle wind, existed in the Pacific between about 80 and 50 million years ago, and shifted the Hawaiian mantle plume southwards by about 15° of latitude. Here we use 40Ar/39Ar age dating and palaeomagnetic inclination data from four seamounts associated with the Louisville hotspot in the South Pacific Ocean to show that this hotspot has been relatively stable in terms of its location. Specifically, the Louisville hotspot--the southern hemisphere counterpart of Hawai'i--has remained within 3-5° of its present-day latitude of about 51°S between 70 and 50 million years ago. Although we cannot exclude a more significant southward motion before that time, we suggest that the Louisville and Hawaiian hotspots are moving independently, and not as part of a large-scale mantle wind in the Pacific.

  18. Anatomy of mantle plumes: hot heads and cold stems (United States)

    Davaille, A. B.; Kumagai, I.; Vatteville, J.; Touitou, F.; Brandeis, G.


    Recent petrological studies show evidences for secular cooling in mantle plumes: the source temperature of oceanic plateaus could be 100°C hotter than the source temperature of volcanic island chains (Herzberg and Gazel, Nature, 2009). In terms of mantle plumes, it would mean that the temperature of the plume head is hotter than that of the plume stem. This is at odd with a model where a plume head would entrain so much ambient mantle on its journey towards the Earth's surface that it would end up being considerably colder than its narrow stem. So we revisited the problem using laboratory experiments and new visualization techniques to measure in situ simultaneously the temperature, velocity and composition fields. At time t=0, a hot instability is created by heating a patch of a given radius at constant power or constant temperature. The fluids are mixtures of sugar syrups , with a strongly temperature-dependent viscosity, and salt. Rayleigh numbers were varied from 104 to 108, viscosity ratios between 1.8 and 4000, and buoyancy ratios between 0 and 2. After a stage where heat transport is by conduction only, the hot fluid gathers in a sphere and begins to rise, followed by a stem anchored on the hot patch. In all cases, temperatures in the head start with higher values than in the subsequent stem. This is also the case for the thermal instabilities rising from a infinite plate heated uniformly. However, the head also cools faster than the stem as they rise, so that they will eventually have the same temperature if the mantle is deep enough. Moreover, all the material sampled by partial melting in the plume head or stem would be coming from the heated area around the deep source, and very little entrainment from the ambient mantle is predicted. The difference in temperature between head and stem strongly depends on the mantle depth, the viscosity ratio and the buoyancy ratio. Our scaling laws predict that Earth's mantle plumes can indeed have hot heads and colder

  19. Growth and mixing dynamics of mantle wedge plumes (United States)

    Gorczyk, Weronika; Gerya, Taras V.; Connolly, James A. D.; Yuen, David A.


    Recent work suggests that hydrated partially molten thermal-chemical plumes that originate from subducted slab as a consequence of Rayleigh-Taylor instability are responsible for the heterogeneous composition of the mantle wedge. We use a two-dimensional ultrahigh-resolution numerical simulation involving 10 × 109 active markers to anticipate the detailed evolution of the internal structure of natural plumes beneath volcanic arcs in intraoceanic subduction settings. The plumes consist of partially molten hydrated peridotite, dry solid mantle, and subducted oceanic crust, which may compose as much as 12% of the plume. As plumes grow and mature these materials mix chaotically, resulting in attenuation and duplication of the original layering on scales of 1-1000 m. Comparison of numerical results with geological observations from the Horoman ultramafic complex in Japan suggests that mixing and differentiation processes related to development of partially molten plumes above slabs may be responsible for the strongly layered lithologically mixed (marble cake) structure of asthenospheric mantle wedges.

  20. Petrological evidence for secular cooling in mantle plumes. (United States)

    Herzberg, Claude; Gazel, Esteban


    Geological mapping and geochronological studies have shown much lower eruption rates for ocean island basalts (OIBs) in comparison with those of lavas from large igneous provinces (LIPs) such as oceanic plateaux and continental flood provinces. However, a quantitative petrological comparison has never been made between mantle source temperature and the extent of melting for OIB and LIP sources. Here we show that the MgO and FeO contents of Galapagos-related lavas and their primary magmas have decreased since the Cretaceous period. From petrological modelling, we infer that these changes reflect a cooling of the Galapagos mantle plume from a potential temperature of 1,560-1,620 degrees C in the Cretaceous to 1,500 degrees C at present. Iceland also exhibits secular cooling, in agreement with previous studies. Our work provides quantitative petrological evidence that, in general, mantle plumes for LIPs with Palaeocene-Permian ages were hotter and melted more extensively than plumes of more modern ocean islands. We interpret this to reflect episodic flow from lower-mantle domains that are lithologically and geochemically heterogeneous.

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

    Gazel, E.; Herzberg, C. T.


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

  2. A mantle plume below the Eifel volcanic fields, Germany


    Ritter, Joachim R. R.; Jordan, Michael; Christensen, Ulrich R.; Achauer, Ulrich


    We present seismic images of the upper mantle below the Quaternary Eifel volcanic fields, Germany, determined by teleseismic travel time tomography. The data were measured at a dedicated network of more than 200 stations. Our results show a columnar low P-velocity anomaly in the upper mantle with a lateral contrast of up to 2%. The 100 km wide structure extends to at least 400 km depth and is equivalent to about 150–200 K excess temperature. This clear evidence for a plume below a region of c...

  3. Chondritic Xenon in the Earth's mantle: new constrains on a mantle plume below central Europe (United States)

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


    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

  4. Tracing Mantle Plumes: Quantifying their Morphology and Behavior from Seismic Tomography (United States)

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


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

  5. The He isotope composition of the earliest picrites erupted by the Ethiopia plume, implications for mantle plume source (United States)

    Stuart, Finlay; Rogers, Nick; Davies, Marc


    The earliest basalts erupted by mantle plumes are Mg-rich, and typically derived from mantle with higher potential temperature than those derived from the convecting upper mantle at mid-ocean ridges and ocean islands. The chemistry and isotopic composition of picrites from CFB provide constraints on the composition of deep Earth and thus the origin and differentiation history. We report new He-Sr-Nd-Pb isotopic composition of the picrites from the Ethiopian flood basalt province from the Dilb (Chinese Road) section. They are characterized by high Fe and Ti contents for MgO = 10-22 wt. % implying that the parent magma was derived from a high temperature low melt fraction, most probably from the Afar plume head. The picrite 3He/4He does not exceed 21 Ra, and there is a negative correlation with MgO, the highest 3He/4He corresponding to MgO = 15.4 wt. %. Age-corrected 87Sr/86Sr (0.70392-0.70408) and 143Nd/144Nd (0.512912-0.512987) display little variation and are distinct from MORB and OIB. Age-corrected Pb isotopes display a significant range (e.g. 206Pb/204Pb = 18.70-19.04) and plot above the NHRL. These values contrast with estimates of the modern Afar mantle plume which has lower 3He/4He and Sr, Nd and Pb isotope ratios that are more comparable with typical OIB. These results imply either interaction between melts derived from the Afar mantle plume and a lithospheric component, or that the original Afar mantle plume had a rather unique radiogenic isotope composition. Regardless of the details of the origins of this unusual signal, our observations place a minimum 3He/4He value of 21 Ra for the Afar mantle plume, significantly greater than the present day value of 16 Ra, implying a significant reduction over 30 Myr. In addition the Afar source was less degassed than convecting mantle but more degassed than mantle sampled by the proto-Iceland plume (3He/4He ~50 Ra). This suggests that the largest mantle plumes are not sourced in a single deep mantle domain with a

  6. Cascaded Evolution of Mantle Plumes and Metallogenesis of Core- and Mantle-derived Elements

    Institute of Scientific and Technical Information of China (English)

    NIU Shuyin; HOU Quanlin; HOU Zengqian; SUN Aiqun; WANG Baode; LI Hongyang; XU Chuanshi


    Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation andevolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion,lighter elements, such as radioactive, halogen-family, rare and rare earth elements and alkali metals. migrated upwards;whereas heavier elements, such as iron-family and platinum-family elements, base metals and noble metals, had atendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in theEarth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressureand viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly bycascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth wereinterdependent and constituted the motive force of the mantle-core movement. The cascaded evolution of mantle plumesopens the passageways for the migration of deep-seated ore-forming material, and thus elements such as gold and silverconcentrated in the core and on the core-mantle boundary migrate as the gaseous state together with the hot material flowof mantle plumes against the gravitational force through the passageways to the lithosphere, then migrate as the mixed gas-liquid state to the near-surface level and finally are concentrated in favorable structural expansion zones, forming mineraldeposits. This is possibly the important metallogenic mechanism for gold, silver, lead, zinc, copper and other manyelements. Take for example the NE-plunging crown of the Fuping mantle-branch structure, the paper analyzes ductile-brittle shear zone-type gold fields (Weijiayu) at the core of the magmatic-metamorphic complex, principal detachment-type gold fields (Shangmingyu) and hanging-wall cover fissure-vein-type lead-zinc polymetallic ore fields

  7. New observational and experimental evidence for a plume-fed asthenosphere boundary layer in mantle convection (United States)

    Morgan, J. P.; Hasenclever, J.; Shi, C.


    The textbook view is that the asthenosphere is the place beneath the tectonic plates where competing temperature and pressure effects on mantle rheology result in the lowest viscosity region of Earth's mantle. We think the sub-oceanic asthenosphere exists for a different reason, that instead it is where rising plumes of hot mantle stall and spread out beneath the strong tectonic plates. Below this plume-fed asthenosphere is a thermal and density inversion with cooler underlying average-temperature mantle. Here we show several recent seismic studies that are consistent with a plume-fed asthenosphere. These include the seismic inferences that asthenosphere appears to resist being dragged down at subduction zones, that a sub-oceanic thermal inversion ∼250-350 km deep is needed to explain the seismic velocity gradient there for an isochemical mantle, that a fast 'halo' of shear-wave travel-times surrounds the Hawaiian plume conduit, and that an apparent seismic reflector is found ∼300 km beneath Pacific seafloor near Hawaii. We also present 2D axisymmetric and 3D numerical experiments that demonstrate these effects in internally consistent models with a plume-fed asthenosphere. If confirmed, the existence of a plume-fed asthenosphere will change our understanding of the dynamics of mantle convection and melting, and the links between surface plate motions and mantle convection.

  8. Geodynamically Consistent Interpretation of Seismic Tomography for Thermal and Thermochemical Mantle Plumes (United States)

    Samuel, H.; Bercovici, D.


    Recent theoretical developments as well as increased data quality and coverage have allowed seismic tomographic imaging to better resolve narrower structures at both shallow and deep mantle depths. However, despite these improvements, the interpretation of tomographic images remains problematic mainly because of: (1) the trade off between temperature and composition and their different influence on mantle flow; (2) the difficulty in determining the extent and continuity of structures revealed by seismic tomography. We present two geodynamic studies on mantle plumes which illustrate the need to consider both geodynamic and mineral physics for a consistent interpretation of tomographic images in terms of temperature composition and flow. The first study aims to investigate the coupled effect of pressure and composition on thermochemical plumes. Using both high resolution 2D numerical modeling and simple analytical theory we show that the coupled effect of composition and pressure have a first order impact on the dynamics of mantle thermochemical plumes in the lower mantle: (1) For low Si enrichment of the plume relative to a reference pyrolitic mantle, an oscillatory behavior of the plume head is observed; (2) For Si-enriched plume compositions, the chemical density excess of the plume increases with height, leading to stagnation of large plume heads at various depths in the lower mantle. As a consequence, these thermochemical plumes may display broad (~ 1200 km wide and more) negative seismic velocity anomalies at various lower mantle depths, which may not necessarily be associated with upwelling currents. The second study focuses on the identification of thermal mantle plumes by seismic tomography beneath the Hawaiian hot spot: we performed a set of 3D numerical experiments in a spherical shell to model a rising plume beneath a moving plate. The thermal structure obtained is converted into P and S wave seismic velocities using mineral physics considerations. We

  9. Modeling of Mauritius as a Heterogeneous Mantle Plume (United States)

    Moore, J. C.; White, W. M.; Paul, D.; Duncan, R. A.


    Mauritius Island (20°20' S, 57°30' E) is located in the western Indian Ocean and is the penultimate volcanic island of the Réunion mantle plume. Mauritius has a well-established history of episodic volcanism and erosional hiatus, traditionally characterized by three chemically and temporally distinct eruptive phases: 1) the voluminous shield-building lavas of the Older Series (8.4-5.5 Ma), 2) the Intermediate Series (3.5-1.9 Ma), and 3) the Younger Series (1.0-0.00 Ma; Duncan, unpub. data). Recent collaboration with the Mauritian Water Resource Unit has permitted the study of a series of newly available drill cores, facilitating an advanced subsurface investigation into the evolution of the island. Radiometric dating of deep lava units from these cores has identified the earliest known sample from Mauritius (B18-1; 8.4 Ma) and demonstrated the existence of Intermediate and Younger Series lavas at previously unanticipated depths, some greater than 150 meters. Calculated volumes for the combined post- erosional lavas exceed 35 km3, closely resembling new results for Hawaiian analogues (20-60 km3; Garcia, pers. comm.). While these two post-erosional series remain temporally distinct (a 0.9 M.y. hiatus remains despite new dates), they are indistinguishable in major, trace, and isotopic composition. The shield building Older Series lavas are enriched in incompatible trace elements relative to the post-erosional lavas, an inverse relationship to that observed at both Hawaii (Maui, Oahu, and Kauai) and Tahaa (Societies). In contrast isotope systematics are consistent, with shield building lavas having more enriched isotopic signatures than post-erosional lavas. The observed differences cannot be explained solely by variations in the extent of partial melting and require distinct and heterogeneous sources for the shield and post-erosional lavas. Two magma generation scenarios for a heterogeneous mantle plume with enriched (eclogitic) and depleted (peridotitic

  10. Evidence for recycled Archaean oceanic mantle lithosphere in the Azores plume. (United States)

    Schaefer, Bruce F; Turner, Simon; Parkinson, Ian; Rogers, Nick; Hawkesworth, Chris


    The compositional differences between mid-ocean-ridge and ocean-island basalts place important constraints on the form of mantle convection. Also, it is thought that the scale and nature of heterogeneities within plumes and the degree to which heterogeneous material endures within the mantle might be reflected in spatial variations of basalt composition observed at the Earth's surface. Here we report osmium isotope data on lavas from a transect across the Azores archipelago which vary in a symmetrical pattern across what is thought to be a mantle plume. Many of the lavas from the centre of the plume have lower 187Os/188Os ratios than most ocean-island basalts and some extend to subchondritic 187Os/188Os ratios-lower than any yet reported from ocean-island basalts. These low ratios require derivation from a depleted, harzburgitic mantle, consistent with the low-iron signature of the Azores plume. Rhenium-depletion model ages extend to 2.5 Gyr, and we infer that the osmium isotope signature is unlikely to be derived from Iberian subcontinental lithospheric mantle. Instead, we interpret the osmium isotope signature as having a deep origin and infer that it may be recycled, Archaean oceanic mantle lithosphere that has delaminated from its overlying oceanic crust. If correct, our data provide evidence for deep mantle subduction and storage of oceanic mantle lithosphere during the Archaean era.

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

    Lenardic, A.; Kaula, W. M.


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

  12. Triggers and sources of volatile-bearing plumes in the mantle transition zone

    Institute of Scientific and Technical Information of China (English)

    Inna Safonova; Konstantin Litasov; Shigenori Maruyama


    The paper discusses generation of volatile-bearing plumes in the mantle transition zone (MTZ) in terms of mineral-fluid petrology and their related formation of numerous localities of intra-plate bimodal volcanic series in Central and East Asia. The plume generation in the MTZ can be triggered by the tectonic erosion of continental crust at Pacific-type convergent margins and by the presence of water and carbon dioxide in the mantle. Most probable sources of volatiles are the hydrated/carbonated sediments and basalts and serpentinite of oceanic slabs, which can be subducted down to the deep mantle. Tectonic erosion of continental crust supplies crustal material enriched in uranium and thorium into the mantle, which can serve source of heat in the MTZ. The heating in the MTZ induces melting of subducted slabs and continental crust and mantle upwelling, to produce OIB-type mafic and felsic melts, respectively.

  13. Triggers and sources of volatile-bearing plumes in the mantle transition zone

    Directory of Open Access Journals (Sweden)

    Inna Safonova


    Full Text Available The paper discusses generation of volatile-bearing plumes in the mantle transition zone (MTZ in terms of mineral-fluid petrology and their related formation of numerous localities of intra-plate bimodal volcanic series in Central and East Asia. The plume generation in the MTZ can be triggered by the tectonic erosion of continental crust at Pacific-type convergent margins and by the presence of water and carbon dioxide in the mantle. Most probable sources of volatiles are the hydrated/carbonated sediments and basalts and serpentinite of oceanic slabs, which can be subducted down to the deep mantle. Tectonic erosion of continental crust supplies crustal material enriched in uranium and thorium into the mantle, which can serve source of heat in the MTZ. The heating in the MTZ induces melting of subducted slabs and continental crust and mantle upwelling, to produce OIB-type mafic and felsic melts, respectively.

  14. Double layering of a thermochemical plume in the upper mantle beneath Hawaii (United States)

    Ballmer, M. D.; Ito, G.; Wolfe, C. J.; Cadio, C.; Solomon, S. C.


    Volcanism far from plate boundaries has traditionally been explained by "classical" plume theory. Classical plumes are typically described as narrow thermal upwellings that rise through the entire mantle to be deflected into a thin (Iceland, are indeed well explained by near-classical thermal plumes. High-resolution seismic velocity images obtained from the PLUME project support the concept of a deep-rooted mantle plume beneath the Hawaiian hotspot. However, in detail these images challenge traditional concepts inasmuch as they indicate a low-velocity body in the upper mantle that is too thick (~400 km) and asymmetric to be interpreted as a classical pancake. Classical plume theory is, moreover, inconsistent with several geochemical characteristics of Hawaiian magmas, which point to a heterogeneous mantle source involving mafic lithologies such as eclogite and not an exclusively thermal (i.e., isochemical) origin¹. To explore the dynamical and melting behavior of plumes containing a substantial fraction (~15%) of eclogite, we performed three-dimensional numerical simulations of thermochemical convection. Relative to ambient-mantle peridotite, eclogite is intrinsically dense. This density contrast is sensitive to phase changes in the upper mantle; the contrast peaks at 410-300 km and lessens at about 250-190 km depth, where eclogite is subsequently removed by melting. For a plume core with an eclogite content >12%, these effects locally increase the density beyond that of the ambient mantle. Therefore, the upwelling column forms a broad and thick pool at depths of 450-300 km (which we term the deep eclogite pool, or DEP). As the DEP is well supported by the deeper stem of the plume and its non-eclogitic outskirts, it inflates to release a shallow thermal plume. This latter plume sustains hotspot volcanism and feeds a hot shallow pancake that compensates the seafloor swell. Our model predictions reconcile a range of characteristics for Hawaiian volcanism. We find

  15. Past Plate Motions and The Evolution of Earth's Lower Mantle: Relating LLSVPs and Plume Distribution (United States)

    Bull, A. L.; Torsvik, T. H.; Shephard, G. E.


    Seismic tomography elucidates broad, low shear-wave velocity structures in the lower mantle beneath Africa and the central Pacific with uncertain physical and compositional origins. The anomalously slow areas, which cover nearly 50% of the core-mantle boundary, are often referred to as Large Low Shear Velocity Provinces (LLSVPs) due to the reduced velocity of seismic waves passing through them. Several hypotheses have arisen to explain the LLSVPs in the context of large-scale mantle convection. One end-member scenario infers a spatial correlation between LLSVP margins at depth and the reconstructed surface eruption sites of hotspots, kimberlites, and Large Igneous Provinces. Such a correlation has been explained by the preferential triggering of plumes at LLSVP margins by impingement of the subducting lithosphere upon the lower thermal boundary layer at the interface between ambient mantle and the higher density structures. This scenario propounds that Earth's plate motion history plays a controlling role in plume development, and that the location, geometry and morphology of plumes may be influenced by the movement of subducting slabs. Here, we investigate what is necessary to create such a pattern of plume distribution in relation to LLSVPs. We consider what effect past plate motions may have had on the evolution of Earth's lower mantle, and discuss the development of mantle plumes in terms of subduction dynamics. We integrate plate tectonic histories and numerical models of mantle convection to investigate the role that subduction history plays in the development and evolution of plumes in the presence of LLSVPs. To test whether an interaction exists between the surface location of subduction and plume eruption sites, and if so, to what degree over time, we apply varying shifts to the absolute reference frame of the plate reconstruction. With this method, we are able to change the location of subduction at the surface and thus the global flow field. This in turn

  16. Tharsis Formation by Chemical Plume Due to Giant Impact Event (United States)

    Fleck, J.; Weeraratne, D. S.; Olson, P.


    Tharsis formed early in the history of Mars, likely during the Noachian but later than the hemispheric crustal dichotomy that it partially overprints (Johnson and Phillips, 2005; Solomon et al., 2005; Wenzel et al., 2004). It has been suggested that the crustal dichotomy may have been formed by a giant impact (Andrews-Hanna et al., 2008; Marinova et al., 2008; Nimmo et al., 2008). Several models have been proposed to explain a localized orogeny, but predict multiple, evenly-spaced plumes or have instability growth and rise times which are longer than Tharsis formation. We use fluid dynamic experiments to model the differentiation process during Mars accretion using low viscosity glucose syrup solutions and an emulsion of liquid gallium for the metal-rich magma ocean and a high viscosity glucose syrup for the mantle. Our experiments demonstrate the formation of metal-silicate diapirs from metal emulsion drops that form a pond at the base of the magma ocean. The diapirs descend through the underlying mantle with trailing conduit of low viscosity silicate material. The silicate material is buoyant and eventually ascends back through the conduit. Remaining emulsion drops that do not adhere with the diapir fall through the conduit, forcing the buoyant molten silicate material to exit the conduit laterally and ascend along a new trajectory. The time elapsed between diapir formation and ascent of the chemical plume in experiments scales with the time between the formation of the crustal dichotomy on Mars and the formation of Tharsis. Our model offers an explanation for the rapid formation of Tharsis on the edge of the crustal dichotomy via a single large upwelling event followed by smaller upwellings producing and the late stages of effusive volcanism observed in the Tharsis region.

  17. The High Arctic Large Igneous Province Mantle Plume caused uplift of Arctic Canada (United States)

    Galloway, Jennifer; Ernst, Richard; Hadlari, Thomas


    The Sverdrup Basin is an east-west-trending extensional sedimentary basin underlying the northern Canadian Arctic Archipelago. The tectonic history of the basin began with Carboniferous-Early Permian rifting followed by thermal subsidence with minor tectonism. Tectonic activity rejuvenated in the Hauterivian-Aptian by renewed rifting and extension. Strata were deformed by diapiric structures that developed during episodic flow of Carboniferous evaporites during the Mesozoic and the basin contains igneous components associated with the High Arctic Large Igneous Province (HALIP). HALIP was a widespread event emplaced in multiple pulses spanning ca. 180 to 80 Ma, with igneous rocks on Svalbard, Franz Josef Island, New Siberian Islands, and also in the Sverdrup Basin on Ellef Ringnes, Axel Heiberg, and Ellesmere islands. Broadly contemporaneous igneous activity across this broad Arctic region along with a reconstructed giant radiating dyke swarm suggests that HALIP is a manifestation of large mantle plume activity probably centred near the Alpha Ridge. Significant surface uplift associated with the rise of a mantle plume is predicted to start ~10-20 my prior to the generation of flood basalt magmatism and to vary in shape and size subsequently throughout the LIP event (1,2,3) Initial uplift is due to dynamical support associated with the top of the ascending plume reaching a depth of about 1000 km, and with continued ascent the uplift topography broadens. Additional effects (erosion of the ductile lithosphere and thermal expansion caused by longer-term heating of the mechanical lithosphere) also affect the shape of the uplift. Topographic uplift can be between 1 to 4 km depending on various factors and may be followed by subsidence as the plume head decays or become permanent due to magmatic underplating. In the High Arctic, field and geochronological data from HALIP relevant to the timing of uplift, deformation, and volcanism are few. Here we present new evidence

  18. The mantle transition zone beneath the Afar Depression and adjacent regions: implications for mantle plumes and hydration (United States)

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


    The Afar Depression and its adjacent areas are underlain by an upper mantle marked by some of the world's largest negative velocity anomalies, which are frequently attributed to the thermal influences of a lower-mantle plume. In spite of numerous studies, however, the existence of a plume beneath the area remains enigmatic, partially due to inadequate quantities of broad-band seismic data and the limited vertical resolution at the mantle transition zone (MTZ) depth of the techniques employed by previous investigations. In this study, we use an unprecedented quantity (over 14 500) of P-to-S receiver functions (RFs) recorded by 139 stations from 12 networks to image the 410 and 660 km discontinuities and map the spatial variation of the thickness of the MTZ. Non-linear stacking of the RFs under a 1-D velocity model shows robust P-to-S conversions from both discontinuities, and their apparent depths indicate the presence of an upper-mantle low-velocity zone beneath the entire study area. The Afar Depression and the northern Main Ethiopian Rift are characterized by an apparent 40-60 km depression of both MTZ discontinuities and a normal MTZ thickness. The simplest and most probable interpretation of these observations is that the apparent depressions are solely caused by velocity perturbations in the upper mantle and not by deeper processes causing temperature or hydration anomalies within the MTZ. Thickening of the MTZ on the order of 15 km beneath the southern Arabian Plate, southern Red Sea and western Gulf of Aden, which comprise the southward extension of the Afro-Arabian Dome, could reflect long-term hydration of the MTZ. A 20 km thinning of the MTZ beneath the western Ethiopian Plateau is observed and interpreted as evidence for a possible mantle plume stem originating from the lower mantle.

  19. Identification of mantle plumes in the Emeishan Large Igneous Province

    Institute of Scientific and Technical Information of China (English)

    Yi-Gang Xu; Jifeng Xu; Yue-Jun Wang; Bin He; Xiaolong Huang; Zhenyu Luo; Sun-Lin Chung; Long Xiao; Dan Zhu; Hui Shao; Wei-Ming Fan


    @@ The plume hypothesis has been recently challengedlargely because some fundamental aspects predicted bythe modeling of plumes are found to be lacking in someclassic hotspot regions. This review paper summarizesrecent achievements made in the late Permian Emeishan continental flood basalt province in southwest China.

  20. Reconstructing the Cenozoic evolution of the mantle: Implications for mantle plume dynamics under the Pacific and Indian plates (United States)

    Glišović, Petar; Forte, Alessandro M.


    The lack of knowledge of the initial thermal state of the mantle in the geological past is an outstanding problem in mantle convection. The resolution of this problem also requires the modelling of 3-D mantle evolution that yields maximum consistency with a wide suite of geophysical constraints. Quantifying the robustness of the reconstructed thermal evolution is another major concern. To solve and estimate the robustness of the time-reversed (inverse) problem of mantle convection, we analyse two different numerical techniques: the quasi-reversible (QRV) and the backward advection (BAD) methods. Our investigation extends over the 65 Myr interval encompassing the Cenozoic era using a pseudo-spectral solution for compressible-flow thermal convection in 3-D spherical geometry. We find that the two dominant issues for solving the inverse problem of mantle convection are the choice of horizontally-averaged temperature (i.e., geotherm) and mechanical surface boundary conditions. We find, in particular, that the inclusion of thermal boundary layers that yield Earth-like heat flux at the top and bottom of the mantle has a critical impact on the reconstruction of mantle evolution. We have developed a new regularisation scheme for the QRV method using a time-dependent regularisation function. This revised implementation of the QRV method delivers time-dependent reconstructions of mantle heterogeneity that reveal: (1) the stability of Pacific and African ‘large low shear velocity provinces’ (LLSVP) over the last 65 Myr; (2) strong upward deflections of the CMB topography at 65 Ma beneath: the North Atlantic, the south-central Pacific, the East Pacific Rise (EPR) and the eastern Antarctica; (3) an anchored deep-mantle plume ascending directly under the EPR (Easter and Pitcairn hotspots) throughout the Cenozoic era; and (4) the appearance of the transient Reunion plume head beneath the western edge of the Deccan Plateau at 65 Ma. Our reconstructions of Cenozoic mantle

  1. The LIP-OIB transitional phase in the Galapagos mantle plume (United States)

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


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

  2. Triggers and sources of volatile-bearing plumes in the mantle transition zone


    Inna Safonova; Konstantin Litasov; Shigenori Maruyama


    The paper discusses generation of volatile-bearing plumes in the mantle transition zone (MTZ) in terms of mineral-fluid petrology and their related formation of numerous localities of intra-plate bimodal volcanic series in Central and East Asia. The plume generation in the MTZ can be triggered by the tectonic erosion of continental crust at Pacific-type convergent margins and by the presence of water and carbon dioxide in the mantle. Most probable sources of volatiles are the hydrated/carbona...

  3. Upper- and mid-mantle interaction between the Samoan plume and the Tonga–Kermadec slabs (United States)

    Chang, Sung-Joon; Ferreira, Ana M. G.; Faccenda, Manuele


    Mantle plumes are thought to play a key role in transferring heat from the core–mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topography. However, the active role of mantle plumes on subducting slabs remains poorly understood. Here we show that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3D anisotropic tomography images and 3D petrological-thermo-mechanical models, which self-consistently explain several unique features of the Fiji–Tonga region. We identify four possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab (VSH>VSV) with thermo-mechanical calculations. PMID:26924190

  4. Upper- and mid-mantle interaction between the Samoan plume and the Tonga-Kermadec slabs (United States)

    Chang, Sung-Joon; Ferreira, Ana M. G.; Faccenda, Manuele


    Mantle plumes are thought to play a key role in transferring heat from the core-mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topography. However, the active role of mantle plumes on subducting slabs remains poorly understood. Here we show that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3D anisotropic tomography images and 3D petrological-thermo-mechanical models, which self-consistently explain several unique features of the Fiji-Tonga region. We identify four possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab (VSH>VSV) with thermo-mechanical calculations.

  5. Upper- and mid-mantle interaction between the Samoan plume and the Tonga-Kermadec slabs. (United States)

    Chang, Sung-Joon; Ferreira, Ana M G; Faccenda, Manuele


    Mantle plumes are thought to play a key role in transferring heat from the core-mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topography. However, the active role of mantle plumes on subducting slabs remains poorly understood. Here we show that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3D anisotropic tomography images and 3D petrological-thermo-mechanical models, which self-consistently explain several unique features of the Fiji-Tonga region. We identify four possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab (V(SH)>V(SV)) with thermo-mechanical calculations.

  6. Accumulation of 'anti-continent' at the base of the mantle and its recycling in mantle plumes (United States)

    Tatsumi, Yoshiyuki; Suzuki, Toshihiro; Ozawa, Haruka; Hirose, Kei; Hanyu, Takeshi; Ohishi, Yasuo


    The continental crust is a unique reservoir of light elements in the solid Earth; it possesses an intermediate composition and is believed to have been created principally along volcanic arcs, which are major sites of terrestrial andesitic magmatism. Mantle-derived arc magmas are, however, generally mafic or basaltic. A simple mechanism to overcome this apparent dilemma and generate andesitic melts in such a setting is through the partial remelting of an initial mafic arc crust by heat supplied from underplating basaltic magmas. An antithesis to the formation of continental crust in this way should be the production of refractory melting residue, here referred to as 'anti-continent'. This anti-continent is likely to detach from arc crust as a result of a density inversion and descend into the upper mantle. High-pressure experiments demonstrate that sinking anti-continent is, in contrast to the subducting oceanic crust, always denser than the surrounding mantle, suggesting that it penetrates through the upper-lower mantle boundary, without stagnation, and accumulates at the base of the mantle to form a 200-400 km thick mass known as the D″ layer. Geochemical modeling provides further evidence that this accumulating anti-continent contributes to a deep-seated hotspot source. Therefore, through complementary processes, Earth creates buoyant continents and dense anti-continents at the top and the base of the mantle, respectively, and has recycled portions of anti-continent in mantle plumes.

  7. Evidence from Sardinian basalt geochemistry for recycling of plume heads into the Earth's mantle. (United States)

    Gasperini, D; Blichert-Toft, J; Bosch, D; Del Moro, A; Macera, P; Télouk, P; Albarède, F


    Up to 10 per cent of the ocean floor consists of plateaux--regions of unusually thick oceanic crust thought to be formed by the heads of mantle plumes. Given the ubiquitous presence of recycled oceanic crust in the mantle source of hotspot basalts, it follows that plateau material should also be an important mantle constituent. Here we show that the geochemistry of the Pleistocene basalts from Logudoro, Sardinia, is compatible with the remelting of ancient ocean plateau material that has been recycled into the mantle. The Sr, Nd and Hf isotope compositions of these basalts do not show the signature of pelagic sediments. The basalts' low CaO/Al2O3 and Ce/Pb ratios, their unradiogenic 206Pb and 208Pb, and their Sr, Ba, Eu and Pb excesses indicate that their mantle source contains ancient gabbros formed initially by plagioclase accumulation, typical of plateau material. Also, the high Th/U ratios of the mantle source resemble those of plume magmas. Geochemically, the Logudoro basalts resemble those from Pitcairn Island, which contain the controversial EM-1 component that has been interpreted as arising from a mantle source sprinkled with remains of pelagic sediments. We argue, instead, that the EM-1 source from these two localities is essentially free of sedimentary material, the geochemical characteristics of these lavas being better explained by the presence of recycled oceanic plateaux. The storage of plume heads in the deep mantle through time offers a convenient explanation for the persistence of chemical and mineralogical layering in the mantle.

  8. The role of viscosity contrast on plume structure in laboratory modeling of mantle convection

    CERN Document Server

    Prakash, Vivek N; Arakeri, Jaywant H


    We have conducted laboratory experiments to model important aspects of plumes in mantle convection. We focus on the role of the viscosity ratio U (between the ambient fluid and the plume fluid) in determining the plume structure and dynamics. In our experiments, we are able to capture geophysical convection regimes relevant to mantle convection both for hot spots (when U > 1) and plate-subduction (when U < 1) regimes. The planar laser induced fluorescence (PLIF) technique is used for flow visualization and characterizing the plume structures. The convection is driven by compositional buoyancy generated by the perfusion of lighter fluid across a permeable mesh and the viscosity ratio U is systematically varied over a range from 1/300 to 2500. The planform, near the bottom boundary for U=1, exhibits a well-known dendritic line plume structure. As the value of U is increased, a progressive morphological transition is observed from the dendritic-plume structure to discrete spherical plumes, accompanied with th...

  9. Simple scaling relations in geodynamics:the role of pressure in mantle convection and plume formation

    Institute of Scientific and Technical Information of China (English)

    Don L. Anderson


    Scaling relations are important in extrapolating laboratory experiments to the Earth's mantle. In planetary interiors, compression becomes an important parameter and it is useful to explore scalings that involve volume. I use simple volume scaling relations that allow one to extrapolate laboratory experiments and upper mantle behavior, in a thermodynamically self-consistent way, to predict lower mantle behavior. The relations are similar to the quasi- harmonic approximation. Slabs and plates have characteristic dimensions of hundreds of kilometers and time constants of 100 million years, but the volume scalings predict order of magnitude higher values in the deep mantle. The scaling relations imply that the deep mantle is a sluggish system with ancient features. They imply irreversible chemical stratification and do not favor the plume hypothesis.

  10. Seismic velocity variations beneath central Mongolia: Evidence for upper mantle plumes? (United States)

    Zhang, Fengxue; Wu, Qingju; Grand, Stephen P.; Li, Yonghua; Gao, Mengtan; Demberel, Sodnomsambuu; Ulziibat, Munkhuu; Sukhbaatar, Usnikh


    Central Mongolia is marked by wide spread recent volcanism as well as significant topographic relief even though it is far from any plate tectonic boundaries. The cause of the recent magmatism and topography remains uncertain partially because little is known of the underlying mantle seismic structure due to the lack of seismic instrumentation in the region. From August 2011 through August 2013, 69 broadband seismic stations were deployed in central Mongolia. Teleseismic traveltime residuals were measured using waveform correlation and were inverted to image upper mantle P and S velocity variations. Significant lateral variations in seismic velocity are imaged in the deep upper mantle (100 to 800 km depth). Most significant are two continuous slow anomalies from the deep upper mantle to near the surface. One slow feature has been imaged previously and may be a zone of deep upwelling bringing warm mantle to beneath the Hangay Dome resulting in uplift and magmatism including the active Khanuy Gol and Middle Gobi volcanoes. The second, deep low velocity anomaly is seen in the east from 800 to 150 km depth. The anomaly ends beneath the Gobi Desert that is found to have fast shallow mantle indicating a relatively thick lithosphere. We interpret the second deep slow anomaly as a mantle upwelling that is deflected by the thick Gobi Desert lithosphere to surrounding regions such as the Hentay Mountains to the north. The upwellings are a means of feeding warmer than normal asthenospheric mantle over a widely distributed region beneath Mongolia resulting in distributed volcanic activity and uplift. There is no indication that the upwellings are rooted in the deep lower mantle i.e. classic plumes. We speculate the upwellings may be related to deep subduction of the Pacific and Indian plates and are thus plumes anchored in the upper mantle.

  11. The Kea- and Loa- trends and magma genesis in the Hawaiian mantle plume (United States)

    Ren, Z.; Ingle, S.; Takahashi, E.; Hirano, N.; Hirata, T.; Tatsumi, Y.


    The Hawaiian-Emperor volcanic island and seamount chain has been created by a hot mantle plume located beneath the Pacific lithosphere. The shield volcanoes of the Hawaiian islands are distributed in two curvilinear parallel trends, termed _eKea_Eand _eLoa_E(Jackson et al., 1972). Lavas from these two trends are commonly believed to have different geochemical characteristics (Tatsumoto, 1978; Frey et al., 1994; Hauri, 1996; Lassiter et al., 1996; Abouchami et al., 2005). The Kea- and Loa- geochemical trends within the Hawaiian shield volcanoes have been interpreted to reflect melting above a compositionally concentrically zoned (Hauri, 1996; Lassiter et al., 1996; Kurz et al., 1996; DePaolo et al., 2001) or compositionally left-right asymmetrically zoned mantle plume (Abouchami et al., 2005). In order to evaluate the homogeneity of the mantle plume source sampled by the Kea- and Loa- trends, we analyzed major and trace element compositions of olivine-hosted melt inclusions from Hawaiian shield lavas, using EPMA and Laser ICP-MS. We selected lava samples form submarine Hana Ridge, Haleakala volcano (Kea trend) and submarine exposures of the Makapuu stage, Koolau volcano (Loa trend), respectively. We found both Kea- and Loa-like major and trace element compositions from olivine-hosted melt inclusions in individual, shield-stage Hawaiian volcanoes, even within single rock samples. We infer from these data that although one mantle source component may dominate a single lava flow, the two (or more) mantle source components are consistently represented to some extent in all lavas, regardless of the specific geographic location of the volcano. On the basis of whole rock geochemical characteristics (Ren et al., J. pet., 2004; 2005) combined with the melt inclusion data (Ren et al., 2005, Nature), we propose a Hawaiian mantle plume characterized by more random heterogeneity than would be present in a simple compositionally zoned mantle plume. The geochemical differences in

  12. Successful and Failing plumes in a Heterogeneous Mantle: the Icelandic Case (United States)

    Kumagai, I.; Davaille, A.; Kurita, K.; Stutzmann, E.


    Although Iceland is always cited as an exemple of hot spot volcanism produced by a deep mantle plume, an increasing number of observations cannot be explained by the classical plume model of a mushroom-shaped plume out of a sustained localized heat source. Volcanic episodes with moderate temperature predate the major episode of mafic magma emplacement (~60Ma) containing hot picrite magma with strong rare gas anomalies. Present-day Iceland shows moderate temperatures, a strong rare gas anomaly, and an apparent disconnection between slow seismic anomalies in the upper and lower mantle. Noteworthy, the same mixture of geochemical ingredients are found in Icelandic lavas during its 80 Myr of activity. We present a new experimental study of the more realistic case of thermochemical convective instabilities developping out of a heterogeneous bottom hot thermal boundary layer. Depending on the buoyancy ratio B, two end-member regimes are observed. For large B, a thermal plume develops above the denser layer and only a small amount of denser fluid is entrained in the plume. For small B, the dense layer can be sufficently heated to become buoyant and rise: the thermo-chemical plume is therefore mainly constituted of material from the chemically denser layer. The fate of the heterogeneous material in the plume then depends on time since the instability cools as it ascends. As a result, the core of the plume head, which consists of initially hotter but chemically heavier material, can cool enough to become denser than the ambient fluid before reaching the surface of the tank: the heterogeneous material then sinks back and a new thermal plume with a lower temperature anomaly is generated from the top edge of the heavier collapsing blob. In this "failing-plume" mode, the thermo-chemical plume fails to deliver most of the chemical heterogeneity to the surface. Hence, the thermal and compositional structure of a thermo-chemical plume changes with time and is quite irregular. In

  13. The Elephants' Graveyard: Constraints from Mantle Plumes on the Fate of Subducted Slabs and Implications for the Style of Mantle Convection (United States)

    Lassiter, J. C.


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

  14. Interactions of the Greater Ontong Java mantle plume component with the Osbourn Trough (United States)

    Zhang, Guo-Liang; Li, Chao


    The Ontong Java-Manihiki-Hikurangi plateau (OJMHP) is considered to have originated from a starting mantle plume, and have been rifted apart by two spreading ridges. However, the ages of these spreading ridges and their possible interactions with the presumed mantle plume are unclear. The Manihiki-Hikurangi plateau has been rifted apart by the Osbourn Trough which formed the southwestern Pacific crust to the east of the Tonga-Kermadec trench. Here we report Pb-Hf-Os isotopes of the basaltic crust (Site U1365 of IODP Expedition 329) formed by the Osbourn Trough. Linear regression of Re-Os isotopes results in an age of 103.7 ± 2.3 Ma for Site U1365 basalts, indicating that the Manihiki-Hikurangi plateau was rifted apart by the Osbourn Trough with a spreading rate of ~190 mm/yr. The superfast spreading rate supports the Osbourn as an abandoned segment of the early Pacific spreading ridge, which initially overlapped with the giant starting plume. Moreover, the Pb-Hf isotopes of some of Site U1365 basalts show distinct differences from those of the Pacific mid-ocean ridge basalts, while they are similar to the basalts of the Ontong Java and Manihiki plateaus. We suggest that the OJMHP mantle plume components has been involved by the Osbourn spreading center.

  15. Processes accompanying of mantle plume emplacement into continental lithosphere: Evidence from NW Arabian plate, Western Syria (United States)

    Sharkov, E. V.


    Lower crustal xenoliths occurred in the Middle Cretaceous lamprophyre diatremes in Jabel Ansaria (Western Syria) (Sharkov et al., 1992). They are represented mainly garnet granulites and eclogite-like rocks, which underwent by deformations and retrograde metamorphism, and younger fresh pegmatoid garnet-kaersutite-clinopyroxene (Al-Ti augite) rocks; mantle peridotites are absent in these populations. According to mineralogical geothermobarometers, forming of garnet-granulite suite rocks occurred under pressure 13.5-15.4 kbar (depths 45-54 kn) and temperature 965-1115oC. At the same time, among populations of mantle xenoliths in the Late Cenozoic platobasalts of the region, quite the contrary, lower crustal xenoliths are absent, however, predominated spinel lherzolites (fragments of upper cooled rim of a plume head), derived from the close depths (30-40 km: Sharkov, Bogatikov, 2015). From this follows that ancient continental crust was existed here even in the Middle Cretaceous, but in the Late Cenozoic was removed by extended mantle plume head; at that upper sialic crust was not involved in geomechanic processes, because Precambrian metamorphic rocks survived as a basement for Cambrian to Cenozoic sedimentary cover of Arabian platform. In other words, though cardinal rebuilding of deep-seated structure of the region occurred in the Late Cenozoic but it did not affect on the upper shell of the ancient lithosphere. Because composition of mantle xenolithis in basalts is practically similar worldwide, we suggest that deep-seated processes are analogous also. As emplacement of the mantle plume heads accompanied by powerful basaltic magmatism, very likely that range of lower (mafic) continental crust existence is very convenient for extension of plume heads and their adiabatic melting. If such level, because of whatever reasons, was not reached, melting was limited but appeared excess of volatile matters which led to forming of lamprophyre or even kimberlite.

  16. Laboratory models of three-dimensional mantle flow: Implications on Northwest U.S. volcanism for plume and non-plume sources (Invited) (United States)

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


    We present results from laboratory modeling addressing the question of whether a plume is required for reconciling the existing data sets of the Cascade subduction system in the Northwest U.S. Three-dimensional analog models are used to map the spatial and temporal patterns of subduction-induced upwelling associated with decompression melting. A series of experiments with varied combinations of down-dip, rollback and steepening plate motions, as well as extension in the overriding plate, were run with particle tracking techniques to focus on vertical velocities (e.g. favorable to decompression melting) in the mantle wedge. An overriding plate with varied depth is also incorporated to the model in order to more accurately approximate the lithosphere structure of the Northwest U.S. Glucose syrup, with a temperature dependent viscosity, and a phenolic plate were used to model the upper mantle and subducting plate, respectively. Hydraulic pistons control longitudinal, translational and steepening motions of the slab as a simplified kinematic approach to mimic dynamic experiments. Results show that the strongest vertical velocities occur in response to the onset of trench retreat and extension of the overriding plate, independent of the lithospheric “bottom topography”, with the largest occurring when there is an asymmetric style of extension. Spatial and temporal melt patterns mapped from these upwelling events, in addition to experiments with a buoyant plume source, are compared with the Northwest U.S. volcanism over the last 20 Ma. Preliminary results show non-plume melt patterns initially follow a trench parallel (north/south) orientation, which is progressively distorted trench-normal (east/west) with continued rollback subduction.

  17. Rapid Mantle Ascent Rates Beneath Brazil: Diamond Bullets from a Smoking Plume? (United States)

    Walter, M. J.; Frost, D. J.


    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

  18. RHUM-RUM investigates La Réunion mantle plume from crust to core (United States)

    Sigloch, Karin; Barruol, Guilhem


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

  19. Deep Drilling into a Mantle Plume Volcano: The Hawaii Scientific Drilling Project

    Directory of Open Access Journals (Sweden)

    Donald M. Thomas


    Full Text Available Oceanic volcanoes formed by mantle plumes, such as those of Hawaii and Iceland, strongly influence our views about the deep Earth (Morgan, 1971; Sleep, 2006. These volcanoes are the principal geochemical probe into the deep mantle, a testing ground for understanding mantle convection, plate tectonics and volcanism, and an archive of information on Earth’s magnetic field and lithospheredynamics. Study of the petrology, geochemistry, and structure of oceanic volcanoes has contributed immensely to our present understanding of deep Earth processes, but virtually all of this study has been concentrated on rocks available at the surface. In favorable circumstances, surface exposures penetrate to a depth of a few hundred meters, which is a small fraction of the 10- to 15-kilometer height of Hawaiian volcanoes above the depressed seafloor (Moore, 1987; Watts, 2001.

  20. Regional uplift associated with continental large igneous provinces: The roles of mantle plumes and the lithosphere (United States)

    Saunders, A.D.; Jones, S.M.; Morgan, L.A.; Pierce, K.L.; Widdowson, M.; Xu, Y.G.


    Provinces. In these examples, rifting is not a requirement for onset of LIP magmatism but melting rates are significantly increased when rifting occurs. Models that attempt to explain emplacement of these five LIPs without hot mantle supplied by mantle plumes often have difficulties in explaining the observations of surface uplift, rifting and magmatism. For example, small-scale convection related to craton or rift boundaries (edge-driven convection) cannot easily explain widespread (1000??km scale) transient surface uplift (Emeishan, Deccan, North Atlantic), and upper mantle convection initiated by differential incubation beneath cratons (the hotcell model) is at odds with rapid onset of surface uplift (Emeishan, North Atlantic). The start-up plume concept is still the most parsimonious way of explaining the observations presented here. However, observations of surface uplift cannot directly constrain the depth of origin of the hot mantle in a plume head. The short time interval between onset of transient surface uplift and magmatism in the North Atlantic and Emeishan means that the associated starting plume heads were probably not large (??? 1000??km diameter) roughly spherical diapirs and are likely to have formed narrow (??? 100??km radius) upwelling jets, with hot mantle then spreading rapidly outward within the asthenosphere. In cases where rifting post-dates magmatism (N Atlantic Phase 1) or where the degree of lithospheric extension may not have been great (Siberia), a secondary mechanism of lithospheric thinning, such as gravitational instability or delamination of the lower lithosphere, may be required to allow hot mantle to decompress sufficiently to explain the observed volume of magma with a shallow melting geochemical signature. Any such additional thinning mechanisms are probably a direct consequence of plume head emplacement. ?? 2007 Elsevier B.V. All rights reserved.

  1. Abnormal high surface heat flow caused by the Emeishan mantle plume (United States)

    Jiang, Qiang; Qiu, Nansheng; Zhu, Chuanqing


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

  2. Effect of partial melting on small scale convection atop a mantle plume (United States)

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


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

  3. Geodynamic models of plumes from the margins of large thermo-chemical piles in the Earth's lowermost mantle (United States)

    Steinberger, B. M.; Gassmoeller, R.; Mulyukova, E.


    We present geodynamic models featuring mantle plumes that are almost exclusively created at the margins of large thermo-chemical piles in the lowermost mantle. The models are based on global plate reconstructions since 300 Ma. Sinking subducted slabs not only push a heavy chemical layer ahead, such that dome-shaped structures form, but also push the thermal boundary layer (TBL) toward the chemical domes. At the steep edges it is forced upwards and begins to rise — in the lower part of the mantle as sheets, which then split into individual plumes higher in the mantle. The models explain why Large Igneous Provinces - commonly assumed to be caused by plumes forming in the TBL above the core-mantle boundary (CMB) - and kimberlites during the last few hundred Myr erupted mostly above the margins of the African and Pacific Large Low Shear Velocity Provinces (LLSVPs) of the lowermost mantle, which are probably chemically distinct from and heavier than the overlying mantle. Computations are done with two different codes, one based on spherical harmonic expansion, and CITCOM-S. The latter is combined with a self-consistent thermodynamic material model for basalt, harzburgite, and peridotite, which is used to derive a temperature- and presssure dependent database for parameters like density, thermal expansivity and specific heat. In terms of number and distribution of plumes, results are similar in both cases, but in the latter model, plume conduits are narrower, due to consideration of realistic lateral - in addition to radial - viscosity variations. For the latter case, we quantitatively compare the computed plume locations with actual hotspots and find that the good agreement is very unlikely (probability geometry, we also show results obtained with a 2-D finite element code. These results allow us to assess how much the computed long-term stability of the piles is affected by numerical diffusion. We have also conducted a systematic investigation, which configurations

  4. Hunting for the Tristan mantle plume - An upper mantle tomography around the volcanic island of Tristan da Cunha (United States)

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


    The active volcanic island Tristan da Cunha, located at the southwestern and youngest end of the Walvis Ridge - Tristan/Gough hotspot track, is believed to be the surface expression of a huge thermal mantle anomaly. While several criteria for the diagnosis of a classical hotspot track are met, the Tristan region also shows some peculiarities. Consequently, it is vigorously debated if the active volcanism in this region is the expression of a deep mantle plume, or if it is caused by shallow plate tectonics and the interaction with the nearby Mid-Atlantic Ridge. Because of a lack of geophysical data in the study area, no model or assumption has been completely confirmed. We present the first amphibian P-wave finite-frequency travel time tomography of the Tristan da Cunha region, based on cross-correlated travel time residuals of teleseismic earthquakes recorded by 24 ocean-bottom seismometers. The data can be used to image a low velocity structure southwest of the island. The feature is cylindrical with a radius of ∼100 km down to a depth of 250 km. We relate this structure to the origin of Tristan da Cunha and name it the Tristan conduit. Below 250 km the low velocity structure ramifies into narrow veins, each with a radius of ∼50 km. Furthermore, we imaged a linkage between young seamounts southeast of Tristan da Cunha and the Tristan conduit.

  5. Peridotite xenoliths from Ethiopia: inferences on mantle processes from Plume to Rift settings (United States)

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


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

  6. Geoid anomalies and dynamic topography from convection in cylindrical geometry - Applications to mantle plumes on earth and Venus (United States)

    Kiefer, Walter S.; Hager, Bradford H.


    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.

  7. Mantle plume related dynamic uplift and plate kinematics: The NE Atlantic case with global implications. (United States)

    Skogseid, Jakob; Khabbaz Ghazian, Reza; Lunt, Ian


    At present a pronounced residual depth anomaly (RDA), centred on Iceland, is characterizing the bathymetry of the NE Atlantic region. For the oceanic lithosphere this anomaly represents a 2500 m elevation difference compared to 'normal' oceanic lithosphere. The observed depth anomaly has since Cochran and Talwani (1978) been ascribed to a 200 -300 km thick moderate thermal anomaly beneath the oceanic lithosphere, the existence of which today has been proven by a sizable low velocity zone on seismic tomography data. The sub-lithosphere low velocities are, however, not limited to the oceanic domain, but also underlie the adjacent continental lithosphere, thus causing a similar magnitude anomalous elevation of the continental shelves and landmasses. The thermal anomaly is presumed to relate to the arrival of the Iceland mantle plume demonstrated by excess Paleocene and Early Eocene magmatism and the formation of the North Atlantic Volcanic Province (NAVP), and subsequent volcanic margin formation. The present width of the RDA compares with the size of the regions that experienced excess magmatism during rifting and breakup, which implies that the sub-lithospheric thermally anomalous body was emplaced in Paleocene time, but still resides in the area. This presentation aims to describe the temporal and spatial development of uplift based on combining plate kinematic modeling with models of lithospheric and plume body thickness development through Late Cretaceous-Paleocene extension, and subsequent seafloor spreading. The model prediction of uplift compares well with descriptions of erosional episodes and depositional sequences off Greenland, in the Northern North Sea, off mid-Norway and in the SW Barents Sea, and represents a mechanism that explains the present elevation of East Greenland as well as western Norway. In a global perspective the close correlation between Large Igneous Provinces (LIP's), the arrival of known mantle plumes and formation of volcanic margins

  8. A mantle plume beneath California? The mid-Miocene Lovejoy Flood Basalt, northern California (United States)

    Garrison, N.J.; Busby, C.J.; Gans, P.B.; Putirka, K.; Wagner, D.L.


    The Lovejoy basalt represents the largest eruptive unit identified in California, and its age, volume, and chemistry indicate a genetic affinity with the Columbia River Basalt Group and its associated mantle-plume activity. Recent field mapping, geochemical analyses, and radiometric dating suggest that the Lovejoy basalt erupted during the mid-Miocene from a fissure at Thompson Peak, south of Susanville, California. The Lovejoy flowed through a paleovalley across the northern end of the Sierra Nevada to the Sacramento Valley, a distance of 240 km. Approximately 150 km3 of basalt were erupted over a span of only a few centuries. Our age dates for the Lovejoy basalt cluster are near 15.4 Ma and suggest that it is coeval with the 16.1-15.0 Ma Imnaha and Grande Ronde flows of the Columbia River Basalt Group. Our new mapping and age dating support the interpretation that the Lovejoy basalt erupted in a forearc position relative to the ancestral Cascades arc, in contrast with the Columbia River Basalt Group, which erupted in a backarc position. The arc front shifted trenchward into the Sierran block after 15.4 Ma. However, the Lovejoy basalt appears to be unrelated to volcanism of the predominantly calc-alkaline Cascade arc; instead, the Lovejoy is broadly tholeiitic, with trace-element characteristics similar to the Columbia River Basalt Group. Association of the Lovejoy basalt with mid-Miocene flood basalt volcanism has considerable implications for North American plume dynamics and strengthens the thermal "point source" explanation, as provided by the mantle-plume hypothesis. Alternatives to the plume hypothesis usually call upon lithosphere-scale cracks to control magmatic migrations in the Yellowstone-Columbia River basalt region. However, it is difficult to imagine a lithosphere-scale flaw that crosses Precambrian basement and accreted terranes to reach the Sierra microplate, where the Lovejoy is located. Therefore, we propose that the Lovejoy represents a rapid

  9. Mantle Plume Upwelling Rates: Evidence from U-Series in Young Ocean Island Basalts (United States)

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


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

  10. Interaction of mantle plume heads with the earth's surface and onset of small-scale convection (United States)

    Griffiths, R. W.; Campbell, I. H.


    The interaction of a mantle plume head with the earth's surface was examined by studying the behavior of a spherical blob of a buoyant fluid under the effect of gravity which forces it toward either a rigid horizontal boundary or a free surface. In the experiments, buoyant spheres of diapir fluid having no surface tension and extremely small Reynolds numbers but diameters as large as are practical in the laboratory were injected into wide cylindrical tanks filled with viscous (nu = 149 sq cm/sec) glucose syrup. Experimental results are presented for the thinning and lateral spreading of the bouyant fluid and for the thinning of the squeeze layer for both the case of a rigid, nonslip boundary (a rigid Perspex lid) and that of a free surface. These are compared with similarity scaling laws based on a balance between the buoyancy of the diapir and the viscous stresses in the diapir's surroundings.

  11. Al-in-olivine thermometry evidence for the mantle plume origin of the Emeishan large igneous province (United States)

    Xu, Rong; Liu, Yongsheng


    The Emeishan large igneous province (ELIP) is renowned for its world-class Ni-Cu-(PGE) deposits and its link with the Capitanian mass extinction. The ELIP is generally thought to be associated with a deep mantle plume; however, evidence for such a model has been challenged through geology, geophysics and geochemistry. In many large igneous province settings, olivine-melt equilibrium thermometry has been used to argue for or against the existence of plumes. However, this method involves large uncertainties such as assumptions regarding melt compositions and crystallisation pressures. The Al-in-olivine thermometer avoids these uncertainties and is used here to estimate the temperatures of picrites in the ELIP. The calculated maximum temperature (1440 °C) is significantly ( 250 °C) higher than the Al-in-olivine temperature estimated for the average MORB, thus providing compelling evidence for the existence of thermal mantle plumes in the ELIP.

  12. Constraints on Mantle Plume Melting Conditions in the Martian Mantle Based on Improved Melting Phase Relationships of Olivine-Phyric Shergottite Yamato 980459 (United States)

    Kiefer, Walter S.; Rapp, Jennifer F.; Usui, Tomohiro; Draper, David S.; Filiberto, Justin


    Martian meteorite Yamato 980459 (hereafter Y98) is an olivine-phyric shergottite that has been interpreted as closely approximating a martian mantle melt [1-4], making it an important constraint on adiabatic decompression melting models. It has long been recognized that low pressure melting of the Y98 composition occurs at extremely high temperatures relative to martian basalts (1430 degC at 1 bar), which caused great difficulties in a previous attempt to explain Y98 magma generation via a mantle plume model [2]. However, previous studies of the phase diagram were limited to pressures of 2 GPa and less [2, 5], whereas decompression melting in the present-day martian mantle occurs at pressures of 3-7 GPa, with the shallow boundary of the melt production zone occurring just below the base of the thermal lithosphere [6]. Recent experimental work has now extended our knowledge of the Y98 melting phase relationships to 8 GPa. In light of this improved petrological knowledge, we are therefore reassessing the constraints that Y98 imposes on melting conditions in martian mantle plumes. Two recently discovered olivine- phyric shergottites, Northwest Africa (NWA) 5789 and NWA 6234, may also be primary melts from the martian mantle [7, 8]. However, these latter meteorites have not been the subject of detailed experimental petrology studies, so we focus here on Y98.

  13. Petrological processes in mantle plume heads: Evidence from study of mantle xenoliths in the late Cenozoic alkali Fe-Ti basalts in Western Syria (United States)

    Sharkov, Evgenii


    It is consensus now that within-plate magmatism is considered with ascending of mantle plumes and adiabatic melting of their head. At the same time composition of the plumes' matter and conditions of its adiabatic melting are unclear yet. The major source of objective information about it can be mantle xenoliths in alkali basalts and basanites which represent fragments of material of the plume heads above magma-generation zone. They are not represent material in melting zone, however, carry important information about material of modern mantle plumes, its phase composition and components, involved in melting. Populations of mantle xenoliths in basalts are characterized by surprising sameness in the world and represented by two major types: (1) dominated rocks of ``green'' series, and (2) more rare rocks of ``black'' series, which formed veins in the ``green'' series matrix. It can evidence about common composition of plume material in global scale. In other words, the both series of xenoliths represent two types of material of thermochemical mantle plumes, ascended from core-mantle boundary (Maruyama, 1994; Dobretsov et al., 2001). The same types of xenoliths are found in basalts and basanites of Western Syria (Sharkov et al., 1996). Rocks of ``green'' series are represented by Sp peridotites with cataclastic and protogranular structures and vary in composition from dominated spinel lherzolites to spinel harzburgites and rare spinel pyroxenites (websterites). It is probably evidence about incomplete homogenizing of the plume head matter, where material, underwent by partial melting, adjoins with more fertile material. Such heterogeneity was survived due to quick cooling of upper rim of the plume head in contact with relatively cold lithosphere. Essential role among xenoliths of the ``black'' series play Al-Ti-augite and water-bearing phases like hornblende (kaersutute) and Ti-phlogopite. Rocks of this series are represented by wehrlite, clinopyroxenite, amphibole

  14. Mongolian plateau: Evidence for a late Cenozoic mantle plume under central Asia (United States)

    Windley, Brian F.; Allen, Mark B.


    The 2500 x 700 km Mongolian plateau (average elevation 2000 m) is situated between the Altai orogen and the Siberian craton and occupies much of Mongolia and Transbaikalia in Russia. The plateau is characterized by (1) basin and range topography and two major domes(Hentai, 600 x 300 km, and Hangai, 800 x 550 km), where altitudes reach 3905 m; (2) lithosphere that is thinner than adjacent areas (minimum ˜50 km); (3) elevated heat flow (up to 120 mW/m2); (4) dominantly alkaline basaltic volcanism in the form of cones, lava fields, and volcanic plateaus mostly of Miocene-Quaternary age, and (5) rifts, including Baikal (main evolution in the Pliocene-Quaternary), Tunka (Oligocene-early Miocene), and Hobsogol (Pliocene-Quaternary). Existing models explain these features in terms of diapiric upwelling of a mantle asthenolith below the main rifts and/or as a long-distance effect of the India-Asia collision. We propose that the late Cenozoic uplift of the whole Mongolian plateau and associated rifting, magmatism, high heat flow, and lithospherec thinning are not externally driven by the India-Asia collision, but are the expression of the interaction of a mantle plume with overlying lithosphere. Some rifts link and interact with major strike-slip faults, such as the Bolnai. Such faults may be the major expression of the India-Asia collision in this region.

  15. Helium, heat, and the generation of hydrothermal event plumes at mid-ocean ridges (United States)

    Lupton, John E.; Baker, Edward T.; Massoth, Gary J.


    Hydrothermal event plumes are unique water-column features observed over mid-ocean ridges, presumably generated by the sudden release of large volumes of hot, buoyant fluid. Although the specifics of event plume generation are unknown, event plumes have been attributed to the rapid emptying of a hydrothermal reservoir or to rapid heat extraction from a recently emplaced dike or seafloor lava flows. The chemical and thermal signatures of event plumes as compared to the underlying steady-state plumes offer important clues to the generation of event plumes. Event plumes have low 3He/heat ratios of ˜0.4 × 10-17 mol J-1, similar to vent fluids from mature hydrothermal systems. In contrast, the steady-state plumes found beneath the event plumes have elevated and variable 3He/heat ratios of 2 to 5 × 10-17 mol J-1. Fluids collected directly over fresh lava flows have even higher 3He/heat ratios of 2 to 8 × 10-17 mol J-1, up to 30 times the event plume values. These disparate 3He/heat ratios place strong constraints on models of event plume generation, especially models which rely on heat extraction from seafloor eruptions. Published by Elsevier Science B.V.

  16. Contourite Deposition in the North Atlantic Ocean Moderated By Mantle Plume Activity: Evidence from Seismic Reflection Images (United States)

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


    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.

  17. The effect of plumes and a free surface on mantle dynamics with continents and self-consistent plate tectonics (United States)

    Jain, Charitra; Rozel, Antoine; Tackley, Paul


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

  18. Hot Spots and Mantle Plumes: A Window Into the Deep Earth and a Lesson on How Science Really Works (United States)

    Caplan-Auerbach, J.


    Despite years of discussion, debate and controversy over the causes of ocean island volcanism, most students simply learn that such features form from fixed plumes of hot material rising from the core mantle boundary. Although we know that the Hawaiian plume exhibited substantial southward motion, most introductory geology textbooks still report that hot spots are fixed and that the Hawaiian-Emperor bend reflects a change in plate motion. That mantle plumes are the focus of significant controversy within the scientific community is rarely, if ever, discussed, and alternative models for the formation of intraplate volcanoes are ignored. Students may thus complete their studies without learning about the dynamic debate focused on the existence and formation of mantle plumes. This issue represents an opportunity for students to see how science really works, how new models are constructed, and what distinguishes a hypothesis from a theory. The culminating project in Western Washington University’s Introduction to Geophysics class, a course required for the BS degree in geology, focuses on the hot spot and mantle plume debate. For the first nine weeks of the quarter students learn about general topics in geophysics including plate tectonics, magnetism, seismology, gravity and heat flow. At the end of the course, students break into small research groups with the goal of investigating how geophysics may be used to address three questions: (1) Do ocean island volcanoes form from mantle plumes? (2) Are “hot spots” actually hot? (3) Are hot spots stationary? Each group examines how these questions may be addressed using a specific geophysical tool. In addition to the five topics described above, a sixth group investigates the question of “if not hot spots/mantle plumes, how do ocean island volcanoes form?” Students read the current literature on the topic and present their results to their classmates. Presentations focus on topics such as the use of seismic

  19. The Hawaiian Mantle Plume from Toe to Head along the Northwest Hawaiian Ridge (United States)

    Harrison, L.; Weis, D.; Garcia, M. O.


    The Hawaiian-Emperor (HE) chain records ~82 Myr of volcanism1 with two distinct geochemical and geographical trends, Kea and Loa, identified on the archipelago. The Northwest Hawaiian Ridge (NWHR) includes 51 volcanoes, spanning ~42 Myr between the bend in the HE chain and the Hawaiian Islands (47% of the HE chain2), that has no high-precision isotopic data aside from two volcanoes near the bend1. Only Kea compositions have been observed on Emperor seamounts (>50 Ma)1,3, whereas the Hawaiian Islands (Kea and Loa lavas3,4. We have analyzed 23 samples of shield stage tholeiitic lavas from 13 NWHR volcanoes for Pb isotopes to test if the Loa trend exhibits a persistent presence along the ridge after Diakakuji seamount1. Age corrected 206Pb/204Pb range from 17.870 at Diakakuji to 18.654 at Midway atoll. The most enriched Loa isotopic compositions are erupted at Diakakuji (comparable to Lanai), and Mokumanamana, West Nihoa, and Nihoa have isotopic compositions similar to Mauna Loa. These observations suggest an ephemeral presence of the Loa geochemical trend along the NWHR. When shield-stage lavas of each Hawaiian volcano is averaged, NWHR volcanoes shows the most and least radiogenic Pb of the entire HE dataset: Diakakuji (0.9703) and Midway (0.9247). The NWHR exhibits the most geochemically extreme lava compositions along a region where many geophysical parameters (volcanic propagation rate, magmatic flux, mantle potential temperature) were changing significantly2,5. At a broader scale, correlation between radiogenic Pb and magmatic flux suggests source composition may control some of these changes, and help explain why the Hawaiian mantle plume seems to be strengthening5 rather than waning like classic plumes and LIPs. 1Regelous et al., 2003, J. Pet., 44, 1, 113-140. 2Garcia et al., 2015, GSA Sp. Pap. 511. 3Tanaka et al., 2008, EPSL, 265, 450-465. 4Weis et al., 2011, Nat. Geosci., 4, 831-838. 5Vidal & Bonneville, 2004, J. Geophy. Res., 109.

  20. Continental Break-up Above A Mantle Plume: Opening of The Southern Red Sea (United States)

    Ebinger, C.; Eagles, G.; Elders, C.; Gloaguen, R.; McClay, K.; Tiberi, C.; Wolfenden, E.

    Initial rifting in the Red Sea occurred concurrent with, or soon after flood basaltic mag- matism at~31 Ma in the Ethiopia-Yemen plume province. Yet, the development of the ca. 400 km-wide extensional province of the southern Red Sea between 31 Ma and the onset of seafloor spreading at ~4 Ma has been poorly understood, in large part owing to inaccessibility in the Afar depression. The Afar depression is a diffuse extensional province marking a triple point zone between plate boundaries in the Red Sea (Arabia Nubia), the Gulf of Aden (Arabia Somalia); and the Main Ethiopian Rift (Somalia Nu- bia). Complicating this setting, the Danakil horst is a microplate lying between oceanic provinces in the southernmost Red Sea and incipient seafloor spreading in the northern Afar depression. We have integrated exploration seismic, gravity, well, and magnetic data from offshore regions with remote sensing, geological and geophysical data from Ethiopia, Eritrea, and Yemen to evaluate models for continental break-up above mantle plumes. Plate kinematic reconstructions using a pole of rotation within the error ellipse of the Chu and Gordon (1999) pole predict real features in remote sensing and gravity data; these reconstructions provide a general framework for our interpretations. Field and geochronology studies along the western margin of Afar show a southward prop- agation of rifting since about 25 Ma when extension commenced offshore Red Sea and in Yemen. We also see an eastward migration of strain from the western border fault to narrow zones of primarily basaltic magmatism since mid-Miocene time. These magmatic sequences, where not onlapped by Pliocene-Recent sedimentary strata, dip steeply seaward and define a regional eastward flexure into transitional oceanic crust, as suggested by gravity models constrained by existing seismic data. Our synthesis suggests that the southern Afar depression, assumed to be most proximal to the plume, was the site of incipient seafloor

  1. Project Hotspot - The Snake River Scientific Drilling Project - Investigating the Interactions of Mantle Plumes and Continental Lithosphere (United States)

    Shervais, J. W.


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

  2. Tracking the Tristan-Gough Mantle Plume Using Discrete Chains of Intraplate Volcanic Centers Buried in the Walvis Ridge (United States)

    O'Connor, John; Jokat, Wilfried; Wijbrans, Jan


    Explanations for hotspot trails range from deep mantle plumes rising from the core-mantle boundary (CMB) to shallow plate cracking. Such mechanisms cannot explain uniquely the scattered hotspot trails distributed across a 2,000-km-wide swell in the sea floor of the southeast Atlantic Ocean. While these hotspot trails formed synchronously, in a pattern consistent with movement of the African Plate over plumes rising from the edge of the African LLSVP, their distribution is controlled by the interplay between plumes and the motion and structure of the African Plate (O'Connor et al. 2012). A significant challenge is to establish how the vigor and flow of hotspot material to the mid-ocean ridge constructed the Walvis Ridge. 40Ar/39Ar stratigraphy for three sites across the central Walvis Ridge sampled by Ocean Drilling (DSDP Leg 74) (Rohde et al., 2013; O'Connor & Jokat 2015a) indicates an apparent inverse relation between the volume flux of hotspot volcanism and the distance between the mid-ocean ridge and the Tristan-Gough hotspot. Moreover, since ˜93 Ma the geometry and motion of the mid-ocean ridge determined where hotspot material was channeled to the plate surface to build the Walvis Ridge. Interplay between hotspot flow, and the changing geometry of the mid-ocean ridge as it migrated relative to the Tristan-Gough hotspot, might explain much of the age and morphology of the Walvis Ridge. Thus, tracking the location of the Tristan-Gough plume might not be practicable if most of the complex morphology of the massive Walvis Ridge is related to the proximity of the South Atlantic mid-ocean ridge. But 40Ar/39Ar basement ages for the Tristan-Gough hotspot track (Rohde et al., 2013; O'Connor & Jokat 2015b), together with information about morphology and crustal structure from new swath maps and seismic profiles, suggest that separated age-progressive intraplate segments track the location of the Tristan-Gough mantle plume. The apparent continuity of the inferred age

  3. Boron isotopes reveal multiple metasomatic events in the mantle beneath the eastern North China Craton (United States)

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


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

  4. Heat and mass transfer in the mushroom-shaped head of mantle plume

    Directory of Open Access Journals (Sweden)

    Kirdyashkin Anatoly


    Full Text Available The results of experimental and theoretical modeling of free-convection flows in the melt of the plume conduit and in the mushroom-shaped head are presented. It was shown that the plumes with the mushroom-shaped heads can be responsible for the batholith formation. The main parameters of such plumes are estimated.

  5. Petrology, Mineralogy and Geochemistry of the Emeishan Continental Flood Basalts, SW China:Evidence for Activity of Mantle Plumes

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhaochong; HAO Yanli; WANG Fusheng; John J. MAHONEY


    Electronic microprobe analyses for olivine, clinopyroxene and Cr-spinel in picrites, which we have discovered recently in the Emeishan continental flood basalt province (ECFBP), show that the olivine is rich in Mg, and that Cr-spinel is rich in Cr. Based on the olivine-melt equilibrium, the primary parental melt compositions are calculated. The high-Mg olivine-hosted picrite can be regarded as parental melt. Thus, the melting temperature and pressure are estimated:T=1600℃ and P=4.5 GPa. It suggests that the picrites are connected with the activity of mantle plumes. Their major element composition is comparable to many other CFBs by their high Fe8, (CaO/Al2O3)8 and low Nas, indicating a high pressure. All rocks display a similar chondrite-normalized REE patterns, i.e., enrichment of LREE, relative depletion of HFSE and absence of negative Nb and Ta but depletion in P and K. Some incompatible element ratios, such as La/Ta, La/Sm, (La/Nb)pM, (Th/Ta)pM, are in a limited range, show that they were derived from the mantle plume, and there was no or little crustal contamination during magma ascent en route to the surface. They were generated by 7% partial melting of garnet peridotite. The axis of the plume might be located beneath Lijiang Town, Yunnan province.

  6. Metallogenic Series Related to Permian Mafic Complex in North Xinjiang: Post-collisional Stage or Mantle Plume Result?

    Institute of Scientific and Technical Information of China (English)

    WANG Yuwang; WANG Jingbin; WANG Lijuan; LONG Lingli


    There are four deposit types related to a Permian mafic complex in northern Xinjiang, i.e.,copper-nickel sulfide deposit, vanadic titanomagnetite deposit, magnetite (-cobalt) deposit and Cu-Ni-VTiFe composite deposit. The deposits are distributed spanning tectonic units with dose andconsecutive metallogenic ages. A transitional deposit type can occur among the end-member deposits.Trace elements of host rocks show that they can derive from similar source area. Hence, theyconstitute a particular metallogenic series related to a mafic-ultramafic complex that is also a symbolseries of the post-collisional stage of the Central Asia Metallogenic Province (CAMP). Themetallogenic ages of the series are between 260 Ma and 300 Ma throughout the Permian. Unlikemineralization from a mantle plume, the metallogenic period of this series spans at least 40 Ma.Compared with related deposits of the Emeishan mantle plume, the North Xinjiang series has asimilar ore-forming element assemblage but has preferably developed Cu-Ni sulfide deposits ratherthan vanadic titanomagnetite deposits. In concomitance with this series, North Xinjiang area hasdeveloped a set of syntectonic Au-Cu-Mo metailogenic series related to a felsic volcanic-intrusivecomplex, which might indicate that there is no direct relationship with mantle plume activity. Fromearly to late, i.e., the sequence of copper-nickel sulfide to magnetite (-cobalt) to vanadictitanomagnetite deposit, the host rock series evolves from mafic-ultramafic and tholeiite series tomafic and alkalic series, the ∑REE content tends to increase with increasing of REE fractionation, andsome of the trace elements (particularly LIL) also show an increasing tendency. The aboveevolutionary regularity possibly reflects a course where the magma source deepens and thermalinterface moves down, energy gradually exhausts, and neo-continentai crust forming in the post-collision stage tends to stabilize.

  7. Isotopic (Pb, Sr, Nd, C, O) evidence for plume-related sampling of an ancient, depleted mantle reservoir (United States)

    Chen, Wei; Simonetti, Antonio


    The exact mantle source for carbonatite melts remains highly controversial. Despite their predominant occurrence within continental (lithospheric) domains, the radiogenic isotope data from young (oceanic island basalts (OIBs). This feature suggests an intimate petrogenetic relationship with asthenospheric mantle. New Pb, Sr, C, and O isotopic data are reported here for constituent minerals from the Oka carbonatite complex, which is associated with the Cretaceous Monteregian Igneous Province (MIP), northeastern North America. The Pb isotope data define linear arrays in Pb-Pb isotope diagrams, with the corresponding Sr isotope ratios being highly variable (0.70314-0.70343); both these features are consistent with open system behavior involving at least three distinct mantle reservoirs. Compared to the isotope composition of known mantle sources for OIBs and carbonatite occurrences worldwide, the least radiogenic 207Pb/204Pb (14.96 ± 0.07) and 208Pb/204Pb (37.29 ± 0.15) isotopic compositions relative to their corresponding 206Pb/204Pb ratios (18.86 ± 0.08) reported here are distinct, and indicate the involvement of an ancient depleted mantle (ADM) source. The extremely unradiogenic Pb isotope compositions necessitate U/Pb fractionation early in Earth's history (prior to 4.0 Ga ago) and growth via a multi-stage Pb evolution model. The combined stable (C and O) and radiogenic isotopic compositions effectively rule out crustal/lithosphere contamination during the petrogenetic history of the Oka complex. Instead, the isotopic variations reported here most likely result from the mixing of discrete, small volume partial melts derived from a heterogeneous plume source characterized by a mixed HIMU-EM1-ADM signature.

  8. On the relationship between tectonic plates and thermal mantle plume morphology (United States)

    Lenardic, A.; Kaula, W. M.


    Models incorporating plate-like behavior, i.e., near uniform surface velocity and deformation concentrated at plate boundaries, into a convective system, heated by a mix of internal and basal heating and allowing for temperature dependent viscosity, were constructed and compared to similar models not possessing plate-like behavior. The simplified numerical models are used to explore how plate-like behavior in a convective system can effect the lower boundary layer from which thermal plumes form. A principal conclusion is that plate-like behavior can significantly increase the temperature drop across the lower thermal boundary layer. This temperature drop affects the morphology of plumes by determining the viscosity drop across the boundary layer. Model results suggest that plumes on planets possessing plate-like behavior, e.g., the Earth, may differ in morphologic type from plumes on planets not possessing plate-like behavior, e.g., Venus and Mars.

  9. Osmium isotope compositions of detrital Os-rich alloys from the Rhine River provide evidence for a global late Mesoproterozoic mantle depletion event (United States)

    Dijkstra, Arjan H.; Dale, Christopher W.; Oberthür, Thomas; Nowell, Geoffrey M.; Graham Pearson, D.


    We report osmium isotopic compositions for 297 mantle-derived detrital Ru-Os-Ir alloy grains found in gold and platinum-group mineral bearing placers of the Rhine River. These alloys were likely formed as a result of high degree melting in the convective mantle and derived from residual Paleozoic mantle peridotites in the Alps of Central Europe that were accreted as part of a collage of Gondwana-derived 'Armorican' terranes before the Variscan Orogeny. The 187Os/188Os isotope ratios of the Os-rich alloys show a wide distribution, with two modes at 0.1244 and 0.1205. These two modes correspond to rhenium depletion ages, interpreted to correspond with episodes of high-degree mantle melting, at ∼0.5 and ∼1.1 Ga. The data confirm the ability of the oceanic mantle to preserve evidence of ancient melting events. Our new data, in combination with published data on Os-rich alloys from the Urals and Tasmania and with data for abyssal peridotites, indicate a geographically widespread record of a major global Late Mesoproterozoic (1.0-1.2 Ga) high-degree melting event in Paleozoic oceanic mantle rocks. This model age peak is essentially absent from the crustal record of Central-Western Europe, but does coincide with the apparent peak in global continental crust zircon ages at this time. Thus, high-degree mantle melting peaking in the 1.0-1.2 Ga interval may have affected a large part of Earth's mantle. This interval occurred during a period of relative super-continental stability, which may have been accompanied in the oceanic realm by rapid seafloor spreading and extensive subduction, and by unusually high activity of mantle plumes forming two active mantle superswells.

  10. Geochemistry of Two Types of Basalts in the Emeishan Basaltic Province: Evidence for Mantle Plume-Lithosphere Interaction

    Institute of Scientific and Technical Information of China (English)

    张招崇; 王福生


    Based on the temporal-spatial distribution and geochemical characteristics, the Emeishan basalts can be divided into two types: high-P2O-TiO2 basalt (HPT) and low-P2O5-TiO2 basalt (LPT), which differ distinctly in geochemistry: the LPTs are characterized by relatively high abundances of MgO, total FeO and P2O5 and compatible elements (Cr, Ni, Sc), and relatively low contents of moderately compatible elements (V, Y, Yb, Co), LREE and other incompatible elements compared with the HPT. On the diagrams of trace element ratios, they are plotted on an approximately linear mixing line between depleted and enriched mantle sources, suggesting that these two types of basalts resulted from interactions of varying degrees between mantle plume and lithospheric mantle containing such volatile-rich minerals as amphibole and apatite. The source region of the LPT involves a smaller proportion of lithospheric components, while that of the HTP has a larger proportion of lithospheric components. Trachyte is generated by partial melting of the basic igneous rocks at the base of the lower continental crust. Both the two types of magmas underwent certain crystal fractionation and contamination of the lower crust at high-level magma chambers and en route to the surface.

  11. Two decades of Indian research on Ninetyeast Ridge reveal how seafloor spreading and mantle plume activities have shaped the eastern Indian Ocean.

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.

    It is widely accepted that the Ninetyeast Ridge ridge is a product of volcanic trace of the Kerguelen mantle plume (hot spot) on the northward-drifting Indian plate between ~85 and 42 Ma. Studies carried out from the early 1990s to 2013 have brought...

  12. Plume-subduction interaction in southern Central America: Mantle upwelling and slab melting (United States)

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


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

  13. Low velocities in the oceanic upper mantle and their relation to plumes: insights from SEM-based waveform tomography (United States)

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


    into several vertically coherent "conduits", the most prominent under Hawaii and the Pacific superswell, where they appear to be rooted in the lower mantle. These conduits have complex shapes, in particular, the one associated with Hawaii undulates as it "rises", and is deflected towards the ridge as it reaches the bottom of the "fingering" layer. Individual hotspots do not lie immediately above the conduits but in their general vicinity. Nor are the fingers always associated with prominent hotspots. This morphology in the top 400 km of the oceanic mantle suggests the presence of a complex dynamic interplay between plate-driven flow just below the lithosphere, return flow directed toward the ridges, and influx from the deep plume conduits.

  14. Plasma observations during the Mars atmospheric "plume" event of March-April 2012

    CERN Document Server

    Andrews, D J; Edberg, N J T; Gurnett, D A; Hall, B E S; Holmström, M; Lester, M; Morgan, D D; Opgenoorth, H J; Ramstad, R; Sanchez-Cano, B; Way, M; Witasse, O


    We present initial analysis and conclusions from plasma observations made during the reported "Mars plume event" of March - April 2012. During this period, multiple independent amateur observers detected a localized, high-altitude "plume" over the Martian dawn terminator [Sanchez-Lavega et al., Nature, 2015, doi:10.1038/nature14162], the cause of which remains to be explained. The estimated brightness of the plume exceeds that expected for auroral emissions, and its projected altitude greatly exceeds that at which clouds are expected to form. We report on in-situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by Mars Express, obtained over the same surface region, but at the opposing terminator. Measurements in the ionosphere at the corresponding location frequently show a disturbed structure, though this is not atypical for such regions with intense crustal magnetic fields. We tentatively conclude that the formation and/or transport of this plume to the alt...

  15. Sulfur and lead isotopic evidence of relic Archean sediments in the Pitcairn mantle plume (United States)

    Delavault, Hélène; Chauvel, Catherine; Thomassot, Emilie; Devey, Colin W.; Dazas, Baptiste


    The isotopic diversity of oceanic island basalts (OIB) is usually attributed to the influence, in their sources, of ancient material recycled into the mantle, although the nature, age, and quantities of this material remain controversial. The unradiogenic Pb isotope signature of the enriched mantle I (EM I) source of basalts from, for example, Pitcairn or Walvis Ridge has been variously attributed to recycled pelagic sediments, lower continental crust, or recycled subcontinental lithosphere. Our study helps resolve this debate by showing that Pitcairn lavas contain sulfides whose sulfur isotopic compositions are affected by mass-independent fractionation (S-MIF down to Δ33S = -0.8), something which is thought to have occurred on Earth only before 2.45 Ga, constraining the youngest possible age of the EM I source component. With this independent age constraint and a Monte Carlo refinement modeling of lead isotopes, we place the likely Pitcairn source age at 2.5 Ga to 2.6 Ga. The Pb, Sr, Nd, and Hf isotopic mixing arrays show that the Archean EM I material was poor in trace elements, resembling Archean sediment. After subduction, this Archean sediment apparently remained stored in the deep Earth for billions of years before returning to the surface as Pitcairńs characteristic EM I signature. The presence of negative S-MIF in the deep mantle may also help resolve the problem of an apparent deficit of negative Δ33S anomalies so far found in surface reservoirs.

  16. Garnet-bearing ultramafic rocks from the Dominican Republic: Fossil mantle plume fragments in an ultra high pressure oceanic complex? (United States)

    Gazel, Esteban; Abbott, Richard N.; Draper, Grenville


    Ultra high pressure (UHP) garnet-bearing ultramafic rocks from the Dominican Republic may represent the only known example where such rocks were exhumed at an ocean-ocean convergent plate boundary, and where the protolith crystallized from a UHP magma (> 3.2 GPa, > 1500 °C). This study focuses on the petrology and geochemistry of one of the ultramafic lithologies, the pegmatitic garnet-clinopyroxenite (garnet + clinopyroxene + spinel + corundum + hornblende). Three distinct types of garnet were recognized: Type-1 garnet (low Ca, high Mg) is interpreted as near magmatic (P > 3.2 GPa, > 1500 °C). Type-1‧ garnet (high Ca, low Mg) is interpreted as having formed approximately isochemically from magmatic high-Al clinopyroxene. Type-2 garnet (intermediate Ca, high Mg, and low Fe + Mn) formed together with hornblende as a result of late, low-pressure retrograde hydration. Clinopyroxene is close to diopside-hedenbergite (Mg# ~ 88) and metasomatized by arc-related fluids. Spinel and corundum occur as microinclusions in type-1 and type-1‧ garnets in the only reported natural occurrence of coexisting garnet + spinel + corundum, indicative of very high pressure. Chondrite-normalized REEs (rare earth elements) of the garnets show humped or weakly sinusoidal patterns, typically associated with garnet inclusions in diamond and garnet in kimberlite that crystallized at UHP conditions. These humped to weakly sinusoidal REE patterns developed as the result of interaction with a light REE-enriched metasomatic fluid. Partitioning of REEs between type-1‧ and type-1 garnets is consistent with the former having inherited its REEs from a high-Al clinopyroxene predecessor. The partitioning preserves a record of near-solidus temperatures (~ 1475 °C). Petrology and phase relationships independently suggest near-solidus conditions > 1500 °C (the highest temperature conditions reported in a UHP orogenic setting), providing evidence for an origin in a mantle plume. Therefore, the

  17. What can seafloor fabric tell us about the nature of the 50 Ma plate-mantle event? (United States)

    Müller, R. D.; Matthews, K. J.


    Several different mechanisms have been proposed to account for the 50 Ma plate-mantle event, including India-Eurasia collision, the time dependence of the Reunion plume-push force, the subduction of the Izanagi-Pacific mid-ocean ridge, and transient ridge capture of the Hawaiian plume. We use a recent digital global seafloor tectonic fabric map derived from vertical gravity gradients together with magnetic anomaly identifications to analyse the geometry and timing of Late Cretaceous-Early Cenozoic fracture zone (FZ) bends. Two sets of closely spaced FZ bends in the North Atlantic, Weddell Sea and at the Southwest Indian Ridge between Antarctica and Africa produce an S-shape in the seafloor fabric. The older spreading ridge reorganisation initiated close to 70 Ma, and was completed around 55 Ma. The younger FZ bends are sharper, were initiated approximately 55-49 Ma and completed around 40-42 Ma, after which time spreading returned to its pre-S-bend azimuth. Additionally there is a distinct increase in seafloor roughness at the mid-Atlantic ridge at about 70 Ma reflecting a decrease in spreading rate. Seafloor fabric indicators of plate motion change produced at around 70 Ma coincide with emplacement of the Reunion plume and are restricted to parts of the Atlantic-Indian realm. The Pacific domain appears unaffected by the mechanism that drove plate motion changes in the Atlantic and Indian Oceans at this time. Yet, from ~55-40 Ma Pacific FZ bends and other oceanic and plate margin events are widespread. Along with formation of the younger part of the Atlantic-Indian S-bends, FZ bends and changes in FZ morphology in the northeast Pacific signify a reorientation of the Pacific-Farallon spreading ridge, a northward propagation of the Pacific-Antarctic ridge, increases in spreading rates at the Australia-Pacific ridge and a change in the direction of plate motion, with spreading terminating in the Tasman Sea. And initiation of Izu-Bonin-Mariana subduction. This

  18. Cocos Plate Seamounts offshore NW Costa Rica and SW Nicaragua: Implications for large-scale distribution of Galápagos plume material in the upper mantle (United States)

    Herbrich, Antje; Hoernle, Kaj; Werner, Reinhard; Hauff, Folkmar; Bogaard, Paul v. d.; Garbe-Schönberg, Dieter


    The origin of intraplate volcanism not directly part of a hotspot track, such as diffuse seamount provinces, and the extent of mantle plume influence on the upper mantle remain enigmatic. Here we present new 40Ar/39Ar age data and geochemical (major and trace-element and Sr-Nd-Pb isotopic) data from seamounts on the Cocos Plate presently located offshore of NW Costa Rica and SW Nicaragua. The seamounts (~ 7-24 Ma) require mixing of an enriched ocean island basalt composition, similar to that of the Northern Galápagos Domain, with two depleted components. One of the depleted components is similar to East Pacific Rise normal mid-ocean ridge basalt and the other has more depleted incompatible elements, either reflecting secondary melting of MORB or a depleted Galápagos plume component. Seamounts with ages significantly younger than the ocean crust formed in an intraplate setting and can be explained by northward transport of Galápagos plume material along the base of the Cocos Plate up to 900 km away from the hotspot and 250-500 km north of the Galápagos hotspot track. We propose that melting occurs due to decompression as the mantle upwells to shallower depth as it flows northwards, either due to changes in lithospheric thickness or as a result of upwelling at the edge of a viscous plug of accumulated plume material at the base of the lithosphere. The tholeiitic to alkaline basalt compositions of the Cocos Plate Seamounts compared to the more silica under-saturated compositions of Hawaiian rejuvenated and arch (alkali basalts to nephelinites) lavas are likely to reflect the significant difference in age (< 25 vs ~ 90 Ma) and thus thickness of the lithosphere on which the lavas were erupted.

  19. 峨眉山地幔柱轴部位置的讨论%The Location of the Tail of Emeishan Mantle Plume

    Institute of Scientific and Technical Information of China (English)

    李宏博; 张招崇; 李永生; 汪云峰


    This paper discusses the tail of Emeishan mantle plume and suggests that it locates in Miyi-Yongren area, southern Sichuan-northern Yunnan. On the basis of the classic mantle plume theory, the estimated diameter of Emeishan plume tail was 65 ~ 105km when it reached the upper mantle. Picrite distributions and sedimentary responses showed that the center zone of the Emeishan plume was ca. 260 ~ 300km wide. Eruption and outcropping of flood basalts were constrained by deep-seated faults and paleogeomorphology, which resulted in the concentration of picrite in the west of the Emeishan large igneous province.%本文对峨眉山地幔柱的轴部位置进行了探讨,认为其应在米易—永仁一带.利用经典地幔柱模型,估算出峨眉山地幔柱到达上地幔时轴部直径大约为65 ~ 105km,高温苦橄岩的分布和差异剥蚀程度显示中心区的范围约为260 ~ 300km.深大断裂带、古地貌等因素控制了溢流玄武岩的喷发和展布,使得轴部岩浆的喷发偏于西部,形成了大理-丽江一带的苦橄岩分布较多的现象.

  20. Fortuitous Plasma Observations During the Mars Atmospheric "Plume" Event of March-April 2012 (United States)

    Andrews, David; Barabash, Stas; Edberg, Niklas; Gurnett, Donald; Hall, Ben; Holmström, Mats; Lester, Mark; Opgenoorth, Hermann; Ramstad, Robin; Sanchez-Cano, Beatriz; Way, Michael; Witasse, Olivier; Morgan, David


    We present initial analysis and conclusions from plasma observations made during the reported `Mars Dust plume event' of March - April 2012.During this period, multiple independent amateur observers detected a localized, high-altitude feature over the Martian terminator [Sanchez-Lavega et al., Nature, 2015, doi:10.1038/nature14162], the explanation for which remains incomplete. The brightness of the feature in visible light is too extreme for auroral emissions to explain, despite its occurrence at a location where these have been previously reported. Likewise, the (projected) altitude of the feature is significantly too high to allow for the local formation of clouds. Fortuitously, the orbit of ESA's Mars Express allowed the measurement of ionospheric plasma density and solar wind parameters over the precise location of the plume sighting at multiple points during this interval. Based on these observations, we tentatively conclude that the formation and/or transport of this plume to the altitudes where it was observed was in part the result of a large Coronal Mass Ejection encountering the Martian system. However, while measurements of ionospheric plasma density at the corresponding altitudes indicate a disturbed structure, this is not a-typical of this location over Mars. Finally, we briefly discuss some possible mechanisms that may lead to the formation of this plume.

  1. Extreme dissipation event due to plume collision in a turbulent convection cell

    CERN Document Server

    Schumacher, Joerg


    An extreme dissipation event in the bulk of a closed three-dimensional turbulent convection cell is found to be correlated with a strong reduction of the large-scale circulation flow in the system that happens at the same time as a plume emission event from the bottom plate. The reduction in the large-scale circulation opens the possibility for a nearly frontal collision of down- and upwelling plumes and the generation of a high-amplitude thermal dissipation layer in the bulk. This collision is locally connected to a subsequent high-amplitude energy dissipation event in the form of a strong shear layer. Our analysis illustrates the impact of transitions in the large-scale structures on extreme events at the smallest scales of the turbulence, a direct link that is observed in a flow with boundary layers. We also show that detection of extreme dissipation events which determine the far-tail statistics of the dissipation fields in the bulk requires long-time integrations of the equations of motion over at least ...

  2. Extreme dissipation event due to plume collision in a turbulent convection cell (United States)

    Schumacher, Jörg; Scheel, Janet D.


    An extreme dissipation event in the bulk of a closed three-dimensional turbulent convection cell is found to be correlated with a strong reduction of the large-scale circulation flow in the system that happens at the same time as a plume emission event from the bottom plate. The reduction in the large-scale circulation opens the possibility for a nearly frontal collision of down- and upwelling plumes and the generation of a high-amplitude thermal dissipation layer in the bulk. This collision is locally connected to a subsequent high-amplitude energy dissipation event in the form of a strong shear layer. Our analysis illustrates the impact of transitions in the large-scale structures on extreme events at the smallest scales of the turbulence, a direct link that is observed in a flow with boundary layers. We also show that detection of extreme dissipation events which determine the far-tail statistics of the dissipation fields in the bulk requires long-time integrations of the equations of motion over at least a hundred convective time units.

  3. Plume-derived rare gases in 380 Ma carbonatites from the Kola region (Russia) and the argon isotopic composition in the deep mantle (United States)

    Marty, Bernard; Tolstikhin, Igor; Kamensky, Igor L.; Nivin, Valentin; Balaganskaya, Elena; Zimmermann, Jean-Louis


    In an effort to document the source of the parental melts to carbonatites, we have measured rare gases in 380 Ma carbonatites and associated mineral assemblages from the Kola Peninsula, eastern part of the Baltic shield in Russia. These series were emplaced during widespread Devonian magmatism when several large ultrabasic-alkaline-carbonatite massifs were formed. 4He/ 3He ratios vary from 1×10 6 to 1×10 7 in the bulk He extracted by melting of samples from three localities, including the large Kovdor massif. A comparison of measured abundances of 3He and 4He with those expected from in-situ production revealed a large (up to 10 5 times) excess of 3He, implying a significant contribution from a mantle-derived 3He-bearing fluid. Crushing of these samples allowed extraction of fluids with 4He/ 3He ratios down to 38,000, lower than those of mid-ocean ridge basalts and in the range of 4He/ 3He observed in 3He-rich ocean island basalts (OIBs) related to mantle plumes. 20Ne/ 22Ne up to 12.1±0.2 are higher than the atmospheric value of 9.80, implying the occurrence of primordial (solar-type) neon in the carbonatite source. 20Ne/ 22Ne and 21Ne/ 22Ne ratios display a good correlation, with the regression line close to (slightly to the right of) the Loihi Seamount correlation. Extrapolation of the regression to solar 20Ne/ 22Ne of 13.8 gives a 21Ne/ 22Ne of 0.045 for the plume end-member, well below the mid-ocean ridge basalt (MORB) source (upper mantle) end-member of 0.07. The measured 40Ar/ 36Ar ratios up to 2790 correlate very well with the Ne isotopic ratios, and the best estimate of the 40Ar/ 36Ar ratio of the plume source is within 5000±1000. Although the 3He/ 22Ne ratio in the plume source appears to be comparable to the solar value within a factor of 2, the 22Ne/ 36Ar ratio, computed from Ne-Ar isotope correlation, is two orders of magnitude lower than the solar value. Such difference is unlikely to be due to magmatic fractionation since the observed 4He/ 40Ar

  4. Rare gas isotopes and parent trace elements in ultrabasic-alkaline-carbonatite complexes, Kola Peninsula: identification of lower mantle plume component (United States)

    Tolstikhin, I. N.; Kamensky, I. L.; Marty, B.; Nivin, V. A.; Vetrin, V. R.; Balaganskaya, E. G.; Ikorsky, S. V.; Gannibal, M. A.; Weiss, D.; Verhulst, A.; Demaiffe, D.


    During the Devonian magmatism (370 Ma ago) ∼20 ultrabasic-alkaline-carbonatite complexes (UACC) were formed in the Kola Peninsula (north-east of the Baltic Shield). In order to understand mantle and crust sources and processes having set these complexes, rare gases were studied in ∼300 rocks and mineral separates from 9 UACC, and concentrations of parent Li, K, U, and Th were measured in ∼70 samples. 4He/3He ratios in He released by fusion vary from pure radiogenic values ∼108 down to 6 × 104. The cosmogenic and extraterrestrial sources as well as the radiogenic production are unable to account for the extremely high abundances of 3He, up to 4 × 10-9 cc/g, indicating a mantle-derived fluid in the Kola rocks. In some samples helium extracted by crushing shows quite low 4He/3He = 3 × 104, well below the mean ratio in mid ocean ridge basalts (MORB), (8.9 ± 1.0) × 104, indicating the contribution of 3He-rich plume component. Magnetites are principal carriers of this component. Trapped 3He is extracted from these minerals at high temperatures 1100°C to 1600°C which may correspond to decrepitation or annealing primary fluid inclusions, whereas radiogenic 4He is manly released at a temperature range of 500°C to 1200°C, probably corresponding to activation of 4He sites degraded by U, Th decay. Similar 4He/3He ratios were observed in Oligocene flood basalts from the Ethiopian plume. According to a paleo-plate-tectonic reconstruction, 450 Ma ago the Baltica (including the Kola Peninsula) continent drifted not far from the present-day site of that plume. It appears that both magmatic provinces could relate to one and the same deep-seated mantle source. The neon isotopic compositions confirm the occurrence of a plume component since, within a conventional 20Ne/22Ne versus 21Ne/22Ne diagram, the regression line for Kola samples is indistinguishable from those typical of plumes, such as Loihi (Hawaii). 20Ne/22Ne ratios (up to 12.1) correlate well with 40Ar/36Ar

  5. Interaction of extended mantle plume head with ancient lithosphere: evidence from deep-seated xenoliths in basalts and lamprophyre diatremes in Western Syria (United States)

    Sharkov, Evgenii


    The Middle Cretaceous lamprophyric diatremes of the Jabel Ansaria Ridge contain xenoliths of ancient lower crustal rocks mainly represented by the suite of partly altered garnet granulite and eclogite-like rocks, which were formed at the expense of ferrogabbros and ferroclinopyroxenites most likely in the course of underplating of Fe-Ti basalt. Garnet (Alm26Grs11Py63) megacrysts and coarse-granular garnet-clinopyroxene intergrowths are most likely the varieties of rocks of this series. Garnet megacrysts are represented by large (up to 10 cm in diameter) round "nodules," often molten from the surface. Garnet is usually fractured, and the kelyphite material similar to that in rocks of the eclogite-granulite series occurs in fractures. In addition, we found several intergrowths of garnet with large (up to 3-5 cm in length) crystals of high-Al augite with the low of Ti and Na contents like in rocks of the eclogite-granulite suite. Coarse-grained garnet-clinopyroxene-hornblende rocks with spinel, as well as megacrysts of Al-Ti augite with kaersutite, form the second group in prevalence. This group is close to mantle xenoliths of the "black series" in alkali Fe-Ti basalt worldwide. Kaersutite in these rocks contains gaseous cavities, which provides evidence for the origin of rocks at the expense of a strongly fluidized melt/fluid. In contrast to rocks of the eclogite-granulite series, these rocks did not undergo alteration. Garnet Alm19-26Grs12-13.5Py59-67.5 usually associates with dark opaque spinel. In contrast, the Late Cenozoic plateaubasalts of the region practically do not contain lower crustal xenoliths, whereas xenoliths of mantle spinel lherzolite (fragments of the upper cooled rim of the plume head) are widely abundant. According to data of mineralogical thermobarometry, rocks of the eclogite-granulite suite were formed at 13.5-15.4 kbar (depths of 45-54 km) and 965-1115°C. Rocks of this suite are typical representatives of the continental lower crust

  6. New Rb-Sr mineral ages temporally link plume events with accretion at the margin of Gondwana (United States)

    Flowerdew, M.J.; Daly, J.S.; Riley, T.R.


    Five of six Rb-Sr muscovite mineral isochron ages from the Scotia Metamorphic Complex of the South Orkney Islands, West Antarctica, average 190 ± 4 Ma. The muscovite ages are interpreted to date foliation-formation and thus also accretion and subduction at the Gondwana margin. Coincident picrite and ferropicrite magmatism, indicative of melts from deep-seated depleted mantle, permits a causative link between accretion and the arrival of the Karoo – Ferrar – Chon Aike mantle plume in the Early Jurassic. Three biotite Rb-Sr mineral isochron ages are consistently younger and average 176 ± 5 Ma. The biotite ages may record post-metamorphic cooling or more likely retrogressive metamorphic effects during uplift.

  7. Multiple plume events in the genesis of the peri-Caribbean Cretaceous oceanic plateau province (United States)

    Lapierre, Henriette; Bosch, Delphine; Dupuis, Vincent; Polvé, Mireille; Maury, René C.; Hernandez, Jean; Monié, Patrick; Yeghicheyan, Delphine; Jaillard, Etienne; Tardy, Marc; de Lépinay, Bernard Mercier; Mamberti, Marc; Desmet, Alain; Keller, Francine; Sénebier, François


    The oceanic crust fragments exposed in central America, in north-western South America, and in the Caribbean islands have been considered to represent accreted remnants of the Caribbean-Colombian Oceanic Plateau (CCOP). On the basis of trace element and Nd, Sr, and Pb isotopic compositions we infer that cumulate rocks, basalts, and diabases from coastal Ecuador have a different source than the basalts from the Dominican Republic. The latter suite includes the 86 Ma basalts of the Duarte Complex which are light rare earth element (REE) -enriched and display (relative to normal mid-ocean ridge basalts, NMORB) moderate enrichments in large ion lithophile elements, together with high Nb, Ta, Pb, and low Th contents. Moreover, they exhibit a rather restricted range of Nd and Pb isotopic ratios consistent with their derivation from an ocean island-type mantle source, the composition of which includes the HIMU (high 238U/204Pb) component characteristic of the Galapágos hotspot. In contrast, the 123 Ma Ecuadorian oceanic rocks have flat REE patterns and (relative to NMORB) are depleted in Zr, Hf, Th, and U. Moreover, they show a wide range of Nd and Pb isotopic ratios intermediate between those of ocean island basalts and NMORB. It is unlikely, on geochemical grounds, that the plume source of the Ecuadorian fragments was similar to that of the Galapágos. In addition, because of the NNE motion of the Farallon plate during the Early Cretaceous, the Ecuadorian oceanic plateau fragments could not have been derived from the Galapagos hotspot but were likely formed at a ridge-centered or near-ridge hotspot somewhere in the SE Pacific.

  8. Why is it downhill from Tonopah to Las Vegas?: A case for mantle plume support of the high northern Basin and Range (United States)

    Saltus, R. W.; Thompson, G. A.


    A major, abrupt, southward decline in elevation (˜800 m) with an accompanying increase in Bouguer gravity anomaly (˜80 mGal) crosses a seismically active region of southern Nevada at about 37°N. The steepness of the gravity gradient requires significant crustal density contrast, some of which is probably caused by the plutonic roots of voluminous Tertiary volcanism to the north, but the amplitude of the anomaly requires additional contrast within the mantle. The topographic step probably developed in mid-Miocene time, coincident with the arrival of the starting head of the Yellowstone thermal plume at the base of the lithosphere. A plausible combination of crustal and deep buoyancy sources, related to the heat and melt input of an anomalously hot asthenospheric source, is consistent with gravity, seismic, heat flow, and isotopic observations and explains the origin of the topographic step.

  9. Elastic plate flexure above mantle plumes explains the upstream offset of volcanic activity at la Réunion and Hawaii (United States)

    Gerbault, Muriel; Fontaine, Fabrice; Rabinowicz, Michel; Bystricky, Micha


    Surface volcanism at la Réunion and Hawaii occurs with an offset of 150-180 km upstream to the plume axis with respect to the plate motion. This striking observation raises questions about the forcing of plume-lithosphere thermo-mechanical interactions on melt trajectories beneath these islands. Based on visco-elasto-plastic numerical models handled at kilometric resolution, we propose to explain this offset by the development of compressional stresses at the base of the lithosphere, that result from elastic plate bending above the upward load exerted by the plume head. This horizontal compression adopts a disc shape centered around the plume axis, 20 km thick and 150 km in radius, at 50-70 km depth where the temperature varies from 600°C to 750°C. It lasts for 5 to 10 My in an oceanic plate of age greater than 70 My, a timing that is controlled by the visco-elastic relaxation time at 50-70 km depth. This period of time exceeds the time during which both the Somalian/East-African and Pacific plates drift over the Reunion and Hawaii plumes, respectively, thus rendering this basal compression a persistent feature. It is inferred that the buoyant melts percolating in the plume head pond below this zone of compression and eventually spread laterally until the most compressive principal elastic stresses reverse to the vertical, i.e., 150 km away from the plume head. There, melts propagate through dikes upwards to 35 km depth, where the plate curvature reverses and ambient compression diminishes. This 30-35 km depth may thus host magmatic reservoirs where melts pond, until further differentiation can relaunch ascension up to the surface and form a volcanic edifice. In a second stage, as the volcano grows because of melt accumulation at the top of the plate, the lithosphere is flexed downwards, inducing extra tensile stress at 30-35 km depth and compression at 15 km depth. It implies that now the melts pond at 15 km and form another magmatic reservoir lying just

  10. RHUM-RUM, a Large-Scale Effort to Seismologically Image a Mantle Plume Under the Reunion Hotspot: Experiment Presentation and Initial Results (United States)

    Sigloch, K.; Barruol, G.


    RHUM-RUM is a German-French geophysical experiment based on the seafloor and on islands surrounding the hotspot of La Réunion, western Indian Ocean. Its primary objective is to clarify the presence or absence of a mantle plume beneath the Reunion hotspot, which is thought to have first pierced the surface 65 million years ago with the eruption of the Deccan Traps on India. RHUM-RUM's central component is a one-year deployment (Oct 2012 - Nov 2013) of 57 broadband ocean-bottom seismometers (OBS) and hydrophones on an area of 2000x2000 km2 surrounding the hotspot. All OBS have been successfully recovered. We also have been operating 37 land seismometers on the islands of La Réunion, Mauritius, Rodrigues, southern Seychelles, îles Eparses, and on Madagascar between 2011 and 2014. As the data collection stage is drawing to a close, we discuss data yield and quality with respect to RHUM-RUM's primary purpose (passive seismological imaging through all depth levels of the mantle) and secondary applications ("environmental seismology" in a sparsely instrumented area, e.g., tracking of tropical cyclones). We give an overview of the research questions investigated by the RHUM-RUM group, and present preliminary results.

  11. Plume-Lithosphere Interaction: Geochemical Evidence from Upper Mantle and Lower Crustal Xenoliths from the Kerguelen Islands (United States)


    recrystalized under granulite facies conditions. On the basis of the whole rock major element characteristics and trace element abundance patterns in...from the sub-Gondwanaland lithosphere. On the basis of major and trace element compositions, the granulite xenoliths were found to be originally...under granulite conditions. The Sr, Nd and Os isotopic compositions of the peridotite and granulite xenoliths demonstrate that the Kerguelen plume is

  12. Isotope-geochemical Nd-Sr evidence of Palaeoproterozoic plume magmatism in Fennoscandia and mantle-crust interaction on stages of layered intrusions formation (United States)

    Serov, Pavel; Bayanova, Tamara; Kunakkuzin, Evgeniy; Steshenko, Ekaterina


    characteristic feature is that in most cases, the proportion of mantle component decreases from the central parts of intrusions to their boundary zones. This may indicate a slight degree of contamination of the magma intrusion by crustal material near the contacts with the frame- rocks. Thus, our investigations show that Palaeoproterozoic layered PGE-bearing intrusions in the N-E Fennoscandian Shield were derived from intraplate magmatism. The same Palaeoproterozoic layered intrusions are known on the Fennoscandian Shield, Superior and Wyoming provinces of the world, and according to [Heaman, 1997; Ernst, 2008] they were derived from the mantle plumes which caused the breakup of the oldest Kenorland supercontinent. These studies were supported by the RFBR 15-35-20501.

  13. MORB melting processes beneath the southern Mid-Atlantic Ridge (40-55°S): a role for mantle plume-derived pyroxenite (United States)

    le Roux, P. J.; le Roex, A. P.; Schilling, J.-G.


    Major and selected trace element abundances of MORB dredged from the moderately slow spreading southern MAR (40-55°S), in the vicinity of the Shona and Discovery mantle plumes, are used to constrain their melting conditions. All samples plot to high Fe8 relative to the Na8-Fe8 global trend, the high Fe8 of N-MORB in particular being anomalous. Shona-influenced MORB plot at lower Na8 and towards higher Fe8 values along the global trend than associated N-MORB, consistent with deeper initiation of melting. Discovery-influenced MORB extend to higher Na8 and lower Fe8 compositions than associated N-MORB. Anomalous Na8 and Fe8, and Si8, Ca8 and Al8, of most Discovery-influenced MORB are interpreted to reflect increased modal clinopyroxene in their source regions. Calculated Fmean range from 15-17% for N-MORB, 16-19% for Shona-influenced MORB, and 11-18.5% for selected, least-anomalous Discovery(+LOMU)-influenced MORB. Calculated Pinitial are fairly constant for N-MORB ( 18+/-2 kbar), slightly greater for Shona-influenced MORB ( 20+/-3 kbar), whereas for least anomalous Discovery(+LOMU)-influenced MORB calculated Pinitial group around 16+/-2 and 22 kbar. Calculated crustal thicknesses range mostly between 6-9 km, but for Shona- and a single Discovery(+LOMU)-influenced MORB location the range is 8-12 km. Anomalous compositions of some Discovery-influenced MORB are interpreted to reflect variable melting of pyroxenite veins, initially formed as small-degree (2-3%) melts of garnet lherzolite within the upwelling off-axis Discovery mantle plume, and subsequently entrained in the ambient spinel lherzolite beneath the ridge axis. Because of lower solidus temperatures relative to ambient spinel lherzolite, initial melting preferentially consumed the low abundance (2.5-3.5%) pyroxenite veins. Variable mixing between vein- and host mantle-derived melts led to the range of Discovery(+LOMU)-influenced MORB compositions. In the vicinity of transform off-sets, melting is restricted

  14. Mantle plumes beneath the South Pacific superswell revealed by finite frequency P tomography using regional seafloor and island data (United States)

    Obayashi, M.; Yoshimitsu, J.; Sugioka, H.; Ito, A.; Isse, T.; Shiobara, H.; Reymond, D.; Suetsugu, D.


    We present a new tomographic image beneath the South Pacific superswell, using finite frequency P wave travel time tomography with global and regional data. The regional stations include broadband ocean-bottom seismograph stations. The tomographic image shows slow anomalies of 200-300 km in diameter beneath most hot spots in the studied region, extending continuously from the shallow upper mantle to 400 km depth. Narrow and weak slow anomalies are detected at depths of 500-1000 km, connecting the upper mantle slow anomalies with large-scale slow anomalies with lateral dimension of 1000-2000 km prevailing below 1000 km depth down to the core-mantle boundary. There are two slow anomalies around the Society hot spot at depths shallower than 400 km, which both emerge from the same slow anomaly at 500 km depth. One of them is located beneath the Society hot spot and the other underlies 500 km east of the Society hot spot, where no volcanism is observed.

  15. The 89 Ma Tortugal komatiitic suite, Costa Rica: Implications for a common geological origin of the Caribbean and Eastern Pacific region from a mantle plume (United States)

    Alvarado, Guillermo E.; Denyer, Percy; Sinton, Christopher W.


    Komatiites are reported for the first time in the northern part of the Gulf of Nicoya, Costa Rica. These rocks, dated at 89.7 ± 1.4 Ma (Turonian) by 40Ar/39Ar methods, occur as a large, elongated (14 km long, 1.5 km wide) N60°W striking body in the ophiolitic Nicoya Complex. These lavas have high MgO (26% 29%), Ni, and Cr, have high CaO/Al2O3 (0.98 1.08) and moderate Al2O3/TiO2 (5.55 8.44) ratios, and are depleted in Al2O3 (4% 5.5%), K2O (0.02% 0.37%), and TiO2 (0.59% 0.9%). Although these lavas are cumulates, their geochemical composition indicates an origin from a primary komatiitic magma, with a melting temperature of 1700 °C at a depth of 150 km. Similarities in the petrology and age (88 90 Ma) of Gorgona, Curaìao, and Nicoya-Tortugal mafic and ultramafic volcanic rocks suggest that these rocks had a common origin. These occurrences suggest a single hotspot center over a large area of the Caribbean and Eastern Pacific Mesozoic region due to a major thermal anomaly in the mantle, such as a hot, rising, convective plume.

  16. Hafnium and iron isotopes in early Archean komatiites record a plume-driven convection cycle in the Hadean Earth (United States)

    Nebel, Oliver; Campbell, Ian H.; Sossi, Paolo A.; Van Kranendonk, Martin J.


    Archean (>2.5 billion years) komatiites are considered expressions of mantle plumes that originate from and thereby sample the lowermost mantle overlying the Earth's core. Some komatiites have reported Hf isotope signatures that require a mantle source with a time-integrated Lu/Hf that is appreciably higher than average modern depleted mantle. The systematic study of the time and locus of parent-daughter fractionation of the mantle sources of these komatiites potentially constrains differentiation processes in the early Earth, and subsequent distribution and storage of early mantle reservoirs. We present radiogenic Hf and stable Fe isotopes for a series of komatiites from the Pilbara craton in Western Australia (aged 3.5 to 2.9 Ga). After careful evaluation of the effects of alteration, we find that pristine samples are characterised by a light Fe isotope mantle source and initial 176Hf/177Hf well above the age-corrected depleted mantle. Taken together these observations require a component of an old, melt-depleted reservoir in their mantle source. The Hf isotope signature of this component appears to be complementary to the first terrestrial crust, as preserved in Hadean (i.e., >4 Ga) detrital zircon cores, suggesting a causal relationship and a Hadean age for this depletion event. We propose that this Early Refractory Reservoir (ERR) is the residue formed by deep melting in hot Hadean mantle plumes, which then accumulated at the base of the first crust. Parts of this primordial lithosphere were destabilised and sank to the core-mantle boundary in cold drips and subsequently returned in hot mantle plumes, whose thermal capacity allows melting of such refractory mantle with its archetype isotope signature. The cycling of this material via cold drips and hot plumes suggests a plume-dominated convection prior to ∼3.9 Ga, which is then replaced by Archean-style plate tectonics.

  17. An Investigation of Crust and Upper Mantle Structure in Western Argentina Utilizing Local Event Receiver Functions (United States)

    Calkins, J. A.; Zandt, G.; Gilbert, H.; Beck, S.


    Images of the crust-mantle boundary and crustal structure obtained using the traditional analysis of teleseismic receiver functions (RFs) exhibit an unusually weak P-S conversion from the Moho in Western Argentina, where the subducting Nazca plate temporarily flattens out beneath the overriding South American plate. In order to better estimate depth to the Moho and search for mid-crustal impedance contrasts, we calculate and stack receiver functions using approximately 45 local earthquakes occurring in the downgoing slab between December of 2000 and February of 2001. The events occurred over a depth range of 76 to 165 km and were all within 128 km horizontal distance of the recording station and thus traveled with ray parameters less than .09 s/km. Radial receiver functions are calculated at two temporary broadband seismic stations located between San Juan and Mendoza, in the region where the Precordillera transitions eastward to the Sierras Pampeanas. Plots of stacked RFs as a function of ray parameter show a strong signal from the Moho at 7 seconds corresponding to a depth near 50 km, as well as conversions from interfaces within the crust at depths of ˜ 20 and 35 km. It should be noted that the narrow time interval between the P and S arrivals, due to the close proximity of events to the stations, precludes the analysis of reverberations within the crust to better constrain crustal Vp/Vs estimates and to refine the depth to interfaces. The observed Moho depth is in good agreement with estimates made using Pn apparent phase velocities along a transect through tectonically similar terrain 200 km to the north. In both cases, areas of relatively low topography are underlain by anomalously thick crust. The discrepancy in the clarity of the Moho Ps between RFs obtained using teleseismic versus local events currently remains unexplained but is an area of ongoing research.

  18. Aerosol Plume during a Polluted Event Occuring Over Paris Area and its Potential Photochemical Effect (United States)

    Randriamiarisoa, H.; Chazette, P.; Sanak, J.; Hauglustaine, D.


    As in many big cities, there are several pollution events in Paris area. A thorough understanding of the processes leading on the formation of pollutants and their transport during pollution episodes is necessary. One of the pertinent factors, which contributions on atmospheric chemistry and radiative effect are not yet well known, is the aerosol. ESQUIF (Etude et Simulation de la QUalité de l?air en Ile de France) is the first program dedicated to study such issues over the Paris area. It was carried out from summer 1998 to winter 2000 (Menut et al., 2000). To characterize all the properties of the urban aerosol, many campaigns were coordinated using both ground and airborne measurements (Chazette et al., 2000). We are focusing on the 31st of July 2000 where a well-defined polluted plume has been observed. Aerosol number concentrations in different size classes were measured and show that urban aerosol in Paris area is mainly submicronic. The absorbent part of the aerosol, mainly associated to the black carbon component, has been observed to be associated to particles with diameter less than 0.1 æm. The single scattering albedo has been assessed to be close to 0.85 leading to a significant influence on the photochemical chemistry. Indeed, a significant decrease of the daily maximum ozone concentration has been calculated using the INCA model and will be presented. ACKNOWLEDGEMENTS The Programme National de Chimie Atmosphérique, INSU supported this work. REFERENCES Chazette P., H. Randriamiarisoa, J. Sanak, C. Flamant, J. Pelon, M. Sicard, H. Cachier, F. Aulagnier, R. Sarda-Esteve, L. Gomes, S. Alfaro and A. Gaudichet (2001). ESQUIF 2000 : Aerosol survey over the Ile-de-France area, J. Aerosol Sci ., 32/suppl. 1, S439-S440. Menut, L., R. Vautard, C. Flamant, A. Abonnel, M. Beekmann, P. Chazette, P.H. Flamant, D. Gombert, D. Guédalia, D. Kley, M.P. Lefebvre, B. Lossec, D. Martin, G. Mégie, P. Perros, M. Sicard and G. Toupance (2000). Measurements and modelling

  19. Petrology and geochronology of lavas from Ka'ula Volcano: Implications for rejuvenated volcanism of the Hawaiian mantle plume (United States)

    Garcia, Michael O.; Weis, Dominique; Jicha, Brian R.; Ito, Garrett; Hanano, Diane


    Marine surveying and submersible sampling of Ka'ula Volcano, located 100 km off the axis of the Hawaiian chain, revealed widespread areas of young volcanism. New 40Ar/39Ar and geochemical analyses of the olivine-phyric submarine and subaerial volcanic rocks show that Ka'ula is shrouded with 1.9-0.5 Ma alkalic basalts. The ages and chemistry of these rocks overlap with rejuvenated lavas on nearby, northern Hawaiian Island shields (Ni'ihau, Kaua'i and South Kaua'i Swell). Collectively, these rejuvenated lavas cover a vast area (∼7000 km2), much more extensive than any other area of rejuvenated volcanism worldwide. Ka'ula rejuvenated lavas range widely in alkalinity and incompatible element abundances (e.g., up to 10× P2O5 at a given MgO value) and ratios indicating variable degrees of melting of a heterogeneous source. Heavy REE elements in Ka'ula lavas are pinned at a mantle normalized Yb value of 10 ± 1, reflecting the presence of garnet in the source. Trace element ratios indicate the source also contained phlogopite and an Fe-Ti oxide. The new Ka'ula ages show that rejuvenated volcanism was nearly coeval from ∼0.3 to 0.6 Ma along a 450 km segment of the Hawaiian Islands (from West Maui to north of Ka'ula). The ages and volumes for rejuvenated volcanism are inconsistent with all but one geodynamic melting model proposed to date. This model advocates a significant contribution of pyroxenite to rejuvenated magmas. Analyses of olivine phenocryst compositions suggest a major (33-69%) pyroxenite component in Ka'ula rejuvenated lavas, which correlates positively with radiogenic Pb isotope ratios for Ka'ula. This correlation is also observed in lavas from nearby South Kaua'i lavas, as was reported for Atlantic oceanic islands. The presence of pyroxenite in the source may have extended the duration and volume of Hawaiian rejuvenated volcanism.

  20. Proceedings of plumes, plates and mineralisation symposium: an introduction

    CSIR Research Space (South Africa)

    Hatton, CJ


    Full Text Available of plume-theory. Mechanisms of magma formation are identified and plume positions and distances to their surface expression considered. Mantle plumes are considered as a heat and fluid source for the Witwatersrand gold deposits....

  1. Geochemical characteristics of aluminum depleted and undepleted komatiites and HREE-enriched low-Ti tholeiites, western Abitibi greenstone belt: A heterogeneous mantle plume-convergent margin environment (United States)

    Fan, J.; Kerrich, R.


    A compositionally diverse suite of komatiites, komatiitic basalts, and basalts coexist in the Tisdale volcanic assemblage of the late-Archean (˜2.7 Ga) Abitibi greenstone belt. The komatiites are characterized by a spectrum of REE patterns, from low total REE contents (9 ppm) and pronounced convex-up patterns to greater total REE (18 ppm) and approximately flat-distributions. Thorium and niobium are codepleted with LREE. Komatiites with the most convex-up patterns have low Al 2O 3 (4.7 wt%) contents and Al 2O 3/TiO 2(12) ratios; they are interpreted to be the Al-depleted variety of komatiite derived from a depleted mantle source. Those komatiites and komatiitic basalts with flatter REE patterns are characterized by greater Al 2O 3 (7.0 wt%) and near chondritic Al 2O 3/TiO 2 (20) ratios; they are interpreted to be Al-undepleted komatiites generated from trace element undepleted mantle. For the komatiites and komatiitic basalts collectively, Gd/Ybn ratios are negatively correlated with La/Smn, but positively with MgO and Ni. The spectrum of patterns is interpreted as mixing between Al, HREE, Y-depleted, and Sc-depleted komatiites and Al-undepleted komatiites in a heterogeneous mantle plume. Auminum-depleted komatiites are characterized by negative Zr and Hf anomalies, consistent with majorite garnet-liquid D's for HFSE and REEs, signifying melt segregation at depths of >400 km. Tisdale Al-undepleted komatiites and komatiitic basalts have small negative to zero Zr(Hf)/MREE fractionation, signifying melt segregation in or above the garnet stability field. Collectively, the komatiites have correlations of Zr/Zr∗ and Hf/Hf ∗ with Gd/Ybn, and hence the Zr(Hf)/MREE fractionations are unlikely to have stemmed from alteration or crustal contamination. Two types of basalts are present. Type I basalts are Mg-tholeiites with near flat REE and primitive mantle normalized patterns, compositionally similar to abundant Mg-tholeiites associated with both Al-undepleted and Al

  2. Miocene-Pliocene mantle depletion event in the northern Fossa Magna, western NE Japan (United States)

    Okamura, Satoshi; Inaba, Mitsuru; Adachi, Yoshiko; Shinjo, Ryuichi


    New isotopic and trace element data presented here imply a temporal change in magma sources and thermal conditions beneath the northern Fossa Magna of NE Japan from the Miocene to the Pliocene. Less radiogenic 176Hf/177Hf and 143Nd/144Nd, high Zr/Hf, and little or no Hf anomaly characterize the Early Miocene volcanism in the northern Fossa Magna region. The mantle wedge consisted of chemically heterogeneous mantle source. Based on out isotope proxies, we propose that during the onset of subduction, influx of hot asthenospheric mantle provided sufficient heat to partially melt newly subducting sediment. Geochemical modeling demonstrates that slab-derived melt mixed with mantle wedge produces the observed isotopic and trace elemental characteristics. In the Middle Miocene, the injection of hot and depleted asthenospheric material replaced the mantle beneath the northern Fossa Magna region of NE Japan. This caused the isotopic signature of the rocks to change from enriched to depleted. Then, the mantle wedge was gradually cooled during the Middle Miocene to the Pliocene with back-arc opening ending in the Late Miocene. Slab surface temperatures were still high enough for sediments to melt but not too high (<∼780 °C) to lose zircon as a residual phase. The Late Miocene and Pliocene volcanism at the post stage of the back-arc opening is best explained by a partial melting of subducted metasediment saturated with trace quantities of zircon and rutile.

  3. Where Plumes Live (United States)

    King, S. D.


    From the perspective of fluid dynamics, `Plumes or not?' might be the wrong question. Let me begin by defining a few terms. Plume with a `P' is the well-known thermal structure with thin (order 100 km) tail and large, bulbous head that originates at the core-mantle boundary. The thin tail/large, bulbous-head morphology has been generated in a number of laboratory and numerical experiments. It can be seen, for example, on the cover of the famous fluid dynamics text by Batchelor. There is a clearly-defined range of parameters for which this structure is the preferred solution for instabilities arising from a bottom boundary layer in a convecting fluid. For example, a strong temperature-dependent rheology is needed. By contrast, plume with a `p' is any cylindrical or quasi-cylindrical instability originating from a thermal (or thermo-chemical) boundary layer. In fluid dynamics plume is sometimes used interchangeable with jet. Unless there is a very small temperature drop across the core-mantle boundary or a rather remarkable balance between temperature and composition at the base of the mantle, there are almost certainly plumes. (Note the little p.) Are these plumes the thermal structures with thin (order 100 km) tails and large bulbous heads or could they be broad, hot regions such as the degree 2 pattern seen in global seismic tomography images of the lower mantle, or the disconnected droplets seen in chaotic convection? To study this question, I will present a sequence of numerical `experiments' that illustrate the morphology of instabilities from a basal thermal boundary layer, i.e., plumes. Some of the aspects I will present include: spherical geometry, temperature-and pressure-dependence of rheology, internal heating, pressure-dependent coefficient of thermal expansion, variable coefficient of thermal diffusivity, phase transformations, and compositional layering at the base of the mantle. The goal is to map out the parameters and conditions where Plumes live

  4. Integrated “plume winter” scenario for the double-phased extinction during the Paleozoic-Mesozoic transition: The G-LB and P-TB events from a Panthalassan perspective (United States)

    Isozaki, Yukio


    changes have appeared twice in the second half of the Permian in a global extent. It is emphasized here that everything geologically unusual started in the Late Guadalupian; i.e., (1) the first mass extinction, (2) onset of the superanoxia, (3) sea-level drop down to the Phanerozoic minimum, (4) onset of volatile fluctuation in carbon isotope ratio, 5) 87Sr/ 86Sr ratio of the Paleozoic minimum, (6) extensive felsic alkaline volcanism, and (7) Illawarra Reversal. The felsic alkaline volcanism and the concurrent formation of several large igneous provinces (LIPs) in the eastern Pangea suggest that the Permian biosphere was involved in severe volcanic hazards twice at the G-LB and the P-TB. This episodic magmatism was likely related to the activity of a mantle superplume that initially rifted Pangea. The supercontinent-dividing superplume branched into several secondary plumes in the mantle transition zone (410-660 km deep) beneath Pangea. These secondary plumes induced the decompressional melting of mantle peridotite and pre-existing Pangean crust to form several LIPs that likely caused a "plume winter" with global cooling by dust/aerosol screens in the stratosphere, gas poisoning, acid rain damage to surface vegetation etc. After the main eruption of plume-derived flood basalt, global warming (plume summer) took over cooling, delayed the recovery of biodiversity, and intensified the ocean stratification. It was repeated twice at the G-LB and P-TB. A unique geomagnetic episode called the Illawarra Reversal around the Wordian-Capitanian boundary (ca. 265 Ma) recorded the appearance of a large instability in the geomagnetic dipole in the Earth's outer core. This rapid change was triggered likely by the episodic fall-down of a cold megalith (subducted oceanic slabs) from the upper mantle to the D″ layer above the 2900 km-deep core-mantle boundary, in tight association with the launching of a mantle superplume. The initial changes in the surface environment in the Capitanian

  5. Elastic flexure controls magma trajectories and explains the offset of primary volcanic activity upstream of mantle plume axis at la Réunion and Hawaii hotspot islands (United States)

    Gerbault, Muriel; Fontaine, Fabrice J.; Rabinowicz, Michel; Bystricky, Misha


    Surface volcanism at la Réunion and Hawaii occurs with an offset of 150-180 km upstream to the plume axis with respect to the plate motion. This striking observation raises questions about the forcing of plume-lithosphere thermo-mechanical interactions on melt trajectories beneath these islands. Based on visco-elasto-plastic numerical models handled at kilometric resolution, we propose to explain this offset by the development of compressional stresses at the base of the lithosphere, that result from elastic plate bending above the upward load exerted by the plume head. This horizontal compression adopts a disc shape centered around the plume axis: (i) it is 20 km thick, (ii) it has a 150 km radius, (iii) it lays at the base of the elastic part of the lithosphere, i.e., around ∼50-70 km depth where the temperature varies from ∼600 °C to ∼750 °C, (iv) it lasts for 5 to 10 My in an oceanic plate of age greater than 70 My, and (vi) it is controlled by the visco-elastic relaxation time at ∼50-70 km depth. This period of time exceeds the time during which both the Somalian/East-African and Pacific plates drift over the Reunion and Hawaii plumes, respectively. This indicates that this basal compression is actually a persistent feature. It is inferred that the buoyant melts percolating in the plume head pond below this zone of compression and eventually spread laterally until the most compressive principal elastic stresses reverse to the vertical, i.e., ∼150 km away from the plume head. There, melts propagate through dikes upwards to ∼35 km depth, where the plate curvature reverses and ambient compression diminishes. This 30-35 km depth may thus host a magmatic reservoir where melts transported by dykes pond. Only after further magmatic differentiation can dykes resume their ascension up to the surface and begin forming a volcanic edifice. As the volcano grows because of melt accumulation at the top of the plate, the lithosphere is flexed downwards

  6. Relationship between plume and plate tectonics (United States)

    Puchkov, V. N.


    The relationship between plate- and plume-tectonics is considered in view of the growth and breakdown of supercontinents, active rifting, the formation of passive volcanic-type continental margins, and the origin of time-progressive volcanic chains on oceanic and continental plates. The mantle wind phenomenon is described, as well as its effect on plume morphology and anisotropy of the ambient mantle. The interaction of plumes and mid-ocean ridges is discussed. The principles and problems of plume activity analysis in subduction- and collision-related foldbelts are considered and illustrated with examples.

  7. Perinucleolar relocalization and nucleolin as crucial events in the transcriptional activation of key genes in mantle cell lymphoma. (United States)

    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


    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.

  8. On the great plume debate

    Institute of Scientific and Technical Information of China (English)

    Yaoling Niu


    @@ 1 Introductory note Geological processes are ultimately consequences of Earth's thermal evolution. Plate tectonic theory, which explains geological phenomena along plate boundaries, elegantly illustrates this concept. For example, the origin of oceanic plates at ocean ridges, the movement and growth of these plates, and their ultimate consumption back into the Earth's deep interior through subduction zones provide an efficient mechanism to cool the earth's mantle, leading to large-scale mantle convection. Mantle plumes, which explain another set of global geological phenomena such as within-plate volcanism, cool the earth's deep interior (probably the Earth's core) and represent another mode of Earth's thermal convection. Plate tectonic theory and mantle plume hypothesis thus complement each other to explain much of the whole picture of Earth processes and phenomena.

  9. Pb - Isotopes and Pulses of the Deccan Plume (United States)

    Basu, A. R.; Yannopoulos, A. S.


    Mantle plumes are generally implicated for flood basalt generation in both continental and oceanic environments by impact of large plume heads beneath or within the lithosphere. The Deccan and Siberian flood basalt eruptions, synchronous with the Cretaceous-Paleogene and end-Permian extinctions, respectively, continue to fascinate geoscientists in search for the "kill-mechanisms" by impacts, volcanisms or both. Recently, Richards et al. (2015) proposed that bulk of the Deccan eruption was triggered by the Chicxulub impact. We showed (Basu et al., 1993) that early (68.5 Ma) and late (65 Ma) alkalic pulses of the Deccan were before and after the impact event at 66 Ma. Here, we focus on an extensive volcano-stratigraphic study of Pb isotopic systematics of 69 basaltic samples from 3 subgroups and 12 formations of the Deccan, each sampled from bottom to top along the stratigraphic section, covering the 3km thick 12 Deccan formations. Pb is sensitive to crustal contamination of mantle plume-derived magmas as both the upper and lower mantle are low in Pb (0.02 - 0.15 ppm) compared to ~ 4 ppm in continental crust. The lower Deccan formations of Kalsubai and Lonavala have initial 206Pb/204Pb with a widely varying range (16.543 - 22.823) indicating continental crustal contamination. In contrast, the upper formations of the Wai subgroup show a narrow range of 16.883 to 18.956, reflecting the plume signature. In addition, the 206Pb/204Pb and 207Pb/204Pb data of the Kalsubai subgroup lavas give an isochron age of 2603±140 Ma (single-stage, µ = 8). The Wai subgroup shows a narrow and restricted Pb isotopic range plotting closer to the Geochron. We interpret these data to infer that the basement rocks of the Deccan, the Archean Indian craton, were assimilated by the upwelling melt, ultimately clearing the conduit passages for the lavas sourced from direct melting of the plume head.

  10. Plumes Do Not Exist (United States)

    Hamilton, W. B.; Anderson, D. L.; Foulger, G. R.; Winterer, E. L.

    Hypothetical plumes from the deep mantle are widely assumed to provide an abso- lute hotspot reference frame, inaugurate rifting, drive plates, and profoundly influence magmatic and tectonic evolution of oceans and continents. Many papers on local to global tectonics, magmatism, and geochemistry invoke plumes, and assign to the man- tle whatever properties, dynamics, and composition are needed to enable them. The fixed-plume concept arose from the Emperor-Hawaii seamount-and-island province, the 45 Ma inflection in which was assumed to record a 60-degree change in direction by the Pacific plate. Paleomagnetic latitudes and smooth Pacific spreading patterns show that such a change did not occur. Other Pacific chains once assumed to be syn- chronous with, and Euler-parallel to, Hawaii have proved to be neither. Thermal and physical properties of Hawaiian lithosphere falsify plume predictions. Rationales for fixed hotspots elsewhere also have become untenable as databases enlarged. Astheno- sphere is everywhere near solidus temperature, so buoyant melt does not require a local heat source but, rather, needs a thin roof or crack or tensional setting for egress. MORB and ocean-island basalt (OIB) broadly intergrade in composition, but MORB typically is richer in refractory elements and their radiogenic daughters, whereas OIB commonly is richer in fusible elements and their daughters. MORB and OIB contrasts are required by melt behavior and do not indicate unlike source reservoirs. MORB melts rise, with minimal reaction, through hot asthenosphere, whereas OIB melts re- act, and thereby lose substance, by crystallizing refractories and retaining and assim- ilating subordinate fusibles, with thick, cool lithosphere and crust. There is no need for hypotheses involving chaotic plume behavior or thousands of km of lateral flow of plume material, nor for postulates of SprimitiveT lower mantle contrary to cos- & cedil;mological and thermodynamic considerations. Plume

  11. Plumes and Earth's Dynamic History : from Core to Biosphere (United States)

    Courtillot, V. E.


    The last half century has been dominated by the general acceptance of plate tectonics. Although the plume concept emerged early in this story, its role has remained ambiguous. Because plumes are singularities, both in space and time, they tend to lie dangerously close to catastrophism, as opposed to the calm uniformitarian view of plate tectonics. Yet, it has become apparent that singular events and transient phenomena are of great importance, even if by definition they cover only a small fraction of geological time, in diverse observational and theoretical fields such as 1) magnetic reversals and the geodynamo, 2) tomography and mantle convection, 3) continental rifting and collision, and 4) evolution of the fluid envelopes (atmospheric and oceanic "climate"; evolution of species in the biosphere). I will emphasize recent work on different types of plumes and on the correlation between flood basalts and mass extinctions. The origin of mantle plumes remains a controversial topic. We suggest that three types of plumes exist, which originate at the three main discontinuities in the Earth's mantle (base of lithosphere, transition zone and core-mantle boundary). Most of the hotspots are short lived (~ 10Ma) and seem to come from the transition zone or above. Important concentrations occur above the Pacific and African superswells. Less than 10 hotspots have been long lived (~ 100Ma) and may have a very deep origin. In the last 50 Ma, these deep-seated plumes in the Pacific and Indo-Atlantic hemispheres have moved slowly, but motion was much faster prior to that. This change correlates with major episodes of true polar wander. The deeper ("primary") plumes are thought to trace global shifts in quadrupolar convection in the lower mantle. These are the plumes that were born as major flood basalts or oceanic plateaus (designated as large igneous provinces or LIPs). Most have an original volume on the order or in excess of 2.5 Mkm3. In most provinces, volcanism lasted on

  12. In situ Re-Os isotope ages of sulfides in Hannuoba peridotitic xenoliths: Significance for the frequently-occurring mantle events beneath the North China Block

    Institute of Scientific and Technical Information of China (English)


    In situ Re-Os isotopes of sulfides in peridotitic xenoliths from Cenozoic Hannuoba basalts were analyzed by LAM-MC-ICPMS. The suifides developed two types of occurrences including silicate-enclosed and interstitial. In the enclosed sulfides, 187Os/188Os vary from 0.1124 to 0.1362 and 187Re/188Os from 0.0026 to 1.8027. In the interstitial ones, 187Os/188Os have a range from 0.1174 to 0.1354 and 187Re/188Os from 0.0365 to 1.4469. The oldest age, calculated by TRD for the enclosed sulfides, is 2.1 Ga. An isochron age of 2.3±1.2 Ga is obtained by five grains of enclosed sulfides and primitive mantle. The sulfides used have lower Re-Os isotopic ratio than primitive mantle. Meanwhile, an isochron age of 645±225 Ma is given by all interstitial sulfides and the enclosed sulfides with higher Re-Os isotopic ratio due to Re addition after mantle formation. In addition, the model age of 1.3 Ga recorded by one interstitial sulfide, having similar TDM and TRD, should be meaningful to deep thermal event. The coexistence of different ages, revealed by in situ Re-Os isotope, indicates frequently-occurring mantle events beneath Hannuoba area.

  13. Stress drops for intermediate-depth intraslab earthquakes beneath Hokkaido, northern Japan: Differences between the subducting oceanic crust and mantle events (United States)

    Kita, Saeko; Katsumata, Kei


    Spatial variations in the stress drop for 1726 intermediate-depth intraslab earthquakes were examined in the subducting Pacific plate beneath Hokkaido, using precisely relocated hypocenters, the corner frequencies of events, and detailed determined geometry of the upper interface of the Pacific plate. The results show that median stress drop for intraslab earthquakes generally increases with an increase in depth from ˜10 to 157 Mpa at depths of 70-300 km. More specifically, median stress drops for events in the oceanic crust decrease (9.9-6.8 MPa) at depths of 70-120 km and increase (6.8-17 MPa) at depths of 120-170 km, whereas median stress drop for events in the oceanic mantle decrease (21.6-14.0 MPa) at depths of 70-170 km, where the geometry of the Pacific plate is well determined. The increase in stress drop with depth in the oceanic crust at depths of 120-170 km, for which several studies have shown an increase in velocity, can be explained by an increase in the velocity and a decrease in the water content due to the phase boundary with dehydration in the oceanic crust. Stress drops for events in the oceanic mantle were larger than those for events in the oceanic crust at depths of 70-120 km. Differences in both the rigidity of the rock types and in the rupture mechanisms for events between the oceanic crust and mantle could be causes for the stress drop differences within a slab.

  14. Paradoxical co-existing base metal sulphides in the mantle: The multi-event record preserved in Loch Roag peridotite xenoliths, North Atlantic Craton (United States)

    Hughes, Hannah S. R.; McDonald, Iain; Loocke, Matthew; Butler, Ian B.; Upton, Brian G. J.; Faithfull, John W.


    The role of the subcontinental lithospheric mantle as a source of precious metals for mafic magmas is contentious and, given the chalcophile (and siderophile) character of metals such as the platinum-group elements (PGE), Se, Te, Re, Cu and Au, the mobility of these metals is intimately linked with that of sulphur. Hence the nature of the host phase(s), and their age and stability in the subcontinental lithospheric mantle may be of critical importance. We investigate the sulphide mineralogy and sulphide in situ trace element compositions in base metal sulphides (BMS) in a suite of spinel lherzolite mantle xenoliths from northwest Scotland (Loch Roag, Isle of Lewis). This area is situated on the margin of the North Atlantic Craton which has been overprinted by a Palaeoproterozoic orogenic belt, and occurs in a region which has undergone magmatic events from the Palaeoproterozoic to the Eocene. We identify two populations of co-existing BMS within a single spinel lherzolite xenolith (LR80) and which can also be recognised in the peridotite xenolith suite as a whole. Both populations consist of a mixture of Fe-Ni-Cu sulphide minerals, and we distinguished between these according to BMS texture, petrographic setting (i.e., location within the xenolith in terms of 'interstitial' or within feldspar-spinel symplectites, as demonstrated by X-ray Computed Microtomography) and in situ trace element composition. Group A BMS are coarse, metasomatic, have low concentrations of total PGE (relationships of the symplectites, it is possible to infer the relative ages of each metasomatic BMS population. We tally these with major tectono-magmatic events for the North Atlantic region by making comparisons to carbonatite events recorded in crustal and mantle rocks, and we suggest that the Pt-enrichment was associated with a pre-Carboniferous carbonatite episode. This method of mantle xenolith base metal sulphide documentation may ultimately permit the temporal and spatial mapping of

  15. 40Ar/39Ar dating of magmatic activities in the Donbas Foldbelt and the Scythian Platform (Eastern Europe) indicating a possible mantle plume source (United States)

    Alexandre, P.; Saintot, A.; Wijbrans, J.; Stephenson, R.; Wilson, M.; Kitchka, A.; Chalot-Prat, F.


    , Early Permian (275--280 Ma) and Early Triassic (245--250 Ma) magmatic activity is present. In the Late Triassic, the ages of magmatic activity are slightly different (220 and 205 Ma), and they are entirely different thereafter. These data suggest that for both areas there was a common deep magmatic source (probably a large plume, as previously proposed) until the Triassic. Subsequently, the two areas had distinct magmatic sources.

  16. Asteroids and Archaean crustal evolution: Tests of possible genetic links between major mantle/crust melting events and clustered extraterrestrial bombardments (United States)

    Glikson, A. Y.


    Since the oldest intact terrestrial rocks of ca. 4.0 Ga and oldest zircon xenocrysts of ca. 4.3 Ga measured to date overlap with the lunar late heavy bombardment, the early Precambrian record requires close reexamination vis a vis the effects of megaimpacts. The identification of microtektite-bearing horizons containing spinals of chondritic chemistry and Ir anomalies in 3.5-3.4-Ga greenstone belts provides the first direct evidence for large-scale Archaean impacts. The Archaean crustal record contains evidence for several major greenstone-granite-forming episodes where deep upwelling and adiabatic fusion of the mantle was accompanied by contemporaneous crustal anatexis. Isotopic age studies suggest evidence for principal age clusters about 3.5, 3.0, and 2.7 (+/- 0.8) Ga, relics of a ca. 3.8-Ga event, and several less well defined episodes. These peak events were accompanied and followed by protracted thermal fluctuations in intracrustal high-grade metamorphic zones. Interpretations of these events in terms of internal dynamics of the Earth are difficult to reconcile with the thermal behavior of silicate rheologies in a continuously convecting mantle regime. A triggering of these episodes by mantle rebound response to intermittent extraterrestrial asteroid impacts is supported by (1) identification of major Archaean impacts from microtektite and distal ejecta horizons marked by Ir anomalies; (2) geochemical and experimental evidence for mantle upwelling, possibly from levels as deep as the transition zone; and (3) catastrophic adiabatic melting required to generate peridotitic komatites. Episodic differentiation/accretion growth of sial consequent on these events is capable of resolving the volume problem that arises from comparisons between modern continental crust and the estimated sial produced by continuous two-stage mantle melting processes. The volume problem is exacerbated by projected high accretion rates under Archaean geotherms. It is suggested that

  17. Zoned mantle convection. (United States)

    Albarède, Francis; Van Der Hilst, Rob D


    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

  18. Eastern Dharwar Craton, India: Continental lithosphere growth by accretion of diverse plume and arc terranes

    Directory of Open Access Journals (Sweden)

    C. Manikyamba


    Archean lithospheric mantle, distinctive in being thick, refractory, and buoyant, formed complementary to the accreted plume and convergent margin terranes, as migrating arcs captured thick plume-plateaus, and the refractory, low density, residue of plume melting coupled with accreted imbricated plume-arc crust.

  19. Plume or no Plume, the Case of the Siberian Trap Formation (United States)

    Reichow, M. K.; Saunders, A. D.; White, R. V.; Al'Mukhamedov, A. I.; Medvedev, A. I.; Inger, S.


    The generation mechanism of continental large igneous provinces, such as the Siberian Traps, are matters of recent debate, particularly their relation to mantle plumes derived from the Earth's interior. Alternative models relate the formation of large igneous provinces to bolide impacts or small-scale convection at the boundary of asymmetric lithospheres. Neither of these models is without criticism and each model cannot explain all characteristics of continental flood basalt formation alone. However, strong support for the involvement of a mantle plume comes from the observation that large volumes of basaltic melts ( ˜3 x 106 km3) erupted within a short period of time (pulse of volcanism extruded over large areas of the Siberian craton. Although the major and trace element data are consistent with a plume origin for the Siberian Traps, they cannot prove it; however, magma volume and timing constraints do strongly suggest that a mantle plume was involved in the formation of the Earth's largest continental flood basalt province.

  20. The validation and analysis of novel stereo-derived smoke plume products from AATSR and their application to fire events from the 2008 Russian fire season (United States)

    Fisher, D.; Muller, J.-P.; Yershov, V.


    Biomass burning events in Boreal forests generate significant amounts of important greenhouse gases; including CO2, CO, NOx [1,2]. When the injection height is above the boundary layer (BL), the lifespan of these chemicals is greatly extended, as is their spatial distribution [2]. Typically, in chemical transport models (CTMs), BL injection heights are simplified and assumed to be constant. This is in part due to poor data availability. This leads to a reduction in the accuracy of the distribution outputs from such models. To generate better smoke-plume injection height (SPIH) inputs into CTMs, measurements need to be made of smoke plume heights, which can be used as a proxy for aerosol injection height into the atmosphere. One method of measuring SPIH is through stereo-photogrammetry [5], originally applied to optically thick clouds [3,4]. Here, we present validation and analysis of the M6 stereo matching method [5] for the determination of SPIHs applied to AATSR. It is referred to as M6 due to a shared heritage with the other M-series matchers [3,4]. M6 utilizes novel normalization and matching techniques to generate improved results, in terms of coverage and accuracy, over these afore-referenced matchers of similar type. Validation is carried out against independent, coincident and higher resolution SPIH measurements obtained from both the CALIOP instrument carried onboard the NASA-CNES CALIPSO satellite and also against measurements from the MISR Smoke Plume Product obtained by manual measurements using the MINX system ( with the MISR instrument onboard the NASA satellite Terra. The results of this inter-comparison show an excellent agreement between AATSR and the CALIOP and MISR measurements. Further an inter-comparison between a heritage M-series matcher, M4 [3], also against MISR data demonstrates the significant improvement in SPIH generated by M6. [1] Crutzen, P. J., L. E. Heidt, et al. (1979). "Biomass

  1. Preservation of Primordial Mantle in the Aftermath of a Giant Impact (United States)

    Lock, S. J.; Stewart, S. T.; Mukhopadhyay, S.


    Terrestrial planets experience a number of giant impacts in the final stages of accretion. These highly energetic events force planets into hot, partially vaporized, and occasionally rapidly-rotating states. However, recent measurements of Xe and W isotopes in mantle plume-derived basalts imply that the terrestrial mantle was not homogenized during this violent stage of Earth's accretion. Understanding the physical structure of post-impact states is key for interpreting these primitive mantle signatures. Post-impact states are highly thermally stratified: the lowermost mantle has lower entropy than the rest of the mantle. Usually, the lowermost mantle is near the solidus or partially molten. The high-entropy portion of the mantle is super-liquidus, smoothly grading to a silicate vapor atmosphere. Here, we consider the competing processes acting on these distinct layers as the mantle establishes a single thermal gradient. If the whole mantle chemically mixed during cooling, then any pre-impact chemical signature would be erased. Previous work has neglected the critical time period between the highly vaporized post-impact state and a fully-condensed silicate body, i.e., a separated magma ocean and atmosphere. The post-impact structure cools rapidly by radiation from the photosphere, causing contraction of the body and redistribution of mass and angular momentum. One consequence of contraction is that the pressure in the mantle increases significantly (on the order of several to 10s GPa at the core mantle boundary) over 10s-1000s years. The increased pressure causes part of the mantle to solidify. Significantly, the timescale for pressure-induced freezing is shorter than the timescale for thermal equilibration between the low and high entropy mantle layers and the timescale for melt percolation (both >100s yrs). Therefore, pressure-induced freezing in the aftermath of a giant impact may be an important factor in preserving primordial Xe and W signatures in the lower

  2. Viscosity jump in Earth's mid-mantle. (United States)

    Rudolph, Maxwell L; Lekić, Vedran; Lithgow-Bertelloni, Carolina


    The viscosity structure of Earth's deep mantle affects the thermal evolution of Earth, the ascent of mantle plumes, settling of subducted oceanic lithosphere, and the mixing of compositional heterogeneities in the mantle. Based on a reanalysis of the long-wavelength nonhydrostatic geoid, we infer viscous layering of the mantle using a method that allows us to avoid a priori assumptions about its variation with depth. We detect an increase in viscosity at 800- to 1200-kilometers depth, far greater than the depth of the mineral phase transformations that define the mantle transition zone. The viscosity increase is coincident in depth with regions where seismic tomography has imaged slab stagnation, plume deflection, and changes in large-scale structure and offers a simple explanation of these phenomena.

  3. The effect of recycled oceanic crust in the thermal evolution of the Galapagos Plume (United States)

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


    Current models suggest that the massive basaltic production responsible for the emplacement of Large Igneous Provinces (LIPS) during the Permian-Paleocene may represent the initial phases (plume heads) of some of the mantle plumes that feed the current ocean island basalts (OIB). In many cases, magmatism associated with the initiation of mantle plumes was so voluminous that produced global environmental impacts. The origin of these intra-plate magmatism is still debated but recent petrological, geochemical and geophysical studies of some of these localities like Samoa, Hawaii, Galapagos, provide evidence that melting is related to a true mantle plume, representing a geochemically heterogeneous, hot-buoyant domain that originates from a boundary layer beneath the upper mantle. Thus, plume-related magmas produced in OIB and LIPS and their connecting plume tracks are windows into the Earth's mantle, providing evidence on mantle temperature, size and composition of heterogeneities, and the deep earth geochemical cycles. Our preliminary petrological modeling suggests that mantle plumes for LIPS with Permian-Paleocene ages were generally hotter and melted more extensively than plumes of more modern oceanic islands. Although a lot of work has been done on LIPS and OIB, no complete record of the evolution of a mantle plume is available to this point, mostly due to the inaccessibility of the submerged sections of almost all plume tracks. Galapagos-related lavas provide a complete record of the evolution of a mantle plume since the plume's initial stages in the Cretaceous. In the case of the Galapagos, our work suggests a decrease from TP(max) of1650 C in the Cretaceous to 1500 C in the present day. Our recent work on the Galapagos Islands and the preliminary work on older Galapagos-related terranes suggest that this secular cooling is directly related with increasing amounts of recycled crust in the plume.

  4. Ultramafic xenoliths from the Bearpaw Mountains, Montana, USA: Evidence for multiple metasomatic events in the lithospheric mantle beneath the Wyoming craton (United States)

    Downes, H.; Macdonald, R.; Upton, B.G.J.; Cox, K.G.; Bodinier, J.-L.; Mason, P.R.D.; James, D.; Hill, P.G.; Hearn, B.C.


    /144Nd values (0??5113) and extremely high 87Sr/86Sr ratios in their constituent phlogopite, indicating an ancient (probably mid-Proterozoic) enrichment. This enriched mantle lithosphere later contributed to the formation of the high-K Eocene host magmas. The cumulate group ranges from clinopyroxene-rich mica peridotites (including abundant mica wehrlites) to mica clinopyroxenites. Most contain >30% phlogopite. Their mineral compositions are similar to those of phenocrysts in the host minettes. Their whole-rock compositions are generally poorer in MgO but richer in incompatible trace elements than those of the tectonite peridotites. Whole-rock trace element patterns are enriched in large ion lithophile elements (LILE; Rb, Cs, U and Pb) and depleted in HFSE (Nb, Ta Zr and Hf as in the host minettes, and their Sr-Nd isotopic compositions are also identical to those of the minettes. Their clinopyroxenes are LREE-enriched and formed in equilibrium with a LREE-enriched melt closely resembling the minettes. The cumulates therefore represent a much younger magmatic event, related to crystallization at mantle depths of minette magmas in Eocene times, that caused further metasomatic enrichment of the lithosphere. ?? Oxford University Press 2004; all rights reserved.

  5. Nannofossils in 2011 El Hierro eruptive products reinstate plume model for Canary Islands (United States)

    Zaczek, Kirsten; Troll, Valentin R.; Cachao, Mario; Ferreira, Jorge; Deegan, Frances M.; Carracedo, Juan Carlos; Soler, Vicente; Meade, Fiona C.; Burchardt, Steffi


    The origin and life cycle of ocean islands have been debated since the early days of Geology. In the case of the Canary archipelago, its proximity to the Atlas orogen led to initial fracture-controlled models for island genesis, while later workers cited a Miocene-Quaternary east-west age-progression to support an underlying mantle-plume. The recent discovery of submarine Cretaceous volcanic rocks near the westernmost island of El Hierro now questions this systematic age-progression within the archipelago. If a mantle-plume is indeed responsible for the Canaries, the onshore volcanic age-progression should be complemented by progressively younger pre-island sedimentary strata towards the west, however, direct age constraints for the westernmost pre-island sediments are lacking. Here we report on new age data obtained from calcareous nannofossils in sedimentary xenoliths erupted during the 2011 El Hierro events, which date the sub-island sedimentary rocks to between late Cretaceous and Pliocene in age. This age-range includes substantially younger pre-volcanic sedimentary rocks than the Jurassic to Miocene strata known from the older eastern islands and now reinstate the mantle-plume hypothesis as the most plausible explanation for Canary volcanism. The recently discovered Cretaceous submarine volcanic rocks in the region are, in turn, part of an older, fracture-related tectonic episode.

  6. Plume tectonics and cratons formation in the early Earth (United States)

    Gerya, T.; Stern, R. J.; Baes, M.; Fischer, R.; Sizova, E.; Sobolev, S. V.; Whattam, S. A.


    Modern geodynamics and continental growth are critically driven by subduction and plate tectonics, however how this tectonic regime started and what geodynamic regime was before remains controversial. Most present-day subduction initiation mechanisms require acting plate forces and/or pre-existing zones of lithospheric weakness, which are themselves the consequence of plate tectonics. Here, we focus on plume-lithosphere interactions and spontaneous plume-induced subduction initiation, which does not require pre-existing lithospheric fabric and is viable for both stagnant lid and mobile/deformable lid conditions. We present results of 2D and 3D numerical modeling of plume-induced deformation and associated crustal growth resulting from tectono-magmatic interaction of ascending mantle plumes with oceanic-type lithosphere. We demonstrate that weakening of the lithosphere by plume-induced magmatism is the key factor allowing for its internal deformation and differentiation resulting in continental crust growth. We also show that plume-lithosphere interaction can enable subduction and rudimentary plate tectonics initiation at the margins of a crustal plateau growing above the plume head. We argue that frequent plume-arc interactions recorded in Archean crust could reflect either short-term plume-induced subduction or plume-induced episodic lithospheric drips. We furthermore suggest a distinct plume-tectonics regime operated on Earth before plate tectonics, which was associated with widespread tectono-magmatic heat and mass exchange between the crust and the mantle. This regime was characterized by weak deformable plates with low topography, massive juvenile crust production from mantle derived melts, mantle-flows-driven crustal deformation, magma-assisted crustal convection and widespread development of lithospheric delamination and crustal drips. Plume tectonics also resulted in growth of hot depleted chemically buoyant subcrustal proto-cratonic mantle layer. Later

  7. Numerical modeling of mantle wedge processes and exhumation of UHP mantle in subduction zones (United States)

    Gorczyk, W.; Gerya, T. V.; Guillot, S.; Connolly, J. A.; Yuen, D.


    The upwelling of subduction generated partially molten rocks is potentially a mechanism for the exhumation of UHP rocks through the mantle wedge. We investigated this processes using a 2-D coupled petrological- thermomechanical model that incorporates slab dehydration and water transport as well as partial melting of mantle and crustal rocks. This approach allows us to study the dynamics of mantle wedge processes including evolution of partially molten plumes and their interaction with surrounding dry mantle. To study the internal structure of the plumes we used ultra-high resolution numerical simulations with 10 billion active markers to detail the internal structure of natural plumes originating from the slab. The plumes consist of partially molten hydrated peridotite, dry solid mantle and subducted oceanic crust, which may comprise up to 12 volume % of the plume. As the plumes grow and mature these materials mix chaotically resulting in attenuation and duplication of the original layering on scales of 1-1000 m. Comparison of numerical results with geological observations from the Horoman ultramafic complex in Japan suggests that mixing and differentiation processes related to development of partially molten plumes above slabs may be responsible for strongly layered lithologically mixed (marble cake) structure of asthenospheric mantle wedges. The recent discovery of garnet bearing peridotites in the subduction zone of the Great Antilles in Hispaniola has raised questions about the process that leads to their exhumation. To evaluate whether upwelling plumes are a plausible exhumation mechanism we investigated the dynamics of subduction of slow spreading ridges. The results show that subduction of strongly serpentinized oceanic plate causes strong dehydration of the slab and leads to a rheological weakening of the interface between subducting and overriding plate. This weakening triggers trench retreat and massive asthenospheric upwelling into the gap between the

  8. Seismic evidence for a chemically distinct thermochemical reservoir in Earth's deep mantle beneath Hawaii (United States)

    Zhao, Chunpeng; Garnero, Edward J.; McNamara, Allen K.; Schmerr, Nicholas; Carlson, Richard W.


    Nearly antipodal continent-sized zones of reduced seismic shear wave velocities exist at the base of Earth's mantle, one beneath the Pacific Ocean, the other beneath the South Atlantic Ocean and Africa. Geophysicists have attributed the low velocity zones to elevated temperatures associated with large-scale mantle convection processes, specifically, hot mantle upwelling in response to cooler subduction-related downwelling currents. Hypotheses have included superplumes, isochemical heterogeneity, and stable as well as metastable basal thermochemical piles. Here we analyze waveform broadening and travel times of S waves from 11 deep focus earthquakes in the southwest Pacific recorded in North America, resulting in 8500 seismograms studied that sample the deep mantle beneath the Pacific. Waveform broadening is referenced to a mean S-wave shape constructed for each event, to define a relative "misfit". Large misfits are consistent with multipathing that can broaden wave pulses. Misfits of deep mantle sampling S-waves infer that the structure in the northeast part of the low velocity province beneath the Pacific has a sharp side as well as a sloping sharp top to the feature. This sharp boundary morphology is consistent with geodynamic predictions for a stable thermochemical reservoir. The peak of the imaged pile is below Hawaii, supporting the hypothesis of a whole mantle plume beneath the hotspot.

  9. Timing of Precambrian melt depletion and Phanerozoic refertilization events in the lithospheric mantle of the Wyoming Craton and adjacent Central Plains Orogen (United States)

    Carlson, R.W.; Irving, A.J.; Schulze, D.J.; Hearn, B.C.


    Garnet peridotite xenoliths from the Sloan kimberlite (Colorado) are variably depleted in their major magmaphile (Ca, Al) element compositions with whole rock Re-depletion model ages generally consistent with this depletion occurring in the mid-Proterozoic. Unlike many lithospheric peridotites, the Sloan samples are also depleted in incompatible trace elements, as shown by the composition of separated garnet and clinopyroxene. Most of the Sloan peridotites have intermineral Sm-Nd and Lu-Hf isotope systematics consistent with this depletion occurring in the mid-Proterozoic, though the precise age of this event is poorly defined. Thus, when sampled by the Devonian Sloan kimberlite, the compositional characteristics of the lithospheric mantle in this area primarily reflected the initial melt extraction event that presumably is associated with crust formation in the Proterozoic-a relatively simple history that may also explain the cold geotherm measured for the Sloan xenoliths. The Williams and Homestead kimberlites erupted through the Wyoming Craton in the Eocene, near the end of the Laramide Orogeny, the major tectonomagmatic event responsible for the formation of the Rocky Mountains in the late Cretaceous-early Tertiary. Rhenium-depletion model ages for the Homestead peridotites are mostly Archean, consistent with their origin in the Archean lithospheric mantle of the Wyoming Craton. Both the Williams and Homestead peridotites, however, clearly show the consequences of metasomatism by incompatible-element-rich melts. Intermineral isotope systematics in both the Homestead and Williams peridotites are highly disturbed with the Sr and Nd isotopic compositions of the minerals being dominated by the metasomatic component. Some Homestead samples preserve an incompatible element depleted signature in their radiogenic Hf isotopic compositions. Sm-Nd tie lines for garnet and clinopyroxene separates from most Homestead samples provide Mesozoic or younger "ages" suggesting

  10. Mapping the Hawaiian plume conduit with converted seismic waves (United States)

    Li; Kind; Priestley; Sobolev; Tilmann; Yuan; Weber


    The volcanic edifice of the Hawaiian islands and seamounts, as well as the surrounding area of shallow sea floor known as the Hawaiian swell, are believed to result from the passage of the oceanic lithosphere over a mantle hotspot. Although geochemical and gravity observations indicate the existence of a mantle thermal plume beneath Hawaii, no direct seismic evidence for such a plume in the upper mantle has yet been found. Here we present an analysis of compressional-to-shear (P-to-S) converted seismic phases, recorded on seismograph stations on the Hawaiian islands, that indicate a zone of very low shear-wave velocity (effects of the Hawaiian plume conduit in the asthenosphere and mantle transition zone with excess temperature of approximately 300 degrees C. Large variations in the transition-zone thickness suggest a lower-mantle origin of the Hawaiian plume similar to the Iceland plume, but our results indicate a 100 degrees C higher temperature for the Hawaiian plume.

  11. A Global 3D P-Velocity Model of the Earth's Crust and Mantle for Improved Event Location (United States)

    Ballard, S.; Young, C. J.; Hipp, J. R.; Chang, M.; Lewis, J.; Begnaud, M. L.; Rowe, C. A.


    Effectively monitoring for small nuclear tests (Java-based distributed computing framework developed by Sandia National Laboratories (SNL), providing us with 300+ processors having an efficiency of better than 90% for the calculations. We evaluate our model both in terms of travel time residual variance reduction and in location improvement for GT events. For the latter, we use a new multi-threaded version of the SNL-developed LocOO code modified to use 3D velocity models.

  12. Propagating buoyant mantle upwelling on the Reykjanes Ridge (United States)

    Martinez, Fernando; Hey, Richard


    Crustal features of the Reykjanes Ridge have been attributed to mantle plume flow radiating outward from the Iceland hotspot. This model requires very rapid mantle upwelling and a "rheological boundary" at the solidus to deflect plume material laterally and prevent extreme melting above the plume stem. Here we propose an alternative explanation in which shallow buoyant mantle upwelling instabilities propagate along axis to form the crustal features of the ridge and flanks. As only the locus of buoyant upwelling propagates this mechanism removes the need for rapid mantle plume flow. Based on new geophysical mapping we show that a persistent sub-axial low viscosity channel supporting buoyant mantle upwelling can explain the current oblique geometry of the ridge as a reestablishment of its original configuration following an abrupt change in opening direction. This mechanism further explains the replacement of ridge-orthogonal crustal segmentation with V-shaped crustal ridges and troughs. Our findings indicate that crustal features of the Reykjanes Ridge and flanks are formed by shallow buoyant mantle instabilities, fundamentally like at other slow spreading ridges, and need not reflect deep mantle plume flow.

  13. Upper mantle viscosity and lithospheric thickness under Iceland determined from a microphysical modelling approach of mantle rheology (United States)

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


    The Vatnajökull glacier, located in the south-east of Iceland is the largest ice cap of Iceland having a mean radius of ~50 km covering an area of ˜8100 km2. The Vatnajökull glacier is situated directly on top of the spreading axis in the eastern volcanic zone (EVZ) of the Icelandic mid-ocean ridge and near the inferred center of the Icelandic hotspot. Due to the vicinity of the glacier to the active tectonic area, the response of the solid earth to melting of the ice cap is strongly controlled by the properties of the hot newly formed upper mantle underneath the mid-ocean ridge. The relatively high temperatures in the mantle during rifting result in relatively low upper mantle viscosities and fast relaxation times in comparison with tectonically inactive glaciated areas such as in. In this study, estimates for lithospheric thickness and upper mantle viscosity under Iceland are produced by a microphysical modelling approach using the theoretical temperature distribution under mid-ocean ridges combined with olivine diffusion and dislocation creep flow laws. Large lateral variations in upper mantle viscosity and especially lithospheric thickness are expected for Iceland perpendicular to the ridge axis due to the large changes in temperatures away from the ridge axis. The lithospheric thickness (27-40 km) and upper mantle viscosity (2 × 1018-1019 Pa s) outcomes for the recent glaciation are consistent with previous reports of viscosity and lithospheric thickness from glacial isostatic adjustment studies. A combination of a 40 km thick elastic lithosphere and an average upper mantle viscosity of 5 × 1018 Pa s would suggest that the upper mantle under Iceland is most likely dry. Also, the results indicate that the presence of a plume under Iceland cannot explain the recent low viscosity values reported for Iceland. Using a larger extent and larger thickness of the Icelandic icecap during the Weichselian glaciation event (˜10,000 BP) this study predicts that during

  14. Vertically Discontinuous Seismic Signatures From Continuous Thermochemical Plumes (United States)

    Harris, A. C.; Kincaid, C.; Savage, B.


    To interpret seismic signatures associated with mantle upwellings, we must understand the distribution of thermochemical heterogeneities within mantle plumes. Thermochemical heterogeneities are expected to arise within plumes by the incorporation of subducted lithosphere (Eclogite and Harzburgite) that has reached the plume source region (thermal boundary layers in the mantle). We analyze laboratory experiments in conjunction with seismic velocity models to predict the seismic signature of thermochemical plumes. Laboratory experiments are fully three-dimensional and use glucose syrup (Rayleigh number: 106) to model the mantle and a two-layer subducted lithosphere, where composition (viscosity and density) is controlled by water content. Experiments show heterogeneous upwellings with variations in both temperature and composition that are more complex than predicted in previous plume models. Spatial distributions for temperature and composition in representative, repeatable types of thermochemical upwellings are tracked through time, scaled to mantle values and used to calculate predicted seismic velocities. Apparent seismic velocity signals are estimated for patterns in thermochemical heterogeneity with length scales ranging from 1 to 300 km and excess temperatures from 50 to 300°C. Results show that if plumes are purely thermal they can be identified in the usual way, by slow velocities. However, if plumes are a mixture of compositions, as predicted by laboratory models, their velocity structure is more complex. An Ecolgite lens within a plume at ~300km depth with an excess temperature of 250°C can have the same velocity as regular mantle with no excess temperature. A Harzburgite lobe of a plume head (up to half of the plume volume) at 300km depth with an excess temperature of 225°C can have the same Vs as regular mantle with no excess temperature, but can only mask up to 55°C in Vp. Spatial variations in temperature control velocity structure above 300km

  15. Multi-variable X-band radar observation and tracking of ash plume from Mt. Etna volcano on November 23, 2013 event (United States)

    Montopoli, Mario; Vulpiani, Gianfranco; Riccci, Matteo; Corradini, Stefano; Merucci, Luca; Marzano, Frank S.


    Ground based weather radar observations of volcanic ash clouds are gaining momentum after recent works which demonstrated their potential use either as stand alone tool or in combination with satellite retrievals. From an operational standpoint, radar data have been mainly exploited to derive the height of ash plume and its temporal-spatial development, taking into account the radar limitation of detecting coarse ash particles (from approximately 20 microns to 10 millimeters and above in terms of particle's radius). More sophisticated radar retrievals can include airborne ash concentration, ash fall rate and out-flux rate. Marzano et al. developed several volcanic ash radar retrieval (VARR) schemes, even though their practical use is still subject to a robust validation activity. The latter is made particularly difficult due to the lack of field campaigns with multiple observations and the scarce repetition of volcanic events. The radar variable, often used to infer the physical features of actual ash clouds, is the radar reflectivity named ZHH. It is related to ash particle size distribution and it shows a nice power law relationship with ash concentration. This makes ZHH largely used in radar-volcanology studies. However, weather radars are often able to detect Doppler frequency shifts and, more and more, they have a polarization-diversity capability. The former means that wind speed spectrum of the ash cloud is potentially inferable, whereas the latter implies that variables other than ZHH are available. Theoretically, these additional radar variables are linked to the degree of eccentricity of ash particles, their orientation and density as well as the presence of strong turbulence effects. Thus, the opportunity to refine the ash radar estimates so far developed can benefit from the thorough analysis of radar Doppler and polarization diversity. In this work we show a detailed analysis of Doppler shifts and polarization variables measured by the X band radar

  16. Water-column geochemical anomalies associated with the remnants of a mega plume: A case study after CR-2003 hydrothermal event in Carlsberg Ridge, NW Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Ray, D.; Mirza, I.H.; Prakash, L.S.; Kaisary, S.; Sarma, Y.V.B.; Rao, B.R.; Somayajulu, Y.K.; Drolia, R.K.; KameshRaju, K.A.

    to analyse certain geochemical aspects of a plume. The oxidative particulates make plume waters turbid and this turbidity in turn can be detected with optical sensors mounted on a CTD or attached to deep tow. The optical backscatter profiles along... below 2400 m, we restricted our water sampling mainly in deep (>2000 m) water. A Seabird CTD system (SBE 9/11 plus), bottle rosette along with light scattering sensors (WET Labs 633 and 634) was used for water-column survey. Water samples were...

  17. SALSA3D - A Global 3D P-Velocity Model of the Earth's Crust and Mantle for Improved Event Location (United States)

    Ballard, S.; Begnaud, M. L.; Young, C. J.; Hipp, J. R.; Chang, M.; Encarnacao, A. V.; Rowe, C. A.; Phillips, W. S.; Steck, L.


    To test the hypothesis that high quality 3D Earth models will produce seismic event locations which are more accurate and more precise, we are developing a global 3D P wave velocity model of the Earth’s crust and mantle using seismic tomography. In this paper, we present the most recent version of our model, SALSA3D version 1.5, and demonstrate its ability to reduce mislocations for a large set of realizations derived from a carefully chosen set of globally-distributed ground truth events. Our model is derived from the latest version of the Ground Truth (GT) catalog of P and Pn travel time picks assembled by Los Alamos National Laboratory. To prevent over-weighting due to ray path redundancy and to reduce the computational burden, we cluster rays to produce representative rays. Reduction in the total number of ray paths is ~50%. The model is represented using the triangular tessellation system described by Ballard et al. (2009), which incorporates variable resolution in both the geographic and radial dimensions.. For our starting model, we use a simplified two layer crustal model derived from the Crust 2.0 model over a uniform AK135 mantle. Sufficient damping is used to reduce velocity adjustments so that ray path changes between iterations are small. We obtain proper model smoothness by using progressive grid refinement, refining the grid only around areas with significant velocity changes from the starting model. At each grid refinement level except the last one we limit the number of iterations to prevent convergence thereby preserving aspects of broad features resolved at coarser resolutions. Our approach produces a smooth, multi-resolution model with node density appropriate to both ray coverage and the velocity gradients required by the data. This scheme is computationally expensive, so we use a distributed computing framework based on the Java Parallel Processing Framework, providing us with ~400 processors. Resolution of our model is assessed using a

  18. Multiscale seismic tomography and mantle dynamics (United States)

    Zhao, Dapeng


    Multiscale (local, regional and global) tomographic studies are made to determine the 3-D structure of the Earth, particularly for imaging mantle plumes and subducting slabs. Plume-like slow anomalies are clearly visible under the major hotspot regions in most parts of the mantle, in particular, under Hawaii, Iceland, Kerguelen, South Pacific and Africa (Zhao, 2001, 2004, 2009). The slow anomalies under South Pacific and Africa have lateral extensions of over 1000 km and exist in the entire mantle, representing two superplumes. The Pacific superplume has a larger spatial extent and stronger slow anomalies than that of the Africa superplume. The Hawaiian plume is not part of the Pacific superplume but an independent whole-mantle plume (Zhao, 2004, 2009). The slow anomalies under hotspots usually do not show a straight pillar shape, but exhibit winding images, suggesting that plumes are not fixed in the mantle but can be deflected by the mantle flow. As a consequence, hotspots are not really fixed but can wander on the Earth's surface, as evidenced by the recent paleomagnetic and numeric modeling studies. Wider and more prominent slow anomalies are visible at the core-mantle boundary (CMB) than most of the lower mantle, and there is a good correlation between the distribution of slow anomalies at the CMB and that of hotspots on the surface, suggesting that most of the strong mantle plumes under the hotspots originate from the CMB. However, there are some small-scaled, weak plumes originating from the transition zone or mid mantle depths (Zhao et al., 2006; Zhao, 2009; Lei et al., 2009; Gupta et al., 2009). Clear images of subducting slabs and magma chambers in the upper-mantle wedge beneath active arc volcanoes are obtained, indicating that geodynamic systems associated with arc magmatism and back-arc spreading are related to deep processes, such as convective circulation in the mantle wedge and dehydration reactions of the subducting slab (Zhao et al., 2002, 2007

  19. P- and S-wave delays caused by thermal plumes (United States)

    Maguire, Ross; Ritsema, Jeroen; van Keken, Peter E.; Fichtner, Andreas; Goes, Saskia


    Many studies have sought to seismically image plumes rising from the deep mantle in order to settle the debate about their presence and role in mantle dynamics, yet the predicted seismic signature of realistic plumes remains poorly understood. By combining numerical simulations of flow, mineral-physics constraints on the relationships between thermal anomalies and wave speeds, and spectral-element method based computations of seismograms, we estimate the delay times of teleseismic S and P waves caused by thermal plumes. Wave front healing is incomplete for seismic periods ranging from 10 s (relevant in traveltime tomography) to 40 s (relevant in waveform tomography). We estimate P-wave delays to be immeasurably small (20 s), measurements of instantaneous phase misfit may be more useful in resolving narrow plume conduits. To detect S-wave delays of 0.4-0.8 s and the diagnostic frequency dependence imparted by plumes, it is key to minimize the influence of the heterogeneous crust and upper mantle. We argue that seismic imaging of plumes will advance significantly if data from wide-aperture ocean-bottom networks were available since, compared to continents, the oceanic crust and upper mantle are relatively simple.

  20. P and S wave delays caused by thermal plumes (United States)

    Maguire, Ross; Ritsema, Jeroen; van Keken, Peter E.; Fichtner, Andreas; Goes, Saskia


    Many studies have sought to seismically image plumes rising from the deep mantle in order to settle the debate about their presence and role in mantle dynamics, yet the predicted seismic signature of realistic plumes remains poorly understood. By combining numerical simulations of flow, mineral-physics constraints on the relationships between thermal anomalies and wave speeds, and spectral-element method based computations of seismograms, we estimate the delay times of teleseismic S and P waves caused by thermal plumes. Wavefront healing is incomplete for seismic periods ranging from 10 s (relevant in traveltime tomography) to 40 s (relevant in waveform tomography). We estimate P wave delays to be immeasurably small ( 20 s), measurements of instantaneous phase misfit may be more useful in resolving narrow plume conduits. To detect S wave delays of 0.4-0.8 s and the diagnostic frequency dependence imparted by plumes, it is key to minimize the influence of the heterogeneous crust and upper mantle. We argue that seismic imaging of plumes will advance significantly if data from wide-aperture ocean-bottom networks were available since, compared to continents, the oceanic crust and upper mantle is relatively simple.

  1. Cenozoic vertical motions in the Moray Firth Basin associated with initiation of the Iceland Plume (United States)

    Mackay, L. M.; Turner, J.; Jones, S. M.; White, N. J.


    It is likely that the Iceland mantle plume generated transient uplift across the North Atlantic region when it initiated in earliest Cenozoic time. However, transient uplift recorded in sedimentary basins fringing the region can be overprinted by the effects of permanent uplift. Identifying and quantifying transient uplift can only be achieved in areas which have a well-constrained stratigraphic record and across which the relative importance of permanent and transient uplift varies (e.g., the Moray Firth Basin, North Sea). By analyzing the subsidence of 50 boreholes from the Moray Firth Basin (MFB), residual vertical motions unrelated to rifting have been isolated. Transient uplift of 180-425 m occurred during Paleocene times. The western MFB has also been affected by permanent Cenozoic uplift, with denudation decreasing from 1.3 ± 0.1 km in the west of the basin to zero denudation east of 1°W. Dynamic support above the Iceland Plume led to transient uplift of the entire MFB in early Paleocene times, peaking in latest Paleocene times. In early Eocene times the effect of the plume waned, and subsidence occurred. Paleocene permanent uplift of the NW British Isles is generally accepted to have been due to magmatic underplating of the crust emplaced during the British Tertiary Igneous Province (61-58.5 Ma). The cause of Neogene uplift events is poorly understood, but it could also be associated with the Iceland Plume.

  2. Helium and lead isotopes reveal the geochemical geometry of the Samoan plume. (United States)

    Jackson, M G; Hart, S R; Konter, J G; Kurz, M D; Blusztajn, J; Farley, K A


    Hotspot lavas erupted at ocean islands exhibit tremendous isotopic variability, indicating that there are numerous mantle components hosted in upwelling mantle plumes that generate volcanism at hotspots like Hawaii and Samoa. However, it is not known how the surface expression of the various geochemical components observed in hotspot volcanoes relates to their spatial distribution within the plume. Here we present a relationship between He and Pb isotopes in Samoan lavas that places severe constraints on the distribution of geochemical species within the plume. The Pb-isotopic compositions of the Samoan lavas reveal several distinct geochemical groups, each corresponding to a different geographic lineament of volcanoes. Each group has a signature associated with one of four mantle endmembers with low (3)He/(4)He: EMII (enriched mantle 2), EMI (enriched mantle 1), HIMU (high µ = (238)U/(204)Pb) and DM (depleted mantle). Critically, these four geochemical groups trend towards a common region of Pb-isotopic space with high (3)He/(4)He. This observation is consistent with several low-(3)He/(4)He components in the plume mixing with a common high-(3)He/(4)He component, but not mixing much with each other. The mixing relationships inferred from the new He and Pb isotopic data provide the clearest picture yet of the geochemical geometry of a mantle plume, and are best explained by a high-(3)He/(4)He plume matrix that hosts, and mixes with, several distinct low-(3)He/(4)He components.


    This presentation presents an assessment of plume diving. Observations included: vertical plume delineation at East Patchogue, NY showed BTEX and MTBE plumes sinking on either side of a gravel pit; Lake Druid TCE plume sank beneath unlined drainage ditch; and aquifer recharge/dis...

  4. Full seismic waveform inversion of the African crust and Mantle - Initial Results (United States)

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


    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. Recycled dehydrated lithosphere observed in plume-influenced mid-ocean-ridge basalt. (United States)

    Dixon, Jacqueline Eaby; Leist, Loretta; Langmuir, Charles; Schilling, Jean-Guy


    A substantial uncertainty in the Earth's global geochemical water cycle is the amount of water that enters the deep mantle through the subduction and recycling of hydrated oceanic lithosphere. Here we address the question of recycling of water into the deep mantle by characterizing the volatile contents of different mantle components as sampled by ocean island basalts and mid-ocean-ridge basalts. Although all mantle plume (ocean island) basalts seem to contain more water than mid-ocean-ridge basalts, we demonstrate that basalts associated with mantle plume components containing subducted lithosphere--'enriched-mantle' or 'EM-type' basalts--contain less water than those associated with a common mantle source. We interpret this depletion as indicating that water is extracted from the lithosphere during the subduction process, with greater than 92 per cent efficiency.

  6. Plume-tectonics for exploring the past and future of the earth. Marugoto chikyukan 'plume tectonics' towa

    Energy Technology Data Exchange (ETDEWEB)

    Maruyama, S. (Tokyo Institute of Technology, Tokyo (Japan). Faculty of Science)


    This paper briefly explains the behavior of the inside of the Earth that has been becoming clearer as the seismic wave tomography and other instruments have been improved. It also describes the plume-tectonics. A plume represents a mass of mantle in the mantle layer that is hotter or colder than the sounding part of the layer. The seismic wave tomography provides a view of two large hot areas on the Earth, one below the South Pacific Ocean and the other below Southern Africa, and a cold area below Asia. There are huge rising and falling flows (plumes) in the mantle, forming a convection. Plumes are very huge; the diameter of a plume may be about 5,000 km, rising high from the bottom of the mantle to the plate level, and extending as long as about 2,900 km. When a cold plume falls on the core and causes a slight difference in temperature between the core and the plume in any part of the interface, a hot plume is produced in the part where temperature is not even. The mechanism of the continents joining or separating from each other in the periods of hundreds of millions of years. The first key to a new theory is cooling of the Earth. 3 figs.

  7. Reply to Comment on “Garnet-bearing ultramafic rocks from the Dominican Republic: Fossil mantle plume fragments in an ultra high pressure oceanic complex?” by Jan C.M. De Hoog (United States)

    Gazel, Esteban; Abbott, Richard N.; Draper, Grenville


    Two competing hypotheses have been proposed for garnet-bearing ultramafic rocks in the Dominican Republic: (1) The ultrahigh pressure (UHP) - ultrahigh temperature (UHT) hypothesis involves a magmatic protolith of mantle origin, which was then delivered to, and incorporated into deep-subducted oceanic crust (eclogite) at UHP conditions (Abbott et al., 2005, 2006, 2007; Abbott and Draper, 2010; Gazel et al., 2011). (2) The low-pressure (LP) hypothesis involves a plagioclase-bearing, arc-related protolith of crustal origin, which was then subducted to UHP conditions (De Hoog, 2011; Hattori et al., 2010a,b). In both hypotheses, the rocks were uplifted to the surface by an as yet poorly understood mechanism. Here we respond to concerns regarding the integrity of REE analyses, Cpx-Grt REE partitioning, other matters related to the interpretation of the trace element data, and Grt-Spl major-element thermometry. We show that none of the concerns precludes a UHP magmatic origin.

  8. Impact of volcanic plume emissions on rain water chemistry during the January 2010 Nyamuragira eruptive event: implications for essential potable water resources. (United States)

    Cuoco, Emilio; Tedesco, Dario; Poreda, Robert J; Williams, Jeremy C; De Francesco, Stefano; Balagizi, Charles; Darrah, Thomas H


    On January 2, 2010 the Nyamuragira volcano erupted lava fountains extending up to 300 m vertically along an ~1.5 km segment of its southern flank cascading ash and gas on nearby villages and cities along the western side of the rift valley. Because rain water is the only available potable water resource within this region, volcanic impacts on drinking water constitutes a major potential hazard to public health within the region. During the 2010 eruption, concerns were expressed by local inhabitants about water quality and feelings of physical discomfort (e.g. nausea, bloating, indigestion, etc.) after consuming rain water collected after the eruption began. We present the elemental and ionic chemistry of drinking water samples collected within the region on the third day of the eruption (January 5, 2010). We identify a significant impact on water quality associated with the eruption including lower pH (i.e. acidification) and increases in acidic halogens (e.g. F(-) and Cl(-)), major ions (e.g. SO(4)(2-), NH(4)(+), Na(+), Ca(2+)), potentially toxic metals (e.g. Al(3+), Mn(2+), Cd(2+), Pb(2+), Hf(4+)), and particulate load. In many cases, the water's composition significantly exceeds World Health Organization (WHO) drinking water standards. The degree of pollution depends upon: (1) ash plume direction and (2) ash plume density. The potential negative health impacts are a function of the water's pH, which regulates the elements and their chemical form that are released into drinking water.

  9. Source of magma for Elet-Ozero pluton (NE Baltic Shield) - subduction or plume-related material? (United States)

    Ryabchikov, Igor; Kogarko, Liya


    Eletozero pluton is located in the northeastern part of the Karelian Craton, it covers an area of about 100 km2 and cuts through Archaean granite-gneisses. The complex has a concentric zoned structure, the peripheral part being composed of a layered gabbro series; the central area is occupied by nepheline syenites. Mafic and ultramafic rocks in this intrusion often contain potassium feldspar (olivine monzonites and monzonites). Gabbroids are characterized by rhythmic layering expressed in the alternation of leucocratic layers predominantly composed of plagioclase and melanocratic layers with pyroxenes, olivine, titanomagnetite and ilmenite. The rocks of the pluton are enriched in highly incompatible elements by comparison with moderately incompatible elements: average primitive mantle normalized La/Lu ratio is 18.3. At the same time, all the rocks from Elet-Ozero massif including the most primitive ones (high Mg-numbers and high Ni contents) exhibit distinct positive Ba anomaly: mean chondrite normalized Ba/Th ratio is 15.3 (both elements have similar incompatibility-[1]). Enrichment of parent magma in Ba is also confirmed by the presence of high-Ba feldspars and micas in some samples of gabbroids. The most Ba-rich feldspar contains 75% of celsian component: K0.09Na0.04Ca0.008Sr0.04Ba0.75Al1.73Fe0.14Si2.20O8. Ba is a fluid mobile incompatible lithophile element that is probably the most sensitive indicator of subduction fluid addition to the mantle wedge. Thus, positive Ba anomaly suggests input of subduction related component into the source of Elet-Ozero magma. The presence of subduction related material in the lithosphere of Karelian craton has been proposed on the basis of Os isotope studies of mantle xenoliths from Finnish kimberlites [2]. The age of this subduction event is similar to the age of Elet-Ozero pluton. On the other hand, there are certain arguments in favor of connection of Elet-Ozero intrusive complex with mantle plume activity. In particular it

  10. The Shangzhuang Fe-Ti oxide-bearing layered mafic intrusion, northeast of Beijing (North China): Implications for the mantle source of the giant Late Mesozoic magmatic event in the North China Craton (United States)

    Liu, Ping-Ping; Zhou, Mei-Fu; Yan, Dan-Ping; Zhao, Guo-Chun; Su, Shang-Guo; Wang, Xiao-Lin


    The Early Cretaceous Shangzhuang Fe-Ti oxide-bearing layered mafic intrusion in the Yanshan Belt northeast of Beijing is coeval with the giant Late Mesozoic igneous province in the eastern part of the North China Craton (NCC). This magmatic event was associated with lithospheric thinning and thus the igneous rocks have been used to characterize the nature of the Mesozoic mantle beneath the NCC. The Shangzhuang mafic pluton intruded a large granodioritic complex and crystallized at ~ 850-872°C at a depth of 13-14 km. It is composed, from the base upward, of troctolite, Fe-Ti oxide-bearing gabbronorite and gabbro. Rocks from this intrusion have low initial 87Sr/86Sr ratios (0.7053-0.7058), negative initial εNd values (- 9.4 to - 10.7), highly differentiated LREE and nearly flat HREE patterns indicative of an EMI-like mantle source unaffected by upper crustal contamination. The occurrence of Fe-Ti oxide ore layers, magnetite-ilmenite exsolution lamellae in hornblende and high TiO2 contents of the silicate rocks indicate that they formed from Fe- and Ti-rich ferrobasaltic magmas, which may have been generated by addition of magmas from a deeper mantle source. The presence of orthopyroxene, high-Mg ilmenite (up to 8.5 wt %), hornblende, biotite and high oxygen fugacities calculated from coexisting titanomagnetite-ilmenite pairs can be explained by derivation from an enriched EMI-type mantle modified by fluids from a subducted slab and mixed with asthenospheric or deeper-mantle materials in an extensional setting. Exposure of the complex occurred during large-scale uplift (at least 13 km) and exhumation of the Yanshan orogenic belt in the Early Cretaceous. Chemical metasomatism triggered by water and enhanced by heat from a deep magma source may have played an important role in removing the ancient cratonic root, generating partial melting of the lithospheric mantle and producing coeval magmatic activity in the Mesozoic eastern NCC.

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

    DEFF Research Database (Denmark)

    Søager, Nina; Holm, Paul Martin

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

  12. Mantle Dynamics of Australia-Banda Arc Collision as Inferred from Shear Wave Splitting Analysis of Teleseismic and Local Slab Events (United States)

    Harris, C. W.; Miller, M. S.; O'Driscoll, L.; Porritt, R. W.; Roosmawati, N.; Widiyantoro, S.


    Arc-continent collision is an important factor in continent building, orogensis, and ocean closure, yet the details associated with it are not fully understood. East-Timor and the Nusa Tenggara Timur region of Indonesia provide a unique setting to study a young arc-continent collision (~8 Ma) and incipient orogenesis. The NSF funded Banda Arc project affords a rare opportunity to investigate unconstrained processes such as active continental subduction and slab rupture beneath a regional deployment of broadband seismometers. We use data from 35 broadband sensors to analyze seismic anisotropy through measuring shear wave splitting. These stations span the roughly east-west transition from normal oceanic subduction at the Sunda Arc to collision at the Banda Arc, and cross areas associated with back-arc thrusting, arc volcanism, extinct volcanism and a rapidly exhuming forearc. Thirty of the sensors used in the analysis are temporary stations installed by our research team in 2014 and will remain in the field until 2016 or later. The remaining stations are part of the open-access GFZ GEOFON global seismic network. We present preliminary shear wave splitting results for teleseismic (*KS core phases) and local (direct S phase) arrivals in order to inspect the sub-slab mantle and the supra-slab mantle wedge for anisotropic patterns related to olivine flow fabric. These results can be used to assess regional strain linked to ongoing collision and may elucidate any slab tearing that has resulted from the (partial) subduction of buoyant continental material of Australian affinity. Presently, we observe a trend of primarily trench-parallel sub-slab fast polarization directions and perhaps more complicated anisotropy in the mantle wedge. Relative to the trench, there appears to be more spatial variation in fast axis orientation for direct arrivals than teleseismic phases. We discuss how the interpretation of our initial results provides insight into the mantle dynamics of the

  13. The role of thermodynamics in mantle convection: is mantle-layering intermittent? (United States)

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


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

  14. Pyroxenite in the Galapagos plume source at 65 Ma (United States)

    Whalen, W. T.; Gazel, E.; Vidito, C. A.; Herzberg, C. T.; Class, C.; Bizimis, M.; Alvarado-Induni, G.


    Mantle plumes originate from boundary layers below the upper mantle. Their surface expressions as hotspot tracks have been linked to voluminous outpourings of lava in the form of large igneous provinces. The Galapagos hotspot has been active since ~90 Ma and the oldest lavas of its associated submarine ridge have been dated to ~14 Ma, subducting at the Middle America Trench, off Costa Rica. The Galapagos plume head magmatic production is preserved as the Caribbean Large Igneous Province (CLIP). A series of 15-65 Ma accreted Galapagos paleo-ridges and islands/seamounts are accreted in the Pacific coast of Costa Rica and Panama. One of these accreted terranes, the Quepos block on the west coast of Costa Rica is an ancient, ~65 Ma Galapagos island. Olivine phenocrysts from Quepos picrites have elevated Ni and low Ca and Mn and Fe/Mn indicative of a dominant pyroxenite source component while CLIP samples are dominated by a peridotite source. The mantle potential temperature (max) of the plume changed from ~1650 to ~1550 C at 65 Ma. This change correlates with the first appearance of the pyroxenite component and an EMII signature (Northern Galapagos Domain) in the Galapagos plume. A relatively dense pyroxenite component may provide a mechanism for the change in Tp due to its effect on the plume's bouyancy. Alternatively, the pyroxenite component was diluted by high peridotite melt fraction during the massive production of the CLIP.

  15. Plume Ascent Tracker: Interactive Matlab software for analysis of ascending plumes in image data (United States)

    Valade, S. A.; Harris, A. J. L.; Cerminara, M.


    This paper presents Matlab-based software designed to track and analyze an ascending plume as it rises above its source, in image data. It reads data recorded in various formats (video files, image files, or web-camera image streams), and at various wavelengths (infrared, visible, or ultra-violet). Using a set of filters which can be set interactively, the plume is first isolated from its background. A user-friendly interface then allows tracking of plume ascent and various parameters that characterize plume evolution during emission and ascent. These include records of plume height, velocity, acceleration, shape, volume, ash (fine-particle) loading, spreading rate, entrainment coefficient and inclination angle, as well as axial and radial profiles for radius and temperature (if data are radiometric). Image transformations (dilatation, rotation, resampling) can be performed to create new images with a vent-centered metric coordinate system. Applications may interest both plume observers (monitoring agencies) and modelers. For the first group, the software is capable of providing quantitative assessments of plume characteristics from image data, for post-event analysis or in near real-time analysis. For the second group, extracted data can serve as benchmarks for plume ascent models, and as inputs for cloud dispersal models. We here describe the software's tracking methodology and main graphical interfaces, using thermal infrared image data of an ascending volcanic ash plume at Santiaguito volcano.

  16. Three-dimensional laboratory modeling of the Tonga trench and Samoan plume interaction (United States)

    Druken, K. A.; Kincaid, C. R.; Pockalny, R. A.; Griffiths, R. W.; Hart, S. R.


    Plume processes occurring near ridge centers (e.g. Iceland) or mid-plate (e.g. Hawaii) have been well studied; however, the behavior of a plume near a subducting plate is still poorly understood and may in fact differ from the typical expected plume surfacing patterns. We investigate how three-dimensional subduction-driven flow relates to the deformation and dispersal of nearby upwelling plume material and the associated geochemical spatial patterns, with site-specific comparisons to the Tonga trench and Samoan plume system. Eighteen plume-trench laboratory experiments were conducted with varied combinations of subduction motions (down-dip, trench rollback, slab steepening and back-arc extension) and plume parameters (position and temperature.) A phenolic plate and glucose syrup, with a temperature dependent viscosity, are used to model the slab and upper mantle, respectively. Hydraulic pistons control longitudinal, translational and steepening motions of the slab as a simplified kinematic approach to mimic dynamic experiments. Results show that the subduction-induced flow dominates the upwelling strength of the plume, causing a significant portion of the plume head to subduct before reaching the melt zone. The remaining material is entrained around the slab edge into the mantle wedge by the trench rollback-induced flow. The proportion of subducted verses entrained material is predominantly dependent on plume location (relative to the trench) and thermal strength, with additional effects from back-arc extension and plate steepening.

  17. Comparing the nature of the western and eastern Azores mantle (United States)

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


    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.

  18. Water Distribution in the Continental and Oceanic Upper Mantle (United States)

    Peslier, Anne H.


    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).

  19. Wet plume atop of the flattening slab: Insight into intraplate volcanism in East Asia (United States)

    He, Lijuan


    Geophysical observations imply the intraplate volcanism in East Asia is related to dehydration of slab stagnating in the transition zone. To better understand the dynamics of such process, a thermochemical mantle convection model is constructed to simulate numerically the thermal evolution of slab and the transportation of water in the process of slab downgoing, flattening and stagnation. Equation of water transfer is included, and water effects on density and viscosity are considered. Model results indicate the warming of slab by surrounding mantle is rather slow. Water could be successfully dragged into the transition zone if the reference viscosity of the hydrous layer (with initial water of 2 wt%) is higher than 1017 Pa s and that of mantle is 1021 Pa s. Wet plumes could then originate in the flat-lying part of the slab, relatively far from the trench. Generally, the viscosity of the hydrous layer governs the initiation of wet plume, whereas the viscosity of the overlying mantle wedge controls the activity of the ascending wet plumes - they are more active in the weaker wedge. The complex fluid flow superposed by corner flow and free thermal convection influences greatly the water transport pattern in the upper mantle. Modeling results together with previous modeling infer three stages of water circulation in the big mantle wedge: 1) water is brought into the mantle transition zone by downward subducting slab under some specific thermo-rheological conditions, otherwise water is released at shallow depth near wedge tip; 2) wet plume generates from surface of the flattening slab warmed by surrounding mantle, and 3) water spreads over the big mantle wedge. Wet plume from the flattening Pacific Plate arrives at the lithospheric base and induces melting, which can explain the intraplate Cenozoic volcanoes in East Asia.

  20. Primary magmas and mantle temperatures through time (United States)

    Ganne, Jérôme; Feng, Xiaojun


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

  1. Experiments on metal-silicate plumes and core formation. (United States)

    Olson, Peter; Weeraratne, Dayanthie


    Short-lived isotope systematics, mantle siderophile abundances and the power requirements of the geodynamo favour an early and high-temperature core-formation process, in which metals concentrate and partially equilibrate with silicates in a deep magma ocean before descending to the core. We report results of laboratory experiments on liquid metal dynamics in a two-layer stratified viscous fluid, using sucrose solutions to represent the magma ocean and the crystalline, more primitive mantle and liquid gallium to represent the core-forming metals. Single gallium drop experiments and experiments on Rayleigh-Taylor instabilities with gallium layers and gallium mixtures produce metal diapirs that entrain the less viscous upper layer fluid and produce trailing plume conduits in the high-viscosity lower layer. Calculations indicate that viscous dissipation in metal-silicate plumes in the early Earth would result in a large initial core superheat. Our experiments suggest that metal-silicate mantle plumes facilitate high-pressure metal-silicate interaction and may later evolve into buoyant thermal plumes, connecting core formation to ancient hotspot activity on the Earth and possibly on other terrestrial planets.

  2. An olivine-free mantle source of Hawaiian shield basalts. (United States)

    Sobolev, Alexander V; Hofmann, Albrecht W; Sobolev, Stephan V; Nikogosian, Igor K


    More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both nickel and silicon at lower levels. This can be resolved if the olivine of the mantle peridotite is consumed by reaction with melts derived from recycled oceanic crust, to form a secondary pyroxenitic source. Our modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from this source. In addition, we estimate that the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plume edge. These results are also consistent with volcano volumes, magma volume flux and seismological observations.

  3. Sediment plume response to surface melting and supraglacial lake drainages on the Greenland ice sheet

    DEFF Research Database (Denmark)

    Chu, Vena W.; Smith, Laurence C; Rennermalm, Asa K.


    of a downstream sediment plume in Kangerlussuaq Fjord by comparing: (1) plume area and suspended sediment concentration from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and field data; (2) ice-sheet melt extent from Special Sensor Microwave/Imager (SSM/I) passive microwave data; and (3......) supraglacial lake drainage events from MODIS. Results confirm that the origin of the sediment plume is meltwater release from the ice sheet. Interannual variations in plume area reflect interannual variations in surface melting. Plumes appear almost immediately with seasonal surface-melt onset, provided...... the estuary is free of landfast sea ice. A seasonal hysteresis between melt extent and plume area suggests late-season exhaustion in sediment supply. Analysis of plume sensitivity to supraglacial events is less conclusive, with 69% of melt pulses and 38% of lake drainage events triggering an increase in plume...

  4. Evidence for melt channelization in Galapagos plume-ridge interaction (United States)

    Mittal, T.; Richards, M. A.


    Many present-day hot spots are located within ~ 1000 km of a mid-ocean ridge, either currently or in the geologic past, leading to frequent interaction between these two magmatic regimes. The consequent plume-ridge interactions provide a unique opportunity to test models for asthenosphere-lithosphere dynamics, with the plume acting as a tracer fluid in the problem, and excess magmatism reflecting otherwise unsampled sub-surface phenomena. Galapagos is an off-ridge hotspot with the mantle plume located ~150-250 km south of the plate boundary. Plume-ridge interaction in Galapagos is expressed by the formation of volcanic lineaments of islands and seamounts - e.g., the Wolf-Darwin lineament (WDL) - providing a direct probe of the plume-ridge interaction process, especially in regards to geochemical data. Although several models have been proposed to explain plume-ridge interaction in Galapagos, none adequately explain the observed characteristics, especially the WDL. In particular, predicted lithospheric fault orientations and melt density considerations appear at odds with observations, suggesting that lithospheric extension is not the primary process for formation of these islands. Other off-ridge hotspots interacting with nearby spreading ridges, such as Reunion and Louisville, also exhibit volcanic lineaments linking the plume and the ridge. Thus these lineament-type features are a common outcome of plume-ridge interaction that are indicative of the underlying physics. We propose that the lineaments are surface expressions of narrow sub-lithospheric melt channels focused towards the spreading ridge. These channels should form naturally due to the reactive infiltration instability in a two-phase flow of magma and solid mantle as demonstrated in two-phase flow simulations (e.g., Katz & Weatherley 2012). For Galapagos, we show that melt channels can persist thermodynamically over sufficient length-scales to link the plume and nearby ridge segments. We also show that

  5. Mantle convection, tectonics and the evolution of the Tethyan subduction zone (United States)

    Jolivet, Laurent; Sternai, Pietro; Menant, Armel; Faccenna, Claudio; Becker, Thorsten; Burov, Evguenii


    side of Africa from the Jurassic until the collision in the Oligocene, and even afterward when Arabia formed by opening of the Red Sea and the Gulf of Aden. This also suggests a dominant role of an underlying flow at large scale, dragging and mechanically eroding plates and breaking them into fragments, then passively carried. Only during a short period of the Late Cretaceous did the situation change drastically with the obduction event giving the large ophiolitic nappes observed from Oman to Turkey. This obduction event has never been really explained. It has been shown to be coeval with faster plate velocities and more active formation of oceanic crust globally, which in turn suggests a link with deep mantle convection. We discuss this succession of events and propose to relate them with the basal drag induced by convective mantle flow below the African continental lithosphere. We discuss the effects of convection on crustal deformation at different scales from deep convection related to plumes and subduction zones to more local mantle flow due to slab retreat and tearing.

  6. On the possibility of crater formation associated with an ascending plume (United States)

    Medvedev, A. B.


    A hypothetical possibility of a qualitative explanation of large crater formation on the surfaces of the Moon and Mercury is discussed in terms of the concept of thermal mantle plumes. Prerequisites to this hypothesis are revealed under the assumption that the model equation of state of SiO2 exhibiting an anomaly (a negative coefficient of thermal expansion) in the range of states approximately corresponding to average conditions typical of mantles of minor planets is applicable, in a first approximation, to mantle material. The anomaly reduces the buoyancy of hot plume material in such a way that, under conditions of moderate overheating, only relatively high columns comparable in size to the mantle are capable of ascending from the mantle bottom to the crust; allows cold peripheral material surrounding the hot column to be pushed away; causes compaction of the vertical zone of the contact of the column with the surrounding medium at the first stages after the plume ascent; and leads to compaction of the deep mantle due to the long-term heat supply. Such phenomena can lead to vertical craterlike deformations of the crust in areas of ascending large plumes whose presence can be supposed at early stages of the existence of minor planets. Significant implications of such an anomaly for geophysical processes can also be postulated.

  7. Recycled crust in the Galápagos Plume source at 70 Ma: Implications for plume evolution (United States)

    Trela, Jarek; Vidito, Christopher; Gazel, Esteban; Herzberg, Claude; Class, Cornelia; Whalen, William; Jicha, Brian; Bizimis, Michael; Alvarado, Guillermo E.


    Galápagos plume-related lavas in the accreted terranes of the Caribbean and along the west coast of Costa Rica and Panama provide evidence on the evolution of the Galápagos mantle plume, specifically its mantle temperature, size and composition of heterogeneities, and dynamics. Here we provide new 40Ar/39Ar ages, major and trace element data, Sr-Nd-Pb isotopic compositions, and high-precision olivine analyses for samples from the Quepos terrane (Costa Rica) to closely examine the transitional phase of the Galápagos Plume from Large Igneous Province (LIP) to ocean island basalt (OIB) forming stages. The new ages indicate that the record of Quepos volcanism began at 70 Ma and persisted for 10 Ma. Petrological evidence suggests that the maximum mantle potential temperature (Tp) of the plume changed from ∼1650° to ∼1550 °C between 90-70 Ma. This change correlates with a dominant pyroxenite component in the Galapagos source as indicated by high Ni and Fe/Mn and low Ca olivines relative to those that crystallized in normal peridotite derived melts. The decrease in Tp also correlates with an increase in high-field strength element enrichments, e.g., Nb/Nb*, of the erupted lavas. Radiogenic isotope ratios (Nd-Pb) suggest that the Quepos terrane samples have intermediate (Central Domain) radiogenic signatures. The Galápagos plume at 70 Ma represents elevated pyroxenite melt productivity relative to peridotite in a cooling lithologically heterogeneous mantle.

  8. Os-He Isotope Systematics of Iceland Picrites: Evidence for a Deep Origin of the Iceland Plume (United States)

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


    Recent work on the origin of the Iceland hotspot suggests that it may result from upwelling upper mantle material rather than a deep plume. To constrain the depths of origins of Iceland mantle sources, Os and He isotope systematics were obtained on a suite picrites that span the compositional range observed within the neovolcanic zones.

  9. An overview of the Mesozoic-Cenozoic magmatism and tectonics in Eastern Paraguay and central Andes (Western Gondwana): Implications for the composition of mantle sources (United States)

    Omarini, Ricardo H.; Gasparon, Massimo; De Min, Angelo; Comin-Chiaramonti, Piero


    The amalgamation of the Western Gondwana (including the Greater Gondwana supercraton) occurred at 600 Ma during the Brazilian - Pan African orogeny. A plate junction related to this event is marked by the Transbrazilian lineament which separates the South American continent into two sectors: the Eastern Paraguay-Brazilian and Central Andean domains. An overview of the geodynamic data from these two sectors indicates that the two domains were subjected to distinct evolutions from the Proterozoic to the present. The Andean domain is characterized by long-lived subduction processes linked to the convergence and consequent collision of microplates since the Middle Proterozoic (western Amazonian Craton) with a peak at about 600-580 Ma. The Paraguay-Brazilian domain remained relatively stable but was affected by extension episodes that reactivated ancient (Early and Middle Proterozoic) suture zones. These different geodynamic evolutions seem to reflect broadly distinct mantle compositions. In the subduction zones of the Andean domain the mantle was deeply modified by metasomatic processes following the subduction of oceanic plates. Consequently, the Andean type magma sources show a clear HIMU imprint inherited from the MORB, whereas the Paraguay-Brazilian sector shows a prevalent EMI and subordinate EMII character. The petrological data mainly from Mesozoic and Cenozoic magmatic events in the two sectors are reviewed to investigate the current mantle plume and mantle dome models for the uprising of the asthenospheric (or sub-lithospheric) material.

  10. Solar Coronal Plumes

    Directory of Open Access Journals (Sweden)

    Giannina Poletto


    Full Text Available Polar plumes are thin long ray-like structures that project beyond the limb of the Sun polar regions, maintaining their identity over distances of several solar radii. Plumes have been first observed in white-light (WL images of the Sun, but, with the advent of the space era, they have been identified also in X-ray and UV wavelengths (XUV and, possibly, even in in situ data. This review traces the history of plumes, from the time they have been first imaged, to the complex means by which nowadays we attempt to reconstruct their 3-D structure. Spectroscopic techniques allowed us also to infer the physical parameters of plumes and estimate their electron and kinetic temperatures and their densities. However, perhaps the most interesting problem we need to solve is the role they cover in the solar wind origin and acceleration: Does the solar wind emanate from plumes or from the ambient coronal hole wherein they are embedded? Do plumes have a role in solar wind acceleration and mass loading? Answers to these questions are still somewhat ambiguous and theoretical modeling does not provide definite answers either. Recent data, with an unprecedented high spatial and temporal resolution, provide new information on the fine structure of plumes, their temporal evolution and relationship with other transient phenomena that may shed further light on these elusive features.

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

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


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

  12. Events

    Directory of Open Access Journals (Sweden)

    Igor V. Karyakin


    Full Text Available The 9th ARRCN Symposium 2015 was held during 21st–25th October 2015 at the Novotel Hotel, Chumphon, Thailand, one of the most favored travel destinations in Asia. The 10th ARRCN Symposium 2017 will be held during October 2017 in the Davao, Philippines. International Symposium on the Montagu's Harrier (Circus pygargus «The Montagu's Harrier in Europe. Status. Threats. Protection», organized by the environmental organization «Landesbund für Vogelschutz in Bayern e.V.» (LBV was held on November 20-22, 2015 in Germany. The location of this event was the city of Wurzburg in Bavaria.

  13. Chemistry in aircraft plumes

    Energy Technology Data Exchange (ETDEWEB)

    Kraabol, A.G.; Stordal, F.; Knudsen, S. [Norwegian Inst. for Air Research, Kjeller (Norway); Konopka, P. [Deutsche Forschungsanstalt fuer Luft- und Raumfahrt e.V. (DLR), Wessling (Germany). Inst. fuer Physik der Atmosphaere


    An expanding plume model with chemistry has been used to study the chemical conversion of NO{sub x} to reservoir species in aircraft plumes. The heterogeneous conversion of N{sub 2}O{sub 5} to HNO{sub 3}(s) has been investigated when the emissions take place during night-time. The plume from an B747 has been simulated. During a ten-hour calculation the most important reservoir species was HNO{sub 3} for emissions at noon. The heterogeneous reactions had little impact on the chemical loss of NO{sub x} to reservoir species for emissions at night. (author) 4 refs.

  14. Laboratory-Scale Simulation of Spiral Plumes in Fluid with Hight Ptandtl Number

    CERN Document Server

    Sharifulin, A N


    We experimentally investigated the appearance of a plumes from local hot spot and study its interaction with cellular flow in closed cavity filled by silicon oil with Prandtl number Pr ~2*10^3 . Convective plume is generated by a local heat source, located on the top of the small rubber cylinder, which is located in the center of the bottom of the rectangular cell. Green laser has been used to simulate the hot-spot. Roll-type large-scale convective flow is generated by heating of the one vertical sides of cavity. Influence of power of hot point on the shape of plume has been investigated. It is shown that the presence of cellular convective motion may lead to the formation of a strange spiral convective plume. This plume looks like Archimedes spiral replaced on vertical plane. Physical mechanism of the formation of strange spiral plume and application of obtained results for mantle convection problems are discussed.

  15. Deep Mantle Cycling of Oceanic Crust: Evidence from Diamonds and Their Mineral Inclusions (United States)

    Walter, M. J.; Kohn, S. C.; Araujo, D.; Bulanova, G. P.; Smith, C. B.; Gaillou, E.; Wang, J.; Steele, A.; Shirey, S. B.


    A primary consequence of plate tectonics is that basaltic oceanic crust subducts with lithospheric slabs into the mantle. Seismological studies extend this process to the lower mantle, and geochemical observations indicate return of oceanic crust to the upper mantle in plumes. There has been no direct petrologic evidence, however, of the return of subducted oceanic crustal components from the lower mantle. We analyzed superdeep diamonds from Juina-5 kimberlite, Brazil, which host inclusions with compositions comprising the entire phase assemblage expected to crystallize from basalt under lower-mantle conditions. The inclusion mineralogies require exhumation from the lower to upper mantle. Because the diamond hosts have carbon isotope signatures consistent with surface-derived carbon, we conclude that the deep carbon cycle extends into the lower mantle.

  16. Abundant carbon in the mantle beneath Hawai`i (United States)

    Anderson, Kyle R.; Poland, Michael


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

  17. 3-D numerical modeling of plume-induced subduction initiation (United States)

    Baes, Marzieh; Gerya, taras; Sobolev, Stephan


    Investigation of mechanisms involved in formation of a new subduction zone can help us to better understand plate tectonics. Despite numerous previous studies, it is still unclear how and where an old oceanic plate starts to subduct beneath the other plate. One of the proposed scenarios for nucleation of subduction is plume-induced subduction initiation, which was investigated in detail, using 2-D models, by Ueda et al. (2008). Recently. Gerya et al. (2015), using 3D numerical models, proposed that plume-lithosphere interaction in the Archean led to the subduction initiation and onset of plate tectonic. In this study, we aim to pursue work of Ueda et al. (2008) by incorporation of 3-D thermo-mechanical models to investigate conditions leading to oceanic subduction initiation as a result of thermal-chemical mantle plume-lithosphere interaction in the modern earth. Results of our experiments show four different deformation regimes in response to plume-lithosphere interaction, that are a) self-sustaining subduction initiation where subduction becomes self-sustained, b) freezing subduction initiation where subduction stops at shallow depths, c) slab break-off where subducting circular slab breaks off soon after formation and d) plume underplating where plume does not pass through the lithosphere but spreads beneath it (failed subduction initiation). These different regimes depend on several parameters such as plume's size, composition and temperature, lithospheric brittle/plastic strength, age of the oceanic lithosphere and presence/absence of lithospheric heterogeneities. Results show that subduction initiates and becomes self-sustained when lithosphere is older than 10 Myr and non-dimensional ratio of the plume buoyancy force and lithospheric strength above the plume is higher than 2.

  18. Lithology and temperature: How key mantle variables control rift volcanism (United States)

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


    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

  19. Plume Measurement System (PLUMES) Calibration Experiment (United States)


    Atle Lohrmann SonTek, Inc. 7940 Silverton Avenue, No. 105 San Diego, California 92126 and Craig Huhta JIMAR University of Hawaii, Honolulu, Hawaii 96822...Measurement System (PLUMES) Calibration Experiment by Age Lohrmann SonTek, Inc. 7940 Silverton Avenue, No. 105 San Diego, CA 92126 Craig Huhta JIMAR...PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) &. PERFORMING ORGANIZATION SonTek, Inc., 7940 Silverton Avenue, No. 105, San Diego, CA 92126 REPORT NUMBER

  20. Geochemical Characterization of Endmember Mantle Components (United States)


    in Figs. 7 & 8). Production of the EM component by deep mantle fractionations involving high-pressure phases such as Ca or Mg perovskite likewise... Hafnium isotopes in basalts from the southern Mid-Atlantic Ridge from 40°S to 55°S: Discovery and Shona plume-ridge interactions and the role of recycled...171 (1999) 49-61. Bowring, S. A. and T. Housh, The Earth’s Early Evolution, Science 269 (1995) 1535-1540. Chauvel, C. and J. Blichert-Toft, A hafnium

  1. The Great Plume Debate

    Institute of Scientific and Technical Information of China (English)

    Ian H. Campbell


    @@ It is forty years since J. Tuzo Wilson first suggested that the Hawaiian Islands were produced by the oceanic lithosphere moving over a stationary "hotspot" in the mantle, and thirty years since W.

  2. Vertical velocity of mantle flow of East Asia and adjacent areas

    Institute of Scientific and Technical Information of China (English)

    CHENG Xianqiong; ZHU Jieshou; CAI Xuelin


    Based on the high-resolution body wave tomo- graphic image and relevant geophysical data, we calculated the form and the vertical and tangential velocities of mantle flow. We obtained the pattern of mantle convection for East Asia and the West Pacific. Some important results and under- standings are gained from the images of the vertical velocity of mantle flow for East Asia and the West Pacific. There is an upwelling plume beneath East Asia and West Pacific, which is the earth's deep origin for the huge rift valley there. We have especially outlined the tectonic features of the South China Sea, which is of the "工" type in the upper mantle shield type in the middle and divergent in the lower; the Siberian clod downwelling dives from the surface to near Core and mantle bounary (CMB), which is convergent in the upper mantle and divergent in the lower mantle; the Tethyan subduction region, centered in the Qinghai-Tibet plateau, is visible from 300 to 2 000 km, which is also convergent in the upper mantle and divergent in the lower mantle. The three regions of mantle convection beneath East Asia and the West Pacific are in accordance with the West Pacific, Ancient Asia and the Tethyan structure regions. The mantle upwelling orig- inates from the core-mantle boundary and mostly occurs in the middle mantle and the lower part of the upper mantle. The velocities of the vertical mantle flow are about 1-4 cm per year and the tangential velocities are 1-10 cm per year. The mantle flow has an effect on controlling the movement of plates and the distributions of ocean ridges, subduction zones and collision zones. The mantle upwelling regions are clearly related with the locations ofhotspots on the earth's surface.

  3. The deep Earth origin of the Iceland plume and its effects on regional surface uplift and subsidence (United States)

    Barnett-Moore, Nicholas; Hassan, Rakib; Flament, Nicolas; Müller, Dietmar


    The present-day seismic structure of the mantle under the North Atlantic Ocean indicates that the Iceland hotspot represents the surface expression of a deep mantle plume, which is thought to have erupted in the North Atlantic domain during the Palaeocene. The spatial and temporal evolution of the plume since its eruption is still highly debated, and little is known about its deep mantle history. Here, we use palaeogeographically constrained global mantle flow models to investigate the evolution of deep Earth flow beneath the North Atlantic since the Jurassic. The models show that over the last ˜ 100 Myr a remarkably stable pattern of convergent flow has prevailed in the lowermost mantle near the tip of the African Large Low-Shear Velocity Province (LLSVP), making it an ideal plume nucleation site. We extract model dynamic topography representative of a plume beneath the North Atlantic region since eruption at ˜ 60 Ma to present day and compare its evolution to available offshore geological and geophysical observations across the region. This comparison confirms that a widespread episode of Palaeocene transient uplift followed by early Eocene anomalous subsidence can be explained by the mantle-driven effects of a plume head ˜ 2500 km in diameter, arriving beneath central eastern Greenland during the Palaeocene. The location of the model plume eruption beneath eastern Greenland is compatible with several previous models. The predicted dynamic topography is within a few hundred metres of Palaeocene anomalous subsidence derived from well data. This is to be expected given the current limitations involved in modelling the evolution of Earth's mantle flow in 3-D, particularly its interactions with the base of a heterogeneous lithosphere as well as short-wavelength advective upper mantle flow, not captured in the presented global models.

  4. Early Earth plume-lid tectonics: A high-resolution 3D numerical modelling approach (United States)

    Fischer, R.; Gerya, T.


    Geological-geochemical evidence point towards higher mantle potential temperature and a different type of tectonics (global plume-lid tectonics) in the early Earth (>3.2 Ga) compared to the present day (global plate tectonics). In order to investigate tectono-magmatic processes associated with plume-lid tectonics and crustal growth under hotter mantle temperature conditions, we conduct a series of 3D high-resolution magmatic-thermomechanical models with the finite-difference code I3ELVIS. No external plate tectonic forces are applied to isolate 3D effects of various plume-lithosphere and crust-mantle interactions. Results of the numerical experiments show two distinct phases in coupled crust-mantle evolution: (1) a longer (80-100 Myr) and relatively quiet 'growth phase' which is marked by growth of crust and lithosphere, followed by (2) a short (∼20 Myr) and catastrophic 'removal phase', where unstable parts of the crust and mantle lithosphere are removed by eclogitic dripping and later delamination. This modelling suggests that the early Earth plume-lid tectonic regime followed a pattern of episodic growth and removal also called episodic overturn with a periodicity of ∼100 Myr.

  5. Properties of industrial dense gas plumes (United States)

    Shaver, E. M.; Forney, L. J.

    Hazardous gases and vapors are often discharged into the atmosphere from industrial plants during catastrophic events (e.g. Union Carbide incident in Bhopal, India). In many cases the discharged components are more dense than air and settle to the ground surface downstream from the stack exit. In the present paper, the buoyant plume model of Hoult, Fay and Forney (1969, J. Air Pollut. Control Ass. 19, 585-590.) has been altered to predict the properties of hazardous discharges. In particular, the plume impingement point, radius and concentration are predicted for typical stack exit conditions, wind speeds and temperature profiles. Asymptotic expressions for plume properties at the impingement point are also derived for a constant crosswind and neutral temperature profile. These formulae are shown to be useful for all conditions.

  6. Long-distance impact of Iceland plume on Norway's rifted margin. (United States)

    Koptev, Alexander; Cloetingh, Sierd; Burov, Evgueni; François, Thomas; Gerya, Taras


    Results of a 3D modeling study inspired by recent seismic tomography of the Northern Atlantic mantle suggest that a complex pattern of hot mantle distribution with long horizontal flows originating from the Iceland mantle plume has been the norm in the geological past. In the Northern Atlantic the Iceland plume has a strong long-distance impact on intraplate deformation affecting both onshore and offshore parts of Norway's rifted margin. As a result, this margin is characterized by large magnitude differential topography sustained over at least several tens of Myr. Here we use high-resolution 3D thermo-mechanical modeling to demonstrate that the long-distance plume impact can be explained by its fast lateral propagation controlled by pre-existing lithosphere structures. Numerical models show that these structures strongly affect the style of horizontal flow of plume head material. This results in long-distance propagation of hot material emplaced at the lithosphere-asthenosphere boundary causing long-wavelength anomalies in onshore topography of Norway's rifted margin. Short-wavelength offshore topographic domes are likely caused by joint occurrence of plume-related thermal perturbations and gravitational forces related to plate thickening (ridge push). Our 3D modeling brings together plume impingement, spreading ridge dynamics, and the formation of anomalous intraplate structures offshore Norway in one scenario.

  7. Martian Atmospheric Plumes: Behavior, Detectability and Plume Tracing (United States)

    Banfield, Don; Mischna, M.; Sykes, R.; Dissly, R.


    We will present our recent work simulating neutrally buoyant plumes in the martian atmosphere. This work is primarily directed at understanding the behavior of discrete plumes of biogenic tracer gases, and thus increasing our understanding of their detectability (both from orbit and from in situ measurements), and finally how to use the plumes to identify their precise source locations. We have modeled the detailed behavior of martian atmospheric plumes using MarsWRF for the atmospheric dynamics and SCIPUFF (a terrestrial state of the art plume modeling code that we have modified to represent martian conditions) for the plume dynamics. This combination of tools allows us to accurately simulate plumes not only from a regional scale from which an orbital observing platform would witness the plume, but also from an in situ perspective, with the instantaneous concentration variations that a turbulent flow would present to a point sampler in situ instrument. Our initial work has focused on the detectability of discrete plumes from an orbital perspective and we will present those results for a variety of notional orbital trace gas detection instruments. We have also begun simulating the behavior of the plumes from the perspective of a sampler on a rover within the martian atmospheric boundary layer. The detectability of plumes within the boundary layer has a very strong dependence on the atmospheric stability, with plume concentrations increasing by a factor of 10-1000 during nighttime when compared to daytime. In the equatorial regions of the planet where we have simulated plumes, the diurnal tidal “clocking” of the winds is strongly evident in the plume trail, which similarly “clocks” around its source. This behavior, combined with the strong diurnal concentration variations suggests that a rover hunting a plume source would be well suited to approach it from a particular azimuth (downwind at night) to maximize detectability of the plume and the ability to

  8. Numerical Modeling of Deep Mantle Flow: Thermochemical Convection and Entrainment (United States)

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


    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

  9. Noble gases in hydrothermal plumes of Loihi Seamount

    Energy Technology Data Exchange (ETDEWEB)

    Kodera, Masako; Igarashi, G.; Ozima, Minoru


    Seawater samples from hydrothermal plumes of Loihi Seamount show very high /sup 3/He//sup 4/He ratios (up to 15.8x10/sup -6/) and /sup 4/He//sup 20/Ne ratios higher than that of air-saturated seawater (ASSW). The /sup 3/He//sup 4/He ratio in the source from which the helium is released into the seawater is estimated as (23.1 +- 2.3)x10/sup -6/ from the correlation plot of /sup 3/He//sup 20/Ne vs. /sup 4/He//sup 20/Ne. The /sup 3/He/heat ratio at Loihi is 5-49 times higher than that at the Galapagos Rift and at 21/sup 0/N EPR. The difference may be attributed to the differences in the structure of the mantle beneath hot spots and the mid-ocean ridge, the former representing the deeper mantle region and the latter the shallower, depleted mantle. These observations are consistent with the view that helium in hydrothermal plumes of Loihi Seamount was derived from a deeper mantle region via a hot spot, where more primordial helium is still preserved.


    Energy Technology Data Exchange (ETDEWEB)

    Miyagoshi, Takehiro [Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001 (Japan); Tachinami, Chihiro [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan); Kameyama, Masanori [Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577 (Japan); Ogawa, Masaki, E-mail:, E-mail:, E-mail:, E-mail: [Department of Earth Sciences and Astronomy, University of Tokyo at Komaba, 3-8-1 Komaba, Meguro, Tokyo 153-8902 (Japan)


    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.

  11. Unsteady turbulent buoyant plumes

    CERN Document Server

    Woodhouse, Mark J; Hogg, Andrew J


    We model the unsteady evolution of turbulent buoyant plumes following temporal changes to the source conditions. The integral model is derived from radial integration of the governing equations expressing the conservation of mass, axial momentum and buoyancy. The non-uniform radial profiles of the axial velocity and density deficit in the plume are explicitly described by shape factors in the integral equations; the commonly-assumed top-hat profiles lead to shape factors equal to unity. The resultant model is hyperbolic when the momentum shape factor, determined from the radial profile of the mean axial velocity, differs from unity. The solutions of the model when source conditions are maintained at constant values retain the form of the well-established steady plume solutions. We demonstrate that the inclusion of a momentum shape factor that differs from unity leads to a well-posed integral model. Therefore, our model does not exhibit the mathematical pathologies that appear in previously proposed unsteady i...

  12. Dilution in Transition Zone between Rising Plumes and Surface Plumes

    DEFF Research Database (Denmark)

    Larsen, Torben


    The papers presents some physical experiments with the dilution of sea outfall plumes with emphasize on the transition zone where the relative fast flowing vertical plume turns to a horizontal surface plume following the slow sea surface currents. The experiments show that a considerable dilution...

  13. 3-D thermo-mechanical modeling of plume-induced subduction initiation (United States)

    Baes, M.; Gerya, T.; Sobolev, S. V.


    Here, we study the 3-D subduction initiation process induced by the interaction between a hot thermo-chemical mantle plume and oceanic lithosphere using thermo-mechanical viscoplastic finite difference marker-in-cell models. Our numerical modeling results show that self-sustaining subduction is induced by plume-lithosphere interaction when the plume is sufficiently buoyant, the oceanic lithosphere is sufficiently old and the plate is weak enough to allow the buoyant plume to pass through it. Subduction initiation occurs following penetration of the lithosphere by the hot plume and the downward displacement of broken, nearly circular segments of lithosphere (proto-slabs) as a result of partially molten plume rocks overriding the proto-slabs. Our experiments show four different deformation regimes in response to plume-lithosphere interaction: a) self-sustaining subduction initiation, in which subduction becomes self-sustaining; b) frozen subduction initiation, in which subduction stops at shallow depths; c) slab break-off, in which the subducting circular slab breaks off soon after formation; and d) plume underplating, in which the plume does not pass through the lithosphere and instead spreads beneath it (i.e., failed subduction initiation). These regimes depend on several parameters, such as the size, composition, and temperature of the plume, the brittle/plastic strength and age of the oceanic lithosphere, and the presence/absence of lithospheric heterogeneities. The results show that subduction initiates and becomes self-sustaining when the lithosphere is older than 10 Myr and the non-dimensional ratio of the plume buoyancy force and lithospheric strength above the plume is higher than approximately 2. The outcomes of our numerical experiments are applicable for subduction initiation in the modern and Precambrian Earth and for the origin of plume-related corona structures on Venus.

  14. Turbulent buoyant jets and plumes

    CERN Document Server

    Rodi, Wolfgang

    The Science & Applications of Heat and Mass Transfer: Reports, Reviews, & Computer Programs, Volume 6: Turbulent Buoyant Jets and Plumes focuses on the formation, properties, characteristics, and reactions of turbulent jets and plumes. The selection first offers information on the mechanics of turbulent buoyant jets and plumes and turbulent buoyant jets in shallow fluid layers. Discussions focus on submerged buoyant jets into shallow fluid, horizontal surface or interface jets into shallow layers, fundamental considerations, and turbulent buoyant jets (forced plumes). The manuscript then exami

  15. Role of the subduction filter in mantle recycling (United States)

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


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

  16. Thermal plumes in ventilated rooms

    DEFF Research Database (Denmark)

    Kofoed, Peter; Nielsen, Peter V.


    The design of a displacement ventilation system involves determination of the flow rate in the thermal plumes. The flow rate in the plumes and the vertical temperature gradient influence each other, and they are influenced by many factors. This paper shows some descriptions of these effects. Free...... to be the only possible approach to obtain the volume flow in: thermal plumes in ventilated rooms....

  17. Ultraslow, slow, or fast spreading ridges: Arm wrestling between mantle convection and far-field tectonics (United States)

    Husson, Laurent; Yamato, Philippe; Bezos, Antoine


    Oceanic spreading rates are highly variable, and these variations are known to correlate to a variety of surface observables, like magmatic production, heat flow or bathymetry. This correlation lead to classify ridges into fast and slow spreading ridges, but also into the more peculiar ultraslow spreading regime. Here we explore the dynamic relationships between spreading ridges, plate tectonics and mantle flow. We first focus on the thermal signature of the mantle, that we infer from the global S-wave seismic tomography model of Debayle and Ricard (2012). We show that the thermal structure of ridges gradually departs from the half-space cooling model for slow, and above all ultraslow spreading ridges. We also infer that the sublithospheric mantle temperature decreases by more than 150 degrees C from fast to ultraslow spreading regimes. Both observations overall indicate that the mantle convection pattern is increasingly chaotic underneath slow and ultraslow spreading ridges. We suggest that this is due to far-field tectonics at the other ends of lithospheric plates: not only it modulates the spreading rates but it also alters the convection regime by obstructing the circulation of plates, which in turn modifies the surface kinematic conditions for the convecting mantle. We test this hypothesis using a thermo-mechanical model that represents a convection cell carrying a continental lithosphere atop. The continent gradually drifts away from the spreading ridge, from which the oceanic lithosphere grows and cools while the continent eventually collides at the opposite side. In turn, this event drastically modifies the upper kinematic condition for the convecting mantle that evolves from a mobile lid regime to an almost stagnant lid regime. Implications on spreading ridges are prominent: heat advection decreases with respect to thermal conduction, which causes the oceanic lithosphere to thicken faster; the oceanic plates get compressed and destabilized by a growing

  18. Lower mantle thermal structure deduced from seismic tomography, mineral physics and numerical modelling (United States)

    Cadek, O.; Yuen, D. A.; Steinbach, V.; Chopelas, A.; Matyska, C.


    The long-wavelength thermal anomalies in the lower mantle have been mapped out using several seismic tomographic models in conjunction with thermodynamic parameters derived from high-pressure mineral physics experiments. These parameters are the depth variations of thermal expansivity and of the proportionality factor between changes in density and seismic velocity. The giant plume-like structures in the lower mantle under the Pacific Ocean and Africa have outer fringes with thermal anomalies around 300-400 K, but very high temperatures are found in the center of the plumes near the base of the core-mantle boundary. These extreme values can exceed +1500 K and may reflect large hot thermal anomalies in the lower mantle, which are supported by recent measurements of high melting temperatures of perovskite and iron. Extremely cold anomalies, around -1500 K, are found for anomalies in the deep mantle around the Pacific rim and under South America. Numerical simulations show that large negative thermal anomalies in the mid-lower mantle have modest magnitudes of around -500 K. correlation pattern exists between the present-day locations of cold masses in the lower mantle and the sites of past subduction since the Cretaceous. Results from correlation analysis show that the slab mass-flux in the lower mantle did not conform to a steady-state nature but exhibited time-dependent behavior.

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

    Directory of Open Access Journals (Sweden)

    Kent C. Condie


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

  20. Mineralogy and composition of the oceanic mantle (United States)

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


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

  1. Geochemistry and petrogenesis of Quaternary volcanism from the islets in the eastern Beibu Gulf:evidence for Hainan plume

    Institute of Scientific and Technical Information of China (English)

    LI Naisheng; YAN Quanshu; CHEN Zhihua; SHI Xuefa


    Some of the islets in the eastern Beibu Gulf are covered by Quaternary volcano strata. The rock samples from these islets mainly consist of quartz tholeiites (at Shenjiandao), olivine tholeiites (at Linshidao and Xieyang-dao) and alkali basalts (at Yangpubi and Jianshidao), and basically represent four periods of the Quaternary volcanism of Hainan Island and its adjacent regions. Except for the samples from Shenjiandao, most of the Quaternary volcanics of these islets belong to alkali magma series. The trace element characteristics of all of these samples show they are OIB (oceanic island basalt)-like, which implies that their deep geodynamic setting may be related to a mantle plume. The Sr-Nd-Pb isotopic compositions show that the mantle source beneath the Quaternary strata can be regarded as a result of binary mixing between a depleted, DMM (de-pleted MORB mantle)-like source and an enriched mantle type 2 (EM2). The EM2 may be originated from the Hainan mantle plume, and has been metasomatized by carbonaceous fluids released from ancient re-cycled oceanic crust at an asthenospheric mantle level. These features, together with typical trace element ratios, reflect that the parent magma was not subjected to crustal contamination during its ascent to the surface. This study provides further petrological and geochemical evidence for the existence of the Hainan mantle plume.

  2. Mantle updrafts and mechanisms of oceanic volcanism (United States)

    Anderson, Don L.; Natland, James H.


    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.

  3. Chemical Plume Detection with an Iterative Background Estimation Technique (United States)


    this paper, we focus on cases where the plume is large (relative to the image ), and provide a method for handling this scenario. The method we develop...the locations of the events, the operation in (11) is a convolution of a binary image with a filter function h. To get an estimate of the probability...background statistics, including the mean and covariance. Diffuse plumes with a large spatial extent are particularly difficult to detect in single- image

  4. High-3He plume origin and temporal-spatial evolution of the Siberian flood basalts (United States)

    Basu, A.R.; Poreda, R.J.; Renne, P.R.; Teichmann, F.; Vasiliev, Y.R.; Sobolev, N.V.; Turrin, B.D.


    An olivine nephelinite from the lower part of a thick alkalic ultrabasic and mafic sequence of volcanic rocks of the northeastern part of the Siberian flood basalt province (SFBP) yielded a 40ArX39Ar plateau age of 253.3 ?? 2.6 million years, distinctly older than the main tholeiitic pulse of the SFBP at 250.0 million years. Olivine phenocrysts of this rock showed 3He/4He ratios up to 12.7 times the atmospheric ratio; these values suggest a lower mantle plume origin. The neodymium and strontium isotopes, rare earth element concentration patterns, and cerium/lead ratios of the associated rocks were also consistent with their derivation from a near-cnondritic, primitive plume. Geochemical data from the 250-million-year-old volcanic rocks higher up in the sequence indicate interaction of this high-3He SFBP plume with a suboceanic-type upper mantle beneath Siberia.

  5. A Consensus on Mantle Potential Temperatures? (Invited) (United States)

    Putirka, K. D.


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

  6. Influence of the Afar plume on the deep structure of Aden and Red Sea margins - Insight from teleseismic tomography in western Yemen (United States)

    Korostelev, Félicie; Basuyau, Clémence; Leroy, Sylvie; Ahmed, Abdulhakim; Keir, Derek; Stuart, Graham; Rolandone, Frédérique; Ganad, Ismail Al; Khanbari, Khaled


    Continental rupture processes under mantle plume influence are still poorly known although extensively studied. The Afar plume has been largely investigated in Ethiopia to study early stages of continental break-up. Here we imaged the lithospheric structure of western continental Yemen to evaluate the role of the Afar plume on the evolution of the continental margin and its extent towards the East. A part of the YOCMAL project (YOung Conjugate MArgins Laboratory) permitted the deployment of twenty-three broadband stations in Yemen (from 2009 to 2010). Using a classical teleseismic tomography (Aki et al., 1974) on these stations together with a permanent GFZ station, we image the relative velocity variations of P-waves in the crust and lithosphere down to 300 km depth, with a maximum lateral resolution of about ~20 km. The model thus obtained shows (1) a dramatic and localized thinning of the crust in the vicinity of the Red Sea and the Gulf of Aden (2) the presence of magmatic underplating related to seaward dipping reflectors under those two volcanic margins (3) two granitic syn-rift intrusions on the border of the great escarpment (4) a low velocity anomaly in which with evidence of partial melting, just below thick Oligocene trapps series and other volcanic events (from 15 Ma to present). This low velocity anomaly could correspond to an abnormally hot mantle and could be responsible for dynamic topography and recent magmatism in western Yemen. (5) Finally, we infer the presence of hot material under the Southwestern corner of Yemen that could be related to Miocene volcanism in Jabal an Nar.

  7. How plume-ridge interaction shapes the crustal thickness pattern of the Réunion hotspot track (United States)

    Bredow, Eva; Steinberger, Bernhard; Gassmöller, Rene; Dannberg, Juliane


    The Réunion mantle plume has shaped a large area of the Earth's surface over the past 65 million years: from the Deccan Traps in India along the hotspot track comprising the island chains of the Laccadives, Maldives, and Chagos Bank on the Indian plate and the Mascarene Plateau on the African plate up to the currently active volcanism at La Réunion Island. This study addresses the question how the Réunion plume, especially in interaction with the Central Indian Ridge, created the complex crustal thickness pattern of the hotspot track. For this purpose, the mantle convection code ASPECT was used to design three-dimensional numerical models, which consider the specific location of the plume underneath moving plates and surrounded by large-scale mantle flow. The results show the crustal thickness pattern produced by the plume, which altogether agrees well with topographic maps. Especially two features are consistently reproduced by the models: the distinctive gap in the hotspot track between the Maldives and Chagos is created by the combination of the ridge geometry and plume-ridge interaction; and the Rodrigues Ridge, a narrow crustal structure which connects the hotspot track and the Central Indian Ridge, appears as the surface expression of a long-distance sublithospheric flow channel. This study therefore provides further insight how small-scale surface features are generated by the complex interplay between mantle and lithospheric processes.

  8. Where is mantle's carbon? (United States)

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


    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

  9. The Sytykanskaya kimberlite pipe:Evidence from deep-seated xenoliths and xenocrysts for the evolution of the mantle beneath Alakit, Yakutia, Russia

    Institute of Scientific and Technical Information of China (English)

    I.V. Ashchepkov; I.V. Makovchuk; V.S. Palesskiy; 0.S. Khmel’nikova; A.M. Logvinova; L.F. Reimers; T. Ntaflos; Z.V. Spetsius; N.V. Vladykin; H. Downes; D.S. Yudin; A.V. Travin


    Mantle xenoliths (>150) and concentrates from late autolithic breccia and porphyritic kimberlite from the Sytykanskaya pipe of the Alakit field (Yakutia) were analyzed by EPMA and LAM ICP methods. In P-T-X-f(O2) diagrams minerals from xenoliths show widest variations, the trends P-Fe#-CaO, f(O2) for minerals from porphyric kimberlites are more stepped than for xenocrysts from breccia. Ilmenite PTX points mark moving for protokimberlites from the lithosphere base (7.5 GPa) to pyroxenite lens (5e3.5 GPa) accompanied by Cr increase by AFC and creation of two trends P-Fe#Ol w10e12% and 13e15%. The Opx-Gar-based mantle geotherm in Alakit field is close to 35 mW/m2 at 65 GPa and 600 ?C near Moho was determined. The oxidation state for the megacrystalline ilmenites is lower for the metasomatic associations due to reduction of protokimberlites on peridotites than for uncontaminated varieties at the lithosphere base. Highly inclined linear REE patterns with deep HFSE troughs for the parental melts of clinopyroxene and garnet xenocrysts from breccia were influenced by differentiated protokimberlite. Melts for metasomatic xenoliths reveal less inclined slopes without deep troughs in spider diagrams. Garnets reveal S-shaped REE patterns. The clinopyroxenes from graphite bearing Cr-websterites show inclined and inflected in Gd spectrums with LREE variations due to AFC differen-tiation. Melts for garnets display less inclined patterns and Ba-Sr troughs but enrichment in Nb-Ta-U. The 40Ar/39Ar ages for micas from the Alakit mantle xenoliths for disseminated phlogopites reveal Proterozoic (1154 Ma) age of metasomatism in early Rodinia mantle. Veined glimmerites with richterite e like amphiboles mark w1015 Ma plume event in Rodinia mantle. The w600e550 Ma stage manifests final Rodinia break-up. The last 385 Ma metasomatism is protokimberlite-related.

  10. NW Iberia Shelf Dynamics. Study of the Douro River Plume.

    Directory of Open Access Journals (Sweden)

    Isabel Iglesias


    Douro River plume is wind-driven. The simulations show important differences in the plume structure and dispersion pathways depending on the wind strength and direction that was simulated. When southerly winds are implemented, it can be seen that those winds push the river water to the north. With this scenario, the water associated with the Douro River can be found in the Galician Rías. The upwelling favorable winds (northerly winds induce plumes with a narrow coastal current. The high surface salinity on the plume regions during strong wind events suggests that the wind enhances the vertical mixing. Several analysis shows that the plume is affected by Coriolis effect but its influence is mitigated by a strong wind forcing. The multi-year climatological study showed a variation of the plume structure with the climatological conditions in the area. During the first months of the simulation, a southwest protruding jet-like plume can be seem, meanwhile, during winter months the bulge and the coastal current seem to evolve to the north, according with the climatic wind conditions. On this simulation it was observed a plume response with the behavior of the offshore geostrophic current system. Offshore eddies and filaments are also responsible for the cross-shore transport, through the horizontal advection of plume waters. Extreme river discharges, associated with southerly winds, can transport debris to the Galician coast in about 60 h, helping to explain the tragic events of the Entre-os-Rios accident of March 2001. Analysis of the Rossby deformation radius and the Kelvin number confirm that the Douro supercritical plumes are strongly affected by the planetary rotation. The supercritical plumes coincided with the coastal current maximum widths. The values obtained for the densimetric Richardson number showed that the supercritical plumes are less mixed than the subcritical ones.

  11. Terrestrial Plume Impingement Testbed Project (United States)

    National Aeronautics and Space Administration — Masten Space Systems proposes to create a terrestrial plume impingement testbed for generating novel datasets for extraterrestrial robotic missions. This testbed...

  12. Mantle source heterogeneity of the Early Jurassic basalt of eastern North America (United States)

    Gregory Shellnutt, J.; Dostal, Jaroslav; Yeh, Meng-Wan


    One of the defining characteristics of the basaltic rocks from the Early Jurassic Eastern North America (ENA) sub-province of the Central Atlantic Magmatic Province (CAMP) is the systematic compositional variation from South to North. Moreover, the tectono-thermal regime of the CAMP is debated as it demonstrates geological and structural characteristics (size, radial dyke pattern) that are commonly associated with mantle plume-derived mafic continental large igneous provinces but is considered to be unrelated to a plume. Mantle potential temperature (T P) estimates of the northern-most CAMP flood basalts (North Mountain basalt, Fundy Basin) indicate that they were likely produced under a thermal regime (T P ≈ 1450 °C) that is closer to ambient mantle (T P ≈ 1400 °C) conditions and are indistinguishable from other regions of the ENA sub-province (T Psouth = 1320-1490 °C, T Pnorth = 1390-1480 °C). The regional mantle potential temperatures are consistent along the 3000-km-long ENA sub-province suggesting that the CAMP was unlikely to be generated by a mantle plume. Furthermore, the mantle potential temperature calculation using the rocks from the Northern Appalachians favors an Fe-rich mantle (FeOt = 8.6 wt %) source, whereas the rocks from the South Appalachians favor a less Fe-rich (FeOt = 8.3 wt %) source. The results indicate that the spatial-compositional variation of the ENA basaltic rocks is likely related to differing amounts of melting of mantle sources that reflect the uniqueness of their regional accreted terranes (Carolinia and West Avalonia) and their post-accretion, pre-rift structural histories.

  13. On the Modes of Mantle Convection in Super-Earths (Invited) (United States)

    Bercovici, D.


    The relatively recent discovery of larger-than-Earth extra-solar terrestrial planets has opened up many possibilities for different modes of interior dynamics, including mantle convection. A great deal of basic mineral physics is still needed to understand the state of matter and rheology of these super terrestrials, even assuming similar compositions to Earth (which is itself unlikely given the effect of singular events such as giant impacts and lunar formation). There has been speculation and debate as to whether the larger Rayleigh numbers of super-Earth's would promote plate tectonic style recycling, which is considered a crucial negative feedback for buffering atmospheric CO2 and stabilizing climate through weathering and mineral carbonation. However, models of plate generation through grainsize-reducing damage (see Foley & Bercovici this session) show that the effect of larger Rayleigh numbers is offset by an increase in the lithosphere-mantle viscosity contrast (due to a hotter mantle). Super-Earth's are therefore probably no more (or less) prone to plate tectonics than "normal" Earths; other conditions like surface temperature (and thus orbital position) are more important than size for facilitating plate tectonic cycling, which is of course more in keeping with observations in our own solar system (i.e., the disparity between Earth and Venus). Regardless, two major questions remain. First, what are the other modes of convective recycling that would possibly buffer CO2 and allow for a negative feedback that stabilizes climate? For example, subarial basaltic volcanism associated with plume or diapiric convection could potentially draw down CO2 because of the reactibility of mafic minerals; this mechanism possibly helped trigger Snow Ball events in the Proterozoic Earth during break-up of near-equatorial super-continents. Second, what observations of exo-planets provide tests for theories of tectonics or convective cycling? Spectroscopic techniques are most

  14. Rejuvenation of the lithosphere by the Hawaiian plume. (United States)

    Li, Xueqing; Kind, Rainer; Yuan, Xiaohui; Wölbern, Ingo; Hanka, Winfried


    The volcanism responsible for creating the chain of the Hawaiian islands and seamounts is believed to mark the passage of the oceanic lithosphere over a mantle plume. In this picture hot material rises from great depth within a fixed narrow conduit to the surface, penetrating the moving lithosphere. Although a number of models describe possible plume-lithosphere interactions, seismic imaging techniques have not had sufficient resolution to distinguish between them. Here we apply the S-wave 'receiver function' technique to data of three permanent seismic broadband stations on the Hawaiian islands, to map the thickness of the underlying lithosphere. We find that under Big Island the lithosphere is 100-110 km thick, as expected for an oceanic plate 90-100 million years old that is not modified by a plume. But the lithosphere thins gradually along the island chain to about 50-60 km below Kauai. The width of the thinning is about 300 km. In this zone, well within the larger-scale topographic swell, we infer that the rejuvenation model (where the plume thins the lithosphere) is operative; however, the larger-scale topographic swell is probably supported dynamically.

  15. Lithological structure of the Galápagos Plume (United States)

    Vidito, Christopher; Herzberg, Claude; Gazel, Esteban; Geist, Dennis; Harpp, Karen


    We have measured Ni, Ca, and Mn in olivine phenocrysts from volcanoes in the Galápagos Archipelago to infer the mantle source lithologies. Results show that peridotite is the dominant source lithology for Fernandina, Floreana, Genovesa, Wolf Island, and Darwin Island. These volcanoes largely characterize the PLUME, WD, FLO, and DUM Nd, Sr, and Pb isotopic endmembers of Harpp and White (2001). Volcan Wolf, Alcedo, Marchena, and Cerro Azul, also produced from the melting of peridotite sources, have isotopic compositions that can be defined by mixing of the four isotopic endmembers. Our analysis suggests that peridotite was present in the sources of the volcanoes covered in this study and therefore is the dominant source lithology of the Galápagos plume. Pyroxenite melting is generally focused in two isotopically distinct domains: Roca Redonda, Volcan Ecuador, and Sierra Negra in the enriched western part of the archipelago and Santiago, Santa Cruz, and Santa Fe in the depleted east. One implication of this finding is that the Western and Eastern Pyroxenite Domains represent two separate bodies of recycled crust within the Galápagos mantle plume. Furthermore, both isotopically enriched and depleted domains of the archipelago were generated from mixtures of peridotite and pyroxenite. This suggests that there is no relationship between the source lithology of the Galápagos plume and its isotopic characteristics. The identification of peridotite-source melting in volcanoes with isotopic characteristics that have been attributed to recycled crust points to the importance of mixing in OIB genesis, consistent with studies in the Canary Islands.


    Directory of Open Access Journals (Sweden)

    A. I. Kiselev


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

  17. Dilution of Buoyant Surface Plumes

    DEFF Research Database (Denmark)

    Larsen, Torben; Petersen, Ole

    The purpose of present work is to establish a quantitative description of a surface plume which is valid for the range of density differences occurring in relation to sewage outfalls.......The purpose of present work is to establish a quantitative description of a surface plume which is valid for the range of density differences occurring in relation to sewage outfalls....

  18. Thermal Plumes in Ventilated Rooms

    DEFF Research Database (Denmark)

    Kofoed, Peter; Nielsen, Peter V.

    The design of a displacement ventilation system involves determination of the flow rate in the thermal plumes. The flow rate in the plumes and the vertical temperature gradient influence each other, and they are influenced by many factors. This paper shows some descriptions of these effects....

  19. Atmospheric chemistry in volcanic plumes. (United States)

    von Glasow, Roland


    Recent field observations have shown that the atmospheric plumes of quiescently degassing volcanoes are chemically very active, pointing to the role of chemical cycles involving halogen species and heterogeneous reactions on aerosol particles that have previously been unexplored for this type of volcanic plumes. Key features of these measurements can be reproduced by numerical models such as the one employed in this study. The model shows sustained high levels of reactive bromine in the plume, leading to extensive ozone destruction, that, depending on plume dispersal, can be maintained for several days. The very high concentrations of sulfur dioxide in the volcanic plume reduces the lifetime of the OH radical drastically, so that it is virtually absent in the volcanic plume. This would imply an increased lifetime of methane in volcanic plumes, unless reactive chlorine chemistry in the plume is strong enough to offset the lack of OH chemistry. A further effect of bromine chemistry in addition to ozone destruction shown by the model studies presented here, is the oxidation of mercury. This relates to mercury that has been coemitted with bromine from the volcano but also to background atmospheric mercury. The rapid oxidation of mercury implies a drastically reduced atmospheric lifetime of mercury so that the contribution of volcanic mercury to the atmospheric background might be less than previously thought. However, the implications, especially health and environmental effects due to deposition, might be substantial and warrant further studies, especially field measurements to test this hypothesis.

  20. 186Os and 187Os enrichments and high-3He/4He sources in the Earth's mantle

    DEFF Research Database (Denmark)

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


    . These Os isotope systematics are best explained by ancient recycled crust or melt enrichment in the mantle source region. If so, then the coupled enrichments displayed in 186Os/188Os and 187Os/188Os from lavas of other plume systems must result from an independent process, the most viable candidate...... picrites is best modeled as mixtures of 1 Ga or older ancient recycled crust mixed with primitive mantle or incompletely degassed depleted mantle isolated since 1-1.5 Ga, which preserves the high 3He/4He of the depleted mantle at the time. These mixtures create a hybrid source region that subsequently...... be interpreted as an increase in the proportion of ancient recycled crust in the upwelling plume over this time period. The positive correlation between 187Os/188Os and 3He/4He demonstrates that the Iceland lava He isotopic compositions do not result from simple melt depletion histories and consequent removal...

  1. A two Layer Convecting Mantle With Exchange : A Unified Model Based on Geochemical, Seismic and Heat Flow Observations (United States)

    Allègre, C. J.; Jaupart, C.; Nolet, G.


    -penetrating slabs as emphasized by Fukao and al.(2001) and the recent observation of the large energy spectrum differences at 670 km depth (Gu and al., 2006). We discuss the problem of return flow, which is crucial for both energy budget and convection regime. The recent work on plume by Montelli and al. (2004, 2006) shows the existence of broad plumes in the lower mantle and thin plumes in the upper mantle. d) The estimate of heat flow coming from the lower mantle of 35-32 TW. The work of Davies(1990) and Sleep(1992) shows clearly that this transfer is not the result of plumes reaching the surface, because they correspond at most to 3TW. At the reverse the estimated heat flow carried by the lower mantle plumes is much higher (Nolet and al., 2006). We also discuss the heat flow paradox to explain a Urey ratio of 0.4 with whole mantle convection. In conclusion, we propose mantle with two layers convecting separately but with some exchange of matter, this global exchange corresponding to 1.1024kg since 4.4 Gy. Plume genesis is a two-stage process. Lower mantle plumes heat the Mesosphere boundary layer generating second generation plumes which reach the surface (Allègre and Turcotte; 1983; Allègre, 1987). In the upper mantle itself, we have to distinguish between a vigorously convecting asthenosphere and a sluggish convecting transition zone, both convecting in same cells.

  2. Monitoring and forecasting Etna volcanic plumes

    Directory of Open Access Journals (Sweden)

    S. Scollo


    Full Text Available In this paper we describe the results of a project ongoing at the Istituto Nazionale di Geofisica e Vulcanologia (INGV. The objective is to develop and implement a system for monitoring and forecasting volcanic plumes of Etna. Monitoring is based at present by multispectral infrared measurements from the Spin Enhanced Visible and Infrared Imager on board the Meteosat Second Generation geosynchronous satellite, visual and thermal cameras, and three radar disdrometers able to detect ash dispersal and fallout. Forecasting is performed by using automatic procedures for: i downloading weather forecast data from meteorological mesoscale models; ii running models of tephra dispersal, iii plotting hazard maps of volcanic ash dispersal and deposition for certain scenarios and, iv publishing the results on a web-site dedicated to the Italian Civil Protection. Simulations are based on eruptive scenarios obtained by analysing field data collected after the end of recent Etna eruptions. Forecasting is, hence, supported by plume observations carried out by the monitoring system. The system was tested on some explosive events occurred during 2006 and 2007 successfully. The potentiality use of monitoring and forecasting Etna volcanic plumes, in a way to prevent threats to aviation from volcanic ash, is finally discussed.

  3. Remote Sensing and Underwater Glider Observations of a Springtime Plume in Western Lake Superior (United States)

    Plumes are commonly observed in satellite imagery of western Lake Superior following storm events, and represent a significant cross-shelf pathway for sediment and other constituents. However, their subsurface extent is poorly understood. This study reports results from plume ob...

  4. 3D Numeric modeling of slab-plume interaction in Kamchatka (United States)

    Constantin Manea, Vlad; Portnyagin, Maxim; Manea, Marina


    Volcanic rocks located in the central segment of the Eastern Volcanic Belt of Kamchatka show a high variability, both in age as well as in the geochemical composition. Three principal groups have been identified, an older group (7-12 my) represented by rich alkaline and transitional basalts, a 7-8 my group exemplified by alkaline basalts of extreme plume type, and a younger group (3-8 my) characterized by calc-alkaline andesites and dacites rocks. Moreover, the younger group shows an adakitic signature. The magmas are assumed to originate from two principle sources: from a subduction modified Pacific MORB-type and from plume-type mantle. In this paper we study the interaction of a cold subducting slab and a hot plume by means of 3D numeric modeling integrated 30 my back in time. Our preliminary modeling results show a short episode of plume material inflowing into the mantle wedge at ~10 my consistent with the second rocks group (plume like). Also our models predict slab edge melting consistent with the youngest group.

  5. On the deep-mantle origin of the Deccan Traps (United States)

    Glišović, Petar; Forte, Alessandro M.


    The Deccan Traps in west-central India constitute one of Earth’s largest continental flood basalt provinces, whose eruption played a role in the Cretaceous-Paleogene extinction event. The unknown mantle structure under the Indian Ocean at the start of the Cenozoic presents a challenge for connecting the event to a deep mantle origin. We used a back-and-forth iterative method for time-reversed convection modeling, which incorporates tomography-based, present-day mantle heterogeneity to reconstruct mantle structure at the start of the Cenozoic. We show a very low-density, deep-seated upwelling that ascends beneath the Réunion hot spot at the time of the Deccan eruptions. We found a second active upwelling below the Comores hot spot that likely contributed to the region of partial melt feeding the massive eruption.

  6. Depleted basaltic lavas from the proto-Iceland plume, Central East Greenland

    DEFF Research Database (Denmark)

    Waight, Tod Earle; Baker, Joel A.


    ridges considered to be derived from upper mantle sources polluted by the Iceland plume. However, small positive Pb peaks when normalised to MORB, and lower Nb distinguish the CEG low-Ti basalts from depleted Icelandic compositions. The lower ¿Nb (... in crustally uncontaminated parental melts implies a closer affinity to compositions from the oceanic ridges surrounding Iceland (especially Reykjanes), yet they are subtly distinct on the basis of available trace element data. We suggest that this depleted component was an integral part of the plume...

  7. Orbital Maneuvering Vehicle (OMV) plume and plume effects study (United States)

    Smith, Sheldon D.


    The objective was to characterize the Orbital Maneuvering Vehicle (OMV) propulsion and attitude control system engine exhaust plumes and predict the resultant plume impingement pressure, heat loads, forces, and moments. Detailed description is provided of the OMV gaseous nitrogen (GN2) thruster exhaust plume flow field characteristics calculated with the RAMP2 snd SFPGEN computer codes. Brief descriptions are included of the two models, GN2 thruster characteristics and RAMP2 input data files. The RAMP2 flow field could be recalculated by other organizations using the information presented. The GN2 flow field can be readily used by other organizations who are interested in GN2 plume induced environments which require local flow field properties which can be supplied using the SFPGEN GN2 model.

  8. Mapping the mass distribution of Earth's mantle using satellite-derived gravity gradients (United States)

    Panet, Isabelle; Pajot-Métivier, Gwendoline; Greff-Lefftz, Marianne; Métivier, Laurent; Diament, Michel; Mandea, Mioara


    The dynamics of Earth's mantle are not well known. Deciphering mantle flow patterns requires an understanding of the global distribution of mantle density. Seismic tomography has been used to derive mantle density distributions, but converting seismic velocities into densities is not straightforward. Here we show that data from the GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission can be used to probe our planet's deep mass structure. We construct global anomaly maps of the Earth's gravitational gradients at satellite altitude and use a sensitivity analysis to show that these gravitational gradients image the geometry of mantle mass down to mid-mantle depths. Our maps highlight north-south-elongated gravity gradient anomalies over Asia and America that follow a belt of ancient subduction boundaries, as well as gravity gradient anomalies over the central Pacific Ocean and south of Africa that coincide with the locations of deep mantle plumes. We interpret these anomalies as sinking tectonic plates and convective instabilities between 1,000 and 2,500km depth, consistent with seismic tomography results. Along the former Tethyan Margin, our data also identify an east-west-oriented mass anomaly likely in the upper mantle. We suggest that by combining gravity gradients with seismic and geodynamic data, an integrated dynamic model for Earth can be achieved.

  9. Continent-sized anomalous zones with low seismic velocity at the base of Earth's mantle (United States)

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


    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.

  10. Biogeochemistry of landfill leachate plumes

    DEFF Research Database (Denmark)

    Christensen, Thomas Højlund; Kjeldsen, Peter; Bjerg, Poul Løgstrup


    is on dissolved organic matter, xenobiotic organic compounds, inorganic macrocomponents as anions and cations, and heavy metals. Laboratory as well as field investigations are included. This review is an up-date of an earlier comprehensive review. The review shows that most leachate contamination plumes...... the behavior of the contaminants in the plume as the leachate migrates away from the landfill. Diverse microbial communities have been identified in leachate plumes and are believed to be responsible for the redox processes. Dissolved organic C in the leachate, although it appears to be only slowly degradable...

  11. The Large-scale Component of Mantle Convection (United States)

    Cserepes, L.

    Circulation in the Earth's mantle occurs on multiple spatial scales: this review dis- cusses the character of its large-scale or global components. Direct and strong evi- dence concerning the global flow comes, first of all, from the pattern of plate motion. Further indirect observational data which can be transformed into flow velocities by the equation of motion are the internal density heterogeneities revealed by seismic to- mography, and the geoid can also be used as an observational constraint. Due to their limited spatial resolution, global tomographic data automatically filter out the small- scale features and are therefore relevant to the global flow pattern. Flow solutions obtained from tomographic models, using the plate motion as boundary condition, re- veal that subduction is the downwelling of the global mantle circulation and that the deep-rooted upwellings are concentrated in 2-3 superplumes. Spectral analysis of the tomographic heterogeneities shows that the power of global flow appears dominantly in the lowest spherical harmonic orders 2-5. Theoretical convection calculations con- tribute substantially to the understanding of global flow. If basal heating of the mantle is significant, numerical models can reproduce the basic 2 to 5 cell pattern of con- vection even without the inclusion of surface plates. If plates are superimposed on the solution with their present arrangement and motion, the dominance of these low spherical harmonic orders is more pronounced. The cells are not necessarily closed, rather they show chaotic time-dependence, but they are normally bordered by long downwelling features, and they have usually a single superplume in the cell interior. Swarms of small plumes can develop in the large cells, especially when convection is partially layered due to an internal boundary such as the 670 km discontinuity (source of small plumes). These small plumes are usually tilted by the background large-scale flow which shows that they are

  12. Multiscale plume modeling of the Deepwater Horizon oil-well blowout for environmental impact assessment and mitigation (United States)

    Socolofsky, S. A.; Rezvani, M.


    The accidental blowout plume of the Deepwater Horizon (DH) oil well is an unprecedented event that will have far-reaching environmental, economic, and societal impact. The subsurface structure of the blowout plume, including its layered system of intrusions, conforms qualitatively to that predicted in the literature; however, new modeling tools are currently needed to produce highly-resolved predictions of such a complex plume in the stratified and flowing ocean. We present laboratory experiments of multiphase plumes in stratification and crossflow to understand the physical mechanisms that lead to separation among the buoyant dispersed phases (oil and gas) and the entrained and dissolved constituents in the continuous phase. Scale analysis indicates that the DH plume is stratification dominated, and observed locations of hydrocarbon intrusion layers agree well with the experimentally derived empirical scaling laws. New flow visualization measurements in gas plumes in stratification demonstrate that unsteady plume oscillation and detrainment events result from regular shedding of coherent structures on the order of the plume width and are not directly related to the stratification frequency. Similar particle image velocimetry (PIV) measurements in weak crossflows characterize the transport mechanisms in the plume wake. The results of these experiments will be used in the context of a National Science Foundation RAPID grant to validate a nested large eddy simulations (LES) / Reynolds averaged Navier-Stokes (RANS) model of the DH plume, and early results from this model demonstrate its feasibility to capture the unsteady and complex structure of the plume evolution.

  13. Mantle Convection, Plate Tectonics, and the Asthenosphere: A Bootstrap Model of the Earth's Internal Dynamics (United States)

    Lenardic, A.; Hoink, T.


    Several studies have highlighted the role of a low viscosity asthenosphere in promoting plate-like behavior in mantle convection models. It has also been argued that the asthenosphere is fed by mantle plumes (Phipps- Morgan et al. 1993; Deffeyes 1972) and that the existence of the specific plume types required for this depends on plate subduction (Lenardic and Kaula 1995; Jellinek et al. 2002). Independent of plumes, plate subduction can generate a non-adiabatic temperature gradient which, together with temperature dependent mantle viscosity, leads to a low viscosity near surface region. The above suggests a conceptual model in which the asthenosphere can not be defined solely in terms of material properties but must also be defined in terms of an active process, plate tectonics, which both maintains it and is maintained by it. The bootstrap aspect of the model is its circular causality between plates and the asthenosphere, neither being more fundamental than the other and the existence of each depending on the other. Several of the feedbacks key to the conceptual model will be quantified. The implications for modeling mantle convection in a plate-tectonic mode will also be discussed: 1) A key is to get numerical simulations into the bootstrap mode of operation and this is dependent on assumed initial conditions; 2) The model implies potentially strong hysteresis effects (e.g., transition between convection states, associated with variable yield stress, will occur at different values depending on whether the yield stress is systematically lowered or raised between successive models).

  14. Smoke plumes: Emissions and effects (United States)

    Susan O' Neill; Shawn Urbanski; Scott Goodrick; Sim Larkin


    Smoke can manifest itself as a towering plume rising against the clear blue sky-or as a vast swath of thick haze, with fingers that settle into valleys overnight. It comes in many forms and colors, from fluffy and white to thick and black. Smoke plumes can rise high into the atmosphere and travel great distances across oceans and continents. Or smoke can remain close...

  15. Helium isotope studies of the mantle xenoliths and megac-rysts from the Cenozoic basalts in the eastern China

    Institute of Scientific and Technical Information of China (English)

    LI; Yanhe


    [1]Molan, E., Zhao Dasheng, The Cenozoic Basalts and Plutonic Xenoliths in the Eastern China (in Chinese), Beijing: Scien-ce Press, 1987.[2]Liu Ruoxin, ed. The Chronology and the Geochemistry of the Cenozoic Volcanic Rocks in the Eastern China (in Chinese), Beijing: Seismology Press, 1992.[3]Liu, C. Q., Masuda, A., Xie, G. H., Isotope and trace element geochemistry of alkali basalts and associated megacrysts from the Huangyishan volcano, Kuandian, Liaoning, NE China, Chem. Geol., 1991, 97: 219-231.[4]Liu Congqiang, Masuda, A., Xie Guanghong, REE, Sr and Nd isotope geochemistry of the mantle xenoliths from Huan-gyishan basalt in Kuandian of Liaoning, Geological Sciences (in Chinese), 1994, 28(3): 228-234.[5]Xie Guanghong, Zhang Ming, Liu Congqiang, Mantle enrichment events and hydrated minerals-- The evidence from mantle xenoliths and high-pressure megacrysts, in the Geochemistry of the Mantle Fluids and the Asthenosphere (Asthe-noliths) (in Chinese) (eds. Du Letian et al.), Beijing: Geological Publishing House, 1996, 272-310.[6]Du Letian, Geochemistry of Mantle Fluids and Asthenosphere (Asthenoliths) (in Chinese), Beijing: Geological Publishing House, 1996.[7]Xia Qunke, Chen Daogong, Deloule, E. et al., Hydrogen isotope compositions of mantle-derived mica megacrysts from ion microprobe analysis, Science in China, Ser. D, 1999, 42(4): 392-398.[8]Zheng Jianping, Lu Fengxiang, O'Reilly, S. Y. et al., The mantle transformation and replacement in the eastern North China: Laser probe study on clinopyroxenes, Science in China (in Chinese), Ser, D, 2000, 30(4): 373-382.[9]Ozima, M., Podosek, F. A., Noble gas geochemistry, New York: Cambridge Univ. Press, 1983.[10]Anderson, D. L., Helium-3 from the mantle: Primordial signal or cosmic dust? Science, 1993, 261: 170-176.[11]Kurz, M., Jenkins, W. J., Hart, S. R. et al., Helium isotopic variations in volcanic rocks from Loihi Seamount and the is-land of Hawaii, Earth Planet Sci. Lett

  16. Equatorial spread F fossil plumes

    Directory of Open Access Journals (Sweden)

    S. L. Ossakow


    Full Text Available Behaviour of equatorial spread F (ESF fossil plumes, i.e., ESF plumes that have stopped rising, is examined using the NRL SAMI3/ESF three-dimensional simulation code. We find that fossil bubbles, plasma density depletions associated with fossil plumes, can persist as high-altitude equatorial depletions even while being "blown" by zonal winds. Corresponding airglow-proxy images of fossil plumes, plots of electron density versus longitude and latitude at a constant altitude of 288 km, are shown to partially "fill in" in most cases, beginning with the highest altitude field lines within the plume. Specifically, field lines upon which the E field has fallen entirely to zero are affected and only the low altitude (≤600 km portion if each field line fills in. This suggests that it should be possible to observe a bubble at high altitude on a field line for which the corresponding airglow image no longer shows a depletion. In all cases ESF plumes stop rising when the flux-tube-integrated ion mass density inside the upper edge of the bubble is equal to that of the nearby background, further supporting the result of Krall et al. (2010b.

  17. Dynamic topography as constraints on stress and viscosity in the mantle and lithosphere (United States)

    Zhong, S.


    Pas, and convection-induced lithospheric stress is unlikely to exceed 200 MPa (i.e., the yield stress for plate interiors). I will discuss the general implications of the results for mantle dynamics including dynamic generation of plate tectonics and the nature of mantle structures (i.e., slabs and plumes) as imaged seismically.

  18. Do plumes exist beneath Northwest Kyushu southwest Japan? (United States)

    Mashima, H.


    A thermal plume model was proposed for the Hot-spot type volcanism at Northwest Kyushu, southwest Japan in the post period of opening of the Sea of Japan. The model regards the Northwest Kyushu Basalts (NWKBs) were magmas fractionated from parental magmas with MgO = 12.8 - 18.8 wt. %, indicating that partial melting occurred at temperatures from 1330 to 1500 °C and at pressures from 1.5 to 3.0 GPa (Sakuyama et al., 2009; 2014). Previous petrological and observations, however, indicate that the NWKBs separated from the source mantle at pressures shallower than those inferred from the plume model. The Mg-Fe-Ni compositions of some NWKBs suggest that they could have been in equilibrium with mantle olivines with Fo = 81 - 87, meaning that they would have been not fractionated but primitive magmas. The NWKBs are associated with primitive high magnesium andesites, indicating that partial melting continued at low pressure such as 0.5 GPa (Mashima, 2009a, b). NWKBs include not garnet lherzolite xenoliths but spinel lherzolite, showing that primitive melt separation occurred at pressure lower than 2GPa (Arai et al., 2001). These lines of evidence indicate that the separation of primitive NWKBs occurred at temperature up to 1250 °C and pressures from 0.5 to 1.5 GPa, significantly lower than those assumed by the plume model. Instead of the plume model, geology of NW Kyushu infers that the volcanism was a consequence of the tectonic evolution of NW Kyushu. The volcanism was leaks of asthenosphere thickened extensional tectonics from the Paleogene to the early Miocene. Orientations of NWKB dikes indicate their eruption was induced by the reactivation of preexisting faults under horizontal compressive stress field oriented to a NW-SE direction. This horizontally compressive stress field would have been caused by mechanical interactions between the subducting Philippine Sea pate and the Eurasian Plate. The NW Kyushu volcanism could be explained in the context of plate

  19. Water in the Cratonic Mantle Lithosphere (United States)

    Peslier, A. H.


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

  20. Capabilities of 3-D wavelet transforms to detect plume-like structures from seismic tomography (United States)

    Bergeron, Stephen Y.; Yuen, David A.; Vincent, Alain P.


    The wavelet transform methods have been applied to viewing 3-D seismic tomography by casting the transformed quantities into two proxy distributions, E-max, the maximum of the magnitude of the local spectra about a local point and the associated local wavenumber, k-max. Using a stochastic background noise, we test the capability of this procedure in picking up the coherent structures of upper-mantle plumes. Plumes with a Gaussian shape and a characteristic width up to 2250 km have been tested for various amounts of the signal-to-noise ratios (SNR). We have found that plumes can be picked out for SNR as low as 0.08 db and that the optimal plume width for detection is around 1500 km. For plume width ranging between 700 km and 2000 km, the SNR can be lower than 1 db. This length-scale falls within the range for plume-detection based on the signal-to-noise levels associated with the current global tomographical models.

  1. Effect of width, amplitude, and position of a core mantle boundary hot spot on core convection and dynamo action

    CERN Document Server

    Dietrich, Wieland; Hori, Kumiko


    Within the fluid iron cores of terrestrial planets, convection and the resulting generation of global magnetic fields are controlled by the overlying rocky mantle. The thermal structure of the lower mantle determines how much heat is allowed to escape the core. Hot lower mantle features, such as the thermal footprint of a giant impact or hot mantle plumes, will locally reduce the heat flux through the core mantle boundary (CMB), thereby weakening core convection and affecting the magnetic field generation process. In this study, we numerically investigate how parametrised hot spots at the CMB with arbitrary sizes, amplitudes, and positions affect core convection and hence the dynamo. The effect of the heat flux anomaly is quantified by changes in global flow symmetry properties, such as the emergence of equatorial antisymmetric, axisymmetric (EAA) zonal flows. For purely hydrodynamic models, the EAA symmetry scales almost linearly with the CMB amplitude and size, whereas self-consistent dynamo simulations typ...

  2. Insights into the formation and dynamics of coignimbrite plumes from one-dimensional models (United States)

    Engwell, S. L.; de'Michieli Vitturi, M.; Esposti Ongaro, T.; Neri, A.


    Coignimbrite plumes provide a common and effective mechanism by which large volumes of fine-grained ash are injected into the atmosphere. Nevertheless, controls on formation of these plumes as a function of eruptive conditions are still poorly constrained. Herein, two 1-D axysymmetric steady state models were coupled, the first describing the parent pyroclastic density current and the second describing plume rise. Global sensitivity analysis is applied to investigate controls on coignimbrite plume formation and describe coignimbrite source and the maximum plume height attained. For a range of initial mass flow rates between 108 and 1010 kg/s, modeled liftoff distance (the distance at which neutral buoyancy is attained), assuming radial supercritical flow, is controlled by the initial flow radius, gas mass fraction, flow thickness, and temperature. The predicted decrease in median grain size between flow initiation and plume liftoff is negligible. Calculated initial plume vertical velocities, assuming uniform liftoff velocity over the pyroclastic density current invasion area, are much greater (several tens of m/s) than those previously used in modeling coignimbrite plumes (1 m/s). Such velocities are inconsistent with the fine grain size of particles lofted into coignimbrite plumes, highlighting an unavailability of large clasts, possibly due to particle segregation within the flow, prior to plume formation. Source radius and initial vertical velocity have the largest effect on maximum plume height, closely followed by initial temperature. Modeled plume heights are between 25 and 47 km, comparable with Plinian eruption columns, highlighting the potential of such events for distributing fine-grained ash over significant areas.

  3. Moho vs crust-mantle boundary: Evolution of an idea (United States)

    O'Reilly, Suzanne Y.; Griffin, W. L.


    The concept that the Mohorovicic Discontinuity (Moho) does not necessarily coincide with the base of the continental crust as defined by rock-type compositions was introduced in the early 1980s. This had an important impact on understanding the nature of the crust-mantle boundary using information from seismology and from deep-seated samples brought to the surface as xenoliths in magmas, or as tectonic terranes. The use of empirically-constrained P-T estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment. The xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere, and revealed that the crust-mantle boundary in off-craton regions commonly is transitional over a depth range of about 5-20 km. Early seismic-reflection data showed common layering near the Moho, correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust-mantle boundary. Developments in seismology, petrophysics and experimental petrology have refined interpretation of lithospheric domains. The expansion of in situ geochronology (especially zircon U-Pb ages and Hf-isotopes; Os isotopes of mantle sulfides) has defined tectonic events that affected whole crust-mantle sections, and revealed that the crust-mantle boundary can change in depth through time. However, the nature of the crust-mantle boundary in cratonic regions remains enigmatic, mainly due to lack of key xenoliths or exposed sections. The observation that the Moho may lie significantly deeper than the crust-mantle boundary has important implications for modeling the volume of the crust. Mapping the crust using seismic techniques alone, without consideration of the petrological problems, may lead to an overestimation of crustal thickness by 15-30%. This will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust-formation processes

  4. Restitic or not? Insights from trace element content and crystal - Structure of spinels in African mantle xenoliths (United States)

    Lenaz, Davide; Musco, Maria Elena; Petrelli, Maurizio; Caldeira, Rita; De Min, Angelo; Marzoli, Andrea; Mata, Joao; Perugini, Diego; Princivalle, Francesco; Boumehdi, Moulay Ahmed; Bensaid, Idris Ali Ahmadi; Youbi, Nasrrddine


    The lithospheric architecture of Africa consists of several Archean cratons and smaller cratonic fragments, stitched together and flanked by polycyclic fold belts. Here we investigate the structure and chemistry of spinels from lithospheric mantle xenoliths from distinct tectonic settings, i.e. from the Saharan metacraton in Libya (Waw-En-Namus) which could show archaic chemical features, Cameroon (Barombi Koto and Nyos Lakes) where the Sub Continental Lithospheric Mantle was modified during the Pan-African event and fluxed by asthenospheric melts of the Tertiary Cameroon Volcanic Line and Morocco (Tafraoute, Bou-Ibalrhatene maars) in the Middle Atlas where different metasomatic events have been recorded. From a structural point of view it is to notice that the Libyan spinels can be divided into two groups having different oxygen positional parameter (u > 0.2632 and u different among the different samples with one Libyan group (LB I) showing Tc in the range 490-640 °C and the other 680-950 °C (LB II). Cameroon and Morocco spinels show a Tc in the range 630-760 °C. About 150 different spinels have been studied for their trace element content and it can be seen that many of them are related to Cr content, while Zn and Co are not and clearly distinguish the occurrences. Differences in the trace element chemistry, in the structural parameters and in the intracrystalline closure temperatures suggest that a different history should be considered for Cameroon, Morocco and LB I and LB II spinels. Even if it was not considered for this purpose, we tentatively used the Fe2 +/Fe3 + vs. TiO2 diagram that discriminate between peridotitic and the so-called ;magmatic; spinels, i.e. spinel crystallized from melts. LB I and LB II spinels plot in the peridotitic field while Cameroon and Morocco spinels fall in the magmatic one. Consequently, the xenoliths sampled from a probably juvenile SCLM at the edge of the most important lithospheric roots (i.e. Cameroon and Morocco

  5. The Effect of Plumes on the Dynamics of Supercontinents in a Self-Consistent Plate Tectonics Setting (United States)

    Jain, C.; Rozel, A.; Tackley, P. J.


    Strong mantle plumes arising from the deep mantle can impose stresses on the continents, thereby facilitating continental rifting and disrupting the supercontinent cycle (Storey, Nature 1995; Santosh et al., Gondwana Research 2009). In recent years, several studies have characterized the relation between the location of the plumes and the continents, but with contradicting observations. While Heron and Lowman (GRL, 2010; Tectonophysics, 2011) propose regions where downwelling has ceased (irrespective of overlying plate) as the preferred location for plumes, O'Neill et al. (Gondwana Research, 2009) show an anti-correlation between the average positions of subducting slabs at continental margins, and mantle plumes at continental/oceanic interiors. Extent of continental motion depends on the heat budget of the mantle (CMB heat flux, radiogenic heating, mantle cooling). 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), much higher than early estimates of 3-4 TW (Lay et al., Nature 2008). Thus, it is necessary to characterize the effect of increased CMB heat flux on mantle dynamics. In almost all mantle convection simulations, the top boundary is treated as a free-slip surface whereas Earth's surface is a deformable free surface. Unlike free-slip, a free surface boundary condition allows for the development of topography and leads to realistic single-sided (asymmetric) subduction (Crameri et al., GJI 2012; Crameri et al., GRL 2012). Using StagYY code (Tackley, PEPI 2008), we test (i) the impact of increased basal heating on mantle dynamics with continents and self-consistent plate tectonics, including whether plumes prefer to develop under continents; (ii) the influence of a free surface on continents using the 'sticky air' approach, in which a low density and a small viscosity fluid layer is

  6. Observations of geometry and ages constrain relative motion of Hawaii and Louisville plumes (United States)

    Wessel, Paul; Kroenke, Loren W.


    The classic view of linear island chains as volcanic expressions of interactions between changing plate tectonic motions and fixed mantle plumes has come under renewed scrutiny. In particular, observed paleolatitudes from the Emperor seamounts imply that the Hawaii hotspot was > 5-15° further north during formation of these seamounts and that rapid retardation of its southward migration was the primary agent forming the angular Hawaii-Emperor bend. Supporting this view are predictions from fluid dynamic experiments that suggest the general mantle circulation may displace narrow mantle plumes; consequently the surface locations of hotspots are not fixed and may have varied considerably in the past. However, the locations and ages of available rock samples place fundamental limits on the relative motion between the Hawaii and Louisville hotspots. Here we use such data to estimate empirical age progression curves for separate chains and calculate the continuous variations in hotspot separations through time. While the data are sparse, the inferred inter-hotspot motion for ages > 55 Myr appears significant but the observed relative motion is only about half of what is predicted by mantle dynamics models. To reconcile the observed paleolatitudes with our observed relative motion requires either a larger contemporaneous southward motion of the Louisville hotspot than previously suggested or a moderate component of true polar wander.

  7. Supercontinents, mantle dynamics and plate tectonics: A perspective based on conceptual vs. numerical models (United States)

    Yoshida, Masaki; Santosh, M.


    The periodic assembly and dispersal of supercontinents through the history of the Earth had considerable impact on mantle dynamics and surface processes. Here we synthesize some of the conceptual models on supercontinent amalgamation and disruption and combine it with recent information from numerical studies to provide a unified approach in understanding Wilson Cycle and supercontinent cycle. Plate tectonic models predict that superdownwelling along multiple subduction zones might provide an effective mechanism to pull together dispersed continental fragments into a closely packed assembly. The recycled subducted material that accumulates at the mantle transition zone and sinks down into the core-mantle boundary (CMB) provides the potential fuel for the generation of plumes and superplumes which ultimately fragment the supercontinent. Geological evidence related to the disruption of two major supercontinents (Columbia and Gondwana) attest to the involvement of plumes. The re-assembly of dispersed continental fragments after the breakup of a supercontinent occurs through complex processes involving 'introversion', 'extroversion' or a combination of both, with the closure of the intervening ocean occurring through Pacific-type or Atlantic-type processes. The timescales of the assembly and dispersion of supercontinents have varied through the Earth history, and appear to be closely linked with the processes and duration of superplume genesis. The widely held view that the volume of continental crust has increased over time has been challenged in recent works and current models propose that plate tectonics creates and destroys Earth's continental crust with more crust being destroyed than created. The creation-destruction balance changes over a supercontinent cycle, with a higher crustal growth through magmatic influx during supercontinent break-up as compared to the tectonic erosion and sediment-trapped subduction in convergent margins associated with supercontinent

  8. Mantle hydrocarbons: abiotic or biotic? (United States)

    Sugisaki, R; Mimura, K


    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.

  9. Plumes in stellar convection zones

    CERN Document Server

    Zahn, J P


    All numerical simulations of compressible convection reveal the presence of strong downwards directed flows. Thanks to helioseismology, such plumes have now been detected also at the top of the solar convection zone, on super- granular scales. Their properties may be crudely described by adopting Taylor's turbulent entrainment hypothesis, whose validity is well established under various conditions. Using this model, one finds that the strong density stratification does not prevent the plumes from traversing the whole convection zone, and that they carry upwards a net energy flux (Rieutord & Zahn 1995). They penetrate to some extent in the adjacent stable region, where they establish a nearly adiabatic stratification. These plumes have a strong impact on the dynamics of stellar convection zones, and they play probably a key role in the dynamo mechanism.

  10. Origin of the Luobusa diamond-bearing peridotites from the sub-arc mantle (United States)

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


    Ophiolites are the remnants of ancient oceanic lithosphere that were emplaced onto continental margins. Ophiolites along the E-W trending Yarlung-Tsangpo Suture (YTS), which separates the Indian plate from the Eurasian plate, have been regarded as relics of the Neo-Tethys Ocean. The Luobusa ophiolite outcrops at the eastern YTS and mainly consists of harzburgites and dunites that have been intruded by gabbroic/diabase dykes at ca 130 Ma (Zhang et al., 2015). Basaltic lavas are rarely outcropped, and volumetrically minor (ocean ridge and subsequently reacted with boninitic magmas in subduction zone, which gave rise to podifiorm chromitites (Zhou et al., 1996). However, such a shallow depth origin fails to explain the occurrence of diamond and other ultra-high pressure (UHP) minerals in both peridotites and chromitites (Yang et al., 2007, 2014). A mantle plume origin has been proposed for the Luobusa ophiolite to explain the UHP minerals. However, this model is not reconciled with the occurrence of low-pressure crustal minerals in both chromitites and peridotites (Robinson et al., 2015). Here we report whole-rock Re-Os isotope data, which suggest that most Luobusa peridotites have subjected to ancient melting events older than 1.9 billion years. High contents of heavy rare earth elements in clinopyroxenes support the occurrence of ancient melting in garnet stability field. Hf-Nd isotopes of clinopyroxenes, which yield young model ages as 110 Ma, with one showing the lowest ɛNd(T) value of -3, do not preserve the signatures of ancient melting but record metasomatism by subduction-related agents. Consequently, we argue that protoliths of the Luobusa peridotites originated from ancient domains in the transition zone and, together with diamond-bearing chromitites, were accreted through a plume activity (Yang et al., 2014) up to the lithospheric mantle beneath the Lhasa terrane, where they have been metasomatized by Neo-Tethyan subduction processes. This sub

  11. Using 3He/4He to Map the flow of the Samoan-Plume into the Lau Basin (United States)

    Price, A.; Jackson, M. G.; Hall, P. S.; Sinton, J. M.; Kurz, M. D.


    Understanding how the upper mantle flows beneath oceanic lithosphere is crucial to understanding mantle melting, the distribution of geochemical reservoirs, and movement of plate tectonics. Spatial variations in the geochemistry of igneous rocks can provide an understanding of flow in the upper mantle. Numerous geochemical and geophysical anomalies within the northern portion of the Lau basin--the presence of high 3He/4He (up to 28 times atmospheric), latitudinal gradients in trace element and isotopic (Sr-Nd-Pb) enrichment, and trench parallel shear wave splitting near the Tonga arc--have been attributed to the southward flow of mantle material from the nearby Samoan hotspot. The Samoan plume is located only 200 km east of the northern terminus of the Tonga trench. North of the terminus, the Pacific plate "tears" and, instead of subducting into the trench, continues to the West. To the South of the terminus, the Pacific plate subducts into the Tonga Trench. The resulting tear generated a "slab window", allowing the Samoan mantle to flow southward beneath the Vitiaz lineament and penetrate into the shallow mantle of the Lau Basin. The juxtaposition of the Samoan hotspot and the Tonga Trench create a unique setting in which the southward flow of the distinctive high 3He/4He Samoan plume mantle can be readily detected in the Lau Basin. High 3He/4He ratios (up to 28.1 Ra) have been reported in a swath within the northern Lau Basin, which drop rapidly to both the South (~400km south of Peggy ridge) and East (Lupton, 2009) of this narrow incursion. It was suggested that the 3He/ 4He would also decline to the west, creating a "finger-like" corridor of Samoan Plume (Turner & Hawkesworth ,1998). However, such a model is not constrained, as 3He/4He ratios have not been reported in the region to the West of the infiltrating plume. Does the Samoan plume material extend broadly to the west, or is it confined to a narrow "finger-like" corridor in the North Lau Basin? We present

  12. Coastal river plumes: Collisions and coalescence (United States)

    Warrick, Jonathan A.; Farnsworth, Katherine L.


    Plumes of buoyant river water spread in the ocean from river mouths, and these plumes influence water quality, sediment dispersal, primary productivity, and circulation along the world's coasts. Most investigations of river plumes have focused on large rivers in a coastal region, for which the physical spreading of the plume is assumed to be independent from the influence of other buoyant plumes. Here we provide new understanding of the spreading patterns of multiple plumes interacting along simplified coastal settings by investigating: (i) the relative likelihood of plume-to-plume interactions at different settings using geophysical scaling, (ii) the diversity of plume frontal collision types and the effects of these collisions on spreading patterns of plume waters using a two-dimensional hydrodynamic model, and (iii) the fundamental differences in plume spreading patterns between coasts with single and multiple rivers using a three-dimensional hydrodynamic model. Geophysical scaling suggests that coastal margins with numerous small rivers (watershed areas 100,000 km2). When two plume fronts meet, several types of collision attributes were found, including refection, subduction and occlusion. We found that the relative differences in pre-collision plume densities and thicknesses strongly influenced the resulting collision types. The three-dimensional spreading of buoyant plumes was found to be influenced by the presence of additional rivers for all modeled scenarios, including those with and without Coriolis and wind. Combined, these results suggest that plume-to-plume interactions are common phenomena for coastal regions offshore of the world's smaller rivers and for coastal settings with multiple river mouths in close proximity, and that the spreading and fate of river waters in these settings will be strongly influenced by these interactions. We conclude that new investigations are needed to characterize how plumes interact offshore of river mouths to better

  13. Coastal river plumes: Collisions and coalescence (United States)

    Warrick, Jonathan; Farnsworth, Katherine L


    Plumes of buoyant river water spread in the ocean from river mouths, and these plumes influence water quality, sediment dispersal, primary productivity, and circulation along the world’s coasts. Most investigations of river plumes have focused on large rivers in a coastal region, for which the physical spreading of the plume is assumed to be independent from the influence of other buoyant plumes. Here we provide new understanding of the spreading patterns of multiple plumes interacting along simplified coastal settings by investigating: (i) the relative likelihood of plume-to-plume interactions at different settings using geophysical scaling, (ii) the diversity of plume frontal collision types and the effects of these collisions on spreading patterns of plume waters using a two-dimensional hydrodynamic model, and (iii) the fundamental differences in plume spreading patterns between coasts with single and multiple rivers using a three-dimensional hydrodynamic model. Geophysical scaling suggests that coastal margins with numerous small rivers (watershed areas  100,000 km2). When two plume fronts meet, several types of collision attributes were found, including refection, subduction and occlusion. We found that the relative differences in pre-collision plume densities and thicknesses strongly influenced the resulting collision types. The three-dimensional spreading of buoyant plumes was found to be influenced by the presence of additional rivers for all modeled scenarios, including those with and without Coriolis and wind. Combined, these results suggest that plume-to-plume interactions are common phenomena for coastal regions offshore of the world’s smaller rivers and for coastal settings with multiple river mouths in close proximity, and that the spreading and fate of river waters in these settings will be strongly influenced by these interactions. We conclude that new investigations are needed to characterize how plumes interact offshore of river mouths to

  14. Global Circulation and Impact of Plasmaspheric Plumes (United States)

    Moore, Thomas E.; Fok, Mei-Ching; Chen, Sheng-Hsiem; Delcourt, Dominique C.; Fedder, Joel A.; Slinker, Steven P.


    We report results from the global circulation model of Lyon, Fedder, and Mobarry with an embedded model of the inner magnetosphere including the plasmasphere. The combination is used to initiate large numbers of representative protons on the geosynchronous orbit L shell, to assign particle weightings, to track their: subsequent trajectories in the 3D fields. This permits us to study the global circulation of plasmaspheric plumes and to compare these with Polar observations from the dayside magnetopause region . A range of events is studied from an isolated period of SBz in the solar wind,to a large storm sequence. We consider effects on circulating plasma reaching the dayside reconnection X-line, the population of the plasma sheet with ionospheric protons and the generation of ring current pressure from this source, compared with solar wind, polar wind, and auroral wind sources. We find that the transient plasmaspheric plume source is large in terms of total fluence, but of modest proportions in terms of contribution to the ring current. Implications of this and other results for improved space weather modeling and prediction will be discussed.

  15. Importance of Mantle Viscosity in Interseismic Deformation (United States)

    Wang, K.; He, J.; Hu, Y.


    the seismic moment of the earthquake, such that for small events, the first two phases are brief or even absent. With modern geodetic observations and advanced modeling demonstrating the first-order importance of mantle viscosity in interseismic deformation, we argue that it is time to revise all the elastic interseismic models to address the effect of mantle viscosity. Using an elastic model to represent the real Earth of very low mantle-wedge viscosity leads to under- or over-estimates of the downdip width of the zone of fault locking or "partial locking", depending on the time since the previous earthquake. The effect of viscoelastic relaxation is strong regardless of how long after the earthquake and whether the deformation field is still changing with time. The use of an elastic model may also cause the interseismic elastic strain to be misidentified as due to permanent upper-plate deformation (commonly described in terms of block motion). Revising these models therefore will improve our view of subduction zone earthquake/tsunami hazards and geodynamic processes.

  16. The 2010 Eyjafjallajökull and 2011 Grimsvötn ash plumes as seen by GPS (United States)

    Grapenthin, R.; Hreinsdottir, S.; Gudmundsson, M. T.


    The injection of a volcanic plume introduces a dynamic, localized, short-term heterogeneity in the atmosphere. Satellite-imagery based remote sensing techniques provide good spatial coverage for the detection of such plumes, but slow satellite repeat times (>30 minutes) and cloud cover can delay, if not entirely prevent, the detection. GPS, in turn, provides excellent temporal coverage, but requires favorable satellite-station-geometry such that the signal propagates through the plume if it is to be used for plume detection and analysis. Two methods exist to detect / analyze ash plumes with GPS: (a) Ash-heavy plumes result in signal dispersion and hence a lowered signal-to-noise ratio (SNR). A lowered SNR, recorded by some receivers, can provide useful information about the plume, such as location and velocity of ascent. These data can be evaluated directly as they are recorded by the receiver; without the need of solving for a receiver's position. (b) Wet plumes refract the GPS signals piercing the plume and hence induce a propagation delay. When solving for a receiver position GPS analysis tools do not model this localized phase delay effect and solutions for plume-piercing satellites do not fit the data well. This can be exploited for plume analysis such as the estimation of changes to the atmospheric refractivity index. We analyze GPS data of the ~2 month 2010 Eyafjallajökull erption and the week-long 2011 Grímsvötn eruption to infer a first order estimate of plume geometry and its progression. Using SNR and phase delay information, we evaluate the evolution of the partitioning of wet versus dry parts of the plume. During the GPS processing we iteratively solve for phase-delay and position and fix other parameters, hence reducing the mapping of least-squares misfit into position estimates and other parameters. Nearly continuous webcam imagery provides independent observations of first-order plume characteristics for the Eyafjallajökull event.

  17. Mantle source provinces beneath the Northwestern USA delimited by helium isotopes in young basalts (United States)

    Graham, D. W.; Reid, M. R.; Jordan, B. T.; Grunder, A. L.; Leeman, W. P.; Lupton, J. E.


    We report new He, Nd and Sr isotope results for basalts from the northwestern United States. The new 3He/ 4He results for olivine phenocrysts in basalts from the eastern Snake River Plain (SRP), the Owyhee Plateau (OP) and the Oregon High Lava Plains (HLP), together with published He isotope data for Yellowstone and the Cascades volcanic arc, delineate distinct mantle sources for each of these sub-provinces. All basalts from the eastern SRP (8 Quaternary localities plus 1 Miocene locality) have 3He/ 4He ratios higher than observed in normal mid-ocean ridge basalts, but overlapping with ranges observed in hotspot-related oceanic islands. For a lateral distance of some 400 km along the SRP, 3He/ 4He ranges from ~ 11 RA in the west to > 19 RA adjacent to Yellowstone. Such high ratios have not been observed elsewhere in the western U.S., and are consistent with the presence of a mantle plume. The lateral gradient in 3He/ 4He suggests that the proportion of plume-derived He decreases westward, but this interpretation is complicated by possible addition of crustal helium during open-system crystal fractionation in some SRP basaltic magmas. Although crustal contamination may modulate 3He/ 4He in basalts along the SRP, the effect is not strong and it does not obscure the elevated 3He/ 4He mantle source signature. In contrast, young basalts from the HLP and the OP have 3He/ 4He values of 8.8-9.3 RA, within the range for mid-ocean ridge basalts; these data reflect a shallow asthenospheric source with no discernible influence from the Yellowstone hotspot. Basalts from Newberry volcano have slightly lower 3He/ 4He (7.6-8.3 RA), within the range for other Cascades arc lavas (7.0-8.4 RA). Three alternative explanations are possible for the origin of the high 3He/ 4He signature along the SRP: (1) multi-component mixing of (a) magmas and/or CO 2-rich fluids derived from plume mantle having high 3He/ 4He, (b) continental lithosphere having low 3He/ 4He, and (c) shallow

  18. Converted phases from sharp 1000 km depth mid-mantle heterogeneity beneath Western Europe (United States)

    Jenkins, J.; Deuss, A.; Cottaar, S.


    Until recently, most of the lower mantle was generally considered to be well-mixed with strong heterogeneity restricted to the lowermost several hundred kilometres above the core-mantle boundary, known as the D″ layer. However several recent studies have started to hint at a potential change in Earth's structure at mid-mantle depths beneath the transition zone. Here we present a continental-wide search of Europe and the North Atlantic for mid-mantle P-to-s wave converted phases. Our data set consists of close to 50,000 high quality receiver functions. These are combined in slowness and depth stacks to identify seismic discontinuities in the range of 800-1400 km depth to determine at which depths and in which tectonic settings these features exist. Receiver functions are computed in different frequency bands to resolve the sharpness of the observed discontinuities. We find most seismic velocity jumps are observed between 975-1050 km depth, localised beneath western Europe and Iceland. The shear wave velocity jumps are roughly 1-2.5% velocity increase with depth occurring over less than 8 km in width. The most robust observations are coincident with areas of active upwelling (under Iceland) and an elongate lateral low velocity anomaly imaged in recent tomographic models which has been interpreted as diverted plume material at depth. The lack of any suggested phase change in a normal pyrolitic mantle composition at around 1000 km depth indicates the presence of regional chemical heterogeneity within the mid-mantle, potentially caused by diverted plume material. We hypothesise that our observations represent either a phase change within chemically distinct plume material itself, or are caused by small scale chemical heterogeneities entrained within the upwelling plume, either in the form of recycled basaltic material or deep sourced chemically distinct material from LLSVPs. Our observations, which cannot be directly linked to an area of either active or ancient

  19. Lidar measurements of plume statistics

    DEFF Research Database (Denmark)

    Ejsing Jørgensen, Hans; Mikkelsen, T.


    the source, instantaneous crosswind plume profiles were detected repetitively at high spatial (1.5 m) and temporal (3 sec) intervals by use of a mini LIDAR system. The experiments were accompanied by measurement of the surface-layer mean wind and turbulence quantities by sonic anemometers. On the basis...

  20. Ship exhaust gas plume cooling

    NARCIS (Netherlands)

    Schleijpen, H.M.A.; Neele, P.P.


    The exhaust gas plume is an important and sometimes dominating contributor to the infrared signature of ships. Suppression of the infrared ship signatures has been studied by TNO for the Royal Netherlands Navy over considerable time. This study deals with the suppression effects, which can be achiev

  1. Satellite detection of wastewater diversion plumes in Southern California (United States)

    Gierach, Michelle M.; Holt, Benjamin; Trinh, Rebecca; Jack Pan, B.; Rains, Christine


    Multi-sensor satellite observations proved useful in detecting surfacing wastewater plumes during the 2006 Hyperion Treatment Plant (HTP) and 2012 Orange County Sanitation District (OCSD) wastewater diversion events in Southern California. Satellite sensors were capable of detecting biophysical signatures associated with the wastewater, compared to ambient ocean waters, enabling monitoring of environmental impacts over a greater spatial extent than in situ sampling alone. Thermal satellite sensors measured decreased sea surface temperatures (SSTs) associated with the surfacing plumes. Ocean color satellite sensors did not measure a distinguishable biological response in terms of chlorophyll-a (chl-a) concentrations during the short lived, three-day long, 2006 HTP diversion. A period of decreased chl-a concentration was observed during the three-week long 2012 OCSD diversion, likely in association with enhanced chlorination of the discharged wastewater that suppressed the phytoplankton response and/or significant uptake by heterotrophic bacteria. Synthetic aperture radar (SAR) satellite data were able to identify and track the 2006 HTP wastewater plume through changes in surface roughness related to the oily components of the treated surfacing wastewater. Overall, it was found that chl-a and SST values must have differences of at least 1 mg m-3 and 0.5 °C, respectively, in comparison with adjacent waters for wastewater plumes and their biophysical impact to be detectable from satellite. For a wastewater plume to be identifiable in SAR imagery, wind speeds must range between ∼3 and 8 m s-1. The findings of this study illustrate the benefit of utilizing multiple satellite sensors to monitor the rapidly changing environmental response to surfacing wastewater plumes, and can help inform future wastewater diversions in coastal areas.

  2. Downwelling wind, tides, and estuarine plume dynamics (United States)

    Lai, Zhigang; Ma, Ronghua; Huang, Mingfen; Chen, Changsheng; Chen, Yong; Xie, Congbin; Beardsley, Robert C.


    The estuarine plume dynamics under a downwelling-favorable wind condition were examined in the windy dry season of the Pearl River Estuary (PRE) using the PRE primitive-equation Finite-Volume Community Ocean Model (FVCOM). The wind and tide-driven estuarine circulation had a significant influence on the plume dynamics on both local and remote scales. Specifically, the local effect of downwelling-favorable winds on the plume was similar to the theoretical descriptions of coastal plumes, narrowing the plume width, and setting up a vertically uniform downstream current at the plume edge. Tides tended to reduce these plume responses through local turbulent mixing and advection from upstream regions, resulting in an adjustment of the isohalines in the plume and a weakening of the vertically uniform downstream current. The remote effect of downwelling-favorable winds on the plume was due to the wind-induced estuarine sea surface height (SSH), which strengthened the estuarine circulation and enhanced the plume transport accordingly. Associated with these processes, tide-induced mixing tended to weaken the SSH gradient and thus the estuarine circulation over a remote influence scale. Overall, the typical features of downwelling-favorable wind-driven estuarine plumes revealed in this study enhanced our understanding of the estuarine plume dynamics under downwelling-favorable wind conditions.

  3. Characterization of redox conditions in pollution plumes

    DEFF Research Database (Denmark)

    Christensen, Thomas Højlund; Bjerg, Poul Løgstrup; Banwart, Steven A.


    Evalution of redox conditions in groundwater pollution plumes is often a prerequisite for understanding the behviour of the pollutants in the plume and for selecting remediation approaches. Measuring of redox conditions in pollution plumes is, however, a fairly recent issue and yet relative few...

  4. Characterization of redox conditions in pollution plumes

    DEFF Research Database (Denmark)

    Christensen, Thomas Højlund; Bjerg, Poul Løgstrup; Banwart, Steven A.


    Evalution of redox conditions in groundwater pollution plumes is often a prerequisite for understanding the behviour of the pollutants in the plume and for selecting remediation approaches. Measuring of redox conditions in pollution plumes is, however, a fairly recent issue and yet relative few...

  5. Iron geochemistry of the mantle (United States)

    Humayun, M.; Campbell, T. J.; Brandon, A. D.; Davis, F. A.; Hirschmann, M. M.


    The Fe/Mg ratio is an important constraint on the compositionally controlled density of the mantle. However, this ratio cannot be inferred from erupted lavas from OIB or MORB sources, but must be determined directly from mantle peridotites. Recently, the Fe/Mn ratio of erupted lavas has been used as an indicator of potential Fe variability in the mantle driven by core-mantle interaction, recycled oceanic crust, or even variations in the temperature of mantle melting. The classic compilation of McDonough & Sun (1995) provided the currently accepted Fe/Mn ratio of the upper mantle, 60±10. The uncertainty on this ratio allows for 15-30% variability in mantle iron abundances, which is equivalent to a density variation larger than observed by seismic tomography in the mantle. To better understand the relationship between mantle peridotites and erupted lavas, and to search for real variability in the Fe/Mn ratio of mantle peridotites, we report precise new ICP-MS measurements of the transition element geochemistry of suites of mantle xenoliths that have known Fe/Mg ratios. For 12 Kilbourne Hole xenoliths, we observe a clear correlation between Fe/Mn and MgO (or Fe/Mg) over an Fe/Mn range of 59-72. Extrapolation of this trend to a Primitive Mantle (PM) MgO content of 37.8 yields an Fe/Mn of 59±1 for the PM. Our new analyses of KLB-1 powder and fused glass beads yield an Fe/Mn of 61.4 for both samples, which plots on the Kilbourne Hole Fe/Mn vs. MgO trend. A set of ten xenoliths from San Carlos yield a wide range of Fe/Mn (56-65) not correlated with MgO content. The San Carlos xenoliths may have experienced a metasomatic effect that imprinted variable Fe/Mn. A clinopyroxene-rich lithology from San Carlos yields an Fe/Mn of 38, which plots on an extension of the Kilbourne Hole Fe/Mn vs. MgO trend. These new results, and those from other xenolith localities being measured in our lab, provide new constraints on the compositional variability of the Earth's upper mantle. Mc

  6. Origin of geochemical mantle components: Role of subduction filter (United States)

    Kimura, Jun-Ichi; Gill, James B.; Skora, Susanne; van Keken, Peter E.; Kawabata, Hiroshi


    We quantitatively explore element redistribution at subduction zones using numerical mass balance models to evaluate the roles of the subduction zone filter in the Earth's geochemical cycle. Our models of slab residues after arc magma genesis differ from previous ones by being internally consistent with geodynamic models of modern arcs that successfully explain arc magma genesis and include element fluxes from the dehydration/melting of each underlying slab component. We assume that the mantle potential temperature (Tp) was 1400-1650°C at 3.5-1.7 Ga and gradually decreased to 1300-1350°C today. Hot subduction zones with Tp ˜1650°C have a thermal structure like modern SW Japan where high-Mg andesite is formed which is chemically like continental crust. After 2.5-1.7 Gyr of storage in the mantle, the residual igneous oceanic crust from hot subduction zones can evolve isotopically to the HIMU mantle component, the residual base of the mantle wedge to EMI, the residual sediment becomes an essential part of EMII, and the residual top of the mantle wedge can become the subcontinental lithosphere component. The Common or Focal Zone component is a stable mixture of the first three residues occasionally mixed with early depleted mantle. Slab residues that recycled earlier (˜2.5 Ga) form the DUPAL anomaly in the southern hemisphere, whereas residues of more recent recycling (˜1.7 Ga) underlie the northern hemisphere. These ages correspond to major continental crust forming events. The east-west heterogeneity of the depleted upper mantle involves subcontinental mantle except in the Pacific.

  7. Heterogeneity of Water Concentrations in the Mantle Lithosphere Beneath Hawaii (United States)

    Bizimis, M.; Peslier, A. H.; Clague, D.


    The amount and distribution of water in the oceanic mantle lithosphere has implications on its strength and of the role of volatiles during plume/lithosphere interaction. The latter plays a role in the Earth's deep water cycle as water-rich plume lavas could re-enrich an oceanic lithosphere depleted in water at the ridge, and when this heterogeneous lithosphere gets recycled back into the deep mantle. The main host of water in mantle lithologies are nominally anhydrous minerals like olivine, pyroxene and garnet, where hydrogen (H) is incorporated in mineral defects by bonding to structural oxygen. Here, we report water concentrations by Fourier transform infrared spectrometry (FTIR) on olivine, clino- and orthopyroxenes (Cpx & Opx) from spinel peridotites from the Pali vent and garnet pyroxenite xenoliths from Aliamanu vent, both part of the rejuvenated volcanism at Oahu (Hawaii). Pyroxenes from the Aliamanu pyroxenites have high water concentrations, similar to the adjacent Salt Lake Crater (SLC) pyroxenites (Cpx 400-500 ppm H2O, Opx 200 ppm H2O). This confirms that pyroxenite cumulates form water-rich lithologies within the oceanic lithosphere. In contrast, the Pali peridotites have much lower water concentrations than the SLC ones (10% modal Cpx and low spinel Cr# (0.09-0.10). The contrast between the two peridotite suites is also evident in their trace elements and radiogenic isotopes. The Pali Cpx are depleted in light REE, consistent with minimal metasomatism. Those of SLC have enriched light REE patterns and Nd and Hf isotopes consistent with metasomatism by alkaline melts. These observations are consistent with heterogeneous water distribution in the oceanic lithosphere that may be related to metasomatism, as well as relatively dry peridotites cross-cut by narrow (?) water-rich melt reaction zones.

  8. Observing Volcanic Plumes Using Singular Vector Decomposition of MIPAS Spectra (United States)

    Smith, Andrew J. A.; Dudhia, A.; Grainger, R. G.


    A simple flagging of MIPAS spectra based on ratios of radiances in a narrow section of the A-Band (685-970 cm-1) can mark suspected volcanic plumes when their signal is strong and uncontaminated, but is not hugely sensitive to weaker signals. Using singular vector decomposition (SVD) to remove modes of spectral variability due to normal atmospheric conditions, a more accurate indicator of volcanic ash plumes in the Oxford MIPAS cloud retrieval can be obtained. As time progresses, the strength of the signal can fall off, but it is still possible to be tracked. SVD also allows one to obtain information about the spectral signature of a specific eruption. Since individual events have different signatures, once a training set has been obtained, signals from different events can be distinguished.

  9. Dynamics of Pre-3 Ga Crust-Mantle Evolution (United States)

    Patchett, P. J.; Chase, C. G.; Vervoort, J. D.


    in view of the apparent Proterozoic Pb age of some present mantle plume sources, we believe sequestration of enriched material in the deep mantle is still underestimated, and that isotopic mass balance calculations involving only continent and upper mantle will overestimate the mean continental age.

  10. Plume spectrometry for liquid rocket engine health monitoring (United States)

    Powers, William T.; Sherrell, F. G.; Bridges, J. H., III; Bratcher, T. W.


    An investigation of Space Shuttle Main Engine (SSME) testing failures identified optical events which appeared to be precursors of those failures. A program was therefore undertaken to detect plume trace phenomena characteristic of the engine and to design a monitoring system, responsive to excessive activity in the plume, capable of delivering a warning of an anomalous condition. By sensing the amount of extraneous material entrained in the plume and considering engine history, it may be possible to identify wearing of failing components in time for a safe shutdown and thus prevent a catastrophic event. To investigate the possibilities of safe shutdown and thus prevent a monitor to initiate the shutdown procedure, a large amount of plume data were taken from SSME firings using laboratory instrumentation. Those data were used to design a more specialized instrument dedicated to rocket plume diagnostics. The spectral wavelength range of the baseline data was about 220 nanometers (nm) to 15 micrometer with special attention given to visible and near UV. The data indicates that a satisfactory design will include a polychromator covering the range of 250 nM to 1000 nM, along with a continuous coverage spectrometer, each having a resolution of at least 5A degrees. The concurrent requirements for high resolution and broad coverage are normally at odds with one another in commercial instruments, therefore necessitating the development of special instrumentation. The design of a polychromator is reviewed herein, with a detailed discussion of the continuous coverage spectrometer delayed to a later forum. The program also requires the development of applications software providing detection, variable background discrimination, noise reduction, filtering, and decision making based on varying historical data.

  11. Mapping the subducted Nazca plate in the lower mantle beneath South America (United States)

    Contenti, S. M.; Gu, Y. J.; Okeler, A.


    Recent improvements in data coverage have enabled high-resolution imaging of the morphology of subduction zones and mantle plumes. In this study, we migrate the SS precursors from over 5000 seismograms to obtain a detailed map of mid- and upper-mantle reflectors beneath the northern portion of the South American subduction zone, where the oceanic Nazca plate is descending below the South American plate. In addition to an elevated 410 and depressed 660 (as expected for a subduction zone), strong mid-mantle reflectors at 800-1100 km depth are also apparent. The amplitudes of these steeply dipping reflectors are comparable to that of the 660-kilometer discontinuity. This anomaly outlines a high-velocity (therefore presumably cold) region present in recent finite-frequency based mantle velocity models, suggesting the extension of slab material into the lower mantle. The strength of the reflection is interpreted to be caused by a relatively sharp velocity change, likely due to a strong temperature gradient in combination with mineral phase transitions, the presence of water, or other chemical heterogeneities. Significant mass and heat exchange is therefore expected between the upper- and lower-mantle beneath the study region.

  12. Variation of thermal conductivity and heat flux at the Earth's core mantle boundary (United States)

    Ammann, Michael W.; Walker, Andrew M.; Stackhouse, Stephen; Wookey, James; Forte, Alessandro M.; Brodholt, John P.; Dobson, David P.


    The two convective systems that dominate Earth's internal dynamics meet at the boundary between the rocky mantle and metallic liquid core. Energy transfer between processes driving plate tectonics and the geodynamo is controlled by thermal conduction in the lowermost mantle (D″). We use atomic scale simulations to determine the thermal conductivity of MgSiO3 perovskite and post-perovskite under D″ conditions and probe how these two convective systems interact. We show that the thermal conductivity of post-perovskite (∼12 W/mK) is 50% larger than that of perovskite under the same conditions (∼8.5 W/mK) and is anisotropic, with conductivity along the a-axis being 40% higher than conductivity along the c-axis. This enhances the high heat flux into cold regions of D″ where post-perovskite is stable, strengthening the feedback between convection in the core and mantle. Reminiscent of the situation in the lithosphere, there is potential for deformation induced texturing associated with mantle convection to modify how the mantle is heated from below. We test this by coupling our atomic scale results to models of texture in D″ and suggest that anisotropic thermal conductivity may help to stabilise the roots of mantle plumes over their protracted lifetime.

  13. Diverse Igneous Protolith Contributions to Sediments in Gale Crater: Variable Metasomatism of the Mars Mantle (United States)

    Schmidt, M. E.; Izawa, M. R. M.; Thomas, A. P.; Thompson, L.; Gellert, R.


    Igneous float rocks and least altered basaltic sedimentary bedrock examined in Gale Crater provide insight to the petrogenesis of the crystalline basement and suggest the mantle source was alkali and Ni-enriched by an oxidizing metasomatic event.

  14. U-Pb isotopic geochemistry of the post-collisional mafic-ultramafic rocks from the Dabie Mountains--Crust-mantle interaction and LOMU component

    Institute of Scientific and Technical Information of China (English)

    黄方; 李曙光; 周红英; 李惠民


    The U-Pb isotope geochemical study of the pyroxenite-gabbro intrusion in the Dabie Mountains shows that the post-collisional mafic-ultramafic rocks of the Dabie Mountains are characterized by relative high Pb contents, low U contents and low U/Pb ratios. These characters may be results of interaction between lithosphere or depleted asthenospheric mantle (DMM) and lower crust, but have nothing to do with mantle plume and subducted continental crust. It was first observed that some samples with lower 206Pb/204Pb and higher 207Pb/204Pb ratios show typical characters of the LOMU component. The Pb, Sr, and Nd isotopic tracing shows that three components are needed in the source of the Zhujiapu pyroxenite-gabbro intrusion. They could be old enriched sub-continental lithospheric mantle (LOMU component), lower crust and depleted asthenospheric mantle. The crust-mantle interaction process producing primitive magma of post-collisional mafic-ultramafic rocks in the Dabie Mountains could be described by a lithospheric delamination and magma underplating model. After continent-continent collision, delamination of the thickened lithosphere induced the upwelling of depleted asthenospheric mantle, which caused partial melting of asthenospheric mantle and residual sub-continental lithospheric mantle. The basaltic magma produced in this process underplated in the boundary between the crust and mantle and interacted with lower crust resulting in the geochemical characters of both enriched lithospheric mantle and lower crust.

  15. Compositional differentiation of Enceladus' plume (United States)

    Khawaja, N.; Postberg, F.; Schmidt, J.


    The Cosmic Dust Analyser (CDA) on board the Cassini spacecraft sampled Enceladus' plume ice particles emanated directly from Enceladus' fractured south polar terrain (SPT), the so-called "Tiger Stripes", during two consecutive flybys (E17 and E18) in 2012. The spacecraft passed through the dense plume with a moderate velocity of ~7.5km/s, horizontally to the SPT with a closest approach (CA) at an altitude of ~75km almost directly over the south pole. In both flybys, spectra were recorded during a time interval of ~ ±3 minutes with respect to the closest approach achieving an average sampling rate of about 0.6 sec-1. We assume that the spacecraft passed through the plume during an interval of about ±60(sec) from the CA. Particles encountered before and after this period are predominately from the E-ring background in which Enceladus is embedded. Most CDA TOF-mass spectra are identified as one of three compositional types: (i) almost pure water (ii) organic rich and (iii) salt rich [2]. A Boxcar Analysis (BCA) is performed from a count database for compositional mapping of the plume along the space-craft trajectory. In BCA, counts of each spectrum type are integrated for a certain interval of time (box size). The integral of counts represents frequencies of compositional types in absolute abundances, which are converted later into proportions. This technique has been proven to be a suitable for inferring the compositional profiles from an earlier flyby (E5) [1]. The inferred compositional profiles show similar trends on E17 and E18. The abundances of different compositional types in the plume clearly differ from the Ering background and imply a compositional differentiation inside the plume. Following up the work of Schmidt et al, 2008 and Postberg et al, 2011 we can link different compositional types to different origins. The E17/E18 results are compared with the E5 flyby in 2008, which yielded the currently best compositional profile [2] but was executed at much

  16. Deep-seated xenoliths and xenocrysts from Sytykanskaya pipe: evidence for the evolution of the mantle beneath Alakit, Yakutia. (United States)

    Ashchepkov, Igor; Vladykin, Nikolai; Ntaflos, Theodoros; Logvinova, Alla; Yudin, Denis; Karpenko, Mikhail; Palessky, Stanislav; Khmelnikova, Olga; Travin, Alexey; Salikhov, Ravil


    . Minerals of the metasomatic xenoliths are less inclined with lower La/Cen ratios and without troughs in spider diagrams. The garnets often show S-shaped patterns. Garnets from the Cr websterites show round REE patterns and deep troughs in Ba-Sr but enrichment in Nb-Ta-U. The clinopyroxenes reveal the inclined and inflected on Gd spectrums with variations in LREE due to AFC differentiation. The 40Ar-39Ar ages for micas from the Alakit field reveal three intervals for the metasomatism. The first (1154 Ma) relates to dispersed phlogopites found throughout the mantle column, and probably corresponds to the continental arc stage in the early stage of Rodinia. Veined highly alkaline and Ti-rich veins with richterite ~1015 Ma corresponds to the plume event within the Rodinia mantle. The ~600-550 Ma stage marks the final Rodinia break-up. The last one near 385 Ma is protokimberlite related. supported by RBRF 11-05-00060; 11-05-91060-PICS

  17. Vapor plumes: A neglected aspect of impact cratering (United States)

    Melosh, H. J.


    When a meteorite or comet strikes the surface of the planet or satellite at typical interplanetary velocities of 10-40 km/sec, the projectile and a quantity of the target body vaporize and expand out of the growing crater at high speed. The crater continues to grow after the vapor plume has formed and the series of ejecta deposits is laid down ballistically while the crater collapses into its final morphology. Although the vapor plume leaves little evidence of its existence in the crater structure of surface deposits, it may play a major role in a number of impact-related processes. The vapor plume expanding away from the site of an impact carries 25-50 percent of the total impact energy. Although the plume's total mass is only a few times the mass of the projectile, its high specific energy content means that it is the fastest and most highly shocked material in the cratering event. The mean velocity of expansion can easily exceed the escape velocity of the target plane, so that the net effect of a sufficiently high-speed impact is to erode material from the planet.

  18. Compositional Evolution of the Mantle (United States)

    Bennett, V. C.


    The mantle is the Earth's largest chemical reservoir comprising 82% of its total volume and 65% of its mass. The mantle constitutes almost all of the silicate Earth, extending from the base of the crust (which comprises only 0.6% of the silicate mass) to the top of the metallic core at 2,900 km depth. The chemical compositions of direct mantle samples such as abyssal peridotites (Chapter 2.04) and peridotite xenoliths (Chapter 2.05), and of indirect probes of the mantle such as basalts from mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) (Chapter 2.03), and some types of primitive granites, tell us about the compositional state of the modern mantle, with ever increasingly detailed information providing strong evidence for chemical complexity and heterogeneity at all scales (Chapter 2.03). This chemical heterogeneity must reflect the complex physical interplay of a number of distinct long-lived geochemical reservoirs that are identified primarily by their radiogenic isotopic compositions.Many of the chapters in this volume provide detailed images of the current chemical and physical state of the Earth's mantle, whereas other contributions examine the starting composition for the Earth (Chapter 2.01). This chapter attempts to link these two areas by tracking the composition of the mantle through time. The first part of this chapter is a summary of the empirical evidence for secular change in the chemical composition of the mantle from the formation of the Earth at 4.56 Ga throughto the present day. The emphasis is on results from the long-lived radiogenic isotopic systems, in particular 147Sm-143Nd, 176Lu-176Hf, 87Rb-87Sr, and 187Re-187Os systems as these isotopic data provide some of the best constraints on the composition of the mantle in the first half of Earth history, and the timing and extent of chemical differentiation that has affected the mantle over geologic time. Selected trace element data and the "short-lived" 146Sm-142Nd isotopic systems

  19. Chemical and Trajectory Analysis of an Air Mass Plume from Asia (United States)

    Guo, J. J.; Marrero, J. E.; Blake, D. R.


    Tracking the source of pollution events is important in understanding the transport of pollution plumes and impact on areas far from the source. Previous studies have shown that the rising contribution of Asian air pollution to the US has increased the number of days that pollution events exceed National Ambient Air Quality Standards (NAAQS). Whole air samples collected over the Edwards Air Force Base during a June 2014 NASA Student Airborne Research Program (SARP) flight exhibited enhancements in the concentrations of several compounds between 23-32 thousand feet. Chemical tracer analysis of these high altitude samples reveal that the air does not correspond to California emitted air. Chemical signatures in the plume, including high levels of OCS, chloroform, and methyl chloride, and low levels of methyl bromide, indicate that the plume was most heavily influence by coal combustion with contributions from biomass burning events from Asia. Low concentrations of ethene at the high altitude despite enhanced concentrations of ethane and ethyne suggest that this plume was aged. Further analysis of the plume using meteorological wind trajectories reveal that the plume had originated in China approximately 4-5 days prior. This is faster than results from previous studies that had found a Spring transport time of approximately 6 days.

  20. Constraints on Structure and Melting of Heterogeneous Plumes From Laboratory Experiments With Three Components (United States)

    Harris, A. C.; Kincaid, C.; Kelley, K. A.


    Many studies of chemical geodynamics consider the fate of a single, compositionally distinct layer at the base of the mantle, but subducted oceanic lithosphere introduces two distinct lithologies (higher-density eclogite and lower-density harzburgite) into the mantle (a third lithology, intermediate-density lherzolitic peridotite). To address the dynamic complexities of interactions between these materials, we conducted three-dimensional laboratory experiments that use glucose syrup (Rayleigh number: 106\\)) to model the mantle and a two-layer subducted lithosphere. The viscosity and density of the syrup are controlled by its water content, which is varied to simulate the distinct physical properties of each of the three lithologies. Experiments were conducted in a 20cc tank, heated from below to create a basal thermal boundary layer (BTBL). The two-layer glucose slab was frozen and placed within the tank, where it sank into the BTBL. These experiments produced heterogeneous upwellings with temporal and spatial variations in both temperature and composition that are much more complex than predicted by classic plume theory. Temperature, composition, and distribution of material in the tank through space and time were recorded during each experiment. We scale these data to mantle-equivalent conditions and address the observational implication for melting such heterogeneous plumes, both within larger (200 - 600 km) plume heads and smaller (<100 km) trailing conduits. Results show length scales of chemical heterogeneity range from <10 km up to 300 km. Thermal heterogeneity was often correlated with composition, where the denser, eclogite analog had higher temperatures than the lighter, harzburgite analog. Distinct domains form within plumes and melting begins at different depths, dependent on the temperature and composition of each domain and the solidus of each composition (e.g. eclogite melts at lower temperatures than harzburgite). The combination of thermo

  1. Investigation of BrO in volcanic plumes: Comparing satellite data from OMI and GOME-2 (United States)

    Warnach, Simon; Hörmann, Christoph; Sihler, Holger; Bobrowski, Nicole; Beirle, Steffen; Penning de Vries, Marloes; Dinger, Florian; Platt, Ulrich; Wagner, Thomas


    It has been repeatedly shown in the past by measurements from the ground and from space that volcanic plumes contain widely varying amounts of bromine monoxide (BrO). The relative amount of BrO in a volcanic plume, i. e. with respect to sulphur dioxide (SO2), is mainly affected by degassing composition as well as chemical processes, but the reasons for the variation is still not fully understood. Our study aims at obtaining a better understanding of bromine emissions from volcanoes. The high spatial resolution of current satellite instruments such as OMI (13x24 km2) and GOME-2 (40x80 km2), and particularly that of future instruments like TROPOMI (3.5x7 km2) allows to resolve the volcanic plume of eruptive events and makes. The combination of the high spatial resolution and the global coverage of satellite instruments make it possible to study the spatial variability of trace gases in a large number of volcanic plumes from a large number of volcanoes. In this study, we investigate the BrO and SO2 distribution as well as the BrO/SO2 ratio within volcanic plumes observed by OMI since 2007. We apply a plume detection algorithm which uses the retrieved SO2 column for plume identification. These data obtained from OMI measurements are compared to plumes identified from GOME-2 data. Differences in the number of identified plumes and the degree of agreement regarding the retrieved spatial distribution of BrO and SO2, as well as the calculated BrO/SO2 ratio between plumes observed by both instruments, are discussed. Differences are mainly attributed to the differences between the two instruments with respect to spatial resolution and overpass time (GOME-2 at 9:30, OMI at 13:30 local time).

  2. Lead isotope composition of Central American volcanoes: Influence of the Galapagos plume (United States)

    Feigenson, Mark D.; Carr, Michael J.; Maharaj, Susan V.; Juliano, Scott; Bolge, Louise L.


    Lead isotopic analyses of lavas from Central America, both along and behind the volcanic arc, help to clarify source components in the mantle wedge. Analysis of previous Pb isotopic data had implied that little or no marine sediment lead was added to the Central American source region, as all samples fell within the MORB field, in contrast to other information (e.g., Ba/La, 10Be, 87Sr/86Sr) that indicated a high subduction component. The data presented here include several analyses of local marine sediment, showing it to be exceptionally unradiogenic in Pb and thus permitting high sediment contributions to the mantle source region without significant changes in Pb isotopes. Combined Pb-Nd and Pb-Sr isotopic diagrams clearly illustrate the influence of crustal contamination for samples from Guatemala and Honduras, and of subducted sediment for all lavas of the volcanic front. Samples collected behind the volcanic front are derived from mixing between enriched and depleted mantle sources, and in central Costa Rica (extending to the back arc) overlap Pb, Sr and Nd isotope values for both Cocos Island and some components of the Galapagos hot spot. The restricted geographical occurrence of the enriched mantle signature in Central America, coupled with the persistence of the signal well into the back arc region, imply that these lavas are sampling Galapagos plume-influenced mantle. The presence of this plume component beneath southern Central America and extending to the northeast beneath the Caribbean confirms a Galapagos hot spot origin for this part of Caribbean Plate.

  3. Mantle Volatiles - Distribution and Consequences (United States)

    Luth, R. W.


    Volatiles in the mantle have, for many years, been the subject of intensive study from a number of perspectives. They are of interest because of their potential effects on melting relationships, on transport of major and trace elements, and on the rheological and other physical properties of the mantle. By convention, "volatiles" in this context are constituents that are liquid or gaseous at normal Earth surface conditions. This review will look at the behavior of C-O-H-S-halogen volatiles, beginning with H2O and C-O volatiles.There have been tremendous strides made recently towards understanding how volatiles in general and water in particular is transported and stored in the mantle. This progress is based on research on a number of fronts: studies of mantle-derived samples have provided insight into the nature and occurrence of hydrous phases such as amphibole, mica, and chlorite, and have provided constraints on the capacity of nominally anhydrous minerals (NAMs) such as olivine, pyroxenes, and garnet to contain "water" by a variety of substitution mechanisms. Experimental studies on mantle-derived magmas have provided constraints on volatile contents in their source regions. Other studies have constrained the pressure, temperature, and composition conditions over which hydrous phases are stable in the mantle.Fundamental questions remain about the geochemical cycling of volatiles in the mantle, and between the mantle and the surface. Much attention has focused on the capability of hydrous phases such as amphibole, mica, serpentine, chlorite, and a family of "dense hydrous magnesian silicates" (DHMSs) to act as carriers of water in subducting slabs back into the mantle. It has been clear since the work of Ito et al. (1983) that there is a discrepancy between the amount of volatiles subducted into the mantle and those returned to the surface by arc magmatism. A recent overview of volatile cycling in subduction systems by Bebout (1996) suggests that 5-15% of the H2

  4. Modelling the fate of the Tijuana River discharge plume (United States)

    van Ormondt, M.; Terrill, E.; Hibler, L. F.; van Dongeren, A. R.


    After rainfall events, the Tijuana River discharges excess runoff into the ocean in a highly turbid plume. The runoff waters contain large suspended solids concentrations, as well as high levels of toxic contaminants, bacteria, and hepatitis and enteroviruses. Public health hazards posed by the effluent often result in beach closures for several kilometers northward along the U.S. shoreline. A Delft3D model has been set up to predict the fate of the Tijuana River plume. The model takes into account the effects of tides, wind, waves, salinity, and temperature stratification. Heat exchange with the atmosphere is also included. The model consists of a relatively coarse outer domain and a high-resolution surf zone domain that are coupled with Domain Decomposition. The offshore boundary conditions are obtained from the larger NCOM SoCal model (operated by the US Navy) that spans the entire Southern California Bight. A number of discharge events are investigated, in which model results are validated against a wide range of field measurements in the San Diego Bight. These include HF Radar surface currents, REMUS tracks, drifter deployments, satellite imagery, as well as current and temperature profile measurements at a number of locations. The model is able to reproduce the observed current and temperature patterns reasonably well. Under calm conditions, the model results suggest that the hydrodynamics in the San Diego Bight are largely governed by internal waves. During rainfall events, which are typically accompanied by strong winds and high waves, wind and wave driven currents become dominant. An analysis will be made of what conditions determine the trapping and mixing of the plume inside the surfzone and/or the propagation of the plume through the breakers and onto the coastal shelf. The model is now also running in operational mode. Three day forecasts are made every 24 hours. This study was funded by the Office of Naval Research.

  5. Searching for structure in the mid-mantle: Observations of converted phases beneath Iceland and Europe (United States)

    Jenkins, J.; Deuss, A. F.; Cottaar, S.


    Until recently, most of the lower mantle was considered to be well-mixed with strong heterogeneity restricted to the lowermost several hundred kilometers above the core-mantle boundary, also known as the D'' layer. However, several recent studies have started to hint at a potential change in earth structure at mid-mantle depths, with evidence from both seismic tomography (Fukao and Obayashi 2013, French and Romanowichz, 2015) and global viscosity structure (Rudolph et al., 2015). We present the first continental-wide search for mid-mantle P to S wave converted phases and find most observations come from approximately 1000 km depth beneath Iceland and Western Europe. Conversions are identified using a data set of 50,000 high quality receiver functions which are systematically searched for robust signals from the mid-mantle. Potential P to s conversions are analysed in terms of slowness to determine whether they are true observations from depth or simply surface multiples arriving at similar times. We find broad regions with robust signals from approximately 1000 km depth in several locations; beneath Iceland and across Western Europe, beneath Ireland, Scotland, Eifel and south towards NW Italy and Spain. Similar observations have previously been observed mainly in subduction zone settings, and have been hypothesised to be caused by down-going oceanic crustal material. Here we present observations which correlate with slow seismic velocities in recent tomographic models (Rickers et al., (2013); French and Romanowicz, (2015)). These low velocities appear to be a channel deviating from the broad mantle plume beneath Iceland at mid-mantle depths. We hypothesise that the mid-mantle seismic signals we observe are caused by either a phase transition occurring locally in a specific composition or by small-scale chemical heterogeneities swept along with upwelling material and ponding around 1000 km.

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

    Energy Technology Data Exchange (ETDEWEB)

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


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

  7. A 1.5 Ma record of plume-ridge interaction at the Western Galápagos Spreading Center (91°40‧-92°00‧W) (United States)

    Herbrich, Antje; Hauff, Folkmar; Hoernle, Kaj; Werner, Reinhard; Garbe-Schönberg, Dieter; White, Scott


    Shallow (elevated) portions of mid-ocean ridges with enriched geochemical compositions near hotspots document the interaction of hot, geochemically-enriched plume mantle with shallow depleted upper mantle. Whereas the spatial variations in geochemical composition of ocean crust along the ridge axis in areas where plume-ridge interaction is taking place have been studied globally, only restricted information exists concerning temporal variations in geochemistry of ocean crust formed through plume-ridge interaction. Here we present a detailed geochemical study of 0-1.5 Ma ocean crust sampled from the Western Galápagos Spreading Center (WGSC) axis to 50 km north of the axis, an area that is presently experiencing a high influx of mantle material from the Galápagos hotspot. The tholeiitic to basaltic andesitic fresh glass and few bulk rock samples have incompatible element abundances and Sr-Nd-Pb isotopic compositions intermediate between depleted normal mid-ocean-ridge basalt (N-MORB) from >95.5°W along the WGSC and enriched lavas from the Galápagos Archipelago, displaying enriched (E-)MORB type compositions. Only limited and no systematic geochemical variations are observed with distance from the ridge axis for offshore Costa Rica, indicating that this composition is derived from the northern portion of the Galápagos plume. The older WGSC requires involvement of an enriched mantle two (EMII) type source, not recognized thus far in the Galápagos system, and is interpreted to reflect entrained material either from small-scale heterogeneities within the upper mantle or from the mantle transition zone. Overall the source material for the 0-1.5 Ma WGSC ocean crust appears to represent mixing of depleted upper mantle with Northern Galápagos Plume material of relatively uniform composition in relatively constant proportions.

  8. The survival of early Earth mantle reservoirs: Evidence from flood basalts (United States)

    Jackson, M. G.


    Over geologic time, large quantities of oceanic crust and sediment have been injected into the mantle at subduction zones, thereby generating heterogeneities in the mantle. The mantle has been further modified by melt extraction at mid-ocean ridges, a process that has generated large depleted reservoirs throughout the mantle. Owing to the fact that the Earth's mantle mixes and stirs chaotically on geologic timescales, it has long been thought that any evidence of an early terrestrial primitive mantle reservoir has either been erased by melt extraction, or has been overprinted by mixing with recycled materials. This hypothesis was supported by a lack of evidence for chondritic primitive mantle material in the mantle sources of oceanic hotspots, which are thought to yield material from the Earth's deep mantle. Instead, ocean island basalts (OIB) exhibit median 143Nd/144Nd isotopic ratios near 0.5130, suggesting that plume fed hotspots sample a largely-depleted mantle. However, the discovery of Boyet and Carlson (2005, Science) presented evidence that the Earth's primitive mantle may not be chondritic in composition. Boyet and Carlson (2005) found that modern terrestrial lavas have 142Nd/144Nd ratios ~18 ppm higher than chondrites. This result implies that all modern crustal and mantle reservoirs derive from a reservoir with Sm/Nd ratios ~5% higher than chondritic. Today, the 143Nd/144Nd of the primitive (albeit non-chondritic) reservoir would be ~0.5130. Critically, this value is similar to the median 143Nd/144Nd ratio identified in OIB lavas, suggesting that the OIB mantle may in fact be a largely primitive reservoir. However, most OIB lavas fail to exhibit the elevated 3He/4He ratios associated with primitive mantle reservoirs. Similarly, OIB lavas generally lack primitive Pb-isotopic compositions that plot on the geochron, a requirement for all early-Earth reservoirs. To date, no terrestrial OIB lavas have been found that exhibit the required He, Nd and Pb

  9. Mantle hydrous-fluid interaction with Archaean granite. (United States)

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


    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

  10. 3D spherical models of Martian mantle convection constrained by melting history (United States)

    Sekhar, Pavithra; King, Scott D.


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

  11. Beyond the vent: New perspectives on hydrothermal plumes and pelagic biology (United States)

    Phillips, Brennan T.


    Submarine hydrothermal vent fields introduce buoyant plumes of chemically altered seawater to the deep-sea water column. Chemoautotrophic microbes exploit this energy source, facilitating seafloor-based primary production that evidence suggests may transfer to pelagic consumers. While most hydrothermal plumes have relatively small volumes, there are recent examples of large-scale plume events associated with periods of eruptive activity, which have had a pronounced effect on water-column biology. This correlation suggests that hydrothermal plumes may have influenced basin-scale ocean chemistry during periods of increased submarine volcanism during the Phanerozoic eon. This paper synthesizes a growing body of scientific evidence supporting the hypothesis that hydrothermal plumes are the energetic basis of unique deep-sea pelagic food webs. While many important questions remain concerning the biology of hydrothermal plumes, this discussion is not present in ongoing management efforts related to seafloor massive sulfide (SMS) mining. Increased research efforts, focused on high-resolution surveys of midwater biology relative to plume structures, are recommended to establish baseline conditions and monitor the impact of future mining-based disturbances to the pelagic biosphere.

  12. Determining the geochemical structure of the mantle from surface isotope distribution patterns? Insights from Ne and He isotopes and abundance ratios (United States)

    Stroncik, N.; Niedermann, S.; Schnabel, E.; Erzinger, J.


    It is a common procedure among geochemists to use surface distribution patterns of e.g. Sr, Nd, Pb or He isotopes of lavas erupted at oceanic islands to map the geochemical structure of the Earth's mantle. Advances in noble gas mass spectrometry within the last decade resulting in an increasing availability of Ne isotope data sets allow us to test the strength of this approach. 4He and 21Ne are coupled through the same parent nuclides and therefore should show analogous isotope distribution patterns. Here we present He and Ne fusion data of fresh olivines derived from Big Island, Hawaii, together with He and Ne fusion data of fresh glasses from the Easter Seamount Chain (ESC), indicating that the observed isotope distribution patterns are mainly controlled by melting and shallow mixing processes. He isotopic ratios of the investigated olivines vary from MORB-like (8 ± 1 RA) to ratios more typical for a primitive mantle source (up to 20 and 26 RA for Hawaii and the ESC, respectively; RA = atmospheric 3He/4He ratio of 1.39 x 10-6). In contrast, all Ne isotope data plot within error limits along the Loihi-Kilauea line in a Ne three-isotope diagram. The Loihi-Kilauea line is regarded to be typical for a primitive mantle source. Thus, the Ne isotope data are inconsistent with any kind of zoned plume model or even a heterogeneous mantle source. The combined He and Ne data show that these He and Ne isotope systematics are produced by a pre-degassing fractionation process and subsequent melt mixing. Basically, this process causes a He deficit in melts generated by the plume, as shown by 3He/22NeS below current estimates of solar or planetary composition and 4He/21Ne* lower than the production ratio, making the He isotopic composition more susceptible to changes than the Ne isotopic composition. This can best be explained by a model in which He is fractionated from Ne during formation of melts from a plume (or enriched parts of a plume) at low melting degrees, which

  13. Contrasting origins of the upper mantle revealed by hafnium and lead isotopes from the Southeast Indian Ridge. (United States)

    Hanan, Barry B; Blichert-Toft, Janne; Pyle, Douglas G; Christie, David M


    The origin of the isotopic signature of Indian mid-ocean ridge basalts has remained enigmatic, because the geochemical composition of these basalts is consistent either with pollution from recycled, ancient altered oceanic crust and sediments, or with ancient continental crust or lithosphere. The radiogenic isotopic signature may therefore be the result of contamination of the upper mantle by plumes containing recycled altered ancient oceanic crust and sediments, detachment and dispersal of continental material into the shallow mantle during rifting and breakup of Gondwana, or contamination of the upper mantle by ancient subduction processes. The identification of a process operating on a scale large enough to affect major portions of the Indian mid-ocean ridge basalt source region has been a long-standing problem. Here we present hafnium and lead isotope data from across the Indian-Pacific mantle boundary at the Australian-Antarctic discordance region of the Southeast Indian Ridge, which demonstrate that the Pacific and Indian upper mantle basalt source domains were each affected by different mechanisms. We infer that the Indian upper-mantle isotope signature in this region is affected mainly by lower continental crust entrained during Gondwana rifting, whereas the isotope signature of the Pacific upper mantle is influenced predominantly by ocean floor subduction-related processes.

  14. Mantle Structure Beneath Central South America (United States)

    Vandecar, J. C.; Silver, P. G.; James, D. E.; Assumpcao, M.; Schimmel, M.; Zandt, G.


    Making use of 60 digital broadband seismic stations that have operated across central South America in recent years, we have undertaken an inversion for the upper- and uppermost lower-mantle P- and S-wave velocity structures beneath the region. We have combined data from four portable PASSCAL-type experiments as well as the 3 GTSN permanent stations (LPAZ, BDFB and CPUP) and 1 Geoscope station (SPB) located in the region. The portable data were deployed at various times between 1992 and 1999 and include: 28 sites from the Brazilian Lithosphere Seismic Project (BLSP: Carnegie Institution of Washington and Universidade de Sao Paulo), 16 sites from the Broadband ANdean JOint experiment (BANJO: Carnegie Institution of Washington and University of Arizona), 8 sites from the Seismic Exploration of the Deep Altiplano project (SEDA: Lawrence Livermore National Laboratory) and 4 sites from the University of Brasilia. The P- and S-wave relative delay times are independently obtained via a multi-channel cross correlation of band-passed waveforms for each teleseismic event. These data are then inverted using an iterative, robust, non-linear scheme which parameterizes the 3-D velocity variations as splines under tension constrained at over 120,000 nodes across South America between latitudes of 15 and 30 degrees South. Amongst other features, we robustly image the high-velocity subducting Nazca plate penetrating into the lower mantle and the high-velocity root of the ~3.2 Gyr old Sao Francisco Craton extending to depths of 200-300 km. We will discuss the consistency between our tomographic models and predictions of dynamic mantle models based on plate tectonic reconstructions of subduction.

  15. Trans-Pacific whole mantle structure (United States)

    Liu, Lijun; Tan, Ying; Sun, Daoyuan; Chen, Min; Helmberger, Don


    Recent reports on modeling USArray data reveal mostly vertical microplates with little resemblance to preliminary reference Earth model (PREM). Such complexity at plate boundaries makes it difficult to form reliable images of ocean basins using global paths. Here, we report on modeling stacked seismograms obtained from the first broadband array (TriNet) situated on the edge of the Pacific Plate, southern California, with no major subduction zone blocking its view. Extended records, including multi-S and ScS waves up to four bounces from 18 Tonga-Fiji deep events (140 to 620 km) are analyzed to check the validity of existing models and derive the whole mantle shear velocity structure along this corridor. Synthetics generated from 3-D tomographic models do not fit the upper mantle triplication data or the mantle reverberations associated with the ScS multiples as well as the 1-D model PAC06. We construct a hybrid model (HPAC), which remains one dimensional down to 800 km (PAC06). The lower portion of HPAC is essentially the tomography model S20RTS with velocity variation inflated by a factor of 2 for the lowermost 600 km. Thus, the mid-Pacific large low shear velocity province (LLSVP) has a lower shear velocity of about 2% relative to PREM and extends into the midmantle, similar to that beneath South Africa. Moreover, rapid changes in the differential (ScS-S) and (ScS2-S) times as a function of distance suggest ultra low velocity zones near the eastern edge and under the LLSVP, again similar to that found beneath Africa.

  16. Variability of Yellow River turbid plume detected with satellite remote sensing during water-sediment regulation (United States)

    Guo, Kai; Zou, Tao; Jiang, Dejuan; Tang, Cheng; Zhang, Hua


    Water Sediment Regulations (WSRs) of the Yellow River (YR) have fundamentally altered the dynamics of freshwater and sediment transport in YR estuary and might profoundly affect water quality and ecosystem of the adjacent Bohai Sea. In this study, empirical algorithms were established to infer sea surface salinity and turbidity of YR plume using on surface reflectance products of MODIS and GOCI satellites in combination with observations from hydrographic surveys during the 2014 WSR event. Inter- and intraday variability of salinity and turbidity were quantitatively assessed and correlated with external forces including river discharge, tides, Coriolis force, and wind-driven circulation. The results revealed the enhanced offshore extension of turbid plume as WSR drastically increased freshwater and sediment discharge to river mouth. During WSR event, the area of low salinity plume (0.12sr-1) occupied a maximum area of 162 km2. Intraday variation observed from geostationary GOCI data clearly illustrated the dominance of tidal current on short term dispersal pattern of freshwater and sediment plume. In comparison, wind field dominated the seasonal variation in flume transport but had insignificant impact on short term river plume dynamic during WSR. Overall, this study demonstrated that the spatial and temporal dynamic of YR plume was successfully captured by satellite remote sensing, which provided an effective tool for evaluating the environmental and ecological impact of WSRs.

  17. The mantle transition zone and the upper mantle in Central-Eastern Greenland (United States)

    Anja Kraft, Helene; Thybo, Hans; Vinnik, Lev


    We present a receiver function (RF) study of the mantle transition zone (MTZ) and upper mantle in central-eastern Greenland. Our results are based on data from 18 temporary broad-band seismometers and 5 additional stations from the GLISN and GLATIS networks. The stations were operating in the region between Scoresby Sund and Summit (~ 70 ° N) with half of them installed on ice, the other half on bedrock. For our analysis we calculated low frequency PRF and SRF, which use the difference in travel times between converted and not converted phases at discontinuities. We see clear signals from P410s and P660s in most of our PRF and from S410p in the SRF. Their delay times suggest a surprisingly thin MTZ for most parts of the study area with up to 25 km of thinning compared to standard Earth models. The only exception is a small region in the centre of the study area, which shows times close to standard. It is mainly the delay time for P410s, that varies, while P660s is stable throughout our study area. This indicates, that the thinning of the MTZ is mainly due to topography on the 410-discontinuity. We furthermore observe an M-shaped signal for P410s at stations in the western part around Summit. A similar, complicated signal has been observed previously in different settings and is interpreted as a thin low velocity layer between 410 km and 520 km. In addition we jointly inverted the PRF and SRF for upper mantle velocities. These results show velocities slower than IASP91 for the entire study area. Both the low velocities in the upper mantle and the thinning of the MTZ are in contrary to simple models of old continental shields and might indicate a fairly recent heating event.

  18. Reconciling laboratory and observational models of mantle rheology in geodynamic modelling (United States)

    King, Scott D.


    -stress regions of the lower mantle, may be in the dislocation creep (power-law) regime. Due to our limited knowledge of mantle grain size, the best hope to resolve the question of whether a region is in diffusion creep (Newtonian rheology) or dislocation or grain-boundary creep (power-law rheology), may be the presence of absence of seismic anisotropy, because there is no mechanism to rotate crystals in diffusion creep which would be necessary to develop anisotropy from lattice preferred orientation. While non-intuitive, the presence or absence of a weak region in the upper mantle has a profound effect on lower mantle flow. With an asthenosphere, the lower mantle organizes into a long-wavelength plan form with one or two (degree 1 or degree 2) large downwellings and updrafts, which may contain a cluster of plumes. The boundary between the long-wavelength lower mantle flow and upper region flow may be deeper, likely 800-1200 km, than the usually assumed base of the transition zone. There are competing hypotheses as to whether this change in flow pattern is caused by a change in rheology, composition, or phase.

  19. Pulsed Plasma Thruster plume analysis

    Energy Technology Data Exchange (ETDEWEB)

    Parker, K. [Washington Univ., Aerospace and Energetics Research Program, Seattle, WA (United States)


    Micro-Pulsed Plasma Thrusters ({mu}PPTs) are a promising method for precision attitude control for small spacecraft in formation flying. They create an ionized plasma plume, which may interfere with other spacecraft in the formation. To characterize the ions in the plume, a diagnostic has been built that couples a drift tube with an energy analyzer. The drift tube provides time of flight measurements to determine the exhaust velocity, and the energy analyzer discriminates the ion energies. The energy analyzer measures the current on a collector plate downstream of four grids that repel electrons and ions below a specified energy. The first grid lowers the density of the plasma, therefore increasing Debye length. The second and fourth grids have a negative potential applied to them so they repel the electrons, while the third grid's voltage can be varied to repel lower energy ions. The ion energies can be computed by differentiating the data. Combining the information of the ion energies and their velocities identifies the ion masses in the PPT plume. The PPT used for this diagnostic is the micro-PPT developed for the Dawgstar satellite. This PPT uses 5.2 Joules per pulse and has a 2.3 cm{sup 2} propellant area, a 1.3 cm electrode length, and an estimated thrust of 85 {mu}N [C. Rayburn et al., AIAA-2000-3256]. This paper will describe the development and design of the time of flight/gridded energy analyzer diagnostic and present recent experimental results. (Author)

  20. The Importance of Grain Size to Mantle Dynamics and Seismological Observations: A Multidisciplinary Approach (United States)

    Gassmöller, Rene; Dannberg, Juliane; Eilon, Zach; Moulik, Pritwiraj; Myhill, Robert; Faul, Ulrich


    orders of magnitude due to grain size alone, in addition to the effects of temperature and strain rate. In mantle plumes, grain size reduction, caused by strain localisation at their edges, competes with fast grain growth due to high plume temperatures. As a result, the viscosity in the center of plumes reaches similar values as in the surrounding mantle, while it decreases more than an order of magnitude towards their margins. Similarly, low viscosities at the edges of slabs favor bending over thickening as mode of deformation. Benchmarking our dynamic models against seismic observations will involve further adjustments to the grain size evolution in the lower mantle as well as the tuning of these constitutive relationships. The very slow grain growth in the lower mantle predicted by some high pressure experiments [Yamazaki et al., 1996] would produce unrealistically large attenuation in the lower mantle. We therefore explore models that include faster grain growth. A change in physical parameters such as activation volume is required across the 660 km discontinuity to match the higher Q observed seismically in the lower mantle. Dynamic recrystallisation and slow grain growth in subducting slabs results in lower seismic velocities and Q than would be predicted from purely thermal models. Negative feedbacks between thermal controls on anharmonic and (through grain size) anelastic velocity variations mean that simple mapping of tomographic velocities to temperatures may systematically underestimate true thermal anomalies.

  1. Detection of Volcanic Plumes by GPS: the 23 November 2013 Episode on Mt. Etna

    Directory of Open Access Journals (Sweden)

    Massimo Aranzulla


    Full Text Available The detection of volcanic plumes produced during explosive eruptions is important to improve our understanding on dispersal processes and reduce risks to aviation operations. The ability of Global Position-ing System (GPS to retrieve volcanic plumes is one of the new challenges of the last years in volcanic plume detection. In this work, we analyze the Signal to Noise Ratio (SNR data from 21 permanent stations of the GPS network of the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, that are located on the Mt. Etna (Italy flanks. Being one of the most explosive events since 2011, the eruption of November 23, 2013 was chosen as a test-case. Results show some variations in the SNR data that can be correlated with the presence of an ash-laden plume in the atmosphere. Benefits and limitations of the method are highlighted. 

  2. Plume spread and atmospheric stability

    Energy Technology Data Exchange (ETDEWEB)

    Weber, R.O. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)


    The horizontal spread of a plume in atmospheric dispersion can be described by the standard deviation of horizontal direction. The widely used Pasquill-Gifford classes of atmospheric stability have assigned typical values of the standard deviation of horizontal wind direction and of the lapse rate. A measured lapse rate can thus be used to estimate the standard deviation of wind direction. It is examined by means of a large dataset of fast wind measurements how good these estimates are. (author) 1 fig., 2 refs.

  3. Geochemical heterogeneity in the Arctic mantle at Gakkel Ridge (United States)

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


    Conductive cooling due to ultraslow spreading has been suggested to limit partial melting of the mantle and crustal production at Gakkel Ridge. In addition, the thick lithosphere induced by cooling should significantly control melt migration and extraction. To explore these effects at ultraslow spreading rates, major and trace element concentrations in pyroxene minerals are presented for 14 dredged Gakkel abyssal peridotites. Samples from the same dredge and among dredges reveal wide compositional variation. Trace element compositions of lherzolites reflect 4-6% non-modal fractional mantle melting. However, these high degrees of melting without a corresponding amount of oceanic crust suggest the occurrence of infertile mantle due to ancient melting event(s). In addition, high degrees of melt depletion at short length-scales (earth elements that can be fit by 6 to ≥13% non-modal melting, but this results in modeled light rare earth element contents that are too low relative to observed concentrations. Instead, harzburgite trace element patterns require open-system melting involving interaction with a percolating melt. Extreme enrichments in highly incompatible elements also suggest the occurrence of late-stage refertilization and melt entrapment. Modeling of several different source melt compositions indicates that the trapped melt was generated from garnet field-equilibrated peridotite. Overall, the compositional variability in Gakkel peridotite samples reflects a heterogeneous mantle resulting from inherited depletion and recent melt percolation and entrapment.

  4. Proposed law of nature linking impacts, plume volcanism, and Milankovitch cycles to terrestrial vertebrate mass extinctions via greenhouse-embryo death coupling (United States)

    Mclean, D. M.


    A greenhouse-physiological coupling killing mechanism active among mammals, birds, and reptiles has been identified. Operating via environmental thermal effects upon the maternal core-skin blood flow critical to the survival and development of embryos, it reduces the flow of blood to the uterine tract. Today, during hot summers, this phenomena kills embryos on a vast, global scale. Because of sensitivity of many mammals to modern heat, a major modern greenhouse could reduce population numbers on a global scale, and potentially trigger population collapses in the more vulnerable parts of the world. In the geological past, the killing mechanism has likely been triggered into action by greenhouse warming via impact events, plume volcanism, and Earth orbital variations (Milankovitch cycles). Earth's biosphere is maintained and molded by the flow of energy from the solar energy source to Earth and on to the space energy sink (SES). This SES energy flow maintains Earth's biosphere and its living components, as open, intermediate, dissipative, nonequilibrium systems whose states are dependent upon the rate of energy flowing through them. Greenhouse gases such as CO2 in the atmosphere influence the SES energy flow rate. Steady-state flow is necessary for global ecological stability (autopoiesis). Natural fluctuations of the C cycle such as rapid releases of CO2 from the mantle, or oceans, disrupt steady-state SES flow. These fluctuations constantly challenge the biosphere; slowdown of SES energy flow drives it toward thermodynamical equilibrium and stagnation. Fluctuations induced by impact event, mantle plume volcanism, and Milankovitch cycles can grow into structure-breaking waves triggering major perturbations of Earth's C cycle and mass extinctions. A major C cycle perturbation involves readjustment of the outer physiochemical spheres of the Earth: the atmosphere, hydrosphere, and lithosphere; and by necessity, the biosphere. A greenhouse, one manifestation of a major

  5. Characteristics of bubble plumes, bubble-plume bubbles and waves from wind-steepened wave breaking

    NARCIS (Netherlands)

    Leifer, I.; Caulliez, G.; Leeuw, G. de


    Observations of breaking waves, associated bubble plumes and bubble-plume size distributions were used to explore the coupled evolution of wave-breaking, wave properties and bubble-plume characteristics. Experiments were made in a large, freshwater, wind-wave channel with mechanical wind-steepened w

  6. Mantle convection modeling of the supercontinent cycle:Introversion, extroversion, or a combination?

    Institute of Scientific and Technical Information of China (English)

    Masaki Yoshida; M. Santosh


    The periodic assembly and dispersal of continental fragments, referred to as the supercontinent cycle, bear close relation to the evolution of mantle convection and plate tectonics. Supercontinent formation involves complex processes of “introversion” (closure of interior oceans), “extroversion” (closure of exterior oceans), or a combination of these processes in uniting dispersed continental fragments. Recent developments in numerical modeling and advancements in computation techniques enable us to simulate Earth’s mantle convection with drifting continents under realistic convection vigor and rheology in Earth-like geometry (i.e., 3D spherical-shell). We report a numerical simulation of 3D mantle convection, incorporating drifting deformable continents, to evaluate supercontinent processes in a realistic mantle convection regime. Our results show that supercontinents are assembled by a combi-nation of introversion and extroversion processes. Small-scale thermal heterogeneity dominates deep mantle convection during the supercontinent cycle, although large-scale upwelling plumes intermit-tently originate under the drifting continents and/or the supercontinent.

  7. Mantle potential temperature estimates of basalt from the surface of Venus (United States)

    Shellnutt, J. Gregory


    The crater density and distribution of Venus indicates the average surface age is younger (≤1 Ga) than most terrestrial planets and satellites in the Solar System. The type and rate (i.e. equilibrium, catastrophic or differential) of volcanism associated with the stagnant lid tectonic system of Venus is a first order problem that has yet to be resolved but is directly related to the thermal conditions of the mantle. The calculated primary melt composition of basalt at the Venera 14 landing site is high-Mg basalt to picrite with a mantle potential temperature estimate similar to terrestrial ambient mantle (1370 ± 70 °C). The calculated accumulated fractional melting curves indicate the olivine compositions from the melt have Mg# of 89-91. The results show that the thermal regime required to generate the primary melt composition of the Venera 14 basalt was not anomalously high (i.e. mantle-plume system) but rather consistent with a lithospheric tensional rift system. The juxtaposition of high thermal regime structures (e.g. Beta Regio) and 'ambient' mantle potential temperature estimates of the Venera 14 basalt suggests that the relatively young surface of Venus is the result of volcanism from a combination of thermal systems that resurfaced the planet at variable rates.

  8. Subduction of young oceanic plates: A numerical study with application to aborted thermal-chemical plumes (United States)

    Blanco-Quintero, Idael Francisco; Gerya, Taras V.; GarcíA-Casco, Antonio; Castro, Antonio


    We investigated numerical models of initiation and subsequent evolution of subduction of young (10-30 Myr) oceanic lithosphere. Systematic numerical experiments were carried out by varying the age of the subducting plate (10, 12.5, 15, 17.5, 20, 25 and 30 Myr), the rate of induced convergence (2, 4 and 5 cm/yr) and the degree of hydration (0 and 2 wt% H2O) of the pre-existing weak oceanic fracture zone along which subduction is initiated. Despite the prescribed plate forcing, spontaneously retreating oceanic subduction with a pronounced magmatic arc and a backarc basin was obtained in a majority of the experiments. It was also found that the younger age of oceanic lithosphere results in more intense dehydration and partial melting of the slab during and after the induced subduction initiation due to the shallow dispositions of the isotherms. Partial melting of the subducted young crust may create thermal-chemical instabilities (cold plumes) that ascend along the slab-mantle interface until they either freeze at depth or detach from the slab and penetrate the upper plate lithosphere contributing to the nucleation and growth of a volcanic arc. Freezing of the plumes in the slab-mantle interface is favored by subduction of very young lithosphere (i.e., 10 Myr) at moderate rate (4 cm/yr) of convergence. Such aborted plumes may correspond to Cretaceous partially melted MORB-derived slab material and associated adakitic tonalitic-trondhjemitic rocks crystallized at ca. 50 km depth in the slab-mantle interface and exhumed in a subduction channel (serpentinite mélanges) in eastern Cuba.

  9. Rogue mantle helium and neon. (United States)

    Albarède, Francis


    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.

  10. Compositional Variation of Terrestrial Mantle Apatites and Implications for the Halogen and Water Budgets of the Terrestrial Mantle (United States)

    Roden, M.; Patino Douce, A. E.; Chaumba, J. B.; Fleisher, C.; Yogodzinski, G. M.


    Apatite in ultramafic xenoliths from various tectonic enviroments including arc (Kamchatka), plume (Hawaii), and intraplate (Lunar Crater, Nunivak, Colorado Plateau) were analyzed by electron microprobe with the aim of characterizing the Cl and F contents, and from these measured compositions to infer the nature of fluids/melts that the apatites equilibrated with. The impetus for the study derived from the generalization of O'Reilly and Griffin (1) that mantle-derived metasomatic apatites tend to be Cl-rich and mantle-derived igneous apatites tend to be F-rich. Our work largely corroborates their generalization with Cl- and/or H2O-rich compositions characterizing the apatites from Nunivak and Kamchatka while apatites from igneous or Group II xenoliths tend to be Cl-poor and be either nearly pure fluorapatite or a mix of hydroxylapatite and fluorapatite. We attribute the Cl-rich nature of the Kamchatka apatites to formation from Cl-rich fluids generated from subducted lithosphere; however the Nunivak occurrence is far removed from subducted lithosphere and may reflect a deep seated source for Cl as also indicated by brine inclusions in diamonds, Cl-rich apatites in carbonate-bearing xenoliths and a Cl-rich signature in some plumes such as Iceland, Azores and Samoa. One curious aspect of mantle-derived apatite compositions is that xenoliths with evidence of carbonatitic metasomatism commonly have Cl-rich apatites while apatites from carbonatites are invariably Cl-poor - perhaps reflecting loss of Cl in fluids evolved from the carbonatitic magma. Apatites from Group II xenoliths at Hawaii are solid solutions between fluorapatite and hydroxylapatite and show no evidence for deep-seated Cl at Hawaii. Samples of the terrestrial mantle are almost uniformly characterized by mineral assemblages with a single Ca-rich phosphate phase but the mantles of Mars, Vesta and the Moon have two Ca-rich phosphates, apatite and volatile-poor merrillite - apatite compositions existing

  11. Towards a Global Upper Mantle Attenuation Model (United States)

    Karaoglu, Haydar; Romanowicz, Barbara


    Global anelastic tomography is crucial for addressing the nature of heterogeneity in the Earth's interior. The intrinsic attenuation manifests itself through dispersion and amplitude decay. These are contaminated by elastic effects such as (de)focusing and scattering. Therefore, mapping anelasticity accurately requires separation of elastic effects from the anelastic ones. To achieve this, a possible approach is to try and first predict elastic effects through the computation of seismic waveforms in a high resolution 3D elastic model, which can now be achieved accurately using numerical wavefield computations. Building upon the recent construction of such a whole mantle elastic and radially anisotropic shear velocity model (SEMUCB_WM1, French and Romanowicz, 2014), which will be used as starting model, our goal is to develop a higher resolution 3D attenuation model of the upper mantle based on full waveform inversion. As in the development of SEMUCB_WM1, forward modeling will be performed using the spectral element method, while the inverse problem will be treated approximately, using normal mode asymptotics. Both fundamental and overtone time domain long period waveforms (T>60s) will be used from a dataset of over 200 events observed at several hundred stations globally. Here we present preliminary results of synthetic tests, exploring different iterative inversion strategies.

  12. Compositional layering within the large low shear-wave velocity provinces (LLSVPs) in the lower mantle (United States)

    Ballmer, Maxim; Lekic, Vedran; Schumacher, Lina; Ito, Garrett; Thomas, Christine


    to entrain basaltic material that has evolved in the lower mantle. Long-lived "primary" plumes rise from LLSVP margins and entrain a mix of materials, including small fractions of primordial mantle material. These predictions address the geochemical and geochronological record of intraplate hotspot volcanism on the Pacific plate. In general, the parameter range spanned by models that are able to reconcile observations provides a constraint for the intrinsic density anomaly (or composition) of DDDs. We use this constraint to evaluate a possible origin of DDDs from (basal) magma ocean cumulates. The study of LLSVP compositional layering has indeed important implications for our understanding of heat and material fluxes through mantle reservoirs, as well as bulk Earth chemistry and evolution.

  13. Triple oxygen isotopic composition of the high-3He/4He mantle (United States)

    Starkey, N. A.; Jackson, C. R. M.; Greenwood, R. C.; Parman, S.; Franchi, I. A.; Jackson, M.; Fitton, J. G.; Stuart, F. M.; Kurz, M.; Larsen, L. M.


    Measurements of Xe isotope ratios in ocean island basalts (OIB) suggest that Earth's mantle accreted heterogeneously, and that compositional remnants of accretion are sampled by modern, high-3He/4He OIB associated with the Icelandic and Samoan plumes. If so, the high-3He/4He source may also have a distinct oxygen isotopic composition from the rest of the mantle. Here, we test if the major elements of the high-3He/4He source preserve any evidence of heterogeneous accretion using measurements of three oxygen isotopes on olivine from a variety of high-3He/4He OIB locations. To high precision, the Δ17O value of high-3He/4He olivines from Hawaii, Pitcairn, Baffin Island and Samoa, are indistinguishable from bulk mantle olivine (Δ17OBulk Mantle - Δ17OHigh 3He/4He olivine = -0.002 ± 0.004 (2 × SEM)‰). Thus, there is no resolvable oxygen isotope evidence for heterogeneous accretion in the high-3He/4He source. Modelling of mixing processes indicates that if an early-forming, oxygen-isotope distinct mantle did exist, either the anomaly was extremely small, or the anomaly was homogenised away by later mantle convection. The δ18O values of olivine with the highest 3He/4He ratios from a variety of OIB locations have a relatively uniform composition (∼5‰). This composition is intermediate to values associated with the depleted MORB mantle and the average mantle. Similarly, δ18O values of olivine from high-3He/4He OIB correlate with radiogenic isotope ratios of He, Sr, and Nd. Combined, this suggests that magmatic oxygen is sourced from the same mantle as other, more incompatible elements and that the intermediate δ18O value is a feature of the high-3He/4He mantle source. The processes responsible for the δ18O signature of high-3He/4He mantle are not certain, but δ18O-87Sr/86Sr correlations indicate that it may be connected to a predominance of a HIMU-like (high U/Pb) component or other moderate δ18O components recycled into the high-3He/4He source.

  14. Impacts of the July 2012 Siberian fire plume on air quality in the Pacific Northwest (United States)

    Teakles, Andrew D.; So, Rita; Ainslie, Bruce; Nissen, Robert; Schiller, Corinne; Vingarzan, Roxanne; McKendry, Ian; Macdonald, Anne Marie; Jaffe, Daniel A.; Bertram, Allan K.; Strawbridge, Kevin B.; Leaitch, W. Richard; Hanna, Sarah; Toom, Desiree; Baik, Jonathan; Huang, Lin


    Biomass burning emissions emit a significant amount of trace gases and aerosols and can affect atmospheric chemistry and radiative forcing for hundreds or thousands of kilometres downwind. They can also contribute to exceedances of air quality standards and have negative impacts on human health. We present a case study of an intense wildfire plume from Siberia that affected the air quality across the Pacific Northwest on 6-10 July 2012. Using satellite measurements (MODIS True Colour RGB imagery and MODIS AOD), we track the wildfire smoke plume from its origin in Siberia to the Pacific Northwest where subsidence ahead of a subtropical Pacific High made the plume settle over the region. The normalized enhancement ratios of O3 and PM1 relative to CO of 0.26 and 0.08 are consistent with a plume aged 6-10 days. The aerosol mass in the plume was mainly submicron in diameter (PM1 / PM2.5 = 0.96) and the part of the plume sampled at the Whistler High Elevation Monitoring Site (2182 m a.s.l.) was 88 % organic material. Stable atmospheric conditions along the coast limited the initial entrainment of the plume and caused local anthropogenic emissions to build up. A synthesis of air quality from the regional surface monitoring networks describes changes in ambient O3 and PM2.5 during the event and contrasts them to baseline air quality estimates from the AURAMS chemical transport model without wildfire emissions. Overall, the smoke plume contributed significantly to the exceedances in O3 and PM2.5 air quality standards and objectives that occurred at several communities in the region during the event. Peak enhancements in 8 h O3 of 34-44 ppbv and 24 h PM2.5 of 10-32 µg m-3 were attributed to the effects of the smoke plume across the Interior of British Columbia and at the Whistler Peak High Elevation Site. Lesser enhancements of 10-12 ppbv for 8 h O3 and of 4-9 µg m-3 for 24 h PM2.5 occurred across coastal British Columbia and Washington State. The findings suggest that the

  15. Radiation Chemistry of Potential Europa Plumes (United States)

    Gudipati, M. S.; Henderson, B. L.


    Recent detection of atomic hydrogen and atomic oxygen and their correlation to potential water plumes on Europa [Roth, Saur et al. 2014] invoked significant interest in further understanding of these potential/putative plumes on Europa. Unlike on Enceladus, Europa receives significant amount of electron and particle radiation. If the plumes come from trailing hemisphere and in the high radiation flux regions, then it is expected that the plume molecules be subjected to radiation processing. Our interest is to understand to what extent such radiation alterations occur and how they can be correlated to the plume original composition, whether organic or inorganic in nature. We will present laboratory studies [Henderson and Gudipati 2014] involving pulsed infrared laser ablation of ice that generates plumes similar to those observed on Enceladus [Hansen, Esposito et al. 2006; Hansen, Shemansky et al. 2011] and expected to be similar on Europa as a starting point; demonstrating the applicability of laser ablation to simulate plumes of Europa and Enceladus. We will present results from electron irradiation of these plumes to determine how organic and inorganic composition is altered due to radiation. Acknowledgments:This research was enabled through partial funding from NASA funding through Planetary Atmospheres, and the Europa Clipper Pre-Project. B.L.H. acknowledges funding from the NASA Postdoctoral Program for an NPP fellowship. Hansen, C. J., L. Esposito, et al. (2006). "Enceladus' water vapor plume." Science 311(5766): 1422-1425. Hansen, C. J., D. E. Shemansky, et al. (2011). "The composition and structure of the Enceladus plume." Geophysical Research Letters 38. Henderson, B. L. and M. S. Gudipati (2014). "Plume Composition and Evolution in Multicomponent Ices Using Resonant Two-Step Laser Ablation and Ionization Mass Spectrometry." The Journal of Physical Chemistry A 118(29): 5454-5463. Roth, L., J. Saur, et al. (2014). "Transient Water Vapor at Europa's South

  16. Variability and Composition of Io's Pele Plume (United States)

    Jessup, K. L.; Spencer, J.; Yelle, R.


    The Pele plume is one of the largest and most dynamic of the plumes on Io. While sulfur dioxide (SO2) gas was always assumed to be a constituent of this plume, spectral observations obtained in 1999 were the first to positively identify elemental sulfur (S2) (Spencer et al. 2000) within the Pele plume. The S2/SO2 ratio derived from this observation provided a critical component necessary for the constraint of the magma chemistry and vent conditions of the Pele plume (Zolotov and Fegley 1998). But, because the Pele plume has long been known to be variable in its eruptive behavior, it is not likely that the vent conditions are invariant. Consequently, additional observations were needed to constrain the extent of the variability of the plume's composition and gas abundances. To this end, in February 2003, March 2003 and January 2004 we obtained spectra of Pele with Hubble's Space Telescope Imaging Spectrograph (STIS) in transit of Jupiter, using the 0.1 arcsec slit, for the wavelength region extending from 2100-3100 Å. Contemporaneous with the spectral data we also obtained UV and visible-wavelength images of the plume in reflected sunlight with the Advanced Camera for Surveys (ACS) prior to Jupiter transit, in order to constrain plume dust abundance. The newly acquired STIS data show both the S2 and SO2 absorption signatures, and provide concrete evidence of temporal variability in the abundance of these gases. Likewise, the degree of dust scattering recorded in the ACS data varied as a function of the date of observation. We will present preliminary constraints on the composition and variability of the gas abundances of the Pele plume as recorded within the STIS data. We will also give a brief overview of the variability of the plume dust signatures relative to the gas signatures as a function of time.

  17. Skylon Aerodynamics and SABRE Plumes (United States)

    Mehta, Unmeel; Afosmis, Michael; Bowles, Jeffrey; Pandya, Shishir


    An independent partial assessment is provided of the technical viability of the Skylon aerospace plane concept, developed by Reaction Engines Limited (REL). The objectives are to verify REL's engineering estimates of airframe aerodynamics during powered flight and to assess the impact of Synergetic Air-Breathing Rocket Engine (SABRE) plumes on the aft fuselage. Pressure lift and drag coefficients derived from simulations conducted with Euler equations for unpowered flight compare very well with those REL computed with engineering methods. The REL coefficients for powered flight are increasingly less acceptable as the freestream Mach number is increased beyond 8.5, because the engineering estimates did not account for the increasing favorable (in terms of drag and lift coefficients) effect of underexpanded rocket engine plumes on the aft fuselage. At Mach numbers greater than 8.5, the thermal environment around the aft fuselage is a known unknown-a potential design and/or performance risk issue. The adverse effects of shock waves on the aft fuselage and plumeinduced flow separation are other potential risks. The development of an operational reusable launcher from the Skylon concept necessitates the judicious use of a combination of engineering methods, advanced methods based on required physics or analytical fidelity, test data, and independent assessments.

  18. Evolution of Australian Bushfire 2009 Plume in the UTLS region investigated using the OSIRIS limb profiles (United States)

    Siddaway, J. M.; Petelina, S. V.


    Major Bushfires in south-eastern Victoria, Australia, produced a smoke plume on 7 February 2009 that was injected into the troposphere, vertically advecting to the lower stratosphere. In order to investigate both horizontal and vertical evolution of this smoke plume, global maps of limb-scattered radiances were produced. These maps were plotted using observations at various altitudes from the OSIRIS (Optical Spectrograph and Infrared Imager System) instrument onboard the Odin satellite. The OSIRIS Level 1 radiances, taken at a 2 km vertical step, were averaged for OSIRIS CCD pixels 1205-1220 (at around 800 nm), and were used to monitor the position and intensity of the aerosol smoke plume as it was transported vertically and horizontally. The results of this analysis suggest that the plume moved eastward from its initial source to New Zealand and reached an altitude of 14 km by 11 February. The plume remained fairly stationary until 13 February, during which time other large radiance perturbations over Indonesia, northern Australia and the Tasman Sea were observed, often extending from 12 to 18 km. On 14 February the bushfire plume was observed at about 19 km and remained over the Tasman Sea until 19 February, gradually moving upwards to 21 km. Subsequently the plume was observed to be moving westward within the 19-21 altitude range over the Indian Ocean, reaching Madagascar at the end of February. It remained stationary over Madagascar until late February and then moved across southern Africa. At that time another convection event was observed by OSIRIS over southern Africa from the beginning of March which had a vertical distribution from ~14-18 km, which the bushfire plume was seen to pass through. This resulted in radiance perturbations over southern Africa for over a week. The plume arrived at South America on 9 March and was observed at 20-22 km altitude. Over the next few weeks it remained over the South American region. Throughout this period the aerosol

  19. Compositional and temperature variations of the Pacific upper mantle since the Cretaceous

    Institute of Scientific and Technical Information of China (English)

    ZHANG Guoliang


    The geological evolution of the Earth during the mid-Cretaceous were shown to be anomalous, e.g., the pause of the geomagnetic field, the global sea level rise, and increased intra-plate volcanic activities, which could be attributed to deep mantle processes. As the anomalous volcanic activities occurred mainly in the Cretaceous Pacific, here we use basalt chemical compositions from the oceanic drilling (DSDP/ODP/IODP) sites to investigate their mantle sources and melting conditions. Based on locations relative to the Pacific plateaus, we classified these sites as oceanic plateau basalts, normal mid-ocean ridge basalts, and near-plateau seafloor basalts. This study shows that those normal mid-ocean ridge basalts formed during mid-Cretaceous are broadly similar in average Na8, La/Sm and Sm/Yb ratios and Sr-Nd isotopic compositions to modern Pacific spreading ridge (the East Pacific Rise). The Ontong Java plateau (125–90 Ma) basalts have distinctly lower Na8 and 143Nd/144Nd, and higher La/Sm and87Sr/86Sr than normal seafloor basalts, whereas those for the near-plateau seafloor basalts are similar to the plateau basalts, indicating influences from the Ontong Java mantle source. The super mantle plume activity that might have formed the Ontong Java plateau influenced the mantle source of the simultaneously formed large areas of seafloor basalts. Based on the chemical data from normal seafloor basalts, I propose that the mantle compositions and melting conditions of the normal mid-ocean ridges during the Cretaceous are similar to the fast spreading East Pacific Rise. Slight variations of mid-Cretaceous normal seafloor basalts in melting conditions could be related to the local mantle source and spreading rate.

  20. Mantle xenoliths from Marosticano area (Northern Italy): a comparison with Veneto Volcanic Province lithospheric mantle (United States)

    Brombin, Valentina; Bonadiman, Costanza; Coltorti, Massimo


    redox conditions (Δlog fO2: +1.2 to -0.7, Ballhaus, 1991) to Lessinean and Val d'Adige xenoliths which may indicate a local oxidation of the mantle below this portion of VVP. References • Beccaluva L., Bianchini G., Bonadiman C., Coltorti M., Milani L., Salvini L., Siena F., Tassinari R. (2007). Intraplate lithospheric and sublithospheric components in the Adriatic domain: Nephelinite to tholeiite magma generation in the Paleogene Veneto Volcanic Province, Southern Alps. Geological Society of America, 131-152. • Beccaluva L., Bonadiman C., Coltorti M., Salvini L., Siena F. (2001). Depletion events, nature of metasomatizing agent and timing of enrichment processes in lithospheric mantle xenoliths from the Veneto Volcanic Province. Journal of Petrology, 42, 173-187. • Gasperini D., Bosch D., Braga R., Bondi M., Macera P., Morten L. (2006). Ultramafic xenoliths from the Veneto Volcanic Province (Italy): Petrological and geochemical evidence for multiple metasomatism of the SE Alps mantle lithospere. Geochemical Journal, 40, 377-404. • Siena F., Coltorti M. (1989). Lithospheric mantle evolution: evidences from ultramafic xenoliths in the Lessinean volcanics (Northern Itlay). Chemical Geology, 77, 347-364.

  1. Aggregate Particles in the Plumes of Enceladus

    CERN Document Server

    Gao, Peter; Zhang, Xi; Ingersoll, Andrew P


    Estimates of the total particulate mass of the plumes of Enceladus are important to constrain theories of particle formation and transport at the surface and interior of the satellite. We revisit the calculations of Ingersoll and Ewald (2011), who estimated the particulate mass of the Enceladus plumes from strongly forward scattered light in Cassini ISS images. We model the plume as a combination of spherical particles and irregular aggregates resulting from the coagulation of spherical monomers, the latter of which allows for plumes of lower particulate mass. Though a continuum of solutions are permitted by the model, the best fits to the ISS data consist either of low mass plumes composed entirely of small aggregates or high mass plumes composed of large aggregates and spheres. The high mass plumes can be divided into a population of large aggregates with total particulate mass of 116 +/- 12 X 10^3 kg, and a mixed population of spheres and aggregates consisting of a few large monomers that has a total plume...

  2. Infrared Sensing of Buoyant Surface Plumes

    DEFF Research Database (Denmark)

    Petersen, Ole; Larsen, Torben


    This paper is concerned with laboratory experiments on buoyant surface plumes where heat is the source of buoyancy. Temperature distributions were measured at the water surface using infra-red sensing, and inside the waterbody a computer based measurement system was applied. The plume is described...

  3. Europa's Ocean Can Be Sustained By Hydrothermal Plumes and Salt Transport (United States)

    Travis, B. J.; Palguta, J.; Schubert, G.


    Data returned by the Galileo spacecraft provide considerable evidence that Jupiter's satellite Europa possesses a liquid ocean beneath its solid, icy outer shell. However, it is not known if that ocean has existed throughout Europa's history. Previous thermal evolution models of Europa suggest that without active tidal dissipative heating (TDH), a global liquid ocean layer would eventually freeze long before the present. However, previous models have not coupled all the various thermal and flow processes that may be operating in Europa. Recently, we have developed a whole-moon numerical model for Europa. This model couples radiogenic heating, thermal diffusion, hydrothermal convection and salt transport in mantle pore water, hydrothermal flow and transport in an ocean layer, parameterized convection in the ice shell, and change of phase between ice and liquid water. Application of our model suggests that, even without TDH active until recently, hydrothermal convection in a salty, rocky mantle can sustain flow in an ocean layer throughout Europa's post-differentiation history. The model thermal history covers three phases: (i) an initial, roughly 0.5 Gyr-long period of radiogenic heating and differentiation, (ii) a long period from 0.5 Gyr to 4 Gyr with continuing radiogenic heating but no TDH (following Yoder, Nature 279: 767-770, 1979), and (iii) a final period covering the last 0.5 Gyr until present day, during which TDH is active. In our model, hydrothermal plumes develop throughout phases II and III, transporting heat and salt from Europa's silicate mantle to its ocean. The outer ice shell thickens over time, growing to about 75 km in depth. When TDH becomes active, the ice shell melts quickly to a thickness of about 10 km, and then stabilizes at roughly 20 to 25 km thickness, leaving an ocean 80 km deep. Parameterized convection in the ice shell is spatially non-uniform and changes over time, reflecting its ties to the evolving deeper ocean-mantle dynamics. A

  4. Alternative model for the Great Oxidation Event (United States)

    Bekker, A.


    Transition from the Archean, largely anoxic atmosphere and ocean to the Proterozoic oxidizing surface conditions has been inferred in Zimbabwe from the geochemical and geological evidence as early as 1927. Subsequent studies provided additional support for this interpretation, bracketed the transition between 2.45 and 2.32 Ga, and suggested temporal and cause-and-effect relationship with a series of the early Paleoproterozoic ice ages (including 4 discrete events). Recently recognized transient oxidation events of the Archean add texture to this pattern, but do not change it. The rise of atmospheric oxygen requires a misbalance between oxygen sinks and sources and most attention was focused on sinks. In contrast, change in oxygen supply related to low organic productivity in Archean oceans with limited nutrient contents are considered here. Although carbon isotope values of carbonates and organic carbon indicate substantial relative burial rate of organic carbon during the Archean, most of the earlier buried organic matter at that time was recycled to sediments during continental weathering, implying very low productivity and burial of 'new' organic carbon. Low contents of redox-sensitive elements, such as Mo, Cu, Zn, and V, in Archean seawater could have kept organic productivity and oxygen production at low levels. The GOE was immediately preceded by deposition of giant iron formations, accounting for more than 70% of world iron resources, and worldwide emplacement of a number of LIPs between 2.5 and 2.45 Ga, indicating enhanced delivery of nutrients and redox-sensitive elements to the oceans via submarine hydrothermal processes and continental weathering under CO2- and SO2-rich atmosphere and associated terrestrial acidic runoff. This enhanced emplacement of LIPs has been linked with the growth of continental crust, emergence of the first supercontinent, and mantle overturn at the Archean-Proterozoic boundary. The GOE could have thus been triggered by enhanced

  5. Mantle superplumes induce geomagnetic superchrons

    Directory of Open Access Journals (Sweden)

    Peter eOlson


    Full Text Available We use polarity reversal systematics from numerical dynamos to quantify the hypothesis that the modulation of geomagnetic reversal frequency, including geomagnetic superchrons, results from changes in core heat flux related to growth and collapse of lower mantle superplumes. We parameterize the reversal frequency sensitivity from numerical dynamos in terms of average core heat flux normalized by the difference between the present-day core heat flux and the core heat flux at geomagnetic superchron onset. A low-order polynomial fit to the 0-300 Ma Geomagnetic Polarity Time Scale (GPTS reveals that a decrease in core heat flux relative to present-day of approximately 30% can account for the Cretaceous Normal Polarity and Kiaman Reverse Polarity Superchrons, whereas the hyper-reversing periods in the Jurassic require a core heat flux equal to or higher than present-day. Possible links between GPTS transitions, large igneous provinces (LIPs, and the two lower mantle superplumes are explored. Lower mantle superplume growth and collapse induce GPTS transitions by increasing and decreasing core heat flux, respectively. Age clusters of major LIPs postdate transitions from hyper-reversing to superchron geodynamo states by 30-60 Myr, suggesting that superchron onset may be contemporaneous with LIP-forming instabilities produced during collapses of lower mantle superplumes.

  6. Modelling oil plumes from subsurface spills. (United States)

    Lardner, Robin; Zodiatis, George


    An oil plume model to simulate the behavior of oil from spills located at any given depth below the sea surface is presented, following major modifications to a plume model developed earlier by Malačič (2001) and drawing on ideas in a paper by Yapa and Zheng (1997). The paper presents improvements in those models and numerical testing of the various parameters in the plume model. The plume model described in this paper is one of the numerous modules of the well-established MEDSLIK oil spill model. The deep blowout scenario of the MEDEXPOL 2013 oil spill modelling exercise, organized by REMPEC, has been applied using the improved oil plume module of the MEDSLIK model and inter-comparison with results having the oil spill source at the sea surface are discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.

  7. No coincidence? Exploring the connection between the Great Oxidation Event and craton stabilization during the Archean-Proterozoic transition (United States)

    Kump, L. R.


    As geochronological constraints on the timing of the Great Oxidation Event (here defined as the passage of atmospheric oxygen levels through the proposed upper limit of 10-5 of present) have improved, it has become increasingly clear that this event is somehow tied to the tectonic factors that have defined the Archean-Proterozoic boundary for decades, namely the stabilization of continental cratons allowing for the growth of large continents. We have proposed two connections in the past: 1) elevated late Archean mantle plume activity brought oxidized material from the lithospheric graveyard to the upper mantle, reducing the oxygen fugacity of post-Archean volcanism, and 2) that the stabilization of the cratons allowed for a proportional increase in less-reducing, subaerial volcanism at the expense of more reducing, submarine volcanism. Critiques of these two proposals will be addressed in the context of subsequent work by the geosciences community on the geodynamics and geochemistry of the Archean-Proterozoic transition, and a synthetic hypothesis for a tectonic driver for atmospheric oxygenation will be presented.

  8. Origin and Distribution of Water Contents in Continental and Oceanic Lithospheric Mantle (United States)

    Peslier, Anne H.


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

  9. Galileo observations of volcanic plumes on Io (United States)

    Geissler, P.E.; McMillan, M.T.


    Io's volcanic plumes erupt in a dazzling variety of sizes, shapes, colors and opacities. In general, the plumes fall into two classes, representing distinct source gas temperatures. Most of the Galileo imaging observations were of the smaller, more numerous Prometheus-type plumes that are produced when hot flows of silicate lava impinge on volatile surface ices of SO2. Few detections were made of the giant, Pele-type plumes that vent high temperature, sulfur-rich gases from the interior of Io; this was partly because of the insensitivity of Galileo's camera to ultraviolet wavelengths. Both gas and dust spout from plumes of each class. Favorably located gas plumes were detected during eclipse, when Io was in Jupiter's shadow. Dense dust columns were imaged in daylight above several Prometheus-type eruptions, reaching heights typically less than 100 km. Comparisons between eclipse observations, sunlit images, and the record of surface changes show that these optically thick dust columns are much smaller in stature than the corresponding gas plumes but are adequate to produce the observed surface deposits. Mie scattering calculations suggest that these conspicuous dust plumes are made up of coarse grained “ash” particles with radii on the order of 100 nm, and total masses on the order of 106 kg per plume. Long exposure images of Thor in sunlight show a faint outer envelope apparently populated by particles small enough to be carried along with the gas flow, perhaps formed by condensation of sulfurous “snowflakes” as suggested by the plasma instrumentation aboard Galileo as it flew through Thor's plume [Frank, L.A., Paterson, W.R., 2002. J. Geophys. Res. (Space Phys.) 107, doi:10.1029/2002JA009240. 31-1]. If so, the total mass of these fine, nearly invisible particles may be comparable to the mass of the gas, and could account for much of Io's rapid resurfacing.

  10. The origin of the Line Islands: plate or plume controlled volcanism? (United States)

    Storm, L. P.; Konter, J. G.; Koppers, A. A.


    Geochemical compositions of melts produced in the Earth's mantle provide key data for our understanding of the Earth's internal structure. Particularly, the range in compositions for oceanic intraplate volcanism has fueled the ongoing debate on the dynamic origin of hotspots. Traditionally, hotspots have been interpreted to originate from narrow, upwelling plumes of hot mantle material that reach the bottom of the tectonic plates. Progressively younger volcanoes, as seen at, for example, Hawaii, are then derived from plume melts. However, such a plume may originate from the core-mantle boundary, the top of seismically defined superplumes, or the origin may not lie in a buoyantly upwelling plume at all. The presence of an age progressive volcanic chain and a large igneous province, a high buoyancy flux, the geochemical composition of the erupted lavas, and seismically slow velocities have been used to distinguish different hotspot origins. Volcanic chains that lack most of these features may originate from the eruption of shallow melts along lithospherically controlled cracks. A unique area to study this type of volcanism is the Line Islands. These islands define a complex chain of volcanoes south of Hawaii that morphologically define multiple sub-groups. Moreover, recent age dating has revealed a complex geochronology. Combined geochronological and geochemical data from the Line Islands allude to the presence of shallow mantle melts that feed eruptions where there are weaknesses in the plates due to fractures or fissures. The Line Islands consist of elongated ridges, seamounts, atolls and islands that form the northern segment of the Line-Tuamotu chain of volcanoes. The volcanic chain is divided into three morphologically distinct regions; the northern, central and southern provinces. Long en echelon ridges of the Line Islands Cross Trend intersect the northern province at 14-16°N, which consists of the section between the Molokai and Clarion fracture zones. The

  11. Effect of Spin Transition onComposition and Seismic Structure of the Lower Mantle (United States)

    Wu, Z.


    hotspots: Search for mantle plumes. Gondwana Res 12, 335-355. [5] van der Hilst, R.D., Karason, H., 1999. Science 283, 1885-1888. [6] Huang,C., Leng, W., Wu, Z. Q., 2015. Iron-spin transition controls structure and stability of LLSVPs in the lower mantle, Earth Planet. Sci. Lett. 423, 173-181.

  12. Water contents in pyroxenes of intraplate lithospheric mantle (United States)

    Bonadiman, C.; Hao, Y.-T.; Coltorti, M.; Dallai, L.; Faccini, B.; Hu, H.; Qunke, X.


    Water contents of clinopyroxene and orthopyroxene in mantle peridotites from various xenolith occurrences in intraplate settings (both oceanic and continental) were determined by Fourier Transform Infrared Spectroscopy (FTIR). The localities are as follow: Sal Island (Cape Verde Archipelago); Baker Rocks and Greene Point (Northern Victoria Land, Antarctica); Panshishan and Lianshan (Subei Basin, Eastern China). They represent well-known localities where detailed petrographical and geochemical studies have already been carried out or areas which are currently under investigation. The water incorporated in these pyroxenes is low (cpx, 37-399ppm; opx: 9-166ppm)(or very low as in Greene Point, Antarctica; cpx, 5-16ppm; opx: 9-16ppm) and, among each population, no clear correlation with melting parameters (MgO contents) in single mineral is evident. Results are compared with the available literature data on water contents in mantle pyroxene which includes peridotites from on-craton (hosted by kimberlitic-type magmas) and off-craton (hosted by alkaline basic magmas), as well as subarc mantle settings. The "relatively dry" (cpx: 140-528 ppm; opx: 38-280 ppm) sub-arc mantle xenoliths (Peslier et al., 2002) are shown to be wetter than the intraplate (off-craton) xenoliths. Cratonic mantle pyroxenes are only represented by a few determinations on garnet peridotites and eclogite from Kaapvaal and Colorado Plateau. They record the highest water contents (cpx: 342-1012 ppm; opx: 180-491 ppm) so far measured in mantle pyroxenes from various tectonic settings. Despite the limited data set, the indication that the cratonic mantle is strongly hydrated is compelling. Rehydration for the Colorado Plateau craton may be due to the Farallon plate subduction (Li et al., 2008), while for Kaapvaal Craton it might be related to young (<100Ma) metasomatic enrichments (Griffin et al., 2003a; Kobussen et al., 2008). If this is the case then the Archean mantle water content needs to be

  13. Impact of wind and tides on the Lena River freshwater plume dynamics in the summer season (United States)

    Fofonova, Vera; Danilov, Sergey; Androsov, Alexey; Janout, Markus; Bauer, Martin; Overduin, Paul; Itkin, Polona; Wiltshire, Karen Helen


    The Lena plume dynamics in the Lena Delta region of the Laptev Sea are explored in simulations performed with the Finite Volume Coastal Ocean Model (FVCOM) on a mesh with the horizontal resolution 0.4-5 km. The impact of wind and tides on the Lena plume propagation is analysed based on simulations for the summer season of 2008 and also on idealised experiments. All main Lena River freshwater channels (Trofimovskaya, Bykovskaya, Tumatskaya and Olenekskaya) produce buoyant outflows in the summer season. The surface plume buoyancy signature proves to be highly variable in time, especially in case of upwelling favourable wind events. Winds stronger than 6 m s-1 can already turn the dynamics of flows from all main freshwater channels to the wind-driven state. During the summer season, the bulk of freshwater from the Lena River stays in the eastern Laptev Sea because of location of the main Lena River freshwater channels, their large Kelvin numbers and light summer winds. Westward and northward plume excursions are wind-driven, and the model skill in simulating them depends on the available wind forcing. The main mechanism of tidal influence in the freshwater plume zone is through tidally induced mixing, except for the northern vicinity of the delta, where residual circulation may contribute to the plume eastward transport significantly.

  14. Sediment plume response to surface melting and supraglacial lake drainages on the Greenland ice sheet

    DEFF Research Database (Denmark)

    Chu, Vena W.; Smith, Laurence C; Rennermalm, Asa K.


    Increased mass losses from the Greenland ice sheet and inferred contributions to sea-level rise have heightened the need for hydrologic observations of meltwater exiting the ice sheet. We explore whether temporal variations in ice-sheet surface hydrology can be linked to the development of a down...... area. We conclude that remote sensing of sediment plume behavior offers a novel tool for detecting the presence, timing and interannual variability of meltwater release from the ice sheet....... of a downstream sediment plume in Kangerlussuaq Fjord by comparing: (1) plume area and suspended sediment concentration from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and field data; (2) ice-sheet melt extent from Special Sensor Microwave/Imager (SSM/I) passive microwave data; and (3......) supraglacial lake drainage events from MODIS. Results confirm that the origin of the sediment plume is meltwater release from the ice sheet. Interannual variations in plume area reflect interannual variations in surface melting. Plumes appear almost immediately with seasonal surface-melt onset, provided...

  15. Mantle convection and plate tectonics on Earth-like exoplanets (United States)

    Sotin, C.; Schubert, G.


    plumes for calculating the driving force. It is suggested that the formation of hot plumes at the core-mantle boundary and their interaction with the upper thermal boundary layer may play an important role in triggering plate tectonics. Part of this work has been carried out at the Jet Propulsion Laboratory-California Institute of Technology, under contract with NASA.

  16. Yellowstone plume trigger for Basin and Range extension and emplacement of the Nevada-Columbia Basin magmatic belt (United States)

    Camp, Victor E; Pierce, Kenneth L.; Morgan Morzel, Lisa Ann.


    Widespread extension began across the northern and central Basin and Range Province at 17–16 Ma, contemporaneous with magmatism along the Nevada–Columbia Basin magmatic belt, a linear zone of dikes and volcanic centers that extends for >1000 km, from southern Nevada to the Columbia Basin of eastern Washington. This belt was generated above an elongated sublithospheric melt zone associated with arrival of the Yellowstone mantle plume, with a north-south tabular shape attributed to plume ascent through a propagating fracture in the Juan de Fuca slab. Dike orientation along the magmatic belt suggests an extension direction of 245°–250°, but this trend lies oblique to the regional extension direction of 280°–300° during coeval and younger Basin and Range faulting, an ∼45° difference. Field relationships suggest that this magmatic trend was not controlled by regional stress in the upper crust, but rather by magma overpressure from below and forceful dike injection with an orientation inherited from a deeper process in the sublithospheric mantle. The southern half of the elongated zone of mantle upwelling was emplaced beneath a cratonic lithosphere with an elevated surface derived from Late Cretaceous to mid-Tertiary crustal thickening. This high Nevadaplano was primed for collapse with high gravitational potential energy under the influence of regional stress, partly derived from boundary forces due to Pacific–North American plate interaction. Plume arrival at 17–16 Ma resulted in advective thermal weakening of the lithosphere, mantle traction, delamination, and added buoyancy to the northern and central Basin and Range. It was not the sole cause of Basin and Range extension, but rather the catalyst for extension of the Nevadaplano, which was already on the verge of regional collapse.

  17. Mantle geoneutrinos in KamLAND and Borexino

    CERN Document Server

    Fiorentini, G; Lisi, E; Mantovani, F; Rotunno, A M


    The KamLAND and Borexino experiments have observed, each at ~4 sigma level, signals of electron antineutrinos produced in the decay chains of thorium and uranium in the Earth's crust and mantle (Th and U geoneutrinos). Various pieces of geochemical and geophysical information allow an estimation of the crustal geoneutrino flux components with relatively small uncertainties. The mantle component may then be inferred by subtracting the estimated crustal flux from the measured total flux. To this purpose, we analyze in detail the experimental Th and U geoneutrino event rates in KamLAND and Borexino, including neutrino oscillation effects. We estimate the crustal flux at the two detector sites, using state-of-the-art information about the Th and U distribution on global and local scales. We find that crust-subtracted signals show hints of a residual mantle component, emerging at ~2.4 sigma level by combining the KamLAND and Borexino data. The inferred mantle flux slightly favors scenarios with relatively high Th ...

  18. GeoFramework: Coupling multiple models of mantle convection within a computational framework (United States)

    Tan, E.; Choi, E.; Thoutireddy, P.; Gurnis, M.; Aivazis, M.


    Geological processes usually encompass a broad spectrum of length and time scales. Traditionally, a modeling code (solver) is developed for a problem of specific length and time scales, but the utility of the solver beyond the designated purpose is usually limited. As we have come to recognize that geological processes often result from the dynamic coupling of deformation across a wide range of time and spatial scales, more robust methods are needed. One means to address this need is through the integration of complementary modeling codes, while attempting to reuse existing software as much as possible. The GeoFramework project addresses this by developing a suite of reusable and combinable tools for the Earth science community. GeoFramework is based on and extends Pyre, a Python-based modeling framework, developed to link solid (Lagrangian) and fluid (Eulerian) solvers, as well as mesh generators, visualization packages, and databases, with one another for engineering applications. Under the framework, a solver is aware of the presence of other solvers and can interact with each other via exchanging information across adjacent mesh boundary. We will show an example of linking two instances of the CitcomS finite element solver within GeoFramework. A high-resolution regional mantle convection model is linked with a global mantle convection model. The global solver has a resolution of ˜180 km horizontally and 35-100 km (with mesh refinement) vertically. The fine mesh has a resolution of ˜40 km horizontally and vertically. The fine mesh is center on the Hawaii hotspot. A vertical plume is used as an initial condition. Time-varying plate velocity models are imposed since 80 Ma and we have investigated how the plume conduit is deflected by the global circulation patterns as a function of mantle viscosity, plume flux, and plate motion.

  19. Melting the lithosphere: Metasomes as a source for mantle-derived magmas (United States)

    Rooney, Tyrone O.; Nelson, Wendy R.; Ayalew, Dereje; Hanan, Barry; Yirgu, Gezahegn; Kappelman, John


    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 an olivine-dominated source. Although there is mounting evidence 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. Here we present major and trace element analyses of 66 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 units identified in the later cinder cones and associated lava flows; (B) a clinopyroxene-phyric high Ti group (3.1-6.5 wt.% TiO2; 2.8-9.2 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. A characteristic negative K anomaly in primitive-mantle normalized diagrams, and Na2O > K2O, suggests a source rich in amphibole, devoid of olivine, and perhaps containing some carbonate and magnetite. While melt generation during rift development in Ethiopia is strongly correlated with the thermo-chemical anomalies associated with the African Superplume, thermobaric destabilization and melting of mantle metasomes may also contribute to lithospheric thinning. In regions impacted by mantle plumes, such melts may be critical to weakening

  20. Digital filtering of plume emission spectra (United States)

    Madzsar, George C.


    Fourier transformation and digital filtering techniques were used to separate the superpositioned spectral phenomena observed in the exhaust plumes of liquid propellant rocket engines. Space shuttle main engine (SSME) spectral data were used to show that extraction of spectral lines in the spatial frequency domain does not introduce error, and extraction of the background continuum introduces only minimal error. Error introduced during band extraction could not be quantified due to poor spectrometer resolution. Based on the atomic and molecular species found in the SSME plume, it was determined that spectrometer resolution must be 0.03 nm for SSME plume spectral monitoring.

  1. Merging Thermal Plumes in the Indoor Environment

    DEFF Research Database (Denmark)

    Bjørn, Erik; Nielsen, Peter V.

    This experimental work deals with the basic problem of merging thermal plumes from heat sources situated in the vicinity of each other. No studies have been made yet of how close two heat sources must be to each other, before they can be considered as a single source with a cumulative heat effect......, and how far apart they must be to be considered separate. Also, it is not known how the flow field behaves in the intermediate fase, where the plumes are neither completely joined nor completely separate. A possible, very simple, solution of the velocity distribution between two plumes is to assume...

  2. How stratified is mantle convection? (United States)

    Puster, Peter; Jordan, Thomas H.


    We quantify the flow stratification in the Earth's mid-mantle (600-1500 km) in terms of a stratification index for the vertical mass flux, Sƒ (z) = 1 - ƒ(z) / ƒref (z), in which the reference value ƒref(z) approximates the local flux at depth z expected for unstratified convection (Sƒ=0). Although this flux stratification index cannot be directly constrained by observations, we show from a series of two-dimensional convection simulations that its value can be related to a thermal stratification index ST(Z) defined in terms of the radial correlation length of the temperature-perturbation field δT(z, Ω). ST is a good proxy for Sƒ at low stratifications (SƒUniformitarian Principle. The bound obtained here from global tomography is consistent with local seismological evidence for slab flux into the lower mantle; however, the total material flux has to be significantly greater (by a factor of 2-3) than that 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.

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

    Institute of Scientific and Technical Information of China (English)

    Y.A. Cook; I.V. Sanislav; J. Hammerli; T.G. Blenkinsop; P.H.G.M. Dirks


    Mafic rocks comprising tholeiitic pillow basalt, dolerite and minor gabbro form the basal stratigraphic unit in the ca. 2.8 to 2.6 Ga Geita Greenstone Belt situated in the NW Tanzania Craton. They outcrop mainly along the southern margin of the belt, and are at least 50 million years older than the supracrustal assemblages against which they have been juxtaposed. Geochemical analyses indicate that parts of the assemblage approach high Mg-tholeiite (more than 8 wt.%MgO). This suite of samples has a restricted compositional range suggesting derivation from a chemically homogenous reservoir. Trace element modeling suggests that the mafic rocks were derived by partial melting within the spinel peridotite field from a source rock with a primitive mantle composition. That is, trace elements maintain primitive mantle ratios (Zr/Hf ¼ 32e35, Ti/Zr ¼ 107e147), producing flat REE and HFSE profiles [(La/Yb)pm ¼ 0.9 e1.3], with abundances of 3e10 times primitive mantle and with minor negative anomalies of Nb [(Nb/La)pm ¼ 0.6e0.8] and Th [(Th/La)pm ¼ 0.6e0.9]. Initial isotope compositions (3Nd) range from 1.6 to 2.9 at 2.8 Ga and plot below the depleted mantle line suggesting derivation from a more enriched source compared to present day MORB mantle. The trace element composition and Nd isotopic ratios are similar to the mafic rocks outcropping w50 km south. The mafic rocks outcropping in the Geita area were erupted through oceanic crust over a short time period, between w2830 and w2820 Ma; are compo-sitionally homogenous, contain little to no associated terrigenous sediments, and their trace element composition and short emplacement time resemble oceanic plateau basalts. They have been interpreted to be derived from a plume head with a primitive mantle composition.

  4. Assessment of analytical techniques for predicting solid propellant exhaust plumes and plume impingement environments (United States)

    Tevepaugh, J. A.; Smith, S. D.; Penny, M. M.


    An analysis of experimental nozzle, exhaust plume, and exhaust plume impingement data is presented. The data were obtained for subscale solid propellant motors with propellant Al loadings of 2, 10 and 15% exhausting to simulated altitudes of 50,000, 100,000 and 112,000 ft. Analytical predictions were made using a fully coupled two-phase method of characteristics numerical solution and a technique for defining thermal and pressure environments experienced by bodies immersed in two-phase exhaust plumes.

  5. Mid-mantle heterogeneities and iron spin transition in the lower mantle: Implications for mid-mantle slab stagnation (United States)

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


    Recent high pressure experimental results reveal that the elastic and transport properties of mantle materials are impacted by the electronic spin transition in iron under lower mantle pressure and temperature conditions. The electronic transition in ferropericlase (Fp), the second major constituent mineral of the lower mantle material, is associated with a smooth increase in density starting from the mid-mantle depth to the core-mantle boundary (CMB). The transition also yields softening in the elastic moduli and an increase in the thermal expansivity over the transition zone in the lower mantle. Although there is not yet robust experimental evidence for spin-transition induced density change in the perovskite (Pv) phase (the major constituent mineral in the lower mantle), the spin transition in the octahedral (B) site in Al-free perovskite causes a bulk modulus hardening (increase in the bulk modulus) in the mineral. We have incorporated these physical processes into high resolution 3D-spherical control volume models for mantle convection. A series of numerical experiments explore how the electronic spin transition in iron modifies the mantle flow, and in particular the fate of sinking cold slabs. Such mid-mantle stagnations are prevalent globally in seismic tomographic inversions, but previous explanations for their existence are not satisfactory. Employing density anomalies from the iron spin transition in ferropericlase and density anomaly models for perovskite, we study the influence of the spin transition in the minerals of the lower mantle on mantle flow. Our model results reveal that while the spin transition-induced property variations in ferropericlase enhance mixing in the lower depths of the mantle, the density anomaly arising from the hardening in the bulk modulus of Al-free perovskite can be effective in slowing the descent of slabs and may cause stagnation at mid-mantle levels. A viscosity hill in the lower mantle may further enhance the stagnation

  6. Sensitivity of air quality simulation to smoke plume rise (United States)

    Yongqiang Liu; Gary Achtemeier; Scott Goodrick


    Plume rise is the height smoke plumes can reach. This information is needed by air quality models such as the Community Multiscale Air Quality (CMAQ) model to simulate physical and chemical processes of point-source fire emissions. This study seeks to understand the importance of plume rise to CMAQ air quality simulation of prescribed burning to plume rise. CMAQ...

  7. Extreme Mantle Heterogeneity beneath the Jingpohu Area, Northeastern China-Geochemical Evidence of Holocene Basaltic Rock

    Institute of Scientific and Technical Information of China (English)


    Holocene basaltic rocks of the Jingpohu area are located in the "Crater Forest" and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, their petrological characteristics are very different: alkaline olivine basalt without any megacrysts in the former, and leucite tephrite with Ti-amphibole, phlogopite and anorthoclasite megacrysts in the latter. On the basis of their geochemical characteristics, the two types of basaltic rocks should belong to weakly sodian alkaline basalts. But leucite tephrite is characterized by higher Al2O3, Na2O and K2O, higher enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), lower MgO and CaO, compatible elements and moderately compatible elements and lower Mg# values and Na/K ratios in comparison with alkaline olivine basalt. However, the two types of basaltic rocks have similar Sr, Nd, Pb isotopic compositions, which suggests that the mantle beneath the Jingpohu area was homogeneous before undergoing some geological processes about 3490 years ago. As the activity of the mantle plume led to different degrees of metasomatism, extreme mantle source heterogeneities occurred beneath the Jingpohu area. In comparison with alkaline olivine basalt, the leucite tephrite was derived from the more enriched mantle source region and resulted from strong metasomatism.

  8. Characteristics of the Great Whale River plume (United States)

    Ingram, R. Grant


    Observations of the motion field and dilution effects associated with the plume of Great Whale River in Hudson Bay are presented for both open water and ice-covered conditions. In the summer months a distinct plume of about 100 km2 in area is formed offshore which is characterized by a 1-2 m thickness and large velocities directed away from the river mouth in contrast to slower currents parallel to the shore in the ambient waters underneath. Surface drifter results suggest that the outer boundary of plume may be a zone of frontal convergence. Under ice-covered conditions the plume was significantly thicker and extended much farther offshore in spite of a marked reduction in river runoff at this time.

  9. Plume Diagnostics for Combustion Stability Project (United States)

    National Aeronautics and Space Administration — Sierra Engineering Inc. and Purdue University propose to develop a non-intrusive plume instrument capable of detecting and diagnosing combustion instability. This...

  10. Hydroxyl Tagging Velocimetry for Rocket Plumes Project (United States)

    National Aeronautics and Space Administration — To address the need for non-intrusive sensors for rocket plume properties, we propose a laser-based velocity diagnostic that does not require seeding, works in high...

  11. Novel plume deflection concept testing Project (United States)

    National Aeronautics and Space Administration — The proposed effort will explore the feasibility and effectiveness of utilizing an electrically driven thermal shield for use as part of rocket plume deflectors. To...

  12. Mantle wedge serpentinization effects on slab dips

    Directory of Open Access Journals (Sweden)

    Eh Tan


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

  13. Fire analog: a comparison between fire plumes and energy center cooling tower plumes

    Energy Technology Data Exchange (ETDEWEB)

    Orgill, M.M.


    Thermal plumes or convection columns associated with large fires are compared to thermal plumes from cooling towers and proposed energy centers to evaluate the fire analog concept. Energy release rates of mass fires are generally larger than for single or small groups of cooling towers but are comparable to proposed large energy centers. However, significant physical differences exist between cooling tower plumes and fire plumes. Cooling tower plumes are generally dominated by ambient wind, stability and turbulence conditions. Fire plumes, depending on burning rates and other factors, can transform into convective columns which may cause the fire behavior to become more violent. This transformation can cause strong inflow winds and updrafts, turbulence and concentrated vortices. Intense convective columns may interact with ambient winds to create significant downwind effects such as wakes and Karman vortex streets. These characteristics have not been observed with cooling tower plumes to date. The differences in physical characteristics between cooling tower and fire plumes makes the fire analog concept very questionable even though the approximate energy requirements appear to be satisfied in case of large energy centers. Additional research is suggested in studying the upper-level plume characteristics of small experimental fires so this information can be correlated with similar data from cooling towers. Numerical simulation of fires and proposed multiple cooling tower systems could also provide comparative data.

  14. Near-glacier surveying of a subglacial discharge plume: Implications for plume parameterizations (United States)

    Jackson, R. H.; Shroyer, E. L.; Nash, J. D.; Sutherland, D. A.; Carroll, D.; Fried, M. J.; Catania, G. A.; Bartholomaus, T. C.; Stearns, L. A.


    At tidewater glaciers, plume dynamics affect submarine melting, fjord circulation, and the mixing of meltwater. Models often rely on buoyant plume theory to parameterize plumes and submarine melting; however, these parameterizations are largely untested due to a dearth of near-glacier measurements. Here we present a high-resolution ocean survey by ship and remotely operated boat near the terminus of Kangerlussuup Sermia in west Greenland. These novel observations reveal the 3-D structure and transport of a near-surface plume, originating at a large undercut conduit in the glacier terminus, that is inconsistent with axisymmetric plume theory, the most common representation of plumes in ocean-glacier models. Instead, the observations suggest a wider upwelling plume—a "truncated" line plume of ˜200 m width—with higher entrainment and plume-driven melt compared to the typical axisymmetric representation. Our results highlight the importance of a subglacial outlet's geometry in controlling plume dynamics, with implications for parameterizing the exchange flow and submarine melt in glacial fjord models.

  15. Grain size evolution in the mantle and its effect on geodynamics, seismic velocities and attenuation (United States)

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


    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

  16. High-Resolution Imaging of Structure and Dynamics of the Lowermost Mantle (United States)

    Zhao, Chunpeng

    This research investigates Earth structure in the core-mantle boundary (CMB) region, where the solid rocky mantle meets the molten iron alloy core. At long wavelengths, the lower mantle is characterized by two nearly antipodal large low shear velocity provinces (LLSVPs), one beneath the Pacific Ocean the other beneath Africa and the southern Atlantic Ocean. However, fine-scale LLSVP structure as well as its relationship with plate tectonics, mantle convection, hotspot volcanism, and Earth's outer core remains poorly understood. The recent dramatic increase in seismic data coverage due to the EarthScope experiment presents an unprecedented opportunity to utilize large concentrated datasets of seismic data to improve resolution of lowermost mantle structures. I developed an algorithm that identifies anomalously broadened seismic waveforms to locate sharp contrasts in shear velocity properties across the margins of the LLSVP beneath the Pacific. The result suggests that a nearly vertical mantle plume underlies Hawaii that originates from a peak of a chemically distinct reservoir at the base of the mantle, some 600-900 km above the CMB. Additionally, acute horizontal Vs variations across and within the northern margin of the LLSVP beneath the central Pacific Ocean are inferred from forward modeling of differential travel times between S (and Sdiff) and SKS, and also between ScS and S. I developed a new approach to expand the geographic detection of ultra-low velocity zones (ULVZs) with a new ScS stacking approach that simultaneously utilizes the pre- and post-cursor wavefield. Strong lateral variations in ULVZ thicknesses and properties are found across the LLSVP margins, where ULVZs are thicker and stronger within the LLSVP than outside of it, consistent with convection model predictions. Differential travel times, amplitude ratios, and waveshapes of core waves SKKS and SKS are used to investigate CMB topography and outermost core velocity structure. 1D and 2D

  17. STRATAFORM Plume Study: Analysis and Modeling (United States)


    of settling is explained by the variation of plume speed, rather than by variations in settling velocity (Hill et al., submitted). Floculation is an...mouth. However, the fraction of floculated sediment does not vary as much as expected with changes in forcing conditions. There do appear to be large...differences in the floculation rate between the extreme flood conditions of 1997 and the more moderate floods of 1998. The detailed examination of plume

  18. Rocket plume tomography of combustion species



    Interest in accurate detection and targeting of aggressor missiles has received considerable interest with the national priority of developing a missile defense system. Understanding the thermal signatures of the exhaust plumes of such missiles is key to accomplishing that mission. Before signature models can be precisely developed for specific rockets, the radiation of the molecular or combustion species within those plumes must be accurately predicted. A combination translation / rotation s...

  19. OPAD data analysis. [Optical Plumes Anomaly Detection (United States)

    Buntine, Wray L.; Kraft, Richard; Whitaker, Kevin; Cooper, Anita E.; Powers, W. T.; Wallace, Tim L.


    Data obtained in the framework of an Optical Plume Anomaly Detection (OPAD) program intended to create a rocket engine health monitor based on spectrometric detections of anomalous atomic and molecular species in the exhaust plume are analyzed. The major results include techniques for handling data noise, methods for registration of spectra to wavelength, and a simple automatic process for estimating the metallic component of a spectrum.

  20. Cretaceous Arctic magmatism: Slab vs. plume? Or slab and plume? (United States)

    Gottlieb, E. S.; Miller, E. L.; Andronikov, A. V.; Brumley, K.; Mayer, L. A.; Mukasa, S. B.


    Tectonic models for the Cretaceous paleogeographic evolution of the Arctic Ocean and its adjacent landmasses propose that rifting in the Amerasia Basin (AB) began in Jura-Cretaceous time, accompanied by the development of the High Arctic Large Igneous Province (HALIP). During the same timespan, deformation and slab-related magmatism, followed by intra-arc rifting, took place along the Pacific side of what was to become the Arctic Ocean. A compilation and comparison of the ages, characteristics and space-time variation of circum-Arctic magmatism allows for a better understanding of the role of Pacific margin versus Arctic-Atlantic plate tectonics and the role of plume-related magmatism in the origin of the Arctic Ocean. In Jura-Cretaceous time, an arc built upon older terranes overthrust the Arctic continental margins of North America and Eurasia, shedding debris into foreland basins in the Brooks Range, Alaska, across Chukotka, Russia, to the Lena Delta and New Siberian Islands region of the Russian Arctic. These syn-tectonic sediments have some common sources (e.g., ~250-300 Ma magmatic rocks) as determined by U-Pb detrital zircon geochronology. They are as young as Valanginian-Berriasian (~136 Ma, Gradstein et al., 2004) and place a lower limit on the age of formation of the AB. Subsequent intrusions of granitoid plutons, inferred to be ultimately slab-retreat related, form a belt along the far eastern Russian Arctic continental margin onto Seward Peninsula and have yielded a continuous succession of zircon U-Pb ages from ~137-95 Ma (n=28) and a younger suite ~91-82 Ma (n=16). All plutons dated were intruded in an extensional tectonic setting based on their relations to wall-rock deformation. Regional distribution of ages shows a southward migration of the locus of magmatism during Cretaceous time. Basaltic lavas as old as 130 Ma and as young as 80 Ma (40Ar/39Ar)) erupted across the Canadian Arctic Islands, Svalbard and Franz Josef Land and are associated with

  1. Petrological features of suprasubuction mantle: evidence from northern, central and southern Patagonian mantle xenoliths (United States)

    Melchiorre, M.; Coltorti, M.; Gregoire, M.; Benoit, M.


    Patagonia has a number of outcrops where xenoliths-bearing lavas can be found. It thus represents a good opportunity to study mantle material in supra-subduction environment both on arc and back-arc position, from as near as 300 km to as far as 600 km from the Chile trench. A wealth of data is nowadays available on these xenoliths, starting from petrographic observations, whole-rock and mineral major and trace element analyses plus few isotopic analyses on whole rock and mineral separates. To this already large dataset the petrological features of another locality (Estancia Sol de Mayo, ESM) were added, allowing a comparison between as much as eight localities coming from northern (Cerro Aznare, Praguaniyeu, Cerro Rio Chubut, Cerro de los Chenques), central (Cerro Clark and Gobernador Gregores) and southern Patagonia (Pali Aike), covering approximately an area of 1000 x 300 km. Most xenoliths are harzburgites, with minor amount of lherzolites, wehrlites and dunites. In the Al2O3 vs mg# [MgO/(MgO+FeO) mol %] diagram clinopyroxene (cpx) compositions highlight three different trends, with orthopyroxene (opx) compositions plotting on two of these. In the first trend Al2O3 content increases at almost constant mg# mol % (trend 1). The second trend comprises only cpx from wehrlites (trend 2) and is situated between the first and the third trend. In the third trend the slight increases of Al2O3 is associated with a remarkable decrease in mg# (trend 3). LREE and LILE abundances in cpx from Tres Lagos and Cerro Rio Chubut are directly correlated to the Al2O3, while they are inversely correlated at Cerro de Los Chenques and Cerro Fraile. In the first case it is likely that a metasomatic process affects the mantle domains beneath those areas, while in the second case a refertilization event caused by a tholeiitic melt is favorite. In other cases, as for Gobernador Gregores, a more complex situation is recorded, with two groups of samples showing both negative and positive

  2. Alkaline lavas from southern Mendoza, Argentina, extend the Patagonian DUPAL mantle field to the north (United States)

    Soager, N.; Holm, P. M.; Llambias, E.


    The lavas sampled around Río Colorado ~37°S at the border of Mendoza and Neuquén provinces, Argentina, define an OIB-like end-member composition for the Pleistocene and Holocene activity in the Payún Matrú volcanic field. Although positioned in the far back-arc of the Andes, only a few lavas show signs of involvement of slab fluids or crustal contamination such as relatively high LILEs relative to Nb. The very low La/Nb (~0.66) and Zr/Nb (~5) and high U/Pb (0.3-0.4) of the end-member composition clearly distinguish the source from normal MORB mantle, while high Ba/Nb (~10) and K/Nb (370-400) compared to FOZO and HIMU type OIBs suggest an EM type of mantle. Overall, the trace element patterns of the Río Colorado lavas are similar to the central and north Patagonian intraplate basalts and to South Atlantic E-MORB affected by the Discovery plume and the LOMU component (le Roux et al., 2002, EPSL 203). The isotopic composition of the Río Colorado component has a 206Pb/204Pb = 18.4, 207Pb/204Pb = 15.58, 208Pb/204Pb = 38.3, 87Sr/86Sr = 0.70353 and 143Nd/144Nd = 0.51285. This composition overlaps the central and north Patagonian intraplate basalts in Pb-isotopic space but is slightly less enriched in Sr and Nd-isotopes. It is distinctly different from the FOZO like composition of the south Patagonian intraplate basalts and the nearby Juan Fernandéz plume but similar to the South Atlantic N-MORB and MORB from the southern Chile Ridge segment 4 (Sturm et al., 1999, JGR 104) described as DUPAL type. The DUPAL-MORB type isotopic composition and the plume-like trace element patterns of the Río Colorado lavas suggest the presence of a weak plume beneath the area. The eruption of the large Payún Matrú volcano and the gigantic Pleistocene flood basalts also calls for a thermal anomaly to produce these melts during a weakly compressive tectonic regime with no significant addition of slab fluids. This was supported by Burd et al. (2008, Abstr., 7th Int. Sym. And. Geo

  3. Radioactivity released from burning gas lantern mantles. (United States)

    Luetzelschwab, J W; Googins, S W


    Gas lantern mantles contain thorium to produce incandescence when lantern fuel is burned on the mantle. Although only thorium is initially present on the mantle, the thorium daughters build up, some over a period of weeks and some over a period of years, and significant quantities of these daughters are present when the mantle is used. Some of these daughters are released when the lantern fuel is burned on the mantle. The amounts of radioactivity released during burning is studied by measuring the gamma radiation emitted by the daughters. Results of this study show that some of the radium (224Ra and 228Ra) and more than half the 212Pb and 212Bi is released during the first hour of a burn. The actual amounts release depend on the age of the mantle.

  4. A global sensitivity analysis of the PlumeRise model of volcanic plumes (United States)

    Woodhouse, Mark J.; Hogg, Andrew J.; Phillips, Jeremy C.


    Integral models of volcanic plumes allow predictions of plume dynamics to be made and the rapid estimation of volcanic source conditions from observations of the plume height by model inversion. Here we introduce PlumeRise, an integral model of volcanic plumes that incorporates a description of the state of the atmosphere, includes the effects of wind and the phase change of water, and has been developed as a freely available web-based tool. The model can be used to estimate the height of a volcanic plume when the source conditions are specified, or to infer the strength of the source from an observed plume height through a model inversion. The predictions of the volcanic plume dynamics produced by the model are analysed in four case studies in which the atmospheric conditions and the strength of the source are varied. A global sensitivity analysis of the model to a selection of model inputs is performed and the results are analysed using parallel coordinate plots for visualisation and variance-based sensitivity indices to quantify the sensitivity of model outputs. We find that if the atmospheric conditions do not vary widely then there is a small set of model inputs that strongly influence the model predictions. When estimating the height of the plume, the source mass flux has a controlling influence on the model prediction, while variations in the plume height strongly effect the inferred value of the source mass flux when performing inversion studies. The values taken for the entrainment coefficients have a particularly important effect on the quantitative predictions. The dependencies of the model outputs to variations in the inputs are discussed and compared to simple algebraic expressions that relate source conditions to the height of the plume.

  5. Sulfur chemistry in a copper smelter plume (United States)

    Eatough, D. J.; Christensen, J. J.; Eatough, N. I.; Hill, M. W.; Major, T. D.; Mangelson, N. F.; Post, M. E.; Ryder, J. F.; Hansen, L. D.; Meisenheimer, R. G.; Fischer, J. W.

    Sulfur transformation chemistry was studied in the plume of the Utah smelter of Kennecott Copper Corporation from April to October 1977. Samples were taken at up to four locations from 4 to 60 km from the stacks. Data collected at each station included: SO 2 concentration, low-volume collected total paniculate matter, high-volume collected size fractionated paniculate matter, wind velocity and direction, temperature, and relative humidity. Paniculate samples were analyzed for S(IV). sulfate, strong acid, anions, cations, and elemental concentrations using calorimetric, ion Chromatographie, FIXE, ESCA, ion microprobe, and SEM-ion microprobe techniques. The concentration of As in the paniculate matter was used as a conservative plume tracer. The ratios Mo/As, Pb/As, and Zn/As were constant in particulate matter collected at all sampling sites for any particle size. Strong mineral acid was neutralized by background metal oxide and/or carbonate particulates within 40km of the smelter. This neutralization process is limited only by the rate of incorporation of basic material into the plume. Two distinct metal-S(IV) species similar to those observed in laboratory aerosol experiments were found in the plume. The formation of paniculate S(IV) species occurs by interaction of SO 2 (g) with both ambient and plume derived aerosol and is equilibrium controlled. The extent of formation of S(IV) complexes in the aerosol is directly proportional to the SO 2(g) and paniculate (Cu + Fe) concentration and inversely proportional to the paniculate acidity. S(IV) species were stable in collected paniculate matter only in the neutralized material, but with proper sampling techniques could be demonstrated to also be present in very acidic particles at high ambient SO 2(g) concentrations. Reduction of arsenate to arsenite by the aerosol S(IV) complexes during plume transport is suggested. The SO 2(g)-sulfate conversion process in the plume is described by a mechanism which is first order

  6. Isotopic evidence for internal oxidation of the Earth's mantle during accretion (United States)

    Williams, Helen M.; Wood, Bernard J.; Wade, Jon; Frost, Daniel J.; Tuff, James


    The Earth's mantle is currently oxidised and out of chemical equilibrium with the core. The reasons for this and for the relatively oxidised state of Earth's mantle relative to the mantles of other terrestrial planets are unclear. It has been proposed that the oxidised nature and high ferric iron (Fe3 +) content of Earth's mantle was produced internally by disproportionation of ferrous iron (Fe2 +) into Fe3 + and metallic iron by perovskite crystallisation during accretion. Here we show that there is substantial Fe isotope fractionation between experimentally equilibrated metal and Fe3 +-bearing perovskite (≥ 0.45‰/amu), which can account for the heavy Fe isotope compositions of terrestrial basalts relative to equivalent samples derived from Mars and Vesta as the latter bodies are too small to stabilise significant perovskite. Mass balance calculations indicate that all of the mantle's Fe3 + could readily have been generated from a single disproportionation event, consistent with dissolution of perovskite in the lower mantle during a process such as the Moon-forming giant impact. The similar Fe isotope compositions of primitive terrestrial and low-titanium lunar basalts is consistent with models of equilibration between the mantles of the Earth and Moon in the aftermath of the giant impact and suggests that the heavy Fe isotope composition of the Earth's mantle was established prior to, or during the giant impact. The oxidation state and ferric iron content of the Earth's mantle was therefore plausibly set by the end of accretion, and may be decoupled from later volatile additions and the rise of oxygen in the Earth's atmosphere at 2.45 Ga.

  7. Thermal Stratification in Vertical Mantle Tanks

    DEFF Research Database (Denmark)

    Knudsen, Søren; Furbo, Simon


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

  8. Microbial populations in contaminant plumes (United States)

    Haack, Sheridan K.; Bekins, Barbara A.

    Efficient biodegradation of subsurface contaminants requires two elements: (1) microbial populations with the necessary degradative capabilities, and (2) favorable subsurface geochemical and hydrological conditions. Practical constraints on experimental design and interpretation in both the hydrogeological and microbiological sciences have resulted in limited knowledge of the interaction between hydrogeological and microbiological features of subsurface environments. These practical constraints include: (1) inconsistencies between the scales of investigation in the hydrogeological and microbiological sciences, and (2) practical limitations on the ability to accurately define microbial populations in environmental samples. However, advances in application of small-scale sampling methods and interdisciplinary approaches to site investigations are beginning to significantly improve understanding of hydrogeological and microbiological interactions. Likewise, culture-based and molecular analyses of microbial populations in subsurface contaminant plumes have revealed significant adaptation of microbial populations to plume environmental conditions. Results of recent studies suggest that variability in subsurface geochemical and hydrological conditions significantly influences subsurface microbial-community structure. Combined investigations of site conditions and microbial-community structure provide the knowledge needed to understand interactions between subsurface microbial populations, plume geochemistry, and contaminant biodegradation. La biodégradation efficace des polluants souterrains requiert deux éléments: des populations microbiennes possédant les aptitudes nécessaires à la dégradation, et des conditions géochimiques et hydrologiques souterraines favorables. Des contraintes pratiques sur la conception et l'interprétation des expériences à la fois en microbiologie et en hydrogéologie ont conduit à une connaissance limitée des interactions entre les

  9. Diamond growth in mantle fluids (United States)

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


    In the upper mantle, diamonds can potentially grow from various forms of media (solid, gas, fluid) with a range of compositions (e.g. graphite, C-O-H fluids, silicate or carbonate melts). Inclusions trapped in diamonds are one of the few diagnostic tools that can constrain diamond growth conditions in the Earth's mantle. In this study, inclusion-bearing diamonds have been synthesized to understand the growth conditions of natural diamonds in the upper mantle. Diamonds containing syngenetic inclusions were synthesized in multi-anvil presses employing starting mixtures of carbonates, and silicate compositions in the presence of pure water and saline fluids (H2O-NaCl). Experiments were performed at conditions compatible with the Earth's geotherm (7 GPa, 1300-1400 °C). Results show that within the timescale of the experiments (6 to 30 h) diamond growth occurs if water and carbonates are present in the fluid phase. Water promotes faster diamond growth (up to 14 mm/year at 1400 °C, 7 GPa, 10 g/l NaCl), which is favorable to the inclusion trapping process. At 7 GPa, temperature and fluid composition are the main factors controlling diamond growth. In these experiments, diamonds grew in the presence of two fluids: an aqueous fluid and a hydrous silicate melt. The carbon source for diamond growth must be carbonate (CO32) dissolved in the melt or carbon dioxide species in the aqueous fluid (CO2aq). The presence of NaCl affects the growth kinetics but is not a prerequisite for inclusion-bearing diamond formation. The presence of small discrete or isolated volumes of water-rich fluids is necessary to grow inclusion-bearing peridotitic, eclogitic, fibrous, cloudy and coated diamonds, and may also be involved in the growth of ultradeep, ultrahigh-pressure metamorphic diamonds.

  10. Analysis of plasmaspheric plumes: CLUSTER and IMAGE observations and numerical simulations (United States)

    Darouzet, Fabien; DeKeyser, Johan; Decreau, Pierrette; Gallagher, Dennis; Pierrard, Viviane; Lemaire, Joseph; Dandouras, Iannis; Matsui, Hiroshi; Dunlop, Malcolm; Andre, Mats


    Plasmaspheric plumes have been routinely observed by CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. Total electron density profiles can be derived from the plasma frequency and/or from the spacecraft potential (note that the electron spectrometer is usually not operating inside the plasmasphere); ion velocity is also measured onboard these satellites (but ion density is not reliable because of instrumental limitations). The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 RE every 10 minutes; such images acquired near apogee from high above the pole show the geometry of plasmaspheric plumes, their evolution and motion. We present coordinated observations for 3 plume events and compare CLUSTER in-situ data (panel A) with global images of the plasmasphere obtained from IMAGE (panel B), and with numerical simulations for the formation of plumes based on a model that includes the interchange instability mechanism (panel C). In particular, we study the geometry and the orientation of plasmaspheric plumes by using a four-point analysis method, the spatial gradient. We also compare several aspects of their motion as determined by different methods: (i) inner and outer plume boundary velocity calculated from time delays of this boundary observed by the wave experiment WHISPER on the four spacecraft, (ii) ion velocity derived from the ion spectrometer CIS onboard CLUSTER, (iii) drift velocity measured by the electron drift instrument ED1 onboard CLUSTER and (iv) global velocity determined from successive EUV images. These different techniques consistently indicate that plasmaspheric plumes rotate around the Earth, with their foot fully co-rotating, but with their tip rotating slower and moving farther out.

  11. Analysis of plasmaspheric plumes: CLUSTER and IMAGE observations and numerical simulations (United States)

    Darouzet, Fabien; DeKeyser, Johan; Decreau, Pierrette; Gallagher, Dennis; Pierrard, Viviane; Lemaire, Joseph; Dandouras, Iannis; Matsui, Hiroshi; Dunlop, Malcolm; Andre, Mats


    Plasmaspheric plumes have been routinely observed by CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. Total electron density profiles can be derived from the plasma frequency and/or from the spacecraft potential (note that the electron spectrometer is usually not operating inside the plasmasphere); ion velocity is also measured onboard these satellites (but ion density is not reliable because of instrumental limitations). The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 RE every 10 minutes; such images acquired near apogee from high above the pole show the geometry of plasmaspheric plumes, their evolution and motion. We present coordinated observations for 3 plume events and compare CLUSTER in-situ data (panel A) with global images of the plasmasphere obtained from IMAGE (panel B), and with numerical simulations for the formation of plumes based on a model that includes the interchange instability mechanism (panel C). In particular, we study the geometry and the orientation of plasmaspheric plumes by using a four-point analysis method, the spatial gradient. We also compare several aspects of their motion as determined by different methods: (i) inner and outer plume boundary velocity calculated from time delays of this boundary observed by the wave experiment WHISPER on the four spacecraft, (ii) ion velocity derived from the ion spectrometer CIS onboard CLUSTER, (iii) drift velocity measured by the electron drift instrument ED1 onboard CLUSTER and (iv) global velocity determined from successive EUV images. These different techniques consistently indicate that plasmaspheric plumes rotate around the Earth, with their foot fully co-rotating, but with their tip rotating slower and moving farther out.

  12. PlumeSat: A Micro-Satellite Based Plume Imagery Collection Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Ledebuhr, A.G.; Ng, L.C.


    This paper describes a technical approach to cost-effectively collect plume imagery of boosting targets using a novel micro-satellite based platform operating in low earth orbit (LEO). The plume collection Micro-satellite or PlueSat for short, will be capable of carrying an array of multi-spectral (UV through LWIR) passive and active (Imaging LADAR) sensors and maneuvering with a lateral divert propulsion system to different observation altitudes (100 to 300 km) and different closing geometries to achieve a range of aspect angles (15 to 60 degrees) in order to simulate a variety of boost phase intercept missions. The PlumeSat will be a cost effective platform to collect boost phase plume imagery from within 1 to 10 km ranges, resulting in 0.1 to 1 meter resolution imagery of a variety of potential target missiles with a goal of demonstrating reliable plume-to-hardbody handover algorithms for future boost phase intercept missions. Once deployed on orbit, the PlumeSat would perform a series phenomenology collection experiments until expends its on-board propellants. The baseline PlumeSat concept is sized to provide from 5 to 7 separate fly by data collects of boosting targets. The total number of data collects will depend on the orbital basing altitude and the accuracy in delivering the boosting target vehicle to the nominal PlumeSat fly-by volume.

  13. Extensional crustal tectonics and crust-mantle coupling, a view from the geological record (United States)

    Jolivet, Laurent; Menant, Armel; Clerc, Camille; Sternai, Pietro; Ringenbach, Jean-Claude; Bellahsen, Nicolas; Leroy, Sylvie; Faccenna, Claudio; Gorini, Christian


    In passive margins or back-arc regions, extensional deformation is often asymmetric, i.e. normal faults or extensional ductile shear zones dip in the same direction over large distances. We examine a number of geological examples in convergent or divergent contexts suggesting that this asymmetry results from a coupling between asthenospheric flow and crustal deformation. This is the case of the Mediterranean back-arc basins, such as the Aegean Sea, the northern Tyrrhenian Sea, the Alboran domain or the Gulf of Lion passive margin. Similar types of observation can be made on some of the Atlantic volcanic passive margins and the Afar region, which were all formed above a mantle plume. We discuss these contexts and search for the main controlling parameters for this asymmetric distributed deformation that imply a simple shear component at the scale of the lithosphere. The different geodynamic settings and tectonic histories of these different examples provide natural case-studies of the different controlling parameters, including a pre-existing heterogeneity of the crust and lithosphere (tectonic heritage) and the possible contribution of the underlying asthenospheric flow through basal drag or basal push. We show that mantle flow can induce deformation in the overlying crust in case of high heat flow and thin lithosphere. In back-arc regions, the cause of asymmetry resides in the relative motion between the asthenosphere below the overriding plate and the crust. When convergence and slab retreat work concurrently the asthenosphere flows faster than the crust toward the trench and the sense of shear is toward the upper plate. When slab retreat is the only cause of subduction, the sense of shear is opposite. In both cases, mantle flow is mostly the consequence of slab retreat and convergence. Mantle flow can however result also from larger-scale convection, controlling rifting dynamics prior to the formation of oceanic crust. In volcanic passive margins, in most cases

  14. The role of solid-solid phase transitions in mantle convection (United States)

    Faccenda, Manuele; Dal Zilio, Luca


    With changing pressure and temperature conditions, downwelling and upwelling crustal and mantle rocks experience several solid-solid phase transitions that affect the mineral physical properties owing to structural changes in the crystal lattice and to the absorption or release of latent heat. Variations in density, together with phase boundary deflections related to the non-null reaction slope, generate important buoyancy forces that add to those induced by thermal perturbations. These buoyancy forces are proportional to the density contrast between reactant and product phases, their volume fraction, the slope and the sharpness of the reaction, and affect the style of mantle convection depending on the system composition. In a homogeneous pyrolitic mantle there is little tendency for layered convection, with slabs that may stagnate in the transition zone because of the positive buoyancy caused by post-spinel and post-ilmenite reactions, and hot plumes that are accelerated by phase transformations in the 600-800 km depth range. By adding chemical and mineralogical heterogeneities as on Earth, phase transitions introduce bulk rock and volatiles filtering effects that generate a compositional gradient throughout the entire mantle, with levels that are enriched or depleted in one or more of these components. Phase transitions often lead to mechanical softening or hardening that can be related to a different intrinsic mechanical behaviour and volatile solubility of the product phases, the heating or cooling associated with latent heat, and the transient grain size reduction in downwelling cold material. Strong variations in viscosity would enhance layered mantle convection, causing slab stagnation and plume ponding. At low temperatures and relatively dry conditions, reactions are delayed due to the sluggish kinetics, so that non-equilibrium phase aggregates can persist metastably beyond the equilibrium phase boundary. Survival of low-density metastable olivine

  15. Coronal Plumes in the Fast Solar Wind (United States)

    Velli, Marco; Lionello, Roberto; Linker, Jon A.; Mikic, Zoran


    The expansion of a coronal hole filled with a discrete number of higher density coronal plumes is simulated using a time-dependent two-dimensional code. A solar wind model including an exponential coronal heating function and a flux of Alfven waves propagating both inside and outside the structures is taken as a basic state. Different plasma plume profiles are obtained by using different scale heights for the heating rates. Remote sensing and solar wind in situ observations are used to constrain the parameter range of the study. Time dependence due to plume ignition and disappearance is also discussed. Velocity differences of the order of approximately 50 km/s, such as those found in microstreams in the high-speed solar wind, may be easily explained by slightly different heat deposition profiles in different plumes. Statistical pressure balance in the fast wind data may be masked by the large variety of body and surface waves which the higher density filaments may carry, so the absence of pressure balance in the microstreams should not rule out their interpretation as the extension of coronal plumes into interplanetary space. Mixing of plume-interplume material via the Kelvin-Helmholtz instability seems to be possible within the parameter ranges of the models defined here, only at large di stances from the Sun, beyond 0.2-0.3 AU. Plasma and composition measurements in the inner heliosphere, such as those which will become available with Solar Orbiter and Solar Probe Plus, should therefore definitely be able to identify plume remnants in the solar wind.

  16. Wind-Forced Baroclinic Beta-Plumes (United States)

    Belmadani, A.; Maximenko, N. A.; Melnichenko, O.; Schneider, N.; Di Lorenzo, E.


    A planetary beta-plume is a classical example of oceanic circulation induced by a localized vorticity source or sink that allows an analytical description in simplistic cases. Its barotropic structure is a zonally-elongated, gyre-like cell governed by the Sverdrup circulation on the beta-plane. The dominant zonal currents, found west of the source/sink, are often referred to as zonal jets. This simple picture describes the depth-integrated flow. Previous studies have investigated beta-plumes in a reduced-gravity framework or using other simple models with a small number of vertical layers, thereby lacking representation of the vertical structure. In addition, most previous studies use a purely linear regime without considering the role of eddies. However, these jets are often associated with strong lateral shear that makes them unstable under increased forcing. The circulation in such a nonlinear regime may involve eddy-mean flow interactions, which modify the time-averaged circulation. Here, the baroclinic structures of linear and nonlinear wind-forced beta-plumes are studied using a continuously-stratified, primitive equation, eddy-permitting ocean model (ROMS). The model is configured in an idealized rectangular domain for the subtropical ocean with a flat bottom. The surface wind forcing is a steady anticyclonic Gaussian wind vortex, which provides a localized vorticity source in the center of the domain. The associated wind stress curl and Ekman pumping comprise downwelling in the vortex center surrounded by a ring of weaker upwelling. Under weak forcing, the simulated steady-state circulation corresponds well with a theoretical linear beta-plume. While its depth-integrated transport exhibits a set of zonal jets, consistent with Sverdrup theory, the baroclinic structure of the plume is remarkably complex. Relatively fast westward decay of the surface currents occurs simultaneously with the deepening of the lower boundary of the plume. This deepening suggests

  17. Confirmation of Water Plumes on Europa (United States)

    Sparks, William

    Evidence was found for plumes of water ice venting from the polar regions of Europa (Roth et al 2014a) - FUV detection of off-limb line emission from the dissociation products of water. We find additional evidence for the presence of ice plumes on Europa from HST transit imaging observations (Sparks et al 2016). The evidence for plumes remains marginal, 4-sigma, and there is considerable debate as to their reality. SOFIA can potentially resolve this issue with an unambiguous direct detection of water vapor using EXES. Detection of the fundamental vibrational mode of water vapor at 6 micron, as opposed to the atomic constituents of water, would prove that the plumes exist and inform us of their physical chemistry through quantitative consideration of the balance between water vapor and its dissociation products, hydrogen and oxygen. We propose to obtain spectra of the leading and trailing hemispheres separately, with trailing as the higher priority. These provide two very different physical environments and plausibly different degrees of activity. If the plumes of Europa arise from the deep ocean, we have gained access to probably the most astrobiologically interesting location in the Solar System, and clarify an issue of major strategic importance in NASAs planning for its multi-billion dollar mission to Europa.

  18. Modelling of aerosol processes in plumes

    Energy Technology Data Exchange (ETDEWEB)

    Lazaridis, M.; Isukapalli, S.S.; Georgopoulos, P.G. [Norwegian Institute of Air Research, Kjeller (Norway)


    A modelling platform for studying photochemical gaseous and aerosol phase processes from localized (e.g., point) sources has been presented. The current approach employs a reactive plume model which extends the regulatory model RPM-IV by incorporating aerosol processes and heterogeneous chemistry. The physics and chemistry of elemental carbon, organic carbon, sulfate, nitrate, ammonium material of aerosols are treated and attributed to the PM size distribution. A modified version of the carbon bond IV chemical mechanism is included to model the formation of organic aerosol. Aerosol dynamics modeled include mechanisms of nucleation, condensation, dry deposition and gas/particle partitioning of organic matter. The model is first applied to a number of case studies involving emissions from point sources and sulfate particle formation in plumes. Model calculations show that homogeneous nucleation is an efficient process for new particle formation in plumes, in agreement with previous field studies and theoretical predictions. In addition, the model is compared with field data from power plant plumes with satisfactory predictions against gaseous species and total sulphate mass measurements. Finally, the plume model is applied to study secondary organic matter formation due to various emission categories such as vehicles and the oil production sector.

  19. Intermittent heat instabilities in an air plume (United States)

    Le Mouël, Jean-Louis; Kossobokov, Vladimir G.; Perrier, Frederic; Morat, Pierre


    We report the results of heating experiments carried out in an abandoned limestone quarry close to Paris, in an isolated room of a volume of about 400 m3. A heat source made of a metallic resistor of power 100 W was installed on the floor of the room, at distance from the walls. High-quality temperature sensors, with a response time of 20 s, were fixed on a 2 m long bar. In a series of 24 h heating experiments the bar had been set up horizontally at different heights or vertically along the axis of the plume to record changes in temperature distribution with a sampling time varying from 20 to 120 s. When taken in averages over 24 h, the temperatures present the classical shape of steady-state plumes, as described by classical models. On the contrary, the temperature time series show a rich dynamic plume flow with intermittent trains of oscillations, spatially coherent, of large amplitude and a period around 400 s, separated by intervals of relative quiescence whose duration can reach several hours. To our knowledge, no specific theory is available to explain this behavior, which appears to be a chaotic interaction between a turbulent plume and a stratified environment. The observed behavior, with first-order factorization of a smooth spatial function with a global temporal intermittent function, could be a universal feature of some turbulent plumes in geophysical environments.

  20. Near field characteristics of buoyant helium plumes

    Indian Academy of Sciences (India)

    Kuchimanchi K Bharadwaj; Debopam Das; Pavan K Sharma


    Puffing and entrainment characteristics of helium plumes emanating out into ambient air from a circular orifice are investigated in the present study. Velocity and density fields are measured across a diametric plane using Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) respectively in phase resolved manner. Experiments are performed in Froude numbers range 0.2–0.4 and for Reynolds numbers 58–248. Puffing frequency measurements reveal that the plume puffing frequencies are insensitive to the plume exit conditions, since the instability is buoyancy driven. The frequencies obtained in the present case are in agreement with frequencies obtained by Cetegen & Kasper (1996) for plumes originating from circular nozzles of various L/D ratios. Velocity and density measurements reveal that toroidal vortex formed during a puffing cycle entrains ambient air as it traverses downstream and this periodic engulfment governs the entrainment mechanism in pulsating plumes. The obtained velocity and density fields are used to calculate mass entrainment rates. It is revealed that though the flow is unsteady, the contribution of unsteady term in mass conservation to entrainment is negligible, and it becomes zero over a puff cycle. Finally, an empirical relation for variation of mass entrainment with height has been proposed, in which the non-dimensional mass entrainment is found to follow a power law with the non-dimensional height.

  1. Long-term, deep-mantle support of the Ethiopia-Yemen Plateau (United States)

    Sembroni, Andrea; Faccenna, Claudio; Becker, Thorsten W.; Molin, Paola; Abebe, Bekele


    Ethiopia is a key site to investigate the interactions between mantle dynamics and surface processes because of the presence of the Main Ethiopian Rift (MER), Cenozoic continental flood basalt volcanism, and plateau uplift. The role of mantle plumes in causing Ethiopia's flood basalts and tectonics has been commonly accepted. However, the location and number of plumes and their impact on surface uplift are still uncertain. Here, we present new constraints on the geological and topographic evolution of the Ethiopian Plateau (NW Ethiopia) prior to and after the emplacement of the large flood basalts (40-20 Ma). Using geological information and topographic reconstructions, we show that the large topographic dome that we see today is a long-term feature, already present prior the emplacement of the flood basalts. We also infer that large-scale doming operated even after the emplacement of the flood basalts. Using a comparison with the present-day topographic setting we show that an important component of the topography has been and is presently represented by a residual, non-isostatic, dynamic contribution. We conclude that the growth of the Ethiopian Plateau is a long-term, probably still active, dynamically supported process. Our arguments provide constraints on the processes leading to the formation of one of the largest igneous plateaus on Earth.

  2. Plume composition and volatile flux from Nyamulagira volcano (United States)

    Calabrese, Sergio; Bobrowski, Nicole; Giuffrida, Giovanni Bruno; Scaglione, Sarah; Liotta, Marcello; Brusca, Lorenzo; D'Alessandro, Walter; Arellano, Santiago; Yalire, Matiew; Galle, Bo; Tedesco, Dario


    applied inside the crater as well as downwind the volcano and active alkaline traps (Raschig-Tube and Drechsel bottle) were exposed. The alkaline solution traps acidic species (CO2, SO2, H2S, HCl, HF, HBr, HI) due to the acid-base reactions. Moreover, filter packs technique have also been used to collect both the volatile phase of the plume (sulphur and halogen species) and the particulate phase (major and trace metals) emitted from the volcano. These new results will add to our lacking knowledge of volcanic degassing in VVP, and will increase constraints on the abundances and origins of volatiles from the mantle source which feeds volcanism in the western branch of the EARS.

  3. Deep Mantle Seismic Modeling and Imaging (United States)

    Lay, Thorne; Garnero, Edward J.


    Detailed seismic modeling and imaging of Earth's deep interior is providing key information about lower-mantle structures and processes, including heat flow across the core-mantle boundary, the configuration of mantle upwellings and downwellings, phase equilibria and transport properties of deep mantle materials, and mechanisms of core-mantle coupling. Multichannel seismic wave analysis methods that provide the highest-resolution deep mantle structural information include network waveform modeling and stacking, array processing, and 3D migrations of P- and S-wave seismograms. These methods detect and identify weak signals from structures that cannot be resolved by global seismic tomography. Some methods are adapted from oil exploration seismology, but all are constrained by the source and receiver distributions, long travel paths, and strong attenuation experienced by seismic waves that penetrate to the deep mantle. Large- and small-scale structures, with velocity variations ranging from a fraction of a percent to tens of percent, have been detected and are guiding geophysicists to new perspectives of thermochemical mantle convection and evolution.

  4. Between a rock and a hot place: the core-mantle boundary. (United States)

    Wookey, James; Dobson, David P


    The boundary between the rocky mantle and iron core, almost 2900 km below the surface, is physically the most significant in the Earth's interior. It may be the terminus for subducted surface material, the source of mantle plumes and a control on the Earth's magnetic field. Its properties also have profound significance for the thermochemical and dynamic evolution of the solid Earth. Evidence from seismology shows that D'' (the lowermost few hundred kilometres of the mantle) has a variety of anomalous features. Understanding the origin of these observations requires an understanding of the elastic and deformation properties of the deep Earth minerals. Core-mantle boundary pressures and temperatures are achievable in the laboratory using diamond anvil cell (DAC) apparatus. Such experiments have led to the recent discovery of a new phase, 'post-perovskite', which may explain many hitherto poorly understood properties of D''. Experimental work is also done using analogue minerals at lower pressures and temperatures; these circumvent some of the limits imposed by the small sample size allowed by the DAC. A considerable contribution also comes from theoretical methods that provide a wealth of otherwise unavailable information, as well as verification and refinement of experimental results. The future of the study of the lowermost mantle will involve the linking of the ever-improving seismic observations with predictions of material properties from theoretical and experimental mineral physics in a quantitative fashion, including simulations of the dynamics of the deep Earth. This has the potential to dispel much of the mystery that still surrounds this remote but important region.

  5. Simple model of a cooling tower plume (United States)

    Jan, Cizek; Jiri, Nozicka


    This article discusses the possibilities in the area of modeling of the so called cooling tower plume emergent at operating evaporating cooling systems. As opposed to recent publication, this text focuses on the possibilities of a simplified analytic description of the whole problem where this description shall - in the future - form the base of a calculation algorithms enabling to simulate the efficiency of systems reducing this cooling tower plume. The procedure is based on the application of basic formula for the calculation of the velocity and concentration fields in the area above the cooling tower. These calculation is then used to determine the form and the total volume of the plume. Although this approach does not offer more exact results, it can provide a basic understanding of the impact of individual quantities relating to this problem.

  6. A collisionless plasma thruster plume expansion model (United States)

    Merino, Mario; Cichocki, Filippo; Ahedo, Eduardo


    A two-fluid model of the unmagnetized, collisionless far region expansion of the plasma plume for gridded ion thrusters and Hall effect thrusters is presented. The model is integrated into two semi-analytical solutions valid in the hypersonic case. These solutions are discussed and compared against the results from the (exact) method of characteristics; the relative errors in density and velocity increase slowly axially and radially and are of the order of 10-2-10-3 in the cases studied. The plasma density, ion flux and ambipolar electric field are investigated. A sensitivity analysis of the problem parameters and initial conditions is carried out in order to characterize the far plume divergence angle in the range of interest for space electric propulsion. A qualitative discussion of the physics of the secondary plasma plume is also provided.

  7. Numerical and approximate solutions for plume rise (United States)

    Krishnamurthy, Ramesh; Gordon Hall, J.

    Numerical and approximate analytical solutions are compared for turbulent plume rise in a crosswind. The numerical solutions were calculated using the plume rise model of Hoult, Fay and Forney (1969, J. Air Pollut. Control Ass.19, 585-590), over a wide range of pertinent parameters. Some wind shear and elevated inversion effects are included. The numerical solutions are seen to agree with the approximate solutions over a fairly wide range of the parameters. For the conditions considered in the study, wind shear effects are seen to be quite small. A limited study was made of the penetration of elevated inversions by plumes. The results indicate the adequacy of a simple criterion proposed by Briggs (1969, AEC Critical Review Series, USAEC Division of Technical Information extension, Oak Ridge, Tennesse).

  8. Modeling the Enceladus plume--plasma interaction

    CERN Document Server

    Fleshman, B L; Bagenal, F


    We investigate the chemical interaction between Saturn's corotating plasma and Enceladus' volcanic plumes. We evolve plasma as it passes through a prescribed H2O plume using a physical chemistry model adapted for water-group reactions. The flow field is assumed to be that of a plasma around an electrically-conducting obstacle centered on Enceladus and aligned with Saturn's magnetic field, consistent with Cassini magnetometer data. We explore the effects on the physical chemistry due to: (1) a small population of hot electrons; (2) a plasma flow decelerated in response to the pickup of fresh ions; (3) the source rate of neutral H2O. The model confirms that charge exchange dominates the local chemistry and that H3O+ dominates the water-group composition downstream of the Enceladus plumes. We also find that the amount of fresh pickup ions depends heavily on both the neutral source strength and on the presence of a persistent population of hot electrons.

  9. Tomography images of the Alpine roots and surrounding upper mantle (United States)

    Plomerova, Jaroslava; Babuska, Vladislav


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

  10. Heat transfer correlations in mantle tanks

    DEFF Research Database (Denmark)

    Furbo, Simon; Knudsen, Søren


    Small solar domestic hot water systems are best designed as low flow systems based on vertical mantle tanks. Theoretical investigations of the heat transfer in differently designed vertical mantle tanks during different operation conditions have been carried out. The investigations are based...... of the inner hot water tank and the domestic water in all levels of the tank. The heat transfer analysis showed that the heat transfer near the mantle inlet port between the solar collector fluid in the mantle and the walls surrounding the mantle is in the mixed convection regime, and as the distance from...... the inlet increases, natural convection starts to dominate. The heat transfer between the wall of the inner hot water tank and the domestic water is governed by natural convection. The results of the CFD-calculations are used to determine improved heat transfer correlations based on dimensionless analysis...

  11. The geobiological nitrogen cycle: From microbes to the mantle. (United States)

    Zerkle, A L; Mikhail, S


    Nitrogen forms an integral part of the main building blocks of life, including DNA, RNA, and proteins. N2 is the dominant gas in Earth's atmosphere, and nitrogen is stored in all of Earth's geological reservoirs, including the crust, the mantle, and the core. As such, nitrogen geochemistry is fundamental to the evolution of planet Earth and the life it supports. Despite the importance of nitrogen in the Earth system, large gaps remain in our knowledge of how the surface and deep nitrogen cycles have evolved over geologic time. Here, we discuss the current understanding (or lack thereof) for how the unique interaction of biological innovation, geodynamics, and mantle petrology has acted to regulate Earth's nitrogen cycle over geologic timescales. In particular, we explore how temporal variations in the external (biosphere and atmosphere) and internal (crust and mantle) nitrogen cycles could have regulated atmospheric pN2 . We consider three potential scenarios for the evolution of the geobiological nitrogen cycle over Earth's history: two in which atmospheric pN2 has changed unidirectionally (increased or decreased) over geologic time and one in which pN2 could have taken a dramatic deflection following the Great Oxidation Event. It is impossible to discriminate between these scenarios with the currently available models and datasets. However, we are optimistic that this problem can be solved, following a sustained, open-minded, and multidisciplinary effort between surface and deep Earth communities. © 2017 The Authors Geobiology Published by John Wiley & Sons Ltd.

  12. Effects of meteorological conditions on spore plumes (United States)

    Burch, M.; Levetin, E.


    Fungal spores are an ever-present component of the atmosphere, and have long been known to trigger asthma and hay fever symptoms in sensitive individuals. The atmosphere around Tulsa has been monitored for airborne spores and pollen with Burkard spore traps at several sampling stations. This study involved the examination of the hourly spore concentrations on days that had average daily concentrations near 50,000 spores/m3 or greater. Hourly concentrations of Cladosporium, Alternaria, Epicoccum, Curvularia, Pithomyces, Drechslera, smut spores, ascospores, basidiospores, other, and total spores were determined on 4 days at three sites and then correlated with hourly meteorological data including temperature, rainfall, wind speed, dew point, air pressure, and wind direction. On each of these days there was a spore plume, a phenomenon in which spore concentrations increased dramatically over a very short period of time. Spore plumes generally occurred near midday, and concentrations were seen to increase from lows around 20,000 total spores/m3 to highs over 170,000 total spores/m3 in 2 h. Multiple regression analysis of the data indicated that increases in temperature, dew point, and air pressure correlated with the increase in spore concentrations, but no single weather variable predicted the appearance of a spore plume. The proper combination of changes in these meteorological parameters that result in a spore plume may be due to the changing weather conditions associated with thunderstorms, as on 3 of the 4 days when spore plumes occurred there were thunderstorms later that evening. The occurrence of spore plumes may have clinical significance, because other studies have shown that sensitization to certain spore types can occur during exposure to high spore concentrations.

  13. Cassini Radio Occultation by Enceladus Plume (United States)

    Kliore, A.; Armstrong, J.; Flasar, F.; French, R.; Marouf, E.; Nagy, A.; Rappaport, N.; McGhee, C.; Schinder, P.; Anabtawi, A.; Asmar, S.; Barbinis, E.; Fleischman, D.; Goltz, G.; Aguilar, R.; Rochblatt, D.


    A fortuitous Cassini radio occultation by Enceladus plume occurs on September 15, 2006. The occultation track (the spacecraft trajectory in the plane of the sky as viewed from the Earth) has been designed to pass behind the plume (to pass above the south polar region of Enceladus) in a roughly symmetrical geometry centered on a minimum altitude above the surface of about 20 km. The minimum altitude was selected primarily to ensure probing much of the plume with good confidence given the uncertainty in the spacecraft trajectory. Three nearly-pure sinusoidal signals of 0.94, 3.6, and 13 cm-wavelength (Ka-, X-, and S-band, respectively) are simultaneously transmitted from Cassini and are monitored at two 34-m Earth receiving stations of the Deep Space Network (DSN) in Madrid, Spain (DSS-55 and DSS-65). The occultation of the visible plume is extremely fast, lasting less than about two minutes. The actual observation time extends over a much longer time interval, however, to provide a good reference baseline for potential detection of signal perturbations introduced by the tenuous neutral and ionized plume environment. Given the likely very small fraction of optical depth due to neutral particles of sizes larger than about 1 mm, detectable changes in signal intensity is perhaps unlikely. Detection of plume plasma along the radio path as perturbations in the signals frequency/phase is more likely and the magnitude will depend on the electron columnar density probed. The occultation time occurs not far from solar conjunction time (Sun-Earth-probe angle of about 33 degrees), causing phase scintillations due to the solar wind to be the primary limiting noise source. We estimate a delectability limit of about 1 to 3E16 electrons per square meter columnar density assuming about 100 seconds integration time. Potential measurement of the profile of electron columnar density along the occultation track is an exciting prospect at this time.

  14. Plume head - trench interaction: impact on subduction dynamics (United States)

    Betts, P. G.; Moresi, L. N.; Mason, W. G.; Willis, D.


    The geologic record provides numerous examples where plumes and their associated buoyancy swell have disrupted convergent plate margins. These interactions have produced a variety of responses in the overriding plate including transient episodes of arc amagmatism, transient episodes of crustal shortening followed by plume-related magmatism in the overriding plate. The latter observation implies the plume must have transitioned from the subducting plate to the overriding plate. We present several 3D Underworld numerical models of plume heads of variable dimension and buoyancy interacting with a subduction trench. The models indicate that plume heads impact enormously on trench geometry. Arcuate trenches are created as the trench retreats around the edges of the plume head, whereas trench advance occurs in front of the plume resulting in transient crustal shortening in the overriding plate. Stalling of subduction when the plume head impacts the trench causes slab windowing. The size of the slab window is dependent on the size and buoyancy of the plume. The creation of the slab window provides a potential conduit for plume migration to the overriding plate. Alternatively, the plume head may be transferred to the overriding plate as subduction is re-established behind the plume. Models with "strong" slabs, characterized by high yield strengths, display different behavior. Plume-heads are entrained in the slab and are subducted without the development of a slab window.

  15. EUV Sunspot Plumes Observed with SOHO

    CERN Document Server

    Maltby, P; Brekke, P; Haugan, S V H; Kjeldseth-Moe, O; Wikstøl, O; Rimmele, T R; Wikstøl, O


    Bright EUV sunspot plumes have been observed in five out of nine sunspot regions with the Coronal Diagnostic Spectrometer -- CDS on SOHO. In the other four regions the brightest line emissions may appear inside the sunspot but are mainly concentrated in small regions outside the sunspot areas. These results are in contrast to those obtained during the Solar Maximum Mission, but are compatible with the Skylab mission results. The present observations show that sunspot plumes are formed in the upper part of the transition region, occur both in magnetic unipolar-- and bipolar regions, and may extend from the umbra into the penumbra.

  16. Halogen Chemistry in Volcanic Plumes (Invited) (United States)

    Roberts, Tjarda


    Volcanoes release vast amounts of gases and particles in the atmosphere. Volcanic halogens (HF, HCl, HBr, HI) are co-emitted alongside SO2, and observations show rapid formation of BrO and OClO in the plume as it disperses into the troposphere. The development of 1D and Box models (e.g. PlumeChem) that simulate volcanic plume halogen chemistry aims to characterise how volcanic reactive halogens form and quantify their atmospheric impacts. Following recent advances, these models can broadly reproduce the observed downwind BrO/SO2 ratios using "bromine-explosion" chemistry schemes, provided they use a "high-temperature initialisation" to inject radicals (OH, Cl, Br and possibly NOx) which "kick-start" the low-temperature chemistry cycles that convert HBr into reactive bromine (initially as Br2). The modelled rise in BrO/SO2 and subsequent plateau/decline as the plume disperses downwind reflects cycling between reactive bromine, particularly Br-BrO, and BrO-HOBr-BrONO2. BrCl is produced when aerosol becomes HBr-depleted. Recent model simulations suggest this mechanism for reactive chlorine formation can broadly account for OClO/SO2 reported at Mt Etna. Predicted impacts of volcanic reactive halogen chemistry include the formation of HNO3 from NOx and depletion of ozone. This concurs with HNO3 widely reported in volcanic plumes (although the source of NOx remains under question), as well as observations of ozone depletion reported in plumes from several volcanoes (Mt Redoubt, Mt Etna, Eyjafjallajokull). The plume chemistry can transform mercury into more easily deposited and potentially toxic forms, for which observations are limited. Recent incorporation of volcanic halogen chemistry in a 3D regional model of degassing from Ambrym (Vanuatu) also predicts how halogen chemistry causes depletion of OH to lengthen the SO2 lifetime, and highlights the potential for halogen transport from the troposphere to the stratosphere. However, the model parameter-space is vast and

  17. The upper mantle structure of the Tibetan Plateau and its implication for the continent-continent collision

    Institute of Scientific and Technical Information of China (English)

    WU; Qingju; ZENG; Rongsheng; ZHAO; Wenjin


    The upper mantle structures of Himalayas-Tibet have been obtained from the migration of receiver functions of the teleseismic events recorded by INDEPTH-III. The result of migration imaging shows a dipping interface subducting northward from the depth of 100 km to the 410-km discontinuity underneath southern Tibet. It indicates that the lithospheric mantle of the Indian continent had been detached from the crust and deeply subducted to the upper mantle of Eurasia during the Indo-Eurasian collision. This kind of continent-continent collision process is fundamentally different from the oceanic collision.

  18. New method for calculation of integral characteristics of thermal plumes

    DEFF Research Database (Denmark)

    Zukowska, Daria; Popiolek, Zbigniew; Melikov, Arsen Krikor


    A method for calculation of integral characteristics of thermal plumes is proposed. The method allows for determination of the integral parameters of plumes based on speed measurements performed with omnidirectional low velocity thermoanemometers. The method includes a procedure for calculation...

  19. New method for calculation of integral characteristics of thermal plumes

    DEFF Research Database (Denmark)


    A method for calculation of integral characteristics of thermal plumes is proposed. The method allows for determination of the integral parameters of plumes based on speed measurements performed with omnidirectional low velocity thermoanemometers. The method includes a procedure for calculation...

  20. Phosphorus-bearing Aerosol Particles From Volcanic Plumes (United States)

    Obenholzner, J. H.; Schroettner, H.; Poelt, P.; Delgado, H.; Caltabiano, T.


    Particles rich in P or bulk geochemical data of volcanic aerosol particles showing high P contents are known from many volcanic plumes (Stanton, 1994; Obenholzner et al., 2003). FESEM/EDS analysis of individual particles obtained from the passively degassing plume of Popocatepetl volcano, Mx. (1997) and from the plume of Stromboli (May 2003) show P frequently. Even at the high resolution of the FESEM, euhedral apatite crystals could not be observed. At Popocatepetl (1997) spherical Ca-P-O particles are common. Fluffy, fractal or botryoidal particles also can contain EDS-detectable amounts of P. The EDS spectrum of such particles can comprise various elements. However most particles show P, S and Cl. P-S and P-S-metal species are known in chemistry but do they occur in volcanic plumes? Stoichiometric considerations had been made in the past suggesting the existence of P-S species in plumes (Stanton 1994), gas sampling and remote gas monitoring systems have not detected yet such molecules in plumes. The particle spectrum of the reawakened Popocateptel volcano might be related to accumulation of volatiles at the top of a magma chamber during the phase of dormancy. P-Fe rich, Ca-free aggregates are also known from the eruption of El Chichon 1982 (SEM/EDS by M. Sheridan, per. comm. 08-24-2003). Persistently active volcanoes (i.e. Stromboli) represent a different category according to continuous degassing and aerosol particle formation. A particle collector ( ca. 90 ml/min) accompanied a COSPEC helicopter flight at Stromboli (May 15, 2003) after one of the rare types of sub-plinian events on April 5 2003. P-bearing particles are very common. For instance, an Fe oxide grain (diam. = 2 æm) is partially covered by fluffy and euhedral P-bearing matter. The elements detected are P, Cl, Na, Mg, Al, Si, K, Ca, Ti and (Fe). The fluffy and the euhedral (rhombohedral?) matter show in SE-BSE-mix image almost identical grey colors. At Stromboli and Popocatepetl particles on which

  1. The Upper Mantle Flow Field around South-Africa as Reflected by Isotopic Provinciality (United States)

    Meyzen, C.; Blichert-Toft, J.; Ludden, J.; Humler, E.; Mevel, C.; Albarede, F.


    Isotopic studies of MORB have established the existence of broad isotopic provinces within the underlying asthenosphere, such as in the Indian Ocean (DUPAL). How these features relate to mantle circulation is, however, still unknown. The steepness of the transition between such isotopic provinces will define the geometry of the velocity field in the upper mantle. In this respect, the transition between the Indian and South Atlantic provinces, two domains that are isotopically contrasted, should be readily identifiable over this long ridge segment. Here, we present Hf isotope data for 60 samples dredged along the SWIR between 35° and 69°E. The new Hf isotope data show that the Indian asthenosphere does not spill directly into the South Atlantic upper mantle: the general decreasing southward gradient observed for ^{176}Hf/^{177}Hf down the mid- Atlantic Ridge, and also for Sr isotopes and model Th/U ratios (derived from Pb isotopes), is overprinted by material with radiogenic Sr, unradiogenic Hf and high Th/U. The Indian domain grades into the South Atlantic around Bouvet, while the South Atlantic collides with the Atlantic province around Tristan. We interpret these features to represent fronts between three adjacent isotopic provinces similar to what has been suggested for the Australian-Antarctic Discordance. The common DUPAL signature of MORB and OIB from the Indian province and the geochemistry of Gulf of Aden MORB and the Afar plume suggest that the source of this distinctive mantle component is deep and lies to the north of the province. This is also what the three-dimensional flow field computed by Behn et al. (2004) from shear-wave splitting shows with a major lower mantle upwelling radiating at the base of the asthenosphere under the Afar plume. Lower mantle gushing out from this source flows southward unimpeded along the Indian ridges, whereas it only reaches the South Atlantic ridge after first having been deflected under the deep roots of the South

  2. Upper and mid mantle fabric developing during subduction-induced mantle flow (United States)

    Faccenda, Manuele


    Subduction zones are convergent margins where the rigid lithosphere sinks into the Earth's mantle inducing complex 3D flow patterns. Seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals is commonly used to study flow in the mantle and its relations with plate motions. We computed the seismic anisotropy of the upper and mid mantle due to strain-induced LPO in 3D mechanical models of dynamic subduction by using, respectively, D-Rex and Underworld. Subsequently, FSTRACK was used to compute seismogram synthetics and SKS splitting patterns. Strong anisotropy develops in the upper mantle, while weak or null seismic anisotropy is formed in the upper transition zone/lower mantle and lower transition zone, respectively. The distribution of the fabric in the mantle depends on the distribution and amount of the deformation, and not on the rate at which the slab subducts. The SKS splitting patterns are controlled by the anisotropy in the upper mantle because SKS waves are more sensitive to the anisotropy in the shallowest layers. Horizontally propagating shear waves in the mid mantle originating from local earthquakes are characterized by significant splitting that is mostly due to the fabric in the uppermost lower mantle. We discuss the implications of our results for real subduction settings like Tonga, where a discrete amount of observations have been collected in the past 10 years on the anisotropy in the upper and mid mantle.

  3. Visualising volcanic gas plumes with virtual globes (United States)

    Wright, T. E.; Burton, M.; Pyle, D. M.; Caltabiano, T.


    The recent availability of small, cheap ultraviolet spectrometers has facilitated the rapid deployment of automated networks of scanning instruments at several volcanoes, measuring volcanic SO 2 gas flux at high frequency. These networks open up a range of other applications, including tomographic reconstruction of the gas distribution which is of potential use for both risk mitigation, particularly to air traffic, and environmental impact modelling. Here we present a methodology for visualising reconstructed plumes using virtual globes, such as Google Earth, which allows animations of the evolution of the gas plume to be displayed and easily shared on a common platform. We detail the process used to convert tomographically reconstructed cross-sections into animated gas plume models, describe how this process is automated and present results from the scanning network around Mt. Etna, Sicily. We achieved an average rate of one frame every 12 min, providing a good visual representation of the plume which can be examined from all angles. In creating these models, an approximation to turbulent diffusion in the atmosphere was required. To this end we derived the value of the turbulent diffusion coefficient for quiescent conditions near Etna to be around 200- 500m2s-1.

  4. Detection of contaminant plumes released from landfills (United States)

    Yenigül, N. B.; Hendsbergen, A. T.; Elfeki, A. M. M.; Dekking, F. M.


    Contaminant leaks released from landfills are a significant threat to groundwater quality. The groundwater detection monitoring systems installed in the vicinity of such facilities are vital. In this study the detection probability of a contaminant plume released from a landfill has been investigated by means of both a simulation and an analytical model for both homogeneous and heterogeneous aquifer conditions. The results of the two models are compared for homogeneous aquifer conditions to illustrate the errors that might be encountered with the simulation model. For heterogeneous aquifer conditions contaminant transport is modelled by an analytical model using effective (macro) dispersivities. The results of the analysis show that the simulation model gives the concentration values correctly over most of the plume length for homogeneous aquifer conditions, and that the detection probability of a contaminant plume at given monitoring well locations match quite well. For heterogeneous aquifer conditions the approximating analytical model based on effective (macro) dispersivities yields the average concentration distribution satisfactorily. However, it is insufficient in monitoring system design since the discrepancy between the detection probabilities of contaminant plumes at given monitoring well locations computed by the two models is significant, particularly with high dispersivity and heterogeneity.

  5. Diagnostics of laser ablated plasma plumes

    DEFF Research Database (Denmark)

    Amoruso, S.; Toftmann, B.; Schou, Jørgen;


    The effect of an ambient gas on the expansion dynamics of laser ablated plasmas has been studied for two systems by exploiting different diagnostic techniques. First, the dynamics of a MgB2 laser produced plasma plume in an Ar atmosphere has been investigated by space-and time-resolved optical...

  6. Ablation plume dynamics in a background gas

    DEFF Research Database (Denmark)

    Amoruso, Salvatore; Schou, Jørgen; Lunney, James G.


    The expansion of a plume in a background gas of pressure comparable to that used in pulsed laser deposition (PLD) has been analyzed in terms of the model of Predtechensky and Mayorov (PM). This approach gives a relatively clear and simple description of the essential hydrodynamics during the expa...

  7. DSMC simulation of Europa water vapor plumes (United States)

    Berg, J. J.; Goldstein, D. B.; Varghese, P. L.; Trafton, L. M.


    A computational investigation of the physics of water vapor plumes on Europa was performed with a focus on characteristics relevant to observation and spacecraft mission operations. The direct simulation Monte Carlo (DSMC) method was used to model the plume expansion assuming a supersonic vent source. The structure of the plume was determined, including the number density, temperature, and velocity fields. The possibility of ice grain growth above the vent was considered and deemed probable for large (diameter > ∼20 m) vents at certain Mach numbers. Additionally, preexisting grains of three diameters (0.1, 1, 50 μm) were included and their trajectories examined. A preliminary study of photodissociation of H2O into OH and H was performed to demonstrate the behavior of daughter species. A set of vent parameters was evaluated including Mach number (Mach 2, 3, 5), reduced temperature as a proxy for flow energy loss to the region surrounding the vent, and mass flow rate. Plume behavior was relatively insensitive to these factors, with the notable exception of mass flow rate. With an assumed mass flow rate of ∼1000 kg/s, a canopy shock occurred and a maximum integrated line of sight column density of ∼1020 H2O molecules/m2 was calculated, comparing favorably with observation (Roth et al., 2014a).

  8. Propagation of light through ship exhaust plumes

    NARCIS (Netherlands)

    Iersel, M. van; Mack, A.; Eijk, A.M.J. van; Schleijpen, H.M.A.


    Looking through the atmosphere, it is sometimes difficult to see the details of an object. Effects like scintillation and blur are the cause of these difficulties. Exhaust plumes of e.g. a ship can cause extreme scintillation and blur, making it even harder to see the details of what lies behind the

  9. Plume dynamics in heterogeneous porous media (United States)

    Neufeld, Jerome A.; Huppert, Herbert E.


    Buoyancy driven flows in layered porous media are present in many geological settings and play an important role in the mixing of fluids, from the dispersal of pollutants in underground aquifers to enhanced oil recovery techniques and, of more recent importance, the sequestration of carbon dioxide (CO2). Seismic images of the rise of a buoyant CO2 plume at Sleipner in the North Sea indicate that these plumes are greatly influenced by a vertical array of thin lenses of relatively low permeability material. We model propagation of CO2 at each layer as a gravity current in a porous medium which propagates along, and drains through, a thin, low permeability seal. Drainage, driven both by hydrostatic pressure and the body force on the draining fluid, leads to an initial rapid advance followed by a gradual retreat of the current to a steady-state. By incorporating a vertical array of these single layer models we are able to capture the rise of the buoyant plume in layered reservoirs. We find that the plume is characterized by a broad head with a tail given by the steady state extent.

  10. DSMC simulation of Io's unsteady Tvashtar plume (United States)

    Hoey, W. A.; Ackley, P. C.; Trafton, L. M.; Goldstein, D. B.; Varghese, P. L.


    Jupiter's moon Io supports its rarefied atmosphere with prolific tidally-driven episodic volcanism. Its largest volcanic plumes erupt violently and exhibit intricate structure, their canopies rising to hundreds of km above the Ionian surface. In early 2007, the NASA New Horizons (NH) spacecraft captured the active Tvashtar plume in a time sequence of panchromatic images at high spatial resolution and observed both discrete "filamentary" patterns in the descending particulate structure, and a prominent traveling canopy wave. These are transient and asymmetric features, indicative of Tvashtar's unresolved and complex vent processes. In this work, we introduce a methodology for identifying vent spatial and temporal scales in the rarefied plume. Three-dimensional DSMC simulations of the collisional gas flowfield are combined with a flow-tracking dust particle model, enabling a broad exploration of parameter space in pursuit of the critical frequencies that qualitatively reproduce the dynamical phenomena observed in Tvashtar's collisional canopy and providing insight into the dynamics of transient extra-terrestrial volcanic plumes.

  11. Relative Abundance Measurements in Plumes and Interplumes

    CERN Document Server

    Guennou, Chloé; Savin, Daniel Wolf


    We present measurements of relative elemental abundances in plumes and interplumes. Plumes are bright, narrow structures in coronal holes that extend along open magnetic field lines far out into the corona. Previous work has found that in some coronal structures the abundances of elements with a low first ionization potential (FIP) 10 eV). We have used EIS spectroscopic observations made on 2007 March 13 and 14 over an ~24 hour period to characterize abundance variations in plumes and interplumes. To assess their elemental composition, we have used a differential emission measure (DEM) analysis, which accounts for the thermal structure of the observed plasma. We have used lines from ions of iron, silicon, and sulfur. From these we have estimated the ratio of the iron and silicon FIP bias relative to that for sulfur. From the results, we have created FIP-bias-ratio maps. We find that the FIP-bias ratio is sometimes higher in plumes than in interplumes and that this enhancement can be time dependent. These res...

  12. Mantle wedge dynamics from seismic anisotropy (Invited) (United States)

    Long, M. D.; Wirth, E. A.


    The mantle wedge above subducting slabs plays a critical role in many of the physical processes associated with subduction, including water transport into the upper mantle and the generation and transport of melts. Our understanding of mantle wedge dynamics is incomplete; in particular, the mantle flow field above subducting slabs remains poorly understood. Because seismic anisotropy is a consequence of deformation, observations of anisotropy (such as shear wave splitting and P-to-SH converted waves) can constrain the geometry of the wedge flow field. Additionally, because the presence of water (either in nominally anhydrous minerals or as hydrous phases) can have a large effect on anisotropic structure, a detailed understanding of mantle wedge anisotropy can help to constrain processes related to water cycling in subduction systems. We present a global, synoptic view of anisotropy observations in subduction zone mantle wedges, compiled from a large number of individual studies, with the goal of understanding the first-order controls on wedge anisotropy and flow patterns. This compilation allows us to explicitly test the predictions made by many different conceptual models for wedge anisotropy, as well as to explore the relationships between observed anisotropy parameters and other parameters that describe subduction. We find that no simple model can explain all of the trends observed in the global data set. Mantle wedge flow is likely controlled by a combination of downdip motion of the slab, trench migration, ambient mantle flow, small-scale convection, proximity to slab edges, and slab morphology, with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology. There is also a likely contribution from B-type olivine and/or serpentinite fabric in many subduction zones, governed by the local thermal structure and volatile distribution.

  13. Heat transport in the high-pressure ice mantle of large icy moons (United States)

    Choblet, G.; Tobie, G.; Sotin, C.; Kalousová, K.; Grasset, O.


    While the existence of a buried ocean sandwiched between surface ice and high-pressure (HP) polymorphs of ice emerges as the most plausible structure for the hundreds-of-kilometers thick hydrospheres within large icy moons of the Solar System (Ganymede, Callisto, Titan), little is known about the thermal structure of the deep HP ice mantle and its dynamics, possibly involving melt production and extraction. This has major implications for the thermal history of these objects as well as on the habitability of their ocean as the HP ice mantle is presumed to limit chemical transport from the rock component to the ocean. Here, we describe 3D spherical simulations of subsolidus thermal convection tailored to the specific structure of the HP ice mantle of large icy moons. Melt production is monitored and melt transport is simplified by assuming instantaneous extraction to the ocean above. The two controlling parameters for these models are the rheology of ice VI and the heat flux from the rock core. Reasonable end-members are considered for both parameters as disagreement remains on the former (especially the pressure effect on viscosity) and as the latter is expected to vary significantly during the moon's history. We show that the heat power produced by radioactive decay within the rock core is mainly transported through the HP ice mantle by melt extraction to the ocean, with most of the melt produced directly above the rock/water interface. While the average temperature in the bulk of the HP ice mantle is always relatively cool when compared to the value at the interface with the rock core (∼ 5 K above the value at the surface of the HP ice mantle), maximum temperatures at all depths are close to the melting point, often leading to the interconnection of a melt path via hot convective plume conduits throughout the HP ice mantle. Overall, we predict long periods of time during these moons' history where water generated in contact with the rock core is transported to

  14. Volcanic Plume Measurements with UAV (Invited) (United States)

    Shinohara, H.; Kaneko, T.; Ohminato, T.


    Volatiles in magmas are the driving force of volcanic eruptions and quantification of volcanic gas flux and composition is important for the volcano monitoring. Recently we developed a portable gas sensor system (Multi-GAS) to quantify the volcanic gas composition by measuring volcanic plumes and obtained volcanic gas compositions of actively degassing volcanoes. As the Multi-GAS measures variation of volcanic gas component concentrations in the pumped air (volcanic plume), we need to bring the apparatus into the volcanic plume. Commonly the observer brings the apparatus to the summit crater by himself but such measurements are not possible under conditions of high risk of volcanic eruption or difficulty to approach the summit due to topography etc. In order to overcome these difficulties, volcanic plume measurements were performed by using manned and unmanned aerial vehicles. The volcanic plume measurements by manned aerial vehicles, however, are also not possible under high risk of eruption. The strict regulation against the modification of the aircraft, such as installing sampling pipes, also causes difficulty due to the high cost. Application of the UAVs for the volcanic plume measurements has a big advantage to avoid these problems. The Multi-GAS consists of IR-CO2 and H2O gas analyzer, SO2-H2O chemical sensors and H2 semiconductor sensor and the total weight ranges 3-6 kg including batteries. The necessary conditions of the UAV for the volcanic plumes measurements with the Multi-GAS are the payloads larger than 3 kg, maximum altitude larger than the plume height and installation of the sampling pipe without contamination of the exhaust gases, as the exhaust gases contain high concentrations of H2, SO2 and CO2. Up to now, three different types of UAVs were applied for the measurements; Kite-plane (Sky Remote) at Miyakejima operated by JMA, Unmanned airplane (Air Photo Service) at Shinomoedake, Kirishima volcano, and Unmanned helicopter (Yamaha) at Sakurajima

  15. Lidar measurements of launch vehicle exhaust plumes (United States)

    Dao, Phan D.; Curtis, David; Farley, Robert; Soletsky, Philip; Davidson, Gilbert; Gelbwachs, Jerry A.


    The Mobile Lidar Trailer (MLT) was developed and operated to characterize launch vehicle exhaust plume and its effects on the environment. Two recent applications of this facility are discussed in this paper. In the first application, the MLT was used to characterize plumes in the stratosphere up to 45 km in support of the Air Force Space and Missile Center's Rocket Impact on Stratospheric Ozone program. Solid rocket motors used by Titan IV and other heavy launch vehicles release large quantities of gaseous hydrochloric acid in the exhaust and cause concerns about a possible depletion of the ozone layer. The MLT was deployed to Cape Canaveral Air Station since October 1995 to monitor ozone and to investigate plume dynamics and properties. Six campaigns have been conducted and more are planned to provide unique data with the objective of addressing the environmental issues. The plume was observed to disperse rapidly into horizontally extended yet surprisingly thin layer with thickness recorded in over 700 lidar profiles to be less than 250 meters. MLT operates with the laser wavelengths of 532, 355 and 308 nm and a scanning receiving telescope. Data on particle backscattering at the three wavelengths suggest a consistent growth of particle size in the 2-3 hour observation sessions following the launch. In the second type of application, the MLT was used as a remote sensor of nitrogen dioxide, a caustic gaseous by-product of common liquid propellant oxidizer. Two campaigns were conducted at the Sol Se Mete Canyon test site in New Mexico in December 1996 an January 1997 to study the dispersion of nitrogen dioxide and rocket plume.

  16. A comparison of the turbulent entrainment process in line plumes and wall plumes (United States)

    Parker, David; Burridge, Henry; Partridge, Jamie; Linden, Paul


    Flows driven by sources of buoyancy appear in a large number of geophysical and industrial applications. The process of turbulent entrainment in these flows is key to understanding how they evolve and how one might model them. It has been observed that the entrainment is reduced when a line source of buoyancy is positioned immediately adjacent to a wall. To gain insight into the effect of the wall on the entrainment process we perform simultaneous PIV and LIF on both line plumes, in the absence of any boundary, and when the source is adjacent to a vertical boundary forming a wall plume. The experiments are designed to isolate the effect of the wall by using the same experimental setup and parameters for both flows with the addition of the wall and half the buoyancy flux used in the wall plume case. Of particular interest is the effect the large scale eddies, forming at the edge of the plume and engulfing ambient fluid, have on the entrainment process. By using velocity statistics in a coordinate system based on the instantaneous scalar edge of the plume, a technique we have recently used to analyse similar effects in an axisymmetric plume, the significance of this large scale engulfment will be quantified.

  17. Californian forest fire plumes over Southwestern British Columbia: lidar, sunphotometry, and mountaintop chemistry observations

    Directory of Open Access Journals (Sweden)

    I. McKendry


    Full Text Available Forest fires in Northern California and Oregon were responsible for two significant regional scale aerosol transport events observed in southern British Columbia during summer 2008. A combination of ground based (CORALNet and satellite (CALIPSO lidar, sunphotometry and high altitude chemistry observations permitted unprecedented characterization of forest fire plume height and mixing as well as description of optical properties and physicochemistry of the aerosol. In southwestern BC, lidar observations show the smoke to be mixed through a layer extending to 5–6 km a.g.l. where the aerosol was confined by an elevated inversion in both cases. Depolarization ratios for a trans-Pacific dust event (providing a basis for comparison and the two smoke events were consistent with observations of dust and smoke events elsewhere and permit discrimination of aerosol events in the region. Based on sunphotometry, the Aerosol Optical Thicknesses (AOT reached maxima of ~0.7 and ~0.4 for the two events respectively. Dubovik-retrieval values of reff, f during both the June/July and August events varied between about 0.13 and 0.15 μm and confirm the dominance of accumulation mode size particles in the forest fire plumes. Both Whistler Peak and Mount Bachelor Observatory data show that smoke events are accompanied by elevated CO and O3 concentrations as well as elevated K+/SO4 ratios. In addition to documenting the meteorology and physic-chemical characteristics of two regional scale biomass burning plumes, this study demonstrates the positive analytical synergies arising from the suite of measurements now in place in the Pacific Northwest, and complemented by satellite borne instruments.

  18. Lowermost mantle anisotropy near the eastern edge of the Pacific LLSVP: constraints from SKS-SKKS splitting intensity measurements (United States)

    Deng, Jie; Long, Maureen D.; Creasy, Neala; Wagner, Lara; Beck, Susan; Zandt, George; Tavera, Hernando; Minaya, Estela


    Seismic anisotropy has been documented in many portions of the lowermost mantle, with particularly strong anisotropy thought to be present along the edges of large low shear velocity provinces (LLSVPs). The region surrounding the Pacific LLSVP, however, has not yet been studied extensively in terms of its anisotropic structure. In this study, we use seismic data from southern Peru, northern Bolivia and Easter Island to probe lowermost mantle anisotropy beneath the eastern Pacific Ocean, mostly relying on data from the Peru Lithosphere and Slab Experiment and Central Andean Uplift and Geodynamics of High Topography experiments. Differential shear wave splitting measurements from phases that have similar ray paths in the upper mantle but different ray paths in the lowermost mantle, such as SKS and SKKS, are used to constrain anisotropy in D″. We measured splitting for 215 same station-event SKS-SKKS pairs that sample the eastern Pacific LLSVP at the base of the mantle. We used measurements of splitting intensity(SI), a measure of the amount of energy on the transverse component, to objectively and quantitatively analyse any discrepancies between SKS and SKKS phases. While the overall splitting signal is dominated by the upper-mantle anisotropy, a minority of SKS-SKKS pairs (˜10 per cent) exhibit strongly discrepant splitting between the phases (i.e. the waveforms require a difference in SI of at least 0.4), indicating a likely contribution from lowermost mantle anisotropy. In order to enhance lower mantle signals, we also stacked waveforms within individual subregions and applied a waveform differencing technique to isolate the signal from the lowermost mantle. Our stacking procedure yields evidence for substantial splitting due to lowermost mantle anisotropy only for a specific region that likely straddles the edge of Pacific LLSVP. Our observations are consistent with the localization of deformation and anisotropy near the eastern boundary of the Pacific LLSVP

  19. Lithospheric contributions to high-MgO basanites from the Cumbre Vieja Volcano, La Palma, Canary Islands and evidence for temporal variation in plume influence (United States)

    Prægel, N.-O.; Holm, P. M.


    New geochemical and isotopic data are presented from the oldest part of the Cumbre Vieja volcano, La Palma (Canary Islands), located near the assumed emergence of the Canary mantle plume. The volcanics comprise a suite dominated by basanite flows with subordinate amounts of phono-tephrite, tephri-phonolite and phonolite flows and intrusives. Two compositionally different basanite groups have been identified, both with HIMU (high-μ)-type incompatible trace element characteristics: Primitive high-MgO basanites (10.7-12.1% MgO), found only at the base of a stratigraphic profile near Fuencaliente on the south coast, and intermediate-MgO basanites (6.0-7.3% MgO), exposed in the upper part of the profile and widespread on the east coast of La Palma. The high-MgO basanites are interpreted as near-primary mantle melts (primary composition 14-15% MgO) derived by progressive melting (2.9% to 4.5%) of a common lithospheric mantle source. Model calculations indicate that it is not possible to generate the intermediate-MgO basanites from the high-MgO group by crystal fractionation of observed phenocrysts. Relative to intermediate-MgO basanites, the high-MgO flows have lower concentrations of LIL and HFS elements, except for Ti, which is markedly enriched in the primitive rocks (3.7-4.7% TiO 2 vs 3.4-3.9% TiO 2). Fuencaliente volcanics display limited temporal isotopic variations suggested to be a result of mixing of melts originating from the rising plume and the metazomatized lithospheric mantle. 87Sr / 86Sr and 143Nd / 144Nd ratios range 0.70305-0.70311 and 0.51285-0.51291, respectively, while the corresponding ranges in Pb-isotope ratios are 206Pb / 204Pb = 19.46-19.64, 207Pb / 204Pb = 15.55-15.61, and 208Pb / 204Pb = 39.16-39.53. The overall variation of the Cumbre Vieja isotopic data can be accounted for by mixtures of three mantle components in the proportions 72-79% plume source (LVC = low velocity component), 9-16% depleted mantle (DM) and up to 12% enriched mantle

  20. Topographic Expression of Deep Crustal and Mantle Processes (United States)

    Whipple, K. X.; Ouimet, W. B.; Baldwin, J. A.


    The topography of mountain ranges records much information about the history of tectonic events and climatic conditions. Although this record is not easily read, as there are many imperfectly understood factors that influence landscape morphology, there is much encouraging evidence that the river steepness index (a cousin of the Hack gradient index) exhibits a robust correlation with rock uplift rate. Published, and soon to be published, examples span a wide range of field conditions from sites around the globe (e.g., Western US, Bolivia, Nepal, China, Taiwan). Differences in substrate rock properties can have a pronounced influence on channel steepness for a given rock uplift rate, however, and analyses are best limited to regional studies where climatic conditions and lithology are largely uniform. In such settings, careful analysis of river profiles and the relief structure of the landscape can reveal important information about the history of rock uplift, recording temporal changes in uplift/river incision rates. This potential adds considerably to the value of topographic analyses, especially where uplift is driven by deep crustal or mantle processes and not clearly expressed in upper crustal structures and geodetic shortening data. However, this potential comes at the price of complicating the interpretation of the relationship between topography and the modern snapshot of deep crustal/mantle conditions provided by geophysical imaging techniques. Over what timescales does topography retain a record of past events in earth's interior? Important questions remain unanswered about the age of topography in many landscapes where deep crustal or mantle dynamics have been invoked. We discuss the factors that control landscape response time, both to an increase in rock uplift rate and to the cessation of tectonic activity, and present constraints on the antiquity of topography in several field settings.

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

    DEFF Research Database (Denmark)

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


    exchangers was also developed for detailed evaluation of the heat flux distribution over the mantle surface. Both the experimental and simulation results indicate that distribution of the flow around the mantle gap is governed by buoyancy driven recirculation in the mantle. The operation of the mantle...

  2. Trace-element geochemistry of mantle olivine and application to mantle petrogenesis and geothermobarometry


    De Hoog, Cees-Jan; Gall, Louise; Cornell, David H.


    Trace-element compositions of olivine from 75 mantle rocks of diverse origin, including xenoliths from kimberlites, basaltic lavas and orogenic peridotites, were determined by laser ablation ICP-MS to study systematic variations between mantle lithologies, partitioning mechanisms in olivine and their potential for geothermobarometry and unravelling mantle processes. Samples were selected to cover a wide range of forsterite contents (89.1-93.4), equilibration temperatures and pressures (750-14...

  3. Plume collimation for laser ablation electrospray ionization mass spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Vertes, Akos; Stolee, Jessica A.


    In various embodiments, a device may generally comprise a capillary having a first end and a second end; a laser to emit energy at a sample in the capillary to ablate the sample and generate an ablation plume in the capillary; an electrospray apparatus to generate an electrospray plume to intercept the ablation plume to produce ions; and a mass spectrometer having an ion transfer inlet to capture the ions. The ablation plume may comprise a collimated ablation plume. The device may comprise a flow cytometer. Methods of making and using the