Sample records for ma oceanic crust

  1. Aleutian basin oceanic crust (United States)

    Christeson, Gail L.; Barth, Ginger A.


    We present two-dimensional P-wave velocity structure along two wide-angle ocean bottom seismometer profiles from the Aleutian basin in the Bering Sea. The basement here is commonly considered to be trapped oceanic crust, yet there is a change in orientation of magnetic lineations and gravity features within the basin that might reflect later processes. Line 1 extends ?225 km from southwest to northeast, while Line 2 extends ?225 km from northwest to southeast and crosses the observed change in magnetic lineation orientation. Velocities of the sediment layer increase from 2.0 km/s at the seafloor to 3.0–3.4 km/s just above basement, crustal velocities increase from 5.1–5.6 km/s at the top of basement to 7.0–7.1 km/s at the base of the crust, and upper mantle velocities are 8.1–8.2 km/s. Average sediment thickness is 3.8–3.9 km for both profiles. Crustal thickness varies from 6.2 to 9.6 km, with average thickness of 7.2 km on Line 1 and 8.8 km on Line 2. There is no clear change in crustal structure associated with a change in orientation of magnetic lineations and gravity features. The velocity structure is consistent with that of normal or thickened oceanic crust. The observed increase in crustal thickness from west to east is interpreted as reflecting an increase in melt supply during crustal formation.

  2. Multiple-scale hydrothermal circulation in 135 Ma oceanic crust of the Japan Trench outer rise: Numerical models constrained with heat flow observations (United States)

    Ray, Labani; Kawada, Yoshifumi; Hamamoto, Hideki; Yamano, Makoto


    Anomalous high heat flow is observed within 150 km seaward of the trench axis at the Japan Trench offshore of Sanriku, where the old Pacific Plate (˜135 Ma) is subducting. Individual heat flow values range between 42 and 114 mW m-2, with an average of ˜70 mW m-2. These values are higher than those expected from the seafloor age based on thermal models of the oceanic plate, i.e., ˜50 mW m-2. The heat flow exhibits spatial variations at multiple scales: regional high average heat flow (˜100 km) and smaller-scale heat flow peaks (˜1 km). We found that hydrothermal mining of heat from depth due to gradual thickening of an aquifer in the oceanic crust toward the trench axis can yield elevated heat flow of the spatial scale of ˜100 km. Topographic effects combined with hydrothermal circulation may account for the observed smaller-scale heat flow variations. Hydrothermal circulation in high-permeability faults may result in heat flow peaks of a subkilometer spatial scale. Volcanic intrusions are unlikely to be a major source of heat flow variations at any scale because of limited occurrence of young volcanoes in the study area. Hydrothermal heat transport may work at various scales on outer rises of other subduction zones as well, since fractures and faults have been well developed due to bending of the incoming plate.

  3. Field and geochemical characterisitics of the Mesoarchean (~3075 ma) Ivisaartoq greenstone belt, southern West Greenland: Evidence for seafloor hydrothermal alteration in a supra-subduction oceanic crust.

    DEFF Research Database (Denmark)

    Polat, A.; Appel, P.W.U.


    The Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt in southern West Greenland includes variably deformed and metamorphosed pillow basalts, ultramafic flows (picrites), serpentinized ultramafic rocks, gabbros, sulphide-rich siliceous layers, and minor siliciclastic sedimentary rocks. Primary magmatic features such as concentric cooling-cracks and drainage cavities in pillows, volcanic breccia, ocelli interpreted as liquid immiscibility textures in pillows and gabbros, magmatic layering in gabbros, and clinopyroxene cumulates in ultramafic flows are well preserved in low-strain domains. The belt underwent at least two stages of calc-silicate metasomatic alteration and polyphase deformation between 2963 and 3075 Ma. The stage I metasomatic assemblage is composed predominantly of epidote (now mostly diopside) + quartz + plagioclase ± hornblende ± scapolite, and occurs mainly in pillow cores, pillow interstitials, and along pillow basalt-gabbro contacts. The origin of this metasomatic assemblage is attributed to seafloor hydrothermal alteration. On the basis of the common presence of epidote inclusions in diopside and the local occurrence of epidote-rich aggregates, the stage I metasomatic assemblage is interpreted as relict epidosite. The stage II metasomatic assemblage occurs as concordant discontinuous layered calc-silicate bodies to discordant calc-silicate veins commonly associated with shear zones. The stage II metasomatic assemblage consists mainly of diopside + garnet + amphibole + plagioclase + quartz ± vesuvianite ± scapolite ± epidote ± titanite ± calcite ± scheelite. Given that the second stage of metasomatism is closely associated with shear zones and replaced rocks with an early metamorphic fabric, its origin is attributed to regional dynamothermal metamorphism. The least altered pillow basalts, picrites, gabbros, and diorites are characterized by LREE-enriched, near-flat HREE, and HFSE (especially Nb)-depleted trace element patterns, indicating a subduction zone geochemical signature. Ultramafic pillows and cumulates display large positive initial eNd values of + 1.3 to + 5.0, consistent with a strongly depleted mantle source. Given the geological similarities between the Ivisaartoq greenstone belt and Phanerozoic forearc ophiolites, we suggest that the Ivisaartoq greenstone belt represents Mesoarchean supra-subduction zone oceanic crust.

  4. Metamorphic processes in subducting oceanic crust

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, M.W. [CNRS, Lab. Magmas et Volcans, Clermont-Ferrand (France)


    In subduction zones, crust is recycled back into the mantle. Three principal processes of interaction between oceanic crust and mantle may intervene: (i) dehydration (or more general devolatilization) which leads to the transfer of volatiles and hydrophile elements into the mantle wedge, (ii) partial melting of the oceanic crust which might mobilize 10-30% of the crust, and finally (iii) assimilation of the mostly dry residual crust into the mantle at great depth. This lecture deals mostly with the first process but will also discuss some aspects of melting of subducting crust. First, the state of the oceanic crust before subduction will be characterized and some typical metamorphic reactions taking place between 10 and 300 km depth investigated. Next, some principles of devolatilization reactions are described and some thermodynamic calculations will illustrate the prediction of phase equilibria and thus P-T determinations. Furthermore, some consequences for geochemical processes are outlined. Slab melting will be briefly characterized and finally, a quantification of the dehydration process is outlined.

  5. Field and geochemical characterisitics of the Mesoarchean (~3075 ma) Ivisaartoq greenstone belt, southern West Greenland: Evidence for seafloor hydrothermal alteration in a supra-subduction oceanic crust

    DEFF Research Database (Denmark)

    Polat, A.; Appel, P.W.U.; Frei, Robert; Pan, Y.; Dilek, Y.; Ordonez-Calderon, J.C.; Fryer, B.; Hollis, J.A.; Raith, J.G.


    The Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt in southern West Greenland includes variably deformed and metamorphosed pillow basalts, ultramafic flows (picrites), serpentinized ultramafic rocks, gabbros, sulphide-rich siliceous layers, and minor siliciclastic sedimentary rocks. Primary magmatic features such as concentric cooling-cracks and drainage cavities in pillows, volcanic breccia, ocelli interpreted as liquid immiscibility textures in pillows and gabbros, magmatic layering in g...

  6. Magnetization of the oceanic crust: TRM or CRM? (United States)

    Raymond, C. A.; Labrecque, J. L.


    A model was proposed in which chemical remanent magnetization (CRM) acquired within the first 20 Ma of crustal evolution may account for 80% of the bulk natural remanent magnetization (NRM) of older basalts. The CRM of the crust is acquired as the original thermoremanent magnetization (TRM) is lost through low temperature alteration. The CRM intensity and direction are controlled by the post-emplacement polarity history. This model explains several independent observations concerning the magnetization of the oceanic crust. The model accounts for amplitude and skewness discrepancies observed in both the intermediate wavelength satellite field and the short wavelength sea surface magnetic anomaly pattern. It also explains the decay of magnetization away from the spreading axis, and the enhanced magnetization of the Cretaceous Quiet Zones while predicting other systematic variations with age in the bulk magnetization of the oceanic crust. The model also explains discrepancies in the anomaly skewness parameter observed for anomalies of Cretaceous age. Further studies indicate varying rates of TRM decay in very young crust which depicts the advance of low temperature alteration through the magnetized layer.

  7. Helium isotopes in ferromanganese crusts from the central Pacific Ocean (United States)

    Basu, S.; Stuart, F.M.; Klemm, V.; Korschinek, G.; Knie, K.; Hein, J.R.


    Helium isotopes have been measured in samples of two ferromanganese crusts (VA13/2 and CD29-2) from the central Pacific Ocean. With the exception of the deepest part of crust CD29-2 the data can be explained by a mixture of implanted solar- and galactic cosmic ray-produced (GCR) He, in extraterrestrial grains, and radiogenic He in wind-borne continental dust grains. 4He concentrations are invariant and require retention of less than 12% of the in situ He produced since crust formation. Loss has occurred by recoil and diffusion. High 4He in CD29-2 samples older than 42 Ma are correlated with phosphatization and can be explained by retention of up to 12% of the in situ-produced 4He. 3He/4He of VA13/2 samples varies from 18.5 to 1852 Ra due almost entirely to variation in the extraterrestrial He contribution. The highest 3He/4He is comparable to the highest values measured in interplanetary dust particles (IDPs) and micrometeorites (MMs). Helium concentrations are orders of magnitude lower than in oceanic sediments reflecting the low trapping efficiency for in-falling terrestrial and extraterrestrial grains of Fe-Mn crusts. The extraterrestrial 3He concentration of the crusts rules out whole, undegassed 4–40 ?m diameter IDPs as the host. Instead it requires that the extraterrestrial He inventory is carried by numerous particles with significantly lower He concentrations, and occasional high concentration GCR-He-bearing particles.

  8. Estimation of seismic velocities of upper oceanic crust from ocean bottom reflection loss data. (United States)

    Dong, Hefeng; Chapman, N Ross; Hannay, David E; Dosso, Stan E


    This paper describes a Bayesian inversion of acoustic reflection loss versus angle measurements to estimate the compressional and shear wave velocities in young uppermost oceanic crust, Layer 2A. The data were obtained in an experiment on the thinly sedimented western flank of the Endeavor segment of the Juan de Fuca Ridge, using a towed horizontal hydrophone array and small explosive charges as sound sources. Measurements were made at three sites at increasing distance from the ridge spreading center to determine the effect of age of the crust on seismic velocities. The inversion used reflection loss data in a 1/3-octave band centered at 16 Hz. The compressional and shear wave velocities of the basalt were highly sensitive parameters in the inversion. The compressional wave velocity increased from 2547 + or - 30 to 2710 + or - 18 m/s over an age span of 1.4 million years (Ma) from the spreading center, an increase of 4.5 + or - 1.0%/Ma. The basalt shear wave velocity increased by nearly a factor of 2, from approximately 725 to 1320 m/s over the same age span. These results show a decreasing trend of Poisson's ratio with age, from a value of 0.46 at the youngest site closest to the ridge axis. PMID:20369999

  9. Another one bites the rust: Microbes weathering subsurface oceanic crust (United States)

    Orcutt, B.


    The marine deep biosphere consists of deeply buried sediment and igneous oceanic crust; yet, the existence, extent, and activity of life hosted in igneous oceanic crust is considerably less understood than in the sedimentaty realm. The role of microbial metabolic reactions in altering basaltic crust is not yet clear. This presentation will summarize what is currently known or speculated about rates of microbial activity in crust, focusing on the cycling of iron and oxygen, based on data from a few basalt-dominated sites that have been examined recently, including the eastern flank of the Juan de Fuca Ridge, the western flank of the Mid-Atlantic Ridge, and the Dorado Outcrop. Microbial community diversity, activity and genomic data will seek to address the question: how do you think microbes get along without iron when it's gone?

  10. Alpha Ridge: Oceanic or Continental Crust? Constraints from Crustal Thickness Mapping using Gravity Inversion (United States)

    Kusznir, N. J.; Alvey, A.


    The ocean basins of the Arctic formed during the Late Jurassic, Cretaceous and Tertiary as a series of small distinct ocean basins leading to a complex distribution of oceanic crust, thinned continental crust and rifted continental margins. The structure and origin of the Alpha and Mendeleev Ridges within the Amerasia Basin are contentious; possibilities include thick oceanic crust formed by ocean ridge - mantle plume interaction, micro-continents or thinned continental crust with mantle plume volcanic addition. We use gravity inversion, incorporating a lithosphere thermal gravity anomaly correction, to map Moho depth, crustal thickness and continental lithosphere thinning factor for the Amerasia Basin in order to determine the distribution of oceanic and continental lithosphere and the ocean-continent transition location. Data used in the gravity inversion are gravity data from the NGA (U) Arctic Gravity Project, IBCAO bathymetry and sediment thickness from Laske et al. (1997). Our gravity inversion predicts thin crust (5-10 km thickness) and high continental lithosphere thinning factors in the Makarov, Podvodnikov, Nautilus and Canada Basins consistent with these basins being oceanic or highly thinned continental crust. Larger crustal thicknesses, in the range 20-30 km, are predicted for the Alpha, Mendeleev and Lomonosov Ridges. Moho depths predicted by gravity inversion compare well with estimates from the TransArctica-Arctica seismic profiles. Moho depths from the gravity inversion are dependent on the age of oceanic lithosphere and continental breakup because of the lithosphere thermal gravity anomaly correction; these ages are uncertain for the Amerasia Basin. Gravity inversion sensitivities to break-up ages between 150 Ma (late Jurassic Triassic) and 60 Ma (early Tertiary) have been examined. Alpha Ridge has in its centre a crustal thickness of 25-30 km and possesses sharp angular edges. While Alpha Ridge has been compared with Iceland for structure and origin, its very large positive satellite derived MF6 total magnetic field anomaly at 350 km elevation (Maus et al. 2009) is an order of magnitude larger in amplitude and spatial extent than of Iceland suggesting a different origin. A global search shows that Kerguelen and Broken Ridge have similar 25-30 km crustal thicknesses, sharp angular edges, and large positive MF6-dt350 satellite magnetic anomalies. Evidence suggests that Kerguelen and Broken Ridge are micro-continents formed by poly-phase continental breakup (giving their angular sharp edges) with LIP volcanic addition. Our interpretation is that, by analogy, Alpha Ridge is also a micro-continent formed by poly-phase continental breakup with LIP volcanic addition.

  11. Chemical Composition of Ferromanganese Crusts in the World Ocean: A Review and Comprehensive Database. U.S. Geological Survey. (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The USGS Ferromanganese Crust data set was compiled by F.T. Manheim and C.M. Lane-Bostwick of the U.S. Geological Survey, Woods Hole, MA. The data set consists of...

  12. Changes in erosion and ocean circulation recorded in the Hf isotopic compositions of North Atlantic and Indian Ocean ferromanganese crusts (United States)

    Piotrowski, Alexander M.; Lee, Der-Chuen; Christensen, John N.; Burton, Kevin W.; Halliday, Alex N.; Hein, James R.; Günther, Detlef


    High-resolution Hf isotopic records are presented for hydrogenetic Fe–Mn crusts from the North Atlantic and Indian Oceans. BM1969 from the western North Atlantic has previously been shown to record systematically decreasing Nd isotopic compositions from about 60 to ?4 Ma, at which time both show a rapid decrease to unradiogenic Nd composition, thought to be related to the increasing influence of NADW or glaciation in the northern hemisphere. During the Oligocene, North Atlantic Hf became progressively less radiogenic until in the mid-Miocene (?15 Ma) it reached +1. It then shifted gradually back to an ?Hf value of +3 at 4 Ma, since when it has decreased rapidly to about ?1 at the present day. The observed shifts in the Hf isotopic composition were probably caused by variation in intensity of erosion as glaciation progressed in the northern hemisphere. Ferromanganese crusts SS663 and 109D are from about 5500 m depth in the Indian Ocean and are now separated by ?2300 km across the Mid-Indian Ridge. They display similar trends in Hf isotopic composition from 20 to 5 Ma, with the more northern crust having a composition that is consistently more radiogenic (by ?2 ?Hf units). Paradoxically, during the last 20 Ma the Hf isotopic compositions of the two crusts have converged despite increased separation and subsidence relative to the ridge. A correlatable negative excursion at ?5 Ma in the two records may reflect a short-term increase in erosion caused by the activation of the Himalayan main central thrust. Changes to unradiogenic Hf in the central Indian Ocean after 5 Ma may alternatively have been caused by the expanding influence of NADW into the Mid-Indian Basin via circum-Antarctic deep water or a reduction of Pacific flow through the Indonesian gateway. In either case, these results illustrate the utility of the Hf isotope system as a tracer of paleoceanographic changes, capable of responding to subtle changes in erosional regime not readily resolved using other isotope systems.

  13. Growth response of a deep-water ferromanganese crust to evolution of the Neogene Indian Ocean (United States)

    Banakar, V.K.; Hein, J.R.


    A deep-water ferromanganese crust from a Central Indian Ocean seamount dated previously by 10Be and 230Th(excess) was studied for compositional and textural variations that occurred throughout its growth history. The 10Be/9Be dated interval (upper 32 mm) yields an uniform growth rate of 2.8 ?? 0.1 mm/Ma [Frank, M., O'Nions, R.K., 1998. Sources of Pb for Indian Ocean ferromanganese crusts: a record of Himalayan erosion. Earth Planet. Sci. Lett., 158, pp. 121-130.] which gives an extrapolated age of ~ 26 Ma for the base of the crust at 72 mm and is comparable to the maximum age derived from the Co-model based growth rate estimates. This study shows that Fe-Mn oxyhydroxide precipitation did not occur from the time of emplacement of the seamount during the Eocene (~ 53 Ma) until the late Oligocene (~ 26 Ma). This paucity probably was the result of a nearly overlapping palaeo-CCD and palaeo-depth of crust formation, increased early Eocene productivity, instability and reworking of the surface rocks on the flanks of the seamount, and lack of oxic deep-water in the nascent Indian Ocean. Crust accretion began (older zone) with the formation of isolated cusps of Fe-Mn oxide during a time of high detritus influx, probably due to the early-Miocene intense erosion associated with maximum exhumation of the Himalayas (op. cit.). This cuspate textured zone extends from 72 mm to 42 mm representing the early-Miocene period. Intense polar cooling and increased mixing of deep and intermediate waters at the close of the Oligocene might have led to the increased oxygenation of the bottom-water in the basin. A considerable expansion in the vertical distance between the seafloor depth and the CCD during the early Miocene in addition to the influx of oxygenated bottom-water likely initiated Fe-Mn crust formation. Pillar structure characterises the younger zone, which extends from 40 mm to the surface of the crust, i.e., ~ 15 Ma to Present. This zone is characterised by > 25% higher content of oxide-bound elements than in the older zone, possibly corresponding to further increased oxygenation of bottom-waters, increased stability of the seamount slope, and gradually reduced input of continental detritus from the erosion of the Himalayas. Middle Miocene Antarctic glaciation, which peaked ~ 12-13 Ma ago, increased the oxic bottom-water influx to the basin resulting in accretion of the crust with low detritus. Therefore, the younger crust started to accrete in response to a shift in bottom-water circulation towards the contemporary pattern, which produced a uniform growth rate and pillar structure up to the present. (C) 2000 Published by Elsevier Science B.V.

  14. Geochemical constraints on the origin of the late Jurassic proto-Caribbean oceanic crust in Hispaniola (United States)

    Viruete, J. Escuder; Pérez-Estaún, A.; Weis, D.


    The nature of the oceanic crust produced through rifting and oceanic spreading between North and South America during the Late Jurassic is a key element for the Caribbean plate tectonic model reconstruction. Located in the Cordillera Central of Hispaniola, the Loma La Monja volcano-plutonic assemblage (LMA) is composed of gabbros, dolerites, basalts, and oceanic sediments, as well as metamorphic equivalents, which represent a dismembered fragment of this proto-Caribbean oceanic crust. Petrologic and geochemical data show that the LMA have a relatively broad diversity in composition, which represent the crystallization products of a typical low-pressure tholeiitic fractionation of mid-ocean ridge basalts (MORB)-type parental magmas, ranging from N- to E-MORB. Three geochemical groups have been distinguished in the volcanic sequence: LREE-flat to slightly LREE-enriched basalts of groups II and III occur interlayered in the lower stratigraphic levels; and LREE-depleted basalts of group I in the upper levels. Mantle melt modeling suggests that group III magmas are consistent by mixing within a mantle melt column of low-degree (15%) melts of a shallow spinel source, and groups II and I magmas are explained with moderate to high (14-18%) and very high (>20%) fractional melting degrees of a shallower spinel mantle source, respectively. Thus, upward in the volcanic sequence of the LMA, the magmas represent progressively more extensive melting of shallower sources, in a plume-influenced spreading ridge of the proto-Caribbean oceanic crust. Nb/Y versus Zr/Y systematics combined with recent plate tectonic model reconstructions reveal that Caribbean Colombian oceanic plateau fragments in Hispaniola formed through melting of heterogeneous mantle source regions related with distinct plumes during at least from Aptian-Albian (>96 Ma) to Late Campanian.

  15. Primary carbonatite melt from deeply subducted oceanic crust

    Energy Technology Data Exchange (ETDEWEB)

    Walter, M.J.; Bulanova, G.P.; Armstrong, L.S.; Keshav, S.; Blundy, J.D.; Gudfinnesson, G.; Lord, O.T.; Lennie, A.R.; Clark, S.M.; Smith, C.B.; Gobbo, L.


    Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here they provide exper8imental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.

  16. Geophysical and geochemical nature of relaminated arc-derived lower crust underneath oceanic domain in southern Mongolia (United States)

    Guy, Alexandra; Schulmann, Karel; Janoušek, Vojt?ch; Å típská, Pavla; Armstrong, Robin; Belousova, Elena; Dolgopolova, Alla; Seltmann, Reimar; Lexa, Ondrej; Jiang, Yingde; Hanžl, Pavel


    The Central Asian Orogenic Belt (CAOB) in southern Mongolia consists of E-W trending Neoproterozoic cratons and Silurian-Devonian oceanic tectonic zones. Previous study revealed that the Early Paleozoic accretionary wedge and the oceanic tectonic zone are underlain by a layer giving a homogeneous gravity signal. Forward gravity modelling suggests that this layer is not formed of high-density material typical of lower oceanic crust but is composed of low- to intermediate-density rocks resembling continental crust. The nature of this lower crust is constrained by the whole-rock geochemistry and zircon Hf isotopic signature of abundant Late Carboniferous high-K calc-alkaline and Early Permian A-type granitoids intruding the two Early Paleozoic domains. It is possible to explain the genesis of these granitoids by anatexis of juvenile, metaigneous (tonalitic-gabbroic) rocks of Late Cambrian age, the source of which is presumed to lie in the "Khantaishir" arc (520-495 Ma) further north. In order to test this hypothesis, the likely modal composition and density of Khantaishir arc-like protoliths are thermodynamically modelled at granulite- and higher amphibolite-facies conditions. It is shown that the current average density of the lower crust inferred by gravity modelling (2730 ± 20 kg/m3) matches best metamorphosed leucotonalite to diorite. Based on these results, it is now proposed that Mongolian CAOB has an architecture in which the accretionary wedge and oceanic upper crust is underlain by allochthonous lower crust that originated in a Cambrian arc. A tectonic model explaining relamination of allochthonous felsic to intermediate lower crust beneath mafic upper crust is proposed.

  17. Exploring the oceanic crust deep biosphere through subsurface borehole observatories (United States)

    Orcutt, Beth


    During Integrated Ocean Drilling Program Expeditions 327 and 336, several new subsurface borehole observatories were installed in oceanic crust, with a primary motivation to access the deep biosphere in these poorly understood environments. These new observatories have enabled unprecedented opportunities to collect high-quality samples for microbiological analysis, including metagenomic and single cell genomic investigations of the unique microbial communities living "on the rocks." This presentation will provide an overview of recent discoveries, focusing on the observatories on the Juan de Fuca Ridge flank and highlighting adaptations to life in the subsurface gleaned from genomic approaches. The presentation will also highlight opportunities for continued observatory-based research within the International Ocean Discovery Program.

  18. Origin of dipping structures in fast-spreading oceanic lower crust offshore Alaska imaged by multichannel seismic data (United States)

    Bécel, Anne; Shillington, Donna J.; Nedimovi?, Mladen R.; Webb, Spahr C.; Kuehn, Harold


    Multi-channel seismic (MCS) reflection profiles across the Pacific Plate south of the Alaska Peninsula reveal the internal structure of mature oceanic crust (48-56 Ma) formed at fast to intermediate spreading rates during and after a major plate re-organization. Oceanic crust formed at fast spreading rates (half spreading rate ? 74 mm /yr) has smoother basement topography, thinner sediment cover with less faulting, and an igneous section that is at least 1 km thicker than crust formed at intermediate spreading rates (half spreading rate ? 28- 34 mm /yr). MCS data across fast-spreading oceanic crust formed during plate re-organization contain abundant bright reflections, mostly confined to the lower crust above a highly reflective Moho transition zone, which has a reflection coefficient (RC) of ?0.1. The lower crustal events dip predominantly toward the paleo-ridge axis at ?10-30°. Reflections are also imaged in the uppermost mantle, which primarily dip away from the ridge at ?10-25°, the opposite direction to those observed in the lower crust. Dipping events in both the lower crust and upper mantle are absent on profiles acquired across the oceanic crust formed at intermediate spreading rates emplaced after plate re-organization, where a Moho reflection is weak or absent. Our preferred interpretation is that the imaged lower crustal dipping reflections within the fast spread crust arise from shear zones that form near the spreading center in the region characterized by interstitial melt. The abundance and reflection amplitude strength of these events (RC ? 0.15) can be explained by a combination of solidified melt that was segregated within the shear structures, mylonitization of the shear zones, and crystal alignment, all of which can result in anisotropy and constructive signal interference. Formation of shear zones with this geometry requires differential motion between the crust and upper mantle, where the upper mantle moves away from the ridge faster than the crust. Active asthenospheric upwelling is one possible explanation for these conditions. The other possible interpretation is that lower crustal reflections are caused by magmatic (mafic/ultramafic) layering associated with accretion from a central mid-crustal magma chamber. Considering that the lower crustal dipping events have only been imaged in regions that have experienced plate re-organizations associated with ridge jumps or rift propagation, we speculate that locally enhanced mantle flow associated with these settings may lead to differential motion between the crust and the uppermost mantle, and therefore to shearing in the ductile lower crust or, alternatively, that plate reorganization could produce magmatic pulses which may lead to mafic/ultramafic banding.

  19. Thermochemical convection in the mantle with oceanic crust recirculation (United States)

    Trubitsyn, V. P.


    Basalts of mid-ocean ridges are depleted in incompatible elements that have passed into the continental crust. Basalts of hot spots (oceanic islands and igneous provinces) have a chemical composition close to the primary uniform mantle and are even somewhat enriched in incompatible elements. At present, for explaining the reason for this difference, there are different qualitative schemes of differentiation and mixing of substance in the mantle. In the present work, the results of numerical modeling of the two-component thermochemical convection in the mantle are given. They quantitatively demonstrate with which parameters in the mantle the layers of different chemical composition can remain unchanged. Models with different density contrasts and with variable viscosity are examined. The times of the partial mixing of layers depending on the values of these parameters are calculated. For retaining the stratified mantle for two Ga, the density contrast must be more than 2%. If the layer D? contains a substance of the primary composition, then, its upper boundary can be the place of origin of the plumes that feed the hot spots of the Earth. The enrichment in the incompatible elements and the variety of the chemical composition of hot spots can be explained by the mixing of the substance of the slowly eroded D? layer and the oceanic crust accumulated in it.

  20. Periodic deformation of oceanic crust in the central Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.; Ramana, M.V.; Rao, D.G.; Murthy, K.S.R.; Rao, M.M.M.; Subrahmanyam, V.; Sarma, K.V.L.N.S.

    of the equatorial central Indian Ocean. Analyses of the data revealed basement and sedimentary structures and structural unconformities that resulted from the release of compressional forces. Long-wavelength (150-300 km) anticlinal basement structures with 1-2 km...

  1. Early Carboniferous (˜357 Ma) crust beneath northern Arabia: Tales from Tell Thannoun (southern Syria) (United States)

    Stern, Robert J.; Ren, Minghua; Ali, Kamal; Förster, Hans-Jürgen; Al Safarjalani, Abdulrahman; Nasir, Sobhi; Whitehouse, Martin J.; Leybourne, Matthew I.; Romer, Rolf L.


    Continental crust beneath northern Arabia is deeply buried and poorly known. To advance our knowledge of this crust, we studied 8 xenoliths brought to the surface by Neogene eruptions of Tell Thannoun, S. Syria. The xenolith suite consists of two peridotites, one pyroxenite, four mafic granulites, and one charnockite. The four mafic granulites and charnockite are probably samples of the lower crust, and two mafic granulites gave 2-pyroxene equilibration temperatures of 780-800 °C, which we take to reflect temperatures at the time of formation. Peridotite and pyroxenite gave significantly higher temperatures of ?900 °C, consistent with derivation from the underlying lithospheric mantle. Fe-rich peridotite yielded T?800 °C, perhaps representing a cumulate layer in the crust. Three samples spanning the lithologic range of the suite (pyroxenite, mafic granulite, and charnockite) yielded indistinguishable concordant U-Pb zircon ages of ?357 Ma, interpreted to approximate when these magmas crystallized. These igneous rocks are mostly juvenile additions from the mantle, as indicated by low initial 87Sr/86Sr (0.70312 to 0.70510) and strongly positive initial ?Nd(357 Ma) (+4 to +9.5). Nd model ages range from 0.55 to 0.71 Ga. We were unable to unequivocally infer a tectonic setting where these melts formed: convergent margin, rift, or hotspot. These xenoliths differ from those of Jordan and Saudi Arabia to the south in four principal ways: 1) age, being least 200 Ma younger than the presumed Neoproterozoic (533-1000 Ma) crust beneath Jordan and Saudi Arabia; 2) the presence of charnockite; 3) abundance of Fe-rich mafic and ultramafic lithologies; and 4) the presence of sapphirine. Our studies indicate that northern Arabian plate lithosphere contains a significant proportion of juvenile Late Paleozoic crust, the extent of which remains to be elucidated. This discovery helps explain fission track resetting documented for rocks from Israel and provides insights into the nature of Late Paleozoic (Hercynian) deformation that affected Arabia near the Persian Gulf.

  2. Geo-neutrino Detection From the Oceanic Crust (United States)

    Dye, S.


    It is well established that radioactivity within the Earth contributes to terrestrial heat flow and dynamic activity of the planet. At present, the extent of the contribution is predicted by models rather than measured by observation. Radioactive heat is dominated by long-lived isotopes of uranium, thorium, and potassium. It is now demonstrated that uranium and thorium in the Earth can be measured by geo-neutrino detectors. Geo- neutrino detectors at both continental and oceanic locations are needed to determine the partitioning of uranium and thorium between the crusts and mantle. The key role of the marine geo-neutrino detector for measuring mantle radioactivity, searching for the putative geo-reactor, and monitoring nuclear activity is described.

  3. Partial separation of halogens during the subduction of oceanic crust (United States)

    Joachim, Bastian; Pawley, Alison; Lyon, Ian; Henkel, Torsten; Clay, Patricia L.; Ruzié, Lorraine; Burgess, Ray; Ballentine, Christopher J.


    Incompatible elements, such as halogens, have the potential to act as key tracers for volatile transport processes in Earth and planetary systems. The determination of halogen abundances and ratios in different mantle reservoirs gives us the ability to better understand volatile input mechanisms into the Earth's mantle through subduction of oceanic crust. Halogen partition coefficients were experimentally determined between forsterite, orthopyroxene and silicate melt at pressures ranging from 1.0 to 2.3 GPa and temperatures ranging from 1500-1600°C, thus representing partial melting conditions of the Earth's mantle. Combining our data with results of recent studies (Beyer et al. 2012; Dalou et al. 2012) shows that halogen partitioning between forsterite and melt increases by factors of about 1000 (fluorine) and 100 (chlorine) between 1300°C and 1600°C and does not show any pressure dependence. Chlorine partitioning between orthopyroxene and melt increases by a factor of about 1500 for a temperature increase of 100°C (anywhere between 1300°C and 1600°C), but decreases by a factor of about 1500 for a pressure increase of 1.0 GPa (anywhere between 1.0 GPa and 2.5 GPa). At similar P-T conditions, a comparable effect is observed for the fluorine partitioning behaviour, which increases by 500-fold for a temperature increase of 100°C and decreases with increasing pressure. Halogen abundances in mid-ocean ridge basalts (MORB; F=3-15, Cl=0.5-14ppm) and ocean island basalts (OIB; F=35-65, Cl=21-55 ppm) source regions were estimated by combining our experimentally determined partition coefficients with natural halogen concentrations in oceanic basalts (e.g. Ruzié et al. 2012). The estimated chlorine OIB source mantle concentration is in almost perfect agreement with primitive mantle estimates (Palme and O'Neill 2003). If we expect an OIB source mantle slightly depleted in incompatible elements, this suggests that at least small amounts of chlorine are recycled deep into the mantle through subduction of oceanic crust, possibly via marine pore fluids (Sumino et al. 2010). The OIB source region is, however, significantly enriched in fluorine relative to the primitive mantle by a factor of 1.4-3.6, which indicates that significantly larger amounts of fluorine are transported deep into the Earth's mantle through subduction. An explanation for the partial separation of chlorine and fluorine during subduction is that the heavy halogens are more likely to escape from the subducting slab in hydrous fluids at an early subduction stage whereas significant amounts of fluorine are likely to remain in the slab, possibly incorporated in the lattice of hydrous amphibole or mica, or in anhydrous high-pressure phases of eclogite. The MORB source mantle is degassed in fluorine (17-88%) and chlorine (22-99%) relative to primitive mantle estimates. Preliminary data suggest that the bromine partitioning behaviour between forsterite and melt is roughly comparable to the behaviour of fluorine and chlorine. If true, this would imply that the Earth's upper mantle is presumably degassed of all halogens despite the more likely escape of heavy halogens from the slab at an early subduction stage, implying that these halogens are at least partly accumulating in the crust after leaving the slab. Beyer C, Klemme S, Wiedenbeck M, Stracke A, Vollmer C (2012) Earth Planet Sci. Lett. 337-338, pp. 1-9. Dalou C, Koga KT, Shimizu N, Boulon J, Devidal JL (2012) Contrib. Mineral. Petrol. 163, pp. 591-609. Palme H, O'Neill HSTC (2003) Treatise Geochem. 2, pp. 1-38. Ruzié L, Burgess R, Hilton DR, Ballentine CJ (2012) AGU Fall Meeting 2012. V31A-2762 (abstr.). Sumino H, Burgess R, Mizukami T, Wallis SR, Holland G, Ballentine CJ (2010) Earth Planet. Sci. Lett. 294, pp. 163-172.

  4. First findings of Paleo- and Mesoarchean zircons in the rocks from the Central Arctic province of oceanic rises as an evidence of the ancient continental crust (United States)

    Sergeev, S. A.; Presnyakov, S. L.; Antonov, A. V.; Belyatsky, B. V.; Rodionov, N. V.; Shevchenko, S. S.


    This report presents the results of local U-Pb zircon dating (SIMS SHRIMP II) for a sample of migmatite gneiss dredged on the western slope of Alpha Ridge in the Arctic Ocean in the course of the "Arktika-2012" Russian polar expedition. The distribution of U-Pb ages of the examined zircon points to the Early Precambrian origin of this gneiss, for the bulk of the zircon was crystallized at least 3450 Ma ago from a magmatic melt under acidic volcanism at the primary crust formation. Zircon of the second generation was crystallized 3300 Ma ago under the remelting of acid volcanics and appearance of migmatite gneisses under the amphibolite facies of metamorphism. Most likely, a partial recrystallization of zircon and formation of microfolded structures and foliation took place 3000 Ma ago at the stage of rocks deformation. The latest zircon was formed 1900 Ma ago from the crust fluid or melt under the low-gradient metamorphism. In view of the possibility of the appearance of the treated clastogenic gneiss fragment under current oceanic erosion, the obtained results allow one to affirm that the occurrence of a fragment of the most ancient sialic continental crust formed at least 3450 Ma ago is possible at the submarine rises of the Arctic Ocean (Alpha Ridge and the Mendeleev Rise).

  5. Deformation and rupture of the oceanic crust may control growth of Hawaiian volcanoes. (United States)

    Got, Jean-Luc; Monteiller, Vadim; Monteux, Julien; Hassani, Riad; Okubo, Paul


    Hawaiian volcanoes are formed by the eruption of large quantities of basaltic magma related to hot-spot activity below the Pacific Plate. Despite the apparent simplicity of the parent process--emission of magma onto the oceanic crust--the resulting edifices display some topographic complexity. Certain features, such as rift zones and large flank slides, are common to all Hawaiian volcanoes, indicating similarities in their genesis; however, the underlying mechanism controlling this process remains unknown. Here we use seismological investigations and finite-element mechanical modelling to show that the load exerted by large Hawaiian volcanoes can be sufficient to rupture the oceanic crust. This intense deformation, combined with the accelerated subsidence of the oceanic crust and the weakness of the volcanic edifice/oceanic crust interface, may control the surface morphology of Hawaiian volcanoes, especially the existence of their giant flank instabilities. Further studies are needed to determine whether such processes occur in other active intraplate volcanoes. PMID:18216852

  6. Continental Growth and Recycling in Convergent Orogens with Large Turbidite Fans on Oceanic Crust

    Directory of Open Access Journals (Sweden)

    Ben D. Goscombe


    Full Text Available Convergent plate margins where large turbidite fans with slivers of oceanic basement are accreted to continents represent important sites of continental crustal growth and recycling. Crust accreted in these settings is dominated by an upper layer of recycled crustal and arc detritus (turbidites underlain by a layer of tectonically imbricated upper oceanic crust and/or thinned continental crust. When oceanic crust is converted to lower continental crust it represents a juvenile addition to the continental growth budget. This two-tiered accreted crust is often the same thickness as average continental crustal and is isostatically balanced near sea level. The Paleozoic Lachlan Orogen of eastern Australia is the archetypical example of a tubidite-dominated accretionary orogeny. The Neoproterozoic-Cambrian Damaran Orogen of SW Africa is similar to the Lachlan Orogen except that it was incorporated into Gondwana via a continent-continent collision. The Mesozoic Rangitatan Orogen of New Zealand illustrates the transition of convergent margin from a Lachlan-type to more typical accretionary wedge type orogen. The spatial and temporal variations in deformation, metamorphism, and magmatism across these orogens illustrate how large volumes of turbidite and their relict oceanic basement eventually become stable continental crust. The timing of deformation and metamorphism recorded in these rocks reflects the crustal thickening phase, whereas post-tectonic magmatism constrains the timing of chemical maturation and cratonization. Cratonization of continental crust is fostered because turbidites represent fertile sources for felsic magmatism. Recognition of similar orogens in the Proterozoic and Archean is important for the evaluation of crustal growth models, particularly for those based on detrital zircon age patterns, because crustal growth by accretion of upper oceanic crust or mafic underplating does not readily result in the addition of voluminous zircon-bearing magmas at the time of accretion. This crust only produces significant zircon when and if it partially melts, which may occur long after accretion.

  7. First Investigation of the Microbiology of the Deepest Layer of Ocean Crust


    Mason, Olivia U; Nakagawa, Tatsunori; Rosner, Martin; Van Nostrand, Joy D.; Zhou, Jizhong; Maruyama, Akihiko; Fisk, Martin R.; Giovannoni, Stephen J


    The gabbroic layer comprises the majority of ocean crust. Opportunities to sample this expansive crustal environment are rare because of the technological demands of deep ocean drilling; thus, gabbroic microbial communities have not yet been studied. During the Integrated Ocean Drilling Program Expeditions 304 and 305, igneous rock samples were collected from 0.45-1391.01 meters below seafloor at Hole 1309D, located on the Atlantis Massif (30 °N, 42 °W). Microbial diversity in the rocks was a...

  8. The Davis Strait crust—a transform margin between two oceanic basins (United States)

    Suckro, Sonja K.; Gohl, Karsten; Funck, Thomas; Heyde, Ingo; Schreckenberger, Bernd; Gerlings, Joanna; Damm, Volkmar


    The Davis Strait is located between Canada and Greenland and connects the Labrador Sea and the Baffin Bay basins. Both basins formed in Cretaceous to Eocene time and were connected by a transform fault system in the Davis Strait. Whether the crust in the central Davis Strait is oceanic or continental has been disputed. This information is needed to understand the evolution of this transform margin during the separation of the North American plate and Greenland. We here present a 315-km-long east-west-oriented profile that crosses the Davis Strait and two major transform fault systems-the Ungava Fault Complex and the Hudson Fracture Zone. By forward modelling of data from 12 ocean bottom seismographs, we develop a P-wave velocity model. We compare this model with a density model from ship-borne gravity data. Seismic reflection and magnetic anomaly data support and complement the interpretation. Most of the crust is covered by basalt flows that indicate extensive volcanism in the Davis Strait. While the upper crust is uniform, the middle and lower crust are characterized by higher P-wave velocities and densities at the location of the Ungava Fault Complex. Here, P-wave velocities of the middle crust are 6.6 km s-1 and of the lower crust are 7.1 km s-1 compared to 6.3 and 6.8 km s-1 outside this area; densities are 2850 and 3050 kg m-3 compared to 2800 and 2900 kg m-3. We here interpret a 45-km-long section as stretched and intruded crust or as new igneous crust that correlates with oceanic crust in the southern Davis Strait. A high-velocity lower crust (6.9-7.3 km s-1) indicates a high content of mafic material. This mantle-derived material gradually intruded the lower crust of the adjacent continental crust and can be related to the Iceland mantle plume. With plate kinematic modelling, we can demonstrate the importance of two transform fault systems in the Davis Strait: the Ungava Fault Complex with transpression and the Hudson Fracture Zone with pure strike-slip motion. We show that with recent poles of rotation, most of the relative motion between the North American plate and Greenland took place along the Hudson Fracture Zone.

  9. Transition from oceanic to continental lithosphere subduction in southern Tibet: Evidence from the Late Cretaceous-Early Oligocene (~ 91-30 Ma) intrusive rocks in the Chanang-Zedong area, southern Gangdese (United States)

    Jiang, Zi-Qi; Wang, Qiang; Wyman, Derek A.; Li, Zheng-Xiang; Yang, Jin-Hui; Shi, Xiao-Bing; Ma, Lin; Tang, Gong-Jian; Gou, Guo-Ning; Jia, Xiao-Hui; Guo, Hai-Feng


    Little is known about the detailed processes associated with the transition from oceanic to continental lithosphere subduction in the Gangdese Belt of southern Tibet (GBST). Here, we report zircon U-Pb age, major and trace element and Sr-Nd-Hf isotopic data for Late Cretaceous-Early Oligocene (~ 91-30 Ma) intermediate-acid intrusive rocks in the Chanang-Zedong area immediately north of the Yarlung-Tsangpo suture zone. These rocks represent five magmatic episodes at ~ 91, ~ 77, ~ 62, ~ 48, and ~ 30 Ma, respectively. The 91-48 Ma rocks have slightly lower initial 87Sr/86Sr (0.7037 to 0.7047), and higher ?Nd(t) (+ 1.8 to + 4.3) and ?Hf(t) (+ 3.5 to + 14.7) values in comparison with those (0.7057 to 0.7062, - 3.3 to - 2.5 and + 2.2 to + 6.6) of the ~ 30 Ma intrusive rocks. The ~ 91, ~ 62 and ~ 30 Ma rocks are geochemically similar to slab-derived adakites. The ~ 91 Ma Somka adakitic granodiorites were likely derived by partial melting of the subducting Neo-Tethyan oceanic crust with minor oceanic sediments, and the ~ 91 Ma Somka dioritic rocks with a geochemical affinity of adakitic magnesian andesites likely resulted from interactions between adakitic magmas and overlying mantle wedge peridotite. The ~ 77 Ma Luomu diorites were probably generated by partial melting of juvenile basaltic lower crust. The ~ 62 Ma Naika and Zedong adakitic diorites and granodiorites were likely generated mainly by partial melting of thickened juvenile mafic lower crust but the source region of the Zedong adakitic rocks also contained enriched components corresponding to Indian continental crust. The ~ 48 Ma Lamda granites were possibly generated by melting of a juvenile basaltic crust. The younger (~ 30 Ma) Chongmuda adakitic quartz monzonites and minor granodiorites were most probably derived by partial melting of Early Oligocene northward-subducted Indian lower crust beneath the southern Lhasa Block. Taking into account the regional tectonic and magmatic data, we suggest that the Gangdese Belt of southern Tibet (GBST) underwent a tectonodynamic transition from oceanic subduction to continental subduction between 100 and 30 Ma. It evolved through four stages: 100-65 Ma roll-back of subducted Neo-Tethyan oceanic lithosphere; 65-60 Ma initial collision between Indian and Asian continents; 60-40 Ma breakoff of subducted Neo-Tethyan oceanic lithosphere; and ~ 30 Ma northward subduction of the Indian continent.

  10. Compositional variation and genesis of ferromanganese crusts of the Afanasiy-Nikitin Seamount, Equatorial Indian Ocean

    Indian Academy of Sciences (India)

    R P Rajani; V K Banakar; G Parthiban; A V Mudholkar; A R Chodankar


    Eight ferromanganese crusts (Fe-Mn crusts) with igneous and sedimentary substrates collected at different water depths from the Afanasiy-Nikitin Seamount are studied for their bulk major, minor and rare earth element composition. The Mn/Fe ratios > 1.5 indicate the hydrogenetic accretion of the Fe-Mn hydroxides. These Fe-Mn crusts are enriched in Co (up to 0.9%, average ?0.5%) and Ce. The Ce-content is the highest reported so far (up to 3763 ppm, average ?2250 ppm) for global ocean seamount Fe-Mn crusts. In spite of general similarity in the range of major, minor, and strictly trivalent rare earth element composition, the dissimilarity between the present Fe-Mn crusts and the Pacific seamount Fe-Mn crusts in Co and Ce associations with major mineral phases indicates inter-oceanic heterogeneity and region-specific conditions responsible for their enrichment. The decrease in Ce-anomaly (from ?8 to ?1.5) with increasing water depth (from ?1.7km to ?3.2 km) might suggest that the modern intermediate depth low oxygen layer was shifted and sustained at a deeper depth for a long period in the past.

  11. Yttrium and rare earth element contents in seamount cobalt crusts in the Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Balaram, V.; Banakar, V.K.; Subramanyam, K.S.V.; Roy, P.; Satyanarayan, M.; RamMohan, M.; Sawant, S.S.

    reports high concentrations of rare earth elements (REE) and yttrium ranging from 1,727 to 2,511 mu g/g in the crust samples collected from the Afanasy Niktin Seamount (ANS) in the Eastern Equatorial Indian Ocean. The concentrations of REE in the ANS Fe...

  12. Europa's Crust and Ocean: Origin, Composition, and the Prospects for Life (United States)

    Kargel, J.S.; Kaye, J.Z.; Head, J. W., III; Marion, G.M.; Sassen, R.; Crowley, J.K.; Ballesteros, O.P.; Grant, S.A.; Hogenboom, D.L.


    We have considered a wide array of scenarios for Europa's chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below. We postulate that, following formation of the jovian system, the europan evolutionary sequence has as its major links: (a) initial carbonaceous chondrite rock, (b) global primordial aqueous differentiation and formation of an impure primordial hydrous crust, (c) brine evolution and intracrustal differentiation, (d) degassing of Europa's mantle and gas venting, (e) hydrothermal processes, and (f) chemical surface alteration. Our models were developed in the context of constraints provided by Galileo imaging, near infrared reflectance spectroscopy, and gravity and magnetometer data. Low-temperature aqueous differentiation from a carbonaceous CI or CM chondrite precursor, without further chemical processing, would result in a crust/ocean enriched in magnesium sulfate and sodium sulfate, consistent with Galileo spectroscopy. Within the bounds of this simple model, a wide range of possible layered structures may result; the final state depends on the details of intracrustal differentiation. Devolatilization of the rocky mantle and hydrothermal brine reactions could have produced very different ocean/crust compositions, e.g., an ocean/crust of sodium carbonate or sulfuric acid, or a crust containing abundant clathrate hydrates. Realistic chemical-physical evolution scenarios differ greatly in detailed predictions, but they generally call for a highly impure and chemically layered crust. Some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and/or cryovolcanism. We describe some plausible geological consequences of the physical-chemical structures predicted from these scenarios. These predicted consequences and observed aspects of Europa's geology may serve as a basis for further analys is and discrimination among several alternative scenarios. Most chemical pathways could support viable ecosystems based on analogy with the metabolic and physiological versatility of terrestrial microorganisms. ?? 2000 Academic Press.

  13. Palaeoceanographic conditions during the formation of ferromanganese crust from the Afanasiy Nikitin seamount, north central Indian Ocean: geochemical evidence

    Digital Repository Service at National Institute of Oceanography (India)

    Banakar, V.K.; Pattan, J.N.; Mudholkar, A.V.

    subaerial exposure during the Oligocene (approx 30 Ma) global sealevel drop. The mineralogy, major, trace and REE element geochemistry and CO-model age estimates suggest three distinct accretionary environments during the crust growth: (1) a period...

  14. Glacial cycles drive variations in the production of oceanic crust

    CERN Document Server

    Crowley, John W; Huybers, Peter; Langmuir, Charles H; Park, Sung-Hyun


    Glacial cycles redistribute water between the oceans and continents causing pressure changes in the upper mantle, with potential consequences for melting of Earth's interior. A numerical model of mid-ocean ridge dynamics that explicitly includes melt transport is used to calculate the melting effects that would be caused by Plio-Pleistocene sea-level variations. Model results interpreted in the context of an analytical approximation predict sea-level induced variations in crustal thickness on the order of hundreds of meters. The specifics of the response depend on rates of sea-level change, mid-ocean ridge spreading rates, and mantle permeability. Spectral analysis of the bathymetry of the Australian-Antarctic ridge shows significant spectral energy near 23, 41, and 100 ky periods, consistent with model results and with the spectral content of Pleistocene sea-level variability. These results support the hypothesis that sea-floor topography records the magmatic response to changes in sea level, reinforcing the...



    Got, Jean-Luc; Monteiller, Vadim; Monteux, Julien; Hassani, Riad; Okubo, Paul


    Hawaiian volcanoes are formed by the eruption of large quantities of basaltic magma related to hot- spot activity below the Pacific Plate(1,2). Despite the apparent simplicity of the parent process emission of magma onto the oceanic crust - the resulting edifices display some topographic complexity(3-5). Certain features, such as rift zones and large flank slides, are common to all Hawaiian volcanoes, indicating similarities in their genesis; however, the underlying mechanism controlling this...

  16. Positive geothermal anomalies in oceanic crust of Cretaceous age offshore Kamchatka


    Delisle, G


    Heat flow measurements were carried out in 2009 offshore Kamchatka during the German-Russian joint-expedition KALMAR. An area with elevated heat flow in oceanic crust of Cretaceous age – detected ~30 years ago in the course of several Russian heat flow surveys – was revisited. One previous interpretation postulated anomalous lithospheric conditions or a connection between a postulated mantle plume at great depth (> 200 km) as the source for the observed high heat flow. However, the positiv...

  17. Positive geothermal anomalies in oceanic crust of Cretaceous age offshore Kamchatka


    Delisle, G


    Heat flow measurements were carried out in 2009 offshore Kamchatka during the German-Russian joint-expedition KALMAR. An area with elevated heat flow in oceanic crust of Cretaceous age – detected ~30 yr ago in the course of several Russian heat flow surveys – was revisited. One previous interpretation postulated anomalous lithospheric conditions or a connection between a postulated mantle plume at great depth (>200 km) as the source for the observed high heat flow. However, the positive he...

  18. Global distribution of beryllium isotopes in deep ocean water as derived from Fe-Mn crusts (United States)

    Von Blanckenburg, F.; O'Nions, R. K.; Belshaw, N.S.; Gibb, A.; Hein, J.R.


    The direct measurement of the ratio of cosmogenic 10Be (T1/2 = 1.5 Ma) to stable terrigenously sourced 9Be in deep seawater or marine deposits can be used to trace water mass movements and to quantify the incorporation of trace metals into the deep sea. In this study a SIMS-based technique has been used to determine the 10Be/9Be ratios of the outermost millimetre of hydrogenetic ferromanganese crusts from the worlds oceans. 10Be/9Be ratios, time-corrected for radioactive decay of cosmogenic 10Be using 234U/ 238U, are in good agreement with AMS measurements of modern deep seawater. Ratios are relatively low in the North and equatorial Atlantic samples (0.4-0.5 ?? 10-7). In the Southwest Atlantic ratios increase up to 1 ?? 10-7, they vary between 0.7 and 1.0 ?? 10-7 in Indian Ocean samples, and have a near constant value of 1.1 ?? 0.2 ?? 10-7 for all Pacific samples. If the residence time of 10Be (??10Be) in deep water is constant globally, then the observed variations in 10Be/9Be ratios could be caused by accumulation of 10Be in deep water as it flows and ages along the conveyor, following a transient depletion upon its formation in the Northern Atlantic. In this view both 10Be and 9Be reach local steady-state concentration in Pacific deep water and the global ??10Be ??? 600 a. An alternative possibility is that the Be isotope abundances are controlled by local scavenging. For this scenario ??10Be would vary according to local particle concentration and would ??? 600 a in the central Pacific, but ??10Be ??? 230 a in the Atlantic. Mass balance considerations indicate that hydrothermal additions of 9Be to the oceans are negligible and that the dissolved riverine source is also small. Furthermore, aeolian dust input of 9Be appears insufficient to provide the dissolved Be inventory. The dissolution of only a small proportion (2%) of river-derived particulates could in principle supply the observed seawater Be content. If true, ocean margins would be the sites for 9Be addition. Due to the particle-reactive nature of Be, these would also be the primary sites of Be removal. A possible net result of horizontal water masses passing through these marginal areas might be a decrease in seawater 10Be/9Be, and establishment of a relatively constant 9Be concentration. As ??10Be ( ??? 600 a) is less than the apparent age of deep water in the Pacific ( ??? 1500 a), the Pacific record of 10Be/ 9Be is not expected to show secular variations due to changes in deep-water flow, despite the large variations in 10Be/ 9Be between different water masses. Because of this insensitivity to deep-water flow, however, it is suggested that the 10Be/ 9Be ratio, determined in the authigenic phase of marine sediments or hydrogenetic precipitates, should be a suitable tool for monitoring changes in continental input or cosmic ray intensity on longer time scales.

  19. Vertical tectonics at a continental crust-oceanic plateau plate boundary zone: Fission track thermochronology of the Sierra Nevada de Santa Marta, Colombia (United States)

    Villagómez, Diego; Spikings, Richard; Mora, AndréS.; GuzmáN, Georgina; Ojeda, GermáN.; CortéS, Elizabeth; van der Lelij, Roelant


    The topographically prominent Sierra Nevada de Santa Marta forms part of a faulted block of continental crust located along the northern boundary of the South American Plate, hosts the highest elevation in the world (˜5.75 km) whose local base is at sea level, and juxtaposes oceanic plateau rocks of the Caribbean Plate. Quantification of the amount and timing of exhumation constrains interpretations of the history of the plate boundary, and the driving forces of rock uplift along the active margin. The Sierra Nevada Province of the southernmost Sierra Nevada de Santa Marta exhumed at elevated rates (?0.2 Km/My) during 65-58 Ma in response to the collision of the Caribbean Plateau with northwestern South America. A second pulse of exhumation (?0.32 Km/My) during 50-40 Ma was driven by underthrusting of the Caribbean Plate beneath northern South America. Subsequent exhumation at 40-25 Ma (?0.15 Km/My) is recorded proximal to the Santa Marta-Bucaramanga Fault. More northerly regions of the Sierra Nevada Province exhumed rapidly during 26-29 Ma (˜0.7 Km/My). Further northward, the Santa Marta Province exhumed at elevated rates during 30-25 Ma and 25-16 Ma. The highest exhumation rates within the Sierra Nevada de Santa Marta progressed toward the northwest via the propagation of NW verging thrusts. Exhumation is not recorded after ˜16 Ma, which is unexpected given the high elevation and high erosive power of the climate, implying that rock and surface uplift that gave rise to the current topography was very recent (i.e., ?1 Ma?), and there has been insufficient time to expose the fossil apatite partial annealing zone.

  20. Seismic wave velocity of rocks in the Oman ophiolite: constraints for petrological structure of oceanic crust (United States)

    Saito, S.; Ishikawa, M.; Shibata, S.; Akizuki, R.; Arima, M.; Tatsumi, Y.; Arai, S.


    Evaluation of rock velocities and comparison with velocity profiles defined by seismic refraction experiments are a crucial approach for understanding the petrological structure of the crust. In this study, we calculated the seismic wave velocities of various types of rocks from the Oman ophiolite in order to constrain a petrological structure of the oceanic crust. Christensen & Smewing (1981, JGR) have reported experimental elastic velocities of rocks from the Oman ophiolite under oceanic crust-mantle conditions (6-430 MPa). However, in their relatively low-pressure experiments, internal pore-spaces might affect the velocity and resulted in lower values than the intrinsic velocity of sample. In this study we calculated the velocities of samples based on their modal proportions and chemical compositions of mineral constituents. Our calculated velocities represent the ‘pore-space-free’ intrinsic velocities of the sample. We calculated seismic velocities of rocks from the Oman ophiolite including pillow lavas, dolerites, plagiogranites, gabbros and peridotites at high-pressure-temperature conditions with an Excel macro (Hacker & Avers 2004, G-cubed). The minerals used for calculations for pillow lavas, dolerites and plagiogranites were Qtz, Pl, Prh, Pmp, Chl, Ep, Act, Hbl, Cpx and Mag. Pl, Hbl, Cpx, Opx and Ol were used for the calculations for gabbros and peridotites. Assuming thermal gradient of 20° C/km and pressure gradient of 25 MPa/km, the velocities were calculated in the ranges from the atmospheric pressure (0° C) to 200 MPa (160° C). The calculation yielded P-wave velocities (Vp) of 6.5-6.7 km/s for the pillow lavas, 6.6-6.8 km/s for the dolerites, 6.1-6.3 km/s for the plagiogranites, 6.9-7.5 km/s for the gabbros and 8.1-8.2 km/s for the peridotites. On the other hand, experimental results reported by Christensen & Smewing (1981, JGR) were 4.5-5.9 km/s for the pillow lavas, 5.5-6.3 km/s for the dolerites, 6.1-6.3 km/s for the plagiogranites, 6.5-7.7 km/s for the gabbros and 6.3-7.9 km/s for the peridotites. Although the two results are broadly comparable to each other for plagiogranites and gabbros, the calculated velocities are considerably higher than the experimental ones for pillow lavas, dolerites and peridotites. The discrepancy for the pillow lavas and dolerites can be attributed to the presence of pore-spaces in the experimental samples. On the other hand, serpentinization of peridotite samples likely resulted in lower velocities in experiments than in calculation. We compared our results with Vp structure of the oceanic crust and mantle (White et al. 1992, JGR). The calculated Vp of peridotites and gabbros are comparable to those of mantle and layer-3, respectively. The calculated Vp of dolerites is comparable to layer-3 and considerably higher than layer-2 velocities. However, recent deep drilling results (Holes 504B and 1256D) indicate the seismic layer-2 of oceanic crust mainly composed of dolerites, which is consistent with the experimental P-wave velocities of dolerites (Christensen & Smewing, 1981, JGR). These results imply that the velocity structure of seismic layer-2 reflects the distribution of pore-spaces in the upper oceanic crust.

  1. Insights into magmatic processes and hydrothermal alteration of in situ superfast spreading ocean crust at ODP/IODP site 1256 from a cluster analysis of rock magnetic properties (United States)

    Dekkers, Mark J.; Heslop, David; Herrero-Bervera, Emilio; Acton, Gary; Krasa, David


    analyze magnetic properties from Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6°44.1' N, 91°56.1' W) on the Cocos Plate in ˜15.2 Ma oceanic crust generated by superfast seafloor spreading, the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Fuzzy c-means cluster analysis and nonlinear mapping are utilized to study down-hole trends in the ratio of the saturation remanent magnetization and the saturation magnetization, the coercive force, the ratio of the remanent coercive force and coercive force, the low-field magnetic susceptibility, and the Curie temperature, to evaluate the effects of magmatic and hydrothermal processes on magnetic properties. A statistically robust five cluster solution separates the data predominantly into three clusters that express increasing hydrothermal alteration of the lavas, which differ from two distinct clusters mainly representing the dikes and gabbros. Extensive alteration can obliterate magnetic property differences between lavas, dikes, and gabbros. The imprint of thermochemical alteration on the iron-titanium oxides is only partially related to the porosity of the rocks. Thus, the analysis complements interpretation based on electrofacies analysis. All clusters display rock magnetic characteristics compatible with an ability to retain a stable natural remanent magnetization suggesting that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Paleointensity determination is difficult because of the propensity of oxyexsolution during laboratory heating and/or the presence of intergrowths. The upper part of the extrusive sequence, the granoblastic dikes, and moderately altered gabbros may contain a comparatively uncontaminated thermoremanent magnetization.

  2. North Atlantic Deep Water export to the Southern Ocean over the past 14 Myr: Evidence from Nd and Pb isotopes in ferromanganese crusts (United States)

    Frank, M.; Whiteley, N.; Kasten, S.; Hein, J.R.; O'Nions, K.


    The intensity of North Atlantic Deep Water (NADW) production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate. Here we present a new approach to reconstruct the overall strength of NADW export from the North Atlantic to the Southern Ocean over the past 14 Myr applying the deep water Nd and Pb isotope composition as recorded by ferromanganese crusts and nodules. We present the first long-term Nd and Pb isotope time series for deep Southern Ocean water masses, which are compared with previously published time series for NADW from the NW Atlantic Ocean. These data suggest a continuous and strong export of NADW, or a precursor of it, into the Southern Ocean between 14 and 3 Ma. An increasing difference in Nd and Pb isotope compositions between the NW Atlantic and the Southern Ocean over the past 3 Myr gives evidence for a progressive overall reduction of NADW export since the onset of Northern Hemisphere glaciation (NHG). The Nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37% depending on location.

  3. High-Albedo Salt Crusts on the Tropical Ocean of Snowball Earth: Measurements and Modeling (United States)

    Carns, R.; Light, B.; Warren, S. G.


    During a Snowball Earth event, almost all of the ocean surface first freezes as sea ice. As in modern sea ice, trapped inclusions of liquid brine permeate the ice cover. As the ice grows and cools, salt crystals precipitate within the inclusions. At -23C, the most abundant salt in seawater, sodium chloride, begins to precipitate as the dihydrate mineral hydrohalite (NaCl·2H2O). Crystals of hydrohalite within the sea ice scatter light. Measurements of cold, natural sea ice show a broadband albedo increase of 10-20% when salt precipitates. Such snow-free natural sea ice with a surface temperature below -23C is rare on modern Earth, but would have been common in tropical regions of a Snowball Earth where evaporation exceeded precipitation. The persistent cold and lack of summer melt on the Snowball ocean surface, combined with net evaporation, is hypothesized to yield lag deposits of hydrohalite crystals on the ice surface. To investigate this process, we prepared laboratory-grown sea ice in a 1000 liter tank in a walk-in freezer laboratory. The ice was cooled below -23 C and the surface sprayed with a 23% NaCl solution to create a layer of hydrohalite-enriched ice, a proxy for lag deposits that would have formed over long periods of surface sublimation. We have developed a novel technique for measuring the spectral albedo of ice surfaces in the laboratory; this technique was used to monitor the evolution of the surface albedo of our salt crust as the ice matrix sublimated away leaving a layer of fine-grained hydrohalite crystals. Measurements of this hydrohalite surface crust show a very high albedo, comparable to fresh snow at visible wavelengths and significantly larger than fresh snow at near infrared wavelengths. Broadband albedos are 0.55 for bare artificial sea ice at -30C, 0.75 for ice containing 25% hydrohalite by volume, 0.84 after five days of desiccation and 0.93 after 47 days of desiccation. Using our laboratory measurements, along with estimates of grain size and crust optical depth, as inputs to Mie scattering and radiative transfer models allowed us to infer the imaginary refractive index of hydrohalite. The model can calculate albedo for pure hydrohalite crusts of varying thickness and for mixtures of ice and hydrohalite. A parameterization is presented for albedo as a function of the thickness of the hydrohalite crust.

  4. The strontium isotopic composition of seawater, and seawater-oceanic crust interaction

    International Nuclear Information System (INIS)

    The 87Sr/86Sr ratio of seawater strontium (0.7091) is less than the 87Sr/86Sr ratio of dissolved strontium delivered to the oceans by continental run-off (approximately 0.716). Isotope exchange with strontium isotopically lighter oceanic crust during hydrothermal convection within spreading oceanic ridges can explain this observation. In quantitative terms, the current 87Sr/86Sr ratio of seawater (0.7091) may be maintained by balancing the continental run-off flux of strontium (0.59 x 1012g/yr) against a hydrothermal recirculation flux of 3.6 x 1012g/yr, during which the 87Sr/86Sr ratio of seawater drops by 0.0011. A concomitant mean increase in the 87Sr/86Sr ratio of the upper 4.5 km of oceanic crust of 0.0010 (0.7029-0.7039) should be produced. This required 87Sr enrichment has been observed in hydrothermally metamorphosed ophiolitic rocks from the Troodos Massif, Cyprus. The post-Upper Cretaceous increase in the strontium isotopic composition of seawater (approximately 0.7075-0.7091) covaries smoothly with inferred increase in land area. This suggests that during this period the main factor which has caused variability in the 87Sr/86Sr ratio of seawater strontium could have been variation in the magnitude of the continental run-off flux caused by variation in land area. Variations in land area may themselves have been partly a consequence of variations in global mean sea-floor spreading rate. (Auth.)

  5. Araxa Group in the type-area: A fragment of Neoproterozoic oceanic crust in the Brasilia Fold Belt

    International Nuclear Information System (INIS)

    This study reviews the geological characteristics and puts forward a new evolution model for the Araxa Group in its type-area, the southern segment of the Neo proterozoic Brasilia Belt, Minas Gerais, Brazil. The Araxa Group is confined within a thrust sheet belonging to a syn formal regional fold, the Araxa Syn form, overlying two other thrust sheets made of the Ibia and Canastra Groups. The Araxa Group is described as a tectono stratigraphic terrane in the sense of Howell (1993). It comprises an igneous mafic sequence, with fine and coarse grained amphibolites, associated with pelitic meta sedimentary rocks, and subordinate psanmites. All rocks were metamorphosed to amphibolite facies at ca. 630 Ma ago and were intruded by collisional granites. The amphibolites represent original basaltic and gabbroic rocks, with minor ultramafic (serpentinite/ amphibole-talc schist). The basalts are similar to high Fe O tholeiites, with REE signatures that resemble E-MORB and ?Nd(T) =+ 1.1. The meta sedimentary rocks are interpreted as the result of a marine deep-water sedimentation. They have Sm-Nd model ages of 1,9 Ga, and ?Nd(T) = -10.21. The amphibolites and metasediments could represent a fragment of back-arc oceanic crust. The data presented here differ significantly from the original definition of Barbosa et al. (1970) who describe the Araxa Group as a pelitic/psanmitic sequence and the collisional granites as a basement complex. (author)

  6. Positive geothermal anomalies in oceanic crust of Cretaceous age offshore Kamchatka (United States)

    Delisle, G.


    Heat flow measurements were carried out in 2009 offshore Kamchatka during the German-Russian joint-expedition KALMAR. An area with elevated heat flow in oceanic crust of Cretaceous age - detected ~30 yr ago in the course of several Russian heat flow surveys - was revisited. One previous interpretation postulated anomalous lithospheric conditions or a connection between a postulated mantle plume at great depth (>200 km) as the source for the observed high heat flow. However, the positive heat flow anomaly - as our bathymetric data show - is closely associated with the fragmentation of the western flank of the Meiji Seamount into a horst and graben structure initiated during descent of the oceanic crust into the subduction zone offshore Kamchatka. This paper offers an alternative interpretation, which connects high heat flow primarily with natural convection of fluids in the fragmented rock mass and, as a potential additional factor, high rates of erosion, for which evidence is available from our collected bathymetric image. Given high erosion rates, warm rock material at depth rises to nearer the sea floor, where it cools and causes temporary elevated heat flow.

  7. Positive geothermal anomalies in oceanic crust of Cretaceous age offshore Kamchatka

    Directory of Open Access Journals (Sweden)

    G. Delisle


    Full Text Available Heat flow measurements were carried out in 2009 offshore Kamchatka during the German-Russian joint-expedition KALMAR. An area with elevated heat flow in oceanic crust of Cretaceous age – detected ~30 years ago in the course of several Russian heat flow surveys – was revisited. One previous interpretation postulated anomalous lithospheric conditions or a connection between a postulated mantle plume at great depth (> 200 km as the source for the observed high heat flow. However, the positive heat flow anomaly – as our bathymetric data show – is closely associated with the fragmentation of the western flank of the Meiji Seamount into a horst and graben structure, initiated during descend of the oceanic crust into the subduction zone offshore Kamchatka. This paper offers an alternative interpretation, which connects high heat flow primarily with natural convection of fluids in the fragmented rock mass and, as a potential additional factor, high rates of erosion, for which evidence is available from our collected bathymetric image. Given high erosion rates, warm rock material at depth rises to nearer the sea floor, where it cools and causes temporary elevated heat flow.

  8. Intraterrestrial life in igneous ocean crust: advances, technologies, and the future (Invited) (United States)

    Edwards, K. J.; Wheat, C. G.


    The “next frontier” of scientific investigation in the deep sub-seafloor microbial biosphere lies in a realm that has been a completely unexplored until just the past decade: the igneous oceanic crust. Problems that have hampered exploration of the “hard rock” marine deep biosphere have revolved around sample access (hard rock drilling is technologically complex), contamination (a major hurdle), momentum (why take on this challenge when the relatively “easier” marine muds also have been a frontier) and suspicion that microbes in more readily accessed using (simpler) non-drilling technologies - like vents - are truly are endemic of subsurface clades/activities. Since the late 1990’s, however, technologies and resultant studies on microbes in the igneous ocean crust deep biosphere have risen sharply, and offer a new and distinct view on this biome. Moreover, microbiologists are now taking leading roles in technological developments that are critically required to address this biosphere - interfacing and collaborating closely with engineers, genomic biologists, geologists, seismologists, and geochemists to accomplish logistically complex and long-term studies that bring observatory research to this deep realm. The future of this field for the least decade is rich - opportunities abound for microbiologists to play new roles in how we study microbiology in the deep subsurface in an oceanographic and Earth system science perspective.

  9. Positive geothermal anomalies in oceanic crust of Cretaceous age offshore Kamchatka

    Directory of Open Access Journals (Sweden)

    G. Delisle


    Full Text Available Heat flow measurements were carried out in 2009 offshore Kamchatka during the German-Russian joint-expedition KALMAR. An area with elevated heat flow in oceanic crust of Cretaceous age – detected ~30 yr ago in the course of several Russian heat flow surveys – was revisited. One previous interpretation postulated anomalous lithospheric conditions or a connection between a postulated mantle plume at great depth (>200 km as the source for the observed high heat flow. However, the positive heat flow anomaly – as our bathymetric data show – is closely associated with the fragmentation of the western flank of the Meiji Seamount into a horst and graben structure initiated during descent of the oceanic crust into the subduction zone offshore Kamchatka. This paper offers an alternative interpretation, which connects high heat flow primarily with natural convection of fluids in the fragmented rock mass and, as a potential additional factor, high rates of erosion, for which evidence is available from our collected bathymetric image. Given high erosion rates, warm rock material at depth rises to nearer the sea floor, where it cools and causes temporary elevated heat flow.

  10. 75 FR 34929 - Safety Zones: Neptune Deep Water Port, Atlantic Ocean, Boston, MA (United States)


    ... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zones: Neptune Deep Water Port, Atlantic Ocean... comment at the Web site . These safety zones are needed pending implementation... Deep Water Port, Atlantic Ocean, Boston, MA; Final Rule (USCG-2009-0589), to protect vessels from...

  11. A Cross-Hole, Multi-Year Tracer Injection Experiment in the Volcanic Ocean Crust (United States)

    Fisher, A. T.; Neira, N. M.; Wheat, C. G.; Clark, J. F.; Becker, K.; Hsieh, C. C.; Rappe, M. S.


    We present preliminary results from the first cross-hole tracer injection experiment in the volcanic ocean crust. The test site is on 3.5 to 3.6 M.y. old seafloor on the eastern flank of the Juan de Fuca Ridge. Six borehole subseafloor observatories (CORKs) were installed during three scientific ocean drilling expeditions, five arrayed along a 1 km profile aligned with the strike of underlying abyssal hills (Holes 1026B, 1301A/B, and 1362A/B), and one offset 2.4 km to the east (1027C). Before installing the sixth CORK in Hole 1362B, in 2010, we injected a mixture of tracers (dissolved gas, metal salts, particles) during 24 hours into the upper ocean crust. Seafloor samplers connected CORKs, sampling from different locations in the crust, were recovered during servicing expeditions in 2011 and 2013; downhole samplers that contain records from the full four years following tracer injection will be recovered in Summer 2014. Analyses of dissolved gas tracers collected with wellhead samplers through 2013 suggest that the dominant flow direction in upper basement is south to north, as inferred from regional thermal data and the chemistry of geochemical (pore fluid and borehole) samples. The apparent tracer flow rate in upper basement is on the order of meters/day, but calculations are complicated by an incomplete CORK seal in Hole 1301A, which resulted in discharge from this system that also "pulled" water and tracer to the south. Samples were collected from the tracer injection borehole, Hole 1362B, and a sampling site 200 m to the north, Hole 1362A, beginning one year after tracer injection, after opening a large-diameter ball valve on the wellhead of Hole 1362B to initiate a long-term free flow experiment. Analyses of these samples suggest that much of the tracer injected in 2010 remained close to Hole 1362B rather than being advected and dispersed into the formation. It also appears that much of the tracer transport to Hole 1362A occurred within one or more relatively thin/isolated zones, because tracer concentrations remain relatively high and there is a long tail of gradually decreasing values during the last two years of sampling. This interpretation is consistent with the highly layered and laterally continuous volcanic stratigraphy observed in basement boreholes drilled at Sites 1301 and 1362.

  12. Deep Continental Lithosphere Keels as Impediments to Asthenosphere Flow and Cause of Ocean Crust Depth Anomalies (United States)

    Ryan, W. B.; Muhlenkamp, B. M.; Haxby, W. F.; Carbotte, S. M.; Buck, W. R.


    The Australian-Antarctic Discordance (AAD) lies directly in the wake of a deep keel of 2.5 billion year old Australian lithosphere that severed from and moved northward in the hot spot reference frame from a near-stationary Antarctica. Adopting the model of a plume-fed sub-ocean asthenosphere (Morgan, 1971,1972; Phipps Morgan,et al, 1995), this keel, like others of similar ancient age beneath South Africa and Laurentia could have served as a dam to isolate different pools of asthenosphere and thus allow each pool to evolve independently from their supplying plumes. A NSF-funded Antarctic database effort has allowed us to digitize a large set of seismic reflection profiles, map sediment thickness and remove the subsidence caused by sediment load. This effort confirms not only that the ocean crust between the keels of Australia and Antarctica was always manufactured at an anomalously deep spreading center, but the depth anomaly was greatest right after continental separation, and the crust beneath the faster moving Australian plate is deeper for all ages than counterparts on the Antarctic Plate. The same depth asymmetry and a similar geoid anomaly are observed in the South Atlantic where South America is traveling faster than Africa relative to the mantle. Upon separation of the continents, asthenosphere from both sides of the keel flows into the wake of the moving continent to replenish the void created by the initial dam. The Pacific asthenosphere, with its distinct geochemical composition, is currently observed to be propagating into the AAD. Since asthenosphere is consumed as it is frozen onto the diverging oceanic lithosphere, a dammed region with a limited asthenosphere supply might act as a brake, or governor, for seafloor spreading. We point out that spreading started very slowly upon the breakup of Australia and Antarctica, the aborted spreading center in the Labrador Sea occurs in a narrow ocean between very ancient cratons, and the boundary between the geochemical distinct Indian and Atlantic mid-ocean ridges occur where deep continental keels were severed.

  13. The Ocean and Crust of a Rapidly Accreting Neutron Star Implications for Magnetic Field Evolution and Thermonuclear Flashes

    CERN Document Server

    Brown, E F; Brown, Edward F.; Bildsten, Lars


    We investigate the atmosphere, ocean, and crust of neutron stars accreting at rates sufficiently high (typically in excess of the local Eddington limit) to stabilize the burning of accreted hydrogen and helium. For hydrogen-rich accretion at global rates in excess of 10^-8 solar masses per year (typical of a few neutron stars), we discuss the thermal state of the deep ocean and crust and their coupling to the neutron star core, which is heated by conduction (from the crust) and cooled by neutrino emission. We estimate the Ohmic diffusion time in the hot, deep crust and find that it is noticeably shortened (to less than 10^8 yr) from the values characteristic of the colder crusts in slowly accreting neutron stars. We speculate on the implications of these calculations for magnetic field evolution in the bright accreting X-ray sources. We also explore the consequences of rapid compression at local accretion rates exceeding ten times the Eddington rate. This rapid accretion heats the atmosphere/ocean to temperat...

  14. The tectonic history of southern Baffin Bay and Davis Strait - seismic refraction experiments and the evolution of oceanic crust (United States)

    Suckro, S. K.; Gohl, K.; Funck, T.; Heyde, I.; Schreckenberger, B.; Ehrhardt, A.; Gerlings, J.; Damm, V.; Jokat, W.


    Located between the Canadian Baffin Island and Greenland, Baffin Bay represents the northern extension of the rift system in Labrador Sea. Davis Strait is a bathymetric high, that connects Baffin Bay with the Labrador Sea and acts as a gateway for the water exchange between the two basins. The strait is dominated by the Ungava Fault Complex, a major transform fault, characterized by a series of positive gravity anomalies. It is generally agreed, that the extensional motion of the rift system in Labrador Sea was connected with the opening of Baffin Bay by the Ungava Fault Complex. Unlike in Labrador Sea, no magnetic spreading anomalies have clearly been identified in Baffin Bay, hence the nature of the crust remains a subject of discussion. In order to determine the character of the crust in southern Baffin Bay, a 710-km-long seismic refraction experiment was set up in two research cruises (MSM09/3 of RV Maria S. Merian in 2008 and ARK25/3 of RV Polarstern in 2010). P-wave velocity and density modeling display the following crustal units from southeast to northwest: transitional crust near Baffin Island, more than 300 km of oceanic crust with an extinct spreading center, 100 km of transitional crust of a volcanic type margin on the Greenland side of the profile, and Greenland continental crust. The nature of the crust in Davis Strait is also disputed. Both, blocks of continental crust or a thick pile of oceanic crust have been proposed. To identify the character of the crust, a 226-km-long seismic refraction line was set up across the strait (MSM09/3 expedition). The P-wave velocity and density models image continental blocks with deep reaching faults. The lower crust displays abnormally high P-wave velocities, which we attribute to intense intrusions of mafic material, most likely related to the arrival of the Iceland mantle plume beneath Greenland in the Paleocene. To set the crustal units along the two profiles into context with the tectonic history of the Labrador Sea and Baffin Bay region, we visualized the opening of these basins in GPlates with published poles of rotation. It became clear, that the existing tectonic map of this region needs modifications, which we present here. Furthermore, the reconstruction images the compression of previously rifted crust in Davis Strait which adds up to an overlap of 70 km.

  15. Oceanographer transform fault structure compared to that of surrounding oceanic crust: Results from seismic refraction data analysis (United States)

    Ambos, E. L.; Hussong, D. M.


    A high quality seismic refraction data set was collected near the intersection of the tranform portion of the Oceanographer Fracture Zone (OFZ) with the adjacent northern limb of the Mid-Atlantic Ridge spreading center (MAR). One seismic line was shot down the axis of the transform valley. Another was shot parallel to the spreading center, crossing from normal oceanic crust into the transform valley, and out again. This latter line was recorded by four Ocean Bottom Seismometers (OBSs) spaced along its length, providing complete reversed coverage over the crucial transform valley zone. Findings indicate that whereas the crust of the transform valley is only slightly thinner (4.5 km) compared to normal oceanic crust (5-8 km), the structure is different. Velocities in the range of 6.9 to 7.7. km/sec, which are characteristics of seismic layer 3B, are absent, although a substantial thickness (approximately 3 km) of 6.1-6.8 km/sec material does appear to be present. The upper crust, some 2 km in thickness, is characterized by a high velocity gradient (1.5 sec -1) in which veloxity increases from 2.7 km/sec at the seafloor to 5.8 km/sec at the base of the section. A centrally-located deep of the transform valley has thinner crust (1-2 km), whereas the crust gradually thickens past the transform valley-spreading center intersection. Analysis of the seismic line crossing sub-perpendicular to the transform valley demonstrates abrupt thinning of the upper crustal section, and thickening of the lower crust outside of the trasform valley. In addition, high-velocity material seems to occur under the valley flanks, particularly the southern flanking ridge. This ridge, which is on the side of the transform opposite to the intersection of spreading ridge and transform, may be an expression of uplifted, partially serpentinized upper mantle rocks.

  16. Reactive overprint of the Central Indian Ridge mantle and formation of hybrid troctolites: reassessing the significance of bulk oceanic crust (United States)

    Sanfilippo, A.; Morishita, T.; Kumagai, H.; Nakamura, K.; Okino, K.; Tamura, A.; Arai, S.


    The idea that hybridized mantle rocks can contribute to the oceanic crust composition has recently emerged thanks to studies on primitive (olivine-rich) troctolites [e.g. 1]. These rocks are considered to be formed by melt-rock interaction, but the exact reaction process by which they originate is still debated and their role on the bulk oceanic crust composition has been never defined. Olivine-rich troctolites have been mostly found at slow spreading ridges [2] or at their fossil analogues [3]. Similar rocks have been recently collected in the 25ºS area of the intermediate spreading Central Indian Ridge (CIR), and rarely characterize the crust mantle boundary at fast spreading ridges [4]. We show that textural and chemical inheritances of the pre-existing mantle are preserved in the CIR troctolites. In particular, the local occurrence of granular, mantle-derived orthopyroxenes and the composition of the associated clinopyroxene indicate that these crustal rocks formed through a direct (one-stage) conversion of a mantle peridotite. We use chemical evidence to infer the same origin of the olivine-rich troctolites worldwide, concluding that the reactive overprint of the oceanic mantle is a process diffused over the entire spreading rate spectrum. Bulk oceanic crust estimates of the Hess Deep (Pacific) and Atlantis Massif (Atlantic) crustal sections are used to quantify and compare the effect of these rocks on the bulk crust composition at fast and slow spreading ridges. Our inferences suggest that the significance of the bulk oceanic crust should be reassessed. When hybrid troctolites are included at crustal levels, the oceanic crust cannot be considered equal to the composition of the melt extracted from the mantle, but it results more primitive and importantly thicker. References: [1] Suhr G., Hellebrand E., Johnson K., Brunelli D., 2008, Geochem. Geophys. Geosyst. 9, doi:10.1029/2008GC002012; [2] Drouin M., Godard M., Ildefonse B., Bruguier O., Garrido C.J. , 2009, Chem. Geol. 264, 71-88; [3] Renna M. R., Tribuzio R., 2011, J. Petrol. 52, 1763-1790; [4] Dick H.J.B. and Natland J.H., 1996, Proceedings Ocean Drill. Prog., 147, 103-134.

  17. Static and fault-related alteration in the lower ocean crust, IODP Expedition 345, Hess Deep (United States)

    McCaig, Andrew; Faak, Kathrin; Marks, Naomi; Nozaka, Toshio; Python, Marie; Wintsch, Robert; Harigane, Yumiko; Titarenko, Sofya


    IODP Expedition 345 drilled the first holes in the lower plutonic crust at a fast-spreading ridge, recovering primitive layered gabbros (Gillis et al 2014). Alteration can be subdivided into two series: 1) a largely static pseudomorphic alteration affecting predominantly olivine. This began in the amphibolite facies with minor secondary cinopyroxene and hornblendic amphibole replacing primary pyroxene, and sporadically developed corona textures with tremolite and chlorite replacing olivine and plagioclase respectively, but was predominantly in the greenschist and sub-greenschist facies with talc, serpentine, clay minerals,oxides andsulphides replacing olivine, and prehnite and locally other calcsilicates replacing plagioclase, commonly in micro-vein networks. Albitic plagioclase is sporadically developed, and locally zeolite and carbonate. 2) An overprinting metasomatic alteration under sub-greenschist or perhaps lowermost greenschist conditions(zeolite. This alteration is spatially related to cataclastic fault zones and macroscopic veins. Comminuted plagioclase in cataclasites is commonly completely replaced by prehnite, while chlorite may completely pseudomorph olivine, locally with textures suggesting replacement of previous secondary minerals such as talc and serpentine. Chlorite also ubiquitously occurs as patches replacing plagioclase along grain boundaries, locally associated with carbonate and amphibole needles. Metamorphosed dykes show chilled margins within the cataclasites, and are affected by cataclastic deformation. Faults, dykes and overprinting alteration are all inferred to be related to the westward propagation of Cocos-Nazca spreading that formed Hess Deep. Samples of different alteration and cataclastic domains were cut out of this section chips for isotopic analysis. 87Sr/86Sr ratios of cataclasites and dyke rocks are in the range 0.7037 - 0.7048, indicating alteration by seawater at moderate integrated fluxes. The highest values were in cataclasites overprinted by prehnite. ?18O values range from +1 to + 6 per mil, indicating alteration at temperatures generally >200 °C. Preliminary modelling using Comsol Multiphysics suggests that the temperatures of the overprinting alteration could be achieved in a permeable fault slot cutting through crust 0.5 to 1 m.y. old. Our study reveals a low temperature alteration assemblage dominated by prehnite and chlorite that is not normally associated with the lower oceanic crust. Yet it is likely to be common in any location where faults intersect the Moho off-axis, including transform faults, near axis normal faults at slow spreading ridges, and bending faults at subduction zones, and would be accompanied by serpentinites in upper mantle rocks, as seen at ODP site 895 in Hess Deep. This prehnite + chlorite assemblage may therefore be significant in the release of volatiles in subduction zones. Gillis, K.M., Snow J. E. and Shipboard Science Party (2014) Primitive layered gabbros from fast-spreading lower oceanic crust. Nature, 505,204-207, doi: 10.1038/nature12778

  18. Lithium and Li-isotopes in young altered upper oceanic crust from the East Pacific Rise (United States)

    Brant, C.; Coogan, L. A.; Gillis, K. M.; Seyfried, W. E.; Pester, N. J.; Spence, J.


    Lithium contents and Li-isotope ratios have been measured in a section of young oceanic upper crust formed at the East Pacific Rise and exposed in the Hess Deep rift. The Li contents of both lavas and sheeted dikes are lower than in the fresh protolith (by 43% and 74%, respectively) suggesting that axial hydrothermal systems leach Li from the entire upper crust. The Li-isotopic composition of the lavas (4.1 ± 1.7‰) is similar to the protolith (3.4 ± 1.4‰) whereas the dikes extend to both higher and lower isotopic compositions (?7Li from -11 to 14‰). Loss of Li from all lava samples was unexpected due to the petrographically fresh appearance of these rocks and the relatively cool fluids generally thought to exist within the lava pile. This Li loss is interpreted as indicating that warm (50-100 °C) fluids pervade the lava pile, at least episodically, leaching Li from the lavas without recrystallization of the primary igneous minerals. This hypothesis has been tested experimentally. Hydrothermal experiments at 125 °C, using synthetic basalts cooled at different rates to produce different starting material texture (glass to crystalline rock), demonstrate that Li is leached rapidly at this temperature and substantially more rapidly from crystalline rock than from glass. The natural and experimental data are consistent with Li diffusion out of plagioclase into warm hydrothermal fluids acting to leach Li from the lavas without any concomitant mineralogical changes. The wide range of ?7Li in the sheeted dike complex, and the lack of a systematic correlation of ?7Li with the concentration of Li, suggest that more than one process leads to Li depletion. A combination of mineral-fluid reactions that break-down igneous minerals and produce secondary minerals (principally amphibole, chlorite and secondary plagioclase), along with diffusive loss of Li from plagioclase into the fluid, can explain the Li-systematics of the sheeted dike complex at Hess Deep.

  19. Separate zones of sulfate and sulfide release from subducted mafic oceanic crust (United States)

    Tomkins, Andrew G.; Evans, Katy A.


    Liberation of fluids during subduction of oceanic crust is thought to transfer sulfur into the overlying sub-arc mantle. However, despite the importance of sulfur cycling through magmatic arcs to climate change, magma oxidation and ore formation, there has been little investigation of the metamorphic reactions responsible for sulfur release from subducting slabs. Here, we investigate the relative stability of anhydrite (CaSO4) and pyrite (FeS2) in subducted basaltic oceanic crust, the largest contributor to the subducted sulfur budget, to place constraints on the processes controlling sulfur release. Our analysis of anhydrite stability at high pressures suggests that this mineral should dominantly dissolve into metamorphic fluids released across the transition from blueschist to eclogite facies (?450-650 °C), disappearing at lower temperatures on colder geothermal trajectories. In contrast, we suggest that sulfur release via conversion of pyrite to pyrrhotite occurs at temperatures above 750 °C. This higher temperature stability is indicated by the preservation of pyrite-bornite inclusions in coesite-bearing eclogites from the Sulu Belt in China, which reached temperatures of at least 750 °C. Thus, sulfur may be released from subducting slabs in two separate pulses; (1) varying proportions of SO2, HSO4- and H2S are released via anhydrite breakdown at the blueschist-eclogite transition, promoting oxidation of remaining silicates in some domains, and (2) H2S is released via pyrite breakdown well into the eclogite facies, which may in some circumstances coincide with slab melting or supercritical liquid generation driven by influx of serpentinite-derived fluids. These results imply that the metallogenic potential in the sub-arc mantle above the subducting slab varies as a function of subduction depth, having the greatest potential above the blueschist-eclogite transition given the association between oxidised magmas and porphyry Cu(-Au-Mo) deposits. We speculate that this zoned sulfur liberation might be one of the factors that lead to the apparently redox-influenced zoned distribution of ore deposit types in the Andean arc. Furthermore, given the lack of sulfate-associated sea floor oxidation prior to the second great oxidation event, the pattern of sulfur transfer from the slab to the sub-arc mantle likely changed over time, becoming shallower and more oxidised from the Neoproterozoic onwards.

  20. High Temperature Logging and Monitoring Instruments to Explore and Drill Deep into Hot Oceanic Crust. (United States)

    Denchik, N.; Pezard, P. A.; Ragnar, A.; Jean-Luc, D.; Jan, H.


    Drilling an entire section of the oceanic crust and through the Moho has been a goal of the scientific community for more than half of a century. On the basis of ODP and IODP experience and data, this will require instruments and strategies working at temperature far above 200°C (reached, for example, at the bottom of DSDP/ODP Hole 504B), and possibly beyond 300°C. Concerning logging and monitoring instruments, progress were made over the past ten years in the context of the HiTI ("High Temperature Instruments") project funded by the european community for deep drilling in hot Icelandic geothermal holes where supercritical conditions and a highly corrosive environment are expected at depth (with temperatures above 374 °C and pressures exceeding 22 MPa). For example, a slickline tool (memory tool) tolerating up to 400°C and wireline tools up to 300°C were developed and tested in Icelandic high-temperature geothermal fields. The temperature limitation of logging tools was defined to comply with the present limitation in wireline cables (320°C). As part of this new set of downhole tools, temperature, pressure, fluid flow and casing collar location might be measured up to 400°C from a single multisensor tool. Natural gamma radiation spectrum, borehole wall ultrasonic images signal, and fiber optic cables (using distributed temperature sensing methods) were also developed for wireline deployment up to 300°C and tested in the field. A wireline, dual laterolog electrical resistivity tool was also developed but could not be field tested as part of HiTI. This new set of tools constitutes a basis for the deep exploration of the oceanic crust in the future. In addition, new strategies including the real-time integration of drilling parameters with modeling of the thermo-mechanical status of the borehole could be developed, using time-lapse logging of temperature (for heat flow determination) and borehole wall images (for hole stability and in-situ stress determination) as boundary conditions for the models. In all, and with limited integration of existing tools, to deployment of high-temperature downhole tools could contribute largely to the success of the long awaited Mohole project.

  1. Do Two Deep Drill Holes Into the Upper Ocean Crust Quantify the Hydrothermal Contribution to Global Geochemical Cycles? (United States)

    Teagle, D. A. H.; Alt, J.; Coggon, R. M.; Harris, M.; Smith-Duque, C. E.; Rehkamper, M.


    Vigorous circulation of seawater at the ocean ridges is required to cool and crystallize magma to form new ocean crust. Axial and ridge flank hydrothermal fluid circulation is accompanied by seawater-basalt exchanges over a spectrum of temperatures that buffer the chemistry of seawater, provide unique microbial niches, alter the chemistry and mineralogy of the ocean crust, and through subduction return surface-derived geochemical tracers to the interior of our planet. In many models of axial and ridge flank hydrothermal circulation, most fluid-rock interaction occurs in the upper oceanic crust. Hence inventories of seawater exchange should be captured by relatively shallow (Penrose-type layering, albeit with different thicknesses of lavas and dikes. However, what was not anticipated was the contrasting distribution and nature of elemental and isotopic hydrothermal exchanges. Differences reflect the influence of local crustal structure, such as lava morphology and flow thicknesses, and thermal gradients on hydrothermal processes. These contrasts highlight the importance of further deep drilling to at least the upper gabbros in a range of spreading rates and ages to robustly extrapolate the results from what will always be a limited number of bore holes to quantify global hydrothermal exchanges.

  2. Constraints on the accretion of the gabbroic lower oceanic crust from plagioclase lattice preferred orientation in the Samail ophiolite (United States)

    VanTongeren, J. A.; Hirth, G.; Kelemen, P. B.


    Oceanic crust represents more than 60% of the earth's surface and despite a large body of knowledge regarding the formation and chemistry of the extrusive upper oceanic crust, there still remains significant debate over how the intrusive gabbroic lower oceanic crust is accreted at the ridge axis. The two proposed end-member models, the Gabbro Glacier and the Sheeted Sills, predict radically different strain accumulation in the lower crust during accretion. In order to determine which of these two hypotheses is most applicable to a well-studied lower crustal section, we present data on plagioclase lattice preferred orientations (LPO) in the Wadi Khafifah section of the Samail ophiolite. We observe no systematic change in the strength of the plagioclase LPO with height above the crust-mantle transition, no dominant orientation of the plagioclase a-axis lineation, and no systematic change in the obliquity of the plagioclase LPO with respect to the modal layering and macroscopic foliation evident in outcrop. These observations are most consistent with the Sheeted Sills hypothesis, in which gabbros are crystallized in situ and fabrics are dominated by compaction and localized extension rather than by systematically increasing shear strain with increasing depth in a Gabbro Glacier. Our data support the hypothesis of MacLeod and Yaouancq (2000) that the rotation of the outcrop-scale layering from sub-horizontal in the layered gabbros to sub-vertical near the sheeted dikes is due to rapid vertical melt migration through upper gabbros close to the axial magma chamber. Additionally, our results support the hypothesis that the majority of extensional strain in fast spreading ridges is accommodated in partially molten regions at the ridge axis, whereas in slow and ultra-slow ridges large shear strains are accommodated by plastic deformation.

  3. Scattering beneath Western Pacific subduction zones: evidence for oceanic crust in the mid-mantle (United States)

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


    Small-scale heterogeneities in the mantle can give important insight into the dynamics and composition of the Earth's interior. Here, we analyse seismic energy found as precursors to PP, which is scattered off small-scale heterogeneities related to subduction zones in the upper and mid-mantle. We use data from shallow earthquakes (less than 100 km depth) in the epicentral distance range of 90°-110° and use array methods to study a 100 s window prior to the PP arrival. Our analysis focuses on energy arriving off the great circle path between source and receiver. We select coherent arrivals automatically, based on a semblance weighted beampower spectrum, maximizing the selection of weak amplitude arrivals. Assuming single P-to-P scattering and using the directivity information from array processing, we locate the scattering origin by ray tracing through a 1-D velocity model. Using data from the small-aperture Eielson Array (ILAR) in Alaska, we are able to image structure related to heterogeneities in western Pacific subduction zones. We find evidence for ˜300 small-scale heterogeneities in the region around the present-day Japan, Izu-Bonin, Mariana and West Philippine subduction zones. Most of the detected heterogeneities are located in the crust and upper mantle, but 6 per cent of scatterers are located deeper than 600 km. Scatterers in the transition zone correlate well with edges of fast features in tomographic images and subducted slab contours derived from slab seismicity. We locate deeper scatterers beneath the Izu-Bonin/Mariana subduction zones, which outline a steeply dipping pseudo-planar feature to 1480 km depth, and beneath the ancient (84-144 Ma) Indonesian subduction trench down to 1880 km depth. We image the remnants of subducted crustal material, likely the underside reflection of the subducted Moho. The presence of deep scatterers related to past and present subduction provides evidence that the subducted crust does descend into the lower mantle at least for these steeply dipping subduction zones. Applying the same technique to other source-receiver paths will increase our knowledge of the small-scale structure of the mantle and will provide further constraints on geodynamic models.

  4. Oceanic crust within the paleozoic Granjeno Schist, northeastern Mexico. Remnants of the Rheic and paleo-Pacific Ocean. (United States)

    Torres Sanchez, Sonia Alejandra; Augustsson, Carita; Rafael Barboza Gudiño, Jose; Jenchen, Uwe; Torres Sanchez, Dario; Aleman Gallardo, Eduardo; Abratis, Michael


    Late Paleozoic metamorphic rocks in Mexico are related to the Laurentia-Gondwana collision in Carboniferous time, during Pangaea amalgamation. Vestiges of the Mexican Paleozoic continental configuration are present in the Granjeno Schist, the metamorphic basement of the Sierra Madre Oriental. Field work and petrographic analysis reveal that the Granjeno Schist comprises metamorphic rocks with both sedimentary (psammite, pelite, turbidite, conglomerate, black shale) and igneous (tuff, lava flows, pillow lava and ultramafic bodies) protoliths. The chlorite geothermometer and the presence of phengite in the metasedimentary units as well as 40Ar/39Ar ages on metavolcanic and metaultramafic rocks indicate that the Granjeno Schist was metamorphosed under sub-greenschist to greenschist facies with temperatures ranging from 250-345°C with 2.5 kbar during Carboniferous time (330±30 Ma). The presence of metabasalt, metacumulate, serpentinite and talc bodies suggests an oceanic tectonic setting for the evolution of the Granjeno Schist. Serpetinite rocks have mesh, granular and ribbon textures which indicate recrystallization and metasomatic events. The serpentinite rocks are enriched in the very large incompatible elements Cs, U, and Zr and depleted in Ba, Sr, Pb, Zr and Ce. Normalized REE patterns (LaN/YbN = 0.51 - 19.95 and LaN/SmN = 0.72 - 9.08) of the serpentinite and talc/soapstone are characteristic of peridotite from both suprasubduction and mid-ocean ridge zones. Serpentinite from the Granjeno Schist have spinel content which can reveal different stages of evolution in host serpentinite. The composition of chromite indicates that they belong to podiform chromite that may have crystallized from mid-ocean ridge magma. Al-chromite in the serpentinite is characterized by #Cr 0.48 to 0.55, which indicates a depleted mantle source affected by 17 to 18% of partial melting. The ferritchromite has #Cr values of 0.93 to 1.00 which indicates a metamorphic origin. Our study suggests at least two serpentinization stages. The first serpentinization stage is related to an ocean-floor environment. At this stage, mesh-textured serpentinite formed under static conditions under subgreenschist to greenschist conditions. The second serpentinization stage occurred under greenschist to low amphibole conditions. During this stage Cr-spinel progressively was replaced by ferritchromite with magnetite rims due to regional metamorphism. Tectonic contact of the serpentinite with metavolcanic and metasedimentary rocks indicates lithospheric mantle slivers juxtaposed during the metamorphism of the Granjeno Schist during Pennsylvanian time. This metamorphic event occurred in an active continental margin. It represents the last events of the southern closure of the Rheic Ocean and Permo-Carboniferous convergence of Pacific plates on the western margin of Pangea.

  5. Folding instabilities and cracking of thin coatings on a soft polymer substrate as a model of the oceanic crust

    Directory of Open Access Journals (Sweden)

    S. L. Bazhenov


    Full Text Available Nucleation and development of microrelief and fragmentation of coating under tensile extension of polymer films coated with a thin rigid layer is studied, and the mechanisms responsible for the development of both types of structures are discussed. The development of regular folding is controlled by compression-induced buckling instabilities in a rigid coating on a compliant support. Parallel cracks are due to features of mechanical stress transfer from a soft substratum to a rigid coating via an interface. Micro-relief is similar to relief of the oceanic floor in the vicinity of mid-oceanic ridges. We suggest that the young oceanic crust and the upper mantle may behave as a solid coating on a soft basement system.

  6. Himalayan sedimentary pulses recorded by silicate detritus within a ferromanganese crust from the Central Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Banakar, V.K.; Galy, A.; Sukumaran, N.P.; Parthiban, G.; Volvaiker, A.Y.

    in the accumulation rate of the Himalayan-derived silicate-detritus during the last 25 Ma. The result shows three periods of high accumulation rates (modern, around 10 Ma and prior to 16 Ma). These sedimentary pulses have already been recognised and described...

  7. Fe-XANES analyses of Reykjanes Ridge basalts: Implications for oceanic crust's role in the solid Earth oxygen cycle (United States)

    Shorttle, Oliver; Moussallam, Yves; Hartley, Margaret E.; Maclennan, John; Edmonds, Marie; Murton, Bramley J.


    The cycling of material from Earth's surface environment into its interior can couple mantle oxidation state to the evolution of the oceans and atmosphere. A major uncertainty in this exchange is whether altered oceanic crust entering subduction zones can carry the oxidised signal it inherits during alteration at the ridge into the deep mantle for long-term storage. Recycled oceanic crust may be entrained into mantle upwellings and melt under ocean islands, creating the potential for basalt chemistry to constrain solid Earth-hydrosphere redox coupling. Numerous independent observations suggest that Iceland contains a significant recycled oceanic crustal component, making it an ideal locality to investigate links between redox proxies and geochemical indices of enrichment. We have interrogated the elemental, isotope and redox geochemistry of basalts from the Reykjanes Ridge, which forms a 700 km transect of the Iceland plume. Over this distance, geophysical and geochemical tracers of plume influence vary dramatically, with the basalts recording both long- and short-wavelength heterogeneity in the Iceland plume. We present new high-precision Fe-XANES measurements of Fe3+ / ? Fe on a suite of 64 basalt glasses from the Reykjanes Ridge. These basalts exhibit positive correlations between Fe3+ / ? Fe and trace element and isotopic signals of enrichment, and become progressively oxidised towards Iceland: fractionation-corrected Fe3+ / ? Fe increases by ?0.015 and ?QFM by ?0.2 log units. We rule out a role for sulfur degassing in creating this trend, and by considering various redox melting processes and metasomatic source enrichment mechanisms, conclude that an intrinsically oxidised component within the Icelandic mantle is required. Given the previous evidence for entrained oceanic crustal material within the Iceland plume, we consider this the most plausible carrier of the oxidised signal. To determine the ferric iron content of the recycled component ([Fe2O3]source) we project observed liquid compositions to an estimate of Fe2O3 in the pure enriched endmember melt, and then apply simple fractional melting models, considering lherzolitic and pyroxenitic source mineralogies, to estimate [Fe2O3](source) content. Propagating uncertainty through these steps, we obtain a range of [Fe2O3](source) for the enriched melts (0.9-1.4 wt%) that is significantly greater than the ferric iron content of typical upper mantle lherzolites. This range of ferric iron contents is consistent with a hybridised lherzolite-basalt (pyroxenite) mantle component. The oxidised signal in enriched Icelandic basalts is therefore potential evidence for seafloor-hydrosphere interaction having oxidised ancient mid-ocean ridge crust, generating a return flux of oxygen into the deep mantle.

  8. Atmospheric contamination of the primary Ne and Ar signal in mid-ocean ridge basalts and its implications for ocean crust formation (United States)

    Stroncik, N. A.; Niedermann, S.


    Both, terrestrial and extra-terrestrial applications of noble gases have demonstrated their importance as tracers for source identification, process characterisation and mass and heat flux quantification. However, the interpretation of noble gas isotope data from terrestrial igneous rocks is often complicated by the ubiquitous presence of heavy noble gases (Ne, Ar, Kr, Xe) with an atmospheric origin. Up to now there has been no consensus on how atmospheric noble gases are entrained into igneous rocks. Suggested processes range from contamination during sample preparation to mantle recycling through subduction. Here we present Ne, Ar, Mg, K, and Cl data of fresh glasses from the Mid-Atlantic Ridge north and south of the Ascension Fracture Zone which show that incorporation of atmospheric noble gases into igneous rocks is in general a two-step process: (1) magma contamination by assimilation of altered oceanic crust results in the entrainment of noble gases from air-equilibrated seawater; (2) atmospheric noble gases are adsorbed onto grain surfaces during sample preparation. This implies, considering the ubiquitous presence of the contamination signal, that magma contamination by assimilation of a seawater-sourced component is an integral part of mid-ocean ridge basalt evolution. Combining the results obtained from noble gas and Cl/K data with estimates of crystallisation pressures for the sample suite shows that the magma contamination must have taken place at a depth between 9 and 13 km. Taking thickness estimates for the local oceanic crust into account, this implies that seawater penetration in this area reaches lower crustal levels, indicating that hydrothermal circulation might be an effective cooling mechanism even for the deep parts of the oceanic crust.

  9. Distribution and sources of pre-anthropogenic lead isotopes in deep ocean water from Fe-Mn crusts (United States)

    Von Blanckenburg, F.; O'Nions, R. K.; Hein, J.R.


    The lead isotope composition of ocean water is not well constrained due to contamination by anthropogenic lead. Here the global distribution of lead isotopes in deep ocean water is presented as derived from dated (ca. 100 ka) surface layers of hydrogenetic Fe-Mn crusts. The results indicate that the radiogenic lead in North Atlantic deep water is probably supplied from the continents by river particulates, and that lead in Pacific deep water is similar to that characteristic of island and continental volcanic arcs. Despite a short residence time in deep water (80-100 a), the isotopes of lead appear to be exceedingly well mixed in the Pacific basin. There is no evidence for the import of North Atlantic deep water-derived lead into the Pacific ocean, nor into the North Indian Ocean. This implies that the short residence time of lead in deep water prohibits advection over such long distances. Consequently, any climate-induced changes in deep-water flow are not expected to result in major changes in the seawater Pb-isotope record of the Pacific Ocean.

  10. Platinum group elements and gold in ferromanganese crusts from Afanasiy–Nikitin seamount, equatorial Indian Ocean: Sources and fractionation

    Indian Academy of Sciences (India)

    V K Banakar; J R Hein; R P Rajani; A R Chodankar


    The major element relationships in ferromanganese (Fe-Mn) crusts from Afanasiy-Nikitin seamount (ANS), eastern equatorial Indian Ocean, appear to be atypical. High positive correlations ( = 0.99) between Mn/Co and Fe/Co ratios, and lack of correlation of those ratios with Co, Ce, and Ce/Co, indicate that the ANS Fe-Mn crusts are distinct from Pacific seamount Fe-Mn crusts, and reflect region-specific chemical characteristics. The platinum group elements (PGE: Ir, Ru, Rh, Pt, and Pd) and Au in ANS Fe-Mn crusts are derived from seawater and are mainly of terrestrial origin, with a minor cosmogenic component. The Ru/Rh (0.5-2) and Pt/Ru ratios (7-28) are closely comparable to ratios in continental basalts, whereas Pd/Ir ratios exhibit values (> 2) similar to CI-chondrite (?1). The chondrite-normalized PGE patterns are similar to those of igneous rocks, except that Pd is relatively depleted. The water depth of Fe-Mn crust formation appears to have a first-order control on both major element and PGE enrichments. These relationships are defined statistically by significant ( < 0.75) correlations between water depth and Mn/Co, Fe/Co, Ce/Co, Co, and the PGEs. Fractionation of the PGE-Au from seawater during colloidal precipitation of the major-oxide phases is indicated by well-defined linear positive correlations ( < 0.8) of Co and Ce with Ir, Ru, Rh, and Pt; Au/Co with Mn/Co; and by weak or no correlations of Pd with water depth, Co-normalized major-element ratios, and with the other PGE ( $mt; 0.5). The strong enrichment of Pt (up to 1 ppm) relative to the other PGE and its positive correlations with Ce and Co demonstrate a common link for the high concentrations of all three elements, which likely involves an oxidation reaction on the Mn-oxide and Fe-oxyhydroxide surfaces. The documented fractionation of PGE-Au and their positive association with redox sensitive Co and Ce may have applications in reconstructing past-ocean redox conditions and water masses.

  11. Compositional variation and genesis of ferromanganese crusts of the Afanasiy-Nikitin Seamount, Equatorial Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Rajani, R.P.; Banakar, V.K.; Parthiban, G.; Mudholkar, A.V.; Chodankar, A.R.

    to fractionate during the Fe{Mn crust formation (Elder?eld 1988; De Carlo 1991; De Carlo and McMurtry 1992; Bau et al 1996; Banakar et al 1997). The Co and Ce were shown to readily oxidize to their higher oxidation state on adsorption to negatively charged Mn... as indicators of redox conditions (Elder?eld 1988; De Carlo 1991; De Carlo and McMurtry 1992; Bau et al 1996; Banakar et al 1997), the ANS Fe{Mn crusts appear to have accreted in better oxygenated waters compared with the ambient waters of the Paci?c Fe...

  12. Molybdenum evidence for expansive sulfidic water masses in ~ 750 Ma oceans

    DEFF Research Database (Denmark)

    Dahl, Tais Wittchen; Canfield, Donald Eugene


    The Ediacaran appearance of large animals, including motile bilaterians, is commonly hypothesized to reflect a physiologically enabling increase in atmospheric and oceanic oxygen abundances (pO2). To date, direct evidence for low oxygen in pre-Ediacaran oceans has focused on chemical signatures in the rock record that reflect conditions in local basins, but this approach is both biased to constrain only shallower basins and statistically limited when we seek to follow the evolution of mean ocean chemical state through time. Because the abundance and isotopic composition of molybdenum (Mo) in organic-rich euxinic sediments can vary in response to changes in global redox conditions, Mo geochemistry provides independent constraints on the global evolution of well-oxygenated environments. Here, we establish a theoretical framework to access global marine Mo cycle in the past from the abundance and isotope composition of ancient seawater. Further, we investigate the ~ 750 Ma Walcott Member of the Chuar Group, Grand Canyon, which accumulated in a rift basin with open connection to the ocean. Iron speciation data from upper Walcott shales indicate that local bottom waters were anoxic and sulfidic, consistent with their high organic content (up to 20 wt.%). Similar facies in Phanerozoic successions contain high concentrations of redox-sensitive metals, but in the Walcott Member, abundances of Mo and U, as well as Mo/TOC (~ 0.5 ppm/wt.%) are low. ?98Mo values also fall well below modern equivalents (0.99 ± 0.13‰ versus ~ 2.35‰ today). These signatures are consistent with model predictions where sulfidic waters cover ~ 1–4% of the global continental shelf area, corresponding to a ~ 400–800 fold increase compared to the modern ocean. Therefore, our results suggest globally expansive sulfidic water masses in mid-Neoproterozoic oceans, bridging a nearly 700 million-year gap in previous Mo data. We propose that anoxic and sulfidic (euxinic) conditions governed Mo cycling in the oceans even as ferruginous subsurface waters re-appeared 800–750 Ma, and we interpret this anoxic ocean state to reflect a markedly lower atmospheric and oceanic O2 level, consistent with the hypothesis that pO2 acted as an evolutionary barrier to the emergence of large motile bilaterian animals prior to the Ediacaran Period.

  13. Age, spreading rates, and spreading asymmetry of the world's ocean crust (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The authors present four companion digital models of the age, age uncertainty, spreading rates and spreading asymmetries of the world's ocean basins as geographic...

  14. Baltican versus Laurentian Crust in the Norwegian Caledonides between Latitudes 67° and 69° N: Implications for Mountains across oceans (United States)

    Steltenpohl, Mark G.; Yaw Nana Yaw, Nana; Andresen, Arild; Verellen, Devon


    Field and geochronological data (U-Pb ID-TIMS, SHRIMP, and LA ICPMS) on granitoids and their metasedimentary hosts are reported for rocks of the Bodø and Ofoten regions of north-central Norway documenting the distribution of Baltican versus Laurentian crust and allowing for tectonostratigraphic correlations across the EW-trending Tysfjord basement culmination. In the Bodø region, large areas previously interpreted as domes cored by Baltic basement (ca. 1.8 Ga; e.g., Heggmovatn and Landegode domes) are in fact Caledonian thrust sheets belonging to the exotic (Laurentian) Uppermost Allochthon. The Bratten orthogneiss, the Landegode augen gneiss, and the batholithic Tårnvika augen gneiss each has a ca. 950 Ma age of crystallization, and are together called the Rørstad complex. Orthogneisses that intrude metasedimentary units of the Heggmo allochthon (formerly the Heggmovatn dome) are dated to ca. 930 Ma, and these are intruded by 430 Ma leucogranites; U-Pb analysis of detrital zircons from metasiliciclastic rocks constrain the age of deposition to between 1100-930 Ma. We lithologically correlate the metasedimentary rocks between the Heggmo and Rørstad complexes. The Rørstad complex was migmatized at ca. 450 Ma and then was intruded by 430 Ma granitoids. Ordovician migmatites have not been documented in the Heggmo unit but such relics might have been masked by intense Scandian magmatic and metamorphic activity. The Rørstad and Heggmo units have straightforward age correlations to Mesoproterozoic to Neoproterozoic rock complexes in southern East Greenland and in other parts of the North Atlantic realm (i.e., Krummedal sequence and Eleonore Bay Supergroup). Laurentian Grenville-continental crust preserved in the Uppermost Allochthon of the Bodø region, therefore, records tectonic events that took place on the northeastern Laurentian continental margin prior to its Scandian continent-continent collision with Baltica. In Ofoten, ~150 km north of Bodø, the basal units of the Uppermost Allochthon comprise a thick sequence of platformal marbles (Evenes Group) that overlie a fragmented ophiolite complex dated at ca. 474 Ma. Multiple suites of felsic intrusions occur within the overlying Bogen and Niingen nappes and in the underlying Narvik nappe (Upper Allochthon) but none are found in the Evenes Group. A geochemically distinct (A-type) suite of ca. 470 Ma granites (Snaufjell granite) intrudes the Bogen Group and implies correlation to parts of the Uppermost Allochthon in the Helgeland nappe far to the south of Bodø; lithologically correlative units also occur directly south of Tysfjord in the Engeløy synform, the southern counterpart to the Ofoten synform. Ordovician magmatism and metamorphism and Grenville detrital zircon age populations within rocks of Lofoten-Vesterålen imply slivers of the Uppermost Allochthon exist far to the west of exposed Baltic basement. Although we have not identified Tonian-aged plutonic rocks north of Tysfjord, U-Pb detrital zircon age populations in quartzites from Lofoten-Vesterålen (Leknes and Gullesfjord), and the Evenes, Bogen, and Niingen groups indicate that they too likely have Laurentian origins. We speculate on potential Laurentian source areas and possible interactions between the two conjugate continental sides of the orogen that could have resulted in the Scandian amalgamation of these orphaned terranes.

  15. Downhole variation of lithium and oxygen isotopic compositions of oceanic crust at East Pacific Rise, ODP Site 1256 (United States)

    Gao, Y.; Vils, F.; Cooper, K. M.; Banerjee, N.; Harris, M.; Hoefs, J.; Teagle, D. A. H.; Casey, J. F.; Elliott, T.; Laverne, C.; Alt, J. C.; Muehlenbachs, K.


    Bulk rock lithium and oxygen isotope compositions from ODP Site 1256 were analyzed to investigate the seawater circulation in the upper oceanic crust formed at the East Pacific Rise (EPR). The upper extrusive basalts have ?18O values from +6.1‰ to +9.2‰, reflecting alteration of oceanic crust by seawater at low temperatures (<200-250°C). Bulk rocks from the sheeted dike complex and plutonic section have overall lower ?18O values (+3.0‰-+5.5‰). In the sheeted dike complex bulk rock ?18O values gradually decrease with depth, and then increase toward the fresh MORB ?18O value after reaching a minimum of +3.0‰ at ˜1350 m below seafloor (mbsf). The entire sampled crust is dominated by rocks with low lithium contents relative to fresh MORBs except for a few localized Li enrichment. The upper volcanic zone is characterized by a spread of ?7Li from low to high values relative to average unaltered MORB values (?7Li = +3.4 ± 1.4‰). The presence of rocks with low ?7Li values in the upper crust most likely indicates zones of upwelling of relatively hot (˜200-250°C) hydrothermal fluids. In the sheeted dike complex, bulk rock ?7Li values show wide range of variation, but exhibit a general trend from enriched to depleted values at ˜1280 mbsf and then return to that for fresh MORB within the upper tens of meters of the plutonic section at the bottom of the after reaching a minimum at ˜1350 mbsf (?7Li = -1.6‰). The downhole pattern of ?7Li principally reflects variations in water-rock ratio (w/r) together with a downhole increase of temperature. Seawater flow in the upper volcanic zone is likely to be channeled with generally small but variable w/r ratios. The w/r ratios increase rapidly with depth in the lower volcanic section into the sheeted dike complex indicating water dominated pervasive hydrothermal flow due to intensive upwelling of hydrothermal fluids.

  16. Growth response of a deep-water ferromanganese crust to evolution of the Neogene Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Banakar, V.K.; Hein, J.R.

    greatly pre- venting the release of Mn in organic matter to the ambient water. It has been shown that metabolically fixed Mn in organic matter and Fe in carbonate skeletons are released to deep-waters on oxidation . and dissolution, respectively Halbach... 2000 529–540538 precipitation of oxyhydroxides at the margins of the OMZ. Separation of the crust palaeo-depth from the CCD caused increased dissolution of biogenic car- bonate and release of Fe and other skeleton bound elements to deep...

  17. Depth profiles of 230Th excess, transition metals and mineralogy of ferromanganese crusts of the Central Indian Ocean basin and implications for palaeoceanographic influence on crust genesis

    Digital Repository Service at National Institute of Oceanography (India)

    Banakar, V.K.; Borole, D.V.

    was done following the proce- dures of Ku and Broecker ( 1967 ) in order to obtain lo- 15 subsamples in each area within the top 1-2-mm-thick crust layer. The subsam- ples were obtained by uniform scraping of crust material from the marked areas using... of the crust (assuming 2 g cmM3). The errors in such depth estimates are within + 20% as reported previously (Ku and Broecker, 1967 ) and as observed by comparing the total depth measured after completion of subsam- pling and the total depth estimated...

  18. Pliocene (3.2-2.4 Ma) ostracode faunal cycles and deep ocean circulation, North Atlantic Ocean (United States)

    Cronin, T. M.; Raymo, M.E.; Kyle, K.P.


    Ostracode assemblages from Deep Sea Drilling Project Sites 607 (western Mid-Atlantic Ridge) and 610 (southeast Rockall Plateau) show rapid, systematic shifts during late Pliocene glacial-interglacial cycles that reflect deep-sea environmental change. Progressive decreases in North Atlantic deep-water taxa and increases in Southern Ocean taxa occur from 3.4 to 2.4 Ma, and high-amplitude faunal cycles begin near 2.8 Ma. Four ostracode assemblages, each with a characteristic phase relative to 41 k.y. obliquity glacial-interglacial ??18O cycles, characterize the benthic faunal record at Site 607. Cross-spectral analysis shows that the Site 607 glacial assemblage has a 41 k.y. periodicity significant at the 95% level; other assemblages show a less significant, but still obvious, concentration of variance at 41 k.y. Faunal patterns suggest climatically controlled reorganization of deep-sea benthic communities during glacial-interglacial cycles due to oscillating deep-sea environments.

  19. New ichthyoliths from ferromanganese crusts and nodules from the Central Indian Ocean Basin

    Digital Repository Service at National Institute of Oceanography (India)

    Gupta, S.M.

    Ferromanganese encrusted hardgrounds, their intraclasts and the nuclei of manganese nodules collected from the Central Indian Ocean basin have yielded plentiful numbers of ichthyoliths. Forty well-knon ichthyoliths, one new type and 35 new subtypes...

  20. Lithium isotope as a proxy for water/rock interaction between hydrothermal fluids and oceanic crust at Milos, Greece (United States)

    Lou, U.-Lat; You, Chen-Feng; Wu, Shein-Fu; Chung, Chuan-Hsiung


    Hydrothermal activity at Milos in the Aegean island (Greece) is mainly located at rather shallow depth (about 5 m). It is interesting to compare these chemical compositions and the evolution processes of the hydrothermal fluids at deep sea hydrothermal vents in Mid-ocean Ridge (MOR). Lithium (Li) is a highly mobile element and its isotopic composition varies at different geological settings. Therefore, Li and its isotope could be used as an indicator for many geochemical processes. Since 6Li preferential retained in the mineral phase where 7Li is leached into fluid phase during basalt alteration, the Li isotopic fractionation between the rocks and the fluids reflect sensitively the degree of water-rock interaction. In this study, Bio-Rad AG-50W X8 cation exchange resin was used for purifying the hydrothermal fluids to separate Li from other matrix elements. The Li isotopic composition (?7Li) was determined by Multi-collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) with precision better than 0.2‰ (2?, n=20). The Li concentration in the hydrothermal fluids falls between 0.02 to 10.31 mM. The ?7Li values vary from +1.9 to +29.7‰, indicating significant seawater contamination have occurred. These hydrothermal fluids fit well with seawater and brine two end-member binary mixing model. During phase separation, lithium, boron, chlorine, iodine, bromine, sodium and potassium were enriched in the brine phase. On the other hand, aluminum, sulphur and iron were enriched in the vapor phase. There is no significant isotope fractionation between the two phases. The water/rock ratio (W/R) calculated is low (about 1.5 to 1.8) for the Milos fluids, restricted seawater recharge into the oceanic crust. Moreover, the oceanic crust in the region becomes less altered since the W/R is low. The ?7Li value of the hydrothermal fluids can be used as a sensitive tool for studying water-rock interaction.

  1. Internal time marker (Q1) of the Cretaceous super chron in the Bay of Bengal - a new age constraint for the oceanic crust evolved between India and Elan Bank (United States)

    Krishna, K. S.; Ismaiel, M.; Karlapati, S.; Saha, D.; Mishra, J.


    Analysis of marine magnetic data of the Bay of Bengal (BOB) led to suggest two different tectonic models for the evolution of lithosphere between India and East Antarctica. The first model explains the presence of M-series (M11 to M0) magnetic anomalies in BOB with a small room leaving for accommodating the crust evolved during the long Cretaceous Magnetic Quiet Period. Second model explains in other way that most part of the crust in BOB was evolved during the quite period together with the possible presence of oldest magnetic chron M1/ M0 in close vicinity of ECMI. It is with this perspective we have reinvestigated the existing and recently acquired magnetic data together with regional magnetic model of BOB for identification of new tectonic constraints, thereby to better understand the evolution of lithosphere. Analysis of magnetic data revealed the presence of spreading anomalies C33 and C34 in the vicinity of 8°N, and internal time marker (Q1) corresponding to the age 92 Ma at 12°N in a corridor between 85°E and Ninetyeast ridges. The new time marker and its location, indeed, become a point of reference and benchmark in BOB for estimating the age of oceanic crust towards ECMI. The magnetic model further reveals the presence of network of fracture zones (FZs) with different orientations. Between 85°E and Ninetyeast ridges, two near N-S FZs, approximately followed 87°E and 89.5°E are found to extend into BOB up to 12°N, from there the FZs reorient in N60°W direction and reach to the continental margin region. Along ECMI two sets of FZs are identified with a northern set oriented in N60°W and southern one in N40°W direction. This suggests that both north and south segments of the ECMI were evolved in two different tectonic settings. The bend in FZs marks the timing (92 Ma) of occurrence of first major plate reorganisation of the Indian Ocean and becomes a very critical constraint for understanding the plate tectonic process in early opening of the Indian Ocean.

  2. Carbonate formation in the ocean crust as a proxy for water-rock interactions


    Eickmann, Benjamin


    The main objective of this thesis was to elucidate the authigenesis of carbonate minerals in modern and Devonian ocean-floor volcanic rocks and to demonstrate that Late Devonian (Frasnian) pillow basalts from the Saxothuringian zone once harbored microbial life. The ultramafic-hosted Logatchev hydrothermal field (LHF) at the Mid-Atlantic Ridge, the Arctic Gakkel Ridge (GR) and the Late Devonian Frankenwald feature carbonate precipitates (aragonite, calcite, dolomite) in voids and fractures of...

  3. Can Fractional Crystallization of a Lunar Magma Ocean Produce the Lunar Crust? (United States)

    Rapp, Jennifer F.; Draper, David S.


    New techniques enable the study of Apollo samples and lunar meteorites in unprecedented detail, and recent orbital spectral data reveal more about the lunar farside than ever before, raising new questions about the supposed simplicity of lunar geology. Nevertheless, crystallization of a global-scale magma ocean remains the best model to account for known lunar lithologies. Crystallization of a lunar magma ocean (LMO) is modeled to proceed by two end-member processes - fractional crystallization from (mostly) the bottom up, or initial equilibrium crystallization as the magma is vigorously convecting and crystals remain entrained, followed by crystal settling and a final period of fractional crystallization [1]. Physical models of magma viscosity and convection at this scale suggest that both processes are possible. We have been carrying out high-fidelity experimental simulations of LMO crystallization using two bulk compositions that can be regarded as end-members in the likely relevant range: Taylor Whole Moon (TWM) [2] and Lunar Primitive Upper Mantle (LPUM) [3]. TWM is enriched in refractory elements by 1.5 times relative to Earth, whereas LPUM is similar to the terrestrial primitive upper mantle, with adjustments made for the depletion of volatile alkalis observed on the Moon. Here we extend our earlier equilibrium-crystallization experiments [4] with runs simulating full fractional crystallization

  4. Uranium isotopic compositions of the crust and ocean: Age corrections, U budget and global extent of modern anoxia (United States)

    Tissot, François L. H.; Dauphas, Nicolas


    The 238U/235U isotopic composition of uranium in seawater can provide important insights into the modern U budget of the oceans. Using the double spike technique and a new data reduction method, we analyzed an array of seawater samples and 41 geostandards covering a broad range of geological settings relevant to low and high temperature geochemistry. Analyses of 18 seawater samples from geographically diverse sites from the Atlantic and Pacific oceans, Mediterranean Sea, Gulf of Mexico, Persian Gulf, and English Channel, together with literature data (n = 17), yield a ?238U value for modern seawater of -0.392 ± 0.005‰ relative to CRM-112a. Measurements of the uranium isotopic compositions of river water, lake water, evaporites, modern coral, shales, and various igneous rocks (n = 64), together with compilations of literature data (n = 380), allow us to estimate the uranium isotopic compositions of the various reservoirs involved in the modern oceanic uranium budget, as well as the fractionation factors associated with U incorporation into those reservoirs. Because the incorporation of U into anoxic/euxinic sediments is accompanied by large isotopic fractionation (?Anoxic/Euxinic-SW = +0.6‰), the size of the anoxic/euxinic sink strongly influences the ?238U value of seawater. Keeping all other fluxes constant, the flux of uranium in the anoxic/euxinic sink is constrained to be 7.0 ± 3.1 Mmol/yr (or 14 ± 3% of the total flux out of the ocean). This translates into an areal extent of anoxia into the modern ocean of 0.21 ± 0.09% of the total seafloor. This agrees with independent estimates and rules out a recent uranium budget estimate by Henderson and Anderson (2003). Using the mass fractions and isotopic compositions of various rock types in Earth's crust, we further calculate an average ?238U isotopic composition for the continental crust of -0.29 ± 0.03‰ corresponding to a 238U/235U isotopic ratio of 137.797 ± 0.005. We discuss the implications of the variability of the 238U/235U ratio on Pb-Pb and U-Pb ages and provide analytical formulas to calculate age corrections as a function of the age and isotopic composition of the sample. The crustal ratio may be used in calculation of Pb-Pb and U-Pb ages of continental crust rocks and minerals when the U isotopic composition is unknown. In cosmochemistry, the search for 247Cm (t1/2 = 15.6 Myr), an extinct short-lived radionuclide that decays into 235U, is important for understanding how r-process nuclides were synthesized in stars and learning about the astrophysical context of solar system formation (Chen and Wasserburg, 1981; Wasserburg et al., 1996; Nittler and Dauphas, 2006; Brennecka et al., 2010b; Tissot et al., 2015). In both terrestrial and extraterrestrial samples, variations in the 238U/235U ratio affect Pb-Pb ages (and depending on the analytical protocols, U-Pb ages). Therefore, samples dated by these techniques need to have their U isotopic compositions measured (Stirling et al., 2005, 2006; Weyer et al., 2008; Amelin et al., 2010; Brennecka et al., 2010b; Brennecka and Wadhwa, 2012; Connelly et al., 2012; Goldmann et al., 2015) or uncertainties on the U isotopic composition should be propagated into age calculations. In low temperature aqueous geochemistry, U isotopic fractionation between U4+ and U6+ (driven in part by nuclear field shift effects; Bigeleisen, 1996; Schauble, 2007; Abe et al., 2008), makes U isotopes potential tracers of paleoredox conditions (Montoya-Pino et al., 2010; Brennecka et al., 2011a; Kendall et al., 2013, 2015; Asael et al., 2013; Andersen et al., 2014; Dahl et al., 2014; Goto et al., 2014; Noordmann et al., 2015). The present paper aims at constraining some aspects of the global budget of uranium in the modern oceans using 238U/235U isotope variations, which involves characterizing the U isotopic composition of seawater and several reservoirs involved in the uranium oceanic budget. Uranium can exist in two oxidation states in terrestrial surface en

  5. Untangling Magmatic Processes and Hydrothermal Alteration of in situ Superfast Spreading Ocean Crust at ODP/IODP Site 1256 with Fuzzy c-means Cluster Analysis of Rock Magnetic Properties (United States)

    Dekkers, M. J.; Heslop, D.; Herrero-Bervera, E.; Acton, G.; Krasa, D.


    Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6.44.1' N, 91.56.1' W) on the Cocos Plate occurs in 15.2 Ma oceanic crust generated by superfast seafloor spreading. Presently, it is the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Here we interpret down-hole trends in several rock-magnetic parameters with fuzzy c-means cluster analysis, a multivariate statistical technique. The parameters include the magnetization ratio, the coercivity ratio, the coercive force, the low-field susceptibility, and the Curie temperature. By their combined, multivariate, analysis the effects of magmatic and hydrothermal processes can be evaluated. The optimal number of clusters - a key point in the analysis because there is no a priori information on this - was determined through a combination of approaches: by calculation of several cluster validity indices, by testing for coherent cluster distributions on non-linear-map plots, and importantly by testing for stability of the cluster solution from all possible starting points. Here, we consider a solution robust if the cluster allocation is independent of the starting configuration. The five-cluster solution appeared to be robust. Three clusters are distinguished in the extrusive segment of the Hole that express increasing hydrothermal alteration of the lavas. The sheeted dike and gabbro portions are characterized by two clusters, both with higher coercivities than in lava samples. Extensive alteration, however, can obliterate magnetic property differences between lavas, dikes, and gabbros. The imprint of thermochemical alteration on the iron-titanium oxides is only partially related to the porosity of the rocks. All clusters display rock magnetic characteristics in line with a stable NRM. This implies that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Determination of the absolute paleointensity with thermal techniques is not straightforward because of the propensity of oxyexsolution during laboratory heating and/or the presence of intergrowths. The upper part of the extrusive sequence, the granoblastic portion of the dikes, and moderately altered gabbros may contain a comparatively uncontaminated thermoremanent magnetization.

  6. Does seismic activity control carbon exchanges between transform-faults in old ocean crust and the deep sea? A hypothesis examined by the EU COST network FLOWS (United States)

    Lever, M. A.


    The European Cooperation in Science and Technology (COST)-Action FLOWS ( was initiated on the 25th of October 2013. It is a consortium formed by members of currently 14 COST countries and external partners striving to better understand the interplay between earthquakes and fluid flow at transform-faults in old oceanic crust. The recent occurrence of large earthquakes and discovery of deep fluid seepage calls for a revision of the postulated hydrogeological inactivity and low seismic activity of old oceanic transform-type plate boundaries, and indicates that earthquakes and fluid flow are intrinsically associated. This Action merges the expertise of a large number of research groups and supports the development of multidisciplinary knowledge on how seep fluid (bio)chemistry relates to seismicity. It aims to identify (bio)geochemical proxies for the detection of precursory seismic signals and to develop innovative physico-chemical sensors for deep-ocean seismogenic faults. National efforts are coordinated through Working Groups (WGs) focused on 1) geophysical and (bio)geochemical data acquisition; 2) modelling of structure and seismicity of faults; 3) engineering of deep-ocean physico-chemical seismic sensors; and 4) integration and dissemination. This poster will illustrate the overarching goals of the FLOWS Group, with special focus to research goals concerning the role of seismic activity in controlling the release of carbon from the old ocean crust into the deep ocean.

  7. Evidence for hydrothermal venting in Fe isotope compositions of the deep Pacific Ocean through time


    Chu, N; Johnson, C.; Beard, B; German, C; Nesbitt, R; Frank, M; Bohn, Marcel; Kubik, P.; Usui, A.; Graham, I.


    Temporal variations in Fe isotope compositions at three locations in the Pacific Ocean over the last 10 Ma are inferred from high-resolution analyses of three hydrogenetic ferromanganese crusts. Iron pathways to the central deep Pacific Ocean appear to have remained constant over the past 10 Ma, reflected by a remarkably constant Fe isotope composition, despite large changes in the Fe delivery rates to the surface ocean via dust. These results suggest that the Fe cycle in the deep ocean is de...

  8. Reactive flow as dominant evolution process in the lowermost oceanic crust: evidence from olivine of the Pineto ophiolite (Corsica) (United States)

    Sanfilippo, Alessio; Tribuzio, Riccardo; Tiepolo, Massimo; Berno, Davide


    The Jurassic Pineto ophiolite from Corsica exposes a ~1-km-thick troctolite-olivine-gabbro sequence, interpreted to represent a lowermost sector of the gabbroic oceanic crust from a (ultra-)slow spreading system. To constrain the petrogenesis of the olivine-gabbros, minor and trace element analyses of olivine (forsterite = 84-82 mol%) were carried out. Olivine from the olivine-gabbros is depleted in incompatible trace elements (Sc, V, Ti, Y, Zr and heavy rare earth elements) with respect to olivines from associated troctolites. Depleted incompatible element compositions are also shown by olivine (forsterite = 86 mol%) from a clinopyroxene-rich troctolite. The incompatible element compositions of olivine argue against a petrogenetic process entirely driven by fractional crystallization. We propose that melts migrating through an olivine-plagioclase crystal mush chemically evolved by reaction with the existing minerals, changing in composition as it flowed upward. The melt residual from these interactions led to partial dissolution of preexisting olivine and to crystallization of clinopyroxene, generating olivine-gabbro bodies within a troctolite matrix. Reactive flow was the major evolution process active in the ~1-km crustal transect exposed at the Pineto ophiolite, producing lithological variations classically attributed to fractional crystallization processes.

  9. Ocean crust vein mineral deposition: Rb/Sr ages, U-Th-Pb geochemistry, and duration of circulation at DSDP sites 261, 462 and 516

    International Nuclear Information System (INIS)

    Cation exchange experiments (ammonium acetate and cation resin) on celadonite-smectite vein minerals from three DSDP holes demonstrate selective removal of common Sr relative to Rb and radiogenic Sr. This technique increases the Rb/Sr ratio by factors of 2.3 to 22 without significantly altering the age of the minerals, allowing easier and more precise dating of such vein minerals. Celadonites show U and Pb contents and Pb isotopic compositions little changed from their basalt precursors, while Tb contents are significantly lower. Celadonites thus have unusually high alkali/U,Th ratios and low Th/U ratios. If this celadonite alteration signature is significantly imprinted on oceanic crust as a whole, it will lead to very distinctive Pb isotope signatures for any hot spot magmas which contain a component of aged subducted recycled oceanic crust. Initial Sr isotope ratios of ocean crust vein minerals (smectite, celadonite, zeolite, calcite) are intermediate between primary basalt values and contemporary sea water values, and indicate formation under seawater-dominated systems with effective water-rock ratios of 20-200. (author)

  10. Linear inversion of a negative gravity anomaly in se Rio Grande cone: a graben on oceanic crust?

    Scientific Electronic Library Online (English)

    Emilson Pereira, Leite; Naomi, Ussami.


    Full Text Available Uma anomalia ar-livre com amplitude negativa de 23 mGal em uma região no oceano Atlântico Sul, centrada em 48ºW e 35ºS, foi observada pela primeira vez devido à integração de dados de gravimetria marinha convencionais e dados de gravidade derivados de altimetria por satélite, adquiridos pela missão [...] GEOSAT/ERM. O limite norte desta anomalia coincide com o Lineamento Chuí e o limite sul indica outro lineamento, que é uma extensão da Zona de Fratura Meteoro. A anomalia tem direção NE-SW, sua largura é de 400 km e seu comprimento é de 600 km. Foi utilizada uma metodologia de inversão linear bidimensional, com vínculos relativos e absolutos, para calcular a distribuição de densidades ao longo de três perfis paralelos ao eixo principal da anomalia. O resultado sugere que a espessura de sedimentos na parte mais profunda da bacia é de no mínimo 3,0 km onde a batimetria oceânica é de 4.800 m. Esta feição tectônica, um semi-gráben assimétrico formado entre dois lineamentos, provavelmente situa-se sobre uma crosta oceânica. O volume de sedimentos estimado para esta bacia é de cerca de 50% do volume de sedimentos pós-Mioceno depositados no Rio Grande Cone, onde hidratos de gás foram encontrados. Abstract in english We detect, for the first time, a negative free-air gravity anomaly of 23 mGal amplitude over a region in the South Atlantic Ocean centered at 48ºW and 35ºS. To this end, we used the integration of conventional shipborne gravity data and gravity data derived from GEOSAT/ERM satellite altimetry. The n [...] orth bound of this anomaly coincides with the Chuí Lineament and the south bound indicates another lineament, which is the extension of the Meteor Fracture Zone. The anomaly trend is NE-SW, its width is 400 km and its length is 600 km. Two-dimensional linear inversion with relative and absolute equality constraints was used to calculate the density distribution along three profiles perpendicular to the main axis of the anomaly. The result suggests that the sediment thickness in the deepest part of the basin is at least 3.0 km where the ocean bathymetry is 4,800 m. This tectonic feature, an asymmetric half-graben formed between two lineaments, probably lies over an oceanic crust. The estimated volume of sediments in this basin is approximately 50% of the post-Miocene sediments volume deposited in the Rio Grande Cone where gas-hydrates were found.

  11. Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits (United States)

    Patten, Clifford G. C.; Pitcairn, Iain K.; Teagle, Damon A. H.; Harris, Michelle


    Volcanogenic massive sulphide (VMS) deposits are commonly enriched in Cu, Zn and Pb and can also be variably enriched in Au, As, Sb, Se and Te. The behaviour of these elements during hydrothermal alteration of the oceanic crust is not well known. Ocean Drilling Program (ODP) Hole 1256D penetrates a complete in situ section of the upper oceanic crust, providing a unique sample suite to investigate the behaviour of metals during hydrothermal alteration. A representative suite of samples was analysed for Au, As, Sb, Se and Te using low detection limit methods, and a mass balance of metal mobility has been carried out through comparison with a fresh Mid-Oceanic Ridge Basalt (MORB) glass database. The mass balance shows that Au, As, Se, Sb, S, Cu, Zn and Pb are depleted in the sheeted dyke and plutonic complexes by -46 ± 12, -27 ± 5, -2.5 ± 0.5, -27 ± 6, -8.4 ± 0.7, -9.6 ± 1.6, -7.9 ± 0.5 and -44 ± 6 %, respectively. Arsenic and Sb are enriched in the volcanic section due to seawater-derived fluid circulation. Calculations suggest that large quantities of metal are mobilised from the oceanic crust but only a small proportion is eventually trapped as VMS mineralisation. The quantity of Au mobilised and the ratio of Au to base metals are similar to those of mafic VMS, and ten times enrichment of Au would be needed to form a Au-rich VMS. The Cu-rich affinity of mafic VMS deposits could be explained by base metal fractionation both in the upper sheeted dykes and during VMS deposit formation.

  12. An oxygen isotope profile in a section of Cretaceous oceanic crust, Samail Ophiolite, Oman: Evidence for ?18O buffering of the oceans by deep (>5 km) seawater-hydrothermal circulation at mid-ocean ridges (United States)

    Gregory, Robert T.; Taylor, Hugh P., Jr.


    Isotopic analyses of 75 samples from the Samail ophiolite indicate that pervasive subsolidus hydrothermal exchange with seawater occurred throughout the upper 75% of this 8-km-thick oceanic crustal section; locally, the H2O even penetrated down into the tectonized peridotite. Pillow lavas (?18O = 10.7 to 12.7) and sheeted dikes (4.9 to 11.3) are typically enriched in 18O, and the gabbros (3.7 to 5.9) are depleted in 18O. In the latter rocks, water/rock ? 0.3, and ?18Ocpx ? 2.9 + 0.44 ?18Ofeld, indicating pronounced isotopic disequilibrium. The mineral ?18O values approximately follow an exchange (mixing) trajectory which requires that plagioclase must exchange with H2O about 3 to 5 times faster than clinopyroxene. The minimum ?18Ofeld value (3.6) occurs about 2.5 km below the diabase-gabbro contact. Although the gabbro plagioclase appears to be generally petrographically unaltered, its oxygen has been thoroughly exchanged; the absence of hydrous alteration minerals, except for minor talc and/or amphibole, suggests that this exchange occurred at T > 400°-500°C. Plagioclase ?18O values increase up section from their minimum values, becoming coincident with primary magmatic values near the gabbro-sheeted diabase contact and reaching 11.8 in the diabase dikes. These 18O enrichments in greenschist facies diabases are in part due to exchange with strongly 18O-shifted fluids, in addition to retrograde exchange at much lower temperatures. The ?18O data and the geometry of the mid-ocean ridge (MOR) magma chamber require that two decoupled hydrothermal systems must be present during much of the early spreading history of the oceanic crust (approximately the first 106 years); one system is centered over the ridge axis and probably involves several convective cells that circulate downward to the roof of the magma chamber, while the other system operates underneath the wings of the chamber, in the layered gabbros. Upward discharge of 18O-shifted water into the altered dikes from the lower system, just beyond the distal edge of the magma chamber, combined with the effects of continued low-T hydrothermal activity, produces the 18O enrichments in the dike complex. Integrating ?18O as a function of depth for the entire ophiolite establishes (within geologic and analytical error) that the average ?18O (5.7 ± 0.2) of the oceanic crust did not change as a result of all these hydrothermal interactions with seawater. Therefore the net change in ?18O of seawater was also zero, indicating that seawater is buffered by MOR hydrothermal circulation. Under steady state conditions the overall bulk 18O fractionation (?) between the oceans and primary mid-ocean ridge basalt magmas is calculated to be +6.1 ± 0.3, implying that seawater has had a constant ?18O?-0.4 (in the absence of transient effects such as continental glaciation). Utilizing these new data on the depth of interaction of seawater with the oceanic crust, numerical modeling of the hydrothermal exchange shows that as long as worldwide spreading rates are greater than 1 km2/yr, 18O buffering of seawater will occur. These conclusions can be extended as far back in time as the Archean (> 2.6 eons) with the proviso that ? may have been slightly smaller (about 5?) because of the overall higher temperatures that could have prevailed then. Thus ocean water has probably had a constant ?18O value of about -1.0 to +1.0 during almost all of earth's history.

  13. Molybdenum evidence for expansive sulfidic water masses in ~ 750 Ma oceans

    DEFF Research Database (Denmark)

    Dahl, Tais Wittchen; Canfield, Donald Eugene; Rosing, Minik Thorleif; Frei, Robert; Gordon, Gwyneth; Knoll, Andrew; Anbar, Ariel


    The Ediacaran appearance of large animals, including motile bilaterians, is commonly hypothesized to reflect a physiologically enabling increase in atmospheric and oceanic oxygen abundances (pO2). To date, direct evidence for low oxygen in pre-Ediacaran oceans has focused on chemical signatures in the rock record that reflect conditions in local basins, but this approach is both biased to constrain only shallower basins and statistically limited when we seek to follow the evolution of mean ocean...

  14. Araxa Group in the type-area: A fragment of Neoproterozoic oceanic crust in the Brasilia Fold Belt; Grupo Araxa em sua area tipo: um fragmento de crosta oceanica Neoproterozoica na faixa de dobramentos Brasilia

    Energy Technology Data Exchange (ETDEWEB)

    Seer, Hildor Jose [Centro Federal de Educacao Tecnologica de Araxa, (CEFET), MG (Brazil); Brod, Jose Affonso; Fuck, Reinhardt Adolfo; Pimentel, Marcio Martins; Boaventura, Geraldo Resende; Dardenne, Marcel Auguste [Brasilia Univ., DF (Brazil). Inst. de Geociencias


    This study reviews the geological characteristics and puts forward a new evolution model for the Araxa Group in its type-area, the southern segment of the Neo proterozoic Brasilia Belt, Minas Gerais, Brazil. The Araxa Group is confined within a thrust sheet belonging to a syn formal regional fold, the Araxa Syn form, overlying two other thrust sheets made of the Ibia and Canastra Groups. The Araxa Group is described as a tectono stratigraphic terrane in the sense of Howell (1993). It comprises an igneous mafic sequence, with fine and coarse grained amphibolites, associated with pelitic meta sedimentary rocks, and subordinate psanmites. All rocks were metamorphosed to amphibolite facies at ca. 630 Ma ago and were intruded by collisional granites. The amphibolites represent original basaltic and gabbroic rocks, with minor ultramafic (serpentinite/ amphibole-talc schist). The basalts are similar to high Fe O tholeiites, with REE signatures that resemble E-MORB and {epsilon}{sub Nd(T)} =+ 1.1. The meta sedimentary rocks are interpreted as the result of a marine deep-water sedimentation. They have Sm-Nd model ages of 1,9 Ga, and {epsilon}{sub Nd(T)} = -10.21. The amphibolites and metasediments could represent a fragment of back-arc oceanic crust. The data presented here differ significantly from the original definition of Barbosa et al. (1970) who describe the Araxa Group as a pelitic/psanmitic sequence and the collisional granites as a basement complex. (author)

  15. 75 FR 34929 - Safety Zones: Neptune Deep Water Port, Atlantic Ocean, Boston, MA (United States)


    ...1625-AA00 Safety Zones: Neptune Deep Water Port, Atlantic Ocean...for review and comment at the Web site http://www.regulations...rulemaking docket titled: Neptune Deep Water Port, Atlantic Ocean...infrastructure of the Neptune Deep Water Port. Extensive...

  16. Platinum group elements and gold in ferromanganese crusts from Afanasiy-Nikitin seamount, equatorial Indian Ocean: Sources and fractionation

    Digital Repository Service at National Institute of Oceanography (India)

    Banakar, V.K.; Hein, J.R.; Rajani, R.P.; Chodankar, A.R.

    in ANS Fe–Mn crusts are derived from seawater and are mainly of terrestrial origin, with a minor cosmogenic component. The Ru/Rh (0.5–2) and Pt/Ru ratios (7-28) are closely comparable to ratios in continental basalts, whereas Pd/Ir ratios exhibit values...

  17. Chemistry and possible resource potential of cobalt rich ferromanganese crust from Afanasiy-Nikitin seamount in the Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Parthiban, G.; Banakar, V.K.

    , Ni, Co, Zn and V and found to be rich in Co (upto 0.88%) mineralogically, the studied Fe-Mn crust samples contain poorly crystalline d-MnO sub(2) and minor amount of Carbonate Fluorapatite (CFA) and feldspars. The low Mn/Fe ratios (less than 2), d...


    Scientific Electronic Library Online (English)



    Full Text Available El Batolito de Sabanalarga es a un cuerpo alargado de 410 Km2 que se extiende entre las Cordilleras Central y Occidental de Colombia, intruye en el borde occidental la Formación Barroso y las Diabasas de San José de Urama y en el borde oriental las rocas metamórficas del Complejo Cajamarca. El Batol [...] ito de Sabanalarga está formado por al menos dos pulsos magmáticos: uno inicial representado por gabros y dioritas de afinidad subalcalina toleítica y un segundo pulso constituido por cuarzodioritas y tonalitas de afinidad subalcalina de la serie calcoalcalina baja en K. El magmatismo se generó en un ambiente localizado por encima de la zona de subducción, en un arco volcánico plutónico localizado en el borde de sutura entre la corteza continental y la corteza oceánica, afectando ambas cortezas. Hace parte del arco las rocas volcánicas de la Formación Barroso. La edad del Batolito y del arco en general, en concordancia con los datos radiométricos, las relaciones intrusivas y el registro fósil, ocurrió dentro del rango comprendido entre el Cenomaniano-Aptiano superior, localizándose el plutonismo en el rango de edad entre 83 M.a y 102 M.a. Magmatismo como el de la Diorita de Altavista, el Gabro de San Diego y el Batolito Antioqueño, es contemporáneo con el arco que generó el Batolito de Sabanalarga, pudiendo ser parte del mismo evento magmático. Abstract in english The Sabanalarga Batholith is a long shape body reaching 410 Km2, located between the Central and Western cordilleras of Colombia. It intrudes rocks of the Barroso Formation and San Jose de Urama diabases along its western margin and rocks belonging to the Cajamarca complex towards the eastern side o [...] f the pluton. The Sabanalarga batholith is formed by at least two magmatic pulses. The first pulse is represented by gabbros and diorites with tholeiitic sub-alkaline affinity. The second pulse corresponds to cuarzodiorites and tonalites with sub-alkaline to calco-alkalyne low-K affinity. Magmatism is interpreted as being of supra-subduction environment, where the plutonic-volcanic arc is located right into the suture zone bonding and affecting both, continental and oceanic crust. The batholith is part of the volcanic arc of the Barroso Formation. The age of the batholith and related arc, according to available radiometric data, intrusive character and fossil record, occurred between the Cenomanian-Upper Aptian range, constraining the plutonism in the age range between 83 Ma and 102 Ma. The magmatic arc represented by the Sabanalarga batholith is contemporary with the Altavista diorite, San Diego Gabbro and Antioquian batholith and eventually belong to the same magmatic event.

  19. Late Quaternary Sedimentary Records of Core MA01 in the Mendeleev Ridge, the Western Arctic Ocean: Preliminary Results (United States)

    Park, K.; Kim, S.; Khim, B. K.; Wang, R.; Mei, J.; Xiao, W.; Polyak, L. V.


    Late Quaternary deep sea sediments in the Arctic Ocean are characterized by brown layers intercalated with yellowish to olive gray layers. It has been known that the brown and gray layers were deposited during interglacial (or interstadial) and glacial (or stadial) periods, respectively. A 5.5-m long gravity core MA01 was obtained from the Mendeleev Ridge in the western Arctic Ocean by R/V Xue Long during scientific cruise CHINARE-V. Age (~1.0 Ma) of core MA01 was tentatively decided by correlation of sediment color cycles, XRF Mn and Ca cycles, and geomagnetic inclinations with core HLY0503-8JPC (Adler et al., 2009) and core HLY0503-06JPC(Cronin et al., 2013) that were also collected from the Mendeleev Ridge area. A total of 23 brown layers are characterized by low L* and b*, high Mn concentration, and abundant foraminifera. In contrast, gray layers are characterized by high L* and b*, low Mn concentration, and few foraminiferal tests. Foraminifera abundance peaks are not well correlated to CaCO3 peaks which are accompanied with the coarse-grained (>63 ?m) fractions (i.e., IRD) both in brown and gray layers. A strong positive correlation coefficient (r2=0.89) between TOC content and C/N ratio indicates that the major source of organic matter is terrestrial. The good correlations of CaCO3 content to TOC (r2=0.56) and C/N ratio (r2=0.69) imply that IRDs contain detrital CaCO3 fraction which mainly originated from the Canadian Arctic Archipelago. In addition, high kaolinite/chlorite (K/C) ratios mostly correspond to CaCO3 peaks, also suggesting that the fine-grained particles in the Mendeleev Ridge were transported from the northern coasts of the Alaska and Canada. Thus, the Beaufort Gyre, the predominant surface current in the western Arctic Ocean, has played an important role in the sediment delivery to the Mendeleev Ridge. It is worthy of note that TOC and CaCO3 peaks are obviously distinct in the upper part of core MA01, whereas these peaks are reduced in the lower part of the core. More study on these contrasting features is in progress.

  20. Insights into Oceanic Crust Accretion from a Comparison of Rock Magnetic and Silicate Fabrics from Lower Crustal Gabbros from Hess Deep Rift (United States)

    Horst, A. J.; Morris, A.; Friedman, S. A.; Cheadle, M. J.


    The mechanisms of lower crustal accretion remain a long-standing question for those who study fast-spreading mid-ocean ridges. One of the goals of Integrated Ocean Drilling Program (IODP) Expedition 345 is to test accretionary models by investigating the structure of the lower oceanic crust exposed within the Hess Deep Rift. Located near the tip of the westward-propagating Cocos-Nazca spreading center, Hess Deep Rift exposes crust formed at the East Pacific Rise. During IODP Expedition 345, primitive gabbroic rocks were recovered from a dismembered lower crustal section at ~4850 meters below sealevel. Constraints on physical processes during magmatic accretion are provided by the relative orientation and strength of rock fabrics. We present anisotropy of magnetic susceptibility (AMS) fabric data from gabbros recovered from the two deepest holes (U1415J and U1415P). AMS measurements provide petrofabric data that may be used to constrain magma emplacement and subsequent magmatic flow. Bulk susceptibility ranges from 1.15 x 10-4 to 5.73 x 10-2 SI, with a majority of the samples having susceptibility greater than 10-3 SI, suggesting magnetite is the dominant contributor to the AMS signal. Low-temperature demagnetization data show Verwey transitions near 125K indicating the presence of nearly stoichiometric magnetite in most samples. AMS reveals dominantly oblate fabrics with a moderate degree of anisotropy (P') ranging from 1.01 to 1.38 (average P' = 1.13). Fabric strength varies within each of the petrologically-defined units recovered from different crustal blocks. Additional remanence anisotropy fabric analyses of a few specimens reveal nearly identical directions of principal axes compared to AMS, but with larger degrees of anisotropy. Electron backscatter diffraction (EBSD) data from one sample shows a moderate plagioclase crystallographic preferred orientation best defined by a b-axis maxima that is coincident with the AMS minimum principal axis. This comparison between silicate and magnetic fabric data suggests that AMS is a good proxy for bulk silicate fabrics in these samples from Hess Deep. By integrating AMS and EBSD, both sensitive indicators of magnetic and silicate fabrics in gabbroic rocks, we seek a better understanding of the formation of gabbro in oceanic crust.

  1. A neodymium, strontium, and oxygen isotopic study of the Cretaceous Samail ophiolite and implications for the petrogenesis and seawater-hydrothermal alteration of oceanic crust (United States)

    McCulloch, Malcolm T.; Gregory, Robert T.; Wasserburg, G. J.; Taylor, Hugh P.


    In the Samail ophiolite, 147Sm- 143Nd, 87Rb- 87Sr, and 18O/ 16O isotopic systems have been used to distinguish between sea-floor hydrothermal alteration and primary magmatic isotopic variations. The Rb-Sr and 18O/ 16O isotopic systems clearly exhibit sensitivity to hydrothermal interactions with seawater while the Sm-Nd system appears essentially undisturbed. Internal isochrons have been determined by the 147Sm- 143Nd method using coexisting plagioclase and pyroxene and give crystallization ages of 130 ± 12m.y. from Ibra and 100 ± 20 m.y. from Wadi Fizh. These ages are interpreted as the time of formation of the Samail oceanic crust and are older than the inferred emplacement age of 65-85 m.y. The initial 143Nd/ 144Nd ratios for a tectonized harzburgite, cumulate gabbros, plagiogranite, sheeted dikes and a basalt have a limited range in ? Nd of from 7.5 to 8.6 for all lithologies, demonstrating a clear oceanic affinity and supporting earlier interpretations based on geologic observations and geochemistry. The 87Sr/ 86Sr initial ratios on the same rocks have an extremely large range of from 0.70296 to 0.70650 (? Sr = -19.7 to +30.5) and the ? 18O values vary from 2.6 to 12.7. These large variations are clearly consistent with hydrothermal interaction of seawater with the oceanic crust. A model is presented for the closed system exchange of Sr and O, that in principle illustrates how the Sr isotopic data may be utilized to estimate the water/rock ratio and subsequently used to evaluate the temperature of equilibration between the water and silicates from the 18O/ 16O water-rock fractionation.

  2. Tectonic model for the evolution of oceanic crust in the northeastern Indian Ocean from the Late Cretaceous to the Early Tertiary

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.; Rao, D.G.; Ramana, M.V.; Subrahmanyam, V.; Sarma, K.V.L.N.S.; Pilipenko, A.I.; Shcherbakov, V.S.; Murthy, I.V.R.

    Bathymetry and magnetic studies (part of the Trans Indian Ocean Geotraverse investigations) in the northeastern Indian Ocean revealed seafloor topographic features, magnetic Lineations (19 through 32B) and abandonaed spreading centers. The seafloor...

  3. Ocean circulation in the tropical Indo-Pacific during early Pliocene (5.6 - 4.2 Ma): Paleobiogeographic and isotopic evidence

    Indian Academy of Sciences (India)

    M. S. Srinivasan; D. K. Sinha


    A Comparison of late Neogene planktic foraminferal biogeography and stable isotopic records of shallow dwelling and deep dwelling planktic foraminifera from DSDP sites 214 (Ninetyeast Ridge, northeast Indian Ocean) and 586B (ontong-Java Plateau, western Equatorial Pacific) provides a clue to the nature of the ocean circulation in the tropical Indo-Pacific during early Pliocene. The Present study reveals that the late Neogene planktic foraminiferal data from the eastern and western sides of the Indonesian Seaway are very similar. The only distinct inter-ocean difference however is the absence of Pulleniatina spectablis from the Indian Ocean. This species makes its first evolutionary appearance in the Equatorial Pacific at about 5.6 Ma (Early Gilbert reversed) and ranges up to 4.2 Ma (Top Conhiti subchron). The complete absence of Pulleniatina spectablis from the Indian Ocean is attributed to blocking of westward flow of tropical waters of the Pacific to the Indian Ocean resulting in a major change in the tropical Pacific and Indian oceans during 5.6 to 4.2 ma. In order to understand the nature of this blockage, isotopic depth ranking of selected planktic foraminifera and thus may be interpreted that the shallow sills that mark the Seaway in modern times were present as early as 5.6 Ma. The distribution of Pulleniatina spectablis throughout the Equatorial Pacific reveals that Modern Equatorial Pacific Under Current (Cromwell Current) flowing towards east at a depth of 200-300 m (which is also the depth habitat of Pulleniatina spectablis) was present at the beginning of the Pliocene (5.6 Ma). As a dequel to the blocking of the Indonesian Seaway and the resultant interruption in the flow of central Equatorial Current System of the Pacific to the west there was an increase in the western Pacific Warm Pool Waters and strengthening of the gyral circulation in the Pacific and Indian Oceans. This eventually triggered the intensification of the Asian Monsoon System.

  4. Crustal thickness controlled by plate tectonics : a review of crust-mantle interaction processes illustrated by European examples

    DEFF Research Database (Denmark)

    Artemieva, Irina M.; Meissner, Rolf


    The continental crust on Earth cannot be extracted directly from the mantle, and the primary crust extracted directly from an early magma ocean is not preserved on Earth. We review geophysical and geochemical aspects of global crust–mantle material exchange processes and examine the processes which, on one side, form and transform the continental crust and, on the other side, chemically modify the mantle residue from which the continental crust has been extracted. Major mechanisms that provide crust–mantle material exchange are oceanic and continental subduction, lithosphere delamination, and mafic magmatism. While both subduction and delamination recycle crustal material into the mantle, mafic magmatism transports mantle material upward and participates in growth of new oceanic and continental crusts and significant structural and chemical modification of the latter. We discuss the role of basalt/gabbro–eclogite phase transition in crustal evolution and the links between lithosphere recycling, mafic magmatism, and crustal underplating. We advocate that plate tectonics processes, together with basalt/gabbro–eclogite transition, limit crustal thickness worldwide by providing effective mechanisms of crustal (lithosphere) recycling. The processes of crust–mantle interaction have created very dissimilar crustal styles in Europe, as seen by its seismic structure, crustal thickness, and average seismic velocities in the basement. Our special focus is on processes responsible for the formation of the thin crust of central and western Europe, which was largely formed during the Variscan (430–280 Ma) orogeny but has the present structure of an “extended” crust, similar to that of the Basin and Range province in western USA. Major geophysical characteristics of the Variscan lithosphere are discussed within the frame of possible sequences of crust–mantle material exchange mechanisms during and after main orogenic events in the European Variscides.

  5. From the lavas to the gabbros: 1.25 km of geochemical characterization of upper oceanic crust at ODP/IODP Site 1256, eastern equatorial Pacific (United States)

    Höfig, Tobias W.; Geldmacher, Jörg; Hoernle, Kaj; Hauff, Folkmar; Duggen, Svend; Garbe-Schönberg, Dieter


    Here we present trace element and Sr-Nd-Hf-Pb (double spike) isotopic data covering the entire igneous section of oceanic crust drilled at Ocean Drilling Program (ODP)/Integrated Ocean Drilling Program (IODP) Site 1256 on the Cocos Plate. The penetrated interval extends from the upper lavas through the sheeted dike complex to the gabbroic plutonic rocks, formed during superfast spreading at the mid-Miocene equatorial East Pacific Rise. The data are used to characterize the effects of chemical alteration, resulting from convection of seawater and hydrothermal fluids, on the trace element and isotopic composition of oceanic crust. Compared to normal mid-ocean-ridge basalt, the igneous basement of Site 1256 (Holes 1256C/D) is isotopically slightly enriched but shows only narrow downhole variations in Nd-Hf-Pb isotope ratios: 143Nd/144Nd = 0.513089 ± 0.000028 (2?), 176Hf/177Hf = 0.283194 ± 0.000033 (2?), 206Pb/204Pb = 18.61 ± 0.11 (2?), 207Pb/204Pb = 15.521 ± 0.014 (2?), 208Pb/204Pb = 38.24 ± 0.15 (2?). We believe that this minor variability is mainly of primary (magmatic) origin. The Sr isotopic composition shows considerably larger variation and, as expected, serves as sensitive tracer of seawater influence, which is particularly pronounced in the lava-dike transition zone and the sheeted dikes. The seawater influence is most prominent in a highly metal sulfide-enriched breccia layer encountered in the transition zone with 87Sr/86Sr of ~ 0.706, indicating a maximum water-rock mixing ratio of ~ 12. However, compared to the igneous section drilled at Site 504 (Hole 504B), which formed at intermediate, i.e., slower spreading rates at the Galápagos Spreading Center and hosting a much thicker sulfide-rich stockwork zone, the average intensity of water-rock interaction is lower. This is expressed by lesser mobility of base metals, narrower variability of alteration-sensitive incompatible elements, and less radiogenic Sr isotopic compositions on average at Site 1256. The amount of metal sulfide precipitation seems to be positively correlated with the degree of hydrothermal overprint. The less intense alteration of the Site 1256 transition zone, compared to Site 504, most likely reflects the higher rate of spreading, eventually resulting in a shorter period of time of continuous exposure to hydrothermal convection at the ridge crest. The observed seafloor alteration, leading to modified radiogenic parent/daughter ratios in the Site 1256 rocks, is ultimately not sufficient to develop time-integrative high 206Pb/204Pb and moderate 87Sr/86Sr ratios, as being characteristic of the HIMU (high ? = high 238U/204Pb) mantle signature proposed to originate from hydrothermally altered, subducted oceanic crust. Therefore, additional modification during the subduction process must be taken into account.

  6. Oceanic crust and island arc formation in Central Asia during late Neoproterozoic times - evidence from petrological and geochemical studies


    Pfänder, Jörg A.


    Die vorliegende Arbeit behandelt die Entwicklung des 570 Ma alten, neoproterozoischen Agardagh - Tes-Chem Ophioliths (ATCO) in Zentralasien. Dieser Ophiolith liegt südwestlich des Baikalsees (50.5° N, 95° E) und wurde im frühen Stadium der Akkretion des Zentralasiatischen Mobilgürtels auf den nordwestlichen Rand des Tuvinisch-Mongolischen Mikrokontinentes aufgeschoben. Bei dem Zentralasiatische Mobilgürtel handelt es sich um einen riesigen Akkretions-Subduktionskomplex, der heute das größte z...

  7. Crusted scabies

    Directory of Open Access Journals (Sweden)

    Karthikeyan Kaliaperumal


    Full Text Available Crusted scabies is a rare manifestation of scabies characterized by uncontrolled proliferation of mites in the skin. In immunocompromised patients, this infestation is characterized by crusted lesions. The occurrence of the disease in human immunodeficiency virus-infected patients and the widespread use of immunosuppressive agents has led to a renewed interest in the disease. Early recognition and treatment is necessary to avoid an outbreak of scabies. This review highlights the pathogenesis, predisposing factors, clinical features and treatment of crusted scabies.

  8. Two stage melt-rock interaction in the lower oceanic crust of the Parece Vela basin (Philippine sea), evidence from the primitive troctolites from the Godzilla Megamullion (United States)

    Sanfilippo, A.; Dick, H. J.; Ohara, Y.


    Godzilla Megamullion is a giant oceanic core complex exposed in an extinct slow- to intermediate-spreading segment of the Parece Vela Basin (Philippine sea) [1; 2]. It exposes lower crust and mantle rocks on the sea-floor, offering a unique opportunity to unravel the architecture and the composition of the lower oceanic lithosphere of an extinct back arc basin. Here we present data on primitive troctolites and associated olivine-gabbros from the breakaway area of the Godzilla Megamullion. On the basis of the olivine/plagioclase volume ratio, the troctolites are subdivided into Ol-troctolites (Ol/Pl >1) and Pl-troctolites (Ol/PlNews 12, 27-29. [2]Tani et al., 2011. Geology 39, 47-50. doi:10.1130/G3132. [3] Suhr et al., 2008.Geochem. Geophys. Geosyst., 9, Q10007, doi:10.1029/2008GC002012 [4] Renna and Tribuzio, 2011, Journal of Petrology, doi:10.1093/petrology/egr029

  9. Long-term records of erosional change from marine ferromanganese crusts

    Indian Academy of Sciences (India)

    R Keith O'Nions; Martin Frank


    Ferromanganese crusts from the Atlantic, Indian and Pacific Oceans record the Nd and Pb isotope compositions of the water masses from which they form as hydrogenous precipitates. The 10Be/9Be-calibrated time series for crusts are compared to estimates based on Co-contents, from which the equatorial Pacific crusts studied are inferred to have recorded ca. 60 Ma of Pacific deep water history. Time series of Nd show that the oceans have maintained a strong provinciality in Nd isotopic composition, determined by terrigenous inputs, over periods of up to 60 Ma. Superimposed on the distinct basin-specific signatures are variations in Nd and Pb isotope time series which have been particularly marked over the last 5 Ma. It is shown that changes in erosional inputs, particularly associated with Himalayan uplift and the northern hemisphere glaciation have influenced Indian and Atlantic Ocean deep water isotopic composi- tions respectively. There is no evidence so far for an imprint of the final closure of the Panama Isthmus on the Pb and Nd isotopic composition in either Atlantic or Pacific deep water masses.

  10. Crusted scabies


    Karthikeyan Kaliaperumal


    Crusted scabies is a rare manifestation of scabies characterized by uncontrolled proliferation of mites in the skin. In immunocompromised patients, this infestation is characterized by crusted lesions. The occurrence of the disease in human immunodeficiency virus-infected patients and the widespread use of immunosuppressive agents has led to a renewed interest in the disease. Early recognition and treatment is necessary to avoid an outbreak of scabies. This review highlights the pathogenesis,...

  11. Late Quaternary sediment deposition of core MA01 in the Mendeleev Ridge, the western Arctic Ocean: Preliminary results (United States)

    Park, Kwang-Kyu; Kim, Sunghan; Khim, Boo-Keun; Xiao, Wenshen; Wang, Rujian


    Late Quaternary deep marine sediments in the Arctic Ocean are characterized by brown layers intercalated with yellowish to olive gray layers (Poore et al., 1999; Polyak et al., 2004). Previous studies reported that the brown and gray layers were deposited during interglacial (or interstadial) and glacial (or stadial) periods, respectively. A 5.5-m long gravity core MA01 was obtained from the Mendeleev Ridge in the western Arctic Ocean by R/V Xue Long during scientific cruise CHINARE-V. Age (~450 ka) of core MA01 was tentatively estimated by correlation of brown layers with an adjacent core HLY0503-8JPC (Adler et al., 2009). A total of 22 brown layers characterized by low L* and b*, high Mn concentration, and abundant foraminifera were identified. Corresponding gray layers are characterized by high L* and b*, low Mn concentration, and few foraminiferal tests. Foraminifera abundance peaks are not well correlated to CaCO3 peaks which occurred with the coarse-grained (>0.063 mm) fractions (i.e., IRD) both in brown and gray layers. IRDs are transported presumably by sea ice for the deposition of brown layers and by iceberg for the deposition of gray layers (Polyak et al., 2004). A strong correlation coefficient (r2=0.89) between TOC content and C/N ratio indicates that the major source of organic matter is terrestrial. The good correlations of CaCO3 content to TOC (r2=0.56) and C/N ratio (r2=0.69) imply that IRDs contain detrital CaCO3 which mainly originated from the Canadian Arctic Archipelago. In addition, high kaolinite/chlorite (K/C) ratios mostly correspond to CaCO3 peaks, which suggests that the fine-grained particles in the Mendeleev Ridge are transported from the north coast Alaska and Canada where Mesozoic and Cenozoic strata are widely distributed. Thus, the Beaufort Gyre, the predominant surface current in the western Arctic Ocean, played an important role in the sediment delivery to the Mendeleev Ridge. It is worthy of note that the TOC and CaCO3 peaks are obviously distinct in the upper part of core MA01, whereas these peaks are reduced in the lower part of the core. More study on these contrasting features is in progress. References Adler, R.E., Polyak, L., Ortiz, J.D., Kaufman, D.S., Channell, J.E.T., Xuan, C., Grottoli, A.G., Sellén, E., and Crawford, K.A., 2009. Global and Planetary Change 68(1-2), 18-29. Polyak, L., Curry, W.B., Darby, D.A., Bischof, J., and Cronin, T.M., 2004. Palaeogeography, Palaeoclimatology, Palaeoecology 203, 73-93. Poore, R., Osterman, L., Curry, W., and Phillips, R., 1999. Geology 27, 759-762.

  12. The hydrothermal power of oceanic lithosphere

    Directory of Open Access Journals (Sweden)

    C. J. Grose


    Full Text Available We have estimated the power of ventilated hydrothermal heat transport, and its spatial distribution, using a set of recently developed plate models which highlight the effects of hydrothermal circulation and thermal insulation by oceanic crust. Testing lithospheric cooling models with these two effects, we estimate that global advective heat transport is about 6.6 TW, significantly lower than previous estimates, and that the fraction of that extracted by vigorous circulation on the ridge axes (<1 Ma is about 50% of the total, significantly higher than previous estimates. This low hydrothermal power estimate originates from the thermally insulating properties of oceanic crust in relation to the mantle. Since the crust is relatively insulating, the effective properties of the lithosphere are "crust dominated" near ridge axes (yielding lower heat flow, and gradually approach mantle values over time. Thus, cooling models with crustal insulation predict low heat flow over young seafloor, implying that the difference of modeled and measured heat flow is due to the heat transport properties of the lithosphere, in addition to ventilated hydrothermal circulation as generally accepted. These estimates may bear on important problems in the physics and chemistry of the Earth because the magnitude of hydrothermal power affects chemical exchanges between the oceans and the lithosphere, thereby affecting both thermal and chemical budgets in the oceanic crust and lithosphere, the subduction factory, and convective mantle.

  13. Tectonic implications of post-30 Ma Pacific and North American relative plate motions (United States)

    Bohannon, R.G.; Parsons, T.


    The Pacific plate moved northwest relative to North America since 42 Ma. The rapid half rate of Pacific-Farallon spreading allowed the ridge to approach the continent at about 29 Ma. Extinct spreading ridges that occur offshore along 65% of the margin document that fragments of the subducted Farallon slab became captured by the Pacific plate and assumed its motion proper to the actual subduction of the spreading ridge. This plate-capture process can be used to explain much of the post-29 Ma Cordilleran North America extension, strike slip, and the inland jump of oceanic spreading in the Gulf of California. Much of the post-29 Ma continental tectonism is the result of the strong traction imposed on the deep part of the continental crust by the gently inclined slab of subducted oceanic lithosphere as it moved to the northwest relative to the overlying continent. -from Authors

  14. Building the oceanic crust: Insights on volcanic emplacement processes at the hotspot-influenced Galápagos Spreading Center, 92°W (United States)

    McClinton, J. T.; White, S. M.; Colman, A.; Sinton, J. M.


    The Galápagos Spreading Center (GSC) displays a range of axial morphology due to increased magma supply from the adjacent Galápagos mantle plume. Over 30 years of scientific exploration has also documented the associated variations in volcanic terrain, crustal thickness, and geochemistry of erupted basalts, but until recently the fine-scale ("lava flow scale") volcanic features of the GSC had not been investigated. Using the Alvin submersible and aided by near-bottom photographic surveys by TowCam and sub-meter-scale sonar surveys by AUV Sentry, we mapped and sampled 12 individual eruptive units covering ~16km2 of seafloor on the ridge axis of the GSC at 92°W. Variations in AUV Sentry bathymetry and DSL-120A backscatter enabled us to characterize the fine-scale surface morphology within each eruptive unit. Lava flow morphologies within each unit were identified using a neuro-fuzzy classifier which assigns pixels as pillows, lobates, sheets, or fissures by using attributes derived from high-resolution sonar bathymetry and backscatter (McClinton et al., submitted PE&RS). An accuracy assessment indicates approximately 90% agreement between the lava morphology map and an independent set of visual observations. The result of this classification effort is that we are able to quantitatively examine the spatial distribution of lava flow morphology as it relates to the emplacement of lava flows within each eruptive unit at a mid-ocean ridge. Preliminary analyses show that a large, segment-centered volcanic cone which straddles the axial summit graben (the "Empanada") is constructed mostly of pillow lavas, while volcanism in the rifted center of the cone consists of lobate and sheet flows. Conversely, along the rest of the segment, on-axis eruptions consist mainly of pillow lava with most sheet and lobate flows found outside of a small axial summit graben. At least some of these sheet flows are fed by lava channels, suggesting emplacement over distances up to 1km, while pillow lava within the summit graben form low mounds; we speculate that eruption effusion rates decreased over the eruptive episode, producing changes in lava morphology within the larger eruptive units. Many axial mounds are also cut by the graben faults. The relatively young appearance of the lava surfaces at 92°W argues for a close relationship between volcanism and graben faulting on this part of the ridge.

  15. Abandoned Paleocene spreading center in the northeastern Indian Ocean: evidence from magnetic and seismic reflection data

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.; Rao, D.G.

    separating oceanic crust with different magnetic isochron patterns. The pairs of magnetic lineations 30 through 32n.2 between the 86 degrees E FZ and the Ninetyeast Ridge reveal an ASC of about 65 Ma age; parallel to approx. equal to 0.5 degrees S latitude...

  16. A geochemical traverse across the North Chilean Andes: Evidence for crust generation from the mantle wedge

    International Nuclear Information System (INIS)

    Major and trace element and Sr- and Nd-isotope analyses are presented on 186-0 Ma magmatic rocks along an east-west traverse across North Chile at 220S. ?Sr ranges from -25 to +100 and ?Nd from +6 to -9, but the low ?Nd and high ?Sr values are in rocks generated in the last 15 Ma. It is argued that previous discussions of petrogenesis in North Chile have been hampered because the changes in magma chemistry in this area of unusually thick crust reflect not one, but two processes. One results in a progressive shift of ?Sr from -25 to +20 and ?Nd from +6 to -6 in Jurassic to Recent rocks, which is accompanied by increasing Ta/Sm and Sr decreasing Th/Ta. The second is largely confined to the younger rocks and it is characterised by ?Sr increasing up to +100 with increasing SiO2 and decreasing Sr, and it results in relatively shallow trends on an ?Nd-?Sr diagram. The preferred interpretation is that trend 1 is due to the mobilisation of old, late Proterozoic mantle lithosphere as magmatism migrated eastwards, and that trend 2 is due to crustal melting and contamination with differentiation in this area of thickened continental crust. It follows that the mantle wedge is the principal site of crust generation, and it is argued that <20% of the Sr in the recent northern Chile rocks is derived from the subducted ocean crust. (orig.)

  17. ACEX Arctic Coring Expedition : paleoceanographic and tectonic evolution of the central Arctic Ocean


    Backman, Jan; Moran, Kathryn; Evans, Dan


    The first scientific drilling expedition to the central Arctic Ocean was completed in late summer 2004. Integrated Ocean Drilling Program Expedition 302, Arctic Coring Expedition (ACEX), recovered sediment cores deeper than 400 meters below seafloor (mbsf) in water depths of ~1300 m at the top of the world, only 250 km from the North Pole. ACEX's destination was the Lomonosov Ridge, hypothesized to be a sliver of continental crust that broke away from the Eurasian plate at ~56 Ma. As the ...

  18. Gondwanaland from 650-500 Ma assembly through 320 Ma merger in Pangea to 185-100 Ma breakup: supercontinental tectonics via stratigraphy and radiometric dating (United States)

    Veevers, J. J.


    Gondwanaland lasted from the 650-500 Ma (late Neoproterozoic-Cambrian) amalgamation of African and South American terranes to Antarctica-Australia-India through 320 Ma (mid-Carboniferous) merging with Laurussia in Pangea to breakup from 185 to 100 Ma (Jurassic and Early Cretaceous). Gondwanaland straddled the equator at 540 Ma, lay wholly in the Southern Hemisphere by 350 Ma, and then rotated clockwise so that at 250 Ma Australia reached the S pole and Africa the equator. By initial breakup of Pangea at 185 Ma, Gondwanaland had moved northward such that North Africa reached 35°N. The first clear picture of Gondwanaland, in the Cambrian, shows the assembly of continents with later Laurentian, European and Asian terranes along the "northern" margin, and with a trench along the "western" and "southern" margins, reflected by a 10,000-km-long chain of 530-500 Ma granites. The interior was crossed by the Prydz-Leeuwin and Mozambique Orogenic Belts. The shoreline lapped the flanks of uplifts generated during this complex terminal Pan-Gondwanaland (650-500 Ma) deformation, which endowed Gondwanaland with a thick, buoyant crust and lithosphere and a nonmarine siliciclastic facies. During the Ordovician, terranes drifted from Africa as the first of many transfers of material to the "northern" continents. Central Australia was crossed by the sea, and the eastern margin and ocean floor were flooded by grains of quartz (and 600-500 Ma zircon) from Antarctica. Ice centres in North Africa and southern South America/Africa waxed and waned in the latest Ordovician, Early Silurian, latest Devonian, and Early Carboniferous. In the mid-Carboniferous, Laurussia and Gondwanaland merged in the composite called Pangea by definitive right-lateral contact along the Variscan suture, with collisional stress and subsequent uplift felt as far afield as Australia. Ice sheets developed on the tectonic uplands of Gondwanaland south of 30°S. In the Early Permian, the self-induced heat beneath Pangea drove the first stage of differential subsidence of the Gondwanaland platform to intercept sediment from the melting ice, then to accumulate coal measures with Glossopteris, and subsequently Early Triassic redbeds. An orogenic zone along the Panthalassan margin propagated from South America to Australia and was terminally deformed in the mid-Triassic. Coal deposition resumed during Late Triassic relaxation in the second stage of Pangean extension. In the Early Jurassic, the vast ˜200 Ma Central Atlantic magmatic province of tholeiite anticipated the 185 Ma breakup in the Central Atlantic. Another magmatic province was erupted at this time between southern Africa and southeastern Australia. The northeastern Indian Ocean opened from 156 Ma, and the western Indian Ocean from 150 Ma. By the 100 Ma mid-Cretaceous, the Gondwanaland province of Pangea had split into its five constituents, and the Earth had entered the thalassocratic state of dispersed continents. The 650-500 Ma "Pan-Gondwanaland" events (? by mafic underplating) rendered Gondwanaland permanently geocratic. Pangean (320-185 Ma) tectonics, driven by pulses of self-induced heat, promoted widespread subsidence at 300 Ma Early Permian and 230 Ma Late Triassic. Pangea initially broke up at 185 Ma and the five continental pieces of Gondwanaland had broken apart by the 100 Ma mid-Cretaceous. Another long-lasting feature of Gondwanaland was subduction beneath the "southern" margin and export of terranes from the "northern" and "northwestern" margins. Export of terranes was promoted by Gondwanaland-induced heat, and internal breakup by Pangea-induced heat.

  19. Global Paleobathymetry for the Cenomanian-Turonian (90 Ma) (United States)

    Goswami, A.; Olson, P.; Hinnov, L. A.; Gnanadesikan, A.


    We present a paleo-ocean bathymetry reconstruction for Cenomanian-Turonian (90 Ma) time in a 0.1°x0.1° resolution for use in paleo-climate studies. Age of the ocean floor for the Cenomanian-Turonian (90 Ma) is from Müller et al. (2008 a,b); coastlines are from the PALEOMAP Project (Scotese, 2011). To reconstruct paleo-ocean bathymetry, we use a plate model equation to model depth to basement (Turcotte and Schubert, 2002). We estimate plate model equation parameter values from measurements of modern oceans (Crosby et al., 2006). On top of the depth to basement, we isostatically add a multilayer sediment model derived from area-corrected sediment thickness data (Divins, 2003; Whittaker et al., 2013). Lastly, we parameterize the modern continental shelf, slope, and rise in a "sediment wedge model" to connect the coastline with the closest ocean crust as defined by Müller et al. (2008 a, b). These parameters are defined using empirical relationships obtained from study of modern ocean transects where a complete rifting history is preserved (Atlantic and Southern oceans), and the closest approach of the respective oceanic crust (Müller et al., 2008a,b) to the coastline. We use the modern ocean as a test, comparing maps and cross sections of modern ocean bathymetry modeled using our reconstruction method with that of ETOPO1 (Amante and Eakins, 2009). Adding sea plateaus and seamounts minimize the difference between our modeled bathymetry and ETOPO1. Finally, we also present a comparison of our reconstructed paleo-bathymetry to that of Müller et al. (2008 a,b) for the Cenomanian-Turonian (90 Ma). References: Amante, C., Eakins, B.W., 2009, NOAA Tech. Memo. NESDIS NGDC-24, 19 p. Crosby, A., McKenzie, D., Sclater, J.G., 2006, Geophysical Journal Int. 166.2, 553-573. Divins, D., 2003, NOAA NGDC, Boulder, CO. Müller, R., Sdrolias, M., Gaina, C., Roest, W., 2008b, Geochemistry, Geophysics, Geosystems, 9, Q04006, doi:10.1029/2007GC001743 Müller, R., Sdrolias, M., Gaina, C., Steinberger, B., Heine, C., 2008a, Science, 319, 1357-1362. Scotese, C., 2011, PALEOMAP Project, Arlington, Texas. Turcotte, D., Schubert, G., 2002, Cambridge University Press, Cambridge, 456 p. Whittaker, J., Goncharov, A., Williams, S., Müller, R., Leitchenkov, G., 2013, Geochemistry, Geophysics, Geosystems. DOI:10.1002/ggge.20181

  20. Crustal structure of the ocean-continent transition at Flemish Cap: Seismic refraction results (United States)

    Funck, Thomas; Hopper, John R.; Larsen, Hans Christian; Louden, Keith E.; Tucholke, Brian E.; Holbrook, W. Steven


    We conducted a seismic refraction experiment across Flemish Cap and into the deep basin east of Newfoundland, Canada, and developed a velocity model for the crust and mantle from forward and inverse modeling of data from 25 ocean bottom seismometers and dense air gun shots. The continental crust at Flemish Cap is 30 km thick and is divided into three layers with P wave velocities of 6.0-6.7 km/s. Across the southeast Flemish Cap margin, the continental crust thins over a 90-km-wide zone to only 1.2 km. The ocean-continent boundary is near the base of Flemish Cap and is marked by a fault between thinned continental crust and 3-km-thick crust with velocities of 4.7-7.0 km/s interpreted as crust from magma-starved oceanic accretion. This thin crust continues seaward for 55 km and thins locally to ˜1.5 km. Below a sediment cover (1.9-3.1 km/s), oceanic layer 2 (4.7-4.9 km/s) is ˜1.5 km thick, while layer 3 (6.9 km/s) seems to disappear in the thinnest segment of the oceanic crust. At the seawardmost end of the line the crust thickens to ˜6 km. Mantle with velocities of 7.6-8.0 km/s underlies both the thin continental and thin oceanic crust in an 80-km-wide zone. A gradual downward increase to normal mantle velocities is interpreted to reflect decreasing degree of serpentinization with depth. Normal mantle velocities of 8.0 km/s are observed ˜6 km below basement. There are major differences compared to the conjugate Galicia Bank margin, which has a wide zone of extended continental crust, more faulting, and prominent detachment faults. Crust formed by seafloor spreading appears symmetric, however, with 30-km-wide zones of oceanic crust accreted on both margins beginning about 4.5 m.y. before formation of magnetic anomaly M0 (˜118 Ma).

  1. Investigating the link between an iron-60 anomaly in the deep ocean's crust and the origin of the Local Bubble

    Energy Technology Data Exchange (ETDEWEB)

    Schulreich, Michael; Breitschwerdt, Dieter [Zentrum fuer Astronomie und Astrophysik, TU Berlin, Berlin (Germany)


    Supernova explosions responsible for the creation of the Local Bubble (LB) and its associated HI cavity should have caused geological isotope anomalies via deposition of debris on Earth. The discovery of a highly significant increase of {sup 60}Fe (a radionuclide that is exclusively produced in explosive nucleosynthesis) in layers of a deep sea ferromanganese crust corresponding to a time of 2.2 Myr before present, appears very promising in this context. We report on our progress in relating these measurements to the formation of the LB by means of 3D hydrodynamical adaptive mesh refinement simulations of the turbulent interstellar medium in the solar neighborhood. Our calculations are based on a sophisticated selection procedure for the LB's progenitor stars and take advantage of passive scalars for following the chemical mixing process.

  2. Biological productivity, terrigenous influence and noncrustal elements supply to the Central Indian Ocean Basin: Paleoceanography during the past ?1Ma

    Indian Academy of Sciences (India)

    J N Pattan; Toshiyuki Masuzawa; D V Borole; G Parthiban; Pratima Jauhari; Mineko Yamamoto


    A 2 m-long sediment core from the siliceous ooze domain in the Central Indian Ocean Basin (CIOB; 13° 03?S: 74° 44?E; water depth 5099 m) is studied for calcium carbonate, total organic carbon, total nitrogen, biogenic opal, major and few trace elements (Al, Ti, Fe, K, Mg, Zr, Sc,V, Mn, Cu, Ni, Zn, Co, and Ba) to understand the productivity and intensity of terrigenous supply. The age model of the sediment core is based on U-Th dating, occurrence of Youngest Toba Tuff of ?74 ka and Australasian microtektites of ?770ka. Low carbonate content (> 1%) of sediment core indicates deposition below the carbonate compensation depth. Organic carbon content is also very low, almost uniform (mean 0.2 wt%) and is of marine origin. This suggests a well-oxygenated bottom water environment during the past ?1100 ka. Our data suggest that during ?1100 ka and ?400 ka siliceous productivity was lower, complimented by higher supply of terrigenous material mostly derived from the metasedimentary rocks of High Himalayan crystalline. However, during the last ?400ka, siliceous productivity increased with substantial reduction in the terrigenous sediment supply. The results suggest that intensity of Himalayan weathering, erosion associated with monsoons was comparatively higher prior to 400 ka. Manganese, Ba, Cu, Ni, Zn, and Co have around 90% of their supply from noncrustal (excess) source and their burial to seafloor remained unaffected throughout the past ?1100ka.

  3. Variability of low temperature hydrothermal alteration in upper ocean crust: Juan de Fuca Ridge and North Pond, Mid-Atlantic Ridge (United States)

    Rutter, J.; Harris, M.; Coggon, R. M.; Alt, J.; Teagle, D. A. H.


    Over 2/3 of the global hydrothermal heat flux occurs at low temperatures (discharge. Understanding ridge flank hydrothermal exchange is important to quantify global geochemical cycles. Hydrothermal chemical pathways are complex and the effects of water-rock reactions remain poorly constrained. Factors controlling fluid flow include volcanic structure, sediment thickness, and basement topography. This study compares the effects of low temperature alteration in two locations with contrasting hydrogeological regimes. The intermediate spreading Juan de Fuca ridge flank (JdF) in the northeast Pacific sports a thick sediment blanket. Rare basement outcrops are sites of fluid recharge and discharge. The average alteration extent (~10% secondary minerals), oxidation ratio (Fe3+/FeTOT=34%), and alteration character (orange, green, grey halos) of basement is constant with crustal age and depth along a 0.97-3.6 m.yr transect of ODP basement holes. However, vesicle fills record an increasingly complex history of successive alteration with age. In contrast, North Pond, a ~8 m.yr-old sediment-filled basin at 22N on the slow spreading Mid Atlantic Ridge, hosts rapid, relatively cool SE to NW basinal fluid flow. Average alteration extent (~10%) and oxidation ratio (33%) of Hole 395A basalts are similar to JdF. However, 395A cores are dominated by orange alteration halos, lack celadonite, but have abundant zeolite. Vesicle fill combinations are highly variable, but the most common fill progression is from oxidising to less oxidising secondary assemblages. The comparable extent of alteration between these two sites and the absence of an age relationship on the JdF suggests that the alteration extent of the upper crust is uniform and mostly established by 1 Myr. However, the variable alteration character reflects the influence of regional hydrology on hydrothermal alteration.

  4. Does subduction zone magmatism produce average continental crust

    International Nuclear Information System (INIS)

    The question of whether present day subduction zone magmatism produces material of average continental crust composition, which perhaps most would agree is andesitic, is addressed. It was argued that modern andesitic to dacitic rocks in Andean-type settings are produced by plagioclase fractionation of mantle derived basalts, leaving a complementary residue with low Rb/Sr and a positive Eu anomaly. This residue must be removed, for example by delamination, if the average crust produced in these settings is andesitic. The author argued against this, pointing out the absence of evidence for such a signature in the mantle. Either the average crust is not andesitic, a conclusion the author was not entirely comfortable with, or other crust forming processes must be sought. One possibility is that during the Archean, direct slab melting of basaltic or eclogitic oceanic crust produced felsic melts, which together with about 65 percent mafic material, yielded an average crust of andesitic composition

  5. The evolution of the Bangong-Nujiang Neo-Tethys ocean: Evidence from zircon U-Pb and Lu-Hf isotopic analyses of Early Cretaceous oceanic islands and ophiolites (United States)

    Fan, Jian-Jun; Li, Cai; Xie, Chao-Ming; Wang, Ming; Chen, Jing-Wen


    We conducted in situ U-Pb analyses of zircons from three basalts and one gabbro from the Zhonggang oceanic island, one basalt from the Zhaga oceanic island, and one gabbro from the Kangqiong ophiolite (all located in the middle segments of the Bangong-Nujiang suture zone of Tibetan Plateau), as well as in situ Hf isotope analyses of zircons from one gabbro from the Zhonggang oceanic island to constrain the tectonic evolution of the Bangong-Nujiang Neo-Tethys ocean. All samples contain numerous inherited zircons, and all the zircons contain magmatic oscillatory zoning and have Th/U ratios exceeding 0.4. Moreover, the average ?REE content of these zircons is less than 2000 ppm, and they display clear negative Eu and variable positive Ce anomalies, indicating a magmatic origin. LA-ICP-MS U-Pb dating of the zircons revealed three clear peaks in the age distribution, at 248-255, 162-168, and 117-120 Ma; Lu-Hf isotopic analyses of zircons from the gabbro of the Zhonggang oceanic island yielded a 269 Ma crust-mantle separation age. Taking into account the regional geology, previous data, and our new analyses, we infer that the middle and western segments of the Bangong-Nujiang Neo-Tethys ocean had initially opened in the late Permian (254-269 Ma) and that the ocean opened substantially between the late Permian and the Early Triassic (248-255 Ma). In addition, we infer that the initiation of subduction of the Bangong-Nujiang Neo-Tethys ocean took place at ~ 162-168 Ma, which is Middle Jurassic. The 117-120 Ma age is the time when the oceanic islands and ophiolites were formed, indicating that the Bangong-Nujiang Neo-Tethys ocean was, to some extent, still open at that time.

  6. On the dynamics and the geochemical mechanism of the evolution of the continental crust. 1

    International Nuclear Information System (INIS)

    An investigation of the isotopic composition of oxygen in the continental crust, in the oceans, in the oceanic crust and in the upper mantle shows the dynamics of plate tectonics and continental growthto be more or less constant during the last three or four aeons independent on the geochemical mechanism of continental growth. (author)

  7. Forward modelling of petrological crust-forming processes on the early Earth


    Ziaja, Karen


    Tonalite-trondhjemite-granodiorite (TTG) gneisses form up to two-thirds of the preserved Archean continental crust and there is considerable debate regarding the primary magmatic processes of the generation of these rocks. The popular theories indicate that these rocks were formed by partial melting of basaltic oceanic crust which was previously metamorphosed to garnet-amphibolite and/or eclogite facies conditions either at the base of thick oceanic crust or by subduction processes.rnThis stu...

  8. Corium crust strength measurements

    International Nuclear Information System (INIS)

    Corium strength is of interest in the context of a severe reactor accident in which molten core material melts through the reactor vessel and collects on the containment basemat. Some accident management strategies involve pouring water over the melt to solidify it and halt corium/concrete interactions. The effectiveness of this method could be influenced by the strength of the corium crust at the interface between the melt and coolant. A strong, coherent crust anchored to the containment walls could allow the yet-molten corium to fall away from the crust as it erodes the basemat, thereby thermally decoupling the melt from the coolant and sharply reducing the cooling rate. This paper presents a diverse collection of measurements of the mechanical strength of corium. The data is based on load tests of corium samples in three different contexts: (1) small blocks cut from the debris of the large-scale MACE experiments, (2) 30 cm-diameter, 75 kg ingots produced by SSWICS quench tests, and (3) high temperature crusts loaded during large-scale corium/concrete interaction (CCI) tests. In every case the corium consisted of varying proportions of UO2, ZrO2, and the constituents of concrete to represent a LWR melt at different stages of a molten core/concrete interaction. The collection of data was used to assess the strength and stability of an anchored, plant-scale crust. The results indicate that such a crust is likely to be too weak to support itself above the melt. It is therefore improbable that an anchored crust configuration could persist and the melt become thermally decoupled from the water layer to restrict cooling and prolong an attack of the reactor cavity concrete.

  9. Weathering crusts on peridotite (United States)

    Bucher, Kurt; Stober, Ingrid; Müller-Sigmund, Hiltrud


    Chemical weathering of dark-green massive peridotite, including partly serpentinized peridotite, produces a distinct and remarkable brown weathering rind when exposed to the atmosphere long enough. The structure and mineral composition of crusts on rocks from the Ronda peridotite, Spain, have been studied in some detail. The generic overall weathering reaction serpentinized peridotite + rainwater = weathering rind + runoff water describes the crust-forming process. This hydration reaction depends on water supply from the outcrop surface to the reaction front separating green peridotite from the brown crust. The reaction pauses after drying and resumes at the front after wetting. The overall net reaction transforms olivine to serpentine in a volume-conserving replacement reaction. The crust formation can be viewed as secondary serpentinization of peridotite that has been strongly altered by primary hydrothermal serpentinization. The reaction stoichiometry of the crust-related serpentinization is preserved and reflected by the composition of runoff waters in the peridotite massif. The brown color of the rind is caused by amorphous Fe(III) hydroxide, a side product from the oxidation of Fe(II) released by the dissolution of fayalite component in olivine.

  10. Petrological studies on the mantle peridotites recovered from the ocean floor in the western Pacific (United States)

    Ishii, T.; Hirano, N.; Ohara, Y.; Bloomer, S.


    Geological and geophysical models for the various oceanic crusts (or lithosphere) have been proposed on the basis of the combined studies between seismic observation for the oceanic crusts and petrological models of the onland ophiolites, which have been assumed as fossil of oceanic crusts. It is very important to collect basement rocks constituting various oceanic crusts and to characterize those petrological features. Ocean floor is commonly covered by effusive volcanic rocks, however occasionally hypabyssal and plutonic rocks are observed among the unique geological environments in the Western Pacific as partly shown in the followings. VOLCANIC DIATREME(?): Very unique volcanic knolls have been recently discovered by N. Hirano at the typical oceanic crust in the Northwestern Pacific, off Tohoku of Northeastern Japan. The constituting rocks for the main volcanic edifice are porous alkaline lavas with 1-5Ma age containing abundant lithic fragments including gabbros as well as mantle peridotites. They are assumed as a volcanic diatreme induced in the Cretaceous oceanic lithosphere . Geological and petrological analyses on those volcano and volcanic rocks can make clear the geological cross (or columnar) section of the typical oceanic lithosphere including crust as well as upper mantle down to 100 km deep asthenospheric mantle. PARECE VERA BASIN: The Parece Vela Basin (PVB) is an extinct backarc basin in the Philippine Sea. The NNE extending escarpments and depressions (maximum depth 7500 m) are fossil fracture zones and extinct segmented spreading axes (first-order segments), respectively. Oceanic core complexes (OCCs), or megamullions, develop at each first-order segment. Recently discovered OCCs at slow-spreading ridges have been interpreted as exhumed footwalls of oceanic detachment faults in magma-starved ridge environments. Godzilla Mullion, one of the OCC in the PVR, is the worlds largest OCC, 10 times larger in area than the normal OCCs in the Mid-Atlantic Ridge (Ohara et al., 2001). Various plutonic rocks including mantle peridotites were recovered from the megamullion. TONGA FOREARC: The serpentine seamounts have never been observed along the forearc, on the other hand, geological cross section is recognized along the Tonga Trench inner wall including fresh mantle peridotite. IZU-OGASAWARA(BONIN)-MARIANA FOREARC: Many topographic highs are recognized along the Izu- Ogasawara-Mariana forearc. A number of igneous rocks including lavas, gabbros and serpentinized depleted peridotites; so called ophiolitic rocks were dredged from those seamounts by several investigators, who concluded that these seamounts originated from serpentinite diapirs derived from the upper parts of the mantle wedge. Remnant mantle diapir is assumed to be the depleted source peridotite of diapiric serpentinite seamount. Tonga forearc and Izu-Ogasawara-Mariana forearc may be assumed as modern analogue of the Oman ophiolite and the Trodos ophiolite, respectively.

  11. Tectonic evolution of the Caribbean and northwestern South America: The case for accretion of two Late Cretaceous oceanic plateaus (United States)

    Kerr, Andrew C.; Tarney, John


    It is widely accepted that the thickened oceanic crust of the Caribbean plate, its basaltic accreted margins, and accreted mafic terranes in northwestern South America represent the remnants of a single ca. 90 Ma oceanic plateau. We review geologic, geochemical, and paleomagnetic evidence that suggests that the Caribbean-Colombian oceanic plateau in fact represents the remnants of two different oceanic plateaus, both dated as ca. 90 Ma. The first of these plateaus, the Caribbean Plateau, formed ca. 90 Ma in the vicinity of the present-day Galapagos hotspot. Northeastward movement of the Farallon plate meant that this plateau collided with the proto Caribbean arc and northwestern South America <10 m.y. after the plateau's main phase of formation. Paleomagnetic evidence suggests that the second of these plateaus, the Gorgona Plateau, formed at 26° 30°S, possibly at the site of the present-day Sala y Gomez hotspot. Over the next ˜45 m.y., this plateau was carried progressively northeastward on the Farallon plate and collided in the middle Eocene with the proto Andean subduction zone in northwestern South America. The recognition of a second ca. 90 Ma Pacific oceanic plateau strengthens the link between plateau formation and global oceanic anoxic events.

  12. Seismic structure of crust formed by back-arc spreading (United States)

    Grevemeyer, I.; Ranero, C. R.


    About three quarters of today Earth crust and most of the past subducted crust have been formed at oceanic spreading centers. Soon after the discovery that oceanic crust underlies most of the world ocean basins it was defined its ubiquitous three-velocity-layers structure, a structure that has been found to date in the vast majority of seismic experiments at mid ocean ridges (MOR) and old oceanic plates, defining the most prevalent crustal structure on Earth. Layer 1 was quickly identified as sediment, but interpretation of layers 2 and 3 remains a topic of intense research since more than half century. The nature of the oceanic crust is primarily inferred from indirect geophysical measurements and rocks sampled at the seafloor. Current models propose that the formation of oceanic crust at MOR -away from hotspot anomalies- is essentially controlled by the rate of plate separation, with crustal types classified as ultraslow, slow, intermediate, and fast spreading crust. However, evaluation of the deep structure has been limited to only a few drill sites (sites 504, 894, 1256) and exposures in tectonic windows (Hess Deep) by sampling of lower crust rocks. Attempting to overcome this limitation, models of oceanic accretion rely strongly on observations from ophiolitic rock assemblages found in orogenic belts, and long interpreted as slices of oceanic lithosphere obducted during subduction-collision processes. After realization that ophiolite stratigraphy -so-called Penrose model - comprises, from bottom to top, peridotites, gabbros, diabase, and basalt, it was proposed that the oceanic layered velocity structure corresponds to that stratigraphy. Although the oceanic "Penrose" stratigraphy was supported by a comparable structure and velocity values measured at some ophiolites, crustal models have subsequently evolved to account for a variable rock-type architecture related to spreading rate. Today the original "Penrose" ophiolite model is regarded appropriate for intermediate- to fast-spreading crust, although in practice most data from MOR are interpreted following a "Penrose" model derivative. Yet, the geodynamic origin of ophiolite assemblages remains an unresolved research subject. Ophiolite geochemistry has been long interpreted to support a supra-subduction-zone arc or back-arc setting, but ophiolite's considerable structural and geochemical variability are interpreted to indicate that at least some of them may have a MOR origin. This uncertainty is fueled by a lack of systematics on back-arc crustal structure due to sparse seismic experiments, contrasting to the wealth of studies of present-day MOR. Here we present the first extensive seismic study of back-arc oceanic crust providing constrains on accretion processes and ophiolite origin. The depth-velocity distribution of back-arc crust resembles MOR layered structure, but velocities are systematically different to MOR crust formed at any spreading rate. In particular, Layer 3 display lower velocities, indicating either a considerable different rock composition or deformation process. Taken with results from other back-arc basins, the substantial range of crustal velocities may explain ophiolite structural and geochemical variability. In sum, the seismic structure of the crust indicates that back-arc spreading represents a class in its own.

  13. Emergence of modern continental crust about 3 billion years ago (United States)

    Dhuime, Bruno; Wuestefeld, Andreas; Hawkesworth, Chris J.


    The continental crust is the principal record of conditions on the Earth during the past 4.4 billion years. However, how the continental crust formed and evolved through time remains highly controversial. In particular, the composition and thickness of juvenile continental crust are unknown. Here we show that Rb/Sr ratios can be used as a proxy for both the silica content and the thickness of the continental crust. We calculate Rb/Sr ratios of the juvenile crust for over 13,000 samples, with Nd model ages ranging from the Hadean to Phanerozoic. The ratios were calculated based on the evolution of Sr isotopes in the period between the TDM Nd model age and the crystallization of the samples analysed. We find that the juvenile crust had a low silica content and was largely mafic in composition during the first 1.5 billion years of Earth’s evolution, consistent with magmatism on a pre-plate tectonics planet. About 3 billion years ago, the Rb/Sr ratios of the juvenile continental crust increased, indicating that the newly formed crust became more silica-rich and probably thicker. This transition is in turn linked to the onset of plate tectonics and an increase of continental detritus into the oceans.

  14. H11079_SURFGEOL.SHP: Interpretations of the Surficial Geology from National Oceanic and Atmospheric Administration (NOAA) Survey H11079 of Great Round Shoal Channel, MA (Geographic) (United States)

    U.S. Geological Survey, Department of the Interior — The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone...

  15. H11076_INTERP.SHP: Interpretations of Bottom Features from National Oceanic and Atmospheric Administration (NOAA) Survey H11076 of Quicks Hole, MA (Geographic) (United States)

    U.S. Geological Survey, Department of the Interior — The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone...

  16. H11077_INTERP.SHP: Interpretation of Bottom Features from National Oceanic and Atmospheric Administration (NOAA) Survey H11077 of Woods Hole, MA (Geographic) (United States)

    U.S. Geological Survey, Department of the Interior — The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone...

  17. A ~400 ka supra-Milankovitch cycle in the Na, Mg, Pb, Ni, and Co records of a ferromanganese crust from the Vityaz fracture zone, central Indian ridge

    Directory of Open Access Journals (Sweden)

    R. Banerjee


    Full Text Available A ~400 ka (kilo years supra-Milankovitch cycle, recorded in the sodium, magnesium, lead, nickel and cobalt contents of a 32 mm thick ferromanganese crust from Vityaz fracture zone, central Indian ridge is reported here. To arrive at the geological ages, we used both 230Thexeccs and Co-chronometric datings. The correlation coefficient between the 230Thexeccs based dates and Co-chronometric dates for the top 0–8 mm is very high (r=0.9734, at 99.9% significance. The cobalt chronometric age for the bottom most oxide layer of this crust is computed as 3.5 Ma. Red-fit and multi-taper spectral analyses of time series data revealed the existence of the significant ~400 ka cycle, representing the changes in the hydrogeochemical conditions in the ocean due to the Earth's orbital eccentricity related summer insolation at the equator. This is the first report of such cycle from a hydrogenous ferromanganese crust from equatorial Indian ocean.

  18. Andean Adakites: Products of Slab Melting, Magma Evolution in Thickened Crust and Crustal Recycling by Forearc Subduction Erosion (United States)

    Kay, S. M.; Kay, R. W.; Goss, A.


    Adakites in the southern and central Andes show a residual garnet signature that can variously be related to local slab melting associated with subduction of hot oceanic crust at the Chile Triple Junction, widespread interaction of mafic magmas in regions of thickened crust, and episodic melting of crust removed by forearc subduction erosion, particularly at times of frontal arc migration. Among the most convincing slab-melt adakites on Earth are the late Miocene Cerro Pampa type dacitic adakites east of the Chile Triple Junction whose low 87Sr/86Sr ratios (0.7028-0.7033) and high Sr contents (up to 2300 ppm) are difficult to explain by any other mechanism. Elsewhere the appearance of transient extreme adakitic signatures at times of frontal arc migration can be explained by forearc subduction erosion and the evolution of magmas at deep crustal levels in a contractional regime provided the crust is thick. Transient steep adakitic-like REE patterns at times of arc migration fit with forearc crust being transported down the subduction channel, entering the tip of the asthenospheric wedge and being incorporated into the arc mantle source. Evidence for a genetic link for transient adakite signatures, arc migration and forearc subduction erosion comes from changing isotopic ratios in mafic magmas erupted before and after arc migration on the edges of the Chilean flat-slab near 27°S and 34°S (Kay et al 2005) where the arc front has migrated up to 50 km eastward in the last 8 Ma. The chemistry of these mafic magmas cannot be explained by enriched mantle or incorporation of subducted sediments or in situ crust. Sharp increases in 87Sr/86Sr ratios and transient steep REE patterns in Andean arc rocks erupted in the final stages of Cretaceous to early Tertiary magmatic cycles at 21°S to 26°S (see Haschke et al. 2002) can also be attributed to forearc subduction erosion. Forearc subduction erosion provides a better explanation for the formation of Aleutian and Central American adakitic magmas erupted through crust that is less than 40 km thick than slab melting or crystallization of garnet from hydrous magmas.

  19. Evidence of Himalayan erosional event at approx. 0.5 Ma from a sediment core from the equatorial Indian Ocean in the vicinityof ODP Leg 116 sites

    Digital Repository Service at National Institute of Oceanography (India)

    Nath, B.N.; Gupta, S.M.; Mislankar, P.G.; Rao, B.R.; Parthiban, G.; Roelandts, I.; Patil, S.K.

    ) to the end of the Pleistocene ice age of 0.2Ma. While all these records are long and provide a long-term history of mountain building and resultant tectonic and geological changes, some studies have concen- trated on the erosional historyof the Himalayan... Table 1 Mineral grains recovered and their optical properties Mineral Optical properties Muscovites Transparent ?akes with basal cleavage, low relief show acute bisetrix interference ?gure with low Biotites Smooth edges with basal cleavage. Other...

  20. Composition and origin of ferromanganese crusts from equatorial western Pacific seamounts (United States)

    Wang, Guozhi; Jansa, Luba; Chu, Fengyou; Zou, Can; Sun, Guosheng


    In the equatorial western Pacific, iron-manganese oxyhydroxide crusts (Fe-Mn crusts) and nodules form on basaltic seamounts and on the top of drowned carbonate platform guyots that have been swept free of pelagic sediments. To date, the Fe-Mn crusts have been considered to be almost exclusively of abiotic origin. However, it has recently been suggested that these crusts may be a result of biomineralization. Although the Fe-Mn crust textures in the equatorial western Pacific are similar to those constructed by bacteria and algae, and biomarkers also document the existence of bacteria and algae dispersed within the Fe-Mn crusts, the precipitation, accumulation and distribution of elements, such as Fe, Mn, Ni and Co in Fe-Mn crusts are not controlled by microbial activity. Bacteria and algae are only physically incorporated into the crusts when dead plankton settle on the ocean floor and are trapped on the crust surface. Geochemical evidence suggests a hydrogenous origin of Fe-Mn crusts in the equatorial western Pacific, thus verifying a process for Fe-Mn crusts that involves the precipitation of colloidal phases from seawater followed by extensive scavenging of dissolved trace metals into the mineral phase during crust formation.

  1. Global Ocean Sedimentation Patterns: Plate Tectonic History Versus Climate Change (United States)

    Goswami, A.; Reynolds, E.; Olson, P.; Hinnov, L. A.; Gnanadesikan, A.


    Global sediment data (Whittaker et al., 2013) and carbonate content data (Archer, 1996) allows examination of ocean sedimentation evolution with respect to age of the underlying ocean crust (Müller et al., 2008). From these data, we construct time series of ocean sediment thickness and carbonate deposition rate for the Atlantic, Pacific, and Indian ocean basins for the past 120 Ma. These time series are unique to each basin and reflect an integrated response to plate tectonics and climate change. The goal is to parameterize ocean sedimentation tied to crustal age for paleoclimate studies. For each basin, total sediment thickness and carbonate deposition rate from 0.1 x 0.1 degree cells are binned according to basement crustal age; area-corrected moments (mean, variance, etc.) are calculated for each bin. Segmented linear fits identify trends in present-day carbonate deposition rates and changes in ocean sedimentation from 0 to 120 Ma. In the North and South Atlantic and Indian oceans, mean sediment thickness versus crustal age is well represented by three linear segments, with the slope of each segment increasing with increasing crustal age. However, the transition age between linear segments varies among the three basins. In contrast, mean sediment thickness in the North and South Pacific oceans are numerically smaller and well represented by two linear segments with slopes that decrease with increasing crustal age. These opposing trends are more consistent with the plate tectonic history of each basin being the controlling factor in sedimentation rates, rather than climate change. Unlike total sediment thickness, carbonate deposition rates decrease smoothly with crustal age in all basins, with the primary controls being ocean chemistry and water column depth.References: Archer, D., 1996, Global Biogeochem. Cycles 10, 159-174.Müller, R.D., et al., 2008, Science, 319, 1357-1362.Whittaker, J., et al., 2013, Geochem., Geophys., Geosyst. DOI: 10.1002/ggge.20181

  2. Investigating an Apparent Warming Event in the Southern Ocean During the Late Miocene (11.5-11.0 Ma): Foraminiferal and Geochemical Results from IODP Expedition 318 Site U1361 Wilkes Land, Antarctica (United States)

    DeCesare, M.; Pekar, S. F.


    High-resolution isotope and foraminiferal biofacies records are being developed from samples obtained from IODP Expedition 318 Site U1361 to investigate a transient warming event that effected the Southern Ocean and Antarctica during the Late Miocene (11.5-11.0 Ma). The Pagodroma Group are proximal glaciomarine strata and provide evidence that the Lambert Glacier had receded up 300 km inland from its present-day grounding line between 12.1 and 8.5 Ma. Four cores, 34X-37X (311.6-349.99 mbsf), recovered from Site U1361 and dated at 11.5-11.0 Ma, contain a sedimentary archive suggestive of a transient warming event. With excellent core recovery and good preservation of foraminifers, it will be possible to document the extent and duration of this warming event. Integrated biostratigraphy and magnetostratigraphy, as well as high sedimentation rates of ~69 m/106 yr allow for excellent age control. These cores were drilled in 3,466 meters water depth on the continental rise, ~280km offshore from Wilkes Land. Foraminiferal abundances are variable, with specimens ranging from rare to relatively high abundances. Planktonic foraminifers are dominated by Globigerina bulloides, while benthic foraminiferal assemblages include Oridorsalis Umbonatus, Cibicidoides Wuellertorfi, Cibicidoides Bradyi, and Epistominella Exigua. Shipboard studies recognized apparent cyclicity in the sediments, which shows good correlation with 41-kyr obliquity cycles. This is supported by comparing foraminiferal abundances to sediment luminosity (total light reflectance or L*). These changes in foraminiferal abundances are interpreted to represent a periodic deepening of the lysocline and carbonate compensation depth. Stable isotope (?18O and ?13C) records are being developed to reconstruct bottom and surface water conditions and place constraints on changes in Southern Ocean dynamics. Mg/Ca and Li/Ca ratio records are being obtained using laser ablation-inductively coupled plasma-mass spectrometry and will provide estimates on temperature. Li/Ca ratios will quantify carbonate ion saturation and reduce uncertainty in Mg/Ca ratio temperature estimates. These records will be developed at 3.5-kyr resolution for intervals in which the above species are present. Biofacies are being used to infer paleoceaographic conditions and will fill any gaps in the isotope record.

  3. Copper-nickel-rich, amalgamated ferromanganese crust-nodule deposits from Shatsky Rise, NW Pacific (United States)

    Hein, J.R.; Conrad, T.A.; Frank, M.; Christl, M.; Sager, W.W.


    A unique set of ferromanganese crusts and nodules collected from Shatsky Rise (SR), NW Pacific, were analyzed for mineralogical and chemical compositions, and dated using Be isotopes and cobalt chronometry. The composition of these midlatitude, deep-water deposits is markedly different from northwest-equatorial Pacific (PCZ) crusts, where most studies have been conducted. Crusts and nodules on SR formed in close proximity and some nodule deposits were cemented and overgrown by crusts, forming amalgamated deposits. The deep-water SR crusts are high in Cu, Li, and Th and low in Co, Te, and Tl concentrations compared to PCZ crusts. Thorium concentrations (ppm) are especially striking with a high of 152 (mean 56), compared to PCZ crusts (mean 11). The deep-water SR crusts show a diagenetic chemical signal, but not a diagenetic mineralogy, which together constrain the redox conditions to early oxic diagenesis. Diagenetic input to crusts is rare, but unequivocal in these deep-water crusts. Copper, Ni, and Li are strongly enriched in SR deep-water deposits, but only in layers older than about 3.4 Ma. Diagenetic reactions in the sediment and dissolution of biogenic calcite in the water column are the likely sources of these metals. The highest concentrations of Li are in crust layers that formed near the calcite compensation depth. The onset of Ni, Cu, and Li enrichment in the middle Miocene and cessation at about 3.4 Ma were accompanied by changes in the deep-water environment, especially composition and flow rates of water masses, and location of the carbonate compensation depth.

  4. Physics of Neutron Star Crusts

    Directory of Open Access Journals (Sweden)

    Chamel Nicolas


    Full Text Available The physics of neutron star crusts is vast, involving many different research fields, from nuclear and condensed matter physics to general relativity. This review summarizes the progress, which has been achieved over the last few years, in modeling neutron star crusts, both at the microscopic and macroscopic levels. The confrontation of these theoretical models with observations is also briefly discussed.

  5. Paleo-elevation and subsidence of ˜145Ma Shatsky Rise inferred from CO2 and H2O in fresh volcanic glass (United States)

    Shimizu, Kenji; Shimizu, Nobumichi; Sano, Takashi; Matsubara, Noritaka; Sager, William


    Shatsky Rise, a large Mesozoic oceanic plateau in the northwest Pacific, consists of three massifs (Tamu, Ori, and Shirshov) that formed near a mid-ocean-ridge triple junction. Published depth estimates imply that Shatsky Rise has not subsided normally, like typical oceanic lithosphere. We estimated paleo-eruption depths of Shatsky Rise massifs on the basis of dissolved CO2 and H2O in volcanic glass and descriptions of cores recovered from five sites of Integrated Ocean Drilling Program Expedition 324. Initial maximum elevations of Shatsky Rise are estimated to be 2500-3500 m above the surrounding seafloor and the ensuing subsidence of Shatsky Rise is estimated to be 2600-3400 m. We did not observe the anomalously low subsidence that has been reported for both Shatsky Rise and the Ontong Java Plateau. Although we could not resolve whether Shatsky Rise originated from a hot mantle plume or non-plume fusible mantle, uplift and subsidence histories of Shatsky Rise for the both cases are constrained based on the subsidence trend from the center of Tamu Massif (˜2600 m) toward the flank of Ori Massif (˜3400 m). In the case of a hot mantle plume origin, Shatsky Rise may have formed on young (˜5 Ma) pre-existing oceanic crust with a total crustal thickness of ˜20 km. For this scenario, the center of Shatsky Rise is subsequently uplifted by later (prolonged) crustal growth, forming the observed ˜30 km thickness crust. For a non-plume origin, Shatsky Rise may have formed at the spreading ridge center as initially thick crust (˜30 km thickness), with later reduced subsidence caused by the emplacement of a buoyant mass-perhaps a refractory mantle residuum-beneath the center of Shatsky Rise.

  6. Did phosphorus derived from the weathering of large igneous provinces fertilize the Neoproterozoic ocean? (United States)

    Horton, Forrest


    Primary productivity and organic carbon burial rates in the Precambrian were highly sensitive to fluxes of phosphorus (P) from the weathering of continental crust. Large igneous provinces (LIPs)—containing substantial P and highly susceptible to chemical weathering—occurred regularly during the breakup of the Rodinia supercontinent, and flood basalts probably covered 3.7-7.4 × 106 km2 at a time when a low-latitude continental configuration expedited weathering. Assuming chemical weathering liberated much of the P contained in the flood basalts, an estimated 1-4 × 1017 mol of biologically available P entered the ocean from LIPs between 900 and 500 Ma. Especially, voluminous LIP magmatism began at ˜850 Ma and culminated with the Franklin Province at 720 Ma, after which an estimated bioavailable P flux from flood basalts of 1-5 × 109 mol/yr may have been sustained for millions of years, elevating primary production and organic carbon burial rates. P enrichment of LIP magmas prior to eruption could have contributed to efficient reactive P delivery to the ocean: liquid-crystal fractionation beneath thick cratonic lithosphere and the incorporation of metasomatic P potentially enriched Neoproterozoic LIP magmas more than anytime previously. Thus, a unique convergence of tectonic conditions—supercontinent breakup, voluminous mafic volcanism containing abundant P, and a low-latitude continental configuration—may have facilitated an unprecedented flux of bioavailable P to the ocean that was capable of triggering oxidation of the ocean-atmosphere system and enabling accelerated biologic diversification.

  7. Structure and Composition of the Lunar Crust (United States)

    Spudis, P. D.; Bussey, D. B. J.; Hawke, B. R.


    Since the first return of lunar samples indicated that global differentiation of the Moon had occurred, numerous models of crustal structure have been proposed. With the completion of the first global reconnaissance mapping by Clementine and Lunar Prospector, we are now in position to re-evaluate crustal structure and composition at a global scale. Although this is a difficult and complex task, and one requiring significant study, some first-order results are apparent now and are quite telling. We here summarize our current view of crustal structure and identify some required knowledge to better understand the origin and evolution of the lunar crust. Wood et al. attempted to estimate the amount of plagioclase in the crust, based on the average elevation difference between mare and highlands and some simple assumptions about anorthosite and basalt as responsible for the principal lunar rock types. Later, more complex models emerged, involving layered crusts of feldspathic material over more basaltic material or a laterally variable crust, with Mg-suite plutons intruding a grossly anorthositic crust. Later models attempted to reconcile these contrasting styles by incorporating both features. In part, crustal structure was inferred by the envisioned mode of crustal formation. A decade-long debate on the reality of the lunar "magma ocean," stimulated by the provocative notion of Walker that the Moon never had a magma ocean, and the recognition that the anorthosites and Mg suite probably recorded different and unrelated magmatic events. Such a scenario leaves much about crustal structure an open question, but allows for both lateral and vertical heterogeneity, thus accommodating both principal crustal models. Global maps of Fe , Ti, and Th both confirm old ideas and create new problems. It is clear that vast areas of the lunar highlands are extremely low in Fe, consistent with a significant amount of anorthosite. Such a distribution supports the magma ocean. However, the average lunar highlands composition is, as long suspected, that of "anorthositic norite", a mixed rock type, somewhat similar to many of the lunar meteorites (e.g,., ALHA 81005 and more mafic than pure ferroan anorthosite. Anorthosite proper does occur on the Moon; it is found almost exclusively within the inner rings of multiring basins. These basins span a range of ages and distributions. Mafic provinces occur in the central Procellarum region of the front side and on the floor of the South Pole Aitken Basin. In these areas, the lunar surface is "highland basaltic" composition (FeO about 9-10 wt%). Additional highland basaltic areas occur in the vicinity of nearside basins, such as Serenitatis. The major lunar "hot spot" of high Th concentration (about 10 ppm) occurs within a broad, oval depression approximately coincident with Oceanus Procellarum. Slightly less elevated amounts (about ppm) are associated with the basaltic floor of SPA Basin on the farside. Aside from this, Th highs are isolated and minor. On the basis of the new global data, as well as from our continuing study of the composition of basin ejecta to probe the deep crust, we have modified slightly our existing crustal model to accommodate the new findings. We propose a three-layer model of crustal configuration. The uppermost zone, down to depths of about 15-20 km, consists of mega breccia of mostly anorthositic norite composition (FeO about 4-6 wt%; Al2O3 about 26 wt%). This zone is neither laterally or vertically uniform, displaying anomalous compositional zones at scales of tens to hundreds of kilometers, but is remarkably homogeneous at planetwide scales. In bulk composition, it resembles the "ferroan anorthositic norite" suite of mixed rocks described by Lindstorm et al. and many of the highlands regolith breccias found as lunar meteorites. It is also similar to the average crustal composition inferred by Taylor , on the basis of Apollo granulitic breccias and limited orbital chemical data. Although some areas on the northern farside app

  8. Evaluating Complex Magma Mixing via Polytopic Vector Analysis (PVA in the Papagayo Tuff, Northern Costa Rica: Processes that Form Continental Crust

    Directory of Open Access Journals (Sweden)

    Guillermo E. Alvarado


    Full Text Available Over the last forty years, research has revealed the importance of magma mixing as a trigger for volcanic eruptions, as well as its role in creating the diversity of magma compositions in arcs. Sensitive isotopic and microchemical techniques can reveal subtle evidence of magma mixing in igneous rocks, but more robust statistical techniques for bulk chemical data can help evaluate complex mixing relationships. Polytopic vector analysis (PVA is a multivariate technique that can be used to evaluate suites of samples that are produced by mixing of two or more magma batches. The Papagayo Tuff of the Miocene-Pleistocene Bagaces Formation in northern Costa Rica is associated with a segment of the Central American Volcanic Arc. While this segment of the arc is located on oceanic plateau, recent (<8 Ma ignimbrites bear the chemical signatures of upper continental crust, marking the transition from oceanic to continental crust. The Papagayo Tuff contains banded pumice fragments consistent with one or more episodes of mixing/mingling to produce a single volcanic deposit. The PVA solution for the sample set is consistent with observations from bulk chemistry, microchemistry and petrographic data from the rocks. However, without PVA, the unequivocal identification of the three end-member solution would not have been possible.

  9. Direct observations on the interaction between lower- and upper-crustal magmatic systems in a virtually complete section through 25 km of pre-Apline crust in the Sesia Valley, northwest Italy (United States)

    Quick, J. E.; Sinigoi, S.; Sbisa, A.; Demarchi, G.; Richards, I.


    The linkage between "magmatic underplating" and continental silicic volcanism is uniquely exposed in the Sesia Valley, where a virtually complete section through the pre-Alpine crust is capped by a Permian bimodal volcanic field with a >15-km, rhyolitic caldera and floored by the famous deep-crustal section of the Ivrea-Verbano Zone (IVZ). Volcanic rocks are intruded by granophyre and fine-grained granite with miarolitic cavities that grade downward into coarse-grained granite "rooted" in paragneiss of the IVZ. Intruding the paragneiss at deeper crustal levels is a >8-km-thick, layered gabbronorite pluton referred to as the Mafic Complex (MC). SHRIMP zircon ages indicate that bimodal volcanism (288 ± 2 to 282 ± 3 Ma) and granitic plutonism (289 ± 3 to 275 ± 5 Ma) were coincident with intrusion of the MC in the lower crust (289 ± 3 to 286 ± 6 Ma). Palinspastic restoration of the Sesia section places the roof of the MC at a depth of 15 to 20 km, consistent with equilibration pressures in its contact aureole, and provides a petrologic model for interpretation of the seismic structure beneath large calderas and silicic volcanic fields analogous to that provided by ophiolites for the seismic structure of the oceanic crust. The interplay between the lower- and upper-crustal magmatic systems is recorded in field relations and geochemistry. Mafic enclaves and andesitic volcanism demonstrate that a mantle component reached the upper crust, contributing to its magmatic evolution, but peraluminous compositions and whole-rock ?18O (10-11.5) of the volumetrically more significant silicic volcanic and granitic rocks are consistent with crustal anatexis within a narrow (interface across which significant transfer of both mass and heat occurred. Uniformity of contamination, arcuate internal structure, and the distribution of strain and paragneiss inclusions are consistent with growth of the MC as a "gabbro glacier" during crustal extension, with focused delivery of mantle-derived melt to its roof and flow of contaminated crystal mush away from the resulting perched magma chamber. Thermal modeling indicates that (1) focused delivery of mantle melt was efficient in driving anatexis in overlying crustal rocks, (2) migration of anatectic melts to the upper crust was efficient in removing heat from the MC and restricting its thermal impact on the overlying crust, and (3) lower- and upper-crustal plutons were dominated by crystal mush rather than large magma chambers during their formation.

  10. The thermal effect of fluid circulation in the subducting crust on slab melting in the Chile subduction zone (United States)

    Spinelli, Glenn A.; Wada, Ikuko; He, Jiangheng; Perry, Matthew


    Fluids released from subducting slabs affect geochemical recycling and melt generation in the mantle wedge. The distribution of slab dehydration and the potential for slab melting are controlled by the composition/hydration of the slab entering a subduction zone and the pressure-temperature path that the slab follows. We examine the potential for along-strike changes in temperatures, fluid release, and slab melting for the subduction zone beneath the southern portion of the Southern Volcanic Zone (SVZ) in south central Chile. Because the age of the Nazca Plate entering the subduction zone decreases from ?14 Ma north of the Guafo Fracture Zone to ?6 Ma to the south, a southward warming of the subduction zone has been hypothesized. However, both north and south of Guafo Fracture Zone the geochemical signatures of southern SVZ arc lavas are similar, indicating 3-5 wt.% sediment melt and little to no contribution from melt of subducted basalt or aqueous fluids from subducted crust. We model temperatures in the system, use results of the thermal models and the thermodynamic calculation code Perple_X to estimate the pattern of dehydration-derived fluid release, and examine the potential locations for the onset of melting of the subducting slab. Surface heat flux observations in the region are most consistent with fluid circulation in the high permeability upper oceanic crust redistributing heat. This hydrothermal circulation preferentially cools the hottest parts of the system (i.e. those with the youngest subducting lithosphere). Models including the thermal effects of fluid circulation in the oceanic crust predict melting of the subducting sediment but not the basalt, consistent with the geochemical observations. In contrast, models that do not account for fluid circulation predict melting of both subducting sediment and basalt below the volcanic arc south of Guafo Fracture Zone. In our simulations with the effects of fluid circulation, the onset of sediment melting occurs under the volcanic arc, but dewatering of the subducting sediment and basalt is focused farther seaward (below the landward boundary of the stagnant mantle wedge corner). Thus, the sediment melt could enter the mantle wedge, contributing to the composition of the southern SVZ magmas, yet remain separate from the fluid derived from sediment dewatering which could migrate updip within the slab or into the wedge corner. Preferential hydrothermal cooling of the hottest segments of the system can help explain how there can be fairly uniform magma composition along the arc, despite large along-arc differences in the age of the subducting plate.

  11. Models of a partially hydrated Titan interior with clathrate crust (United States)

    Lunine, J. I.; Castillo-Rogez, J.


    We present an updated model of the interior evolution of Titan over time, assuming the silicate core was hydrated early in Titan's history and is dehydrating over time. The original model presented in Castillo-Rogez and Lunine (2010) was motivated by a Cassini-derived moment of inertia (Iess et al., 2010) for Titan too large to be accommodated by classical fully differentiated models in which an anhydrous silicate core was overlain by a water ice (with possible perched ocean) mantle. Our model consisted of a silicate core still in the process of dehydrating today, a situation made possible by the leaching of radiogenic potassium from the silicates into the liquid water ocean. The crust of Titan was assumed to be pure water ice I. The model was consistent with the moment of inertia of Titan, but neglected the presence of large amounts of methane in the upper crust invoked to explain methane's persistence at present and through geologic time (Tobie et al. 2006). We have updated our model with such a feature. We have also improved our modeling with a better physical model for the dehydration of antigorite and other hydrated minerals. In particular our modeling now simulates heat advection resulting from water circulation (e.g., Seipold and Schilling 2003), rather than the purely conductive heat transfer regime assumed in the first version of our model. The modeling proceeds as in Castillo-Rogez and Lunine (2010), with the thermal conductivity of the methane clathrate crust rather than that of ice I. The former is several times lower than that of the latter, and the two have rather different temperature dependences (English and Tse, 2009). The crust turns out to have essentially no bearing on the temperature of the silicate core and hence the timing of dehydration, but it profoundly affects the thickness of the high-pressure ice layer beneath the ocean. Indeed, with the insulating methane clathrate crust, there must be a liquid water ocean beneath the methane clathrate crust and in contact with the silicates beneath for most of Titan's history. Although a high-pressure ice layer is likely in place today, it is thin enough that plumes of hot water from the dehydrating core probably breach the high pressure ice layer maintaining contact between the ocean and the silicate core. Part of this work has been performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged.

  12. Crust Formation in Aluminum Cells (United States)

    Oedegard, R.; Roenning, S.; Rolseth, S.; Thonstad, J.


    This paper examines the catalytic effects offlourides on the ???-Al2O3 phase transformation by heat treating commercial alumina samples with 2wt% additions of different flouride compounds. The various additives were ranked according to their effect on transformation temperature. Experiments were conducted to explain the high temperature coherence of crusts. The findings indicate that an alumina network is formed during ??? phase transformation, which reinforces the crust on top of the cryolite bath.

  13. Adjoint tomography of the southern California crust. (United States)

    Tape, Carl; Liu, Qinya; Maggi, Alessia; Tromp, Jeroen


    Using an inversion strategy based on adjoint methods, we developed a three-dimensional seismological model of the southern California crust. The resulting model involved 16 tomographic iterations, which required 6800 wavefield simulations and a total of 0.8 million central processing unit hours. The new crustal model reveals strong heterogeneity, including local changes of +/-30% with respect to the initial three-dimensional model provided by the Southern California Earthquake Center. The model illuminates shallow features such as sedimentary basins and compositional contrasts across faults. It also reveals crustal features at depth that aid in the tectonic reconstruction of southern California, such as subduction-captured oceanic crustal fragments. The new model enables more realistic and accurate assessments of seismic hazard. PMID:19696349

  14. Mantle composition controls the development of an Oceanic Core Complex


    Wilson, S C; Murton, B.J.; Taylor, R.N.


    The thickness and continuity of oceanic crust is variable. Slow-spreading ridge segments often contain areas of ‘amagmatic’ or tectonic extension, exposing areas of lower-crust and upper-mantle, and having little or no recent volcanism. These are interspersed with areas of ‘normal’ volcanic crust generated by ‘robust’ magmatic accretion. Tectonic spreading is accommodated by displacement on low-angle extensional detachment faults, forming Oceanic Core Complexes. Although ‘amagmatic’ extension...

  15. Oceanic slab melting and mantle metasomatism


    Scaillet, Bruno; Prouteau, Gaëlle


    Modern plate tectonic brings down oceanic crust along subduction zones where it either dehydrates or melts. Those hydrous fluids or melts migrate into the overlying mantle wedge trigerring its melting which produces arc magmas and thus additional continental crust. Nowadays, melting seems to be restricted to cases of young (

  16. Palaeomagnetism and the continental crust

    Energy Technology Data Exchange (ETDEWEB)

    Piper, J.D.A.


    This book is an introduction to palaeomagnetism offering treatment of theory and practice. It analyzes the palaeomagnetic record over the whole of geological time, from the Archaean to the Cenozoic, and goes on to examine the impact of past geometries and movements of the continental crust at each geological stage. Topics covered include theory of rock and mineral magnetism, field and laboratory methods, growth and consolidation of the continental crust in Archaean and Proterozoic times, Palaeozoic palaeomagnetism and the formation of Pangaea, the geomagnetic fields, continental movements, configurations and mantle convection.

  17. Nature of crust in the central Red Sea (United States)

    Mitchell, Neil C.; Park, Yongcheol


    A transition between continental crust in the northern Red Sea and oceanic crust in the southern Red Sea coincides broadly with a southward increase in plate tectonic separation rate and with a decrease in upper mantle seismic velocity. We re-evaluate here the nature of crust in the intervening central Red Sea with the results of legacy seismic refraction experiments and recently released marine gravity anomalies derived from satellite altimeter measurements. In the refraction data, collected east of Thetis Deep, velocities of 6.6-6.9 km s- 1 of a deep refracting layer, which are similar to measured velocities of unaltered gabbro samples, extend outside the deep to 65 km from the axis. The new version of the marine gravity field reveals trends crossing the central Red Sea. Whereas some of them connect with major lineaments in the surrounding African-Arabian shield, those around Thetis Deep die out towards the coastlines. They can be paired across the ridge and lie slightly oblique to plate motions, as is typical of oceanic fracture zones or non-transform discontinuities migrating away from hotspots. Taken together these observations support the view that an oceanic rather than extended continental crust underlies this part of the central Red Sea. The crestal mountains around the median valleys of slow-spreading ridges are typically 500-1000 m lower at spreading discontinuities. Around Thetis Deep, the similar pattern in the gravity field to those of slow-spreading ridges suggests that the crestal mountains may variably block or impede flowage of evaporites towards the spreading centre, whereas the discontinuities may mark areas where flowage is unobstructed. Limited multibeam data collected in transits outside Thetis Deep show oblique fabrics as expected from these predicted movements.

  18. Crust and Mantle Structure Beneath the Samoan Islands (United States)

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


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

  19. Nonvolcanic tectonic islands in ancient and modern oceans (United States)

    Palmiotto, Camilla; Corda, Laura; Ligi, Marco; Cipriani, Anna; Dick, Henry J. B.; Douville, Eric; Gasperini, Luca; Montagna, Paolo; Thil, François; Borsetti, Anna Maria; Balestra, Barbara; Bonatti, Enrico


    Most oceanic islands are due to excess volcanism caused by thermal and/or compositional mantle melting anomalies. We call attention here to another class of oceanic islands, due not to volcanism but to vertical motions of blocks of oceanic lithosphere related to transform tectonics. Sunken tectonic islands capped by carbonate platforms have been previously identified along the Vema and Romanche transforms in the equatorial Atlantic. We reprocessed seismic reflection lines, did new facies analyses and 87Sr/86Sr dating of carbonate samples from the carbonate platforms. A 50 km long narrow paleoisland flanking the Vema transform, underwent subsidence, erosion, and truncation at sea level; it was then capped by a 500 m thick carbonate platform dated by 87Sr/86Sr at ˜11-10 Ma. Three former islands on the crest of the Romanche transverse ridge are now at ˜900 m bsl; they show horizontal truncated surfaces of oceanic crust capped by ˜300 m thick carbonate platforms, with 10-6 Ma Sr isotopic ages. These sunken islands formed due to vertical tectonics related to transtension/transpression along long-offset slow-slip transforms. Another tectonic sunken island is Atlantis Bank, an uplifted gabbroic block along the Atlantis II transform (SW Indian Ridge) ˜700 m bsl. A modern tectonic island is St. Peter and St. Paul Rocks, a rising slab of upper mantle located at the St. Paul transform (equatorial Atlantic). "Cold" tectonic islands contrast with "hot" volcanic islands related to mantle thermal and/or compositional anomalies along accretionary boundaries and within oceanic plates, or to supra-subduction mantle melting that gives rise to islands arcs.

  20. A New Estimate for Global Hydrothermal Exchange Between the Oceans and Lithosphere (United States)

    Hasterok, D. P.


    We revise the estimated global power deficit due to ventilated hydrothermal circulation (8.0 TW) using an updated global heat flow dataset with >14000 oceanic measurements and a new conductive cooling model of the oceanic lithosphere. This study differs from previous estimates by taking into account (1) non-Gaussian statistics, (2) an improved seafloor age model, (3) a new plate cooling model calibrated directly to heat flow, and (4) the effect of sediment cover on the heat flow deficit and ventilated cutoff age. We obtain the maximum heat flow deficit (difference between predicted and observed) when the data are separated by seafloor areas with power deficit (integrated heat flow deficit with respect to area) for areas of thin (total power deficit, 8.0 TW with 50% of estimates falling between 5.0 and 10.0 TW, represents a 30% reduction in magnitude compared with previous heat flow and fluid flow based estimates. Regions with thick, 400 m, sediment cover experience half the heat flow deficit for one-third of the duration (25 Ma) of regions with thin sediment cover (75 Ma). Based on this study, vigorous fluid exchange between the oceans and seafloor redistributes 30% of heat lost through young oceanic crust. Spatial variation in heat flow deficit relative to estimated conductive heat loss. Variations are calibrated to observed heat flow and constrained by sediment thickness variations.

  1. Eocene deep crust at Ama Drime, Tibet : Early evolution of the Himalayan orogen

    DEFF Research Database (Denmark)

    Kellett, Dawn; Cottle, John


    Granulitized eclogite-facies rocks exposed in the Ama Drime Massif, south Tibet, were dated by Lu-Hf garnet geochronology. Garnet from the three samples analyzed yielded Lu-Hf ages of 37.5 ± 0.8 Ma, 36.0 ± 1.9 Ma, and 33.9 ± 0.8 Ma. Eclogitic garnet growth is estimated at ca. 38 Ma, the oldest age for burial of the lower Indian crust beneath Tibet reported from the central-eastern Himalaya. Granulite-facies overprinting followed at ca. 15–13 Ma, as indicated by U-Pb zircon ages. Unlike ultrahigh-pressure eclogites of the northwest Himalaya, the Ama Drime eclogites are not characteristic of rapid burial and exhumation of a cold subducted slab. The rocks instead resulted from crustal thickening during the early stages of continental collision, and resided in the lower-middle crust for >20 m.y. before they were exhumed and reheated. These new data provide solid evidence for the Indian crust having already reached at least ?60 km thickness by the late Eocene.

  2. Genesis of adakitic granitoids by partial melting of thickened lower crust and its implications for early crustal growth: A case study from the Huichizi pluton, Qinling orogen, central China (United States)

    Qin, Zhengwei; Wu, Yuanbao; Siebel, Wolfgang; Gao, Shan; Wang, Hao; Abdallsamed, Mohammed. I. M.; Zhang, Wenxiang; Yang, Saihong


    Adakitic rocks are often considered as a key to deciphering the genesis of Archean TTGs and the early crustal growth. Granites from the Huichizi pluton in the North Qinling (NQ) unit have high Sr/Y and (La/Yb)N ratios similar to adakites. Their relatively high SiO2, K2O, and Na2O and very low MgO, Cr, and Ni contents are in the range of high-SiO2 adakites and early Archean TTGs and are compositionally similar to experimental melts derived from metabasalt sources. New SIMS zircon U-Pb dating constrains the emplacement age of the Huichizi pluton at 422 ± 5 Ma. Rock samples from the Huichizi pluton have ?Nd(t) and zircon ?Hf(t) values similar to the Neoproterozoic metabasalts in the NQ unit. In combination with their normal mantle-like ?18Ozir values, these adakites are best explained by partial melting of the Neoproterozoic mafic crustal root due to subduction of the Shangdan ocean. Regional geological data suggest that the crust was probably thickened by a ca. 490 Ma arc-collision process prior to the emplacement of the Huichizi pluton. Our results confirm that underplating of mafic magma and its subsequent fusion triggered by slab subduction under high pressure conditions could be an important mechanism for the formation of early continental crust.

  3. Galenicals in the treatment of crusted scabies

    Directory of Open Access Journals (Sweden)

    Sugathan P


    Full Text Available Crusted scabies is rare. It is a therapeutic challenge, as the common drugs used against scabies are unsatisfactory. The successful use of galenicals in a 10-year-old girl with crusted scabies is reported.



    Sugathan P.; Martin Abhay


    Crusted scabies is rare. It is a therapeutic challenge, as the common drugs used against scabies are unsatisfactory. The successful use of galenicals in a 10-year-old girl with crusted scabies is reported.

  5. Seasonal Methane Oxidation Potential in Manure Crusts


    Nielsen, Daniel A.; Schramm, Andreas; Lars P. Nielsen; Revsbech, Niels P.


    Organic crusts on liquid manure storage tanks harbor ammonia- and nitrite-resistant methane oxidizers and may significantly reduce methane emissions. Methane oxidation potential (0.6 mol CH4 m?2 day?1) peaked during fall and winter, after 4 months of crust development. Consequences for methane mitigation potential of crusts are discussed.

  6. Continental crust subducted deeply into lithospheric mantle: the driving force of Early Carboniferous magmatism in the Variscan collisional orogen (Bohemian Massif) (United States)

    Janoušek, Vojt?ch; Schulmann, Karel; Lexa, Ondrej; Holub, František; Fran?k, Jan; Vrána, Stanislav


    The vigorous Late Devonian-Early Carboniferous plutonic activity in the core of the Bohemian Massif was marked by a transition from normal-K calc-alkaline, arc-related (~375-355 Ma), through high-K calc-alkaline (~346 Ma) to (ultra-)potassic (343-335 Ma) suites, the latter associated with mainly felsic HP granulites enclosing Grt/Spl mantle peridotite bodies. The changing chemistry, especially an increase in K2O/Na2O and 87Sr/86Sri with decrease in 143Nd/144Ndi in the basic end-members, cannot be reconciled by contamination during ascent. Instead it has to reflect the character of the mantle sources, changing over time. The tectonic model invokes an oceanic subduction passing to subduction of the attenuated Saxothuringian crust under the rifted Gondwana margin (Teplá-Barrandian and Moldanubian domains). The deep burial of this mostly refractory felsic metaigneous material is evidenced by the presence of coesite/diamond (Massonne 2001; Kotková et al. 2011) in the detached UHP slices exhumed through the subduction channel and thrusted over the Saxothuringian basement, and by the abundance of felsic HP granulites (> 2.3 GPa), some bearing evidence for small-scale HP melt separation, in the orogen's core (Vrána et al. 2013). The subduction channel was most likely formed by 'dirty' serpentinites contaminated by the melts/fluids derived from the underlying continental-crust slab (Zheng 2012). Upon the passage through the orogenic mantle, the continental crust-slab derived material not only contaminated the adjacent mantle forming small bodies/veins of pyroxenites (Becker 1996), glimmerites (Becker et al. 1999) or even phlogopite- and apatite-bearing peridotites (Naemura et al. 2009) but the felsic HP-HT granulites also sampled the individual peridotite types at various levels. Eventually the subducted felsic material would form an (U)HP continental wedge under the forearc/arc region, to be later redistributed under the Moldanubian crust by channel flow and crustal relamination mechanisms. The presence of refractory light material rich in radioactive elements under the denser upper plate would eventually result in gravity-driven overturns in the thickened crust. The contaminated lithospheric mantle domains yielded, soon thereafter, ultrapotassic magmas whose major- and compatible-trace element signatures point to equilibration with the mantle peridotite, while their LILE contents and radiogenic isotope signatures are reminiscent of the subducted continental crust. This research was financially supported by the GA?R Project P210-11-2358 (to VJ) and Ministry of Education of the Czech Republic program LK11202 (to KS). Becker, H. 1996. Journal of Petrology 37, 785-810. Kotková, J. et al. 2011. Geology 39, 667-670. Massonne, H.-J. 2001. European Journal of Mineralogy 13, 565-570. Naemura, K. et al. 2009. Journal of Petrolology 50, 1795-1827. Schulmann, K., et al., 2014. Geology, in print. Vrána, S. 2013. Journal of Geosciences 58, 347-378. Zheng, Y. F. 2012. Chemical Geology 328, 5-48.

  7. Physics of the earth crust

    International Nuclear Information System (INIS)

    This book deals in 12 chapters, amongst other things, with the subjects: Structure of the crust and the upper earth mantle, geology and geophysics of sea beds, satellite and aero-methods of geophysics, state of the art of geothermal research, geophysical potential fields and their anomalies, applied seismology, electrical methods of geophysics, geophysics in engineering and rock engineering, borehole geophysics, petrophysics, and geochemistry. (RW)

  8. Opening of the Gulf of Mexico and the Nature of the Crust in the Deep Gulf: New Evidence from Seafloor Spreading Magnetic Anomalies (United States)

    Harry, D. L.; Eskamani, P. K.


    The seafloor spreading history in the Gulf of Mexico is poorly constrained due to a lack of recognized seafloor spreading magnetic anomalies, a paucity of deep penetrating seismic data, and absence of drilling to constrain crystalline ocean floor composition and ages. We have identified lineated magnetic anomalies in the eastern Gulf on profiles collected during the Woods Hole R/V Farnella FRNL85-2 cruise that correlate with magnetic chrons M21R to M10. Forward modeling shows that these anomalies formed during creation of weakly magnetized new seafloor in the eastern Gulf between 149-134 Ma at an average half-spreading rate of 3.2 cm/yr. The oldest anomalies are located against stretched continental crust beneath the western Florida shelf on the east and the Yucatan shelf on the west. The youngest anomalies form a juxtaposed conjugate pair that mark the location of an extinct spreading ridge between Yucatan and Florida. Seismic velocities of the crust in the eastern Gulf and the amplitude of the magnetic anomalies are similar to the Iberian and Newfoundland rifted margins, where the early stages of continental breakup were accommodated by exhumation of subcontinental lithosphere rather than creation of new basaltic oceanic crust. We infer that the eastern Gulf of Mexico is underlain by exhumed sub-continental peridotitic mantle intruded by lesser volumes of basaltic igneous rocks generated by decompression melting of the asthenosphere during the late stages of opening of the Gulf. The long wavelength characteristics of the magnetic and gravity fields in the eastern Gulf, as well as the seismic velocity structure of the crust, differ from those in the central and western Gulf, which are more similar to typical magmatic rifted margins. This suggests that the character of the Gulf changes along strike, from a magmatic western portion to an amagmatic eastern portion. Paleogeographic restoration of the lineated magnetic anomaly pattern suggests a 4-phase model for opening of the Gulf. During phase 1 (Early Permian-Late Triassic), Yucatan and associated tectonic blocks that now comprise eastern Mexico were translated eastward from the Pacific realm into positions near the modern western Gulf. During phase 2 (Late Triassic-ca. 160 Ma) Yucatan and the South Florida block were translated southeastward relative to North America, rotating 6.7? counterclockwise about a pole located at 34?N, 74?W. This resulted in ca. 430 km of southeastward extension on the North American coastal plain, 120 km of southward extension on the northern Yucatan shelf, and displacement of the South Florida Block from a pre-rift position on the northwest Florida shelf to its modern position. During phase 3 (ca. 160-149 Ma), Yucatan rotated counterclockwise 46? relative to North America about a pole located at 27.6?N, 84.0?W. Phase 3 may have coincided with seafloor spreading in the central and western Gulf, but predated seafloor spreading in the eastern Gulf. During phase 4 (149-134 Ma), Yucatan moved southwestward relative to North America, rotating counterclockwise 2.2? about a pole located at 17.6?N, 74.2?W and completing opening of the Gulf.

  9. Ductile extensional shear zones in the lower crust of a passive margin (United States)

    Clerc, Camille; Jolivet, Laurent; Ringenbach, Jean-Claude


    We describe and interpret an unpublished set of ION Geophysical seismic reflection profile showing strong organized seismic reflectors at the base of the continental crust of the Uruguayan volcanic rifted margin. We distinguish two main groups of reflectors in the lowermost continental crust. A first group, at depths ranging from 32 km below the continent to 16 km in the continent-ocean transition, comprises reflectors continuous over tens of kilometers, peculiarly visible near the mantle-crust boundary. A second group of reflectors dipping toward the ESE (oceanward) is widely distributed in the lower crust. These reflectors are slightly curved and tend to merge and become sub-parallel with the first group of reflectors. Together they draw the pattern of thick shallow-dipping top-to-the continent shear zones affecting the lower continental crust. Such sense of shear is also consistent with the continentward dip of the normal faults that control the deposition of the thick syn-tectonic volcanic formations (SDR). A major portion of the continental crust behaved in a ductile manner and recorded a component of top-to-the continent penetrative simple shear during rifting indicative of a lateral movement between the upper crust and the mantle.

  10. nantucket_ma.grd (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NGDC builds and distributes high-resolution, coastal digital elevation models (DEMs) that integrate ocean bathymetry and land topography to support NOAA's mission...

  11. Archean Arctic continental crust fingerprints revealing by zircons from Alpha Ridge bottom rocks (United States)

    Sergeev, Sergey; Petrov, Oleg; Morozov, Andrey; Shevchenko, Sergey; Presnyakov, Sergey; Antonov, Anton; Belyatsky, Boris


    Whereas thick Cenozoic sedimentary cover overlapping bedrock of the Arctic Ocean, some tectonic windows were sampled by scientific submarine manipulator, as well as by grabbing, dredging and drilling during «Arctic-2012» Russian High-Arctic expedition (21 thousands samples in total, from 400-km profile along Alpha-Mendeleev Ridges). Among others, on the western slope of Alpha Ridge one 10x10 cm fragment without any tracks of glacial transportation of fine-layered migmatitic-gneiss with prominent quartz veinlets was studied. Its mineral (47.5 vol.% plagioclase + 29.6% quartz + 16.6% biotite + 6.1% orthoclase) and chemical composition (SiO2:68.2, Al2O3:14.9, Fe2O3:4.44, TiO2:0.54, MgO:2.03, CaO:3.13, Na2O:3.23, K2O:2.16%) corresponds to trachydacite vulcanite, deformed and metamorphozed under amphibolite facies. Most zircon grains (>80%) from this sample has an concordant U-Pb age 3450 Ma with Th/U 0.8-1.4 and U content of 100-400 ppm, epsilon Hf from -4 up to 0, and ca 20% - ca 3.3 Ga with Th/U 0.7-1.4 and 90-190 ppm U, epsilon Hf -6.5 to -4.5, while only 2% of the grains show Proterozoic age of ca 1.9 Ga (Th/U: 0.02-0.07, U~500 ppm, epsilon Hf about 0). No younger zircons were revealed at all. We suppose that magmatic zircon crystallized as early as 3450 Ma ago during acid volcanism, the second phase zircon crystallization from partial melt (or by volcanics remelting) under amphibolite facies metamorphism was at 3.3 Ga ago with formation of migmatitie gneisses. Last zircon formation from crustal fluids under low-grade metamorphic conditions was 1.9 Ga ago. There are two principal possibilities for the provenance of this metavolcanic rock. The first one - this is ice-rafted debris deposited by melted glacial iceberg. However, presently there are no temporal and compositional analogues of such rocks in basement geology of peri-oceanic regions, including Archean Itsaq Gneiss Complex, Lewisian Complex and Baltic Shield but these regions are far from the places of nowadays iceberg formation. Moreover, no Grenvillian-age zircons were revealed in studied sample. The nearest areas of Paleo- and Mesoarchean rocks appearance are deeply inland territories like Acasta Gneiss Complex, Uivak Gneisses, the Superior Province, Anabar and Aldan Shields, Northern China craton (Anshan complex), thus, a only possibility to bring some fragments of basement rocks from these areas to oceanic coast is transcontinental river transportation. The second possibility - this gneissic clast has a local provenance and has undergone a submarine weathering, shallow marine avalanche, proximal transportation by alongside ocean flows, tidal waves abrasion, and as so, reflects local bedrock geology, i.e. adjacent Alpha Ridge rock composition. Additional confirmation of this can be seen in a wide distribution of Qu-sandstones with Paleo-Mezoarchean zircons, and finds of similar allochtonous zircons in dolerites along Alpha-Mendeleev Ridge profile. The studied fragment is a unique evidence for the possible existence of Paleoarchean continental crust within the submarine Alpha-Mendeleev Ridge in Arctic Ocean.

  12. Late Cretaceous modification of deep continental crust in the NE Paleo Pacific: additional evidence from Viliga lower crust xenoliths (United States)

    Akinin, V. V.; Miller, E. L.; Layer, P.


    The Viliga volcanic field is located ~200 km NE of Magadan, Russia, near the junction of North America-Eurasia-Okhotsk Sea plates. 40Ar/39Ar dating of whole rock olivine melanephelinite samples indicates two magmatic pulses at 8.5 and 10.8 Ma. Volcanism of this age in NE Russia (outside of Kamchatka) is not common but the ages obtained from this newly dated volcanic field are similar to reported ages from intraplate alkali basalts located far to the north (Enmelen volcanoes on the Chukotka Peninsula) and to the south in Primorie (Vladivostok area). The volcanism at Viliga and in Primorie could be controlled by NE trending, leaky strike-slip like faults related to geologically recent plate boundary interactions. The Viliga olivine melanephelinites are highly depleted in radiogenic isotopes (Sr, Nd, Pb) but are quite enriched in incompatible trace elements. The generation of an alkaline magma in such depleted sources requires a relatively recent metasomatic even, which occurred less than 200 Ma and led to an enrichment of incompatible elements but of insufficient time elapsed to shift isotopic ratios. The lavas contain peridotite mantle xenoliths mainly with fertile major element signatures that lead to the conclusion that the lithospheric mantle beneath Viliga has not been affected by Late Cretaceous subduction of the paleo - Pacific plate as it was suggested for region. Viliga lower crustal xenoliths, however, contain zircons with U-Pb SHRIMP ages ranging from 63 to 100 Ma (24 dated zircon grains from two samples). These ages of lower crustal xenoliths are the same as those obtained from lower crustal xenoliths collected from Enmelen and St. Lawrence Island basalts located 1500 km to the NE in the Bering Strait area. This remarkable similarity in lower crustal ages suggests that the lower crust beneath a very wide portion of the continental margin of NE Russia and western Alaska has been affected by a similar Late Cretaceous magmatic/metamorphic event that modified the deep crust across the region.

  13. Petrological, geochemical and geochronological evidence for a Neoproterozoic ocean basin recorded in the Marlborough terrane of the northern New England Fold Belt

    International Nuclear Information System (INIS)

    Petrological, geochemical and radiogenic isotopic data on ophiolitic-type rocks from the Marlborough terrane, the largest (?700 km2) ultramafic-mafic rock association in eastern Australia, argue strongly for a sea-floor spreading centre origin. Chromium spinel from partially serpentinised mantle harzburgite record average Cr/(Cr + Al) = 0.4 with associated mafic rocks displaying depleted MORB-like trace-element characteristics. A Sm/Nd isochron defined by whole-rock mafic samples yields a crystallisation age of 562 ± 22 Ma (2?). These rocks are thus amongst the oldest rocks so far identified in the New England Fold Belt and suggest the presence of a late Neoproterozoic ocean basin to the east of the Tasman Line. The next oldest ultramafic rock association dated from the New England Fold Belt is ca 530 Ma and is interpreted as backarc in origin. These data suggest that the New England Fold Belt may have developed on oceanic crust, following an oceanward migration of the subduction zone at ca 540 Ma as recorded by deformation and metamorphism in the Anakie Inlier. Fragments of late Neoproterozoic oceanic lithosphere were accreted during progressive cratonisation of the east Australian margin. Copyright (1999) Geological Society of Australia

  14. H11076_GEO_1MMBES.TIF: Color Shaded-Relief GeoTIFF Image Showing the 1-m Bathymetry Generated from National Oceanic and Atmospheric Administration (NOAA) Survey H11076 in Quicks Hole, Elizabeth Islands, MA (Geographic) (United States)

    U.S. Geological Survey, Department of the Interior — The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone...

  15. H11076_GEO_1MSSS.TIF: Composite Grayscale Image of the Sidescan Sonar Data From National Oceanic and Atmospheric Administration (NOAA) Survey H11076 of the Sea Floor in Quicks Hole, MA (Geographic) (United States)

    U.S. Geological Survey, Department of the Interior — The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone...

  16. Depth anomalies in the Arabian Basin, NW Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Ajay, K.K.; Chaubey, A.K.

    as the difference between the observed depth to oceanic basement (corrected for sediment load) and the calculated depth to oceanic basement of the same age. The results indicate an anomalous depth to basement of oceanic crust in the Arabian Basin in the age bracket...

  17. Dry and strong quartz during deformation of the lower crust in the presence of melt


    Menegon, Luca; Nasipuri, Pritam; Stunitz, Holger; Behrens, Harald; Ravna, Erling J Krogh


    Granulite facies migmatitic gneisses from the Seiland Igneous Province (northern Norway) were deformed during deep crustal shearing in the presence of melt, which formed by dehydration melting of biotite. Partial melting and deformation occurred during the intrusion of large gabbroic plutons at the base of the lower crust at 570 to 520 Ma in an intracontinental rift setting. The migmatitic gneisses consist of high-aspect-ratio leucosome-rich domains and a leucosome-poor, restitic domain of qu...

  18. Modelling the volatile and organic content of Enceladus' ocean (United States)

    Sotin, Christophe; Lunine, Jonathan


    A variety of Cassini data on Enceladus suggest that the jets of material spraying out of the south polar region of this Saturnian moon are connected to a regional or global ocean below an icy crust -- an ocean in contact with a rocky core [1, 2, 3]. In this study we construct models of the mineralogical and elemental composition of Enceladus' rocky core so as to predict the abundance of species that may provide more detail on the extent of hydrothermal evolution of the ocean and its interaction with the rocky core. Using equations of state of the relevant material, the models are made consistent with the values of the gravity coefficients [1]. We investigate the amount of organic molecules (amino acids and fatty acids) as well as the amount of 40Ar that could be present in Enceladus' deep ocean and, therefore, in the icy grains expelled into space. Some models show that the conditions in Enceladus rocky core can be very similar to those existing in the Earth's oceanic crust, suggesting that all of Enceladus rocky core would have been leached over the age of the solar system. The amount of 40Ar dissolved in the ocean provides constraints on the amount of K in the building blocks of Enceladus, the amount of leaching of the silicate fraction, and the extent of the ocean. Based on chondritic abundances for K, we have calculated that the total potential of 40Ar is about 5.6x1012 kg. We also investigate the amount of organic material that would have been concentrated in the ocean. The Murchison meteorite contains about 60 ppm of amino acids, mainly glycine [4]. Assuming that all the rocky core has been leached by water, the modelled concentration of amino acids exceeds 150 ppm. Carboxylic acids were detected in the Asuka carbonaceous chondrites in Antarctica with values, for example, of 90 nmol/g of benzoic acid. Assuming this value, about 35 ppm of benzoic acid would be present in Enceladus' ocean. The concentrations are larger if the ocean is not global, but rather limited to the South Pole [1], and assuming that all the leached material is concentrated in the regional ocean (and not partially trapped elsewhere in ice). A future mission to Enceladus could eventually measure these quantities in order to assess the extent of evolution of Enceladus, and the potential presence of the building blocks of life in its ocean. This work has been performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. [1] Iess L. et al. (2014) Science, 344, 78. [2] Porco C. et al. (2014) The Astronomical Journal, 148:45. [3] Hedman M. M. et al. (2013) Nature, 500, 182-184. [4] Sephton M.A. (2002) Nat. Prod. Rep., 19, 292-311.

  19. Rb–Sr and Sm–Nd isotope systematics and geochemical studies on metavolcanic rocks from Peddavura greenstone belt: Evidence for presence of Mesoarchean continental crust in easternmost part of Dharwar Craton, India

    Indian Academy of Sciences (India)

    M Rajamanickam; S Balakrishnan; R Bhutani


    Linear, north–south trending Peddavura greenstone belt occurs in easternmost part of the Dharwar Craton. It consists of pillowed basalts, basaltic andesites, andesites (BBA) and rhyolites interlayered with ferruginous chert that were formed under submarine condition. Rhyolites were divided into type-I and II based on their REE abundances and HREE fractionation. Rb–Sr and Sm–Nd isotope studies were carried out on the rock types to understand the evolution of the Dharwar Craton. Due to source heterogeneity Sm–Nd isotope system has not yielded any precise age. Rb–Sr whole-rock isochron age of 2551 ± 19 (MSWD = 1.16) Ma for BBA group could represent time of seafloor metamorphism after the formation of basaltic rocks. Magmas representing BBA group of samples do not show evidence for crustal contamination while magmas representing type-II rhyolites had undergone variable extents of assimilation of Mesoarchean continental crust (< 3.3 Ga) as evident from their initial Nd isotope values. Trace element and Nd isotope characteristics of type I rhyolites are consistent with model of generation of their magmas by partial melting of mixed sources consisting of basalt and oceanic sediments with continental crustal components. Thus this study shows evidence for presence of Mesoarchean continental crust in Peddavura area in eastern part of Dharwar Craton.

  20. Kitoy sillimanite deposit (Eastern Siberia): an example of Neoarchaean-Paleoproterozoic paleoweathering crust (United States)

    Salnikova, Ekaterina; Yakovleva, Sonya; Levitsky, Ivan; Kotov, Alexander; Levitsky, Valery; Reznitsky, Leonid; Anisimova, Irina


    We present the first reliable geochronological data on the age of the Kitoy sillimanite deposit (south-western Siberian craton) composed by andalusite-sillimanite, garnet-sillimanite and essentially sillimanite rocks intercalated with quartzite. These rocks experienced metamorphic reworking under amphibolite facies condition. Geochemical data indicates that hydrolysate clay rocks with kaolin, kaolinite and metalaterite or pyrophyllite have been a protholites of the high-alumina Kitoy rocks. Thus the Kitoy deposit high-alumina schist corresponds to mature paleoweathering crust (laterite and bauxite) with negligible amount of clastic material. U-Pb zircon geochronological investigations were undertaken for leucocratic biotite gneisses directly subjacent productive high-alumina suite as well as for migmatitic orthotektite vein cutting the andalusite-sillimanite rocks. Both samples contain typical magmatic zircon which was dated at 2578+/-16 Ma in the biotite gneisses and at 2483+/-4 Ma in the veined orthotektite. Pb-Pb age of sillimanite from high-alumina rocks is at 2536+/-27 Ma (Levchenkov et al., 2009) that is in good correspondence with our data. Results of our study allow to bracket the formation of the Kitoy deposit in the age interval 2536-2483 Ma and consider the high-alumina rocks of this deposit as example of the ancient paleoweathering crust recognized in the Eastern Siberia.

  1. Biogenic crust dynamics on sand dunes

    CERN Document Server

    Kinast, Shai; Yizhaq, Hezi; Ashkenazy, Yosef


    Sand dunes are often covered by vegetation and biogenic crusts. Despite their significant role in dune stabilization, biogenic crusts have rarely been considered in studies of dune dynamics. Using a simple model, we study the existence and stability ranges of different dune-cover states along gradients of rainfall and wind power. Two ranges of alternative stable states are identified: fixed crusted dunes and fixed vegetated dunes at low wind power, and fixed vegetated dunes and active dunes at high wind power. These results suggest a cross-over between two different forms of desertification.

  2. The hydrothermal power of oceanic lithosphere (United States)

    Grose, C. J.; Afonso, J. C.


    We have estimated the power of ventilated hydrothermal heat transport, and its spatial distribution, using a set of recently developed plate models which highlight the effects of hydrothermal circulation and thermal insulation by oceanic crust. Testing lithospheric cooling models with these two effects, we estimate that global advective heat transport is about 6.6 TW, significantly lower than previous estimates, and that the fraction of that extracted by vigorous circulation on the ridge axes (total, significantly higher than previous estimates. This low hydrothermal power estimate originates from the thermally insulating properties of oceanic crust in relation to the mantle. Since the crust is relatively insulating, the effective properties of the lithosphere are "crust dominated" near ridge axes (yielding lower heat flow), and gradually approach mantle values over time. Thus, cooling models with crustal insulation predict low heat flow over young seafloor, implying that the difference of modeled and measured heat flow is due to the heat transport properties of the lithosphere, in addition to ventilated hydrothermal circulation as generally accepted. These estimates may bear on important problems in the physics and chemistry of the Earth because the magnitude of hydrothermal power affects chemical exchanges between the oceans and the lithosphere, thereby affecting both thermal and chemical budgets in the oceanic crust and lithosphere, the subduction factory, and convective mantle.

  3. Eocene magmatic processes and crustal thickening in southern Tibet: Insights from strongly fractionated ca. 43 Ma granites in the western Gangdese Batholith (United States)

    Wang, Qing; Zhu, Di-Cheng; Cawood, Peter A.; Zhao, Zhi-Dan; Liu, Sheng-Ao; Chung, Sun-Lin; Zhang, Liang-Liang; Liu, Dong; Zheng, Yuan-Chuan; Dai, Jin-Gen


    This study reports zircon U-Pb age and Hf isotope, whole-rock major and trace element, and Sr-Nd-Pb-Hf isotope data for the Dajia pluton, western Gangdese Batholith, in southern Tibet. These data indicate that the pluton consists of moderately (Group 1) and strongly (Group 2) fractionated granites that were emplaced synchronously at ca. 43 Ma. Group 1 samples have SiO2 contents of 69-72 wt.% and vary in terms of the differentiation index (DI = 84-93). These rocks are depleted in Ba, Nb, Sr, P, and Ti, with moderate negative Eu anomalies, and display low heavy rare earth elements (HREEs) and Y abundances. Group 2 samples are characterized by high SiO2 (75-78 wt.%) and DI (95-97); significantly negative Eu anomalies; marked concave-upward middle REE (Gd-Ho) patterns; and Ba, Sr, P, and Ti anomalies that are significantly more negative than those of Group 1 samples. Group 1 samples have whole-rock ?Nd(t) (- 5.9 to - 6.0), ?Hf(t) (- 4.0 to - 4.5), and zircon ?Hf(t) (- 6.0 to + 5.8) values identical to those of Group 2 samples [?Nd(t) = - 5.7 to - 6.7, ?Hf(t) = - 3.5 to - 2.9, and zircon ?Hf(t) = - 2.0 to + 4.2], as well as similar initial Pb isotopic compositions. These data indicate that the two groups were derived from a common source region with garnet as a residual mineral phase. Group 1 samples were most likely derived from partial melting of garnet-bearing amphibolite (rather than eclogite) within the juvenile southern Lhasa crust and mixed with the enriched components from the subducting ancient Indian continental crust and/or the ancient central Lhasa basement. Group 2 samples are interpreted as the products of extensive fractional crystallization (plagioclase, K-feldspar, biotite, apatite, allanite, titanite, monazite, and ilmenite) of the melts represented by Group 1 samples. Low HREEs and Y abundances of the Dajia pluton, together with the presence of strongly fractionated granites (Group 2) identified for the first time in the Gangdese Batholith, indicate that the crust beneath the Dajia region had already been thickened by ca. 43 Ma. High whole-rock zircon saturation temperatures (815 °C-869 °C) of Group 1 samples and the other ca. 43 Ma coeval magmatism documented both in the Gangdese Batholith and in the Tethyan Himalaya can be best interpreted as the final consequences of the magmatic responses to the Neo-Tethyan oceanic slab breakoff.

  4. The unstable CO2 feedback cycle on ocean planets


    Kitzmann, D.; Alibert, Y.; Godolt, M; Grenfell, J.L.; Heng, K; Patzer, A. B. C.; Rauer, H.; Stracke, B.; von Paris, P.


    Ocean planets are volatile rich planets, not present in our Solar System, which are thought to be dominated by deep, global oceans. This results in the formation of high-pressure water ice, separating the planetary crust from the liquid ocean and, thus, also from the atmosphere. Therefore, instead of a carbonate-silicate cycle like on the Earth, the atmospheric carbon dioxide concentration is governed by the capability of the ocean to dissolve carbon dioxide (CO2). In o...

  5. The tectonic structure of the Song Ma fault zone, Vietnam (United States)

    Wen, Strong; Yeh, Yu-Lien; Tang, Chi-Cha; Phong, Lai Hop; Toan, Dinh Van; Chang, Wen-Yen; Chen, Chau-Huei


    Indochina area is a tectonic active region where creates complex topographies and tectonic structures. In particular, the Song Ma fault zone plays an important role in understanding the mechanism and revolution of the collision between the Indian plate and Eurasian plate. In order to have better understanding the seismotectonic structures of the Song Ma fault zone, a three-year project is proposed to study the seismotectonic structures of crust in this region. The main goal of this project is to deploy temporary broad-band seismic stations around/near the shear zone to record high quality microearthquakes. By using the data recorded by the temporary array and the local seismic network, we are able to conduct seismological studies which include using waveform inversion to obtain precise fault plane solutions of microearthquakes, one-dimensional (1-D) velocity structure of the crust in the region as well as the characteristics of seismogeneric zone. From the results of earthquake relocation and focal mechanisms, we find that the spatial distribution of events occurred in Song Ma fault zone forms in several distinct groups which are well correlated local geological structures and further use to gain insights on tectonic evolution.

  6. Post-rift km-scale uplift of passive continental margins can be caused by compressive stresses within continental crust (United States)

    Chalmers, J. A.


    Many passive continental margins are flanked by a mountain range up to more than 2 km high (Elevated Passive Continental Margins; EPCMs), e.g. Norway, east and west Greenland, East Brazil, eastern Australia and other margins elsewhere, that have been uplifted long after continental break-up. Explanations for these uplifted margins have been ad hoc, but there has hitherto been no explanation that accounts for their presence at both volcanic and non-volcanic margins and in both polar and tropical climatic environments. A continent breaks up by extension and thinning of the continental crust. Thinning varies from small amounts in the proximal rift to perhaps a factor of 5 or more adjacent to oceanic crust. Continental crust > ca. 25 km thick contains two weak layers, one between strong upper (quartz-rich) and lower (dioritic) crust and the other between strong lower crust and strong mantle. Continental crust data exists, all EPCMs are currently under compression. Continental crust responds to moderate compression stress in two modes; flow in the weak lower crust and by forming gentle buckle-folds with a wavelength of 200-400 km and an amplitude of ca. 0.5 km. Under moderate compression, material in the crust's weak layers starts to flow towards the rift from under the adjacent continent. The lack of weak layers under the thinned, distal rift basin means, however, that flow cannot continue towards the ocean. Mid- and lower crustal material therefore accumulates under the proximal rift, thickening the crust there and lifting it by isostatic response to the thickening. Material flows into the rift until the crust under it is once more as thick as it was prior to extension, but no thicker. This thickened layer extends gradually further and further below the rift, at speeds of a few km per million years, uplifting it and exposing post-rift sediments. At higher stress, buckling may enhance this uplift, and it may be enhanced even more by the isostatic response to the erosion of deep valleys in the rising mountains. Both the thickening and folding continues until there is a reduction in imposed far-field compressive stress, after which the thickened crust 'freezes' in place.

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

    DEFF Research Database (Denmark)

    Frassetto, Andrew; Thybo, Hans


    The mountains across southern Norway and other margins of the North Atlantic Ocean appear conspicuously high in the absence of recent convergent tectonics. We investigate this phenomenon with receiver functions calculated for seismometers deployed across southern Fennoscandia. These are used to constrain the structure and seismic properties of the lithosphere and primarily to measure the thickness and infer the bulk composition of the crust. Such parameters are key to understanding crustal isostasy and assessing its role, or lack thereof, in supporting the observed elevations. Our study focuses on the southern Scandes mountain range that has an average elevation >1.0 km above mean sea level. The crust-mantle boundary (Moho) is ubiquitously imaged, and we occasionally observe structures that may represent the base of the continental lithosphere or other thermal, chemical, or viscous boundaries in the upper mantle. The Moho resides at similar to 25-30 km depth below mean sea level in southeastern coastal Norwayand parts of Denmark, similar to 35-45 km across the southern Scandes, and similar to 50-60 km near the Norwegian-Swedish border. That section of thickest crust coincides with much of the Transscandinavian Igneous Belt and often exhibits a diffuse conversion at the Moho, which probably results from the presence of a high wave speed, mafic lower crust across inner Fennoscandia. A zone of thinned crust (

  8. The Siquisique basalts and gabbros, Los Algodones, Venezuela: late Cretaceous oceanic plateau formed within the proto-Caribbean plate? (United States)

    Kerr, A. C.; Neill, I.; Urbani, F.; Spikings, R.; Barry, T.; Tarney, J.


    Basalts and gabbros, exposed near Siquisique, Venezuela have previously been interpreted as Jurassic mid-ocean ridge basalts, on the basis of an ammonite found in nearby, but not obviously intercalated, sediments (Bartok, 1985). This, combined with their current tectonic position, well within the continent, and because they accreted before the Cretaceous ‘Great Arc’ of the Caribbean, has led to the Siquisique igneous rocks being widely regarded as Jurassic ‘normal’ mid-ocean ridge basalts and gabbros formed as North and South America rifted apart. We present new geochemical and chronological data which shows that the Siquisique igneous rocks are 95-90Ma and have a chemistry which is more consistent with derivation from a deep mantle plume, than a mid-ocean ridge. It is clear that these basalts represent part of the original ocean floor of the Caribbean, which formed before the tectonic emplacement of the present-day Caribbean from the Pacific. Chemically similar basalts and gabbros at El Copey on Araya Peninsula and Sans Souci in northern Trinidad also accreted to the continental margin of South America before the ‘Great Arc’ of the Caribbean and may well be part of the same intra-Caribbean ‘plume event’. These exposures all indicate that the oceanic crust of the proto-Caribbean, was likely to have consisted (at least in part) of thickened oceanic crust formed by melting of a hot-mantle plume. Although the Siquisique rocks formed at a similar time to the Caribbean-Colombian oceanic plateau they were not derived from the same mantle plume. This supports previous suggestions (Kerr & Tarney, 2005; Snow et al. 2005) that the period around ~90Ma (like that around 120Ma) was marked by a significant upsurge in global plume-related magmatic activity. This activity is likely to have contributed significantly to the major worldwide oceanic anoxia event (OAE2) around the Cenomanian-Turonian boundary (93.4Ma)(Kerr, 1998; Snow et al. 2005). Significantly, this discovery requires a revision of our current understanding of Caribbean plate tectonic evolution. References Bartok, P.E., et al. 1985. The Siquisique Ophiolites, Northern Lara State, Venezuela - a discussion on their Middle Jurassic Ammonites and Tectonic Implications. GSA Bulletin 96, 1050-1055. Kerr, A.C., 1998. Oceanic plateau formation: A cause of mass extinction and black shale deposition around the Cenomanian-Turonian boundary. J Geol Soc London 155, 619-626. Kerr, A.C., Tarney, J., 2005. Tectonic evolution of the Caribbean and northwestern South America: The case for accretion of two Late Cretaceous oceanic plateaus. Geology 33, 269-272. Snow, L.G. et al. 2005. Trace element abundances in the Rock Canyon Anticline, Pueblo, Colorado, marine sedimentary section and their relationship to Caribbean plateau construction and oxygen anoxic event 2. Paleoceanography 20, doi. 10.1029/2004PA001093.

  9. Boron isotopes in tourmaline from the ca. 3.7-3.8 Ga Isua supracrustal belt, Greenland: Sources for boron in Eoarchean continental crust and seawater (United States)

    Grew, Edward S.; Dymek, Robert F.; De Hoog, Jan C. M.; Harley, Simon L.; Boak, Jeremy; Hazen, Robert M.; Yates, Martin G.


    Boron is highly concentrated in Earth's crust relative to primitive mantle. However, when present-day crustal concentrations were achieved remains debatable. It has been proposed that seawater boron ?11B was lower than at present, consistent with a model relating increase in sea-water ?11B to the proportion of B extracted from Earth's mantle into the oceans and crust. Our in situ ion microprobe analyses of tourmaline in 17 samples from the Eoarchean Isua supracrustal belt, Southwest Greenland, gave the following average ?11B with uncertainties ranging from ±0.4 to ±1.9‰: ?11B = -7.1 to -11.5‰ in amphibolite; ?11B = -10.5 to -25.3‰ in mica schist; ?11B = -19.2‰ in metachert (one sample), and ?11B = -21.9‰ in metaconglomerate (one sample). Tourmaline is largely schorl-dravite, rarely uvite-feruvite, and shows color and compositional zoning. ?11B varies from grain to grain in most samples; grains in a kyanite-staurolite schist are isotopically zoned, possibly because the rims incorporated B released by muscovite breakdown. The patterns in color-zoned tourmaline grains in our samples are not consistent with detrital origin of the cores, which rules out the possibility of there being tourmaline detritus from pre-existing continental crust in the studied samples. The tourmaline-bearing rocks are found in both the ca. 3700 Ma northern and ca. 3800 Ma southern terranes in the Isua supracrustal belt. Following an approach suggested by Chaussidon and Appel, we estimated Eoarchean seawater ?11B by calculating back from ?11B of tourmaline in metasedimentary rocks using fractionation of boron isotopes between clays and muscovite, tourmaline and aqueous fluid. This calculation gave an estimated ?11B ? +14 ± 15‰ for Eoarchean seawater, 25‰ lower than present-day seawater (?11B = +39.5‰). For comparison, an estimate obtained simply by direct comparison of ?11B for Eoarchean and Phanerozoic tourmaline presumed to have crystallized in similar environments gives ?11B ? +30‰ for Eoarchean seawater. At first, our results appear to be contradictory. On the one hand, tourmaline is as widespread and abundant in the Isua supracrustal rocks as it is in many younger complexes, which suggests that extraction of boron from the mantle had reached levels close to present day levels. On the other hand, there is no evidence of boron having been extracted prior to ca. 3800 Ma and a seawater ?11B lower than present-day ?11B = 39.5‰ implies that extraction of B from the mantle had not reached the present-day extent. The proto-arc scenario proposed by A. Nutman and co-authors offers a possible resolution to the contradiction by considering the abundance and isotopic composition of B in the Isua supracrustal rocks as a localized phenomenon that should not be interpreted to reflect B concentrations in an Earth-circling ocean. Accumulation of boron in seawater in a partially isolated basin associated with a proto-arc and the attendant volcanism might have been sufficiently rapid for the needed concentrations to be attained in a relatively short time.

  10. Ocean Ridges and Oxygen (United States)

    Langmuir, C. H.


    The history of oxygen and the fluxes and feedbacks that lead to its evolution through time remain poorly constrained. It is not clear whether oxygen has had discrete steady state levels at different times in Earth's history, or whether oxygen evolution is more progressive, with trigger points that lead to discrete changes in markers such as mass independent sulfur isotopes. Whatever this history may have been, ocean ridges play an important and poorly recognized part in the overall mass balance of oxidants and reductants that contribute to electron mass balance and the oxygen budget. One example is the current steady state O2 in the atmosphere. The carbon isotope data suggest that the fraction of carbon has increased in the Phanerozoic, and CO2 outgassing followed by organic matter burial should continually supply more O2 to the surface reservoirs. Why is O2 not then increasing? A traditional answer to this question would relate to variations in the fraction of burial of organic matter, but this fraction appears to have been relatively high throughout the Phanerozoic. Furthermore, subduction of carbon in the 1/5 organic/carbonate proportions would contribute further to an increasingly oxidized surface. What is needed is a flux of oxidized material out of the system. One solution would be a modern oxidized flux to the mantle. The current outgassing flux of CO2 is ~3.4*1012 moles per year. If 20% of that becomes stored organic carbon, that is a flux of .68*1012 moles per year of reduced carbon. The current flux of oxidized iron in subducting ocean crust is ~2*1012 moles per year of O2 equivalents, based on the Fe3+/Fe2+ ratios in old ocean crust compared to fresh basalts at the ridge axis. This flux more than accounts for the incremental oxidizing power produced by modern life. It also suggests a possible feedback through oxygenation of the ocean. A reduced deep ocean would inhibit oxidation of ocean crust, in which case there would be no subduction flux of oxidized material, and oxygen could rise. Once the ocean becomes fully oxidized, a substantial subduction flux operates as a negative feedback. Plate tectonic geochemical cycles may have played a very significant role in the oxygen balance in both the ancient and modern Earth.

  11. The magma ocean as an impediment to lunar plate tectonics (United States)

    Warren, Paul H.


    The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the magma ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the magma ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the magma ocean.

  12. Implications of Laurentian Grenville crust in the northern Scandinavian Caledonides (United States)

    Steltenpohl, Mark; Andresen, Arild; Augland, Lars; Prouty, Jonathan; Corfu, Fernando


    Field and geochronological data (40Ar/39Ar and U-Pb ID-TIMS and SHRIMP) on granitoids and their metasedimentary host rocks in the Salten region, northern Norway, document large Early Neoproterozoic plutons intruding slightly older metasedimentary protoliths. The Bratten-Landegode-Tårnvika gneiss complex, herein called the Rørstad complex, and the Heggmo unit have traditionally been interpreted to represent Baltican basement culminations (~ 1.8 Ga), but we document them to be exotic Grenville elements within separate thrust sheets at the structurally highest preserved tectonostratigraphic level (Uppermost Allochthon) of the Scandinavian Caledonides. Neoproterozoic ages for magmatism in these two tectonic units range between ~ 950 and 926 Ma, whereas metasedimentary host rocks of the Heggmo unit were deposited after ~1050 Ma (youngest zircon) prior to their intrusion. We suggest correlation of the metasedimentary rocks between the Heggmo and the Rørstad, although differences in their tectonometamorphic histories are clear. The Rørstad complex was migmatized in the Late Ordovician (~450 Ma) and later intruded by pegmatites and diorite sheets at ~433 and 428 Ma, respectively. Ordovician migmatites have not been found in the Heggmo unit, but relics of ~450 Ma activity might be masked by intense migmatization and associated leuocogranite activity are documented. 40Ar/39Ar step-heating analysis of hornblende and K-feldspar locally record pre-Scandian thermal effects, whereas muscovites and phlogopites indicate Siluro-Devonian metamorphism and cooling from Scandian emplacement. The Rørstad complex and the Heggmo unit show one-to-one correlations in ages with Mesoproterozoic to Neoproterozoic rock complexes from the southern segment of the East Greenland Caledonides, as well as affinities to other complexes throughout the North Atlantic realm. The discovery of Laurentian Grenville-continental crust in the Uppermost Allochthon of the Scandinavian Caledonides requires substantial revision of the tectonostratigraphy of this part of the Caledonides. The Rørstad and Heggmo preserve a record of tectonic events that had taken place on the northeastern Laurentian continent prior to its Caledonian continent-continent collision with Baltica. We hypothesize on interactions and displacements between the two conjugate continental margins during the Scandian phase of the Caledonian orogeny.

  13. MaTeam-projektet

    DEFF Research Database (Denmark)

    Andreasen, Marikka; Damkjær, Helle Sejer; Højgaard, Tomas


    Projektet MaTeam beskrives med fokus på et toårigt forsøg hvor matematiklærerne på 4.-6. klassetrin på fire skoler i Silkeborg Kommune samarbejdede med forfatterne. Projektet handlede om udvikling af matematiklærerkompetencer med fokus på samarbejdet i de fire skolers matematiklærerfagteam. Hovedformålet var at etablere en eksplicit målstyret matematikundervisning med særlig vægt på faglige kompetencemål. Analysen her handler bl.a. om forhold der påvirker den enkelte matematiklærers fagidentitet...

  14. Platinum stable isotopes in ferromanganese crust and nodules (United States)

    Corcoran, Loretta; Seward, Terry; Handler, Monica R.


    Hydrogenetic ferromanganese (Fe-Mn) crust and nodules are slow-growing chemical sediments that form by direct precipitation from seawater, resulting in a record of changing seawater chemistry. These sediments are the primary sink for platinum in the modern oxic marine environment, hosting well-documented enrichments over other platinum-group elements (PGEs): the Pt anomaly [1]. Platinum is a non-bio-essential, highly siderophile, transition metal with six stable isotopes (190Pt, 192Pt, 194Pt, 195Pt, 196Pt, and 198Pt) with several oxidation states (Pt0, Pt2+ and Pt4+). Platinum is generally considered to exist in the hydrosphere as Pt2+ although its behaviour in the marine environment is poorly constrained, and Pt4+may also be present. Variations in ocean redox state, together with changes in source fluxes to the oceans, may therefore lead to small variations (< ±1) in the stable isotopic composition of marine platinum, raising the potential of adding platinum to the growing arsenal of paleoceanographic tracers. A method has been developed to measure the platinum isotopic composition using double spike MC-ICPMS analysis [2]and applied to a global suite of modern Fe-Mn crust and nodules. Combining synchrotron XAFS analyses of platinum adsorbed onto Fe-Mn oxide and oxyhydroxide surfaces to determine oxidation state and bonding environment, with platinum stable isotopic measurements allowing us to evaluate both platinum incorporation onto these sediments and the associated degree of platinum isotopic fractionation. Leaching experiments conducted on platinum rich terrestrial materials underwent platinum stable isotopic measurement as an analogue for the Pt isotopic fractionation associated with continental weathering. [1] Hodge, V.F. et al. (1985) Earth and Planetary Science Letters, 72, 158-162. [2] Creech, J. et al. (2013) Journal of Analytical Atomic Spectrometry, 28. 853-865.

  15. Hydroacoustic Monitoring of Oceanic Spreading Centers: Past, Present, and Future

    Directory of Open Access Journals (Sweden)

    Robert P. Dziak


    Full Text Available Mid-ocean ridge volcanism and extensional faulting are the fundamental processes that lead to the creation and rifting of oceanic crust, yet these events go largely undetected in the deep ocean. Currently, the only means available to observe seafloor-spreading events in real time is via the remote detection of the seismicity generated during faulting or intrusion of magma into brittle oceanic crust. Hydrophones moored in the ocean provide an effective means for detecting these small-magnitude earthquakes, and the use of this technology during the last two decades has facilitated the real-time detection of mid-ocean ridge seafloor eruptions and confirmation of subseafloor microbial ecosystems. As technology evolves and mid-ocean ridge studies move into a new era, we anticipate an expanding network of seismo-acoustic sensors integrated into seafloor fiber-optic cabled observatories, satellite-telemetered surface buoys, and autonomous vehicle platforms.

  16. 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 neighboring ridges of the Indian Ocean. There is in particular a long-standing hypothesis, not yet examined seismically, that channelized plume flow beneath the aseismic Rodrigues Ridge could feed the Central Indian Ridge at 1000 km distance. The RHUM-RUM group ( * IPG Paris & Géosciences Réunion: G. Barruol, J.P. Montagner, E. Stutzmann, F.R. Fontaine, C. Deplus, M. Cannat, G. Roult, J. Dyment, S. Singh, W. Crawford, C. Farnetani, N. Villeneuve, L. Michon. V. Ferrazzini, Y. Capdeville. * Univ. Munich (LMU): K. Sigloch, H. Igel. AWI Bremerhaven: V. Schlindwein. Univ. Frankfurt: G. Rümpker. Univ. Münster: C. Thomas. Univ. Bonn: S. Miller. * Géosciences Montpellier: C. Tiberi, A. Tommasi, D. Arcay, C. Thoraval. * Mauritius Oceanography Institute: D. Bissessur. Univ. Antananarivo: G. Rambolamanana. SEYPEC Seychelles Petroleum: P. Samson, P. Joseph. * Other institutes: A. Davaille, M. Jegen, M. Maia, G. Nolet, D. Sauter, B. Steinberger.

  17. Growth of the Afanasy Nikitin seamount and its relationship with the 85°E Ridge, northeastern Indian Ocean

    Indian Academy of Sciences (India)

    K S Krishna; J M Bull; O Ishizuka; R A Scrutton; S Jaishankar; V K Banakar


    The Afanasy Nikitin seamount (ANS) is a major structural feature (400 km-long and 150 km-wide) in the Central Indian Basin, situated at the southern end of the so-called 85°E Ridge. Combined analyses of new multibeam bathymetric, seismic reflection and geochronological data together with previously described magnetic data provide new insights into the growth of the ANS through time, and its relationship with the 85°E Ridge. The ANS comprises a main plateau, rising 1200 m above the surrounding ocean floor (4800 m), and secondary elevated seamount highs, two of which (lie at 1600 and 2050 m water depths) have the morphology of a guyot, suggesting that they were formed above or close to sea-level. An unbroken sequence of spreading anomalies 34 through 32n.1 identified over the ANS reveal that the main plateau of the ANS was formed at 80–73 Ma, at around the same time as that of the underlying oceanic crust. The 40Ar/39Ar dates for two basalt samples dredged from the seamount highs are consistent, within error, at 67 Ma. These results, together with published results of late Cretaceous to early Cenozoic Indian Ocean plate reconstructions, indicate that the Conrad Rise hotspot emplaced both the main plateau of the ANS and Conrad Rise (including the Marion Dufresne, Ob and Lena seamounts) at 80–73 Ma, close to the India–Antarctica Ridge system. Subsequently, the seamount highs were formed by late-stage volcanism c. 6–13 Myr after the main constructional phase of the seamount plateau. Flexural analysis indicates that the main plateau and seamount highs of the ANS are consistent with Airy-type isostatic compensation, which suggest emplacement of the entire seamount in a near spreading-center setting. This is contrary to the flexural compensation of the 85°E Ridge further north, which is interpreted as being emplaced in an intraplate setting, i.e., 25–35 Myr later than the underlying oceanic crust. Therefore, we suggest that the ANS and the 85°E Ridge appear to be unrelated as they were formed by different mantle sources, and that the proximity of the southern end of the 85°E Ridge to the ANS is coincidental.

  18. Nuclei in Strongly Magnetised Neutron Star Crusts

    CERN Document Server

    Nandi, Rana


    We discuss the ground state properties of matter in outer and inner crusts of neutron stars under the influence of strong magnetic fields. In particular, we demonstrate the effects of Landau quantization of electrons on compositions of neutron star crusts. First we revisit the sequence of nuclei and the equation of state of the outer crust adopting the Baym, Pethick and Sutherland (BPS) model in the presence of strong magnetic fields and most recent versions of the theoretical and experimental nuclear mass tables. Next we deal with nuclei in the inner crust. Nuclei which are arranged in a lattice, are immersed in a nucleonic gas as well as a uniform background of electrons in the inner crust. The Wigner-Seitz approximation is adopted in this calculation and each lattice volume is replaced by a spherical cell. The coexistence of two phases of nuclear matter - liquid and gas, is considered in this case. We obtain the equilibrium nucleus corresponding to each baryon density by minimizing the free energy of the c...

  19. The crust role at Paramillos Altos intrusive belt: Sr and Pb isotope evidence

    International Nuclear Information System (INIS)

    Paramillos Altos Intrusive Belt (PAIB) (Ostera, 1996) is located in the thick skinned folded-thrust belt of Malargue, southwestern Mendoza, Argentina. Geochemical, geochronologic and isotopic studies were carried out in it (Ostera 1996, 1997, Ostera et al. 1999; Ostera et al. 2000) and these previous papers suggested a minor involvement of the crust in the genesis of the PAIB. According with Ostera et al. (2000) it is composed by stocks, laccoliths, dykes and sills which range in composition from diorites to granodiorites, and from andesites to rhyolites, and divided in five Members, which range in age from Middle Miocene to Early Miocene: a- Calle del Yeso Dyke Complex (CYDC), with sills and dykes of andesitic composition (age: 20±2 Ma). b- Puchenque-Atravesadas Intrusive Complex (PAIC), composed by dykes and stocks ranging from diorites to granodiorites (age: 12.5±1 Ma). c- Arroyo Serrucho Stock (SAS), an epizonal and zoned stock, with four facies, with K/Ar and Ar/Ar dates of 10±1 and 9.5±0.5 Ma. d- Portezuelo de los Cerros Bayos (PCB), that includes porphyritic rocks of rhyolitic composition, of 7.5±0.5 Ma. e- Cerro Bayo Vitrophyres (CBV), with andesitic sills and dykes (age: 4.8±0.2 Ma). We present in this paper new Sr and Pb isotopes data that constrain the evolution of the PAIB (au)

  20. Resonant Shattering of Neutron Star Crusts


    Tsang, D.; Read, J. S.; Hinderer, T; Piro, A. L.; Bondarescu, R.


    The resonant excitation of neutron star (NS) modes by tides is investigated as a source of short gamma-ray burst (sGRB) precursors. We find that the driving of a crust-core interface mode can lead to shattering of the NS crust, liberating ~10^46-10^47 erg of energy seconds before the merger of a NS-NS or NS-black hole binary. Such properties are consistent with Swift/BAT detections of sGRB precursors, and we use the timing of the observed precursors to place weak constraints...

  1. The atypical Caribbean-Colombia oceanic plateau and its role in the deformation of the Northern Andes (United States)

    Ferrari, L.; Lopez-Martinez, M.; Petrone, C. M.; Serrano, L.


    The Late Cretaceous to Early Tertiary tectono-magmatic evolution of the Northern Andes has been strongly influenced by the dextral oblique interaction of the Caribbean-Colombian oceanic plateau (CCOP) with northwestern South America. This complex interaction has resulted in several pulses of transpressional deformation and crustal accretion to the South America plate but also in a widespread deformation in the plateau itself. In this peculiar type of orogeny one of the factors controlling the deformation is the crustal structure and thus the rheological profiles of the two lithospheric sections that interact. The genesis of the CCOP has been traditionally associated to the melting of the Galapagos plume head when it impacted the Farallon plate, which is supposed to have built an unsubductable and thick crustal section. This interpretation was based on the apparent clustering of ages at ~91-89 Ma for several obducted fragments of the CCOP in northwestern South America and in the Caribbean islands. However, seismic profiles show that magmatism added a very variable amount but no more than 10 km of igneous material to the original crust of the Farallon plate, making the CCOP much more irregular than other oceanic plateaus. Recent studies of key areas of the obducted part of the CCOP contradict the notion that the plateau formed by melting of a plume head at ~ 90 Ma. Particularly, new geochronologic data and petrologic modeling from the small Gorgona Island document a magmatic activity spanning the whole Late Cretaceous (98.7±7.7 to 64.4±5 Ma) and a progressive increase in the degree of melting and melt extraction with time. Multiple magmatic pulses over several tens of Ma in small areas like Gorgona, are also recognized in other areas of the CCOP, documenting a long period of igneous activity with peaks at 74-76, 80-82, and 88-90 Ma in decreasing order of importance. Even older, Early Cretaceous ages, have been reported for fragments in Costa Rica and Curaçao. A prolonged period of igneous activity over several tens of Ma is not consistent with a short, voluminous outburst of magmatism from a plume head at ~91-89 Ma and the geographic distribution of ages does not point to a definite pattern of migration as it would be expected if magmatism would be the result of the passage of the Farallon plate over a stationary, or slowly moving, hotspot. However, the age span of this magmatism is broadly concurrent with the existence of the Caribbean slab window, formed by the intersection of the proto- Caribbean spreading ridge with the Great Caribbean Arc. During this time span the Farallon oceanic lithosphere advanced eastward ~1500 km, overriding the astenosphere feeding the proto-Caribbean spreading ridge. This hotter mantle flowed westward into, and mixed with, the opening mantle wedge, promoting increasing melting with time. This mechanism may explain the irregularly thickened oceanic crust of the CCOP and its internal deformation but also the evidence of partial subduction of some of its parts.

  2. Actual timing of neodymium isotopic variations recorded by Fe-Mn crusts in the western North Atlantic (United States)

    Burton, K.W.; Lee, D.-C.; Christensen, J.N.; Halliday, A.N.; Hein, J.R.


    Hydrogenetic ferromanganese (Fe-Mn) crusts from the western North Atlantic record variations in the Nd and Pb isotopic composition of Cenozoic deep water preserved during their growth. The timing and cause of the most striking change have been the subject of debate. Some have proposed that the shift took place after 4 Ma in response to the closure of the Panama gateway. Others have argued that the major change in isotope composition occurred as early as 8 Ma. This study presents high-resolution Nd isotope records for crusts previously dated using 10Be/9Be chronology. These data confirm that the shifts in Nd occurred after 4 Ma, consistent with a likely relationship with the closure of the Central American Isthmus and intensification of Northern Hemisphere Glaciation, and in accordance with changes seen in other physical and chemical records. These results illustrate the need for both a robust chronological framework and high-resolution records before a reliable paleoceanographic interpretation can be made of the variations recorded by Fe-Mn crusts.

  3. Early Cretaceous intra-oceanic rifting in the Proto-Indian Ocean recorded in the Masirah Ophiolite, Sultanate of Oman


    Marquer, Didier; Mercolli, Ivan; Peters, Tjerk


    The Masirah Ophiolite (Sultanate of Oman) was part of an oceanic basin (Proto-Indian Ocean) formed by the break-up of Gondwana in Late Jurassic times similar to the Somali basin. It was obducted onto the Arabian continental margin in the Early Paleocene, 100 Ma after its formation. Hence, it is possible to investigate the different tectonic and magmatic processes that have affected the oceanic lithosphere during these 100 Ma. Tithonian ridge magmatism, tectonism and hydrothermal alteration ar...

  4. Nagssugtoqidian mobile belt of West Greenland: A cryptic 1850 Ma suture between two Archaean continents - chemical and isotopic evidence

    International Nuclear Information System (INIS)

    New chemical and isotopic data permit the recognition of a cryptic suture zone between two Archean continental masses within the Nagssugtoqidian mobile belt of West Greenland. This discovery has important implications for Precambrian crustal evolution: suture zones may not always be identifiable from geologic field observations, with the consequence that mobile belts in which undetected sutures exist may be mis-identified as ensialic, and thought to require special non-plate tectonic models to account for their development. The Nagssugtoqidian belt consists mainly of Archaean gneisses reworked during the Proterozoic, with metamorphic grade and degree of isotopic disturbance increasing towards the center of the belt. At the centre of the belt the Nagssugtoqidian includes metasediments and calc-alkaline volcanic and plutonic rocks of Proterozoic age, almost always strongly deformed and metamorphosed. From isotopic evidence (Sri ca. 0.703; model ?1 values ca. 8.0; initial ?Nd ca. 0) it is clear that the Proterozoic igneous rocks do not include any significant contributions derived from the Archaean crust, and the chemistry of rocks, together with the isotope data, suggests that they were formed at a destructive plate margin. The Proterozoic rocks are found in a narrow zone (up to 30 km wide) between the Archaean gneisses to the north and south of Nordre Stroemfjord, and are interpreted as reflecting the existence of a suture between two Archaean continental blocks. Zircon U-Pb data and other isotope evidence show that subduction started before ca. 1920 Ma ago, and lasted until ca. 1850 Ma when collision occurred, with consequent crustal thickening, high-grade metamorphism and local anatexis. Given the time-span for the operation of subduction, the existence of a wide Nagssugtoqidian ocean can be inferred, even for slow rates of plate motion. (orig./SHOE)

  5. Fusion of neutron rich oxygen isotopes in the crust of accreting neutron stars

    CERN Document Server

    Horowitz, C J; Berry, D K


    Fusion reactions in the crust of an accreting neutron star are an important source of heat, and the depth at which these reactions occur is important for determining the temperature profile of the star. Fusion reactions depend strongly on the nuclear charge $Z$. Nuclei with $Z\\le 6$ can fuse at low densities in a liquid ocean. However, nuclei with $Z=8$ or 10 may not burn until higher densities where the crust is solid and electron capture has made the nuclei neutron rich. We calculate the $S$ factor for fusion reactions of neutron rich nuclei including $^{24}$O + $^{24}$O and $^{28}$Ne + $^{28}$Ne. We use a simple barrier penetration model. The $S$ factor could be further enhanced by dynamical effects involving the neutron rich skin. This possible enhancement in $S$ should be studied in the laboratory with neutron rich radioactive beams. We model the structure of the crust with molecular dynamics simulations. We find that the crust of accreting neutron stars may contain micro-crystals or regions of phase sep...

  6. Crust-mantle contribution to Andean magmatism

    International Nuclear Information System (INIS)

    There has long been great interest in quantifying the contributions of the continental crust to continental arc magmas, such as those of the Andes using osmium isotopes (Alves et al., 1999; Borg et al., 2000; Brandon et al., 1996; McInnes et al., 1999). In general, Andean volcanic rocks of all compositions show relatively low Sr-isotope ratios and positive to mildly negative epsilon Nd values. Nonetheless, in the Southern Volcanic Zone of central Chile, basalt-andesite-dacite volcanoes along the Quaternary volcanic front were shown (by Hildreth and Moorbath, 1988) to have latitudinally systematic chemical variations, as well as a monotonic increase in 87Sr/Sr86 from ca. 0.7035 to 0.7055 and a decrease in epsilon Nd values from ca. +3 to -1. The isotopic variations correlate with basement elevation of the volcanic edifices and with Bouguer gravity anomalies, both of which are thought to reflect along-arc variations in thickness and average age of the underlying crust. Volcanoes with the most evolved isotopic signatures were fed through the thickest crust. Correlation of chemical and isotopic variations with crustal thickness was interpreted to be caused by Melting (of deep-crustal host rocks), Assimilation, Storage, and Homogenization (MASH) of mantle-derived magmas in long-lived lower-crustal reservoirs beneath each center prior to eruption. We have now determined Os-isotope ratios for a sample suite from these volcanoes (33-36 S lat.), representing a range of crustal thickness from ca. 60-35 km. The samples range in MgO from ca. 8-4% and in SiO2 from 51-57%. The most evolved eruptive products occur above the thickest crust and have 87Sr/86Sr ratios of 0.7054 and epsilon Nd values of -1.5. The 187Os/188Os ratios correlate with the other isotopic systems and with crustal thickness. Volcanoes on the thinnest crust have 187Os/188Os ratios of 0.18-0.21. Those on the thickest crust have 187Os/188Os ratios as high as 0.64. All the Os values are much too radiogenic to represent purely mantle-derived melts (nominally ca. 0.13). The Os-isotopic system mimics the variations recorded by the other isotopic systems but is significantly magnified, demonstrating its power for evaluating crustal contributions to arc-magma genesis. Mixing calculations suggest that the Os isotopic values of the Chilean samples represent mixing of mantle-derived magmas with 20% or more of material derived from mafic lower crust (au)

  7. Millennium Ecosystem Assessment: MA Scenarios (United States)

    National Aeronautics and Space Administration — The Millennium Ecosystem Assessment: MA Scenarios provide useful insight into the complex factors that drive ecosystem change, estimating the magnitude of regional...

  8. Stability of clathrate hydrates in Martian crust (United States)

    Gloesener, Elodie; Karatekin, Özgür; Dehant, Véronique


    Clathrate hydrates are crystalline compounds constituted by cages formed by hydrogen-bonded water molecules inside of which guest gas molecules are trapped. These materials are typically stable at high pressure and low temperature and are present on Earth mainly in marine sediments and in permafrost. Moreover, clathrate hydrates are expected to exist on celestial bodies like the icy moons Titan, Europa or Enceladus. Current conditions in the Martian crust are favourable to the presence of clathrate hydrates. In this study, we focused on the stability of methane and carbon dioxide clathrates in the Martian crust. We coupled the stability conditions of clathrates with a 1D thermal model in order to obtain the variations of the clathrate stability zone in the crust of Mars with time and for different crust compositions. Indeed, the type of soil directly controls the geothermal conditions and therefore the depth of clathrates formation. Unconsolidated soil acts as a thermal insulator and prevents the clathrates formation in the crust except on a small part of a few tens of meters thick. In contrast, sandstone or ice-cemented soil allows the clathrates formation with a stability zone of several kilometers. This is explained by the fact that they evacuate heat more efficiently and thus maintain lower temperatures. We also studied the stability zone of clathrates formed from a mixture of methane and hydrogen sulphide as well as from a mixture of methane and nitrogen. Contrary to the addition of N2, the addition of H2S to CH4 clathrates extends the stability zone and thus brings it closer to the surface. Therefore, mixed clathrates CH4-H2S will be more easily destabilized by changes in surface temperature than CH4 clathrates.

  9. Composition and genesis of zeolitic claystones from the central Indian Ocean Basin

    Digital Repository Service at National Institute of Oceanography (India)

    Iyer, S.D.; Sudhakar, M.; Das, P.

    More than fifty indurated sediments recovered from the Central Indian Ocean Basin (CIoB) are examined during the course of collection for manganese nodules and crusts. The samples occur as slabs either over which ferromanganese oxides are present...

  10. Tectonomagmatic setting and provenance of the Santa Marta Schists, northern Colombia: Insights on the growth and approach of Cretaceous Caribbean oceanic terranes to the South American continent (United States)

    Cardona, A.; Valencia, V.; Bustamante, C.; García-Casco, A.; Ojeda, G.; Ruiz, J.; Saldarriaga, M.; Weber, M.


    Metamorphosed volcano-sedimentary rocks accreted to the northern South American continental margin are major vestiges of the Caribbean oceanic plate evolution and its interactions with the continent. Selected whole rock geochemistry, Nd-Sr isotopes and detrital zircon geochronology were obtained in metabasic and metasedimentary rocks from the Santa Marta and San Lorenzo Schists in northernmost Colombia. Trace element patterns are characterized by primitive island arc and MORB signatures. Similarly initial 87Sr/ 86Sr-? Nd isotopic relations correlate with oceanic arcs and MORB reservoirs, suggesting that the protoliths were formed within a back-arc setting or at the transition between the inta-oceanic arc and the Caribbean oceanic crust. Trace element trends from associated metasedimentary rocks show that the provenance was controlled by a volcanic arc and a sialic continental domain, whereas detrital U/Pb zircons from the Santa Marta Schists and adjacent southeastern metamorphic units show Late Cretaceous and older Mesozoic, Late Paleozoic and Mesoproterozoic sources. Comparison with continental inland basins suggests that this arc-basin is allocthonous to its current position, and was still active by ca. 82 Ma. The geological features are comparable to other arc remnants found in northeastern Colombia and the Netherland Antilles. The geochemical and U/Pb detrital signatures from the metasedimentary rocks suggest that this tectonic domain was already in proximity to the continental margin, in a configuration similar to the modern Antilles or the Kermadec arc in the Pacific. The older continental detritus were derived from the ongoing Andean uplift feeding the intra-oceanic tectonic environment. Cross-cutting relations with granitoids and metamorphic ages suggest that metamorphism was completed by ca. 65 Ma.

  11. Crust and subduction zone structure of Southwestern Mexico (United States)

    Suhardja, Sandy Kurniawan; Grand, Stephen P.; Wilson, David; Guzman-Speziale, Marco; Gomez-Gonzalez, Juan Martin; Dominguez-Reyes, Tonatiuh; Ni, James


    Southwestern Mexico is a region of complex active tectonics with subduction of the young Rivera and Cocos plates to the south and widespread magmatism and rifting in the continental interior. Here we use receiver function analysis on data recorded by a 50 station temporary deployment of seismometers known as the MARS (MApping the Rivera Subduction zone) array to investigate crustal structure as well as the nature of the subduction interface near the coast. The array was deployed in the Mexican states of Jalisco, Colima, and Michoacan. Crustal thickness varies from 20 km near the coast to 42 km in the continental interior. The Rivera plate has steeper dip than the Cocos plate and is also deeper along the coast than previous estimates have shown. Inland, there is not a correlation between the thickness of the crust and topography indicating that the high topography in northern Jalisco and Michoacan is likely supported by buoyant mantle. High crustal Vp/Vs ratios (greater than 1.82) are found beneath the trenchward edge of magmatism including below the Central Jalisco Volcanic Lineament and the Michoacan-Guanajuato Volcanic Field implying a new arc is forming closer to the trench than the Trans Mexican Volcanic Belt. Elsewhere in the region, crustal Vp/Vs ratios are normal. The subducting Rivera and Cocos plates are marked by a dipping shear wave low-velocity layer. We estimate the thickness of the low-velocity layer to be 3 to 4 km with an unusually high Vp/Vs ratio of 2.0 to 2.1 and a drop in S velocity of 25%. We postulate that the low-velocity zone is the upper oceanic crust with high pore pressures. The low-velocity zone ends from 45 to 50 km depth and likely marks the basalt to eclogite transition.

  12. Accurate focal depth determination of oceanic earthquakes using water-column reverberation and some implications for the shrinking plate hypothesis (United States)

    Huang, Jianping; Niu, Fenglin; Gordon, Richard G.; Cui, Chao


    Investigation of oceanic earthquakes is useful for constraining the lateral and depth variations of the stress and strain-rate fields in oceanic lithosphere, and the thickness of the seismogenic layer as a function of lithosphere age, thereby providing us with critical insight into thermal and dynamic processes associated with the cooling and evolution of oceanic lithosphere. With the goal of estimating hypocentral depths more accurately, we observe clear water reverberations after the direct P wave on teleseismic records of oceanic earthquakes and develop a technique to estimate earthquake depths by using these reverberations. The Z-H grid search method allows the simultaneous determination of the sea floor depth (H) and earthquake depth (Z) with an uncertainty less than 1 km, which compares favorably with alternative approaches. We apply this method to two closely located earthquakes beneath the eastern Pacific. These earthquakes occurred in ?25 Ma-old lithosphere and were previously estimated to have similar depths of ?10-12 km. We find that the two events actually occurred at dissimilar depths of 2.5 km and 16.8 km beneath the seafloor, respectively, within the oceanic crust and lithospheric mantle. The shallow and deep events are determined to be a thrust and normal earthquake, respectively, indicating that the stress field within the oceanic lithosphere changes from horizontal deviatoric compression to horizontal deviatoric tension as depth increases, which is consistent with the prediction of lithospheric cooling models. Furthermore, we show that the P-axis of the newly investigated thrust-faulting earthquake is perpendicular to that of the previously studied thrust event, consistent with the predictions of the shrinking-plate hypothesis.

  13. Widespread, Miocene, Large-Magnitude Exhumation of the Pamir Deep Crust Driven by the India-Asia Collision (United States)

    Hacker, B. R.; Ratschbacher, L.; Stearns, M.; McGraw, J.; Stübner, K.; Kylander-Clark, A. R.; Pfander, J.; Weise, C.; Minaev, V.; Gadoev, M.; Oimahmadov, I.


    Thermobarometry, thermochronology, and structural geology provide insight into the formation and exhumation histories of the high-grade crustal domes across the Pamir. P-T histories were reconstructed from thermobarometry based on major elements and pseudosections. Intrusion, recrystallization, and cooling histories were determined by SIMS and LA-MC-ICP-MS U-Th-Pb zircon, monazite, titanite, and rutile; Rb-Sr mica; 40Ar/39Ar hornblende and mica; apatite fission-track, and (U-Th)/He apatite dating. For the northern Pamir Kurgovat dome we find peak conditions of 600-650 °C and 6.5-8.2 kbar. Hornblende and biotite 40Ar/39Ar ages indicate that this metamorphism is Jurassic and Early Cretaceous (ca. 200 and ca. 130 Ma), overprinting Devonian arc intrusions (350 Ma U-Pb zircon). The western central Pamir Yazgulom dome yields P-T conditions of 575 °C and 9.4 kbar; U-Pb zircon ages of 21-18 Ma from igneous rocks; a U-Pb titanite age of 19 Ma and 40Ar/39Ar biotite ages of 17-16 Ma tightly constrain an early Miocene exhumation. The eastern central Pamir Muskol-Sares dome yields hotter P-T conditions of 700-800 °C and 9.1-11.7 kbar; U-Pb zircon ages as young as 23-17 Ma, U-Pb titanite ages of ca. 17 Ma, 40Ar/39Ar hornblende ages of 22-15 Ma, and 40Ar/39Ar mica ages of 19-13 Ma indicate an essentially identical exhumation history. U-Pb zircon and titanite ages indicate a Triassic magmatic protolith, intruding Paleozoic meta-sedimentary strata. The enormous Shakhdara dome in the southwestern Pamir gives higher peak metamorphic conditions at 6.5-14.6 kbar and 700-800 °C. U-Pb zircon ages indicate ca. 1.8 and 2.5 Ga basement, strongly remobilized by 134-73 Ma Cretaceous magmatism. U-Pb metamorphic zircon ages of 22-12 Ma, U-Pb titanite ages of 18-10 Ma, Th-Pb metamorphic monazite ages of 30-18 Ma, U-Pb titanite ages of 18-10 Ma, 40Ar/39Ar biotite ages of 18-10 Ma, and apatite fission-track ages of 8-5 Ma imply early to late Miocene exhumation. These data, combined with those of earlier studies (e.g., Hubbard, 1989; Schwab et al., 2004; Robinson et al., 2007), indicate that the bulk of the Pamir high-grade crystalline rocks were exhumed from ~35 km depth, beginning in the central Pamir in the early Miocene and progressing north and south in the middle Miocene. If the crust of the Pamir prior to the India-Asia collision was <30 km thick and convergence within the Pamir was <600 km, shortening could have been accommodated by homogeneous plane-strain vertical thickening; each of the Pamir domes then represents a zone of unusually great exhumation compensated by a corresponding zone of less exhumation. Alternatively, if the pre-collisional crust was thicker or the amount of convergence was larger, vast amounts of crust must have been removed from the Pamir orogenic system by i) subhorizontal extrusion along the strike of the orogenic belt, ii) erosion, or-most likely-iii) recycling into the mantle.

  14. Regional anomalies of sediment thickness, basement depth and isostatic crustal thickness in the North Atlantic Ocean (United States)

    Louden, Keith E.; Tucholke, Brian E.; Oakey, Gordon N.


    We calculate the anomalous basement topography for the North Atlantic Ocean from 30° to 70°N latitude and from 0° to 70°W longitude at a resolution of roughly 6×6 km, using grids of total sediment thickness and observed and predicted sea-floor bathymetry to correct for the effects of isostatic sediment loading and lithospheric age. Plotting this residual topography for various plate reconstructions during opening of the North Atlantic, we delineate consistent patterns of basement highs related to variations in hotspot-related volcanism. In addition to Iceland and the Azores, we recognize three centers of excess volcanism at the mid-Atlantic ridge: the Milne Seamounts and Azores-Biscay Rise (˜75-40 Ma), the Southeast Newfoundland Ridge and Madeira-Tore Rise (˜130-110 Ma), and the East and West Thulean Rises (˜60-50 Ma). The duration of volcanic activity ranges from 8 to 10 m.y. (Thulean Rises) to 60 m.y. (Iceland) and thus it appears that both long- and short-lived hotspots coexist, even in relatively close proximity. In contrast, during the period 110-60 Ma we observe little excess volcanism during either continental breakup or seafloor spreading. We estimate isostatic crustal thickness from the anomalous basement depths, after first removing dynamic effects created by mantle flow. Maximum thicknesses of volcanic features, from 30 km beneath the Greenland-Iceland-Faeroe ridge to ˜15 km beneath the Azores-Biscay Rise, are broadly consistent with seismic data and predictions of decompression melting. Widths of volcanic features indicate that thickening primarily occurs within 100-200 km of hotspots except along continental margins that rifted at the time of the hotspot activity (i.e. East Greenland and the Hatton-Rockall Bank). We observe conjugate structures south of Greenland and Edoras Bank, where excess volcanism appears to have extended beyond the margin proper and into oceanic crust. Similar conjugate features appear in the Labrador Sea south of Davis Strait. Finally, we identify anomalous oceanic regions adjacent to some continental margins, where unusually low values of predicted crustal thickness suggest either additional variations in plate properties or non-isostatic effects within the mantle.

  15. Millennial-scale ocean acidification and late Quaternary

    Energy Technology Data Exchange (ETDEWEB)

    Riding, Dr Robert E [University of Tennessee (UT); Liang, Liyuan [ORNL; Braga, Dr Juan Carlos [Universidad de Granada, Departamento de Estratigraf?a y Paleontolog?a, Granada, Spain


    Ocean acidification by atmospheric carbon dioxide has increased almost continuously since the last glacial maximum (LGM), 21 000 years ago. It is expected to impair tropical reef development, but effects on reefs at the present day and in the recent past have proved difficult to evaluate. We present evidence that acidification has already significantly reduced the formation of calcified bacterial crusts in tropical reefs. Unlike major reef builders such as coralline algae and corals that more closely control their calcification, bacterial calcification is very sensitive to ambient changes in carbonate chemistry. Bacterial crusts in reef cavities have declined in thickness over the past 14 000 years with largest reduction occurring 12 000 10 000 years ago. We interpret this as an early effect of deglacial ocean acidification on reef calcification and infer that similar crusts were likely to have been thicker when seawater carbonate saturation was increased during earlier glacial intervals, and thinner during interglacials. These changes in crust thickness could have substantially affected reef development over glacial cycles, as rigid crusts significantly strengthen framework and their reduction would have increased the susceptibility of reefs to biological and physical erosion. Bacterial crust decline reveals previously unrecognized millennial-scale acidification effects on tropical reefs. This directs attention to the role of crusts in reef formation and the ability of bioinduced calcification to reflect changes in seawater chemistry. It also provides a long-term context for assessing anticipated anthropogenic effects.

  16. The fate of Ceres' original crust (United States)

    Roberts, James H.; Rivkin, Andrew S.


    The bulk density of Ceres implies that water ice comprises a substantial fraction of Ceres’ interior. However, water ice is not stable at Ceres orbital distance and if exposed would have a loss rate of 1 km Myr-1 or more. The near-hydrostatic shape of Ceres, and relatively low melting point of ice suggests that the interior is at least partly differentiated. Because Ceres’ surface remains exposed to space, it radiates very effectively, and models predicting differentiation retain an undifferentiated crust. This would be denser than the ice shell beneath it resulting in an unstable stratification. This has led to expectations that the crust would founder and the surface of Ceres might be very smooth and relaxed. But could the crust have remained to the present day?Here, we model global-scale overturn on Ceres using both analytical two-layer linear stability analyses, and numerical models to predict the most unstable wavelength, and growth timescales for Rayleigh-Taylor instabilities. We find that for a 10 km-thick crust above a 75 km-thick ice layer, instabilities grow fastest at spherical harmonic degree l=4. The growth timescale is a function of the viscosity of the upper layer. This timescale is less than the age of the solar system unless the effective viscosity of the crust is > 1024 Pa s. We conclude that the crust of Ceres could remain at the surface if it either has some finite elastic strength over a ~800 km length scale, or is an unconsolidated regolith with a large, (> 50%) macro-porosity, such that the regolith is buoyant relative to water ice.Neither end-member for the crustal strength precludes convective activity in the underlying ice layer. However we note that a thick, porous regolith is a fantastic insulator and may promote heating of the interior and potential foundering of the regolith if the top of the ice becomes too warm. This possibility can be evaluated by models of thermal evolution (e.g., Castillo-Rogez et al., 2010). An episode of global overturn may have been preserved as spatially correlated long-wavelength (l=3-5) variations in albedo, composition, and topography, which could be measured by Dawn.

  17. Melt evolution and residence in extending crust: Thermal modeling of the crust and crustal magmas (United States)

    Karakas, Ozge; Dufek, Josef


    Tectonic extension and magmatism often act in concert to modify the thermal, mechanical, and chemical structure of the crust. Quantifying the effects of extension and magma flux on melting relationships in the crust is fundamental to determining the rate of crustal melting versus fractionation, magma residence time, and the growth of continental crust in rift environments. In order to understand the coupled control of tectonic extension and magma emplacement on crustal thermal evolution, we develop a numerical model that accounts for extension and thermal-petrographic processes in diverse extensional settings. We show that magma flux exerts the primary control on melt generation and tectonic extension amplifies the volume of melt residing in the crustal column. Diking into an extending crust produces hybrid magmas composed of 1) residual melt remaining after partial crystallization of basalt (mantle-derived melt) and 2) melt from partial melting of the crust (crustal melt). In an extending crust, mantle-derived melts are more prevalent than crustal melts across a range of magma fluxes, tectonic extension rates, and magmatic water contents. In most of the conditions, crustal temperatures do not reach their solidus temperatures to initiate partial melting of these igneous lithologies. Energy balance calculations show that the total enthalpy transported by dikes is primarily used for increasing the sensible heat of the cold surrounding crust with little energy contributing to latent heat of melting the crust (maximum crustal melting efficiency is 6%). In the lower crust, an extensive mush region develops for most of the conditions. Upper crustal crystalline mush is produced by continuous emplacement of magma with geologically reasonable flux and extension rates on timescales of 106 yr. Addition of tectonic effects and non-linear melt fraction relationships demonstrates that the magma flux required to sustain partially molten regions in the upper crust is within the range of estimates of magmatic flux in many rifting regions (?10-4 to 10-3km3 /yr) and at least an order of magnitude lower than previous modeling estimates. Our results demonstrate the importance of tectonics in augmenting melt production, composition, and crustal evolution in active magmatic systems.

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

    International Nuclear Information System (INIS)

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

  19. Outer crust of nonaccreting cold neutron stars (United States)

    Rüster, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Jürgen


    The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.

  20. Towards a metallurgy of neutron star crusts

    CERN Document Server

    Kobyakov, D


    In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic (bcc) lattice of nuclei immersed in an essentially uniform electron gas. We show that at densities above that for neutron drip ($\\sim4\\times10^11$) g cm$^{-3}$ or roughly one thousandth of nuclear matter density, the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as BaTiO$_3$. As a consequence, properties of matter in the inner crust are expected to be much richer than previously appreciated and we mention consequences for observable neutron star properties.

  1. Seismic Structure of Eastern Anatolia Crust

    International Nuclear Information System (INIS)

    Regional crustal structure, which is mainly, affected by the collision of the Eurasian and the Arabian Plates beneath Eastern Anatolia plateau has been investigated using seismological data. P-wave first arrivals and P-S waveforms of the earthquakes recorded by ETSE (1999-2001) and KOERI (Kandilli) stations were simulated. The crust has an average depth of 38 - 42 km and low velocity zones due to the partially melting were modeled

  2. Breaking stress of neutron star crust


    Chugunov, A. I.; Horowitz, C. J.


    The breaking stress (the maximum of the stress-strain curve) of neutron star crust is important for neutron star physics including pulsar glitches, emission of gravitational waves from static mountains, and flares from star quakes. We perform many molecular dynamic simulations of the breaking stress at different coupling parameters (inverse temperatures) and strain rates. We describe our results with the Zhurkov model of strength. We apply this model to estimate the breaking...

  3. Evolution of the long-wavelength, subduction-driven topography of South America since 150 Ma (United States)

    Flament, N. E.; Gurnis, M.; Williams, S.; Bower, D. J.; Seton, M.; Müller, D.


    Subduction to the west of South America spans 6000 km along strike and has been active for over 250 Myr. The influence of the history of subduction on the geodynamics of South America has been profound, driving mountain building and arc volcanism in the Andean Cordillera. Here, we investigate the long-wavelength changes in the topography of South America associated with subduction and plate motion and their interplay with the lithospheric deformation associated with the opening of the South Atlantic. We pay particular attention to the topographic expression of flat-lying subduction zones. We develop time-dependent geodynamic models of mantle flow and lithosphere deformation to investigate the evolution of South American dynamic and total topography since the late Jurassic (150 Ma). Our models are semi-empirical because the computational cost of fully dynamic, evolutionary models is still prohibitive. We impose the kinematics of global plate reconstructions with deforming continents in forward global mantle convection models with compositionally distinct crust and continental lithosphere embedded within the thermal lithosphere. The shallow thermal structure of subducting slabs is imposed, allowing us to investigate the evolution of dynamic topography around flat slab segments in time-dependent models. Multiple cases are used to investigate how the evolution of South American dynamic topography is influenced by mantle viscosity, the kinematics of the opening of the South Atlantic and alternative scenarios for recent and past flat-slab subduction. We predict that the migration of South America over sinking oceanic lithosphere resulted in continental tilt to the west until ~ 45 Ma, inverting to an eastward tilt thereafter. This first-order result is consistent with the reversal of the drainage of the Amazon River system. We investigate which scenarios of flat-slab subduction since the Eocene are compatible with geological constraints on the evolution of the Solimoes Basin, the Chaco Basin, the Sierras Pampeanas and the Central Patagonian Basin. To broadly constrain mantle viscosity, we compare models to the total subsidence inferred from well data offshore Argentina and Brazil, and to mantle tomography, since the initial and boundary conditions are based on independent plate reconstructions.

  4. The morphostructure of the atlantic ocean floor its development in the meso-cenozoic

    CERN Document Server

    Litvin, V M


    The study of the topography and structure of the ocean floor is one of the most important stages in ascertaining the geological structure and history of development of the Earth's oceanic crust. This, in its turn, provides a means for purposeful, scientifically-substantiated prospecting, exploration and development of the mineral resources of the ocean. The Atlantic Ocean has been geologically and geophysically studied to a great extent and many years of investigating its floor have revealed the laws governing the structure of the major forms of its submarine relief (e. g. , the continental shelf, the continental slope, the transition zones, the ocean bed, and the Mid-Oceanic Ridge). The basic features of the Earth's oceanic crust structure, anomalous geophysical fields, and the thickness and structure of its sedimentary cover have also been studied. Based on the investigations of the Atlantic Ocean floor and its surrounding continents, the presently prevalent concept of new global tectonics has appeared. A g...

  5. Syn-volcanic cannibalisation of juvenile felsic crust: Superimposed giant 18O-depleted rhyolite systems in the hot and thinned crust of Mesoproterozoic central Australia (United States)

    Smithies, R. H.; Kirkland, C. L.; Cliff, J. B.; Howard, H. M.; Quentin de Gromard, R.


    Eruptions of voluminous 18O-depleted rhyolite provide the best evidence that the extreme conditions required to produce and accumulate huge volumes of felsic magma can occur in the upper 10 km of the crust. Mesoproterozoic bimodal volcanic sequences from the Talbot Sub-basin in central Australia contain possibly the world's most voluminous accumulation of 18O-depleted rhyolite. This volcanic system differs from the better known, but geochemically similar, Miocene Snake River Plain - Yellowstone Plateau of North America. Both systems witnessed 'super' sized eruptions from shallow crustal chambers, and produced 18O-depleted rhyolite. The Talbot system, however, accumulated over a much longer period (>30 Ma), at a single depositional centre, and from a magma with mantle-like isotopic compositions that contrast strongly with the isotopically evolved basement and country-rock compositions. Nevertheless, although the Talbot rhyolites are exclusively 18O-depleted, the unavoidable inference of an 18O-undepleted precursor requires high-temperature rejuvenation of crust in an upper-crustal chamber, and in this respect the evolution of the Talbot rhyolites and 18O-depleted rhyolites of the Snake River Plain - Yellowstone Plateau is very similar. However, instead of older crustal material, the primary upper-crustal source recycled into Talbot rhyolites was comagmatic (or nearly so) felsic rock itself derived from a contemporaneous juvenile basement hot-zone. Whereas giant low ?18O volcanic systems show that voluminous melting of upper crust can occur, our studies indicate that felsic magmas generated at lower crustal depths can also contribute significantly to the thermal and material budget of these systems. The requirement that very high-temperatures be achieved and sustained in the upper crust means that voluminous low ?18O magmatism is rare, primarily restricted to bimodal tholeiitic, high-K rhyolite (A-type) magmatic associations in highly attenuated lithosphere. In the case of the Talbot system, at least, our data suggest that an unusually hot pre-history might also be required to thermally prime the crust.

  6. Reconciling evidence for Tethyan intra-oceanic subduction and a two-stage collision between India and Eurasia (United States)

    Gibbons, Ana D.; Zahirovic, Sabin; Dietmar Müller, R.; Whittaker, Joanne M.; Yatheesh, Vadakkeyakath


    We present a plate tectonic model for the India-Eurasia collision that includes a time-dependent network of evolving plate boundaries with synthetic plates constructed for now-subducted Tethyan ocean floor, including back-arc basins that formed on the southern Eurasian margin. Southern Eurasia and Southeast Asia are riddled with dismembered oceanic arcs indicating long-lived intra-oceanic subduction. This intra-oceanic subduction may have extended further west into the India-Eurasia convergence zone in the NeoTethys, which was consumed during Greater India's northward trajectory towards Eurasia from the Early Cretaceous. Fragments of obducted oceanic crust within the Himalayan Yarlung-Tsangpo Suture Zone, between India and Eurasia, cluster around two age groups, the Late Jurassic and mid Cretaceous (Barremian-Aptian). The adakitic, boninitic and MORB-affinities of the various ophiolites along strike suggest that there was at least one generation of intra-oceanic subduction, whose plate boundary configuration remains uncertain, though it is best preserved in the Kohistan-Ladakh Arc. Paleomagnetic and magmatic characterisation studies from the ophiolites suggest that the intra-oceanic arc was as far south as the equator during the Early Cretaceous before subduction resumed further north beneath the southern Eurasian margin (Lhasa terrane) to consume the back-arc basin. During ~80-65 Ma, a hiatus in subduction-related magmatism along the southern Lhasa terrane may indicate the approach of the back-arc spreading centre towards the active Andean-style margin. We incorporate these observations into a regional, self-consistent plate tectonic model for the dispersal of East Gondwana, simultaneously considering geophysical data and seafloor spreading histories from abyssal plains offshore West Australia and East Antarctica, including Jurassic seafloor age data from offshore NW Australia that limits northern Greater India to a maximum of ~1000 km. This Greater India collided with the Tethyan intra-oceanic arc, including the Kohistan and Ladakh arcs, from the Mid Paleocene. Greater India's leading edge, bearing the intra-oceanic arc, finally closed the Tethyan seaway with progressive suturing to Eurasia from the Mid-Late Eocene, which coincides with the age of the youngest marine deposits found between India and Eurasia. Our model of mid-ocean ridge and subduction zone geometries, locations and divergence/convergence vectors through time can be represented as a time-dependent plate velocity mesh and is testable by combining coupled plate-mantle simulations with mantle seismic tomography. The model also provides a basis for future modifications in order to assimilate new data and test alternative tectonic scenarios.

  7. High Tech High interns develop a mid-ocean ridge database for research and education (United States)

    Staudigel, D.; Delaney, R.; Staudigel, H.; Koppers, A.; Miller, S.


    Mid-ocean ridges (MOR) represent one of the most important geographic features on planet Earth. MORs are the locations where plates spread apart, they are the locations of most of the earths' volcanoes that harbor some of the most extreme life forms. These concepts attract much research, but mid-ocean ridges are still effectively not represented in the earth science class rooms. We began an internship at Scripps to develop a database for mid-ocean ridges as a resource for science and for education. Major research goals of this project include the development of an archival structure for data, images or any other arbitrary digital objects relating to MORs, and to compile a global data set for some of the most defining characteristics of every ridge segment. One of the challenges included the need of making MOR data useful to the scientist as well as the teacher in the class room. While this data base remains a long term project, we completed a series of first order steps that establish an archival structure and lay out the defining information for each ridge segment. To create this database we used existing maps of the age of the ocean floor (University of Sidney) and the MOR locations from the University of Texas database. We divided the global MOR system into segments through their end-point coordinates, using the mid-point lat/lon as a generic name and we digitized the area of the 11 Ma isochron. Each ridge segment was also characterized with the ocean it is in, and the names of the plates. This allowed us to create a database structure for MOR segments, similar to the seamount catalogue ( The data compiled allow us to determine the length of the ridges, spreading rates, the ocean crust production rates, and plate motion vectors for every ridge segment, ocean or the global ocean ridge system. The process of creating this data base introduced us to the excitement of MOR research, allowing us to create a resource that is equally useful for researchers as well as the members of the educational community.

  8. Melting in the Hawaiian plume at 1-2 Ma as recorded at Maui Nui: The role of eclogite, peridotite, and source mixing (United States)

    Gaffney, Amy M.; Nelson, Bruce K.; Blichert-Toft, Janne


    The volcanoes of Maui Nui (West Moloka'i, East Moloka'i, Lana'i, West Maui, Haleakala, and Kaho'olawe) record Hawaiian magmatism at ˜1-2 Ma. Lavas from these volcanoes nearly span the compositional range erupted from all the Hawaiian volcanoes over the past 5 Myr and represent both the Kea and Ko'olau compositional end-members of Hawaiian lavas. Many aspects of major and trace element and isotope compositions of Hawaiian shield-stage lavas are consistent with ancient, recycled oceanic lithosphere in the plume sources of Kea- and Ko'olau-type magmas (Lassiter and Hauri, 1998; Blichert-Toft et al., 1999). Hypotheses that describe the compositional range of Hawaiian lavas as originating from ancient oceanic lithosphere in the Hawaiian plume implicitly or explicitly infer lithologic heterogeneity in the plume. We present trace element models for the origin of these end-members that explicitly address the petrologic complexities of melting eclogite (derived from ancient oceanic lithosphere) in the plume. Trace element (La/Nb, Sm/Yb, Sm/Hf, and Sm/Nb), major element, and isotope compositions of Lana'i, which erupts dominantly Ko'olau-type lavas, are consistent with the origin of these lavas in large-degree (˜60-70%) melts of ancient upper oceanic crust (basalt + sediment) that mix with plume-derived Haleakala-type melts. Trace element (Sm/Yb, Hf/Zr, and Hf/Nb) and isotope compositions of West Maui and East Moloka'i, which erupt dominantly Kea-type magmas, are consistent with an origin in ancient depleted oceanic lithosphere that has been refertilized with moderate-degree melts (10-30%) of associated crustal gabbro. The physical mechanisms (melt-melt versus melt-solid mixing) through which the oceanic crustal components melt and mix within the plume lead to the generation of isotopically homogeneous Kea-type lavas and isotopically heterogeneous Ko'olau-type lavas. The volcanoes of Maui Nui record the exhaustion of the Ko'olau component and the initiation of the Kea component as dominant compositional end-members in the Hawaiian plume.

  9. Nature of the crust in the Laxmi Basin (14°-20°N), western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.; Rao, D.G.; Sar, D.

    observed west of the Laxmi Ridge (Figures 2 and 6) are not associated with basement structures. The velocity-depth results obtained from seismic refraction experiments of Laxmi Ridge, Laxmi Basin, Western Basin, Seychelles Bank and Indian continental... combined (Figure 10) with a view to compare the Laxmi Basin velocity structure with that of known oceanic (Western Basin) and continental (Seychelles Bank, Laxmi Ridge and Indian subcontinent) crust. No refraction signals have been received from Moho...

  10. Millennium Ecosystem Assessment: MA Population (United States)

    National Aeronautics and Space Administration — The Millennium Ecosystem Assessment: MA Population data sets provide baseline population information as one of the drivers of ecosystem change. The data helped in...

  11. “Imaging” the cross section of oceanic lithosphere: The development and future of electrical microresistivity logging through scientific ocean drilling (United States)

    Tominaga, Masako


    A detailed understanding of the architecture of volcanic and magmatic lithologies present within the oceanic lithosphere is essential to advance our knowledge of the geodynamics of spreading ridges and subduction zones. Undertaking sub-meter scale observations of oceanic lithosphere is challenging, primarily because of the difficulty in direct continuous sampling (e.g., by scientific ocean drilling) and the limited resolution of the majority of geophysical remote sensing methods. Downhole logging data from drillholes through basement formations, when integrated with recovered core and geophysical remote sensing data, can provide new insights into crustal accretion processes, lithosphere hydrogeology and associated alteration processes, and variations in the physical properties of the oceanic lithosphere over time. Here, we introduce an alternative approach to determine the formation architecture and lithofacies of the oceanic sub-basement by using logging data, particularly utilizing downhole microresistivity imagery (e.g. Formation MicroScanner (FMS) imagery), which has the potential to become a key tool in deciphering the high-resolution internal architecture of the intact upper ocean crust. A novel ocean crust lithostratigraphy model based on meticulously deciphered lava morphology determined by in situ FMS electrofacies analysis of holes drilled during Ocean Drilling Program legs (1) advances our understanding of ocean crust formation and accretionary processes over both time and space; and (2) allows the linking of local igneous histories deciphered from the drillholes to the regional magmatic and tectonic histories. Furthermore, microresistivity imagery can potentially allow the investigation of (i) magmatic lithology and architecture in the lower ocean crust and upper mantle; and, (ii) void space abundances in crustal material and the determination of complex lithology-dependent void geometries.

  12. The feasibility of MA transmutation in CEFR

    International Nuclear Information System (INIS)

    The feasibility of MA transmutation in CEFR (China Experimental Fast Reactor) is described. The nuclear characteristics of reference core and those of MA-loaded core are compared, the MA-transmutation amount is presented. Although the amount of MA transmutation in CEFR is limited, CEFR still has a significant role in MA fuel irradiation tests and MA transmutation technique studies. (author). 6 refs, 1 fig., 3 tabs

  13. Tectonic evolution of the Perth Abyssal Plain's Quiet Zone, Southeast Indian Ocean (United States)

    Ehrlich, Zohar Louis; Granot, Roi; Williams, Simon E.


    During the Late Jurassic period, the Greater-Indian plate was torn away from Australia, dissociating East Gondwanaland. The Perth Abyssal Plain (PAP) is the southernmost rift segment along the western Australian margin, and has an onset age of ~136 Ma. New marine magnetic and swath bathymetry data, crossing the entire PAP, were acquired recently on geophysical cruise ss2011v06 aboard the R/V Southern Surveyor. These have lead to the outline of conjugate Indian and Australian M-series isochrons in the east and west PAP, respectively [1]. Yet, most of the PAP was created during the Cretaceous Normal Superchron (CNS, 121-83 Ma), a period of no geomagnetic field reversals, hence no comprehensive tectonic model for the PAP exists . Here we present preliminary findings of an analytic bathymetric and magnetic investigation aimed at elucidating the PAP's quiet zone. Recent discoveries regarding the evolution of the geomagnetic field during the CNS [2] provide new time markers that can be utilized to date the oceanic crust. The magnetic anomaly data exhibit the Q2 anomaly marker (~108 Ma), further constraining the spreading history of the PAP. Together with the ridgelet transform method [3] for automated abyssal hill delineation, we present new constraints on the development of crustal construction processes (spreading location, direction and rates) that took place along the PAP spreading center. References: [1] S.E. Williams, J.M. Whittaker, R. Granot, R.D. Muller (in preparation), New constraints on the seafloor spreading history in the Perth Abyssal Plain. [2] Granot, R., J. Dyment, and Y. Gallet (2012), Geomagnetic field variability during the Cretaceous Normal Superchron, Nature Geoscience, 5(3), 220-223. [3] Downey, N. J. and R. W. Clayton (2007), A ridgelet transform method for constraining tectonic models via abyssal-hill morphology, Geochemistry Geophysics Geosystems, 8, Q03004, doi: 10.1029/2006GC001440.

  14. Kinetics of the crust thickness development of bread during baking. (United States)

    Soleimani Pour-Damanab, Alireza; Jafary, A; Rafiee, Sh


    The development of crust thickness of bread during baking is an important aspect of bread quality and shelf-life. Computer vision system was used for measuring the crust thickness via colorimetric properties of bread surface during baking process. Crust thickness had a negative and positive relationship with Lightness (L (*) ) and total color change (E (*) ) of bread surface, respectively. A linear negative trend was found between crust thickness and moisture ratio of bread samples. A simple mathematical model was proposed to predict the development of crust thickness of bread during baking, where the crust thickness was depended on moisture ratio that was described by the Page moisture losing model. The independent variables of the model were baking conditions, i.e. oven temperature and air velocity, and baking time. Consequently, the proposed model had well prediction ability, as the mean absolute estimation error of the model was 7.93 %. PMID:26396343

  15. Mineral chemistry and density of subducted basaltic crust at lower-mantle pressures (United States)

    Kesson, S. E.; Fitz Gerald, J. D.; Shelley, J. M. G.


    SUBDUCTED slabs are less dense than the surrounding mantle near the base of the transition zone (˜660 km depth) because of the survival of garnet in former basaltic crust: by this depth mantle peridotite has transformed to denser perovskitite1'2. The buoyancy of the former basaltic crust may contribute to the observed accu-mulation or horizontal displacement of many slabs at the base of the transition zone3. Here we report experimental confirmation of the widely held belief that the basaltic crust of slabs eventually transforms to a dense perovskititic lithology, stable in the lower mantle. Synthetic mid-ocean-ridge basalt (MORE) glass subjected to pressures of 45, 80 and 100 GPa in a laser-heated diamond anvil cell transforms to an assemblage of aluminous Mg,Fe silicate perovskite, non-quenchable CaSiO3 perovskite, stishovite and a sodic, aluminous phase with the Ca-ferrite structure (Fig. 1). Per-ovskititic MORE is about 0.06 g cm-3 more dense than a model lower mantle (PREM) derived from seismological data. Thus even thermally equilibrated perovskititic slabs should encounter no sig-nificant hindrance to subduction and convection in the lower mantle.

  16. Crust formation and its effect on the molten pool coolability

    Energy Technology Data Exchange (ETDEWEB)

    Park, R.J.; Lee, S.J.; Sim, S.K. [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)


    Experimental and analytical studies of the crust formation and its effect on the molten pool coolability have been performed to examine the crust formation process as a function of boundary temperatures as well as to investigate heat transfer characteristics between molten pool and overlying water in order to evaluate coolability of the molten pool. The experimental test results have shown that the surface temperature of the bottom plate is a dominant parameter in the crust formation process of the molten pool. It is also found that the crust thickness of the case with direct coolant injection into the molten pool is greater than that of the case with a heat exchanger. Increasing mass flow rate of direct coolant injection to the molten pool does not affect the temperature of molten pool after the crust has been formed in the molten pool because the crust behaves as a thermal barrier. The Nusselt number between the molten pool and the coolant of the case with no crust formation is greater than that of the case with crust formation. The results of FLOW-3D analyses have shown that the temperature distribution contributes to the crust formation process due to Rayleigh-Benard natural convection flow.

  17. Thinning and flow of Tibetan crust constrained by seismic anisotropy. (United States)

    Shapiro, Nikolai M; Ritzwoller, Michael H; Molnar, Peter; Levin, Vadim


    Intermediate-period Rayleigh and Love waves propagating across Tibet indicate marked radial anisotropy within the middle-to-lower crust, consistent with a thinning of the middle crust by about 30%. The anisotropy is largest in the western part of the plateau, where moment tensors of earthquakes indicate active crustal thinning. The preferred orientation of mica crystals resulting from the crustal thinning can account for the observed anisotropy. The middle-to-lower crust of Tibet appears to have thinned more than the upper crust, consistent with deformation of a mechanically weak layer that flows as if confined to a channel. PMID:15247475

  18. Crusted Scabies in the Burned Patient

    DEFF Research Database (Denmark)

    Berg, Jais Oliver; AlsbjØrn, Bjarne


    The objectives of this study were 1) to describe a case of crusted scabies (CS) in a burned patient, which was primarily undiagnosed and led to a nosocomial outbreak in the burn unit; 2) to analyze and discuss the difficulties in diagnosing and treating this subset of patients with burn injury; and 3) to design a treatment strategy for future patients. Case analysis and literature review were performed. The index patient had undiagnosed crusted scabies (sive Scabies norvegica) with the ensuing mite hyperinfestation when admitted to the department with minor acute dermal burns. Conservative healing and autograft healing were impaired because of the condition. Successful treatment of the burns was only accomplished secondarily to scabicide treatment. An outbreak of scabies among staff members indirectly led to diagnosis. CS is ubiquitous, and diagnosis may be difficult. This is the first report of a burned patient with CS in the English language literature. CS is also highly contagious and may lead to a nosocomial outbreak. Furthermore, CS seems to have a detrimental impact on the burned patient's course of treatment. A scabicide treatment is necessary to guarantee successful treatment of the burns.

  19. The Early?Middle Palaeozoic Oceanic Events Along the Southern European Margin: The Deli Jovan Ophiolite Massif (NE Serbia) and Palaeo-oceanic Zones of the Great Caucasus




    The paper deals with the Middle Palaeozoic oceanic events on the northern margin of the Eastern Mediterranean Hercynides. The Balkan-Carpathian Ophiolite Belt (BCO) and palaeo-oceanic zones of the Great Caucasus, all framing the East European Platform from the south, are correlated. The BCO palaeo-oceanic complex was widely thought to be a Late Precambrian-earliest Cambrian oceanic thrust sheet (563±5 Ma), a part of the South European Palaeo-oceanic Suture. The geochronological studies carrie...

  20. The Neoproterozoic Malani magmatism of the northwestern Indian shield: Implications for crust-building processes

    Indian Academy of Sciences (India)

    Kamal K Sharma


    Malani is the largest event of anorogenic felsic magmatism (covering ?50,000km2) in India. This magmatic activity took place at ?750Ma post-dating the Erinpura granite (850 Ma) and ended prior to Marwar Supergroup (680 Ma) sedimentation. Malani eruptions occurred mostly on land, but locally sub-aqueous conditions are shown by the presence of conglomerate, grits and pillow lava. The Malani rocks do not show any type of regional deformation effects. The Malanis are characterised by bimodal volcanism with a dominant felsic component, followed by granitic plutonism and a terminal dyke phase. An angular unconformity between Malani lavas and basement is observed, with the presence of conglomerate at Sindreth, Diri, and Kankani. This indicates that the crust was quite stable and peneplained prior to the Malani activity. Similarly, the absence of any thrust zone, tectonic m´elange and tectonised contact of the Malanis with the basement goes against a plate subduction setting for their genesis. After the closure of orogenic cycles in the Aravalli craton of the northwestern shield, this anorogenic intraplate magmatic activity took place in a cratonic rift setting under an extensional tectonic regime.

  1. Sensitivity of climate and atmospheric CO2 to deep-ocean and shallow-ocean carbonate burial (United States)

    Volk, Tyler


    A model of the carbonate-silicate geochemical cycle is presented that distinguishes carbonate masses produced by shallow-ocean and deep-ocean carbonate burial and shows that reasonable increases in deep-ocean burial could produce substantial warmings over a few hundred million years. The model includes exchanges between crust and mantle; transients from burial shifts are found to be sensitive to the fraction of nondegassed carbonates subducted into the mantle. Without the habitation of the open ocean by plankton such as foraminifera and coccolithophores, today's climate would be substantially colder.

  2. Late Cretaceous (ca. 90 Ma) adakitic intrusive rocks in the Kelu area, Gangdese Belt (southern Tibet): Slab melting and implications for Cu-Au mineralization (United States)

    Jiang, Zi-Qi; Wang, Qiang; Li, Zheng-Xiang; Wyman, Derek A.; Tang, Gong-Jian; Jia, Xiao-Hui; Yang, Yue-Heng


    The Gangdese Belt in southern Tibet (GBST) is a major Cu-Au-Mo mineralization zone that mostly formed after the India-Asia collision in association with the small-volume, though widespread, Miocene (18-10 Ma) adakitic porphyries. Cu-Au mineralization has scarcely been found in the regional Jurassic-Early Tertiary batholiths related to subduction of the Neo-Tethyan oceanic plate. Here, we report petrological, zircon geochronological and geochemical data for Late Cretaceous (˜90 Ma) intrusive rocks that contain Cu-Au mineralization from the Kelu area in the GBST. These rocks consist of quartz monzonites and diorites. The quartz monzonites, with SiO2 of 58-59 wt.% and Na2O/K2O of 1.1-1.2, are geochemically similar to slab-derived adakites characterized by apparent depletions in heavy rare earth elements (e.g., Yb = 1.4-1.5 ppm) and Y (16-18 ppm) contents, positive Sr but negative Nb and Ti anomalies on multi-element variation diagrams. They have relatively low (87Sr/86Sr)i (0.7038-0.7039) ratios and high ?Nd(t) (+3.4 to +3.9) and in situ zircon ?Hf(t) (+9.3 to +15.8) values. The diorites exhibit high Mg-numbers (0.57-0.61) similar to those of magnesian andesites, and have (87Sr/86Sr)i (0.7040-0.7041) and ?Nd(t) (+3.0 to +4.4) values similar to those of the quartz monzonites. We suggest that the quartz monzonitic magmas were most likely generated by partial melting of the subducted Neo-Tethyan basaltic oceanic crust and minor associated oceanic sediments, with subsequent melt-mantle interaction, and the dioritic magmas were mainly derived by the interaction between slab melts and mantle wedge peridotites, with fractionation of apatite and hornblende. These slab-derived adakitic magmas have high oxygen fugacity that may have facilitated Cu-Au mineralization. The close association of the Late Cretaceous adakitic intrusive rocks and Cu-Au mineralization in the Kelu area suggests that the arc magmatic rocks in the GBST may have higher potential than previously thought for Cu-Au mineralization.

  3. Lunar Magma Ocean Crystallization: Constraints from Fractional Crystallization Experiments (United States)

    Rapp, J. F.; Draper, D. S.


    The currently accepted paradigm of lunar formation is that of accretion from the ejecta of a giant impact, followed by crystallization of a global scale magma ocean. This model accounts for the formation of the anorthosite highlands crust, which is globally distributed and old, and the formation of the younger mare basalts which are derived from a source region that has experienced plagioclase extraction. Several attempts at modelling the crystallization of such a lunar magma ocean (LMO) have been made, but our ever-increasing knowledge of the lunar samples and surface have raised as many questions as these models have answered. Geodynamic models of lunar accretion suggest that shortly following accretion the bulk of the lunar mass was hot, likely at least above the solidus]. Models of LMO crystallization that assume a deep magma ocean are therefore geodynamically favorable, but they have been difficult to reconcile with a thick plagioclase-rich crust. A refractory element enriched bulk composition, a shallow magma ocean, or a combination of the two have been suggested as a way to produce enough plagioclase to account for the assumed thickness of the crust. Recently however, geophysical data from the GRAIL mission have indicated that the lunar anorthositic crust is not as thick as was initially estimated, which allows for both a deeper magma ocean and a bulk composition more similar to the terrestrial upper mantle. We report on experimental simulations of the fractional crystallization of a deep (approximately 100km) LMO with a terrestrial upper mantle-like (LPUM) bulk composition. Our experimental results will help to define the composition of the lunar crust and mantle cumulates, and allow us to consider important questions such as source regions of the mare basalts and Mg-suite, the role of mantle overturn after magma ocean crystallization and the nature of KREEP

  4. Provenance And Tectonomagmatic Setting Of The Santa Marta Schists, Northern Colombia Caribbean Region: Insights On The Styles Of Growth And Approach Of Caribbean Intra- Oceanic Domains To The Continental Margin (United States)

    Cardona, A.; Jaramillo, C.; Ojeda, G.; Ruiz, J.; Valencia, V.; Weber, M.


    The life cycle of an intra-oceanic terranemincludes different phases and styles of magmatic growth, accretion with other terranes and translation before reaching a continental margin. In order to unveil the nature of these phases in crystalline rocks from northern Colombia, U/Pb LA-MC-ICP-MS detrital geochronology and whole rock geochemical data were obtained from stacks of intercalated metavolcanic-sedimentary rocks of the Santa Marta Schists in the Sierra Nevada de Santa Marta. Immobile elements whole rock geochemistry from greenschist to amphibolite facies units are characterized by low to moderate LREE/HREE, variable Th enrichment and weakly negative Nb and Ti anomalies, which are similar to island arc and MORB signatures. The intercalated metasedimentary rocks show a REE pattern similar to the PAAS and high Zr/Sc vs Th/Sc ratios, which suggest a felsic and highly diferentiated upper crust sources for the protoliths. Detrital zircons from three different units were obtained, The maximum depositional age for the northwestern unit is limited to the late Cretaceous, with a major peak of 83 Ma. Variable input of older crustal sources with Jurassic (153 Ma), Permo-Triassic (250-290 Ma), Cambrian to Late Neoproterozoic (520-560 Ma) and Middle Mesoproterozic (1000-1500 Ma) ages which are clearly recognized in older units of the Sierra Nevada de Santa Marta massif and the northern South American basement are also recorded. This type of volcano-sedimentary record within an intra-oceanic arc bears strong similarities with the modern Lesser-Antilles and the Tonga-Kermadec arcs, where continentally derived sediments can be transported houndred of kilometers to the fore-arc, back-arc or the accretionary prism of the active intra-oceanic arc. This record also suggests that this arc has an intra-Americas position, near to its final accretionary stop. Although the metamorphic overprint has obliterated the stratigraphic relations, apparent variations of the LREE/HREE in the metavolcanics and the preservation of continentally derived sediments, can be ascribed to variation in the sediment subduction vs accretion sediment budget in an evolving back-arc basin. Similar lithostratigraphic associations within the Caribbean metamorphosed and unmetamorphosed magmatic and sedimentary units can be related to a similar detrital continental input, whereas, the existence of coherent metamorphosed pre-Mesozoic crustal elements within subduction-accretion complexes, may reflect the existence of continental islands that were detached during the initial proto-Caribbean rifting phases and mixed within intra-oceanic accretionary prisms.

  5. Experimental Fractional Crystallization of the Lunar Magma Ocean (United States)

    Rapp, J. F.; Draper, D. S.


    The current paradigm for lunar evolution is of crystallization of a global scale magma ocean, giving rise to the anorthositic crust and mafic cumulate interior. It is thought that all other lunar rocks have arisen from this differentiated interior. However, until recently this paradigm has remained untested experimentally. Presented here are the first experimental results of fractional crystallization of a Lunar Magma Ocean (LMO) using the Taylor Whole Moon (TWM) bulk lunar composition [1].

  6. Reference crust-mantle density contrast beneath Antarctica based on the Vening Meinesz-Moritz isostatic inverse problem and CRUST2.0 seismic model

    Scientific Electronic Library Online (English)

    Robert, Tenzer; Mohammad, Bagherbandi.


    Full Text Available El contraste de densidad de la discontinuidad de Mohorovicic (Moho) debajo de la Antártida fue estimado con base en la solución del problema isostático Vening Meinesz-Moritz y a partir de datos obtenidos con el modelo sísmico de la corteza global (CRUST2.0). La solución se encontró a través de un aj [...] uste al método de mínimos cuadrados por el método de elementos. El modelo geopotencial global (GOCO02S), el modelo topográfico/batimétrico (DTM2006.0), los datos de espesor del hielo para la Antártida (reunidos por el proyecto BEDMAP) y el modelo sísmico de corteza global (CRUST2.0) fueron utilizados para calcular las anomalías gravitatorias isostáticas. Ya que los datos de CRUST2.0 para las estructuras de la corteza en la Antártida no son exactos (debido a la falta de información sísmica para esta parte del planeta), el contraste de densidad de la Discontinuidad de Mohorovicic fue determinado a partir de un modelo de corteza homogéneo que tiene una densidad constante de 2,670 kg/m³. Los valores estimados del contraste de densidad de la Moho se encontraron entre 160 y 682kg/m³. La distribución espacial del contraste de densidad de la Moho exhibe mayores rasgos en la configuración de la plancha tectónica de la Antártida continental y su alrededor oceánico. El valor máximo encontrado excede los 500 kg/m³ y se ubica en la parte Este continental, con extensión en las Montañas Transantárticas. El contraste de densidad de la Moho (zona de transición entre la corteza y el manto terrestre) en el Oeste de la Antártida osciló entre 400-500 kg/m³, excepto para la máxima local de ? 550 kg/m³, en el centro de la Península Antártida. Abstract in english The crust-mantle (Moho) density contrast beneath Antarctica was estimated based on solving the Vening Meinesz-Moritz isostatic problem and using constraining information from a seismic global crustal model (CRUST2.0). The solution was found by applying a least-squares adjustment by elements method. [...] Global geopotential model (GOCO02S), global topographic/bathymetric model (DTM2006.0), ice-thickness data for Antarctica (assembled by the BEDMAP project) and global crustal model (CRUST2.0) were used for computing isostatic gravity anomalies. Since CRUST2.0 data for crustal structures under Antarctica are not accurate (due to a lack of seismic data in this part of the world), Moho density contrast was determined relative to a reference homogenous crustal model having 2,670 kg/m³ constant density. Estimated values of Moho density contrast were between 160 and 682 kg/m³. The spatial distribution of Moho density contrast resembled major features of the Antarctic’s continental and surrounding oceanic tectonic plate configuration; maxima exceeding 500 kg/m³ were found throughout the central part of East Antarctica, with an extension beneath the Transantarctic mountain range. Moho density contrast in West Antarctica decreased to 400-500 kg/m³, except for local maxima up to ? 550 kg/m³ in the central Antarctic Peninsula.

  7. IODP Expeditions 304 & 305 Characterize the Lithology, Structure, and Alteration of an Oceanic Core Complex

    Directory of Open Access Journals (Sweden)

    Christopher J. MacLeod


    Full Text Available More than forty years after the Mohole Project (Bascom, 1961, the goal of drilling a complete section through in situ oceanic crust remains unachieved. Deep Sea Drilling Project – Ocean Drilling Program (DSDP-ODP Hole 504B within the eastern Pacifi c (Alt et al., 1993 is the deepest hole ever drilled into ocean crust (2111 mbsf, but it failed to reach lower crustal plutonic rocks below the pillow basalts and sheeted dikes. IODP Expeditions 309 and 312 eventuallyrecovered the long-sought transition from sheeted dikes into underlying gabbros by drilling into very fast-spreading Pacifi c crust (Wilson et al., 2006. The lithology and structure of oceanic crust produced at slow-spreading ridges are heterogeneous (e.g., Cannat et al., 1997 and offer unique drilling access to lower crust and upper mantle rocks. After ODP Hole 735B penetrated 1500 m of gabbro at the Southwest Indian Ridge (Dick et al., 2000, IODP Expeditions 304 and 305 recently recovered just over 1400 m of little-deformed, gabbroic lower crust from a tectonic window along the slowspreading Mid-Atlantic Ridge.

  8. Breaking stress of neutron star crust

    CERN Document Server

    Chugunov, A I


    The breaking stress (the maximum of the stress-strain curve) of neutron star crust is important for neutron star physics including pulsar glitches, emission of gravitational waves from static mountains, and flares from star quakes. We perform many molecular dynamic simulations of the breaking stress at different coupling parameters (inverse temperatures) and strain rates. We describe our results with the Zhurkov model of strength. We apply this model to estimate the breaking stress for timescales ~1 s - 1 year, which are most important for applications, but much longer than can be directly simulated. At these timescales the breaking stress depends strongly on the temperature. For coupling parameter <200, matter breaks at very small stress, if it is applied for a few years. This viscoelastic creep can limit the lifetime of mountains on neutron stars. We also suggest an alternative model of timescale-independent breaking stress, which can be used to estimate an upper limit on the breaking stress.

  9. Shear viscosity in magnetized neutron star crust

    CERN Document Server

    Ofengeim, D D


    The electron shear viscosity due to Coulomb scattering of degenerate electrons by atomic nuclei throughout a magnetized neutron star crust is calculated. The theory is based on the shear viscosity coefficient calculated neglecting magnetic fields but taking into account gaseous, liquid and solid states of atomic nuclei, multiphonon scattering processes, and finite sizes of the nuclei albeit neglecting the effects of electron band structure. The effects of strong magnetic fields are included in the relaxation time approximation with the effective electron relaxation time taken from the field-free theory. The viscosity in a magnetized matter is described by five shear viscosity coefficients. They are calculated and their dependence on the magnetic field and other parameters of dense matter is analyzed. Possible applications and open problems are outlined.

  10. Structure of the Crust Beneath Cameroon, West Africa, from the Joint Inversion of Rayleigh Wave Group Velocities and Receiver Functions

    International Nuclear Information System (INIS)

    The joint inversion of Rayleigh wave group velocities and receiver functions was carried out to investigate the crustal and uppermost mantle structures beneath Cameroon. This was achieved using data from 32 broadband seismic stations installed for 2 years across Cameroon. The Moho depth estimates reveal that the Precambrian crust is variable across the country and shows some significant differences compared to other similar geologic units in East and South Africa. These differences suggest that the setting of the Cameroon Volcanic Line (CVL) and the eastward extension of the Benue Trough have modified the crust of the Panafrican mobile belt in Cameroon by thinning beneath the Rift area and CVL. The velocity models obtained from the joint inversion show at most stations, a layer with shear wave velocities ? 4.0 km/s, indicating the presence of a mafic component in the lower crust, predominant beneath the Congo Craton. The lack of this layer at stations within the Panafrican mobile belt may partly explain the crustal thinning observed beneath the CVL and rift area. The significant presence of this layer beneath the Craton, results from the 2100 Ma magmatic events at the origin of the emplacement of swarms of mafic dykes in the region. The CVL stations are underlain by a crust of 35 km on average except near Mt-Cameroon where it is about 25 km. The crustal thinning observed beneath Mt. Cameroon supported by the observed positive gravity anomalies here, suggests the presence of dense astenospheric material within the lithosphere. Shear wave velocities are found to be slower in the crust and uppermost mantle beneath the CVL than the nearby tectonic terrains, suggesting that the origin of the line may be an entirely mantle process through the edge-flow convection process. (author)

  11. Symmetry energy effects in the neutron star crust properties

    CERN Document Server

    Porebska, J


    Different shapes of the nuclear symmetry energy leads to a different crust-core transition point in the neutron star. The basic properties of a crust, like thickness, mass and moment of inertia were investigated for various forms of the symmetry energy.

  12. Calculation of fluid fluxes in Earth's crust (United States)

    Lasaga, Antonio C.; Rye, Danny M.; Lüttge, Andreas; Bolton, Edward W.


    The movement of fluids in the crust and upper mantle not only lead to important mineral reactions but also play an essential role in the geochemical cycling of elements and in controlling global change. Numerous papers have focused on calculation of fluid fluxes driving metamorphic reactions in the earth's crust. The extent of reaction in nature has been "inverted" to predict the total amount of fluid that was required to drive that much reaction. These models, although based on thermodynamic equilibrium, have extended the earlier concept of water-rock ratio. Any quantitative treatment of the fluid fluxes and the relationship between these fluxes and other variables such as temperature and mineral abundances requires a kinetic model. A simple model is presented that incorporates the essential dynamics of metamorphic processes including both heat flow by conduction and convection as well as fluid flow in and out of a representative volume. Overall mineral reactions can then take place within this rock volume in response to internal and external factors. The production and subsequent expulsion of excess fluids (H 2O and CO 2) as a result of these reactions leads to increased fluid fluxes, which the model can also handle. Using this kinetic model, the assumption of thermodynamic equilibrium can be tested and forward calculations can compare the numbers "inverted" for total integrated fluid fluxes based on equilibrium with the "actual" integrated fluid fluxes. Other effects such as changes in the temperature field or the presence of dispersion/diffusion can also be readily quantified with this kinetic model. The nontrivial consequences of heterogeneity in natural systems make the kinetic approach much more essential but at the same time much more "invertible" than earlier approaches. Ultimately, the effects of the rates of overall mineral reactions and their interplay with the other kinetic processes taking place in these open systems have to be evaluated to guide us in developing much more powerful and correct ways of extracting fluid velocities from petrologic field data.

  13. Multidisciplinary Collaborations in Mid-Ocean Ridge Research (United States)

    Rubin, Kennneth H.; Fornari, Daniel


    The global mid-ocean ridge (MOR) is one of Earth's most fundamental geologic structures. Active volcanic, tectonic, hydrothermal, and biological processes occurring at the MOR affect nearly every attribute of the world's oceans and oceanic crust. For the past quarter century the overarching goal of the U.S. National Science Foundation (NSF)-funded multidisciplinary Ridge 2000 program ( and its predecessor, Ridge Interdisciplinary Global Experiments (RIDGE), here collectively called “R2K,” has been to use observations, experiments, and models to answer fundamental questions about oceanic spreading center processes. Since its inception, R2K has worked to develop a holistic understanding of MORs. There are multiple interrelated consequences of oceanic crust generation at MORs, including transfer of material and energy from the mantle to the crust and ocean; impacts on marine ecology; and temporal, spatial, and rate-dependent interactions between biological and geological processes. Consequently, a diverse yet tightly knit community of collaborating scientists, including geologists, chemists, geophysical modelers, microbiologists, and oceanographers, has developed under R2K programs. This research community has spanned multiple generations of investigative effort, requiring it to confront transformations in communications technology, tools for use and access of data, and attitudes about cooperative approaches to scientific discovery. The tools and approaches R2K has used to enhance cross-disciplinary understanding of complex problems are adaptable to other multidisciplinary research efforts.

  14. BaMa / Raivo Juurak

    Index Scriptorium Estoniae

    Juurak, Raivo, 1949-


    Eesti ülikoolide üleminekust 3+2 süsteemile. Lühend BaMa on tulnud kasutusele seoses Euroopa ülikoolide õppekavade reformimisega ning tähistab õppekava, kus esimese astme läbimise järel omandatakse bakalaureuse- ja teise järel magistrikraad. Õppekavade tüüpidest Eesti ja Euroopa Liidu kõrgkoolides ning Bologna deklaratsioonist

  15. Thermalisation time and specific heat of neutron stars crust

    CERN Document Server

    Fortin, M; Margueron, J; Sandulescu, N


    We discuss the thermalisation process of the neutron stars crust described by solving the heat transport equation with a microscopic input for the specific heat of baryonic matter. The heat equation is solved with initial conditions specific to a rapid cooling of the core. To calculate the specific heat of inner crust baryonic matter, i.e., nuclear clusters and unbound neutrons, we use the quasiparticle spectrum provided by the Hartree-Fock-Bogoliubov approach at finite temperature. In this framework we analyse the dependence of the crust thermalisation on pairing properties and on cluster structure of inner crust matter. It is shown that the pairing correlations reduce the crust thermalisation time by a very large fraction. The calculations show also that the nuclear clusters have a non-negligible influence on the time evolution of the surface temperature of the neutron star.

  16. Persistent crust-core spin lag in neutron stars (United States)

    Glampedakis, Kostas; Lasky, Paul D.


    It is commonly believed that the magnetic field threading a neutron star provides the ultimate mechanism (on top of fluid viscosity) for enforcing long-term corotation between the slowly spun-down solid crust and the liquid core. We show that this argument fails for axisymmetric magnetic fields with closed field lines in the core, the commonly used `twisted torus' field being the most prominent example. The failure of such magnetic fields to enforce global crust-core corotation leads to the development of a persistent spin lag between the core region occupied by the closed field lines and the rest of the crust and core. We discuss the repercussions of this spin lag for the evolution of the magnetic field, suggesting that, in order for a neutron star to settle to a stable state of crust-core corotation, the bulk of the toroidal field component should be deposited into the crust soon after the neutron star's birth.

  17. Persistent crust-core spin lag in neutron stars

    CERN Document Server

    Glampedakis, Kostas


    It is commonly believed that the magnetic field threading a neutron star provides the ultimate mechanism (on top of fluid viscosity) for enforcing long-term corotation between the slowly spun down solid crust and the liquid core. We show that this argument fails for axisymmetric magnetic fields with closed field lines in the core, the commonly used `twisted torus' field being the most prominent example. The failure of such magnetic fields to enforce global crust-core corotation leads to the development of a persistent spin lag between the core region occupied by the closed field lines and the rest of the crust and core. We discuss the repercussions of this spin lag for the evolution of the magnetic field, suggesting that, in order for a neutron star to settle to a stable state of crust-core corotation, the bulk of the toroidal field component should be deposited into the crust soon after the neutron star's birth.

  18. Origin and evolution of a submarine large igneous province: The Kerguelen Plateau and Broken Ridge, southern Indian Ocean


    Frey, FA; Coffin, MF; Wallace, PJ; Weis, D; Zhao , X.; Wise Jr, SW; Wähnert, V; Teagle, DAH; Saccocia, PJ; Reusch, DN; Pringle, MS; Nicolaysen, KE; Neal, CR; Müller, RD; Moore, CL


    Oceanic plateaus form by mantle processes distinct from those forming oceanic crust at divergent plate boundaries. Eleven drillsites into igneous basement of Kerguelen Plateau and Broken Ridge, including seven from the recent Ocean Drilling Program Leg 183 (1998-99) and four from Legs 119 and 120 (1987-88), show that the dominant rocks are basalts with geochemical characteristics distinct from those of mid-ocean ridge basalts. Moreover, the physical characteristics of the lava flows and the p...

  19. Paleomagnetism continents and oceans

    CERN Document Server

    McElhinny, Michael W; Dmowska, Renata; Holton, James R; Rossby, H Thomas


    Paleomagnetism is the study of the fossil magnetism in rocks. It has been paramount in determining that the continents have drifted over the surface of the Earth throughout geological time. The fossil magnetism preserved in the ocean floor has demonstrated how continental drift takes place through the process of sea-floor spreading. The methods and techniques used in paleomagnetic studies of continental rocks and of the ocean floor are described and then applied to determining horizontal movements of the Earth''s crust over geological time. An up-to-date review of global paleomagnetic data enables 1000 millionyears of Earth history to be summarized in terms of the drift of the major crustal blocks over the surface of the Earth. The first edition of McElhinny''s book was heralded as a "classic and definitive text." It thoroughly discussed the theory of geomagnetism, the geologicreversals of the Earth''s magnetic field, and the shifting of magnetic poles. In the 25 years since the highly successful first editio...

  20. The sedimentary supply of African sedimentary basins over the last 250 Ma (United States)

    Rouby, Delphine; Guillocheau, Francois; Robin, Cecile; Helm, Catherine


    The African continent is bordered by passive margins and bears intracontinental basins preserving the terrigeneous sediment resulting from its erosion, and as such, recording the dynamics of its relief variation. Our objective is to bring new constraints on the uplift and erosion of the African continent over the last 250 Ma from the perspective of the stratigraphic architecture of its sedimentary basins. The novel aspect of our approach is to integrate the evolution of both the domains in erosion and in sedimentation (i.e. from the drainage divide of the domain in erosion down to the most distal deposits over the oceanic crust), and to review published data to quantify the terrigeneous supply eroded in the drainage area and preserved in the basins. One objective is to evaluate the conditions under which this simple approach, based on already published data, can be used to infer continental relief variations, the sedimentary archives of the domain in erosion being by definition scarce and denudation evaluation by thermochronology usually relying on hypotheses on past heat flows. We quantify the siliciclastic sedimentary volumes preserved in African basins correcting from porosity and in-situ (e.g. carbonate) production, with a particular attention to the determination of uncertainties resulting from parameters such as: velocity laws used to depth conversion of TWT data, biostratigraphic used for calibration in absolute ages, lithology assumed for porosity removal. We use two approaches with complementary spatial and temporal resolutions. (1) When data are available (e.g along the South African and Namibian Atlantic margins), we determine the long-term signal of sedimentary supply (x10 Ma) from 3D mass balance calculations comparing sedimentary volumes deduced from offshore isopach maps on one hand and erosion volumes deduced from the present day geometry of geomorphic markers and thermochronology data on the other hand. We show that our approach provide a good estimation of the long-term denudation of the drainage basins. (2) 3D dataset are not always available and allow most of the time only a long-term description of the sedimentary supply. We therefore develop a GIS database of 2D regional cross-sections across the major sedimentary basins established from published seismic lines. We homogenise the sections in spatial and temporal scale and then extrapolate them down to the most distal part of the basin so that geometries of our sedimentary wedges are not restricted to the platform domain (Figure 4), this, taking into account several hypotheses. On each cross-section, we then measure the 2D area of each stratigraphic interval (x1 Ma) and, in doing so, determine the average sedimentation "areas" and rates. We then determine the spatial extension of the basins for each time increment and use it to extrapolate average sedimentation "areas" and rate into sedimentation volumes.

  1. Shear wave velocity structure of the Anatolian Plate: anomalously slow crust in southwestern Turkey (United States)

    Delph, Jonathan R.; Biryol, C. Berk; Beck, Susan L.; Zandt, George; Ward, Kevin M.


    The Anatolian Plate is composed of different lithospheric blocks and ribbon continents amalgamated during the closure of the Paleotethys Ocean and Neotethys Ocean along a subduction margin. Using ambient noise tomography, we investigate the crustal and uppermost mantle shear wave velocity structure of the Anatolian Plate. A total of 215 broad-band seismic stations were used spanning 7 yr of recording to compute 13 778 cross-correlations and obtain Rayleigh wave dispersion measurements for periods between 8 and 40 s. We then perform a shear wave inversion to calculate the seismic velocity structure of the crust and uppermost mantle. Our results show that the overall crustal shear wave velocities of the Anatolian crust are low (˜3.4 km s-1), indicative of a felsic overall composition. We find that prominent lateral seismic velocity gradients correlate with Tethyan suture zones, supporting the idea that the neotectonic structures of Turkey are exploiting the lithospheric weaknesses associated with the amalgamation of Anatolia. Anomalously slow shear wave velocities (˜3.15 km s-1 at 25 km) are located in the western limb of the Isparta Angle in southwestern Turkey. In the upper crust, we find that these low shear wave velocities correlate well with the projected location of a carbonate platform unit (Bey Da?lari) beneath the Lycian Nappe complex. In the lower crust and upper mantle of this region, we propose that the anomalously slow velocities are due to the introduction of aqueous fluids related to the underplating of accretionary material from the underthrusting of a buoyant, attenuated continental fragment similar to the Eratosthenes seamount. We suggest that this fragment controlled the location of the formation of the Subduction-Transform Edge Propagator fault in the eastern Aegean Sea during rapid slab rollback of the Aegean Arc in early Miocene times. Lastly, we observe that the uppermost mantle beneath continental Anatolia is generally slow (˜4.2 km s-1), indicating higher than usual temperatures consistent with the influx of asthenosphere to shallow depths as a result of the segmentation and break-up of the subducting African lithosphere.

  2. ???? ???????? / Ma?????? ?????????

    Index Scriptorium Estoniae

    Ta???????, ????????


    Koolilaste järjest kehvenev tervis sundis sotsiaalministeeriumi uuest õppeaastast kehtestama korra, mis päästab õpilased raske ranitsa tassimisest ja keelab koduste ülesannete andmise nädalavahetusteks

  3. Transition metal isotope fractionation in marine hydrothermal deposits of the Mohns Ridge, North Atlantic Ocean


    Möller, Kirsten


    Seafloor hydrothermal vent systems form along mid-ocean ridges in all of the Earth’s oceans. They have a major impact on the chemical exchange between the lithosphere and the hydrosphere, as vast volumes of seawater cycle through these systems, thereby interacting with young, oceanic crust. Furthermore, seafloor hydrothermal vent systems provide an excellent environment for organisms to thrive, resulting in diverse and unique vent faunas. Due to their favourable ecological cond...

  4. The 17 Ma old Turkana beaked whale fossil: new paleoaltimetry constraints for uplift and environmental change in East Africa (United States)

    Wichura, Henry; Jacobs, Louis L.; Strecker, Manfred R.; Lin, Andrew; Polcyn, Michael J.; Manthi, Fredrick K.; Winkler, Dale A.; Matthew, Clemens


    Timing and magnitude of vertical motions of the Earth's crust is key to evaluate the impact of tectonic processes on changes in atmospheric circulation patterns, rainfall, and environmental conditions. The East African Plateau (EAP) is a major topographic feature that fundamentally impacts the patterns of the Indian-African Monsoon and the eastward transport of air masses from the Congo Basin. Uplift of the EAP in Kenya has been linked to mantle processes, but due to the lack of reliable palaeoaltimetric data it has been challenging to unambiguously constrain plateau evolution, vertical motions associated with late Cenozoic rifting of the East African Rift System, and ensuing environmental change. We explored the fossil remains of a beaked whale (Ziphiidae) from the Turkana region in the northern Kenya Rift, 700 km inland from the present-day coastline of the Indian Ocean. The whale fossil, preserved near sea level, was discovered at an elevation of 620 m and thus constrains the uplift of the northeastern flanks of the EAP. The Kenyan ziphiid was discovered in fluvio-lacustrine sediments of the extensional Oligo-Miocene Lokichar basin (Mead, 1975) along with terrestrial mammals and freshwater molluscs below a basalt dated at 17.1 ± 1.0 Ma (Boschetto et al., 1992). The unifying characteristics of riverine occurrences of modern marine mammals include sufficient discharge in low-gradient rivers to maintain pathways deep enough to facilitate migration, and the absence of shallow bedrock, rapids, and waterfalls. The most likely route, which may have had these characteristics is a fluvial corridor controlled by protracted thermal subsidence of the Cretaceous Anza Rift, which once linked extensional processes in Central and East Africa with the continental margin of northeastern Africa. The fossil locality and analogies with present-day occurrences of marine mammals in terrestrial realms suggest that the ziphiid stranded slightly above sea level. In combination with Miocene lava flows that utilized eastward-directed drainages away from the EAP the fossil find thus provides the older of only two empirical palaeoelevation points that constrain the onset of uplift of the EAP to the interval between approximately 17 and 13 Ma. Our results show that topographic uplift of the EAP is a viable mechanism that induced palaeoclimatic change from a low-elevation humid environment to highly variable, much drier conditions, which altered biotic communities and drove evolution in East Africa, including that of primates.

  5. Ma's identity and its application

    Directory of Open Access Journals (Sweden)

    Damian S?ota


    Full Text Available In the paper we distinguish the, so called, Ma's polynomials and we introduce connections of these polynomials with the classic Cauchy polynomials and the Ferrers-Jackson's polynomials. Presented connections enable to receive certain interesting divisibility relations for all these three types of polynomials and some other symmetric polynomials. Application of the discussed identities for determining the limits of quotients of the respective polynomials in two variables are also presented here.

  6. Ocean gravitational-modes in transient neutron stars

    CERN Document Server

    Deibel, Alex


    The neutron star ocean is a plasma of ions and electrons that extends from the base of the neutron star's envelope to a depth where the plasma crystallizes into a solid crust. During an accretion outburst in an X-ray transient, material accumulates in the envelope of the neutron star primary. This accumulation compresses the neutron star's outer layers and induces nuclear reactions in the ocean and crust. Accretion-driven heating raises the ocean's temperature and increases the frequencies of g-modes in the ocean; when accretion halts, the ocean cools and ocean g-mode frequencies decrease. If the observed low frequency quasi-periodic oscillations on accreting neutron stars are g-modes in the ocean, the observed quasi-periodic oscillation frequencies will increase during outburst --- reaching a maximum when the ocean temperature reaches steady state --- and subsequently decrease during quiescence. For time-averaged accretion rates during outburst between $\\langle \\dot{M} \\rangle = 0.1 \\textrm{--} 1.0\\, \\dot{\\r...

  7. Ocean Color (United States)

    National Aeronautics and Space Administration — Satellite-derived Ocean Color Data sets from historical and currently operational NASA and International Satellite missions including the NASA Coastal Zone Color...

  8. LOCV approach and core-crust transition in neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Bigdeli, M.; Elyasi, S. [University of Zanjan, Department of Physics, Zanjan (Iran, Islamic Republic of)


    In this paper, we have calculated the core-crust transition parameters and the location of inner edge for crust in the neutron stars. We have also investigated the structural properties of neutron stars, such as mass and radius for the core and crust, the moment of inertia, and its crustal fraction. Here we have employed the lowest-order constrained variational approach and used the UV{sub 14} + TNI and AV{sub 18} potentials to compute the equation of state of nuclear matter. Finally, we have compared our results with those of other techniques. (orig.)

  9. Collective Modes in the Superfluid Inner Crust of Neutron Stars

    CERN Document Server

    Urban, Michael


    The neutron-star inner crust is assumed to be superfluid at relevant temperatures. The contribution of neutron quasiparticles to thermodynamic and transport properties of the crust is therefore strongly suppressed by the pairing gap. Nevertheless, the neutron gas still has low-energy excitations, namely long-wavelength collective modes. We summarize different approaches to describe the collective modes in the crystalline phases of the inner crust and present an improved model for the description of the collective modes in the pasta phases within superfluid hydrodynamics.

  10. An elderly long-term care resident with crusted scabies. (United States)

    Sandre, Matthew; Ralevski, Filip; Rau, Neil


    Crusted scabies is a highly contagious form of scabies. Altered immune response, nutritional deficiencies and modified host response are all risk factors for crusted scabies. The authors report a case involving a patient found to have a chronic maculopapular, erythematous rash with large hyperkeratotic, white and grey plaques on the soles of both feet. An ultimate diagnosis of crusted scabies was reached after a delay in diagnosis suspected to be caused by the similarity in appearance to more common skin conditions such as psoriasis. After topical permethrin was unsuccessful, intermittent dosing of oral ivermectin resulted in a rapid reduction in cutaneous plaques. PMID:25798153

  11. Thermal conductivity of the crust of accreting neutron stars

    CERN Document Server

    Horowitz, C J; Berry, D K


    Recently, crust cooling times have been measured for neutron stars after extended outbursts. These observations are very sensitive to the thermal conductivity $\\kappa$ of the crust and strongly suggest that $\\kappa$ is large. We perform molecular dynamics simulations of the structure of the crust of an accreting neutron star using a complex composition that includes many impurities. The composition comes from simulations of rapid proton capture nucleosynthesys followed by electron captures. We find an ordered crystal structure with a high thermal conductivity that is in agreement with observation. We do not find an amorphous solid that could have a low conductivity.

  12. Solvent evaporation of spin cast films crust effects

    CERN Document Server

    De Gennes, Pierre Gilles


    When a glassy polymer film is formed by evaporation, the region near the free surface is polymer rich and becomes glassy first, as noticed long ago by Scriven et al. We discuss the thickness of this "crust" and the time interval where it is present -before freezing of the whole film. We argue that the crust is under mechanical tension, nd should form some cracks. This may be the source of the roughness observed on the final, dry films, when the solvent vapor pressure is high (and leads to thin crusts).

  13. An elderly long-term care resident with crusted scabies (United States)

    Sandre, Matthew; Ralevski, Filip; Rau, Neil


    Crusted scabies is a highly contagious form of scabies. Altered immune response, nutritional deficiencies and modified host response are all risk factors for crusted scabies. The authors report a case involving a patient found to have a chronic maculopapular, erythematous rash with large hyperkeratotic, white and grey plaques on the soles of both feet. An ultimate diagnosis of crusted scabies was reached after a delay in diagnosis suspected to be caused by the similarity in appearance to more common skin conditions such as psoriasis. After topical permethrin was unsuccessful, intermittent dosing of oral ivermectin resulted in a rapid reduction in cutaneous plaques. PMID:25798153

  14. Breaking stress of neutron star crust

    International Nuclear Information System (INIS)

    Complete text of publication follows. The breaking stress (the maximum of the stress-strain curve) of neutron star crust is important for neutron star physics including pulsar glitches, emission of gravitational waves from static mountains, and flares from star quakes. We perform many molecular dynamic simulations of the breaking stress at different coupling parameters (inverse temperatures), strain rates and composition of matter. We describe our results with the Zhurkov model of strength. We apply this model to estimate the breaking stress for timescales ?1 s - 1 year, which are most important for applications, but much longer than can be directly simulated. At these timescales the breaking stress depends strongly on the temperature. For coupling parameter ?<200 matter breaks at very small stress, if it is applied for a few years. This viscoelastic creep can limit the lifetime of mountains on neutron stars. We also suggest an alternative model of timescale-independent breaking stress, which can be used to estimate an upper limit on the breaking stress. This work was partially supported by the Russian Foundation for Basic Research (grant 11-02-00253-a), by the State Program 'Leading Scientific Schools of Russian Federation' (grant NSh 3769.2010.2), by the President grant for young Russian scientists (MK-5857.2010.2), by United States DOE grant (DE-FG02-87ER40365) and by Shared University Research grants from IBM, Inc. to Indiana University.

  15. Late Triassic adakitic plutons within the Archean terrane of the North China Craton: Melting of the ancient lower crust at the onset of the lithospheric destruction (United States)

    Wang, Chao; Song, Shuguang; Niu, Yaoling; Su, Li


    We present the results of a geochemical and geochronological study for Late Triassic (230?220 Ma) adakitic plutons within the Archean terrane of the eastern part of the North China Craton (NCC). These plutons show adakitic signatures with high Sr, Sr/Y, (La/Yb)N, and low Cr and Ni. The enriched Nd-Hf isotopic compositions (?Nd(t) = - 13.3 to - 12.9; ?Hf(t) = - 17.4 to - 14.6) and old Nd (TDM2 = 2078-2037 Ma) and Hf (TDM2 = 2366-2192 Ma) isotope model ages suggest that the adakitic pluton may be derived from the underplated mafic lower crust of Paleoproterozoic age. The relatively low Cr and Ni contents and lower ?Nd(t) and ?Hf(t) values of the Taili adakitic plutons imply negligible input of mantle materials. Calculations of equilibrium mineral assemblages and modeling of trace element partition between melts and residual phases at different pressures confirm the interpretation that the petrogenesis of the Taili adakitic plutons is consistent with partial melting of the Paleoproterozoic mafic lower crust at 10-12 kbar (36-43 km) with a garnet granulite residue. Melting of the ancient mafic lower crust may be triggered by excess heating of the upwelling mantle in an extensional setting evoked by the contemporary subduction toward beneath the NCC from both north and south, which could serve as one possible mechanism for the destruction or lithospheric thinning of the NCC. Complex mantle-crust interaction through various mechanisms may have been responsible for the long-lived process of destruction or lithospheric thinning, which might have begun as early as in the late Triassic.

  16. Models of a partially hydrated Titan interior with a clathrate crust (United States)

    Lunine, J. I.; Castillo-Rogez, J. C.; Choukroun, M.; Sotin, C.


    We present a model of the interior evolution of Titan over time, assuming the silicate core was hydrated early in Titan’s history and is dehydrating over time. The original model presented in Castillo-Rogez and Lunine (2010) was motivated by a Cassini-derived moment of inertia (Iess et al., 2010) for Titan too large to be accommodated by classical fully differentiated models in which an anhydrous silicate core was overlain by a water ice (with possible perched ocean) mantle. Our model consists of a silicate core still in the process of dehydrating today, a situation made possible by the leaching of radiogenic potassium from the silicates into the perched liquid water ocean. The most recent version of our model accounts for the likely presence of large amounts of methane in the upper crust invoked to explain methane’s persistence at present and through geologic time (Tobie et al. 2006). The methane-rich crust turns out to have essentially no bearing on the temperature of the silicate core and hence the timing of dehydration, but it profoundly affects the thickness of the high-pressure ice layer beneath the ocean. Indeed, the insulating effect of the methane clathrate crust could have delayed the formation of the high-pressure layer, resulting in the interaction of liquid water with the silicate core for extended periods of time. Although a high-pressure ice layer is likely in place today, it is thin enough that plumes of hot water from the dehydrating core probably breach that layer. The implications of such a deep hydrothermal system for the later stages of the evolution of Titan’s interior and surface will be discussed. Part of this work has been performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged. References: Castillo-Rogez, J., Lunine, J.: “Evolution of Titan’s rocky core constrained by Cassini observations”. GRL, Vol. 37, L20205, 2010. Iess, L., et al.: “Gravity field, shape, and moment of inertia of Titan”. Science, Vol. 327, 1367-1369. Tobie, G., et al.: “Episodic outgassing as the origin of atmospheric methane on Titan”. Nature 440: 61-64, 2006.

  17. Natural constraints on the rheology of the lower continental crust (Musgrave Ranges, Central Australia) (United States)

    Hawemann, Friedrich; Mancktelow, Neil; Wex, Sebastian; Camacho, Alfredo; Pennacchioni, Giorgio


    Current models and extrapolated laboratory data generally predict viscous flow in the lower continental crust and any localized brittle deformation at these depths has been proposed to reflect downward propagation of the frictional-viscous transition zone during short-term seismic events and related high strain rates. Better natural constraints on this proposed rheological behaviour can be obtained directly from currently exposed lower crust that has not been strongly overprinted during its exhumation. One of the largest and best preserved lower crustal sections is located in the Musgrave Ranges, Central Australia. The Petermann Orogeny (550 Ma) in this area is characterized by the development of localized shear zones on a wide range of scales, overprinting water-deficient granulites of Musgravian age (1.2 Ga) as well as younger granites and gabbros. Shearing is rarely localized on lithological inhomogeneities, but rather on precursor fractures and on commonly associated pseudotachylytes. The only exception is that older dolerite dykes are often exploited, possibly because they are planar layers of markedly smaller grain size. Sheared pseudotachylyte often appears caramel-coloured in the field and has a fine grained assemblage of Grt+Cpx+Fsp. Multiple generations of pseudotachylyte formed broadly coeval with shearing are indicated by clasts of sheared pseudotachylyte within pseudotachylyte veins that then themselves subsequently sheared. The ductile shear zones formed under sub-eclogitic conditions of ca. 650°C and 1.2 GPa, generally typical of the lower continental crust. However, the P-T conditions during pseudotachylyte formation cannot be readily determined using classical geothermobarometry, because of the fine grain sizes and possible disequilibrium. The software "Xmaptools" (by Pierre Lanari) allows the quantification of X-ray maps produced by EDS or WDS. It provides both very precise definition of local mineral compositions for exchange geothermobarometry on a statistical basis, and an estimate of the bulk pseudotachylyte composition for small areas, avoiding clasts and heterogeneous composition of the former melt. The combination with thermodynamic modelling using PerpleX is used to test the results from geothermobarometry. The estimated conditions are similar to the ductile shear zones and support evidence for synchronous action of brittle faulting and viscous shearing in the lower crust.

  18. On the relief of the crust-mantle boundary and strain-compression stresses in the crust of Venus

    International Nuclear Information System (INIS)

    An associated analysis of the topography and the non-equilibrium part of the gravitational field of the planet for spherical harmonics with n=3-18 allows one to obtaine some hinst about character of crust-mantle boundary and strain-compression stresses in the crust for series of realistic models of Venus taking into consideration an astenosphere. Moho's undulation amplitudes from the midle level for different models are in the limits from ?+80km (downward) to ?-20km (upward). On the whole, the crust - mantle boundary of Venus is smooth enough. The stresses varies from ?+600 bars(strain) to ?-700 bars(compression) depending on the planet interior model

  19. Ocean technology

    Digital Repository Service at National Institute of Oceanography (India)

    Peshwe, V.B

    stream_size 2 stream_content_type text/plain stream_name Voices_Oceans_1996_113.pdf.txt stream_source_info Voices_Oceans_1996_113.pdf.txt Content-Encoding ISO-8859-1 Content-Type text/plain; charset=ISO-8859-1 ...

  20. Yellow sorediate crusts called Caloplaca citrina in England.

    Czech Academy of Sciences Publication Activity Database

    Powell, M.; Vondrák, Jan


    Ro?. 2012, ?. 110 (2012), s. 20-24. ISSN 0300-4562 Institutional research plan: CEZ:AV0Z60050516 Institutional support: RVO:67985939 Keywords : biodiversity * crytic species * sorediate crusts Subject RIV: EF - Botanics

  1. Biological soil crusts in post-mining areas.

    Czech Academy of Sciences Publication Activity Database

    Lukešová, Alena; Zahradníková, M.; Frouz, J.

    Boca Raton : Taylor & Francis CRC Press, 2013, s. 53-65. ISBN 978-1-4665-9931-4 Institutional support: RVO:60077344 Keywords : biological soil crusts * post-mining areas Subject RIV: DF - Soil Science

  2. Nuclear superfluidity and cooling time of neutron-star crust

    Energy Technology Data Exchange (ETDEWEB)

    Monrozeau, C.; Margueron, J. [Institut de Physique Nucleaire, Universite Paris Sud, F-91406 Orsay CEDEX (France); Sandulescu, N. [Institut de Physique Nucleaire, Universite Paris Sud, F-91406 Orsay CEDEX (France); Institute of Physics and Nuclear Engineering, RO-76900 Bucharest (Romania)


    We analyse the effect of neutron superfluidity on the cooling time of inner crust matter in neutron stars, in the case of a rapid cooling of the core. The specific heat of the inner crust, which determines the thermal response of the crust, is calculated in the framework of HFB approach at finite temperature. The calculations are performed with two paring forces chosen to simulate the pairing properties of uniform neutron matter corresponding respectively to Gogny-BCS approximation and to many-body techniques including polarisation effects. Using a simple model for the heat transport across the inner crust, it is shown that the two pairing forces give very different values for the cooling time. (authors)

  3. Nuclear superfluidity and cooling time of neutron-star crust

    International Nuclear Information System (INIS)

    We analyse the effect of neutron superfluidity on the cooling time of inner crust matter in neutron stars, in the case of a rapid cooling of the core. The specific heat of the inner crust, which determines the thermal response of the crust, is calculated in the framework of HFB approach at finite temperature. The calculations are performed with two paring forces chosen to simulate the pairing properties of uniform neutron matter corresponding respectively to Gogny-BCS approximation and to many-body techniques including polarisation effects. Using a simple model for the heat transport across the inner crust, it is shown that the two pairing forces give very different values for the cooling time. (authors)

  4. Dust or Crust?: Surface Soil Nutrients in the Kalahari (United States)

    Thomas, A. D.; Dougill, A. J.


    The Kalahari covers 2.5 million km2 of southern Africa and consists of 95% fine sand-sized, aeolian-deposited sediment. Soils are predominantly deep, structureless and lacking in N, P and organic matter. Plant available nutrients are concentrated in the top centimetre and thus vulnerable to degradation and transportation by wind erosion. The fertility of Kalahari soils is important for nutritious grass production as livestock grazing remains the predominant livelihood throughout the region. The aim of the research was to investigate the interrelationships between dust, biological crusts, vegetation and disturbance across the Kalahari. Crust, vegetation and surface nutrient characteristics were determined at five locations of different land uses. The spatial and temporal variability of rainfall results in an incomplete vegetation cover and spatially heterogeneous soil nutrients. Our studies show that nutrient heterogeneity is controlled by various factors operating at different scales and is important for ecosystem functioning and degradation vulnerability. At a landscape scale, variability is minimal due to limited topography and a relatively uniform Kalahari Sand cover. At a smaller scale, spatial heterogeneity of soil N and P is also low (11 to 28%) compared to shrublands in the SW United States. Wind erosion is not the principal cause of nutrient heterogeneity because the amount of dust movement and associated nutrient fluxes are low. This is because of an extensive vegetation cover that reduces erodibility and coarse grain sizes, aggregation and biological crusts which reduce surface erosivity. Enrichment occurs under bush canopies due to organic inputs from the vegetation as well as fixation by biological soil crusts that develop preferentially in protected sub-canopy niches. Biological soil crusts are widespread and are able to persist in landscapes where there is a high level of disturbance. However, crust composition is largely restricted to simple Microcoleus spp. Crustal succession is limited by both breakage of crusts and burial by wind blown sediment. In a typical communal grazing area, 48% of the surface was unconsolidated, 44% was crusted and 8% buried crusts compared to up to 95% crust cover in National Parks. Bush sub-canopies are sites of preferential crust development and thus nutrient enrichment, but are also subjected to periodic burial by wind blown dust and plant litter. The overall impact on surface nutrients will depend upon the bush species composition, canopy structure and degree of disturbance.

  5. Cost synergies in M&A


    Nowak, Daniel; Nyman, Robert,


    Background: Today, M&A carried out by European companies stands for a significant share of the total M&A (Gaughan, 2002). One example, is the M&A between two of Europe’s superior truck manufacturers, MAN and Scania. In fact, M&A with Swedish companies have reached a level, close to all time high, during the year of 2006. However, it still prevails an ambiguity whether M&A are followed by success or by failure. An explanation is synergies in general and cost synergies in pa...

  6. Seismic characteristics of central Brazil crust and upper mantle: A deep seismic refraction study (United States)

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


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

  7. Impacts of the Nuclear Symmetry Energy on Neutron Star Crusts

    CERN Document Server

    Bao, Shishao


    Using the relativistic mean-field theory, we adopt two different methods, namely, the coexisting phase method and the self-consistent Thomas-Fermi approximation, to study the impacts of the nuclear symmetry energy on properties of neutron star crusts within a wide range of densities. It is found that the nuclear symmetry energy and its density slope play an important role in determining the pasta phases and the crust-core transition.

  8. Fracture behaviour of bread crust: Effect of bread cooling conditions


    Primo Martin, C.; Beukelaer, H.J., de; Hamer, R.J.; Vliet, T.


    The effect of air and vacuum cooling on the fracture behaviour and accompanying sound emission, moisture content and crispness of bread crust were investigated. Vacuum cooling resulted in rapid evaporative cooling of products that contained high moisture content. Fracture experiments showed a clear dependence of fracture properties on the way the bread was cooled. Vacuum cooling gave breads with a lower moisture content in the crust than the air cooled breads. Both fracture behaviour and soun...

  9. Deep Crustal Heating in a Multicomponent Accreted Neutron Star Crust


    Steiner, Andrew W.


    A quasi-statistical equilibrium model is constructed to simulate the multicomponent composition of the crust of an accreting neutron star. The ashes of rp-process nucleosynthesis are driven by accretion through a series of electron captures, neutron emissions, and pycnonuclear fusions up to densities near the transition between the neutron star crust and core. A liquid droplet model which includes nuclear shell effects is used to provide nuclear masses far from stability. Re...

  10. Crusted scabies-associated immune reconstitution inflammatory syndrome


    Fernández-Sánchez Mónica; Saeb-Lima Marcela; Alvarado-de la Barrera Claudia; Reyes-Terán Gustavo


    Abstract Background Despite the widely accepted association between crusted scabies and human immunodeficiency virus (HIV)-infection, crusted scabies has not been included in the spectrum of infections associated with immune reconstitution inflammatory syndrome in HIV-infected patients initiating antiretroviral therapy. Case presentation We report a case of a 28-year-old Mexican individual with late HIV-infection, who had no apparent skin lesions but soon after initiation of antiretroviral th...

  11. An elderly long-term care resident with crusted scabies


    Sandre, Matthew; Ralevski, Filip; Rau, Neil


    Crusted scabies, also referred to as Norwegian scabies, is a highly contagious infection of the skin caused by Sarcoptes scabiei mites. The authors report a case involving a 94-year-old woman with dementia who presented with symptoms of crusted scabies, which were initially believed to be due to a different skin condition. The risk factors as well as appropriate treatment courses for this infection are also reviewed.

  12. Magnetar activity mediated by plastic deformations of neutron star crust


    Lyutikov, Maxim


    We advance a "Solar flare" model of magnetar activity, whereas a slow evolution of the magnetic field in the upper crust, driven by electron MHD (EMHD) flows, twists the external magnetic flux tubes, producing persistent emission, bursts and flares. At the same time the neutron star crust plastically relieves the imposed magnetic field stress, limiting the strain $ \\epsilon_t $ to values well below the critical strain $ \\epsilon_{crit}$ of a brittle fracture, $ \\epsilon_t \\s...

  13. Soil invertebrate activity in biological crusts on tropical inselbergs


    Vaçulik, Anne; Kounda-Kiki, Charlotte; Sarthou, Corinne; Ponge, Jean-François


    Granite inselbergs protrude from forest and savanna in the tropics. They are exposed to harsh climates (alternation of heavy rain and severe drought) and provide little nutrient for plants. Soil animals and humus components were investigated in cyanobacterial crusts close to patches of epilithic vegetation on the surface of the Nouragues inselberg (French Guiana). Three biological crust samples, corresponding to bromeliacean carpets of increasing size (supposed of increasing age), were sample...

  14. The Indian Ocean Nodule Field: Petrotectonic evolution and ferromanganese deposits

    Digital Repository Service at National Institute of Oceanography (India)

    Mukhopadhyay, R.; Iyer, S.D.; Ghosh, A.K.

    to global mid-ocean ridge mor- phology. For instance, the crust generated from slow spreading ridges (i.e., sector D) is characterised by episodic mode of accretion, discontinuous faulting and rugged flanking morphology. In contrast, the crust generated from... Tapascott et al. (1980). However, Munschy and Schlich (1989) rejected the concept of ridge–ridge–ridge configura- tion and proposed a ridge–ridge–fault configuration suggesting that both the CIR and SEIR are progres- sively offset at a rate of 1.4 mm...

  15. Rapid hydrothermal cooling above the axial melt lens at fast-spreading mid-ocean ridge. (United States)

    Zhang, Chao; Koepke, Juergen; Kirchner, Clemens; Götze, Niko; Behrens, Harald


    Axial melt lenses sandwiched between the lower oceanic crust and the sheeted dike sequences at fast-spreading mid-ocean ridges are assumed to be the major magma source of oceanic crust accretion. According to the widely discussed "gabbro glacier" model, the formation of the lower oceanic crust requires efficient cooling of the axial melt lens, leading to partial crystallization and crystal-melt mush subsiding down to lower crust. These processes are believed to be controlled by periodical magma replenishment and hydrothermal circulation above the melt lens. Here we quantify the cooling rate above melt lens using chemical zoning of plagioclase from hornfelsic recrystallized sheeted dikes drilled from the East Pacific at the Integrated Ocean Drilling Program Hole 1256D. We estimate the cooling rate using a forward modelling approach based on CaAl-NaSi interdiffusion in plagioclase. The results show that cooling from the peak thermal overprint at 1000-1050°C to 600°C are yielded within about 10-30 years as a result of hydrothermal circulation above melt lens during magma starvation. The estimated rapid hydrothermal cooling explains how the effective heat extraction from melt lens is achieved at fast-spreading mid-ocean ridges. PMID:25209311

  16. Obama vu de ma banlieue.

    Directory of Open Access Journals (Sweden)

    Olga Stanislawska


    Full Text Available Une petite brocante est organisée tous les jeudis sur une place proche de la Basilique de Saint-Denis. On y vend des livres, des bibelots, des bijoux fantaisies et des masques africains. L’un des vendeurs a visiblement décidé de bénéficier de l’effet Obama. J’ai pris la photo de ma fenêtre, située au dessus de ce marché. J’ai adoré ce stand, mais ce n’est qu’une fois sur l’écran de mon ordinateur que j’ai vu les petites images Banania... ! Si j’avais su, je serais ...

  17. Gold in the oceans through time (United States)

    Large, Ross R.; Gregory, Daniel D.; Steadman, Jeffrey A.; Tomkins, Andrew G.; Lounejeva, Elena; Danyushevsky, Leonid V.; Halpin, Jacqueline A.; Maslennikov, Valeriy; Sack, Patrick J.; Mukherjee, Indrani; Berry, Ron; Hickman, Arthur


    During sedimentation and diagenesis of carbonaceous shales in marine continental margin settings, Au is adsorbed from seawater and organic matter and becomes incorporated into sedimentary pyrite. LA-ICPMS analysis of over 4000 sedimentary pyrite grains in 308 samples from 33 locations around the world, grouped over 123 determined ages, has enabled us to track, in a first order sense, the Au content of the ocean over the last 3.5 billion years. Gold was enriched in the Meso- and Neoarchean oceans, several times above present values, then dropped by an order of magnitude from the first Great Oxidation Event (GOE1) through the Paleoproterozoic to reach a minimum value around 1600 Ma. Gold content of the oceans then rose, with perturbations, through the Meso- and Neoproterozoic, showing a steady rise at the end of the Proterozoic (800 to 520 Ma), which most likely represents the effects of the second Great Oxidation Event (GOE2). Gold in the oceans was at a maximum at 520 Ma, when oxygen in the oceans rose to match current maximum values. In the Archean and Proterozoic, the Au content of seawater correlates with the time distribution of high-Mg greenstone belts, black shales and banded iron formations, suggesting that increases in atmospheric oxygen and marine bio-productivity, combined with the higher background of Au in komatiitic and Mg-rich basalts were the first order causes of the pattern of Au enrichment in seawater. We suggest the lack of major Au deposits from 1800 to 800 Ma, is explained by the low levels of Au in the oceans during this period.

  18. Development of biological soil crusts and their influence on soil hydrology in the recultivation area of lignite open-cast mining district in Lower Lusatia (Germany) (United States)

    Spröte, R.; Veste, M.; Fischer, T.; Raab, T.; Bens, O.; Hüttl, R. F.


    Cyanobacteria, green algae, mosses and lichens are often the first colonizers of substrate and initial soil surfaces. They are an important factor of initial soil formation as they stabilize the substrate and decrease erosion processes. Biological soil crusts accumulate the initial soil organic matter and provide nitrogen fixation. Once settled, the crusts influence the soil water regime by delaying or limiting infiltration through enhanced water repellency. Aim of this study was to compare the influence of biological soil crusts on soil hydrology under conditions on various substrates and of different ages in recultivated areas of the open-cast mining district of Lower Lusatia (Brandenburg, NE Germany) with various recultivation aims. In Brandenburg (NE Germany), where the climate is transitional between oceanic and continental and the summers are characterized by generally low of precipitation (mean annual rainfall 559 mm, mean annual temperature 9.3° C) open landscapes provide ideal conditions for biological soil crusts, e. g. on mobile sand dunes in former military training areas and in recultivation areas related to open-cast mining with initial soil development. Here biological soil crusts are commonly found (Spröte et al., 2010). At five study sites in recultivation areas with different reclamation approaches (natural development, pine reforestation, birch reforestation) we defined four types of biological soil crusts: i) cyanobacterial and green algae crusts on the soil surface with no vegetation where dominating sand grains were physically stabilized in their contact zones by this crust type (type 1), ii) cyanobacteria and green algae partially filled in the matrix pores and enmeshed sand grains between sparse vegetation cover (type 2), iii) biological soil crusts with mosses which covered most of the surface between the vegetation (type 3) and (iv) with soil lichens (type 4). We investigated the development of the amount of chlorophyll a which is an indicator for biomass productivity and depends from the species composition and crust type, and the water repellency index which shows the influence of biological soil crusts on hydrological parameters. Additionally, organic matter content (dry combustion) as well as soil pH (soil: H2O = 1:2.5) were determined. Texture was analysed by wet sieving and fractionation pipette method. At all study sites and for all crust types soil pH ranged between 7.2 to 4.7 and decreased from type 1 to type 4. Soil organic matter and chlorophyll a concentrations ranged from 0.3 and 1.7% and from 0.95 to 16.44 mg m-2, respectively, and increased from type 1 to type 4. With few exceptions, water repellency indices ranging between 1.0 and 1.85, followed this trend. Constrarily, infiltration rates decreased from type 1 to type 4. The cause for limited infiltration is the swelling of extracellular polysaccharides in the biological soil crusts (Fischer et al., 2010) and the influence of the particle size distribution and porosity of the substrate with a relatively high content of silt and clay at some study sites. Fischer, T., Veste, M., Wiehe, W. & Lange, P. (2010): Water repellency and pore clogging at early succesional stages of microbiotic crusts on inland dunes, Brandenburg, NE Germany. - Catena, 80, 47-52. Spröte, R.,Fischer, T., Veste, M., Raab, T., Wiehe, W., Lange, P., Bens, O., Hüttl, R.F. (2010): Biological topsoil crusts at early successional stages on Quaternary substrates dumped by mining in Brandenburg, NE Germany. Géomorphologie: relief, processus, environnement 4/2010: 359-370.

  19. Multipolarity remanences in lower oceanic crustal gabbros recovered by drilling at Hess Deep (Integrated Ocean Drilling Program Expedition 345) (United States)

    Morris, Antony; Horst, Andrew; Friedman, Sarah; Nozaka, Toshio


    A long-term goal of the scientific ocean drilling community is to understand the processes by which the ocean crust is constructed through magmatism, deformation, metamorphism and hydrothermal cooling. Insights into the magnetic properties of the lower crust have come from drilling at oceanic core complexes and in tectonic windows. At the Hess Deep Rift, propagation of the Cocos-Nazca Ridge into young, fast-spreading East Pacific Rise crust exposes a dismembered, but nearly complete lower crustal section. Here, IODP Expedition 345 (Site U1415) recovered primitive plutonic lithologies including gabbro, troctolitic gabbro and olivine gabbronorite. These rocks exhibit cumulate textures similar to those found in layered basic intrusions and some ophiolite complexes. Metamorphism is dominated by background greenschist facies alteration associated with cataclastic deformation that likely results from Cocos-Nazca rifting. Some intervals display complex, multiple remanence components within individual samples. A high temperature component unblocks above 500°-520°C and an intermediate temperature component of nearly antipodal direction unblocks between 425°-450°C and 500°-520°C. In addition, a few samples display a third component that unblocks between 100-350°C that is nearly parallel to the highest temperature component. These multiple, nearly antipodal components suggest that remanence was acquired in different geomagnetic chrons, and represent the first multipolarity remanences seen in Pacific lower oceanic crust. Similar remanence structures, however, have been reported in lower crustal gabbros recovered from slow-spreading rate crust along the Mid-Atlantic Ridge, and have been interpreted to reflect protracted accretion or protracted cooling. In contrast, at Hess Deep unblocking temperatures appear consistent with temperatures inferred for successive phases of alteration, suggesting an alteration history spanning at least two polarity chrons.

  20. Exploring the Earth's crust: history and results of controlled-source seismology (United States)

    Prodehl, Claus; Mooney, Walter D.


    This volume contains a comprehensive, worldwide history of seismological studies of the Earth’s crust using controlled sources from 1850 to 2005. Essentially all major seismic projects on land and the most important oceanic projects are covered. The time period 1850 to 1939 is presented as a general synthesis, and from 1940 onward the history and results are presented in separate chapters for each decade, with the material organized by geographical region. Each chapter highlights the major advances achieved during that decade in terms of data acquisition, processing technology, and interpretation methods. For all major seismic projects, the authors provide specific details on field observations, interpreted crustal cross sections, and key references. They conclude with global and continental-scale maps of all field measurements and interpreted Moho contours. An accompanying DVD contains important out-of-print publications and an extensive collection of controlled-source data, location maps, and crustal cross sections.

  1. Enhanced anatexis as a consequence of mantle-derived magma intrusion in the middle crust: a case study from the Eastern French Massif Central (United States)

    Couzinié, Simon; Moyen, Jean-François; Villaros, Arnaud; Paquette, Jean-Louis; Scarrow, Jane H.; Marignac, Christian


    The post-collisional stage of orogens corresponds to a dramatic change in mountain belts dynamics. During this period, large volumes of granitic melts are generated in the crust thus impacting its rheology and overall behavior. Evolving from compression/transpression to extension/transtension enhances exhumation of high-grade metamorphic rocks and subsequent decompression crustal melting. However, other processes can trigger anatexis such as heat or fluid fluxes from the mantle and the crust. The Early Carboniferous nappe stack of the Eastern French Massif Central (EFMC) underwent two successive low-pressure melting events at the end of its evolution, during the Late Carboniferous. They are particularily evident in the southern edge of the Velay Complex, a 100 km-diameter migmatite-granite dome. The M3 'pre-Velay' event corresponds to water-saturated melting in the amphibolite facies at T heat input at the M3-M4 transition. The EFMC anatectic crust is intruded by widespread, Mg-K-rich biotite-rich diorites locally called 'vaugnerites'. These mantle-derived melts emplaced in a partially molten setting, as evidenced by mingling features between vaugnerites and anatectic melts, as well as the presence of hybrid granitoids including a 'vaugnerite' component. In situ (LA-ICP-MS) U-Pb zircon and monazite dating of vaugnerites or coeval granites in the Southern Velay area yielded ages mostly indistinguishable within analytical uncertainties, spanning from 307.4 ± 1.8 to 303.7 ± 3.1 Ma. Thus, mantle-derived magmas emplaced at ca. 305 Ma which is the very transition from M3 to M4. This striking synchronism between enhanced crustal melting and mantle-derived magmatism suggests that vaugnerites could be the cause of the M3-M4 transition. Depending on the volume involved, the emplacement of hot (ca. 1000 ° C) melts in mid crustal levels would have supplied significant amounts of heat. Vaugnerites could also be the manifestation of a (yet unconstrained) process enhancing the conductive mantle heat flux to the crust. For instance, delamination of a lithospheric mantle root or slab break-off would result in generation of mantle-derived melts as well as increase the heat conduction into the crust. Therefore, the relevant system that must be considered to study late-orogenic periods is not only the crust but the whole lithosphere, taking into account mass/heat transfer from the mantle to the overlying crust.

  2. The unstable CO2 feedback cycle on ocean planets (United States)

    Kitzmann, Daniel; Alibert, Yann; Godolt, Mareike; Grenfell, John Lee; Heng, Kevin; Patzer, Beate; Rauer, Heike; Stracke, Barbara; von Paris, Philip


    Ocean planets are volatile rich planets, not present in our Solar System, which are dominated by deep, global oceans. Theoretical considerations and planet formation modeling studies suggest that extrasolar ocean planets should be a very common type of planet. One might therefore expect that low-mass ocean planets would be ideal candidates when searching for habitable exoplanets, since water is considered to be an essential requirement for life. However, a very large global ocean can also strongly influence the climate.The high pressure at the oceans bottom results in the formation of high-pressure water ice, separating the planetary crust from the liquid ocean and, thus, also from the atmosphere. In our study we, therefore, focus on the CO2 cycle between the atmosphere and the ocean which determines the atmospheric CO2 content. The atmospheric amount of CO2 is a fundamental quantity for assessing the potential habitability of the planet's surface because of its strong greenhouse effect, which determines the planetary surface temperature to a large degree.In contrast to the stabilising carbonate-silicate cycle regulating the long-term CO2 inventory of the Earth atmosphere, we find that the CO2 cycle on ocean planets is positive and has strong destabilising effects on the planetary climate. By using a chemistry model for oceanic CO2 dissolution and an atmospheric model for exoplanets, we show that the CO2 feedback cycle is severely limiting the potential habitability of ocean planets.

  3. Triassic "adakitic" rocks in an extensional setting (North China): Melts from the cratonic lower crust (United States)

    Ma, Qiang; Zheng, Jianping; Griffin, W. L.; Zhang, Ming; Tang, Huayun; Su, Yuping; Ping, Xianquan


    Adakite was originally defined as a specific type of magmatic rock derived from melting of subducted oceanic plates (Defant, M.J., Drummond, M.S., 1990. Derivation of some modern arc magmas by melting of young subducted lithosphere. Nature 347 (6294), 662-665), producing unique chemical signatures with high Sr/Y and La/Yb. However, widespread occurrences of igneous rocks that are geochemically similar to the adakites, but from diverse tectonic settings, suggest that "adakitic" rocks may have a variety of origins. Late Triassic high Sr/Y lavas, mainly trachytes with minor pyroxene andesite and rhyolite, are found at Shuiquangou, in the Yanshanian fold-and-thrust belt on the northern margin of the North China Craton. Data on mineral chemistry, major and trace elements and Sr-Nd isotopes of whole rocks, and in situ U-Pb age and Hf-isotope analyses of zircons are reported here. The Shuiquangou volcanic rocks with high Sr/Y (> 72) and (La/Yb)N (> 24) also show enrichment in light rare-earth elements and large-ion lithophile elements (e.g., Rb, Ba and Pb), and depletion in high-field-strength elements (e.g., Nb, Ta and Ti). They have low Ce/Pb (Asian Ocean. Their high Sr/Y is inherited from their source, and does not necessarily imply melting at great depths (e.g., garnet-bearing lower crust). We suggest that partial melting of the ancient lower crust may be important for the petrogenesis of "adakitic" magmas in a continental extensional setting.

  4. MA transmutation performance in the optimized MYRRHA

    International Nuclear Information System (INIS)

    MYRRHA (multi-purpose hybrid research reactor for high-tech applications) is a multipurpose research facility currently being developed at SCK-CEN. It will be able to work in both critical and subcritical modes and, cooled by lead-bismuth eutectic. In this paper the minor actinides (MA) transmutation capabilities of MYRRHA are investigated. (Pu + Am, U) MOX fuel and (Np + Am + Cm, Pu) Inert Matrix Fuel test samples have been loaded in the central channel of the MYRRHA critical core and have been irradiated during five cycles, each one consisting of 90 days of operation at 100 MWth and 30 days of shutdown. The reactivity worth of the test fuel assembly was about 1.1 dollar. A wide range of burn-up level has been achieved, extending from 42 to 110 MWd/kg HM, the samples with lower MA-to-Pu ratios reaching the highest burn-up. This study has highlighted the importance of the initial MA content, expressed in terms of MA/Pu ratio, on the transmutation rate of MA elements. For (Pu + Am, U) MOX fuel samples, a net build-up of MA is observed when the initial content of MA is very low (here, 1.77 wt% MA/Pu) while a net decrease in MA is observed in the sample with an initial content of 5 wt%. This suggests the existence of some 'equilibrium' initial MA content value beyond which a net transmutation is achievable

  5. MA transmutation performance in the optimized MYRRHA

    Energy Technology Data Exchange (ETDEWEB)

    Malambu, E.; Van den Eynde, G.; Fernandez, R.; Baeten, P.; Ait Abderrahim, H. [SCK-CEN, Boeretang 200, BE-2400 Mol (Belgium)


    MYRRHA (multi-purpose hybrid research reactor for high-tech applications) is a multipurpose research facility currently being developed at SCK-CEN. It will be able to work in both critical and subcritical modes and, cooled by lead-bismuth eutectic. In this paper the minor actinides (MA) transmutation capabilities of MYRRHA are investigated. (Pu + Am, U) MOX fuel and (Np + Am + Cm, Pu) Inert Matrix Fuel test samples have been loaded in the central channel of the MYRRHA critical core and have been irradiated during five cycles, each one consisting of 90 days of operation at 100 MWth and 30 days of shutdown. The reactivity worth of the test fuel assembly was about 1.1 dollar. A wide range of burn-up level has been achieved, extending from 42 to 110 MWd/kg HM, the samples with lower MA-to-Pu ratios reaching the highest burn-up. This study has highlighted the importance of the initial MA content, expressed in terms of MA/Pu ratio, on the transmutation rate of MA elements. For (Pu + Am, U) MOX fuel samples, a net build-up of MA is observed when the initial content of MA is very low (here, 1.77 wt% MA/Pu) while a net decrease in MA is observed in the sample with an initial content of 5 wt%. This suggests the existence of some 'equilibrium' initial MA content value beyond which a net transmutation is achievable.

  6. H11346_MB25M_GEO.TIF: Color Shaded-Relief GeoTIFF Image Showing the 25-m Bathymetry Generated from National Oceanic and Atmospheric Administration (NOAA) Survey H11346 in the vicinity of Edgartown Harbor, MA (Geographic, WGS84) (United States)

    U.S. Geological Survey, Department of the Interior — The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone...

  7. H11346_MB25M_UTM19.TIF: Color Shaded-Relief GeoTIFF Image Showing the 25-m Bathymetry Generated from National Oceanic and Atmospheric Administration (NOAA) Survey H11346 in the vicinity of Edgartown Harbor, MA (UTM Zone 19, WGS84) (United States)

    U.S. Geological Survey, Department of the Interior — The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone...

  8. Widespread and synchronous change in deep-ocean circulation in the North and South Atlantic during the Late Cretaceous


    Robinson, SA; Vance, D


    Modern thermohaline circulation plays a role in latitudinal heat transport and in deep-ocean ventilation, yet ocean circulation may have functioned differently during past periods of extreme warmth, such as the Cretaceous. The Late Cretaceous (100-65Ma) was an important period in the evolution of the North Atlantic Ocean, characterized by opening ocean gateways, long-term climatic cooling and the cessation of intermittent periods of anoxia (oceanic anoxic events, OAEs). However, how these phe...

  9. Indian Ocean Triple Junction

    Energy Technology Data Exchange (ETDEWEB)

    Tapscott, C.R.; Patriat, P.; Fisher, R.L.; Sclater, J.G.; Hoskins, H.; Parsons, B.


    The boundaries of three major plates (Africa, India, and Antarctica) meet in a triple junction in the Indian Ocean near 25 /sup 0/S, 70 /sup 0/E. Using observed bathymetry and magnetic anomalies, we locate the junction to within 5 km and show that it is a ridge-ridge-ridge type. Relative plate motion is N60 /sup 0/E at 50 mm/yr (full rate) across the Central Indian Ridge, N47 /sup 0/E at 60 mm/yr across the Southeast Indian Ridge, and N3 /sup 0/W at 15 mm/yr across te Southwest Indian Ridge; the observed velocity triangle is closed. Poles of instantaneous relative plate motion are determined for all plate pairs. The data in the South Atlantic and Indian oceans are consistent with a rigid African plate without significant internal deformation. Two of the ridges at the triple junction are normal midocean spreading centers with well-defined median valleys. The Southwest Indian Ridge, however, has a peculiar morphology near the triple junction, that of an elongate triangular deep, with the triple junction at its apex. The floor of the deep represents crust formed at the Southwest Indian Ridge, and the morphology is a consequence of the evolution of the triple junction and is similar to that at the Galapagos Triple Junction. Though one cannot determine with precision the stability conditions at the triple junction, the development of the junction over the last 10 m.y. can be mapped, and the topographic expressions of the triple junction traces may be detected on the three plates.

  10. Improving Earthquake-Explosion Discrimination using Attenuation Models of the Crust and Upper Mantle

    Energy Technology Data Exchange (ETDEWEB)

    Pasyanos, M E; Walter, W R; Matzel, E M; Rodgers, A J; Ford, S R; Gok, R; Sweeney, J J


    In the past year, we have made significant progress on developing and calibrating methodologies to improve earthquake-explosion discrimination using high-frequency regional P/S amplitude ratios. Closely-spaced earthquakes and explosions generally discriminate easily using this method, as demonstrated by recordings of explosions from test sites around the world. In relatively simple geophysical regions such as the continental parts of the Yellow Sea and Korean Peninsula (YSKP) we have successfully used a 1-D Magnitude and Distance Amplitude Correction methodology (1-D MDAC) to extend the regional P/S technique over large areas. However in tectonically complex regions such as the Middle East, or the mixed oceanic-continental paths for the YSKP the lateral variations in amplitudes are not well predicted by 1-D corrections and 1-D MDAC P/S discrimination over broad areas can perform poorly. We have developed a new technique to map 2-D attenuation structure in the crust and upper mantle. We retain the MDAC source model and geometrical spreading formulation and use the amplitudes of the four primary regional phases (Pn, Pg, Sn, Lg), to develop a simultaneous multi-phase approach to determine the P-wave and S-wave attenuation of the lithosphere. The methodology allows solving for attenuation structure in different depth layers. Here we show results for the P and S-wave attenuation in crust and upper mantle layers. When applied to the Middle East, we find variations in the attenuation quality factor Q that are consistent with the complex tectonics of the region. For example, provinces along the tectonically-active Tethys collision zone (e.g. Turkish Plateau, Zagros) have high attenuation in both the crust and upper mantle, while the stable outlying regions like the Indian Shield generally have low attenuation. In the Arabian Shield, however, we find that the low attenuation in this Precambrian crust is underlain by a high-attenuation upper mantle similar to the nearby Red Sea Rift. Applying this 2-D MDAC methodology with the new attenuation models can significantly improve earthquake-explosion discrimination using regional P/S amplitude ratios. We demonstrate applications of this technique, including a study at station NIL (Nilore, Pakistan) using broad area earthquakes and the 1998 Indian nuclear explosion using a number of regional amplitude ratio discriminants. We are currently applying the technique in the YSKP region as well.

  11. Crust-Poor Lithosphere at Cold Spots in the Mid Atlantic and SW Indian Ridges (United States)

    Brunelli, D.; Bonatti, E.; Cipriani, A.; Grindlay, N. R.; Ligi, M.; Paganelli, E.; Sclater, J.


    The Equatorial portion of the Mid Atlantic Ridge is thought to reflect a thermal minimum in the subridge structure, with deeper than normal axial topography underlain by high upper mantle seismic velocities revealed by tomography. This stretch of Ridge is intersected by a number of long offset transforms, the longest being the Romanche (offset ~950 km corresponding to ~50 Myr). As the Mid Atlantic Ridge axis approaches the Romanche transform from the south, it gradually deepens; its rift valley disappears, and, starting roughly 50 km from the transform, the basaltic crust becomes patchy and then disappears, leaving mantle ultramafics outcropping on the sea floor. Modelling the "cold edge" effect of the transform on the axial Ridge segment shows that partial melting of the subridge mantle decreases as the transform is approached. Crust-free lithosphere outcrops continuously for several hundred kilometers in a ~30 km wide belt south of the Romanche, indicating that the present-day lack of crustal production has been prevailing for at least 30 million years. The mantle derived serpentinized peridotites are of two types. The majority of the samples show evidence of strong impregnation by basaltic melts. The mineral chemistry of the samples that are free of impregnation suggests that they have undergone a very low degree of melting. These results suggest a quasi-crust-free lithosphere, produce by a mantle that has undergone little or no partial melting, unable to expel the small quantities of melt it generates. The small quantities of basalt produced in this area tend to have alkali affinity and are strongly enriched in H2O. Their REE content show a strong garnet signature, suggesting that they were generated mostly in the garnet peridotite mantle zone (> 20 kbar). This quasi-crust-free impregnated lithosphere probably prevails at cold spots along mid ocean ridges. Peridotites obtained recently from the SW end of the Andrew Bain transform, that offsets the SW Indian Ridge by ~750 km (~50 Myr), are strongly impregnated by basaltic melt, in a situation very similar to that observed near the Romanche. In contrast, peridotites from the NE end of the Andrew Bain transform are not impregnated, and are residual of a significant degree of melting, probably due to the influence of the Marion plume located a few hundred km away.

  12. Microbial Turnover of Fixed Nitrogen Compounds in Oceanic Crustal Fluids (United States)

    Kraft, B.; Wankel, S. D.; Glazer, B. T.; Huber, J. A.; Girguis, P. R.


    Oceanic crust is the largest aquifer on Earth, with a massive volume of seawater advecting through the basaltic crust. The microbiome of this deep marine subsurface biosphere has been estimated to be substantial, and consequently their metabolic activity may have major influences on global biogeochemical cycles. While earlier and recent studies provide insight into the microbial community composition of oceanic crustal fluids, information on the microbial ecophysiology is broadly missing. Therefore, to investigate the microbial transformation of fixed nitrogen compounds in crustal aquifer fluids, fluids were sampled from different horizons of two neighbouring CORK (Circulation Obviation Retrofit Kit) observatories at the North Pond sediment pond. This site is located on the western flank of the Mid Atlantic Ridge and is characterized by relatively young oceanic crust and cold fluids. The crustal fluids contain oxygen and nitrate, which potentially both may serve as electron acceptor for respiration. In a multidisciplinary approach we combined stable isotope incubations, determination of the natural isotopic compositions and plan to analyse relevant functional genes from a metagenomic dataset to investigate the nitrogen cycling at North Pond. The turnover of fixed nitrogen in oceanic crustal fluids may have important implications for the understanding of the global nitrogen cycle.

  13. Geochemical stratigraphy of submarine lavas (3-5 Ma) from the Flamengos Valley, Santiago, Cape Verde

    DEFF Research Database (Denmark)

    Barker, Abigail K; Holm, Paul Martin; Peate, David W.; Baker, Joel A.


    New high-precision Pb-Sr-Nd isotope, major and trace element and mineral chemistry data are presented for the submarine stage of ocean island volcanism on Santiago, one of the southern islands of the Cape Verde archipelago. Pillow basalts and hyaloclastites in the Flamengos Valley are divided into three petrographic and compositional groups; the Flamengos Formation lavas ( 4·6 Ma) dominate the sequence, with the younger Low Si and Coastal groups ( 2·8 Ma) found near the shoreline. Olivine and cl...

  14. Ma Ying-jeou’s Presidential Discourse


    Jonathan Sullivan; Sapir, Eliyahu V.


    "Despite the substantial advances made in cross-Strait relations during Ma Ying-jeou's (Ma Yingjiu) first term, the ROC president's rhetoric varied considerably as he grappled with the difficult reality of implementing campaign and inauguration pledges to establish better relations with China while striving to maintain national respect and sovereignty. In this article, the authors put forward a framework for measuring, analyzing and explaining this variation in President Ma's first-term disco...

  15. Magnetised Neutron Star Crusts and Torsional Shear Modes of Magnetars

    CERN Document Server

    Nandi, Rana


    We discuss outer and inner crusts of neutron stars in strong magnetic fields. Here, we demonstrate the effect of Landau quantization of electrons on the ground state properties of matter in outer and inner crusts in magnetars. This effect leads to the enhancement of the electron number density in strong magnetic fields with respect to the zero field case. For the outer crust, we adopt the magnetic Baym-Pethick-Sutherland model and obtain the sequence of nuclei and equation of state (EoS). The properties of nuclei in the inner crust in the presence of strong magnetic fields are investigated using the Thomas-Fermi model. The coexistence of two phases of nuclear matter - liquid and gas, is assumed in this case. The proton number density in the Wigner-Seitz cell is affected in strong magnetic fields through the charge neutrality. We perform this calculation using the Skyrme nucleon-nucleon interaction with different parameterisations. We find nuclei with larger mass and atomic numbers in the inner crust in the pr...

  16. Interaction of sea water and lava during submarine eruptions at mid-ocean ridges (United States)

    Perfit, M.R.; Cann, J.R.; Fornari, D.J.; Engels, J.; Smith, D.K.; Ridley, W.I.; Edwards, M.H.


    Lava erupts into cold sea water on the ocean floor at mid-ocean ridges (at depths of 2,500 m and greater), and the resulting flows make up the upper part of the global oceanic crust. Interactions between heated sea water and molten basaltic lava could exert significant control on the dynamics of lava flows and on their chemistry. But it has been thought that heating sea water at pressures of several hundred bars cannot produce significant amounts of vapour and that a thick crust of chilled glass on the exterior of lava flows minimizes the interaction of lava with sea water. Here we present evidence to the contrary, and show that bubbles of vaporized sea water often rise through the base of lava flows and collect beneath the chilled upper crust. These bubbles of steam at magmatic temperatures may interact both chemically and physically with flowing lava, which could influence our understanding of deep-sea volcanic processes and oceanic crustal construction more generally. We infer that vapour formation plays an important role in creating the collapse features that characterize much of the upper oceanic crust and may accordingly contribute to the measured low seismic velocities in this layer.

  17. Titanite petrochronology of the Pamir gneiss domes: Implications for middle to deep crust exhumation and titanite closure to Pb and Zr diffusion (United States)

    Stearns, M. A.; Hacker, B. R.; Ratschbacher, L.; Rutte, D.; Kylander-Clark, A. R. C.


    The Pamir Plateau, a result of the India-Asia collision, contains extensive exposures of Cenozoic middle to lower crust in domes exhumed by north-south crustal extension. Titanite grains from 60 igneous and metamorphic rocks were investigated with U-Pb + trace element petrochronology (including Zr thermometry) to constrain the timing and temperatures of crustal thickening and exhumation. Titanite from the Pamir domes records thickening from ~44 to 25 Ma. Retrograde titanite from the Yazgulem, Sarez, and Muskol-Shatput domes records a transition from thickening to exhumation at ~20-16 Ma, whereas titanite from the Shakhadara dome records prolonged exhumation from ~20 to 8 Ma. The synchronous onset of exhumation may have been initiated by breakoff of the Indian slab and possible convective removal of the Asian lower crust and/or mantle lithosphere. The prolonged exhumation of the Shakhdara and Muztaghata-Kongur Shan domes may have been driven by continued rollback of the Asian lithosphere concurrent with shortening and northwestward translation of the Pamir Plateau.

  18. High?resolution image of the oceanic moho in the subducting Nazca Plate from P?S converted waves


    Günther Bock; Bernd Schurr; Günther Asch


    Short?period P?S converted waves outline the oceanic Moho of the descending Nazca plate in northern Chile at 24°S. Comparison with hypocentral locations obtained with temporary local seismic networks show that earthquakes inside the subducting oceanic lithosphere of the Nazca plate are located predominantly in the oceanic crust at depths between 70 and 120 km, and probably in the upper mantle at depths below 120 km. The results suggest that dehydration embrittlement as mechanism for intermedi...

  19. Crust-mantle density distribution in the eastern Qinghai-Tibet Plateau revealed by satellite-derived gravity gradients (United States)

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


    As the highest, largest and most active plateau on Earth, the Qinghai-Tibet Plateau has a complex crust-mantle structure, especially in its eastern part. In response to the subduction of the lithospheric mantle of the Indian plate, large-scale crustal motion occurs in this area. Despite the many previous studies, geodynamic processes at depth remain unclear. Knowledge of crust and upper mantle density distribution allows a better definition of the deeper geological structure and thus provides critically needed information for understanding of the underlying geodynamic processes. With an unprecedented precision of 1-2 mGal and a spatial resolution better than 100 km, GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission products can be used to constrain the crust-mantle density distribution. Here we used GOCE gravitational gradients at an altitude of 10km after reducing the effects of terrain, sediment thickness variations, and Moho undulations to image the density structures of eastern Tibet up to 200 km depths. We inverted the residual satellite gravitational gradients using a least square approach. The initial density model for the inversion is based on seismic velocities from the tomography. The model is composed of rectangular blocks, having a uniform density, with widths of about 100 km and variable thickness and depths. The thickness of the rectangular cells changes from10 to 60km in accordance with the seismic model. Our results reveal some large-scale, structurally controlled density variations at depths. The lithospheric root defined by higher-density contrast features from southwest to northeast, with shallowing in the central part: base of lithosphere reaches a depth of180 km, less than 100km, and 200 km underneath the Lhasa, Songpan-Ganzi, and Ordos crustal blocks, respectively. However, these depth values only represent a first-order parameterization because they depend on model discretization inherited from the original seismic tomography model. For example, the thickness of the uniform density blocks centered at140 km depth is as large as 60 km. Low-density crustal anomalies beneath the southern Lhasa and Songpan-Ganzi blocks in our model support the idea of weak lower crust and possible crustal flow, as a result of the thermal anomalies caused by the upwelling of hot deep materials. The weak lower crust may cause the decoupling of the upper crust and the mantle. These results are consistent with many other geophysical studies, confirming the effectiveness of the GOCE gravitational gradient data. Using these data in combination with other geodynamic constraints (e.g., gravity and seismic structure and preliminary reference Earth model), an improved dynamic model can be derived.

  20. Fabrics and Rheology of the Mojave Lower Crust and Lithospheric Mantle (United States)

    Bernard, R. E.; Behr, W. M.


    We use xenoliths from young (3 Ma to present) cinder cones in the tectonically active Mojave desert region of southern California to characterize the rheological properties of the lower crust and upper mantle. The xenoliths were collected from two localities ~90 km apart: the Cima and Dish Hill volcanic fields. The xenolith suites represent a depth range of ~25-60 km and include spinel and plagioclase facies peridotites and lower crustal gabbros. We document how stress, temperature, water content, deformation mechanism, lattice preferred orientation, and style of localization vary with increasing depth in both xenolith suites. Key findings thus far include the following: (1) Both xenolith suites exhibit a wide range of deformation textures, ranging from granular, to protogranular, to porphyroclastic and mylonitic. The higher strain fabrics show no evidence for static annealing, thus are likely reflecting youthful deformation and strain gradients at depth. (2) Both xenolith suites show abundant dynamic recrystallization and other evidence for dislocation creep as the dominant deformation mechanism. This is consistent with recent models of upper mantle post-seismic relaxation following the Landers and Hector Mine earthquakes, which require a component of power-law creep in order to fit the post-seismic surface response. (3) A- and E-type olivine LPOs occur in both xenolith suites. Further work will determine whether these fabrics are related to changes in water content as inferred from experimental studies. (4) Deformation in most lower crustal gabbros is weak, but some show strong fabrics associated with plagioclase-rich zones. (5) Measurements of olivine subgrain sizes in Dish Hill samples are similar to previously published measurements from Cima, suggesting similar stress magnitudes at depth in both locations. Paleopiezometers for olivine and plagioclase indicate stress magnitudes of 11-20 MPa for the uppermost mantle, and 0.1 MPa for the lowermost crust.

  1. The Composition of the Prebasin Crust in the Central Highlands of the Moon (United States)

    Korotev, R. L.


    The Apollo 16 regolith consists of a large amount of material derived from the prebasin crust, i.e., (1) plutonic ferroan anorthosite and brecciated derivatives (>90% plagioclase), (2) a variety of noritic anor-thosites (plutonic, feldspathic fragmental breccias [FFBs], granulitic breccias [GrBs], feldspathic impact-melt breccias), and (3) a minor amount of gabbronorites of highland affinity. However, the site is sufficiently close to nearside mare basins that the regolith also contains a substantial fraction of basin ejecta as well as some mare-derived materials (MDMs) delivered to the site by volcanism and impacts since filling of the basins with mare basalt. These syn- and postbasin products include (4) mafic impact-melt breccias [MIMBs, i.e., "LKFM" and "VHA"], (5) MDMS, i.e., glasses and some crystalline mare basalt, and (6) meteoritic material (largely from micrometeorites) accumulated in the regolith since basin for-ma-tion ~3.9 Ga ago. The MIMBs, which are rich in incompatible trace elements, were formed during the time of basin formation by impacts large enough to penetrate the outer feldspathic crust and melt mafic underlying material, although not all of the several known varieties at the Apollo 16 site may actually have been formed by impacts that produced basins. The Central Highlands, as sampled by the Apollo 16 mission, differs from highlands regions distant from mare basins in its high abundance of mafic syn- and postbasin material. For example, some feldspathic lunar meteorites (ALHA81005, Yamato-86032, MAC 88104/5, QUE93069) contain virtually no MDMSor MIMBs.

  2. Rapid rotational crust-core relaxation in magnetars

    CERN Document Server

    Sedrakian, Armen


    If a magnetar interior $B$-field exceeds $10^{15}$ G it will unpair the proton superconductor in the star's core by inducing diamagnetic currents which destroy the Cooper pair coherence. Then, the $P$-wave neutron superfluid in these non-superconducting regions will couple to the stellar plasma by scattering of protons off the quasiparticles confined in the cores of neutron vortices via the strong (nuclear) force. The dynamical time-scales associated with this interaction span from several minutes at the crust-core interface to a few seconds in the deep core. We show that (a) the rapid crust-core coupling is incompatible with oscillation models of magnetars which decouple completely the core superfluid from the crust and (b) magnetar precession is damped by the coupling of normal fluids to the superfluid core and, if observed, needs to be forced or continuously excited by seismic activity.

  3. Structure of the Crust and the Lithosperic Mantle in Siberia

    DEFF Research Database (Denmark)

    Cherepanova, Yulia


    The study addresses the structure of the lithosphere of Siberia, including the Siberian Craton and the West Siberian Basin, with a particular focus on the crustal structure of the entire region and the density structure of its lithospheric mantle. The first part of the study included the development of a new regional crustal model, SibCrust, that is a digital crustal model for both the Siberian Craton and the West Siberian Basin. The SibCrust model, constrained by digitizing of all available sei...

  4. Recovery rates of cryptobiotic crusts: inoculant use and assessment methods (United States)

    Belnap, Jayne


    Recovery rates of cyanobacterial-lichen soil crusts from disturbance were examined. Plots were either undisturbed or scalped, and scalped plots were either inoculated with surrounding biological crust material or left to recover naturally. Natural recovery rates were found to be very slow. Inoculation significantly hastened recovery for the cyanobacterial/green algal component, lichen cover, lichen species richness, and moss cover. Even with inoculation, however, lichen and moss recovery was minimal. Traditional techniques of assessing recovery visually were found to underestimate time for total recovery. Other techniques, such as extraction of chlorophyll a from surface soil and measurement of sheath material accumulation, were used and are discussed.

  5. Soil stabilization by biological soil crusts in arid Tunisia (United States)

    Guidez, Sabine; Couté, Alain; Bardat, Jacques


    As part of the fight against desertification (LCD) in arid Tunisia, we have been able to highlight the important role played by biological soil crusts (BSC) in soil stabilization. The identification of the major species of cyanobacteria, lichens and bryophytes, their adaptation and terrestrial colonization strategies in this high climatic constraints area through their morpho-anatomical criteria have been set. In addition to their biological composition, their internal arrangement (i.e. texture and microstructure) reflects the structural stability of BSC against erosion. Precisely, the aggregative power of cyanobacteria and their ways of moving inside a soil, the capacity of mosses to grow through the sediments and lichens ability to bind at particles on surface, thus stabilizing the substrate have been demonstrated. Then, the three biological components ability to capture soil particles has been widely illustrated, proving the major environmental contribution of BSC in arid areas biological crusts formation, providing that soils will experience an increase of organic matter and fine particles rates subsequently gaining faster and better stability. Although the thickness and the morphology of crusts are related to the cover rates of these different biological components, the water properties of the latter, studied at the environmental SEM, illustrate their important role in altering the water cycle. Thus, the mixed crusts, i.e. with good presence of three biological components, cause the highest runoff rates by their ability to retain the water and spread on the surface. In spite of a swelling coefficient in presence of water higher than cryptogams, the cyanobacterial crusts located in newly stabilized areas of our studied region, remain finally insufficiently dense to impact surface hydrology. But, we showed after all that the cyanobacteria, pioneer species, have a certain environmental role. The lichen crusts cause a increased runoff because the lichens have a ability to extend them horizontally on the soil surface. Despite the water capture for their metabolism, the water flows; it isn't released in the depth. The moss crusts show an opposite process with an increased infiltration thanks to the possibility of a vertical transit of water through their sheets, stem and roots. So, in relation to bare soils, a crust with a good microbial and cryptogamic development causes more runoff. As part of the fight against the desertification in arid Tunisia, hydrological impact of BSC may lead to elaborate some ecosystem strategies in water and soils management. Indeed, climate aridity is not synonymous with edaphic aridity.

  6. Recent Advances in Multichannel Seismic Imaging for Academic Research in Deep Oceanic Environments

    Directory of Open Access Journals (Sweden)

    Juan Pablo Canales


    Full Text Available Academic research using marine multichannel seismic (MCS methods to investigate processes related to Earth's oceanic crust has made substantial advances in the last decade. These advances were made possible by access to state-of-the-art MCS acquisition systems, and by development of data processing and modeling techniques that specifically deal with the particularities of oceanic crustal structure and the challenges of subseafloor imaging in the deep ocean. Among these methods, we highlight multistreamer three-dimensional (3D imaging, streamer refraction tomography, synthetic ocean bottom experiments (SOBE, and time-lapse (4D studies.

  7. Petrology of seamounts in the Central Indian Ocean Basin: Evidence for near-axis origin

    Digital Repository Service at National Institute of Oceanography (India)

    Mukhopadhyay, R.; Batiza, R.; Iyer, S.D.

    the Cretaceous. In: Moberly R, Schlanger SO, et al. (Eds.), Initial Reports of the Deep Sea Drilling Projects 89:555 576 Dyment J (1993) Evolution of the Indian Ocean triple junction be- tween 65 and 49 Ma (anomalies 28 to 21 Ma). Journal of Geo- physical...

  8. Using Google Earth to Visualize the Core, Mantle, and Crust in Four Dimensions (Invited) (United States)

    de Paor, D. G.; Dordevic, M.; Wild, S. C.; Scientific Team Of Digitalplanet. Org


    Google Earth is generally recognized as a powerful tool for visualizing the Earth’s atmosphere, hydrosphere, and solid surface. However, it’s opaque terrain imagery would seem to preclude most solid earth applications. We have previously described how to visualize the subsurface using emergent COLLADA models. The KML "timespan" element was intended for time series but it can be redeployed to lift models out of the sub surface. We have used this technique mainly to display relatively shallow crustal and lithospheric structures. For studies of the Earth’s interior in four dimensions, we need to use the time slider as originally intended. Therefore, we make the surface transparent in the Primary Layers sidebar and represent deep structures with in situ COLLADA models. This approach enables us to model major stages in Earth’s internal evolution, including differentiation of the liquid core and magma ocean, the formation of the Moon, and the growth of a solid inner core and magnetic field. We can also follow subducted oceanic crust into the lower mantle and model the rise of deep mantle plumes from the core-mantle boundary. There are alternative virtual globes and 3D or 4D modeling tools that may be more powerful than Google Earth but none competes in terms of usability and universal accessibility. The extra effort required at the content creation stage is therefore well worthwhile.

  9. Fundamental properties of MA-cont

    International Nuclear Information System (INIS)

    The thermal and mechanical properties of minor actinide (MA) containing mixed oxide (MOX) fuel were studied from the properties measurements of simulated fuel materials and computer simulations. The simulated fuel materials were prepared, in which MA is substituted by rare earth elements such as Nd. the effect of Nd content to the elastic moduli and thermal conductivity of simulated fuel materials was studied. The molecular dynamics (MD) calculation was performed for MA containing MOX fuels in the temperature range from 300 K to 2500 K to evaluate the thermophysical properties viz., the lattice parameter, thermal expansion coefficient, compressibility, heat capacity, and thermal conductivity. The thermodynamic modelling was carried out for the O-MA-Pu-U system and the oxygen potentials of MA containing MOX fuels were evaluated from the assessed thermodynamic database. The results were compared with the experimental results obtained by JNC groups. (author)

  10. Th, Pb and Sr isotope variations in young island arc volcanics and oceanic sediments

    International Nuclear Information System (INIS)

    Destructive plate margin rocks have (230Th/232Th) values in the range 0.5-2.5, which is similar to those in MORB and OIB. Approximately 60% of the available data on subduction-related rocks plot within 10% of the (230Th/232Th)-(238U/232Th) equiline, and most of the remaining analyses are displaced to high (238U/230Th). Moreover, despite the large range of Th isotope ratios in sediments and altered MORB in the subducted slab, the majority (?70%) of destructive margin rocks plot within the Th-Sr and Th-Pb mantle arrays defined by MORB-OIB. Th/U ranges from 1.0 to 6.6 in the rocks analysed, and both the measured and the source Th/U inferred from initial (230Th/232Th) correlate with 208Pb*/206Pb*. Thus, the major (six-fold) difference in Th/U between different arc suites was established several 100 Ma prior to subduction, and it does not appear to reflect element fractionation processes associated with Recent subduction. Oceanic sediments exhibit a wide range in Th/U but relatively restricted 208Pb*/206Pb* suggesting that the average residence age of pelagic sediments is less than 350 Ma. Th isotopes are sensitive tracers of subducted carbonate, hydrothermally altered oceanic crust and detrital sediments. However, only those from Nicaragua and Tonga exhibit unusually high (230Th/232Th) consistent with a significant contribution of Th from altered MORB and/or carbonate. Most of the water in the subducted slab is in sediments and altered MORB, and so they should dominate the slab-derived contribution. Their bulk (230Th/232Th) values are likely to be >4, which suggests that subducted materials constitute <15% of the Th in arc magmas. Finally, Th/Nb and Ba/Nb ratios are high in subduction-related rocks, but whereas the latter primarily reflects a high Ba/Nb slab flux, the high Th/Nb ratios also reflect partial melting processes in the mantle wedge. (orig./WL)

  11. New Zealand maritime glaciation: millennial-scale southern climate change since 3.9 Ma. (United States)

    Carter, Robert M; Gammon, Paul


    Ocean Drilling Program Site 1119 is ideally located to intercept discharges of sediment from the mid-latitude glaciers of the New Zealand Southern Alps. The natural gamma ray signal from the site's sediment core contains a history of the South Island mountain ice cap since 3.9 million years ago (Ma). The younger record, to 0.37 Ma, resembles the climatic history of Antarctica as manifested by the Vostok ice core. Beyond, and back to the late Pliocene, the record may serve as a proxy for both mid-latitude and Antarctic polar plateau air temperature. The gamma ray signal, which is atmospheric, also resembles the ocean climate history represented by oxygen isotope time series. PMID:15192226

  12. Analysis of environmental factors determining development and succession in biological soil crusts. (United States)

    Lan, Shubin; Wu, Li; Zhang, Delu; Hu, Chunxiang


    Biological soil crusts play important ecological functions in arid and semi-arid regions, while different crust successional patterns appeared in different regions. Therefore in this study, the environmental conditions between Shapotou (with cyanobacterial, lichen and moss crusts) and Dalate Banner (with only cyanobacterial and moss crusts) regions of China were compared to investigate why lichen crusts only appeared in Shapotou; at the same time, artificial moss inoculation was conducted to find out the environmental factors promoting crust succession to moss stage. The results showed lichen crusts always developed from cyanobacterial crusts, which provide not only the stable soil surface, but also the biomass basis for lichen formation; furthermore, addition of crust physicochemical characteristics (primarily silt content) play a facilitating effect on lichen emergence (R(2)=0.53). The inoculation experiment demonstrated early crust soil surface and enough water holding content (>4%) provided the essential guarantee for moss germination. Our results show that there is heterogeneity in crust succession in different regions, which may be mainly affected by the ambient soil microenvironments. It is concluded that a positive feedback mechanism is expected between crust succession and ambient soil microenvironments; while a negative feedback mechanism forms between crust succession and free living cyanobacteria and algae. PMID:26318686

  13. Stable isotope composition and volume of Early Archaean oceans

    DEFF Research Database (Denmark)

    Pope, Emily Catherine; Rosing, Minik Thorleif; Bird, Dennis K.


    Oxygen and hydrogen isotope compositions of seawater are controlled by volatile fluxes between mantle, lithospheric (oceanic and continental crust) and atmospheric reservoirs. Throughout geologic time oxygen was likely conserved within these Earth system reservoirs, but hydrogen was not, as it can escape to space [1]. Hydrogen isotope ratios of serpentinites from the ~3.8Ga Isua Supracrustal Belt in West Greenland are between -53 and -99‰; the highest values are in antigorite ± lizardite serpent...

  14. Titan's rotation reveals an internal ocean and changing zonal winds (United States)

    Lorenz, R.D.; Stiles, B.W.; Kirk, R.L.; Allison, M.D.; Del Marmo, P.P.; Iess, L.; Lunine, J.I.; Ostro, S.J.; Hensley, S.


    Cassini radar observations of Saturn's moon Titan over several years show that its rotational period is changing and is different from its orbital period. The present-day rotation period difference from synchronous spin leads to a shift of ???0.36?? per year in apparent longitude and is consistent with seasonal exchange of angular momentum between the surface and Titan's dense superrotating atmosphere, but only if Titan's crust is decoupled from the core by an internal water ocean like that on Europa.

  15. Isotope composition and volume of Earth´s early oceans

    DEFF Research Database (Denmark)

    Pope, Emily Catherine; Bird, Dennis K.; Rosing, Minik Thorleif


    Oxygen and hydrogen isotope compositions of Earth´s seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen´s was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope c...

  16. Ocean nutrients (United States)

    Boyd, Philip W.; Hurd, Catriona L.

    Nutrients provide the chemical life-support system for phytoplankton in the ocean. Together with the carbon fixed during photosynthesis, nutrients provide the other elements, such as N and P, needed to synthesize macromolecules to build cellular constituents such as ribosomes. The makeup of these various biochemicals, such as proteins, pigments, and nucleic acids, together determine the elemental stoichiometry of an individual phytoplankton cell. The stoichiometry of different phytoplankton species or groups will vary depending on the proportions of distinct cellular machinery, such as for growth or resource acquisition, they require for their life strategies. The uptake of nutrients by phytoplankton helps to set the primary productivity, and drives the biological pump, of the global ocean. In the case of nitrogen, the supply of nutrients is categorized as either new or regenerated. The supply of new nitrogen, such as nitrate upwelled from the ocean' interior or biological nitrogen fixation, is equal to the vertical export of particular organic matter from the upper ocean on a timescale of years. Nutrients such as silica can also play a structural role in some phytoplankton groups, such as diatoms, where they are used to synthesize a siliceous frustule that offers some mechanical protection from grazers. In this chapter, we also explore nutrient uptake kinetics, patterns in nutrient distributions in space and time, the biogeochemical cycle of nitrogen, the atmospheric supply of nutrients, departures from the Redfield ratio, and whether nutrient distributions and cycling will be altered in the future

  17. Crusted scabies in a chid with systemic lupus erythematosus

    Directory of Open Access Journals (Sweden)

    Nurimar C.F. Wanke


    Full Text Available A child with systemic lupus erythematosus who has been treated with prednisone for three years, developed crusted scabies. Scrapings from lesions revealed Sarcoptes scabiei adult mites mad eggs. The patient died with septicemia and renal failure soon after starting topical 20% sulfur. A marked improvement was observed in the cutaneous lesions.

  18. Estimate of plasticity in the crust of neutron stars

    International Nuclear Information System (INIS)

    The influence of plasticity in the crust of a neutron star on the frequency of crustquakes has been estimated and found to be small. The resulting rate of creep, assuming it is a classical, thermally activated process, is obtained and compared to the results of others. (orig.)

  19. Structure of the crust and the lithospheric mantle in Siberia

    DEFF Research Database (Denmark)

    Cherepanova, Yulia


    The study addresses the structure of the lithosphere of Siberia, including the Siberian Craton and the West Siberian Basin, with a particular focus on the crustal structure of the entire region and the density structure of its lithospheric mantle. The first part of the study included the development of a new regional crustal model, SibCrust, that is a digital crustal model for both the Siberian Craton and the West Siberian Basin. The SibCrust model, constrained by digitizing of all available seismic profiles and crustal velocity models across the Siberia, also includes a critical quality assessment of regional seismic data and crustal regionalization based on seismic structure of the crust. The second part of the study included the development of the SibDensity model that is the density model of the lithospheric mantle calculated by the mass balance method. Mantle density modeling involved calculation of the crustal correction based on the SibCrust model. The SibDensity model is made of two independent parts calculated for two major tectonic provinces with contrasting geodynamic evolution: the West Siberian Basin and the Siberian Craton. The modeling results, that are lateral variations in the lithospheric mantle density, are interpreted in terms of regional tectonic evolution, namely the mechanism by which the Paleozoic intracontinental basin has been formed and the tectono-magmatic processes by which the Archean-Proterozoic craton has been modified as reflected in the composition of its mantle.

  20. Symmetry Energy, Neutron Star Crust and Neutron Skin Thickness

    International Nuclear Information System (INIS)

    We analyze the correlations of the slope and curvature parameters of the symmetry energy with the neutron skin thickness of neutron-rich isotopes, and the crust-core transition density in neutron stars. The results are obtained within the microscopic Brueckner-Hartree-Fock approach, and are compared with those obtained with several Skyrme and relativistic mean field models. (author)

  1. Geoelectrical and geological structure of the crust in Western Slovakia.

    Czech Academy of Sciences Publication Activity Database

    Bezák, V.; Pek, Josef; Vozár, J.; Bielik, M.; Vozár, J.


    Ro?. 58, ?. 3 (2014), s. 473-488. ISSN 0039-3169 Institutional support: RVO:67985530 Keywords : magnetotellurics * MT15 profile * Western Carpathians * applied geophysics * Earth’s crust Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 0.806, year: 2014

  2. Sr and Nd isotope geochemistry of oceanic basalts and mantle evolution

    International Nuclear Information System (INIS)

    Sr and Nd isotope ratios are reported for 17 mid-ocean ridge basalts and for 11 oceanic islands and island groups. Data from the Azores, Samoa and the Society Islands diverge significantly from the mantle array. These results are not explained by binary mixing of depleted and undepleted mantle reservoirs or by variable magmatic depletion of a planetary reservoir, but support mantle evolution models involving re-injection of crust material into the mantle. (author)

  3. Harnessing Ocean Energy by Tidal Current Technologies


    Nasir Mehmood; Zhang Liang; Jawad Khan


    The world is heavily dependent on fossil fuels since most of its energy requirements are fulfilled by conventional methods of burning these fuels. The energy demand is increasing by day with growing population. The energy production by fossil fuels is devastating the environment and survival of life on globe is endangered. The renewal energy technologies are vital to ensure future energy sustenance and environmental issues. Ocean is a vast resource of renewable energy. The technology today ma...

  4. Geochemistry and Geochronology of the Lower Crust Beneath Central Mongolia (United States)

    Ancuta, L. D.; Carlson, R. W.; Ionov, D. A.; Zeitler, P. K.


    Two-pyroxene granulite xenoliths recovered from the Shavaryn-Tsaram Quaternary basaltic breccia pipe near Tariat Mongolia provide a snapshot of the modern lower crust beneath the elevated Hangay Dome in central Mongolia. Two-pyroxene thermometry indicates the xenoliths equilibrated at temperatures of 840 ± 30ºC. Previous studies using the Grt-Opx-Pl barometer indicated an upper limit on pressures between 12.5 and 15.5 kbar for samples collected from the same locality (Stosch et al., 1995). Whole-rock trace-element data for the xenoliths show similar trends to arc-derived magmatic rocks, with enrichments in the large-ion lithophile elements and rare earth elements compared to depletion in the high field-strength elements. The arc-like geochemical signature of the lower crust suggests it did not form through underplating during the most recent phase of Cenozoic volcanism, which has geochemical characteristics typical of intraplate volcanism. Instead, the lower crust beneath the Hangay dome may have formed during the accretion of the Central Asian Orogenic Belt (CAOB) in the Late Paleozoic to Early Mesozoic. Alternatively, it could include remnants of older Precambrian basement accreted during the formation of the CAOB. Abundant zircon observed in the samples will be dated by U-Pb laser ablation ICP-MS and ID-TIMS to better determine the timing of lower-crust formation and metamorphism. To the extent that a crustal root supports the high elevation of Hangay region, constraining the age of the root will help place constraints on the timing of crustal thickening and the attainment of high elevation. The post-orogenic, long-term thermal evolution of the lower crust can be assessed using U-Pb analyses of a number of trace phases, including monazite and apatite. Results from these measurements will address the timing and evolution of the high topography in central Mongolia.

  5. Glauconitic laminated crusts from Jurassic pillow-lava deposits (Betic Cordillera, South Spain)


    Reolid, Matías; Abad, Isabel


    An exceptional record of Jurassic glauconitic laminated crusts is reported from veins of spaces among pillow-lava bodies in the Middle Subbetic (Betic Cordillera). The veins are composed by green crusts with planar (

  6. Geochronologic and isotopic evidence for involvement of pre-Pan-African crust in the Nubian shield, Egypt

    Energy Technology Data Exchange (ETDEWEB)

    Sultan, M.; Chamberlain, K.R.; Bowring, S.A.; Arvidson, R.E. (Washington Univ., St. Louis, MO (USA)); Abuzied, H. (Cairo Univ. (Egypt)); El Kaliouby, B. (Ain Shams Univ., Abassia, Cairo (Egypt))


    Two Late Proterozoic granitic bodies from the Eastern Desert of Egypt, the ca. 578 Ma Nakhil and the ca. 595 Ma Aswan granites, provide insights into processes of crust formation in the Arabian-Nubian shield. Evidence for involvement of an older crustal component in the formation of the Nakhil granite includes (1) U/Pb zircon data that establish a crystallization age of 578 {plus minus} 15 Ma and indicate the presence of inherited zircons possibly as old as 1.6 Ga; (2) an elevated model initial {sup 87}Sr/{sup 86}Sr (0.7136); and (3) an elevated initial {sup 207}Pb/{sup 204}Pb (15.561) relative to model mantle compositions at 578 Ma. Evidence for involvement of an older crustal component in the Aswan granite comes from the elevated initial {sup 207}Pb/{sup 204}Pb (15.611). In contrast, extensive crustal contamination is not reflected in the high initial {epsilon}{sub Nd} (+5.7) for the Nakhil and the low initial {sup 87}Sr/{sup 86}Sr (0.7029) for the Aswan granite. The contrasting inferences from the different isotopic systems can be explained by the high whole-rock Nd and Sr concentration for the the Nakhil (87 ppm Nd) and the Aswan (173 ppm Sr) granites, respectively, that suggest that the Nd and Sr isotopic composition of the older component has been overshadowed by the more primitive material. Similar contrasts in Pb, Sr, and Nd isotopic data from the eastern and western shield margins can be interpreted in the same manner and might suggest widespread involvement of older crustal components in the formation of the Late Proterozoic Arabian-Nubian shield.

  7. The Mohorovi?i? discontinuity beneath the continental crust: An overview of seismic constraints (United States)

    Carbonell, Ramon; Levander, Alan; Kind, Rainer


    The seismic signature of the Moho from which geologic and tectonic evolution hypotheses are derived is to a large degree a result of the seismic methodology which has been used to obtain the image. Seismic data of different types, passive source (earthquake) broad-band recordings, and controlled source seismic refraction, densely recorded wide-angle deep seismic reflection, and normal incidence reflection (using VibroseisTM, explosives, or airguns), have contributed to the description of the Moho as a relatively complex transition zone. Of critical importance for the quality and resolution of the seismic image are the acquisition parameters, used in the imaging experiments. A variety of signatures have been obtained for the Moho at different scales generally dependent upon bandwidth of the seismic source. This variety prevents the development of a single universally applicable interpretation. In this way source frequency content, and source and sensor spacing determine the vertical and lateral resolution of the images, respectively. In most cases the different seismic probes provide complementary data that gives a fuller picture of the physical structure of the Moho, and its relationship to a petrologic crust-mantle transition. In regional seismic studies carried out using passive source recordings the Moho is a relatively well defined structure with marked lateral continuity. The characteristics of this boundary change depending on the geology and tectonic evolution of the targeted area. Refraction and wide-angle studies suggest the Moho to be often a relatively sharp velocity contrast, whereas the Moho in coincident high quality seismic reflection images is often seen as the abrupt downward decrease in seismic reflectivity. The origin of the Moho and its relation to the crust-mantle boundary is probably better constrained by careful analysis of its internal details, which can be complex and geographically varied. Unlike the oceanic Moho which is formed in a relatively simple, well understood process, the continental Moho can be subject to an extensive variety of tectonic processes, making overarching conclusions about the continental Moho difficult. Speaking very broadly: 1) In orogenic belts still undergoing compression and active continental volcanic arcs, the Moho evolves with the mountain belt, 2) In collapsed Phanerozoic orogenic belts the Moho under the collapse structure was formed during the collapse, often by a combination of processes. 3) In regions having experienced widespread basaltic volcanism, the Moho can result from underplated basalt and basaltic residuum. In Precambrian terranes the Moho may be as ancient as the formation of the crust, in others Precambrian tectonic and magmatic processes have reset it. We note that seismic reflection data in Phanerosoic orogens as well as from Precambrian cratonic terranes often show thrust type structures extending as deep as the Moho, and suggest that even where crust and mantle xenoliths provide similar age of formation dates, the crust may be semi-allochothonous.

  8. Zircon Lu-Hf isotopes and granite geochemistry of the Murchison Domain of the Yilgarn Craton: Evidence for reworking of Eoarchean crust during Meso-Neoarchean plume-driven magmatism (United States)

    Ivanic, Timothy J.; Van Kranendonk, Martin J.; Kirkland, Christopher L.; Wyche, Stephen; Wingate, Michael T. D.; Belousova, Elena A.


    New in situ Lu-Hf data on zircons from GSWA geochronology samples has provided a unique isotopic dataset with a high temporal resolution for the Murchison Domain of the Yilgarn Craton in Western Australia. These data identify extended periods of juvenile mantle input (positive ?Hf values) into the crust firstly at c. 2980 Ma and then from c. 2820 Ma to c. 2640 Ma with significant pulses of crustal recycling at c. 2750 Ma and c. 2620 Ma (highly negative ?Hf values). Geochemical data from well-characterised granitic suites of the Murchison Domain provide additional constraints on the crustal evolution of the area and indicate a prolonged period of crustal melting and remelting at progressively shallower depths from c. 2750 to c. 2600 Ma. At c. 2760-2753 Ma, widespread calc-alkaline, intermediate to silicic volcanic rocks of the Polelle Group were erupted, accompanied by intrusion of felsic to intermediate melts derived from a variety of crustal sources that likely formed by partial mixing with basaltic melts. The intrusive rocks include a wide geochemical array of rocks in the Cullculli and Eelya suites that were sourced over a wide range of crustal depths. At this time a major departure to negative ?Hf values (Bald Rock Supersuite, resulting in cratonization of this part of the Yilgarn Craton.

  9. Propagation of coupled Rayleigh-gravity waves on the ocean floor


    Vladimir V. Grimalsky; J. Sánchez-Mondragón; Masashi Hayakawa; Svetlana V. Koshevaya; Gennadiy N. Burlak


    It is shown that the Ocean-Earth crust interface can propagate gravity-sound Rayleigh waves. Dispersion properties of waves and flux of energy are derived. It is shown that the waves split into low and fast velocity branches. The fast branch has a multimode structure and has a cutoff in frequency and wave number. Numerical solutions are discussed.

  10. Propagation of coupled Rayleigh-gravity waves on the ocean floor

    Directory of Open Access Journals (Sweden)

    Vladimir V. Grimalsky


    Full Text Available It is shown that the Ocean-Earth crust interface can propagate gravity-sound Rayleigh waves. Dispersion properties of waves and flux of energy are derived. It is shown that the waves split into low and fast velocity branches. The fast branch has a multimode structure and has a cutoff in frequency and wave number. Numerical solutions are discussed.

  11. Dating of the 85 degrees E Ridge (northeastern Indian Ocean) using marine magnetic anomalies

    Digital Repository Service at National Institute of Oceanography (India)

    Michael, L.; Krishna, K.S.

    , in general, by a relief of the ridge and polarity contrast between the ridge material and adjacent oceanic crust, respectively. On correlation of the ridge’s magnetization pattern to the geomagnetic polarity timescale, we believe that the 85 degrees E Ridge...

  12. The worship of Bh?ma


    Duijker, Marijke


    This study deals with stone representations of Bh?ma, one of the protagonists of the Hindu epic Mah?bh?rata. This epic which originates from India, is already known on Java in the tenth century. The Bh?ma representations which include statues and reliefs appeared during the Majapahit Period (1296-1527 C.E.) and were mainly found on mountain sanctuaries in present East and Central Java. Given the number of statues found, there was a worship of Bh?ma going on during the Majapahit Period. ...

  13. Exposure to natural radiation from the earth's crust, atmosphere and outer space - the natural radioactivity of the earth's crust

    International Nuclear Information System (INIS)

    Any conclusions to be drawn from the geochemical distribution pattern of radioactive elements for one's own conduct require to study their distribution in soil, earth crust, magmatic differentiation, rock disintegration zone and biosphere. The author notes that high activities in soils and rocks are contrasted by relatively low radiation dose levels absorbed by the human body. This is different for incorporated radiation. (DG)

  14. Mossbauer studies and oxidised manganese ratio in ferromanganese nodules and crusts from the Central Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Pattan, J; Mudholkar, A.V

    stream_size 5 stream_content_type text/plain stream_name Geo-Mar_Lett_11_51.pdf.txt stream_source_info Geo-Mar_Lett_11_51.pdf.txt Content-Encoding ISO-8859-1 Content-Type text/plain; charset=ISO-8859-1 ...

  15. Thermal Coupling Between the Ocean and Mantle of Europa: Implications for Ocean Convection (United States)

    Soderlund, Krista M.; Schmidt, Britney E.


    Magnetic induction signatures at Europa indicate the presence of a subsurface ocean beneath the cold icy crust. The underlying mantle is heated by radioactive decay and tidal dissipation, leading to a thermal contrast sufficient to drive convection and active dynamics within the ocean. Radiogenic heat sources may be distributed uniformly in the interior, while tidal heating varies spatially with a pattern that depends on whether eccentricity or obliquity tides are dominant. The distribution of mantle heat flow along the seafloor may therefore be heterogeneous and impact the regional vigor of ocean convection. Here, we use numerical simulations of thermal convection in a global, Europa-like ocean to test the sensitivity of ocean dynamics to variations in mantle heat flow patterns. Towards this end, three end-member cases are considered: an isothermal seafloor associated with dominant radiogenic heating, enhanced seafloor temperatures at high latitudes associated with eccentricity tides, and enhanced equatorial seafloor temperatures associated with obliquity tides. Our analyses will focus on convective heat transfer since the heat flux pattern along the ice-ocean interface can directly impact the ice shell and the potential for geologic activity within it.

  16. The Petrology and Geochemistry of Feldspathic Granulitic Breccia NWA 3163: Implications for the Lunar Crust (United States)

    McLeod, C. L.; Brandon, A. D.; Lapen, T. J.; Shafer, J. T.; Peslier, A. H.; Irvine, A. J.


    Lunar meteorites are crucial to understand the Moon s geological history because, being samples of the lunar crust that have been ejected by random impact events, they potentially originate from areas outside the small regions of the lunar surface sampled by the Apollo and Luna missions. The Apollo and Luna sample sites are contained within the Procellarum KREEP Terrain (PKT, Jolliff et al., 2000), where KREEP refers to potassium, rare earth element, and phosphorus-rich lithologies. The KREEP-rich rocks in the PKT are thought to be derived from late-stage residual liquids after approx.95-99% crystallization of a lunar magma ocean (LMO). These are understood to represent late-stage liquids which were enriched in incompatible trace elements (ITE) relative to older rocks (Snyder et al., 1992). As a consequence, the PKT is a significant reservoir for Th and KREEP. However, the majority of the lunar surface is likely to be significantly more depleted in ITE (84%, Jolliff et al., 2000). Lunar meteorites that are low in KREEP and Th may thus sample regions distinct from the PKT and are therefore a valuable source of information regarding the composition of KREEP-poor lunar crust. Northwest Africa (NWA) 3163 is a thermally metamorphosed ferroan, feldspathic, granulitic breccia composed of igneous clasts with a bulk anorthositic, noritic bulk composition. It is relatively mafic (approx.5.8 wt.% FeO; approx.5 wt.% MgO) and has some of the lowest concentrations of ITEs (17ppm Ba) compared to the feldspathic lunar meteorite (FLM) and Apollo sample suites (Hudgins et al., 2011). Localized plagioclase melting and incipient melting of mafic minerals require localized peak shock pressures in excess of 45 GPa (Chen and El Goresy, 2000; Hiesinger and Head, 2006). NWA 3163, and paired samples NWA 4481 and 4883, have previously been interpreted to represent an annealed micro-breccia which was produced by burial metamorphism at depth in the ancient lunar crust (Fernandes et al., 2009). This is in contrast to the interpretation of Hudgins et al. (2009) where NWA 3163 was interpreted to have formed through contact metamorphism. To further constrain its origin, we examine the petrogenesis of NWA 3163 with a particular emphasis on in-situ measurement of trace elements within constituent minerals, Sm-Nd and Rb-Sr isotopic systematics on separated mineral fractions and petrogenetic modeling.

  17. Mafic magma underplating and convection in a partially molten metasedimentary crust (United States)

    Riel, Nicolas; Mercier, Jonathan; Weinberg, Roberto; van Hunen, Jeroen; Lanari, Pierre


    The El Oro Complex, southwestern Ecuador, is a tilted section of the metasedimentary Ecuadorian forearc, which has been partially molten during Triassic times due to gabbroic magma emplacement. This complex underwent a single and short (less than 10 Ma) anatectic event and is an ideal location to study magmatic underplating, migmatite formation, magma migration and granitoid emplacement. In the garnet-bearing diatexite zone of the migmatitic unit the metamorphic conditions indicate that the maximum temperature across this 7-8 km thick unit varies between 880°C at the base and 760°C at the top, thus giving an anomalously low geothermal gradient of ~16°C/km. In order to investigate the heat transfer processes in the El Oro Complex during the anatectic event, we carried out 1D thermal modelling of basic magma emplacement. Our results show that neither diffusive nor advective models account for the low metamorphic gradient in the garnet-bearing diatexites. We demonstrate that in the El Oro Complex convection of the migmatite/diatexite layer is the only heat transfer process that explains all the petrological, geochemical and metamorphic data. This study has implications for the persistance of partially molten mid-crust region such as for the "channel flow" model in Tibet. Moreover, the early stages of the plutonic sequence exhibit a compositional trend from tonalite to granodiorite that can be used as an analogue to study archean T.T.G. formation.

  18. Crust and upper mantle of the western Mediterranean - Constraints from full-waveform inversion (United States)

    Fichtner, Andreas; Villaseñor, Antonio


    We present a full-waveform tomographic model of the western Mediterranean crust and mantle constructed from complete three-component recordings from permanent and temporary networks. The incorporation of body and multi-mode surface waves in the period range from 12-150 s allows us to jointly resolve crustal and mantle structures, including the Guadalquivir, Tajo and Ebro basins at shallow depth, as well as the western Mediterranean subduction system in the transition zone. No mantle plumes can be detected beneath the European Cenozoic rift system, including the Massif Central. In addition to the well-studied Alboran slab, a strong E-W trending high-velocity anomaly is present around 200-300 km depth beneath the Algerian coast. This previously undetected African slab is detached from the surface and broken into two segments. It may be interpreted as the slab that caused the opening of the Liguro-Provençal basin through successive roll-back between 35-15 Ma.

  19. Big Impacts and Transient Oceans on Titan (United States)

    Zahnle, K. J.; Korycansky, D. G.; Nixon, C. A.


    We have studied the thermal consequences of very big impacts on Titan [1]. Titan's thick atmosphere and volatile-rich surface cause it to respond to big impacts in a somewhat Earth-like manner. Here we construct a simple globally-averaged model that tracks the flow of energy through the environment in the weeks, years, and millenia after a big comet strikes Titan. The model Titan is endowed with 1.4 bars of N2 and 0.07 bars of CH4, methane lakes, a water ice crust, and enough methane underground to saturate the regolith to the surface. We assume that half of the impact energy is immediately available to the atmosphere and surface while the other half is buried at the site of the crater and is unavailable on time scales of interest. The atmosphere and surface are treated as isothermal. We make the simplifying assumptions that the crust is everywhere as methane saturated as it was at the Huygens landing site, that the concentration of methane in the regolith is the same as it is at the surface, and that the crust is made of water ice. Heat flow into and out of the crust is approximated by step-functions. If the impact is great enough, ice melts. The meltwater oceans cool to the atmosphere conductively through an ice lid while at the base melting their way into the interior, driven down in part through Rayleigh-Taylor instabilities between the dense water and the warm ice. Topography, CO2, and hydrocarbons other than methane are ignored. Methane and ethane clathrate hydrates are discussed quantitatively but not fully incorporated into the model.

  20. The continent-ocean transition at the southern margin of the South China Sea (United States)

    Franke, Dieter


    The South China Sea is surrounded by magma-poor or non-volcanic rifted margins like Iberia, Newfoundland and southern Australia. Seafloor spreading started in the Early Oligocene. The area thus is at an evolutionary stage in between the Late Miocene Woodlark Basin and the Cretaceous Iberia/Newfoundland margins or the ancient Mesozoic margins preserved in the Alps. We focus on the southern margin of the South China Sea and the transition area from oceanic crust to extended continental crust between the continental blocks of Reed Bank and the islands of Palawan/Calamian Group. Several BGR surveys, the last one in 2008, have established a database of more than 5.000 km of regional multi-channel reflection seismic lines, accompanied with magnetic and gravity profiles. One of the key issues of the 2008 survey was to investigate the structure and architecture of the transitional area between continental and oceanic crust (COT). Our approach to define the COT was based on • identification of the outermost fault-blocks defining stretched continental crust • identification of typical high-frequency diffractive oceanic crust reflections in the stacked sections • identification of seafloor-spreading anomalies and the transition to small-scale magnetic variation of presumably continental crust • identification of the landward extent of the oceanic Moho reflection • Lateral extent of the break-up unconformity • Gravity modelling The COT was found to be highly variable along the newly acquired lines. We distinguish between two types showing different styles of continent-ocean transitions. One type of continent-ocean transition shows a distinct outer ridge at the COT. The recent seafloor relief is steep. The ridge is elevated for about 1-1.5 s (TWT) with respect to the rift-onset unconformity or top oceanic crust, respectively. A clear magnetic signal might imply a volcanic/magmatic origin for the ridge. However, we observe extensional faults at the rims and also within this ridge that are not expected for volcanic intrusions. The other type is characterized by rotated fault blocks, bounded by listric normal faults that ramp down to a common detachment surface. Above the strongly eroded pre-rift basement half-grabens developed. Small-scale offsets in the basement are levelled out by the overlying sediments. The seafloor relief is smooth across this type of COT. There are examples of continuous listric extensional faults of more or less equal through and also equal block geometry from the continental to the oceanic crust. This results in a gradual deepening of the continental basement to the oceanic crust. Alternatively horst structures of varying size are located between the rotated faults blocks. A common observation here is a major listric normal fault that bounds the oceanic crust to the most seaward located fault block or local high.

  1. Salatoimikud : ma tahan uskuda / Mart Rummo

    Index Scriptorium Estoniae

    Rummo, Mart


    USA sarjale "The X-Files" põhinev teine järjefilm "Salatoimikud: Ma tahan uskuda" ("The X-Files: I Want to Believe") : režissöör Chris Carter : peaosades David Duchovny, Gillian Anderson : Ameerika Ühendriigid - Kanada 2008

  2. Oxygen isotope variations in ocean island basalt phenocrysts

    International Nuclear Information System (INIS)

    Oxygen isotope ratios are reported for olivine phenocrysts from sixty-seven samples of ocean island basalts (OIBs), mid-ocean ridge basalts (MORBs), and related peridotites, including representatives of the various isotopic endmembers defined by radiogenic isotope ratios. OIBs are more homogeneous in ?18O by this analysis than suggested by previous studies of whole rocks and glasses. Most OIB samples have oxygen isotope ratios within a restricted range (?18Oolivine = 5.0-5.4 per-thousand), comparable to those of olivines in peridotites from ophiolites, in most peridotitic mantle xenoliths, and inferred for the sources of mid-ocean ridge basalts. The exceptions are EM2 lavas, which are enriched in 18O (?18Oolivine = 5.4-6.1 per-thousand), and a small number of samples characterized by low 3He/4He and distinctive lead isotope ratios, which are 18O depleted (?18O = 4.7-5.1 per-thousand). The observed range in ?18O and the correlations with radiogenic isotope ratios are similar to those observed in a detailed study of Hawaiian samples. These results indicate that recycled crust and/or sediments (or the imprint of extensive metasomatism by fluids derived from such materials) is present as at most a small mass fraction (approx-lt%) in the mantle sources of most OIBs. The results on most EM2 lavas are consistent with the presence of ?2-6% recycled sediment in their source regions. Low ?18O values in OIBs can be produced by assimilation of altered lavas from high-levels in the volcanic edifice, assimilation of the oceanic crust underlying the volcano, or incorporation of subducted oceanic crust in mantle sources. 75 refs., 4 figs., 2 tabs

  3. The unstable CO2 feedback cycle on ocean planets (United States)

    Kitzmann, D.; Alibert, Y.; Godolt, M.; Grenfell, J. L.; Heng, K.; Patzer, A. B. C.; Rauer, H.; Stracke, B.; von Paris, P.


    Ocean planets are volatile-rich planets, not present in our Solar system, which are thought to be dominated by deep, global oceans. This results in the formation of high-pressure water ice, separating the planetary crust from the liquid ocean and, thus, also from the atmosphere. Therefore, instead of a carbonate-silicate cycle like on the Earth, the atmospheric carbon dioxide concentration is governed by the capability of the ocean to dissolve carbon dioxide (CO2). In our study, we focus on the CO2 cycle between the atmosphere and the ocean which determines the atmospheric CO2 content. The atmospheric amount of CO2 is a fundamental quantity for assessing the potential habitability of the planet's surface because of its strong greenhouse effect, which determines the planetary surface temperature to a large degree. In contrast to the stabilizing carbonate-silicate cycle regulating the long-term CO2 inventory of the Earth atmosphere, we find that the CO2 cycle feedback on ocean planets is negative and has strong destabilizing effects on the planetary climate. By using a chemistry model for oceanic CO2 dissolution and an atmospheric model for exoplanets, we show that the CO2 feedback cycle can severely limit the extension of the habitable zone for ocean planets.

  4. Lower crust exhumation and ongoing continental convergence in the Variscan Maures-Tanneron Massif, France, geological synthesis and numerical models (United States)

    Gerbault, Muriel; Schneider, Julie; Corsini, Michel; Reverso-Peila, Alexandre


    The Maures-Tanneron Massif together with Corsica and Sardinia compose the present day southeastern part of the Variscan belt. Pressure-temperature-time patterns were compiled to adress how rocks once forming a thick orogenic crust were exhumed, from burial conditions of ca. 10 kb and ca. 800°C. A continuous evolution from subduction to collision, from ca. 420 Ma to 290 Ma has recently been proposed by Schneider et al., 2014, ending with orthogonal Permean rifting. Here we complement this study by exploring the thermo-mechanical conditions prevailing during the massive exhumation of this orogenic crust. Based on field observations and petrological analysis indicative of the acceleration of partial melting during ongoing convergence, our numerical models test a scenario in which pre-thickened units located at 40-60 km depth, would have molten due to internal heating and burrial, and were progressively exhumed by gravitationally-driven instabilities to the surface, within ~15-25 Myrs. Assuming temperature dependent elasto-visco-plastic behavior, we have tested rheological layering including mafic or felsic units, far-field convergence and surface processes, as well as temperature-dependent melting conditions and density and viscosity evolution. In order to reproduce asymmetrical exhumation over the given time-scales and over an extent area of more than 50 km synchroneous with the development of compressional folds in the upper crust, a best fit was obtained for an applied far-field convergence of 0.5 cm/yr, equivalent to present day Alpine convergence rates, and a bulk crustal viscosity of at least 102° Pa.s. Crustal heat source had to contribute significantly, whereas a too shallow mantle heat source triggers exceedingly warm and fast exhumation. We propose that the evolution from transpressional to tensile conditions perpendicular to the orogenic axis (north-south Permean rifting versus East-West vergence of the orogenic structures), occurred progressively as internal volume forces rose and exceeded far-field boundary forces, linked with the balancing of masses in all three directions. The original location of this portion of the Variscan belt remains unclear but it presents consistent transitional characteristics between the Massif Central and the Bohemian massif.

  5. Lithium isotope constraints on crust-mantle interactions and surface processes on Mars (United States)

    Magna, Tomáš; Day, James M. D.; Mezger, Klaus; Fehr, Manuela A.; Dohmen, Ralf; Aoudjehane, Hasnaa Chennaoui; Agee, Carl B.


    Lithium abundances and isotope compositions are reported for a suite of martian meteorites that span the range of petrological and geochemical types recognized to date for Mars. Samples include twenty-one bulk-rock enriched, intermediate and depleted shergottites, six nakhlites, two chassignites, the orthopyroxenite Allan Hills (ALH) 84001 and the polymict breccia Northwest Africa (NWA) 7034. Shergottites unaffected by terrestrial weathering exhibit a range in ?7Li from 2.1 to 6.2‰, similar to that reported for pristine terrestrial peridotites and unaltered mid-ocean ridge and ocean island basalts. Two chassignites have ?7Li values (4.0‰) intermediate to the shergottite range, and combined, these meteorites provide the most robust current constraints on ?7Li of the martian mantle. The polymict breccia NWA 7034 has the lowest ?7Li (-0.2‰) of all terrestrially unaltered martian meteorites measured to date and may represent an isotopically light surface end-member. The new data for NWA 7034 imply that martian crustal surface materials had both a lighter Li isotope composition and elevated Li abundance compared with their associated mantle. These findings are supported by Li data for olivine-phyric shergotitte NWA 1068, a black glass phase isolated from the Tissint meteorite fall, and some nakhlites, which all show evidence for assimilation of a low-?7Li crustal component. The range in ?7Li for nakhlites (1.8 to 5.2‰), and co-variations with chlorine abundance, suggests crustal contamination by Cl-rich brines. The differences in Li isotope composition and abundance between the martian mantle and estimated crust are not as large as the fractionations observed for terrestrial continental crust and mantle, suggesting a difference in the styles of alteration and weathering between water-dominated processes on Earth versus possibly Cl-S-rich brines on Mars. Using high-MgO shergottites (>15 wt.% MgO) it is possible to estimate the ?7Li of Bulk Silicate Mars (BSM) to be 4.2 ± 0.9‰ (2?). This value is at the higher end of estimates for the Bulk Silicate Earth (BSE; 3.5 ± 1.0‰, 2?), but overlaps within uncertainty.

  6. The outer crust of non-accreting cold neutron stars

    CERN Document Server

    Ruster, S B; Schaffner-Bielich, J; Ruster, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Jurgen


    The properties of the outer crust of non-accreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables updating in particular the classic work of Baym, Pethick and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 is used and a thorough comparison of many modern theoretical nuclear models, relativistic and non-relativistic ones, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared in order to check their differences concerning the neutron dripline, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the dripline in the outer crust of non-accreting cold neutron stars.

  7. Symmetry energy, unstable nuclei and neutron star crusts

    Energy Technology Data Exchange (ETDEWEB)

    Iida, Kei [Kochi University, Department of Natural Science, Kochi (Japan); RIKEN Nishina Center, Saitama (Japan); Oyamatsu, Kazuhiro [RIKEN Nishina Center, Saitama (Japan); Aichi Shukutoku University, Department of Human Informatics, Aichi (Japan)


    The phenomenological approach to inhomogeneous nuclear matter is useful to describe fundamental properties of atomic nuclei and neutron star crusts in terms of the equation of state of uniform nuclear matter. We review a series of researches that we have developed by following this approach. We start with more than 200 equations of state that are consistent with empirical masses and charge radii of stable nuclei and then apply them to describe matter radii and masses of unstable nuclei, proton elastic scattering and total reaction cross sections off unstable nuclei, and nuclei in neutron star crusts including nuclear pasta. We finally discuss the possibility of constraining the density dependence of the symmetry energy from experiments on unstable nuclei and even observations of quasi-periodic oscillations in giant flares of soft gamma-ray repeaters. (orig.)

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

    CERN Document Server

    Rokityansky, Igor I


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

  9. Luna 24 - Lateral heterogeneity in the lunar crust (United States)

    Warner, J. L.; Simonds, C. H.; Mcgee, P. E.; Cochran, A.


    Results of petrological investigations of Luna 24 soil samples are compared with data from Apollo and other Luna missions in order to determine the large scale composition of the lunar surface and crust. Modal analysis of the 90 to 150 micron soil fraction and electron microprobe analysis of glass spheres and fragments of the Luna 24 core sample are presented. High and low MgO mare basalt compositional clusters are found, suggesting the derivation of southern Mare Crisium basalts from two magmas. A model of Luna 24 soils as being composed of a mixture of glass-poor mare material and glass-rich highland material is found to be consistent with glass and agglutinate modal abundances. Comparisons show that potassium, and by inference all lithophile trace elements, are depleted on the eastern limb of the moon relative to the central nearside. The observed depletion is interpreted to be characteristic of the underlying crust and mantle as well as the surface.

  10. Spin diffusive modes and thermal transport in neutron star crusts

    CERN Document Server

    Sedrakian, Armen


    In this contribution we first review a method for obtaining the collective modes of pair-correlated neutron matter as found in a neutron star inner crust. We discuss two classes of modes corresponding to density and spin perturbations with energy spectra $\\omega = \\omega_0 + \\alpha q^2$, where $\\omega_0 = 2\\Delta$ is the threshold frequency and $\\Delta$ is the gap in the neutron fluid spectrum. For characteristic values of Landau parameters in neutron star crusts the exitonic density modes have $\\alpha 0$ and they exist above $\\omega_0$ which implies that these modes are damped. As an application of these findings we compute the thermal conductivity due to spin diffusive modes and show that it scales as $T^{1/2} \\exp(-2\\omega_0/T)$ in the case where their two-by-two scattering cross-section is weakly dependent on temperature.

  11. Applicability of salt reduction strategies in pizza crust. (United States)

    Mueller, Eva; Koehler, Peter; Scherf, Katharina Anne


    In an effort to reduce population-wide sodium intake from processed foods, due to major health concerns, several different strategies for sodium reduction in pizza crust without any topping were evaluated by sensory analyses. It was possible to reduce sodium by 10% in one single step or to replace 30% of NaCl by KCl without a noticeable loss of salty taste. The late addition of coarse-grained NaCl (crystal size: 0.4-1.4 mm) to pizza dough led to an enhancement of saltiness through taste contrast and an accelerated sodium delivery measured in the mouth and in a model mastication simulator. Likewise, the application of an aqueous salt solution to one side of the pizza crust led to an enhancement of saltiness perception through faster sodium availability, leading to a greater contrast in sodium concentration. Each of these two strategies allowed a sodium reduction of up to 25% while maintaining taste quality. PMID:26304455

  12. The origin and crust/mantle mass balance of Central Andean ignimbrite magmatism constrained by oxygen and strontium isotopes and erupted volumes (United States)

    Freymuth, Heye; Brandmeier, Melanie; Wörner, Gerhard


    Volcanism during the Neogene in the Central Volcanic Zone (CVZ) of the Andes produced (1) stratovolcanoes, (2) rhyodacitic to rhyolitic ignimbrites which reach volumes of generally less than 300 km3 and (3) large-volume monotonous dacitic ignimbrites of up to several thousand cubic kilometres. We present models for the origin of these magma types using O and Sr isotopes to constrain crust/mantle proportions for the large-volume ignimbrites and explore the relationship to the evolution of the Andean crust. Oxygen isotope ratios were measured on phenocrysts in order to avoid the effects of secondary alteration. Our results show a complete overlap in the Sr-O isotope compositions of lavas from stratovolcanoes and low-volume rhyolitic ignimbrites as well as older (>9 Ma) large-volume dacitic ignimbrites. This suggests that the mass balance of crustal and mantle components are largely similar. By contrast, younger (70 km3 Ma-1 km-1 (assuming plutonic/volcanic ratios of 1:5) which are additional to, but within the order of, the arc background magmatic flux. Comparing our results to average shortening rates observed in the Andes, we observe a "lag-time" with large-volume eruptions occurring after accelerated shortening. A similar delay exists between the ignimbrite pulses and the subduction of the Juan Fernandez ridge. This is consistent with the idea that large-volume ignimbrite eruptions occurred in the wake of the N-S passage of the ridge after slab steepening has allowed hot asthenospheric mantle to ascend into and cause the melting of the mantle wedge. In our model, the older large-volume dacitic ignimbrites in the northern part of the CVZ have lower (15-37 %) crustal contributions because they were produced at times when the Central Andean crust was thinner and colder, and large-scale melting in the middle crust could not be achieved. Younger ignimbrite flare-ups further south (22°S) formed with a significantly higher crustal contribution (22-68 %) because at that time the Andean crust was thicker and hotter and, therefore primed for more extensive crustal melting. The rhyolitic lower-volume ignimbrites are more equally distributed in the CVZ in time and space and are produced by mechanisms similar to those operating below large stratovolcanoes, but at times of higher melt fluxes from the mantle wedge.

  13. Syn-collapse eclogite metamorphism and exhumation of deep crust in a migmatite dome: The P-T-t record of the youngest Variscan eclogite (Montagne Noire, French Massif Central) (United States)

    Whitney, Donna L.; Roger, Françoise; Teyssier, Christian; Rey, Patrice F.; Respaut, J.-P.


    In many orogens, high-pressure (HP) metamorphic rocks such as eclogite occur as lenses in quartzofeldspathic gneiss that equilibrated at much lower pressures. The pressure-temperature-time (P-T-t) history of eclogite relative to host gneiss provides information about mechanisms and timescales of exhumation of orogenic crust. The Montagne Noire of the southern Massif Central, France, is an eclogite-bearing gneiss (migmatite) dome located at the orogen-foreland transition of the Variscan belt. Results of our study show that it contains the youngest eclogite in the orogen, similar in age to migmatite and granite that crystallized under low-pressure conditions. P-T conditions for an exceptionally unaltered eclogite from the central Montagne Noire were estimated using a pseudosection supplemented by garnet-clinopyroxene and Zr-in-rutile thermometry. Results indicate peak P ˜ 1.4 GPa and T ˜ 725°C for Mg-rich garnet rim (50 mol% pyrope) + omphacite (36 mol% jadeite) + rutile + quartz. U-Pb geochronology (LA-ICP-MS) of 16 zoned zircon grains yielded ˜360 Ma (4 cores) and ˜315 Ma (12 rims and cores). Rare earth element abundances determined by LA-ICP-MS for dated zircon are consistent with crystallization of ˜315 Ma zircon under garnet-stable, plagioclase-unstable conditions that we interpret to indicate high pressure; in contrast, the ˜360 Ma zircon core corresponds to crystallization under lower pressure plagioclase-stable conditions. Based on garnet zoning and inclusion suites, rutile textures and Zr zoning, P-T results, and zircon petrochronology, we interpret the ˜315 Ma date as the age of eclogite-facies metamorphism that only slightly preceded dome formation and crystallization at 315-300 Ma. This age relation indicates that eclogite formation at high pressure and migmatite dome emplacement at low pressure were closely spaced in time. We propose that collapse-driven material transfer from the hot orogen to the cool foreland resulted in thickening of the orogen edge, leading to eclogite facies metamorphism of the deep crust. Soon after, the low-viscosity partially molten crust flowed from the plateau toward the foreland, incorporating and exhuming eclogite. The P-T-t history of the Montagne Noire eclogite shows that some dome material ascended from >40 km depth to shallow crustal levels, likely in a single decompression event, and that migmatite domes are therefore very efficient at exhuming the deep crust.

  14. Effects of termites on infiltration in crusted soil.


    Mando, A.; Stroosnijder, L.; Brussaard, L.


    In northern Burkina Faso (West Africa), a study was undertaken to explore the possibilities of restoring the infiltration capacity of crusted soils through the stimulation of termite activity. Treatments consisted of the application of a mulch of a mixture of wood and straw without insecticides (resulting in ''termite plots'') and the application of the same mulch and an insecticide (Dursban with chloropyrifos as the active ingredient) to prevent termite activity (resulting in ''non-termite p...

  15. The outer crust of non-accreting cold neutron stars


    Rüster, Stefan Bernhard; Hempel, Matthias; Schaffner-Bielich, Jürgen


    The properties of the outer crust of non-accreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables updating in particular the classic work of Baym, Pethick and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 is used and a thorough comparison of many modern theoretical nuclear models, relativistic and non-relativistic ones, is performed for the first time. In addition, the influences of ...

  16. Crusted (Norwegian) Scabies Following Systemic and Topical Corticosteroid Therapy


    Bini?, Ivana; Jankovi?, Aleksandar; Dragan JOVANOVI?; Ljubenovi?, Milanka


    It is a case study of a 62-yr-old female with crusted (Norwegian) scabies, which appeared during her treatment with systemic and topical corticosteroid therapy, under the diagnosis of erythroderma. In the same time, the patient had been suffered from hypothyoidism, and her skin changes were misdiagnosed, because it was thought that they are associated with her endocrine disorder. Suddenly, beside the erythema, her skin became hyperkeratotic, with widespread scaling over the trunk and limbs, a...

  17. Magnetic crust concept and magnetic anomalies of Slovakia

    International Nuclear Information System (INIS)

    Complete text of publication follows. The magnetic map of Slovakia was compiled as part of a project titled Atlas of Geophysical maps and profiles in 2001. Reduction to pole transformation (RTP) was applied to the magnetic anomalies using the magnetization angle of the induced magnetization to remove distortion of magnetic anomalies caused by the Earth's magnetic field. The reduced to the pole anomalies have good correlations with tectonic structures. To remove effects of topography, 3 km upward continuation was applied to RTP anomalies. Curie point depth (CPD) map was produced using 3 km upward continuation aeromagnetic anomalies. The depth to the tops and centroid of the magnetic anomalies were calculated by azimuthally averaged power spectrum method for the whole area. Such estimates can be indicative of temperatures in the crust; because magnetic minerals lose their spontaneous magnetization at the Curie temperature of the dominant magnetic minerals in the rocks. The Curie point depths of Slovakia vary from 15.2 km and 20.9 km. Higher heat-flow areas (>100 mWm-2) are around at the central volcanics and eastern part of Slovakia. CPD values are shallow in these areas. Two cross sections of E-W direction were produced for determining to correlation between CPD, heat flow and crustal thickness. There is a good correlation between CPD and heat flow values, however a better correlation between CPD and crust depth. The Curie point isotherm also separates the magnetic and non-magnetic level in the crust which investigated for two cross sections. In this correlation, shallow CPD is supported by high heat flow and shallow crust depth except Central Volcanics. In the Central Volcanics, the correlation is different from other sides due to intensive magnetized rocks and isostasy.

  18. Instability of Superfluid Flow in the Neutron Star Inner Crust

    CERN Document Server

    Link, Bennett


    I examine the hydrodynamic stability of a pinned superfluid vortex lattice undergoing thermal creep under the Magnus force in the inner crust of a spinning down neutron star. The superfluid flow is unstable over length scales $\\lap 10$ m, possibly over timescales of days to minutes. The vortex lattice could degenerate into a tangle, and the superfluid flow could become turbulent. Unexpectedly large dissipation would suppress the instability.

  19. Processes of formation of ferromanganese manganese nodules and crusts

    Digital Repository Service at National Institute of Oceanography (India)

    Nath, B.N.

    of the nucleus present in them. Local bottom topography, relief, geology, currents and sediment facies control the nature of the nucleus. Therefore, large local variations are seen in the seamount environment. Fig. 5. Various types of nuclei occurring... term climatic history in its oxide material. Oxide material slowly precipitates from seawater and is least altered diagenetically as the crusts are devoid of sediment cover. The structural, mineralogical, chemical and isotopic changes...

  20. Inner crust of neutron stars with finite range interactions

    Directory of Open Access Journals (Sweden)

    Khan Elias


    Full Text Available The microscopic structure of the inner crust of neutron stars is generally studied in the framework of local energy density functionals (EDF. Here, we discuss other possible frameworks, either based on non-relativistic EDF which are fully non-local, or covariant EDF of the relativistic mean field (RMF type. These other approaches must be more widely used in the context of neutron stars in order to gain confidence in predicting general trends.

  1. Neutron-Phonon Interaction in Neutron Star Crusts


    Sedrakian, Armen


    The phonon spectrum of Coulomb lattice in neutron star crusts above the neutron drip density is affected by the interaction with the ambient neutron Fermi-liquid. For the values of the neutron-phonon coupling constant in the range $0.1 \\le \\lambda \\le 1$ an appreciable renormalization of the phonon spectrum occurs which can lead to a lattice instability manifested in an exponential growth of the density fluctuations. The BCS phonon exchange mechanism of superconductivity lea...

  2. The formation and rejuvenation of continental crust in the central North China Craton: Evidence from zircon U-Pb geochronology and Hf isotope (United States)

    Li, Qing; Santosh, M.; Li, Sheng-Rong; Guo, Pu


    The Trans-North China Orogen (TNCO) along the central part of the North China Craton (NCC) is considered as a Paleoproterozoic suture along which the Eastern and Western Blocks of the NCC were amalgamated. Here we investigate the Precambrian crustal evolution history in the Fuping segment of the TNCO and the subsequent reactivation associated with extensive craton destruction during Mesozoic. We present zircon LA-ICP-MS U-Pb and Lu-Hf data on TTG (tonalite-trondhjemite-granodiorite) gneiss, felsic orthogneiss, amphibolite and granite from the Paleoproterozoic suite which show magmatic ages in the range of 2450-1900 Ma suggesting a long-lived convergent margin. The ?Hf(t) values of these zircons range from -11.9 to 12 and their model ages suggest magma derivation from both juvenile components and reworked Archean crust. The Mesozoic magmatic units in the Fuping area includes granite, diorite and mafic microgranular enclaves, the zircons from which define a tight range of 120-130 Ma ages suggesting a prominent Early Cretaceous magmatic event. However, the ?Hf(t) values of these zircons show wide a range from -30.3 to 0.2, indicating that the magmatic activity involved extensive rejuvenation of the older continental crust.

  3. Rb-Sr geochronology from Barro Alto Complex, Goias: metamorphism evidence of high degree and continental collision around 1300 Ma ago in Central Brazil

    International Nuclear Information System (INIS)

    Rb-Sr geochronologic investigation carried out on rocks from the Barro Alto Complex, Goias, yielded iso chronic ages of 1266 +- 17 Ma, for felsic rocks from the granulite belt and 1330 +- 67 Ma, for gneisses belonging to the Juscelandia Sequence. Rb-Sr isotope measurements suggest that Barro Alto rocks have undergone an important metamorphic event during middle Proterozoic times, around 1300 Ma ago. During that event, volcanic and sedimentary rocks of Juscelandia Sequence, as well as the underlying gabbros-anorthosite layered complex, underwent deformation and recrystallization under amphibolite facies conditions. Deformation and metamorphism took place during the collision of two continental blocks, which resulted in a southeastward directed thrust complex, allowing the exposure of granulite slices from the middle-lower crust of the overthrusted block. (author)

  4. OESbathy version 1.0: a method for reconstructing ocean bathymetry with realistic continental shelf-slope-rise structures

    Directory of Open Access Journals (Sweden)

    A. Goswami


    Full Text Available We present a method for reconstructing global ocean bathymetry that uses a plate cooling model for the oceanic lithosphere, the age distribution of the oceanic crust, global oceanic sediment thicknesses, plus shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to reconstruct realistic ocean bathymetry based on parameterized relationships of present-day variables that can be applied to global oceans in the geologic past, and to isolate locations where anomalous processes such as mantle convection may affect bathymetry. Parameters of the plate cooling model are combined with ocean crustal age to calculate depth-to-basement. To the depth-to-basement we add an isostatically adjusted, multicomponent sediment layer, constrained by sediment thickness in the modern oceans and marginal seas. A continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Shelf-slope-rise structures at active and passive margins are parameterized using modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and Central Atlantic Ocean, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth-to-basement, ocean bathymetry with an isostatically adjusted, multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

  5. OESbathy version 1.0: a method for reconstructing ocean bathymetry with realistic continental shelf-slope-rise structures (United States)

    Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.


    We present a method for reconstructing global ocean bathymetry that uses a plate cooling model for the oceanic lithosphere, the age distribution of the oceanic crust, global oceanic sediment thicknesses, plus shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to reconstruct realistic ocean bathymetry based on parameterized relationships of present-day variables that can be applied to global oceans in the geologic past, and to isolate locations where anomalous processes such as mantle convection may affect bathymetry. Parameters of the plate cooling model are combined with ocean crustal age to calculate depth-to-basement. To the depth-to-basement we add an isostatically adjusted, multicomponent sediment layer, constrained by sediment thickness in the modern oceans and marginal seas. A continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Shelf-slope-rise structures at active and passive margins are parameterized using modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and Central Atlantic Ocean, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth-to-basement, ocean bathymetry with an isostatically adjusted, multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

  6. Nitrogen fixation and leaching of biological soil crust communities in mesic temperate soils. (United States)

    Veluci, Roberta M; Neher, Deborah A; Weicht, Thomas R


    Biological soil crust is composed of lichens, cyanobacteria, green algae, mosses, and fungi. Although crusts are a dominant source of nitrogen (N) in arid ecosystems, this study is among the first to demonstrate their contribution to N availability in xeric temperate habitats. The study site is located in Lucas County of Northwest Ohio. Using an acetylene reduction technique, we demonstrated potential N fixation for these crusts covering sandy, acidic, low N soil. Similar fixation rates were observed for crust whether dominated by moss, lichen, or bare soil. N inputs from biological crusts in northwestern Ohio are comparable to those in arid regions, but contribute substantially less N than by atmospheric deposition. Nitrate and ammonium leaching from the crust layer were quantified using ion exchange resin bags inserted within intact soil cores at 4 cm depth. Leaching of ammonium was greater and nitrate less in lichen than moss crusts or bare soil, and was less than that deposited from atmospheric sources. Therefore, biological crusts in these mesic, temperate soils may be immobilizing excess ammonium and nitrate that would otherwise be leached through the sandy soil. Moreover, automated monitoring of microclimate in the surface 7 cm of soil suggests that moisture and temperature fluctuations in soil are moderated under crust compared to bare soil without crust. We conclude that biological crusts in northwestern Ohio contribute potential N fixation, reduce N leaching, and moderate soil microclimate. PMID:16453200

  7. Rapid continental crust formation at 1.7 Ga from a reservoir with chondritic isotope signatures, eastern Labrador

    International Nuclear Information System (INIS)

    The origin of the 1.71-1.64 Ga tonalitic to granitic continental crust in eastern Labrador was studied by major-, trace-, and rare earth-element analyses, as well as by Rb-Sr and Sm-Nd geochronology and Pb, Nd, and Sr isotope systematics. Apart from a few exceptions, U-Pb ages of the rocks are identical to: (1) their isochron-ages of 1.712±0.066 Ga (2?-error) for Sm-Nd, and 1.617±0.021 Ga for Rb-Sr; (2) TCHURNd of the individual rocks lying between 1.68 and 1.63 Ga, and (3) TCHURNd of the isochron, yielding 1.693±0.040 Ga. All TDMNd are too old by 200-350 Ma, relative to TCHURNd and U-PB, Sm-Nd and Rb-Sr-ages. ?iNd lie between -0.13 and +0.42 for individual rocks, and at +0.48±0.96 for the isochron, overlapping the chondrite zero-value. ?iSr of most rocks range between -1.29 and +3.63 (ISr:0.70259-0.70277), and ?iSr of the isochron lies at +2.72±2.03 (ISr:0.70277±0.00022). Pb isotopes, measured in leached K-feldspar from the same samples define a distinct field for initial isotopic compositions (?: 15.85-16.14, ?: 15.26-15.32 and ?: 35.34-35.61) which is an agreement with crust formation from a mantle source with time-integrated ?-values of 9.11-9.36, ?-values of 36.0-36.74, and Th/U of 3.86-4.01. Relative to model-compositions of lower-, bulk-, and upper-continental crust, the Labradorian rocks show distinct overall enrichment in K, Ba, Fe/Mg, and La/Y, but normal patterns for trace elements such as Th, Ta, Zr, Ti, Sc and Co. The data are consistent with rapid juvenile crust formation from a mantle reservoir having chondritic Nd, Sr, and Th/U at 1.7 Ga, whereas Pb isotopes are more radiogenic than single-stage evolution from primordial Pb. It appears that these characteristics are primary signatures of the mantle segment sampled, and not an effect of sediment mixing or melting of older arc material. (orig./WL)

  8. Investigation of Biological Soil Crusts Metabolic Webs Using Exometabolomic Analysis (United States)

    Northen, T.; Karaoz, U.; Jenkins, S.; Lau, R.; Bowen, B.; Cadillo-Quiroz, H.; Garcia-Pichel, F.; Brodie, E.; Richard, B.


    Desert biological soil crusts are simple cyanobacteria-dominated surface soil microbial communities found in areas with infrequent wetting, often extreme temperatures, low coverage of vascular plants and constitute the world's largest biofilm. They exist for extended periods in a desiccated dormant state, yet rapidly re-boot metabolism within minutes of wetting. These soil microbial communities are highly dependent on filamentous cyanobacteria such as Microcoleus vaginatusto stabilize the soil and to act as primary producers for the community through the release carbon sources to feed a diversity of heterotrophs. Exometabolomic analysis was performed using liquid chromatography coupled to tandem mass spectrometry on biological soil crust pore water and spent media of key soil bacterial isolates. Comparison of spent vs. fresh media was used to determine uptake or release of metabolites by specific microbes. To link pore water experiments with isolate studies, metabolite extracts of authentic soil were used as supplements for isolate exometabolomic profiling. Our soil metabolomics methods detected hundreds of metabolites from soils including may novel compounds. Only a small set of which being targeted by all isolates. Beyond these few metabolites, the individual bacteria examined showed specialization towards specific metabolites. Surprisingly, many of the most abundant oligosaccharides and other metabolites were ignored by these isolates. The observed specialization of biological soil crust bacteria may play a significant role in determining community structure.

  9. Pinned vortex hopping in a neutron star crust

    CERN Document Server

    Haskell, Brynmor


    The motion of superfluid vortices in a neutron star crust is at the heart of most theories of pulsar glitches. Pinning of vortices to ions can decouple the superfluid from the crust and create a reservoir of angular momentum. Sudden large scale unpinning can lead to an observable glitch. In this paper we investigate the scattering of a free vortex off a pinning potential and calculate its mean free path, in order to assess whether unpinned vortices can skip multiple pinning sites and come close enough to their neighbours to trigger avalanches, or whether they simply hop from one pinning site to another giving rise to a more gradual creep. We find that there is a significant range of parameter space in which avalanches can be triggered, thus supporting the hypothesis that they may lie at the origin of pulsar glitches. For realistic values of the pinning force and superfluid drag parameters we find that avalanches are more likely in the higher density regions of the crust where pinning is stronger. Physical dif...

  10. In situ evidence for continental crust on early Mars (United States)

    Sautter, V.; Toplis, M. J.; Wiens, R. C.; Cousin, A.; Fabre, C.; Gasnault, O.; Maurice, S.; Forni, O.; Lasue, J.; Ollila, A.; Bridges, J. C.; Mangold, N.; Le Mouélic, S.; Fisk, M.; Meslin, P.-Y.; Beck, P.; Pinet, P.; Le Deit, L.; Rapin, W.; Stolper, E. M.; Newsom, H.; Dyar, D.; Lanza, N.; Vaniman, D.; Clegg, S.; Wray, J. J.


    Understanding of the geologic evolution of Mars has been greatly improved by recent orbital, in situ and meteorite data, but insights into the earliest period of Martian magmatism (4.1 to 3.7 billion years ago) remain scarce. The landing site of NASA’s Curiosity rover, Gale crater, which formed 3.61 billion years ago within older terrain, provides a window into this earliest igneous history. Along its traverse, Curiosity has discovered light-toned rocks that contrast with basaltic samples found in younger regions. Here we present geochemical data and images of 22 specimens analysed by Curiosity that demonstrate that these light-toned materials are feldspar-rich magmatic rocks. The rocks belong to two distinct geochemical types: alkaline compositions containing up to 67 wt% SiO2 and 14 wt% total alkalis (Na2O + K2O) with fine-grained to porphyritic textures on the one hand, and coarser-grained textures consistent with quartz diorite and granodiorite on the other hand. Our analysis reveals unexpected magmatic diversity and the widespread presence of silica- and feldspar-rich materials in the vicinity of the landing site at Gale crater. Combined with the identification of feldspar-rich rocks elsewhere and the low average density of the crust in the Martian southern hemisphere, we conclude that silica-rich magmatic rocks may constitute a significant fraction of ancient Martian crust and may be analogous to the earliest continental crust on Earth.

  11. Biogenic black crusts on buildings in unpolluted environments. (United States)

    Gaylarde, Christine C; Ortega-Morales, B Otto; Bartolo-Pérez, Pascual


    Samples of peeling black crusts from modern and historic buildings in Campeche, Mexico, from a gravestone on the island of Dom Khon, Lao, and from the Anglican cathedral in Belize City were analyzed microbiologically, by scanning electron microscopy plus electron dispersive spectroscopy (EDS) and for pigment composition. In all cases, the surface was covered by a thick mat of cyanobacteria with dark brown sheaths. These were filamentous organisms of the genera Scytonema or Fischerella/Mastigocladus, except for one sample, where coccoid cyanobacteria of Subsection II were predominant. Fungi were not present at all sites and, where seen, were not the major biomass. High scytonemin:chlorophyll a ratios correlated with the dark pigmentation of the cyanobacterial cells and indicated the stressful conditions under which these organisms were living (high temperatures and ultraviolet levels, frequent desiccation). The absence, or low levels, of sulfur in the biofilms confirmed that there was little urban pollution at the sites and the EDS analysis showed that the black coloration was caused solely by cell pigmentation; no dark-colored elements were present at high concentrations. These results demonstrate that, unlike chemically formed thick black crusts found in polluted atmospheres, thin black crusts (which could be called patinas) in clean environments may be predominantly composed of filamentous cyanobacteria. PMID:17211538

  12. Outer crust of a cold non-accreting magnetar (United States)

    Basilico, D.; Arteaga, D. Peña; Roca-Maza, X.; Colò, G.


    The outer-crust structure and composition of a cold, non-accreting magnetar are studied. We model the outer crust to be made of fully equilibrated matter where ionized nuclei form a Coulomb crystal embedded in an electron gas. The main effects of the strong magnetic field are those of quantizing the electron motion in Landau levels and of modifying the nuclear single-particle levels producing, on average, an increased binding of nucleons in nuclei present in the Coulomb lattice. The effect of a homogeneous and constant magnetic field on nuclear masses has been predicted by using a covariant density functional in which induced currents and axial deformation due to the presence of a magnetic field that breaks time-reversal symmetry have been included self-consistently in the nucleon and meson equations of motion. Although not yet observed, for B ?1016 G both effects contribute to produce different compositions—odd-mass nuclei are frequently predicted—and to increase the neutron-drip pressure as compared to a typical neutron star. Specifically, in such a regime, the magnetic-field effects on nuclei favor the appearance of heavier nuclei at low pressures. As B increases, such heavier nuclei are also preferred up to larger pressures. For the most extreme magnetic field considered, B =1018 G, and for the models studied, almost the whole outer crust is made of 4092Zr52.

  13. Equation of state and thickness of the inner crust of neutron stars

    CERN Document Server

    Grill, Fabrizio; Providência, Constança; Vidaña, Isaac; Avancini, Sidney S


    The cell structure of $\\beta$-stable clusters in the inner crust of cold and warm neutron stars is studied within the Thomas-Fermi approach using relativistic mean field nuclear models. The relative size of the inner crust and the pasta phase of neutron stars is calculated, and the effect of the symmetry energy slope parameter, $L$, on the profile of the neutron star crust is discussed. It is shown that while the size of the total crust is mainly determined by the incompressibility modulus, the relative size of the inner crust depends on $L$. It is found that the inner crust represents a larger fraction of the total crust for smaller values of $L$. Finally, it is shown that at finite temperature the pasta phase in $\\beta$-equilibrium matter essentially melts above $5-6$ MeV, and that the onset density of the rodlike and slablike structures does not depend on the temperature.


    International Nuclear Information System (INIS)

    The transition density ? t and pressure Pt at the inner edge separating the liquid core from the solid crust of neutron stars are systematically studied using a modified Gogny (MDI) and 51 popular Skyrme interactions within well established dynamical and thermodynamical methods. First of all, it is shown that the widely used parabolic approximation to the full equation of state (EOS) of isospin asymmetric nuclear matter may lead to huge errors in estimating the transition density and pressure, especially for stiffer symmetry energy functionals E sym(?), compared to calculations using the full EOS within both the dynamical and thermodynamical methods mainly because of the energy curvatures involved. Thus, fine details of the EOS of asymmetric nuclear matter are important for locating accurately the inner edge of the neutron star crust. Second, the transition density and pressure decrease roughly linearly with increasing slope parameter L of E sym(?) at normal nuclear matter density using the full EOS within both the dynamical and thermodynamical methods. It is also shown that the thickness, fractional mass, and moment of inertia of the neutron star crust are all very sensitive to the parameter L through the transition density ? t whether one uses the full EOS or its parabolic approximation. Moreover, it is shown that E sym(?) constrained in the same subsaturation density range as the neutron star crust by the isospin diffusion data in heavy-ion collisions at intermediate energies limits the transition density and pressure to 0.040 fm-3 ?? t ? 0.065 fm-3 and 0.01 MeV fm-3 ?Pt ? 0.26 MeV fm-3, respectively. These constrained values for the transition density and pressure are significantly lower than their fiducial values currently used in the literature. Furthermore, the mass-radius relation and several other properties closely related to the neutron star crust are studied by using the MDI interaction. It is found that the newly constrained ? t and Pt together with the earlier estimate of ?I/I>0.014 for the crustal fraction of the moment of inertia of the Vela pulsar impose a more stringent constraint of R ? 4.7 + 4.0M/M sun km for the radius R and mass M of neutron stars compared to previous studies in the literature.

  15. Sulfuric Acid Speleogenesis: Microbial Karst and Microbial Crust (United States)

    Engel, A. S.; Bennett, P. C.; Stern, L. A.


    Sulfuric acid speleogenesis is a fundamental mechanism of karst formation, and is potentially responsible for the formation of some of the most extensive cave systems yet discovered. Speleogenesis occurs from the rapid dissolution of the host limestone by sulfuric acid produced from biotic and abiotic sulfide oxidation, and with the release of carbon dioxide, secondary gypsum crusts form. This crust develops predominately on the cave walls, often preserving original bedding indicators, until it finally collapses under its own weight to expose fresh limestone for dissolution. While this general speleogenetic process can be inferred from secondary residues in some caves, directly observing this process is difficult, and involves entry into an extreme environment with toxic atmospheres and low pH solutions. Kane Cave, Big Horn County, WY, offers the unique opportunity to study microbe-rock interactions directly. Kane Cave presently contains 3 springs that discharge hydrogen sulfide-rich waters, supporting thick subaqueous mats of diverse microbial communities in the stream passage. Condensation droplets and elemental sulfur form on subaerially exposed gypsum surfaces. Droplets have an average pH of 1.7, and are dominated by dissolved sulfate, Ca, Mg, Al, and Si, with minor Sr and Fe, and trace Mn and U. SEM and EDS examination of the crusts reveal the presence of C, O, and S, as well as authigenic, doubly-terminated quartz crystals. An average ? 13C value of -36 ‰ suggests that the crusts are biogenic and are composed of chemoautotrophic microorganisms. Enrichment cultures of biofilms and acid droplets rapidly produce sulfuric acid, demonstrating the dominance of sulfur-oxidizing bacteria. Colonization of gypsum surfaces by acidophilic microorganisms enhances acid dissolution of the limestone, and hence the growth of the cave itself. Limestone dissolution also results in mineralized crusts and biofilms that accumulate insoluble residues, which serve as sources of nutrient Fe, P, and N to the microbes. Other elements, such as Si, increase in concentration in the acid solutions and low-temperature mineral precipitation occurs. >

  16. New Constraints on Baja California-North America Relative Plate Motion Since 11 Ma (United States)

    Bennett, S. E.; Skinner, L. A.; Darin, M. H.; Umhoefer, P. J.; Oskin, M. E.; Dorsey, R. J.


    Tectonic reconstructions of the Pacific-North America (PAC-NAM) plate boundary across the Gulf of California and Salton Trough (GCAST) constrain the controversial magnitude of Baja California microplate-North America (BCM-NAM) relative motion since middle Miocene time. We use estimates of total PAC-NAM relative dextral-oblique motion from the updated global plate-circuit model (Atwater and Stock, 2013; GSA Cordilleran Mtg) to resolve the proportion of this motion on faults east of the BCM. Modern GPS studies and offset of late Miocene cross-gulf geologic tie points both suggest that BCM has never been completely coupled to the Pacific plate. Thus, our preferred GCAST reconstruction uses 93% BCM-PAC coupling from the present back to 6 Ma. We assume BCM-PAC coupling of 60% between 6 and 7 Ma, and 25% between 7 and 11 Ma, to avoid unacceptable overlap of continental crustal blocks between Baja California and the Sierra Madre Occidental (on stable NAM). Using these coupling ratios and PAC-NAM stage Euler poles, we determine the azimuth and velocity of individual points on the BCM in 1 million year increments back to 11 Ma. This procedure accounts for minor clockwise rotation of BCM that occurred during oblique rifting, and shows how total BCM-NAM relative motion increases from north to south due to greater distance from the Euler pole. Finer-scale restoration of tectonic blocks along significant (>1 km offset) faults, across extensional (e.g. pull-apart and half-graben) basins, and by vertical-axis rotation is constrained by local geologic and marine-geophysical datasets and accomplished via the open-source Tectonic Reconstruct ArcGIS tool. We find that restoration across the Gulf of California completely closes marine basins and their terrestrial predecessors between 6 and 9 Ma. Latest Miocene opening of these basins was coincident with a ~10° clockwise azimuthal change from 8 to 6 Ma in PAC-NAM relative motion, as revealed by the global plate circuit model. The coupling ratios used in our reconstruction produce important changes in BCM-NAM relative motion, where a point at the latitude of the Guaymas rift corridor experienced a ~10° clockwise azimuthal change from ~119° to ~129° between 8 and 6 Ma, and a ~27 mm/yr rifting rate increase from ~13 to ~40 mm/yr between 9 and 6 Ma. This increase in obliquity and rate of rifting likely drove localization of plate boundary strain into the North American continent and ultimately formed the Gulf of California. Initiation of these basins ca. 9 Ma requires that the residual ~20 - 40 km of dextral-oblique motion from 9 to 11 Ma occurred immediately offshore or east of the present-day Sonora-Sinaloa shoreline on as-yet undocumented structures. Total preferred BCM-NAM dextral-oblique motion since 11 Ma varies from ~385 km in the southern Gulf of California to ~365 km at the Midriff Islands. These values and the south-north gradient are consistent with recent estimates of ~340 × 40 km of relative dextral plate motion across southern California and the Eastern California Shear Zone. Attempts to restore larger amounts (e.g. 450 - 500 km) of BCM-NAM motion require a higher percent of late Miocene BCM-PAC coupling and result in unacceptable overlap between continental tectonic blocks in western Sonora and Sinaloa and submerged, extended continental crust in the southern Gulf of California.

  17. Ma Ying-jeou’s Presidential Discourse

    Directory of Open Access Journals (Sweden)

    Jonathan Sullivan


    Full Text Available Despite the substantial advances made in cross-Strait relations during Ma Ying-jeou’s (Ma Yingjiu first term, the ROC president’s rhetoric varied considerably as he grappled with the difficult reality of implementing campaign and inauguration pledges to establish better relations with China while striving to maintain national respect and sovereignty. In this article, we put forward a framework for measuring, analysing and explaining this variation in President Ma’s first-term discourse. Analysing a very large number of Ma’s speeches, addresses, etc., we provide empirical assessments of how the content of Ma’s public pronouncements has developed over time, how his rhetoric varies according to the strategic context and timing of a speech, and how his discourse compares to that of his predecessor, Chen Shui-bian (Chen Shuibian. In addressing these questions, the article contributes a quantitative perspective to existing work on political discourse in Taiwan and to the growing methodological and applied literature on how to systematically analyse Chinese political text.

  18. The 1590-1520 Ma Cachoeirinha magmatic arc and its tectonic implications for the Mesoproterozoic SW Amazonian craton crustal evolution

    Directory of Open Access Journals (Sweden)

    Ruiz Amarildo S.


    Full Text Available Isotopic and chemical data of rocks from the Cachoeirinha suite provide new insights on the Proterozoic evolution of the Rio Negro/Juruena Province in SW Amazonian craton. Six U-Pb and Sm-Nd analyses in granitoid rocks of the Cachoeirinha suite yielded ages of 1587-1522 Ma and T DM model ages of 1.88-1.75 Ga (EpsilonNd values of -0.8 to +1.0. In addition, three post-tectonic plutonic rocks yielded U-Pb ages from 1485-1389 Ma (T DM of 1.77-1.74 Ga and EpsilonNd values from -1.3 to +1.7. Variations in major and trace elements of the Cachoeirinha suite rocks indicate fractional crystallization process and magmatic arc geologic setting. These results suggest the following interpretations: (1 The interval of 1590-1520 Ma represents an important magmatic activity in SW Amazonian craton. (2 T DM and arc-related chemical affinity supportthe hypothesis that the rocks are genetically associated with an east-dipping subduction zone under the older (1.79-1.74 Ga continental margin. (3 The 1590-1520 Ma age of intrusive rocks adjacent to an older crust represents similar geological framework along the southern margin of Baltica, corroborating the hypothesis of tectonic relationship at that time.

  19. Dynamics of the Cretaceous Oceans: A Numerical Recipe (United States)

    Ridgwell, A. J.


    Recipe for OAE layer-cake: Take one whole fresh super-continent and break into pieces. Pick out the rock phosphate and place to one side. Immerse the continental fragments in seawater until the shelves and interior seaways are thoroughly flooded. Add a pinch of CO2 and heat gently. While the ocean is warming and de-oxygenating, gradually stir in the phosphate that was put aside earlier. Keep stirring and adding CO2 and phosphate until a thick black carbon crust suddenly forms. Remove the crust. Repeat to create as many carbon layers as possible before the cake starts to cool and the ocean re-oxygenates. In this talk I will test this recipe using an Earth system model, discussing the potential role of sedimentary phosphate regeneration feedbacks in triggering carbon burial events, and the role of massive carbon burial in creating the necessary conditions to exit an OAE. I will also illustrate how the dynamics of entering and exiting an OAE depend on boundary conditions such as continental configuration and whether enhanced CO2 out-gassing and weathering (and its attendant higher rate of nutrient supply to the ocean) is a sufficient trigger. Finally, in utilizing an isotope-enabled Earth system model ('GENIE' - in generating an OAE-like event, the plausibility of the recipe can be tested by analyzing the simulated phasing of climate, d13C, ocean redox, and carbon burial, which I will show contrasted with the geological record.

  20. Ocean Uses: Hawaii (PROUA) (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This Pacific Regional Ocean Uses Atlas (PROUA) Project is an innovative partnership between NOAA and the Bureau of Ocean Energy Management (BOEM) designed to...

  1. Ocean Maps Coordinate Planes

    CERN Document Server

    Wall, Julia


    Learn about ocean maps and the concepts surrounding coordinate planes as Ocean Maps explores geography under the sea, early and current navigation practices, and the variety of ways the ocean can be mapped such as sonar, submersibles, and satellites.

  2. Growth of continental crust: Clues from Nd isotopes and Nb-Th relationships in mantle-derived magmas

    International Nuclear Information System (INIS)

    Isotope and trace element geochemistry of Precambrian mantle derived rocks and implications for the formation of the continental crust is discussed. Epsilon Nd values of Archean komatiites are variable, but range up to at least +5, suggesting that the Archean mantle was heterogeneous and, in part, very depleted as far back as 3.4 to 3.5 Ga. This may be taken as evidence for separation of continental crust very early in Earth history. If these komatiite sources were allowed to evolve in a closed system, they would produce modern day reservoirs with much higher epsilon Nd values than is observed. This implies recycling of some sort of enriched material, perhaps subducted sediments, although other possibilities exist. Archean volcanics show lower Nb/Th than modern volcanics, suggesting a more primitive mantle source than that observed nowadays. However, Cretaceous komatiites from Gorgona island have similar Nb/Th to Archean volcanics, indicating either the Archean mantle source was indeed more primitive, or Archean magmas were derived from a deep ocean island source like that proposed for Gorgona

  3. Oceans, Ice Shells, and Life on Europa (United States)

    Schenk, Paul


    The four large satellites of Jupiter are famous for their planet-like diversity and complexity, but none more so than ice-covered Europa. Since the provocative Voyager images of Europa in 1979, evidence has been mounting that a vast liquid water ocean may lurk beneath the moon's icy surface. Europa has since been the target of increasing and sometimes reckless speculation regarding the possibility that giant squid and other creatures may be swimming its purported cold, dark ocean. No wonder Europa tops everyone's list for future exploration in the outer solar system (after the very first reconnaissance of Pluto and the Kuiper belt, of course). Europa may be the smallest of the Galilean moons (so-called because they were discovered by Galileo Galilei in the early 17th century) but more than makes up for its diminutive size with a crazed, alien landscape. The surface is covered with ridges hundreds of meters high, domes tens of kilometers across, and large areas of broken and disrupted crust called chaos. Some of the geologic features seen on Europa resemble ice rafts floating in polar seas here on Earth-reinforcing the idea that an ice shell is floating over an ocean on this Moon-size satellite. However, such features do not prove that an ocean exists or ever did. Warm ice is unusually soft and will flow under its own weight. If the ice shell is thick enough, the warm bottom of the shell will flow, as do terrestrial glaciers. This could produce all the observed surface features on Europa through a variety of processes, the most important of which is convection. (Convection is the vertical overturn of a layer due to heating or density differences-think of porridge or sauce boiling on the stove.) Rising blobs from the base of the crust would then create the oval domes dotting Europa's surface. The strongest evidence for a hidden ocean beneath Europa's surface comes from the Galileo spacecraft's onboard magnetometer, which detected fluctuations in Jupiter's magnetic field consistent with a conductor inside Europa. The most likely conductor: a somewhat salty ocean.

  4. Mismo field experiment in the equatorial Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Masumoto, Y.; Kuroda, Y.; Katsumata, M.; Mizuno, K.; Takayabu, Y.N.; Yoshizaki, M.; Shareef, A.; Fujiyoshi, Y.; McPhaden, M.J.; Murty, V.S.N.; Shirooka, R.; Yasunaga, K.; Yamada, H.; Sato, N.; Ushiyama, T.; Moteki, Q.; Seiki, A.; Fujita, M.; Ando, K.; Hase, H.; Ueki, I.; Horii, T.; Yokoyama, C.; Miyakawa, T.

    EXPERIMENT IN THE EQUATORIAL INDIAN OCEAN * b y Ku n i o yo n e y a m a , yu K i o ma s u m o t o , yo s h i f u m i Ku r o d a , ma s a K i Ka t s u m a t a , Ke i s u K e mi z u n o , yu K a r i n. ta K a y a b u , ma s a n o r i yo s h i z a K i..., Japan; ma s u m o t o —IORGC, JAMSTEC, Yokosuka, and Department of Earth and Planetary Sciences, University of Tokyo, Tokyo, Japan; Ku r o d a # —Marine Technology Center, JAMSTEC, Yokosuka, Japan; ta K a y a b u —Center for Climate System Research...

  5. OESbathy version 1.0: a method for reconstructing ocean bathymetry with generalized continental shelf-slope-rise structures (United States)

    Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.


    We present a method for reconstructing global ocean bathymetry that combines a standard plate cooling model for the oceanic lithosphere based on the age of the oceanic crust, global oceanic sediment thicknesses, plus generalized shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to develop a methodology for reconstructing ocean bathymetry in the geologic past that includes heterogeneous continental margins in addition to abyssal ocean floor. First, the plate cooling model is applied to maps of ocean crustal age to calculate depth to basement. To the depth to basement we add an isostatically adjusted, multicomponent sediment layer constrained by sediment thickness in the modern oceans and marginal seas. A three-parameter continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Parameters of the shelf-slope-rise structures at active and passive margins are determined from modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and central Atlantic, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth to basement, ocean bathymetry with an isostatically adjusted multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

  6. Tectonic events recorded in the sediments and crust of the Caribbean sea floor

    Energy Technology Data Exchange (ETDEWEB)

    Holcombe, T.L.


    A reconnaissance review of reflection-seismic sections from the Caribbean, together with limited information derived from dredged rocks, sediment cores, and drillholes, yields or contributes to first-order conclusions regarding the tectonic history of the water-covered Caribbean. Broadly speaking, tectonic episodes for which there is some evidence are: (1) late Cenozoic convergence and accretion along deformed continental or island margins off Panama, Colombia/Venezuela, and Hispaniola/Puerto Rico; (2) late Cenozoic generation of oceanic crust within the Cayman Trough; (3) late Cenozoic secondary deformation along the Caribbean-North American plate boundary zone, in the form of small pull-apart basins, transcurrent faults, tensional rift basins, and compressional features; (4) late Cenozoic slow disintegration of the western part of the Caribbean plate; (5) Cenozoic rift-basin formation on the upper Nicaraguan rise; (6) early Cenozoic or late Cretaceous opening of the Yucatan Basin; (7) late Cretaceous through early Cenozoic island arc formation; and (8) late Cretaceous and earlier emplacement of flow basalts in the northwestern Venezuelan Basin and possibly beneath large areas of the Caribbean. There is no evidence that except along their active margins, the Venezuelan Basin, Beata Ridge, Colombian Basin, and Nicaraguan rise areas have been sites for large-scale relative movements which created or destroyed plate material since late Cretaceous time - or earlier.

  7. Arctic and N Atlantic Crustal Thickness and Oceanic Lithosphere Distribution from Gravity Inversion (United States)

    Kusznir, Nick; Alvey, Andy


    The ocean basins of the Arctic and N. Atlantic formed during the Mesozoic and Cenozoic as a series of distinct ocean basins, both small and large, leading to a complex distribution of oceanic crust, thinned continental crust and rifted continental margins. The plate tectonic framework of this region was demonstrated by the pioneering work of Peter Ziegler in AAPG Memoir 43 " Evolution of the Arctic-North Atlantic and the Western Tethys" published in 1988. The spatial evolution of Arctic Ocean and N Atlantic ocean basin geometry and bathymetry are critical not only for hydrocarbon exploration but also for understanding regional palaeo-oceanography and ocean gateway connectivity, and its influence on global climate. Mapping crustal thickness and oceanic lithosphere distribution represents a substantial challenge for the Polar Regions. Using gravity anomaly inversion we have produced comprehensive maps of crustal thickness and oceanic lithosphere distribution for the Arctic and N Atlantic region, We determine Moho depth, crustal basement thickness, continental lithosphere thinning and ocean-continent transition location using a 3D spectral domain gravity inversion method, which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir 2008). Gravity anomaly and bathymetry data used in the gravity inversion are from the NGA (U) Arctic Gravity Project and IBCAO respectively; sediment thickness is from a new regional compilation. The resulting maps of crustal thickness and continental lithosphere thinning factor are used to determine continent-ocean boundary location and the distribution of oceanic lithosphere. Crustal cross-sections using Moho depth from the gravity inversion allow continent-ocean transition structure to be determined and magmatic type (magma poor, "normal" or magma rich). Our gravity inversion predicts thin crust and high continental lithosphere thinning factors in the Eurasia, Canada, Makarov, Podvodnikov and Baffin Basins consistent with these basins being oceanic. Larger crustal thicknesses, in the range 20 - 30 km, are predicted for the Lomonosov, Alpha and Mendeleev Ridges. Crustal basement thicknesses of 10-15 km are predicted under the Laptev Sea which is interpreted as highly thinned continental crust formed at the eastward continuation of Eurasia Basin sea-floor spreading. Thin continental or oceanic crust of thickness 7 km or less is predicted under the North Chukchi Basin and has major implications for understanding the Mesozoic and Cenozoic plate tectonic history of the Siberian and Chukchi Amerasia Basin margins. Restoration of crustal thickness and continent-ocean boundary location from gravity inversion may be used to test and refine plate tectonic reconstructions. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we improve the determination of pre-breakup rifted margin conjugacy and sea-floor spreading trajectory within the Arctic and N Atlantic basins. By restoring crustal thickness & continental lithosphere thinning maps of the Eurasia Basin & NE Atlantic to their initial post-breakup configuration we show the geometry and segmentation of the rifted continental margins at their time of breakup, together with the location of highly-stretched failed breakup basins and rifted micro-continents. We interpret gravity inversion crustal thicknesses underneath Morris Jessop Rise & Yermak Plateau as continental crust which provided a barrier to the tectonic and palaeo-oceanic linkage between the Arctic & North Atlantic until the Oligocene. Before this time, we link the seafloor spreading within the Eurasia Basin to that in Baffin Bay.

  8. Crust-core coupling and r-mode damping in neutron stars a toy model

    CERN Document Server

    Levin, Y; Levin, Yuri; Ushomirsky, Greg


    R-modes in neutron stars with crusts are damped by viscous friction at the crust-core boundary. The magnitude of this damping, evaluated by Bildsten and Ushomirsky (BU) under the assumption of a perfectly rigid crust, sets the maximum spin frequency for a neutron star spun up by accretion in a Low-Mass X-ray binary (LMXB). In this paper we explore the mechanical coupling between the core r-modes and the elastic crust, using a toy model of a constant density neutron star with a constant shear modulus crust. We find that, at spin frequencies in excess of ~50 Hz, the r-modes strongly penetrate the crust. This reduces the relative motion (slippage) between the crust and the core compared to the rigid crust limit. We therefore revise down, by as much as a factor of 10^2-10^3, the damping rate computed by BU, significantly reducing the maximal possible spin frequency of neutron star with a solid crust. The dependence of the crust-core slippage on the spin frequency is complicated, and is very sensitive to the physi...

  9. A study on the crust formation of molten core material without coolant boiling

    International Nuclear Information System (INIS)

    Experimental and analytical studies have been performed for crust formation and for associated the heat transfer mechanisms in molten pool without coolant boiling. From the simple analysis, the heat transfer coefficients between the molten pool and the coolant were estimated in order to predict the crust thickness accurately. The results of FLOW-3D analysis have shown that the temperature distribution affects to the crust formation process due to convection flow. The experimental test results have shown that the surface temperatures of the bottom and the top are influential parameters in the crust formation process of the molten pool. The experimental and analytical studies showed that the coolant injection methods and the boundary temperature changes were the major controlling parameters in the crust formation process. Increasing mass flow rate of coolant injection did not affect the crust thickness growth after the crust was formed in the molten pool because the crust behaves as a thermal barrier. The heat transfer rate between the molten pool and the coolant in the case of no crust formation was greater than the case with crust formation. (Author) 54 refs., 35 figs.,7 tabs

  10. Methanotrophs, methanogens, and microbial community structure in livestock slurry surface crusts

    DEFF Research Database (Denmark)

    Duan, Yun-Feng (Kevin); Abu Al-Soud, Waleed


    Aims: Crusts forming at the surface of liquid manure (slurry) during storage has been shown to harbor a potential for mitigating CH4 emissions. This study investigated the microbial community in surface crusts, with a focus on microorganisms related to CH4 metabolism. Methods and Results: Microbial communities in four crusts from cattle and swine slurries were investigated using DGGE and tag-encoded amplicon pyrosequencing. All crusts had distinct compositions of bacteria and archaea. The genera Methylobacter, Methylomicrobium, Methylomonas, and Methylosarcina of Type I, and Methylocystis of Type II, dominated the MOB community, whereas Methanocorpusculum was the predominant methanogen. Higher numbers of OTUs representing Type I than Type II MOB were found in all crusts. Potential CH4 oxidation rates were determined by incubations of crusts with CH4, and CH4 oxidization was observed in cattle, but not in swine slurry crusts. Conclusions: Slurry surface crusts harbor a diverse microbial community. Type IMOB are more diverse and abundant than Type II MOB in this environment. The distinct CH4 oxidation rates could be related to microbial compositions. Significance and Impact of Study: This study is the first to present the overall microbial community structure in slurry surface crusts. A better understanding of microbial community in surface crusts could contribute to mitigation of CH4 emissions from livestock manure management.

  11. Methanotrophs, methanogens and microbial community structure in livestock slurry surface crusts

    DEFF Research Database (Denmark)

    Duan, Y.F.; Abu Al-Soud, Waleed


    Aims: Crusts forming at the surface of liquid manure (slurry) during storage have been shown to harbour a potential for mitigating CH4 emissions. This study investigated the microbial community in surface crusts, with a focus on micro-organisms related to CH4 metabolism. Methods and Results: Microbial communities in four crusts from cattle and swine slurries were investigated using denaturing gradient gel electrophoresis and tag-encoded amplicon pyrosequencing. All crusts had distinct compositions of bacteria and archaea. The genera Methylobacter, Methylomicrobium, Methylomonas, and Methylosarcina of Type I, and Methylocystis of Type II, dominated the methane-oxidizing bacteria (MOB) community, whereas Methanocorpusculum was the predominant methanogen. Higher numbers of operational taxonomic units (OTUs) representing Type I than Type II MOB were found in all crusts. Potential CH4 oxidation rates were determined by incubating crusts with CH4, and CH4 oxidization was observed in cattle, but not in swine slurry crusts. Conclusions: Slurry surface crusts harbour a diverse microbial community. Type I MOB are more diverse and abundant than Type II MOB in this environment. The distinct CH4 oxidation rates could be related to microbial compositions. Significance and Impact of the Study: This study is the first to present the overall microbial community structure in slurry surface crusts. A better understanding of microbial community in surface crusts could support strategies for mitigation of CH4 emissions from livestock manure management. © 2014 The Society for Applied Microbiology.

  12. M&A information technology best practices

    CERN Document Server

    Roehl-Anderson, Janice M


    Add value to your organization via the mergers & acquisitions IT function  As part of Deloitte Consulting, one of the largest mergers and acquisitions (M&A) consulting practice in the world, author Janice Roehl-Anderson reveals in M&A Information Technology Best Practices how companies can effectively and efficiently address the IT aspects of mergers, acquisitions, and divestitures. Filled with best practices for implementing and maintaining systems, this book helps financial and technology executives in every field to add value to their mergers, acquisitions, and/or divestitures via the IT

  13. 70 Ma nonmarine diatoms from northern Mexico (United States)

    Chacón-Baca, Elizabeth; Beraldi-Campesi, H.; Cevallos-Ferriz, S. R. S.; Knoll, A. H.; Golubic, S.


    Carbonaceous cherts of the Tarahumara Formation, exposed near Huepac, Sonora, Mexico, contain abundant diatom frustules occurring as benthic filamentous colonies. Stratigraphic and paleontological observations indicate that Tarahumara sediments accumulated in a nonmarine setting; radiometric ages on encompassing volcanic rocks delimit their depositional age to ca. 70 Ma. Tarahumara fossils therefore extend the paleontological record of nonmarine diatoms from middle Eocene to Late Cretaceous. Preserved populations include forms similar to species of the extant genera Amphora and Melosira, as well as filament-forming araphid pennates comparable to species of Fragilaria and Tabellaria. Tarahumara fossils indicate that by 70 Ma, nonmarine diatoms had achieved considerable environmental as well as taxonomic diversity.

  14. Persistence of deeply sourced iron in the Pacific Ocean. (United States)

    Horner, Tristan J; Williams, Helen M; Hein, James R; Saito, Mak A; Burton, Kevin W; Halliday, Alex N; Nielsen, Sune G


    Biological carbon fixation is limited by the supply of Fe in vast regions of the global ocean. Dissolved Fe in seawater is primarily sourced from continental mineral dust, submarine hydrothermalism, and sediment dissolution along continental margins. However, the relative contributions of these three sources to the Fe budget of the open ocean remains contentious. By exploiting the Fe stable isotopic fingerprints of these sources, it is possible to trace distinct Fe pools through marine environments, and through time using sedimentary records. We present a reconstruction of deep-sea Fe isotopic compositions from a Pacific Fe-Mn crust spanning the past 76 My. We find that there have been large and systematic changes in the Fe isotopic composition of seawater over the Cenozoic that reflect the influence of several, distinct Fe sources to the central Pacific Ocean. Given that deeply sourced Fe from hydrothermalism and marginal sediment dissolution exhibit the largest Fe isotopic variations in modern oceanic settings, the record requires that these deep Fe sources have exerted a major control over the Fe inventory of the Pacific for the past 76 My. The persistence of deeply sourced Fe in the Pacific Ocean illustrates that multiple sources contribute to the total Fe budget of the ocean and highlights the importance of oceanic circulation in determining if deeply sourced Fe is ever ventilated at the surface. PMID:25605900

  15. Magnetic Fields Induced in the Solid Earth and Oceans

    DEFF Research Database (Denmark)

    Kuvshinov, Alexei Technical University of Denmark

    Electromagnetic induction in the Earth's interior is an important contributor to the near-Earth magnetic field. Oceans play a special role in the induction, due to their relatively high conductance of large lateral variability. Electric currents that generate secondary magnetic fields are induced in the oceans by two different sources: by time varying external magnetic fields, and by motion of the conducting ocean water through the Earth's main magnetic field. Significant progress in the accurate and detailed prediction of magnetic fields induced by these sources has been achieved during the last years, utilizing realistic 3-D conductivity models of the oceans, crust and mantle. In addition to these improvements in the prediction of 3-D induction effects, much attention has been paid to identifying magnetic signals of oceanic origin in observatory and satellite data. During the talk we will present the results of 3-D model studies that aim at estimating magnetic signals (at ground and satellite altitude) induced by a variety of realistic sources. In particular we will consider induction from ionospheric currents (Sq and electrojets), magnetospheric currents (magnetic storms), ocean tides, and global ocean circulation. Finally, we will discuss how the results of 3-D predictions can be utilized in geomagnetic field modeling and in a recovery of deep conductivity structures.

  16. Late Pliocene climate change 3.4-2.3 Ma: paleoceanographic record from the Yabuta Formation, Sea of Japan (United States)

    Cronin, T. M.; Kitamura, A.; Ikeya, Noriyuki; Watanabe, M. E.; Kamiya, T.


    Late Pliocene paleoceanographic changes in the Sea of Japan between 3.4 and2.3 Ma were investigated through study of molluscs, diatoms, and ostracodes from the Yabuta Formation in Toyama Prefecture. The period 3.4-2.7 Ma was characterized by relatively high sea level and cool water benthic faunas. A progressive paleoceanographic shift towards colder oceanic conditions and lower sea level occurred beginning near 2.7 Ma, intenifying about 2.5 Ma, when important changes in ostracode and molluscan faunas occurred. Between 2.7 and 2.3 Ma, eight glacial events can be inferred based on drops in sea level of 50-60 m and increasing proportions of cold, shallow water ostracode species whose modern ecology and zoogeography indicate colder winter water temperatures (3-4??C). The glacial events between 2.5 and 2.3 Ma were the most intense. Preliminary interpretation of the faunal and oceanographic events of the Yabuta Formation suggests that they correspond to Northern Hemispheric cooling also known from North Atlantic deep-sea oxygen isotope, IRD, and planktic foraminiferal records, North Pacific diatom and radiolarian record, and the Chinese loess sequences. The eight glacial events may record a 41,000-yr obliquity cycle which characterized other late Pliocene climate proxy records. Inferred sea level drops near 2.5-2.3 Ma of about 50-60 m provide direct evidence from an ocean margin setting that supports deep sea oxygen isotopic evidence indicating major changes in global ice volume changes. ?? 1994.

  17. Reconstruction of food webs in biological soil crusts using metabolomics. (United States)

    Baran, Richard; Brodie, Eoin L.; Mayberry-Lewis, Jazmine; Nunes Da Rocha, Ulisses; Bowen, Benjamin P.; Karaoz, Ulas; Cadillo-Quiroz, Hinsby; Garcia-Pichel, Ferran; Northen, Trent R.


    Biological soil crusts (BSCs) are communities of organisms inhabiting the upper layer of soil in arid environments. BSCs persist in a dessicated dormant state for extended periods of time and experience pulsed periods of activity facilitated by infrequent rainfall. Microcoleus vaginatus, a non-diazotrophic filamentous cyanobacterium, is the key primary producer in BSCs in the Colorado Plateau and is an early pioneer in colonizing arid environments. Over decades, BSCs proceed through developmental stages with increasing complexity of constituent microorganisms and macroscopic properties. Metabolic interactions among BSC microorganisms probably play a key role in determining the community dynamics and cycling of carbon and nitrogen. However, these metabolic interactions have not been studied systematically. Towards this goal, exometabolomic analysis was performed using liquid chromatography coupled to tandem mass spectrometry on biological soil crust pore water and spent media of key soil bacterial isolates. Comparison of spent vs. fresh media was used to determine uptake or release of metabolites by specific microbes. To link pore water experiments with isolate studies, metabolite extracts of authentic soil were used as supplements for isolate exometabolomic profiling. Our soil metabolomics methods detected hundreds of metabolites from soils including many novel compounds. Overall, Microcoleus vaginatus was found to release and utilize a broad range of metabolites. Many of these metabolites were also taken up by heterotrophs but there were surprisingly few metabolites uptaken by all isolates. This points to a competition for a small set of central metabolites and specialization of individual heterotrophs towards a diverse pool of available organic nutrients. Overall, these data suggest that understanding the substrate specialization of biological soil crust bacteria can help link community structure to nutrient cycling.

  18. Can a Warm (Aqueous Ammonium Sulfate) Ocean Survive Inside Titan? (United States)

    Grindrod, P.; Fortes, A.; Nimmo, F.; Feltham, D.; Brodholt, J.; Vocadlo, L.


    The presence of an ocean inside Titan has yet to be confirmed, but is not unexpected. If gravity data do confirm a subsurface ocean, then what might its composition be? A recent model [1] predicts that it will be made of aqueous ammonium sulfate solution (AS), rather than an ammonia-water (AW) mixture [e.g. 2], formed by the leaching of sulfates from a hydrated core during differentiation. The freezing temperature of AS is significantly higher than that of AW, and therefore such an ocean would crystallize quicker upon cooling. The implications of the new internal structure model [1] are significant for surface chemistry and the nature of volcanism on Titan, and so the goal of this paper is to determine under what conditions such an ocean could survive to the present day. We model the thermal evolution of Titan using a parameterized convection scheme, using the new structural model as the starting reference. In this model, Titan consists initially of a rocky core (1900 km radius) made of the hydrated mineral antigorite, overlain by an icy mantle (700 km thick). At the base of the mantle there exists a high pressure ice VI phase (434 km thick), overlain by the AS ocean (153 km thick), and a crust made predominantly of methane clathrate (123 km thick) with small amounts of AS and ice I present. We allow the top and bottom boundaries of the ocean to change according to the rate of crystallization/melting over time. We use detailed material properties derived from experimental data to derive accurate models of each layer. Our nominal model predicts a present-day heterogeneous crust of 176 km above a warm (249 K) AS ocean 56 km thick. The exact thickness of the ocean is sensitive to parameter choice, but, for a wide range of input parameters and different scaling laws, an ocean made of AS can survive to the present day. Therefore this, and other, warm ocean compositions are plausible candidates for a sub-surface ocean inside Titan. References [1] Fortes et al., 2007. Icarus, 188, 139-153. [2] Tobie et al., 2006. Nature, 440, 61-64.

  19. The Search for Water in the Lunar Crust (United States)

    Smith, D. E.; Zuber, M. T.


    There is evidence from several sources that water ice is present at a number of locations on the surface at the lunar poles. But there seems little agreement on the source of the ice with most suggestions being of external nature, such as impacts by ice-rich comets. Here we discuss the lunar crust as a possible source of the water ice and investigate whether there is any evidence from the recent GRAIL [1,2] and Lunar Reconnaissance Orbiter (LRO) [3] missions to support this possibility.

  20. Thermal conductivity of the neutron star crust: A reappraisal


    Abbar, Sajad; Carlson, Joe; Duan, Huaiyu; Reddy, Sanjay


    We use classical and quantum Monte Carlo techniques to study the static structure function $S(q)$ of a one-component ion lattice and use it to calculate the thermal conductivity $\\kappa$ of high-density solid matter expected in the neutron star crust. We also calculate the phonon spectrum using the dynamic-matrix method and use it to obtain $\\kappa$ in the one-phonon approximation. We compare the results obtained with these methods and assess the validity of some commonly us...

  1. Coastal Analysis Submission for Plymouth County, MA (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Coastal study data as defined in FEMA Guidelines and Specifications, Appendix D: Guidance for Coastal Flooding Analyses and Mapping (April 2003) and Atlantic Ocean...

  2. Locating inner edge of the neutron star crust from stability of neutron star matter

    International Nuclear Information System (INIS)

    One of the most important predictions of nuclear equation of state (EoS) is the location of the inner edge of neutron star crust. Knowledge of the properties of the crust plays an important role in understanding many astrophysical observations. The inner crust spans the region from the neutron drip point to the inner edge separating the solid crust from the homogeneous liquid core. In the present work, stability of the ?-equilibrated dense nuclear matter is analyzed with respect to the thermodynamic stability conditions. Based on the density dependent M3Y (DDM3Y) effective nucleon-nucleon (NN) interaction, the effects of nuclear incompressibility on proton fraction in neutron stars and location of the inner edge of their crusts and core-crust transition density and pressure are investigated

  3. On the formation and lifetime of large silicic magma chambers in the shallow crust (United States)

    Schöpa, A.; Annen, C.


    Most large silicic intrusion are believed to have formed by repeated injections of smaller magma pulses that eventually constitute the whole pluton. Geochronology helps to calculate long-term average emplacement rates of intrusions that are in the order of few mm/a. However, numerical simulations showed that these rates are too low to create large magma chambers. The incremental emplacement style limits the size and lifetime of any large magma chamber because the earlier injected magma pulse would cool down below solidus temperature before the next pulse is injected. To better constrain the formation of large-volume magma chambers, we investigate the influence of a changing emplacement rate over the lifetime of a composite plutonic body. That means that the emplacement rate can be temporarily high although the long-term average rate is low and is in agreement with the geochronological data. This is achieved by thermal modelling via an explicit finite difference scheme. The models calculate temperatures in the Earth's crust according to the equation of conductive heat transfer. They also take heat production of radioactive decay and phase changes into account. The conditions necessary to form a magma chamber that is larger than one single magma pulse, in this case a sill intrusion, are investigated and applied to the Tuolumne Intrusive Suite. This granitic intrusion is part of the Mesozoic Sierra Nevada Batholith in California and covers an area of more than 1000 km2. The Tuolumne Intrusive Suite is normally zoned with nested map units getting progressively younger and more evolved towards the centre. Data provided by U-Pb geochronology give an age range from 93.5 Ma for the outermost unit to 85.4 Ma for the core of the intrusive suite. The modelling results show that specific conditions need to be fulfilled to form a magma chamber for the Tuolumne Intrusive Suite. For most models, one sill intrusion cools down before the emplacement of the next sill. Thus, no more melt than delivered by a single sill is present at any time of the model run. A transient emplacement rate of more than several cm/a sustained for more than 300 ka is necessary that eruptible volumes of magma with a melt fraction higher than 60% can accumulate. The results suggest that processes like fractional crystallisation and settling of crystals which are believed to take place in magma chambers and can account for chemical and textural variations across a pluton, need to be reconsidered when looking at large silicic intrusions.

  4. Multi-MA reflex triode research.

    Energy Technology Data Exchange (ETDEWEB)

    Swanekamp, Stephen Brian (Naval Research Laboratory, Washington, DC); Commisso, Robert J. (Naval Research Laboratory, Washington, DC); Weber, Bruce V. (Naval Research Laboratory, Washington, DC); Riordan, John C. (L-3 Pulse Sciences Division, San Leandro, CA); Allen, Raymond J. (Naval Research Laboratory, Washington, DC); Goyer, John R. (L-3 Pulse Sciences Division, San Leandro, CA); Murphy, Donald P. (Naval Research Laboratory, Washington, DC); Mikkelson, Kenneth A.; Harper-Slaboszewicz, Victor Jozef


    The Reflex Triode can efficiently produce and transmit medium energy (10-100 keV) x-rays. Perfect reflexing through thin converter can increase transmission of 10-100 keV x-rays. Gamble II experiment at 1 MV, 1 MA, 60 ns - maximum dose with 25 micron tantalum. Electron orbits depend on the foil thickness. Electron orbits from LSP used to calculate path length inside tantalum. A simple formula predicts the optimum foil thickness for reflexing converters. The I(V) characteristics of the diode can be understood using simple models. Critical current dominates high voltage triodes, bipolar current is more important at low voltage. Higher current (2.5 MA), lower voltage (250 kV) triodes are being tested on Saturn at Sandia. Small, precise, anode-cathode gaps enable low impedance operation. Sample Saturn results at 2.5 MA, 250 kV. Saturn dose rate could be about two times greater. Cylindrical triode may improve x-ray transmission. Cylindrical triode design will be tested at 1/2 scale on Gamble II. For higher current on Saturn, could use two cylindrical triodes in parallel. 3 triodes in parallel require positive polarity operation. 'Triodes in series' would improve matching low impedance triodes to generator. Conclusions of this presentation are: (1) Physics of reflex triodes from Gamble II experiments (1 MA, 1 MV) - (a) Converter thickness 1/20 of CSDA range optimizes x-ray dose; (b) Simple model based on electron orbits predicts optimum thickness from LSP/ITS calculations and experiment; (c) I(V) analysis: beam dynamics different between 1 MV and 250 kV; (2) Multi-MA triode experiments on Saturn (2.5 MA, 250 kV) - (a) Polarity inversion in vacuum, (b) No-convolute configuration, accurate gap settings, (c) About half of current produces useful x-rays, (d) Cylindrical triode one option to increase x-ray transmission; and (3) Potential to increase Saturn current toward 10 MA, maintaining voltage and outer diameter - (a) 2 (or 3) cylindrical triodes in parallel, (b) Triodes in series to improve matching, (c) These concepts will be tested first on Gamble II.

  5. Structure of the Crust beneath Cameroon, West Africa, from the Joint Inversion of Rayleigh Wave Group Velocities and Receiver Functions

    Energy Technology Data Exchange (ETDEWEB)

    Tokam, A K; Tabod, C T; Nyblade, A A; Julia, J; Wiens, D A; Pasyanos, M E


    The Cameroon Volcanic Line (CVL) is a major geologic feature that cuts across Cameroon from the south west to the north east. It is a unique volcanic lineament which has both an oceanic and a continental sector and consists of a chain of Tertiary to Recent, generally alkaline volcanoes stretching from the Atlantic island of Pagalu to the interior of the African continent. The oceanic sector includes the islands of Bioko (formerly Fernando Po) and Sao Tome and Principe while the continental sector includes the Etinde, Cameroon, Manengouba, Bamboutos, Oku and Mandara mountains, as well as the Adamawa and Biu Plateaus. In addition to the CVL, three other major tectonic features characterize the region: the Benue Trough located northwest of the CVL, the Central African Shear Zone (CASZ), trending N70 degrees E, roughly parallel to the CVL, and the Congo Craton in southern Cameroon. The origin of the CVL is still the subject of considerable debate, with both plume and non-plume models invoked by many authors (e.g., Deruelle et al., 2007; Ngako et al, 2006; Ritsema and Allen, 2003; Burke, 2001; Ebinger and Sleep, 1998; Lee et al, 1994; Dorbath et al., 1986; Fairhead and Binks, 1991; King and Ritsema, 2000; Reusch et al., 2010). Crustal structure beneath Cameroon has been investigated previously using active (Stuart et al, 1985) and passive (Dorbath et al., 1986; Tabod, 1991; Tabod et al, 1992; Plomerova et al, 1993) source seismic data, revealing a crust about 33 km thick at the south-western end of the continental portion of the CVL (Tabod, 1991) and the Adamawa Plateau, and thinner crust (23 km thick) beneath the Garoua Rift in the north (Stuart et al, 1985) (Figure 1). Estimates of crustal thickness obtained using gravity data show similar variations between the Garoua rift, Adamawa Plateau, and southern part of the CVL (Poudjom et al., 1995; Nnange et al., 2000). In this study, we investigate further crustal structure beneath the CVL and the adjacent regions in Cameroon using 1-D shear wave velocity models obtained from the joint inversion of Rayleigh wave group velocities and P-receiver functions for 32 broadband seismic stations. From the 1-D shear wave velocity models, we obtain new insights into the composition and structure of the crust and upper mantle across Cameroon. After briefly reviewing the geological framework of Cameroon, we describe the data and the joint inversion method, and then interpret variations in crustal structure found beneath Cameroon in terms of the tectonic history of the region.

  6. Simulating the Late Ordovician (445Ma) with the fully coupled Community Climate System Model (CCSM3). (United States)

    Shields, C. A.; Kiehl, J. T.; Scotese, C. R.


    The first of earth's five major extinctions occurred during the late Ordovician (445Ma) and was the only extinction to occur during a glaciated climate. Current theory suggests a rigorous ocean circulation, present during the onset of glaciation, increased ocean ventilation and promoted eutrophic conditions and a massive marine die-off. Despite glacial conditions, C02 levels for this period were thought to be elevated. Estimates range from as high as 15X to, more recently, 4X pre-industrial levels. We apply the fully coupled Climate System Model, Version 3 (CCSM3), to a series of experiments simulating the earth's climate for the late Ordovician and show results from both our 15X CO2 and 4X CO2 integrations. Of technical note, we are the first modelling group to accurately represent, in a fully coupled (or ocean only) model, the geographical land distribution for the Orodivican, a period with virtually no land in the northern mid- or polar latitudes. Previously, ocean models have required a small land mass at the north pole for numerical purposes. We apply a grid rotation technique to eliminate this problem. Preliminary results from simulations show a very well ventilated Panthalassic Ocean and an atmospheric general circulation which are both supported by proxy records.

  7. How relevant are Tidal Effects on Past Ocean Circulation? (United States)

    Weber, T.; Thomas, M.


    Global ocean models can generally be divided into Ocean General Circulation and tidal models. Paleoclimate simulations consider dynamics due to the ocean's general, i.e., thermohaline, wind and pressure driven circulation, while tidal dynamics most commonly are neglected due to their strict periodicity and high frequencies. Nevertheless, residual tidal currents have the potential to alter the ocean's mean circulation and therefore climate relevant dynamics. Using the coupled atmosphere-ocean general circulation model ECHAM5/MPIOM with an integrated tidal module based on luni-solar ephemerides, we simultaneously model circulation and tidal dynamics for the Early Eocene (50Ma). The additional tidal forcing changes the ocean's mean circulation, in particular below 1000m depth compared to an Early Eocene control run without tides. Maximum velocities of the order of 1cm/s are obtained in the control run in the intermediate and deep ocean, while by a factor of 2 stronger mean currents are obtained when tidal dynamics are considered. A stronger ocean circulation leads to modified temperature transports and thus altered energy exchange at the atmosphere-ocean boundary. This affects winds and thereby energy transports in the atmosphere. As a result, near surface temperatures are locally altered by more than 1°C.

  8. Impact of Environmental Factors and Biological Soil Crust Types on Soil Respiration in a Desert Ecosystem


    Feng, Wei; Zhang, Yuqing; JIA, XIN; WU Bin; Zha, Tianshan; Qin, Shugao; Wang, Ben; Shao, Chenxi; Liu, Jiabin; Fa, Keyu


    The responses of soil respiration to environmental conditions have been studied extensively in various ecosystems. However, little is known about the impacts of temperature and moisture on soils respiration under biological soil crusts. In this study, CO2 efflux from biologically-crusted soils was measured continuously with an automated chamber system in Ningxia, northwest China, from June to October 2012. The highest soil respiration was observed in lichen-crusted soil (0.93±0.43 µmol m?2 s?...

  9. The continent-ocean transition on the northwestern South China Sea (United States)

    Cameselle, Alejandra L.; Ranero, César R.; Franke, Dieter; Barckhausen, Udo


    Rifted margins are created as a result of stretching and breakup of continental lithosphere that eventually leads to oceanic spreading and formation of a new oceanic basin. A cornerstone for understanding how rift characteristics vary along strike in the same system and what processes control the final transition to seafloor spreading is the continent-ocean transition (COT). We use four regional multichannel seismic profiles and published magnetic lineations to study the structure and variability of COT on the northwest subbasin (NWSB) of the South China Sea and to discern continental from oceanic domains. The continental domain is characterized by tilted fault blocks overlaid by thick syn-rift sedimentary units and fairly continuous Moho reflections typically at 8-10 s twtt. Thickness of the continental crust changes from ~20-25 km under the uppermost slope to ~9-6 km under the lower slope. The oceanic domain is interpreted where a highly reflective top of basement, little faulting, no syntectonic strata, and fairly constant thickness basement (4-8 km) occur. The COT is imaged as a ~5-10 km wide zone where oceanic-type features abut continental-type structures. The South China margin is deformed by abundant normal faults dissecting the continental crust, whereas the conjugate Macclesfield Bank margin displays comparatively abrupt thinning and little faulting. Seismic profiles show an along-strike variation in the tectonic structure of the continental margin. The NE-most lines display ~20-40 km wide segments of intense faulting under the slope and associated continental-crust thinning. Towards the SW, faulting and thinning of the continental crust occurs across a ~100-110 km wide segment. We interpret this 3D structural variability and the narrow COT as a consequence of the abrupt termination of continental rifting tectonics by the NE to SW propagation of a spreading center. We suggest that breakup occurred by spreading center propagation to a larger degree than by lithospheric thinning during continental rifting. Based on the sedimentary successions overlying the oceanic crust, we propose a kinematic evolution for the oceanic domain of the NWSB consisting of a southward spreading center propagation followed by a first narrow ridge jump to the north, and then a younger larger jump to the SW into the east subbasin.

  10. The tholeiite-TTG connection during Eoarchean crust formation in Isua, southern West Greenland: the role of subduction processes (United States)

    Hoffmann, J. E.; Münker, C.; Nagel, T. J.; Næraa, T.; Polat, A.; Rosing, M. T.


    The processes and the geodynamic settings that generated Earth's oldest parts of continental crust are still a matter of debate. A pertinent issue is the genetic relationship between the tonalite-trondhjemite-granodiorite (TTG) suite and the mafic fragments that are found as inclusions within this felsic crust. Here we propose a coherent model for the geodynamic evolution of the oldest (3.65 to 3.85 Ga) continental crust in southern West Greenland. Within the Isua Supracrustal Belt, the best preserved and largest fragment of mafic Eoarchean crust worldwide, tholeiitic and boninite-like amphibolites dominate the sequence, both yielding trace element patterns consistent with a subduction-related origin. The tholeiites yield correlated trace element variations in Nb/Th, La/Yb, Gd/Yb, Zr/Nb, in agreement with a subduction zone setting where a depleted mantle source is overprinted by melt-like slab components (Hoffmann et al., 2011a). Boninite-like rocks in Isua are derived from ultradepleted sources with epsHf(3720) of up to ca. +12.9 (Hoffmann et al., 2010). Petrological phase equilibrium modeling combined with trace element modeling suggests a relationship between the typical Isua arc tholeiites and the TTGs (Nagel et al., 2012). Notably, Hf-Nd isotope signatures between the two lithologies overlap (epsHf(t) = -0.7 to +2.5; epsNd(t) = -0.8 to +4.4), both showing the characteristic decoupling of initial Hf-Nd isotope compositions. Systematically elevated 142Nd anomalies of tholeiites and TTGs are also in agreement with a related origin of both rock types (e.g., Caro et al., 2006). Trace element modeling shows that the Isua TTGs likely formed by melting of thickened mafic arc crust with tholeiite compositions (Hoffmann et al., 2011b) and that the decoupled Hf-Nd signature is likely an inherited feature from melting of the tholeiites. This is also underlined by new Hf and O in zircon data from TTGs in the area (Næraa et al., submitted) that indicate melting of a thickened mafic crust to form the TTGs. The cause for the decoupled behavior of the Hf and Nd isotope compositions is most likely a subduction-related mantle source overprint, because Nd behaves more mobile in subduction components compared to the less mobile Hf (Hoffmann et al., 2011a). Other scenarios explaining the Hf-Nd decoupling may include cumulate segregation processes in an early magma ocean or an early metamorphic overprint during intrusion of the TTGs might also (Hoffmann et al., 2011a; Rizo et al., 2011). These scenarios are possible, however, they are only very difficult to reconcile with all observed trace element and isotope features of Isua rocks. Overall, we therefore propose that the most likely geodynamic setting to form the TTGs in the Isua region is an arc-arc collisional model, where the arc tholeiites melt at 10-20% of partial melting to form the TTGs. Caro, G., Bourdon, B. et al. (2006) Geochim. Cosmochim. Acta 70, 164-191. Hoffmann, J.E., Münker, C. et al. (2010) Geochim. Cosmochim. Acta 74, 7236-7260. Hoffmann, J.E., Münker, C. et al. (2011a) Geochim. Cosmochim. Acta 75, 6610-6628. Hoffmann, J.E., Münker, C. et al. (2011b) Geochim. Cosmochim. Acta 75, 4157-4178. Nagel, T., Hoffmann, J.E., Münker, C. (2012) Geology DOI: doi:10.1130/G32729.1. Næraa, T., Scherstén, A., et al., (submitted). Rizo, H., Boyet, M. et al. (2011) Earth Planet. Sci. Lett. 312, 267-279.

  11. Magnetic Field-Decay-Induced Electron Captures: a Strong Heat Source in Magnetar Crusts

    CERN Document Server

    Cooper, Randall L


    We propose a new heating mechanism in magnetar crusts. Magnetars' crustal magnetic fields are much stronger than their surface fields; therefore, magnetic pressure partially supports the crust against gravity. The crust loses magnetic pressure support as the field decays and must compensate by increasing the electron degeneracy pressure; the accompanying increase in the electron Fermi energy induces exothermic electron captures. The total heat released via field-decay electron captures is comparable to the total magnetic energy in the crust. Thus, field-decay electron captures are an important, if not the primary, mechanism powering magnetars' soft X-ray emission.

  12. A Novel Clinical Grading Scale to Guide the Management of Crusted Scabies


    Davis, Joshua S; McGloughlin, Steven; Steven Y C Tong; Walton, Shelley F.; Bart J Currie


    Crusted scabies is a severe skin condition caused by a microscopic parasitic mite. It occurs in people whose immune system does not react properly to the mite and it leads to crusting and cracking of the skin and can cause death. The usual treatment for crusted scabies is a tablet called ivermectin combined with anti-scabies skin creams. However, there is no current method of measuring the severity of crusted scabies and thus deciding how long to continue the treatment for. We have developed ...

  13. Equation of state and thickness of the inner crust of neutron stars


    Grill, Fabrizio; Pais, Helena; Providência, Constança; Vidaña, Isaac; Avancini, Sidney S.


    The cell structure of $\\beta$-stable clusters in the inner crust of cold and warm neutron stars is studied within the Thomas-Fermi approach using relativistic mean field nuclear models. The relative size of the inner crust and the pasta phase of neutron stars is calculated, and the effect of the symmetry energy slope parameter, $L$, on the profile of the neutron star crust is discussed. It is shown that while the size of the total crust is mainly determined by the incompress...

  14. Spatial Pattern of Biological Soil Crust with Fractal Geometry (United States)

    Ospina, Abelardo; Florentino, Adriana; Tarquis, Ana M.


    Soil surface characteristics are subjected to changes driven by several interactions between water, air, biotic and abiotic components. One of the examples of such interactions is provided through biological soil crusts (BSC) in arid and semi-arid environments. BSC are communities composed of cyanobacteria, fungi, mosses, lichens, algae and liverworts covering the soil surface and play an important role in ecosystem functioning. The characteristics and formation of these BSC influence the soil hydrological balance, control the mass of eroded sediment, increase stability of soil surface, and influence plant productivity through the modification of nitrogen and carbon cycle. This study focus on characterize the spatial arrangements of the BSC based on image analysis and fractal concepts. To this end, RGB images of different types of biological soil crust where taken, each image corresponding to an area of 3.6 cm2 with a resolution of 1024x1024 pixels. For each image and channel, mass dimension and entropy were calculated. Preliminary results indicate that fractal methods are useful to describe changes associated to different types of BSC. Further research is necessary to apply these methodologies to several situations.

  15. Stability of Hall equilibria in neutron star crusts

    Energy Technology Data Exchange (ETDEWEB)

    Marchant, Pablo; Reisenegger, Andreas [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Macul 7820436, Santiago (Chile); Valdivia, Juan Alejandro [Departamento de Física, Facultad de Ciencias, Universidad de Chile Casilla 653, Santiago (Chile); Hoyos, Jaime H., E-mail: [Departamento de Ciencias Básicas, Universidad de Medellín Cra. 87 # 30-65, Medellín (Colombia)


    In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are 'Hall equilibria', i.e., field configurations that are unaffected by Hall drift. Here we address the crucial question of the stability of these equilibria through axially symmetric (two-dimensional (2D)) numerical simulations of Hall drift and ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D stability of a purely poloidal equilibrium, for which ohmic dissipation makes the field evolve toward an attractor state through adjacent stable configurations, around which damped oscillations occur. For this field, the decay scales with the ohmic timescale. We also study the case of an unstable equilibrium consisting of both poloidal and toroidal field components that are confined within the crust. This field evolves into a stable configuration, which undergoes damped oscillations superimposed on a slow evolution toward an attractor, just as the purely poloidal one.

  16. Magnetar activity mediated by plastic deformations of neutron star crust (United States)

    Lyutikov, Maxim


    We advance a `solar flare' model of magnetar activity, whereas a slow evolution of the magnetic field in the upper crust, driven by electron magnetohydrodynamic flows, twists the external magnetic flux tubes, producing persistent emission, bursts, and flares. At the same time, the neutron star crust plastically relieves the imposed magnetic field stress, limiting the strain ?t to values well below the critical strain ?crit of a brittle fracture, ?t ˜ 10-2?crit. Magnetar-like behaviour, occurring near the magnetic equator, takes place in all neutron stars, but to a different extent. The persistent luminosity is proportional to cubic power of the magnetic field (at a given age), and hence is hardly observable in most rotationally powered neutron stars. Giant flares can occur only if the magnetic field exceeds some threshold value, while smaller bursts and flares may take place in relatively small magnetic fields. Bursts and flares are magnetospheric reconnection events that launch Alfvén shocks which convert into high-frequency whistlers upon hitting the neutron star surface. The resulting whistler pulse induces a strain that increases with depth both due to the increasing electron density (and the resulting slowing of the waves), and due to the increasing coherence of a whistler pulse with depth. The whistler pulse is dissipated on a time-scale of approximately a day at shallow depths corresponding to ? ˜ 1010 g cm-3; this energy is detected as enhanced post-flare surface emission.

  17. Magnetar activity mediated by plastic deformations of neutron star crust

    CERN Document Server

    Lyutikov, Maxim


    We advance a "Solar flare" model of magnetar activity, whereas a slow evolution of the magnetic field in the upper crust, driven by electron MHD (EMHD) flows, twists the external magnetic flux tubes, producing persistent emission, bursts and flares. At the same time the neutron star crust plastically relieves the imposed magnetic field stress, limiting the strain $ \\epsilon_t $ to values well below the critical strain $ \\epsilon_{crit}$ of a brittle fracture, $ \\epsilon_t \\sim 10^{-2}\\epsilon_{crit} $. Magnetar-like behavior, occurring near the magnetic equator, takes place in all neutron stars, but to a different extent. The persistent luminosity is proportional to cubic power of the magnetic field (at a given age), and hence is hardly observable in most rotationally powered neutron stars. Giant flares can occur only if the magnetic field exceeds some threshold value, while smaller bursts and flares may take place in relatively small magnetic fields. Bursts and flares are magnetospheric reconnection events t...

  18. Outer crust of a cold non-accreting magnetar

    CERN Document Server

    Basilico, D; Roca-Maza, X; Colò, G


    The outer crust structure and composition of a cold, non-accreting magnetar is studied. We model the outer crust to be made of fully equilibrated matter where ionized nuclei form a Coulomb crystal embedded in an electron gas. The main effects of the strong magnetic field are those of quantizing the electron motion in Landau levels and of modifying the nuclear single particle levels producing, on average, an increased binding of nucleons in nuclei present in the Coulomb lattice. The effect of an homogeneous and constant magnetic field on nuclear masses has been predicted by using a covariant density functional, in which induced currents and axial deformation due to the presence of a magnetic field that breaks time-reversal symmetry have been included self-consistently in the nucleon and meson equations of motion. Although not yet observed, for $B\\gtrsim 10^{16}$G both effects contribute to produce different compositions and to enlarge the range of pressures typically present in common neutron stars. Specifical...

  19. One View of the Genesis of Cratonic Mantle and Crust (United States)

    Kelemen, P. B.; Jull, M.; Kelly, R.


    Kelemen et al. [1] proposed that SiO2-rich, cratonic mantle peridotite xenoliths from Kaapvaal and Siberia had a two stage history. First, they underwent ca. 40% polybaric decompression melting, ending in spinel peridotite facies, to produce depleted, SiO2-poor residues [2]. Second, residues reacted with migrating, felsic melt to become SiO2-rich and light REE-enriched, in accord with previous work [3-5]. Modified melt rose to form continental crust. In this way, cratonic upper mantle and crust may be genetically linked. This differs from theories in which SiO2-rich cratonic mantle formed via high pressure melting and crystal fractionation involving komatiitic melts, with a coincidental relationship between SiO2-rich peridotites and SiO2-rich crust. With regard to Stage 1, average melt removed from primitive mantle [6] to form depleted, SiO2-poor, Archean mantle in Greenland is similar to experimental partial melts at 2.5 to 3 GPa [2]. Also, heavy REE in cratonic peridotite xenoliths are correlated with Ca, suggesting that residual garnet was exhausted early in melting, long before residual clinopyroxene [1]. This, combined with data on melting as a function of pressure [7], yields an average pressure for polybaric melting ca. 3 GPa. Thus, depleted cratonic peridotites recording equilibration pressures greater than 3 GPa have undergone subsolidus pressure increase and garnet growth. Pressure increase could be in response to thickening via tectonic imbrication, pure shear during continental collision, viscous flow in a "mantle wedge", or diapirism of buoyant, depleted residues through dense, subducting, basaltic crust. We will examine these hypotheses in the light of new calculations of the density of cratonic peridotites as a function of P and T. With regard to Stage 2, this provides an explanation for positive correlation between Ni in olivine and modal orthopyroxene, seen in xenolith suites from some kimberlites, and in a global comparison of cratonic xenoliths from Greenland, Kaapvaal and Siberia. To model reaction between peridotite and melt, we used a system of equations for phase equilibrium (Fe/Mg Kd between olivine and melt, Fe/Mg Kd between olivine and orthopyroxene, Mg partitioning between olivine and melt) and mass balance constraints. [1] reported results in terms of Ni in olivine versus modal orthopyroxene. Here, we report calculated melt compositions. Reaction of komatiiite, picrite, and basalt with peridotite are unable to produce the observed trend of Ni in olivine versus orthopyroxene. Reaction between tonalite (11% melt of eclogite at 3.2 GPa [8]) and peridotite does reproduce the observed trend. Modified melt compositions are similar to high Mg# andesite and continental crust. In order to evaluate these results in a more complicated chemical system, we will supplement these earlier calculations with modeling from MELTS. We also will consider the possible effect of dissolved sulfur on the crystal/liquid distribution coefficients used in our calculations. Finally, the lack of SiO2-rich peridotites with depleted light REE contents suggests a genetic link between SiO2- and light REE-enrichment in the cratonic mantle, supporting the idea that both were imparted by reaction with SiO2-rich melt. We will present compiled whole rock data and new microbeam data to support this point. [1]Kelemen et al. EPSL 164 1998 [2] Bernstein et al. EPSL 154 1998 [3] Ringwood J. Geol. Soc. Lond. 130 1974 [4] Kesson, Ringwood Chem. Geol. 78 1989 [5] Rudnick et al., Proc. 5th Kimberlite Conf. 1994 [6] Ringwood Advances in Earth Science, P. Hurley ed. 1966 [7] Walter J. Petrol. 39 1998 [8] Rapp, Watson J. Petrol. 36 1995.

  20. Ocean anoxia and large igneous provinces (United States)

    Ruhl, Micha; Bjerrum, Christian J.; Canfield, Donald E.; Korte, Christoph; Stemmerik, Lars; Frei, Robert


    Earth's history is marked by multiple events of ocean anoxia developing along continental margins and potentially into the open ocean realm. These events often coincide with the emplacement of large igneous provinces (LIPs) on continents, major perturbations of global geochemical cycles and marine (mass) extinction. The geographic and temporal extend and the intensity (ferruginous vs. euxinic) of anoxic conditions is often, however, poorly constraint. This complicates understanding of close coupling between Earth's physical, chemical and biological processes. We studied ocean redox change over two major mass extinction events in Earth history, the Permian-Triassic (at ~252 Ma) and Triassic-Jurassic (at ~201.3 Ma) mass extinctions. Both extinction events are marked by a major perturbation of the global exogenic carbon cycle (and associated major negative carbon isotope excursion (CIE)), likely initiated by carbon outgassing of the Siberian Traps and the Central Atlantic Magmatic Province (CAMP), respectively. We compare Permian-Triassic and Triassic-Jurassic ocean redox change along continental margins in different geographic regions (Permian-Triassic: Greenland, Svalbard, Iran; Triassic-Jurassic: UK, Austria) and discuss its role in marine mass extinction. We show strongly enhanced sedimentary redox-sensitive trace element concentrations (e.g. Mo) during both events. However, increased Permian-Triassic values are in all localities distinctly delayed relative to the associated negative CIE. Triassic-Jurassic values are only delayed in the oceanographically restricted western Germanic basin (UK) while increased Mo-values in the north-western Tethys Ocean (Austria) directly match the onset of the associated negative CIE. Speciation of iron [giving (Fe-HR/ Fe-T) and (Fe(Py)/ Fe-HR)] in the Triassic-Jurassic western Germanic basin (UK) however shows close coupling between the onset of the global carbon cycle perturbation and a shift to anoxic and even euxinic conditions. Delayed molybdenum enrichment in this basin suggests strong initial depletion of the molybdenum reservoir. Triassic-Jurassic molybdenum drawdown does however occur in more well-connected marine basins along continental margins. Iron speciation and delayed Mo-enrichments along Permian-Triassic continental margins in different geographic regions suggest more widely, potentially global ocean, molybdenum drawdown and more widespread ocean anoxia. Further, our data shows that anoxic (and euxinic) conditions directly matches extinction of marine organisms, suggesting ocean anoxia as contributor to marine ecosystem collapse.

  1. Satellite-Respondent Buoys Identify Ocean Debris (United States)


    NASA operates a series of Earth-observing satellites, which help scientists learn more about our home planet. Through partnerships with universities and other government agencies, like the National Oceanic and Atmospheric Administration (NOAA), the Space Agency helps scientists around the world capture precise movements of the Earth s crust to learn more about the underground processes related to earthquakes and volcanic eruptions, create accurate assessments of wind resources for future energy use, and preserve endangered species by generating much-needed data about their environments. This work, done primarily from space with satellites using a variety of complex instruments to take readings of the surface below, generates leagues of valuable data that aid scientists on the ground - or in some cases on the water. As much of the Earth is covered in water liquid, frozen, saltwater, or fresh much of NASA s remote sensing work focuses on the oceans and their health. This valuable, mammoth (yet fragile) resource provides insight into the overall health of our planet, as water, in addition to being abundant, is a key ingredient to all known life on Earth. As part of its ocean-observing work, NASA partnered with NOAA and private industry to develop remote sensing technologies for protecting the seas of the North Pacific from a nefarious and pervasive problem: derelict fishing gear.

  2. Water Cycling Between Ocean and Mantle: Super-Earths Need Not be Waterworlds

    CERN Document Server

    Cowan, Nicolas B


    Large terrestrial planets are expected to have muted topography and deep oceans, implying that most super-Earths should be entirely covered in water, so-called waterworlds. This is important because waterworlds lack a silicate weathering thermostat so their climate is predicted to be less stable than that of planets with exposed continents. In other words, the continuously habitable zone for waterworlds is much narrower than for Earth-like planets. A planet's water is partitioned, however, between a surface reservoir, the ocean, and an interior reservoir, the mantle. Plate tectonics transports water between these reservoirs on geological timescales. Degassing of melt at mid-ocean ridges and serpentinization of oceanic crust depend negatively and positively on seafloor pressure, respectively, providing a stabilizing feedback on long-term ocean volume. Motivated by Earth's approximately steady-state deep water cycle, we develop a two-box model of the hydrosphere and derive steady-state solutions to the water pa...

  3. Model for Analysis of the Energy Demand (MAED) users' manual for version MAED-1

    International Nuclear Information System (INIS)

    This manual is organized in two major parts. The first part includes eight main sections describing how to use the MAED-1 computer program and the second one consists of five appendices giving some additional information about the program. Concerning the main sections of the manual, Section 1 gives a summary description and some background information about the MAED-1 model. Section 2 extends the description of the MAED-1 model in more detail. Section 3 introduces some concepts, mainly related to the computer requirements imposed by the program, that are used throughout this document. Sections 4 to 7 describe how to execute each of the various programs (or modules) of the MAED-1 package. The description for each module shows the user how to prepare the control and data cards needed to execute the module and how to interpret the printed output produced. Section 8 recapitulates about the use of MAED-1 for carrying out energy and electricity planning studies, describes the several phases normally involved in this type of study and provides the user with practical hints about the most important aspects that need to be verified at each phase while executing the various MAED modules

  4. The unstable CO2 feedback cycle on ocean planets

    CERN Document Server

    Kitzmann, D; Godolt, M; Grenfell, J L; Heng, K; Patzer, A B C; Rauer, H; Stracke, B; von Paris, P


    Ocean planets are volatile rich planets, not present in our Solar System, which are thought to be dominated by deep, global oceans. This results in the formation of high-pressure water ice, separating the planetary crust from the liquid ocean and, thus, also from the atmosphere. Therefore, instead of a carbonate-silicate cycle like on the Earth, the atmospheric carbon dioxide concentration is governed by the capability of the ocean to dissolve carbon dioxide (CO2). In our study, we focus on the CO2 cycle between the atmosphere and the ocean which determines the atmospheric CO2 content. The atmospheric amount of CO2 is a fundamental quantity for assessing the potential habitability of the planet's surface because of its strong greenhouse effect, which determines the planetary surface temperature to a large degree. In contrast to the stabilising carbonate-silicate cycle regulating the long-term CO2 inventory of the Earth atmosphere, we find that the CO2 cycle feedback on ocean planets is negative and has strong...

  5. Microradiometers Reveal Ocean Health, Climate Change (United States)


    When NASA researcher Stanford Hooker is in the field, he pays close attention to color. For Hooker, being in the field means being at sea. On one such research trip to the frigid waters of the Arctic, with a Coast Guard icebreaker looming nearby and the snow-crusted ice shelf a few feet away, Hooker leaned over the edge of his small boat and lowered a tethered device into the bright turquoise water, a new product devised by a NASA partner and enabled by a promising technology for oceanographers and atmospheric scientists alike. Color is a function of light. Pure water is clear, but the variation in color observed during a visit to the beach or a flight along a coastline depends on the water s depth and the constituents in it, how far down the light penetrates and how it is absorbed and scattered by dissolved and suspended material. Hooker cares about ocean color because of what it can reveal about the health of the ocean, and in turn, the health of our planet. "The main thing we are interested in is the productivity of the water," Hooker says. The seawater contains phytoplankton, microscopic plants, which are the food base for the ocean s ecosystems. Changes in the water s properties, whether due to natural seasonal effects or human influence, can lead to problems for delicate ecosystems such as coral reefs. Ocean color can inform researchers about the quantities and distribution of phytoplankton and other materials, providing clues as to how the world ocean is changing. NASA s Coastal Zone Color Scanner, launched in 1978, was the first ocean color instrument flown on a spacecraft. Since then, the Agency s ocean color research capabilities have become increasingly sophisticated with the launch of the SeaWiFS instrument in 1997 and the twin MODIS instruments carried into orbit on NASA s Terra (1999) and Aqua (2002) satellites. The technology provides sweeping, global information on ocean color on a scale unattainable by any other means. One issue that arises from satellite observation, however, is that the instruments must be continuously calibrated over time to maintain the quality of the data they gather from orbit. To validate and calibrate the satellites, researchers must also gather data at sea level.

  6. Rheology and Thermal State of Titan's Crust: Potential Role of Methane Clathrates (United States)

    Basu Sarkar, D.; Elwood Madden, M.


    Gravity and topography data including new results obtained from recent Cassini RADAR and Visible and Infrared Mapping Spectrometer (VIMS) observations suggest that Titan has a rigid and conductive crust, greater than 40 km in thickness (Beghin et al., 2012; Hemingway et al., 2013; Lopes et al., 2013; Mitri et al., 2014; Lefevre et al., 2014; Baland et al., 2014). In this work we employed rheological models based on clathrate hydrate stability fields and modeled geothermal gradients to investigate how clathrate hydrates may influence the rheology of Titan's crust. Our findings suggest that a thick, rigid, and conductive crust composed of pure water ice is unlikely. Instead, a mixed phase crust comprised of water ice and clathrate hydrates, with up to 40 to 50% methane clathrates, results in thermal conductivity, viscosity, and density values consistent with Cassini observations. We modeled variations in Rayleigh number with crustal thickness for different crustal compositions assuming constant viscosity. Addition of methane clathrates makes the mixed ice-clathrate crust more viscous resulting in smaller Rayleigh numbers with depth compared to ice-only models. This slower rate of increase in Rayleigh number is also associated with increasing critical Rayleigh numbers, and hence, the potential thickness of a rigid, conductive crust. Modeling basal viscosity for different crustal compositions, following McKinnon (2006), we also determined that a methane clathrate-rich conductive crust would likely be much thicker (~60 km) than a non-convecting pure water-ice crust (~12 km). Titan's carbon content constrained by different formation models (Tobie et al., 2012) shows that even a pure methane clathrate crust is possible. However, a pure methane clathrate crust is unlikely because it would be relatively thin, less than 20 km due to clathrate's low thermal conductivity. Therefore, a mixed phase crust may explain both the geophysical observations and significant methane concentrations in Titan's atmosphere.

  7. Spatial and temporal distribution of cyanobacterial soil crusts in the Kalahari: Implications for soil surface properties (United States)

    Thomas, A. D.; Dougill, A. J.


    Localised patterns of erosion and deposition in vegetated semi-arid rangelands have been shown to influence ecological change and biogeochemical cycles. In the flat, vegetated Kalahari rangelands of Southern Africa the factors regulating erodibility of the fine sand soils and the erosivity of wind regimes require further investigation. This paper reports on the spatial and temporal patterns of cyanobacterial soil crust cover from ten sites at five sampling locations in the semi-arid Kalahari and discusses the likely impact on factors regulating surface erodibility and erosivity. Cyanobacterial soil crust cover on Kalahari Sand varied between 11% and 95% of the ground surface and was higher than previously reported. Cover was inversely related to grazing with the lowest crust cover found close to boreholes and the highest in the Game Reserve and Wildlife Management Zone. In grazed areas, crusts form under the protective canopies of the thorny shrub Acacia mellifera. Fenced plot data showed that crusts recover quickly from disturbance, with a near complete surface crust cover forming within 15 months of disturbance. Crust development is restricted by burial by wind blown sediment and by raindrop impact. Crusts had significantly greater organic matter and total nitrogen compared to unconsolidated surfaces. Crusts also significantly increased the compressive strength of the surface (and thus decreased erodibility) and changed the surface roughness. Establishing exactly how these changes affect aeolian erosion requires further process-based studies. The proportion of shear velocity acting on the surface in this complex mixed bush-grass-crust environment will be the key to understanding how crusts affect erodibility.

  8. Geochemical characteristics and metal element enrichment in crusts from seamounts of the Western Pacific (United States)

    Zhang, Xiaoyu; Zhu, Kechao; Du, Yong; Zhang, Fuyuan; Zhang, Weiyan; Ren, Xiangwen; Jiang, Binbin; Huang, Dasong


    Elemental geochemistry is an essential part of understanding mineralization mechanisms. In this paper, a data set of 544 cobalt crust samples from seamounts of the Western Pacific are used to study the enrichment characteristics of metal elements. REE normalization is utilized to reveal the origin of the crusts; effects of water depth on Co enrichment and impacts of phosphatization on mineral quality are discussed to obtain the evolution of these marine mineral deposits, which gives support to further resource assessment. Conclusions are reached as follows: 1) Elemental abundances, inter-element relationships, and shale-normalized REE patterns for phosphate-poor crusts from different locations reflect hydrogenetic origin of the crusts. EFs (enrichment coefficients) of REE exhibit exponential increase from surface sediments to phosphorite to polymetallic nodules to crusts, suggesting that the improved degree of hydrogeneous origin induces the enrichment of REE. 2) The crusts in the Western Pacific, formed through hotspot produced guyots trails, have relatively lower REE than those in the Mid-Pacific. The latter could be attributed to the peculiar submarine topography of seamounts formed by intraplate volcanism. 3) The non-phosphatized younger crust layers have 40% higher Co than the phosphatized older layers. This indicates the modification of the elemental composition in these crusts by phosphatization. A general depletion of hydroxide-dominated elements such as Co, Ni, and Mn and enrichment of P, Ca, Ba, and Sr is evident in phosphatized crusts, whereas non-phosphatized younger generation crusts are rich in terrigenous aluminosilicate detrital matter. 4) Co increases above the carbonate compensation depth (CCD) from less than 0.53% to over 0.65% in seamount regions with water depth of less than 2,500 m, suggesting the significance of the dissolution of carbonate in the sea water column to the growth and composition of crusts.

  9. Microbial ecology of the dark ocean above, at, and below the seafloor

    DEFF Research Database (Denmark)

    Orcutt, Beth; Sylvan, Jason B


    The majority of life on Earth--notably, microbial life--occurs in places that do not receive sunlight, with the habitats of the oceans being the largest of these reservoirs. Sunlight penetrates only a few tens to hundreds of meters into the ocean, resulting in large-scale microbial ecosystems that function in the dark. Our knowledge of microbial processes in the dark ocean-the aphotic pelagic ocean, sediments, oceanic crust, hydrothermal vents, etc.-has increased substantially in recent decades. Studies that try to decipher the activity of microorganisms in the dark ocean, where we cannot easily observe them, are yielding paradigm-shifting discoveries that are fundamentally changing our understanding of the role of the dark ocean in the global Earth system and its biogeochemical cycles. New generations of researchers and experimental tools have emerged, in the last decade in particular, owing to dedicated research programs to explore the dark ocean biosphere. This review focuses on our current understanding of microbiology in the dark ocean, outlining salient features of various habitats and discussing known and still unexplored types of microbial metabolism and their consequences in global biogeochemical cycling. We also focus on patterns of microbial diversity in the dark ocean and on processes and communities that are characteristic of the different habitats.

  10. Rehabilitation of European Biological Soil Crusts - The SCIN project (United States)

    Williams, Laura; Zheng, Lingjuan; Maier, Stefanie; Weber, Bettina; Büdel, Burkhard


    The ''Soil Crust INternational'' (SCIN) Project aims to improve the appreciation and understanding of European Biological Soil Crusts (BSC) with the goal of developing biodiversity conservation and sustainable management strategies. Our objective is to study the uniqueness of European BSC on a local scale and investigate how these communities thrive in areas with such great macroclimatic differences. In order to cover a wide diversity of European BSC a latitudinal transect was established, extending from the Great Alvar of Öland, Sweden in the north, down to Gössenheim, Central Germany and Hochtor in the Hohe Tauern National Park, Austria, continuing to the Badlands of Tabernas, in southern Spain. The transect stretches over 20° latitude and 2,300 m in altitude and includes natural and also semi-natural sites that require maintenance, for instance, by grazing. Within the SCIN project a rehabilitation study was initiated in order to investigate the recovery potential of BSC under different environmental conditions. This entailed the construction of 10 times 1m2 plots, alongside control plots, at each of the 4 sites, where the BSC was completely removed. Over the course of 2 years (2012-2014) the plots were sampled regularly to assess recovery in the form of returning organisms (cyanobacteria, algae, lichens, bryophytes, higher plants), soil stability, chlorophyll and carbon content and nutrient composition. Cyanobacteria are considered as the pioneering functional group of BSC establishment in many regions, especially arid, and may be critical for the successful formation of any of the further BSC successional stages. Therefore, the cyanobacterial assemblages of recovering plots are being investigated to shed light on the importance of cyanobacteria in the rehabilitation of BSC and whether individual species or specific communities can be ascribed to a local or wide geographical range. It also has to be considered the proximity of recovering BSC to established crust; in our case a major contributing factor to successful recovery has to be the mature BSC surrounding the plots. Our results so far show however, that this may not be as simple as it seems due to the physical properties of the treated plot, the erosion caused by the lack of BSC may severely affect the ability of returning communities to establish themselves, and therefore the geographical and climatic aspects of the rehabilitation sites play a crucial factor in the sense of minimising erosion as much as possible. Two years is clearly not a significant amount of time in the rehabilitation of BSC, but this study throws light on the initial stages of recovery and can suggest management practices for future rehabilitation projects.

  11. 42 CFR 422.520 - Prompt payment by MA organization. (United States)


    ...2010-10-01 false Prompt payment by MA organization. 422.520 Section 422.520 ...and Contracts for Medicare Advantage Organizations § 422.520 Prompt payment by MA organization. (a) Contract between CMS and...

  12. 42 CFR 422.2268 - Standards for MA organization marketing. (United States)


    ...false Standards for MA organization marketing. 422.2268 Section 422.2268...ADVANTAGE PROGRAM Medicare Advantage Marketing Requirements § 422.2268 Standards for MA organization marketing. In conducting marketing...

  13. High temperature constitutive models for MA957

    International Nuclear Information System (INIS)

    Full text of publication follows: MA957 has outstanding low-temperature tensile and high-temperature creep strength and potential for managing radiation damage, including high helium levels in fusion environment. The excellent properties of nano-structured ferritic alloys (NFAs), such as MA957, derive from a high density of nm-sized Y-Ti-O precipitate cluster and/or complex oxides (NF), such as Y2Ti2O7 and Y2TiO5, which form during hot consolidation following mechanical alloying. The low temperature strengthening contributions have been evaluated in previous studies. However, the strengthening contributions of NF at high temperatures are not well understood. In this study we develop high temperature constitutive models for MA957, primarily from interrupted compression tests in the temperature (Tt) range from about 600 to 900 deg. C, over a range of strain rates down to less than 10-6/s. In probing the high stress regime for power law creep, our objective is to characterize the NF dislocation pinning dynamics. This information will then be used to build physical creep models, such as those based on threshold stress concepts, which can be extrapolated to lower stress regimes. Comparing this data to actual lower stress creep data we generate, as well as that taken from the literature, will help to discriminate the contributions of the NF to overall creep strength. The models will be used to construct Ashby type creep maps and to guide future experimental studies. (authors)

  14. Microcap M&A: An Exploratory Study

    Directory of Open Access Journals (Sweden)

    Keith Turpie


    Full Text Available A substantial body of accounting and finance literature has been devoted to the study of Mergers and Acquisitions (M&As dominated by discussions relating to the gains and losses that accrue from transactions involving large public companies. This paper makes a unique contribution to the literature by investigating the M&A experience of microcap businesses. Transactions involving microcap M&A are substantially different to those involving large companies on a number of dimensions. This paper explores the determinants of microcap M&A success and pitfalls and problems from an integration perspective. Due to the paucity of research in the area an exploratory research design is employed, conducting interviews with five CEOs of companies that had each managed multiple transactions. We find microcap M&As are successful when measured against identified goals but generally take longer and cost more than expected. Further, culture and communication are key issues in determining success/failure. We also find the in-house management of integration aspects is problematic for these businesses and suggest this warrants further study.

  15. Production of mildly alkaline basalts at complex ocean ridge settings: Perspectives from basalts emitted during the 2010 eruption at the Eyjafjallajökull volcano, Iceland (United States)

    Viccaro, Marco; Nicotra, Eugenio; Urso, Salvatore


    The early phase of the 2010 eruption at the Eyjafjallajökull volcano (Iceland) produced poorly evolved mildly alkaline basalts that have a signature more enriched with respect to the typically depleted basalts emitted at ocean ridges. The whole rock geochemistry of these basaltic magmas offers a great opportunity to investigate the mantle source characteristics and reasons leading to this enriched fingerprint in proximity of the ocean ridge system. Some basaltic products of Katla volcano, ?25 km east of Eyjafjallajökull, have been chosen from the literature, as they display a similar mildly alkaline signature and can be therefore useful to explore the same target. Major and trace element variations of the whole rock suggest a very limited evolutionary degree for the 2010 Eyjafjallajökull products and the selected Katla magmas, highlighting the minor role played by differentiation processes such as fractional crystallization. Nevertheless, effects of the limited fractionation have been erased through re-equilibration of the major and trace element abundances at primary conditions. Concentrations of Th after re-equilibration have been assumed as indexes of the partial melting degree, given the high incompatibility of the element, and enrichment ratios calculated for each trace element. Especially for LILE (Rb, Ba, K, Sr), the pattern of resulting enrichment ratios well matches that obtained from fractional melting of peridotite bearing hydrous phases (amphibole/phlogopite). This put forward the idea that magmas have been generated through partial melting of enriched mantle domains where hydrous minerals have been stabilized as a consequence of metasomatic processes. Refertilization of the mantle has been attributed to intrusion of hydrous silicate melts and fractional crystallization of hydrous cumulates. These refertilizing melts, inherited from an ancient subducted oceanic crust, intruded into a depleted oceanic lithosphere that remained stored for a long time (hundreds of Ma or Ga) before being re-entrained in partial melting. This means that magmas could have acquired their main geochemical differences in response of the variable depletion/enrichment degree of the heterogeneous mantle portion tapped at rather shallow depth (?100 km). Our finding is another tessera in the open debate on the plume-related vs. non plume-related origin of Icelandic magmatism.

  16. Realistic electrostatic potentials in a neutron star crust (United States)

    Ebel, Claudio; Mishustin, Igor; Greiner, Walter


    We study the electrostatic properties of inhomogeneous nuclear matter which can be formed in the crusts of neutron stars or in supernova explosions. Such matter is represented by Wigner-Seitz cells of different geometries (spherical, cylindrical, cartesian), which contain nuclei, free neutrons and electrons under the conditions of electrical neutrality. Using the Thomas-Fermi approximation, we have solved the Poisson equation for the electrostatic potential and calculated the corresponding electron density distributions in individual cells. The calculations are done for different shapes and sizes of the cells and different average baryon densities. The electron-to-baryon fraction was fixed at 0.3. Using realistic electron distributions leads to a significant reduction in electrostatic energy and electron chemical potential.

  17. Structure of lunar crust from KAGUYA selenodesy data (United States)

    Sasaki, S.; Ishihara, Y.; Goossens, S.; Matsumoto, K.; Araki, H.; Hanada, H.; Kikuchi, F.; Noda, H.; Iwata, T.; Ohtake, M.


    Using 4-way Doppler tracking with relay satellite OKINA, KAGUYA obtained the first precise gravity field of the lunar farside. Multi-frequency differential VLBI observation of subsatellites OKINA and OUNA improved the accuracy of gravity. KAGUYA also has a laser altimeter (LALT) which obtained the first global topography of the moon including polar regions. Assuming uniform crustal density, we obtain crustal thickness distribution where crustal thickness is nearly zero beneath Mare Moscoviense. The interior structure of the South Pole-Aitken basin (SPA) is investigated using localized representation of gravity potential where Slepian functions were used to estimate the gravity field over certain areas of the Moon. The direction of an ellipse denoting the depression is similar to the previous result. The region with the thinnest crust is nearly circular and offset southward from the center of SPA. We analyzed interior structure of small basins in and around SPA.

  18. P-wave Receiver Functions reveal the Bohemian Massif crust (United States)

    Kampfova Exnerova, Hana; Plomerova, Jaroslava; Vecsey, Ludek


    In this study we present initial results of P-wave Receiver Functions (RF) calculated from broad-band waveforms of teleseismic events recorded by temporary and permanent stations in the Bohemian Massif (BM, Central Europe). Temporary arrays BOHEMA I (2001-2003), BOHEMA II (2004-2005) and BOHEMA III (2005-2006) operated during passive seismic experiments oriented towards studying velocity structure of the lithosphere and the upper mantle. Receiver Functions show relative response of the Earth structure under a seismic station and nowadays represent frequently-used method to retrieve structure of the crust, whose knowledge is needed in various studies of the upper mantle. The recorded waveforms are composites of direct P and P-to-S converted waves that reverberate in the structure beneath the receiver (Ammon, 1997). The RFs are sensitive to seismic velocity contrast and are thus suited to identifying velocity discontinuities in the crust, including the Mohorovi?i? discontinuity (Moho). Relative travel-time delays of the converted phases detected in the RFs are transformed into estimates of discontinuity depths assuming external information on the vp/vs and P velocity. To evaluate RFs we use the Multiple-taper spectral correlation (MTC) method (Park and Levin, 2000) and process signals from teleseismic events at epicentral distances of 30 - 100° with magnitude Mw > 5.5. Recordings are filtered with Butterworth band-pass filter of 2 - 8 s. To select automatically signals which are strong enough, we calculate signal-to-noise ratios (SNR) in two steps. In the first step we calculate SNR for signals from intervals (-1s, 3s)/(-10s, -2s), where P-arrival time represent time zero. In the second step we broaden the intervals and calculate SNR for (-1s, 9s)/(-60s, -2s). We also employ forward modelling of the RFs using Interactive Receiver Functions Forward Modeller (IRFFM) (Tkal?i? et al., 2010) to produce, in the first step, one-dimensional velocity models under individual seismic station. Stacked traces of the RFs show strong conversions with positive polarity (indicating a velocity increase across the discontinuity) between 3.3 and 4.5 s after the P-wave arrival at almost all stations. We relate these pulses to conversions at the Moho discontinuity. Assuming a constant crustal vp/vs ratio (1.73) and average crustal velocity vp=6.3 km/s for all stations, analogically to Geissler et al (2012), we multiply the evaluated Ps delay times by factor of 8.3 km/s and estimate the Moho beneath the Bohemian Massif at depths between 27 and 37 km. The crust is thinnest in the western part of the BM, beneath the SW end of the Eger Rift. The Moldanubian part of the BM exhibits the thickest crust. At most of the stations we also see one or two intra-crustal conversions, sometimes stronger than that related to the Moho. Several stations exhibit significant variations of the RF with back-azimuth. The aim of this study is to update existing three dimensional P-velocity crustal model of the Bohemian Massif (Karousová et al., 2012) compiled from control-source seismic results.

  19. Crusted scabies in a chid with systemic lupus erythematosus

    Scientific Electronic Library Online (English)

    Nurimar C.F., Wanke; Claudia, Melo; Viviam, Balassiano.


    Full Text Available E descrito um caso de sarna crostosa em criança portadora de lupus eritematoso sistêmico em tratamento com prednisona há três anos. O raspado das lesões cutâneas revelou ovos e ácaros adultos de Sarcoptes scabiei. A paciente faleceu por sepsis e insuficiência renal pouco tempo após início da terapêu [...] tica tópica com enxofre a 20%. Melhora importante foi observada no quadro dermatológico. Abstract in english A child with systemic lupus erythematosus who has been treated with prednisone for three years, developed crusted scabies. Scrapings from lesions revealed Sarcoptes scabiei adult mites mad eggs. The patient died with septicemia and renal failure soon after starting topical 20% sulfur. A marked impro [...] vement was observed in the cutaneous lesions.

  20. Clinopyroxene precursors to amphibole sponge in arc crust (United States)

    Smith, Daniel J.


    The formation of amphibole cumulates beneath arc volcanoes is a key control on magma geochemistry, and generates a hydrous lower crust. Despite being widely inferred from trace element geochemistry as a major lower crustal phase, amphibole is neither abundant nor common as a phenocryst phase in arc lavas and erupted pyroclasts, prompting some authors to refer to it as a ‘cryptic’ fractionating phase. This study provides evidence that amphibole develops by evolved melts overprinting earlier clinopyroxene—a near-ubiquitous mineral in arc magmas. Reaction-replacement of clinopyroxene ultimately forms granoblastic amphibole lithologies. Reaction-replacement amphiboles have more primitive trace element chemistry (for example, lower concentrations of incompatible Pb) than amphibole phenocrysts, but still have chemistries suitable for producing La/Yb and Dy/Yb ‘amphibole sponge’ signatures. Amphibole can fractionate cryptically as reactions between melt and mush in lower crustal ‘hot zones’ produce amphibole-rich assemblages, without significant nucleation and growth of amphibole phenocrysts.

  1. Research for the physics and structure of earth's crust in Romania

    International Nuclear Information System (INIS)

    Systematic research for the deciphering of the physic and structure of Earth's crust in our country by geophysical methods were performed in the frame of Romanian Geological Institute since 1925. We put into evidence the principle achievements obtained by the geological and geophysical research for the mineral resources existing in the Romanian earth's crust. (authors)

  2. Comparison of internal features and microchemistry of ferromanganese crusts from the Central Indian Basin

    Digital Repository Service at National Institute of Oceanography (India)

    Iyer, S.D.

    are enriched in Ni and Cu. Microstructural and elemental variations, from the ferromanganese crust outer surface to the basalt substrate, probably reflect changes in the accretion or in the source of metals. The major source of the crust metals in seawater...

  3. Fast Episodes of West-Mediterranean-Tyrrhenian Oceanic Opening and Revisited Relations with Tectonic Setting (United States)

    Savelli, Carlo


    Extension and calc-alkaline volcanism of the submerged orogen of alpine age (OAA) initiated in Early Oligocene (~33/32?Ma) and reached the stage of oceanic opening in Early-Miocene (Burdigalian), Late-Miocene and Late-Pliocene. In the Burdigalian (~20-16?Ma) period of widespread volcanism of calcalkaline type on the margins of oceanic domain, seafloor spreading originated the deep basins of north Algeria (western part of OAA) and Sardinia/Provence (European margin). Conversely, when conjugate margins’ volcanism has been absent or scarce seafloor spreading formed the plains Vavilov (7.5-6.3?Ma) and Marsili (1.87-1.67?Ma) within OAA eastern part (Tyrrhenian Sea). The contrast between occurrence and lack of margin’s igneous activity probably implies the diversity of the geotectonic setting at the times of oceanization. It appears that the Burdigalian calcalkaline volcanism on the continental margins developed in the absence of subduction. The WNW-directed subduction of African plate probably commenced at ~16/15?Ma (waning Burdigalian seafloor spreading) after ~18/16?Ma of rifting. Space-time features indicate that calcalkaline volcanism is not linked only to subduction. From this view, temporal gap would exist between the steep subduction beneath the Apennines and the previous, flat-type plunge of European plate with opposite direction producing the OAA accretion and double vergence.

  4. Titan's rotation reveals an internal ocean and changing zonal winds. (United States)

    Lorenz, Ralph D; Stiles, Bryan W; Kirk, Randolph L; Allison, Michael D; Del Marmo, Paolo Persi; Iess, Luciano; Lunine, Jonathan I; Ostro, Steven J; Hensley, Scott


    Cassini radar observations of Saturn's moon Titan over several years show that its rotational period is changing and is different from its orbital period. The present-day rotation period difference from synchronous spin leads to a shift of approximately 0.36 degrees per year in apparent longitude and is consistent with seasonal exchange of angular momentum between the surface and Titan's dense superrotating atmosphere, but only if Titan's crust is decoupled from the core by an internal water ocean like that on Europa. PMID:18356521

  5. The helium flux from the continents and ubiquity of low-3He/4He recycled crust and lithosphere (United States)

    Day, James M. D.; Barry, Peter H.; Hilton, David R.; Burgess, Ray; Pearson, D. Graham; Taylor, Lawrence A.


    New helium isotope and trace-element abundance data are reported for pyroxenites and eclogites from South Africa, Siberia, and the Beni Bousera Massif, Morocco that are widely interpreted to form from recycled oceanic crustal protoliths. The first He isotope data are also presented for Archaean peridotites from the Kaapvaal (South Africa), Slave (Canada), and Siberian cratons, along with recently emplaced off-craton peridotite xenoliths from Kilbourne Hole, San Carlos (USA) and Vitim (Siberia), to complement existing 3He/4He values obtained for continental and oceanic peridotites. Helium isotope compositions of peridotite xenoliths vary from 7.3 to 9.6 RA in recently (Africa. The helium isotope compositions of the peridotites can be explained through progressive sampling of 4He produced from radiogenic decay of U and Th in the mineral lattice in the older emplaced peridotite xenoliths. Ingrowth of 4He is consistent with generally higher 4He concentrations measured in olivine from older emplaced peridotite xenoliths relative to those from younger peridotite xenoliths. Collectively, the new data are consistent with pervasive open-system behaviour of He in peridotite xenoliths from cratons, mobile belts and tectonically-active regions. However, there is probable bias in the estimate of the helium isotope composition of the continental lithospheric mantle (6.1 ± 2.1 RA), since previously published databases were largely derived from peridotite xenoliths from non-cratonic lithosphere, or phenocrysts/xenocrysts obtained within continental intraplate alkaline volcanics that contain a contribution from asthenospheric sources. Using the new He isotope data for cratonic peridotites and assuming that significant portions (>50%) of the Archaean and Proterozoic continental lithospheric mantle are stable and unaffected by melt or fluid infiltration on geological timescales (>0.1 Ga), and that U and Th contents vary between cratonic lithosphere and non-cratonic lithosphere, calculations yield a 3He flux of 0.25-2.2 atoms/s/cm2 for the continental lithospheric mantle. These estimates differ by a factor of ten from non-cratonic lithospheric mantle and are closer to the observed 3He flux from the continents (<1 atoms/s/cm2). Pyroxenites and eclogites from the continental regions are all characterized by 3He/4He (0.03-5.6 RA) less than the depleted upper mantle, and relatively high U and Th contents. Together with oceanic and continental lithospheric peridotites, these materials represent reservoirs with low time-integrated 3He/(U + Th) in the mantle. Pyroxenites and eclogites are also characterized by higher Fe/Mg, more radiogenic Os-Pb isotope compositions, and more variable ?18O values (?3‰ to 7‰), compared with peridotitic mantle. These xenoliths are widely interpreted to be the metamorphic/metasomatic equivalents of recycled oceanic crustal protoliths. The low-3He/4He values of these reservoirs and their distinctive compositions make them probable end-members to explain the compositions of some low-3He/4He OIB, and provide an explanation for the low-3He/4He measured in most HIMU lavas. Continental lithospheric mantle and recycled oceanic crust protoliths are not reservoirs for high-3He/4He and so alternative, volumetrically significant, He-rich reservoirs, such as less-degassed (lower?) mantle, are required to explain high-3He/4He signatures measured in some intraplate lavas. Recycling of oceanic crust represents a fundamental process for the generation of radiogenic noble gases in the mantle, and can therefore be used effectively as tracers for volatile recycling.

  6. Identification and characterization of novel NuMA isoforms

    International Nuclear Information System (INIS)

    Highlights: • Seven NuMA isoforms generated by alternative splicing were categorized into 3 groups: long, middle and short. • Both exons 15 and 16 in long NuMA were “hotspot” for alternative splicing. • Lower expression of short NuMA was observed in cancer cells compared with nonneoplastic controls. • Distinct localization pattern of short isoforms indicated different function from that of long and middle NuMA. - Abstract: The large nuclear mitotic apparatus (NuMA) has been investigated for over 30 years with functions related to the formation and maintenance of mitotic spindle poles during mitosis. However, the existence and functions of NuMA isoforms generated by alternative splicing remains unclear. In the present work, we show that at least seven NuMA isoforms (categorized into long, middle and short groups) generated by alternative splicing from a common NuMA mRNA precursor were discovered in HeLa cells and these isoforms differ mainly at the carboxyl terminus and the coiled-coil domains. Two “hotspot” exons with molecular mass of 3366-nt and 42-nt tend to be spliced during alternative splicing in long and middle groups. Furthermore, full-length coding sequences of long and middle NuMA obtained by using fusion PCR were constructed into GFP-tagged vector to illustrate their cellular localization. Long NuMA mainly localized in the nucleus with absence from nucleoli during interphase and translocated to the spindle poles in mitosis. Middle NuMA displayed the similar cell cycle-dependent distribution pattern as long NuMA. However, expression of NuMA short isoforms revealed a distinct subcellular localization. Short NuMA were present in the cytosol during the whole cycle, without colocalization with mitotic apparatus. These results have allowed us tentatively to explore a new research direction for NuMA’s various functions

  7. Was there a global-scale plate reorganisation event at 100 Ma? (United States)

    Matthews, K. J.; Seton, M.; Müller, R. D.


    A plate reorganisation event that occurred at 50 Ma has received much attention due to its association with the well-known bend in the Hawaiian-Emperor seamount chain. We review the major tectonic events that occurred between 110 and 90 Ma and find strong evidence that a plate reorganisation at this time was global in scale, occurred over a period of 3-8 Myr, and may have been more dramatic than the 50 Ma event. While the Hawaiian-Emperor bend is synonymous with the 50 Ma event, prominent fracture zone bends in the Wharton Basin west of Australia record a drastic 50° change in the direction of spreading between Australia and India, and have long been discussed in terms of a mid-Cretaceous plate reorganisation in the Indian Ocean. Yet to-date there has been no attempt at a complete global investigation of this reorganisation to determine its magnitude and continental impact. Key tectonic events in the Atlantic-realm include a major compressional episode in the Antarctic Peninsula, a 75° counter-clockwise rotation of the Antarctic-South American spreading ridge in the Weddell Sea, an increase in spreading rate at the mid-Atlantic ridge, a change in the tectonic regime along the western convergent margin of South America from extensional to compressional, a subduction polarity reversal in the Caribbean, and changes in sedimentation pa