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Sample records for ma oceanic crust

  1. Recycled oceanic crust in the source of 90-40 Ma basalts in North and Northeast China: Evidence, provenance and significance

    Xu, Yi-Gang

    2014-10-01

    Major, trace element and Sr-Nd-Pb isotopic data of basalts emplaced during 90-40 Ma in the North and Northeast China are compiled in this review, with aims of constraining their petrogenesis, and by inference the evolution of the North China Craton during the late Cretaceous and early Cenozoic. Three major components are identified in magma source, including depleted component I and II, and an enriched component. The depleted component I, which is characterized by relatively low 87Sr/86Sr (1.1) and HIMU-like trace element characteristics, is most likely derived from gabbroic cumulate of the oceanic crust. The depleted component II, which distinguishes itself by its high ?Nd (?8) and moderate 87Sr/86Sr (?0.7038), is probably derived from a sub-lithospheric ambient mantle. The enriched component has low ?Nd (2-3), high 87Sr/86Sr (>0.7065), low 206Pb/204Pb (17), excess Sr, Rb, Ba and a deficiency of Zr and Hf relative to the REE. This component is likely from the basaltic portion of the oceanic crust, which is variably altered by seawater and contains minor sediments. Comparison with experimental melts and trace element modeling suggest that these recycled oceanic components may be in form of garnet pyroxenite/eclogite. These components are young (influence of Pacific subduction on the deep processes in the North China Craton, which can be traced back at least to the late Cretaceous. This, along with the conjugation of crustal deformation pattern in this region with the movement of the Pacific plate, makes the Pacific subduction as a potential trigger of the destruction of the North China Craton. Geophysical investigations and morphological analyses indicate that decratonization is largely confined to east of the NSGL, whereas to west of NSGL, in particular the Ordos basin, characteristics typical of a craton are observed (Menzies et al., 2007; Zhu et al., 2011). This spatial pattern of craton destruction, together with NE-NNE-oriented extensional basins, main structural alignments and metamorphic core complexes (Zheng et al., 1978; Ye et al., 1987; Ren et al., 2002; Liu et al., 2006; Zhu G et al., 2012), is consistent with the subduction direction of the Pacific plate. Two main episodes of late Mesozoic magmatism have been identified in the Jurassic and the early Cretaceous. These correspond to the subduction of the Pacific plate underneath the Eurasian content and to subsequent extensions, respectively (Wu et al., 2005, 2006). Global tomography studies indicate that the subducted Pacific oceanic slab has become stagnant within the mantle transition zone and extended subhorizontally westward beneath the East Asian continent (Fukao et al., 1992; Huang and Zhao, 2006; Chen and Ai, 2009; Van der Hilst and Li, 2010). The western end of this stagnant slab does not go beyond the NNE-trending NSGL (Huang and Zh

  2. The global oxidation state of the upper oceanic crust

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

    2012-12-01

    The oxidation state of the oceanic crust is an important component of the Earth system. The widespread oxidation of the crust is a major contributor to the redox state of the mantle due to the subduction of hydrothermally altered oceanic crust, which supplies 10 - 25 % of the net ferric iron flux to the global mantle Fe3+/FeTOT budget (Lcuyer and Ricard, 1999). Secondly, the degree of oxidation of the upper oceanic crust provides a measure of the biomass of microbial life sub-basement (Bach and Edwards, 2003). Thirdly, oxidation state analyses of oceanic basalt give information on the environment and relative timings of local hydrothermal alteration events. To date comprehensive measurements of Fe3+/FeTOT for the oceanic crust are lacking. Post crystallisation oxidation processes, occurring predominantly in the upper basaltic layers of the crust, elevate ratios of ferric to total iron (Fe3+/FeTOT) from mantle levels of 0.16 0.01 (Cottrell and Kelley, 2011). Ferrous (Fe2+/) iron is oxidised to ferric (Fe3+/) iron during reaction with oxidised seawater, which circulates through oceanic crust for tens of millions of years following crustal formation. This study integrates published data with new analyses from six ocean crustal boreholes to categorise the global oxidation state of the upper crust. Samples range from <1 to 129 Ma, and represent basalt from medium to superfast spreading centres, depths between <100 - 2000 mbsf, and at a variety of sedimentary cover rates and thicknesses. Results show that by 1 Ma, the Fe3+/FeTOT ratio of the bulk crust is already raised to an average of 0.28 0.07, implying that the oxidation state is established very early in the lifetime of the ocean crust. Post 1 Ma, Fe3+/FeTOT ratios are more variable, reflecting the effects of prolonged exposure to circulating seawater, but are on average ~0.35.

  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

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

    2006-01-01

    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...

  4. Metamorphic processes in subducting oceanic crust

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

    2000-07-01

    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. Thin oceanic crust and flood basalts: India-Seychelles breakup

    Armitage, J. J.; Collier, J. S.; Minshull, T. A.; Henstock, T. J.

    2011-05-01

    Recent seismic experiments showed that separation of India from the Seychelles occurred in two phases of rifting. The first brief phase of rifting between India and the Laxmi Ridge formed the Gop Rift, which is characterized by thick oceanic crust and underplating of the adjacent continental margins. The age of the Gop Rift is uncertain, initiation of seafloor spreading being some time between 71 and 66 Ma. This was then followed by rifting and seafloor spreading between the Laxmi Ridge and the Seychelles, the onset of which is well dated by magnetic anomalies at 63.4 Ma and characterized by thin oceanic crust. Both of these rift events occurred within 1000 km of the center of the Deccan flood basalts, which formed at 65 ± 1 Ma. To constrain the age of the Gop Rift and to explore the reasons for the change in crustal structure between the Gop Rift and Seychelles-Laxmi Ridge margins, we employ a geodynamic model of rift evolution in which melt volumes, seismic velocity, and rare earth element (REE) chemistry of the melt are estimated. We explore the consequences of different thermal structures, hydration, and depletion on the melt production during the India-Seychelles breakup to understand the reasons behind the thin oceanic crust observed. Magmatism at the Gop Rift is consistent with a model in which the seafloor spreading began at 71 Ma, ca. 6 Myr prior to the Deccan. The opening occurred above a hot mantle layer (temperature of 200°C, thickness of 50 km) that we interpret as incubated Deccan material, which had spread laterally beneath the lithosphere. This scenario is consistent with observed lower crustal seismic velocities of 7.4 km s-1 and 12 km igneous crustal thickness. The model indicates that when the seafloor spreading migrated to the Seychelles-Laxmi Ridge at 63 Ma, the thermal anomaly was reduced significantly but not sufficient to explain the observed reduction in breakup magmatism. From observations here of 5.2 km oceanic crust, lower crustal seismic velocities of 6.9 km s-1 and a flat REE profile, we infer that breakup occurred in a region of mantle that became depleted by prior extension related to the Gop Rift.

  6. Magnetization of the oceanic crust: TRM or CRM?

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

    1987-01-01

    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

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

    2006-01-01

    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 440 ?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. Post-glacial ocean acidification and the decline of reefal microbial crusts

    Riding, R.; Liang, L.; Braga, J.

    2011-12-01

    Data from Pacific, Indian Ocean and Caribbean coral reefs indicate marked Late Pleistocene to Holocene decline in the maximum thickness of microbial carbonate crusts in reef cavities. Using estimated values of pH, temperature, CO2, and ionic composition, we calculated calcite saturation ratio (?calcite) of tropical surface seawater for the past 16 Ka. This shows a declining trend of ?calcite, paralleling that of reefal microbial crust thickness. We suggest that thinning of reefal microbial crusts could reflect decrease in seawater carbonate saturation due to ocean acidification in response to deglacial CO2 increase. Previously, decline in reefal microbial crusts, for example at Tahiti in the Pacific Ocean, has mainly been attributed to changes in nutrient supply associated with ocean upwelling and/or terrestrial run-off. Ocean acidification does not preclude such effects on microbial crust development produced by localized changes, but two features in particular are consistent with a global link with carbonate saturation state. Firstly, post-glacial decline in reefal microbial crust thickness affected tropical coral reefs in several oceans. Secondly, seawater carbonate saturation is a major long-term control on microbial carbonate abundance; microbially-induced biocalcification requires elevated seawater saturation for CaCO3 minerals and can be expected to fluctuate with carbonate saturation. In addition to compiling published crust thickness data, we measured thicknesses of microbial carbonate crusts in cavities in Tahiti reefs sampled by Integrated Ocean Drilling Program coring in 2005. This indicates halving of maximum crust thickness, during the same period as steep decline in mean-ocean calcite saturation, near the Pleistocene-Holocene transition. Reefal microbial crusts have been common since skeletal reefs became widespread during the Ordovician Period, 475 Ma ago. The habitat for cryptic crusts expanded as scleractinian corals developed cavernous frameworks. These typically form late-stage stromatolitic veneers on coral and other reef skeletons in framework cavities, and can make a substantial contribution to reef structure. In some tropical reefs of the past 10 Ma, microbial crusts constitute up to 80% of the CaCO3 framework. The thinning and/or elimination of crusts affects the wave-resistance and mechanical stability of skeletal frames, and can be expected to influence overall patterns of coral reef growth and architecture. If the deglacial decline in reefal microbial crusts recorded by our data does reflect reduction in carbonate saturation ratio due to CO2 increase, then this natural ocean acidification can be expected to have occurred with similar effects during earlier interglacial periods.

  9. Deep-ocean ferromanganese crusts and nodules

    Hein, James R.; Koschinsky, Andrea

    2013-01-01

    Ferromanganese crusts and nodules may provide a future resource for a large variety of metals, including many that are essential for emerging high- and green-technology applications. A brief review of nodules and crusts provides a setting for a discussion on the latest (past 10 years) research related to the geochemistry of sequestration of metals from seawater. Special attention is given to cobalt, nickel, titanium, rare earth elements and yttrium, bismuth, platinum, tungsten, tantalum, hafnium, tellurium, molybdenum, niobium, zirconium, and lithium. Sequestration from seawater by sorption, surface oxidation, substitution, and precipitation of discrete phases is discussed. Mechanisms of metal enrichment reflect modes of formation of the crusts and nodules, such as hydrogenetic (from seawater), diagenetic (from porewaters), and mixed diagenetic–hydrogenetic processes.

  10. Thickened juvenile lower crust-derived ~ 90 Ma adakitic rocks in the central Lhasa terrane, Tibet

    Sun, Gao-Yuan; Hu, Xiu-Mian; Zhu, Di-Cheng; Hong, Wen-Tao; Wang, Jian-Gang; Wang, Qing

    2015-05-01

    The questions of why the Late Cretaceous magmatism generated and how the nature of the lower crust evolves in central Tibet remain poorly constrained. In this paper, we report the presence of early Late Cretaceous adakitic rocks from the Azhang area, northern edge of the central Lhasa subterrane, central Tibet. These rocks are rhyodacites/dacites in composition and have geochemical characteristics of adakitic rocks, e.g., high Sr (554-836 ppm), Sr/Y (66-100), and (La/Yb)N (20-21), low Y (7.96-8.96 ppm) and heavy rare earth elements (HREE). In situ zircon U-Pb dating for two samples yields an early Late Cretaceous age (90 ± 1 Ma and 87 ± 1 Ma). The low MgO (1.4-1.9 wt.%) contents and compatible element abundances (e.g., Cr = 22-30 ppm; Ni = 19-25 ppm) indicate that these rocks were most likely derived from the partial melting of a garnet-bearing amphibolite under a thickened lower crust condition. The positive whole-rock εNd(t) (+ 2.5 to + 5.6) and zircon εHf(t) (+ 8.9 to + 16.0) values suggest that this thickened lower crust was juvenile. The crust beneath the central Lhasa subterrane may have been significantly thickened due to tectonic shortening in response to the Lhasa-Qiangtang collision and magma underplating before the emplacement of Azhang adakitic rocks (~ 90 Ma). We argue that regional lithospheric delamination at ~ 90 Ma triggered the partial melting of the lowermost garnet-bearing crust that is still attached to the middle crust to generate the Azhang adakitic rocks. The presence of the ~ 90 Ma Azhang adakitic rocks provides valuable constraints on the origin of the early Late Cretaceous magmatism in the central Lhasa subterrane and on the crustal evolution beneath the Lhasa-Qiangtang collisional zone prior to the Cenozoic India-Asia collision.

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

    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

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

    2000-01-01

    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 ϵHf 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 ϵHf 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. Anorthositic oceanic crust in the Archean Earth

    Jagoutz, E.; Dawson, J. B.; Hoernes, S.; Spettel, B.; Waenke, H.

    1985-01-01

    Ultrapure minerals separated from eclogite inclusions in kimberlites were analyzed for Sm, Nd, Sr, and oxygen isotopes and for major and trace elements. Clinopyroxene (cpx) and garnet (gnt) are the only primary mineral phases in these rocks, and mineral phases and their alteration products. The WR sub calc. is the reconstructed bulk composition excluding all the contamination influences. Two groups of eclogites: are distinguished: (1) type A Noritic-anorthositic eclogites; and (2) type B Ti-ferrogabbroic eclogites. The oxygen isotopes are primary mantle-derived features of these rocks and are not caused by posteruption processes, as they were measured on unaltered, clean mineral separates and show a correlation with REE pattern and Sr and Nd isotopes. It is suggested that the variation of the oxygen isotopes are caused by crustal-level fluid-rock interaction at relatively low temperature. It is shown that oxygen isotopes variation in MORB basalts caused by the hydrothermal system are in the same range as the observed oxygen isotope variation in eclogites. A model to explain the new set of data is proposed. It is thought that some of these eclogites might be emplaced into the upper lithosphere or lower crust at the time corresponding to their internal isochron age. The calculated WR composition was used to estimate model ages for these rocks.

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

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

    2000-01-01

    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.

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

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

    2014-05-01

    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 εNd(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.

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

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

    New seismic reflection profiles of ~~ 5370 km, running through the Ocean Drilling Program Leg 116 sites and Deep Sea Drilling Project Sites 215 and 218, were obtained to investigate the spatial extent, timing, and nature of the Tertiary deformation...

  17. Primary carbonatite melt from deeply subducted oceanic crust

    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.

    2008-07-01

    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.

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

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

    2015-08-01

    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. Boron isotope exchange between seawater and the oceanic crust

    Dissolved boron in seawater from the Atlantic and Pacific is isotopically homogeneous at 39.5 per mil(11B/10B ratios are expressed as per mil deviations from NBS SRM 951). Unaltered mid-ocean ridge basalts (MORB) from the crest of the East Pacific Rise (EPR) at 210 and 130N have B contents of 0.39 +- 0.03 and 0.46 +-0.03 ppm (about one order of magnitude lower than previous estimates) and delta11B of -3.6 +- 0.4 and -2.2 +- 0.6 per mil respectively. Large scale B exchange between seawater and the oceanic crust has been demonstrated at both high and low temperature. Hydrothermal solutions from nine separate vent fields at 210 and 130N (EPR) have variable B enrichments, relative to seawater (416 μmoles/kg), of between 8 and 32% and have 11B values between 30.0 +- 0.4 and 36.8 +- 0.4 per mil. Boron has been extracted from the basalts with no resolvable isotopic fractionation. High temperature water/rock ratios, based on the B concentrations, are between 0.28 and 3.0. The hydrothermal flux of B into the oceans is between 0.4 and 0.8 x 109 moles/yr, assuming that only pristine basalts are present in the reaction zone. Basalts altered at low temperature and serpentinites are variably enriched in B. The B content of altered whole rocks correlates strongly with 18O, and increases with degree of alteration. Altered basalts (n = 7) containing between 8.9 and 69 ppm B have 11B between 0.1 and 9.2 +- 0.4 per mil. Model calculations give water/rock ratios greater than 100 for rocks recovered from DSDP Hole 418A. Serpentinized peridotites (n = 4) with between 50 and 81 ppm B have 11B between 8.3 +- 0.4 and 12.6 +- 0.4 per mil. The flux of B into the crust during low temperature alteration is about 13 x 109 moles/yr. The maximum diffusive flux of B into the crust from sediment pore waters is 0.8 x 109 moles/yr with a 11B less than 43 per mil. (author)

  20. Million year cycles in the Fe, Mg and Ni records of a ferromanganese crust from the equatorial Indian Ocean

    Banerjee, R.; Gupta, S. M.; Miura, H.

    2008-12-01

    In search of long term productivity signals, a high resolution geochemical study was undertaken by using the life sustaining iron and magnesium contents in a slowly accreting 26 mm thick hydrogenous Fe-Mn crust representing around 12 Million years (Ma) record from the equatorial Indian Ocean. We analyzed Fe, Mg, Ni, Co, and other trace metals by using electron probe micro-analyzer at 100 micron interval. The geochemical data was averaged at every 1 mm interval and subjected to statistical analyses. The crust was dated using standard cobalt-chronometry (Manheim and Lane-Bostwick, 1998). Mixed age-depth model (Heegaard et al., 2005) was applied to ascertain the error limits in the computed ages for each millimeter of the crust. Thereafter, the Red-fit (Schulz and Mudelsee, 2002) and multi-taper (Thompson, 1990) spectral analyses of Fe, Mg and Ni revealed the existence of the significant (>90%) cycles at around 3, 1.5, and 1.2 Ma. We surmise that Fe and Mg cycles represented the changes in oceanic productivity as these metals are essentially used in sustaining the oceanic phyto- and zoo-plankton productivity in the surface water. The Fe/Ni ratio, which is attributed to meteoritic dust influx (Johnson, 2001), also revealed the similar cycles suggesting a possibility of Ni input from the meteoritic dust in the past. We compared the geochemical time- series data with the Earth's orbital eccentricity and summer solar insolation (Berger, 1979) at the equator for the last 10 million years. The Redfit and multi-taper analyses of the eccentricity and the insolation also resulted similar cycles at around 1.5 and 1.2 Ma. Therefore, we surmise that the Fe, Mg, and Ni cycles at 1.5, and 1.2 Ma could be result of the geochemical response to the Earth's eccentricity related solar insolation changes. Earlier studies reported cycles due to eccentricity (0.4, 0.126, 0.95 Ma), tilt (0.041 Ma) and precession (0.023 Ma) in Indian Ocean, whereas we report here 3, 1.5 and 1.2 Ma supra-Milankovitch cycles for the first time from the equatorial Indian Ocean.

  1. Recycled crust in the Galpagos Plume source at 70 Ma: Implications for plume evolution

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

    2015-09-01

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

  2. Crust-ocean interactions during midocean ridge eruptions

    Baker, E. T.

    2011-12-01

    Eruptions are the "quantum event" of crustal accretion, occurring daily to monthly (depending on spreading rate) along the global midocean ridge system. The number of eruptions detected and responded to remain very few, however, so our knowledge of the magnitude and rate of crust-ocean interaction at the instant of an eruption is almost entirely circumstantial. The discovery of uniquely different plumes over a 2008 eruption on the NE Lau spreading center greatly broadened the known range of eruption-initiated transfer of heat, chemicals, and perhaps biota from the crust to the ocean. Serendipitous observations and rapid response cruises have now documented that the "event (mega-) plumes" accompanying eruptions range over a factor of 100 in volume (1-150 km3), yet maintain a distinctive and consistent chemical signature (much lower 3He/heat and Mn/heat and higher H2/heat than typical black smokers). Confirmed event plumes have formed at spreading rates from 55-~90 mm/yr, with some incompletely sampled but "event-like" plumes observed at even slower rates (11-30 mm/yr; Gakkel and Carlsberg Ridges). Presently, only four event plumes can be associated with specific eruptions. Large event plumes in the NE Pacific were found over thick (up to ~75 m), voluminous, and slowly extruded pillow mounds. The 2008 eruption on the fast-spreading NE Lau spreading center demonstrated that thin (a few meters), small, and rapidly emplaced sheet flows can generate smaller event plumes. Available evidence suggests that massive fluid discharge occurs virtually simultaneously with an eruption. At Gorda Ridge in 1996, eruption-indicative seismicity began on the same day and location an event plume was found. At Axial Volcano in 1998, moorings 2 km apart both recorded the appearance of a >100-m-thick plume within minutes of the start of a 72-min-long sheet flow eruption. These observations support inferences from plume modeling and chemistry that event plume generation time is hours, not days. Candidates for the source of event plume fluids include the release of high-temperature, pre-formed hydrothermal fluid from the crust or magma chamber; the heating of crustal fluid by a cooling dike; or the conversion of seawater to hydrothermal fluid by cooling lava. The requirements of very high crustal permeabilities and/or a large volume of stored fluids hinder the first two hypotheses. The slow rate of lava cooling relative to event plume formation hinders the third hypothesis. Whatever the process, the uniform and unique chemistry of event plumes requires a consistent formation process during all types and sizes of eruptions. High concentrations of H2 and abundant basalt shards in the 2008 event plumes necessitate interaction between source fluids and molten lava. The 2008 observations also preclude source fluid salinities <~15 psu, much higher than the values as low as ~2 psu measured in post-eruption vent fluids at some sites. Source fluids with salinities fresher than ~15 psu would have produced unreasonably high or negative temperature anomaly values in the event plumes. The immediate generation of copious hydrothermal fluids now seems a common consequence of any midocean ridge eruption at any depth. The difficulty of formulating a convincing theory to explain this conclusion implies that we remain ignorant about some of the most fundamental processes that occur during events of ocean crust accretion.

  3. Deep-sea mud volcanoes - a window to alteration processes in old oceanic crust?

    Hensen, Christian; Scholz, Florian; Nuzzo, Marianne; Valadares, Vasco; Terrinha, Pedro; Liebetrau, Volker; Kaul, Norbert; Manzoni, Sonia; Schmidt, Mark; Gràcia, Eulàlia

    2013-04-01

    A number of deep sea mud volcanoes (>4700 m water depth) were discovered during a recent expedition with the German research vessel Meteor along a prominent WSW-ENE trending strike-slip fault (SWIM 1; Zitellini et al., 2009) in the western extension of the Gulf of Cadiz (NE Atlantic). Mud volcanism was unambiguously related to tectonic activity along the fault and fluids expelled at these sites show a very distinct geochemical composition that has not been reported from any other mud volcano to date. In previous studies on deep-water mud volcanoes in the Western Gulf of Cadiz accretionary wedge it was hypothesized that the discharge fluids were affected by alteration processes occurring in the old (>140 Ma) and deeply buried (>4 km) oceanic crust (Scholz et al., 2009; Sallarès et al, 2011). This hypothesis is supported by recent findings at the mud volcanoes located to the west of the realm of tectonic deformation driven by the accretionary wedge of the Gulf of Cadiz. Pore water geochemical analyses revealed fluid sources from oceanic crust and oldest sedimentary strata. Regardless of the ultimate source, these findings suggest that large strike-slip faults may play a significant, yet unrecognized role in terms of fluid circulation and element redistribution. To date, hot vents and cold seeps occurring at active spreading centers and forearcs of subduction zones have been pinpointed as hotspots of fluid activity. However, bearing in mind that transform-type plate boundaries are equal in length compared to other types of plate boundaries, fluid exchange at this type of plate boundary may provide a similarly important pathway for water and element exchange between the lithosphere and ocean. Sallarès V., Gailler A., Gutscher M.-A., Graindorge D., Bartolomé R., Gràcia E., Díaz J., Dañobeitia J.J. and Zitellini N. (2011) Seismic evidence for the presence of Jurassic oceanic crust in the central Gulf of Cadiz (SW Iberian margin), Earth and Planetary Science Letters 311(1-2), 112-123. Scholz F., Hensen C., Reitz A., Romer R.L., Liebetrau V., Meixner A., Weise S.M., and Haeckel M. (2009) Isotopic evidence (87Sr/86Sr, δ7Li) for alteration of the oceanic crust at deep-rooted mud volcanoes in the Gulf of Cadiz, NE Atlantic Ocean. Geochimica et Cosmochimica Acta 73, 5444-5459. Zitellini N., Gràcia E., Matias L., Terrinha P., Abreu M.A., Dealteriis G., Henriet J.P., Dañobeitia J.J., Masson D.G., Mulder T., Ramella R., Somoza L., and Diez S. (2009) The quest for the Africa-Eurasia plate boundary west of the Strait of Gibraltar. Earth and Planetary Science Letters 280, 13-50.

  4. Metasomatic modification of oceanic crust during early stages of subduction recorded in Mariana blueschist

    Zack, Thomas; Savov, Ivan P.; Pabst, Sonja; Schmitt, Axel K.

    2013-04-01

    Serpentine mud volcanoes from the Mariana forearc bear unique witness of metasomatic processes in an active subduction zone in the form of centimeter-size blueschist-facies xenoliths. Charcateristic metamorphic assemblages point to conditions of ca 400°C and a formation depth of 27 km. Bulk rock compositions of amphibole-talc schists and chlorite-rich schists lie on a mixing line, extending from typical MORB towards SiO2-enriched mantle. Such mixing trends are remarkably similar to findings from the amphibolite-facies assemblages of the Catalina schist, although they equilibrated at much lower temperatures (Pabst et al. 2012). These observations demonstrate that the material experienced severe metasomatic changes at the slab-mantle interface in the shallow forearc. Further supporting evidence derives from δ11B measurements: phengite, amphibole and chlorite within the clasts have boron isotope values of -6±4‰, significantly lighter than oceanic crust, requiring isotopic fractionation by fluids carrying an isotopically heavy B component (Pabst et al. 2012). Although most current models assume that the Mariana blueschists record conditions of the ongoing subduction process, our recent findings indicate otherwise. Large (>100 µm) rutiles with high U (ca 20 ppm) found in one blueschist clast were dated by HR-SIMS at UCLA employing recently established U/Pb dating techniques (Schmitt & Zack 2012). Rutile concordia ages were tightly constrained at 48.1±2.9 Ma and are reproduced by concordia ages of low Th/U zircons at 47.5±1.5 Ma in the same sample. As those ages are interpreted to be formation ages of metasomatically modified blueschists and are only a few million years older than subduction initiation (at ca 50-52 Ma), we draw the following conclusions: (1) fast cooling of the downgoing oceanic crust must occur right after subduction initiation; (2) effective metasomatic and mechanical mixing processes (subduction channels?) must be established early in subduction zones and (3) the forearc mantle (source region of serpentine mud volcanoes) must contain stable areas where 48 Ma old low-grade samples are not being reset. Pabst S et al. 2012: Lithos 132-133, pp. 162-179; Schmitt AK & Zack T 2012: Chem Geol 332-333, pp. 65-73.

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

    Ben D. Goscombe

    2013-07-01

    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.

  6. Controls on ferromanganese crust composition and reconnaissance resource potential, Ninetyeast Ridge, Indian Ocean

    Hein, James; Conrad, Tracey A.; Mizell, Kira; Banakar, Virupaxa K.; Frey, Frederick A.; Sager, William W.

    2016-01-01

    A reconnaissance survey of Fe-Mn crusts from the 5000 km long (~31°S to 10°N) Ninetyeast Ridge (NER) in the Indian Ocean shows their widespread occurrence along the ridge as well as with water depth on the ridge flanks. The crusts are hydrogenetic based in growth rates and discrimination plots. Twenty samples from 12 crusts from 9 locations along the ridge were analyzed for chemical and mineralogical compositions, growth rates, and statistical relationships (Q-mode factor analysis, correlation coefficients) were calculated. The crusts collected are relatively thin (maximum 40 mm), and those analyzed varied from 4 mm to 32 mm. However, crusts as thick as 80 mm can be expected to occur based on the age of rocks that comprise the NER and the growth rates calculated here. Growth rates of the crusts increase to the north along the NER and with water depth. The increase to the north resulted from an increased supply of Mn from the oxygen minimum zone (OMZ) to depths below the OMZ combined with an increased supply of Fe at depth from the dissolution of biogenic carbonate and from deep-sourced hydrothermal Fe. These increased supplies of Fe increased growth rates of the deeper-water crusts along the entire NER. Because of the huge terrigenous (rivers, eolian, pyroclastic) and hydrothermal (three spreading centers) inputs to the Indian Ocean, and the history of primary productivity, Fe-Mn crust compositions vary from those analyzed from open-ocean locations in the Pacific.

  7. Imaging The Flat Slab Beneath The Sierras Pampeanas, Argentina, Using Receiver Function Analysis: Evidence For Overthickened Subducted Oceanic Crust

    Gans, C.; Beck, S. L.; Zandt, G.; Gilbert, H. J.; Alvarado, P. M.; Linkimer, L.; Porter, R. C.

    2009-12-01

    The western margin of the South American continent between 30and 32 S is characterized by the flat slab subduction of the ~43 Ma oceanic Nazca plate beneath the continental South American plate. Several arrays of broadband seismic instruments have been deployed in Chile and western Argentina to study this phenomenon (e.g., CHARGE, 2000-2002; SIEMBRA, 2007-2009; ESP, 2008-2010). The low angle subduction has prevented magmatism in the area since the late Miocene due to reduced mantle flow above the subducting slab, and spatially correlates with the formation of both thick-skinned (Sierras Pampeanas) and thin-skinned (Andean Precordillera) thrust belts within the region. In order to better constrain the crust and upper mantle structure in the transition region between flat slab and normal subduction to the south and east, we have calculated receiver functions (RFs) from teleseismic earthquakes. Using our dense SIEMBRA array, combined with the broader CHARGE and ESP arrays, we are able to image in detail the flat slab, which contains a distinct negative arrival (indicative of a low velocity zone) at the top of the flat slab, followed by a strong positive P-to-S conversion. While the exact causes of flat slab subduction continue to be debated, one overriding theme is the necessity of having an overthickened crust in order to increase the buoyancy of the subducting slab. In this region, the hotspot seamount chain of the Juan Fernandez Ridge (JFR) is thought to provide such a mechanism. Kopp et al. (2004), however, did not find overthickened crust in the offshore portion of the JFR, but rather moderately thick oceanic crust. Preliminary results from our receiver functions, compared with synthetic RFs containing either a normal (7 km) or an overthickened (17km) crust, indicate that the oceanic crust at the top of the slab (the low velocity zone) must be at least ~15 km thick. Our results support the idea of an overthickened crust in the subducted flat slab beneath western Argentina.

  8. Emergence of blueschists on Earth linked to secular changes in oceanic crust composition

    Palin, Richard M.; White, Richard W.

    2016-01-01

    The oldest blueschists--metamorphic rocks formed during subduction--are of Neoproterozoic age, and 0.7-0.8 billion years old. Yet, subduction of oceanic crust to mantle depths is thought to have occurred since the Hadean, over 4 billion years ago. Blueschists typically form under cold geothermal gradients of less than 400 °C GPa-1, so their absence in the ancient rock record is typically attributed to hotter pre-Neoproterozoic mantle prohibiting such low-temperature metamorphism; however, modern analogues of Archaean subduction suggest that blueschist-facies metamorphic conditions are attainable at the slab surface. Here we show that the absence of blueschists in the ancient geological record can be attributed to the changing composition of oceanic crust throughout Earth history, which is a consequence of secular cooling of the mantle since the Archaean. Oceanic crust formed on the hot, early Earth would have been rich in magnesium oxide (MgO). We use phase equilibria calculations to show that blueschists do not form in high-MgO rocks under subduction-related geothermal gradients. Instead, the subduction of MgO-rich oceanic crust would have created greenschist-like rocks--metamorphic rocks formed today at low temperatures and pressures. These ancient metamorphic products can hold about 20% more water than younger metamorphosed oceanic crust, implying that the global hydrologic cycle was more efficient in the deep geological past than today.

  9. Density and porosity of the upper oceanic crust from seafloor gravity measurements

    Johnson, H. Paul; Pruis, M. J.; Van Patten, D.; Tivey, M. A.

    2000-04-01

    The exposure of 1300 meters of upper oceanic crust at the Blanco Fracture Zone allows near-bottom gravity measurements to determine the in situ density of the seafloor as a function of depth. Gravity measurements along the north wall of the Blanco Depression indicate an outcrop density of 2530 Kg/m for the upper 800 meters of crust and a calculated porosity of 23%. The lower 500 meters of crust (800 to 1300 meters below the sea floor) has a measured density of 2710 130 Kg/m and a porosity of 14%. These data indicate that most of the extrusive volcanic oceanic crust is highly porous and can act as an aquifer and large-scale reservoir for hydrothermal fluids. These direct crustal density measurements also support previous interpretations that low seismic velocities observed in Layer 2 are due to the high porosity of the upper extrusive section.

  10. Controls on ferromanganese crust composition and reconnaissance resource potential, Ninetyeast Ridge, Indian Ocean

    Hein, James R.; Conrad, Tracey; Mizell, Kira; Banakar, Virupaxa K.; Frey, Frederick A.; Sager, William W.

    2016-04-01

    A reconnaissance survey of Fe-Mn crusts from the 5000 km long (~31°S to 10°N) Ninetyeast Ridge (NER) in the Indian Ocean shows their widespread occurrence along the ridge as well as with water depth on the ridge flanks. The crusts are hydrogenetic based in growth rates and discrimination plots. Twenty samples from 12 crusts from 9 locations along the ridge were analyzed for chemical and mineralogical compositions, growth rates, and statistical relationships (Q-mode factor analysis, correlation coefficients) were calculated. The crusts collected are relatively thin (maximum 40 mm), and those analyzed varied from 4 mm to 32 mm. However, crusts as thick as 80 mm can be expected to occur based on the age of rocks that comprise the NER and the growth rates calculated here. Growth rates of the crusts increase to the north along the NER and with water depth. The increase to the north resulted from an increased supply of Mn from the oxygen minimum zone (OMZ) to depths below the OMZ combined with an increased supply of Fe at depth from the dissolution of biogenic carbonate and from deep-sourced hydrothermal Fe. These increased supplies of Fe increased growth rates of the deeper-water crusts along the entire NER. Because of the huge terrigenous (rivers, eolian, pyroclastic) and hydrothermal (three spreading centers) inputs to the Indian Ocean, and the history of primary productivity, Fe-Mn crust compositions vary from those analyzed from open-ocean locations in the Pacific. The sources of detrital material in the crusts change along the NER and reflect, from north to south, the decreasing influence of the Ganga River system and volcanic arcs located to the east, with increasing influence of sediment derived from Australia to the south. In addition, weathering of NER basalt likely contributed to the aluminosilicate fraction of the crusts. The southernmost sample has a relatively large detrital component compared to other southern NER crust samples, which was probably derived predominantly from weathering of local volcanic outcrops. Fe-Mn crusts from a dredge haul at 3412 m water depth, 2°S latitude, are pervasively phosphatized along with the substrate rocks (site D7). Phosphatization took place through replacement of carbonate, preferential replacement of Fe oxyhydroxide relative to Mn oxide in the crusts, preferential replacement of silica-rich phases relative to Al-rich phases in the crusts, and precipitation of carbonate fluorapatite in pore space. The preferentially replaced silica may have been Si adsorbed on the Fe oxyhydroxide. The enrichment of Ni, Zn, and Cu in the phosphatized crust reflects preferential adsorption into the tunnel structure of todorokite. The rare earth element plus yttrium (REY) patterns indicate a lower oxidation potential during phosphatization of the NER crusts compared to Pacific phosphatized crusts. NER phosphatization occurred in a deeper-water environment than typical for phosphatization of Pacific crusts, occurred post-middle Miocene, a younger age than phosphatization the Pacific crusts, and had in part a different set of chemical changes produced by the phosphatization than did the Pacific crusts. The southern third of NER has Fe-Mn crusts with the highest Co (0.91%), Ni (0.43%), ΣREY (0.33%), Cu (0.22%), Te (146 ppm), Pt (1.5 ppm), Ru (52 ppb), and Rh (99 ppb) contents. These are among the highest Pt, Ru, and Rh concentrations measured in marine Fe-Mn deposits. Because of these high metal concentrations, exploration is warranted for the southern sector of the NER, especially at shallower-water sites where the platinum group elements (PGE) and Co are likely to be even more enriched.

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

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

    -1 Compositional variation and genesis of ferromanganese crusts of the Afanasiy{Nikitin Seamount, Equatorial Indian Ocean R P Rajani, V K Banakarcurrency1, G Parthiban, A V Mudholkar and A R Chodankar National Institute of Oceanography, Dona Paula, Goa 403 004... to show this initial fractionation of Fe and Mn from the ambient water because they are inti- mately intermixed. The dominant controls on the incorporation of various metals in the Fe{Mn crusts Composition and genesis of seamount Fe{Mn crusts from...

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

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

    2005-02-01

    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.

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

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

    2014-01-01

    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...

  14. Precambrian U-Pb zircon ages in eclogites and garnet pyroxenites from South Brittany (France): an old oceanic crust in the West European Hercynian belt?

    Peucat, J. J.; Vidal, Ph.; Godard, G.; Postaire, B.

    1982-08-01

    U-Pb zircon ages have been determined for two eclogites from the Vende and for two garnet pyroxenites from the Baie d'Audierne. In an episodic Pb loss model, the two discordia would give upper intercept ages around 1300-1250 Ma and lower intercepts ages of 436-384 Ma. Two interpretations are proposed: (1) The 1250-1300 Ma ages may reflect an unspecified upper mantle event or process; the Paleozoic ages correspond to the tectonic emplacement of an eclogitic mantle fragment into the continental crust. (2) The protolith may have been extracted from the upper mantle 1250-1300 Ma ago and stored in a crustal environment until it was metamorphosed under high-pressure conditions around 400 Ma ago. This latter model is favoured by available geologic and isotopic data. Consequently, we propose that a 1300 Ma old oceanic crust was tectonicly incorporated into a sialic basement during the Proterozoic. This mixture was subsequently subducted during the Paleozoic.

  15. Tectonic slicing of subducting oceanic crust along plate interfaces: Numerical modeling

    Ruh, J. B.; Le Pourhiet, L.; Agard, Ph.; Burov, E.; Gerya, T.

    2015-10-01

    Multikilometer-sized slivers of high-pressure low-temperature metamorphic oceanic crust and mantle are observed in many mountain belts. These blueschist and eclogite units were detached from the descending plate during subduction. Large-scale thermo-mechanical numerical models based on finite difference marker-in-cell staggered grid technique are implemented to investigate slicing processes that lead to the detachment of oceanic slivers and their exhumation before the onset of the continental collision phase. In particular, we investigate the role of the serpentinized subcrustal slab mantle in the mechanisms of shallow and deep crustal slicing. Results show that spatially homogeneous serpentinization of the sub-Moho slab mantle leads to complete accretion of oceanic crust within the accretionary wedge. Spatially discontinuous serpentinization of the slab mantle in form of unconnected patches can lead to shallow slicing of the oceanic crust below the accretionary wedge and to its deep slicing at mantle depths depending on the patch length, slab angle, convergence velocity and continental geothermal gradient. P-T paths obtained in this study are compared to natural examples of shallow slicing of the Crescent Terrane below Vancouver Island and deeply sliced crust of the Lago Superiore and Saas-Zermatt units in the Western Alps.

  16. Europa's Crust and Ocean: Origin, Composition, and the Prospects for Life

    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.

    2000-01-01

    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.

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

    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...

  18. Cadomian (˜560 Ma) crust buried beneath the northern Arabian Peninsula: Mineral, chemical, geochronological, and isotopic constraints from NE Jordan xenoliths

    Stern, Robert J.; Ali, Kamal A.; Ren, Minghua; Jarrar, Ghaleb H.; Romer, Rolf L.; Leybourne, Matthew I.; Whitehouse, Martin J.; Ibrahim, Khalil M.

    2016-02-01

    In order to better understand the nature and formation of the lower continental crust beneath northern Arabia, we studied lower crustal xenoliths brought up by Neogene basalts in NE Jordan. Most of these xenoliths are comprised of primary phases plagioclase + two-pyroxenes with magnetite and ilmenite. Most clinopyroxene are augite whereas orthopyroxene mostly are hypersthene (Mg# = 50-80). Plagioclase feldspar is dominantly andesine-labradorite; pyrope-rich garnet and Fe-rich olivine (Fo75 to Fo62) are rare. These xenoliths represent cumulates formed from intermediate magmas that pooled in the lower crust. Many xenoliths also contain small, fine-grained K-rich zones interpreted as melt pockets reflecting late magmatic infiltration of the lower crust. The xenoliths display a wide range in major element compositions (37-51 wt.% SiO2, 4-15 wt.% MgO and 0.1-6.3 wt.% TiO2), enrichment in Ba, K, Sr, Pb and Eu, and some trace element ratios atypical of bulk continental crust (e.g., K/Rb = 1265 ± 565, K/U = 63 000 ± 60 080 and Th/U = 0.96 ± 0.56); these extreme ratios reflect widespread K-metasomatism associated with melt pockets. The magmas from which these cumulates formed may have been generated at a reararc convergent margin setting. Four U-Pb zircon populations yield indistinguishable ages of 554 ± 4 Ma; 559 ± 5 Ma; 559 ± 6 Ma, and 563 ± 5 Ma. Initial 87Sr/86Sr values (0.70260-0.70352) and positive ɛNd(560) (with the exception of a single, more radiogenic sample (+9.6), range = + 1.3 to +4.8) indicate that the lower crust sampled by the xenoliths originated in the asthenospheric mantle, with little or no interaction with older crust, although Pb isotopic compositions allow for some interaction with older or subducted crustal materials. We interpret the geochemistry and mineralogy of these xenoliths to indicate that the lower crust beneath NE Jordan is mafic and comprised of plagioclase-rich 2-pyroxene igneous rocks. The lower crust of this area formed by magmatic underplating over less than 18 Ma. The crust of NE Jordan is significantly younger than the crust of the northernmost Arabian-Nubian Shield and represents a fragment of Cadomian (600-520 Ma) crust that may make up the NE margin of the Arabian Plate.

  19. Recycled oceanic crust observed in 'ghost plagioclase' within the source of Mauna Loa lavas

    Sobolev; Hofmann; Nikogosian

    2000-04-27

    The hypothesis that mantle plumes contain recycled oceanic crust is now widely accepted. Some specific source components of the Hawaiian plume have been inferred to represent recycled oceanic basalts, pelagic sediments or oceanic gabbros. Bulk lava compositions, however, retain the specific trace-element fingerprint of the original crustal component in only a highly attenuated form. Here we report the discovery of exotic, strontium-enriched melt inclusions in Mauna Loa olivines. Their complete trace-element patterns strongly resemble those of layered gabbros found in ophiolites, which are characterized by cumulus plagioclase with very high strontium abundances. The major-element compositions of these melts indicate that their composition cannot be the result of the assimilation of present-day oceanic crust through which the melts have travelled. Instead, the gabbro has been transformed into a (high-pressure) eclogite by subduction and recycling, and this eclogite has then been incorporated into the Hawaiian mantle plume. The trace-element signature of the original plagioclase is present only as a 'ghost' signature, which permits specific identification of the recycled rock type. The 'ghost plagioclase' trace-element signature demonstrates that the former gabbro can retain much of its original chemical identity through the convective cycle without completely mixing with other portions of the former oceanic crust. PMID:10801125

  20. the Deep Biosphere Archaeal Microbial Community in Igneous Ocean Crust

    Edwards, K. J.

    2014-12-01

    Ridge flank hydrothermal systems represent vast environments that may be habitable by subseafloor microbial life. Oceanic ridge flanks, areas far from the magmatic and tectonic influence of seafloor spreading, comprise one of the largest and least explored microbial habitats on the planet. These potential ecosystems may play a significant role in biogeochemical processes and elemental fluxes that are known to be regulated by these systems. I will discuss the nature of ridge flank hydrothermal environments, and present a framework for delineating a continuum of conditions and processes that are likely to be important for defining subseafloor microbial "provinces." The basis for this framework is three governing conditions that help to determine the nature of subseafloor biomes: crustal age, extent of fluid flow, and thermal state. A brief overview of subseafloor conditions, within the context of these three characteristics for select sites will be described. Technical challenges remain and likely will limit progress in studies of microbial ridge flank hydrothermal ecosystems, which is why it is vital to select and design future studies so as to leverage as much general understanding as possible from work focused at a small number of sites. A characterization framework that perhaps includes alternative or additional physical or chemical characteristics is essential for achieving the greatest benefit from multidisciplinary microbial investigations of oceanic ridge flank hydrothermal systems.

  1. Constancy of oceanic deposition of 10Be as recorded in manganese crusts

    Measurements of 10Be and 9Be in two ferromanganese oxide crusts from the sea floor of the equatorial Atlantic and the North Pacific, are reported, that indicate deposition of 10Be and 10Be/9Be during the past 7-9 Myr has been constant. Averaged over time intervals of approximately 1 Myr, the variation is within +- 6%. Before that time, both crusts show similar significant deviations. It is considered that the 7-9 Myr demarcation may be related to the reported late Miocene global abyssal circulation change in the ocean. (U.K.)

  2. Small, monogenetic volcanoes: building blocks of the upper oceanic crust

    Yeo, Isobel A.; Achenbach, Kay L.; Searle, Roger C.; Le Bas, Tim P.

    2010-05-01

    The study of slow-spreading mid-ocean ridge volcanism provides important insights into the mechanisms of oceanic crustal accretion. This study uses a combination of sidescan sonar and recently developed methods of high resolution bathymetry and video data collection to describe the volcanic features on the Mid-Atlantic Ridge axis at 45°N in more detail than has previously been possible. Within most axial valleys lie axial volcanic ridges (AVRs), linear volcanic features thought to be the focus of volcanism at slow spreading ridges. AVR volcanic morphologies have been described independently in a number of studies, through combinations of remote sensing (predominantly through the use of sidescan sonar) and deep towed cameras or submersibles. These different methods have led to classification of volcanic features on two very different scales. While the resolution of the sidescan sonar studies allows only for the identification and classification of features tens to hundreds of metres in size, the photographic and submersible studies describe features from centimetre to metre scale. Until now it has been difficult to reliably link these observations together as no intermediate sensing method has been available. This study uses 1m resolution ROV multibeam bathymetry to address this problem and link features identified at different scales together. We identify a prominent 22km long axial volcanic ridge within a 1km deep axial valley that ranges from 6 to 14km across. We find that 'hummocks' described in previous sidescan sonar studies (of which the AVR is composed) are individual, monogenetic volcanic cones. These cones range from 2 to 200m in height and 40 to 400m in diameter and we identify over 8000 of them on the surface of the AVR. We calculate the average volume of a cone to be 220,000m3 and estimate the AVR is built of approximately 73,000 such cones. We estimate these edifices form on time scales ranging from less than one hour to several months so are likely the products of single eruptions. Cones of all heights, but particularly those over 70m, are prone to collapse soon after forming. A variety of mechanisms are examined and collapse triggers may include: a) flank over-steepening, b) building on unstable material, and c) cutting by fissuring. Collapse scarps show two strong alignments, one ridge parallel and one at 30° to the ridge trend; however as cones always collapse downslope, these alignments may be due to the slope angles produced as a result of cone emplacement rather than first order controls on collapses themselves. We estimate the minimum magmatic flux to the surface for this segment to be at least 64,000m3 yr -1, which is equivalent to producing one average volume cone every 3.5 years.

  3. 75 FR 34929 - Safety Zones: Neptune Deep Water Port, Atlantic Ocean, Boston, MA

    2010-06-21

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

  4. Global distribution of beryllium isotopes in deep ocean water as derived from Fe-Mn crusts

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

    1996-01-01

    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.

  5. The fate of oceanic crust in Paleozoic subduction zones: the metamorphic evolution of (ultra-)high-pressure rocks of the Tianshan (Kazakhstan, Kyrgyzstan, NW China)

    Meyer, Melanie

    2014-01-01

    Subduction zones are the place in the global subduction factory where crustal rocks are buried to mantle depths. Due to its higher density, most oceanic crust is irreversibly buried and thus, processes, which result in the exhumation of deeply subducted oceanic crust have received less attention, compared to continental crust. This may be due to the rare occurrences of exhumed ultra-high-pressure oceanic crust. Given that processes in modern subduction zones cannot be investigated directly, (...

  6. Imaging the Moho and Subducted Oceanic Crust at the Isthmus of Tehuantepec, Mexico, from Receiver Functions

    Melgar, Diego; Pérez-Campos, Xyoli

    2011-08-01

    Using teleseismic data recorded along a transect, which we call VEOX (for Veracruz-Oaxaca seismic line), of 46 broadband stations installed across the Isthmus of Tehuantepec in southern Mexico, we obtained receiver functions and stacked them to study the Moho topography and back projected them to visualize the subducted slab geometry beneath the isthmus. We observed a back-azimuth dependent Moho thickness across the transect, particularly beneath the Los Tuxtlas Volcanic Field. Also, we observed the Cocos plate which subducts with an angle of 26° between 140 and 310 km from the trench. Comparison with regional seismicity indicates that it occurs below the oceanic crust.

  7. High-Albedo Salt Crusts on the Tropical Ocean of Snowball Earth: Measurements and Modeling

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

    2014-12-01

    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 (NaCl2H2O). 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.

  8. Seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing.

    Audet, Pascal; Bostock, Michael G; Christensen, Nikolas I; Peacock, Simon M

    2009-01-01

    Water and hydrous minerals play a key part in geodynamic processes at subduction zones by weakening the plate boundary, aiding slip and permitting subduction-and indeed plate tectonics-to occur. The seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization. However, seismological observations bearing on the presence of water within the subducting plate itself are less well documented. Here we use converted teleseismic waves to obtain observations of anomalously high Poisson's ratios within the subducted oceanic crust from the Cascadia continental margin to its intersection with forearc mantle. On the basis of pressure, temperature and compositional considerations, the elevated Poisson's ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values. Combined with observations of a strong negative velocity contrast at the top of the oceanic crust, our results imply that the megathrust is a low-permeability boundary. The transition from a low- to high-permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization. These results may have important implications for our understanding of seismogenesis, subduction zone structure and the mechanism of episodic tremor and slip. PMID:19122639

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

    G. Delisle

    2011-09-01

    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. Faulting induced by precipitation of water at grain boundaries in hot subducting oceanic crust.

    Zhang, Junfeng; Green, Harry W; Bozhilov, Krassimir; Jin, Zhenmin

    2004-04-01

    Dehydration embrittlement has been proposed to explain both intermediate- and deep-focus earthquakes in subduction zones. Because such earthquakes primarily occur at shallow depths or within the core of the subducting plate, dehydration at relatively low temperatures has been emphasized. However, recent careful relocation of subduction-zone earthquakes shows that at depths of 100-250 km, earthquakes continue in the uppermost part of the slab (probably the former oceanic crust that has been converted to eclogite) where temperatures are higher. Here we show that at such pressures and temperatures, eclogite lacking hydrous phases but with significant hydroxyl incorporated as defects in pyroxene and garnet develops a faulting instability associated with precipitation of water at grain boundaries and the production of very small amounts of melt. This new faulting mechanism satisfactorily explains high-temperature earthquakes in subducting oceanic crust and could potentially be involved in much deeper earthquakes in connection with similar precipitation of water in the mantle transition zone (400-700 km depth). Of potential importance for all proposed high-pressure earthquake mechanisms is the very small amount of fluid required to trigger this instability. PMID:15071590

  11. Deformation Experiments on Blueschist and Greenschist: Implications for the Rheology of Subducted Oceanic Crust

    Okazaki, K.; Hirth, G.

    2014-12-01

    To understand the spatial and temporal distribution of deformation (e.g., underplating and exhumation of metamorphic rocks) and earthquakes in subduction zones, it is important to constrain the rheological properties of metamorphic rocks (i.e., altered oceanic crust and sediments), and how they evolve during metamorphic reactions following hydration, carbonation and dehydration of the down-going slab. We conducted triaxial deformation experiments on three mafic schists with various peak metamorphic conditions: a lawsonite-blueschist, a greenschist, and an epidote-amphibole schist, using Griggs-type solid pressure- medium apparatus. Constant strain rate experiments and strain rate stepping experiments were conducted at confining pressures (Pc) from 0.76-2GPa, temperatures (T) from 300-600C and strain rates from 10-5-10-71/s. At a confining pressure of 1 GPa, temperature of 400C and strain rate of 10-5 1/s, differential stresses σd for all mafic schists were higher than 1 GPa. The lawsonite-blueschist and greenschist samples were weaker than epidote-amphibolite samples under all experimental conditions. All types of samples exhibit high stress exponent (> 15) and strain rate strengthening; frictional behavior that inhibits earthquake nucleation. Differential stress increased with increasing confining pressure, while friction coefficient decreased with increasing confining pressure and temperature. The nominal friction coefficient for the lawsonite-blueschist and the greenschist samples was 0.3 to 0.35, values which predict stresses below the Goetze criterion (σd < Pc). Microstructures of recovered samples showed modest buckling and several localized shear zones. These features suggest that the deformation of mafic schist is accommodated by semi-brittle deformation resulting in strain localization on faults. Such weak and aseismic fault zones in subducting slab might promote detachment of oceanic crust from the subducting slab and allow underplating to forearc crust.

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

    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 εNd(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 εNd(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)

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

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

    2002-01-01

    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.

  14. Static and fault-related alteration in the lower ocean crust, IODP Expedition 345, Hess Deep

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

    2014-05-01

    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(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. δ18O 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

  15. Deep Continental Lithosphere Keels as Impediments to Asthenosphere Flow and Cause of Ocean Crust Depth Anomalies

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

    2003-12-01

    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.

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

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

    1998-01-01

    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...

  17. Ocean Circulation and Gateway Closures During the Late Miocene (~13-5 Ma)

    Nathan, S. A.; Leckie, R. M.

    2004-12-01

    Long-term climate change is driven by tectonic influences, including changes in ocean circulation that are the result of ocean gateway closure. During the middle to late Miocene (~13-5 Ma), both tropical ocean circulation and deep water production were reorganized due to the increasing constriction of the Indonesian and Central American seaways. For example, the waters of the modern Pacific equatorial current system do not move freely into the Indian Ocean (i.e., via the Indonesian Throughflow, ITF) but instead pile up to form the Western Pacific Warm Pool (a thermal anomaly that greatly influences tropical Pacific climate and ocean circulation). Here we use a continuous record of multispecies stable isotope stratigraphy and foraminiferal assemblage counts from Ontong Java Plateau to demonstrate that during middle to late Miocene time, progressive restriction of the ITF, modulated by sea level fluctuations, resulted in the waxing and waning of a proto-warm pool in the western equatorial Pacific (WEP). The proto-warm pool profoundly affected the early late Miocene "carbonate crash" (an anomalous decrease of carbonate in deep sea sediments) and the late Miocene "biogenic bloom" (sharp increase in carbonate accumulation rates across the tropical Indo-Pacific). We hypothesize that El Niño/La Niña-like alternations of tropical carbonate preservation and productivity between the western and eastern equatorial Pacific during the late Miocene were the consequence of early warm pool development and decay. A proto-warm pool was formed ~12.1-10.6 Ma, which initiated a nutrient-rich Equatorial Undercurrent and/or increased Trade Wind strength. These La Niña-like conditions sustained carbonate productivity in the eastern equatorial Pacific (EEP) at a time when carbonate preservation sharply declined in the Caribbean. Proto-warm pool weakening and El Niño-like conditions ~10.6-8.8 Ma intensified a "carbonate crash" in the EEP, while resurgence of the warm pool and La Niña-like conditions after ~6.5 Ma spurred a "biogenic bloom". The production of deep water in the northern North Atlantic (i.e., Northern Component Water, NCW) may also have been modulated by sea level fluctuations as the Central American Seaway became increasingly constricted by the uplift of the Panama sill during the late Miocene. We suggest that the sea level fluctuations that facilitated the early development of a proto-warm pool in the WEP, particularly the Mi5 event at 11.4 Ma, also constricted flow through the Central American Seaway and controlled NCW production at this time in the North Atlantic.

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

    Parthiban, G.; Banakar, V.K.

    Samples of ferromanganese encrustations (fe-Mn crusts) dredged from the upper flank of the Afanasiy-Nikitin seamount, above the Carbonate Compensation Depth (CCD) in the Northern Central Indian Ocean (NCIO) were analysed for Al, Fe, Mn, Ca, Ba, Cu...

  19. Geological storage of CO2 within the oceanic crust by gravitational trapping

    Marieni, Chiara; Henstock, Timothy J.; Teagle, Damon A. H.

    2013-12-01

    rise of atmospheric carbon dioxide (CO2) principally due to the burning of fossil fuels is a key driver of anthropogenic climate change. Mitigation strategies include improved efficiency, using renewable energy, and capture and long-term sequestration of CO2. Most sequestration research considers CO2 injection into deep saline aquifers or depleted hydrocarbon reservoirs. Unconventional suggestions include CO2 storage in the porous volcanic lavas of uppermost oceanic crust. Here we test the feasibility of injecting CO2 into deep-sea basalts and identify sites where CO2 should be both physically and gravitationally trapped. We use global databases to estimate pressure and temperature, hence density of CO2 and seawater at the sediment-basement interface. At previously suggested sites on the Juan de Fuca Plate and in the eastern equatorial Pacific Ocean, CO2 is gravitationally unstable. However, we identify five sediment-covered regions where CO2 is denser than seawater, each sufficient for several centuries of anthropogenic CO2 emissions.

  20. Seawater recharge into oceanic crust: IODP Exp 327 Site U1363 Grizzly Bare outcrop

    Wheat, C. Geoffrey; Hulme, Samuel M.; Fisher, Andrew T.; Orcutt, Beth N.; Becker, Keir

    2013-06-01

    Systematic differences in sediment thermal and pore water chemical profiles from Integrated Ocean Drilling Program Site U1363 document mixing and reaction within the basaltic crust adjacent to Grizzly Bare outcrop, a site of hydrothermal recharge into 3.6 My-old basaltic crust. A transect of seven holes was drilled ~50 m to ~750 m away from the base of the outcrop. Temperatures at the sediment-basement interface increase from ~6°C to >30°C with increasing distance from the outcrop, and heat flow is suppressed within several hundred meters from the outcrop. Calculated fluid compositions at the sediment-basement interface are generally explained by mixing between bottom seawater and altered crustal basement fluids, with a composition similar but not identical to fluids from seeps at Baby Bare outcrop, located ~45 km to the northeast. Reactions within upper basement and overlying sediment affect a variety of ions (Mn, Fe, Mo, Si, PO43-, V, and U) and δ13DIC, indicating a diagenetic influence and diffusive exchange with overlying sediment pore waters. The apparent 14C age of basal pore fluids is much older than bottom seawater. Collectively, these results are consistent with seawater recharge at Grizzly Bare outcrop; however, there are strong gradients in fluid composition within 50 m of the outcrop, providing evidence for complex flow paths and vigorous mixing of young, recently recharged seawater with much older, more reacted basement fluid. The proximity of these altered fluids to the edge of the outcrop raises the possibility for fluid seepage from the outcrop in addition to seawater recharge.

  1. Transient Hydrothermal Alteration in Fault Zones Cutting the Lower Oceanic Crust, Hess Deep Rift

    McCaig, Andrew; Titarenko, Sofya; Cliff, Robert; Ivan, Savov; Adrian, Boyce

    2015-04-01

    IODP Expedition 345 drilled the first holes in the lower plutonic crust at a fast-spreading ridge, recovering primitive layered gabbros [1]. Alteration occurred as: 1) a largely static pseudomorphic alteration, predominantly in the greenschist and sub-greenschist facies with mainly talc and serpentine replacing olivine, and prehnite replacing plagioclase. Talc sometimes overprints serpentine mesh texture. 2) an overprinting metasomatic alteration, spatially related to cataclastic fault zones and macroscopic veins, dominated by prehnite and chlorite. Secondary clinopyroxene and epidote locally overprint the prehnite-chlorite assemblage, but the last events are veins of prehnite and zeolite. Metamorphosed dykes show chilled margins within the cataclasites, and are themselves affected by cataclastic deformation. Faults, dykes and overprinting alteration are all inferred to be related to the westward propagation of Cocos-Nazca spreading forming Hess Deep. 87Sr/86Sr ratios of small whole rock samples 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. Sampling of individual minerals has been undertaken using a microscope mounted drill, and shows that alteration is mainly affecting secondary minerals, with late prehnite veins ranging up to Sr isotope ratios of 0.7054. δ18O values range from +1 to + 6 per mil. Combined with metamorphic data this indicates alteration at temperatures between 200 and 400 °C. Secondary clinopyroxene and talc replacing serpentine are interpreted to indicate transient prograde hydrothermal events. Preliminary modelling using Comsol Multiphysics suggests that the temperatures of the overprinting alteration, as well as transient prograde events, could be achieved in a permeable fault slot cutting through crust 0.5 to 1 m.y. old. The prehnite-chlorite assemblage is predicted to be important in off-axis alteration, common in any location where faults intersect the Moho, including transform faults, near axis normal faults at slow spreading ridges, and perhaps bending faults at subduction zones. [1] Gillis, K.M., Snow J. E. and Shipboard Science Party (2014) Primitive layered gabbros from fast-spreading lower oceanic crust. Nature, 505, 204-207.

  2. Slow-Spreading Oceanic Crust Formed By Steady-State Axial Volcanic Ridges

    Murton, B. J.; Schroth, N.; LeBas, T.; Van Calsteren, P. W.; Yeo, I. A.; Achenbach, K. L.; Searle, R. C.

    2012-12-01

    Oceanic crust originates at mid-ocean spreading ridges (MORs), covers almost three quarters of the earth's surface and dominates the global magmatic flux. Axial volcanic ridges (AVRs) are almost ubiquitous features of orthogonal slow-spreading ridges, which account for three quarters of the global mid-ocean spreading ridge system today. Typically 3-6 km wide, 200-500 m high and 10-20 km long, AVRs are the loci of recent volcanic activity and form the most prominent topography rising above the otherwise flat-lying Median Valley floor. Previous studies indicate that AVRs, and their related crustal magma reservoirs are episodic, on a time scale of 150-300 ka. Yet their near ubiquitous occurrence at slow-spreading ridge segments provides us with a paradox: if AVRs have a life cycle of formation and degradation, does their near ubiquitous presence at slow spreading ridges imply their life-cycles are synchronised? In this contribution, we report the findings from a high-resolution study of a well-developed axial volcanic ridge (AVR) at 45°N on the Mid-Atlantic Ridge (MAR). Here, the MAR is typical of most slow-spreading ridges: it spreads generally symmetrically and orthogonally, at a full rate of 23.6 mm per year, has second and third-order segmentation, and contains a typical AVR. Using a combination of detailed micro-bathymetry, sidescan sonar, visual surveying and petrology, we suggest that the AVR is the product of quasi-steady state volcanotectonic processes. Small volume lava flows, originating at or near the crest and with short run-out lengths, form ~60 m high hummocky pillow-lava mounds that dominate the construction of the AVR. The lavas are the product of moderate degrees of mantle melting that are typical for normal mid-ocean ridge basalt. Synchronous with these eruptions the flanks of the AVR subside forming a structural horst. Subsidence is partially accommodated by a series of outward-facing volcanic growth faults that step-down and away from the AVR crest and towards the Median Valley floor. Here, much larger volume, yet less frequent, effusions of massive lava flows erupt rapidly from large flat-topped seamounts, found almost exclusively outside of the AVR. The sheet-flows have run-out lengths of up to several kilometres, a combined thickness sufficient to bury the hummocky topography of the AVR flanks, producing smooth flat-lying seafloor typical of the Median Valley floor and its uplifted flanks. These lavas are relatively enriched geochemically and are characteristic of small melt fractions from the mantle. Thus it appears that the volcanic crust at slow-spreading ridges is formed through a continuous process of small volcanic eruptions along AVRs that evolve through syn-volcanic subsidence and episodic burial by large volume massive lava eruptions. From this, we conclude that AVRs have neither a particular life cycle nor are they synchronised along the global mid-ocean ridge system. Rather, they approximate steady-state features in which subsidence plays as large a part in their origin as volcanic construction.

  3. Petrology and geochemistry of primitive lower oceanic crust from Pito Deep: Implications for the accretion of the lower crust at the Southern East Pacific Rise

    Perk, N.W.; Coogan, L.A.; Karson, J.A.; Klein, E.M.; Hanna, H.D.

    2007-01-01

    A suite of samples collected from the uppermost part of the plutonic section of the oceanic crust formed at the southern East Pacific Rise and exposed at the Pito Deep has been examined. These rocks were sampled in situ by ROV and lie beneath a complete upper crustal section providing geological context. This is only the second area (after the Hess Deep) in which a substantial depth into the plutonic complex formed at the East Pacific Rise has been sampled in situ and reveals significant spatial heterogeneity in the plutonic complex. In contrast to the uppermost plutonic rocks at Hess Deep, the rocks studied here are generally primitive with olivine forsterite contents mainly between 85 and 88 and including many troctolites. The melt that the majority of the samples crystallized from was aggregated normal mid-ocean ridge basalt (MORB). Despite this high Mg# clinopyroxene is common despite model predictions that clinopyroxene should not reach the liquidus early during low-pressure crystallization of MORB. Stochastic modeling of melt crystallisation at various levels in the crust suggests that it is unlikely that a significant melt mass crystallized in the deeper crust (for example in sills) because this would lead to more evolved shallow level plutonic rocks. Similar to the upper plutonic section at Hess Deep, and in the Oman ophiolite, many samples show a steeply dipping, axis-parallel, magmatic fabric. This suggests that vertical magmatic flow is an important process in the upper part of the seismic low velocity zone beneath fast-spreading ridges. We suggest that both temporal and spatial (along-axis) variability in the magmatic and hydrothermal systems can explain the differences observed between the Hess Deep and Pito Deep plutonics. ?? Springer-Verlag 2007.

  4. High Temperature Logging and Monitoring Instruments to Explore and Drill Deep into Hot Oceanic Crust.

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

    2014-12-01

    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 200C (reached, for example, at the bottom of DSDP/ODP Hole 504B), and possibly beyond 300C. 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 400C and wireline tools up to 300C 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 (320C). As part of this new set of downhole tools, temperature, pressure, fluid flow and casing collar location might be measured up to 400C 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 300C 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.

  5. Separate zones of sulfate and sulfide release from subducted mafic oceanic crust

    Tomkins, Andrew G.; Evans, Katy A.

    2015-10-01

    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.

  6. Oceanic crust within the paleozoic Granjeno Schist, northeastern Mexico. Remnants of the Rheic and paleo-Pacific Ocean.

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

    2015-04-01

    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.

  7. Chlorine isotope geochemistry of hydrothermally altered oceanic crust: Mineralogical controls and experimental constraints

    Cisneros, M.; Barnes, J.; Jenkins, D. M.; Gardner, J. E.

    2012-12-01

    Chlorine stable isotopes (37Cl and 35Cl) can provide an important fingerprint for geochemical recycling of subducted oceanic lithosphere and fluid-rock interaction due to chlorine's high solubility in aqueous phases. To implement Cl isotopes as a tracer of volatile element recycling, we must constrain the δ37Cl value of potential Cl reservoirs and determine fractionation factors between Cl-bearing phases. δ37Cl and Cl concentrations of hydrothermally altered oceanic crust (AOC) samples from seven IODP/ODP/DSDP drill sites have been measured on bulk rock samples (n = 50). For ease of comparing results, samples are categorized into three lithologies: 1) extrusive lavas, 2) sheeted dikes, and 3) gabbros. Extrusive lava Cl concentrations vary from factors between hydrous minerals and co-existing fluid often also provides the ability of determining the isotopic composition of the water removed from the original mineral-water pair. 'Pseudo' isotope exchange experiments (O'Neil, 1986) are currently being carried out in cold-seal pressure vessels by synthesizing hastingsite in the presence of a Cl bearing solution of known isotopic composition. Several variable hornblende compositions (near ferro-pargasite or hastingsite) have successfully been synthesized at 700°C and 0.2 GPa, carrying out experiments for 2-4 days, approximately at the wuestite-magnetite buffer. Fractionation experiments are being run at a constant pressure and varying temperatures that will successfully synthesize amphibole and approach reasonable kinetic rates in order to achieve equilibrium. It will also be important to note the variation in equilibrium fractionation factors based on amphibole composition and fluid/rock ratio (Graham et al., 1984). Graham et al. (1984). Am. Mineral., 69, pp. 128-138. O'Neil, J.R. (1986). Rev. Mineral., 16, pp. 1-40.

  8. Do Two Deep Drill Holes Into the Upper Ocean Crust Quantify the Hydrothermal Contribution to Global Geochemical Cycles?

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

    2014-12-01

    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 (textbook 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.

  9. Dehydration of lawsonite could directly trigger earthquakes in subducting oceanic crust

    Okazaki, Keishi; Hirth, Greg

    2016-02-01

    Intermediate-depth earthquakes in cold subduction zones are observed within the subducting oceanic crust, as well as the mantle. In contrast, intermediate-depth earthquakes in hot subduction zones predominantly occur just below the Mohorovičić discontinuity. These observations have stimulated interest in relationships between blueschist-facies metamorphism and seismicity, particularly through dehydration reactions involving the mineral lawsonite. Here we conducted deformation experiments on lawsonite, while monitoring acoustic emissions, in a Griggs-type deformation apparatus. The temperature was increased above the thermal stability of lawsonite, while the sample was deforming, to test whether the lawsonite dehydration reaction induces unstable fault slip. In contrast to similar tests on antigorite, unstable fault slip (that is, stick-slip) occurred during dehydration reactions in the lawsonite and acoustic emission signals were continuously observed. Microstructural observations indicate that strain is highly localized along the fault (R1 and B shears), and that the fault surface develops slickensides (very smooth fault surfaces polished by frictional sliding). The unloading slope during the unstable slip follows the stiffness of the apparatus at all experimental conditions, regardless of the strain rate and temperature ramping rate. A thermomechanical scaling factor for the experiments is within the range estimated for natural subduction zones, indicating the potential for unstable frictional sliding within natural lawsonite layers.

  10. A hydrologic model for the uppermost oceanic crust constrained by temperature estimates from carbonate minerals

    Anderson, B. W.; Gillis, K. M.; Coogan, L. A.

    2013-08-01

    models of the oceanic crust commonly assume that the uppermost igneous extrusive layer of the aquifer is thermally well mixed, although this assumption has not been rigorously tested. Here, the assumption of a thermally well-mixed aquifer is tested against the geological record using O isotope-derived crystallization temperatures of carbonates in the lavas as a record of the temperatures experienced by the aquifer. It is found that carbonate formation temperatures are higher than can be explained by a model of outcrop-to-outcrop flow in a well-mixed aquifer at four of the seven drilling locations analyzed. A poorly mixed aquifer is developed to further explore the crustal hydrology at these locations. Relative to a well-mixed aquifer, a poorly mixed aquifer can achieve higher average temperatures, develops larger lateral pressure gradients driving flow, and requires a lower permeability to achieve a given lateral fluid flux. O isotope data from most of the carbonate samples analyzed are consistent with temperatures achievable in a poorly mixed aquifer; those samples which are not consistent can be explained by plausible special circumstances (such as formation at a discharge zone, where ascending fluid may warm the uppermost aquifer).

  11. Magnetic mapping of (carbonated) oceanic crust-mantle boundary: New insights from Linnajavri, northern Norway

    Tominaga, M.; Beinlich, A.; Tivey, M.; Andrade Lima, E.; Weiss, B. P.

    2012-12-01

    The contribution of lower oceanic crust and upper mantle to marine magnetic anomalies has long been recognized, but the detailed magnetic character of this non-volcanic source layer remains to be fully defined. Here, we report preliminary results of a magnetic survey and source characterization of a "carbonated" oceanic Moho (petrological "Mohorovicic discontinuity") sequence observed at the Linnajavri Serpentinite Complex (LSC), northern Norway. The LSC is located at 67 36'N and 16 24'E within the upper Allochthon of the Norwegian Caledonides and represents a dismembered ophiolite. Particularly in the southern ("Ridoalggicohkka") area of the LSC, gabbro, serpentinite and its talc-carbonate (soapstone) and quartz-carbonate (listvenite) altered equivalents are extraordinarily well-exposed [1]. An intact oceanic Moho is exposed here, despite its complex tectonic setting. The small degree of arctic rock weathering (? 2 mm weathering surface) allowed for detailed regional-scale surface magnetic mapping across alteration fronts (serpentinite-soapstone; soapstone-listvenite) and lithological contacts (soapstone-gabbro). Magnetic mapping was conducted using a handheld 3-axis magnetometer, surface-towed resistivity meter and Teka surface magnetic susceptometer with sample spacing of 1 m. Geophysical field mapping was combined with petrological observations and scanning SQUID microscopy (SM) mapping conducted on thin sections from rock samples that were drilled along the survey lines. Regional scale magnetic mapping indicates that the total magnetic field across both the "carbonated" Moho and the soapstone-serpentinite interfaces show higher frequency changes in their magnetic anomaly character and amplitudes than the surface-towed resistivity data. SQUID microscopy mapping of both natural remanence magnetization (NRM) and anhysteretic remanence magnetization (ARM) on gabbro, serpentinite, soapstone, and listvenite samples, with a sensor-sample separation of 190 ?m, show that the distribution of microscopically measurable ferromagnetic and possibly sulfide minerals produces a different bulk intensity for each of the rock types. SM vector magnetic field maps of these samples also reveal that the magnetization associated with these grains (observed as dipole-like fields in SM maps) is variable in direction from grain to grain, which may result from different alteration histories for each grain. These complex magnetization patterns acquired through thermal and chemical alteration history may explain the short wavelength magnetic anomalies observed along our traverse lines. [1] Beinlich, A., Plmper, O., Hvelmann, J., Austrheim, H. and Jamtveit, B. (2012), Terra Nova, in press.

  12. Structure, porosity and stress regime of the upper oceanic crust: Sonic and ultrasonic logging of DSDP Hole 504B

    Newmark, R.L.; Anderson, R.N.; Moos, D.; Zoback, M.D.

    1985-01-01

    The layered structure of the oceanic crust is characterized by changes in geophysical gradients rather than by abrupt layer boundaries. Correlation of geophysical logs and cores recovered from DSDP Hole 504B provides some insight into the physical properties which control these gradient changes. Borehole televiewer logging in Hole 504B provides a continuous image of wellbore reflectivity into the oceanic crust, revealing detailed structures not apparent otherwise, due to the low percentage of core recovery. Physical characteristics of the crustal layers 2A, 2B and 2C such as the detailed sonic velocity and lithostratigraphic structure are obtained through analysis of the sonic, borehole televiewer and electrical resistivity logs. A prediction of bulk hydrated mineral content, consistent with comparison to the recovered material, suggests a change in the nature of the alteration with depth. Data from the sonic, borehole televiewer, electrical resistivity and other porosity-sensitive logs are used to calculate the variation of porosity in the crustal layers 2A, 2B and 2C. Several of the well logs which are sensitive to the presence of fractures and open porosity in the formation indicate many zones of intense fracturing. Interpretation of these observations suggests that there may be a fundamental pattern of cooling-induced structure in the oceanic crust. ?? 1985.

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

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

    1996-01-01

    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.

  14. Nd isotope systematics on ODP Sites 756 and 762 sediments reveal major volcanic, oceanic and climatic changes in South Indian Ocean over the last 35 Ma

    Le Houedec, Sandrine; Meynadier, Laure; Allègre, Claude J.

    2012-04-01

    We have analyzed the Nd isotopic composition of both ancient seawater and detrital material from long sequences of carbonated oozes of the South Indian Ocean which are ODP Site 756 (Ninety East Ridge (- 30°S), 1518 m water depth) and ODP Site 762 (Northwest Australian margin, 1360 m water depth). The measurements indicate that the ɛNd changes in Indian seawater over the last 35 Ma result from changes in the oceanic circulation, large volcanic and continental weathering Nd inputs. This highlights the diverse nature of those controls and their interconnections in a small area of the ocean. These new records combined with those previously obtained at the equatorial ODP Sites 757 and 707 in the Indian Ocean (Gourlan et al., 2008) established that the distribution of intermediate seawater ɛNd was uniform over most of the Indian Ocean from 35 Ma to 10 Ma within a geographical area extending from 40°S to the equator and from - 60°E to 120°E. However, the ɛNd value of Indian Ocean seawater which kept an almost constant value (at about - 7 to - 8) from 35 to 15 Ma rose by 3 ɛNd units from 15 to 10 Ma. This sharp increase has been caused by a radiogenic Nd enrichment of the water mass originating from the Pacific flowing through the Indonesian Passage. Using a two end-members model we calculated that the Nd transported to the Indian Ocean through the Indonesian Pathway was 1.7 times larger at 10 Ma than at 15 Ma. The Nd isotopic composition of ancient seawater and that of the sediment detrital component appear to be strongly correlated for some specific events. A first evidence occurs between 20 and 15 Ma with two positive spikes recorded in both ɛNd signals that are clearly induced by a volcanic crisis of, most likely, the St. Paul hot-spot. A second evidence is the very large ɛNd decrease recorded at ODP Sites 756 and 762 during the past 10 Ma which has never been previously observed. The synchronism between the ɛNd decrease in seawater from 10 to 5 Ma and evidences of desertification in the western part of the nearly Australian continent suggests enhanced weathering inputs in this ocean from this continent as a result of climatic changes.

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

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

    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... is dark-brown, compact, and typical of most Fe–Mn crusts. The remainder of the crust, ;40 mm to ;70 mm is earthy yellow, porous, and . detritus rich older zone . A polished section of the crust was observed under reflected light microscope to delineate...

  16. Radiocarbon dating of basalts from middle oceanic ridges using lithified carbonate crust samples

    Results of radiocarbon dating of basalts using lithified carbonate crust samples are presented. Core samples were samples in Red sea deep-water cavities during joint Picar expedition of two scientific research ships ''Academic Kurchatov'' and ''Professor Shtockman''. Crust samples were dated according to benzene variant. Age values obtained are varied in the interval from 2980 to 20700 yeras. Dating of basalts using lithified carbonate crusts is efficient in the range of radiocarbon dating (up to 40000-45000 years). This range is inaccessible for other methods of nuclear geochronology that makes the above method more valuable

  17. Fe-XANES analyses of Reykjanes Ridge basalts: Implications for oceanic crust's role in the solid Earth oxygen cycle

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

    2015-10-01

    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 ΔQFM 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.

  18. Atmospheric contamination of the primary Ne and Ar signal in mid-ocean ridge basalts and its implications for ocean crust formation

    Stroncik, N. A.; Niedermann, S.

    2016-01-01

    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.

  19. Age, spreading rates, and spreading asymmetry of the world's ocean crust

    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...

  20. The magmatic-hydrothermal transition in the lower oceanic crust: Clues from the Ligurian ophiolites, Italy

    Tribuzio, Riccardo; Renna, Maria Rosaria; Dallai, Luigi; Zanetti, Alberto

    2014-04-01

    The gabbroic bodies from the Jurassic Ligurian ophiolites are structurally and compositionally similar to the gabbroic sequences from the oceanic core complexes of the Mid Atlantic Ridge. Initial cooling of the Ligurian gabbros is associated with local development of hornblende-bearing felsic dykes and hornblende vein networks. The hornblende veining is correlated with the widespread development of hornblende as coronas/pseudomorphs after the clinopyroxene in the host gabbros. In addition, the studied gabbroic body includes a mantle sliver locally containing hornblende gabbros and hornblendite veins. The hornblendes from the felsic dykes and the hornblende-rich rocks within the mantle sliver show a similar geochemical signature, characterized by low Mg#, CaO and Al2O3, negligible Cl, and high TiO2, K2O, REE, Y, Zr and Nb concentrations. The whole-rock Sm-Nd isotopic compositions of the felsic dykes and the hornblende-rich rocks define a Sm-Nd isochron corresponding to an age of 154 ± 20 Ma and an initial ɛNd of 9.2 ± 0.5. The δ18O of the hornblendes and coexisting zircons from these rocks (about +4.5‰ and +5.8‰, respectively) do not indicate the presence of a seawater component in these melts. The formation of the felsic dykes and of the hornblende-rich rocks within the mantle sliver involved SiO2-rich silicate melts with negligible seawater component, which presumably were derived from high degree fractional crystallization of MOR-type basalts. The vein and the coronitic/pseudomorphic hornblendes show high Mg# and CaO, significant Cl (0.02-0.17 wt%) and low TiO2 and K2O concentrations. The coronitic/pseudomorphic hornblendes have trace element compositions similar to those of the clinopyroxenes from the gabbros and δ18O values (+1.0‰ to 0.7‰) close to seawater, suggesting an origin by reaction between migrating seawater-derived fluids and the host gabbros. The vein hornblendes commonly show slight LREE enrichment, relatively high concentrations of Nb (up to 2.5 ppm) and δ18O ranging from +3.7‰ to +0.8‰. The crystallization of these hornblendes most likely involved both seawater and magmatic components.

  1. Distribution and sources of pre-anthropogenic lead isotopes in deep ocean water from Fe-Mn crusts

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

    1996-01-01

    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.

  2. Platinum group elements and gold in ferromanganese crusts from AfanasiyNikitin seamount, equatorial Indian Ocean: Sources and fractionation

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

    2007-02-01

    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.

  3. Continental growth through time by underplating of subducted oceanic crust: evidence from kimberlites in South Africa and SW Pacific

    In the dynamic model of plate tectonics, it is evident that crustal components are returned to the mantle by subduction. Chemical signatures of these subducted components were identified in ocean island volcanics and in island arc volcanics. Indeed, an origin involving a subducted protolith was postulated for certain types of xenoliths in kimberlite, including diamonds. Recent studies of eclogite xenoliths in kimberlite from southern Africa and megacrysts form the Malaitan alnoite, Solomon islands, indicate that lithospheric underplating by subducted oceanic crust has occurred in these two contrasting areas. The results of new eclogite studies from the Bellsbank kimberlite, South Africa, and isotopic data from the Malaitan alnoite megacryst suite. This forms the basis for discerning the role of lithospheric underplating in the growth of cratons and in the evolution of mantle-derived magma

  4. Continental growth through time by underplating of subducted oceanic crust: Evidence from kimberlites in South Africa and SW Pacific

    Taylor, Lawrence A.; Neal, Clive R.

    1988-01-01

    In the dynamic model of plate tectonics, it is evident that crustal components are returned to the mantle by subduction. Chemical signatures of these subducted components were identified in ocean island volcanics and in island arc volcanics. Indeed, an origin involving a subducted protolith was postulated for certain types of xenoliths in kimberlite, including diamonds. Recent studies of eclogite xenoliths in kimberlite from southern Africa and megacrysts form the Malaitan alnoite, Solomon islands, indicate that lithospheric underplating by subducted oceanic crust has occurred in these two contrasting areas. The results of new eclogite studies from the Bellsbank kimberlite, South Africa, and isotopic data from the Malaitan alnoite megacryst suite. This forms the basis for discerning the role of lithospheric underplating in the growth of cratons and in the evolution of mantle-derived magma.

  5. Intermediate crust (IC); its construction at continent edges, distinctive epeirogenic behaviour and identification as sedimentary basins within continents: new light on pre-oceanic plate motions

    Osmaston, Miles F.

    2014-05-01

    Introduction. The plate tectonics paradigm currently posits that the Earth has only two kinds of crust - continental and oceanic - and that the former may be stretched to form sedimentary basins or the latter may be modified by arc or collision until it looks continental. But global analysis of the dynamics of actual plate motions for the past 150 Ma indicates [1 - 3] that continental tectospheres must be immensely thicker and rheologically stiffer than previously thought; almost certainly too thick to be stretched with the forces available. In the extreme case of cratons, these tectospheric keels evidently extend to 600 km or more [2, 3]. This thick-plate behaviour is attributable, not to cooling but to a petrological 'stiffening' effect, associated with a loss of water-weakening of the mineral crystals, which also applies to the hitherto supposedly mobile LVZ below MORs [4, 5]. The corresponding thick-plate version of the mid-ocean ridge (MOR) process [6 - 8], replacing the divergent mantle flow model, has a deep, narrow wall-accreting axial crack which not only provides the seismic anisotropy beneath the flanks but also brings two outstanding additional benefits:- (i) why, at medium to fast spreading rates, MOR axes become straight and orthogonally segmented [6], (ii) not being driven by body forces, it can achieve the sudden jumps of axis, spreading-rate and direction widely present in the ocean-floor record. Furthermore, as we will illustrate, the crack walls push themselves apart at depth by a thermodynamic mechanism, so the plates are not being pulled apart. So the presence of this process at a continental edge would not imply the application of extensional force to the margin. Intermediate Crust (IC). In seeking to resolve the paradox that superficially extensional structures are often seen at margins we will first consider how this MOR process would be affected by the heavy concurrent sedimentation to be expected when splitting a mature continent. I reason that, by blocking the hydrothermal cooling widely seen along MOR axes this must inhibit the freezing-in of diagnostic spreading-type magnetic anomalies and would prolong magmagenesis to give a thicker-than-oceanic mafic crust. I have called this Intermediate Crust (IC) [9, 10], to distinguish it from Mature Continental Crust (MCC). Plate separation will continue to generate IC along the margins for as long/far as the sedimentation input is sufficient to have this effect. Transition to the MOR process will then follow. But if, contrary to the general plate tectonics assumption, based on body forces, plate separation ceases after a limited separation (or perhaps several in differing directions), without proceeding to the oceanic condition, the resulting IC areas will be incorporated within the continent [11]. Where does this lead us? With examples drawn from 40 years' study, I will contend that this is indeed the way the Earth has worked and that it offers potential plate kinematic explanation of the origin of the block-and-sedimentary basin layouts abundantly present in the non-craton areas of continents. I will show that in some cases the intricacy of block outlines and the precision with which they can be fitted together in a kinematically consistent manner rules out that this was purely by chance. The evidently meaningful character of those outlines means that they have been drawn by a narrow-crack separative mechanism which reflects that of our new MOR model. To provide a basis for such Plate Kinematic Analysis (PKA) we now link and compare some features of IC-formation at continental edges and of the crust of sedimentary basins. Characteristics of IC and of sedimentary basin crust (SBC). 1. IC basement, with expected seismic Vp around 6km/s, must look deceptively like that assigned to supposedly stretched MCC. 2. For thermodynamic reasons, the hydrous metamorphic content of deep MCC and of deeply subducted UHP slices of it gives them a big thermal epeirogenic sensitivity which IC lacks. Calculation [8, 9] shows that this type of process yields some 12-30 t

  6. The age and emplacement of obducted oceanic crust in the Urals from Sm-Nd and Rb-Sr systematics

    The Urals contain a 2000 km belt of mafic-ultramafic bodies. The Sm-Nd and Rb-Sr systematics of two of these bodies, the Kempersai Massif in the South Ural Mountains and the Voykar-Syninsky Ophiolite Complex in the Polar Ural Mountains have been examined. These data confirm the hypothesis that these bodies represent fragments of pre-collision oceanic crust and establish constraints on the nature and timing of events in the Uralian Orogeny. Two Kempersai gabbros define Sm-Nd internal isochrons of 397 +- 20 My and 396 +- 33 My with epsilonsub(Nd)(T) = +8.7 -+ 0.6 and +8.4 -+ 1.3, respectively. Whole rock samples of pillow basalt, diabase, gabbros, troctolite, and a metasediment give Sm-Nd values which lie on this isochron indicating that these rocks are genetically related and have an igneous crystallization age of 397 My. Whole rock samples of Voykar-Syninsky diabase, gabbros, and clinopyroxenite give Sm-Nd values which lie on or within proportional 1 epsilon-unit of this isochron indicating an age and epsilonsub(Nd)(T) virtually identical to those of Kempersai. epsilonsub(Nd)(T) for the Kempersai and Voykar-Syninsky mafic samples range from +7.3 to +9.0 with an average value of +8.4. This indicates that the Urals ophiolites are derived from an ancient depleted mantle source and are most plausibly pieces of the oceanic crust and lithosphere. The fact that a metasediment has the same epsilonsub(Nd)(397 My) as the other samples indicates derivation from an oceanic source with negligible continental input. epsilonsub(Nd)(T) for the massifs is proportional 1.5 epsilon-units lower than the average for modern MORBs. (orig./HSI)

  7. Reconstructing the carbonate compensation depth from 0 to 100 Ma using ocean ion concentrations and bathymetry models

    Davis, Joel; Lithgow-Bertelloni, Carolina

    2014-05-01

    The oceans play an important part in regulating the carbon cycle and climate system, acting as a buffer between the carbon in the atmosphere and the deep earth. Of all dissolved inorganic carbon (DIC) in the ocean, only carbonate can exist in a solid state (mostly as calcite). In the near-surface ocean, calcite is supersaturated and thus precipitates. Deeper in the ocean, the solubility of calcite increases and all is entirely dissolved at the carbonate compensation depth (CCD), where the rate of falling carbonate equals the rate of dissolution. The CCD today is around 4.5 km depth, though previous work that looked at the composition of sediments on the ocean floor has suggested that CCD was different in the past (e.g. Pälike et al., 2012; Sclater et al., 1977). These studies mostly show the CCD decreasing to shallower depths through the Cenozoic and the Mesozoic. The deepening of the CCD through time is consistent with the decrease in atmospheric CO2 over time shown in the GEOCARB models (Berner, 1987; Berner and Kothavala, 2001; Berner, 2006); more carbon is being stored in the ocean as sediment. We look at the evolution of the CCD since 100 Ma by focusing on changes in the volume of the ocean basins. We combine recent advancements in determining palaeobathymetry into the Mesozoic from reconstructed ages of the ocean floor (Müller et al., 2008) in conjunction with a geochemical model by Boudreau et al. (2010) for the average CCD today, applying it from 0 to 100 Ma. A history of global ocean ion concentrations produced by Tyrrell and Zeebe (2004) was used. Various assumptions about productivity rates, solubility constants and other conditions in the past oceans were necessary to make a first order working model. The model was found to be very sensitive to even minor changes in the dissolved concentration of carbonate. In the reconstruction where the surface saturation state was decreased going back to 100 Ma, the CCD gradually deepens with time, consistent with other independent studies. Changes in CO2 concentrations likely influenced this, which would have affected the amount of silicate weathering from continents (Misra and Froelich, 2012). We will show maps of the extent of the global carbonate cover for the last 100 my, which suggest that the amount of sedimentary carbon being subducted has increased with time, despite an overall decrease in volcanic activity since the Mesozoic.

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

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

    rate of the silicate-detritus has been calculated, which shows an overall decrease during the past 25 plus or minus 2 Ma growth history of the specimen. This silicate-detritus displays epsilon Nd(0) between -7.7 and -12.7, and u87Sr/ u86Sr between 0...

  9. Seismic properties of subducting oceanic crust: Constraints from natural lawsonite-bearing blueschist and eclogite in Sivrihisar Massif, Turkey

    Cao, Yi; Jung, Haemyeong

    2016-01-01

    Investigating the seismic properties of natural lawsonite (Lws)-bearing blueschist and eclogite is particularly important for constraining the seismic interpretation of subducting oceanic crust based on seismological observations. To achieve this end, we analyzed in detail the mineral fabrics and seismic properties of foliated Lws-blueschist and Lws-eclogites from Sivrihisar Massif in Turkey. In both blueschists and eclogites, the lawsonite fabric is characterized by three different patterns: [0 0 1] axes aligning sub-normal to foliation, and [0 1 0] axes aligning sub-parallel to lineation (normal type); [0 0 1] axes aligning sub-parallel to lineation, and [1 0 0] axes aligning sub-normal to foliation with a girdle sub-normal to lineation (abnormal type); and [0 0 1] axes aligning both sub-normal to foliation and sub-parallel to lineation, [0 1 0] axes aligning sub-parallel to lineation, and [1 0 0] axes aligning sub-normal to foliation (transitional pattern). In contrast, glaucophane and omphacite mostly present consistent axial fabrics with the [0 0 1] axes aligning to lineation. These mineral fabrics produce whole-rock seismic anisotropies with similar patterns. However, the variations in seismic anisotropies are mainly controlled by the rock type, to a lesser extent are determined by the lawsonite fabric type, and to only a small extent are affected by mineral fabric strength. Despite the constructive abnormal-type lawsonite fabric on whole-rock seismic anisotropies, because of their weaker mineral fabric strength (or deformation degree), the abnormal-type Lws-blueschist still exhibit comparatively lower seismic anisotropies than those normal-type Lws-blueschist from other localities. Based on the calculated seismic anisotropies and velocities, we estimated that when oceanic crust transforms from Lws-blueschist to Lws-eclogite with increasing subduction depth, (1) P-wave and max. S-wave polarization anisotropies reduce about 70% and 40%, respectively; and (2) variations of Vp and Vs contrasts relative to mantle peridotites are about -7% to -3% and -8% to -6%, respectively. These results corroborate the important roles of Lws-bearing blueschist and eclogite in interpreting the existence and gradual weakening of low-velocity layers in subducting oceanic crust, during the subduction process.

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

    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...

  11. 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

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

    on crust genesis V.K. Banakar and D.V. Borole NationaI Institute of Oceanography, Dona Paula, Goa 403 004, India (Received August 16, 1989; revised and accepted May 29, 199 1) ABSTRACT Banakar, V.K. and Borole, D.V., 1991. Depth profiles of 23”Thcrecu..., transition metals and mineralogy of ferromanganese crusts of the Central Indian basin and implications for palaeoceanographic influence on crusts genesis. Chem. Geol. (Isot. Geosci. Sect.), 94: 33-44. Two ferromanganese encrustations of hydrogenetic origin...

  12. In situ Detection of Microbial Life in the Deep Biosphere in Igneous Ocean Crust

    Salas, Everett C.; Bhartia, Rohit; Anderson, Louise; Hug, William F.; Reid, Ray D.; Iturrino, Gerardo; Edwards, Katrina J.

    2015-01-01

    The deep biosphere is a major frontier to science. Recent studies have shown the presence and activity of cells in deep marine sediments and in the continental deep biosphere. Volcanic lavas in the deep ocean subsurface, through which substantial fluid flow occurs, present another potentially massive deep biosphere. We present results from the deployment of a novel in situ logging tool designed to detect microbial life harbored in a deep, native, borehole environment within igneous oceanic cr...

  13. Pillow basalts of the Angayucham terrane: oceanic plateau and island crust accreted to the Brooks Range

    Pallister, J.S.; Budahn, J.R.; Murchey, B.L.

    1989-01-01

    The Angayucham Mountains (north margin of the Yukon-Koyukuk province) are made up of an imbricate stack of four to eight east-west trending, steeply dipping, fault slabs composed of Paleozoic, Middle to Late Triassic, and Early Jurassic oceanic upper crustal rocks. Field relations and geochemical characteristics of the basaltic rocks suggest that the fault slabs were derived from an oceanic plateau or island setting and were emplaced onto the Brooks Range continental margin. The basalts are variably metamorphosed to prehnite-pumpellyite and low-greenschist facies. Major element analyses suggest that many are hypersthene-normative olivine tholeiites. The Triassic and Jurassic basalts are geochemically most akin to modern oceanic plateau and island basalts. Field evidence also favors an oceanic plateau or island setting. The great composite thickness of pillow basalt probably resulted from obduction faulting, but the lack of fault slabs of gabbro or peridotite suggests that obduction faults did not penetrate below oceanic layer 2, a likely occurrence if layer 2 were anomalously thick, as in the vicinity of an oceanic island. -from Authors

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

    Kita, Saeko; Katsumata, Kei

    2015-02-01

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

  15. Uranium isotopic compositions of the crust and ocean: Age corrections, U budget and global extent of modern anoxia

    Tissot, François L. H.; Dauphas, Nicolas

    2015-10-01

    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 δ238U 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 (ΔAnoxic/Euxinic-SW = +0.6‰), the size of the anoxic/euxinic sink strongly influences the δ238U 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 δ238U 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 environments: U4+ is insoluble in seawater while U6+ is soluble (Langmuir, 1978). The contrasting behaviors of the two oxidation states of uranium explains why the disappearance of detrital uraninite after the Archean marks the rise of oxygen in Earth's atmosphere/hydrosphere (Ramdohr, 1958; Rasmussen and Buick, 1999; Frimmel, 2005). More recently, significant effort has focused on using U isotopes to constrain the past extents of anoxic/euxinic vs. oxic or suboxic sediments in modern and ancient oceans (Montoya-Pino et al., 2010; Brennecka et al., 2011a; Asael et al., 2013; Kendall et al., 2013, 2015; Andersen et al., 2014; Dahl et al., 2014; Goto et al., 2014; Noordmann et al., 2015). A virtue of this system is that it can potentially reflect the global redox state of Earth's oceans. At the same time, several difficulties have been encountered in applying U isotopes as paleo-redox indicators. For example, detrital contributions can blur the authigenic signal and have to be corrected for (Asael et al., 2013; Andersen et al., 2014; Noordmann et al., 2015), uranium isotopes can be affected by diagenesis and exchange with porewater (Romaniello et al., 2013; Andersen et al., 2014), and the exact isotopic fractionation factors relevant to various conditions of deposition are uncertain. While significant progress has already been made to address these difficulties (Asael et al., 2013; Romaniello et al., 2013; Andersen et al., 2014; Noordmann et al., 2015), this system and others are missing some of the groundwork studies on modern environments that are needed to gain trust in their applications to ancient sediments.In the modern ocean, water-soluble uranium behaves conservatively (i.e., U concentration correlates linearly to water salinity, Ku et al., 1977; Owens et al., 2011) and has a long residence time of ∼400 kyr (Ku et al., 1977). The ocean is therefore a large repository of uranium, exceeding the total inventory of land-based deposits (Lu, 2014). The riverine input (40-46 Mmol/yr) is balanced by several sinks; including suboxic sediments, anoxic/euxinic sediments, carbonates, altered oceanic crust, salt marshes and Fe-Mn nodules. Barnes and Cochran (1990), Morford and Emerson (1999), Dunk et al. (2002), and Henderson and Anderson (2003) each proposed estimates for the oceanic uranium budget that differ substantially in the fluxes that they use. Uranium isotopes are sensitive to ocean redox conditions because uranium removal in anoxic/euxinic sediments imparts large uranium isotopic fractionation, so that the areal extent of this sink influences greatly the U isotopic composition of seawater relative to the riverine input. In the present paper, we report double-spike uranium isotopic measurements of 18 seawater samples, 18 continental crust lithologies, 7 individual minerals, 6 oyster samples, 3 modern evaporites samples, 2 lake water samples, 1 large river water sample and 1 coral sample. These measurements are supplemented by compilations of literature data. With this large data set (n = 444), we are able to constrain the flux of uranium into anoxic/euxinic sediments, as well as the global extent of anoxia in the modern ocean (percent of seafloor covered by anoxic/euxinic sediments). Our findings compare well with independent estimates and rule out the most recent U budget of Henderson and Anderson (2003).As part of our effort, we also present a data reduction method for double-spike measurements that is both comprehensive in the way the errors are propagated and simple to implement.

  16. The origin of layered gabbros from the mid lower ocean crust, Hess Deep, East Pacific Rise

    Cheadle, M. J.; Brown, T. C.; Ceuleneer, G.; Meyer, R.

    2014-12-01

    IODP Exp. 345 Holes U1415 I & J cored a ~30m thick unit of conspicuously layered gabbroic rocks from the lower plutonic crust at Hess Deep. These rocks likely come from >1500m below the dike gabbro transition and thus provide an unique opportunity to study the origin of layering and the formation of relatively deep, fast spread plutonic crust formed at the EPR. Here we report the initial results of a comprehensive high-resolution petrologic, geochemical and petrographic study of this unit, which focuses on a fairly continuous 1.5m long section recovered at Hole I. The rocks consist of opx-bearing olivine gabbro, olivine gabbro and gabbro and exhibit 1-10cm scale modal layering. Some layers host spectacular 2-3 cm diameter cpx oikocrysts encapsulating partially resorbed plagioclase laths. Downhole variations in mineral chemistry are complicated. Olivine, cpx and opx Mg#'s partly reflect equilibration and show a subtle metre-scale variation (1-2 Mg#), whereas, for example, plagioclase anorthite, and cpx TiO2 contents reveal a more complicated 10-20 cm-scale variation (2-4 An, and 0.2 TiO2). Mineral zonation, for all but Mg# in equilibrated olivine, is of higher magnitude than downhole variations in average mineral compositions. Trace element geochemistry reveals rather homogeneous plagioclase and opx compositions; however cpx exhibits variation at the mineral scale. Cpx shows an increased range of, and highest REE concentrations, in the more olivine rich, near cotectic, composition gabbros, whereas the more plagioclase rich, cumulates show no variation of, and low REE, concentrations.Plagioclase fabrics are moderate to weak and partially modally controlled, but the strength of the plagioclase crystallographic preferred orientation (CPO) varies dramatically, within the 1.5m core showing a significant part of the variation recorded by Oman ophiolite plutonic crust. Plagioclase shape preferred orientation and CPO match well suggesting that diffusion enabled compaction was not significant. Overall, our combined observations and the similarity of composition and textures to those found in the Rum layered mafic intrusion (Scotland); an intrusion built by multiple ~100m thick replenishments of magma, suggests that the studied layered sequence is best interpreted as having formed in a lower crustal sill.

  17. New constraints on the sources and behavior of neodymium and hafnium in seawater from Pacific Ocean ferromanganese crusts

    van de Flierdt, T.; Frank, M.; Lee, D.-C.; Halliday, A.N.; Reynolds, B.C.; Hein, J.R.

    2004-01-01

    The behavior of dissolved Hf in the marine environment is not well understood due to the lack of direct seawater measurements of Hf isotopes and the limited number of Hf isotope time-series obtained from ferromanganese crusts. In order to place better constraints on input sources and develop further applications, a combined Nd-Hf isotope time-series study of five Pacific ferromanganese crusts was carried out. The samples cover the past 38 Myr and their locations range from sites at the margin of the ocean to remote areas, sites from previously unstudied North and South Pacific areas, and water depths corresponding to deep and bottom waters. For most of the samples a broad coupling of Nd and Hf isotopes is observed. In the Equatorial Pacific ENd and EHf both decrease with water depth. Similarly, ENd and EHf both increase from the South to the North Pacific. These data indicate that the Hf isotopic composition is, in general terms, a suitable tracer for ocean circulation, since inflow and progressive admixture of bottom water is clearly identifiable. The time-series data indicate that inputs and outputs have been balanced throughout much of the late Cenozoic. A simple box model can constrain the relative importance of potential input sources to the North Pacific. Assuming steady state, the model implies significant contributions of radiogenic Nd and Hf from young circum-Pacific arcs and a subordinate role of dust inputs from the Asian continent for the dissolved Nd and Hf budget of the North Pacific. Some changes in ocean circulation that are clearly recognizable in Nd isotopes do not appear to be reflected by Hf isotopic compositions. At two locations within the Pacific Ocean a decoupling of Nd and Hf isotopes is found, indicating limited potential for Hf isotopes as a stand-alone oceanographic tracer and providing evidence of additional local processes that govern the Hf isotopic composition of deep water masses. In the case of the Southwest Pacific there is evidence that decoupling may have been the result of changes in weathering style related to the buildup of Antarctic glaciation. Copyright ?? 2004 Elsevier Ltd.

  18. Constraints on Lu-Hf and Nb-Ta systematics in globally subducted oceanic crust from a survey of orogenic eclogites and amphibolites

    Zirakparvar, N. Alex

    2016-04-01

    To further understand Lu-Hf and Nb-Ta systematics in globally subducted oceanic crust, this paper evaluates all available Lu-Hf garnet isochron ages and initial ɛHf values in conjunction with present-day bulk-rock Lu-Hf isotope and trace element (K, Nb, Ta, Zr, and Ti in addition to Lu-Hf) data from the world's orogenic eclogites and amphibolites (OEAs). Approximately half of OEAs exhibit Lu-Hf and Nb-Ta systematics mimicking those of unsubducted oceanic crust whereas the rest exhibit variability in one or both systems. For the Lu-Hf system, mixing calculations demonstrate that subduction-related phase transformations, in conjunction with open system behavior, can shift subducted oceanic crust toward higher Lu/Hf, or toward lower Lu/Hf that can also be associated with unradiogenic ɛHf values. However, evaluation of potential mechanisms for fractionating Nb from Ta is more complicated because many of the OEAs have Nb-Ta systematics that are decoupled from Lu-Hf and the behavior of K, Zr, and Ti. Nonetheless, the global data set demonstrates that the association between unradiogenic ɛHf and elevated Nb/Ta observed in some kimberlitic eclogite xenoliths can be inherited from processes that occurred during subduction of their oceanic crustal protoliths. This allows for a geologically based estimate of the Nb concentration in a reservoir composed of deeply subducted oceanic crust. However, mass balance calculations confirm that such a reservoir, when considered as a whole, likely has a Nb concentration similar to unsubducted oceanic crust and is therefore not the solution to the problem of the Earth's "missing" Nb.

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

    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...... 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....

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

    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 i...

  1. Reconciling hydrological models with geological constraints in the upper oceanic crust at ODP Holes 504B and 896A

    Anderson, B. W.; Gillis, K. M.; Coogan, L. A.

    2011-12-01

    It has been proposed that ridge flank hydrothermal circulation by outcrop-to-outcrop (lateral) flow may be the dominant mode of advective heat extraction from the oceanic crust globally[1]. In this model the upper crust is an aquifer overlain by low permeability sediments, and aquifer-ocean fluid exchange occurs through basement outcrops. Thermally-induced pressure gradients drive fluid laterally from recharge outcrops to discharge outcrops. Drilling at ODP Holes 504B and 896A (in 6.9 Myr crust), along with hydrological monitoring and geophysical surveys of the area, provide a wealth of data to test the model of outcrop-to-outcrop flow in a young, rapidly sedimented area. Outcrop-to-outcrop flow in this region has been shown to be consistent with heat flow data and measured upper crustal temperatures[2], but has not been tested against geological constraints. With a numerical model of sedimentation, and constraints from geophysical data, the time-dependant distribution of outcrops near Holes 504B and 896A is estimated. From this, temperature histories and fluid fluxes in the upper crust are estimated for the drilling locations with a quantitative model of outcrop-to-outcrop fluid flow and heat exchange. Temperatures predicted by the outcrop-to-outcrop flow model for both holes are outcrop-to-outcrop flow. We consider whether ?18O-derived carbonate temperatures may be overestimated due to uncertainty in the hydrothermal fluid composition. Although there is a 1-2% enrichment in the ?18Orock of Hole 896A lavas[3], the modeled water-rock ratio of ~50 requires a relatively small corresponding decrease in ?18Ofluid relative to seawater, insufficient to lower carbonate temperatures to within range of the outcrop-to-outcrop flow model. These high temperature carbonates could be explained if vertical heat advection is important. The solubility of calcium carbonate is determined for temperatures predicted for outcrop-to-outcrop flow. Carbonate solubility and modeled water/rock ratios are used to estimate the timing and abundance of carbonate precipitation. Outcrop-to-outcrop flow requires that most upper crustal carbonates in both holes precipitated within the last ~2 Myrs. The 2-3x enrichment of bulk rock CO2 at Hole 896A[6] is consistent with greater fluid fluxes at Hole 896A relative to Hole 504B and/or a closer proximity of Hole 896A to a focused recharge site. Ongoing modeling of carbonate precipitation in off-axis hydrothermal systems near other drill holes will also be presented. [1] Fisher and Becker, Nature 2000, v403, p71. [2] Davis et al., EPSL 2004, v222, p863. [3] Teagle et al., Proc. ODP, Sci. Res. v148, p119. [4] Coggon et al., Science 2010, v327, p1114. [5] Alt et al., Proc. ODP, Sci. Res. 1996, v148, p435. [6] Alt and Teagle, Geochim. Cosmochim. Acta 1999, v63, p1527.

  2. Can Fractional Crystallization of a Lunar Magma Ocean Produce the Lunar Crust?

    Rapp, Jennifer F.; Draper, David S.

    2013-01-01

    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

  3. 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

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

    2014-12-01

    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 8N, and internal time marker (Q1) corresponding to the age 92 Ma at 12N in a corridor between 85E 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 85E and Ninetyeast ridges, two near N-S FZs, approximately followed 87E and 89.5E are found to extend into BOB up to 12N, from there the FZs reorient in N60W direction and reach to the continental margin region. Along ECMI two sets of FZs are identified with a northern set oriented in N60W and southern one in N40W 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.

  4. Canterbury Drifts, SW Pacific Ocean: Record of Antarctic Intermediate Water Flow Since 24 Ma

    Carter, R. M.

    2005-12-01

    The Canterbury Drifts were deposited in water depths between 400 and 1500 m by northward flowing, cold, intermediate depth water masses - Subantarctic Mode Water, Antarctic Intermediate Water, and their predecessor current flows. Drift accumulation started at 24 Ma, fed by terrigenous sediment derived from the newly rising Alpine Fault plate boundary in the west, which has built a progradational shelf-slope sediment prism up to 130 km wide at rates of eastward advance of up to 5.4 km/My. These regionally extensive, intermediate-depth sediment drifts can be examined in outcrop, in marine drillcore (ODP Site 1119) and at the modern seabed. The drifts comprise planar-bedded units up to several metres thick. Sand intervals have either reverse graded or sharp, erosive bases and normally graded tops. Bioturbation is moderate and the sands occur within a pervasive background of cm-scale, planar or wispy alternating muddy and sandy silts, consistent with deposition from rhythmically fluctuating bottom currents. In the Plio-Pleistocene, the sand:silt lithological rhythmicity occurs in synchroneity with Milankovitch-scale climate cycling; periods of inferred faster current flow (sand beds) mostly correspond to warm climatic intervals. The drifts vary in thickness from 300 m near the early Miocene shoreline, where they were accumulating in limited shallow water accommodation, to 2000+ m under the modern shelf edge. Mounded drifts first occur at 15 Ma (Middle Miocene), their appearance perhaps reflecting more vigorous intermediate water flow consequent upon the worldwide climatic deterioration between 15 and 13 Ma. A further change from large (more than 10 km wide) to smaller (1-3 km wide) mounded slope drifts occurs at 3.1 Ma, marking further cooling, the inception of discrete SAMW flows, and initiation of the Subantarctic Front. The natural gamma ray record from Site 1119 contains a history since 3.9 Ma of the waxing and waning of the New Zealand mountain ice cap. Back to 0.37 Ma, this record closely mirrors the climate history of Antarctica, as manifested in the Vostok ice core, at 0.1-0.6 ky resolution. Beyond, and back to 3.9 Ma, the gamma record reflects southern mid-latitude ice-volumes and perhaps Antarctic polar plateau temperature at a resolution of 1.3 ky.

  5. Experimental Simulations of Lunar Magma Ocean Crystallization: The Plot (But Not the Crust) Thickens

    Draper, D. S.; Rapp, J. F.; Elardo, S. M.; Shearer, C. K., Jr.; Neal, C. R.

    2016-01-01

    Numerical models of differentiation of a global-scale lunar magma ocean (LMO) have raised as many questions as they have answered. Recent orbital missions and sample studies have provided new context for a large range of lithologies, from the comparatively magnesian "purest anorthosite" reported by to Si-rich domes and spinel-rich clasts with widespread areal distributions. In addition, the GRAIL mission provided strong constraints on lunar crustal density and average thickness. Can this increasingly complex geology be accounted for via the formation and evolution of the LMO? We have in recent years been conducting extensive sets of petrologic experiments designed to fully simulate LMO crystallization, which had not been attempted previously. Here we review the key results from these experiments, which show that LMO differentiation is more complex than initial models suggested. Several important features expected from LMO crystallization models have yet to be reproduced experimentally; combined modelling and experimental work by our group is ongoing.

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

    Dahl, Tais; Canfield, Donald E; Rosing, Minik T; Frei, Robert E.; Gordon, Gwyneth W.; Knoll, Andrew Herbert; Anbar, Ariel D.

    2011-01-01

    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 oc...

  7. Deeply dredged submarine HIMU glasses from the Tuvalu Islands, Polynesia: Implications for volatile budgets of recycled oceanic crust

    Jackson, M. G.; Koga, K. T.; Price, A.; Konter, J. G.; Koppers, A. A. P.; Finlayson, V. A.; Konrad, K.; Hauri, E. H.; Kylander-Clark, A.; Kelley, K. A.; Kendrick, M. A.

    2015-09-01

    Ocean island basalts (OIB) with extremely radiogenic Pb-isotopic signatures are melts of a mantle component called HIMU (high µ, high 238U/204Pb). Until now, deeply dredged submarine HIMU glasses have not been available, which has inhibited complete geochemical (in particular, volatile element) characterization of the HIMU mantle. We report major, trace and volatile element abundances in a suite of deeply dredged glasses from the Tuvalu Islands. Three Tuvalu glasses with the most extreme HIMU signatures have F/Nd ratios (35.6 ± 3.6) that are higher than the ratio (˜21) for global OIB and MORB, consistent with elevated F/Nd ratios in end-member HIMU Mangaia melt inclusions. The Tuvalu glasses with the most extreme HIMU composition have Cl/K (0.11-0.12), Br/Cl (0.0024), and I/Cl (5-6 × 10-5) ratios that preclude significant assimilation of seawater-derived Cl. The new HIMU glasses that are least degassed for H2O have low H2O/Ce ratios (75-84), similar to ratios identified in end-member OIB glasses with EM1 and EM2 signatures, but significantly lower than H2O/Ce ratios (119-245) previously measured in melt inclusions from Mangaia. CO2-H2O equilibrium solubility models suggest that these HIMU glasses (recovered in two different dredges at 2500-3600 m water depth) have eruption pressures of 295-400 bars. We argue that degassing is unlikely to significantly reduce the primary melt H2O. Thus, the lower H2O/Ce in the HIMU Tuvalu glasses is a mantle signature. We explore oceanic crust recycling as the origin of the low H2O/Ce (˜50-80) in the EM1, EM2, and HIMU mantle domains.

  8. Sulu-Celebes-Banda basins: a trapped piece of Cretaceous to Eocene oceanic crust

    McCabe, R.J.; Hilde, T.W.; Cole, J.T.; Sager, W.; Lee, C.S.

    1986-07-01

    The Sulu-Celebes-Banda basin is composed of three poorly understood marginal basins located between northwest Australia and southeast Asia. Recent studies have proposed that these three basins are remnants of once-continuous ocean basin. The on-land geology of this region is complicated. However, numerous stratigraphic and paleomagnetic studies on pre-Oligocene rocks are consistent with the interpretation that older landmasses presently dissecting the basin were translated into their present position during the middle to late Tertiary. Paleomagnetic data from the Philippines suggest that the Philippine arc is a composite of Early Cretaceous to Holocene arcs that were translated clockwise and from the southeast. Paleomagnetic and stratigraphic data from Kalimantan and Sulawesi suggest that these landmasses share a common origin and that Sulawesi was rifted eastward off of Borneo during the late Tertiary. Stratigraphic studies from the Sula microcontinent, Buru, Ceram, and Timor show close correlation to the stratigraphy of northwest Australia or New Guinea. In addition, paleomagnetic studies from Timor suggest that a portion of the island was part of Australia since the early Mesozoic.

  9. Reconstructing ocean carbonate chemistry and atmospheric CO2 over the last 100 Ma: A new approach

    Zeebe, R. E.; Tyrrell, T.

    2003-04-01

    Recent data from fluid inclusions and fossil sea urchins provide compelling evidence that seawater calcium concentrations, [Ca2+], and Mg/Ca ratios have significantly changed over the last 100~Ma. In particular, [Ca2+] probably more than halved since the Cretaceous. We use this evidence to develop the first proxy for seawater carbonate ion concentration, [CO_32-], over this period of time. As documented in deep sea sediments, the calcite compensation depth and hence the CaCO_3 saturation has varied little over the last 100~Ma. From the saturation state (which is proportional to the product of [Ca2+] times [CO_32-]) we can calculate seawater [CO_32-]. Our results show that [CO_32-] has increased approximately three-fold since the Cretaceous. Furthermore, using our [CO_32-] proxy and recent paleo-pH proxy records, we provide the first calculation of the entire seawater carbonate system (including CO_2, HCO_3^-, ΣCO_2 and alkalinity) and atmospheric CO_2 from independent reconstructions of two CO_2 system parameters. Based on this, reconstructed atmospheric CO_2 is relatively low during the Miocene but high in the early Eocene. Finally, we make a strong case that seawater pH has increased over the last 100~Ma.

  10. Late Quaternary Sedimentary Records of Core MA01 in the Mendeleev Ridge, the Western Arctic Ocean: Preliminary Results

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

    2014-12-01

    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 μm) 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.

  11. Morphology and genesis of slow-spreading ridges-seabed scattering and seismic imaging within the oceanic crust

    Peirce, Christine; Sinha, Martin; Topping, Simon; Gill, Christopher

    2007-01-01

    A grid of 32 across-axis and five axis-parallel multichannel seismic (MCS) reflection profiles were acquired at an axial volcanic ridge (AVR) segment at 57° 45'N, 32° 35'W on the slow-spreading Reykjanes Ridge, Mid-Atlantic Ridge, to determine the along-axis variation and geometry of the axial magmatic system and to investigate the relationship between magma chamber structure, the along-axis continuity and segmentation of melt supply to the crust, the development of faulting and the thickness of oceanic layer 2A. Seismic reflection profiles acquired at mid-ocean ridges are prone to being swamped by high amplitude seabed scattered noise which can either mask or be mistaken for intracrustal reflection events. In this paper, we present the results of two approaches to this problem which simulate seabed scatter and which can either be used to remove or simply predict events within processed MCS profiles. The 37 MCS profiles show clear intracrustal seismic events which are related to the structure of oceanic layer 2, to the axial magmatic system and to the faults which dismember each AVR as it ages through its tectono-magmatic life cycle and which form the median valley walls. The layer 2A event can be mapped around the entirety of the survey area between 0.1 and 0.5 s two-way traveltime below the seabed, being thickest at AVR centres, and thinning both off-axis and along-axis towards AVR tips. Both AVR-parallel and ridge-parallel trends are observed, with the pattern of on-axis layer 2A thickness variation preserved beneath relict AVRs which are rafted off-axis largely intact. Each active AVR is underlain by a mid-crustal melt lens reflection extending almost along its entire length. Similar reflection events are observed beneath the offset basins between adjacent AVRs. These are interpreted as new AVRs at the start of their life cycle, developing centrally within the median valley. The east-west spacings of relict AVRs and offset basins is ~5-7 km, corresponding to a life span of the order of 0.5-0.7 Myr, during which AVRs appear to undergo multiple 20-60 Kyr tectono-magmatic cycles.

  12. Evolution of the Late Cretaceous crust in the equatorial region of the Northern Indian Ocean and its implication in understanding the plate kinematics

    Desa, M.; Ramana, M.V.; Ramprasad, T.

    version: Geophys. J. Int.: 177(3); 2009; 1265-1278 Evolution of the Late Cretaceous crust in the equatorial region of the Northern Indian Ocean and its implication in understanding the plate kinematics M. Desa 1* , M. V. Ramana 1 , T. Ramprasad 1 1..., National Institute of Oceanography, Dona Paula, Goa India. Tel. No.: +91 832 2450492; Fax. No.: +91 832 2450601; Email: mdesa@nio.org 2 1 INTRODUCTION The Late Cretaceous-Cenozoic evolution of the Indian Ocean is well documented using seafloor...

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

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

    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...

  14. 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.

    2006-01-01

    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...

  15. Updated maps of Moho topography and the earth crust thickness in the Deep Arctic Ocean based on results of potential field zoning and 3-D gravity modeling

    Glebovsky, Yury; Astafurova, Ekaterina; Chernykh, Andrey; Egorova, Alena; Kaminsky, Valeriy; Korneva, Mariya; Redko, Anton

    2014-05-01

    Both initial (Glebovsky et al., 2013) and updated maps and digital models (DM) of Moho topography and earth crust thickness in the deep Arctic Ocean were compiled using the same procedure. It included several steps: analysis of potential fields information compiled under CAMPGM and ArcGP projects and updating by new Russian data; separation of the study area into individual geostructures; calculation of gravitational effects from two main boundaries lying above Moho, presented by IBCAO grid, and by grid of basement relief (Kaminsky et al., 2012); subtraction of these effects from observed gravity anomalies, and converting of residual anomalies to depths to Moho using Parker's (1974) algorithm. Averaged depth to Moho required by Parker's algorithm to estimate its relative variations was determined from available deep refraction seismic data. It varies for different regional geological structures (basins, ridges and rises) which boundaries were contoured based on results of potential fields zoning. Modeling process for each structure was iterative and calibrated by seismic data. Results that best fit with seismic sections were merged to compile the grid of depths to Moho. This grid was specified by estimation of gravitational effects related both with increasing of density of sediments with depth and with uplift of asthenosphere beneath the Gakkel Ridge (GR). Grids of total and consolidated crust thickness were computed by sequential subtracting the IBCAO and sediment thickness grids from the final grid of depths to Moho. Updated versions of maps and DM of Moho topography and earth crust thickness are specified by recent Russian multi-channel and DSS seismic data collected in 2011-2012. It is confirmed the significant differences in crustal structure between the Eurasian (EB) and Amerasian Basins (AB). The thickness of the consolidated crust in the EB shows a fairly clear bilateral symmetry with respect to the GR. In the Nansen and Amundsen basins it varies from 3 to 8 km. The GR is underlain by the thinnest crust (2 km or less km). The crustal thickness of the Lomonosov Ridge varies along its strike within 16-26 km which may indicate its block structure. Within the AB there are a number of large highs and deep basins. The Mendeleev and Alpha ridges are underlain by crust that varies from 24 to 30 km and reaches maximum values of 30-32 km, respectively. The thickest crust that reaches 32-34 km is observed at the Northwind Ridge and Chukchi Plateau. Thickness of crust in deep basins of the AB varies widely. In the Canada and Makarov basins, it ranges from 10 to 16 km, and in the Podvodnikov Basin, from 16 to 20 km.

  16. Compositional variations in spinel-hosted pargasite inclusions in the olivine-rich rock from the oceanic crust-mantle boundary zone

    Tamura, Akihiro; Morishita, Tomoaki; Ishimaru, Satoko; Hara, Kaori; Sanfilippo, Alessio; Arai, Shoji

    2016-05-01

    The crust-mantle boundary zone of the oceanic lithosphere is composed mainly of olivine-rich rocks represented by dunite and troctolite. However, we still do not fully understand the global variations in the boundary zone, and an effective classification of the boundary rocks, in terms of their petrographical features and origin, is an essential step in achieving such an understanding. In this paper, to highlight variations in olivine-rich rocks from the crust-mantle boundary, we describe the compositional variations in spinel-hosted hydrous silicate mineral inclusions in rock samples from the ocean floor near a mid-ocean ridge and trench. Pargasite is the dominant mineral among the inclusions, and all of them are exceptionally rich in incompatible elements. The host spinel grains are considered to be products of melt-peridotite reactions, because their origin cannot be ascribed to simple fractional crystallization of a melt. Trace-element compositions of pargasite inclusions are characteristically different between olivine-rich rock samples, in terms of the degree of Eu and Zr anomalies in the trace-element pattern. When considering the nature of the reaction that produced the inclusion-hosting spinel, the compositional differences between samples were found to reflect a diversity in the origin of the olivine-rich rocks, as for example in whether or not a reaction was accompanied by the fractional crystallization of plagioclase. The differences also reflect the fact that the melt flow system (porous or focused flow) controlled the melt/rock ratios during reaction. The pargasite inclusions provide useful data for constraining the history and origin of the olivine-rich rocks and therefore assist in our understanding of the crust-mantle boundary of the oceanic lithosphere.

  17. The early terrestrial crust

    Bourdon, Bernard; Caro, Guillaume

    2007-01-01

    Recent geochemical evidence based on the ^(146)Sm–^(142)Nd system and Hadean zircons shows that the Earth's mantle experienced depletion approximately 100 Ma after the formation of the solar system, and possibly even before (earlier than 30 Ma), due to the extraction of a crust enriched in incompatible elements. Depending on the model ^(142)Nd abundance assumed for the Bulk Earth, the early crust may have been stored in the deep mantle, or may have been remixed in the mantle with a timescale ...

  18. Reconstruction of seawater chemistry from deeply subducted oceanic crust; hydrogen and oxygen isotope of lawsonite eclogites preserving pillow structure

    Hamabata, D., VI; Masuyama, Y.; Tomiyasu, F.; Ueno, Y.; Yui, T. F.; Okamoto, K.

    2014-12-01

    In order to understand evolution of life, change of seawater chemistry from Hadean, Archean to present is significant. Pillow structure is well-preserved in the Archean greenstone belt (e.g. Komiya et al., 1999). Oxygen and hydrogen isotope of rims in the pillow is useful conventional tool to decipher chemistry of Paleao-seawater from Archean to Present. However, Archean greenstone belt suffered regional metamorphism from greenschist to Amphibolite facies conditions. Therefore, it is necessary to testify the validity of pillow chemistry from recent (Phanerozoic) metamorphosed greenstone. We have systematically collected pillowed greenstone from blueschist and eclogites. Two eclogite exhibiting pillow structures were chosen for oxygen and hydrogen isotope analysis. One is from Corsica (lawsonite eclogite collected with Dr. Alberto Vidale Barbarone) and another is from Cazadero, Franciscan belt (collected by Dr. Tatsuki Tsujimori). The both are ascribed as MORB from major and trace bulk chemistry and Ca is rich in the core and Na is poor in the rims. The former exhibits garnet, omphacite, lawsonite, and glacophane. Phengite is in core of the pillow and chlorite is in the rims. In the latter, besides garnet, omphacite, epdiote and glaucophane, chlorite is recognized with phengite in the core. Glaucophane is richer in the rims from the both samples, therefore istope analysis of glaucophane was done. Mineral separation was carefully done using micro-mill, heavy liquid and isodynamic separator. 20 mg specimens were used for oxygen isotope analysis and 2mg were for hydrogen analysis. δ18O of the all analysis (7.7 to 8.3) is within the range of unaltered igneous oceanic crust and high temperature hydrothermal alteration although rims (8.3 for Franciscan and 8.0 for Corsica) are higher than cores (7.7 for Franciscan and Corsica). δD data is also consistent with hydrothermal alteration. It is relative higher in core from the Corsica and Franciscan (-45 and -56) than of the rims (-49 and -57, respectively), suggesting dehydration in deep subduction zone.

  19. Late Quaternary sediment deposition of core MA01 in the Mendeleev Ridge, the western Arctic Ocean: Preliminary results

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

    2014-05-01

    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.

  20. Pliocene stratigraphy and the impact of Panama uplift on changes in Caribbean and tropical east Pacific upper ocean stratification (6 - 2.5 Ma).

    Steph, Silke

    2005-01-01

    This thesis examines the closure history of the Central American Seaway (CAS) and its effect on changes in ocean circulation and climate during the time interval from ~6 – 2.5 Ma. It was accomplished within the DFG Research Unit "Impact of Gateways on Ocean Circulation, Climate and Evolution" at the University of Kiel. Proxy records from Ocean Drilling Program (ODP) Sites 999 and 1000 (Caribbean), and from ODP Sites 1237, 1239 and 1241 (low-latitude east Pacific) are developed and examined. I...

  1. Long-distance fluid and heat transport in the oceanic crust entering the Nankai subduction zone, NanTroSEIZE transect

    Spinelli, Glenn A.

    2014-03-01

    I examine the potential causes of anomalous seafloor heat flux on the oceanic plate in the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) transect offshore southern Japan. The most prominent anomaly is a 50 mW m change in heat flux between Integrated Ocean Drilling Program Sites C0011 and C0012 over a distance of process in the shallow subsurface; variations in heat input from ?5 km depth would generate a >30 km wide transition at the seafloor. The observed surface heat flux pattern is indicative of hydrothermal circulation in the basement aquifer and advection of heat from the subducted crust into the aquifer on the incoming plate. For a 600 m thick aquifer, the permeability is likely ?710-11 m, and hydrothermal circulation transports at least 300 times more heat than conduction alone. The heat flux from the subduction zone seaward to the incoming plate is consistent with hydrothermal circulation in the subducting crust persisting to 100 km landward of the deformation front. Vigorous fluid circulation in the basaltic basement is consistent with both the seafloor thermal anomalies and geochemical anomalies near the sediment-basement interface.

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

    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. 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

    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

    2001-09-01

    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)

  4. Oxygen consumption rates in subseafloor basaltic crust derived from a reaction transport model.

    Orcutt, Beth N; Wheat, C Geoffrey; Rouxel, Olivier; Hulme, Samuel; Edwards, Katrina J; Bach, Wolfgang

    2013-01-01

    Oceanic crust is the largest potential habitat for life on Earth and may contain a significant fraction of Earth's total microbial biomass; yet, empirical analysis of reaction rates in basaltic crust is lacking. Here we report the first assessment of oxygen consumption in young (~8?Ma) and cool (strontium pore water gradients in basal sediments collected during Integrated Ocean Drilling Program Expedition 336 to 'North Pond' on the western flank of the Mid-Atlantic Ridge. Dissolved oxygen is completely consumed within the upper to middle section of the sediment column, with an increase in concentration towards the sediment-basement interface, indicating an upward supply from oxic fluids circulating within the crust. A parametric reaction transport model of oxygen behaviour in upper basement suggests oxygen consumption rates of 1?nmol? cm(-3)ROCK d(-1) or less in young and cool basaltic crust. PMID:24071791

  5. BATOLITO DE SABANALARGA, PLUTONISMO DE ARCO EN LA ZONA DE SUTURA ENTRE LAS CORTEZAS OCENICA Y CONTINENTAL DE LOS ANDES DEL NORTE / THE SABANALARGA BATHOLITH, ARC PLUTONISM IN THE SUTURE ZONE BETWEEN CONTINENTAL AND OCEANIC CRUST IN THE NORTHERN ANDES

    GABRIEL, RODRGUEZ G.; MARA ISABEL, ARANGO; JOS GILBERTO, BERMDEZ.

    2012-12-01

    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 Formacin Barroso y las Diabasas de San Jos de Urama y en el borde oriental las rocas metamrficas del Complejo Cajamarca. El Batol [...] ito de Sabanalarga est formado por al menos dos pulsos magmticos: uno inicial representado por gabros y dioritas de afinidad subalcalina toletica y un segundo pulso constituido por cuarzodioritas y tonalitas de afinidad subalcalina de la serie calcoalcalina baja en K. El magmatismo se gener en un ambiente localizado por encima de la zona de subduccin, en un arco volcnico plutnico localizado en el borde de sutura entre la corteza continental y la corteza ocenica, afectando ambas cortezas. Hace parte del arco las rocas volcnicas de la Formacin Barroso. La edad del Batolito y del arco en general, en concordancia con los datos radiomtricos, las relaciones intrusivas y el registro fsil, ocurri dentro del rango comprendido entre el Cenomaniano-Aptiano superior, localizndose 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 Antioqueo, es contemporneo con el arco que gener el Batolito de Sabanalarga, pudiendo ser parte del mismo evento magmtico. 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.

  6. Insights into Oceanic Crust Accretion from a Comparison of Rock Magnetic and Silicate Fabrics from Lower Crustal Gabbros from Hess Deep Rift

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

    2014-12-01

    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.

  7. Motion between the Indian, Capricorn and Somalian plates since 20 Ma: implications for the timing and magnitude of distributed lithospheric deformation in the equatorial Indian ocean

    DeMets, Charles; Gordon, Richard G.; Royer, Jean-Yves

    2005-05-01

    Approximately 2200 magnetic anomaly crossings and 800 fracture zone crossings flanking the Carlsberg ridge and Central Indian ridge are used to estimate the rotations of the Indian and Capricorn plates relative to the Somalian Plate for 20 distinct points in time since 20 Ma. The data are further used to place limits on the locations of the northern edge of the rigid Capricorn Plate and of the southern edge of the rigid Indian Plate along the Central Indian ridge. Data south of and including fracture zone N (the fracture zone immediately south of the Vema fracture zone), which intersects the Central Indian ridge near 10°S, are well fit assuming rigid Capricorn and Somalian plates, while data north of fracture zone N are not, in agreement with prior results. Data north of fracture zone H, which intersects the Central Indian ridge near 3.2°S, are well fit assuming rigid Indian and Somalian plates, while data south of and including fracture zone H are not, resulting in a smaller rigid Indian Plate and a wider diffuse oceanic plate boundary than found before. The data are consistent with Capricorn-Somalia motion about a fixed pole since ~8 Ma, but require rotation about a pole 15° farther away from the Central Indian ridge from 20 to ~8 Ma. The post-8-Ma pole also indicates Capricorn-Somalia displacement directions that are 7° clockwise of those indicated by the pre-8-Ma stage pole. In contrast, India-Somalia anomaly and fracture crossings are well fit by a single fixed pole of rotation for the past 20 Ma. India-Somalia motion has changed little during the past 20 Myr. Nonetheless, astronomically calibrated ages for reversals younger than 12.9 Ma allow resolution of the following small but significant changes in spreading rate: India-Somalia spreading slowed from 31 to 28 mm yr-1 near 7.9 Ma and later sped up to 31 mm yr-1 near 3.6 Ma; Capricorn-Somalia spreading slowed from 40 to 36 mm yr-1 near 11.0 Ma, later sped up to 38 mm yr-1 near 5.1 Ma and further sped up to 40 mm yr-1 near 2.6 Ma. The motion between the Indian and Capricorn plates is estimated by differencing India-Somalia and Capricorn-Somalia rotations, which differ significantly for all 20 pairs of reconstructions. India has rotated relative to the Capricorn Plate since at least ~20 Ma. If about a pole located near 4°S, 75°E, the rate of rotation was slow, 0.11°+/- 0.01° Myr-1 (95 per cent confidence limits), from 20 to 8 Ma, but increased to 0.28°+/- 0.01° Myr-1 (95 per cent confidence limits) at ~8 Ma. The onset of more rapid rotation coincides, within uncertainty, with the inferred onset at 7-8 Ma of widespread thrust faulting in the Central Indian basin, and with the hypothesized attainment of maximum elevation and initiation of collapse of the Tibetan plateau at ~8 Ma. The plate kinematic data are consistent with steady India-Capricorn motion since 8 Ma and provide no evidence for previously hypothesized episodic motions during that interval. The convergence since 8 Ma between the Indian and Capricorn plates significantly exceeds (by 13 to 20 km) the convergence estimated from three north-south marine seismic profiles in the Central Indian basin. Where and how the additional convergence was accommodated is unclear.

  8. A documentation on burrows in hard substrates of ferromanganese crusts and associated soft sediments from the Central Indian Ocean

    Banerjee, R.

    COMMUNICATIONS CURRENT SCIENCE, VOL. 79, NO. 4, 25 AUGUST 2000 517 A documentation on burrows in hard substrates of ferromanganese crusts and associated soft sediments from the Central Indian Basin Ranadip Banerjee Geological Oceanography Division... (Figure 3 a?g). Among the ob- served relict burrow features, at least in one of the semiconsolidated claystone substrates, which appears to RESEARCH COMMUNICATIONS CURRENT SCIENCE, VOL. 79, NO. 4, 25 AUGUST 2000 Figure 1. Detailed bathymetry...

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

    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 60Fe (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.

  10. Double-layer structure of the crust beneath the Zhongdian arc, SW China: U-Pb geochronology and Hf isotope evidence

    Cao, Kang; Xu, Ji-Feng; Chen, Jian-Lin; Huang, Xiao-Xiao; Ren, Jiang-Bo; Zhao, Xiang-Dong; Liu, Zhen-Xing

    2016-01-01

    U-Pb ages and Hf isotopes of zircons in Late Triassic and Cretaceous intrusive rocks from the Zhongdian arc, SW China, are used to decipher the tectonic, magmatic, and metallogenic processes that occurred during this period. New U-Pb dating of zircons from Late Triassic porphyries yielded ages of ca. 216 Ma and εHf(t) values of -2.1 to +6.1. Combined with previous results, the data indicate that these Late Triassic rocks were most likely derived from a juvenile mafic lower-crust with minor old crust material. However, the Cretaceous granites (∼80 Ma) have lower εHf(t) values (-7.6 to -2.4) than the Late Triassic rocks, indicating that the former originated from old crust. Based on the new data and previous studies of Mesozoic magmatic activity, a plausible model for the tectono-magmatism and metallogenesis of the Zhongdian arc is proposed. The westwards subduction of the Ganzi-Litang oceanic crust began before ∼230 Ma, resulting in the formation of a juvenile lower crust beneath the Zhongdian arc due to the underplating of mafic arc magmas during ca. 230-216 Ma. At ca. 216 Ma, break-off or slab-tearing of the west-dipping Ganzi-Litang oceanic slab led to partial melting of the juvenile lower crust, which gave rise to Cu-bearing porphyries. In the Late Cretaceous, the Zhongdian arc probably underwent post-collision extension, triggering the partial melting of the old middle-upper crustal materials and producing various granites and related Mo-Cu deposits. According to this model, the crust beneath the Zhongdian arc probably has a double-layer structure, with older crust at shallow levels and juvenile crust at deeper levels.

  11. Evolution of biogeochemical cycling of phosphorus during 45~50 Ma revealed by sequential extraction analysis of IODP Expedition 302 cores from the Arctic Ocean

    Hashimoto, S.; Yamaguchi, K. E.; Takahashi, K.

    2012-12-01

    The modern Arctic Ocean plays crucial roles in controlling global climate system with the driving force of global thermohaline circulation through the formation of dense deep water and high albedo due to the presence of perennial sea-ice. However, the Arctic sea-ice has not always existed in the past. Integrated Ocean Drilling Program (IODP) Expedition 302 Arctic Coring Expedition (ACEX) has clarified that global warming (water temperature: ca. 14~16?C) during 48~49 Ma Azolla Event induced the loss of sea-ice and desalination of surface ocean, and that sea-ice formed again some million years later (45 Ma). In the Arctic Ocean, warming and cooling events repeated over and over (e.g., Brinkhuis et al., 2006; Moran et al., 2006; Mrz et al., 2010). Large variations in the extent of thermohaline circulation through time often caused stagnation of seawater and appearance of anaerobic environment where hydrogen sulfide was produced by bacterial sulfate reduction. Ogawa et al. (2009) confirmed occurrence of framboidal pyrite in the ACEX sediments, and suggested that the Arctic Ocean at the time was anoxic, analogous to the modern Black Sea, mainly based on sulfur isotope analysis. To further clarify the variations in the nutrient status of the Arctic Ocean, we focus on the geochemical cycle of phosphorus. We performed sequential extraction analysis of sedimentary phosphorus in the ACEX sediments, using the method that we improvped based on the original SEDEX method by Ruttenberg (1992) and Schenau et al. (2000). In our method, phosphorus fractions are divided into five forms; (1) absorbed P, (2) Feoxide-P, (4) carbonate fluorapatite (CFAP) + CaCO3-P + hydroxylapatite (HAP), (4) detrital P, and (5) organic P. Schenau et al. (2000) divided the (3) fraction into non-biological CFAP and biological HAP and CaCO3-P. When the Arctic Ocean was closed and in its warming period, the water mass was most likely stratified and an anaerobic condition would have prevailed where bacterial sulfate reduction was active. In this case, most of the phosphorus in sediment was stored as organic P, which was originally derived as sinking particles of detrital plankton from the surface ocean. Increased rainfalls during such a warming period would have enhanced continental weathering and delivery of phosphorus to the surface ocean, and biological activity using increased amounts of phosphorus supply would also have increased. Feoxide-P is considered to be less important as a sink for phosphorus because of the likely formation of pyrite through the reductive dissolution of Fe oxide. CFAP could be a sink for phosphorus, because the formation of CFAP tends to increase with increasing age and depth.

  12. Barium geochemistry in sediment pore waters and formation waters of the oceanic crust on the eastern flank of the Juan de Fuca Ridge (ODP Leg 168)

    Monnin, Christophe; Wheat, C. Geoffrey; Dupre, Bernard; Elderfield, Henry; Mottl, Mike M.

    2001-01-01

    Sediment pore waters collected on the eastern flank of the Juan de Fuca Ridge at 10 sites drilled during Ocean Drilling Program (ODP) Leg 168 and basement fluids discharging at the seafloor on a basaltic outcrop called Baby Bare located at 100 km east of the Juan de Fuca Ridge were analyzed for barium. The data show an overall symmetrical behavior between Ba and sulfate, suggesting that the pore water Ba content is controlled by equilibrium with barium sulfate. Barite saturation indices calculated with a thermodynamic model of the Na-K-Ca-Mg-Ba-Sr-Cl-SO4-H2O system show that barite does not equilibrate with the pore waters at the shipboard conditions (20C, 1 bar) but reflects an overall equilibrium between pore waters and barite at in situ temperatures and pressures, for depths below 20 m below the seafloor. Barite supersaturation is found for conditions in the upper 20 m of the sediment column. Ba concentrations in pore waters at the base of the sediment section exceed those in the underlying formation fluids, based on the direct sampling of these fluids in the open borehole at ODP Sites 1026 and the hydrothermal springs at Baby Bare. This suggests that Ba is supplied to basement by the sediment. Despite this, the formation fluids are undersaturated with respect to barite. These fluids, which contain 2-3 times more Ba than bottom seawater, vent at the seafloor resulting in a net flux of Ba to bottom seawater. The calculated flux from warm (63C) ridge flank hydrothermal systems is insignificant to the oceanic budget for Ba, but the flux associated from cool (less than 25C) ridge flank hydrothermal systems, which dispense most of the heat and fluid flux through the oceanic crust, is unconstrained.

  13. The Archean Dongwanzi ophiolite complex, North China craton: 2.505-billion-year-old oceanic crust and mantle.

    Kusky, T M; Li, J H; Tucker, R D

    2001-05-11

    We report a thick, laterally extensive 2505 +/- 2.2-million-year-old (uranium-lead ratio in zircon) Archean ophiolite complex in the North China craton. Basal harzburgite tectonite is overlain by cumulate ultramafic rocks, a mafic-ultramafic transition zone of interlayered gabbro and ultramafic cumulates, compositionally layered olivine-gabbro and pyroxenite, and isotropic gabbro. A sheeted dike complex is rooted in the gabbro and overlain by a mixed dike-pillow lava section, chert, and banded iron formation. The documentation of a complete Archean ophiolite implies that mechanisms of oceanic crustal accretion similar to those of today were in operation by 2.5 billion years ago at divergent plate margins and that the temperature of the early mantle was not extremely elevated, as compared to the present-day temperature. Plate tectonic processes similar to those of the present must also have emplaced the ophiolite in a convergent margin setting. PMID:11349144

  14. Crusted scabies

    Karthikeyan Kaliaperumal

    2009-01-01

    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,...

  15. Canterbury Drifts at Ocean Drilling Program Site 1119, New Zealand: Climatic modulation of southwest Pacific intermediate water flows since 3.9 Ma

    Carter, R. M.; Fulthorpe, C. S.; Lu, H.

    2004-11-01

    We provide a record of variations in southwest Pacific Ocean intermediate water flow that shows a strong correlation between periods of vigorous flow and warm climate phases. Ocean Drilling Program Site 1119, located at 395 m water depth on the upper continental slope east of New Zealand, penetrated 514 m of silts and silty clays (glacial deposits) punctuated by muds and episodic 0.02 1.2-m-thick terrigenous sands (interglacial deposits). The natural gamma-ray record reflects the waxing and waning of the South Island ice cap since 3.91 Ma. Below 86.19 m composite depth, the succession comprises drift sediments deposited from north-flowing intermediate Subantarctic Mode Water (SAMW, ˜250 800 m depth) and Antarctic Intermediate Water (˜800 1100 m depth). A change from the deposition of large, low-energy drifts on the middle slope to smaller, higher-energy drifts on the upper slope coincided with global climatic deterioration that occurred after ca. 3.25 Ma. This change marks an upward expansion of intermediate cold waters, perhaps caused by the inception of the Subantarctic Front and the consequent commencement of Southland Current driven SAMW flow.

  16. Tectonic implications of post-30 Ma Pacific and North American relative plate motions

    Bohannon, R.G.; Parsons, T.

    1995-01-01

    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

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

    R Keith O'Nions; Martin Frank

    2000-03-01

    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.

  18. Subduction-modified oceanic crust mixed with a depleted mantle reservoir in the sources of the Karoo continental flood basalt province

    Heinonen, Jussi S.; Carlson, Richard W.; Riley, Teal R.; Luttinen, Arto V.; Horan, Mary F.

    2014-05-01

    The great majority of continental flood basalts (CFBs) have a marked lithospheric geochemical signature, suggesting derivation from the continental lithosphere, or contamination by it. Here we present new Pb and Os isotopic data and review previously published major element, trace element, mineral chemical, and Sr and Nd isotopic data for geochemically unusual mafic and ultramafic dikes located in the Antarctic segment (Ahlmannryggen, western Dronning Maud Land) of the Karoo CFB province. Some of the dikes show evidence of minor contamination with continental crust, but the least contaminated dikes exhibit depleted mantle - like initial ɛNd (+9) and 187Os/188Os (0.1244-0.1251) at 180 Ma. In contrast, their initial Sr and Pb isotopic compositions (87Sr/86Sr = 0.7035-0.7062, 206Pb/204Pb = 18.2-18.4, 207Pb/204Pb = 15.49-15.52, 208Pb/204Pb = 37.7-37.9 at 180 Ma) are more enriched than expected for depleted mantle, and the major element and mineral chemical evidence indicate contribution from (recycled) pyroxenite sources. Our Sr, Nd, Pb, and Os isotopic and trace element modeling indicate mixed peridotite-pyroxenite sources that contain ˜10-30% of seawater-altered and subduction-modified MORB with a recycling age of less than 1.0 Ga entrained in a depleted Os-rich peridotite matrix. Such a source would explain the unusual combination of elevated initial 87Sr/86Sr and Pb isotopic ratios and relative depletion in LILE, U, Th, Pb and LREE, high initial ɛNd, and low initial 187Os/188Os. Although the sources of the dikes probably did not play a major part in the generation of the Karoo CFBs in general, different kind of recycled source components (e.g., sediment-influenced) would be more difficult to distinguish from lithospheric CFB geochemical signatures. In addition to underlying continental lithosphere, the involvement of recycled sources in causing the apparent lithospheric geochemical affinity of CFBs should thus be carefully assessed in every case.

  19. Recycling of oceanic crust from a stagnant slab in the mantle transition zone: Evidence from Cenozoic continental basalts in Zhejiang Province, SE China

    Li, Yan-Qing; Ma, Chang-Qian; Robinson, Paul T.; Zhou, Qin; Liu, Ming-Liang

    2015-08-01

    Cenozoic continental basalts from Zhejiang Province, southeast China are tholeiitic to weakly alkalic in composition, with moderate MgO contents (6-11 wt.%) and an average Mg# of 62. They display typical OIB-like trace element features, including enrichment in most incompatible elements, both LILE and LREE, and negative K, Pb, Zr, Hf anomalies. In particular, they are characterized by high Fe/Mn (73 ± 5), La/Yb (19 ± 6) and Nb/Ta (18.8 ± 0.4) ratios, which can be attributed to the presence of residual clinopyroxene, garnet and rutile in the mantle source. Based on these minerals, the following hybrid source rocks are hypothesized: garnet pyroxenite/eclogite and peridotite. Clinopyroxene-liquid thermobarometry indicates clinopyroxene crystallization temperatures of > 1257 °C. This is higher than the assumed temperature at the base of the sub-continental lithospheric mantle (SCLM) (~ 1220 °C) beneath Zhejiang, thus the magmas were presumably derived from the asthenosphere. Some typical geochemical features such as negative K, Pb anomalies, positive Ba, Sr, Nb, Ta anomalies and the extremely high Os isotopic signatures, suggest participation of EM-like mantle sources, indicative of ancient subducted oceanic crust. (87Sr/86Sr)i (0.7037-0.7046) and 143Nd/144Nd (0.512832-0.512990) isotope ratios point to the presence of mixed components in the source region, i.e., DMM, EM1 and EM2. Recent seismic tomographic images of the mantle beneath Zhejiang suggest the presence of a subducted slab of oceanic lithosphere in the transition zone. Based on the combined geophysical and geochemical evidence, we propose that the major source of the Zhejiang basaltic magmas was the ancient subducted oceanic slab in the transition zone with an EM-like signature. The other magma sources include depleted asthenospheric peridotite possessing a DMM-like signature. The dynamics of this upwelling hybrid magma was apparently related to westward subduction of the Pacific plate underneath the eastern Asian continent. This process may have triggered the widespread Cenozoic volcanism related to the lithospheric thinning in East China in the Mesozoic and Cenozoic.

  20. High-resolution grain size analysis and its significance for detecting ocean acidification at the onset of the Paleocene-Eocene Thermal Maximum (PETM; 55Ma) (Invited)

    Bralower, T. J.; Kump, L.; Eccles, L.; Smith, G. J.; Lindemann, T. L.; Bowen, G. J.; Schneider Mor, A.; Thomas, E.

    2010-12-01

    The Paleocene-Eocene Thermal Maximum (PETM; 55Ma) is widely considered a close ancient analog to modern global warming. A host of recent investigations have elucidated the scale and nature of the climate forcing during the PETM, as well as the range of atmospheric, oceanographic and biotic impacts. Introduction of massive amounts of greenhouse gases into the ocean-atmosphere system at the onset of the event is known to have led to abrupt shoaling of the lysocline and calcite compensation depth in the oceans as observed at deep-sea locations by a marked increase in the dissolution of calcareous microfossils and correspondingly sharp lithologic changes. The occurrence of surface ocean acidification during the initial stages of the PETM is not documented largely because the potential evidence is overprinted by pervasive dissolution at the sea floor. We present detailed grain size analysis from a high-resolution sample set across the PETM at Ocean Drilling Program Sites 690 (Maud Rise, Southern Ocean), 1209 (Shatsky Rise, Pacific Ocean) and 1262 (Walvis Ridge, South Atlantic Ocean) and at the Wilson Lake drill hole from the New Jersey coastal plain. The Wilson Lake section is dominated by clastic material, thus samples were processed to obtain the grain size distribution of the carbonate fraction. Grain size data were collected using a Malvern Mastersizer, an instrument that optically measures particle size between 0.1 and 1000 micrometer in diameter. The results show dramatic differences is size trends between sites that are consistent with their depths with respect to the CCD and lysocline. At the same time, the base of the PETM is characterized by very sharp changes in grain size distribution at Site 1262, where dissolution is most severe and progressively less abrupt changes at Site 1209, Site 690 and Wilson Lake. This progression is consistent with known differences in the magnitude of the lysocline and CCD shoaling at these sites. Comparison of grain size, carbonate and stable isotope data produces more accurate estimates of the depth of carbonate “burn down” at Sites 1209 and 1262. At the other sites, comparison of nannofossil and benthic foraminiferal preservation across the base of the PETM allows us to evaluate whether there was a brief period of surface-water acidification prior to the onset of deep-water acidification. For all sites, grain size data provide more quantitative estimates of the changes in flux of planktonic foraminifera and nannoplankton during the course of the PETM. Nannoplankton dominate the carbonate flux at all sites except Site 690 where the event is marked by complex pattern of variation in foraminiferal flux.

  1. Preservation and Recycling of Crust during Accretionary and Collisional Phases of Proterozoic Orogens: A Bumpy Road from Nuna to Rodinia

    Kent C. Condie

    2013-05-01

    Full Text Available Zircon age peaks at 2100–1650 and 1200–1000 Ma correlate with craton collisions in the growth of supercontinents Nuna and Rodinia, respectively, with a time interval between collisions mostly <50 Myr (range 0–250 Myr. Collisional orogens are two types: those with subduction durations <500 Myr and those ≥500 Myr. The latter group comprises orogens with long-lived accretionary stages between Nuna and Rodinia assemblies. Neither orogen age nor duration of either subduction or collision correlates with the volume of orogen preserved. Most rocks preserved date to the pre-collisional, subduction (ocean-basin closing stage and not to the collisional stage. The most widely preserved tectonic setting in Proterozoic orogens is the continental arc (10%–90%, mean 60%, with oceanic tectonic settings (oceanic crust, arcs, islands and plateaus, serpentinites, pelagic sediments comprising <20% and mostly <10%. Reworked components comprise 20%–80% (mean 32% and microcratons comprise a minor but poorly known fraction. Nd and Hf isotopic data indicate that Proterozoic orogens contain from 10% to 60% of juvenile crust (mean 36% and 40%–75% reworked crust (mean 64%. Neither the fraction nor the rate of preservation of juvenile crust is related to the collision age nor to the duration of subduction. Regardless of the duration of subduction, the amount of juvenile crust preserved reaches a maximum of about 60%, and 37% of the volume of juvenile continental crust preserved between 2000 and 1000 Ma was produced in the Great Proterozoic Accretionary Orogen (GPAO. Pronounced minima occur in frequency of zircon ages of rocks preserved in the GPAO; with minima at 1600–1500 Ma in Laurentia; 1700–1600 Ma in Amazonia; and 1750–1700 Ma in Baltica. If these minima are due to subduction erosion and delamination as in the Andes in the last 250 Myr; approximately one third of the volume of the Laurentian part of the GPAO could have been recycled into the mantle between 1500 and 1250 Ma. This may have enriched the mantle wedge in incompatible elements and water leading to the production of felsic magmas responsible for the widespread granite-rhyolite province of this age. A rapid decrease in global Nd and in detrital zircon Hf model ages between about 1600 and 1250 Ma could reflect an increase in recycling rate of juvenile crust into the mantle; possibly in response to partial fragmentation of Nuna.

  2. From continent to intra-oceanic arc: zircon xenocrysts record the crustal evolution of the Solomon island arc

    Tapster, Simon; Roberts, N.M.W.; Petterson, M.G; Saunders, A.D.; Naden, J.

    2014-01-01

    The first U-Pb ages from a ca. 26–24 Ma pluton on Guadalcanal, in the intra-oceanic Solomon island arc (southwest Pacific Ocean), reveal Eocene- to Archean-aged zircon xenocrysts. Xenocryst populations at ca. 39–33 Ma and ca. 71–63 Ma correlate with previously obtained ages of supra-subduction magmatism within the arc. A ca. 96 Ma zircon population may be derived from Cretaceous ophiolite basement crust or region-wide continental rift-related magmatism. Xenocryst age populations alternate wit...

  3. Refertilization of mantle peridotite in embryonic ocean basins: trace element and Nd isotopic evidence and implications for crust-mantle relationships

    Mntener, Othmar; Pettke, Thomas; Desmurs, Laurent; Meier, Martin; Schaltegger, Urs

    2004-04-01

    Many mantle peridotites exhumed along ancient and present-day magma-poor passive continental margins, along (ultra-) slow spreading ridges and fracture zones are plagioclase-bearing and generally too fertile to be the residue of partial melting processes alone. Likewise, the associated gabbroic and basaltic rocks are not a priori genetically linked to the underlying mantle rocks. Trace element and Nd isotopic studies in the eastern Central Alps peridotites in eastern Switzerland and northern Italy provide evidence for near-fractional melting and depletion at high pressure in Permian time followed by refertilization of subcontinental mantle by ascending melts at low pressure in Jurassic time. These results suggest regional-scale modification of ancient subcontinental mantle by melt infiltration and melt-rock reaction during incipient opening of oceanic basins. The similar Nd isotopic composition of plagioclase peridotite (?Nd 160: 7.4-10.6) and associated mafic crust (?Nd 160: 7.3-9.6) indicates that the liquids, which reacted with the peridotites derived from similar N-MORB type mantle sources. Plagioclase peridotites in magma-poor passive margins may predominantly form as a consequence of diffuse porous flow of melt in the thermal boundary layer above an upwelling asthenosphere and probably represent modified ancient subcontinental mantle. Thus, plagioclase peridotites exhumed in passive margins and possibly in (ultra-) slow spreading ridges may represent magma-poor periods where liquids stagnate in the thermal boundary layer and react with the surrounding peridotites. Once the effects of conductive heat loss dominate over advection of heat from below, diffuse porous flow of melt becomes less important and might be replaced by the formation of gabbro bodies.

  4. Widely distributed thrust and strike-slip faults within subducting oceanic crust in the Nankai Trough off the Kii Peninsula, Japan

    Tsuji, Takeshi; Kodaira, Shuichi; Ashi, Juichiro; Park, Jin-Oh

    2013-07-01

    We identified widely distributed thrust and strike-slip faults within subducting oceanic crust in the Nankai Trough, southeast of the Kii Peninsula, Japan, on the basis of 2D and 3D seismic reflection data. The seafloor seaward of the trough axis is deformed by displacement on these intraoceanic reverse faults, producing topographic highs (part of Kashinosaki Knoll). Because the thrust faults extend to the Moho and offset the Moho reflection, they may be related to serpentinization of the mantle due to seawater invasion. These faults are seismically active, given that their geometries are consistent with the focal mechanisms of intraplate earthquakes and microearthquakes. The thrust faults appear to extend landward to a high-density dome within the accretionary prism off the Kii Peninsula. Because the dome and the associated thick accretionary prism are expected to generate high friction at the plate interface due to their large vertical load, the intraoceanic thrusts are likely to have grown with ongoing subduction. Furthermore, because the geometry of the fault system we identified off the Kii Peninsula has characteristics similar to faults at Zenisu Ridge east of our study area, the thrusts observed in the study area may be considered to be the westward continuation of those at Zenisu Ridge. Since the Euler rotation pole of relative motion between the Philippine Sea plate and Zenisu Ridge is consistent with the high-density dome off the Kii Peninsula, we interpret the high-density dome as well as Kashinosaki Knoll as a westward termination of the Zenisu compression zone.

  5. Recycled oceanic crust and marine sediment in the source of alkali basalts in Shandong, eastern China: Evidence from magma water content and oxygen isotopes

    Liu, Jia; Xia, Qun-Ke; Deloule, Etienne; Chen, Huan; Feng, Min

    2015-12-01

    The magma water contents and cpx δ18O values in alkali basalts from the Fuyanyshan (FYS) volcano in Shandong, eastern China, were investigated by an inverse calculation based on the water content of clinopyroxene (cpx) phenocrysts, the ivAlcpx-dependent water partitioning coefficient Dwatercpx>/melt, and secondary ion mass spectrometer, respectively. The calculated water content (H2O wt.) of magma ranges from 0.58% to 3.89%. It positively correlates with heavy rare earth element concentrations and bulk rock 87Sr/86Sr ratios, and it negatively correlates with Nb/U ratios. However, it is not correlated with bulk Mg# (Mg# = 100 × Mg / (Mg + Fe)) and (La/Yb)n (n represents primitive mantle normalization). Combined with the rather homogenous distribution of water content within cpx grains, these correlations indicate that the water variations among different samples represent the original magma signature, rather than results of a shallow process, such as degassing and diffusion. The δ18O of cpx phenocrysts varies from 3.6‰ to 6.3‰ (±0.5‰, 2SD), which may be best explained by the involvement of components from the lower and upper oceanic crust with marine sediments within the mantle source. The H2O/Ce ratios of the calculated melts range from 113 to 696 and form a positive trend with bulk rock 87Sr/86Sr, which cannot be explained by the recycled Sulu eclogite or by the metasomatized lithospheric mantle. Our modeling calculation shows that the decoupling of ɛHf and ɛNd could be caused by the involvement of marine sediments. Combing the high Ba/Th ratios, positive Sr spikes, and low Ce/Pb ratios for the Fuyanshan basalts, we suggest that the hydrous nature of the FYS basalts was derived from the hydrous mantle transition zone with ancient sediments.

  6. Microstructures and petro-fabrics of lawsonite blueschist in the North Qilian suture zone, NW China: Implications for seismic anisotropy of subducting oceanic crust

    Cao, Yi; Jung, Haemyeong; Song, Shuguang

    2014-07-01

    We conducted a detailed study on the microstructures and petro-fabrics of massive and foliated lawsonite blueschist (LBS) in North Qilian suture zone, NW China. The lattice preferred orientation (LPO) of glaucophane and lawsonite in foliated lawsonite blueschist (LBS) is considered to be dominantly formed by the deformation mechanism of dislocation creep and rigid-body rotation, respectively. The LPO of glaucophane is mainly characterized by the [001] axis aligning parallel to lineation and the [100] axis and (110) pole plunging perpendicular to foliation. In contrast, the LPO of lawsonite features the maximum [010] axis concentrated close to lineation and the [001] axis strongly clustered normal to foliation. The preferred orientation of [010] axis of lawsonite parallel to lineation is supported by a two-dimensional numerical modeling using the finite-volume method (FVM). The mineral LPOs are much stronger in foliated LBS than in massive LBS. In addition, a kinematic vorticity analysis suggests that both pure shear dominant (Wm = 0.18-0.26) and simple shear dominant (Wm = 0.86-0.93) deformation regimes are present in foliated LBS. The [001] axis and (010) pole of glaucophane, and the [100] and [010] axes of lawsonite, tend to distribute in a foliation-parallel girdle in the pure shear dominant samples, but simple shear dominant samples display more lineation-parallel concentrations of a [001] axis of glaucophane and a [010] axis of lawsonite. Because the whole-rock seismic anisotropies in foliated LBS are significantly higher than those in massive LBS and a counteracting effect on seismic anisotropies occurs between glaucophane and lawsonite, the delay time of fast S-wave polarization anisotropy induced by an actual subducting oceanic crust with a high subducting angle (> 45-60°) is expected to range from 0.03 to 0.09 s (lower bound for massive LBS) and from 0.1 to 0.3 s (upper bound for foliated epidote blueschist).

  7. Birth of an ocean in the Red Sea: Initial pangs

    Ligi, M.; CNR-ISMAR Bologna; Bonatti, E.; CNR-ISMAR Bologna; Bortoluzzi, G.; CNR-ISMAR Bologna; Cipriani, A.; CNR-ISMAR Bologna; Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Caratori Tontini, F.; GNS Science; Carminati, E.; Università di Roma "La Sapienza"; Ottolini, L.; CNR -Pavia; Schettino, A.; Università di Camerino

    2012-01-01

    We obtained areal variations of crustal thickness, magnetic intensity, and degree of melting of the sub- axial upwelling mantle at Thetis and Nereus Deeps, the two northernmost axial segments of initial oceanic crustal accretion in the Red Sea, where Arabia is separating from Africa. The initial emplacement of oceanic crust occurred at South Thetis and Central Nereus roughly $2.2 and $2 Ma, respectively, and is taking place today in the northern Thetis and southern Nereus tips. Basaltic glass...

  8. Interaction between seawater and magma or very hot rock in the deep fast-spreading oceanic crust: Constraints from experimental petrology

    Koepke, J.; Botcharnikov, R. E.; Berndt, J.; Feig, S.; France, L.

    2011-12-01

    More and more publications on the dynamics of magmatic system at fast spreading ridges refer to deep interaction of seawater with magma or with just frozen rocks. Prominent models focus on deep hydrothermal circulation at magmatic temperatures [1], seawater involvement into magmatic processes due to ridge tectonics [2], or on stoping/assimilation of hydrothermally altered dikes at the top of the axial melt lens [3]. In order to understand the underlying hydrous MORB magmatism and the corresponding hydrous melting reactions at fast-spreading ocean ridges, we performed different series of crystallization and partial melting experiments in hydrous MORB-type systems at shallow pressures. (1) To understand the magmatic processes ongoing in the top of the axial melt lenses, we present here new phase diagrams for hydrous MORB systems at a pressure of 50 MPa, by extrapolating results of phase equilibria experiments in hydrous systems performed at shallow pressures in primitive to evolved tholeiitic, MORB-type systems. We applied our new phase diagrams to rocks from the sheeted dike/gabbro transition from the EPR crust (IODP Site 1256D) and from the Oman ophiolite, opening interesting perspectives to explain specific aspects of petrogenesis of these rocks. (2) Experimental hydrous partial melting of gabbro results not only in the production of oceanic plagiogranites, but also in the formation of characteristic interstitial residual parageneses like plagioclase with An-rich rims, orthopyroxene, and pargasitic amphibole rimming the primary phases. Such parageneses can be observed in gabbros from IODP Site 1256D and from the Oman ophiolite, documenting that hydrous partial melting proceeded. (3) Experimental partial melting of hydrated dikes results in the formation of plagiogranitic melts and of a typical residual granoblastic mineral paragenesis. Domains with a characteristic texture (microgranular wormy intergrowth of clino- and orthopyroxene, plagioclase, and oxides) can be observed rather often in Gabbros from IODP Site 1256D, implying that partial melting of stoped hydrated sheeted dikes was a major magmatic process which resulted in locally high water activities enabling primary amphibole crystallization. [1] Nicolas, A., and D. Mainprice (2005), Terra Nova, 17, 326-330. [2] Abily, B., G. Ceuleneer, and P. Launeau (2011), Geology, 39, 391-394. [3] Koepke, J., L. France, T. Mller, F. Faure, N. Goetze, W. Dziony, and B. Ildefonse (2011 accepted), Geochem. Geophys. Geosyst.

  9. Absolute palaeointensity of Oligocene (28-30 Ma) lava flows from the Kerguelen Archipelago (southern Indian Ocean)

    Plenier, G; Coe, R S; Perrin, M; Plenier, Guillaume; Camps, Pierre; Coe, Robert S.; Proxy, Mireille Perrin

    2003-01-01

    We report palaeointensity estimates obtained from three Oligocene volcanic sections from the Kerguelen Archipelago (Mont des Ruches, Mont des Tempetes, and Mont Rabouillere). Of 402 available samples, 102 were suitable for a palaeofield strength determination after a preliminary selection, among which 49 provide a reliable estimate. Application of strict a posteriori criteria make us confident about the quality of the 12 new mean-flow determinations, which are the first reliable data available for the Kerguelen Archipelago. The Virtual Dipole Moments (VDM) calculated for these flows vary from 2.78 to 9.47 10e22 Am2 with an arithmetic mean value of 6.15+-2.1 10e22 Am2. Compilation of these results with a selection of the 2002 updated IAGA palaeointensity database lead to a higher (5.4+-2.3 10e22 Am2) Oligocene mean VDM than previously reported, identical to the 5.5+-2.4 10e22 Am2 mean VDM obtained for the 0.3-5 Ma time window. However, these Kerguelen palaeointensity estimates represent half of the reliable Ol...

  10. Seismic azimuthal anisotropy in the oceanic lithosphere and asthenosphere from broadband surface wave analysis of OBS array records at 60 Ma seafloor

    Takeo, A.; Kawakatsu, H.; Isse, T.; Nishida, K.; Sugioka, H.; Ito, A.; Shiobara, H.; Suetsugu, D.

    2016-03-01

    We analyzed seismic ambient noise and teleseismic waveforms of nine broadband ocean bottom seismometers deployed at a 60 Ma seafloor in the southeastward of Tahiti island, the South Pacific, by the Tomographic Investigation by seafloor ARray Experiment for the Society hotspot project. We first obtained one-dimensional shear wave velocity model beneath the array from average phase velocities of Rayleigh waves at a broadband period range of 5-200 s. The obtained model shows a large velocity reduction at depths between 40 and 80 km, where the lithosphere-asthenosphere boundary might exist. We then estimated shear wave azimuthal anisotropy at depths of 20-100 km by measuring azimuthal dependence of phase velocities of Rayleigh waves. The obtained model shows peak-to-peak intensity of the azimuthal anisotropy of 2%-4% with the fastest azimuth of NW-SE direction both in the lithosphere and asthenosphere. This result suggests that the ancient flow frozen in the lithosphere is not perpendicular to the strike of the ancient mid-ocean ridge but is roughly parallel to the ancient plate motion at depths of 20-60 km. The fastest azimuths in the current asthenosphere are subparallel to current plate motion at depths of 60-100 km. Additional shear wave splitting analysis revealed possible perturbations of flow in the mantle by the hot spot activities and implied the presence of azimuthal anisotropy in the asthenosphere down to a depth of 190-210 km.

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

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

    2005-02-01

    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.

  12. Growth of planetary crusts

    The solid planets and satellites mostly have crusts which differ markedly in composition both from their interior, and from primordial solar nebula composition. Primary crusts, mercury, icy crusts, early intense cratering, Mars, Venus, Ganymede, and tertiary crusts are discussed

  13. Deep seismic reflection images of the Wharton Basin oceanic crust and uppermost mantle offshore Northern Sumatra: Relation with active and past deformation

    Carton, Hélène; Singh, Satish C.; Hananto, Nugroho D.; Martin, James; Djajadihardja, Yusuf S.; Udrekh; Franke, Dieter; Gaedicke, Christoph

    2014-01-01

    present deep seismic reflection images along two profiles collected in 2006 in the Wharton Basin offshore Northern Sumatra. The main profile is located subparallel to the Sumatran trench at a distance of 32-66 km. Faulting of the entire sedimentary section (strike-slip deformation sometimes accompanied by a dip-slip component) is imaged over two fracture zones of the extinct Wharton Spreading Center that prior studies have shown to be reactivated as left-lateral faults. The western fracture zone is associated with a wide region of strong basement topography, a difference in crustal thickness of ~1.5 km, and an age offset of 9 Ma. The epicenters of the 11 April 2012 Mw 8.6 great strike-slip earthquake, its Mw 7.2 foreshock, and Mw 8.2 aftershock align along this major structure > 100 km south of the profile intersection. Our high-quality long-offset seismic reflection data also reveal bright dipping reflections extending down to a maximum of ~24 km into the oceanic mantle (~37 km below sea level). Apparent dips are mostly 25-35°, corresponding to 30-55° along either N-S to NNE-SSW or E-W to WNW-ESE directions, which encompass the directions of plate fabric and nodal planes of the Mw 8.6 event. We suggest that these enigmatic reflections arise from presently inactive dip-slip fault planes reaching for the deepest ones to the base of the brittle layer. Possible origins include extension related to plate bending or an episode of now inactive thrust-type deformation reactivating paleonormal faults, similar to that taking place in the Central Indian Basin.

  14. Dynamical tides in icy satellites with subsurface oceans

    Beuthe, M.; Rivoldini, A.; Trinh, A.; Van Hoolst, T.

    2015-10-01

    Subsurface oceans are a generic feature of large icy bodies, if not now, then at some point in their past evolution. Various datasets already point to the existence of oceans within Europa, Ganymede, Callisto, Titan,Enceladus, and Mimas, while other bodies like Ceres,Pluto, and Triton await their turn. Subsurface oceans partially decouple the crust and thus greatly enhance tidal effect, unless the crust is very thick and hard. Dynamical effects are usually neglected when computing tidal deformations of solid bodies. It is well known,however, that various oscillation modes have a ma- jor impact on tidal dissipation within shallow surface oceans [1]. We show here that the dynamical Love numbers of a non-rotating body exhibit a simple resonant behavior if the ocean is very shallow. We also examine how the resonance is affected by rotation.

  15. Precambrian U-Pb zircon ages in eclogites and garnet pyroxenites from South Brittany (France): An old oceanic crust in the West European Hercynian belt

    U-Pb zircon ages have been determined for tow eclogites from the Vendee and for two garnet pyroxenites from the Baie d'Audierne. In an episodic Pb loss model, the two discordia could give upper intercept ages around 1300-1250 Ma and lower intercepts ages of 436-384 Ma. (orig.)

  16. Cenozoic marine geochemistry of thallium deduced from isotopic studies of ferromanganese crusts and pelagic sediments

    Rehkamper, M.; Frank, M.; Hein, J.R.; Halliday, A.

    2004-01-01

    Cenozoic records of Tl isotope compositions recorded by ferromanganese (Fe-Mn) crusts have been obtained. Such records are of interest because recent growth surfaces of Fe-Mn crusts display a nearly constant Tl isotope fractionation relative to seawater. The time-series data are complemented by results for bulk samples and leachates of various marine sediments. Oxic pelagic sediments and anoxic marine deposits can be distinguished by their Tl isotope compositions. Both pelagic clays and biogenic oozes are typically characterized by ??205Tl greater than +2.5, whereas anoxic sediments have ??205Tl of less than -1.5 (??205Tl is the deviation of the 205Tl/203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 104). Leaching experiments indicate that the high ??205Tl values of oxic sediments probably reflect authigenic Fe-Mn oxyhydroxides. Time-resolved Tl isotope compositions were obtained from six Fe-Mn crusts from the Atlantic, Indian, and Pacific oceans and a number of observations indicate that these records were not biased by diagenetic alteration. Over the last 25 Myr, the data do not show isotopic variations that significantly exceed the range of Tl isotope compositions observed for surface layers of Fe-Mn crusts distributed globally (??205 Tl=+12.8??1.2). This indicates that variations in deep-ocean temperature were not recorded by Tl isotopes. The results most likely reflect a constant Tl isotope composition for seawater. The growth layers of three Fe-Mn crusts that are older than 25 Ma show a systematic increase of ??205Tl with decreasing age, from about +6 at 60-50 Ma to about +12 at 25 Ma. These trends are thought to be due to variations in the Tl isotope composition of seawater, which requires that the oceans of the early Cenozoic either had smaller output fluxes or received larger input fluxes of Tl with low ??205Tl. Larger inputs of isotopically light Tl may have been supplied by benthic fluxes from reducing sediments, rivers, and/or volcanic emanations. Alternatively, the Tl isotope trends may reflect the increasing importance of Tl fluxes to altered ocean crust through time. ?? 2004 Elsevier B.V. All rights reserved.

  17. Genesis and evolution of the upper oceanic crust (ODP-IODP site 1256, East Pacific Rise): inferences from structure and composition of late magmatic veins in a lava pond

    Panseri, M.

    2009-04-01

    A complete intact "in situ" section of upper oceanic crust, from extrusive lavas, through dikes into gabbros has been recently drilled for the first time in a 15 Ma old crust that formed at the East Pacific Rise with a full spreading rate of >200 mm/yr. The study area is ODP-IODP Site 1256 (644.2N, 9156.1W, Pacific Ocean). Holes 1256C and 1256D have been drilled into the basaltic basement during ODP Leg 206, IODP Expeditions 309 and 312. Hole 1256D has been deepened to a depth of ca. 1500 meters below seafloor (mbsf). The upper section of the igneous basement consists of thin (3m). The massive flows include a ponded lava flow, located near the top of both Hole 1256C and 1256D, where it has a thickness of 32m and 74m, respectively. The lava pond is interpreted as a thick lava flow delivered either on-axis or off-axis and accumulated in a topographic depression. Although very close (ca. 30m), the two holes record different structural patterns of the lava pond, probably related to different steps of the lava flow emplacement. In the lava pond, both igneous (magmatic foliation, flow-related folds, late-magmatic veins) and post-magmatic (joints, veins, shear veins, and microfaults) structures were recognized. Late magmatic veins (LMVs), which were identified as primary features typical of the lava pond, are the main goal of this work. Mm-thick LMVs are mainly clustered in the middle (290-300 mbsf in hole 1256C and 282-297 mbsf in hole 1256D) and bottom (312-313 mbsf in hole 1256C and 311-328 mbsf in hole 1256D) parts of the lava pond. Structural measurements on cores suggest that they are mostly gently dipping structures, but we also observed sub-vertical LMVs. At the bottom of the lava pond in hole 1256C, late magmatic veins are often arranged in en echelon arrays and sigmoidal pull aparts, suggesting a syn/post-magmatic shear component. Thin-section observations show that basalt including LMVs consists of plagioclase, clinopyroxene, ilmenite, and spinel. LMVs cutting basalt are filled with quartz, quartz + plagioclase intergrowth showing a granophyric texture, clinopyroxene, ilmenite, spinel, and apatite. Rarely we observed pyrite crystals at the LMV core that cut plagioclase + quartz intergrowth. Quartz + plagioclase intergrowth (with apatite) are also present in the basalt as mm-size interstitial domains or rimming plagioclase (IDs = intergrowth domains). Rare samples display IDs with interstitial K-feldspar growing around plagioclase. LMVs often show sharp contacts with basalt. Plagioclase or pyroxene crystals of the basalt may be fragmented at the contact with LMVs (brittle rheology of basalt). Differently, IDs commonly corrode plagioclase crystals, without fragmentation (ductile rheology). The composition of basalt plagioclase ranges from Ab37 to Ab62, with a main concentration around Ab50. On the contrary, plagioclase in the LMVs intergrowth as well as that in the mm-sized IDs are Na-rich (Ab64-Ab98). Mineral analyses also highlight homogeneous clinopyroxene, spinel and ilmenite, without variations in the LMVs and IDs. Clinopyroxene usually shows a Ca-poor core (mainly augite or pigeonite) and a diopsidic rim. Opaque minerals often exhibit ilmenite-ulvospinel lamellae intergrowths. EDS mapping of IDs and LMVs cutting basalt supports the previous observations. LMVs and IDs have higher Si, Na and lower Al, Ca values than basalt. This distribution is only due to albitic plagioclase concentration in LMVs and IDs. K has low and homogeneous concentrations: rarely IDs are characterized by interstitial K enrichment (K-feldspar). Incompatible (Zr, Rb, Sr, Ba), hydrothermal elements (Cu, Cl), and F are undetectable or absent. We infer that LMVs and IDs likely crystallized from a pure Si-Al-Na-(Ca) melt. K, rarely noticed in the IDs, may be related to late magmatic fluids differentiation or to subsequent hydrothermal fluids. Core description, microstructural observations, mineral compositions and EDS mapping of the studied samples suggest that: - the middle and bottom parts of the lava pond has been affected by Si-Na rich late magmatic melts, without chemical interactions between host rock and melt; - IDs may represent the diffused reservoir of late magmatic felsic material; - LMVs could be the migration channels for Si-Al-Na-(Ca) melt through the basalt mush during the late stages of crystallization; - late magmatic material rapidly cooled producing granophyric textures in veins and interstitial patches.

  18. Habitability Of Europa's Crust

    Greenberg, R.; Tufts, B. R.; Geissler, P.; Hoppa, G.

    Physical characterization of Europa's crust shows it to be rich in potentially habitable niches, with several timescales for change that would allow stability for organisms to prosper and still require and drive evolution and adaptation. Studies of tectonics on Europa indicate that tidal stress causes much of the surface cracking, that cracks pen- etrate through to liquid water (so the ice must be thin), and that cracks continue to be worked by tidal stress. Thus a global ocean is (or was until recently) well linked to the surface. Daily tidal flow (period~days) transports substances up and down through the active cracks, mixing surface oxidants and fuels (cometary material) with the oceanic reservoir of endogenic and exogenic substances. Organisms moving with the flow or anchored to the walls could exploit the disequilibrium chemistry, and those within a few meters of the surface could photosynthesize. Cracks remain active for at least ~10,000 yr, but deactivate as nonsynchronous rotation moves them to different stress regimes in less than a million yr. Thus, to survive, organisms squeezed into the ocean must migrate to new cracks, and those frozen in place must hibernate. Most sites remelt and would release captive organisms within about a million yr based on the prevalence of chaotic terrain, which covers nearly half of Europa. Linkage of the ocean to the surface also could help sustain life in the ocean by delivering oxidants and fuels. Suboceanic volcanism (if any) could provide additional sites and support for life, but is not necessary. Recent results support this model. We further constrain the non-synchronous rotation rate, demonstrate the plausibility of episodic melt-through, show that characteristics of pits and uplift features do not imply thick ice, and demonstrate polar wander, i.e. that the ice crust is detached from the solid interior and has slipped as a unit relative to the spin axis. Thus Europa's biosphere (habitable if not inhabited) likely extends from within the ocean up to the surface, with important implications for exploration strategies: Life or its products may be relatively easy to reach, but Europa may be highly susceptible to biological contamination.

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

    Backman, Jan; Moran, Kathryn; Evans, Dan

    2004-01-01

    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 ...

  20. The Gop Basin - A Possible Imprint of Early Oceanic Spreading Between Greater Seychelles and India

    Bhattacharya, G. C.; Yatheesh, V.; Dyment, J.

    2009-04-01

    The Arabian and its conjugate Eastern Somali basins were formed by the seafloor spreading at the Carlsberg Ridge since Early Tertiary (anomaly 28n; ~62.5 Ma). The reconstruction model at anomaly 28n suggested existence of a wide swath of deep offshore region (Gop and Laxmi basins) between the Laxmi Ridge and the India-Pakistan continental shelf. In the present study we focus on the Gop Basin, where the important constraints about the early geodynamic evolution of the Arabian Sea appear to exist. The nature of the crust underlying this basin remains a matter of debate, with views varying from volcanics-intruded thinned continental crust to oceanic crust formed by a now extinct spreading centre. Our interpretation of an updated compilation of marine geophysical data supports the oceanic nature of the crust underlying the Gop Basin, where the Palitana Ridge represents the extinct spreading centre related to an episode of early oceanic spreading between Greater Seychelles (Seychelles-Laxmi Ridge block) and India. Our magnetic modelling shows that the well correlatable, prominent but short sequence of magnetic anomalies in the Gop Basin does not allow a unique identification; it can be reasonably explained either as A31r - A25r (~69 - 56 Ma) or as A29r - A25r (~65 - 56 Ma) sequence. Both the models suggest that spreading in the Gop Basin was significantly affected by the nearby onset of the Reunion hotspot at ~65 Ma, which formed the Deccan Traps on the adjacent western Indian mainland.

  1. Chapter 50 Geology and tectonic development of the Amerasia and Canada Basins, Arctic Ocean

    Grantz, Arthur; Hart, Patrick E.; Childers, Vicki A

    2011-01-01

    Amerasia Basin is the product of two phases of counterclockwise rotational opening about a pole in the lower Mackenzie Valley of NW Canada. Phase 1 opening brought oceancontinent transition crust (serpentinized peridotite?) to near the seafloor of the proto-Amerasia Basin, created detachment on the Eskimo Lakes Fault Zone of the Canadian Arctic margin and thinned the continental crust between the fault zone and the proto-Amerasia Basin to the west, beginning about 195 Ma and ending prior to perhaps about 160 Ma. The symmetry of the proto-Amerasia Basin was disrupted by clockwise rotation of the Chukchi Microcontinent into the basin from an original position along the Eurasia margin about a pole near 72N, 165 W about 145.5140 Ma. Phase 2 opening enlarged the proto-Amerasia Basin by intrusion of mid-ocean ridge basalt along its axis between about 131 and 127.5 Ma. Following intrusion of the Phase 2 crust an oceanic volcanic plateau, the AlphaMendeleev Ridge LIP (large igneous province), was extruded over the northern Amerasia Basin from about 127 to 8975 Ma. Emplacement of the LIP halved the area of the Amerasia Basin, and the area lying south of the LIP became the Canada Basin.

  2. Chapter 50: Geology and tectonic development of the Amerasia and Canada Basins, Arctic Ocean

    Grantz, A.; Hart, P.E.; Childers, V.A.

    2011-01-01

    Amerasia Basin is the product of two phases of counterclockwise rotational opening about a pole in the lower Mackenzie Valley of NW Canada. Phase 1 opening brought ocean-continent transition crust (serpentinized peridotite?) to near the seafloor of the proto-Amerasia Basin, created detachment on the Eskimo Lakes Fault Zone of the Canadian Arctic margin and thinned the continental crust between the fault zone and the proto-Amerasia Basin to the west, beginning about 195 Ma and ending prior to perhaps about 160 Ma. The symmetry of the proto-Amerasia Basin was disrupted by clockwise rotation of the Chukchi Microcontinent into the basin from an original position along the Eurasia margin about a pole near 72??N, 165 Wabout 145.5-140 Ma. Phase 2 opening enlarged the proto-Amerasia Basin by intrusion of mid-ocean ridge basalt along its axis between about 131 and 127.5 Ma. Following intrusion of the Phase 2 crust an oceanic volcanic plateau, the Alpha-Mendeleev Ridge LIP (large igneous province), was extruded over the northern Amerasia Basin from about 127 to 89-75 Ma. Emplacement of the LIP halved the area of the Amerasia Basin, and the area lying south of the LIP became the Canada Basin. ?? 2011 The Geological Society of London.

  3. Seismic evidence for hydrothermally altered mantle beneath old crust in the Tydeman fracture zone

    Calvert, A. J.; Potts, C. G.

    1985-11-01

    To study the structure of old Atlantic fracture zones, seismic refraction profiles were obtained using ocean-bottom seismometers and two-ship multichannel expanding spread experiments on two inactive sections of the Tydeman fracture zone. The results indicate that: (a) crustal seismic velocities are low compared with "normal" oceanic crust; (b) there is a marked absence of an identifiable layer 3; (c) the depth to the Moho is shallow, though not exceptionally so; and (d) anomalously low seismic velocities of 7.2-7.5 km s -1 are observed over ranges at which upper mantle velocities are normally detected. S-wave arrivals, corresponding to both crustal and mantle refractions, are also observed, which enable the first estimates of Poisson's ratio within a fracture zone to be made. Using these results, and those from other surveys, we show that the seismic velocity in the upper mantle beneath fracture zones decreases systematically with increasing age. These findings suggest that hydrothermal circulation, which can lower the upper mantle velocity by serpentinization, persists under fracture zones for at least 70 Ma, and occurs at greater depths than for normal oceanic crust. The serpentinization process is not sufficiently rapid to obscure the location of the original crust-mantle boundary.

  4. Fluid kinematics, fluid residence times, and rock degassing in oceanic crust determined from noble gas contents of deep sea drilling project pore waters

    Barnes, Ross O.; Clarke, W. Brian

    1987-11-01

    The 3He, 4He, Ne, and Ar in sedimentary pore fluids, extracted in situ, were measured on samples from Deep Sea Drilling Project (DSDP) sites 398, 410, 419, 420, 424, 436, and 438. Earlier results from DSDP leg 15 are also discussed. Where regional sediment cover prevents direct penetration of seawater into basement rocks at sites 149, 436, and 438, He concentration profiles indicate slow vertical and/or horizontal advection of sedimentary pore fluids, suggesting that fluids can ventilate through the sediment cover either in diffuse, bulk flow or in "aquifers" confined to regions of relatively high permeability such as ash beds, sand/silt layers, or fracture channels in lithified sediments. At site 410, where basement outcrops are prevalent, no advection was detectable in the sediments; however, the basement was well flushed by seawater. On fluid velocities. However, most juvenile helium is degassed from the crust in fluids advecting in deep fissures or faults. Fluid residence times in upper basement rocks increased from 5 103 years in 10 m.y. crust open to direct seawater penetration to 105-106 years in Cretaceous basement sealed by hundreds of meters of sediment, to >1-5 108 years (apparent age) in sediments on the active continental margin off NE Japan.

  5. Noble gas isotopic systematics of Fe-Ti-V oxide ore-related mafic-ultramafic layered intrusions in the Panxi area, China: The role of recycled oceanic crust in their petrogenesis

    Hou, Tong; Zhang, Zhaochong; Ye, Xianren; Encarnacion, John; Reichow, Marc K.

    2011-11-01

    Olivine and clinopyroxene grains have been separated from four large Fe-Ti-V oxide ore-bearing intrusions (Panzhihua, Hongge, Baima and Taihe) in the Panxi area, Emeishan large igneous province, Southwest China, for He and Ar isotope studies. The samples examined revealed extremely low 3He/ 4He ratios (0.078-4.34 Ra with the mean value 0.78 Ra) for gases extracted by stepwise heating. This feature, combined with low 40Ar/ 36Ar ratios can be interpreted as due to addition of subduction-related fluids and melts that had been stored in the lithospheric mantle for long periods. Considering the regional geologic history, such addition can be attributed to the paleo subduction that occurred along the western margin of the Yangtze Block during the Neoproterozoic. The subducted oceanic crust beneath the Panxi area underwent eclogite-facies metamorphism and subsequent exhumation. The infiltration of subduction-related melts and fluids into the lithospheric mantle led to enriched isotopic signatures from that of the slightly depleted asthenopheric mantle which has been suggested by the Sr, Nd and Pb isotopic data of the Emeishan basalts and picrites. In addition, considerable amounts of eclogitic melts produced by partial melting of eclogite-facies oceanic crust extensively contaminated the lithospheric mantle. During the late Permian, partial melting of an upwelling mantle plume that contained an eclogite or pyroxenite component generated the parental Fe-rich magma that supplied the ore-bearing intrusions. The combination of these factors may have been the crucial reason that many world-class Fe-Ti-V oxides deposits are clustered in the Panxi area.

  6. Incorporation of transition and platinum group elements (PGE) in Co-rich Mn crusts at Afanasiy-Nikitin Seamount (AFS) in the equatorial S Indian Ocean

    Glasby, G.P.

    of these elements in Co-rich manganese crusts relative to seawater. Five of these elements are transition elements (Mn, Fe, Co, Ni and Cu), six PGE (Ru, Rh, Pd, Os, Ir, Pt) plus Au. It is seen that Mn and Fe are the most enriched of the transition elements in Co... CuCO 3 0 5,000 0.15% 25 – 1 0 ¥ 10 6 Ru < 50 fmol kg - 1 < 5 ¥ 10 - 15 – – 20 ppb 0.1 – > 4 ¥ 10 6 Rh 780 fmol kg - 1 79 ¥ 10 - 15 – – 20 ppb 0.06 – 0.25 ¥ 10 6 Pd 560 fmol kg - 1 59 ¥ 10 - 15 PdCl 4 2 - 10,000 9 ppb 0.4 0.65 0.15 ¥ 10 6 Os 15–56 fmol...

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

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

    2013-07-01

    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.

  8. Spreading rate dependent seafloor deformation in response to India-Eurasia collision: results of a hydrosweep survey in the Central Indian Ocean basin

    Mukhopadhyay, R.; George, P.; Ranade, G.

    by ancient oceanic crust formed under a variable spreading condition. This crust was formed at fast, intermediate fast, and slow rates, from north to south. The CIOB began forming at least 84 Ma ago as India moved northwards from the Antarctic...) and moderate to fast spreading South East Indian Ridge (SEIR). The rate of spreading along these ridges has undergone several distinct changes in the past. In particular, the SEIR was spreading at a faster rate (180 mm/yr, full rate) until 58.2 Ma (i...

  9. Eocene deep crust at Ama Drime, Tibet

    Kellett, Dawn; Cottle, John; Smit, Matthijs Arjen

    2014-01-01

    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...

  10. High-resolution geology, petrology and age of a tectonically accreted section of Paleoarchean oceanic crust, Barberton greenstone belt, South Africa

    Grosch, Eugene; Vidal, Olivier; McLoughlin, Nicola; Whitehouse, Martin

    2015-04-01

    The ca. 3.53 to 3.29 Ga Onverwacht Group of the Barberton greenstone belt (BGB), South Africa records a rare sequence of exceptionally well-preserved volcanic, intrusive and volcani-clastic Paleaoarchean rocks. Numerous conflicting models exist for the geologic evolution and stratigraphy of this early Archean greenstone belt, ranging from plume-type dynamics to modern-style plate tectonics. Although much work has focussed on the komatiites of the ca. 3.48 Ga Komati Formation since their discovery in 1969, far less petrological attention has been given to the younger oceanic rock sequences of the Kromberg type-section in the mid-Onverwacht Group. In this study, we present new field observations from a detailed re-mapping of the Kromberg type-section, and combine this with high-resolution lithological observations from continuous drill core of the Barberton Scientific Drilling Project [1]. The new mapping and field observations are compared to a recent preliminary study of the Kromberg type-section [2]. A U-Pb detrital provenance study was conducted on a reworked, volcani-clastic unit in the upper Kromberg type-section for the first time. This included U-Pb age determination of 110 detrital zircons by secondary ion microprobe analyses (SIMS), providing constraints on maximum depositional age, provenance of the ocean-floor detritus, and timing for the onset of Kromberg ocean basin formation. These new zircon age data are compared to a previous U-Pb detrital zircon study conducted on the structurally underlying sediments of the ca. 3.43 Ga Noisy formation [3]. A multi-pronged petrological approach has been applied to various rock units across the Kromberg, including thermodynamic modelling techniques applied to metabasalts and metapyroxenites for PT-estimates, bulk- and in-situ isotope geochemistry providing constraints on protolith geochemistry and metamorphic history. Consequently, it is shown that this previously poorly studied Kromberg oceanic rock sequence of the mid-Onverwacht, is a key area in resolving stratigraphy models and understanding the geologic evolution of the BGB. The combined field and petrological data provide new insight into mid-Paleoarchean ocean basin formation and subsequent tectonic destruction. [1]. Grosch et al., (2009b). EOS 90, 350-351. [2] Furnes et al., (2011) Precam. Research 186, 28-50. [3] Grosch et al. (2011) Precam. Research 191, 85-99.

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

    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...

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

    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...

  13. H11346_INTERP.SHP: Interpretation of Bottom Features from National Oceanic and Atmospheric Administration (NOAA) Survey H11346 of Edgartown Harbor, MA (Geographic, WGS84)

    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...

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

    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. Crustal magnetization and accretion at the Southwest Indian Ridge near the Atlantis II fracture zone, 0-25 Ma

    Hosford, A.; Tivey, M.; Matsumoto, T.; Dick, H.; Schouten, Hans; Kinoshita, H.

    2003-01-01

    We analyze geophysical data that extend from 0 to 25-Myr-old seafloor on both flanks of the Southwest Indian Ridge (SWIR). Lineated marine magnetic anomalies are consistent and identifiable within the study area, even over seafloor lacking a basaltic upper crust. The full spreading rate of 14 km/Myr has remained nearly constant since at least 20 Ma, but crustal accretion has been highly asymmetric, with half rates of 8.5 and 5.5 km/Myr on the Antarctic and African flanks, respectively. This asymmetry may be unique to a ???400 km wide corridor between large-offset fracture zones of the SWIR. In contrast to the Mid-Atlantic Ridge, crustal magnetization amplitudes correlate directly with seafloor topography along the present-day rift valleys. This pattern appears to be primarily a function of along-axis variations in crustal thickness, rather than magnetic mineralogy. Off-axis, magnetization amplitudes at paleo-segment ends are more positive than at paleo-segment midpoints, suggesting the presence of an induced component of magnetization within the lower crust or serpentinized upper mantle. Alteration of the magnetic source layer at paleo-segment midpoints reduces magnetization amplitudes by 70-80% within 20 Myr of accretion. Magnetic and Ocean Drilling Program (ODP) Hole 735B data suggest that the lower crust cooled quickly enough to lock in a primary thermoremanent magnetization that is in phase with that of the overlying upper crust. Thus magnetic polarity boundaries within the intrusive lower crust may be steeper than envisioned in prior models of ocean crustal magnetization. As the crust ages, the lower crust becomes increasingly important in preserving marine magnetic stripes.

  16. Geochemical evidence for the tectonic setting of the Coast Range ophiolite: A composite island arc oceanic crust terrane in western California

    Shervais, John W.; Kimbrough, David L.

    1985-01-01

    The Middle to Late Jurassic age Coast Range ophiolite (CRO) of California contains two geochemically distinct volcanic rock associations that formed in different tectonic settings. Volcanic rocks from the southern CRO (Point Sal, Cuesta Ridge, Stanley Mountain, Llanada, Quinto Creek, and Del Puerto) and parts of the northern CRO (Healdsburg, Elder Creek) are similar to low-K tholeiites and calc-alkaline rocks of the island-arc suite. The thin volcanic sections of these ophiolite remnants suggest formation by intra-arc rifting. In contrast, volcanic rocks from Stonyford seamount and Paskenta in the northern CRO are transitional subalkaline metabasalts with geochemical characteristics similar to enriched mid-ocean ridge basalts or ocean-island tholeiites. These rocks are associated with Tithonian radiolarian cherts and may be part of the Franciscan Complex. Alternatively, they may represent a change in tectonic setting within the CRO during the Late Jurassic. Regardless, the CRO as currently conceived cannot be considered a single terrane with one mode of origin.

  17. The role of recycled oceanic crust in magmatism and metallogeny: Os-Sr-Nd isotopes, U-Pb geochronology and geochemistry of picritic dykes in the Panzhihua giant Fe-Ti oxide deposit, central Emeishan large igneous province, SW China

    Hou, Tong; Zhang, Zhaochong; Encarnacion, John; Santosh, M.; Sun, Yali

    2013-04-01

    The picritic dykes occurring within fine-grained gabbro in the marginal zone and in the surrounding Proterozoic wall-rock marbles of the Panzhihua Fe-Ti oxide deposit closely correspond in bulk composition with the nearby Panzhihua intrusion. These dykes offer important constraints on the nature of the mantle source of the Panzhihua ore-bearing intrusion and its possible link to the Emeishan plume. U-Pb zircon dating of the picritic dyke yields a crystallization age of 261.4 ± 4.6 Ma, coeval with the timing of the main Panzhihua gabbroic intrusion and Late Permian Emeishan flood basalts. The Panzhihua picritic dykes contain 37.63-43.41 wt% SiO2, 1.15-1.56 wt% TiO2, 11.43-13.25 wt% TFe2O3, and 20.96-28.87 wt% MgO. Primitive-mantle-normalized patterns of the rocks are comparable to those of ocean island basalt. The rocks define a relatively small range of Os isotopic compositions and a low Os signature of -0.13 to +2.76 for γOs (261 Ma). In combination with their Sr-Nd-Os isotopic compositions, we interpret that these rocks were derived from the Emeishan plume sources as well as the interactions of plume melts with the overlying lithosphere which had been extensively affected by eclogite-derived melts from the deep-subducted oceanic slab. Partial melting induced by an upwelling mantle plume that involved an eclogite or pyroxenite component in the lithospheric mantle could have produced the parental Fe-rich magma. Our study suggests that plume-lithosphere interaction might have played a key role in generating many world-class Fe-Ti oxide deposits clustered in the Panxi area.

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

    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. εSr ranges from -25 to +100 and εNd from +6 to -9, but the low εNd and high εSr 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 εSr from -25 to +20 and εNd 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 εSr increasing up to +100 with increasing SiO2 and decreasing Sr, and it results in relatively shallow trends on an εNd-εSr 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.)

  19. Core and early crust formation on Mars

    Golabek, G. J.; Keller, T.; Gerya, T.; Tackley, P. J.; Connolly, J.; Zhu, G.

    2010-12-01

    One of the most striking surface features on Mars is the crustal dichotomy. It is the oldest geological feature on Mars and was formed more than 4.1 Ga ago by either exogenic or endogenic processes [1,2]. In order to find an internal origin of the crustal dichotomy, located within a maximum of 400 Ma of planetary differentiation, the thermal state of the planet resulting from core formation needs to be considered. Additionally, it was suggested that a primordial crust with up to 45 km thickness can be formed already during the Martian core formation [3]. We suggest that the sinking of iron diapirs delivered by predifferentiated impactors induced impact- and shear heating-related temperature anomalies in the mantle that fostered the formation of early Martian crust. Thus, the crustal thickness distribution would largely be a result of planetary core formation, late impact history and the onset of mantle convection. To test this hypothesis we use numerical models to simulate the formation of the Martian iron core and the resulting mantle convection pattern, while peridotite melting is enabled to track melting caused by shear and radioactive heating. We perform 2D simulations using the spherical-Cartesian code I2ELVIS for planetary accretion and the spherical code STAGYY for the consequent onset of mantle convection. We apply a temperature-, stress- and melt-fraction dependent viscoplastic rheology. Radioactive and shear heating as well as consumption of latent heat by silicate melting are taken into account. The depth of neutral buoyancy of silicate melt with respect to solid silicates is determined by the difference in compressibility of the liquid and solid phase. To self-consistently simulate the silicate phase changes expected inside a Mars-sized body, we use the thermodynamical database Perple_X. As initial condition for core formation, we apply randomly distributed iron diapirs with 75 km radius inside the planet, representing the cores of stochastically distributed impactors. Additionally, we explore the effect of one giant impactor core on the planetary evolution. Results indicate that the presence of a large impactor core induces hemispherically asymmetrical core formation. The amplitude of shear heating anomalies often exceeds the solidus of primitive mantle material and thus, the formation of a considerable amount of silicate melt is observed. The resulting temperature field after core formation is then read into the mantle convection code STAYY. The hemispherical magma ocean induced by one late giant impactor favours a dichotomous crust formation during and shortly after core formation. Afterwards, the extraction of excess heat produced by the sinking of the giant impactor through the mantle leads to a localized region of massive magmatism, comparable to Tharsis, which is sustained during later evolution by a single plume forming beneath the province. The rest of the mantle is dominated by a sluggish convection pattern with limited crust formation that preserves the early formed dichotomous crustal structure until recent time. References [1] Nimmo, F. et al., Nature, 453, 1220-1223, 2008. [2] Keller, T. & Tackley, P.J., Icarus, 202, 429-443, 2009. [3] Norman, M.D., Meteorit. Planet. Sci., 34, 439-449, 1999.

  20. Earth's partial pressure of CO2 over the past 120 Ma; evidence from Ce anomalies in the deep (greater than 600 m) Pacific Ocean, 1

    Liu, Y.-G; Schmitt, R. A.

    1993-01-01

    It was found that Ce serves as a chemical tracer of paleo-oceanic redox conditions. It was shown that the unoxidized and soluble Ce(3+) in modern seawater exhibits a negative anomaly relative to the other soluble REE(3+). An expression of soluble Ce(3+) in seawater that was approximately 1900X greater than the average observed in Ce in 600-5000 m Pacific seawater was derived. Since Ce(CO3)(+) and Ce(CO3)2(-) complexes greatly exceed the Ce(PO4) complexes in seawater, the formulations of using carbonate complexes were followed and it was found that the calculated Ce and observed concentrations in the deep 600-5000 m Pacific Ocean agree within the uncertainties of the thermodynamic data. As expected, the calculated Ce concentrations are a strong function of pH and found to be lesser functions of CO3(2-) activities.

  1. Paleoceanography/climate and taphonomy at intermediate water depth in the Subtropical Western North Pacific Ocean over the last 1 Ma from IODP Exp 350 Sites U1436C and U1437B, Izu arc area.

    Vautravers, Maryline

    2015-04-01

    IODP Expedition 350 Site U1436C lies in the western part of the Izu fore arc basin, ~60 km east of the arc front volcano Aogashima, at 1776 m water depth. This site is a technical hole (only a 150 m long record) for a potential future deep drilling by Chikyu. Site U1437 is located in the Izu rear arc, ~90 km west of the arc front volcanoes Myojinsho and Myojin Knoll, at 2117 m water depth. At this site in order to study the evolution of the IZU rear arc crust we recovered a 1800 meter long sequence of mud and volcaniclastic sediments. These sites provide a rich and well-preserved record of volcanic eruptions within the area of the Izu Bonin-Arc. However, the material recovered, mostly mud with ash containing generally abundant planktonic foraminifera, can support additional paleoceanographic goals in an area affected by the Kuroshio Current. Also, the hydrographic divide created by the Izu rise provides a rare opportunity to gain some insight into the operation of the global intermediate circulation. The Antarctic Intermediate Water Mass is more influential at the depth of U1437B in the West and the North Pacific Intermediate Water at Site U1436C to the East. We analyzed 460 samples recovered at Sites U1436C and U1437B for a quantitative planktonic foraminifer study, and also for carbonate preservation indices, including: shell weight, percent planktonic foraminifera fragments planktonic foraminifer concentrations, various faunal proxies, and benthic/planktonic ratio. We measured the stable isotopes for a similar number of samples using the thermocline dwelling Neogloboquadrina dutertrei. The dataset presented here covers the last 1 Ma at Site U1437B and 0.9 Ma at Site U1436C. The age models for the two sites are largely established through stable isotope stratigraphy (this study). On their respective age models we evidence based on polar/subpolar versus subtropical faunal assemblages changes qualitative surface water temperature variations recording the changing influences in the Kuroshio/Oyashio currents at orbital time scales over the last 1 Ma. However, the 2 main findings are i.) that of the intense and pervasive carbonate dissolution at such an intermediate water depth, especially during interglacials, and in particular at site U1436C, and ii.) the good and improving carbonate preservation at Site U1437B during glacials, particularly in the upper part of the record.

  2. 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

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

    2015-08-01

    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 ΣREE 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.

  3. 60 Myr records of major elements and Pb-Nd isotopes from hydrogenous ferromanganese crusts: Reconstruction of seawater paleochemistry

    Frank, M.; O'Nions, R.K.; Hein, J.R.; Banakar, V.K.

    The time series of major element geochemical and Pb- and Ni-isotopic composition obtained for seven hydrogenous ferromanganese crusts from the Atlantic, Indian, and Pacific Oceans which cover the last 60 Myr are compared. Average crust growth rates...

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

    Ziaja, Karen

    2012-01-01

    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...

  5. Enrichment mechanisms of tellurium in ferromanganese crusts

    Sakaguchi, A.; Sugiyama, T.; Usui, A.; Takahashi, Y.

    2012-04-01

    Marine ferromanganese crusts (FMCs) consist of iron (Fe) hydroxides and manganese (Mn) oxides with various minor and trace elements. Especially for tellurium (Te), which is recognized as one of the rare metals, it has been reported that this element is concentrated about 105 times in FMCs compared with earth's crust, and the host phase might be Fe (oxy)hydroxide (Hein et al., 2003). Actually, in our previous study, the high concentration of Te in very surface layers of FMCs was found from the top to halfway down of a seamount in the Pacific Ocean. However, the concentration of Te in surface layers through the seamount showed good correlation with that of Mn instead of Fe. In this study, we attempted to clarify the enrichment mechanism of Te in FMCs with some methods including X-ray absorption fine structure (XAFS) technique for synthesised /natural samples. Seventeen FMC samples were collected from the Takuyo-Daigo seamount, from 950 m (summit) to 3000 m in water depth, with hyper-dolphin (remotely operated vehicle) equipped with live video camera and manipulators. The growth rates of all FMC samples were estimated to be about 3 mm/Ma. Very surface layer (less than 1 mm) of all FMC was analyzed with XRD and XAFS to confirm the mineral composition and speciation of Te. Furthermore, to serve as an aid to clarify the adsorption mechanism of Te on FMCs, distribution coefficients (Kd) and oxidation states were determined through the adsorption experiments of Te(IV) and Te(VI) on ferrihydrite and δ-MnO2. In all the experiments, pH and ionic strength were adjusted to pH 7.5 and 0.7 M, respectively. The oxidation state of Te in water phase was determined with HPLC-ICP-MS. As for the analysis of oxidation and adsorption states on the solid phase, XAFS was employed. The major mineral composition of Fe and Mn had no significant variation through the water depth of Takuyo-Daigo seamount. The oxidation state of Te in all samples showed hexavalent, and there was no significant difference of adsorption state independent of the DO, salinity and temperature in water. It has been reported that Te exists as tetravalent and hexavalent in sea water of the Pacific Ocean (Nozaki, 1996). Thus, it can be said that the Te in sea water is oxidised and incorporated into FMCs. As a result of the adsorption experiments in laboratory, the Kd of Te on ferrihydrite was larger than that of δ-MnO2, and Te(IV) was adsorbed to a larger degree than Te(VI) on both minerals. The adsorption experiments of Te(IV) on δ-MnO2 showed that the solid phase has only hexavalent Te, although the water phase has both tetra and hexavalent species of Te. Te(IV) on ferrihydrite was not oxidized to Te(VI). From these results, it can be suggested that Te(IV) was oxidized by δ-MnO2 and would be adsorbed onto ferrihydrite. Actually, the results of double-cell adsorption experiments support this hypothesis. The detail of our results and discussion will be given in the presentation.

  6. Weathering crusts on peridotite

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

    2015-05-01

    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.

  7. The syncollisional granitoid magmatism and continental crust growth in the West Kunlun Orogen, China - Evidence from geochronology and geochemistry of the Arkarz pluton

    Zhang, Yu; Niu, Yaoling; Hu, Yan; Liu, Jinju; Ye, Lei; Kong, Juanjuan; Duan, Meng

    2016-02-01

    The West Kunlun orogenic belt (WKOB) at the northwest margin of the Greater Tibetan Plateau records seafloor subduction, ocean basin closing and continental collision with abundant syncollisional granitoids in response to the evolution of the Proto- and Paleo-Tethys Oceans from the early-Paleozoic to the Triassic. Here we present a combined study of detailed zircon U-Pb geochronology, whole-rock major and trace elements and Sr-Nd-Hf isotopic geochemistry on the syncollisional Arkarz (AKAZ) pluton with mafic magmatic enclaves (MMEs) exposed north of the Mazha-Kangxiwa suture (MKS) zone. The granitoid host rocks and MMEs of the AKAZ pluton give the same late Triassic age of ~ 225 Ma. The granitoid host rocks are metaluminous granodiorite and monzogranite. They have initial 87Sr/86Sr of 0.70818 to 0.70930, εNd(225 Ma) = - 4.61 to - 3.91 and εHf(225 Ma) = - 3.01 to 0.74. The MMEs are more mafic than the host with varying SiO2 (51.00-63.24 wt.%) and relatively low K2O (1.24-3.02 wt.%), but have similar Sr-Nd-Hf isotope compositions to the host ((87Sr/86Sr)i = 0.70830-0.70955, εNd(225 Ma) = - 4.88 to - 4.29, εHf(225 Ma) = - 2.57 to 0.25). Both the host and MMEs have rare earth element (REE) and trace element patterns resembling those of bulk continental crust (BCC). The MMEs most likely represent cumulate formed from common magmas parental to the granitoid host. The granitoid magmatism is best explained as resulting from melting of amphibolite of MORB protolith during continental collision, which produces andesitic melts with a remarkable compositional similarity to the BCC and the inherited mantle-like isotopic compositions. Simple isotopic mixing calculations suggest that ~ 80% ocean crust and ~ 20% continental materials contribute to the source of the AKAZ pluton. Thus, the hypothesis "continental collision zones as primary sites for net continental crust growth" is applicable in the WKOB as shown by studies in southern Tibet, East Kunlun and Qilian orogens. In addition, we also propose a new view for the tectonic evolution of the Paleo-Tethys Ocean in geological regions recorded and represented by the MKS.

  8. Comment on "207Pb-206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the Central Anatolian crust, Turkey" - Boztug, D., Tichomirowa, M. & Bombach, K., 2007, JAES 31, 71-86

    Göncüoglu, M. Cemal

    A continent-oceanic island arc collision model was proposed as a new geodynamic scenario for the evolution of the Cretaceous Central Anatolian granitoids in the Central Anatolian crystalline complex (CACC) by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb-206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust, Turkey. Journal of Asian Earth Sciences 31, 71-86]. The key aspects of this model include an intra-oceanic subduction in the Neotethyan Izmir-Ankara Ocean, formation of an island arc and its subsequent collision with the northern margin of the Tauride-Anatolide Platform. The identical scenario was initially proposed by Göncüoglu et al. (1992) [Göncüoglu, M.C., Erler, A., Toprak, V., Yalınız, K., Olgun, E., Rojay, B., 1992. Geology of the western Central Anatolian Massif, Part II: Central Areas. TPAO Report No: 3155, 76 p] . Moreover, the weighted mean values of the reported 207Pb-206Pb single-zircon evaporation ages by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb-206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust: Turkey. Journal of Asian Earth Sciences 31, 71-86] from A-type granitoids in the CACC seem to be miscalculated and contrast with the field data.

  9. 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

    R. Banerjee

    2010-07-01

    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 08 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.

  10. The early-stage evolution of the Neo-Tethys ocean: Evidence from granitoids in the middle Gangdese batholith, southern Tibet

    Meng, Yuanku; Dong, Hanwen; Cong, Yuan; Xu, Zhiqin; Cao, Hui

    2016-03-01

    The Gangdese magmatic belt, located along the southern margin of the Lhasa terrane, plays a critical role in understanding the tectonic framework associated with the Indian-Eurasian collision and the crustal growth of the southern Tibet. In this paper, we present a series of results from new petrological, geochemical and geochronological investigations of the granitoid rocks. The granitoids mainly have sub-alkaline compositions and show medium K calc-alkaline affinities, as well as I-type granitoid characteristics. Significant depletions of Nb and Ta, combined with other geochemical features including enrichments of LILEs and LREEs confirm that the parental magmas of these rocks were generated in a subduction-related active continental margin (continental arc environment). Lu-Hf isotopic compositions and relatively low MgO contents indicate that the granitoids might be generated from partial melting of juvenile crust and basaltic lower crust, which is caused by the underplating of mantle materials, and the mantle materials that have been involved in this process. The 191.2-169.2 Ma zircon U-Pb ages of the granitoids reveal middle-early Jurassic magmatic events. Combined with published data in the Gangdese magmatic belt, our study suggests that the northward subduction of the Neo-Tethys oceanic crust beneath the southern margin of the Lhasa terrane probably started no later than 191.2 Ma. Zircons from the granitoids suite display positive ɛHf(t) values between 10.1 and 15.4 (mean value is 12.7), which correspond to the two-stage model ages (tDM2) in the range of 198-415 Ma, attesting to crustal growth in the southern Lhasa terrane associated with the subduction of the Neo-Tethys oceanic crust. Our study is a systematic report of the granitoid suite in the Gangdese magmatic belt and strengthens the concept that the Neo-Tethys oceanic crust might have experienced a long evolution history.

  11. Origin of enriched components in the South Atlantic: Evidence from 40 Ma geochemical zonation of the Discovery Seamounts

    Schwindrofska, Antje; Hoernle, Kaj; Hauff, Folkmar; van den Bogaard, Paul; Werner, Reinhard; Garbe-Schönberg, Dieter

    2016-05-01

    Spatial geochemical zonation is being increasingly recognized in Pacific and Atlantic hotspot tracks and is believed to reflect zonation within plumes upwelling from the margins of the Large Low Shear Velocity Provinces (LLSVPs) at the base of Earth's mantle. We present new 40Ar/39Ar age data for the Discovery Rise (South Atlantic Ocean) that show an age progression in the direction of plate motion from 23 Ma in the southwest to 40 Ma in the northeast of the Rise, consistent with formation of the Rise above a mantle plume. The lavas have incompatible element and Sr-Nd-Pb-Hf radiogenic isotope characteristics similar to the enriched DUPAL anomaly occurring in the southern hemisphere. The northern chain of seamounts is compositionally similar to the adjacent Gough subtrack of the bilaterally-zoned Tristan-Gough hotspot track, whereas the southern chain has some of the most extreme DUPAL compositions found in South Atlantic intraplate lavas thus far. The nearby southern Mid-Atlantic Ridge, believed to interact with the Discovery hotspot, shows a similar spatial geochemical distribution, consistent with the Discovery hotspot being zoned over its entire 40 Ma history. Our study implies a deep origin for the DUPAL anomaly, suggesting recycling of subcontinental lithospheric mantle (± lower crust) and oceanic crust through the lower mantle. The presence of an additional (Southern Discovery) DUPAL-like component, in addition to the Tristan and Gough/Northern Discovery components, in long-term zoned South Atlantic hotspots, points to the presence of a third lower mantle reservoir and thus is not consistent with the simple model that bilaterally-zoned plumes sample a chemically distinct LLSVP and the ambient mantle outside of the LLSVP.

  12. Primary estimation of forming date for carbonate weathering crust in Guizhou province

    The problem of directed dating of carbonate weathering crust in Guizhou Province hasn't been resolved. On the base of our previous study, we tested in detail the ages of antigenic quartz grains by fission track dating method and give a limitation of the forming date to carbonate weathering crust. The results show that the age of Xinpu profile is younger than 8.5 Ma, and the age of Guanba profile is younger than 7.3 Ma, and the age of Daxing profile is younger than 4.6 Ma. (authors)

  13. Birth of an ocean in the Red Sea: Initial pangs

    Ligi, Marco; Bonatti, Enrico; Bortoluzzi, Giovanni; Cipriani, Anna; Cocchi, Luca; Caratori Tontini, Fabio; Carminati, Eugenio; Ottolini, Luisa; Schettino, Antonio

    2012-08-01

    We obtained areal variations of crustal thickness, magnetic intensity, and degree of melting of the sub-axial upwelling mantle at Thetis and Nereus Deeps, the two northernmost axial segments of initial oceanic crustal accretion in the Red Sea, where Arabia is separating from Africa. The initial emplacement of oceanic crust occurred at South Thetis and Central Nereus roughly ˜2.2 and ˜2 Ma, respectively, and is taking place today in the northern Thetis and southern Nereus tips. Basaltic glasses major and trace element composition suggests a rift-to-drift transition marked by magmatic activity with typical MORB signature, with no contamination by continental lithosphere, but with slight differences in mantle source composition and/or potential temperature between Thetis and Nereus. Eruption rate, spreading rate, magnetic intensity, crustal thickness and degree of mantle melting were highest at both Thetis and Nereus in the very initial phases of oceanic crust accretion, immediately after continental breakup, probably due to fast mantle upwelling enhanced by an initially strong horizontal thermal gradient. This is consistent with a rift model where the lower continental lithosphere has been replaced by upwelling asthenosphere before continental rupturing, implying depth-dependent extension due to decoupling between the upper and lower lithosphere with mantle-lithosphere-necking breakup before crustal-necking breakup. Independent along-axis centers of upwelling form at the rifting stage just before oceanic crust accretion, with buoyancy-driven convection within a hot, low viscosity asthenosphere. Each initial axial cell taps a different asthenospheric source and serves as nucleus for axial propagation of oceanic accretion, resulting in linear segments of spreading.

  14. nantucket_ma.grd

    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...

  15. Highly extended oceanic lithosphere: The basement and wallrocks for the Late Jurassic Rogue-Chetco oceanic arc, Oregon Klamath Mountains

    Yule, J.D.; Saleeby, J.B.

    1993-04-01

    The superbly preserved, coeval Late Jurassic Rogue-Chetco oceanic arc and Josephine inter-arc basin exposed in the western Jurassic belt of the Oregon Klamath Mountains provide a unique opportunity to (1) directly observe the oceanic lithosphere upon which this oceanic arc was constructed, and (2) gain a better understanding of the pre-accretionary dynamic processes that shape oceanic arc and inter-arc basin lithosphere. Field relations exposed in the Roque, Illinois, and Chetco River areas show that (1) plutonic and volcanic rocks of the Rogue-Chetco arc both intruded and conformably overlapped fragmented composite blocks of oceanic crust and serpentinized, dike-filled depleted mantle rocks; and (2) arc growth occurred during regional oblique extension of the oceanic lithosphere resulting in the extreme fragmentation of oceanic crustal rocks and the local exposure of serpentinized mantle rocks on the sea floor. The Rogue-Chetco overlap sequence consists of rhythmically bedded volcanogenic turbidites, chert, argillite, and local deposits of polymict basal breccias. The clasts which comprise the distinctive basal breccias indicate derivation from a dominantly ophiolitic crust and serpentinized mantle source. Source materials for the basal breccias comprise the basement and wallrocks for the Roque-Chetco arc and consist of (1) rifted fragments of western Paleozoic and Triassic belt rocks (Yule and others, 1991) cut by heterogeneous mafic complexes inferred to represent early Josephine age rifting at approximately 165 Ma, (2) fault bounded blocks of massive gabbro, sheeted mafic dikes, pillow lava and breccia overlain by Callovian age chert, and (3) serpentinized depleted mantle peridotite cut by multiple generation of mafic and intermediate dikes. The basement rock types all share a pervasive brittle fragmentation and hydrothermal alteration history that is conspicuously absent in the arc volcanic and plutonic rocks.

  16. Arc-continent collision and the formation of continental crust: A new geochemical and isotopic record from the Ordovician Tyrone Igneous Complex, Ireland

    Draut, Amy E.; Clift, Peter D.; Amato, Jeffrey M.; Blusztajn, Jerzy; Schouten, Hans

    2009-01-01

    Collisions between oceanic island-arc terranes and passive continental margins are thought to have been important in the formation of continental crust throughout much of Earth's history. Magmatic evolution during this stage of the plate-tectonic cycle is evident in several areas of the Ordovician Grampian-Taconic orogen, as we demonstrate in the first detailed geochemical study of the Tyrone Igneous Complex, Ireland. New U-Pb zircon dating yields ages of 493 2 Ma from a primitive mafic intrusion, indicating intra-oceanic subduction in Tremadoc time, and 475 10 Ma from a light rare earth element (LREE)-enriched tonalite intrusion that incorporated Laurentian continental material by early Arenig time (Early Ordovician, Stage 2) during arc-continent collision. Notably, LREE enrichment in volcanism and silicic intrusions of the Tyrone Igneous Complex exceeds that of average Dalradian (Laurentian) continental material that would have been thrust under the colliding forearc and potentially recycled into arc magmatism. This implies that crystal fractionation, in addition to magmatic mixing and assimilation, was important to the formation of new crust in the Grampian-Taconic orogeny. Because similar super-enrichment of orogenic melts occurred elsewhere in the Caledonides in the British Isles and Newfoundland, the addition of new, highly enriched melt to this accreted arc terrane was apparently widespread spatially and temporally. Such super-enrichment of magmatism, especially if accompanied by loss of corresponding lower crustal residues, supports the theory that arc-continent collision plays an important role in altering bulk crustal composition toward typical values for ancient continental crust. ?? 2009 Geological Society of London.

  17. Volcanic Origin of the Lunar Highland Crust

    Lowman, P. D.

    2006-05-01

    Introduction: This paper reviews evidence from Apollo missions, returned lunar samples, and earth-based reflection spectroscopy, bearing on the composition, structure, and origin of the "highland" crust (actually the global crust, underlying the maria as well as the nominal highlands). Current views are that the crust is primarily anorthosite, formed in a magma ocean, with a layered structure formed of superimposed impact ejecta blankets. Several lines of independent evidence contradict this concept. Structure: Retrospective analysis of lunar surface photos taken by the astronauts on Apollos 15, 16, and 17 reveal pervasive layering, best exposed on the Apennine Front near the Apollo 15 landing site, at Silver Spur. These layers, more than 90, average 16 meters in thickness. Similar layers were found on photos from Apollo 16, of Stone Mountain, and from Apollo 17, of the Sculptured Hills. In thickness, geometry, and regularity they are similar to basaltic lava flows of the Columbia Plateau, the island of Hawaii, and Kauai. The generally- accepted explanation of these layers as overlapping ejecta blankets from mare basins or craters is contradicted by their number and thickness, and the fact that no such layers were found by seismic methods in the Fra Mauro Formation (Imbrium ejecta). Composition: Remote sensing data, from Apollo orbital X-ray fluorescence surveys and earth-based reflection spectroscopy, show that anorthosite is a subordinate constituent of the lunar crust, not the major one. Returned lunar samples support this, despite the masking effects of pervasive brecciation and impact melting. Dominant highland rock types are basalt, frequently feldspar-rich; norite; troctolite; KREEP; and anorthosite, the bulk surface composition corresponding chemically to a high-Al norite. Five-km resolution reflectance traverses by Pieters and others show that anorthosite is a widespread but subordinate component, occurring in central peaks that probably expose anorthosite intrusions. The "magma ocean" concept is petrologically valid but probably applicable only to these intrusions. Conclusion: It is proposed that the highland crust layers are flows of alumnum-rich noritic lavas, collectively several kilometers thick, and that they represent a "first differentiation" of the Moon by massive global volcanism in the first few hundred million years of the Moon's history,concurrent with intense impact cratering.

  18. The effect of hydrothermal circulation on subsidence on ocean basins : evidence from the South East Indian Ocean

    Gli, L.; Francheteau, J.

    2003-04-01

    While it is generally accepted that off-axis hydrothermal circulation is responsible for the majority of the observed oceanic heat flow anomalies (e. g. for the "missing" conductive heatflow through oceanic lithosphere), the effect of water circulation on the subsidence of ocean basins at the scale of tens of millions years has not been thoroughly recognized. We present a very simple model (based on the half-space model) showing that, that in some particular circumstances, hydrothermal circulation may be held responsible for unexplained subsidence rate anomalies at the scale of ocean basins. An example is given for the poorly sedimented South-East Indian Ridge flanks of age Ma1/2 ) can be more readily explained by the observed sedimentation pattern and the subsequent pattern in hydrothermal circulation than by ad hoc variations in the mantle thermal parameters. Our model assumes that in absence of sedimentation, hydrothermal circulation convectively maintains low temperatures within the upper crust at ages as old as 20 to 30 Ma. Agreement with re-assesed subsidence estimates supports the model hypothesis.

  19. Update on CRUST1.0 - A 1-degree Global Model of Earth's Crust

    Laske, Gabi; Masters, Guy; Ma, Zhitu; Pasyanos, Mike

    2013-04-01

    Our new 1-by-1 degree global crustal model, CRUST1.0, was introduced last year and serves as starting model in a comprehensive effort to compile a global model of Earth's crust and lithosphere, LITHO1.0 (Pasyanos et al., 2012). The Moho depth in CRUST1.0 is based on 1-degree averages of a recently updated database of crustal thickness data from active source seismic studies as well as from receiver function studies. In areas where such constraints are still missing, for example in Antarctica, crustal thicknesses are estimated using gravity constraints. The compilation of the new crustal model initially followed the philosophy of the widely used crustal model CRUST2.0 (Bassin et al., 2000; http://igppweb.ucsd.edu/~gabi/crust2.html) to assign elastic properties in the crystalline crust according to basement age or tectonic setting (loosely following an updated map by Artemieva and Mooney (2001; http://www.lithosphere.info). For cells with no local seismic or gravity constraints, statistical averages of crustal properties, including crustal thickness, were extrapolated. However, in places with constraints the depth to basement and mantle are given explicitly and no longer assigned by crustal type. This allows for much smaller errors in both. In each 1-degree cell, boundary depth, compressional and shear velocity as well as density is given for 8 layers: water, ice, 3 sediment layers and upper, middle and lower crystalline crust. Topography, bathymetry and ice cover are taken from ETOPO1. The sediment cover is based on our sediment model (Laske and Masters, 1997; http://igppweb.ucsd.edu/~sediment.html), with some near-coastal updates. In an initial step toward LITHO1.0, the model is then validated against new global surface wave disperison maps and adjusted in areas of extreme misfit. This poster presents the next validation step: compare the new Moho depths with in-situ active source and receiver function results. We also present comparisons with CRUST2.0. CRUST1.0 is available for download. References: Pasyanos, M.E., Masters, G., Laske, G. and Ma, Z., LITHO1.0 - An Updated Crust and Lithospheric Model of the Earth Developed Using Multiple Data Constraints, Abstract T11D-09 presented at 2012 Fall Meeting, AGU, San Francisco, Calif., 3-7 Dec, 2012. Artemieva, I.M. and Mooney, W.D., Thermal thickness and evolution of Precambrian lithosphere: A global study, J. Geophys. Res., 106, 16,387-16,414, 2001. Bassin, C., Laske, G. and Masters, G., The Current Limits of Resolution for Surface Wave Tomography in North America, EOS Trans AGU, 81, F897, 2000. Laske, G. and Masters, G., A Global Digital Map of Sediment Thickness, EOS Trans. AGU, 78, F483, 1997. URL: http://igppweb.ucsd.edu/~gabi/crust1.html

  20. A 17 Ma onset for the post-collisional K-rich calc-alkaline magmatism in the Maghrebides: Evidence from Bougaroun (northeastern Algeria) and geodynamic implications

    Abbassene, Fatiha; Chazot, Gilles; Bellon, Hervé; Bruguier, Olivier; Ouabadi, Aziouz; Maury, René C.; Déverchére, Jacques; Bosch, Delphine; Monié, Patrick

    2016-04-01

    Bougaroun is the largest pluton (~ 200 km2) in the 1200 km-long Neogene magmatic belt located along the Mediterranean coast of Maghreb. New U-Pb dating on zircons and K-Ar ages on whole rocks and separated minerals document its emplacement at 17 Ma within the Lesser Kabylian basement, a continental block that collided with the African margin during the Neogene. This Upper Burdigalian intrusion is therefore the oldest presently identified K-rich calc-alkaline massif in the whole Maghrebides magmatic lineament and marks the onset of its activity. The Bougaroun peraluminous felsic rocks display a very strong crustal imprint. Associated mafic rocks (LREE-enriched gabbros) have preserved the "orogenic" (subduction-related) geochemical signature of their mantle source. Older depleted gabbros cropping out at Cap Bougaroun are devoid of clear subduction-related imprint and yielded Ar-Ar hornblende ages of 27.0 ± 3.0 Ma and 23.3 ± 3.2 Ma. We suggest that they are related to the Upper Oligocene back-arc rifted margin and Early Miocene oceanic crust formation of the nearby Jijel basin, an extension of the Algerian basin developed during the African (Tethyan) slab rollback. The fact that the Bougaroun pluton intrudes exhumed Kabylian lower crustal units, mantle slices and flysch nappes indicates that the Kabylian margin was already stretched and in a post-collisional setting at 17 Ma. We propose a tectono-magmatic model involving an Early Miocene Tethyan slab breakoff combined with delamination of the edges of the African and Kabylian continental lithospheres. At 17 Ma, the asthenospheric thermal flux upwelling through the slab tear induced the thermal erosion of the Kabylian lithospheric mantle metasomatized during the previous subduction event and triggered its partial melting. We attribute the strong trace element and isotopic crustal signature of Bougaroun felsic rocks to extensive interactions between ascending mafic melts and the African crust underthrust beneath the Kabylie de Collo basement.

  1. Physics of Neutron Star Crusts

    Chamel Nicolas; Haensel Pawel

    2008-01-01

    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.

  2. Physics of Neutron Star Crusts

    Chamel Nicolas

    2008-12-01

    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.

  3. MaTeam-projektet

    Andreasen, Marikka; Damkjr, Helle Sejer; Hjgaard, Tomas

    Projektet MaTeam beskrives med fokus p et torigt forsg hvor matematiklrerne p 4.-6. klassetrin p fire skoler i Silkeborg Kommune samarbejdede med forfatterne. Projektet handlede om udvikling af matematiklrerkompetencer med fokus p samarbejdet i de fire skolers matematiklrerfagteam...... matematiklrerfagteam og samarbejdsrelationer der indgr i projektet. Desuden beskriver vi forskellige typer af fagteam og lrere. Metodisk var MaTeam-projektet struktureret som en didaktisk modelleringsproces....

  4. Continued Evidence for Input of Chlorine into the Martian Crust from Degassing of Chlorine-Rich Martian Magmas with Implications for Potential Habitability

    Filiberto, J.; Gross, J.

    2014-12-01

    The chlorine-concentration (or salinity) of a fluid affects the potential for that fluid to be a habitable environment, with most known terrestrial organisms preferring low salinity fluids [1, 2]. The Martian crust (as analyzed by the Gamma Ray Spectrometer) is chlorine-rich with up to 0.8 wt% Cl; while the MER rovers Spirit and Opportunity as well as MSL Curiosity have analyzed rocks with even higher chlorine concentrations [e.g., 3]. This suggests that any potential fluid flowing through the crust would have high chlorine concentrations and therefore high salinity. Here we investigate the bulk and mineral chemistry of the SNC meteorites to constrain the pre-eruptive chlorine concentrations of Martian magmas as the potential source of chlorine in the Martian crust. Bulk SNC meteorites have Cl concentrations similar to terrestrial Mid Ocean Ridge Basalts which would suggest a Cl content of the Martian interior similar to that of the Earth [4]. However, based on Cl/La ratios, the Martian interior actually has 2-3 times more Cl than the Earth [5]. This is also reflected in the composition of Cl-rich minerals within the SNC meteorites [5, 6] and suggests that the pre-eruptive parental magmas to the SNC meteorites were Cl-rich. Eruption and degassing of such Cl-rich magmas would have delivered Cl to the Martian crust, thereby increasing the salinity of any fluids within the crust. [1] Rothschild L.J. and R.L. Mancinelli (2001) Nature. 409: 1092-1101. [2] Sharp Z.D. and D.S. Draper (2013) EPSL. 369-370: 71-77. [3] Taylor G.J. et al. (2010) GRL. 37: L12204. [4]. Burgess R. et al (2013) GCA 77: 793. [5] Filiberto J. and A.H. Treiman (2009) Geology. 37: 1087-1090. [6] McCubbin F.M. et al. (2013) MaPS. 48: 819-853.

  5. A model of oceanic development by ridge jumping: Opening of the Scotia Sea

    Maldonado, Andrs; Bohoyo, Fernando; Galindo-Zaldvar, Jess; Hernndez-Molina, F. Javier; Lobo, Francisco J.; Lodolo, Emanuele; Martos, Yasmina M.; Prez, Lara F.; Schreider, Anatoly A.; Somoza, Luis

    2014-12-01

    Ona Basin is a small intra-oceanic basin located in the southwestern corner of the Scotia Sea. This region is crucial for an understanding of the early phases of opening of Drake Passage, since it may contain the oldest oceanic crust of the entire western Scotia Sea, where conflicting age differences from Eocene to Oligocene have been proposed to date. The precise timing of the gateway opening between the Pacific and Atlantic oceans, moreover, has significant paleoceanographic and global implications. Two sub-basins are identified in this region, the eastern and western Ona basins, separated by the submarine relief of the Ona High. A dense geophysical data set collected during the last two decades is analyzed here. The data include multichannel seismic reflection profiles, and magnetic and gravimetric data. The oceanic basement is highly deformed by normal, reverse and transcurrent faults, as well as affected by deep intrusions from the mantle. The initial extension and continental thinning, with subsequent oceanic spreading, were followed by compression and thrusting. Several elongated troughs, bounded by faults, depict a thick sequence of depositional units in the basin. Eight seismic units are identified in a deep trough of the eastern Ona Basin. The deposits reach a thickness of 5 km, a consistent value not previously reported from the Scotia Sea. A body of chaotic seismic facies is also observed above the thinned continental crust of the Ona High. Magnetic seafloor anomalies older than C10 (~ 28.5 Ma) may be present in the region. The anomalies could include up to chron C12r (~ 32 Ma), although their identification is difficult, since the amplitude is subdued and the original oceanic crust was highly deformed by later faulting and thrusting. The magnetic anomaly distribution is not congruent with seafloor spreading from a single ridge. The basin plain is tilted and subducted southwestward below the South Shetland Islands Block, particularly in the western part, where an accretionary prism is identified. Such tectonics, locally affecting up to the most recent deposits, imply that a portion of the primitive oceanic crust is absent. Based on the stratigraphy of the deposits and the magnetic anomalies, an age of 44 Ma is postulated for the initiation of oceanic spreading in the eastern Ona basin, while spreading in the western Ona Basin would have occurred during the early Oligocene. The tectonics, depositional units and the age of the oceanic crust provide additional evidence regarding the Eocene opening of Drake Passage. The initial tectonic fragmentation of the South America-Antarctic Bridge, followed by oceanic spreading, was characterized by jumping of the spreading centers. An Eocene spreading center in the eastern Ona Basin was the precursor of the Scotia Sea. A model comprising four tectonic evolutionary phases is proposed: Phase I, Pacific subduction - Paleocene to middle Eocene; Phase II, eastern Ona back-arc spreading - middle to late Eocene; Phase III, ridge jumping and western Ona back-arc spreading - early Oligocene; and Phase IV, ridge jumping and West Scotia Ridge spreading - early Oligocene to late Miocene. The development of shallow gateways allowed for an initial connection between the Pacific and Atlantic oceans and, hence, initiated the thermal isolation of Antarctica during the middle and late Eocene. Deep gateways that enhanced the full isolation of Antarctica developed in Drake Passage from the Eocene/Oligocene transition onward. A significant correlation is observed between the tectonics, stratigraphic units and major climate events, thereby indicating the influence of the local tectonic and paleoceanographic events of the Southern Ocean on global evolution.

  6. Copper-nickel-rich, amalgamated ferromanganese crust-nodule deposits from Shatsky Rise, NW Pacific

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

    2012-10-01

    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.

  7. Origin of the 'Gabbro' Signature in Ocean Island Basalts: Constraints from Osmium Isotopic Ratios of Galapagos Basalts

    Gibson, S. A.; Dale, C. W.; Geist, D.; Harpp, K. S.

    2014-12-01

    The Re-Os isotope system has become increasingly used as a tracer of lithological heterogeneity in the convecting mantle, with radiogenic 187Os/188Os in high-Os oceanic basalts and picrites widely interpreted as evidence of a melt contribution from ancient recycled oceanic crust. When combined with 206Pb/204Pb and O isotopes, 187Os/188Os ratios have been used to identify distinct lithological units (i.e. sediments, gabbros and basalts). We report new 187Os/188Os for basalts with high Os (>40 ppt) and MgO from Galpagos, which range from near primitive mantle values (0.130) to highly radiogenic (0.155). While co-variations in 187Os/188Os and 206Pb/204Pb for some Galpagos basalts (Floreana-type) are HIMU like, and consistent with melting of ancient recycled oceanic crust, others have variable 187Os/188Os ratios and primitive to depleted mantle like 206Pb/204Pb. Similar variations in Os and Pb isotopic space have been interpreted in other OIB suites as melts from recycled ancient oceanic gabbros, entrained by upwelling mantle plumes. Nevertheless, a marked east-west spatial variation in 187Os/188Os of Galpagos basalts does not correlate with postulated lithological variations in the Galpagos plume (Vidito et al., 2013). We show that basalts in eastern Galpagos with elevated 187Os/188Os and positive Sr anomalies occur in the vicinity of over-thickened 10 Ma gabbroic crust, that formed when the Galpagos plume was on-axis. We propose the elevated 187Os/188Os of Galpagos basalts are due to in-situ assimilation of young gabbroic lower crust, with high Re/Os, rather than melting of ancient recycled material in the Galpagos plume. In western Galpagos recent plume accreted crust is thick but more mafic, the melt flux higher and assimilation more sporadic. The contamination thresholds of Os and MgO in Galpagos basalts occur at higher contents than for many global OIBs (Azores, Iceland, Hawaii) and may reflect both a relatively low melt flux into the crust from the weak Galpagos plume (Tp=1400 oC) and excess thickness of ridge-formed gabbro in the east of the archipelago. Similar in-situ assimilation of lower oceanic crust by high-Os and MgO-rich OIBs suites may have been overlooked in the quest for establishing melting of ancient recycled oceanic gabbro in hotspots and heterogeneity in the convecting mantle.

  8. Geology of Nascent Ocean Basins: Insights from Western Pacific Back-arc Basins and the Gulf of California

    Hawkins, J. W.; Castillo, P. R.

    2001-12-01

    The origin of ocean basins must involve complex interplay between heat transfer, lithosphere extension, attenuation, and rupture, and emplacement of mantle-derived melts. Petrologic details of early evolution of present Atlantic-style basins are masked by thick sedimentary prisms of passive margins. Ophiolites are lithosphere remnants from aborted ocean basins, but few seem to have originated in deep ocean. We propose that supra-subduction zone (SSZ) forearcs and backarc basins, e.g., Lau Basin, Mariana Trough, and intra-continental rifts, e.g., Salton Trough - Gulf of Calif. are analogues for two types of nascent ocean basins. In both types upwelling fertile mantle partly melts to form MORB-like crust. Silici-clastic arc/continental sediments, deposited coeval with mafic volcanics, in rift basins, is distinctive. In both settings characteristic rock age relations and petrology/chemistry are useful in recognizing them in the geologic record. Cenozoic SSZ systems exhibit multi-stage evolution of crust/mantle owing to mantle upwelling and local extension in broad regions of crustal contraction. Volcanic island arc tholeiite (IAT) eruptions are accompanied by forearc extension, rift basins fill with silici-clastics and basalts, forearc volcanism includes boninites and IAT. These have HFSE depletion and varied LILE enrichment. MORB, IAT, Fe-Ti basalts and transitional types erupt on propagating rifts to form "backarc" basin crust. "New" volcanic arcs form outboard of backarc ridges. "Remnant" arc, "new" arc, backarc and forearc magmas may erupt nearly coeval for ~5 Ma. They may be interbedded with arc-clastic rocks. The Salton Trough - Gulf of Calif. developed by mantle upwelling, coupled with crustal extension, causing continental crust thinning, detachment faults, rifting, and volcanism having varied chemistry. There is a N-S transition from extended (Basin-Range) continental crust, to inter-continental rifts having both sediments and basalt, to intra-continental ocean crust (Alarcon Rise, 23-24oN). Regionally, ~40 my lithosphere extension culminated at 3.6 Ma with seafloor spreading forming N-MORB on Alarcon Rise. There is a N-S progression from mantle-derived basalts modified by extensive fractionation /crustal assimilation to N-MORB on Alarcon Rise.

  9. High-precision TIMS U-Pb dating and SHRIMP trace element analyses of zircons from plutonic crust from ODP Hole 735B, Atlantis Bank, Southwest Indian Ridge

    Rioux, M. E.; Cheadle, M. J.; John, B. E.; Bowring, S. A.; Wooden, J. L.; Baines, G.

    2012-12-01

    Ocean Drilling Program Hole 735B at Atlantis Bank on the Southwest Indian Ridge is the deepest drill hole (1508m) into plutonic oceanic crust. The recovered core provides the opportunity to study both the processes and timescales of lower crustal accretion at a slow-spreading mid-ocean ridge. Major element chemistry suggests that the crust is made up of three 200-1000m thick igneous series (Natland and Dick, 2002). Previous SHRIMP U/Pb dating of zircons from oxide gabbro and felsic/dioritic dikes/veins from the length of the core found no resolvable age differences, suggesting rapid crustal growth; SHRIMP Th-corrected weighted mean 206Pb/238U dates ranged from 11.86 ± 0.20 to 12.13 ± 0.21 Ma (Baines et al., 2009). Here we report combined SHRIMP chemical analyses and high precision TIMS U-Pb geochronology on zircons from a suite of fifteen samples from depths of 26-1430 mbsf. The samples are from each of the three main intrusive series and range from oxide gabbro to diorite and granodiorite dikes/veins. Single grain TIMS 206Pb/238U date uncertainties for most analyses range from ~0.01-0.2 Ma and weighted mean 206Pb/238U date uncertainties range from ~0.004-0.07 Ma, providing precise constraints on the timing and duration of magmatism. Zircon chemistry is variable between samples (John et al., this meeting). Ti and Hf from spot analyses within individual samples range from tight clusters of data to linear trends of decreasing Ti with increasing Hf. Apparent Ti-in-zircon temperature variations within samples range from ~60-230°C, and variations within single grains are as large as 160°C. For zircons with significant chemical zoning, the cores are typically higher in Ti and lower in Hf than the rims. Th-corrected single grain 206Pb/238U dates from individual samples typically overlap within uncertainty, consistent with crystallization of a single batch of magma with no evidence for assimilation of older crust or protracted crystallization, as has been seen in high precision dates from the Mid-Atlantic Ridge and East Pacific Rise (Lissenberg et al., 2009; Rioux et al., 2012). However, two diorite dikes each contain populations of younger zircons with dates of ~11.9 Ma and a single older zircon with a date of ~12.4 Ma, suggesting that these magmas entrained zircons from older but so far unrecognized wall rocks. Resolvable age differences between the most precisely dated rocks suggest that the upper-two magmatic series (0-540 mbsf) under went final crystallization before the lowest series (540-1508 mbsf). Two precisely dated samples from the top two magmatic series have weighted mean 206Pb/238U dates of 12.00 ± 0.02 Ma and 11.96 ± 0.02 Ma. Six precisely dated samples from a range of depths in the deepest magmatic series all have younger weighted mean 206Pb/238U dates of 11.94 ± 0.02 to 11.91 ± 0.01 Ma. The current data do not show resolvable correlations between Th-corrected 206Pb/238U dates and zircon chemistry within individual samples.

  10. 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 (H11076_GEO_1MSSS.TIF, Geographic)

    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...

  11. 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 (H11076_GEO_1MMBES.TIF, Geographic)

    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...

  12. [MaRS Project

    Aruljothi, Arunvenkatesh

    2016-01-01

    The Space Exploration Division of the Safety and Mission Assurances Directorate is responsible for reducing the risk to Human Space Flight Programs by providing system safety, reliability, and risk analysis. The Risk & Reliability Analysis branch plays a part in this by utilizing Probabilistic Risk Assessment (PRA) and Reliability and Maintainability (R&M) tools to identify possible types of failure and effective solutions. A continuous effort of this branch is MaRS, or Mass and Reliability System, a tool that was the focus of this internship. Future long duration space missions will have to find a balance between the mass and reliability of their spare parts. They will be unable take spares of everything and will have to determine what is most likely to require maintenance and spares. Currently there is no database that combines mass and reliability data of low level space-grade components. MaRS aims to be the first database to do this. The data in MaRS will be based on the hardware flown on the International Space Stations (ISS). The components on the ISS have a long history and are well documented, making them the perfect source. Currently, MaRS is a functioning excel workbook database; the backend is complete and only requires optimization. MaRS has been populated with all the assemblies and their components that are used on the ISS; the failures of these components are updated regularly. This project was a continuation on the efforts of previous intern groups. Once complete, R&M engineers working on future space flight missions will be able to quickly access failure and mass data on assemblies and components, allowing them to make important decisions and tradeoffs.

  13. The thermal effect of fluid circulation in the subducting crust on slab melting in the Chile subduction zone

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

    2016-01-01

    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.

  14. Color characterization of Arctic Biological Soil Crusts

    Mele, Giacono; Gargiulo, Laura; Ventura, Stefano

    2015-04-01

    Global climate change makes large areas lacking the vegetation coverage continuously available to primary colonization by biological soil crusts (BSCs). This happens in many different environments, included high mountains and Polar Regions where new areas can become available due to glaciers retreat. Presence of BSCs leads to the stabilization of the substrate and to a possible development of protosoil, with an increase of fertility and resilience against erosion. Polar BSCs can exhibit many different proportions of cyanobacteria, algae, microfungi, lichens, and bryophytes which induce a large variability of the crust morphology and specific ecosystem functions. An effective and easy way for identifying the BSCs in the field would be very useful to rapidly recognize their development stage and help in understanding the overall impact of climate change in the delicate polar environments. Color analysis has long been applied as an easily measurable physical attribute of soil closely correlated with pedogenic processes and some soil functions. In this preliminary work we used RGB and CIE-L*a*b* color models in order to physically characterize fourteen different BSCs identified in Spitsbergen island of Svalbard archipelago in Arctic Ocean at 79 north latitude. We found that the "redness parameter "a*" of CIE-L*a*b* model was well correlated to the succession process of some BSCs at given geomorphology condition. Most of color parameters showed, moreover, a great potential to be correlated to photosynthetic activity and other ecosystem functions of BSCs.

  15. {sup 238}U-{sup 234}U-{sup 230}Th chronometry of Fe-Mn crusts: Growth processes and recovery of thorium isotopic ratios of seawater

    Chabaux, F.; Cohen, A.S.; O`Nions, R.K. [Univ. of Cambridge (United Kingdom); Hein, J.R. [Geological Survey, Menlo Park, CA (United States)

    1995-02-01

    Comparison of ({sup 234}U){sub excess}/({sup 238}U) and ({sup 230}Th)/({sup 232}Th) activity ratios in oceanic Fe-Mn deposits provides a method for assessing the closed-system behaviour of {sup 238}U-{sup 234}U-{sup 230}Th, as well as variations in the initial uranium and thorium isotopic ratios of the precipitated metal oxides. This approach is illustrated using a Fe-Mn crust from Lotab seamount (Marshall Islands, west equatorial Pacific). Here we report uranium and thorium isotopic compositions in five subsamples from the surface of one large 5 cm diameter botyroid of this crust, and from two depth profiles of the outermost rim of the same botyroid. The decrease of ({sup 234}U){sub excess}/({sup 238}U) and ({sup 230}Th/{sup 232}Th) activity ratio with depth in the two profiles gives mean growth rates, for the last 150 ka, of 7.8 {+-} 2 mm/Ma and 6.6 {+-} 1 mm/Ma, respectively. All data points (surface and core samples) but one, define a linear correlation in the Ln ({sup 230}Th/{sup 232}Th) - Ln [({sup 234}U){sub excess}({sup 238}U)] diagram. This correlation indicates that for all points the U-Th system remained closed after the Fe-Mn layer precipitated, and that the different samples possessed the same initial Uranium and thorium isotope ratios. Furthermore, these results show that the preserved surface of this Fe-Mn crust may not be the present-day growth surface, and that the thorium and uranium isotopic ratios of seawater in west equatorial Pacific have not changed during the past 150 ka. The initial thorium activity ratio is estimated from the correlation obtained between Ln({sup 230}Th/{sup 232}Th) and Ln [({sup 234}U){sub excess}/({sup 238}U)].

  16. 238U-234U-230Th chronometry of Fe-Mn crusts: Growth processes and recovery of thorium isotopic ratios of seawater

    Comparison of (234U)excess/(238U) and (230Th)/(232Th) activity ratios in oceanic Fe-Mn deposits provides a method for assessing the closed-system behaviour of 238U-234U-230Th, as well as variations in the initial uranium and thorium isotopic ratios of the precipitated metal oxides. This approach is illustrated using a Fe-Mn crust from Lotab seamount (Marshall Islands, west equatorial Pacific). Here we report uranium and thorium isotopic compositions in five subsamples from the surface of one large 5 cm diameter botyroid of this crust, and from two depth profiles of the outermost rim of the same botyroid. The decrease of (234U)excess/(238U) and (230Th/232Th) activity ratio with depth in the two profiles gives mean growth rates, for the last 150 ka, of 7.8 ± 2 mm/Ma and 6.6 ± 1 mm/Ma, respectively. All data points (surface and core samples) but one, define a linear correlation in the Ln (230Th/232Th) - Ln [(234U)excess(238U)] diagram. This correlation indicates that for all points the U-Th system remained closed after the Fe-Mn layer precipitated, and that the different samples possessed the same initial Uranium and thorium isotope ratios. Furthermore, these results show that the preserved surface of this Fe-Mn crust may not be the present-day growth surface, and that the thorium and uranium isotopic ratios of seawater in west equatorial Pacific have not changed during the past 150 ka. The initial thorium activity ratio is estimated from the correlation obtained between Ln(230Th/232Th) and Ln [(234U)excess/(238U)

  17. Obduction of old oceanic lithosphere due to reheating and plate reorganization: Insights from numerical modelling and the NE Anatolia - Lesser Caucasus case example

    Hässig, Marc; Duretz, Thibault; Rolland, Yann; Sosson, Marc

    2016-05-01

    The ophiolites of NE Anatolia and of the Lesser Caucasus (NALC) evidence an obduction over ∼200 km of oceanic lithosphere of Middle Jurassic age (c. 175-165 Ma) along an entire tectonic boundary (>1000 km) at around 90 Ma. The obduction process is characterized by four first order geological constraints: Ophiolites represent remnants of a single ophiolite nappe currently of only a few kilometres thick and 200 km long. The oceanic crust was old (∼80 Ma) at the time of its obduction. The presence of OIB-type magmatism emplaced up to 10 Ma prior to obduction preserved on top of the ophiolites is indicative of mantle upwelling processes (hotspot). The leading edge of the Taurides-Anatolides, represented by the South Armenian Block, did not experience pressures exceeding 0.8 GPa nor temperatures greater than ∼300 °C during underthrusting below the obducting oceanic lithosphere. An oceanic domain of a maximum 1000 km (from north to south) remained between Taurides-Anatolides and Pontides-Southern Eurasian Margin after the obduction. We employ two-dimensional thermo-mechanical numerical modelling in order to investigate obduction dynamics of a re-heated oceanic lithosphere. Our results suggest that thermal rejuvenation (i.e. reheating) of the oceanic domain, tectonic compression, and the structure of the passive margin are essential ingredients for enabling obduction. Afterwards, extension induced by far-field plate kinematics (subduction below Southern Eurasian Margin), facilitates the thinning of the ophiolite, the transport of the ophiolite on the continental domain, and the exhumation of continental basement through the ophiolite. The combined action of thermal rejuvenation and compression are ascribed to a major change in tectonic motions occurring at 110-90 Ma, which led to simultaneous obductions in the Oman (Arabia) and NALC regions.

  18. Sulfur and metal fertilization of the lower continental crust

    Locmelis, Marek; Fiorentini, Marco L.; Rushmer, Tracy; Arevalo, Ricardo; Adam, John; Denyszyn, Steven W.

    2016-02-01

    Mantle-derived melts and metasomatic fluids are considered to be important in the transport and distribution of trace elements in the subcontinental lithospheric mantle. However, the mechanisms that facilitate sulfur and metal transfer from the upper mantle into the lower continental crust are poorly constrained. This study addresses this knowledge gap by examining a series of sulfide- and hydrous mineral-rich alkaline mafic-ultramafic pipes that intruded the lower continental crust of the Ivrea-Verbano Zone in the Italian Western Alps. The pipes are relatively small (asthenospheric rise during the orogenic collapse of the Variscan belt (< 300 Ma). Unlike previous models, outcomes from this study suggest a significant temporal gap between the occurrence of mantle metasomatism, subsequent partial melting and emplacement of the pipes. We argue that this multi-stage process is a very effective mechanism to fertilize the commonly dry and refractory lower continental crust in metals and volatiles. During the four-dimensional evolution of the thermo-tectonic architecture of any given terrain, metals and volatiles stored in the lower continental crust may become available as sources for subsequent ore-forming processes, thus enhancing the prospectivity of continental block margins for a wide range of mineral systems.

  19. Semi-Empirical Oceanic Depth-Age Relationship Inferred from Bathymetric Curve

    Niedzielski, Tomasz; Jurecka, Miros?awa; Migo?, Piotr

    2015-11-01

    In this paper, we report on a preliminary investigation into a semi-empirical method for derivation of depth-age relationship for oceanic lithosphere. The global 30-arcsecond bathymetry data from the General Bathymetric Charts of the Oceans (GEBCO) were corrected for (1) sediment thickness using the Total Sediment Thickness of the World's Oceans and Marginal Seas and (2) isostasy. The corrected bathymetry was processed to obtain the empirical bathymetric curve, the solution computed with 50 m elevation bin. Subsequently, the data-based curve was approximated with the optimal polynomial model. By combining the model with a formula for derivative of area with respect to age, we obtained the approximate differential equation for depth-age relationship. We solved the equation numerically. The solution was compared with (1) depth-age relationships derived empirically using the combination of the corrected GEBCO bathymetry with digital isochrons of the oceans, (2) Parsons Sclater Model (PSM) and (3) Global Depth Heatflow model (GDH1). In the new depth-age curve, three sections with specific relationships of ocean depth versus age of the crust are identified: (1) moderate increase in depth from 2500 to 5900 m for lithospheric ages 0-118 Ma, (2) more pronounced increase in depth from 5900 to 6700 m for the lithosphere 118-147 Ma old, (3) stabilization of ocean depth at 6700-6760 m for the lithosphere older than 147 Ma. The fit to empirical data as well as PSM and GDH1 models is good for the first section, but rather imperfect for the other two. Reasons for mismatches are complex and probably different for dissimilar sections of the curve.

  20. Profiling planktonic foraminiferal crust formation

    Steinhardt, Juliane; de Nooijer, Lennart L. J.; Brummer, Geert-Jan; Reichart, Gert-Jan

    2015-07-01

    Planktonic foraminifera migrate vertically through the water column during their life, thereby growing and calcifying over a range of depth-associated conditions. Some species form a calcite veneer, crust, or cortex at the end of their lifecycle. This additional calcite layer may vary in structure, composition, and thickness, potentially accounting for most of their total shell mass and thereby dominating the element and isotope signature of the whole shell. Here we apply laser ablation ICP-MS depth profiling to assess variability in thickness and Mg/Ca composition of shell walls of three encrusting species derived from sediment traps. Compositionally, Mg/Ca is significantly lower in the crusts of Neogloboquadrina dutertrei and Globorotalia scitula, as well as in the cortex of Pulleniatina obliquiloculata, independent of the species-specific Mg/Ca of their lamellar calcite shell. Wall thickness accounts for nearly half of the total thickness in both crustal species and nearly a third in cortical P. obliquiloculata, regardless of their initial shell wall thickness. Crust thickness and crustal Mg/Ca decreases toward the younger chambers in N. dutertrei and to a lesser extent, also in G. scitula. In contrast, the cortex of P. obliquiloculata shows a nearly constant thickness and uniform Mg/Ca through the complete chamber wall. Patterns in thickness and Mg/Ca of the crust indicate that temperature is not the dominant factor controlling crust formation. Instead, we present a depth-resolved model explaining compositional differences within individuals and between successive chambers as well as compositional heterogeneity of the crust and lamellar calcite in all three species studied here.

  1. Early oceanic opening off Western India-Pakistan margin: The Gop Basin revisited

    Yatheesh, V.; Bhattacharya, G. C.; Dyment, J.

    2009-07-01

    The Deccan Traps, one of the best known examples of rapid flood basalt, are considered as marking of the inception of a mantle plume on the Indian continental lithosphere. Their emplacement may be associated with the continental break-up of India and the Seychelles block and later formation of a new spreading centre, the Carlsberg Ridge, while spreading progressively ceased in the Mascarene Basin. Whether rifting, continental break-up, and seafloor spreading predated or were the consequence of the Deccan Traps emplacement is still a matter of debate. This issue is further complicated by the presence of a continental sliver, the Laxmi Ridge, and large basins lying landward of the Laxmi Ridge, such as the Laxmi and Gop basins, where nature of the crust is still ambiguous. The present study attempts to decipher the tectonic setting and the imprints of plume-ridge interaction in the Gop Basin, where the crust has been interpreted as either volcanic-intruded thinned continental crust or oceanic crust formed by a now-extinct spreading centre. Based on interpretation of an updated compilation of marine geophysical data, the present study supports the oceanic nature of the crust underlying the Gop Basin and proposes the Palitana Ridge as the extinct spreading centre in this region. The prominent but short sequence of fairly linear magnetic anomalies in the Gop Basin does not allow a unique identification; it can be reasonably explained either as A31r-A25r (˜ 69.3-56.4 Ma) or as A29r-A25r (˜ 64.8-56.4 Ma) sequence. The variations of the spreading rates assumed by both these models suggest that spreading in the Gop Basin significantly slowed around 65 Ma, contemporaneous with the magmatic outburst of the Reunion plume on the adjacent western Indian mainland. Subsequently, the Gop Basin spreading centre was waning whereas a new spreading centre was developing further south, close to the (relatively) southward migrating plume. In this last stage, the Gop Basin spreading centre was associated with an abundant magmatism, probably supplied from the plume region.

  2. Tracking the movement of magma through the crust in the East African rift

    Ebinger, Cynthia

    2010-10-01

    Although fault and magmatic processes have achieved plate spreading at mid-ocean ridges throughout Earth's history, intense volcano-tectonic rifting episodes have rarely been observed. A 65 km-long segment of the subaerial Red Sea rift in Ethiopia experienced a major volcano-tectonic rifting episode in September 2005. Incipient seafloor spreading centers in the Afar rift are surrounded by continental crust and mantle lithosphere stretched and intruded during the past 30 Ma as Africa and Arabia have rifted apart above a mantle plume. We use seismic data and complementary space-based geodetic and remote sensing data to determine the length and timescales of magmatism and faulting, the partitioning of strain between faulting and magmatism, and their implications for the maintenance of along-axis segmentation. Most of the magma for the initial and subsequent 12 intrusions was sourced from the center of the Dabbahu-Manda Hararo rift segment. Strain is accommodated primarily by axial dike intrusions fed from mid-segment magma chamber(s). These findings show that episodic (approximate century interval), rapid opening of discrete rift segments is the primary mechanism of plate boundary deformation. The length scale (˜65 km) and intensity of crustal deformation (˜6 m), as well as the volume of intrusive and extrusive magmatism (>3 cubic km) provokes a re-evaluation of seismic and volcanic hazards in subaerial rift zones.

  3. The formation of ultradeep sedimentary basins through metamorphism with rock contraction in continental crust

    Artyushkov, E. V.; Belyaev, I. V.; Kazanin, G. S.; Pavlov, S. P.; Chekhovich, P. A.; Shkarubo, S. I.

    2013-10-01

    Sedimentary covers are up to 15-20 km thick in ultradeep sedimentary basins. Joint interpretation of seismic reflection sounding and gravimetric data indicates that eclogites are located in the basins under the Moho. In these rocks the velocities of P-waves are close to those in mantle peridotites. The basins show only moderate crustal stretching and their formation was caused primarily by the transformation of gabbroids into dense eclogites in the lower part of the continental crust. The transformation took place episodically as mantle fluids infiltrated the lower crust and it was ensured by pressure rise in the lower crust occurring with the accumulation of sediments. Moderate metamorphism developed in silicic upper crust as temperature and pressure increased under thick sedimentary covers. In iron-rich metasedimentary rocks, deep metamorphism resulted in the density increase, and P-wave velocities there increased to those characteristic of the oceanic crust.

  4. Precambrrian continental crust evolution of southeastern Sao Paulo state-Brazil: based on isotopico evidences

    The focussed area comprises five major different tectonic terranes separated by faults, which are named Alto Rio Grande Belt, Socorro-Guaxupe Nappe, Sao Roque, Embu and Costeiro Domains. The geological and geochronological history of these terranes show that the metamorphic episodes of crust-forming occurred involving both mantle-derived magmas and reworking of continental material since 3.4 Ga until 600 Ma. The post-tectonic granitic activities occurred within 1000-500 Ma range and in general, the rocks are progressively younger from the Socorro-Guaxupe Nappe (1000-850 Ma) in the NW towards the Costeiro Domain (550 Ma) in the SE. The Sr and Pb isotopic evidences, together with geological and geophysical informations, suggest that the proportions of the rock-forming processes through the geological time are: Archean, 10%; Lower Proterozoic, 10%; Middle Proterozoic, 38%; Late Proterozaic, 42%. Although the Mid and Late Proterozoic time were a period of a large amount of rocks were formed, they were not a major crustforming period, because these rocks are mainly constituted by recycled continental crust material. In our view, at end of the Early Proterozoic time, at least 85% of continetal crust, in this area, has accreted and differentiate. During the Middle and Late Proterozoic the continental crust grew at small rate. (author)

  5. Processes of Magma-crust Interaction : Insights from Geochemistry and Experimental Petrology

    Deegan, Frances M.

    2010-01-01

    This work focuses on crustal interaction in magmatic systems, drawing on experimental petrology and elemental and isotope geochemistry. Various magma-chamber processes such as magma-mixing, fractional crystallisation and magma-crust interaction are explored throughout the papers comprising the thesis. Emphasis is placed on gaining insights into the extent of crustal contamination in ocean island magmas from the Canary Islands and the processes of magma-crust interaction observed both in natur...

  6. M&A Cooperative Games

    Maria A. Nastych

    2014-01-01

    Cooperative game theory instruments application to the corporate finance M&A research issues provide an ability to extend the field considered and conclusions obtained. The paper presents the M&A cooperative games modeling and its empiri-cal implementation to analyze the airline strategic alliance as M&A deal.

  7. Thickness of Mercury's crust from MESSENGER gravity and altimetry data

    Padovan, S.; Wieczorek, M. A.; Margot, J. L.; Tosi, N.; Solomon, S. C.

    2014-12-01

    The major igneous events that form and shape the crust of a rocky body, such as magma ocean solidification and volcanism, affect the interior thermo-chemical evolution through control on the bulk volatile content, partitioning of heat-producing elements, and heat loss. Therefore, characterizing the crust of a body provides information on that object's origin, differentiation, and subsequent geologic evolution. For Mercury, the crust may hold clues in particular to the still poorly understood processes of formation of this planet. Analysis of geoid-to-topography ratios (GTRs) has been previously applied to infer the thickness of the crust of the Moon, Mars, and Venus. We perform a similar analysis for Mercury with the gravity and altimetry data acquired by the MESSENGER spacecraft. We consider only the northern hemisphere, where the gravity field and topography are well constrained. We assume that Airy isostasy is the principal mechanism of support of variations in topography, and we therefore exclude from the analysis regions that might not be compatible with this assumption, such as large expanses of smooth plains and large impact basins. For a conservative range of densities of the crust, we infer a crustal thickness of 35±18 km (one standard deviation). This new mean value is substantially less than earlier estimates that were based on viscous relaxation of topography, on the relation between the low-degree gravity field and equatorial ellipticity, and on the depth of the brittle-ductile transition as constrained by models of thrust faulting and thermal evolution. This relatively thin crust allows for the possibility of excavation of mantle material during the formation of large impact basins (such as Caloris). Such material might be observed with instruments on MESSENGER and the BepiColombo spacecraft now in development.

  8. Geochemical and Sr-Nd-Pb isotopic evidence for ancient lower continental crust beneath the Xi Ujimqin area of NE China

    Gao, Xiaofeng; Guo, Feng; Xiao, Peixi; Kang, Lei; Xi, Rengang

    2016-05-01

    The Central Asian Orogenic Belt (CAOB) is the largest Phanerozoic accretionary orogen on Earth. The role that Precambrian continental microblocks played in its formation, however, remains a highly controversial topic. New zircon U-Pb age data and whole-rock geochemical and Sr-Nd-Pb isotopic studies on Permian (253-251 Ma) andesites from the Xi Ujimqin area provide the first evidence for the existence of a continental lower mafic crust in the eastern segment of the CAOB. These Permian lavas generally have chemical compositions similar to experimental melts of garnet pyroxenites. Based on Sr-Nd-Pb isotopic compositional differences, they can be further subdivided into two groups. Group 1 has moderately radiogenic Sr (87Sr/86Sr(i) = 0.7060-0.7062) and nonradiogenic Nd (εNd(t) = - 9.0-8.3) and Pb (e.g., 206Pb/204Pb = 17.18-17.23) isotopic compositions similar to the ancient lower mafic crust beneath the North China Craton (NCC). Compared with Group 1, Group 2 has less radiogenic Sr (87Sr/86Sr(i) = 0.7051-0.7055), and more radiogenic Nd (εNd(t) = - 0.2-+1.4) and Pb (e.g., 206Pb/204Pb = 18.04-18.20) isotopic compositions as observed in the Phanerozoic granitoids and felsic lavas of the CAOB. The combined geochemical and isotopic data indicate that Group 1 was derived from ancient lower mafic crust of the NCC affinity, with a residual assemblage of pyroxene + plagioclase + amphibole. The source for Group 2 was a mixture of ancient lower mafic crust and a juvenile crustal component, and melting left a residue of orthopyroxene + clinopyroxene + plagioclase + garnet + amphibole. Generation of these two types of late Permian andesites favors a model whereby breakoff of a subducted slab and subsequent lithospheric extension triggered extensive asthenospheric upwelling and melting of the continental mafic lower crust of the eastern CAOB. The discovery of ancient lower continental crust of the NCC affinity in the CAOB implies that the NCC experienced continental breakup during the opening and spreading of the paleo-Asian Ocean.

  9. GALENICALS IN THE TREATMENT OF CRUSTED SCABIES

    Sugathan P; Martin Abhay

    2010-01-01

    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.

  10. Galenicals in the treatment of crusted scabies

    Sugathan P

    2010-01-01

    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.

  11. 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

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

    2015-12-01

    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 εNd(t) and zircon εHf(t) values similar to the Neoproterozoic metabasalts in the NQ unit. In combination with their normal mantle-like δ18Ozir 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.

  12. Continental crust formation seen through the SR and Nd isotope systematics of S-type granites in the Hercynian belt of western France

    The isotopic composition of Sr, Nd and Pd in leucogranites which are intercorrelated (Bernard-Griffiths et al., 1985) may be explained by the mixing of ancient basement 1800 Ma) with juvenile crust (late Precambrian or early Palaeozoic). This hypothesis does not involve the existence of Mid-Proterozoic crust, as apparently indicated by the TDM model ages of the leucogranites (ranging between 1600 and 1100 Ma). The Nd isotopes reveal the crustal reworking while Sr isotopes mainly record juvenile crust formation. This paradox is explained by the geochemical heterogeneity of the sources involved. (orig.)

  13. Seasonal Methane Oxidation Potential in Manure Crusts

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

    2013-01-01

    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.

  14. Origin of the Martian Crust and Mantle

    Hess, P. C.

    2002-01-01

    The existence of a planet-wide early magma ocean on Mars is supported by a growing base of petrochemical and geophysical observations 1) The parent liquids to the SNC meteorites are significantly depleted in Al2O3 and CaO relative to terrestrial basalts. Only terrestrial komatiites, the products of more than 30% melting of the Archean mantle and boninites, wet melts of the mantle wedge in island arc regions, have similar low Al2O3 and CaO contents. Mare basalts and picrite glasses on the Moon have similar geochemical depletions, and the major element compositions of very low Ti mare basalts bear a striking resemblance to the Shergotty parent magmas. What these terrestrial and lunar magmas have in common is that the parent magmas last equilibrated with a mantle severely depleted in magmaphile elements. The boninites and mare basalts, in particular, last coexisted with a mantle residue of olivine and orthopyroxene. In the lunar case the mantle was a product of crystallization from a magma ocean whereas the harzburgite parent mantle for boninites was a residuum to previous melting events that eliminated diopside from the mantle. 2) W-182 and Nd-142 anomalies date the fractionation of the core and mantle, respectively, within about 50- 100 million years of the origin of the solar system. The large heavily crated Martian crust and the absence of large scale recycling suggests strongly that the crust was also a product of this ancient global differentiation and has experienced only modest volcanic activity, particularly in the southern hemisphere, in subsequent epochs. Whole rock Rb-Sr systematics appear to record this planet wide differentiation at about 4.5 Ga 3) The Nd-143 composition of the Martian mantle is significantly more depleted than the terrestrial mantle and even the cumulate source regions of mare basalts on the Moon. Only Archean lithosphere on earth has the extreme positive and negative epsilon values so characteristic of the Martian mantle. Continental lithosphere, by definition, is stable and has withstood the homogenizing effects of mantle convection. The extreme epsilon values reflect ancient depletion events and subsequent metasomatic perturbations. The data is consistent with the early differentiation of a Martian magma ocean producing a buoyant crust, dense core and a complementary stratified cumulate mantle. The stratified cumulate is likely to be gravitationally unstable, at least, in the shallowmost stratigraphic levels where more iron-rich cumulates overlie dense magnesian cumulates. Under these unstable conditions, solid state differentiation would have carried dense, iron-rich and relatively cool cumulates into the Martian interior ultimately resulting in a lower mantle that is denser and compositional more evolved than the upper mantle. This lower mantle would also contain varying amounts of heat producing radioactive elements.

  15. Metamorphism in the Martian crust

    McSween, Harry Y.; Labotka, Theodore C.; Viviano-Beck, Christina E.

    2015-04-01

    Compositions of basaltic and ultramafic rocks analyzed by Mars rovers and occurring as Martian meteorites allow predictions of metamorphic mineral assemblages that would form under various thermophysical conditions. Key minerals identified by remote sensing roughly constrain temperatures and pressures in the Martian crust. We use a traditional metamorphic approach (phase diagrams) to assess low-grade/hydrothermal equilibrium assemblages. Basaltic rocks should produce chlorite + actinolite + albite + silica, accompanied by laumontite, pumpellyite, prehnite, or serpentine/talc. Only prehnite-bearing assemblages have been spectrally identified on Mars, although laumontite and pumpellyite have spectra similar to other uncharacterized zeolites and phyllosilicates. Ultramafic rocks are predicted to produce serpentine, talc, and magnesite, all of which have been detected spectrally on Mars. Mineral assemblages in both basaltic and ultramafic rocks constrain fluid compositions to be H2O-rich and CO2-poor. We confirm the hypothesis that low-grade/hydrothermal metamorphism affected the Noachian crust on Mars, which has been excavated in large craters. We estimate the geothermal gradient (>20 C km-1) required to produce the observed assemblages. This gradient is higher than that estimated from radiogenic heat-producing elements in the crust, suggesting extra heating by regional hydrothermal activity.

  16. The tectonic structure of the Song Ma fault zone, Vietnam

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

    2015-08-01

    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.

  17. Millennium Ecosystem Assessment: MA Scenarios

    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...

  18. Millennium Ecosystem Assessment: MA Scenarios

    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...

  19. Discovery and utilization of sorghum genes (Ma5/Ma6)

    Mullet, John E; Rooney, William L; Klein, Patricia E; Morishige, Daryl; Murphy, Rebecca; Brady, Jeff A

    2012-11-13

    Methods and composition for the production of non-flowering or late flowering sorghum hybrid. For example, in certain aspects methods for use of molecular markers that constitute the Ma5/Ma6 pathway to modulate photoperiod sensitivity are described. The invention allows the production of plants having improved productivity and biomass generation.

  20. The extent of continental crust beneath the Seychelles

    Hammond, J. O. S.; Kendall, J.-M.; Collier, J. S.; Rümpker, G.

    2013-11-01

    The granitic islands of the Seychelles Plateau have long been recognised to overlie continental crust, isolated from Madagascar and India during the formation of the Indian Ocean. However, to date the extent of continental crust beneath the Seychelles region remains unknown. This is particularly true beneath the Mascarene Basin between the Seychelles Plateau and Madagascar and beneath the Amirante Arc. Constraining the size and shape of the Seychelles continental fragment is needed for accurate plate reconstructions of the breakup of Gondwana and has implications for the processes of continental breakup in general. Here we present new estimates of crustal thickness and VP/VS from H-κ stacking of receiver functions from a year long deployment of seismic stations across the Seychelles covering the topographic plateau, the Amirante Ridge and the northern Mascarene Basin. These results, combined with gravity modelling of historical ship track data, confirm that continental crust is present beneath the Seychelles Plateau. This is ˜30-33 km thick, but with a relatively high velocity lower crustal layer. This layer thins southwards from ˜10 km to ˜1 km over a distance of ˜50 km, which is consistent with the Seychelles being at the edge of the Deccan plume prior to its separation from India. In contrast, the majority of the Seychelles Islands away from the topographic plateau show no direct evidence for continental crust. The exception to this is the island of Desroche on the northern Amirante Ridge, where thicker low density crust, consistent with a block of continental material is present. We suggest that the northern Amirantes are likely continental in nature and that small fragments of continental material are a common feature of plume affected continental breakup.

  1. Lateral Temperature Variations in Upwelling Limbs of the Asthenosphere and its Implications for Thermal Models of the Oceanic Lithosphere

    Hamza, V. M.; Cardoso, R. R.

    2008-05-01

    Thermal models of the lithosphere proposed to date (the Half-Space Cooling and Plate models) have failed to provide satisfactory accounts of some of the important features in large-scale variations of oceanic heat flow. The systematic difference between model values and observational data have given rise to the so-called "oceanic heat flow paradox", for which no satisfactory solution has been found for over the last forty years. In the present work, we point out that this paradox is a consequence of the model assumption that lateral temperature variations are absent in the sublithospheric mantle. We propose a new thermal model of the oceanic lithosphere that can overcome such inconsistencies. Designated CMI, the new model assumes existence of lateral temperature variations in up-welling limbs of the asthenosphere, similar in character to those commonly observed in tectonothermal processes in the upper crust and in laboratory experiments of thermal plumes. CMI model simulations indicate that the thickness of the young lithosphere increases with distance from the ridge axis, at rates faster than those predicted by Half-Space Cooling and Plate models. As a result, the width of magma injection zone at mid-ocean ridges is relatively narrower in CMI model. Another noteworthy feature of the new model is its ability to provide vastly improved fits for observational heat flow data, in both young (ages less than 55 ma) and old (ages greater than 55 ma) oceanic lithosphere. More importantly, the improved fits to heat flow have been achieved without the need to invoke the ad-hoc hypothesis of large-scale hydrothermal circulation in stable ocean crust. Also, use of CMI model does not lead to artificial discontinuities in the temperature field of the lithosphere, as is the case with GDH reference models. The results of the CMI model provide a better understanding of the global heat flow variations and estimates of global heat loss. In particular, the model is capable of reproducing regional-scale features in the thermal field of the oceanic crust, identified in recent higher degree spherical harmonic representations of global heat flow.

  2. Identification of hyper-extended crust east of Davie Ridge in the Mozambique Channel

    Klimke, Jennifer; Franke, Dieter

    2015-04-01

    Davie Ridge is a ~1200 km wide, N-S trending bathymetrical high in the Mozambique Channel. Today, it is widely accepted that Davie Ridge is located along a fossil transform fault that was active during the Middle Jurassic and Early Cretaceous (~165-120 Ma). This transform fault results from the breakup of Gondwana, when Madagascar (together with India and Antarctica) drifted from its northerly position in the Gondwana Supercontinent (adjacent to the coasts of Tanzania, Somalia and Kenya) to its present position (e.g. Coffin and Rabinowitz, 1987; Rabinowitz et al., 1983; Segoufin and Patriat, 1980). The southward motion of Madagascar relative to Africa is constrained by the interpretation of magnetic anomalies in the Western Somali Basin, located north of Madagascar (e.g. Rabinowitz et al., 1983). According to Bird (2001), sheared margins share typical characteristics and a common evolution: 1. The transition from continental to oceanic crust is relatively abrupt (~ 50-80 km). 2. Along the continental side of the margin, complex rift basins form that display a wide range of faults. 3. Prominent marginal ridges form along the sheared margin that probably originate from the propagation of the oceanic spreading center along the plate boundary (Bird, 2001). In February and March 2014, a dense geophysical dataset (multichannel seismic, magnetics, gravimetry and bathymetry) with a total of 4300 profile km along the sheared margin was acquired with the R/V Sonne by the Federal Institute for Geosciences and Natural Resources (BGR). A special objective of the project, amongst others, is the characterization and interpretation of the continent-ocean transition seaward of Davie Ridge in the Mozambique Channel. Seismic profiles located east of Davie Ridge in the Western Somali Basin reveal a wide sequence of half-grabens bounded by listric normal faults. We tentatively suggest that this crust is of continental origin and results from rifting between Africa and Madagascar during the breakup of Gondwana. This implies that the continent-ocean transition is located at least ~ 150 km east of Davie Ridge. References Bird, D., 2001. Shear margins: Continent-ocean transform and fracture zone boundaries. The Leading Edge, 150-159. Coffin, M. F., und Rabinowitz, P. D., 1987. Reconstruction of Madagascar and Africa: Evidence from the Davie Fracture Zone and Western Somali Basin. Journal of Geophysical Research: Solid Earth, vol. 92, no. B9, 9385-9406. Rabinowitz, P.D., Coffin, M.F. and Falvey, D.A., 1983. The separation of Madagascar and Africa. Science 220, 67-69. Segoufin, J., und Patriat, P., 1980. Existence d'anomalies mesozoiques dans le bassin de Somalie. Implications pour les relations Afrique-Antarctique-Madagascar: C.R. Acad. Sci. Paris, v. 291, p. 85-88.

  3. The tectonic transition from oceanic subduction to continental subduction: Zirconological constraints from two types of eclogites in the North Qaidam orogen, northern Tibet

    Zhang, Long; Chen, Ren-Xu; Zheng, Yong-Fei; Li, Wan-Cai; Hu, Zhaochu; Yang, Yueheng; Tang, Haolan

    2016-02-01

    In the plate tectonics theory, continental subduction is pulled by subduction of dense oceanic crust. In practice, however, it is not easy to demonstrate that preceding oceanic crust exposes as oceanic-type eclogite together with continental-type eclogite in collisional orogens. The North Qaidam orogen in northern Tibet is an ultrahigh-pressure (UHP) metamorphic belt that contains the two types of eclogites, providing us with an excellent opportunity to study the tectonic transition from oceanic subduction to continental subduction. In order to constrain the protolith nature and metamorphic evolution of eclogites, we performed a combined study of zircon U-Pb ages, trace elements, mineral inclusions and O-Hf isotopes for various eclogites from the orogen. We discriminate the two types of eclogites by their differences in zircon U-Pb ages and O-Hf isotopes. CL-dark zircon domains exhibit high Th/U ratios, steep HREE patterns and significantly negative Eu anomalies, indicating that they are protolith zircons of magmatic origin with different extents of metamorphic recrystallization. Relict magmatic zircon domains in Type I eclogites yield Neoproterozoic protolith ages of > 830 Ma and Hf model ages of 850-1100 Ma, whereas those in Type II eclogites yield Cambrian protolith U-Pb ages of > 489 Ma and Hf model ages of 500-650 Ma. Most of the CL-bright zircon domains show low Th/U ratios, flat HREE patterns and no negative Eu anomalies, and contain mineral inclusions of garnet, omphacite and rutile, indicating their growth under eclogite-facies metamorphic conditions. These metamorphic domains have consistent eclogite-facies metamorphic ages of 433-440 Ma throughout the North Qaidam orogen, regardless of the eclogite types and locations. The metamorphic zircon domains in Type I eclogites mostly exhibit δ18O values higher than normal mantle values, whereas Type II eclogites mostly have δ18O values lower than the normal mantle values. The difference in the δ18O values indicates that their protoliths underwent different temperatures of hydrothermal alteration at different tectonic settings. Combining zircon U-Pb ages and O-Hf isotope compositions with local tectonics, it is inferred that Type I eclogites were metamorphosed from Neoproterozoic continental mafic rocks, whereas Type II eclogites were metamorphosed from oceanic mafic rocks that were subducted prior to the continental subduction. The consistent eclogite-facies metamorphic ages for the two types of eclogites indicate that the exhumed oceanic-type eclogite was detached from the subducted oceanic crust and then entrained by the exhuming continental crust. Therefore, the coexistence of oceanic- and continental-type eclogites in the North Qaidam orogen demonstrates the tectonic transition from oceanic subduction to continental collision in the early Paleozoic.

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

    Janoušek, Vojtěch; Schulmann, Karel; Lexa, Ondrej; Holub, František; Franěk, Jan; Vrána, Stanislav

    2014-05-01

    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 GAČR 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.

  5. Evidence for at Least Two Different Sources of Asian Dust to the Northwest Pacific Ocean Since the Eocene

    Scudder, R.; Murray, R. W.; Zheng, H.; Tada, R.

    2014-12-01

    Atmospheric dust records in ice cores and marine sediment provide important information regarding global climate, tectonics, and ocean-atmospheric interactions over many different timescales. In particular, marine records from the northwest Pacific are of critical importance to our understanding of the development of the Asian Monsoon, the onset of Northern Hemisphere Glaciation, and other important climatic features. Changes in dust sources have been documented over short timescales related to monsoonal dynamics; however, studies over much longer timescales commonly consider canonical "Chinese Loess" as the sole source of Asian dust. Here we present a new marine record from Ocean Drilling Program Site 1149 that indicates the clear presence of at least two different sources of Asian dust over the past 60 Ma. Using a multi-elemental geochemical and statistical approach we have resolved two disparate eolian dust inputs to Site 1149, in addition to two different ash sources. The first dust source appears to be Chinese Loess (CL); whereas, the second dust source is compositionally distinct from CL and is similar in composition to general Upper Continental Crust. These two sources show contrasting accumulation patterns through the Cenozoic. Our results confirm previous studies that show the CL source increasing in importance over the past 8 Ma. Further, our data show that the second eolian input from Asia decreases in importance from 60 Ma to ~22 Ma. This second dust source shows variability throughout the Cenozoic that can be related to major climatic events and terrestrial climate records from China, yet ceases to be important younger than ~22 Ma. The time period from ~25-20 Ma, therefore, appears to represent a fundamental transition in the hydrologic behavior of the Asian interior. That there are two important dust sources through the Cenozoic, rather than just the single "Chinese Loess", offers new opportunities for inferring the climate and tectonic evolution of Asia and the northern hemisphere.

  6. Methane: Mantle depths to crust

    A few years ago, Thomas Gold, Cornell's famous astronomer, entered the earth sciences by discovering, so he says, that methane gas is released from deep in the earth's mantle and is now trapped in large reservoirs within the crust. For a number of good reasons the idea has continued to bounce around the geological community for a while. The main attraction is that if Gold is correct, abundant energy sources can be tapped into the next millenium. Unless strong evidence is found to dispute his idea that most methane emissions from the crust are abiogenic, it seems wise to go on testing the concept. In spite of the title in ridicule, ‘Mantle methane—Fool's gold?,’ of a recent article by the Planetary Sciences Unit (PSU) of the University of Cambridge, England (Nature, Nov. 25, 1982), it was determined that the idea of commercially exploitable accumulations of abiogenic methane should be checked out. In the words of the PSU, ‘The possibility that primordial methane still outgases from the Earth, forms commercially exploitable accumulations, and is involved with higher hydrocarbon formation cannot be dismissed out of hand; constructive research and exploitation is necessary.’

  7. Biogenic crust dynamics on sand dunes

    Kinast, Shai; Meron, Ehud; Yizhaq, Hezi; Ashkenazy, Yosef

    2012-01-01

    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 a...

  8. Protracted construction of gabbroic crust at a slow spreading ridge: Constraints from 206Pb/238U zircon ages from Atlantis Massif and IODP Hole U1309D (30°N, MAR)

    Grimes, Craig B.; John, Barbara E.; Cheadle, Michael J.; Wooden, Joseph L.

    2008-01-01

    Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages of 24 samples from oceanic crust recovered in Integrated Ocean Drilling Program (IODP) Hole U1309D and from the surface of Atlantis Massif, Mid-Atlantic Ridge (MAR) (30°N) document a protracted history of accretion in the footwall to an oceanic detachment fault. Ages for 18 samples of evolved Fe-Ti oxide gabbro and felsic dikes collected 40–1415 m below seafloor in U1309D yield a weighted mean of 1.20 ± 0.03 Ma (mean square of weighted deviates = 7.1). However, the ages range from 1.08 ± 0.07 Ma and 1.28 ± 0.05 Ma indicating crustal construction occurred over a minimum of 100–200 ka. The zircon ages, along with petrologic observations, indicate at least 2 major periods of intrusive activity with age peaks separated by 70 ka. The oldest ages are observed below 600 mbsf, an observation inconsistent with models requiring constant depth melt intrusion beneath a detachment fault. The data are most consistent with a “multiple sill” model whereby sills intrude at random depths below the ridge axis over a length scale greater than 1.4 km. Zircon ages from broadly spaced samples collected along the southern ridge of Atlantis Massif yield a detachment fault slip rate of 28.7 ± 6.7 mm/a and imply significant asymmetric plate spreading (up to 100% on the North American plate) for at least 200 ka during core complex formation.

  9. Pulsar glitches: the crust is not enough.

    Andersson, N; Glampedakis, K; Ho, W C G; Espinoza, C M

    2012-12-14

    Pulsar glitches are traditionally viewed as a manifestation of vortex dynamics associated with a neutron superfluid reservoir confined to the inner crust of the star. In this Letter we show that the nondissipative entrainment coupling between the neutron superfluid and the nuclear lattice leads to a less mobile crust superfluid, effectively reducing the moment of inertia associated with the angular momentum reservoir. Combining the latest observational data for prolific glitching pulsars with theoretical results for the crust entrainment, we find that the required superfluid reservoir exceeds that available in the crust. This challenges our understanding of the glitch phenomenon, and we discuss possible resolutions to the problem. PMID:23368300

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

    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 (2σ). 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

  11. The return of subducted continental crust in Samoan lavas

    Jackson, Matthew G.; Hart, Stanley R.; Koppers, Anthony A. P.; Staudigel, Hubert; Konter, Jasper; Blusztajn, Jerzy; Kurz, Mark; Russell, Jamie A.

    2007-08-01

    Substantial quantities of terrigenous sediments are known to enter the mantle at subduction zones, but little is known about their fate in the mantle. Subducted sediment may be entrained in buoyantly upwelling plumes and returned to the Earth's surface at hotspots, but the proportion of recycled sediment in the mantle is small, and clear examples of recycled sediment in hotspot lavas are rare. Here we report remarkably enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures in Samoan lavas from three dredge locations on the underwater flanks of Savai'i island, Western Samoa. The submarine Savai'i lavas represent the most extreme 87Sr/86Sr isotope compositions reported for ocean island basalts to date. The data are consistent with the presence of a recycled sediment component (with a composition similar to the upper continental crust) in the Samoan mantle. Trace-element data show affinities similar to those of the upper continental crust-including exceptionally low Ce/Pb and Nb/U ratios-that complement the enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures. The geochemical evidence from these Samoan lavas significantly redefines the composition of the EM2 (enriched mantle 2; ref. 9) mantle endmember, and points to the presence of an ancient recycled upper continental crust component in the Samoan mantle plume.

  12. Propagation of microseisms from the deep ocean to land

    Ying, Yingzi; Bean, Christopher J.; Peter D. Bromirski

    2014-01-01

    Ocean-generated microseisms are faint Earth vibrations that result from pressure fluctuations at the sea floor generated by the interaction between ocean surface gravity waves, and are continuously recorded as low frequency seismic noise. Here we investigate microseism propagation away from deep-ocean source regions using the spectral element method for an oceanic model that contains realistic northeast Atlantic Ocean irregular-layered structure composed of water, sediment, and upper crust. I...

  13. 42 CFR 495.202 - Identification of qualifying MA organizations, MA-EPs and MA-affiliated eligible hospitals.

    2010-10-01

    ... STANDARDS FOR THE ELECTRONIC HEALTH RECORD TECHNOLOGY INCENTIVE PROGRAM Requirements Specific to Medicare Advantage (MA) Organizations § 495.202 Identification of qualifying MA organizations, MA-EPs and MA...) are not meaningful users of certified EHR technology. (b) Identification of qualifying MA EPs...

  14. Early Formation of Terrestrial Crust

    Harrison, T. M.; Schmitt, A. K.; McCulloch, M. T.; Lovera, O. M.

    2007-12-01

    Early (?4.5 Ga) Formation of Terrestrial Crust T.M. Harrison1, A.K. Schmitt1, M.T. McCulloch2, and O.M. Lovera1 1Department of Earth and Space Sciences and IGPP, UCLA, Los Angeles, CA 90095, USA; 2Research School of Earth Sciences, Australian National University, Canberra, A.C.T. 2601 AUSTRALIA Large deviations in ?repsilonHf(T) from bulk silicate Earth seen in >4 Ga detrital zircons from Jack Hills, Western Australia, have been interpreted as reflecting a major differentiation of the silicate Earth at ca. 4.4 to 4.5 Ga. We have expanded the characterization of 176Hf/177Hf (Hf) in Hadean zircons by acquiring a further 116 laser ablation Lu-Hf measurements on 87 grains with ion microprobe 207Pb/206Pb ages up to 4.36 Ga. Most measurements employed concurrent Lu-Hf and 207Pb/206Pb analyses, permitting assessment of the use of ion microprobe data to characterize the age of the volumetrically larger domain sampled by laser drilling. Our new results confirm and extend the earlier observation of significant negative deviations in ?repsilonHf(T) throughout the Hadean, although no positive ?repsilonHf(T) values were documented in this study. These data yields an essentially uniform spectrum of single-stage model ages between 4.54 and 4.20 Ga for extraction of the zircons' protoliths from a chondritic reservoir. We derived the full error propagation expression for a parameter, ?repsilono, which measures the difference of a sample from solar system initial (Hf) (Hfo), and from this conclude that data plotting close to (Hfo), are statistically meaningful and consistent with silicate differentiation at 4.5400.006 Ga. ?18O and Ti thermometry for these Hadean zircons show little obvious correlation with initial (Hf), consistent with their derivation through fusion of a broad suite of crustal rock types under near water-saturated conditions. Together with the inclusion assemblage and other isotopic and trace element data obtained from these ancient zircons, our results indicate essentially continuous derivation of crust from the mantle from 4.5 to 4.2 Ga, concurrent with recycling into the mantle and internal crustal re-working. These results represent further evidence that by 4.35 Ga, portions of the crust had taken on continental characteristics.

  15. Composition of the Primary Crust of Mars: Observations of Deeply Excavated Crater Central Peaks

    Skok, J. R.; Mustard, J. F.; Tornabene, L. L.; Murchie, S. L.

    2011-12-01

    It is predicted that the primary crust of Mars crystallized from a magma ocean and would be well preserved at depth on a single plate planet but poorly exposed as impacts, volcanism and alteration has reworked the upper crust. In a few select locations, extensive excavation by impact or erosion has exposed unaltered mafic minerals of the Martian crust. The majority of these exposures occur within the uplifted central peaks and peak rings of Southern Highland craters. We examine the mafic compositions of these deeply excavated crustal rocks in an attempt to constrain the composition of the Martian crust and test models of planetary formation. The search for deeply excavated bedrock from HiRISE images is ongoing and has so far resulted in nearly 200 potential locations. Over half of these currently have CRISM spectroscopic observations with ~50 locations having good exposures of crustal rocks showing little to no alteration. It is this combination of deeply excavated minerals that has potential to tap the preserved primary crust of Mars. We focus our analysis on olivine and pyroxene as crustal formation models predict that these two minerals would dominate the modal mineralogy of the crystallizing crust with a garnet layer potentially stable at depth. The high-resolution visible and near-infrared spectroscopic data provided by the CRISM instrument is ideally suited for examining these compositional characteristics. Initial in-depth analysis of the central peak of Alga Crater shows excellent exposures of lithologies characterized by both olivine and pyroxene. The olivine-bearing unit here has a fayalitic composition and a dunite lithology. This ancient Fe-rich olivine is in stark contrast to the Mg-enriched olivine of the primitive mantle of Earth. The primary pyroxene-bearing unit was determined to be a low-calcium, high-Fe enstatite orthopyroxenite, consistent with the mineralogy of the ancient Mars meteorite ALH84001. These observations suggest that the crust crystallized into compositionally homogeneous units in close proximity to allow single impact to sample multiple lithologies. The units are consistent with the late-stage crystallization of a hot magma ocean enriched in Fe. Here we expand the results to all suitable Southern Highland exposures to check regional compositional consistency and examine global trends. Initial results support similar compositions in excavated crust throughout the southern highlands, though the presence of both olivine and pyroxene lithologies are rarely well exposed in the same central peak. Additional analysis will continue to test the emerging hypothesis that the upper primary crust is the direct result of the late stage crystallization of a magma ocean, with no density driven overturn, that results in compositionally segregated fayalite and enstatite rich crust.

  16. The formation of deep basins in High Arctic from metamorphism in continental crust

    Artyushkov, Eugene; Belyaev, Igor; Chekhovich, Peter; Petrov, Eugene; Poselov, Viktor

    2014-05-01

    In the East Barents and North Chukchi basins, 16-20 km deep, the crystalline crust is attenuated to 12-18 km (reference profiles 2-AR, 4-AR and 5-AR). P-wave velocities and densities in this layer are characteristic of the oceanic crust. However, the subsidence history in the basins is quite different from that typical of the oceanic crust. In both basins the subsidence continued for several hundred million years and one half of the deposits or more was formed long after the start of the subsidence when cooling of the oceanic plate would be already over. Moreover, the basins are 4-5 km deeper than it could be expected according to the thickness of the crystalline crust above the Moho boundary. In the absence of large free-air gravity anomalies, joint analysis of the gravity and seismic data indicates the existence under the Moho of thick layers of high-density and high-velocity eclogites. As can be seen in high resolution seismic profiles, the intensity of crustal stretching did not exceed 10% in the basins, and their formation can be predominantly attributed to a high-grade metamorphism in the mafic lower part of continental crust. At some episodes, strong increase in the rate of subsidence occurred in the basins. This indicates acceleration of metamorphism catalyzed by infiltration of mantle fluids. A set of the above features, abnormally large depth, long subsidence history with its acceleration at the late stages, and episodes of pronounced acceleration of the subsidence represent characteristic features of some other large hydrocarbon basins, e.g., of the North and South Caspian basins. These features can be used for prospecting new prolific provinces on the Arctic shelf. The Lomonosov ridge, Mendeleev high and the Makarov basin pertain to the same structural type. In the Oligocene they underwent erosion near to sea level with the formation of pronounced unconformity. Then at the end of Oligocene deep-water basins were formed in these regions. Rapid crustal subsidence after a long period of relative stability is atypical of oceanic crust. It can be produced either by intense stretching of continental crust or by a density increase due to metamorphism in this layer. Recent seismic reflection profiles demonstrate only minor stretching of the crystalline basement in the regions. Then metamorphism should be the main cause of formation of deep basins in these regions. This can explain attenuation of crystalline crust and an increase in P-wave velocities in this layer that are typical for many deep basins formed due to intense metamorphism in continental crust.

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

    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...

  18. Millennium Ecosystem Assessment: MA Population

    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...

  19. Millennium Ecosystem Assessment: MA Population

    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...

  20. Himalaya gneiss dome formation, focused radiogenic heating in southern Madagascar, and fertilization of the Neoproterozoic ocean by mantle-derived phosphorus

    Horton, Forrest Miller

    (I) Geochronology, thermochronology, and structural observations across Gianbul gneiss dome provide insight about the exhumation of middle crust in the India-Asia collision zone: Doming (1) initiated during the early stages of extension; (2) was driven by a positive feedback among dehydration melting, buoyancy, and decompression; and (3) culminated with the injection of anatectic melts into the upper levels of the dome. The dome was subsequently exhumed as part of a footwall block beneath a brittle normal fault. (II) Focused internal heating led to melting, metamorphism, and crustal weakening during the Neoproterozoic continent-continent collision between East and West Gondwana. Numerical models based on chronologic and thermal constraints across southern Madagascar indicate that radioactive decay of thorium was the principal heat source responsible for regional metamorphism at temperatures >900 C in the middle to lower crust. (III) The Neoproterozoic era was punctuated by profound tectonic, evolutionary, and environmental change. Biologic and climatic conditions may have been especially sensitive to fluxes of phosphorus (P) from the weathering of continental crust. Large igneous provinces-containing abundant P and highly susceptible to chemical weathering-occurred regularly during the breakup of the Rodinia supercontinent. An estimated bioavailable P flux to the ocean from the weathering of basalt peaked at 720 Ma, immediately prior to rapid biologic diversification and the Sturtian glaciation; I postulate that the burial of organic carbon that resulted from this unprecedented P flux helped facilitate glaciation and triggered the oxidation of the ocean-atmosphere system.

  1. Segmentation of mid-ocean ridges

    Schouten, Hans; Klitgord, Kim D.; Whitehead, J.A.

    1985-01-01

    Studies of mid-ocean ridges in the Pacific and Atlantic oceans show that the volcanism that forms the oceanic crust along the spreading-plate boundaries is concentrated at regular intervals related to spreading rate. This observation and a new calculation for a Rayleigh-Taylor type of gravitational instability of a partially molten mantle region growing under spreading centres yield reasonable estimates of upper mantle viscosities. ?? 1985 Nature Publishing Group.

  2. DTA for superalloy MA6000 and ferritic steel MA956

    Commercialized mechanically alloyed yttria dispersion strengthened alloys exhibit unusual recrystallisation behavior. In spite of their large stored energy content, they tend to recrystallise temperatures close to melting. The recrystallised microstructure is often very coarse and highly anisotropic, characterized by columnar grains. To investigate the factors behind such strange recrystallisation behavior, DTA (Differential Thermal Analysis) experiments were performed for the measurement of stored energy in the as-deformed condition to oxide dispersion strengthened superalloys commercially designated as MA6000 and MA956. The ODS (Oxide Dispersion Strengthened) MA6000 measured and calculated values of energies suggest that the material in deformed condition is primary recrystallized and subsequent change in microstructure by further heat treatment can be described as secondary recrystallization and attributed to the driving force for that is the energy stored in the material in the form of grain boundaries. Whereas, a much higher stored energy was measured for MA956 and a small part of that appears to be due to grain boundary energy. The highly deformed microstructure in as-received condition and higher energy values suggest that the coarse columnar grain is-the product of primary recrystallisation in MA956. (author)

  3. Growth of early continental crust controlled by melting of amphibolite in subduction zones.

    Foley, Stephen; Tiepolo, Massimo; Vannucci, Riccardo

    2002-06-20

    It is thought that the first continental crust formed by melting of either eclogite or amphibolite, either at subduction zones or on the underside of thick oceanic crust. However, the observed compositions of early crustal rocks and experimental studies have been unable to distinguish between these possibilities. Here we show a clear contrast in trace-element ratios of melts derived from amphibolites and those from eclogites. Partial melting of low-magnesium amphibolite can explain the low niobium/tantalum and high zirconium/samarium ratios in melts, as required for the early continental crust, whereas the melting of eclogite cannot. This indicates that the earliest continental crust formed by melting of amphibolites in subduction-zone environments and not by the melting of eclogite or magnesium-rich amphibolites in the lower part of thick oceanic crust. Moreover, the low niobium/tantalum ratio seen in subduction-zone igneous rocks of all ages is evidence that the melting of rutile-eclogite has never been a volumetrically important process. PMID:12075348

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

    Frey, F. A.; Coffin, M. F.; Wallace, P. J.; Weis, D.; Zhao, X.; Wise, S. W.; Wähnert, V.; Teagle, D. A. H.; Saccocia, P. J.; Reusch, D. N.; Pringle, M. S.; Nicolaysen, K. E.; Neal, C. R.; Müller, R. D.; Moore, C. L.; Mahoney, J. J.; Keszthelyi, L.; Inokuchi, H.; Duncan, R. A.; Delius, H.; Damuth, J. E.; Damasceno, D.; Coxall, H. K.; Borre, M. K.; Boehm, F.; Barling, J.; Arndt, N. T.; Antretter, M.

    2000-02-01

    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 presence of wood fragments, charcoal, pollen, spores and seeds in the shallow water sediments overlying the igneous basement show that the growth rate of the plateau was sufficient to form subaerial landmasses. Most of the southern Kerguelen Plateau formed at ˜110 Ma, but the uppermost submarine lavas in the northern Kerguelen Plateau erupted during Cenozoic time. These results are consistent with derivation of the plateau by partial melting of the Kerguelen plume. Leg 183 provided two new major observations about the final growth stages of the Kerguelen Plateau. 1: At several locations, volcanism ended with explosive eruptions of volatile-rich, felsic magmas; although the total volume of felsic volcanic rocks is poorly constrained, the explosive nature of the eruptions may have resulted in globally significant effects on climate and atmospheric chemistry during the late-stage, subaerial growth of the Kerguelen Plateau. 2: At one drillsite, clasts of garnet-biotite gneiss, a continental rock, occur in a fluvial conglomerate intercalated within basaltic flows. Previously, geochemical and geophysical evidence has been used to infer continental lithospheric components within this large igneous province. A continental geochemical signature in an oceanic setting may represent deeply recycled crust incorporated into the Kerguelen plume or continental fragments dispersed during initial formation of the Indian Ocean during breakup of Gondwana. The clasts of garnet-biotite gneiss are the first unequivocal evidence of continental crust in this oceanic plateau. We propose that during initial breakup between India and Antarctica, the spreading center jumped northwards transferring slivers of the continental Indian plate to oceanic portions of the Antarctic plate.

  5. Neutron flux and dynamics of Earth's crust

    Made during many years (from 1990) observations of variation of thermal and slow neutron's fluxes in seismic active (Pamir) and seismic quiet (Moscow) region of the Earth allow to prove following: I .Earth's crust makes a substantial contribution into full flux of such neutrons near the crust. 2. There are observed variations of neutron flux with in amplitude and different duration, part of which correlate with tidal wave in the Earth's crust, which is induced by interaction of the Earth and the Moon and the Sun. These some claims results in following one: deformations of the Earth's crust cause variations of thermal and slow neutrons' flux near the Earth's crust, especially displayed in the seismic active regions

  6. Towards self-consistent modelling of the Martian dichotomy: Coupled models of simultaneous core and crust formation

    Golabek, Gregor; Keller, Tobias; Gerya, Taras; Zhu, Guizhi; Tackley, Paul

    2010-05-01

    One of the most striking surface features on Mars is the crustal dichotomy. It is the oldest geological feature on Mars and was formed more than 4.1 Ga ago by either exogenic or endogenic processes (e.g. Keller and Tackley, 2009). In order to find an internal origin of the crustal dichotomy, located within a maximum of 400 Ma of planetary differentiation, the thermal state of the planet resulting from core formation needs to be considered. Additionally, it was suggested that a primordial crust with up to 45 km thickness can be formed already during the Martian core formation (Norman, 1999). We suggest that the sinking of iron diapirs delivered by pre-differentiated impactors induced impact- and shear heating-related temperature anomalies in the mantle that fostered the formation of early Martian crust. Thus, the crustal thickness distribution would largely be a result of planetary core formation, late impact history and the onset of mantle convection. In this study, we examine parameter sets that will likely cause hemispherical asymmetry in both core formation and onset of mantle convection. To test this hypothesis we use numerical models to simulate the formation of the Martian iron core and the resulting mantle convection pattern, while peridotite melting is enabled to track melting caused by shear and radioactive heating.
We perform 2D simulations using the spherical-Cartesian code I2ELVIS (Gerya and Yuen, 2007) for planetary accretion and the spherical code STAGYY (Tackley, 2008) for the consequent onset of mantle convection. We apply a temperature-, stress- and melt-fraction dependent viscoplastic rheology inside a Mars-sized planet. Radioactive and shear heating as well as consumption of latent heat by silicate melting are taken into account. The depth of neutral buoyancy of silicate melt with respect to solid silicates is determined by the difference in compressibility of the liquid and solid phase. To self-consistently simulate the silicate phase changes expected inside a Mars-sized body, we use the thermodynamical database PerpleX (Connolly, 2005). As initial condition for core formation (I2ELVIS), we apply randomly distributed iron diapirs with 75 km radius inside the planet, representing the cores of stochastically distributed impactors. Additionally, we explore the effect of one giant impactor core on the planetary evolution. Results indicate that the presence of a large impactor core induces hemispherically asymmetrical core formation. The amplitude of shear heating anomalies often exceeds the solidus of primitive mantle material and thus, the formation of a considerable amount of silicate melt is observed. The resulting temperature field after core formation is then read into the mantle convection code STAYY. The hemispherical magma ocean induced by one late giant impactor favours a dichotomous crust formation during a few Ma after core formation. Afterwards, the extraction of excess heat produced by the sinking of the giant impactor through the mantle leads to a localized region of massive magmatism, comparable to Tharsis, whereas the rest of the mantle is dominated by a sluggish convection pattern with limited crust formation that prevails during the further evolution of the planet. REFERENCES
 Connolly, J.A.D. 2005. EPSL, 236. Gerya, T.V. & Yuen, D.A. 2007. PEPI, 163. Keller, T. & Tackley, P.J. 2009. Icarus, 202. Norman, M.D. 1999. Meteorit. Planet. Sci., 34. Tackley, P.J. 2008. PEPI, 171.

  7. The feasibility of MA transmutation in CEFR

    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

  8. Crystallization Age and Impact Resetting of Ancient Lunar Crust from the Descartes Terrane

    Norman, M. D.; Borg, L. E.; Nyquist, L. E.; Bogard, D. D.

    2002-01-01

    Lunar ferroan anorthosites (FANs) are relics of an ancient, primary feldspathic crust that is widely believed to have crystallized from a global magma ocean. Compositions and ages of FANs provide fundamental information about the origin and magmatic evolution of the Moon, while the petrology and thermal history of lunar FANs illustrate the structure and impact history of the lunar crust. Here we report petrologic, geochemical, and isotopic (Nd-Sr-Ar) studies of a ferroan noritic anorthosite clast from lunar breccia 67215 to improve our understanding of the composition, age, and thermal history of the Moon.

  9. Isotopically-diverse rhyolites coeval with the Columbia River Basalts Large Igneous Province: evidence for widespread mantle-plume driven hydrothermal alteration and remelting of the crust

    Colon, D.; Bindeman, I. N.; Stern, R. A.; Fisher, C. M.

    2014-12-01

    The formation of the most recent flood basalt province on Earth, the Columbia River Flood Basalts (CRBs) of the northwestern USA, was accompanied by eruptions of several thousand km3 of rhyolite in a short time window from 16.7 to 15 Ma. These rhyolites span from low (+1‰) to high (+11‰) in δ18O values as recorded by major phenocrysts, and alteration-resistant zircons within each rhyolite commonly display diversity of up to 6‰ δ18O, indicative of batch assembly prior to eruption. Significant variation in ɛHf also exists in zircons, ranging from -39 to 0 in rhyolites erupted through the North American cratonic crust, and from -1 to +9 in rhyolites erupted through accreted oceanic terranes to the east of the Sr87/86Sr = 0.706 line. This isotopic diversity cannot be accounted for by fractionation of a CRB-like parent magma, demonstrating that the syn-CRB rhyolites must have been derived from melting of the crust. Abundant low-δ18Omelt values among syn-CRB rhyolites further constrains this crustal melting to shallow depths of 5-10 km, due to the shallow depths of the necessary hydrothermal alteration of the protolith. By contrast, high-δ18O rhyolites must have been formed by remelting of sedimentary or metasedimentary rocks. Low-δ18O rhyolites are also most common in the vicinity of the crustal suture between the thick lithosphere of the Archean craton and the thin lithosphere of the accreted terranes. Thermomechanical modeling suggests that this contrast concentrates crustal heating and deformation, creating pathways for meteoric water to penetrate the crust and cause extensive hydrothermal alteration less than 1 Ma before those same rocks remelt to form low-δ18O rhyolites. Finally, we suggest that this extensive crustal hydrothermal alteration and melting may be typical of continental flood basalt provinces world wide, and particularly when there is syn-volcanic extension.

  10. Ocean Ridges and Oxygen

    Langmuir, C. H.

    2014-12-01

    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 Future of Deep-Ocean Drilling

    Heirtzler, J. R.; Maxwell, A. E.

    1978-01-01

    Describes the scientific accomplishments of the International Program of Ocean Drilling (IPOD) during its first decade. Notable are the scientific contributions to understanding the sea floor. Critical decisions for the second decade include economic and social implications. (MA)

  12. Biogenic crust dynamics on sand dunes

    Kinast, Shai; Yizhaq, Hezi; Ashkenazy, Yosef

    2012-01-01

    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.

  13. Microphytic crusts: 'topsoil' of the desert

    Belnap, Jayne

    1990-01-01

    Deserts throughout the world are the home of microphytic, or cryptogamic, crusts. These crusts are dominated by cyanobacteria, previously called blue-green algae, and also include lichens, mosses, green algae, microfungi and bacteria. They are critical components of desert ecosystems, significantly modifying the surfaces on which they occur. In the cold deserts of the Colorado Plateau (including parts of Utah, Arizona, Colorado, and New Mexico), these crusts are extraordinarily well-developed, and may represent 70-80% of the living ground cover.

  14. Molecular mobility in crispy bread crust

    Nieuwenhuijzen, van, M.

    2008-01-01

    The aim of the PhD study on molecular mobility was to analyse the molecular grounds for the deterioration of crispy/crunchy characteristics of cellular solid foods. A fresh baguette for example has a crispy crust and a moist and soft interior. Moisture migrates from crumb to crust. Already at a water content of 9% (crumb contains around 45% water) the crispness of the crust decreases. During the study methods were developed to measure the speed of water uptake to test different ingredients on...

  15. Biogenic crust dynamics on sand dunes.

    Kinast, Shai; Meron, Ehud; Yizhaq, Hezi; Ashkenazy, Yosef

    2013-02-01

    Sand dunes are often covered by vegetation and biogenic crusts. Despite their significant role in dune stabilization, biogenic crusts have rarely been considered in model 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 crossover between two different forms of desertification. PMID:23496449

  16. Seismicity, metamorphism and rheology of the lower continental crust

    Austrheim, Håkon

    2014-05-01

    Seismological data document that both normal earthquakes and tremors occur in the lower continental crust. Pseudotachylytes (frictional melts and ultracommunited rocks) have been described from several high grade metamorphic terrains and may be the geological manifestation of this seismicity. The Grenville (c. 930Ma) granulite facies complex (T: 800 °C; P: ≤10kbar) of the Lindås Nappe in the Bergen Arcs, W-Norway underwent a fluid induced partial eclogite (T: 600-650 °C; P: 15-20 kbar) and amphibolite facies metamorphism during the Caledonian (c.400-430 Ma) continent collision. Pseudotachylyte fault and injection veins formed in the dry granulites at or close to the reaction fronts both in the eclogitized (western parts) and the amphibolitized (eastern parts) of the Nappe. They are locally recrystalized with the development of amphibolite and eclogite facies assemblages demonstrating that they formed pre or syn the Caledonian metamorphism. The pseudotachylytes transect lithologies ranging from peridotite to anorthosite and consequently the influence of the seismic energy release on a range of granulite facies minerals including garnet, pyroxenes, olivine, plagioclase, hornblende and scapolite can be observed. The seismic energy released promotes the Caledonian metamorphism and change the petrophysical properties of the lower crust in the following ways: The melting and the ultracommunition of the granulite facies minerals increased the reactive surface area and produce local pathways for fluid. S-rich scapolite, a common mineral in granulities play a key role in this process by releasing S and C to form sulfides and carbonates. Small sulfide grains impregnate the pseudotachylyte veins which may lead to an increased electrical conductivity of the deep crust. The pseudotachylyte veins impose inhomogeneities in the massive rocks through grain size reduction and lead to strain localization with development of amphibolite and eclogite facies shear zones. Formation of eclogite facies breccias where meter size blocks of rotated granulites are enclosed in eclogite may have initiated by the seismic events as indicated by fractures in the relict granulite facies garnet. The seismic events may have been important in large scale transport of fluid required to bring about the metamorphism of the dry granulite facies complex.

  17. 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

    M Rajamanickam; S Balakrishnan; R Bhutani

    2014-07-01

    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.

  18. Microbial communities at the borehole observatory on the Costa Rica Rift flank (Ocean Drilling Program Hole 896A)

    AndreasTeske; BethOrcutt; KeirBecker

    2012-01-01

    The microbiology of subsurface, hydrothermally influenced basaltic crust flanking mid-ocean ridges has remained understudied, due to the difficulty in accessing the subsurface environment. The instrumented boreholes resulting from scientific ocean drilling offer access to samples of the formation fluids circulating through oceanic crust. We analyzed the phylogenetic diversity of bacterial communities of fluid and microbial mat samples collected in situ from the observatory at Ocean Drilling P...

  19. Continental accretion: From oceanic plateaus to allochthonous terranes

    Ben-Avraham, Z.; Nur, A.; Jones, D.; Cox, A.

    1981-01-01

    Some of the regions of the anomalously high sea-floor topography in today's oceans may be modern allochthonous terranes moving with their oceanic plates. Fated to collide with and be accreted to adjacent continents, they may create complex volcanism, cut off and trap oceanic crust, and cause orogenic deformation. The accretion of plateaus during subduction of oceanic plates may be responsible for mountain building comparable to that produced by the collision of continents. Copyright ?? 1981 AAAS.

  20. Crust formation and its role during baking

    Vanin, F.; Lucas, T.; Trystram, Gilles

    2009-01-01

    The final properties of the crumb and crust differ according to their heat-moisture dynamics. Compilations of heating and drying rates reported in the literature are discussed and will serve to validate future models of baking. Their impact on the structural elements in dough films and the porous network are discussed, highlighting the lack of data and the need to reproduce these dynamics inside the instrument of analysis. Some roles of the crust setting during the whole baking process are al...

  1. Neutron Star Crust and Molecular Dynamics Simulation

    Horowitz, C J; Schneider, A; Berry, D K

    2011-01-01

    In this book chapter we review plasma crystals in the laboratory, in the interior of white dwarf stars, and in the crust of neutron stars. We describe a molecular dynamics formalism and show results for many neutron star crust properties including phase separation upon freezing, diffusion, breaking strain, shear viscosity and dynamics response of nuclear pasta. We end with a summary and discuss open questions and challenges for the future.

  2. Methane oxidation in slurry storage surface crusts.

    Petersen, Sren O; Amon, Barbara; Gattinger, Andreas

    2005-01-01

    Livestock manure is a significant source of atmospheric methane (CH4), especially during liquid storage. In liquid manure (slurry) storages a surface crust may form naturally, or an artificial surface crust can be established. We investigated whether there is a potential for CH4 oxidation in this environment. Surface crust materials were sampled from experimental storages with cattle slurry (with natural crust) or anaerobically digested cattle slurry (with straw layer) that had been stored with or without a wooden cover. Extracts of surface crust material were incubated with 5.6% CH4 in the headspace, and methanotrophic activity was demonstrated in all four treatments following a 4- to 10-d lag phase. Subsequent incubation of field-moist surface crust material with 350 microL L(-1) CH4 also showed CH4 oxidation, indicating a potential for CH4 removal under practical storage conditions. There was no CH4 oxidation activity during incubation of autoclaved samples. Methane oxidation rates were 0.1 to 0.5 mg kg(-1) organic matter (OM) h(-1), which is comparable with the activity in wetlands and rice paddies. Partial drying increased CH4 oxidation to 0.2 to 1.4 mg kg(-1) OM h(-1), probably as a result of improved diffusivity within the surface crust. Rewetting reversed the stimulation of methanotrophic activity in some treatments, but not in others, possibly due to a decline in CH4 production in anaerobic volumes, or to growth of methanotrophs during incubation. This study presents direct evidence for methanotrophic activity in slurry storages. Measures to ensure crust formation with or without a solid cover appear to be a cost-effective greenhouse gas mitigation option. PMID:15758097

  3. Geodetic And Geological Analysis Of The Tandilia Crust

    Del Cogliano, D.; Dallasalda, L.

    2007-05-01

    Keywords: Tandilia-Geoid-Anomaly-Collision-Transamazonic The oldest Precambrian rocks of the south-western Gondwana in South America are cropping out in the Río de la Plata craton, it encompasses the western region of Uruguay, the Martín Garcia island and the Tandilia Ranges in the Buenos Aires Province, Argentina. The Tandil Ranges are the oldest region in Argentina (1.8- 2.2Ga); however, some features of the crust still remain unknown. These rocks evolved during two main events:Transamazonian and Brasilian tectonic cycles. The local and regional gravitational effects were analyzed on gravity and height anomalies. The studied are extended on 400 km x 400 km area which includes three geological units: the Tandilia ranges, and the Claromecó and Salado basins. Due the dependence of gravity and height anomalies with the distance, the seconds are more suitable to analyze the crust interior. For this reason a very precise cuasi geoid model was calculated using the point masses method, from gravity and GPS/leveling data. Taking into account the topography (less than 500 m high hills) and the Bouguer anomalies values (| AB | Azul hills (north of Tandilia) it extends to the southwest running mainly along the eastern edge of the ranges until the continental platform. This anomaly is attributed to a basic-ultrabasic tectonic slab, a relict of a suture (oceanic bottom and astenosphere) from a continent-continent collision (Transamazonian orogeny). This collisional model was previously based on the presence of wide areas of gneisses, migmatites and granitoids (leucogranites), of sub volcanic and lava flows, of a polifase metamorphic-deformational style, of swarms of pre-metamorphic belts, and of a strong piling up of the crust, associated to thrusting and transcurrence; as well as minor lenses of ultrabasic rocks, that seem to also be part of the suture as a result of a "mantel pinching" during collision.

  4. The magma ocean as an impediment to lunar plate tectonics

    Warren, Paul H.

    1993-01-01

    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.

  5. Fission track dating of authigenic quartz in red weathering crusts of carbonate rocks in Guizhou province

    The Cenozoic evolution history of Guizhou Province, which is located on the southeastern flank of the Qinghai-Tibet Plateau, is unclear because of the lack of sedimentation records. The red weathering crusts widespread on the Yunnan-Guizhou Plateau may bear critical information about their evolution history. This work firstly determined the ages of four red weathering crusts in eastern, central and northern Guizhou. The material used in fission track dating is well-crystallized quartz occurring in many in-situ weathering crusts of carbonate rocks. The results showed that the fission track ages of quartz vary over a wide range from 1 Ma to 25 Ma in the four profiles, significantly younger than the ages of Triassic and Cambrian parent rocks. In combination with the regionally geological evolution history during the period from 25 Ma to 1 Ma, the ages of quartz can exclude the possibility that the origin of quartz has nothing to do with primary clastic minerals in parent rocks, authigenesis during diagenesis and hydrothermal precipitation or replacement by volcanic activities. It is deduced that the well-crystallized quartz was precipitated from Si-rich weathering fluids during weathering processes of carbonate rocks. The recorded ages of quartz from the four profiles are consistent with the episodes of planation surfaces on the Qinghai-Tibet Plateau, the stages of red soil in the tropics of South China, the tectonically stable periods in Guizhou, and the ages of weathering in other parts of the world during the Cenozoic era. That is to say, the ages of authigenic quartz dated by the fission track method are well feasible and credible. (authors)

  6. Diversity in early crustal evolution: 4100 Ma zircons in the Cathaysia Block of southern China.

    Xing, Guang-Fu; Wang, Xiao-Lei; Wan, Yusheng; Chen, Zhi-Hong; Jiang, Yang; Kitajima, Kouki; Ushikubo, Takayuki; Gopon, Phillip

    2014-01-01

    Zircons are crucial to understanding the first 500 Myr of crustal evolution of Earth. Very few zircons of this age (>4050 Ma) have been found other than from a ~300 km diameter domain of the Yilgarn Craton, Western Australia. Here we report SIMS U-Pb and O isotope ratios and trace element analyses for two ~4100 Ma detrital zircons from a Paleozoic quartzite at the Longquan area of the Cathaysia Block. One zircon ((207)Pb/(206)Pb age of 4127 ± 4 Ma) shows normal oscillatory zonation and constant oxygen isotope ratios (δ(18)O = 5.8 to 6.0‰). The other zircon grain has a ~4100 Ma magmatic core surrounded by a ~4070 Ma metamorphic mantle. The magmatic core has elevated δ(18)O (7.2 ± 0.2‰), high titanium concentration (53 ± 3.4 ppm) and a positive cerium anomaly, yielding anomalously high calculated oxygen fugacity (FMQ + 5) and a high crystallization temperature (910°C). These results are unique among Hadean zircons and suggest a granitoid source generated from dry remelting of partly oxidizing supracrustal sediments altered by surface waters. The ~4100 Ma dry melting and subsequent ~4070 Ma metamorphism provide new evidence for the diversity of the Earth's earliest crust. PMID:24888297

  7. A Seafloor Microbial Biome Hosted within Incipient Ferromanganese Crusts

    Templeton, Alexis S.; Knowles, A. S.; Eldridge, D. L.; Arey, Bruce W.; Dohnalkova, Alice; Webb, Samuel M.; Bailey, B. E.; Tebo, Bradley M.; Staudigel, Hubert

    2009-11-15

    Unsedimented volcanic rocks exposed on the seafloor at ridge systems and Seamounts host complex, abundant and diverse microbial communities that are relatively cosmopolitan in distribution (Lysnes, Thorseth et al. 2004; Mason, Stingl et al. 2007; Santelli, Orcutt et al. 2008). The most commonly held hypothesis is that the energy released by the hydration, dissolution and oxidative alteration of volcanic glasses in seawater drives the formation of an ocean crust biosphere (Thorseth, Furnes et al. 1992; Fisk, Giovannoni et al. 1998; Furnes and Staudigel 1999). The combined thermodynamically favorable weathering reactions could theoretically support anywhere from 105 to 109 cells/gram of rock depending upon the metabolisms utilized and cellular growth rates and turnover (Bach and Edwards 2003; Santelli, Orcutt et al. 2008). Yet microbially-mediated basalt alteration and energy conservation has not been directly demonstrated on the seafloor. By using synchrotron-based x-ray microprobe mapping, x-ray absorption spectroscopy and high-resolution scanning and transmission electron microscopy observations of young volcanic glasses recovered from the outer flanks of Loihi Seamount, we intended to identify the initial rates and mechanisms of microbial basalt colonization and bioalteration. Instead, here we show that microbial biofilms are intimately associated with ferromanganese crusts precipitating onto basalt surfaces from cold seawater. Thus we hypothesize that microbial communities colonizing seafloor rocks are established and sustained by external inputs of potential energy sources, such as dissolved and particulate Fe(II), Mn(II) and organic matter, rather than rock dissolution.

  8. Ma's identity and its application

    Damian Słota; Edyta Hetmaniok; Roman Wituła

    2012-01-01

    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 present...

  9. Ma's identity and its application

    Damian Słota

    2012-04-01

    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.

  10. Evolution of the long-wavelength, subduction-driven topography of South America since 150 Ma

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

    2014-12-01

    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.

  11. Role of the Deep Mantle in Generating EM-I in Ocean Island Basalts: Insight from the Kerguelen Archipelago (Indian Ocean) (Invited)

    Weis, D.

    2013-12-01

    The Kerguelen Plume is responsible for one of the longest (both in length and time) hotspot tracks on Earth, starting at ~120 Ma with the formation of the Rajmahal Traps in India. The tectonic setting evolved from continental break-up at ~120 Ma, to a position above the Southeast Indian Ridge (SEIR) at ~40 Ma, to a purely oceanic environment today. The Cretaceous record of volcanism on the Central and Southern Kerguelen Plateau shows interaction of mantle plume-derived magmas with continental-related material (5000 km-long Ninetyeast Ridge (82-38 Ma) lacks any evidence of such shallow contamination. Upper mantle components (depleted, SEIR-type) participated in the formation of the submarine Northern Kerguelen Plateau (~34 Ma). The Kerguelen Archipelago is covered (>80%) by flood basalts erupted between 30 and 24 Ma. With decreasing age and increasing distance from the SEIR, the compositions evolved from tholeiitic in the northwest, to transitional in the central part of the archipelago, and to alkaline in the Southeast Province. The transition from tholeiitic to mildly alkalic compositions primarily reflects changes in melting conditions (lower extents of partial melting at higher pressures), associated with crust and lithosphere thickening as the distance from the SEIR increased. High-precision Pb-Sr-Nd-Hf isotopic data reveal that the archipelago flood basalts were derived from melting of an enriched component (EM-I) in the plume source, without any trace of continental contamination during eruption. The enriched component dominates the chemistry of the alkalic basalts (25-24 Ma), whereas the older (28-26 Ma) tholeiitic-transitional basalts contain a higher proportion of a depleted-SEIR component. In binary isotope plots, Kerguelen compositions form subparallel trends that are distinctly more enriched than those from Hawaii. Seismic data shows the presence of two large-low-shear-velocity-provinces (LLSVP) in the deep mantle, one centred in the Pacific, the other below Africa. When projected down to the core-mantle boundary (CMB), Kerguelen and Tristan (Atlantic Ocean) are located on the eastern and western edges of the tall steep-sided LLSVP African anomaly, respectively. The other two islands with EM-I signatures, Hawaii and Pitcairn, overlie the edges of the Pacific LLSVP. We infer that these deep zones with velocity anomalies at the CMB are the repositories for enriched components in the mantle that are brought to the surface by strong mantle plumes. Kerguelen and Tristan carry the strongest enriched signature, also referred to as the ';DUPAL anomaly', whereas Pitcairn and Hawaii have a distinct, slightly less pronounced enriched signature. The differences in EM-I compositions indicate that some of the material constituting the LLSVP at the base of the mantle is different in the African and Pacific anomalies. In Hawaii, the EM-I signature can be traced back to at least 5 Ma, whereas in Kerguelen it can be traced back until 34 Ma on the archipelago and Northern Kerguelen Plateau, and until 82 Ma along the Ninetyeast Ridge. This implies that the LLSVPs are long-lived features of the deep mantle; in the case of the African anomaly, on the order of 100 million years.

  12. Implications of regional gravity for state of stress in the earth's crust and upper mantle.

    McNutt, M.

    1980-01-01

    Topography is maintained by stress differences within the earth. Depending on the distribution of the stress we classify the support as either local or regional compensation. In general, the stresses implied in a regional compensation scheme are an order of magnitude larger than those corresponding to local isostasy. Gravity anomalies, a measure of the earth's departure from hydrostatic equilibrium, can be used to distinguish between the two compensation mechanisms and thus to estimate the magnitude of deviatoric stress in the crust and upper mantle. Topography created at an ocean ridge crest or in a major contiental orogenic zone appears to be locally compensated. Such features were formed on weak crust incapable of maintaining stress differences much greater than the stress from the applied load. Oceanic volcanoes formed on an already cooled, thickened lithosphere are regionally supported with elastic stresses. -Author

  13. The amount of recycled crust in sources of mantle-derived melts.

    Sobolev, Alexander V; Hofmann, Albrecht W; Kuzmin, Dmitry V; Yaxley, Gregory M; Arndt, Nicholas T; Chung, Sun-Lin; Danyushevsky, Leonid V; Elliott, Tim; Frey, Frederick A; Garcia, Michael O; Gurenko, Andrey A; Kamenetsky, Vadim S; Kerr, Andrew C; Krivolutskaya, Nadezhda A; Matvienkov, Vladimir V; Nikogosian, Igor K; Rocholl, Alexander; Sigurdsson, Ingvar A; Sushchevskaya, Nadezhda M; Teklay, Mengist

    2007-04-20

    Plate tectonic processes introduce basaltic crust (as eclogite) into the peridotitic mantle. The proportions of these two sources in mantle melts are poorly understood. Silica-rich melts formed from eclogite react with peridotite, converting it to olivine-free pyroxenite. Partial melts of this hybrid pyroxenite are higher in nickel and silicon but poorer in manganese, calcium, and magnesium than melts of peridotite. Olivine phenocrysts' compositions record these differences and were used to quantify the contributions of pyroxenite-derived melts in mid-ocean ridge basalts (10 to 30%), ocean island and continental basalts (many >60%), and komatiites (20 to 30%). These results imply involvement of 2 to 20% (up to 28%) of recycled crust in mantle melting. PMID:17395795

  14. CO 2-depleted fluids from mid-ocean ridge-flank hydrothermal springs

    Sansone, Francis J.; Mottl, Michael J.; Olson, Eric J.; Wheat, C. Geoffrey; Lilley, Marvin D.

    1998-07-01

    Hydrothermal spring fluids were collected from Baby Bare, a basement outcrop on the sediment-covered eastern flank of the Juan de Fuca Ridge overlying 3.5 Ma-old crust. These waters are venting at 25C but have cooled from 64C within the upper 200-300 m of the upflow zone during their ascent. Unlike ridge-axis hydrothermal vent fluids previously sampled, the total CO 2 content of the endmember spring fluids (0.85 ?mol kg -1) is depleted with respect to bottom seawater. The very low alkalinities (0.43 meq L -1) and high Ca 2+ concentrations (55 mmol kg -1) of endmember spring fluids suggest that the removal of C in the spring fluids is associated with carbonate precipitation in the igneous basement. Assuming that 8-20% of the total ridge-flank heat loss rate of 50 10 18 cal yr -1 (6.6 TW) is removed by porewater advecting from the sediment at ?25C (an upper limit dictated by the global input rate of Mg +2 to the oceans; Mottl and Wheat, 1994), a maximum global carbon sink of 1.0-2.6 10 11 mol yr -1 ( 1.2-3.1 Mton-C yr -1) and a maximum global alkalinity sink of 140-340 10 9 eq yr -1 are calculated for warm (?25C) ridge-flank hydrothermal circulation. This carbon flux is only 2-5% of current estimates of subaerial and submarine volcanic CO 2 emissions (50 10 11 mol yr -1), indicating that hydrothermal alteration of oceanic crust on young mid-ocean ridge flanks at temperatures of a few tens of degrees Celsius is only a relatively minor sink for carbon on a global basis. It is still possible, however, that ridge-flank alteration at lower temperatures (<25C) is an important component of the global carbon budget.

  15. Origin of the oceanic basalt basement of the Solomon Islands arc and its relationship to the Ontong Java Plateau-insights from Cenozoic plate motion models

    Wells, R.E.

    1989-01-01

    Cenozoic global plate motion models based on a hotspot reference frame may provide a useful framework for analyzing the tectonic evolution of the Solomon Islands convergent margin. A postulated late Miocene collision of the Ontong Java Plateau (OJP) with a NE-facing arc is consistent with the predicted path of the OJP across the Pacific Basin and its Miocene arrival at the trench. Late-stage igneous activity (65-30 Ma) predicted for the OJP as it rode over the Samoan hotspot occurred in correlative stratigraphic sections on Malaita, the supposed accreted flake of OJP in the Solomon Islands arc. Convergence similar to the present velocities between Australia and the Pacific plates was characteristic of the last 43 million years. Prior to 43 Ma Pacific-Australia plate motions were divergent, seemingly at odds with geologic evidence for early Tertiary convergence, particularly in Papua New Guinea. A postulated South Pacific plate may have existed between Australia and the Pacific plate and would have allowed implied northward subduction along the northeastern Australia plate boundary that lasted into the early Eocene. Subsequent reorganization of plate motions in the middle Eocene correlates with middle Eocene marginal basin formation along ridges oblique to the main plate boundary. Cessation of spreading on the Pacific-South Pacific Ridge and its subsequent subduction beneath Asia followed the change in Pacific plate motion at 43 Ma. A trapped remnant of the extinct, NW-trending ridge may still lie beneath the western Philippine Sea. The terminal deformation, metamorphism and ophiolite obduction in the Eocene orogen of the southwest Pacific also correlates with the major change in Pacific plate motion at 43 Ma and the subsequent compression of the dying Eocene arc against outlying continental and oceanic crustal blocks of the Australian plate. The Solomon Islands oceanic basement may represent juxtaposition of oceanic plateaus of the Australian plate beneath overthrust, dismembered ophiolite derived from adjacent marginal basin crust. ?? 1989.

  16. Reconstructions of subducted ocean floor along the Andes: a framework for assessing Magmatic and Ore Deposit History

    Sdrolias, M.; Müller, R.

    2006-05-01

    The South American-Antarctic margin has been characterised by numerous episodes of volcanic arc activity and ore deposit formation throughout much of the Mesozoic and Cenozoic. Although its Cenozoic subduction history is relatively well known, placing the Mesozoic arc-related volcanics and the emplacement of ore bodies in their plate tectonic context remains poorly constrained. We use a merged moving hotspot (Late Cretaceous- present) and palaeomagnetic /fixed hotspot (Early Cretaceous) reference frame, coupled with reconstructed spreading histories of the Pacific, Phoenix and Farallon plates to understand the convergence history of the South American and Antarctic margins. We compute the age-area distribution of oceanic lithosphere through time, including subducting oceanic lithosphere and estimate convergence rates along the margin. Additionally, we map the location and migration of spreading ridges along the margin and relate this to processes on the overriding plate. The South American-Antarctic margin in the late Jurassic-early Cretaceous was dominated by rapid convergence, the subduction of relatively young oceanic lithosphere (Verdes" in southern South America. The speed of subduction increased again along the South American-Antarctic margin at ~105 Ma after another change in tectonic regime. Newly created crust from the Farallon-Phoenix ridge continued to be subducted along southern South America until the cessation of the Farallon-Phoenix ridge in the latest Cretaceous / beginning of the Cenozoic. The age of the subducting oceanic lithosphere along the South American-Antarctic margin has increased steadily through time.

  17. Spectral expressions for modelling the gravitational field of the Earth’s crust density structure

    R. Tenzer; Novak, P.; Hamayun; Vajda, P.

    2011-01-01

    We derive expressions for computing the gravitational field (potential and its radial derivative) generated by an arbitrary homogeneous or laterally varying density contrast layer with a variable depth and thickness based on methods for a spherical harmonic analysis and synthesis of gravity field. The newly derived expressions are utilised in the gravimetric forward modelling of major known density structures within the Earth’s crust (excluding the ocean density contrast) beneath the geoid su...

  18. Biological soil crust community types differ in key ecological functions

    Pietrasiak, N; Regus, JU; Johansen, JR; LAM, D.; Sachs, JL; Santiago, LS

    2013-01-01

    Soil stability, nitrogen and carbon fixation were assessed for eight biological soil crust community types within a Mojave Desert wilderness site. Cyanolichen crust outperformed all other crusts in multi-functionality whereas incipient crust had the poorest performance. A finely divided classification of biological soil crust communities improves estimation of ecosystem function and strengthens the accuracy of landscape-scale assessments. © 2013 Elsevier Ltd.

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

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

    2014-02-01

    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 85E 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 85E 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 8073 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 8073 Ma, close to the IndiaAntarctica Ridge system. Subsequently, the seamount highs were formed by late-stage volcanism c. 613 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 85E Ridge further north, which is interpreted as being emplaced in an intraplate setting, i.e., 2535 Myr later than the underlying oceanic crust. Therefore, we suggest that the ANS and the 85E Ridge appear to be unrelated as they were formed by different mantle sources, and that the proximity of the southern end of the 85E Ridge to the ANS is coincidental.

  20. Nuclei in Strongly Magnetised Neutron Star Crusts

    Nandi, Rana

    2012-01-01

    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...

  1. Plume-proximal mid-ocean ridge origin of Zhongba mafic rocks in the western Yarlung Zangbo Suture Zone, Southern Tibet

    He, Juan; Li, Yalin; Wang, Chengshan; Dilek, Yildirim; Wei, Yushuai; Chen, Xi; Hou, Yunling; Zhou, Aorigele

    2016-05-01

    The >2000 km-long Yarlung Zangbo Suture Zone (YZSZ) in southern Tibet includes the remnants of the Mesozoic Neotethyan oceanic lithosphere, and is divided by the Zhada-Zhongba microcontinent into northern and southern branches in its western segment. Zircon U-Pb dating of a doleritic rock from the northern branch has revealed a concordant age of 160.5 ± 1.3 Ma. All of the doleritic samples from the northern branch and the pillow basalt and gabbro samples from the southern branch display consistent REE and trace element patterns similar to those of modern OIB-type rocks. The geochemical and Sr-Nd-Pb isotopic signatures of these OIB-type rocks from the western segment are identical with those of OIB-type and alkaline rocks from other ophiolite massifs along the central and eastern segments of the YZSZ, suggesting a common mantle plume source for their melt evolution. The enriched Sr-Nd-Pb isotopic character of the gabbroic dike rocks from the southern branch points to a mantle plume source, contaminated by subducted oceanic crust or pelagic sediments. We infer that the mafic rock associations exposed along the YZSZ represent the remnants of a Neotethyan oceanic lithosphere, which was developed as part of a plume-proximal seafloor-spreading system, reminiscent of the seamount chains along-across the modern mid-ocean ridges in the Pacific Ocean.

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

    Marquer, Didier; Mercolli, Ivan; Peters, Tjerk

    2007-01-01

    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...

  3. Crust formation in drying colloidal suspensions

    Style, R. W.

    2010-06-30

    During the drying of colloidal suspensions, the desiccation process causes the suspension near the air interface to consolidate into a connected porous matrix or crust. Fluid transport in the porous medium is governed by Darcy\\'s law and the equations of poroelasticity, while the equations of colloid physics govern processes in the suspension. We derive new equations describing this process, including unique boundary conditions coupling the two regions, yielding a moving-boundary model of the concentration and stress profiles during drying. A solution is found for the steady-state growth of a nedimensional crust during constant evaporation rate from the surface. The solution is used to demonstrate the importance of the system boundary conditions on stress profiles and diffusivity in a drying crust. © 2011 The Royal Society.

  4. Elemental composition of the Martian crust.

    McSween, Harry Y; Taylor, G Jeffrey; Wyatt, Michael B

    2009-05-01

    The composition of Mars' crust records the planet's integrated geologic history and provides clues to its differentiation. Spacecraft and meteorite data now provide a global view of the chemistry of the igneous crust that can be used to assess this history. Surface rocks on Mars are dominantly tholeiitic basalts formed by extensive partial melting and are not highly weathered. Siliceous or calc-alkaline rocks produced by melting and/or fractional crystallization of hydrated, recycled mantle sources, and silica-poor rocks produced by limited melting of alkali-rich mantle sources, are uncommon or absent. Spacecraft data suggest that martian meteorites are not representative of older, more voluminous crust and prompt questions about their use in defining diagnostic geochemical characteristics and in constraining mantle compositional models for Mars. PMID:19423810

  5. The Subduction of Continental Crust, the Variscan Evolution of the Bohemian Massif, and the Origin of PO Granitoids

    Brueckner, H. K.

    2012-04-01

    Slices of continental crust subducted into the mantle during collisional orogeny may either undergo metamorphism and exhumation towards the surface as coherent slab-like or domal high pressure/ultrahigh pressure (HP/UHP) terranes or, if stalled or delayed in the mantle, melt and return towards the surface as magmas, or undergo a combination of exhumation and melting. Some exhumed HP/UHP terranes contain synorogenic granitoid bodies demonstrating melting does occur during exhumation. Therefore, crust that remains trapped in the mantle will also melt when temperatures reach the appropriate solidi through adiabatic decompression and/or conductive heating and/or radioactive decay. Subducted terranes with hydrous phases will undergo hydrate-breakdown melting and could melt during subduction, when stalled in the mantle or during exhumation. Terranes lacking hydrous phases probably require melting by adiabatic decompression as heated crust becomes ductile and rises as diapirs through the mantle wedge. The generated magmas will intrude through the overlying mantle wedge and into the overlying continental crust to form late orogenic and post orogenic (PO) granitoids depending on the time required to reach solidus temperatures. Geochemical characteristics will depend on P-T conditions, the age/chemistry/mineralogy of the subducted terrane (especially the presence or lack of hydrous phases), and the degree of melt interaction (i.e. the traverse length) with the mantle wedge. Melts that significantly traverse the wedge will acquire the hybrid mantle/crust nature of many PO granitoids. Melts generated by adiabatic decompression close to or within the continental crust will retain ancient crustal signatures. The Variscan evolution of the Bohemian Massif involved two episodes of subduction of continental crust: (1), the southward (present coordinates) subduction of Saxo-Thuringia beneath Bohemia (aka Tapla-Barrandia) along an east-west suture at 400-370 Ma followed by, (2), the east-northeast subduction of Moldanubia beneath Bohemia at 340-320 Ma1. The first subduction was followed by the intrusion of granitoids, including the Central Bohemian Batholith, between 370-340 Ma, all occurring south of the Saxo-Thuringian - Bohemia suture suggesting elements of the subducted Saxo-Thuringian continental crust melted and intruded the overlying Bohemian Craton. The second subduction event was accompanied and followed by multiple intrusions of granites (340 Ma synorogenic granitoids, 340-310 Ma post-orogenic S and high-K granitoids, and 310-290 I-type granitoids2) all occurring west of the of the Moldanubia-Bohemia suture suggesting elements of the subducted Moldanubian crust were melted and intruded the overlying Bohemian/Saxo-Thuringian Craton. Many of the HP/UHP terranes in the Bohemian Massif occur in domal structures suggesting exhumation and melting occurred in part by diapiric upwelling3. It is proposed that both the Saxo-Thuringian and Moldanubian terranes were exhumed by a combination of slab-return and diapiric upwelling and that elements of both terranes were stranded long enough in the mantle to heat up and melt to form most or all of the PO granitoids of the Bohemian Massif. This model involves successive re-distillation of the continental crust and may play a significant role in the evolution of both the continental crust and upper mantle. 1Medaris et al., 2005, Lithos 82. 2Finger et al., 1997, Min & Pet 61. 3Stpsk et a., 04, J. Met. Geol. 22.

  6. Crust and uppermost mantle structure of the Kyushu-Palau Ridge, remnant arc on the Philippine Sea plate

    Nishizawa, Azusa; Kaneda, Kentaro; Oikawa, Mitsuhiro

    2016-02-01

    We acquired 27 wide-angle seismic profiles to investigate variation in crustal structure along the Kyushu-Palau Ridge (KPR), a 2600-km-long remnant island arc in the center of the Philippine Sea plate; 26 lines were shot across the strike of the KPR at 13°-31°N, and one was shot along the northernmost KPR. The derived P-wave velocity (Vp) models show that the KPR has a crustal thickness of 8-23 km, which is thicker than the neighboring backarc basin oceanic crusts of the West Philippine Basin to the west and the Shikoku and Parece Vela Basins to the east. While the KPR crust consists mainly of lower crusts with a Vp of 6.8-7.2 km/s, the thicker crust contains a thick middle crust with Vp of 6.0-6.8 km/s. In general, the KPR crust is thicker in the north than in the south. The uppermost mantle velocities just below the KPR bathymetric highs are lower than 8.0 km/s and are commonly associated with a slightly high Vp of 7.2 km/s at the base of the crust. Large amplitude reflection signals are sometimes observed at far offsets on several lines suggesting the existence of several reflectors at depths of 23-40 km in the mantle beneath the KPR. The characteristics of these reflections are similar to these observed beneath the Izu-Ogasawara (Bonin) island arc, the tectonically conjugate arc of the KPR before backarc basin spreading. Very thin crust and high Pn velocities characterize the transition between the KPR and the eastern basins, which is probably a relic of the initial stage of the rifting. West of the KPR, the crust varies in structure from north to south as a result of the different tectonic settings in which it evolved.

  7. Investigation of thallium fluxes from subaerial volcanism-Implications for the present and past mass balance of thallium in the oceans

    Baker, R.G.A.; Rehkamper, M.; Hinkley, T.K.; Nielsen, S.G.; Toutain, J.P.

    2009-01-01

    A suite of 34 volcanic gas condensates and particulates from Kilauea (Hawaii), Mt. Etna and Vulcano (Italy), Mt. Merapi (Indonesia), White Island and Mt. Nguaruhoe (New Zealand) were analysed for both Tl isotope compositions and Tl/Pb ratios. When considered together with published Tl-Pb abundance data, the measurements provide globally representative best estimates of Tl/Pb = 0.46 ?? 0.25 and ??205Tl = -1.7 ?? 2.0 for the emissions of subaerial volcanism to the atmosphere and oceans (??205Tl is the deviation of the 205Tl/203Tl isotope ratio from NIST SRM 997 isotope standard in parts per 10,000). Compared to igneous rocks of the crust and mantle, volcanic gases were found to have (i) Tl/Pb ratios that are typically about an order of magnitude higher, and (ii) significantly more variable Tl isotope compositions but a mean ??205Tl value that is indistinguishable from estimates for the Earth's mantle and continental crust. The first observation can be explained by the more volatile nature of Tl compared to Pb during the production of volcanic gases, whilst the second reflects the contrasting and approximately balanced isotope fractionation effects that are generated by partial evaporation of Tl during magma degassing and partial Tl condensation as a result of the cooling and differentiation of volcanic gases. Mass balance calculations, based on results from this and other recent Tl isotope studies, were carried out to investigate whether temporal changes in the volcanic Tl fluxes could be responsible for the dramatic shift in the ??205Tl value of the oceans at ???55 Ma, which has been inferred from Tl isotope time series data for ferromanganese crusts. The calculations demonstrate that even large changes in the marine Tl input fluxes from volcanism and other sources are unable to significantly alter the Tl isotope composition of the oceans. Based on modelling, it is shown that the large inferred change in the ??205Tl value of seawater is best explained if the oceans of the early Cenozoic featured significantly larger Tl output fluxes to oxic pelagic sediments, whilst the sink fluxes to altered ocean crust remained approximately constant. ?? 2009 Elsevier Ltd.

  8. Early precambrian continental crust basement and its compositional features in South China

    Based on the compilation of the uranium geological map of Fujian, Zhejiang and Jiangxi Provinces (on the scale of 1000000) and combined with the latest research outcomes in geology, geophysics and isotopic geochronology, the authors preliminarily analyses the compositional features of Early Precambrian (Ar-Pt) continental crust crystalline basement and the relationship between the Yangzi and Cathaysian blocks in South China. It is though that the basement, after Luliang Movement (1700-1800 Ma), gradually disintegrated in middle and late Proterozoic, then it turned into a new regime of polycyclic geosyncline and platform development which was controlled by the plate-tectonic mechanism. Owing to the heterogeneity in composition and the disequilibrium of the ancient continental crust evaluation, uranium was relatively enriched in local areas, thus laying foundation for the formation of various derivative types of U-rich geologic bodies and distribution of uranium mineralization thereafter

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

    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)

  10. The atypical Caribbean-Colombia oceanic plateau and its role in the deformation of the Northern Andes

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

    2013-05-01

    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 (98.77.7 to 64.45 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 Curaao. 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.

  11. Formation of the giant Chalukou porphyry Mo deposit in northern Great Xing'an Range, NE China: Partial melting of the juvenile lower crust in intra-plate extensional environment

    Li, Zhen-Zhen; Qin, Ke-Zhang; Li, Guang-Ming; Ishihara, Shunso; Jin, Lu-Ying; Song, Guo-Xue; Meng, Zhao-Jun

    2014-08-01

    The Chalukou porphyry Mo deposit (2.46 Mt @ 0.087% Mo), located in the northern Great Xing'an Range, NE China, is the largest Mo deposit discovered in China so far. The host rocks consist of aplite porphyry, granite porphyry and quartz porphyry, and are intruded into Lower Ordovician intermediate-felsic volcanic-sedimentary rocks and pre-ore monzogranite and are cut by post-ore feldspar porphyry, diorite porphyry and quartz monzonite porphyry. Here, we present the zircon U-Pb ages, whole-rock geochemistry, Sr-Nd isotopic and zircon Hf isotopic data for the pre-ore, syn-ore and post-ore intrusive rocks. The Chalukou ore-forming porphyries intruded during 147-148 Ma and have high-silica, alkali-rich, metaluminous to slightly peraluminous compositions and are oxidized. They are enriched in large ion lithophile elements (e.g. K, Rb, U and Th), light REE and depleted in high-field strength elements (e.g. Nb, P and Ti). Depletions in Eu, Ba, Sr, Nb, Ta, P and Ti suggest that they have experienced strong fractional crystallization of plagioclase, biotite, hornblende and accessory minerals. The pre-ore monzogranite (~ 172 Ma) also belongs to the high-K calc-alkaline series. Highly fractionated REE patterns ((La/Yb) N = 19.6-21.7), high values of Sr/Y (54-69) and La/Yb (29-32), are adakite-like geochemical features. The post-ore rocks (~ 141-128 Ma) have similar geochemical characteristics with ore-forming porphyries except that quartz monzonite porphyry shows no Ba-Sr negative anomaly. All intrusive rocks have relative low initial 87Sr/86Sr (0.705413-0.707889) and εNd (t) values (- 1.28 to + 0.92), positive εHf (t) values (+ 2.4 to + 10.1) and young two-stage Nd and Hf model ages (TDM2 (Nd) = 863-977 Ma, TDM2 (Hf) = 552-976 Ma). These geochemical and isotopic data are interpreted to demonstrate that the ore-forming porphyries formed by partial melting of the juvenile lower crust caused by underplating of mafic magmas in an intra-plate extensional setting. The pre-ore monzogranite formed by partial melting of thickened lower crust in a collisional setting caused by closure of Mongol-Okhotsk Ocean. The post-ore feldspar porphyry shares a similar magma source with ore-forming porphyry, but the quartz monzonite porphyry has a relatively deeper magma source region and has not experienced as much fractional crystallization. The transformation from middle Jurassic compression to late Jurassic extension created favorable conditions for the generation and emplacement of the ore-forming magma. The juvenile lower crust provided the main source of molybdenum for Chalukou deposit. Enrichment of Mo by fractional crystallization played an important role in concentrating Mo during formation of the Chalukou Mo deposit. The age (~ 147 Ma), high fluorine, and associated Pb-Zn deposits are all different from other major porphyry Mo deposits in NE China; Chalukou is a new mineral deposit type in the Great Xing'an Range.

  12. A relatively reduced Hadean continental crust

    Yang, Xiaozhi; Gaillard, Fabrice; Scaillet, Bruno

    2014-05-01

    Among the physical and chemical parameters used to characterize the Earth, oxidation state, as reflected by its prevailing oxygen fugacity (fO2), is a particularly important one. It controls many physicochemical properties and geological processes of the Earth's different reservoirs, and affects the partitioning of elements between coexisting phases and the speciation of degassed volatiles in melts. In the past decades, numerous studies have been conducted to document the evolution of mantle and atmospheric oxidation state with time and in particular the possible transition from an early reduced state to the present oxidized conditions. So far, it has been established that the oxidation state of the uppermost mantle is within ±2 log units of the quartz-fayalite-magnetite (QFM) buffer, probably back to ~4.4 billion years ago (Ga) based on trace-elements studies of mantle-derived komatiites, kimberlites, basalts, volcanics and zircons, and that the O2 levels of atmosphere were initially low and rose markedly ~2.3 Ga known as the Great Oxidation Event (GOE), progressively reaching its present oxidation state of ~10 log units above QFM. In contrast, the secular evolution of oxidation state of the continental crust, an important boundary separating the underlying upper mantle from the surrounding atmosphere and buffering the exchanges and interactions between the Earth's interior and exterior, has rarely been addressed, although the presence of evolved crustal materials on the Earth can be traced back to ~4.4 Ga, e.g. by detrital zircons. Zircon is a common accessory mineral in nature, occurring in a wide variety of igneous, sedimentary and metamorphic rocks, and is almost ubiquitous in crustal rocks. The physical and chemical durability of zircons makes them widely used in geochemical studies in terms of trace-elements, isotopes, ages and melt/mineral inclusions; in particular, zircons are persistent under most crustal conditions and can survive many secondary processes such as metamorphism, weathering and erosion. Thus, zircons in granites of shallow crust may record the chemical/isotopic composition of the deep crust that is otherwise inaccessible, and offer robust records of the magmatic and crust-forming events preserved in the continental crust. In fact, due to the absence of suitable rock records (in particular for periods older than ~4.0 Ga), studies in recent years concerning the nature, composition, growth and evolution of the continental crust, and especially the Hadean crust, have heavily relied on inherited/detrital zircons. Natural igneous zircons incorporate rare-earth elements (REE) and other trace elements in their structure at concentrations controlled by the temperature, pressure, fO2 and composition of their crystallization environment. Petrological observations and recent experiments have shown that the concentration of Ce relative to other REE in igneous zircons can be used to constrain the fO2 during their growth. By combining available trace-elements data of igneous zircons of crustal origin, we show that the Hadean continental crust was significantly more reduced than its modern counterpart and experienced progressive oxidation till ~3.6 billions years ago. We suggest that the increase in the oxidation state of the Hadean continental crust is related to the progressive decline in the intensity of meteorite impacts during the late veneer. Impacts of carbon- and hydrogen-rich materials during the formation of Hadean granitic crust must have favoured strongly reduced magmatism. The conjunction of cold, wet and reduced granitic magmatism during the Hadean implies the degassing of methane and water. When impacts ended, magma produced by normal decompression melting of the mantle imparted more oxidizing conditions to erupted lavas and the related crust.

  13. Oman Ophiolite: Petrological and Geochemical Investigation of Fast-Spreading Crust Formation Processes

    Mller, T.; Koepke, J.; Garbe-Schoenberg, C. D.; Schuth, S.; Wolff, P. E.

    2014-12-01

    We undertook a detailed field campaign in the Wadi Gideah, which is located in the Wadi-Tayin Massif in the southern part of the Oman Ophiolite, to sample a complete section of fast-spreading oceanic crust. Our concept of performing different analytical and structural investigations on the same samples enabled us to create a coherent data set. The thickness of the layered and virtually undeformed oceanic crust, containing pillow lavas and sheeted dikes as well as varitextured, foliated and layered gabbros resting on a relatively thin MOHO transition zone, was recalculated to approximately 6km. Here we present our data focusing on the petrological and geochemical logs obtained. Samples from the layered gabbro sequence show modal compositions of ~50 vol% plagioclase, ~40 vol% clinopyroxene and ~10 vol% olivine in average. The samples from the foliated gabbro sequence display a slightly higher amount of plagioclase. In very few samples up to 20 vol% of orthopyroxene is present. The layered gabbro sequence display Mg# 71-82 for olivine, Mg# 75-83 for clinopyroxene and An% in plagioclase of 71-93 mol%. The foliated gabbro sequence display Mg# 67-79 for olivine, Mg# 76-85 for clinopyroxene and An% in plagioclase of 58-85 mol%. The varitextured gabbro sequence display Mg# 74-80 for clinopyroxene and An% 59-86 in plagioclase mol%. The generally evolving trends in mineral major element composition from bottom to top of the profile are also observed for bulk rock major and trace element data. The average Sr87/Sr86 ratio is 0.7033 0.0002 for the entire foliated and layered gabbro with significantly higher values for samples from fault zones cutting the gabbros at all crustal level which here are interpreted as possible hydrothermal pathways for cooling of the deep crust. We calculated the Wadi Gideah bulk crust composition and modeled possible fractionation paths, implying significant crystallization in the deep crust.

  14. Central Andean Giant Ore Deposits: Links to Forearc Subduction Erosion, Shallowing Subduction and Thickening Crust

    Kay, S. M.; Mpodozis, C.

    2013-05-01

    An outstanding question on the Central Andean margin is the relationship between tectonic processes like ebbing arc volcanism, shallowing of the subducting slab and crustal thickening, and the origin of giant porphyry and epithermal Cu, Au and Ag deposits. Another potentially important factor in forming these major mineral deposits is forearc subduction erosion, which is postulated to have removed up to ~250 km of Central Andean forearc crust since the Jurassic. Geochemical and geophysical studies provide insights into possible links. Evidence for partial melts of removed and subducted forearc crust reaching the arc magma source and thus the magmas that host the ore deposits comes from the chemistry of late Neogene volcanic rocks on both the northern and southern margin of the Chilean-Pampean flat-slab (28-33S), where the frontal arc was displaced ~50 km into the foreland between ~10 and 3 Ma. This chemical evidence consists of transient ultra-steep REE patterns, elevated Mg, Cr and Ni contents and steps in isotopic ratios that are particularly notable in the glassy adakitic 8-3 Ma (Pircas Negras) andesites on the northern flat-slab margin at 27-28S. Well constrained reconstructions of the margin near 26-28S that assume a sustained 300 km wide arc-trench gap and ~50 km of forearc removal suggest an accelerated average forearc subduction erosion rate over 150 km3/my/km between 8 and 3 Ma. Noting that the late Miocene arc is now at least ~ 260 km from the trench from 26S to 34S and that the active arc extrapolates through the amagmatic flat-slab region (28-33S) at 300 km from the trench, accelerated forearc removal could be inferred from ~34S to 26S at ~10 to 3 Ma. Geophysical evidence for forearc crust entering the mantle wedge as the flatslab shallowed could come from low Vp/Vs seismic ratios in the mantle wedge under the flatslab, which Wagner et al. (2010) attribute to orthopyroxene. Formation of this orthopyroxene could be explained by forearc crust reacting with the mantle wedge. Thus, the slab shallowing, crustal thickening and forearc subduction erosion in the flatslab region, which began at ca 20-18 Ma and accelerated after 11-10 Ma could have set the stage for the formation of the Los Pelambres, Rio Blanco and El Teniente giant Cu porphyries between ~ 11-4 Ma. The backarc 8-6 Ma Bajo de la Alumbrera Cu-Au district near 27S, also formed east of the migrating volcanic arc on the northern flatslab margin at this time. This deposit is notable for now being above a high Qp mantle seismic anomaly overlying the slab, which is at a depth of ~150 km. Elsewhere, Ag-Zn mineralization in the ~14-12 Ma Potosi district near 19.5S in the Altiplano backarc, which has been suggested to have occurred in the early stages of steepening of a shallow slab, would potentially predate flushing of eroded forearc material from an expanding mantle wedge. In the same vein, a lack of known big Cu-Au-Ag deposits associated with the late Neogene giant plateau ignimbrite complexes, considered to be fomed over steepening subduction zones characterized by low Vp and Vs and high Qp tomographic seismic anomalies, could also partially reflect loss of forearc subducted components from an expanding wedge.

  15. Early magma ocean and core formation on Vesta

    Neumann, Wladimir; Breuer, Doris; Spohn, Tilman

    2013-04-01

    The Dawn mission confirms predictions that the asteroid 4 Vesta is differentiated in an iron rich core, a silicate mantle and a basaltic crust, supports its identification as the parent body of the HEDs and provides revised values of e.g. the mass, the bulk density and the dimensions of the asteroid 4 Vesta. Although no distinct volcanic regions have been identified, resurfacing by igneous processes distinguishes Vesta from asteroids like Ceres with its primitive surface, or Lutetia, which retained its primordial surface composition (and may still be partially differentiated[1]). Vesta's core radius is estimated to be 107-113 km[2] (derived from the mass concentration towards the centre). We performed numerical calculations of the thermo-chemical evolution of Vesta adopting the new data obtained by the Dawn mission (mass, bulk density, radius). We have expanded the thermo-chemical evolution model of [3], which includes accretion, compaction, melting, associated changes of the material properties, advective heat transport and differentiation by porous flow, by considering convection and thus effective cooling in a magma ocean to analyse its formation and evolution on Vesta. For melt fractions below the rheologically critical melt fraction (RCMF) of ?50% the heat transport by melt segregation is modeled assuming melt flow in porous media and by supplementing the energy balance equation with additional advection terms. Above the RCMF the effective thermal conductivity keff is computed from the convective heat flux in the soft turbulence regime[4]. The parameter keff mimics the vigorous convection and heat flux of the magma ocean with a low viscosity. It amounts to O(106) W m-1K-1 and substitutes the thermal conductivity in the energy balance equation. We consider both instantaneous and continuous accretion (assuming late runaway material accumulation). In particular, we compare the evolution scenarios arising from the instantaneous accretion of Vesta at different formation times t0 (relative to the formation of the CAIs) with those for which the accretion durations ta is between 0.5 and 2.0 Ma. According to our results core formation is possible for formation times of up to 2.5 Ma after the CAIs. An important process for the formation and evolution of a magma ocean is the partitioning of 26Al and its relocation with the silicate melt. Previous models[5] suggest the formation of an internal magma ocean throughout the whole mantle beneath a solid crust. Thereby, the partitioning of 26Al is neglected. In contrast to that, if partitioning of 26Al into the melt is considered we obtain an about 1 km thick superficial magma ocean due to the enrichment of the radioactive nuclides in the liquid phase and redistribution towards the surface with the rising melt (for t0

  16. Superfluid Dynamics in Neutron Star Crusts

    Pethick, C.J.; Chamel, Nicolas; Reddy, S.

    2010-01-01

    A simple description of superfluid hydrodynamics in the inner crust of a neutron star is given. Particular attention is paid to the effect of the lattice of nuclei on the properties of the superfluid neutrons, and the effects of entrainment, the fact that some fraction of the neutrons are locked to the motion of the protons in nuclei.

  17. Resonant shattering of neutron star crusts.

    Tsang, David; Read, Jocelyn S; Hinderer, Tanja; Piro, Anthony L; Bondarescu, Ruxandra

    2012-01-01

    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 on the crust equation of state. We describe how a larger sample of precursor detections could be used alongside coincident gravitational wave detections of the inspiral by Advanced LIGO class detectors to probe the NS structure. These two types of observations nicely complement one another, since the former constrains the equation of state and structure near the crust-core boundary, while the latter is more sensitive to the core equation of state. PMID:22304251

  18. Collective excitations in neutron-star crusts

    Chamel, N.; Page, D.; Reddy, S.

    2016-01-01

    We explore the spectrum of low-energy collective excitations in the crust of a neutron star, especially in the inner region where neutron-proton clusters are immersed in a sea of superfluid neutrons. The speeds of the different modes are calculated systematically from the nuclear energy density functional theory using a Skyrme functional fitted to essentially all experimental atomic mass data.

  19. Pulsar Glitches: The Crust may be Enough

    Piekarewicz, J; Horowitz, C J

    2014-01-01

    Pulsar glitches-the sudden spin-up in the rotational frequency of a neutron star-suggest the existence of an angular-momentum reservoir confined to the inner crust of the neutron star. Large and regular glitches observed in the Vela pulsar have originally constrained the fraction of the stellar moment of inertia that must reside in the solid crust to about 1.4%. However, crustal entrainment-which until very recently has been ignored-suggests that in order to account for the Vela glitches, the fraction of the moment of inertia residing in the crust must increase to about 7%. This indicates that the required angular momentum reservoir may exceed that which is available in the crust. We explore the possibility that uncertainties in the equation of state provide enough flexibility for the construction of models that predict a large crustal thickness and consequently a large crustal moment of inertia. Given that analytic results suggest that the crustal moment of inertia is sensitive to the transition pressure at ...

  20. Unified Structural Representation of the southern California crust and upper mantle

    Shaw, John H.; Plesch, Andreas; Tape, Carl; Suess, M. Peter; Jordan, Thomas H.; Ely, Geoffrey; Hauksson, Egill; Tromp, Jeroen; Tanimoto, Toshiro; Graves, Robert; Olsen, Kim; Nicholson, Craig; Maechling, Philip J.; Rivero, Carlos; Lovely, Peter; Brankman, Charles M.; Munster, Jason

    2015-04-01

    We present a new, 3D description of crust and upper mantle velocity structure in southern California implemented as a Unified Structural Representation (USR). The USR is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity (Vp, Vs) measurements and incorporates the locations and displacement of major fault zones that influence basin structure. These basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure, which were subsequently iterated and improved using 3D waveform adjoint tomography. A geotechnical layer (GTL) based on Vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component. The resulting model provides a detailed description of the structure of the southern California crust and upper mantle that reflects the complex tectonic history of the region. The crust thickens eastward as Moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust. Deep sedimentary basins and underlying areas of thin crust reflect Neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late Pliocene. To illustrate the impact of this complex structure on strong ground motion forecasting, we simulate rupture of a proposed M 7.9 earthquake source in the Western Transverse Ranges. The results show distinct basin amplification and focusing of energy that reflects crustal structure described by the USR that is not captured by simpler velocity descriptions. We anticipate that the USR will be useful for a broad range of simulation and modeling efforts, including strong ground motion forecasting, dynamic rupture simulations, and fault system modeling. The USR is available through the Southern California Earthquake Center (SCEC) website (

  1. 33 CFR 80.135 - Hull, MA to Race Point, MA.

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Hull, MA to Race Point, MA. 80... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Atlantic Coast 80.135 Hull, MA to Race Point, MA. (a... position latitude 4216.7? N., longitude 7052.6? W., to Race Point on Cape Cod. (b) A line drawn...

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

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

    1999-01-01

    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. Remote sensing evidence for an ancient carbon-bearing crust on Mercury

    Peplowski, Patrick N.; Klima, Rachel L.; Lawrence, David J.; Ernst, Carolyn M.; Denevi, Brett W.; Frank, Elizabeth A.; Goldsten, John O.; Murchie, Scott L.; Nittler, Larry R.; Solomon, Sean C.

    2016-04-01

    Mercury’s global surface is markedly darker than predicted from its measured elemental composition. The darkening agent, which has not been previously identified, is most concentrated within Mercury’s lowest-reflectance spectral unit, the low-reflectance material. This low-reflectance material is generally found in large impact craters and their ejecta, which suggests a mid-to-lower crustal origin. Here we present neutron spectroscopy measurements of Mercury’s surface from the MESSENGER spacecraft that reveal increases in thermal-neutron count rates that correlate spatially with deposits of low-reflectance material. The only element consistent with both the neutron measurements and visible to near-infrared spectra of low-reflectance material is carbon, at an abundance that is 1-3 wt% greater than surrounding, higher-reflectance material. We infer that carbon is the primary darkening agent on Mercury and that the low-reflectance material samples carbon-bearing deposits within the planet’s crust. Our findings are consistent with the formation of a graphite flotation crust from an early magma ocean, and we propose that the heavily disrupted remnants of this ancient layer persist beneath the present upper crust. Under this scenario, Mercury’s globally low reflectance results from mixing of the ancient graphite-rich crust with overlying volcanic materials via impact processes or assimilation of carbon into rising magmas during secondary crustal formation.

  4. Guided wave observations and evidence for the low-velocity subducting crust beneath Hokkaido, northern Japan

    Shiina, Takahiro; Nakajima, Junichi; Toyokuni, Genti; Matsuzawa, Toru

    2014-12-01

    At the western side of the Hidaka Mountain range in Hokkaido, we identify a clear later phase in seismograms for earthquakes occurring at the uppermost part of the Pacific slab beneath the eastern Hokkaido. The later phase is observed after P-wave arrivals and has a larger amplitude than the P wave. In this study, we investigate the origin of the later phase from seismic wave observations and two-dimensional numerical modeling of wave fields and interpret it as a guided P wave propagating in the low-velocity subducting crust of the Pacific plate. In addition, the results of our numerical modeling suggest that the low-velocity subducting crust is in contact with a low-velocity material beneath the Hidaka Mountain range. Based on our interpretation for the later phase, we estimate P-wave velocity in the subducting crust beneath the eastern part of Hokkaido by using the differences in the later phase travel times and obtain velocities of 6.8 to 7.5 km/s at depths of 50 to 80 km. The obtained P-wave velocity is lower than the expected value based on fully hydrated mid-ocean ridge basalt (MORB) materials, suggesting that hydrous minerals are hosted in the subducting crust and aqueous fluids may co-exist down to depths of at least 80 km.

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

    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?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 24O+24O and 28Ne+28Ne. 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 separation. Nevertheless, the screening factors that we determine for the enhancement of the rate of thermonuclear reactions are insensitive to these features. Finally, we calculate the rate of thermonuclear 24O+24O fusion and find that 24O should burn at densities near 1011 g/cm3. The energy released from this and similar reactions may be important for the temperature profile of the star

  6. Seismic structure of the crust and uppermost mantle beneath Caucasus based on regional earthquake tomography

    Zabelina, Irina; Koulakov, Ivan; Amanatashvili, Iason; El Khrepy, Sami; Al-Arifi, Nassir

    2016-04-01

    We present a new seismic model of the crust beneath the Caucasus based on tomographic inversion of P and S arrival times from earthquakes occurred in the region recorded by regional seismic networks in the Caucasian republics. The resulting P and S velocity models clearly delineate major tectonic units of the study area. A high velocity anomaly in Transcaucasian separating the Great and Lesser Caucasus possibly represents a rigid crustal block corresponding to the remnant oceanic lithosphere of Tethys. Another high-velocity pattern coincides with the southern edge of the Scythian Plate. Strongly deformed areas of Great and Lesser Caucasus are mostly associated with low-velocity patterns representing thickened felsic part of the crust and strong fracturing of rocks. Most Cenozoic volcanic centers of Caucasus match to the low-velocity seismic anomalies in the crust. For example, the Kazbegi volcano group is located above an elongated low-velocity anomaly squeezed between high-velocity segments of Transcaucasian and Scythian Plate. We propose that mantle part of the Arabian and Eurasian Plates has been delaminated due to the continental collision in the Caucasus region. As a result, overheated asthenosphere appeared nearly the bottom of the crust and facilitated melting of the crustal material that caused the origin of recent volcanism in Great and Lesser Caucasus.

  7. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-01-01

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins. PMID:24301173

  8. Crust and subduction zone structure of Southwestern Mexico

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

    2015-02-01

    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.

  9. Heat and fluid flux at a crustal scale: Observations and models of coupled transport in young oceanic lithosphere

    Hutnak, Michael

    Hydrothermal circulation of seawater through the oceanic crust profoundly influences lithospheric and oceanic evolution. The upper oceanic crust comprises an aquifer of global proportions, and sedimentation acts to hydrologically isolate the crustal aquifer from the overlying ocean. Thermally-significant exchange of fluids between the crustal aquifer and overlying ocean can only occur where seamounts or other basaltic outcrops penetrate the sediment blanket. Although much progress has been made in the last several decades in elucidating the nature of hydrothermal circulation in oceanic basement, many of the physical properties and processes remain poorly understood or inadequately quantified. My dissertation research addresses several fundamental gaps in our understanding of ridge-flank hydrological processes, namely the roles of seamounts and basement outcrops is facilitating the exchange of fluid between the crustal aquifer and overlying ocean, the extents and rates of hydrothermal circulation in uppermost basement, the bulk crustal permeability distributions required to support the fluid fluxes, the thermal effects of sedimentation on measurements of seafloor heat flux, and the timescales required for conductive thermal rebound to occur once basement outcrops become buried. Interpretation of measurements of seafloor heat flux on relatively young (0.7-24 Ma) on the eastern flanks of the Juan de Fuca Ridge (JFR) and East Pacific Rise (EPR) is facilitated by collocation of measurements on bathymetric maps and along seismic reflection profiles, and these data are used as constraints for numerical models of coupled heat-fluid flow. Observational data from the eastern flank of the JFR indicate that fluids circulate rapidly through upper basement close to the ridge axis, both along- and across-strike of dominant structural trends. Numerical models of both individual and paired recharging and discharging outcrops are most consistent with regional upper basement permeabilities of 10-11 to 10-8 m2, and crustal aquifer thicknesses of 100-600 m. Numerical thermal models of sedimentation indicate that incomplete conductive thermal rebound may be responsible for the observed variability in seafloor heat flux measurements on the JFR, and may also bias measurements made on moderate to old seafloor areas even where there is little evidence for ridge-flank hydrothermal circulation at present.

  10. The fate of Ceres' original crust

    Roberts, James H.; Rivkin, Andrew S.

    2015-11-01

    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.

  11. Kinetics of the crust thickness development of bread during baking

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

    2012-01-01

    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 mathemat...

  12. Compositional Freeze-Out of Neutron Star Crusts

    Hoffman, Kelsey; Heyl, Jeremy

    2009-01-01

    We have investigated the crustal properties of neutron stars without fallback accretion. We have calculated the chemical evolution of the neutron star crust in three different cases (a modified Urca process without the thermal influence of a crust, a thick crust, and a direct Urca process with a thin crust) in order to determine the detailed composition of the envelope and atmosphere as the nuclear reactions freeze out. Using a nuclear reaction network up to technetium, we calculate the distr...

  13. Melt evolution and residence in extending crust: Thermal modeling of the crust and crustal magmas

    Karakas, Ozge; Dufek, Josef

    2015-09-01

    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.

  14. Millennial-scale ocean acidification and late Quaternary

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

    2014-01-01

    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.

  15. Ma Ying-jeou’s Presidential Discourse

    Jonathan Sullivan; Sapir, Eliyahu V.

    2012-01-01

    "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...

  16. Coulomb crystals in neutron star crust

    It is well known that neutron star crust in a wide range of mass densities and temperatures is in a crystal state. At a given density, the crystal is made of fully ionized atomic nuclei of a single species immersed in a nearly incompressible (i.e., constant and uniform) charge compensating background of electrons. This model is known as the Coulomb crystal model. In this talk we analyze thermodynamic and elastic properties of the Coulomb crystals and discuss various deviations from the ideal model. In particular, we study the Coulomb crystal behavior in the presence of a strong magnetic field, consider the effect of the electron gas polarizability, outline the main properties of binary Coulomb crystals, and touch the subject of quasi-free neutrons permeating the Coulomb crystal of ions in deeper layers of neutron star crust.

  17. Composition of weakly altered Martian crust

    Mustard, J. F.; Murchie, S. L.; Erard, S.

    1993-01-01

    The mineralogic and chemical composition of weakly altered crust remains an unresolved question for Mars. Dark regions hold clues to the composition since they are thought to comprise surface exposures of weakly altered crustal materials. Understanding the in situ composition of relatively pristine crustal rocks in greater detail is important for investigating basic volcanic processes. Also, this will provide additional constraints on the chemical pathways by which pristine rocks are altered to produce the observed ferric iron-bearing assemblages and inferred clay silicate, sulphate, and magnetic oxide phases. Reflectance spectra of dark regions obtained with the ISM instrument are being used to determine the basic mineralogy of weakly altered crust for a variety of regions on Mars.

  18. Towards a metallurgy of neutron star crusts.

    Kobyakov, D; Pethick, C J

    2014-03-21

    In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic lattice of nuclei immersed in an essentially uniform electron gas. We show that, at densities above that for neutron drip (∼ 4 × 1 0(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 BaTiO3. As a consequence, the properties of matter in the inner crust are expected to be much richer than previously appreciated, and we mention possible consequences for observable neutron star properties. PMID:24702357

  19. Crusted Scabies in the Burned Patient

    Berg, Jais Oliver; Alsbjørn, Bjarne

    2011-01-01

    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...

  20. Towards a metallurgy of neutron star crusts

    Kobyakov, D

    2013-01-01

    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. Black crusts in the European built environment

    Sáiz-Jiménez, Cesáreo; Hermosín, Bernardo

    2004-01-01

    Buildings and monuments act as repositories of airborne organic pollutants, which accumulate at the surfaces in zones frequently soaked by rainwater but are not washed out. In these areas thick black crust deposits can be found, which contribute to soiling of stone surfaces. The exposed building materials act as a non-selective surface, passively entrapping all deposited airborne particulate matter and organic compounds, which obviously modifies the composition of the materials present in the...

  2. Topological characterization of neutron star crusts

    Dorso, C. O.; Giménez Molinelli, P. A.; López, J. A.

    2012-11-01

    Neutron star crusts are studied using a classical molecular dynamics model developed for heavy-ion reactions. After the model is shown to produce a plethora of the so-called pasta shapes, a series of techniques borrowed from nuclear physics, condensed matter physics, and topology is used to craft a method that can be used to characterize the shape of the pasta structures in an unequivocal way.

  3. Topological characterization of neutron star crusts

    Dorso, C O; López, J A

    2012-01-01

    Neutron star crusts are studied using a classical molecular dynamics model developed for heavy ion reactions. After the model is shown to produce a plethora of the so-called "pasta" shapes, a series of techniques borrowed from nuclear physics, condensed matter physics and topology are used to craft a method that can be used to characterize the shape of the pasta structures in an unequivocal way.

  4. Crusted Demodicosis in an Immunocompetent Pediatric Patient

    Guillermo Antonio Guerrero-González; Maira Elizabeth Herz-Ruelas; Minerva Gómez-Flores; Jorge Ocampo-Candiani

    2014-01-01

    Demodicosis refers to the infestation by Demodex spp., a saprophytic mite of the pilosebaceous unit. Demodex proliferation can result in a number of cutaneous disorders including pustular folliculitis, pityriasis folliculorum, papulopustular, and granulomatous rosacea, among others. We report the case of a 7-year-old female presenting with pruritic grayish crusted lesions over her nose and cheeks, along with facial erythema, papules, and pustules. The father referred chronic use of topical st...

  5. Seismic Structure of Eastern Anatolia Crust

    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

  6. r-process in neutron star crust

    Understanding the formation of heavy and superheavy nuclei in the universe is a challenging problem. It is predicted that the rapid neutron-capture process (r-process) could be responsible for the synthesis of heavy and superheavy elements in supernova explosions and neutron star crust under extreme physical conditions. However, there is much debate about the astrophysical sites, in which ideal r-process conditions are met. Supernova, could not reproduce the observed solar abundances of r-process elements and has been abandoned by recent studies. Neutron-rich ejecta of compact binary mergers are now believed to be a perfect candidate for an astrophysical r-process. In the events of merging of binary neutron star or a neutron star with a black hole, the crust matter can be dynamically stripped and ejected. Once the density decreases below neutron drip, β-decay channels begin opening in full, and a conventional r-process begins leading to the formation of very heavy nuclei when the seed nuclei rapidly capture the free neutrons. Recently it has been shown that the decompression of the neutron star matter from the outer crust provides suitable condition for nucleosynthesis of r-nuclei with A ≤ 140. The decompression is triggered by a phase transition to strange quark matter at the core of a neutron star that ejects neutron-rich matter at the surface

  7. Mesoscopic pinning forces in neutron star crusts

    Seveso, S.; Pizzochero, P. M.; Grill, F.; Haskell, B.

    2016-02-01

    The crust of a neutron star is thought to be comprised of a lattice of nuclei immersed in a sea of free electrons and neutrons. As the neutrons are superfluid, their angular momentum is carried by an array of quantized vortices. These vortices can pin to the nuclear lattice and prevent the neutron superfluid from spinning down, allowing it to store angular momentum which can then be released catastrophically, giving rise to a pulsar glitch. A crucial ingredient for this model is the maximum pinning force that the lattice can exert on the vortices, as this allows us to estimate the angular momentum that can be exchanged during a glitch. In this paper, we perform, for the first time, a detailed and quantitative calculation of the pinning force per unit length acting on a vortex immersed in the crust and resulting from the mesoscopic vortex-lattice interaction. We consider realistic vortex tensions, allow for displacement of the nuclei and average over all possible orientations of the crystal with respect to the vortex. We find that, as expected, the mesoscopic pinning force becomes weaker for longer vortices and is generally much smaller than previous estimates, based on vortices aligned with the crystal. Nevertheless, the forces we obtain still have maximum values of the order of fpin ? 1015 dyn cm-1, which would still allow for enough angular momentum to be stored in the crust to explain large Vela glitches, if part of the star is decoupled during the event.

  8. Thin crust as evidence for depleted mantle supporting the Marion Rise.

    Zhou, Huaiyang; Dick, Henry J B

    2013-02-14

    The global ridge system is dominated by oceanic rises reflecting large variations in axial depth associated with mantle hotspots. The little-studied Marion Rise is as large as the Icelandic Rise, considering both length and depth, but has an axial rift (rather than a high) nearly its entire length. Uniquely along the Southwest Indian Ridge systematic sampling allows direct examination of crustal architecture over its full length. Here we show that, unlike the Icelandic Rise, peridotites are extensively exposed high on the rise, revealing that the crust is generally thin, and often missing, over a rifted rise. Therefore the Marion Rise must be largely an isostatic response to ancient melting events that created low-density depleted mantle beneath the Southwest Indian Ridge rather than thickened crust or a large thermal anomaly. The origin of this depleted mantle is probably the mantle emplaced into the African asthenosphere during the Karoo and Madagascar flood basalt events. PMID:23389441

  9. Recognition of Intermediate Crust (IC), its construction and its distinctive epeirogenic behaviour: an exciting new tool for plate kinematic analysis (PKA) of the Arctic margins and western Siberia

    Osmaston, M. F.

    2012-04-01

    Identification of a microcontinental block within or near a continental margin raises two questions, addressed in this talk - How did it get there? What is the nature of the intervening crust? I will then illustrate briefly how, in the Arctic, the answers, although by no means restricted to that region, do seem to help us a lot to begin unravelling the ancient plate kinematics of its wide margins. The plate tectonics paradigm currently posits that the Earth has only two kinds of crust - continental and oceanic - and that the former may be stretched to form sedimentary basins or the latter may be modified by arc or collision until it looks continental. But global analysis of the dynamics of actual plate motions for the past 150 Ma indicates [1, 2, 3] that continental tectospheres must be immensely thicker than previously thought and almost certainly too thick to be stretched with the forces available. In the extreme case of cratons, these tectospheric keels may commonly extend to 600 km or more [3]. This thick-plate behaviour is attributable, not to cooling but to a petrological 'stiffening' effect, associated with a loss of water-weakening, which also applies to the LVZ below MORs [4, 5, 6]. The corresponding thick-plate version of the MOR process [1, 6] has a deep, narrow wall-accreting axial crack which inherently brings two outstanding additional benefits:- (i) why, at medium to fast spreading rates, MOR axes become straight and orthogonally segmented [7], (ii) not being driven by body forces, it can achieve the sudden jumps of axis, spreading-rate and direction widely recorded in mid-ocean and are necessary after generating the limited separations of microplates near margins. So in seeking the 'continent-ocean boundary' (COB) along passive margins, a site where stretching has often been invoked, we need instead to consider how this MOR process would be affected by the heavy concurrent sedimentation to be expected when splitting a continent. I reason that, by blocking the hydrothermal cooling, this must inhibit magnetic anomaly formation and prolong magmagenesis to give a thicker-than-oceanic mafic crust, which I have called Intermediate Crust (IC) [8, 9], to distinguish it from Mature Continental Crust (MCC). Seismologically, IC basement must look deceptively like that assigned to stretched MCC. For thermodynamic reasons [8, 9] the hydrous content of deep MCC and of deeply subducted UHP crustal slices gives them a big thermal epeirogenic sensitivity which IC lacks. The NE Atlantic offers an example of this distinction. Structurally, the MCC of Greenland and Norway must have been intimately juxtaposed by the Scandian collision, so it was concluded [9] that the crust of the Greenland-Norway continental shelves must mostly be IC of post-Scandian (early Devonian?) age, a character confirmed by their lack of epeirogenic response to laterally conducted heat from the opening N Atlantic, although drainage systems in Norway proper clearly show it. Geometrically, this separation appears to have changed direction sharply, the second and bigger stage also involving separation of Svalbard from near Tromsø, where it had provided northward continuation of a complete Caledonian transect, so it has an IC implication for much of the Barents Sea area (bar the Bjørnøya block). Moving quickly round to the NE side of Baltica, we can begin to trace the separative motions of the Novaya Zemlya - Pay Khoy (NZPK) strip of less-mature MCC, transverse to the Timanian belt, and the associated evolution of the Pechora basin system. In places, faulted IC/MCC epeirogenic contrasts seem to define the size and direction of the IC-generating separation with remarkable precision. A crucial opening-up of this analysis is provided by realizing that the Polar Ural stretch is not MCC, but is merely the huge 585 Ma Voykar-Synya ophiolite, with its metamorphics, resting on a now-crumpled boundary between IC of very different ages. For further understanding we need briefly to extend the analysis, first to the formation of the West Siberian Basin, the IC nature of whose crust (but not its low thermal epeirogenic sensitivity) has been obscured by Permo-Triassic addition of the Siberian flood basalts, and thence to the complicated MCC distribution seen in Khazakhstan. The pattern of the older elements of the latter appears to be a further, but more ancient, example of the plate dynamics evidence [1, 2, 3] for 'deep-keeled' cratons, in that, when they separate, horizontal inflows of mantle are induced which impinge on the lesser keels of MCC blocks in the region, potentially generating IC-floored basins in between them. In this way the geology which now lies between the Baltica and East Siberia cratons can in principle provide powerful constraints on the freedom with which palaeomagnetic data for them has been interpreted. A key element in this is that otherwise-missing components of the Timanian orogen are apparently to be found on the western edge of the Siberian platform. This means that the NZPK strip and Pechora Basin area were formed as part of the Timanian interplay between the then-roughly-parallel sides of the Baltica and Siberian cratons. A final step in this limited analysis suggests that the clockwise bending of northern Novaya Zemlya was the dextral consequence of the final (~2000 km) northwestward cratonic separation of Baltica plus NZPK etc. to form the IC of the West Siberian Basin during the 580-535 Ma interval. This may be older than any of the NZ rocks suitable for palaeomagnetic determination. Resolution of the conflict between this geologically and geometrically secured reconstruction and that prescribed palaeomagnetically for 'Rodinia' appears to lie in the possibility that at some point on the APWP there has been an inadvertent switch between following the N and the S pole, due to the habitual choosing of the lesser of two plate motion speeds during the interval between points on the curve. In that case some of the supposed assemblage will be geographically upside down in relation to the rest. Finally, a quick visit to the Chukchi-Bering-Alaska sector of the Arctic margin. Here, too, recognition of IC may provide a key. I suggest that northward emplacement of the Brooks Range Ophiolite at close to 170 Ma was swiftly followed by the (now) westward extraction of the Seward-Chukchi MCC assemblage to form, as IC, both the extensive Koyukuk basin system which lies south of Brooks Range and, ultimately, the Bering gap in the Pacific rim of cratonic keels, through which mantle to put at depth under the widening Eurasian Basin ocean floor has been drawn, initiating the Aleutian arc in the Palaeocene, trapping OC/IC behind it. I discuss a global reason for the initiation of the Bering gap, and its timing, in another session (GD6.1) of this meeting. [1] Osmaston M. F. (2006) Global tectonic actions emanating from Arctic opening in the circumstances of a two-layer mantle and a thick-plate paradigm involving deep cratonic tectospheres: the Eurekan (Eocene) compressive motion of Greenland and other examples. In, Proc. ICAM IV 2003 (ed. R. Scott & D. Thurston). OCS Study MMS 2006-003, pp.105-124: Also published on: http://www.mms.gov/alaska/icam [2] Osmaston M. F. (2007) Cratonic keels and a two-layer mantle tested: mantle expulsion during Arabia-Russia closure linked to westward enlargement of the Black Sea, formation of the Western Alps and subduction of the Tyrrhenian (not the Ionian) Sea. XXIV IUGG, Session JSS 011 Abstr #2105. http://www.iugg2007perugia.it/webbook/. [3] Osmaston M. F. (2009) Deep cratonic keels and a 2-layer mantle? Tectonic basis for some far-reaching new insights on the dynamical properties of the Earth's mantle: example motions from Mediterranean, Atlantic-Arctic and India. Geophys. Res. Abst. 11, EGU2009-6359 (Solicited). [4] Karato S. (1986) Does partial melting reduce the creep strength of the upper mantle? Nature 319, 309-310. [5] Hirth G. & Kohlstedt D. L. (1996) Water in the oceanic upper mantle: implication for rheology, melt extraction, and the evolution of the lithosphere. EPSL 144, 93-108. [6] Osmaston M. F. (2010) On the actual variety of plate dynamical mechanisms and how mantle evolution affected them through time, from core formation to the Indian collision. Geophys. Res. Abstr. 12, EGU2010-6101. [7] Osmaston M. F. (1995) A straightness mechanism for MORs: a new view of ocean plate genesis and evolution. In IUGG XXI Gen. Assy. Abstracts p. A472. [8] Osmaston M. F. (2011) An introduction to Intermediate Crust (IC): its formation, epeirogenic character, and plate tectonics significance. TSG Ann.Mtg. 2011, Durham University, Technical Programme p.45. [9] Osmaston M. F. (2008) Basal subduction tectonic erosion (STE), butter mélanges and the construction and exhumation of HP-UHP belts: the Alps example and some comparisons. Internat. Geol. Rev. 50(8), 685-754 DOI: 10.2747/00206814.50.8.685.

  10. Formation of the Archean crust of the ancient Vodlozero domain (Baltic shield)

    Arestova, N. A.; Chekulaev, V. P.; Lobach-Zhuchenko, S. B.; Kucherovskii, G. A.

    2015-03-01

    The available geological, petrological, and isotopic data on Archean rocks of the Baltic shield are used to analyze the formation of the crust of the ancient Vodlozero domain. This made it possible to reveal the succession of endogenic processes in different parts of the domain and correlate them between each other. Several stages of magmatic processes reflecting changes in magma-generation environments are definable in the crust formation. The earliest stages of magmatism (3.24 and 3.13-3.15 Ga) are mostly represented by rocks of the tonalite-trondhjemite-granodiorite association. The next stage of endogenic activity (3020-2900 Ma) was marked by the formation of volcanics of the komatiite-basalt and andesite-dacite associations constituting greenstone belts in marginal parts of the Vodlozero domain and basic dikes accompanied by layered pyroxenite-norite-diorite intrusion in its central part. These basic bodies crossing earlier tonalities were formed in extension settings related to the formation of the mantle plume, which is confirmed by the rock composition. This stage culminated in the formation of trondhjemites at margins of greenstone structure. The next stage of endogenic activity commenced at 2890-2840 Ma by the emplacement of high-magnesian gabbro and diorite dikes in the western margin of the domain, where they cross rocks of the tonalitetrondhjemite association. This stage was marked by the formation of intermediate-acid subvolcanic bodies and dikes as well as basite intrusions including the layered and differentiated Semch intrusion, the largest one in the Vodlozero domain. The stage culminated at approximately 2850 Ma in the emplacement of tonalities of the limited distribution being represented by the Shilos massif in the north of the domain and Shal'skii massif on the eastern shore of Lake Onega. The important stage in the geological history of the Vodlozero domain is the formation of the intracratonic Matkalakhta greenstone belt at approximately 2.8 Ga, which includes arenite quartzite and graywackes and polymictic conglomerates developed in the Lake Oster area in addition to volcanics. These rocks indicate a stable tectonic regime, which resulted in deep erosion of the crust. The emplacement of sanukitoids (2.73-2.74 Ga) as well as subsequent two-feldspar granites (2.68-2.70 Ga) and basite dikes (2.61-2.65 Ga) may be considered as resulting from the plume influence on the relatively stabilized sialic crust of the Baltic shield.

  11. High Tech High interns develop a mid-ocean ridge database for research and education

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

    2003-04-01

    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 (http://earthref.org/databases/SC/main.htm). 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.

  12. H11077_MB1.5M_UTM19.TIF: Color Shaded-Relief GeoTIFF Image Showing the 1.5-m Bathymetry Generated from National Oceanic and Atmospheric Administration (NOAA) Survey H11077 in Woods Hole, MA (UTM Zone 19)

    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...

  13. H11077_MB1.5M_GEO.TIF: Color Shaded-Relief GeoTIFF Image Showing the 1.5-m Bathymetry Generated from National Oceanic and Atmospheric Administration (NOAA) Survey H11077 in Woods Hole, MA (Geographic)

    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...

  14. 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)

    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. H11077_MB0.5M_GEO.TIF: Color Shaded-Relief GeoTIFF Image Showing the 0.5-m Bathymetry Generated from National Oceanic and Atmospheric Administration (NOAA) Survey H11077 in Woods Hole, MA (Geographic)

    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_MB0.5M_UTM19.TIF: Color Shaded-Relief GeoTIFF Image Showing the 0.5-m Bathymetry Generated from National Oceanic and Atmospheric Administration (NOAA) Survey H11077 in Woods Hole, MA (UTM Zone 19)

    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. 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)

    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...

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

    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. A new compilation of plate tectonics in the Indian Ocean

    Munschy, M.; Bernard, A.; Rotstein, Y.; Ravaut, P.

    2003-04-01

    A new compilation of plate tectonics in the Indian Ocean is presented. It is based on a synthesis of all magnetic anomaly interpretations and on the identifications of fracture zone in the most recent satellite gravity data. We detail the development of the Indian Ocean by 12 phases. The analysis solves all the problems of gaps and overlaps between the continents that border the Indian Ocean (at a scale of about 50-100 km) and matches well the magnetic anomalies and identified fracture zones. The initial opening of the Indian Ocean started some 180 Ma ago with the breakup between Africa and Madagascar-India-Antarctica, in a northwest-southeast direction and at 160 Ma it turned to a north-south direction. This single ridge geometry continued until 140 Ma, at which time India, Antarctica and Australia all broke from each other. This new plate configuration, with two triple junctions, lasted until 120 Ma, when spreading between Africa and Madagascar stopped. At 96 Ma, a major reorganization of plate movements occurred: spreading stopped between Antarctica and Australia while spreading direction between Antarctica and India rotated by more than 40° and right lateral shear motion began between India and Madagascar. At 84 Ma, spreading started in the Mascarene Basin in a northeast-southwest direction and continued until 63 Ma. From 77 Ma to 54 Ma, spreading between Africa and Antarctica at the Southwest Indian Ridge was oblique by more than 40°. At 63 Ma, spreading stopped in the Mascarene Basin and started along the Carlsberg and Central Indian ridges. This event can be interpreted as a ridge jump. The last large reorganization of plate motions in the Indian Ocean occurred at 44 Ma. At that time, spreading directions between Australia and Antarctica restarted, spreading direction between Antarctica and Africa, Madagascar and India and India and Antarctica, all rotated.

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

    Litvin, V M

    1984-01-01

    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...

  1. Generic Ma\\~n\\'e sets

    Contreras, Gonzalo

    2014-01-01

    We prove that $C^2$ generic hyperbolic Ma\\~n\\'e sets contain a periodic orbit. In dimesion 2, adding a result with A. Figalli and L. Rifford, we obtain Ma\\~n\\'e's Conjecture for surfaces in the $C^2$ topology.

  2. Oceanic ferromanganese deposits: Future resources and past-ocean recorders

    Banakar, V.K.; Nair, R.R.; Parthiban, G.; Pattan, J.N.

    ., Weichowski, A. and Beer, J., 1984. Be-10 dating of a manganese crust from central Pacific and implication for ocean paleocirculations. Nature, 30; 540-543. Somayajulu, B.L.K., 1967. Be-10 in manganese nodule. Science, 156; 1219-1220. Sorem, R.K. and Fewkes, R.H...., 1977. Internal characteristics. In: Marine Manganese Deposits, ed. G.R Glasby, Elsevier, 147-184. 56 V. K. BANAKAR AND OTHERS Sorem, R.K., Fewkes, R.H., McFarland, W.D., Reinhard, W.R., 1979. Physical aspects of the growth environment of manganese...

  3. Maßnahmenmanagement anhand eines Lebenszyklusmodells

    Ulrich Schmidt

    2011-01-01

    Full Text Available Wie im ersten Teil dieser Beitragsserie dargestellt, ist es in der betrieblichen Praxis von großer Bedeutung den Nutzen von Wissensmanagement aufzuzeigen. Als erfolgversprechende Herangehensweise hat sich hierbei die Betrachtung einzelner Maßnahmen des Wissensmanagements herausgestellt. Dieser Erkenntnis folgend wurde bei EnBW ein Ansatz entwickelt, der sich auf die Darstellung des Nutzens von Wissensmanagement-Maßnahmen fokussiert. Dem Ansatz liegt die Überlegung zugrunde, dass sich der Nutzen einer Maßnahme insbesondere über deren Wirkung und ihre Wirkungsdauer beschreiben lässt. Aus diesem Grund wurde ein Modell entwickelt, das es ermöglicht Maßnahmen im Zeitverlauf zu begleiten, dabei die Wirkung zu dokumentieren und somit den Erfolg einer Maßnahme zu beurteilen.

  4. Eocene magmatic processes and crustal thickening in southern Tibet: Insights from strongly fractionated ca. 43 Ma granites in the western Gangdese Batholith

    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

    2015-12-01

    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 εNd(t) (- 5.9 to - 6.0), εHf(t) (- 4.0 to - 4.5), and zircon εHf(t) (- 6.0 to + 5.8) values identical to those of Group 2 samples [εNd(t) = - 5.7 to - 6.7, εHf(t) = - 3.5 to - 2.9, and zircon εHf(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.

  5. Forward modelling of oceanic lithospheric magnetization

    Masterton, S. M.; Gubbins, D.; Müller, R. D.; Singh, K. H.

    2013-03-01

    We construct a model of remanence for the oceans, combine it with a model of induced magnetization for the whole Earth from a previous study, compute the predicted lithospheric geomagnetic field and compare the result with a model, MF7, that is based on satellite data. Remanence is computed by assigning magnetizations to the oceanic lithosphere acquired at the location and time of formation. The magnetizing field is assumed to be an axial dipole that switches polarity with the reversal time scale. The magnetization evolves with time by decay of thermal remanence and acquisition of chemical remanence. The direction of remanence is calculated by Euler rotation of the original geomagnetic field direction with respect to an absolute reference frame, significantly improving previous results which did not include realistic oceanic magnetization computed this way. Remanence only accounts for 24 per cent of the energy of the oceanic magnetization, the induced magnetization being dominant, increasing slightly to 30 per cent of the part of the magnetization responsible for generating geomagnetic anomalies and 39 per cent of the Lowes energy of the geomagnetic anomalies. This is because our model of oceanic crust and lithosphere is fairly uniform, and a uniform layer magnetized by a magnetic field of internal origin produces no external field. The largest anomalies are produced by oceanic lithosphere magnetized during the Cretaceous Normal Superchron. Away from ridges and magnetic quiet zones the prediction fails to match the MF7 values; these are also generally, but not always, somewhat smaller than the observations. This may indicate that the magnetization estimates are too small, in which case the most likely error is in the poorly-known magnetization deep in the crust or upper mantle, or it may indicate some other source such as locally underplated continental lithosphere or anomalous oceanic crust, or even small-scale core fields.

  6. The 17 Ma old Turkana beaked whale fossil: new paleoaltimetry constraints for uplift and environmental change in East Africa

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

    2015-04-01

    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.

  7. Early evolution of the crust-mantle system

    Condie, K. C.

    1985-01-01

    Nd isotopic data indicate that most Archean igneous rocks including compositions ranging from komatiite to tonalite are derived from undepleted or depleted upper mantle sources. If sampling is representative, only a few require enriched sources. A major unresolved question is the fate of the material removed from the upper mantle leaving early depleted sources as residue. One possibility is that widespread depletion of the early mantle resulted from a period of early degassing and magmatism. Rare gas isotopic data, in particular 129Xe/130Xe ratios, seem to demand that the upper mantle was extensively degassed at or before 4.4 b.y. and this led to rapid growth of the atmosphere and oceans. The lower mantle, however, was not significantly degassed during this event. It is likely that such widespread degassing and magmatism of the upper mantle transferred significant quantities of incompatible elements into the uppermost mantle or crust. Once formed, such an enriched fraction should resist recycling into the mantle and collect at or near the Earth's surface. One possibility is that it collects chiefly in a zone of partial melting, analogous to the present low-velocity zone at the base of the lithosphere.

  8. Dew formation and activity of biological crusts

    M. Veste; Heusinkveld, B.G.; Berkowicz, S.M.; Breckle, S.W.; Littmann, T.; Jacobs, A.F.G.

    2008-01-01

    Biological soil crusts are prominent in many drylands and can be found in diverse parts of the globe including the Atacama desert, Chile, the Namib desert, Namibia, the Succulent-Karoo desert, South Africa, and the Negev desert, Israel. Because precipitation can be negligible in deserts the Atacama desert being almost rain-free or restricted to infrequent rains during short rainfall seasons, atmospheric moisture in the form of dew and/or fog can be a major, regular supplier of water for c...

  9. Modelling of heat flow in Earths Crust

    ?urove Juraj B.; Maras Michal; Rybrov Mria; Kuzevi? tefan; Rybr Pavol

    1999-01-01

    The paper deals with the modelling of the heat flow in the Earths crust. The used three-dimensional model utilises the computer environment where the rock masses are modelled by the set of basic structural elements placed in the orthogonal co-ordinate system x, y, z, while the basic structural element is a cube with a chosen size. The physical notion of the diffusion is utilised for modelling the potentials flow from places with higher value of potentials to the surrounding rock masses. With...

  10. Geological cycles and a two-stage history of the Continental Crust (Robert Wilhelm Bunsen Medal Lecture)

    Hawkesworth, Chris J.; Cawood, Peter A.; Dhuime, Bruno

    2014-05-01

    The continental crust is the archive of Earth history, and the apparently cyclical nature of geological evolution is a feature of the geological record. The advent of radiometric ages has highlighted that the spatial and temporal distribution of the Earth's record of rock units and events is heterogeneous with distinctive peaks and troughs in the distribution of ages of igneous crystallization, metamorphism, continental margins and mineralization. It is argued that the temporal distribution largely reflects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly. In contrast there are other signals, such as the Sr isotope ratios of seawater, mantle temperatures, and redox conditions on the Earth, where the records are regarded as primary because they are not sensitive to the numbers of samples of different ages that have been analysed. Models based on the U-Pb, Hf and O isotope ratios of detrital zircons suggest that at least ~60-70% of the present volume of the continental crust had been generated by 3 Ga. The sedimentary record is biased by preferential sampling of relatively young material in their source terrains. The implication is that there were greater volumes of continental crust in the Archaean than might be inferred from the compositions of detrital zircons and sediments. The growth of continental crust was a continuous rather than an episodic process, but the rates of continental growth were significantly higher before 3 Ga than subsequently. The time-integrated Rb/Sr ratios, and the average SiO2 contents, indicate that new continental crust was largely mafic over the first 1.5 Ga of Earth's evolution, and that significant volumes of pre-3 Ga crust may have been associated with intraplate magmatism. Since ~3 Ga there has been an increase in Rb/Sr, SiO2, and the inferred thickness of new crust, consistent with an increase of continental input into the oceans and the onset of plate tectonics. The 60-70% of the present volume of the continental crust estimated to have been present at 3 Ga, contrasts markedly with the <10% of crust of that age apparently still preserved and it requires ongoing destruction (recycling) of early formed crust and subcontinental mantle lithosphere back into the mantle through processes such as subduction and delamination.

  11. 42 CFR 495.204 - Incentive payments to qualifying MA organizations for MA-EPs and MA-affiliated eligible hospitals.

    2010-10-01

    ... CERTIFICATION STANDARDS FOR THE ELECTRONIC HEALTH RECORD TECHNOLOGY INCENTIVE PROGRAM Requirements Specific to Medicare Advantage (MA) Organizations § 495.204 Incentive payments to qualifying MA organizations for...

  12. PiMA Survey Design and Methodology

    Mudhai, Okoth Fred; Abreu Lopes, Claudia; Mitullah, Winnie; Fraser, Alastair; Milapo, Nalukui; Mwangi, Sammy; (PI) Srinivasan, Sharath

    2015-01-01

    The PiMA Working Papers are a series of peer-reviewed working papers that present findings and insights from Centre of Governance and Human Rights? (CGHR) Politics and Interactive Media in Africa (PiMA) research project (2012-14). The project, jointly funded by the ESRC and DFID, focuses on expressions of ?public opinion? in broadcast media via new information and communication technologies (ICT) such as mobile phones in Kenya and Zambia. PiMA examines the political implications of such i...

  13. Critical Metals In Western Arctic Ocean Ferromanganese Mineral Deposits

    Hein, J. R.; Spinardi, F.; Conrad, T. A.; Conrad, J. E.; Genetti, J.

    2013-12-01

    Little exploration for minerals has occurred in the Arctic Ocean due to ice cover and the remote location. Small deposits of seafloor massive sulfides that are rich in copper and zinc occur on Gakkel Ridge, which extends from Greenland to the Laptev Sea, and on Kolbeinsey and Mohns ridges, both located between Greenland and mainland Europe. However, rocks were recently collected by dredge along the western margin of the Canada Basin as part of the U.S. Extended Continental Shelf (ECS) program north of Alaska. Sample sites include steep escarpments on the Chukchi Borderland, a newly discovered seamount informally named Healy seamount, the southern part of Alpha-Mendeleev Ridge, and several basement outcrops in Nautilus Basin. These dredge hauls yielded three types of metal-rich mineralized deposits: ferromanganese crusts, ferromanganese nodules, and hydrothermal iron and manganese deposits. Chemical analyses of 43 crust and nodule samples show high contents of many critical metals needed for high-technology, green-technology, and energy and military applications, including cobalt (to 0.3 wt.%), vanadium (to 0.12 wt.%), zirconium (to 459 grams/tonne=ppm), molybdenum (to 453 g/t), the rare-earth elements (including scandium and yttrium; yttrium to 229 g/t), lithium (to 205 g/t), tungsten (to 64 g/t), and gallium (to 26 g/t). The metal contents of these Arctic Ocean crusts and nodules are comparable to those found throughout the global ocean, however, these Arctic Ocean samples are the first that have been found to be enriched in rare metal scandium. The metal contents of these samples indicate a diagenetic component. Crusts typically form by precipitation of metal oxides solely from seawater (hydrogenetic) onto rock surfaces producing a pavement, whereas nodules form by accretion of metal oxides, from both seawater and pore waters (diagenetic), around a nucleus on the surface of soft sediment. The best evidence for this diagenetic input to the crusts is that crusts typically have low lithium contents, 1-10 g/t while diagenetic nodules can have contents up to 600 g/t; the Arctic Ocean crusts have relatively high lithium contents of up to 205 g/t, indicating that these crusts may be only the second yet discovered to acquire some elements from sediment pore waters. A potential avenue for acquisition of diagenetic metals would be via release from pore waters into the bottom waters that bathe the crusts, or alternatively by partial burial of the crusts in mud. However, the overall composition of the crusts indicates predominantly a hydrogenetic origin. Hydrothermal iron hydroxide samples from the Arctic Ocean were dated using argon isotopes, which produced a Paleozoic age. This indicates that the Chukchi Platform in the SW Arctic Ocean is a piece of continental crust. This age also indicates that hydrothermal iron and manganese deposits are not temporally related to the Neogene ferromanganese crusts and nodules. Our preliminary results suggest that additional exploration in the Arctic Ocean for mineral deposits is warranted.

  14. Non-cyanobacterial diazotrophs mediate dinitrogen fixation in biological soil crusts during early crust formation.

    Pepe-Ranney, Charles; Koechli, Chantal; Potrafka, Ruth; Andam, Cheryl; Eggleston, Erin; Garcia-Pichel, Ferran; Buckley, Daniel H

    2016-02-01

    Biological soil crusts (BSCs) are key components of ecosystem productivity in arid lands and they cover a substantial fraction of the terrestrial surface. In particular, BSC N2-fixation contributes significantly to the nitrogen (N) budget of arid land ecosystems. In mature crusts, N2-fixation is largely attributed to heterocystous cyanobacteria; however, early successional crusts possess few N2-fixing cyanobacteria and this suggests that microorganisms other than cyanobacteria mediate N2-fixation during the critical early stages of BSC development. DNA stable isotope probing with (15)N2 revealed that Clostridiaceae and Proteobacteria are the most common microorganisms that assimilate (15)N2 in early successional crusts. The Clostridiaceae identified are divergent from previously characterized isolates, though N2-fixation has previously been observed in this family. The Proteobacteria identified share >98.5% small subunit rRNA gene sequence identity with isolates from genera known to possess diazotrophs (for example, Pseudomonas, Klebsiella, Shigella and Ideonella). The low abundance of these heterotrophic diazotrophs in BSCs may explain why they have not been characterized previously. Diazotrophs have a critical role in BSC formation and characterization of these organisms represents a crucial step towards understanding how anthropogenic change will affect the formation and ecological function of BSCs in arid ecosystems. PMID:26114889

  15. Shear modulus of neutron star crust

    Baiko, D A

    2011-01-01

    Shear modulus of solid neutron star crust is calculated by thermodynamic perturbation theory taking into account ion motion. At given density the crust is modelled as a body-centered cubic Coulomb crystal of fully ionized atomic nuclei of one type with the uniform charge-compensating electron background. Classic and quantum regimes of ion motion are considered. The calculations in the classic temperature range agree well with previous Monte Carlo simulations. At these temperatures the shear modulus is given by the sum of a positive contribution due to the static lattice and a negative $\\propto T$ contribution due to the ion motion. The quantum calculations are performed for the first time. The main result is that at low temperatures the contribution to the shear modulus due to the ion motion saturates at a constant value, associated with zero-point ion vibrations. Such behavior is qualitatively similar to the zero-point ion motion contribution to the crystal energy. The quantum effects may be important for li...

  16. Crusted Demodicosis in an Immunocompetent Pediatric Patient

    Gómez-Flores, Minerva; Ocampo-Candiani, Jorge

    2014-01-01

    Demodicosis refers to the infestation by Demodex spp., a saprophytic mite of the pilosebaceous unit. Demodex proliferation can result in a number of cutaneous disorders including pustular folliculitis, pityriasis folliculorum, papulopustular, and granulomatous rosacea, among others. We report the case of a 7-year-old female presenting with pruritic grayish crusted lesions over her nose and cheeks, along with facial erythema, papules, and pustules. The father referred chronic use of topical steroids. A potassium hydroxide mount of a pustule scraping revealed several D. folliculorum mites. Oral ivermectin (200 μg/kg, single dose) plus topical permethrin 5% lotion applied for 3 consecutive nights were administered. Oral ivermectin was repeated every week and oral erythromycin plus topical metronidazole cream was added. The facial lesions greatly improved within the following 3 months. While infestation of the pilosebaceous unit by Demodex folliculorum mites is common, only few individuals present symptoms. Demodicosis can present as pruritic papules, pustules, plaques, and granulomatous facial lesions. To our knowledge, this is the first reported case of facial crusted demodicosis in an immunocompetent child. The development of symptoms in this patient could be secondary to local immunosuppression caused by the chronic use of topical steroids. PMID:25371830

  17. Is Ishtar Terra a thickened basaltic crust?

    Arkani-Hamed, Jafar

    1992-01-01

    The mountain belts of Ishtar Terra and the surrounding tesserae are interpreted as compressional regions. The gravity and surface topography of western Ishtar Terra suggest a thick crust of 60-110 km that results from crustal thickening through tectonic processes. Underthrusting was proposed for the regions along Danu Montes and Itzpapalotl Tessera. Crustal thickening was suggested for the entire Ishtar Terra. In this study, three lithospheric models with total thicknesses of 40.75 and 120 km and initial crustal thicknesses of 3.9 and 18 km are examined. These models could be produced by partial melting and chemical differentiation in the upper mantle of a colder, an Earth-like, and a hotter Venus having temperatures of respectively 1300 C, 1400 C, and 1500 C at the base of their thermal boundary layers associated with mantle convection. The effects of basalt-granulite-eclogite transformation (BGET) on the surface topography of a thickening basaltic crust is investigated adopting the experimental phase diagram and density variations through the phase transformation.

  18. Paleomagnetism continents and oceans

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

    1999-01-01

    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...

  19. Titanite evidence for Triassic thickened lower crust along southeastern margin of North China Craton

    Guo, Jing-Liang; Gao, Shan; Wu, Yuan-Bao; Hu, Zhao-Chu; Xu, Wen-Liang; Zong, Ke-Qing; Liu, Yong-Sheng; Yuan, Hong-Lin

    2014-10-01

    Titanite U-Pb isotopic and major and trace element compositions of one mafic garnet granulite from a rare suite of lower crustal xenoliths (e.g., eclogite, garnet pyroxenite, and mafic garnet granulite) hosted in Early Cretaceous dioritic porphyries in the Xu-Huai area along the southeastern margin of the North China Craton (NCC) were analyzed by laser ablation ICP-MS. Titanite occurs as granular grains or coronary rims on rutile. The coronary titanite is clearly a secondary product of rutile decomposition. The granular titanite exhibits zonation in U-Pb age and chemical composition. Petrographic and geochemical evidence suggests that the zonation was formed by thermal diffusion and later fluid-assisted recrystallization. Occurrences of granular titanite between garnet grains point to a pressure of > 10 kbar, while inclusions of rutile inside granular titanite rims imply that the pressure might have reached 15 kbar. Granular titanite cores give U-Pb ages of 237-241 Ma and Zr-temperatures of 794-831 C at 10 kbar and 850-892 C at 15 kbar, indicating high-pressure granulite-facies metamorphism. Together with previous P-T estimates of coeval eclogite-facies xenoliths, a geotherm of above 60 mW m- 2 is implied. The geotherm plots below the temperature field of amphibole dehydration melting, consistent with presence of abundant amphibole. This geotherm is similar to that of the Kohistan arc, which has preserved a 12-km-thick dense lower crust, but significantly cooler than the geotherm of the Talkeetna arc, where most of the dense lower crust has been foundered. Our results provide new evidence for Triassic thickened dense lower crust along the southeastern margin of the NCC. By comparison with the Kohistan and Talkeetna arc crusts, we suggest that this dense lower crust was not hot enough to be foundered in the Triassic. Foundering must have occurred in the Jurassic-Cretaceous in order to explain the present-day seismic velocity structure characterized by a sharp Moho, overall slow velocities in the lower crust, and a thin crustal thickness in the Xu-Huai area and other parts of the eastern NCC. We suggest that the Jurassic-Cretaceous foundering was related to the Pacific subduction. On one hand, the Jurassic subduction may have further thickened the southeastern margin of the NCC prior to Cretaceous extension, leading to greater instability of the lower crust. On the other hand, the subduction-related magma provided heat and water that weakened the lower crust, resulting in the final foundering. The large contrast in mineralogy between the Xu-Huai eclogite-facies xenoliths and nearby Nshan garnet-free granulite xenoliths entrained by Quaternary basalts indicates > 20 km removal of the lower crust along the southeastern margin of the NCC.

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

    Sandre, Matthew; Ralevski, Filip; Rau, Neil

    2015-01-01

    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...

  1. Salatoimikud : ma tahan uskuda / Mart Rummo

    Rummo, Mart

    2008-01-01

    USA sarjale "The X-Files" phinev teine jrjefilm "Salatoimikud: Ma tahan uskuda" ("The X-Files: I Want to Believe") : reissr Chris Carter : peaosades David Duchovny, Gillian Anderson : Ameerika hendriigid - Kanada 2008

  2. 78 FR 2708 - Massachusetts Disaster # MA-00050

    2013-01-14

    ... From the Federal Register Online via the Government Publishing Office SMALL BUSINESS ADMINISTRATION Massachusetts Disaster MA-00050 AGENCY: U.S. Small Business Administration. ACTION: Notice... completed loan applications to: U.S. Small Business Administration, Processing and Disbursement...

  3. Diffusive transfer of oxygen from seamount basaltic crust into overlying sediments: An example from the Clarion-Clipperton Fracture Zone

    Mewes, K.; Mogollón, J. M.; Picard, A.; Rühlemann, C.; Eisenhauer, A.; Kuhn, T.; Ziebis, W.; Kasten, S.

    2016-01-01

    The Clarion-Clipperton Fracture Zone (CCFZ) in the Pacific Ocean is characterized by organic carbon-starved sediments and meter-scale oxygen penetration into the sediment. Furthermore, numerous seamounts occur throughout its deep-sea plain, which may serve as conduits for low-temperature hydrothermal seawater circulation through the oceanic crust. Recent studies in deep-sea environments of the Pacific and Atlantic Oceans have suggested and presented evidence of dissolved constituent exchange between the seawater flowing in the basaltic crust and the pore water of the overlying sediments. Through high-resolution pore-water oxygen and nutrient measurements, we examined fluxes and geochemical interactions between the seamount basaltic basement and pore waters of the overlying sediments at three sites located on a radial transect from the foot of Teddy Bare, a small seamount in the CCFZ. At three sites, located 1000, 700 and 400 m away from the foot of the seamount, we found that oxygen concentrations initially decrease with sediment depth but start to increase at depths of 3 and 7 m toward the basaltic basement. Nitrate (NO3-) concentrations mirror the oxygen concentration profiles, as they increase with sediment depth but decrease towards the basement. These profiles suggest an upward diffusion of oxygen from seawater circulating within the seamount crust into the overlying basal sediments and a downward diffusion of NO32- from sediment pore water into the basaltic crust. At one site, we determined that the 87Sr/86Sr ratios of the bottom water and of the deep sediment near the basaltic crust are similar, further supporting diffusive exchange between basaltic crust fluids and sediment pore water. Transport-reaction modeling performed at two of the study sites revealed that (1) the diffusive flux of oxygen from the basaltic basement outpaces the oxygen consumption through organic matter oxidation and nitrification in the basal sediments and (2) the nutrient exchange between the sediment and the underlying basaltic crust occurs at orders-of-magnitude lower rates than between the upper sediment and the overlying bottom water. These results further show that the diffusion of oxygen from the seamount basaltic basement into the overlying pore waters affects the preservation of organic compounds and helps to maintain a completely oxygenated sedimentary column at all 3 sites near the seamount.

  4. Zircon U-Pb and biotite Rb-Sr dating of the Wami River granulites, Eastern Granulites, Tanzania: evidence for approximately 715 Ma old granulite-facies metamorphism and final Pan-African cooling approximately 475 Ma ago

    A U-Pb investigation of suites of zircons from five granulites in the Wami River area, Tanzania, yields a 17-points discordia with upper and lower intercepts at 714-49+36 Ma and 538-35+49 Ma, respectively. These systematics are interpreted to indicate an age of approximately 715 Ma (Pan African) for the M1 granulite-facies metamorphism, whereas the lower intercept is related to a stage in the uplift and cooling following the M2 amphibolite-facies retrogradation (elsewhere dated at approximately 650 Ma). Three of the granulites contain minor amounts of an inherited, > 1600 Ma old zircon component, probably derived from the igneous precursors of the granulites. A suite of zircons from the adjacent biotite gneisses may signal a provenance age of approximately 2600 Ma (Tanzania craton?), but the U-Pb sytematics do not clearly reflect the amphibolite-facies metamorphism (correlated with the M2 partial retrogradation of the granulites) that transformed the sedimentary sequences into gneisses (any petrographic record of a possible older metamorphic influence being absent). Biotite/whole-rock pairs from the same samples yield Rb-Sr ages between about 470 and 485 Ma for the granulites and about 458 Ma for the gneiss. They are interpreted as 'cooling ages' and set an age between about 485 and 460 Ma to the final cooling of the crust through the closure temperature of biotite to Rb-Sr. The subsequent granulite-facies and amphibolite-facies events and their chronology are fitted in the continent-continent collision model for the evolution of the Mozambique belt advocated by the first author. (Auth.)

  5. Sensitivity of climate and atmospheric CO2 to deep-ocean and shallow-ocean carbonate burial

    Volk, Tyler

    1989-01-01

    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.

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

    Kamal K Sharma

    2004-12-01

    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.

  7. Nitrogen fixation in biological soil crusts from southeast Utah, USA

    Belnap, J.

    2002-01-01

    Biological soil crusts can be the dominant source of N for arid land ecosystems. We measured potential N fixation rates biweekly for 2 years, using three types of soil crusts: (1) crusts whose directly counted cells were >98% Microcoleus vaginatus (light crusts); (2) crusts dominated by M. vaginatus, but with 20% or more of the directly counted cells represented by Nostoc commune and Scytonema myochrous (dark crusts); and (3) the soil lichen Collema sp. At all observation times, Collema had higher nitrogenase activity (NA) than dark crusts, which had higher NA than light crusts, indicating that species composition is critical when estimating N inputs. In addition, all three types of crusts generally responded in a similar fashion to climate conditions. Without precipitation within a week of collection, no NA was recorded, regardless of other conditions being favorable. Low (26??C) temperatures precluded NA, even if soils were moist. If rain or snow melt had occurred 3 or less days before collection, NA levels were highly correlated with daily average temperatures of the previous 3 days (r2=0.93 for Collema crusts; r2=0.86 for dark crusts and r2=0.83 for light crusts) for temperatures between 1??C and 26??C. If a precipitation event followed a long dry period, NA levels were lower than if collection followed a time when soils were wet for extended periods (e.g., winter). Using a combination of data from a recording weather datalogger, time-domain reflectometry, manual dry-down curves, and N fixation rates at different temperatures, annual N input from the different crust types was estimated. Annual N input from dark crusts found at relatively undisturbed sites was estimated at 9 kg ha-1 year-1. With 20% cover of the N-fixing soil lichen Collema, inputs are estimated at 13 kg ha-1 year-1. N input from light crusts, generally indicating soil surface disturbance, was estimated at 1.4 kg ha-1 year-1. The rates in light crusts are expected to be highly variable, as disturbance history will determine cyanobacterial biomass and therefore N fixation rates.

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

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

    1995-09-01

    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.

  9. Computation and analysis for maximal water press of condensator's crust

    As to the failure of the condensator's crust in the system of cold circulation in a enterprise, mechanical evaluations of the maximal water press of the condensator's crust were conducted via the simplified theoretical model an the finite element numerical computation, according to the relationship of the corresponding unisonous deformation between the long fixed bolts on the condensator's crust and themselves. the results show that the structural design of the condensator's crust and the welding quality of the weld lead to these hidden trouble. (authors)

  10. Lunar anorthosite - Identification and distribution of remnants of the primordial crust

    Peterson, C. A.; Hawke, B. R.; Lucey, P. G.; Taylor, G. J.; Blewett, D. T.; Spudis, P. D.

    1997-03-01

    Evidence strongly suggests that Earth's moon was once covered by a magma ocean which differentiated as it cooled. In the later stages of crystallization, plagioclase feldspar formed a cumulate flotation crust composed primarily of anorthosite many kilometers thick. The concurrent and subsequent heavy bombardment experienced by the moon has disrupted or obscured much of this original crust, but portions of it appear to have remained intact, especially on the northern lunar farside and globally at depth. While some other mechanisms for the production of anorthosite, such as the differentiation of plutons, have been suggested, the great majority of anorthosite outcrops present at the surface of the moon today may be portions of the original crust. Several spectral techniques are available for remotely identifying anorthosite on the moon. They utilize multispectral data sets obtained from Earth-based telescopes or from spacecraft orbiting or flying by the moon. While the techniques are related, they differ in their strengths and weaknesses. By comparing and combining the results from the various techniques, we can increase our confidence in our understanding of the global distribution of anorthosite.

  11. Ocean technology

    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 ...

  12. Ocean Acidification

    Iglesias-Rodriguez, Maria Debora

    The oceans play a central role in the maintenance of life on Earth. Oceans provide extensive ecosystems for marine animals and plants covering two-thirds of the Earth's surface, are essential sources of food, economic activity, and biodiversity, and are central to the global biogeochemical cycles. The oceans are the largest reservoir of carbon in the Planet, and absorb approximately one-third of the carbon emissions that are released to the Earth's atmosphere as a result of human activities. Since the beginning of industrialization, humans have been responsible for the increase in one greenhouse gas, carbon dioxide (CO2), from approximately 280 parts per million (ppm) at the end of the nineteenth century to the current levels of 390ppm. As well as affecting the surface ocean pH, and the organisms living at the ocean surface, these increases in CO2 are causing global mean surface temperatures to rise.

  13. Global maps of the step-wise topography corrected and crustal components stripped geoids using the CRUST 2.0 model

    Tenzer, Robert; Hamayun; Vajda, Peter

    2009-01-01

    We compile global maps of the step-wise topography corrected and crustal components stripped geoids based on the geopotential model EGM'08 complete to spherical harmonic degree 180 and the CRUST 2.0 global crustal model. The spectral resolution complete to degree 180 is used to compute the primary indirect bathymetric stripping and topographic effects on the geoid, while degree 90 for the primary indirect ice stripping effect. The primary indirect stripping effects of the soft and hard sediments, and the upper, middle and lower consolidated crust components are forward modeled in spatial form using the 2 2 arc-deg discrete data of the CRUST 2.0 model. The ocean, ice, sediment and consolidated crust density contrasts are defined relative to the adopted reference crustal density of 2670 kg/m3. Finally we compute and apply the primary indirect stripping effect of the density contrast (relative to the mantle) of the reference crust. The constant value of -520 kg/m3 is adopted for this density contrast relative to the mantle. All data are evaluated on a 1 1 arc-deg geographical grid. The complete crust-stripped geoidal undulations, globally having a range of approximately 1.5 km, contain the gravitational signal coming from the global mantle lithosphere (upper mantle) morphology and density composition, and from the sub-lithospheric density heterogeneities. Large errors in the complete crust-stripped geoid are expected due to uncertainties of the CRUST 2.0 model, i.e., due to deviations of the CRUST 2.0 model density from the real earth's crustal density and due to the Moho-boundary uncertainties.

  14. Lunar Magma Ocean Crystallization: Constraints from Fractional Crystallization Experiments

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

    2015-01-01

    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

  15. The seismic Moho structure of Shatsky Rise oceanic plateau, northwest Pacific Ocean

    Zhang, Jinchang; Sager, William W.; Korenaga, Jun

    2016-05-01

    Oceanic plateaus are large igneous provinces formed by extraordinary eruptions that create thick oceanic crust, whose structure is poorly known owing to the lack of deep-penetration seismic data. Multichannel seismic (MCS) reflection and wide-angle refraction data allow us to show Moho structure beneath a large part of the Shatsky Rise oceanic plateau in the northwest Pacific Ocean. Moho reflectors in the two data sets can be connected to trace the interface from the adjacent abyssal plain across much of the interior. The reflectors display varied character in continuity, shape, and amplitude, similar to characteristics reported in other locations. Beneath normal crust, the Moho is observed at ˜13 km depth (˜7 km below the seafloor) in MCS data and disappears at ˜20 km depth (˜17 km below the seafloor) beneath the high plateau. Moho at the distal flanks dips downward towards the center with slopes of ˜0.5°-1°, increasing to 3°-5° at the middle flanks. Seismic Moho topography is consistent with Airy isostasy, confirming this widely-applied assumption. Data from this study show that crustal thickness between the massifs in the interior of the plateau is nearly twice normal crustal thickness, despite the fact that this crust records apparently normal seafloor spreading magnetic lineations. The Moho model allows improved estimates of plateau area (5.33 ×105 km2) and volume (6.90 ×106 km3), the latter assuming that the entire crust was formed by Shatsky Rise volcanism because the massifs formed at spreading ridges. This study is unique in showing Moho depth and structure over an extraordinarily large area beneath an oceanic plateau, giving insight to plateau structure and formation.

  16. Exploring the plutonic crust at a fast-spreading ridge:new drilling at Hess Deep

    Gillis, Kathryn M. [Univ. of Victoria, BC (Canada). School of Earth and Ocean Sciences; Snow, Jonathan E. [Univ. of Houston, Houston, TX (United States). Earth & Atmospheric Sciences; Klaus, Adam [Texas A & M Univ., College Station, TX (United States). Integrated Ocean Drilling Program (IODP). United States Implementing Organization.; Guerin, Gilles [Lamont-Doherty Earth Observatory of Columbia Univ., Palisades, NY (United States). Borehole Research Group; Abe, Natsue [Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka (Japan). Inst. for Research on Earth Evolution (IFREE); Akizawa, Norikatsu [Kanazawa Univ. (Japan). Dept. of Earth Sciences; Ceuleneer, Georges [Univ. Paul Sabatier, Toulouse (France). Observatoire Midi-Pyrenees (UMS 831), CNRS; Cheadle, Michael J. [Univ. of Wyoming, Laramie, WY (United States). Dept. of Geology and Geophysics; Adriao, Alden de Brito [Federal Univ. of Rio Grande do Sul, Porto Alegre (Brazil). Geology Inst. (IGEO); Faak, Kathrin [Ruhr Univ., Bochum (Germany). Geological Inst.; Falloon, Trevor J. [Univ. of Tasmania, Hobart, TAS (Australia). Inst. for Marine and Antarctic Studies; Friedman, Sarah A. [Southern Illinois Univ., Carbondale, IL (United States). Dept. of Geology; Godard, Marguerite M. [Univ. Montpellier II (France). Geosciences Montpellier-UMR 5243; Harigane, Yumiko [National Inst. of Advanced Industrial Science and Technology (AIST), Tsukuba (Japan). Marine Geology Dept.; Horst, Andrew J. [Syracuse Univ., NY (United States). Dept. of Earth Science; Hoshide, Takashi [Tohoku Univ., Sendai (Japan). Graduate School of Science; Ildefonse, Benoit [Univ. Montpellier II (France). Lab. de Tectonophysique; Jean, Marlon M. [Northern Illinois Univ., DeKalb, IL (United States). Dept. of Geology and Environmental Geosciences; John, Barbara E. [Univ. of Wyoming, Laramie, WY (United States). Dept. of Geology and Geophysics; Koepke, Juergen H. [Univ. of Hannover (Germany). Inst. of Mineralogy; Machi, Sumiaki [Kanazawa Univ. (Japan). Dept. of Earth Sciences; Maeda, Jinichiro [Hokkaido Univ., Sapporo (Japan). Dept. of Natural History Sciences; Marks, Naomi E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Chemistry and Material Sciences Dept.; McCaig, Andrew M. [Univ. of Leeds (United Kingdom). School of Earth and Environment; Meyer, Romain [Univ. of Bergen (Norway). Dept. of Earth Science and Centre for Geobiology; Morris, Antony [Univ. of Plymouth (United Kingdom). School of Earth, Ocean & Environmental Sciences; Nozaka, Toshio [Okayama Univ. (Japan). Dept. of Earth Sciences; Python, Marie [Hokkaido Univ., Sapporo (Japan). Dept. of Earth and Planetary Sciences; Saha, Abhishek [Indian Inst. of Science (IISC), Bangalore (India). Centre for Earth Sciences; Wintsch, Robert P. [Indiana Univ., Bloomington, IN (United States). Dept. of Geological Sciences

    2013-02-28

    Integrated Ocean Drilling Program (IODP) Hess Deep Expedition 345 was designed to sample lower crustal primitive gabbroic rocks that formed at the fast-spreading East Pacific Rise (EPR) in order to test models of magmatic accretion and the intensity of hydrothermal cooling at depth. The Hess Deep Rift was selected to exploit tectonic exposures of young EPR plutonic crust, building upon results from ODP Leg 147 as well as more recent submersible, remotely operated vehicle, and near-bottom surveys. The primary goal was to acquire the observations required to test end-member crustal accretion models that were in large part based on relationships from ophiolites, in combination with mid-ocean ridge geophysical studies. This goal was achieved with the recovery of primitive layered olivine gabbros and troctolites with many unexpected mineralogical and textural relationships, such as the abundance of orthopyroxene and the preservation of delicate skeletal olivine textures.

  17. Experimental Fractional Crystallization of the Lunar Magma Ocean

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

    2012-01-01

    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].

  18. Breaking stress of neutron star crust

    Chugunov, A I

    2010-01-01

    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.

  19. Shear viscosity in magnetized neutron star crust

    Ofengeim, D. D.; Yakovlev, D. G.

    2015-12-01

    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.

  20. Shear viscosity in magnetized neutron star crust

    Ofengeim, D D

    2015-01-01

    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.

  1. Crusting susceptibility in some allic Colombian soils

    Many lab methods were used: dry and water soil aggregates stability, instability index and erosion index and their results were related with soil characteristics like texture, Fe and Al oxides and organic matter. Soil samples collected within 0-2.5 and 2.5-5 cm of the soil surface came from terrains with many kinds of both forest and savanna intervened systems. Those results were analyzed like a completely randomized designed. It was found that significative changes in oxides content could increase soil-crusting susceptibility unless soil humus was up to was up to 4%. In this sense, pastures or its rotation with rice and leguminous offer a best alternative for intervening these natural systems. Intensive land husbandry or monocultures with low stubble soil incorporation caused an increase in physical instability at the top of soil. Dry soil stability test and instability index were most adequate for these soils

  2. Anti Ma2-associated myeloradiculopathy: expanding the phenotype of anti-Ma2 associated paraneoplastic syndromes

    Murphy, Sinead M; Khan, Usman,; Alifrangis, Constantine; Hazell, Steven; Hrouda, David; Blake, Julian; Ball, Joanna; Gabriel, Carolyn; Markarian, Pierre; Rees, Jeremy; Karim, Abid; Seckl, Michael J.; Lunn, Michael P.; Reilly, Mary M

    2011-01-01

    Anti-Ma2 associated paraneoplastic syndrome usually presents as limbic encephalitis in association with testicular tumours.1, 2 Only four patients have been reported with involvement outside the CNS, two of whom also had limbic or brainstem encephalitis.2, 3 We report a man with anti- Ma2 associated myeloradiculopathy and previous testicular cancer whose neurological syndrome stabilised and anti-Ma2 titres fell following orchidectomy of a microscopically normal testis.

  3. Geochronology and geochemistry of middle Permian-Middle Triassic intrusive rocks from central-eastern Jilin Province, NE China: Constraints on the tectonic evolution of the eastern segment of the Paleo-Asian Ocean

    Wang, Zi-Jin; Xu, Wen-Liang; Pei, Fu-Ping; Wang, Zhi-Wei; Li, Yu; Cao, Hua-Hua

    2015-12-01

    To constrain the Permian-Early Mesozoic tectonic evolution of the eastern segment of the Paleo-Asian Ocean, we conducted zircon U-Pb dating and whole-rock geochemical analyses on six middle Permian-Middle Triassic intrusive plutons in central-eastern Jilin Province, NE China. Zircons from the six plutons display distinct oscillatory zoning and striped absorption in cathodoluminescence (CL) images, and Th/U ratios of 0.11-1.41, indicating a magmatic origin. Zircon U-Pb dating indicates that the intrusive rocks formed in the middle Permian (ca. 260 Ma) to Middle Triassic (ca. 245 Ma). In central-eastern Jilin Province, the middle Permian and Middle Triassic plutons are composed mainly of strongly deformed monzogranites with affinities to adakitic rocks, which are formed from partial melting of thickened mafic lower crust. In contrast, the late Permian-the Early Triassic plutons in central-eastern Jilin Province consist of a bimodal association (including gabbros and granitoids) and deformed monzonites, which typically form in extensional settings. These observations, along with the results of previous studies on early-middle Permian granitoids in western Jilin Province, indicate that the eastern segment of the Paleo-Asian Ocean underwent the initial closure in central-western Jilin Province during the middle Permian and the final closure in eastern Jilin Province in the Middle Triassic.

  4. Unique Thermophiles Supported by the Ocean Crustal Fluids Exiting From a Borehole in the Eastern Flank of Juan de Fuca Ridge.

    Nakagawa, S.; Inagaki, F.; Suzuki, Y.; Takai, K.; Horikoshi, K.

    2005-12-01

    Very little is known about the potential of ocean crustal fluids on ridge flanks to sustain microbial ecosystem. An unprecedented chance to investigate the occurrence of microbes within the crustal fluids is given by a borehole observatory, CORK (Circulation Obviation Retrofit Kit). The CORK consists of two parts: instruments installed in the sealed part of the cased borehole drilled by the Ocean Drilling Program (ODP), and a data logger and fluids sampling port sitting on the seafloor. Recently, a study using the CORK suggested the presence of unique microorganisms in ~64 deg C of crustal fluids emanated from a 295-meter-deep borehole in the eastern flank of Juan de Fuca Ridge (35 Ma crust) (Cowen et al., 2003, Science, 299, 120-123). Most of the 16S rRNA gene detected in the fluids related to sulfate-reducing genera (Desulfotomaculum, Ammonifex, and Desulfonatronovibrio), implying that fluids circulating within aging ocean crust potentially support microbial sulfate-reduction. When we recovered the CORK during the Juan de Fuca cruise of Integrated Ocean Drilling Program (IODP), sulfide deposits attached to the CORK body was found. The microbial community in the sulfide deposits inferred by clone sequencing of environmental 16S rRNA genes was distinct from those hitherto reported in other microbial habitats including natural deep-sea vents on ridge crests and subduction zones, but similar in part with that reported in the fluids emanated from the same CORK. Most frequently retrieved clones of bacterial and archaeal 16S rRNA gene were related to Ammonifex and Methanococcales, respectively. Semi-quantitative cultivation experiments revealed that over 103 cells per cm3 of the sulfide deposits were culturable. Surprisingly, none of the microbes widely distributing in natural deep-sea hydrothermal environments, i.e. Thermococcales, Aquificales, and epsilon-Proteobacteria, could be detected or cultured. Culturable microbial community consisted mainly of Methanothermococcus sp., members of the hydrogenotrophic and thermophilic methanogen, and which also included diverse thermophilic fermenters and thermophilic sulfate reducers belonging to the previously uncultivated phylogroups. Detection of dissimilatory sulfite reductase (dsrAB) genes, together with the SEM-EDX analysis, confirmed the occurrence of microbial sulfate-reduction. Stable carbon isotopic analysis indicated the microbial community mainly depended on photosynthesis-derived organic matter. Our study demonstrated that the occurrence of diverse, unique, and active thermophiles supported by fluids emanated from the deep basaltic crust, which is probably driven by dissolved nutrients in the hydrothermal fluids.

  5. Recrystallization temperatures in mechanically alloyed oxide-dispersion-strengthened MA956 and MA957 steels

    Chou, T.S. [University of Cambridge, Department of Materials Science and Metallurgy, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); Bhadeshia, H.K.D.H. [University of Cambridge, Department of Materials Science and Metallurgy, Pembroke Street, Cambridge CB2 3QZ (United Kingdom)

    1994-12-20

    Previous work has demonstrated that the mechanically alloyed oxide-dispersion-strengthened steels MA956 and MA957 have significantly different crystallographic textures prior to recrystallization and that their subsequent recrystallization behaviours are also not similar. New experiments confirm that the differences in recrystallization behaviour can indeed be attributed to their initial difference in crystallographic texture. The crystallographic texture of MA957 prior to recrystallization has been manipulated so as to make it similar to that of MA956, and the two alloys have been demonstrated to behave similarly during subsequent recrystallization heat treatments. ((orig.))

  6. Geophysics of an Oceanic Ice Shell on Snowball Earth

    Gaidos, E. J.

    2000-01-01

    Kirschvink proposed Precambrian low-latitude glaciation could result in an albedo-driven catastrophic runaway to a "Snowball Earth" state in which pack ice up to 1 km thick covered the world ocean. The geophysical state of an ice crust on a Snowball Earth is examined.

  7. Petrogenesis of silicic magmatism related to the ˜ 2.44 Ga rifting of Archean crust in Koillismaa, eastern Finland

    Lauri, L. S.; Rämö, O. T.; Huhma, H.; Mänttäri, I.; Räsänen, J.

    2006-01-01

    Early Paleoproterozoic extension in the Archean craton of the Fennoscandian shield led to the emplacement of several 2.44 Ga layered gabbroic intrusive complexes in northern Finland and adjacent Russia. Closely associated with them are felsic rocks of similar age: (1) the Sirniö Group volcanic rocks on top of the Koillismaa layered complex; (2) a quartz alkali feldspar syenite at Kynsijärvi near the Koillismaa complex; and (3) an aluminous A-type granite at Nuorunen near the Oulanka layered complex. In the Koillismaa area, the ruptured Archean crust consists of ortho- and paragneisses that were intruded and migmatized by somewhat younger granites. U-Pb zircon data indicate that the gneisses are at least ˜2.8 Ga old and that the granites were crystallized at ˜2.7 Ga. Both rock types show a common monazite age of 2695 Ma that registers the peak of granulite facies metamorphism and, possibly, the intrusion of the granites. The local Neoarchean crust has ɛNd(at 2440 Ma) values between - 5 and - 8.5. The mafic rocks of the Koillismaa complex show initial ɛNd(at 2440 Ma) values around - 1.5 and those of the Oulanka complex range from - 2.1 to 0. The ɛNd value (- 4.8) and TDM model age (2.9-3.0 Ga) of the Kynsijärvi quartz alkali feldspar syenite are within the limits of the evolution path of the local Archean crust. The corresponding values for the Nuorunen granite are - 2.0 and 2.76 Ga and are thus closer to those of the mafic rocks. The volcanic rocks of the Sirniö Group show more scatter with initial ɛNd(at 2440 Ma) values of - 1.1 to - 5.3; the lowest ɛNd values probably reflect later disturbance-magmatic values cluster around - 2. Major and trace element modeling shows that fractional crystallization of the Koillismaa complex parental magma or partial melting of the Archean crust cannot account for the ˜ 2.44 Ga silicic rocks of Koillismaa. The geochemical and Nd isotope characteristics of the volcanic rocks and the Kynsijärvi quartz alkali feldspar syenite are best explained by a combined assimilation-fractional crystallization model involving a contaminated komatiitic parental magma and intermediate-mafic lower crustal assimilant. Differences in the initial Nd isotope composition of the 2.44 Ga rocks reflect varying source components and evolutionary history for the Archean lithosphere in eastern Fennoscandia.

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

    Christopher J. MacLeod

    2006-09-01

    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.

  9. A Continuous History of Plume-Influenced Rifting in the North Atlantic Ocean

    Parnell-Turner, Ross; White, Nicky; Henstock, Tim; Murton, Bramley; Maclennan, John; Jones, Stephen

    2015-04-01

    Evolution of the North Atlantic Ocean has been dominated the Iceland mantle plume. Here we present an unbroken record of variable mantle plume activity stretching back 55 Ma, through analysis of regional seismic reflection images. Residual depth anomalies of oceanic lithosphere, long wavelength gravity anomalies and seismic tomographic models show that this convective upwelling reaches from Baffin Bay to Western Norway, and from offshore Newfoundland to Spitzbergen. At fringing passive margins, there is strong evidence for present-day dynamic support of the crust (e.g. Scotland, Western Norway). The Iceland plume is bisected by a mid-oceanic ridge, which provides a record of the temporal evolution of the plume. Transient behavior of the plume is indirectly recorded within the fabric of oceanic floor south of Iceland. We exploit regional seismic reflection profiles that traverse the oceanic basin between northwest Europe and Greenland. A diachronous pattern of V-shaped ridges is imaged beneath a thickening blanket of sediment, revealing a complete record of transient periodicity that can be traced continuously. This periodicity increases from ~3 to ~8 Myr with clear evidence for minor, but systematic, asymmetric crustal accretion. V-shaped ridges grow with time and reflect small (e.g. 5-30C) changes in mantle temperature, consistent with quasi-periodic generation of hot solitary waves triggered by growth of thermal boundary layer instabilities within the mantle. Our continuous record of convective activity suggests that the otherwise uniform thermal subsidence of sedimentary basins, which fringe the North Atlantic Ocean, has been periodically interrupted by transient uplift events. These elevation changes can explain a suite of diverse observations from the geologic record. Regional Paleogene erosion surfaces in the Faroe-Shetland Basin, the punctuated deposition of contourite drifts, and the history of denudation on the UK continental shelf can all be explained by transient mantle plume behaviour. These manifestations of convective activity should lead to improved insights into the fluid dynamics of the mantle, with implications for the subsidence history of sedimentary elsewhere.

  10. Persistent crust-core spin lag in neutron stars

    Glampedakis, Kostas

    2015-01-01

    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.

  11. New Zealand Maritime Glaciation: Millennial-Scale Southern Climate Change Since 3.9 Ma

    Carter, Robert M.; Gammon, Paul

    2004-06-01

    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.

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

    Robert, Tenzer; Mohammad, Bagherbandi.

    2013-06-01

    Full Text Available El contraste de densidad de la discontinuidad de Mohorovicic (Moho) debajo de la Antrtida fue estimado con base en la solucin del problema isosttico Vening Meinesz-Moritz y a partir de datos obtenidos con el modelo ssmico de la corteza global (CRUST2.0). La solucin se encontr a travs de un aj [...] uste al mtodo de mnimos cuadrados por el mtodo de elementos. El modelo geopotencial global (GOCO02S), el modelo topogrfico/batimtrico (DTM2006.0), los datos de espesor del hielo para la Antrtida (reunidos por el proyecto BEDMAP) y el modelo ssmico de corteza global (CRUST2.0) fueron utilizados para calcular las anomalas gravitatorias isostticas. Ya que los datos de CRUST2.0 para las estructuras de la corteza en la Antrtida no son exactos (debido a la falta de informacin ssmica para esta parte del planeta), el contraste de densidad de la Discontinuidad de Mohorovicic fue determinado a partir de un modelo de corteza homogneo que tiene una densidad constante de 2,670 kg/m. Los valores estimados del contraste de densidad de la Moho se encontraron entre 160 y 682kg/m. La distribucin espacial del contraste de densidad de la Moho exhibe mayores rasgos en la configuracin de la plancha tectnica de la Antrtida continental y su alrededor ocenico. El valor mximo encontrado excede los 500 kg/m y se ubica en la parte Este continental, con extensin en las Montaas Transantrticas. El contraste de densidad de la Moho (zona de transicin entre la corteza y el manto terrestre) en el Oeste de la Antrtida oscil entre 400-500 kg/m, excepto para la mxima local de ? 550 kg/m, en el centro de la Pennsula Antrtida. 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/m constant density. Estimated values of Moho density contrast were between 160 and 682 kg/m. The spatial distribution of Moho density contrast resembled major features of the Antarctics continental and surrounding oceanic tectonic plate configuration; maxima exceeding 500 kg/m 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/m, except for local maxima up to ? 550 kg/m in the central Antarctic Peninsula.

  13. Ocean Color

    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...

  14. Open Oceans

    Mikuláš, Radek

    Vol. 1. EOLSS Publishers, 2002, s. - Institutional research plan: CEZ:AV0Z3013912 Keywords : environment * ocean * paleogeography Subject RIV: DB - Geology ; Mineralogy http://www.eols.net/eolss/M.asp

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

    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)

  16. The world turns over: Hadean-Archean crust-mantle evolution

    Griffin, W. L.; Belousova, E. A.; O'Neill, C.; O'Reilly, Suzanne Y.; Malkovets, V.; Pearson, N. J.; Spetsius, S.; Wilde, S. A.

    2014-02-01

    We integrate an updated worldwide compilation of U/Pb, Hf-isotope and trace-element data on zircon, and Re-Os model ages on sulfides and alloys in mantle-derived rocks and xenocrysts, to examine patterns of crustal evolution and crust-mantle interaction from 4.5 Ga to 2.4 Ga ago. The data suggest that during the period from 4.5 Ga to ca 3.4 Ga, Earth's crust was essentially stagnant and dominantly mafic in composition. Zircon crystallized mainly from intermediate melts, probably generated both by magmatic differentiation and by impact melting. This quiescent state was broken by pulses of juvenile magmatic activity at ca 4.2 Ga, 3.8 Ga and 3.3-3.4 Ga, which may represent mantle overturns or plume episodes. Between these pulses, there is evidence of reworking and resetting of U-Pb ages (by impact?) but no further generation of new juvenile crust. There is no evidence of plate-tectonic activity, as described for the Phanerozoic Earth, before ca 3.4 Ga, and previous modelling studies indicate that the early Earth may have been characterised by an episodic-overturn, or even stagnant-lid, regime. New thermodynamic modelling confirms that an initially hot Earth could have a stagnant lid for ca 300 Ma, and then would experience a series of massive overturns at intervals on the order of 150 Ma until the end of the EoArchean. The subcontinental lithospheric mantle (SCLM) sampled on Earth today did not exist before ca 3.5 Ga. A lull in crustal production around 3.0 Ga coincides with the rapid buildup of a highly depleted, buoyant SCLM, which peaked around 2.7-2.8 Ga; this pattern is consistent with one or more major mantle overturns. The generation of continental crust peaked later in two main pulses at ca 2.75 Ga and 2.5 Ga; the latter episode was larger and had a greater juvenile component. The age/Hf-isotope patterns of the crust generated from 3.0 to 2.4 Ga are similar to those in the internal orogens of the Gondwana supercontinent, and imply the existence of plate tectonics related to the assembly of the Kenorland (ca 2.5 Ga) supercontinent. There is a clear link in these data between the generation of the SCLM and the emergence of modern plate tectonics; we consider this link to be causal, as well as temporal. The production of both crust and SCLM declined toward a marked low point by ca 2.4 Ga. The data naturally divide the Archean into three periods: PaleoArchean (4.0-3.6 Ga), MesoArchean (3.6-3.0 Ga) and NeoArchean (3.0-2.4 Ga); we suggest that this scheme could usefully replace the current four-fold division of the Archean.

  17. MaRIE Undulator & XFEL Systems

    Nguyen, Dinh Cong [Los Alamos National Laboratory; Marksteiner, Quinn R. [Los Alamos National Laboratory; Anisimov, Petr Mikhaylovich [Los Alamos National Laboratory; Buechler, Cynthia Eileen [Los Alamos National Laboratory

    2015-03-23

    The 22 slides in this presentation treat the subject under the following headings: MaRIE XFEL Performance Parameters, Input Electron Beam Parameters, Undulator Design, Genesis Simulations, Risks, and Summary It is concluded that time-dependent Genesis simulations show the MaRIE XFEL can deliver the number of photons within the required bandwidth, provided a number of assumptions are met; the highest risks are associated with the electron beam driving the XFEL undulator; and risks associated with the undulator and/or distributed seeding technique may be evaluated or retired by performing early validation experiments.

  18. M&A information technology best practices

    Roehl-Anderson, Janice M

    2013-01-01

    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

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

    Frey, F.A.; Coffin, M.F.; Wallace, P.J.; Weis, D.; Zhao, X.; Wise, S.W.; Wahnert, V.; D. A. H. Teagle; Saccocia, P.J.; Reusch, D.N.; Pringle, M.S.; Nicolaysen, K. E.; Neal, C. R.; Muller, R.D.; Moore, C L

    2011-01-01

    Oceanic plateaus form by mantle processes distinct from those farming 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...

  20. Gold in the oceans through time

    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

    2015-10-01

    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.

  1. The timescales of magma evolution at mid-ocean ridges

    Brandl, Philipp A.; Regelous, Marcel; Beier, Christoph; O'Neill, Hugh St. C.; Nebel, Oliver; Haase, Karsten M.

    2016-01-01

    Oceanic crust is continuously created at mid-ocean ridges by decompression melting of the upper mantle as it upwells due to plate separation. Decades of research on active spreading ridges have led to a growing understanding of the complex magmatic, tectonic and hydrothermal processes linked to the formation of new oceanic igneous crust. However, less is known about the timescales of magmatic processes at mid-ocean ridges, including melting in and melt extraction from the mantle, fractional crystallisation, crustal assimilation and/or magma mixing. In this paper, we review the timescales of magmatic processes by integrating radiometric dating, chemical and petrological observations of mid-ocean ridge basalts (MORBs) and geophysical models. These different lines of evidence suggest that melt extraction and migration, and crystallisation and mixing processes occur over timescales of 1 to 10,000 a. High-resolution geochemical stratigraphic profiles of the oceanic crust using drill-core samples further show that at fast-spreading ridges, adjacent flow units may differ in age by only a few 100 a. We use existing chemical data and new major- and trace-element analyses of fresh MORB glasses from drill-cores in ancient Atlantic and Pacific crust, together with model stratigraphic ages to investigate how lava chemistry changes over 10 to 100 ka periods, the timescale of crustal accretion at spreading ridges which is recorded in the basalt stratigraphy in drilled sections through the oceanic crust. We show that drilled MORBs have compositions that are similar to those of young MORB glasses dredged from active spreading ridges (lavas that will eventually be preserved in the lowermost part of the extrusive section covered by younger flows), showing that the dredged samples are indeed representative of the bulk oceanic crust. Model stratigraphic ages calculated for individual flows in boreholes, together with the geochemical stratigraphy of the drilled sections, show that at fast-spreading ridges, magma compositions vary over < 100 to 1000 a, likely due to variations in the relative rates of crystallisation and melt recharge. However, on longer timescales of 10 to 100 ka, variations in the composition of the primitive melt feeding the ridge lead to chemical variations in the erupted lavas, likely as a function of thermal and/or chemical heterogeneity of the mantle source. The further understanding of these temporal variations in magma composition, especially at shorter timescales of less than a few centuries, is a promising area for future research.

  2. Ocean gravitational-modes in transient neutron stars

    Deibel, Alex

    2015-01-01

    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...

  3. Project MA1101; GREEN HARBOR, PLYMOUTH, PROVENCETOWN, CHATHAM, HYANNIS, WOODS HOLE; PORTS OF CAPE COD; MA.

    National Oceanic and Atmospheric Administration, Department of Commerce — The objective of Integrated Ocean and Coastal Mapping (IOCM) is to improvethe coordination among federal, state and local government, non-governmentaland private...

  4. The dual role of soil crusts in desertification

    Assouline, S.; Thompson, S. E.; Chen, L.; Svoray, T.; Sela, S.; Katul, G. G.

    2015-10-01

    Vegetation cover in dry regions is a key variable in determining desertification. Soils exposed to rainfall by desertification can form physical crusts that reduce infiltration, exacerbating water stress on the remaining vegetation. Paradoxically, field studies show that crust removal is associated with plant mortality in desert systems, while artificial biological crusts can improve plant regeneration. Here it is shown how physical crusts can act as either drivers of or buffers against desertification depending on their environmental context. The behavior of crusts is first explored using a simplified theory for water movement on a uniform, partly vegetated slope subject to stationary hydrologic conditions. Numerical model runs supplemented with field data from a semiarid Long-Term Ecological Research site are then applied to represent more realistic environmental conditions. When vegetation cover is significant, crusts can drive desertification, but this process is potentially self-limiting. For low vegetation cover, crusts mitigate against desertification by providing water subsidy to plant communities through a runoff-runon mechanism.

  5. Fabrication technology for ODS Alloy MA957

    A successful fabrication schedule has been developed at Carpenter Technology Corporation for the production of MA957 fuel and blanket cladding. Difficulties with gun drilling, plug drawing and recrystallization were overcome to produce a pilot lot of tubing. This report documents the fabrication efforts of two qualified vendors and the support studies performed at WHC to develop the fabrication-schedule

  6. 78 FR 25336 - Massachusetts Disaster #MA-00054

    2013-04-30

    ... From the Federal Register Online via the Government Publishing Office SMALL BUSINESS ADMINISTRATION Massachusetts Disaster MA-00054 AGENCY: U.S. Small Business Administration. ACTION: Notice...: 01/21/2014. ADDRESSES: Submit completed loan applications to: U.S. Small Business...

  7. Salatoimikud : ma tahan uskuda / Mart Rummo

    Rummo, Mart

    2008-01-01

    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

  8. Maíz I (Zea mays)

    Sánchez Ortega, Iván; Pérez-Urria Carril, Elena

    2014-01-01

    El maíz es uno de los cultivos básicos más importantes y extendidos en todo el mundo. Constituye una de las fuentes principales de alimento de millones depersonas, sobre todo en América y Asia. Se trata de una de las primeras plantas que se domesticaron y se difundieron por todo el mundo.

  9. Direct measurements of oceanic crustal density at the Northern Juan de Fuca Ridge

    Gilbert, Lisa A.; Johnson, H. Paul

    Density and porosity of oceanic crust are critically important to understanding the circulation of hydrothermal fluid at mid-ocean ridges. To determine these parameters directly, we completed a fixed, on-bottom gravity survey on the Endeavour Segment of the Juan de Fuca Ridge, which is a well studied spreading center that is both hydrothermally and tectonically active. A Bell-Aerospace gravity meter mounted within the submersible ALVIN was used to make gravity measurements from the floor of the axial valley to the summit of the west axial ridge. Analysis of these data gave a density of 2240150 kg/m for the upper 130 m of crust. Comparison of the outcrop density with that of recovered rock samples resulted in a calculated porosity of 384%. Forward modeling of the seafloor gravity data indicated that both the valley floor and bounding walls have unusually low density crust that is flanked by higher density crust.

  10. The Origin of Voluminous Dacite (vs. Andesite) at Mature, Thick Continental Arcs: A Reflection of Processes in the Deep Crust

    Lange, R. A.

    2013-12-01

    An outstanding question is why some continental arc segments are characterized by voluminous eruptions of dacite (65-70 wt% SiO2), whereas others erupt more andesite (58-64 wt% SiO2) than any other magma type. An example of the former is the Altiplano-Puna region of the central Andean arc, which has erupted a predominance of dacite over all magma types 10-1 Ma (de Silva, 1989). In contrast, a 200-km arc segment of the Mexican volcanic arc (Michoacán-Guanajuato arc segment) has erupted ~75% andesite, ~26% basaltic andesite and Guanajuato arc segment, on the basis of phenocryst modes, major- and trace-element data, as well as phase-equilibrium experiments from the literature, it is proposed that the andesites were derived by partial melting (>20%) of hornblende-rich (~40%) gabbronorite in the deep crust, driven by mantle-derived basalt intrusions at depths of 30-40 km. The absence of any dacite or rhyolite along this arc segment indicates that interstitial liquid from crystal-rich andesites never segregated to form eruptible magma. Thus, little upper-crust differentiation occurred along this arc segment. On the basis of phase-equilibrium experiments in the literature (e.g., Sisson et al., 2005), it is proposed that rhyolite and dacite did form during partial melting of the lower arc crust, but at melt fractions too low (≤15%) to permit efficient transport to the upper crust (Vigneresse and Tikoff, 1999). It is further proposed that the reason why dacite is so abundant at mature thick continental arcs (e.g., Altiplano-Puno complex) may be because mantle-derived basalts are primarily emplaced at similar depths (~30-40 km) in continental arc crustal columns. If so, in the central Andean arc, a depth of 30-40 km is within the middle dioritic crust (Graeber and Asch, 1999). Partial melts of hornblende diorite (vs. hornblende gabbro) are predicted to be dacitic (vs. andesitic) at melt fractions of 20-25%, which permits transport to the upper crust. It is therefore proposed that it is deep crustal processes that determine whether andesite or dacite is the most voluminous magma type emplaced into the upper crust and erupted at arcs.

  11. El Hierro's floating stones as messengers of crust-magma interaction at depth

    Burchardt, S.; Troll, V. R.; Schmeling, H.; Koyi, H.; Blythe, L. S.; Longpr, M. A.; Deegan, F. M.

    2012-04-01

    During the early stages of the submarine eruption that started on October 10 2011 south of El Hierro, Canary Islands, Spain, peculiar eruption products were found floating on the sea surface. These centimetre- to decimetre-sized "bombs" have been termed "restingolites" after the nearby village La Restinga and consist of a basaltic rind and a white to light grey core that resembles pumice in texture. According to Troll et al. (2011; see also Troll et al. EGU 2012 Abstracts), this material consists of a glassy matrix hosting extensive vesicle networks, which results in extremely low densities allowing these rocks to float on sea water. Mineralogical and geochemical analyses reveal that the "restingolites" originate from the sedimentary rocks (sand-, silt-, and mudstones) that form layer 1 of the oceanic crust beneath El Hierro. During the onset and early stages of the eruption, magma ponded at the base of this sedimentary sequence, breaking its way through the sedimentary rocks to the ocean floor. The textures of the "restingolites" reveal that crust-magma interaction during fragmentation and transport of the xenoliths involved rapid partial melting and volatile exsolution. Xenoliths strikingly similar to those from El Hierro are known from eruptions on other Canary Islands (e.g. La Palma, Gran Canaria, and Lanzarote). In fact, they resemble in texture xenoliths of various protoliths from volcanic areas worldwide (e.g. Krakatao, Indonesia, Cerro Quemado, Guatemala, Laacher See, Germany). This indicates that the process of partial melting and volatile exsolution, which the "restingolites" bear witness of, is probably occurring frequently during shallow crustal magma emplacement. Thermomechanical numerical models of the effect of the density decrease associated with the formation of vesicle networks in partially molten xenoliths show that xenoliths of crustal rocks initially sink in a magma chamber, but may start to float to the chamber roof once they start to heat up and vesiculate. The "floating stones" from El Hierro thus represent the products of crust-magma interaction beneath the Canary Islands, but is probably relevant in most volcanic areas and tectonic settings. In addition, xenolith devolatilisation has important general implications for the mechanics of crustal recycling, magma emplacement into the upper crust and volatile release from active volcanic systems.

  12. Hafnium isotopes in Jack Hills zircons and the formation of the Hadean crust

    Blichert-Toft, Janne; Albarède, Francis

    2008-01-01

    New bulk Hf and Pb isotope data were obtained for 63 leached single zircons from Jack Hills (JH), Western Australia, using solution chemistry and, respectively, MC-ICP MS and ICP-MS. With the exception of one "young" zircon at 3.32 Ga, the remainder of the selected grains were previously dated at > 3.9 Ga by ion-microprobe. This work extends and complements the solution chemistry data of Harrison et al. [Harrison, T.M., Blichert-Toft, J., Müller, W., Albarède, F., Holden, P., Mojzsis, S.J., 2005. Heterogeneous Hadean hafnium: evidence of continental crust at 4.4 to 4.5 Ga. Science 310, 1947-1950.] but uses bulk rather than in situ Pb-Pb ages to interpret the Hf isotope data. This larger data set is used to explore whether the host rocks of the JH zircons formed as a succession of pulses or rather as a single event, and to calculate the age and assess the nature of their crustal protolith. We find that the parent granites of the JH zircons analyzed here formed during a single pulse 4.1 ± 0.1 Ga ago by the remelting of a 4.30-4.36 Ga old protolith. Monte Carlo modeling indicates that the 176Lu/ 177Hf ratios of this material (< 0.01) are unlike the ratios of modern-type oceanic crust and island arc rocks but rather fit a tonalite-trondhjemite-granodiorite (TTG) source. TTGs themselves derived their inordinately enriched character from a basaltic progenitor which corresponds to the missing enriched reservoir identified by the 143Nd- 144Nd, 142Nd- 144Nd, and 176Hf/ 177Hf systematics of Archean rocks. We speculate that crystallization of the magma ocean in the presence of garnet left the upper mantle and an early basaltic crust enriched in incompatible elements. Reaction of this early crust with the overlying hydrosphere and subsequent foundering into the mantle gave rise at ˜ 4.3 Ga to the TTG protolith of the JH granites. Dating the onset of plate tectonics therefore depends on whether TTGs can be considered as subduction zone magmas or not.

  13. Solvent evaporation of spin cast films crust effects

    De Gennes, Pierre Gilles

    2001-01-01

    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).

  14. Superfluidity and entrainment in neutron-star crusts

    Chamel, Nicolas; Pearson, Michael J.; Goriely, Stéphane

    2012-01-01

    Despite the absence of viscous drag, the neutron superfluid permeating the inner crust of a neutron star can still be strongly coupled to nuclei due to non-dissipative entrainment effects. Neutron superfluidity and entrainment have been systematically studied in all regions of the inner crust of a cold non-accreting neutron star in the framework of the band theory of solids. It is shown that in the intermediate layers of the inner crust a large fraction of “free” neutrons are actually entrain...

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

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

    2015-03-01

    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.)

  16. Active Electromagnetics At The Mid-Ocean Ridge

    Everett, Mark E.

    1990-01-01

    The 59,000 km long global mid-ocean ridge system is the site of formation of 20 km3 of oceanic crust yearly. Two-thirds of all heat loss from the interior of our planet is through the ocean floors, 40% of this amount is focused through the ridge. Activity involves complex interactions among a number of processes occurring over wide ranges of depths and lateral distances, including melting of the earth's mantle, delivery of the molten rock to a crustal magma chamber, cooling of the magma intru...

  17. Granite forming events and their role in crust formation of Indian shield

    Continental crustal evolution in the Indian shield appears to have started around the middle Archaean and completed by the early Proterozoic. In this time span of around 700-800 Ma, the primordial gneissic crust has evolved, recycled and stabilized. The earliest phase of the granitoid activity, from the middle-to late Archaean consists predominantly of a tonalite-trondhjemite-granodiorite (TTG) suite, while the second phase of the Archean - Proterozoic transition (APT) period consists predominantly of granodiorite-adamellite suite. Minor granite forming events have occurred in the middle-to late Proterozoic. The compositional changes in the granites from the Archaean to the proterozoic appear to have been mainly controlled by the tectonics and the source composition at each stage and contribution from the appears to be negligible. Increasing of some large ion lithophile (LIL) elements and decreasing of compatible trace elements in the APT granites compared to the earlier gneissic phase and the overall compositions of the latter (the gneisses) suggest that the middle-to late Archaean polyphase gneisses are the partial melts of the mafic rocks from greenstones and the various phases of the tonalite-trondhjemite-granodiorite (TTG), viz., the hornblende-biotite- and feldspathic gneisses (younging in the same order) are the successive fractionate of similar or same source. The tectonic setting at the time of formation of the TTG gneisses is more of a compressive regime and crustal thickening appears to have played a role in the initiation of partial melting of the source. The appearance of extensive K-rich batholithic granites throughout the shield in a limited time span of 200-300 Ma during the early Proterozoic, increase of LIL elements and high Th, Rb and Sr variations in these batholithic granites suggest that these granites are anatectic in nature and have formed due to the release of compressional forces and initiation of an extensional regime in the shield area. though sporadic important alkalic granite bodies have formed in the middle to late Proterozoic, they are mostly restricted to the orogenic belts like the Aravalli, the Delhi, the Satpura and the Eastern Ghats. Many of these post-tectonic granites (mostly A-type) give evidence for crust-mantle interaction in their formation and their emplacement in a stable continental crust setting. (author)

  18. Shallow Moho with aseismic upper crust and deep Moho with seismic lower crust beneath the Japanese Islands obtained by seismic tomography using data from dense seismic network

    Matsubara, Makoto; Obara, Kazushige

    2015-04-01

    P-wave seismic velocity is well known to be up to 7.0 km/s and over 7.5 km/s in the lower crust and in the mantle, respectively. A large velocity gradient is the definition of the Moho discontinuity between the crust and mantle. In this paper, we investigates the configuration of Moho discontinuity defined as an isovelocity plane with large velocity gradient derived from our fine-scale three-dimensional seismic velocity structure beneath Japanese Islands using data obtained by dense seismic network with the tomographic method (Matsubara and Obara, 2011). Japanese Islands are mainly on the Eurasian and North American plates. The Philippine Sea and Pacific plates are subducting beneath these continental plates. We focus on the Moho discontinuity at the continental side. We calculate the P-wave velocity gradients between the vertical grid nodes since the grid inversion as our tomographic method does not produce velocity discontinuity. The largest velocity gradient is 0.078 (km/s)/km at velocities of 7.2 and 7.3 km/s. We define the iso-velocity plane of 7.2 km/s as the Moho discontinuity. We discuss the Moho discontinuity above the upper boundary of the subducting oceanic plates with consideration of configuration of plate boundaries of prior studies (Shiomi et al., 2008; Kita et al., 2010; Hirata et al, 2012) since the Moho depth derived from the iso-velocity plane denotes the oceanic Moho at the contact zones of the overriding continental plates and the subducting oceanic plates. The Moho discontinuity shallower than 30 km depth is distributed within the tension region like northern Kyushu and coastal line of the Pacific Ocean in the northeastern Japan and the tension region at the Cretaceous as the northeastern Kanto district. These regions have low seismicity within the upper crust. Positive Bouguer anomaly beneath the northeastern Kanto district indicates the ductile material with large density in lower crust at the shallower portion and the aseismic upper crust. The Moho discontinuity deepens over 35 km in the collision zone like as Kanto Mountains, the volcanic underplating zone as the Tohoku backbone range, and non-tension region like as Chugoku Mountains. These regions associated with deep Moho are characterized by the crustal seismicity within the depth range from 20 to 30 km. The iso-depth contour of 35 km beneath the southwestern Japan is consistent with that derived from the receiver function method (Shiomi et al. 2006). There are nonvolcanic tremors and short-time slow slip events (SSE) beneath the southwestern Japan (eg. Obara, 2002). Matsubara et al. (2009) consider that the tremors and SSEs occur along the contact zone of Moho discontinuity beneath the Eurasian plate and the subducting Philippine Sea plate beneath southwestern Japan. Our Moho model is consistent with this since they exist along the southern edge of the Moho discontinuity of the continental Eurasian plate. Reference: Hirata, N., Sakai, S., Nakagawa, S., Ishikawa, M., Sato, H., Kasahara, K., Kimura, H. and Honda, R. (2012) A new tomographic image on the Philippine Sea Slab beneath Tokyo - Implication to seismic hazard in the Tokyo metropolitan region, EOS, Transactions, AGU, T11C-06. Kita, S., T. Okada, A. Hasegawa, J. Nakajima, and T. Matsuzawa (2010) Anomalous deepening of a seismic belt in the upper-plane of the double seismic zone in the Pacific slab beneath the Hokkaido corner: Possible evidence for thermal shielding caused by subducted forearc crust materials, Earth Planet. Science Lett., 290, 415-426. Matsubara, M. and K. Obara (2011) The 2011 Off the Pacific Coast of Tohoku earthquake related to a strong velocity gradient with the Pacific plate, Earth Planets Space, 63, 663-667. Matsubara, M., K. Obara, and K. Kasahara (2009) High-Vp/Vs zone accompanying non-volcanic tremors and slow-slip events beneath southwestern Japan, Tectonophysics, 472, 6-17, doi:10.1016/j.tecto.2008.06.013. Obara, K. (2002) Nonvolcanic deep tremor associated with subduction in southwest Japan. Science 296, 1679-1681. Shiomi, K., K. Obara, and H. Sato (2006) Moho depth variation beneath southwestern Japan revealed from the velocity structure based on receiver function inversion , Tectonophysics, 420, 205-221, doi:10.1016/j.tecto.2006.01.017. Shiomi, K., M. Matsubara, Y. Ito, and K. Obara (2008) Simple relationship between seismic activity along Philippine Sea slab and geometry of oceanic Moho beneath southwest Japan, Geophys. J. Int., 173, 1018-1029.

  19. Mass and Reliability System (MaRS)

    Barnes, Sarah

    2016-01-01

    The Safety and Mission Assurance (S&MA) Directorate is responsible for mitigating risk, providing system safety, and lowering risk for space programs from ground to space. The S&MA is divided into 4 divisions: The Space Exploration Division (NC), the International Space Station Division (NE), the Safety & Test Operations Division (NS), and the Quality and Flight Equipment Division (NT). The interns, myself and Arun Aruljothi, will be working with the Risk & Reliability Analysis Branch under the NC Division's. The mission of this division is to identify, characterize, diminish, and communicate risk by implementing an efficient and effective assurance model. The team utilizes Reliability and Maintainability (R&M) and Probabilistic Risk Assessment (PRA) to ensure decisions concerning risks are informed, vehicles are safe and reliable, and program/project requirements are realistic and realized. This project pertains to the Orion mission, so it is geared toward a long duration Human Space Flight Program(s). For space missions, payload is a critical concept; balancing what hardware can be replaced by components verse by Orbital Replacement Units (ORU) or subassemblies is key. For this effort a database was created that combines mass and reliability data, called Mass and Reliability System or MaRS. The U.S. International Space Station (ISS) components are used as reference parts in the MaRS database. Using ISS components as a platform is beneficial because of the historical context and the environment similarities to a space flight mission. MaRS uses a combination of systems: International Space Station PART for failure data, Vehicle Master Database (VMDB) for ORU & components, Maintenance & Analysis Data Set (MADS) for operation hours and other pertinent data, & Hardware History Retrieval System (HHRS) for unit weights. MaRS is populated using a Visual Basic Application. Once populated, the excel spreadsheet is comprised of information on ISS components including: operation hours, random/nonrandom failures, software/hardware failures, quantity, orbital replaceable units (ORU), date of placement, unit weight, frequency of part, etc. The motivation for creating such a database will be the development of a mass/reliability parametric model to estimate mass required for replacement parts. Once complete, engineers working on future space flight missions will have access a mean time to failures and on parts along with their mass, this will be used to make proper decisions for long duration space flight missions

  20. Hydrothermal experiments on serpentinization at crust/mantle boundary

    Oyanagi, R.; Okamoto, A.; Tsuchiya, N.

    2013-12-01

    Serpentinization commonly proceeds in seafloor hydrothermal systems at mid-ocean ridges, along the bending faults, and at the boundary of wedge mantle and subducting plate. Silica activity are key factors in controlling reaction paths and the rate of serpentinization (e.g., Frost and Beard, 2007; Klein et al., 2009; Ogasawara et al.,2013). However, most of the previous experimental studies focused on bulk solid materials and solutions within the reaction vessel, and local changes of products reaction rate in response to concentration gradient have not been clarified. Ogasawara et al. (2013) conducted hydrothermal experiments in Ol-Opx-H2O system, and modeled the progress of serpentinization by coupled reactions and silica diffusion. In their experiment, reaction product is only serpentine and no talc or brucite were found. In this study, we conducted hydrothermal experiments in olivine (Ol)-quartz (Qtz)-H2O and Ol-plagioclase (Pl)-H2O systems as the analogue of crust/mantle boundary. The condition was 250 degreeC and at a vapor-saturated pressure. Composite powders (composed of Qtz/Ol zone, or Pl/Ol zone) were set in tube-in-tube vessels, and then loaded into autocrave with fluid ( NaOHaq, pH = 13.8 at 25 degreeC ). Runnig time is up to 25 days and maximum water content in the products is 12 wt% H2O. After the experiments, solution chemistry and the extent of serpentinization were analyzed in detail. In the Ol-Qtz-H2O experiments, we observed systematic changes of reaction products in the Ol zone. Smectite and serpentine was formed at Ol-Qtz boundary due to high Na concentration although talc is expected to form in MgO-SiO2-H2O system at Ol-Qtz boundary. Mg/Si ratio of products from EDS analyze shows high Si gradient near the boundary indicate that amount of smectite decreased with increasing distance from the Ol-Qtz boundary and only serpentine zone was observed at ~10mm. At >10mm away from Ol-Qtz boundary, serpentine ( chrysotile nano tubes) and brucite was observed. Extent of hydration within the reaction tube is low (TG loss = 3.5 wt% H2O) at ~10mm (smectite zone), and it increases (TG loss =12 wt% H2O) to 40mm (the top of inner tube).Brucite and serpentine zone retreated from the boundary, by probably dehydration reaction due to silica input. In Ol-Pl-H2O experiment, Al-rich lizardite was only formed near the Ol-Pl boundary whreas serpentine (chrysotile nano tubes) + brucite was formed away from Ol-Qtz boundary. Our results imply that input of silica from the crust decelerate the overall hydration within the boundary because it inhibit the brucite formation and enhance formation the less-hydrous minerals (talc/smectite). Reference Klein, F., Bach, W., Jöns, et al (2009). Geochimica et Cosmochimica Acta, 73, 6868-6893. Frost, B. R., & Beard, J. S. (2007). Journal of Petology 48, 1351-1368. Ogasawara et al. (2013), Geochimica et Cosmochimica Acta, 119, 212-230.

  1. Comparisons of Mineralogy Between Cumulate Eucrites and Lunar Meteorites Possibly from the Farside Anorsothitic Crust

    Takeda, H.; Yamaguchi, A.; Hiroi, T.; Nyquist, L. E.; Shih, C.-Y.; Ohtake, M.; Karouji, Y.; Kobayashi, S.

    2011-01-01

    Anorthosites composed of nearly pure anorthite (PAN) at many locations in the farside highlands have been observed by the Kaguya multiband imager and spectral profiler [1]. Mineralogical studies of lunar meteorites of the Dhofar 489 group [2,3] and Yamato (Y-) 86032 [4], all possibly from the farside highlands, showed some aspects of the farside crust. Nyquist et al. [5] performed Sm-Nd and Ar-Ar studies of pristine ferroan anorthosites (FANs) of the returned Apollo samples and of Dhofar 908 and 489, and discussed implications for lunar crustal history. Nyquist et al. [6] reported initial results of a combined mineralogical/chronological study of the Yamato (Y-) 980318 cumulate eucrite with a conventional Sm-Nd age of 4567 24 Ma and suggested that all eucrites, including cumulate eucrites, crystallized from parental magmas within a short interval following differentiation of their parent body, and most eucrites participated in an event or events in the time interval 4400- 4560 Ma in which many isotopic systems were partially reset. During the foregoing studies, we recognized that variations in mineralogy and chronology of lunar anorthosites are more complex than those of the crustal materials of the HED parent body. In this study, we compared the mineralogies and reflectance spectra of the cumulate eucrites, Y-980433 and 980318, to those of the Dhofar 307 lunar meteorite of the Dhofar 489 group [2]. Here we consider information from these samples to gain a better understanding of the feldspathic farside highlands and the Vesta-like body.

  2. MaJAZ1 Attenuates the MaLBD5-Mediated Transcriptional Activation of Jasmonate Biosynthesis Gene MaAOC2 in Regulating Cold Tolerance of Banana Fruit.

    Ba, Liang-Jie; Kuang, Jian-Fei; Chen, Jian-Ye; Lu, Wang-Jin

    2016-02-01

    Previous studies indicated that methyl jasmonate (MeJA) treatment could effectively reduce the chilling injury of many fruits, including banana, but the underlying mechanism is poorly understood. In this study, one lateral organ boundaries (LOB) domain (LBD) gene, designated as MaLBD5, was isolated and characterized from banana fruit. Expression analysis revealed that accumulation of MaLBD5 was induced by cold temperature and MeJA treatment. Subcellular localization and transactivation assays showed that MaLBD5 was localized to the nucleus and possessed transcriptional activation activity. Protein-protein interaction analysis demonstrated that MaLBD5 physically interacted with MaJAZ1, a potential repressor of jasmonate signaling. Furthermore, transient expression assays indicated that MaLBD5 transactivated a jasmonate biosynthesis gene, termed MaAOC2, which was also induced by cold and MeJA. More interestingly, MaJAZ1 attenuated the MaLBD5-mediated transactivation of MaAOC2. These results suggest that MaLBD5 and MaJAZ1 might act antagonistically in relation to MeJA-induced cold tolerance of banana fruit, at least partially via affecting jasmonate biosynthesis. Collectively, our findings expand the knowledge of the transcriptional regulatory network of MeJA-mediated cold tolerance of banana fruit. PMID:26760434

  3. Reconstructing the temperature and salinity of the Mediterranean Sea through the Late Miocene (13 Ma - 6 Ma) prior to the Messinian Salinity Crisis

    Tzanova, Alexandrina; Herbert, Timothy; Peterson, Laura

    2014-05-01

    We present a unique, alkenone-based record of sea surface temperatures spanning 13 Ma to 6 Ma from the uplifted, pelagic, Mediterranean sequence at Monte dei Corvi. The thick salt layers resulting from the isolation of the Mediterranean have so far been an obstacle to conventional drilling in obtaining a high-resolution, continuous record of the basin's conditions prior to ~6 Ma. This is especially important when reconstructing the climate conditions that preceded and contributed to the Messinian Salinity Crisis. Uplifted sections allow access to this otherwise unresolved time period. Planktonic d18O records from uplifted marine sections exist; however, they are hampered by the lack of independent temperature reconstruction in order to detangle the competing influence of both temperature and salinity on such data. Using alkenone paleothermometry we show that the Late Miocene Mediterranean Sea was notably warmer than present with SSTs equivalent and even higher than the warmest parts of the modern ocean. Between ~ 12.9 Ma to ~8.1 Ma temperatures hovered close to 28oC and possibly even higher. At ~8.1 Ma, concurrent with notable changes in the vegetation pattern of the area as well as globally, sea surface temperatures show a distinct cooling trend punctuated with a cold episode at ~7 Ma which coincides with the first appearance of desert conditions in the Sahara. The cooling trend continues up to the Messinian Salinity Crisis at which point marine sedimentation was interrupted at the site. Our dataset contains four high-resolution windows where we examine the precession scale SST changes that contributed to sapropel formation and comparing them with the regime established for the Plio-Pleistocene. The reconstructed sea surface temperatures allow us to reconstruct the paleo-salinity of the Mediterranean leading up to the Messinian Salinity Crisis. The uncorrected the published d18O planktonic records show a sharp enrichment at ~7.5 Ma. Once corrected for temperature the residual salinity component shows a much more gradual change. We suggest that the isolation of the basin was a gradual restriction. We show that even when the basin became restricted the mechanisms of sapropel formation remained the same with strong freshwater pulses and warmer temperatures leading up to the MSC.

  4. [Crusted scabies induced by topical corticosteroids: A case report].

    Bilan, P; Colin-Gorski, A-M; Chapelon, E; Sigal, M-L; Mahé, E

    2015-12-01

    The frequency of scabies is increasing in France. Crusted (or Norwegian) scabies is a very contagious form of scabies because of the huge number of mites in the skin. It is observed in patients suffering from immunodepression, motor or sensory deficiency, or mental retardation. The clinical presentation, except for the classic manifestation of scabies, is characterized by crusted lesions. Treatment is not easy and requires hospitalization. Topical corticosteroids are frequently used for children's dermatological diseases. Their long-term and inappropriate application in an infested scabies child can induce crusted scabies. We report on a case of an 8-year-old boy who developed crusted scabies induced by topical corticosteroid application. We discuss the therapeutic aspects of this severe form of scabies. PMID:26459132

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

    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)

    2007-03-15

    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)

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

    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)

  7. Biological soil crusts in post-mining areas

    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

  8. Intensive Ammonia and Methane Oxidation in Organic Liquid Manure Crusts

    Nielsen, Daniel Aagren; Nielsen, Lars Peter; Schramm, Andreas; Revsbech, Niels Peter

    the crusts. PCR targeting the unique methane and ammonia monooxygenases were applied together with FISH to detect the presence of the two bacterial groups. Potential activity was assessed by short term slurry incubations of crust samples while monitoring NO2- production or CH4 consumption. Crusts were......Intensive agricultural practice leads to periodic accumulation of enormous amounts of liquid manure (slurry) from animal husbandry, and large quantities of environmentally hazardous ammonia and methane are emitted from the manure storages. Floating surface crusts have been suggested to harbour...... methane oxidizing bacteria (MOB) and are known to accumulate nitrite and nitrate, indicating the presence of ammonia oxidizers (AOB). We have surveyed six manure tanks with organic covers to investigate the prevalence of MOB and AOB and to link the potential activity with physical and chemical aspects of...

  9. Oceans Past

    Based on research for the History of Marine Animal Populations project, Oceans Past examines the complex relationship our forebears had with the sea and the animals that inhabit it. It presents eleven studies ranging from fisheries and invasive species to offshore technology and the study of marine...

  10. Ocean optics

    This paper provides an introduction and overview of the discipline known as ocean optics. Emphasis is on basic concepts, the optical quantities involved, their measurement, and inter-connecting theoretical relationships. Topics include radiometric quantities, inherent optical properties, apparent optical properties, measuring the spectral absorption coefficient, measuring the volume scattering function, effect of the deep chlorophyll layer, and future directions

  11. Crusted scabies-associated immune reconstitution inflammatory syndrome

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

    2012-01-01

    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...

  12. PAIRING CORRELATIONS AND THERMODYNAMIC PROPERTIES OF INNER CRUST MATTER

    Margueron, Jérôme; Sandulescu, N.

    2012-01-01

    In this review paper we discuss the effects of pairing correlations on inner crust matter in the density region where nuclear clusters are supposed to coexist with nonlocalised neutrons. The pairing correlations are treated in the framework of the finite temperature Hartree-Fock-Bogoliubov approach and using zero range nuclear forces. After a short introduction and presentation of the formalism we discuss how the pairing correlations affect the structure of the inner crust matter, i.e., the p...

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

    Bao, Shishao

    2015-01-01

    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.

  14. Ultrafine-scale magnetostratigraphy of marine ferromanganese crust

    Oda, Hirokuni; Usui, Akira; Miyagi, Isoji; Joshima, Masato; Weiss, Benjamin P.; Shantz, Chris; Fong, Luis E.; McBride, Krista K.; Harder, Rene; Baudenbacher, Franz J.

    2011-01-01

    Hydrogenetic ferromanganese crusts are iron-manganese oxide chemical precipitates on the seafloor that grow over periods of tens of millions of years. Their secular records of chemical, mineralogical, and textural variations are archives of deep-sea environmental changes. However, environmental reconstruction requires reliable high-resolution age dating. Earlier chronological methods using radiochemical and stable isotopes provided age models for ferromanganese crusts, but have limitations on...

  15. Ocean energies

    This timely volume provides a comprehensive review of current technology for all ocean energies. It opens with an analysis of ocean thermal energy conversion (OTEC), with and without the use of an intermediate fluid. The historical and economic background is reviewed, and the geographical areas in which this energy could be utilized are pinpointed. The production of hydrogen as a side product, and environmental consequences of OTEC plants are considered. The competitiveness of OTEC with conventional sources of energy is analysed. Optimisation, current research and development potential are also examined. Separate chapters provide a detailed examination of other ocean energy sources. The possible harnessing of solar ponds, ocean currents, and power derived from salinity differences is considered. There is a fascinating study of marine winds, and the question of using the ocean tides as a source of energy is examined, focussing on a number of tidal power plant projects, including data gathered from China, Australia, Great Britain, Korea and the USSR. Wave energy extraction has excited recent interest and activity, with a number of experimental pilot plants being built in northern Europe. This topic is discussed at length in view of its greater chance of implementation. Finally, geothermal and biomass energy are considered, and an assessment of their future is given. The authors also distinguished between energy schemes which might be valuable in less-industrialized regions of the world, but uneconomical in the developed countries. A large number of illustrations support the text. This book will be of particular interest to energy economists, engineers, geologists and oceanographers, and to environmentalists and environmental engineers

  16. PuMa-ECR ion source operation

    The PuMa (Pulsed Magnetic field)-ECR ion source uses a pulsed solenoid coil to improve the peak current by opening the magnetic bottle along the beam axis. After demonstration of the principle of the pulsed magnetic extraction, the ion source was tested with different gases. We got promising results from helium up to krypton. For xenon the enhancement of the analyzed current was only in the same order as the enhancement of the afterglow. The influence of the current in the pulsed coil on the analyzed ion current was measured. With increased current levels in the pulsed coil the pulse height of the PuMa-pulse increases within the given pulse length of the coil. By using the pulsed coil the maximum of the charge state distribution can be shifted to higher charge states. (author)

  17. Neutron Star Asteroseismology. Axial Crust Oscillations in the Cowling Approximation

    Samuelsson, L; Samuelsson, Lars; Andersson, Nils

    2006-01-01

    Recent observations of quasi-periodic oscillations in the aftermath of giant flares in soft gamma-ray repeaters suggest a close coupling between the seismic motion of the crust after a major quake and the modes of oscillations in a magnetar. In this paper we consider the purely elastic modes of oscillation in the crust of a neutron star in the relativistic Cowling approximation (disregarding any magnetic field). We determine the axial crust modes for a large set of stellar models, using a state-of-the-art crust equation of state and a wide range of core masses and radii. We also devise useful approximate formulae for the mode-frequencies. We show that the relative crust thickness is well described by a function of the compactness of the star and a parameter describing the compressibility of the crust only. Considering the observational data for SGR 1900+14 and SGR 1806-20, we demonstrate how our results can be used to constrain the mass and radius of an oscillating neutron star.

  18. Compositional Freeze-Out of Neutron Star Crusts

    Hoffman, Kelsey L.; Heyl, J. S.

    2010-01-01

    We have investigated the crustal properties of neutron stars without fallback accretion. We have calculated the chemical evolution of the neutron star crust in three different cases (a modified Urca process without the thermal influence of a crust, a thick crust, and a direct Urca process with a thin crust) in order to determine the detailed composition of the envelope and atmosphere as the nuclear reactions freeze out. Using a nuclear reaction network up to technetium, we calculate the distribution of nuclei at various depths of the neutron star. The nuclear reactions quench when the cooling timescale is shorter than the inverse of the reaction rate. Trace light elements among the calculated isotopes may have enough time to float to the surface before the layer crystallizes and form the atmosphere or envelope of the neutron star. The composition of the neutron star envelope determines the total photon flux from the surface, and the composition of the atmosphere determines the emergent spectrum. Our calculations using each of the three cooling models indicate that without accretion of fallback the neutron star atmospheres are dependent on the assumed cooling process of the neutron star. Each of the cooling methods have different elements composing the atmosphere: for the modified Urca process the atmosphere is 28Si, the thick crust has an atmosphere of 50Cr, and the thin crust has an atmosphere of 40Ca. In all three cases the atmospheres are composed of elements which are lighter then iron.

  19. Permeability of continental crust influenced by internal and external forcing

    Rojstaczer, S.A.; Ingebritsen, S.E.; Hayba, D.O.

    2008-01-01

    The permeability of continental crust is so highly variable that it is often considered to defy systematic characterization. However, despite this variability, some order has been gleaned from globally compiled data. What accounts for the apparent coherence of mean permeability in the continental crust (and permeability-depth relations) on a very large scale? Here we argue that large-scale crustal permeability adjusts to accommodate rates of internal and external forcing. In the deeper crust, internal forcing - fluxes induced by metamorphism, magmatism, and mantle degassing - is dominant, whereas in the shallow crust, external forcing - the vigor of the hydrologic cycle - is a primary control. Crustal petrologists have long recognized the likelihood of a causal relation between fluid flux and permeability in the deep, ductile crust, where fluid pressures are typically near-lithostatic. It is less obvious that such a relation should pertain in the relatively cool, brittle upper crust, where near-hydrostatic fluid pressures are the norm. We use first-order calculations and numerical modeling to explore the hypothesis that upper-crustal permeability is influenced by the magnitude of external fluid sources, much as lower-crustal permeability is influenced by the magnitude of internal fluid sources. We compare model-generated permeability structures with various observations of crustal permeability. ?? 2008 The Authors Journal compilation ?? 2008 Blackwell Publishing Ltd.

  20. Model for Analysis of the Energy Demand (MAED) users' manual for version MAED-1

    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

  1. The unstable CO2 feedback cycle on ocean planets

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

    2015-12-01

    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.

  2. Microcap M&A: An Exploratory Study

    Keith Turpie

    2014-06-01

    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.

  3. High temperature constitutive models for MA957

    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)

  4. Zircon U-Pb age and Sr-Nd-Hf isotope geochemistry of the Panzhihua A-type syenitic intrusion in the Emeishan large igneous province, southwest China and implications for growth of juvenile crust

    Zhong, Hong; Zhu, Wei-Guang; Hu, Rui-Zhong; Xie, Lie-Wen; He, De-Feng; Liu, Feng; Chu, Zhu-Yin

    2009-06-01

    The late Permian Panzhihua syenitic stock in the Pan-Xi area, SW China, showing the typical association of mantle-derived mafic and alkaline rocks along with silicic units, is genetically related to the upwelling Emeishan plume head. This syenitic intrusion consists mainly of metaluminous syenite, metaluminous to peralkaline quartz syenite with subordinate syenite porphyry and alkali-feldspar granite. SHRIMP U-Pb zircon analysis reveal that the Panzhihua syenitic pluton was emplaced at 253.1 ± 1.9 Ma, and is slightly younger than the crystallization age of the spatially associated gabbroic intrusion. These syenitic and granitic rocks have a distinctive A-type chemistry characterized by elevated high-field-strength elements (HFSE) contents and high Ga/Al ratios (3.95 to 6.79). Nb/Ta and Zr/Hf ratios of the syenitic and granitic rocks, gabbros and syenodiorites are similar to those typical of oceanic island basalt (OIB). These granitoids all have relatively low initial 87Sr/ 86Sr ratios (0.7037-0.7058), positive ɛNd( t) values (+ 2.4 to + 3.5). The magmatic zircons from the syenites exhibit positive ɛHf( t) values between 5.9 and 10.4, which correspond to single-stage depleted mantle Hf model ages ( TDM1) of 494 to 671 Ma. In contrast, the magmatic zircons from the syenite porphyries are characterized by positive ɛHf( t) values of 11.4 to 12.9 with younger TDM1 model ages of 382 to 449 Ma than those of the syenites. The positive ɛNd( t) and ɛHf( t) values of the Panzhihua syenitic intrusion indicate a significant contribution of plume-derived basaltic underplating to magma genesis. The similarity of the Nd isotopic compositions of the syenitic and granitic rocks, gabbros and syenodiorites suggests that their parental magmas were derived from a common reservoir. We propose that the Panzhihua syenitic intrusion was predominantly generated by the emplacement of two distinct syenitic melts from differentiation of newly underplated, mildly alkaline basaltic magmas ponded at depth, with incorporation of little Neoproterozoic lower crustal melts, and subsequent fractional crystallization of individual melts. It is therefore demonstrated that the growth of juvenile crust through mantle-derived underplating during the late Permian was significant in the inner zone of the Emeishan large igneous province.

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

    Robinson, S.A.; Vance, D.

    2012-01-01

    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 (100–65 Ma) 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 ph...

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

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

    2006-01-01

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

  7. New Constraints on Baja California-North America Relative Plate Motion Since 11 Ma

    Bennett, S. E.; Skinner, L. A.; Darin, M. H.; Umhoefer, P. J.; Oskin, M. E.; Dorsey, R. J.

    2013-12-01

    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.

  8. Structure of thinned continental crust across the Orphan Basin from a dense wide-angle seismic profile and gravity data

    Lau, K. W. Helen; Watremez, Louise; Louden, Keith E.; Nedimov?, Mladen R.

    2015-09-01

    We present a 500-km long, 2-D P-wave velocity model across the Orphan Basin, offshore NE Newfoundland, Canada, from Flemish Cap to the Bonavista Platform, formed using refraction and wide-angle reflection data from 89 ocean-bottom seismometers. This layered model builds on a recent traveltime tomography result using additional constraints from coincident multichannel seismic reflection and gravity data plus borehole logs from three wells. The model shows (i) post-rift Tertiary (velocities 1.7-3.5 km s-1) and (ii) both post-rift and syn-rift, Cretaceous and Jurassic sediments (4-5 km s-1), deposited within an eastern and a western sub-basin that are separated by a major basement block. The existence of Jurassic sediments indicates a pre-Cretaceous rifting phase in the eastern sub-basin, and possibly in the western sub-basin. However, there is no evidence that Triassic sediments are widespread across the Orphan Basin. Two upper crustal sublayers and one lower crustal layer are defined by differences in velocities (5.4-6.1, 6.1-6.5 and 6.3-7.1 km s-1, respectively) and vertical velocity gradients (mean = 0.14, 0.10 and 0.05 s-1, respectively). Crustal thinning is asymmetric across the Orphan Basin. Within the eastern sub-basin, continental crust beneath Flemish Cap (32 km thick; ? 1.1) thins westward into a 35-km-wide zone of hyperextended crust ( 3.4) beneath an 11-km-deep sedimentary basin. Within the western sub-basin, the Bonavista Platform crust (32 km thick) thins eastward into a 116-km-wide zone of hyperextended crust. Two zones of thicker crust (? = 2-3.5) exist within the central section, with muted topography within the eastern part and large basement highs in the western part, separated by the eastward dipping White Sail Fault (WSF). The zone to the east of the WSF displays higher velocities in the lower crust than to the west. This can only be explained by a lateral ductile flow across the zone boundary. By combining the two upper crustal sublayers into one, we define the full crustal thicknesses of the upper and lower crusts as 12 and 22 km, respectively. The extension and thinning factors of these two layers are calculated across the basin. Discrepancies between upper crustal thinning and lower crustal thinning are common but only produce a small mass deficit (7 per cent or 1.5 km) in the lower crust. Structural connections are shown between the Rockall Trough and the West Orphan Basin and between the Porcupine Basin and the East Orphan Basin in that a wider hyperextended western basin is paired with a narrower eastern basin by a middle zone of thicker crust. In contrast to the Rockall Trough and the Porcupine Basin, serpentinized mantle is not observed in the East Orphan Basin where hyperextended crust is observed (?max 8.5). One possible cause is that the restricted size of the basin and its location adjacent to Flemish Cap may have permitted a heavier supply of sediment to cover the basement early during its extension. Such a cover would inhibit the flow of water into the crust and thus leave the mantle unchanged.

  9. Temporal Evolution of the Upper Continental Crust: Implications for the Mode of Crustal Growth and the Evolution of the Hydrosphere

    Rud