WorldWideScience
 
 
1

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

DEFF Research Database (Denmark)

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

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

2006-01-01

2

Late Cretaceous (100–89 Ma) magnesian charnockites with adakitic affinities in the Milin area, eastern Gangdese: Partial melting of subducted oceanic crust and implications for crustal growth in southern Tibet  

Science.gov (United States)

Rapid Mesozoic–Early Cenozoic crustal growth in the Gangdese area, southern Tibet, has commonly been attributed to pre-collisional and syn-collisional underplating of mantle-derived magmas. Here, we report on adakitic magnesian charnockites (i.e., hypersthene-bearing diorites and granodiorites) near Milin, in eastern Gangdese, that provide new insights into the crustal growth process of the region. Zircon U–Pb analyses of seven charnockite samples indicate that they were generated in the Late Cretaceous (100–89 Ma). They exhibit variable SiO2 (53.9 to 65.7 wt.%) contents, high Na2O/K2O (1.6 to 14.4) and Sr/Y (27.2 to 138.7) ratios, low Y (6.5 to 18.5 ppm), heavy rare earth element (e.g., Yb = 0.6 to 1.6 ppm) and Th (0.20–2.39 ppm) contents and Th/La (0.02–0.23) ratios, with relatively high Mg# (46 to 56) and MgO (2.0 to 4.5 wt.%) values. They are characterized isotopically by high and slightly variable ?Nd(t) (+ 2.4 to + 4.0) and ?Hf(t) (+ 10.1 to + 15.8) values with relatively low and consistent (87Sr/86Sr)i (0.7042 to 0.7043) ratios. Their pyroxenes have high crystallization temperatures (876 to 949 °C). The Milin charnockites were most probably produced by partial melting of subducted Neo-Tethyan oceanic crust that was followed by adakitic melt–mantle interaction, minor crustal assimilation and fractional crystallization of amphibole + plagioclase. The upwelling asthenosphere, triggered by the roll-back of subducted Neo-Tethyan oceanic lithosphere, provided the heat for slab melting. Therefore, we suggest that, in addition to pre-collisional and syn-collisional underplating of mantle-derived magmas, the recycling of subducted oceanic crust has also played an important role in continental crustal growth in southern Tibet.

Ma, Lin; Wang, Qiang; Wyman, Derek A.; Li, Zheng-Xiang; Jiang, Zi-Qi; Yang, Jin-Hui; Gou, Guo-Ning; Guo, Hai-Feng

2013-08-01

3

Metamorphic processes in subducting oceanic crust  

Energy Technology Data Exchange (ETDEWEB)

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.

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

2000-07-01

4

Chemical remanent magnetization of oceanic crust  

Energy Technology Data Exchange (ETDEWEB)

The effects of chemical remanent magnetization (CRM) of oceanic crust on the anomalous skewness of sea-floor spreading magnetic anomalies are investigated. Considering a realistic constraint that the actual magnetization at anomaly M0 is reversed, the CRM of layer 2A basalts fails to explain the anomalous skewness of the magnetic anomalies. The CRM of the deeper layers does contribute to the anomalous skewness of anomalies 33/34, but the major contribution comes from thermal remanent magnetization.

Verhoef, J. (Bedford Institute of Oceanography, Dartmouth, Nova Scotia (Canada)); Arkani-Hamed, J. (McGill University, Montreal, Quebec (Canada))

1990-10-01

5

New Images Suggest Oceanic Crust Generated from Several Magma Sources  

Science.gov (United States)

... Physics Press Release 05-149New Images Suggest Oceanic Crust Generated from Several Magma ... August 25, 2005 Some of the highest quality images ever taken of the Earth's lower crust reveal that ...

6

Effect of thicker oceanic crust in the Archaean on the growth of continental crust through time  

International Nuclear Information System (INIS)

Present crustal evolution models fail to account for the generation of the large volume of continental crust in the required time intervals. All Archaean plate tectonic models, whether invoking faster spreading rates, similar to today's spreading rates, or longer ridge lengths, essentially propose that continental crust has grown by island arc accretion due to the subduction of oceanic crust. The petrological differences that characterize the Archaean from later terrains result from the subduction of hotter oceanic crust into a hotter mantle. If the oceanic crust was appreciably thicker in the Archaean, as geothermal models would indicate, this thicker crust is surely going to have an effect on tectonic processes. A more valid approach is to compare the possible styles of convergence of thick oceanic crust with modern convergence zones. The best modern analog occurs where thick continental crust is colliding with thick continental crust. Oceanic crustal collision on the scale of the present-day Himalayan continental collision zone may have been a frequent occurrence in the Archaean, resulting in extensive partial melting of the hydrous underthrust oceanic crust to produce voluminous tonalite melts, leaving a depleted stabilized basic residuum. Present-day island arc accretion may not have been the dominant mechanism for the growth of the early Archaean crust.

1987-07-13

7

Continental Crust Growth as a Result of Continental Collision: Ocean Crust Melting and Melt Preservation  

Science.gov (United States)

The significance of the continental crust (CC) on which we live is self-evident. However, our knowledge remains limited on its origin, its way and rate of growth, and how it has acquired the “andesitic” composition from mantle derived magmas. Compared to rocks formed from mantle derived magmas in all tectonic settings, volcanic arc rocks associated with oceanic lithosphere subduction share some common features with the CC; both are relatively depleted in “fluid-insoluble” elements (e.g., Nb, Ta and Ti), but enriched in “fluid-soluble” elements (e.g., U, K and Pb). These chemical characteristics are referred to as the “arc-like signature”, and point to a genetic link between subduction-zone magmatism and CC formation, thus leading to the “island-arc” model widely accepted for the origin of the CC over the past 40 years. However, it has been recognized also that this “island-arc” model has several difficulties. These include (1) bulk arc crust (AC) is basaltic, whereas the bulk CC is andesitic [1]; (2) AC has a variably large Sr excess whereas the CC is Sr deficient [2]; and (3) AC production is mass-balanced by subduction-erosion and sediment recycling, thus contributing no new mass to CC growth, at least in the Phanerozoic [3,4]. Our data on magmatic rocks (both volcanic and intrusive) formed during the India-Asia continental collision (~65 - ~45Ma) [5] show a remarkable compositional similarity to the bulk CC with the typical “arc-like signature” [6]. Also, these syncollisional felsic rocks exhibit strong mantle isotopic signatures, implying that they were recently derived from a mantle source. The petrology and geochemistry of these syncollisional felsic rocks is most consistent with an origin via partial melting of upper oceanic crust (i.e., last fragments of underthrusting oceanic crust) under amphibolite facies conditions, adding net mantle-derived materials to form juvenile CC mass. This leads to the logical and testable hypothesis that continental collision produces and preserves the juvenile crust, and hence maintains net continental growth. References: [1] Gill, Orogenic andesites and plate tectonics, Springer-Verlag, New York., 390 pp, 1981; [2] Niu & O’Hara, Lithos, 112, 1-17, 2009; [3] von Huene & Scholl, Rev. Geophys., 29, 279-316, 1991; [4] Clift & Vannucchi, Rev. Geophys., 42, RG2001., 2004; [5] Mo et al., Chem. Geol., 250, 49-67, 2008; [6] Rudnick & Gao, Treat. Geochem., 3, 1-64, 2003.

Niu, Y.; Zhao, Z.; Zhou, S.; Zhu, D.; Dong, G.; Mo, X.; Xie, G.; Dong, X.

2010-12-01

8

Under the sea: microbial life in volcanic oceanic crust.  

UK PubMed Central (United Kingdom)

Exploration of the microbiology in igneous, 'hard rock' oceanic crust represents a major scientific frontier. The igneous crust harbours the largest aquifer system on Earth, most of which is hydrologically active, resulting in a substantial exchange of fluids, chemicals and microorganisms between oceanic basins and crustal reservoirs. Study of the deep-subsurface biosphere in the igneous crust is technically challenging. However, technologies have improved over the past decade, providing exciting new opportunities for the study of deep-seated marine life, including in situ and cross-disciplinary experimentation in microbiology, geochemistry and hydrogeology. In this Progress article, we describe the recent advances, available technology and remaining challenges in the study of the marine intraterrestrial microbial life that is harboured in igneous oceanic crust.

Edwards KJ; Wheat CG; Sylvan JB

2011-10-01

9

Chemical Evolution of the Oceanic Crust on 103 - 108 Year Timescales  

Science.gov (United States)

The chemical and isotopic composition of mid-ocean ridge basalts (MORB) are widely used to infer the processes of melt generation, melt evolution and eruption at mid-ocean ridges. However, almost all analysed MORB samples analysed to date were collected by dredging from within 1 km of the active spreading centres, and thus represent the very youngest lavas erupted within the neovolcanic zone. These are not necessarily representative of the flows that make up the bulk of the oceanic crust. A more accurate record of the composition of the oceanic crust is provided by samples collected by drilling outside the neovolcanic zone. Drillcore samples can be used to study the chemical evolution of the oceanic crust on 80 My) oceanic crust can be used to test the hypothesis that the average major element composition of Cretaceous MORB was different from that of today, possibly due to changes in mantle potential temperature or 'pollution' of the upper mantle by large-scale 'mantle overturning' events. We will present new major and trace element data, measured using electron microprobe and LA-ICPMS techniques, for more than 360 volcanic glasses from 30 DSDP-ODP-IODP drill sites from the Atlantic (9 sites) and Pacific (21 sites). The age of the oceanic crust at these sites ranges from 6 Ma up to 160-170 Ma, and all sites were drilled in normal oceanic crust far from hotspots. We have analysed exclusively fresh volcanic glasses, because the whole-rock samples used in previous compilations of ancient oceanic crust composition (Humler et al., 1999), may be compromised by alteration and accumulation of phenocrysts, in which case they do not represent melt compositions. For comparison we have compiled a dataset of zero-age MORB glasses from ridges far from hotspots using the PetDB database. After correction for crystal fractionation to either MgO = 8.0 wt. % or Mg# = 72, we find no statistically significant difference between the average major element composition (e.g. Na and Fe) of MORB older than 80 Ma, and young MORB from active spreading centres. Unlike previous studies therefore, we find no evidence for significantly hotter upper mantle beneath spreading centres during the Cretaceous. Work is in progress to compare lavas from ancient Atlantic and Pacific ocean crust in order to see whether differences between slow-spreading and fast-spreading ridges (more MgO-rich more variable for the latter) also existed in the past. Nine of the sites we sampled penetrated more than 100 m into the oceanic crust and we are examining the chemical stratigraphy of individual boreholes in order to test models for crustal accretion (e.g. Hardarson and Fitton, 1997, etc.). Hardarson, B.S., and Fitton, J.G., 1997, Geology, v. 25, no. 11, p. 1043-1046. Humler, E., Langmuir, C.H., and Daux, V., 1999, Earth and Planetary Science Letters, v. 173, no. 1-2, p. 7-23.

Brandl, P. A.; Regelous, M.; Beier, C.; Haase, K. M.

2011-12-01

10

Experimental Constraints on Recycling of Potassium from Subducted Oceanic Crust  

UK PubMed Central (United Kingdom)

Petrological experiments on oceanic crust samples characterize the recycling of potassium from mid-ocean ridge basalts and sediments. Metasomatism could develop directly and continuously from subducted potassium-bearing crust from shallow levels to a maximum depth of 300 kilometers. Phengite (a potassium-rich mica) is the principal potassium host at subsolidus conditions. It transports potassium and water to depths of up to 300 kilometers and could yield over the entire depth range potassium-rich fluids or melts (depending on the specific geotherm), which are likely to constitute one of the primary metasomatic agents for generation of calc-alkaline magmas.

Schmidt MW

1996-06-01

11

Experimental Constraints on Recycling of Potassium from Subducted Oceanic Crust  

Science.gov (United States)

Petrological experiments on oceanic crust samples characterize the recycling of potassium from mid-ocean ridge basalts and sediments. Metasomatism could develop directly and continuously from subducted potassium-bearing crust from shallow levels to a maximum depth of 300 kilometers. Phengite (a potassium-rich mica) is the principal potassium host at subsolidus conditions. It transports potassium and water to depths of up to 300 kilometers and could yield over the entire depth range potassium-rich fluids or melts (depending on the specific geotherm), which are likely to constitute one of the primary metasomatic agents for generation of calc-alkaline magmas. PMID:8662494

Schmidt

1996-06-28

12

Variation of young oceanic crust and upper mantle structure  

International Nuclear Information System (INIS)

[en] Seismic refraction and single-channel reflection data taken along 0.5-, 2.5-, and 4.5-m.y.-age isochrons near the East Pacific Rise during Project ROSE are used to determine if a systematic change in the P velocity-depth function with age can be resolved. Inversion of these data suggests that any change in crustal P velocity structure related to age is smaller than variability in the seismic velocity-depth function along an isochron. The emergence of a 'normal' crust-mantle transition by 4.5-m.y.-age is seen in these data. Crust and crust-mantle transition zone heterogeneity along these isochrons may be related to the along strike variability in processes at the ridge crest. The velocity-depth functions for the threee split profile refractions lines are compared with velocity-depth functions for the Samail ophiolite, which is thought to represent oceanic crust of similar age. The velocity-depth functions for the ROSE data are bounded by different velocity-depth models for the Samail ophiolite; this suggests that those models are not in disagreement but represent the lateral heterogeneity that can be expected in young oceanic crust

1982-10-10

13

Titanium: A Tracer of Mafic Crust in Ocean Island Basalts?  

Science.gov (United States)

The recycling of mafic oceanic crust and its re-sampling in ocean island basalts (OIB) is a long-standing notion (e.g., 1). However, arguments based on trace element ratios and long-lived isotopic measurements fall prey to the uncertain make-up of the mantle source, time-integration and other added 'flavours' the OIB source may contain. Accordingly, the paradigm of crustal recycling continues to be debated (e.g., 2,3). With the advent of large online geochemical databases such as PetDB and GEOROC, major elements are yielding new insight to mantle melting processes. I review why the high field strength elements (HFSE) and titanium in particular appear to be a unique tracers of mafic oceanic crust in the source of ocean island basalts (e.g., 4). I will further explore the use of simple Ti abundances combined with other geochemical parameters in a well-characterised OIB suite from Pico, Azores to estimate the amount of recycled crust in the source. 1. Hofmann and White, 1982; 2. Niu and O'Hara, 2003; 3. Pilet et al. 2008; 4. Prytulak and Elliott, 2007

Prytulak, J.; Elliott, T.

2008-12-01

14

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

Science.gov (United States)

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, ?7Li) 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.

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

2013-04-01

15

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

Science.gov (United States)

...Zones: Neptune Deep Water Port, Atlantic Ocean, Boston, MA AGENCY: Coast Guard...Deepwater Port located in the Atlantic Ocean off of Boston, Massachusetts...titled: Neptune Deep Water Port, Atlantic Ocean, Boston, MA; Final Rule...

2010-06-21

16

Purtuniq ophiolite, Cape Smith belt, northern Quebec, Canada: A reconstructed section of Early Proterozoic oceanic crust  

Science.gov (United States)

The crustal part of a dismembered ophiolite is preserved in the structurally highest thrust sheets of the Early Proterozoic Cape Smith belt in northern Quebec, Canada. The rocks of the ophiolite represent two magmatic suites, each with a mantle source that is Nd isotopically distinct. The older suite comprises pillowed and massive volcanic rocks, sheeted dikes, dominantly gabbroic layered cumulate rocks, and rare plagiogranite sills and dikes in the volcanic sequence. This >5-km-thick tholeiitic suite is ca. 1998 Ma, and is compositionally and petrographically similar to rocks formed at modern oceanic spreading ridges. The younger suite (>4 km) comprises sheeted mafic dikes and layered ultramafic to mafic cumulate rocks that are similar to tholeiitic rocks found in modern plume- generated oceanic islands, such as Hawaii. The composite section is in excess of 9 km. Although the total thickness of the Purtuniq ophiolite may not be typical of that for oceanic crust formed at Early Proterozoic spreading ridges elsewhere, it does suggest that ancient ridge-formed crust was at least as thick as that in modern oceans.

Scott, D. J.; Helmstaedt, H.; Bickle, M. J.

1992-02-01

17

Relict 1.4 Ga oceanic crust in the Zambezi Valley, northern Zimbabwe: Evidence for Mesoproterozoic supercontinental fragmentation  

Science.gov (United States)

The Archean cratons of southern Africa are separated from one another by younger orogenic belts. It is widely believed that these deformation belts developed entirely within continental crust, but in the Zambezi belt of northern Zimbabwe, relict oceanic crust, i.e., ophiolite, has now been discovered. The zircon age of a plagiogranite dike within the ophiolite—1393 ± 22 Ma—makes this the oldest dated remnant of oceanic crust in Africa. Presence of the ophiolite is direct evidence for the rifting and/or assembly of continental fragments within Africa. The age of the ophiolite is consistent with its being a remnant of sea floor formed during the episode of continental fragmentation that immediately preceded the Grenville orogeny, the global event that marked the coalescence of the Late Proterozoic supercontinent of Rodinia.

Oliver, G. J. H.; Johnson, S. P.; Williams, I. S.; Herd, D. A.

1998-06-01

18

Magnetism of the oceanic crust: Evidence from ophiolite complexes  

Energy Technology Data Exchange (ETDEWEB)

The magnetic properties of six ophiolite complexes from around the world, ranging in age from Jurassic to Miocene, are presented. An emphasis is placed in our study on the petrologic and isotopic data from these ophiolite complexes in order to determine first whether the rock samples presently available represent the pristine ocean crust or whether they have been altered subaerially since their formation. Five of the ophiolites are found to be acceptable, and the conclusion is overwhelmingly in favor of a marine magnetic source layer that includes not only the pillow lavas but also the underlying dikes and gabbro. At the moment, however, our observations do not suggest that the magnetic contributions of the basaltic dikes should be overlooked in favor of gabbro. A second important conclusion is that nearly pure magnetite could indeed be a magnetic carrier which contributes to marine magnetic anomanies. It only awaits discovery by deeper ocean crustal penetration by future Deep Sea Drilling Project legs.

Banerjee, S.K.

1980-07-10

19

Fluid flow in ocean crust cools the Cascadia subduction zone  

Science.gov (United States)

Temperatures along subduction zone plate boundary faults have been used to estimate the area and extent of the seismogenic zone. Recent studies of the well-constrained Nankai margin of Japan show that hydrothermal circulation in the subducting crust cools the subduction zone and widens the area of the plate boundary fault that is between the key temperatures of 150 and 350 °C. Here, we present new thermal models for the Cascadia subduction zone that include the effects of fluid flow in the subducting crust. This fluid circulation cools the subduction zone and widens the thermally-defined seismogenic zone by shifting the intersection of 350 °C with the plate boundary fault ˜35-50 km landward. Temperatures in the region of episodic tremor and slip are ~350-450 °C, ˜100 °C cooler than based on estimates that do not include fluid circulation. In contrast to the Nankai margin, the observed surface heat flux pattern for the thickly sedimented Cascadia margin provides only a weak constraint on subduction zone temperature. We use the tomographically-defined basalt-to-eclogite transition in the subducting slab as an additional constraint on the Cascadia subduction zone thermal models. The model most consistent with both the slab alteration observations and surface heat flux measurements includes moderate to vigorous fluid flow in an ocean crust aquifer with permeability ~10-10 to 10-9 m2, consistent with previous observations and inferences.

Cozzens, B. D.; Spinelli, G. A.

2010-12-01

20

Boron isotope geochemistry of the oceanic crust from DSDP/ODP Hole 504B  

Energy Technology Data Exchange (ETDEWEB)

Boron contents and boron isotopic compositions were determined for the uppermost 1.3 km section of typical 6.2 Ma oceanic crust from DSDP/ODP Hole 504B, Costa Rica Rift, Galapagos Spreading Center. Both the boron content and the {delta}{sup 11}B value in the oceanic crust are controlled by two types of alteration: (1) low-temperature alteration (0 to 60C; Zones 1 and 2) and (2) high-temperature hydrothermal alteration (200 to 400C; Zones 3 and 4). Basalts subjected to the low-temperature alteration are characterized by their relatively high boron contents (0.69 to 19.3 ppm) and high {delta}{sup 11}B values (+2.2 to +10.6{per thousand}), indicating uptake of boron into secondary phases in equilibrium with seawater or evolved seawater. Hydrothermally altered basalts contain less abundant boron (0.17 to 0.52 ppm) and relatively constant {delta}{sup 11}B values ({minus}0.1 to +1.0{per thousand}). Although basalts from the upper part of these hydrothermal zones (< 1,300 mbsf) show equilibrated boron content and {delta}{sup 11}B value with aqueous fluid, effective leaching of boron from basalt is predominant in the lower part (> 1,300 mbsf). Original boron content and {delta}{sup 11}B value of the Hole 504B MORB were 0.35 ppm and +0.2{per thousand}, respectively. The present data provide fundamental information in understanding of the distribution of boron and boron isotopes in the oceanic crust.

Ishikawa, Tsuyoshi; Nakamura, Eizo (Okayama Univ., Tottori (Japan))

1992-04-01

 
 
 
 
21

Subducting oceanic crust: The source of deep diamonds  

Science.gov (United States)

Inclusions of majoritic garnet in diamonds from the Jagersfontein kimberlite formed at unusually great depths of ˜250 to >500 km in the asthenosphere and transition zone. The original host rocks were derived from a much shallower, basaltic (eclogitic) source. The presence of negative Eu anomalies in all majoritic garnets requires a crustal origin, thereby linking these very deep diamond sources to subducting oceanic crust. The carbon isotope values (?13C) of the host diamonds fall within a narrow range at ˜-20‰, which is fundamentally different from the broad range (-24‰ to -2‰) and bimodal distribution of carbon isotopes of Jagersfontein diamonds that formed in the shallower lithosphere. This indicates that majoritic garnet-bearing diamonds at Jagersfontein inherited their light carbon isotopic composition directly from organic matter contained in a subducting slab. These diamonds were likely formed by direct conversion from graphite, well within the diamond stability field.

Tappert, Ralf; Stachel, Thomas; Harris, Jeff W.; Muehlenbachs, Karlis; Ludwig, Thomas; Brey, Gerhard P.

2005-07-01

22

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

Science.gov (United States)

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 ?11B 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.

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

2013-04-01

23

Petrology of Alarcon Rise lavas, Gulf of California: Nascent intracontinental ocean crust  

Science.gov (United States)

The Alarcon Basin in the southern Gulf of California originated by intracontinental rifting of the southwestern margin of North America and has evolved into an intercontinental ocean basin by 3.7 m.y. of seafloor spreading. Lava samples collected on the axial ridge along Alarcon Rise, two of the many near-axis seamounts on the northwest flank of the rise, and an abyssal hill on 0.6 Ma crust on the southeast flank were examined petrographically and analyzed for major and trace element and He-Sr-Nd-Pb isotope composition. Most samples are typical mid-ocean ridge basalt (MORB), but rocks at the axial ridge site closest to continent are more differentiated. Rocks from the axial ridge and abyssal hill are genetically related through separate episodes of fractional crystallization. Seamount samples are relatively more primitive than seafloor samples and may have been formed by smaller degree of melting of the same mantle source as the seafloor lavas. Tamayo transform fault has no apparent effect on the geochemistry of axial ridge lavas erupted close to it; this is contrary to the postulated transform fault effect. Alarcon Basin differs from the Salton Trough and Guaymas Basin in that its youngest seafloor shows no evidence for contamination with continental crust or a subduction component. We propose that Pacific MORB source mantle underlies the Gulf of California because the western North American margin has overridden the Pacific suboceanic mantle. Miocene rifting and Pliocene spreading in Alarcon Basin have created a window allowing the most recent MORB melts to rise uncontaminated to the surface.

Castillo, P. R.; Hawkins, J. W.; Lonsdale, P. F.; Hilton, D. R.; Shaw, A. M.; Glascock, M. D.

2002-10-01

24

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

Directory of Open Access Journals (Sweden)

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.

David A. Foster; Ben D. Goscombe

2013-01-01

25

The Red Sea analog for the early Gulf of Mexico: Salt basins on oceanic crust  

Energy Technology Data Exchange (ETDEWEB)

New geophysical data from the Red Sea and the Gulf of Mexico support the concept that the early Gulf closely resembled the modern Red Sea. Oceanic crust like that now forming along the axis of the Red Sea basin may underlie much of the continental slope offshore Louisiana and Texas. Original depositional thicknesses greater than 4 km characterize both salt depocenters. The thickest salt overlies oceanic crust, probably for isostatic reasons. Deep crustal detachment faulting in a simple shear model with ductile flow below 15 km and narrow zones (up to 50 km) of severely extended crust on the hanging wall characterizes the early tectonic development. The landward edge of thick (> 2--4 km) salt generally follows the edge of oceanic crust, but the seaward edge is localized by depositional factors, modified by subsequent gravity spreading.

Hall, D.J. [Excalibur Interpretation Co., Houston, TX (United States)

1996-12-31

26

Distribution of oceanic versus transitional crust in deep Gulf of Mexico Basin - implications for early history  

Energy Technology Data Exchange (ETDEWEB)

Regional studies of seismic reflection and refraction data in the deep Gulf of Mexico basin outline in considerable detail the distribution of oceanic vs. transitional crust. Oceanic crust forms a narrow east-west belt up to 300 km wide across the deep Gulf. Most current models for early Gulf evolution suggest the belt was emplaced in the Late Jurassic following widespread deposition of salt on rifted and attenuated continental crust (transitional crust). The southern boundary is defined by a zone of prominent salt structures along the northern margin of the Sigsbee salt basin. The northern boundary is obscured below the Texas-Louisiana slope, but is inferred from the distribution of large vertical salt structures. The eastern boundary is clearly marked by onlap and pinch-out of thick Jurassic sedimentary sequences. This distribution is corroborated by regional magnetic and gravity data and total tectonic subsidence analysis, and provides constraints for early Gulf basin reconstructions. An appropriate reconstruction must account for plate motion accommodated by ocean crust formation and extension of continental crust. The data seem most consistent with a model in which the Yucatan block moved generally south and rotated somewhat counterclockwise. This reconstruction implies very little lateral displacement along transform faults between Yucatan and Florida during early basin history. This is supported by seismic stratigraphic studies and DSDP drilling in the southeastern Gulf.

Buffler, R.T.; Sawyer, D.S.

1985-02-01

27

The earth's crust of oceans from seismic data  

Energy Technology Data Exchange (ETDEWEB)

A survey is made of modern concepts regarding the seismic stratification of the upper lithosphere of oceans: the questions is examined of the probable nature of zones of reduced velocity of seismic waves isolated from deep seismic sounding observations in 1970-1975 at depths from 2 to 20 km below the bottom of the ocean. A critical evaluation is made of the data on anistropy of velocity of seismic waves in the earth's crust, coefficient of seismic turbidity of the medium, link between the velocity of seismic waves and the age of the crust blocks, determined by the spreading hypothesis. Results are analyzed from the first oceanological deep seismic soundings and basic reasons are examined which cause the development of erroneous evaluation of the structure of the upper lithosphere regarding the thin earth's crust primarily of a basalt composition. Recommendations are made for the direction of deep seismic sounding studies in the oceans.

Bulin, N.K.

1981-01-01

28

Evidence for mantle metasomatism by hydrous silicic melts derived from subducted oceanic crust.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The low concentrations of niobium, tantalum and titanium observed in island-arc basalts are thought to result from modification of the sub-arc mantle by a metasomatic agent, deficient in these elements, that originates from within the subducted oceanic crust 1. Whether this agent is an hydrous fluid...

Prouteau, Gaëlle; Scaillet, Bruno; Pichavant, Michel; Maury, René

29

Deep mantle cycling of oceanic crust: evidence from diamonds and their mineral inclusions.  

UK PubMed Central (United Kingdom)

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

Walter MJ; Kohn SC; Araujo D; Bulanova GP; Smith CB; Gaillou E; Wang J; Steele A; Shirey SB

2011-10-01

30

The role of black smokers in the Cu mass balance of the oceanic crust  

Science.gov (United States)

Seafloor hydrothermal systems play an important role in the metal budgets of the oceans via hydrothermal plumes, accumulation of seafloor massive sulfide deposits, and alteration of the oceanic crust. These processes have resulted in large-scale metal anomalies on the Pacific plate, most notably at the Nazca–Pacific plate boundary. This plate-scale variability in metal deposition has important implications for the fluxes of metals to subduction zones and possibly the metal endowment of arc-related mineral deposits. However, the relative contributions to the metal budget from black smokers, deep-sea sediments, Mn nodules and altered crust remain unclear. The Cu contents of more than 10,000 samples of seafloor massive sulfide deposits, subseafloor stockwork mineralization, nodules and sediments reveal that most of the Cu metal originally mobilized by high-temperature hydrothermal convection at the ridges is retained in the crust as subseafloor alteration and mineralization, never reaching the seafloor. This metal accounts for at least 80% of the labile Cu that may be released to subduction fluids driven off a down-going slab. Copper deposited in deep-sea sediments, which account for 17% of the total budget, is derived in part from plume fallout associated with ridge-crest hydrothermal activity but also from pelagic deposition of marine organic matter enriched in Cu metal. Massive sulfide deposits, nodules and manganiferous crusts account for only ˜3% of the Cu metal of the subducting slab.

Hannington, Mark D.

2013-07-01

31

Closure of western Pacific marginal basins: Rupture of the oceanic crust and the emplacement of ophiolites  

Science.gov (United States)

Most of the marginal basins of the western Pacific region opened in Cenozoic time and many of these are presently closing. Late Cenozoic basin closing has been documented in the recently drilled Celebes and Sulu seas (Ocean Drilling Program leg 124) and in the Japan Sea ?leg 127). The oceanic floors of these young marginal basins were deformed locally before being actively consumed along young subduction zones, with parts of their sedimentary section and crust incorporated into accretionary wedges. The youngest parts of these basins are the first to be deformed, to subduct, or to be incorporated in these accretionary wedges. The initial flexural stage affecting the crust before rupture appears to be a local process.

Rangin, Claude; Silver, Eli A.; Tamaki, Kensaku

32

Seismic evidence for high pore pressures in the oceanic crust: Implications for fluid-related embrittlement  

Science.gov (United States)

estimated the P wave velocity structure of the crust of the subducting Pacific plate beneath northeast Japan using arrival time data of P-to-S-converted waves. The results show that the P wave velocity of the subducting crust varies along the arc and increases abruptly at a depth of ~100 km, from 6.5-7.0 km/s in the fore arc to 7.5-8.5 km/s in the back arc. The P wave velocity in the fore arc is ~10% lower than theoretically expected values for the metamorphosed mid-ocean ridge basalt material. Seismicity in the subducting crust is most active at depths of 70-80 km where P wave velocities are lowest. The marked reduction of P wave velocity suggests the coexistence of aqueous fluids with hydrous minerals. Abundant fluids elevate pore fluid pressures and reduce effective normal stress, promoting intensive seismic activity in the low-velocity crust. Our observations provide seismic evidence that earthquakes in the subducting crust are facilitated by fluid-related embrittlement.

Shiina, Takahiro; Nakajima, Junichi; Matsuzawa, Toru

2013-05-01

33

Lateral continuity of basement seismic reflections in 15 Ma ultrafast-spreading crust at ODP Site 1256  

Science.gov (United States)

The Ocean Drilling Program (ODP) initiated drilling at Site 1256D in the Guatemala Basin, about 1,000 km off the East Pacific Rise to penetrate plutonic rocks, anticipated to be relatively shallow in this region, formed at an ultra-fast spreading rate. IODP Expedition E312 successfully drilled into gabbros at ~1,150 m in basement. Multi-channel seismic traces show weak laterally coherent sub-basement reflections at borehole depths. Synthetic reflectivity seismograms were computed using a Ricker wavelet and impedance profiles from borehole sonic logs. These seismograms show significant sub-basement amplitude peaks. A zero-offset vertical seismic profile, shot on E312, was processed to investigate the authenticity of these reflections and their relationship to borehole geology. A dual scheme of the median filtering and F-K dip filtering was used. Tests with synthetic seismograms indicate the approach is effective at reasonable SNR levels. Downgoing energy is clearly identified but negligible upgoing energy is visible over random noise. These results indicate that lava flows and igneous contacts in upper ocean crust have significant topography on lateral scales less than the Fresnel Zone (~300 m) due to igneous and tectonic processes.

Nag, Sreeja; Swift, Stephen A.

2011-09-01

34

Hydrous magmatism triggered by assimilation of hydrothermally altered rocks in fossil oceanic crust (northern Oman ophiolite)  

Science.gov (United States)

Mid-ocean ridges magmatism is, by and large, considered to be mostly dry. Nevertheless, numerous works in the last decade have shown that a hydrous component is likely to be involved in ocean ridges magmas genesis and/or evolution. The petrology and geochemistry of peculiar coarse grained gabbros sampled in the upper part of the gabbroic sequence from the northern Oman ophiolite (Wadi Rajmi) provide information on the origin and fate of hydrous melts in fast-spreading oceanic settings. Uncommon crystallization sequences for oceanic settings (clinopyroxene crystallizing before plagioclase), extreme mineral compositions (plagioclase An% up to 99, and clinopyroxene Mg # up to 96), and the presence of magmatic amphibole, imply the presence of a high water activity during crystallization. Various petrological and geochemical constraints point to hydration, resulting from the recycling of hydrothermal fluids. This recycling event may have occurred at the top of the axial magma chamber where assimilation of anatectic hydrous melts is recurrent along mid-ocean ridges or close to segments ends where fresh magma intrudes previously hydrothermally altered crust. In ophiolitic settings, hydration and remelting of hydrothermally altered rocks producing hydrous melts may also occur during the obduction process. Although dry magmatism dominates oceanic magmatism, the dynamic behavior of fast-spreading ocean ridge magma chambers has the potential to produce the observed hydrous melts (either in ophiolites or at spreading centers), which are thus part of the general mid-ocean ridges lineage.

France, Lydéric; Ildefonse, Benoit; Koepke, Juergen

2013-08-01

35

Osmium isotope variations in the oceans recorded by Fe-Mn crusts  

Science.gov (United States)

This study presents osmium (Os) isotope data for recent growth surfaces of hydrogenetic ferromanganese (Fe-Mn) crusts from the Pacific, Atlantic and Indian Oceans. In general, these data indicate a relatively uniform Os isotopic composition for modern seawater, but suggest that North Atlantic seawater is slightly more radiogenic than that of the Pacific and Indian Oceans. The systematic difference in the Os isotopic composition between the major oceans probably reflects a greater input of old continental material with a high Re/Os ratio in the North Atlantic Ocean, consistent with the distribution of Nd and Pb isotopes. This spatial variation in the Os isotope composition in seawater is consistent with a residence time for Os of between 2 and 60 kyr. Indian Ocean samples show no evidence of a local source of radiogenic Os, which suggests that the present-day riverine input from the Himalaya-Tibet region is not a major source for Os. Recently formed Fe-Mn crusts from the TAG hydrothermal field in the North Atlantic yield an Os isotopic composition close to that of modern seawater, which indicates that, in this area, the input of unradiogenic Os from the hydrothermal alteration of oceanic crust is small. However, some samples from the deep Pacific (???4 km) possess a remarkably unradiogenic Os isotope composition (187Os/186Os ratios as low as 4.3). The compositional control of Os incorporation into the crusts and mixing relationships suggest that this unradiogenic composition is most likely due to the direct incorporation of micrometeoritic or abyssal peridotite particles, rather than indicating the presence of an unradiogenic deep-water mass. Moreover, this unradiogenic signal appears to be temporary, and local, and has had little apparent effect on the overall evolution of seawater. These results confirm that input of continental material through erosion is the dominant source of Os in seawater, but it is not clear whether global Os variations are due to the input of mantle or meteoritic material, or simply indicate that the continental source itself is not uniform.

Burton, K. W.; Bourdon, B.; Birck, J. -L.; Allegre, C. J.; Hein, J. R.

1999-01-01

36

Seismic structure of the crust and uppermost mantle of South America and surrounding oceanic basins  

Science.gov (United States)

We present a new set of contour maps of the seismic structure of South America and the surrounding ocean basins. These maps include new data, helping to constrain crustal thickness, whole-crustal average P-wave and S-wave velocity, and the seismic velocity of the uppermost mantle (Pn and Sn). We find that: (1) The weighted average thickness of the crust under South America is 38.17 km (standard deviation, s.d. ±8.7 km), which is ˜1 km thinner than the global average of 39.2 km (s.d. ±8.5 km) for continental crust. (2) Histograms of whole-crustal P-wave velocities for the South American crust are bi-modal, with the lower peak occurring for crust that appears to be missing a high-velocity (6.9-7.3 km/s) lower crustal layer. (3) The average P-wave velocity of the crystalline crust (Pcc) is 6.47 km/s (s.d. ±0.25 km/s). This is essentially identical to the global average of 6.45 km/s. (4) The average Pn velocity beneath South America is 8.00 km/s (s.d. ±0.23 km/s), slightly lower than the global average of 8.07 km/s. (5) A region across northern Chile and northeast Argentina has anomalously low P- and S-wave velocities in the crust. Geographically, this corresponds to the shallowly-subducted portion of the Nazca plate (the Pampean flat slab first described by Isacks et al., 1968), which is also a region of crustal extension. (6) The thick crust of the Brazilian craton appears to extend into Venezuela and Colombia. (7) The crust in the Amazon basin and along the western edge of the Brazilian craton may be thinned by extension. (8) The average crustal P-wave velocity under the eastern Pacific seafloor is higher than under the western Atlantic seafloor, most likely due to the thicker sediment layer on the older Atlantic seafloor.

Chulick, Gary S.; Detweiler, Shane; Mooney, Walter D.

2013-03-01

37

Lower crustal variability and the crust/mantle transition at the Atlantis Massif oceanic core complex  

Science.gov (United States)

Seismic refraction data provide new constraints on the structure of the lower oceanic crust and its variability across the Atlantis Massif oceanic core complex, ˜30°N on the Mid-Atlantic Ridge. A 40 km-long spreading-parallel profile constrains P-wave velocities to depths of up to ˜7 km beneath the seafloor. Two shorter spreading-perpendicular lines provide coverage to ˜2 km depth. The anomalous character of the massif's central dome crust is clear compared to the neighboring rift valley and similar-age crust on the opposite ridge flank. The domal core of the massif, unroofed via detachment faulting, has velocities >7.0 km/s at depths below ˜2.5 km sub-seafloor, increasing to 7.5-7.8 km/s over the depth range 4.8-6.8 km. Within the core complex, the Moho does not appear to be sharp as no PmP arrivals are observed. Within the axial valley, velocities do not reach mantle-transition zone values in the uppermost 6 km. We infer that crust there is of normal thickness but that a thinner than average mafic section is present in the central massif. Near IODP Hole U1309D, located on the central dome, there is a low velocity gradient interval at 1-3 km depth with velocities of 6.6-6.8 km/s, that coincides with a 3-5 km wide region where shallower velocities are highest. Given the predominantly gabbroic section recovered from the 1.4 km deep drillhole, this seismic structure suggests that the mafic body extends a few km both laterally and vertically.

Blackman, Donna K.; Collins, John A.

2010-12-01

38

Calcium carbonate veins in ocean crust record a threefold increase of seawater Mg/Ca in the past 30 million years  

Science.gov (United States)

Chemical (Sr, Mg) and isotopic (?18O, 87Sr/86Sr) compositions of calcium carbonate veins (CCV) in the oceanic basement were determined to reconstruct changes in Sr/Ca and Mg/Ca of seawater in the Cenozoic. We examined CCV from 10 basement drill sites in the Atlantic and Pacific, ranging in age between 165 and 2.3 Ma. Six of these sites are from cold ridge flanks in basement mmol/mol) and Mg/Ca (1.12-2.03 mol/mol) between 165 and 30 Ma was followed by a steady increase in Mg/Ca ratios by a factor of three to modern ocean composition. Mg/Ca-Sr/Ca relations suggest that variations in hydrothermal fluxes and riverine input are likely causes driving the seawater compositional changes. However, additional forcing may be involved in explaining the timing and magnitude of changes. A plausible scenario is intensified carbonate production due to increased alkalinity input to the oceans from silicate weathering, which in turn is a result of subduction-zone recycling of CO2 from pelagic carbonate formed after the Cretaceous slow-down in ocean crust production rate.

Rausch, Svenja; Böhm, Florian; Bach, Wolfgang; Klügel, Andreas; Eisenhauer, Anton

2013-01-01

39

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

Science.gov (United States)

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

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

2011-08-01

40

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

International Nuclear Information System (INIS)

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

2001-01-01

 
 
 
 
41

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

UK PubMed Central (United Kingdom)

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.

Audet P; Bostock MG; Christensen NI; Peacock SM

2009-01-01

42

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

DEFF Research Database (Denmark)

The Ediacaran appearance of large animals, including motile bilaterians, is commonly hypothesized to reflect a physiologically enabling increase in atmospheric and oceanic oxygen abundances (pO2). To date, direct evidence for low oxygen in pre-Ediacaran oceans has focused on chemical signatures in the rock record that reflect conditions in local basins, but this approach is both biased to constrain only shallower basins and statistically limited when we seek to follow the evolution of mean ocean chemical state through time. Because the abundance and isotopic composition of molybdenum (Mo) in organic-rich euxinic sediments can vary in response to changes in global redox conditions, Mo geochemistry provides independent constraints on the global evolution of well-oxygenated environments. Here, we establish a theoretical framework to access global marine Mo cycle in the past from the abundance and isotope composition of ancient seawater. Further, we investigate the ~ 750 Ma Walcott Member of the Chuar Group, Grand Canyon, which accumulated in a rift basin with open connection to the ocean. Iron speciation data from upper Walcott shales indicate that local bottom waters were anoxic and sulfidic, consistent with their high organic content (up to 20 wt.%). Similar facies in Phanerozoic successions contain high concentrations of redox-sensitive metals, but in the Walcott Member, abundances of Mo and U, as well as Mo/TOC (~ 0.5 ppm/wt.%) are low. d98Mo values also fall well below modern equivalents (0.99 ± 0.13‰ versus ~ 2.35‰ today). These signatures are consistent with model predictions where sulfidic waters cover ~ 1–4% of the global continental shelf area, corresponding to a ~ 400–800 fold increase compared to the modern ocean. Therefore, our results suggest globally expansive sulfidic water masses in mid-Neoproterozoic oceans, bridging a nearly 700 million-year gap in previous Mo data. We propose that anoxic and sulfidic (euxinic) conditions governed Mo cycling in the oceans even as ferruginous subsurface waters re-appeared 800–750 Ma, and we interpret this anoxic ocean state to reflect a markedly lower atmospheric and oceanic O2 level, consistent with the hypothesis that pO2 acted as an evolutionary barrier to the emergence of large motile bilaterian animals prior to the Ediacaran Period.

Dahl, Tais Wittchen; Canfield, Donald Eugene

2011-01-01

43

Depleted Peridotites of Macquarie Island, an Uplifted Section of In-situ Oceanic Crust  

Science.gov (United States)

Macquarie Island, located 1500 km southeast of southernmost Australia, is thought be the sole complete section of ocean crust uplifted in the ocean basin in which it formed. It is an exposure of the Macquarie Ridge complex, which marks the modern Australian-Pacific plate boundary. The oceanic crust of the island formed in the final stages of spreading, ~6 mya, as indicated by Ar-Ar plateau ages of basaltic glass. Geometries of marine faults on the island suggest that it formed near the intersection of a ridge and a transform. At this latitude, the plate boundary evolved from a spreading ridge to a transpressional boundary between ~33 and ~6 mya, thus the rocks of the island record an interesting tectonic history and may provide clues to the mantle process during a major plate motion re-organization. Residual, plagioclase-free mantle peridotite samples were collected along transects through all of the mantle sections on the island, with an average of 100 meter spacing between samples. Orthopyroxenes, clinopyroxenes and chrome spinels were analysed by electron microprobe. Spinel chrome numbers (Cr-nr) ranged from 0.39 to 0.46 (n=23), which corresponds to 15-16% fractional melting applying the empirical melting equation of Hellebrand et al (2001). Their low Ti contents (0.02-0.07) attest to the residual nature of the Macquarie Island peridotites. Cpx is preserved in only 7 samples (alteration, depletion), and occurs mainly as small interstitial grains or as exsolved blebs in opx porphyroclasts. Cpx titanium (0.00 - 0.04 wt% TiO2) and sodium (0.00 - 0.05 wt% Na2O) contents are extremely low, confirming the high depletion and supporting highly efficient melt extraction. Opx porphyroclast cores have very high Mg-nr (0.92 on average). Spreading rates at the time of formation of the Macquarie Island crust have been calculated to be 30mm/yr (full) which is considered "slow". However, the levels of depletion indicated by the spinel Cr-nr and Ti and Na contents of cpx of the Macquarie Island peridotites are more similar to those seen at fast spreading centers or ophiolites. This depletion could be caused by the progressively changing spreading direction disrupts mixing in the mantle, causing repeated melting of the same mantle source or biased sampling in the existing abyssal peridotite database. Further analyses of peridotites and associated basalts will test which model is most likely. Hellebrand et al., (2001) Nature 410, 677-681.

Wertz, K.; Snow, J. E.; Hellebrand, E.; von der Handt, A.; Mosher, S.

2002-12-01

44

The deep subsurface biosphere in igneous ocean crust: frontier habitats for microbiological exploration.  

UK PubMed Central (United Kingdom)

We discuss ridge flank environments in the ocean crust as habitats for 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. We describe the nature of selected ridge flank crustal 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. We present a brief overview of subseafloor conditions, within the context of these three characteristics, for five field sites where microbial studies have been done, are underway, or have been proposed. Technical challenges remain and likely will limit progress in studies of microbial ridge flank 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 such that as presented in this paper, perhaps including alternative or additional physical or chemical characteristics, is essential for achieving the greatest benefit from multidisciplinary microbial investigations of oceanic ridge flanks.

Edwards KJ; Fisher AT; Wheat CG

2012-01-01

45

Mapping tectonic deformation in the crust and upper mantle beneath Europe and the North Atlantic Ocean.  

Science.gov (United States)

We constructed a three-dimensional azimuthally anisotropic model of Europe and the North Atlantic Ocean based on adjoint seismic tomography. Several features are well correlated with historical tectonic events in this region, such as extension along the North Atlantic Ridge, trench retreat in the Mediterranean, and counterclockwise rotation of the Anatolian Plate. Beneath northeastern Europe, the direction of the fast anisotropic axis follows trends of ancient rift systems older than 350 million years, suggesting "frozen-in" anisotropy related to the formation of the craton. Local anisotropic strength profiles identify the brittle-ductile transitions in lithospheric strength. In continental regions, these profiles also identify the lower crust, characterized by ductile flow. The observed anisotropic fabric is generally consistent with the current surface strain rate measured by geodetic surveys. PMID:23929947

Zhu, Hejun; Tromp, Jeroen

2013-08-08

46

Seismic reflection character of the Cameroon volcanic line: Evidence for uplifted oceanic crust  

Energy Technology Data Exchange (ETDEWEB)

Deep-imaging multifold seismic lines across submarine parts of the Cameroon volcanic line (west Africa-Gulf of Guinea) show asymmetric uplift of oceanic crust associated with extensive magmatism. The main pulse of uplift occurred after creation of a regional sequence boundary believed to be Miocene in age. The apparent synchroneity of uplift argues against the Cameroon line being a simple hotspot trace, as previously inferred. One plausible theory of origin for the seaward part of the Cameroon volcanic line and its asymmetric uplift geometry combines regional asthenospheric upwelling with restriction of magmatic egress to regularly spaced weak spots, corresponding to fracture-zone crossings. Horizontal motion and buckling also may have occurred along the Cameroon volcanic line.

Meyers, J.B.; Rosendahl, B.R. (Univ. of Miami, FL (United States))

1991-11-01

47

Mapping tectonic deformation in the crust and upper mantle beneath Europe and the North Atlantic Ocean.  

UK PubMed Central (United Kingdom)

We constructed a three-dimensional azimuthally anisotropic model of Europe and the North Atlantic Ocean based on adjoint seismic tomography. Several features are well correlated with historical tectonic events in this region, such as extension along the North Atlantic Ridge, trench retreat in the Mediterranean, and counterclockwise rotation of the Anatolian Plate. Beneath northeastern Europe, the direction of the fast anisotropic axis follows trends of ancient rift systems older than 350 million years, suggesting "frozen-in" anisotropy related to the formation of the craton. Local anisotropic strength profiles identify the brittle-ductile transitions in lithospheric strength. In continental regions, these profiles also identify the lower crust, characterized by ductile flow. The observed anisotropic fabric is generally consistent with the current surface strain rate measured by geodetic surveys.

Zhu H; Tromp J

2013-08-01

48

Velocity Structure of Oceanic Crust and the Moho of the Pacific Plate Near Ogasawara Seamount: Insight From Seismic Reflection Data  

Science.gov (United States)

Imaging structures within oceanic crust and Moho geometry using multichannel seismic reflection data has been difficult because of challenges in determining accurate velocities within oceanic crust. To obtain improved velocity models, we apply seismic attribute analysis to Common Mid Point (CMP) gathers. We calculate the instantaneous phase from the CMP gather, use the phase information for velocity analysis, and determine velocity models for oceanic crust. We apply this method to seismic reflection data acquired near Ogasawara seamount, with the result of clear images of structures within oceanic crust and the Moho. Furthermore, we use the velocity models to determine depth to Moho. From structures observed in the depth section and our velocity model, we estimate the velocity of Layer 2 to be from 3900 to 5900 m/s, and of Layer 3 to be from 5500 to 7100 m/s. Furthermore, the Moho reflection may be caused by gradual or steplike changes in acoustic impedance. The characteristics of Moho reflections suggest magmatic intrusions near the seamount.

Tsuji, T.; Nakamura, Y.; Tokuyama, H.; Coffin, M.; Matsuoka, T.; Koda, K.

2005-12-01

49

Oxygen Isotope Composition of the Oceanic Crust in the Oman ophiolite, Wadi Fizh section  

Science.gov (United States)

Oxygen isotope compositions of oceanic crustal rocks of a complete section through the Wadi Fizh area in the Oman ophiolite were determined in order to investigate water-rock interaction at mid-ocean ridges. Bulk rock ?18O values decreased with increasing depth (the mean ?18O values of pillow basalt, sheeted dike and gabbro were 10.9, 7.6 and 4.8 per mil, respectively). Plagiogranites were relatively ?18O-enriched (6.2 to 9.0 per mil), whereas two samples of epidosites showed the lowest ?18O values (1.5 and 2.7 per mil). Average ?18O value (6.1 per mil) of bulk crustal rocks is almost identical to that of MORB basalt (5.7±0.3 per mil). Assuming that the ?18O of hydrothermal solution is 2 per mil and water-rock ratio is 9.4 (calculated from 87Sr/86Sr by the previous study), maximum temperature of alteration in the lower gabbro section is estimated as >500° C, which is consistent with the temperature of alteration estimated from assemblage of secondary minerals. If the reacted solution is more enriched in ?18O, the temperature of alteration might be higher. Although the trend of ?18O depth profile in the Wadi Fizh section is consistent with the previous studies of the other sections (Ibra, Hilti, Shafan and Rajimi) in the Oman ophiolite, the ?18O of the gabbro section in the Wadi Fizh section is highly depleted in comparison with the other sections. It indicates that large volume of high-temperature seawater circulated down to the Moho and the gabbros rarely overprinted by the late stage, low-temperature hydrothermal alteration at off-axis. Thus, the oceanic crust in the Wadi Fizh area is an ideal section to interpret the hydrothermal circulation at fast-spreading ridge system.

Yamaoka, K.; Hiroyasu, Y.; Matsubaya, O.; Ishiyama, D.; Chiba, H.; Kawahata, H.

2008-12-01

50

The effect of recycled oceanic crust in the thermal evolution of the Galapagos Plume  

Science.gov (United States)

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

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

2011-12-01

51

Deep-Ocean Crusts as Telescopes: Using Live Radioisotopes to Probe Supernova Nucleosynthesis  

CERN Document Server

Live 60Fe has recently been detected in a deep-ocean ferromanganese crust, isolated in layers dating from about 3 Myr ago. Since 60Fe has a mean life of 2.2 Myr, a near-Earth supernova is the only likely source for such a signal, and we explore here the consequences of a supernova origin. We combine the 60Fe data with several supernova nucleosynthesis models to calculate the supernova distance as a function of progenitor mass, finding an allowed range of 15-120 pc. We also predict the signals expected for several other radioisotopes, which are independent of the supernova distance. Species likely to be present near or above background levels are 10Be, 26Al, 53Mn, 182Hf and 244Pu. Of these, 182Hf and 244Pu are nearly background-free, presenting the best opportunities to provide strong confirmation of the supernova origin of the 60Fe signal, and to demonstrate that at least some supernovae are the source for the r-process. The accuracies of our predictions are hampered by large uncertainties in the predicted 60...

Fields, B D; Ellis, Jonathan Richard

2005-01-01

52

Evidence for mantle metasomatism by hydrous silicic melts derived from subducted oceanic crust.  

UK PubMed Central (United Kingdom)

The low concentrations of niobium, tantalum and titanium observed in island-arc basalts are thought to result from modification of the sub-arc mantle by a metasomatic agent, deficient in these elements, that originates from within the subducted oceanic crust. Whether this agent is an hydrous fluid or a silica-rich melt has been discussed using mainly a trace-element approach and related to variable thermal regimes of subduction zones. Melting of basalt in the absence of fluid both requires high temperatures and yields melt compositions unlike those found in most modern or Mesozoic island arcs. Thus, metasomatism by fluids has been thought to be the most common situation. Here, however, we show that the melting of basalt under both H2O-added and low-temperature conditions can yield extremely alkali-rich silicic liquids, the alkali content of which increases with pressure. These liquids are deficient in titanium and in the elements niobium and tantalum and are virtually identical to glasses preserved in mantle xenoliths found in subduction zones and to veins found in exhumed metamorphic terranes of fossil convergent zones. We also found that the interaction between such liquids and mantle olivine produces modal mineralogies that are identical to those observed in metasomatized Alpine-type peridotites. We therefore suggest that mantle metasomatism by slab-derived melt is a more common process than previously thought.

Prouteau G; Scaillet B; Pichavant M; Maury R

2001-03-01

53

Evidence for mantle metasomatism by hydrous silicic melts derived from subducted oceanic crust.  

Science.gov (United States)

The low concentrations of niobium, tantalum and titanium observed in island-arc basalts are thought to result from modification of the sub-arc mantle by a metasomatic agent, deficient in these elements, that originates from within the subducted oceanic crust. Whether this agent is an hydrous fluid or a silica-rich melt has been discussed using mainly a trace-element approach and related to variable thermal regimes of subduction zones. Melting of basalt in the absence of fluid both requires high temperatures and yields melt compositions unlike those found in most modern or Mesozoic island arcs. Thus, metasomatism by fluids has been thought to be the most common situation. Here, however, we show that the melting of basalt under both H2O-added and low-temperature conditions can yield extremely alkali-rich silicic liquids, the alkali content of which increases with pressure. These liquids are deficient in titanium and in the elements niobium and tantalum and are virtually identical to glasses preserved in mantle xenoliths found in subduction zones and to veins found in exhumed metamorphic terranes of fossil convergent zones. We also found that the interaction between such liquids and mantle olivine produces modal mineralogies that are identical to those observed in metasomatized Alpine-type peridotites. We therefore suggest that mantle metasomatism by slab-derived melt is a more common process than previously thought. PMID:11242077

Prouteau, G; Scaillet, B; Pichavant, M; Maury, R

2001-03-01

54

Geochronologic and isotopic study of the La Désirade island basement complex: Jurassic oceanic crust in the Lesser Antilles?  

Science.gov (United States)

La Désirade, a small island east of Guadeloupe, is underlain by the only exposed pre-Tertiary basement rocks in the Lesser Antilles. The basement complex comprises spilitic and keratophyric flows and pillow lavas (with interbedded and overlying radiolarian cherts), swarms of mafic to silicic dikes, and subjacent plagiogranite. These features, and the absence of carbonates, terrigenous clastic sediments, or tuffaceous sediments from the complex indicate that it developed in a deep marine environment beyond the reach of terrigenous sedimentation or emergent island arc pyroclastic deposition. Previous workers have suggested that the Désirade basement complex originated either as oceanic crust or during an early (tholeiitic) stage of island arc growth. The isotopic compositions of Sr and Pb from the complex, and previously reported rare earth data (Johnston and Schilling, 1974) do not provide a clear distinction between these two possibilities. Nor does the presence of siliceous keratophyre in the complex rule out an oceanic crustal origin-such rocks are common in well studied ophiolites that originated as oceanic crust. Hence we turn to the age relationships of the complex, the surrounding ocean floor, and adjacent island arcs in an attempt to resolve this problem. The age of the complex strongly supports an oceanic crustal (ophiolitic) origin. The ages of zircons and a previously reported K-Ar age indicate that the complex is 145±5 m.y. old. The complex predates the next oldest volcanic rocks of the Lesser Antilles arc by ca. 110 m.y., and the oldest known rocks of the Aves Ridge, a possible Mesozoic precursor of the Lesser Antilles arc, by 50 60 m.y. This makes it unlikely that the Désirade complex is related to an early phase of either of these arcs. Instead, the age of the complex falls in the range of ages expected for oceanic crust in the vicinity of the Lesser Antilles prior to the development of any subduction zone and resulting arc. Thus we interpret the Désirade complex to be an uplifted segment of oceanic crust that represents the basement on which the later island arcs grew: first the Aves Ridge, an arc that was active in middle to late Cretaceous time (but whose exact mode of origin is enigmatic, and is considered in four alternate tectonic models), then the Eocene to Recent Lesser Antilles arc.

Mattinson, James M.; Fink, L. Kenneth; Hopson, Clifford A.

1980-01-01

55

Gravity evidence of very thin crust at the Gakkel Ridge (Arctic Ocean)  

Science.gov (United States)

Gakkel Ridge, the active spreading center in the Arctic Ocean, is the slowest spreading portion of the global mid-ocean ridge system. Total spreading rates range from 0.6 cm/yr in the east where the ridge disappears beneath the Laptev shelf to 1.3 cm/yr in the west near Greenland. Bathymetry and gravity surveys of four sections of the Gakkel Ridge were carried out in 1996 by the U.S. Navy nuclear submarine USS POGY as part of SCICEX 96 in order to sample variations in seafloor morphology and gravity anomalies as a function of spreading rate. The ridge axis throughout the survey area is characterized by a continuous axial rift valley similar to that observed at other slow spreading ridges. The continuous rift axis suggests that well-organized seafloor spreading is occurring at total spreading rates of less than 1 cm/yr. In three faster spreading (1.13-1.24 cm/yr) western survey areas located between 7°E and 54°E, the Gakkel Ridge is deep compared with other ridge axes. Axial depths range between 4600 and 5100 m and ridge flanks at about 3200 m. The ridge flank morphology is very blocky and is characterized by large scarps and deep fault-bounded troughs. Very large amplitude free-water anomalies with peak-to-trough amplitudes of 85-150 mGal are observed centered on the axis of the Gakkel Ridge. Modeling of the free-water anomalies by varying the crustal thickness and average crustal density, including the gravity effect of the cooling of the mantle away from the axis, implies that if the average crustal density is less than 2900 kg/m 3, the crustal thickness must be less than 4 km. The axial rift valley at the fourth survey area, near 98°E where the total spreading rate is 0.99 cm/yr, is buried by sediments. The axis in this region is associated with a continuous 70 mGal gravity minimum implying the presence of a large buried rift valley. The rift flanks at 95°E are at a depth of greater than 3800 m, 600 m deeper than the average depth at the Gakkel Ridge axis west of 60°E. Simple isostatic calculations suggest that the crust in this region may be vanishingly thin beneath the sediment cover. These observations indicate a relationship between melt production and seafloor spreading rate at very slow spreading rates, suggesting that ultra-slow spreading may suppress melt production or delivery at the Gakkel Ridge.

Coakley, Bernard J.; Cochran, James R.

1998-10-01

56

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

Science.gov (United States)

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 (r = 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 ( 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 (r > 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 (r < 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.

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

2007-01-01

57

Evidence for biogenic processes during formation of ferromanganese crusts from the Pacific Ocean: implications of biologically induced mineralization.  

UK PubMed Central (United Kingdom)

Ferromanganese [Fe/Mn] crusts formed on basaltic seamounts, gain considerable economic importance due to their high content of Co, Ni, Cu, Zn and Pt. The deposits are predominantly found in the Pacific Ocean in depths of over 1000m. They are formed in the mixing layer between the upper oxygen-minimum zone and the lower oxygen-rich bottom zone. At present an almost exclusive abiogenic origin of crust formation is considered. We present evidence that the upper layers of the crusts from the Magellan Seamount cluster are very rich in coccoliths/coccolithophores (calcareous phytoplankton) belonging to different taxa. Rarely intact skeletons of these unicellular algae are found, while most of them are disintegrated into their composing prisms or crystals. Studies on the chemical composition of crust samples by high resolution SEM combined with an electron probe microanalyzer (EPMA) revealed that they are built of distinct stacked piles of individual compartments. In the center of such piles Mn is the dominant element, while the rims of the piles are rich in Fe (mineralization aspect). The compartments contain coccospheres usually at the basal part. Energy dispersive X-ray spectroscopy (EDX) analyses showed that those coccospheres contain, as expected, CaCO3 but also Mn-oxide. Detailed analysis displayed on the surface of the coccolithophores a high level of CaCO3 while the concentration of Mn-oxide is relatively small. With increasing distance from the coccolithophores the concentration of Mn-oxide increases on the expense of residual CaCO3. We conclude that coccoliths/coccolithophores are crucial for the seed/nucleation phase of crust formation (biomineralization aspect). Subsequently, after the biologically induced mineralization phase Mn-oxide deposition proceeds "auto"catalytically.

Wang XH; Schlossmacher U; Natalio F; Schröder HC; Wolf SE; Tremel W; Müller WE

2009-07-01

58

Yin of birthing and the Yang of destroying continental crust at ocean-margin and crust-suturing subduction zones—exploring evidence about processes, amounts, and the Phanerozoic balance  

Science.gov (United States)

INTRODUCTION: Field evidence implies that the creation of juvenile continental crust by mantle melting is paired with the destruction of older crust and its recycling to the mantle. The tectonic notion of birthing and annihilation is philosophically expressed by the Chinese concept of the twained and inseparable processes of yin-yang. Since at least the Phanerozoic these opposing processes appear to have been most active at the subduction zones (SZs) of ocean margins (i.e., Peru-Chile margin) and suture-building collision zones (i.e. closing of Tethys). Crust is also created and destroyed by non-plate tectonic processes, in particular additions by hotspot melting and losses by foundering of lower crust. BASIC OBSERVATIONS: Evidence exists that the creation of juvenile crust is impressively voluminous at newly formed SZs, in particular those that build the massifs of offshore arcs. Modern intra-oceanic arcs (e.g., the Aleutian and IBM arcs) have since the early Tertiary grown at a rate of 100-150 km3/Myr/km of SZ, thus adding to the inventory of continental crust at a global rate of about 1.5 km3/yr (= 1.5 Armstrong units or AU). The arc massifs forming along continental margin (e.g., Andean arc) compile at a much slower rate (30 km3/Myr/km of SZ) but globally account for about +1.0 AU of juvenile growth. An additional +0.7 AU is estimated supplied by continental rift and hotspot volcanism. The opposite or destructive Yang processes of sediment subduction and subduction erosion remove and transport crustal material toward and into the mantle at modern ocean-margin SZs. The global rate is evidentially estimated at about -2.5 AU. Similar observations of missing material estimate that a large volume, at least -0.7 AU or greater, of continental crust is loss at the SZs of colliding or suturing crustal blocks. The greater volume of the loss is effected by the detachment and en-mass sinking of deeply underthrust continental edges. THE BALANCE: During the Phanerozoic, creation and destruction of continental crust has either struck a long-term balance at about 3.2 AU, or that more crust has being destroyed than created. This seems possible or even likely to us because the uncertainty comes from limited observations to assess the en-mass loss of deeply underthrust crust and the foundering (sinking) of densified lower crustal rock to which we have presently assigned no estimate.

Scholl, D. W.; Stern, R. J.

2009-12-01

59

Seismic evidence of bending and unbending of subducting oceanic crust and the presence of mantle megathrust in the 2004 Great Sumatra earthquake rupture zone  

Science.gov (United States)

In subduction zones the plate interface (megathrust) is typically poorly imaged at depths > 12 km, however its precise geometry and nature as well as the positions of updip and downdip limits of the seismogenic zone are important elements to understand the generation of megathrust earthquakes. Using deep marine seismic reflection and refraction data, we observed discontinuous reflections off the top of the subducting oceanic crust down to 60 km depth in the 2004 great Sumatra-Andaman earthquake rupture zone. We find that the top of the downgoing plate does not dip gently into the subduction zone but instead displays a staircase geometry with three successive, 5-15 km vertical steps, spaced ~ 50 km apart. Micro-earthquake data indicate that most of the seismicity lies below this interface, suggesting that the oceanic plate is deforming actively. Along part of the profile, we also image a second reflector located 8-10 km below the top of the oceanic crust. The forward modelling of the gravity data along the profile supports the presence of a high-density material above this reflector. The presence of a staircase shape for the top of the oceanic crust, together with constraints from gravity data and earthquake data, require that the megathrust goes through this second reflector. This leads us to conclude that the megathrust is at least partly located in the oceanic mantle and that underplating of oceanic crust beneath the wedge and underplating of upper mantle beneath the forearc basin are taking place in this region.

Singh, Satish C.; Chauhan, Ajay P. S.; Calvert, Andrew J.; Hananto, Nugroho D.; Ghosal, Dibakar; Rai, Abhishek; Carton, Helene

2012-03-01

60

Depth profiles of trace elements and stable isotopic compositions (O, H, B, Sr) of the hydrothermally altered oceanic crust in the Oman ophiolite  

Science.gov (United States)

Trace elements and stable isotopic compositions of hydrothermally altered oceanic crust could be useful tracers during geochemical processes, such as seawater-rock interaction, arc magmatism at convergent zone, and heterogeneity of mantle. Although previous studies have been reported the chemical compositions of oceanic crustal rocks from dredged and/or drilled modern seafloor and ophiolite, available depth-successive data is still limited. The ancient oceanic crust in the Oman ophiolite is a good material to investigate the geochemistry associated with hydrothermal alteration at fast spreading ridge system because of its continuous exposure and less metamorphism. In this study, we present the depth profiles of trace elements with stable isotopic compositions including oxygen and hydrogen [1], boron [2], and strontium [3] for the complete sequence of the oceanic crust from the Wadi Fizh area, in the northern part of the Oman ophiolite. Based on the types of alteration and oxygen isotopic compositions of bulk rocks, the oceanic crust from the Wadi Fizh area was divided into four zones as follows: (1) Zone I (100-350 m; basalt altered at 10‰), (2) Zone II (350-2000 m; basalt and dolerite altered at 60-350oC; actinolite, prehnite, albite, chlorite, epidote; ?18O = 6-10‰), (3) Zone III (2000-3560 m; dolerite dike, plagiogranite, metagabbro and epidosite altered at 350-450oC; actinolite, albite, chlorite, epidote, quartz; ?18O plagiogranite), (4) Zone IV (3560-5340 m; noncumulate and cumulate gabbro altered at >450oC; hornblende, albite, chlorite; ?18O <6‰). The 87Sr/86Sr ratios and ?11B values of the lower gabbros were highly elevated relative to MORB, indicating that seawater-originated hydrothermal fluid penetrated into deep section of the oceanic crust at or near a spreading center. Furthermore, the obviously D-depleted chlorite and hornblende from the lower oceanic crust suggested interaction with saline brine generated by supercritical phase separation of seawater. Taking into these findings, we discuss the behavior of trace element during hydrothermal alteration of the oceanic crust along mid-ocean ridges. [1] Yamaoka et al., submitted. [2] Yamaoka et al., submitted. [3] Kawahata et al. (2001) JGR 106, 11,083-11,099.

Yamaoka, K.; Ishikawa, T.; Kawahata, H.

2010-12-01

 
 
 
 
61

Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago.  

UK PubMed Central (United Kingdom)

No crustal rocks are known to have survived since the time of the intense meteor bombardment that affected Earth between its formation about 4,550 Myr ago and 4,030 Myr, the age of the oldest known components in the Acasta Gneiss of northwestern Canada. But evidence of an even older crust is provided by detrital zircons in metamorphosed sediments at Mt Narryer and Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, where grains as old as approximately 4,276 Myr have been found. Here we report, based on a detailed micro-analytical study of Jack Hills zircons, the discovery of a detrital zircon with an age as old as 4,404+/-8 Myr--about 130 million years older than any previously identified on Earth. We found that the zircon is zoned with respect to rare earth elements and oxygen isotope ratios (delta18O values from 7.4 to 5.0%), indicating that it formed from an evolving magmatic source. The evolved chemistry, high delta18O value and micro-inclusions of SiO2 are consistent with growth from a granitic melt with a delta18O value from 8.5 to 9.5%. Magmatic oxygen isotope ratios in this range point toward the involvement of supracrustal material that has undergone low-temperature interaction with a liquid hydrosphere. This zircon thus represents the earliest evidence for continental crust and oceans on the Earth.

Wilde SA; Valley JW; Peck WH; Graham CM

2001-01-01

62

Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago.  

Science.gov (United States)

No crustal rocks are known to have survived since the time of the intense meteor bombardment that affected Earth between its formation about 4,550 Myr ago and 4,030 Myr, the age of the oldest known components in the Acasta Gneiss of northwestern Canada. But evidence of an even older crust is provided by detrital zircons in metamorphosed sediments at Mt Narryer and Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, where grains as old as approximately 4,276 Myr have been found. Here we report, based on a detailed micro-analytical study of Jack Hills zircons, the discovery of a detrital zircon with an age as old as 4,404+/-8 Myr--about 130 million years older than any previously identified on Earth. We found that the zircon is zoned with respect to rare earth elements and oxygen isotope ratios (delta18O values from 7.4 to 5.0%), indicating that it formed from an evolving magmatic source. The evolved chemistry, high delta18O value and micro-inclusions of SiO2 are consistent with growth from a granitic melt with a delta18O value from 8.5 to 9.5%. Magmatic oxygen isotope ratios in this range point toward the involvement of supracrustal material that has undergone low-temperature interaction with a liquid hydrosphere. This zircon thus represents the earliest evidence for continental crust and oceans on the Earth. PMID:11196637

Wilde, S A; Valley, J W; Peck, W H; Graham, C M

2001-01-11

63

Banda-Celebes-Sulu basin - a trapped Cretaceous-Eocene oceanic crust  

Energy Technology Data Exchange (ETDEWEB)

The Banda, Celebes and Sulu Basins are three poorly understood marginal seas that are located at the junction of the Eurasian, Indian-Australian, Pacific and Philippine Sea plates. The incomplete data sets from each of these three marginal basins, the complex geological arrangement of the surrounding islands, and the compound late Cenozoic evolutions involving subduction, rifting, transform faulting and island arc collision have complicated any tectonic interpretations of this region. On the bases of marine geophysical data and on-land geology, the authors propose that the Banda, Celebes and Sulu Basins are the remanents of a once-continuous Cretaceous to Eocene ocean basin. Magnetic anomalies from the Banda, Celebes and Sulu Basins show the similar trends of about N70/sup 0/E, N60/sup 0/E and N55/sup 0/E respectively. Their best fit to the reversal models are as follows: (1) anomalies M1-M11 in the Banda Basin, (2) anomalies 30-33 in the Celebes Basin and (3) anomalies 17-20 in the Sulu Basin. The heat flow data from each of these basins is consistent with the relationship of our assigned magnetic ages. The on-land geology of this region is complicated by numerous land masses which dissect this old oceanic basin into the present configuration of marginal seas. The authors argue that each of these land masses arrived at its present location by either late Tertiary tectonic movements or has been built in place upon this older oceanic basement.

Lee, C.S.; McCabe, R.

1985-01-01

64

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

UK PubMed Central (United Kingdom)

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 (<25?°C) basaltic crust, which we calculate from modelling dissolved oxygen and 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.

Orcutt BN; Wheat CG; Rouxel O; Hulme S; Edwards KJ; Bach W

2013-09-01

65

Osmium isotope stratigraphy of a marine ferromanganese crust  

Science.gov (United States)

Ferromanganese crusts provide records of long term change in ocean circulation and continental weathering. However, calibrating their age prior to 10 Ma has been entirely based on empirical growth rate models using Co concentrations, which have inherently large uncertainties and fail to detect hiatuses and erosional events. We present a new method for dating these crusts by measuring their osmium (Os) isotope record and matching it to the well-known marine Os isotope evolution of the past 80 Ma. The well-characterised crust CD29-2 from the central Pacific, was believed to define a record of paleooceanographic change from 50 Ma. Previous growth rate estimates based on the Co method are consistent with the new Os isotope stratigraphy but the dating was grossly inaccurate due to long hiatuses that are now detectable. The new chronology shows that it in fact started growing prior to 70 Ma in the late Cretaceous and stopped growing or was eroded between 13.5 and 47 Ma. With this new technique it is now possible to exploit the full potential of the oceanographic and climatic records stored in Fe-Mn crusts. ?? 2005 Elsevier B.V. All rights reserved.

Klemm, V.; Levasseur, S.; Frank, M.; Hein, J. R.; Halliday, A. N.

2005-01-01

66

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

Scientific Electronic Library Online (English)

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

Leite, Emilson Pereira; Ussami, Naomi

2006-09-01

67

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1986-07-01

68

Processes of brine generation and circulation in the oceanic crust: Fluid inclusion evidence from the Troodos Ophiolite, Cyprus  

Science.gov (United States)

Detailed temporal, thermal, and compositional data on aqueous fluid inclusions from a suite of plutonic and diabase samples from the Troodos ophiolite, Cyprus provide the first documentation that generation of high-temperature brines may be common at depth in the oceanic crust. Anastomosing arrays of fluid inclusions in rocks of the upper intrusive sequence record episodic fracturing events. The earliest fracturing event, at temperatures >450-600°C resulted in entrapment of brine-rich aqueous fluids with salinities of 36-61 wt % NaCl equivalent. Homogenization of the brine inclusions by haute dissolution, the virtual absence of vaporrich fluid inclusions throughout the upper level plutonic sequence, and the restriction of brine inclusions to the most evolved plutonic rocks suggests that exsolution of brines off of the late stage gabbro and plagiogranite melts played a significant role in generating the quartz-hosted, high-salinity inclusions. Cooling of the fluids during pulses of fluid migration associated with episodic fracturing events, resulted in entrapment of the brines in the deep-seated, high-temperature portion of the hydrothermal system. In localized areas, the high-temperature brines (NaCl±KCl±CaCl2) caused extreme alteration of the plagiogranite bodies and in the formation of podiform epidosites. Arrays of low-temperature, low-salinity fluid inclusions, which in some samples crosscut fractures dominated by brine inclusions, indicate downward propagation of a cracking front subsequent to collapse of the high-temperature magmatic system, resulting in penetration of seawaterlike fluids into the plutonic sequence at temperatures >200-400°C. Hydration reactions under greenschist facies conditions, or limited mixing with brine-rich fluids, may have resulted in salinity variations from 70% below to 200% above seawater concentrations. Temperatures and compositions of the low-salinity inclusions are similar to those found in stockwork systems beneath Troodos ore deposits and to those of fluids exiting active submarine hydrothermal vents at mid-ocean ridge spreading centers. The low-temperature fracture networks may represent an extensive deep-seated feeder system which coalesced to form zones of concentrated hydrothermal upflow.

Kelley, Deborah S.; Robinson, Paul T.; Malpas, John G.

1992-06-01

69

Sulfur geochemistry and microbial sulfate reduction during low-temperature alteration of uplifted lower oceanic crust: Insights from ODP Hole 735B  

Science.gov (United States)

Sulfide petrography plus whole rock contents and isotope ratios of sulfur were measured in a 1.5 km section of oceanic gabbros in order to understand the geochemistry of sulfur cycling during low-temperature seawater alteration of the lower oceanic crust, and to test whether microbial effects may be present. Most samples have low SO4/?S values (? 0.15), have retained igneous globules of pyrrhotite ± chalcopyrite ± pentlandite, and host secondary aggregates of pyrrhotite and pyrite laths in smectite ± iron-oxyhydroxide ± magnetite ± calcite pseudomorphs of olivine and clinopyroxene. Compared to fresh gabbro containing 100–1800 ppm sulfur our data indicate an overall addition of sulfide to the lower crust. Selection of samples altered only at temperatures ? 110 °C constrains microbial sulfate reduction as the only viable mechanism for the observed sulfide addition, which may have been enabled by the production of H2 from oxidation of associated olivine and pyroxene. The wide range in ?34Ssulfide values (? 1.5 to + 16.3‰) and variable additions of sulfide are explained by variable ?sulfate-sulfide under open system pathways, with a possible progression into closed system pathways. Some samples underwent oxidation related to seawater penetration along permeable fault horizons and have lost sulfur, have high SO4/?S (? 0.46) and variable ?34Ssulfide (0.7 to 16.9‰). Negative ?34Ssulfate–?34Ssulfide values for the majority of samples indicate kinetic isotope fractionation during oxidation of sulfide minerals. Depth trends in sulfide–sulfur contents and sulfide mineral assemblages indicate a late-stage downward penetration of seawater into the lower 1 km of Hole 735B. Our results show that under appropriate temperature conditions, a subsurface biosphere can persist in the lower oceanic crust and alter its geochemistry.

Alford, Susan E.; Alt, Jeffrey C.; Shanks, Wayne C., III

2011-01-01

70

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  

Science.gov (United States)

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.

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

2005-05-01

71

Global occurrence of tellurium-rich ferromanganese crusts and a model for the enrichment of tellurium  

Science.gov (United States)

Hydrogenetic ferromanganese oxyhydroxide crusts (Fe-Mn crusts) precipitate out of cold ambient ocean water onto hard-rock surfaces (seamounts, plateaus, ridges) at water depths of about 400 to 4000 m throughout the ocean basins. The slow-growing (mm/Ma) Fe-Mn crusts concentrate most elements above their mean concentration in the Earth's crust. Tellurium is enriched more than any other element (up to about 50,000 times) relative to its Earth's crustal mean of about 1 ppb, compared with 250 times for the next most enriched element. We analyzed the Te contents for a suite of 105 bulk hydrogenetic crusts and 140 individual crust layers from the global ocean. For comparison, we analyzed 10 hydrothermal stratabound Mn-oxide samples collected from a variety of tectonic environments in the Pacific. In the Fe-Mn crust samples, Te varies from 3 to 205 ppm, with mean contents for Pacific and Atlantic samples of about 50 ppm and a mean of 39 ppm for Indian crust samples. Hydrothermal Mn samples have Te contents that range from 0.06 to 1 ppm. Continental margin Fe-Mn crusts have lower Te contents than open-ocean crusts, which is the result of dilution by detrital phases and differences in growth rates of the hydrogenetic phases. Correlation coefficient matrices show that for hydrothermal deposits, Te has positive correlations with elements characteristic of detrital minerals. In contrast, Te in open-ocean Fe-Mn crusts usually correlates with elements characteristic of the MnO2, carbonate fluorapatite, and residual biogenic phases. In continental margin crusts, Te also correlates with FeOOH associated elements. In addition, Te is negatively correlated with water depth of occurrence and positively correlated with crust thickness. Q-mode factor analyses support these relationships. However, sequential leaching results show that most of the Te is associated with FeOOH in Fe-Mn crusts and ???10% is leached with the MnO2. Thermodynamic calculations indicate that Te occurs predominantly as H5TeO6- in ocean water. The speciation of Te in ocean water and charge balance considerations indicate that Te should be scavenged by FeOOH, which is in agreement with our leaching results. The thermodynamically more stable Te(IV) is less abundant by factors of 2 to 3.5 than Te(VI) in ocean water. This can be explained by preferential (not exclusive) scavenging of Te(IV) by FeOOH at the Fe-Mn crust surface and by Fe-Mn colloids in the water column. We propose a model in which the extreme enrichment of Te in Fe-Mn crusts is likely the result of an oxidation reaction on the surface of FeOOH. A similar oxidation process has been confirmed for Co, Ce, and Tl at the surface of MnO2 in crusts, but has not been suggested previously to occur in association with FeOOH in Fe-Mn crusts. Mass-balance considerations indicate that ocean floor Fe-Mn deposits are the major sink for Te in the oceans. The concentration and redox chemistry of Te in the global ocean are likely controlled by scavenging on Fe-Mn colloids in the water column and Fe-Mn deposits on the ocean floor, as is also the case for Ce. ?? 2003 Elsevier Science Ltd.

Hein, J. R.; Koschinsky, A.; Halliday, A. N.

2003-01-01

72

Distribution of various components in a hydrogeneous ferromanganese nodule and an Afanasiy Nikitin Seamount crust from Indian Ocean - A geochemical study using micro-PIXE  

Energy Technology Data Exchange (ETDEWEB)

The present study emphasizes the geochemical features pertaining to the distribution of the major and minor elements in a hydrogenous ferromanganese nodule and a seamount crust originating from the Indian Ocean. The micro-PIXE elemental maps indicate the successive layer formation of Fe and Mn in these deposits. A Ni association with Mn has been further confirmed by observing a Ni-Mn spatial correlation together with their compositional correlation. In addition, the core or the nucleus of the ferromanganese nodule was found to be rich in Fe and not Mn, which strengthens the assumptions made earlier that the nodule formation started with Fe deposition which catalysed the growth of a ferromanganese nodule or crust by successive deposition of Mn and Fe. Irregular patterns of Mn and Fe layers were observed and discussed. Instead of the more often studied Co-Fe association in nodules and crusts, the intra nodule microanalysis revealed a Co-Mn correlation that will be discussed in this paper.

Dutta, R.K. E-mail: raja@src.wits.ac.za; Sideras-Haddad, E.; Connell, S.H

2001-07-01

73

Distribution of various components in a hydrogeneous ferromanganese nodule and an Afanasiy Nikitin Seamount crust from Indian Ocean - A geochemical study using micro-PIXE  

International Nuclear Information System (INIS)

The present study emphasizes the geochemical features pertaining to the distribution of the major and minor elements in a hydrogenous ferromanganese nodule and a seamount crust originating from the Indian Ocean. The micro-PIXE elemental maps indicate the successive layer formation of Fe and Mn in these deposits. A Ni association with Mn has been further confirmed by observing a Ni-Mn spatial correlation together with their compositional correlation. In addition, the core or the nucleus of the ferromanganese nodule was found to be rich in Fe and not Mn, which strengthens the assumptions made earlier that the nodule formation started with Fe deposition which catalysed the growth of a ferromanganese nodule or crust by successive deposition of Mn and Fe. Irregular patterns of Mn and Fe layers were observed and discussed. Instead of the more often studied Co-Fe association in nodules and crusts, the intra nodule microanalysis revealed a Co-Mn correlation that will be discussed in this paper

2001-01-01

74

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

Energy Technology Data Exchange (ETDEWEB)

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)

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

75

A neodymium, strontium, and oxygen isotopic study of the Cretaceous Samail ophiolite and implications for the petrogenesis and seawater-hydrothermal alteration of oceanic crust  

Science.gov (United States)

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

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

1980-01-01

76

Highly siderophile element behaviour accompanying subduction of oceanic crust: Whole rock and mineral-scale insights from a high-pressure terrain  

Science.gov (United States)

Highly siderophile element concentrations (HSE: Re and platinum-group elements (PGE)) are presented for gabbros, gabbroic eclogites and basaltic eclogites from the high-pressure Zermatt-Saas ophiolite terrain, Switzerland. Rhenium and PGE (Os, Ir, Ru, Rh, Pt, Pd) abundances in gabbro- and eclogite-hosted sulphides, and Re-Os isotopes and elemental concentrations in silicate phases are also reported. This work, therefore, provides whole rock and mineral-scale insights into the PGE budget of gabbroic oceanic crust and the effects of subduction metamorphism on gabbroic and basaltic crust. Chondrite-normalised PGE patterns for the gabbros are similar to published mid-ocean ridge basalts (MORB), but show less inter-element fractionation. Mean Pt and Pd contents of 360 and 530 pg/g, respectively, are broadly comparable to MORB, but gabbros have somewhat higher abundances of Os, Ir and Ru (mean: 64, 57 and 108 pg/g). Transformation to eclogite has not significantly changed the concentrations of the PGE, except Pd which is severely depleted in gabbroic eclogites relative to gabbros (˜75% loss). In contrast, basaltic eclogites display significant depletion of Pt (?60%), Pd (>85%) and Re (50-60%) compared with published MORB, while Os, Ir and Ru abundances are broadly comparable. Thus, these data suggest that only Pt, Pd and Re, and not Os, Ir and Ru, may be significantly fluxed into the mantle wedge from mafic oceanic crust. Re-Os model ages for gabbroic and gabbroic eclogite minerals are close to age estimates for igneous crystallisation and high-pressure metamorphism, respectively, hence the HSE budgets can be related to both igneous and metamorphic behaviour. The gabbroic budget of Os, Ir, Ru and Pd (but not Pt) is dominated by sulphide, which typically hosts >90% of the Os, whereas silicates account for most of the Re (with up to 75% in plagioclase alone). Sulphides in gabbroic eclogites tend to host a smaller proportion of the total Os (10-90%) while silicates are important hosts, probably reflecting Os inheritance from precursor phases. Garnet contains very high Re concentrations and may account for >50% of Re in some samples. The depletion of Pd in gabbroic eclogites appears linked, at least in part, to the loss of Ni-rich sulphide. Both basaltic and gabbroic oceanic crust have elevated Pt/Os ratios, but Pt/Re ratios are not sufficiently high to generate the coupled 186Os- 187Os enrichments observed in some mantle melts, even without Pt loss from basaltic crust. However, the apparent mobility of Pt and Re in slab fluids provides an alternative mechanism for the generation of Pt- and Re-rich mantle material, recently proposed as a potential source of 187Os- 186Os enrichment.

Dale, C. W.; Burton, K. W.; Pearson, D. G.; Gannoun, A.; Alard, O.; Argles, T. W.; Parkinson, I. J.

2009-03-01

77

Insights on the Formation and Evolution of the Upper Oceanic Crust from Deep Drilling at ODP/IODP Hole 1256D  

Science.gov (United States)

Deep drilling of Hole 1256D on ODP Leg 206 and IODP Expeditions 309/312 provides the first complete section of intact upper oceanic crust down to gabbros. Site 1256 is located on ocean crust of the Cocos Plate that formed at the East Pacific Rise (EPR) 15 million years ago during an episode of superfast rate ocean spreading in excess of 200 mm/yr. Past deep drilling of intact ocean crust has been fraught with difficulties due to the highly fractured nature of oceanic lavas. Site 1256 was specifically chosen because the observed relationship between spreading rate and the depth to axial seismic low velocity zones at modern mid-ocean ridges (thought to be magma chambers), suggests that gabbroic rocks should occur at the shallowest levels in ocean crust formed at the highest spreading rates. In line with pre-drilling predictions, gabbroic rocks were first encountered 1157 m into the basement. Hole 1256D penetrates 754 m of lavas, a 57-m thick transition zone and a thin (346 m) sheeted dike complex. The lower ~60 m of the sheeted dikes are contact metamorphosed to granoblastic textures. After encountering gabbros the hole was deepened a further 100 m before the cessation of drilling operations and the plutonic section comprises two gabbroic sills, 52 and 24 m-thick, intruded into a 24 m screen of granoblastic dikes. The gabbro sills have chilled margins and compositions similar to the overlying lavas and dikes, precluding formation of the cumulate lower oceanic crust from the melt lenses so far penetrated by Hole 1256D. A vertical seismic experiment conducted in Hole 1256D indicates that the bottom of the Hole is still within seismic layer 2 despite gabbroic rocks having been recovered. These data together with 1-D and imaging wire-line logs, have been used to construct a continuous volcano-stratigraphy for Site 1256. Comparison of this data with the recovered cores and the styles of eruption occurring at the modern EPR indicate that ~50% of lava sequences were formed within a few kilometres of the ridge axis, with a further 200 m of lavas that display inflation textures deposited at the base of the axial slope. The great thickness (>75 m) of the ponded lava that makes up the uppermost crust at Site 1256, and an absence of vertical fracturing within those rocks, supports the shipboard interpretation that this unit crystallized a significant distance (~5-10 km) off axis. Geochemical analyses of the Hole 1256D cores have been undertaken to evaluate the melting processes and mantle source heterogeneity under the superfast spreading ancient EPR. Hole 1256D cores have significantly lower incompatible element concentrations than present-day EPR lavas, a signature typically interpreted in terms of greater extents of mantle melting. However, similar crustal thicknesses between Site 1256 (5.5 km) and the EPR (5-7 km) challenge that view. This observation coupled with preliminary radiogenic isotope signatures indicate that the depleted mantle source variation might be caused by upwelling previously depleted Galapagos plume mantle at the paleo-Site 1256. Whole rock and mineral trace element analyses indicate that the gabbros sampled to date cannot be the cumulate rocks remaining after melt extraction. Instead, most of the gabbros represent slowly cooled equivalents of the overlying basaltic rocks. However, some patches of gabbro are magmatically highly evolved, and record late stage melts squeezed out from the crystallizing mush within the melt lens. Secondary mineralogy plus oxygen isotope analyses of vein minerals document the thermal structure of the fossil hydrothermal system penetrated by Hole 1256D, and record a complex history of repeated episodes of magmatism and hydrothermal alteration. The ~800 m volcanic section is partly altered to saponite and celadonite, typical of altered submarine basalts but with little oxidation. There is a stepwise increase in alteration grade across the lava-dike transition and the dikes are variably altered to chlorite and other greenschist minerals (250-350 deg C). The lower 60 m of granoblast

Teagle, D. A. H.

2009-04-01

78

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Die vorliegende Arbeit behandelt die Entwicklung des 570 Ma alten, neoproterozoischen Agardagh - Tes-Chem Ophioliths (ATCO) in Zentralasien. Dieser Ophiolith liegt südwestlich des Baikalsees (50.5° N, 95° E) und wurde im frühen Stadium der Akkretion des Zentralasiatischen Mobilgürtels auf den...

Pfänder, Jörg A.

79

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

Science.gov (United States)

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.

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

2010-12-01

80

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

Directory of Open Access Journals (Sweden)

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.

Kent C. Condie

2013-01-01

 
 
 
 
81

Crusted scabies  

Directory of Open Access Journals (Sweden)

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

Karthikeyan Kaliaperumal

2009-01-01

82

The Sabzevar blueschists of the North-Central Iranian micro-continent as remnants of the Neotethys-related oceanic crust subduction  

Science.gov (United States)

The Sabzevar ophiolites mark the Neotethys suture in east-north-central Iran. The Sabzevar metamorphic rocks, as part of the Cretaceous Sabzevar ophiolitic complex, consist of blueschist, amphibolite and greenschist. The Sabzevar blueschists contain sodic amphibole, epidote, phengite, calcite ± omphacite ± quartz. The epidote amphibolite is composed of sodic-calcic amphibole, epidote, albite, phengite, quartz ± omphacite, ilmenite and titanite. The greenschist contains chlorite, plagioclase and pyrite, as main minerals. Thermobarometry of a blueschist yields a pressure of 13-15.5 kbar at temperatures of 420-500 °C. Peak metamorphic temperature/depth ratios were low (~12 °C/km), consistent with metamorphism in a subduction zone. The presence of epidote in the blueschist shows that the rocks were metamorphosed entirely within the epidote stability field. Amphibole schist samples experienced pressures of 5-7 kbar and temperatures between 450 and 550 °C. The presence of chlorite, actinolite, biotite and titanite indicate greenschist facies metamorphism. Chlorite, albite and biotite replacing garnet or glaucophane suggests temperatures of >300 °C for greenschist facies. The formation of high-pressure metamorphic rocks is related to north-east-dipping subduction of the Neotethys oceanic crust and subsequent closure during lower Eocene between the Central Iranian Micro-continent and Eurasia (North Iran).

Omrani, Hadi; Moazzen, Mohssen; Oberhänsli, Roland; Altenberger, Uwe; Lange, Manuela

2013-07-01

83

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

CERN Multimedia

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...

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

2003-01-01

84

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

Science.gov (United States)

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.

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

2013-07-01

85

Ocean Drilling Program (Program Description)  

Science.gov (United States)

... FOR GEOSCIENCES (GEO) OCEAN SCIENCES (OCE) Ocean Drilling Program The Ocean Drilling Program (ODP ... scale, the Earth's crust beneath the ocean in order to learn more about the composition, structure ...

86

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

Science.gov (United States)

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.

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

2004-01-01

87

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

Science.gov (United States)

We compare the time series of major element geochemical and Pb- and Nd-isotopic composition obtained for seven hydrogenous ferromanganese crusts from the Atlantic, Indian, and Pacific Oceans which cover the last 60 Myr. Average crust growth rates and age-depth relationships were determined directly for the last about 10 Myr using 10Be/ 9Be profiles. In the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial 10Be/ 9Be ratios due to the lack of additional information. Co contents have also been used previously to estimate growth rates in Co-rich Pacific and Atlantic seamount crusts (Puteanus and Halbach, 1988). A comparison of 10Be/ 9Be- and Co-based dating of three Co-rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated 10Be/ 9Be-based growth rates back to 60 Ma. Our data show that the flux of Co into Co-poor crusts has been considerably lower. The relationship between growth rate and Co content for the Co-poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits (Manheim, 1986). The results suggest that the Co content provides detailed information on the growth history of ferromanganese crusts, particularly prior to 10-12 Ma where the 10Be-based method is not applicable. The distributions of Pb and Nd isotopes in the deep oceans over the last 60 Myr are expected to be controlled by two main factors: (a) variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and (b) variability of supply rates or provenance of detrital material delivered to the ocean, linked to climate change (glaciations) or major tectonic uplift. The major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust. Consequently, any interpretation of time series of major element concentrations of a single crust in terms of paleoceanographic variations must be considered with caution. This is because local processes appear to have dominated over more basin-wide paleoceanographic effects. In this study Co is the only element which shows a relationship to Pb and Nd isotopes in Pacific crusts. A possible link to changes of Pacific deep water properties associated with an enhanced northward advection of Antarctic bottom water from about 14 Ma is consistent with the Pb but not with the Nd isotopic results. The self-consistent profiles of the Pb and Nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts, including phosphatization events, have been insignificant for particle reactive elements such as Pb, Be, and Nd. Isotope time series of Pb and Nd show no systematic relationships with major element contents of the crusts, which supports their use as tracers of paleo-seawater isotopic composition.

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

1999-06-01

88

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

Science.gov (United States)

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.

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

2009-04-01

89

Timescales of Crustal Accretion at a Medium to Fast Spreading Ridge: High Precision U- Pb Zircon Dating of the Intrusive Crust of the Cretaceous Oman Ophiolite  

Science.gov (United States)

The Oman ophiolite is one of the largest subaerial exposures of oceanic lithosphere on Earth. We present new high-precision single grain U-Pb zircon dates from both gabbro and plagiogranite plutons in the ophiolite, which provide new insight into the temporal evolution of oceanic crust. In the Ibra area, at the southern end of the ophiolite, a large and laterally coherent block of oceanic lithosphere exposes a cross section through mantle harzburgites, layered gabbros, massive gabbros, sheeted dikes and rare basaltic flows and pillows. We have dated five upper level massive gabbros and a single plagiogranite from a ~25 km transect perpendicular to the inferred ridge axis. The 206Pb/238U dates range from ~96.2-95.7 Ma and generally confirm that the crust formed at a medium to fast spreading ridge. However, the spatial distribution and spread of dates do not follow the pattern predicted by current models of simple spreading, and suggest that either i) there was significant off-axis magmatism, ii) older plutons crystallized in the mantle and were incorporated into the crust at the ridge axis, or iii) the crust was imbricated by post magmatic strike- slip faulting. Two new dates from the Samail Massif provide insight into the origin of oceanic plagiogranites. A plagioclase- hornblende vein that crosscuts layered gabbros yielded a 206Pb/238U date of ~95.8 Ma, providing a minimum age for the layered gabbros. In contrast, an adjacent plagiogranite pluton generated a range of 206Pb/238U dates of ~95.4-95.2 Ma, indicating that the plagiogranite intrusion post- dates gabbro crystallization by a minimum of ~400,000-600,000 years and likely reflects protracted off- axis modification of the crust.

Rioux, M.; Bowring, S. A.; Kelemen, P. B.

2008-12-01

90

Nature of the Crust in the Laxmi Basin, Western Continental Margin of India  

Science.gov (United States)

The nature of the crust in the Laxmi Basin, western margin of India is an uncertain issue; more importantly this has implications on paleo-geographic reconstructions of the western Indian Ocean. We have analysed three geophysical datasets and modelled gravity and magnetic anomalies for determining nature of the crust. Basement of the Laxmi Basin includes numerous highs, which make the basement uneven and shallower compared to the Western Basin. The Laxmi Basin is characterised by a broad gravity high and a narrower prominent gravity low within it, while within the basin the broad anomaly gradually increases towards north. The Panikkar Ridge is associated with the gravity low, which is comparable, at least in sign, to known negative gravity anomaly of Laxmi Ridge. Intrusive structures mapped in the Laxmi Basin coincide with significant magnetic anomalies, which were earlier interpreted as seafloor-spreading anomalies. Model studies reveal that the Laxmi Basin consists of ~14 km thick stretched continental crust, in which magmatic bodies have been emplaced, whereas Panikkar Ridge remains less altered stretched continental crust. The crust of the Laxmi Basin is mostly thinner than crust under Laxmi Ridge and continental margin. In addition to the rift-drift related stretching of the continental margin the Laxmi Basin possibly has undergone extra stretching in E-W direction during the pre-Tertiary period. At ~68 Ma Deccan volcanism on western India may have disrupted the initial conditions that were leading to onset of spreading in the basin. Subsequently the Réunion hotspot had emplaced the volcanic material within the stretched thinned continental crust. We interpret the Laxmi Basin as a failed rift, undergone stretching following intraplate kinematics prior to Deccan volcanism. Key words: Laxmi Basin, Laxmi Ridge, Panikkar Ridge, stretched continental crust, Deccan volcanism, northwest continental margin of India

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

2006-05-01

91

The exploitation of state of the art digital terrain databases and combined or satellite-only Earth gravity models for the estimation of the crust-mantle interface over oceanic regions  

Science.gov (United States)

The prediction of the geometry of characteristic crustal interfaces, such as bathymetry or Moho, can be carried out efficiently by applying well tested estimation procedures. The computation of the gravity response at the Earth's surface of a characteristic density layer in the Earth's interior in combination with the statistical tool of Least Squares Collocation have been proven to be a flexible and useful prediction tool, especially at regions with lack in primary crustal observations. To investigate the contribution of recently released digital terrain databases to this estimation procedure we use the one-minute global elevation databases GEBCO and TOPO14. Using the combined Earth gravity model EGM2008 and recently released GOCE-only models we produce the observed grid of gravity anomalies over two test areas in the Indian and the Atlantic oceans. The estimation procedure is based on a two-layer model of the upper crust and is driven mainly by the definition and quality of the involved covariance functions. The application leads to independent and much denser estimations of the crust-mantle interface over these regions, in comparison with the available Moho information provided by global databases such as CRUST 2.0. Apart from the direct comparison between the obtained solutions a further assessment was carried out in terms of computing the corresponding isostatic effects on the available regional altimeter data.

Arabelos, D. N.; Tsoulis, D.

2013-06-01

92

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

International Nuclear Information System (INIS)

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.)

1982-01-01

93

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

Energy Technology Data Exchange (ETDEWEB)

U-Pb zircon ages have been determined for two 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.

Peucat, J.J.; Vidal, P.; Postaire, B. (Rennes-1 Univ., 35 (France). Inst. de Geologie); Godard, G. (Nantes Univ., 44 (France). Lab. de Petrologie et Mineralogie)

1982-08-01

94

Neoproterozoic nascent island arc volcanism from the Nubian Shield of Egypt: Magma genesis and generation of continental crust in intra-oceanic arcs  

Science.gov (United States)

The Neoproterozoic Wadi Ranga metavolcanic rocks, South Eastern Desert of Egypt, constitute a slightly metamorphosed bimodal sequence of low-K submarine tholeiitic mafic and felsic volcanic rocks. The mafic volcanic rocks are represented by massive and pillow flows and agglomerates, composed of porphyritic and aphyric basalts and basaltic andesites that are mostly amygdaloidal. The felsic volcanic rocks embrace porphyritic dacites and rhyolites and tuffs, which overlie the mafic volcanic rocks. The geochemical characteristics of Wadi Ranga volcanic rocks, especially a strong Nb depletion, indicate that they were formed from subduction-related melts. The clinopyroxene phenocrysts of basalts are more akin to those crystallizing from island-arc tholeiitic magmas. The tholeiitic nature of the Wadi Ranga volcanics as well as their LREE-depleted or nearly flat REE patterns and their low K2O contents suggest that they were developed in an immature island arc setting. The subchondritic Nb/Ta ratios (with the lowest ratio reported for any arc rocks) and low Nb/Yb ratios indicate that the mantle source of the Wadi Ranga mafic volcanic rocks was more depleted than N-MORB-source mantle. Subduction signature was dominated by aqueous fluids derived from slab dehydration, whereas the role of subducted sediments in mantle-wedge metasomatization was subordinate, implying that the subduction system was sediment-starved and far from continental clastic input. The amount of slab-derived fluids was enough to produce hydrous magmas that follow the tholeiitic but not the calc-alkaline differentiation trend. With Mg# > 64, few samples of Wadi Ranga mafic volcanic rocks are similar to primitive arc magmas, whereas the other samples have clearly experienced considerable fractional crystallization.The low abundances of trace elements, together with low K2O contents of the felsic metavolcanic rocks indicate that they were erupted in a primitive island arc setting. The felsic volcanic rocks are characterized by lower K/Rb ratios compared to the mafic volcanic rocks, higher trace element abundances (~ 2 to ~ 9 times basalt) on primitive arc basalt-normalized pattern and nearly flat chondrite-normalized REE patterns, which display a negative Eu anomaly. These features are largely consistent with fractional crystallization model for the origin of the felsic volcanic rocks. Moreover, SiO2-REE variations for the Wadi Ranga volcanic rocks display steadily increasing LREE over the entire mafic to felsic range and enriched La abundances in the felsic lavas relative to the most mafic lavas, features which are consistent with production of the felsic volcanic rocks through fractional crystallization of basaltic melts. The relatively large volume of Wadi Ranga silicic volcanic rocks implies that significant volume of silicic magmas can be generated in immature island arcs by fractional crystallization and indicates the significant role of intra-oceanic arcs in the production of Neoproterozoic continental crust. We emphasize that the geochemical characteristics of these rocks such as their low LILE and nearly flat REE patterns can successfully discriminate them from other Egyptian Neoproterozoic felsic volcanic rocks, which have higher LILE, Zr and Nb and fractionated REE patterns.

Maurice, Ayman E.; Basta, Fawzy F.; Khiamy, Ali A.

2012-02-01

95

Distribution of crust in deep eastern Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

Most current models for the evolution of the Gulf of Mexico suggest that Upper Jurassic oceanic crust underlies the deep part of the basin, surrounded by older, attenuated continental crust (thin transitional crust). Based on a detailed analysis of existing University of Texas Institute for Geophysics multifold seismic reflection data and a recently available grid of industry data, they have redefined the oceanic/transitional crust boundary as well as characterized and mapped basement trends in areas of oceanic crust in the deep eastern gulf. Along the eastern part of the study area, the crust boundary is defined where Middle Jurassic(.) salt and equivalent strata, deposited on transitional crust prior to the emplacement of oceanic crust, onlap and pinch out basinward onto a basement block. In the northern and southern parts of the study area, the boundary is obscured by low-relief salt tongues. Regional basement highs and lows associated with oceanic crust within the central part of the deep eastern Gulf trend east-northeast-west-southwest. Deep marine rocks overlying oceanic crust appear to onlap both north and south onto a median high, suggesting that this linear feature may represent a segment of an extinct mid-ocean spreading ridge. A north-northwest-striking trough perpendicular to and bisecting the median ridge could represent an extinct fracture zone. These trends indicate that in the central gulf, sea-floor spreading was probably in a north-northwest-south-southeast direction. Apparent lack of regional structural trends in the eastern part of the study area, however, suggest a different origin for this part of the oceanic crust. These boundaries are structural trends provide important constraints for Gulf of Mexico reconstructions.

Rosenthal, D.B.; Buffler, R.T.; Corso, W.P.; Weimer, P.

1987-05-01

96

Triassic - Jurassic kinematic relationships between the Gulf of Mexico, Central Atlantic Ocean, and Mexico  

Science.gov (United States)

Closing ocean basins along geomagnetic isochrons can be an objective method for analyzing reconstructed continental margins because, in general, tectonic extension at passive margins stops once new oceanic lithosphere is created. Holding Africa fixed, we close the South Atlantic Ocean to Chron M4 (126.6 Ma) and the Central Atlantic Ocean to Chron M40 (165.1 Ma). In this configuration, and with the Gulf of Mexico closed by clockwise rotation of the Yucatan continental block (~42 degrees), the positions of North America and South America indicate that the Gulf of Mexico opened at least 20 My after the opening of the Central Atlantic Ocean (ca. 180 Ma) and the earlier breakup of Pangea (ca. 200 Ma). The Gondwanan terranes of eastern Mexico, Yucatan, Florida, and the United States south of the Ouachita-Marathon Suture, remained attached to Laurasia after the breakup of the supercontinent. The Gulf of Mexico then formed in Late Jurassic to earliest Cretaceous times (ca. 160 Ma to 140 Ma) by counterclockwise rotation of the Yucatan block. Two prominent basement structures, defined by seismic refraction and gravity data, are interpreted to be hotspot tracks created by a single mantle plume during this rotation. A third prominent basement structure is interpreted to be a marginal ridge that developed along the ocean-continental transform boundary between the Yucatan block and eastern Mexico. The Gulf of Mexico formed after initial rifting and extension of continental crust and widespread salt deposition (ca. 160 Ma to 150 Ma), followed by the mantle plume eruption and sea-floor spreading (ca. 150 Ma to 140 Ma).

Bird, D. E.; Burke, K.; Hall, S. A.; Casey, J. F.

2008-05-01

97

Oceans  

Energy Technology Data Exchange (ETDEWEB)

This chapter of the Intergovernmental Panel on Climate Change describes the potential impacts of climate change on the world`s oceans. Previous work on sea-surface temperature and sea level has been extended to examine climate change effects on ice cover, oceanic circulation and wave climate. Global biogeochemical cycles, ecosystem structures and functions, and many time and space scales are likely to be effected by climate change. The nature and likelihood of the various changes are discussed. Areas needing further research, such as the development of methodologies to assess the sensitivity of oceans to climate change, are noted. (UK)

Ittekkot, V. [Hamburg Univ. (Germany)

1996-12-31

98

Chronology of early lunar crust  

International Nuclear Information System (INIS)

The chronology of lunar rocks is summarized. The oldest pristine (i.e., lacking meteoritic contamination of admixed components) lunar rock, recently dated with Sm-Nd by Lugmair, is a ferroan anorthosite, with an age of 4.44 + 0.02 Ga. Ages of Mg-suite rocks (4.1 to 4.5 Ga) have large uncertainties, so that age differences between lunar plutonic rock suites cannot yet be resolved. Most mare basalts crystallized between 3.1 and 3.9 Ga. The vast bulk of the lunar crust, therefore, formed before the oldest preserved terrestrial rocks. If the Moon accreted at 4.56 Ga, then 120 Ma may have elapsed before lunar crust was formed.

1987-07-13

99

Channelized lava flows at the East Pacific Rise crest 9??-10??N: The importance of off-axis lava transport in developing the architecture of young oceanic crust  

Science.gov (United States)

Submarine lava flows are the building blocks of young oceanic crust. Lava erupted at the ridge axis is transported across the ridge crest in a manner dictated by the rheology of the lava, the characteristics of the eruption, and the topography it encounters. The resulting lava flows can vary dramatically in form and consequently in their impact on the physical characteristics of the seafloor and the architecture of the upper 50-500 m of the oceanic crust. We have mapped and measured numerous submarine channelized lava flows at the East Pacific Rise (EPR) crest 9?? - 10??N that reflect the high-effusion-rate and high-flow-velocity end-member of lava eruption and transport at mid-ocean ridges. Channel systems composed of identifiable segments 50 - 1000 m in length extend up to 3 km from the axial summit trough (AST) and have widths of 10 - 50 m and depths of 2 - 3 m. Samples collected within the channels are N-MORB with Mg# indicating eruption from the AST. We produce detailed maps of lava surface morphology across the channel surface from mosaics of digital images that show lineated or flat sheets at the channel center bounded by brecciated lava at the channel margins. Modeled velocity profiles across the channel surface allow us to determine flux through the channels from 0.4 to 4.7 ?? 103 m3/s, and modeled shear rates help explain the surface morphology variation. We suggest that channelized lava flows are a primary mechanism by which lava accumulates in the off-axis region (1 - 3 km) and produces the layer 2A thickening that is observed at fast and superfast spreading ridges. In addition, the rapid, high-volume-flux eruptions necessary to produce channelized flows may act as an indicator of the local magma budget along the EPR. We find that high concentrations of channelized lava flows correlate with local, across-axis ridge morphology indicative of an elevated magma budget. Additionally, in locations where channelized flows are located dominantly to the east or west of the AST, the ridge crest is asymmetric, and layer 2A appears to thicken over a greater distance from the AST toward the side of the ridge crest where the channels are located. Copyright 2005 by the American Geophysical Union.

Soule, S. A.; Fornari, D. J.; Perfit, M. R.; Tivey, M. A.; Ridley, W. I.; Schouten, H.

2005-01-01

100

Phase separation in the crust of accreting neutron stars.  

UK PubMed Central (United Kingdom)

Nucleosynthesis, on the surface of accreting neutron stars, produces a range of chemical elements. We perform molecular dynamics simulations of crystallization to see how this complex composition forms new neutron star crust. We find chemical separation, with the liquid ocean phase greatly enriched in low atomic number elements compared to the solid crust. This phase separation should change many crust properties such as the thermal conductivity and shear modulus.

Horowitz CJ; Berry DK; Brown EF

2007-06-01

 
 
 
 
101

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

Science.gov (United States)

The nature of the crust in the Laxmi Basin, western margin of India, is an uncertain issue; more importantly, this has implications on paleogeographic reconstructions of the western Indian Ocean. We have analyzed three geophysical data sets and modeled gravity and magnetic anomalies for determining nature of the crust. Basement of the Laxmi Basin includes numerous highs, which make the basement uneven and shallower compared to the Western Basin. The Laxmi Basin is characterized by a broad gravity high and a narrower prominent gravity low within it, while within the basin the broad anomaly gradually increases toward north. The Panikkar Ridge is associated with the gravity low, which is comparable, at least in sign, to known negative gravity anomaly of the Laxmi Ridge. Intrusive structures mapped in the Laxmi Basin coincide with significant magnetic anomalies, which were earlier interpreted as seafloor-spreading anomalies. Model studies reveal that the Laxmi Basin consists of ˜14 km thick stretched continental crust, in which magmatic bodies have been emplaced, whereas the Panikkar Ridge remains less altered stretched continental crust. The crust of the Laxmi Basin is mostly thinner than crust under the Laxmi Ridge and continental margin. In addition to the rift-drift-related stretching of the continental margin, the Laxmi Basin possibly has undergone extra stretching in E-W direction during the pre-Tertiary period. At ˜68 Ma Deccan volcanism on western India may have disrupted the initial conditions that were leading to onset of spreading in the basin. Subsequently the Réunion hot spot had emplaced the volcanic material within the stretched thinned continental crust. We interpret the Laxmi Basin as a failed rift, undergone stretching following intraplate kinematics prior to Deccan volcanism.

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

2006-02-01

102

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  

Science.gov (United States)

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 ?Os (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.

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

2013-04-01

103

Factitious lip crusting.  

UK PubMed Central (United Kingdom)

Four cases of factitious crusting of the lips in women are reported. Two of the women had hemorrhagic crusts, and two had keratotic yellow crusts. All four patients had personality disturbances. Biting, picking, or unconscious licking of the lips may be the underlying mechanism for trauma and crust formation. This entity should be distinguished from contact cheilitis, actinic cheilitis, infectious cheilitis glandularis, and cheilitis granulomatosa. Some cases of exfoliative cheilitis may also be factitious. The presence of bizarre hemorrhagic or keratotic crusts on the lips should alert the clinician to a possible factitious origin, and a psychiatric evaluation should be done.

Crotty CP; Dicken CH

1981-06-01

104

Factitious lip crusting.  

Science.gov (United States)

Four cases of factitious crusting of the lips in women are reported. Two of the women had hemorrhagic crusts, and two had keratotic yellow crusts. All four patients had personality disturbances. Biting, picking, or unconscious licking of the lips may be the underlying mechanism for trauma and crust formation. This entity should be distinguished from contact cheilitis, actinic cheilitis, infectious cheilitis glandularis, and cheilitis granulomatosa. Some cases of exfoliative cheilitis may also be factitious. The presence of bizarre hemorrhagic or keratotic crusts on the lips should alert the clinician to a possible factitious origin, and a psychiatric evaluation should be done. PMID:6972736

Crotty, C P; Dicken, C H

1981-06-01

105

Dynamics and the geochemical mechanism of the evolution of the continental crust. 1. The dynamics of the evolution of the continental crust  

Energy Technology Data Exchange (ETDEWEB)

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

Wetzel, K. (Akademie der Wissenschaften der DDR, Leipzig. Zentralinstitut fuer Isotopen- und Strahlenforschung)

1983-01-01

106

Early formation of evolved asteroidal crust.  

Science.gov (United States)

Mechanisms for the formation of crust on planetary bodies remain poorly understood. It is generally accepted that Earth's andesitic continental crust is the product of plate tectonics, whereas the Moon acquired its feldspar-rich crust by way of plagioclase flotation in a magma ocean. Basaltic meteorites provide evidence that, like the terrestrial planets, some asteroids generated crust and underwent large-scale differentiation processes. Until now, however, no evolved felsic asteroidal crust has been sampled or observed. Here we report age and compositional data for the newly discovered, paired and differentiated meteorites Graves Nunatak (GRA) 06128 and GRA 06129. These meteorites are feldspar-rich, with andesite bulk compositions. Their age of 4.52 +/- 0.06 Gyr demonstrates formation early in Solar System history. The isotopic and elemental compositions, degree of metamorphic re-equilibration and sulphide-rich nature of the meteorites are most consistent with an origin as partial melts from a volatile-rich, oxidized asteroid. GRA 06128 and 06129 are the result of a newly recognized style of evolved crust formation, bearing witness to incomplete differentiation of their parent asteroid and to previously unrecognized diversity of early-formed materials in the Solar System. PMID:19129845

Day, James M D; Ash, Richard D; Liu, Yang; Bellucci, Jeremy J; Rumble, Douglas; McDonough, William F; Walker, Richard J; Taylor, Lawrence A

2009-01-01

107

Early formation of evolved asteroidal crust.  

UK PubMed Central (United Kingdom)

Mechanisms for the formation of crust on planetary bodies remain poorly understood. It is generally accepted that Earth's andesitic continental crust is the product of plate tectonics, whereas the Moon acquired its feldspar-rich crust by way of plagioclase flotation in a magma ocean. Basaltic meteorites provide evidence that, like the terrestrial planets, some asteroids generated crust and underwent large-scale differentiation processes. Until now, however, no evolved felsic asteroidal crust has been sampled or observed. Here we report age and compositional data for the newly discovered, paired and differentiated meteorites Graves Nunatak (GRA) 06128 and GRA 06129. These meteorites are feldspar-rich, with andesite bulk compositions. Their age of 4.52 +/- 0.06 Gyr demonstrates formation early in Solar System history. The isotopic and elemental compositions, degree of metamorphic re-equilibration and sulphide-rich nature of the meteorites are most consistent with an origin as partial melts from a volatile-rich, oxidized asteroid. GRA 06128 and 06129 are the result of a newly recognized style of evolved crust formation, bearing witness to incomplete differentiation of their parent asteroid and to previously unrecognized diversity of early-formed materials in the Solar System.

Day JM; Ash RD; Liu Y; Bellucci JJ; Rumble D 3rd; McDonough WF; Walker RJ; Taylor LA

2009-01-01

108

Evidence for ˜80-75 Ma subduction jump during Anatolide-Tauride-Armenian block accretion and ˜48 Ma Arabia-Eurasia collision in Lesser Caucasus-East Anatolia  

Science.gov (United States)

Orogens formed by a combination of subduction and accretion are featured by a short-lived collisional history. They preserve crustal geometries acquired prior to the collisional event. These geometries comprise obducted oceanic crust sequences that may propagate somewhat far away from the suture zone, preserved accretionary prism and subduction channel at the interplate boundary. The cessation of deformation is ascribed to rapid jump of the subduction zone at the passive margin rim of the opposite side of the accreted block. Geological investigation and 40Ar/39Ar dating on the main tectonic boundaries of the Anatolide-Tauride-Armenian (ATA) block in Eastern Turkey, Armenia and Georgia provide temporal constraints of subduction and accretion on both sides of this small continental block, and final collisional history of Eurasian and Arabian plates. On the northern side, 40Ar/39Ar ages give insights for the subduction and collage from the Middle to Upper Cretaceous (95-80 Ma). To the south, younger magmatic and metamorphic ages exhibit subduction of Neotethys and accretion of the Bitlis-Pütürge block during the Upper Cretaceous (74-71 Ma). These data are interpreted as a subduction jump from the northern to the southern boundary of the ATA continental block at 80-75 Ma. Similar back-arc type geochemistry of obducted ophiolites in the two subduction-accretion domains point to a similar intra-oceanic evolution prior to accretion, featured by slab steepening and roll-back as for the current Mediterranean domain. Final closure of Neotethys and initiation of collision with Arabian Plate occurred in the Middle-Upper Eocene as featured by the development of a Himalayan-type thrust sheet exhuming amphibolite facies rocks in its hanging-wall at c. 48 Ma.

Rolland, Yann; Perincek, Dogan; Kaymakci, Nuretdin; Sosson, Marc; Barrier, Eric; Avagyan, Ara

2012-05-01

109

Crustal Thickness and the Distribution of Oceanic Lithosphere in the Western Mediterranean from Gravity Inversion  

Science.gov (United States)

Gravity inversion has been used to map Moho depth, crustal thickness and continental lithosphere thinning for the western Mediterranean in order to determine the distribution of oceanic and continental lithosphere and the location of the ocean-continent transition. Data used in the gravity inversion are bathymetry, free-air gravity, sediment thickness and age isochrons, where available, from Smith and Sandwell (2009), Sandwell and Smith (2009), Laske and Masters (1997) and Muller et al (2008) respectively. The gravity inversion method, which is carried out in the 3D spectral domain and predicts Moho depth, incorporates a lithosphere thermal gravity anomaly correction because of the elevated geothermal gradient within oceanic and rifted continental margin lithosphere (Chappell & Kusznir 2008). Gravity inversion results are dependent on the age of the oceanic lithosphere and continental break-up; the lithosphere thermal gravity anomaly correction is dependent on the lithosphere thermal re-equilibration time. Gravity inversion sensitivities to break-up ages of 30Ma, 20Ma and 5Ma have been examined, for the western Mediterranean corresponding to break-up ages in the North Balearic Basin and Gulf of Lion, in the South Balearic and Ligurian Basins, and in the Tyrrhenian Basin. The resulting maps of Moho depth, crustal basement thickness and continental lithosphere thinning from gravity inversion predict the distribution of oceanic and thinned continental crust within these basins. Gravity inversion results suggest that a reference Moho depth of 45km is required in order to predict crustal thicknesses consistent with oceanic crust in the Balearic Basins and the Tyrrhenian Sea. The high reference Moho depth (45km or greater) required by the gravity inversion to predict sensible oceanic crustal thicknesses suggests that the western Mediterranean region is subjected to regional mantle dynamic subsidence. This is consistent with mantle dynamic topography predictions by Mueller et al (2008). Maps of Moho depth, crustal basement thickness and continental lithosphere thinning have been corrected for regional variations in mantle dynamic topography.

Cowie, L.; Kusznir, N.

2012-04-01

110

On- and off-axis chemical heterogeneities along the South Atlantic Mid-Ocean-Ridge (5-11°S): Shallow or deep recycling of ocean crust and/or intraplate volcanism?  

Science.gov (United States)

The Mid-Atlantic Ridge between the Ascension and Bode Verde Fracture Zones exhibits anomalous crustal thickness and geochemical compositions, which could reflect the presence of either small, enriched heterogeneities in the upper mantle or a weak, diffuse mantle plume. We report new trace element (106 samples) and Sr, Nd and Pb (double spike) isotope data from 72 ridge axis samples and 9 off-axis seamount samples between 5 and 11°S, as well as U-Th-Ra disequilibria data for the seamounts. The U-series data constrain the age of one sample from Seamount D, furthest (120 km) east of the shallowest part of the ridge, to be ocean island basalt (OIB) type volcanic islands and seamounts that have either been recycled through 1) the shallow mantle, upwelling passively beneath the ridge system or 2) the deep mantle via an actively upwelling heterogeneous mantle plume that interacts with the ridge system.

Hoernle, Kaj; Hauff, Folkmar; Kokfelt, Thomas F.; Haase, Karsten; Garbe-Schönberg, Dieter; Werner, Reinhard

2011-06-01

111

Deep dish pizza crust  

UK PubMed Central (United Kingdom)

A fully baked, deep dish pizza crust is provided having a water activity in the range of about 0.9 to about 0.95. The deep dish pizza crust is ideally suited for use in a refrigerated, ready-to-eat pizza kit. The deep dish pizza crust is of a convenient size and shape (generally square and about 4 by about 4 by about 0.75 in. deep) and is especially adapted as a single serving or snack food product. Also provided is a kit for preparing ready-to-eat deep dish pizza, the kit including one or more deep dish pizza crusts, pizza sauce, cheese, and one or more pizza toppings. The deep dish pizza crusts are designed so that they can be nested so as to reduce the volume requirements in the kit. Each of the components of the pizza kit, including the deep dish pizza crusts, is hermetically sealed from the other food items to substantially retard or prevent flavor, moisture, and microbial migration from one food item to another. The deep dish pizza crusts retain a soft, desirable texture throughout their anticipated shelf lives.

LAMP MARY A; FORNECK KEITH; PAULOS WILLIAM T

112

Deep dish pizza crust  

UK PubMed Central (United Kingdom)

A fully baked, deep dish pizza crust is provided having a water activity in the range of about 0.9 to about 0.95. The deep dish pizza crust is ideally suited for use in a refrigerated, ready-to-eat pizza kit. The deep dish pizza crust is of a convenient size and shape (generally square and about 4 by about 4 by about 0.75 in. deep) and is especially adapted as a single serving or snack food product. Also provided is a kit for preparing ready-to-eat deep dish pizza, the kit including one or more deep dish pizza crusts, pizza sauce, cheese, and one or more pizza toppings. The deep dish pizza crusts are designed so that they can be nested so as to reduce the volume requirements in the kit.Each of the components of the pizza kit, including the deep dish pizza crusts, is hermetically sealed from the other food items to substantially retard or prevent flavor, moisture, and microbial migration from one food item to another. The deep dish pizza crusts retain a soft, desirable texture throughout their anticipated shelf lives.

LAMP MARY A; FORNECK KEITH; PAULOS WILLIAM T

113

Millet rice crust  

UK PubMed Central (United Kingdom)

The invention provides a millet rice crust, relating to a natural total nutrient rice crust and a manufacturing method thereof. The invention adopts millet as a major ingredient, and uses natural nutrient materials such as beans, nuts, shrimpbran powder and vegetable protein powder, cereal germ powder, fresh bone calcium powder, animal liver powder, dried marine algae powder, spirulina powder and the like for nutrition enrichment and flavoring, thus having balanced and overall nutrition. In the manufacturing process, the rice and bean materials are cooked and ripened for two times, and natural nutrition enrichment and flavoring are carried out for three times in different processing stages, thus providing finished products of rice crust slice and roasted semi-finished products of rice crust slice billet and rice crust cookie billet. The invention has the following beneficial effects that as millet has unique edible value and is abundant in a plurality of amino acids and vitamins and the like, the rice crust has more health functions, more sweet taste and natural color.

HEPING FU

114

Oceanic slab melting and mantle metasomatism.  

UK PubMed Central (United Kingdom)

Modern plate tectonic brings down oceanic crust along subduction zones where it either dehydrates or melts. Those hydrous fluids or melts migrate into the overlying mantle wedge trigerring its melting which produces arc magmas and thus additional continental crust. Nowadays, melting seems to be restricted to cases of young (< 50 Ma) subducted plates. Slab melts are silicic and strongly sodic (trondhjemitic). They are produced at low temperatures (< 1000 degrees C) and under water excess conditions. Their interaction with mantle peridotite produces hydrous metasomatic phases such as amphibole and phlogopite that can be more or less sodium rich. Upon interaction the slab melt becomes less silicic (dacitic to andesitic), and Mg, Ni and Cr richer. Virtually all exposed slab melts display geochemical evidence of ingestion of mantle material. Modern slab melts are thus unlike Archean Trondhjemite-Tonalite-Granodiorite rocks (TTG), which suggests that both types of magmas were generated via different petrogenetic pathways which may imply an Archean tectonic model of crust production different from that of the present-day, subduction-related, one.

Scaillet B; Prouteau G

2001-01-01

115

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

Directory of Open Access Journals (Sweden)

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

R. Banerjee; S. M. Gupta; H. Miura; D. V. Borole

2010-01-01

116

Crustal Thickness and Oceanic Lithosphere Distribution in the Eastern Mediterranean from Satellite Gravity Anomaly Inversion  

Science.gov (United States)

The distribution of oceanic and continental lithosphere in the eastern Mediterranean is not well understood. Gravity inversion, incorporating a lithosphere thermal gravity anomaly correction, has been used to map Moho depth, crustal thickness and continental lithosphere thinning factor for the eastern Mediterranean in order to determine the distribution of oceanic and continental lithosphere and the ocean-continent transition location. Data used in the gravity inversion are bathymetry, free-air gravity and sediment thickness data from Smith and Sandwell (1997), Sandwell and Smith (2009) and Laske and Masters (1997) respectively. Moho depths from the gravity inversion are dependent on the age of oceanic lithosphere and continental breakup because of the lithosphere thermal gravity correction; however, these ages are uncertain for the eastern Mediterranean. Gravity inversion sensitivities to break-up ages of 225Ma (late Triassic) and 100Ma (early Cretaceous) have been examined. Gravity inversion results show thin crust (5 - 10km thickness) for the Ionian Sea and the Herodotus Basin of the eastern Mediterranean consistent with these basins being underlain by oceanic or highly thinned continental crust. Predicted Moho depths from the gravity inversion are in agreement with published Ionian Sea ESP results (Voogd et al, 1992) and suggest a gravity inversion reference Moho depth increasing to the north, which we attribute to subduction dynamic subsidence. Calibration of gravity inversion Moho against ESP results show a trade-off between break-up age and reference Moho depth; a Cretaceous age ocean requires a larger Moho reference depth than a Triassic age ocean. Lithosphere thinning factor maps from gravity inversion for Africa do not show continuity between the Cretaceous African rift system (Benue Trough, Chad, CASZ and Sudan basins) and eastern Mediterranean basins. If the Ionian Sea is of Cretaceous age then it more probably links to Cretaceous rifting and sea-floor spreading to its north and north-west.

Cowie, L.; Kusznir, N. J.

2010-12-01

117

Crust-Mantle Interactions  

Energy Technology Data Exchange (ETDEWEB)

The topic of crust-mantle interactions covers two orders of problems. On the one hand, there is an observational problem, dealing with the petrological, geochemical, and geophysical properties of the transition, approached through experiment and field work; on the other hand, there is a modelling problem, dealing with the role of the crust/mantle system in various igneous, metamorphic, and tectonic processes. These two problems, however, are so closely interconnected that a division along observational and modelling lines, as defined above, would be difficult and not very fruitful. As in many other topics in Earth Science, there is a continuous feedback loop among observation, inference, model, and model verification. It has been therefore preferred to organize the volume in three parts, according to subject matter. The first part groups together the lectures dealing with large-scale geophysical observations and geodynamic modelling. The second part deals with the field studies, mineral physics, magmatism and metamorphism of the crust/mantle system. The third part presents a survey of geological and geophysical data, together with their interpretation, from selected areas which provide particularly interesting instances of crust/mantle interactions.

Ranalli, G. [Ottawa Carleton University, Ottawa (Canada). Dept. of Earth Sciences; Ricci, C.A. [Siena Univ., Siena (Italy). Dipt. di Scienze della Terra; Trommsdorff, V. [ETH-Zentrum, Institut fuer Mineralogie und Petrographie, Zuerich (Switzerland)

2000-07-01

118

[Factitious crusting cheilitis].  

Science.gov (United States)

The authors report 4 cases of factitious crusting cheilitis seen in young women. The lesions are crusty, yellowish or even black, forming as a mould casting the lip. The crusts are sometimes very thick just as an oyster-shell. When removed the underlying mucosa appears either normal or erosive and the crusts reappear rapidly. Emotional factors and personality disturbances are often present. Most probably the crusts are the result of a traumatic mechanism induced by chewing or sucking the lip. In the 4 reported patients the clinical aspect and the psychological status of the patients are similar, the 4 of them being not at all bothered by their cheilitis. The factitious keratotic cheilitis has to be differentiated from other cheilitis induced by Candida albicans (although Candida albicans may superinfect any cheilitis) or by an actinic phenomenon, from glandular cheilitis (of the Puente-Acevedo or of the Volkmann type) and from dermatitis localized on the lips. In some instances an exfoliative cheilitis may also to be of factitious origin. The factitious origin of such a cheilitis is always difficult to demonstrate but its possibility should be kept in mind. PMID:6524813

Jeanmougin, M; Civatte, J; Bertail, M A

1984-01-01

119

[Factitious crusting cheilitis  

UK PubMed Central (United Kingdom)

The authors report 4 cases of factitious crusting cheilitis seen in young women. The lesions are crusty, yellowish or even black, forming as a mould casting the lip. The crusts are sometimes very thick just as an oyster-shell. When removed the underlying mucosa appears either normal or erosive and the crusts reappear rapidly. Emotional factors and personality disturbances are often present. Most probably the crusts are the result of a traumatic mechanism induced by chewing or sucking the lip. In the 4 reported patients the clinical aspect and the psychological status of the patients are similar, the 4 of them being not at all bothered by their cheilitis. The factitious keratotic cheilitis has to be differentiated from other cheilitis induced by Candida albicans (although Candida albicans may superinfect any cheilitis) or by an actinic phenomenon, from glandular cheilitis (of the Puente-Acevedo or of the Volkmann type) and from dermatitis localized on the lips. In some instances an exfoliative cheilitis may also to be of factitious origin. The factitious origin of such a cheilitis is always difficult to demonstrate but its possibility should be kept in mind.

Jeanmougin M; Civatte J; Bertail MA

1984-01-01

120

Gulf of Mexico plate reconstruction by palinspastic restoration of extended continental crust  

Energy Technology Data Exchange (ETDEWEB)

In this study, total tectonic subsidence analysis was used to estimate the mount of crust extension in the Gulf of Mexico to determine its effects on the proposed plate reconstructions. This involves the calculation and mapping of the sediment-unloaded-basement depth from observations of the basement depth, water depth, and sediment compaction properties. The well-known depth-age relation for oceanic crust and a model for the subsidence of extended continental crust allowed within the limits of available data the identification and mapping of crust type and the amount of extension of transitional crust. The zone of extended continental crust under the northern margin of the Gulf is extraordinarily wide, more than 800 km (500 mi) in a cross section through east Texas. The zone of extended crust to the south is much narrower, about 150 km (90 mi) on the margin of the Yucatan Block. Palinspastic restoration shows that the total 950 km (590 mi) of extended and thinned continental crust corresponds to 490 km (300 mi) of continental crust of original thickness. Therefore 460 km (280 mi) of crustal extension occurred during rifting and prior to ocean crust formation. The 460 km (280 mi) of extension along this cross section, and the results of similar calculations on the other cross sections, must be accounted for properly when reconstructing the prerift configuration of the Gulf of Mexico.

Sawyer, D.S.

1984-04-01

 
 
 
 
121

Continent- Ocean Transition Across the Alarcon Basin, Gulf of California from Seismic Reflection and Refraction Data.  

Science.gov (United States)

A transect of seismic reflection and onshore/offshore refraction data was collected across the Alarcon Basin, Gulf of California in Fall 2002 as part of the MARGINS Rupturing Continental Lithosphere (RCL) initiative. The dataset consists of ~600 km of seismic reflection data together with data from 53 ocean-bottom seismometers and 11 land seismometers along a coincident ~900 km refraction line. This transect crosses the entire conjugate rift system from continent to the thinned and faulted crust of the transition zone, and then to oceanic crust with an active seafloor spreading center. The Alarcon Rise is the southernmost spreading segment in the Gulf of California, separated from the East Pacific Rise by the Tamayo transform fault. Extension in the gulf began about 12 Ma and rifting was initiated at the mouth of the Gulf at the now inactive Magdalena spreading ridge about 5 Ma. Magnetic anomalies reveal that the Alarcon Rise has been spreading at an intermediate rate since 3.6 Ma. The current ridge crest is about 10 km wide, 150 m high and with a small axial valley. The data quality from the ocean-bottom seismometers is excellent, with first arrivals to at least 75 km offset, and past 100 km on many instruments. Land seismometers also produced excellent results- first arrivals are typically observed out to 200 km offset. Pg/Pn crossover distances are around 40 km in the oceanic crust of the Alarcon basin, increase to about 60-75 km in the transition zone and reach a maximum of about 100km for the continental land instruments. The total width of oceanic crust created at the Alarcon Rise, as determined from reflection profiles and initial refraction processing is about 130 km, which agrees with the bathymetric data. The transition zone is characterized by normal faulting- synrift faulting created sedimentary basins, which were later modified by additional normal faulting. The rifted margin appears to be symmetric, with about 180 km of transition zone on either side. However the southern margin is complicated by the fossil Magdalena spreading ridge, which lies about 150 km southeast of the Alarcon rise. We will present MCS results and an initial velocity model across the Alarcon basin.

Sutherland, F. H.; Harding, A. J.; Kent, G. M.; Lizarralde, D.; Holbrook, W. S.; González-Ferná; ndez, A.; Fletcher, J. M.; Umhoefer, P. J.; Axen, G. J.

2003-12-01

122

Crust-mantle density contrast derived globally using gravity and seismic models  

Science.gov (United States)

We utilize the combined least-squares approach to determine jointly the crustal thickness and the crust-mantle density contrast using gravity data and constraining information from seismic model. The principle of this combined approach is based on solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy. The EGM2008 global gravity model coefficients, the DTM2006.0 global topographic/bathymetric model coefficients, global ice thickness data, and the sediment and consolidated crust thickness and density data from the global crustal model CRUST2.0 are used to generate the isostatic gravity anomalies. All computations are realized and presented globally on a 1×1 arc-deg geographical grid. The estimated values of the crust-mantle density contrast (defined relative to the adopted value of the reference crust density of 2670 kg/m3) are between 81 and 965 kg/m3. The minima correspond with locations of the divergent oceanic tectonic plate boundaries. The maxima are found along the convergent tectonic plate boundaries in Andes and in Himalayas (extending under the Tibetan plateau). We demonstrate that the spatial distribution of the crust-mantle density underneath the oceanic crust is attributed to the age of oceanic lithosphere. The corresponding distribution beneath the continental crust is significantly correlated with the crustal thickness.

Tenzer, R.; Bagherbandi, M.; Novak, P.

2012-04-01

123

Macquarie island and the cause of oceanic linear magnetic anomalies.  

UK PubMed Central (United Kingdom)

Macquarie Islands is formed of probably Pliocene oceanic crust. Intruded into pillow lavas is a belt of harzburgite and layered gabbro mnasses cut by dike swarms. Similar belt-like structures may cause the linear magnetic anomalies of the ocean.

Varne R; Gee RD; Quilty PG

1969-10-01

124

ConcepTest: Oceans by South America #6  

Science.gov (United States)

Examine the image of part of the South American continent and neighboring oceans. (Image courtesy the National Geophysical Data Center.) Which sites are most likely to be located on oceanic crust? a. A, B, C, & ...

125

Mechanisms of continental crust formation in the Central Asian Foldbelt  

Science.gov (United States)

Geological and isotopic study of rocks occurring in the Early and Late Baikalian, Caledonian, Hercynian, and Indosinian fold regions of Central Asia is carried out. The juvenile crust formation occurred in these fold regions have determined the systematic differences in isotopic compositions of the crust. In the course of the subsequent (postaccretion) evolution, the crust of these domains underwent multiple reworking. These processes were accompanied by variations in the Nd isotopic compositions of the crust, which, in turn, are recorded in the isotopic compositions of granites and felsic volcanics as products of crust melting. Three types of crust differing in Nd isotopic composition and structure and, as a consequence, in formation mechanisms, are distinguished. The isotopically homogeneous crust is a source of igneous rocks with constant model Nd isotopic age (TNd(DM2st)) irrespective of the age of the crustal igneous rocks. These are the isotopic provinces, the crust of which remained isolated from addition of alien materials during postaccretion evolution. The axial zone of the Hercynides in the Central Asian Foldbelt is an example. The isotopically heterogeneous layered crust consists of fragments differing in isotopic composition. The products of its melting are characterized by widely scattered ?Nd(T) and (TNd(DM2st). The appearance of alien sources of melt is considered in terms of underplating. This mechanism develops either due to subduction of the juvenile oceanic lithosphere beneath the mature continental lithosphere at convergent boundaries or as a result of plume-lithosphere interaction. The first mechanism operated during the formation of granitoids pertaining to the Tuva-Mongolia microcontinent. The second mechanism was responsible for the formation of batholiths in the zonal Hangay, Barguzin, and Mongolia-Transbaikalia magmatic fields. The isotopically heterogeneous mixed crust is composed of fragments differing in isotopic composition, which are tectonically mixed, resulting in the formation of an isotopically uniform reservoir in the domain of magma generation. As a result, the products of melting acquire isotopic parameters substantially distinct from the juvenile rocks of the corresponding structural zone. The formation of such a crust is related to the tectonic delamination, which provides for juxtaposition and a high degree of tectonic mingling of heterogeneous fragments at deep levels. The Caledonides of the Central Asian Foldbelt are characterized by such a mechanism of crust formation.

Yarmolyuk, V. V.; Kovach, V. P.; Kozakov, I. K.; Kozlovsky, A. M.; Kotov, A. B.; Rytsk, E. Yu.

2012-07-01

126

UV - BOSTON MA  

Science.gov (United States)

Brewer 103 is located in Boston MA, measuring ultraviolet solar radiation. Irradiance and column ozone are derived from this data. Ultraviolet solar radiation is measured with a Brewer Mark IV, single-monochrometer, spectrophotometer manufactured by SCI-TEC Instruments, Inc. of S...

127

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

Science.gov (United States)

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.

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

2012-10-01

128

Continental Paleoclimate of Southern Argentina, 38Ma to the Present  

Science.gov (United States)

Recent advances in isotope geochemistry have shown that the stable isotopes of oxygen preserved in the tooth enamel of mammals can be used to develop continental climate records. Enamel isotope ratios are highly correlated with rain water compositions, which in turn correlate strongly with temperature. In this study we developed a baseline climatic record for southern South America from 38 Ma to the present, to compare the continental and marine climate records. Fossil teeth were analyzed from the Sarmiento Formation of the Gran Baranca (S45° 42'49", W68° 44'16") in the Chubut Province, Argentina. Zoning profiles were collected along the length of the teeth and show smoothly changing compositions (variations = 3-7 ‰ ), consistent with preserved seasonal isotope variations. Average isotope values (which reflect average yearly climate) show important temporal changes. Median ? 18O values are 15.6‰ (38.3Ma), 16.0‰ (36.9Ma), 16.8‰ (33.3Ma), 16.3‰ (30.5Ma), 14.2‰ (22.9Ma), 14.4‰ (19.8Ma), 15.5‰ (19.5Ma), 19.2‰ (15.8Ma), 14.9‰ (11.8Ma), and 14.9‰ (0Ma). Changes in median isotope compositions show gross similarities as well as differences compared to the global marine record. In general, median ? 18O values of tooth enamel should increase as climate warms, and decrease as climate cools, because rainwater ? 18O correlates positively with temperature. As expected, the mid-Miocene warming event (15Ma) resulted in both a global and regional shift in isotope compositions. However, major global cooling during the early-to mid-Oligocene (34-26Ma) and post-Miocene cooling (12 Ma to the present) had little obvious effect on isotopic records of continental climate in southern South America. Processes such as tectonics, ocean and atmospheric circulation evidently decouple terrestrial and marine climate histories.

Josef, J. A.; Kohn, M. J.

2002-05-01

129

Physics of Neutron Star Crusts  

Directory of Open Access Journals (Sweden)

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.

Chamel Nicolas; Haensel Pawel

2008-01-01

130

Ocean Drilling Program: Recent highlights and future expeditions  

Energy Technology Data Exchange (ETDEWEB)

During the past year, exploration of the deep ocean floor through scientific ocean drilling has yielded important results with respect to evolution of ocean crust and continental margins and paleoceanography. This paper describes the Ocean Drilling Program's (ODP's) scientific and technical achievements during its ninth year of field operations and discusses areas of future study.

Rabinowitz, P.D. (Texas A M Univ., College Station, TX (United States). Ocean Drilling Program)

1994-04-01

131

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

Science.gov (United States)

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.

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

2009-07-01

132

Nicoya Peninsula, Costa Rica: A single suite of Caribbean oceanic plateau magmas  

Science.gov (United States)

The pre-Tertiary oceanic crust exposed on the west coast of Costa Rica has been broadly referred to as the Nicoya Complex. This study was designed to determine the age of the Nicoya Complex in the Nicoya Peninsula, Playa Jacó, and the Quepos Peninsula using 40Ar-39Ar radiometric dating and to assess the petrologic relationships between the different localities using major element, trace element, and Sr, Nd, Pb isotopic data. Radiometric ages of basalts and diabases from the Nicoya Peninsula are 88-90 Ma (with a weighted mean of 88.5 Ma), and those of two intrusive rocks (a gabbro and plagiogranite) are both 83-84 Ma. The combined geochemical data indicate that the sampled Nicoya Peninsula rocks belong to a single suite related by fractional crystallization of similar parental magmas. Nd and Pb isotopic ratios indicate a common mantle source distinct from that of mid-ocean ridge basalts. Both the age and composition of the Nicoya rocks are consistent with the idea that they are a part of the Caribbean Cretaceous oceanic plateau [Donnelly, 1994]. The Jacó lavas are geochemically similar to the Nicoya Peninsula suite, and a single age of 84 Ma is identical to the age of the Nicoya Peninsula intrusives. The one analyzed Quepos basalt has a radiometric age of ˜64 Ma, and it is enriched in incompatible elements relative to the Nicoya rocks. Similarities in Nd and Pb isotopic ratios indicate that the Quepos and Nicoya/Jacó lavas were derived from a similar mantle source to that which produced the Nicoya rocks, possibly the Galapagos plume.

Sinton, Christopher W.; Duncan, Robert A.; Denyer, Percy

1997-07-01

133

Adjoint tomography of the southern California crust.  

UK PubMed Central (United Kingdom)

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

Tape C; Liu Q; Maggi A; Tromp J

2009-08-01

134

Dynamics of ocean tides  

Energy Technology Data Exchange (ETDEWEB)

Ocean tide information can solve vital problems in oceanology and geophysics. Elastic properties of the Earth's crust, tidal gravity variations and deviations in trajectories of artificial satellites can be studied from the dynamics of ocean tides. This book contains mathematical models and applications on several problems related to ocean tide dynamics. The first part serves as an introduction to studies of tidal dynamics equations and the application in experimental studies. Specific problems like free oscillations and forced tidal oscillations in the oceans and the ocean-shelf system are discussed. The book deals with tidal flow in the bottom boundary layer. Data and models are presented and experimental and theoretical results are compared.

Maarchuk, G.I.; Kagan, B.A. (P.P. Shirshov Inst. of Oceanology, Moscow (SU))

1989-01-01

135

U-Pb Zircon geochronology, Hf isotope and trace element geochemistry of a unique lower crustal - upper mantle section of a dying slow-spreading mid-ocean ridge (Macquarie Island, Southern Ocean)  

Science.gov (United States)

Macquarie Island, located in the Southern Ocean, is a section of oceanic crust formed at the now extinct proto-Macquarie, slow-spreading, mid-ocean ridge. The northernmost part of Macquarie Island is composed primarily of lower crustal gabbro and upper mantle peridotite. The mantle sequence consists of harzburgite intruded by a variety of gabbro dikes/dikelettes and zircon and phlogopite-bearing veins. Here, we report integrated Pb/U zircon ages and Hf isotopic and trace element data from six samples of the lower crust-upper mantle sequence. Samples consist of two lower crustal gabbros, and three gabbro dikes/dikelettes and one phlogopite-bearing vein from the upper mantle sequence. 206Pb/238U SHRIMP-RG zircon ages for the gabbros range from 8.7 ± 0.3 Ma to 9.0 ± 0.2 Ma, whereas gabbro dikes/dikelettes yield overlapping ages of 8.7 ± 0.2 Ma, 8.7 ± 0.3 Ma, and 8.9 ± 0.2 Ma (all errors 2s). The phlogopitic vein yielded a slightly younger age of 8.5 ± 0.1 Ma. Initial epsilon Hf results for zircons from the same samples show a broad distribution ranging from +9.5 to +13.3 for the lower crustal gabbro (N=28), +7.0 to +16.4 for the gabbro dikes/diklettes (N=24), and +8.4 to +12.2 for the phlogopite vein (N=12). The wide range in values (particularly from the gabbro dikes/diklettes) is consistent with a heterogeneous source region composed of a range of relatively long-lived depleted- and enriched mantle sources. Zircon trace element concentrations also support a heterogeneous source, displaying enrichment in U/Yb relative to N-MORB zircons from the Mid-Atlantic and Southwest Indian Ridge systems. We interpret these results to indicate that magmatic construction of Macquarie Island occurred from 8.7 to 9.0 Ma and involved sampling of at least two distinct mantle sources.

Jeffcoat, C. R.; Schwartz, J. J.; Wooden, J. L.; Mueller, P. A.; Saal, A. E.

2011-12-01

136

Discovery and utilization of sorghum genes (Ma5/Ma6)  

Energy Technology Data Exchange (ETDEWEB)

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.

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

2012-11-13

137

Evolution Of The Alpha Ride, The Arctic Ocean, On The Basis Of The Geohistorical Analysis Of The Magnetic Anomalies  

Science.gov (United States)

A new magnetic anomaly map of the Amerasian Basin has been created owing to a joint reprocessing of the Russian and American aeromagnetic data [Glebovsky, Kovacs at all., 2000]. This model produced the base for the magnetic data interpretation on the more qualitative level. As a result three series of seafloor spreading-type magnetic anomalies have been identified within the area of the Alpha Ridge and the adjacent part of the Canada Basin [Gurevich et all, 2003]. Their sources were formed from three spreading centers (SC). Two spreading centers: the western and the eastern, are situated at the axial part of the Alpha Ridge, the third one - the southern, is located on the southern slope of the Alpha Ridge and on the adjacent part of the Canada Basin. The triple junction of these SC had been located in the central part of the recent Alpha Ridge. The geohistorical analysis of these magnetic anomalies is fulfilled using an original computer programs. In consequence of this analysis: the geochronological characteristics are specified; the kinematic characteristics of the oceanic floor movement are determined and the main stages of the area evolution are found. The magnetic anomalies M16r (140 Ma), which signify the position of all three SC, and pair anomalies M20r (146.5 Ma) and M23r (151.5 Ma) are identified enough sure for all three SC and pair anomalies M30r (157.5 Ma) - fore the eastern and the southern SC. Finite and differential Euler poles of the lithospheric plates rotation were calculated for all three SC from best-fit pair magnetic anomalies. All the poles are concentrated around the Nares strait and at the northeastern part of the Ellesmere island. Angle and linear spreading rates were calculated using Euler poles. The calculation has showed that all three SC had low spreading rates. Three stages of the area evolution are found on the basis of the plate tectonic reconstruction for the periods 146.5, 151.5 and 157.5 Ma ago. The first stage, slightly earlier 157.5 Ma ago: the initiation of the oceanic crust formation to the north-west from the recent shelf of the Prince Patrick island. The second stage, from about 157.5 Ma ago: SC had advanced to the north-east; the oceanic crust was forming from one SC. The third stage, from slightly earlier 151.5 Ma ago to 140 Ma ago: the oceanic floor spreading from three SC took place, 140 Ma ago spreading ceased in this area. During the third stage the triple junction of the spreading centers was not stable and changed from type "ridge - ridge - ridge" to type " ridge - ridge - transform". The intraplate volcano-tectonic activity of the oceanic floor that created the Alpha Ridge was t8he fourth stage of the area evolution The kinematic characteristics of the spreading imply of crustal compression in the north of the Greenland and in the north-east of the Ellesmere island and of crustal stretching in the area of the Queen Elizabeth Islands, that agrees with their geological structure. The main stages of the Amerasian Basin evolution correspond by age to unconformities that A. Embry determined in the Mesozoic strata of the Sverdrup Basin [Embry, 1991]. The work has been supported by the Russian Foundation for basic Research (Grant 01-05-65481).

Gurevich, N. I.; Merkouriev, S. A.

2004-12-01

138

Mineral behaviour across the crust-mantle boundary  

Energy Technology Data Exchange (ETDEWEB)

The aim of this lecture is to present of this lecture is to present an appraisal of the expected behaviour of minerals, along a transect extending from the crust down to the upper mantle, along the outer 700 kms of the Earth, as well as of the methods necessary to approach this issue. The system under investigation corresponds to: continental and oceanic crust (CC and OC, respectively), upper mantle (UM), transition zone (TZ). These shells extend 10, 50, 400 and 670 km in depth, respectively; close to 670 km, the lower mantle (LM) is found. Rather than being specialistic and updated, the lecture wants to cover basic and simple topics, even if possibly old.

Mellini, M. [Siena Univ., Siena (Italy). Dipt. di Scienze Terra

2000-07-01

139

Galenicals in the treatment of crusted scabies  

Directory of Open Access Journals (Sweden)

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

Sugathan P; Martin Abhay

2010-01-01

140

Segmentation of mid-ocean ridges  

Science.gov (United States)

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.

Schouten, H.; Klitgord, K. D.; Whitehead, J. A.

1985-01-01

 
 
 
 
141

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)  

Science.gov (United States)

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. Copyright 2008 by the American Geophysical Union.

Grimes, C. B.; John, B. E.; Cheadle, M. J.; Wooden, J. L.

2008-01-01

142

Seasonal methane oxidation potential in manure crusts.  

UK PubMed Central (United Kingdom)

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 CH(4) m(-2) day(-1)) peaked during fall and winter, after 4 months of crust development. Consequences for methane mitigation potential of crusts are discussed.

Nielsen DA; Schramm A; Nielsen LP; Revsbech NP

2013-01-01

143

Mesozoic adakitic rocks from the Xuzhou Suzhou area, eastern China: Evidence for partial melting of delaminated lower continental crust  

Science.gov (United States)

Adakitic rocks in the Xuzhou Suzhou area, eastern China, consist of dioritic and monzodioritic porphyries and were dated at 131 132 Ma by the SHRIMP U Pb zircon method. These rocks have high MgO content (1.47 5.73%), high Mg# values (0.49 0.61), and high La/Yb and Sr/Y ratios. These features are similar to rocks derived from partial melting of a subducted oceanic slab. However, their high initial 87Sr/86Sr (0.7053 0.7075) and low ?Nd(t) values (-4.43 to -13.14) are inconsistent with the origin from slab melting. These rocks often contain garnet residual crystals and eclogite, garnet clinopyroxenite, and garnet amphibolite xenoliths. Petrographical characteristics and estimated P T conditions of these xenoliths indicate that they were once deeply subducted and subsequently underwent rapid exhumation in the early Mesozoic. Garnet residual crystals from the porphyries show similar chemical compositions to garnets from garnet clinopyroxenite and garnet amphibolite xenoliths. Ages of the inherited zircons of the xenoliths and their host rocks likely indicate that sources for the adakitic magma and protoliths of the eclogite and garnet clinopyroxenite xenoliths in the study area were from Precambrian basement of the North China Craton. The data also suggest that the lower continental crust in the eastern North China Craton was thickened during the early Mesozoic and delaminated in the early Cretaceous. The high-Mg adakitic magma resulted from partial melting of this delaminated lower continental crust and its subsequent interaction with the mantle during upward transport, leaving garnet as the residual phase.

Xu, Wen-Liang; Wang, Qing-Hai; Wang, Dong-Yan; Guo, Jing-Hui; Pei, Fu-Ping

2006-07-01

144

Mesozoic adakitic rocks from the Xuzhou-Suzhou area, eastern China: Evidence for partial melting of delaminated lower continental crust  

Science.gov (United States)

Adakitic rocks in the Xuzhou-Suzhou area, eastern China, consist of dioritic and monzodioritic porphyries and were dated at 131 132 Ma by the SHRIMP U Pb zircon method. These rocks have high MgO content (1.47 5.73%), high Mg# values (0.49 0.61), and high La/Yb and Sr/Y ratios. These features are similar to rocks derived from partial melting of a subducted oceanic slab. However, their high initial 87Sr/86Sr (0.7053 0.7075) and low ?Nd(t) values (-4.43˜-13.14) are inconsistent with the origin from slab melting. These rocks often contain garnet residual crystals and eclogite, garnet clinopyroxenite, and garnet amphibolite xenoliths. Petrographical characteristics and estimated P T conditions of these xenoliths indicate that they were once deeply subducted and subsequently underwent rapid exhumation in the early Mesozoic. Garnet residual crystals from the porphyries show similar chemical compositions to garnets from garnet clinopyroxenite and garnet amphibolite xenoliths. Ages of the inherited zircons of the xenoliths and their host rocks likely indicate that sources for the adakitic magma and protoliths of the eclogite and garnet clinopyroxenite xenoliths in the study area were from Precambrian basement of the North China Craton. The data also suggest that the lower continental crust in the eastern North China Craton was thickened during the early Mesozoic and delaminated in the early Cretaceous. The high-Mg adakitic magma resulted from partial melting of this delaminated lower continental crust and its subsequent interaction with the mantle during upward transport, leaving garnet as the residual phase.

Xu, Wen-Liang; Wang, Qing-Hai; Wang, Dong-Yan; Guo, Jing-Hui; Pei, Fu-Ping

2006-09-01

145

Seawater osmium isotope evidence for a middle Miocene flood basalt event in ferromanganese crust records  

Science.gov (United States)

Three ferromanganese crusts from the northeast, northwest and central Atlantic were re-dated using osmium (Os) isotope stratigraphy and yield ages from middle Miocene to the present. The three Os isotope records do not show evidence for growth hiatuses. The reconstructed Os isotope-based growth rates for the sections older than 10??Ma are higher than those determined previously by the combined beryllium isotope (10Be/9Be) and cobalt (Co) constant-flux methods, which results in a decrease in the maximum age of each crust. This re-dating does not lead to significant changes to the interpretation of previously determined radiogenic isotope neodymium, lead (Nd, Pb) time series because the variability of these isotopes was very small in the records of the three crusts prior to 10??Ma. The Os isotope record of the central Atlantic crust shows a pronounced minimum during the middle Miocene between 15 and 12??Ma, similar to a minimum previously observed in two ferromanganese crusts from the central Pacific. For the other two Atlantic crusts, the Os isotope records and their calibration to the global seawater curve for the middle Miocene are either more uncertain or too short and thus do not allow for a reliable identification of an isotopic minimum. Similar to pronounced minima reported previously for the Cretaceous/Tertiary and Eocene/Oligocene boundaries, possible interpretations for the newly identified middle Miocene Os isotope minimum include changes in weathering intensity and/or a meteorite impact coinciding with the formation of the No??rdlinger Ries Crater. It is suggested that the eruption and weathering of the Columbia River flood basalts provided a significant amount of the unradiogenic Os required to produce the middle Miocene minimum. ?? 2008 Elsevier B.V.

Klemm, V.; Frank, M.; Levasseur, S.; Halliday, A. N.; Hein, J. R.

2008-01-01

146

Evolution of the earth's crust in regions of active continental riftogenesis  

Energy Technology Data Exchange (ETDEWEB)

Destruction of the continental crust whose extreme manifestation is leading to the formation of an oceanic type crust is taking place in the regions of active continental riftogenesis of the Afar type such as the articulation zones of the Red Sea, Aden, and Ethiopian rifts. The destruction is found to occur through the crushing, stretching, and saturation of continental crust by base and ultra-base rock of mantle origin. The similarity between the evolution of volcanism - the basic indicator of lithospheric plutonic dynamics - of the Afar and mobile oceanic structures, makes it possible to relate the singularity of the destructive process in the earth's history which results in a better understanding of the mechanism that underlies the formation of peripheral and interior seas as well as their analogs in the geological past. The specificity of Afar type structures is manifested in the scattered nature of the endogenic conditions. 42 references, 2 figures.

Razvalyaev, A.V.; Ponikarov, V.P.

1980-05-01

147

Two contemporaneous magma series on Mayotte Island, Comores Archipelago, Indian Ocean  

Science.gov (United States)

The Comores archipelago is comprised of four islands all of which are characterised by alkaline lavas. On Mayotte, two clearly separate magma series can be defined. The origin of such contemporaneous but compositionally different series in several oceanic islands is still a subject of a debate. The mineralogy and geographically locations allow to identify three different lava groups. (1) The north lava group composed of relatively homogeneous alkaline basalts. (2) The north-east group comprised of tephrites to trachy-phonolites series and (3) the south lava group is made up of a nephelinite to phonolite series. Ol+cpx+plag are the main phenocryst phases in the north and north-east lavas, whereas the south lava series have ol+cpx+nepheline as phenocrysts. Composition of clinopyroxene is variable with diopside compositions in the north alkaline basalts and tephrites, and diopside to aegerine compositions in the south nephelinite lavas. A regular enrichment of Na content in plagioclases phenocrysts and groundmass crystals from the lavas of the north group to those from the north-east is observed. In contrast, alkali-feldspars are present in the south lavas. The crystallisation of clinopyroxene instead of plagioclase after olivine fractionation in the north lavas suggests that fractionation occurred at pressure between 0.4 and 0.9 GPa, which is consistent with the presence of Na-rich cpx-cores in all lava groups. The major element composition of lavas from Mayotte allow to define two distinct magma series: a moderately undersaturated and a highly undersaturated series. The moderately undersaturated series is composed of the north alkali basalt and the north-east tephrite lavas, whereas the south nephlinites represent the highly undersaturated series. Compilation of published age determinations and new Ar/Ar datings suggest that the north lavas erupted from 7.7 Ma to 4.4 Ma, followed by the north-east lavas erupted from 4.7 Ma to 1.4 Ma. The south lavas erupted contemporaneously from 7.7 Ma to 2.7 Ma. Basic volcanic activity resumed in the North between 2.9 Ma and 1.2 Ma, and from 2 Ma to 1.5 Ma in the South. Taken together, these preliminary petrological and geochemical results suggest that Mayotte island was constructed by two volcanoes. These volcanoes were active at the same time producing two distinct magma series. Migration of the activity of the northern volcano to the east occurred with emission of increasingly differentiated lavas with time. Depth of crystallisation can be evaluated at more than 15 km for alkaline basalt and tephrite lavas, which corresponds to the mantle-crust interface.

Debeuf, D.; Bachèlery, P.; Sigmarsson, O.

2003-04-01

148

Effect of thermal stress on oxide crusts  

International Nuclear Information System (INIS)

[en] In the transition phase in LMFBR hypothetical accidents, the existence of an insulating crust of frozen fuel between molten fuel and cold structure is of key importance. The disruption of such a crust for fuel flowing through the axial blanket regions can lead to rapid freezing and subsequent blockage formation. In a boiling pool of molten fuel and steel, the presence of the crust may be necessary in order to reduce the convective heat transfer rate and allow a subcritical boilup. This paper describes the effect of thermal stress on such a crust and points out that such crusts may be far weaker than previously believed

1977-12-02

149

Paleozoic to Triassic ocean opening and closure preserved in Central Iran: Constraints from the geochemistry of meta-igneous rocks of the Anarak area  

Science.gov (United States)

The Anarak area belongs to an ophiolitic belt along the northern border of the Central-East Iranian Microcontinent, and is thought to contain fragments of the former Paleotethys and Neotethys oceans. A wide range of meta-igneous rocks from the Late Paleozoic to Triassic Anarak Metamorphic Complex (AMC) and nearby Meraji area have been studied to constrain the origins and modes of emplacement of oceanic remnants in Central Iran. Our samples occur as layers and lenses embedded in extensive sequences of deformed meta-sediments and smaller bodies of serpentinized ultramafic rocks. Petrographical and geochemical data combined with field and satellite observations allow recognition of seven types of meta-igneous rocks preserved from low grade to blueschist facies conditions. Their origins based on relative abundances of immobile trace elements include subduction zone, mid-ocean ridge, ocean intraplate, and continental rift settings. These data and existing geochronological constraints show the AMC formed an accretionary complex formed/exhumed incrementally during the Carboniferous, Permo-triassic and Triassic. Igneous rocks from Meraji formed in the Early Devonian due to opening of the Paleotethys, and belong to a rift sequence extending over 300 km along the edge of the Central-East Iranian Microcontinent. The AMC and nearby rock associations record the evolution of the Paleotethys during a complete Wilson Cycle between ca. 450 and 225 Ma, with implications for: (1) continental rifting; (2) ocean opening; (3) subduction initiation; (4) ocean intraplate and continued mid-ocean volcanism; (5) ridge subduction; and (6) final closure of the ocean during continent–continent collision. Alternate interpretations of the Anarak metabasites are possible, but require radical departures from the widely accepted model for tectonic evolution of the Paleotethys, with the existence of Paleotethyan backarc basin(s) and Permian or earlier collision of continental blocks in Central Iran. In any case, our results show accretionary complexes preserved along suture zones contain an important record of the evolution of oceanic crust from ancient ocean basins.

Buchs, David M.; Bagheri, Sasan; Martin, Laure; Hermann, Joerg; Arculus, Richard

2013-07-01

150

DTA for superalloy MA6000 and ferritic steel MA956  

International Nuclear Information System (INIS)

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)

2008-01-01

151

Ocean drilling surveys planned  

Science.gov (United States)

As a continuation of the International Phase of Ocean Drilling (IPOD), the Glomar Challenger is slated to drill in the Pacific and North Atlantic oceans during 1982-83. In preparation for the drilling, the Joint Oceanographic Institutions (JOI), Inc. will manage the site survey program during 1981-82. These site surveys will be focused to support four programs: a hydrogeology study on the equatorial East Pacific Rise flank; a study of Mesozoic sediments in the western Pacific; a study in sedimentation of the equatorial Pacific basin; and a study of the geochemistry of the North Atlantic ocean crust.JOI has issued a request for proposals for the United States site survey program. Proposal deadline is March 5. For additional information, contact JOI, Inc., 2600 Virginia Avenue, N.W., Suite 512, Washington, D.C. 20037.

152

Continental crust/mantle transition in Malenco (Eastern Central Alps)  

Energy Technology Data Exchange (ETDEWEB)

The fossil crust/mantle transition preserved in the Val Malenco area (N-Italy) is situated at the Penninic-Austroalpine boundary in the Eastern Central Alps. This boundary region originated from the remnants of the Adriatic passive continental margin (Austroalpine) and the Piemonte-Ligurian ocean (South Penninic domain). This area was involved in polyphase Alpine deformation and metamorphism which have been the main research focus for a long time. Much less attention has been paid on the pre-Alpine evolution. In the last few years a big effort has been made by a research group at ETH-Zuerich to decipher the tectonic evolution which predates the Alpine convergence. This contribution summarizes the results of this project. In the first part of this paper, evidence for and characteristics of the Permian Malenco crust/mantle section are presented. In the second part, exhumation of the crust/mantle transition and emplacement at the Adriatic passive continental margin during Jurassic rifting are discussed.

Hermann, J. [Canberra The Australian National University, Canberra (Australia). Research School of Earth Sciences

2000-07-01

153

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

International Nuclear Information System (INIS)

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

1987-01-01

154

The Siquisique basalts and gabbros, Los Algodones, Venezuela: late Cretaceous oceanic plateau formed within the proto-Caribbean plate?  

Science.gov (United States)

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

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

2009-12-01

155

Strange crusts on strange stars  

International Nuclear Information System (INIS)

[en] We re-examine the surface composition of strange stars. It is widely accepted that they are characterized by an enormous density gradient (1026 g cm-4) and large electric fields at surface. By investigating the possibility of realizing a heterogeneous crust, comprised of nuggets of strange quark matter embedded in a uniform electron background, we find that the strange star surface has a much reduced density gradient and negligible electric field. We discuss the role of Debye screening in estimating the critical surface which will disfavour the nugget phase. We comment on how our findings will impact various proposed observable signatures for strange stars

2006-01-01

156

Scaling of X pinches from 1 MA to 6 MA.  

Energy Technology Data Exchange (ETDEWEB)

This final report for Project 117863 summarizes progress made toward understanding how X-pinch load designs scale to high currents. The X-pinch load geometry was conceived in 1982 as a method to study the formation and properties of bright x-ray spots in z-pinch plasmas. X-pinch plasmas driven by 0.2 MA currents were found to have source sizes of 1 micron, temperatures >1 keV, lifetimes of 10-100 ps, and densities >0.1 times solid density. These conditions are believed to result from the direct magnetic compression of matter. Physical models that capture the behavior of 0.2 MA X pinches predict more extreme parameters at currents >1 MA. This project developed load designs for up to 6 MA on the SATURN facility and attempted to measure the resulting plasma parameters. Source sizes of 5-8 microns were observed in some cases along with evidence for high temperatures (several keV) and short time durations (<500 ps).

Bland, Simon Nicholas (Imperial College, London, United Kingdom); McBride, Ryan D.; Wenger, David Franklin; Sinars, Daniel Brian; Chittenden, Jeremy Paul (imperial College, London, United Kingdom); Pikuz, Sergei A. (Cornell University, Ithaca, NY); Harding, Eric; Jennings, Christopher A.; Ampleford, David J.; Yu, Edmund P.; Cuneo, Michael Edward; Shelkovenko, Tatiana A. (Cornell University, Ithaca, NY); Hansen, Stephanie B.

2010-09-01

157

Zircon dating of oceanic crustal accretion.  

UK PubMed Central (United Kingdom)

Most of Earth's present-day crust formed at mid-ocean ridges. High-precision uranium-lead dating of zircons in gabbros from the Vema Fracture Zone on the Mid-Atlantic Ridge reveals that the crust there grew in a highly regular pattern characterized by shallow melt delivery. Combined with results from previous dating studies, this finding suggests that two distinct modes of crustal accretion occur along slow-spreading ridges. Individual samples record a zircon date range of 90,000 to 235,000 years, which is interpreted to reflect the time scale of zircon crystallization in oceanic plutonic rocks.

Lissenberg CJ; Rioux M; Shimizu N; Bowring SA; Mével C

2009-02-01

158

Ocean Planet: Ocean Market  

Science.gov (United States)

Unit from Smithsonian multidisciplinary ocean curriculum. Lesson plan focuses on foods, materials and medicines that comes form marine life, how these resources are harvested and processed and the impacts of fisheries. Students identify and classify consumer goods from the ocean and calculate their cost. Unit includes: background essay; teacher instructions; forms for student activity; discussion questions; all online in PDF format. Resources include online version of Smithsonian Ocean Planet exhibition.

159

Pulsar glitches: the crust is not enough.  

UK PubMed Central (United Kingdom)

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.

Andersson N; Glampedakis K; Ho WC; Espinoza CM

2012-12-01

160

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

Directory of Open Access Journals (Sweden)

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

Robert P. Dziak; DelWayne R. Bohnenstiehl; Deborah K. Smith

2012-01-01

 
 
 
 
161

Comparison of Oceanic and Continental Ultramafic Hosted Hydrothermal Sulfide Deposits under Slow-spreading Mid-ocean Ridge Setting  

Science.gov (United States)

Recently, slow-spreading mid-ocean ridges have attracted lots of researchers, especially in the MAR (Mid-Atlantic Ridge) and the Indian Ocean Ridge. People have found many hydrothermal vents or hydrothermal sulfide deposits around MAR, such as TAG, Rainbow and Lost City. The slow-spreading ridges are characterized by variations in magmatic, tectonic, and alteration processes along ridge segments. Because of the difficulties of the seafloor exploration, we need an example on the continent for compare with the hydrothermal sulfide deposits on mid-ocean ridge. So we found De'erni Cu (Co) ore deposit on the north of Tibet. De'erni Cu (Co) ore deposit is a typical VHMS developing in the north of Tibet, China. The ore body is hosted by the ultramafic rocks of the A'nyemagen ophiolite suite, which is the symbol of the residual crust of Paleo-Tethys Ocean. Through the detailed geological analysis to De'erni Cu (Co) ore deposit, lots of reminded geological records of submarine hydrothermal system, including: 1) thin-layer exhalative rock covering on the ore body; 2) the colloform structure, raspberry-like structure and breccia structure reserved in the porous-type ores; 3) the main mineral composition; 4) the calcite and felsic cement in the synchronization with the pyrite clast; 4) the ore zonality similar to the TAG hydrothermal sulfide deposit. According to the TiO2 content in the MORB basalts, the approximate half-spreading rate is 1.1-2.5cm/a, of the Paleo-Tethys Ocean represented by the De'erni ophiolite. Comparing to the mineralization processes of present mid-ocean hydrothermal sulfide deposits, we insist that De'erni Cu (Co) deposit has experienced three stages: submarine exhalation stage, cooling deposition and subduction emplacement. And the OCC (Oceanic Core Complex) may be the host setting of the submarine hydrothermal exhalation stage. Compared to other similar sulfide deposits on the continent in the world, De'erni Cu (Co) sulfide deposit has a younger age (340Ma Carboniferous) and a more completed ore deposit structure. De'erni Cu (Co) ore deposit is a typical case of ultramafic hosted hydrothermal sulfide deposits.

Li, Honglin; Li, Jianghai; Zhang, Huatian

2013-04-01

162

Resonant shattering of neutron star crusts  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ˜1046-1047erg of energy seconds before the merger of a NS-NS ...

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

163

Water Uptake Mechanism in Crispy Bread Crust  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Crispness is an important quality characteristic of dry solid food products such as crispy rolls. Its retention is directly related to the kinetics of water uptake by the crust. In this study, a method for the evaluation of the water sorption kinetics in bread crust is proposed. Two different sorpti...

Nieuwenhuijzen, N.H., van; Meinders, M.B.J.; Tromp, R.H.; Hamer, R.J.; Vliet, T., van

164

Thermalization time of hot neutron star crust  

International Nuclear Information System (INIS)

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

2011-09-16

165

MoMA: Gabriel Orozco  

Science.gov (United States)

This exhibition website from MoMA tackles the difficult task of presenting the work of Gabriel Orozco, an artist about whom the exhibition catalog states, "There is no way to identify a work by Orozco in terms of physical product". In a post from the MoMA blog "Inside/Out", Shannon Darrough, Senior Media Developer, stated that in order to achieve a playful interactive feeling for the online exhibition, the underlying metaphor of the Orozco site is a game of cards. When the site is loaded, the visitor sees an array of about 150 thumbnail images of different works. When any of these works is selected, the others skitter away to let the selected piece enlarge and come to the fore, with full captions, and sometimes audio of Orozco's comments. There is also a set of 6 videos available, documenting the installation of the show, and more commentary from Orozco.

166

Sources of continental crust: neodymium isotope evidence from the Sierra Nevada and Peninsular ranges  

Energy Technology Data Exchange (ETDEWEB)

Granitic rocks from batholiths of the Sierra Nevada and Peninsular Ranges exhibit initial /sup 143/Nd//sup 144/Nd ratios that vary over a large range and correlate with /sup 87/Sr//sup 86/Sr ratios. The data suggest that the batholiths represent mixtures of materials derived from (i) chemically depleted mantle identical to the source of island arcs and (ii) old continental crust, probably sediments or metasediments with a provenance age of approx. 1.6 x 10/sup 9/ years. These conclusions are consistent with a model for continental growth whereby new crustal additions are repeatedly extracted from the same limited volume of the upper mantle, which has consequently become depleted in elements that are enriched in the crust. There is little evidence that hydrothermally altered, subducted oceanic crust is a primary source of the magmas.

DePaolo, D.J.

1980-08-08

167

Sources of continental crust: neodymium isotope evidence from the Sierra Nevada and Peninsular ranges  

International Nuclear Information System (INIS)

Granitic rocks from batholiths of the Sierra Nevada and Peninsular Ranges exhibit initial 143Nd/144Nd ratios that vary over a large range and correlate with 87Sr/86Sr ratios. The data suggest that the batholiths represent mixtures of materials derived from (i) chemically depleted mantle identical to the source of island arcs and (ii) old continental crust, probably sediments or metasediments with a provenance age of approx. 1.6 x 109 years. These conclusions are consistent with a model for continental growth whereby new crustal additions are repeatedly extracted from the same limited volume of the upper mantle, which has consequently become depleted in elements that are enriched in the crust. There is little evidence that hydrothermally altered, subducted oceanic crust is a primary source of the magmas

1980-08-08

168

The 140 Ma (?) Evolution of the Galápagos Hotspot  

Science.gov (United States)

The Galápagos Islands and hotspot tracks on the Cocos and Nazca Plates (Cocos, Carnegie, Malpelo and Coiba Ridges) extend the activity of the Galápagos hotspot to nearly 20 Ma (Malpelo and Carnegie Ridges). The complex spatial zonation in trace element and isotopic composition found at the Galápagos Islands is also preserved in the hotspot tracks. Older parts of the hotspot tracks have presumably been subducted beneath South and Central America and therefore are not directly available for sampling. Detailed field, geochemical and 40Ar/39Ar age dating studies of accreted volcanic terranes in Costa Rica and Panama, however, show that they represent parts of the subducted history of the Galápagos hotspot. Samples from accreted ocean island, seamount and submarine ridge volcanoes range in age from 20-70 Ma and have intraplate major element, trace element and Sr-Nd-Pb isotopic compositions consistent with their derivation from the Galápagos hotspot. Our preliminary geochemical data also suggests that the unique spatial zonation of the Galápagos hotspot can be traced as far back as 65 Ma. Outcrops of radiolarian chert, which have been intruded by gabbros or basaltic dikes and sills or are overlain by basaltic sheet flows and pillow lavas, are also common along the Pacific margin of Central American. These rocks are tholeiitic in composition, have very uniform trace element and Sr-Nd-Pb isotopic characteristics, which are identical to other basalts from the Caribbean Large Igneous Province (CLIP). Despite their homogeneous geochemistry, 40Ar/39Ar dating yields a surprisingly large age range of 70-140 Ma. The oldest ages (133-139 Ma) are derived from pristine glasses from pillow rinds from three separate outcrops in North Nicoya. Questions posed by these data include: 1) Has the Galápagos hotspot been active for the last 140 Ma? and 2) Over what age span was the CLIP formed?

Hoernle, K.; Bogaard, P.; Hauff, F.; Werner, R.; Lissinna, B.

2001-12-01

169

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

UK PubMed Central (United Kingdom)

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.

Sobolev AV; Hofmann AW; Kuzmin DV; Yaxley GM; Arndt NT; Chung SL; Danyushevsky LV; Elliott T; Frey FA; Garcia MO; Gurenko AA; Kamenetsky VS; Kerr AC; Krivolutskaya NA; Matvienkov VV; Nikogosian IK; Rocholl A; Sigurdsson IA; Sushchevskaya NM; Teklay M

2007-04-01

170

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

Science.gov (United States)

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

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

2007-03-29

171

Constraining timescales of focused magmatic accretion and extension in the Afar crust using lava geochronology.  

UK PubMed Central (United Kingdom)

As continental rift zones mature the tectonic and volcanic processes associated with crustal extension become confined to narrow magmatic rift zones, reminiscent of oceanic spreading ridges. The formation of these rift zones and the development of ocean-ridge type topography is a significant milestone in rift evolution as it signifies the localization of crustal extension and rift-related volcanism. Here we show that lavas, which erupted since ~200?ka along part of the on-land Red Sea rift system in Afar, Ethiopia, have a consistent age-progression from the rift axis outwards, indicating that axial dyke intrusion has been the primary mechanism of segment growth and that focused magmatic accretion and extension in the crust have remained stable here over this period. Our results suggest that as this rift segment has formed, in thinned and intruded continental crust, the time-averaged surface opening rate has closely approximated the total extension rate between Africa and Arabia.

Ferguson DJ; Calvert AT; Pyle DM; Blundy JD; Yirgu G; Wright TJ

2013-01-01

172

Constraining timescales of focused magmatic accretion and extension in the Afar crust using lava geochronology.  

Science.gov (United States)

As continental rift zones mature the tectonic and volcanic processes associated with crustal extension become confined to narrow magmatic rift zones, reminiscent of oceanic spreading ridges. The formation of these rift zones and the development of ocean-ridge type topography is a significant milestone in rift evolution as it signifies the localization of crustal extension and rift-related volcanism. Here we show that lavas, which erupted since ~200?ka along part of the on-land Red Sea rift system in Afar, Ethiopia, have a consistent age-progression from the rift axis outwards, indicating that axial dyke intrusion has been the primary mechanism of segment growth and that focused magmatic accretion and extension in the crust have remained stable here over this period. Our results suggest that as this rift segment has formed, in thinned and intruded continental crust, the time-averaged surface opening rate has closely approximated the total extension rate between Africa and Arabia. PMID:23361007

Ferguson, David J; Calvert, Andrew T; Pyle, David M; Blundy, Jon D; Yirgu, Gezahegn; Wright, Tim J

2013-01-01

173

Biogenic crust dynamics on sand dunes.  

UK PubMed Central (United Kingdom)

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.

Kinast S; Meron E; Yizhaq H; Ashkenazy Y

2013-02-01

174

Biogenic crust dynamics on sand dunes  

CERN Document Server

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.

Kinast, Shai; Yizhaq, Hezi; Ashkenazy, Yosef

2012-01-01

175

Obama vu de ma banlieue.  

Directory of Open Access Journals (Sweden)

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

Olga Stanislawska

2008-01-01

176

Index of Memoranda of Interpretation (Ma)  

Science.gov (United States)

... Sup. 1 (Revised), Withdrawal of Ma-57-Supplement 1, 8r, 9-17-1993, ACTIVE. Ma-58, Lowfat Milk with Lactobacillus acidophilus Culture added, Sec ... More results from www.fda.gov/food/guidanceregulation/guidancedocumentsregulatoryinformation

177

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

Science.gov (United States)

RHUM-RUM (Réunion Hotspot and Upper Mantle - Réunions Unterer Mantel) is a French-German passive seismic experiment designed to image an oceanic mantle plume - or lack of plume - from crust to core beneath La Réunion Island, and to understand these results in terms of material, heat flow and plume dynamics. La Réunion hotspot is one of the most active volcanoes in the world, and its hotspot track leads unambiguously to the Deccan Traps of India, one of the largest flood basalt provinces on Earth, which erupted 65 Ma ago. The genesis and the origin at depth of the mantle upwelling and of the hotspot are still very controversial. In the RHUM-RUM project, 57 German and French ocean-bottom seismometers (OBS) are deployed over an area of 2000 km x 2000 km2 centered on La Réunion Island, using the "Marion Dufresne" and "Meteor" vessels. The one-year OBS deployment (Oct. 2012 - Oct. 2013) will be augmented by terrestrial deployments in the Iles Eparses in the Mozambique Channel, in Madagascar, Seychelles, Mauritius, Rodrigues and La Réunion islands. A significant number of OBS will be also distributed along the Central and South West Indian Ridges to image the lower-mantle beneath the hotspot, but also to provide independent opportunity for the study of these slow to ultra-slow ridges and of possible plume-ridge interactions. RHUM-RUM aims to characterize the vertically ascending flow in the plume conduit, as well as any lateral flow spreading into the asthenosphere beneath the western Indian Ocean. We want to establish the origin of the heat source that has been fueling this powerful hotspot, by answering the following questions: Is there a direct, isolated conduit into the deepest mantle, which sources its heat and material from the core-mantle boundary? Is there a plume connection to the African superswell at mid-mantle depths? Might the volcanism reflect merely an upper mantle instability? RHUM-RUM also aims at studying the hotspot's interaction with the neighboring ridges of the Indian Ocean. There is in particular a long-standing hypothesis, not yet examined seismically, that channelized plume flow beneath the aseismic Rodrigues Ridge could feed the Central Indian Ridge at 1000 km distance. The RHUM-RUM group (www.rhum-rum.net): * IPG Paris & Géosciences Réunion: G. Barruol, J.P. Montagner, E. Stutzmann, F.R. Fontaine, C. Deplus, M. Cannat, G. Roult, J. Dyment, S. Singh, W. Crawford, C. Farnetani, N. Villeneuve, L. Michon. V. Ferrazzini, Y. Capdeville. * Univ. Munich (LMU): K. Sigloch, H. Igel. AWI Bremerhaven: V. Schlindwein. Univ. Frankfurt: G. Rümpker. Univ. Münster: C. Thomas. Univ. Bonn: S. Miller. * Géosciences Montpellier: C. Tiberi, A. Tommasi, D. Arcay, C. Thoraval. * Mauritius Oceanography Institute: D. Bissessur. Univ. Antananarivo: G. Rambolamanana. SEYPEC Seychelles Petroleum: P. Samson, P. Joseph. * Other institutes: A. Davaille, M. Jegen, M. Maia, G. Nolet, D. Sauter, B. Steinberger.

Sigloch, Karin; Barruol, Guilhem

2013-04-01

178

Early magma ocean and core formation on Vesta  

Science.gov (United States)

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

Neumann, Wladimir; Breuer, Doris; Spohn, Tilman

2013-04-01

179

Resolving ontogenetic from gametogenic and outer crust calcification in planktic foraminifers (Invited)  

Science.gov (United States)

Late outer crust and gametogenic crust calcification is a feature of many planktic foraminifer species including several that are widely used for paleoceanographic reconstruction. The presence of outer/gametogenic crusts on the latter species is of particular significance because it complicates the interpretation of bulk shell compositions, as it remains unclear whether ontogenetic and crust calcite components are precipitated under different water mass compositions and physical conditions, and/or the product of different calcification control mechanisms. It is also important that the variable development of outer/gametogenic crusts is a significant driver of observed changes in ‘calcification rate’ that are recorded as differences in size normalised shell mass. Changes in the latter have been used as evidence for the impacts of ocean acidification on foraminifer calcification, despite it being unclear from down-core, core-top and sediment trap studies whether temperature or [CO32-] are the primary drivers of calcification changes. We have combined elemental and isotopic tracer techniques with laser ablation ICPMS and nanoSIMS microanalysis that enable a variety of labelling and pulse-chase experiments to be performed in cultures under tightly controlled conditions in laboratory cultures. By transferring foraminifers between different seawater compositions labelled with various isotopes (e.g. 25Mg, 43,44Ca, 86Sr) and trace metal spikes (Ba) at defined times/intervals, we are able to determine the amount of calcification during crust formation, and determine any differences in precipitated ontogenetic and crust calcite compositions grown over a range of temperature, seawater carbonate equilibria, etc. These approaches provide the means to: (1) isolate the variables that control gametogenic/outer crust development in planktic forams; (2) test whether ‘crust’ calcite compositions are in accord with environmental calibrations (e.g. temperature sensitivity of Mg/Ca ratio) that apply to ontogenetic calcite; and (3) investigate calcification mechanisms such as putative Ca and Mg pumps and the role of a putative Ca pool in planktic foraminifer calcification. We will show laser ablation ICPMS results that resolve gametogenetic crust developed on G. sacculifer and O. universa grown in culture.

Eggins, S. M.; Spero, H. J.; Vetter, L.; Hoenisch, B.

2010-12-01

180

PRODUCTION OF CRUST PIZZA COATED WITH SWEET SYRUP BY APPLYING SWEET SYRUPS TO BAKED PIZZA CRUST  

UK PubMed Central (United Kingdom)

PURPOSE: A method of producing crust pizza coated with sweet syrups by applying sweet syrup containing glucose syrup to the surface of the baked pizza crust is provided. The pizza has various tastes and flavors without a greasy taste. CONSTITUTION: The crust pizza is prepared by the steps of: kneading dough for pizza crust placing the dough on a pizza plate while applying a little pressure thereto applying pizza sauce to the center of the dough and placing cheese, ham, onion, Agaricus bisporus, olive, pimentos, chili, Caper(Capparis spinosa), sausage and chopped meat on the pizza sauce baking the pizza crust at 230 to 350deg.C for 5 to 10min in an oven preheating glucose syrup at 160 to 260deg.C for 30sec to 4min and uniformly applying the preheated syrup to the pizza crust.

KANG WON MUK

 
 
 
 
181

The breaking strain of neutron star crust  

Energy Technology Data Exchange (ETDEWEB)

Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of neutron star crust. With multimillion ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Due to the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gTavitational wave radiation could limit the spin periods of some stars and might be detectable in large scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in Magnetar Giant and Micro Flares.

Kadau, Kai [Los Alamos National Laboratory; Horowitz, C J [INDIANA UNIV

2009-01-01

182

Is Macquarie Island a Section of Slow-spread Crust?  

Science.gov (United States)

Peridotite melting at mid-ocean ridges is believed to be affected by spreading rate, with faster spreading rates leading to higher degrees of melting. Macquarie Island, located 1500 km southeast of southernmost Australia, is thought be the sole complete section of ocean crust uplifted in the ocean basin in which it formed; moreover it has been proposed that it formed during slow spreading (30mm/yr full rate, calculated from geophysical studies). The oceanic crust of the island formed in the final stages of spreading, ˜6 mya, as indicated by Ar-Ar plateau ages of basaltic glass. At this latitude, the plate boundary evolved from a spreading ridge to a transpressional boundary between ˜33 and ˜6 mya, thus the rocks of the island record an interesting tectonic history and may provide clues to the mantle processes during a major plate motion re-organization, and slow spreading. Residual, plag-free peridotites were collected along transects through all of the mantle sections on the island, with an average of 100 meter spacing between samples. Spinel chrome numbers (Cr#) ranged from 0.39 to 0.46 (n=23), which corresponds to 15-16% fractional melting [1]. Their low Ti contents (0.02-0.07) attest to the residual nature of the Macquarie Island peridotites. Cpx is preserved in only 7 samples (alteration, depletion), and occurs mainly as small interstitial grains or as exsolved blebs in opx porphyroclasts. Cpx titanium (0.00-0.04 wt% TiO_2) and sodium (0.00-0.05 wt% Na_2O) contents are extremely low, confirming the high depletion and supporting highly efficient melt extraction. Opx porphyroclast cores have very high Mg# (0.92 on average). Trace element analysis (SIMS) revealed a strong depletion of HREE, and enrichment of LREE, as well as a positive Sr anomaly in some samples. Exsolved and matrix grains have identical compositions. The levels of depletion indicated by the spinel Cr# and HREE contents of cpx of the Macquarie Island peridotites are more similar to those seen at fast spreading centers or ophiolites, not at most slow spreading centers. This depletion could be caused by the progressively changing spreading direction disrupting mixing in the mantle, causing repeated melting of the same mantle source. Alternately, this depletion may be caused by melting enhanced by the presence of fluids, possibly introduced by some limited (temporal?) subduction in the region. This could also explain the LREE- and fluid mobile element enrichment. Further analyses of associated gabbros and basalts will test which model is most likely. [1] Hellebrand et al., (2001) Nature 410, 677-681.

Wertz, K.; Hellebrand, E.; Snow, J. E.; von der Handt, A.; Mosher, S.

2003-04-01

183

Hydrotaxis of cyanobacteria in desert crusts.  

Science.gov (United States)

We studied the migration of cyanobacteria in desert crusts from Las Bárdenas Reales (Spain). The crusts were almost exclusively colonized by the filamentous cyanobacterium Oscillatoria, which formed a dense layer approximately 600 microm thick located between 1.5 and 2.1 mm deep. Laboratory and field experiments showed that saturation of the crust with liquid water induced a migration of the cyanobacteria leading to a significant greening of the surface within a few minutes. Under light and rapid evaporation, the green color rapidly disappeared and the crust surface was completely devoid of filaments within 60 min. In contrast, 260 min was required to recover the original white color of the crust when slow evaporation was experimentally imposed. The up and down migration following wetting and drying occurred also in the dark. This demonstrates that light was not a required stimulus. Addition of ATP synthesis inhibitors prevented the cyanobacterium from migrating down into the crust, with filaments remaining on the surface. Therefore, the disappearance of the green color observed during desiccation can only be attributed to an active cyanobacterial motility response to the decrease in the water content. The simplest explanation that can account for the evidence gathered is the presence of a mechanism that links, directly or indirectly, these motility responses to gradients in water content, namely a form of hydrotaxis. PMID:14605777

Pringault, O; Garcia-Pichel, F

2003-11-20

184

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

Science.gov (United States)

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

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

2013-04-25

185

Frozen pizza crust and pizza suitable for microwave cooking  

UK PubMed Central (United Kingdom)

A frozen pizza product, particularly adapted for cooking and/or reheating in a microwave oven, and method of making such product. The pizza product of the invention includes a crust comprised of first and second crust elements with the first crust element being comprised of a baked cracker-type dough material having a moisture content of about 5% or less, with the second crust element being a baked bread dough type crust having a moisture content of about 20%-40%. The bread dough crust portion immediately overlies the cracker dough crust portion and, in use, the cracker crust is adapted to absorb excess moisture created during microwave cooking of the product. The method includes separately forming and, in some cases, baking the crust portions and then placing the two crust portions for overlying relation before adding a pizza sauce or other topping to the product.

BONE DAVID P; MANOSKI PAULA M

186

Diachronic and different metamorphic evolution in the fossil Variscan lower crust of Calabria  

Science.gov (United States)

Different P- T- t paths and Variscan tectonic evolution have been described for the lower crust of Calabria. New data have been collected through retrieval technique and construction of pseudosections to control the validity of the previous data and to check the appropriate model to describe the tectono-thermal evolution of the lower crust of the Serre (southern Calabria). The time-period from ~350 and ~270 Ma has been considered to depict the evolution from Variscan crustal thickening to exhumation as happens in the peri-Mediterranean blocks of south European Variscides and consistently with the available geochronological data. It results that: (1) P-peak at 0.9 and 1.03 GPa at the top and bottom, respectively, was reached earlier than T-peak, (2) crustal thickening developed likely earlier than 325 Ma within the stability field of kyanite, in agreement with previous studies, up to the P-peak along a geothermal gradient of about 21-22°C km-1, (3) the T-peak of 700 and 880°C at the top and bottom, respectively, was reached in the stability field of sillimanite after a nearly isobaric heating and (4) Variscan exhumation occurred under increasing T/depth ratio and stopped 270-280 Ma ago. The P-T paths for the upper and lower portions of the section, qualitatively comparable to the numerical simulation, reflect different styles of exhumation, cooling and, according to the available geochronological data, diachronic evolution.

Fornelli, A.; Pascazio, A.; Piccarreta, G.

2012-07-01

187

Anomalous Subsidence at the Ocean Continent Transition of the Gulf of Aden Rifted Continental Margin  

Science.gov (United States)

It has been proposed that some rifted continental margins have anomalous subsidence and that at break-up they were elevated at shallower bathymetries than the isostatic response predicted by classical rift models (McKenzie, 1978). The existence of anomalous syn- or early-post break-up subsidence of this form would have important implications for our understanding of the geodynamics of continental break-up and sea-floor spreading initiation. We have investigated subsidence of the young rifted continental margin of the eastern Gulf of Aden, focussing on the western Oman margin (break-up age 17.6 Ma). Lucazeau et al. (2008) have found that the observed bathymetry here is approximately 1 km shallower than the predicted bathymetry. In order to examine the proposition of an anomalous early post break-up subsidence history of the Omani Gulf of Aden rifted continental margin, we have determined the subsidence of the oldest oceanic crust adjacent to the continent-ocean boundary (COB) using residual depth anomaly (RDA) analysis corrected for sediment loading and oceanic crustal thickness variation. RDAs corrected for sediment loading using flexural backstripping and decompaction have been calculated by comparing observed and age predicted oceanic bathymetries in order to identify anomalous subsidence of the Gulf of Aden rifted continental margin. Age predicted bathymetric anomalies have been calculated using the thermal plate model predictions of Crosby and McKenzie (2009). Non-zero RDAs at the Omani Gulf of Aden rifted continental margin can be the result of non standard oceanic crustal thickness or the effect of mantle dynamic topography or a non-classical rift and break-up model. Oceanic crustal basement thicknesses from gravity inversion together with Airy isostasy have been used to predict a "synthetic" gravity RDA, in order to determine the RDA contribution from non-standard oceanic crustal thickness. Gravity inversion, used to determine crustal basement thickness, incorporates a lithosphere thermal gravity anomaly correction and uses sediment thicknesses from 2D seismic data. Reference Moho depths used in the gravity inversion have been calibrated against seismic refraction Moho depths. The difference between the sediment corrected RDA and the "synthetic" gravity derived RDA gives the component of the RDA which is not due to variations in oceanic crustal thickness. This RDA corrected for sediment loading and crustal thickness variation has a magnitude between +600m and +1000m (corresponding to anomalous uplift) and is comparable to that reported (+1km) by Lucazeau et al. (2008). We are unable to distinguish whether this anomalous uplift is due to mantle dynamic topography or anomalous subsidence with respect to classical rift model predictions.

Cowie, Leanne; Kusznir, Nick; Leroy, Sylvie

2013-04-01

188

Scanning electron microscopy of eggs of Mansonia uniformis, Ma. indiana, Ma. annulifera, and Ma. annulata (Diptera: Culicidae).  

UK PubMed Central (United Kingdom)

The eggs of Mansonia uniformis, Ma. indiana, Ma. annulifera, and Ma. annulata are described with the aid of scanning electron micrographs. Comparisons of egg structure among the four species showed that the eggs differed discernibly with respect to the outer chorionic tubercles on the anterior tube, the spines surrounding the raised central micropyle within the anterior cup, and the outer chorionic tubercles in the posterior region. Attempts to produce a key for identification of these eggs under scanning electron microscopy are discussed.

Iwaki M; Choochote W

1991-05-01

189

Rheological gravity model of the crust and upper mantle of Transbaikalia  

Science.gov (United States)

Based on rheological interpretation of formalized gravity models, earlier known deep-seated structures in the Earth’s crust and mantle of Transbaikalia have been detailed and new ones discovered. The structures are asymmetric and transverse relative to the Baikal rift zone. Their presence explains the peculiar features of the Baikal rift, including the one-way southeasterly direction of horizontal displacement of tectonic masses and northwestern migration of the Earth’s crust extension processes. The prolonged history (more than 250 Ma) of the Baikal rift zone and Transbaikalia mountainous country involved gravity or rotational detachments of rigid tectonic slabs from the craton and their sliding along intracrustal and subcrustal decollement zones into the above-dome area of the Transbaikalia asthenolith.

Petrishchevsky, A. M.

2009-06-01

190

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

International Nuclear Information System (INIS)

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

2001-01-01

191

Using of the Passive Remote Sensing for the Study of a two Layered Crust on the Europa Satellite  

Science.gov (United States)

On December 7th 1995, the Galileo mission began the study the jovian system. Among the results that his mission has obtained, it is the evidence of the existence of a liquid water ocean beneath the icy crust of Europa. Liquid water is one of the main factors that make life possible, so then life might exist in Europa. Some of the scenes that have been settled out to explain how living organisms could be present in such an extreme environment involve suppositions about the width of the icy crust. The explanation of other geological structures on the satellite also implies an estimation of the crust's width, that is why a good estimation about this parameter is very important in the geological study of this satellite. In this work, we analyze one electrodynamic model of the crust considering a two layered crust. The purpose is to obtain the optimal electrophysical parameters of measurement that permit us to estimate the crust's width. These parameters are calculated from the inverse elements of the Fisher matrix. The results obtained from this work can be used to plan future space missions to jovian satellites (in particular it could be useful for JIMO mission). The optimal algorithms for these measurements can be modified to be used in active systems of remote sensing.

Velasco Herrera, Victor Manuel; Cordero, Guadalupe; Velasco Herrera, Graciela

192

Red Studio - MoMA  

Science.gov (United States)

By collaborating with high school students, the Museum of Modern Art (MoMA) put together Red Studio, a Web site designed to connect teens with modern art and today's working artists. Currently, Red Studio features an interview with Shahzia Sikander, an artist born in Pakistan in 1969, who was educated, and now lives here in the US. Conducted by six students, interview questions range from what it's like for a young woman with a Muslim family to pursue a career as an artist, if she's ever felt she has to censor her art, to what type of music she likes. Red Studio visitors can view the interview as a Flash presentation with sound, or read the complete transcript. There is also an earlier interview with Vito Acconci, who is asked if he is an artist or an architect, and why he always wears black. Another teen-orientated part of the site is polls, so that kids can find out what other kids think about the purpose of art, and what they like to do after school.

2005-01-01

193

Ocean margin drilling: a technical memorandum  

Energy Technology Data Exchange (ETDEWEB)

The ocean margin drilling (OMD) program is both a continuation of deep ocean drilling under NSF earth sciences and a new thrust to investigate the geology of continental margins and ocean crust where very deep drilling is necessary to penetrate unknown regions. Some of the margin regions, which are the borders between continental shelves and the deep ocean, could contain substantial oil and gas resources, but very little evidence has yet been collected. This Technical Memorandum reviews the present plans for the Ocean Margin Drilling program and addresses questions on the merits of the program and alternatives to it. It analyzes problems associated with the approach proposed by NSF and suggests possible improvements. It also discusses the institutional capability of the Federal agencies which are to manage this program; the technology development aspects, and the problems and opportunities associated with industry participation.

1980-05-01

194

Elemental composition of the Martian crust.  

UK PubMed Central (United Kingdom)

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.

McSween HY Jr; Taylor GJ; Wyatt MB

2009-05-01

195

Spatial variations in effective elastic thickness in the Western Pacific Ocean and their implications for Mesozoic volcanism  

Science.gov (United States)

We have used free-air gravity anomaly and bathymetric data, together with a moving window admittance technique, to determine the spatial variation in oceanic elastic thickness, Te, in the Western Pacific ocean. Synthetic tests using representative seamounts show that Te can be recovered to an accuracy of ± 5 km for plates up to 30 km thick, with increased accuracy of ± 3 km for Te ? 20 km. The Western Pacific has a Te range of 0-50 km, with a mean of 9.4 km and a standard deviation of 6.8 km. The Te structure of the region is dominated by relatively high Te over the Hawaiian-Emperor Seamount Chain, intermediate values over the Marshall Islands, Gilbert Ridge, and Marcus-Wake Guyots, and low values over the Line Islands, Mid-Pacific Mountains, Caroline Islands, Shatsky Rise, Hess Rise, and Musician Seamounts. Plots of Te at sites with radiometric ages suggest that Te is to first order controlled by the age of the lithosphere at the time of loading. In areas that backtrack into the South Pacific Isotopic and Thermal Anomaly (SOPITA), Te may be as low as the depth to the 180 ± 120 °C isotherm at least locally. In the northern part of the study area including the Hawaiian-Emperor Seamount Chain, Te correlates with the depth to 310 ± 120 °C. These best-fitting isotherms imply peak rates of volcanism during 100-120 Ma (Early Cretaceous) and 140-150 Ma (Late Jurassic). The corresponding addition of 8 × 106 km3 and 4 × 106 km3 of volcanic material to the surface of the oceanic crust would result in long-term sea-level rises of 20 m and 10 m respectively. The Late Jurassic volcanic event, like the later Early Cretaceous event, appears to have influenced the tectonic evolution of the Pacific plate convergent boundaries, resulting in increased volcanism and orogenesis.

Kalnins, L. M.; Watts, A. B.

2009-08-01

196

Laboratory colonization of Mansonia uniformis, Ma. indiana and Ma. bonneae in Malaysia.  

UK PubMed Central (United Kingdom)

Methods are described for the laboratory colonization of Mansonia uniformis, Ma. indiana and Ma. bonneae in Malaysia. Gravid females oviposited in 500 ml beakers with a layer of water covered with small leaves of Salvinia. Newly hatched larvae were set up in a basal medium of guinea pig dung and water or liver powder, yeast powder and water. Larvae attached to aquatic plants or 'Keaykolour' ruffia snow white paper. The cultures with paper gave better yields than those with plants. Production of Ma. uniformis was higher than the other two species. Twelve generations of Ma. uniformis and 11 generations of Ma. indiana and Ma. bonneae were monitored in the laboratory.

Chiang GL; Cheong WH; Loong KP; Eng KL; Samarawickrema WA

1985-06-01

197

An integrated approach for determination of nature of the crust in the Laxmi Basin, western continental margin of India  

Science.gov (United States)

The nature of the crust in the Laxmi Basin, northwest continental margin of India is an uncertain issue and more importantly this is limiting our understanding of the evolution of the lithosphere in the Arabian Sea. The aspect has become a key issue principally from the point of paleogeographic reconstructions of the western Indian Ocean. In order to determine the nature of the crust below the Laxmi Basin we have analysed two new geophysical datasets in combination with previously published datasets, thereafter gravity and magnetic anomalies were modelled with the constraints from seismic reflection and refraction results. The sediments derived mostly from the Indus cone are generally thicker on west of the Laxmi Ridge than that in the Laxmi Basin. The basement in the Laxmi Basin includes numerous intrusive structures and faulted blocks, thus the basement topography becomes highly irregular and shallower compared to that of the Western Basin. The ship-borne and satellite gravity anomalies had enabled to map the regional extent of the structures in the basin especially the gravity lows associated with the Laxmi and Panikkar ridges. Intrusive structures mapped in the Laxmi Basin are seen coinciding with significant magnetic anomalies, but these anomalies were earlier considered as pre-Tertiary spreading-related anomalies. Free-air gravity anomalies of the Laxmi Ridge and Laxmi Basin are in general anomalous as they are associated with negative and positive gravity anomalies respectively. Within the basin the gravity anomaly is gradually rising toward north, reaches 40 mGal more, indicating the accretion of additional magmatic material toward north within crust. The velocity structures of the Laxmi Ridge, Laxmi Basin, Western Basin, Seychelles Bank and Indian continental shield reveal the Moho boundary only below the Seychelles Bank, Western Basin and Indian subcontinent. An anomalous velocity layer, 7.15 to 7.19 km/s is observed in the lower crust of the Laxmi Basin and Laxmi Ridge. The velocities are contrastingly deviating from the normal velocity structure of both continental and oceanic crust. On close observation of velocity structure we found that 6.2 - 6.3 km/s layer is conspicuously present in the upper crust of all the geological provinces except below the Western Basin. Instead the Western Basin bears about 6.7 km/s velocity layer, which is considered as a normal velocity for layer 3 of the oceanic crust. As the velocity layer 6.2 - 6.3 km/s in general represents the upper crustal rocks (granitic gneisses) of the continental crust, the similar velocity layer below the Laxmi Basin may be attributed to upper crustal rocks of the continental crust. The gravity and magnetic model studies have revealed that the Laxmi Basin consists of 11-14 km stretched continental crust, in which magmatic bodies have been emplaced, while the Panikkar Ridge in the middle of the basin has relatively less disturbed stretched continental crust. The seaward dipping reflectors (SDRs) on western margin of the Laxmi Ridge and sharp changes in regional gravity and magnetic fields across it lead to place the ocean-continent boundary on west of the Laxmi Ridge. The Reunion hotspot, when the basin was passing over it, had emplaced the volcanic material in the form of dykes and sills within existing stretched continental crust. We, therefore, believe that the Laxmi Basin basically consists of continental crust, which subsequently got modified by extensive stretching and volcanic outpourings of the Reunion hotspot.

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

2004-12-01

198

Oscillatory water sorption dynamics of bread crust  

UK PubMed Central (United Kingdom)

Step-wise and oscillatory gravimetric sorption experiments were used to study the equilibrium and dynamic water sorption behavior of bread crust. Water uptake kinetics is strongly related to crispness retention of composite products consisting of a dry crispy part and a more humid and soft part. We show that oscillatory sorption experiments of bread crusts could be very well described by a Fickian diffusion model. Many essential features, such as the shape of the oscillatory sorption curves, and the dependency of water sorption rates on time, time-interval between successive step-wise changes in relative humidity, and particle size are understood now to a great detail.

Meinders MBJ; van Vliet T

2011-11-01

199

Crusted scabies and multiple dosages of ivermectin.  

UK PubMed Central (United Kingdom)

We present the case of a bone marrow transplant patient who was diagnosed with crusted scabies but did not respond to the usual approach with topical permethrin and ivermectin. The Centers for Disease Control and Prevention were contacted and suggested a 7-dose regimen of ivermectin. The patient started to improve remarkably after the third dose, and the skin eruption was resolved after 7 doses. This case supports the use of a more prolonged course of oral ivermectin for crusted scabies in those who fail the conventional approach.

Ortega-Loayza AG; McCall CO; Nunley JR

2013-05-01

200

Crusted scabies and multiple dosages of ivermectin.  

Science.gov (United States)

We present the case of a bone marrow transplant patient who was diagnosed with crusted scabies but did not respond to the usual approach with topical permethrin and ivermectin. The Centers for Disease Control and Prevention were contacted and suggested a 7-dose regimen of ivermectin. The patient started to improve remarkably after the third dose, and the skin eruption was resolved after 7 doses. This case supports the use of a more prolonged course of oral ivermectin for crusted scabies in those who fail the conventional approach. PMID:23652958

Ortega-Loayza, Alex G; McCall, Calvin O; Nunley, Julia R

2013-05-01

 
 
 
 
201

Ocean Animals  

Science.gov (United States)

There are many types of Ocean Animals, today we wil be going to identify several Ocean Anumals through specific body parts that makeOcean Animals different from one another. To begin examine the links below to see what different types of ocean animals there are and what makes those animals different from one another Beluga Whales- National Geographic Kids Dolphins- Who lives in the sea? Puffer fish- National Geographic Stingrays- National Geographic Kids ...

2011-12-05

202

Osmium isotope systematics of historical lavas from Piton de la Fournaise (Réunion Island, Indian Ocean)  

Science.gov (United States)

Re-Os isotope and elemental data have been obtained for 20 historical picrites and basalts (1931-2006) from the Piton de la Fournaise volcano on Réunion Island and two old (>0.78 Ma) cumulates from a drill hole in the eastern part of the volcano. The 187Os/188Os ratios of the historical lava samples, selected to cover the MgO concentration and Pb isotopic ranges of Piton de la Fournaise lavas, range from 0.1311 to 0.1374. This result, together with previous results on 66-Ma-old lavas from the Deccan Traps (Allègre et al. in. Earth Planet Sci Lett, 170:197-204, 1999), supports the idea that the Os isotopic signature of the Réunion plume is relatively uniform and is at the less radiogenic end of the ocean island basalt spectrum. In detail, lavas erupted before 1992 seem to have higher 187Os/188Os than the lavas erupted after the 1992-1998 period of quiescence. Comparison of 187Os/188Os ratios with Pb, Sr and Nd isotopic data on the same set of samples shows no correlation between Os and Sr-Nd isotopes, whereas a broad positive relationship with Pb isotopes is observed, which is interpreted to reflect coupled fractionation of Re/Os and U-Th/Pb in the mantle due to the partitioning of Pb and Os into sulphides. Lavas inferred to be recording the Os isotopic signature of the Réunion plume source have higher 187Os/188Os ratios than the primitive mantle values. While this might be ascribed to melting of a lithologically heterogeneous source comprising recycled oceanic crust and/or continental sediment, the expected coupled Os-Sr-Nd-Pb isotopic variations are not observed. It is thus proposed that the mantle source for Piton de la Fournaise has inherently slightly radiogenic 187Os/188Os values that could reflect a mantle domain almost isolated from recycling processes.

Schiano, P.; David, K.; Vlastélic, I.; Gannoun, A.; Klein, M.; Nauret, F.; Bonnand, P.

2012-11-01

203

Paleoarchaean rhyolitic volcanism and the origin of the granitic continental crust  

Science.gov (United States)

Earth’s continental crust is dominated by granitic (s. s.) rocks with substantial K2O contents and K/Na > 0.6. However, 75% of Earth’s continental crust formed during the Archaean (4.0—2.5 Ga), as sodic Tonalite-Trondhjemite-Granodiorite (TTG) granitoids (K/Na ~ 0.23). It is generally assumed that the more potassic granites arose by intracrustal recycling of this material. This assumption predicts that Earth’s bulk crustal composition remains TTG-like, limiting the volume of granitic material that can form and necessitating that it would be counterbalanced by a substantially larger volume of refractory residua from the partial melting of TTGs. Consequently, the composition of the post-Archaean crust requires an additional source of crustal K2O. Here we present evidence that in the Barberton Greenstone Belt (BGB) in South Africa, TTG magmas were formed concurrently with sub-volcanic granitic and rhyolitic magmas. This granitic magmatism occurred during each of three documented cycles of TTG magmatism at ca 3550, 3450 and 3230 Ma. The granites and rhyolites from each episode display the same major- and trace- element compositions, which preclude their derivation through fractional crystallization or partial melting of a protolith of TTG composition and indicate their source to be potassic clay-bearing sediments derived predominantly from the weathering of mafic rocks. The production of these granitic magmas that lack crustal residency and are destined to erupt, during each tectono-magmatic episode of crust production, provides a path for the accumulation of potassium in volcano-sedimentary depositories, despite the absence of granites in the plutonic record at the time. In the BGB, the orogenic reworking of the first major accumulation of these sediments (the Fig Tree Group) coincided with the last TTG producing event and fertilised the middle and lower crust for the subsequent production of granitic magmas.

Sanchez-Garrido, C.; Stevens, G.; Armstrong, R.; Moyen, J.; Herve, M.; Doucelance, R.

2009-12-01

204

What determines the volume of the oceans?  

UK PubMed Central (United Kingdom)

The volume of Earth's oceans may be determined by a dynamic mechanism involving exchange of water between the crust and the mantle. Fast-spreading mid-ocean ridges are currently submerged to a depth at which the pressure is close to the critical pressure for seawater. This ensures optimal convective heat transport and, hence, maximal penetration of hydrothermal circulation along the ridge axes. The oceanic crust is hydrated to a depth of a kilometer or more and can therefore carry a substantial flux of water to the upper mantle when it is subducted. The current ingassing rate of water by this process is probably at least sufficient to balance the outgassing rate. If the oceans were shallower, as they may have been in the distant past, convective heat transport would be reduced and the depth of hydrothermal penetration and crustal hydration would decrease. Outgassing would exceed ingassing and ocean volume would increase. The system is self-stabilizing as long as the depth of the oceans does not exceed its present value. This mechanism could explain why continental freeboard has remained approximately constant since the Archean despite probable increases in continental area.

Kasting JF; Holm NG

1992-04-01

205

Ma Ying-jeou’s Presidential Discourse  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 s...

Jonathan Sullivan; University of Southampton; Eliyahu V. Sapir; Maastricht University

206

Termination agreements in M&A contracting  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper extends information economics research on M&A by examining the difficulty acquirers encounter when seeking to purchase targets that have the option of selling to other bidders. We use signaling theory to develop theoretical arguments on the dual effects of signals in M&A markets: Signals ...

Wu, CW; Reuer, JJ

207

The worship of Bh?ma  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This study deals with stone representations of Bh?ma, one of the protagonists of the Hindu epic Mah?bh?rata. This epic which originates from India, is already known on Java in the tenth century. The Bh?ma representations which include statues and reliefs appeared during the Majapahit Period (1296-1...

Duijker, Marijke

208

Crust–mantle interaction beneath the Luxi Block, eastern North China Craton: Evidence from coexisting mantle- and crust-derived enclaves in a quartz monzonite pluton  

Science.gov (United States)

The Laiwu quartz monzonite in the Luxi Block of eastern North China Craton (NCC) is characterized by the presence of abundant plagioclase amphibolite and gabbro–diorite enclaves. Here we present LA-ICPMS zircon U–Pb ages which show that the host quartz monzonite was emplaced at 129.8 ± 1.0 Ma, whereas the protolith of the plagioclase amphibolite enclaves formed during early Paleoproterozoic. The gabbro–diorite enclaves were produced simultaneously with or slightly earlier than the formation of the host quartz monzonite. Combined with the Archean and Paleoproterozoic zircons as well as the low ?Nd(0) values (? 18.4 to ? 18.0) in the plagioclase amphibolite enclaves, the equilibrium temperature and pressure conditions (645–670 °C and 4.8–6.5 Kb) suggest that the plagioclase amphibolite enclaves are fragments of the middle crust. The gabbro–diorite enclaves mainly originated from an enriched lithospheric mantle metasomatized by melts/fluids derived from the continental crust, as indicated by their low SiO2 (54.4–54.7 wt.%) and high MgO (10.9–11.1 wt.%) contents as well as the negative ?Nd(t) values (? 13.5 to ? 10.7) and enrichment of LILEs (e.g., Ba and Sr) and depletion of HFSEs (e.g., Nb, Ta, P and Ti). Compared with the ancient crustal rocks and the mafic plutons considered to have been derived from lithospheric mantle in the Luxi Block, the moderate ?Nd(t) (? 15.7 to ? 15.1) and ?Hf(t) (? 20.7 to ? 13.0) values of the quartz monzonite in our study suggest that both mantle- and crust-derived melts were involved in the magma generation. Thus we propose a model involving magma mixing between mantle- and crust-derived melts for the formation of the quartz monzonite. Since significant crust–mantle interaction is recorded not only in the quartz monzonite and its enclaves in the Luxi Block but also in the other granitoids widespread in the NCC, it is considered that large-scale crust–mantle interaction and magmatic underplating were associated with the Mesozoic lithospheric mantle thinning and crustal reactivation in the eastern NCC.

Lan, Ting-Guang; Fan, Hong-Rui; Santosh, M.; Hu, Fang-Fang; Yang, Kui-Feng; Yang, Yue-Heng; Liu, Yongsheng

2013-09-01

209

A crust-scale 3D structural model of the Beaufort-Mackenzie Basin (Arctic Canada)  

Science.gov (United States)

The Beaufort-Mackenzie Basin was initiated in the Early Jurassic as part of an Arctic rifted passive continental margin which soon after became overprinted by Cordilleran foreland tectonics. Decades of industrial exploration and scientific research in this petroliferous region have produced a wide spectrum of geological and geophysical data as well as geoscientific knowledge. We have integrated available grids of sedimentary horizons, well data, seismic reflection and refraction data, and the observed regional gravity field into the first crust-scale 3D structural model of the Beaufort-Mackenzie Basin. Many characteristics of this model reflect the complex geodynamic and tectonostratigraphic history of the basin.The Mesozoic-Cenozoic sedimentary part of the model comprises seven clastic units (predominantly sandy shales) of which the modelled thickness distributions allow to retrace the well-established history of the basin comprising a gradual north(east)ward shift of the main depocentres as well as diverse phases of localised erosion. As a result of this development, the present-day configuration of the basin reveals that the sedimentary units tend to be younger, more porous, and thus less dense towards the north at a constant depth level.By integrating three refraction seismic profiles and performing combined isostatic and 3D gravity modelling, we have modelled the sub-sedimentary basement of the Beaufort-Mackenzie Basin. The continental basement spans from unstretched domains (as thick as about 42 km) in the south to extremely thinned domains (of less than 5 km thickness) in the north where it probably represents transitional crust attached to the oceanic crust of the Canada Basin. The uppermost parts of the continental crust are less dense (? = 2710 kg/m3) and most probably made up by pre-Mesozoic meta-sediments overlying a heavier igneous and metamorphic crust (? = 2850 kg/m3).The presented crust-scale 3D structural model shows that the greatest thicknesses of Mesozoic-Cenozoic sediments (almost 17 km) are not found in the north where the sub-sedimentary crust is thinnest, but farther south where the crust is thicker and the Moho quite deep. We causally relate the huge amounts of foredeep deposits overlying a Moho depression to a flexural response of the lithosphere to orogenic loading induced by the Brooks Range orogen in the south. Our 3D model provides an ideal base and reference for future numerical studies including reconstructions of the development from a passive margin to a foreland basin and simulations of the present-day thermal field of the basin.

Sippel, Judith; Scheck-Wenderoth, Magdalena; Lewerenz, Björn; Kroeger, Karsten Friedrich

2013-04-01

210

Oceanic slab melting and mantle metasomatism.  

Science.gov (United States)

Modern plate tectonic brings down oceanic crust along subduction zones where it either dehydrates or melts. Those hydrous fluids or melts migrate into the overlying mantle wedge trigerring its melting which produces arc magmas and thus additional continental crust. Nowadays, melting seems to be restricted to cases of young (metasomatic phases such as amphibole and phlogopite that can be more or less sodium rich. Upon interaction the slab melt becomes less silicic (dacitic to andesitic), and Mg, Ni and Cr richer. Virtually all exposed slab melts display geochemical evidence of ingestion of mantle material. Modern slab melts are thus unlike Archean Trondhjemite-Tonalite-Granodiorite rocks (TTG), which suggests that both types of magmas were generated via different petrogenetic pathways which may imply an Archean tectonic model of crust production different from that of the present-day, subduction-related, one. PMID:11838241

Scaillet, B; Prouteau, G

2001-01-01

211

The nature of the lower continental crust  

Energy Technology Data Exchange (ETDEWEB)

This book reviews the physical and geochemical properties of the lower continental crust. Reviews cover heat flow, rheology, seismic properties, electrical resistivity, metasomatism, geochemistry and isotope characteristics. The terrains include the western USA, Canada, Labrador, West Greenland, northern Britain, Finland, West Germany, Massif Central, the Alps, the Himalayas, southern India, South Africa and Australia.

Dawson, J.B.; Carswell, D.A. (Dept. of Geology, Univ. of Sheffield, Sheffield (GB)); Hall, J. (Dept. of Geology, Univ. of Glasgoq, Glasgow (GB)); Wedepohl, K.H. (Geochemisches Institut der Universitat, Gottingen (DE))

1986-01-01

212

Fluid Flow in the Deep Crust  

Science.gov (United States)

The heating and burial of rock masses during mountain building drives chemical reactions that liberate volatile fluid species (Figure 1). These volatiles, including H2O, CO2, and CH4, are much less dense and viscous than the surrounding rock and will, therefore, have a strong tendency to migrate along grain boundaries or fractures through the Earth's crust. Fluids released in the deep crust interact geochemically with their surroundings (Rye et al., 1976) as they ascend to shallow levels where they invade hydrothermal and groundwater systems and, ultimately, interact with the hydrosphere and atmosphere. This flux of fluid from active mountain belts to the surface is a major contributor to planetary volatile cycling and is estimated to be currently in excess of ˜1017 kg Myr-1 (based on Kerrick and Caldeira, 1998; Wallmann, 2001a, b). (13K)Figure 1. Diagram of crustal fluid cycling. The deep crust is composed largely of metamorphic rock (cf. Rudnick and Fountain, 1995; Wedepohl, 1995; see Chapter 3.01). Fluids and magmas are the primary agents of chemical mass transport through the deep crust; fluid flow dominates at temperatures ˜15 km depth), although many of the concepts discussed are general and also apply to shallower levels.

Ague, J. J.

2003-12-01

213

Oscillatory water sorption dynamics of bread crust  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Step-wise and oscillatory gravimetric sorption experiments were used to study the equilibrium and dynamic water sorption behavior of bread crust. Water uptake kinetics is strongly related to crispness retention of composite products consisting of a dry crispy part and a more humid and soft part. We ...

Meinders, M.B.J.; Vliet, T., van

214

Crusted Scabies In An HIV Seropositive Woman  

Directory of Open Access Journals (Sweden)

Full Text Available A 27 year old female presented with itchy lesions over the trunk and extremities of six month duration. She had typical lesions of scabies in hands, besides crusted hyperkeratotic lesions over the lumber and gluteal areas, and was found to have underlying HIV infection. The case is reported for unusual presentation and its rarity.

Thappa Devinder Mohan; Laxmisha Chandrashekhar; Karthikeyan Kaliaperumal

2002-01-01

215

Superfluid dynamics in neutron star crusts  

CERN Multimedia

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.

Pethick, C J; Reddy, S

2010-01-01

216

Resonant shattering of neutron star crusts.  

UK PubMed Central (United Kingdom)

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.

Tsang D; Read JS; Hinderer T; Piro AL; Bondarescu R

2012-01-01

217

Collective excitations in neutron-star crusts  

CERN Multimedia

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.

Chamel, N; Reddy, S

2013-01-01

218

Age, origin and geodynamic significance of plagiogranites in lherzolites and gabbros of the Piedmont-Ligurian ocean basin  

Science.gov (United States)

U-Pb zircon dating, Sr-Nd isotope tracing and major/trace/RE element analyses were performed to constrain the age, origin and geodynamic significance of plagiogranites that intrude lherzolites and gabbros in the Ligurian Alps and the Northern Apennines. In addition, a host Fe-diorite was investigated. Samples from the Ligurian Alps were collected from the Voltri Group and the Sestri-Voltaggio Zone, whereas the plagiogranites from the Northern Apennines were taken in the Bracco unit. All these units have been affected by Alpine metamorphism reaching eclogite facies in the Voltri Group, blueschist degree in the Sestri Voltaggio samples, and prehnite-pumpellyite facies in the Bracco Unit, which has additionally been affected by rodingitization. U-Pb zircon ages of 150 ± 1, 153 ± 1 and 156 Ma were obtained, respectively, for two plagiogranites and the host Fe-diorite in the Ligurian Alps, and an age of 153 ± 1 Ma was determined for the plagiogranite in Northern Apennines. Inherited components in zircon and initial Pb in plagioclase indicate mixing of variously differentiated basaltic magmas with small amounts of roughly 1.7-2.1 Ga old continental crust material. REE patterns in both the plagiogranites and the host diorite are characterized by high REE abundance, and moderate LREE enrichment. Nd isotopic compositions lie in the range of N-MORB sources, yielding initial epsilon Nd values between +8.8 and +9.7, whereas Sr is isotopically heterogeneous. The geochemical pattern of the plagiogranites and the host Fe-diorite requires melting of a MORB-type mantle source that experienced LREE enrichment shortly before melting. The most likely explanation for such enrichment is the injection of melts derived by small degrees of melting from an adjacent mantle region. The basaltic, LREE-enriched parent magmas generated from this enriched domain have probably undergone up to about 72% of low-pressure fractional crystallization prior to their emplacement into the gabbro-peridotite complex. The 156-150 Ma magmatism occurred in close relation to normal faulting, sedimentation of breccias, and detachment of the mantle complex from its overlying continental crust, followed by exposure on the ocean floor. This tectono-magmatic event in the Ligurian Alps and the Northern Apennines reflects rifting of the Adriatic-Iberian continental plate segment, preceding wider opening of the Piedmont-Ligurian ocean basin and pillow basalt deposition.

Borsi, Laura; Schärer, Urs; Gaggero, Laura; Crispini, Laura

1996-05-01

219

Sm--Nd Garnet Geochronology Demonstrates Wholesale Transformation of Continental Crust During UHP Subduction---Western Gneiss Region, Norway  

Science.gov (United States)

Determining the extent to which ultrahigh-pressure (UHP) terranes transform to high-pressure (HP) minerals during subduction is central to understanding the processes attending the subduction of continental margins. The Western Gneiss Region (WGR) of Norway is one of two giant UHP terranes on Earth, and as such constitutes an important natural laboratory for investigating these processes. The distribution of UHP and HP eclogites shows that a 60,000 km2 area was subducted, but these eclogites are sparse (1--2 vol%) blocks in a sea of chiefly quartzofeldspathic, amphibolite-facies orthogneiss. Aside from the eclogites, the only widespread indicator of (U)HP metamorphism in this enclosing orthogneiss is garnet. This study uses high- precision Sm--Nd geochronology of these garnets to evaluate the degree of transformation of the WGR to high- pressure minerals during subduction and back to low-pressure minerals during exhumation. We compare these garnet ages to the 420--400 Ma Sm--Nd ages reported for WGR eclogites (e.g., Kylander-Clark et al., 2007). Eight garnet samples dated using the garnet--whole-rock isochron technique yielded the following results: 1) 921.7 ± 1.3 Ma for a sample from the easternmost section of the WGR; 2) 418.1 ± 1.7 Ma, 417.3 ± 1.2 Ma and 403.9 ± 0.8 Ma for three UHP samples; 3) 410.3 ± 2.5, 406.9 ± 1.5 Ma and 398.5 ± 0.8 Ma for three HP samples; 4) 587.3 ± 4.3 Ma for a fourth HP sample. These ages are interpreted to represent 1) the Proterozoic granulite-facies metamorphism of ca. 950 Ma; 2 & 3) (U)HP prograde metamorphism of the continental crust; and 4) a mixed age derived from the granulite-facies and (U)HP metamorphic events. The Proterozoic garnet age implies that the easternmost WGR did not transform to eclogite-facies minerals. In contrast, the good agreement between the 420--400 Ma eclogite ages (e.g., Kylander-Clark et al., 2007) and the 418--398 Ma gneiss ages reported here, indicates that the bulk of the WGR continental crust underwent wholesale transformation at (U)HP conditions. That the garnets are the only HP silicate mineral (other than quartz) surviving within a quartzofeldspathic gneiss composed of otherwise amphibolite-facies minerals indicates wholesale retrogression during exhumation.

Peterman, E. M.; Hacker, B. R.; Baxter, E. F.

2007-12-01

220

Ocean Fertilization and Ocean Acidification  

Science.gov (United States)

It has been suggested that ocean fertilization could help diminish ocean acidification. Here, we quantitatively evaluate this suggestion. Ocean fertilization is one of several ocean methods proposed to mitigate atmospheric CO2 concentrations. The basic idea of this method is to enhance the biological uptake of atmospheric CO2 by stimulating net phytoplankton growth through the addition of iron to the surface ocean. Concern has been expressed that ocean fertilization may not be very effective at reducing atmospheric CO2 concentrations and may produce unintended environmental consequences. The rationale for thinking that ocean fertilization might help diminish ocean acidification is that dissolved inorganic carbon concentrations in the near-surface equilibrate with the atmosphere in about a year. If ocean fertilization could reduce atmospheric CO2 concentrations, it would also reduce surface ocean dissolved inorganic carbon concentrations, and thus diminish the degree of ocean acidification. To evaluate this line of thinking, we use a global ocean carbon cycle model with a simple representation of marine biology and investigate the maximum potential effect of ocean fertilization on ocean carbonate chemistry. We find that the effect of ocean fertilization on ocean acidification depends, in part, on the context in which ocean fertilization is performed. With fixed emissions of CO2 to the atmosphere, ocean fertilization moderately mitigates changes in ocean carbonate chemistry near the ocean surface, but at the expense of further acidifying the deep ocean. Under the SRES A2 CO2 emission scenario, by year 2100 simulated atmospheric CO2, global mean surface pH, and saturation state of aragonite is 965 ppm, 7.74, and 1.55 for the scenario without fertilization and 833 ppm, 7.80, and 1.71 for the scenario with 100-year (between 2000 and 2100) continuous fertilization for the global ocean (For comparison, pre-industrial global mean surface pH and saturation state of aragonite is 8.18 and 3.5). As a result of ocean fertilization, 10 years from now, the depth of saturation horizon (the depth below which ocean water is undersaturated with respect to calcium carbonate) for aragonite in the Southern Ocean shoals from its present average value of about 700 m to 100 m. In contrast, no significant change in the depth of aragonite saturation horizontal is seen in the scenario without fertilization for the corresponding period. By year 2100, global mean calcite saturation horizon shoals from its present value of 3150 m to 2965 and 2534 m in the case without fertilization and with it. In contrast, if the sale of carbon credits from ocean fertilization leads to greater CO2 emissions to the atmosphere (e.g., if carbon credits from ocean fertilization are used to offset CO2 emissions from a coal plant), then there is the potential that ocean fertilization would further acidify the deep ocean without conferring any chemical benefit to surface ocean waters.

Cao, L.; Caldeira, K.

2008-12-01

 
 
 
 
221

Crust-mantle relations in Antarctica. The evolution of the east antarctic shield and tectonic settings of UHT metamorphism  

Energy Technology Data Exchange (ETDEWEB)

In this lecture it will be considered the geology of the East Antarctic Shield and its bearing on models of crust-mantle relations associated with high-grade metamorphism and deformation, focussing in particular on the evidence in East Antarctica for ultra-high temperature (UHT) metamorphism. It will be begun with a broad summary of the principal geological domains in the EAS, arranged according to the principal events preserved in them, followed by a brief outline of the concept of UHT metamorphism and the general evidence for it. These background topics will then lead into a more detailed consideration of the metamorphic geology and potential tectonic contexts of selected terrains that illustrate three of the key tectonothermal events or cycles recorded in the EAT: late Archaean to earliest Proterozoic (<2840 Ma but > 2480 Ma), mid-Proterozoic (1100-930 Ma) Grenvillian or Kibaran, and latest Proterozoic to Cambrian (600-500 Ma) Pan African. The terms event and cycle in this case are intended to be broad and will embrace, in many cases, several local events (e.g. deformation phases, magma pulses) that do not precisely correlate with each other on the larger scale. The potential crust-mantle relations involved in each of these major events or cycles will be discussed within the context of each event, but also considered in a broader final discussion to end the topic.

Harley, S. [Edinburgh Univ., Edinburgh (United Kingdom). Dept. of Geology and Geophysics

2000-07-01

222

Permeability of crust is key to crispness retention  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Bread loses crispness rapidly after baking because water originating from the wet crumb accumulates in the dry crust. This water accumulation might be increased by the dense and low permeable character of the bread crust. Our objective was to investigate the influence of permeability of the crust on...

Hirte, A.; Hamer, R.J.; Meinders, M.B.J.; Primo-Martin, C.

223

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

International Nuclear Information System (INIS)

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

2004-01-01

224

Evolution of high Arctic ocean basins and continental margins  

Energy Technology Data Exchange (ETDEWEB)

Taking advantage of the much increased detail offered by new data, the dissertation attempts to answer some of the remaining questions about the ocean basins and continental margins flanking the Eurasia-North America plate boundary. Its four constituent papers result from integrated geophysical analysis of gravity and magnetic anomalies, bathymetry, seismic reflection and refraction profiles, earthquake locations and focal mechanisms, and onshore and offshore geological data. The overall objectives are to: 1) Elucidate aspects of the structure, composition and evolution of the Eurasia Basin and Norwegian-Greenland Sea and their passive continental margins. 2) Relate the findings to fundamental Earth processes, specifically associated with lithospheric break-up and seafloor spreading. Summary of Papers: The present-day global seismograph network is capable of detecting earthquakes with nearly uniform magnitude threshold throughout the Eurasia Basin region. Given that the location of each earthquake is constrained by at least 12 recording stations, global earthquake catalogues confidently show that 1) earthquakes along the oceanic part of the plate boundary occur in swarms; 2) plate boundary stress decreases eastwards, in accordance with decreasing spreading rates; and 3) deformation takes place in a narrow zone in the oceanic domain but is abruptly defocused at the transition to the Laptev Sea continental rift system. When integrated with bathymetry and potential field data, the earthquake distribution indicates four distinct plate boundary provinces. The Spitsbergen Transform System is a series of oblique ridges and transform faults where the seismicity becomes increasingly diffuse to the north. The western Gakkel Ridge (west of 60{sup E}) has clustered and focused seismicity, accentuated topography and highamplitude magnetic anomalies, whereas the eastern Gakkel Ridge has smoother topographic relief, lower magnetic amplitudes, and slightly more focused seismicity. At the Laptev Sea continental slope, the change from ultra-slow seafloor spreading to active continental rifting takes place over a less than 60-km-wide continent-ocean transition featuring a 150-200-km-long sheared margin segment. The western Gakkel Ridge province is magmatically segmented. The central, sparsely magmatic segment is characterised by discrete magmatic centres that have been stationary with respect to the spreading axis since at least Chron 6 times (apprx. 19.6 Ma) and possibly since before Chron 18 times (apprx. 39.9 Ma). The westernmost, volcanic segment may have been amagmatic during Chron 13-5 times (apprx. 33.3-9.8 Ma). Sedimentary rocks in the Nansen Basin comprise four turbidite units with typical seismic velocities of 2.3, 2.2, 1.9 and 1.8 km s-1. The upper unit is associated with glaciomarine deposition in the Franz-Victoria Fan system and dates accordingly to approx. 2.3 Ma. The deeper, regional velocity contrast from 2.2 to 1.9 km s-1 probably represents a late Miocene (apprx. 10 Ma) response to major paleoceanographic changes during the opening of the Fram Strait gateway. A location of the continent-ocean transition (COT) on conjugate margins of the western Eurasia Basin and the northern Norwegian-Greenland Sea is proposed from the relation between seismically observed crustal thinning and seaward increasing mantle Bouguer anomalies. A refined location of the COT around the Hovgaard and Greenland ridges is also provided. The new COT location indicates that the distinct segmentation of the western Barents Sea margin is mirrored on the conjugate northeast Greenland margin. The Hinlopen margin north of Svalbard is characterised by a steep boundary fault on the COT and may be a sheared margin segment. The present geological and geophysical data base favours a continental origin of the Yermak Plateau and the Morris Jesup Rise, but a firm conclusion on their crustal structure cannot yet be drawn. A continuous oceanic corridor formed through shear-rifted continental crust in the Fram Strait between Chron 5B (14.8 Ma) and Chron 5 times (9.8

Engen, Oeyvind

2005-08-01

225

Uranium and thorium in magmatic rocks of oceanic regions  

International Nuclear Information System (INIS)

[en] New estimations of uranium and thorium oncentrations in magmaic rocks of oc eanic crust have been obtained. An indicator role of uranium and thorium with respect to magmatic processes of oceanic regions has been shown on the base of d ata analysis. Coefficients of uranium and thorium distribution between phenocry sts and basalt groundmass have been considered along with distributions of their contents in mantle spinel therzolites of oceanic and continental regions

1983-01-01

226

Salatoimikud : ma tahan uskuda / Mart Rummo  

Index Scriptorium Estoniae

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

Rummo, Mart

2008-01-01

227

77 FR 76585 - Massachusetts Disaster # MA-00052  

Science.gov (United States)

...Disaster Declaration 13417 and 13418] Massachusetts Disaster MA-00052 AGENCY: U...a disaster for the Commonwealth of Massachusetts dated 12/11/2012. Incident...Counties: Hampden. Contiguous Counties: Massachusetts: Berkshire, Hampshire,...

2012-12-28

228

77 FR 76584 - Massachusetts Disaster # MA-00051  

Science.gov (United States)

...Disaster Declaration 13420 and 13421] Massachusetts Disaster MA-00051 AGENCY: U...a disaster for the Commonwealth of Massachusetts dated 12/12/2012. Incident...Worcester. Contiguous Counties: Massachusetts: Franklin, Hampden,...

2012-12-28

229

Missing history (16 71 Ma) of the Galápagos hotspot: Implications for the tectonic and biological evolution of the Americas  

Science.gov (United States)

We present the results of volcanological, geochemical, and geochronological studies of volcanic rocks from Malpelo Island on the Nazca plate (15.8 17.3 Ma) belonging to the Galápagos hotspot tracks, and igneous complexes (20.8 71.3 Ma) along the Pacific margin of Costa Rica and Panama. The igneous complexes consist of accreted portions of ocean island and seamount volcanoes and aseismic ridges, representing the missing (primarily subducted) history of the Galápagos hotspot. The age and geochemical data directly link the Galápagos hotspot tracks on the Pacific Ocean floor to the Caribbean large igneous province (ca. 72 95 Ma), confirming a Pacific origin for the Caribbean oceanic plateau from the Galápagos hotspot. We propose that emplacement of this oceanic plateau between the Americas and interaction of the Galápagos hotspot tracks with the Central American Arc played a fundamental role in the formation of land bridges between the Americas in Late Cretaceous Paleocene and Pliocene-Holocene time. The land bridges allowed the exchange of terrestrial faunas (e.g., dinosaurs, mastodons, saber-tooth cats, and ground sloths) between the Americas and served as barriers for the exchange of marine organisms between the central Pacific Ocean and the Caribbean Sea and the central Atlantic Ocean.

Hoernle, Kaj; van den Bogaard, Paul; Werner, Reinhard; Lissinna, Britta; Hauff, Folkmar; Alvarado, Guillermo; Garbe-Schönberg, Dieter

2002-09-01

230

Towards a metallurgy of neutron star crusts  

CERN Document Server

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.

Kobyakov, D

2013-01-01

231

Ocean energy  

Energy Technology Data Exchange (ETDEWEB)

Extraction of renewable energy from the ocean has long term potential of satisfying much of the world's requirements for energy. The important sources of energy from the ocean are: ocean thermal (OTEC), waves, tides, salinity gradients, and currents. On the basis of source potential, the level of technology development and possible economic viability, ocean thermal, waves and tides appear to be the most promising for India. A brief review of the state-of-the art on OTEC, wave and tidal energies is presented in this paper.

Raju, S.; Bhattacarya, S.K.; Vendhan, C.P.

1983-07-01

232

Excited nuclei in neutron star crusts  

CERN Document Server

The paper considers the chains of successive electron capture reactions by nuclei of the iron group which take place in the crystal structures of neutron star envelopes. It is shown that as a result of such reactions the daughter nuclei in excited states accumulate within certain layers of neutron star crusts. The phonon model of interactions is proposed between the excited nuclei in the crystalline structure, as well as formation of highly excited nuclear states which emit neutrons and higher energy photons.

Takibayev, Nurgali; Nasirova, Diana

2012-01-01

233

Pyrolysis of waste plastic crusts of televisions.  

UK PubMed Central (United Kingdom)

The disposal of waste plastic crusts of televisions is an issue that is gaining increasing interest around the world. In this investigation, the pyrolysis and catalytic cracking of the waste television crusts mainly composed of acrylonitrile--butadiene-styrene copolymer was studied. Thermogravimetric analysis was used for initial characterization of the pyrolysis of the waste plastic, but most of the investigations were carried out using a 600 mL tubing reactor. Effects of temperature, reaction time and catalyst on the pyrolysis of the waste television crusts were investigated. The results showed that the oil yield increased with increasing temperature or with prolongation of reaction time. With increasing temperature, the generating percentage of gasoline and diesel oil increased, but the heavy oil yield decreased. Zinc oxide, iron oxide and fluid catalytic cracking catalyst (FCC catalyst) were employed to perform a series of experiments. It was demonstrated that the liquid product was markedly improved and the reaction temperature decreased 100 degrees C when FCC was used. The composition ofpyrolysis oils was analysed using gas chromatography-mass spectrometry, and they contained 36.49% styrene, 19.72% benzenebutanenitrile, 12.1% alpha-methylstyrene and 9.69% dimethylbenzene.

Liu X; Wang Z; Xu D; Guo Q

2012-09-01

234

Deformations of Accreting Neutron Star Crusts and Gravitational Wave Emission  

CERN Document Server

Motivated by the narrow range of spin frequencies of nearly 20 accreting neutron stars, Bildsten (1998) conjectured that their spin-up had been halted by the emission of gravitational waves. He also pointed out that small nonaxisymmetric temperature variations in the accreted crust will lead to "wavy" electron capture layers, whose horizontal density variations naturally create a mass quadrupole moment. We present a full calculation of the crust's elastic adjustment to these density perturbations and find that the elastic response of the crust reduces Bildsten's original estimate of the quadrupole moment in the thin outer crust by a factor of 20-50. However, this basic picture, when applied to capture layers in the deep inner crust, can generate quadrupoles in the necessary range as long as there are ~5% lateral temperature variations in the inner crust. By calculating the thermal flow throughout the core and the crust, we find that temperature gradients this large are easily maintained by asymmetric heat sou...

Ushomirsky, G; Bildsten, L; Ushomirsky, Greg; Cutler, Curt; Bildsten, Lars

2000-01-01

235

Tectonomagmatic evolution of the Earth: from the primordial crust to Phanerozoic type of activit  

Science.gov (United States)

There are two dominating hypotheses about composition of the primordial Earth's crust now: basic or sialic. Both models require a global melting of primary chondritic material, and final result would depend on degree of melt differentiation during hardening of global magma ocean some hundreds km deep. Such solidification, due to difference in adiabatic and melting point gradients proceeded in bottom-top direction and resulted in accumulation of low-temperature derivates in outer shell of the planet. Geological data, namely granite-dominated Archean crust, composed mainly by tonalite-trondhjemite-granodiorite (TTG) rocks, and Hadean detrital zircons from Australia with U-Pb age 4.4-4.2 Ga supports the primordial-sialic crust hypothesis. Formation of the sialic crust was responsible for the depletion of the upper mantle matter. Tectonomagmatic activity in the Early Precambrian was rather different from the Phanerozoic. Granite-greenstone terranes (GGTs) and their separating granulite belts were major Archean tectonic structures. The GGTs consisting of irregular network of greenstone belts with high-Mg komatiite-basaltic and boninite-like magmatism, "submerged" in TTG granite-gneiss matrix, probably, strongly reworked primordial sialic crust. They were areas of extension, uplifting and denudation, whereas the granulite belts were dominated by compression, sinking and sedimentation. By the Proterozoic the crust became rigid resulting in formation of rift structures, huge dike swarms and large mafic-ultramafic layered intrusions. In early Paleoroterozoic character of the tectonomagmatic activity remained almost the same: cratons, separated by granulite belts, appeared on the place of GGTs. Magmatism was dominated by siliceous high-Mg (boninite-like) series (SHMS), which formed large igneous provinces. SHMS are close in composition to the Phanerozoic subduction-related magmas; however, instead of them, SHMS had intracontinental tectonic settings. Negative ?Nd in these rocks suggests an important assimilation of the Archean lower-crustal rocks. We assume that origin of the SHMS magmas was linked with floating up of magma chambers of high-temperature mantle-derived ultramafic melts through the crust according to zone refinement principle, i.e. by melting of roof accompanied by crystallization at bottom. It suggests that the Early Precambrian tectonomagmatic activity was linked with ascending of the first generation mantle superplumes, composed by depleted ultramafic material Cardinal change of tectonomagmatic processes occurred in the period of 2.35 to 2.0 Ga, which was characterized by voluminous eruption of Fe-Ti picrites and basalts similar to the Phanerozoic within-plate magmas, derived from geochemical-enriched mantle source. Simultaneously, important compositional changes occurred in the atmosphere, hydrosphere and biosphere (Melezhik et al., 2005). The first Phanerozoic-type orogens (Svecofennian of the Baltic Shield, Trans-Hudson and others of the Canadian Shield, etc.) appeared ca. 2 Ga. Since then, subduction of the ancient sialic continental crust (together with newly-formed oceanic crust) is a permanent process and the crustal material has stored in the "slab graveyard", revealed in the mantle by seismic tomography. We believe that the ascending of the second generation mantle plumes (thermochemical), enriched in Fe, Ti, P, LREE, etc., was responsible for those changes. Those plumes were generated at the core-mantle boundary and this process is active so far. The thermochemical plume matter possessed less density and could reach shallower depths; triggering plate tectonics processes. So, previously absent geochemical-enriched material started to involve from ~2.3 Ga in the Earth's tectonomagmatic processes. Where such material was "conserved" and how it was activated? The established succession of events could be provided by a combination of two independent factors: (1) the Earth originally was heterogeneous, and (2) the downward heating of the Earth (from the surface to the core) was f

Sharkov, Evgenii

2010-05-01

236

Strontium isotope stratigraphy and geochemistry of the late Neogene ocean  

International Nuclear Information System (INIS)

A curve describing the variation of the strontium isotopic composition of seawater for the late Neogene (9 to 2 Ma) was constructed from 87Sr/86Sr analyses of marine carbonate in five Deep Sea Drilling Project (DSDP) sites: 502, 519, 588, 590, and 593. The strontium isotopic composition of the oceans increased between 9 and 2 Ma with several changes in slope. From 9 to 5.5 Ma 87Sr/86Sr values were nearly constant at ? 0.708925. Between 5.5 and 4.5 Ma, 87Sr/86Sr ratios increased monotonically at a rate of ? 1 x 10-4 per million years. The steep slope during this interval provides the potential for high resolution strontium isotope stratigraphy across the Miocene/Pliocene boundary. The rate of change of 87Sr/86Sr decreases to near zero again during the interval 4.5-2.5 Ma, and ratios average 0.709025. The relatively rapid increase of 87Sr/86Sr between 5.5 and 4.5 Ma must be related to changes in the flux or average 87Sr/86Sr ratios of the major inputs of Sr to the oceans. Quantitative modelling of these inputs suggests that the increase was most probably caused by an increase in the dissolved riverine flux of strontium to the oceans, an increase in the average 87Sr/86Sr composition of river water, or some combination of these parameters. Modelling of this period as a transient-state requires a pulse-like increase in the input of 87Sr to the oceans between 5.5 and 4.5 Ma. Alternatively, the 5.5-4.5 Ma period can be modelled as a simple transition from one steady-state to another if the oceanic residence time of strontium was eight times less than the currently accepted value of 4 Ma. (orig./Shoe).

1989-01-01

237

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

Directory of Open Access Journals (Sweden)

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.

Benoit Ildefonse; Donna Blackman; Barbara E. John; Yasuhiko Ohara; D. Jay Miller; Christopher J. MacLeod; the IODP Expeditions 304–305 Scientists

2006-01-01

238

Ocean Science ????  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Ocean Science (OS) is a new international and free to web scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of ocean science, experimental, theoretical and laboratory. The primary objective is to publish ...

239

"Sõnu mis ma kõige rohkem vajan..." : [luuletused] / Aarne Puu  

Index Scriptorium Estoniae

Sisu: "Sõnu mis ma kõige rohkem vajan..." ; "Pühade-eelses tänavasaginas..." ; "Alati leidub keegi..." ; "Ma nägin und..." ; "Ma luban et ulatan sulle oma käe..." ; "Ühel ööl hakkas toanurgas nutma..." ; Hitchcock naeratab jälle

Puu, Aarne

2007-01-01

240

Global Crust-Mantle Density Contrast Estimated from EGM2008, DTM2008, CRUST2.0, and ICE-5G  

Science.gov (United States)

We compute globally the consolidated crust-stripped gravity disturbances/anomalies. These refined gravity field quantities are obtained from the EGM2008 gravity data after applying the topographic and crust density contrasts stripping corrections computed using the global topography/bathymetry model DTM2006.0, the global continental ice-thickness data ICE-5G, and the global crustal model CRUST2.0. All crust components density contrasts are defined relative to the reference crustal density of 2,670 kg/m3. We demonstrate that the consolidated crust-stripped gravity data have the strongest correlation with the crustal thickness. Therefore, they are the most suitable gravity data type for the recovery of the Moho density interface by means of the gravimetric modelling or inversion. The consolidated crust-stripped gravity data and the CRUST2.0 crust-thickness data are used to estimate the global average value of the crust-mantle density contrast. This is done by minimising the correlation between these refined gravity and crust-thickness data by adding the crust-mantle density contrast to the original reference crustal density of 2,670 kg/m3. The estimated values of 485 kg/m3 (for the refined gravity disturbances) and 481 kg/m3 (for the refined gravity anomalies) very closely agree with the value of the crust-mantle density contrast of 480 kg/m3, which is adopted in the definition of the Preliminary Reference Earth Model (PREM). This agreement is more likely due to the fact that our results of the gravimetric forward modelling are significantly constrained by the CRUST2.0 model density structure and crust-thickness data derived purely based on methods of seismic refraction.

Tenzer, Robert; Hamayun; Novák, Pavel; Gladkikh, Vladislav; Vajda, Peter

2012-09-01

 
 
 
 
241

Environmental/Ocean Systems  

Science.gov (United States)

... Environmental/Ocean Systems   NSF 99-20 Environmental/Ocean Systems Bioengineering and ... ocean and sea floor data as well as ocean energy, power sources, and environmentally benign ocean ...

242

Rivera Ocean seismic experiment (ROSE) overview  

Energy Technology Data Exchange (ETDEWEB)

The Rivera Ocean Seismic Experiment (ROSE) was designed as a combined sea and land seismic program to utilize both explosive and earthquakes to study a number of features of the structure and evolution of a mid-ocean ridge, a major oceanic fracture zone, and the transition region between ocean and continent. The primary region selected for the experiment included the Rivera Fracture Zone, the crest and eastern flank of the East Pacific north of the Rivera and adjacent areas of Baja California and mainland Mexico. The experiment included: (1) study of the East Pacific Rise south of the Orozco Fracture Zone primarily using ocean bottom recording and explosive sources. (2) a seismicity program at the Orozco, and (3) a land-based program of recording natural events along the coastal region of Mexico. A considerable amount of useful data was obtained in each of the three subprograms. In the marine parts of the experiment we were able to address a variety of problems including structure and evolution of young oceanic crust and mantle, structure and dynamics of the East Pacific Rise, seismicity of the Orozco Fracture Zone, and partitioning of energy transmission between the ocean volume and the crust/lithosphere. On land, the fortuitous occurrence of the Petatlan M7.6 earthquake of March 14, 1979, permitted the acquisition of an excellent data set of foreshocks and aftershocks of this large event, which provide new insight into the filling of a major seismic gap in the region. This overview describes the scientific rationale and the design of the experiments, along with some general results.

Ewing, J.I.; Meyer, R.P.

1982-10-10

243

MA-1, MA-2 system for beam analysis and transportation within the acceleration complex in IFNE  

Energy Technology Data Exchange (ETDEWEB)

The experimental conditions were established to test the magnetic analysers MA-1 an MA-2 of the heavy ions accelerating system in IFNE. The energy resolution, transmission and focusing conditions for the proton beam with the energy of E = 5-14 MeV were determined.

Berceanu, I.; Brancus, I.; Buta, A.; Dobrescu, S.; Grama, C.; Indreas, G.; Lazar, I.; Mihai, I.; Papureanu, S.; Petrascu, M.

1981-01-01

244

Ma Ying-jeou's presidential discourse Ma Ying-jeou's präsidentieller Diskurs  

Digital Repository Infrastructure Vision for European Research (DRIVER)

"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 ...

Sullivan, Jonathan; Sapir, Eliyahu V.

245

Moored systems designed to sense deep ocean earthquakes  

International Nuclear Information System (INIS)

The ability to predict earthquakes and tsunamis is becoming increasingly important as world population continues to grow in high-density coastal metropolitan areas. Earthquakes which occur in and near undersea subduction zones where the earth's crust slides under continental masses generate highly destructive tsunamis. Deep ocean buoy systems and sensor implantation techniques are being developed to obtain seismic data from the earth's crust in water depths of 6000 m. For the first time, deep-sea drilling, high-resolution seismic sensors, and long-term, deep-ocean mooring technology are being combined to provide systems which continuously monitor earthquake activity in the deep ocean. Such systems provide vital seismic research information to the scientific community.

1982-01-01

246

The Cenozoic Arctic Ocean Unveiled through Scientific Ocean Drilling  

Science.gov (United States)

In late summer 2004, the Integrated Ocean Drilling Program (IODP) conducted one of the most transformational missions in the almost 40 year history of scientific ocean drilling: the Arctic Coring Expedition (ACEX). This technically-challenging expedition recovered the first Cenozoic sediment record from the Arctic Ocean-extending previous records from ~1.5 Ma to an unprecedented ~56 Ma. Glimpses of the breadth of this transformation were even seen during ACEX when the massulae from fresh water ferns were found and the presence of Apectodinium augustum confirmed that the Paleocene-Eocene Thermal Maximum (PETM) was unexpectedly recovered. Soon after the expedition, when the cores were opened and analyzed, ice-rafted debris was found to have occurred much earlier than previously thought-in the Eocene in an environment of high organic carbon content. The initial analyses also revealed an extensive hiatus that occurred between several of the most spectacular sediment cores in terms of color, e.g. turquoise, and structure, starkly contrasting black and white crossbedding that is now dubbed the "zebra" core. The exciting early results attracted other investigators that expanded the scientific investigating team to more than 40 people. This, in turn, extended the analyses to include new studies that revealed surprisingly high Arctic Ocean surface water temperatures and a hydrologically active system during the PETM. Although the hiatus is a lost window in time for the Arctic paleoclimate record, it spawned other studies that integrated the regional tectonic history with ACEX results revealing a major oceanographic reorganization at 17.5 Ma-ventilation of the Arctic Ocean to the North Atlantic through the Fram Strait. In this overview, recent results from the large ACEX scientific "family" are summarized and include: a new age model; detailed analyses of the middle Eocene that document a unique brackish water environment; sea ice and iceberg history reconstructions and provenance from the Eocene to present; evolution of depositional environments that are linked to broader tectonic & subsidence histories; times of isolation and connection to the global ocean; geochemical analyses of the organic carbon-rich sediments; and unique applications of high resolution proxies and cyclostratigraphy.

Mayer, L.; Moran, K.; Backman, J.

2007-12-01

247

Hydrothermal alteration in a modern suprasubduction zone: The Tonga forearc crust  

Science.gov (United States)

An extensive suite of hydrothermally altered basalts, gabbros, and plagiogranites was recovered from the trench-facing slope of the Tonga forearc. The tectonic setting, lithology, and geochemistry of these samples make them a unique collection for comparison with suprasubduction zone (SSZ) ophiolites. Petrography, mineral chemistry, and geothermometry are used to constrain the metamorphic evolution of ocean crust formed in a modern SSZ setting. Seawater-derived hydrothermal fluids first penetrated the lower crust along grain boundaries and microscopic fracture networks at temperatures >800°C. As the plutonic sequence cooled, amphibole progressively replaced the mafic phases, followed by chlorite and epidote below ˜550°C. Basalts record peak alteration temperatures up to 773°C; however, most were altered at lower temperatures typical of mid-ocean ridge (MOR) volcanic sequences [Kelman, 1998]. Epidosites formed by pervasive alteration of basalt and plagiogranite at greenschist facies conditions and at high water-rock ratios. Pervasively altered gabbros and basalts display evidence of late cataclastic deformation and/or contain veins that is likely related to a later tectonic event such as trench rollback. The range of alteration temperatures and mineral assemblages in basalts and gabbros are similar to those described from both SSZ ophiolites and MORs. However, the degree of alteration in basalts and the presence of epidosites in the Tonga collection are most similar to alteration characteristics in SSZ ophiolites. The initiation of high-temperature brittle deformation in the absence of ductile deformation suggests that the Tonga forearc crust was constructed in a magma-rich environment, similar to fast spreading MORs.

Banerjee, Neil R.; Gillis, Kathryn M.

2001-10-01

248

Ocean Motion  

Science.gov (United States)

This Website offers a review of the surface circulation of Earth's ocean and classroom investigations appropriate for various disciplines at the high school level. Articles and video interviews about ocean current research, interactive data visualizes, news articles, simplified models, teacher and student guides will create resources for diverse audiences who are impacted by ocean surface currents. This site highlights use of data derived from the on-line satellite data of Earth for understanding patterns of ocean surface currents and how they relate to issues of human exploration, commerce, science, weather/climate, and pollution. Classroom-ready, interdisciplinary investigation swill help high school students practice science, mathematics and writing skills matched to national standards and will be keyed to topics covered in the traditional high school curriculum. Each investigation is keyed to the stages of the 5 E's teacher/learning model.

Tweedie, Sara

2010-09-17

249

Earth at 200 Ma: Global palaeogeography refined from CAMP palaeomagnetic data  

Science.gov (United States)

The Central Atlantic Magmatic Province was formed approximately 200 Ma ago as a prelude to the breakup of Pangea, and may have been a cause of the Triassic-Jurassic mass extinction. Based on a combination of (i) a new palaeomagnetic pole from the CAMP related Argana lavas (Moroccan Meseta Block), (ii) a global compilation of 190-210 Ma poles, and (iii) a re-evaluation of relative fits between NW Africa, the Moroccan Meseta Block and Iberia, we calculate a new global 200 Ma pole (latitude = 70.1° S, longitude = 56.7° E and A95 = 2.7°; N = 40 poles; NW Africa co-ordinates). We consider the palaeomagnetic database to be robust at 200 ± 10 Ma, which allows us to craft precise reconstructions near the Triassic-Jurassic boundary: at this very important time in Earth history, Pangea was near-equatorially centered, the western sector was dominated by plate convergence and subduction, while in the eastern sector, the Palaeotethys oceanic domain was almost consumed because of a widening Neothethys. We show that there has been negligible net displacement of the Moroccan Meseta relative to Africa since 200 Ma. We calculate a new fit between Iberia and NW Africa, showing that models inferring minor Cretaceous rotation and major Cretaceous sinistral translation of Iberia relative to Europe are inconsistent with palaeomagnetic Iberia-Africa fits at 200 Ma. During Pangea breakup (~ 195 Ma, opening of the Central Atlantic), and shortly after the CAMP outburst, Laurasia rotated clockwise relative to Gondwana around an Euler pole located in SE Iberia. The CAMP and its likely contribution to climate change, mass extinction and Pangea breakup profoundly changed planet Earth and we show that CAMP was sourced by a deep mantle plume that started its disturbing journey from the core-mantle boundary.

Ruiz-Martínez, Vicente Carlos; Torsvik, Trond H.; van Hinsbergen, Douwe J. J.; Gaina, Carmen

2012-05-01

250

Crusted Scabies in the Burned Patient  

DEFF Research Database (Denmark)

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

Berg, Jais Oliver; AlsbjØrn, Bjarne

2011-01-01

251

Method for manufacturing sandwich bread with no crust  

UK PubMed Central (United Kingdom)

The process comprises preparing a dough roll of batch bread (5) by kneading, shaping and fermenting it in a mold, baking the dough roll in the mold, cooling the baked batch bread, and removing the crust of bread on its sides. The crust of bread is removed by scraping the peripheral surface of the bread using a rotating cutting unit (20). Before and during the removal of the crust, the batch bread is frozen at a surface temperature of 10-30[deg] C to preserve a firm crust for its elimination. The freezing of the bread is carried out by cryogenics or by the producing mechanical cooling. The process comprises preparing a dough roll of batch bread (5) by kneading, shaping and fermenting it in a mold, baking the dough roll in the mold, cooling the baked batch bread, and removing the crust of bread on its sides. The crust of bread is removed by scraping the peripheral surface of the bread using a rotating cutting unit (20). Before and during the removal of the crust, the batch bread is frozen at a surface temperature of 10-30[deg] C to preserve a firm crust for its elimination. The freezing of the bread is carried out by cryogenics or by producing mechanical cooling such as ventilation. During the removal of the crust, the bread is moved in a direction of tangential (T) displacement to the rotary cutting unit or along the direction perpendicular to the axis of rotation (X) of the rotary cutting unit towards the rotation movement of the cutting tools (26). The bread is moved on rollers for forming a moving support by pinching between two mobile strips, by a lug chain, or by a pusher arm having alternating movement. The bread is alternately moved at several times before the rotary cutting unit to remove the crust on its entire periphery, and then simultaneously or successively to the rotary cutting units arranged around the bread to remove the entire crust on its sides. During the removal of the crust, the pieces of the bread crust are aspirated closer to the rotary cutting unit. The pieces of the torn bread crust are evacuated by a simple conveyor belt system, bucket conveyor or rope and button conveyor. After the removal of the crust, the stubs are removed and then the bread is sliced and packaged. The crust is removed to create the final form of the bread in a longitudinal shape with straight, curved, symmetric or non-symmetric, and polygonal or curved such as square, rectangular, triangular, round, oval, heart or star.

DU REAU DE LA GAIGNONNIERE ENGUERRAN; NADAUD FRANCIS

252

Comment on Ahmadi and Ma (1990).  

Science.gov (United States)

A model to predict flow of a particular mixture is described in Ahmadi and Ma (1990):the full model, with closures, appears to result in predictions of unphysical behavior. Specifically, the model with its closure appears to result in spurious creation of...

L. M. Liljegren

1997-01-01

253

Marker Sequential Test (MaST) design.  

UK PubMed Central (United Kingdom)

BACKGROUND: New targeted anticancer therapies often benefit only a subset of patients with a given cancer. Definitive evaluation of these agents may require phase III randomized clinical trial designs that integrate evaluation of the new treatment and the predictive ability of the biomarker that putatively determines the sensitive subset. PURPOSE: We propose a new integrated biomarker design, the Marker Sequential Test (MaST) design, that allows sequential testing of the treatment effect in the biomarker subgroups and overall population while controlling the relevant type I error rates. METHODS: After defining the testing and error framework for integrated biomarker designs, we review the commonly used approaches to integrated biomarker testing. We then present a general form of the MaST design and describe how it can be used to provide proper control of false-positive error rates for biomarker-positive and biomarker-negative subgroups. The operating characteristics of the MaST design are compared by analytical methods and simulations to the sequential subgroup-specific design that sequentially assesses the treatment effect in the biomarker subgroups. Practical aspects of MaST design implementation are discussed. RESULTS: The MaST design is shown to have higher power relative to the sequential subgroup-specific design in situations where the treatment effect is homogeneous across biomarker subgroups, while preserving the power for settings where treatment benefit is limited to biomarker-positive subgroup. For example, in the time-to-event setting considered with 30% biomarker-positive prevalence, the MaST design provides up to a 30% increase in power in the biomarker-positive and biomarker-negative subgroups when the treatment benefits all patients equally, while sustaining less than a 2% loss of power against alternatives where the benefit is limited to the biomarker-positive subgroup. LIMITATIONS: The proposed design is appropriate for settings where it is reasonable to assume that the treatment will not be effective in the biomarker-negative patients unless it is effective in the biomarker-positive patients. CONCLUSION: The MaST trial design is a useful alternative to the sequential subgroup-specific design when it is important to consider the treatment effect in the biomarker-positive and biomarker-negative subgroups.

Freidlin B; Korn EL; Gray R

2013-10-01

254

The ocean-continent transition of western Iberia  

Energy Technology Data Exchange (ETDEWEB)

The western continental margin of the Iberian peninsular has the characteristic of a rifted non-volcanic continental margin with half-graben and tilted fault blocks seen in several places on multichannel seismic reflection profiles. The ocean-continent transition (OCT) is therefore expected to be where thinned continental crust and oceanic crust are juxtaposed, as elsewhere. The authors located the OCT off western Iberia in order to constrain the pre-lift fit of Iberia to North America. This fit is only marginally constrained by sea-floor spreading magnetic anomalies because the Cretaceous constant polarity interval is adjacent to the OCT. Thinned continental crust can be distinguished from oceanic crust by the nature of the lower crustal velocity structure. In 1986-1987, a series of seismic refraction profiles was shot across three parts of the Iberian Abyssal Plain, the OCT can be detected not only from seismic velocities but also by modeling magnetic anomalies. The chosen location of the OCT is consistent with the interpretation of subsequently acquired multichannel profiles. Off Galicia Bank, the OCT, recognized from seismic velocities and multichannel profiles, corresponds to a seabed peridotite ridge, which has been extensively sampled. In the Tagus Abyssal Plain, limited seismic data gives a less clear picture of the OCT.

Whitmarsh, R.B.; Miles, P.R.; Pinheiro, L.M. (Inst. of Oceanographic Sciences Deacon Lab., Surrey (United Kingdom)); Boillot, G. (Univ. Pierre et Marie Curie, Villefranchesur-Mer (France)); Recq, M. (Univ. de Bretagne Occidentale, Brest (France))

1991-08-01

255

Central South Atlantic kinematics: a 3D ocean basin-scale model of the Walvis Ridge and Rio Grande Rise  

Science.gov (United States)

Prior to the breakup of western Gondwana, ca. 130 Ma, the Tristan da Cuhna mantle plume produced the eastern South American Parana, and western African Etendeka, flood basalts. As the South Atlantic basin opened, the ridge-centered plume produced seaward extending hotspot tracks: Rio Grande Rise on the South American Plate, and Walvis Ridge on the African Plate. Several ocean floor edifices on the hotspot trends appear to produce lower than expected amplitude free air gravity anomalies, suggesting that they are composed of lower density material. We have constructed a 3D gravity model of the South Atlantic basin to examine variations in crustal density associated with the hot spot trends. The model, which encompasses a region that extends from 46°S to 10 °S and from 20°E to 60°W, comprises the following layers: water, sediment, crust, and upper mantle. Variable density sediment and upper mantle layers are incorporated to estimate density changes related to sediment thickness and compaction, and upper mantle temperatures, respectively. The initial Moho horizon is estimated from isostatic equilibrium calculations; however the isostatic effect is scaled away from the seafloor spreading center to simulate the active spreading center. Three open-file grids were used to generate the model: satellite-derived free air gravity, global topography, and sediment thickness of the world. Inverting the model for crustal density reveals a distribution of low-density areas: along the coasts, the seafloor spreading axis, and along the Rio Grande Rise and Walvis Ridge hotspot trends. Coastal and spreading axis low density areas are thought to be related to continental crust and high temperature upper mantle. Hotspot track low density areas might be related to variable densities within the volcanic edifices, variations in their crustal thickness, or upper mantle densities beneath them. Detailed 2D models approximate reasonable density and geometry limits along select transects. Holding the African Plate fixed, we have rotated the South American Plate for 16 times corresponding to Chrons C5, C6, C13, C18, C21, C25, C31, C34, five interpolated times (ca. 89, 93, 100, 105, and 112 Ma), and Chrons M0, M2 and M4. Reconstructions, displaying inversion results illustrate the development of the hotspot tracks as the South Atlantic opened, suggest that Tristan da Cuhna was a ridge-centered plume until about 30 Ma.

Bird, D. E.; Hall, S. A.

2009-12-01

256

Laboratory colonization of Mansonia mosquitoes with an emphasis on Ma. annulata and Ma. bonneae.  

Science.gov (United States)

The present study records the first successful colonization of Mansonia annulata and describes colony maintenance with modification of rearing medium and host plants. Three species of Mansonia mosquitoes (Ma. uniformis, Ma. indiana and Ma annulifera) were successfully reared in ambient environments with adult emergence rates > 50%, while Ma. bonneae and Ma. dives yielded emergence rates > 30%. Colonization of Ma. annulata was modified and improved so that they were successfully raised to adult with emergence rates of 23%. Tube sedge, Lepironia articulata, was utilized as a host plant and peat swamp water was used as a rearing medium. Yeast and small lizard droppings were added daily to the larval medium to maintain microorganisms and pH in the infusion. However, identifying suitable culture medium remains an obstacle to establishing colonies of Ma. annulata, as the culture medium is difficult to mimic in the laboratory. Further study, focusing particularly on larval attachment substrates and rearing medium, is needed to develop a standardized and practical rearing technique for Mansonia mosquitoes. PMID:17121290

Samung, Yudthana; Palakul, Kaewmala; Apiwathnasorn, Chamnarn; Prummongkol, Samrerng; Asavanich, Achara; Leemingsawat, Somjai

2006-07-01

257

The closed-system approximation for evolution of argon and helium in the mantle, crust and atmosphere  

International Nuclear Information System (INIS)

The atmosphere formed by the outgassing of the depleted mantle, leaving a remnant of non-degassed mantle which forms the source of some ocean-island basalts such as Hawaii and Iceland. The 40Ar in the atmosphere degassed from 50% to 90% of the mantle possibly synchronous with sea-floor spreading, ocean-ridge hydrothermal activity and continent formation. The bulk of the degassing ended 1.2-1.8 Ga ago. The similarity of the 40Ar/36Ar ratio between the atmosphere and non-degassed mantle suggest both have approximated closed systems. On the other hand, more than 99% of He outgassed from the mantle has been lost to space from the upper atmosphere. Portions of the oceanic crust and mantle contaminated by atmospheric noble gases are distinguished from non-degassed mantle by this He depletion. Uranium isotope ratios are estimated starting from earth degassing models. (Auth.).

1982-07-02

258

Early Cambrian oceanic plagiogranite in the Silvretta Nappe, eastern Alps: geochemical, zircon U-Pb and Rb-Sr data from garnet-hornblende-plagioclase gneisses  

Science.gov (United States)

Garnet-hornblende-plagioclase gneisses rich in incompatible elements occur in the crystalline basement of the Austro-Alpine Silvretta nappe and are associated with clinopyroxene norites and harzburgite cumulates. It is proposed here that the gneisses were formerly oceanic plagiogranites. An ?Nd(530) value of +5.6 for the gneisses as well as initial87Sr/86Sr values of 0.7036 0.7037 for the gabbroic rocks and 0.7026 0.7027 for the ultramafic rocks suggest a mantle source for this rock association. The geochemical characteristics of the garnet-hornblende-plagioclase gneisses indicate that their precursors were derived by fractional crystallization from a basaltic parent magma, by the same process which produced the adjacent clinopyroxene norites and ultramafic cumulates as well. The combined U-Pb upper intercept ages of zircons from two gneiss samples yield an igneous crystallization age of 532 ± 30 Ma, similar to previously dated (mostly calcalkaline) orthogneisses in the same area. High-quality transparent zircons showed the least degree of discordance, but contain extremely low U and Pb levels. The rock suite, including this plagiogranite, was emplaced within oceanic crust which formed in the latest Precambrian-early Palaeozoic off the northern continental margin of Gondwana.

Müller, Bernhard; Schaltegger, Urs; Klötzli, Urs; Flisch, Markus

1996-12-01

259

Physical constraints on dolomite crust formation, Ambergris Cay Belize  

Energy Technology Data Exchange (ETDEWEB)

Dolomitic crusts forming on a peritidal flat on Ambergris Cay, Belize, occur beneath surface sediment adjacent to, but not within, small saline (60-90 ppt) ponds. Upper crusts, 2-12 cm thick forming at or slightly below the water table (approximately equivalent to lagoon water level) are areally restricted by (1) ponds where sediment lies below 20-50 cm of water, (2) high and relatively dry areas where sediment accumulation of more than 15 cm above water level supports diverse vegetation, and (3) low areas affected by mangrove encroachment where preexisting crusts are perforated by roots and displaced. The lower crusts occur immediately above the Pleistocene in lows beneath the Holocene sediment and on exposed Pleistocene surfaces. Estimates from x-ray diffraction analysis indicate 80-100% dolomite content within the upper crusts and 50-60% dolomite content in the lower crusts. Unlithified sediment above and below the upper crust contain up to 80% dolomite. Compositions range from Ca{sub 56}, Mg{sub 44} in the upper crusts to Ca{sub 60} Mg{sub 40} in the lower crusts. There is no correlation between stoichiometry and ordering in the dolomites; all are poorly ordered as indicated by very weak (015) and (021) superstructure peaks. Where crusts are not 100% dolomite, the dolomite is evident as euhedral cements within pores, especially within foraminiferal tests, and as micrite along algal laminations and walls of burrows. However, preliminary examinations with scanning electron microscopy and energy dispersive x-ray mapping show that magnesium enrichment is pervasive within these crusts and may represent Mg-enrichment of calcite as an intermediate stage in dolomite formation.

Birdwell, B.A.; Bischoff, W.D.; Mazzullo, S.J. (Wichita State Univ., KS (USA))

1990-05-01

260

Indian Ocean Triple Junction  

Energy Technology Data Exchange (ETDEWEB)

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

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

1980-09-10

 
 
 
 
261

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

International Nuclear Information System (INIS)

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

2009-01-01

262

Sequestering atmospheric carbon dioxide by increasing ocean alkalinity  

Energy Technology Data Exchange (ETDEWEB)

We present a preliminary analysis of a geoengineering option based on the intentional increase of ocean alkalinity to enhance marine storage of atmospheric CO{sub 2}. Like all geoengineering techniques to limit climate change, with today`s limited understanding of the climate system, this approach must be regarded as a potential strategic option that requires ongoing assessment to establish its potential benefits and side effects. CO{sub 2} would be absorbed from the atmosphere by the oceans at an increased rate if ocean alkalinity were raised. Ocean alkalinity might be raised by introducing the dissolution products of alkaline minerals into the oceans. The limited deposits of naturally occurring soda ash (Na{sub 2}CO{sub 3}) are readily soluble and easily mined. Limestone (CaCO{sub 3}) is abundant in the Earth`s crust but is not readily soluble. This analysis explores the potential feasibility and limits of such approaches. (author)

Kheshgi, H.S. [Exxon Research and Engineering Company, Annandale (United States). Corporate Research Labs.

1995-09-01

263

Breaking stress of neutron star crust  

CERN Multimedia

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.

Chugunov, A I

2010-01-01

264

Frozen pizza with low fat pastry crust  

UK PubMed Central (United Kingdom)

Frozen pizza product with special baked pastry shell is produced from a dough comprising a specified mixture of high protein and low protein wheat flours, and containing between 10 and 17% by weight of solid fat pieces, preferably flakes, of specified dimensions, wherein the fat pieces have a melting point in the range 118 DEG -128 DEG F. by the Wiley method, and wherein the mixing takes place so that the solid fat pieces remain as such as the dough goes into the oven for baking. After topping with pizza sauce and freezing, the resulting crust is tender in the inside and crisp on the bottom, after final rebaking by the consumer, even after freeze-thaw cycles which sometimes occur during shipping and storage.

WILMES JOHN H

265

Measurement of palladium crust thickness on catalyst by EPMA  

International Nuclear Information System (INIS)

[en] Selective hydrogenation is a key process in petrochemistry to obtain good feedstock for polymers synthesis. Common catalysts for this process consist in metallic palladium deposited with an eggshell distribution on porous alumina. For this system, the catalytic activity is known to be in strong relation with the thickness of the palladium crust. Typical catalyst consists of 2 - 4 mm diameter spherical beads having a 200 - 400 ?m thick palladium crust and a total palladium amount of about 0.3 to 0.5 wt%. The palladium distribution in the catalyst bead can be easily characterized by electron probe microanalysis (EPMA) using polished cross-sections of the beads trough their diameter. By measuring the local concentration of palladium on several points along the bead diameter we obtain the distribution profile of palladium in the bead. Two strategies are proposed to measure this palladium crust thickness by EPMA. First the crust thickness is defined by the distance to the catalyst bead surface containing a fixed amount of total palladium (for example 95 % or 98 %). Second, the palladium profile is modelled by a parameterized analytical function from which a crust thickness can be extracted. Catalytic tests on four samples having different palladium crust thicknesses confirm the strong relation between activity and crust thickness. However the crust thickness containing 98 % of the palladium content shows the best correlation with activity.

2012-03-07

266

Bacterial-Paleontological Study of Early Precambrian Weathering Crusts  

Directory of Open Access Journals (Sweden)

Full Text Available Existence of diverse microorganisms, bacteria (? Cyanobacteria) in the Early Precambrian (Archaean and Early Proterozoic) weathering crusts is determined. Presence of eukaryots can’t be excluded also. So it is possible to speak about the colonization of land by microbes already at that time and about existence of single series from weathering crusts (primitive soils) to real soils.

Marina M. Astafieva; Alexei Yu. Rozanov

2012-01-01

267

Seismic anisotropy in the continental crust of northwestern Canada  

Science.gov (United States)

Most studies of the seismic structure of continental crust assume that the wave speeds are isotropic at seismic wavelengths. The ability to measure surface wave propagation speed from the cross-correlation of ambient seismic noise provides new opportunities to image the crust and uppermost mantle. We investigate radial anisotropy in the continental crust of northwestern Canada from group-velocity curves of Love and Rayleigh waves obtained from ambient-noise cross-correlation. We test the null hypothesis that the Love and Rayleigh group-speed curves can be simultaneously fit by an earth model containing isotropic seismic velocities throughout the crust. Group velocity is predicted for 200 000 one-dimensional earth models, which are generated by randomly varying the crustal shear velocity and radial anisotropy within a prescribed range. The goodness-of-fit of the predictions is assessed by comparison with two sets of observed dispersion curves that correspond to two tectonically distinct terranes: the Archean/early Proterozoic craton and the transition from craton to Cordillera. The majority of best-fitting models contain VSH > VSV (4-5 per cent) in the middle crust. The finding that the middle/lower crust is seismically anisotropic across a large swath of northwestern Canada, combined with recent observations of anisotropic crust in much of the western United States, suggests that anisotropy may be ubiquitous in the continental crust.

Dalton, Colleen A.; Gaherty, James B.

2013-04-01

268

Precipitation pulse size effects on Sonoran Desert soil microbial crusts.  

Science.gov (United States)

Deserts are characterized by low productivity and substantial unvegetated space, which is often covered by soil microbial crust communities. Microbial crusts are important for nitrogen fixation, soil stabilization and water infiltration, but their role in ecosystem production is not well understood. This study addresses the following questions: what are the CO2 exchange responses of crusts to pulses of water, does the contribution of crusts to ecosystem flux differ from the soil respiratory flux, and is this contribution pulse size dependent? Following water application to crusts and soils, CO2 exchange was measured and respiration was partitioned through mixing model analysis of Keeling plots across treatments. Following small precipitation pulse sizes, crusts contributed 80% of soil-level CO2 fluxes to the atmosphere. However, following a large pulse event, roots and soil microbes contributed nearly 100% of the soil-level flux. Rainfall events in southern Arizona are dominated by small pulse sizes, suggesting that crusts may frequently contribute to ecosystem production. Carbon cycle studies of arid land systems should consider crusts as important contributors because of their dynamic responses to different pulse sizes as compared to the remaining ecosystem components. PMID:14669007

Cable, Jessica M; Huxman, Travis E

2003-12-11

269

PuMa-ECR ion source operation  

International Nuclear Information System (INIS)

[en] 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)

1995-01-01

270

Model for Analysis of the Energy Demand (MAED) users' manual for version MAED-1  

International Nuclear Information System (INIS)

This manual is organized in two major parts. The first part includes eight main sections describing how to use the MAED-1 computer program and the second one consists of five appendices giving some additional information about the program. Concerning the main sections of the manual, Section 1 gives a summary description and some background information about the MAED-1 model. Section 2 extends the description of the MAED-1 model in more detail. Section 3 introduces some concepts, mainly related to the computer requirements imposed by the program, that are used throughout this document. Sections 4 to 7 describe how to execute each of the various programs (or modules) of the MAED-1 package. The description for each module shows the user how to prepare the control and data cards needed to execute the module and how to interpret the printed output produced. Section 8 recapitulates about the use of MAED-1 for carrying out energy and electricity planning studies, describes the several phases normally involved in this type of study and provides the user with practical hints about the most important aspects that need to be verified at each phase while executing the various MAED modules

1986-01-01

271

Thermalization time and specific heat of the neutron stars crust  

International Nuclear Information System (INIS)

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

2010-01-01

272

Thermalisation time and specific heat of neutron stars crust  

CERN Document Server

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

Fortin, M; Margueron, J; Sandulescu, N

2009-01-01

273

The giant Dexing porphyry Cu-Mo-Au deposit in east China: product of melting of juvenile lower crust in an intracontinental setting  

Science.gov (United States)

The Dexing porphyry Cu-Mo-Au deposit in east China (1,168 Mt at 0.45 % Cu) is located in the interior of the South China Craton (SCC), made up of two lithospheric blocks, the Yangtze and Cathaysia blocks. The Cu-Mo-Au mineralization is associated with mid-Jurassic granodioritic porphyries with three high-level intrusive centers, controlled by a series of lineaments at the southeastern edge of the Yangtze block. Available age data define a short duration (172-170 Ma) of the felsic magmatism and the mineralization (171 ± 1 Ma). The deposit shows broad similarities with deposits in volcanoplutonic arcs, although it was formed in an intracontinental setting. Porphyries associated with mineralization are mainly granodiorites, which contain abundant phenocrysts (40-60 %) and carry contemporaneous microgranular mafic enclaves (MMEs). They are mainly high-K calc-alkaline and show geochemical affinities with adakite, characterized by relatively high MgO, Cr, Ni, Th, and Th/Ce ratios. The least-altered porphyries yielded relatively uniform ? Nd(t) values from -0.9 to +0.6, and wide (87Sr/86Sr)i range between 0.7046 and 0.7058 partially overlapping with the Sr-Nd isotopic compositions of the MMEs and mid-Jurassic mafic rocks in the SCC. Zircons from the porphyries have positive ? Hf(t) values (3.4 to 6.9), and low ?18O values (4.7 to 6.3 ‰), generally close to those of depleted mantle. All data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components (e.g., Neoproterozoic mafic arc magmas), triggered by invasion of contemporaneous mafic melts at Dexing. The MMEs show textural, mineralogical, and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas. These MMEs usually contain magmatic chalcopyrite, and have original, variable contents of Cu (up to 500 ppm). Their geochemical characteristics suggest that they were derived from an enriched mantle source, metasomatized by Proterozoic slab-derived fluids, and supplied a part of Cu, Au, and S for the Dexing porphyry system during their injection into the felsic magmas. The 171 ± 1 Ma magmatic-hydrothermal event at Dexing is contemporaneous with the mid-Jurassic extension in the SCC, followed by 160-90 Ma arc-like magmatism in southeastern China. With respect to the tectono-magmatic evolution of the SCC, the emplacement of Cu-bearing porphyries and the associated Cu mineralization occurred in response to the transformation from a tensional regime, related to mid-Jurassic extension, to a transpressional regime, related to the subduction of the Paleo-Pacific oceanic lithosphere.

Hou, Zengqian; Pan, Xiaofei; Li, Qiuyun; Yang, Zhiming; Song, Yucai

2013-05-01

274

Understanding Oceans  

Science.gov (United States)

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on oceans currents and their effects. Students do a lab activity to show that temperature is what causes ocean currents. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, an audio-enhanced vocabulary list, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

Cahill, Mary

275

Proceedings of oceans '91  

International Nuclear Information System (INIS)

This volume contains the proceedings of the Oceans '91 Conference. Topics addressed include: ocean energy conversion, marine communications and navigation, ocean wave energy conversion, environmental modeling, global climate change, ocean minerals technology, oil spill technology, and submersible vehicles

1991-01-01

276

Intensive Ammonia and Methane Oxidation in Organic Liquid Manure Crusts  

DEFF Research Database (Denmark)

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 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 characterized with respect to O2 availability by in situ profiling with electrochemical microsensors. Results show that oxygen penetration increased from few micrometers up to several centimetres with crust age. AOB and ammonium oxidation are ubiquitously present in well-developed manure crusts whereas MOB were only present in old crusts which then could have very high potential rates of methane oxidation. In old crusts the potential rates of both processes were in the range of reported fluxes of CH4 and NH3 from slurry storages without surface crust. Results indicate that with respect to NH3 and possibly also CH4 emission mitigation, an organic surface crust can be effective if populations of MOB and AOB are allowed to build up.

Nielsen, Daniel Aagren; Nielsen, Lars Peter

277

Ocean Acoustics.  

Science.gov (United States)

The main element of this final report is a discussion of the development of the trace method for determining the acoustic properties of the ocean bottom sediments and basement. In addition a method is reported for the uniform determination of the continuo...

D. Stickler

1984-01-01

278

Geochronology of the Baltica crust in the Western Gneiss Region, Norway: Palaeoproterozoic augen gneisses, Sveconorwegian zircon neocrystallization and Caledonian zircon deformation  

Science.gov (United States)

The Western Gneiss Region, Western Norway, is dominated by Palaeoproterozoic to Mesoproterozoic felsic crust of Baltica ancestry (Baltican Basement), partly subducted to high- and ultrahigh-pressure (HP-UHP) conditions during the Caledonian (Scandian) orogeny between 415 and 395 Ma. The dominant felsic gneisses, in contrast with mafic rocks, carry little evidence for the HP-UHP history, but were affected by amphibolite-facies reworking during exhumation. LA-ICPMS and SIMS zircon U-Pb data were collected in augen orthogneiss samples to constrain the magmatic and metamorphic geochronology in this crust. Five samples from the eclogite-bearing HP-UHP basement near Molde yield intrusion ages ranging from 1644 +/-6 to 1594 +/-10 Ma. Two samples of the structurally underlying eclogite-free basement yield ages of 1685 ±18 and 1644 +/-13 Ma, and a sample from the infolded Middle Allochthon Risberget Nappe yields an equivalent age of 1676 +/-18 Ma. Two samples of the eclogite-bearing basement contain low Th/U neocrystallized zircon with an age of 950 +/-26 Ma. This zircon provides the northernmost direct evidence for at least amphibolite-facies Sveconorwegian metamorphism in unquestionable Baltican crust, close to the known "Sveconorwegian boundary" in the Western Gneiss Region. The Western Gneiss Region characterized by 1686-1594 Ma magmatism, the Eastern Segment of the Sveconorwegian Orogen characterized by 1795-1640 Ma magmatism, and the Idefjorden terrane hosting the type Gothian active margin magmatism dated between 1659 and 1520 Ma, probably represent three distinct Proterozoic growth zones of Baltica into which Sveconorwegian reworking propagated. Samples of the eclogite-bearing basement lack Scandian neocrystallization of zircon, but show partial recrystallization of zircon. Paired CL and EBSD images indicate that zircon crystals underwent crystal-plastic deformation during the Scandian subduction-exhumation cycle. They illustrate a relationship between crystal-plastic deformation by dislocation creep, fading of oscillatory growth zoning and loss of radiogenic lead. No precise age for the Scandian reworking can be extracted from the data.

Røhr, Torkil S.; Bingen, Bernard; Robinson, Peter; Reddy, Steven M.

2013-04-01

279

Ocean energies  

Energy Technology Data Exchange (ETDEWEB)

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

Charlier, R.H. (Univ. of Brussels (Belgium)); Justus, J.R. (The Library of Congress, CRS/SPRD, Washington, DC (United States))

1993-09-01

280

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

Directory of Open Access Journals (Sweden)

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

Juan Pablo Canales; Hélène Carton; John C. Mutter; Alistair Harding; Suzanne M. Carbotte; Mladen R. Nedimovi?

2012-01-01

 
 
 
 
281

Crustal Growth of the Izu - Ogasawara (Bonin) - Mariana Oceanic Island arc Inferred from Seismic Velocity Structures  

Science.gov (United States)

It is said that ancient earth consists of the basaltic materials without granitic ones, despite of current large continents has thick granitic materials. Because the oceanic island arc has andesitic middle crust despite of the initial arc has no andesitic materials, the arc is regarded as one of steps of crustal evolution to a continent. Suyehiro et al. (1996), Takahashi et al. (2004) and Crawford et al. (2003) found thick andesitic middle crust with velocity of 6 km/s in northern Izu, Mariana, and Tonga arcs, respectively. However, the central and the eastern Aleutian arcs have little or no andesitic middle crust (Holbrook et al., 1999). To understand the nature of the crustal growth, we have to clarify not only the andesitic middle crust but also the lower crust and the upper mantle, because repeated crustal differentiation may occur within the middle and lower crusts. In 2005, JAMSTEC performed an active seismic experiment across the southern Ogasawara (Bonin) arc using an airgun array and 110 ocean bottom seismographs. A seismic main line runs perpendicularly across the Eocene arc of initial oceanic island arc (the Ogasawara ridge), the current active arc with non-mature and the old Miocene arc. From the preliminary results, the three arcs have similar crustal thickness. However, these crustal components seem to be different each other. The Eocene arc has relative thin middle crust and thick lower crust. The current active arc has thin middle crust and thick lower crust with high velocity of over 7 km/s. The Miocene arc has thick middle crust similar to the northern Izu arc. The Ogasawara trough, which is regarded as a part of Oligocene arc just before the backarc opening, has a crustal thickness of 15-20 km. Moreover, according to reflection imaging recorded by OBSs, we clarified the large fault between the current active arc and the Ogasawara trough, which cuts entire of the crust. This fault suggests that a process of the initial stage of the backarc opening might follow the simple shear mechanism. Using above three velocity models within this arc, we discuss crustal transformation accompanied to the crustal growth to the upper mantle.

Takahashi, N.; Kaiho, Y.; Sato, T.; Fujie, G.; Kodaira, S.; Kaneda, Y.

2005-12-01

282

Seismic structure of the lithosphere beneath the ocean islands near the mid-oceanic ridges  

Science.gov (United States)

Deciphering the seismic character of the young lithosphere near the mid-oceanic ridges (MOR) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs, using the P-to-s conversions isolated from good quality data recorded at 5 broadband seismological stations situated on the ocean Islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform modeling of the P receiver function stacks reveal that the crustal thickness varies between 6 and 8 km with the corresponding depths to the lithosphere asthenosphere boundary (LAB) varying between 43 and 68 km. However, the depth to the LAB at Macquire Island is intriguing in view of the observation of a thick (~ 87 km) lithosphere beneath a relatively young crust. At three other stations i.e., Ascension Island, Sao Jorge and Easter Island, we find evidence for an additional deeper low velocity layer probably related to the presence of a hotspot.

Haldar, C.; Kumar, P.; Kumar, M. Ravi

2013-10-01

283

Composition of the lunar upper crust estimated from Kaguya spectral data  

Science.gov (United States)

The magma ocean hypothesis has been the most widely accepted mechanism explaining the generation of the lunar highland crust. This hypothesis is based on analyses of returned samples [1] and an assumption that Fe-bearing, plagioclase-rich rocks exist globally as the major component of the lunar crust. However, no crystalline plagioclase had been detected by remote sensing before SELENE [2], except for some ambiguous or indirect indications of the existence of plagioclase. Subsequently, a global distribution of rocks of extremely high plagioclase abundance (approaching 100 vol%; called purest anorthosite (PAN)) was reported using an unambiguous plagioclase absorption band around 1250 nm found by the SELENE Multiband Imager (MI) [3]. The estimated plagioclase abundance is significantly higher than previous estimates of 82 to 92 vol% [1], providing a valuable constraint on models for lunar magma ocean evolution. Further study using continuous reflectance spectra derived by the SELENE Spectral Profiler (SP) [4] revealed a global and common distribution of the PAN over the entire lunar surface, supporting the high abundance of PAN rocks within the upper crust. In this study, we investigated a vertical compositional (modal abundance and/or mineral composition) trend of the PAN rocks within the crust using their reflectance spectra derived from SP and MI. Knowing the compositional trend of the lunar upper crust may enable us to understand the mechanism of the lunar crustal growth. All of the SP data observed throughout SELENE mission periods were used in this study (about 7,000 orbits and roughly 10,000 spectra for each orbit). The absorption depth at each wavelength was calculated after a linear continuum was removed. Spectra with the deepest absorption depth, around 1250 nm, which is caused by a minor amount of Fe2+ (in the order of 0.1 wt% FeO) contained in the plagioclase, were selected to detect the PAN rocks. The original burial depth of each PAN rock outcrop was estimated from a crater scaling law using the crater diameter of each outcrop observed in MI data. Results indicate that the majority of the derived absorption depths (strengths) of the detected PAN rock spectra around 1250 nm appear to form a trend which increases as their estimated original burial depths increase within the crust (the trend is observed up to 30 km of the original burial depth). Although understanding the actual cause of this trend requires further studies, such a trend may indicate a decrease in the mafic mineral abundance within the already very mafic-poor rock and/or an increase in the Fe2+ content of plagioclase with depth. References: [1] Warren P. H. (1990) Am. Mineral., 75, 46-58. [2] Matsunaga T. et al. (2008) Geophys. Res. Let., 35, L23201, doi:10.1029/2008GL035868. [3] Ohtake M. et al. (2009) Nature, 461, doi:10.1038. [4] Ohtake et al. (2010) Lunar Planet. Sci. Conf. XXXXI, 1628.

Ohtake, M.; Matsunaga, T.; Takeda, H.; Yokota, Y.; Yamamoto, S.; Moroda, T.; Ogawa, Y.; Hiroi, T.; Nakamura, R.; Haruyama, J.

2010-12-01

284

Influence of plateau buoyancy, geometry and rheology on oceanic plateau subduction  

Science.gov (United States)

Oceanic plateaus are classified as large igneous provinces (LIP) and form relief on the seafloor due to buoyant, thickened crust. Around 10% of present-day subduction zones are associated with oceanic plateaus. The thick crust has a positive buoyancy due a thicker basaltic crust and harzburgitic mantle which modifies the dynamic behavior of the slab and the overriding plate. As a consequence, some plateaus are trapped as terranes in the overriding plate (eg., Caribbean plateau) while others are subducted and cause flattening (eg., Nazca ridge) of the slab. Furthermore, plateau subduction is generally related to a regional uplift of the overriding plate. A study on the feasibility of subducting oceanic plateaus has shown that features with a crust thinner than 17 km should subduct while features with a crust thicker than 35 km should not subduct (1). Using the 2D/3D visco-plastic numerical code Gale, we investigate thermo-mechanical deformation of the crust and lithosphere of the subducting and overriding plate due to oceanic plateau subduction. We use a combined diffusion-dislocation viscosity for the mantle and a visco-plastic strain-dependent rheology, which can lead to formation of localized shear zones, for the plates. Moreover, topography is modeled in Gale with a deforming free surface. We present models in which we systematically explore the individual and coupled effects of plateau shape, size, crustal thickness and density, and the plastic rheology of the plate. Reference: (1) CLOOS, M., Lithospheric buoyancy and collisional orogenesis: Subduction of oceanic plateaus, continental margins, island arcs, spreading ridges, and seamounts, Geological Society of America Bulletin, 1993, v. 105, p. 715-737

Arrial, P.; Billen, M. I.

2010-12-01

285

The 1590-1520 Ma Cachoeirinha magmatic arc and its tectonic implications for the Mesoproterozoic SW Amazonian craton crustal evolution  

Directory of Open Access Journals (Sweden)

Full Text Available Isotopic and chemical data of rocks from the Cachoeirinha suite provide new insights on the Proterozoic evolution of the Rio Negro/Juruena Province in SW Amazonian craton. Six U-Pb and Sm-Nd analyses in granitoid rocks of the Cachoeirinha suite yielded ages of 1587-1522 Ma and T DM model ages of 1.88-1.75 Ga (EpsilonNd values of -0.8 to +1.0). In addition, three post-tectonic plutonic rocks yielded U-Pb ages from 1485-1389 Ma (T DM of 1.77-1.74 Ga and EpsilonNd values from -1.3 to +1.7). Variations in major and trace elements of the Cachoeirinha suite rocks indicate fractional crystallization process and magmatic arc geologic setting. These results suggest the following interpretations: (1) The interval of 1590-1520 Ma represents an important magmatic activity in SW Amazonian craton. (2) T DM and arc-related chemical affinity supportthe hypothesis that the rocks are genetically associated with an east-dipping subduction zone under the older (1.79-1.74 Ga) continental margin. (3) The 1590-1520 Ma age of intrusive rocks adjacent to an older crust represents similar geological framework along the southern margin of Baltica, corroborating the hypothesis of tectonic relationship at that time.

Ruiz Amarildo S.; Geraldes Mauro C.; Matos João B.; Teixeira Wilson; Van Schumus William R.; Schmitt Renata S.

2004-01-01

286

Solvent evaporation of spin cast films crust effects  

CERN Document Server

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).

De Gennes, Pierre Gilles

2001-01-01

287

Electrically Conductive Crust in Southern Tibet from INDEPTH Magnetotelluric Surveying  

UK PubMed Central (United Kingdom)

The crust north of the Himalaya is generally electrically conductive below depths of 10 to 20 km. This conductive zone approaches the surface beneath the Kangmar dome (dipping north) and extends beneath the Zangbo suture. A profile crossing the northern Yadong-Gulu rift shows that the high conductivity region extends outside the rift, and its top within the rift coincides with a bright spot horizon imaged on the INDEPTH CMP (common midpoint) profiles. The high conductivity of the middle crust is atypical of stable continental regions and suggests that there is a regionally interconnected fluid phase in the crust of the region.

Chen L; Booker JR; Jones AG; Wu N; Unsworth MJ; Wei W; Tan H

1996-12-01

288

Electrically Conductive Crust in Southern Tibet from INDEPTH Magnetotelluric Surveying  

Science.gov (United States)

The crust north of the Himalaya is generally electrically conductive below depths of 10 to 20 km. This conductive zone approaches the surface beneath the Kangmar dome (dipping north) and extends beneath the Zangbo suture. A profile crossing the northern Yadong-Gulu rift shows that the high conductivity region extends outside the rift, and its top within the rift coincides with a bright spot horizon imaged on the INDEPTH CMP (common midpoint) profiles. The high conductivity of the middle crust is atypical of stable continental regions and suggests that there is a regionally interconnected fluid phase in the crust of the region. PMID:8939855

Chen; Booker; Jones; Wu; Unsworth; Wei; Tan

1996-12-01

289

Disseminated crusted papules in a newborn  

Directory of Open Access Journals (Sweden)

Full Text Available Background. Congenital self-healing Langerhans cell histiocytosis (Hashimoto-Pritzker disease) is the rarest form of Langerhans cell histiocytosis, usually confined to the skin and/or mucous membranes. Cutaneous eruption is mostly generalized, papular, nodular or vesicular. Despite impressive clinical presentation in a newborn it infrequently spreads to internal organs (which then portends a grave prognosis, indistinguishable from Letterer-Siwe disease). Case report. We presented a full-term newborn, female, 3.3 kg who had a multitude of erythematous and crusted papules, nodules and pseudovesicles distributed all over the body, except for the mucous membranes. A biopsy and haematoxylin ? eosin stain revealed dermal infiltration of pleomorphic histiocytes with eosinophilic ground-glass cytoplasm and round to bean-shaped nuclei. Over the next six weeks the eruption gradually subsided leaving no residues, or a few atrophic scars. Conclusion. There is no need for specific treatment of congenital self-healing Langerhans cell-histiocytosis in the absence of multiorgan involvement. However, a close and regular follow-up is necessary to evaluate the children for systemic symptoms and signs.

Pavlovi? Miloš D.; Mini? Aleksandra; Zolotarevski Lidija; Vesi? Sonja

2006-01-01

290

Rb-Sr geochronology from Barro Alto Complex, Goias: metamorphism evidence of high degree and continental collision around 1300 Ma ago in Central Brazil  

International Nuclear Information System (INIS)

Rb-Sr geochronologic investigation carried out on rocks from the Barro Alto Complex, Goias, yielded iso chronic ages of 1266 +- 17 Ma, for felsic rocks from the granulite belt and 1330 +- 67 Ma, for gneisses belonging to the Juscelandia Sequence. Rb-Sr isotope measurements suggest that Barro Alto rocks have undergone an important metamorphic event during middle Proterozoic times, around 1300 Ma ago. During that event, volcanic and sedimentary rocks of Juscelandia Sequence, as well as the underlying gabbros-anorthosite layered complex, underwent deformation and recrystallization under amphibolite facies conditions. Deformation and metamorphism took place during the collision of two continental blocks, which resulted in a southeastward directed thrust complex, allowing the exposure of granulite slices from the middle-lower crust of the overthrusted block. (author)

1989-01-01

291

MaRV Penetration Study Project: MaRV discrimination studies: Final report for FY87  

Energy Technology Data Exchange (ETDEWEB)

This report describes the MaRV discrimination studies results obtained during FY87 in support of the MaRV Penetration Study Project. Several single-sensor discrimination algorithms and a multi-sensor ''Data Fusion'' technique are proposed for inclusion in the MaRV penetration study simulator under development. The goal of this fiscal year's investigation was to provide algorithms that are immediately useable with the simulator, and that support the testing of the simulator and its subsystems. The algorithms presented, consequently, are of relatively low complexity and have explicit predicted performance expressions. The model assumptions required to achieve these results, and future efforts proposed to refine the models and resulting algorithms, are briefly discussed. 9 refs., 13 figs.

Morris, J.M.

1988-04-01

292

Along-arc segmentation and interaction of subducting ridges with the Lesser Antilles Subduction forearc crust revealed by MCS imaging  

Science.gov (United States)

We present the results from a new grid of deep penetration multichannel seismic (MCS) profiles over the 280-km-long north-central segment of the Lesser Antilles subduction zone. The 14 dip-lines and 7 strike-lines image the topographical variations of (i) the subduction interplate décollement, (ii) the top of the arcward subducting Atlantic oceanic crust (TOC) under the huge accretionary wedge up to 7 km thick, and (iii) the trenchward dipping basement of the deeply buried forearc backstop of the Caribbean upper plate.

Laigle, Mireille; Becel, Anne; de Voogd, Béatrice; Sachpazi, Maria; Bayrakci, Gaye; Lebrun, Jean-Frédéric; Evain, Mikael

2013-09-01

293

Scanning electron microscopy of the eggs of Mansonia uniformis, Ma. indiana and Ma. annulifera (Diptera: Culicidae).  

UK PubMed Central (United Kingdom)

Descriptions of the eggs of Mansonia uniformis, Ma. indiana and Ma. annulifera are provided with the aid of scanning electron micrographs. Eggs of these three species, although similar in shape and colour, are covered by outer chorionic reticulum and tubercles which provide reliable morphological character for their identification. Size, distribution and number of lobes on the large tubercles present in the region between the anterior tube and posterior region, are important distinguishing features. Measurements of egg sizes and other chorionic differences are also discussed.

Eng KL; Chiang GL; Hamidah T; Loong KP

1990-03-01

294

Ocean Voyagers  

Science.gov (United States)

Ocean Voyagers is an educational outreach initiative consisting of an interdisciplinary curriculum program. It is designed to allow middle school teachers and students to gain real-world knowledge about oceanographic science, social science, maritime cultures, communication, literature, and the language arts. This site includes: integrated lesson plans on oceanographic science, maritime life and lore, technology and communications, and profiles of the Navy oceanographic survey fleet.

295

The Ocean Drilling Program: The next phase in scientific ocean drilling  

Energy Technology Data Exchange (ETDEWEB)

Texas AandM University has been designated as Science Operator for a new National Science Foundation sponsored program of scientific ocean drilling - the Ocean Drilling Program. The responsibilities of the Science Operator include implementing the science plans under the guidance of the Joint Oceanographic Institutions for Deep Earth Sampling, providing logistical and technical support for a shipboard science team, managing post-cruise activities, the long term curation and distribution of core samples, and coordinating, editing and publication of the final research product. The scientific programs will be carried out with the drilling vessel SEDCO/BP 471, a dynamically positioned drillship capable of deploying 30,000 ft. of drill string and operating with a riser in 6000 ft. of water. The primary scientific objectives of the Ocean Drilling Program will be in studying the origin and evolution of the oceanic crust, the tectonic evolution of continental margins, the origin and evolution of marine sedimentary sequences, studies of long term changes in the atmosphere, oceans, cryosphere, biosphere and magnetic field and development of new tools and technology for deep ocean exploration and drilling.

Rabinowitz, P.D.; Carlson, R.; Garrison, L.; Gartner, S.; Herrig, S.; Mazzollo, J.; Merrell, W.J.

1984-05-01

296

Breaking strain of neutron star crust and gravitational waves.  

UK PubMed Central (United Kingdom)

Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of the neutron star crust. With multimillion ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Because of the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gravitational wave radiation could limit the spin periods of some stars and might be detectable in large-scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in magnetar giant flares and microflares.

Horowitz CJ; Kadau K

2009-05-01

297

Early Intense Cratering: Effects on Growth of Earth's Crust.  

Science.gov (United States)

The disrupting effects of early intense meteorite bombardment on Earth's protocrustal evolution is discussed. The author emphasized that one should not consider the Earth's impact history as a discrete phase separate from an early crust forming event, and...

W. K. Hartmann

1988-01-01

298

Sr and Nd isotope geochemistry of oceanic basalts and mantle evolution  

International Nuclear Information System (INIS)

Sr and Nd isotope ratios are reported for 17 mid-ocean ridge basalts and for 11 oceanic islands and island groups. Data from the Azores, Samoa and the Society Islands diverge significantly from the mantle array. These results are not explained by binary mixing of depleted and undepleted mantle reservoirs or by variable magmatic depletion of a planetary reservoir, but support mantle evolution models involving re-injection of crust material into the mantle. (author)

1982-04-29

299

Alteration of oceanic volcanic glass: textural evidence of microbial activity  

Science.gov (United States)

The subsurface biosphere may constitute as much as 50 percent of Earth's biomass. Direct and indirect evidence suggests that an extensive biosphere exists in the rocks below the sea floor. This survey of basalts of the Atlantic, Pacific, and Indian Oceans supports the hypothesis that bacteria have colonized much of the upper oceanic crust, which has a volume estimated at 10(18) cubic meters. Although this is the largest habitat on Earth, its low abundance of bacteria constitutes much less than 1 percent of Earth's biomass. PMID:9703510

Fisk; Giovannoni; Thorseth

1998-08-14

300

Alteration of oceanic volcanic glass: textural evidence of microbial activity  

UK PubMed Central (United Kingdom)

The subsurface biosphere may constitute as much as 50 percent of Earth's biomass. Direct and indirect evidence suggests that an extensive biosphere exists in the rocks below the sea floor. This survey of basalts of the Atlantic, Pacific, and Indian Oceans supports the hypothesis that bacteria have colonized much of the upper oceanic crust, which has a volume estimated at 10(18) cubic meters. Although this is the largest habitat on Earth, its low abundance of bacteria constitutes much less than 1 percent of Earth's biomass.

Fisk MR; Giovannoni SJ; Thorseth IH

1998-08-01

 
 
 
 
301

Structure of the Highly Magnetized Neutron Star Crust  

Science.gov (United States)

Sharma & Reddy recently investigated how the potential between two ions at high density is modified by the presence of a very strong magnetic field. If the field is high enough, only the first Landau level is filled and this leads to an anisotropic potential with magnetic screening. We take this potential and use Molecular Dynamics to model the crust of a magnetar. We determine the structure of the highly magnetized crust and also compute various transport properties.

Hughto, Joseph; Horowitz, Charles; Pons, Jose

2012-10-01

302

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

Science.gov (United States)

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

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

2012-04-01

303

Carbon in black crusts from the Tower of London  

Energy Technology Data Exchange (ETDEWEB)

This paper investigates the origin, fluxes, and transformation of carbon compounds within black crusts on the stone walls of the Tower of London. The crusts were analyzed for elemental and organic carbon, including the water soluble fraction. The stratigraphy of the old, thicker crusts highlighted the presence of prismatic particles, spherical aluminosilicates and metals, and carbonaceous particles. These are indicative of wood, coal and oil combustion processes. Elemental carbon and low solubility compounds such as oxalates appeared to be conserved because of long residence times. Conversely, more soluble ions, like chloride and formate would be removed from the layers relatively quickly by rainfall. At higher organic carbon concentrations acetic acid may be produced within the crusts from biological transformations. Currently, traffic sources contribute to increasingly organic rich crusts. The deposition of elemental carbon to buildings darkens surfaces and has important aesthetic implications. The increased organic content may have further aesthetic consequence by changing the color of buildings to warmer tones, particularly browns and yellows. Management of historic buildings requires us to recognize the shift away from simple gypsum crusts to those richer in organic materials. 26 refs., 6 figs., 1 tab.

Alessandra Bonazza; Peter Brimblecombe; Carlota M. Grossi; Cristina Sabbioni [Institute ISAC-CNR, Bologna (Italy)

2007-06-15

304

Changes in dip of subducted slabs at great depth: Petrological and geochronological evidence from oceanic eclogite-facies rocks in the Chinese Tianshan  

Science.gov (United States)

Previous high-resolution seismic imaging has shown abrupt changes in the dip of subducted oceanic plates [e.g., Rondenay et al., 2008]. In any subduction zone, such 'kinking' apparently coincides with the disappearance of the low-velocity layers associated with subducted oceanic crust. In the present study [for details see Klemd et al., 2011], we provide petrographical, petrological, and geochemical evidence for kinking derived from oceanic blueschist- and eclogite-facies rocks from the Chinese Tianshan. The investigated samples show a wide range of peak metamorphic conditions (330-580 °C at 1.5-2.3 GPa). Such a wide range in peak metamorphic conditions in high- and ultrahigh-pressure rocks, which are interlayered on a meter-scale, have also been reported from other Tianshan localities [Lü et al., 2009; Wei et al., 2009]. This suggests that the rocks equilibrated at varying depths within the subduction zone before being juxtaposed during exhumation in the subduction channel. Four Lu­-Hf mineral isochrons defined by high-pressure rocks yielded consistent garnet-growth ages of 313±12, 315.8±2.9, 313.9±4.8, and 315.2±1.6 Ma, confirming that the eclogite-facies metamorphism of the Tianshan high-pressure rocks occurred during a single subduction cycle in the Late Carboniferous. Interestingly, all previously reported estimates of peak metamorphic conditions from UHP metasediments and eclogites define a lower geothermal gradient than that indicated by the HP blueschists and eclogites from the present study. These data are consistent with a sudden increase in slab-subduction angle occurring between the equilibration depths of the HP and UHP rocks, i.e., > ca. 90 km. Such kinking may act in concert with the negative buoyancy of mafic UHP rocks in subduction zones to hinder the exhumation of such rocks, perhaps explaining their paucity on Earth's surface.

Klemd, R.; John, T.; Scherer, E. E.; Rondenay, S.; Gao, J.

2012-04-01

305

Chuar Group of the Grand Canyon: Record of Breakup of Rodinia, Associated Change in the Global Carbon Cycle, and Ecosystem Expansion by 740 Ma  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Chuar Group (similar to 1.600 m thick) preserves a record of extensional tectonism, ocean-chemistry fluctuations, and biological diversification during the late Neoproterozoic Era. An ash layer from the top of the section has a U-Pb zircon age of 742 +/- 6 Ma. The Chuar Group was deposited at lo...

Weil, Arlo B.; Des Marais, David J.; Crossey, Laura J.; Sharp, Zachary D.; Karlstrom, Karl E.; Elrick, Maya B.

306

Transmutation of minor actinides (MA) with pebble bed type HTGRs  

International Nuclear Information System (INIS)

[en] It has been proposed to transmute minor actinides (MA) in LWRs, FBRs or actinide burning reactors. In FBRs and actinide burning reactor, MA is transmuted only about 10%. In LWRs, MA could not transmuted because MA is produce more than that of transmuted. Therefore, the large number of reprocessing process has to be carried out for further transmutation of MA repeatedly. HTGRs can achieve higher burnup with its coated fuel particles. We have found a reactor system that can transmuted more of MA in fuel for one burnup cycle. This system is a pebble bed type HTGR using MA balls and Pu balls. The Pu is obtained from reprocessing LWR fuel. The criticality maintains with the Pu. MA is converted to fissile nuclides by neutron absorption reaction, then transmuted by fission reaction. The fuels are loaded and removed from the core continuously. The burnups of the fuel ball are evaluated by measuring the strength of Y-rays when they are exhausted from the core. They are reloaded again if the burnups are still under the expected burnups. They are discharged form the reactor system as spent fuels if the expected burnups are achieved. So for, the achievable burnup of the fuel is about 600GWd/t. The ratio of the residual MA to initially loaded MA is about 40%. The MA transmutation ratio is five times higher than that of reactors above mentioned. As the same time, about 50% of plutonium is also transmuted. Moreover, it is expected that the MA will transmuted nearly 100% by many improvements. For example, MA balls are reloaded into the core more times than Pu balls, low outlet coolant temperature, diluted fuel kernel, and so on. We think that the reactor system is one of the most promising options with which the transmutation of MA can be carried out effectively. (author)

1996-01-01

307

Neodymium, strontium, and oxygen isotopic variations in the crust of the western United States: Origin of Proterozoic continental crust and tectonic implications  

Energy Technology Data Exchange (ETDEWEB)

Initial Nd isotopic ratios of crystalline rocks from an area of about 1.5 {times} 10{sup 6} km{sup 2} of the western United States have been determined in order to map Precambrian age province boundaries and thus document the growth and modification of the North American continent in the Proterozoic. Three age provinces have been delineated. It is demonstrated that large regions of Early Proterozoic continental crust were formed with anomalous isotopic compositions ({sup 143}Nd/{sup 144}Nd ratios lower than Early Proterozoic depleted-mantle). The variations in the initial {epsilon}{sub Nd} and {delta}{sup 18}O values correlate with each other, and correspond to the previously determined Nd isotopic provinces. The Pelona, Rand, Chocolate Mountain and Orocopia Schists are represented by 15 lithologically and structurally similar schist bodies exposed along the San Andreas and Garlock faults in southern California. The grayschists have measured {epsilon}{sub Nd} values from -1.7 to -11.7 with depleted-mantle model ages of 0.9 to 1.7 Ga. The Nd isotopic compositions can be modeled as variable mixtures of Early Proterozoic continental crust with a Mesozoic are component. The measured {sup 87}Sr/{sup 86}Sr ratios are from 0.7087 to 0.7129 and reflect the presence of an old continental source. Independent of age, the high initial {epsilon}{sub Nd} values ({sup +}9 {plus minus} 1.5) are consistent with derivation at an oceanic spreading center, either at a MORB or in a back-arc basin environment. The presence of both Early Proterozoic continental detritus and a younger sedimentary component in the grayschist protolith, and the MORB affinity of the metabasalts are compatible with formation of the protoliths of the Pelona and related schists in a Mesozoic basin adjacent to the southwestern United States continental margin.

Bennett, V.C.

1989-01-01

308

Spreading of the ocean floor: undeformed sediments in the peru-chile trench.  

UK PubMed Central (United Kingdom)

None of the expected stratigraphic and structural effects of a spreading sea floor have been imposed on the sedimentary fill of the Peru-Chile Trench. During at least the last several million years, and perhaps during much of the Cenozoic, the trench has not been affected by an oceanic crust thrusting under the continent.

Scholl DW; von Huene R; Ridlon JB

1968-02-01

309

Propagation of coupled Rayleigh-gravity waves on the ocean floor  

Directory of Open Access Journals (Sweden)

Full Text Available It is shown that the Ocean-Earth crust interface can propagate gravity-sound Rayleigh waves. Dispersion properties of waves and flux of energy are derived. It is shown that the waves split into low and fast velocity branches. The fast branch has a multimode structure and has a cutoff in frequency and wave number. Numerical solutions are discussed.

Gennadiy N. Burlak; Svetlana V. Koshevaya; Masashi Hayakawa; J. Sánchez-Mondragón; Vladimir V. Grimalsky

1999-01-01

310

Galactic-cosmic-ray-produced 3He in a ferromanganese crust: any supernova 60Fe excess on earth?  

UK PubMed Central (United Kingdom)

An excess of 60Fe in 2.4-3.2 x 10(6) year old ferromanganese crust (237 KD) from the deep Pacific Ocean has been considered as evidence for the delivery of debris from a nearby supernova explosion to Earth. Extremely high ;{3}He/;{4}He (up to 6.12 x 10(-3)) and 3He concentrations (up to 8 x 10(9) atoms/g) measured in 237 KD cannot be supernova-derived. The helium is produced by galactic cosmic rays (GCR) and delivered in micrometeorites that have survived atmospheric entry to be trapped by the crust. 60Fe is produced by GCR reactions on Ni in extraterrestrial material. The maximum (3)He/(60)Fe of 237 KD (80-850) is comparable to the GCR (3)He/(60)Fe production ratio (400-500) predicted for Ni-bearing minerals in iron meteorites. The excess 60Fe can be plausibly explained by the presence of micrometeorites trapped by the crust, rather than injection from a supernova source.

Basu S; Stuart FM; Schnabel C; Klemm V

2007-04-01

311

Interpretation of X-ray diffraction analysis and TEM microstructure of MA'ed powders with peritectic reaction  

International Nuclear Information System (INIS)

Various microstructural changes take place simultaneously during the mechanical alloying process. Reduction in the crystalline size and the lattice strain cause a significant peak broadening, and dissolution of solute atoms results in peak shift in X-ray diffraction (XRD) spectrum. Therefore application of conventional XRD analysis routes is not straight forward, and could lead to incorrect information. When XRD method is used to analyze MA'ed powders, the spectrum needs to be carefully interpreted in order to extract the meaningful quantitative information. In this study, the possible sources of the error are addressed when MA'ed powders of Al-X (X = Ti, Nb) system are characterized by the XRD method, and proper XRD analysis methods are suggested to determine on lattice parameter, solubility of minor elements, crystallite size and strain variance in the MA'ed Al-X samples. The TEM observation is done to evaluate the formation of solid solution during MA.

2009-08-26

312

Ocean Maps Coordinate Planes  

CERN Multimedia

Learn about ocean maps and the concepts surrounding coordinate planes as Ocean Maps explores geography under the sea, early and current navigation practices, and the variety of ways the ocean can be mapped such as sonar, submersibles, and satellites.

Wall, Julia

2009-01-01

313

Constraints on Indian plate motion since 20 Ma from dense Russian magnetic data: Implications for Indian plate dynamics  

Science.gov (United States)

We use more than 230,000 km of Russian marine magnetic and bathymetric data from the Carlsberg and northern Central Indian ridges, comprising one of the most geographically extensive, dense shipboard surveys anywhere in the ocean basins, to describe in detail seafloor spreading since 20 Ma along the trailing edge of the Indian plate. India-Somalia plate rotations for ˜1 Myr intervals over the past 20 Myr are derived from inversions of more than 6600 crossings of 20 magnetic reversals and ˜1400 crossings of fracture zones that offset these two ridges. Statistical analysis of the numerous data indicates that outward displacement of reversal boundaries due to finite seafloor emplacement widths and correlated noise for anomaly crossings from individual spreading segments constitute two distinct sources of systematic bias in the locations of magnetic anomaly crossings, contrary to the often-made assumption that random, Gaussian-distributed noise dominates the error budget. Seafloor spreading rates slowed gradually by 30% from 20 Ma to 10 ± 1 Ma about a relatively stationary pole of rotation. From 11 Ma to 9 Ma the rotation axis migrated several angular degrees toward the plate boundary, modestly increasing the spreading gradient along the plate boundary. India-Somalia kinematic data for times since ˜9 Ma are consistent with remarkably steady motion, with no evidence for a change in either the rotation pole or rate of angular opening within the few percent precision of our data. The timing and nature of changes in India-Somalia motion since 20 Ma closely resemble those for the Capricorn-Somalia plate pair, indicating that India and Capricorn plate motions are strongly coupled. We speculate that the slowdown in seafloor spreading at the trailing edges of the Indo-Capricorn composite plate from 20 Ma to 10 ± 1 Ma resulted from the increasing amount of work that was needed to build topography in the Himalayan collisional zone. The transition to stable India-Somalia and Capricorn-Somalia seafloor spreading at ˜10-9 Ma corresponds well with the onset at 8 Ma of folding and faulting across an equatorial plate boundary separating the Indian and Capricorn plates, suggesting that the latter may have played a fundamental role in restoring equilibrium between the torques that were driving and resisting the northward motions of the Indian and Capricorn plates.

Merkouriev, S.; Demets, C.

2006-02-01

314

New age (ca. 2970 Ma), mantle source composition and geodynamic constraints on the Archean Fiskenæsset anorthosite complex, SW Greenland.  

DEFF Research Database (Denmark)

The Archean Fiskenæsset Complex, SW Greenland, consists of an association of ca. 550-meter-thick layered anorthosite, leucogabbro, gabbro, and ultramafic rocks (peridotite, pyroxenite, dunite, hornblendite). The complex was intruded by tonalite, trondhjemite, and granodiorite (TTG) sheets (now orthogneisses) during thrusting that was followed by several phases of isoclinal folding. The trace element systematics of the Fiskenæsset Complex and associated volcanic rocks are consistent with a supra-subduction zone geodynamic setting. The Fiskenæsset anorthosites, leucogabbros, gabbros and ultramafic rocks collectively yield an Sm–Nd errorchron age of 2973 ± 28 Ma (MSWD = 33), with an average initial eNd = + 3.3 ± 0.7, consistent with a long-term depleted mantle source. Regression of Pb isotope data define an age of 2945 ± 36 Ma (MSWD = 44); and the regression line intersects the average growth curve at 3036 Ma. Slightly lower Pb–Pb errorchron age is interpreted as reflecting partial disturbance of the U–Pb system in gabbros, leucogabbros and ultramafic rocks during intrusion of TTGs. Complex internal structures in zircons from orthogneisses reveal several episodes of zircon growth and recrystallization taking place between ca. 3200 and 2650 Ma. Zircon ages peak at about 3200, 3100, 3000, 2950, 2820, and 2750 Ma. The 3200–3000 Ma zircon cores are interpreted as inherited xenocrysts from older reworked crustal rocks. 2950 Ma is considered as an approximate intrusion age of sampled TTGs. The 2940–2650 Ma ages are attributed to metamorphic overgrowth and recrystallization in response to multiple tectonothermal events that affected the Fiskenæsset region. On the basis of recently published trace element data, and new Nd and Pb isotope and U–Pb zircon age data, a three-stage geodynamic model is proposed to explain the evolution of the Fiskenæsset Complex. Stage 1 represents the formation of depleted shallow mantle source > 3000 Ma (eNd = + 3.3 ± 0.7) for the complex. Stage 2 corresponds to the development ofan intra-oceanic island arc between 3000–2950 Ma. Stage 3 is characterized by the collision of the island arc with either a passive continental margin or with an older arc between 2950–2940 Ma.

Polat, A; Frei, Robert

2010-01-01

315

Oxygen isotope variations in ocean island basalt phenocrysts  

Energy Technology Data Exchange (ETDEWEB)

Oxygen isotope ratios are reported for olivine phenocrysts from sixty-seven samples of ocean island basalts (OIBs), mid-ocean ridge basalts (MORBs), and related peridotites, including representatives of the various isotopic endmembers defined by radiogenic isotope ratios. OIBs are more homogeneous in {delta}{sup 18}O by this analysis than suggested by previous studies of whole rocks and glasses. Most OIB samples have oxygen isotope ratios within a restricted range ({delta}{sup 18}O{sub olivine} = 5.0-5.4{per_thousand}), comparable to those of olivines in peridotites from ophiolites, in most peridotitic mantle xenoliths, and inferred for the sources of mid-ocean ridge basalts. The exceptions are EM2 lavas, which are enriched in {sup 18}O ({delta}{sup 18}O{sub olivine} = 5.4-6.1{per_thousand}), and a small number of samples characterized by low {sup 3}He/{sup 4}He and distinctive lead isotope ratios, which are {sup 18}O depleted ({delta}{sup 18}O = 4.7-5.1{per_thousand}). The observed range in {delta}{sup 18}O and the correlations with radiogenic isotope ratios are similar to those observed in a detailed study of Hawaiian samples. These results indicate that recycled crust and/or sediments (or the imprint of extensive metasomatism by fluids derived from such materials) is present as at most a small mass fraction ({approx_lt}%) in the mantle sources of most OIBs. The results on most EM2 lavas are consistent with the presence of {approximately}2-6% recycled sediment in their source regions. Low {delta}{sup 18}O values in OIBs can be produced by assimilation of altered lavas from high-levels in the volcanic edifice, assimilation of the oceanic crust underlying the volcano, or incorporation of subducted oceanic crust in mantle sources. 75 refs., 4 figs., 2 tabs.

Eiler, J.M.; Farley, K.A.; Stolper, E.M. [California Institute of Technology, Pasadena, CA (United States)] [and others

1997-06-01

316

Oxygen isotope variations in ocean island basalt phenocrysts  

International Nuclear Information System (INIS)

Oxygen isotope ratios are reported for olivine phenocrysts from sixty-seven samples of ocean island basalts (OIBs), mid-ocean ridge basalts (MORBs), and related peridotites, including representatives of the various isotopic endmembers defined by radiogenic isotope ratios. OIBs are more homogeneous in ?18O by this analysis than suggested by previous studies of whole rocks and glasses. Most OIB samples have oxygen isotope ratios within a restricted range (?18Oolivine = 5.0-5.4 per-thousand), comparable to those of olivines in peridotites from ophiolites, in most peridotitic mantle xenoliths, and inferred for the sources of mid-ocean ridge basalts. The exceptions are EM2 lavas, which are enriched in 18O (?18Oolivine = 5.4-6.1 per-thousand), and a small number of samples characterized by low 3He/4He and distinctive lead isotope ratios, which are 18O depleted (?18O = 4.7-5.1 per-thousand). The observed range in ?18O and the correlations with radiogenic isotope ratios are similar to those observed in a detailed study of Hawaiian samples. These results indicate that recycled crust and/or sediments (or the imprint of extensive metasomatism by fluids derived from such materials) is present as at most a small mass fraction (approx-lt%) in the mantle sources of most OIBs. The results on most EM2 lavas are consistent with the presence of ?2-6% recycled sediment in their source regions. Low ?18O values in OIBs can be produced by assimilation of altered lavas from high-levels in the volcanic edifice, assimilation of the oceanic crust underlying the volcano, or incorporation of subducted oceanic crust in mantle sources. 75 refs., 4 figs., 2 tabs

1997-01-01

317

El Margen Atlántico Ibérico al W de Galicia. Evolución en régimen extensional y sedimentación. (Resultados preliminares del Leg. 103, Ocean Drilling Program.)  

Directory of Open Access Journals (Sweden)

Full Text Available Leg 101 of the Ocean Drilling Program (ODP) was devoted discovering the tectonic and sedimentary evolution of the Atlantic Margin of the lberian Peninsula. A transect of five sites, with a total of 14 drill-holes was undertaken to the South of the Galicia Bank on the seaward edge of the margin. The data obtained revealed a complex history of subsidence and rifting preceding the initiation of sea floor spreading between Newfoundland and Iberia. The main findings include: 1) The Upper Jurassic-Lowermost Cretaceous shallow-water carbonate platform are the first Messozoic deposits at the margin. The «basement seismic reflector» is made-up of these carbonates. 2) The platform drowning, tilting of fault blocks and rapid subsidence preceded the spreading by as much as 25 million years. 3) A ridge of serpentiniced peridotites is located near the boundary between the oceanic and continental crusts. 4) The seismic reflector «S» does not, as widely believed represent a ductile-brinle boundary within the continental crust but is instead a reflector at the base of the synrift sediments.La campaña oceanográfica 103 del Ocean Drilling Program (ODP) ha estado dedicada a dilucidar la evolución tectónica y sedimentación del Margen Atlántico-Ibérico. Se realizaron un total de 14 sondeos., en cinco puntos de posicionamiento, sobre el extremo más profundo del margen; al S del Banco de Galicia. Los resultados obtenidos revelan que previamente al inicio de la expansión oceánica entre Terranova e Iberia ocurrió una historia compleja de distensión cortical, fracturación y subsidencia asociadas. Los resultados fundamentales son los siguientes: 1) Carbonatos de plataforma marina somera, de edad Jurásico superior-Cretáceo basal constituyen los primeros depósitos mesozóicos en ese ámbito del margen y dan lugar a un reflector sísmico considerado interiormente como basamento, 2) El hundimiento de la plataforma, fallamiento y basculamiento de los bloques ocurre desde 25 m.a. antes de iniciarse la acreción oceánica. 3) En el límite entre corteza oceánica-corteza continental se ubica una cresta constituida por peridotitas serpetinizadas. 4) El reflector sísmico «S», generalmente considerado como el límite dúctil-frágil en la corteza continental, corresponde realmente a la base de los depósitos sinrift.

Boillot, G.; Winterer, E. L.; Meyer, A. W.; Applegate, J.; Baltuck, M.; Bergen, J. A.; Davies, T. A.; Dunham, K.; Evans, C. A.; Girardeau, J.; Goldberg, D.; Haggerty, J.; Jansa, L. F.; Johnson, J. A.; Kasahara, J.; Loreau, J. P.; Luna, E.; Moullade, H.; Ogg, J.; Sarti, M.; Thurow, J.; Williansom, M. W.

1986-01-01

318

Mass independently fractionated sulfur isotopes reveal recycling of Archean lithosphere in modern oceanic hotspot lavas  

Science.gov (United States)

Oceanic crust and sediments are introduced to the mantle at subduction zones, but the fate of this subducted material within the mantle, as well as the antiquity of this process, is unknown. The mantle is compositionally and isotopically heterogeneous, and it is thought that much of this heterogeneity derives from incorporation of diverse subducted components—both crustal and oceanic lithosphere—over geologic time. Basaltic lavas erupted at some oceanic hotspot volcanoes have long been considered to be melts of ancient subducted lithosphere. However, compelling evidence for the return of subducted materials in mantle plumes is lacking. We report mass independently fractionated (MIF) S-isotope signatures in olivine-hosted sulfides from 20-million-year-old ocean island basalts (OIBs) from Mangaia, Cook Islands (Polynesia). Terrestrial MIF S-isotope signatures were generated exclusively through atmospheric photochemical reactions until ~2.45 billion years ago. Therefore, the discovery of MIF-S in young OIBs indicates that sulfur—likely derived from hydrothermally-altered oceanic crust—was subducted into the mantle before 2.45 Ga and recycled into the mantle source of Mangaia lavas. These new data provide evidence for ancient materials, with MIF 33S depletions, in the mantle source for Mangaia lavas. An Archean age for recycled oceanic crust provides key constraints on the length of time that subducted crustal material can survive in the mantle and on the timescales of mantle convection from subduction to melting and eruption at plume-fed hotspots. The new S-isotope measurements confirm inferences about the cycling of sulfur between the major reservoirs from the Archean to the Phanerozoic, extending from the atmosphere and oceans to the crust and mantle, and ultimately through a return cycle to the surface that, here, is completed in Mangaia lavas. It remains to be seen whether hotspots lavas sampling different compositional mantle endmembers (e.g., EM1, EM2, DMM) will exhibit evidence for recycling of Archean protoliths.

Jackson, Matthew; Cabral, Rita; Rose-Koga, Estelle; Koga, Ken; Whitehouse, Martin; Antonelli, Michael; Farquhar, James; Day, James; Hauri, Erik

2013-04-01

319

Crusted scabies-associated immune reconstitution inflammatory syndrome.  

UK PubMed Central (United Kingdom)

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 therapy, he developed an aggressive form of crusted scabies with rapid progression of lesions. Severe infestation by Sarcoptes scabiei was confirmed by microscopic examination of the scale and skin biopsy. Due to the atypical presentation of scabies in a patient responding to antiretroviral therapy, preceded by no apparent skin lesions at initiation of antiretroviral therapy, the episode was interpreted for the first time as "unmasking crusted scabies-associated immune reconstitution inflammatory syndrome". CONCLUSION: This case illustrates that when crusted scabies is observed in HIV-infected patients responding to antiretroviral therapy, it might as well be considered as a possible manifestation of immune reconstitution inflammatory syndrome. Patient context should be considered for adequate diagnosis and treatment of conditions exacerbated by antiretroviral therapy-induced immune reconstitution.

Fernández-Sánchez M; Saeb-Lima M; Alvarado-de la Barrera C; Reyes-Terán G

2012-01-01

320

Control of crust permeability and crispness retention in crispy breads  

UK PubMed Central (United Kingdom)

Crispness of bread crust is rapidly lost after baking. It is known that the speed of this loss is influenced by the water vapor permeability of the crust. A high water vapor permeability benefits crispness retention but could lead to crumb dryness. In this paper we aimed to determine the water vapor permeability that is optimal for both crispness retention and crumb softness retention. The water vapor permeability of crust was changed by creating different quantities and sizes of channels in the crust. The instrumental and sensory evaluation of the breads stored at 40% relative humidity showed that the water vapor permeability for optimal crispness and crumb softness retention was 8×10?9g/(msPa). Based on this knowledge we suggest possible combinations of the quantities and sizes of channels to create breads with an up to eight-fold longer sensory crispness retention without decreasing crumb softness retention. In addition, our data allowed us to develop a model describing the water vapor permeability of crust with channels.

Hirte A; Hamer RJ; Meinders MBJ; van de Hoek K; Primo-Martín C

2012-04-01

 
 
 
 
321

Magnetised Neutron Star Crusts and Torsional Shear Modes of Magnetars  

CERN Multimedia

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

Nandi, Rana

2012-01-01

322

The Composition of the Prebasin Crust in the Central Highlands of the Moon  

Science.gov (United States)

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

Korotev, R. L.

1996-03-01

323

Deep Crustal Heating in a Multicomponent Accreted Neutron Star Crust  

CERN Document Server

A quasi-statistical equilibrium model is constructed to simulate the multicomponent composition of the crust of an accreting neutron star. The ashes of rp-process nucleosynthesis are driven by accretion through a series of electron captures, neutron emissions, and pycnonuclear fusions up to densities near the transition between the neutron star crust and core. A liquid droplet model which includes nuclear shell effects is used to provide nuclear masses far from stability. Reaction pathways are determined consistently with the nuclear mass model. The nuclear symmetry energy is an important uncertainty in the masses of the exotic nuclei in the inner crust and varying the symmetry energy changes the amount of deep crustal heating by as much as a factor of two.

Steiner, Andrew W

2012-01-01

324

Eclogites with oceanic crustal and mantle signatures from the Bellsbank kimberlite, South Africa. Pt. 2  

International Nuclear Information System (INIS)

The Sr, Nd, and O isotopic compositions of garnet and clinopyroxene mineral separates from nine eclogite xenoliths from the Bellsbank kimberlite (erupted at 120 Ma) define three groups. Group A eclogites, considered to be mantle cumulates, are characterized by ?18O and 87Sr/86Sr values typical of mantle-derived materials (+5.1 to +5.6per mille and 0.7042-0.7046, respectively), and very low Sm/Nd ratios, (apparent) Rb/Sr ratios and ?Nd[120] values (0.057-0.078, 0.00005-0.00136 and -14 to -16 respectively). The REE and isotopic data for these eclogites can be modelled in terms of crystallization from a Group II kimberlite magma at ? 1-1.5 Ga. Group B and C eclogites, believed to be the metamorphosed products of ancient subducted oceanic crust, are characterized by low ?18O (+2.9 to +4.7), extremely high ?Nd[120] (?+40 to +219), and radiogenic 87Sr/86Sr ratios (0.708-0.710). The Sm/Nd ratios of the Group B eclogites are very high (up to 1.6). The data for Group B and C eclogites define a linear correlation on Sm/Nd and 1/Nd vs. ?Nd[120] diagrams. These relationships are consistent with mixing of the Bellsbank kimberlite (?Nd[120] = -10; Sm/Nd = 0.10) with a depleted eclogite end-member (?Nd[120] + 219; Sm/Nd = 1.6) during a cryptic metasomatic event. The Sr isotopic variations in Group B and C eclogites cannot be generated by simple two-component mixing. The Sr, Nd, and O isotope data for Group B and C eclogittes probably reflect a complex sequence of depletion and enrichment events, in both crust and mantle settings. Enrichments which possibly affected the Group B and C eclogites include seawater-alteration of a MORB-like protolith, which lowered the ?18O and raised the 87Sr/86Sr ratio, but left the Nd isotopic compositions unchanged, and cryptic metasomatism by the magmatism that produced the Bellsbank kimberlite. (orig./WB).

1990-01-01

325

IODP Expeditions 309 and 312 Drill an Intact Section of Upper Oceanic Basement into Gabbros  

Directory of Open Access Journals (Sweden)

Full Text Available The Integrated Ocean Drilling Program’s (IODP) Expeditions 309 and 312 successfully completed the first sampling of an intact section of upper oceanic crust, through lavas and the sheeted dikes into the uppermost gabbros. Hole 1256D, which was initiated on the Ocean Drilling Program’s (ODP) Leg 206, now penetrates to >1500 mbsf and >1250 m sub-basement. The first gabbroic rocks were encountered at 1407 mbsf. Below this, the hole penetrates ~100 m into a complex zone of fractionated gabbros intruded into contact metamorphosed dikes.

Jeffrey C. Alt; Damon A.H. Teagle; Susumu Umino; Sumio Miyashita; Neil R. Banerjee; Douglas S. Wilson; the IODP Expeditions 309 and 312 Scientists; the ODP Leg 206 Scientific Party

2007-01-01

326

Intrusion of Oceanic-type Basaltic Melts Precedes Continental Break up in the Red Sea Rift  

Science.gov (United States)

The role of magmatism in continental rifting and break up and in the birth of a new ocean are not well understood. Continental break up can take place with intense and voluminous volcanism, as in the Southern Red Sea/Afar Rift, or in a relatively amagmatic mode, as in the Mesozoic Iberian Atlantic rift. Studies of gabbros from the Brothers and Zabargad islands suggest that continental break up in the northern Red Sea, a relatively non-volcanic rift, is preceded by intrusion of oceanic-type basaltic melts that crystallize at progressively shallower crustal depths as rifting progresses towards continental break-up. A seismic reflection profile running across the central part of the southern Thetis basin, shows a ~5 km wide reflector ~1.25 s below the axial neovolcanic zone. We interpret it as marking the roof of a magma chamber or melt lens, similar to those identified below several mid-ocean ridges. Assuming a 4.5 km/s acoustic velocity for the upper oceanic crust at Thetis, this reflector is ~3.5 km below the seafloor. The presence of a few kilometers deep subrift magma chamber soon after the initiation of oceanic spreading implies the crystallization of lower oceanic crust intrusives as a last step in a sequence of basaltic melt intrusion from pre-oceanic continental rifting to oceanic spreading. Thus, oceanic crust accretion in the Red Sea rift starts at depth before continental break up, emplacement of oceanic basalt at the sea floor, and development of Vine-Matthews magnetic anomalies, pointing to a rift model, where the lower continental lithosphere has been replaced by upwelling asthenosphere before continental rupturing. This model would imply depth-dependent extension due to decoupling between the upper and lower lithosphere with mantle-lithosphere-necking breakup before crustal-necking breakup. This mode of initial oceanic crust accretion may have been common in Mesozoic Atlantic-type rifts, in addition to wider, amagmatic, Iberian-type continent-ocean zones of transition.

Bonatti, Enrico; Ligi, Marco; Ronca, Sara; Seyler, Monique; Bosworth, William; Cipriani, Anna

2013-04-01

327

Mission Moho Workshop: Drilling Through the Oceanic Crust to the Mantle  

Directory of Open Access Journals (Sweden)

Full Text Available The Mission Moho workshop was held in Portland Oregon on 7–9 September 2006. It was funded by the IODP, the Joint Oceanographic Institutions (JOI), the Ridge 2000 program, and the InterRidge initiative. This report builds on many fruitful and passionate discussions during the workshop, and we express our deepest thanks to all workshop participants. Several of them contributed to the writing of the full workshop report.

Benoit Ildefonse; David M. Christie; Mission Moho Workshop Steering Committee

2007-01-01

328

Magnetic Fields Induced in the Solid Earth and Oceans  

DEFF Research Database (Denmark)

Electromagnetic induction in the Earth's interior is an important contributor to the near-Earth magnetic field. Oceans play a special role in the induction, due to their relatively high conductance of large lateral variability. Electric currents that generate secondary magnetic fields are induced in the oceans by two different sources: by time varying external magnetic fields, and by motion of the conducting ocean water through the Earth's main magnetic field. Significant progress in the accurate and detailed prediction of magnetic fields induced by these sources has been achieved during the last years, utilizing realistic 3-D conductivity models of the oceans, crust and mantle. In addition to these improvements in the prediction of 3-D induction effects, much attention has been paid to identifying magnetic signals of oceanic origin in observatory and satellite data. During the talk we will present the results of 3-D model studies that aim at estimating magnetic signals (at ground and satellite altitude) induced by a variety of realistic sources. In particular we will consider induction from ionospheric currents (Sq and electrojets), magnetospheric currents (magnetic storms), ocean tides, and global ocean circulation. Finally, we will discuss how the results of 3-D predictions can be utilized in geomagnetic field modeling and in a recovery of deep conductivity structures.

Kuvshinov, Alexei Technical University of Denmark, Danish National Space Center

329

The Pacific Ocean  

Energy Technology Data Exchange (ETDEWEB)

The monograph The Pacific Ocean is one of the regional volumes in the series The Geography of the World Ocean. Physical, geographic, and economic traits of the Pacific Ocean are examined and its specific physical, geographic, biological, and geomorphological regions are outlined. Detailed economic and geographic characteristics are presented for different regions of the ocean as are its economic regions.

Kort, V.G.; Sal' nikov, S.S.

1981-01-01

330

[Nanobiology of the ocean  

UK PubMed Central (United Kingdom)

The concepts of nanobiotic forms and their relationships with oceanic organic matter and feeding as well as their role in oceanic communities are proposed on the basis of long-term electron microscopy and microbiological studies initiated in 1969 in the Barents Sea, Atlantic and Pacific oceans, and marginal seas of the Arctic Ocean.

Mishustina IE

2004-09-01

331

M&A decisions cause to pause  

Energy Technology Data Exchange (ETDEWEB)

It`s big news in the business world: Electric companies are on a merger/acquisition rampage unlike anything seen since the early part of this century, when fewer than 10 holding companies controlled most of the nation`s power supply. According to the New York Times (December 10, 1996), the year had already witnessed 52 mergers or acquisitions in the electric utility and natural gas industries. Now, as Congress considers legislation to deregulate the electric utility industry, most observes say, {open_quotes}You ain`t seen nothing yet.{close_quotes} Some prognosticators believe that within the next five to ten years we`ll once again see a massive consolidation in the generation sector, a dozen or fewer giant transmission entities, and comparable shrinkage in the distribution sector. But does merging for scale always make sense? Is gargantuan size the only survival guarantee? Unless the company`s strategy specifically requires scale, merging with another vertically integrated utility can be a poor investment and create chaos in the organization for years to come. Mergers in this industry are often a growth trap, where the pure desire to get bigger can have negative impact on the strategy. Before they jump onto the M&A bandwagon, utility executives should reevaluate the potential downsides to mergers and acquisitions, which range from uncertain public policy to enormous human resource challenges. The worth while mergers will be those that take place after utilities functionally unbundle and then selectively acquire businesses that improve their strategic position. The ultimate object, executives should remind themselves, is to increase shareholder value. And, despite the pressure to merge, there are other ways to cut costs and build revenues. No company, no matter how big or savvy, can afford to pursue them all. Options must be weighed against each other to see which create the most shareholder value.

Buttorff, L.A. [A.T. Kearney, Inc., Englewood, CO (United States)

1997-03-01

332

Lineament tectonics of the earth's crust  

Energy Technology Data Exchange (ETDEWEB)

Discussed are linear structures of the crust: lineaments identified practically in all regions of the earth according to various satellite, photographic, and cartographic materials. Given is a system of classifying lineaments according to the type of source materials for decoding, the length of the lineaments and their zones, and also according to their depth. A conclusion is formed about the importance of purposeful study of the lineament tectonics of the earth, which makes a positive contribution to the development of the deep geological mapping--a constituent part of comprehensive study of the earth's crust and tectonosphere.

Poletaev, A.I.

1981-01-01

333

The time reversal effect of the impulse response of crust  

Science.gov (United States)

In this paper, the time reversal processes of impulse response of crust are simulated by means of a dynamical finite element method (DFEM). The results indicate that a small undulating load during a long period may cause a focused brevity impact in a chaos-response system. The physical principle for this phenomenon is that the wave interferes or multiples superposition. Based on this knowledge, a new view toward the mechanism for preparing and triggering an earthquake is proposed. Finally, an interpretation of crust response to the sea tides is given.

Zheng, Wen-Heng; Wang, Cheng; Chen, Xiang-Peng

2001-07-01

334

Are oceanic plateaus sites of komatiite formation?  

Science.gov (United States)

During Cretaceous and Tertiary time a series of oceanic terranes were accreted onto the Pacific continental margin of Colombia. The island of Gorgona is thought to represent part of the most recent, early Eocene, terrane-forming event. Gorgona is remarkable for the occurrence of komatiites of middle Cretaceous age, having MgO contents up to 24%. The geochemistry of spatially and temporally associated tholeiites suggests that Gorgona is an obducted fragment of the oceanic Caribbean Plateau, postulated by Duncan and Hargraves (1984) to have formed at 100 to 75 Ma over the Galapagos hotspot. Further examples of high-MgO oceanic lavas that may represent fragments of the Caribbean Plateau occur in allochthonous terranes on the island of Curaçao in the Netherlands Antilles and in the Romeral zone ophiolites in the southwestern Colombian Andes. These and other examples suggest that the formation of high-MgO liquids may be a feature of oceanic-plateau settings. The association of Phanerozoic komatiites with oceanic plateaus, coupled with thermal considerations, provides a plausible analogue for the origin of some komatiite-tholeiite sequences in Archean greenstone belts.

Storey, M.; Mahoney, J. J.; Kroenke, L. W.; Saunders, A. D.

1991-04-01

335

Ocean Planet: Sea Secrets  

Science.gov (United States)

Unit from Smithsonian multidisciplinary ocean curriculum. Lesson plan focuses on ocean bottom features including continental shelf, deep ocean plain, and mid-ocean ridges. Students study the discovery and mapping of seafloor features, learn to read seafloor maps, then create a map of Atlantic seafloor features. Unit includes: background essay; teacher instructions; maps and forms for student activity; discussion questions; all online in PDF format. Resources include online version of Smithsonian Ocean Planet exhibition.

336

MA transmutation using accelerator-driven subcritical system  

International Nuclear Information System (INIS)

[en] Long-lived radioactive waste disposal is an important issue for nuclear power development. Based on recent research in the field, a multi-purpose accelerator-driven, lead-cooled fast neutron subcritical system is proposed, and MA transmutation chain is analysed. The system is able to transmute MA, generate energy, breed fissile materials, and has better safe characteristics

2000-01-01

337

Ocean anoxia and large igneous provinces  

Science.gov (United States)

Earth's history is marked by multiple events of ocean anoxia developing along continental margins and potentially into the open ocean realm. These events often coincide with the emplacement of large igneous provinces (LIPs) on continents, major perturbations of global geochemical cycles and marine (mass) extinction. The geographic and temporal extend and the intensity (ferruginous vs. euxinic) of anoxic conditions is often, however, poorly constraint. This complicates understanding of close coupling between Earth's physical, chemical and biological processes. We studied ocean redox change over two major mass extinction events in Earth history, the Permian-Triassic (at ~252 Ma) and Triassic-Jurassic (at ~201.3 Ma) mass extinctions. Both extinction events are marked by a major perturbation of the global exogenic carbon cycle (and associated major negative carbon isotope excursion (CIE)), likely initiated by carbon outgassing of the Siberian Traps and the Central Atlantic Magmatic Province (CAMP), respectively. We compare Permian-Triassic and Triassic-Jurassic ocean redox change along continental margins in different geographic regions (Permian-Triassic: Greenland, Svalbard, Iran; Triassic-Jurassic: UK, Austria) and discuss its role in marine mass extinction. We show strongly enhanced sedimentary redox-sensitive trace element concentrations (e.g. Mo) during both events. However, increased Permian-Triassic values are in all localities distinctly delayed relative to the associated negative CIE. Triassic-Jurassic values are only delayed in the oceanographically restricted western Germanic basin (UK) while increased Mo-values in the north-western Tethys Ocean (Austria) directly match the onset of the associated negative CIE. Speciation of iron [giving (Fe-HR/ Fe-T) and (Fe(Py)/ Fe-HR)] in the Triassic-Jurassic western Germanic basin (UK) however shows close coupling between the onset of the global carbon cycle perturbation and a shift to anoxic and even euxinic conditions. Delayed molybdenum enrichment in this basin suggests strong initial depletion of the molybdenum reservoir. Triassic-Jurassic molybdenum drawdown does however occur in more well-connected marine basins along continental margins. Iron speciation and delayed Mo-enrichments along Permian-Triassic continental margins in different geographic regions suggest more widely, potentially global ocean, molybdenum drawdown and more widespread ocean anoxia. Further, our data shows that anoxic (and euxinic) conditions directly matches extinction of marine organisms, suggesting ocean anoxia as contributor to marine ecosystem collapse.

Ruhl, Micha; Bjerrum, Christian J.; Canfield, Donald E.; Korte, Christoph; Stemmerik, Lars; Frei, Robert

2013-04-01

338

Crustal structure of the ocean-island arc transition at the mid Izu-Ogasawara (Bonin) arc margin  

Science.gov (United States)

Wide-angle refraction experiments were conducted to reveal the crustal structure at the transition between the intra-oceanic island arc crust of the mid Izu-Ogasawara (Bonin) arc and the backarc oceanic crust of the Shikoku Basin. The island arc crust consists of an upper crust about 5 km thick with a P-wave velocity Ogasawara arc (IOA). These features are very similar to those of the northern IOA, which indicates that the crustal structure is relatively constant within 200 km at the northern and mid IOA. The Kinan Escarpment, a 500-km-long fault with a maximum offset of 800 m, characterizes the transition zone between the IOA and Shikoku Basin. The seismic crustal model indicates that the escarpment is a fault which tears the whole oceanic crust along the western margin of the IOA. However, no significant differences exist in the crustal structure on either side of the escarpment, and the Kinan Escarpment seems to be a zone of the structural weakness from its birth.

Nishizawa, A.; Kaneda, K.; Nakanishi, A.; Takahashi, N.; Kodaira, S.

2006-08-01

339

Generation of plagiogranite by amphibolite anatexis in oceanic shear zones  

Science.gov (United States)

Field, geochronological, and rare earth element (REE) evidence obtained from the Fournier oceanic fragment of the Canadian Appalachians indicates that its plagiogranite component was generated by the anatexis of amphibolite and not by the fractionation of basic magma. We propose that the process occurred in two stages: first, gabbro was plastically deformed at high temperature to form dry, low-angle shear zones that subsequently evolved to amphibolite via the addition of light REE-enriched hydrothermal solutions; second, the amphibolite underwent partial melting during shear to yield a migmatite comprising bands of plagiogranite alternating with amphibolite restite. The plagiogranite locally coalesced to form pods, dikes, and lenses that injected the surrounding undeformed gabbro. We attribute the development of the Fournier plagiogranite to dynamothermal processes occurring in proximity to a spreading center due to asthenosphere-induced shear within ocean layer 3. This serves as an important illustration of the dynamic nature of metamorphism and melting that can occur in the ocean crust.

Flagler, Patricia A.; Spray, John G.

1991-01-01

340

Oxygen Distribution and Potential Ammonia Oxidation in Floating, Liquid Manure Crusts  

DEFF Research Database (Denmark)

Floating, organic crusts on liquid manure, stored as a result of animal production, reduce emission of ammonia (NH3) and other volatile compounds during storage. The occurrence of NO2- and NO3- in the crusts indicate the presence of actively metabolizing NH3 oxidizing bacteria (AOB) which may be partly responsible for this mitigation effect. Six manure tanks with organic covers (straw and natural) were surveyed to investigate the prevalence and potential activity of AOB and its dependence on the O2 availability in the crust matrix as studied by electrochemical profiling. Oxygen penetration varied from <1 mm in young, poorly developed natural crusts and old straw crusts, to several centimeters in the old, natural crusts. AOB were ubiquitously present in all crusts investigated but nitrifying activity could only be detected in old natural crusts and young straw crust with high O2 availability. In old natural crusts total potential NH3 oxidation rates were similar to reported fluxes of NH3 from slurry without surface crust. These results indicate that old, natural surface crusts may develop into a porous matrix with high O2 availability that harbors an active population of aerobic microorganisms, including AOB. The microbial activity may thus contribute to a considerable reduction of ammonia emissions from slurry tanks with well-developed crusts.

Nielsen, Daniel Aagren; Nielsen, Lars Peter

2010-01-01

 
 
 
 
341

Assessing level of development and successional stages in biological soil crusts with biological indicators.  

UK PubMed Central (United Kingdom)

Biological soil crusts (BSCs) perform vital ecosystem services, but the difference in biological components or developmental level still affects the rate and type of these services. In order to differentiate crust successional stages in quantity and analyze the relationship between crust developmental level and successional stages, this work determined several biological indicators in a series of different developmental BSCs in the Shapotou region of China. The results showed that crust developmental level (level of development index) can be well indicated by crust biological indicators. Photosynthetic biomass was the most appropriate to differentiate crust successional stages, although both photosynthetic biomass and respiration intensity increased with the development and succession of BSCs. Based on of the different biological compositions, BSCs were quantificationally categorized into different successional stages including cyanobacterial crusts (lichen and moss coverages <20 %), lichen crusts (lichen coverage >20 % but moss coverage <20 %), semi-moss crusts (moss coverage >20 % but <75 %), and moss crusts (moss coverage >75 %). In addition, it was found that cyanobacterial and microalgal biomass first increased as cyanobacterial crusts formed, then decreased when lots of mosses emerged on the crust surface; however nitrogen-fixing cyanobacteria and heterotrophic microbes increased in the later developmental BSCs. The structural adjustment of biological components in the different developmental BSCs may reflect the requirement of crust survival and material transition.

Lan S; Wu L; Zhang D; Hu C

2013-08-01

342

[Effects of soil crusts on surface hydrology in the semiarid Loess hilly area].  

UK PubMed Central (United Kingdom)

Soil crusts are distributed extensively in the Chinese Loess Plateau and play key roles in surface hydrological processes. In this study, a typical loess hilly region in Anjiagou catchment, Dingxi city, Gansu province was selected as the study region, and soil crusts in the catchment were investigated. Then, the hydrological effect of soil crusts was studied by using multi-sampling and hydrological monitoring experiments. Several key results were shown as follows. Firstly, compared with bared soil without crust cover, soil crusts can greatly reduce the bulk density, improve the porosity of soil, and raise the holding capacity of soil moisture which ranges from 1.4 to 1.9 times of that of bared soil. Secondly, the role of soil crust on rainfall interception was very significant. Moss crust was found to be strongest on rainfall interception, followed by synantectic crusts and lichen crusts. Bared soil without covering crusts was poorest in resisting rainfall splash. Thirdly, hydrological simulation experiments indicate that soil crusts play a certain positive role in promoting the water infiltration capacity, and the mean infiltration rate of the crusted soil was 2 times higher than that of the no-crust covered soils. While the accumulated infiltrated water amounts was also far higher than that of the bared soil.

Wei W; Wen Z; Chen LD; Chen J; Wu DP

2012-11-01

343

Reflection seismology: The continental crust (1986). Volume 14  

Energy Technology Data Exchange (ETDEWEB)

This volume explores the major problems of deep geology and continental tectonics, the issues of deep crustal fluids, and the geological significance of deep reflections. It reports on seismic results from Precambrian crust to Paleozoic structures, including seismic results from the Appalachian-Hercynian system and new results from the Cordillera of western North America, the young subduction zone of western Canada, and Antarctica.

Barazangi, M.; Brown, L.

1986-01-01

344

Chlorine isotope homogeneity of the mantle, crust and carbonaceous chondrites.  

UK PubMed Central (United Kingdom)

Chlorine in the Earth is highly depleted relative to carbonaceous chondrites and solar abundances. Knowledge of the Cl concentrations and distribution on Earth is essential for understanding the origin of these depletions. Large differences in the stable chlorine isotope ratios of meteoritic, mantle and crustal materials have been used as evidence for distinct reservoirs in the solar nebula and to calculate the relative proportions of Cl in the mantle and crust. Here we report that large isotopic differences do not exist, and that carbonaceous chondrites, mantle and crust all have the same 37Cl/35Cl ratios. We have further analysed crustal sediments from the early Archaean era to the Recent epoch and find no systematic isotopic variations with age, demonstrating that the mantle and crust have always had the same delta37Cl value. The similarity of mantle, crust and carbonaceous chondrites establishes that there were no nebular reservoirs with distinct isotopic compositions, no isotopic fractionation during differentiation of the Earth and no late (post-core formation) Cl-bearing volatile additions to the crustal veneer with a unique isotopic composition.

Sharp ZD; Barnes JD; Brearley AJ; Chaussidon M; Fischer TP; Kamenetsky VS

2007-04-01

345

Chlorine isotope homogeneity of the mantle, crust and carbonaceous chondrites.  

Science.gov (United States)

Chlorine in the Earth is highly depleted relative to carbonaceous chondrites and solar abundances. Knowledge of the Cl concentrations and distribution on Earth is essential for understanding the origin of these depletions. Large differences in the stable chlorine isotope ratios of meteoritic, mantle and crustal materials have been used as evidence for distinct reservoirs in the solar nebula and to calculate the relative proportions of Cl in the mantle and crust. Here we report that large isotopic differences do not exist, and that carbonaceous chondrites, mantle and crust all have the same 37Cl/35Cl ratios. We have further analysed crustal sediments from the early Archaean era to the Recent epoch and find no systematic isotopic variations with age, demonstrating that the mantle and crust have always had the same delta37Cl value. The similarity of mantle, crust and carbonaceous chondrites establishes that there were no nebular reservoirs with distinct isotopic compositions, no isotopic fractionation during differentiation of the Earth and no late (post-core formation) Cl-bearing volatile additions to the crustal veneer with a unique isotopic composition. PMID:17460668

Sharp, Z D; Barnes, J D; Brearley, A J; Chaussidon, M; Fischer, T P; Kamenetsky, V S

2007-04-26

346

Symmetry Energy, Neutron Star Crust and Neutron Skin Thickness  

International Nuclear Information System (INIS)

We analyze the correlations of the slope and curvature parameters of the symmetry energy with the neutron skin thickness of neutron-rich isotopes, and the crust-core transition density in neutron stars. The results are obtained within the microscopic Brueckner-Hartree-Fock approach, and are compared with those obtained with several Skyrme and relativistic mean field models. (author)

2011-01-01

347

Water sorption and transport in dry crispy bread crust  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Water sorption and dynamical properties of bread crust have been studied using gravimetric sorption experiments. Water uptake and loss were followed while relative humidity (RH) was stepwise in- or decreased (isotherm experiment) or varied between two adjusted values (oscillatory experiment). Experi...

Meinders, M.B.J.; Nieuwenhuijzen, N.H., van; Tromp, R.H.; Hamer, R.J.; Vliet, T., van

348

Drilling of Early Cretaceous Oceanic Anoxic Event 1a in Southern France  

Directory of Open Access Journals (Sweden)

Full Text Available The massive concentration of black, laminated, organic carbon-rich shales at certain time periods during the Cretaceous period (?140–65 Ma) led to the concept of Oceanic Anoxic Events (OAEs). These events are characterized by unusually enhanced preservation of organic matteracross environments ranging from the deep oceans to shelf seas. Enhanced productivity of siliceous and organic-walled primary producers and/or strongly dysaerobic or anoxic conditions in all major oceans were both suggested as likely causes (Meyer and Kump, 2008). Fundamental chemical and biological changes in the world ocean must have been associated with these events.

Sascha Flögel; Wolfgang Kuhnt; Michel Moullade

2010-01-01

349

Complete hydrothermal re-equilibration of zircon in the Maniitsoq structure, West Greenland: A 3001 Ma minimum age of impact?  

Science.gov (United States)

Zircon in five samples of variably comminuted, melted, and hydrothermally altered orthogneiss from the Maniitsoq structure of southern West Greenland yield a weighted mean 207Pb/206Pb age of 3000.9 ± 1.9 Ma (ion probe data, n = 37). The age data constitute a rare example of pervasive and nearly complete isotopic resetting of zircon during a regional hydrothermal event. Many zircon grains are homogeneous or display weak flame-like patterns in backscattered electron images. Other grains show complex internal textures, where homogeneous, high-U fronts commonly cut across relict igneous-type oscillatory zonation. Inclusions of quartz, plagioclase, mica, and other Al ± Na ± Ca ± Fe-bearing silicates are very common. In two samples, selective replacement of zircon with baddeleyite occurs along concentric zones with relict igneous zonation, and as specks a few microns large within recrystallized, high-U areas. We interpret the 3000.9 ± 1.9 Ma date as the minimum age of the recently proposed impact structure at Maniitsoq. The great geographical extent and intensity of the hydrothermal event suggest massive invasion of water into the currently exposed crust, implying that the age of the hydrothermal alteration would closely approximate the age of the proposed impact at Maniitsoq. At the western margin of the Taserssuaq tonalite complex, which postdates the Maniitsoq event, a 207Pb/206Pb mean age of 2994.6 ± 3.4 Ma obtained from zircon has mostly retained igneous-type oscillatory zonation. A subsequent thermal event at approximately 2975 Ma is recorded in several samples by zircon with baddeleyite replacement textures.

ScherstéN, Anders; Garde, Adam A.

2013-08-01

350

Evidence for a Large Bolide Impact in the Proto-Pacific Ocean Preceding the Chicxulub Impact by About 2 Million Years  

Science.gov (United States)

Although the Cretaceous-Tertiary (K-T) transition is generally accepted as having been caused by a single large asteroid impact at ~65 Ma near Chicxulub on the Yucatán Peninsula, a `comet shower' or multiple-impact hypothesis has also been proposed to explain multiple extinction pulses in latest Cretaceous time. The contributory effects of contemporaneous Deccan volcanism and rapid sea level changes also remain controversial. We have discovered spherule layers several meters below the K-T boundary (Chicxulub impact layer) in giant piston core GPC-3 and in DSDP drill cores 576-8-1 (43-45 cm) and 596-3-6 (142-144 cm) from the northern and southern Pacific Ocean, respectively. We have also found a spherule layer ~8 cm below the peak K-T Ir anomaly in core 596-3-4 (50-51 cm); this layer contains the farthest known spherules from the Chicxulub crater (>10,000 km at 65 Ma). Corliss and Hollister [Nature, 282, 1979, p. 707-9] initially reported small (~20 ?m) cristobalite spherules in core GPC-3 within a zone of disrupted layering, between ~2 m below the K-T boundary and the core bottom (~2 m thick), but considered them of volcanic origin. We have found larger spherules and mineral crystals (up to >200 ?m) dispersed within this disturbed zone. The spherule layers found ~5.5 m below the peak K-T Ir anomaly in hole 576, and ~3.8 m below the peak K-T Ir anomaly in hole 596 are relatively undisturbed. Hole GPC-3 is the easternmost on Mesozoic crust in the Pacific Ocean, and we interpret the pre-K-T spherules and mineral crystals as ejecta and vapor-phase condensates, respectively, from an oceanic impact site farther east on crust now subducted beneath western North America. Apparently, the pre-K-T spherule layers are related to an earlier large impact because of the size of the condensed particles (>100 ?m) in the GPC-3 core, and because some of the particles have chemical compositions (Fe-Ti-C-O) that are not of volcanic origin. Disruption of the sediments and dispersal of the spherules and mineral grains in core GPC-3 were probably caused by megatsunami waves associated with nearby impact. Such waves (initially up to 4 km high) might account for an abrupt anomaly in the seawater 87Sr/86Sr ratio, also preceding the K-T boundary by several m.y., because the waves likely washed vast amounts of 87Sr-rich continental soils into the oceans. In addition, erosion of shallow continental margins or deposition of higher-energy sediments by megatsunami waves left a stratigraphic record that may be erroneously interpreted as indicating a regression-transgression pulse in sea level near the time of impact.

Hagstrum, J. T.; Abbott, D.

2002-12-01

351

77 FR 22523 - Safety Zone; 2012 Ocean City Air Show; Atlantic Ocean, Ocean City, MD  

Science.gov (United States)

...Zone; 2012 Ocean City Air Show; Atlantic Ocean, Ocean City, MD AGENCY: Coast...on the navigable waters of the Atlantic Ocean in Ocean City, MD. This action...host an air show event over the Atlantic Ocean in Ocean City, MD. In...

2012-04-16

352

530 Ma zircon age for ophiolite from the New England orogen: Oldest rocks known from eastern Australia  

Science.gov (United States)

New ion microprobe data provide constraints on the timing of formation of ophiolitic rocks in the New England tectonic collage in eastern Australia. Results for analyses of magmatic zircons from plagiogranite of the Weraerai terrane ophiolite at Upper Bingara give a 206Pb/238U age of 530 ±6 Ma (2?). This plagiogranite is the oldest rock from eastern Australia yet identified. Existing tectonic models suggest that progressively younger crust was accreted to the eastern margin of Gondwanan Australia throughout the Paleozoic. This cannot be reconciled easily with the Cambrian age for these ophiolitic rocks, which are juxtaposed between Devonian terranes and are at least 1000 km east of the nearest lithologically similar rocks of comparable age. We speculate that younger, thin-skinned terranes may have been thrust westward over the continental freeboard of eastern Australia during the late Paleozoic.

Aitchison, J. C.; Ireland, T. R.; Blake, M. C., Jr.; Flood, P. G.

1992-02-01

353

Low velocity and low electricalresistivity layers in the middle crust  

Directory of Open Access Journals (Sweden)

Full Text Available Some Deep Seismic Sounding (DSS) revealed low velocity layers in the upper and middle crust of old platforms. The layers are often characterised by a lower electrical resistivity. It is not clear, however, how reliable the layers recognized from DSS data are, if they are regular or occasional events and how they correlate with other geophysical parameters. To answer these questions the experimental DSS data obtained in the Baltic and Ukranian shields by different institutions were reinterpreted by the author with unified methods. The shield areas are well studied using both the DSS and high-frequency magnetotelluric sounding (MTS) methods. As a result a marked velocity inversion (waveguide) was observed in a 10 to 20 km depth range in the majority of the DSS profiles. An increase in the electrical conductivity is typical for the waveguide. A comparison of the results with the data from other platform regions allow the conclusion that this low velocity and high electrical conductivity layer has a global significance. In the continental crust, the layer is characterised by changes in the reflectivity pattern, earthquakes number and changes in velocity pattern where the block structure is transformed into a subhorizontal layering. These structural features suggest that the layers separate brittle and weak parts of the crust. Usually they play the role of detachment zones at crustal block moving. A possible factor responsible for this phenomenon is an increase in porosity and in the salinity of the waveguide pore water compared with the upper crust. This suggestion is confirmed by the Kola superdeep borehole data. Porosity increasing in the middle crust is explained by the change in rock mechanical properties with depth, by fracturing porosity and by dilatancy effect, at a depth of 10-20 km.

N. I. Pavlenkova

2004-01-01

354

Postglacial Iron-Rich Crusts in Hemipelagic Deep-Sea Sediment.  

Science.gov (United States)

An iron-rich crust separates terrigenous hemipelagic lutites and turbidites from overlying pelagic foraminiferal oozes and lutites on the Amazon abyssal fan and adjacent continental rise and abyssal plains. This crust is found over wide areas of the weste...

D. F. R. McGeary J. E. Damuth

1972-01-01

355

Inferences from Io: The Possible Role of Volcanic Heat Pipes and Emergent Mountain Blocks in Creating Earth's First Sialic Crust  

Science.gov (United States)

Io is the most volcanically active body in the solar system. More than 2.5 W m-2 of tidal energy is volcanically brought to its surface. Of the hundreds of volcanic features identified, 70% are caldera-like depressions sunk into the surface. Coexisting with these volcanic features are more than 100 tilted mountain blocks, reaching heights up to ~18 km. Downward advection of the cooled volcanic crustal stack generates 1) tensile elastic overburden stress; 2) potentially strong compressive radial confinement stress; and if volcanism locally or regionally falters, 3) potentially strong compressive thermal stress as the lower crust reheats. The combination of these effects, especially the last two, plausibly explains the origin of Io's spectacular mountains by means of thrust faulting (McKinnon et al. 2001, Geology 29, 103-106; McEwen et al. 2004, in press in \\ Jupiter - The Planet, Satellites, and Magnetosphere; Kirchoff and McKinnon 2003, LPSC XXXIV, abs. 2030). The earliest Earth was also quite hot, from accretional and initially high radiogenic heating. Arguably the early Hadean Earth, like Io, dominantly shed its interior heat via vertical magma transport rather than by conduction or lateral plate tectonics. If so, the early Earth plausibly had a cool volcanic crust thick enough to support substantial topography. But what would create the topography? A lack of stable plumes, copious partial melt at shallow levels, and possibly, a lack of water in the earliest (pre-plate tectonics) mantle could have resulted in muted surface topography so that little or no emergent land existed beneath the early global ocean (<3-km deep). Regardless, mountain formation by thrust faulting may have occurred by the mechanisms above. The greater gravity and size (radius of curvature) of the Earth compared with Io would have increased the elastic overburden stress and decreased the radial confinement stress so that they approximately canceled, leaving the dominant role for compressive thermal stresses (as long as the advective heat flow was high). Greater gravity also implies the Earth's crust was stronger than Io's at similar depths (Byerlee's rule), but pore pressure (due to downward advection of H2O in the volcanics) and "semibrittle" failure would have limited crustal strength. Mountain heights would have been lower than on Io today, but gravitational scaling from Io implies maximum heights exceeding 3 km - emergent land subject to erosion - and possibly the Earth's first source of substantial sediment. Eventual mountain collapse, as seen on Io, volcanic burial, and downward advection would have brought water, crust and wet sediment into the partially molten upper mantle, where wet remelting would have resulted in more silica-rich magma, and possibly, embryonic continental crust.

McKinnon, W. B.; Kirchoff, M.

2004-05-01

356

Utility of low mA 1.5 pitch helical versus conventional high mA abdominal CT.  

Science.gov (United States)

The objective of this study was to evaluate the utility of a low mA 1.5 pitch helical versus conventional high mA conventional technique in abdominal computed tomography (CT). Twenty-five patients who had both a conventional high mA (> 300) and a 1.5 pitch low mA (80-125) helical CT within 3 months were selected for inclusion in the study. Patients were excluded who had a significant change in pathology between the two studies. The other parameters (injection rate, contrast type and volume, and filming window/level) were constant. The studies were randomized and blinded to five separate experienced readers who graded the studies by a variety of normal anatomical structures and pathological criteria. Overview questions also assessed noise, resolution, contrast, and overall quality. The abdominal wall/retroperitoneum and hiatal hernias were statistically better visualized on the conventional high mA studies. However, for all other normal anatomical and pathological sites, there was equivalent or better visualization on the helical versus the conventional CT examinations. The resolution of the helical studies was graded statistically better than the high mA conventional CT scans as was the amount of noise present on the images. While there was some advantage for conventional high mA CT with respect to contrast enhancement and low contrast sensitivity, these differences were not statistically significant. It appears from the data of this study that a low mA technique in evaluating the abdomen may be a useful option in performing routine abdominal CT. The radiation dose savings to the patient is significant and there appears to be little degradation of image quality using a low mA 1.5 helical versus mA conventional CT technique. PMID:9421657

Hopper, K D; Keeton, N C; Kasales, C J; Mahraj, R; Van Slyke, M A; Patrone, S V; Singer, P S; Tenhave, T R

357

Ma tean, et päike liigub : [luuletused] / Hando Runnel  

Index Scriptorium Estoniae

Sisu: Ma tean et päike liigub ; Ma tean, et ma tulen kord jälle ; Jaanipäevaks kõrgeks kasvab rohi ; Luigelaul ; Pühapäev lastepargis ; Kui päike loojub ; Kohvik ; "Kui veel..." ; Muruks kummel, muruks linnurohi ; Ei mullast sul olegi enam suurt lugu ; Vanaema ; Hauakiri ; Testament ; Üks veski seisab vete pääl ; Kui sa tuled ; Töölispoiss ; Sõbrad ; Mõnitus ; Naine naturaalne ; Kõigevägevam ja kõigelahjem ; Kehv kõhn poiss ; Keldrikakand ; Loogikaloksed ; Tume rahvas ; Võllalaul ; Kodu ; Ei ole ma käinud Komorras ; Mäletaja ; Hingede aeg ; Kui pidud on peetud ; Muusikat olgu ; Kaua sa kannatad ; Üle maa, üle mäda ; Jutt ; "Mis on me pääl, kas jumalate viha..." ; Jälle hakkab ; Müüt ; Vähid ; Muuda ennast ; Mõistmine ; Lindprii ; Kolm külameest 1-3 ; Meie õnn on kindel ; Ei saa me läbi Lätita ; Saadik ; Jälle ; Unistus ; Mets on kõrge ; "Marssis majja majuline..." ; "Üks väga vana rahvas..." ; "Ma polegi isa näinud..." ; "Ilus on ikkagi isamaa pale ; "Kiri algab kirikust..." ; "Mehepoegi läheb pätiks..." ; "Isa oli joodik..." "Hiired veavad pabereid..." ; "Talisman on Talli-Mannil..." ; "Täna ma luuletan läbi öö..." ; "Küll ma ootasin sind tollel tuulisel õhtul..." ; "Me liigume loogeldes loojangu poole... 1-10"

Runnel, Hando, 1938-

1998-01-01

358

Model for Analysis of Energy Demand (MAED-2). User's manual  

International Nuclear Information System (INIS)

The IAEA has been supporting its Member States in the area of energy planning for sustainable development. Development and dissemination of appropriate methodologies and their computer codes are important parts of this support. This manual has been produced to facilitate the use of the MAED model: Model for Analysis of Energy Demand. The methodology of the MAED model was originally developed by. B. Chateau and B. Lapillonne of the Institute Economique et Juridique de l'Energie (IEJE) of the University of Grenoble, France, and was presented as the MEDEE model. Since then the MEDEE model has been developed and adopted to be appropriate for modelling of various energy demand system. The IAEA adopted MEDEE-2 model and incorporated important modifications to make it more suitable for application in the developing countries, and it was named as the MAED model. The first version of the MAED model was designed for the DOS based system, which was later on converted for the Windows system. This manual presents the latest version of the MAED model. The most prominent feature of this version is its flexibility for representing structure of energy consumption. The model now allows country-specific representations of energy consumption patterns using the MAED methodology. The user can now disaggregate energy consumption according to the needs and/or data availability in her/his country. As such, MAED has now become a powerful tool for modelling widely diverse energy consumption patterns. This manual presents the model in details and provides guidelines for its application

2007-01-01

359

Model for Analysis of Energy Demand (MAED-2). User's manual  

International Nuclear Information System (INIS)

The IAEA has been supporting its Member States in the area of energy planning for sustainable development. Development and dissemination of appropriate methodologies and their computer codes are important parts of this support. This manual has been produced to facilitate the use of the MAED model: Model for Analysis of Energy Demand. The methodology of the MAED model was originally developed by. B. Chateau and B. Lapillonne of the Institute Economique et Juridique de l'Energie (IEJE) of the University of Grenoble, France, and was presented as the MEDEE model. Since then the MEDEE model has been developed and adopted to be appropriate for modelling of various energy demand system. The IAEA adopted MEDEE-2 model and incorporated important modifications to make it more suitable for application in the developing countries, and it was named as the MAED model. The first version of the MAED model was designed for the DOS based system, which was later on converted for the Windows system. This manual presents the latest version of the MAED model. The most prominent feature of this version is its flexibility for representing structure of energy consumption. The model now allows country-specific representations of energy consumption patterns using the MAED methodology. The user can now disaggregate energy consumption according to the needs and/or data availability in her/his country. As such, MAED has now become a powerful tool for modelling widely diverse energy consumption patterns. This manual presents the model in details and provides guidelines for its application

2006-01-01

360

Ocean drilling program for Georges Bank, Eastern Pacific Rise, Mid American Trench, and Antarctica (Weddell sea)  

Energy Technology Data Exchange (ETDEWEB)

The draft form of an environmental impact statement (EPA No. 850262D) on a proposed 10-year international ocean drilling program describes plans for drilling in the Georges Bank, Eastern Pacific Rise, Mid-American Trench, and Weddell Sea areas. Core samples from the ocean floor in the four study areas will examine oceanic crust, active and passive margins, and ocean paleoenvironment. The program would generate information on sea floor spreading, plate tectonics, the structure of the earth's interior, evolution of ocean life, climatic changes through time, and the structure of the planet. Negative impacts would be damage to the sea floor, drilling muds, possible gas or brine blowouts, and a possible effect on the sonar or hearing of marine mammals. Legal mandates for the impact statement are laws addressing water pollution, international conventions of the sea, and protection for marine life.

1985-06-01

 
 
 
 
361

Mapping Ganymede's time variable aurora in the search for a subsurface ocean  

Science.gov (United States)

A very exciting, unresolved question about JupiterÕs moon Ganymede is whether Ganymede harbors a saline subsurface water ocean under its icy crust. A saline, electrically conductive water ocean will modifiy Ganymede's magnetic field enviorment and thus also the locations of Ganymede's northern and southern auroral ovals. Without an ocean, Ganymede's auroral ovals will rock by ~10 degrees towards and away from Jupiter within 5.25 hours. However, with an ocean the shift will be up to only ~4 degrees. We propose two visits of five consecutive STIS orbits at eastern elongation to monitor and resolve with sufficient precision the shift in locations of Ganymede's auroral ovals to determine wheter an ocean is present on Ganymede. Addressing this question is timely as NASA/ESA are planing a Jupiter system mission including a Ganymede orbiter with the objective to characterize Ganymede as potential habitat.;

Saur, Joachim

2009-07-01

362

Fuzzy comprehensive evaluation of earth crust stability of Beishan and nerghbouring areas, Gansu province  

International Nuclear Information System (INIS)

The evaluation of earth crust stability is a research project priot to siting of the repository of high-radioactive waste disposal. Based on fuzzy mathematics authors have developed a fuzzy comprehensive evaluation model of earth crust stability, then divided the studied region into eight a reas with different stability of earth crust on the basis of analysing the structure of earth crust, seismic characteristics, active faults and recent tectonic stress field. (author)

2004-01-01

363

Microbial ecology of the dark ocean above, at, and below the seafloor  

DEFF Research Database (Denmark)

The majority of life on Earth--notably, microbial life--occurs in places that do not receive sunlight, with the habitats of the oceans being the largest of these reservoirs. Sunlight penetrates only a few tens to hundreds of meters into the ocean, resulting in large-scale microbial ecosystems that function in the dark. Our knowledge of microbial processes in the dark ocean-the aphotic pelagic ocean, sediments, oceanic crust, hydrothermal vents, etc.-has increased substantially in recent decades. Studies that try to decipher the activity of microorganisms in the dark ocean, where we cannot easily observe them, are yielding paradigm-shifting discoveries that are fundamentally changing our understanding of the role of the dark ocean in the global Earth system and its biogeochemical cycles. New generations of researchers and experimental tools have emerged, in the last decade in particular, owing to dedicated research programs to explore the dark ocean biosphere. This review focuses on our current understanding of microbiology in the dark ocean, outlining salient features of various habitats and discussing known and still unexplored types of microbial metabolism and their consequences in global biogeochemical cycling. We also focus on patterns of microbial diversity in the dark ocean and on processes and communities that are characteristic of the different habitats.

Orcutt, Beth; Sylvan, Jason B

2011-01-01

364