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

Kay L. Achenbach  Michael J. Cheadle  Ulrich Faul  Peter Kelemen  Susan Swapp 《Earth and Planetary Science Letters》2011,301(1-2):199-212

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

Near-surface electromagnetic, rock magnetic, and geochemical fingerprinting of submarine freshwater seepage at Eckernf?rde Bay (SW Baltic Sea)   总被引：1，自引：1，他引：0  

Hendrik M��ller  Tilo von Dobeneck  Wiebke Nehmiz  Kay Hamer 《Geo-Marine Letters》2011,31(2):123-140

Submarine groundwater discharge in coastal settings can massively modify the hydraulic and geochemical conditions of the seafloor. Resulting local anomalies in the morphology and physical properties of surface sediments are usually explored with seismo-acoustic imaging techniques. Controlled source electromagnetic imaging offers an innovative dual approach to seep characterization by its ability to detect pore-water electrical conductivity, hence salinity, as well as sediment magnetic susceptibility, hence preservation or diagenetic alteration of iron oxides. The newly developed electromagnetic (EM) profiler Neridis II successfully realized this concept for a first time with a high-resolution survey of freshwater seeps in Eckernf?rde Bay (SW Baltic Sea). We demonstrate that EM profiling, complemented and validated by acoustic as well as sample-based rock magnetic and geochemical methods, can create a crisp and revealing fingerprint image of freshwater seepage and related reductive alteration of near-surface sediments. Our findings imply that (1) freshwater penetrates the pore space of Holocene mud sediments by both diffuse and focused advection, (2) pockmarks are marked by focused freshwater seepage, underlying sand highs, reduced mud thickness, higher porosity, fining of grain size, and anoxic conditions, (3) depletion of Fe oxides, especially magnetite, is more pervasive within pockmarks due to higher concentrations of organic and sulfidic reaction partners, and (4) freshwater advection reduces sediment magnetic susceptibility by a combination of pore-water injection (dilution) and magnetite reduction (depletion). The conductivity vs. susceptibility biplot resolves subtle lateral litho- and hydrofacies variations.  相似文献   

Sea-ice retreat in the Sea of Okhotsk and the ice–ocean albedo feedback effect on it     

Sohey Nihashi  Kay I. Ohshima  Haruka Nakasato 《Journal of Oceanography》2011,67(5):551-562

Sea-ice retreat processes are examined in the Sea of Okhotsk. A heat budget analysis in the sea-ice zone shows that net heat flux from the atmosphere at the water surface is about 77 W m⁻² on average in the active ice melt season (April) due to large solar heating, while that at the ice surface is about 12 W m⁻² because of the difference in surface albedo. The temporal variation of the heat input into the upper ocean through the open water fraction corresponds well to that of the latent heat required for ice retreat. These results suggest that heat input into the ice–upper ocean system from the atmosphere mainly occurs at the open water fraction, and this heat input into the upper ocean is an important heat source for ice melting. The decrease in ice area in the active melt season (April) and the geostrophic wind just before the melt season (March) show a correlation: the decrease is large when the offshoreward wind is strong. This relationship can be explained by the following process. Once ice concentration is decreased (increased) by the offshoreward (onshoreward) wind just before the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration. This positive feedback is regarded as the ice–ocean albedo feedback, and explains in part the large interannual variability of the ice cover in the ice melt season.  相似文献   

The extragalactic submillimetre population: predictions for the SCUBA Half-Degree Extragalactic Survey (SHADES)     

Eelco van Kampen  Will J. Percival  Miller Crawford  James S. Dunlop  Susie E. Scott  Neil Bevis  Seb Oliver  Frazer Pearce  Scott T. Kay  Enrique Gaztañaga  David H. Hughes  Itziar Aretxaga 《Monthly notices of the Royal Astronomical Society》2005,359(2):469-480

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Morphology,sedimentary bedforms and sand transport across a ridge- and- runnel beach under the action of summer waves     

Christopher E. Vincent  Robert C. Kay  Chen Chenghui  Li Li  Jack Jarvis 《中国海洋湖沼学报》1990,8(3):197-212

As part of a collaborative study between the 3rd Institute of Oceanography, Xiamen, and the U. K. Universities of East Anglia and St. Andrews, a 4-day experiment was conducted on a ridge- and- runnel beach of north Norfolk on the North Sea coast. Detailed surveys were made of every low water of an area 10m by 30m and electromagnetic current meters were used to measure wave-induced currents over the ridge and in the runnel. The locations of bedform fields were noted, fluorescent sand was used to follow the sand movement and, at the end of the experiment, lacquer peels were taken of the top 0.2m of a vertical section through the ridge- and- runnel. During the 4 days 0.75m³ of sand per metre width of beach accreted in the runnel and a similar volume was eroded from the upper foreshore. The dominant shoreward transport, identified qualitatively by the movement of the fluorescent sand, suggests the ridge- and- runnel system migrated shorewards up the general beach slope of 1^o by 2–3m. The wave orbital currents were used to predict the bedforms to be expected over the tidal cycle: an upper phase plane- bed was predicted for most of the period but vortex and rolling- grain ripples were predicted and observed when the water level over the ridge was low. As the tide dropped ripples on the ridge were eliminated by swash action but the ripples in the runnel were protected by the ridge and remained on the beach after the tide dropped. The observed accretion of the beach in the runnel and on the lee slope of the ridge was used to calculate that a net average shoreward transport of 0.11g/cm·s⁻¹ occurred over the ridge crest during the period it was underwater. The current meter measurements of the wave orbital currents and the mean currents over the ridge crest were used with the wave- current interaction model of Grant and Madsen (1982), ripple dimensions defined by Nielsen (1981), and resuspension coefficient of Vincent and Green (1990), to compute bedload sand transport rates from the equations of Madsen and Grant (1976), Sleath (1978), and Vincent et al. (1981), and also the suspended sand transport rates. The results from one of these bedload equations (Madsen and Grant, 1976) compared well with the observed net transport. The calculated suspended load transport rates (due to steady currents alone) were a factor of 5 too great, and were also several orders of magnitude greater than suspended transport rates measured directly under similar or more energetic wave and current conditions.  相似文献   

Ca ii K interstellar observations towards early-type disc and halo stars     

J. V. Smoker  W. R. J. Rolleston  H. R. M. Kay  D. Kilkenny  R. Morras  M. Arnal  F. P. Keenan  C. J. Mooney  P. L. Dufton  R. S. I. Ryans  N. C. Hambly  D. O'Donoghue  H. McGillivray 《Monthly notices of the Royal Astronomical Society》2003,346(1):119-134

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长江河源地区河流水文特性分析   总被引：3，自引：0，他引：3  

吴凯  刘彩棠  王广德 《地理研究》1983,2(2):72-81

本文简要介绍了青藏高原长江河源地区冰川,冻土和地质构造对水系发育和河况的影响,初步分析了该地区河流的经流、洪水、枯水、水温和冰情的变化规律.文中着重阐明河流洪水形成的基本特征,并据观测资料和洪水调查资料,探讨了百年一遇洪峰流量的分布规律,该成果可供长江河源地区铁路,公路桥涵设计参照使用.  相似文献   

The Somuncura Large Igneous Province in Patagonia: Interaction of a Transient Mantle Thermal Anomaly with a Subducting Slab     

Kay  S. Mahlburg; Ardolino  A. A.; Gorring  M. L.; Ramos  V. A. 《Journal of Petrology》2007,48(1):43-77

The Oligo-Miocene Somuncura province is the largest (55 000km²) back-arc mafic volcanic field in Patagonia, and one ofEarth's largest with no clear link to a hotspot or major extension.Major and trace element and Sr–Nd–Pb isotopic datasuggest involvement of a plume-like component in the mantlemagma source mixed with hydrous, but not high field strengthelement (HFSE)-depleted components, from a disintegrating subductingplate. Magmatism is attributed to mantle upwelling related todisturbances during plate reorganization, possibly at a timewhen the South America plate was nearly stationary over theunderlying mantle. Melting was enhanced by hydration of themantle during Paleogene subduction. Crustal contamination wasminimal in a refractory crust that had been extensively meltedin the Jurassic. Eruption began with low-volume intraplate alkalinemafic flows with depleted Nd–Sr isotopic signatures. Thesewere followed by voluminous 29–25 Ma tholeiitic maficflows with flat light and steep heavy rare earth element (REE)patterns, intraplate-like La/Ta ratios, arc-like Ba/La ratiosand enriched Sr–Nd isotopic signatures. Their source canbe explained by mixing EM1–Tristan da Cunha-like and depletedmantle components with subduction-related components. Post-plateau24–17 Ma alkaline flows with steep REE patterns, highincompatible element abundances, and depleted Sr–Nd isotopicsignatures mark the ebbing of the mantle upwelling. KEY WORDS: Somuncura plateau; slab interaction; Patagonia; large igneous province (LIP); plume-like upwelling  相似文献   

Cone morphologies associated with shallow marine eruptions: east Pico Island, Azores     

Neil C. Mitchell  Rachelle Stretch  Clive Oppenheimer  Daniel Kay  Christoph Beier 《Bulletin of Volcanology》2012,74(10):2289-2301

Eruptions in shallow water typically produce cones of volcaniclastic material. In order to identify any systematic effects of water depth and other environmental parameters on cone morphology, we have measured the heights and widths of cones in multibeam echo-sounder data from a submarine ridge extending southeast from Pico Island, Azores. XRF analyses of dredged samples show that lavas here vary compositionally from alkali basalt to trachybasalt and trachyandesite. Cones in deeper water are generally steep-sided with upper flanks close to 30°, the dip of talus at the angle of repose. However, height/width ratios of cones vary more in shallow water (200?C400-m summit depth) with extreme values below 0.1; while some shallow-water cones are steep-sided as in deep water, others are much flatter. Three such cones lie on a bench at 300-m depth immediately east of Pico Island and have flank slopes of only 10?C20°. We speculate that exceptionally shallow cone slopes here were produced by forced spreading of the erupting columns on reaching the water?Cair density barrier.  相似文献   

The Sunyaev–Zel'dovich temperature of the intracluster medium     

Scott T. Kay  Leila C. Powell  rew R. Liddle  Peter A. Thomas 《Monthly notices of the Royal Astronomical Society》2008,386(4):2110-2114

The relativistic Sunyaev–Zel'dovich (SZ) effect offers a method, independent of X-ray, for measuring the temperature of the intracluster medium (ICM) in the hottest systems. Here, using N -body/hydrodynamic simulations of three galaxy clusters, we compare the two quantities for a non-radiative ICM, and for one that is subject both to radiative cooling and to strong energy feedback from galaxies. Our study has yielded two interesting results. First, in all cases, the SZ temperature is hotter than the X-ray temperature and is within 10 per cent of the virial temperature of the cluster. Secondly, the mean SZ temperature is less affected by cooling and feedback than the X-ray temperature. Both these results can be explained by the SZ temperature being less sensitive to the distribution of cool gas associated with cluster substructure. A comparison of the SZ and X-ray temperatures (measured for a sample of hot clusters) would therefore yield interesting constraints on the thermodynamic structure of the intracluster gas.  相似文献