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971.
Bernard D. Zetler 《Marine Geodesy》2013,36(3):237-248
Abstract The tides at Port Mansfield are so small (mean diurnal range of about 2 cm) that they are nearly lost in a noisy (meteorological) continuum. Nevertheless, a precise tidal analysis is necessary to provide the data for a determination of the elevation of mean high water, the boundary between private and state ownership in an oil‐producing area with a very flat terrain. Although response tidal analysis has been shown to be somewhat superior to classical harmonic analysis in various previous tests, no advantage is found in these circumstances of extremely low sighal‐to‐noise ratio. 相似文献
972.
Bernard Charlier Olivier Namur Simon Malpas Cédric de Marneffe Jean-Clair Duchesne Jacqueline Vander Auwera Olivier Bolle 《Lithos》2010,117(1-4):119-134
The late-Proterozoic Allard Lake ilmenite deposit is located in the Havre-Saint-Pierre anorthosite complex, part of the allochtonous polycyclic belt of the Grenville Province. Presently the world's largest Fe–Ti oxide deposit, it had a pre-mining amount in excess of 200 Mt at grades over 60 wt.% hemo-ilmenite. The main ore body is a funnel-shaped intrusion, measuring 1.03 × 1.10 km and 100–300 m-thick. Two smaller bodies are separated by faults and anorthosite. The ore is an ilmenite-rich norite (or ilmenitite) made up of hemo-ilmenite (Hem22.6–29.4, 66.2 wt.% on average), andesine plagioclase (An45–50), aluminous spinel and locally orthopyroxene. Whole-rock chemical compositions are controlled by the proportions of ilmenite and plagioclase ± orthopyroxene which supports the cumulate origin of the deposit. Ore-forming processes are further constrained by normal and reverse fractionation trends of Cr concentration in cumulus ilmenite that reveal multiple magma emplacements and alternating periods of fractional crystallization and magma mixing. Mixing of magmas produced hybrids located in the stability field of ilmenite resulted in periodic crystallization of ilmenite alone. The unsystematic differentiation trends in the Allard Lake deposit, arising from a succession of magma pulses, hybridisation, and the fractionation of hemo-ilmenite alone or together with plagioclase suggest that the deposit formed within a magma conduit. This dynamic emplacement mechanism associated with continuous gravity driven accumulation of Fe–Ti oxides and possibly plagioclase buoyancy in a fractionating ferrobasalt explains the huge concentration of hemo-ilmenite. The occurrence of sapphirine associated with aluminous spinel and high-alumina orthopyroxene (7.6–9.1 wt.% Al2O3) lacking exsolved plagioclase supports the involvement of a metamorphic overprint during the synchronous Ottawan orogeny, which is also responsible for strong textural equilibration and external granule of exsolved aluminous spinel due to slow cooling. 相似文献
973.
Bathymetric and sub-bottom acoustic data were collected in Laguna San Rafael, Chile, to determine sediment yields during the Little Ice Age advance and subsequent retreat of San Rafael Glacier. The sediment volumes and subaqueous landforms imaged are used to interpret the proglacial dynamics and estimate erosion rates from a temperate tidewater glacier over a complete advance-retreat cycle. Sediment yields from San Rafael Glacier averaged 2.7 × 107 m3/a since the end of the Little Ice Age, circa AD 1898, corresponding to average basin-wide erosion rates of 23 ± 9 mm/a; the highest erosion rates, 68 ± 23 mm/a, occurred at the start of the retreat phase, and have since been steadily decreasing. Erosion rates were much lower during glacial advance, averaging at most 7 mm/a, than during retreat. Such large glacial sediment yields over two centuries of advance and retreat suggest that the contribution of sediments stored subglacially cannot account for much of the sediment being delivered to the terminus today. The detailed sub-bottom information of a proglacial lagoon yields important clues as to the timing of erosion, deposition and transfer of glacigenic sediments from orogens to the continental shelves, and the influence of glacier dynamics on this process. 相似文献
974.
Magnesium isotopic composition of the Earth and chondrites 总被引:3,自引:0,他引:3
Fang-Zhen Teng Wang-Ye Li Shan Ke Bernard Marty Shichun Huang Ali Pourmand 《Geochimica et cosmochimica acta》2010,74(14):4150-74
To constrain further the Mg isotopic composition of the Earth and chondrites, and investigate the behavior of Mg isotopes during planetary formation and magmatic processes, we report high-precision (±0.06‰ on δ25Mg and ±0.07‰ on δ26Mg, 2SD) analyses of Mg isotopes for (1) 47 mid-ocean ridge basalts covering global major ridge segments and spanning a broad range in latitudes, geochemical and radiogenic isotopic compositions; (2) 63 ocean island basalts from Hawaii (Kilauea, Koolau and Loihi) and French Polynesia (Society Island and Cook-Austral chain); (3) 29 peridotite xenoliths from Australia, China, France, Tanzania and USA; and (4) 38 carbonaceous, ordinary and enstatite chondrites including 9 chondrite groups (CI, CM, CO, CV, L, LL, H, EH and EL).Oceanic basalts and peridotite xenoliths have similar Mg isotopic compositions, with average values of δ25Mg = −0.13 ± 0.05 (2SD) and δ26Mg = −0.26 ± 0.07 (2SD) for global oceanic basalts (n = 110) and δ25Mg = −0.13 ± 0.03 (2SD) and δ26Mg = −0.25 ± 0.04 (2SD) for global peridotite xenoliths (n = 29). The identical Mg isotopic compositions in oceanic basalts and peridotites suggest that equilibrium Mg isotope fractionation during partial melting of peridotite mantle and magmatic differentiation of basaltic magma is negligible. Thirty-eight chondrites have indistinguishable Mg isotopic compositions, with δ25Mg = −0.15 ± 0.04 (2SD) and δ26Mg = −0.28 ± 0.06 (2SD). The constancy of Mg isotopic compositions in all major types of chondrites suggest that primary and secondary processes that affected the chemical and oxygen isotopic compositions of chondrites did not significantly fractionate Mg isotopes.Collectively, the Mg isotopic composition of the Earth’s mantle, based on oceanic basalts and peridotites, is estimated to be −0.13 ± 0.04 for δ25Mg and −0.25 ± 0.07 for δ26Mg (2SD, n = 139). The Mg isotopic composition of the Earth, as represented by the mantle, is similar to chondrites. The chondritic composition of the Earth implies that Mg isotopes were well mixed during accretion of the inner solar system. 相似文献
975.
Catherine Larose Aurélien Dommergue Martine De Angelis Bernard Averty Nicolas Soumis Christophe Ferrari 《Geochimica et cosmochimica acta》2010,74(22):6263-6275
Seasonal snow is an active media and an important climate factor that governs nutrient transfer in Arctic ecosystems. Since the snow stores and transforms nutrients and contaminants, it is of crucial importance to gain a better understanding of the dynamics of contaminant cycling within the snowpack and its subsequent release to catchments via meltwater. Over the course of a two-month field study in the spring of 2008, we collected snow and meltwater samples from a seasonal snowpack in Ny-Ålesund, Norway (78°56′N, 11°52′E), which were analyzed for major inorganic ions and some organic acids, as well as total, dissolved, bioavailable mercury (THg, DHg, BioHg, respectively) and monomethylmercury (MMHg) species. We observe a seasonal gradient for ion concentrations, with surface samples becoming less concentrated as the season progressed. A significant negative correlation between BioHg and MMHg was observed in the snowpack. MMHg was positively and significantly correlated to methanesulfonate concentrations. Based on these results, we propose a new model for aerobic methylation of mercury involving species in the dimethylsulfoniopropionate cycle. 相似文献
976.
977.
Damien Sous Frédéric Bouchette Erik Doerflinger Samuel Meulé Raphael Certain Gwladys Toulemonde Benjamin Dubarbier Bernard Salvat 《地球表面变化过程与地形》2020,45(12):3042-3054
The topographical complexity of coral reefs is of primary importance for a number of hydrodynamical and ecological processes. The present study is based on a series of high-resolution seabottom elevation measurements along the Maupiti Barrier Reef, French Polynesia. Several statistical metrics and spectral analysis are used to characterize the spatial evolution of the coral geometrical structure from the reef crest to the backreef. A consistent fractal-like power law exists in the spectral density of bottom elevation for length scales between 0.1 and 7 m, while at larger scale, the reef structure shows a different pattern. Such a fine characterization of the reef geometrical structure provides key elements to reconstruct the reef history, to improve the representation of reef roughness in hydrodynamical models and to monitor the evolution of coral reef systems in the context of global change. © 2020 John Wiley & Sons, Ltd. 相似文献
978.
Smirnov V. B. Ponomarev A. V. Stanchits S. A. Potanina M. G. Patonin A. V. Dresen G. Narteau C. Bernard P. Stroganova S. M. 《Izvestiya Physics of the Solid Earth》2019,55(1):124-137
Izvestiya, Physics of the Solid Earth - Laboratory experiments on studying the aftershock regime are carried out on sandstone specimens at different levels of axial loading and uniform compression... 相似文献
979.
It is proposed that the observed differences between odd and even solar cycles are a consequence of the nonlinear interactions that provide the stabilizing mechanism for the cycle's amplitude. If, for example, the magnetic field is larger than average for a given cycle (say odd), the nonlinear feedback mechanism can generate a magnetic field that is smaller than average for the next cycle (even), and then one that is larger than average for the following cycle (odd), etc. As a consequence the odd cycles have larger amplitudes than even cycles. A very simply model having a nonlinear interaction that reproduces this behavior is discussed. 相似文献
980.