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1.
Monique Seyler J. -P. Lorand H. J. B. Dick M. Drouin 《Contributions to Mineralogy and Petrology》2007,153(3):303-319
ODP Leg 209 Site 1274 mantle peridotites are highly refractory in terms of lack of residual clinopyroxene, olivine Mg# (up
to 0.92) and spinel Cr# (∼0.5), suggesting high degree of partial melting (>20%). Detailed studies of their microstructures
show that they have extensively reacted with a pervading intergranular melt prior to cooling in the lithosphere, leading to
crystallization of olivine, clinopyroxene and spinel at the expense of orthopyroxene. The least reacted harzburgites are too
rich in orthopyroxene to be simple residues of low-pressure (spinel field) partial melting. Cu-rich sulfides that precipitated
with the clinopyroxenes indicate that the intergranular melt was generated by no more than 12% melting of a MORB mantle or
by more extensive melting of a clinopyroxene-rich lithology. Rare olivine-rich lherzolitic domains, characterized by relics
of coarse clinopyroxenes intergrown with magmatic sulfides, support the second interpretation. Further, coarse and intergranular
clinopyroxenes are highly depleted in REE, Zr and Ti. A two-stage partial melting/melt–rock reaction history is proposed,
in which initial mantle underwent depletion and refertilization after an earlier high pressure (garnet field) melting event
before upwelling and remelting beneath the present-day ridge. The ultra-depleted compositions were acquired through melt re-equilibration
with residual harzburgites.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
2.
Dissolved Ba, Cd, Co, Mn, Mo, Ni, Rb, Sb, Sr, U and V were measured in the Oubangui river (Central African Republic) during a complete flood period. The dissolved concentrations vary by factors ranging from 1.4 to 8.2 as a function of river discharge: Sr, Ba, Rb and Mo concentrations decrease with rising stage; Ni, U, Sb, Cd, V and Mn concentrations increase with rising stage. These distributions are explained by a mixing of quick flow, mostly surface runoff with delayed flow, mostly groundwater. The dual origin of stream waters is demonstrated by the major element ratios, which are close to a silicate end-member during the high-flow period and trend towards a carbonate end-member during the low-flow period. Moreover, geological heterogeneities in the Oubangui basin may play a role in the variation of concentrations observed at the basin outlet. The previously indicated presence of a subsurface carbonate sequence in the lower part of the basin is confirmed. Cd, V, Mn and Co show peak concentrations during decreasing stage. We suggest that biological processes such as release from phytoplanktonic material and dissolution of oxides or carbonate phases may explain this maximum. 相似文献
3.
Two peridotite suites collected by submersible in the equatorial Atlantic Ocean (Hekinian et al., 2000) were studied for textures, modes, and in situ major and trace element compositions in pyroxenes. Dive SP12 runs along the immersed flank of the St. Peter and Paul Rocks islets where amphibole-bearing, ultramafic mylonites enriched in alkalies and incompatible elements are exposed (Roden et al., 1984), whereas dive SP03 sampled a small intra-transform spreading centre situated about 370 km east of the St. Peter and Paul Rocks. Both suites are characterized by undeformed, coarse-grained granular textures typical of abyssal peridotites, derived from residual mantle after ～ 15% melting of a DMM source, starting in the garnet stability field. Trace element modelling, textures and lack of mineral zoning indicate that the residual peridotites were percolated, reacted and refertilized by ～ 2.6% partially aggregated melts in the uppermost level of the melting region. This relatively large amount of refertilization is in agreement with the cold and thick lithosphere inferred by previous studies. Freezing of trapped melts occurred as the peridotite entered the conductive layer, resulting in late-stage crystallization of olivine, clinopyroxene, spinel, ± plagioclase. Chondrite-normalized REE patterns in clinopyroxenes from SP03 indicate that they last equilibrated with (ultra-) depleted partial melts. In contrast, REE concentrations in clinopyroxenes from SP12 display U and S shaped LREE-enriched patterns and the calculated compositions of the impregnating melts span the compositional range of the regional basalts, which vary from normal MORB to alkali basalt sometimes modified by chromatographic fractionation with no, or very limited, mineral reaction. Thus the mylonitic band forming the St. Peter and St. Paul Rocks ridge is not a fragment of subcontinental lithospheric mantle left behind during the opening of the Central Atlantic, nor the source of the alkaline basalts as previously suggested. Rather, dive SP12 sampled residual peridotites of normal MORB mantle that were located close to channels transporting alkali basalts. Reacted melts escaping from these channels, infiltrated, and locally equilibrated with, the peridotite matrix by ion exchange reactions. Relicts of the source of the alkaline basalts were not sampled but our study suggests that it was a component of the MORB mantle underlying the St. Paul region. 相似文献
4.
G. Figueres J.M. Martin M. Meybeck P. Seyler 《Estuarine, Coastal and Shelf Science》1985,20(2):183-203
Concentrations of mercury were determined for the waters, suspended matter and sediments of the Tagus and of major French estuaries.The Tagus estuary is one of the most contaminated by mercury derived from the outfalls of a chloralkali plant and from other industrial sources. In deposited sediments the median level, 1·0 μg Hg g?1, is twenty times higher than the natural background and Hg contents depend on the sediment grain-size, age and the distance from waste-outfalls. Suspended matter is more regularly and highly contaminated (median value: 4·5 μg Hg g?1). In the French estuaries Hg levels in the suspended material decrease with salinity due to dilution and/or remobilization processes. In June 1982, in the Loire estuary, high values of Hg are observed in the middle estuary and attributed to urban and industrial sources.In the Tagus estuary, the general distribution of total dissolved Hg confirms the contamination: it increases seaward from 10 ng 1?1 in the river to 80 ng 1?1 in the estuary outlet. The dissolved Hg is almost totally organic in the river, inorganic in the middle estuary due to inorganic Hg effluents and again organic in the lower estuary. This variation is related to the dissolved organic carbon values. The dissolved Hg levels in the Loire Estuary (5–300 ng 1?1) are much higher than in the Gironde estuary (3–6 ng 1?1) and of the same order as those observed in the Tagus estuary. 相似文献
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6.
Dieudonné Bitom Boris Volkoff Anicet Beauvais Frédérique Seyler Paul-Désiré Ndjigui 《Comptes Rendus Geoscience》2004,336(13):1161-1170
Analysis of landscapes and soil covers from the outer to the inner part of a watershed in the South-Cameroon rainforest zone, characterized by important remnants of inherited ferricretes and stable hydrostatic base levels, indicates that the development of present landforms has not involved significant erosion by slope retreat because of the relative preservation of downslope residual ferricrete and that soil covers have vertically decayed under in situ geochemical process. To cite this article: D. Bitom et al., C. R. Geoscience 336 (2004). 相似文献
7.
Amazonian floodplain water balance based on modelling and analyses of hydrologic and electrical conductivity data 
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下载免费PDF全文 Marie‐Paule Bonnet Sébastien Pinel Jérémie Garnier Julie Bois Géraldo Resende Boaventura Patrick Seyler David Motta Marques 《水文研究》2017,31(9):1702-1718
In the Amazon basin, floodplains form a complex mosaic of freshwater systems with differing morphologies, resulting in varied inundation patterns and heterogeneous chemical and ecological characteristics. In this study, we focused on the Janauacá floodplain, a medium‐sized system (786 km2, including the local watershed) located along the Solimões River. Based on in situ and satellite observations acquired from November 2006 to November 2011, we computed water fluxes between the mainstream and the floodplain and examined the temporal dynamics of floodplain storage from river flooding, rainfall, runoff, and exchanges with groundwater through bank seepage for the 5 years from 2006 to 2011. The mainstream was the main input of water to the flooded area, accounting on average for 93% of total water inputs by the end of the water year. Direct precipitation and runoff from uplands contributed less than or equal to 5% and 10%, respectively. The seepage contribution was less than 1%. Model uncertainties, evaluated using Monte Carlo analysis of the input data and model parameters, showed that all water fluxes were relatively well constrained except for outflow through seepage, which had a standard deviation across simulations greater than 60%. The water balance computation was verified using electrical conductivity as an assumed non‐reactive tracer. Except during periods of very low water, the simulated and measured conductivities agreed well. Moreover, conductivity data analysis confirmed that the Janauacá system can be considered homogeneous in terms of electrical conductivity for filling percentages equal to or greater than 40% (i.e., when the water level is above 19.5 m, generally from April to August) but presented large heterogeneities during the rest of the hydrological cycle. 相似文献
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9.
Monitoring Continental Surface Waters by Satellite Altimetry 总被引：4，自引：1，他引：3
Stéphane Calmant Frédérique Seyler Jean François Cretaux 《Surveys in Geophysics》2008,29(4-5):247-269
The monitoring of continental water stages is a requirement for meeting human needs and assessing ongoing climatic changes. However, regular gauging networks fail to provide the information needed for spatial coverage and timely delivery. Although the space missions discussed here were not primarily dedicated to hydrology, 18 years of satellite altimetry have furnished complementary data that can be used to create hydrological products, such as time series of stages, estimated discharges of rivers or volume change of lakes, river altitude profiles or leveling of in situ stations. Raw data still suffer uncertainties of one to several decimeters. These require specific reprocessing such as waveform retracking or geophysical correction editing; much work still remains to be done. Besides, measuring the flow velocity appears feasible owing to SAR interferometer techniques. Inundated surfaces, and the time variations of their extent, are currently almost routinely computed using satellite imagery. Thus, the compilation of the continuous efforts of the scientific community in these various investigative directions, such as recording from space the discharges of rivers or the change in water volume stored in lakes, can be foreseen in the near future. 相似文献
10.
Didier?LaporteEmail author Michael?J.?Toplis Monique?Seyler Jean-Luc?Devidal 《Contributions to Mineralogy and Petrology》2004,146(4):463-484
A new technique that allows extraction of liquids from peridotite at degrees of melting as low as 0.2 wt% is presented. Microfractures that formed in the graphite sample container at the beginning of the experiments were used as traps for the liquid phase. Glass-filled cracks (or 'microdikes') unaffected by quench crystallisation were produced in all experiments and were analysed using standard electron microprobe techniques. Reversal experiments demonstrated that, at moderate degrees of melting (4.4 and 6.5 wt%), the segregated liquid was in equilibrium with the neighbouring peridotite. At very low degrees of melting (0.3 wt%), the liquid in the microdikes failed to fully equilibrate with the peridotite after 5 days and the sandwich technique was used in combination with the microdike technique to approach more closely the equilibrium composition of near-solidus partial melts. The microdike technique was used to study melting of a depleted peridotite at 1 GPa and 1,220 to 1,360 °C.Editorial responsibility: T.L. Grove 相似文献