Seismic heterogeneity of Mt Etna: structure and activity   总被引：3，自引：0，他引：3  

Alfred Hirn  Alexandre Nercessian  Martine Sapin  Fabrizio Ferrucci  Gérard Wittlinger 《Geophysical Journal International》1991,105(1):139-153

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High to low velocity succession in the upper crust related to tectonic emplacement: Tras os Montes-Galicia (Iberia), Brittany and Limousin (France)     

Alfred Hirn  Luisa Senos  Martine Sapin  Luis Mendes Victor 《Geophysical Journal International》1982,70(1):1-10

Summary. Seismic probing of the upper crust in a catazonal massif in Tras os Montes, Hercynian Iberia, demonstrates the absence of a root towards the lower crust and favours a mechanism of thrust and nappe emplacement. Similar high to low velocity successions in the upper crust are evidenced in particular segments of the Hercynian domain of France. All these occurrences are related to a type region to which a particular meaning has been given in a recent plate tectonics interpretation of the Hercynian orogenesis. This model, implying large-scale nappe displacement and intracrustal thrusts furnishes in turn a general mechanism for the tectonic formation of upper crustal high and low velocity layers of limited extent in orogenic cycles.  相似文献   

Phillipsite formation in nephelinitic rocks in response to hydrothermal alteration at Mount Etinde,Cameroon     

Jacques Etame  Che Emmanuel Suh  Martine Gerard  Paul Bilong 《Chemie der Erde / Geochemistry》2012,72(1):31-37

Fresh nephelinitic rocks and hydrothermally altered rocks at Mount Etinde (Cameroon Volcanic Line, West Africa) have been studied by combined whole rock geochemistry (ICP-MS), mineralogy and mineral chemistry (SEM-EDS, WDS, XRD) techniques. The nephelinites have feldspathoids, clinopyroxene, perovskite and titanomagnetite as the principal minerals in the mode with subsidiary apatite and sphene. The mineralogy of their hydrothermally altered counterparts includes phillipsite, calcite and analcime which are secondary phases developed in response to hydrothermal fluid events. Correspondingly, the bulk rock geochemical data show elevated SiO₂, CaO, Na₂O and K₂O concentrations with increasing alteration and Al₂O₃ and Fe₂O₃ depletion while MgO, MnO and TiO₂ concentrations are largely unaffected. The nephelinites also have high concentrations of LILLE, HFSE and REE and upon hydrothermal alteration they show an enrichment of LREE and MREE over HREE. Phillipsite is the principal alteration mineral in the rocks and it occurs along cracks, vesicles and also forms alteromorphs after feldspathoids. The Ce content of these categories of phillipsite varies. Phillipsite along cracks is richer in Ce while phillipsite associated with calcite has lower Ce concentration and the phillipsite alteromorphs very little or no Ce. Various stages of fluid circulation are proposed hereby to explain the variations in phillipsite generation and composition.  相似文献   

Raman spectroscopic properties and Raman identification of CaS‐MgS‐MnS‐FeS‐Cr2FeS4 sulfides in meteorites and reduced sulfur‐rich systems     

Caroline Avril  Valérie Malavergne  Razvan Caracas  Brigitte Zanda  Bruno Reynard  Emeline Charon  Ema Bobocioiu  Fabrice Brunet  Stephan Borensztajn  Sylvain Pont  Martine Tarrida  François Guyot 《Meteoritics & planetary science》2013,48(8):1415-1426

Raman spectra were acquired on a series of natural and synthetic sulfide minerals, commonly found in enstatite meteorites: oldhamite (CaS), niningerite or keilite ((Mg,Fe)S), alabandite (MnS), troilite (FeS), and daubreelite (Cr₂FeS₄). Natural samples come from three enstatite chondrites, three aubrites, and one anomalous ungrouped enstatite meteorite. Synthetic samples range from pure endmembers (CaS, FeS, MgS) to complex solid solutions (Fe, Mg, Ca)S. The main Raman peaks are localized at 225, 285, 360, and 470 cm^?1 for the Mg‐rich sulfides; at 185, 205, and 285 cm^?1 for the Ca‐rich sulfides; at 250, 370, and 580 cm^?1 for the Mn‐rich sulfides; at 255, 290, and 365 cm^?1 for the Cr‐rich sulfides; and at 290 and 335 cm^?1 for troilite with, occasionally, an extra peak at 240 cm^?1. A peak at 160 cm^?1 is present in all Raman spectra and cannot be used to discriminate between the different sulfide compositions. According to group theory, none of the cubic monosulfides oldhamite, niningerite, or alabandite should present first‐order Raman spectra because of their ideal rocksalt structure. The occurrence of broad Raman peaks is tentatively explained by local breaking of symmetry rules. Measurements compare well with the infrared frequencies calculated from first‐principles calculations. Raman spectra arise from activation of certain vibrational modes due to clustering in the solid solutions or to coupling with electronic transitions in semiconductor sulfides.  相似文献   

Impact of gamma densitometry on the luminescence signal of quartz grains     

Martine J. J. Couapel  Christopher J. Bowles 《Geo-Marine Letters》2006,26(1):1-5

Most of the marine sediment cores collected in the past 10 years by the ODP and IMAGES programs have been processed using a multi-sensor core logger (MSCL, Geotek). This system estimates the density of sediment using the γ-ray attenuation of a ¹³⁷Cs source. To date, optically stimulated luminescence (OSL) dating has not been applied to sediments from cores treated in this way, because of the possible impact of this exposure on the existing luminescence signal. We have investigated the effect of such γ-ray irradiation by test exposure, measurement and estimation, and conclude that the usual ¹³⁷Cs exposure from γ-ray attenuation densitometry has no impact on the luminescence signal of quartz grains in sediment cores. For longer exposure to the ¹³⁷Cs source, a formula is provided to calculate the received dose. This result will permit the OSL dating technique to be applied to the voluminous body of marine cores already collected and processed by MSCL.  相似文献   

Export flux of particles at the equator in the western and central Pacific ocean     

Martine Rodier  Robert Le Borgne 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)

Export of particles was studied at the equator during an El Nin˜o warm event (October 1994) as part of the French ORSTOM/FLUPAC program. Particulate mass, carbon (organic and inorganic) (C), nitrogen (N), and phosphorus (P) export fluxes were measured at the equator in the western and central Pacific during two 6–7 day-long time-series stations located in the warm pool (TS-I at 0°, 167°E) and in the equatorial HNLC situation (TS-II at 0°, 150°W), using drifting sediment traps deployed for 48 h at four depths (between, approximately, 100 and 300 m).The particulate organic carbon (POC) fluxes at the base of the euphotic zone (0.1 % light level), were approximately four times lower at TS-I than at TS-11 (4.1 vs. 17.0 mmol C m^-2 day^-1). Conversely, fluxes measured at 300 m were similar at both sites (3.6vs. 3.7 mmol C m⁻² day⁻¹ at TS-I and TS-11, respectively). This change in export fluxes was in good agreement with food-web dynamics in the euphotic zone characterized by an increase in plankton biomasses and metabolic rates and a shift towards larger size from TS-1 to TS-II. The POC flux profiles indicated high remineralization (up to 78%) of the exported particles at TS-II, between 100 and 200 m in the Equatorial Undercurrent. According to zooplankton ingestion estimates from 100 – 300 m, 60% of this POC loss could be accounted for by zooplankton grazing. At TS-I, no marked increase of flux with depth was observed, and we assume that loss of particles was compensated by in-situ particle production by zooplankton. Fluxes of particulate nitrogen and phosphorus followed the same general patterns as the POC fluxes. The elemental and pigment composition of the exported particles was not very different between the two stations. In particular, the POCYN flux molar ratio at the base of the euphotic zone was low, 6.9 and 6.2 at TS-1 and TS-II, respectively.For particulate inorganic carbon (mainly carbonate) flux, values at the base of the euphotic zone averaged 0.9 mmol C m-2 day-1 at TS-I and 2.3 mmol C m-2 day-1 at TS-11 (corresponding to a 2.6-fold increase) and showed low depth changes at both stations.POC export flux (including active flux associated with the interzonal migrants) at the 0.1 % light level depth represented only 8% of primary production (1°C uptake) measured at TS-1 and 19% at TS-II. For the time and space scales considered in the present study, new primary production, as measured by the 15N method, was in good agreement with the total export flux in the HNLC situation, thus leading to negligible dissolved organic carbon (DOC) or nitrogen (DON) losses from the photic zone. Conversely, export flux was found to be only 50% (C units) and 60% (N) of new production in the oligotrophic system, either because of an overestimation by the 15N method or of a significant export of DOC and DON.Comparison with other oceanic regions shows that export flux in the warm pool was within the same range as in the central gyres. On the other hand, comparison with EgPac data in the central Pacific suggests that there is no straightforward relation between the magnitude of the export and surface nitrate concentrations.  相似文献   

The Western Boundary of the Equatorial Pacific Upwelling: Some Consequences of Climatic Variability on Hydrological and Planktonic Properties     

Martine Rodier  Gérard Eldin  Robert Le Borgne 《Journal of Oceanography》2000,56(4):463-471

The longitude of the western limit of the equatorial Pacific upwelling is a key parameter for studies of carbon budget and pelagic fisheries variability. Although it is well defined at the surface on the equator by a salinity front and a sharp variation of the partial pressure of CO₂, data from two equatorial cruises make it clear that this hydrological limit does not necessarily coincide with the boundary of the nitrate and chlorophyll enriched area. In January-February 1991 during a non-El Niño period, when trade winds and the South Equatorial current (SEC) were favorable to upwelling, the two limits were at the same longitude. Conversely, in September-October 1994 during El Niño conditions, when the equatorial upwelling had stopped, the nitrate and chlorophyll enriched zone was found a few degrees of longitude east of the hydrological boundary (5.5° at the surface and 2.5° for the 50 m upper layer), whereas no such offset was observed for zooplankton biomass. A simple model, based on the HNLC (High Nutrient - Low Chlorophyll) ecosystem functioning, was initialized with nitrate uptake measurements and estimates of upwelling break duration. The model results support the hypothesis that zonal separation of the limits arises from biological processes (i.e. nitrate uptake and phytoplankton grazing) achieved during that upwelling break.  相似文献   

Unprecedented risk of spring frost damage in Switzerland and Germany in 2017     

Yann Vitasse  Martine Rebetez 《Climatic change》2018,149(2):233-246

Spring frosts are feared by farmers, fruit growers, and wine growers as they can cause significant damage to crops when they occur during the development of the plants. In the second half of April 2017, following a very warm period that had caused premature vegetation growth, a cold air mass from the Arctic penetrated central and western Europe, causing severe damage to natural and cultivated vegetation over broad areas. Here, we analyze how exceptional this event was in Switzerland and Germany in relation to the accumulated growing degree days (GDD), used as a proxy for plant phenology advancement. Although this damaging frost was not the latest on record in terms of calendar days, our results show that it was, in some regions, unprecedented in relation to the accumulated warmth during the preceding period, at least since the beginning of instrumental temperature records (1864). Our results also highlight how global warming has considerably increased the number of days with mean temperature above 5 °C in late winter and early spring, especially since 1970 (+?16.8?±?4.7 °C days decade^?1). However, in spite of earlier spring phenology due to climate warming, our results suggest that the risk of damaging frost events to vegetation has remained unchanged over the last 150 years in lowlands of Switzerland and Germany, due to the concurring earlier occurrence of the last potentially damaging frosts (about ??20 days since 1864). Our analyses reveal therefore that the April 2017 damaging frost was a true outlier in terms of risk of frost damage to plants.  相似文献   

Shorter snow cover duration since 1970 in the Swiss Alps due to earlier snowmelt more than to later snow onset   总被引：1，自引：0，他引：1  

Geoffrey Klein  Yann Vitasse  Christian Rixen  Christoph Marty  Martine Rebetez 《Climatic change》2016,139(3-4):637-649

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New data on the kinetics of the dissolution of alkali feldspars at 200°C in CO₂ charged water     

Martine Lagache 《Geochimica et cosmochimica acta》1976,40(2):157-161

The kinetics of the dissolution of a (Na. K) sanidine in CO₂-charged water, were studied experimentally at 200°C as a function of the surface area s and of the time t. The molalities of Na⁺ and K⁺ have been plotted against the product st. As for albite and adularia (Lagache, Bull. Soc. Fr. Minéral. Cristallogr. 88, 223–253, 1965), the rates of dissolution of Na² and K⁺ are smooth continuous functions of st, which implies that they are controlled by the composition of the solution.The comparison between the dissolution of pure sodic or potassic feldspars and that of an intermediate feldspar shows that the sanidine dissolves as if it were composed of albite and K-feldspar grains in the proportions corresponding to its composition.Theoretical considerations presented by Helgeson (Geochim. Cosmochim. Acta35, 421–169, 1971; The Feldspars, pp. 184–217, 1972) and Pa?es (Geochim. Cosmochim. Acta37, 2641–2663, 1973) are reviewed: both had suggested, arguing from my first experimental results, that the dissolution could be described by a process of diffusional mass transfer through a surface layer of reaction products.The present experiments do not agree with such an interpretation of the mechanism of dissolution.  相似文献