Mössbauer studies of synthetic and natural micas on the polylithionite-siderophyllite join     

Christian Levillain  Pierre Maurel  Francis Menil 《Physics and Chemistry of Minerals》1981,7(2):71-76

Mössbauer studies of micas on the polylithionite-side-rophyllite join show the existence of a relation between the quadrupole splitting (ΔE _Q) values of Fe²⁺ high spin doublets and both cationic and anionic composition of micas. This linear relation is positive as Li₂O content increases and negative as F content increases. In the lithium iron micas, the inner ferrous quadrupole doublet is assigned to the cis-site M(2), while the outer doublet is assigned to the trans-site M(1). A random distribution of Fe²⁺ is observed in fluorine-rich compositions, while slight enrichment of the M(1) site is noticed in hydroxyl compositions, perhaps due to a more sensitive oxidation in situ in M(2) than M(1) sites. The Mössbauer spectrum of siderophyllite K₂(Fe ₄ ²⁺ Al₂)(Si₄Al₄)O₂₀(OH)₄ shows the presence of only one ferrous doublet, which is assigned to M(2) sites. Hence from Mössbauer data we must consider a clintonite (“xanthophyllite”) structure for this mica. The ordered octahedral layer has two distorted ferrous cis-sites and one, more symmetrical, aluminum trans-site.  相似文献   

Traces d'un pergélisol villafranchien dans les alluvions du sundgau     

Pierre Gangloff 《Geoforum》1981,12(3):273-280

Evidence of villafranchian permafrost has been found at the southern end of the Rhine graben, 20km west of Basel. Two syngenetic ice-wedge casts were discovered in the “alluvions du Sundgau”. From a stratigraphical point of view, these coarse gravels were deposited after the Miocene and before the Günz glaciation. The occurrence of syngenetic periglacial structures shows that they must be of Pleistocene (Villafranchian) age. A SEM study of sand from the infilling of one of the cryogenic structures showed numerous marks of glacial origin on the quartz grains. They are indicative of a pre-Günz glaciation in the Alps. It is suggested that permafrost in villafranchian time developed only on the fringe of the alpine glaciation, but further studies will be needed for a better picture of villafranchian palaeogeography.  相似文献   

A new theory of bed-blending derived from the theory of sampling — Development and full-scale experimental check     

Pierre M. Gy 《International Journal of Mineral Processing》1981,8(3):201-238

  相似文献   

Sedimentary inputs and oxygen uptake by the sediment in Lake Geneva (Switzerland)     

Pierre Hutter  Dr. Claude Lang 《Aquatic Sciences - Research Across Boundaries》1981,43(2):253-264

Sediment cores and sediment traps were collected twice a month in two 35 m deep stations of Lake Geneva (Switzerland). The organic input sedimenting to the bottom is equal to 157 g C m⁻²y⁻¹ in station 1, to 214 g C in station 2. In spite of this difference, the oxygen uptake by the sediment (OUS) is similar in both locations (46–47 g C m⁻²y⁻¹). The oxygen uptake by the matter sedimenting to the bottom (OUSM) is respectively 45 g C m⁻²y⁻¹ and 41 g C in stations 1 and 2. The equivalence between OUS and OUSM implies that most of the sedimented matter arriving to the bottom is directly oxidized at the sediment surface. In station 1, OUS is positively correlated to OUSM, and OUSM is positively correlated to chlorophyll-a concentrations in the water column (0–20 m) one week before sediment sampling. In location 2, OUS is positively correlated to the percentage of organic carbon and nitrogen in the sedimented matter, negatively to its C:N ratio. Increasing allochthonous inputs have a negative influence on benthic respiration. At both sites, OUS is not directly related to macrobenthic biomass or to temperature of bottom water.  相似文献   

Magnetic transition at 30–34 Kelvin in pyrrhotite: insight into a widespread occurrence of this mineral in rocks     

Pierre Rochette  Grard Fillion  Jean-Luc Matti  Marinus J. Dekkers 《Earth and Planetary Science Letters》1990,98(3-4)

A characteristic magnetic transition at 30–34 K is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low-temperature techniques as applied to magnetite and hematite, extended down to liquid helium temperature. A review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals. Unblocking temperature up to 350°C and extreme resistance against AF may be encountered in fine grained pyrrhotite.  相似文献   

The 2 Ga peraluminous magmatism of the Jacobina — Contendas Mirante Belt (Bahia) Brazil): Major and trace-element geochemistry and metallogenic potential     

Michel Cuney  Pierre Sabat  Philippe Vidal  Moacyr M. Marinho  Herbet Conceiao 《Journal of Volcanology and Geothermal Research》1990,44(1-2)

The Jacobina — Contendas Mirante belt represents a Transamazonian (2 Ga), N-S, 500-km long, elongated orogenic domain in the central part of the São Francisco craton, Bahia state. Numerous syntectonic to post-tectonic peraluminous leucogranites were emplaced along the major structures of the belt. Their mineralogical and geochemical and some of their metallogenetic characteristics are very similar to their Hercynian and Himalayan equivalents. However, their average peraluminous index varies from one granitic pluton to another and biotite is, on average, slightly more magnesian in the Transamazonian leucogranites. Higher oxygen fugacity is indicated by the general occurrence of magnetite, the stability of allanite and sometimes epidote in most of the plutons and by biotite chemistry. The peraluminous magmatism of the Jacobina-Contendas Mirante belt results from crustal partial melting during a continental collision event at 2 Ga.Trace-element geochemistry implies variable source composition and/or melting conditions for the different granitic plutons and some different facies within the same plutonic unit. The scarcity of ilmenite, the general occurrence of magnetite, and the relatively low peraluminous index of some of these granites suggest that graphite-beating sediments are not a significantly source material. From their mineralogical and geochemical characteristics, acid meta-igneous rocks such as the Sete Voltas TTG suite of presumed Archaean age, seem to represent a suitable source for these granites.Sn, W, Li, F and Be enrichment of most Transamazonian leucogranites is much weaker than in the mineralized Variscan equivalents. The Caetano-Aliança and Riacho das Pedras granites represent the most specialized granitic bodies. Beryl (emerald), molybdenite and scheelite mineralizations are related to some of these granites which intrude ultrabasic formations: the Campo Formoso and the Carnaiba granites. In many of these granites, uranium content is comparable to values measured in mineralized Hercynian leucogranites. The occurrence of hexavalent uranium minerals, mineralization and episyenitic alteration are favourable criteria for finding Variscan-type uranium ore deposits.  相似文献   

Shelf to basin transition in the Cambrian-Lower Ordovician of Sardinia (Italy) reply     

Anna Gandin  Pierre Courjault-Radé 《International Journal of Earth Sciences》1989,78(2):685-688

  相似文献   

Ritz vectors and generation criteria for mode superposition analysis     

Kuan-Jung Joo  Edward L. Wilson  Pierre Leger 《地震工程与结构动力学》1989,18(2):149-167

A generation procedure of Ritz vectors to control the inclusion of static effect and the number of vectors in mode superposition dynamic analysis is presented. The original algorithm of the Ritz vectors¹⁵ is modified to improve stability in the generation procedure and to include the use of static residual. To reject unimportant Ritz vectors, cut-off criteria, which are based on the participation of mass distribution and spatial load distribution, are proposed. Numerical examples are presented to illustrate the effectiveness of the derived Ritz vectors over the eigenvectors and the performance of the cutoff criteria in the mode superposition dynamic analysis.  相似文献   

Recent dynamics of subarctic dunes as determined by tree-ring analysis of white spruce, Hudson Bay, Québec     

Pierre Marin  Louise Filion   《Quaternary Research》1992,38(3)

The radial-growth patterns of white spruce were studied on a number of trees growing in subarctic dunes along the eastern coast of Hudson Bay to calculate the rates of accumulation, erosion, and migration of cold-climate sand dunes. The average rate of sand accumulation in sheltered dunes (forest sites) was 2.5 to 3.3 cm/yr, which is two to three times lower than in highly exposed dunes with a rate of sedimentation of 7.65 cm/yr. The average erosion rate was 1.4–1.7 cm/yr, about two times lower than the accumulation rate. The migration rate of sheltered dunes was 18 to 30 cm/yr, three to five times lower than for an exposed dune which advanced at a speed of 74 cm/yr. This migration rate established for highly exposed dunes in the Subarctic with tree-ring methods is about 10 times lower than that established for a barchan in the Sahara with other methods.  相似文献   

A critical discussion of numerical models for multiaquifer systems     

Ismael Herrera  Jean Pierre Hennart  Robert Yates 《Advances in water resources》1980,3(4):159-163

Leaky aquifers constitute complicated hydrological structures, whose inclusion in numerical models of hydrological systems is difficult, because of their three-dimensional nature. Methods for treating such systems can be classified as fully three-dimensional and quasi-three-dimensional. The latter have clear numerical advantages when applicable. In this paper a critical discussion of existing quasi-three-dimensional models is presented.  相似文献