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171.
Origin of Fe-rich lherzolites and wehrlites from Tok,SE Siberia by reactive melt percolation in refractory mantle peridotites 总被引:2,自引:2,他引:0
Dmitri?A.?IonovEmail author Ingrid?Chanefo Jean-Louis?Bodinier 《Contributions to Mineralogy and Petrology》2005,150(3):335-353
Lherzolite–wehrlite (LW) series xenoliths from the quaternary Tok volcanic field in the southeastern Siberian craton are distinguished
from the more common lherzolite–harzburgite (LH) series by (a) low Mg numbers (0.84–0.89) at high modal olivine (66–84%) and
(b) widespread replacement of orthopyroxene (0–12%) and spinel by clinopyroxene (7–22%). The LW series peridotites are typically
enriched in Ca, Fe, Mn and Ti, and depleted in Si, Ni and Cr relative to refractory LH series rocks (Mg number ≥0.89), which
are metasomatised partial melting residues. Numerical modelling of Fe–Mg solid/liquid exchange during melt percolation demonstrates
that LW series rocks can form by reaction of host refractory peridotites with evolved (Mg numbers 0.6–0.7), silica-undersaturated
silicate melts at high melt/rock ratios, which replace orthopyroxene with clinopyroxene and decrease Mg numbers. This process
is most likely related to underplating and fractionation of basaltic magma in the shallow mantle, which also produced olivine–clinopyroxene
cumulates found among the Tok xenoliths. 相似文献
172.
173.
Jean-Louis?PaquetteEmail author Philippe?Goncalves Bertrand?Devouard Christian?Nicollet 《Contributions to Mineralogy and Petrology》2004,147(1):110-122
In terranes subject to complex metamorphic evolution, zircon and monazite U-Pb system can record successive growth and/or resetting episodes. Conventional isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) dating of fractions or single grains from conventionally separated zircon and monazite populations may produce inaccurate ages. A new technique combining textural analysis and ID-TIMS dating on single monazite crystals is proposed. This method is applied directly on thin sections with three successive steps comprising (1) a characterisation of textural relationships using electron microprobe analyses and images, (2) extraction by micro-drilling of selected monazites and (3) U-Pb dating of each extracted grain by ID-TIMS. The potential for this in situ dating technique are tested on Ultra High Temperature (UHT) granulites from North-Central Madagascar. Four distinct events on a single thin section were distinguished. The UHT metamorphism was dated at 2.5 Ga, while two retrogression events were dated at 790 and 500 Ma. Finally, a single crystal shielded in quartz seems to preserve a pre-metamorphic age around 2.7 Ga.Editorial responsibility: J. Hoefs 相似文献
174.
The hydrogeomorphological method for delimiting flood risk zones in France was developed some twenty years ago. It is based on a simple principle: the outer limits of a stream's flood plain constitute the outer envelope of past floods. These limits are determined with the use of aerial photographs and field surveys of micro-topography as well as analyses of deposit granulometry and colour. Indications of present or past land use (fields, location and distribution of archaeological sites, houses and farm buildings, roads) are also useful. This field-based method long remained ignored, but being reliable, easy to use and inexpensive, it has now been incorporated into the package of methods recommended by French risk-prevention plans (PPRI). The many recent catastrophes that have occurred over the past fifteen years in the Mediterranean regions of southern France demonstrated both the inadequacy of the hydrological–hydraulic method and the reliability of the hydrogeomorphological method, which can, however, be improved by setting observations for the present period against information on the more ancient Holocene evolution of flood plains. To cite this article: J.-L. Ballais et al., C. R. Geoscience 337 (2005). 相似文献
175.
176.
Dominique Cluzel Delphine Bosch Jean-Louis Paquette Yves Lemennicier Philippe Montjoie René-Pierre Ménot 《Island Arc》2005,14(3):254-271
Abstract In southern New Caledonia, Late Oligocene granodiorite and adamellite are intruded into an ultramafic allochthon emplaced in the Late Eocene period. Previous studies of these granitoids proposed an origin associated with the melting of the underlying continental crust, but our new data show that these high-K to medium-K calc-alkaline granitoids display the geochemical and isotopic features of volcanic arc magmas uncontaminated by crust-derived melts. These magmas were probably generated in a post-Eocene and pre-Miocene subduction, the geophysical traces of which have been detected along the western coast of New Caledonia. Sr, Nd and Pb isotopic ratios indicate derivation from an almost isotopically homogeneous mantle wedge, but in contrast, some variation in trace element ratios uncorrelated to differentiation is indicative of source heterogeneity. Prominent heavy rare earth element (HREE) depletion of some of the younger granitoids may be the result of an equilibrium achieved with garnet-bearing subcrustal material (granulite) found as xenoliths, while a relative Nb, Ta and Hf enrichment, irrespective of crystal fractionation, may be related to either a modest contamination by previously underplated mafic material, heterogeneous hydration of the mantle wedge, or mixing with uplifted Nb-rich mantle. Post-obduction slab break-off can be proposed to have played a role in sublithospheric mantle mixing and the subsequent heterogeneity. The Late Oligocene subduction described here may be tentatively extended southward into northern New Zealand allochthons. 相似文献
177.
Susan E. Kayser Jean-Louis Bougeret Joseph Fainberg Robert G. Stone 《Solar physics》1971,109(1):107-118
The trajectories of 38 type III storms in the interplanetary medium have been deduced from ISEE-3 radio observations and extrapolated back to the Sun to determine the Carrington coordinates of their footpoints. The analysis assumes radial motion of the solar wind, and the trajectories are projected radially back toward the surface for the last few solar radii. To identify the storm sources, the footpoints were compared to a variety of solar features: to the large-scale neutral line at the base of the current sheet, to active regions, to the small-scale neutral lines and H filaments which trace out active regions, and to coronal holes. Most of the footpoints were found to lie near active regions, in agreement with metric storm locations. There is a weak correlation with H filaments, no apparent association with the current sheet, and an anticorrelation with coronal holes. There is a small excess of storms in the leading half of magnetic sectors. 相似文献
178.
The age of the inner core 总被引:1,自引:0,他引:1
Stphane Labrosse Jean-Paul Poirier Jean-Louis Le Mouël 《Earth and Planetary Science Letters》2001,190(3-4):111-123
The energy conservation law, when applied to the Earth’s core and integrated between the onset of the crystallization of the inner core and the present time, gives an equation for the age of the inner core. In this equation, all the terms can be expressed theoretically and, given values and uncertainties of all relevant physical parameters, the age of the inner core can be obtained as a function of the heat flux at the core–mantle boundary and the concentrations in radioactive elements. It is found that in absence of radioactive elements in the core, the age of the inner core cannot exceed 2.5 Ga and is most likely around 1 Ga. In addition, to have an inner core as old as the Earth, concentrations in radioactive elements needed in the core are too high to be acceptable on geochemical grounds. 相似文献
179.
Jean-Pierre Ivaldi Hervé Bellon Pierre Guardia Christian Mangan Carla Müller Jean-Louis Perez Serge Terramorsi 《Comptes Rendus Geoscience》2003,335(4):411-421
Lithostratigraphic and structural framework, chronology and geochemistry of the Tertiary calc-alkaline volcanism of Cap-d'Ail (French Maritime Alps) are specified according to the new data collected during the earthworks of the recent railway tunnel built between Cap-d'Ail and Monaco. Two different magmatic events were dated: the first one, to Palaeogene, the other one, to Neogene. To cite this article: J.-P. Ivaldi et al., C. R. Geoscience 335 (2003). 相似文献
180.
Marwan Alkattan Eric H. Oelkers Jean-Louis Dandurand Jacques Schott 《Chemical Geology》2002,190(1-4):291-302
Dissolution rates of single calcite crystals were determined from sample weight loss using free-drift rotating disk techniques. Experiments were performed at 25 °C in aqueous HCl solutions over the bulk solution pH range −1 to 3 and in the presence of trace concentrations of aqueous NaPO3 and MgCl2. These salts were chosen for this study because aqueous magnesium and phosphate are known to strongly inhibit calcite dissolution at neutral to basic pH. Reactive solutions were undersaturated with respect to possible secondary phases. Neither an inhibition or enhancement of calcite dissolution rates was observed in the presence of aqueous MgCl2 at pH 1 and 3. The presence of trace quantities of NaPO3, which dissociates in solution to Na+ and H2PO4−, decreased the overall calcite dissolution rate at pH≤2. This contrasting behavior could be attributed to the different adsorption behavior of these dissolved species. As calcite surfaces are positively charged in acidic solutions, aqueous Mg2+ may not adsorb, whereas aqueous phosphate, present as either the anion H2PO4− or the neutral species H3PO40, readily adsorbs on calcite surfaces leading to significant dissolution inhibition. 相似文献