Mantle xenoliths édité par P. H. Nixon, 1987

Mével Catherine. Mantle xenoliths édité par P. H. Nixon, 1987. In: Bulletin de Minéralogie, volume 111, 5, 1988. p. 553

William Julius Wilson, Les oubliés de l'Amérique, 1994, tr. Ivan Ermakoff. Titre original «The truly disadvantaged», 1987

Mével Catherine. William Julius Wilson, Les oubliés de l'Amérique, 1994, tr. Ivan Ermakoff. Titre original «The truly disadvantaged», 1987. In: Les Annales de la recherche urbaine, N°67, 1995. Densités et espacements. pp. 150-151

La participation : entre construction d’un pouvoir et accomplissement d’un devoir. Les corporations de développement communautaire et le développement social urbain

Les politiques américaine et française en direction des zones urbaines défavorisées sont conduites à travers des formules d’action qui divergent par leurs modalités organisationnelles et leurs objectifs stratégiques, mais se rejoignent par le rôle qu’elles accordent à la participation des habitants. Cet article propose une comparaison entre la formule américaine des corporations de développement communautaire (CDC) et la formule française du développement social urbain (DSU). Distincts par leurs structures et par leurs ambitions, les deux dispositifs se rapprochent toutefois par l’égale insistance qu’ils mettent sur la nécessité de la participation des habitants. La comparaison confronte les acceptions données à celle-ci, éclairant le cas français par les concepts usités outre-Atlantique.While American and French development policies in poor urban areas differ in their organisational details and strategic objectives, they converge around the notion that residents should participate. This article compares the American use of community development corporations and France’s programme for urban social development. Despite different structures and goals, the two policy instruments resemble each other in their emphasis on community participation. The comparison clarifies the French system by employing concepts in use on the other side of the Atlantic

Jadeite-kosmochlor solid solution and chromian sodic amphiboles in jadeitites and associated rocks from Tawmaw (Burma)

Jadeitites from Tawmaw (Burma) and associated amphibolites display chromian pyroxene — and amphibole-bearing parageneses, formed during a high pressure — low temperature metamorphic event. Sodic pyroxene compositions confirm the occurrence of kosmochlor in terrestrial rocks ; they show a wide range of solid solution between pure jadeite and kosmochlor 85, but suggest the existence of a miscibility gap between Ko25 and Ko50 under these metamorphic conditions. The sodic amphiboles, katophorite, glaucophane and eckermannite, contain up to 10 % Cr2O3. These exceptional compositions were formed in a particular chemical environment resulting from metasomatic reaction between an albitite dyke containing chromite xenocrysts and the enclosing serpentinites during metamorphism.Les jadéitites de Tawmaw (Birmanie) et les amphibolites associées présentent des paragenèses à pyroxènes et amphiboles sodiques chromifères, formées pendant un épisode de métamorphisme de haute pression — basse température. Les compositions des pyroxènes sodiques confirment l'existence de kosmochlor dans les roches terrestres. Elles montrent une large extension des solutions solides entre jadéite et kosmochlor 85 mais suggèrent toutefois l'existence d'une lacune de miscibilité entre Ko25 et Ko50 dans ces conditions de métamorphisme. Les amphiboles sodiques, katophorite, glaucophane et eckermannite, contiennent jusqu'à 10 % de Cr2O3. Ces compositions exceptionnelles ont pu se former dans un environnement chimique particulier résultant d'une réaction métasomatique au contact entre un filon d'albitite contenant des xénocristaux de chromite, et la serpentinite encaissante, pendant le métamorphisme.Mével Catherine, Kienast Jean-Robert. Jadeite-kosmochlor solid solution and chromian sodic amphiboles in jadeitites and associated rocks from Tawmaw (Burma). In: Bulletin de Minéralogie, volume 109, 6, 1986. pp. 617-633

Evidence for major-element heterogeneity in the mantle source of abyssal peridotites from the Southwest Indian Ridge (52° to 68°E)

International audienceA suite of 53 samples of mantle spinel lherzolites and harzburgites dredged at 13 sites between 52°E and 68°E along the Southwest Indian Ridge has been studied for petrography and mineral major element chemistry. Results show that the residual mantle beneath this very slow-spreading/cold ridge is strongly heterogeneous in modal and mineral compositions at local and regional scales and underwent greater extents of melting than predicted by melting model and by compositions of the basalts dredged with the peridotites. Along-axis, the peridotite compositional variability defines a concave pattern with increasing depletion at both ends of the studied section (e.g., approaching Rodrigues Triple Junction to the East and Gallieni fracture zone to the west) that cannot be matched with the basalt compositions. Clinoyroxenes reflect depleted compositions (low modal abundances, high Cr and Mg, low Ti contents) but are paradoxally enriched in jadeite component, a feature that distinguishes these peridotites from common abyssal peridotites. Textural data show that major depletion in basaltic components and pyroxene Na enrichment are early features of the studied peridotites. In most samples, Na is nevertheless correlated with Ti suggesting that initial clinopyroxenes had high Na/Ti contents. Samples at both ends of the studied area have even higher Na/Ti ratios because of higher Na enrichment and higher Ti depletion, indicating metasomatic interaction. We conclude that along-axis compositional variations characterizing these peridotites are primary controlled by major element heterogeneity in the initial mantle, that have been preserved because of low degrees of melting beneath the Southwest Indian Ridge

GEOTECTONIC SIGNIFICANCE OF GNEISSIC AMPHIBOLITES FROM THE VEMA FRACTURE ZONE, EQUATORIAL MID-ATLANTIC RIDGE

International audienceA large collection of gneissic amphibolites was recovered by two close dredge hauls from the deepest part of the north facing slope of the transverse ridge forming the south wall of the Vema Fracture Zone. Serpentinites and various types of gabbroic rocks ranging from undeformed slightly uralitized gabbros and norites to flaser and mylonitic gabbros were associated with the gneissic amphibolites (in the shallowest of the dredge hauls). Petrological studies indicate that the amphibolites were derived from similar gabbroic rocks that reequilibrated under stress in the conditions of the amphibolite facies. On the other hand, the associated meta‐gabbros display sequences of secondary minerals, indicating complex cooling and cataclastic histories without reaching metamorphic equilibrium. We tentatively suggest that the gneissic amphibolites and associated metagabbros formed in a vertical shear zone generated in oceanic layer 3 by tectonism associated with the Vema Fracture Zone. Hydrothermal circulation of seawater along the highly permeable shear zone was activated by magmatic intrusions. K/Ar dating suggests, within relatively large analytical uncertainties, that the amphibolite metamorphism took place 10 m.y. ago, i.e., at a time when the dredging sites were located in the vicinity of the spreading center

Geochemistry and stable isotopes of peridotites of ODP Hole 103-637A

A ridge of strongly serpentinized, plagioclase-bearing peridotite crops out at the boundary between the Atlantic oceanic crust and the Galicia continental margin (western Spain). These peridotites, cored at Hole 637A (ODP Leg 103) have been mylonitized at high-temperature, low-pressure conditions and under large deviatoric stress during their uplift (Girardeau et al., 1988, doi:10.2973/odp.proc.sr.103.135.1988). After this main ductile deformation event, the peridotite underwent a polyphase metamorphic static episode in the presence of water, with the crystallization of Ti- and Cr-rich pargasites at high-temperature (800°-900°C) interaction with a metasomatic fluid or alkaline magma. Introduction of water produced destabilization of the pyroxenes and the subsequent development of hornblendes and tremolite at temperatures decreasing from 750° to 350°C. The main serpentinization of the peridotite occurred at a temperature below 300°C, and possibly around 50°C, as a consequence of the introduction of a large amount of seawater, which is suggested by stable isotope (d18O and SD) data. Finally, calcite derived from seawater precipitated in late-formed fractures or locally pervasively impregnated the peridotite at low temperature (~10°C)