Filters
Results 1 - 10 of 1406
Results 1 - 10 of 1406.
Search took: 0.025 seconds
| Sort by: date | relevance |
[en] Several mineral phases of the Chainpur meteorite are very enriched in deuterium. D /H ratios ranging between 600 and 900 ppm have been measured (i.e. 4 to 6 times the terrestrial value). These data are explained as the result of nuclear reactions on solid grains by an integrated flux of protons of 1019 to 1020 cm-2, for energies larger than 10 MeV. These proton fluxes must have been produced at the very beginning of the solar system (for instance T Tauri radiation). These results are discussed in the light of other cosmochemical data
[fr]
La plupart des phases minerales de la meteorite Chainpur contiennent d'enormes exces de deuterium. Le rapport D/H atteint des valeurs de 600 a 900.10-6 (4 a 6 fois le rapport terrestre). Ces resultats sont interpretes par un modele de spallation par des fluences de protons de l'ordre de 1019 a 1020/cm2 pour les energies superieures a 10 MeV. Ces flux ne peuvent avoir ete produits que pendant l'histoire precoce du systeme solaire (par exemple rayonnement T Tauri). Ce modele est discute en fonction des autres donnees cosmochimiquesJournal
Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences. Serie B; ISSN 0302-8437; 
; v. 288(21); p. 375-378
; v. 288(21); p. 375-378
[en] A hypersthene-cordierite-quartz granulite (delta18O/16O = 2.70/00) contains hypersthene porphyroblasts (delta = 1.80/00) which enclose (and thus preserve from the effects of later metamorphic events) inclusions of quartz (delta = 4.30/00) and cordierite (delta = 2.80/00). Initial granulite facies metamorphism (about 1860 m.y.) took place at about 7600C. Fluids responsible for the introduction of 1470 m.y. phlogopite were not greatly different in 18O from those prevailing during the 1860 m.y. metamorphism. Many other granulites (siliceous, feldspathic and basic) over a wide area contain very light oxygen; although several causal mechanisms are suggested, the ultimate source of the widespread light oxygen is still unknown.(auth.)
Source
Robinson, B.W. (ed.) (Department of Scientific and Industrial Research, Lower Hutt (New Zealand). Inst. of Nuclear Sciences); New Zealand DSIR bulletins; p. 175-179; 1978; p. 175-179; DSIR Science Information Division; Wellington; International stable isotope conference; Lower Hutt, New Zealand; 4 - 6 Aug 1976; ISSN 0077-961X;
[en] Rocks altered by volcanic gases rich in HCl, HF and SO2, and their fresh counterparts, have been studied chemically, mineralogically and isotopically. In addition, alteration of fresh rock powders of different rock types has been artificially induced by leaving the powders inside fumaroles at various temperatures. As alteration proceeds the rocks as well as the artificially exposed powders become leached and enriched in silica until they consist of almost nothing else with gradual disappearance of original rock-forming minerals. The alteration is also accompanied by the enrichment of 18O. More siliceous rocks become resistant to this type of alteration, in the order basalt, andesite and obsidian. The increase in delta18O of altered rocks may be caused by the following factors:(1) Kinetic isotope effects involved in the net loss of oxygen from rocks during leaching processes at low temperatures; (2) Oxygen isotope exchange between rocks and water vapour in volcanic gases at submagmatic temperatures with a high water/rock ratio during alteration.(auth.)
Source
Robinson, B.W. (ed.) (Department of Scientific and Industrial Research, Lower Hutt (New Zealand). Inst. of Nuclear Sciences); New Zealand DSIR bulletins; p. 127-137; 1978; p. 127-137; DSIR Science Information Division; Wellington; International stable isotope conference; Lower Hutt, New Zealand; 4 - 6 Aug 1976; ISSN 0077-961X;
| 1 | 2 | 3 | Next |