Meteoritics & Planetary Science, Volume 37, Number 7 (2002)
http://hdl.handle.net/10150/641311
2024-03-27T22:06:51ZThe Third International Conference on Magnetism, Metamorphism and Associated Mineralizations "3MA", Casablanca, Morocco 2003 May 8-10
http://hdl.handle.net/10150/656668
The Third International Conference on Magnetism, Metamorphism and Associated Mineralizations "3MA", Casablanca, Morocco 2003 May 8-10
Announcement: The Third International Conference on Magnetism, Metamorphism and Associated Mineralizations "3MA"
2002-01-01T00:00:00ZAluminum-26 in H4 chondrites: Implications for its production and its usefulness as a fine-scale chronometer for early solar system events
http://hdl.handle.net/10150/655545
Aluminum-26 in H4 chondrites: Implications for its production and its usefulness as a fine-scale chronometer for early solar system events
Zinner, Ernst; Göpel, Christa
In order to investigate whether or not 26Al can be used as a fine-scale chronometer for early-solar-system events we measured, with an ion microprobe, Mg isotopes and Al/Mg ratios in separated plagioclase, olivine, and pyroxene crystals from the H4 chondrites Ste. Marguerite, Forest Vale, Beaver Creek and Quenggouk and compared the results with the canonical 26Al/27Al ratio for Ca,Al-rich inclusions (CAIs). For Ste. Marguerite (SM) and Forest Vale (FV) Pb/Pb and Mn-Cr ages have previously been determined (Gpel et al., 1994; Polnau et al., 2000; Polnau and Lugmair, 2001). Plagioclase grains from these two meteorites show clear excesses of 26Mg. The 26Al/27Al ratios inferred from these excesses and from isotopically normal Mg in pyroxene and olivine are (2.87 +/- 0.64) x 10^(-7) for SM and (1.52 +/- 0.52) x 10^(-7) for FV. The differences between these ratios and the ratio of 5 x 10^(-5) in CAIs indicate time differences of 5.4 +/- 0.1 Ma and 6.1 +/- 0.2 Ma for SM and FV, respectively. These differences are in agreement with the absolute Pb/Pb ages for CAIs and SM and FV phosphates but there are large discrepancies between the U-Pb and Mn-Cr system for the relative ages for CAIs, SM and FV. For example, Mn-Cr ages of carbonates from Kaidun are older than the Pb/Pb age of CAIs. However, even if we require that CAIs are older than these carbonates, the time difference between this "adjusted" CAI age and the Mn-Cr ages of SM and FV require that 26Al was widely distributed in the early solar system at the time of CAI formation and was not mostly present in CAIs, a feature of the X-wind model proposed by Shu and collaborators (Gounelle et al., 2001; Shu et al., 2001). From this we conclude that there was enough 26Al to melt small planetary bodies as long as they formed within 2 Ma of CAIs, and that 26Al can serve as a fine-scale chronometer for early solar system events.
2002-01-01T00:00:00ZPre-atmospheric depths and thermal histories of Canyon Diablo spheroids
http://hdl.handle.net/10150/655546
Pre-atmospheric depths and thermal histories of Canyon Diablo spheroids
Leya, I.; Wieler, R.; Ma, P.; Schnabel, C.; Herzog, G. F.
Despite having melted during formation, seven of eight Canyon Diablo spheroids weighing from 0.6 to 13 mg retain cosmic-ray-produced 38Ar (38Arcos) in concentrations [10^(-10) cm^3 STP/g] ranging from 0.35 to 68. The presence of 38Arcos is consistent with pre-atmospheric depths of <2.3 meters and most likely rules out an origin for the spheroids deep within the projectile, which had a radius of ~15 m. Low levels of 21Necos indicate gas loss from these spheroids. Relative to most Canyon Diablo meteorites, the spheroids contain lower concentrations of cosmogenic noble gases. The difference partly reflects diffusion losses from the spheroids, especially for 3He and 21Ne, but also suggests deeper locations on average for the precursor material, consistent with independent results from 59Ni.
2002-01-01T00:00:00ZProduction of krypton and xenon isotopes in thick stony and iron targets isotropically irradiated with 1600 MeV protons
http://hdl.handle.net/10150/655542
Production of krypton and xenon isotopes in thick stony and iron targets isotropically irradiated with 1600 MeV protons
Gilabert, E.; Lavielle, B.; Michel, R.; Leya, I.; Neumann, S.; Herpers, U.
Two spherical targets made of gabbro with a radius of 25 cm and of steel with a radius of 10 cm were irradiated isotropically with 1600 MeV protons at the SATURNE synchrotron at Laboratoire National Saturne (LNS)/CEN Saclay, in order to simulate the production of nuclides in meteorites induced by galactic cosmic-ray protons in space. These experiments supply depth-dependent production rate data for a wide range of radioactive and stable isotopes in up to 28 target elements. In this paper, we report results for 78Kr, 80-86Kr isotopes in Rb, Sr, Y and Zr and for 124Xe, 126Xe, 128-132Xe, 134Xe, 136Xe isotopes in Ba and La. Krypton and xenon concentrations have been measured at different depths in the spheres by using conventional mass spectrometry. Based on Monte-Carlo techniques, theoretical production rates are calculated by folding depth-dependent spectra of primary and secondary protons and secondary neutrons with the excitation functions of the relevant nuclear reactions. The comparison of the model calculation results with experimental data in the thick target experiments performed at LNS and previously at CERN have allowed adjustments of the poorly known excitation functions of neutron-induced reactions. Thus, for the two experiments at SATURNE, excellent agreement is obtained between experimental and calculated production rates for most Kr and Xe isotopes in all investigated target elements. Only Xe production in Ba in the gabbro is underestimated by the calculations by ~25%. This work validates the approach of the thin-target model calculations of cosmogenic nuclide production rates in the attempt of modeling the interaction of galactic cosmic-ray protons with stony and iron meteorites in space as well as with the lunar samples.
2002-01-01T00:00:00Z