Computer Science
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..466y&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 466
Computer Science
Allende, Chondrules, Experiments, Exchange, Isotopes, Oxygen, Ornans
Scientific paper
Chondrules in carbonaceous and ordinary chondrites show slope-1 mixing lines on the oxygen three-isotope diagram, suggestive of a gas-melt exchange process during chondrule formation. In order to test this conjecture and to extend our existing knowledge of chondrule thermal history and the kinetics of reaction of interstellar dust with solar nebula gas, an experiment involving high- temperature oxygen isotope exchange between a 16O-rich sample (meteorite) and water vapor (terrestrial) has been designed. The experiment was conducted with a DELTECH vertical tube furnace with ceramic parts shielded with metal foil. The starting meteorite powder (one of two C3 carbonaceous chondrites--bulk Allende and Ornans) was pressed into a pellet and suspended at the hot spot inside the furnace. The furnace gas was a mixture of H2O vapor and H2 (1 atm total pressure, fO2 = IW-0.5) [1]. The preliminary experiments were performed at 1400 degrees C for durations from 5 minutes to 36 hours, and were terminated by quenching the samples into liquid nitrogen. The meteorite charges and the water samples collected were later analyzed for their oxygen isotope compositions. The experimental results (Fig.1) show that the exchange process has greatly modified delta-18O and delta-17O for both meteorites, which move towards the projected equilibrium point as the heating time increases. For Allende samples, the exchange proceeds quickly in the first 5 minutes, which accounts for most of the isotope exchange (~84% of total change in delta-18O(sub)A-W, and ~57% of total change in delta-17O). Then the exchange is dramatically slowed down, and takes at least 12 hours to finally reach equilibrium with the ambient water vapor. The approach to equilibrium is not a straight line on the three-isotope graph, possibly due to the presence of residual 16O-rich solids in the molten sample. A similar exchange profile is observed for Ornans samples. However, it takes longer for the Ornans sample to reach equilibrium after the initial fast exchange. The 15-hour run for Ornans is still away from the TF line, and it is moving toward the TF line about 1 permil lighter than the expected equilibrium value. Microscopic and electron microprobe studies on the heated Allende and Ornans samples (parallel runs) show that the quenched charges are composed of olivine relics and glass. The initial fast exchange observed is probably due to the rapid exchange between the ambient gas and the molten part of the meteorite sample, and the existence of olivine crystals eventually slows down the exchange process because of its much lower rate of oxygen diffusion [2]. The concentration of exchangeable gas molecules in our experiments is much greater than that in the solar nebula. The next step of this study will be experiments at higher temperatures, under conditions more similar to the chondrule-forming environment, such as flash heating and with gas diluted with Ar to obtain fewer oxygen molecules. Acknowledgments: We thank T. Grove for technical guidance, E. Jarosewich (NMNH, Washington) and B. Zanda (MNHN, Paris) for meteorite samples, and NASA (OSS) and NSF for financial support. References: [1] Baker M. B. and Grove T. L. (1985) Am. Mineral., 70, 279-287. [2] Jaoul O. et al. (1983) JGR, 88, 613-624.
Clayton Robert N.
Hewins Roger H.
Mayeda Toshiko K.
Yu Yue
No associations
LandOfFree
High-Temperature Oxygen Isotope Exchange Between Meteorite Sample and Water Vapor: Preliminary Experimental Results does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with High-Temperature Oxygen Isotope Exchange Between Meteorite Sample and Water Vapor: Preliminary Experimental Results, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High-Temperature Oxygen Isotope Exchange Between Meteorite Sample and Water Vapor: Preliminary Experimental Results will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1072451