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Record 75 of 666
The effect of Na vapor on the Na content of chondrules
Author and Affiliation:
Lewis, R. Dean(Iowa State University, Ames, IA, United States)
Lofgren, Gary E.(NASA Johnson Space Center, Houston, TX, United States)
Franzen, Hugo F.(Iowa State University, Ames, IA, United States)
Windom, Kenneth E.(Iowa State University, Ames, IA, United States)
Abstract: Chondrules contain higher concentrations of volatiles (Na) than expected for melt droplets in the solar nebula. Recent studies have proposed that chondrules may have formed under non-canonical nebular conditions such as in particle/gas-rich clumps. Such chondrule formation areas may have contained significant Na vapor. To test the hypothesis of whether a Na-rich vapor would minimize Na volatilization reaction rates in a chondrule analog and maintain the Na value of the melt, experiments were designed where a Na-rich vapor could be maintained around the sample. A starting material with a melting point lower that typical chondrules was required to keep the logistics of working with Na volatilization from NaCl within the realm of feasibility. The Knippa basalt, a MgO-rich alkali olivine basalt with a melting temperature of 1325 +/- 5 C and a Na2O content of 3.05 wt%, was used as the chondrule analog. Experiments were conducted in a 1 atm, gas-mixing furnace with the fO2 controlled by a CO/CO2 gas mixture and fixed at the I-W buffer curve. To determine the extent of Na loss from the sample, initial experiments were conducted at high temperatures (1300 C - 1350 C) for duration of up to 72 h without a Na-rich vapor present. Almost all (up to 98%) Na was volatilized in runs of 72 h. Subsequent trials were conducted at 1330 C for 16 h in the presence of a Na-rich vapor, supplied by a NaCl-filled crucible placed in the bottom of the furnace. Succeeding Knudsen cell weight-loss mass-spectrometry analysis of NaCl determined the P(sub Na) for these experimental conditions to be in the 10(exp -6) atm range. This value is considered high for nebula conditions but is still plausible for non-canonical environments. In these trials the Na2O content of the glass was maintained or in some cases increased; Na2O values ranged from 2.62% wt to 4.37% wt. The Na content of chondrules may be controlled by the Na vapor pressure in the chondrule formation region. Most heating events capable of producing chondrules are sufficient to volatile Na. Sodium volatilization reaction rates will be reduced to varying degrees from melt droplets, depending on the magnitude of the P(sub Na) generated. A combination of Na vapor during, and Na diffusion back into chondrules after, formation could maintain and/or enrich Na concentrations in chondrules.
Publication Date: Dec 01, 1993
Document ID:
19950047177
(Acquired Dec 28, 1995)
Accession Number: 95A78776
Subject Category: LUNAR AND PLANETARY EXPLORATION
Document Type: Journal Article
Publication Information: Meteoritics (ISSN 0026-1114); 28; 5; p. 622-628
Publisher Information: United States
Financial Sponsor: NASA; United States
Organization Source: NASA Johnson Space Center; Houston, TX, United States
Description: 7p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: CHONDRITES; CHONDRULE; METAL VAPORS; METEORITIC COMPOSITION; NUCLEAR REACTIONS; PETROLOGY; SODIUM; SOLAR CORONA; ATOMIC WEIGHTS; PRESSURE DISTRIBUTION; SOLAR CONVECTION (ASTRONOMY); THERMAL DIFFUSION
Imprint And Other Notes: Meteoritics vol. 28, no. 5 p. 622-628 December 1993
Availability Source: Other Sources
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