The Thermal Retentive Nature of the I-Xe System in the Meteorite Bjurbole: Implications for the I-Xe System as a Chronometer of Early Solar System Events

Details The Thermal Retentive Nature of the I-Xe System in the Meteorite Bjurbole: Implications for the I-Xe System as a Chronometer of Early Solar System Events The Thermal Retentive Nature of the I-Xe System in the Meteorite Bjurbole: Implications for the I-Xe System as a Chronometer of Early Solar System Events

Oct 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt........13b&link_type=abstract

Thesis (PHD). THE UNIVERSITY OF ARIZONA , Source DAI-B 59/04, p. 1693, Oct 1998, 254 pages.

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Scientific paper

To understand the response of the I-Xe system to thermal alteration, isothermal heating experiments were performed on the Bjurbole (L4) standard used for I-Xe dating. The time dependence of the release of radiogenic 129Xe ('129Xe*') and 127I was determined by analyzing Bjurbole heated for various times at temperatures of 1000, 1100, and 1200oC using noble gas mass spectrometry. Microprobe analyses on thin sections of heated Bjurbole were done to correlate chemical, mineralogical, and textural alterations with Xe and I release in the hope of constraining the identity of the host phase(s) of I. Results for the release of 129Xe* indicate that a single domain (site of 129Xe*) model is insufficient to describe the release. At least three, and possible more, domains are present in Bjurbole. At least one domain outgasses in one hour at a temperature <=1000oC by a mechanism that is not indicative of volume diffusion. For the 1100oC heating, one domain containing the majority of 129Xe* in Bjurbole is seen to outgas in a manner suggestive of volume diffusion. Release characteristics at 1200oC indicate the presence of at least one high temperature domain. The release of 127I is similar to that of 129Xe* for the three isothermal heating temperatures. In domains that contain I-correlated Xe, assuming loss by volume diffusion, Dodson closure temperatures for 129Xe* (along with more retentive 127I) are at least as high, and perhaps much higher than, the peak metamorphic temperature experienced by Bjurbole. Based on diffusion parameters, the diffusion lengths of both 129Xe* and 127I, at peak metamorphic temperatures, are much less than a characteristic domain size of 10-3 cm. The data suggest that the degree of thermal retention of both isotopes is great enough under thermal metamorphic conditions that the initial iodine ratio was not altered. Correlation with I and Xe release patterns suggest that the low retentive domain exists in troilite. The domain exhibiting diffusive release likely resides in pyroxene and∨ olivine crystalline structures that remain stable throughout the 1100oC heatings. The most retentive domain surviving the 1200oC heating also presumably resides in the silicate crystals, which have yet to become molten.

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