Mathematics – Probability
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28q.348f&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 348
Mathematics
Probability
Cosmochemistry, Earth, Mantle, Isotopic Anomalies, Noble Gases, Xenon
Scientific paper
I have performed replicate crushing experiments on two glass MORB (East Pacific Rise and Mid Atlantic Ridge) in which previous whole-rock melting experiments showed ^40Ar/^36Ar ratios ranging up to ~15,000, indicating efficient trapping of gases from the mantle [1,2]. I loaded nearly a gram of mm-sized pieces and crushed varying portions of them under vacuum, transferring the released gases directly into the mass spectrometer and obtaining more than 20 separate aliquots. Though the Xe/Ar ratio was higher than atmospheric in all aliquots, indicating the presence of mantle xenon, none of the data show any excess ^129Xe from the decay of ^129I early in earth history. It is clear that some terrestrial xenon contains the anomaly [3], but it is not at all clear that the MORB source region does, though some models of mantle and atmospheric evolution rely heavily on this result [4]. I have gone through the literature, and find a diversity of results. Four papers, all from the same laboratory, present clear evidence of the anomaly [4-7], five others do not [8-12], and one straddles the fence [1]. The situation is complicatedby the ubiquitous presence in MORB of a component withatmospheric-like rare gas isotopic ratios. I shall discuss the attempts of various workers to separate these components, and the probability that a true anomaly exists in all or in some MORB source regions, by comparing Xe isotopic data obtained through stepwise heating, total fusion, or crushing experiments, with other pertinent ratios. "I have forgot much, Cynara, gone with the wind; Have flung roses, roses riotously with the throng." References: [1] Fisher D. E. (1986) GCA, 50, 2531-2541. [2] Fisher D. E. (1985) JGR, 90, B2, 1801-1807. [3] Boulos M. S. and Manuel O. K. (1971) Science, 174, 837-840. [4] Allegre C. J. (1983) Nature, 303, 762-766. [5] Staudacher T. and Allegre C. J. (1982) EPSL, 60, 389-406. [6] Staudacher T. (1989) EPSL, 96, 119- 133. [7] Marty B. (1989) EPSL, 94, 45-56. [8] Fisher D. E., EPSL, for publ. [9] Hiyagon H. (1992) GCA, 56, 1301-1316. [10] Ozima M. and Zashu S. (1983) EPSL, 62, 24-40. [11] Takaoka N. and Nagao K. (1978) Nature, 276, 491-492. [12] Kirsten T. and Richter H. (1981) Meteoritics, 16, 341.
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