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A specific comment on “an alternative model for the formation of iron meteorites”
EARTH AND PLANETARY SCIENCE LETTERS 15 (1972) 220. NORTH-HOLLAND PUBLISHING COMPANY
A SPECIFIC COMMENT ON "AN ALTERNATIVE MODEL FOR THE FORMATION OF IRON METEORITES", by M.R. Bloch and O. Miiller, Earth Planet, Sci. Letters 12 (1971) 1 3 4 - 1 3 6 . Wulf A. KAISER Department of Physics, University of California, Berkeley, California 94 720, USA Received 11 November 1971 Revised version received 24 January 1972
My comment is limited to the five lines in which Bloch and Mi~ller [ 1] suggest that the high 4°Ar/4°K ratios found by MOiler and ZLhringer [2] in the metal phase of iron meteorites might represent a "trapped cometary atmosphere" containing excess *OAr. A complete review of the voluminous literature on the (very difficult) determination of 4°Ar/4°K ratios in the metal phase of iron meteorites is beyond the scope of this short comment. It is sufficient to note that Bloch and Moiler have chosen to reference the work [2] which best supports their model even though that work is known to be in serious error. Kaiser and Z~hringer [3,4] have clearly shown that the work of MOiler and Zfihringer was subject to three different and major experimental problems, each of which produced spuriously high 4°Ar/4°K ratios. The results of Miiller and Zalaringer are of very doubtful validity. Admittedly, some iron meteorites examined by Kaiser and ZbJaringer still appear to show high 4°Ar/4°K ratios and unreasonable K/Ar ages. It is impossible to prove that these high apparent 4°Ar/~U~K
ratios are not due to an "excess 4°Ar" component of unknown origin. However, the meteorite samples which show the high apparent 4°Ar/4°K ratios are those which are most subject to the experimental-problems described by Kaiser and Z/ihringer [3,4]. In view of the other plausible explanations [3,4] of the high apparent 4°Ar/4°K ratios, the existence of any "excess" 4°Ar in iron meteorites is rather improbable.
References [1] M.R. Bloch and O. Miiller, An alternative model for the formation of iron meteorites, Earth Planet. Sci. Letters 12 (1971) 134. [2] O. Mfiller and J. Zghringer, K-Ar-Altersbestimmungen an Eisenmeteoriten-III. Kalium- und Argonbestimmungen, Geochim. Cosmochim. Acta, 30 (1966) 1075. [3] W. Kaiser and J. Z/ihringer, K/Ar age determinations of iron meteorites IV. New results with refined experimental procedures, Earth Planet. Sci. Letters. 4 (1968) 84. [4] W. Kaiser and J. Z~ihringer, K/Ar age determinations of iron meteorites V, in: Meteorite research, ed. P.M. Millman, (Springer Verlag Inc., New York, 1968) p. 429
A SPECIFIC COMMENT ON "AN ALTERNATIVE MODEL FOR THE FORMATION OF IRON METEORITES", by M.R. Bloch and O. Miiller, Earth Planet, Sci. Letters 12 (1971) 1 3 4 - 1 3 6 . Wulf A. KAISER Department of Physics, University of California, Berkeley, California 94 720, USA Received 11 November 1971 Revised version received 24 January 1972
My comment is limited to the five lines in which Bloch and Mi~ller [ 1] suggest that the high 4°Ar/4°K ratios found by MOiler and ZLhringer [2] in the metal phase of iron meteorites might represent a "trapped cometary atmosphere" containing excess *OAr. A complete review of the voluminous literature on the (very difficult) determination of 4°Ar/4°K ratios in the metal phase of iron meteorites is beyond the scope of this short comment. It is sufficient to note that Bloch and Moiler have chosen to reference the work [2] which best supports their model even though that work is known to be in serious error. Kaiser and Z~hringer [3,4] have clearly shown that the work of MOiler and Zfihringer was subject to three different and major experimental problems, each of which produced spuriously high 4°Ar/4°K ratios. The results of Miiller and Zalaringer are of very doubtful validity. Admittedly, some iron meteorites examined by Kaiser and ZbJaringer still appear to show high 4°Ar/4°K ratios and unreasonable K/Ar ages. It is impossible to prove that these high apparent 4°Ar/~U~K
ratios are not due to an "excess 4°Ar" component of unknown origin. However, the meteorite samples which show the high apparent 4°Ar/4°K ratios are those which are most subject to the experimental-problems described by Kaiser and Z/ihringer [3,4]. In view of the other plausible explanations [3,4] of the high apparent 4°Ar/4°K ratios, the existence of any "excess" 4°Ar in iron meteorites is rather improbable.
References [1] M.R. Bloch and O. Miiller, An alternative model for the formation of iron meteorites, Earth Planet. Sci. Letters 12 (1971) 134. [2] O. Mfiller and J. Zghringer, K-Ar-Altersbestimmungen an Eisenmeteoriten-III. Kalium- und Argonbestimmungen, Geochim. Cosmochim. Acta, 30 (1966) 1075. [3] W. Kaiser and J. Z/ihringer, K/Ar age determinations of iron meteorites IV. New results with refined experimental procedures, Earth Planet. Sci. Letters. 4 (1968) 84. [4] W. Kaiser and J. Z~ihringer, K/Ar age determinations of iron meteorites V, in: Meteorite research, ed. P.M. Millman, (Springer Verlag Inc., New York, 1968) p. 429