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At 04:10 PM 2000/05/18 +0600, Nina Volkova wrote: >... >Help me with references concerning the examples of diffusion metasomatism... >... Shohei Banno responded: >... >Theoretical part is well written in Korzhinskii. ... The prevailing theory of metasomatic zoning is flawed by a usually tacit assumption that pressure is constant and uniform regardless of whatever local volume-changes may be dictated by the metasomatic reactions. In rock systems this assumption is not tenable, because rocks and minerals resist deformation. Any metasomatic reaction that would tend to change the volume is resisted by an induced stress field, and the stress field induces secondary chemical-potential gradients that drive secondary mass transfer. Provided that the secondary mass transfer is not the rate-limiting step in the overall metasomatic process, the induced stress field tends to relax towards constant and uniform pressure and the metasomatism tends to take place at virtually constant volume. Thus nature neatly circumvents the strength of rocks and minimizes the mechanical work of metasomatic alteration (Carmichael 1986, Induced stress and secondary mass transfer: Thermodynamic basis for the tendency toward constant-volume constraint in diffusion metasomatism. in Helgeson HC editor, Chemical Transport in Metasomatic Processes, NATO ASI Series C 218, 239-264). This natural tendency toward constant-volume constraint in metasomatism was understood by Lindgren as early as 1912 (Econ Geol 8, 521-535). In 1947 Ramberg provided a sound thermodynamic explanation for the induced-stress part of the story (Geol Foren Forhandl 69, 189-194), and in his 1952 textbook the secondary-mass-transfer part is also clearly explained. But despite additional explanations by Maliva & Siever (1988 Geology 16, 688-691) and Merino et al (1993 Am J Sci 293, 135-155), respectable journals still promulgate a flawed theory of metasomatic zoning that is capable of predicting only primary mass transfer with uninhibited changes of volume at constant and uniform pressure (e.g. Joesten 1991 Am Mineral 76, 743-755; Guy 1993 Eur J Mineral 5, 317-399; Lichtner & Balashov 1993 Geochim Cosmochim Acta 57, 369-387; Ashworth & Sheplev 1997 ibid 61, 3671-3689; Rusinov & Zhukov 1998 Geochem Internat 36, 934-947). Dugald Dugald M Carmichael Phone/V-mail: 613-533-6182 Dept of Geological Sciences and Geological Engineering Queen's University FAX: 613-533-6592 Kingston ON K7L3N6 E-mail: [log in to unmask] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%