I agree entirely with Dugald and John and it has also been my impression
that this is the way the term has been used in most metamorphic papers.
Specifically, without any connotation about the mode of origin (i.e.
fluids, melts, solid state reaction), which is probably the best way to
go - at least that would be my two cents worth on the matter.
I would just like to add a line about development of zoning by
resorption, which seemed to be the point of departure for the original
mail. Resorption by itself can only shorten a zoning profile, not
produce any new patterns / gradients. Development of a new pattern /
gradient requires diffusion, and therefore, the broad classification of
zoning patterns arising due to "growth" or "diffusion" should be
adequate. That is, if one is willing to include patterns formed by
dissolution - reprecipitation (e.g. Ostwald ripening, if it happens;
pressure solution type processes etc.) under the broad term "growth" in
the sense it involves addition of a new garnet composition to an
existing one to produce the zoning. One of the earliest examples I know
where zoning patterns (in garnets) were interpreted to have formed due
resorption and diffusion is Grant and Weiblen, AJS, 1971 (where I
believe they used the term "resorption", do not have it on hand to
check); also a few early papers by Hollister, Hess and Loomis in the
seventies deal with similar stuff and many more since then.
And finally, as John's (Clemens) mail just came in - there are plenty of
instances in metamorphic rocks where garnets are "chewed up" without
forming a corona / product assemblage in the immediate vicinity...so
"resorption" may not be so out of place.
Hope this helps,
Sumit
|