That is a remarkable occurrence. The "Fe-wollastonite" may be
ferrobustamite, which could exsolve wollastonite. The rocks remind me of
some calcareous melt rocks we have seen in Utah, and that have been
described in the Monterey Fm. in southern California and in the Mottled
Zone of Israel. I hope that you are able to get microprobe analyses of the
phases. Sulfur and oxygen isotope study of the buchites and anhydrites is
essential to identify their origin. Is anhydrite found as a phenocryst in
the El Popo lavas?
>I am writing a manuscript on new textural, mineralogical and chemical results
>on volcanic ash and aerosols: SEM and FE SEM examinations. All data are from
>the recent activity of Popocatepetl volcano, Mexico. One part is dedicated to
>the occurrence of Fe-rich wollastonite, hercynite and buchites (glasses
>origin of contact metamorphism [CM]) as a population of fragments of the
>volcanic ash. The wollastonite is not homogeneous, it shows Fe-rich and
>parts which are intergrown. Some grains show vesiculation-like textures.
>Does anybody know SEM studies of similar wollastonites etc.? Also the buchites
>are highly heterogeneous.
>The main question is: Are these fragments products of ongoing CM underneath
>Popocatepetl, or are they fragments of an old aureol. Popocatepetl is situated
>on a ca. 3 km thick sequence of lime/dolostones/evaporites etc. of Cretaceous
>Buchites show wild compositions, they are rich in S, Cl and P. Anhydrite and
>inheritated zircons are enbedded in this glassy/devitrified matrix.
>Ideas, references and coauthorship for essential contributions are welcome.
>Thanks and best wishes
>Johannes H. Obenholzner, PhD
>email: [log in to unmask]
Professor of Geology
Department of Geological Sciences
2534 C.C. Little Bldg.
425 E. University Ave.
University of Michigan
Ann Arbor MI 48109-1063 USA