Hi all,
it appears to me that the compositional dependence of both amphibole and
biotite on Cl incorporation is RELATIVELY similar. That means: if in a rock
biotite and amphibole coexist, then the partition coefficient DCl (Cl in
biotite/Cl in amphibole) will be relatively constant - for samples from
Lofoten about 3 and - interestingly - for samples from Antarctica about 3
as well (similar rock types, retrogressed charnockites).
So DCl depends on mineral chemistry (and, presumably, on P and T), while
the absolute XCl is naturally a function of the fluid H2O/HCl fugacity
ratio for a given biotite or amphibole composition. Mineral chemistry in
turn is a function of whole rock chemistry (a complex function, admittably)
and of P and T, but in principle, I guess that DCl as defined above can be
related to whole rock chemistry in quite a simple manner (well, let us see
how simple) - I still lack enough data for coexisting hydrosilicates from a
wide variety of rock types at similar P-T conditions, however, to be able
to test this.
Cheers
Gregor
Prof. Dr. Gregor Markl
Institut für Mineralogie, Petrologie und Geochemie
Wilhelmstrasse 56
72074 Tuebingen
Germany
Tel: ++49-7071-2972930
FAX: ++49-7071-293060
email: [log in to unmask]
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