Hi Steve you'll probably get a raft of responses on this. The presence of quartz-chlorite-biotite together with Kfeldspar will restrict it fairly nicely. Without knowing the Fe number of the ferromagnesians you won't get much closer than a minimum temperature of about 380 to 400 depending on pressure; the upper limit is constrained by the coexistence of chlorite and quartz and given the detrital Kfeldspar, the chlorite, Kspar and quartz will keep reacting to produce biotite but probably not too much higher than 420 or so, by which time chlorite will be gone.
But wait for a response from one of the regular thermocalc users (e.g. Kurt Stuewe) who use this forum frequently; these figures I quote you are from working on greenstones from around the world but not routinely trying to calculate P-T
cheers
Nick Oliver
Adjunct Professor of Economic Geology
Economic Geology Research Unit
James Cook University
(see also http://www.holcombecoughlinoliver.com/)
-----Original Message-----
From: Metamorphic Studies Group [mailto:[log in to unmask]] On Behalf Of Steven Kidder
Sent: Thursday, 15 December 2011 6:07 AM
To: [log in to unmask]
Subject: Minimum T for biotite?
Hi, I'd like to know the minimum temperature needed for the appearance of
metamorphic biotite in a typical metamorphosed sandstone. I'm a structural
geologist and couldn't find a relevant reference after a couple hours
literature search. The quartzite I'm working on contains ~70% quartz,
lithic fragments (predominantly volcanics and slate), detrital feldspar,
mica, and some Fe and FeTi oxides. The only clearly metamorphic minerals
I've see are chlorite and biotite growing in pressure shadows.
thanks,
Steve Kidder
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