Interesting to hear Nick say this - my best guess would also have to be a range, and the one I would have picked would be 350 - 425. Lots of variables here (I agree with his assessment of the assemblage limitations), but for a metapsammite, I think that's about right. I also agree that hearing from the regular Thermocalc users would be instructive.
Bob T.
Robert Tracy
Professor of Geosciences
Virginia Tech
Blacksburg VA 24061-0420
O: 540-231-5980
F: 540-231-3386
On Dec 14, 2011, at 7:52 PM, Oliver, Nick wrote:
> 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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