Hi again everybody,
Thanks for all the discussion. I would like to add one more paper to the
list of material that has been provided so far - thank you all, it has
been great for updating my databank.
In the attached paper (Anckiewicz et al.) we looked at dates and
chemistry of garnets systematically across a coherent Barrovian
sequence, and then in some nearby rocks (but separated by a fault -
different history) that were metamorphosed to higher grades.
We could show that the garnets in the prograde sequence retained growth
zoning, and essentially dated the initiation of garnet growth (because
most of the Lu is concentrated in the core, and there is no sign of
diffusive modification). In one case we could do a core - rim dating to
substantiate that more. In contrast, in the higher grade rocks where
significant melts were present (migmatite), the zoning is homogenized
and the dates refer to the peak temperatures (or nearby) of
metamorphism. We could show (and there are additional independent
evidence not discussed in detail in the paper - e.g. the presence of
melt inclusions all over the garnets) that this was caused by melt
facilitated recrystallization rather than diffusion.
I hope this provides a systematic study of how the Lu-Hf system behaves
during metamorphism, the different stages of metamorphism that the
system may date depending on the grade of metamorphism (and the
resulting implications for tectonic interpretations), and the
complexities that can arise in the presence of melts.
I hope this helps.
Best wishes,
Sumit
Am 22/04/2019 um 16:50 schrieb Gregory Dumond:
> These are a few questions about Lu-Hf garnet dating:
>
> 1) How well do we know the closure temperature of the Lu-Hf system in garnet?
>
> 2) How reliable is this technique for dating granulites, especially granulites that have experience protracted high-T metamorphism and/or residence in the lower crust?
>
> If you have any references that pertain to the above questions, I would sincerely appreciate them.
>
> With best regards,
> Greg
>
> Department of Geosciences
> University of Arkansas, USA
>
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Sumit Chakraborty
Professor, Institut für Geologie, Mineralogie und Geophysik
and
Director, RUBION
ACS Earth and Space Chemistry, Associate-Editor
Ruhr Universität Bochum,
Universitaetstrasse 150, D-44801 Bochum
Germany
Phone: +49 – 234 322 4395
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Fax: +49 – 234 – 321 4433
Email: [log in to unmask]
Web: http://www.gmg.rub.de/petrologie/
http://www.rubion.rub.de/
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