Hi All,
A couple of weeks ago, I sent a request to the List concerning a
suitable pelitic starting material for a set of shock and annealing
experiments that I would like to do. Thanks to Dave Waters and
Nathalie Marchildon for their offers of crd-pl-qtz-ksp-bt+-sil+-opx
assemblages. These samples are fine-grained enough (<200
microns) and have most, but not all, of the ingredients for which I
am looking. In particular, grt is absent. I have a grt-bearing sample,
but it lacks plag and ksp. Does this mean there are no fine-grained
grt-crd-bt-sil-pl-ksp-qtz hornfelses out there? As my petrographic
observations from the Vredefort Dome suggest that crd, pl and ksp
melt under shock conditions of >20 GPa and that grt and bt may
melt in reponse to the ensuing high post-shock temperatures (>850
oC), I would, ideally, like to have all these minerals present (opx is
optional). I would need no more than a fist-sized sample, as long
as alteration and fracturing is minimal (as this will affect the shock
wave propagation).
If anyone has any grt-bearing hornfels assemblages in their
personal or teaching collections, I would REALLY appreciate being
dropped a (life)line!
Thanks,
Roger Gibson.
Dr. Roger Gibson
Department of Geology
University of the Witwatersrand
Private Bag 3
P O WITS
Johannesburg 2050
REPUBLIC OF SOUTH AFRICA
Tel. + 11 717 6553 (Sec. + 11 717 6547)
Fax + 11 339 1697
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