[Rockhounds] giant garnets exposed: a field trip gone awry

[DonH]

Lanny wrote:

> Great, thanks Don for looking that up. It's been too long since I've 
> read Hietanen's reports on the metamorphism in the region 


Well not to beat the dead horse too much, but motivated readers can look 
up these papers at used booksellers and in libraries:

Geology Along the Northwest Border Zone of the Idaho Batholith, Northern 
Idaho (Bulletin 1608)

Anorthosite and Associated Rocks in the Boehls Butte Quadrangle and 
Vicinity Idaho

Metamorphism of the Belt Series in the Elk River-Clarkia Area Idaho

Belt Series in the Region Around Snow Peak and Mallard Peak, Idaho

Metasomatic Metamorphism in Western Clearwater County Idaho

Everyone calls this area "a mess," and I certainly can't add much to the 
discussion, except to confirm that it is a mess.  But it has huge 
kyanite and huge garnet, and some of the whitest and most porcelainous 
feldspar I've ever seen.

> Have you looked at the rock closely in those areas? 

Oh yes indeed.  very closely.  I am passing around slices of the garnet 
amphibolite to professors.  The folks over at WSU just did some 
radiometric dating on the rims, and then the cores, of these garnets and 
determined there were two significant periods of growth spaced millions 
of years apart.  Now I found one with three growth rings, and they want 
to look at it.  Cutting these open is like an adventure, you never know 
what kind of toy surprise is inside.


best,
Don