Nordfjord
On the north shore of Nordfjord, there are a few preserved basic eclogites, found
in small metabasic pods. These can preserve prograde peak conditions of
(P = 20-24 kbar; T = 650-800.C).
However, the critical feature of the Nordfjord outcrops is the occurrence of
metamorphic overprinting textures, within which are relict HP minerals. The
overprint lies in the amphibolite to greenschist facies. These younger assemblages
record conditions where temperature and pressure have near normal relationships
to each other (i.e. a near normal geotherm gradient).
Estimates of PT conditions for various units here are:
- P = 8-12 kbar, T = c. 650.C
- P = 4.3-8.2 kbar; T = 520-610.C.
These conditions are recorded for different parts of the same site - so they represent
snap-shots along the common exhumation/cooling paths for the WGR. Consequently
you can plot these onto the PT diagram to construct more of the PT path for the
WGR.
Once-eclogitic metabasic unit largely overprinted
by new mineral growth. The garnet is largely replace by epidote, which
also dominates the groundmass. There is a dark rim around the garnet of chlorite
± amphibole (hornblende). Note that the new mineral growth occurs
upon the old texture and is not associated here with significant post-HP deformation
at this site. Of course there was some deformation related to the retrograde
metamorphism but this occurred away from these locations - in other words it
was heterogeneous.
Partially retrogressed eclogite. The core of the garnet
is partially preserved but is rimmed by albite. Note that at eclogite
facies the albite would not be stable (the composition of albite would be represented
by the minerals jadeite + quartz). The dark mineral(s) here are chlorite ±
hornblende.
Western Gneiss Region front page : Introduction : Hornelen map : Hornelen
Basin N-S section