Summary: [The Journal of Geology, 1999, volume 107, p. 353374] 1999 by The University of Chicago. All rights reserved. 0022-1376/99/10703-0007$01.00
Early Carboniferous Unroofing in Western Norway: A Tale of Alkali
E. A. Eide, T. H. Torsvik,1
T. B. Andersen,2
and N. O. Arnaud3
Geological Survey of Norway, N-7491 Trondheim, Norway
A B S T R A C T
Ar thermochronologic data from an extensional detachment zone in western Norway document punctuated
late Paleozoic through Mesozoic tectonothermal activity. Diffusion and thermal modeling of alkali feldspars sampled
in a profile through the detachment replicate laboratory argon release patterns when feldspars comprise three or four
diffusion domains with differing activation energies that represent high-, intermediate-, and low-closure temperatures.
These domains correspond to distinct changes in late Paleozoic cooling rates: (1) slow cooling at 0.4 2.2 C/m.yr.
from ca. 380360 Ma; (2) rapid cooling at 15 C/m.yr. in Late DevonianEarly Carboniferous time (360340 Ma); (3)
slow cooling at 0.4 1.7 C/m.yr. after ca. 340 Ma, with partial argon loss in Permian and Late JurassicEarly Cretaceous
times. The Early Carboniferous rapid cooling event recorded by the feldspars links the western Norway margin to