Journal of Petrology | Volume 1 | Number 1 | Pages 99-120 | 1960
© Oxford University Press 1960
research-article |
Banded Gneisses
Mineralogisk-Geologisk Museum Oslo, Norway1
ABSTRACT
Banded gneisses are of diverse origins. A possibly theoretically inclusive genetic classification is proposed.
Criteria that may serve to aid distinction between possible geneses are given and their applicabilities discussed and evaluated. It is emphasized that conclusions concerning origins of multilithic rocks such as banded gneisses must take into consideration the origins of all constituent units.
On the basis of an intensive investigation of banded gneisses of the Randesund area of south-eastern Norway; cursory examinations of banded gneisses from southern Finland, the northern Pyrenees of France, the south-western Black Forest of Germany, Ornö Huvud of eastern Sweden, and two ‘root zone’ areas of the southern Alps of Switzerland; and a review of the geological literature concerned with banded gneisses the following conclusions are made. (1) The banding of nearly all banded gneisses reflects directly or reflects formation controlled by supracrustal layering; (2) some banded gneisses may reflect formation controlled by structural features such as cleavage; (3) some banded gneisses could have been formed by lit par lit injection (controlled by (1) or (2)); and, (4) presently observable banding of many banded gneisses is probably hybrid in that after it was formed originally it was subsequently modified (commonly accentuated) as the result of differential anatexis, permeation, metamorphic differentiation, differential cataclasis, or some combination of such processes.