NGT43-1-06
1963
Banded gneisses of eight localities.
43
1
89-120

The banding of most of the metamorphic and composite rock units observed in Southern Finland, the Pyrenees of France, Southwestern Black Forest of Germany, the Otago District of New Zealand, Ornö Huvud off the coast of Eastern Sweden, two "root zone" areas of the Southern Alps of Switzerland, and the Fish Creek "Phacolith" of the Northwestern Adirondack Mountains of New York, U.S . A. , appears to reflect supracrustal layering. The banding of a few of the observed rocks, e.g., some of the "laminated schists" of Otago, New Zealand, appears to reflect preexisting structural discontinuities. Almost all of the banding is hybrid in that the preexisting sedimentary or structural discontinuities have been modified, commonly accentuated, as the result of some process(es) such as differential anatexis, permeation, or metamorphic differentiation. Nevertheless, in a general way "type" localities for each of the genetic categories of banded gneisses may be and are suggested. A few observations relating to banded gneisses support the conclusion that "granite" has been formed as the result of isochemical (or topochemical) metamorphism, herein named treptomorphism, of granitic composition supracrustal rocks as well as by consolidation of magma and by metasomatism. Thus, granites may be classified, according to processes of formation, as follows:

Magmatism
  Differentiation
  Anatexis

Metamorphism
  Metasomatism
  Treptomorphism

0029-196x
Print