Greinar (Vísindafélag Íslendinga) - 01.01.1977, Page 113

Chapter 8
GEOSYNCLINES AND FOLDED MOIJNTAIN CIIAINS.
CONTENTS
Geosynclines are in the first place due to the load produced by denuda-
tion of the continents, and carried by the rivers to the coasts. Longshore
drifting of the material is an important factor, as well as major changes
of drainage. The initial troughs are of normal isostatic nature, but after
a certain depth of the trough is reached, it is considered that dense nano-
crystals begin to form, so as to enable a further deepening of the trough
without violation of isostasy.
At all depths in a geosyncline, the external pressure is greater than
the internal one. This external overpressure would replace the colliding
continents of theories of older times.
This is a very old problem, and just therefore there is every
reason to suspect that still today there lurk in our minds
dogmas which are the result of conclusions and generaliza-
tions made at an early stage of the study of the problem.
Perhaps the main pitfall lies in the fact that up to the end
of the 19th century, the solution of the problem seemed quite
obvious. The mountain chains were naturally the result of the
cooiling and shrinking of the earth. Which dogmas remain from
that stage? They are easy to find.
In this “obvious” explanation of folded mountains was all
the thrust that so clearly was needed to push all the material
together and fold it thoroughly. Here was also the explana-
tion of the global occurence of the main phases of orogeny:
the crust was naturally everywhere under increasing pressure
until the yielding point was reached. And it was quite natural
that those wrinkles on the surface of the “dried apple”, which
had been filled with weak sediments and formed those long
narrow troughs (geosynclines) should yield to the compression.
Still in the 6th edition of his classic treatise, The Earth (84),