Greinar (Vísindafélag Íslendinga) - 01.01.1977, Page 123

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The Orogeny and Mountain building. It is quite clear that
the deepening and final depth of a geosyncline is not just due
to the sediment load in it, in a straightforward way, i.e. usual
reference to isostasy. But the solution of the problem is really
quite simple on the basis of dense nanocrystals. We are led
here to just the same conclusion as when considering the den-
sity jump at the Moho in Chapter 5: Under burial of a gra-
dually thickening pile of sediments in an isostatically formed
depression, there ultimately begins the formation of higher
density nanocrystals at or below the bottom of the depres-
sion.
Thus the depression is deepened and can receive more load.
At a stage which needs more consideration in its details than
can be given here (regional differences in deepening within
the trough will cause dip and flowage), the orogenic phase
sets in, with internal flow in the weak masses, as can now be
no surprise, leading to, and ending in recrystallization and
extensive consolidation. (One wonders, whether the addition
“from below” of small amounts of various substances, called
emanation, is not due to the elements expelled from dense nano-
crystals, when lower density crystallization sets in).
Now, it will be clear that all the time, even to the present
point of development, there has been lighter material in the
geosyncline than in the crust or mantle on both sides. This
means that also all the time there was, at any depth, a greater
hydro- or lithostatic pressure outside than inside the geo-
syncline. With the densities 2.67 and 2.2 g./cm- outside and
inside, we get a pressure difference of 235—470 kg/cm2 at a
depth of 5—10 km.
However, at such or greater depth the flanking crust is to
some degree plastic, as we have derived from the shallow'ness
of earthquakes in Chapter 3 and from seismic layering in
Chapter 5, and tends to flow into the geosyncline.
Already prior to the orogenic stage, such flow may exist,
but it would only affect layers of the weak sediments which
are closest to the boundary of the depression. After the oro-