Greinar (Vísindafélag Íslendinga) - 01.01.1977, Blaðsíða 115

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way to an understanding of the still mysterious, endogenous
processes in the Upper Mantle which were thought to have
such a striking influence on the main tectonic processes in
the crust.
The Preface, by V. V. Beloussov, begins with the words:
“We have many reasons to believe that the history of the
development of the earth’s crust is fundamentally dependent
on processes in the upper mantle to a depth not exceeding
1000 km. Because of this relation, the Upper Mantle Project
was organized as an international program of geophysical, geo-
chemical, and geological studies concerning the upper mantle
and its influence on the development of the earth’s crust”.
This formulation of the problems reflects the views of a
classically thinking, experienced geologist, and in 1968 I would
have had no objections to his formulation, and at that time
I was still telling my students that the sinking of a geosyn-
clinal trough could not be entirely due to the weight of its
contents of sediments; some unknown process in the mantle
would have to be postulated. And I twisted my mind about
that process and tried to imagine a stress field, which could
explain the formation of these winding global troughs. Only
now, I realize that the formation of dense nanocrystals at or
below the bottom of a developing geosyncline is the answer
to its continued deepening. And the swaying lines of global
extension, most obvious in the Alpine orogenic system, are
naturally coastal lines, where rivers deposit most of the mate-
rial denuded from the continents. The direction of the con-
tinental drainage, and the longshore transport of the so de-
posited material are therefore also main factors in the forma-
tion of geosynclines.
We shall now point out several examples, the North Ame-
rican geosynclinal history being particularly easy to interpret.
We know by seismic evidence that there is a syncline-like
depression, filled with sediments, along the NE coast of North
America. We know further, that along this coast there are
thick Lower Mesozoic sediments, depressed towards the ocean,
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