Greinar (Vísindafélag Íslendinga) - 01.01.1977, Side 129

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one pole near the middle of the Pacific Ocean (10°N, 150°W
in a recent approximation) and the other in South Africa
(10°S, 30°E). Just the latter position would very well explain
flat shear planes in all island arcs, the Bahamas included,
whereas in the Atlantic the maximum shear would be near-
vertical. The stresses were calculated on the basis of the as-
sumption of an internal cause, i.e. zero surface shear, and
will be later revised, as we have recognized that just surface
shear is the cause of most global fields. But the inference from
the global tectonic features remains otherwise unchanged.
This global field does not seem to fit very well the present
position of the poles, and we feel it rather stretching the in-
formation to try to explain the formation of the planes of
the island arcs by e.g. Tertiary stress fields as mentioned in
Chapter 1. But we have pointed out that the island arcs of
the Pacific follow Hercynian arcs at both ends of their chain.
This is highly suggestive in the present connection, although
the close connection of this Alpine phenomenon with Her-
cynian arcs cannot be directly verified by observation except
at these ends. The position of the axis in case b) would be
in fine agreement with an equilibrium position of the earth’s
axis (90, 91, 92) at a time when the Pacific was overwhel-
mingly the main ocean, and it would be in a striking agree-
ment with the Carbo-Permian climate of Africa and its neigh-
bourhood, which in time followed the Hercynian, most rea-
sonably by a very similar axial position, as this was still the
equilibrium position. The torsional field would be a natural
result of the great difference in wind stress over land, in one
hemisphere, and demanding a right screw, the African pole
must have been a South Pole. So it had not to move very far
in later geological times.
The Carbo-Permian ice age of the southern hemisphere may,
thus, very likely have been accompanied by a strong torsional
stress field. This means not unlikely the formation of high
volcanoes, and these eould become glaciated in Gondwana
areas, even by low humidity. The geological evidence is thought
to indicate individual mountain glaciers (98). By a lack of