Greinar (Vísindafélag Íslendinga) - 01.01.1977, Page 106

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cularly detailed study (36) of an axial area on the ridge in
the 22nd to 23rd north latitude, then consider the antiquated
and untenable dogma about red clay, as being a safe indi-
cation of deep sea, and finally extract important conclusions
from the thickness of sediments on the flanks and away from
the flanks of submarine ridges, as given in (35).
In (36, Fig. 7), reproduced here as Fig. 16, is shown a sche-
matic structural diagram of the (relatively young) tectonic
median valley and the eastern crestal range of the Mid-Atlan-
tic ridge in this particular area. This crestal range is formed
of east-dipping layers of (from below) greenschist, green-
stone, and basalt. The surface of the latter (at a depth of
1.5—2.5 km) very much suggests subaerial denudation, which
on the basis of metamorphic consideration, the authors think
should represent a removal of a 2 km thick layer. But the
authors conclude: “Since removal of 2 km of overburden by
erosion seems impossible in such deep water and since there
is no evidence of thick sediments in the adjacent depressions,
tectonic displacement [gliding down-dip] must be assumed”
(36, p. 1287). However, it is too much to expect of tectonic
displacement in this particular case, that it leaves a surface
which so closely simulates the work of subaerial denuda-
tion. Also the profiles on the flanks (36, Fig. 3) Fig. 17 here,
are most familiar in regions of tilted plateau basalts, such as
are common in Iceland. This cannot be anything but the work
of subaerial denudation. And as to the sediments correspond-
ing to the denudation, they are simply a part of that rela-
Fig. 16. Layers of greenschist, greenstone and basalt in the wall of n
median ridge valley. (After (36), Fig. 7).