1961 cont.
The Geological History of Atlantis, Dr.
Th. Zhirov (Atlantis Notes from Russia, cont.2)
Tolstoy notes further, that there is synchronization
between the periods of the greatest volcanic activity, both in Iceland and in
the Azores, which may be tentative and not sufficiently accurately known, but
which might help to establish in some degree at what period in the history of
the North Atlantic ridge the structural displacement could have occurred. L. Hawkes considered that the greatest flow of basalts in Iceland (so called Thule basalts) could have taken place in the
pre-Miocene period. On the other hand, J. Agostinho
also thought that there is evidence of pre-Miocene volcanic activity in the Azores. Similarly, for both Iceland
and the Azores, there is synchronization in
activity of volcanic action in post-Miocene times and even later, quite
recently. Thus there are two great periods of activity in the history of both
islands. One of them extends from the late Tertiary period up to the present
day; the other relates to the middle or early Tertiary period. Recently, H.
Hess expressed the original idea that the formation of the Central
Atlantic ridge may be connected with the processes of serpentinization. Serpentine is fairly easily formed by the
hydratization of olivine basalts, especially when
carbonic acid is present. On the strength of the finding of some serpentines
dredged up the sea bottom on the slopes of the North Atlantic ridge, H. Hess considers
that the formation of terrace series on both sides of the ridge was caused by
the processes of serpentinization, and then, after
the period of maximum serpentinization, some de-serpentinization occurred. One can not disagree with H.
Hess in that serpentinization process could play a
vital role in the topographic formation of the North
Atlantic ridge. Yet it would seem that ascribing the dominant role
to them is due to the author's quite understandable desire to give his
hypothesis the widest possible application. Moreover, the discoveries of
serpentine are not as plentiful as might be expected from his hypothesis. Among
Soviet scientists studying the nature of the Central
Atlantic ridge, V.V. Belousov writes as
follows:
"There is no doubt for
us now that this vallation represents a mighty
upheaval of the earth's crust in the area where the geo-synclinal of the alpine
cycle completed its development, that is to say, we are concerned with mountain
erections homological with these of the earliest mountain ranges such as the
Alps, Caucasus, Himalayas, etc. What confirmation is there for this viewpoint?
The islands located on the ridge are volcanic nature. It can be established
that these volcanoes arose in the Tertiary period, i.e. at the end of the alpine
cycle. We have seen that when the geo-synclinal development is completed and
the period of macro-fluctuation sets in, the earth's crust cracks at its utmost
distention and the magma flows out to the surface. This scheme applies exactly
in the present instance. "More over, it must also be added that to the
north of England, at Spitzbergen, and on the eastern coast of Greenland,
there is evident fold-formation of the alpine era. In the areas mentioned, it
has a marginal character, but in the indicated regions of the North
Atlantic it should be of greater intensity. "Consequently, in
the course of the alpine cycle in the central part of the Atlantic Ocean, the
geo-synclinal extended approximately in a meridional
direction, limited on the west and on the east by plateaus, and dispersed into
sub-geosynclinal and sub-geoantisynclinals.
When the cycle ended and the epoch of macro-fluctuation began (at the end of
the Tertiary period), intensive swelling of the earth's crust occurred in the
geo-synclinal area. Accompanied by cracks, and
volcanic eruptions".
This opinion finds
confirmation in the data obtained by the Swedish submarine expedition led by
Prof. H. Pettersson, which established that an area
east of the North Atlantic ridge, extending as far as Madeira, is covered with
a layer of deposits 3500 meters thick. It is shown that deposit accumulations
of great thickness are characteristics of geo-synclinal areas. According to I. Tolstoy, even on the terraces of the ridge itself,
deposits over 300 meters thick were found. The answer to the question of when
the North Atlantic ridge arose, is given on the other hand, by the discovery of
limestone on the Azores, where Miocene limestone was found on the island of
Santa Maria, and on the other hand, by direct determination of the age of the
samples obtained by dredging near the base of the ridge. This dating by the
method of radio-activity was carried out by D. R. Carr and J. L. Kulp on a sample of Grey basalt, taken at a depth of 4,279
meters at Lat. 30' 01'' N, Long. 45' 01'' W. The
resultant figure, taking into account the accuracy of this method, gives a date
of 30 + or - 15 million years ago. Therefore, according to this calculation,
the ridge was formed, at the earliest, at the beginning of the Miocene, at the
latest, at the end of it. Comparison with the age of the Miocene limestone's of
the Azores would argue in favor of a later origin, as their presence indicates
the existence of a shallow sea in that era. According to information received
by the present writer, it seems that drilling on the Azores has brought up
sample of Oligocene limestone's, which likewise indicate the existence here of
a shallow sea in the earlier stages of the Tertiary period. In general, it
seems undoubted that the Central Atlantic
ridge represents a very singular boundary between the western or American, and
the eastern or Eurasian-African hemispheres. The fact is not that J. P. Rothe's surmise has not been justified, because deep basins
lacking of granite layer were discovered to the west of the ridge, but it lies
in the structure common to both halves of the Atlantic.
Thus, the curves of the European alpine orogenesis do
not penetrate beyond the Straits of Gibraltar, but, on the other hand,
earthquakes epicenters are concentrated in the region of the middle ridge and
to the east of it, which more readily indicates connection with the eastern and
not the western hemisphere. The latter is separated from the central ridge by
deep basins of greater extent and magnitude. And this means, evidently, that
the fusion processes for the bottom of the western deeps began earlier than
those for the eastern. The extraordinary topography of the North
Atlantic, in fact, has no analogy with that of any mountain system
on dry land. This leads to the conclusion that various factors played equally
important parts in its formation, including such processes as fold-formations,
and rifts, accompanied by risings and subsidences. In
this, the processes occurring during the formation of the ridge did not follow
the course taken in the formation of the great mountain systems of the old
continents, such as in the Alps of the Himalayas. The explanation may be that
the earth's crust had greater mobility here, due to its lesser thickness, and
the material was different-pure basalt. Therefore all the processes of altering
topography proceeded with greater contrasts than those on the old continents.
The fact of the matter is not that the central ridge is apparently of purely
submarine origin and therefore better preserved, not having been subjected to
erosion. The fact is that it is very young, is formed of material other than
granite of the old continents, and furthermore, under conditions of
considerable pressures. Careful study of the topographic peculiarities leads to
the surmise that the first historical process was probably that of fold
formation. Then, as the accumulation of hardened basalt material piled up and
the thickness of its layers increased, there followed the processes of
splitting and the formation of cracks which, in the case of the Azores plinth,
were caused by distensions. Then, finally, came the last subsidences
and depressions with which, again, were connected new splits, shelf formations,
and so forth. The submarine location of the ridge has not yet afforded the
possibility for detailed study of the whole system of rifts, but from data
available it is evident that these rifts are meridional
and latitudinal in extension. An example of this is afforded by the great rift
at Lat. 30'-31' N. which cuts across the ridge (we have named it the Straits of
Poseidon). This split fairly evenly divides Poseidonia
from Antilia, according to the nomenclature for the
sectors of Atlantis suggested by ourselves and other writers. As yet, it is
more difficult to fix the time for the formation of this or that type of rift.
Particular difficulty is met in explaining the huge meridional
split known as the middle trough of the main chain of the North
Atlantic ridge, which divides the ridge lengthwise almost for the
whole of its known extent. There are some considerations in favor of the
surmise that the middle trough extended before Atlantis was submerged, being
(according to G.T. Wilson) of comparatively ancient formation. On the other
hand, from other considerations it seems undoubted that part of the terraces
bordering the ridge came into being after the main submergence of Atlantis,
possibly even in current historical times. How do we envisage the history of
the Central Atlantic Ridge in the light of the hypotheses and propositions
which we uphold? We believe that this ridge arose in the weakest area of the
earth's crust between the western and eastern hemispheres and was formed
originally as a result of folds caused by two processes of widening the bed of
oceanic basins, which proceeded in parallel and were directed from the edges of
the continent towards the middle of the future ocean. Supporting basically the
hypothesis of N. H. Odhner and R. Malaise (the
constriction theory), we also believe that widening of the bottom of these basins
occurred as a result of a prolonged duration of the warm waters of shallow seas
at the end of the Mesozoic and in the first half of the Tertiary period. The
warmth of the ocean waters of that time and the resultant warming of the ocean
bed due to decreased loss of warmth (water's great capacity for retaining heat)
led to distension of the bottom crust, to its sinking and partial fusion, as a
result of which deep basins begun to appear. Since inter-continental reserves
of granite materials were already insignificant at the time when the basic
massif of the Central Atlantic ridge arose, it was formed chiefly out of
basaltic magma, and only in some parts of the South Atlantic, nearer to the equitorial bridge of earlier epochs, are encountered
scattered fragments of sialytic and "semi-sialytic" species (e.g. Ascension Island).
The Geological History of
Atlantis, By Dr. N. Th. Zhirov (cont. 3) cont. 1961
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