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The metallogenic zoning on survey maps of such small scale it is
possible conducting only at the level of the metallogenic provinces. The
separation the structural metallogenic belts, zones, ore districts and knots is
practically impossible; it would be overstrain the map. Whereas the fact,
that every separate
geodynamic system with their mineral deposits
indicated one age metallogenic province, on the present map had not
provided more detailed metallogenic zoning.
4. METALLOGENY OF GEODYNAMIC CYCLES ,STAGES AND SYSTEMS
We selected the following geodynamic cycles based on systematic
analysis of the geological development of the primordial hydride Earth
from protoplanetary up to the modern time:
I . protoplanetary (4,600-3,600 Ma);
II . permobilic (3,600-2,000 Ma);
III. protocontinental and protooceanic (2,000-900 Ma);
IV. platform-geosynclinal and oceanic (900-200 Ma);
V. continental - oceanic (200 – 0 Ma).
The other factors that were considered are: the harmonically analysis
of oscillation of the earth’s crust (Grozdilov, 1974); the periodicity of the
epochs of kimberlite magmatism on radiological dates as compared to the
sidereal calendar about 215-225 Ma (Milashev,1994). Each of the
geodynamic cycles is subdivided into three stages: early, middle and late.
The exception from this subdivision is the protoplanetary cycle, in which
only the middle and late stages have been selected. The early stage,
apparently, falls into the accretion and the condensation stages of forming
the planet from the gas-dust nebula (Figure 2).
I
. P r o t o p l a n e t a r y c y c l e (4,600-3,600 Ma) of
development of the Earth had begun immediately after the collapse of the
planet, when the gravity was approximately in 3 times more, and the radius
at 2.5 times less than the modern ones (Larin, 1980). The protoplanetary
cycle is subdivided in two stages – l u n a r and n u c l e a r.
I. 1. L u n a r s t a g e (4,600-4,200 Ma) was selected by analogy
with the most ancient
mafic rocks on the Moon,
the age of which is dated by
radiological dimension in 4,600-4,300 Ma.
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composition, pitted on the surface by basalt volcanic craters and calderas.
The oldest members of the world’s largest anorthosite massifs have mafic
compositions and exhibit circular structural forms. These features are now
recognized as characteristic of the earliest era in Earth history – a unique
“lunar” stage in Katarchean (Glukhovskiy & Pavlovskiy, 1973). Most
probably, at this time the Earth protocontinental crust had been of a
gabbro-norite-anorthosite
It is possible to explain the
formation of lunar craters on the Moon and the
Earth in Katarchean not only by external actions (bombardment of the
surface by asteroids and meteorites), but also by internal conditions of the
development of these related planets
. So, from the position of primordial
hydridic Earth, at radioactive warming up, the hydridic core began to
emphasize scattered gas jets of protonal hydrogen, above which in
the upper
mantle the areas of compressing and downing of silicides metals were
arisen. The reaction of some more thin and plastic silicate crust above such
areas of downing was formation depression craters and on the surface of the
Earth orbed depressions, where the basalt magma was effused. Thus, than
less the deep of location the focal point of a blast of the volcano, then wider
on the surface was the diameter of a “lunar” crater, and vice versa.
The most believable skyscape on the surface of the Earth in early
Katarchean are vast orbed-oval deep depressions filled with basalt’s lavas («
the lunar seas»), which are disparted by low «continental plateaus »,
composed by massifs of anorthosites, gabbro-norites, gabbro-dolerites and
products of their differentiation. The terrain surface at that time was warm
up to several hundred of grades Celsius and was enwrapped in a dense
carbonic atmosphere still completely dispossessed of oxygen, such as on
modern planet Venus. The basic rocks of the lunar stage were subsequently
overlapped by younger geological formations and immersed in the depth of
earth crust, where as a result of regional metamorphism they were turned
into eclogites, composing the upper horizons of mantle together with
unltrabasic rocks.
The type of magma at the «lunar» stage of development of the Earth is
instituted as primitively basic (tholeiite-basalts, gabbro and аnorthosites)
with clearly expressed homjdromic evolution. The low activity of oxygen in
tholeiitic magma explains the restorer forms of metals in trapps and
presence the native nuggets crystals of iron, aluminum and copper in them
(Oleynikov et al., 1978). There are finds of native nuggets of iron in
Siberian trapps and on the island of Disco. The tellure’s iron nuggets
weighing up to several tons are met in Greenland (Betechtin, 1950).
Аrchean and Proterozoic аnorthosites are specialized in iron, titanium,
aluminum and phosphorus. On this basis, it is possible to guess, that
Katarchean metallogenic epoch of the «lunar» stage of development of the
Earth, was specialized on initial concentration for the siderophile (titanium,
iron), as well as on the lithophile (phosphorus, aluminum) elements,
reflecting the conditions of forming the primitive basalt crust.