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In the early Archean, oxygen-silicate lithosphere of the Earth was still
strongly heated, the geothermal gradient compounded 54
o
C / km, and the
heat stream in 2-3 times exceeded modern (Crambling, 1981). The early
Archean lithosphere, more probably, had elastic-tenacious consistency and
was rather plastic. The degassing of protonic hydrogen from hydridic core
of the Earth in accordance with raising thickness of the mantle and crust has
become to turn from universal surfaces to lateral-jet. At the location of the
thermal hydrogen stream in intermetallic midlle mantle (zone С) and
saturation of protonic hydrogen the heat-conducting zone (tectonogen), the
metals, composing it should be undergoing compression. As a
consequence, in mouth part of the heat stream at intrusion it in silicate
sphere of the upper mantle (zone В) will be reshaped a zone of downing, on
which silicate mantle will be immersed in metallic (Larin, 1980). The
reaction of the astenosphere to such downing will be the formation a
lengthwise depression. The consequence of these processes on the surface
of the Earth, will be appearance a protogeosinclinal baths and sedimentary –
volcanic infill them. Alongside with it, if the location of such depressions
originated in linking to a rifting zone, it acquired features «eugeosyncline»
with early primitive basalt and comatiitic volcanism, which once was ended
by the intrusion of granitoids sodium of rank. The foundation of such
volcanic-plutonic greenstones belts, as a rule, is represented by introduction
of more ancient «greygneissic» complex or granulites of Katarchean or
Archean age. The Аrchean granite – greenstone belts are detected on all
continents, occupying not less than two-third of the areas of the shields. The
rest areas of protocratons are represented by granulite-gneisis formations
of Archean age (Khain, Bozhko, 1988).
In the Archean the lithosphere became more stable as evidenced by the
appearence of large intrusive massifs, among them 3,500 – 3,300 Ma old
granitoides (Pavlovskiy,1975). Their emplacement marked the first sign of
an emerging granite crustal layer. Where the granitoids, characteristically
with low-K and primary enderbite, were sporadic; and the crust remained
largely mafic, later in the Archean, metamorphism became more diverse so
that, along with granulites, scattered sediments were deposited.
Nevertheless, these now-metamorphosed rocks still do not exceed the
greenschist facies in volume. Everywhere, the feature left from the
geodynamic regime of that era is persistently irregular in orientation and
form.
The close of Archean was marked by perturbation of the existing
tectonic regime on a massive scale. An intense pulse of potassium
granitization pervasively affected Archean mafic basement. The granite
layer of earth’s crust was initiated and commenced to evolve and expand at
this time. Typically Archean, anhydrous granulites gave way everywhere to
the hydrous metamorphism of greenschist and amphibolites facies.
Commencing in early Proterozoic time, geothermal gradients decreased
rapidly, lithosphere stability increased, and sedimentation acquired a
protoplatform character. However, sedimentation under these conditions, in
contrast to that of the platforms of the Neogaicum, was accompanied by
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high-grade metamorphism (up to amphibolites grade) and intense
granitization of the Archean mafic basement and its protoplatformal cover.
The altered cover was then subject to folding on the peripheries of its
growing granite-gneiss domes (Pavlovskiy, 1975).
The fundamental manifestation of perturbation of the tectonic regime at
the Archean-Proterozoic boundary was the emergence of extended linear
feature, which expressed the existence of horizontally directed fields of
stress and deformation (Pavlovskiy & Markov, 1963). These formations
have been accepted into the literature as “greenstone belts”, which was
differing from Phanerozoic geosynclinal fold belts (Markov, 1962). They
were being smaller in area, relatively simple in internal structure (without
observed differentiation into geanticlinal or intra-geosynclinal zones),
absence of foredeeps, and a reduced tendency toward orogenesis (absence of
typical molasse). Researches tend to view them as prototypes for later
geosynclines of Neogaicum.
Simultaneously with the evolution of greenstone belts, intense
granitization of the crust continued through the early- and the part of the
middle Proterozoic. As a result, about 80 % of the area of the present
continental crust dates back to this span of time, making this period the
main stage of granitization and granite formation in all of Earth’s history.
II.1. E a r l y A r c h e a n s t a g e (3,600-3,000 Ma) of permobile cycle of
geological development of the Earth represent by the protocontinental cratons,
that are composed from granulite-gneisis, granite - gneisis, granulite-
greenstone and granite–greenstone areas and belts. On the modern continents,
they constitute deep eroded uplifted Precambrian shields. At the Northern
Lavrasia hemisphere they are represented by Canadian, Baltic, Аnabar, Аldan
and Chinese shields, and on the Southern Gondvan hemisphere - African,
Guinean, Brazilian, Indian, East - Antarctic and West-Australian shields. In the
central parts of shields granulite-basic and granulite-gneisis complexes
dominate, which are almost deprived of carbonates formations. The last are
dispersed in lugs on the margin parts of shields. On Archean shields the
composite complex of magmatic, pegmatitic, hydrothermal, sedimentary and
especially wide metamorphic of genesis deposits are detected. Among them
there are the well-known world’s deposits of iron, titanium, manganese,
muscovite, phlogopite,
graphite, emery and kyanite.
The displays of emery, sillimanite and great deposits of graphite are
connected with granulite-gneisis belts of andalusite-sillimanite facies of
metamorphism ( Sri-Lanka and Madagascar). The massifs of gabbro –
anorthosites, containing apatite – ilmenitite-titanemagnetitite ores, are
connected to the belts of sillimanite-kyanite facies of metamorphism, for
example, the anorthosites of Aldan shield and Adirondike in Northern
America. The ferriferous deposits Baikal (Аldan shield), Olenegorsk (Kola
peninsula) are linked to granulite-gneisis belts of highly and modest
gradient. To the indicated types of the metamorphism and deposits can be
regarded Granville belt (Canadian shield), Limpopo belt (Southern Africa),