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contours of these blocks as structural borders of kimberlites fields (Мilashev,
1981).
Two basic types of kimberlite fields are differed at the orientation and
interaction of dispositions, which internal structure is characterized by mesh or
subparallel arrangement of kimberlite-localize dislocations. In the fields where
the systems of dislocations refer to mesh type, kimberlite bodies localized in
places of crossing supervising and locating dispositions, which are distributed
without equability plan.
On the contrary, in the fields
with subparallel systems of
dislocations the order of disposition diatrems and dikes are determinated by the
presence of two-three similar orientated and convergent linear groups of
kimberlites bodies pulled together in tracer space.
The most perspective on diamonds are the kimberlite fields of diamonds
subfacies with a mesh structure of systems dispositions, many stages of
formations and much diversity of rocks composition. The absence of
commercial deposits of diamonds in two kimberlite fields of Yakutian with
subparallel systems of dislocations is, probably, caused by belonging these fields
to subgroup of few stages and their localization in
a zone of mutual development
kimberlites of diamond and pyrope subfacies.
Two basic types of kimberlites bodies - explosive and hypabyssal - are
clearly defined. The explosive types of rocks are submitted by actually pipes of
explosion, flattened-tubular bodies and inflations on dikes, consisted of
kimberlites breccias. The hypabyssal types are represented by massive
kimberlites fulfilled dikes, sills, lenses, injections in karstic cavities, and also
"columns” inside the diatrems.
Under the earths crust the pyrolite mantle (restite) reach up to depth of 200
km. In Cenozoic the non-depleted mantle (hypolite) reaches up to death of 300
km and is represented by garnet peridotite. According to the data by study
mineral and gas inclusion in diamond crystals, at the depth ranging from 170 up
to 240 km, there are the places of origin alkaline-ultramafic melts above the
"hot points” at the pressure more than 4-7GPa. As a result of long differentiation
of the initial melts or numerous "zoning melting"of the garnet peridotite came
the formation of all gammas of alkaline-ultramafic rocks, starting from
kimberlites, lamproites to picrites and carbonatites (Milashev,1994).
The "hot points " in non-depleted mantle, most likely, have arisen above the
jets of superheated protonic hydrogen, which rose from the top of liquid
environment of the
hydridic core, represented by metals
with dissolved hydrogen
(Larin, 1980). The decomposition of hydridic core of the Earth on metals and
protonic hydrogen occurred, apparently, influenced by "pumping up” the
galactic energy at the passage our planet together with the Sun through magnetic
and radiating belts (zones) at the time of their rotation around the center of the
Galaxy in current of the sidereal year, with the duration of approximately 212-
225 Ма.
It is necessary to note, that inside the same Kaapvaal-Zimbabwe craton in
the Southern Africa the diamond-bearing kimberlite magmatism was reiterated
for three times: in late Archean (2700-2600 Ма), in late Proterozoic (1200-1100
Ма) and in Mesozoic (200-80 Ма) with intervals of approximately 1500 and
1000 Ма. It testifies to the fact that the Southern Africa, since late Archean
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including up to Mesozoic, at all time stood above the same " hot area " in the
upper mantle, which was the source of kimberlite magma in the various periods
of tectono-magmatic activity. It is possible to explain that cratons and
continents always remain rigidly connected with their roots in the upper mantle.
The continents are disjointed along the deep riftogen zones, which were
established in the mantle. The riftgen zones are served as ways of degassing
protonic hydrogen while warming up and decomposing the hydridic core at the
expansion of the Earth.
Most likely, that repeated occurrence of diamond-bearing kimberlites within
the same area in the upper mantle take place as the result of a long processes of
transformation from hypolite to pyrolite. The new centers of kimberlite magmas
arose at the greater depths in the non-depleted mantle (hypolite) from garnet
peridotite, above the jets of protonic hydrogen during the new tectono-magmatic
activity. Probably, at deeper levels in the non-depleted mantle the
thermodynamic conditions were more favorable for crystallization diamonds
from alkaline-ultramafic melts. Therefore, in the later epochs of tectono-
magmatic activities in Southern Africa more diamond enriched kimberlites
deposits of Mezozoic age were generated (Table 2), (Krutoyarskiy et al., 2000).
In our opinion, each of the diamond-bearing kimberlite epoch within the
limits of platforms finished by formation of the large ring impact structures,
caused by brisant evolution of superheated hydrogen gases of huge capacity
from hydridic earth’s core in places of crossing the deep faults. If in such places
are available graphite gneisses or layers of carbonic schists, under influence of
high temperatures (2000 C
o
) and extreme impact pressure graphite passes in
hexagonal diamond – lonsdaleite. For example, in the Popigay ring impact
structure 36 Ma (diameter about 100 km), which is located at the North Siberian
platform, had been determined small diamond crystals (Masaitis et al., 1998).
The conditions of genesis and location of impact diamonds are sharply differ
from all known magmatic and metamorphic deposits of diamonds. The
resources of diamonds, located in impact rocks of the Popigay ring structure, as
a whole, exceed those in all known in the World diamond-bearing kimberlite
provinces.
The impact diamonds which have recovered from original impactites rocks
(tagamites and suevites) have sizes from 0.05 to 2 mm across. Diamonds found
at nearby placers seldom have grains up to 8 - 10 mm in diameter. Most
diamonds are shades of yellow and some are colorless, gray and black. The
impact diamonds are usually represented by polycrystalline aggregates of cubic
and hexagonal modification (lonsdaleite) of carbon. They often form
paramorphs with graphitic crystals. Lonsdaleite in impactites forms small
elongated or irregular grains in fine-grained aggregates with graphite and
diamond, or with diamond only. It can also form a type of matrix in relation to
small cubic or cubic-octahedral diamond crystals. The lonsdaleite can form as
much as 60 % of fine-grained aggregates. In contrast, the chaoite is rarely found
in the graphitic and diamond-lonsdaleite aggregates of the Popigay impactites. It
reflects the fact that the temperature of impactogenesis exceeded 2,000 C
o
(Masaitis et al. 1998).