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magmatic melts were undergone to the processes of differentiation on the
eclogite (top), pyroxenite (average) and peridotite (bottom) magmatic layers.
Under the high thermodynamic conditions from volatile components (Н
2
, C,
СН
4
, СО
2
, CO, Н
2
О) the crystallization of diamonds was derived,
corresponding to the specified three types of melts: diamond Е-type from
eclogites, diamonds Рх-type from pyroxenites and diamonds Р-type from
peridotites (Figura 9) (M
arakushev et al., 1995)
.
4. Diamond and its barophilic mineral - satellites in the listed rocks concern
to intratelluric mineralizations, arising in these centers
before the introduction
of diamond-bearing magmas to more high levels in earth's crust, where they
were finally consolidated to forming diamond-bearihg initial intrusives.
Basing on the definitions of radiometric age of inclusion minerals in
diamonds, the following epochs of generation diamonds in non-depleted
mantle (gipolite) we can emphasize: 3300, 2700, 1600, 1200, 900 and 300
Ма ago.
5. The processes of formation diamondiferous ultrabasic and alkaline-
ultramafic rocks in the upper mantle are characterized by the long periods of
maturation from 600-300 up to 1500-1000 Ma. During these periods there
were heating, melting, magmatic differentiation and crystallization of
diamond and its barophilic mineral - satellites in the intratelluric stage.
Simultaneously, or somewhat later, there occured the transformation of non-
depleted garnet peridotite in the upper mantle (gipolite)
in depleted pyroxene-
olivine mantle (pyrolite), enriched by lithophile and terra-rare elements. But
the thickness of new pyrolite upper mantle is sharply increased because of
increasing the volume of pyroxene-olivine rocks at such transformation. All
it causes the uplift the surface of Mohorovichic discontinuity under
continents and the swelling of earth’s crust with the formation cratons on the
platforms.
6. The intrusives of diamondiferous peridotites, pyroxenites and eclogites,
which have intruded into the bottom of platforms, represented the substrata
for generation of the centers of secondary fluidalic kimberlite and lamproite
magmas, developing by their replacement with an inherited diamond
mineralization (the plutonic stage). These secondary, but related
diamondiferous magmas, by the process of zonic melting, periodically
derived from the upper mantle up to the bottom of earth’s crust (the
hypabyssal stage). Along the deep faults and cracks in the earth crust
kimberlite and lamproite magmas, eventually, reached the surface of the
Earth, where they were preserved in the forms of the diamondiferous dikes,
sills and explosive pipes (the explosive stage).
7. The generation of deep diamondiferous centers in the upper mantle,
considering the absolute age of mineral inclusions in diamonds, occurred in
Pre-Cambrian time, whereas the impulses of kimberlite and lamproite
volcanism periodically renewed during an enormous geological time. These
118
processes sometimes combined on the same territory, for example, in South-
African and West-Australian cratons. Judging by the absolute age of mineral
inclusions in diamonds and nodules of garnet peridotites, pyroxenites and
eclogites in diamondiferous kimberlites and the time of kimberlite intrusions,
the following epochs of kimberlite generation can be suggested: 3300, 2700,
2000, 1600,1000, 1200, 900, 600, 400-350, 380-340, 250-200, 160-
140,110-90,70-50, 40-20 (Ma) (Table 1, Figure 1).
8. The formation of every separate kimberlite or lamproite pipe of explosion
also occurred at some stages of repeated intrusion and explosion, that was
accompanied by disintegration of rocks and minerals of the previous stages.
For example, in kimberlite pipe Udachnaya (Siberian, Yakutian), which time
of intrusion is defined as late Devonian (367-353 Ма), nodules of garnet
peridotites, pyroxenites, eclogites and mineral inclusions in diamonds are
found with absolute age: 3300, 2700, 2000, 1580, 1200, 650, 420, 370 Ма.
9. Kimberlite and lamproite are naturally entered in the general system of
development of alkaline-ultramafic magmatism on platforms, representing
facies of extremely high fluid pressure with its increasing alkaline
magmatism gets more and more alkaline ultrabasic character. On the
diagram Nb - Sr (Figure 7) we can see the gradual transitions from
olivine kimberlite I type to olivine-phlogopite kimberlite II type, further to K-
richterite-olivine lamproite (kimberlite III type) and, at last, to K-richterite-
leucite lamproite (kimberlite IV type) (Milashev, 1994).
10. In the fluid pegmatite stage of development of kimberlite magmatism,
selected by A.A.Marakushev (1995), the collective over-crystallization
emanated from some fine diamonds to huge rare megacrystals of non-
nitrogen diamonds of cubic habit and high quality, cleared from intratelluric
mineral inclusions. The recordsman of size on the world are the famous
diamond "Cullinan", which was found in kimberlite pipe Premier in Southern
Africa and weighted 3,106 carats.
11. The most significant condition of preserving the degree of
diamondiferous of the initial magmatic sources, except for the favorable
chemical compound of alkaline-ultramafic magmas and thermodynamic
conditions of diamond crystallization, is the speed of transportation
diamondiferous kimberlites and lamproites from the upper mantle
to the earth
crust and, at last, to the surface of the Earth, where the diamond deposits
were preserved. It is necessary to note, that the mantle diamonds are very
stable against temperature influence, because the melting of diamond occurs
at high temperature about 3570
o
C without any access of oxygen. The phase
transition of diamond to graphite also happens without any access of oxygen,
when the pressure in melts falls below 4.7-3,3 GPa (Figure 11). But in the
presence of oxygen, crystals of diamond burn down at 1000
o
C, thus curved
facet crystals of diamond are formed, and the weight of them decreases up to
their full disappearance.