Donskoy A.N.
N.P. Semenenko Institute of Geochemistry, Mineralogy and Ore
Formation of NAS, Kiev, Ukraine
Proterozoic alkaline massifs
of nepheline syenite series
are predominantly concentrated in margin zones of Ukrainian Crystalline Shield.
They are located nearby huge tectonic structure. This structure is Dnieper-Donetsk avlakogene, which divides
Ukrainian Crystalline Shield (USh) from North and
East. The formation of these alkaline complexes is connected with a period of
platform development in this region.
Most of alkaline
massifs of this type such as Octyabrskiy, Malaya Tersa, Sherbakovka (next to
border of Rostov district in Russia) alkaline massifs and Chernigovka
carbonatite one are located at Azov block (domain) in
USh. Lately massifs of same type were found at
Western margin of USh. There were Proskurovka
and Antonovka massifs and Yastrebetskiy
one (North-Western part of USh). Alkaline massif in Proterozoic shield was discovered at Lithuania, Vareny zone. There is a prediction of finds of same massifs
in Belarus. Alkaline syenites were discovered next to
city of Pinsk. These rocks use to frame alkaline massifs of nepheline
series. As a rule the complexes of this type are located into zone of deep
fault intersection.
Tectonics of Azov
block of USh has been the best studied (fig.). The
alkaline massifs were forming in Proterozoic era
after the main structures of Azov block had been formed. Zones of deep faults
frame the block. It is got up regarding Northern and Eastern its borders. Joint
zone is got up regarding the block.
Fig. Schematic
tectonic map of Eastern part of Azov block. (Roman numerals in circle):
I Azov block; II Orekhovo-Pavlograd joint zone;
IA Western Azov block on 1st tectonic range, Iโ - Central Azov interblock
structure; I๗ - Eastern Azov block of 1st
tectonic range.
The blocks of 2nd
tectonic range (Arabic numeral): 1- Volchanka, 2 Huliaipole, Andreevka.
Faults (Arabic
numerals in circle): 1 Azov-Pavlograd, 2 Malaya Yanisol, 3 South Donbass (Volnovaha), 4 Berdyansk-Kalmiuss,
5 Konka, 6 Gruzskiy Elanchik, 7 Krivoy Rog-Pavlovka.
Deep faults: 1 1st
range, 2 2nd range, 3 3rd and upper range, 4 -faults,
5 - upthrow faults, 6 slide apart faults.
Massifs: granite (1
Ekaterinovka, 2 Starodubovka,
3 Tokovka); 8 undefined alkaline (1 Octyabrskiy, 2 Kalmius, 3
South-Kalchik, 4 Elanchik);
9 ultrabasic alkaline (1 Chernigovka,
Begim-Chokrak, 2 Pokrovo-Kireevo);
10 plagiogranite-migmatite Saltychansk
dome; 11 anticlines; 12 troughs; 13 trough structures (Kuibyshevsk-Sorokin, 2 Fedorov);
14 projections of basis strong metamorphised; 15
dykes.
Inasmuch as the
alkaline massifs were forming under great influence of metasomatic
processes which been controlled by tectonic structures, we refer to appointed
types of tectonic zones. The 1st range tectonic zones frame
structures of 1st range. They use to be a great length and zonal.
There are occurrences of igneous and metasomatic
rocks of different age on the territory of these zones.
The 2nd
range tectonic zones are structures with deep faults, which divide blocks of 1st
and upper tectonic range. There are dykes, occurrences of acid and basic magmatism, ultramafic and metasomatic rocks on territory of these blocks. These zones
have North-Western direction and a lot of feathering faults.
Deep fault zones,
which associate with occurrences of alkaline metasomatic
rocks, depend on the fault zones of North-Western direction.
Over fault zones of
North-Western direction ultrabasic and alkaline
rocks, zones of fenitization, alkalization, metasomatic rocks and carbonatites
were developing. These structures were repeatedly renewed; dyke complex rocks
were developed there. They were of importance for forming a block structure of
the massifs.
Peculiarities of a formation
of Octyabrskiy massif and its frame are suggested to
be in the following way. Formation of large folded structures of North-Western
direction was simultaneously occurring with slow block elevation
Some tectonic stages have been
established in North-Western part of Octyabrskiy
massif (Mazurova Balka
deposit). These stages are related with faults' renewing along old fault zones.
The two fault systems of North-Western and North-Eastern direction are noted.
Some tectonic
stages have been established in Northwestern part of Octyabrskiy
massif (Mazurova Balka
deposit). These stages are related with renewing of fault displacements over
old direction fault zones. Two fault displacement directions have been noted to
be Northwestern direction and North-Eastern one.
The appointed types of faults
are distinguished:
1) which have been preceded
formation of syenites of North-Western direction and
45-60º in contact zone of base rock and syenites
(pre-ore bearing stage);
2) controlled
by albitite intrusion (ore-bearing stage);
3) related
with albitite intrusions (ore-bearing stage);
4) fault
zones formed until ore-bearing period, it occurred the renewing of displacement
movement which slide and crush ore bodies
5) small
displacements, breccia post ore-bearing zones
initiate steep displacements of North-Western direction in nepheline
rocks; they are related with lamprophyre dykes.
6) younger faults of slide type shift lamprophyre dykes
The nepheline complexes massifs of syenite
series are related with ancient platforms such as USh,
Belarus shield, Lithuanian plate, Baltic Shield, Transvaal province, Canadian
platform, which had been formed in Proterozoic era.
The nepheline series suite epochs of ectonic and igneous activity, which correspond periods of
global reconstruction.