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.