Home – Home – Jornals – Russian Geology and Geophysics 2001 number 9

Three petrochemical groups of basic rocks are statistically recognized among the intrusive traps of the Siberian Platform (SP) and Taimyr Peninsula. These are: (1) normal tholeiitic (predominant), (2) Ti- and Fe-enriched, with increased contents of alkalies (ferrodolerites), (3) low-Ti picritoid (of Noril'sk type), which are least abundant. The platform cover is most saturated with intrusions in the west, where in places up to 17 separate magmatic bodies occur and their total thickness may be more than 2000-2500 meters. In some sections two or three petrochemical groups of intrusions are present, whereas others are denominated by bodies of one type.
There is distinct regional zoning in distribution of compositions of intrusive traps. In the southern and southwestern SP, the Noril'sk-type massifs are rare to absent. Only one deposit contained about 15 wt.% MgO, whereas the maximum contents of MgO at the bottom of differentiated sills are, as a rule, less than 11 wt.%. Striking differences are observed in occurrence of ferrobasites. In the western SP they make up no more than 11%, and in the southern SP, about one quarter of all rock groups. The rock enriched in TiO₂ and FeO* (ferrodolerites) amount to about 70% in the south of the platform. The most basic, magnesian, and low-Ti melts occur within the Noril'sk-Kharaelakh district. South and north of it, the intrusive traps are, on average, more silicic, high-Ti, and alkaline. The molten intrusive basites in the north and south are richer in iron than those in the central part of the platform. In the east of the platform the melts are close to "normal tholeiitic". They contain less iron but are richer in Ca and Mg than the melts in the southwestern SP. The compositional zoning of intrusive traps is correlated with structure-formational zones and the structure of the Earth's crust: (1) magnesian and trachybasaltic differentiated intrusions are conjugate chiefly with the Yenisei-Khatanga depression, (2) Fe- and Ti-enriched basites are predominant in the Angara block, which is characterized by the thinnest consolidated Earth's crust in its central part, (3) normal tholeiitic basites seem to dominate in localities with the thick consolidated Earth' crust.