Lunov E. Petrology of alkaline rocks from the Pokrovo-Kiriyivo massif (Ukraine).

The dissertation is devoted to the study of alkaline rocks from Pokrovo-Kiriyivo massif. The intrusion of alkaline rocks is composed by malignites and juvites. It is believed that between malignites and juvites there are gradual transitions but according to the results of our research these rocks are discrete. In the primary rocks (using a microprobe analysis) the chemical composition of the rock-forming (pyroxenes, amphiboles, feldspathoids, micas, feldspars, magnetite) and accessory minerals was first identified, and a number of their features are revealed. The unchanged malignites and juvites belong to the agpaitic series, the agpaitic coefficient of which reaches to 1,3. According to the poikilite structure (the inclusions of nepheline in other minerals) the investigated alkaline rocks are similar to the rischorites of Khibin massif. Like alkaline rocks of the agpaitic series malignites and juvites of Pokrovo-Kiriyivo massif enriched such incompatible elements as Zr, REE, Y, Nb the accessory minerals of which are represented by bastnaesite, britholite, titanoniobates, catapleiite etc. These minerals are also characterized by a high content of strontium, which is fixed in such minerals as strontianite, burbankite, Sr-apatite. The results of petrological research indicate that the alkaline rocks of Pokrovo- Kiriyivo massif were formed during the evolution of initial undersaturated silica (nepheline normative) melts in hypabysical conditions. This is evidenced by their structures, high oxidation of iron and the presence of hypabysal and subvolcanic analogues.