Ryabinovyi

This rather irregularly shaped complex has an area of about 50 km2 and involves both volcanic and plutonic rocks. The enclosing rocks are granite gneisses and granites which are fenitized adjacent to the margins of the complex. In the contact zone, as well as in the roof, are blocks and fragments of limestones of the Cambrian basement cover, which have been altered to marble and skarns, and Jurassic sandstones that have been hornfelsed. The complex includes a considerable diversity of volcanic, plutonic and hypabyssal rocks which alternated temporally but the major stages of magmatism, according to geological evidence, are as follows. The first stage is represented by quartz and alkaline peralkaline trachytes. They are encountered only in the form of xenoliths in other rocks. The second stage comprises volcanic rocks which include peralkaline trachyte, pseudoleucite phonolite and their brecciated equivalents. They have been preserved at the summits of mountain peaks and form a partial cover to the laccoliths. The third stage encompasses aegirine syenite and pulaskite, nepheline syenite and alkaline syenite porphyries. They form about 80% of the area of the complex and are extensively metamorphosed and replaced by K-feldspar, which may comprise up to 80-90% of the rock, albite and aegirine. The ratio of primary rock to metasomatic products varies from 70:30 to 50:50. The metasomatised rocks are characterized by the abundance of accessory minerals including apatite, magnetite, titanite, melanite, leucoxene and rarer xenotime. The fourth and fifth stages include alkaline trachytes and their tuff equivalents, lava breccias, lamproite, solvsbergite porphyry, grorudite, nordmarkite and peralkaline granites; many of these rock types are present in the form of dykes. The nepheline syenites contain alkali feldspar (70-80%), nepheline (4-5%), aegirine (11-20%) and biotite and albite in small quantities. In pulaskites the content of feldspar increases up to 87% and, in addition, albite (7%) and clinopyroxene (9%) are present; accessories include magnetite and apatite. Aegirine syenites are formed in the main of alkali feldspar (up to 75%) and clinopyroxene (17-20%) with small amounts of albite, biotite and accessory magnetite, apatite, titanite, fluorite and garnet. In addition to K-feldspar (80%) and clinopyroxene (5%) the nordmarkites contain up to 15% quartz. More detailed data on the composition of the rocks can be found in papers by Orlova (1990), Kravchenko (1972), Kochetkov et al. (1989) and Eremeyev et al. (1993).