Geology Reference
In-Depth Information
4.12 K-Rich Feldspathoid-Bearing Rocks from the Former
U.S.S.R
Ultrapotassic feldspathoid-bearing rocks are found in widely scattered localities
throughout the former U.S.S.R. (Bazarova and Kazaryan 1977). Of these localities
the rocks occurring at Elpinsky, Talyshskii and Tezhsar (all from Caucasus),
Andriyanovka (Kamchatka province), Tokko and Anomaly (Aldan), Artem (Pri-
morye province) and Pastistennyl (Omolon province) are genuinely leucite-bearing.
4.12.1 Tezhsar (40 ° 41 N, 44 ° 39 E)
The alkaline complex of Tezhsar (37
39 Ma, Abovyan et al. 1981) covers an area
of 80 km 2 and occurs at the Prisevanskaya zone of the Pambaksky range (Kogarko
et al. 1995). The complex is ring-shaped comprising both intrusive and extrusive
rocks. The effusive series occurs in a circular area (15 km 2 ), and is 600 m thick.
There are three pyroclastic formations (from bottom to top): (a) trachyandesites, (b)
trachytes, and (c) leucite phonolites or pseudoleucite porphyries. Leucite tephrites,
shoshonites, sanidine- and leucite-bearing trachytes, phonolites, leucitophyres and
italites (containing essentially leucite) also occur in this complex. The intrusive
rocks of concentric zones are as follows: (1) alkaline syenites, (2) pseudoleucite
syenites, (3) nepheline syenites, (4) nordmarkites, (5) alkali syenites and (6) quartz
syenites. Nepheline-rich pseudoleucite syenites are con
-
ned to the marginal part of
the core of the complex. These syenites comprise pseudoleucites (30
-
40 vol%,
1
35 wt%) and orthoclase
(Or 90 Ab 10 ). The central part of the intrusive is composed of alkaline to peralkaline
syenite grading to peralkaline monzonite, nordmarkite and pulaskites.
-
6 cm in diameter) in a matrix of nepheline (25
-
4.12.2 Elpinskii (39 ° 27 N, 46 ° 09 E)
The Elpinskii complex was emplaced 12.50
14.53 Ma ago. They occur in the
tectonically depressed area of Zavozhen (Kogarko et al. 1995) near Akhavnad-
zorskaya, south of Armenia (Bazarova and Kazaryan 1986). The igneous activity
started with eruption of analcite-bearing alkalic basalt (25
-
30 m). Analcite-bearing
tephrites and explosive breccias occur in the upper part of the volcanic section
underlain by trachyandesites, trachytes and further below by leucite tephrites and
dykes of ha
-
ü
yne-bearing ma
c rocks.
 
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